Shoe lifts are able to correct the leg-length discrepancies (LLDs) and relieve limp gaits of patients with unilateral developmental dysplasia of the hip (DDH). Four unilateral DDH patients were treated for leg-length equalization using shoe lifts. We evaluated gait parameters and the performance of the shoe lifts. The results showed that shoe lifts not
only improved pelvic levelness, but also reduced supinatory forces within the shorter limb and pronatory forces within the longer limb. However, shoe lifts added vertical ground-reaction force (GRF) on the affected side which may cause increases of joint stress of the lower limbs. To diminish the reaction force, the heels and outsoles should be made of materials with proper shock-absorbing capabilities and as little mass as possible. Moreover, the forefoot rocker in the shoe lifts provided easier and smoother motion during the process of propelling the body forward, however, the rocker also reduced the support force for the contraction of the gastrocnemius and soleus muscles, and thus diminished the propelled force.