gms | German Medical Science

Objectives: Kinematic alignment (KA) in total knee arthroplasty (TKA) is largely biomimetic in terms of restoring pre-arthritic distal femoral joint lines. Less is known regarding changes to the patellofemoral joint with both KA and MA (mechanical axis) TKA. The persistence of patellofemoral complications with both techniques underscores the need for further evaluation of whether a TKA femoral component appropriately replicates a patient's native trochlear orientation and dimensions. The purpose of this study was to assess whether a TKA femoral component aligned in either mechanical axis alignment (MA) or KA more closely replicates the native trochlear groove of the knee.

Methods: A modelling and analytics system was used to segment bone surfaces from 1,098 lower limb CT scans. A total of eleven coaxial cutting planes were rotated equally about a trochlear sulcus axis. The deepest point of the trochlear sulcus was found at the cross-section of each cutting plane and collectively defined the sulcus.The distal trochlear sulcus angle (DTSA) was the angle between the distal femoral joint line (DFJL) and a straight line fitted through trochlear sulcus points projected onto the coronal plane. The distance of the trochlear medial apex and the lateral apex to the trochlear sulcus axis was also measured at each of the eleven coaxial cutting planes. The same method was used to define the prosthetic sulcus of the implant oriented in MA and KA in each of the 1,098 femora so measurements relative to the native trochlea could be made.

Figure 1 [Fig. 1]

Results and conclusion: Kinematic alignment of the femoral component more closely restored native trochlear groove orientation in the coronal plane, particularly in higher valgus femora.KA is more biomimetic than MA with respect to restoration of lateral trochlear height in early and late flexion. Both KA and MA under-stuff the lateral trochlea in mid-flexion whereas MA overstuffs in late flexion, particularly in femora with larger valgus angles.

Depending on the native DFJL, the DTSA of the implant and the implant positioning technique applied (MA or KA), large deviations between native and prosthetic sulcus orientations are possible.It is currently unknown what the ideal solution to each potential anatomic variation is, but a universal prosthetic position is unlikely to be the answer, especially in the circumstances of more extreme anatomy. KA is more biomimetic in terms of restoring native sulcus orientation and lateral trochlear height