ACL graft failure location differs between allografts and autografts

Dynamic Deformation Behavior of the Porcine Anterior Cruciate Ligament Enthesis Under Anterior Tibial Loading

This study determined the insertion angle at the porcine anterior cruciate ligament (ACL) enthesis under joint loading to provide information on the structure and mechanical function of the enthesis. Ten intact porcine knee joints were harvested, and an anterior tibial load was applied using a robotic testing system. After dissecting a portion of the ACL enthesis along ligament fibers, the remaining enthesis was imaged using a digital microscope while reproducing the three-dimensional intact knee motion. Fiber orientation angles (FOAs) in the enthesis region (0-300 µm from the ligament-bone boundary) and the ligament region (500-2000 µm from the ligament-bone boundary) were analyzed in the femoral and tibial entheses of the anteromedial bundle (AMB) of the ACL under loading. On the femoral side, the FOA in the enthesis region was significantly higher than that in the ligament region by approximately 10 degrees under loading (n = 5, p < 0.05 in paired t-test). In contrast, the FOAs in the enthesis and ligament regions on the tibial side were nearly equal under loading, with no significant difference (n = 5, p > 0.15 in paired t-test). Histological examination indicated that uncalcified fibrocartilage (UF) was abundant in the enthesis region of the AMB femoral enthesis while the UF was not observed in the enthesis region of the AMB tibial enthesis. Thus, the current data suggest that the regional dependence and independence in FOA are caused by the presence or absence of UF and contributes to a moderate and subtle load-transduction in the ACL enthesis.

Evaluation of Failed ACL Reconstruction: An Updated Review

Failure rates among primary Anterior Cruciate Ligament Reconstruction (ACLR) range from 3.2% to 11.1%. Recently, there has been increased focus on surgical and anatomic considerations which predispose patients to failure, including excessive posterior tibial slope (PTS), unaddressed high-grade pivot shift, and improper tunnel placement. The purpose of this review was to provide a current summary and analysis of the literature regarding patient-related and technical factors surrounding revision ACLR, rehabilitation considerations, overall outcomes and return to sport (RTS) for patients who undergo revision ACLR. There is a convincingly higher re-tear and revision rate in patients who undergo ACLR with allograft than autograft, especially amongst the young, athletic population. Unrecognized Posterior Cruciate Ligament (PLC) injury is a common cause of ACLR failure and current literature suggests concurrent operative management of high-grade PLC injuries. Given the high rates of revision surgery in young active patients who return to pivoting sports, the authors recommend strong consideration of a combined ACLR + Anterolateral Ligament (ALL) or Lateral extra-articular tenodesis (LET) procedure in this population. Excessive PTS has been identified as an independent risk factor for ACL graft failure. Careful consideration of patient-specific factors such as age and activity level may influence the success of ACL reconstruction. Additional technical considerations including graft choice and fixation method, tunnel position, evaluation of concomitant posterolateral corner and high-grade pivot shift injuries, and the role of excessive posterior tibial slope may play a significant role in preventing failure.

Increased ACL direct insertion coverage provided more positive biomechanical effects on graft and bone tunnel during knee flexion: a simulation study

PURPOSE

Flattened femoral tunnels were recently applied in anatomical single-bundle anterior cruciate ligament (ACL) reconstruction. Little is known about the biomechanical effect of such changes during knee flexion. The aim of the present simulation study was to assess the effect of altered ACL direct insertion coverage on the biomechanics of the graft and bone tunnel.

METHODS

Five finite element (FE) models, including a round femoral tunnel and four progressively flattened rounded rectangular femoral tunnels, were established to represent the ACL reconstructions. In vivo knee kinematics data obtained from the validated dual fluoroscopic imaging techniques controlled the FE models to simulate lunge motions. The maximal principal stress of the graft and the volume of equivalent strain within 1000-3000 microstrain (V1000-3000) of the cancellous bone were subsequently calculated at 0°, 30°, 60° and 90° of knee flexion.

RESULTS

A lower stress state on the graft and a more beneficial strain state on the cancellous bone were observed when the femoral tunnel better covered the ACL direct insertion. The average maximal principal stress of each model were 3.93 ± 0.60 MPa, 3.82 ± 0.54 MPa, 3.43 ± 0.44 MPa, 3.45 ± 0.44 MPa and 3.05 ± 0.43 MPa, respectively. The average V1000-3000 of the cancellous bone of each model were 179.06 ± 89.62 mm3, 221.40 ± 129.83 mm3, 247.57 ± 157.78 mm3, 282.74 ± 178.51 mm3 and 295.71 ± 162.59 mm3, respectively. Both the stress and strain values exhibited two peaks during the flexion simulation. The highest value occurred at 30° of flexion, and the second highest value occurred at 90° of flexion.

CONCLUSIONS

Increased ACL direct insertion coverage provided more positive biomechanical effects after anatomical single-bundle ACL reconstruction during knee flexion.

Fatigue-driven compliance increase and collagen unravelling in mechanically tested anterior cruciate ligament

Approximately 300,000 anterior cruciate ligament (ACL) tears occur annually in the United States, half of which lead to the onset of knee osteoarthritis within 10 years of injury. Repetitive loading is known to result in fatigue damage of both ligament and tendon in the form of collagen unravelling, which can lead to structural failure. However, the relationship between tissue's structural, compositional, and mechanical changes are poorly understood. Herein we show that repetitive submaximal loading of cadaver knees causes an increase in co-localised induction of collagen unravelling and tissue compliance, especially in regions of greater mineralisation at the ACL femoral enthesis. Upon 100 cycles of 4× bodyweight knee loading, the ACL exhibited greater unravelled collagen in highly mineralized regions across varying levels of stiffness domains as compared to unloaded controls. A decrease in the total area of the most rigid domain, and an increase in the total area of the most compliant domain was also found. The results highlight fatigue-driven changes in both protein structure and mechanics in the more mineralized regions of the ACL enthesis, a known site of clinical ACL failure. The results provide a starting point for designing studies to limit ligament overuse injury.

Graft-Specific Surgical and Rehabilitation Considerations for Anterior Cruciate Ligament Reconstruction with the Quadriceps Tendon Autograft

Anterior cruciate ligament reconstruction (ACLR) with a bone-patellar tendon-bone (BPTB) or hamstring tendon (HT) autograft has traditionally been the preferred surgical treatment for patients returning to Level 1 sports. More recently, international utilization of the quadriceps tendon (QT) autograft for primary and revision ACLR has increased in popularity. Recent literature suggests that ACLR with the QT may yield less donor site morbidity than the BPTB and better patient-reported outcomes than the HT. Additionally, anatomic and biomechanical studies have highlighted the robust properties of the QT itself, with superior levels of collagen density, length, size, and load-to-failure strength compared to the BPTB. Although previous literature has described rehabilitation considerations for the BPTB and HT autografts, there is less published with respect to the QT. Given the known impact of the various ACLR surgical techniques on postoperative rehabilitation, the purpose of this clinical commentary is to present the procedure-specific surgical and rehabilitation considerations for ACLR with the QT, as well as further highlight the need for procedure-specific rehabilitation strategies after ACLR by comparing the QT to the BPTB and HT autografts.

Level of Evidence

Level 5.

High initial graft tension is a post-operative risk factor for high UTE T2* value of the graft 6 months after anterior cruciate ligament reconstruction

BACKGROUND

To evaluate the risk factor of "ligamentization" using the ultrashort echo time (UTE)-T2* imaging.

METHODS

Fifty-nine patients (23 males and 36 females, age of 21.9 ± 10.6 years old) who underwent anterior cruciate ligament (ACL) reconstruction with hamstring tendon were evaluated. The UTE T2* values of the reconstructed ACL at 6 months postoperatively were calculated. Circular regions of interest (5-10 mm²) were set at the proximal, mid-substance, and distal regions of the reconstructed ACL. The UTE T2* values of the entire reconstructed ACL were calculated as the average of these three points. Patients were divided into high (27 knees) and low (32 knees) UTE T2* groups by calculating whether their UTE T2* values were greater than the median of the UTE T2* values of all patients. Risk factors for high UTE T2* values were evaluated. Clinical outcomes were compared between the two groups.

RESULTS

There were no significant differences in any measured parameters and clinical outcomes between the two UTE T2* groups. Logistic regression analysis revealed that graft tension was a significant risk factor for patients with high UTE-T2* values (P = 0.047, odds ratio [OR] = 2.285). The UTE-T2* values of the 20 N graft tension using the Tension loc system were significantly lower than those of the 40 N using double-spike plate (DSP) with screws at each site and the 30 N using the Tension loc system at the distal site.

CONCLUSIONS

Higher graft tension was an independent risk factor for high UTE T2* values of the reconstructed ACL.

A retrospective cohort study of anterior half peroneus longus tendon vs hamstring tendon for anterior cruciate ligament reconstruction: A minimum 3-years follow-up

Background: The anterior half of the peroneus longus tendon (AHPLT) has recently gained popularity to become the alternate graft choice for anterior cruciate ligament reconstruction due to its acceptable biomechanical properties, easy and safe to harvest. Methods: A retrospective study was conducted to compare the results of anterior cruciate ligament (ACL) reconstruction with AHPLT and hamstring graft at the minimum of 3 years follow-up. Knee stability, International Knee Documentation Committee (IKDC) subjective score and Tegner activity level were collected. Results: There was no clinical significance regarding physical examination. Postoperative IKDC score was higher in the hamstring group compared with AHPLT group. Multiple regression analysis was done. The parsimonious model revealed graft types and gender were the most optimal variables explained postoperative IKDC score. Conclusion: AHPLT graft can be an alternative choice to conventional graft for single anatomic ACL reconstruction with less donor site morbidity, however there must be concern for smaller graft in short and thin female patients.

Local variations in mechanical properties of human hamstring tendon autografts for anterior cruciate ligament reconstruction do not translate to a mechanically inferior strand

A ruptured anterior cruciate ligament (ACL) is often reconstructed with a multiple-strand autograft of a semitendinosus tendon alone or combined with a gracilis tendon. Up to 10% of patients experience graft rupture. This potentially results from excessive local tissue strains under physiological loading which could either result in direct mechanical failure of the graft or induce mechanobiological weakening. Since the original location in the hamstring tendon cannot be traced back from an autograft rupture site, this study explored whether clinical outcome could be further improved by avoiding specific locations or regions of human semitendinosus and/or gracilis tendons in ACL grafts due to potential mechanical or biochemical inferiority. Additionally, it examined numerically which clinically relevant graft configurations experience the lowest strains - and therefore the lowest rupture risk - when loaded with equal force. Remnant full-length gracilis tendons from human ACL reconstructions and full-length semitendinosus- and ipsilateral gracilis tendons of human cadaveric specimens were subjected to a stress-relaxation test. Locations at high risk of mechanical failure were identified using particle tracking to calculate local axial strains. As biochemical properties, the water-, collagen-, glycosaminoglycan- and DNA content per tissue region (representing graft strands) were determined. A viscoelastic lumped parameter model per tendon region was calculated. These models were applied in clinically relevant virtual graft configurations, which were exposed to physiological loading. Configurations that provided lower stiffness - i.e., experiencing higher strains under equal force - were assumed to be at higher risk of failure. Suitability of the gracilis tendon proper to replace semitendinosus muscle-tendon junction strands was examined. Deviations in local axial strains from the globally applied strain were of similar magnitude as the applied strain. Locations of maximum strains were uniformly distributed over tendon lengths. Biochemical compositions varied between tissue regions, but no trends were detected. Viscoelastic parameters were not significantly different between regions within a tendon, although semitendinosus tendons were stiffer than gracilis tendons. Virtual grafts with a full-length semitendinosus tendon alone or combined with a gracilis tendon displayed the lowest strains, whereas strains increased when gracilis tendon strands were tested for their suitability to replace semitendinosus muscle-tendon junction strands. Locations experiencing high local axial strains - which could increase risk of rupture - were present, but no specific region within any of the investigated graft configurations was found to be mechanically or biochemically deviant. Consequently, no specific tendon region could be indicated to provide a higher risk of rupture for mechanical or biochemical reasons. The semitendinosus tendon provided superior stiffness to a graft compared to the gracilis tendon. Therefore, based on our results it would be recommended to use the semitendinosus tendon, and use the gracilis tendon in cases where further reinforcement of the graft is needed to attain the desired length and cross-sectional area. All these data support current clinical standards.

The use of gold nanoparticles in improving ACL graft performance in an ovine model

Surgical repair of the anterior cruciate ligament (ACL) can involve autograft or allograft materials. Allografts are typically chosen to avoid donor site morbidity associated with autografts harvest, but they can also result in a prolonged inflammatory period and delayed graft remodeling when compared to autografts. The aim of this study was to investigate the use of gold nanoparticles (AuNPs) conjugated to allografts to determine if AuNPs can reduce inflammation and enhance graft remodeling in an ovine model. Six sheep had their ACL surgically removed and replaced with a decellularized human gracilis tendon. Three of the sheep received grafts conjugated with 20 nm gold nanoparticles, while three of the sheep received grafts without the gold nanoparticles. The sheep were sacrificed 8 weeks after ACL reconstruction. Immediately following sacrifice, joint fluid was collected for cytology. Semi-quantitative histological scoring of the bone tunnel portion and the intra-articular portion of the grafts were performed independently along with descriptive analysis of histologic changes and quantitative analysis of revascularization. The results demonstrated that AuNP experimental grafts had an overall better histological scores than the non-AuNPs graft. The AuNPs grafts exhibited decreased inflammation in the bone tunnel portion of the graft, the intra-articular portion of the graft, and in the synovial fluid cell count. Overall, the results demonstrated that the grafts conjugated with nanoparticles have the potential to be influence inflammation and overall remodeling response.

Influence of femoral tunnel exit on the 3D graft bending angle in anterior cruciate ligament reconstruction

Purpose

To quantify the influence of the femoral tunnel exit (FTE) on the graft bending angle (GBA) and GBA-excursion throughout a full range of motion (ROM) in single-bundle anterior cruciate ligament (ACL) reconstruction.

Methods

Three-dimensional (3D) surface models of five healthy knees were generated from a weight-bearing CT obtained throughout a full ROM (0, 30, 60, 90, 120°) and femoral and tibial ACL insertions were computed. The FTE was simulated for 16 predefined positions, referenced to the Blumensaat's line, for each patient throughout a full ROM (0, 30, 60, 90, 120°) resulting in a total of 400 simulations. 3D GBA was calculated between the 3D directional vector of the ACL and the femoral tunnel, while the intra-articular ACL insertions remained unchanged. For each simulation the 3D GBA, GBA-excursion, tunnel length and posterior tunnel blow-out were analysed.

Results

Overall, mean GBA decreased with increasing knee flexion for each FTE (p < 0.001). A more distal location of the FTE along the Blumensaat's line resulted in an increase of GBA and GBA-excursion of 8.5 ± 0.6° and 17.6 ± 1.1° /cm respectively (p < 0.001), while a more anterior location resulted in a change of GBA and GBA-excursion of -2.3 ± 0.6° /cm (+ 0.6 ± 0.4°/ cm from 0–60° flexion) and 9.8 ± 1.1 /cm respectively (p < 0.001).

Mean tunnel length was 38.5 ± 5.2 mm (range 29.6–50.5). Posterior tunnel blow-out did not occur for any FTE.

Conclusion

Aiming for a more proximal and posterior FTE, with respect to Blumensaat’s line, reliably reduces GBA and GBA-excursion, while preserving adequate tunnel length. This might aid to reduce excessive graft stress at the femoral tunnel aperture, decrease femoral tunnel widening and promote graft-healing.

Level of Evidence

IV

Femoral Intercondylar Notch: Gross Anatomy and Histology of the Connective Tissue Lining of its Roof: A Pilot Study

PURPOSE

We have consistently observed a connective tissue lining over the intercondylar notch's roof (CTLINR) during arthroscopic surgeries of the knee joint. As there is a strong association of the intercondylar fossa with the anterior cruciate ligament (ACL), we believe that this tissue must be having some role in the functioning of the ACL. The purpose of this pilot study was to investigate the anatomic characteristics of the CTLINR.

METHODS

In this observational anatomical study, we have investigated the gross anatomical and histological features of the CTLINR in four knees of two fresh frozen non-embalmed cadavers. We have also studied its ultrastructural characteristics by obtaining an arthroscopic biopsy of the tissue from a patient undergoing ACL reconstruction.

RESULTS

At gross examination, the CTLINR had a typical glistening white surface with transversely oriented fibres. It entirely covered the roof of the intercondylar notch and was soft to touch. Histological examination with haematoxylin-eosin stain revealed fibro-collagenous tissue with intervening blood vessels. Transmission electron microscopy manifested loosely arranged collagen fibres of variable diameter.

CONCLUSION

The histological and electron microscopic characteristics of the tissue differentiate it from the ACL and its femoral enthesis, suggesting that it was a distinct anatomical structure. As it entirely covered the roof of the intercondylar fossa and had a smooth surface and soft consistency, it may protect the reconstructed ACL from graft abrasion. Furthermore, as it had a characteristic arthroscopic appearance, future research can investigate its role in femoral tunnel positioning.

Trauma and femoral tunnel position are the most common failure modes of anterior cruciate ligament reconstruction: a systematic review

PURPOSE

To improve outcomes of anterior cruciate ligament reconstruction (ACLR), it is important to understand the reasons for failure of this procedure. This systematic review was performed to identify current failure modes of ACLR.

METHODS

A systematic search was performed using PubMed, EMBASE, Cochrane, and annual registries for ACLR failures. Studies were included when failure modes were reported (I) of ≥ 10 patients and (II) at a minimum of two-year follow-up. Modes of failure were also compared between different graft types and in femoral tunnel positions.

RESULTS

This review included 24 cohort studies and 4 registry-based studies (1 level I, 1 level II, 10 level III, and 16 level IV studies). Overall, a total of 3657 failures were identified. The most common single failure mode of ACLR was new trauma (38%), followed by technical errors (22%), combined causes (i.e. multiple failure mechanisms; 19%), and biological failures (i.e. failure due to infection or laxity without traumatic or technical considerations; 8%). Technical causes also played a contributing role in 17% of all failures. Femoral tunnel malposition was the most common cause of technical failure (63%). When specifically looking at the bone-patellar tendon-bone (BPTB) or hamstring (HT) autografts, trauma was the most common failure mode in both, whereas biological failure was more pronounced in the HT group (4% vs. 22%, respectively). Technical errors were more common following transtibial as compared to anteromedial portal techniques (49% vs. 26%).

CONCLUSION

Trauma is the single leading cause of ACLR failure, followed by technical errors, and combined causes. Technical errors seemed to play a major or contributing role in large part of reported failures, with femoral tunnel malposition being the leading cause of failure. Trauma was also the most common failure mode in both BPTB and HT grafts. Technical errors were a more common failure mode following transtibial than anteromedial portal technique.

LEVEL OF EVIDENCE

IV.

[The killer turn in the posterior cruciate ligament reconstruction: mechanism and improvement]

OBJECTIVE

To summarize the research progress of killer turn in posterior cruciate ligament (PCL) reconstruction.

METHODS

The literature related to the killer turn in PCL reconstruction in recent years was searched and summarized.

RESULTS

The recent studies show that the killer turn is considered to be the most critical cause of graft relaxation after PCL reconstruction. In clinic, this effect can be reduced by changing the fixation mode of bone tunnel, changing the orientation of bone tunnel, squeezing screw fixation, retaining the remnant, and grinding the bone at the exit of bone tunnel. But there is still a lack of long-term follow-up.

CONCLUSION

There are still a lot of controversies on the improved strategies of the killer turn. More detailed basic researches focusing on biomechanics to further explore the mechanism of the reconstructed graft abrasion are needed.

Fibril deformation under load of the rabbit Achilles tendon and medial collateral ligament femoral entheses

Microscopic visualization under load of the region connecting ligaments/tendons to bone, the enthesis, has been performed previously; however, specific investigation of individual fibril deformation may add insight to such studies. Detailed visualization of fibril deformation would inform on the mechanical strategies employed by this tissue in connecting two mechanically disparate materials. Clinically, an improved understanding of enthesis mechanics may help guide future restorative efforts for torn or injured ligaments/tendons, where the enthesis is often a point of weakness. In this study, a custom ligament/tendon enthesis loading device was designed and built, a unique method of sample preparation was devised, and second harmonic and two-photon fluorescence microscopy were used to capture the fibril-level load response of the rabbit Achilles tendon and medial collateral ligament femoral entheses. A focus was given to investigation of the mechanical problem of fibril embedment. Resultant images indicate a rapid (occurring over approximately 60 μm) change in fibril orientation at the interface of ligament/tendon and calcified fibrocartilage early in the loading regime, before becoming relatively constant. Such a change in fibril angle helps confirm the materially graded region demonstrated by others, while, in this case, providing additional insight into fibril bending. We speculate that the scale of the mechanical problem (i.e., fibril diameters being on the order of 250 nm) allows fibrils to bend over the small (relative to the imaging field of view, but large relative to fibril diameter) distances observed; thus, potentially lessening required embedment lengths. Nevertheless, this behavior merits further investigation to be confirmed. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2506-2515, 2018.

Peak stresses shift from femoral tunnel aperture to tibial tunnel aperture in lateral tibial tunnel ACL reconstructions: a 3D graft-bending angle measurement and finite-element analysis

PURPOSE

To investigate the effect of tibial tunnel orientation on graft-bending angle and stress distribution in the ACL graft.

METHODS

Eight cadaveric knees were scanned in extension, 45°, 90°, and full flexion. 3D reconstructions with anatomically placed anterior cruciate ligament (ACL) grafts were constructed with Mimics 14.12^®. 3D graft-bending angles were measured for classic medial tibial tunnels (MTT) and lateral tibial tunnels (LTT) with different drill-guide angles (DGA) (45°, 55°, 65°, and 75°). A pivot shift was performed on 1 knee in a finite-element analysis. The peak stresses in the graft were calculated for eight different tibial tunnel orientations.

RESULTS

In a classic anatomical ACL repair, the largest graft-bending angle and peak stresses are seen at the femoral tunnel aperture. The use of a different DGA at the tibial side does not change the graft-bending angle at the femoral side or magnitude of peak stresses significantly. When using LTT, the largest graft-bending angles and peak stresses are seen at the tibial tunnel aperture.

CONCLUSION

In a classic anatomical ACL repair, peak stresses in the ACL graft are found at the femoral tunnel aperture. When an LTT is used, peak stresses are similar compared to classic ACL repairs, but the location of the peak stress will shift from the femoral tunnel aperture towards the tibial tunnel aperture.

CLINICAL RELEVANCE

the risk of graft rupture is similar for both MTTs and LTTs, but the location of graft rupture changes from the femoral tunnel aperture towards the tibial tunnel aperture, respectively.

LEVEL OF EVIDENCE

I.

Change in Anterior Cruciate Ligament Graft Choice and Outcomes Over Time

PURPOSE

To analyze failure rate in 2-year increments to determine if graft choice changed over time and graft failure rate.

METHODS

A prospective 2002-2008 database was used to identify risk factors for anterior cruciate ligament (ACL) retear. Subjects who had primary ACL retear with no history of contralateral surgery and 2-year follow-up were included. Subjects who underwent a multiligament reconstruction were excluded. Graft type, age, sex, smoking status, body mass index, Marx activity level at index surgery, medial and lateral meniscus status at time of ACL retear, sport played after ACL reconstruction, and clinical site were evaluated. Analysis was repeated using 2002-2003 (early) and 2007-2008 (late) 2-year databases. Analysis of variance with post hoc analysis was performed to detect significant differences in age and Marx score by graft type over time.

RESULTS

Two-year follow-up for graft failure was obtained on 2,497 of 2,692 (93%) subjects. There were 112 of 2,497 (4.5%) ACL retears identified at 2-year follow-up. The only predictor that changed between early/late periods was allograft use. Allograft odds ratio decreased from 13.1 to 9.5 (P < .01). Allografts were used in older patients (31-40 years) and with lower Marx scores (10-8) from early to late periods. The mean age of subjects who received bone-patellar tendon-bone autografts did not significantly change over time (22.8-23.5). The mean age of subjects who received hamstring autografts fell (27.9-25.5). The mean age of subjects who received allografts rose significantly (31.3-39.8, P < .01). The mean Marx score of subjects who received bone-patellar tendon-bone and hamstring autografts did not significantly change over time. The mean Marx score of subjects who received allografts decreased significantly (P < .01).

CONCLUSIONS

After early recognition, allograft use in young active patients was a risk factor for retear; graft choice by surgeons changed in the late period to use of allografts in older and less-active patients, which correlated with a significant decrease in retear risk.

LEVEL OF EVIDENCE

Level III, case control study.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Risk Factors and Predictors of Subsequent ACL Injury in Either Knee After ACL Reconstruction: Prospective Analysis of 2488 Primary ACL Reconstructions From the MOON Cohort

BACKGROUND

Anterior cruciate ligament (ACL) reinjury results in worse outcomes and increases the risk of posttraumatic osteoarthritis.

PURPOSE

To identify the risk factors for both ipsilateral and contralateral ACL tears after primary ACL reconstruction (ACLR).

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Data from the Multicenter Orthopaedic Outcomes Network (MOON), a prospective longitudinal cohort, were used to identify risk factors for ACL retear. Subjects with primary ACLR, no history of contralateral knee surgery, and a minimum of 2-year follow-up data were included. Age, sex, Marx activity score, graft type, lateral meniscal tear, medial meniscal tear, sport played at index injury, and surgical facility were evaluated to determine their contribution to both ipsilateral retear and contralateral ACL tear.

RESULTS

A total of 2683 subjects with average age of 27 ± 11 years (1498 men; 56%) met all study inclusion/exclusion criteria. Overall there were 4.4% ipsilateral graft tears and 3.5% contralateral ACL tears. The odds of ipsilateral ACL retear were 5.2 times greater for an allograft (P < .01) compared with a bone-patellar tendon-bone (BTB) autograft; the odds of retear were not significantly different between BTB autograft and hamstring autograft (P = .12). The odds of an ipsilateral ACL retear decreased by 0.09 for every yearly increase in age (P < .01) and increased by 0.11 for every increased point on the Marx score (P < .01). These odds were not significantly influenced by sex, smoking status, sport played, medial or lateral meniscal tear, or consortium site (P > .05). The odds of a contralateral ACL tear decreased by 0.04 for every yearly increase in age (P = .04) and increased by 0.12 for every increased point on the Marx score (P < .01); these odds were not significantly different between sex, smoking status, sport played, graft type, medial meniscal tear, or lateral meniscal tear (P > .05).

CONCLUSION

Younger age, higher activity level, and allograft graft type were predictors of increased odds of ipsilateral graft failure. Higher activity and younger age were found to be risk factors in contralateral ACL tears.

The role of the RNFA in anterior cruciate ligament graft preparation

Anterior cruciate ligament (ACL) reconstruction is one of the most commonly performed orthopedic procedures in the United States. Repair of the ACL often requires the use of autografts or allografts, and the RN first assistant (RNFA) often is the team member responsible for preparing the graft. Common grafts used in ACL repair include bone-patellar tendon-bone, hamstring, Achilles tendon, quadriceps tendon, and tibialis anterior tendon. The RNFA must be competent in preparing all of these grafts and in understanding the advantages and disadvantages of using each graft, such as the reasons for graft choice, and must ensure that all graft-related supplies and equipment are available and ready for use. The ability to prepare all graft types expands treatment options, reduces surgical time, and enhances the role of the RNFA.

Neuromuscular training to target deficits associated with second anterior cruciate ligament injury

SYNOPSIS

Successful return to previous level of activity following anterior cruciate ligament (ACL) reconstruction is not guaranteed, and the prevalence of second ACL injury may be as high as 30%. In particular, younger athletes who return to sports activities within the first several months after ACL reconstruction may be at significantly greater risk of a second ACL rupture compared to older, less active individuals. Significant neuromuscular deficits and functional limitations are commonly identified in athletes following ACL reconstruction, and these abnormal movement and neuromuscular control profiles may be both residual of deficits existing prior to the initial injury and exacerbated by the injury and subsequent ACL reconstruction surgery. Following ACL reconstruction, neuromuscular deficits are present in both the surgical and nonsurgical limbs, and accurately predict second-ACL injury risk in adolescent athletes. While second ACL injury in highly active individuals may be predicated on a number of modifiable and nonmodifiable factors, clinicians have the greatest potential to address the modifiable postsurgical risk factors through targeted neuromuscular interventions. This manuscript will (1) summarize the neuromuscular deficits commonly identified at medical discharge to return to sport, (2) provide the evidence underlying second-ACL injury risk factors, (3) propose a method to assess the modifiable deficits related to second-ACL injury risk, and (4) outline a method of intervention to prevent second ACL injury. The program described in this clinical commentary was developed with consideration for the modifiable factors related to second-injury risk, the principles of motor learning, and careful selection of the exercises that may most effectively modify aberrant neuromuscular patterns. Future validation of this evidence-based, late-phase rehabilitation program may be a critical factor in maximizing return-to-activity success and reduction of second-injury risk in highly active individuals.

LEVEL OF EVIDENCE

Therapy, level 5.