Relationships between the changes in flexion contracture and standing flexion angle of the knee and sagittal spinal alignment after total knee arthroplasty

BackgroundThe sagittal spinal alignment interacts with the lower extremity in patients with combined degenerative disease of the spine and lower extremity. This study aimed to clarify the relationships between the reciprocal changes in sagittal alignment of the knee, pelvis, and spine after total knee arthroplasty (TKA) in osteoarthritis patients.MethodsProspectively, 36 patients who underwent primary TKA for severe knee osteoarthritis were enrolled. Their clinical and radiological evaluation included assessments of the knee flexion contracture (KFC) and standing knee flexion angle (KFA), as well as spinopelvic parameters and the global sagittal spinal alignment from standing whole-lower-extremity and whole-spine radiographs preoperatively and at postoperative 2 weeks, 6 weeks, 6 months, 1 year, and 2 years. Linear mixed models were used to assess the relationships between KFC/KFA and between spinopelvic/global sagittal spinal alignments.ResultsThe KFC decreased abruptly immediately after TKA, and the correction was maintained for 2 years postoperatively. The KFA decreased gradually and approached the value of the KFC after 2 years. Of the spinopelvic parameters, sacral slope and pelvic incidence decreased significantly, in ways related to changes in KFA. There was no significant relationship between sagittal spinal alignment and postoperative changes in KFC.ConclusionAlthough the flexion contracture was corrected immediately after TKA, the standing KFA improved gradually over 2 years. The pelvic parameters showed compensatory changes according to the KFA. The decompensated sagittal spinal malalignment was not related to a relapse in flexion contracture.