Alteration in Energy Efficiency Resulting from Hip Arthritis

Coronal hip motion is one of the early aspects of function to reduce as a result of arthritic changes in the hip joint. Limited abduction or the presence of an adduction contracture leads to a limp. Normal gait requires 15 degrees of hip abduction and an extra degree for each mm of shortening. If this prerequisite range is missing the stance phase control of centre of mass has to either be undertaken by excessive truncal motion or the deficiency of the hip abductors substituted by means of a stick held in the opposite hand. Tida demonstrated the alterations in the centre of mass displacements resulting from pathological gait.

Sagittal plane abnormalities also result in altered energy consumption with a diminution in the power generated at the hip in terms of loading response eccentric extensor contraction and preswing hip flexion. Waters recorded a 53% increase in oxygen cost in patients who had undergone hip arthrodesis compared with normals.

Significant levels of hip flexion contracture will lead to knee flexion once the ability of the lumbar spine to hide te deformity with increased lordosis, particularly in terminal stance. Increased mid stance knee flexion will lead to a need for stance phase quadriceps activity where there should only be soleus activity controlling the advance of the knee joint centr relative to the ground reaction vector.

Transverse plane stiffness often with an external rotation contracture will lead to a minor restriction in step length as a result of limitation in pelvic rotation as a method of step length extension. The effect is however small and the coronal plane restrictions are the major component with the sagittal plane deficiencies following shortly behind.

References

Iida H, Yamamuro T. Kinetic analysis of the center of gravity of the human body in normal and pathological gaits. J Biomec 1987;20(10):987-95.

Waters RL, Barnes G, Husserl T, Silver L, Liss R. Comparable energy expenditure after arthrodesis of the hip and ankle. J Bone Joint Surg Am 1988;70(7):1032-7.