Knee recurvatum in gait: a study of associated knee biomechanics.

OBJECTIVES: To quantitatively evaluate peak knee extensor torque values imparted to the posterior knee structures during gait in patients with knee recurvatum compared with torque values observed in control subjects, and to assess the predictive value of the degree of knee hyperextension and other clinical factors in estimating peak knee extensor torque.
DESIGN: A retrospective analysis of clinical and quantitative gait data obtained from patients and control subjects. SETTINGS: A gait laboratory.
SUBJECTS: Forty-one consecutive patients with neurologically based impairments presenting with knee hyperextension during gait (52 limbs) and 46 able-bodied control subjects. MAIN OUTCOME MEASURE: Peak knee extensor torque during the stance period of the gait cycle.
RESULTS: Although overall, the patient average peak extensor torque was significantly greater (p < .001) than the control subjects' average value, knee extensor torques were within or below a +/- 1 standard deviation range for control subjects in 25% (13) of limbs tested. Peak knee hyperextension angle was a poor predictor of peak extensor torque; there was statistical significance (coefficient .061,p < .001) only for hyperextension angles of < or = 4 degrees. Multiple regression incorporating hyperextension angle and other clinical variables to predict peak knee extensor torque resulted in an adjusted r2 of .53.
CONCLUSION: Patients with knee recurvatum have variable peak extensor torque values associated with their knee hyperextension. Knowledge of knee hyperextension angle and other clinical factors are only partially useful in predicting a patient's peak knee extensor torque imparted to the posterior knee structures during walking.