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Objective: To evaluate the mechanical properties of locking screw placement in hybrid plating in comparison to all-locked and all nonlocked constructs., Study Design: Completely randomized design. Forty-eight synthetic bone cylinders (4th generation composite Sawbones(®)) across 6 construct types (n = 8 each)., Methods: An 8-hole 3.5 mm LCP was placed across a 2 mm cylinder gap to mimic an unstable fracture model. The plates were secured with all locking screws, all nonlocking screws, or a combination of locking screws and nonlocking screws in the hybrid constructs. Constructs were cyclically tested nondestructively in 4-point bending, axial compression, and torsion, and then tested to failure in torsion. The stiffness and strength of each construct were calculated and compared across construct types., Results: Constructs with a locking screw located adjacent to the fracture gap were stiffer in bending and stronger in torsion to failure than constructs without an adjacent locking screw. Hybrid and nonlocking screw constructs more frequently failed by catastrophic breakage of the bone cylinder, compared to all locking screw constructs that failed by plastic deformation of the plate., Conclusions: Mechanical testing of synthetic bone model constructs shows that hybrid constructs are at least as stiff and strong as entirely nonlocked constructs, and with some screw configurations, are not statistically different from entirely locked constructs., (© Copyright 2015 by The American College of Veterinary Surgeons.)

Objective: To compare the in vitro biomechanical properties of a novel subcuticular stapling device to current methods of abdominal skin closure for equine abdominal surgery., Study Design: In vitro randomized, matched design., Sample Population: Equine ventral median abdominal skin specimens (n = 24 horses)., Methods: Subcuticular absorbable staples (SAS), metallic staples (MS), polyglyconate suture (PG), and nylon monofilament (NYL) were applied to longitudinally transected portions of equine ventral midline skin. Loads that resulted in an initial failure point and the ultimate failure load and mechanism were recorded., Results: Mean ± SD loads at initial failure for PG (86 N ± 64 N), NYL (81 N ± 142 N), and SAS (70 N ± 20 N) were not significantly different from each other. PG and SAS were significantly higher than MS (43 N ± 17 N; P < .05). Ultimate failure load for PG (563 N ± 157 N) and NYL (558 N ± 162 N) were significantly higher than either MS (175 N ± 44 N) or SAS (96 N ± 20N; P < .001). For the suture groups, nearly all failures occurred because of skin pull through whereas all SAS staples failed because of staple fracture. Failure patterns were mixed for MS., Conclusions: SAS had the lowest ultimate failure load; however, other measured variables identified characteristics of SAS that may be clinically beneficial., (© Copyright 2014 by The American College of Veterinary Surgeons.)

Objective: To (1) investigate the tissue response to a novel urethral bulking agent, polyethylene glycol carboxymethyl cellulose hydrogel (PEG-CMC) injected submucosally in the canine urethra and (2) compare PEG-CMC with bovine collagen (BC), the current standard for urethral bulking., Study Design: Experimental study., Animals: Purpose-bred female hound dogs (n = 8)., Methods: Standardized submucosal urethral injections of BC and PEG-CMC were performed in 8 female dogs. Injection sites were evaluated by cystoscopy on days 0 (n = 8), 30 (n = 4), and 90 (n = 4), magnetic resonance imaging on days 0 (n = 8), 30 (n = 8), and 90 (n = 4) and by histopathology on days 30 (n = 4) and 90 (n = 4)., Results: Both PEG-CMC and BC were detectable on MRI as hyperintense foci on T2-weighted images. Grossly, PEG-CMC formed more prominent blebs than BC. On follow-up cystoscopic examination, 6/8 PEG-CMC injection needle tracts were visible, and 3 of these sites had mucosal erosions. Histopathologic scores for foreign body reaction and inflammation were significantly higher for PEG-CMC compared with BC (P < 0.005). BC elicited a lymphoplasmacytic reaction whereas PEG-CMC incited a granulomatous response., Conclusions: The overall physical characteristics and histologic response associated with PEG-CMC support its use as a urethral bulking agent; however, the current formulation needs to be adjusted for clinical use., (© Copyright 2012 by The American College of Veterinary Surgeons.)

Objective: To compare digital radiography (DR), computed tomography (CT), and magnetic resonance imaging (MRI) for detection of pathology of the distal aspect of the third metacarpal bone (MC3) and to assess whether arthrography would improve detection of articular cartilage or subchondral bone cracking., Study Design: Cross-sectional study., Sample Population: Limb specimens from 17 Thoroughbred horses after catastrophic injury and 4 age-matched control horses., Methods: Standard DR, CT, and MRI images of the metacarpophalangeal joint were acquired before and after iohexol injection. Pathologic features detected with imaging and on visual inspection of cartilage and subchondral bone of the distal aspect of MC3 were graded. Imaging observations were compared with pathologic abnormalities., Results: Inspection revealed obvious changes in the cartilage and subchondral bone surfaces in Thoroughbreds. Both CT and MRI were superior to DR for detection of subchondral bone pathology. Cracking of cartilage was not detected by any imaging modality. Signal changes associated with cartilage loss and development of repair tissue were evident on MRI in 9/19 cases. There was significant correlation (P < .05) between subchondral bone pathology detected on both CT and MRI, and cartilage pathology on gross examination. Contrast arthrography did not improve the detection of articular cartilage or subchondral plate cracking., Conclusion: Both CT and MRI are superior to DR for detection of subchondral bone pathology, but underestimate the extent of joint adaptation and pathologic damage. MRI was able to detect cartilage degeneration., (© Copyright 2011 by The American College of Veterinary Surgeons.)

Objective: To evaluate stifle joints of dogs for synovitis, before development of joint instability and cranial cruciate ligament rupture (CrCLR)., Study Design: Cross-sectional study., Animals: Dogs (n = 16) with CrCLR and stable contralateral stifles; 10 control dogs with intact CrCL., Methods: Arthritis and tibial translation were graded radiographically. Synovitis severity and cruciate pathology were assessed arthroscopically. Presence of inflammatory cells in synovial membrane biopsies was scored histologically. CrCLR stifle pairs and control stifles were compared., Results: Radiographic evidence of arthritis, cranial tibial translation, and arthroscopic synovitis were increased in unstable stifles, when compared with stable contralateral stifles in CrCLR dogs (P < .05). Arthroscopic synovitis in both joints of CrCLR dogs was increased compared with controls, was correlated with radiographic arthritis (S(R) = 0.71, P < .05), and was present in all stable contralateral stifles. Arthroscopically, 75% of stable stifle joints had CrCL fiber disruption, which correlated with severity of synovitis (S(R) = 0.56, P < .05). Histologic evidence of synovitis was identified in all CrCLR dogs, but was only significantly correlated with arthroscopic observations in stable stifles (r(2) = 0.57, P < .005)., Conclusion: Synovitis is an early feature of the CrCLR arthropathy in dogs before development of joint instability clinically. Severity of synovitis is correlated with radiographic arthritis in joints with minimal to no clinically detectable CrCL damage., (© Copyright 2011 by The American College of Veterinary Surgeons.)

Objective: To investigate the incidence of caudal cruciate ligament (CaCL) damage in dogs with cranial cruciate ligament rupture (CCLR)., Study Design: Prospective clinical study., Animals: Dogs (n=24) admitted for surgical stabilization of the stifle after CCLR and 8 healthy dogs with intact cranial cruciate ligament (CCL) and CaCL studied as controls., Methods: Preoperative radiographs and stifle joint images (arthrotomy, 6; arthroscopy, 18) were collected from dogs with CCLR. Severity of arthritis, synovitis, CCL damage, and CaCL damage were assessed using numerical rating scales. The CaCL was probed to determine whether minor fraying or a full thickness defect in the ligament was present. Data collected from the study population were compared with the control population of dogs., Results: The CaCL was damaged in 21/24 (88%) of dogs with CCLR; 6/24 (25%) had a full thickness defect in the CaCL. Severity of stifle synovitis and severity of damage to the CaCL were positively correlated (P<.05)., Conclusions: The CaCL is damaged in a high percentage of dogs with CCLR. A significant and positive correlation exists between the degree of synovitis present and the extent of CaCL damage., Clinical Relevance: In dogs with CCLR, cruciate ligament pathology typically involves both the CCL and CaCL. As the severity of synovitis and the extent of CaCL damage are related, this observation supports the hypothesis that stifle synovitis may contribute to CCL and CaCL degeneration and subsequent damage., (© Copyright 2010 by The American College of Veterinary Surgeons.)

Objectives: To determine interobserver repeatability of measurements on computed tomography (CT) images of lax canine hip joints at different ages and in the presence of degenerative joint disease at maturity., Study Design: Longitudinal observational investigation., Animals: Sibling crossbreed hounds., Methods: Pelvic CT was performed at 20, 24, 32, 48, 68, and 104 weeks of age. Measures were performed on 3 contiguous two-dimensional (2D) transverse CT images of both hips at each time point by 3 investigators. Center-edge angle (CEA), horizontal toit externe angle (HTEA), ventral (VASA), dorsal (DASA), and horizontal (HASA) acetabular sector angles, acetabular index (AI), and percent femoral head coverage (CPC) were measured. Interobserver repeatability was quantified with the intraclass correlation coefficient (ICC). Satisfactory repeatability was considered when ICC >or=0.75., Results: DASA, CEA, and CPC were repeatable in all age groups. HASA and HTEA were repeatable for all but 1 time point. At 20 weeks of age, all measures but AI were repeatable, and at 104 weeks of age, DASA, CEA, CPC, and HASA were repeatable. Measures were repeatable in hips with and without degenerative changes with the exceptions of AI and HASA in normal hips and VASA and HTEA in osteoarthritic hips., Conclusions: Most 2D CT measurements examined were repeatable regardless of age or joint disease., Clinical Relevance: Two-dimensional CT measures may augment current techniques for assessing joint changes in lax canine hips.

Objectives: To compare bone healing of tibial osteotomy repaired with Nitinol wire braid and hardened steel rods (Braid system) and polymethylmethacrylate bone cement with an interlocking intramedullary (IM) nail fixation in an ovine model., Study Design: In vitro and in vivo experimental study., Animals: Adult female sheep (n=22)., Methods: Using sheep tibia, a middiaphyseal transverse osteotomy was performed in the right tibia, which were then randomly assigned to the Braid system group or IM nail group (n=5). The left tibia were used as controls. The torsional properties of tibial constructs were compared. The study was repeated in vivo in 12 sheep and mechanical properties and bone healing were evaluated at 12 weeks., Results: In vitro, there was no significant difference in torsional stiffness between the groups. In vivo, operative time for the Braid system group was significantly shorter than the IM nail group. At 12 weeks, there were no significant differences in maximum torque and torsional stiffness between IM nail and Braid system groups nor were there significant radiographic or histologic differences between the groups., Conclusions: The Braid system might decrease operative time for repair of transverse middiaphyseal tibial fractures and result in similar bone healing at 12 weeks after surgery compared with an interlocking IM nail repair., Clinical Relevance: A Nitinol Braid system may be a treatment option for transverse midshaft tibial fractures.

Objective: To evaluate the accuracy of numerical rating (NRS) and visual analogue (VAS) scoring scales compared with force plate gait analysis and agreement between observers for each scoring scale., Study Design: Experimental study., Animals: Mixed breed dogs (n=21) with a right limb tibial osteotomy repaired with an external fixator., Methods: Three small-animal veterinarians with orthopedic training scored lameness using NRS and VAS before surgery, and at 4 and 8 weeks after surgery. Peak force and impulse were determined at the same time points using a force plate. Agreement between observers and with force plate data was assessed. Significance was set at P< or =.05., Results: Agreement was generally low among observers for both NRS and VAS scores. When evaluated at each time point, an acceptable level of agreement was present only at 4 weeks after surgery. Only impulse had a significant relationship with some of the observers' subjective scores. No significant relationships between any observer's scores and force plate data existed if very lame dogs were omitted., Conclusions: Subjective scoring scales do not replace force plate gait analysis. Agreement is low unless lameness is severe, and each observer uses an individually unique scale. Subjective scoring scales most accurately reflect force plate gait analysis when lameness is severe., Clinical Relevance: Subjective lameness scoring scales may not accurately reflect lameness and do not replace force plate gait analysis. Observers must stay the same during the duration of a study for accurate analyses.

Objective: To compare the efficacy of 2 doses of recombinant human bone morphogenetic protein-2 (rhBMP-2) on tibial osteotomy healing in dogs., Study Design: Experimental, randomized complete block (n=7)., Animals: Adult female dogs (n=21)., Methods: Right midshaft tibial osteotomies were created and stabilized with a 1-mm gap using type I external fixators. Seven dogs were untreated controls and 14 with osteotomies were treated with either 0.05 or 0.2 mg/mL rhBMP-2 delivered in an absorbable collagen sponge (ACS). At 8 weeks, dogs were euthanatized and bones were mechanically tested and examined by microscopy., Results: Bone healing based on radiographic scoring, was significantly improved in dogs treated with 0.2 mg/mL of rhBMP-2 compared with the other groups; these tibiae were also significantly stronger and stiffer than 0.05 mg/mL rhBMP-2 and control osteotomized tibiae. Histologic scores were significantly better for 0.2 mg/mL rhBMP-2 group than 0.05 mg/mL rhBMP-2 group, but neither was significantly different from control., Conclusions: rhBMP-2 in ACS at a concentration of 0.2 mg/mL improves healing of tibial osteotomies in dogs compared with untreated controls and 0.05 mg/mL rhBMP-2 based on force plate analysis and radiographic evaluation. This was not confirmed histologically but treated bones had improved mechanical properties at 8 weeks., Clinical Relevance: After a long bone fracture, dogs may face a long recovery period before full return of limb function. rhBMP-2, in association with good fracture fixation principles, may enhance bone healing in dogs with diaphyseal fractures.

Objectives: To evaluate the effects of intra-articular protection (IAP) on the canine cranial cruciate ligament (CrCL) and stifle in a CrCL midsubstance elongation injury model., Study Design: Experimental longitudinal cohort study., Animals: Skeletally mature female mixed breed hounds (n=12; mean+/-SEM weight, 25.6+/-0.7 kg)., Methods: After CrCL elongation in 1 stifle of each dog, IAP was applied in 6 joints. In vivo assessment included radiographs, cranial-caudal joint translation, gait analysis, and synovial fluid levels of 3B3(-) (proteoglycan epitope) and C2C (collagen II neoepitope) up to 12 weeks after surgery. Joint translation and rotation were quantified at necropsy. CrCL midsubstance length was determined before and after elongation and at necropsy. CrCLs were subjectively assessed with light microscopy. Comparisons were made between stifles containing elongated CrCLs with and without IAP and unoperated controls., Results: Four weeks after surgery, ground reaction forces were significantly decreased in operated limbs. Absolute C2C levels were significantly elevated in operated stifles 4 weeks post-surgery. C2C and 3B3(-) levels normalized to total protein were significantly elevated in IAP+ stifles 8 weeks after surgery. Protected CrCLs appeared to have decreased granulation tissue and better collagen fiber alignment., Conclusions: IAP has negligible effects on the canine stifle based on the response variables evaluated in this 12-week study. Protection of elongated CrCLs may promote reduced, organized scar formation., Clinical Relevance: These results support the healing capacity of the canine CrCL midsubstance following elongation injury and IAP application to potentially reduce cicatrix formation in elongated CrCLs.

Objective: To compare the orthogonal radiographic (OR) and computed tomographic (CT) appearance of paired Thoroughbred racehorse limbs with severe condylar fracture., Study Design: In vitro study., Sample Population: Cadaveric paired limbs with severe condylar fracture (n=11 horses)., Methods: Four standard radiographic and multiple transverse CT images were obtained of the fractured and contralateral limbs centering on the metacarpo/metatarsophalangeal (fetlock) joints. Radiographs and CT images were graded by 4 raters, and interobserver agreement was calculated. Imaging evaluations were supplemented by fetlock joint dissection. A consensus description of actual injury and the detection accuracy of OR and CT for that injury was determined. Results- Rater agreement for OR and CT for most pathologic features was good or excellent. OR was similar to CT for the detection of condylar and diaphyseal third metacarpal and metatarsal (MC/MT3) fractures, diaphyseal fractures of the first phalanx (P1), and fracture location on the condyle. CT was superior to OR for detection of MC/MT3 proximal fissures and articular comminution, condylar small cracks and lucencies, and proximal sesamoid fractures. OR was superior to CT for detection of proximal P1 dorsal fractures. Both OR and CT were poor at detecting palmar/planter proximal P1 fractures and coalescing cracks in the subchondral bone of MC/MT3., Conclusions: CT is better than OR for detection of pathology in limbs with condylar fractures, but does not detect every pathologic feature., Clinical Relevance: CT provides superior information of pathology in Thoroughbred racehorses with condylar fractures.

Objective: Evaluation of the relationship between canine weight gain from 6 to 15 weeks of age and passive coxofemoral joint (CFJ) laxity at 16 weeks of age., Study Design: Longitudinal cohort study., Animals: Full- or half-sibling hounds (n = 56)., Methods: Hounds were weighed weekly from 6 to 15 weeks of age. Individual average daily gain (ADG) was calculated for each week (weekly) and for the study (overall). PennHIP distraction index (DI) was determined for each CFJ at 16 weeks. Mixed effects linear models were evaluated for associations of DI (highest and mean) with 15-week weight and ADGs (actual or normalized). Left and right DIs were compared with a Student's paired t-test. Significance was set at P<.05. Trends were considered at P<.10., Results: Mean (+/-SD) 16-week DI score and 15-week weight was 0.67 +/- 0.16 and 12.5 +/- 1.8 kg, respectively. Within animal left and right DIs were not significantly different. There were no significant associations between DI and any of the weight gains evaluated. There was a trend for a negative relationship between normalized 14-week ADG and DI in one statistical model., Conclusions: Weight gain from 6 to 15 weeks of age was unrelated to 16-week PennHIP DI in a homogenous canine population with moderate-to-severe CFJ joint laxity., Clinical Relevance: Based on our results, ad libitum feeding between 6 and 15 weeks of age does not appear to have an adverse impact on joint laxity at 16 weeks of age as measured by the PennHIP DI.

Objective: To evaluate femoral adaptation after unstable long-term cemented total hip arthroplasty (cTHA) in dogs., Study Design: Clinical study., Animals: Four dogs., Methods: Paired femurs were examined from client-owned dogs that were donated to a retrieval program after death from causes unrelated to their cTHA. Mean (+/-SEM) dog age was 10.0+/-1.5 years and implant duration was 6.0+/-1.4 years. Implanted femurs had radiographic changes associated with implant loosening and gross mechanical instability at femur retrieval. Femurs were evaluated at 3 levels relative to implant length. Cortical area and medullary area were measured at each level, and cortical porosity was assessed at each level in 4 quadrants and in 3 regions. Implanted femurs were compared with the contralateral non-implanted femurs., Results: Cortical area and cortical porosity were increased at all levels in femurs with unstable implants. Implanted femurs had increased porosity in all quadrants and regions at the proximal 2 levels, and increased porosity in only the cranial quadrant and mid-cortical area at the distal level, when compared with contralateral non-implanted femurs. Corresponding medullary areas were not different., Conclusions: Significant histomorphometric changes occur in femurs after unstable cTHA. The patterns of periosteal bone formation and endosteal bone resorption support mechanisms of stress shielding and wear debris-mediated osteolysis as factors that may contribute to femoral adaptation and implant loosening., Clinical Relevance: Despite popularity and excellent return to function with cTHA, aseptic loosening remains a serious long-term complication. Substantial net bone loss and unfavorable environment with unstable cTHA may make revision surgery less successful.

Objective: To quantify long-term bone adaptation after stable cemented total hip arthroplasty (cTHA) in dogs., Study Design: Clinical study., Animals: Fourteen dogs., Methods: Femoral specimens were collected from client-owned dogs that were donated after death because of causes unrelated to their cTHA. Mean (+/-SEM) dog age was 11.4+/-0.7 years and implant duration was 5.3+/-0.7 years. Implant stability was established from radiographic signs and gross mechanical stability. Femurs were evaluated at 3 levels based on implant length: proximal stem (PS), mid-stem (MS), and distal to stem (DS). Cortical area, medullary area, and porosity were measured at each level. Implanted femurs were compared to contralateral nonimplanted femurs., Results: Cortical area and cortical porosity were significantly increased in implanted femurs compared to nonimplanted femurs. Cortical area was increased at the MS and DS levels, and porosity was increased at the PS and MS levels in implanted femurs. Porosity was greatest in the endosteal region at the PS and MS levels in implanted femurs., Conclusions: Significant differences in femoral geometry and cortical porosity were detected after long-term stable cTHA. Net bone loss proximally and increased bone mass distally support stress shielding as a important mechanical factor associated with bone adaptation. Distribution of porosity shifts to endosteal regions after long-term cTHA., Clinical Relevance: Significant site-specific femoral adaptation occurs in response to stable cTHA and may precede implant loosening.

Objectives: To determine whether bone microcracks are altered after application of focused and radial extracorporeal shock wave therapy (ESWT) to the equine distal limb., Study Design: An ex vivo experimental model., Sample Population: A contralateral limb specimen was obtained from 11 Thoroughbred racehorses with a unilateral catastrophic injury. Distal limb specimens were also obtained from 5 non-racing horses., Methods: Three separate skin-covered bone segments were obtained from the mid-diaphysis of the metacarpus (MC3) or metatarsus (MT3). Focused (9,000 shockwaves, 0.15 mJ/mm2, 4 Hz) and radial (9,000 shockwaves, 0.175 mJ/mm2, 4 Hz) ESWT treatments were randomized to the proximal and distal segments and the middle segment was used as a treatment control for pre-existing microcracks. After treatment, bone specimens were bulk-stained with basic fuchsin and microcracks were quantified in transverse calcified bone sections., Results: ESWT had small but significant effects on microcracks. Microcrack density (Cr.Dn) and microcrack surface density (Cr.S.Dn) were increased after focused ESWT, whereas Cr.Le was increased after radial ESWT. In racing Thoroughbreds, Cr.Le increased with increased number of races undertaken. Cr.Dn and Cr.S.Dn were not significantly influenced by the number of races undertaken., Conclusion: ESWT has small but significant effects on bone microcracking ex vivo., Clinical Relevance: These preliminary data suggest that ESWT has the potential to increase bone microcracking in equine distal limb bone in vivo. Such effects may be more pronounced in Thoroughbreds that are actively being raced, because in vivo microcracking increases with increased number of races undertaken.

Objective: To examine the fracture failure surfaces from Thoroughbred horses that had sustained a catastrophic condylar fracture., Sample Population: Bone specimens from the failure surface were obtained from 12 Thoroughbred racehorses with catastrophic injury and 2 non-racing horses with accidental long bone fracture., Methods: Bone specimens from the failure surface of each fracture were incubated with gold microspheres to label microcracks before examination at x50 to x60,000 using scanning electron microscopy. Microcracking at the failure surface was assessed using a visual analog scale., Results: Branching arrays or clusters of microcracks were seen over a range of magnifications in adapted subchondral bone in the distal end of the MC3/MT3 bone from racing Thoroughbreds with a catastrophic displaced condylar fracture. In the palmar/plantar region, microcracking was associated with the formation of an array of macroscopic cracks in the condylar groove. A different pattern of microcracking was seen in specimens of bone from distal metaphyseal and diaphyseal MC3/MT3 failure surfaces from Thoroughbred racehorses with catastrophic fracture and non-racing horses with an accidental diaphyseal long bone fracture. Few microcracks were seen and typically did not form branching arrays., Conclusion: These data suggest that propagation of condylar fracture in Thoroughbred racehorses is initiated by the formation of nanoscale microcracks in adapted subchondral bone that form during exercise-induced bone adaptation., Clinical Relevance: Accumulation and coalescence of branching microcracks into arrays or clusters appears to eventually lead to the development of macroscopic subchondral cracks in the condylar groove and initiation of a condylar fracture.

Objective: To investigate the harvest and application of hamstring grafts for canine cranial cruciate ligament (CrCL) reconstruction., Study Design: Experimental study., Animals: Four adult female hounds, weighing 26.3 +/- 1.6 kg (mean +/- SEM). METHODS-One stifle in each dog was randomly chosen for hamstring graft CrCL reconstruction after native CrCL transection. Arthroscopy was performed to evaluate graft integrity at 12 weeks. Gait analysis and stifle radiographs were performed preoperatively and up to 52 weeks after graft placement. Dogs were killed 12 (n = 2) or 52 weeks (n = 2) after CrCL reconstruction. Tissues were evaluated grossly and with light and confocal laser microscopy., Results: Hamstring grafts were intact in all stifles at 12 weeks (n = 4) and 52 weeks (n = 2). Grossly, there was no osteoarthritis in stifles at 12 weeks and only chondrophytes along the trochlear ridges at 52 weeks. Minimal radiographic evidence of osteoarthritis developed in stifles with grafts during the study. Lameness in limbs with grafts resolved by 52 weeks. Graft tissue was highly vascular, ligamentized, and undergoing active remodeling at 12 weeks. Fifty-two weeks after graft placement, intraarticular graft tissue was well vascularized, mature, and encapsulated by synovium, and graft-bone interfaces were characterized by Sharpey's fiber insertions. There was no evidence of graft necrosis using confocal laser microscopy at either time point., Conclusions: The hamstring graft technique may be a viable method of canine CrCL reconstruction., Clinical Relevance: Hamstring grafts may be an alternative technique for canine CrCL reconstruction. Further study is needed before clinical application., (Copyright 2003 by The American College of Veterinary Surgeons)

Objective: To determine the optimal fixation technique for equine interdental space fractures by evaluating the biomechanical characteristics of 4 fixation techniques., Study Design: In vitro randomized block design., Sample Population: Twenty-seven adult equine mandibles., Methods: Mandibles with interdental osteotomies were randomly divided into 4 fixation groups (n = 6/group). Fixation techniques were the following: (1) dynamic compression plates (DCP), (2) external fixator (EF), (3) external fixator with interdental wires (EFW), and (4) intraoral splint with interdental wires (ISW). Three intact (nonosteotomized) mandibles were tested as controls. Mandibles were subjected to monotonic cantilever bending until failure. Angular displacement data (radians) were derived from continuously recorded gap width measurements provided by extensometers placed across the osteotomy site. Osteotomy gap width data (mm) at 50 and 100 Nm were selected for standardized comparison of gap width before the yield point and failure point, respectively of all constructs tested. Stiffness (Nm/radian), yield strength (Nm), and failure strength (Nm) were determined from bending moment-angular displacement curves and were compared using ANOVA with appropriate post hoc testing when indicated. Radiographs were obtained prefixation, postfixation, and posttesting., Results: Bending stiffness, yield, and ultimate failure loads were greatest for intact mandibles. Among osteotomized mandibles, stiffness was greatest for DCP constructs (P <.05) and was not significantly different among EF, EFW, and ISW constructs. Yield load was greatest for ISW constructs (P <.05) and was not significantly different among DCP and EFW constructs. Yield and ultimate failure loads were lowest (P <.05) and osteotomy gap width at 50 and 100 Nm were greatest for EF constructs (P =.09 and P <.05, respectively). There was no significant difference in failure loads and osteotomy gap widths among DCP, EFW, and ISW constructs (P <.05). Failure occurred through the screw-bone interface (DCP), acrylic splint (ISW), acrylic connecting bar and/or pin-bone interface (EF, EFW), and wire loosening (EFW). All 3 intact mandibles fractured through the vertical ramus at its attachment to the testing apparatus., Conclusions: Among osteotomized mandibles, DCP fixation had the greatest stiffness under monotonic bending to failure; however, the relatively low yield value may predispose it to earlier failure in fatigue testing without supplemental fixation. Techniques using tension-band wiring (EFW and ISW) were similar to DCP constructs in yield, failure, and osteotomy displacement, whereas EF constructs were biomechanically inferior to all other constructs., Clinical Relevance: DCP fixation is most likely the most stable form of fixation for comminuted interdental space fractures. However, for simple interdental space fractures, ISW fixation may provide adequate stability with minimal invasiveness and decreased expense. Tension-band wiring significantly enhances the strength of type II external skeletal fixators and should be used to augment mandibular fracture repairs., (Copyright 2003 by The American College of Veterinary Surgeons)

Objectives: To determine changes to the cells and collagenous and amorphous extracellular matrix (ECM) structure in ruptured canine cranial cruciate ligaments (CCL)., Study Design: Prospective clinical study., Animals: CCL specimens obtained from 29 dogs with ruptured CCL and 6 young dogs with intact CCL., Methods: Ligament fibroblast number density and phenotype were determined in the core and epiligamentous regions. ECM birefringence and crimp structure in the core region were also studied., Results: Loss of fibroblasts from the core region of ruptured CCL was seen (P <.001), whereas, in the epiligamentous region, cell number densities were similar in ruptured and intact CCL (P =.7). In ruptured CCL, numbers of typical ligament fibroblasts (fusiform and ovoid cells) were decreased, and numbers of cells exhibiting chondroid transformation (spheroid cells) were increased in the core region (P <.001). Expansion of the volume of the epiligamentous region was also seen, although bridging scar tissue was not seen between the ends of ruptured CCL. The structure of the ECM collagen in the core region was extensively disrupted in ruptured CCL. This was, in part, because of decreased birefringence and elongation of the crimp in the remaining collagen fibers when compared with intact CCL (P <.01)., Conclusions: Extensive alterations to the cell populations and collagenous ECM structure were seen in ruptured CCL. Although a proliferative epiligamentous repair response was seen in ruptured CCL, there was a lack of any bridging scar between the ruptured ends of the CCL., Clinical Relevance: The cellular and ECM changes in ruptured CCL that we have described appear to result from the cumulative effects of remodeling and adaptation to mechanical loading and microinjury. Treatment of early cruciate disease in dogs will need to inhibit or reverse these progressive changes to CCL tissue, which are directly associated with partial or complete structural failure of the CCL under conditions of normal activity., (Copyright 2003 by The American College of Veterinary Surgeons)

Objective: To compare the biomechanical characteristics and mode of failure of two different dynamic compression plate (DCP) techniques for proximal interphalangeal joint (PIPJ) arthrodesis in horses., Study Design: Randomized block-design blocking on horse (1-5), method of fixation (two 7-hole, 3.5-mm broad DCP vs two 5-hole, 4.5-mm narrow DCP), side (left, right), and end (front, hind). Constructs were loaded to failure in 3-point bending in a dorsal-to-palmar (plantar) direction., Sample Population: Ten paired limbs from 5 equine cadavers., Methods: Two 7-hole, 3.5-mm broad dynamic compression plates (bDCP) were used in 1 limb of a pair, and two 5-hole 4.5-mm narrow dynamic compression plates (nDCP) were used on the contralateral limb. Plates were positioned abaxially across the dorsomedial and dorsolateral aspect of the PIPJ. Arthrodesis constructs were loaded (19 mm/s) in 3-point bending in a dorsal-to-palmar (plantar) direction using a materials-testing machine. Composite stiffness, yield point, and maximal bending moment at failure were obtained from bending moment-angular deformation curves. Data were analyzed using ANOVA, X(2) analysis, and Fisher's exact tests; the power of the test was calculated when differences were not significant., Results: There were no significant differences in composite stiffness (P >.05; power = 0.8 @ delta = 21.9%), yield point (P >.05; power = 0.8 @ delta = 34.4%), or maximal bending moment (P >.05; power = 0.8 @ delta = 17.8%) between the two fixation techniques. For bDCP constructs, 11% (15 of 140) of the 3.5-mm screws were damaged; 7 of the screw heads pulled through plates where the plates bent, 1 screw head broke off, and 7 screws were bent or pulled out of the phalanx. For nDCP constructs, 8% (8 of 100) of the 4.5-mm screws were damaged; 1 screw head pulled through a plate, 1 screw head broke off, and 6 screws were bent or pulled out of the phalanx., Conclusions: There were no biomechanical or failure differences between bDCP and nDCP fixation of the PIPJ in horses when evaluated in single-cycle 3-point bending to failure., Clinical Relevance: There is no biomechanical advantage to the use of two 7-hole, 3.5-mm bDCP in equine proximal interphalangeal arthrodesis compared with two 5-hole, 4.5-mm nDCP. Two 5-hole, 4.5-mm nDCP may be easier to place, whereas two 7-hole, 3.5-mm bDCP may provide more versatility in fracture repair., (Copyright 2002 by The American College of Veterinary Surgeons)