Biomechanical Comparison of Subsidence Between Patient-Specific and Non-Patient-Specific Lumbar Interbody Fusion Cages.

STUDY DESIGN: Biomechanical study. OBJECTIVES: Several strategies to improve the surface of contact between an interbody device and the endplate have been employed to attenuate the risk of cage subsidence. 3D-printed patient-specific cages have been presented as a promising alternative to help mitigate that risk, but there is a lack of biomechanical evidence supporting their use. We aim to evaluate the biomechanical performance of 3D printed patient-specific lumbar interbody fusion cages in relation to commercial cages in preventing subsidence. METHODS: A cadaveric model is used to investigate the possible advantage of 3D printed patient-specific cages matching the endplate contour using CT-scan imaging in preventing subsidence in relation to commercially available cages (Medtronic Fuse and Capstone). Peak failure force and stiffness were analyzed outcomes for both comparison groups. RESULTS: PS cages resulted in significantly higher construct stiffness when compared to both commercial cages tested (>59%). PS cage peak failure force was 64% higher when compared to Fuse cage (P < .001) and 18% higher when compared to Capstone cage (P = .086). CONCLUSIONS: Patient-specific cages required higher compression forces to produce failure and increased the cage-endplate construct' stiffness, decreasing subsidence risk.

Extended Intraoperative Longitudinal 3-Dimensional Cone Beam Computed Tomography Imaging With a Continuous Multi-Turn Reverse Helical Scan.

OBJECTIVES: Cone beam computed tomography (CBCT) imaging is becoming an indispensable intraoperative tool; however, the current field of view prevents visualization of long anatomical sites, limiting clinical utility. Here, we demonstrate the longitudinal extension of the intraoperative CBCT field of view using a multi-turn reverse helical scan and assess potential clinical utility in interventional procedures. MATERIALS AND METHODS: A fixed-room robotic CBCT imaging system, with additional real-time control, was used to implement a multi-turn reverse helical scan. The scan consists of C-arm rotation, through a series of clockwise and anticlockwise rotations, combined with simultaneous programmed table translation. The motion properties and geometric accuracy of the multi-turn reverse helical imaging trajectory were examined using a simple geometric phantom. To assess potential clinical utility, a pedicle screw posterior fixation procedure in the thoracic spine from T1 to T12 was performed on an ovine cadaver. The multi-turn reverse helical scan was used to provide postoperative assessment of the screw insertion via cortical breach grading and mean screw angle error measurements (axial and sagittal) from 2 observers. For all screw angle measurements, the intraclass correlation coefficient was calculated to determine observer reliability. RESULTS: The multi-turn reverse helical scans took 100 seconds to complete and increased the longitudinal coverage by 370% from 17 cm to 80 cm. Geometric accuracy was examined by comparing the measured to actual dimensions (0.2 ± 0.1 mm) and angles (0.2 ± 0.1 degrees) of a simple geometric phantom, indicating that the multi-turn reverse helical scan provided submillimeter and degree accuracy with no distortion. During the pedicle screw procedure in an ovine cadaver, the multi-turn reverse helical scan identified 4 cortical breaches, confirmed via the postoperative CT scan. Directly comparing the screw insertion angles (n = 22) measured in the postoperative multi-turn reverse helical and CT scans revealed an average difference of 3.3 ± 2.6 degrees in axial angle and 1.9 ± 1.5 degrees in the sagittal angle from 2 expert observers. The intraclass correlation coefficient was above 0.900 for all measurements (axial and sagittal) across all scan types (conventional CT, multi-turn reverse helical, and conventional CBCT), indicating excellent reliability between observers. CONCLUSIONS: Extended longitudinal field-of-view intraoperative 3-dimensional imaging with a multi-turn reverse helical scan is feasible on a clinical robotic CBCT imaging system, enabling long anatomical sites to be visualized in a single image, including in the presence of metal hardware.

Accuracy of Patient-Specific Drill Guide Template for Bilateral C1-C2 Laminar Screw Placement: A Cadaveric Study.

OBJECTIVE: We sought to evaluate the accuracy of using patient-specific drill guides to place bilateral laminar screws in C1 and C2. METHODS: Nine cervical specimens (8 males; mean age: 66.6 [56-73]) with the occiput attached (C0-C3) were used in this study. Preoperative computed tomography (CT) scans were used to create digital anatomic models for templating and guide creation. A total of 36 screws were placed with the aid of 3-dimensional printed, patient-specific guides (2 screws at C1 and C2). Postoperative CT scans were performed following screw insertion. The planned and actual trajectories were compared using preoperative and postoperative imaging based on the angular and entry point deviation. After screw placement and postoperative imaging, each specimen was dissected and performed a visual inspection for breaches. RESULTS: No breaches or violations were observed on postprocedural CT and visual inspection. The average variation of the entry point in the X, Y, and Z axes was 0.3 ± 0.28, 0.41 ± 0.38, and 0.29 ± 0.24, respectively. No statistically significant difference (P > 0.05) was observed between the planned and obtained entry points. There was no significant difference (P > 0.05) in the deviation analysis between the planned and obtained angles in the axial and coronal planes. CONCLUSIONS: The study demonstrates that patient-specific drill guides allow for accurate C1 and C2 bilateral laminar screw placement, with a low risk of cortical breach.

Biomechanical comparison of 3 types of transdiscal fixation implants for fixing high-grade L5/S1 spine spondylolisthesis.

BACKGROUND CONTEXT: There are several options for the stabilization of high-grade lumbosacral spondylolisthesis including transdiscal screws, the Bohlman technique (transdiscal fibular strut) and the modified Bohlman technique (transdiscal titanium mesh cage). The choice of an optimum construct remains controversial; therefore, we endeavoured to study and compare the biomechanical performance of these 3 techniques. PURPOSE: The aim of this study was to compare 3 types of transdiscal fixation biomechanically in an in vitro porcine lumbar-sacral spine model. STUDY DESIGN/SETTING: Porcine cadaveric biomechanical study. METHODS: 18 complete lumbar-sacral porcine spines were split into 3 repair groups, transdiscal screws (TS), Bohlman technique, and a modified Bohlman technique (MBT). Range of motion (L3 - S1) was measured in an intact and repaired state for flexion, extension, left/right lateral bending, and left/right torsion. To recreate a high-grade lumbosacral spondylolisthesis a bilateral L5/S1 facetectomy, removing the intervertebral disc completely, and the L5 body was displaced 50%-60% over the sacral promontory. Results were analyzed and compared to intact baseline measurements. Standard quasi-static moments (5 Nm) were applied in all modes. RESULTS: All range of motion (ROM) were in reference to intact baseline values. TS had the lowest ROM in all modes (p=.006-.495). Statistical difference was found only in extension for TS vs. BT (p=.011) and TS vs. MBT (p=.014). No bone or implant failures occurred. CONCLUSION: TS provided the lowest ROM in all modes of loading compared to Bohlman technique and MBT. Our study indicates that TS results in the most biomechanically stable construct. CLINICAL SIGNIFICANCE: Knowledge of the biomechanical attributes of various constructs could aid physicians in choosing a surgical construct for their patients.

Anatomical relationship between the accessory process of the lumbar spine and the pedicle screw entry point.

INTRODUCTION: The vertebra accessory process (or tubercle) of the lumbar spine is an understated landmark which lies caudal to the mammillary process at the base of the transverse process. To our knowledge, no studies compare its relation to pedicle entry point for screw placement. We proposed to evaluate whether a valid and reliable relationship exists between the accessory process and the projected pedicle axis. MATERIAL AND METHODS: The distance between the tip of the accessory process and the entry point of the pedicle screw was measured for 50 pedicles. The angle between this axis and the midline was measured. Interrater reliability was assessed intraclass correlation coefficient for two raters. Statistical analysis of the results was performed using SPSS. RESULTS: The mean distance between the tip of accessory process and pedicle screw entry point was 6.58 mm (SD ±2.05), and the mean angle between this axis and the midline was 29.4° medial (SD ±10.08). The ICC for the two raters for the mean distance and the mean angle was 0.974 and 0.894. The calculated mean distance between the tip of the accessory process and pedicle screw entry point was 3.2 mm (SD ±1.3) and 5.7 mm (SD ±1.9) medial and cranial respectively. CONCLUSIONS: The accessory process is a consistent and reliable landmark to guide pedicle screw entry point, and compliments other screw insertion techniques. To our knowledge, this is the first study in the published literature to assess this relationship.

Extensile lateral versus sinus tarsi approach for displaced, intra-articular calcaneal fractures: a meta-analysis.

BACKGROUND: Operative management of displaced, intra-articular calcaneal fractures is associated with improved functional outcomes but associated with frequent complications due to poor soft tissue healing. The use of a minimally invasive sinus tarsi approach to the fixation of these fractures may be associated with a lower rate of complications and therefore provide superior outcomes without the associated morbidity of operative intervention. METHODS: We reviewed four prospective and seven retrospective trials that compared the outcomes from the operative fixation of displaced intra-articular calcaneal fractures via either an extensile lateral approach or minimally invasive fixation via a sinus tarsi approach. RESULTS: Patients managed with a sinus tarsi approach were less likely to suffer complications (OR = 2.98, 95% CI = 1.62-5.49, p = 0.0005) and had a shorter duration of surgery (OR = 44.29, 95% CI = 2.94-85.64, p = 0.04). CONCLUSION: In displaced intra-articular calcaneal fractures, a minimally invasive sinus tarsi approach is associated with a lower complication rate and quicker operation duration compared to open reduction and internal fixation via an extensile lateral approach.

Position of the sciatic nerve and effect of gluteus maximus release during hip arthroplasty.

Eight Thiel embalmed hips were dissected. The distance between the sciatic nerve and the femoral neck was measured before and after hip dislocation, and before and after release of the gluteus maximus tendon. There was a significant reduction in the mean distance between the neck of femur and the sciatic nerve in both the gluteus maximus tendon release and the unreleased groups at 60° and 90° of hip flexion, p < 0.05. The mean distance between the neck of femur and sciatic nerve was greater in the release group for all positions.

The Distance of the Common Peroneal Nerve to the Posterolateral Structures of the Knee.

BACKGROUND: The common peroneal nerve (CPN) is an important structure of the lower limb and is at risk of injury during total knee arthroplasty. The aim of this study was to use a tibial reference system to determine the position of the CPN relative to the knee center and popliteus. METHODS: Two hundred consecutive knee magnetic resonance images at the level of a standard tibial arthroplasty cut were evaluated for (1) distance of the CPN from the posterolateral capsule; (2) angle of the CPN from the center of the tibial anteroposterior axis; and (3) location of CPN with respect to the popliteus. RESULTS: The mean distance between the CPN and the posterolateral joint capsule was 11.9 mm (range, 4.7-22.13 mm), which correlated positively with the medial-lateral axis of the tibia (Pearson correlation, 0.157; P = .026) and negatively with the angle of the nerve from the midline (Pearson correlation, -0.237, P = .001). The mean angle of the nerve from the midline was 42.2° (range, 25.0°-64.0°). In 116 knees (58%), the CPN was in line with the popliteus from the center of the knee, in 69 knees (34.5%) the CPN was lateral to the popliteus, and in 15 knees (7.5%), the CPN was medial to the popliteus. A danger zone was identified as between 29.95° and 54.57° from the anteroposterior axis. CONCLUSION: The CPN is at risk during total knee arthroplasty. This study describes a method to help predict the location of the CPN intraoperatively and therefore avoid direct injury.

Safe zone for the superficial femoral artery demonstrated on computed tomography angiography.

INTRODUCTION: Internal or external fixation of the femur is common following trauma. Neurovascular structures around the shaft of the femur are at risk, particularly the superficial femoral artery (SFA). Damage to this structure, when it is medial to the femur, can occur during the lateral approach, when drills, pins or screws are inserted. This anatomical study aims to delineate a safe zone for operative intervention to the shaft of the femur with respect to the SFA, and describe the relationship between this zone and the width and length of the femur. MATERIALS AND METHODS: 41 limbs from 22 patients were examined using Computed Tomography Angiography to determine the relationship between the SFA and the medial shaft of the femur. The danger zone where the SFA lies medial to the shaft of the femur in the sagittal plane was identified and measured, and the width and length of the femur were measured for reference points. RESULTS: The SFA begins anterior to the shaft of the femur proximally and passes posteriorly, crossing the shaft of the femur in the sagittal plane at points 239.6±39.8mm and 172.5±40.9mm proximal to the adductor tubercle (AT). The width of the femur correlates to the inferior crossing point of the SFA on the femur with a mean ratio of 1:2.05, p=0.000, the length of the femur correlates to the mid crossing point of the SFA on the femur with a ratio of 2.00:1, p=0.000. CONCLUSIONS: There is a safe zone along the medial shaft of the femur, which can be estimated intraoperatively using anatomical reference points.

The influence of entry point and radius of curvature on femoral intramedullary nail position in the distal femur.

AIM: Perforation of the anterior cortex during femoral intramedullary nailing can be a major complication. We aim to determine the influence of entry point and radius of curvature on intramedullary nail position in the distal femur using a synthetic bone model. METHODS: Using synthetic femora, the greater trochanter was measured and entry points marked in two planes. A standard recommended technique was used to insert two different Stryker Gamma 3 intramedullary nails of different radius of curvature. The synthetic femora were sectioned and the centre of nail to anterior cortex distance (CAD) was measured. Statistical interpretation of the results was performed using linear regression analyses. RESULTS: We found that the more posterior entry points led to a more anterior placement in the distal femur in both nails of differing radius of curvature (11 mm and 13.5 mm CAD). The smaller radius of curvature led to a more central placement of the nail tip in the distal femur. CONCLUSION: Anterior penetration of the distal femur can be minimized by a more anterior entry point and with the use of a femoral intramedullary nail with a smaller radius of curvature.