The effect of the cam deformity on the insertion of the femoral component in hip resurfacing.

Surface arthroplasty simulations were generated using 3-dimensional computed tomographic scans from 61 consecutive patients presenting with idiopathic osteoarthritis to evaluate the change in femoral component positioning that would allow optimal alignment when resurfacing a cam-type deformity. Anatomical parameters were measured to quantify the influence of the deformity on the insertion technique of the femoral implant. A modified femoral head ratio was initially calculated from plain radiographs to define the severity of cam deformity in these patients. A severe deformity required more superior translation of the entry point and greater reaming depth to allow safe insertion with optimal implant alignment. This could be achieved while preserving the leg length, minimizing the component size, and maximizing the amount of host bone contact, although the horizontal femoral offset was reduced. These findings suggest that the femoral component can be safely inserted by modifying the surgical technique despite progressive deformity of the femoral head.