Alteration of distal tarsal subchondral bone thickness pattern in horses with tarsal pain

REASONS FOR PERFORMING STUDY: Understanding of the development of pathology and source of pain in distal tarsal osteoarthritis is poorly understood. Magnetic resonance imaging is often used in the analysis of human osteoarthritis (OA) because it is sensitive to early changes. HYPOTHESIS: In association with distal tarsal joint (DTJ) pain, there will be an alteration in the characteristic subchondral bone (SCB) thickness pattern of horses with no history of pain when subjected to low-level exercise. METHODS: Sixteen cadaver tarsal joints were collected from 9 mature horses with a history of tarsal pain and radiographic evidence of OA; 3 cadaver tarsi were collected from 2 mature horses with a history of tarsal pain and no radiographic abnormality. Magnetic resonance images were acquired using high-resolution sagittal 3D T1 weighted spoiled gradient echo sequence. Subchondral bone thickness was measured on sagittal images at dorsal and plantar locations on the proximal and distal aspects of the central (CT) and third (T3) tarsal bones and proximal aspect of the third metatarsal bone (MT3). RESULTS: In tarsi with radiographic evidence of OA medial and lateral SCB thicknesses were greater than midline on the proximal and distal aspects of CT and T3. Lateral SCB thickness was greater than medial on the proximal aspect of MT3. There was an increase in SCB thickness at the majority of sites compared with normal horses. There were too few joints in the group without radiographic changes to analyse statistically. In painful tarsi SCB thickness was greater medially than laterally at all sites. In horses without tarsal pain all lateral sites had greater SCB thickness, except the proximal aspect of CT. CONCLUSIONS: There is alteration of normal SCB thickness patterns in painful tarsi. Different thickness patterns could represent different types of pathological processes. Potential clinical relevance: Further work is required to elucidate the pathological processes leading to OA of the DTJs.     

Radiographic and clinical survey of degenerative joint disease in the distal tarsal joints in Icelandic horses

The prevalence of degenerative joint disease (DJD) in the distal tarsal joints and the relation between radiographic and clinical signs compatible with the disease were estimated in a population of Icelandic horses used for riding. The material consisted of 614 horses age 6-12 years (mean age = 7.9 years). Radiographs with 3 projections of each tarsus were made and a clinical examination, including palpation of the medial aspect of the distal tarsus and motion evaluation of the hindlimbs before and after a flexion test of the tarsus, was performed. Radiographic signs of DJD in the distal tarsal joints were found in 30.3% of the horses and the prevalence was strongly correlated with age. Hindlimb lameness before and after flexion test and palpation abnormalities were significantly associated with the radiographic findings. The lameness was usually mild and, in most cases, detectable only after the flexion test. The prevalence of lameness was not significantly correlated with age. Lameness could not be predicted by details of the radiographic findings.     

Is there a characteristic distal tarsal subchondral bone plate thickness pattern in horses with no history of hindlimb lameness?

REASONS FOR PERFORMING STUDY: Osteoarthritis (OA) is a common cause of distal tarsal pain, but disease development is poorly understood. Awareness of normal tarsal structure and function is important in order to understand the pathogenesis of OA. Thickening of the subchondral bone (SCB) plate has been related to the development of OA, but SCB plate patterns in the equine tarsus have not been documented. HYPOTHESES: There is a repeatable pattern of SCB thickness across the distal tarsal joints, and specifically that thickness would be greatest dorsally and laterally. METHODS: Twenty cadaver tarsi were collected from mature horses that had undertaken low-level exercise only with no history of hindlimb lameness. Magnetic resonance images were acquired using a high-resolution sagittal 3-dimensional T1-weighted spoiled gradient echo sequence. Subchondral bone thickness was measured on sagittal images at dorsal and plantar locations on the proximal and distal aspects of the central (CT) and third (T3) tarsal bones and proximal aspect of the third metatarsal bone (Mt3). RESULTS: On the proximal aspect of CT, medial and lateral SCB thickness were significantly greater than midline. On the distal aspect of CT and T3 and proximal Mt3, lateral SCB thickness was significantly greater than medial and midline sites. Dorsal SCB thickness was greatest on the proximal and distal aspects of CT and proximal Mt3. Subchondral bone accounted for a greater proportion of CT and T3 on the dorsal aspect than the plantar. CONCLUSIONS: There is a repeatable pattern of SCB thickness in the distal tarsal bones of horses with no history of hindlimb lameness. This reflects the pattern of loading across the joints. POTENTIAL RELEVANCE: This study provides evidence of a consistent osteochondral pattern in the equine tarsus for reference in identification of osteoarticular pathologies.     

Comparison of three methods for arthrodesis of the distal intertarsal and tarsometatarsal joints in horses

OBJECTIVE: To evaluate the effects of diode laser surgery (LS), surgical drilling (SD), and intraarticular sodium monoiodoacetate (MIA) as methods for fusing the distal intertarsal (DIT) and tarsometatarsal (TMT) joints in horses. STUDY DESIGN: Experimental study. ANIMALS: Adult horses (15) without radiographic signs of osteoarthritis (OA) of the DIT and TMT joints. METHODS: Group 1 (n=3) had LS performed bilaterally on DIT and TMT joints; 1 horse was evaluated for 1 week and 2 horses were evaluated for 2 weeks. Group 2 (n=6) had LS on DIT and TMT joints of 1 tarsus and MIA administration into the contralateral DIT and TMT joints and were evaluated for 6 months. Group 3 (n=6) had LS performed on DIT and TMT joints of 1 tarsus and SD of the contralateral DIT and TMT joints and were evaluated for 12 months. Postoperative comfort, lameness, radiography, microradiography, and histology scores were compared using repeated measures ANOVA, and paired or 2 sample t-tests; significance was set at P<.05. RESULTS: LS caused the least postoperative morbidity. In group 2, horses were less lame in 4 LS-treated limbs and 2 MIA-treated limbs at 6 months when compared with the contralateral limb. In group 3, horses were less lame in 5 LS-treated limbs and 1 SD-treated limb at 6 and 12 months compared with the contralateral limb. On microradiography, 11 MIA joints and 2 LS joints had bone bridging the joint at 6 months whereas 8 SD joints and 5 LS joints had bone bridging at 12 months. Significantly more joint space was bridged by bone in MIA- (51.4%) and SD (46.2%)-treated joints compared with LS joints at 6 (30.6%) and 12 (28.5%) months, respectively (P<.05). CLINICAL RELEVANCE: SD and MIA resulted in more bone bridging of the distal 2 tarsal joints, than LS. However, LS seemingly caused less pain and discomfort to horses in the immediate postoperative period; horses were generally less lame in the LS limb. More laser energy may need to be applied to these joints to promote fusion; however, it may also have beneficial effects beyond fusion. Further research on horses with OA of the distal 2 tarsal joints is needed to determine whether LS can cause soundness without facilitating bony fusion.     

Study of cartilage and bone layers of the bearing surface of the equine metacarpophalangeal joint relative to different timescales of maturation

REASONS FOR PERFORMING STUDY: A detailed and comprehensive insight into the normal maturation process of the different tissues that make up functional units of the locomotor system such as joints is necessary to understand the influence of early training on musculoskeletal tissues. OBJECTIVES: To study simultaneously the maturation process in the entire composite structure that makes up the bearing surface of a joint (cartilage, subchondral and trabecular bone) in terms of biochemical changes in the tissues of juvenile horses at 2 differently loaded sites of the metacarpophalangeal joint, compared to a group of mature horses. HYPOTHESIS: In all the structures described above developmental changes may follow a different timescale. METHODS: Age-related changes in biochemical characteristics of the collagen part of the extracellular matrix (hydroxylysine, hydroxyproline, hydroxypyridinum crosslinks) of articular cartilage and of the underlying subchondral and trabecular bone were determined in a group of juvenile horses (n = 13) (Group 1, age 6 months-4 years) and compared to a group of mature horses (n = 30) (Group 2, >4 years). In both bony layers, bone mineral density, ash content and levels of individual minerals were determined. RESULTS: In cartilage, subchondral bone and trabecular bone, virtually all collagen parameters in juvenile horses were already at a similar (stable) level as in mature horses. In both bony layers, bone mineral density, ash- and calcium content were also stable in the mature horses, but continued to increase in the juvenile group. For magnesium there was a decrease in the juvenile animals, followed by a steady state in the mature horses. CONCLUSIONS: In horses age 6 months-4 years, the collagen network of all 3 layers within the joint has already attained a mature biochemical composition, but the mineral composition of both subchondral and trabecular bone continues to develop until approximately age 4 years. POTENTIAL RELEVANCE: The disparity in maturation of the various extracellular matrix components of a joint can be assumed to have consequences for the capacity to sustain load and should hence be taken into account when training or racing young animals.     

Use of a three-drill-tract technique for arthrodesis of the distal tarsal joints in horses with distal tarsal osteoarthritis: 54 cases (1990-1999)

OBJECTIVE: To assess the long-term clinical outcome of horses with distal tarsal osteoarthritis (OA) in which a 3-drill-tract technique was used to induce arthrodesis of the affected joints, identify any preoperative or operative factors associated with outcome, and describe any complications associated with the technique. DESIGN: Retrospective study. ANIMALS: 54 horses. PROCEDURE: Medical records were reviewed for information on signalment, use, history, physical and lameness examination findings, surgical technique, and postoperative care. Radiographs were examined, and severity of OA was graded. Follow-up information was obtained through telephone interviews with owners at least 13 months after the procedure. RESULTS: 32 (59%) horses had a successful outcome, 6 (11%) improved but were not sound after surgery, and 16 (30%) did not improve following surgery. Outcome was negatively associated with the previous use of intra-articular injections. Few postoperative complications were evident. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that distal tarsal OA in horses can be successfully treated by means of distal tarsal arthrodesis with a 3-drill-tract technique. Horses with advanced distal tarsal OA are likely to have poorer outcomes, and the procedure will likely be of minimal benefit in horses with concomitant causes of hind limb lameness prior to surgery and in horses with preexisting proximal intertarsal joint disease.     

Prevalence and distribution of radiographically evident lesions on repository films in the hock and stifle joints of yearling Thoroughbred horses in New Zealand

AIM: To characterise the prevalence and distribution of radiographic changes in the hocks and stifles of Thoroughbred yearling colts and fillies in New Zealand and compare them with other populations of young horses. METHODS: Repository radiographs taken in New Zealand for the 2003-2006 Thoroughbred national yearling sales were evaluated by two individual readers. The distribution of radiographic changes was classified as left side only, right side only, or bilateral. Lesions were categorised by type, location, and sex of the yearling. Complete sets of hock and stifle radiographs of 1,505 yearlings were evaluated. RESULTS: Osteophytes or enthesophytes were seen radiographically in the distal tarsal joints of 460/1,505 (31%) horses. Osteochondrosis was seen in the tibiotarsal joint of 66/1,505 (4%) horses, and in the femoropatellar joint of 40/1,505 (3%) horses. Radiographic lucency in the distal or axial aspect of the medial femoral condyle was seen in 247/1,505 (16%) horses, and lucencies consistent with subchondral cyst-like lesions were seen in 26/1,505 (2%) horses. No significant difference was seen in the proportion of colts and fillies with radiographic changes in the hock or stifle. The prevalence of osteochondrosis and subchondral cyst-like lesions in the stifles of the yearlings examined were similar to those reported in Thoroughbred yearling sale horses in the United States of America (USA). The prevalence of changes in the distal tarsal joints was similar to those reported in Standardbred and Thoroughbred yearlings from Scandinavia and the USA. CONCLUSIONS: There was no significant difference in the prevalence of osteochondrosis in the hock and stifle, lucencies in the distal medial femoral condyle, or radiographic changes in the distal tarsal joints between colts and fillies. CLINICAL RELEVANCE: Establishment of the normal prevalence and distribution of radiographic changes in the hocks and stifles of Thoroughbred yearlings in New Zealand will allow comparison with populations of young horses in other countries. Knowledge of the normal prevalence will assist veterinarians to identify abnormally high or low prevalences on individual farms, to further investigate the pathogenesis of the lesions.     

Radiographic, high detail radiographic, microangiographic and histological findings of the distal portion of the tarsus in weanling, young and adult horses.

Clinical radiographic (LM and D35L-P1MO views), high detail radiographic, microangiographic and histological findings of the distal portion of the tarsus of 16 horses (five weanling, four young and six adult), without known clinical histories, were evaluated to determine the sensitivity of clinical radiographs for the detection of abnormalities in the distal tarsus and the prevalence of abnormalities in this population. Clinical radiographic and high detail radiographic abnormalities were observed in at least 30 per cent of the tarsi examined. Statistical agreement between observations from clinical radiographs and corresponding post mortem high detail radiographs was not good for subchondral bone plate irregularities and joint margin changes. Three patterns of sclerosis of the medullary spongiosa were visualised on high detail radiographs: thickening of the subchondral bone plate was seen commonly in the weanling group, whereas arching and bridging patterns were more prevalent in the young and adult groups. Bone production on the dorsal cortex of the central and third tarsal bones did not increase with age. Abnormalities in vascular perfusion and articular cartilage histology were observed in association with subchondral bone plate irregularities and focal regions of osteopenia observed on high detail radiographs.     

Use of ethanol in the treatment of distal tarsal joint osteoarthritis: 24 cases

Reasons for performing this study: Intra‐articular ethanol has been described to promote distal tarsal joint ankylosis. Its use and results in clinical cases affected by osteoarthritis (OA) have not been reported. Objectives: To describe and evaluate the results of treatment of distal tarsal joint OA by facilitated ankylosis stimulated by intra‐articular ethanol injection. Methods: Twenty‐four horses met the inclusion criteria of tarsometatarsal and centrodistal joint OA diagnosed by a positive response to intra‐articular analgesia, radiographic evaluation and recurrence of lameness ≤4 months after intra‐articular medication with a corticosteroid. Horses were sedated and, following a radiographic contrast study of the tarsometatarsal joint, medication with 2–4 ml of either 100% pure ethanol (G100) or a 70% ethanol (G70) solution was applied. Horses were classified as improved based on a 50% reduction from initial lameness grade combined with an increase in exercise level. Results: Of the 24 horses included in this study, 20 had the treatment performed bilaterally and 4 unilaterally. All horses were available for initial follow‐up examination and 21 for a second one 6–9 months after treatment. This represented a total of 44 treated limbs and 35 available for long‐term follow‐up. Of these, 21/35 (60%) were considered improved, which corresponds to 11/21 horses (52%). Of 21 horses, 4 (19%) deteriorated and 2 of these developed significant complications related to treatment. Conclusions: Distal tarsal joint ankylosis with ethanol should be considered a safe and economic treatment in cases of distal tarsal joint OA that fail to show long‐term improvement with intra‐articular corticosteroid treatment. Potential relevance: Ethanol should be considered in the treatment of certain cases of distal tarsal joint OA. The importance of performing an adequate radiographic contrast study of the tarsometatarsal joint prior to treatment is highlighted.     

Clinical significance of osseous spurs on the dorsoproximal aspect of the third metatarsal bone

Reasons for performing study: Osseous spurs on the dorsoproximal aspect of the third metatarsal bone (MtIII) are common, but their clinical significance is unknown. Objectives: To verify the sites of insertion of the dorsal metatarsal ligament and the tendons of tibialis cranialis and fibularis tertius in order to determine if periarticular osteophytes and entheseophytes could be differentiated radiologically; and to determine the frequency of occurrence of osseous spurs on the dorsoproximal aspect of MtIII. Hypotheses: The frequency of osseous spurs on the dorsoproximal aspect of MtIII would be higher in lame than in clinically normal horses and higher in horses with distal hock joint pain or proximal suspensory desmitis than in horses with other causes of hindlimb lameness. Methods: A retrospective study of data from the clinical work up and tarsal radiographs of 455 horses was performed. Horses were divided into: Group 1, clinically normal horses; Groups 2–5, according to the diagnosis of hindlimb lameness. Radiographs were examined for the presence of an osseous spur on the dorsoproximal aspect of MtIII; pathology of the distal tarsal joints was graded. The associations between the presence of a spur and lameness, diagnosis group and the grade of distal tarsal joint abnormalities were analysed statistically using Chi‐squared tests. Results: An osseous spur was present in 25% of horses; 13% of horses with bilateral radiographs had bilateral spurs. There was no significant difference in frequency of the presence of a spur between lame and nonlame horses, or between horses with other causes of hindlimb lameness and horses with proximal suspensory desmitis and/or distal tarsal joint pain. The presence of an osseous spur was significantly associated with the grade of radiological abnormality in the distal tarsal joints (tarsometatarsal joint P = 0.018: centrodistal joint P = 0.027). In many horses it was not possible to differentiate accurately between osteophytes and entheseophytes. Conclusions and potential relevance: The presence of an osseous spur on the dorsoproximal aspect of MtIII in the absence of other radiological abnormalities may be an incidental finding. Osseous spurs occur more frequently in hocks with radiological abnormalities in the distal tarsal joints and may be an indicator of distal tarsal joint osteoarthritis. The clinical significance must be established by intra‐articular analgesia.     

Biochemical analysis of the articular cartilage and subchondral and trabecular bone of the metacarpophalangeal joint of horses with early osteoarthritis

OBJECTIVE: To assess whether site-related changes in biochemical composition are present in the cartilage and subchondral and trabecular bone of the metacarpophalangeal joint of horses with early osteoarthritis. SAMPLE POPULATION: Right metacarpophalangeal joints from 59 mature warmblood horses. PROCEDURE: Biochemical data (cross-link, amino acid, DNA, and ash contents; denatured collagen and glycosaminoglycan [GAG] concentrations; bone mineral density; and mineral composition) were obtained from 2 differently loaded sites of phalanx I cartilage and subchondral and trabecular bone samples; data were compared with previously published values from nonosteoarthritic equine joints. RESULTS: Compared with findings in nonosteoarthritic joints, GAG concentration was lower in cartilage from osteoarthritic joints and there was a loss of site differences in cellularity and lysylpyridinoline (LP) cross-link content. In subchondral bone, LP cross-link content was decreased overall and there was a loss of site differences in osteoarthritic joints; ash content was higher in the osteoarthritic joints. Hydroxyproline content in trabecular bone from osteoarthritic joints was greater than that in nonosteoarthritic trabecular bone. In all 3 layers and at both sites, the linear increase of the pentosidine cross-link content with age had diminished or was not apparent in the horses with osteoarthritic joints. CONCLUSIONS AND CLINICAL RELEVANCE: In equine metacarpophalangeal joints with early osteoarthritis, distinct biochemical changes were detected in the cartilage and subchondral and trabecular bone. The dissimilarity in response of the different tissues and differences between the sites that are affected may be related to differences in biomechanical loading and transmission and dissipation of force.     

Osteochondral Defects of the Lateral Trochlear Ridge of the Distal Femur of the Horse Clinical, Radiographic, and Pathological Examination and Results of Surgical Treatment

Osteochondral defects of the lateral trochlear ridge of the distal femur were identified in 15 joints of 10 horses. Lesions were bilateral in five horses and unilateral in five horses. Thirteen of these 15 defects were treated by curettage through a craniolateral femoropatellar arthrotomy. Subcutaneous seroma formation and partial skin dehiscence occurred in nine stifles. Lameness attributable to the stifle joint was no longer apparent at 6 and 12 months after surgery. The normal subchondral bony contour of the lateral trochlear ridge was altered in all joints after surgery. The subchondral bone was uniformly increased in density in all joints, and six lateral trochlear ridges had small focal radiolucent regions within the subchondral bone, which suggested that complete removal of the original lesion had not been achieved. Healing of the surgical site between 2 weeks and 14 months was evaluated in four joints. Granulation tissue from mesenchymal elements in subchondral marrow spaces gradually filled the defects with fibrocartilage.     

Clinical effects of exercise on subchondral bone of carpal and metacarpophalangeal joints in horses

OBJECTIVE: To determine effects of treadmill exercise on subchondral bone of carpal and metacarpophalangeal joints of 2-year-old horses. ANIMALS: 12 healthy 2-year-old horses. PROCEDURE: Horses were randomly assigned to the control (n = 6) or exercised (6) groups. Horses in the exercised group ran on a high-speed treadmill 5 d/wk for 6 months. Horses in the control group were hand walked for the same amount of time. Results of clinical, radiographic, nuclear scintigraphic, and computed tomographic examinations, and serum and synovial concentrations of biochemical markers of bone metabolism were compared between groups. RESULTS: Exercised horses were significantly lamer at the end of the study than control horses. Radionuclide uptake in the metacarpal condyles, but not in the carpal joints, was greater in exercised horses, compared with control horses. Exercised horses also had a higher subchondral bone density in the metacarpal condyles than control horses, but such differences were not detected in the carpal bones. CONCLUSIONS AND CLINICAL RELEVANCE: None of the diagnostic techniques evaluated was sufficiently sensitive to detect all osteochondral damage. Computed tomography and computed tomographic osteoabsorptiometry were superior to conventional radiography for detecting small osteochondral fragments. Nuclear scintigraphy was a sensitive indicator of subchondral bone change but lacked specificity for describing lesions and discerning normal bone remodeling from damage. Newer techniques such as computed tomography may help clinicians better diagnose early and subtle joint lesions in horses prior to development of gross joint damage.     

Concentration of methylprednisolone in the centrodistal joint after administration of methylprednisolone acetate in the tarsometatarsal joint

REASONS FOR PERFORMING STUDY: The centrodistal (CD) and tarsometatarsal (TMT) joints are often injected individually with a corticosteroid to resolve lameness caused by osteoarthritis (OA). There are no data available regarding diffusion of methylprednisolone (MP) from the TMT joint to the CD joint. HYPOTHESIS: A therapeutic concentration of MP diffuses into the CD joint after methylprednisolone acetate (MPA) is administered into the TMT joint. OBJECTIVE: To measure the concentration of MP in the CD joint after MPA was administered into the TMT joint. METHODS: MPA was administered into a TMT joint of 16 horses. At different times, the ipsilateral CD joint of these horses was injected with a small amount of saline and recovered saline was measured for concentration of MP using high performance liquid chromatography. RESULTS: Six hours after administration of MPA into the TMT joint, a therapeutic concentration of MP was found in all 10 CD joints sampled at this time. CONCLUSIONS: Horses with pain arising from the distal 2 joints of the hock can be treated by administering MPA into the TMT joint alone. POTENTIAL RELEVANCE: Administering MPA into the TMT joint only, to treat OA of the distal 2 hock joints, reduces the difficulties and risks associated with centesis of the CD joint.     

Use of magnetic resonance imaging for identifying subchondral bone damage in horses: 11 cases (1999-2003)

OBJECTIVE: To assess the use of magnetic resonance (MR) imaging for identifying subchondral bone damage in the distal limbs of horses. DESIGN: Retrospective study. ANIMALS: 11 horses. PROCEDURE: Medical records of horses with lameness and subsequent evidence of subchondral bone damage as determined by MR imaging were reviewed. Severity and duration of lameness, results of diagnostic local anesthesia and diagnostic testing, surgical and necropsy findings, and treatment were recorded. Outcome was determined by follow-up information obtained from the owner or referring veterinarian. RESULTS: Lameness was localized by physical examination and diagnostic local anesthesia. Lameness was localized to the metacarpophalangeal or metatarsophalangeal joint in 4 horses, distal interphalangeal joint in 5 horses, and tarsocrural joint in 2 horses. The duration of lameness ranged from 2 weeks to 20 months. Magnetic resonance imaging of the affected joints revealed abnormal fluid accumulation within the subchondral bone. None of the abnormalities observed by MR imaging were detected by radiography. Subchondral bone damage was diagnosed in all horses. Arthroscopy of the affected joint was performed in 4 horses. Communication with the articular surface of the affected bone was suspected on the basis of results of MR imaging in 4 horses and was confirmed by arthroscopy in 1 horse and by necropsy in 1 horse. CONCLUSIONS AND CLINICAL RELEVANCE: Magnetic resonance imaging was useful for providing a diagnosis when other imaging techniques did not definitively identify the cause of lameness. Subchondral bone damage was clearly identified by MR imaging and should be considered as a cause of lameness in horses in which radiographic findings are unremarkable.     

Effects of exercise on chondrocyte viability and subchondral bone sclerosis in the distal third metacarpal and metatarsal bones of young horses

The objective was to determine the effects of early exercise on the articular cartilage and subchondral bone at specific sites of the distal third metacarpal and metatarsal bones of 12 young Thoroughbred horses allowed free choice exercise at pasture. Six of the horses had additional controlled exercise 5 days per week from mean age of 21+/-20 days of age (range: 3-83 days) until 17.1 months of age. Confocal laser scanning microscopy was used to quantify viable and non-viable chondrocytes. Proteoglycan scoring and modified Mankin scoring was performed and subchondral bone mineral density measured by computed tomography. The number of viable chondrocytes was significantly greater in the conditioned group, which also had a higher Safranin O/Fast Green (SOFG) score than did the group which could exercise only at pasture. There was no difference in mean bone mineral density between groups, nor was there relationship between subchondral bone mineral density and chondrocyte viability. The apparent beneficial effects of early conditioning exercise may support the use of exercise to optimise development of articular cartilage in young individuals.     

Comparison of mean bone densities of three preparations of the distal portion of the equine third metacarpal bone measured by use of quantitative computed tomography

OBJECTIVE: To evaluate whether cutting equine subchondral bone to demarcate specific regions of interest (ROIs) influences the mean density for that bone as measured via quantitative computed tomography (QCT). Sample population-2 metacarpophalangeal joints from equine cadavers. PROCEDURES: The distal portion of the third metacarpal bone of each intact metacarpophalangeal joint was scanned via CT to simulate in vivo conditions. Each joint was subsequently disarticulated and dissected, and the distal portion of the dissected third metacarpal bone in air was scanned. Then, six 1-cm(2) areas representing ROIs were cut into the distal condylar surfaces to depths of approximately 1 cm, and the bone was scanned again. Three-dimensional CT models of the 3 bone preparations were generated for each third metacarpal bone on the basis of data from each set of scan images, and densities of the 6 ROIs were measured. Mean bone densities for the 6 ROIs were compared among models of intact, dissected, and cut third metacarpal bone scans. RESULTS: Mean bone density was significantly lower in cut bone preparations, compared with that in intact or dissected bone. Differences between mean bone densities for intact and dissected bone preparations were not significant. CONCLUSIONS AND CLINICAL RELEVANCE: Cutting subchondral bone to demarcate specific ROIs prior to CT imaging significantly lowered mean bone density as measured via QCT and thus introduced substantial artifacts. These findings have direct implications on techniques for CT modeling of equine subchondral bone in the characterization of joint diseases in horses.     

EVALUATION OF DIFFERENT PROJECTIONS FOR RADIOGRAPHIC DETECTION OF TARSAL DEGENERATIVE JOINT DISEASE IN ICELANDIC HORSES

Radiographs from 196 tarsi in 98 Icelandic horses were evaluated to compare the accuracy of four different projections in detecting radiographic signs of degenerative joint disease in the distal tarsus. The extent and localization of tarsal degenerative joint disease found in one projection when reading all four projections of the same tarsus together was compared with the combined findings from all four projections. The results of reading individual radiographic projections without knowledge of the other three projections was also evaluated. Degenerative joint disease was detected most frequently in the plantarolateral-dorsomedial oblique (P1L-DMO) projection. The location with the highest relative frequency of radiographic findings was the dorsolateral aspect of the centrodistal and tarsometatarsal joints respectively. Radiographic signs of active bone remodelling was detected in 30 (33%) and periarticular osteophytes in 51 (56%) of 91 tarsi with degenerative joint disease.     

Risk factors associated with hindlimb lameness and degenerative joint disease in the distal tarsus of Icelandic horses

The aim of this study was to evaluate potential risk factors associated with hindlimb lameness and radiographic signs of degenerative joint disease (DJD) in the distal tarsus in Icelandic horses. The material consisted of riding horses (n = 420) age 6-12 years sired by 17 selected sires representing all major breeding lines, and of riding horses (n = 194) in the same age range sired by other sires. The examination protocol included the following: interview with owners/trainers, assessment of conformation, motion evaluation and radiographic examination. At the interview, data related to factors outside the horse (environmental variables) and data associated directly with the horse (intrinsic variables) were obtained. Data analysis was performed in 2 steps: screening using bivariate analysis, followed by testing with a multivariate logistic regression model. In the multivariate analysis, the factors of sire, age when broken to saddle and stud show participation were strongly associated with the prevalence of lameness. Height at the croup and ability to perform different gaits were also associated with the prevalence of lameness, but to a lesser degree. The risk factors of age, tarsal angle and birthplace were significantly associated with radiographic signs of DJD in the distal tarsus. Neither the variation in applied training intensity, the use of a professional or amateur trainer nor the temperament or front limb action of the individual horse was significantly associated with the prevalence of hindlimb lameness and/or radiographic signs of DJD in the distal tarsus in the Icelandic horse.     

The use of advanced vs. conventional imaging modalities for the diagnosis of subchondral bone injuries

Damage to the subchondral bone has been associated with a number of orthopaedic diseases. Diagnostic imaging is, therefore, critical in identifying disease and damage of the subchondral bone, not only for the diagnosis of joint and subchondral bone disease causing lameness, but also for identifying early/pre-symptomatic damage. The aims of this Critically Appraised Topic (CAT) were to assess the published evidence for the use of advanced imaging techniques (magnetic resonance imaging [MRI] and computed tomography [CT]) in the diagnosis of subchondral bone disease in the distal limb joints (metacarpo/metatarsophalangeal and interphalangeal joints) of the adult horse, and to compare the diagnostic value of these techniques with radiography. In the studies reviewed in this CAT, advanced imaging modalities (MRI and CT) were superior to routine radiography for the diagnosis of subchondral bone injury of the distal limb joints. In a small percentage of horses, post-MRI reevaluation of the initial radiographs or acquiring further lesion-orientated radiographs allowed the identification of the subchondral bone injury. Extended radiographic examinations, including non-standard views, might increase the sensitivity of radiography to detect subchondral bone injuries, however, currently CT and MRI may be considered the “gold standard” imaging modalities. More studies comparing the identification of subchondral bone lesions on imaging and by histopathological/gross examination would be useful to assess more precisely the sensitivity and specificity of the different modalities.