Assessing the contributions of soft tissue to the stability of total knee replacements

Abstract

Total knee arthroplasty (TKA) is a common surgical procedure to combat the onset of osteoarthritis; however failure of TKA may occur due to instability of the knee joint as a result of soft-tissue deficiency or imbalance, or incorrect implant choice. The aim of this PhD was to investigate how soft-tissues help stabilise knees implanted with different TKA designs and thus provide more quantifiable data to help clinicians choose the correct implant and soft-tissue release for patients. Cadaveric experiments utilising a robotic testing system investigated soft-tissue contributions in three different implants, and found that the collateral ligaments are the primary restraints in the implanted knee. On the lateral aspect of the knee, the lateral collateral ligament (LCL) provided restraint to varus and internal-external rotations in a primary TKA implant. On the medial side of the knee, the superficial medial collateral ligament (sMCL) is the main valgus, internal-external and anterior stabiliser in primary TKA: this was also the case in a more constrained implant which may have been expected to provide inherent stability to reduce the reliance on the sMCL. After resecting the medial structures in the constrained TKA knee, a soft-tissue reconstruction of the structures using a hamstring tendon was tested, and this was found to restore internal-external and varus-valgus rotational stability to pre-sectioned values. Therefore it is advised that surgeons should preserve the sMCL/ LCL when attempting to correct a varus/ valgus deformity, as it may result in a combined laxity pattern that cannot be compensated by the other soft-tissues. In the event of collateral deficiency, either a more constrained implant such as a hinged implant would be required to provide enough stability, or performing a soft-tissue reconstruction in conjunction with a less constrained implant may restore stability to the knee.