Objective To evaluate the effectiveness of posterior unilateral pedicle screw fixation plus lumbar interbody fusion in treatment of degenerative lumbar instability. Methods Between February 2008 and December 2011, 33 patients with degenerative lumbar instability were treated with posterior unilateral pedicle screw fixation plus lumbar interbody fusion, including 14 cases of lumbar disc protrusion with instability, 15 cases of lumbar spinal stenosis with instability, 3 recurrent cases of lumbar disc protrusion at 1 year after discectomy, and 1 case of extreme lateral lumbar disc protrusion. There were 20 males and 13 females with an average age of 47.2 years (range, 39-75 years). The average disease duration was 12.8 months (range, 6-25 months). Single-segment-fixation was performed in 28 cases (L4, 5 in 21 cases, L5, S1 in 6 cases, and L5, 6 in 1 case), and double-segment-fixation was performed in 5 cases (L3, 4 and L4, 5). The clinical results were evaluated by using Oswestry disability index (ODI) and modified Japanese Orthopaedic Association (JOA) score for low back pain. Results Infection occurred in 1 case, and was cured after dressing change; primary healing was obtained in the other patients. Thirty-one patients were followed up 32.3 months on average (range, 15-53 months). Cage displacement occurred in 1 case who received bilateral pedicle screw fixation plus lumbar interbody fusion; no screw breaking, Cage displacement, or pseudoarthrosis was observed in the others. X-ray films showed bone fusion in the other patients except 1 case of bone fusion failure. ODI and JOA score at last follow-up were significantly improved when compared with the ones before operation and at 2 weeks after operation (P lt; 0.05); the improvement rates were 74.0% ± 10.1% and 83.6% ± 9.4%, respectively. Conclusion Posterior unilateral pedicle screw fixation plus lumbar interbody fusion is an effective and reliable method for patients with degenerative lumbar instability because it has the advantages of simple operation and less trauma.
Objective To evaluate the effects of sacrectomy extent on the stabil ity of lumbo-il iac fixation using single or dual il iac screw technique, and to determine which conditions require the dual il iac screw technique. Methods Nine fresh L2 to pelvic specimens were harvested from donated adult cadavers. After testing the intact state simulated by L3-5 pedicle screw fixation, sequential partial sacrectomies and L3 to il iac fixation using bilateral single il iac screw (Single) wereconducted on the same specimen as follows: in group A, under S1 partial sacrectomy and Single; in group B, under 1/2 S1 partial sacrectomy and Single; in group C, one-side (left) sacroil iac joint resection and Single; in group D, total sacrectomy and Single; and in group E, the single il iac screw was replaced by dual il iac screws based on group D. Biomechanical testing was performed on a material testing machine under 0-800 N compression and —7-7 N•m torsion loading modes for construct stiffness evaluation. Results The compressive stiffness of intact condition was (392 ± 119) N/mm, groups A, B, C, D, and E obtained 106.4% ± 9.5%, 102.7% ± 8.0%, 92.2% ± 10.1%, 72.7% ± 8.0%, and 107.7% ± 10.7% of intact condition, respectively. No significant differences were found among groups A, B, C, and the intact state (P gt; 0.05), however, the four groups showed significantly higher compressive stiffness than group D (P lt; 0.05). Although group E exhibited a comparable compressive stiffness with groups A, B, and intact state (P gt; 0.05), it displayed markedly higher compressive stiffness than groups C and D (P lt; 0.05). The torsional stiffness of intact state was (3.22 ± 1.23) N•m/deg. Groups A, B, C, D, and E acquired 105.4% ± 10.1%, 89.8% ± 12.3%, 75.9% ± 10.6%, 71.2% ± 10.2%, and 109.1% ± 16.9% of intact state, respectively. No significant differences were detected among groups A, B, E, and the intact state (P gt; 0.05). However, groups C and D showed remarkably lower torsional stiffness than groups A, E, and the intact state (P lt; 0.05). Importantly, group E offered remarkably higher torsional stiffness than group B (P lt; 0.05). Conclusion After under 1/2 S1 partial sacrectomy, single il iac screw technique could effectively restore local stabil ity; whereas it could hardly provide adequate stabil ity for further resection of one-side sacroil iac joint or total sacrectomy; in such situation, the use of dual il iac screw technique could obtain sufficient construct stabil ity. Therefore, in the surgical treatment of sacral tumor, the dual il iac screw technique should be considered for the unstable conditions of totalsacrectomy or under 1/2 S1 sacrectomy with one-side sacroil iac joint resection.
Objective To compare the maximum pull-out strength of the upper il iac screw and lower il iac screw with and without polymethylmethacrylate (PMMA) augmentation, and to provide the experimental evidences for the rational use of il iacscrews. Methods Ten intact human il ium from 5 donated cadavers with formal in embalmed were selected. The bone mineral density (BMD) of L1-4 of each cadaver was measured with a dual energy X-ray absorptiometry. The screws placed in the upper and lower il iac column were named as the upper and lower il iac screw, respectively. Using 70 mm length and 7.5 mm diameter screws with and without PMMA augmentation, 4 il iac screw technique models were sequentially establ ished and tested as follows: upper il iac screw (group A), upper il iac screw with PMMA augmentation (group B), lower il iac screw (group C), and lower il iac screw with PMMA augmentation (group D). Each il ium was mounted on a material testing machine with its position similar to standing. Under 2 000 cycl ic compressive loadings of 100-300 N to the screw, the maximum pull-out strength of il iac screw was measured. Results The BMD value of the 5 human cadavers was (0.88 ± 0.06) g/cm2. All the il iac screws were inserted into the screw tracts accurately as expected. No screw penetrations of acetabulum or cortex was not observed through visual inspection. There was no “halo” ring sign surrounding any screw after the 2 000 cycle loading. The maximum pull-out strengths of groupsA, B, C, and D were (964 ± 250), (1 462 ± 266), (1 537 ± 279), and (1 964 ± 422) N, respectively. Group D exhibited the highest maximum pull-out strength among the 4 groups (P lt; 0.05). No significant difference was detected between groups B and C (P gt; 0.05); however, groups B, C showed higher maximum pull-out strength than group A (P lt; 0.05). Conclusion The lower il iac screw offers significantly higher fixation strength than the upper il iac screw; PMMA augmentation could effectively increase the fixation strength of il iac screws and therefore could be appl ied in the salvage of il iac screw loosening.