Effect of rotational malalignment of components on functional outcome of total knee arthroplasty: A prospective observational study

Abstract

Background: Correction of coronal alignment alone may not translate into optimum functional outcome after total knee arthroplasty. Painful knees and patellofemoral complications are quite common after total knee arthroplasty, and rotational malalignment of the prosthetic components may be responsible. Objectives: We conducted a prospective observational study to compare functional outcomes following total knee arthroplasty among subjects with and without rotational malalignment. Methods: We studied 396 patients (contributing 709 knees with Kellgren-Lawrence grade 4 osteoarthritis) undergoing total knee arthroplasty in a tertiary care hospital setting, with 2-3 years of follow-up. Postoperative axial CT scans were obtained to estimate the rotational alignment of femoral and tibial components. External and internal rotation of components was measured with software to estimate combined external rotation, combined internal rotation, or component mismatch, based on which knees were grouped into two cohorts: having rotational malalignment or with normal alignment. Functional outcome was assessed by Knee Society Score, Oxford Knee Score, Knee Society Pain Score, Lower Extremity Functional Scale, and Public Health Questionnaire-9. Results: Normal alignment (combined external rotation < 10 degrees) was observed in 475 knees, while the rest of 234 knees had rotational malalignment in the form of combined external rotation of 10 degree or above, combined internal rotation or component mismatch. A significant difference in outcome scores was found between these two cohorts at the first follow-up itself. Knee Society Pain Score clearly indicated painful knees in the rotational malalignment cohort. Poorer improvement in outcome scores occurred in this cohort, throughout the duration of follow-up. Conclusions: Rotational malalignment of components is almost invariably associated with the poorer outcome of total knee arthroplasty; manifested by anterior knee pain or incomplete functional recovery, compared to the knees with normal alignment.