ANALYSIS OF 10-YEAR SURVIVAL RATES OF 100 CEMENTLESS ZWEYMÜLLER STEMS IN PRIMARY TOTAL HIP PROSTHESES

Abstract

Introduction and Objectives: At present, cementless stems offer a reliable alternative for survival of total hip prostheses (THP). This study analyzes the clinical and radiographic results obtained using the Zweymüller SL stem in patients with an average follow-up time of 10 years.

Materials and Methods: This is a study of 100 cement-less THP (Balgrist cups, SL stems) implanted between June 1991 and February 1995 in 93 patients (7 bilateral). Patients were 55% male and 45% female, with an average age of 58.5 years (20–74). Diagnoses were 72% coxarthrosis, 13% avascular necrosis, 5% fractures, 4% rheumatism, 2% Perthes disease, 2% dysplasia, and 2% post-infection sequelae. Two deaths occurred during the follow-up period (unrelated to THP). No cases were lost. Average follow-up time was 10 years (range: 8 to 12 years). Clinical evaluation was done using the Merle D’Aubigné scale as modified by Kramer and Maichl, to numerically evaluate degree of pain and walking capacity. Radiographic evaluation included determining radiolucent lines, sclerosis, osteolysis in the Gruen zones, stem subsidence, heterotopic ossification, and type of stem fixation. Survival analysis was done according to Kaplan-Meier at 10 years using prosthetic revision as the endpoint.

Results: Clinical evaluation based on the modified Merle D’Aubigné scale was as follows: 81% very good results, 2% good, 3% satisfactory, 2% fair, and 11% poor (this last group included revision THP). Radiographic evaluation showed 9% with radiolucent lines in zone 1, 6% in zone VII, and one case with osteolysis in zones II and VI, the latter in conjuction with aseptic loosening of the stem. There was heterotopic ossification in 28% of cases and subsidence in 2 cases (one asymptomatic and the other aseptic loosening, which is pending revision). Stem fixation was excellent in 67% of cases, good in 32%, and poor in 1%. There were 7 revisions in the survival analysis: 4 of the cup, 2 of the entire prosthesis due to septic loosening, and one of the head of the stem. All of this resulted in 10-year survival rates of 92% (0.92 +/− 0.06; p< 0.05) for the THP and 97% (0.97 +/− 0.03; p< 0.05) for the SL stem.

Discussion and Conclusions: Cementless Zweymüller SL stems offer excellent survival rates. In our series, only one stem failed (1%), and is currently awaiting revision.