Current trends in anterior cruciate ligament reconstruction. Part 1: Biology and biomechanics of reconstruction

Comparison of hamstring tendon and patellar tendon grafts in anterior cruciate ligament reconstruction in a nationwide population-based cohort study: results from the danish registry of knee ligament reconstruction

BACKGROUND

The choice of graft for anterior cruciate ligament reconstruction (ACLR) remains controversial, and despite numerous studies, there is still an ongoing debate on this topic. The 2 most widely used grafts are the hamstring tendon and patellar tendon.

HYPOTHESIS

In this study, we hypothesized that the revision rate after primary ACLR is greater when using hamstring tendon grafts compared with patellar tendon grafts.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

From the nationwide population-based Danish Knee Ligament Reconstruction Registry, we identified all primary ACLR procedures (n = 13,647) performed in Denmark between July 2005 and December 2011. The end point was revision ACLR. As other end points, we used objective measurements and patient-reported outcome scores. Revision rates and relative risk estimates for revision ACLR were calculated using Cox multiple regression.

RESULTS

The use of hamstring tendon grafts increased from 68% in 2005 to 85% in 2011. The cumulative revision rates for hamstring tendon grafts at 1 and 5 years were 0.65% (95% confidence interval [CI], 0.51%-0.82%) and 4.45% (95% CI, 3.94%-5.01%), respectively. For patellar tendon grafts, the revision rate was 0.16% (95% CI, 0.05%-0.50%) at 1 year and 3.03% (95% CI, 2.27%-4.05%) at 5 years. The adjusted overall relative risk of revision surgery in the hamstring tendon group compared with the patellar tendon group was 1.41 (95% CI, 1.03-1.92), and the adjusted relative risk of undergoing revision surgery performed after 1 and 5 years was 3.82 (95% CI, 1.20-12.2) and 1.90 (95% CI, 0.43-8.40), respectively.

CONCLUSION

In this population-based study, the use of hamstring tendon grafts in ACLR was associated with an increased risk of revision compared with patellar tendon grafts, in particular during the first year after surgery. These results demonstrate that both hamstring and patellar tendon grafts reveal good results after ACLR and suggest that graft selection should be based on an individual evaluation of patient demands and graft morbidity.

Surgical management of partial tears of the anterior cruciate ligament

PURPOSE

Partial anterior cruciate ligament (ACL) tears involving the posterolateral (PL) bundle can lead to rotatory laxity of the knee, while tears involving the anteromedial (AM) bundle result in abnormal anteroposterior laxity of the knee. In this systematic review, we examine the best evidence on the management of partial tears of the ACL.

METHODS

A comprehensive search of several databases was performed from the inception of the database to December 2011, using various combinations of keywords focusing on clinical outcomes of human patients who had partial tears of ACL and who had undergone ACL augmentation. We evaluated the methodological quality of each article using the Coleman Methodology Score.

RESULTS

Ten articles published in peer-reviewed journals were identified (392 males and 242 females), with a mean modified Coleman methodology of 66.1 ± 10.2. Only two studies compared standard ACL reconstruction and augmentation techniques. No study has a sample large enough to allow establishing guidelines. Validated and standardized proprioception assessment methods should be used to report outcomes. Imaging outcomes should be compared to functional outcomes, and a control group consisting of traditional complete ACL reconstruction should be present.

CONCLUSION

There is a need to perform appropriately powered randomized controlled trials presenting clinical outcome with homogeneous score systems to allow accurate statistical analysis. ACL augmentation technique, preserving the intact AM or PL bundle of the ACL, is encouraging but currently available evidences are too weak to support his routine use in clinical practice.

Anterior cruciate ligament reconstruction using bone plug-free quadriceps tendon autograft: intermediate-term clinical outcome after 24-36 months

Introduction

Although known as a possible graft option for decades, quadriceps tendon grafts have often been termed a second-line graft option. We report a consecutive case series using this method as the primary treatment line. The rationale for this study was to evaluate the midterm results of this method in a prospective and consecutive case series. The primary study question was to determine the clinical results 24–36 months after primary anterior cruciate ligament (ACL) reconstruction using a bone plug-free quadriceps tendon autograft fixed with bioabsorbable cross-pins.

Materials and methods

The study population included 55 patients, of whom 24 were female (43.6%). The mean age at the index procedure was 31.7 years (15–58 years). All patients received an ACL construction using a bone block-free quadriceps tendon graft fixed with resorbable cross-pins. The postoperative regimen included partial weight-bearing for 3 weeks and flexion limited to 90° for six weeks; an orthosis was not used. The mean follow-up duration was 29.5 months (24.3–38.5 months) after the index procedure. The International Knee Documentation Committee (IKDC) subjective score and examination form was assessed, as well as the Lysholm and Gillquist score and the Tegner activity index. The Rolimeter arthrometer was used to assess the anterior laxity of the knee.

Results

Graft harvesting was possible in all cases; a bony extension was never required. On average, graft length was measured at 8.8 cm (7.5–10 cm). The mean IKDC subjective score at follow-up was 80.44 points (55.17–100 points, standard deviation [SD] 12.05). The mean preinjury Tegner activity index was 4.98 (2–7) compared to a mean value of 4.16 (2–7, SD 0.8) at follow-up. There was a mean loss of 0.82 index points. The average Lysholm and Gillquist score was 89 points (65–100, SD 17.7). Of the results, 89.1% were in the good or very good groups; in one case (1.8%), the result was poor, while the rest were fair.

Conclusion

ACL reconstruction using a bone plug-free quadriceps tendon autograft achieved satisfactory results in a midterm review.

How to read post-operative radiographs and CT scans after single-bundle anterior cruciate ligament reconstruction

Reconstruction of the anterior cruciate ligament (ACL) is a well-established surgical procedure. However, post-operative imaging in the early phase is not routinely performed. The rationale for performing such imaging is to provide a baseline examination for future controls, to provide immediate feedback to surgeons regarding tunnel placement, and to assess placement of fixation devices. The purpose of this paper is to enable the reader to accurately read post-operative radiographs and CT scans after single-bundle ACL reconstruction.

Anterior cruciate ligament bundle measurement by MRI

OBJECTIVE

An accurate in vivo method of measuring dimensions of the anteromedial (AM) and posterolateral (PL) anterior cruciate ligament (ACL) bundles has not been established. The purpose of this study was to measure each individual bundle using double oblique axial MR imaging of the ACL, to compare this with cadaveric measurements, and to investigate the range of measurements seen in normal subjects.

MATERIALS AND METHODS

In five cadaveric knees, measurements obtained of the proximal, middle, and distal segments of each ACL bundle from double oblique axial MR images were compared with direct measurements following anatomical dissection. Thereafter, the size of both bundles from 24 normal knees was measured using an identical MR technique. Inter-observer variation was calculated using intraclass correlation.

RESULTS

ACL bundle measurement in the cadaveric knees had a strong correlation (r = 0.93) with measurements obtained following anatomical dissection. No significant difference existed between measurements obtained from cadaveric knees and living normal subjects (p > 0.05). Interobserver correlation for MR measurements was excellent (R = 0.92-0.93). Overall, the long and short axis of the AM bundle were significantly larger than those of the PL bundle (p < 0.05). Also, men showed significantly larger AM and PL bundles than women (p < 0.05). Bundle size was not related to age or knee dominance.

CONCLUSION

The individual ACL bundles can be accurately measured on double oblique axial MR imaging. The AM bundle is larger in caliber than the PL bundle. Both bundles are larger in men than in women and there is no significant side-to side difference.

Semitendinosus muscle fatty infiltration following tendon harvest in rabbits

The hamstring tendon autograft is one of the most commonly used graft choices in Anterior cruciate ligament (ACL) reconstruction. There are conflicting results regarding postoperative hamstring strength deficits in patients who have had a hamstring graft. The semitendinosus tendon has been shown to regenerate after harvesting for ACL autograft, suggesting that the muscle has the potential to regain normal function. However, no studies have been performed to define the microstructural changes that occur in the semitendinosus muscle after tendon resection. In this study, we hypothesized that fatty infiltration of the semitendinosus muscle after tendon harvest in New Zealand White rabbits increases postoperatively and remains constant or increases during the first year of repair. The semitendinosus tendon was unilaterally detached and harvested from 15 rabbits. Five rabbits were sacrificed at 3-, 6-, and 12-month intervals, and the semitendinosus muscle-tendon units were analyzed. The contralateral unoperated limb served as the control. The gross tendon and muscle dimensions and histologic percentage of fatty infiltration were measured. We found no significant difference in fatty infiltration at any time point between the control muscle and test specimens and that there was no progression of fatty infiltration over time. If these results hold true in humans, natural repair of the hamstring muscle following tendon harvest during ACL autograft reconstruction is not inhibited by fatty infiltration.

Radioprotection provides functional mechanics but delays healing of irradiated tendon allografts after ACL reconstruction in sheep

Successful protection of tissue properties against ionizing radiation effects could allow its use for terminal sterilization of musculoskeletal allografts. In this study we functionally evaluate Achilles tendon allografts processed with a previously developed radioprotective treatment based on (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide) crosslinking and free radical scavenging using ascorbate and riboflavin, for ovine anterior cruciate ligament reconstruction. Arthroscopic anterior cruciate ligament (ACL) reconstruction was performed using double looped allografts, while comparing radioprotected irradiated and fresh frozen allografts after 12 and 24 weeks post-implantation, and to control irradiated grafts after 12 weeks. Radioprotection was successful at preserving early subfailure mechanical properties comparable to fresh frozen allografts. Twelve week graft stiffness and anterior-tibial (A-T) translation for radioprotected and fresh frozen allografts were comparable at 30 % of native stiffness, and 4.6 and 5 times native A-T translation, respectively. Fresh frozen allograft possessed the greatest 24 week peak load at 840 N and stiffness at 177 N/mm. Histological evidence suggested a delay in tendon to bone healing for radioprotected allografts, which was reflected in mechanical properties. There was no evidence that radioprotective treatment inhibited intra-articular graft healing. This specific radioprotective method cannot be recommended for ACL reconstruction allografts, and data suggest that future efforts to improve allograft sterilization procedures should focus on modifying or eliminating the pre-crosslinking procedure.

Single-bundle versus double-bundle anterior cruciate ligament reconstruction: assessment with vertical jump test

PURPOSE

The study was designed to compare the clinical results of traditional single-bundle (SB) anterior cruciate ligament (ACL) reconstruction with those of double-bundle (DB) ACL reconstruction.

METHODS

This study comprised 80 patients aged 18 to 45 years with an isolated ACL lesion: 40 patients underwent SB reconstruction, and 40 patients underwent DB reconstruction. Patients were assessed preoperatively with functional assessment including the International Knee Documentation Committee 2000 knee subjective form and visual analog scale, as well as physical examination (including the pivot-shift test and instrumented knee laxity measurement). Vertical jump assessment with the Optojump system (Microgate, Bolzano, Italy) has been introduced as a method to compare functional ability between the 2 surgical techniques. The same protocol was repeated 6 months, 12 months, and 2 years after surgery.

RESULTS

No statistically significant differences were noted between the groups concerning subjective evaluation, thigh girth difference, mean visual analog scale score, range of motion, and Lachman and anterior drawer tests (P = not significant). A statistically higher number of patients in the SB group showed a positive pivot-shift test and a higher side-to-side difference when measured with the KT-1000 arthrometer (MEDmetric, San Diego, CA) than in the DB group (P < .001). Better mean jumping performance results were reported in the DB group compared with the SB group (P < .001). The average performance results for the injured limb were not significantly reduced compared with those of the uninjured limb in the DB group 12 months after surgery. At 2 years, a restoration of jumping ability in the ACL-reconstructed limb was achieved in both groups regardless of the technique used.

CONCLUSIONS

DB ACL reconstruction has been proven to be superior to the SB technique with regard to knee stability and vertical jump performance.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

Anterior cruciate ligament reconstruction with LARS™ artificial ligament results at a mean follow-up of eight years

PURPOSE

The aim of this study was to review patients that underwent ACL reconstruction with the LARS™ ligament in the First Orthopaedic Division of Pisa University during the period between January 2003 and December 2005.

METHODS

Twenty-six patients were reviewed with an average follow-up of 95.3 months (7.9 years). The review protocol was articulated in three phases: (1) a subjective evaluation using three grading scales: VAS, KOOS and the Cincinnati knee rating scale, (2) a clinical and objective evaluation, and (3) a biomechanical evaluation of the knee stability.

RESULTS

A global positive result was obtained in 92.3 % of the patients (16 optimal results and eight good results), with a fast functional recovery and a high knee stability. A global poor result was reported in two cases. In our series we did not record cases of infection or knee synovitis. We recorded only one case of mechanical graft failure. The results obtained from our study are encouraging and similar to those in the literature.

CONCLUSIONS

We conclude that the LARS™ ligament can be considered a suitable option for ACL reconstruction in carefully selected cases, especially for older patients needing a fast functional recovery.

A review of anterior cruciate ligament injuries and reconstructive techniques. Part 2: Treatment

The aims of treatment of anterior cruciate ligament rupture are to eliminate pain, restore stability and allow early return to activity while preventing early degeneration. Ruptures can be treated conservatively, which requires careful patient selection and avoidance of high-risk activity. Each patient must be treated on an individual basis with consideration given to the level of activity, desire to return to sport, donor site morbidity and compliance with post-operative regimes. Through the evolution of single incision, arthroscopic anatomic reconstruction, our knowledge of the native anterior cruciate ligament anatomy and knee kinematics has progressed. The current gold standard uses four-stranded hamstring autograft with endobutton and interference screw fixation. Double-bundle reconstruction is technically challenging with greater risk and best reserved for larger knees with larger native ligaments. Although treatment has advanced considerably over the years, there are still a number of contentious issues which are considered in this review. Part two of this review discusses the short- and long-term objectives of surgery, the indications and timing of surgery, different graft materials, tunnel positions and rehabilitation programmes. We also evaluate the role of anatomical reconstruction and single- versus double-bundle anterior cruciate ligament reconstructions.

A review of anterior cruciate ligament injuries and reconstructive techniques. Part 1: Basic science

Anterior cruciate ligament rupture is a common soft tissue knee injury, often affecting young athletic individuals keen to return to pre-injury levels of function. Increasing sporting activity is reflected by an increasing incidence of anterior cruciate ligament rupture. Although treatment has advanced considerably over the years, there are still a number of contentious issues that are considered in this review. The anterior cruciate ligament is a dense band of connective tissue, comprising an anteromedial and posterolateral bundle based on tibial insertion sites. It is important to appreciate the position and orientation of these bundles at the time of reconstructive surgery. The bundles, with their load sharing behaviour through knee flexion, affect antero-posterior and rotational stability of the knee. In the first part of this review, we consider the clinical presentation of anterior cruciate ligament injury and relevant anatomy, knee kinematics, mechanism of injury and incidence of anterior cruciate ligament ruptures.

The Effect of the Variation in ACL Constitutive Model on Joint Kinematics and Biomechanics Under Different Loads: A Finite Element Study

The biomechanics and function of the anterior cruciate ligament (ACL) have been widely studied using both experimental and simulation methods. It is known that a constitutive model of joint tissue is a critical factor in the numerical simulation. Some different ligament constitutive models have been presented to describe the ACL material behavior. However, the effect of the variation in the ligament constitutive model on joint kinematics and biomechanics has still not been studied. In this paper, a three-dimensional finite element model of an intact tibiofemoral joint was reconstructed. Three ACL constitutive models were compared under different joint loads (such as anterior tibial force, varus tibial torque, and valgus tibial torque) to investigate the effect of the change of the ACL constitutive model. The three constitutive models corresponded to an isotropic hyperelasticity model, a transversely isotropic hyperelasticity model with neo-Hookean ground substance description, and a transversely isotropic hyperelastic model with nonlinear ground substance description. Although the material properties of these constitutive equations were fitted on the same uniaxial tension stress-strain curve, the change of the ACL material constitutive model was found to induce altered joint kinematics and biomechanics. The effect of different ACL constitutive equations on joint kinematics depended on both deformation direction and load type. The variation in the ACL constitutive models would influence the joint kinematic results greatly in both the anterior and internal directions under anterior tibial force as well as some other deformations such as the anterior and medial tibial translations under valgus tibial torque, and the medial tibial translation and internal rotation under varus torque. It was revealed that the transversely isotropic hyperelastic model with nonlinear ground substance description (FE model III) was the best representation of the realistic ACL property by a linear regression between the simulated and the experiment deformation results. But the comparison of the predicted and experiment force of ligaments showed that all the three ACL constitutive models represented similar force results. The stress value and distribution of ACL were also altered by the change in the constitutive equation. In brief, although different ACL constitutive models have been fitted using the same uniaxial tension curve and have the similar longitudinal material property, the ACL constitutive equation should still be carefully chosen to investigate joint kinematics and biomechanics due to the different transverse material behavior.

Revision ACL reconstruction using contralateral hamstrings

PURPOSE

Due to the increasing number of primary anterior cruciate ligament (ACL) reconstructions, the need for revision surgery has risen. The aim of this study was to evaluate the use of contralateral doubled semitendinosus and gracilis tendon (DGST) for revision anterior cruciate ligament reconstruction.

METHODS

Twelve patients undergoing revision ACL reconstruction with hamstring tendon were examined at an average follow-up of 3 years. All patients underwent a thorough subjective and objective evaluation, which included a KT-1000 arthrometric evaluation, and a radiographic examination.

RESULTS

Subjective evaluation yielded a median score of 5.5 (range 2-9) on the Tegner activity scale. The mean Lysholm score was 95 (SD 9.5), and the mean subjective IKDC 2000 score was 95.4 (SD 7.8). At physical examination, a negative Lachman test was found in ten patients; one patient had a positive Lachman test with a firm end-point, and one other patient had a clearly positive Lachman test. Two patients had a grade 1+ on pivot shift testing. Only 1 patient showed a side-to-side difference more than 5 mm at the maximum manual KT-1000 arthrometer. Three patients (25 %) showed initial signs of osteoarthritis.

CONCLUSIONS

The results of the study show that the use of hamstring tendons harvested from the unaffected knee represents a valid option for revision surgery following a failed primary ACL reconstruction using DGST grafts.

LEVEL OF EVIDENCE

IV.

Anterior cruciate ligament fixation: is radial force a predictor of the pullout strength of soft-tissue interference devices?

BACKGROUND

In anterior cruciate ligament (ACL) reconstruction, an interference device achieves soft-tissue graft fixation by radially compressing the graft against the bone.

PURPOSE

The objective of this study was to measure the radial force generated by different interference devices and evaluate the effect of this radial force on the pullout strength of graft-device constructs.

STUDY DESIGN

Controlled laboratory study.

METHODS

A resultant force (F(R)) was used as a representative measure of the total radial force generated. Bovine tendons were fixated in either synthetic bone or porcine tibia using one of following devices: (1) RCI titanium screw, (2) PEEK screw, (3) IntraFix sheath-and-screw device, and (4) ExoShape sheath-and-insert device. F(R) was measured while each device was inserted into synthetic bone mounted on a test machine (n=5 for each device). In a subsequent test series, graft-device constructs were loaded to failure at 50mm/min. The pullout strength was measured as the ultimate load before failure (n=10 for each device).

RESULTS

The F(R) values generated during insertion into synthetic bone were 777 ± 86N, 865 ± 140N, 1313 ± 198N, and 1780 ± 255N for the RCI screw, PEEK screw, IntraFix, and ExoShape, respectively. The pullout strengths in synthetic bone for the RCI screw, PEEK screw, IntraFix and ExoShape were 883 ± 125N, 716 ± 249N, 1147 ± 142N, and 1233 ± 190N, respectively.

CONCLUSIONS

These results suggest that the F(R) generated during interference fixation affects the pullout strength with sheath-based devices providing superior F(R) compared with interference screws. The use of synthetic bone was validated by comparing the pullout strengths to those when tested in porcine tibia.

CLINICAL RELEVANCE

These results could be valuable to a surgeon when determining the best fixation device to use in the clinical setting.

Design Considerations for a Prosthetic Anterior Cruciate Ligament

Anterior cruciate ligament (ACL) tearing is a common knee injury often requiring reconstruction with an autograft or an allograft. A prosthetic ligament replacement with off-the-shelf availability could potentially provide significant advantages over the current options for both patients and surgeons. Limitations of previous prosthetics include lack of biocompatibility and susceptibility to fatigue, creep, and failure of bony incorporation. This paper describes design considerations and possible improvements for the next generation prosthetic ACL. Design controls, as mandated by the FDA, are a systematic set of practices within the design and development process used to ensure that a new medical device meets the needs of the intended users. The specified requirements, called the design inputs, for a prosthetic ACL are discussed pertaining to material and structural properties, resistance to creep and fatigue, ability to support secure initial fixation, biocompatibility, and long-term osseointegration. Design innovations to satisfy the design inputs are discussed with regards to material selection, textile pattern, bone tunnel features, and short term fixation. A risk analysis is presented along with descriptions of proposed testing. Design control methodology and tissue engineering may be used to develop a next generation prosthetic ligament, solving multiple problems, simultaneously, on a holistic level, providing major improvements over earlier devices and current treatment options.

Effect of bone morphogenetic protein 2 on tendon-to-bone healing in a canine flexor tendon model

Tendon-to-bone healing is typically poor, with a high rate of repair-site rupture. Bone loss after tendon-to-bone repair may contribute to poor outcomes. Therefore, we hypothesized that the local application of the osteogenic growth factor bone morphogenetic protein 2 (BMP-2) would promote bone formation, leading to improved repair-site mechanical properties. Intrasynovial canine flexor tendons were injured in Zone 1 and repaired into bone tunnels in the distal phalanx. BMP-2 was delivered to the repair site using either a calcium phosphate matrix (CPM) or a collagen sponge (COL) carrier. Each animal also received carrier alone in an adjacent repair to serve as an internal control. Repairs were evaluated at 21 days using biomechanical, radiographic, and histologic assays. Although an increase in osteoid formation was noted histologically, no significant increases in bone mineral density occurred. When excluding functional failures (i.e., ruptured and gapped repairs), mechanical properties were not different when comparing BMP-2/CPM groups with carrier controls. A significantly higher percentage of BMP-2 treated specimens had a maximum force <20 N compared to carrier controls. While tendon-to-bone healing can be enhanced by addressing the bone loss that typically occurs after surgical repair, the delivery of BMP-2 using the concentrations and methods of the current study did not improve mechanical properties over carrier alone. The anticipated anabolic effect of BMP-2 was insufficient in the short time frame of this study to counter the post-repair loss of bone.

Donor-site-related functional problems following anterior cruciate ligament reconstruction: development of a self-administered questionnaire

PURPOSE

To develop a self-administered questionnaire for the evaluation of donor-site-related functional problems after anterior cruciate ligament (ACL) reconstruction with autograft harvested from the hamstring tendon or patellar tendon and to determine the content validity, reliability and preliminary factor structure of this new instrument.

METHODS

Seven physiotherapists with long clinical experience of rehabilitation after ACL reconstruction and 60 patients from the target population participated as experts in the developmental stages of the questionnaire. Content validity was determined and quantified with the content validity index (CVI). Test-retest reliability, internal consistency and factor structure were evaluated in another 64 patients reconstructed with an autograft.

RESULTS

The final questionnaire included 16 items on symptoms and function during activities of daily living and exercise. Excellent content validity on both item level (I-CVI ≥ 0.83, range 0.83-1.00) and scale level (S-CVI = 0.93) was found. The test-retest reliability was good, ICC = 0.94. Internal consistency was high, and Cronbach's α was 0.92 and 0.94 at each test occasion. The principal components analysis yielded a four-component structure.

CONCLUSIONS

The questionnaire "Donor-site-Related Functional Problems following Anterior Cruciate Ligament (ACL) Reconstruction" is a patient-reported questionnaire with high content validity and reliability for the evaluation of donor-site-related functional problems after ACL reconstruction, with autograft harvested from the hamstring tendon or patellar tendon. The results of this study support the use of this questionnaire as a standardized outcome measure for both research purposes and in clinical settings.

Biomechanical comparison between single-bundle and double-bundle anterior cruciate ligament reconstruction with hamstring tendon under cyclic loading condition

PURPOSE

The purpose of this study was to compare the anterior tibial translation (ATT) of the anterior cruciate ligament (ACL) reconstructed-knee between single-bundle and double-bundle ACL reconstruction under cyclic loading.

METHODS

Single-bundle and double-bundle reconstructions of the knee were performed sequentially in randomized order on the same side using eight human amputated knees. After each reconstruction, the reconstructed-knee was subjected to 500-cycles of 0 to 100-N anterior tibial loads using a material testing machine. The ATT before and after cyclic loading and "laxity increase", which indicated a permanent elongation of the graft construct, was also determined.

RESULTS

The ATT after cyclic loading increased in both single-bundle and double-bundle reconstruction techniques compared to that without cyclic loading. Changes in ATT before and after cyclic loading were 3.9 ± 0.9 mm and 2.9 ± 0.6 mm respectively, and were significantly different. Laxity increase was also significantly different (4.3 ± 0.9 mm and 3.2 ± 0.8 mm respectively). Although no graft rupture or graft fixation failure was found during cyclic loading, the graft deviated into an eccentric position within the tunnel.

CONCLUSIONS

Although ATT was significantly increased in both single-bundle and double-bundle reconstruction with hamstring tendon after cyclic loading test, there was significant difference. Double-bundle reconstruction might be superior to prevent increasing ATT under cyclic loading. Deformation of hamstring tendon after cyclic loading might result in deterioration of knee stability after ACL reconstruction, and is one of disadvantages of soft tissue graft.

A between sex comparison of anterior-posterior knee laxity after anterior cruciate ligament reconstruction with patellar tendon or hamstrings autograft: a systematic review

Anterior-posterior (AP) knee laxity after anterior cruciate ligament (ACL) reconstruction may differ between sexes for different graft types. Females may experience an increase in AP knee laxity following an ACL reconstruction with a hamstrings graft, which is not seen in males with a hamstrings graft or in males or females with a bone-patellar tendon-bone (BTB) graft. The hypothesis of this review is sex differences in AP knee laxity and this will be identified in patients who undergo an ACL reconstruction with a hamstrings graft, while no sex differences will be observed in patients who have an ACL reconstruction with a BTB graft. A systematic search was performed in PubMed, CINAHL and SPORTDiscus. Inclusion criteria were articles published in the English language that studied human subjects who underwent an ACL reconstruction with a BTB or hamstrings autograft, and the presence of a sex comparison on outcome measures including side-to-side difference in AP knee laxity. Methodological quality was assessed using a Modified Coleman Methodology Score. Eleven cohort studies met the inclusion criteria. Six investigated sex differences in both hamstrings and BTB grafts. Three only investigated BTB grafts and two only investigated hamstrings grafts. These studies consistently reported increases in AP knee laxity in females after an ACL reconstruction with a hamstrings graft that was not observed in the other cohorts. This systematic review indicates that female patients have greater AP knee laxity following an ACL reconstruction with a hamstrings autograft compared with males with a similar procedure, and both females and males following an ACL reconstruction with a BTB autograft. These results are derived from lower level evidence, as no randomized control trials have attempted to answer this question. Future studies need to rigorously address this clinical question to confirm the results currently in the literature.

Lateral femoral cortical breach during anterior cruciate ligament reconstruction: a biomechanical analysis

PURPOSE

The purpose of our study was to determine whether secondary fixation is needed when lateral femoral wall breach occurs and whether the diameter of the femoral tunnel affects the cyclical and ultimate load to failure of 3 different suspensory fixation devices.

METHODS

Sixty fresh-frozen porcine femora were dissected to isolate the anterior cruciate ligament (ACL) footprint. Femoral ACL tunnels were then drilled at diameters of 7, 8, 9, and 10 mm. We conducted 5 separate cyclical and ultimate load testing trials, at each tunnel diameter, for 3 different cortical suspension devices.

RESULTS

The mean load to failure decreased as the tunnel size enlarged for all 3 devices. In 7-mm tunnels, mean failure load ranged from 1,163.7 to 1,455.0 N across the 3 devices; in 8-mm tunnels, 1,154.7 to 1,643.2 N; in 9-mm tunnels, 820.8 to 1,125.21 N; and in 10-mm tunnels, 314.7 to 917.8 N. Modes of failure also varied as the tunnel sizes enlarged. The ultimate load was not different among the 3 manufacturers (P = .08), but there was a difference in the ultimate load across the 4 tunnel diameters (P < .05), except when we compared the 7-mm tunnel with the 8-mm tunnel (P = .91).

CONCLUSIONS

With 7- and 8-mm-diameter tunnels, failure loads with each of the suspensory devices tested exceeded the documented interference screw load to failure.

CLINICAL RELEVANCE

Our findings suggest that, for soft-tissue ACL grafts, femoral tunnels of 8 mm or less can be drilled through the lateral femoral cortex while still using a suspensory device for graft fixation. With pediatric, double-bundle, and anatomic ACL reconstructions, smaller and shorter tunnels are routinely used. Thus, breaching the lateral cortex when using suspensory fixation may increase tunnel length while still achieving stable fixation.

BIOMECHANICAL STUDY OF TRANSCORTICAL OR TRANSTRABECULAR BONE FIXATION OF PATELLAR TENDON GRAFT WITH BIOABSORBABLE PINS IN ACL RECONSTRUCTION IN SHEEP

Objective: To determine the initial resistance of fixation using the Rigid Fix^® system, and compare it with traditional fixation methods using metal interference screws; and to evaluate the resistance of the fixation with the rigid fix system when the rotational position of the bone block is altered in the interior of the femoral tunnel. Methods: forty ovine knee specimens (stifle joints) were submitted to anterior cruciate ligament reconstruction (ACL) using a bone-tendon-bone graft. In twenty specimens, the Rigid Fix method was used; this group was subdivided into two groups: ten knees the pins transfixed only the spongious area of the bone block, and ten for fixation passing through the layer of cortical bone. In the twenty remaining specimens, the graft was fixed with 9mm metal interference screws. Results: comparison of the RIGIDFIX^® method with the metal interference screw fixation method did not show any statistically significant differences in terms of maximum load and rigidity; also, there were no statistically significant differences when the rotational position of the bone block was altered inside the femoral tunnel. For these evaluations, a level of significance of p < 0.017 was considered. Conclusion: fixation of the bone-tendon-bone graft with 2 bioabsorbable pines, regardless of the rotational position inside the femoral tunnel, gave a comparable fixation in terms of initial resistance to the metal interference screw, in this experimental model.

Biomechanics of the anterior cruciate ligament and implications for surgical reconstruction

Injury to the anterior cruciate ligament (ACL) is regarded as critical to the physiological kinematics of the femoral-tibial joint, its disruption eventually causing long-term functional impairment. Both the initial trauma and the pathologic motion pattern of the injured knee may result in primary degenerative lesions of the secondary stabilisers of the knee, each of which are associated with the early onset of osteoarthritis. Consequently, there is a wide consensus that young and active patients may profit from reconstructing the ACL. Several factors have been identified as significantly influencing the biomechanical characteristics and the functional outcome of an ACL reconstructed knee joint. These factors are: (1) individual choice of autologous graft material using either patellar tendon-bone grafts or quadrupled hamstring tendon grafts, (2) anatomical bone tunnel placement within the footprints of the native ACL, (3) adequate substitute tension after cyclic graft preconditioning, and (4) graft fixation close to the joint line using biodegradable graft fixation materials that provide an initial fixation strength exceeding those loads commonly expected during rehabilitation. Under observance of these factors, the literature encourages mid-to long-term clinical and functional outcomes after ACL reconstruction.

The impact of tensioning device mal-positioning on strand tension during anterior cruciate ligament reconstruction

Background

In order to confer optimal strength and stiffness to the graft in Anterior Cruciate Ligament (ACL) reconstruction, the maintenance of equal strand tension prior to fixation, is desired; positioning of the tensioning device can significantly affect strand tension This study aimed to determine the effect of tensioning device mal-positioning on individual strand tension in simulated cadaveric ACL reconstructions.

Methods

Twenty cadaveric specimens, comprising bovine tibia and tendon harvested from sheep, were used to simulate ACL reconstruction with a looped four-strand tendon graft. A proprietary tensioning device was used to tension the graft during tibial component fixation with graft tension recorded using load cells. The effects of the tensioning device at extreme angles, and in various locking states, was evaluated.

Results

Strand tension varied significantly when the tensioning device was held at extreme angles (p < 0.001) or in 'locked' configurations of the tensioning device (p < 0.046). Tendon position also produced significant effects (p < 0.016) on the resultant strand tension.

Conclusion

An even distribution of tension among individual graft strands is obtained by maintaining the tensioning device in an unlocked state, aligned with the longitudinal axis of the tibial tunnel. If the maintenance of equal strand tension during tibial fixation of grafts is important, close attention must be paid to positioning of the tensioning device in order to optimize the resultant graft tension and, by implication, the strength and stiffness of the graft and ultimately, surgical outcome.

Biomechanical evaluation of pediatric anterior cruciate ligament reconstruction techniques

BACKGROUND

Anterior cruciate ligament (ACL) reconstruction rates in skeletally immature patients have risen recently because of increased injury frequency combined with growing awareness of the importance of treating them in an acute setting. Concerns over potential growth disturbances caused by traditional tunnel placement have prompted the description of several partial and complete physeal-sparing techniques.

HYPOTHESIS

Native knee kinematics will most closely be restored by the all-epiphyseal technique because it best re-creates the intra-articular ACL anatomy.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six cadaveric knees were subjected to static anteroposterior, varus, and internal rotation forces at 0°,15°, 30°, 45°, 60°, and 90° of flexion. Displacement and rotation of the tibia with respect to the femur were measured in the intact knee, after ACL disruption, and again after ACL reconstruction using all-epiphyseal, transtibial over-the-top, and iliotibial band physeal-sparing techniques.

RESULTS

Peak anteroposterior translation in the ACL intact and deficient states was 2.8 ± 1.4 mm and 7.2 ± 2.7 mm, respectively, at 30°. The all-epiphyseal reconstruction had a peak translation of 5.1 ± 2.3 mm at 30°, and the transtibial over-the-top reconstruction had a peak of 4.8 ± 1.8 mm at 30°, both significantly greater than the ACL intact state. The iliotibial band technique had a peak anteroposterior translation of 1.7 ± 1.1 mm at 45°, which was significantly less than the ACL-deficient state. Internal rotation was significantly increased in the all-epiphyseal reconstruction compared with the ACL intact state and significantly decreased at all flexion angles except 0° in the iliotibial band reconstruction. The only technique to affect varus rotation was the iliotibial band reconstruction, which significantly decreased varus rotation from the ACL-deficient state at flexion angles greater than 30°.

CONCLUSION

All physeal-sparing reconstruction techniques restored some stability to the knee. The iliotibial band reconstruction best restored anteroposterior stability and rotational control, although it appeared to overconstrain the knee to rotational forces at some flexion angles.

CLINICAL RELEVANCE

This study provides orthopaedic surgeons with objective knee kinematic data to help guide them in making more informed decisions on the optimal technique for ACL reconstruction in skeletally immature patients.

Arthroscopically pertinent landmarks for tunnel positioning in single-bundle and double-bundle anterior cruciate ligament reconstructions

BACKGROUND

Quantification of the overall anterior cruciate ligament (ACL) and anteromedial (AM) and posterolateral (PL) bundle centers in respect to arthroscopically pertinent bony and soft tissue landmarks has not been thoroughly assessed.

HYPOTHESIS

A standardized anatomical measurement method can quantitate the locations of the ACL and AM and PL bundle centers in reference to each other and anatomical landmarks.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Quantification of the ACL and its bundle attachments was performed on 11 cadaveric knees using a radio frequency-tracking device.

RESULTS

The tibial ACL attachment center was 7.5 mm medial to the anterior horn of the lateral meniscus, 13.0 mm anterior to the retro-eminence ridge, and 10.5 mm posterior to the ACL ridge. The femoral ACL attachment center was 1.7 mm proximal to the bifurcate ridge and 6.1 mm posterior to the lateral intercondylar ridge. The tibial AM attachment center was 8.3 mm medial to the anteromedial aspect of the lateral meniscus anterior horn, 17.8 mm anterior to the retro-eminence ridge, and 5.6 mm posterior to the ACL ridge. The femoral AM attachment center was 4.8 mm proximal to the bifurcate ridge and 7.1 mm posterior to the lateral intercondylar ridge. The tibial PL bundle attachment center was 6.6 mm medial to the posteromedial aspect of the lateral meniscus anterior horn, 10.8 mm anteromedial to the root attachment of the lateral meniscus posterior horn, and 8.4 mm anterior to the retro-eminence ridge. The femoral PL bundle attachment center was 5.2 mm distal to the bifurcate ridge and 3.6 mm posterior to the lateral intercondylar ridge.

CONCLUSION

The authors developed a comprehensive compilation of measurements of arthroscopically pertinent bony and soft tissue landmarks that quantitate the ACL and its individual bundle attachment centers on the tibia and femur.

CLINICAL RELEVANCE

These clinically relevant arthroscopic landmarks may enhance single- and double-bundle ACL reconstructions through improved tunnel placement.

What is the best femoral fixation of hamstring autografts in anterior cruciate ligament reconstruction?: a meta-analysis

BACKGROUND

Several methods are available for fixing the femoral side of a hamstring autograft in ACL reconstruction and the best method is unclear. Biomechanical studies have shown varying results with regard to fixation failure.

QUESTIONS/PURPOSES

We asked whether there were any differences with regard to graft failures and functional outcome measures with differing methods of femoral fixation of hamstring autografts in ACL reconstruction.

METHODS

We systematically reviewed the literature using PubMed, MEDLINE, Scopus, and Cochrane Controlled Trial Register databases with regard to interference screw fixation (aperture fixation) versus noninterference screw fixation (fixation away from the joint line). A meta-analysis was performed of those studies reporting on surgical failures and postoperative International Knee Documentation Committee score. Eight studies met our inclusion criteria of Level I or II evidence.

RESULTS

Use of interference screws for femoral fixation resulted in a trend toward decreased risk of surgical failure (relative risk = 0.57; confidence interval, 0.1678-1.0918). When only Level I trials were evaluated, the same trend was noted toward a decreased risk of surgical failures using femoral interference screws (relative risk = 0.52; confidence interval, 0.1794-1.3122). There was no difference in postoperative International Knee Documentation Committee score with Level I and II studies (relative risk = 0.9940; confidence interval, 0.6230-1.5860) or only Level I studies (relative risk = 1.0380; confidence interval, 0.6381-1.6886).

CONCLUSIONS

The literature suggests a trend toward decreased surgical failures with femoral fixation at the joint line with an interference screw. However, there is no difference when postoperative functional outcomes are compared. Future studies are needed with standardized fixation methods and outcomes assessment to determine the importance of femoral fixation.

[Is it possible to predict the length of knee flexor tendons by anthropometry?]

OBJECTIVE

To compare the anthropometric data and the sportive way of life with the hamstring tendons dimensions, prospectively, in order to create a rule to predetermine its dimensions.

METHODS

General and anthropometric data were collected from 30 patients that were submitted to anterior cruciate ligament reconstruction. These data were correlated to the diameter and length of the hamstring tendons. The data collected were: height, weight, age, knee lesion side, body mass, sportive training level, femoral length, tibia length, thigh circumference, and knee circumference. The correlation was made by Pearson coefficient.

RESULTS

Statistic significant correlation occurred only with height and tibia length versus the gracilis and semitendinous tendon length. Using linear regression the relations found could be expressed with the following formulas: semitendinous length = -2.276 + 0.177 x height; semitendinous length = 13.048 + 0.46 x tibia height; gracilis length = -9.413 + 0.207 x height; gracilis length = 7.036 + 0.583 x tibia height.

CONCLUSION

It is possible to predetermine hamstring tendons length through linear regression formulas before surgical intervention.

Is supplementary fixation necessary in anterior cruciate ligament reconstructions?

BACKGROUND

There has been concern regarding the fixation of anterior cruciate ligament reconstruction, with soft tissue grafts being strong and stiff enough to allow for early accelerated postoperative rehabilitation. Therefore, some have recommended supplementary fixation for soft tissue tibia interference screw fixation with a staple, to improve the strength and stiffness of the fixation. Unfortunately, with staple supplementation, there is a risk for symptomatic hardware, which may require a second surgery to remove the staple.

HYPOTHESIS

Supplementary fixation with a bioabsorbable knotless suture anchor will improve the structural properties of soft tissue tibia bioabsorbable interference screw (BIS) fixation and be comparable with supplementary fixation with a staple.

STUDY DESIGN

Controlled laboratory study.

METHOD

Fifteen porcine tibias and flexor profundus tendons were randomized into 3 fixation study groups: group 1, BIS; group 2, BIS + staple; and group 3, BIS + push-lock screw. The structural properties of the 3 fixation groups were tested under displacement-controlled cyclic loading and load to failure.

RESULTS

No significant difference in mean stiffness (N/mm ± SEM) under cyclic loading was found for BIS (335.31 ± 15.43), BIS + staple (344.81 ± 44.97), and BIS + push-lock (353.28 ± 38.93). Under load-to-failure testing, there were no differences found in stiffness, yield load, displacement at yield load, displacement at ultimate load, and energy absorbed among the 3 fixation methods. BIS + push-lock fixation had a significantly higher ultimate load than BIS alone and BIS + staple (917.85 ± 58.30 N vs 479.83 ± 66.04 N, P = .0003 vs 618.89 ± 8.94 N, P = .004).

CONCLUSION

Supplementary fixation with staple or push-lock screw did not significantly increase the structural strength and stiffness of the BIS soft tissue graft fixation under cyclic loading, but it did show improvement under load-to-failure testing for ultimate tensile load.

CLINICAL RELEVANCE

The indication for supplementary fixation for tibial BIS soft tissue graft fixation depends on the fixation that the BIS achieves at the time of the surgery because the tensile load is transferred to the secondary fixation if and only when there is slippage of graft at the primary fixation. The supplementary fixation may be of value in those cases with poor bone quality, such as revision surgery with tunnel widening and/or graft-tunnel mismatch, or possibly in cases with older patients or patients with disorders affecting bone mineral density.

Augmentation of bone tunnel healing in anterior cruciate ligament grafts: application of calcium phosphates and other materials

Bone tunnel healing is an important consideration after anterior cruciate ligament (ACL) replacement surgery. Recently, a variety of materials have been proposed for improving this healing process, including autologous bone tissue, cells, artificial proteins, and calcium salts. Amongst these materials are calcium phosphates (CaPs), which are known for their biocompatibility and are widely commercially available. As with the majority of the materials investigated, CaPs have been shown to advance the healing of bone tunnel tissue in animal studies. Mechanical testing shows fixation strengths to be improved, particularly by the application of CaP-based cement in the bone tunnel. Significantly, CaP-based cements have been shown to produce improvements comparable to those induced by potentially more complex treatments such as biologics (including fibronectin and chitin) and cultured cells. Further investigation of CaP-based treatment in the bone tunnels during ACL replacement is therefore warranted in order to establish what improvements in healing and resulting clinical benefits may be achieved through its application.

Mechanical evaluation of cross pins used for femoral fixation of hamstring grafts in ACL reconstructions

The goal of this study was to test the mechanical strength of 4 different cross pins currently available for femoral fixation by loading each cross pin to failure as received and determine the effect of 1 million cycles of fatigue loading. Additionally, the strength of resorbable pins was tested after prolonged exposure to biologic conditions. Six implants each of the Arthrotek LactoSorb (Biomet, Warsaw, Indiana), Mitek RigidFix (DePuy Mitek Inc, Raynham, Massachusetts), Arthrotek Bone Mulch Screw (Biomet), cortical allograft, and control were tested for 3-point failure without prior loading and after cyclic loading between 50 to 200 N at 10 Hz for 1 million cycles. The bioabsorbable pins were placed in sterile water at 37°C and tested after 2, 4, and 6 months for 3-point failure strength. All implants tested without antecedent loading demonstrated adequate strength for initial fixation for hamstring grafts. During fatigue testing, RigidFix implants (n=6) failed at 18,893±8365 cycles (with a central deformation of 0.48±0.11 mm prior to fracture). All of the other implants tested endured 1 million cycles of loading (50-200 N) without fracture or 1.5 mm central deformation. Neither of the bioabsorbable pins demonstrated a significant change in yield strength after prolonged exposure to water. All implants tested demonstrated adequate strength for initial fixation of hamstring grafts. The metal and bone implants far exceed the strength required to sustain mechanical fixation until biological fixation occurs; both polymeric implants demonstrated that they maintained enough mechanical strength to achieve this goal.

A comparison of the effect of central anatomical single-bundle anterior cruciate ligament reconstruction and double-bundle anterior cruciate ligament reconstruction on pivot-shift kinematics

BACKGROUND

Biomechanical differences between anatomical double-bundle and central single-bundle anterior cruciate ligament reconstruction using the same graft tissue have not been defined.

PURPOSE

The purpose of this study was to compare these reconstructions in their ability to restore native knee kinematics during a reproducible Lachman and pivot-shift examination.

STUDY DESIGN

Controlled laboratory study.

METHODS

Using a computer-assisted navigation system, 10 paired knees were subjected to biomechanical testing with a standardized Lachman and mechanized pivot-shift examination. The navigation system recorded the 3D motion path of a tracked point at the center of the tibia, center of the medial tibial plateau, and center of the lateral tibial plateau with each maneuver. The testing protocol consisted of evaluation in the intact state, after complete anterior cruciate ligament transection, after medial and lateral meniscectomy, and after anterior cruciate ligament reconstruction with (1) a single-bundle center-center or (2) anatomical double-bundle technique. Repeated-measures analysis of variance with a post hoc Tukey test was used to compare the measured translations with each test condition.

RESULTS

A significant difference in anterior translation was seen with Lachman examination between the anterior cruciate ligament- and medial and lateral meniscus-deficient condition compared with both the double-bundle and single-bundle center-center anterior cruciate ligament reconstruction (P < .001); no significant difference was observed between reconstructions. The double-bundle construct was significantly better in limiting anterior translation of the lateral compartment compared with the single-bundle reconstruction during a pivot-shift maneuver (2.0 +/- 5.7 mm vs 7.8 +/- 1.8 mm, P < .001) and was not significantly different than the intact anterior cruciate ligament condition (2.7 mm +/- 4.7 mm, P > .05).

DISCUSSION

Although double-bundle and single-bundle, center-center anterior cruciate ligament reconstructions appear equally effective in controlling anterior translation during a Lachman examination, analysis of pivot-shift kinematics reveals significant differences between these surgical reconstructions. An altered rotational axis resulted in significantly greater translation of the lateral compartment in the single-bundle compared with double-bundle reconstruction.

CLINICAL RELEVANCE

A double-bundle anterior cruciate ligament reconstruction may be a favorable construct for restoration of knee kinematics in the at-risk knee with associated meniscal injuries and/or significant pivot shift on preoperative examination.

Inorganic-organic hybrid scaffolds for osteochondral regeneration

Ligament graft failure frequently results from poor integration of the replacement tissue with associated bone. Thus, the ability to regenerate the bone-ligament osteochondral interface would be advantageous in ligament reconstruction. At the osteochondral interface, the tissue transitions from a bone-like matrix to fibrocartilage. Therefore, a scaffold which promotes a spatially regulated transition in cell behavior from osteoblast-like to chondrocyte-like would be desirable. Previous research indicates that addition of inorganic components to organic scaffolds can enhance the deposition of bone-like matrix by associated osteoblasts. We therefore reasoned that a gradient in the inorganic content of a hybrid inorganic-organic scaffold may induce an osteochondral-like transition in cell phenotype and matrix production. To test this hypothesis, hydrogels were prepared from poly(ethylene glycol) (PEG) and star poly(dimethylsiloxane) (PDMS(star)). As anticipated, both the matrix deposition and phenotype of encapsulated osteoblasts varied with scaffold inorganic content, although the directionality of this modulation was contrary to expectation. Specifically, osteoblasts appeared to transdifferentiate into chondrocyte-like cells with increasing scaffold inorganic content, as indicated by increased chondroitin sulfate and collagen type II production and by upregulation of sox9, a transcription factor associated with chondrocytic differentiation. Furthermore, the deposition of bone-like matrix (collagen type I, calcium phosphate, and osteocalcin) decreased with increasing PDMS(star) content. The resistance of the PDMS(star)-PEG scaffolds to protein adsorption and/or the changes in gel modulus/mesh structure accompanying PDMS(star) incorporation may underlie the unexpected increase in chondrocytic phenotype with increasing inorganic content. Combined, the present results indicate that PDMS(star)-PEG hybrid gels may prove promising for osteochondral regeneration. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Comparison between bovine bone and titanium interference screws for implant fixation in ACL reconstruction: a biomechanical study

INTRODUCTION

The application of interference screws for the fixation of bone-patellar tendon-bone (BPTB) grafts is a well-established technique in anterior-cruciate ligament reconstruction. Interference screws derived from bovine compact bone are a biological alternative to metallic or biodegradable polymer interference screws.

MATERIALS AND METHODS

In 60 porcine specimens, the tibial part of an anterior-cruciate ligament reconstruction was performed using a BPTB graft. To secure the graft, either an 8-mm titanium interference screw or a self-made bovine interference screw (BC), or a commercial bovine compact bone screw (Tutofix) was used. The maximum failure load was determined by means of a universal testing machine with computer interface at a testing speed of 50 mm/min. In a second test series, cyclic sub-maximal load was applied to the test specimen from 40 to 400 N with a number of 1,000 load cycles and a frequency of 1 Hz. Subsequently, the maximum failure load was determined. The stiffness of the test specimen was investigated in both test series. Each type of interference screw was tested 10 times.

RESULTS

A secure fixation of the grafts was achieved with all interference screws. In the experiments on the maximum load to failures, the titanium screws showed significantly higher failure loads than the Tutofix screws (P = 0.005). The stiffness of the grafts fixed with BC screws was significantly higher as compared to the fixation with Tutofix screws (P = 0.005). After cyclic sub-maximal loading, the maximum failure load of the titanium screws was significantly higher than that of the Tutofix screws (P = 0.033). The fixation of the BC screws showed a significantly higher failure load (P = 0.021) and stiffness (P = 0.032) than the Tutofix screw fixation. Except for two screw head fractures and two intra-tendinous graft ruptures, the failure mode was slippage in the interface between interference screw and bone plug.

CONCLUSION

Interference screws derived from bovine compact bone show similar good results as the titanium interference screws. Therefore, the safety and in vivo performance of products derived from xenogenic bone should be the focus of further investigations.

Pretensioning of quadruple flexor tendon grafts in two types of femoral fixation: quasi-randomised controlled pilot study

Pretensioning of the flexor tendon graft of the knee is used to improve the stability of anterior cruciate ligament (ACL) reconstructions. The objective was to demonstrate the pretensioning of grafts of the semitendinosus and gracilis in situ with range of flexion and extension of 0-110°, and determine the appropriate number of cycles in two types of femoral fixation. ACL reconstruction was performed in 60 patients, aged 16-48 years, 90% male, with 50% right knees and 50% left knees, divided into two groups of 30 patients: One with the femur fixed using interference screws (direct form) and the other with the transcondylar cross-pin screw (from a distance). Total length of the grafts, their circumference and the measurements on the radiographs of length of the grafts submitted to pretensioning and the measurements with ten, 25 and 50 cycles of flexion and extension were determined. There was no significant difference in relation to the total tendon lengths and their circumferences. The lengths of the portions submitted to pretensioning were significantly different: 7.90 cm for the interference and 10.92 cm for the transcondylar (mean). After tensioning, in the interference and transcondylar groups, respectively, lengthening was 3.57 mm/3.97 mm with ten, 6.30 mm/7.03 mm with 25, and 6.83 mm/7.7 mm with 50 cycles. The greater the length of the graft, the greater the lengthening on pretensioning throughout the substance; the shorter the length, the earlier the end of the lengthening was achieved, close to 25 cycles; more than ten cycles were necessary, 25 being sufficient.

Torsional stability of interference screws derived from bovine bone--a biomechanical study

Background

In the present biomechanical study, the torsional stability of different interference screws, made of bovine bone, was tested. Interference screws derived from bovine bone are a possible biological alternative to conventional metallic or bioabsorbable polymer interference screws.

Methods

In the first part of the study we compared the torsional stability of self-made 8 mm Interference screws (BC) and a commercial 8 mm interference screw (Tutofix^®). Furthermore, we compared the torsional strength of BC screws with different diameters. For screwing in, a hexagon head and an octagon head were tested. Maximum breaking torques in polymethyl methacrylate resin were recorded by means of an electronic torque screw driver. In the second part of the study the tibial part of a bone-patellar tendon-bone graft was fixed in porcine test specimens using an 8 mm BC screw and the maximum insertion torques were recorded. Each interference screw type was tested 5 times.

Results

There was no statistically significant difference between the different 8 mm interference screws (p = 0.121). Pairwise comparisons did not reveal statistically significant differences, either. It was demonstrated for the BC screws, that a larger screw diameter significantly leads to higher torsional stability (p = 9.779 × 10^-5). Pairwise comparisons showed a significantly lower torsional stability for the 7 mm BC screw than for the 8 mm BC screw (p = 0.0079) and the 9 mm BC screw (p = 0.0079). Statistically significant differences between the 8 mm and the 9 mm BC screw could not be found (p = 0.15). During screwing into the tibial graft channel of the porcine specimens, insertion torques between 0.5 Nm and 3.2 Nm were recorded. In one case the hexagon head of a BC screw broke off during the last turn.

Conclusions

The BC screws show comparable torsional stability to Tutofix^® interference screws. As expected the torsional strength of the screws increases significantly with the diameter. The safety and in vivo performance of products derived from xenogeneic bone should be the focus of further investigations.

Rehabilitation results following anterior cruciate ligament reconstruction using a hard brace compared to a fluid-filled soft brace

The purpose of this study was to compare the clinical outcomes of rehabilitation after ACL reconstruction using a water-filled soft brace to those using a hard brace. The method used in this study was a prospective randomised clinical trial including 36 patients wearing a hard brace and 37 patients wearing a water-filled soft brace for 6 weeks after surgery. Preoperative and postoperative (seven examinations) clinical evaluation within a follow-up period of 1 year including effusion status, swelling and range of motion (ROM), IKDC 2000, KT1000 Arthrometer, Lysholm knee scoring scale and Tegner activity score. Mean values are presented with standard deviations. Data was analysed using descriptive statistics and Student's t-test for unpaired samples. Significantly less effusion was found in the soft brace group from 5 days (p=0.002) to 12 weeks (p<0.024) postoperative. Hard brace patients presented with significantly more extension deficit from 5 days (p=0.036) to 12 months (p=0.014) postoperative but no significant difference was detected in complete ROM, laxity or thigh atrophy at any follow-up examination. Patients treated with a soft brace had significantly higher IKDC subjective ratings at 6 weeks (p=0.02) up to 12 months after operation (p=0.002) and rated significantly higher in Tegner activity score (p=0.004) and Lysholm knee scoring scale (p=0.006) 6 and 12 months (p<0.001 for both scores) postoperatively. The water-filled soft brace was superior regarding effusion, swelling, extension deficit and patient-measured midterm outcome. The soft brace presents a safe, easy-to-use and effective alternative to the hard brace.

How to avoid the risk of intraoperative cartilage damage in anatomic four tunnel double bundle anterior cruciate ligament reconstruction

Double bundle (DB) anterior cruciate ligament (ACL) reconstruction is technically demanding. In order to create four anatomical anteromedial (AM) and posterolateral (PL) bone tunnels many surgeons adopt new ways of tibial and femoral bone tunnel drilling. From surgical experience, these technical changes might increase the risk for intraoperative pitfalls. An intraoperative articular cartilage damage to the medial femoral condyle or the medial tibial plateau could be disastrous for the patient. It may be caused by an insufficient anteromedial portal technique for femoral AM and PL bone tunnel drilling or flat tibial AM or PL bone tunnel reaming. Potential pitfalls may be avoided by small modifications to the surgical technique. In this present technical note, a sequence of surgical steps are described, which may help to avoid articular cartilage damage to the medial femoral condyle and medial tibial plateau in anatomical four tunnel DB ACL reconstruction.

Collagen-platelet composite enhances biomechanical and histologic healing of the porcine anterior cruciate ligament

BACKGROUND

The anterior cruciate ligament (ACL) fails to heal after traumatic rupture. Furthermore, large-animal models have recently shown that 1-month functional ACL healing is augmented after suture repair when a bioactive scaffold is placed in the tear site.

HYPOTHESIS

At the time of suture repair, placement of a bioactive scaffold in the ACL wound site would improve the structural properties of the tissue.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-seven knees in immature pigs underwent ACL transection and suture repair. A collagen-platelet composite (CPC) was used to supplement the repair in 14 knees. Knees were harvested at 4 weeks, 6 weeks, and 3 months. Mechanical testing and histologic analysis were performed.

RESULTS

The addition of a CPC to a suture repair resulted in improvements in yield load and linear stiffness of the repair tissue at 3 months, as well as a significant increase in cell density. A reduction in yield load and stiffness occurred at the 6-week time point in both groups, a phase when revascularization was noted.

CONCLUSION

The addition of a CPC to a suture repair enhanced the structural properties of the ACL, and the improvement was associated with increased cellularity within the healing ligament.

CLINICAL RELEVANCE

The addition of a bioactive scaffold to the wound site improved the functional healing of the ACL after suture repair. The decreased repair strength during revascularization may indicate a need to protect the repair site through this period.

Influence of bone adaptation on tendon-to-bone healing in bone tunnel after anterior cruciate ligament reconstruction in a rabbit model

Anterior cruciate ligament (ACL) reconstruction with placement of grafted tendon in bone tunnel is a common surgical procedure. Bone tunnel creation may result in stress shielding of postero-lateral regions of tibial tunnel. The present study was designed to characterize the changes of peri-graft bone and compare with tendon-to-bone (T-B) healing in spatial and temporal manners after ACL reconstruction in rabbit. Surgical reconstruction using digital extensor tendon in bone tunnel was performed on 48 rabbits. Twelve rabbits were sacrificed at 0, 2, 6, and 12 weeks postoperatively for radiological and histological examinations. Bone mass and microarchitecture at the anterior, posterior, medial, and lateral regions of tunnel wall at distal femur and proximal tibia were evaluated. Using peripheral quantitative computed tomography, a 26, 22, and 42% decrease in bone mineral density (BMD) relative to baseline was present in the medial region of the femoral tunnel and the posterior and lateral regions of the tibial tunnel, respectively, at week 12 postoperatively (p < 0.05). It was accompanied by a decrease in trabecular number and increase in trabecular spacing, the shift of platelike to rodlike trabeculae, and loss of anisotropy under micro-computed tomography evaluation. This finding was echoed by histology showing increased osteoclastic activities and poor T-B healing in these regions. In conclusion, the postoperative bone loss and associated poor T-B healing was region-dependent, which may result from adaptive changes after tunnel creation.

Functional grading of mineral and collagen in the attachment of tendon to bone

Attachment of dissimilar materials is a major challenge because high levels of localized stress may develop at their interfaces. An effective biologic solution to this problem exists at one of nature's most extreme interfaces: the attachment of tendon (a compliant, structural "soft tissue") to bone (a stiff, structural "hard tissue"). The goal of our study was to develop biomechanical models to describe how the tendon-to-bone insertion derives its mechanical properties. We examined the tendon-to-bone insertion and found two factors that give the tendon-to-bone transition a unique grading in mechanical properties: 1), a gradation in mineral concentration, measured by Raman spectroscopy; and 2), a gradation in collagen fiber orientation, measured by polarized light microscopy. Our measurements motivate a new physiological picture of the tissue that achieves this transition, the tendon-to-bone insertion, as a continuous, functionally graded material. Our biomechanical model suggests that the experimentally observed increase in mineral accumulation within collagen fibers can provide significant stiffening of the partially mineralized fibers, but only for concentrations of mineral above a "percolation threshold" corresponding to formation of a mechanically continuous mineral network within each collagen fiber (e.g., the case of mineral connectivity extending from one end of the fiber to the other). Increasing dispersion in the orientation distribution of collagen fibers from tendon to bone is a second major determinant of tissue stiffness. The combination of these two factors may explain the nonmonotonic variation of stiffness over the length of the tendon-to-bone insertion reported previously. Our models explain how tendon-to-bone attachment is achieved through a functionally graded material composition, and provide targets for tissue engineered surgical interventions and biomimetic material interfaces.

MRI measurement of the 2 bundles of the normal anterior cruciate ligament

Anatomical studies have shown that the normal anterior cruciate ligament (ACL) consists of 2 distinct functional bundles: the anteromedial and posterolateral bundles. To date, no study has assessed the magnetic resonance imaging (MRI) appearance of the anteromedial and posterolateral bundles. The purpose of this study was to measure the anteromedial and posterolateral bundles using high-field digital MRI. Fifty MRIs of the knees of 50 patients were prospectively collected using a 1.5-T magnet. The length and width of each ACL bundle was measured on sagittal and coronal digital MRIs, independently performed by 2 observers blinded to each other's measurements. The average length and width of the anteromedial and posterolateral bundles were determined for all patients. Intraclass correlation coefficients were calculated to determine intertester test-retest reliability. In the sagittal plane, the anteromedial bundle averaged 36.9+/-2.8 mm in length and 5.1+/-0.7 mm in width. The posterolateral bundle, by contrast, averaged 20.5+/-2.4 mm in length and 4.4+/-0.8 mm in width. In the coronal plane, the width of the anteromedial bundle averaged 4.2+/-0.8 mm and of the posterolateral bundle averaged 3.7+/-0.8 mm. Interobserver reliability for length of the ACL in the sagittal plane was 0.85, with a 95% CI of 0.75 to 0.91 for the anteromedial bundle and 0.75 with a 95% CI of 0.60 to 0.85 for the posterolateral bundle. Providing precise measurement of the ACL anteromedial and posterolateral bundles on MRI may improve the ability to detect damage to 1 or both of the bundles following injury.