INTRODUCTION

Metallic ion release may be related to bearing surface wear and thus serve as an indicator of in-vivo performance of metal on metal (MOM) articulations.

Summary

Management of metal on metal hip replacements can be accomplished with a simple algorithm including easily available metal ion levels and hip MRI with metal artifact reducing software. After revision serum metal ion levels can be expected to fall rapidly.

Various reports confirm that elevations in serum markers associated with skeletal muscle injury exist and can occur after orthopaedic surgery in the absence of overt clinical manifestations of myocardial injury. The purpose of this study is to measure the influence surgical approach on these serum markers following primary Minimally Invasive THA. Consecutive enrollment of 30 patients into three different groups of 10 was performed. The MIS Modified Watson Jones THA is an approach using an inter-muscular plane, the Mini Posterior is a trans-muscular approach with some muscle detachment and repair, while the MIS II Incision THA is an inter-muscular approach anteriorly and a trans-muscular approach posteriorly. Blood samples for total creatine kinase (CK), creatine phospho-kinase (CPK), and serum myoglobin were obtained at screening and the morning before surgery as a baseline, immediately post-operatively in the recovery room and 8, 16, 24, 36, 48, and 72 hours post-operatively. Hemoglobin and hematocrit was obtained pre-operatively, 16, 36, and 72 hours (±6 hours) post-operatively. Cardiac troponin-I was measured the morning before surgery (pre-operatively) and 16 hours following surgery to monitor any contributory effect of myocardial injury. We report measurable and reproducible trends in serum enzyme levels consistent with skeletal muscle damage due to THA. Troponin-I remained normal in all but one case throughout the entire study indicating no myocardial contribution to measured serum enzyme levels. While these trends may have slight correlation with surgical approach, they were not statistically significant. We conclude that all three procedures do affect serum enzyme markers and are safe from this standpoint, but no surgical approach appears to affect the degree of muscle trauma more or less than another.

The purpose of this study was to compare the clinical, radiographic, and DEXA results of Epoch® Femoral Component for primary THA with other non-cemented femoral components. The Epoch and Epoch 14+ (Zimmer, Warsaw, IN) Composite Femoral Components were studied in conjunction with the VerSys® Fiber Metal Taper, Fiber Metal Mid coat and Beaded Fullcoat Femoral Components (Zimmer, Warsaw, IN). All patients were randomized into one of five component groups and followed prospectively. All patients across the five groups were matched with respect to demographics and body mass index (BMI) (Table 1). Diagnoses were evenly distributed across all study groups. There was no significant change in BMD at 5-years when compared to the baseline (6 month) DEXA measurements for all component groups except for the Beaded Fullcoat component subset which had significant decreases in BMD in proximal zones 1, 6 and 7, The Fiber Metal Taper showed similar decreases in BMD in zones 1 and 7, and the Epoch Component had a significant decrease in BMD in zone 7 only. Additionally, our DEXA findings complement and support the subjective radiographic interpretations performed for this study cohort. The results from this prospective, randomized controlled clinical trial showed that the Epoch Composite Femoral Component for primary THA can achieve results equal to standard alloy components of varying design. Based on these early results, the Epoch and Epoch 14+ Femoral Components for primary THA are justified for continuance of further prospective study.