EVALUATION OF STABILITY OF ROTATING HINGE KNEE PROSTHESES

Abstract

Introduction: Rotating hinge knee prostheses are fully constrained with three degrees of motional freedom (flexion-extension, internal-external rotation and distraction). They are used for reconstruction of the knee in cases of severe articular compromise and major bone loss. The main indications are revision surgeries and reconstructions following distal femoral or proximal tibial tumor resections. The aim of this study was to examine the stability of various rotating hinge knee prostheses. Materials and Methods: We performed a biomechanical analysis of three different prosthesis designs (Limb Preservation System-LPS/M.B.T., S-ROM Noiles and Global Modular Resection System-GMRS) to establish the association between the design of the central rotational stem (length and taper) and the implants stability in vitro. Therefore we used a self-constructed biomechanical apparatus on a test bench in the laboratory. Additionally, we retrospectively evaluated short- and mid-term results of LPS/M.B.T. and S-ROM Noiles rotating hinge knee replacement after primary implantation, wide resection of malignancies or revision total knee arthroplasty, including three questionnaires, clinical examination, ultrasound and plain radiographs. Results: The measurements with the biomechanical apparatus resulted that the GMRS device was superior to the LPS/M.B.T. and S-ROM Noiles implant design concerning stability and maximum amount of distraction before implants dislocation (38 mm vs. 27 mm vs. 26 mm). Clinical and radiographic evaluation showed that the S-ROM Noiles knee had better results for medial and lateral lift-off than the LPS/M.B.T. design, although the more tapered central rotational stem. Only the distraction was higher in patients with the S-ROM Noiles rotating hinge knee. Overall, statistical analysis revealed that there were no significant differences in clinical and functional outcome between the tested devices. Differences in implant survival were also insignificant, neither between the groups nor between the implants. Discussion: Rotating hinge knee prostheses with a short and markedly tapered central rotational stem seem to have the highest instability/angular laxity at any given amount of distraction. On the other hand, testing the stability of the LPS/M.B.T. and S-ROM Noiles in vivo showed no significant differences between the implants. Despite the assimilable results, we recommend prosthetic designs with a long, cylindrical central rotational stem, especially in patients with severe compromised knees.

Date of Award	2011
Original language	English
Awarding Institution	Medical University Graz
Supervisor	Andreas Leithner (Supervisor) & Mathias Glehr (Co-supervisor)