Summary

Kinematically aligned TKA frequently restored the limb and knee alignment within 0 ± 3° of native while improving patient reported outcomes.

Abstract

Background

Mechanical alignment targets a hip-knee-ankle angle (HKA) of 0 ± 3°. The targets for kinematically aligned total knee arthroplasty (TKA) are to restore the native limb and joint lines within 0 ± 3°, however whether these targets are achieved with low risk of varus and valgus malalignment has not been reported. The present study determined 1) whether the average alignments of the HKA angle, distal lateral femoral angle (DLFA), and or proximal medial tibial angle (PMTA) of the kinematically aligned TKA are different from the native contralateral leg, 2) the frequency that each alignment was within 0 ± 3°, > 3° varus, and > 3° valgus from native, 3) and the improvement in patient-reported function as measured by the Oxford Knee Score (48 best, 0 worst).

Methods

A retrospective analysis of 562 consecutive patients treated with a primary kinematically aligned TKA with manual instruments between August 2014 and March 2016 was performed. A post-operative anterior-posterior CT scanogram of both limbs was available for 561 subjects. Excluded were 459 subjects because the scanogram showed an arthroplasty or degenerative arthritis in the contralateral limb (N=305), asymmetric rotation between limbs (N=133), or a healed fracture, arthroplasty of the hip or ankle in the treated or contralateral limb (N=41). Alignment measurements were performed on 102 subjects (63 female) with a mean BMI of 28, a preoperative Oxford Knee Score of 20, and a Kellgren Lawrence classification of IV in 41%, III in 47%, and II in 12%.

Results

The average alignments were not different between the kinematically aligned TKA versus native limb with a HKA of 0.6° varus (6.8° valgus to 8.1° varus) versus 1.1° varus (6.8° valgus to 9.6° varus) (p = 0.7) (Figure 1), LDFA of 86.8° (81.7° to 92.4°) versus 87.4° (81.7° to 92.2°) (p =0.5) (Figure 2), and MPTA of 86.9° (81.9° to 90.6°) versus 86.8° (79.8° to 90.9°) (p =0.6) (Figure 3). The frequency that the kinematically aligned TKAs were within 0 ± 3°, > 3° varus, and > 3° valgus of native was 97%, 0% and 3% for the HKA, 98%, 0% and 2% for the DLFA, and 98%, 0% and 2% for the PMTA. The average Oxford Knee Score improved from 23 to 44 points at a mean follow-up of 15 months.

Conclusion

Kinematically aligned TKA frequently restored the HKA, DLFA, and PMTA within 0 ± 3° of native while improving patient reported outcomes. The low risk of varus and valgus malalignment from native when kinematic alignment is performed with manual instruments is compatible to the alignments associated with a negligible risk of component loosening at 2, 3 and 6 years reported for kinematically aligned TKA performed with patient-specific instruments.