OBJECTIVE: We endeavored to introduce a novel scoring system (Lumbar Functional Index, LFI) capable of evaluating lumbar function in pelvic bone sarcoma patients who underwent surgical resection and spinal pelvic fixation, while simultaneously identifying the incidence, outcomes, and risk factors of lumbar function impairment among these populations.
METHODS: A cohort of 304 primary bone sarcoma patients were recruited. The LFI was created based on the Oswestry Dysfunction Index (ODI) and Japanese Orthopaedic Association (JOA) scores. Lumbar function impairment was defined as LFI score ≥ 18 points, which was identified as high LFI. Demographic data, clinical characteristics, and oncological outcomes were analyzed.
RESULTS: The cohort included chondrosarcoma (39.8%), osteosarcoma (29.9%), Ewing sarcoma (8.6%), bone-derived undifferentiated pleomorphic sarcoma (7.2%), giant cell tumor of bone (7.2%), chordoma (2.3%), and other bone sarcomas (5.0%). The LFI score exhibited significant negative correlation with common scoring systems of bone sarcoma. The incidence of high LFI was 23.0%. Patients with high LFI demonstrated a higher prevalence of type I + II + III + IV pelvic tumor, more sacrificed nerve roots and bilateral lumbar spine fixation during surgery, while lower percentage of R0 resection and local control of pelvic tumor. Decreased median overall survival (30 vs. 52 months, p < 0.001) and recurrence-free survival (14 vs. 24 months, p < 0.001) time were observed in these patients. Type I + II + III + IV pelvic tumor and sacrificed nerve roots≥2 were identified as risk factors for high LFI, while R0 resection and local control were identified as protective factors.
CONCLUSIONS: The LFI scoring system exhibited a significant negative correlation to current scoring systems. High LFI patients had worse prognosis and distinct characteristics. The risk factors of high LFI included type I + II + III + IV pelvic tumor and sacrificed nerve roots≥2, and the protective factors included R0 resection and local control.

BACKGROUND: To investigate the ideal trajectory for the S2AI screw and to clinically validate its safety feasibility.
METHODS: The 3D model was reconstructed from CT data of the pelvis of 30 selected adults, and the 3D coordinate system was established with the first sacral superior endplate as the horizontal plane. A set of cutting planes was made at 3 mm intervals in the coronal plane, and the cross-sectional internal tangent circles were divided in the target area. Using the linear fitting function, the axis of 90 mm length was calculated by the least squares method for each inner tangent circle center. The diameter of the axis is gradually increased until the first contact with the cortex, and the cylindrical model is the ideal screw trajectory. The intersection of the axis and the dorsal cortex is the screw placement point, which is located by Horizon Distance (HD) and Vertical Distance (VD); the diameter of the screw trajectory (d) is the diameter of the cylindrical model; the direction of the screw trajectory is determined by Sagittal Angle (SA) and Transverse Angle (TA). The screw trajectory orientation is determined by Sagittal Angle (SA) and Transverse Angle (TA). Based on the ideal screw trajectory, the 3D printed surgical guide and freehand techniques were used to verify its safety feasibility, respectively.
RESULTS: The screw placement points [HD (4.7 ± 1.0) mm, VD (19.7 ± 1.9) mm], screw placement directions [SA (31.3°±2.3°), TA (42.4°±2.3°)], and screw dimensions for the ideal screw trajectory of the S2AI were combined for analysis. (L is 90 mm, d is 13.2 ± 1.4 mm). The S2AI screw superiority rate [96.6% (56/58)] and reasonable rate [100%] were higher in the guide group than in the freehand group [90.0% (63/70), 97.1% (68/70)], but the differences were not statistically significant (P > 0.05). Although screws invaded the cortex in both groups, there were no associated adverse events in either group.
CONCLUSIONS: The S2AI screw-based ideal trajectory placement is a safe, feasible and accurate method of screw placement.