CEMENTLESS TOTAL HIP ARTHROPLASTY WITH A CLOSE PROXIMAL FIT AND TAPERED DISTAL STEM: (THIRD-GENERATION) PROSTHESIS IN PATIENTS UNDER 50 YEARS OF AGE

Abstract

To determine the results critically of cementless third generation prosthesis (proximal fit, porous coated, and tapered distal stem), a prospective study was performed only in Charnley class A patients under 50 years of age who underwent primary total hip arthroplasty. 50 patients (50 hips) were included in study (37 were male and 13 were female). Average age of patients was 45.4 years (26–50 years). IPS(Immediate Postoperative Stability) stems (DePuy, Leeds, UK) were implanted in all hips. Cementless Duraloc cups (DePuy, warsaw, IN.) were used in all hips. 22 mm zirconia femoral head was used in all hips. All surgeries were performed by one surgeon (YHK). The redominant Dx. was osteonecrosis (30 hips or 60%), O.A. 2° to childhood T.B. or pyogenic arthritis (8 hips or 16%) and others (12 hips or 24%). The average F.U. was 6.3 years (5–7 years). Thigh pain was evaluated using a visual analog scale (10 points). Clinical (Harris hip score) and x-ray follow-up was performed at 6 weeks, 3 months, 6 months, 1 year and then annually. Linear and volumetric wear were measured by software program. Abductor moment arm, femoral offset, neck and limb length, center of rotation of hips, cup angle and anteversion were measured and the results were compared between normal and operated hips. All hips had satisfactory fit in A-P and lateral planes. There was no aseptic loosening or subsidence of components. Incidence of thigh pain was 14% (7 of 50 hips). All thigh pain disappeared at 3 years postoperatively. Preoperative Harris hip score was 52.3 (7–64) points and 92.9 (80–100) points at the final F.U. The values of abductor moment arm, femoral offset, neck and limb length, center of rotation of hips, cup angle and anteversion of operated hips were comparable to normal unoperated hips. The average linear wear and annual wear rate were 1.25 and 0.21 mm, respectively. The average volumetric wear was 473.48 mm3. There was statistically significant relationship between the liner wear, age (under 40), male patient, and the cup angle. Yet there was no statistical relationship between the wear and Dx., wt., hip score, R-O-M, anteversion, abductor moment arm, femoral offset, neck and limb length and center of rotation of hip. Osteolysis was identified in zones 1A and 7A in 4 hips (8%). No hip had distal osteolysis. Close fit cementless stem in coronal and saggital planes without having distal stem fixation were proved to have an excellent mechanical fixation and provided favorable mechanical loading. Close fit in the proximal canal with a circumferential porous coating reduced the incidence of osteolysis. Factors contributing to good results in this young patient group are improved design of the prosthesis, improved surgical technique, strong trabecular bone and the use of smaller femoral head and thick polys. Although there was no aseptic loosening of the hip, high incidence of linear and volumetric wear of polyethylene liner in these young patients remains to be a challenging problem.