Summary

Choice of alignment philosophy in TKA lead to significant differences in trochlea groove recreation using a standard femoral component. The findings of this study may explain why patellofemoral aetiology is the most common cause for revision of kinematically aligned total knee arthroplasty.

Abstract

Aim

The ability of kinematic alignment (KA) to consistently restore trochlea anatomy in total knee arthroplasty (TKA) is unknown despite recreation of constitutional anatomy being its rationale for use. The purpose of this study was to assess if alignment choice in TKA effects the ability to restore the native trochlea groove.

Methods

122 consecutive patients undergoing robotic-assisted TKA using the MAKO image-based robotic platform had simulated femoral components placed according to kinematic, mechanical and functional alignment principals. Implant position and trochlea restoration between groups were compared. Restoration was assessed by shift (medial-lateral) and depth relative to the native groove from 3 consistent positions on the femoral implant; full extension (0°), mid-flexion (30°- 40°) and deep flexion (70° - 80°).

Results

366 alignment options were analyzed. Femoral alignment was significantly different between groups. 13.1% of KA compared to 3.3% of FA plans were outside safe coronal boundaries.Majority of these occurred by placement of femoral component in more than 6° of valgus. For femoral rotation using the TEA as reference, KA placed 3.3% outside of a safe zone limit of 3° ER to 6° IR, with 25% being placed in more than 3° IR compared to FA which had 1.6% outside the safe-zone and 4.1% being placed in more than 3° IR


The trochlear groove was translated most using a mechanical alignment (MA) technique. In full extension, a MA femoral component was a mean 7.84 +/- 1.99mm lateral to the native groove compared to KA 6.40 +/- 2.43mm and functional alignment (FA) 6.88 +/- 1.74mm (p = < 0.001). This difference was less in mid-flexion (p = 0.003) and not significant in deep flexion. In full extension, KA overstuffed by a mean of 1.36 +/- 1.16mm compared to MA 1.28 +/- 1.21mm and FA 0.83 +/- 1.18mm (p = < 0.001). In mid-flexion and deep flexion, all alignments resulted in a mean under-stuffing of the groove, most with KA, followed by MA and FA (p = < 0.001). FA most closely restored the trochlear groove depth.

Conclusion

Choice of alignment philosophy led to significant variations in trochlear groove restoration. MA resulted in the greatest translation shift and KA created the most understuffing overall. FA and KA were equally consistent in reproducing the trochlear groove in terms of translation, however KA resulted in femoral coronal component positioning that is considered unsafe in 13.2% of cases, compared to FA in 3.7% of cases. A KA philosophy also resulted in a femoral component that was IR beyond 3° relative to the TEA in more than 25% of cases compared to 3.3% with a FA philosophy. These findings confirm our hypothesis that a KA placed femoral component better restores the constitutional trochlea groove alignment but frequently results in unsafe coronal or axial implant positioning. These findings may explain why patellofemoral complications are the most common reason for revision in KA TKA.