Fulcrum to Generate Maximum Extension of the Spine and Hip—Proposing A New Strategy using EOS Imaging for Patient-specific Assessment of Degenerated Lumbar Spines

STUDY DESIGN A retrospective, radiographic comparative study conducted in a single academic institution. OBJECTIVE This study aims to compare fulcrum extension with conventional extension imaging to determine maximum "hip lordosis" (HL), an important novel patient-specific parameter in spinal realignment surgery, as well as understand the extension capabilities of the lower lumbar spine, which together, are key contributors to whole-body balancing. SUMMARY OF BACKGROUND DATA Recent literature recognizes the hip as an important contributor to whole-body lordosis beyond a compensator for spinal imbalance. METHODS Patients >45 years' old with mechanical low back pain due to degenerative spinal conditions were included and grouped based on the imaging performed-fulcrum or conventional extension. All imaging was performed using EOS under standardized instructions and visual aids. Radiographic parameters include global lumbar angle (GLA), inflexion-S1 (Inf-S1) angle, segmental lumbar angles, pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), femoral alignment angle (FAA), HL and spinocoxa angle (SCA). Unpaired t test was used to compare between radiographic parameters. RESULTS One hundred patients (40 males and 60 females, mean age 63.0 years) underwent either fulcrum or conventional extension EOS® imaging. Both groups had comparable baseline radiographic parameters. Fulcrum extension gave a larger mean GLA (-60.7° vs. -48.5°, P = 0.001), Inf-S1 angle (-58.8° vs. -48.8°, P = 0.003), SCA (-36.5° vs. -24.8°, P < 0.001), L4/5 and L5/S1 lordosis (-20.7° vs. -17.7°, P = 0.041, and -22.3° vs. -17.1°, P = 0.018, respectively), compared to conventional extension. PI, SS, PT, FAA, and HL were similar between both extension postures. CONCLUSION Fulcrum extension, compared to conventional extension, is better at generating lordosis in the lower lumbar spine, thus improving preoperative assessment of stiffness or instability of the lumbar spine. Both extension methods were equally effective at determining the patient-specific maximum HL to assess the flexibility and compensation occurring at the hip, potentially guiding surgical management of patients with degenerative spines.Level of Evidence: 3.