Clinical and roentgenographic evaluation of hydroxyapatite-augmented and nonaugmented porous total hip arthroplasty

Sixty osteoarthritic patients undergoing primary, uncemented total hip arthroplasty were matched for age and weight and randomized into one of four groups with respect to implant coating and postoperative, protected weight-bearing status: group 1, hydroxyapatite-augmented, 12 weeks; group 2, nonaugmented, 12 weeks; group 3, hydroxyapatite-augmented, 6 weeks; and group 4, nonaugmented, 6 weeks. Tantalum spheres were implanted periprosthetically into the femur at the time of the arthroplasty, thus providing constant references for stereoscopic radiographs. Patients were then evaluated over a 2-year period with clinical examination, plain radiography, and roentgen stereophotogrammetric analysis. Clinical evaluation using the Charnley scoring system showed no significant preoperative or postoperative intergroup differences, whereas visual analog testing noted less thigh pain with hydroxyapatite-augmented stems at the 12-week and 6-month follow-up evaluations. Plain radiographic analysis produced no significant differences, with no instability detected, and bony ingrowth was uniform in all groups. Stereographic evaluation showed migration in all groups, but there were no significant differences between the augmented and nonaugmented stems or the 6-week and 12-week partial weight-bearing protocols. Charnley, plain radiographic, and stereogrammetric evaluations all suggest that migration is unaltered by enhanced surfaces and early, unprotected weight bearing does not jeopardize implant fixation regardless of coating design. The lower incidence of visual analog thigh pain with the hydroxyapatite-augmented stems, however, may be a reflection of bony ingrowth and, as such, add some validity to the theoretic advantages of enhanced surface prostheses.