Purpose of the study: The authors deal with the issues of loosening of Walter cementless total hip replacement. The intention was to develop the curve of survival of components of the implant and analyze the causes of their failure.
Material: On the group of 127 patients on between 1988 and 1991 with the average follow-up of 9.4 years the authors operated analyze results of this type of implant which was applied in the whole main spectre of orthopaedic indications.
Methods: Based on the results survival curves were drawn by the method after Kaplan-Meier and they were compared from different views.
Results: Loosening requiring revision was recorded in 33 cases, a marked decline of the curve was evident after the fifth year. Ten-year survival was recorded in 66% of cups. The comparison of the implant survival diagram in patients operated on by different surgeons revealed the substantial impact of the surgical technique on the implant survival. Loosening of the stem was recorded in 16 cases. More than 80% of stems have survived ten years.
Discussion: As potential causes of the failure of the cup the authors consider errors in the surgical technique, excessive pitch of cup thread and material composition of the used alloy from which the primary series of cups was manufactured. The error was also caused by the indication of a conical cup in cases of oval defects solved by the combination of the cup and a solid homogenous bone graft (21% of loosened cups). In stem loosening the cause again consists in incorrect surgical technical and material composition of the used alloy. A marked improvement of the survival curve may be achieved by the stem surface finish in the form of a combined plasmatic hydroxyapatite coating.
Conclusion: Results obtained from the preceding model of the Walter cup led to the change of the design of both the cup and the stem. The original titanium alloy VT6 was replaced by Tl6A14V ELI (Extra Low Interstitial) according to a more strict ASTM F136 standard. Osteointegration of both components has been improved by porous titanic surface combined with hydroxyapatite.