Lower limb flexibility and muscle strength in Osgood-Schlatter disease

BACKGROUND: Osgood- Schlatter disease (OSD), a disorder of the knee common in 10-15 year olds, is thought to be a result of microavulsions caused by repeated traction of the patellar tendon on the tibial apophysis. We hypothesized that patients with OSD lack flexibility in the knee joints and may have an imbalance of muscle strength in the lower limbs. METHODS: 9 adolescents (7 male) aged 9-15 (x=11.8yrs) with OSD of one or both knees were matched for age, sex, height and weight with 9 adolescents with no known knee complaints or disease. Participants completed a structured interview questionnaire about type and frequency of sports participation. Quantitative static flexibility of both the hamstring and quadriceps muscles was measured. Isokinetic knee extensor and flexor muscle strength was measured at speeds of 90, 180, & 360 degrees/second was done using a Biodex III system dynamometer. Maximal concentric quadriceps muscle strength (peak torque and total work) during isokinetic movement was calculated. RESULTS: A comparison of the quadriceps and hamstring flexibility by goniometer between the OSD and control groups showed similar flexibility (x= 127.4 degrees and 129.6 degrees, respectively for quadriceps and 39.8 degrees and 41.2 degrees for hamstrings, p=ns). Subjects in the OSD group who engaged in sports more than 3 times a week (n=7) were significantly less flexible than the remainder (n=11) of the participants (mean quadriceps flexibility 141.1 degrees vs. 128 degrees, p<0.05). Isokinetic strength testing of bilateral knee extensor and flexor muscle groups was not significantly different between the OSD and control groups. However, the ratio of knee extensor strength to knee flexor muscle strength was greater in affected knees of OSD subjects than in knees of controls at all speeds. (Mean knee extension/flexion ratio in OSD subjects 73 ft. lbs./30 ft. lbs.= 2.4, in controls 78 ft. lbs/42 ft. lbs.=1.85, p<0.05). CONCLUSION: Lck of flexibility and strength imbalance of the leg muscles is associated with Osgood-Schlatter disease. While this cross-sectional study cannot determine cause and effect, training aimed at improving the flexibility and balancing the strength of the leg muscle groups in youngsters during their growth spurt may help to prevent Osgood-Schlatter disease.