Anatomic trajectory for iliac screw placement adapts better to the morphological features of the pelvis of each individual than the S2 alar iliac screw: a radiological study.

PURPOSE: The iliac fixation (IF) through the S2 ala permits the minimization of implant prominence and tissue dissection. An alternative to this technique is the anatomic iliac screw fixation (AI), which considers the perpendicular axis to the narrowest width of the ileum and the width of the screw. The morphological accuracy of the iliac screw insertion of two low profile iliac fixation (IF) techniques is investigated in this study. METHODS: Twenty-nine patients operated on via low profile IF technique were divided into two groups, those treated using 28 screws with the starting point at S2, and those treated with 30 AI entry point. Radiological parameters (Tsv-angle, Sag-Angle, Max-length, sacral-distance, iliac-width, S2-midline, skin-distance, iliac-wing, and PSIS distance) and clinical outcomes (early and clinic complications) were evaluated by two blinded expert radiologists, and the results were compared in both groups with the real trajectory of the screws placed. RESULTS: Differences between ideal and real trajectories were observed in 6 of the 9 evaluated parameters in the S2AI group. In the AI group, these trajectories were similar, except for TSV-Angle, Max-length, Iliac-width, and distance to iliac-wing parameters. Moreover, compared with S2AI, AI provided better adaptation to the pelvic morphology in all parameters, except for sagittal plane angulation, skin distance, and iliac width. CONCLUSIONS: AI ensures the advantages of low profile pelvic fixation like S2AI, with a starting point in line with S1 pedicle anchors and low implant prominence, and moreover adapts better to the morphological features of the pelvis of each individual.

Timing of PMMA cement application for pedicle screw augmentation affects screw anchorage.

INTRODUCTION: Cement augmentation is an established method to increase the pedicle screw (PS) anchorage in osteoporotic vertebral bodies. The ideal timing for augmentation when a reposition maneuver is necessary is controversial. While augmentation of the PS before reposition maneuver may increase the force applied it on the vertebrae, it bears the risk to impair PS anchorage, whereas augmenting the PS after the maneuver may restore this anchorage and prevent early screw loosening. The purpose of the present study was to evaluate the effect of cement application timing on PS anchorage in the osteoporotic vertebral body. METHODS: Ten lumbar vertebrae (L1-L5) were used for testing. The left and right pedicles of each vertebra were instrumented with the same PS size and used for pairwise comparison of the two timing points for augmentation. For the reposition maneuver, the left PS was loaded axially under displacement control (2 × ±2 mm, 3 × ±6 mm, 3 × ±10 mm) to simulate a reposition maneuver. Subsequently, both PS were augmented with 2 ml PMMA cement. The same force as measured during the left PS maneuver was applied to the previously augmented right hand side PS [2 × F (±2 mm), 3 × F (±6 mm), 3 × F (±10 mm)]. Both PS were cyclically loaded with initial forces of +50 and -50 N, while the lower force was increased by 5 N every 100 cycles until total failure of the PS. The PS motion was measured with a 3D motion analysis system. After cyclic loading stress, X-rays were taken to identify the PS loosening mechanism. RESULTS: In comparison with PS augmented prior to the reposition maneuver, PS augmented after the reposition maneuver showed a significant higher number of load cycles until failure (5930 ± 1899 vs 3830 ± 1706, p = 0.015). The predominant loosening mechanism for PS augmented after the reposition maneuver was PS toggling with the attached cement cloud within the trabecular bone. While PS augmented prior to the reposition, maneuver showed a motion of the screw within the cement cloud. CONCLUSION: The time of cement application has an effect on PS anchorage in the osteoporotic vertebral body if a reposition maneuver of the instrumented vertebrae is carried out. PS augmented after the reposition maneuver showed a significant higher number of load cycles until screw loosening.

Biomechanical, histological and histomorphometric analyses of calcium phosphate cement compared to PMMA for vertebral augmentation in a validated animal model.

INTRODUCTION: Calcium phosphate cements (biocements) are alternative materials for use in vertebral augmentation procedures, and are a potential solution to problems associated with polymethylmethacrylate (PMMA) cements. The aim of this study is to demonstrate the utility of percutaneously injected biocements compared with PMMA in a validated animal model of osteoporosis. MATERIALS AND METHODS: Fortyseven augmentation procedures were performed on 11 osteoporotic sheep. 9 vertebrae were augmented with PMMA and 38 with a biocement. The animals were killed in four groups: at 7 days, 3 months, 6 months, and 1 year after intervention. Radiological study and TC of the pieces were obtained to evaluate for leakage, cement diffusion, and integration. In total, 26 biomechanic studies and 27 histomorphometry analyses were performed, included control vertebrae. RESULTS: In 20.9% of the vertebrae, the hole was empty at sacrifice. The pattern of fracture was heterogeneous, and cement augmentation did not increase vertebral strength or decrease vertebral stiffness compared to control vertebrae, with neither PMMA or biocement. The rate of remodeling of the biocement was not predictable. In the single majority, there is peripheral remodeling, staying the volume of injected biocement stable. CONCLUSIONS: Even though this animal model may not be useful to analyze the biomechanical pattern of treated vertebrae, it demonstrates that the percutaneous use of biocements in vertebral augmentation techniques is not predictable. This is one reason not to recommend its use presently as a substitute for PMMA in vertebral reinforcement procedures.

Indication Variability in Degenerative Lumbar Spine Surgery: A Four-nation Survey.

STUDY DESIGN: Electronic survey. OBJECTIVE: The aim of this study was to identify the international nuances in surgical treatment patterns for severals lumbar degenerative conditions, specifically, to identify differences in responses in each country groupand different treatment trends across countries. SUMMARY OF BACKGROUND DATA: Significant variations in treatment of lumbar degenerative conditions exist among spine surgeons, related to the lack of established consensus in the literature. METHODS: An online survey with preformulated answers was submitted to 52 orthopedic surgeons, 50 neurosurgeons from four different countries (United States, France, Spain, and Germany) regarding five vignette-cases. Cases included: multilevel stenosis, monolevel stenosis, lytic spondylolisthesis, isthmic lysis, and degenerative scoliosis. The variability for each country was calculated according to the Index of Qualitative Variation (IQV = 0: no variability and 1: maximal variability). We used Fleiss kappa (range: from -1, poor agreement, to 1, almost perfect agreement) for assessing the reliability of agreement between the participants concerning specialties, countries, and age groups. RESULTS: For the two stenosis cases, US surgeons were more likely to propose decompression (IQV multilevel = 0.47 and monolevel = 0.32) comparing with European countries more heterogeneous (all IQV >0.70) and more frequently proposing fusion. As regards degenerative scoliosis, all attitudes were extremely heterogeneous with IQV >0.8. Fusion for isthmic spondylolisthesis was more consensual (all IQV <0.63), but attitudes were more heterogeneous for isthmic lysis (IQV ranged from 0.48 to 0.76) with anterior approach proposed in France (37%) and United States (19.2%).The overall interrater agreement was equally slight not only for neurosurgeons (Fleiss Kappa = 0.04) and orthopedic surgeons (Kappa = 0.13), but also for countries (Kappa <0.13) and age groups (Kappa <0.1). CONCLUSION: In this study, we found substantial agreement for some spinal conditions but a high variability in some others: intranational and international variations were observed, reflecting the lack of literature consensus. LEVEL OF EVIDENCE: 2.