Impact on spino-pelvic alignment by total knee arthroplasty to correct knee flexion deformity in osteoarthritis patients: a retrospective cohort study.

BACKGROUND

Knee osteoarthritis (KOA) is a common knee joint degenerative disorder. Total knee arthroplasty (TKA) is a surgical treatment option that not only corrects knee flexion contraction but also impacts spino-pelvic alignment, leading to altered standing posture and gait. This study aimed to utilize a low-dose biplanar X-ray device (EOS) whole-body X-ray imaging to assess the impact of knee flexion deformity correction by TKA on spino-pelvic alignment in patients with KOA.

METHODS

A retrospective cohort study was conducted in patients with varus-type KOA who underwent TKA between April 2023 and May 2024. Both sagittal and coronal alignments were measured in preoperative and postoperative EOS images. Patients were categorized into Group A or B based on Δknee flexion angle (ΔKFA) (<10° and ≥10°, respectively). Changes in postoperative alignment were analyzed using the paired t-test or the Wilcoxon signed-rank test. Pearson or Spearman correlation and multivariate linear regression analysis were employed to evaluate the relationship between changes in KFA and spino-pelvic parameters.

RESULTS

Among the 70 patients, the average knee flexion corrections were 5.1° in Group A (n=39) and 13.2° in Group B (n=31). Postoperative assessments showed decreases in hip-knee-ankle, pelvic tilt, spino sacral angle, T1 spinopelvic inclination (T1SPI), and T9 spinopelvic inclination, whereas increases in sacral slope, lumbar lordosis (LL), and C7 sagittal vertical axis (P<0.001). No significant inter-group differences were observed in these changes, except that LL increased in Group B and remained unchanged in Group A following surgery. Statistically significant correlations were noted between ΔKFA and both ΔT1SPI [Pearson correlation coefficient (PCC): -0.330, P=0.019] and ΔT9 spinopelvic inclination (ΔT9SPI) (PCC: -0.404, P=0.004). Multivariate linear regression analysis revealed that ΔKFA was significantly associated with ΔT1SPI [β=-0.341, 95% confidence interval (CI): -0.741 to 0.059, P=0.037] and ΔT9SPI (β=-0.437, 95% CI: -0.962 to 0.089, P=0.011).

CONCLUSIONS

Following TKA in patients with KOA, knee flexion deformity changes may lead to improved spino-pelvic sagittal alignment, but not coronal alignment. Additionally, the KFA change was correlated with changes in T1SPI and T9SPI in these patients. Therefore, clinicians should be aware of potential changes in spino-pelvic alignment when correcting lower limb alignment. A comprehensive preoperative evaluation may enhance surgical outcomes and prognosis.