Long-term results after thoracoscopic anterior spondylodesis with or without posterior stabilization of unstable incomplete burst fractures of the thoracolumbar junction: a prospective cohort study.

BACKGROUND: Minimally invasive, thoracoscopic anterior spondylodesis (MIAS) is an established treatment for burst fractures of the thoracolumbar spine. Good restoration of the local sagittal alignment and good functional results have been reported. The aim of this study was to evaluate long-term results of MIAS in patients with incomplete burst fractures and to analyze the influence on global sagittal alignment, clinical outcomes, and adjacent segment degeneration. METHODS: From 2002 to 2003, 18 patients were treated with MIAS for incomplete thoracolumbar burst fractures. Mono-segmental spondylodesis was performed with an iliac crest bone graft and bisegmental spondylodesis with a titanium cage. In this single-center prospective cohort study, 15 patients were available for follow-up (FU) after an average of 12.9 years (12.1-14.4). Seven patients were treated with a combined anterior and posterior instrumentation and eight patients with anterior spondylodesis only. The primary clinical outcome parameter was the Oswestry Disability Index (ODI); secondary parameters were the Short Form 36 (SF36) and the visual analog scale (VAS spine). Full spine radiographs were assessed for bisegmental Cobb angle, alignment parameters, and signs of adjacent segment degeneration (ASD). RESULTS: ODI evaluation showed a mean impairment of 11.7% with minimal limitations in 13 patients. Neither a significant deterioration over time nor significant differences between both therapy strategies were found in the clinical scores at the latest follow-up. The mean bisegmental increase of regional malalignment of reduction was 8.8° (± 7.3°) with no significant correlation to any clinical outcome scores. The majority of patients had no signs of adjacent segment degeneration. Two patients showed minor radiologic changes. All patients had a balanced sagittal spine profile. CONCLUSIONS: In conclusion, MIAS leads to good clinical results with-in majority-minimal spine-related impairment at the latest follow-up. No significant deterioration at 12-year FU was detectable compared to the 6-year results for the SF36 and VAS spine scores. There was no association between sagittal alignment, clinical outcome scores, and ASD. TRIAL REGISTRATION: The study was retrospectively registered in the German Clinical Trials Register ( Nr.00015656 ).

Biomechanical evaluation of interlocking lag screw design in intramedullary nailing of unstable pertrochanteric fractures.

OBJECTIVES: Intramedullary nails with special lag screw designs may provide improved mechanical performance and alleviate clinical problems. We hypothesize that the proximal design of trochanteric nails affects mechanical performance. METHODS: Ten pairs of human cadaveric femora were implanted with 2 different short intramedullary nails without (Gamma3) and with an interlocking lag screw (Intertan). An unstable, multifragmentary, pertrochanteric fracture was created. Bones were tested in a cyclic testing protocol with increasing loads until failure simulating 1 leg stance. Stiffness, failure load, cycles to failure, and fracture gap movements were measured. RESULTS: Initially stiffness of the interlocking lag screw nail was almost 40% larger (P = 0.005) compared with the noninterlocking nail. During the test, the difference in stiffness gradually decreased. Failure load (13%, P = 0.02) and cycles to failure (18%, P = 0.02) were larger for the interlocking nail construct. Rotation and varus collapse of the head were initially up to 84% lower (P = 0.013) for the interlocking technique. During the test, the rate of rotational instability gradually increased for both techniques. CONCLUSIONS: The interlocking lag screw design reduced movement of the femoral head and relative movement between fracture fragments. Beyond that the trapezoidal nail design of the Intertan reduced toggling within the trochanteric area and prolonged survival. Although this study showed a decrease in the retention of stability over time, failure did not occur until the equivalent of 2-3 months of reduced physical activity in which healing may have occurred under normal clinical conditions.