Retrospective Study of Biomechanical Factors Influencing Early Clinical Results of the Munting Stemless Hip Prosthesis
The Munting stemless hip prosthesis was developed in the early eighties by Pr E. Munting and Pr A. Vincent (UCL, Brussels, Belgium). This device was designed for young and active patients to prevent the bone loss commonly associated with femoral components having intramedullary stems. Previous in-vitro experiments and clinical densitometric follow-up confirmed that it preserved physiological loading and reduced stress shielding compared to traditional hip designs. Nevertheless, some early clinical failures were reported up to 2 years after surgery and were always related to inadequate implant positioning (varus) or partial seating of the implant on the proximal bone resection.
The aim of this study was to evaluate the relationship between the first 2 years clinical response (qualitative analysis of proximal bone remodeling) and 5 independent biomechanical factors such as patient age (A), implant position angle (IPA), pre-operative bone quality (BQ), body mass (BM) and height (H). We reviewed clinical results of a consecutive series of 103 patients operated between 1989 and 1998. Classification Tree and a Multinomial Logistic regression model (Systat.11) were used to retrospectively analyse the clinical results.
As per our hypothesis, this study confirmed the significant influence of implant position angle (IPA) to the clinical response in varus and valgus positions (p=0.001 and p=0.008). Influence of patient weight was close to statistical significance in valgus (p=0.063), confirming well known role of mechanical stress and strain in BMD homeostasis of the femoral bone. Rapid bone loss at the medial bone/implant interface was statistically related to varus position, 77% of which became early clinical failures.
Keywordsstemless hip prosthesis physiological loading bone remodeling short term clinical results young and active patients
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