Limb reconstruction using modular tumour megaendoprostheses is a standard procedure nowadays in patients with malignant tumours [1
]. Particularly with modern imaging and surgical techniques, limb salvage is possible in most cases. Rates of major complications such as periprosthetic infections, aseptic loosening, and luxations have been significantly reduced over the last few decades, and good functional results can be achieved in the lower limb [1
]. In the upper limb, the rate of implant-associated complications is low, but the functional results are poor [1
]. This is due firstly to the resection of the axillary nerve that is often required for oncological reasons; secondly, even if the nerve can be preserved, relevant parts of the rotator cuff have to be sacrificed, resulting in loss of congruity of the humeral head and loss of function of the deltoid muscle.
Reconstruction with an anatomical proximal humerus replacement has been the standard procedure to date. In our department, the prosthesis was embedded in an attachment tube and the remaining muscles were attached to it. This procedure provided a stable situation in the joint, but the patient was unable to actively abduct and elevate the arm [1
]. Even techniques such as the Bateman procedure in cases of axillary nerve resection were unsuccessful with a conventional prosthesis, due to the residual loss of congruity of the humeral head [7
Reversed shoulder arthroplasty is an established procedure in patients with loss of rotator cuff function [8
]. The medialised and semi-constrained artificial joint restores stability and mobility [9
]. In the past, this procedure was only used in older patients, due to its high complication rates [10
] and declining function after eight to ten years [11
]. Complications observed during the long-term follow-up included periprosthetic infection, instability and dislocation, infraglenoid notching, and also abrasive wear [10
]. Wear in particular represents an underestimated risk for loosening of the prosthesis. In addition to permanent deformation of the component, small particles of polyethylene can cause an inflammatory response in the surrounding bone [14
]. Particles of debris generated by wear are also responsible for changes in osteogenesis, producing an imbalance between osteoclastic and osteoblastic activity that may result in resorption of bone at the implant–bone interface, leading to failure of the bond between the implant and the bone [14
The Modular Universal Tumour and Replacement System (MUTARS) inverse proximal humerus replacement is indicated in young patients in whom the axillary nerve can be preserved and little muscle resection is necessary. A low degree of wear on the polyethylene is required because of the patients’ youth and the expected high demands on shoulder function. A special type of polyethylene with shock-absorbing properties has been developed to minimise polyethylene wear in the MUTARS inverse proximal humerus replacement (Implantcast Ltd., Buxtehude, Germany). This study compared tribological data for the new MUTARS inverse proximal humerus replacement with those for a standard anatomical prosthesis (Capica, Implantcast Ltd., Buxtehude).