Allograft-prosthetic composite versus megaprosthesis in the proximal tibia—What works best?

Abstract

Modular megaprosthesis (MP) and allograft-prosthetic composite (APC) are the most commonly used reconstructions for large bone defects of the proximal tibia. The primary objective of this study was to compare the two different techniques in terms of failures and functional results.

A total of 42 consecutive patients with a mean age of 39.6 years (range 15–81 years) who underwent a reconstruction of the proximal tibia between 2001 and 2012 were included. Twenty-three patients were given an MP, and 19 patients received an APC. There were nine reconstruction failures after an average follow-up of 62 months: five in the MP group and four in the APC group (p = 0.957). The 10-year implant survival rate was 78.8% for the MP and 93.7% for the APC (p = 0.224). There were no relevant differences between the two groups in functional results. Both MP and APC are valid and satisfactory reconstructive options for massive bone defects in the proximal tibia. In high-demanding patients with no further risk factors, an APC should be considered to provide the best possible functional result for the extensor mechanism.

Introduction

Resection of bone tumours, failed total knee replacements and failed previous reconstructions can lead to an important osseous defect of the proximal tibia. The main concerns for the surgeon are the sparse soft tissue coverage and, more importantly, restoring the patellar tendon insertion to achieve a functioning extensor mechanism. In most cases a knee arthrodesis can be avoided and the preservation of the joint leads to better functional results. There are three different techniques to reconstruct the knee articulation: an osteoarticular allograft, a modular and custom-made megaprosthesis (MP) or an allograft-prosthetic composite (APC) [1]. Osteoarticular allografts are associated with high long-term failure rates [2]. In our experience, osteoarticular allografts are a valid method of biological reconstruction in children to preserve the uninvolved half of the joint, but often they have to be replaced with a definitive implant after the end of growth. Modular and custom-made MP is a straightforward surgical technique and is easy to assemble intraoperatively. The postoperative rehabilitation programme and the time until full weight-bearing are short. Furthermore, the economic costs and the infrastructure required are less compared to allograft devices from a bone bank. However, the main disadvantage of MP is the sacrifice of the insertion of the extensor mechanism, which requires a fixation of the tendon to the metallic surface afterwards [3], [4], [5]. In contrast, the APC restores the bone stock of the tibia and, therefore, leads to a better load distribution. The allograft also enables the biological reattachment of the patellar tendon to the tibia, which leads to good functional results [6], [7]. The resurfacing of the allograft by a prosthetic device avoids the long-term joint destruction associated with osteoarticular allografts. APC appears to combine the advantages of prosthetic and biological devices in restoring the proximal tibia [5], [6], [8].

The aim of this study was to compare (1) implant survival, (2) complications and (3) functional outcome between MP and APC in patients who underwent resection of the proximal tibia.

We hypothesised that APC of the proximal tibia should provide better functional results than MP, at the expense of a higher complication rate.