Muscle function after mid-shaft femoral shortening. A prospective study with a two-year follow-up.

We performed isokinetic knee testing to assess thigh muscle function in ten patients (12 legs) before and after mid-shaft femoral shortening averaging 46 mm (27 to 70). Tests were at angular velocities of 60 degrees/sec and 180 degrees/sec, and were performed preoperatively and after 3, 6, 12 and 24 months. Isokinetic tests at two years showed a significant reduction in muscle function in both quadriceps and hamstrings, but recovery of function was significantly better for the hamstrings. There was a linear relationship with correlation of r2 = 0.31 to 0.86 between loss of muscle force at two years and the magnitude of shortening. Long-term loss of muscle force should be expected after a mid-shaft shortening of the femur of more than 10%.