Osteoarthrosis of the Antebrachiocarpal Joint of 7 Riding Horses
© The Author(s) 2001
Received: 02 April 2001
Accepted: 25 June 2001
Published: 31 December 2001
Osteoarthrosis (OA) of the antebrachiocarpal joint from 7 riding horses is described. The horses were old mares and developed severe OA, with ankylosis in some of the joints. The lesions were bilateral, and the owners noticed the lameness in a late event. The cause of severe OA in these mares is not clear. The fact that OA was bilateral indicates that a single traumatic injury is unlikely as an etiologic factor. Considering the severe joint lesions it took long time before the horse-owners noticed the lameness. It is discussed if the threshold of pain is higher in the antebrachiocarpal joint compared with the middle carpal joint.
Osteoarthros i övre karpalleden från sju ridhästar.
Sju äldre ridston med en svårartad, bilateral osteoarthros i radiokarpalleden har undersökts kliniskt upprepade gånger under åren 93-98. Symtomen dominerades av en tilltagande ledstyvhet, smärta vidsammanböjning, konturstörning framtill runt leden samt hälta. Trots vila förvärrades ledbesvären ochsamtliga hästar avlivades efter en tid. Vid makroskopisk och radiologisk undersökning postmortalt påvisades förlust av ledbrosk distalt på radius och proximalt på radiokarpalbenet, ledrandsosteofyter, subkondral benscleros samt förtjockad ledkapsel med villiproliferationer. I samtliga fall har det dröjt länge innan ägarna noterat hälta. Detta kan tala för att smärttröskeln i radiokarpalleden är högre jämförtmed den i interkrapallederna. Orsaken till ostearthrosen i dessa fall har ej kunnat fastställas och uppgifter om predisponerande faktorer saknas.
Lameness originating from the carpal joints is common in the racehorse, where excessive, rapid and repetitive or inappropriate loading and movement are thought to induce joint damage . During the protraction phase the carpus is freely movable in an anterioposterior direction. The different joints within the carpal joint do not fit perfectly but slide into position when loaded, with an increased fitting of the articular cartilages at high loads [3, 4]. showed that the carpus of the racehorse is overextended for most of the stance phase. The ability of joint surfaces to dissipate axial force by transfer to the interosseous ligaments is the principal means by which carpal injury is avoided . In racehorses, most interest is focused on the middle carpal joint because of a higher rate of injuries compared with the antebrachiocarpal joint [5, 7].
The aim of this case report was to point out the severe chronic osteoarthrosis (OA) that can develop in the antebrachiocarpal joint compared to the middle carpal joint, in order to make clinicians aware of this. We wanted to describe the clinical features of 7 riding horses with severe chronic OA of the antebrachiocarpal joints and in some of these also describe the radiological and pathological changes.
Materials and methods
Data of the 7 mares included in the study.
Age (years) at first examination
Number of examinations
Age (years) at euthanasia
The following breeds were represented: 3 Swedish warmblood horses, 2 mixed Swedish warmblood horses – Standardbred trotters, 1 Arabian horse and 1 pony of unknown breed. The carpal joints from 4 of these horses (nos. 1,2,3,5) were collected after euthanasia and stored in a freezer until examination. All 8 joints were opened for a macroscopical examination of the articular cartilage and synovium. Four joints were macerated allowing examination of the osteophyte formations. The other joints from 3 horses were not available for postmortem examination.
Three of the joints were radiographed and 2 (left carpal joint from horses nos. 1 and 3) were sampled for microscopic examination. The joint for microscopic examination was thawed and then fixed in buffered formalin and 1 cm thick slabs were cut with a bandsaw. These slabs were radiographed and samples from the articular cartilage and subchondral bone of the distal radius and the radial carpal bone were decalcified in formic acid, embedded in paraffin, cut into 6 μm sections and stained with Hematoxylin & Eosin (H&E).
Three (nos. 1,2,3) of the horses had, according to the owners, shown a short stride with decreased shoulder action for a long time (years) prior to the first clinical examination. The other 4 were diagnosed at a routine health control at a riding school (nos. 4,5,6,7). All the horses except 1 (no. 3), a brood mare, were used for all-round riding prior to the first noted lameness. The horses had not been treated for carpal lameness prior to the first examination.
All horses showed bilateral frontleg lameness with pain in flexion of the carpal joints. The lameness was located to the antebrachiocarpal joints by intra-articular anaesthesia. Horses 1, 2 and 3 revealed moderate synovial distension on palpation of the antebrachiocarpal joints at the first clinical examination. Some years later, marginal osteophytes and severe periosteal proliferations were palpated. The lameness increased and joint stiffness changed from mild, moderate to severe. The other horses (nos. 4, 5, 6, and 7) all had moderate to severe synovial effusion, bony enlargements around the antebrachiocarpal joints and joint stiffness of the carpal joints, at the first examination. Horse no 4 was slaughtered soon after the second examination due to severe lameness and nos. 5, 6 and 7 all developed more severe symptoms with increased lameness and joint stiffness.
In the most severe case (no. 1), the joint stiffness only permitted 50 degrees of flexion. For 4 years, this mare was used for breeding, but the signs deteriorated to the point that when the mare rested, she always lay on her side, and euthanasia was strongly suggested by the clinician.
The second mare (no. 2) was treated with hyaluronic acid and corticosteroids in the initial stage with mild synovial effusion and mild bilateral frontleg lameness. In spite of a long period of rest, and being used only for breeding, the horse developed severe osteoarthritis of the antebrachiocarpal joints during a 4-year period. The severe joint stiffness did not allow the mare to rest on the chest in a natural way and euthanasia was elected. These 2 mares (nos. 1,2) had moderately bucked knees and were wide at the knees at the time of euthanasia. A tendency to develop these specific faulty limb confirmations was also found in the other horses. There was no history of broken limb axis prior to the lameness.
Macroscopical and radiological examination
All (nos. 1, 2, 3, and 5) antebrachiocarpal joints that were examined showed severe villi hypertrophy of the synovial membrane and severe fibrosis of the synovial capsule.
On histologic examination of the left distal radius and the proximal radial carpal bones from 2 horses (nos. 1, 3), the articular cartilage fraying, ulcerations and loss of cartilage were verified. The subchondral bone showed thick trabeculae with lamellar bone (bone sclerosis). Areas of woven bone outlined some of the trabeculae, where also osteoblast and osteoclast activity was increased and an intertrabecular fibrosis was present. The synovial membrane of the proximal carpal joint of these horses was characterised by villi proliferations, marked proliferation of synoviocytes and mild to moderate subsynovial accumulations, mostly perivascular, of lymphocytes.
This paper describes a severe chronic osteoarthrosis (OA) of the antebrachiocarpal joints from 7 mares.
Considering the severe joint lesions, it took a surprisingly long time before the horse-owners noticed the lameness. This can be explained by the bilateral lameness present prior to the lameness being dominant in 1 leg. The first sign of injury in the antebrachiocarpal joints of the horses in this study was a short stride with decreased shoulder action. A clinical examination revealed bilateral lameness with marked reaction after flexion and marked synovial distension. When a frontleg lameness is present in racehorses or riding horses, it usually originates from the middle carpal joint even if the radiological lesions are more severe in the antebrachiocarpal joint (Ingela Liwång, personal communication). Hence, it has been suggested that the threshold of pain is higher in the antebrachiocarpal joint compared to the middle carpal joint.
The destruction of articular cartilage, subchondral bone sclerosis, marginal osteophyte formation with large periosteal bony proliferation and subsequent anchylosis resulted in pain and joint dysfunction. The most striking signs were loss of normal joint motion and a severe pain at flexion. Surprisingly, all the horses in this study were mares. This is perhaps a random effect, but it is also more acceptable to keep a lame mare for breeding.
Repeated micro trauma and/or an impact load to the joint tissues can be the central etiologic concept in the degenerative changes in these joints. The initial cartilage lesions are often disruption of the superficial zone with fraying, erosion and loss of cartilage. The progression of the cartilage lesions is linked together with the subchondral bone sclerosis creating a stiff inelastic tissue . The degenerative debris will cause low-grade synovitis, which will contribute to the progression of the OA . OA in the antebrachiocarpal joints of horses can also develop due to trauma , subchondral bonecysts  and chip fractures .
In the present material, the OA was bilateral and the destruction of the articular cartilage was most severe at the most weight-bearing parts in the antebrachiocarpal joint. Together with the lack of a history of predisposing disorders such as septic arthritis, articular fractures or subchondral bonecysts, this suggests a repetitive joint trauma in a high-load-high-motion joint as a cause of the OA. The fact that the OA was bilateral in all 7 mares indicates that a single traumatic injury is unlikely as an etiologic factor. However, a previous subchondral bonecyst may be a factor in the pathogenesis of the OA of the antebrachiocarpal joints. All the horses had been used for all-round riding performance in riding schools and none had been competing in jumping or dressage.
The cause of the severe OA of the antebrachiocarpal joints in these old mares is not clear. None of the owners did report lameness from the 7 mares early in the disease, which may suggest that the antebrachiocarpal joint have a high threshold for pain, which must be important to consider in equine clinical practise.
The authors would like to thank Drs Ingela Liwång and Nino Gerbino for valuable discussions and Bengt Ekberg for excellent photographic assistance. The study was funded by the Sten-Erik Olsson foundation.
- Bertone AL, Schneiter HL, Turner AS, Shoemaker RS: Pancarpal arthrodesis for treatment of carpal collapse in the adult horse. A report of two cases Vet Surg. 1989, 18: 353-9.PubMedGoogle Scholar
- Bramlage LR, Schneider RK, Gabel AA: A clinical perspective on lameness originating in the carpus. Equine Vet J Suppl. 1988, 6: 12-8.PubMedGoogle Scholar
- Firth EC, Hartman W: An in vitro study on joint fitting and cartilage thickness in the radiocarpal joint of foals. Research in Veterinary Science. 1983, 34: 320-6.PubMedGoogle Scholar
- Johnston C, Drevemo S, Roepstorff L: Kinematics and kinetics of the carpus. Equine Vet J Suppl. 1997, 23: 84-8.PubMedGoogle Scholar
- McIlwraith CW, Yovich JV, Martin GS: Arthroscopic surgery for the treatment of osteochondral chip fractures in the equine carpus. J Am Vet Me Assoc. 1987, 191: 531-40.Google Scholar
- Norrdin RW, Kawacak CE, Capwell BA, McIlwraith CW: Subchondral bone failure in an equine model of overload arthrosis. Bone. 1998, 22: 133-9. 10.1016/S8756-3282(97)00253-6.View ArticlePubMedGoogle Scholar
- Palmer SE: Prevalence of carpal fractures in Thoroughbred and Standardbred racehorses. J Am Vet Med Assoc. 1986, 188: 1171-3.PubMedGoogle Scholar
- Palmer SE, Bertrone AL: Joint structure, biochemistry and biochemical disequilibrium in synovitis and equine joint disease. Equine Vet J. 1994, 26: 263-77.View ArticlePubMedGoogle Scholar
- Specht TE, Nixon AJ, Colahan PT, Moore BG, Brown MP: Subchondral cyst-like lesions in the distal portion of the radius of four horses. J Am Vet Med Assoc. 1988, 193: 949-52.PubMedGoogle Scholar