DISTAL FEMORAL STEM/BONE ANCHORAGE OF A CEMENTLESS REVISION TOTAL HIP ARTHROPLASTY – EVALUATION BY USING COMPUTER ASSISTED TOMOGRAPHY

Abstract

Introduction: Proximal bone loss in patients undergoing femoral hip revision surgery is a challenging and complex problem, as it is often impossible to implant a proximally anchored prosthesis in such cases. Fluted tapered cementless prosthesis stems, such as the Link MP reconstruction prosthesis represent a distal fixation option, allowing axial and rotational control of the implant in the femoral diaphysis.

The manufacturer of the MP hip stem recommends a distal femoral implant/bone anchorage of at least 80 mm to gain implant stability. However, there are no in vivo studies showing that this fixation length is achieved in clinical practice and that this distance is needed for clinical satisfying results. Therefore, the aim of this study was to assess the distal femoral fixation length of the MP reconstruction prosthesis by using computer assisted tomography (CT).

Patients and Methods: To evaluate stem anchorage of the MP reconstruction stem, we performed CT-scans on 14 patients at a median follow-up of 12 months (IQR 12–25) after surgery. All CT-scans were separately analysed by 2 blinded radiologists. Clinical outcome was assessed by VAS for pain and Harris Hip Score (HHS) both at 12 (IQR 12–25) and 68 (IQR 61–73) months after surgery.

Results: We found the CT-scans of good quality and almost free from disturbing metal artefacts, which made it easy to interpret the images. Intraclass correlation between the measurements of the two blinded radiologists was 0.935 corresponding to an outstanding inter-rater reliability.

The median length of femoral stem/bone anchorage was 33 mm (IQR 10–60) which was too short according to the manufacturer’s guidelines. Still, all patients were fully weight-bearing and only 1/14 complaint about mild thigh pain. 7/14 patients did not experience any pain at rest or movement in the affected hip.

The patients reached median 85 (IQR 77–94) points in the HHS, corresponding to a good result. At 62 months follow-up, the patients described the same pain scores and the HHS had still a good result with 81 (IQR 62–92) points.

Discussion: We could show that it is possible to analyse the distal stem/bone anchorage of cementless femoral implants by using CT. Moreover, we could show a clear discrepancy between the manufacturer’s guidelines and clinical practice concerning anchorage of the MP reconstruction prosthesis. It is difficult to achieve femoral stem/bone anchorage of at least 80 mm, which otherwise is not necessary to achieve stability and clinically satisfying results.