Assessment of Knee Flexor Muscles Strength in Patients With Patellar Instability

The study enrolled 33 patients with confirmed recurrent patellar dislocation, including 6 patients with bilateral involvement. The study group consisted of 20 girls and 13 boys with average age at the time of the study 16.2 years (range: 8 to 17 years, SD 2.7). For the purpose of the study, a control group of 18 healthy subjects (12 girls and 6 boys) aged on the average 15.7 years (range:13 to 17 years, SD 1.5), was recruited.

The following study inclusion criteria were applied: recurrent patellar dislocation, correctly completed testing protocol, age under 18 years at the time of testing. Subjects with osteochondral fracture and those with a history of the knee surgery were excluded.

Each patient underwent an isokinetic examination on Biodex System 3 (Biodex Multi-Joint System - Pro, Biodex Medical Systems, Inc. New York, USA). In the study group, both side hamstring muscle were evaluated at the velocities of 60 and180 deg/s for the following parameters: peak torque (PT), torque in 30 degree of the knee flexion (T 30 deg.), angle of peak torque (APT) and peak torque hamstring to quadriceps ratio (H/Q ratio).

Isokinetic measurements were made by a trained, experienced physiotherapist. After a proper warm-up and instruction, the test performed 10 full repetitions, the best result was recorded. The results of the peak torque (PT) of both test and control limbs were then compared with the normative data for age and gender available in the literature. In addition, we compared the peak torque (PT), torque in 30 degrees of the knee flexion (T 30 deg.), angle of peak torque (APT) and peak torque hamstring to quadriceps ratio (H/Q ratio) of involved and uninvolved knee flexor strength in the study group. Depending on the data distribution, the nonparametric Wilcoxon's test or the parametric t-test for the related data was applied. Statistical significance was assumed for p<0.05. The study was approved by our Institutional Review Board. Informed consent was obtained and the rights of subjects were protected.

Inclusion criteria

• recurrent patellar dislocation,
• correctly completed testing protocol,
• age under 18 years at the time of testing

Exclusion criteria

• osteochondral fracture
• those with a history of the knee surgery