Search

OBJECTIVES To evaluate the effects of the chondrodystrophy-associated FGF4L2 retrogene on intervertebral disc (IVD) calcification and vertebral geometry. ANIMALS 22 Nova Scotia Duck Tolling Retrievers (NSDTR) with no FGF4L2 retrogene (n = 7, wild-type dogs), 1 retrogene copy (8, heterozygous dogs), or 2 retrogene copies (7, homozygous dogs). PROCEDURES Computed tomography (CT) scans of the vertebral column were analyzed using computer-aided design (CAD) software. IVD calcification, vertebral column length, and vertebral geometry of the third cervical (C3), 13th thoracic (T13), and first lumbar (L1) vertebrae were compared. RESULTS IVD calcification was not found in wild-type dogs. IVD calcification was more frequent in homozygous dogs than heterozygous (P = .008) or wild-type dogs (P < .001) and in heterozygous dogs compared to wild-type dogs (P < .001). Four IVDs were subclinically herniated in 3 dogs (2 homozygous, 1 heterozygous). Calcified IVD had a greater volume and surface area in heterozygous dogs than homozygous dogs. C3 vertebral canal height-to-width ratio was greater in homozygous dogs than heterozygous dogs (P = .044) and wild-type dogs (P = .010). CLINICAL RELEVANCE IVD calcification and vertebral geometry can be analyzed using CAD software. The presence of 1 or 2 FGF4L2 copies in the absence of the FGF4L1 retrogene has an additive effect on the number of calcified IVD and a minor effect on vertebral geometry in NSDTR dogs. Data support the use of FGF4L2 phenotyping to reduce clinical disease in segregating breeds and to monitor the introduction of wild-type alleles into fixed breed populations.

OBJECTIVE Determine whether dogs with well-functioning orthopedic metal implants can develop metal reactivity. SAMPLE Client-owned dogs that had tibial plateau leveling osteotomy (TPLO) or total hip replacement (THR) implants for 12 months or more and control dogs with no implants. PROCEDURES Lymphocyte transformation testing was performed by exposing peripheral blood lymphocytes to nickel (Ni), chromium (Cr), cobalt (Co), or a combination of these metals. Lymphocyte proliferation was assessed with flow cytometry. Lymphocyte stimulation indexes (SIs) were calculated. A SI > 2 was considered reactive. Median SIs of dogs in response to metal exposure were compared statistically. RESULTS Samples from 10 dogs with TPLO, 12 dogs with THR, and 7 control dogs were analyzed. Six dogs out of 22 with metal implants had a reactive SI to 1 or more metals, while 2 of 7 control dogs had a SI > 2 when exposed to nickel only. When all metals were considered, no differences in metal reactivity were found between TPLO, THR, and control groups. CLINICAL RELEVANCE Metal reactivity is present in dogs and can be identified using lymphocyte transformation testing. Reactivity to Ni is present in dogs with and without metal implants. Reactivity to Co and Cr occurs in some dogs with metal implants.

During the stance phase of equine locomotion, ground reaction forces are exerted on the hoof, leading first to rapid deceleration (“braking”) and later to acceleration (“propulsion”) as the hoof leaves the ground. Excessive hoof deceleration has been identified as a risk factor for musculoskeletal injury and may be influenced by arena surface properties. Therefore, our objective was to evaluate the effect of arena surface type (dirt, synthetic) on hoof translation of the leading and trailing forelimbs during jump takeoff and landing. Solar hoof angle, displacement, velocity, and deceleration were captured using kinematic markers and high-speed video for four horses jumping over a 1.1 m oxer at 12 different arenas (5 dirt, 7 synthetic). Surface vertical impact and horizontal shear properties were measured simultaneously. The effects of surface type (dirt, synthetic), jump phase (takeoff, landing), and limb (leading, trailing) on hoof movement were assessed using ANOVA (p < 0.05), while the relationships of hoof movement with surface mechanical properties were examined with correlation. Slide time (p = 0.032), horizontal velocity of the hoof (p < 0.001), and deceleration (p < 0.001) were greater in the leading limb, suggesting a higher risk of injury to the leading limb when braking. However, surface type and jump phase did not significantly affect deceleration during braking.

Racehorses are susceptible to underrun heel hoof conformation. Racehorses are often shod with nails placed toward the heel. It is unknown if palmar nails restrict or alter hoof deformation in a manner that could promote the development of underrun heel conformation over time with repeated loading. To determine how the addition of palmar nails affects heel deformation during limb loading, hoof expansion and hoof wall deformations were quantified using rosette strain gauges and kinematic markers during in the vitro limb loading of cadaveric limbs that simulated midstance for walk, trot, and canter loads. Nail treatments used to attach a horseshoe to the hoof included: toe nails (T), toe and quarter nails (TQ), and toe, quarter, and heel nails (TQH). The effects of nail treatment on heel expansion and hoof wall deformations were assessed using repeated measures analysis of variance (p < 0.05). Nails placed palmar to the quarters of the hoof decreased heel expansion (p < 0.001). Heel nails resulted in the largest changes in hoof wall principal strain directions distally. The application of nails palmar to the hoof quarters alters hoof wall deformation during limb loading. The continued loading of the hoof with palmer nails could alter hoof conformation over time.

Medial proximal sesamoid bones (PSBs) from Thoroughbred racehorses that did (Case) or did not (Control) experience unilateral biaxial PSB fracture were evaluated for bone volume fraction (BVF), apparent mineral density (AMD), tissue mineral density (TMD), and microdamage in Case fractured, Case contralateral limb intact, and Control bones. A majority of Case bones had a subchondral lesion with high microdamage density, and low BVF, AMD, and TMD. Lesion microdamage and densitometric measures were associated with training history by robust linear regression. Exercise intensity was negatively related to BVF (0.07 ≤ R2 ≤ 0.12) and positively related to microcrack areal density (0.21 ≤ R2 ≤ 0.29) in the lesion; however, in an undamaged site, the relationships were opposite in direction. Regardless of location, TMD decreased with event frequency for both Case and Control, suggesting increased bone remodeling with exercise. Measures of how often animals were removed from active training (layups) predicted a decrease in TMD, AMD, BVF, and microdamage at regions away from the lesion site. A steady-state compartment model was used to organize the differences in the correlations between variables within the data set. The overall conclusions are that at the osteopenic lesion site, repair of microdamage by remodeling was not successful (e.g., lower bone mass, increased damage, and lower mineralization) but that in regions away from the lesion remodeling successfully controlled damage (e.g., higher bone mass, less microdamage, and lower mineralization).

OBJECTIVE To evaluate the accuracy of six depth gauges used in three tibial plateau leveling osteotomy (TPLO) plate holes. STUDY DESIGN Ex vivo experimental study. ANIMALS AND SAMPLE POPULATION Cadaveric canine limbs (n = 10), one 25-mm-thick wood board, and one 33.8-mm-diameter polyvinyl chloride (PVC) pipe. METHODS A TPLO was performed on 10 canine cadaveric pelvic limbs. Three 3.5-mm plate holes were filled with screws. The remaining three plate holes: a compression hole, a combination compression-locking hole, and a stacked combination compression-locking hole were measured by three observers using six commercial depth gauges and using a micrometer as gold standard. The process was repeated on one wood board and one PVC pipe. RESULTS Bone measurements collected using two depth gauges with base diameter 5.5 mm (p ranging from < .001 to .038). Mean depth gauge measurements were smaller than micrometer measurements by 2.20 mm for the compression hole, 0.82 mm for the combination hole, and 3.57 mm for the stacked combination hole. Measurement differences among depth gauges were also present for wood board and PVC pipe measurements. Bone measurement variability between depth gauges was less for the combination and compression holes than for the stacked combination hole. CONCLUSION Depth gauges lacked accuracy. Measurements differed among gauges and measurement variability varied based on plate hole geometry. CLINICAL RELEVANCE Depth gauge measurement accuracy varies based on measuring devices and on 3.5-mm plate hole geometry.

This retrospective observational study aimed to characterize the severity and distribution of OA in the stifle joints of small and medium dogs with CCL injury and/or MPL. Radiographs of the stifle joints from 218 dogs from 10 small and medium breeds were included; 127 joints had CCL injury, 76 joints had MPL, and 73 joints had CCL injury and MPL. OA was graded at 33 sites within the joint. The mean ± SD OA score was 20.3 ± 9.9. For all joints, OA was more severe in heavier than lighter dogs (P = 0.003). Joints with MPL (14.9 ± 8.2) had lower OA scores than joints with CCL injury (22.2 ± 10.0, P = 0.003) or CCL injury and MPL (22.6 ± 9.4, P0.001). OA scores were higher in joints with MPL for older dogs (r = 0.408, P0.001) but did not change with age in joints with CCL injury. The pattern of OA did not differ among joints with CCL injury or MPL. The retrospective nature of the study limited findings to associations but did not allow conclusions regarding factors causing OA or enhancing its progression. We concluded that, in small- and medium-breed dogs, the patterns of stifle OA joint after CCL injury and MPL are similar. Radiographic OA after CCL injury is more severe than MPL. An increase in age leads to an increase in OA at the time of presentation at a referral hospital in stifle joints with MPL and without CCL injury.

Objective The aim of this study was to assess bone density, bone architecture and clinical function of canine nonunion distal appendicular long bone fractures with a defect treated with fixation, compression-resistant matrix and recombinant human bone morphogenetic protein-2 (rhBMP-2). Study Design Prospective cohort study with dogs at least 1-year post treatment. Computed tomography was performed and quantitative measurements from previous fracture sites were compared with measurements from contralateral limbs. Subjective evaluation included gait assessment and palpation. Results Six patients met the inclusion criteria. The rhBMP-2 treated bone exhibited higher density at the periphery and lower density in the centre, similar to the contralateral limb. All patients were weight bearing on the treated limb and all fractures were healed. Conclusion The rhBMP-2-treated bone underwent restoration of normal architecture and density. Acceptable limb function was present in all patients. The results of this study can serve as a basis for long-term response in treating nonunion fractures in veterinary patients.

OBJECTIVE To evaluate the biomechanical properties of the mandibles of cats with experimentally created osteotomies simulating oblique ramus fractures, which were stabilized with malleable L-miniplates with either locking screws [locking construct (LC)] or nonlocking screws [nonlocking construct (NLC)], compared with those for intact mandibles. SAMPLES 20 mandibles from 10 adult cat cadavers. PROCEDURES A block study design was adopted to allocate the mandibles of each cadaver to 2 of the 3 test groups (LC, NLC, or intact mandible). Mandibles within each cadaver were allocated systematically to a test group. For mandibles assigned to an LC and an NLC, a complete oblique osteotomy was performed from the mid rostral aspect of the ramus in a caudoventral direction. All mandibles were loaded in a single-load-to-failure test through cantilever bending. Load and actuator displacement were recorded simultaneously. Mode of failure and radiographic evidence of damage to tooth roots and the mandibular canal were evaluated. Biomechanical properties were compared among the groups. RESULTS No iatrogenic tooth root damage was evident, but all mandibles with an LC and an NLC had evidence of screw invasion into the mandibular canal. Plated mandibles had significantly less stiffness and bending moment than intact mandibles. Stiffness was not significantly different between the LC and the NLC; the NLC had a greater bending moment at failure than the LC. The pre-yield stiffness of plated mandibles decreased when the number of screw holes overlapping the mandibular canal increased. CLINICAL RELEVANCE The use of a malleable L-miniplate in a caudal mandibular fracture model is feasible. Both the LC and the NLC were inferior mechanically to intact mandibles. Type of construct used did not affect the construct stiffness significantly in tested mandibles.

OBJECTIVE To compare the torsional mechanical properties of 2 external skeletal fixators (ESFs) placed with 2 intramedullary pin (IP) and transfixation pin (TP) size combinations in a model of raptor tibiotarsal bone fracture. SAMPLE 24 ESF-synthetic tibiotarsal bone model (polyoxymethylene) constructs. PROCEDURES Synthetic bone models were fabricated with an 8-mm (simulated fracture) gap. Four types of ESF-synthetic bone model constructs (6/group) were tested: a FESSA with a 1.6-mm IP and 1.6-mm TPs, a FESSA with a 2.0-mm IP and 1.1-mm TPs, an acrylic connecting bar with a 1.6-mm IP and 1.6-mm TPs, and an acrylic connecting bar with a 2.0-mm IP and 1.1-mm TPs. Models were rotated in torsion (5°/s) to failure or the machine angle limit (80°). Mechanical variables at yield and at failure were determined from load deformation curves. Effects of overall construct type, connecting bar type, and IP and TP size combination on mechanical properties were assessed with mixed-model ANOVAs. RESULTS Both FESSA constructs had significantly greater median stiffness and median torque at yield than both acrylic bar constructs; FESSA constructs with a 1.6-mm IP and 1.6-mm TPs had greatest stiffness of all tested constructs and lowest gap strain at yield. No FESSA constructs failed during testing; 7 of 12 acrylic bar constructs failed by fracture of the connecting bar at the interface with a TP. CONCLUSIONS AND CLINICAL RELEVANCE Although acrylic bar ESFs have been successfully used in avian patients, the FESSA constructs in this study were mechanically superior to acrylic bar constructs, with greatest benefit resulting from use with the larger TP configuration.

Objective To describe the novel placement of percutaneous radiologically guided gastrostomy (PRG) tubes in a canine cadaveric model and to biomechanically compare PRG and percutaneous endoscopic gastrostomy (PEG) tube constructs. Study design Descriptive and biomechanical experimental study. Animals Fifteen large breed (>25 kg) canine cadavers. Methods Percutaneous endoscopic gastrostomy tubes, low-profile PRG tubes, and standard PRG tubes were each placed in five canine cadavers. Body wall and stomach (with attached gastrostomy tube constructs) were harvested and biomechanically tested. Data regarding the maximal load to failure and procedure time were statistically analyzed. Results Percutaneous endoscopic gastrostomy and PRG tube placement was successful in all cadavers with no procedure-related complications. Gastrostomy tube placement time was longer for the PEG group vs the low-profile PRG (P = .005) and standard PRG (P = .037) groups. Peak construct strength was lower for the PEG group vs the low-profile PRG (P = .002) and standard PRG (P = .010) groups. The site of failure varied among groups. Conclusion Percutaneous radiologically guided gastrostomy tubes were successfully placed in all cases with shorter placement time and greater peak construct strength compared with PEG tubes. Clinical significance Due to the increased load to failure as well as decreased placement time recorded for PRG tubes relative to PEG tubes, PRG tubes may be considered as an alternative minimally invasive gastrostomy option in large breed canine patients. Further evaluation in clinical animals is required. Results of this work were presented at the 2019 American College of Veterinary Surgeons Surgery Summit; October 16-19, 2019; Las Vegas, Nevada.

OBJECTIVE To describe methods to measure the 3-D orientation of the proximal, diaphyseal, and distal segments of the canine radius by use of computer-aided design software (CADS) and to compare the repeatability and reliability of measurements derived by those methods. SAMPLE 31 canine radii with biapical deformities and 24 clinically normal (control) canine radii. PROCEDURES Select CT scans of radii were imported into a CADS program. Cartesian coordinate systems for the humerus and proximal, diaphyseal, and distal radial segments were developed. The orientation of each radial segment in the frontal, sagittal, and transverse planes was measured in triplicate by 3 methods. The repeatability and reliability of those measurements were calculated and compared among the 3 measurement methods. RESULTS The mean ± SD within-subject repeatability of radial angular measurements for all 3 methods was 1.40 ± 0.67° in the frontal plane, 3.17 ± 2.21° in the sagittal plane, and 3.01 ± 1.11° in the transverse plane for control radii and 2.56 ± 1.95° in the frontal plane, 3.59 ± 2.39° in the sagittal plane, and 3.47 ± 1.19° in the transverse plane for abnormal radii. Mean ± SD bias between radial measurement methods was 1.88 ± 2.07° in the frontal plane, 6.44 ± 6.80° in the sagittal plane, and 2.27 ± 2.81° in the transverse plane. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that use of CADS to assess the 3-D orientation of the proximal, diaphyseal, and distal segments of normal and abnormal canine radii yielded highly repeatable and reliable measurements.

OBJECTIVE To determine the influence of interlocking screw threads on the biomechanical properties of repaired canine humeral condylar fractures. STUDY DESIGN Ex vivo biomechanical study. SAMPLE POPULATION Thirty-six humeral condyles. METHODS Simulated fractures of the lateral aspect of the humeral condyle were stabilized by a 3.5 mm interlocking thread screw (ITS) or 3.5 mm buttress thread screw placed in lag (BTS-L) or positional fashion (BTS-P) and axially loaded at a walk, trot, 2-mm displacement, and failure cycles. Compact flute drill bits (CFBs) were used for ITS constructs and standard flute drill bits (SFB) for BTS constructs. The effects of bit type on drilling parameters and screw type on screw insertion properties and fragment stability were assessed. RESULTS CFB produced a 6°C greater temperature increase (p = .042) and required 20 N higher torque (p = .003) than SFB. Insertional torque was greater for ITS than BTS-P (p = .001) and BTS-L (p = .001). Condylar fragment rotation at failure was lower in ITS (lsmean ± SE, 8.3° ± 1.9°) than BTS-L constructs (14.5° ± 2.3°, p = .011). ITS resisted greater loads (1503 ± 105 N) than BTS-P (1189 ± 99 N, p = .038) but not BTS-L (1249 ± 123 N, p = .121) constructs. CONCLUSION Biomechanical performance of constructs was improved with ITS rather than BTS fixation. CLINICAL SIGNIFICANCE ITS can be considered for stabilization of humeral condylar fractures in adult dogs.

OBJECTIVE To assess the motion of the proximal sesamoid bones (PSBs) relative to the third metacarpal bone (MC3) of equine forelimbs during physiologic midstance loads. SAMPLE 8 musculoskeletally normal forelimbs (7 right and 1 left) from 8 adult equine cadavers. PROCEDURES Each forelimb was harvested at the mid-radius level and mounted in a material testing system so the hoof could be moved in a dorsal direction while the radius and MC3 remained vertical. The PSBs were instrumented with 2 linear variable differential transformers to record movement between the 2 bones. The limb was sequentially loaded at a displacement rate of 5 mm/s from 500 N to each of 4 loads (1.8 [standing], 3.6 [walking], 4.5 [trotting], and 10.5 [galloping] kN), held at the designated load for 30 seconds while lateromedial radiographs were obtained, and then unloaded back to 500 N. The position of the PSBs relative to the transverse ridge of the MC3 condyle and angle of the metacarpophalangeal (fetlock) joint were measured on each radiograph. RESULTS The distal edge of the PSBs moved distal to the transverse ridge of the MC3 condyle at 10.5 kN (gallop) but not at lower loads. The palmar surfaces of the PSBs rotated away from each other during fetlock joint extension, and the amount of rotation increased with load. CONCLUSIONS AND CLINICAL RELEVANCE At loads consistent with a high-speed gallop, PSB translations may create an articular incongruity and abnormal bone stress distribution that contribute to focal subchondral bone lesions and PSB fracture in racehorses.

Author(s): Hersh-Boyle, Rebecca A; Chou, Po-Yen; Kapatkin, Amy S; Spriet, Mathieu; Filliquist, Barbro; Garcia, Tanya C; Marcellin-Little, Denis J | Abstract: ObjectiveTo evaluate the diagnostic value of still images of needle arthroscopy (SNAR), still images of traditional arthroscopy (STAR), and computed tomography (CT) to diagnose medial coronoid process (MCP) pathology.Study designProspective clinical trial.AnimalsDogs (nn=n17) presented for evaluation of elbow dysplasia.MethodsFor each case, two SNAR and STAR images of the MCP were reviewed independently and in random order by three board-certified surgeons. Computed tomographic images were reviewed by one board-certified radiologist. Reviewers were blinded to surgical and clinical findings. Surgical findings from real-time TAR with palpation were used as the gold standard. Receiver operating characteristic (ROC) curves and concordance statistics tests for the diagnostic accuracy of MCP fissure, MCP fragment, medial compartment condition, and cartilage score were calculated.ResultsImages of 27 elbows joints were reviewed. For MCP fissure detection, areas under the ROC curves for CT (0.84), STAR (0.73), and SNAR (0.57) did not differ. For the detection of MCP fragment, STAR had a larger area under the ROC curve (0.93) compared with SNAR (0.74, Pn=n.015) and CT (0.54, P l .001). Still images of TAR and SNAR had comparable concordance for cartilage score (0.80 and 0.77, respectively) and medial compartment pathology (0.80 and 0.73, respectively).ConclusionStill images of NAR, STAR, and CT had similar diagnostic value to identify MCP fissures. Still images of TAR was superior to SNAR and CT to identify MCP fragments.Clinical significanceThe diagnostic accuracy of SNAR varied on the basis of the coronoid lesion being evaluated.

Strain parameters at injury prone sites of the equine third metacarpal (MC3) and proximal phalangeal (P1) bones were investigated with the aim of improving understanding of injury pathogenesis. We hypothesized that dorsal principal and shear strain patterns, magnitudes and directions would differ from proximal-to-distal; and would be similar from medial-to-lateral across each bone. Unilateral limbs from nine equine cadavers were instrumented with rosette strain gauges during limb loading to 10,500 N. Gauges were attached at seven dorsal sites: middle MC3, distal MC3 (medial, middle, lateral) and proximal P1 (medial, middle, lateral). Outcome measures were analysed with repeated measures analysis of variance. Distal MC3 had the greatest, and proximal P1 the smallest magnitude of minimum principal and shear strains. Directions of maximum and minimum principal strain were similar at the middle and distal MC3 sites with a 20-40° direction difference compared to proximal P1. The patterns of strain magnitude and direction were similar from medial-to-lateral on distal MC3 but varied in pattern and magnitude among the P1 sites. Overall, as load reached maximum, direction of minimum principal strain became more axial in orientation, converging from opposite directions between bones, potentially maximising stability of the distal limb. The difference in strain parameters and strain ratio for adjacent anatomic sites on distal MC3 and proximal P1 was not anticipated, in light of the anatomic congruity of the metacarpophalangeal joint. Based on the predominance of shear strain across proximal P1, shear forces are likely the predominant biomechanical contributor to sagittal fractures of P1.

To compare the torsional mechanical properties of 2 external skeletal fixators (ESFs) placed with 2 intramedullary pin (IP) and transfixation pin (TP) size combinations in a model of raptor tibiotarsal bone fracture.24 ESF-synthetic tibiotarsal bone model (polyoxymethylene) constructs.Synthetic bone models were fabricated with an 8-mm (simulated fracture) gap. Four types of ESF-synthetic bone model constructs (6/group) were tested: a FESSA with a 1.6-mm IP and 1.6-mm TPs, a FESSA with a 2.0-mm IP and 1.1-mm TPs, an acrylic connecting bar with a 1.6-mm IP and 1.6-mm TPs, and an acrylic connecting bar with a 2.0-mm IP and 1.1-mm TPs. Models were rotated in torsion (5°/s) to failure or the machine angle limit (80°). Mechanical variables at yield and at failure were determined from load deformation curves. Effects of overall construct type, connecting bar type, and IP and TP size combination on mechanical properties were assessed with mixed-model ANOVAs.Both FESSA constructs had significantly greater median stiffness and median torque at yield than both acrylic bar constructs; FESSA constructs with a 1.6-mm IP and 1.6-mm TPs had greatest stiffness of all tested constructs and lowest gap strain at yield. No FESSA constructs failed during testing; 7 of 12 acrylic bar constructs failed by fracture of the connecting bar at the interface with a TP.Although acrylic bar ESFs have been successfully used in avian patients, the FESSA constructs in this study were mechanically superior to acrylic bar constructs, with greatest benefit resulting from use with the larger TP configuration.

Background Proximal sesamoid bone (PSB) fracture is the most common fatal injury in Thoroughbred (TB) racehorses in the United States. Epidemiological and pathological evidence indicates PSB fracture is likely the acute culmination of a chronic stress-related process. However, the aetiopathogenesis of PSB fracture is poorly understood. Objective To characterise bone abnormalities that precede PSB fracture. Study design Two retrospective case-control groups of PSBs from TB racehorses with, and without, unilateral biaxial PSB fracture. Methods Proximal sesamoid bones were harvested post-mortem from TB racehorses subjected to euthanasia for unilateral biaxial PSB fracture (cases) or causes unrelated to PSB fracture (controls) while racing or training. The fractured medial PSB (FX-PSB) and contralateral intact medial PSB (CLI-PSB) from racehorses that sustained PSB fracture, and an intact medial PSB (CTRL-PSB) from racehorses that did not have a PSB fracture were collected as case and control specimens. Study 1 distributions of morphological features were compared among case and control groups using visual examination, photographs, radiographs and histology of whole PSBs and serial sagittal sections (10 FX-PSB, 10 CLI-PSB and 10 CTRL-PSB). Study 2 local bone volume fraction and mineral densities were compared among case and control PSBs using microcomputed tomography (9 FX-PSB, 9 CLI-PSB and 9 CTRL-PSB). Results A focal subchondral lesion characterised by colocalised focal discoloration, radiolucency, osteopenia, low tissue mineral density and a surrounding region of dense cancellous bone was identified in most case horses but not in controls. This subchondral lesion was found in a slightly abaxial mid-body location and was bilaterally present in most case horses. Main limitations The post-mortem samples may not represent the spectrum of abnormalities that occur throughout the development of the subchondral lesion. Lateral PSBs were not examined, so their contribution to biaxial PSB fracture pathogenesis is unknown. Conclusion Abaxial subchondral lesions are consistent with pre-existing injury and likely associated with PSB fracture.

Proximal sesamoid bone (PSB) fractures in racehorses are likely fatigue fractures that occur due to repetitive loads and stress remodeling. The loading circumstances that may induce damage in the PSBs are not well understood. The goal of this study was to determine in three-dimensions, PSB motions relative to the opposing metacarpal condyle during simulated mid-stance loads. Seven equine cadaveric forelimbs were axially loaded in a material testing system to simulate standing and mid-stance walk, trot, and gallop load conditions (1.8-10.5 kN). Joint angles were determined by tracking the positions of bone-fixed kinematic markers. Internal-external rotation, abduction-adduction, and flexion-extension of each PSB relative to the third metacarpal condyle were compared between loads and between PSBs using an ANOVA with Tukey-Kramer post hoc tests for pairwise comparisons. The medial PSB rotated externally and the lateral PSB apex abducted during limb loading. Medial PSB external rotation was significantly greater at the gallop load condition than at the walk or trot load conditions. The medial and lateral PSB motions observed in this study are consistent with location of fatigue damage and fracture configurations frequently seen in medial and lateral PSBs from Thoroughbred racehorses. Specifically, medial PSB external rotation is consistent with the development of an abaxial subchondral medial PSB lesion that is reported in association with medial PSB transverse fracture and lateral PSB abduction is consistent with axial longitudinal fracture of the lateral PSB.

Objective To improve the prediction of fractures in dogs with bone tumors of the distal radius by identifying computed tomography (CT) indices that correlate with antebrachial bone strength and fracture location. Study design Prospective experimental study. Animals Dogs with antebrachial osteosarcoma (n = 10), and normal cadaver bones (n=9). Methods Antebrachia were imaged with quantitative CT prior to biomechanical testing to failure. CT indices of structural properties were compared to yield force and maximum force using Pearson correlation tests. Results Straight beam failure (Fs), axial rigidity, curved beam failure (Fc), and craniocaudal bending moment of inertia (MOICrCd) CT indices most highly correlated (0.77 > R > 0.57) with yield and maximum forces when iOSA-affected and control bones were included in the analysis. Considering only OSA-affected bones, Fs, Fc, and axial rigidity correlated highly (0.85 > R > 0.80) with maximum force. In affected bones, the location of minimum axial rigidity and maximum MOICrCd correlated highly (R > 0.85) with the actual fracture location. Conclusions CT-derived axial rigidity, Fs, and MOICrCd have strong linear relationships with yield and maximum force. These indices should be further evaluated prospectively in OSA-affected dogs that do, and do not, experience pathologic fracture.

Objective To determine the influence of neoplasia on the biomechanical properties of canine antebrachia. Study design Ex vivo biomechanical study. Sample population: Osteosarcoma (OSA)-affected canine antebrachia (n = 12) and unaffected canine antebrachia (n = 9). Methods Antebrachia were compressed in axial loading until failure. A load-deformation curve was used to acquire the structural mechanical properties of neoplastic and unaffected specimens. Structural properties and properties normalized by body weight (BW) and radius length were compared using analysis of variance (ANOVA). Modes of failure were compared descriptively. Results Neoplastic antebrachia fractured at, or adjacent to, the OSA in the distal radial diaphysis. Unaffected antebrachia failed via mid-diaphyseal radial fractures with a transverse cranial component and an oblique caudal component. Structural mechanical properties were more variable in neoplastic antebrachia than unaffected antebrachia, which was partially attributable to differences in bone geometry related to dog size. When normalized by dog BW and radial length, strength, stiffness, and energy to yield and failure, were lower in neoplastic antebrachia than in unaffected antebrachia. Conclusions OSA of the distal radial metaphysis in dogs presented for limb amputation markedly compromises the structural integrity of affected antebrachia. However, biomechanical properties of affected bones was sufficient for weight-bearing, as none of the neoplastic antebrachia fractured before amputation. The behavior of tumor invaded bone under cyclic loading warrants further investigations to evaluate the viability of in situ therapies for bone tumors in dogs.

OBJECTIVE To evaluate and quantify the kinematic behavior of canine mandibles before and after bilateral rostral or unilateral segmental mandibulectomy as well as after mandibular reconstruction with a locking reconstruction plate in ex vivo conditions. SAMPLE Head specimens from cadavers of 16 dogs (range in body weight, 30 to 35 kg). PROCEDURE Specimens were assigned to undergo unilateral segmental (n = 8) or bilateral rostral (8) mandibulectomy and then mandibular reconstruction by internal fixation with locking plates. Kinematic markers were attached to each specimen in a custom-built load frame. Markers were tracked in 3-D space during standardized loading conditions, and mandibular motions were quantified. Differences in mandibular range of motion among 3 experimental conditions (before mandibulectomy [ie, with mandibles intact], after mandibulectomy, and after reconstruction) were assessed by means of repeated-measures ANOVA. RESULTS Both unilateral segmental and bilateral rostral mandibulectomy resulted in significantly greater mandibular motion and instability, compared with results for intact mandibles. No significant differences in motion were detected between mandibles reconstructed after unilateral segmental mandibulectomy and intact mandibles. Similarly, the motion of mandibles reconstructed after rostral mandibulectomy was no different from that of intact mandibles, except in the lateral direction. CONCLUSIONS AND CLINICAL RELEVANCE Mandibular kinematics in head specimens from canine cadavers were significantly altered after unilateral segmental and bilateral rostral mandibulectomy. These alterations were corrected after mandibular reconstruction with locking reconstruction plates. Findings reinforced the clinical observations of the beneficial effect of reconstruction on mandibular function and the need for reconstructive surgery after mandibulectomy in dogs.

Objective The aim of this study was to evaluate and compare the effect of three clinically applicable screw hole diameters on rabbit femoral torsional structural properties. Sample Eighteen pairs of skeletally mature New Zealand White rabbit femora (36 bones). Materials and Methods Femora with a bicortical hole at mid-diaphysis from one of the 3-drill bit sizes, 1.1 mm, 1.5 mm, 2.0 mm, and intact bones were studied. Each bone was bi-axially loaded in a servo-hydraulic load frame with the bone positioned so the neutral axis of torsion was aligned with the centre of the bone diaphysis. Axial compression to 35% body weight was applied to represent compression at stance, and rapid external torsion was applied to failure. Torque and angular deformation data were plotted for each test, with pre-yield and post-yield stiffnesses derived. Yield and failure torques and angles were determined, along with calculated yield, failure and post-yield energies. Results Failure torque was reduced compared with that of intact bone; weakened by 37% in 1.1-mm hole models, 53% in 1.5-mm hole models and 65% in 2.0-mm hole models. The torque angular deformation curves lacked plastic deformation. Conclusions and Clinical Relevance This study demonstrates the unique, brittle biomechanics of rabbit bone. Based on data from other species that strength loss of no more than 50% is acceptable when placing orthopaedic implants, no defect greater than 1.1 mm (15% bone diameter) is recommended in rabbit femora.

OBJECTIVE To compare the biomechanical behavior of mandibular critical-sized defects stabilized with 2 plating configurations under in vitro conditions resembling clinical situations. SAMPLE 24 mandibles harvested from 12 adult canine cadavers. PROCEDURES 8 mandibles were kept intact as control samples. A critical-sized defect was created in 16 mandibles; these mandibles were stabilized by use of a single locking plate (LP [n = 8]) or an LP combined with an alveolar miniplate (LMP [8]). Mandibles were loaded in cantilever bending in a single-load-to-failure test with simultaneous recording of load and actuator displacement. Stiffness, yield, and failure properties were compared among groups. Mode of failure was recorded. Radiographic evidence of tooth root and mandibular canal damage was quantified and compared between groups. RESULTS Stiffness and yield loads of single LP and LMP constructs were < 30% of values for intact mandibles, and failure loads were < 45% of values for intact mandibles. There were no consistent biomechanical differences at failure between single LP and LMP constructs, but the LMP construct had greater stiffness and strength prior to yield. Frequency of screw penetration of teeth and the mandibular canal was significantly greater for LMP than for single LP constructs. CONCLUSIONS AND CLINICAL RELEVANCE Both fixation methods were mechanically inferior to an intact mandible. The LMP construct was mechanically stronger than the LP construct but may not be clinically justifiable. Addition of an alveolar miniplate provided additional strength to the construct but resulted in more frequent penetration of tooth roots and the mandibular canal.

Objective To describe a novel percutaneous radiologic gastropexy (PRG) technique in a canine model and to biomechanically compare this technique to open incisional gastropexy (OIG) and laparoscopic-assisted incisional gastropexy (LAG). Study Design Randomized ex vivo biomechanical study. Animals: Canine cadavers. Methods Fifteen cadavers were randomized to 1 of 3 surgical interventions: OIG, LAG, and PRG. For the PRG procedure, the stomach was distended with air, and a preloaded T-fastener device was utilized to attach the stomach to the body wall with fluoroscopic-guidance. The procedural times of the 3 techniques were recorded. After completion of the procedure, the stomach and body wall overlying the stomach wall were harvested and the maximum tensile strength of the gastropexies was determined. Results The maximal tensile strength was not significantly different between groups. The total procedural time for the PRG procedure (5 minutes) was significantly shorter than both OIG (28 minutes) and LAG (20 minutes) procedures. Conclusion The PRG technique described in this study demonstrated a similar maximal tensile strength to commonly employed gastropexy techniques (OIG and LAG) in an acute canine model. Additionally, the PRG procedure was significantly faster to perform. The clinical relevance of this technique will be determined by further study to assess the applicability and efficacy of this procedure in clinical patients by determining the likelihood of adhesion development and the ability of the adhesion to prevent gastric volvulus.

Objective To compare the stiffness, angular deformation, and mode of failure of lumbar vertebral column constructs stabilized with bilateral pins and polymethylmethacrylate (Pin-PMMA) or with a unilateral (left) locking compression plate (LCP) with monocortical screws. Study Design Ex vivo biomechanical, non-randomized. Samples: Cadaveric canine thoracolumbar specimens (n=16). Methods Thoracolumbar (T13-L3) vertebral specimens had the L1-L2 vertebral motion unit stabilized with either Pin-PMMA or LCP. Stiffness in flexion, extension, and right and left lateral bending after nondestructive testing were compared between intact (pretreated) specimens and Pin-PMMA, and LCP constructs. The Pin-PMMA and LCP constructs were then tested to failure in flexion and left lateral bending. Results Both the Pin-PMMA and LCP constructs had reduced range of motion at the stabilized L1-L2 vertebral motion unit compared to intact specimens. The Pin-PMMA constructs had less range of motion for the flexion elastic zone than LCP constructs. The Pin-PMMA constructs were stiffer than intact specimens in flexion, extension, and lateral bending, and stiffer than LCP constructs in flexion and left lateral bending. The Pin-PMMA constructs had less angular deformation at construct yield and lower residual deformation at L1-L2 than LCP constructs after destructive testing to failure in flexion. The Pin-PMMA constructs were stiffer, stronger, and had less deformation at yield than LCP constructs after destructive testing to failure in lateral bending. Most constructs failed distant to the implant and fixation site. Conclusions Pin-PMMA constructs had greater lumbar vertebral stiffness and reduced ROM than LCP constructs; however, both Pin-PMMA and LCP constructs were stronger than intact specimens.

Objective To use micro-computed tomography (CT) to evaluate the fissure–fracture pattern in dogs affected by medial coronoid disease (MCD). Study Design Prospective case-controlled study. Sample Population Client owned (n = 21) and cadaver dogs (n = 5). Methods Segments were excised by subtotal coronoid ostectomy from dogs with MCD. Two categories were identified: fissured (Fi) or fractured (F). Three subcategories were contingent on fissure–fracture orientation: tip (T), radial incisure (RI), and radial incisure encroaching tip (RIT). Control segments were from nondiseased cadavers. High-resolution micro-CT (3 dimensional and 2 dimensional) was performed on all segments. Measurements included mean bone mineral density, trabecular number and thickness, and the angle of the fissure–fracture relative to the predominant trabecular orientation. Results A total of 28 diseased segments from 21 dogs (mean age 23.3 months, mean bodyweight 31.5 kg) were analyzed and categorized according to fissure–fragment location as Fi-T (n = 2), Fi-RIT (n = 2), Fi-RI (n = 3), F-T (n = 5), F-RIT (n = 9), F-RI (n = 7). The 3D analysis revealed subchondral micro-fracturing occurred in association with fragmentation. Canalicular impaction was associated with increase in trabecular number and decrease in trabecular space, most notably in RI categories. The 2D analysis showed that predominant trabecular orientation in control segments was significantly different to RI but not to T. The mean (SD) angle difference between the orientation of fissure–fracture and the predominant trabecular pattern was 6.9 (6.9)° for RI and 44.6 (49.6) ° for T. Conclusion T and RI fissure–fracture patterns show morphologic differences and likely arise from different supraphysiologic loading. Medial compartment disease is not homogenous and pattern recognition may assist further investigation of etiopathogenesis.

This study is the first biomechanical research of headless compression screws for fixation of vertical shear fractures of the medial malleolus, a promising alternative that potentially offers several advantages for fixation. Vertical shear fractures were simulated by osteotomies in 20 synthetic distal tibiae. Models were randomly assigned to fixation with either 2 parallel cancellous screws or 2 parallel Acutrak 2 headless compression screws (Acumed). Specimens were subjected to offset axial loading to simulate supination-adduction loading and tracked using high-resolution video. The headless compression screw construct was significantly stiffer (P < .0001) (360 ± 131 N/mm) than the partially threaded cancellous screws (180 ± 48 N/mm) and demonstrated a significantly increased (P < .0001) mean load to clinical failure (719 ± 91 N vs 343 ± 83 N). When specimens were displaced to 6 mm and allowed to relax, the headless compression screw constructs demonstrated an elastic recoil and were reduced to the pretesting fragment alignment, whereas the parallel cancellous screw constructs remained displaced. Along with the headless design that may decrease soft tissue irritation, the increased stiffness and elastic recoil of the headless compression screw construct offers improved fixation of medial malleolus vertical shear fractures over the traditional methods.

OBJECTIVE To describe the torsional and axial compressive properties of tibiotarsal bones of red-tailed hawks (Buteo jamaicensis). SAMPLE 16 cadaveric tibiotarsal bones from 8 red-tailed hawks. PROCEDURES 1 tibiotarsal bone from each bird was randomly assigned to be tested in torsion, and the contralateral bone was tested in axial compression. Intact bones were monotonically loaded in either torsion (n = 8) or axial compression (8) to failure. Mechanical variables were derived from load-deformation curves. Fracture configurations were described. Effects of sex, limb side, and bone dimensions on mechanical properties were assessed with a mixed-model ANOVA. Correlations between equivalent torsional and compressive properties were determined. RESULTS Limb side and bone dimensions were not associated with any mechanical property. During compression tests, mean ultimate cumulative energy and postyield energy for female bones were significantly greater than those for male bones. All 8 bones developed a spiral diaphyseal fracture and a metaphyseal fissure or fracture during torsional tests. During compression tests, all bones developed a crushed metaphysis and a fissure or comminuted fracture of the diaphysis. Positive correlations were apparent between most yield and ultimate torsional and compressive properties. CONCLUSIONS AND CLINICAL RELEVANCE The torsional and axial compressive properties of tibiotarsal bones described in this study can be used as a reference for investigations into fixation methods for tibiotarsal fractures in red-tailed hawks. Although the comminuted and spiral diaphyseal fractures induced in this study were consistent with those observed in clinical practice, the metaphyseal disruption observed was not and warrants further research.

Sagittal fractures of the proximal phalanx (P1) in the racehorse appear to be associated with turf racing surfaces, which are known to restrict forward slide of the foot at impact. We hypothesized that restriction of forward foot slip would result in higher P1 bone strains during metacarpophalangeal joint (MCPJ) hyperextension. Unilateral limbs from six equine cadavers were instrumented with strain gauges and bone reference markers to measure dorsoproximal P1 bone strains and MCPJ extension, collateromotion and axial rotation during in vitro limb loading to 10,500 N. By limiting movement of the distal actuator platform, three different foot conditions (forward, free, and restricted) were applied in a randomised block design. Bone reference markers, recorded by video, were analyzed to determine motion of P1 relative to MC3. Rosette strain data were reduced to principal and shear magnitudes and directions. A mixed model ANOVA determined the effect of foot position on P1 bone strains and MCPJ angles. At 10,000 N load, the restricted condition resulted in higher P1 axial compressive (p=0.015), maximum shear (p=0.043) and engineering shear (p=0.046) strains compared to the forward condition. The restricted condition had higher compressive (p=0.025) and lower tensile (p=0.043) principal strains compared to the free condition. For the same magnitude of principal or shear strains, axial rotation and collateromotion angles were greatest for the restricted condition. Therefore, the increase in P1 principal compressive and shear bone strains associated with restricted foot slip indicate that alterations in foot:ground interaction may play a role in fracture occurrence in horses.

Category: Sports, Biomechanics Introduction/Purpose: Lisfranc injuries are characterized by disruption between the medial cuneiform and base of the second metatarsal. Conventional interfragmentary screws decreases the amount of diastasis, however is believed to decrease the natural physiological movement of the joint compared to suture button (Tightrope, Arthrex, Inc., Naples, FL). The InternalBrace (IB, Arthrex, Inc., Naples, FL) allows physiologic movement and collagen ingrowth, while also decreasing iatrogenic bone loss. It also prevents erosion of the suture button into the medial cuneiform and prevents irritation of the tibialis anterior tendon. We hypothesized that there was no significant difference in the mechanical properties of these three constructs. Methods: Three groups of 10 sawbone models were used in this study. Two fourth generation 20 mm cylinder sawbones with open cell foam were fixed together with either a 3.5 mm conventional screw, mini Tightrope or IB with a curved button and 4.75 mm biotenodesis screw. Sawbone constructs were held in a mechanical testing system (Model 809, MTS Systems Corp, Minneapolis MN) using custom fixtures. Constructs were loaded in axial tension at 0.5mm/sec until failure. Load-displacement data were plotted for each test. Yield, stiffness, ultimate strength (US), yield energy, post-yield energy and ultimate strength energy were calculated Additionally, the load and energy to 0.5 mm, 1.0 mm and 1.5 mm of displacement were captured to relate strength at clinically relevant displacements. The residuals of an ANOVA on all mechanical testing results were not normally distributed. Therefore non-parametric comparison was used to compare fixation types (Proc NPAR1WAY, SAS 9.4, SAS Institute). Results: Compared to IB, the screw demonstrated greater stiffness, yield load and energy, and ultimate load and energy, with smaller yield, ultimate and failure displacement. When comparing the Tightrope and IB, there was no difference in stiffness (p=0.82), although the Tightrope performed greater in terms of having a larger yield load, energy and displacement, a larger ultimate strength load, energy and displacement, and a larger failure load, energy and displacement. When assessing the load at various distances of displacement, there was no significant difference between the load at 0.5 mm displacement (p=0.5, Figure 1). At greater displacement, the load was greater in the Tightrope than the IB (Figure 1). Conclusion: In this study, IB has shown proper stiffness and strength for fixation of ligamentous lisfranc injury. However, if a diastasis of >0.5 mm is evident, concerns for a clinical failure should be examined. This is the first study examining the use of an IB for treatment of a ligamentous lisfranc injury. The data supports its current clinical indications and further studies in cadaveric models are recommended.

OBJECTIVE To evaluate biomechanical properties of intact feline mandibles, compared with those for mandibles with an experimentally created osteotomy that was stabilized with 1 of 2 internal fixation configurations. SAMPLE 20 mandibles from 10 adult feline cadavers. PROCEDURES An incomplete block study design was used to assign the mandibles of each cadaver to 2 of 3 groups (locking plate with locking screws [locking construct], locking plate with nonlocking screws [nonlocking construct], or intact). Within each cadaver, mandibles were randomly assigned to the assigned treatments. For mandibles assigned to the locking and nonlocking constructs, a simple transverse osteotomy was created caudal to the mandibular first molar tooth after plate application. All mandibles were loaded in cantilever bending in a single-load-to-failure test while simultaneously recording load and actuator displacement. Mode of failure (bone or plate failure) was recorded, and radiographic evidence of tooth root and mandibular canal damage was evaluated. Mechanical properties were compared among the 3 groups. RESULTS Stiffness, bending moments, and most post-yield energies for mandibles with the locking and nonlocking constructs were significantly lower than those for intact mandibles. Peak bending moment and stiffness for mandibles with the locking construct were significantly greater than those for mandibles with the nonlocking construct. Mode of failure and frequency of screw damage to tooth roots and the mandibular canal did not differ between the locking and nonlocking constructs. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that both fixation constructs were mechanically inferior to intact mandibles. The locking construct was mechanically stronger than the nonlocking construct.

We characterized features of complete diaphyseal fractures of third metacarpal bones in Thoroughbred racehorses. Given that stress fractures are known to occur in the third metacarpal bone, an additional aim was to determine if complete fractures are associated with signs of a preexisting incomplete stress fracture. Bilateral metacarpi from 12 Thoroughbred racehorses euthanized because of complete unilateral metacarpal diaphyseal fracture were examined visually and radiographically. Open, comminuted, transverse or short oblique fractures occurred in the middle of the diaphysis or supracondylar region. Periosteal surface discoloration and bone callus formation contiguous with the fracture line were present in fractured bones. All contralateral intact metacarpi had gross anatomic lesions, and 10 had radiographic abnormalities similar to those observed on fractured metacarpi. Catastrophic metacarpal fractures occurred in racehorses with bilateral evidence of preexisting bone injury.

Horizontal fractures of the medial malleolus occur through application of valgus or abduction force through the ankle that creates a tension failure of the medial malleolus. The authors hypothesize that mini-fragment T-plates may offer improved fixation, but the optimal fixation construct for these fractures remains unclear. Forty synthetic distal tibiae with identical osteotomies were randomized into 4 fixation constructs: (1) two parallel unicortical cancellous screws; (2) two parallel bicortical cortical screws; (3) a contoured mini-fragment T-plate with 2 unicortical screws in the fragment and 2 bicortical screws in the shaft; and (4) a contoured mini-fragment T-plate with 2 bicortical screws in the fragment and 2 unicortical screws in the shaft. Specimens were subjected to offset axial tension loading on a servohydraulic testing system and tracked using high-resolution video. Failure was defined as 2 mm of articular displacement. Analysis of variance followed by a Tukey–Kramer post hoc test was used to assess for differences between groups, with significance defined as P Orthopedics . 2018; 41(3):e395–e399.]

Objectives To develop a nonterminal large animal bone defect model for assessing the efficacy of regenerative and pharmacologic treatments designed to enhance bone healing. Study Design In vivo experimental. Sample Population Adult gelding horses (n = 6). Methods Under general anesthesia, using radiographic guidance, 13.5 mm diameter bilateral, full thickness mandibular defects were created in 6 horses using a custom surgical jig and coring bit. After 16 weeks, under general anesthesia, 23 mm diameter cores that encompassed the original healing defects and surrounding parent bone material were removed for evaluation. Oxytetracycline was administered 14 days before final core harvest to label bone-forming surfaces. Healing was qualitatively assessed from decalcified hematoxylin and eosin (H&E) stained and undecalcified fluorescent labeled sections. Trabecular to cortical bone fraction (Tb.V/Ct.V), bone volume fraction (BV/TV), tissue mineral density (TMD), and apparent bone mineral density (aBMD) were quantified using microcomputed tomography and compared between left and right sides using Wilcoxon signed rank test. Results BV/TV was not significantly different between left and right-sided defects. Bone deposition occurred centripetally from the border of the original defect, filling 67% ± 16% (SD) of the defect at 16 weeks. Conclusion This model has potential use for comparison of regenerative and pharmacologic products aimed to augment bone healing.

SummaryObjectives: To compare the bending and torsional mechanical properties of mono- and bicortical locking screws in a canine cadaveric tibial gap ostectomy bridged by a locking compression plate (LCP).Methods: A 10-hole 3.5 mm LCP was applied medially to the tibia with a gap ostectomy using locking screws in the two proximal and distal plate holes. One tibia of each pair was randomly assigned monocortical screws and the other bicortical screws. Constructs were tested non-destructively in mediolateral and caudocranial four-point bending and torsion, and then to failure in four-point bending. Stiffness, yield and failure variables were compared between screw lengths and load conditions using analysis of variance.Results: Caudocranial and mediolateral fourpoint bending stiffnesses were not different between screw constructs. Torsional stiffness was greater and neutral zone smaller for bicortical constructs. Constructs were stiffer and stronger in caudocranial bending than in mediolateral bending. In caudocranial bending, bicortical constructs failed by bone fracture and monocortical constructs by screw loosening.Conclusion: Bicortical constructs were stiffer than monocortical constructs in torsion but not bending. Bicortical screw constructs failed by bone fracture under the applied loads whereas monocortical screw constructs failed at the bone-screw interface.Clinical relevance: Bicortical screw placement may be a safer clinical alternative than monocortical screw placement for minimally invasive percutaneous osteosynthesis LCPplated canine tibiae with comminuted diaphyseal fractures.

The incidence of age-related bone fracture is increasing with average population age. Bone scatters more light (stress-whitens) during loading, immediately prior to failure, in a manner visually similar to polymer crazing. We wish to understand the stress-whitening process because of its possible effect on bone toughness. The goals of this investigation were a) to establish that stress-whitening is a property of the demineralized organic matrix of bone rather than only a property of mineralized tissue and that stress whitening within the demineralized bone is dependent upon both b) hydrogen bonding and, c) the orientation of loading.Demineralized cortical bone specimens were loaded in tension to failure (0.08 strain/s). The effect of hydrogen bonding on mechanical properties and the stress-whitening process was probed by altering the Hansen's hydrogen bonding parameter (δh) of the immersing solution.Stress-whitening occurred in the demineralized bone. Stress-whitening was negatively correlated with δh (R(2)=0.81, p0.0001). Stress-whitening was significantly lower (p0.0001) in specimens loaded orthogonally compared to those loaded parallel to the long (strong) axis.The stress-whitening observed was consistent with increased Mie scattering. We suggest that the change in Mie scattering was due to collagen fibril dehydration driven by the externally applied stress. The presence of stress-whitening in demineralized bone suggests that this process may be a property of the collagenous matrix and hence may be present in other collagenous tissues rather than an emergent property of the bone composite.