STUDY DESIGN: Cross-sectional. OBJECTIVE: To investigate predictors of increased frontal plane knee projection angle (FPKPA) in athletes. BACKGROUND: The underlying mechanisms that lead to increased FPKPA are likely multifactorial and depend on how the musculoskeletal system adapts to the possible interactions between its distal and proximal segments. Bivariate and linear analyses traditionally employed to analyze the occurrence of increased FPKPA are not sufficiently robust to capture complex relationships among predictors. The investigation of nonlinear interactions among biomechanical factors is necessary to further our understanding of the interdependence of lower-limb segments and resultant dynamic knee alignment. METHODS: The FPKPA was assessed in 101 athletes during a single-leg squat and in 72 athletes at the moment of landing from a jump. The investigated predictors were sex, hip abductor isometric torque, passive range of motion (ROM) of hip internal rotation (IR), and shank-forefoot alignment. Classification and regression trees were used to investigate nonlinear interactions among predictors and their influence on the occurrence of increased FPKPA. RESULTS: During single-leg squatting, the occurrence of high FPKPA was predicted by the interaction between hip abductor isometric torque and passive hip IR ROM. At the moment of landing, the shank-forefoot alignment, abductor isometric torque, and passive hip IR ROM were predictors of high FPKPA. In addition, the classification and regression trees established cutoff points that could be used in clinical practice to identify athletes who are at potential risk for excessive FPKPA. CONCLUSION: The models captured nonlinear interactions between hip abductor isometric torque, passive hip IR ROM, and shank-forefoot alignment.

J Orthop Sports Phys Ther 2012;42(12):996-1004, Epub 18 September 2012. doi:10.2519/jospt.2012.4041

KEY WORDS: anterior cruciate ligament, CART, dynamic knee alignment, hip strength, patellofemoral joint

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To investigate the impact of quadriceps femoris (QF) muscle strength asymmetry at the time of return to sport on self-reported function and functional performance of individuals following anterior cruciate ligament reconstruction (ACLR). BACKGROUND: Evidence-based QF strength guidelines for return-to-sport decision making are lacking. Objective guidelines necessitate understanding the impact of QF strength deficits at the time of return to sport on function and performance. METHODS: Fifty-five individuals (mean age, 17.3 years) who were cleared for return to sport following primary ACLR (ACLR group) and 35 uninjured individuals (mean age, 17.0 years) in a control group participated in the study. QF strength (maximum voluntary isometric contraction) was assessed, and the quadriceps index (QI) was calculated [(involved strength/uninvolved strength) × 100%]. The ACLR group was further subdivided into 2 groups, based on the QI: high quadriceps (QI of 90% or greater) and low quadriceps (QI of less than 85%). The International Knee Documentation Committee Subjective Knee Evaluation Form score was used to assess self-reported function, and hop tests were used to assess functional performance. Multivariate analysis of variance and hierarchical regression analyses were performed. RESULTS: The individuals in the ACLR group were weaker, reported worse function, and performed worse on hop tests compared to those in the control group (P<.05). The low-quadriceps group demonstrated worse performance on the hop tests compared to the high-quadriceps group and the control group (P≤.016). Hop test performance did not differ between the high-quadriceps and control groups (P≥.14). QF strength predicted performance on the hop tests beyond graft type, presence of meniscus injury, knee pain, and knee symptoms. CONCLUSION: At the time of return to sport, individuals post-ACLR who had weaker QF (QI of less than 85%) demonstrated decreased function, whereas those with minimal QF strength deficits (QI of 90% or greater) demonstrated functional performance similar to uninjured individuals. QF strength deficits predicted hop test performance beyond the influences of graft type, presence of meniscus injury, knee pain, and knee symptoms.

J Orthop Sports Phys Ther 2012;42(9):750-759, Epub 19 July 2012. doi:10.2519/jospt.2012.4194

KEY WORDS: ACL, ACL reconstruction, function, hop test, knee, performance, weakness

Over the past few months we have been afforded a unique opportunity to evaluate injury rate data prior to, during, and following the historical aberration created by the recent National Football League (NFL) Lockout. During this period (March 11th to July 25th, 2011), professional football players underwent an uncommon offseason, without the normal access to their team’s healthcare providers, strength and conditioning professionals, and high-level coaches. With limited access to these professionals and an absence of the structured preseason preparatory conditioning normally progressed over a 14-week period between May and July, we had a unique window of opportunity to evaluate the effects of an alarmingly rapid transition from the start of training camp, which took place 2 days after the end of the Lockout, to the initiation of preseason competition. A glimpse at early data, limited to Achilles tendon injuries, is cause for concern due to an unprecedented number of Achilles tendon ruptures in training camp and the beginning of preseason.

J Orthop Sports Phys Ther 2011;41(10):702-705. doi:10.2519/jospt.2011.0107

KEY WORDS: Achilles tendon rupture, football

STUDY DESIGN: Controlled laboratory, cross-sectional, cohort design. OBJECTIVE: To determine if a sex-specific pattern of lower limb asymmetries is present during a drop vertical jump (DVJ) maneuver at the time of return to sport after anterior cruciate ligament (ACL) reconstruction. BACKGROUND: A high incidence of second ACL injury is reported after reconstruction; however, the underlying mechanisms of this injury are unclear. While asymmetrical dynamic loading patterns predictive of primary ACL injury in healthy female athletes were observed in female athletes 2 years after ACL reconstruction, it is unknown if similar asymmetries are present in male athletes after ACL reconstruction at the time of return to sport. METHODS: A total of 98 participants were included in the study, 56 of whom had unilateral ACL reconstruction (35 female, 21 male) and had been released to return to unrestricted level 1 and 2 sports, and 42 of whom were uninjured, activity-matched control participants (29 female, 13 male). Lower extremity kinetic data were analyzed during a bilateral drop vertical jump maneuver from a 31-cm box. Peak vertical ground reaction force (VGRF) was calculated during the landing phase of the drop vertical jump and normalized to body weight (BW). A 2-by-2-by-2 analysis of variance was used to determine differences between side (involved versus uninvolved), group (ACL reconstruction versus control), and sex (female versus male) for the peak VGRF. RESULTS: A significant side-by-group interaction for peak VGRF (P = .002) was observed during the landing phase of the drop vertical jump in the entire cohort. The involved limb of the ACL reconstructed group displayed significantly lower VGRF (mean ± SD, 1.77 ± 0.35 BW) than the uninvolved limb (2.2 ± 0.4 BW, P<.001) and both the preferred limb (2.0 ± 0.4 BW, P = .002) and nonpreferred limb (2.09 ± 0.42 BW, P<.001) in the control group. No effect of sex was noted. CONCLUSION: After ACL reconstruction, both male and female participants at the time of return to sport demonstrated involved limb asymmetries in peak VGRF during landing from a bipedal task. These deficits, which persist at the time of return to sport, may increase the risk of future injury and indicate that rehabilitation after ACL reconstruction may require more targeted interventions to address involved limb biomechanical deficits in athletes of both sexes prior to return to sport participation.

J Orthop Sports Phys Ther 2011;41(8):553-559. doi:10.2519/jospt.2011.3591

KEY WORDS: ACL, drop vertical jump, female, male, vertical ground reaction force

STUDY DESIGN: Case control. OBJECTIVES: To use modified NFL Combine testing methodology to test for functional deficits in athletes following anterior cruciate ligament (ACL) reconstruction following return to sport. BACKGROUND: There is a need to develop objective, performance-based, on-field assessment methods designed to identify potential lower extremity performance deficits and related impairments in this population. METHODS: Eighteen patients (mean ± SD age, 16.9 ± 2.1 years; height, 170.0 ± 8.7 cm; body mass, 71.9 ± 21.8 kg) who returned to their sport within a year following ACL reconstruction (95% CI: 7.8 to 11.9 months from surgery) participated (ACLR group). These individuals were asked to bring 1 or 2 teammates to serve as control participants, who were matched for sex, sport, and age (n = 20; mean ± SD age, 16.9 ± 1.1 years; height, 169.7 ± 8.4 cm; body mass, 70.1 ± 20.7 kg). Functional performance was tested using the broad jump, vertical jump, modified long shuttle, modified pro shuttle, modified agility T-test, timed hop, triple hop, single hop, and crossover hop tests. A 1-way multivariate analysis of variance (MANOVA) was used to evaluate group differences for dependent performance variables. RESULTS: The functional performance measurements of skills requiring bilateral involvement of both lower extremities showed no group differences between the ACLR and control groups (P>.05). An overall group difference (P = .006) was observed for the combined limb symmetry index (LSI) measures. However, the modified double-limb performance tasks (long shuttle, modified agility T-test, and pro shuttle) were not, independently, sufficiently sensitive to detect limb deficits in individuals with ACL reconstruction. Conversely, the LSI on the distance measures of the single-limb performance tasks all provided moderate to large effect sizes to differentiate between the ACLR and control groups, as the individuals who had ACL reconstruction demonstrated involved limb deficits on all measures (P<.05). Finally, the LSI for the timed hop test was not different between groups (P>.05). CONCLUSIONS: These findings indicate that, while unilateral deficits are present in individuals following ACL reconstruction, they may not be evident during bipedal performance or during modified versions of double-limb performance activities. Isolation of the involved limb with unilateral hopping tasks should be used to identify deficits in performance.

J Orthop Sports Phys Ther 2011;41(6):377-387, Epub 2 February 2011. doi:10.2519/jospt.2011.3547

KEY WORDS: anterior cruciate ligament, hop tests, knee, prevention

STUDY DESIGN: Controlled cohort repeated-measures experimental design. OBJECTIVES: To determine if a neuromuscular training program (NMTP) focused on core stability and lower extremity strength would affect performance on the star excursion balance test (SEBT). We hypothesized that NMTP would improve SEBT performance in the experimental group and there would be no side-to-side differences in either group. BACKGROUND: The SEBT is a functional screening tool that is used to assess dynamic stability, monitor rehabilitation progress, assess deficits following an injury, and identify athletes at high risk for lower extremity injury. The SEBT requires lower extremity coordination, balance, flexibility, and strength. METHODS: Twenty uninjured female soccer players (13 experimental, 7 control) participated. Players trained together as a team, so group allocation was not randomized. The SEBT was administered prior to and following 8 weeks of NMTP in the experimental group and 8 weeks of no NMTP in the control group. A 3-way mixed-model ANOVA was used to determine the effect of group (experimental versus control), training (pretraining versus posttraining), and limb (right versus left). RESULTS: After participation in a NMTP, subjects demonstrated a significant improvement in the SEBT composite score (mean ± SD) on the right limb (pretraining, 96.4% ± 11.7%; posttraining, 104.6% ± 6.1%; P = .03) and the left limb (pretraining, 96.9% ± 10.1%; posttraining, 103.4% ± 8.0%; P = .04). The control group had no change on the SEBT composite score for the right (pretraining, 95.7% ± 5.2%; posttraining, 94.4% ± 5.2%; P = .15) or the left (97.4% ± 7.2%; 93.6% ± 5.0%; P = .09) limb. Further analysis identified significant improvement for the SEBT in the posterolateral direction on both the right (P = .008) and left (P = .040) limb and the posteromedial direction of the left limb (P = .028) in the experimental group. CONCLUSION: Female soccer players demonstrated an improved performance on the SEBT after NMTP that focused on core stability and lower extremity strength. LEVEL OF EVIDENCE: Performance enhancement, level 2b-.

J Orthop Sports Phys Ther 2010;40(9):551-558, Epub 6 August 2010. doi:10.2519/jospt.2010.3325

KEY WORDS: core stability, core strengthening, injury prevention training, trunk neuromuscular control

Study Design: Controlled single-group pretest/posttest design. Objective: The purpose of this study was to determine if a 6-week neuromuscular training program designed to decrease the incidence of anterior cruciate ligament (ACL) injuries would improve single-limb postural stability in young female athletes. We hypothesized neuromuscular training would result in an improvement in postural stability, with the greatest improvement taking place in the medial-lateral direction. Background: Balance training has become a common component of programs designed to prevent ACL injury. Rehabilitation programs can improve postural stability following ACL injury and reconstruction; however, there is limited information available which quantifies improvement of postural stability following neuromuscular training designed to prevent ACL injuries in a healthy population. Methods and Measures: Forty-one healthy female high school athletes (mean age, 15.3 years; age range, 13-17 years) participated in this study. Single-limb postural stability for both lower extremities was assessed with a Biodex Stability System. The neuromuscular training program consisted of three 90-minute training sessions per week for 6 weeks. Following the completion of the training program, each subject was re-evaluated to determine change in total, anterior-posterior, and medial-lateral single-limb stability. Two-way analysis of variance models were used to determine differences between pretraining and posttraining and between limbs. Results: The subjects showed a significant improvement in single-limb total stability (P = .004) and anterior-posterior stability (P = .001), but not medial-lateral stability (P = .650) for both the right and left lower extremity following training. In addition, the subjects demonstrated significantly better total postural stability on the right side as compared to the left (P = .026). Conclusions: A 6-week neuromuscular training program designed to decrease the incidence of ACL injuries improves objective measures of total and anterior-posterior single-limb postural stability in high school female athletes.

J Orthop Sports Phys Ther. 2004;34(6):305-316. doi:10.2519/jospt.2004.1325

Key Words: anterior cruciate ligament, balance, knee, prevention, proprioception

Study Design: Controlled laboratory study. Objectives: To determine whether gender differences in electromyographic (EMG) activity of hip-stabilizing muscles are present during single-leg landing. Background: Numerous factors may explain the greater rate of anterior cruciate ligament (ACL) injuries in female athletes. However, gender differences in hip muscle activity during dynamic events have not been well characterized. Methods and Measures: Twenty-two Division I collegiate athletes (13 female, 9 male) performed drop landings from 30.5- and 45.8-cm heights. Surface EMG was used to examine relative muscle activity from 200 milliseconds prior to initial contact to 250 milliseconds postcontact. Peak and mean values for each muscle (gluteus maximus, gluteus medius, rectus femoris) in each time epoch were analyzed using 2 ×2 (group by height) analyses of variance (ANOVAs) to determine significance. Results: Females demonstrated lower gluteus maximus peak (mean ± SD, 69.5 ± 30.2 versus 98.0 ± 33.4 percent maximum voluntary contraction [%MVIC]; P = .019) and mean (mean ± SD, 37.5 ± 15.6 versus 53.9 ± 18.0 %MVIC; P = .018) muscle activation during the postcontact phase of landing than males. Furthermore, females demonstrated greater peak rectus femoris activity during the precontact phase (mean ± SD, 33.6 ± 18.5 versus 18.7 ± 8.2 %MVIC; P = .029). A positive effect of drop height on relative activity of all muscles was observed during both phases (P<.05). Conclusions: Females utilize different muscular activation patterns compared to males (ie, decreased gluteus maximus and increased rectus femoris muscle activity) during landing maneuvers. Decreased hip muscle activity and increased quadriceps activity may be important contributors to the increased susceptibility of female athletes to noncontact ACL injuries.

J Orthop Sports Phys Ther. 2005;35(5):292-299. doi:10.2519/jospt.2005.1734

Key Words: ACL, hip stability, knee

A systematic approach to the clinical history, physical, and arthroscopic examination of patellofemoral disorders will lead to improved diagnostic accuracy and clinical treatment success. We review important aspects of physical and arthroscopic examination of patellofemoral disorders. Basic and advanced physical examination techniques are presented, and their clinical significance is reviewed. Arthroscopic examination of the patellofemoral joint is used as an adjunct to physical examination to evaluate chondral lesions of the patella and femoral sulcus and to visualize patellar tracking. Techniques to assess patellar tracking and the integrity of patellar restraints and to grade chondral lesions are outlined. Utilization of these techniques will improve clinical studies on the treatment of patellofemoral disorders.

J Orthop Sports Phys Ther. 1998;28(5):277-285.

Key Words: knee pain, physical examination, extensor mechanism, malalignment

Rehabilitation following anterior cruciate ligament (ACL) reconstruction has undergone a relatively rapid and global evolution over the past 25 years. However, there is an absence of standardized, objective criteria to accurately assess an athlete’s ability to progress through the end stages of rehabilitation and safe return to sport. Return-to-sport rehabilitation, progressed by quantitatively measured functional goals, may improve the athlete’s integration back into sport participation. The purpose of this clinical commentary is to introduce an example of a criteria-driven algorithm for progression through return-to-sport rehabilitation following ACL reconstruction. Our criteria-based protocol incorporates a dynamic assessment of baseline limb strength, patient-reported outcomes, functional knee stability, bilateral limb symmetry with functional tasks, postural control, power, endurance, agility, and technique with sport-specific tasks. Although this algorithm has limitations, it serves as a foundation to expand future evidence-based evaluation and to foster critical investigation into the development of objective measures to accurately determine readiness to safely return to sport following injury.

J Orthop Sports Phys Ther. 2006; 36(6):385-402. doi:10.2519/jospt.2006.2222

Key Words: anterior cruciate ligament, knee rehabilitation, lower extremity, sport injury