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Background: Loss of knee extension has been reported by many authors to be the most common complication following anterior cruciate ligament reconstruction. The objective of this in vitro study was to determine the effect, on loss of knee extension, of the knee flexion angle and the tension of the bone-patellar tendon-bone graft during graft fixation in a reconstruction of an anterior cruciate ligament.Methods: The anterior cruciate ligament was reconstructed with use of tibial and femoral bone tunnels placed in the footprint of the native anterior cruciate ligament in ten cadavers. The graft was secured with an initial tension of either 44 N (10 lb) or 89 N (20 lb) applied with the knee at 0 degrees or 30 degrees of flexion. The knee flexion angle was measured with use of digital images following graft fixation.Results: Tensioning of the graft at 30 degrees of knee flexion was associated with loss of knee extension in this cadaver model. Graft tension did not affect knee extension under the conditions tested.Conclusions: The results suggest that one of the common causes of the loss of full knee extension may be diminished if the graft is secured in full knee extension when the tibial and femoral tunnels are placed in the footprint of the native anterior cruciate ligament. More importantly, even when the femoral and tibial tunnels are placed in the femoral and tibial footprints of the native anterior cruciate ligament, fixing a graft in knee flexion can result in the loss of knee extension. [ABSTRACT FROM AUTHOR]

The medial soft-tissue restraints of the patella, specifically the medial patellofemoral ligament and the vastus medialis obliquus muscle, are critical to patellofemoral joint stability. A reliable and inexpensive imaging technique would be clinically useful especially after acute patellar dislocation. The medial patellofemoral ligament and the vastus medialis obliquus muscle were identified in cadaveric dissection. The attachments of the medial patellofemoral ligament to the patella and the adductor tubercle, and the attachments of the vastus medialis obliquus muscle to the adductor magnus tendon, adductor tubercle, and patella were carefully observed. Sonography then was performed on four thawed fresh frozen cadaver knees. After sonographic examination of these structures, the knees were dissected and the structures previously identified by sonography were verified. In all four specimens, these restraints of the patellofemoral joint were identified by sonography based on their imaging characteristics and surrounding bony and soft-tissue landmarks. [ABSTRACT FROM AUTHOR]

BACKGROUND: Athletes often employ prophylactic braces to reduce the risk of ankle injuries. HYPOTHESIS: Ankle braces do not significantly decrease the risk of forced inversion on a standardized one-footed jump landing. STUDY DESIGN: Controlled laboratory study. METHODS: Fourteen healthy men with a mean age of 25.1 years were tested. Three braces, two semirigid (Aircast and Bledsoe) and one lace-up (Swede-O), were fitted to each subject. Forced dynamic ankle inversion of 24 degrees was to be resisted as the subjects landed on one foot with a force of two body weights on a stimulus presented randomly in 5 of 15 jump trial blocks onto a hard, level force plate. Subjects first completed 1 no-brace block of 5 trials to establish baseline performance, then 3 randomly ordered 15-trial blocks testing performance with each of the braces, and then finally a no-brace 5-trial block. RESULTS: The average no-brace success rate was 24%, which demonstrated the challenging nature of the task. All three braces increased the success rate (average, 44%); however, only the two semirigid braces proved to be significantly better than the unbraced state. CONCLUSION: This test holds promise for evaluating brace efficacy when landing with one foot unexpectedly on an object that acts to forcibly invert the ankle. [ABSTRACT FROM AUTHOR]

Background: Female athletes who participate in sports involving jumping and cutting maneuvers are up to eight times more likely to sustain a rupture of the anterior cruciate ligament than are men participating in the same sports. We tested the hypothesis that healthy young women are able to volitionally increase the apparent torsional stiffness of the knee, by maximally activating the knee muscles, significantly less than are size-matched men participating in the same type of sport.Methods: Twenty-four NCAA (National Collegiate Athletic Association) Division-I athletes (twelve men and twelve women) competing in sports associated with a high risk of injury to the anterior cruciate ligament (basketball, volleyball, and soccer) were compared with twenty-eight collegiate endurance athletes (fourteen men and fourteen women) participating in sports associated with a low risk of such injuries (bicycling, crew, and running). Male and female pairs were matched for age, height, weight, body mass index, shoe size, and activity level. Testing was performed with a weighted pendulum that applied a medially directed 80-N impulse force to the lateral aspect of the right forefoot. The resulting internal rotation of the leg was measured optically, to the nearest 0.25 degrees, at 30 degrees and 60 degrees of knee flexion, both with and without maximal activation of the knee muscles.Results: Maximal rotations of the leg were greater in women than in men in both the passive and the active muscle state (16% and 27% greater [p = 0.01 and p = 0.02], respectively). Moreover, female athletes exhibited a significantly (18%) smaller volitional increase in apparent torsional stiffness of the knee under internal rotation loading than did the matched male athletes (p = 0.014); this was particularly the case for those who participated in sports involving jumping and pivoting maneuvers (42% difference between genders, p = 0.001).Conclusions: The collegiate female athletes involved in high-risk sports exhibited less muscular protection of the knee ligaments during external loading of the knee than did size and sport-matched male athletes. [ABSTRACT FROM AUTHOR]

Background: Women's susceptibility to injuries involving the anterior cruciate ligament remains unexplained. Volitional contraction of the knee musculature is known to increase the resistance of the knee to shear deformation, raising the possibility that muscles play a part in protecting the anterior cruciate ligament during hazardous activities. We therefore tested the hypothesis that a volitional co-contraction of the knee muscles increases the sagittal-plane shear stiffness (or resistance to anterior tibial translation) of the knee more in men than in women.Methods: Twenty-three volunteers (ten men and thirteen women; mean age, 24.7 +/- 5.4 years), all with anterior tibial translation of 6 mm, agreed to participate in the study. Each subject underwent a subjective evaluation of knee function and activity level, an arthrometric measurement of passive anterior tibial translation, and an isokinetic dynamometer strength test at 60 degrees/sec. A dynamic stress test was then performed to measure anterior tibial translation while simultaneously monitoring lower-extremity muscle response.Results: Maximum co-contraction of the knee musculature significantly decreased mean anterior tibial translation in both men and women (from 7.8 mm to 2.2 mm in men and from 6.5 mm to 3.1 mm in women). The corresponding percentage increase in shear stiffness of the knee was significantly greater (p = 0.003) in men (379%) than in women (212%).Conclusions: The results suggested that women have a diminished potential for muscular protection of passive structures of the knee in anterior tibial translation.Clinical Relevance: Maximal muscular protection of the anterior cruciate ligament in women may be less than that in men. This may be one factor explaining why more women than men are apt to sustain injuries to the anterior cruciate ligament. [ABSTRACT FROM AUTHOR]

Maximum isometric ankle inversion and eversion muscle strengths were measured under full unipedal weightbearing in 20 healthy young adult women. When the women wore a low-top shoe, the mean (standard deviation) maximum external eversion moments resisted with the foot in 0 degrees and 32 degrees of ankle plantar flexion were 24.1 (7.6) and 24.1 (8.1) N x m, respectively, while the corresponding values for maximum inversion moments resisted were 14.7 (6.8) and 17.4 (6.4) N x m, respectively. Both shoe height and ankle plantar flexion affected the overall inversion moment resisted by 17% (P = 0.03) at 0 degrees of ankle plantar flexion to 11.9% (P = 0.003) at 32 degrees of ankle plantar flexion. However, neither shoe height nor ankle plantar flexion significantly affected the maximum eversion moment resisted. Although eversion muscle strength of the young women averaged 39% less than the corresponding value found in young men, the sex difference was not significant when ankle strengths were normalized by body size (body weight x height). Thus, when data from healthy young men and women were averaged, eversion and inversion strengths averaged 1.6% and 2.7%, respectively, of body weight x height. [ABSTRACT FROM AUTHOR]

We examined persons after anterior cruciate ligament injury and for 1.5 years after anterior cruciate ligament reconstruction to analyze changes in anterior knee laxity, lower extremity muscle strength, endurance, and several parameters of neuromuscular function. Sixteen men and nine women (average age, 23.8 years) were evaluated preoperatively, then underwent intraarticular autogenous patellar tendon anterior cruciate ligament reconstruction by the same surgeon and were evaluated at 6, 12, and 18 months postoperatively. Muscle strength was measured isokinetically and neuromuscular function was quantified with simultaneous anterior tibial translation and surface electromyography tests. Forty subjects (26 men and 14 women; average age, 23.5 years) with no known knee abnormalities served as the control group. Subjective questionnaire results showed that by 18 months postoperatively, 20 subjects (80%) believed they had regained their preoperative levels of function. Unfortunately, muscle function in most subjects had not returned to normal. At 12 to 18 months postoperatively, when knee rehabilitation was terminated, significant deficiencies in muscle performance persisted in most patients. Interestingly, in this group of stable knees, quadriceps and hamstring muscle reaction times appeared to be the best objective indicators of subjective knee function. [ABSTRACT FROM AUTHOR]

Anterior cruciate ligament injury rates are four to eight times higher in women than in men. Because of estrogen's direct effect on collagen metabolism and behavior and because neuromuscular performance varies during the menstrual cycle, it is logical to question the menstrual cycle's effect on knee injury rates. Of 40 consecutive female athletes with acute anterior cruciate ligament injuries (less than 3 months), 28 (average age, 23 +/- 11 years) met the study criteria of regular menstrual periods and noncontact injury. Details concerning mechanism of injury, menstrual cycle, contraceptive use, and previous injury history were collected. A chi-square test was used to compute observed and expected frequencies of anterior cruciate ligament injury based on three different phases of the menstrual cycle: follicular (days 1 to 9), ovulatory (days 10 to 14), and luteal (day 15 to end of cycle). A significant statistical association was found between the stage of the menstrual cycle and the likelihood for an anterior cruciate ligament injury (P = 0.03). In particular, there were more injuries than expected in the ovulatory phase of the cycle. In contrast, significantly fewer injuries occurred in the follicular phase. These hormones may be a factor in the knee ligament injury dilemma in women. [ABSTRACT FROM AUTHOR]

We investigated the effect of quadriceps and hamstring muscle fatigue on anterior tibial translation and muscle reaction time in 10 healthy subjects. The six men and four women had an average age of 21.3 years and had no known pathologic knee conditions. Each patient underwent a knee examination, arthrometer measurements of tibial translation, subjective functional assessment, and an anterior tibial translation stress test before and after quadriceps and hamstring muscle fatiguing exercise. The recruitment order of the lower extremity muscles in response to anterior tibial translation did not change with muscle fatigue. However, the results showed an average increase of 32.5% in anterior tibial translation (range, 11.4% to 85.2%) after fatigue. Muscle responses in the gastrocnemius, hamstring, and quadriceps originating at the spinal cord and cortical level showed significant slowing and, in some cases, an absence of activity after the quadriceps and hamstring muscles were fatigued. The increases in displacement after fatigue strongly correlated (0.62 to 0.96) with a delay in cortical-level activity (intermediate and voluntary). Muscle fatigue, which appears to affect the dynamic stability of the knee, alters the neuromuscular response to anterior tibial translation. Therefore, fatigue may play an important role in the pathomechanics of knee injuries in physically demanding sports. [ABSTRACT FROM AUTHOR]

The routine use of functional knee braces in the anterior cruciate ligament-deficient, injured, or reconstructed knee, lacks biomechanical support. Although subjective reports favoring bracing are plentiful, objective proof of significant control of tibial translation is not. This in vivo study was designed to assess the effect of six popular braces on anterior tibial translation, isokinetic performance, and neuromuscular function in five chronically unstable anterior cruciate ligament-deficient knees. A knee stress test was performed on a specially designed device that allowed free tibial movement while monitoring anterior tibial translation and muscle function in the quadriceps, hamstring, and gastrocnemius muscles. Results show that braces can decrease anterior tibial translation between 28.8% and 39.1% without the stabilizing contractions of the hamstring, quadriceps, and gastrocnemius muscles. With lower extremity muscle activation and bracing, anterior tibial translation was decreased between 69.8% and 84.9%. Some improvement in spinal level muscle reaction times was seen with brace use, especially in the quadriceps muscle. Unfortunately, most braces appear to consistently slow hamstring muscle reaction times at the voluntary level. [ABSTRACT FROM AUTHOR]

The purpose of this research was to identify possible predisposing neuromuscular factors for knee injuries, particularly anterior cruciate ligament tears in female athletes by investigating anterior knee laxity, lower extremity muscle strength, endurance, muscle reaction time, and muscle recruitment order in response to anterior tibial translation. We recruited four subject groups: elite female (N = 40) and male (N = 60) athletes and sex-matched nonathletic controls (N = 40). All participants underwent a subjective evaluation of knee function, arthrometer measurement of anterior tibial translation, isokinetic dynamometer strength and endurance tests at 60 and 240 deg/sec, and anterior tibial translation stress tests. Dynamic stress testing of muscles demonstrated less anterior tibial translation in the knees of the athletes (both men and women) compared with the nonathletic controls. Female athletes and controls demonstrated more anterior tibial laxity than their male counterparts and significantly less muscle strength and endurance. Compared with the male athletes, the female athletes took significantly longer to generate maximum hamstring muscle torque during isokinetic testing. Although no significant differences were found in either spinal or cortical muscle reaction times, the muscle recruitment order in some female athletes was markedly different. The female athletes appeared to rely more on their quadriceps muscles in response to anterior tibial translation; the three other test groups relied more on their hamstring muscles for initial knee stabilization. [ABSTRACT FROM AUTHOR]

Weight training is an integral part of most athletic conditioning programs; yet, the effect of these programs on neuromuscular function remains unclear. To examine the neuromuscular effects of training and conditioning at the knee joint, 32 volunteers (16 men and 16 women; average age, 25.4 years) were placed into one of four groups: isokinetic, isotonic, agility, or control. Each group trained 3 days per week for 6 weeks. The knee function of all participants was evaluated just before and after the 6-week training period. The agility-trained group significantly improved the spinal reflex times of the lateral and medial quadriceps muscles in response to anterior tibial translation. The cortical response time of the agility group also significantly improved in the gastrocnemius, medial hamstring, and the lateral quadriceps muscles. Interestingly, the cortical response time of the medial hamstring and the medial quadriceps muscles in the isokinetic group slowed significantly, by 39.1 and 32.4 msec, respectively, after 6 weeks of training. Isotonic and isokinetic strength training of the lower extremities do not appear to improve muscle reaction time to anterior tibial translation, whereas agility exercises potentially improve this parameter. [ABSTRACT FROM AUTHOR]

Knee injuries are painful and disabling and can result in lifelong dysfunction. A comprehensive knee examination is essential if you're to identify the cause of knee pain and appropriately guide treatment decisions. [ABSTRACT FROM AUTHOR]

We measured the maximal isometric eversion moment developed under full weightbearing in 20 healthy adult men (age 24.4 +/- 3.4 years; mean +/- SD) with their ankles in 15 degrees of inversion. Tests were performed at both 0 degrees and 32 degrees of ankle plantar flexion in low- and in three-quarter-top shoes with and without adhesive athletic tape or one of three proprietary ankle orthoses. At 0 degrees of ankle plantar flexion, the mean maximal voluntary resistance of the unprotected ankle to an inversion moment was 50 +/- 8 N-m; this increased by an average of 12% (or 6 N-m) when the subject wore a three-quarter-top basketball shoe. The maximal voluntary resistances to inversion moments developed with the ankles further protected by athletic tape or any of three orthoses were not significantly different. Biomechanical calculations suggest that at 15 degrees of inversion the fully active ankle evertor muscles isometrically developed a moment up to six times larger than that developed when an athlete wears a three-quarter-top shoe alone and more than three times larger than that developed passively when the athlete has tape or an orthosis worn inside a three-quarter-top shoe. We conclude that fully activated and strong ankle evertor muscles are the best protection for a near-maximally inverted ankle at footstrike. [ABSTRACT FROM AUTHOR]

To determine if the height of a basketball shoe alters the maximal inversion and eversion moment that can be actively resisted by the ankle in the frontal plane, we tested 20 healthy, young adult men with no recent ankle injuries. Subjects underwent unipedal functional ankle strength testing under weightbearing conditions at 0 degrees, 16 degrees, and 32 degrees of ankle plantar flexion using a specially designed testing apparatus. Testing was performed with the subject wearing either a low- or a three quartertop basketball shoe. Shoe height did not significantly affect an individual's ability to actively resist an eversion moment at any angle of ankle plantar flexion. However, tests at 0 degrees of ankle plantar flexion demonstrated that the three quarter-top basketball shoe we tested significantly increased the maximal resistance to an inversion moment by 29.4%. At 16 degrees of ankle plantar flexion, inversion resistance was also significantly improved by 20.4%. These results show that athletic shoe height can significantly increase the active resistance to an inversion moment in moderate ankle plantar flexion. The findings apply to a neutral foot position in the frontal plane, an orientation equivalent to the early phase of a potential ankle sprain. [ABSTRACT FROM AUTHOR]

Of 353 arthroscopic peripheral meniscal repairs performed using the 'outside to inside' suturing technique with rasp preparation of the tear region, 74 repairs (50 medial and 24 lateral) were assessed by second-look arthroscopy and are the basis of this report. Results were graded as either healed, incompletely healed, or failed; these findings were correlated with clinical symptoms and associated ACL deficiency. Overall, asymptomatic healing occurred in 84%, with 65% healed and 19% incompletely healed. The failure rate was 16%. All failures were symptomatic while all healed and incompletely healed menisci were asymptomatic. Failure was associated with ACL deficiency in all cases. No failures occurred in either an ACL uninjured knee or an ACL reconstructed knee. Failure was also associated with tear location in the posterior horn of the medial meniscus. Eleven of 12 failures (92%) involved posterior medial meniscal tears with only 1 failure located posterolaterally. Visual evidence of healing required a 4 month time interval. [ABSTRACT FROM AUTHOR]

Objective: To review 16 years of NCAA injury surveillance data for women's volleyball and to identify potential areas for injury prevention initiatives. Background: Participation in NCAA women's volleyball has increased greatly over the past 16 years. As with all sports, women participating in volleyball assume an inherent risk of injury each time they practice or participate in a game. In order for clinicians to better understand the risks associated with volleyball, it is critical to gather data that illustrates injury rates and patterns among volleyball athletes. Furthermore, with knowledge of injury mechanisms and risk factors comes the ability to initiate prevention strategies to minimize future injury. Main Results: Over the past 16 years, the rate of injury in a game situation was slightly higher than in practice (4.58 versus 4.10 game injuries per 1000 athlete-exposures, rate ratio = 1.1, 95% confidence interval = -1.0, 1.2, P < .01). A total of 2216 injuries from more than 50000 games and 4725 injuries from more than 90 000 practices were reported. The lower extremity accounted for more than 55% of all game and practice injuries, with ankle ligament sprains representing 44.1% of game injuries and 29.4% of practice injuries. Approximately 20% of all game injuries involved the upper extremity. The majority of injuries during a game situation occurred while athletes were in one of the front 3 positions. A player landing on another player and contact with the floor each accounted for 21% of game injuries. Recommendations: Ankle injuries appear to be the most common injuries in women's volleyball. Future preventive efforts should focus on preventing first-time ankle sprains and acute traumatic knee injuries, as well as reducing the risk of ankle sprain recurrence. [ABSTRACT FROM AUTHOR]

Context: Knee joint effusion and quadriceps strength and activation deficits are common consequences of anterior cruciate ligament (ACL) injury and reconstruction. The presence of an effusion may initiate or worsen the quadriceps dysfunction present after ACL trauma. In simulated effusion studies, evidence indicates an inverse relationship between effusion size and quadriceps dysfunction. While this relationship was not found in patients after ACL injury, prior research was limited by a subjective clinical assessment of effusion grade., Objective: The purpose of this study was to determine if the size of the knee joint effusion, measured via ultrasound, after ACL injury and reconstruction influences quadriceps strength and activation., Design: Descriptive Laboratory Study., Setting: Research Laboratory., Patients or Other Participants: 41 individuals (23 females, age=21.8±7.5years, height =171.7±7.9cm, 15 mass =72.3±14.2kg), with an ACL injury reported for 2 sessions [one before 16 reconstruction and one ∽16 weeks after ACL reconstruction]., Main Outcome Measure: Three ultrasound images of the suprapatellar pouch and three trials of quadriceps strength and activation using the interpolated twitch technique were gathered from the ACL knee. Effusion cross-sectional area was measured using ImageJ, averaged and inputted into linear regression models to predict muscle strength and interpolated twitch activation. Analyses were considered significant at p≤0.05., Results: No relationship was found between effusion size and strength (R2 = 0.086) or activation (R2=0.056) after ACL injury (p>0.05). After reconstruction, however, there was a small negative relationship between effusion size 24 and activation (R2=0.122; Standardized β=-0.349; p=0.025), while no relationship was found for effusion size and strength (R2=0.000; p≤0.05)., Conclusions: The size of the effusion after ACL injury does not influence strength or activation. However, after ACL reconstruction, effusion size does have a small influence on quadriceps activation, with a larger effusion being related to lower activation. Prior research using simulated effusions appear to overestimate the effects of effusion on quadriceps function.

Background: Young patients are 6 times more likely than adults to have a primary anterior cruciate ligament (ACL) graft failure. Biological factors (ie, tunnel osteolysis) may account for up to a third of these failures. Previous evaluations of patient ACL explants indicated significant bone loss within the entheseal regions. However, it remains unknown if the degree of bone loss within the ACL insertion regions, wherein ACL grafts are fixated, exceeds that of the femoral and tibial condylar bone., Hypothesis: Bone loss in the mineralized matrices of the femoral and tibial ACL entheses is distinct from that clinically reported across the whole knee after injury., Study Design: Controlled laboratory study., Methods: We developed a clinically relevant in vivo mouse ACL injury model to cross-sectionally track the morphological and physiological postinjury changes within the ACL, femoral and tibial entheses, synovial joint space, and load-bearing epiphyseal cortical and trabecular bone components of the knee joint. Right ACLs of 10-week-old C57BL/6J female mice (N = 75) were injured in vivo with the contralateral ACLs serving as controls. Mice were euthanized at 1, 3, 7, 14, or 28 days after injury (n = 12/cohort). Downstream analyses included volumetric cortical and trabecular bone analyses and histopathologic assessments of the knee joint after injury. Gait analyses across all time points were also performed (n = 15 mice)., Results: The majority of the ACL injuries in mice were partial tears. The femoral and tibial cortical bone volumes were 39% and 32% lower, respectively, at 28 days after injury than those of the uninjured contralateral knees ( P < .01). Trabecular bone measures demonstrated little difference between injured and control knees after injury. Across all bone measures, bone loss was similar between the injured knee condyles and ACL entheses. There was also significant inflammatory activity within the knee after injury. By 7 days after injury, synovitis and fibrosis were sigificantly elevated in the injured knee compared with the controls ( P < .01), which corresponded with significantly higher osteoclast activity in bone at this time point compared with the controls. This inflammatory response signficantly persisted throughout the duration of the study ( P < .01). The hindlimb gait after injury deviated from normal, but mice habitually loaded their injured knee throughout the study., Conclusion: Bone loss was acute and persisted for 4 weeks after injury in mice. However, the authors' hypothesis was not confirmed, as bone quality was not significantly lower in the entheses compared with the condylar bone regions after injury. With relatively normal hindlimb loading but a significant physiological response after injury, bone loss in this model may be driven by inflammation., Clinical Relevance: There is persistent bone resorption and fibrotic tissue development after injury that is not resolved. Inflammatory and catabolic activity may have a significant role in the postinjury decline of bone quality in the knee.

Background: It is not known mechanistically whether a steeper lateral posterior tibial slope (LTS) leads to an increase in anterior tibial translation (ATT) as well as internal tibial rotation (ITR) during a given jump landing., Hypothesis: A steeper LTS will result in increased ATT and ITR during simulated jump landings when applying knee compression, flexion, and internal tibial torque of increasing severity., Study Design: Descriptive laboratory study., Methods: Seven pairs of cadaveric knees were harvested from young male adult donors (mean ± SD; age, 25.71 ± 5.53 years; weight, 71.51 ± 4.81 kg). The LTS of each knee was measured by a blinded observer from 3-T magnetic resonance images. Two sets of 25 impact trials of ∼700 N (1× body weight [BW] ±10%) followed by 2 sets of 25 trials of 1400 N (2× BW ±10%) were applied to a randomly selected knee of each pair. Similarly, on the contralateral knee, 2 sets of 25 impact trials of ∼1800 N (2.5× BW ±10%) followed by 2 sets of 25 trials of ∼2100 N (3× BW ±10%) were applied. Three-dimensional knee kinematics, including ATT and ITR, were measured at 400 Hz using optoelectronic motion capture. Two-factor linear mixed effect models were used to determine the relationship of LTS to ATT and ITR as impact loading increased., Results: As LTS increased, so did ATT and ITR during increasingly severe landings. LTS had an increasing effect on ATT (coefficient, 0.50; 95% CI, 0.29-0.71) relative to impact force (coefficient, 0.52; 95% CI, 0.50-0.53). ITR was proportional to LTS (coefficient, 1.36; 95% CI, 0.80-1.93) under increasing impact force (coefficient, 0.49; 95% CI, 0.47-0.52). For steeper LTS, the increase in ITR was proportionally greater than the increase in ATT., Conclusion: In male knee specimens, a steeper LTS significantly increased ATT and ITR during jump landings., Clinical Relevance: Increases in ITR and ATT during jump landings lead to increased strain on the anterior cruciate ligament and are therefore associated with greater risk of ligament failure., Competing Interests: One or more of the authors has declared the following potential conflict of interest or source of funding: Funding was received from the National Institutes of Health (grant R01 AR054821 to J.A.A-M. and E.M.W.). E.M.W. is a paid editor for Sports Health: A Multidisciplinary Approach. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto., (© The Author(s) 2023.)

Background: Anterior cruciate ligament (ACL) tears are a high-frequency injury requiring a lengthy recovery in professional American football players. Concomitant pathology associated with ACL tears as identified on magnetic resonance imaging (MRI) is not well understood in these athletes., Purpose: To describe the MRI findings of concomitant injuries associated with ACL tears among athletes in the National Football League (NFL)., Study Design: Cross-sectional study; Level of evidence, 3., Methods: Of 314 ACL injuries in NFL athletes from 2015 through 2019, 191 complete MRI scans from the time of primary ACL injury were identified and reviewed by 2 fellowship-trained musculoskeletal radiologists. Data were collected on ACL tear type and location, as well as presence and location of bone bruises, meniscal tears, articular cartilage pathology, and concomitant ligament pathology. Mechanism data from video review were linked with imaging data to assess association between injury mechanism (contact vs noncontact) and presence of concomitant pathology., Results: Bone bruises were evident in 94.8% of ACL tears in this cohort, most often in the lateral tibial plateau (81%). Meniscal, additional ligamentous, and/or cartilage injury was present in 89% of these knees. Meniscal tears were present in 70% of knees, lateral (59%) more than medial (41%). Additional ligamentous injury was present in 71% of all MRI scans, more often a grade 1/2 sprain (67%) rather than a grade 3 tear (33%), and most often involving the medial collateral ligament (MCL) (57%) and least often the posterior cruciate ligament (10%). Chondral damage was evident in 49% of all MRI scans, with ≥1 full-thickness defect in 25% of all MRI scans, most often lateral. Most (79%) ACL tears did not involve direct contact to the injured lower extremity. Direct contact injuries (21%) were more likely to have a concomitant MCL tear and/or medial patellofemoral ligament injury and less likely to have a medial meniscal tear., Conclusion: ACL tears were rarely isolated injuries in this cohort of professional American football athletes. Bone bruises were almost always present, and additional meniscal, ligamentous, and chondral injuries were also common. MRI findings varied by injury mechanism., Competing Interests: One or more of the authors has declared the following potential conflict of interest or source of funding: R.H.B. has received education payments from Elite Orthopedics. J.C.B. has received consulting fees from Alnylam Pharmaceutical. M.M.H. and C.D.M. are full-time employees of IQVIA, which is in a paid research consultancy with the National Football League. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto. Ethical approval for this study was obtained from Mount Sinai School of Medicine (reference No. STUDY-17-NFL16-CR001)., (© The Author(s) 2023.)

Background: Overuse ligament and tendon injuries are prevalent among recreational and competitive adolescent athletes. In vitro studies of the ligament and tendon suggest that mechanical overuse musculoskeletal injuries begin with collagen triple-helix unraveling, leading to collagen laxity and matrix damage. However, there are little in vivo data concerning this mechanism or the physiomechanical response to collagen disruption, particularly regarding the anterior cruciate ligament (ACL)., Purpose: To develop and validate a novel in vivo animal model for investigating the physiomechanical response to ACL collagen matrix damage accumulation and propagation in the ACL midsubstance, fibrocartilaginous entheses, and subchondral bone., Study Design: Controlled laboratory study., Methods: C57BL/6J adolescent inbred mice underwent 3 moderate to strenuous ACL fatigue loading sessions with a 72-hour recovery between sessions. Before each session, randomly selected subsets of mice (n = 12) were euthanized for quantifying collagen matrix damage (percent collagen unraveling) and ACL mechanics (strength and stiffness). This enabled the quasi-longitudinal assessment of collagen matrix damage accrual and whole tissue mechanical property changes across fatigue sessions. Additionally, all cyclic loading data were quantified to evaluate changes in knee mechanics (stiffness and hysteresis) across fatigue sessions., Results: Moderate to strenuous fatigue loading across 3 sessions led to a 24% weaker ( P = .07) and 35% less stiff ( P < .01) ACL compared with nonloaded controls. The unraveled collagen densities within the fatigued ACL and entheseal matrices after the second and third sessions were 38% ( P < .01) and 15% ( P = .02) higher compared with the nonloaded controls., Conclusion: This study confirmed the hypothesis that in vivo ACL collagen matrix damage increases with tissue fatigue sessions, adversely impacting ACL mechanical properties. Moreover, the in vivo ACL findings were consistent with in vitro overloading research in humans., Clinical Relevance: The outcomes from this study support the use of this model for investigating ACL overuse injuries.

Approximately 300,000 anterior cruciate ligament (ACL) tears occur annually in the United States, half of which lead to the onset of knee osteoarthritis within 10 years of injury. Repetitive loading is known to result in fatigue damage of both ligament and tendon in the form of collagen unravelling, which can lead to structural failure. However, the relationship between tissue's structural, compositional, and mechanical changes are poorly understood. Herein we show that repetitive submaximal loading of cadaver knees causes an increase in co-localised induction of collagen unravelling and tissue compliance, especially in regions of greater mineralisation at the ACL femoral enthesis. Upon 100 cycles of 4× bodyweight knee loading, the ACL exhibited greater unravelled collagen in highly mineralized regions across varying levels of stiffness domains as compared to unloaded controls. A decrease in the total area of the most rigid domain, and an increase in the total area of the most compliant domain was also found. The results highlight fatigue-driven changes in both protein structure and mechanics in the more mineralized regions of the ACL enthesis, a known site of clinical ACL failure. The results provide a starting point for designing studies to limit ligament overuse injury., (© 2023. The Author(s).)

Introduction: Recent evidence has emerged suggesting that a non-contact anterior cruciate ligament (ACL) tear can result from repetitive submaximal loading of the ligament. In other words, when the intensity of ACL-straining athletic activities is increased too rapidly, microdamage can accumulate in the ligament beyond the rate at which it can be repaired, thereby leading to material fatigue in the ligament and its eventual failure. The objective of this survey-based exploratory study was to retrospectively determine whether the levels of various athletic activities performed by ACL-injured patients significantly changed during the 6 months before injury. Methods: Forty-eight ACL-injured patients completed a survey to characterize their participation in various activities (weightlifting, sport-specific drills, running, jumping, cutting, pivoting/twisting, and decelerating) at three timepoints (1 week, 3 months, 6 months) prior to ACL injury. Activity scores, which summarized the frequency and intensity of each activity, were calculated for each patient at each time interval. A series of linear mixed-effects regression models was used to test whether there was a significant change in levels of the various activities in the 6-month period leading up to ACL injury. Results: Patients who sustained a non-contact ACL injury markedly increased their sport-specific drills activity levels in the time leading up to injury ( p = 0.098), while those patients who sustained a contact ACL injury exhibited no change in this activity during the same time period ( p = 0.829). Levels of running, jumping, cutting, pivoting/twisting, and decelerating increased for non-contact ACL-injured patients but decreased for contact ACL-injured patients, though not significantly ( p values > 0.10). Weightlifting activity significantly decreased leading up to injury among contact ACL-injured patients ( p = 0.002). Discussion: We conclude that levels of ACL-straining athletic activities or maneuvers in non-contact ACL-injured patients markedly increased in the 6 months leading up to their injury, providing evidence that changing levels of certain activities or maneuvers may play a role in ACL injury risk. This warrants further investigation of the hypothesis that too rapid an increase in activities or maneuvers known to place large loads on the ACL can cause microdamage to accumulate in the ligament, thereby leading to failure., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Grodman, Beaulieu, Ashton-Miller and Wojtys.)

This review identifies the three-dimensional knee loads that have the highest risk of injuring the anterior cruciate ligament (ACL) in the athlete. It is the combination of the muscular resistance to a large knee flexion moment, an external reaction force generating knee compression, an internal tibial torque, and a knee abduction moment during a single-leg athletic manoeuvre such as landing from a jump, abruptly changing direction, or rapidly decelerating that results in the greatest ACL loads. While there is consensus that an anterior tibial shear force is the primary ACL loading mechanism, controversy exists regarding the secondary order of importance of transverse-plane and frontal-plane loading in ACL injury scenarios. Large knee compression forces combined with a posteriorly and inferiorly sloped tibial plateau, especially the lateral plateau-an important ACL injury risk factor-causes anterior tibial translation and internal tibial rotation, which increases ACL loading. Furthermore, while the ACL can fail under a single supramaximal loading cycle, recent evidence shows that it can also fail following repeated submaximal loading cycles due to microdamage accumulating in the ligament with each cycle. This challenges the existing dogma that non-contact ACL injuries are predominantly due to a single manoeuvre that catastrophically overloads the ACL.

Purpose: Quadriceps weakness is common after anterior cruciate ligament (ACL) reconstruction, resulting in prolonged disability and increased risk for reinjury and osteoarthritis. Functional resistance training (FRT) combines resistance training with task-specific training and may prove beneficial in restoring quadriceps strength. The primary purpose of this study was to determine if a walking-specific FRT program (e.g., resisted walking) improves knee strength in individuals after ACL reconstruction., Methods: Thirty participants were randomized into one of three groups: 1) FRT with a customized knee BRACE applied to the ACL leg, 2) FRT with elastic BAND tethered to the ankle of the ACL leg, or 3) a TARGET MATCH condition where no resistance was externally applied. Participants in all groups received training while walking on a treadmill 2-3 times per week for 8 wk. Isometric knee extension and flexion strength were measured before the start of the intervention, after the intervention (POST), and 8 wk after intervention completion (POST-2)., Results: The BRACE group had greater knee extensor strength compared with the TARGET MATCH group at POST and POST-2 ( P < 0.05). The BRACE group had greater knee flexor strength than the TARGET MATCH group at POST and POST-2 ( P < 0.05) and the BAND group at POST ( P < 0.05)., Conclusions: FRT applied via a customized knee brace results in improvements in knee extensor and flexor strength after ACL reconstruction. FRT is a beneficial adjuvant to ACL rehabilitation and leads to better strength compared with standard of care., (Copyright © 2022 by the American College of Sports Medicine.)

Purpose: Certain types of repetitive sub-maximal knee loading cause microfatigue damage in the human anterior cruciate ligament (ACL) that can accumulate to produce macroscopic tissue failure. However, monitoring the progression of that ACL microfatigue damage as a function of loading cycles has not been reported. To explore the fatigue process, a confocal laser endomicroscope (CLEM) was employed to capture sub-micron resolution fluorescence images of the tissue in situ. The goal of this study was to quantify the in situ changes in ACL autofluorescence (AF) signal intensity and collagen microstructure as a function of the number of loading cycles., Methods: Three paired and four single cadaveric knees were subjected to a repeated 4 times bodyweight landing maneuver known to strain the ACL. The paired knees were used to compare the development of ACL microfatigue damage on the loaded knee after 100 consecutive loading cycles, relative to the contralateral unloaded control knee, through second harmonic generation (SHG) and AF imaging using confocal microscopy (CM). The four single knees were used for monitoring progressive ACL microfatigue damage development by AF imaging using CLEM., Results: The loaded knees from each pair exhibited a statistically significant increase in AF signal intensity and decrease in SHG signal intensity as compared to the contralateral control knees. Additionally, the anisotropy of the collagen fibers in the loaded knees increased as indicated by the reduced coherency coefficient. Two out of the four single knee ACLs failed during fatigue loading, and they exhibited an order of magnitude higher increase in autofluorescence intensity per loading cycle as compared to the intact knees. Of the three regions of the ACL - proximal, midsubstance and distal - the proximal region of ACL fibers exhibited the highest AF intensity change and anisotropy of fibers., Conclusions: CLEM can capture changes in ACL AF and collagen microstructures in situ during and after microfatigue damage development. Results suggest a large increase in AF may occur in the final few cycles immediately prior to or at failure, representing a greater plastic deformation of the tissue. This reinforces the argument that existing microfatigue damage can accumulate to induce bulk mechanical failure in ACL injuries. The variation in fiber organization changes in the ACL regions with application of load is consistent with the known differences in loading distribution at the ACL femoral enthesis., (© 2022. The Author(s).)

Despite poor graft integration among some patients that undergo an anterior cruciate ligament (ACL) reconstruction, there has been little consideration of the bone quality into which the ACL femoral tunnel is drilled and the graft is placed. Bone mineral density of the knee decreases following ACL injury. However, trabecular and cortical architecture differences between injured and non-injured femoral ACL entheses have not been reported. We hypothesize that injured femoral ACL entheses will show significantly less cortical and trabecular mass compared with non-injured controls. Femoral ACL enthesis explants from 54 female patients (13-25 years) were collected during ACL reconstructive surgery. Control explants (n = 12) were collected from seven donors (18-36 years). Injured (I) femoral explants differed from those of non-injured (NI) controls with significantly less (p ≤ 0.001) cortical volumetric bone mineral density (vBMD) (NI: 736.1-867.6 mg/cm 3 ; I: 451.2-891.9 mg/cm 3 ), relative bone volume (BV/TV) (NI: 0.674-0.867; I: 0.401-0.792) and porosity (Ct.Po) (NI: 0.133-0.326; I: 0.209-0.600). Injured explants showed significantly less trabecular vBMD (p = 0.013) but not trabecular BV/TV (p = 0.314), thickness (p = 0.412), or separation (p = 0.828). We found significantly less cortical bone within injured femoral entheses compared to NI controls. Lower cortical and trabecular bone mass within patient femoral ACL entheses may help explain poor ACL graft osseointegration outcomes in the young and may be a contributor to the osteolytic phenomenon that often occurs within the graft tunnel following ACL reconstruction., (© 2021 Orthopaedic Research Society. Published by Wiley Periodicals LLC.)

Background: Anterior cruciate ligament (ACL) injury rates continue to rise among youth involved in recreational and competitive athletics, requiring a better understanding of how the knee structurally and mechanically responds to activity during musculoskeletal growth. Little is understood about how anatomical risk factors for ACL injury (e.g., small ACL size, narrow intercondylar notch, and steep posterior tibial slope) develop and respond to increased physical activity throughout growth. We hypothesized that the ACL-complex of mice engaged in moderate to strenuous physical activity (i.e., endurance running) throughout late adolescence and young adulthood would positively functionally adapt to repetitive load perturbations., Methods: Female C57BL6/J mice (8 weeks of age) were either provided free access to a standard cage wheel with added resistance (n = 18) or normal cage activity (n = 18), for a duration of 4 weeks. Daily distance ran, weekly body and food weights, and pre- and post-study body composition measures were recorded. At study completion, muscle weights, three-dimensional knee morphology, ACL cross-sectional area, and ACL mechanical properties of runners and nonrunners were quantified. Statistical comparisons between runners and nonrunners were assessed using a two-way analysis of variance and a Tukey multiple comparisons test, with body weight included as a covariate., Results: Runners had larger quadriceps (p = 0.02) and gastrocnemius (p = 0.05) muscles, but smaller hamstring (p = 0.05) muscles, compared to nonrunners. Though there was no significant difference in ACL size (p = 0.24), it was 13% stronger in runners (p = 0.03). Additionally, both the posterior medial and lateral tibial slopes were 1.2 to 2.2 degrees flatter than those of nonrunners (p < 0.01)., Conclusions: Positive functional adaptations of the knee joint to moderate to strenuous exercise in inbred mice offers hope that that some anatomical risk factors for ACL injury may be reduced through habitual physical activity. However, confirmation that a similar response to loading occurs in humans is needed., (© 2021. The Author(s).)

Background: The lateral femoral condyle index (LFCI)-a recently developed measure of the sphericity of the lateral femoral condyle-was reported to be a risk factor for anterior cruciate ligament (ACL) injury. However, issues have been raised regarding how the index was measured and regarding the patient group and the knee in which it was measured., Purpose: To investigate the association between the LFCI and the risk of sustaining a primary, noncontact ACL injury, and to examine whether this association was moderated by the posterior-inferior-directed slope of the lateral tibial plateau., Study Design: Cross-sectional study; Level of evidence, 3., Methods: A secondary analysis was conducted of deidentified magnetic resonance images of the uninjured knees of 86 athletes with ACL injury and the corresponding knees of 86 control athletes, matched for sports team, sex, and age. From those images, we measured the LFCI and the posterior-inferior-directed slope of the middle region articular cartilage surface of the tibial plateau's lateral compartment. Conditional logistic regressions were performed to determine whether the LFCI was significantly associated with ACL injury risk and whether the lateral tibial compartment middle cartilage slope moderated this association. Data were analyzed for female and male participants separately as well as for both groups combined., Results: The LFCI was not found to be significantly associated with experiencing a primary, noncontact ACL injury for all analyses. The lateral tibial slope measure was not found to moderate the association between the LFCI and ACL injury. A conditional logistic regression analysis using the LFCI data of the injured knees, instead of the uninjured knees, of the participants with ACL injury revealed that the LFCI was significantly associated with ACL injury., Conclusion: In this population of athletically active female and male participants, the LFCI was not found to be a risk factor for noncontact ACL injury, regardless of the geometric features of the lateral tibial slope.

Background: The factors associated with anterior cruciate ligament (ACL) injury mechanism in professional American football players are not well-understood., Hypothesis: It was hypothesized that football-related and player-specific factors, such as position and body mass index (BMI), are associated with ACL injury mechanism in these athletes., Study Design: Descriptive epidemiology study., Methods: Videos of ACL tears occurring in National Football League (NFL) games over 6 consecutive seasons from 2014 to 2019 were reviewed by 2 orthopaedic surgeons who specialize in sports medicine. For each injury, the role of contact ( direct contact [contact to the injured knee/lower extremity], indirect contact [contact not involving the injured knee/lower extremity], or no contact ) as well as playing situation and lower extremity position were recorded. Additional player characteristics, timing of injury, and surface information were obtained from NFL game-day and injury database statistics., Results: Of the 140 ACL tears, a minority occurred via direct contact to the injured lower extremity (30%), although this varied by position. Just over two-thirds (70%) of ACL tears in offensive linemen occurred via direct contact to the injured lower extremity, while wide receivers had no direct contact ACL tears. Elevated BMI was associated with a greater likelihood of ACL tears occurring via direct contact (53% in players with BMI ≥35 kg/m 2 vs 24% in players with BMI <35 kg/m 2 ; P = <.01). Rookies had the lowest percentage of direct contact ACL tears (18%; P = .22). ACL tears that occurred during the middle 8 weeks of the regular season resulted more often from direct contact (38%; P = .06). ACL tears that occurred in the third quarter were the most likely to occur via direct contact (44%), while those that occurred in the fourth quarter were the least likely to occur via direct contact (13%; P < .01)., Conclusion: Although most NFL players sustained ACL tears via a noncontact mechanism (ie, through indirect or no contact), players with an elevated BMI, especially on the offensive line, were more likely to injure their ACL through direct contact. Position-dependent variance in injury mechanism may help guide injury prevention efforts in these athletes., Competing Interests: One or more of the authors has declared the following potential conflict of interest or source of funding: R.H.B. has received education payments from Arthrex, Breg, and Smith & Nephew; consulting fees from Sanofi; and nonconsulting fees from Arthrex. E.M.W. has received payments from the National Football League (NFL) and NIAMS/KAI, has served on the scientific advisory board for Miach, is a co-founder of STEL, and is the editor-in-chief of Sports Health. C.D.M., K.H., and M.M.H. are full-time employees of IQVIA, which is engaged in a paid consultancy with the NFL. B.D.O. has received consulting fees from ConMed, Miach, Mitek, Musculoskeletal Transplant Foundation, and Vericel; royalties from ConMed; and honoraria from Vericel; hasstock/stock options in Vivorte; and is a paid associate editor for The American Journal of Sports Medicine. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto., (© The Author(s) 2021.)