Standard anatomical medullary locking (AML) versus tricalcium phosphate-coated AML femoral prostheses

Objectives: To compare the preliminary rate and amount of bony ingrowth and calcar resorption between patients receiving either a standard anatomical medullary locking (AML) or a tricalcium phosphate (TCP)-coated AML femoral prosthesis and to compare preliminary clinical results. Design: A prospecti ve, randomized, double-blind clinical trial. Setting: An acute care tertiar y institution. Patients: Between January 1993 and March 1995, 92 patients u nderwent primary total hip arthroplasty (THA). They were randomized to 2 gr oups of 46 - a control group or a treatment group. Of the 46 subjects enrol led in each group, no significant differences were seen preoperatively with respect to age, sex, diagnosis, clinical and radiographic assessment. Seve nty-one patients were followed up for 24 months. Interventions: Insertion o f either a standard AML femoral implant (control group) or a TCP-coated AML femoral implant (treatment group). Outcome measures: The degree of hypertr ophy, calcar atrophy and the number of spot welds on standard postoperative radiographs at 6, 12 and 24 months. Clinically, assessment according to th e Societe internationale de chirurgie orthopedique et de traumatologie (SIC OT) scale and a 100-point visual analogue scale (VAS) for pain. Results: Th ere were no prosthetic stem revisions in either group at the 24-month follo w-up. Radiographically, bony ingrowth was not significantly different in th e TCP-coated stem, by chi (2) analysis of the degree of hypertrophy and num ber of spot welds present. Also by chi (2) analysis, the degree of calcar a trophy was not significantly different between groups. The mean VAS score f or pain at 24 months was 12.5 for the control and 12.1 for the treatment gr oup. No significant differences were seen in any of the clinical categories of the SICOT Scale over the 24-month interval. Conclusion: The objective o f TCP-coating - to increase the rate and amount of bony ingrowth while redu cing the rate of calcar resorption in non-cemented THA - was not achieved b y 24 months postoperatively in our study.