142 Journal of Equine Veterinary Science April 2003

Osteochondrosis is thought to be a failure or disruptionin endochondral ossification at the ends of growing

bone. This produces an area of hypertrophied cartilagewhich can (1) cleave a section of bone from its parent por-tion, usually at the articular surface (osteochondritis disse-cans, OCD) or (2) produce an island of cartilage in the endof a maturing bone which results in a cyst like structure.The causes of this developmental anomaly are many andpoorly understood. Heredity seems to play a role as themanifestations have a tendency to be quite specific for dif-ferent breeds of horses and to certain lines within a breed.For example, Standardbreds and Warmbloods have a highincidence of osteochondral lesion at palmar/plantar aspectof the ankle and the distal intermediate ridge of the hock,while Thoroughbreds tend to develop more shoulder andstifle problems. Certain lines within a breed produce phe-notypic individuals more prone to developing OCD. Theseindividuals tend to grow rapidly in short intervals of time.

Nutrition has long been implicated as playing a role in thedevelopment of osteochondrosis. In particular, deficiencies intrace minerals such as copper and zinc have been associatedwith the development of the disease. Supplementation of thediet with these minerals has had limited success in preventingproblems. Caloric intake also seems to be a factor in the prob-lem. High energy diets allow individuals to grow at their max-imum genetic potential which translates into rapid bonedevelopment and the opportunity for errors in endochondralossification. Restricting caloric intake during periods of rapidgrowth would be the ideal approach. Since these growth spurtsare difficult to detect, it is very hard to implement this tech-nique. Total dietary restriction has been used with some suc-cess to treat animals already exhibiting symptoms ofosteochondrosis.

Trauma also seems to play a role in some cases. It ap-pears that some OCD lesions (particularly the stifle joint)can lie dormant for some period of time. A traumatic inci-dent may occur which destabilizes the fragment or breaks itentirely free. Symptoms then become obvious in a previ-ously sound horse and the diagnosis is made.

Before osteochondrosis was well recognized, affectedanimals were frequently misdiagnosed as having chip frac-tures or joint mice. While certainly not all osteochondralfragments located within or at the margins of a joint are os-

teochondritis dissecans, we are recognizing with increasingfrequency that more are OCD. Radiographically there aresimilarities between osteochondral lesions and chip frac-tures but there are also significant differences. The most ob-vious difference between the two is that osteochondrallesion always appear to be radiographically “old” and areoften bilateral. They are well rounded and separated fromparent bone. There is no callus formation and the defect inthe parent bone tends to fill in with bone. Even more char-acteristic is the fact that while the lesions can be quite large,the symptoms are often clinically subtle. Fractures are usu-ally small lesions with more profound clinical symptoms.

COFFIN JOINT

The most common manifestation of osteochondrosis ofthe pedal bone is osteochondral fragment of the extensorprocess. These lesions are fairly common in all breeds, par-ticularly in the Warmblood. They usually occur in the frontlegs and are often bilateral. These lesions can be clinicallysilent. Diagnosis requires intraarticular anesthesia and ap-propriate radiographs. If the joint block is positive, they canbe treated with the usual intraarticular medications such assteroids, hyaluronic acid or polysulfated glycosaminogly-can or a combination of these products. Rest and correctiveshoeing, i.e. rolled toe, can also be important in therapy.Surgical removal of the lesion is also a treatment alternativeespecially if unresponsive to conservative methods.Arthrotomy was the usual surgical approach but now is re-served only for extremely large fragments. Arthroscopy hasbecome the approach of choice particularly using a smallerscope to reduce trauma to the joint.

The prognosis if responsive to medical therapy is ex-cellent although there is a tendency for symptoms to recur.Surgical removal usually has a good prognosis but on rareoccasions will cause degenerative joint disease due to ia-trogenic trauma.

Cystic manifestation of osteochondrosis is rare and canoccur anywhere within the pedal bone including the exten-sor process. These cases are asymptomatic unless the cystcommunicates with the joint. Treatment of these lesions isunrewarding; they rarely will respond to intraarticular ther-apy and the surgical approach is extremely difficult. Theprognosis of these cases is poor.

Osteochondrosis in the HorseJoseph J. Foerner, DVM

Veterinary Review

Volume 23, Number 4 143

PASTERN JOINT

Osteochondral fragments in the pastern joint are quiterare, usually incidentally found on survey radiographs.Lesions originating from the proximal aspect of the shortpastern bone occur on the palmar or plantar aspect. They areoften bilateral and if unilateral must be differentiated fromavulsion fractures of the caudal eminence of the pasternbone. While surgical removal has been reported, jointarthrodesis seems to be the treatment of choice if symp-tomatic. The prognosis if nonsymptomatic is excellent.

If the osteochondral fragment originates from the longpastern (P-I) bone, it is on the dorso-medial or dorso-lat-eral aspect. These lesions are unilateral, quite large and ex-hibit only a mild lameness. The only treatment option forthese lesions is surgical removal by arthrotomy. The prog-nosis on these cases is surprisingly good in spite of the sizeof the lesions.

There are many manifestations of osteochondrosis in thefetlock joint and it is the joint most often affected. Whilemany osteochondral fragments at the dorsal aspect of thisjoint are traumatic in origin, there is considerable clinical ev-idence that many may be yet another manifestation of osteo-chondritis dissecans. These lesions occur just medial orlateral to the sagittal groove - the frequency of the medial po-sition is much higher than lateral. These lesions are fre-quently bilateral and can be quadrilateral. They are verycommon in the rear limb and usually will not manifest anysymptoms until these horses are put into hard training. Thesecases can be treated conservatively with intraarticular medi-cation and rest but symptoms will often recur. Arthroscopicremoval is the treatment of choice and results in an excellentprognosis if degenerative changes aren’t present.

Osteochondral fragments at the palmar/plantar aspect ofthis joint are almost always manifestations of osteochondro-sis. There are two types of lesions that occur and each onerequires different treatment modalities. Special radiographicviews dorso-palmar, medio-lateral and latero-medialobliques are required to differentiate between the 2 types.

Type I lesions occur just medial or lateral to the sagit-tal groove and like dorsal fragments, the majority are me-dial (78%). This type lesion is most often seen in theStandardbred with frequencies as high as 20% on somefarms. The Warmbloods are the breed with the next highestfrequency but it is much lower than Standardbreds. Sincethe lesions can be observed radiographically at 3 months ofage, an entire population of weanlings can be screened forthe problem. Lesions can occur as a single entity or in somecombination of multiple lesions. Of 124 cases in 1 study, 73were single lesion-single joint, 4 had multiple lesionswithin the same joint, 17 had single lesions in multiplejoints and 30 had different type OCD lesions in other joints.

Symptoms of this disease are quite subtle. Horses willusually not show symptoms until they approach maximumperformance levels (under 2:20 in Standardbreds).

Symptoms in the Standardbred include “putting in extrasteps” or “getting rough in the turns.” Warmbloods are re-ported to “cross canter” or be “reluctant to take a lead.”Clinically the joints look normal and diagnosis is made byregional anesthesia. Intraarticular anesthesia is an unreliablediagnostic tool. The diagnosis is confirmed radiographically.

Treatment for this condition is arthroscopic removal ofthe fragment(s). Medical therapy can be tried but symp-toms usually return. The prognosis with surgical removal isquite good, approaching 90% in 1 study.

Type II lesions are large fragments off the wing of P-1,usually lateral. These may or may not have an articular com-ponent and are considered by some as un-united processes.There is no breed predilection associated with these andmost are seen in the rear limbs. In some horses there may bea type I lesion also seen in the same joint, either on the sameside or on the opposite side of the joint. Type II lesions usu-ally are asymptomatic and present only a cosmetic flaw. Ifthe lesions are quite large and have an articular component,or if there is also a type I lesion present, lameness may occur.

Treatment, if necessary, is surgery. If Type I lesions arepresent, these are removed arthroscopically and the nonar-ticular component is not removed. If the type II lesion isdetermined to be the cause of the lameness it can be re-moved through an arthrotomy approach. The prognosis isquite good for removal of the type I lesions but only fair forremoval of the entire wing of P-1.

Osteochrondrosis of the sagittal ridge of the distalmetacarpal/metatarsal bone occurs in 3 different locationsand causes a wide variety of symptoms. Lesions on theproximo-dorsal end of the ridge are the most common.These lesions can be unilateral but are often bilateral andcan be quadrilateral. They are most commonly seen inArabians but can occur in any breed. Horses may beasymptomatic, exhibit chronic synovial effusion, or showsome degree of lameness.

Treatment depends on the type of lesion. Cases withonly a defect in the ridge may respond to intraarticularmedication. When there is a separate fragment of bone pre-sent, arthroscopic removal is the treatment of choice. Theprognosis in theses cases is 75% depending on degenera-tive changes already present.

Osteochondrosis at the distal end of the sagittal ridgepresents a very different clinical picture. These lesionsoccur most often in the Standardbred but again can occurin all breeds. The lameness seen is mild to severe: mildwithout bone fragmentation and severe with fragmenta-tion. Synovial effusion is also present if there is fragmen-tation. Treatment options are the same as proximal ridgelesions but surgical removal is best accomplished byarthrotomy. The prognosis on these cases is not as favor-able as proximal ridge lesion (50%) due to the tendencyfor development of other osteochondritis lesions else-where in the body.

144 Journal of Equine Veterinary Science April 2003

The third type occurring in the palmar/plantar aspect ofthe sagittal ridge is extremely rare. The low frequency of thelesion may be due in part to the fact that they are very diffi-cult to diagnose. Standard radiographic views will notdemonstrate the lesion. A caudal flexed tangential view willshow the fragmentation if it is displaced. The most reliable di-agnostic technique is exploratory arthroscopy. If this tech-nique is used, the fragment can be easily removed during theprocedure. The prognosis is similar to dorso-proximal lesions.

Osteochondrosis lesions of the metacarpal/metatarsalcondyles are infrequently encountered. They usually are lo-cated on either side of the sagittal ridge on the dorsal aspectof the condyle. Clinical signs, treatment and prognosis aresimilar to dorsal sagittal ridge lesions.

The cystic form of osteochondrosis of the fetlock usu-ally occurs in the distal condyle of the metacarpal/metatarsal bone. These are usually in the front leg and uni-lateral. Some are nonarticular and do not cause symptoms.They are symptomatic if they communicate with the jointor are just under the articular cartilage. Like other cystic le-sions, they can be treated conservatively, particularly inyounger animals. These lesions are readily accessiblethrough an arthrotomy approach and this is the usual treat-ment option. Prognosis on these cases is fair to good de-pending on degenerative disease already present.

Cystic lesions in the proximal end of P-1 are much lesscommon than the distal condyle. Clinical signs are generallymore severe than other types of cystic lesions. There is oftenconsiderable boney reaction associated with these lesionsdue to the compromise in structural support. The only treat-ment option is curettage of the lesion through a transcorticalapproach. The prognosis for this condition is poor becausethere is normally extensive degenerative disease present.

CARPUSPresently there are no known forms of osteochondritis

dissecans in the carpus. Cystic lesions can form anywherein the carpal bone or distal radius but are quite rare. Surveyradiographs of carpi may show remnant of a physeal plateat the styloid process or a defect in the fourth carpal asso-ciated with development of the fifth carpal bone but none ofthese are pathologic. These cystic lesions are difficult totreat and have a very poor prognosis because they oftenlead to a collapse of one side of the carpus.

ELBOW

Again there are no known cases of osteochondritis dis-secans in the elbow joint but some cystic lesions have beenreported. The proximal radius is the usual location for cys-tic lesions. Diagnosis can be challenging because they maymanifest only periodic bouts of lameness and are difficultto isolate with diagnostic anesthesia. Good quality radio-graphs will demonstrate the lesion readily. The only treat-ment alternative is surgical curettage by a transcortical

approach. Even though this is a somewhat difficult surgicalprocedure, it is usually very rewarding.

SHOULDER

Osteochondral fragments in the shoulder joint nor-mally originate from the head of the humerus. They areseen most often in the Quarter Horse, less often in theThoroughbred and rarely in the Standardbred and otherbreeds. These lesions can occur bilaterally which makes thediagnosis more difficult. Horses exhibit variable degrees oflameness but joint effusion is difficult to detect.Intraarticular anesthesia and good quality radiographs arethe major diagnostic tools in these cases. Arthroscopy is thetreatment of choice for this condition. The prognosis onmany of these cases is surprisingly good; depending on thesuccess of fragment removal and the amount of joint de-generation already present. It seems that larger joints of thebody tolerate degenerative joint disease much better thansmaller joints, once the inciting cause is removed.

Cystic lesions in the shoulder are very rare and are lo-cated in the glenoid when present. The prognosis for theseanimals is very poor due to the surgical inaccessibility.

HOCK

Osteochondral fragments in the hock joint are found in5 locations. By far, lesions on the distal intermediate ridgeare the most common. These occur with the highest fre-quency in the Quarter Horse and Standardbred. Affectedhorses may or may not show synovial effusion and the gaitchanges are very similar to lameness seen withpalmar/plantar P-1 lesions. There is normally little degen-erative disease with these fragments unless the fragmenthas been broken loose or crushed. On radiographic screen-ing of an equine population, the lesions are detectable by 6months of age. At this age it can be difficult to differentiatebetween the physis and large bone. If this is the case,surgery should be postponed until further maturation unlessthe animals are showing symptoms. Treatment for this con-dition is surgical removal with the arthroscope and theprognosis is generally excellent. In some cases, particularlywhere there has been a chronic bog spavin, the joint disten-tion may remain.

Lesions off the distal lateral trochlear ridge can bequite large and usually manifest more intense symptoms.Most cases have synovial effusion and show some lame-ness. Unlike distal intermediate ridge lesions, these aremostly unilateral. On rare occasions they are seen with dis-tal intermediate ridge fragments and if so, the lateraltrochlear lesion is small. Large fragments are most easilyremoved through an arthrotomy approach. Smaller frag-ments or cases where there is a distal intermediate lesionare best removed by arthroscopy. In spite of the large sizeof the fragments, the prognosis on these cases is good un-less the lesions extend well up the trochlea.

Volume 23, Number 4 145

Fragments off the distal end of the medial trochlearridge are called “dew drop” syndrome. These lesions are in-cidental findings because they are embedded in the syn-ovial membrane and produce no symptoms. No treatment isnecessary for this condition and their prognosis is excellent.

Fragmentation of the medial malleolus presents moreof a diagnostic challenge. Affected individuals show mildlameness and synovial effusion. Cases are mostly unilateralbut can be bilateral and seen with other forms of hock os-teochondrosis. The lesions can be difficult to detect radio-graphically particularly if there is little displacement. Thebest view for visualization is the dorso-plantar or slightoblique. Occasionally they will be totally silent radiograph-ically and found on exploratory arthroscopy. Arthroscopicremoval of the fragments leads to an excellent prognosis.

Fragmentation of the lateral malleolus is almost alwaysan avulsion fracture and manifests appropriate symptoms.There is severe lameness and soft tissue swelling alongwith the synovial effusion. Treatment includes removal ofsmall pieces or internal fixation of large fragments. Theprognosis is much poorer than osteochondrosis due to thesevere osteoarthritis that often develops.

STIFLE

Osteochondritis dissecans of the stifle joint is mostcommon in the Thoroughbred but can be seen in all otherbreeds. The lesion is usually located in the lateral trochlearridge and rarely both ridges are involved. The condition canbe unilateral but frequently is bilateral. Symptoms are mostoften manifested as yearlings but may be symptom free untilmuch later in life. In the latter case particularly, trauma ap-pears to “activate” a pre-existing lesion. Symptomatic ani-mals will manifest some degree of lameness and/or synovialeffusion. Treatment for this problem is removal of the frag-ments and curettage of underlying bone using the arthro-scope. The prognosis with this lesion is variable. Lesionsconfined to the lateral ridge will have a good to excellentoutcome. Like the shoulder, fragmentation can be quite ex-tensive and still have a favorable prognosis. If the medialridge is involved, the prognosis deteriorates. This seems tobe due to the fact that medial ridge lesions are more axial,

affecting the movement of the patella. Involvement of bothridges decreases the prognosis even more and patellar le-sions warrant a guarded prognosis. The detection of patellarlesions on preoperative radiographs is an extremely poorprognostic sign and justification of surgery is questionable.

Cystic lesions of the stifle joint are most often found inthe distal medial femoral condyle and rarely in the lateral.It is seen in all breeds. It is normally unilateral but can bebilateral. This condition appears to require considerabletime to develop as symptoms are almost always seen in ma-ture horses. Diagnostics can be challenging with this con-dition as lameness is the only clinical sign. Intraarticularanesthesia is the ultimate diagnostic tool. Good quality ra-diographs will usually demonstrate the lesion but occasion-ally the lesions are so small that there is no radiographicevidence or perhaps only a flat spot in the medial condyle.Treatment offers several options. Some advocate the use ofintraarticular medications only. Steroids with hyaluronicacid seems to be the therapy of choice. People who favorsurgery are divided between arthrotomy and arthroscopy.Arthroscopy lends itself well to exploratory diagnostics andtreatment of smaller lesions. Arthrotomy seems more effec-tive in the treatment of larger lesions because the exposureof the lesion is greater.

Prognosis in this condition is also variable but in gen-eral worse than osteochondral fragmentation. If the indi-vidual responds to intraarticular medications, the prognosisis good. Surgical intervention before the presence of de-generative joint disease is fair to good. Once there is sec-ondary joint disease, the prognosis is poor.

Cystic lesions of the proximal tibia are rare and presentboth a diagnostic as well as therapeutic challenge. Like othercystic lesions of the stifle, lameness is the only clinical symp-toms. Diagnosis is achieved by intraarticular anesthesia andquality radiographs. The only surgical treatment is curettagethrough a transcortical approach. The prognosis is usuallypoor with this condition because of the extensive joint dis-ease that is present by the time the diagnosis is made.

Reprinted with permission from Proceedings of Alamo Pintado EquineMedical Center Symposium, 2003.doi: 1053/jevs.2003.42