Arthroscopic visualisation of the third metacarpal and metatarsal condyles in the horse

Reasons for performing study: Arthroscopy of the fetlock joints is a routine surgical procedure in the horse. It is unclear how much of the articular surface of the condyles of the metacarpal (MCIII)/metatarsal (MTIII) bone can be visualised using either the dorsal or palmar/plantar arthroscopic approach. Objectives: To investigate which part of the articular surface of the MCIII/MTIII condyles of the fetlock joints can be evaluated arthroscopically using: 1) dorsal approach in combination with flexion; 2) standard palmar/plantar approach; or 3) additional portal at the base of the sesamoid bone with joint extension. Methods: All 3 arthroscopic approaches were performed on 20 fore‐ and 20 hindlimbs of 14 cadavers. For each approach, a curette was inserted ipsilaterally to create a lesion at the most distal part of the condyle that could be seen. After disarticulation and placement of a nail in each lesion, the maximally reachable angle was calculated on a perfect lateromedial radiograph. The 0° angle was determined as the distal crossing of the best fitting circle around the condyle with a line parallel to the dorsal MCIII/MTIII bone running through the circle centre (positive angle dorsal to 0°, negative palmar/plantar to 0°). Results: Using the dorsal approach with flexion, a significantly larger area of visualisation was present in the hind‐ (?23.4°) compared to the forelimb (+2.7°). Using the palmar/plantar approach (fore: ?60.4°; hind: ?70.7°) and the approach at the base of the sesamoid bone (fore: ?36.3°; hind: ?47.6°) more cartilage could be seen in the fore‐ compared to the hindlimb. When combining the 3 approaches, the remaining nonvisible part measured 38.9° in the fore‐ and 24.2° in the hindlimb, both located palmaro/plantarodistally. Conclusions: The use of dorsal and palmar/plantar arthroscopic approaches in combination with flexion and extension of the fetlock joint allows visualisation of the majority of the cartilage of the MCIII/MTIII condyles. The nonvisible section is smaller in the hindlimb compared to the forelimb. Potential relevance: Knowledge of the specific areas of visualisation of the condyles on arthroscopy is important for both diagnostic and therapeutic planning of fetlock disorders.     

Pathology of the distal condyles of the third metacarpal and third metatarsal bones of the horse

This study examined material from Thoroughbred horses, the majority of which had been in race training, for evidence of pathology in the third metacarpal (McIII) and third metatarsal (MtIII) bones which might be related to the occurrence of distal condylar fractures. Whole bone samples were studied and documented by macrophotography prior to macroradiography and computed tomographic (CT) imaging. Microradiographs were made from 100 microm thick mediolateral sections cut perpendicular to the dorsal and palmar/plantar articular surfaces of distal condylar regions of McIII and MtIII. Blocks were prepared for morphological imaging using the backscattered electron mode of scanning electron microscopy (BSE SEM). Linear defects in mineralised articular cartilage and subchondral bone were found in the palmar/plantar aspects of the condylar grooves adjacent to the sagittal ridge. These were closely related to the pattern of densification of the subchondral bone and were associated with intense focal remodelling of the immediately adjacent and subjacent bone. Parasagittal fractures of the condyles originated in similar defects. A unifying hypothesis for the aetiopathogenesis of these fractures is presented.     

Structural variation of the distal condyles of the third metacarpal and third metatarsal bones in the horse

This study examined 3-dimensional (3D) distribution of sectors with contrasting density in the equine third metacarpal (McIII) and third metatarsal (MtIII) bones with a view to explaining the aetiology of distal condylar fractures. Macroradiography and computed tomographic (CT) imaging were used in the nondestructive study of bones obtained from horses, most of which were Thoroughbreds in race training. Distal condylar regions of McIII and MtIII were also studied in microradiographs of 100 microm thick mediolateral sections cut perpendicular to the dorsal and palmar/plantar articular surfaces. Qualitative and quantitative results from all methods used (radiography, CT and microradiographic stereology) demonstrated a densification (sclerosis) of subchondral bone located in the palmar/plantar regions of the medial and lateral condyles of both McIII and MtIII. Substantial density gradients between the denser condyles and the subchondral bone of the sagittal groove were shown to equate with anatomical differences in loading intensity during locomotion. It is hypothesised that such differences in bone density results in stress concentration at the palmar/plantar aspect of the condylar grooves, which may predispose to fracture.     

Aetiopathogenesis of parasagittal fractures of the distal condyles of the third metacarpal and third metatarsal bones--review of the literature

Fractures are the cause of considerable morbidity and mortality among Thoroughbred racehorses. A significant proportion of these injuries occur in the absence of any particular traumatic incident. Evidence of prefracture pathology interpreted as fatigue damage has been identified in some such cases, but the aetiology of many of these so-called 'spontaneous' fractures remains obscure. Parasagittal fractures of the third metacarpal (McIII) and third metatarsal (MtIII) bones are one of the more common fractures to affect Thoroughbred racehorses. The configuration of each of these fracture types is highly consistent, suggesting a predisposition of the bones to these injuries. Several theories have been proposed to explain the aetiopathogenesis of these fractures although none has so far stood up to critical examination. The current paper reviews the literature relating to parasagittal fractures of McIII and MtIII.     

Results of treatment of 145 fractures of the third metacarpal/metatarsal condyles in 135 horses (1986-1994).

The objectives of this study were to correlate condylar fracture characteristics and type of treatment with subsequent capacity for athletic ability, and to determine the characteristics of healing that affect prognosis after fracture fixation. Medical records, post operative radiographic studies and race records were examined for 135 horses sustaining 145 fractures. Sixty-five percent of horses overall started in a race post injury (SPI) in a mean time of 9.7 months with a mean of 13.7 races post injury. Having raced pre-injury did not confer an advantage to starting post injury, though nonstarters pre-injury tended to take longer to return. For horses starting pre- and post injury, 66% improved or maintained their race class level after injury, whereas 64.2% decreased their race earnings post injury. Eighty-five percent of the fractures received internal fixation, of which 70% were complete fractures. Eighty-seven percent of horses with incomplete-nondisplaced fractures treated conservatively raced post injury. The percent SPI for incomplete-nondisplaced, complete-nondisplaced and complete-displaced fractures treated with internal fixation were 74%, 58%, and 60%, respectively. Males (72%) raced post injury more frequently than fillies (53%), and may represent a truer probability of SPI. Spiral fractures tended to take longer until their first start (mean 13.3 months). Fifty-two percent of horses with articular fragments were able to race post injury. Horses were more likely to start if 2-4 month radiographic healing revealed no evidence of the fracture except the presence of lag screws. Based on this series of cases, the majority of horses, with proper treatment, were able to return to racing regardless of fracture characteristic. Prognosis appeared to be affected by the severity of the injury to the joint, the presence of articular comminution and the quality of surgical repair.     

Frequency distributions of 174 fractures of the distal condyles of the third metacarpal and metatarsal bones in 167 Thoroughbred racehorses (1999–2009)

Reasons for performing study: Although fractures of the metacarpal and metatarsal condyles are the most common long‐bone fractures of Thoroughbred horses in training, limited data on variations in morphology and incidence have been published. Additionally, grouped analyses of previous studies from the UK and USA would permit comparison between study groups and the creation of a substantial pool of international data. Methods: Retrospective analysis of case records of horses with fractures of the distal condyles of third metacarpal/metatarsal bones seen over the last 10 years at Newmarket Equine Hospital. The current series was compared with a prior series from the UK; pooled analyses of these, and series from the USA were also compared. Results: One hundred and seventy‐four fractures were identified in 167 racehorses. The current series contained a significantly lower proportion of medial condylar fractures than in a similar population 17 years earlier. Fractures that originated more abaxially tended to be shorter, and a significant proportion of lateral condylar fractures arose outside of the condylar groove. There was also some apparent seasonality of fractures of the lateral condyles in 2‐year‐old horses, but not so in older horses or those with medial condylar fractures. Conclusions and potential relevance: A substantial portion (approximately 50%) of fractures in the present series cannot be explained by unifying theories of aetiopathogenesis, which suggest that fractures usually arise within the condylar groove, as a focus of cumulative fatigue and failure of adaptation of bone. A separate aetiopathogenesis may be responsible for a proportion of condylar fractures encountered in racehorses, and further work is required to elucidate this. Changes in the number of medial condylar fractures encountered may reflect the introduction of artificial racing and training surfaces, and also may reflect changes in the age demographic of horses racing in the UK since the introduction of year‐round ‘all‐weather’ racing.     

Long incomplete longitudinal fractures of the third metacarpal and metatarsal bone in horses

Five horses with long incomplete longitudinal fractures of the third metacarpal bone and three horses with similar fractures of the third metatarsal bone were examined. In three of the metacarpal fractures a long incomplete fissure extended proximomedially, in association with the more common lateral condylar fracture of the third metacarpal bone, and in the other two cases the fracture originated from the medial aspect of the distal articular surface. In the three horses with fractures of the third metatarsal bone the fractures had a consistent spiral configuration.     

Surgical treatment of osteomyelitis in the metacarpal and metatarsal bones of the horse.

The case histories of four horses with osteomyelitis involving the metacarpal and metatarsal bones are reviewed and the surgical treatments discussed. The horses recovered after curettage of all infected tissue and post operative drainage. The role of antibiotics in treatment is considered and reference is made to the acute treatment of deep wounds to avoid osteomyelitis.     

Subchondral bone density and cartilage degeneration patterns in osteoarthritic metacarpal condyles of horses

OBJECTIVE: To evaluate and correlate patterns of subchondral bone density and articular cartilage degeneration (derived by use of gross, histologic, and computed tomographic [CT] examinations) in equine third metacarpal condyles with and without osteoarthritis. SAMPLE POPULATION: 8 metacarpophalangeal (MCP) joints (n = 4 horses) without osteoarthritis and 6 osteoarthritis-affected MCP joints (4). PROCEDURES: Horses were euthanized. The third metacarpal condyles of the joints were examined grossly and via CT (3 slice images/condyle). For 6 condylar zones, mean bone density and pattern of density distribution were determined. Data for osteoarthritis-affected and control joints were compared. Histomorphometric point count analyses identified areas of bone density for comparison with CT density measurements. RESULTS: Osteoarthritis-affected condyles had heterogeneous subchondral bone with focal resorptive lesions and patterned sclerosis, whereas control condyles had symmetric bone density distribution. In osteoarthritis-affected condyles, bone density determined via gray scale image density analysis was greater (dorsal and medial pattern), compared with control condyles, and differed among zones because of resorption and sclerosis. With regard to bone density in osteoarthritis-affected condyles, histologic findings correlated with CT images, and bone lesions were significantly correlated with cartilage lesions. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, heterogeneous distribution and greater subchondral bone density were characteristic of osteoarthritis-affected condyles, compared with control condyles. Subchondral bone lesions correlated with overlying cartilage lesions in osteoarthritis-affected MCP joints. Identification of CT image characteristics appears to predict the presence of a cartilage lesion in MCP joints of horses with osteoarthritis.     

Standing surgical repair of propagating metacarpal and metatarsal condylar fractures in racehorses

REASONS FOR PERFORMING STUDY: Repair of spiral and long diaphyseal metacarpal and metatarsal fractures under anaesthesia can be problematic and associated with a high incidence of complications, including fracture propagation necessitating euthanasia. OBJECTIVE: To report on a practical repair technique for which general anaesthesia is not required. METHODS: Thirteen racehorses with a spiral/propagating condylar fracture had the fracture repaired using local anaesthesia and sedation, without the need for general anaesthetic. RESULTS: Ten of the horses returned to training and 8 raced again. Two horses were retired directly to stud. One horse had propagation of the fracture 3 days post surgery, and was subjected to euthanasia. CONCLUSIONS AND POTENTIAL RELEVANCE: Results achieved were comparable to those gained using standard repair techniques under general anaesthesia. The described technique removes the need for general anaesthesia for repair of selected condylar fractures.     

Early changes of osteochondrosis in medial femoral condyles from rats

Osteochondrosis developed from the early growing process of articular cartilage at the caudal-central region of the medial femoral condyle in rats. Articular cartilage was thick at the region. Mineralization of the matrix in the thick deep zone was incomplete and major parts remained unmineralized. Cavity formation in the mineralized matrix resulting in osteochondrotic lesions was present in the deep zone at 6 weeks of age and was followed by an appearance of viable chondrocytes around it. Osteochondrotic lesions were present from the age of 10 weeks for females and 12 weeks for males. Cavities were expanded and increased in number, and eosinophilic necrotic foci were additionally seen. These changes were extended throughout the deep zone, and viable chondrocytes were also increased in number. The thick deep zone was retained and had no detectable invasions of blood vessels from the subchondral bone. At 20 weeks of age, necrotic areas containing large clefts were present in the basal layer of the thick deep zone and fibrotic lesions were seen beneath them. In normal cases, invasions of blood vessels were seen in the basal layer of the deep zone and also in the cavities of the cartilage; the deep zone was markedly thinned at 20 weeks of age.     

Osteochondritis dissecans of the sagittal ridge of the third metacarpal and metatarsal bones in horses

Osteochondritis dissecans of the sagittal ridge of the third metacarpal and metatarsal bones was diagnosed in 8 horses during an 18-month period. Seven of the horses were less than or equal to 2 1/2 years old. Synovial distention of the affected fetlock joints and a pain response to fetlock flexion were typical findings. Lameness predominated in 1 limb at a trot, although fetlock flexion frequently elicited lameness in other affected limbs. Radiography revealed bony lesions (flattening, erosion, or fragmentation) of the sagittal ridge in at least 2 fetlock joints in all horses. The onset of signs was not correlated with the severity of radiographic changes in all horses.     

Three dimensional structure of the distal condyles of the third metacarpal bone of the horse

This study examined the three-dimensional (3D) microarchitecture of regions of the equine third metacarpal bone (McIII) commonly involved in distal condylar fractures. Limbs were obtained from Thoroughbred horses (neonates to age 24 years) destroyed for inoperable fractures and a variety of other conditions. Beams, blocks and sections were cut in the principal axes, some embedded in PMMA and others examined unembedded. Several methods were used to study the 3D structure, including conventional and confocal optical microscopy, scanning electron microscopy (SEM) and radiography. The mineralised articular cartilage tends to cleave in the sagittal plane. Proximal to the subchondral bone, the main trabeculae are robust plates running in the sagittal direction with less significant mediolateral connections. Small blood vessel canals lie inside the sagittal plates. This structure gives maximum strength and protection in the sagittal plane in which the bone rotates, but offers minimal resistance to fracture propagation in this plane. The anatomical course of the common distal condylar fractures of the third metacarpal bones can be explained by underlying anisotropic structural features of the mineralised tissues.     

Nuclear scintigraphic evaluation of third metacarpal and metatarsal bone fractures in three horses

Nuclear scintigraphy was used to evaluate healing of third metacarpal bone (MC III) fractures in 2 horses (horses 1 and 2) and a third metatarsal bone fracture in 1 horse (horse 3) after stabilization of each fracture with 2 broad dynamic compression plates. In horse 1, the fracture had uniform uptake of 99mTc methylene diphosphonate on days 1, 15, and 30 after surgery. The fracture healed, and the horse was discharged from the clinic on day 52. In horse 2, a 6-cm photopenic region (ie, area of low radioactivity) was seen over the diaphysis of MC III on day 3. The region persisted and became more distinct by day 32. The diaphysis of MC III sequestered, and horse 2 was euthanatized on day 44. In horse 3, vascularity was seen bridging the fracture on day 5, with a 3-cm photopenic region over the dorsal diaphysis of the third metatarsal bone. By days 18 and 32, uptake of 99mTc methylene diphosphonate in the region had increased, indicating vascularization of the site. the fracture healed, and horse 3 was discharged from the clinic on day 47. Our findings indicated that serial nuclear scintigraphy can be used to evaluate fracture vascularization after surgery in horses.     

Quantitative evaluation of subchondral bone injury of the plantaro‐lateral condyles of the third metatarsal bone in Thoroughbred horses identified using nuclear scintigraphy: 48 cases

Reasons for performing study: Increased radio‐isotope uptake (IRU) in the subchondral bone of the plantaro‐lateral condyle of the third metatarsus (MTIII) is a commonly reported scintigraphic finding and potential cause of lameness in UK Thoroughbred racehorses in training and has not been fully documented. Objectives: To characterise lameness attributable to IRU of the subchondral bone of MTIII, compare the scintigraphic findings of these horses with a normal population and evaluate the use of scintigraphy as an indicator of prognosis. Hypothesis: IRU will be in significantly higher in horses with subchondral bone injury and will be related to prognosis and future racing performance. Methods: Data were analysed from 48 horses in which subchondral bone injury of the plantaro‐lateral condyle of MTIII had been diagnosed using nuclear scintigraphy and that met the inclusion criteria. Data recorded included age, sex, trainer, racing discipline, lameness assessment, treatment regimes, radiographic and scintigraphic findings, response to diagnostic analgesia where performed and racing performance pre‐ and post diagnosis. Region of interest (ROI) counts were obtained for the plantar condyle and the mid diaphysis from the latero‐medial view, the ratio calculated and then compared with a control group of clinically unaffected horses. Results: The mean condyle mid‐diaphysis ROI ratio was significantly (P<0.001) higher in the affected population and with positively correlation (P = 0.024) with the level of lameness. The presence of radiographic findings had no significant effect on the ROI ratio. Conclusion: Subchondral bone injury of the plantar lateral condyles of MTIII is a significant cause of lameness in UK Thoroughbred racehorses. Nuclear scintigraphy is a useful diagnostic imaging modality in the detection of affected horses but is a poor indicator of prognosis for the condition. Potential relevance: Better understanding of the clinical manifestations, diagnosis of and prognosis for subchondral bone injury will benefit the Thoroughbred industry in the UK.