Predictive value of pelvic incidence in progression of spondylolisthesis

Study Design. Retrospective analysis of pelvic incidence and other radiographic parameters as a predictor of progression of isthmic spondylolisthesis. Objectives. To evaluate the predictive value of various radiographic parameters, including pelvic incidence, in determining the risk for progression of lumbosacral isthmic spondylolisthesis. Summary of Background Data. Although pelvic incidence has recently been shown to be positively correlated to the severity of spondylolisthesis, it has not been confirmed as a predictor of spondylolisthetic progression. Materials and Methods. Thirty-six patients who have undergone primary posterior lumbosacral fusion for isthmic spondylolisthesis at our institution from 1977 to 2001 were retrospectively analyzed. There were 24 females and 12 males with a mean age of 21.3 +/- 2.0 years ( range, 12 to 53 y). Twenty-two patients had high-grade (Meyerding class III, IV, V) and 14 patients had low-grade ( Meyerding class I, II) spondylolisthesis, respectively. Factors evaluated included age, gender, neurologic deficits, reason for surgery, and documented evidence of progression. Slip percentage, high-grade or low-grade slip, slip angle, sacral inclination, sacral rounding, trapezoidal L5 vertebra, and pelvic incidence were measured from immediate preoperative standing lateral radiographs. These factors were statistically analyzed for risk of progression. Continuous variables were analyzed using one-way analysis of variance. Nominal variables were analyzed using chi(2) test. Results. Pelvic incidence ( P = 0.66) was not predictive of spondylolisthetic progression. Of the other radiographic measurements, slip percentage ( P < 0.001), slip angle ( P = 0.016), and high-grade spondylolisthesis ( P < 0.0001) were highly predictive of progression. Interestingly, sacral inclination ( P = 0.33) was not predictive of progression. Conclusions. Pelvic incidence cannot adequately predict the probability of spondylolisthetic progression. Analysis of the other clinical and radiographic parameters revealed that slip percentage and high-grade spondylolisthesis remain the most positive predictors of progression.