Subsidence of the femoral prosthesis. A stereophotogrammetric evaluation.

A quantitative three-dimensional measurement method, radiographic stereophotogrammetry (SPG), was employed to assess the relation between early subsidence of the femoral prosthesis after total hip arthroplasty (THA) and subsequent clinical course. The SPG technique and the authors' error control mechanisms are described in 15 patients in the early postoperative period, and the findings are correlated with those of follow-up clinical examinations. Among the 12 patients who remained clinically asymptomatic with respect to pain, only one had an SPG estimate of subsidence in excess of 1 mm at any point in time. Each of the three patients who later became symptomatic had SPG estimates of subsidence in excess of 1.75 mm within six months of the operation. Thus far, the patient with the largest estimate of subsidence is the only one who required surgical revision.