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Objective—To describe the anatomic and histologic features of the collateral ligaments (CLs) of the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints in cadaveric limbs obtained from nonlame horses and to compare the histologic findings with the ultrasonographic appearance of the CLs. Sample—Medial and lateral CLs of the MCP and MTP joints of 28 limbs (16 forelimbs and 12 hind limbs) from 9 adult nonlame horses euthanized for reasons unrelated to the study. Procedures—26 limbs of 8 horses were examined by ultrasonography immediately after euthanasia. Postmortem gross and histologic examinations were performed for all 28 limbs. Histologic and ultrasonographic images were graded and compared. Results—Ultrasonographically, the mean ± SD depth and width of the superficial CL were 5.1 ± 0.7 mm and 20.5 ± 1.7 mm, respectively. On histologic examination, only 125 of 319 (39%) specimens obtained from 56 medial and lateral CLs appeared normal. Histopathologic findings varied from mild changes in cellular density and collagen fiber orientation to severe fibrocartilaginous metaplasia. The degree of CL lesion severity increased distally, and the lateral CL was affected more frequently than was the medial CL. Ultrasonographically detectable abnormalities were not correlated with the histologic findings. Conclusions and Clinical Relevance—In horses, histologic abnormalities within the CLs of the MCP and MTP joints may be an adaptive response to joint hyperextension and compression and might predispose horses to desmopathy and ligament failure in the event of trauma. Ultrasonography did not detect morphologic changes of the CL matrix. For an accurate diagnosis of subclinical lesions, more sensitive imaging techniques (eg, MRI) should be considered.

Summary Reasons for performing study Selection of suture material in equine surgery is often based on costs or subjective factors, such as the surgeon's personal experience, rather than objective facts. The amount of objective data available on durability of suture materials with regard to specific equine physiological conditions is limited. Objectives To evaluate the effect of various equine physiological and pathological fluids on the rate of degradation of a number of commonly used suture materials. Study design In vitro material testing. Methods Suture materials were exposed in vitro to physiological fluid, followed by biomechanical analysis. Three absorbable suture materials, glycolide/lactide copolymer, polyglactin 910 and polydioxanone were incubated at 37°C for 7, 14 or 28 days in phosphate-buffered saline, equine serum, equine urine and equine peritoneal fluid from an animal with peritonitis. Five strands of each suture material type were tested to failure in a materials testing machine for each time point and each incubation medium. Yield strength, strain and Young's modulus were calculated, analysed and reported. Results For all suture types, the incubation time had a significant effect on yield strength, percentage elongation and Young's modulus in all culture media (P

REASONS FOR PERFORMING STUDY: Equine embryogenesis post implantation is not well studied, and only two-dimensional illustrations are available. A thorough appreciation of the complex three-dimensional relationship between tissues and organs and their development is, however, crucial for understanding physiological and pathological mechanisms. OBJECTIVES: The goals were 2-fold: 1) to establish a freely accessible online atlas as a reference tool for the scientific and pedagogic communities; and 2) to create a framework for integration of data with known spatiotemporal distribution, such as gene expression or cell lineage. STUDY DESIGN: Descriptive anatomical study. METHODS: Magnetic resonance microscopy was performed on embryos of 28, 32, 35, 37, 39, 40, 42, 45, 50 and 65 days gestation using a 9.4 T magnet. Equine embryos were staged according to the Carnegie system. Acquired images were optimised using histogram optimisation and processed for easy online access. RESULTS: Magnetic resonance microscopy protocols for imaging of equine embryos and fetuses were developed. The wider spread of signal intensity values achieved by histogram equalisation increased visual contrast considerably. Despite their longer gestation, equine conceptuses appeared to reach the various Carnegie staging benchmarks earlier than human embryos. CONCLUSIONS: The equine atlas is designed to serve as an online reference tool for research and teaching. POTENTIAL RELEVANCE: The equine atlas may serve as a foundation and scaffold for improved anatomical labelling, spatial and temporal data integration and further understanding of physiological and pathophysiological processes involved in development and disease.

Objective: To determine the physiologic response of the equine navicular bone to core decompression surgery in healthy horses. Study Design: Experimental in vivo study. Materials: Healthy adult horses (n=6). Methods: Core decompression was completed by creating three 2.5-mm-diameter drill channels into the navicular bone under arthroscopic control. The venous (PV), arterial (PA), articular (PDIPJ), and intraosseous pressures (IOP) were recorded before and after decompression drilling. Each IOP measurement consisted of a baseline (IOPB) and a stress test (intramedullary injection of saline solution, IOPS) recording. Lameness was assessed subjectively and using force plate gait analysis. Fluorochrome bone labeling was performed. Horses were euthanatized at 12 weeks. Navicular bone mineral density (BMD) was measured, and bone histology evaluated. Results: Peak IOP (IOPmax) after stress testing was significantly (P

Objective: To determine the effect of core decompression surgery and bone mineral density (BMD) on the mechanical properties of equine navicular bones. Study Design: Experimental, in vitro study. Sample Population: Fore limb navicular bones (n=36 pairs) from sound 2–5-year-old horses with no radiographic abnormalities of the distal aspect of the forelimbs. Methods: Navicular BMD was measured using dual energy X-ray absorptiometry. One randomly assigned navicular bone from each pair served as control. The contralateral test specimen was allocated to 1 of 6 treatment groups defined by drill bit size (3.2 versus 2.5 mm diameter) and by the number of drill channels (1, 2, or 3) created in the proximal border of the bone. Bones were then tested until failure in 3-point bending. Data were statistically analyzed using ANOVA and regression analysis. Results: There were significant (P .05) influence the extent of the reduction in mechanical strength. Conclusion: In vitro core decompression significantly decreases the breaking strength of the equine navicular bone.

REASONS FOR PERFORMING STUDY: Articular cartilage regeneration is the focus and goal of considerable research effort. Since articular chondrocytes descend from a distinct cohort of progenitor cells located in embryonic nascent joints (interzones), establishing the timing of equine interzone formation is an essential first step towards understanding equine joint and articular cartilage development. OBJECTIVES: To establish the time frame during which the equine femorotibial interzone forms. STUDY DESIGN: Descriptive anatomical study. METHODS: Equine embryos were harvested at 37 (E37), 40, 42, 45, 50 and 65 days' gestation. The femorotibial interzone was examined using high-resolution episcopic microscopy of E37, E42, E45, E50 and E65. Additional histology and collagen-II-immunohistochemistry were performed on E42. RESULTS: At E37, the femorotibial interzone is first visible as a uniform layer, while at E42 the interzone is fully formed and consists of 3 morphologically distinct layers. The first evidence of cavitation was seen at E45. At E50, the cruciate ligaments were well formed and by E65, joint formation appeared complete. CONCLUSIONS: The embryogenesis of the equine femorotibial joint is similar to the developmental timeline of stage-matched human and murine embryos. Further studies looking at interzone formation on a cellular and molecular level may further our understanding of the intricate developmental patterns and pathways of articular cartilage development.

Summary A comminuted fracture of the central tarsal bone, fragmentation of the fourth tarsal bone and associated joint instability was diagnosed in a 14-year-old Sport Horse mare who presented for investigation of acute nonweightbearing hindlimb lameness. The mare responded well to conservative management and, unlike previously reported cases of similar injuries, returned to a similar level of athletic activity.

Summary Objectives: To review the outcome of equine shoulder osteochondrosis (OC) with surgical or conservative treatment. Methods: Retrospective study of 32 horses, less than two years of age, with scapulohumeral joint (SHJ) OC. The lesion severity was graded based on measurements taken from lateromedial radiographs. Follo–up information was obtained from racing records or telephone conversations with owners. Successful outcome was defined as the ability of the horse to perform its intended use. Results: Sixteen of 32 horses were affected bilaterally (48 joints). Eleven of 16 horses with bilateral OC underwent arthroscopic surgery; five had bilateral arthroscopy, six had unilateral arthroscopy of the most severely affected joint. Eight of 16 horses with unilateral OC underwent arthroscopy. The overall outcome was ′poor′. Only 15.4% (4/26) of potential race horses started a race, whereas 67% (4/6) non-racehorses were ′sound′ for the intended use. Statistical analysis evaluating the effect of breed on outcome showed a statistically significant difference. There were no significant interactions between outcome and gender, affected limb, unilateral versus bilateral involvement, treatment or severity of the radiographic lesion. However, radiographic lesion severity on the humerus and glenoid showed significant positive correlation. Clinical significance: The overall poor prognosis for shoulder OC in young horses appears to be, in part, dependent on breed and intended use. There was not any difference in outcome between surgically and conservatively treated horses.

To evaluate knot security for 3 knot types created in 3 commonly used 5 metric suture materials incubated in physiological and pathological fluids.In vitro mechanical study.Knotted suture loops (n = 5/group).Loops of 3 different suture materials (glycolide/lactide copolymer; polyglactin 910; polydioxanone) were created around a 20 mm rod using 3 knot types (square [SQ], surgeon's [SK], and triple knot [TK]) and were tested to failure in distraction (6 mm/min) after tying (day 0) and after being incubated for 14 and 28 days in phosphate buffered saline (PBS) or inflamed peritoneal fluid. Failure load (N) and mode were recorded and compared.For polydioxanone, significant differences in force to knot failure were found between SQ and SK/TK but not between SK and TK. The force required to break all constructs increased after incubation in phosphate buffered saline (PBS). With glycolide/lactide copolymer no differences in force to knot failure were observed. With polyglactin 910, a significant difference between SQ and TK was observed, which was not seen between the other knot types. Incubation in inflamed peritoneal fluid caused a larger and more rapid decrease in force required to cause knot failure than incubation in PBS.Mechanical properties of suture materials have significant effects on knot security. For polydioxanone, SQ is insufficient to create a secure knot. Additional wraps above a SK confer extra stability in some materials, but this increase may not be clinically relevant or justifiable. Glycolide/lactide copolymer had excellent knot security.

Objective: Articular chondrocytes originate from a distinct cohort of progenitor cells located in the so-called interzone in embryonic developing joints. We conducted this study 1) to determine if it is possible to identify the intermediate and outer interzone layers histologically (using cresyl violet) without adjunct in situ hybridization or immunohistochemistry; 2) to establish whether sufficient amounts of RNA can be harvested from each interzone layer of individual embryos to allow gene expression analysis; 3) to develop measurements that can provide an estimation of the RNA yield prior to costly amplification steps. Methods: Cells from the outer (OI) and intermediate (II) interzone of the nascent femorotibial joint and the epiphyseal cartilage (EC) of femur and tibia of murine embryos of 13.5 and 15.5 days gestation were harvested using laser capture microdissection (LCM). Subsequently, microarray analysis was performed to confirm appropriate layer selection. The surface area harvested and the grey value (gv) of photomicrographs taken during LCM was measured and the corresponding relative optical density (ROD) was calculated and degree and significance of the correlation with RNA yield were determined. Results: Cells from the OI, II and EC could be identified histologically using cresyl violet staining and were successfully harvested with LCM yielding sufficient amounts of RNA for linear amplification and microarray analysis. The RNA yield correlated significantly with the tissue surface area harvested, the mean gv and the corresponding ROD. Conclusions: This study provides a technique for selective laser capture microdissection and subsequent microarray analysis of murine interzone cells of the intermediate and outer layer and presents a method to estimate the RNA yield by measuring the tissue area harvested and calculating the ROD. We recommend to harvest a minimum of 1×106 μm2 of 13.5 days murine embryos and 3×106 μm2 of 15.5 days murine embryos to obtain approximately 10 ng total RNA that can be used for linear T7-based amplification and subsequent microarray analysis.

To determine the physiologic response of the equine navicular bone to core decompression surgery in healthy horses.Experimental in vivo study.Healthy adult horses (n=6).Core decompression was completed by creating three 2.5-mm-diameter drill channels into the navicular bone under arthroscopic control. The venous (P(V)), arterial (P(A)), articular (P(DIPJ)), and intraosseous pressures (IOP) were recorded before and after decompression drilling. Each IOP measurement consisted of a baseline (IOP(B)) and a stress test (intramedullary injection of saline solution, IOP(S)) recording. Lameness was assessed subjectively and using force plate gait analysis. Fluorochrome bone labeling was performed. Horses were euthanatized at 12 weeks. Navicular bone mineral density (BMD) was measured, and bone histology evaluated.Peak IOP (IOP(max)) after stress testing was significantly (P.05) reduced immediately after core decompression; however, the magnitude of these effects was decreased at 3 and 6 weeks after decompression. A significant (P.05) correlation existed between IOP(max) and BMD. No lameness was observed beyond the first week after surgery. Substantial remodeling and neovascularization was evident adjacent the surgery sites.Navicular bone core decompression surgery reduced IOP(max), and, with the exception of a mild short-lived lameness, caused no other adverse effects in healthy horses during the 12-week study period.

To determine the effect of core decompression surgery and bone mineral density (BMD) on the mechanical properties of equine navicular bones.Experimental, in vitro study.Fore limb navicular bones (n=36 pairs) from sound 2-5-year-old horses with no radiographic abnormalities of the distal aspect of the forelimbs.Navicular BMD was measured using dual energy X-ray absorptiometry. One randomly assigned navicular bone from each pair served as control. The contralateral test specimen was allocated to 1 of 6 treatment groups defined by drill bit size (3.2 versus 2.5 mm diameter) and by the number of drill channels (1, 2, or 3) created in the proximal border of the bone. Bones were then tested until failure in 3-point bending. Data were statistically analyzed using ANOVA and regression analysis.There were significant (P.001) positive correlations between BMD and biomechanical data. A significant (P.001) reduction in breaking strength was noted between intact and drilled bone pairs; however, the diameter and number of decompression channels did not significantly (P.05) influence the extent of the reduction in mechanical strength.In vitro core decompression significantly decreases the breaking strength of the equine navicular bone.

Objective—To evaluate the use of hydrothermal ablation of articular cartilage for arthrodesis in horses through investigation of the effects of joint lavage with physiologic saline (0.9% NaCl) solution (80°C) for various treatment times on chondrocyte viability in the articular cartilage of the metacarpophalangeal and metatarsophalangeal joints of cadaveric horse limbs. Sample Population—7 pairs of metacarpophalangeal and 8 pairs of metatarsophalangeal joints from 8 Thoroughbreds. Procedure—The horses were euthanatized for reasons unrelated to musculoskeletal disease. On a random basis, 1 joint of each pair underwent intra-articular lavage for 5, 10, or 15 minutes with heated saline solution (80°C); the other joint underwent sham treatment of similar duration with saline solution at 22°C (control). Cartilage samples from the distal articular surface of metacarpus III (or metatarsus III), the proximal surface of the proximal phalanx, and the lateral and medial proximal sesamoid bones were assessed for chondrocyte viability via confocal microscopy and viability staining following enzymatic digestion. Results—Compared with the control joints, findings of both viability assays indicated that the percentage of sites containing viable chondrocytes in heat-treated joints was decreased. Treatment hazard ratios of 0.048 (confocal microscopy) and 0.2 (digestion assay) were estimated. Histologically, periarticular soft tissues had minimal detrimental effects after heat treatment. Conclusions and Clinical Relevance—Ex vivo intraarticular lavage with saline solution at 80°C resulted in the death of almost all articular chondrocytes in the joint. This technique may be a satisfactory method for extensive cartilage ablation when performing arthrodesis by minimally invasive techniques. (Am J Vet Res 2005;66:36–42)

Objective—To determine whether triamcinolone acetonide diffuses from the distal interphalangeal joint (DIPJ) to the navicular bursa, diffusion is direct or systemic, and addition of sodium hyaluronan has an effect on diffusion in horses. Animals—11 adult horses without forelimb lameness. Procedures—1 randomly chosen forelimb DIPJ of each horse received an injection of 10 mg of triamcinolone acetonide plus 20 mg of sodium hyaluronan (group 1), and the contralateral forelimb DIPJ received an injection of 10 mg of triamcinolone acetonide plus 2 mL of lactated Ringer's solution (group 2). Synovial fluid samples were taken from both forelimb navicular bursae and 1 hind limb navicular bursa (systemic control group) at 6 hours. Triamcinolone acetonide concentrations in synovial fluid were quantified by use of high-performance liquid chromatography plus tandem mass spectrometry. Data were logarithmically transformed, and contrast analysis was performed on the 3 groups. Results—Triamcinolone acetonide was detected in navicular bursal samples in all groups. Groups 1 and 2 had significantly greater concentrations of triamcinolone acetonide than the systemic control group. There was no significant difference between groups 1 and 2. Conclusions and Clinical Relevance—Triamcinolone acetonide diffused directly from the DIPJ into the navicular bursa in clinically normal horses, and diffusion was not affected by addition of hyaluronan. Injection into the DIPJ with triamcinolone acetonide or a triamcinolone acetonide–hyaluronan combination can potentially be used for treatment of navicular syndrome, but further studies are needed to determine whether triamcinolone acetonide diffuses similarly in horses with navicular syndrome.