Introduction: In cases of lumbar spinal stenosis, there can be an increase in lumbar lordosis (LL) after decompression surgery. The necessity of postoperative LL increase varies depending on the presence of preoperative lumbar kyphosis. This study aimed to compare the changes in LL after surgery between patients with pelvic incidence (PI) minus LL greater than 10 degrees and those with PI minus LL less than or equal to 10 degrees, and to investigate preoperative factors influencing postoperative LL increase.
Methods: We performed posterior decompression surgery (without fixation) on 47 patients with lumbar spinal stenosis, who were followed up for more than two years. The patients were divided into two groups: PI-LL >10 degrees (Mismatch group, mean age 68.7 ± 8.4 years, 16 males, 9 females) and PI-LL ≤10 degrees (Match group, mean age 69.1 ± 8.0 years, 18 males, 4 females). We compared the preoperative and 2-year postoperative LL between the groups. We then analyzed the correlation between various preoperative factors previously reported to be associated with postoperative LL increase and the change in LL using Pearson`s correlation analysis. Factors with p-values of 0.1 or less were further examined for correlation with postoperative LL increase using multiple regression analysis, including age, gender, and Body Mass Index (BMI).
Results: Over the 2-year postoperative period, the Mismatch group showed a significant increase in LL (3.7 ± 7.4 degrees) compared to the Match group (-0.7 ± 5.1 degrees). Pearson correlation analysis indicated that the difference in LL between standing and supine positions (Difference in LL: DiLL) and the degree of intermittent claudication (JOA score) had p-values of 0.1 or less. However, multiple regression analysis revealed that only DiLL had a significant correlation with postoperative LL increase (t-value: 2.34, p=0.028).
Discussion: Cases with preoperative PI-LL mismatch tend to show an increase in LL after surgery, whereas patients without mismatch do not require LL increase, resulting in no change in LL. Among the preoperative factors suggested to influence postoperative LL change (such as back pain, leg pain, intermittent claudication, PI, and disc vacuum phenomenon), DiLL was found to have the strongest impact on postoperative LL increase.
Conclusion: Patients with PI-LL >10 degrees are likely to experience an increase in LL after lumbar decompression surgery, with DiLL being the most important preoperative predictor of this increase.