Small differences in tibial contact locations following kinematically aligned TKA from the native contralateral knee

Purpose

Kinematically aligned (KA) TKA strives to restore native limb and knee alignments without ligament release with the premise that knee function likewise will be closely restored to native to the extent enabled by the components used. This study determined differences in anterior–posterior (AP) tibial contact locations of a KA TKA performed with asymmetric, fixed bearing, posterior cruciate-retaining (PCR) components from those of the native contralateral knee and also determined the incidence of posterior rim contact of the tibial insert during a deep knee bend and a step-up.

Methods

Both knees were imaged using single-plane fluoroscopy for 25 patients with a calipered KA TKA and a native knee in the contralateral limb. AP tibial contact locations in each compartment were determined following 3D model-to-2D image registration. Differences in mean AP tibial contact locations in each compartment between the KA TKA knees and the native contralateral knees were analysed. Contact locations either on or beyond the most posterior point of the tibial insert determined the occurrence of posterior rim contact.

Results

Mean AP tibial contact locations for both native and KA TKA knees remained relatively centred in the medial compartment but moved posterior in the lateral compartment during flexion. In both the medial and lateral compartments, differences in mean AP tibial contact locations between the KA TKA knees and the native contralateral knees were more posterior and greatest at 0° flexion for both activities (4 mm, p = 0.0009 and 7 mm, p < 0.0001 for deep knee bend and 6 mm, p < 0.0001 and 8 mm, p < 0.0001 for step-up in the medial and lateral compartments, respectively). The incidence of posterior rim contact of the tibial insert was 16% (4 of 25 patients) but the lowest Oxford Knee Score was 43 for these patients. The median Oxford Knee Score for all patients was 46 (out of 48).

Conclusions

Calipered KA TKA with asymmetric, fixed bearing, PCR components resulted in mean AP tibial contact locations which were relatively centred in the compartments and differed at most from those of the native contralateral knee by approximately 15% of the AP dimension of a mid-sized tibial baseplate. Although posterior rim contact occurred in some patients, all such patients had high patient-reported outcome scores.

Level of evidence

Therapeutic, Level III.