Preliminary experience with a novel facet-based lateral mass drill guide for the placement of lateral mass screws compared to freehand technique: a cadaveric study.

BACKGROUND CONTEXT: Lateral mass screw fixation is the standard for posterior subaxial cervical fixation. Several freehand surgical techniques for placing lateral mass screws have been described which rely on anatomical landmarks and surgeon mastery of the technique to safely place screws. The accuracy of these freehand techniques is inherently variable and can be influenced by a surgeon's level of clinical experience. A novel technique was developed that utilizes the plane of the facet joint to create lateral mass screw pilot holes parallel with the joint line to improve the safety and accuracy of lateral mass screw placement regardless of experience. PURPOSE: To assess the safety and accuracy of lateral mass screw placement using a novel lateral mass drill guide instrument (LM Guide), compared to standard freehand technique. STUDY DESIGN: Randomized cadaveric study utilizing multiple surgeon evaluators to compare the safety and accuracy of guided cervical lateral mass placement compared to traditional freehand techniques. MATERIALS AND METHODS: Lateral mass screws were placed from C3 to C7 in 20 cadaver specimens by 8 spine surgeons of varying levels of clinical experience (4 attendings, 4 fellows). Screws were placed bilaterally using standard anatomic landmarks ("freehand") randomly allocated on one side and using the LM Guide on the other. Cadaveric specimens were imaged with high-resolution CT to assess screw placement. Zone grading for safety was conducted based on screw tip position and clinical severity of screw breach was based on proximity to surrounding neurovascular anatomy. Screws were graded as safe, at-risk, or critical, with at-risk and critical screws considered malpositioned. To assess the accuracy of screw trajectory placed using the LM Guide compared to freehand, sagittal screw angle was measured and compared to an "ideal" screw path parallel to the facet joint line. Freehand and LM Guide groups were compared using Pearson's chi-square correlation. RESULTS: Screw placement using the LM guide yielded a significantly lower rate of screw malpositioning, with 7 of 91 (7.7%) compared with 18 of 99 (18.2%) screws placed in the At-Risk or Critical Zones, p<.05. Of the 91 screws inserted using the LM Guide, 84 (92.3%) were in the Safe Zone, 7 (7.7%) were At-Risk, and 0 were in Critical zones. There was no incidence of neural or transverse foramen breaches with the LM Guide. In comparison, for the 99 screws inserted freehand, 81 (81.8%) were Safe, 14 (14.1%) were At-Risk, and 4 (4.1%) were in Critical zones. The 4 Critical zone freehand screw breaches included 1 neural foramen breach, 2 transverse foramen breaches, and 1 facet breach. The LM Guide also resulted in higher accuracy of screw trajectory, as indicated by a significant reduction in sagittal screw angle compared with freehand, p<.01. Notably, in the less-experienced surgeon cohort, the LM Guide significantly reduced the sagittal screw angle and resulted in no critical screw breaches compared to 3 critical breaches with freehand technique suggesting there might be a benefit in decreasing the learning curve associated with lateral mass screw placement. CONCLUSIONS: Lateral mass screw placement with a novel LM Guide that uses the facet joint to control screw trajectory improved the accuracy and reproducibility of screw placement with a significant reduction in screw breach rate and sagittal screw angle compared to freehand techniques regardless of surgeon experience level. CLINICAL SIGNIFICANCE: The inherent variability of freehand lateral mass screw placement can increase the risk of clinical complications associated with screw malpositioning. The technique presented in this cadaveric study may be a viable alternative to standard freehand technique that can improve the overall safety of lateral mass screw placement.

Dexmedetomidine Infusion for Routine Dental Management of an ASA IV Patient: A Case Report.

Anesthetic management of elderly patients requires numerous physiological considerations. With aging, degenerative changes occur in the structure and functional capacity of tissues and organs. Typically, these patients experience clinical effects with lower doses of medication. Important considerations for the geriatric populations following anesthesia include increased time to recovery and avoidance of functional decline. A case is reported in which an 83-year-old Caucasian female with a complex medical history presented for routine dental treatment under intravenous sedation via dexmedetomidine infusion.

The Impact of Nitinol Staples on the Compressive Forces, Contact Area, and Mechanical Properties in Comparison to a Claw Plate and Crossed Screws for the First Tarsometatarsal Arthrodesis.

UNLABELLED: Background The optimal fixation method for the first tarsometatarsal arthrodesis remains controversial. This study aimed to develop a reproducible first tarsometatarsal testing model to evaluate the biomechanical performance of different reconstruction techniques. Methods Crossed screws or a claw plate were compared with a single or double shape memory alloy staple configuration in 20 Sawbones models. Constructs were mechanically tested in 4-point bending to 1, 2, and 3 mm of plantar displacement. The joint contact force and area were measured at time zero, and following 1 and 2 mm of bending. Peak load, stiffness, and plantar gapping were determined. Results Both staple configurations induced a significantly greater contact force and area across the arthrodesis than the crossed screw and claw plate constructs at all measurements. The staple constructs completely recovered their plantar gapping following each test. The claw plate generated the least contact force and area at the joint interface and had significantly greater plantar gapping than all other constructs. The crossed screw constructs were significantly stiffer and had significantly less plantar gapping than the other constructs, but this gapping was not recoverable. Conclusions Crossed screw fixation provides a rigid arthrodesis with limited compression and contact footprint across the joint. Shape memory alloy staples afford dynamic fixation with sustained compression across the arthrodesis. A rigid polyurethane foam model provides an anatomically relevant comparison for evaluating the interface between different fixation techniques. Clinical Relevance The dynamic nature of shape memory alloy staples offers the potential to permit early weight bearing and could be a useful adjunctive device to impart compression across an arthrodesis of the first tarsometatarsal joint. LEVELS OF EVIDENCE: Therapeutic, Level V: Bench testing.

Evaluation of Nitinol Staples for the Lapidus Arthrodesis in a Reproducible Biomechanical Model.

While the Lapidus procedure is a widely accepted technique for treatment of hallux valgus, the optimal fixation method to maintain joint stability remains controversial. The purpose of this study is to evaluate the biomechanical properties of new shape memory alloy (SMA) staples arranged in different configurations in a repeatable first tarsometatarsal arthrodesis model. Ten sawbones models of the whole foot (n = 5 per group) were reconstructed using a single dorsal staple or two staples in a delta configuration. Each construct was mechanically tested non-destructively in dorsal four-point bending, medial four-point bending, dorsal three-point bending, and plantar cantilever bending with the staples activated at 37°C. The peak load (newton), stiffness (newton per millimeter), and plantar gapping (millimeter) were determined for each test. Pressure sensors were used to measure the contact force and area of the joint footprint in each group. There was a statistically significant increase in peak load in the two staple constructs compared to the single staple constructs for all testing modalities with P values range from 0.016 to 0.000. Stiffness also increased significantly in all tests except dorsal four-point bending. Pressure sensor readings showed a significantly higher contact force at time zero (P = 0.037) and contact area following loading in the two staple constructs (P = 0.045). Both groups completely recovered any plantar gapping following unloading and restored their initial contact footprint. The biomechanical integrity and repeatability of the models was demonstrated with no construct failures due to hardware or model breakdown. SMA staples provide fixation with the ability to dynamically apply and maintain compression across a simulated arthrodesis following a range of loading conditions.

The effect of sterilization on the mechanical properties of intact rabbit humeri in three-point bending, four-point bending and torsion.

Load bearing bone allografts are used to replace the mechanical function of bone that has been removed or to augment bone that has been damaged in trauma. In order to minimize the risk of infection and immune response, the bone is delipidated and terminally sterilized prior to implantation. The optimal method for bone graft sterilization has been the topic of considerable research. Recently, supercritical carbon dioxide (SCCO(2)) treatments have been shown to terminally sterilize bone against a range of bacteria and viruses. This study aimed to evaluate the effect of SCCO(2) treatment compared with two doses of gamma irradiation, on the mechanical properties of whole bone. Paired rabbit humeri were dissected and randomly assigned into either SCCO(2) control, SCCO(2) additive or gamma irradiation at 10 or 25 kGy treatment groups. The bones were mechanically tested in three-point and four-point bending and torsion, with the lefts acting as controls for the treated rights. Maximum load, energy to failure and stiffness were evaluated. This study found that SCCO(2) treatment with or without additive did not alter maximum load, energy to failure or stiffness significantly under any loading modality. Gamma irradiation had a deleterious dose dependant effect, with statistically significant decreases in all mechanical tests at 25 kGy; while at 10 kGy there were reductions in all loading profiles, though only reaching statistical significance in torsion. This study highlights the expediency of SCCO(2) treatment for bone allograft processing as terminal sterilization can be achieved while maintaining the intrinsic mechanical properties of the graft.

The effect of gamma irradiation on the anisotropy of bovine cortical bone.

Bone is an anisotropic non-homogenous composite material composed of inorganic bone mineral embedded in an organic matrix. The mechanical behaviour of bone is governed by the volume fraction of these constituents, their mechanical properties, the degree of crystallite-collagen orientation and the bonding between phases. This study aims to evaluate the mechanical role of these constituents in the expression of anisotropy by using gamma irradiation to alter the mineralised collagen fibrils. Bovine cortical cubes were prepared, treated and mechanically tested in uniaxial compression in the axial, radial and tangential orientations. Ultimate stress, ultimate strain, energy to failure and stiffness were evaluated. This study confirmed deleterious effect of gamma irradiation on the axial compressive properties of cortical bone with a dose dependent decrease in ultimate stress of 6% (P=0.231) and 16% (P=0.001) at 15 and 25 kGy respectively. This corresponded to a 39% (P=0.058) and 30% (P=0.167) reduction in energy to failure. In the radial orientation there was also a dose dependant decrease in ultimate stress which was consistent with a statistically significant decline in ultimate strain (31% (P=0.003) and 36% (P=0.000)) and energy to failure (36% (P=0.053) and 45% (P=0.008)) at both doses. In the tangential orientation there was a significant 22% (P=0.01) and 23% (P=0.02) decrease in stiffness; though these changes did not alter ultimate stress considerably. This study provides valuable insights into the role of collagen in the radial and tangential orientation when loaded in compression; while also building on the body of work related to the use of gamma irradiation for load bearing bone allografts.