Hewett, Timothy E.

ABSTRACTThe mechanism underlying non‐contact anterior cruciate ligament (ACL) injury is multi‐factorial and still an object of debate. Computational models, in combination with in vivo and cadaveric studies, can provide valuable insight into the contribution of the different factors involved. The goal of this study was to validate four knee finite element models (two males and two females) to kinematic and strain data collected in vitro with an impact‐driven simulator and use them to assess how secondary external knee loads (knee abduction moment [KAM], anterior shear force, and internal rotation torque [ITR]) affect tibiofemoral contact forces and ACL force during impact. Four subject‐specific knee models were developed from specimen computed tomography and magnetic resonance imaging. Patellofemoral and tibiofemoral ligament properties were calibrated to match experimentally measured kinematics and ligament strain. Average root mean square errors and correlations between experimental and model‐predicted knee kinematics were below 1.5 mm and 2°, and above 0.75, respectively. Similar errors and correlations were obtained for ACL strain (< 2% and > 0.9). Model‐predicted ACL forces were highly correlated with the anterior component of the tibiofemoral contact force on the lateral plateau occurring during impact (r = 0.99), which was increased by larger KAM and ITR through the posterior tibial slope and a larger contact force on the lateral side. This study provides a better understanding of the mechanism through which secondary external knee loads increase ACL injury risk during landing. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1730–1742, 2019

Background: Avulsion fractures involving the tibial eminence are considered equivalent in etiology to anterior cruciate ligament tears, however there is limited data comparing outcomes of adolescent patients undergoing surgical fixation of tibial eminence fractures to those undergoing anterior cruciate ligament (ACL) reconstruction. Purpose: The purpose of this study was to compare clinical outcomes, subsequent ACL injury rates, and activity levels between adolescent patients who underwent tibial eminence fracture fixation to patients with mid-substance ACL tears who required acute ligament reconstruction. Methods: This study included a group of patients with tibial eminence fractures treated with surgical fixation matched to a group of similar patients with ACL tears treated with reconstruction between the years of 2001 and 2015. Data regarding initial injury, surgical intervention, ACL/ACL graft injury rates, and physical examination findings were recorded. Clinical and functional outcomes were obtained using physical examination, IKDC subjective scores, Lysholm scores, and Tegner Activity levels. Results: Sixty patients with a mean follow-up of 57.7 (24-206) months were included. 20 patients (11 M:9 F) who underwent surgical fixation for tibial eminence fractures (TEF) with a mean age of 11.9 (7-15) years were matched to a group of 40 patients (23 M:17 F) who underwent ACL reconstruction for ACL tears with a mean age of 12.5 (8-15) years. The TEF group demonstrated significantly lower postoperative IKDC (TEF group: 94.0, ACL group: 97.2 (p=0.04)) and Lysholm scores (TEF group: 92.4, ACL group: 96.9 (p=0.02)). The TEF group returned to sport 121 days sooner (p<0.01), but there was no difference in postoperative Tegner scores (TEF group: 7.3, ACL group: 7.6 (p=0.16)). The TEF group demonstrated increased postoperative anterior laxity (p=0.02) and a higher rate of postoperative arthrofibrosis (p=0.04). There was no difference in subsequent ACL injury (p=0.41). Conclusion: Patients with tibial eminence fractures demonstrated lower mean clinical outcome scores compared to patients with ACL tears at minimum 2-year follow up. Additionally, they experienced more postoperative anterior laxity and had a higher rate of postoperative arthrofibrosis. There was no difference in subsequent ACL injury rate. The TEF group returned to sport sooner than the ACL group, but the postoperative activity level was similar.

Purpose: The goal of this study was to evaluate patient and surgical factors predictive of excellent functional and isokinetic test results 6-months following anterior cruciate ligament (ACL) reconstruction in a group of pediatric patients with open physes. Methods: We retrospectively reviewed the records of all patients 14 years of age or younger that underwent ACL reconstruction from 2000 to 2015. An excellent 6-month outcome was defined as greater than 85% in isokinetic strength and greater than 90% in functional tests when compared to the non-operative extremity. We then utilized univariate and multivariate statistical models to identify patient and/or surgical factors associated with excellent 6-month outcomes. Results: Eighty-six patients (46 male, 42 female) with open physes on preoperative radiographs were included in the study, with a mean age of 13.6 (range, 8.4-14.9), body mass index (BMI) of 22.1 (range, 15.6-36.0), Tegner activity score of 8.8 (6.0-9.0). Thirty-four patients (40%) met the criteria for the excellent 6-month group, which left 52 (60%) in the delayed 6-month group. In univariate analysis, no single preoperative factor correlated with excellent 6-month outcome. The two groups were statistically similar in terms of age, BMI, time to surgery, preoperative arc of motion, presence of concomitant meniscal tear, cartilage damage, graft size, use of a nerve block or tourniquet, operative time, and tourniquet time. Use of a nerve block trended towards delayed outcomes (p = 0.051). Conclusion: Children undergoing ACL reconstruction only have a 40% chance of achieving an excellent rehabilitation result at 6 months. We found no statistically significant patient or surgical characteristics that could predict this outcome. Utilizing a nerve block is a factor which will need to be further evaluated. Significance: Studies in the adult population have identified preoperative patient and surgical factors associated with excellent 6-month isokinetic and functional test results. This pediatric cohort did not find similar results as many of these children were young, healthy and fit. However, the variability of the outcome casts doubts on applying adult rehabilitation protocols to children.

Introduction: It is unknown whether functional and isokinetic testing at 6 months following ACL reconstruction in patients with open-physes correlates with longer term outcomes. The purpose of this study was to compare subsequent ACL rupture risk, knee function, and activity level in patients with open-physes who had excellent 6-month testing to those who did not. Methods: Between the years of 2000 and 2015, 86 patients with open-physes underwent ACL reconstruction and had functional and isokinetic testing performed at 6-months post-operatively. Thirty-four (40%) tested in the excellent range in all categories of both functional and isokinetic testing and were labeled the excellent group. The remaining 52 (60%) patients were labeled the delayed testing group. Data regarding patient, injury, and surgical characteristics were retrospectively collected. The rate of second ACL injury as well as clinical outcome scores were collected postoperatively. Results: Graft rupture rate was 23.4% (n = 8) in the excellent group and 15.4% (n = 8) in the delayed group (p = 0.51). In the excellent group, 20.5% (n = 7) had a contralateral ACL tear versus 11.5% (n = 6) in the delayed group (p = 0.40). Five patients in the excellent group and 4 patients in the delayed group sustained both graft failure and contralateral ACL tear. The overall prevalence of second ACL injury was 29% in the excellent group and 23% in the delayed group. The delayed group returned to sport at an average of 8.8 months whereas the excellent group returned at an average of 6.6 months (p < 0.01). At mean follow up of 3.59 years, the excellent group had a higher Tegner activity level (8.9 versus 8.3) than the delayed group (p < 0.02). Conclusion: Pediatric patients with open-physes who had excellent isokinetic strength and functional testing 6-months postoperatively returned to sport sooner than those who did not. There was no statistical difference in either graft failure or contralateral ACL disruption between these groups. However, both groups had unacceptably high rates of second ACL injury (29% for the excellent group and 23% for the delayed group). Significance: Excellent 6 month return of strength and function was not protective of subsequent ACL disruption, the rate of which remains dismal within this pediatric population. Development of more sensitive functional measures for children could help to change these poor outcomes and guide clinicians when to allow return to sport.

Background: Achilles tendon tears are potentially career-ending injuries for professional athletes. For players in the National Football League (NFL), return requires not only surgery and extensive rehabilitation but also the ability to compete in a market with limited positions that annually introduces new recruits. Purpose/Hypothesis: We authors sought to evaluate factors related to return to play (RTP) and changes in performance following a primary Achilles tear. Our hypothesis was that “skilled” position players and those drafted in later rounds would return at a lower rate as compared with “unskilled” position players and higher draft-round players. Study Design: Case-control study; Level of evidence, 3. Methods: From a previously established database, 80 NFL players were identified as having primary Achilles tendon tears between the 2009 and 2014 seasons. RTP was defined as playing in a regular season or postseason game following injury. Probability of RTP was modeled as a function of time after injury in Kaplan-Meier analysis with demographic variables assessed via generalized linear models. Twelve players (15%) experienced a subsequent Achilles tendon tear during or after the study period and were included in the overall RTP rate but were excluded from performance analyses owing to the confounding effects of an ipsilateral retear or contralateral tear. Results: The overall RTP rate was 61.3%. Age, number of prior seasons, position type, or draft round status did not significantly affect RTP when evaluated with Kaplan-Meier analysis. In the season before their injury, players who did RTP played in a significantly greater number of regular season games (13.7) compared with players who did not RTP (8.71) ( P = .011). Players who did not RTP exhibited a significant decrease in performance in the season preceding injury (12.7 regular season games played 2 seasons preinjury vs 8.71 regular season games played 1 season prior preinjury;, P = .019). Players who returned did not display a significant change in the number of games played or started in seasons following injury when >1 season after return was evaluated. Conclusion: Rate of RTP following primary Achilles tendon tears may be lower than previously published. However, for those able to return, performance only in the season immediately following injury appears to be affected; players return to preinjury levels if given the opportunity to play >1 season after injury.

Background: Lower psychological readiness to return to sport has been reported for younger patients (≤20 years) who go on to a second anterior cruciate ligament (ACL) injury. However, changes in psychological readiness and specific psychological responses associated with second injury have not been identified. Purpose/Hypothesis: To identify changes in psychological readiness over time associated with a second ACL injury. It was hypothesized that younger patients who suffered a second injury would have smaller changes in psychological readiness to return to sport when compared with those who did not have a second injury. Study Design: Case-control study; Level of evidence, 2. Methods: Patients ≤20 years old at the time of surgery who had a primary ACL reconstruction procedure between June 2014 and June 2016 were recruited for this study. The short version of the Anterior Cruciate Ligament Return to Sport After Injury (ACL-RSI) scale was completed by patients before their ACL reconstruction and repeated at 12 months after surgery to assess psychological readiness to return to sport. The primary outcome of interest was the relationship between the change in psychological readiness and second ACL injuries. Results: Among 115 young patients who returned to sport after ACL reconstruction, 21 (18%) experienced a second ACL injury. Injured patients did not show improvement in their ACL-RSI score between the preoperative assessment and 12-month time point (58.5 vs 60.8 points, P = .60) and had a significantly smaller change when compared with noninjured patients (9.2 vs 24.9 points, P = .01). When compared with the noninjured group, the injured group reported they were more nervous about playing sport, less confident in playing sport without concern for the knee, more frustrated with having to consider the knee with respect to sport, and more fearful of reinjuring the knee by playing sport ( P≤ .05). Conclusion: Injured patients exhibited less improvement in psychological readiness at a group level and reported different psychological characteristics with regard to return to sport at 12 months after ACL reconstruction as monitored by the ACL-RSI scale.

Background: Psychological responses after anterior cruciate ligament (ACL) injury and ACL reconstruction (ACLR) have been identified as predictors of return to sport but have not been investigated in relation to further injury. Purpose/Hypothesis: To determine whether psychological readiness to return to sport is associated with second ACL injury. It was hypothesized a priori that at both preoperative and 12-month postoperative time points, patients who sustained a second ACL injury would have lower psychological readiness than patients who did not have a second injury. Study Design: Cohort study; Level of evidence, 2. Methods: Patients who had a primary ACLR procedure between June 2014 and June 2016 completed the ACL–Return to Sport after Injury (ACL-RSI) (short version) scale before their ACLR and repeated the scale at 12 months after surgery to assess psychological readiness to return to sport. Patients were followed for a minimum of 2 years (range, 2-4 years) after surgery to determine further injury. The primary outcome was the relationship between ACL-RSI scores and the incidence of second ACL injury. Results: In 329 patients who returned to sport after ACLR, 52 (16%) sustained a second ACL injury. No difference in psychological readiness was observed at the preoperative time point, but patients who sustained a second injury trended toward lower psychological readiness at 12 months compared with noninjured patients (60.9 vs 67.2 points; P = .11). Younger (≤20 years) patients with injury had significantly lower psychological readiness to return to sport than young noninjured patients (60.8 vs 71.5 points; P = .02), but no difference was found in older patients (60.9 vs 64.6 points; P = .58). In younger patients, receiver operating characteristic curve analysis revealed a cutoff score of 76.7 points with 90% sensitivity to identify younger patients who sustained a second ACL injury. Conclusion: Younger patients with lower psychological readiness are at higher risk for a second ACL injury after return to sport.

Objective: Athletes who return to sport after anterior cruciate ligament reconstruction (ACLR) demonstrate persistent biomechanical and neuromuscular deficits of the knee. There is limited evidence on what effect a neuromuscular training (NMT) program has on knee biomechanics in a cohort of athletes with ACLR. Therefore, the primary aim of this study was to quantify the effect of an NMT program on knee biomechanics in a cohort of ACLR athletes. Second, the post-training knee biomechanics were compared between the cohort of ACLR and control athletes. Design: Cohort study. Setting: Controlled laboratory setting. Participants: Eighteen athletes with ACLR and 10 control athletes. Interventions: Neuromuscular training. Main Outcome Measures: Knee kinematics and kinetics during a double-limb jump-landing task. Results: There were no significant interactions (P > 0.05) observed for the athletes with ACLR. However, there was a significant main effect of biomechanics testing session (P < 0.05) for knee flexion angle and moments; athletes with ACLR demonstrated greater knee flexion angle and lower knee flexion moment during the post-training biomechanics testing session. Post-training comparison between the ACLR and control athletes demonstrated no significant interactions (P > 0.05) between the groups. There was a significant main effect of group (P < 0.05) for knee frontal angle, as athletes with ACLR landed with greater knee adduction than the control athletes. Conclusions: Significant improvements in knee sagittal plane biomechanical measures were observed after the NMT program by the athletes with ACLR. In addition, post-training comparison of the ACLR and control groups demonstrates comparable knee biomechanics.

Purpose To describe the clinical history of a series of primary, lateral patellar dislocations and determine long‐term predictors of recurrent instability while accounting for patients undergoing early operative management. Methods A large geographic database of more than 500,000 patients was used to identify patients who sustained a first‐time lateral patellar dislocation between 1990 and 2010. Charts were individually reviewed to document demographics, radiographic measures including tibial tubercle to trochlear groove distance (TT‐TG) and patellar length (PL), recurrent episodes of instability, and patellar stabilization surgery. A risk score that accounted for early surgical management was calculated using Fine and Gray competing risk regression, and its ability to stratify patients was examined using cumulative incidence curves. Results Eighty‐one patients (mean age 19.9 ± 9.4 years, 38 male, 43 female) were identified and followed for a mean of 10.1 years (range 4.1‐20.2). Thirty‐eight patients (46.9%) experienced an episode of recurrent instability and 30 (37.0%) underwent patellar stabilization surgery, including 7 who did so before recurrent dislocation. A multivariate, statistically derived scoring system, the Recurrent Instability of the Patella Score (RIP Score), that employed age, skeletal maturity, trochlear dysplasia, and TT‐TG/PL ratio to predict recurrent instability while accounting for patients managed surgically, was generated. The resulting RIP score stratified patients into low‐, intermediate‐, and high‐risk categories, with 0.0%, 30.6%, and 79.2% 10‐year recurrent instability rates, respectively ( P = .000004), and an area under the curve of 0.875 ( P = .00002). Conclusions Patients who sustain a first‐time, lateral patellar dislocation can be readily classified into low‐, intermediate‐, and high‐risk categories employing the RIP score based on age, skeletal maturity, trochlear dysplasia, and TT‐TG/PL ratio. This long‐term risk stratification holds significant potential clinical utility for determination of patients who are at high risk for recurrent instability after primary patellar dislocation. Level of Evidence Level III, retrospective comparative study.