Philippe Gédet

Mechanical anchorage and peri‐implant bone formation of surface‐modified zirconia in minipigs

AIM To test the hypothesis that peri-implant bone formation and mechanical stability of surface-modified zirconia and titanium implants are equivalent. MATERIALS AND METHODS Twelve minipigs received three types of implants on either side of the mandible 8 weeks after removal of all pre-molar teeth: (i) a zirconia implant with a sandblasted surface; (ii) a zirconia implants with a sandblasted and etched surface; and (iii) a titanium implant with a sandblasted and acid-etched surface that served as a control. Removal torque and peri-implant bone regeneration were evaluated in six animals each after 4 and 13 weeks. RESULTS The titanium surface was significantly rougher than both tested zirconia surfaces. Mean bone to implant contact (BIC) did not differ significantly between the three implant types after 4 weeks but was significantly higher for titanium compared with both zirconia implants after 13 weeks (p<0.05). Bone volume density (BVD) did not differ significantly at any interval. Removal torque was significantly higher for titanium compared with both zirconia surfaces after 4 and 13 weeks (p<0.001). The sandblasted and etched zirconia surface showed a significantly higher removal torque after 4 weeks compared with sandblasted zirconia (p<0.05); this difference levelled out after 13 weeks. CONCLUSIONS It is concluded that all implants achieved osseointegration with similar degrees of BIC and BVD; however, titanium implants showed a higher resistance to removal torque, probably due to higher surface roughness.

The influence of different osteosynthesis configurations with locking compression plates (LCP) on stability and fracture healing after an oblique 45° angle osteotomy

BACKGROUND Locking compression plates are used in various configurations with lack of detailed information on consequent bone healing. STUDY DESIGN In this in vivo study in sheep 5 different applications of locking compression plate (LCP) were tested using a 45° oblique osteotomy simulating simple fracture pattern. 60 Swiss Alpine sheep where assigned to 5 different groups with 12 sheep each (Group 1: interfragmentary lag screw and an LCP fixed with standard cortex screws as neutralisation plate; Group 2: interfragmentary lag screw and LCP with locking head screws; Group 3: compression plate technique (hybrid construct); Group 4: internal fixator without fracture gap; Group 5: internal fixator with 3mm gap at the osteotomy site). One half of each group (6 sheep) was monitored for 6 weeks, and the other half (6 sheep) where followed for 12 weeks. METHODS X-rays at 3, 6, 9 and 12 weeks were performed to monitor the healing process. After sacrifice operated tibiae were tested biomechanically for nondestructive torsion and compared to the tibia of the healthy opposite side. After testing specimens were processed for microradiography, histology, histomorphometry and assessment of calcium deposition by fluorescence microscopy. RESULTS In all groups bone healing occurred without complications. Stiffness in biomechanical testing showed a tendency for higher values in G2 but results were not statistically significant. Values for G5 were significantly lower after 6 weeks, but after 12 weeks values had improved to comparable results. For all groups, except G3, stiffness values improved between 6 and 12 weeks. Histomorphometrical data demonstrate endosteal callus to be more marked in G2 at 6 weeks. DISCUSSION AND CONCLUSION All five configurations resulted in undisturbed bone healing and are considered safe for clinical application.

Biomechanical Analysis of the Three‐Dimensional Motion Pattern of the Canine Cervical Spine Segment C4–C5

OBJECTIVE To study the kinematics of cervical spine segment C(4)-C(5) and its association with disc dimensions and the coupled motion (CM) in relation to primary motion (PM). STUDY DESIGN Cadaveric biomechanical study. ANIMALS Cadavers of large breed dogs (>20 kg; n=11). METHODS Spines were freed from muscles. Radiographs were taken orthogonal to the C(4)-C(5) disc space and disc thickness, endplate width, and height were measured. Spines were mounted on a simulator for 3-dimensional motion analysis. Data were recorded with an optoelectronic motion analysis system. Range of motion (ROM) and neutral zone (NZ) were determined in the direction of flexion/extension, left/right lateral bending, and left/right axial rotation, as well as the ROM of CM. RESULTS ROM in flexion and extension was similar; there was no CM in flexion/extension. Left/right axial rotation and left/right lateral bending were coupled to the same side. CM was 1.72 and 3.56 times the ROM of the PM in lateral bending and axial rotation, respectively. Disc dimensions were positively correlated with body weight. Flexion/extension magnitude was significantly reduced for larger endplates, but axial rotation was not influenced. Lateral bending had no correlation with weight or disc dimensions. CONCLUSION Left/right lateral bending and left/right axial rotation are coupled differently in the C(4)-C(5) segment in dogs compared with humans. CLINICAL RELEVANCE The canine C(4)-C(5) spinal segment has unique motion coupling patterns that should be considered for dynamic implant designs.

Viscoelastic properties of the ovine posterior spinal ligaments are strain dependent

BACKGROUND The biomechanical role of the posterior spinal ligaments for spinal stability has been stated in previous studies. The investigation of the viscoelastic properties of human lumbar spinal ligaments is essential for the understanding of physiological differences between healthy and degenerated tissues. The stress-relaxation behavior of biological tissues is commonly described with the quasi-linear viscoelastic model of Fung, which assumes that the stress-relaxation response is independent of the applied strain. The goal of this study was to investigate the stress-relaxation response of ovine posterior spinal ligaments at different elongations to verify the above-mentioned hypothesis. METHODS Twenty-four ovine lumbar spinal segments, consisting of only the supraspinous and interspinous ligaments and adjoining spinous processes, were elongated uniaxially to different strain levels within the physiological elastic region (5-20%). The experimental data were described with a non-linear viscoelastic model: the modified superposition method of Findley. FINDINGS A linear dependency of the relaxation rate to the applied strains was observed on intact segments, when both ligaments were considered, as well as on each individual ligament. This result can be applied to the human spinal ligaments, due to similarities observed between the sheep and human spinal segment under physiological loading. INTERPRETATION The non-linear viscoelastic modified superposition method of Findley is an appropriate model for describing the viscoelastic properties of lumbar spinal ligaments in vitro due to its ability to address variation in applied strain during the force relaxation measurements.

A Robust and Accurate Two-Stage Approach for Automatic Recovery of Distal Locking Holes in Computer-Assisted Intramedullary Nailing of Femoral Shaft Fractures

It has been recognized that one of the most difficult steps in intramedullary nailing of femoral shaft fractures is the distal locking- the insertion of distal transverse interlocking screws, for which it is necessary to know the positions and orientations of the distal locking holes (DLHs) of the intramedullary nail (IMN). This paper presents a robust and accurate approach for solving this problem based on two calibrated and registered fluoroscopic images. The problem is formulated as a two-stage model-based optimal fitting process. The first stage, nail detection, automatically estimates the axis of the distal part of the IMN (DP-IMN) by iteratively fitting a cylindrical model to the images. The second stage, pose recovery, resolves the translations and the rotations of the DLHs around the estimated axis by iteratively fitting the geometrical models of the DLHs to the images. An iterative best matched projection point (IBMPP) algorithm is combined with random sample strategies to effectively and robustly solve the fitting problems in both stages. We designed and conducted comprehensive experiments to validate the robustness and the accuracy of the present approach. Our in vitro experiments show on average less than 14 s execution time on a Linux machine, a mean angular error of 0.48deg (std = 0.25deg), and a mean translational error of 0.09 mm (std = 0.04 mm). We conclude that the present approach is fast, robust, and accurate for distal locking applications.

Biomechanical analysis of torsion and shear forces in lumbar and lumbosacral spine segments of nonchondrodystrophic dogs.

OBJECTIVE To determine stiffness and load-displacement curves as a biomechanical response to applied torsion and shear forces in cadaveric canine lumbar and lumbosacral specimens. STUDY DESIGN Biomechanical study. ANIMALS Caudal lumbar and lumbosacral functional spine units (FSU) of nonchondrodystrophic large-breed dogs (n=31) with radiographically normal spines. METHODS FSU from dogs without musculoskeletal disease were tested in torsion in a custom-built spine loading simulator with 6 degrees of freedom, which uses orthogonally mounted electric motors to apply pure axial rotation. For shear tests, specimens were mounted to a custom-made shear-testing device, driven by a servo hydraulic testing machine. Load-displacement curves were recorded for torsion and shear. RESULTS Left and right torsion stiffness was not different within each FSU level; however, torsional stiffness of L7-S1 was significantly smaller compared with lumbar FSU (L4-5-L6-7). Ventral/dorsal stiffness was significantly different from lateral stiffness within an individual FSU level for L5-6, L6-7, and L7-S1 but not for L4-5. When the data from 4 tested shear directions from the same specimen were pooled, level L5-6 was significantly stiffer than L7-S1. CONCLUSIONS Increased range of motion of the lumbosacral joint is reflected by an overall decreased shear and rotational stiffness at the lumbosacral FSU. CLINICAL RELEVANCE Data from dogs with disc degeneration have to be collected, analyzed, and compared with results from our chondrodystrophic large-breed dogs with radiographically normal spines.

Prediction of dental implant torque with a fast and automatic finite element analysis: a pilot study

OBJECTIVES Despite its importance, implant removal torque can be assessed at present only after implantation. This paper presents a new technique to help clinicians preoperatively evaluate implant stability. STUDY DESIGN Planning software has been combined with an in-house finite element solver. Once the clinician has chosen the implant position on the planner, a finite element analysis automatically calculates the primary stability. The process was designed to be as simple and fast as possible for clinical use. This paper describes application of the method to the prediction of removal torque. A preliminary validation has been performed in both polyurethane foam and sheep bone. RESULTS The predicted torque is quantitatively equivalent to experimental values with correlation coefficients of >0.7 in both materials. CONCLUSIONS This preliminary study is a first step toward the introduction of finite element models in computer-assisted surgery. The fact that the process is fast and automatic makes it suitable for a clinical use.

Accurate and reliable pose recovery of distal locking holes in computer-assisted intra-medullary nailing of femoral shaft fractures: A preliminary study

Objective: One of the difficult steps in intra-medullary nailing of femoral shaft fractures is distal locking – the insertion of distal interlocking screws. Conventionally, this is performed using repeated image acquisitions, which leads to considerable irradiation of the patient and surgical team. Virtual fluoroscopy has been used to reduce radiation exposure, but can only provide multi-planar two-dimensional projection views. In this study, two calibrated fluoroscopic images were used to automatically recover the positions and orientations of the distal locking holes (DLHs). The ultimate goal is to provide precise three-dimensional guidance during distal locking. Methods: A model-based optimal fitting process was used to reconstruct the positions and orientations of the DLHs from two calibrated fluoroscopic images. No human intervention is required. A preliminary in vitro validation study was conducted to analyze the accuracy and reliability of the technique using images acquired from different viewpoints. The ground truths of the DLH were obtained by inserting a custom-made steel rod through the hole and then digitizing both the top and bottom centers of the rod using a sharp pointer. The recovery errors were computed by comparing the computed results to the ground truths. Results: In all experiments, the poses of the DLHs could be recovered fully automatically. When the recovered positions and orientations of the DLHs were compared to their associated ground truths, a mean angular error of 0.5° (STD = 0.2°), and a mean translational error of 0.1 mm (STD = 0.0 mm) were found. Conclusions: Accurate and reliable pose recovery of distal locking holes from two calibrated fluoroscopic images is achievable. Our preliminary in vitro experimental results demonstrate that the recovered poses of the distal locking holes are sufficiently accurate for intra-operative use.

Combining 3D tracking and surgical instrumentation to determine the stiffness of spinal motion segments: a validation study.

The spine is a complex structure that provides motion in three directions: flexion and extension, lateral bending and axial rotation. So far, the investigation of the mechanical and kinematic behavior of the basic unit of the spine, a motion segment, is predominantly a domain of in vitro experiments on spinal loading simulators. Most existing approaches to measure spinal stiffness intraoperatively in an in vivo environment use a distractor. However, these concepts usually assume a planar loading and motion. The objective of our study was to develop and validate an apparatus, that allows to perform intraoperative in vivo measurements to determine both the applied force and the resulting motion in three dimensional space. The proposed setup combines force measurement with an instrumented distractor and motion tracking with an optoelectronic system. As the orientation of the applied force and the three dimensional motion is known, not only force-displacement, but also moment-angle relations could be determined. The validation was performed using three cadaveric lumbar ovine spines. The lateral bending stiffness of two motion segments per specimen was determined with the proposed concept and compared with the stiffness acquired on a spinal loading simulator which was considered to be gold standard. The mean values of the stiffness computed with the proposed concept were within a range of ±15% compared to data obtained with the spinal loading simulator under applied loads of less than 5 Nm.

Validation of Intra-Operative Measurement Apparatus to Determine the Stiffness Properties of Spinal Motion Segments

The load-displacement behavior of spinal motion segments is commonly determined from in-vitro experiments on cadaveric spines. However, clinically, it is often desirable to quantify the patient specific biomechanical properties of the spine in-vivo. Load-displacement measurement requires direct access to the appropriate anatomy, which is typically available in spinal surgeries that aim to correct lumbar spinal instability or scoliosis. We propose an approach to measure the spinal load-displacement behavior for use during these surgeries.Copyright