The Journal of Bone and Joint Surgery, Vol 77, Issue 2 247-250, Copyright © 1995 by Journal of Bone and Joint Surgery, Inc
The effect of lengthening of the femur on the extensors of the knee. An electromyographic study
U Kaljumae, A Martson, T Haviko and O Hanninen
Department of Orthopaedics, University of Tartu Hospital, Estonia.
Surface electromyography of the quadriceps femoris muscle was performed in
seven patients in order to determine the effect of extensive lengthening of
the femur on the muscles that extend the knee. Electromyograms were made
during sustained (thirty-second) isometric extension of the knee, at an
angle of flexion of the knee of 30 degrees, while a load equal to 15 per
cent of body weight was applied to the leg just proximal to the ankle. The
average circumference of the thigh was smaller, the motor-unit recruitment
of the muscles was slower, and the fatigability was greater on the involved
side compared with the uninvolved side. The vastus medialis exhibited
greater fatigability and slower motor-unit recruitment than the rectus
femoris or the vastus lateralis. The atrophy index of the involved muscles
correlated well with the muscle fatigability, the preoperative limb-length
discrepancy, the percentage of lengthening, and the motor-unit recruitment.
Analysis also revealed a correlation between muscle fatigability and the
percentage of lengthening of the bone and between muscle fatigability and
the preoperative limb-length discrepancy. The percentage of lengthening
correlated with the extent of motor-unit recruitment. The results of this
study suggest that the amount of damage to neuromuscular tissue varies
according to the extent of the lengthening of the femur. Of all of the knee
extensors, the vastus medialis was affected the most.
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