Biomechanics of the anterior cruciate ligament and implications for surgical reconstruction

Bone-patellar tendon-bone, hamstring, and quadriceps tendon autografts for anterior cruciate ligament reconstruction in skeletally immature patients: a systematic review

INTRODUCTION

Historically, anterior cruciate ligament (ACL) ruptures in the paediatric age group were managed conservatively with bracing, casting, activity modification, and physical therapy. However, most of these patients had to reduce their sports activities, and secondary damages to the affected knee were prevalent.

SOURCE OF DATA

Published scientific literature in Embase, Web of Science, PubMed, and Google Scholar databases.

AREAS OF AGREEMENT

ACL reconstruction in children with open physes patients is debated. Any damage to the physes around the knee could lead to growth abnormalities and axial deviation of the knee.

AREAS OF CONTROVERSY

Different grafts are available and suitable for ACL reconstruction in skeletally immature patients; however, which graft performs better remains unclear.

GROWING POINTS

This systematic review compared bone-patellar tendon-bone (BPTB), hamstring tendon (HT), and quadriceps tendon (QT) autografts for ACL reconstruction in skeletally immature patients. The joint laxity, Patient-reported outcome measures (PROMs), return to sport, and complications were compared.

AREAS TIMELY FOR DEVELOPING RESEARCH

In skeletally immature patients, HT, BPTB, and QT autografts for ACL reconstruction yielded good outcomes. Comparative studies are strongly required to establish the most suitable autograft.

A Comprehensive Review of Graft Choices and Surgical Techniques in Primary Anterior Cruciate Ligament Reconstruction: An Outcome Analysis

Anterior cruciate ligament (ACL) injuries are among the most prevalent knee injuries, particularly in athletes engaged in high-impact sports. ACL reconstruction is a widely performed surgical procedure to restore knee stability, prevent further knee damage, and enable patients to return to their previous physical activity levels. However, the success of ACL reconstruction is influenced by various factors, including the choice of graft and the surgical technique employed. This comprehensive review explores the outcomes of different graft options - autografts, allografts, and synthetic grafts - and various surgical techniques such as single-bundle versus double-bundle reconstruction and anatomic versus non-anatomic tunnel placement. The review analyzes the short- and long-term outcomes, including functional recovery, return to sports, complication rates, and the impact of patient-specific factors such as age, activity level, and comorbidities. Additionally, the review discusses the role of rehabilitation protocols in optimizing surgical outcomes. By synthesizing current evidence, this review aims to provide clinicians with insights into the most effective graft choices and surgical techniques for primary ACL reconstruction, ultimately guiding the optimization of patient outcomes and highlighting areas for future research.

Understanding the Structure-Function Relationship through 3D Imaging and Biomechanical Analysis: A Novel Methodological Approach Applied to Anterior Cruciate Ligaments

Understanding the microstructure of fibrous tissues, like ligaments, is crucial due to their nonlinear stress-strain behavior from unique fiber arrangements. This study introduces a new method to analyze the relationship between the microstructure and function of anterior cruciate ligaments (ACL). We tested the procedure on two ACL samples, one from a healthy individual and one from an osteoarthritis patient, using a custom tensioning device within a micro-CT scanner. The samples were stretched and scanned at various strain levels (namely 0%, 1%, 2%, 3%, 4%, 6%, 8%) to observe the effects of mechanical stress on the microstructure. The micro-CT images were processed to identify and map fibers, assessing their orientations and volume fractions. A probabilistic mathematical model was then proposed to relate the geometric and structural characteristics of the ACL to its mechanical properties, considering fiber orientation and thickness. Our feasibility test indicated differences in mechanical behavior, fiber orientation, and volume distribution between ligaments of different origins. These indicative results align with existing literature, validating the proposed methodology. However, further research is needed to confirm these preliminary observations. Overall, our comprehensive methodology shows promise for improving ACL diagnosis and treatment and for guiding the creation of tissue-engineered grafts that mimic the natural properties and microstructure of healthy tissue, thereby enhancing integration and performance in biomedical applications.

Predictive Refined Computational Modeling of ACL Tear Injury Patterns

Anterior cruciate ligament (ACL) ruptures are prevalent knee injuries, with approximately 200,000 ruptures annually, and treatment costs exceed USD two billion in the United States alone. Typically, the initial detection of ACL tears and anterior tibial laxity (ATL) involves manual assessments like the Lachman test, which examines anterior knee laxity. Partial ACL tears can go unnoticed if they minimally affect knee laxity; however, they will progress to a complete ACL tear requiring surgical treatment. In this study, a computational finite element model (FEM) of the knee joint was generated to investigate the effect of partial ACL tears under the Lachman test (GNRB® testing system) boundary conditions. The ACL was modeled as a hyperelastic composite structure with a refined representation of collagen bundles. Five different tear types (I-V), classified by location and size, were modeled to predict the relationship between tear size, location, and anterior tibial translation (ATT). The results demonstrated different levels of ATT that could not be manually detected. Type I tears demonstrated an almost linear increase in ATT, with the growth in tear size ranging from 3.7 mm to 4.2 mm, from 25% to 85%, respectively. Type II partial tears showed a less linear incline in ATT (3.85, 4.1, and 4.75 mm for 25%, 55%, and 85% partial tears, respectively). Types III, IV, and V maintained a nonlinear trend, with ATTs of 3.85 mm, 4.2 mm, and 4.95 mm for Type III, 3.85 mm, 4.25 mm, and 5.1 mm for Type IV, and 3.6 mm, 4.25 mm, and 5.3 mm for Type V, for 25%, 55%, and 85% partial tears, respectively. Therefore, for small tears (25%), knee stability was most affected when the tears were located around the center of the ligament. For moderate tears (55%), the effect on knee stability was the greatest for tears at the proximal half of the ACL. However, severe tears (85%) demonstrated considerable growth in knee instability from the distal to the proximal ends of the tissue, with a substantial increase in knee instability around the insertion sites. The proposed model can enhance the characterization of partial ACL tears, leading to more accurate preliminary diagnoses. It can aid in developing new techniques for repairing partially torn ACLs, potentially preventing more severe injuries.

Plastic and elastic biomechanical properties of anterior cruciate ligament autografts

BACKGROUND

Anterior cruciate ligament (ACL) rupture is a common orthopedic injury, occurring in roughly 68.6 per 100,000 persons annually, with the primary treatment option being ACL reconstruction. However, debate remains about the appropriate graft type for restoring the native biomechanical properties of the knee. Furthermore, plastic graft elongation may promote increased knee laxity and instability without rupture. This study aims to investigate the plastic properties of common ACL-R graft options.

METHODS

Patellar tendon (PT), hamstring tendon (HT), and quadriceps tendon (QT) grafts were harvested from 11 cadaveric knees (6 male and 5 female) with a mean age of 71(range 55-81). All grafts were mechanically tested under uniaxial tension until failure to determine each graft's elastic and plastic biomechanical properties.

RESULTS

Mechanically, the QT graft was the weakest, exhibiting the lowest failure force and the lowest failure stress (QT < HT, p = 0.032). The PT was the stiffest of the grafts, having a significantly higher stiffness (PT > QT, p = 0.0002) and Young's modulus (PT > QT, p = 0.001; PT > HT, p = 0.041). The HT graft had the highest plastic elongation at 4.01 ± 1.32 mm (HT > PT, p = 0.002). The post-yield behavior of the HT tendon shows increased energy storage capabilities with the highest plastic energy storage (HT > QT, p = 0.012) and the highest toughness (HT > QT, p = 0.032).

CONCLUSION

Our study agrees with prior studies indicating that the failure load of all grafts is above the requirements for everyday activities. However, grafts may be susceptible to yielding before failure during daily activities. This may result in the eventual loss of functionality for the neo-ACL, resulting in increased knee laxity and instability.

Radiographic Investigation of Differences in Static Anterior Tibial Translation With Axial Load Between Isolated ACL Injury and Controls

BACKGROUND

Static anterior tibial translation (SATT) is radiographically measured to show the amount of tibial translation during the single-leg stance, and thus it is representative of the physiological axial load subjected to the anterior cruciate ligament (ACL) during the stance. Increased SATT has been associated with increased posterior tibial slope (PTS) and is also associated with increased graft failure.

PURPOSE

To compare the SATT value in a control population with that in a population with an isolated ACL injury, as well as to compare the effect of tibial slope on SATT between the 2 groups.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A consecutive series of patients without ligamentous or meniscal injuries between 2019 and 2022 was reviewed. A matched consecutive cohort of patients with nonacute ACL injuries (surgery between 6 and 12 weeks after injury) without concomitant pathology was reviewed. Preoperative SATT and PTS were measured with a previously validated technique on lateral weightbearing knee radiographs. The SATT value was determined, and regression analysis was performed to investigate the relationship between SATT and PTS.

RESULTS

In total, 101 controls and 115 patients with an ACL injury were included in this study. The mean SATT was 1.31 mm (SD, 2.44 mm) and the mean PTS was 10.61° (SD, 3.28°) in the control cohort. The SATT was larger (mean, 2.27 mm; SD, 3.36 mm) in the ACL-injured cohort despite the tibial slope measurement being less in the ACL-injured cohort (mean, 9.46°; SD, 2.85°; P = .016). Linear regression analysis showed that for every 1° of increase in PTS, there was a 0.34-mm increase in SATT in the control cohort; however, there was a greater increase of 0.5 mm for every 1° of increase in PTS in the ACL-injured cohort. We found no significant differences in SATT when the cohorts were compared by age (P = .26) or sex (P = .10).

CONCLUSION

The present study reports a reference SATT value of 1.31 mm (SD, 2.44 mm) in a non-ACL-injured cohort, which was lower than in the ACL-injured cohort (mean, 2.27 mm; SD, 3.36 mm). The effect of slope on weightbearing anterior tibial translation was greater in the ACL-injured population than in the control cohort.

Sensorimotor Dysfunction Following Anterior Cruciate Ligament Reconstruction- an Afferent Perspective: A Scoping Review

Background

Sensorimotor dysfunction is thought to occur following anterior cruciate ligament (ACL) injury which may have implications on future reinjury risk. Dysfunction has been demonstrated within the efferent component of the sensorimotor system. However, no reviews have examined the two main components of the afferent system: the visual and somatosensory systems.

Hypothesis/Purpose

This study aimed to report differences in function (central processing and local processing) within the (1) somatosensory and (2) visual systems between individuals following anterior cruciate ligament reconstruction (ACLR) and healthy controls (between-subject). The study also aimed to report differences in function within the two systems between the two limbs of an individual following ACLR (within-subject).

Study Design

Scoping review.

Methods

A search was conducted in PubMed, SPORTDiscus, CINAHL, Medline and Embase up until September 2021. Level I-IV studies assessing somatosensory and visual systems were included if they compared ACLR limbs to the uninjured contralateral limb (within-subject) or a healthy control limb (between-group). The function of somatosensory and visual systems was assessed across both central processing (processing of information in the central cortex) and local processing (all other assessments outside of central processing of information).

Results

Seventy studies were identified (52 somatosensory, 18 visual). Studies examining somatosensory central processing demonstrated significant differences; 66% of studies exhibited within-subject differences and 100% of the studies exhibited between-group differences. Studies examining local somatosensory processing had mixed findings; 40% of the 'joint position sense (JPS)' and 'threshold to detect motion (TTDM)' studies showed significant within-subject differences (JPS=0.8°-3.8° and TTDPM=0.2°-1.4°) and 42% demonstrated significant between-group differences (JPS=0.4°-5° and TTDPM=0.3°-2.8°). Eighty-three percent of visual central processing studies demonstrated significant dysfunction between-groups with no studies assessing within-subject differences. Fifty percent of the studies examining local visual processing demonstrated a significant between-group difference.

Conclusion

Significant differences in central processing exist within somatosensory and visual systems following ACLR. There is mixed evidence regarding local somatosensory and visual processing. Increased compensation by the visual system and local visual processing dysfunction may occur in conjunction with somatosensory dysfunction.

Epidemiology of Anterior Cruciate Ligament Tears in National Collegiate Athletic Association Athletes: 2014/2015-2018/2019

PURPOSE

This study aimed to describe the epidemiology of ACL tears in NCAA men's and women's sports.

METHODS

Injury and exposure data collected within the NCAA Injury Surveillance Program from 2014/2015 to 2018/2019 were analyzed. ACL tear frequencies, injury rates (IR), and injury proportions were used to describe injury incidence by sport, event type, injury mechanism, and injury history. Injury rate ratios (IRR) were used to examine differential injury rates, and injury proportion ratios (IPR) were used to examine differential distributions.

RESULTS

A total of 729 ACL tears were reported from 8,474,401 recorded athlete exposures (AE) during the study period (IR = 0.86 per 10,000 AE), and the competition-related ACL tear rate was higher than the practice-related rate (IRR = 5.52, 95% confidence interval [CI] = 4.75-6.39). Among men's sports, the highest overall ACL tear rate was observed in men's football (IR = 1.44 per 10,000 AE), whereas among women's sports, the highest overall rate was observed in women's soccer (IR = 2.60 per 10,000 AE). Among sex-comparable sports, ACL tear rates were higher in women's basketball, softball, and soccer, as compared with their men's counterparts. ACL tears were more prevalently attributed to player contact mechanisms in men's sports than women's sports (IPR = 1.73, 95% CI = 1.37-2.19), but more prevalently attributed to noncontact mechanisms in women's sports than men's sports (IPR = 1.17, 95% CI = 1.01-1.35).

CONCLUSIONS

ACL tear risk in women's sports continues to warrant attention and prevention efforts. Given the differential rates by event type, future research efforts may also evaluate initiatives to reduce competition-related injury burden in NCAA sports.

Traditional suture tape versus multiple high-strength sutures for augmentation of anterior cruciate ligament primary repair: A time-zero biomechanical study

Background/objective

During the initial stages of rehabilitation after anterior cruciate ligament (ACL) surgery, a pivotal role is played in ensuring effective recuperation and averting complications. An often-employed strategy to tackle ACL laxity during this period involves the incorporation of synthetic materials for reinforcement. The objective of this study is to compare the effectiveness of conventional suture tape and multiple high-strength sutures as augmentation techniques for ACL repair.

Methods

Ten preserved cadaveric knees embalmed using the Thiel method were segregated into two groups, each containing five knees. In one group, traditional suture tape was employed for augmentation, while the other group utilized multiple high-strength sutures. Each knee underwent a cyclic load of 1000 sine wave cycles, succeeded by an axial distraction load until failure ensued. The resultant displacement and ultimate load at failure were assessed to contrast the efficacy of the two augmentation techniques.

Results

The group utilizing multiple high-strength sutures exhibited a significantly higher load to failure at time-zero (1690.7 N) compared to the suture tape group (987.6 N) (P = .003). Furthermore, the multiple high-strength sutures group demonstrated significantly reduced displacement after 1000 cyclic loads (6.6 mm) in comparison to the suture tape group (16.3 mm) (P < .001).

Conclusions

Multiple high-strength sutures show better biomechanical properties for the augmentation of ACL repair at time-zero. Both suture tape and multiple high-strength sutures had ultimate load-to-failure values higher than the natural ACL loads. Therefore, these substances might serve as augmentation options to prevent the ACL's gradual elongation, a critical concern particularly in the initial stages of rehabilitation.

Computational modelling of the graft-tunnel interaction in single-bundle ACL reconstructed knee

OBJECTIVES

Tunnel enlargement and graft failure are common complications associated with ACL reconstruction. The mechanical interaction between the graft and the tunnel aperture may play a more important role. This study aims to evaluate graft position within femoral tunnel and the graft force under external loads.

METHODS

An FE model of the femur-graft-tibia complex was constructed from CT images of an anatomically reconstructed knee specimen. The model was subjected to kinematics of passive flexion extension, anterior/posterior translation, internal/external rotation and valgus kinematics, which were collected from experimental testing. Graft shift and rotation of graft-tunnel contact region during flexion/extension and external loadings were recorded and compared to experimental measurements.

RESULTS

Model showed that the graft shifted in the femoral tunnel during flexion and under external loads. The graft-tunnel contact area rotated by up to 55° during flexion from full extension to 90° of extension implying that the so-called "wiper effect" occurs during most of flexion angles.

CONCLUSIONS

Different regions of the femoral tunnel aperture, particularly the anterior region, were under significantly more contact force from the graft than other areas of the aperture during the anterior translation test, potentially leading to femoral tunnel enlargement to the anterior side of the aperture.

Dynamic CT scanning of the knee: Combining weight bearing with real-time motion acquisition

BACKGROUND

Imaging the lower limb during weight-bearing conditions is essential to acquire advanced functional joint information. The horizontal bed position of CT systems however hinders this process. The purpose of this study was to validate and test a device to simulate realistic knee weight-bearing motion in a horizontal position during dynamic CT acquisition and process the acquired images.

METHODS

"Orthostatic squats" was compared to "Horizontal squats" on a device with loads between 35% and 55% of the body weight (%BW) in 20 healthy volunteers. Intraclass Correlation Coefficient (ICC), and standard error of measurement (SEM), were computed as measures of the reliability of curve kinematic and surface EMG (sEMG) data. Afterwards, the device was tested during dynamic CT acquisitions on three healthy volunteers and three patients with patellofemoral pain syndrome. The respective images were processed to extract Tibial-Tuberosity Trochlear-Groove distance, Bisect Offset and Lateral Patellar Tilt metrics.

RESULTS

For sEMG, the highest average ICCs (SEM) of 0.80 (6.9), was found for the load corresponding to 42%BW. Kinematic analysis showed ICCs were the highest for loads of 42%BW during the eccentric phase (0.79-0.87) and from maximum flexion back to 20° (0.76). The device proved to be safe and reliable during the acquisition of dynamic CT images and the three metrics were computed, showing preliminary differences between healthy and pathological participants.

CONCLUSIONS

This device could simulate orthostatic squats in a horizontal position with good reliability. It also successfully provided dynamic CT scan images and kinematic parameters of healthy and pathological knees during weight-bearing movement.

Association between pre- and postoperative rotational mismatches of the femorotibial components and bones in bi-cruciate retaining and posterior stabilized total knee arthroplasty

To clarify the association between pre- and postoperative rotational mismatches of the femorotibial components and bones for total knee arthroplasty (TKA) with bi-cruciate retaining (BCR) design and with fixed bearing posterior stabilized (PS) design. This retrospective cohort study included 40 BCR TKAs and 50 PS TKAs. Pre- and postoperative rotational mismatches of the femorotibial components and bones were measured by three-dimensional assessment based on computed tomography imaging. The mean value and percentage within ± 5° of pre- and postoperative rotational mismatches were compared between BCR TKA and PS TKA. Correlations between pre- and postoperative rotational mismatches of the femorotibial components and bones were investigated in BCR TKA and PS TKA. There was no significant difference in mean preoperative rotational mismatch of femorotibial components and bones between BCR TKA and PS TKA. Mean postoperative rotational mismatch of femorotibial components and bones was significantly greater in BCR TKA than in PS TKA. Postoperative rotational mismatch of the femorotibial components was within ± 5° in 21 knees (52.5%) for BCR TKA and in 43 knees (86.0%) for PS TKA. The rate of postoperative rotational mismatch of the femorotibial components and bones within ± 5° was significantly lower for BCR TKA than for PS TKA. In BCR TKA, there was a positive correlation between pre- and postoperative rotational mismatches of the femorotibial components and of bones. We consider these results can be attributed to the retention of both cruciate ligaments, which may affect the reduction of rotational permittance of the components and bones.

Mechanical properties of a bioabsorbable magnesium interference screw for anterior cruciate ligament reconstruction in various testing bone materials

Tears of the anterior cruciate ligament (ACL) negatively impact the stability and kinematics of the knee. Interference screws (ISs) are used for graft fixation in ACL reconstruction and provide sufficient fixation strength to withstand the patients' activities during the graft-to-bone integration process. Magnesium is a novel material used to manufacture IS given its strength and bioabsorbability. In previous studies, the selected magnesium IS design showed a better fixation performance in comparison to the conventional IS design due to its shape design and surface condition. In this study, bioabsorbable magnesium ISs were tested for their insertion (insertion torque and a number of turns to implement the IS) and fixation performance (pull-out and dynamic test). To obtain a reliable initial assessment of IS performance, ISs were implanted in 15 per cubic foot (PCF) Sawbones polyurethane foam blocks, Sawbones biomechanical tibia models with 17 PCF foam cores, and human cadaveric tibiae. Porcine tendons were used in the foam block pull-out test, and nylon ropes were used in all other test setups to prevent influences of the ligament graft material itself. In the pull-out test, the graft was subjected to tensile stress at a rate of 6 mm/min. For the dynamic test, 1000 cycles between 0 and 200 N were performed, followed by a final pull-out test. After each test, the tunnel widening pattern was observed by measuring the aspect ratio of the tunnel at the insertion site. The insertion torque lies within the normal insertion torque of the ISs as well as the average ligament tension before the insertion. In the foam block setup, the nylon rope showed a higher pull-out force than the porcine tendon. The comparison of each setup using nylon rope for both pull-out and pull-out after the dynamic test showed no significant difference between the foam block and cadaver setup. However, all tibia model setup shows unexpectedly high pull-out force due to the influence of its cortical layer. There were no statistically significant differences in tunnel widening between foam block-porcine tendon and foam block-nylon rope constructs. The pull-out resistance of magnesium ISs falls within the typical ACL tension range during daily activities. Even though the test results of the magnesium ISs are different in each bone material, the magnesium IS shows adequate fixation ability and workability during insertion without material failure.

Comparison of Functional Outcomes of an Anterior Cruciate Ligament (ACL) Reconstruction Using a Peroneus Longus Graft as an Alternative to the Hamstring Tendon Graft

Background Ever since the arthroscopic reconstruction of the anterior cruciate ligament (ACL) has begun, the use of the peroneus longus (PL) graft for primary ACL reconstruction (ACLR) has never been thought of. There is very little literature on it. Hence, our study aims to compare the functional outcomes, knee stability, donor site morbidity, and assessment of thigh muscle wasting in patients with ACL injury managed by arthroscopic single bundle reconstruction with peroneus longus tendon (PLT) and hamstring tendons (HT), respectively. Methods All adults aged 16-50 years of either gender presenting with symptoms of symptomatic ACL deficiency were admitted for arthroscopic single-bundle ACLR and allocated into two groups (peroneus longus and hamstring tendon). Functional scores (International Knee Documentation Committee (IKDC), Lysholm score), clinical knee evaluation (anterior drawer, Lachman, and pivot shift test), donor site morbidity (American Orthopedic Foot and Ankle Society ankle hindfoot score (AOFAS)), and thigh circumference were recorded preoperatively and at six months and one year postoperatively. The same post-op rehabilitation protocol was followed in both groups. Results One hundred and ninety-four patients (hamstring n = 96, peroneus n = 98) met the inclusion criteria. There were no significant differences between the preoperative, six-month postoperative, and one-year postoperative scores between the hamstring and peroneus longus groups in the IKDC (p=0.356) and Lysholm knee score (p=0.289). The mean for the AOFAS was 99.05 ± 3.56 and 99.80 ± 0.70 in the PLT and HT groups, respectively, showing no statistical difference, with a significant improvement in thigh muscle wasting among the PLT group at final follow-up (p < 0.001). Conclusion We observed similar knee stability and functional outcomes and no obvious donor site morbidity among both groups. These patients also had better responses to physiotherapy in recovering from their thigh muscle wasting. So, we can recommend that a PL graft can be a safe, viable, and effective option for usual arthroscopic single-bundle ACL reconstruction.

Publication trends and global productivity about the anterior cruciate ligament: a bibliometric analysis between 1980-2021

Aim: Due to anatomic, biomechanical, kinematic, biological and clinical data obtained as a result of many studies related to treatment and rehabilitation of injuries to the anterior cruciate ligament (ACL), among the most studied anatomic structures in the human body, the literature is continuously being updated and improved. In this study, the aim was to holistically analyze scientific articles about the ACL published between 1980 and 2021 using a variety of statistical methods. Material and Method: Articles published from 1980 to 2021 about the ACL were obtained from the Web of Science (WoS) database and analyzed using statistical methods and bibliometric approaches. To identify trend topics and global cooperation, and to complete citation analysis, network visualization maps were used. The exponential smoothing predictor was used to predict the number of articles that will be published in the next 5 years. Spearman’s correlation coefficient was used for correlation research. Results: A total of 11,077 publications were identified. Of these publications, 9101 (82.1%) were articles. The top 3 countries contributing most to the literature were the USA (3894, 42.7%), Japan (879, 9.6%) and Germany (616, 6.7%). The top 3 active organizations were Pennsylvania Commonwealth System of Higher Education (n=468), University of Pittsburgh (440), and University of California system (279). The top 3 journals publishing most articles were the American Journal of Sports Medicine (n=1614), Knee Surgery Sports Traumatology Arthroscopy (1418), and Arthroscopy: The Journal of Arthroscopic and Related Surgery (915). The most effective journal according to mean number of citations per article was the Journal of Bone and Joint Surgery (average citation per document: 80.7). The most active author was Freddie H. Fu (n=278, from University of Pittsburgh). Conclusion: In this comprehensive bibliometric research about the topic of ACL, with a trend toward increasing publication numbers in recent years, the summary information for 9101 articles published between 1980 and 2021 was shared. According to analysis results to determine trend topics, the keywords studied in recent years include return to sport, ACL injury, anterolateral ligament, pivot shift, quadriceps strength, KOOS, ACL tear, ACL repair, meniscal repair, knee ligaments, tibial slope, posterior tibial slope, return to play, adolescent, graft failure and lateral meniscus.

Factors Influencing the Initial Constraint Level of the Knee Joint and Its Effect on Clinical Outcomes After ACL Reconstruction With Hamstring Graft

Background

A force-based tension protocol that uses a certain amount of tension at graft fixation could still give rise to variations in initial constraint levels of the knee joint in terms of side-to-side difference (SSD) in anterior translation.

Purpose

To investigate the factors influencing the initial constraint level in anterior cruciate ligament (ACL)-reconstructed knees and compare outcomes according to the level of constraint in terms of anterior translation SSD.

Study Design

Cohort study; Level of evidence, 3.

Methods

Included were 113 patients who underwent ipsilateral ACL reconstruction using an autologous hamstring graft and had minimum 2-year follow-up outcomes. All grafts were tensioned and fixed at 80 N using a tensioner at the time of graft fixation. The patients were classified into the following 2 groups according to the initial anterior translation SSD, measured using the KT-2000 arthrometer: a physiologic constraint group with restored anterior laxity ≤2 mm (group P; n = 66) and a high-constraint group with restored anterior laxity >2 mm (group H; n = 47). Clinical outcomes were compared between the groups, and preoperative and intraoperative variables were evaluated to identify factors affecting the initial constraint level.

Results

Between group P and group H, generalized joint laxity (P = .005), posterior tibial slope (P = .022), and anterior translation measured in the contralateral knee (P < .001) were found to differ significantly. Measured anterior translation in the contralateral knee was the only significant predictor of high initial graft tension (P = .001). No significant differences were found between the groups regarding clinical outcomes and subsequent surgery.

Conclusion

Greater anterior translation measured in the contralateral knee was an independent predictor of a more constrained knee after ACL reconstruction. The short-term clinical outcomes after ACL reconstruction were comparable, regardless of the initial constraint level in terms of anterior translation SSD.

Physiotherapy After Anterior Cruciate Ligament Reconstruction a Literature Review

Introduction: The anterior cruciate ligament (ACL) is the main stabiliser that inhibits excessive anterior translation of the tibia and prevents excessive rotational movements of the knee joint. ACL injuries occur at a frequency of 30 to 78 per 100,000 people a year, leading to instability and impaired function of the knee joint. Continuous development of knowledge on the anatomy and functions of the anterior cruciate ligament, along with the improvement of surgical and physiotherapeutic techniques, allowed for the development of satisfactory modern methods for treating ACL lesions.Objective: The aim of the study is to review literature on modern methods of physiotherapy after the reconstruction of the anterior cruciate ligament.Material and methods: Pubmed, Google Scholar and ScienceDirect scientific databases were searched using a combination of keywords: anterior cruciate ligament, ACL, reconstruction, physiotherapy, protocol. The inclusion criteria were: publication date from the last 10 years and a detailed description of the physiotherapy protocol included.Results: Six publications meeting the inclusion criteria were included in the analysis. Selected physiotherapy protocols consisted of 3 to 5 phases. Phase 1 was focused on reducing pain and swelling in all cases. The purpose of the following phases was to increase the range of motion and to strengthen muscle strength as well as neuromuscular coordination. The final stage consisted of dynamic exercises allowing to prepare for a chosen sports activity.Conclusion: Contemporary protocols for physiotherapy after ACL reconstruction are based on early recovery of range of motion in the knee joint, early increase in load on the operated limb as well as shortening (or excluding) the period of immobilisation and the use of orthoses.

3D-Braided Poly-ε-Caprolactone-Based Scaffolds for Ligament Tissue Engineering

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee. Due to its limited intrinsical healing potential and vascularization, injuries of the ACL do not heal satisfactorily, and surgical intervention is usually required. The limitations of existing reconstructive grafts and autologous transplants have prompted interest in tissue-engineered solutions. A tissue engineering scaffold for ACL reconstruction must be able to mimic the mechanical properties of the native ligament, provide sufficient porosity to promote cell growth of the neoligament tissue, and be biodegradable. This study investigates long-term biodegradable poly-ε-caprolactone (PCL)-based scaffolds for ACL replacement using the 3D hexagonal braiding technique. The scaffolds were characterized mechanically as well as morphologically. All scaffolds, regardless of their braid geometry, achieved the maximum tensile load of the native ACL. The diameter of all scaffolds was lower than that of the native ligament, making the scaffolds implantable with established surgical methods. The 3D hexagonal braiding technique offers a high degree of geometrical freedom and, thus, the possibility to develop novel scaffold architectures. Based on the findings of this study, the 3D-braided PCL-based scaffolds studied were found to be a promising construct for tissue engineering of the anterior cruciate ligament.

Rotational Stability of the Knee in a Comparative Study of Anterior Cruciate Ligament Reconstruction Using the Double-Bundle and Single-Bundle Techniques

BACKGROUND

The purpsose of this study was to evaluate the biomechanical outcomes of patients who underwent ACL reconstruction either with the DB or SB technique. We hypothesized that the DB technique would provide better rotation control of the knee following ACL reconstruction.

METHODS

The study included seventy-five participants (26 DB, 22 SB, and 27 healthy volunteers). Only cases with at least one year of postoperative follow-up were included. The participants performed three different demand tasks: walk task, walk and change direction, and stair descent and change direction, which was tracked using a three-dimensional 4-camera optoelectronic system. The following kinematic data were analyzed: tibial rotation amplitude and maximal internal and external rotation. Knees with ACL reconstruction were compared to contralateral knees with intact ACL and healthy knees. Clinical outcomes were determined using the subjective and objective International Knee Documentation Committee (IKDC) questionnaire and a manual arthrometer (KT 1000).

RESULTS

Both surgical groups exhibited similar clinical outcomes (mean subjective IKDC 91 SB vs. 90 DB, P=0.815; KT 1000 difference: 2mm in both groups, P=0.772). The vertical component of the ground force reaction revealed no differences between the surgical and control groups (P>0.05). Tibial rotation amplitude and maximal internal and external rotation were similar between the control, SB, and DB groups in all three different demand tasks (P>0.05).

CONCLUSION

ACL reconstruction using either the SB or DB technique can restore rotational control to the level of a healthy knee. No clinical or functional differences were found between the SB and DB surgical options.

Rehabilitation and functional outcomes in internally braced and standard ACL reconstructions

Purpose

The purpose of this study was to compare surgical outcomes in patients who underwent ACL reconstruction, with and without internal bracing, at 1-3, 4-7, and 8-12 months of postoperative physical therapy. Previous studies show that ACL reconstruction with internal bracing allows earlier and more aggressive rehabilitation. Therefore, it was hypothesized that patients with internal bracing would display superior surgical recovery compared to ACL reconstruction alone after adjusting for length of physical therapy.1, 2, 3.

Methods

Patients who underwent ACL reconstruction and had a minimum two-year follow-up were included. Demographics including age, gender, use of internal bracing, and pre-operative level of activity were collected. Patient-reported outcomes were assessed using KOOS scores.

Results

46 patients underwent ACL reconstruction between January 2013 and December 2015. The mean age was 31.53 ± 8.37 years. Patients who received ACL reconstruction with internal bracing reported similar improvement in KOOS scores (mean = 42.82 ± 15.44; median = 46.39 [34.52-51.80]) compared to ACL reconstruction alone (mean = 38.18 ± 19.91; median = 40.17 [29.49-53.90]) (p = 0.475). Patients who received ACL reconstruction with internal bracing reported comparable improvement to ACL reconstruction alone at 0-3 months (Internal bracing: mean = 35.39 ± 15.26, median = 40.45 [26.49-47.73]; No internal bracing: mean = 42.51 ± 12.33, median = 39.32 [35.69-52.94], p = 0.4113), 4-7 months (Internal bracing: 41.96 ± 14.49, 45.55 [33.94-52.68]; No internal bracing: 30.64 ± 32.29, 41.65 [26.17-46.12], p = 0.7491) and 8+ months groups (Internal bracing: 63.36 ± 13.06, 63.36 [58.74-67.98]; No internal bracing: 47.05 ± 10.14, 47.05 [43.46-50.63]) (p = 0.6985).

Conclusion

This study demonstrates no statistical difference in functional outcome scores when comparing patients with internally braced ACL reconstruction compared to standard reconstruction. Therefore, the increased structural support provided by use of internal bracing in ACL reconstruction does not afford to quicker improvement in patient-reported recovery.

Small laboratory animal models of anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) injuries are common knee ligament injuries. While generally successful, ACL reconstruction that uses a tendon graft to stabilize the knee is still associated with a notable percentage of failures and long-term morbidities. Preclinical research that uses small laboratory species (i.e., mice, rats, and rabbits) to model ACL reconstruction are important to evaluate factors that can impact graft incorporation or posttraumatic osteoarthritis after ACL reconstruction. Small animal ACL reconstruction models are also used for proof-of-concept studies for the development of emerging biological strategies aimed at improving ACL reconstruction healing. The objective of this review is to provide an overview on the use of common small animal laboratory species to model ACL reconstruction. The review includes a discussion on comparative knee anatomy, technical considerations including types of tendon grafts employed amongst the small laboratory species (i.e., mice, rats, and rabbits), and common laboratory evaluative methods used to study healing and outcomes after ACL reconstruction in small laboratory animals. The review will also highlight common research questions addressed with small animal models of ACL reconstruction.

Single versus double hamstring tendon graft in anterior cruciate ligament reconstruction in the paediatric patient: a single-blind randomised controlled trial study protocol

INTRODUCTION

There is currently no clear indication in the literature regarding a single or double hamstring tendon (single bundle) autograft for anterior cruciate ligament (ACL) reconstruction in the paediatric patient. The primary aim of this single blind randomised controlled trial is to determine whether a single or double hamstring tendon graft ACLR leads to superior clinical outcomes postsurgery in paediatric patients with ACL injury.

METHODS AND ANALYSIS

Single site, prospective, single blind, randomised controlled trial with two parallel treatment arms. 100 patients aged 10-18 years who present with an isolated ACL tear±meniscal injury, verified on MRI, will be randomly allocated to one of the two surgical groups. The primary outcomes will be side-to-side difference in anterior tibial translation and graft failure incidence 12 months postsurgery. Primary and secondary outcomes will also be assessed at 2-year and 5-year postsurgery.

ETHICS AND DISSEMINATION

Results will be presented in peer-reviewed journals and at international conferences and disseminated to participants and healthcare professionals via newsletters and hospital presentations. This study is approved by the Children's Health Queensland Hospital and Health Service Human Research Ethics committee.

TRIAL REGISTRATION NUMBER

ACTRN12620001170910p; Australian New Zealand Clinical Trials Registry.

State of the mineralized tissue comprising the femoral ACL enthesis in young women with an ACL failure

Despite poor graft integration among some patients that undergo an anterior cruciate ligament (ACL) reconstruction, there has been little consideration of the bone quality into which the ACL femoral tunnel is drilled and the graft is placed. Bone mineral density of the knee decreases following ACL injury. However, trabecular and cortical architecture differences between injured and non-injured femoral ACL entheses have not been reported. We hypothesize that injured femoral ACL entheses will show significantly less cortical and trabecular mass compared with non-injured controls. Femoral ACL enthesis explants from 54 female patients (13-25 years) were collected during ACL reconstructive surgery. Control explants (n = 12) were collected from seven donors (18-36 years). Injured (I) femoral explants differed from those of non-injured (NI) controls with significantly less (p ≤ 0.001) cortical volumetric bone mineral density (vBMD) (NI: 736.1-867.6 mg/cm3 ; I: 451.2-891.9 mg/cm3 ), relative bone volume (BV/TV) (NI: 0.674-0.867; I: 0.401-0.792) and porosity (Ct.Po) (NI: 0.133-0.326; I: 0.209-0.600). Injured explants showed significantly less trabecular vBMD (p = 0.013) but not trabecular BV/TV (p = 0.314), thickness (p = 0.412), or separation (p = 0.828). We found significantly less cortical bone within injured femoral entheses compared to NI controls. Lower cortical and trabecular bone mass within patient femoral ACL entheses may help explain poor ACL graft osseointegration outcomes in the young and may be a contributor to the osteolytic phenomenon that often occurs within the graft tunnel following ACL reconstruction.

EFFECTS OF A PROPHYLACTIC KNEE SLEEVE ON THE ANTERIOR CRUCIATE LIGAMENT AND LOWER EXTREMITY BIOMECHANICS: AN EXAMINATION USING MUSCULOSKELETAL SIMULATION

The current study aimed using a two-experiment musculoskeletal simulation-based approach, measuring anterior cruciate ligament (ACL) biomechanics, knee joint kinematics, and lower extremity joint loading to examine the effects of both a prophylactic knee sleeve on (1) a sport-specific change of direction movement in female footballers and (2) a single leg landing in male footballers. Experiment 1 examined 12 female university first team level footballers (age [Formula: see text] years, height [Formula: see text][Formula: see text]m, body mass [Formula: see text][Formula: see text]kg) undertaking a [Formula: see text] cutting movement in sleeve and no-sleeve conditions. Experiment 2 examined 10 male university first team level footballers (age [Formula: see text] years, height [Formula: see text][Formula: see text]m, body mass [Formula: see text][Formula: see text]kg) undertaking a single leg drop jump landing in sleeve and no-sleeve conditions. In each experiment, data was collected in a biomechanics laboratory and three-dimensional (3D) motion capture and ground reaction force (GRF) information was collected. 3D kinematics, 3D knee kinetics, and ACL ligament forces/strains were measured using musculoskeletal simulation, and participants were also asked to subjectively rate the knee sleeve in terms of both comfort and stability. Experiment 1 showed that the sleeve condition was associated with greater ACL strain ([Formula: see text]% and no-[Formula: see text]%) and forces ([Formula: see text] BW and no-[Formula: see text] BW). In addition, the brace condition also enhanced lateral compressive tibiofemoral ([Formula: see text] BW and no-[Formula: see text] BW) and total compressive tibiofemoral force ([Formula: see text] BW and no-[Formula: see text] BW). Finally, for the subjective ratings, participants indicated that the knee sleeve significantly improved perceived comfort and stability. Experiment 2 did not reveal any statistical differences between knee sleeve and no-sleeve conditions nor any effects of the knee sleeve on subjective ratings of comfort or stability. Therefore, the findings from the current investigation suggest that the prophylactic knee sleeve examined in the current investigation does not appear to reduce the biomechanical parameters linked to the aetiology of knee pathologies in male/female footballers.

Large lateral tibial slope and lateral-to-medial slope difference are risk factors for poorer clinical outcomes after posterolateral meniscus root tear repair in anterior cruciate ligament reconstruction

BACKGROUND

Meniscus root tear is an uncommon but detrimental injury of the knee. Hoop stress is lost during meniscus root tear, which can lead to excessive tibiofemoral contact pressure and early development of osteoarthritis. Posterolateral meniscus root tears (PLRT) are more commonly associated with anterior cruciate ligament (ACL) tears. As the lateral compartment is less congruent than the medial compartment, it is more susceptible to a shearing force, which is increased in the ACL-deficient knee. In accordance with the compressive axial load, the increase in the tibial slope would generate a greater shearing force. The additional lateral compartment mobility caused by ACL tear should be reduced after ACL reconstruction (ACLR). However, there is a lack of evidence to conclude that ACLR can sufficiently limit the effect of large tibial slope (LTS) on the healing after PLRT repair. This study aimed to evaluate whether a steep LTS would be a risk factor for poorer clinical outcomes after PLRT repair concomitant with ACLR.

METHODS

In this retrospective study, a chart review was conducted to identify patients with concomitant unilateral primary ACLR and PLRT repair. Patients with a partial tear or healed tear were excluded. Postoperative MRI and clinical assessments were performed at a mean follow up of 35 months. MRI data was used to measure the LTS, medial tibial slope (MTS), coronal tibial slope (CTS), the lateral-to-medial slope difference (LTS-MTS) and meniscus healing and extrusion. Functional outcomes were evaluated by patient-reported outcomes (International Knee Documentation Committee [IKDC], Lysholm and Tegner scores) and KT-1000 arthrometer assessment. Interobserver reproducibility was assessed by two reviewers.

RESULTS

Twenty-five patients were identified for the analysis. Patients with larger LTS and larger LTS-MTS differences were shown to be correlated with poorer IKDC scores after surgery (R = -0.472, p = 0.017 and R = -0.429, p = 0.032, respectively). Herein, patients with LTS ≥ 6° or LTS-MTS ≥ 3° demonstrated poorer IKDC scores.

CONCLUSION

A large LTS (≥ 6°) and a large difference of LTS-MTS (≥ 3°) were shown to be risk factors for poorer functional and radiological outcomes for PLRT repair in patients after ACLR. Clinically, closer monitoring and a more stringent rehabilitation plan for patients with LTS ≥ 6° or LTS-MTS ≥ 3° would be recommended.

Current trends in the anterior cruciate ligament part 1: biology and biomechanics

A trend within the orthopedic community is rejection of the belief that "one size fits all." Freddie Fu, among others, strived to individualize the treatment of anterior cruciate ligament (ACL) injuries based on the patient's anatomy. Further, during the last two decades, greater emphasis has been placed on improving the outcomes of ACL reconstruction (ACL-R). Accordingly, anatomic tunnel placement is paramount in preventing graft impingement and restoring knee kinematics. Additionally, identification and management of concomitant knee injuries help to re-establish knee kinematics and prevent lower outcomes and registry studies continue to determine which graft yields the best outcomes. The utilization of registry studies has provided several large-scale epidemiologic studies that have bolstered outcomes data, such as avoiding allografts in pediatric populations and incorporating extra-articular stabilizing procedures in younger athletes to prevent re-rupture. In describing the anatomic and biomechanical understanding of the ACL and the resulting improvements in terms of surgical reconstruction, the purpose of this article is to illustrate how basic science advancements have directly led to improvements in clinical outcomes for ACL-injured patients.Level of evidenceV.

Ligament Regenerative Engineering: Braiding Scalable and Tunable Bioengineered Ligaments Using a Bench-Top Braiding Machine

Anterior cruciate ligament (ACL) injuries are common sports injuries that typically require surgical intervention. Autografts and allografts are used to replace damaged ligaments. The drawbacks of autografts and allografts, which include donor site morbidity and variability in quality, have spurred research in the development of bioengineered ligaments. Herein, the design and development of a cost-effective bench-top 3D braiding machine that fabricates scalable and tunable bioengineered ligaments is described. It was demonstrated that braiding angle and picks per inch can be controlled with the bench-top braiding machine. Pore sizes within the reported range needed for vascularization and bone regeneration are demonstrated. By considering a one-to-one linear relationship between cross-sectional area and peak load, the bench-top braiding machine can theoretically fabricate bioengineered ligaments with a peak load that is 9× greater than the human ACL. This bench-top braiding machine is generalizable to all types of yarns and may be used for regenerative engineering applications.

Morphometric analysis of patella and patellar ligament: a cadaveric study to aid patellar tendon grafts

PURPOSE

Morphometric analysis of the patella and the patellar ligament is crucial in diagnosing and surgical corrections of knee injuries and patellofemoral joint disorders. Dimensions of the patella and the patellar ligament are frequently used in implant design and ACL reconstruction. This study aims to obtain detailed morphometric data on the patellar ligament and its localization based on gross anatomical dissections in the adult cadavers.

METHODS

The present study consisted of 50 lower limbs from formalin-fixed male adult cadavers aged about 70 years (45-85) belonging to the South Indian population. Total length of the quadriceps tendon, patellar height, patellar ligament height, proximal width, distal width and thickness of the patellar ligament were measured meticulously. Mean, standard deviation, median scores of each parameter were computed for groups using SPSS 16.0. Level of significance was considered as p < 0.05. Wilcoxon signed-rank test was used to compare the various parameters on the right and left limbs. The relationships between all parameters were analyzed using Spearman's rank correlation test.

RESULTS

There was no statistically significant difference in the various measurements of the patella and patellar ligament between the right and left lower limbs. Patellar ligament length showed positive correlation with ligament thickness (r = 0.36; p = 0.078 for right limb and r = 0.33; p = 0.104 for left limb). Proximal width of ligament showed significant positive correlation with distal width (r = 0.41; p = 0.041 for right limb and r = 0.54; p = 0.006 for left limb).

CONCLUSION

This morphometric data and analysis might be fundamental in understanding various knee conditions in situ and necessary to orthopedic surgeons for successful planning and execution for ACL reconstruction using patellar ligament graft and other patellofemoral joint disorders.

LEVEL OF EVIDENCE

I.

The Effect of Anterior Cruciate Ligament Reconstruction with an Electropsun Scaffold on Tibiofemoral Contact Mechanics

Surgical reconstruction of the torn ACL is performed to restore native contact mechanics. Drawbacks to traditional ACL repair techniques motivate the development of a tissue engineered ACL scaffold. Our group has developed a hierarchical electrospun polycaprolactone (PCL) scaffold that consists of rolled nanofiber bundles attached at each end with solvent-case blocks of PCL. The goal of this study was to compare ovine cadaver tibiofemoral contact mechanics after ACL reconstruction with the electrospun scaffold to a clinically applicable ACL reconstruction with a soft tissue graft and the ACL transected condition (ACLX). In the ACLX group and after ACL reconstruction with either the electrospun scaffold or soft tissue graft, pressure sensors were inserted under the menisci. Loads up to 890 N were applied at various flexion angles. The scaffold performed the best at restoring contact mechanics in the medial hemijoint to that of the native ACL. The scaffold was good at maintaining a medial-lateral balance of pressures as in the native joint whereas the ACLX shifted pressure off the lateral and on to the medial hemijoint. While the ACL scaffold didn't restore mechanics to that of the native condition, it improved contact mechanics compared to the standard graft replacement and ACLX condition.

Anterior cruciate ligament intactness in osteoarthritic patients indicated for total knee arthroplasty: a systematic literature review and meta-analysis

Bi-cruciate retaining total knee arthroplasty (BCR TKA) is thought to result in more natural knee kinematics compared to conventional TKA designs. This may lead to a reduction in dissatisfied patients after TKA. An intact anterior cruciate ligament (ACL) is a prerequisite for implantation of a BCR TKA but the frequency of an intact ACL in patients indicated for TKA is not well known. The objective of this systematic literature review was to determine the presence of an intact ACL in patients undergoing TKA by intraoperative macroscopic or MRI assessment. A systematic literature review was conducted using PubMed™ and EMBASE™ in June 2020. The ACL of patients with knee osteoarthritis (OA) undergoing TKA was classified as present (including intact and degenerated) vs. absent, and as intact vs. not fully intact. Proportional meta-analyses were performed. 2840 articles were identified and screened. 135 full texts were analyzed and 18 studies met the inclusion criteria for subsequent qualitative and quantitative meta-analysis. Analysis of the status of the ACL when assessed intraoperatively during TKA showed that the ligament was present in 79.4% of patients (CI: 73.5-84.3%), from 14 studies with 2067 cases studied. The ACL was determined to be intact in 55.0% of patients (CI: 45.3-64.4%), from 14 studies with 1916 cases. Preoperative ACL assessment using MRI (2 studies) revealed it was present in 82.9% of 193 cases (CI: 76.9-87.6%), and intact in 56.8% of 176 cases (CI: 8.2-94.7%). This systematic literature review shows that the ACL is macroscopically intact in more than half of patients with knee OA undergoing TKA, based on intraoperative assessment of the ligament. The results suggest BCR TKA may be considered as an alternative to traditional TKA in a large number of TKA patients. More high-quality studies are needed to better understand the functional status of the ACL in TKA patients.Level of evidence III.

Anterior Cruciate Ligament Revision Reconstruction

Revision anterior cruciate ligament (ACL) reconstruction is used in patients with recurrent instability after primary ACL reconstruction. Identifying the etiology of graft failure is critical to the success of revision reconstruction. The most common etiologies include technical errors, trauma, failure to recognize concomitant injuries, young age, incomplete rehabilitation, and hardware failure. Patients should undergo a complete history and physical examination with a specific focus on previous injury mechanism and surgical procedures. A revision ACL reconstruction is a technically demanding procedure, and the surgeon should be prepared to address bone tunnel osteolysis, concurrent meniscal, ligamentous, or cartilage lesions, and limb malalignment. Surgical techniques described in this article include both single-stage and two-stage reconstruction procedures. Rates of return to sport after a revision reconstruction are lower than after primary reconstruction. Future research should be focused on improving both single-stage and two-stage revision techniques, as well as concomitant procedures to address limb malalignment and associated injuries.

Radiological Evaluation of Femoral Intercondylar Notch and Tibial Intercondylar Eminence Morphometries in Anterior Cruciate Ligament Pathologies Using Magnetic Resonance Imaging

PURPOSE

To determine the relationship between femoral-tibial morphometries and anterior cruciate ligament (ACL) pathologies using magnetic resonance imaging (MRI).

METHODS

We retrospectively evaluated 455 patients (211 females and 244 males) who underwent knee MRI with suspected ACL pathology. Imaging findings were classified as normal ACL (n = 119), degeneration of the ACL (n = 116), partial ACL tear (n = 103), and complete ACL tear (n = 117). In all groups, the femoral intercondylar notch width (INW), intercondylar distance (CD), notch width index (NWI), and intercondylar notch angle (INA), the angles between the tibial plateau and tibial spines (MPA and LPA), intercondylar eminence peak angle (IEA), and tibial slope angles (MSA and LSA) were measured.

RESULTS

Femoral INW and NWI were significantly lower in patients with ACL pathology (p < 0.05). They were also lower in patients with tear compared to degeneration. The INA was significantly smaller in patients with ACL pathology (p < 0.001) and the significance continued in both genders. The LSA was only increased in patients with complete tear (p < 0.01) and the difference seems existing in both genders. It was also found that the LPA and IEA demonstrated significant increases in patients with ACL pathology (p < 0.01 and < 0.05, respectively) and the significance in LPA continued in both genders. Significant differences between males and females were found for the INW and CD in all 4 groups (p < 0.001). In addition, the INA, LPA and LSA were independent predictors in determining the risk of ACL pathology.

CONCLUSION

The ACL pathologies are associated with femoral-tibial morphometries and these associations exist in both genders.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43465-021-00490-7.

Biomechanical analysis of three different types of fixators for anterior cruciate ligament reconstruction via finite element method: a patient-specific study

Complication rates of anterior cruciate ligament reconstruction (ACL-R) were reported to be around 15% although it is a common arthroscopic procedure with good outcomes. Breakage and migration of fixators are still possible even months after surgery. A fixator with optimum stability can minimise those two complications. Factors that affect the stability of a fixator are its configuration, material, and design. Thus, this paper aims to analyse the biomechanical effects of different types of fixators (cross-pin, interference screw, and cortical button) towards the stability of the knee joint after ACL-R. In this study, finite element modelling and analyses of a knee joint attached with double semitendinosus graft and fixators were carried out. Mimics and 3-Matic softwares were used in the development of the knee joint models. Meanwhile, the graft and fixators were designed by using SolidWorks software. Once the meshes of all models were finished in 3-Matic, simulation of the configurations was done using MSC Marc Mentat software. A 100-N anterior tibial load was applied onto the tibia to simulate the anterior drawer test. Based on the findings, cross-pin was found to have optimum stability in terms of stress and strain at the femoral fixation site for better treatment of ACL-R.

Can the body slope of interference screw affect initial stability of reconstructed anterior cruciate ligament?: An in-vitro investigation

Background

Superior biomechanical performance of tapered interference screws, compared with non-tapered screws, with reference to the anterior cruciate ligament (ACL) reconstruction process, has been reported in the literature. However, the effect of tapered interference screw’s body slope on the initial stability of ACL is poorly understood. Thus, the main goal of this study was to investigate the effect of the interference screw’s body slope on the initial stability of the reconstructed ACL.

Methods

Based on the best screw-bone tunnel diameter ratios in non-tapered screws, two different tapered interference screws were designed and fabricated. The diameters of both screws were equal to bone tunnel diameter in one-third of their length from screw tip, then they were gradually increased by 1mm, in the lower slope (LSTIS), and 2 mm, in the higher slope (HSTIS) screws. To simulate the ACL reconstruction, sixteen soft tissue grafts were fixed, using HSTIS and LSTIS, in synthetic bone blocks. Through applying sub-failure cyclic incremental tensile load, graft-bone-screw construct’s stiffness and graft laxity in each cycle, also through applying subsequent step of loading graft to the failure, maximum load to failure, and graft’s mode of failure were determined. Accordingly, the performance of the fabricated interference screws was compared with each other.

Results

HSTIS provides a greater graft-bone-screw construct stiffness, and a lower graft laxity, compared to LSTIS. Moreover, transverse rupture of graft fibers for LSTIS, and necking of graft in the HSTIS group were the major types of grafts’ failure.

Conclusions

HSTIS better replicates the intact ACL’s behavior, compared to LSTIS, by causing less damage in graft’s fibers; reducing graft laxity; and increasing fixation stability. Nonetheless, finding the optimal slope remains as an unknown and can be the subject of future studies.

Postoperative Rehabilitation of Anterior Cruciate Ligament Reconstruction: A Systematic Review

Recent studies have investigated the various components of postoperative rehabilitation protocols following anterior cruciate ligament reconstruction (ACLR). The objective of this article was to access and summarize the latest evidence for postoperative rehabilitation protocols following ACLR to evaluate common timeframes, number of phases, exercises, as well as the length of rehabilitation protocol. Common interventions include vibration training, open-chain and closed-chain exercises, electrical stimulation, postoperative bracing, and aquatic therapy. The eligibility criteria included English-language articles published from 2000 to 2019 pertaining to rehabilitation following ACLR, excluding addresses, commentaries, and editorials. Two blinded reviewers screened, graded, and extracted data from articles. Recommendations on various aspects of rehabilitation were summarized. A total of 3651 articles were retrieved from the database search, and 62 level 1 to 2 studies were available for extraction. On the basis of the evidence, vibration training can be safely incorporated into the postoperative rehabilitation protocol following ACLR. Accelerated rehabilitation may give patients short-term functional benefits. Open kinetic chain exercises may have additional strength and endurance benefits. Postoperative bracing does not confer additional benefits. Long-term use of neuromuscular electrical stimulation seems to be more beneficial than short-term use. Aquatic rehabilitation may be beneficial in the early phases of anterior cruciate ligament rehabilitation.

Mechanics of cadaveric anterior cruciate ligament reconstructions during simulated jump landing tasks: Lessons learned from a pilot investigation

BACKGROUND

Around half of anterior cruciate ligament (ACL) injuries are treated through reconstruction, but the literature lacks mechanical investigation of reconstructions in a dynamic athletic task and rupture environment. The current objective was to ascertain the feasibility of investigating ACL reconstructions in a rupture environment during simulated landing tasks in a validated mechanical impact simulator.

METHODS

Four cadaveric lower extremities were subjected to simulated landing in a mechanical impact simulator. External joint loads that mimicked magnitudes recorded from an in vivo population were applied to each joint in a stepwise manner. Simulations were repeated until ACL failure was achieved. Repeated measures design was used to test each specimen in the native ACL and hamstrings, quadriceps, and patellar tendon reconstructed states.

FINDINGS

ACL injuries were generated in 100% of specimens. Graft substance damage occurred in 58% of ACLRs, and in 75% of bone tendon bone grafts. Bone tendon bone and quadriceps grafts survived greater simulated loading than hamstrings grafts, but smaller simulated loading than the native ACL. Median peak strain prior to failure was 20.3% (11.6, 24.5) for the native ACL and 17.4% (9.5, 23.3) across all graft types.

INTERPRETATION

The simulator was a viable construct for mechanical examination of ACLR grafts in rupture environments. Post-surgery, ACL reconstruction complexes are weaker than the native ACL when subjected to equivalent loading. Bone tendon bone grafts most closely resembled the native ligament and provided the most consistently relevant rupture results. This model advocated reconstruction graft capacity to sustain forces generated from immediate gait and weightbearing during rehabilitation from an ACL injury.

Contribution of Lower Extremity Joints on Energy Absorption during Soft Landing

Soft landing after jumping is associated with the prevention of lower extremity injuries during sports activities in terms of the energy absorption mechanisms. In this study, the contribution of lower extremity joints during soft landing was investigated. Subjects comprised 20 healthy females. Kinetics and kinematics data were obtained during drop vertical jumps using a three-dimensional motion analysis system. Negative mechanical work values in the lower extremity joints were calculated during landing. A multiple regression analysis was performed to determine which lower extremity joints contributed more in achieving soft landing. The means of mechanical work of the hip, knee, and ankle in the sagittal plane were −0.30 ± 0.17, −0.62 ± 0.31, and −1.03 ± 0.22 J/kg, respectively. Results showed that negative mechanical work in the hip and knee is effective in achieving soft landing. These findings indicate that energy absorption in the hip and knee joints might be an important factor in achieving soft landing, whereas that in the ankle has a negative effect. Therefore, when improving soft landing techniques, we should consider energy absorption in the hip and knee via eccentric activation of the hip and knee extensors during landing.

Accuracy of magnetic resonance imaging in predicting anterior cruciate ligament tear location and tear degree

Purpose

The purpose of this study is to evaluate the reliability of magnetic resonance imaging (MRI) in predicting the location of ACL tears in preoperative planning for anterior cruciate ligament (ACL) repair.

Methods

Thirty-four patients who underwent ACL repair were retrospectively analyzed to compare intraoperative arthroscopic findings with preoperative MRIs.

Results

For identifying type I tears, the sensitivity of MRI was 9.0% and the accuracy of MRI was 8.8%. There was moderate interrater agreement between MRI findings for tear location and tear degree.

Conclusion

MRI alone may not necessarily be accurate in identifying which ACL tears are amenable to repair.

Study design

Retrospective case series; Level of Evidence: IV.

Anterior Cruciate Ligament Tear Following Operative Treatment of Pediatric Tibial Eminence Fractures in a Multicenter Cohort

BACKGROUND

Postoperative ipsilateral anterior cruciate ligament (ACL) tears after tibial eminence fracture fixation has been previously noted in the literature. This study aims to describe the prevalence of and risk factors for postoperative ACL tears in a cohort of patients operatively treated for tibial eminence fracture.

METHODS

A retrospective review of children undergoing treatment of a tibial eminence fracture at 10 tertiary care children's hospitals was performed. The primary outcome of interest was subsequent ACL rupture. Incidence of ACL tear was recorded for the entire cohort. Patients who sustained a postoperative ACL tear were compared with those without ACL tear and analyzed for demographics and risk factors. A subgroup analysis was performed on patients with a minimum of 2-year follow-up data or those who had met the primary outcome (ACL tear) before 2 years.

RESULTS

A total of 385 pediatric patients were reviewed. 2.6% of the cohort experienced a subsequent ACL tear. The median follow-up time was 6.5 months (SD=6.4 mo). Subsequent ACL tears occurred at a median of 10.2 months (SD=19.5 mo) postoperatively. There was a statistically significant association with higher grade tibial spine fractures (Myers and McKeever type III and IV) and subsequent ACL tear (P=0.01). Patients with a subsequent ACL tear were older on average (13.5 vs. 12.2 y old), however, this difference was not statistically significant (P=0.08). Subgroup analysis of 46 patients who had a 2-year follow-up or sustained an ACL tear before 2 years showed a 21.7% incidence of a subsequent ACL tear. There was a statistically significant association with higher grade tibial spine fractures (Myers and McKeever type III and IV) and subsequent ACL rupture (P=0.006) in this subgroup. Postoperative ACL tears occurred in patients who were older at the time that they sustained their original tibial eminence fracture (13.4 vs. 11.3 y old, P=0.035).

CONCLUSIONS

Ipsilateral ACL tears following operatively treated pediatric tibial eminence fractures in a large multicenter cohort occurred at a rate of 2.6%. However, in those with at least 2 years of follow-up, the incidence was 21.7%. Subsequent ACL tear was more likely in those with completely displaced (type III or IV) tibial eminence fractures and older patients.

LEVEL OF EVIDENCE

Level III-retrospective cohort study.

Estimation of forces on anterior cruciate ligament in dynamic activities

In this work, a nonlinear strain rate dependent plugin developed for the OpenSim® platform was used to estimate the instantaneous strain rate (ISR) and the forces on the ACL's anteromedial (aACL) and posterolateral (pACL) bundles during walking and sudden change of direction of running termed as 'plant-and-cut' (PC). The authors obtained the kinematics data for walking via optical motion capture. PC movements, along with running kinematics, were obtained from the literature. A nonlinear plugin developed for ligaments was interfaced with OpenSim® platform to simulate walking and PC motions with a flexed knee and an extended knee. PC phase is sandwiched between an approach phase and take-off phase and was studied at various event velocities (1.8, 3, and 4.2 m s^-1), and angles of PC (23°, 34°, and 45°) as encountered in adult ball games. In both cases of PC-with-extended knee and PC-with-flexed-knee, the maximum forces on both the ACL bundles were observed after the take-off phase. A maximum force of ~ 35 N kg^-1 of body weight (BW) was observed on aACL after the take-off phase for an event velocity of 4.2 m s^-1. In the posterolateral bundle (pACL), the maximum forces (~ 40 N kg^-1 of BW) were observed towards the end of the mid-swing phase (after the take-off phase) for the various combinations of the parameters studied. The forces observed in the simulation of PC-with-flexed-knee and PC-with-extended-knee has resulted in magnitude higher than sustainable by the adults. This study is novel in attempting to incorporate differing rates-of-strain that have been shown to alter soft tissue properties into the OpenSim® musculoskeletal model. The proposed model can be used by researchers to predict the forces during various kinematic activities for other soft tissues.

Age-related changes in ACL morphology during skeletal growth and maturation are different between females and males

Despite a well-established role of anterior cruciate ligament (ACL) anatomy on its biomechanics, little is known on how ACL anatomy develops and changes during skeletal growth. We hypothesized that ACL size and orientation will change by age during skeletal growth and maturation with different trends in males vs females. Magnetic resonance images of 269 unique knees (3-18 years old; 51% female) were used to measure ACL length, cross-sectional area, length-to-cross-sectional area ratio, and elevation angles. In both males and females, ACLs became longer, thicker, and more vertical in sagittal and coronal planes by increasing age (R2  > 0.2; P < .001 for all associations). ACL cross-sectional area-to-length ratio increased by age only in males (R2  = 0.06; P = .003). Despite similar ACL sizes between males and females at early age, adolescent males had significantly longer and thicker ACLs compared to the age-matched females (P < .05). There were no sex differences in ACL elevation angles (P > .2) except for larger coronal elevation in 7 to 10 years old females compared to age-matched males (P = .012). Observed changes in ACL cross-sectional area-to-length ratio indicate that age- and sex-dependent changes in ACL size are not homogenous. The trends seen in normalized ACL size measurements suggest that unlike ACL cross-sectional area, ACL length is primarily controlled by body size. Smaller ACLs and lower cross-sectional growth rates observed in females may be contributing factors to the higher risk of ACL injuries in females. Further investigations are required to identify the intrinsic and extrinsic factors responsible for these discrepancies.

Porcine bone-patellar tendon-bone xenograft in a caprine model of anterior cruciate ligament repair

The use of human tissue-derived autografts and allografts continues to be the gold standard in anterior cruciate ligament (ACL) repair. However, autografts and allografts have their own set of associated risks. Many alternative options, including synthetic replacements, have failed to demonstrate long-term success. In this study, sterile acellular porcine bone-tendon-bone (BTB) xenografts were created using a proprietary process and tested against BTB autografts in goats for 13 and 52 weeks. At 13 weeks, all xenograft-implanted animals (n = 9) had subjective hind leg motor function (HLMF) that was categorized as either normal (score = 0) or a slight limp (score = 1) compared with two of nine autograft-implanted animals having a moderate limp (score = 2). At 39 weeks, there was HLMF improvement with each autograft-implanted and xenograft-implanted animal having normal HLMF or only a slight limp. At 13 weeks, six of nine animals in each group achieved normal anterior drawer scores, which increased to nine of nine animals in each group by 39 weeks. Both autografts and xenografts exhibited minimal inflammation with excellent integration of the fibrous tendon portion of the graft to host bone, as evidenced histologically by Sharpey's fiber formation. At 52 weeks, maximum mechanical load at failure for xenografts was 1092.0 ± 586.4 N compared with 1037.0 ± 422.6 N for autografts. These results demonstrate that a sterile acellular porcine BTB xenograft can perform equivalently to BTB autograft in a caprine model of ACL repair.

Analysis of Posterior Tibial Slope as Risk Factor to Anterior Cruciate Ligament Tear

Objective  The objective of the present study was to evaluate the relationship between patients with anterior cruciate ligament (ACL) injury by indirect trauma and increased posterior tibial inclination.

Methods  Retrospective study, performed by analysis of medical records and digital radiographs of patients, present in a database of a tertiary orthopedic hospital. The sample consisted of two groups, the first group consisting of patients diagnosed with ACL injury by indirect trauma, and a control group matched by age.

Results  Each group consisted of 275 patients, whose measurements of posterior tibial inclination were measured by three specialists. It was observed that the group of patients with ACL lesion presented a significantly higher tibial slope (in degrees) than the control group in the total sample and in the subsamples stratified by gender. The best cutoff point for the first group was identified as a posterior tibial inclination ≥ 8°, achieving a sensitivity of 63.3% and a specificity of 62.5%. The first group also had a tibial slope ratio ≥ 8° (63.3%), significantly higher than the control group (37.5%), with an odds ratio of 2.8.

Conclusion  It was concluded that the increase of the posterior tibial inclination is associated with an increased risk for injury of the ACL by indirect trauma, mainly for values ≥ 8°.

The Effects of Mechanical Scale on Neural Control and the Regulation of Joint Stability

Recent work has demonstrated how the size of an animal can affect neural control strategies, showing that passive viscoelastic limb properties have a significant role in determining limb movements in small animals but are less important in large animals. We extend that work to consider effects of mechanical scaling on the maintenance of joint integrity; i.e., the prevention of aberrant contact forces within joints that might lead to joint dislocation or cartilage degradation. We first performed a literature review to evaluate how properties of ligaments responsible for joint integrity scale with animal size. Although we found that the cross-sectional area of the anterior cruciate ligament generally scaled with animal size, as expected, the effects of scale on the ligament’s mechanical properties were less clear, suggesting potential adaptations in passive contributions to the maintenance of joint integrity across species. We then analyzed how the neural control of joint stability is altered by body scale. We show how neural control strategies change across mechanical scales, how this scaling is affected by passive muscle properties and the cost function used to specify muscle activations, and the consequences of scaling on internal joint contact forces. This work provides insights into how scale affects the regulation of joint integrity by both passive and active processes and provides directions for studies examining how this regulation might be accomplished by neural systems.

Bi-cruciate retaining total knee arthroplasty: a systematic literature review of clinical outcomes

Total knee arthroplasty (TKA) has been shown to have good long-term outcomes and survivorship. Nonetheless, dissatisfied patients are frequently reported in the literature. Bi-cruciate retaining total knee prostheses (BCR TKA) were designed to address the demand for more kinematically functional implants that better reconstruct natural knee kinematics. In BCR TKA, the anterior cruciate ligament (ACL) is preserved. Improved patient-reported outcomes and satisfaction levels are expected. This review aimed to summarize indications for and clinical outcomes of BCR TKA. A systematic literature review on BCR TKA was performed. 24 articles were included for data analysis. Indications covered osteoarthritis, inflammatory arthritis and others. The degree of deformity was often but not always limited to minor axial deformity and contractures: maximum acceptable varus/valgus deformity reached 10°-30° and flexion contractures of 15°-65°. ACL intactness was macroscopically examined intraoperatively in nine studies and clinically tested in ten studies (e.g., Lachmann Test, drawer-test). Objective and patient-reported outcome scores were reported for follow-up periods of up to 22 years. Survival rates varied significantly. For first generation implants, 22-year survival reached 82% while a second generation design was associated with 13.5% revision rate at 18 months. Reasons for varying outcomes were not clear and may be attributed to the implant itself, surgical techniques and patient specific variables including changed expectations and functional demand. The literature has not shown clear indications and guidelines for the use of BCR implants. The promising results of first generation BCR TKA designs may be optimized through improved implant designs in the future. Further studies are advocated to provide the necessary evidence of second generation BCR TKA designs.

Fibroblasts From Common Anterior Cruciate Ligament Tendon Grafts Exhibit Different Biologic Responses to Mechanical Strain

BACKGROUND

Different tendons are chosen for anterior cruciate ligament (ACL) reconstruction based on perceived advantages and disadvantages, yet there is a relative paucity of information regarding biologic responsiveness of commonly used tendon grafts to mechanical strain.

PURPOSE

To evaluate the in vitro responses of graft fibroblasts derived from tendons used for ACL reconstruction to clinically relevant strain levels.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve quadriceps tendons (QTs), 12 patellar tendons (PTs), and 9 hamstring tendons (HTs) were harvested from skeletally mature dogs (n = 16). Tendon fibroblasts were isolated and seeded onto BioFlex plates (1 × 10⁵ cells/well). Cells were subjected to 3 strain conditions (stress deprivation, 0%; physiologic, 4%; high, 10%) for 5 days. Media were collected for proinflammatory and metabolic assays. RNA was extracted for gene expression analysis using real-time reverse transcription polymerase chain reaction.

RESULTS

Stress deprivation elicited significantly higher metabolic activity from HT and PT cells than from QT cells (P < .001 and P = .001, respectively). There were no differences in metabolic activity among all 3 graft fibroblasts at physiologic and high strain. COL-1 expression was significantly higher in PT versus HT during physiologic strain (P = .007). No significant differences with COL-3 expression were seen. TIMP-1 (P = .01) expression was higher in PT versus HT under physiologic strain. Scleraxis expression was higher in PT versus HT (P = .007) under physiologic strain. A strain-dependent increase in PGE2 levels occurred for all grafts. At physiologic strain conditions, HT produced significantly higher levels of PGE2 versus QT (P < .001) and PT (P = .005).

CONCLUSION

Fibroblasts from common ACL graft tissues exhibited different metabolic responses to mechanical strain. On the basis of these data, we conclude that early production of extracellular matrix and proinflammatory responses from ACL grafts are dependent on mechanical loading and graft source.

CLINICAL RELEVANCE

Graft-specific differences in ACL reconstruction outcomes are known to exist. Our results suggest that there are differences in the biologic responsiveness of cells from the tendon grafts used in ACL reconstruction, which are dependent on strain levels and graft source. The biologic properties of the tissue used for ACL reconstruction should be considered when selecting graft source.

A novel arthroscopically assisted reduction technique for three patterns of posterolateral tibial plateau fractures

Background

Posterolateral tibial plateau fractures (PTPF) remain a challenge for orthopedics surgeons because the special anatomical structures of the posterolateral corner of knee joint including the fibular head, the lateral collateral ligament, and the peroneal nerve, which impedes the exposure of the fracture fragments and need irregular implants to get a stable fixation. The purpose of present study was to introduce a new articular fracture fragments restoration technique for three patterns of PTPF and investigate the relationship between associated soft injuries and fracture patterns.

Methods

From May 2016 to April 2018, 31 patients with PTPF who had undertaken arthroscopically assisted reduction and fixation (AARF) were enrolled in present study. Demographic data, pre-operation, and post-operation X plan films, three-dimensional computed tomography (CT) scans and magnetic resonance imaging (MRI) were reviewed. Present samples were divided into three patterns with lateral inclination (LI), posterior inclination (PI), and parallel compression (PC) according to the orientation of the articular fragment inclination. Rasmussen anatomical score was used to assess the radiological results. Rasmussen functional score, Hospital for Special Surgery knee-rating Score (HSS), and range of motion (ROM) of the knee joint at the final follow-up were measured to evaluate the clinical outcomes.

Results

In this series, the post-operation tibial plateau angle (TPA) was 9.7° ± 3.5°(range 4.0°–15.8°) and the Rasmussen anatomical score was 17.7 ± 0.7(range 16–18); clinical outcomes showed that the HSS score was 92.7 ± 21.8 (range 90–96) and the Rasmussen functional score was 27.9 ± 1.0 (range 26–30). Of all the patients, the anterior cruciate ligament (ACL) injuries including the ACL tibial attachment ruptures occurred in 16 patients (51.6%), meniscus lesions happened in 19 patients (61.3%), medial collateral ligament (MCL) injuries were founded in 13 patients (41.9%). The number of ACL injuries including the ACL tibial attachment ruptures in the PI fracture pattern (12 cases) is significantly higher than LI (2 cases) and PC (2 cases) fracture pattern (p < 0.05).

Conclusion

Profound understanding the different patterns of PTPF and using our reduction technique will facilitate to restore the main articular fracture fragments. The PI fracture patterns have a significant high incidence of the ACL ruptures.

Level of evidence

Therapeutic study, Level IV.

Significant Loss of ACL Graft Force With Tibial-Sided Soft Tissue Interference Screw Fixation Over 24 Hours: A Biomechanical Study

Background

Tibial-sided graft fixation is thought to be critical for the success of anterior cruciate ligament (ACL) reconstruction. Nevertheless, little is known about the graft force after fixation during the first 24 hours after surgery or the influence of screw diameter and length during this time.

Purpose

To investigate the force, over the course of 24 hours, in soft tissue grafts secured with a tibial interference screw and to evaluate the effect of different screw diameters (7, 8, and 9 mm) and lengths (25 and 30 mm) on the force in these grafts.

Study Design

Controlled laboratory study.

Methods

Quadruple-strand flexor tendon grafts were fixed with bioabsorbable interference screws in 60 porcine tibiae. Grafts were pretensioned at 80 N over 10 minutes, and screws were inserted outside-in while a preload force of 80 N was applied. Different screw lengths (25 and 30 mm) and diameters (7, 8, and 9 mm), resulting in 6 groups with 10 specimens each, were tested. After release of the preload, graft force was recorded over 24 hours.

Results

A significant decrease in graft force progressed in all groups over the 24-hour period. In total, a median loss of 75 N (IQR, 68-79 N) compared with the initial loading force was observed. Compared with the loading force of 80 N, this corresponded to a median loss of 91%. No significant differences in the remaining graft force could be found among the 6 different screw length and diameter groups after 10 minutes, 100 minutes, or 24 hours.

Conclusion

Graft force in soft tissue grafts secured with a tibial interference screw decreased substantially over the first 24 hours after fixation. Neither the screw diameter nor the screw length affected the decrease in graft force. This raises substantial questions regarding the remaining fixation strength in vivo.

Clinical Relevance

It should not be expected that ACL reconstruction can mechanically restabilize an injured knee as would an intact ACL. Reconstructed knees should be protected from mechanical overload in the early postoperative period.