The effects of prosthesis mis-alignment on joint biomechanics during gait after limb-salvage surgery—a simulation based on clinical gait data

This study was designed to quantify the effects of mis-alignments in both coronal and sagittal plane on joint biomechanics after total knee replacement following the resection of osteosarcoma. A three-dimensional motion capture system was employed to collect the kinematic data of twelve patients following knee arthroplasty after osteosarcoma, data collected from seven healthy adults set as healthy control group. Subject-specific musculoskeletal models were constructed based on the postoperative measurement. The mis-alignments of prosthesis were simulated by altering the orientation of components ranging from -6º to 6º away from the neutral axis at interval of 2º, in both coronal and sagittal planes. In each model, the joint contact forces (JCFs) of both healthy limb and operated limb were derived and compared. Results indicates that after the limb-salvage surgery, the JCFs for the healthy limb side was 10% larger than those of the operated side. By altering the alignments of the prosthesis in the coronal plane for 6º, the peak JCFs were increased by 24.2% for the hip joint and by 84.7% for the knee joint on the operated limb, respectively. However, the JCFs of the healthy limb side were found to be insensitive to the misalignment of the limb-salvage surgery. It was also found that the centre of mass for each patient has been shifted backwards postoperatively. This study highlighted the importance of accurate implantation during limb-salvage surgery, especially in the coronal plane, a misalignment with the range of ±2º is tolerable, whilst, the sagittal plane was more forgiving for misalignment.