The elongation behavior of the anterior cruciate ligament graft in vivo. A long-term follow-up study

Graft isometry during anatomical ACL reconstruction has little effect on surgical outcomes

PURPOSE

To investigate the surgical outcomes of anatomical anterior cruciate ligament (ACL) reconstruction according to the graft isometry measured during surgery.

METHODS

Electrical medical records of patients who underwent an arthroscopic ACL reconstruction through the transportal technique using hamstring tendon autograft between 2012 and 2016 were retrospectively reviewed. The patients were classified into two groups based on the graft length change throughout the knee range of motion measured just before graft fixation (Group 1, graft length change ≤ 2 mm; Group 2, graft length change > 2 mm). Comparative analyses, including a non-inferiority trial, were performed regarding the clinical scores, knee laxity, and radiographic parameters between the groups.

RESULTS

A total of 67 patients were included in the study. The total change in the length of ACL graft throughout the knee range of motion was 1.4 ± 0.4 mm in Group 1 (range, 0.2-2.0 mm), and 3.0 ± 0.7 mm in Group 2 (range, 2.2-5.0 mm). Group 1 showed a relatively high (proximal) femoral tunnel and shallow (anterior) tibial tunnel compared to Group 2 (P < 0.001 and P = 0.028, respectively), but there were no apparent differences in the macroscopic view. There were no statistically significant differences in the clinical outcomes between groups at 2 years after surgery, which satisfied the non-inferiority criterion of Group 1 in terms of clinical scores and knee laxity compared to Group 2.

CONCLUSION

The surgical outcomes of anatomical ACL reconstruction in patients with non-isometric ACL graft were not inferior in terms of clinical scores and knee laxity, compared to those with nearly-isometric ACL graft. The graft tunnel placement in the isometric position during anatomical ACL reconstruction, which is technically challenging in the clinical setting, is not a crucial factor in terms of clinical outcomes.

LEVEL OF EVIDENCE

Level IV.

Effects of and Response to Mechanical Loading on the Knee

Mechanical loading to the knee joint results in a differential response based on the local capacity of the tissues (ligament, tendon, meniscus, cartilage, and bone) and how those tissues subsequently adapt to that load at the molecular and cellular level. Participation in cutting, pivoting, and jumping sports predisposes the knee to the risk of injury. In this narrative review, we describe different mechanisms of loading that can result in excessive loads to the knee, leading to ligamentous, musculotendinous, meniscal, and chondral injuries or maladaptations. Following injury (or surgery) to structures around the knee, the primary goal of rehabilitation is to maximize the patient's response to exercise at the current level of function, while minimizing the risk of re-injury to the healing tissue. Clinicians should have a clear understanding of the specific injured tissue(s), and rehabilitation should be driven by knowledge of tissue-healing constraints, knee complex and lower extremity biomechanics, neuromuscular physiology, task-specific activities involving weight-bearing and non-weight-bearing conditions, and training principles. We provide a practical application for prescribing loading progressions of exercises, functional activities, and mobility tasks based on their mechanical load profile to knee-specific structures during the rehabilitation process. Various loading interventions can be used by clinicians to produce physical stress to address body function, physical impairments, activity limitations, and participation restrictions. By modifying the mechanical load elements, clinicians can alter the tissue adaptations, facilitate motor learning, and resolve corresponding physical impairments. Providing different loads that create variable tensile, compressive, and shear deformation on the tissue through mechanotransduction and specificity can promote the appropriate stress adaptations to increase tissue capacity and injury tolerance. Tools for monitoring rehabilitation training loads to the knee are proposed to assess the reactivity of the knee joint to mechanical loading to monitor excessive mechanical loads and facilitate optimal rehabilitation.

Creating a Femoral Tunnel Aperture at the Anteromedial Footprint Versus the Central Footprint in ACL Reconstruction: Comparison of Contact Stress Patterns

Background:

It remains unclear whether an anteromedial (AM) footprint or a central footprint anterior cruciate ligament (ACL) graft exhibits less contact stress with the femoral tunnel aperture. This contact stress can generate graft attrition forces, which can lead to potential graft failure.

Purpose/Hypothesis:

The purpose of this study was to compare the difference in contact stress patterns of the graft around a femoral tunnel that is created at the anatomic AM footprint versus the central footprint. It was hypothesized that the difference in femoral tunnel positions would influence the contact stress at the interface between the reconstructed graft and the femoral tunnel orifice.

Study Design:

Controlled laboratory study.

Methods:

A total of 24 patients who underwent anatomic single-bundle ACL reconstruction were included in this study. In 12 patients, the femoral tunnels were created at the center of the native AM footprint (AM group), and in the remaining 12 patients the center of the femoral tunnel was placed in the anatomic central footprint (central group). Three-dimensional knee models were created and manipulated using several modeling programs, and the graft-tunnel angle (GTA) was determined using a special software program. The peak contact stresses generated on the virtual ACL graft around the femoral tunnel orifice were calculated using a finite element method.

Results:

The mean GTA was significantly more obtuse in the AM group than in the central group (124.2° ± 5.9° vs 112.6° ± 7.9°; P = .001). In general, both groups showed high stress distribution on the anterior surface of the graft, which came in contact with the anterior aspect of the femoral tunnel aperture. The degree of stress in the central group (5.3 ± 2.6 MPa) was significantly higher than that in the AM group (1.2 ± 1.1 MPa) (P < .001).

Conclusion:

Compared with the AM footprint ACL graft, the central footprint ACL graft developed significantly higher contact stress in the extended position, especially around the anterior aspect of the femoral tunnel orifice.

Clinical Relevance:

The contact stress of the ACL graft at the extended position of the knee may be minimized by creating the femoral tunnel at the AM-oriented footprint.

Dual fluoroscopic imaging and CT-based finite element modelling to estimate forces and stresses of grafts in anatomical single-bundle ACL reconstruction with different femoral tunnels

PURPOSE

Little is known about the in vivo forces and stresses on grafts used in anterior cruciate ligament (ACL) reconstruction. The aims of this study were to evaluate and compare the forces and stresses on grafts used in anatomical single-bundle ACL reconstruction at different locations of the femoral footprint (anterior vs middle vs posterior; high vs middle vs low) during a lunge motion.

METHODS

Establish subject-specific finite element models with different graft's tunnel loci to represent the primary ACL reconstructions. A displacement controlled finite element method was used to simulate lunge motions (full extension to ~ 100° of flexion) with six-degree-of-freedom knee kinematics data obtained from the validated dual fluoroscopic imaging techniques. The reaction force of the femur and maximal principal stresses of the grafts were subsequently calculated during knee flexion.

RESULTS

Increased and decreased graft forces were observed when the grafts were located higher and lower on the femoral footprint, respectively; anterior and posterior graft placement did not significantly affect the graft force. Lower and posterior graft placement resulted in less stress on the graft at higher degrees of flexion; there were no significant differences in stress when the grafts were placed from 0° to 30° of flexion on the femoral footprint.

CONCLUSION

The proposed method is able to simulate knee joint motion based on in vivo kinematics. The results demonstrate that posterior to the centre of the femoral footprint is the strategic location for graft placement, and this placement results in anatomical graft behaviour with a low stress state.

Anterior Cruciate Ligament Graft Tunnel Placement and Graft Angle Are Primary Determinants of Internal Knee Mechanics After Reconstructive Surgery

BACKGROUND

Graft placement is a modifiable and often discussed surgical factor in anterior cruciate ligament (ACL) reconstruction (ACLR). However, the sensitivity of functional knee mechanics to variability in graft placement is not well understood.

PURPOSE

To (1) investigate the relationship of ACL graft tunnel location and graft angle with tibiofemoral kinematics in patients with ACLR, (2) compare experimentally measured relationships with those observed with a computational model to assess the predictive capabilities of the model, and (3) use the computational model to determine the effect of varying ACL graft tunnel placement on tibiofemoral joint mechanics during walking.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eighteen participants who had undergone ACLR were tested. Bilateral ACL footprint location and graft angle were assessed using magnetic resonance imaging (MRI). Bilateral knee laxity was assessed at the completion of rehabilitation. Dynamic MRI was used to measure tibiofemoral kinematics and cartilage contact during active knee flexion-extension. Additionally, a total of 500 virtual ACLR models were created from a nominal computational knee model by varying ACL footprint locations, graft stiffness, and initial tension. Laxity tests, active knee extension, and walking were simulated with each virtual ACLR model. Linear regressions were performed between internal knee mechanics and ACL graft tunnel locations and angles for the patients with ACLR and the virtual ACLR models.

RESULTS

Static and dynamic MRI revealed that a more vertical graft in the sagittal plane was significantly related (P < .05) to a greater laxity compliance index (R² = 0.40) and greater anterior tibial translation and internal tibial rotation during active knee extension (R² = 0.22 and 0.23, respectively). Similarly, knee extension simulations with the virtual ACLR models revealed that a more vertical graft led to greater laxity compliance index, anterior translation, and internal rotation (R² = 0.56, 0.26, and 0.13). These effects extended to simulations of walking, with a more vertical ACL graft inducing greater anterior tibial translation, ACL loading, and posterior migration of contact on the tibial plateaus.

CONCLUSION

This study provides clinical evidence from patients who underwent ACLR and from complementary modeling that functional postoperative knee mechanics are sensitive to graft tunnel locations and graft angle. Of the factors studied, the sagittal angle of the ACL was particularly influential on knee mechanics.

CLINICAL RELEVANCE

Early-onset osteoarthritis from altered cartilage loading after ACLR is common. This study shows that postoperative cartilage loading is sensitive to graft angle. Therefore, variability in graft tunnel placement resulting in small deviations from the anatomic ACL angle might contribute to the elevated risk of osteoarthritis after ACLR.

The effect of cyclic knee motion on the elongation of four-strand hamstring autograft in anterior cruciate ligament reconstruction: an in-situ pilot study

Background

Pretension of the viscoelastic graft by cyclic knee motion has been confirmed to decrease the graft creep and improve the outcome of anterior cruciate ligament (ACL) reconstruction. The purpose of the present study was to investigate the effect of cyclic knee motion on the elongation of the four-strand hamstring tendon autograft in situ and to explore the stable level cycle, in which the tendon length achieved a stable level.

Methods

The study was performed with 53 consecutive patients undergoing transtibial ACL reconstruction with four strand hamstring tendon from Aug 2013 to Apr 2015. 43 males and 10 females were included with mean age of 29 ± 10 years. The pretension of the tendons was operated by cyclical knee motion ranging from 0 to 110°after the femoral fixation with Endo-button. The tendon length after 10, 20, 30 and 40 cycles was measured respectively and compared by repeated measure ANOVA. Then multivariate logistic regression was used to investigate the effect of the patients’ parameters (age, gender, height, body weight, tendon length, etc.) on the elongation of the graft and the stable level cycle.

Results

The mean lengthening of the graft at 10, 20, 30 and 40 times was 3.0 ± 1.4 mm, 4.3 ± 1.5 mm, 4.8 ± 1.7 mm and 4.8 ± 1.8 mm respectively. No significant correlation was found between the elongation and the patients’ parameters. There was significant difference of the tendon length from 0 to 30 cycles (F = 264.8, df = 1.95, p<0.001). However, the tendon length achieved a stable level after 30 cycles and the median elongation from 30 cycles to 40 cycles was 0 (0–1) mm with no significant difference (F = 2.039, p = 0.159). The male and female tendon length achieved to a stable level at 20 cycles and 30 cycles respectively but with no significant difference (p = 0.074).

Conclusions

The four-strand hamstring tendon was elongated after cyclic knee motion and the elongation achieved a stable level after 30 cycles for the transtibial technique. Both of the tendon elongation and the stable level cycle were not correlated with patients’ gender, age, preoperative duration, graft diameter and length.

Transportal central femoral tunnel placement has a significantly higher revision rate than transtibial AM femoral tunnel placement in hamstring ACL reconstruction

PURPOSE

It is proposed that central femoral ACL graft placement better controls rotational stability. This study evaluates the consequence of changing the femoral tunnel position from the AM position drilled transtibially to the central position drilled transportally. The difference in ACL graft failure is reported.

METHODS

This prospective consecutive patient single surgeon study compares the revision rates of 1016 transtibial hamstring ACL reconstructions followed for 6-15 years with 464 transportal hamstring ACL reconstructions followed for 2-6 years. Sex, age, graft size, time to surgery, meniscal repair and meniscectomy data were evaluated as contributing factors for ACL graft failure to enable a multivariate analysis. To adjust for the variable follow-up a multivariate hazard ratio, failure per 100 graft years and Kaplan-Meier survivorship was determined.

RESULTS

With transtibial ACLR 52/1016 failed (5.1%). With transportal ACLR 32/464 failed (6.9%). Significant differences between transportal and transtibial ACLR were seen for graft diameter, time to surgery, medial meniscal repair rates and meniscal tissue remaining after meniscectomy. Adjusting for these the multivariate hazard ratio was 2.3 times higher in the transportal group (p = 0.001). Central tunnel placement resulted in a significantly 3.5 times higher revision rate compared to an anteromedial tunnel placement per 100 graft years (p = 0.001). Five year survival was 980/1016 (96.5%) for transtibial versus 119/131 (90.5%) for transportal. Transportal ACLR also showed a significantly higher earlier failure rate with 20/32 (61%) of the transportal failing in the first year compared with 14/52 (27%) for transtibial. (p = 0.001.) CONCLUSION: Transportal central femoral tunnel ACLR has a higher failure rate and earlier failure than transtibial AM femoral tunnel ACLR.

LEVEL OF EVIDENCE

Level II-prospective comparative study.

The posterior horn of the lateral meniscus is a reliable novel landmark for femoral tunnel placement in ACL reconstruction

PURPOSE

Femoral tunnel placement is essential for good outcome in anterior cruciate ligament (ACL) reconstruction. In the past, several attempts have been made to optimize femoral tunnel placement. It was observed that the posterior horn of the lateral meniscus was always located directly below to the desired femoral ACL tunnel position, when the knee was brought to deep flexion (> 120°). The goal of the present study was to verify the hypothesis that the posterior horn of the lateral meniscus can be used as a landmark for femoral tunnel placement.

METHODS

Out of a consecutive series of ACL reconstructions done by a single surgeon, 55 lateral radiographs were evaluated according to the quadrant method by Bernard and Hertel. Additionally, on anterior-posterior radiographs the femoral tunnel angle was determined.

RESULTS

In the present case series the posterior horn of the lateral meniscus could be identified and used as a landmark for femoral tunnel placement in all cases. The mean tunnel depth was 24 ± 5.1% and the mean tunnel height was 31.3 ± 5.7%. The mean femoral tunnel angle was 41 ± 4.9° using the anatomical axis as a reference. Compared to previous cadaver studies the data of the present study were within their anatomical range of the native ACL insertion site.

CONCLUSION

The suggested technique using the posterior horn of the lateral meniscus as a landmark for femoral tunnel placement showed reproducible results and matches the native ACL insertion site compared to previous cadaveric studies. In particular, non-experienced ACL surgeons will benefit from this apparent landmark and the corresponding easy-to-use ACL reconstruction method.

LEVEL OF EVIDENCE

IV.

[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.

Timing of Postoperative Mechanical Loading Affects Healing Following Anterior Cruciate Ligament Reconstruction: Analysis in a Murine Model

BACKGROUND

Following anterior cruciate ligament (ACL) reconstruction, the mechanical loading of the tissues has a significant impact on tendon-to-bone healing. The purpose of this study was to determine the effect of the timing of the initiation of mechanical loading on healing of a tendon graft in a bone tunnel.

METHODS

ACL reconstruction using a flexor tendon autograft was performed in 56 mice randomized to 4 groups with differing times to initiation of postoperative mechanical loading: (1) immediate, (2) 5 days, (3) 10 days, or (4) 21 days following surgery. An external fixator was placed across the knee at the time of surgery and removed when mechanical loading was scheduled to commence. Following removal of the external fixator, animals were permitted free, unrestricted cage activity. All mice were killed on postoperative day 28, and tendon-to-bone healing was assessed by biomechanical testing, microcomputed tomography (micro-CT), and histological analysis.

RESULTS

The mean failure force (and standard deviation) of the reconstructed ACL at the time of sacrifice was highest for Group 2 (3.29 ± 0.68 N) compared with Groups 1, 3, and 4 (p = 0.008). Micro-CT bone volume fraction was greatest for Group 2 in the femoral tunnel (p = 0.001), tibial tunnel (p = 0.063), and both bones (p < 0.001). Similarly, histological analysis demonstrated a narrower scar tissue interface and increased direct contact at the tendon-bone interface (p = 0.012) for Group 2.

CONCLUSIONS

Following ACL reconstruction, a defined period of immobilization without weight-bearing appears to improve biomechanical strength of the healing tendon-bone interface, while prolonged periods without mechanical load and motion decrease the ultimate load to failure in this murine model.

CLINICAL RELEVANCE

The ideal period of restricted weight-bearing and motion following ACL reconstruction remains undefined. In a murine model, improved healing was noted for animals immobilized for a brief period of 5 days. This work may serve as an initial step in determining the ideal time period in a clinical population.

The anatomy of the anterior cruciate ligament and its relevance to the technique of reconstruction

Anterior cruciate ligament (ACL) reconstruction is commonly performed and has been for many years. Despite this, the technical details related to ACL anatomy, such as tunnel placement, are still a topic for debate. In this paper, we introduce the flat ribbon concept of the anatomy of the ACL, and its relevance to clinical practice.

Cite this article: Bone Joint J 2016;98-B:1020–6.

Arthroscopic Stabilization of Chronic Acromioclavicular Joint Dislocations: Triple- Versus Single-Bundle Reconstruction

BACKGROUND

Arthroscopically assisted single-bundle (SB) or double-bundle coracoclavicular (CC) ligament reconstruction using autologous tendon grafts has been reported to provide acromioclavicular (AC) joint (ACJ) stability in chronic instability cases. Recently, additional AC ligament reconstruction to provide triple-bundle (TB) stabilization has been introduced but lacks a comparison of clinical and radiological outcomes.

HYPOTHESIS

Arthroscopically assisted anatomic TB CC and AC reconstruction yields superior clinical and radiological results when compared with nonanatomic SB CC reconstruction.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Twenty-six patients (mean [±SD] age, 46.9 ± 12.8 years) suffering from chronic high-grade ACJ instability underwent ACJ stabilization using autologous hamstring grafts. Twelve patients underwent combined anatomic TB CC and AC reconstruction using a semitendinosus tendon with clavicular interference screw fixation (TB group), and 14 underwent isolated SB CC reconstruction using the AC GraftRope system with a gracilis tendon (SB group). After a minimum follow-up of 2 years (mean, 29.0 ± 7.4 months), patients were evaluated radiologically and clinically using the Constant, American Shoulder and Elbow Surgeons (ASES), Taft, and Acromioclavicular Joint Instability Score (ACJI) outcome measures.

RESULTS

The mean Constant score increased significantly in both groups, from 71.6 preoperatively to 88.8 postoperatively in the TB group and from 67.8 to 82.6 in the SB group (P ≤ .009). No intergroup difference was found regarding the final Constant or ASES scores. Regarding the ACJ-specific scores, the final outcomes were significantly different: 10.9 (TB group) versus 9.0 (SB group) for the mean Taft score (P = .018) and 84.7 versus 58.4, respectively, for the mean ACJI score (P = .0001). No significant radiological difference was found regarding the mean CC distance (10.7 mm [TB group] vs 13.1 mm [SB group]). The TB group showed superior horizontal ACJ stability (P = .011), which was associated with a better clinical outcome according to the ACJI and Taft scores. In the SB group, the rate of ACJ instability recurrence was higher (21% vs 8% [TB group]).

CONCLUSION

Combined arthroscopically assisted anatomic TB CC and AC ligament reconstruction using an autologous semitendinosus tendon graft provides superior clinical and radiological results compared with isolated nonanatomic SB CC ligament reconstruction using the AC GraftRope system. In particular, the TB technique can better restore horizontal ACJ stability, which is associated with superior ACJ-specific outcome scores.

Pretensioning of Soft Tissue Grafts in Anterior Cruciate Ligament Reconstruction

To determine which preconditioning and pretensioning techniques should be applied to soft tissue grafts during anterior cruciate ligament (ACL) reconstruction to avoid loss of tension after surgery, fresh semitendinosus and tibialis anterior tendons underwent tensile mechanical testing with 4 pretensioning and/or preconditioning techniques. A mechanical tester was used to collect the data. Group I (n=5) was given only an initial 80 N pull for tensioning, Group II (n=4) was given pretensioning and initial tensioning, Group III (n=5) was given cyclic tensioning and initial tensioning, and Group IV (n=5) was given a combination of the 3 techniques. Group I lost 50% of the initial tension at 30 minutes. The residual tension in Groups II, III, and IV was significantly higher than that in Group I after 1, 10, and 30 minutes (P<.001). Group IV consistently showed significantly higher residual tension than Groups II and III after 10 and 30 minutes (P<.05). All groups experienced elongation during testing: Group I (10.8 mm)<Group IV (14.6 mm)<Group III (15.6 mm)<Group II (16.6 mm), with significant differences observed between groups (P<.05). All experimental groups showed significantly greater stiffness than the control group (Group I) (P<.001). This study confirmed that pretensioning or preconditioning after 30 minutes leaves a graft with higher residual tension. Moreover, pretensioning and preconditioning had an additive effect and resulted in significantly greater retained tension than either method performed individually. A simple pull up to 80 N before fixation does not impart sufficient tension to a graft to prevent it from failing. The authors recommend that clinicians performing ACL reconstructions with soft tissue grafts precondition or pretension the tendons before final tibial fixation to achieve greater retained tension in the graft after placement.

Regional mechanical properties of human patellar tendon allografts

PURPOSE

Very little is known regarding regional biomechanical properties of patellar tendon allografts.

METHODS

Ten human bone-tendon-bone (BTB) patellar grafts were separated into equal thirds and underwent cyclic and failure testing. Grafts were non-irradiated and processed using proprietary sterilization methods.

RESULTS

The central third was the thickest region (4.9 ± 0.4 mm) compared to the medial and lateral (p < 0.05). The lateral third was the longest region (58.8 ± 8.8 mm) compared to the medial (47.9 ± 8.5 mm) and central (47.2 ± 8.8 mm) portions (p < 0.05). Cyclic testing demonstrated no regional differences with respect to elongation (n.s.) and creep strain (n.s.). Failure testing demonstrated increased maximum load and stiffness in the central region (1,680 ± 418 N and 278 ± 67 N/mm, respectively) as compared to the medial (1,033 ± 214 N, p < 0.002, 201 ± 37 N/mm, p < 0.03) and lateral thirds (908 ± 412 N, p < 0.03, 173 ± 66 N/mm, p < 0.002). Elongation at maximum load did not vary between regions. Central region maximum stress (41.0 ± 12.5 MPa) was greater than that of the medial third (28.1 ± 3.6 MPa, p < 0.02), with strain at maximum stress larger in the central third (0.21 ± 0.03) compared to lateral (0.16 ± 0.03, p < 0.01).

CONCLUSIONS

The central third of a non-irradiated, human bone-patellar tendon-bone construct is thicker and biomechanically superior to the medial and lateral regions in most respects. These findings reinforce the use of the central third of a patellar tendon allograft in anterior cruciate ligament reconstruction. Further investigations are required to determine whether the decreased biomechanical properties of the medial and lateral third of the BTB construct negatively influence the mechanical function of hemi-BTB grafts.

Functional bracing of ACL injuries: current state and future directions

PURPOSE

Functional braces are commonly prescribed to treat anterior cruciate ligament (ACL) injury. The results of the existing literature on functional brace use are mixed. The purpose of this study was to evaluate the history and current state of functional ACL bracing and to identify design criteria that could improve upon current bracing technologies.

METHODS

A literature search was performed through the PubMed MEDLINE database in April 2013 for the keywords "anterior cruciate ligament" and "brace". Articles published between January 1, 1980, and April 4, 2013, were retrieved and reviewed. Current functional braces used to treat ACL injury were identified. The function of the native ACL was carefully studied to identify design requirements that could improve upon current bracing technologies.

RESULTS

Biomechanical evaluations of functional brace effects at time zero have been mixed. Functional brace use reportedly does not improve long-term patient outcomes following ACL reconstruction, but has been shown to reduce subsequent injury rates while skiing in both ACL-deficient and reconstructed skiers. In situ force in the ACL varies with flexion angle and activity. Currently, no brace has been designed and validated to replicate the force-flexion behavior of the native ACL.

CONCLUSIONS

Biomechanical and clinical evidence suggests current functional bracing technologies do not sufficiently restore normal biomechanics to the ACL-deficient knee, protect the reconstructed ACL, and improve long-term patient outcomes. Further research into a functional brace designed to apply forces to the knee joint similar in magnitude to the native ACL should be pursued.

LEVEL OF EVIDENCE

III.

Single-bundle anterior cruciate ligament reconstruction in active young men using bone-tendon achilles allograft versus free tendon achilles allograft

PURPOSE

The purpose was to prospectively compare the outcomes of anterior cruciate ligament (ACL) reconstruction using bone-tendon Achilles allograft with those of free tendon Achilles allograft in 2 groups of active young men.

METHODS

We enrolled 72 subjects in the study. Of these, 33 subjects who had ACL reconstruction with Achilles allograft with calcaneal bone block on its end (group I) and 34 who had ACL reconstruction with free tendon Achilles allograft (group II) were followed up for a minimum of 2 years. The Lachman test, pivot-shift test, and 1-leg hop test were evaluated at the last follow-up. The International Knee Documentation Committee classification, Lysholm score, and side-to-side difference were assessed preoperatively and at the last follow-up. The Tegner activity scale was evaluated before injury and at the last follow-up.

RESULTS

The mean follow-up period was 30.9 months (range, 26 to 38 months). At the last follow-up, there were no statistically significant differences between the 2 groups for the Lachman test, pivot-shift test, 1-leg hop test, International Knee Documentation Committee classification, Lysholm score, and side-to-side difference (P > .05). Three subjects in group I and three in group II showed an activity level 2 steps below the preinjury activity level. The rest of the subjects returned to the preinjury activity level or showed a level 1 step below the preinjury activity level.

CONCLUSIONS

There were no significant differences in clinical outcomes of ACL reconstructions using Achilles allograft between the bone-tendon group and the free tendon group in active young men. Free tendon Achilles allograft may be considered an option for ACL reconstruction.

LEVEL OF EVIDENCE

Level II, therapeutic study, randomized controlled trial.

Clinical outcomes after anterior cruciate ligament reconstruction: a meta-analysis of autograft versus allograft tissue

BACKGROUND

Clinical outcomes of autograft and allograft anterior cruciate ligament (ACL) reconstructions are mixed, with some reports of excellent to good outcomes and other reports of early graft failure or significant donor site morbidity.

OBJECTIVE

To determine if there is a difference in functional outcomes, failure rates, and stability between autograft and allograft ACL reconstructions.

DATA SOURCES

Medline, Cochrane Central Register of Controlled Trials (Evidence Based Medicine Reviews Collection), Cochrane Database of Systematic Reviews, Web of Science, CINAHL, and SPORTDiscus were searched for articles on ACL reconstruction. Abstracts from annual meetings of the American Academy of Orthopaedic Surgeons, American Orthopaedic Society for Sports Medicine, and Arthroscopy Association of North America were searched for relevant studies.

STUDY SELECTION

INCLUSION CRITERIA FOR STUDIES WERE AS FOLLOWS: primary unilateral ACL injuries, mean patient age less than 41 years, and follow-up for at least 24 months postreconstruction. Exclusion criteria for studies included the following: skeletally immature patients, multiligament injuries, and publication dates before 1990.

DATA EXTRACTION

Joint stability measures included Lachman test, pivot-shift test, KT-1000 arthrometer assessment, and frequency of graft failures. Functional outcome measures included Tegner activity scores, Cincinnati knee scores, Lysholm scores, and IKDC (International Knee Documentation Committee) total scores.

RESULTS

More than 5000 studies were identified. After full text review of 576 studies, 56 were included, of which only 1 directly compared autograft and allograft reconstruction. Allograft ACL reconstructions were more lax when assessed by the KT-1000 arthrometer. For all other outcome measures, there was no statistically significant difference between autograft and allograft ACL reconstruction. For all outcome measures, there was strong evidence of statistical heterogeneity between studies. The sample size necessary for a randomized clinical trial to detect a difference between autograft and allograft reconstruction varied, depending on the outcome.

CONCLUSIONS

With the current literature, only KT-1000 arthrometer assessment demonstrated more laxity with allograft reconstruction. A randomized clinical trial directly comparing allograft to autograft ACL reconstruction is warranted, but a multicenter study would be required to obtain an adequate sample size.

Effects of cyclic loading on the tensile properties of human patellar tendon

Bone-patellar tendon-bone (BPTB) graft is a popular choice for ACL reconstruction. These grafts are subjected to cyclic loading during the activities of daily living. Significant knee laxity is observed in reconstructed knee shortly after reconstruction. The source of this laxity is not clear. The change in the tensile properties of the graft due to cyclic loading can be one of the reasons for the change in knee laxity. Twenty patellar tendons from fresh frozen cadaver knees were cyclically loaded at a stress amplitude equivalent to 33% of the failure strength of the contralateral patellar tendon for 5000 cycles at 1.4Hz. They were then tested in tension to failure. Failure properties and the low load properties such as toe-region modulus were calculated. The results were compared with those of contralateral patellar tendons that were not subjected to cyclic loading before testing to failure. Fatigue loading did not alter the failure and low load properties with the exception of failure strain which decreased by about 10% (P<.05). Cyclically loaded patellar tendons with higher tissue mass density possess higher strength, modulus of elasticity, toughness, and transition stress (P<.05). The results indicate that there is no significant change in graft properties because of cyclic loading with the above load magnitude. The change in knee laxity observed after reconstruction, hence, is not because of change in graft properties due to moderate cyclic loading. Other factors, such as plastic deformation (yielding) of the graft, might play a role in increased knee laxity after reconstruction.

Tibio-femoral joint constraints for bone pose estimation during movement using multi-body optimization

When using skin markers and stereophotogrammetry for movement analysis, bone pose estimation may be performed using multi-body optimization with the intent of reducing the effect of soft tissue artefacts. When the joint of interest is the knee, improvement of this approach requires defining subject-specific relevant kinematic constraints. The aim of this work was to provide these constraints in the form of plausible values for the distances between origin and insertion of the main ligaments (ligament lengths), during loaded healthy knee flexion, taking into account the indeterminacies associated with landmark identification during anatomical calibration. Ligament attachment sites were identified through virtual palpation on digital bone templates. Attachments sites were estimated for six knee specimens by matching the femur and tibia templates to low-dose stereoradiography images. Movement data were obtained using stereophotogrammetry and pin markers. Relevant ligament lengths for the anterior and posterior cruciate, lateral collateral, and deep and superficial bundles of the medial collateral ligaments (ACL, PCL, LCL, MCLdeep, MCLsup) were calculated. The effect of landmark identification variability was evaluated performing a Monte Carlo simulation on the coordinates of the origin-insertion centroids. The ACL and LCL lengths were found to decrease, and the MCLdeep length to increase significantly during flexion, while variations in PCL and MCLsup length was concealed by the experimental indeterminacy. An analytical model is given that provides subject-specific plausible ligament length variations as functions of the knee flexion angle and that can be incorporated in a multi-body optimization procedure.

Effect of short-duration low-magnitude cyclic loading versus immobilization on tendon-bone healing after ACL reconstruction in a rat model

BACKGROUND

Successful anterior cruciate ligament reconstruction with use of soft-tissue grafts requires healing between tendon and bone. Little is known about the effect of mechanical load on the cellular and molecular cascade of tendon-to-bone healing. Understanding these mechanical influences has critical implications for postoperative rehabilitation following anterior cruciate ligament reconstruction. The purpose of this study was to test the hypothesis that, compared with perioperative immobilization, short-duration low-magnitude cyclic axial loading would result in impaired tendon-to-bone healing after anterior cruciate ligament reconstruction in a rat model.

METHODS

Fifty-two male Sprague-Dawley rats underwent anterior cruciate ligament reconstruction with use of a flexor digitorum longus autograft. The patellar tendon, capsule, and ligamentous structures were circumferentially released, and an external fixator parallel to the anterior cruciate ligament graft was placed across the knee. Mechanical loading, consisting of cyclic displacement of the femur and tibia constrained to axial translation parallel to the graft, was applied daily. The rats were randomly assigned to immobilization or daily loading, for fourteen or twenty-eight days. Biomechanical, micro-computed tomographic, and histomorphometric analysis was performed on the bone-tendon-bone complexes.

RESULTS

The load measured across the knees during cyclic displacement increased over time (p < 0.05). Load-to-failure testing of the isolated femur-anterior cruciate ligament graft-tibia specimens revealed no significant differences between groups at two or four weeks. By two weeks postoperatively, a greater number of ED1+ inflammatory macrophages (phagocytic cells involved in the initial injury response) were seen at the tendon-bone interface after loading in the cyclically loaded group than in the immobilized group (p = 0.01). Compared with the baseline values, the number of trabeculae was significantly lower after loading for four weeks (p = 0.02).

CONCLUSIONS

Short-duration low-magnitude cyclic axial loading of the anterior cruciate ligament graft in the postoperative period is not detrimental to the strength of the healing tendon-bone interface but appears to be associated with greater inflammation and less bone formation in the tunnel in this rat model.

Effect of early and delayed mechanical loading on tendon-to-bone healing after anterior cruciate ligament reconstruction

BACKGROUND

Modulation of the mechanical environment may profoundly affect the healing tendon graft-bone interface. The purpose of this study was to determine how controlled axial loading after anterior cruciate ligament reconstruction affects tendon-to-bone healing. Our hypothesis was that controlled cyclic axial loading after a period of immobilization would improve tendon-to-bone healing compared with that associated with immediate axial loading or prolonged immobilization.

METHODS

One hundred and fifty-six male Sprague-Dawley rats underwent anterior cruciate ligament reconstruction with use of a flexor digitorum longus autograft. A custom-designed fixture was used to apply an external fixator across the knee parallel to the anterior cruciate ligament graft. Animals were randomly assigned to be treated with immobilization (n = 36) or controlled knee distraction along the long axis of the graft to achieve approximately 2% axial strain beginning (1) immediately postoperatively (n = 36), (2) on postoperative day 4 ("early delayed loading," n = 42), or (3) on postoperative day 10 ("late delayed loading," n = 42). The animals were killed at fourteen or twenty-eight days postoperatively for biomechanical testing, micro-computed tomography, and histomorphometric analysis of the bone-tendon-bone complex. Data were analyzed with use of a two-way analysis of variance followed by a post hoc Tukey test with p < 0.05 defined as significant.

RESULTS

Delayed initiation of cyclic axial loading on postoperative day 10 resulted in a load to failure of the femur-anterior cruciate ligament-tibia complex at two weeks that was significantly greater than that resulting from immediate loading or prolonged immobilization of the knee (mean and standard deviation, 9.6 ± 3.3 N versus 4.4 ± 2.3 N and 4.4 ± 1.5 N, respectively; p < 0.01). The new-bone formation observed in the tibial tunnels of the delayed-loading groups was significantly increased compared with that in the immediate-loading and immobilization groups at both two and four weeks postoperatively (1.47 ± 0.11 mm(3) [postoperative-day-10 group] versus 0.89 ± 0.30 mm(3) and 0.85 ± 0.19 mm(3), respectively, at two weeks; p < 0.003). There were significantly fewer ED1+ inflammatory macrophages and significantly more ED2+ resident macrophages at the healing tendon-bone interface in both delayed-loading groups compared with the counts in the immediate-loading and immobilization groups at two and four weeks (2.97 ± 0.7 [postoperative day 10] versus 1.14 ± 0.47 and 1.71 ± 1.5 ED2+ cells, respectively, per high-power field at two weeks; p < 0.02). The numbers of osteoclasts in the delayed-loading groups were significantly lower than those in the immediate-loading and immobilization groups at two and four weeks postoperatively (0.35 ± 0.15 [postoperative-day-10 group] versus 1.02 ± 0.08 and 1.44 ± 0.2 cells, respectively, per high-power field at two weeks; p < 0.01), and the delayed-loading groups also had significantly reduced interface tissue vascularity compared with the other groups (p < 0.003).

CONCLUSIONS

Delayed application of cyclic axial load after anterior cruciate ligament reconstruction resulted in improved mechanical and biological parameters of tendon-to-bone healing compared with those associated with immediate loading or prolonged postoperative immobilization of the knee.

The Effect of the Shoe-Surface Interface in the Development of Anterior Cruciate Ligament Strain

The shoe-surface interface has been implicated as a possible risk factor for anterior cruciate ligament (ACL) injuries. The purpose of this study is to develop a biomechanical, cadaveric model to evaluate the effect of various shoe-surface interfaces on ACL strain. There will be a significant difference in ACL strain between different shoe-surface combinations when a standardized rotational moment (a simulated cutting movement) is applied to an axially loaded lower extremity. The study design was a controlled laboratory study. Eight fresh-frozen cadaveric lower extremities were thawed and the femurs were potted with the knee in 30 deg of flexion. Each specimen was placed in a custom-made testing apparatus, which allowed axial loading and tibial rotation but prevented femoral rotation. For each specimen, a 500 N axial load and a 1.5 Nm internal rotation moment were placed for four different shoe-surface combinations: group I (AstroTurf-turf shoes), group II (modern playing turf-turf shoes), group III (modern playing turf-cleats), and group IV (natural grass-cleats). Maximum strain, initial axial force and moment, and maximum axial force and moment were calculated by a strain gauge and a six component force plate. The preliminary trials confirmed a linear relationship between strain and both the moment and the axial force for our testing configuration. In the experimental trials, the average maximum strain was 3.90, 3.19, 3.14, and 2.16 for groups I–IV, respectively. Group IV had significantly less maximum strain (p<0.05) than each of the other groups. This model can reproducibly create a detectable strain in the anteromedial bundle of the ACL in response to a given axial load and internal rotation moment. Within the elastic range of the stress-strain curve, the natural grass and cleat combination produced less strain in the ACL than the other combinations. The favorable biomechanical properties of the cleat-grass interface may result in fewer noncontact ACL injuries.

Does the use of fluoroscopy and isometry during anterior cruciate ligament reconstruction affect surgical decision making?

OBJECTIVE

Poor results after anterior cruciate ligament (ACL) reconstruction are often due to inaccurate graft placement. Numerous strategies have been advocated to improve accuracy and consistency of tunnel positioning, including computer-assisted navigation. Less expensive alternatives, such as intraoperative fluoroscopy and isometry, have also been advocated for confirming guide pin placement before reaming the femoral tunnel. It is unknown how often these techniques cause surgeons to change the location of their femoral tunnel at the time of surgery. We undertook this study to determine how often this approach results in repositioning of the guide pin before final graft placement. We hypothesized that a lower level of surgeon experience would lead to a higher frequency of repositioning compared to a higher level of experience.

DESIGN

Prospective, case series.

SETTING

Institutional.

PATIENTS

Intraoperative data were gathered prospectively from 413 consecutive, primary ACL reconstructions performed by the sports medicine group at our institution. Of the 413 procedures enrolled in this study, 407 were available for analysis. Six procedures were excluded because the tension isometer was unavailable during the procedure.

INTERVENTIONS

Isometry and fluoroscopy were used in all cases to aid in the accurate placement of the femoral tunnel. Femoral pin change based on the results of isometry or fluoroscopy was recorded. The percentage of cases involving a change in the femoral pin resulting from the use of these techniques was calculated. This percentage was also calculated separately for cases performed by a staff surgeon (fellowship-trained sports medicine staff) as well as less experienced surgeons (current sports medicine fellows).

MAIN OUTCOME MEASURES

The main outcome measurement was whether the femoral pin was changed.

RESULTS

Of the 407 procedures available for review, 62 (15%) of them involved a change in femoral pin position secondary to information provided by intraoperative isometry or fluoroscopy. In the procedures performed by more experienced surgeons, the pin was changed in 40 (16%) of 253 cases; in those performed by less experienced surgeons, it was changed in 22 (14%) of 154 cases.

CONCLUSIONS

The intraoperative use of isometry and fluoroscopy during ACL reconstruction led to changes in the femoral tunnel placement 15% of the time. The influence of these instruments on intraoperative decision making does not seem to diminish with surgical experience.

Tibiofemoral compression force differences using laxity- and force-based initial graft tensioning techniques in the anterior cruciate ligament-reconstructed cadaveric knee

PURPOSE

Our purpose was to document the tibiofemoral (TF) compression forces produced during clinical initial graft tension protocols.

METHODS

An image analysis system was used to track the position of the tibia relative to the femur in 11 cadaveric knees. TF compression forces were quantified by use of thin-film pressure sensors. Before anterior cruciate ligament (ACL) reconstructions were performed with patellar tendon grafts, measurements of TF compression force were obtained from the ACL-intact knee with knee flexion. ACL reconstructions were then performed by use of "force-based" and "laxity-based" graft tension approaches. Within each approach, high- and low-tension conditions were compared with the ACL-intact condition over the range of knee flexion angles.

RESULTS

The TF compression forces for all initial graft tension conditions were significantly greater than those of the normal knee when the knee was in full extension (0 degrees ). The TF compression forces produced with the laxity-based approach were greater than those produced with the force-based approach. However, the laxity-based approach was necessary to restore normal laxity at the time of surgery.

CONCLUSIONS

The results of this study show that initial graft tension conditions influence TF compressive forces at the time of surgery and that clinically relevant initial graft tension conditions produce different TF compressive forces.

CLINICAL RELEVANCE

This study showed that the TF compression forces were greater in the ACL-reconstructed knee for all of the initial graft tension conditions when compared with the ACL-intact knee and that clinically relevant initial graft tension conditions produce different TF compressive forces.

Low-load behaviour of the patellar tendon graft and its relevance to the biomechanics of the reconstructed knee

BACKGROUND

Although the linear elastic (high-load) properties of patellar tendon graft used for anterior cruciate ligament (ACL) reconstruction are studied extensively, the low-load properties of the graft, associated with the toe region of its load-deformation curve, are largely neglected. The objectives of this study were to (i) determine the properties of the patellar tendon in the low-load region and compare to that of the intact ACL, (ii) assess the extent of variability in these properties and relate them to donor factors, and (iii) establish the theoretical importance of low-load properties to the function of the reconstructed knee.

METHODS

The patellar tendons of 20 unpaired fresh frozen human knees (10 males and 10 females) were harvested. The central portions were trimmed, measured, and tested in tension to failure. The stress-strain curves were fitted with a bi-linear model and the graft properties were measured.

FINDINGS

The low-load region modulus of elasticity, E 0, of the patellar tendon, ranged from 49 MPa to 276 MPa in males and 63 MPa to 279 MPa in females. The strain at which the graft transitions from its low-load region to its linear elastic region (epsilon* approximately 4.6%) is on average above the strain levels experienced by the ACL during daily activities (epsilon approximately 4%). Donor sex, height and body mass were found to significantly affect some of the mechanical properties of the low-load region.

INTERPRETATION

The results suggest that the low-load region properties of the patellar tendon, not the linear elastic properties, govern the biomechanics of the tibiofemoral joint during the early healing period. Also, a wide variability of graft properties in the low-load region exists partly due to certain donor factors. Clinicians should be aware of the low-load region behaviour of the graft and its influence on time=0 behaviour of the reconstructed knee.

"Biological failure" of the anterior cruciate ligament graft

Anterior cruciate ligament (ACL) reconstruction has the best chance for success when the graft undergoes extensive biologic remodeling and incorporation after implantation. There are many factors that can lead to graft failure and possible revision surgery. These include patient selection; surgical technique such as graft placement and tensioning; the use of allograft versus autograft; mechanical factors such as secondary restraint laxity; lack of a correct, carefully controlled post-operative rehabilitation program; and biological factors. When a patient presents with knee instability following ligament reconstruction and there is no history of a new trauma or identifiable technical error, biological failure should be considered. However, the biologic response of the grafted tissue is closely linked to the mechanical and biochemical environment into which the graft is placed. Thus, the "biological failure" of the ACL graft is a complex pathological entity whose cause is not fully understood. Failure may be initiated by early extensive graft necrosis, disturbances in revascularization, problems in cell repopulation and proliferation, and as well difficulties in the ligamentization process. However, further study of the biological characterization of a failed graft placed in a correct mechanical environment is warranted.

Viscoelasticity and temperature variations decrease tension and stiffness of hamstring tendon grafts following anterior cruciate ligament reconstruction

BACKGROUND

Hamstring tendon grafts used for anterior cruciate ligament reconstruction are typically harvested early in the surgical procedure and are preconditioned prior to reimplantation. Postoperatively, the grafts undergo stress relaxation and warm from the temperature of the operating room to body temperature. The hypothesis of this study was that the tension within semitendinosus and gracilis tendon grafts and the stiffness of the grafts significantly decrease postoperatively because of both stress relaxation and an increase in temperature.

METHODS

Double-strand grafts were created from six semitendinosus tendons and six gracilis tendons harvested from cadaver specimens. The grafts were loaded to 65 N while at operating-room temperature (20 degrees C). After fifteen minutes of stress relaxation, graft tension was measured and the grafts were stretched by 0.1 mm to determine stiffness. The tension and stiffness measurements represented graft properties immediately following reconstruction. Additional tension and stiffness measurements were made following three hours of stress relaxation and after increasing the temperature to the body temperature at the knee (34 degrees C). Both types of graft were examined for differences in stiffness and tension due to stress relaxation and the temperature increase.

RESULTS

For both types of graft, the tension and stiffness decreased following stress relaxation to approximately 50% and 80%, respectively, of the value immediately after reconstruction. Increasing the temperature decreased the tension and stiffness further to approximately 40% and 70%, respectively, of the value after reconstruction for both types of graft. All changes in tension and stiffness were significant (p < 0.01).

CONCLUSIONS

Graft tension and stiffness achieved immediately following reconstruction are not maintained postoperatively because of stress relaxation and a temperature increase. This could lead to increased knee laxity.

Treatment of anterior cruciate ligament injuries, part 2

Anterior cruciate ligament tears, common among athletes, are functionally disabling; they predispose the knee to subsequent injuries and the early onset of osteoarthritis. A total of 3810 studies published between January 1994 and the present were identified and reviewed to determine the current state of knowledge regarding the treatment of anterior cruciate ligament injuries. Part 1 of this article focused on studies pertaining to the biomechanical behavior of the anterior cruciate ligament, the prevalence of and risk factors for injuries related to it, the natural history of the ligament-deficient knee, injuries associated with anterior cruciate ligament disruption, indications for the treatment of anterior cruciate ligament injuries, as well as nonoperative and operative treatments. Part 2 includes technical aspects of anterior cruciate ligament surgery, bone tunnel widening, graft healing, rehabilitation after anterior cruciate ligament reconstruction, and the effects of sex, age, and activity level on the outcome of such reconstructive surgery.

Treatment of anterior cruciate ligament injuries, part I

Anterior cruciate ligament injuries are common among athletes. Although the true natural history remains unclear, anterior cruciate ligament injuries are functionally disabling; they predispose the knee to subsequent injuries and the early onset of osteoarthritis. This article, the first in a 2-part series, was initiated with the use of the PubMed database and a comprehensive search of articles that appeared between January 1994 to the present, using the keywords anterior cruciate ligament. A total of 3810 citations were identified and reviewed to determine the current state of knowledge about the treatment of these injuries. Articles pertaining to the biomechanical behavior of the anterior cruciate ligament, the prevalence of anterior cruciate ligament injury, the natural history of the anterior cruciate ligament-deficient knee, injuries associated with anterior cruciate ligament disruption, risk factors for anterior cruciate ligament injury, indications for treatment of anterior cruciate ligament injuries, and nonoperative and operative treatments were obtained, reviewed, and served as the basis for part I. Part II, to be presented in another issue of this journal, includes technical aspects of anterior cruciate ligament surgery, bone tunnel widening, graft healing, rehabilitation after reconstruction, and the effect of sex, age, and activity level on the outcome of surgery. Our approach was to build on prior reviews and to provide an overview of the literature for each of the before-mentioned areas of study by summarizing the highest level of scientific evidence available. For the areas that required a descriptive approach to research, we focused on the prospective studies that were available; for the areas that required an experimental approach, we focused on the prospective, randomized controlled trials and, when necessary, the highest level of evidence available. We were surprised to learn that considerable advances have been made during the past decade regarding the treatment of this devastating injury.

The mechanical properties of the human patellar tendon are correlated to its mass density and are independent of sex

BACKGROUND

A diverse range of values for the mechanical properties of the human patellar tendon has been reported in the literature. Donor age has been excluded as a factor that causes this disparity. However, the effects of donor sex and tissue mass density on the mechanical properties of the patellar tendon have not been established. More importantly, predictors of the mechanical properties of the patellar tendon, used as grafts in anterior cruciate ligament reconstruction surgeries, are not available.

METHODS

Uniaxial tension tests were performed to determine the effects of donor sex and mass density of the tissue on the mechanical properties of twenty unpaired human patellar tendons (10 male and 10 female; age, 17-50). Mass density of the patellar tendon was determined by measuring its volume and mass.

FINDINGS

No evidence of sex-based differences in any of the mechanical properties of the patellar tendon was found. The results revealed a diverse range of mass densities extending from a low of 0.76 g/cm(3) to a high of 2.68 g/cm(3) (250% difference). Furthermore, it was determined that the ultimate tensile strength (mean=58.71 MPa), elastic modulus (mean=507.38 MPa) and strain energy density (mean=4.59 MPa) of the patellar tendon were significantly correlated to its mass density. The tensile strength and elastic modulus were significantly higher for those patellar tendons having a mass density greater than 1.67 g/cm(3).

INTERPRETATION

The mass density of the patellar tendon may be considered as an indicator of mechanical properties of the patellar tendon or graft quality.

Varying femoral tunnels between the anatomical footprint and isometric positions: effect on kinematics of the anterior cruciate ligament-reconstructed knee

BACKGROUND

Knee kinematics and in situ forces resulting from anterior cruciate ligament reconstructions with 2 femoral tunnel positions were evaluated.

HYPOTHESIS

A graft placed inside the anatomical footprint of the anterior cruciate ligament will restore knee function better than a graft placed at a position for best graft isometry.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten cadaveric knees were tested in response to a 134-N anterior load and a combined 10-N.m valgus and 5-N.m internal rotation load. A robotic universal force-moment sensor testing system was used to apply loads, and resulting kinematics were recorded. An active surgical robot system was used for positioning tunnels in 2 locations in the femoral notch: inside the anatomical footprint of the anterior cruciate ligament and a position for best graft isometry. The same quadrupled hamstring tendon graft was used for both tunnel positions. The 2 loading conditions were applied.

RESULTS

At 30 degrees of knee flexion, anterior tibial translation in response to the anterior load for the intact knee was 9.8 +/- 3.1 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 13.8 +/- 4.6 mm; position 2: 16.6 +/- 3.7 mm; P < .05). There was a significant difference between the 2 tunnel positions. At the same flexion angle, the anterior tibial translation in response to the combined load for the intact knee was 7.7 +/- 4.0 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 10.4 +/- 5.5 mm; position 2: 12.0 +/- 5.2 mm; P < .05), with a significant difference between the tunnel positions.

CONCLUSION

Neither femoral tunnel position restores normal kinematics of the intact knee. A femoral tunnel position inside the anatomical footprint of the anterior cruciate ligament results in knee kinematics closer to the intact knee than does a tunnel position located for best graft isometry.

CLINICAL RELEVANCE

Anatomical femoral tunnel position is important in reproducing function of the anterior cruciate ligament.

Transtibial tubercle fixation without hardware for anterior cruciate ligament and posterior cruciate ligament reconstruction: A new technique

Tibial fixation with implants for both anterior and posterior cruciate ligament reconstructions (ACLR and PCLR) can be associated with a wide variety of problems. Common problems encountered include graft-tunnel mismatch when using grafts with bone blocks, graft damage or poor graft fixation using metal or absorbable implants, painful retained hardware requiring removal, and hardware interference during revision surgery. A new technique is presented using transosseous graft suture passage across the tibial tubercle followed by knot tying over a bone bridge. The technique provides a quick, simple, safe, and reproducible alternative for primary or supplemental tibial graft fixation without hardware in ACLR and PCLR.

The effect of graft stiffness on knee joint biomechanics after ACL reconstruction--a 3D computational simulation

OBJECTIVE

The objective was to determine the effect of varying graft stiffness and initial graft tension on knee kinematics and graft tension after anterior cruciate ligament reconstruction.

DESIGN

A 3D computational knee model was used.

BACKGROUND

Many factors influencing the biomechanical outcome of anterior cruciate ligament reconstruction have been investigated. However, there are no reports on the effect of variations in graft stiffness on knee behavior.

METHODS

A 3D computational knee model was used to simulate anterior cruciate ligament reconstruction using three different grafts with stiffnesses similar to the anterior cruciate ligament (graft 1), a 10mm bone-patellar tendon-bone graft (graft 2), and a 14 mm bone-patellar tendon-bone graft (graft 3). The initial graft tension was set to 0 or 40 N with the knee at 30 degrees of flexion. A 134 N anterior tibial drawer load and a 400 N quadriceps load were applied to the knee, and kinematics and graft tension were calculated.

RESULTS

When fixed with no initial tension, graft 1 was found to under-constrain the knee, while graft 2 slightly over-constrained the knee, and graft 3 over-constrained the knee when compared to the intact knee. When an initial graft tension of 40 N was used, all of the reconstructed knees were more constrained than when an initial tension of 0 N was used.

CONCLUSIONS

This study suggests that graft stiffness has a direct impact on knee biomechanics after anterior cruciate ligament reconstruction. An optimal anterior cruciate ligament reconstruction can be achieved if the anterior cruciate ligament is replaced by a graft with similar structural stiffness.

RELEVANCE

This study showed that if the graft material and fixation sites are selected such that the anterior cruciate ligament structural stiffness is retained, normal knee kinematics can be restored.

Biology and biomechanics

Increased participation by the general population in athletic activities leads to increased trauma to bones, joint surfaces, and soft tissues. Management and treatment of these injuries has significantly improved over the past few decades. The application of knowledge gained from basic science research in biology and biomechanics has continuously contributed to that. Biological advances have been made in the field of gene therapy, cell therapy, and tissue engineering. Certainly, the greatest focus is bone and cartilage research that will lead to improved fracture repair in the traumatic injured population, as well as prevention of early osteoarthritic changes in the injured athletic population. In biomechanical research, contributions have been made to further understand kinematic behavior of joints that will lead to improved ligament reconstruction techniques and rehabilitation regimens. Various fixation techniques and several different ligament reconstruction techniques have been studied and validated. In the future, improved understanding of ligament healing, graft incorporation, and revascularization will lead to improved outcome of surgical reconstruction techniques in orthopaedic sports medicine. Exciting research has been performed over the past years and will be reviewed in this article.