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The primary stability of the hip transposition type IIb: a biomechanical in vitro study
Martin Wessling1, Mirko Aach, Mirko Herbort
1Department of Orthopaedic Surgery, University Hospital Muenster, Albert-Schweitzer-Str. 33, D-48149 Muenster, Germany. wessling@uni-muenster.de
Background:
The hip transposition is firmly established in pelvic sarcoma surgery. However, the primary stability of the hip transposition has not been tested yet so that the mobilisation, respectively the immobilisation of the patient so far solely relied on the experience of the surgeon. The aim of this study was to test the primary stability reliably with the help of a model and to reveal possible differences in stability between currently used anchor systems (TwinFix 6.5 and MITEK SuperAnchor).
Methods:
A biomechanical model of porcine sacra was developed to document the maximum load capacity (load to failure test) and the performance under cyclic load (100 N, 200 N, 350 N, 700 N, 1400 N, each with 1000 cycles), 28 sacra were tested in total. Macroscopic damages, displacement, yield load, stiffness and F(max) were recorded as well.
Findings:
The load to failure test results showed a 3.9 times higher maximum load capacity for the TwinFix 6.5 anchor (1307 N) compared to the MITEK SuperAnchor (334N). The cyclical test revealed that nearly all MITEK SuperAnchors failed at a load of 350 N. In contrast, the TwinFix 6.5 anchors resisted 4000 cycles up to a load of 1400 N.
Interpretation:
The TwinFix 6.5 anchor proved to be clearly superior to the MITEK SuperAnchor, resulting in the adjustment of the reconstruction technique. Therefore, the immobilisation period of a patient after a hip transposition type IIb could be shortened according to the results of the primary stability test.
