Abstract
Total joint arthroplasty is an extremely high quality medical intervention with measured benefit to individual patients and society as a whole. However, nearly 20% of patients following total knee arthroplasty (TKA) may report some level of dissatisfaction following surgery. Weight-bearing-in-flexion activities such as squatting and ascending/descending stairs are those activities with which patients most frequently report dissatisfaction.
It is assumed that optimal functioning following TKA requires proper femoral and tibial implant positioning in all planes (sagittal, coronal, and axial), proper femoral-tibial balance in the coronal and sagittal plane and durable fixation irrespective of implant design and the manner in which the surgery is executed. Posterior stabilised (PS) and cruciate retaining (CR) TKA designs are the most predominant implants utilised yet their kinematics are infrequently close to normal. In addition, there is little clinical evidence that one design is superior to another. Alternative designs such as bi-cruciate and medially stabilised designs are much less frequently used and much less frequently studied. However, in both cases, isolated centers with relatively small volumes of patients studied have reported outcomes superior to PS and CR designs depending on the metric assessed.
With respect to kinematics, bi-cruciate and medially stabilised designs have displayed certain patterns of behavior that more closely mimic the native knee both in-vitro and in-vivo. Normal knee kinematics, as described by Freeman and Pinskerova, includes lateral sided femoral rollback with progressive knee flexion (alternatively thought of as internal tibial rotation with flexion) and sagittal plane stability achieved through the medial compartment. In theory, both optimal sagittal plane stability and internal tibial rotation with progressive flexion (consistent with normal dynamic changes in tibial tubercle – trochlear groove distance) following TKA should optimise weight-bearing-in-flexion kinematics and load transfer. Patient-related satisfaction with such activities might thus reasonably improve and may help explain the separate findings of Pritchett and Hossain regarding outcomes following medially stabilised TKA.
Medially stabilised TKA affords sagittal plane stability in mid-flexion and internal tibial rotation with flexion without the complexity and unique failure modes seen following bi-cruciate TKA. The work flow of performing medially stabilised TKA is similar to PS and CR surgical techniques and the surgeon need not climb a steep learning curve. In addition, similar to PS TKA, medial stabilised TKA is applicable to any primary state in which coronal plane balance can be achieved.
Further investigation in well-designed trials is necessary to fully develop an understanding of how different contemporary TKA designs might impact patient reported outcome. Larger registry populations of medially stabilised TKA over time are also necessary to best assess survivorship compared to other contemporary designs.
