What Factors Were Associated With Implant Failure After Posterior Vertebral Column Resection for Severe Thoracolumbar Pott Deformity?

Abstract

Background – Posterior vertebral column resection (PVCR) is associated with improved spinal alignment and function in patients with severe thoracolumbar Pott deformity. However, the loads it places on spinal implants can result in those implants breaking or loosening, which can result in instability, pain, and unplanned reoperations. Identifying the controllable factors associated with implants breaking or loosening may be beneficial in the development of more effective surgical strategies.Questions/purposes – What (1) radiographic and (2) clinical factors were associated with implant failure (defined as the mechanical failure of implanted spinal instrumentation) among patients who underwent PVCR surgery for severe thoracolumbar Pott deformity?Methods – Between January 2013 and June 2020, we treated 168 patients who underwent PVCR for severe thoracolumbar Pott deformity. Twenty-four percent (41) of patients, however, were lost because of incomplete data, incompliance, emigration, nonsurgical-related death, less than 2-year minimum follow-up, or they had not been seen in the last 5 years, leaving 76% (127) for analysis here. There were 56% (71) males and 44% (56) females, with a mean ± SD age at surgery of 39 ± 11 years. Mean follow-up time was 45 ± 12 months. Two trained spine surgeons independently measured spinopelvic parameters, demonstrating excellent agreement (intraclass correlation coefficient = 0.99; p < 0.001). Based on the occurrence of implant failure, which we defined as a mechanical compromise of spinal instrumentation (such as screws, rods, plates, titanium mesh, or cages) resulting in loss of structural integrity, spinal instability, or neurologic deficits, participants were categorized into an implant failure group (n = 19) and a no implant failure group (n = 108). Comparative analyses were conducted on surgical-related data (such as apex location, number of resected vertebra, instrumented levels, anterior support, and use of multiple rods) and spinopelvic parameters (such as local kyphosis, residual segmental kyphotic angle [RSKA]—which we defined as the angle formed by the projection lines extending from the upper and lower endplates of the healed focal vertebra—sagittal vertical axis, and pelvic tilt). Notably, before the two-sample t-test, normality distribution and homogeneity of variance test (Levene test) were performed. Cox regression analysis was employed to determine the independent factors associated with postoperative implant failure. DeepSeek-V3 was utilized to enhance the spelling and grammatical accuracy of the writing.Results – After controlling for potentially confounding variables such as age, sex, bone mineral density (BMD), BMI, and the number of instrumented levels, we found that a higher RSKA was associated with increased risk of implant failure (HR 1.15 per 1° increment [95% confidence interval (CI) 1.08 to 1.22]; p < 0.001). We also found that BMI ≥ 24 kg/m2 was associated with an increased risk of implant failure after controlling for variables such as age, sex, BMD, and the number of instrumented levels (HR 6.61 [95% CI 1.99 to 22.00]; p = 0.002), and that use of multiple rods was associated with a decreased risk of implant failure (HR 0.19 [95% CI 0.04 to 0.90]; p = 0.04). Differences were observed between the two groups regarding BMI, instrumented levels, and whether multiple rods were used. Furthermore, there were differences in postoperative spinopelvic parameters such as local kyphosis, RSKA, and sagittal vertical axis between the two groups. However, no difference was found for other spinopelvic parameters including cervical lordosis, thoracic kyphosis, lumbar lordosis, pelvic incidence, sacral slope, pelvic tilt, and coronal balance. The results from Cox regression analysis indicated that RSKA, BMI, and the use of multiple rods are independent factors associated with postoperative implant failure.Conclusion – Larger RSKA, increased BMI, and the absence of multiple-rod constructs were identified as factors associated with implant failure in severe thoracolumbar Pott deformity. PVCR requires adequate anterior column support and kyphosis correction, and multiple-rod constructs are recommended for reducing the risk of implant failure.Level of Evidence – Level III, therapeutic study. © 2025 by the Association of Bone and Joint Surgeons