OBJECTIVE: To investigate whether a combined hip and knee muscle strengthening program is superior to a knee strengthening program for people after lateral patellar dislocation (LPD). DESIGN: Single-blind, superiority, randomized controlled trial with 48 weeks follow-up. SETTING: Physiotherapy out-patient clinic. PARTICIPANTS: Forty individuals aged 16 or older, with a history of non-traumatic LPD were randomized to a knee-based strengthening (KBSG) or quadriceps and hip strengthening exercise (HQSG) program (n = 40). Inclusion criteria included a positive apprehension sign, pain on palpation along the medial retinaculum, and J sign. Exclusion criteria included restricted range of motion (< 90 degree knee flexion), and traumatic or postsurgical LPD. INTERVENTIONS: Concealed randomization was performed using random permuted blocks of size 4. Individuals received their corresponding exercise program according to randomization and group allocation: knee-based strengthening (n = 20) or combined hip and quadriceps strengthening (n = 20) twice weekly for 8 weeks over 16 appointments. MAIN OUTCOME MEASURES: Primary outcome was the Lysholm Knee Score. Secondary outcomes included Numerical Pain Ratings Scale (NPRS) at rest and during effort, Norwich Patellar Instability Score (NPIS), Kujala Anterior Knee Pain Scale (AKPS), Lower Extremity Functional Scale (LEFS), 4 domains of the WHOQOL-Bref, and recurrence rate. Patient-reported outcome measures were assessed from the baseline to 48 weeks. Assessments were performed by a physiotherapist who was blinded to the group allocation. Data were analyzed by using a repeated-measures ANOVA model with Tukey's post hoc test after an intention-to-treat principle. RESULTS: At the primary time-point of 8 weeks, there were no substantial between-group differences in the Lysholm Knee Score: mean difference -6.8 (95% CI -14.3 to 3.7); NPIS: mean difference 23.5 (95% CI 5.6 to 41.3); AKPS: mean difference -1.54 (95% CI -8.6 to 5.6), NPRS at rest and during effort (mean difference 0.32 (95% CI -0.37 to 1); and mean difference 0.68 (95% CI -0.9 to 1.86); LEFS mean difference -1.08 (95% CI -5.9 to 2.4), WHOQOL-Bref domains (physical health: mean difference -0.12, (95% CI -1.26 to 1.02); psychological: mean difference -0.32 (95% CI -2.04 to 1.4); social relations: mean difference -0.7 (95% CI -2.2 to 0.82); environment: mean difference 0.44 (95% CI -1 to 1.9), and recurrence rate (p = 0.69). CONCLUSION: This study indicates that combined hip and knee muscle strengthening is not superior to knee-based strengthening for LPD treatment. The limitations stemming from the underpowered nature of the trial must be acknowledged, concerning the potential oversight of moderate intervention effects.

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