Summary

This study investigated the prevalence and significance of component malalignment in a cohort of patients with painful total knee arthroplasty (TKA) using CT scans and plain radiographs, finding that nearly all patients had some degree of component malalignment, with the sagittal femoral angle, tibial component rotation, and patellar height being most significantly malaligned in these patients.

Abstract

Background

Component malalignment is thought to cause pain and dissatisfaction following total knee arthroplasty (TKA). A currently unknown proportion of patients with pain following TKA have abnormal component alignment. This study aims to investigate what proportion of patients with painful TKA have component malalignment, and which measures in particular are most significant in causing pain.

Methods

This observational study evaluated a cohort of patients with painful primary TKA for component malalignment using computed tomography (CT) scans and a standardised series of plain radiographs. A total of 31 validated radiological measurements were used in this study. Results were then compared to published normative ranges. Furthermore, analysis was conducted comparing patients who underwent revision TKA surgery to those who were unrevised.

Results

A total of 107 patients were included. Overall, 105 (98.1%) demonstrated abnormal component alignment in at least one radiological measurement. Post-TKA pain was associated with significantly flexed femoral components (3.8º ±3.3º, p=0.014) evident on lateral x-rays, and excessive internal rotation of the tibial component (21º ±9.3º, p=0.002) evident on axial CT scans. Patellar baja (Blackburne-Peel ratio measured on CT) was also a significant contributing factor (0.51 ±0.14, p=0.001). Sagittal alignment of the femoral component was the only measurement significantly different between the revision group and unrevised group (4.8º ±3.6º vs 3.3º ±3.1º respectively, p=0.044).

Conclusions

Sagittal femoral angle, tibial component rotation and patellar height are the most significant malalignment variables in patients with pain following TKA. Further refinement is required of many of the published normative values for measures of malalignment in TKA. Patients presenting with persevering pain following TKA should be investigated with CT scans and a standardised series of radiographs.