Introduction: While T1 slope is an critically important parameter in cervical deformity surgery, its importance in posterior cervical fusion (PCF) for myelopathy/radiculopathy remains unknown. Among patients undergoing elective, degenerative PCF, we evaluated the impact of T1 slope on: 1) mechanical complications, 2) reoperation, and 3) patient-reported outcomes measures (PROMs).
Methods: A retrospective, cohort study of patients undergoing elective PCF for degenerative pathology (myelopathy/radiculopathy) from 2010-22 was undertaken. The cohort was trichotomized: 1) entire sample, 2) isolated cervical fusions, and 3) fusions including thoracic spine. The primary exposure variable was postoperative T1 slope (angle between superior T1 endplate and horizontal). Outcomes included mechanical complications, reoperation, and PROMs (NDI/VAS/EQ5D). Bivariate statistic and logistic regression were performed.
Results: Among 257 patients undergoing elective, degenerative PCF, 197 (76.6%) had fusions extending to thoracic spine. Mean age was 62.7±10.3 years with mean follow-up of 3.5±3.2 years. The mean T1 slope was 28.1±9.6º. Mechanical complications occurred in 41 (17.2%) patients: screw/rod fracture (12.2%), pseudarthrosis (24.4%), and symptomatic screw loosening (87.8%). Fourteen (5.9%) patients underwent reoperation.
Entire sample: mechanical complications (29.7±8.0 vs. 27.7±9.9º,p=0.219) and reoperation (28.4±8.4 vs. 28.1±9.7º,p=0.905) had no association with T1 slope. T1 slope was negatively correlated with 12-month NDI% (ρ=-0.151,p=0.035), but significance was lost on multivariable analysis (β=-1.420,95%CI=-0.380-0.062,p=0.157).
Isolated cervical fusions: mechanical complications (26.1±7.8 vs. 29.5±13.1º,p=0.483) and reoperation (23.4±6.4 vs. 29.4±12.8º,p=0.355) had no association with T1 slope. T1 slope had no association with any PROMs.
Fusions including thoracic spine: mechanical complications were associated with a greater T1 slope (30.6±8.0 vs. 27.0±8.4º, p=0.028), though no significant association was found with reoperation (28.7±7.8 vs. 27.8±8.5º,p=0.747). On logistic regression, T1 slope was independently associated with mechanical complications (OR=1.04, 95% CI=1.01–1.09,p=0.020). T1 slope was negatively correlated with 12-month NDI% (ρ=-0.190,p=0.027), but significance was lost on multivariable analysis (β=-0.101,95%CI=-0.555-0.107,p=0.182).
Conclusion : In patients undergoing elective, degenerative PCF for myelopathy/radiculopathy, a higher T1 slope was associated with increased mechanical complications only in patients fused to the thoracic spine but not isolated cervical PCF. T1 slope warrants further study in degenerative cervical fusions.
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