Purpose: The mechanical behavior of human scapholunate ligaments is not described well in the literature regarding torsion. Presently, intact scapholunate specimens were mechanically tested in torsion to determine if any tensile forces were generated as a result.

Method: Scapholunate specimens (n=19) were harvested and inspected visually. Scaphoid and lunate bones were potted in square chambers using epoxy cement. The interposing ligaments remained exposed. Specimens were mounted in a specially designed test jig and remained at a fixed axial length during testing. Using angular displacement control, ligaments were subjected to a torsional motion regime that included cyclic preconditioning (25 cycles, 1 Hz, triangular wave, 5 deg max), ramp-up to 15 deg at 180 deg/min, stress relaxation for 120 sec duration, ramp-down to 0 angulation at 180 deg/min, rest period for 5–10 minutes, and torsion-to-failure at 180 deg/min. Torque and axial tension were monitored simultaneously.

Results: Tests showed a coupled linear relationship between applied torsion and the resultant tensile forces generated for the ligament during ramp-up (Torsion/Tension Ratio = 38.86 +/− 29.00 mm, Linearity Coefficient R-squared = 0.89 +/− 0.15, n=19), stress relaxation (Ratio = 23.43 +/− 15.84 mm, R-squared = 0.90 +/− 0.09, n=16), and failure tests (Ratio = 38.81 +/− 26.39 mm, R-squared = 0.77 +/− 0.20, n=16). No statistically significant differences were detected between the Torsion/Tension ratios (p=0.13) or between the linearity (R-squared) of the best-fit lines (p> 0.085).

Conclusion: A strong linear relationship between applied torsion and resulting tensile forces for the ligament was exhibited during all testing phases. This may suggest that there is interplay between torsion and tension in both the stabilization of the scapholunate ligament during normal physiological motion and during resistance to injury processes. This is the first report in the literature of the coupling of torsion with tension for the scapholunate ligament.

Rodents are often used as preclinical models for investigating the biomechanical consequences of spinal pathologies and interventions. Growth plates are present within rat vertebrae throughout life and may alter the vertebral biomechanics. This study investigates the biomechanical response of rat-tail vertebrae to axial compressive loading using μCT imaging and image registration to spatially resolve strain fields.

The sixth caudal vertebrae of eight immunocompromised (rnu/rnu) rats were μCT scanned (17.5 ×17.5×17.5μm/pixel) in both loaded (27N-32N axial compression) and unloaded configurations. Image registration was used to calculate strain and displacement fields in the bone due to the applied load by finding a spatial mapping between the two scans. Strain was resolved to varying spatial resolutions; high strain gradient regions, such as the growth plates, were analyzed to higher spatial resolutions.

Axial strains calculated by image registration ranged from 2% in tension to 16% in compression with an average axial strain of 1.6% in compression. In seven rats the majority of the strain measured within the vertebrae was concentrated in the growth plate. Very soft growth plates in three specimens resulted in maximum axial strains from 10–16% in compression. The remaining four rats with strain concentrations in the growth plate had maximum axial strains ranging from 2.2%–3.2%. Centrally located strain concentrations of lower magnitudes and more limited spatial extent were observed in the trabecular bone.

The majority of the strain within the rat vertebrae was absorbed by the growth plates. The amount of strain within the growth plate is important to consider when interpreting biomechanical data on rat vertebrae. Load application to rodent vertebrae will first compress the growth plate and only following compression of this structure cause significant development of displacement and strains within the trabecular and cortical bone. This insight into the biomechanical response of rat vertebrae is apparent through the application of image registration to analyse vertebral body behaviour; such information would not be evident in analysing preclinical whole vertebral body response using finite element modeling or experimental testing protocols.

To compare strains measured in a whole rat-tail vertebra by image registration (IM) with those predicted by solid finite element analysis (FEA). Quantification of bone strain allows better understand fracture risk, bone healing and turnover.

The sixth caudal vertebra of an rnu/rnu rat was μCT scanned (17.5×17.5×17.5μm/voxel) while loaded (27N axial compression) and unloaded. IM was used to calculate strain and displacement fields in the bone due to the applied load by finding a spatial mapping between the two scans. Strain was resolved to varying spatial resolution; high strain gradient regions (ie growth plates) were analyzed to higher spatial resolutions. A FE model was created of the unloaded vertebra, consisting of tetrahedral elements with transversely isotropic material properties. Elements were assigned elastic moduli based upon μCT image intensities. Growth plate moduli ranged from 0–150kPa and the bone moduli ranged from 0.2–15000MPa. Vertebral geometry was created through segmentation of μCT images. Displacement boundary conditions were obtained by matching cranial and caudal surfaces in the unloaded and loaded scans. The displacement fields of the two methods were compared by using the fields calculated to deform the unloaded scan to match the loaded scan. The strains were compared by plotting FEA measured axial strain against IM calculated axial strain.

The displacement fields calculated by both methods were able to spatially align the unloaded scan to the loaded scan (Mean Voxel Intensity Difference: FEA=441HU, IM=328HU, Unregistered=969HU). IM and FEA show very limited agreement in axial strain measurement (R2=0.388, Slope=0.75, X-Intercept=0.0037) although both calculated high axial strains in the growth plates and low axial strains in the trabecular and cortical bone. Good agreement was found in the mean axial strain measured by both methods (IM= −0.044, FEA=−0.037). IM was better able to deal with difficulties in quantifying bone strain due to the growth plate than FEA.

IM presents advantages over FEA in measuring strain in complex whole bone trabecular structures, however has lower spatial resolution than is possible with FEA.

Purpose: There is a clinical need for novel effective local therapies to treat spinal metastases at significant risk for fracture. Photodynamic therapy (PDT) is a promising cancer treatment that employs wavelength specific light combined with a photosensitizing agent to induce localized tumour destruction by photochemical generation of singlet oxygen. Using minimally invasive techniques developed for vertebroplasty to deliver light within the vertebral body, PDT is proposed as a potential new treatment for spinal metastases; however, the effects of PDT on bone are largely unknown. This study aims to determine if PDT affects the structural integrity of normal vertebral bone.

Methods: Sixteen Wistar rats were randomly assigned to control, 1-week treatment or 6-week treatment groups. Rats treated with PDT received an intracardiac injection of 2mg/kg BPD-MA activated at 15 minutes post-injection through administration of a non-thermal 690nm diode laser positioned adjacent to the L3 vertebral body via fluoroscopic guidance (150J at 150mW). Rats were sacrificed at 1-week or 6-weeks following a single treatment. |In vitro & #956;CT scans were taken of L2-L4 and 3D stereological quantities measured using a semiautomated volume shrinkage thresholding technique within the trabecular bone centrum. L2, L3 and L4 vertebral bodies were individually tested biomechanically to failure in axial compression. Yield stress and stiffness were calculated from generated load displacement curves.

Results: Bone surface area and bone volume significantly increased with treatment, through trabecular thickening, at both 1-week and 6-weeks vs. control group. The treated group demonstrated an increase in yield stress at 6-weeks vs. control (27%, p=0.023). An increase in stiffness (45%, p=0.010) was found in the 1-week treatment group vs. control, but was not maintained in the 6-week group.

Conclusions: PDT is a promising new treatment for spinal metastases that appears to strengthen vertebral bone. Further research must determine the mechanism of this action and verify if similar effects will occur in metastatically-involved vertebrae. If PDT proves to be effective in both destroying tumour cells and in strengthening remaining bone, it may provide a very attractive minimally invasive treatment option for patients with spinal metastases.

Funding : Other Education Grant

Funding Parties : Canadian Breast Cancer Foundation, Ontario Chapter

Purpose: Effectively quantifying metastatic tumour involvement in the spine requires accurate vertebral segmentation. Automated techniques such as thresholding or region growing have difficulty defining boundaries between tumour tissue and surrounding soft tissue if lytic disease breaches the vertebral cortical shell. It is hypothesized that the application of image registration techniques may afford a potential solution to automating segmentation of metastically-involved vertebrae with cortical shell destruction. The objective of this study is to validate deformable registration as a means to automate the segmentation of tumour-bearing vertebrae through the transformation of atlas segmentations.

Methods: CT scans were collected from 6 patients (T4-L5) with spinal metastases secondary to breast cancer. Healthy levels from the patients were cropped and segmented using a combination of thresholding and manual delineation (Amira 3.1.1, TGS Berlin) to obtain the atlas for each vertebral level. After spatial alignment, metastatically involved vertebral levels were segmented by a registration of the atlas scan by automated affine registration (Amira) and refined by demons deformable registration (ITK, NLM Bethesda). The algorithm was tested through comparison of 10 vertebral bodies (thoracic and lumbar) segmented using the automated approach against a gold standard segmentation produced by semi-manual thresholding. The quality of the automatic segmentation was determined by calculating how many voxels were concurrently within both automatic and manual segmentation of the scan.

Results: Deformable registration successfully segmented metastatically involved vertebrae with and without breach of the cortical shell. Similar performance was evident when using an atlas from an adjacent level as compared to using an atlas of the identical vertebral level. Quality of the automatic segmentation ranged from 87.67%–96.22% concurrency. Comparisons of inter-user semi-manual segmentations yielded a similar maximum of 96% concurrency. Analysis speed was 10 to 15 times faster using the automated technique.

Conclusions: By maintaining the atlas morphology, atlas-based segmentations are able to accurately differentiate between trans-cortical tumours and surrounding soft tissue, overcoming problems inherent to more conventional automated segmentation techniques. Clinical application of this segmentation algorithm centers on tumour quantification and tracking progression of treatment effect and metastatic disease pathology. Funding: Other Education Grant Funding Parties: Canadian Breast Cancer Research Alliance, Sunnybrook & Women`s College Research Institute

Purpose: The objective of this study was to establish an automated and objective method to quantitatively characterize the extent, spatial distribution, and temporal progression of metastatic disease in the bony spine.

Methods: Serial patient CT scans from GE Light-speed Plus CT Scanners were standardized to 120kVp, 1.25mm/2.5mm slice interval/ thickness, standard reconstruction, and 0.468mm/0.468mm pixel spacing. From 3D reconstructed CT images, trabecular regions within vertebral bodies (VBs) were segmented through atlas-based deformable registration (ITK, NLM, Bethesda). Voxel intensity histograms (voxel counts vs. Hounsfield Units) were used to characterize 32 healthy and 11 metastatically involved vertebrae (T5 to L5). Healthy histograms were fitted to Gaussian regression curves and compared using one-way repeated measures ANOVA (p< 0.05). Tumours were segmented as connected areas with voxel intensities between specified thresholds (Amira 3.1.1, TGS, Berlin).

Results: Histograms of healthy vertebrae were found to be Gaussian distributions (avg. RMSD = 30 voxel counts). The Gaussian mean & #956; ranged from 120 to 290HU, presumably due to inter-patient differences in age and activity. However, the histogram data sets were not significantly different (p> 0.8) across intra-patient vertebral levels T5-L5. Consequently, the Gaussian parameters, & #956; and standard deviation & #963;, determined from fitted healthy histograms could be used in adjacent metastatic levels to define patient-specific lytic and blastic thresholds for tumor segmentation. The ideal lytic and blastic segmentation thresholds were determined to be & #956;−& #963; and & #956;+2& #963; respectively: i.e. while histograms of metastatic VBs were non-Gaussian (RMSD of 56 voxels), subtracting from them the tumourous regions segmented accordingly restored the Gaussian nature of the distributions (RMSD of 24 voxels). Metastatic involvement can then be quantified from histograms of metastases in terms of: (1) lytic/ blastic volumes from areas under the curves; (2) severity of the pathologic involvement from the distribution and range; (3) tumor progression over time or treatment effects by taking the difference between sequential scans.

Conclusions: This proposed histogram-based method for characterizing spinal metastases shows great potential in extending the quantitative capacity of CT-based radiographic evaluations, especially in tracking meta-static progression and treatment effectiveness in clinical research applications. Funding: Other Education Grant Funding Parties: NSERC and CBCRA

Introduction: Malrotations following Several complications have been reported in femoral nailing, among them. The aim of this study is to develop an intraoperative method based on cone beam CT (CBCT) to assess comminuted fracture periaxial rotation. We hypothesize that bone surface matching using CBCT image data can precisely predict malrotation in the fractured femur even with severe comminution.

Methods: A mid-shaft osteotomy in a fresh frozen cadaveric femur was performed and a rotational axis was formed. The proximal part of the femur was fixed and the distal part was optically racked for periaxial rotation. At each rotation a CBCT was aquired. The images were segmented at bone threshold. The center of the bone in each axial slice was calculated and the distance from that center to the inner and outer bone surfaces was sampled at 1o intervals (360x). The resulting plot was an unwrapped virtual bone surface consisting of a pattern of ridges and valleys. Fracture gaps were simulated by removing CT slices adjacent to the osteotomy. The fracture gap was reconstituted using an extrapolation algorithm to the midline of the fracture. The two bone surfaces were then continuously shifted relative to one another in order to match the geometric bony features. Calculated malalignments were compared to the measured at each of the 16 rotations with each of the 9 simulated fracture gaps. Three rotational malrotations were tested twice to assess repeatability.

Results: Femoral malrotation was strongly predicted as compared to the rotation measured by optical tracking. The performance was not impacted by gap size up to 100 mm.

Discussion: The high quality of intraoperative CBCT imaging data enables surface matching algorithms to be utilized. The results ratify this novel method for assessing fracture rotation.

Introduction: Lateral compression (LC) is the most common type of pelvic fracture, however there are no clear clinical or radiologic indications to direct conservative versus operative treatment of this pattern of injury. This study aims to determine if improved characterization of LC fracture patterns is possible through 3D radiological analysis.

Methods: CT scans of 61 patients with unilateral LC pelvic fractures were identified. The scans were segmented to generate a 3D model of the pelvis (Amira, MCS Inc). To quantify displacement of the fractured hemipelvis, the spatial orientation of three distinct anatomical landmarks (anteriof superior iliac, posterior superior iliac and ischial spines) on each side of the 3D hemipelvis were identified. Translational and rotational differences between the intact and fractured sides were compared to determine patterns of displacement with respect to a generated mid-sacral sagittal plane.

Results: 36.6% of the LC fractures were classified as non-displaced, 36.6% had an isolated single axis rotation, in another 13.3% had a pure translation with no rotation. 10% demonstrated pure rotational involvement in extension and the remaining patients, 3.3% had dual axis rotation.

Conclusion and Significance: Using 3D geometric analysis we were able to quantify patterns of LC fracture displacements not previously described. We characterized 5 subgroups of displacement patterns in LC fractures of the pelvis. Our 3D findings demonstrated a spectrum of translation and rotation motivating comparison with clinical outcome.

Introduction and Aims: Computer-assisted bone and soft tissue balancing in total knee arthroplasty (TKA) may aid in achieving perfect knee alignment leading to better function and prosthesis survival. The ‘Measured Resection’ technique was compared to a ‘Computer Assisted Gap Equalisation’ (CAGE) technique of knee balancing in TKA.

Method: TKAs were performed on eight pairs of cadaver knees. One side of each pair was randomly selected to the control group in which measured resection was used for balancing. The experimental technique (CAGE) using a computer-assisted ligament-tensioning device to equalise gap symmetry and load was used on the contralateral side. Post-operatively, a simulator applied forces to the quadriceps and hamstring tendons and a tibial load transducer measured compartmental force at five flexion angles (0, 30, 45, 60, 90 degrees). Outcome assessment consisted of measuring gap loads and symmetry under ligament tension pre-component insertion and compartmental force post-component insertion.

Results: Although there was no significant difference between the two groups in the symmetry of the extension (p = 0.27) and flexion (p=0.07) gaps pre-component insertion, there was a trend towards improved gap symmetry in the CAGE group. As well, pre-component insertion there was a significant (p< 0.05) equalisation of flexion and extension gap loads in the CAGE group. However, post-component insertion there was no significant difference (p> 0.05 using 2-way repeated measures ANOVA) in medial to lateral compartment load balance between the two groups. As well, the measured loads with the knee in full extension (zero degrees of flexion) were significantly higher (p< 0.001) in both groups compared to other flexion angles.

Conclusion: CAGE improves knee balance pre-component insertion by improving surgical accuracy with computer-assistance. However, component design, posterior capsular tension and tibial rotation preclude sustaining the improved balance post-component insertion leaving final knee balance unchanged. Further work is needed to translate the improved surgical accuracy into improved balance following component insertion.