Tensile properties of the human femur-anterior cruciate ligament-tibia complex. The effects of specimen age and orientation

New Insights Optimize Landing Strategies to Reduce Lower Limb Injury Risk

Single-leg landing (SL) is often associated with a high injury risk, especially anterior cruciate ligament (ACL) injuries and lateral ankle sprain. This work investigates the relationship between ankle motion patterns (ankle initial contact angle [AICA] and ankle range of motion [AROM]) and the lower limb injury risk during SL, and proposes an optimized landing strategy that can reduce the injury risk. To more realistically revert and simulate the ACL injury mechanics, we developed a knee musculoskeletal model that reverts the ACL ligament to a nonlinear short-term viscoelastic mechanical mechanism (strain rate-dependent) generated by the dense connective tissue as a function of strain. Sixty healthy male subjects were recruited to collect biomechanics data during SL. The correlation analysis was conducted to explore the relationship between AICA, AROM, and peak vertical ground reaction force (PVGRF), joint total energy dissipation (TED), peak ankle knee hip sagittal moment, peak ankle inversion angle (PAIA), and peak ACL force (PAF). AICA exhibits a negative correlation with PVGRF (r = -0.591) and PAF (r = -0.554), and a positive correlation with TED (r = 0.490) and PAIA (r = 0.502). AROM exhibits a positive correlation with TED (r = 0.687) and PAIA (r = 0.600). The results suggested that the appropriate increases in AICA (30° to 40°) and AROM (50° to 70°) may reduce the lower limb injury risk. This study has the potential to offer novel perspectives on the optimized application of landing strategies, thus giving the crucial theoretical basis for decreasing injury risk.

Care of The Older Fighter: Position Statement of the Association of Ringside Physicians

Older Fighters are defined as combat sports athletes older than 35 years, based on heightened medical risks and historical classification. Age-related changes to the neurological, cardiopulmonary, endocrinological, thermoregulatory, osmoregulatory, and musculoskeletal systems increase these athletes' risks for injury and may prolong their recovery. These age-related risks warrant special considerations for competition, licensure, prefight medical clearance, in-fight supervision, post-fight examination, and counseling regarding training practices and retirement from combat sports. Neurological considerations include increased risk of intracranial lesions, intracranial hemorrhage, and sequelae from traumatic brain injury (TBI), warranting more comprehensive neurological evaluation and neuroimaging. Increased risk of myocardial ischemia and infarction warrant careful assessment of cardiac risk factors and scrutiny of cardiovascular fitness. Older fighters may take longer time to recover from musculoskeletal injury; post-injury clearance should be individualized.

Functional knee brace use for 21 h leads to a longer duration to achieve peak vertical ground reaction forces and the removal of the brace after 17.5 h results in faster loading of the knee joint

PURPOSE

To investigate the landing strategies used after discontinuing and continuing the use of a functional knee brace (FKB) while performing a drop jump.

METHODS

Following published methodology and power analysis, 23 uninjured male athletes, mean age of 19.4 ± 3.0 years, performed seven tests, during three test conditions (nonbraced, braced and removed brace or continued brace use), over 6 days of 12 testing sessions (S) for a total of 38.5 h. Each subject was provided with a custom-fitted FKB. This study focuses on the single leg drop jump kinetics during S12 when subjects were randomly selected to remove the FKB after 17.5 h or continued use of FKB. The time to peak vertical ground reaction forces (PVGRF) and PVGRF were recorded on landing in eight trials.

RESULTS

After brace removal, a significantly shorter mean time to PVGRF was recorded (9.4 ± 22.9 msec (3.9%), p = 0.005, 95% confidence interval (95% CI): -168.1, 36.1), while continued brace use required a nonsignificant (n.s.) longer mean duration to achieve PVGRF (19.4 ± 53.6 msec (8.9%), n.s., 95% CI: -49.7, 73.4). No significant mean PVGRF difference was found in brace removal (25.3 ± 65.8 N) and continued brace use (25.1 ± 23.0 N).

CONCLUSION

Removal of FKB after 17.5 h of use led to a significantly shorter time to achieve PVGRF, while continued brace use for 21 h required a longer duration to achieve PVGRF, suggesting faster and slower knee joint loading, respectively. Understanding the concerns associated with the use of FKB and the kinetics of the knee joint will assist clinicians in counselling athletes about the risks and benefits of using an FKB.

LEVEL OF EVIDENCE

Level II.

Comparison of In Vivo Stiffness of Tendons Commonly Used for Anterior Cruciate Ligament Reconstruction - A Shear Wave Elastography Study

RATIONALE AND OBJECTIVES

There are currently no studies investigating the in vivo stiffness of the most commonly used autografts for anterior cruciate ligament reconstruction (ACLR) using Shear wave elastography (SWE). We hypothesize that there are differences regarding the elastic properties between the three tendons commonly used for ACLR and that they are influenced by patient-related factors.

MATERIALS AND METHODS

80 healthy subjects (25 females, 55 males, age: 25.33 ± 4.76 years, BMI: 23.76 ± 3.14 kg/m2, 40 semiprofessional athletes, athlete group [AG], age: 25.51 [19-29]; 40 healthy controls, control group [CG], age: 25.50 [20-29]) were recruited as participants. In addition to patient reported outcome scores, every participant underwent a standardized multimodal ultrasound protocol consisting of B-mode-ultrasound (B-US), Color Doppler-ultrasound (CD-US) and a SWE examination of the bilateral quadriceps tendon (QT), patellar tendon (PT) and semitendinosus tendon (ST).

RESULTS

The highest shear wave velocity (SWV) were observed in ST (4.88 (4.35-5.52) m/s, ST vs QT, p = 0.005; ST vs PT, p < 0.001) followed by QT (4.61 (4.13-5.26) m/s, QT vs PT, p < 0.001) and PT (3.73 (3.30-4.68) m/s). Median QT, PT and ST stiffness was significantly higher in AG compared to CG. Male subjects tend to have stiffer QT and PT than female subjects. Positive correlation with SWV was obtained for age and activity level.

CONCLUSION

There are significant differences regarding in vivo tendon stiffness between the most frequently used autograft tendon options for ACLR. The quantitative information obtained by SWE could be of particular interest for graft choice for ACLR.

Topographically and Chemically Enhanced Textile Polycaprolactone Scaffolds for Tendon and Ligament Tissue Engineering

The use of tissue engineering to address the shortcomings of current procedures for tendons and ligaments is promising, but it requires a suitable scaffold that meets various mechanical, degradation-related, scalability-related, and biological requirements. Macroporous textile scaffolds made from appropriate fiber material have the potential to fulfill the first three requirements. This study aimed to investigate the biocompatibility, sterilizability, and functionalizability of a multilayer braided scaffold. These macroporous scaffolds with dimensions similar to those of the human anterior cruciate ligament consist of fibers with appropriate tensile strength and degradation behavior melt-spun from Polycaprolactone (PCL). Two different cross-sectional geometries resulting in significantly different specific surface areas and morphologies were used at the fiber level, and a Chitosan-graft-PCL (CS-g-PCL) surface modification was applied to the melt-spun substrates for the first time. All scaffolds elicited a positive cell response, and the CS-g-PCL modification provided a platform for incorporating functionalization agents such as drug delivery systems for growth factors, which were successfully released in therapeutically effective quantities. The fiber geometry was found to be a variable that could be manipulated to control the amount released. Therefore, scaled, surface-modified textile scaffolds are a versatile technology that can successfully address the complex requirements of tissue engineering for ligaments and tendons, as well as other structures.

Two-to-three times increase in natural hip and lumbar non-sagittal plane kinematics can lead to anterior cruciate ligament injury and cartilage failure scenarios during single-leg landings

BACKGROUND

Analyzing sports injuries is essential to mitigate risk for injury, but inherently challenging using in vivo approaches. Computational modeling is a powerful engineering tool used to access biomechanical information on tissue failure that cannot be obtained otherwise using traditional motion capture techniques.

METHODS

We extrapolated high-risk kinematics associated with ACL strain and cartilage load and stress from a previous motion analysis of 14 uninjured participants. Computational simulations were used to induce ACL failure strain and cartilage failure load, stress, and contact pressure in two age- and BMI-matched participants, one of each biological sex, during single-leg cross drop and single-leg drop tasks. The high-risk kinematics were exaggerated in 20% intervals, within their physiological range of motion, to determine if injury occurred in the models. Where injury occurred, we reported the kinematic profiles that led to tissue failure.

FINDINGS

Our findings revealed ACL strains up to 9.99%, consistent with reported failure values in existing literature. Cartilage failure was observed in all eight analyzed conditions when increasing each high-risk kinematic parameter by 2.61 ± 0.67 times the participants' natural landing values. The kinematics associated with tissue failure included peak hip internal rotation of 22.48 ± 19.04°, peak hip abduction of 22.51 ± 9.09°, and peak lumbar rotation away from the stance limb of 11.56 ± 9.78°.

INTERPRETATION

Our results support the ability of previously reported high-risk kinematics in the literature to induce injury and add to the literature by reporting extreme motion limits leading to injurious cases. Therefore, training programs able to modify these motions during single-leg landings may reduce the risk of ACL injury and cartilage trauma.

Whip-Lock Stitch Is Biomechanically Superior to Whipstitch for Semitendinosus Tendons

Purpose

To assess the biomechanical performance of different stitching methods using a suturing device by comparing the elongation, stiffness, failure load, and time to stitch completion in cadaveric semitendinosus tendons (STs) and quadriceps tendons (QTs).

Methods

A total of 24 STs and 16 QTs were harvested from cadaveric knee specimens (N = 40). Samples were randomly divided into 2 groups: whipstitch (WS) and whip-lock (WL) stitch. Both tendon ends were clamped to a graft preparation stand, and a 2-part needle was used to place 5 stitches, each 0.5 cm apart. Stitching time was recorded. Samples were preconditioned and then underwent cyclic loading from 50 to 200 N at 1 Hz for 500 cycles, followed by load-to-failure testing at 20 mm/min. Stiffness (in newtons per millimeter), ultimate failure load (in newtons), peak-to-peak displacement (in millimeters), elongation (in millimeters), and failure displacement (in millimeters) were recorded.

Results

Completion of the WS was significantly faster than the WL stitch in the ST (P < .001) and QT (P = .004). For the ST, the WL stitch exhibited higher ultimate failure loads and construct stiffness than the WS. Regarding the QT, the WL stitch showed higher stiffness and displacement than the WS; however, the ultimate failure load was higher for the WS in the QT. The ultimate failure load in the QT was higher than that in the ST for both stitches. In the ST, only 25% of WSs and 100% of WL stitches failed due to suture breakage. In the QT, suture breakage led to the failure of 100% of both the WL stitches and WSs.

Conclusions

In the ST, the WL stitch resulted in improved biomechanical performance through higher ultimate load and fewer failures from tissue damage compared with the WS. In the QT, both the WS and the WL stitch showed similar biomechanical performance with ultimate failure loads above established clinical failure thresholds.

Clinical Relevance

Various types of ligament and tendon injuries require suturing to enable repair or reconstruction. The success of ligament or tendon surgery often relies on soft-tissue quality. It is important to investigate the biomechanical properties of stitching techniques that help preserve soft-tissue quality as a step to determining their clinical suitability.

Tape-Reinforced Graft Suturing and Retensioning of Adjustable-Loop Cortical Buttons Improve Quadriceps Tendon Autograft Biomechanics in Anterior Cruciate Ligament Reconstruction: A Cadaveric Study

PURPOSE

To investigate the biomechanical effects of tape-reinforced graft suturing and graft retensioning for all-soft tissue quadriceps tendon (ASTQT) anterior cruciate ligament reconstruction (ACLR) in a full-construct human cadaveric model.

METHODS

Harvested cadaveric ASTQT grafts were assigned to either (1) double-suspensory adjustable-loop cortical button device (ALD) fixation in which both graft ends were fixed with a suspensory fixation device with (n = 5) or without (n = 5) tape-reinforced suturing or (2) single-suspensory distal tendon fixation in which only the patellar end was fixed with an ALD (n = 5) or fixed-loop cortical button device (FLD) (n = 5). All specimens were prepared using a No. 2 whipstitch technique, and tape-reinforced specimens had an integrated braided tape implant. Graft preparation time was recorded for double-suspensory constructs. Samples were tested on an electromechanical testing machine using a previously published protocol simulating rehabilitative kinematics and loading.

RESULTS

Tape-reinforced graft suturing resulted in greater graft load retention after cycling (11.9% difference, P = .021), less total elongation (mean [95% confidence interval (CI)], 5.57 mm [3.50-7.65 mm] vs 32.14 mm [25.38-38.90 mm]; P < .001), greater ultimate failure stiffness (mean [95% CI], 171.9 N/mm [158.8-185.0 N/mm] vs 119.4 N/mm [108.7-130.0 N/mm]; P < .001), and less graft preparation time (36.4% difference, P < .001) when compared with unreinforced specimens. Retensioned ALD constructs had less cyclic elongation compared with FLD constructs (mean total elongation [95% CI], 7.04 mm [5.47-8.61 mm] vs 12.96 mm [8.67-17.26 mm]; P = .004).

CONCLUSIONS

Tape-reinforced graft suturing improves time-zero ASTQT ACLR construct biomechanics in a cadaveric model with 83% less total elongation, 44% greater stiffness, and reduced preparation time compared with a whipstitched graft without tape reinforcement. ALD fixation improves construct mechanics when compared with FLD fixation as evidenced by 46% less total elongation.

CLINICAL RELEVANCE

Tape-reinforced implants and graft retensioning using ALDs improve time-zero ACLR graft construct biomechanics in a time-zero biomechanical model. Clinical studies will be necessary to determine whether these implants improve clinical outcomes including knee laxity and the incidence of graft rupture.

Shear wave elastography demonstrates different material properties between the medial collateral ligament and anterolateral ligament

BACKGROUND

Anterolateral ligament and medial collateral ligament injuries could happen concomitantly with anterior cruciate ligament ruptures. The anterolateral ligament is injured more often than the medial collateral ligament during concomitant anterior cruciate ligament ruptures although it offers less restraint to knee movement. Comparing the material properties of the medial collateral ligament and anterolateral ligament helps improve our understanding of their structure-function relationship and injury risk before the onset of injury.

METHODS

Eight cadaveric lower extremity specimens were prepared and mechanically tested to failure in a laboratory setting using a hydraulic platform. Measurements of surface strains of superficial surface of each medial collateral ligament and anterolateral ligament specimen were found using three-dimensional digital image correlation. Ligament stiffness was found using ultrasound shear-wave elastography. t-tests were used to assess for significant differences in strain, stress, Young's modulus, and stiffness in the two ligaments.

FINDINGS

The medial collateral ligament exhibited greater ultimate failure strain along its longitudinal axis (p = 0.03) and Young's modulus (p < 0.0018) than the anterolateral ligament. Conversely, the anterolateral ligament exhibited greater ultimate failure stress than the medial collateral ligament (p < 0.0001). Medial collateral ligament failure occurred mostly in the proximal aspect of the ligament, while most anterolateral ligament failure occurred in the distal or midsubstance aspect (P = 0.04).

INTERPRETATION

Despite both being ligamentous structures, the medial collateral ligament and anterolateral ligament exhibited separate material properties during ultimate failure testing. The weaker material properties of the anterolateral ligament likely contribute to higher rates of concomitant injury with anterior cruciate ligament ruptures.

Optimising the Early-Stage Rehabilitation Process Post-ACL Reconstruction

Outcomes following anterior cruciate ligament reconstruction (ACLR) need improving, with poor return-to-sport rates and a high risk of secondary re-injury. There is a need to improve rehabilitation strategies post-ACLR, if we can support enhanced patient outcomes. This paper discusses how to optimise the early-stage rehabilitation process post-ACLR. Early-stage rehabilitation is the vital foundation on which successful rehabilitation post-ACLR can occur. Without high-quality early-stage (and pre-operative) rehabilitation, patients often do not overcome major aspects of dysfunction, which limits knee function and the ability to transition through subsequent stages of rehabilitation optimally. We highlight six main dimensions during the early stage: (1) pain and swelling; (2) knee joint range of motion; (3) arthrogenic muscle inhibition and muscle strength; (4) movement quality/neuromuscular control during activities of daily living (5) psycho-social-cultural and environmental factors and (6) physical fitness preservation. The six do not share equal importance and the extent of time commitment devoted to each will depend on the individual patient. The paper provides recommendations on how to implement these into practice, discussing training planning and programming, and suggests specific screening to monitor work and when the athlete can progress to the next stage (e.g. mid-stage rehabilitation entry criteria).

Tailoring the pore design of embroidered structures by melt electrowriting to enhance the cell alignment in scaffold-based tendon reconstruction

Tissue engineering of ligaments and tendons aims to reproduce the complex and hierarchical tissue structure while meeting the biomechanical and biological requirements. For the first time, the additive manufacturing methods of embroidery technology and melt electrowriting (MEW) were combined to mimic these properties closely. The mechanical benefits of embroidered structures were paired with a superficial micro-scale structure to provide a guide pattern for directional cell growth. An evaluation of several previously reported MEW fiber architectures was performed. The designs with the highest cell orientation of primary dermal fibroblasts were then applied to embroidery structures and subsequently evaluated using human adipose-derived stem cells (AT-MSC). The addition of MEW fibers resulted in the formation of a mechanically robust layer on the embroidered scaffolds, leading to composite structures with mechanical properties comparable to those of the anterior cruciate ligament. Furthermore, the combination of embroidered and MEW structures supports a higher cell orientation of AT-MSC compared to embroidered structures alone. Collagen coating further promoted cell attachment. Thus, these investigations provide a sound basis for the fabrication of heterogeneous and hierarchical synthetic tendon and ligament substitutes.

Subregional analysis of joint stiffness facilitates insight into ligamentous laxity after ACL injury

Purpose: Increased incidence of anterior cruciate ligament injuries has amplified the need for quantitative research in clinical and academic settings. We used a novel digital arthrometer to measure knee laxity in healthy people and patients with anterior cruciate ligament injuries. Changes in stiffness were also assessed to develop new indicators for detecting anterior cruciate ligament injury. The purpose of this study was to use arthrometer to measure the quantitative indicator of knee laxity, bringing clinicians a new perspective on how to identify injury to the ACL. Methods: In this cross-sectional study, anterior tibial displacement under continuous loading was measured using a novel digital arthrometer in 30 patients with unilateral anterior cruciate ligament injury and 30 healthy controls. Load-displacement curves were plotted, using real-time load and displacement changes. Stiffness was defined by the slope of the applied load to tibial displacement. Anterior tibial displacement and instantaneous stiffness values under different loads were compared. The restricting contribution of the anterior cruciate ligament transformed the displacement-stiffness curve from a sharp decrease to a stable increase, resulting in a minimum stiffness value. Using the minimum stiffness as the turning point, the load-displacement curve was divided into regions 1 and 2. The two regions' stiffness changes were compared. Based on the findings, receiver operating characteristic curves were plotted and the area under the curve was calculated to estimate the diagnostic accuracy. Results: Anterior tibial displacement was significantly greater in the anterior cruciate ligament injury group than in the controls under each 10-N increase load (p < 0.05). In the anterior cruciate ligament injury group, instantaneous stiffness was significantly lower on the injured side than on the healthy side (p < 0.05). In the two regions of the load-displacement curve, stiffness was significantly lower in the anterior cruciate ligament injury group than in the control group (all, p < 0.05). Receiver operating characteristic curves were plotted, using changes in stiffness under the two regions in both groups. Stiffness in region 2 had the largest area under the curve (0.94; 95% CI, 0.88-0.99). Using the cut-off value of 9.62 N/mm to detect ACL injury, the sensitivity and specificity were 93% and 82%, respectively. Conclusion: Our investigation of ligament stiffness provides novel insights into the properties of knee laxity. Stiffness in the later stages of increased loading <9.62 N/mm could be a valid indicator for identifying knee laxity.

Reproducibility in modeling and simulation of the knee: Academic, industry, and regulatory perspectives

Stakeholders in the modeling and simulation (M&S) community organized a workshop at the 2019 Annual Meeting of the Orthopaedic Research Society (ORS) entitled "Reproducibility in Modeling and Simulation of the Knee: Academic, Industry, and Regulatory Perspectives." The goal was to discuss efforts among these stakeholders to address irreproducibility in M&S focusing on the knee joint. An academic representative from a leading orthopedic hospital in the United States described a multi-institutional, open effort funded by the National Institutes of Health to assess model reproducibility in computational knee biomechanics. A regulatory representative from the United States Food and Drug Administration indicated the necessity of standards for reproducibility to increase utility of M&S in the regulatory setting. An industry representative from a major orthopedic implant company emphasized improving reproducibility by addressing indeterminacy in personalized modeling through sensitivity analyses, thereby enhancing preclinical evaluation of joint replacement technology. Thought leaders in the M&S community stressed the importance of data sharing to minimize duplication of efforts. A survey comprised 103 attendees revealed strong support for the workshop and for increasing emphasis on computational modeling at future ORS meetings. Nearly all survey respondents (97%) considered reproducibility to be an important issue. Almost half of respondents (45%) tried and failed to reproduce the work of others. Two-thirds of respondents (67%) declared that individual laboratories are most responsible for ensuring reproducible research whereas 44% thought that journals are most responsible. Thought leaders and survey respondents emphasized that computational models must be reproducible and credible to advance knee M&S.

Knee laxity after anterior tibial eminence fracture in children: A 35-case series

INTRODUCTION

Anterior tibial eminence (ATE) fractures are characterized by avulsion of the anterior cruciate ligament insertion. The aim of our study was to evaluate the long-term incidence of laxity and instability in the aftermath of these fractures. The secondary objective was to identify factors for instability.

HYPOTHESIS

ATE fracture in children is responsible for laxity and instability in the medium and long term.

MATERIAL AND METHODS

This retrospective, single-center study included 35 isolated fractures of the tibial intercondylar eminence during skeletal growth between January 2006 and January 2020. Analysis comprised demographics, laxity measured by GNRB™, range of motion and IKDC and Lysholm scores. Clinical reassessment was performed in 24 patients, the other 11 being interviewed by telephone.

RESULTS

Mean laxity on GNRB™ was 1.46mm, and 3 patients had>3mm differential with respect to the healthy knee. Mean IKDC score was 92.2 and mean Lysholm score 93.1. Four patients showed instability, 2 of whom required surgical management. There was no significant difference in occurrence of laxity according to fracture type or reduction quality. Mean follow-up was 5.9years (range, 1.1-14.8).

DISCUSSION

Our clinical and functional results were in accordance with the literature. The long-term clinical results were satisfactory. ATE fractures require long-term follow-up to screen for instability and laxity on GNRB™.

LEVEL OF EVIDENCE

IV, retrospective study.

Injury risk functions for the four primary knee ligaments

The purpose of this study was to develop injury risk functions (IRFs) for the anterior and posterior cruciate ligaments (ACL and PCL, respectively) and the medial and lateral collateral ligaments (MCL and LCL, respectively) in the knee joint. The IRFs were based on post-mortem human subjects (PMHSs). Available specimen-specific failure strains were supplemented with statistically generated failure strains (virtual values) to accommodate for unprovided detailed experimental data in the literature. The virtual values were derived from the reported mean and standard deviation in the experimental studies. All virtual and specimen-specific values were thereafter categorized into groups of static and dynamic rates, respectively, and tested for the best fitting theoretical distribution to derive a ligament-specific IRF. A total of 10 IRFs were derived (three for ACL, two for PCL, two for MCL, and three for LCL). ACL, MCL, and LCL received IRFs in both dynamic and static tensile rates, while a sufficient dataset was achieved only for dynamic rates of the PCL. The log-logistic and Weibull distributions had the best fit (p-values: >0.9, RMSE: 2.3%-4.7%) to the empirical datasets for all the ligaments. These IRFs are, to the best of the authors' knowledge, the first attempt to generate injury prediction tools based on PMHS data for the four knee ligaments. The study has summarized all the relevant literature on PHMS experimental tensile tests on the knee ligaments and utilized the available empirical data to create the IRFs. Future improvements require upcoming experiments to provide comparable testing and strain measurements. Furthermore, emphasis on a clear definition of failure and transparent reporting of each specimen-specific result is necessary.

Meniscal injuries in skeletally immature children with tibial eminence fractures. Systematic review of literature

PURPOSE

Although the mechanisms of injury are similar to ACL rupture in adults, publications dealing with meniscal lesions resulting from fractures of the intercondylar eminence in children are much rarer. The main objective was to measure the frequency of meniscal lesions associated with tibial eminence fractures in children. The second question was to determine whether there is any available evidence on association between meniscal tears diagnostic method, and frequencies of total lesions, total meniscal lesions, and total entrapments.

METHODS

A comprehensive literature search was performed using PubMed and Scopus. Articles were eligible for inclusion if they reported data on intercondylar tibial fracture, or tibial spine fracture, or tibial eminence fracture, or intercondylar eminence fracture. Article selection was performed in accordance with the PRISMA guidelines.

RESULTS

In total, 789 studies were identified by the literature search. At the end of the process, 26 studies were included in the final review. This systematic review identified 18.1% rate of meniscal tears and 20.1% rate of meniscal or IML entrapments during intercondylar eminence fractures. Proportion of total entrapments was significantly different between groups (17.8% in the arthroscopy group vs. 6.2% in the MRI group; p < .0001). Also, we found 20.9% of total associated lesions in the arthroscopy group vs. 26.1% in the MRI group (p = .06).

CONCLUSION

Although incidence of meniscal injuries in children tibial eminence fractures is lower than that in adults ACL rupture, pediatric meniscal tears and entrapments need to be systematically searched. MRI does not appear to provide additional information about the entrapment risk if arthroscopy treatment is performed. However, pretreatment MRI provides important informations about concomitant injuries, such as meniscal tears, and should be mandatory if orthopaedic treatment is retained. MRI modalities have yet to be specified to improve the diagnosis of soft tissues entrapments.

STUDY DESIGN

Systematic review of the literature REGISTRATION: PROSPERO N° CRD42021258384.

Mechanical properties of animal ligaments: a review and comparative study for the identification of the most suitable human ligament surrogates

The interest in the properties of animal soft tissues is often related to the desire to find an animal model to replace human counterparts due to the unsteady availability of human tissues for experimental purposes. Once the most appropriate animal model is identified, it is possible to carry out ex-vivo and in-vivo studies for the repair of ligamentous tissues and performance testing of replacement and support healing devices. This work aims to present a systematic review of the mechanical properties of ligaments reported in the scientific literature by considering different anatomical regions in humans and several animal species. This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method. Moreover, considering the lack of a standard protocol for preconditioning of tissues, this aspect is also addressed. Ninety-six studies were selected for the systematic review and analysed. The mechanical properties of different animal species are reported and summarised in tables. Only results from studies reporting the strain rate parameter were considered for comparison with human ligaments, as they were deemed more reliable. Elastic modulus, ultimate tensile stress, and ultimate strain properties are graphically reported identifying the range of values for each animal species and to facilitate comparison between values reported in the scientific literature in animal and human ligaments. Useful similarities between the mechanical properties of swine, cow, and rat and human ligaments have been found.

Could an Anterior Cruciate Ligament Be Tissue-Engineered from Silk?

Silk has a long history as an exclusive textile, but also as a suture thread in medicine; nowadays, diverse cell carriers are manufactured from silk. Its advantages are manifold, including high biocompatibility, biomechanical strength and processability (approved for nearly all manufacturing techniques). Silk's limitations, such as scarcity and batch to batch variations, are overcome by gene technology, which allows for the upscaled production of recombinant "designed" silk proteins. For processing thin fibroin filaments, the sericin component is generally removed (degumming). In contrast to many synthetic biomaterials, fibroin allows for superior cell adherence and growth. In addition, silk grafts demonstrate superior mechanical performance and long-term stability, making them attractive for anterior cruciate ligament (ACL) tissue engineering. Looking at these promising properties, this review focusses on the responses of cell types to silk variants, as well as their biomechanical properties, which are relevant for ACL tissue engineering. Meanwhile, sericin has also attracted increasing interest and has been proposed as a bioactive biomaterial with antimicrobial properties. But so far, fibroin was exclusively used for experimental ACL tissue engineering approaches, and fibroin from spider silk also seems not to have been applied. To improve the bone integration of ACL grafts, silk scaffolds with osteogenic functionalization, silk-based tunnel fillers and interference screws have been developed. Nevertheless, signaling pathways stimulated by silk components remain barely elucidated, but need to be considered during the development of optimized silk cell carriers for ACL tissue engineering.

Speed whip ripstop technique during anterior cruciate ligament reconstruction using quadriceps tendon results in higher fixation strength

PURPOSE

To compare the biomechanical strength of different fixation configurations using a suspensory button in a soft-tissue quadriceps tendon graft for Anterior Cruciate Ligament (ACL) reconstruction.

METHODS

Thirty fresh-frozen bovine Achilles tendons (10 mm wide, 50 mm long, and 4 mm thick) were used in this study. Tendons were assigned to three groups (n = 10 per group) with different suture configurations using adjustable loops with a suspensory button: group A, with the threads of an adjustable loop fixed by crossing at the tip of the loop and the entire loop; group B, continuous loops with hanging buttons were directly sutured to the tendon with eight simple sutures; group C, fixation was performed using the speed whip ripstop technique. Tensile tests with five cycles of preloading were performed at 50 N, held at 50 N for 1 min, and load-to-failure testing was conducted until rupture at 5 mm/min. The difference in the elongation and the maximum load-to-failure force were measured.

RESULTS

The average elongation was significantly larger in group B (16.6 ± 2.2 mm) than in groups A (10.3 ± 2.4 mm) and C (10.0 ± 1.0 mm), (p < 0.001). The average load-to-failure force varied significantly between the three groups, 157.5 ± 33.4 N in group A, 253.4 ± 45.5 N in group B, and 337.7 ± 21.0 N in group C, (p < 0.001).

CONCLUSION

Fixation using the speed whip ripstop technique to fix the suspensory button and soft-tissue transplant tendon resulted in minimal elongation and higher fixation strength. Simple devices that use this method have already been developed. Since it can be fixed using a relatively simple method, speed whip ripstop technique was shown to be advantageous for femoral fixation in ACL reconstruction using soft-tissue quadriceps tendon. The findings of this study could help surgeons reduce graft re-tear rates in ACL reconstruction using quadriceps tendons.

LEVEL OF EVIDENCE

N/A, laboratory control study.

Biomechanical Comparison of 3 Adjustable-Loop Suspensory Devices for All-Inside ACL Reconstruction: A Time-Zero Full-Construct Model

Background

Little is known about the stability of adjustable-loop devices (ALDs) for anterior cruciate ligament (ACL) reconstruction (ACLR).

Purpose

To evaluate the stabilization behavior of 3 different types of ALDs for all-inside ACLR in a full-construct surgical technique-based manner.

Study Design

Controlled laboratory study.

Methods

The femoral and tibial devices of Ultrabutton (Smith & Nephew), Infinity (Conmed), and TightRope II (Arthrex) were applied to quadrupled bovine tendon grafts (n = 8 each) with tibial-sided traction applied (350 N) for graft tensioning in a simulated fully extended knee. Knotless femoral graft fixation was based on either a suture-locking device (SLD; Ultrabutton), button-locking device (BLD; Infinity), or dual-locking device (DLD; TightRope II). All constructs were progressively loaded (50 N/500 cycles) from 50 to 300 N for 3000 cycles (0.75 Hz), including complete unloading situations and pull to failure (50 mm/min). Construct elongation, stiffness, and ultimate load were analyzed.

Results

BLD showed significantly greater initial elongation (-2.69 ± 0.15 mm) than DLD (-3.19 ± 0.21 mm; P < .001) but behaved similarly to SLD (-2.93 ± 0.23 mm). While DLD and SLD had the smallest initial elongation at the same significance level, they behaved opposite to each other with gradually increasing peak loading. At the end of testing, DLD had the lowest (-0.64 ± 0.32 mm) and SLD the highest (3.41 ± 1.01 mm) total elongation (P < .003 for both). SLD displayed significantly higher dynamic elongation (6.34 ± 0.23 mm) than BLD (3.21 ± 0.61 mm) and DLD (2.56 ± 0.31 mm) (P < .001 for both). The failure load of BLD (865.0 ± 183.8 N) was significantly lower (P < .026) compared with SLD and DLD (>1000 N). The predominant failure mode was suture rupture and tibial bone breakage with button subsidence (SLD, n = 4). No significant difference in stiffness between constructs was found.

Conclusion

While DLD successfully restricted critical construct elongation, BLD partially and SLD completely exceeded the clinical failure threshold (>3 mm) of plastic elongation with loop lengthening during increasing cyclic peak loading with complete unloading. Higher failure loads of SLD and DLD implants (>1000 N) were achieved at similar construct stiffness to BLD.

Clinical Relevance

A detailed biomechanical understanding of the stabilization potential is pertinent to the continued evolution of ALDs to improve clinical outcomes.

How safe are partial squats after the anterior cruciate ligament reconstruction? A finite element analysis

BACKGROUND

Partial squats are a part of many rehabilitation programs. Progress to deeper squats can only be performed through the partial squat position. However, squats safety, onset time, and rational depth are still controversial. Most previous studies have not considered the influence of posterior tibial slope (PTS) and anterolateral ligament (ALL) on the stress on the knee anatomical elements in partial squats.

METHODS

We have created the new comprehensive knee computer models, which considered muscle exertions while weight bearing 75, 100, 125, and 150 kg in partial squats, included the ALL, two variants of PTS (5° and 13.9°), and two variants of anterior cruciate ligament (ACL) (a native 6 mm double-bundle ACL and an 8 mm single-bundle ACL graft). Using the finite element analysis, we have analyzed stresses in 14 anatomical elements in each model in partial squats (55° knee flexion and 10° anterior tibia tilt).

RESULTS

PTS change from 5° to 13.9° in a partial squat increases stress 1.2-1.3 times on the native ACL and 1.3-1.4 times on the ALL. In the case of single-bundle ACL reconstruction, PTS growth from 5° to 13.9° results in stress increasing 1.2-1.3 times on the graft and 1.3-1.4 times on the ALL. Thus, increased PTS is a significant risk factor, especially in the early postoperative period. Weight-bearing predictably increases stress on the ACL, ALL, and other joint elements proportional to the weight growth. Patients with thinner grafts after the ACL reconstruction may already reach the risk level for graft rupture in a single load in partial squatting if they weigh 125 kg or more. The risk rises with increasing PTS angle or the patient's weight. Because of the reduction of the graft strength by six weeks after surgery by 27%, partial squats in six weeks are associated with forces that may exceed the maximal ACL load even in patients with 75 kg of weight without additional load.

CONCLUSION

In the early postoperative period, partial squats can put the ACL graft at risk of failure. This risk is proportional to the patient's weight and PTS angle, and inversely proportional to the graft thickness. The choice of physical therapy strategies after ACL reconstruction, exercises, and their initiation timing is complex and cannot be standardized for all patients. Factors like the thickness of the graft, the method of fixation, the patient's weight, the ALL insufficiency, the PTS angle, and the patient's goals in the short and long term should be considered when planning the rehabilitation program.

Bayesian Calibration of Computational Knee Models to Estimate Subject-Specific Ligament Properties, Tibiofemoral Kinematics, and Anterior Cruciate Ligament Force With Uncertainty Quantification

High-grade knee laxity is associated with early anterior cruciate ligament (ACL) graft failure, poor function, and compromised clinical outcome. Yet, the specific ligaments and ligament properties driving knee laxity remain poorly understood. We described a Bayesian calibration methodology for predicting unknown ligament properties in a computational knee model. Then, we applied the method to estimate unknown ligament properties with uncertainty bounds using tibiofemoral kinematics and ACL force measurements from two cadaver knees that spanned a range of laxities; these knees were tested using a robotic manipulator. The unknown ligament properties were from the Bayesian set of plausible ligament properties, as specified by their posterior distribution. Finally, we developed a calibrated predictor of tibiofemoral kinematics and ACL force with their own uncertainty bounds. The calibrated predictor was developed by first collecting the posterior draws of the kinematics and ACL force that are induced by the posterior draws of the ligament properties and model parameters. Bayesian calibration identified unique ligament slack lengths for the two knee models and produced ACL force and kinematic predictions that were closer to the corresponding in vitro measurement than those from a standard optimization technique. This Bayesian framework quantifies uncertainty in both ligament properties and model outputs; an important step towards developing subject-specific computational models to improve treatment for ACL injury.

Does mechanical loading restore ligament biomechanics after injury? A systematic review of studies using animal models

BACKGROUND

Mechanical loading is purported to restore ligament biomechanics post-injury. But this is difficult to corroborate in clinical research when key ligament tissue properties (e.g. strength, stiffness), cannot be accurately measured. We reviewed experimental animal models, to evaluate if post-injury loading restores tissue biomechanics more favourably than immobilisation or unloading. Our second objective was to explore if outcomes are moderated by loading parameters (e.g. nature, magnitude, duration, frequency of loading).

METHODS

Electronic and supplemental searches were performed in April 2021 and updated in May 2023. We included controlled trials using injured animal ligament models, where at least one group was subjected to a mechanical loading intervention postinjury. There were no restrictions on the dose, time of initiation, intensity, or nature of the load. Animals with concomitant fractures or tendon injuries were excluded. Prespecified primary and secondary outcomes were force/stress at ligament failure, stiffness, laxity/deformation. The Systematic Review Center for Laboratory animal Experimentation tool was used to assess the risk of bias.

RESULTS

There were seven eligible studies; all had a high risk of bias. All studies used surgically induced injury to the medial collateral ligament of the rat or rabbit knee. Three studies recorded large effects in favour of ad libitum loading postinjury (vs. unloading), for force at failure and stiffness at 12-week follow up. However, loaded ligaments had greater laxity at initial recruitment (vs. unloaded) at 6 and 12 weeks postinjury. There were trends from two studies that adding structured exercise intervention (short bouts of daily swimming) to ad libitum activity further enhances ligament behaviour under high loads (force at failure, stiffness). Only one study compared different loading parameters (e.g. type, frequency); reporting that an increase in loading duration (from 5 to 15 min/day) had minimal effect on biomechanical outcomes.

CONCLUSION

There is preliminary evidence that post-injury loading results in stronger, stiffer ligament tissue, but has a negative effect on low load extensibility. Findings are preliminary due to high risk of bias in animal models, and the optimal loading dose for healing ligaments remains unclear.

Anatomical Tissue Engineering of the Anterior Cruciate Ligament Entheses

The firm integration of anterior cruciate ligament (ACL) grafts into bones remains the most demanding challenge in ACL reconstruction, since graft loosening means graft failure. For a functional-tissue-engineered ACL substitute to be realized in future, robust bone attachment sites (entheses) have to be re-established. The latter comprise four tissue compartments (ligament, non-calcified and calcified fibrocartilage, separated by the tidemark, bone) forming a histological and biomechanical gradient at the attachment interface between the ACL and bone. The ACL enthesis is surrounded by the synovium and exposed to the intra-articular micromilieu. This review will picture and explain the peculiarities of these synovioentheseal complexes at the femoral and tibial attachment sites based on published data. Using this, emerging tissue engineering (TE) strategies addressing them will be discussed. Several material composites (e.g., polycaprolactone and silk fibroin) and manufacturing techniques (e.g., three-dimensional-/bio-printing, electrospinning, braiding and embroidering) have been applied to create zonal cell carriers (bi- or triphasic scaffolds) mimicking the ACL enthesis tissue gradients with appropriate topological parameters for zones. Functionalized or bioactive materials (e.g., collagen, tricalcium phosphate, hydroxyapatite and bioactive glass (BG)) or growth factors (e.g., bone morphogenetic proteins [BMP]-2) have been integrated to achieve the zone-dependent differentiation of precursor cells. However, the ACL entheses comprise individual (loading history) asymmetric and polar histoarchitectures. They result from the unique biomechanical microenvironment of overlapping tensile, compressive and shear forces involved in enthesis formation, maturation and maintenance. This review should provide a road map of key parameters to be considered in future in ACL interface TE approaches.

Evaluation of Autografts Used in Anterior Cruciate Ligament Reconstruction in Terms of Tensile Strength

Introduction Anterior cruciate ligament (ACL) injuries increase the likelihood of chronic knee problems in later years, including early onset osteoarthritis. Therefore, ACL treatment is important in preventing knee problems from developing. The treatment of choice for ACL tears is surgery (ACL reconstruction), and the most popular tendons for ACL reconstruction are the patellar tendon, hamstring tendon (semitendinosus and gracilis tendons), and bone-patellar tendon-bone. The present study compares the tensile strength of autografts used in ACL reconstruction to identify the optimum autograft for ACL in terms of mechanical properties. Methods Cadavers were dissected, and the Achilles tendons, quadriceps tendons, hamstring tendons (semitendinosus and gracilis tendons), patellar tendon grafts, and ACLs were harvested. Tensile tests of each tendon graft were performed using a Shimadzu Autograph AG-IS 100 kN tester (Shimadzu, Kyoto, Japan). Results The mean difference in tensile strength between ACL and other grafts was lowest for the quadriceps in both males and females (p ˂ 0.001), meaning that ACL and quadriceps grafts are more compatible than other tendon grafts in terms of tensile strength. Conclusion The present study found the lowest mean difference in tensile strength to be between the ACL and the quadriceps tendon, suggesting that the use of the quadriceps tendon in ACL reconstruction will yield more positive outcomes.

Comparison of side-cutting maneuvers versus low impact baseball swing on knee ligament loading in adolescent populations

BACKGROUND

High impact sports are associated with an increased incidence rate for knee ligament injuries, specifically pertaining to the anterior cruciate ligament and medial collateral ligament. What is less clear is (i) the extent to which high impact activities preferentially load the anterior cruciate ligament versus the medial collateral ligament, and (ii) whether both ligaments experience similar stretch ratios during high loading scenarios. Therefore, the goal of this project was to assess how different loading conditions experienced through more at-risk sporting maneuvers influence the relative displacements of the anterior cruciate ligament and medial collateral ligament. The focus of the study was on adolescent patients - a group that has largely been overlooked when studying knee ligament biomechanics.

METHODS

Through kinetic knee data obtained through motion capture experimentation, two different loading conditions (high vs low impact) were applied to 22 specimen-specific adolescent finite element knee models to investigate the biomechanical impact various sporting maneuvers place on the knee ligaments.

FINDINGS

The high impact side cutting maneuver resulted in 102% and 47% increases in ligament displacement compared to the low impact baseball swing (p < 0.05) for both the anterior cruciate ligament and medial collateral ligament.

INTERPRETATION

Quantifying biomechanical risks that sporting activities place on adolescent subjects provides physicians with insight into knee ligament vulnerability. More specifically, knowing the risks that various sports place on ligaments helps guide the selection of sports for at-risk patients (especially those who have undergone knee ligament surgery).

Current trends in graft choice for anterior cruciate ligament reconstruction - part I: anatomy, biomechanics, graft incorporation and fixation

Graft selection in anterior cruciate ligament (ACL) reconstruction is critical, as it remains one of the most easily adjustable factors affecting graft rupture and reoperation rates. Commonly used autografts, including hamstring tendon, quadriceps tendon and bone-patellar-tendon-bone, are reported to be biomechanically equivalent or superior compared to the native ACL. Despite this, such grafts are unable to perfectly replicate the complex anatomical and histological characteristics of the native ACL. While there remains inconclusive evidence as to the superiority of one autograft in terms of graft incorporation and maturity, allografts appear to demonstrate slower incorporation and maturity compared to autografts. Graft fixation also affects graft properties and subsequent outcomes, with each technique having unique advantages and disadvantages that should be carefully considered during graft selection.

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.

Strain evaluation of axially loaded collateral ligaments: a comparison of digital image correlation and strain gauges

The response of soft tissue to loading can be obtained by strain assessment. Typically, strain can be measured using electrical resistance with strain gauges (SG), or optical sensors based on the digital image correlation (DIC), among others. These sensor systems are already established in other areas of technology. However, sensors have a limited range of applications in medical technology due to various challenges in handling human soft materials. The aim of this study was to compare directly attached foil-type SG and 3D-DIC to determine the strain of axially loaded human ligament structures. Therefore, the medial (MCL) and lateral (LCL) collateral ligaments of 18 human knee joints underwent cyclic displacement-controlled loading at a rate of 20 mm/min in two test trials. In the first trial, strain was recorded with the 3D-DIC system and the reference strain of the testing machine. In the second trial, strain was additionally measured with a directly attached SG. The results of the strain measurement with the 3D-DIC system did not differ significantly from the reference strain in the first trial. The strains assessed in the second trial between reference and SG, as well as between reference and 3D-DIC showed significant differences. This suggests that using an optical system based on the DIC with a given unrestricted view is an effective method to measure the superficial strain of human ligaments. In contrast, directly attached SGs provide only qualitative comparable results. Therefore, their scope on human ligaments is limited to the evaluation of changes under different conditions.

Advanced Graft Development Approaches for ACL Reconstruction or Regeneration

The Anterior Cruciate Ligament (ACL) is one of the major knee ligaments, one which is greatly exposed to injuries. According to the British National Health Society, ACL tears represent around 40% of all knee injuries. The number of ACL injuries has increased rapidly over the past ten years, especially in people from 26-30 years of age. We present a brief background in currently used ACL treatment strategies with a description of surgical reconstruction techniques. According to the well-established method, the PubMed database was then analyzed to scaffold preparation methods and materials. The number of publications and clinical trials over the last almost 30 years were analyzed to determine trends in ACL graft development. Finally, we described selected ACL scaffold development publications of engineering, medical, and business interest. The systematic PubMed database analysis indicated a high interest in collagen for the purpose of ACL graft development, an increased interest in hybrid grafts, a numerical balance in the development of biodegradable and nonbiodegradable grafts, and a low number of clinical trials. The investigation of selected publications indicated that only a few suggest a real possibility of creating healthy tissue. At the same time, many of them focus on specific details and fundamental science. Grafts exhibit a wide range of mechanical properties, mostly because of polymer types and graft morphology. Moreover, most of the research ends at the in vitro stage, using non-certificated polymers, thus requiring a long time before the medical device can be placed on the market. In addition to scientific concerns, official regulations limit the immediate introduction of artificial grafts onto the market.

Biomechanical comparison of different screw-included angles in crossing screw fixation for transverse patellar fracture in level walking: a quasi-dynamic finite element study

BACKGROUND

A minimally invasive technique with various screw configurations without open surgery is currently used for the fixation of transverse patellar fractures. Percutaneous crossing screw configuration has been reported to have a good bone union rate in patellar fractures. However, the difference in mechanical stability of the fractured patella between different screw-included angles has not been fully investigated. Hence, this study aims to compare the mechanical stability of parallel and crossing screw fixations with different screw-included angles for the fixation of transverse patellar fractures during level walking.

METHODS

A finite element knee model containing a patella with a transverse fracture is created. Two headless compression screws with different angles (0°, 30°, 60°, and 90°) are used to fix the fracture. The loading conditions of the knee joint during level walking are used to compare the stability of the fractured patella with different fixation screw configurations.

RESULTS

The results indicate that the maximum fracture gap opening distance increased with an increase in the included angle. Two parallel screws yield the smallest gap distance among all screw configurations. The maximum gap opening distances at the anterior leading edge of the fractured patella with two parallel screws and two screws having an included angle of 90° are 0.73 mm and 1.31 mm, respectively, at 15% walking cycle.

CONCLUSIONS

Based on these results, the superior performance of two parallel screws over crossing screw fixations in the fixation of transverse patellar fractures is established. Furthermore, the smaller the angle between the crossing screws, the better is the stability of the fractured patella.

Comparative analysis of the results of the anterior cruciate ligament reconstruction using an autograft preparation by known and new methods

Background. To date, the problem of choosing the optimal graft for anterior cruciate ligament (ACL) reconstruction and the methods for its formation is one of the main trends in the surgical treatment of patients with anterior knee joint instability.The aim. To compare the results of the anterior cruciate ligament reconstruction using the known method and the new proposed method for autograft formation.Materials and methods. The results of treatment of ACL injury in 44 patients were assessed. In the main group (19 patients), an original technique of ACL reconstruction from 1/2 of the width of m. peroneus longus tendon was used. In the control group (25 patients), ACL reconstruction was performed using a graft from the m. semitendinosus tendon prepared by the Lubowitz method.Results. The mean difference in the circumference of the distal third of the hip in the main group was 1.57 ± 1.162 cm and was statistically significantly better than in the control group, where the mean difference in the hip circumference was 4.74 ± 1.7207 cm.The range of motion of the knee joint in the main group 3 months after the surgery was 128.42 ± 9.287°, and in the control group mean flection was 109.6 ± 9.120°.The functional results in the main group were assessed by the Lisholm scale and were statistically significantly better than the results in the control group. The functional results by the AOFAS (American Orthopedic Foot & Ankle Society) scale in the main group were 100 points before the surgery and at all terms after the surgery: this indicates that the use of 1/2 of the width of m. peroneus longus tendon does not cause the its functional impairement.Conclusion. Anterior cruciate ligament plasty with use of 1/2 of the width of m. peroneus longus tendon prepared by the proposed method showed statistically significantly better results compared to the preparation of autograft from semitendinous muscle tendon using known method.

Electrospun poly(3-hydroxybutyrate-co-3-hydroxyvalerate) scaffolds - a step towards ligament repair applications

The incidence of anterior cruciate ligament (ACL) ruptures is approximately 50 per 100,000 people. ACL rupture repair methods that offer better biomechanics have the potential to reduce long term osteoarthritis. To improve ACL regeneration biomechanically similar, biocompatible and biodegradable tissue scaffolds are required. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), with high 3-hydroxyvalerate (3HV) content, based scaffold materials have been developed, with the advantages of traditional tissue engineering scaffolds combined with attractive mechanical properties, e.g., elasticity and biodegradability. PHBV with 3HV fractions of 0 to 100 mol% were produced in a controlled manner allowing specific compositions to be targeted, giving control over material properties. In conjunction electrospinning conditions were altered, to manipulate the degree of fibre alignment, with increasing collector rotating speed used to obtain random and aligned PHBV fibres. The PHBV based materials produced were characterised, with mechanical properties, thermal properties and surface morphology being studied. An electrospun PHBV fibre mat with 50 mol% 3HV content shows a significant increase in elasticity compared to those with lower 3HV content and could be fabricated into aligned fibres. Biocompatibility testing with L929 fibroblasts demonstrates good cell viability, with the aligned fibre network promoting fibroblast alignment in the axial fibre direction, desirable for ACL repair applications. Dynamic load testing shows that the 50 mol% 3HV PHBV material produced can withstand cyclic loading with reasonable resilience. Electrospun PHBV can be produced with low batch variability and tailored, application specific properties, giving these biomaterials promise in tissue scaffold applications where aligned fibre networks are desired, such as ACL regeneration.   .

A biomechanical analysis of skiing-related anterior cruciate ligament injuries based on biomedical imaging technology

Alpine skiing is an attractive but highly risky sport, and the anterior cruciate ligament (ACL) tear is one of the most common diagnoses of skiing-related injuries. To better prevent such injuries among athletes and recreational skiers, we developed a facile and reliable biomechanical method to analyze the differences between "right" and "wrong" movements during skiing and their impacts on ACL stress loading. Unlike those conventional methods that are very difficult to implement and time-consuming, our method was developed based on inverse dynamics analyses and video capture, which were much easier to implement in the real-world setting. It is shown that, with a harmful skiing action, the knee joint's maximum reaction force significantly increases compared to nonharmful skiing actions. The peak front-and-rear force increased from 1242 N to 3105 N, and the peak axial force increased from 1023 N to 3443 N, which significantly exceeded the maximum tensile loading (2000 N) in the ACL. Our results are proven to be reliable and consistent with findings obtained with other methods. This method may substitute current complex analytical methods and be easier to apply in sports-related injury-prevention applications.

Evolution of functional tissue engineering for tendon and ligament repair

This review paper is motivated by a Back-to-Basics presentation given by the author at the 2022 Orthopaedic Research Society meeting in Tampa, Florida. I was tasked with providing a brief history of research leading up to the introduction of functional tissue engineering (FTE) for tendon and ligament repair. Beginning in the 1970s, this timeline focused on two common orthopedic soft tissue problems, anterior cruciate ligament ruptures in the knee and supraspinatus tendon injuries in the shoulder. Historic changes in the field over the next 5 decades revealed a transformation from a focus more on mechanics (called "bioMECHANICS") on a larger (tissue) scale to a more recent focus on biology (called "mechanoBIOLOGY") on a smaller (cellular and molecular) scale. Early studies by surgeons and engineers revealed the importance of testing conditions for ligaments and tendons (e.g., high strain rates while avoiding subject disuse and immobility) and the need to measure in vivo forces in these tissues. But any true tissue engineering and regeneration in these early decades was limited more to the use of auto-, allo- and xenografts than actual generation of stimulated cell-scaffold constructs in culture. It was only after the discovery of tissue engineering in 1988 and the recognition of frequent rotator cuff injuries in the early 1990s, that biologists joined surgeons and engineers to discover mechanical and biological testing criteria for FTE. This review emphasizes the need for broader and more inclusive collaborations by surgeons, biologists and engineers in the short term with involvement of those in biomaterials, manufacturing, and regulation of new products in the longer term.

Quadriceps tendon autograft for anterior cruciate ligament reconstruction: state of the art

The ideal graft for anterior cruciate ligament reconstruction (ACLR) continues to be debated. Although first described in 1984, use of the quadriceps tendon (QT) autograft has only recently gained popularity. The biomechanical properties of the QT autograft are favourable compared to bone-patellar tendon-bone (BPTB) and doubled hamstring (HS) grafts with a higher load to failure and a modulus of elasticity that more closely approximates the native anterior cruciate ligament (ACL). The QT graft can be harvested with or without a bone plug, as either a full thickness or a partial thickness graft, and even through minimally invasive techniques. The surgeon must be aware of potential harvest risks including patellar fracture or a graft that is of insufficient length. Numerous short-term studies have shown comparable results when compared to BPTB or hamstring HS autografts with similar graft failure rates, patient-reported outcomes. A major advantage of QT ACLR is reduced donor site morbidity compared to BPTB. However, some persistent quadriceps weakness after QT ACLR has also been reported. The current literature shows that use of the QT autograft for ACLR provides equivalent clinical results compared to other autografts with less donor site morbidity. However, future studies with longer follow-up and higher level of evidence are needed to identify specific populations where the QT may have additional advantage.

Probabilistic planning for ligament-balanced TKA-Identification of critical ligament properties

Total knee arthroplasty (TKA) failures are often attributed to unbalanced knee ligament loading. The current study aims to develop a probabilistic planning process to optimize implant component positioning that achieves a ligament-balanced TKA. This planning process accounts for both subject-specific uncertainty, in terms of ligament material properties and attachment sites, and surgical precision related to the TKA process typically used in clinical practice. The consequent uncertainty in the implant position parameters is quantified by means of a surrogate model in combination with a Monte Carlo simulation. The samples for the Monte Carlo simulation are generated through Bayesian parameter estimation on the native knee model in such a way that each sample is physiologically relevant. In this way, a subject-specific uncertainty is accounted for. A sensitivity analysis, using the delta-moment-independent sensitivity measure, is performed to identify the most critical ligament parameters. The designed process is capable of estimating the precision with which the targeted ligament-balanced TKA can be realized and converting this into a success probability. This study shows that without additional subject-specific information (e.g., knee kinematic measurements), a global success probability of only 12% is estimated. Furthermore, accurate measurement of reference strains and attachment sites critically improves the success probability of the pre-operative planning process. To allow more precise planning, more accurate identification of these ligament properties is required. This study underlines the relevance of investigating in vivo or intraoperative measurement techniques to minimize uncertainty in ligament-balanced pre-operative planning results, particularly prioritizing the measurement of ligament reference strains and attachment sites.

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.

Ligaments Laxity and Elongation at Injuryin Flexed knees during Lateral Impact Conditions

The knee is one of the regions of interest for pedestrian safety assessment. Past testing to study knee ligament injuries for pedestrian impact only included knees in full extension and mostly focused on global responses. As the knee flexion angle and the initial ligament laxity may affect the elongation at which ligaments fail, the objectives of this study were (1) to design an experimental protocol to assess the laxity of knee ligaments before measuring their elongation at failure, (2) to apply it in paired knee tests at two flexion angles (10 and 45 degrees). The laxity tests combined strain gauges to measure bone strains near insertions that would result from ligament forces and a custom machine to exercise the knee in all directions. Failure was assessed using a four-point bending setup with additional degrees of freedom on the axial rotation and displacement of the femur. A template was designed to ensure that the two setups used the exact same starting position. The protocol was applied to six pairs of knees which were tested until the failure of all ligaments. In the laxity tests, a higher compliance of the knee was observed at 45 degrees compared to 10 degrees. Minimum lengths associated with the beginning of bone loading were also successfully identified for the collateral ligaments, but the process was less successful for the cruciate ligaments. The failure tests suggested increased elongation and length at failure for the ligaments and their bundles at 45°. This could be consistent with the higher compliance in static test, but the minimum lengths identified on the collaterals did not explain this difference during failure. The results highlight the possible relationship between position, laxity and elongation at failure in a lateral loading and provide a dataset including 3D coordinates of insertions to continue the investigation using a modelling approach. Perspectives are also outlined to improve upon the laxity determination protocol.

Intra-Articular Biomechanical Changes of the Meniscus and Ligaments During Stance Phase of Gait Circle after Different Anterior Cruciate Ligament Reconstruction Surgical Procedures: A Finite Element Analysis

OBJECTIVE

The debate on the superiority of single- or double-bundle for anterior cruciate ligament reconstruction has not ceased. The comparative studies on intra-articular biomechanics after different surgical reconstructions are rare. This study is to evaluate the biomechanical stress distribution intra-knee after single- and double-bundle anterior cruciate ligament reconstruction by three-dimensional finite element analysis, and to observe the change of stress concentration under the condition of vertical gradient loads.

METHODS

In this study, magnetic resonance imaging data were extracted from patients and healthy controls for biomechanical analysis. Patients included in the three models were matched in age and sex. The strength and distribution of induced stresses were analyzed in two frequently used procedures, anatomical single-bundle anterior cruciate ligament reconstruction and anatomical double-bundle anterior cruciate ligament reconstruction, using femoral-graft-tibial system under different loads, to mimic a post-operation mechanical motion. The three-dimensional finite-element models for normal ligament and two surgical methods were applied. A vertical force simulating daily walking was performed on the models to assess the interfacial stresses and displacements of intra-articular tissues and ligaments. The evaluation results mainly included the stress of each part of ligament and meniscus. The stress values of different parts of three models were extracted and compared.

RESULTS

The stress of ligament/graft at femoral side of three finite-element models was significantly higher than at tibial side, while the highest level was observed in single-bundle reconstruction finite-element model. With the increase of force, the maximum stress in the medial (7.1-7.1 MPa) and lateral (4.9-7.4 MPa) meniscus of single-bundle reconstruction finite-element model shifted from the anterior horn to the central area (p = 0.0161, 0.0479, respectively). The stress was shown to be at a lower level at femoral side and posterior cruciate ligament of intra-knee in two reconstruction finite-element models than that in normal finite-element models, while presented higher level at the tibial side than normal knee (p = 0.3528). The displacement of the femoral side and intra-knee areas in reconstruction finite-element models was greater than that in normal finite-element model (p = 0.0855).

CONCLUSION

Compared with the single-bundle technique, the graft of double-bundle anterior cruciate ligament reconstruction has better stress dissipation effect and can prevent postoperative meniscus tear more effectively.

Plantaris tendon is valuable graft for the medial patellofemoral ligament reconstruction: A biomechanical study

BACKGROUND

Medial patellofemoral ligament (MPFL) reconstruction is a standard treatment option for selected patients with patellar instability. Although frequently performed, the optimal graft source for the procedure has not yet been established. This study aimed to determine whether a two-strand plantaris tendon construct possesses the biomechanical properties needed to act as an MPFL reconstruction graft.

METHODS

Thirty paired plantaris and gracilis tendons were harvested from 15 cadavers, mean age at death of 42.7 years. All specimens were frozen and maintained at -20 °C until biomechanical testing. Prior to mechanical testing, specimens were thawed at room temperature. The two-strand plantaris tendon and two-strand gracilis tendon constructs were created and secured in a uniaxial tensile testing machine in a triangular-shaped mode. Biomechanical properties for tensile testing to failure were determined using validated method. Results obtained were compared with the previously published data on native MPFL biomechanical properties.

RESULTS

The mean maximal force was 220.3 ± 108.1 N and 448.1 ± 117 N for the two-strand plantaris tendon construct and two-strand gracilis tendon construct, respectively. Significant differences were observed between all biomechanical properties of two-strand plantaris tendon and two-strand gracilis tendon constructs. The mean maximal force of a two-strand plantaris tendon construct and a two-strand gracilis tendon construct were greater than the mean maximal force of the native MPFL reported in all previous studies.

CONCLUSIONS

This study suggests that, due to its biomechanical properties, the two-strand plantaris tendon graft is suitable as a graft for MPFL reconstruction.

Instabilität des Kniegelenks – medial oder anteromedial?

Hintergrund

Verletzungen des medialen Bandkomplexes gehören zu den häufigsten Knieverletzungen. Sie heilen zwar meist mit konservativer Therapie problemlos aus, persistierende Instabilitäten erhöhen aber die Belastung der Kreuzbänder und benötigen speziell bei deren Beteiligung eine adäquate Therapie.

Anatomie und Biomechanik

Der mediale Seitenbandkomplex besteht im Wesentlichen aus dem oberflächlichen Seitenband (sMCL), welches der primäre Stabilisator gegen Valgus ist, dem tiefen Seitenband (dMCL) mit dessen schräg verlaufendem ventralem Anteil (AML), die nur sekundäre Stabilisatoren gegen Valgus darstellen, aber primär gegen Außenrotation stabilisieren, und dem hinteren Schrägband (POL), das in vollständiger Streckung gegen Valgus sowie gegen Innenrotation stabilisiert.

Therapie

Chronische Instabilitäten bzw. höhergradige Verletzungen mit Dislokation der Bandstümpfe oder multiligamentäre Verletzungen bedürfen einer operativen Versorgung. Im Akutstadium zeigen Avulsionsverletzungen bei anatomischer Refixation gutes Heilungspotenzial, während bei intraligamentären Verletzungen zusätzlich zur Naht der Bandanteile eine Augmentation mit Sehnenmaterial empfohlen wird. Bei chronischen Instabilitäten ist die Differenzierung des Instabilitätsmusters ausschlaggebend für die Wahl der Rekonstruktionstechnik (reine sMCL-Rekonstruktion oder kombinierte Rekonstruktion von sMCL und AML). In beiden Fällen kommt die hier beschriebene Technik mit flachem Transplantat der Anatomie näher als bei konventionellen Verfahren.

Diskussion

Rekonstruktionstechniken unter Verwendung flacher Sehnentransplantate, die alle betroffenen Bandanteile adressieren, haben sich biomechanisch als sehr effektiv erwiesen, komplexe mediale Instabilitäten suffizient zu behandeln. Ob diese auch klinisch überlegen sind, werden zukünftige klinische Studien zeigen müssen.

Consensus Delphi study on guidelines for the assessment of anterior cruciate ligament injuries in children

Background: Knee examination guidelines in minors are intended to aid decision-making in the management of knee instability. Clinical question: A Delphi study was conducted with a formal consensus process using a validated methodology with sufficient scientific evidence. A group consensus meeting was held to develop recommendations and practical guidelines for use in the assessment of instability injuries in children. Key findings: there is a lack of evidence to analyse anterior cruciate ligament injuries in children and their subsequent surgical management if necessary. Diagnostic guidelines and clinical assessment of the patient based on a thorough examination of the knee are performed and a guide to anterior cruciate ligament exploration in children is developed. Clinical application: In the absence of a strong evidence base, these established guidelines are intended to assist in that decision-making process to help the clinician decide on the most optimal treatment with the aim of benefiting the patient as much as possible. Following this expert consensus, surgical treatment is advised when the patient has a subjective sensation of instability accompanied by a pivot shift test ++, and may include an anterior drawer test + and a Lachman test +. If these conditions are not present, the conservative approach should be chosen, as the anatomical and functional development of children, together with a physiotherapy programme, may improve the evolution of the injury.

Revision of Failed Sacroiliac Joint Posterior Interpositional Structural Allograft Stabilization with Lateral Porous Titanium Implants: A Multicenter Case Series

Background

Distraction arthrodesis (DA) and stabilization of the sacroiliac (SI) joint by placing standalone structural allograft (SA) into the joint from a posterior trajectory has recently been introduced as a surgical procedure for chronic SI joint pain refractory to non-operative care.

Methods

Retrospective case series of patients with recurrent and/or persistent pain after placement of one or more interpositional/intraarticular standalone SAs between the ilium and sacrum using a posterior procedure to treat SI joint pain/dysfunction. Patients subsequently underwent surgical revision with porous titanium fusion implants using a lateral transfixing procedure. The demographic, clinical, and radiographic features of these cases are described.

Results

Data were available for 37 patients. The average (SD) age was 57 (13) years, 62% were female, and the average BMI was 31 (5.4). On average, two SA implants were placed per joint; 46% of cases were bilateral. At follow-up, two common themes were identified: lucencies around the implants and suboptimal implant position. None of the cases showed radiographic fusion of the SI joint prior to revision. One patient had an inflammatory reaction to the SA. All patients presented for revision due to either continued (49%) or recurrence (51%) of pain. In one revision case, the SA was forced ventrally, resulting in a sacral fracture, which was treated conservatively without sequelae.

Conclusions

The popularity of standalone SA for SI joint stabilization/fusion with a posterior procedure is increasing. This case series demonstrates that clinical failures from this procedure may require surgical revision. The proposed fusion strategy (DA) for these products is unproven in the SI joint, and, therefore, properly conducted prospective randomized clinical trials with long-term clinical and radiographic follow-up are important to establish the safety and efficacy of this approach. In the meantime, the placement of lateral titanium implants appears to be an effective revision strategy.

Periostin Contributes to Fibrocartilage Layer Growth of the Patella Tendon Tibial Insertion in Mice

Background and Objectives: The influence of periostin on the growth of the patella tendon (PT) tibial insertion is unknown. The research described here aimed to reveal the contribution of periostin to the growth of fibrocartilage layers of the PT tibial insertion using periostin knockout mice. Materials and Methods: In both the wild-type (WD; C57BL/6N, periostin +/+; n = 54) and periostin knockout (KO; periostin −/−; n = 54) groups, six mice were euthanized on day 1 and at 1, 2, 3, 4, 6, 8, 10, and 12 weeks of age. Chondrocyte proliferation and apoptosis, number of chondrocytes, safranin O-stained glycosaminoglycan (GAG) area, staining area of type II collagen, and length of the tidemark were investigated. Results: Chondrocyte proliferation and apoptosis in KO were lower than those in WD on day 1 and at 1, 4, and 8 weeks and on day 1 and at 4, 6, and 12 weeks, respectively. Although the number of chondrocytes in both groups gradually decreased, it was lower in KO than in WD on day 1 and at 8 and 12 weeks. In the extracellular matrix, the GAG-stained area in KO was smaller than that in WD on day 1 and at 1, 4, 8, 10, and 12 weeks. The staining area of type II collagen in KO was smaller than that in WD at 8 weeks. The length of the tidemark in KO was shorter than that in WD at 4 and 6 weeks. Conclusion: Loss of periostin led to decreased chondrocyte proliferation, chondrocyte apoptosis, and the number of chondrocytes in the growth process of the PT tibial insertion. Moreover, periostin decreased and delayed GAG and type II collagen production and delayed tidemark formation in the growth process of the PT tibial insertion. Periostin can, therefore, contribute to the growth of fibrocartilage layers in the PT tibial insertion. Periostin deficiency may result in incomplete growth of the PT tibial insertion.

Anterior cruciate ligament reconstruction with short hamstring grafts: the choice of femoral fixation device matters in controlling overall lengthening

PURPOSE

The purpose was to conduct an independent biomechanical study comparing the main types of femoral fixation adapted to short hamstring grafts in anterior cruciate ligament (ACL) reconstruction surgery and to validate their performance.

METHODS

The ACLip^® Femoral, ToggleLoc™ Ziploop (TLZ), and Tape Locking Screw (TLS^®) implants were tested in tension in the following three different configurations: implant alone, implant fixed on the femur without graft, and implant fixed on the femur with graft. Grafts alone were also tested. The femurs and the 4-strand semi-tendinosus grafts were derived from porcine and human models, respectively. Each set-up was subjected to the same protocol of creep (50 N for 30 s), cycling (1000 cycles between 50 and 250 N, 1 Hz), and load to failure (50 mm/min).

RESULTS

A total of 93 tests were performed (30 ACLip^®, 30 TLZ, 20 TLS^®, and 13 ST4 alone). For the implants tested with femur and graft, the mean ± standard deviation (SD) overall elongation at 250 N after cycling was 5.2 ± 0.2 mm, 8.4 ± 2.1 mm, and 5.3 ± 0.8 mm, the mean ± SD ultimate load to failure was 736 ± 116 N, 830 ± 204 N, and 640 ± 242 N, and the mean ± SD stiffness at the 1000th cycle was 185 ± 15 N/mm, 172 ± 19 N/mm, and 178 ± 21 N/mm for ACLip^®, ToggleLoc™, and TLS^® devices, respectively. There was no significant difference between the implants except for post-cycling elongation between TLZ and the other two implants (p < 0.05).

CONCLUSION

The choice of femoral fixation device plays a decisive role in controlling the overall lengthening of an ACL reconstruction using a short hamstring graft. All implants validated the specifications in terms of ultimate load to failure, the TLS^® system had, however, a low performance limit. ToggleLoc™ with adjustable loop should no longer be used on the femur side; instead the other types of fixation should be used to improve the overall elongation control.

A regeneration process-matching scaffold with appropriate dynamic mechanical properties and spatial adaptability for ligament reconstruction

Ligament regeneration is a complicated process that requires dynamic mechanical properties and allowable space to regulate collagen remodeling. Poor strength and limited space of currently available grafts hinder tissue regeneration, yielding a disappointing success rate in ligament reconstruction. Matching the scaffold retreat rate with the mechanical and spatial properties of the regeneration process remains challenging. Herein, a scaffold matching the regeneration process was designed via regulating the trajectories of fibers with different degradation rates to provide dynamic mechanical properties and spatial adaptability for collagen infiltration. This core-shell structured scaffold exhibited biomimetic fiber orientation, having tri-phasic mechanical behavior and excellent strength. Besides, by the sequential material degradation, the available space of the scaffold increased from day 6 and remained stable on day 24, consistent with the proliferation and deposition phase of the native ligament regeneration process. Furthermore, mature collagen infiltration and increased bone integration in vivo confirmed the promotion of tissue regeneration by the adaptive space, maintaining an excellent failure load of 67.65% of the native ligament at 16 weeks. This study proved the synergistic effects of dynamic strength and adaptive space. The scaffold matching the regeneration process is expected to open new approaches in ligament reconstruction.

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Regeneration process-matching scaffold was made via regulating fiber trajectory.

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The scaffold showed tri-phasic mechanical behavior and fatigue properties.

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Matching repair process with dynamic mechanical property and spatial adaptability.

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A feasible substitute for the T/L reconstruction by spatial adaptability.

Effect of Sectioning of the Anterior Cruciate Ligament and Posterolateral Structures on Lateral Compartment Gapping: A Randomized Biomechanical Study

Background:

The contribution of anterior cruciate ligament (ACL) injury to lateral instability under varus stress, particularly compared with posterolateral structures, is not well known.

Purpose:

To investigate the effect of sectioning the ACL and posterolateral knee structures on lateral compartment gapping under varus stress.

Study Design:

Controlled laboratory study.

Methods:

Fourteen nonpaired cadaveric knees were randomized to 1 of 2 groups: sequential sectioning of the ACL, fibular collateral ligament (FCL), popliteus tendon (PLT), and popliteofibular ligament (PFL) (ACL-first group) or sequential sectioning of the FCL, PLT, PFL, and ACL (FCL-first group). Knees were loaded onto a custom jig at a 20° flexion angle. A standardized 12-N·m varus moment was applied to each specimen in the intact state and after each randomized sequential-sectioning state. Lateral compartment opening was measured on radiographs to assess the contribution to the increase in the lateral gap caused by resecting the respective structure. The distance was measured by 3 observers on 15 images (5 testing states each imaged 3 times) per specimen, for a total of 210 radiographs. The articular cartilage surfaces were not included in the measurements.

Results:

The mean increase in lateral opening after sectioning all structures (ACL and posterolateral corner) was 4.6 ± 1.8 mm (range, 1.9-7.7 mm). The ACL and FCL sectioning contributed the most to lateral knee opening (1.3 ± 0.6 and 2.2 ± 1.3 mm, respectively). In both groups, lateral gapping >3 mm was achieved only after both the ACL and FCL were sectioned. All comparisons of increased mean gapping distances demonstrated a significant difference with subsequent sequential sectioning of structures, except comparisons between the FCL and PLT and the PLT and PFL. When considering the effect of the ACL on lateral opening, no significant difference was found between sectioning the ACL first or FCL first (P = .387).

Conclusion:

ACL deficiency significantly increased lateral opening under varus stress, regardless of the sequence of injury. The effect of injury to the ACL in addition to the lateral structures should be considered when using varus stress radiographs to evaluate knee injuries.

Clinical Relevance:

With the current findings, understanding the effect of ACL and posterolateral corner injuries on lateral gapping under varus stress can aid in correctly diagnosing knee injuries and determining appropriate treatment plans.