Paul W. Kline

Impaired Quadriceps Rate of Torque Development and Knee Mechanics After Anterior Cruciate Ligament Reconstruction With Patellar Tendon Autograft

Background: Rate of torque development (RTD) measures the ability of a muscle to produce torque quickly. Decreased quadriceps RTD may impair performance of sporting tasks after surgery. Currently, little is known about variations in quadriceps RTD between anterior cruciate ligament (ACL)–reconstructed and noninjured limbs. Purpose: To determine the differences in RTD of the quadriceps, the rate and timing of knee extensor moment (KEM) development, and knee flexion excursion during running after ACL reconstruction with patellar tendon autograft. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study involved 21 patients (11 female) 6 months after ACL reconstruction with patellar tendon autograft (median [IQR]: age, 18 [16-20] years; mass, 68.18 [61.34-75] kg; height, 1.74 [1.66-1.78] m). Patients performed four 5-second maximal voluntary isometric strength trials of both limbs on an isokinetic dynamometer. RTD was calculated as the mean slope of the torque-time curve between 20% and 80% of total time to peak torque. Then, patients underwent 3-dimensional motion analysis while running on an instrumented treadmill at a self-selected running speed (mean ± SD, 2.68 ± 0.28 m/s). The rate of knee extensor moment (RKEM) was calculated as the mean slope of the moment curve between 10% and 30% of stance phase. Between-limb comparisons were determined with a paired t test for peak KEM, RKEM, knee flexion excursion during 10% to 30% of stance, and time to generate KEM. Results: In the reconstructed limb, deficits in the peak rate of quadriceps torque development compared with the noninjured limb existed both isometrically (RTD, 257.56 vs 569.11 Nm/s; P < .001) and dynamically (RKEM, 16.47 vs 22.38 Nm/kg·m·s; P < .001). The reconstructed limb also generated a KEM later in the stance phase compared with the noninjured limb (11.37% vs 9.61% stance; P < .001) and underwent less knee flexion excursion (15.5° vs 19.8°; P < .001). Conclusion: After ACL reconstruction with patellar tendon autograft, patients have lower RTD and RKEM in the reconstructed limb. Deviations in RTD and the timing of the KEM can change the way the knee is loaded and can potentially increase injury risk and future development of posttraumatic osteoarthritis. Rehabilitation should consider exercises designed to improve RTD and prepare the limb for the demands of sport performance.

Clinical Predictors of Knee Mechanics at Return to Sport after ACL Reconstruction.

PURPOSE Despite significant rehabilitation, many athletes experience protracted weakness and faulty mechanics after anterior cruciate ligament reconstruction (ACLR). Clinical tests performed early in rehabilitation, which predict knee mechanics at return-to-sport, are virtually unknown and critically needed to guide clinical decision making. The purpose of this study is to determine if quadriceps strength, Y balance anterior (YB-A) reach distance, and single-leg step-down test performance (SLSD) conducted 3 months post-ACLR are predictive of knee flexion excursion (KFLEX) and knee extensor moment (KEM) during running 6 months post-ACLR. METHODS Thirty (16 females) subjects were collected 3 and 6 months post-ACLR. Age, 21.3 ± 7.6 yr; mass, 69.85 ± 11.4 kg; height, 1.73 ± 0.09 m. At 3 months post-ACLR, subjects performed isometric quadriceps strength testing, YB-A, and SLSD assessments. At 6 months post-ACLR, subjects underwent three-dimensional motion analysis while running on an instrumented treadmill. Pearson correlation coefficients and stepwise multiple regression were used to assess the relationships of 3-month and 6-month variables. RESULTS Quadriceps strength (r = 0.493, P < 0.01), YB-A (r = 0.394, P = 0.03), and SLSD (r = 0.648, P < 0.01) were significantly correlated to KFLEX. Quadriceps strength (0.505, P < 0.01) and SLSD (.541, P < 0.01) were significantly correlated with KEM, whereas YB-A (.276, P = 0.06) was not. SLSD and quadriceps strength were predictive of KEM (adj R², 0.36; P = 0.001) whereas only SLSD was predictive of KFLEX (adj R², 0.40; P < 0.001). CONCLUSIONS After ACLR, better performance in SLSD and quadriceps strength 3 months postsurgery is predictive of improved sagittal plane knee mechanics during running 6 months postsurgery.

Kinesiophobia is Strongly Associated with Altered Loading after an ACL Reconstruction: Implications for Re-injury Risk

Objectives: The effect of kinesiophobia (fear of movement) following an anterior cruciate ligament (ACL) reconstruction has recently received greater attention. Elevated kinesiophobia as measured on the Tampa Scale of Kinesiophobia (TSK) has been previously found to be associated with poorer outcomes. However, the effect of kinesiophobia in ACL reconstructed patients on high impact and challenging tasks associated with re injury risk such as jumping has not been investigated. Establishing the relationship between kinesiophobia and jump landing mechanics could result in the development of specific treatments to reduce fear of movement and improve jump landing mechanics after ACL reconstruction, resulting in a diminished re-injury risk. Therefore, the purpose of this study is to define the relationship between landing mechanics (axial loading rates and impact forces) with the TSK score in patients 6 months after ACL reconstruction. Methods: Twenty subjects, 6 months post ACL reconstruction, who had completed post-operative physical therapy, and were cleared by their physician to begin return to sport drills participated in the study. Subjects completed an instrumented drop vertical landing assessment with the ground reaction forces recorded while the subjects performed a drop vertical jump task off a 30.48 cm high box. Three trials were taken and the data were analyzed using custom Labview code and Visual 3D software during the period of time from foot contact until initial impact peak. The average loading rate was defined as the linear portion of the vertical ground reaction curve between 20-80% of foot contact to initial impact peak. Subjects also completed the TSK questionnaire. Associations between loading rate and vertical impact peak to the TSK scale were made with Pearson correlation coefficients with significant relationships defined as p<0.05. Results: 20 subjects (11 female, 9 male, Ages 19 ± 3.3 yrs, H 1.73 ± 0.11 m, M 69.1 ± 12.2 kg) with bone patellar bone autografts completed the study. The mean loading rate was 56.96 ± 18.6 %bodyweight/sec, initial impact peak 0.88 ± 0.24 %bodyweight, and TSK value was 33.1 ± 6.8. There was a significant negative association between poorer responses on the TSK scale and initial impact peak forces (r=-0.624, p=0.003) but not average loading rate (r=-0.243, p=-0.302) (Figure 1). Conclusion: We found greater kinesiophobia to be associated with a lower weight-bearing in the ACL reconstructed limb. Potentially, subjects who are afraid of loading their reconstructed limb transfer weight to the uninjured limb, increasing the demand placed upon that limb. The greater forces that the contra lateral limb must absorb may in part be related to the elevated risk of injury associated with the non injured limb. The lack of relationship to loading rate suggests kinesiophobia is more related to the magnitude of the load and not the subject’s ability to control the load. These results suggest that in patients with elevated kinesiophobia, cognitive training may be needed before initiating movement retraining or other exercises to improve landing mechanics. Additional prospective studies are needed to assess if these relationships improve over time and determine the optimal time to intervene to reduce subsequent injury risk.

Early Objective Clinical Testing Predicts Jump Landing Mechanics Following an ACL Reconstruction: Impact for the Clinician and Return to Play Testing

Objectives: Currently, objective functional assessments are performed at the time of return to play following an anterior cruciate ligament (ACL) reconstruction. While informative, by that time the majority of organized rehabilitation has been completed, leaving little time for clinicians to address remaining impairments. Further, few objective tests have been compared to faulty movement mechanics. Identifying objective clinical tests that can be administered early during recovery from an ACL reconstruction which predict long term joint mechanics would provide sufficient time to address the underlying deficits prior to return to play testing. Thus, the purpose of this study was to determine if objective clinical tests (60 second single leg step down test and quadriceps strength) administered 3 months after surgery predicted jump landing mechanics of the knee (knee extension moment, average loading rate, vertical impact peak) at 6 months following an ACL reconstruction. Methods: 29 subjects completed objective clinical testing at 3 months post operatively that included the 60 second single leg step down test and an assessment of isometric knee strength. To perform the 60 second single leg step down test, subjects performed a single leg squat by touching their heel on a scale with less than 10% of their bodyweight as many times as they could for 60 seconds while standing on an 8-inch box. Isometric knee extension strength was assessed with a hand held dynamometer secured to a table. The subject performed 4 isometric maximum isometric contractions for 5 seconds. At 6 months, performed a instrumented drop vertical landing jumping. Three trials were taken and the data were analyzed using custom Labview and Visual 3D code. The average loading rate was defined as the linear portion of the vertical ground reaction curve between 20-80% of foot contact to initial impact peak. Associations between quadriceps strength and the timed single leg step down test to knee extensor moment, average loading rate, and vertical impact peak were then made with Pearson correlation coefficients. Results: 29 subjects (15 male and 14 female, Ages 20.2 ± 4.7 yrs, 24 bone patellar bone vs 5 hamstring autografts, H 1.75 ± 0.12 m, M 72.2 ± 12.1 kg) completed the study. The mean quadriceps strength was 23.3 ± 10.2 N, timed single leg step down test 20 ± 11 step downs, knee extensor moment 1.32 ± 0.54 Nm/kg, loading rate was 64.5 ± 23.6 %bodyweight/sec, and vertical impact peak 0.97 ± 0.36 %bodyweight. We found significant positive associations between 3 month quadriceps strength and knee extensor moment (r=0.442, p=0.016), average vertical loading rate (r=0.426, p=0.021), and vertical impact peak (r=0.619, p=0.000) (Figure 1). We found no significant associations between 3 month single leg step down performance and landing mechanics. Conclusion: We show the ability of a early, quick, clinically-feasible method of assessing quadriceps strength to predict joint mechanics during a drop vertical jump 6 months after ACL reconstruction. This assessment can be used to screen individuals at much earlier time point who need additional focused treatment to improve their outcomes prior to return to play testing. Further, they can give the orthopedic surgeon additional data to educate the patient and family about the need to not return to higher level activities too early and reinforces the need to be compliant with rehabilitation in order to maximize results at the time individuals begin return to sport drills.

Hip and trunk muscle dysfunction: implications for anterior cruciate ligament injury prevention

Due to the short and long-term consequences of anterior cruciate ligament (ACL) injury, significant efforts have been devoted to identifying injury risk factors and develop screening and prevention tools. A growing body of evidence has identified hip and trunk muscle strength and functional performance as modifiable risk factors in ACL injury. Screening tools have been developed to capture hip and trunk function in order to identify athletes with elevated injury risk. Furthermore, ACL injury prevention programs include activities to improve hip and trunk strength and motor control during dynamic tasks. Because of the considerable focus and the growing body of evidence, the role of the hip and trunk in ACL injury etiology, screening tools, and prevention programs requires review and synthesis for improved implementation in clinical practice. Thus, the purpose of this review is to highlight the role of the hip and trunk in primary ACL injury, identify screening tests that may reveal deficits of the hip and trunk, and discuss the efficacy of prevention programs in correcting hip and trunk risk factors and ACL injury risk.