Knee Extensor Mechanism Strength and Its Relationship to Patellofemoral Kinematics in Individuals With Arthrofibrosis Within 6 Months After Anterior Cruciate Ligament Reconstruction

Abstract

CONTEXT: Performance in strength and assessment of patellar tracking is important for patients with arthrofibrosis after anterior cruciate ligament (ACL) reconstruction. OBJECTIVE: The study was to examine the difference of patellofemoral kinematics between the affected and the contralateral limb and to evaluate the relationship between knee extensor strength and patellofemoral kinematics in patients with arthrofibrosis after ACL reconstruction. DESIGN: Cohort study (diagnosis); level of evidence, 3. SETTING: Laboratory. PATIENTS: A prospective cohort of 20 patients with arthrofibrosis after ACL reconstruction was recruited. INTERVENTIONS: A total of 20 patients who underwent arthroscopic reconstruction of the double-bundle ACL with a hamstring tendon autograft received standardized patellofemoral kinematics testing and knee extensor strength testing within 6 months after primary ACL reconstruction. Computed tomography and dual fluoroscopic imaging were used to evaluate in vivo patellofemoral kinematics of affected and contralateral knees during a lunge task. Knee extensor mechanism strength was measured using a handheld dynamometer. MAIN OUTCOME MEASURES: A limb symmetry index of knee strength and patellar mobility was calculated and satisfactory performance defined as ≥90%. RESULTS: There was a statistically significant decrease in the range of patellar inferior shift (P = .020; d = 0.81), flexion (P = .026; d = 0.95), lateral tilt (P = .001; d = 1.04), and lateral rotation (P < .001; d = 0.89) in the affected knee compared with the contralateral knee from 15° to 75° of knee flexion. There was a strong positive linear correlation between knee extensor strength and patellar inferior shift (r = .747; P = .008). A knee extensor strength limb symmetry index <90% was 89% sensitive and 9% specific for limited patellar inferior shift. CONCLUSIONS: Patients with arthrofibrosis after ACL reconstruction presented decreased patellar mobility in the arthrofibrotic knee compared with the contralateral knee. The strong correlation between knee extensor strength and patellar inferior shift of the arthrofibrotic knee demonstrates the importance of knee extensor strength in the diagnosis and treatment of patients with knee arthrofibrosis. The knee extensor mechanism strength has high sensitivity but low specificity in identifying a decrease in patellar inferior shift in patients with arthrofibrosis after ACL reconstruction.