The Effect of Coronal Alignment on Tibial Component Migration Following Total Knee Arthroplasty: A Cohort Study with Long-Term Radiostereometric Analysis Results.

BACKGROUND

Recent short-term studies of total knee arthroplasty (TKA) have claimed improved clinical outcomes and implant survival when aiming to restore constitutional joint kinematics, as compared with neutral mechanical axis alignment. However, implant durability may be compromised when aligned in varus or valgus. With use of data pooled from 3 long-term radiostereometric analysis (RSA) studies, the aim of the present study was to assess the effects of coronal alignment on tibial component migration.

METHODS

Coronal alignment parameters from full-leg radiographs were measured and the constitutional leg alignment was determined for each patient. We evaluated the effect of the postoperative hip-knee-ankle angle, relative to both the mechanical axis and the constitutional alignment, on tibial component migration. In-range knees were defined as within ±3° of either the neutral mechanical axis or constitutional alignment of the patient. Analysis was performed with a linear mixed-effects model, corrected for study, age, sex, preoperative alignment, diagnosis, and body mass index.

RESULTS

A total of 85 cemented TKAs were included, of which 3 were revised for aseptic loosening and another 4 were considered loose. The median follow-up was 11 years. No loose tibial components were observed in mechanically in-range knees, whereas all loose tibial components were out of range. Mechanically varus knees showed the highest mean migration (maximum total point motion) of 1.55 mm (95% confidence interval [CI], 1.16 to 2.01 mm) after 5 years, compared with 1.07 mm (95% CI, 0.63 to 1.64 mm) and 0.77 mm (95% CI, 0.53 to 1.06 mm) for valgus and in-range knees, respectively (p < 0.001). In contrast, looking at constitutional alignment, loose tibial components were found among both constitutionally in-range and out-of-range knees. Mixed-model analysis showed comparable migration among constitutionally in-range, more-in-varus, and more-in-valgus aligned knees.

CONCLUSIONS

Mechanically out-of-range alignment, especially mechanical varus, led to higher tibial component migration. However, matching the constitutional alignment of the patient did not preclude high implant migration. RSA trials randomizing different alignment techniques are needed to confirm the results of the present study.

LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.