Oliver Tannous

Heterotopic ossification after extremity blast amputation in a Sprague-Dawley rat animal model.

Objective: To create an animal survival model for heterotopic ossification (HO) in the residual limb of the rat after extremity blast amputation. The hypothesis was that extremity blast amputation spontaneously stimulates development of HO in the residual limb. Methods: Twelve Sprague-Dawley rats underwent localized exposure to a controlled, high-energy blast. Seven rats were designated for hind limb amputation and five for forelimb amputation. Our protocol produced extremity amputation through detonation of an explosive while protecting the animal proximal to the specified amputation level. Immediately after injury, the rat underwent wound management and primary surgical closure. Radiographs of the amputated limbs were obtained every 2 weeks. Heterotopic bone was radiographically classified as periosteal growth (Type A) or noncontiguous growth (Type B). A kappa statistic was calculated for interobserver strength of agreement on the presence of HO. Fisher exact test was conducted to assess the significance of the difference in hind limb and forelimb HO rates. Results: Nine of 12 animals survived the procedure. The three nonsurvivors were all hind limb amputees, and each died of various related causes. All four surviving hind limb amputees exhibited Type A HO, and three of four also exhibited Type B HO within the injured stump. One of five forelimb amputees exhibited Types A and B HO. Conclusions: We have developed a reproducible model for HO in the residual limbs of blast-amputated rats without addition of exogenous osteogenic stimulus. Hind limb amputation demonstrated a predilection for HO formation in comparison with forelimb amputation (P < 0.05).

Finding the right fit: studying the biomechanics of under-tapping with varying thread depths and pitches

BACKGROUND CONTEXT Compromise of pedicle screw purchase is a concern in maintaining rigid spinal fixation, especially with osteoporosis. Little consistency exists among various tapping techniques. Pedicle screws are often prepared with taps of a smaller diameter, which can further exacerbate inconsistency. PURPOSE The objective of this study was to determine whether a mismatch between tap thread depth (D) and thread pitch (P) and screw D and P affects fixation when under-tapping in osteoporotic bone. STUDY DESIGN This study is a polyurethane foam block biomechanical analysis. MATERIALS AND METHODS A foam block osteoporotic bone model was used to compare pullout strength of pedicle screws with a 5.3 nominal diameter tap of varying Ds and Ps. Blocks were sorted into seven groups: (1) probe only; (2) 0.5-mm D, 1.5-mm P tap; (3) 0.5-mm D, 2.0-mm P tap; (4) 0.75-mm D, 2.0-mm P tap; (5) 0.75-mm D, 2.5-mm P tap; (6) 0.75-mm D, 3.0-mm P tap; and (7) 1.0-mm D, 2.5-mm P tap. A pedicle screw, 6.5 mm in diameter and 40 mm in length, was inserted to a depth of 40 mm. Axial pullout testing was performed at a rate of 5 mm/min on 10 blocks from each group. RESULTS No significant difference was noted between groups under axial pullout testing. The mode of failure in the probe-only group was block fracture, occurring in 50% of cases. Among the other six groups, only one screw failed because of block fracture. The other 59 failed because of screw pullout. CONCLUSIONS In an osteoporotic bone model, changing the D or P of the tap has no statistically significant effect on axial pullout. Osteoporotic bone might render tap features marginal. Our findings indicate that changing the characteristics of the tap D and P does not help with pullout strength in an osteoporotic model. The high rate of fracture in the probe-only group might imply the potential benefit of tapping to prevent catastrophic failure of bone.

Does Lumbopelvic Fixation Add Stability? A Cadaveric Biomechanical Analysis of an Unstable Pelvic Fracture Model

Objective: We sought to determine the role of lumbopelvic fixation (LPF) in the treatment of zone II sacral fractures with varying levels of sacral comminution combined with anterior pelvic ring (PR) instability. We also sought to determine the proximal extent of LPF necessary for adequate stabilization and the role of LPF in complex sacral fractures when only 1 transiliac–transsacral (TI–TS) screw is feasible. Materials and Methods: Fifteen L4 to pelvis fresh-frozen cadaveric specimens were tested intact in flexion-extension (FE) and axial rotation (AR) in a bilateral stance gliding hip model. Two comminution severities were simulated through the sacral foramen using an oscillating saw, with either a single vertical fracture (small gap, 1 mm) or 2 vertical fractures 10 mm apart with the intermediary bone removed (large gap). We assessed sacral fracture zone (SZ), PR, and total lumbopelvic (TL) stability during FE and AR. The following variables were tested: (1) presence of transverse cross-connector, (2) presence of anterior plate, (3) extent of LPF (L4 vs. L5), (4) fracture gap size (small vs. large), (5) number of TI–TS screws (1 vs. 2). Results: The transverse cross-connector and anterior plate significantly increased PR stability during AR (P = 0.02 and P = 0.01, respectively). Increased sacral comminution significantly affected SZ stability during FE (P = 0.01). Two versus 1 TI–TS screw in a large-gap model significantly affected TL stability (P = 0.04) and trended toward increased SZ stabilization during FE (P = 0.08). Addition of LPF (L4 and L5) significantly improved SZ and TL stability during AR and FE (P < 0.05). LPF in combination with TI–TS screws resulted in the least amount of motion across all 3 zones (SZ, PR, and TL) compared with all other constructs in both small-gap and large-gap models. Conclusions: The role of LPF in the treatment of complex sacral fractures is supported, especially in the setting of sacral comminution. LPF with proximal fixation at L4 in a hybrid approach might be needed in highly comminuted cases and when only 1 TI–TS screw is feasible to obtain maximum biomechanical support across the fracture zone.

Outcomes of lumbopelvic fixation in the treatment of complex sacral fractures using minimally invasive surgical techniques

BACKGROUND CONTEXT Complex sacral fractures with vertical and anterior pelvic ring instability treated with traditional fixation methods are associated with high rates of failure and poor clinical outcomes. Supplemental lumbopelvic fixation (LPF) has been applied for additional stability to help with fracture union. PURPOSE The study aimed to determine whether minimally invasive LPF provides reliable fracture stability and acceptable complication rates in cases of complex sacral fractures. STUDY DESIGN/SETTING This is a retrospective cohort study at a single level I trauma center. PATIENT SAMPLE The sample includes 24 patients who underwent minimally invasive LPF for complex sacral fracture with or without associated pelvic ring injury. OUTCOME MEASURES Reoperation for all causes, loss of fixation, surgical time, transfusion requirements, length of hospital stay, postoperative day at mobilization, and mortality were evaluated. METHODS Patient charts from 2008 to 2014 were reviewed. Of the 32 patients who underwent minimally invasive LPF for complex sacral fractures, 24 (12 male, 12 female) met all inclusion and exclusion criteria. Outcome measures were assessed with a retrospective chart review and radiographic review. The authors did not receive external funding for this study. RESULTS Acute reoperation was 12%, and elective reoperation was 29%. Two (8%) patients returned to the operating room for infection, one (4.2%) required revision for instrumentation malposition, and seven (29%) underwent elective removal of instrumentation. No patient experienced failure of instrumentation or loss of correction. Average surgical time was 3.6 hours, blood loss was 180 mL, transfusion requirement was 2.1 units of packed red blood cells, and postoperative mobilization was on postoperative day 5. No mortalities occurred as a result of the minimally invasive LPF procedure. CONCLUSIONS Compared with historic reports of open LPF, our results demonstrate reliable maintenance of reduction and acceptable complication rates with minimally invasive LPF for complexsacral fractures. The benefits of minimally invasive LPF may be offset with increased elective reoperations for removal of instrumentation.

Low-Density Pedicle Screw Constructs for Adolescent Idiopathic Scoliosis: Evaluation of Effectiveness and Cost:

Introduction Optimal screw density and technique in treatment of idiopathic scoliosis remain unknown. We sought to find if low-density (LD) screw construct can achieve curve correction similar to that achieved with high-density (HD) constructs in adolescent scoliosis at substantial cost savings. Materials and Methods Patients treated operatively for idiopathic scoliosis at our center between 2007 and 2011 were identified through a retrospective database review. Each patient was treated with an LD screw construct. Radiographic outcomes included assessment of screw density, percent correction of major and fractional lumbar curves at follow-up, T5−T12 kyphosis, and angle of lowest instrumented vertebra (LIV). Costs were calculated and compared with costs of HD constructs. Results Forty-five patients met inclusion criteria. Ages ranged from 12 to 19 years (mean age, 14.9 years). Average construct density was 1.2 screws per fused level (range, 1.07−1.33 screws). Mean percent curve correction at latest follow-up: major curve, 67.2%; fractional lumbar curve, 69%. Average postoperative thoracic kyphosis: 30 degrees. Mean LIV angle: 5.6 degrees. Total screw cost was

Minimally Invasive Thoracolumbar Facet Joint Fusion

13,370 per case in the LD group compared with

Can Liposomal Bupivacaine Be Safely Utilized in Elective Spine Surgery

22,340 per case if all levels had been instrumented with 2 screws. Conclusions Our LD screw construct is among the lowest density constructs reported in the literature and achieves curve correction comparable to that reported for HD constructs at substantially lower cost.

Heterotopic Bone Formation About the Hip Undergoes Endochondral Ossification: A Rabbit Model

For minimally invasive spine surgery to be successful, it is mandatory that it achieves the same goals that open surgical procedures achieve. By avoiding collateral damages to anatomic structures, the purported advantages of minimally invasive techniques include reduction in postoperative pain, length of hospitalization, blood loss, and medical and surgical complications. During the past several years, surgeons have been expanding the indications for minimally invasive techniques from degenerative procedures to more complex spinal disorders, including thoracolumbar deformity, trauma, tumor, and infections. Paramount to successful results of treatment of many thoracolumbar pathological conditions is achieving a solid biological fusion.

Anterior surgical treatment for cervical spondylotic myelopathy

Study Design: Single-blinded prospective randomized control trial. Objectives: To compare the incidence of adverse events (AEs) and hospital length of stay between patients who received liposomal bupivacaine (LB) versus a single saline injection, following posterior lumbar decompression and fusion surgery for degenerative spondylosis. Methods: From 2015 to 2016, 59 patients undergoing posterior lumbar decompression and fusion surgery were prospectively enrolled and randomized to receive either 60 mL injection of 266 mg LB or 60 mL of 0.9% sterile saline, intraoperatively. Outcome measures included the incidence of postoperative AEs and hospital length of stay. Results: The most common AEs in the treatment group were nausea (39.3%), emesis (18.1%), and hypotension (18.1%). Nausea (23%), constipation (19.2%), and urinary retention (15.3%) were most common in the control group. Patients who received LB had an increased risk of developing nausea (relative risk [RR] = 1.7; 95% confidence interval [CI] = 0.75-3.8), emesis (RR = 2.3; 95% CI = 0.51-10.7), and headaches (RR = 2.36; 95% CI = 0.26-21.4). Patients receiving LB had a decreased risk of developing constipation (RR = 0.78; 95% CI = 0.25-2.43), urinary retention (RR = 0.78; 95% CI = 0.21-2.85), and pruritus (RR = 0.78; 95% = 0.21-2.8) postoperatively. Relative risk values mentioned above failed to reach statistical significance. No significant difference in the hospital length of stay between both groups was found (3.9 vs 3.9 days; P = .92). Conclusion: Single-dose injections of LB to the surgical site prior to wound closure did not significantly increase or decrease the incidence or risk of developing AEs postoperatively. Furthermore, no significant difference was found in the hospital length of stay between both groups.