The femoral insertion of the anterior cruciate ligament: discrepancy between macroscopic and histological observations

Three-dimensional isotropic magnetic resonance imaging can provide a reliable estimate of the native anterior cruciate ligament insertion site anatomy

PURPOSE

This study quantified the error in anterior cruciate ligament (ACL) insertion site location and area estimated from three-dimensional (3D) isotropic magnetic resonance imaging (MRI) by comparing to native insertion sites determined via 3D laser scanning.

METHODS

Isotropic 3D DESS MRI was acquired from twelve fresh-frozen, ACL-intact cadaver knees. ACL insertion sites were manually outlined in each MRI slice, and the resulting contours combined to determine the 3D insertion site shape. Specimens were then disarticulated, and the boundaries of the ACL insertion sites were digitized using a high-accuracy laser scanner. MRI and laser scan insertion sites were co-registered to determine the percent overlapping area and difference in insertion centroid location.

RESULTS

Femoral ACL insertion site area averaged 112.7 ± 17.9 mm² from MRI and 109.7 ± 10.9 mm² from laser scan (p = 0.345). Tibial insertion area was 134.7 ± 22.9 mm² from MRI and 135.2 ± 15.1 mm² from laser scan (p = 0.881). Percentages of overlapping area between modalities were 82.2 ± 10.2% for femurs and 81.0 ± 9.0% for tibias. The root-mean-square differences for ACL insertion site centroids were 1.87 mm for femurs and 2.49 mm for tibias. The MRI-estimated ACL insertion site centroids were biased on average 0.6 ± 1.6 mm proximally and 0.3 ± 1.9 mm posteriorly for femurs, and 0.3 ± 1.1 mm laterally and 0.5 ± 1.5 mm anteriorly for tibias.

CONCLUSION

Errors in ACL insertion site location and area estimated from 3D-MRI were determined via comparison with a high-accuracy 3D laser scanning. Results indicate that MRI can provide estimates of ACL insertion site area and centroid location with clinically applicable accuracy. MRI-based assessment can provide a reliable estimate of the native ACL anatomy, which can be helpful for surgical planning as well as assessment of graft tunnel placement.

An In Vivo Prediction of Anisometry and Strain in Anterior Cruciate Ligament Reconstruction - A Combined Magnetic Resonance and Dual Fluoroscopic Imaging Analysis

PURPOSE

To evaluate the in vivo anisometry and strain of theoretical anterior cruciate ligament (ACL) grafts in the healthy knee using various socket locations on both the femur and tibia.

METHODS

Eighteen healthy knees were imaged using magnetic resonance imaging and dual fluoroscopic imaging techniques during a step-up and sit-to-stand motion. The anisometry of the medial aspect of the lateral femoral condyle was mapped using 144 theoretical socket positions connected to an anteromedial, central, and posterolateral attachment site on the tibia. The 3-dimensional wrapping paths of each theoretical graft were measured. Comparisons were made between the anatomic, over the top (OTT), and most-isometric (isometric) femoral socket locations, as well as between tibial insertions.

RESULTS

The area of least anisometry was found in the proximal-distal direction just posterior to the intercondylar notch. The most isometric attachment site was found midway on the Blumensaat line with approximately 2% and 6% strain during the step-up and sit-to-stand motion, respectively. Posterior femoral attachments resulted in decreased graft lengths with increasing flexion angles, whereas anterodistal attachments yielded increased lengths with increasing flexion angles. The anisometry of the anatomic, OTT and isometric grafts varied between tibial insertions (P < .001). The anatomic graft was significantly more anisometric than the OTT and isometric graft at deeper flexion angles (P < .001).

CONCLUSIONS

An area of least anisometry was found in the proximal-distal direction just posterior to the intercondylar notch. ACL reconstruction at the isometric and OTT location resulted in nonanatomic graft behavior, which could overconstrain the knee at deeper flexion angles. Tibial location significantly affected graft strains for the anatomic, OTT, and isometric socket location. CLINICAL RELEVANCE: This study improves the knowledge on ACL anisometry and strain and helps surgeons to better understand the consequences of socket positioning during intra-articular ACL reconstruction.

The capsular line reference, a new arthroscopic reference for posterior/anterior femoral tunnel positioning in anterior cruciate ligament reconstruction

BACKGROUND

Femoral malposition is the first cause for graft rupture during ACL reconstruction. Arthroscopic landmarks can be difficult to identify. So, landmark has to be found for reliable tunnel placement. A proximal-distal reference was described as "Apex reference" reported by Hart et al. but no posterior/anterior reference exists in the literature. The purpose of this study was to do a 3D CT-scan assessment of the femoral tunnel positioning using the Capsular Line Reference (CLR) as a landmark for posterior/anterior placement in ACL reconstruction. We hypothesized the CLR could provide a precise and reliable antero/posterior femoral tunnel positioning less than 2 mm from the Bernard & Hertel posterior quarter.

METHODS

Seven cadaveric knee specimens with a mean age of 79.2 ± 11 years were used. Using standard approaches, the CLR was identified corresponding to a white line (the capsule) appearing at the posterior border of the femoral condyle after bony debridement of the medial and posterior part of the lateral femoral condyle. The center of the tunnel was marked. An inside-out technique with anteromedial drilling technique was performed using an 8-mm diameter reamer. The distal femurs were sawed and a CT-scan was done for each specimen to obtain 3-dimensional image reconstructions. These 3D reconstructions were analyzed to measure the position tunnel center on the posterior/anterior axis and the distance from the posterior/anterior quadrant according to the Bernard & Hertel method.

RESULTS

The mean position for the posterior/anterior axis was 27.0 ± 1.8% (25-28.9) with a median of 26.9%. The position from the first quarter of the Bernard & Hertel method was 0.9 ± 0.8 mm (0-1.8) with a median of 0.8 mm.

CONCLUSION

The CLR is a reliable and reproducible arthroscopic landmark to place the femoral tunnel for ACL reconstruction in the anterior/posterior axis. Proximal/distal position depends on the choice of the surgeon to reproduce anteromedial or posterolateral fibers.

[Anatomical study of anterior cruciate ligament and its effect on reconstruction technique]

Objective

To summarize the current research progress of anterior cruciate ligament (ACL) anatomy, and discuss its effect on the reconstruction technique.

Methods

The literature concerning ACL anatomy and reconstruction at home and abroad was extensively reviewed and summarized.

Results

The anatomy and morphology of ACL has gained new recognition in recent years, and the "Ribbon-like" ACL has gradually been paid attention to by researchers. In present researches, it seems the "Ribbon-like" anatomy theory has advantages in theory when compared with the previous anatomy theory. It is more in line with the anatomy and isometric reconstruction.

Conclusion

The understanding of ACL anatomy guided the development of ACL reconstruction. The "Ribbon-like" ACL anatomy theory is the different understanding of the anatomy theory, which remains controversy. The "Ribbon-like" reconstruction maybe has more advantages in theory, but further study is needed.

Anterior cruciate ligament tibial insertion site is elliptical or triangular shaped in healthy young adults: high-resolution 3-T MRI analysis

PURPOSE

To clarify the morphology of anterior cruciate ligament (ACL) tibial insertion site in healthy young knees using high-resolution 3-T MRI.

METHODS

Subjects were 50 ACL-reconstructed patients with a mean age of 21.4 ± 6.8 years. The contralateral healthy knees were scanned using high-resolution 3-T MRI. The tibial insertion sites of the anteromedial (AM) and posterolateral (PL) bundle fibres, and the ACL attachment on the anterior horn of lateral meniscus (AHLM) were segmented from the MR images, and 3D models were reconstructed to evaluate the morphology. The shape of ACL footprint was qualitatively analysed, and the size of AM and PL attachments and AHLM overlapped area was measured digitally.

RESULTS

Tibial AM and PL bundles were clearly identified in 42 of 50 knees (84.0%). Morphology of the whole ACL tibial insertion site was elliptical in 23 knees (54.8%) and triangular in 19 knees (45.2%), but not classified as C-shape in any knees. However, the AM bundle attachment was of C-shape in 29 knees (69.0%) and band-like in 13 knees (31.0%). Overlap of ACL on AHLM was found in 26 knees (61.9%), and the size of the overlapped area was 4.8 ± 4.7% of the whole ACL insertion site.

CONCLUSION

3D morphology of the intact ACL tibial insertion site analysed by high-resolution 3-T MRI was elliptical or triangular in healthy young knees. However, the AM bundle insertion site was of C-shape or band-like. A small lateral portion of the ACL was overlapped with the AHLM. As for clinical relevance, these findings should be considered in order to reproduce the native ACL insertion site sufficiently.

LEVEL OF EVIDENCE

III.

Chronicity of Anterior Cruciate Ligament Deficiency, Part 2: Radiographic Predictors of Early Graft Failure

BACKGROUND

Accumulating evidence suggests that long-term anterior cruciate ligament (ACL) deficiency can give rise to an abnormal tibiofemoral relationship and subsequent intra-articular lesions. However, the effects of chronic ACL deficiency (ACLD) on early graft failure after anatomic reconstruction remain unclear.

HYPOTHESIS

We hypothesized that patients with long-term ACLD lasting more than 5 years would have a greater rate of early graft failure due to insufficient intraoperative reduction of the tibia and that the preoperative and immediately postoperative abnormal tibiofemoral relationship in the sagittal plane, such as anterior tibial subluxation (ATS), would correlate with the graft status on postoperative magnetic resonance imaging (MRI).

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A total of 358 patients who had undergone anatomic ACL reconstruction with hamstring grafts were divided into 5 groups based on chronicity of ACLD: (1) 0 to 6 months, (2) 6 months to 1 year, (3) 1 to 2 years, (4) 2 to 5 years, and (5) longer than 5 years. Preoperatively and immediately postoperatively, lateral radiographs in full extension were taken in all patients to evaluate the tibiofemoral relationship, specifically with regard to ATS, space for the ACL (sACL), and extension angle. All patients underwent MRI at 6 months to reveal graft status. Groups with a high rate of graft failure were further analyzed to compare demographic and radiographic factors between the intact and failure subgroups, followed by multivariate logistic regression analysis to identify predisposing factors.

RESULTS

Graft failure without trauma was observed in 4 (1.8%), 0 (0%), 1 (3.7%), 3 (9.7%), and 8 patients (17.7%) in groups 1, 2, 3, 4, and 5, respectively. Of the 76 patients in groups 4 and 5, significant differences were noted between the failure and intact subgroups in preoperative ATS (4.9 vs 2.4 mm, respectively; P < .01), side-to-side differences in sACL (sACL-SSD) (4.7 vs 1.9 mm, respectively; P < .01), extension deficit (4.4° vs 1.3°, respectively; P < .01), and chondral lesions (P = .02), while postoperative ATS and sACL-SSD showed no differences. Multivariate logistic regression analysis revealed that of these factors, preoperative sACL-SSD could be a risk factor for early graft failure (odds ratio, 3.2; 95% CI, 1.37-7.46).

CONCLUSION

Early graft failure at 6 months increased in patients with ACLD longer than 2 years. In this population, preoperative sACL-SSD was the most significant risk factor for early graft failure on MRI. However, immediately postoperative radiographic measurements had no effect on graft failure rates.

A Method of Accurate Bone Tunnel Placement for Anterior Cruciate Ligament Reconstruction Based on 3-Dimensional Printing Technology: A Cadaveric Study

PURPOSE

To explore a method of bone tunnel placement for anterior cruciate ligament (ACL) reconstruction based on 3-dimensional (3D) printing technology and to assess its accuracy.

METHODS

Twenty human cadaveric knees were scanned by thin-layer computed tomography (CT). To obtain data on bones used to establish a knee joint model by computer software, customized bone anchors were installed before CT. The reference point was determined at the femoral and tibial footprint areas of the ACL. The site and direction of the bone tunnels of the femur and tibia were designed and calibrated on the knee joint model according to the reference point. The resin template was designed and printed by 3D printing. Placement of the bone tunnels was accomplished by use of templates, and the cadaveric knees were scanned again to compare the concordance of the internal opening of the bone tunnels and reference points.

RESULTS

The twenty 3D printing templates were designed and printed successfully. CT data analysis between the planned and actual drilled tunnel positions showed mean deviations of 0.57 mm (range, 0-1.5 mm; standard deviation, 0.42 mm) at the femur and 0.58 mm (range, 0-1.5 mm; standard deviation, 0.47 mm) at the tibia.

CONCLUSIONS

The accuracy of bone tunnel placement for ACL reconstruction in cadaveric adult knees based on 3D printing technology is high.

CLINICAL RELEVANCE

This method can improve the accuracy of bone tunnel placement for ACL reconstruction in clinical sports medicine.

Chronicity of Anterior Cruciate Ligament Deficiency, Part 1: Effects on the Tibiofemoral Relationship Before and Immediately After Anatomic ACL Reconstruction With Autologous Hamstring Grafts

Background:

It remains unclear whether the tibiofemoral relationship in the sagittal plane is restored after anatomic anterior cruciate ligament (ACL) reconstruction, particularly in cases of chronic ACL deficiency (ACLD).

Hypothesis:

Patients with long-term ACLD will exhibit an anteriorly subluxed tibia both preoperatively and immediately postoperatively, even after anatomic reconstruction.

Study Design:

Cohort study; Level of evidence, 2.

Methods:

In total, 358 patients who had undergone anatomic ACL reconstruction with autologous semitendinosus grafts were divided into 5 groups based on chronicity of ACLD: (1) 0 to 6 months, (2) 6 months to 1 year, (3) 1 to 2 years, (4) 2 to 5 years, and (5) longer than 5 years. Preoperatively and immediately postoperatively, all patients underwent lateral radiography in extension to evaluate the tibiofemoral relationship, specifically with regard to anterior tibial subluxation (ATS), space for the ACL (sACL), and extension angle. Demographic and radiographic factors were compared among the 5 groups.

Results:

Preoperative ATS values in groups 4 (mean ± SD, 2.9 ± 2.1 mm) and 5 (2.6 ± 1.9 mm) were significantly greater than in group 1 (1.6 ± 1.9 mm). Postoperatively, the tibia was posteriorly overconstrained in all groups, and there was no difference in immediately postoperative ATS among the 5 groups. Further evaluation of the tibiofemoral relationship in the sagittal plane revealed that the mean preoperative side-to-side difference in sACL (sACL-SSD) was greater in groups 4 (2.5 ± 1.6 mm) and 5 (2.2 ± 1.7 mm) than in group 1 (1.2 ± 1.5 mm). Immediately after ACL reconstruction, however, there were no group-dependent differences in sACL-SSD. No significant group-dependent differences were found for extension deficit.

Conclusion:

Chronicity of ACLD had an effect on the preoperative tibiofemoral relationship in the sagittal plane, including ATS and sACL-SSD, especially in patients with ACLD longer than 2 years. However, preoperative extension deficit was not influenced by chronicity. Immediately postoperatively, chronicity did not affect the ability of anatomic ACL reconstruction to reduce subluxation.

Radiographic positions of femoral ACL, AM and PL centres: accuracy of guidelines based on the lateral quadrant method

PURPOSE

Femoral tunnel positioning is an important factor in anatomical ACL reconstructions. To improve accuracy, lateral radiographic support can be used to determine the correct tunnel location, applying the quadrant method. Piefer et al. (Arthroscopy 28:872-881, 2012) combined various outcomes of eight studies applying this method to one guideline. The studies included in that guideline used various insertion margins, imaging techniques and measurement methods to determine the position of the ACL centres. The question we addressed is whether condensing data from various methods into one guideline, results in a more accurate guideline than the results of one study.

METHODS

The accuracy of the Piefer's guideline was determined and compared to a guideline developed by Luites et al. (2000). For both guidelines, we quantified the mean absolute differences in positions of the actual anatomical centres of the ACL, AM and PL measured on the lateral radiographs of twelve femora with the quadrant method and the positions according to the guidelines.

RESULTS

The accuracy of Piefer's guidelines was 2.4 mm (ACL), 2.7 mm (AM) and 4.6 mm (PL), resulting in positions significantly different from the actual anatomical centres. Applying Luites' guidelines for ACL and PL resulted in positions not significantly different from the actual centres. The accuracies were 1.6 mm (ACL) and 2.2 mm (PL and AM), which were significantly different from Piefer for the PL centres, and therefore more accurate.

CONCLUSIONS

Condensing the outcomes of multiple studies using various insertion margins, imaging techniques and measurement methods, results in inaccurate guidelines for femoral ACL tunnel positioning at the lateral view.

CLINICAL RELEVANCE

An accurate femoral tunnel positioning for anatomical ACL reconstruction is a key issue. The results of this study demonstrate that averaging of various radiographic guidelines for anatomical femoral ACL tunnel placement in daily practice, can result in inaccurate tunnel positions.

LEVEL OF EVIDENCE

Diagnostic study, Level 1.

Tibial insertions of the anterior cruciate ligament and the anterior horn of the lateral meniscus: A histological and computed tomographic study

BACKGROUND

A positional relationship between the anterior cruciate ligament (ACL) and the anterior horn of the lateral meniscus (AHLM) has not previously been a topic of interest in the literature because the AHLM is already known to be obviously adjacent to the ACL and is assumed as a lateral border. The objective of this study was to investigate the positional anatomic relationship between the ACL and AHLM by histological evaluation of sequential slices and computed tomography (CT) of the tibial insertion sites.

HYPOTHESIS/PURPOSE

The ACL has a specific positional relationship with the AHLM and there is an identifiable distinct bony border between them. The position of the AHLM could be an important and useful landmark for accurate tibial tunnel positioning in anatomical ACL reconstruction.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Twelve ACL-intact knees from embalmed cadavers were used in this study. Six knees were sectioned into four slices for histologic examination in the coronal planes parallel to the AHLM alignment. Before sectioning, these knees were subjected to three-dimensional (3-D) volume-rendering CT. Each of the four slices demonstrated the insertion area of the ACL relative to the position of the AHLM. Each histologic slice was compared with the corresponding CT image. Only histological examination in the sagittal planes was performed in the other six knees.

RESULTS

The ACL fibres were broadly attached at the region anterior to the AHLM. However, the ACL and AHLM shared a clear border identifiable on the coronal CT images and appeared as a prominence of the bony ridge on the 3-D CT images. No dense ACL fibres were attached to the region posterior to the AHLM. Based on the histological data, the geometry of the ACL tibial insertion was L-shaped along the AHLM.

CONCLUSION

The ACL and AHLM have a specific positional relationship not only in the mediolateral direction but also anteroposteriorly. The AHLM serves not only as a lateral border, but also as a useful reference in an anterioposterior direction for tunnel positioning in ACL reconstruction. Specifically, the ACL fibres were found to be broadly attached onto the bony surface in the region anterior to the AHLM and there was no firm attachment of the ACL in the region posterior to the AHLM on the tibial side, which is useful in avoiding posterior tunnel placement.

The Bow Tie Shape of the Anterior Cruciate Ligament as Visualized by High-Resolution Magnetic Resonance Imaging

BACKGROUND

Although numerous studies have examined the anatomic characteristics of the anterior cruciate ligament (ACL), its actual shape remains unclear.

PURPOSE

To determine the average shape of the ACL by analyzing its cross section through the use of high-resolution magnetic resonance imaging (MRI) data.

STUDY DESIGN

Descriptive laboratory study.

METHODS

The study included 96 MRIs, conducted using a 3.0-T magnet, to analyze the shape of the ACL. Three-dimensional, curved multiplanar reconstruction was used to obtain cross sections at 7 points (femoral insertion; midsubstance 1, 2, 3, 4, and 5 from the femoral side to the tibial side; and tibial insertion). The width and thickness of cross sections were measured by 2 independent observers, and the ratio of width to thickness was calculated to determine the proportions of each cross section. The 7 cross sections were accumulated and standardized to generate an average model through the use of image analysis software developed by the authors.

RESULTS

The mean ± SD width (femoral insertion, 17.02 ± 2.17 mm; tibial insertion, 17.33 ± 2.03 mm) and thickness (femoral insertion, 11.03 ± 1.75 mm; tibial insertion, 10.09 ± 1.70 mm) of both insertions were significantly larger than those of midsubstance 4 (width, 9.99 ± 1.87 mm; thickness, 6.53 ± 1.25 mm) ( P < .001). The mean ratios of width to thickness of the 7 cross sections from femoral insertion to tibial insertion were 1.57 ± 0.23, 3.36 ± 0.57, 3.07 ± 0.81, 2.18 ± 0.54, 1.56 ± 0.32, 2.16 ± 0.48, and 1.75 ± 0.28, respectively. The shape of the cross section at midsubstance 4 was an oval isthmus, which was the most narrow and well-balanced shape. It was transformed into a wide band at midsubstance 1 and 5. The shape of the femoral insertion was semicircular, with its anterior side slightly straight and its posterior side convex. The tibial insertion was kidney bean-shaped.

CONCLUSION

On 3.0-T MRI, the ACL has a "bow tie" shape, including an oval isthmus, with a semicircular femoral insertion and kidney bean-shaped tibial insertion.

CLINICAL RELEVANCE

The measurement method will allow surgeons to quantitatively diagnose partial injuries of the ACL using a noninvasive system in actual patients.

The Anatomic Centers of the Femoral and Tibial Insertions of the Anterior Cruciate Ligament: A Systematic Review of Imaging and Cadaveric Studies Reporting Normal Center Locations

BACKGROUND

The anterior cruciate ligament (ACL) is regularly reconstructed if knee joint function is impaired. Anatomic graft tunnel placement, often assessed with varying measurement methods, in the femur and tibia is considered important for an optimal clinical outcome. A consensus on the exact location of the femoral and tibial footprint centers is lacking.

PURPOSE

To systematically review the literature regarding anatomic centers of the femoral and tibial ACL footprints and assess the mean, median, and percentiles of normal centers.

STUDY DESIGN

Systematic review.

METHODS

A systematic literature search was performed in the PubMed/Medline database in November 2015. Search terms were the following: "ACL" and "insertion anatomy" or "anatomic footprint" or "radiographic landmarks" or "quadrant methods" or "tunnel placement" or "cadaveric femoral" or "cadaveric tibial." English-language articles that reported the location of the ACL footprint according to the Bernard and Hertel grid in the femur and the Stäubli and Rauschning method in the tibia were included. Weighted means, weighted medians, and weighted 5th and 95th percentiles were calculated.

RESULTS

The initial search yielded 1393 articles. After applying the inclusion and exclusion criteria, 16 studies with measurements on cadaveric specimens or a healthy population were reviewed. The weighted mean of the femoral insertion center based on measurements in 218 knees was 29% in the deep-shallow (DS) direction and 35% in the high-low (HL) direction. The weighted median was 26% for DS and 34% for HL. The weighted 5th and 95th percentiles for DS were 24% and 37%, respectively, and for HL were 28% and 43%, respectively. The weighted mean of the tibial insertion center in the anterior-posterior direction based on measurements in 300 knees was 42%, and the weighted median was 44%; the 5th and 95th percentiles were 39% and 46%, respectively.

CONCLUSION

Our results show slight differences between the weighted means and medians in the femoral and tibial insertion centers. We recommend the use of the 5th and 95th percentiles when considering postoperative placement to be "in or out of the anatomic range."

Permanent knee sensorimotor system changes following ACL injury and surgery

The cruciate ligaments are components of the knee capsuloligamentous system providing vital neurosensory and biomechanical function. Since most historical primary ACL repair attempts were unsuccessful, reconstruction has become the preferred surgery. However, an increased understanding of the efficacy of lesion-site scaffolding, innovative suturing methods and materials, and evolving use of biological healing mediators such as platelet-rich plasma and stem cells has prompted reconsideration of what was once believed to be impossible. A growing number of in vivo animal studies and prospective clinical studies are providing increasing support for this intervention. The significance of ACL repair rather than reconstruction is that it more likely preserves the native neurosensory system, entheses, and ACL footprints. Tissue preservation combined with restored biomechanical function increases the likelihood for premorbid neuromuscular control system and dynamic knee stability recovery. This recovery should increase the potential for more patients to safely return to sports at their desired intensity and frequency. This current concepts paper revisits cruciate ligament neurosensory and neurovascular anatomy from the perspective of knee capsuloligamentous system function. Peripheral and central nerve pathways and central cortical representation mapping are also discussed. Surgical restoration of a more physiologically sound knee joint may be essential to solving the osteoarthritis dilemma. Innovative rehabilitative strategies and outcome measurement methodologies using more holistic and clinically relevant measurements that closely link biomechanical and neurosensory characteristics of physiological ACL function are discussed. Greater consideration of task-specific patient physical function and psychobehavioral links should better delineate the true efficacy of all ACL surgical and non-surgical interventions. Level of evidence IV.

Impingement following anterior cruciate ligament reconstruction: comparing the direct versus indirect femoral tunnel position

PURPOSE

During anterior cruciate ligament (ACL) reconstruction, authors have suggested inserting the femoral tunnel at the biomechanically relevant direct fibres, but this higher position can cause more impingement. Therefore, we aimed to assess ACL graft impingement at the femoral notch for ACL reconstruction at both the direct and indirect tunnel positions.

METHODS

A virtual model was created for twelve cadaveric knees with computed tomography scanning in which a virtual graft was placed at direct and indirect tunnel positions of the anteromedial bundle (AM), posterolateral bundle (PL) or centre of the both bundles (C). In these six tunnel positions, the volume (mm³) and mid-point location of impingement (°) were measured at different flexion angles.

RESULTS

Generally, more impingement was seen with the indirect position compared with the direct position although this was only significant at 90° of flexion for the AM position (97 ± 28 vs. 76 ± 20 mm³, respectively; p = 0.046). The direct tunnel position impinged higher at the notch, whereas the indirect position impinged more towards the lateral wall, but this was only significant at 90° of flexion for the AM (24 ± 5° vs. 34 ± 4°, respectively; p < 0.001) and C position (34 ± 5° vs. 42 ± 5°, respectively; p = 0.003).

CONCLUSION

In this cadaveric study, the direct tunnel position did not cause more impingement than the indirect tunnel position. Based on these results, graft impingement is not a limitation to reconstruct the femoral tunnel at the insertion of the biomechanically more relevant direct fibres.

Is Remnant Preservation Truly Beneficial to Anterior Cruciate Ligament Reconstruction Healing? Clinical and Magnetic Resonance Imaging Evaluations of Remnant-Preserved Reconstruction

BACKGROUND

Remnant-preserved anterior cruciate ligament (ACL) reconstruction was introduced to improve clinical outcomes and biological healing. However, the effects of remnant preservation and the influence of the delay from injury until reconstruction on the outcomes of this technique are still uncertain. Purpose/Hypothesis: The purposes of this study were to evaluate whether remnant preservation improved the clinical outcomes and graft incorporation of ACL reconstruction and to examine the influence of the delay between ACL injury and reconstruction on the usefulness of remnant preservation. We hypothesized that remnant preservation improves clinical results and accelerates graft incorporation and that its effect is dependent on the delay between ACL injury and reconstruction.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

A total of 151 consecutive patients who underwent double-bundle ACL reconstruction using a semitendinosus graft were enrolled in this study: 74 knees underwent ACL reconstruction without a remnant (or the remnant was <25% of the intra-articular portion of the graft; NR group), while 77 knees underwent ACL reconstruction with remnant preservation (RP group). These were divided into 4 subgroups based on the time from injury to surgery: phase 1 was <3 weeks (n = 24), phase 2 was 3 to less than 8 weeks (n = 70), phase 3 was 8 to 20 weeks (n = 32), and phase 4 was >20 weeks (n = 25). Clinical measurements, including KT-1000 arthrometer side-to-side anterior tibial translation measurements, were assessed at 3, 6, 12, and 24 months after reconstruction. Magnetic resonance imaging evaluations of graft maturation and graft-tunnel integration of the anteromedial and posterolateral bundles were assessed at 3, 6, and 12 months after reconstruction.

RESULTS

There was no difference in side-to-side anterior tibial translation between the NR and RP groups. There was also no difference in graft maturation between the 2 groups. Furthermore, the time from ACL injury until reconstruction did not affect graft maturation, except in the case of very long delays before reconstruction (phase 4). Graft-tunnel integration was significantly increased in both groups in a time-dependent manner. However, there was no difference between the NR and RP groups.

CONCLUSION

Remnant preservation did not improve knee stability at 2 years after ACL reconstruction. Furthermore, remnant preservation did not accelerate graft incorporation, especially during the acute and subacute injury phases.

Anterior cruciate ligament reconstruction: principles of treatment

Anterior cruciate ligament (ACL) reconstruction is one of the most common procedures in sports medicine. Several areas of controversy exist in ACL tear management which have engaged surgeons and researchers in debates towards identifying an ideal approach for these patients.

This instructional review discusses the principles of ACL reconstruction in an attempt to provide guidelines and initiate a critical thinking approach on the most common areas of controversy regarding ACL reconstruction.

Using high-level evidence from the literature, as presented in randomised controlled trials, systematic reviews, and meta-analyses, operative versus conservative treatment, timing of surgery, and rehabilitation are discussed. Also, the advantages and disadvantages of the most common types of autografts, such as patellar tendon and hamstrings as well as allografts are presented.

Key considerations for the anatomical, histological, biomechanical and clinical data (‘IDEAL’) graft positioning are reviewed.

Cite this article: Paschos NK, Howell SM. Anterior cruciate ligament reconstruction: principles of treatment. EFORT Open Rev 2016;398-408. DOI: 10.1302/2058-5241.1.160032.

Cortical Bony Thickening of the Lateral Intercondylar Wall: The Functional Attachment of the Anterior Cruciate Ligament

BACKGROUND

The anatomy of the anterior cruciate ligament (ACL) has become the subject of much debate. There has been extensive study into attachment points of the native ligament, especially regarding the femoral attachment. Some of these studies have suggested that fibers in the ACL are of differing functional importance. Fibers with higher functional importance would be expected to exert larger mechanical stress on the bone. According to Wolff's law, cortical thickening would be expected in these areas.

PURPOSE

To examine cortical thickening in the region of the ACL footprint (ie, the functional footprint of the ACL).

STUDY DESIGN

Descriptive laboratory study.

METHODS

Using micro-computed tomography with resolutions ranging from 71 to 91 μm, the cortical thickness of the lateral wall of the intercondylar notch in 17 cadaveric knees was examined, along with surface topography. After image processing, the relationship between the cortical thickening and surface topology was visually compared.

RESULTS

A pattern of cortical thickening consistent with the functional footprint of the ACL was found. On average, this area was 3 times thicker than the surrounding bone and significantly thicker than the remaining lateral wall ( P < .0001). This thickening was roughly elliptical in shape (with a mean centroid at 23.5 h:31 t on a Bernard and Hertel grid) and had areas higher on the wall where greater thickness was present. The relationship to previously reported osseous landmarks was variable, although the patterns were broadly consistent with those reported in previous studies describing direct and indirect fibers of the ACL.

CONCLUSION

The findings of this study are consistent with those of recent studies describing fibers in the ACL of differing functional importance. The area in which the thickening was found has been defined and is likely to represent the functional footprint of the ACL.

CLINICAL RELEVANCE

This information is of value to surgeons when determining the optimal place to position the femoral attachment site of the reconstructed ACL.

Direct versus indirect ACL femoral attachment fibres and their implications on ACL graft placement

PURPOSE

To further elucidate the direct and indirect fibre insertion morphology within the human ACL femoral attachment using scanning electron microscopy and determine where in the footprint each fibre type predominates. The hypothesis was that direct fibre attachment would be found centrally in the insertion site, while indirect fibre attachment would be found posteriorly adjacent to the posterior articular cartilage.

METHODS

Ten cadaveric knees were dissected to preserve and isolate the entirety of the femoral insertion of the ACL. Specimens were then prepared and evaluated with scanning electron microscopy to determine insertional fibre morphology and location.

RESULTS

The entirety of the fan-like projection of the ACL attachment site lay posterior to the lateral intercondylar ridge. In all specimens, a four-phase architecture, consistent with previous descriptions of direct fibres, was found in the centre of the femoral attachment site. The posterior margin of the ACL attachment attached directly adjacent to the posterior articular cartilage with some fibres coursing into it. The posterior portion of the ACL insertion had a two-phase insertion, consistent with previous descriptions of indirect fibres. The transition from the ligament fibres to bone had less interdigitations, and the interdigitations were significantly smaller (p < 0.001) compared to the transition in the direct fibre area. The interdigitations of the direct fibres were 387 ± 81 μm (range 282-515 μm) wide, while the interdigitations of indirect fibres measured 228 ± 75 μm (range 89-331 μm).

CONCLUSIONS

The centre of the ACL femoral attachment consisted of a direct fibre structure, while the posterior portion had an indirect fibre structure. These results support previous animal studies reporting that the centre of the ACL femoral insertion was comprised of the strongest reported fibre type. Clinically, the femoral ACL reconstruction tunnel should be oriented to cover the entirety of the central direct ACL fibres and may need to be customized based on graft type and the fixation device used during surgery.

Management of Anterior Cruciate Ligament Injury: What's In and What's Out?

Sports medicine physicians have a keen clinical and research interest in the anterior cruciate ligament (ACL). The biomechanical, biologic, and clinical data researchers generate, help drive injury management and prevention practices globally. The current concepts in ACL injury and surgery are being shaped by technological advances, expansion in basic science research, resurging interest in ACL preservation, and expanding efforts regarding injury prevention. As new methods are being developed in this field, the primary goal of safely improving patient outcomes will be a unifying principle. With this review, we provide an overview of topics currently in controversy or debate, and we identify paradigm shifts in the understanding, management, and prevention of ACL tears.

A Multibody Knee Model Corroborates Subject-Specific Experimental Measurements of Low Ligament Forces and Kinematic Coupling During Passive Flexion

A multibody model of the knee was developed and the predicted ligament forces and kinematics during passive flexion corroborated subject-specific measurements obtained from a human cadaveric knee that was tested using a robotic manipulator. The model incorporated a novel strategy to estimate the slack length of ligament fibers based on experimentally measured ligament forces at full extension and included multifiber representations for the cruciates. The model captured experimentally measured ligament forces (≤ 5.7 N root mean square (RMS) difference), coupled internal rotation (≤ 1.6 deg RMS difference), and coupled anterior translation (≤ 0.4 mm RMS difference) through 130 deg of passive flexion. This integrated framework of model and experiment improves our understanding of how passive structures, such as ligaments and articular geometries, interact to generate knee kinematics and ligament forces.

Synovial C-Shaped Tibial Footprint of the Anterior Cruciate Ligament

Background:

Although numerous anatomic studies about the anterior cruciate ligament (ACL) structure and attachments have been performed, these studies have not reached consensus on the ACL footprint.

Purpose:

To investigate the existing controversy regarding the morphology of the tibial ACL insertion (footprint) and confirm histologically that the tibial ACL footprint is not completely filled with ligament tissue.

Study Design:

Descriptive laboratory study.

Methods:

The tibial ACL footprint was dissected from 20 different fresh-frozen cadaveric knees (all males; mean age, 68.8 ± 5.4 years [range, 55-80 years]; mean weight, 78 ± 6.6 kg [range, 45-93 kg]). Two knees, 1 with severe osteoarthritis and 1 with previous knee surgery, were excluded. The tibial ACL insertion was observed, and this area was longitudinally divided into 4 parallel slices (0%-25%, 25-50%, 50%-75%, and 75%-100%), embedded in paraffin wax, and stained with hematoxylin-eosin, alcian blue, and picrosirius-polarization. The specimens were measured using a microscope to determine the distances from the anterior to the posterior border of the ACL ligament tibial insertion and the distance from the posterior border to the end of the ligament fibers of the ACL ligament tibial insertions.

Results:

The 18 evaluated knee specimens confirmed the finding of a C-shaped tibial insertion of the ACL. The measurements showed that the ligament (vertical parallel collagen fibers) occupied only 30.8% of the complete insertion. The remaining area was filled with synovial tissue, demonstrating histologically the “C” shape.

Conclusion:

This study confirms macroscopically the C-shaped tibial insertion of the ACL and shows histologically that synovial tissue is an indirect insertion filling the major part of the footprint.

Clinical Relevance:

This anatomic study suggests a different shape of the ACL tibial footprint, which may be useful for new perspectives regarding ACL reconstruction surgery research.

Computed tomography value and tunnel enlargement of round and rounded rectangular femoral bone tunnel for anterior cruciate ligament reconstruction

INTRODUCTION

We developed a novel technique for anatomical single-bundle anterior cruciate ligament (ACL) reconstruction: creation of a rounded rectangular femoral bone tunnel. The purpose of this study was to compare the computed tomography (CT) value and tunnel enlargement ratio of the femoral bone tunnel with those of round tunnel ACL reconstruction.

MATERIALS AND METHODS

We included 39 knees that underwent round tunnel ACL reconstruction and 42 that underwent rounded rectangular ACL reconstruction. To evaluate the CT value, we compared the CT images approximately 1 week after surgery. Making a parallel slice toward the opening of bone tunnels to a depth of 3 mm, we evaluated the CT value of eight directions in the bone tunnel wall. To evaluate tunnel enlargement, we compared CT images approximately 1 week after surgery with images taken 3 months after surgery. Using a parallel slice toward the opening of the bone tunnel, we measured the bone tunnel area and calculated the tunnel enlargement ratio. The level of significance was P < 0.05, and the t test was used for statistical analyses.

RESULTS

The CT value was significantly increased for the rounded rectangular tunnel in comparison with the round tunnel in almost all directions (P < 0.05). The rounded rectangular tunnel area enlargement ratio was significantly lower (round, 110 ± 38 %; rounded rectangular, 73 ± 37 %; P = 0.001).

CONCLUSION

The rounded rectangular tunnel could have a compression effect on the cancellous bone and reduce enlargement of the bone tunnel.

The cross-sectional shape of the fourfold semitendinosus tendon is oval, not round

BACKGROUND

The looped side of the semitendinosus tendon (ST) graft (i.e., the side inserted into the femoral tunnel during anterior cruciate ligament reconstruction) appears to be oval rather than round. The purpose of this study was to investigate the cross section of the fourfold semitendinosus tendon graft and, more specifically, the differences in pressure exerted by a rounded rectangular tunnel versus a round femoral tunnel.

METHODS

Seven STs were harvested from cadaveric knees and a fourfold ST graft was made. Aluminum cubes with round or rectangular tunnels containing four-way pressure-sensitive conductive sensors (vertically and bilaterally) were used. The area of both cubes was the same. The graft was inserted into the tunnels 15 mm from the looped edge. After measuring pressure, the graft was fixed using ultraviolet-curing acrylic resin and was cut at 7.5 mm and 15 mm from the lapel edge. The area, axes for the best fitting ellipse of the cross-section, and ellipticity of the axes were measured.

RESULTS

In the round tunnel, the mean contact pressure was 287.0 ± 136.7 gf at the bilateral sensor; there was no contact pressure detected by the vertical sensor. In the rounded rectangular tunnel, the mean contact pressure was 260.9 ± 186.4 gf at the bilateral sensor and 352.9 ± 49.5 gf at the vertical sensor. Ellipticity was 1.25 ± 0.13 at 7.5 mm, and 1.17 ± 0.07 at 15 mm from the lapel edge of the graft.

CONCLUSIONS

The cross-sectional shape of the fourfold ST graft was not round, but oval. Moreover, the rounded rectangular tunnel was more fitted to the graft than the round tunnel.

ACL Fibers Near the Lateral Intercondylar Ridge Are the Most Load Bearing During Stability Examinations and Isometric Through Passive Flexion

BACKGROUND

The femoral insertion of the anterior cruciate ligament (ACL) has direct and indirect fiber types located within the respective high (anterior) and low (posterior) regions of the femoral footprint.

HYPOTHESIS

The fibers in the high region of the ACL footprint carry more force and are more isometric than the fibers in the low region of the ACL footprint.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten fresh-frozen cadaveric knees were mounted to a robotic manipulator. A 134-N anterior force at 30° and 90° of flexion and combined valgus (8 N·m) and internal (4 N·m) rotation torques at 15° of flexion were applied simulating tests of anterior and rotatory stability. The ACL was sectioned at the femoral footprint by detaching either the higher band of fibers neighboring the lateral intercondylar ridge in the region of the direct insertion or the posterior, crescent-shaped fibers in the region of the indirect insertion, followed by the remainder of the ACL. The kinematics of the ACL-intact knee was replayed, and the reduction in force due to each sectioned portion of insertion fibers was measured. Isometry was assessed at anteromedial, center, and posterolateral locations within the high and low regions of the femoral footprint.

RESULTS

With an anterior tibial force at 30° of flexion, the high fibers carried 83.9% of the total anterior ACL load compared with 16.1% in the low fibers (P < .001). The high fibers also carried more anterior force than the low fibers at 90° of flexion (95.2% vs 4.8%; P < .001). Under combined torques at 15° of flexion, the high fibers carried 84.2% of the anterior ACL force compared with 15.8% in the low fibers (P < .001). Virtual ACL fibers placed at the anteromedial portion of the high region of the femoral footprint were the most isometric, with a maximum length change of 3.9 ± 1.5 mm.

CONCLUSION

ACL fibers located high within the femoral footprint bear more force during stability testing and are more isometric during flexion than low fibers.

CLINICAL RELEVANCE

It may be advantageous to create a "higher" femoral tunnel during ACL reconstruction at the lateral intercondylar ridge.

Behind-remnant arthroscopic observation and scoring of femoral attachment of injured anterior cruciate ligament

PURPOSE

To describe the femoral anterior cruciate ligament (ACL) attachment based on the behind-remnant observation with a new scoring system and to investigate the characteristics of an ACL injured knee.

METHODS

One hundred and twenty-six ACL injured knees with four standardized arthroscopic photos and full evaluation under anaesthesia were included in the study. Sixty non-ACL injured knees were also evaluated as control. A scoring system for the femoral ACL attachment was set as follows based on behind-remnant findings; the direct insertion was divided into three portions as proximal, middle and distal. The fibrous extension from the articular surface (indirect insertion) and the severity of synovitis were also graded into 2, 1 and 0 points. The total score was 10 as full marks. The correlation between each score and total score, as well as age at surgery, gender, anterior laxity, pivot-shift test and meniscus injuries, was statistically evaluated with a significance of 0.05.

RESULTS

The femoral attachment score of the ACL injured knees was statistically different from that of the non-ACL injured knees. Anterior laxity was dependent only on the integrity of the proximal portion. Knee instability was significantly correlated with the status of the direct insertion. Medial and lateral meniscus injuries were correlated with the middle part and the distal part of the direct insertion, respectively. The direct insertion was less preserved in distal and articular sides.

CONCLUSION

Arthroscopic observation behind the remnant of the injured ACL showed clearer findings of the femoral attachment than that from the front. Behind-remnant observation greatly assists in the creation of a correct anatomical tunnel with the preserving remnant. The scoring system indicated several significant correlations between the score and preoperative patient status.

The ACL Graft Has Different Cross-sectional Dimensions Compared With the Native ACL: Implications for Graft Impingement

BACKGROUND

Impingement of anterior cruciate ligament (ACL) grafts against the femoral notch and the posterior cruciate ligament (PCL) is thought to be influenced primarily by tunnel position and graft orientation. Recent data have implied that the native ACL is ribbon-shaped.

PURPOSE

To evaluate the 3-dimensional shape and cross-sectional area of the native ACL versus the ACL graft and to compare the degree of impingement against the femoral notch and PCL.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Bilateral knee magnetic resonance images were analyzed for 27 patients with unilateral bone-patellar tendon-bone (BPTB) ACL reconstruction performed via transtibial or anteromedial portal femoral tunneling techniques. Three-dimensional models of the ACL, PCL, femur, and tibia were digitally rendered. The cross-sectional area and dimensions of the native ACL and the reconstructed graft were determined at 3 equally spaced locations and compared via Wilcoxon-Mann-Whitney and Kruskal-Wallis tests. In addition, impingement of the ACL on the PCL and femoral notch was graded in 3 groups. Chi-square or Fisher exact tests were used to compare the proportional differences of impingement of the native and reconstructed ACL on the PCL and femoral notch, respectively. All analyses were performed using 2-sided hypothesis testing, with statistical significance at P < .05.

RESULTS

Cross-sectional areas at all 3 points on the ACL graft were significantly greater than those of the native ACL (P < .001). The long- to short-axis ratio for the native ACL was significantly greater at each location compared with the corresponding locations along the ACL graft (P < .001), implying that the native ACL is "flatter" than is an ACL graft. There were 19 operated knees (70%) with contact or impingement between the ACL graft and the femoral notch compared with zero knees with a native ACL (P < .001). In addition, 22 operated knees (81%) showed contact or impingement between the ACL graft and the PCL, compared with 7 knees (26%) with a native ACL (P < .001). No significant differences in impingement frequency were noted between the transtibial and anteromedial tunneling techniques for ACL graft specimens (P > .05).

CONCLUSION

Native ACLs have a smaller cross-sectional area, are "flatter," and experience less incidence of impingement compared with anatomically placed BPTB ACL grafts.

A Systematic Review of Anterior Cruciate Ligament Femoral Footprint Location Evaluated by Quadrant Method for Single-Bundle and Double-Bundle Anatomic Reconstruction

PURPOSE

To unravel the standard position of anterior cruciate ligament (ACL) femoral origin and deduce practical arthroscopic localization and postsurgical evaluation method.

METHODS

Two independent reviewers searched PubMed using the terms ACL, footprint, femur, etc. We included studies published since January 1, 2000, in which the results were measured by Bernard's quadrant method. This method consists of 4 distances, including total diameter of lateral condyle along Blumensaat's line (distance t), maximum intercondylar notch height (distance h), distance from center of footprint to proximal border (distance x), and distance from center of footprint to Blumensaat's line (distance y). The data of included studies were combined to calculate theoretical centers and standard area for both ACL as a whole bundle and as anteromedial (AM) and posterolateral (PL) bundles individually. Finally, we translated the combined data to arthroscopic localization and postsurgical evaluation.

RESULTS

A total of 13 studies were included. The theoretical centers of ACL as a whole bundle is 28.4% ± 5.1% (x) of distance t and 35.7% ± 6.9% (y) of distance h, whereas AM bundle is 24.2% ± 4%, 21.6% ± 5.2% (x, y) and PL bundle is 32.8% ± 4.7%, 46.7% ± 4.9% (x, y), respectively. The standard area of ACL footprint is a circle with a center of 27.53%, 35.85% (x, y), and a radius of 4.58%, 9.2% (x, y), respectively. Translation of combined data shows that under arthroscopy, for single-bundle ACL reconstruction, the midpoint of distance from border of proximal to distal articular cartilage is the center of anatomic femoral socket.

CONCLUSIONS

Combined data unravel the standard position of ACL femoral origin. It can be used by clinicians to localize anatomic tunnel both in surgery and postsurgical evaluation. For single-bundle ACL reconstruction, the midpoint of lateral femoral condyle corresponds to anatomic socket.

LEVEL OF EVIDENCE

Level V, systematic review of anatomic studies.

On the heterogeneity of the femoral enthesis of the human ACL: microscopic anatomy and clinical implications

BACKGROUND

Most ruptures of the native anterior cruciate ligament (ACL) and ACL graft occur at, or near, the femoral enthesis, with the posterolateral fibers of the native ligament being especially vulnerable during pivot landings. Characterizing the anatomy of the ACL femoral enthesis may help us explain injury patterns which, in turn, could help guide injury prevention efforts. It may also lead to improved anatomic reconstruction techniques given that the goal of such techniques is to replicate the knee's normal anatomy. Hence, the aim of this study was to investigate the microscopic anatomy of the ACL femoral enthesis and determine whether regional differences exist.

METHODS

Fifteen human ACL femoral entheses were histochemically processed and sectioned along the longitudinal axis of the ACL at 20, 40, 60, and 80 % of the width of the enthesis. Four thick sections (100 μm) per enthesis were prepared, stained, and digitized. From these sections, regional variations in the quantity of calcified and uncalcified fibrocartilage, the angle at which the ligament originates from the bone, and the shape profile of the tidemark were quantified.

RESULTS

At least 33 % more calcified fibrocartilage and 143 % more uncalcified fibrocartilage were found in the antero-inferior region, which corresponds to the inferior margin of the origin of the anteromedial ACL fibers, than all other regions (Ps < 0.05). In addition, the anteromedial fibers of the ACL originated from the femur at an angle six times greater than did its posterolateral fibers (P = 0.032). Finally, average entheseal tidemark profiles correlated bilaterally (Pearson's r = 0.79; P = 0.036), the most common profile being convex with a single re-entrant.

CONCLUSIONS

Systematic regional differences were found in fibrocartilage quantity and collagen fiber attachment angles. The marked differences may reflect differences in the loading history of the various regions of the ACL femoral enthesis. These differences, which could affect the potential for injury, should also be considered when developing new ACL reconstruction approaches.

Height and Depth Guidelines for Anatomic Femoral Tunnels in Anterior Cruciate Ligament Reconstruction: A Cadaveric Study

PURPOSE

To develop guidelines for femoral tunnel placement based on height and depth on the lateral wall of the notch and to apply these guidelines arthroscopically to show tunnel placements within the anterior cruciate ligament (ACL) femoral insertion site.

METHODS

Twelve cadaveric knees were dissected to define the centers of the femoral ACL attachment and its anteromedial (AM) and posterolateral (PL) bundles. In 90° of flexion, the height and depth of each center were determined relative to the low point on the lateral intercondylar notch. Radiographic grid measurements were made to validate these measurements. Subsequently, the measurement guidelines were applied arthroscopically in 10 new cadaveric knees to evaluate their accuracy for an anatomic single-bundle femoral tunnel. Interobserver reliability analysis was evaluated with the intraclass correlation coefficient.

RESULTS

In 90° of flexion, the height of the ACL center was 8.7 ± 0.6 mm from the low point of the lateral notch; PL center, 7.2 ± 1.2 mm; and AM center, 9.6 ± 1.1 mm. Relative to the low point, the ACL center was 1.7 ± 1.7 mm posterior, the PL center was 3.4 ± 1.5 mm anterior, and the AM center was 4.9 ± 1.7 mm posterior (intraclass correlation coefficient, 0.859). Radiographic grid measurements were consistent with the direct measurements. Application of the guidelines arthroscopically with or without the assistance of a 7-mm offset aimer placed all guide pins for tunnels within the femoral ACL footprint, with 90% within 4 mm of the ACL center.

CONCLUSIONS

This study showed in cadaveric knees in 90° of flexion that the center of the ACL can be located on the lateral notch at a height of 8.7 ± 0.6 mm from the lowest point and anterior 11.5 ± 1.3 mm from the deepest point. How anatomic tunnels can be placed using these measurements was also shown in cadaveric knees.

CLINICAL RELEVANCE

An anatomic femoral tunnel for ACL reconstruction can be placed using height and depth guidelines.

Prospective Randomized Study of Objective and Subjective Clinical Results Between Double-Bundle and Single-Bundle Anterior Cruciate Ligament Reconstruction

BACKGROUND

There is controversy as to whether double-bundle anterior cruciate ligament (ACL) reconstruction with hamstring tendon graft (DB-HT) or single-bundle ACL reconstruction with patellar tendon graft (SB-PT) obtains the best clinical outcomes.

PURPOSE

To compare the short-term clinical outcomes of DB-HT with those of rectangular-tunnel SB-PT (RTSB-PT) at 2-year follow-up and to identify the factors that affect subjective knee functional score.

STUDY DESIGN

Randomized controlled trial. Level of evidence, 1.

METHODS

Sixty-three male patients (mean age, 26.1 years) and 87 female patients (mean age, 25.8 years) were included in this study and were randomly distributed to either the DB-HT (n = 76) or RTSB-PT (n = 74) group. Clinical outcomes (knee flexion range of motion [ROM], heel-height difference, side-to-side difference in anterior laxity, rotational laxity, and Tegner activity score) were compared between the DB-HT and RTSB-PT groups, and examination of factors affecting subjective outcomes (Knee Injury and Osteoarthritis and Outcome Score [KOOS] results) was performed by multiple linear regression analysis.

RESULTS

Fourteen patients (9 DB-HT, 5 RTSB-PT) had secondary ACL injury within 2 years after primary ACL reconstruction and were excluded from analysis. In the examination of 136 patients at the 24-month follow-up, there was no significant difference between the 2 groups in clinical or subjective outcomes. The normalized knee extensor strength of the RTSB-PT group showed negative surgical technique effect in the early postoperative phase (P = .005), but there was no significant difference between the 2 groups at the 24-month follow-up (P = .114). There was no significant difference in change of normalized knee flexor strength between the 2 groups (P = .493). Age, sex, body mass index (BMI), and presence of meniscus injury were the factors that affected KOOS subscale scores.

CONCLUSION

In this prospective randomized controlled study, there was no significant difference in the incidence of secondary ACL injury and no difference in objective or subjective outcomes between the DB-HT and RTSB-PT reconstruction at 24-month follow-up. Age, sex, presence of meniscus injury, and BMI affected subjective KOOS subscale scores, while surgical technique did not.

Biomechanics of the anterior cruciate ligament: Physiology, rupture and reconstruction techniques

The influences and mechanisms of the physiology, rupture and reconstruction of the anterior cruciate ligament (ACL) on kinematics and clinical outcomes have been investigated in many biomechanical and clinical studies over the last several decades. The knee is a complex joint with shifting contact points, pressures and axes that are affected when a ligament is injured. The ACL, as one of the intra-articular ligaments, has a strong influence on the resulting kinematics. Often, other meniscal or ligamentous injuries accompany ACL ruptures and further deteriorate the resulting kinematics and clinical outcomes. Knowing the surgical options, anatomic relations and current evidence to restore ACL function and considering the influence of concomitant injuries on resulting kinematics to restore full function can together help to achieve an optimal outcome.

Technique of anatomical single bundle ACL reconstruction with rounded rectangle femoral dilator

BACKGROUND

This study aimed to present a new technique for anatomical single bundle anterior cruciate ligament (ACL) reconstruction. We developed an original rounded rectangular dilator set to create rounded rectangular femoral tunnels. This technique can increase the femoral tunnel size without roof impingement, and has the potential to reduce the graft failure rate. We investigated the tunnel position and the incidence of intraoperative complications.

METHOD

The presented technique is anatomical single bundle ACL reconstruction using a semitendinosus graft (with or without the gracilis tendon). The tunnel was drilled via an additional medial portal. Rounded rectangular tunnels were created using a special dilator. Tibial tunnels were created using conventional rounded tunnels. Fixation was achieved using a suspensory device on the femoral side and a plate and screw on the tibial side.

PATIENTS

Fifty patients underwent this surgery, and intraoperative complications were investigated. The femoral tunnel positions were documented postoperatively from computed tomography scans using the quadrant method. The tibial tunnel positions (anterior-to-posterior, medial-to-lateral) were documented using intraoperative X-ray scans.

RESULTS

Only one patient had a partial posterior tunnel wall blowout. The femoral tunnel length varied between 30 and 40mm (mean, 34.9±3.3mm). All femoral and tibial tunnels were located within the area of the anatomical ACL insertions.

CONCLUSION

We did not experience any serious intraoperative complications during anatomical single bundle ACL reconstruction using a rounded rectangle dilator, and the resulting locations of the femoral and tibial tunnels were within the anatomical ACL footprint.

LEVEL OF EVIDENCE

Level IV.

A new behind-remnant approach for remnant-preserving double-bundle anterior cruciate ligament reconstruction compared with a standard approach

PURPOSE

To introduce a new behind-remnant approach for double-bundle (DB) anterior cruciate ligament (ACL) reconstruction and to compare the femoral tunnel positions of anteromedial (AM) and posterolateral (PL) bundles between the new and standard procedures by a three-dimensional computed tomography (3D-CT).

METHODS

During DB ACL reconstruction, two approaches for femoral tunnel creation were consecutively practiced from 2010 to 2012. The patients were evaluated retrospectively as a cohort study. A total of 200 primary ACL reconstructions have been performed using a transtibial approach. One approach was a standard approach from the front in which the ACL remnant was peeled off from the attachment, and two guide wires were inserted based on anatomic bony landmarks (standard group). The other approach was a new behind-remnant approach in which the ACL remnant was kept untouched and two guide wires were inserted at the posterior margin of the direct ACL insertion (behind-remnant group). The position of the AM and PL femoral tunnels was expressed on a 3D-CT reconstructive image using the quadrant method with a statistical analysis.

RESULTS

The depth of the AM center was 24 ± 6 % (mean and standard deviation) in the standard group and 22 ± 5 % in the behind-remnant group. The height of the AM tunnel center was 22 ± 8 % in the standard group and 31 ± 8 % in the behind-remnant group. The depth of the PL tunnel center was 32 ± 6 % in the standard group and 35 ± 5 % in the behind-remnant group. The height of the PL tunnel center was 47 ± 9 % in the standard group and 55 ± 7 % in the behind-remnant group. The AM and PL femoral tunnels in both groups were created within the normal anatomic footprint of the previous studies. The behind-remnant approach created a significantly lower femoral tunnel for both AM (p = 0.000) and PL tunnels (p = 0.000). The depth of both AM and PL tunnels was not significantly different between the two groups (n.s.).

CONCLUSION

The new behind-remnant procedure is technically simple and reproducible as a remnant-preserving ACL reconstruction.

LEVEL OF EVIDENCE

Cohort study, Level III.

Quantitative comparison of the microscopic anatomy of the human ACL femoral and tibial entheses

The femoral enthesis of the human anterior cruciate ligament (ACL) is known to be more susceptible to injury than the tibial enthesis. To determine whether anatomic differences might help explain this difference, we quantified the microscopic appearance of both entheses in 15 unembalmed knee specimens using light microscopy, toluidine blue stain and image analysis. The amount of calcified fibrocartilage and uncalcified fibrocartilage, and the ligament entheseal attachment angle were then compared between the femoral and tibial entheses via linear mixed-effects models. The results showed marked differences in anatomy between the two entheses. The femoral enthesis exhibited a 3.9-fold more acute ligament attachment angle than the tibial enthesis (p<0.001), a 43% greater calcified fibrocartilage tissue area (p<0.001), and a 226% greater uncalcified fibrocartilage depth (p<0.001), with the latter differences being particularly pronounced in the central region. We conclude that the ACL femoral enthesis has more fibrocartilage and a more acute ligament attachment angle than the tibial enthesis, which provides insight into why it is more vulnerable to failure.

Evaluation of a behind-remnant approach for femoral tunnel creation in remnant-preserving double-bundle anterior cruciate ligament reconstruction - Comparison with a standard approach

PURPOSE

To evaluate a novel approach for femoral tunnel creation, a behind-remnant approach, in remnant-preserving double-bundle anterior cruciate ligament (ACL) reconstruction through comparison with a standard approach.

METHODS

Sixty patients who underwent remnant-preserving double-bundle ACL reconstruction were included. Thirty patients with a standard approach were classified as the standard group, and 30 patients with a behind-remnant approach as the behind-remnant (BR) group. The anteromedial bundle (AMB) and posterolateral bundle (PLB) were provisionally fixed at 20° and 45° of flexion to a graft tensioning system during surgery. Bundle tension was recorded during knee flexion-extension and in response to anterior or rotatory loads. Femoral tunnel positions were then assessed using the quadrant method.

RESULTS

During flexion-extension, the BR group showed equivalent tension curves between AMB and PLB, while the standard group showed reciprocal tension curves. The tension on the PLB was lower than the AMB in response to anterior or rotatory loads in the BR group, while the AMB and PLB shared equivalent loads in the standard group. Tunnel position of the AMB in the BR group was lower and deeper, with smaller variances, than that in the standard group. Tunnel position of the PLB in the BR group was lower than that in the standard group.

CONCLUSIONS

In remnant-preserving double-bundle ACL reconstruction, a behind-remnant approach can be achieved without any removal of the remnant tissue, and could create a deeper and lower AMB tunnel and a lower PLB tunnel with higher reproducibility, showing equivalent tension curves between the AMB and PLB.

Relationship between femoral tunnel location and graft bending angle in outside-in and transportal technique for ACL double bundle reconstruction in 3D-CT study

INTRODUCTION

In anterior cruciate ligament (ACL) reconstruction, sharp angulation of the graft at tunnel aperture increases local strain to the graft. The purpose of this study is to investigate the relationship between femoral tunnel location and femoral graft bending angle after ACL double bundle reconstruction (ACL-DBR) with two different drilling techniques.

MATERIALS AND METHODS

In ACL-DBR, femoral tunnel was created by two techniques; outside-in technique (26 patients, group A) and transportal technique (25 patients, group B). CT scan was taken at 1 week postoperatively. The position of femoral tunnel exit on the lateral femoral cortex, and intra-articular femoral and tibial tunnel aperture of the anteromedial bundle (AMB) and postero-lateral bundle (PLB) was measured using a rectangular frame on three-dimensional CT images. Femoral graft bending angle was measured using two-dimensional CT images.

RESULTS

Femoral tunnel exits of AMB and PLB in group A were significantly anterior and proximal than those in group B (p < 0.05), while there was no significant difference in intra-articular femoral and tibial tunnel apertures between group A and B. A mean femoral graft bending angle of AMB was 80.3° in group A and 69.2 degrees in group B, respectively (p < 0.05). A mean femoral graft bending angle of PLB was 66.3° in group A and 64.6° in group B, respectively. In both groups, a significant (p < 0.05) correlation (r < -0.4) was observed between the position of the femoral tunnel exit (anterior-posterior ratio from femoral anterior border line) and the femoral graft bending angle in AMB.

CONCLUSIONS

Since the femoral tunnel exit in outside-in technique was located more anterior and proximal, femoral graft bending angle of AMB in outside-in technique was greater than that in transportal technique. Anterior position of the femoral tunnel exit in AMB increased femoral graft bending angle in outside-in and transportal techniques.

Twenty-Year Experience of a Double-Bundle Anterior Cruciate Ligament Reconstruction

Double-bundle (DB) anterior cruciate ligament (ACL) reconstruction using a four-strand semitendinosus tendon was started in our department in July 1994. The motivation for starting the procedure was that the EndoButton with an inside-out procedure instrument became available in Japan. A review article of our DB ACL reconstruction procedure was summarized for the twentieth anniversary of the surgical procedure. Initial tension setting of the two grafts was changed in the first 8 years to achieve better stability during DB ACL reconstruction. A randomized clinical trial (RCT) was started in July 2002 to clarify superiority of the DB procedure to single-bundle (SB) reconstruction under the concept of anatomic reconstruction. Several anatomic studies were performed to describe normal ACL anatomy, which is essential for realizing anatomic reconstruction. A remnant-preserving technique would be an additional option for our DB procedure to improve reconstruction outcomes. Thus, a new remnant-preserving DB procedure was started in 2012. The reproducibility of the new procedure was investigated using three-dimensional computed tomography images. More complex procedures were performed using a transtibial technique and EndoButtons. Initial tension balancing between the two grafts was important for a better outcome. Superiority of knee stability after the DB compared to that after the SB procedure was clarified by the RCT. However, no patient consensus has been reached on any subjective advantage to the DB procedure. Studies of normal ACL anatomy have left questions unresolved regarding where the two tunnels should be created for direct and indirect insertions based on normal anatomy. A new remnant-preserving DB ACL procedure has been practiced. The procedure was more reproducible with respect to creating the femoral tunnel. DB ACL reconstruction using a semitendinosus tendon is an attractive option when pursuing a better outcome for patients.

The role of fibers in the femoral attachment of the anterior cruciate ligament in resisting tibial displacement

PURPOSE

The purpose was to clarify the load-bearing functions of the fibers of the femoral anterior cruciate ligament (ACL) attachment in resisting tibial anterior drawer and rotation.

METHODS

A sequential cutting study was performed on 8 fresh-frozen human knees. The femoral attachment of the ACL was divided into a central area that had dense fibers inserting directly into the femur and anterior and posterior fan-like extension areas. The ACL fibers were cut sequentially from the bone: the posterior fan-like area in 2 stages, the central dense area in 4 stages, and then the anterior fan-like area in 2 stages. Each knee was mounted in a robotic joint testing system that applied tibial anteroposterior 6-mm translations and 10° or 15° of internal rotation at 0° to 90° of flexion. The reduction of restraining force or moment was measured after each cut.

RESULTS

The central area resisted 82% to 90% of the anterior drawer force; the anterior fan-like area, 2% to 3%; and the posterior fan-like area, 11% to 15%. Among the 4 central areas, most load was carried close to the roof of the intercondylar notch: the anteromedial bundle resisted 66% to 84% of the force and the posterolateral bundle resisted 16% to 9% from 0° to 90° of flexion. There was no clear pattern for tibial internal rotation, with the load shared among the posterodistal and central areas near extension and mostly the central areas in flexion.

CONCLUSIONS

Under the experimental conditions described, 66% to 84% of the resistance to tibial anterior drawer arose from the ACL fibers at the central-proximal area of the femoral attachment, corresponding to the anteromedial bundle; the fan-like extension fibers contributed very little. This work did not support moving a single-bundle ACL graft to the side wall of the notch or attempting to cover the whole attachment area if the intention was to mimic how the natural ACL resists tibial displacements.

CLINICAL RELEVANCE

There is ongoing debate about how best to reconstruct the ACL to restore normal knee function, including where is the best place for ACL graft tunnels. This study found that the most important area on the femur, in terms of resisting displacement of the tibia, was in the central-anterior part of the femoral ACL attachment, near the roof of the intercondylar notch. The testing protocol did not lead to data that would support using a large ACL graft tunnel that attempts to cover the whole natural femoral attachment area.

Flat midsubstance of the anterior cruciate ligament with tibial "C"-shaped insertion site

PURPOSE

This anatomical cadaver study was performed to investigate the flat appearance of the midsubstance shape of the anterior cruciate ligament (ACL) and its tibial "C"-shaped insertion site.

METHODS

The ACL midsubstance and the tibial ACL insertion were dissected in 20 cadaveric knees (n = 6 fresh frozen and n = 14 paraffined). Magnifying spectacles were used for all dissections. Morphometric measurements were performed using callipers and on digital photographs.

RESULTS

In all specimens, the midsubstance of the ACL was flat with a mean width of 9.9 mm, thickness of 3.9 mm and cross-sectional area of 38.7 mm(2). The "direct" "C"-shaped tibial insertion runs from along the medial tibial spine to the anterior aspect of the lateral meniscus. The mean width (length) of the "C" was 12.6 mm, its thickness 3.3 mm and area 31.4 mm(2). The centre of the "C" was the bony insertion of the anterior root of the lateral meniscus overlayed by fat and crossed by the ACL. No posterolateral (PL) inserting ACL fibres were found. Together with the larger "indirect" part (area 79.6 mm(2)), the "direct" one formed a "duck-foot"-shaped footprint.

CONCLUSION

The tibial ACL midsubstance and tibial "C"-shaped insertion are flat and are resembling a "ribbon". The centre of the "C" is the bony insertion of the anterior root of the lateral meniscus. There are no central or PL inserting ACL fibres. Anatomical ACL reconstruction may therefore require a flat graft and a "C"-shaped tibial footprint reconstruction with an anteromedial bone tunnel for single bundle and an additional posteromedial bone tunnel for double bundle.

Ribbon like appearance of the midsubstance fibres of the anterior cruciate ligament close to its femoral insertion site: a cadaveric study including 111 knees

PURPOSE

Recently, the configuration of the anterior cruciate ligament (ACL) from its direct femoral insertion to midsubstance was found to be flat. This might have an important impact for anatomical ACL reconstruction. The purpose of this anatomical study was to evaluate the macroscopic appearance of the ACL from femoral to midsubstance.

METHODS

The ACL was dissected in 111 human fresh frozen cadaver knees from its femoral insertion to midsubstance, and the shape was described. The anatomical findings were documented on digital photographs and on video. Thirty knees were sent for computed tomography (CT), magnetic resonance imaging (MRI) and histology of the femoral ACL insertion.

RESULTS

Two millimetres from its direct femoral insertion, the ACL fibres formed a flat ribbon in all dissected knees without a clear separation between AM and PL bundles. The ribbon was in exact continuity of the posterior femoral cortex. The width of the ribbon was between 11.43 and 16.18 mm and the thickness of the ACL was only 2.54-3.38 mm. 3D CT, MRI and the histological examination confirmed above findings.

CONCLUSION

This is a detailed anatomical study describing the ribbon-like structure of the ACL from its femoral insertion to midsubstance. A key point was to carefully remove the surface fibrous membrane of the ACL. A total of 2-3 mm from its bony femoral insertion, the ACL formed a flat ribbon without a clear separation between AM and PL bundles. The ribbon was in exact continuity of the posterior femoral cortex. The findings of a flat ligament may change the future approach to femoral ACL footprint and midsubstance ACL reconstruction and to graft selection.

Effect of femoral tunnel position on graft tension curves and knee stability in anatomic double-bundle anterior cruciate ligament reconstruction

PURPOSE

To evaluate the effect of the femoral tunnel position of the anteromedial bundle (AMB) and the posterolateral bundle (PLB) on the graft tension curves and knee stability in anatomic double-bundle anterior cruciate ligament (ACL) reconstruction.

METHODS

Forty-five patients who underwent anatomic double-bundle ACL reconstruction were included. AMB and PLB were provisionally fixed to a graft tensioning system in the following settings during surgery: (1) AMB at 20° and PLB at 0° (A20P0), (2) AMB at 20° and PLB at 20° (A20P20), and (3) AMB at 20° and PLB at 45° (A20P45). Bundle tension was recorded during knee flexion-extension. A pivot shift test was also evaluated. Femoral tunnel positions of the AMB and PLB were then assessed by three-dimensional computed tomography, and the correlation between femoral tunnel position and tension change pattern or residual pivot shift was evaluated.

RESULTS

The depth of the PLB tunnel position was correlated with the extent of tension reduction in the PLB between 0° and 30° irrespective of graft fixation settings, while neither the AMB tunnel position nor the height of the PLB tunnel position affected the tension change pattern. Ten cases showed grade 1 pivot shift only in the A20P0 setting. The PLB tunnel position in the pivot shift-positive cases was significantly deeper than that in the pivot shift-negative cases (27.5 ± 6.2 and 34.1 ± 5.5%, respectively, P = 0.002).

CONCLUSIONS

In anatomic double-bundle reconstruction, deeper PLB tunnel position was correlated with the larger tension reduction in the PLB between 0° and 30°. Fixation of the AMB at 20° and the PLB at 0° resulted in residual pivot shift phenomenon in 10/45 cases, and the PLB tunnel position in the pivot shift-positive cases was significantly deeper than that in the pivot shift-negative cases. In anatomic double-bundle reconstruction, the placement of PLB femoral tunnel must not be too deep, as it might lead to significant tension reduction in the PLB near extension and thus insufficient tension in the PLB, resulting in residual pivot shift phenomenon.

LEVEL OF EVIDENCE

IV.

Kinematic analysis of the indirect femoral insertion of the anterior cruciate ligament: implications for anatomic femoral tunnel placement

PURPOSE

To determine the effect of debriding the indirect insertion component of the femoral anterior cruciate ligament (ACL) attachment on tibiofemoral kinematics when compared with the intact knee.

METHODS

Knee kinematics were measured in 9 cadaveric knees with the ACL intact, after indirect insertion debridement, and after ACL transection. Three loading conditions were used: (1) a 134-N anterior tibial load, (2) a combined 10-Nm valgus and 5-Nm internal tibial torque, and (3) a simulated robotic pivot shift. Anterior tibial translation (ATT) was recorded in response to anterior and combined loads at 0°, 15°, 30°, 45°, 60°, and 90° of flexion. Posterior tibial translation and external tibial rotation were recorded during the simulated pivot shift.

RESULTS

With an anterior load, indirect insertion debridement increased ATT by 0.37 ± 0.24 mm at 0° (P = .002) and by 0.16 ± 0.19 mm at 15° (P = .033; increases <1 mm in all specimens). ACL transection increased ATT in response to an anterior load (P = .0001) with maximum effect at 15° compared with the intact and debrided states (11.26 ± 1.15 mm and 11.04 ± 1.08 mm, respectively). With a combined load, indirect insertion debridement increased ATT by 0.17 ± 0.11 mm at 0° (P = .001; increases <0.3 mm in all specimens) with no effect at other angles. ACL transection increased ATT in response to a combined load (P = .001) with maximum effect at 15° (4.45 ± 0.85 mm v ACL intact and 4.44 ± 0.84 mm v debrided indirect insertion). In the ACL intact condition, the pivot shift produced 1.29 ± 1.34 mm of posterior tibial translation and 1.54 ± 1.61° of external tibial rotation, as compared with 1.28 ± 1.34 mm and 1.54 ± 1.47°, respectively, after debridement (P = .68 and P = .99, respectively) and 12.79 ± 3.22 mm and 17.60 ± 4.30°, respectively, after ACL transection (P = .0001).

CONCLUSIONS

The indirect femoral ACL insertion contributes minimally to restraint of tibial translation and rotation.

CLINICAL RELEVANCE

Femoral tunnel positioning for anatomic ACL reconstruction should aim to recreate the biomechanically significant direct insertion.

Biomechanical comparison between the rectangular-tunnel and the round-tunnel anterior cruciate ligament reconstruction procedures with a bone-patellar tendon-bone graft

PURPOSE

The purpose of this study was to evaluate the effectiveness of 2 anterior cruciate ligament (ACL) reconstruction techniques using a bone-patellar tendon-bone (BPTB) graft with femoral tunnel, either a rectangular tunnel (RET) or a round tunnel (ROT).

METHODS

For experiment 1, nine fresh-frozen human cadaveric knees were tested with a robotic/universal force-moment sensor system to determine the initial optimal tension: the amount of graft tension at 15° of flexion most closely resembling the anterior laxity of a normal knee. The value was estimated by repeatedly measuring anterior laxity when 100 N of anteroposterior drawer load was applied to the knees at 30° of flexion after RET ACL or ROT ACL reconstruction. For experiment 2, six fresh-frozen human cadaveric knees were selected. On the basis of the initial tension determined in experiment 1, RET ACL reconstruction was conducted with the graft tensioned to 10 N, followed by ROT ACL reconstruction on the same knee at 40 N of initial tension, and the biomechanical efficacy of the 2 methods was compared.

RESULTS

For experiment 1, the mean laxity match tension at 15° of flexion was 8.6 ± 4.8 N and 34.8 ± 9.2 N for RET- and ROT-reconstructed knees, respectively. For experiment 2, both RET and ROT ACL reconstructions were successful in controlling anterior tibial translation under anterior tibial loads, with the graft initially tensioned to 10 N in the former and to 40 N in the latter. However, the greater tensioning in ROT reconstruction led to proximal, posterior, and lateral displacement of the tibia along with its external and valgus rotation.

CONCLUSIONS

The RET ACL-reconstructed knee more closely resembled the normal knee in biomechanical behavior. Although ROT reconstruction successfully controlled anterior translation with greater initial tensioning to the graft, the normal positional relation between the tibia and femur was impaired.

CLINICAL RELEVANCE

Rectangular femoral ACL fixation constructs and grafts may prove more efficacious at restoring in vivo ACL kinematics than round femoral tunnels.

MRI analysis of single-, double-, and triple-bundle anterior cruciate ligament grafts

PURPOSE

The purpose of the study was to evaluate the entire course of ACL grafts on coronal oblique MR images, focusing on differences in graft morphology and graft-to-tunnel healing among single-bundle (SB), double-bundle (DB), and triple-bundle (TB) reconstructions.

METHODS

Eighty-three patients underwent anatomical ACL reconstruction using the semitendinosus tendon. SB reconstruction was performed on 20 patients, DB on 29 patients, and TB on 34 patients. The anteromedial-bundle (AMB) and posterolateral-bundle (PLB) images were extracted from coronal oblique images of grafts at 6 months to visualize their entire course. Signal intensity of grafts was measured independently in three regions: (1) intra-femoral tunnel region, (2) intra-articular region, and (3) intra-tibial tunnel region, followed by calculation of the signal-to-noise quotient (SNQ). To evaluate graft-to-tunnel healing, T2-weighted images were examined for the presence of a high signal-intensity lesion between the graft and bone tunnel around the tunnel aperture.

RESULTS

AMB images showed that SB graft was thick throughout the entire course, while DB graft was thinner than SB graft. TB graft showed a fan shape approaching the tibial tunnels. The SNQ in the femoral tunnel of SB graft was significantly lower than in the DB and TB grafts. High signal-intensity lesions were frequently observed around the femoral tunnel aperture in PLB images of DB and TB grafts compared to SB grafts.

CONCLUSION

Gross morphology of TB grafts resembled that of the natural ACL. However, the graft-to-tunnel healing around the femoral tunnel seemed to be insufficient in PLB images of DB and TB compared to SB grafts.

Anatomic variations of the lateral intercondylar ridge: relationship to the anterior margin of the anterior cruciate ligament

BACKGROUND

The lateral intercondylar ridge (LIR) has been recognized as an important landmark to create an appropriate femoral tunnel in single-bundle anterior cruciate ligament (ACL) reconstruction. However, because of variations in the distal part of the LIR or because the relationship between the LIR and the anterior margin of the ACL attachment has not been sufficiently clarified, the utility of the LIR for anatomic single- and double-bundle reconstruction remains controversial.

HYPOTHESES

(1) There is a large degree of positional and dimensional variation in the LIR, specifically concerning the distal part. (2) There may be significant differences between sexes in the LIR. (3) The anterior margin of the ACL attachment may be located anterior to the distal part of the LIR.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A total of 318 femora, which were collected with the donors' demographic data, were examined to determine anatomic variations of the LIR. In addition, 20 cadaveric knees, in which the anterior margin was marked by radiopaque silicon markers, were examined with micro-computed tomography to evaluate the positional relationship between the LIR and the anterior margin of the ACL attachment.

RESULTS

Although the LIR was identified in 94.0% of the 318 femora, the distal half of the LIR was not visible in 18.4% of these femora. Moreover, the LIR was located in an extremely anterior part of the lateral condyle surface in 8.8% in comparison with the common location, and in an extremely posterior part in 8.5%. The length-height ratio (69.9% in men, 63.6% in women) and the length between the inlet of the notch roof and the proximal part of the LIR (19.9 mm in men, 17.9 mm in women) were significantly greater in males than in females (P = .0028 and P < .0001, respectively). The anterior margin of the ACL attachment was commonly located anterior to the middle and distal part of the LIR, having the mean marker-ridge distance of 4.2 mm.

CONCLUSION

There were large positional and dimensional variations in the LIR, specifically concerning the distal part. There are slight but significant differences between the male and female femora. The anterior margin of the ACL attachment is commonly located anterior to the middle and distal parts of the LIR.

CLINICAL RELEVANCE

Utility of the LIR as an osseous landmark for femoral tunnel creation is limited in anatomic reconstruction of the posterolateral bundle and anatomic single-bundle reconstruction.

Anatomic and histologic analysis of the mid-substance and fan-like extension fibres of the anterior cruciate ligament during knee motion, with special reference to the femoral attachment

PURPOSE

The purpose of this study is to evaluate the morphology of the mid-substance and fan-like extension fibres of ACL during knee motion with reference to the femoral attachment.

METHODS

This study used six fresh-frozen cadaveric knees and 22 embalmed cadaveric knees to macroscopically evaluate morphological changes in the ACL attachment during knee motion. Three embalmed specimens fixed at knee extension and another three specimens fixed at 120° flexion were used for histologic observations.

RESULTS

The fan-like extension fibres were adhered to the bone surface and the fibre location and orientation in relation to the femoral surface did not change, regardless of the knee flexion angle, while the orientation of the mid-substance fibres in relation to the femur did change during knee motion. During knee flexion, a fold in the ACL femoral attachment was observed at the border between the mid-substance and the fan-like extension fibres. The attachment of the mid-substance fibres was significantly smaller than the attachment of the fan-like extension fibres.

CONCLUSION

The present study clarified anatomic and histologic character of the mid-substance fibres and fan-like extension fibres, and provided critical information for future clinical and biomechanical studies concerning both two different fibres. Specifically for ACL reconstruction, it is difficult to reconstruct the natural fan-like extension fibres by creating a tunnel at the femoral and tibial ends of each fibre bundle, although the mid-substance fibres can be reconstructed by such procedures.