Unexplained Pain Following Total Knee Arthroplasty – Is Rotational Malalignment the Problem?

OBJECTIVE: Malrotation of both tibial and femoral components has been suggested as a potential source of pain following total knee arthroplasty (TKA). However previous studies have been small, with variable control groups. The aim of this study was to compare component rotational alignment in TKA patients with unexplained pain to a control group with well-functioning TKA. METHOD: Seventy-one patients presenting with unexplained pain following primary TKA were included in this retrospective, comparative study. Diagnostic work-up included clinical examination, blood tests, x-rays, long-leg films, and CT scan. Patients with an identifiable diagnosis or with initially well-functioning TKAs were excluded. A control group of 41 patients with well-functioning TKAs also underwent CT scans. Femoral component rotation was measured relative to the surgical epicondylar axis, and tibial component rotation relative to the medial third of the tibial tubercle using a previously validated method involving 3D-image reconstruction. Findings were compared between painful and control TKA groups. RESULTS: We found no difference in femoral component rotation between the painful and control groups (mean 0.6° vs 1.0° external rotation (ER), p=0.4), and no difference in tibial component rotation (mean 11.2° vs 9.5° internal rotation(IR), p=0.3). Fifty-nine percent of patients in the painful group had tibial component rotation >9°IR versus 49% in the control group. 6% of patients in the painful group and 2% in the control group had femoral component rotation >3°IR. There was no difference in overall coronal alignment between groups (mean 1.3° varus vs 0.5° varus, p=0.23). CONCLUSION: In this the largest study yet reported on component rotation in TKA, we found no difference in the incidence of tibial or femoral component malalignment in painful versus well-functioning TKAs. Tibial component IR in particular appears to be a common finding, and its significance when evaluating the painful TKA should be interpreted with caution.