A computer assessment of the effect of hindfoot alignment on mechanical axis deviation

Lower limb malalignment is a common cause of disability that increases risk of osteoarthritis (OA). Treatment of OA may require an osteotomy or arthroplasty, which mandate accurate evaluation of mechanical loading on the limbs to achieve optimal alignment and minimal implant wear. Surgical planning uses a conventional method of mechanical axis deviation (MADC) measured from the center of the femoral head to the center of the ankle. This method fails to account for hindfoot deformity distal to the ankle. We used a computer model to compare MADC with the ground mechanical axis deviation (MADG), drawn from the center of the hip to the ground reaction point. Average anatomic measurements were analyzed with a range of knee and hindfoot angle variation in single leg stance, double leg stance, toe off and heel strike. MADG was consistently higher than MADC, suggesting a more complete estimate of weight-bearing axis that considers hindfoot deformity.