Antoine Tohmeh

Biomechanical efficacy of unipedicular versus bipedicular vertebroplasty for the management of osteoporotic compression fractures

STUDY DESIGN Cadaveric study on the biomechanics of osteoporotic vertebral bodies augmented and not augmented with polymethylmethacrylate cement. OBJECTIVES To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and 1) not augmented, 2) augmented with unipedicular injection of cement, or 3) augmented with bipedicular injection of cement. SUMMARY OF BACKGROUND DATA Percutaneous vertebroplasty is a relatively new method of managing osteoporotic compression fractures, but it lacks biomechanical confirmation. METHODS Fresh vertebral bodies (L2-L5) were harvested from 10 osteoporotic spines (T scores range, -3.7 to -8.8) and compressed in a materials testing machine to determine intact strength and stiffness. They were then repaired using a transpedicular injection of cement (unipedicular or bipedicular), or they were unaugmented and recrushed. RESULTS Results suggest that unipedicular and bipedicular cement injection restored vertebral body stiffness to intact values, whereas unaugmented vertebral bodies were significantly more compliant than either injected or intact vertebral bodies. Vertebral bodies injected with cement (both bipedicular and unipedicular) were significantly stronger than the intact vertebral bodies, whereas unaugmented vertebral bodies were significantly weaker. There was no significant difference in loss in vertebral body height between any of the augmentation groups. CONCLUSIONS This study suggests that unipedicular and bipedicular injection of cement, as used during percutaneous vertebroplasty, increases acute strength and restores stiffness of vertebral bodies with compression fractures.

Adult degenerative scoliosis treated with XLIF: clinical and radiographical results of a prospective multicenter study with 24-month follow-up.

Study Design. Prospective, multicenter, single-arm study. Objective. The objective of this study was to evaluate the clinical and radiographical results of patients undergoing extreme lateral interbody fusion (XLIF), a minimally disruptive lateral transpsoas retroperitoneal surgical approach for the treatment of degenerative scoliosis (DS). Summary of Background Data. Surgery for the treatment of DS has been reported to have acceptable results but is traditionally associated with high morbidity and complication rates. A minimally disruptive lateral transpsoas retroperitoneal surgical approach (XLIF) has become popular for the treatment of DS. This is the first prospective, multicenter study to quantify outcomes after XLIF in this patient population. Methods. A total of 107 patients with DS who underwent the XLIF procedure with or without supplemental posterior fixation at one or more intervertebral levels were enrolled in this study. Clinical and radiographical results were evaluated up to 24 months after surgery. Results. Mean patient age was 68 years; 73% of patients were female. A mean of 3.0 (range, 1–6) levels were treated with XLIF per patient. Overall complication rate was low compared with traditional surgical treatment of DS. Significant improvement was seen in all clinical outcome measures at 24 months: Oswestry Disability Index, visual analogue scale for back pain and leg pain, and 36-Item Short Form Health Survey mental and physical component summaries (P < 0.001). Eighty-five percent of patients were satisfied with their outcome and would undergo the procedure again. In patients with hypolordosis, lumbar lordosis was corrected from a mean of 27.7° to 33.6° at 24 months (P < 0.001). Overall Cobb angle was corrected from 20.9° to 15.2°, with the greatest correction observed in patients supplemented with bilateral pedicle screws. Conclusion. This study demonstrates the use of the XLIF procedure in the treatment of DS. XLIF is associated with good clinical and radiographical outcomes, with a substantially lower complication rate than has been reported with traditional surgical procedures. Level of Evidence: 3

Two-Year Comparative Outcomes of MIS Lateral and MIS Transforaminal Interbody Fusion in the Treatment of Degenerative Spondylolisthesis: Part II: Radiographic Findings.

Study Design. A prospective, multicenter, institutional review board (IRB) approved study with randomized and observational study arms. Objective. The purpose of this study was to compare clinical outcomes between minimally invasive transforaminal (MIS TLIF) and MIS lateral interbody fusion (XLIF) in the treatment of patients with low-grade degenerative spondylolisthesis with stenosis through two years postoperative. Summary of Background Data. Few reports exist comparing different MIS approaches directly in the treatment of similar pathology, as most studies report differences between MIS and open procedures. Methods. A total of 55 patients undergoing surgical treatment for degenerative spondylolisthesis with spinal stenosis at one or two contiguous levels between L1 and L5 were enrolled. Twenty-nine patients were treated with XLIF and 26 patients were treated with MIS TLIF. Results. Operative time and length of stay were similar between the XLIF and MIS TLIF groups (171 vs 186 minutes; two days for each group). Blood loss was significantly lower in the XLIF group, with 79% of XLIF cases and 27% of MIS TLIF cases resulting in <100 mL of blood loss, P < 0.001. Hip flexion weakness was more common in the XLIF group (31%) than in the MIS TLIF group (0%). One patient in the XLIF group had a new distal motor weakness and three patients in the XLIF group and two patients in the MIS TLIF group had new sensory changes postoperatively, all of which resolved by 12 months postoperative. Back and leg pain for both XLIF and MIS TLIF groups improved significantly from baseline to 24 months postoperative, with 73% improvement in the XLIF and 64% in the MIS TLIF group. Worst leg pain showed similar improvements through two years postoperative, with a 79% decrease seen in the XLIF group and 74% in the MIS TLIF group. Disability (ODI) improved 53% in the XLIF group and 57% in the MIS TLIF group. Conclusion. Despite different mechanisms of action (indirect vs direct decompression), mid-term clinical outcomes between XLIF and MIS TLIF were similar. These two-year results suggest that both XLIF and MIS TLIF are reasonable MIS approaches for the treatment of lumbar degenerative pathology. Level of Evidence: 2

Radiographical and clinical evaluation of extreme lateral interbody fusion: effects of cage size and instrumentation type with a minimum of 1-year follow-up.

Study Design. Prospective single-cohort observational study. Objectives. To compare cage settling rates after extreme lateral interbody fusion (XLIF) across various implant sizes and fixation types. Secondary objectives were to detect factors associated with cage settling and correlation with clinical and radiographical improvement. Summary of Background Data. Intervertebral cage settling can occur postoperatively after interbody fusion, limiting the long-term correction achieved with surgery. Methods. Clinical and radiographical data were collected on 140 consecutive patients treated with extreme lateral interbody fusion at 223 levels (range, 1–5). All patients received supplemental pedicle screw fixation or lateral plating. Results. Average follow-up was 15.5 months (range, 12–36 mo). At 12 months, disability improved by 44%, low back pain improved by 49%, leg pain improved by 48%, and quality of life improved by 50% (P < 0.001). Foraminal height improved from 15.7 mm to 21.2 mm, disc height improved from 4.6 mm to 9.4 mm, discal lordosis improved from 4.0 to 8.1, and segmental lordosis improved from 10.7 to 13.7 (P < 0.001). Cage settling 1 mm or more occurred in 20% of cages immediately postoperatively and in 62% at 12 months. Settling more than 4 mm occurred in 5% of cages immediately postoperatively and in 24% at 12 months postoperatively. Pedicle screw fixation was associated with a higher rate of cage settling 1 mm or more compared with lateral plating, though magnitude of settling at the anterior inferior endplate was higher for lateral plating (4.9 mm vs. 3.5 mm). Taller cage height, narrower cage width, and shorter cage length were significantly associated with increased risk of cage settling more than 4 mm at 12 months postoperatively. In patients with no cage settling immediately postoperatively, risk of settling more than 4 mm at 12 months was 6.8 times greater with narrower cages. Conclusion. Risk of cage settling after extreme lateral interbody fusion may be reduced with the use of wider cages to engage more central endplate bone, longer cages to span the ring apophysis and osteophytes, and avoid overdistraction of the intervertebral disc space with shorter cages. Level of Evidence: 3

The choice of supplemental fixation in lateral interbody fusion: video lecture.

Learning objectives In this video lecture, the factors that influence the biomechanics of lateral interbody fusion and supplemental fixation are reviewed. Considerations for determining the optimal internal spinal fixation are explored. A decisionmaking scoring scheme is also proposed, based on spondylolisthesis, degenerative disc, facet disease and adjacent segment disease scores.

Long Construct Pedicle Screw Reduction and Residual Forces are Decreased Using aComputer-assisted Rod Bending System

Long Construct Pedicle Screw Reduction and Residual Forces are Decreased Using a Computer-assisted Rod Bending System Previous biomechanical studies have shown that reduction loads placed on pedicle screws during assembly of the construct, with a rod that does not adequately fit the screw locations, can reduce the strength of the screw-bone interfaces. In this bench top study, axial pedicle screw forces on a unilateral 7-level construct were evaluated for 2 rod bending techniques: manual and computerassisted.