Review article — Oorsigartikel

Elbow dysplasia in the dog: pathophysiology, diagnosis and control

R M Kirbergera and S L Fouriea

INTRODUCTIONElbow dysplasia is the abnormal

development of the elbow joint. The termdysplasia is derived from the Greek wordsdys meaning abnormal and plasia mean-ing development. Elbow dysplasia is anall-encompassing term comprehensible tothe dog-breeding fraternity and hasgained popular recognition, particularlyin communicating scientific informationto the public2,10,40. In scientific publica-tions, however, specific aetiologies shouldbe referred to where possible10 or, if onlysecondary arthritic changes are seen onroutine radiographic views with noevidence of the primary cause, the termelbow arthrosis should be used40. Aselbow dysplasia is a developmentalcondition, clinical signs are usually seenfrom 4–8 months and are followed byelbow arthrosis. Long-standing elbowarthrosis due to undetected elbowdysplasia may only be diagnosed later inlife. In particular, lameness in bothelbows may result in a peculiar gait thatthe owner may not have realised wasabnormal. Often minor elbow dysplasia

resulting in mild arthrosis may be presentwith no clinical evidence and breeders areunaware of the problem in their breedingstock36. In a study of rottweilers, 57 % ofdogs had radiographic signs of elbowdysplasia but only 15 % were lame36.

Developmental elbow abnormalitiesincluded in the term elbow dysplasia arefragmented medial coronoid process(FMCP), osteochondrosis and osteochon-dritis dissecans (OCD) of the medialhumeral condyle, ununited anconealprocess (UAP), humero-ulnar, humero-radial and radio-ulnar incongruity andarticular cartilage erosion. These condi-tions, singly or in combination, result inirreversible elbow arthrosis with resultantpain and lameness. Osteochondrosis, thedisturbed endochondral ossification ofarticular or physeal cartilage, is most likelythe underlying cause for all the conditionsincluded in elbow dysplasia31-33. Under-development of the trochlear notch withsecondary incongruity is postulated byothers to be the primary cause45,47,50. Inosteochondrosis, normal cartilaginousdevelopment and maturation fails in thehypertrophic zone, resulting in thickenedcartilage31. In the elbow joint, articularcartilage involvement results in OCDwhile non-articular cartilage alterationsare assumed to result in FMCP, UAP and

elbow incongruity, probably as result ofsmall growth abnormalities of the longbones making up the elbow joint32. Thecartilaginous growth disturbance is likelyto have genetic and environmental,mainly traumatic, and nutritionalcauses31. The most important nutritionalfactors are an excess supply of energy andrelative over-nutrition with calcium31.Trauma is usually minimal and associatedwith hyperactivity or excessive bodyweight31. Figure 1 denotes the relationshipof factors involved in elbow dysplasia andthe development of arthrosis. Severetrauma resulting in premature closure ofa physis is a separate clinical entitycausing severe growth disturbance of theaffected long bone that may markedlyinfluence joints adjacent to the trauma-tised physis, and is excluded from theelbow dysplasia syndrome.

Elbow dysplasia is a worldwideproblem in intermediate and heavy-setbreeds and is commonly seen in SouthAfrica in the rottweiler, Labrador andgolden retriever, and German shepherddog. Other breeds commonly affectedworldwide are the Bernese mountaindog, Saint Bernard, Newfoundland,and bull mastiff. The condition is seensporadically in many other breeds. Breedsmay be predisposed to a particular formof elbow dysplasia, e.g. the Germanshepherd dog suffers more from UAP16,the rottweiler rarely has OCD11,17 andthe Labrador retriever is most likely tohave combined OCD and FMCP17. Thecondition is more likely to occur in males,probably owing to their faster rate ofgrowth or a sex-linked factor5,11,17,20. Elbowdysplasia is a polygenic and multifactorialcondition, the incidence of which canbe reduced by selective breeding15,20,40.Affected dogs are more likely to haveoffspring with dysplastic elbows thannormal dogs. The greater the degree ofarthrosis in the parents, the greaterpercentage of puppies are likely to sufferfrom the condition.

Recognition of the condition by veteri-narians and breeders and the institutionof screening and breeding programmesare required to decrease the incidence ofthis often crippling disease. Elbowdysplasia is a progressive disease and

ABSTRACTElbow dysplasia is a non-specific term denoting abnormal development of the elbow. Elbowdysplasia encompasses the clinical and radiographic manifestation of ununited anconealprocess, fragmented medial coronoid process, osteochondritis dissecans, erosive cartilagelesions and elbow incongruity. The net result is elbow arthrosis, which may be clinicallyinapparent or result in marked lameness. These conditions may be diagnosed by means ofroutine or special radiographic views and other imaging modalities, or the precise cause ofthe arthrosis or lameness may remain undetermined. Breeds most commonly affected arethe rottweiler, Bernese mountain dog, Labrador and golden retriever and the Germanshepherd dog. Certain breeds are more susceptible to a particular form of elbow dysplasiaand more than 1 component may occur simultaneously. The various conditions are thoughtto result from osteochondrosis of the articular or physeal cartilage that results in disparategrowth of the radius and ulna. Heritability has been proven for this polygenic conditionand screening programmes to select suitable breeding stock have been initiated in severalcountries and have decreased the incidence of elbow dysplasia.

Key words: elbow dysplasia, elbow incongruity, fragmented medial coronoid process,osteochondritis dissecans, ununited anconeal process, screening programmes.

Kirberger R M, Fourie S L Elbow dysplasia in the dog. Journal of the South African VeterinaryAssociation (1998) 69(2): 43–54 (En.). Department of Surgery, Faculty of Veterinary Science,University of Pretoria, Private Bag X04, Onderstepoort, 0110 South Africa.

aRadiology Section, Department of Surgery, Faculty ofVeterinary Science, University of Pretoria, Private BagX04, Onderstepoort, 0110 South Africa.

Received: January 1998. Accepted: March 1998.

0038-2809 Jl S.Afr.vet.Ass. (1998) 69(2): 43–54 43

owners must be made aware that medicalor surgical treatment may result inimprovement but not normality48. Theobjective of this article is to review thepathophysiology and diagnosis of thevarious conditions involved in elbowdysplasia, briefly consider therapy anddiscuss measures to prevent and controlthe condition.

DIAGNOSTIC IMAGING TECHNIQUESGood quality, well-positioned radio-

graphs remain the most cost-effectivemethod of diagnosing elbow dysplasia.Radiographs, however, do not show allabnormalities or are often only suggestiveof an abnormality. This is often the casein the growing dog when arthrosis hasnot yet developed. Three-dimensionalimaging techniques such as computedtomography (CT) and magnetic resonanceimaging (MRI) are the most reliablemethods, as they allow slices of theaffected joint to be evaluated. Lineartomography has also proven to be ofbenefit9,44. Positive contrast arthrography,although technically fairly easy to per-form, does not contribute to evaluatingFMCP but could assist in the diagnosis ofOCD27. The contralateral elbow shouldalways be imaged because of the highincidence of bilateral disease or as acontrol11,26,32,48. If the origin of a forelimblameness is uncertain, shoulder radio-graphs should also be made to excludeOCD of this region. A small number ofdogs may have lesions in both the

shoulder and elbow32. In the rottweiler,the palmar metacarpal region should beevaluated to exclude palmar metacarpalsesamoid pathology36. Radiographs of therest of the limb may be required to excludeother conditions such as panosteitis.

RadiographyOptimal radiographic detail is essential

to accurately evaluate elbow pathology.This is obtained by using table-toptechniques, non-grid exposures,collimating to the elbow joint, centringthe primary beam on the medialepicondyle of the humerus, using detail-intensifying screens and short-scalecontrast (low kVp and high mAs exposuretechnique). Sedation or anaesthesia maybe indicated for accurate positioning.Standard craniocaudal and mediolateralviews have been supplemented bynumerous additional views in an attemptto highlight certain anatomical locationsor pathological conditions. Minor lesionssuch as erosion of the medial humeralcondyle cartilage will not be visible in anyof these views. Microfocal radiographyof the elbow has been described andyielded more information than standardradiography but some lesions were stillnot detectable and this is not a readilyavailable technique19.

Lateral recumbency – routine mediolat-eral view of the joint (semi-flexed ML)(Fig. 2a)

The angle between the humerus andradius and ulna is about 110°. This view

allows for the most accurate evaluation ofjoint incongruity but true lateralpositioning is vital. Humeral condyles canbe evaluated for OCD but minor changesmay not be detected. The medial coronoidprocess is seen superimposed on theproximal radius with its cranial tip at thelevel of the radial physis. Osteophytereactions on the cranial aspect of the jointare seen more readily than in the flexedML view. Early osteophyte formationdorsally on the anconeal process may beobscured by the medial humeral condyle,particularly on suboptimal radiographs.

Lateral recumbency – mediolateral viewwith the joint maximally flexed (flexedML) (Fig. 2b)

The angle between the humerus andradius and ulna is about 45°. This viewmaximally exposes the anconeal processand thus optimises visibility of UAP andearly osteophyte formation within thedorsal hollow of the anconeal process.This view does not contribute much to thedemonstration of OCD and FMCP com-pared to the other views44.

Lateral recumbency – mediolateral viewwith the joint maximally extended andthe limb supinated approximately 15°(extended supinated ML =Cd75°MCrLO)30,44 (Fig. 2c)

This projection results in a true lateralview of the medial coronoid process. Theradiograph allows the cranial border ofthe medial coronoid process to be seen in94 % of cases as compared to 50 % and

Fig. 1: Flow diagram of interrelationship between elbow dysplasia and elbow arthrosis.

44 0038-2809 Tydskr.S.Afr.vet.Ver. (1998) 69(2): 43–54

Fig. 2a: Lateral recumbency – mediolateral view with the joint semi-flexed (ML).Fig. 2b: Lateral recumbency – mediolateral view with the joint maximally flexed (flexed ML).Fig. 2c: Lateral recumbency – mediolateral view with the joint extended and the limb supinated approximately 15° (extended

supinated ML=Cd75°MCrLO).Fig. 2d: Sternal recumbency – true craniocaudal view (CrCd).Fig. 2e: Sternal recumbency – craniolateral to caudomedial oblique view (Cr30°LCdMO).Fig. 2f: Sternal recumbency – craniomedial to caudolateral oblique view (CrMCdLO).

a

c

e

b

d

f

0038-2809 Jl S.Afr.vet.Ass. (1998) 69(2): 43–54 45

56 % respectively in the semi-flexed MLand flexed ML views30. One study provedthis view to be more reliable in detectingFMCP than the ML view31.

Sternal recumbency – true craniocaudalview (CrCd) (Fig. 2d)

Useful to detect osteochondral defectsof the medial humeral condyle but somelesions may only be seen in the extendedsupinated ML view, or if they are locatedmore cranially, only in the ML view44.Osteophyte reactions on the medialhumeral epicondyle and medial coronoidprocess are readily seen.

Sternal recumbency – craniolateral tocaudomedial oblique views(Cr30°LCdMO)30,44 (Fig. 2e)

This view is also known as the pronatedCrCd view and is used to skyline themedial coronoid process and medialhumeral condyle. The cranial aspect of themedial coronoid process is seen en face inthis view making it difficult to seecleavage lines30. Osteophyte reactions onthe medial humeral epicondyle andmedial coronoid process and osteochon-dral defects of the medial humeralcondyle are readily seen.

Sternal recumbency – craniomedial tocaudolateral oblique view (CrMCdLO)44

(Fig. 2f)Also known as the supinated CrCd view

and highlights the lateral humeral con-dyle and as such does not contribute tothe evaluation of conditions involved inelbow dysplasia.

Computed tomography (Fig. 3)Computed tomography is significantly

more accurate than radiography, lineartomography and xeroradiography for thediagnosis of FMCP owing to its exceptionalcontrast resolution and ability to imagethe medial coronoid process in a 3rdplane6. Non-mineralised cartilage frag-ments occur more commonly thanmineralised cartilage fragments and aremuch more likely to be seen with CT thanwith radiographs6.

Magnetic resonance imagingOwing to cost considerations, MRI is

rarely used for elbow evaluations but ismore accurate and sensitive than radio-graphs for the detection of FMCP and OCD.Additionally it allows non-displaced,non-mineralised fragments to be seen39.

Linear tomography (Fig. 4)Linear tomography is a useful

technique to demonstrate potentialdisease areas that are obscured by super-

Fig. 3: Computed tomography transverse cross-section of the radius and ulna, illustratinga fragmented medial coronoid process (arrow) (courtesy of P Steyn, Colorado StateUniversity).

Fig. 4a: ML linear tomography image of a normal medial coronoid process (arrow).Fig. 4b: ML radiograph of same dog. Note improved visibility of medial coronoid process in Fig. 4a.

a b

46 0038-2809 Tydskr.S.Afr.vet.Ver. (1998) 69(2): 43–54

imposed structures. Linear tomography isperformed in the extended supinated MLview at the level of the medial coronoidprocess with the tube movement perpen-dicular to the axis of the leg and a swingangle of 40° 44. The technique is used to seeFMCP not visible in other views9,44 andmay detect up to 30 % more FMCP cases44.Another study showed no significantdifference between linear tomographyand radiographs but the combination ofthe 2 imaging modalities approached anaccuracy similar to CT for detectingFMCP6.

CLINICAL CONDITIONSClinical signs are usually seen from 5–6

months of age. A stiff, slightly stilted fore-limb gait after rest progresses to lamenessafter exercise and pain on flexion andextension of the elbow joint33. The lowerlimb and elbow are slightly abducted andsupinated. As clinical signs are mild andinsidious, the patient is often onlypresented at about 6–9 months and afterhaving been lame for 3–4 weeks11,33.Occasionally dogs are only presented inlater life due to bilateral arthrosis33. Theinciting condition results in an inflamma-tory reaction within the joint andarthrosis33 and the primary cause is oftenonly established after arthrotomy17 orarthroscopy1.

Fragmented medial coronoid process

PathophysiologyFragmentation of the medial coronoid

process is believed to be a manifestationof the osteochondrosis complex26,33 and isthe most common clinical entity causingelbow arthrosis14. The cartilaginousmedial coronoid process ossifies from itsbase to the tip, i.e. it has no separateossification centre, and ossification iscompleted at 20–22 weeks33. Osteochon-drosis results in the inability of the deeperchondrocytes in the thick layer of cartilageto survive, and they undergo chondro-malacia with eventual fissuring of thecartilage and subsequent fragmentation26.The fragment often mineralises as a resultof receiving blood supply through itsfibrous connection with the annularligament, which inserts on the coronoidprocess33. Mechanical stresses have alsobeen incriminated as a cause of FMCP33.A recent popular hypothesis postulatesasynchronous growth of the radius andulna32. Overgrowth of the ulna relative tothe radius appears to be the main cause ofFMCP32. It places an abnormal load on themedial humeral condyle and medialcoronoid process and if these structuresare weakened by delayed ossification,

pathology occurs in both32. Fragmentedmedial coronoid process is thuscommonly seen together with OCD6 orerosive lesions and rarely with UAP. Thedisparate growth may still be evident atthe time of presentation or may havecorrected itself.

Radiographic changesThe medially located fragment should

not be confused with the sesamoid bonein the origin of the supinator muscleon the lateral side or with osteophyteformation on the medial coronoidprocess. The fragment is rarely seen onradiographs24,26,32, with fragment visibilityreported as low as 9.8 %13. If visible, it maybe seen as a single loose fragment or asseveral smaller fragments (Fig. 5). Factorscontributing to poor or non-visualisationof the fragment include partial fragmen-tation, minimal fragment displacement30,

small fragment, fragment locationbetween the radial head and remainingintact coronoid process31, or that thefragment cleavage line is often oblique tothe X-ray beam, making it impossible tosee30,48. Additionally, the medial coronoidprocess may be only fissured1,14,24,31 andnon-displaced, non-mineralised39 orabnormally shaped24, making radio-graphic evaluation impossible andrequiring more sophisticated imagingtechniques. Additional radiographicchanges that may be indicative of medialcoronoid pathology include loss of sharpdelineation of the cranial edge of themedial coronoid (Fig. 6a) or blunting ofthe coronoid process3. Medial coronoid

changes are most likely to be seen in theextended supinated ML and pronatedCrCd (Fig. 6b) views. Radiographicchanges are often seen only from about 7months and then secondary arthriticchanges may be all that are seen11,32,33. Thearthritic changes are similar to thosecaused by other conditions (see below).Osteophyte reactions tend to be less se-vere than with UAP and more severe thanwith OCD26. Joint incongruity may also beevident, with the lateral coronoid processdisplaced proximally to the radial head,resulting in step formation (Fig. 7). Ifmore sophisticated imaging techniquesare not available, the diagnosis canoften only be confirmed by means ofarthrotomy or arthroscopy1,43. Arthro-scopy allows excellent visualisation ofjoint incongruity, free fragments, jointmice, abrasions, fissures and osteophyteformation of the medial coronoidprocess1. Dogs presented with clinicalevidence of an elbow problem at less than7 months of age with normal radiographsshould undergo arthroscopy1 or mustreturn for follow-up radiographs 4–8weeks later32.

TreatmentSurgical exploration by means of

arthrotomy, or preferably arthroscopy,with the removal of fragments isrecommended in dogs less than 1 year oldbefore the development of severearthrosis1,12,26,28,48. Older dogs with exten-sive arthrosis may improve clinicallyafter surgery26. Weight control, exerciserestriction and analgesic therapy are all

Fig. 5: ML view with 2 separate medial coronoid fragments (arrows) superimposed on theproximal radius, and severe arthrosis.

0038-2809 Jl S.Afr.vet.Ass. (1998) 69(2): 43–54 47

important additional therapeutic aids26,48.Owners should be made aware of theprogressive nature of the condition.Several surgical approaches are possiblebut muscle separation between thepronator teres and flexor carpi radialiscurrently appears to be the method ofchoice28. Other studies cast doubt on thebenefits of surgery. A study comparingsurgical to medical treatment withpentosan polysulphate showed nodifference in clinical status after 9 months,

but a more rapid recovery in the medi-cally treated cases4. Radiographic andrange of motion scores, however, stillshowed progression of arthrosis. A studycomparing surgery to treatment with restand aspirin had similar results23. In earlycases with a step between the radial headand the coronoid process, a proximal ulnasliding osteotomy will reduce the incon-gruency1. Treating the incongruency isprobably more beneficial than removingthe fragment.

Osteochondritis dissecans of themedial humeral condyle

PathophysiologyThe pathophysiology is very similar to

that described for FMCP. Osteochondritisdissecans without concomitant FMCPis very rare6. The cartilage flap rarelymineralises33. The cartilage flap mayseparate and form a joint mouse.

Radiographic changesThe defect is readily seen in the CrCd

or pronated CrCd views as a radiolucentlesion (Fig. 8a) or dished-out defect on themedial humeral condyle and may be seenfrom 5–6 months of age and prior tosecondary arthrosis5,11,33. In more advancedcases the defect may be surrounded by asclerotic rim32. In ML views it may beseen as a flattening of the caudodistaledge of the medial humeral trochlea47

(Fig. 8b). If OCD is the sole lesion,arthrosis is less marked than with FMCPalone11,21 but clinical signs may occurearlier and may be more disabling thanFMCP on its own21. Combined OCD andFMCP lesions result in the most severearthrosis17,21.

TreatmentSurgical exploration and removal of

fragments followed by curettage isperformed as described for FMCP. Themedial coronoid process should beevaluated at the same time.

Medical treatment is the same as forFMCP. Surgical results may be better than

Fig. 6a: ML view of 8-month-old German shepherd dog with poorly-visible medial coronoid process, degenerative changes and mild joint incongruity.

Fig. 6b: Slightly pronated CrCd view of same dog with separate medial coronoid fragment (arrows).

Fig. 7: Sagittal computed tomography images to illustrate proximal displacement of lateralcoronoid process (arrow) in relation to caudal radial head and incongruent humero-ulnar joint space (courtesy of P Steyn, Colorado State University).

a b

48 0038-2809 Tydskr.S.Afr.vet.Ver. (1998) 69(2): 43–54

for FMCP, particularly if surgery isperformed at a young age12.

Erosive lesion/cartilage defect

PathophysiologyAn erosive lesion or cartilage defect is

seen most commonly on the medialhumeral condyle and occasionally on themedial coronoid process1,14,32 and probablyhas the same aetiology as FMCP and OCDand is due to ulnar overgrowth32. It maynot be possible macroscopically todetermine if a medial humeral condylelesion is primary osteochondrosis or asecondary erosive lesion and histopathol-ogy may be required32. Erosive lesionscommonly accompany FMCP17. Erosivelesions are postulated to occur ratherthan FMCP or OCD if the ulnar growthdisparity occurs at a slightly older age whenthe medial coronoid process and medialhumeral condyle cartilage are almostmature32. Alternative hypotheses are thatminor joint incongruity may result in thelesions48 or that they are earlier stages ofFMCP and OCD14. These lesions are alsoknown as ‘kissing’ lesions but Olssondifferentiates this from an erosive lesion32.

Radiographic changesLesions are not seen on radiographs of

affected joints13 but secondary arthroticchanges may be seen.

TreatmentSurgical removal of affected cartilage is

recommended32.

Ununited anconeal process

PathophysiologyThe condition occurs mainly in the

German shepherd dog16,18,38. The separateossification centre of the anconealprocess, only present in larger breeds,appears at 11–14 weeks and the anconealprocess is united with the olecranon at20–22 weeks (greyhound 14–15 weeks,German shepherd dog 16–20 weeks)33,41.The ununited anconeal process may becompletely separated or joined to the ulnaby fibrous or fibrocartilagenous tissue38,41.Overgrowth of the radius with a relativelyshorter ulna is postulated by Olsson22 tobe the cause. The radius forces the hu-meral trochlea in a proximal direction andthe floor of the olecranon fossa exertsmore pressure than normal on the an-coneal process, damaging the anconealprocess ossification centre. If osteochon-drosis is present, the entire structure is lessresistant to trauma and a tear in theweakened cartilage prevents osseousbridging of the gap32. In 2 separatestudies, measurements made of theolecranon in German shepherd dogs withUAP showed a significantly shorterolecranon or proximally displaced radiusin affected limbs18,38. Weis45 and Wind47, onthe other hand, propose a hypothesis of aprimary incongruent joint with anabnormally developed slightly ellipticaltrochlear notch causing UAP (see elbowincongruity). Ununited anconeal processis rarely seen together with FMCP but, ifpresent, has important implications as the

surgical approaches are different6,24,50.

Radiographic changesThe condition is readily seen in

flexed ML view as an irregular verticalradiolucent line through the caudalaspect of the anconeal process (Fig. 9a).Superimposition of the medial humeralepicondyle physis in views that are notfully flexed should not be confused witha UAP in dogs less than 8 months old7.The fragment may separate completelyfrom the olecranon (Fig. 9b). Arthriticchanges become severe over time. It isessential to make multiple views to ensureno other causes of elbow arthrosis arepresent7.

TreatmentConservative therapy is unrewarding

and results in persistent lameness andprogressive arthrosis18,37. Surgical therapyis the treatment of choice but at present notechnique can ensure a functionallynormal joint7. Surgical excision via alateral arthrotomy has been the tradi-tional treatment. This, however, resultsin instability with progressive arthrosis,but if performed early, results in accept-able longterm function7,16,37. Surgicalre-attachment by means of a lag screwaims to prevent arthrosis by providingstability7. This technique may, however,aggravate arthritic changes if incongruitycaused by asynchronous growth ispresent. Proximal ulnar osteotomy is arecently-proposed technique that aims toredress joint incongruity caused by

Fig. 8a: CrCd view with a triangular radiolucent defect in the medial humeral condyle (arrows) in a 4-month-old boerboel with bilateral elbow OCD.

Fig. 8b: ML view of same dog with flattening of the medial condyle (arrows).

a b

0038-2809 Jl S.Afr.vet.Ass. (1998) 69(2): 43–54 49

asynchronous radius or ulnar growth7,32.Results appear good, with olecranonfusion taking place in up to 95 % of cases38,although in 27 % of these a narrowradiolucent line remained. The clinicalresponse appears superior to thatachieved by the other 2 techniques7,38.Olsson’s short olecranon/overgrownradius hypothesis is supported by theulnar ostectomy treatment, whichrelieves the pressure on the anconealprocess, resulting in fusion of theununited anconeal process with theulna32,38. This treatment is unlikely to havea similar effect in relieving olecranonpressure if the UAP was due to trochlearnotch with a smaller radius of curvature,as proposed by Weis45 and Wind47.

Elbow incongruity

PathophysiologyAccording to Weis45 and Wind47, incon-

gruity (described under radiographicchanges) is due to the trochlear notchdeveloping in a slightly elliptic shape withthe articular curvature of the trochlearnotch too small to fully encompass thehumeral trochlea. If the incongruityoccurs after 6 months it may be present onits own, with only elbow arthrosisresulting47. If present before 6 months,incongruity may also predispose the dogto FMCP, OCD and UAP owing toincreased mechanical forces on thesestructures and incongruity may thus beseen together with these conditions47.

Intermediate and heavy-set breeds havea longer proximal ulna relative to theadjacent radius than in other breeds50.Wind50 postulated that this reflects a needto accommodate a trochlear notch ofsufficient size to encompass a heavier andlarger humeral trochlea. Insufficientdevelopment of the trochlear notch withresultant incongruity is thus most likely inthese larger dogs50. Incongruity may notalways be evident at the time of radio-graphic examination, due to compensa-tory adjustments during growth48.According to Olsson32, the incongruity iscaused by asynchronous growth asdiscussed under FMCP.

Radiographic changesIn the semi-flexed ML and CrCd view

of a normal elbow joint there should besmall, even joint spaces between thehumeral trochlea and the ulnar trochlearnotch and between the humeral condyle,radius and medial coronoid process of theulna47. The joint space forms a continuousarc in the ML view47. The lateral coronoidprocess should lie close to and runcontinuously with the adjacent proximalradius47. Incongruity is characterised by agap or step formation between the lateralcoronoid process and the adjacent proxi-mal radius, a more proximally locatedmedial coronoid process, humerusdisplaced cranially on the centre of theradial articulation, increased humero-ulnar and humero-radial joint space andan indistinct outline of the trochlear

notch46,47 (Fig. 10). These changes are wellillustrated in a radiographic guide of theelbow joint49.

TreatmentTreatment is determined by concurrent

FMCP, OCD and UAP, while the trochlearnotch incongruity is treated conserva-tively28.

ArthrosisArthrosis is a chronic, degenerative,

non-infectious joint disease involvingjoint cartilage, joint capsule and subchon-dral bone tissue10.

Radiographic changesEarly changes are best seen in the ML

views with osteophyte formationcommencing on the dorsal anconealprocess and lateral epicondylar ridge,followed by the margins of the cranio-proximal radius and craniodistal humerusarticular surfaces and sclerosis surround-ing the trochlear notch24,48 (Figs 5, 6, 9, 11).The latter tends to start distally and maybe the result of osteophyte formation atthe joint capsule insertion or subchondralsclerosis or both47. The anconeal osteo-phytes correspond to the insertion of theolecranon ligament and joint capsule onthe proximal non-articular surface of theanconeal process24. In CrCd view, osteo-phytes are seen on the medial humeralepicondyle and on the medial aspect ofthe medial coronoid process. Severearthrosis may develop over time and joint

Fig. 9a: Flexed right elbow ML view of a 2-year-old German shepherd with bilateral ununited anconeal process. The dog had a history ofbeing mildly lame in the left front limb. Note vertical radiolucent line through anconeal process and secondary osteophyteformation. Visibility of pathology can be enhanced by making a fully flexed ML view.

Fig. 9b: Flexed left elbow ML view of same dog. Note cranially displaced united anconeal process (arrows).

a b

50 0038-2809 Tydskr.S.Afr.vet.Ver. (1998) 69(2): 43–54

mice may be present cranial to the medialcoronoid process or in the olecranonfossa14. Arthrosis may be present withoutany radiographic evidence of a primarycause and could be due to erosive lesions,healed FMCP or minor incongruity.

HERITABILITYElbow dysplasia is inherited as multifac-

torial polygenic traits15,20,34,40, i.e. requiresmore than 1 gene to cause the phenotypeto be expressed in an individual34. Asimple autosomal recessive mode ofinheritance has been ruled out for theinheritance of OCD and FMCP and theyappear to be inherited independentlyfrom each other as polygenic traits34.

The frequency of elbow arthrosis causedby elbow dysplasia varies from 30–50 %,with males generally more frequently andseverely affected15,21. However, in onestudy in Bernese mountain dogs, thefemale was shown to be more suscepti-ble40. Radiographic studies are usuallyperformed at 12 months. Severelyaffected cases diagnosed at a younger ageand possibly destroyed are thereforeexcluded and consequently the incidenceof elbow dysplasia may be underesti-mated15. The rottweiler is the breed withthe highest incidence but the degree ofarthrosis tends to be more severe in theBernese mountain dog15,22. The risk ofdeveloping elbow dysplasia is higher indogs with affected parents comparedto dogs with unaffected parents15,40.Heritability varies from 0.10–0.4815, 0.28–0.4040, 0.45 (females)20, and 0.77 (males)20.In rottweilers and Bernese mountaindogs, breeding parents that are bothnormal resulted in a 31 % incidence ofelbow dysplasia in the offspring, breeding1 normal with 1 arthritic parent resultedin 44–48 % of offspring affected andbreeding affected parents with each otherresulted in 59–62 % of offspring beingaffected22. In Sweden, concerted efforts todecrease the prevalence of elbowarthrosis have reduced the incidence from60 to 38 % in the Bernese mountain dogand from 60 to 45 % in the rottweiler overa period of 5 years40. During the sameperiod the incidence of moderate tosevere arthrosis decreased from 42 to 14 %in the Bernese mountain dog and from29 to 14 % in the rottweiler40.

Heritability is a definite factor in thedevelopment of elbow arthrosis andelbow joints should be radiographed insusceptible breeds at the same time as hipdysplasia evaluations are performed15.Breeding animals , particularly insusceptible breeds, should be selected bytheir phenotypic status and by informa-tion on the elbow status of parents, grand-

parents, litter mates and offspring alreadyborn15,34.

CONTROL PROGRAMMESScreening programmes to grade elbow

arthrosis have been established to

determine the degree of elbow involve-ment, with the intent to limit breedingwith severely affected dogs. Elbowgrading for degree of arthrosis has beenperformed by numerous investigatorswho often devised their own grading

Fig. 10: ML view of 8-month-old German shepherd dog with incongruent elbow joint.Compare to Fig. 2a. Note slightly proximally displaced lateral coronoid processand widened humero-ulnar and humero-radial joint space. Osteophyte reactionspresent and medial coronoid process poorly seen. Three medial coronoidfragments found at surgery.

Fig. 11: Schematic illustration of International Elbow Working Group elbow arthrosisgrading scheme illustrating osteophyte location in flexed ML and CrCd views.

0038-2809 Jl S.Afr.vet.Ass. (1998) 69(2): 43–54 51

systems15,17,21,25. Many of these pro-grammes involved certain breeds ororganisations e.g. Bernese mountain dogsin Switzerland25, Bernese mountain dogsand rottweilers in Scandinavia15,22,40,rottweilers in Australia36 and Dutchseeing-eye dogs42. The grading systemdoes not, however, predict the type oflesion present and thus does not correlatewith the degree of lameness that may beevident17.

The International Elbow WorkingGroup (IEWG) was established in 1989 tolower the incidence and promote agreater worldwide understanding ofelbow dysplasia. The group consists of

veterinarians, veterinary radiologists,geneticists and dog breeders and meetsannually in different parts of the world todiscuss current knowledge and promoteelbow screening schemes. More informa-tion on the IEWG can be obtained fromtheir web site at:

http://www.vetmed.ucdavis.edu/iewg/iewg.html

The IEWG has established guidelinesfor elbow screening and these have beenadopted by the Fédération InternationaleCynologique and World Small AnimalVeterinary Association as the official

standard2,29. Control programmes indifferent countries are encouraged toutilise the IEWG criteria when initiatingscreening programmes. The currentIEWG elbow screening protocol includessubmission of permanently-identifiedgood quality flexed ML radiographs ofboth elbows from 12 months onwards forosteophyte evaluation (Fig. 11). Theflexed ML view has been proven to be asensitive predictor of elbow arthrosisresulting from elbow dysplasia eventhough the inciting cause is not alwaysevident24. Grading is as follows (Figs 11, 12):

Grade 1 (mild arthrosis) – osteophytes<2 mm anywhere in the elbow but

ba

c

Fig. 12a: Grade 1 elbow arthrosis.Fig. 12b: Grade 2 elbow arthrosis.Fig. 12c: Grade 3 elbow arthrosis.

52 0038-2809 Tydskr.S.Afr.vet.Ver. (1998) 69(2): 43–54

particularly at 1 or more of the followingsites :a) on the dorsal border of the anconeal

process;b) on the cranioproximal edge of the

radius;c) on the proximal edge of the medial

coronoid process;d) on the proximal edge of the lateral

epicondylar ridge;e) and/or sclerosis in the area caudal to

the distal end of the ulnar trochlearnotch and the proximal radius.

Grade 2 (moderate arthrosis) – osteo-phytes 2–5 mm high at 1 or more locationsas described for grade 1.

Grade 3 (severe arthrosis) – osteophytes>5 mm high in 1 or more locations asdescribed for grade 1.

Osteophytes may also be evaluated ona CrCd radiograph at the followinglocations:f) distal aspect of medial humeral

condyle;g) medial aspect of medial coronoid

process.

In addition, if the primary pathology isevident it should be noted. Screeningprogrammes should be performed ata standard and narrow age interval, i.e.as close to 12 months as possible, asincreasing age has a significant influenceof the prevalence and severity of elbowarthrosis40. Dogs with clinical signs ofelbow pathology or offspring bred with ahigh risk of developing elbow arthrosisare radiographed at an earlier age so thataffected dogs may be submitted forsurgery before arthrotic changes develop.

The benefit versus cost ratio of an elbowarthrosis screening programme has beenextensively studied in Sweden40. The costof screening and registration of dogs forelbow dysplasia was found to be less thanthe value of dogs estimated to have beensaved from moderate to severe arthrosis.

Information gained from screeningprogrammes should be available in anopen registry system to researchers andresponsible owners to improve theselection of breeding stock. It is ideal notto breed with a dog with any grade ofarthrosis, but this is likely to result inbreeder resistance and breedingprogrammes should thus be adaptedto the incidence of elbow dysplasia inthe breed to ensure breeder compliance.In Australia, rottweilers have a highincidence of elbow arthrosis and,in accordance with current IEWGrecommendations, it was suggested thatdogs with evidence of grade 2 and 3elbow arthrosis should not be used forbreeding36.

DISCUSSIONEvidence appears to favour osteochon-

drosis in combination with asynchronousgrowth of the radius and ulna to be amajor contributing factor causing elbowarthrosis. This is corroborated by the smallnumber of cases that have simultaneousFMCP and UAP that would, according tothis hypothesis, tend to be mutuallyexclusive. However, asynchronous radiusand ulnar growth could possibly occuralternatively with first the ulna and thenthe radius, or vice versa, growing pasteach other. This hypothesis requiresfurther investigation. The hypothesis ofan abnormally developed slightly ellipti-cal trochlear notch proposed by Weis andWind seems unlikely to be a majorcontributing factor, as combined UAP andFMCP should then occur in much largernumbers of dogs and ulnar ostectomywould have no effect in cases with UAP7,38.It is, however, also possible that the timeat which incongruency develops mayaffect the outcome. Trochlear notchmalformation under 20 weeks of age mayresult in UAP, while such malformationafter the anconeal process has fused to theulna could result in FMCP.

Open registries are essential to combatelbow dysplasia. Evaluating the progeny,particularly of sires, will also make amarked difference as it has been shownthat there is a lower incidence of elbowarthrosis in the progeny of unaffectedsires40. In Sweden, an open registry issponsored by the Swedish kennel cluband has resulted in a marked decrease inthe incidence of elbow arthrosis48. In theUnited States an open registry system forelbow dysplasia is controlled by theInstitute for Genetic Disease Control(GDC) which also maintains opengenetic registries for a multitude of otherinherited diseases. The GDC iscooperating with Canada, Australia,Japan and has been asked to assist inestablishing an open registry in Europe as‘shared knowledge is the greatest tool inthe world for understanding’35.

In South Africa, screening programmesshould be introduced in predisposedbreeds such as the rottweiler, Labradorretriever, golden retriever and Germanshepherd dog. The Kennel Union ofSouth Africa, affected-breed clubs,veterinary clinicians, radiologists andsurgeons should combine their resourcesand expertise to initiate such pro-grammes. Cooperation with the GDC canbe considered. As conditions involved inelbow dysplasia are being recognisedearlier and more frequently and someprogress is being made in their treatment,screening programmes will benefit those

dogs that have elbow dysplasia as well asreduce the incidence of this oftencrippling disease.

REFERENCES1. Bardet J F 1997 Arthroscopy of the elbow in

dogs. Part II: cranial portals in the diagnosisand treatment of the lesions of the coronoidprocess. Veterinary and Comparative Ortho-paedics and Traumology 10: 60–66

2. Bedford P G C 1994 Control of hereditaryelbow disease in pedigree dogs. Journal ofSmall Animal Practice 35: 119–121

3. Berry C R 1992 Evaluation of the canineelbow for fragmented medial coronoidprocess. Veterinary Radiology & Ultrasound33: 273–276

4. Bouck G R, Miller C W, Taves C L 1995 Acomparison of surgical and medical treat-ment of fragmented coronoid process andosteochondritis dissecans of the canineelbow. Veterinary and Comparative Orthopae-dics and Traumatology 8: 177–183

5. Boudrieau R J, Hohn R B, Bardet J F 1983Osteochondritis dissecans of the elbow inthe dog. Journal of the American AnimalHospital Association 19: 627–635

6. Carpenter L G, Schwarz P D, Lowry J E,Park R D, Steyn P F 1993 Comparison ofradiologic imaging techniques for diagnosisof fragmented medial coronoid process ofthe cubital joint in dogs. Journal of theAmerican Veterinary Medical Association 203:78–83

7. Cross A R, Chambers J B 1997 Ununitedanconeal process of the canine elbow. Com-pendium on Continuing Education for the Prac-ticing Veterinarian (Small Animals) 19:349–360

8. Fox S M, Bloomberg M S, Bright R M 1983Developmental anomalies of the canineelbow. Journal of the American AnimalHospital Association 19: 605–615

9. Fox S M, Roberts R E 1987 Lineartomography in diagnosing fragmentedcoronoid processes in canine elbows. Com-pendium on Continuing Education for the Prac-ticing Veterinarian (Small Animals) 9: 61–65

10. Grondalen J 1979 Arthrosis with specialreference to the elbow joint of youngrapidly growing dogs. I. Nordisk Veterinær-medicin 31: 62–68

11. Grondalen J 1979 Arthrosis with specialreference to the elbow joint of youngrapidly growing dogs. II. Nordisk Veterinær-medicin 31: 69–75

12. Grondalen J 1979 Arthrosis in the elbowjoint of young rapidly growing dogs. III.Nordisk Veterinærmedicin 31: 520–527

13. Grondalen J 1982 Arthrosis in the elbowjoint of young rapidly growing dogs. VI.Nordisk Veterinærmedicin 34: 65–75

14. Grondalen J, Grondalen T 1981 Arthrosis inthe elbow joint of young rapidly growingdogs. V. Nordisk Veterinærmedicin 33: 1–16

15. Grondalen J, Lingaas F 1991 Arthrosis in theelbow joint of young rapidly growing dogs:a genetic investigation. Journal of SmallAnimal Practice 32: 460–464

16. Grondalen J, Rorvik A M 1980 Arthrosis inthe elbow of young rapidly growing dogs.IV. Nordisk Veterinærmedicin 32: 212–218

17. Guthrie S 1989 Use of a radiographic scoringtechnique for the assessment of dogs withelbow osteochondrosis. Journal of SmallAnimal Practice 30: 639–644

18. Guthrie S 1989 Some radiographic and

0038-2809 Jl S.Afr.vet.Ass. (1998) 69(2): 43–54 53

clinical aspects of ununited anconealprocess. The Veterinary Record 124: 661–662

19. Guthrie S, Buckland-Wright J C, VaughanL C 1991 Microfocal radiography as an aidto the diagnosis of canine elbow ostechon-drosis. Journal of Small Animal Practice 32:503–508

20. Guthrie S, Pidduck H G 1990 Heritability ofelbow osteochondrosis within a closedpopulation of dogs. Journal of Small AnimalPractice 31: 93–96

21. Hazewinkel H A W, Meij B P, Nap R C,Dijkshoorn N E, Ubbink G, Wolvekamp W1995 Radiographic views for elbow dys-plasia screening in Bernese mountain dogs.Proceedings of the 7th International ElbowWorking Group Meeting, Constance, Germany,1 July 1995: 29–32

22. Hedhammar A A 1991 The hereditary as-pects of canine elbow dysplasia. Proceedingsof the 16th World Small Animal VeterinaryAssociation Congress, Vienna, Austria, 2–5October 1995: 578–579

23. Huibregtse B A, Johnson A L, MuhlbauerM C, Pijanowski G J 1994 The effect of treat-ment of fragmented coronoid process onthe development of osteoarthritis of theelbow. Journal of the American AnimalHospital Association 30: 190–195

24. Keller G G, Kreeger J M, Mann F A, LattimerJ C 1997 Correlation of radiographic,necropsy and histologic findings in 8 dogswith elbow dysplasia. Veterinary Radiology& Ultrasound 38: 272–276

25. Lang J 1995 Comparison of two classifica-tion protocols in the evaluation of elbowdisease in the Bernese mountain dog.Proceedings of the 7th International ElbowWorking Group Meeting, Constance, Germany,1 July 1995: 37–38

26. Lewis D D, Parker R B, Hager D A 1989Fragmented medial coronoid process of thecanine elbow. Compendium on ContinuingEducation for the Practicing Veterinarian(Small Animals) 11: 703–715

27. Lowry J E, Carpenter L G, Park R D, SteynP F, Schwarz P D 1993 Radiographicanatomy and technique for arthrography ofthe cubital joint in clinically normal dogs.Journal of the American Veterinary MedicalAssociation 203: 72–77

28. Meij B P, Hazewinkel H A 1995 Treatmentof canine elbow dysplasia. Proceedings ofthe 7th International Elbow Working GroupMeeting, Constance, Germany, 1 July 1995:18–21

29. Meutstege F J 1995 Aims of the internationalelbow working group. Proceedings of the 7thInternational Elbow Working Group Meeting,

Constance, Germany, 1 July 1995: 3–530. Miyabayashi T, Takiguchi M, Scrader S C,

Biller D S 1995 Radiographic anatomy of themedial coronoid process of dogs. Journal ofthe American Animal Hospital Association 31:125–132

31. Nap R C 1995 Pathophysiology and clinicalaspects of canine elbow dysplasia. Proceed-ings of the 7th International Elbow WorkingGroup Meeting, Constance, Germany, 1 July1995: 6–8

32. Olsson S E 1993 Pathophysiology, morphol-ogy, and clinical signs of osteochondrosisin the dog. In Bojrab M S, Smeak D D,Bloomberg M S (eds) Disease mechanisms insmall animal surgery (2nd edn). Lea &Febiger, Philadelphia: 777–796

33. Olsson S E 1983 The early diagnosis offragmented coronoid process and osteo-chondritis dissecans of the canine elbowjoint. Journal of the American Animal HospitalAssociation 19: 616–626

34. Padgett G A, Mostosky U V, Probst C W,Thomas M W, Krecke C F 1995 Theinheritance of osteochondritis dissecansand fragmented coronoid process of theelbow joint in Labrador retrievers. Journal ofthe American Animal Hospital Association 31:327–330

35. Poulos P W 1997 GDC update: currentstatus and the role in the internationalcommunity. Proceedings of the 8th Interna-tional Elbow Working Group Meeting,Birmingham, Great Britain, 2 April 1997: 18–21

36. Read R A, Armstrong S J, Black A P,Macpherson J C, Davey T 1996 Relationshipbetween physical signs of elbow dysplasiaand radiographic score in growingrottweilers. Journal of the American VeterinaryMedical Association 209: 1427–1430

37. Roy R G, Wallace L J, Johnston G R 1994 Aretrospective long-term evaluation ofununited anconeal process excision on thecanine elbow. Veterinary and ComparativeOrthopaedics and Traumatology 7: 94–97

38. Sjöström L, Kasstöm H, Källber M 1995Ununited anconeal process in the dog.Pathogenesis and treatment by osteotomyof the ulna. Veterinary and ComparativeOrthopaedics and Traumatology 8: 170–176

39. Snaps F, Balligand N, Saunders J, Park R,Daenen B, Dondelinger R F 1996 Compari-son of radiography and MRI for the diagno-sis of fragmented medial coronoid processof cubital joint in dog. Proceedings of the 4thEuropean Association of Diagnostic ImagingConference, Cambridge, Great Britain, 29August – 1 September 1996 (Poster)

40. Swenson L, Audell L, Hedhammar A 1997Prevalence and inheritance of and selectionfor elbow arthrosis in Bernese mountaindogs and rottweilers in Sweden andbenefit:cost analysis of a screening andcontrol program. Journal of the AmericanVeterinary Medicine Association 210: 215–221

41. Thacher C 1993 Ununited anconeal process.In Slatter D (ed.) Textbook of small animalsurgery (2nd edn). W B Saunders, Philadel-phia: 1977–1981

42. Ubbink G, Hazewinkel H A W, WolvekampW th C, Rothuizen J, Van de Broek J 1995Preliminary results of the genetic analysis ofthe ED program of the Dutch seeing eyesdogs. Proceedings of the 7th InternationalElbow Working Group Meeting, Constance,Germany, 1 July 1995: 43–45

43. Van Bree H, Van Ryssen B 1995 Diagnosticand surgical arthroscopy of the canineelbow. Proceedings of the 7th InternationalElbow Working Group Meeting, Constance,Germany, 1 July 1995: 22–23

44. Voorhout G, Hazewinkel H A W 1987Radiographic evaluation of the canineelbow joint with special reference to themedial humeral condyle and the medicalcoronoid process. Veterinary Radiology 28:158–165

45. Weis M 1983 Knochenwachstumunter-suchungen mittels fluoreszenzmikrosko-pischer, mikroradiographischer undphasenkontrastmikroskopischer Tech-niken am Ellbogengelenk sowie distal anRadius und Ulna beim jungen Hund. EinBeitrag zur Aetiologie und Pathogenese derOsteochondrosis des Ellbogengelenkes.Inaugural dissertation, Faculty of Veteri-nary Medicine, University of Zurich

46. Wind A P 1982 Incidence and radiographicappearance of fragmented coronoidprocess. California Veterinarian 6: 19–25

47. Wind A P 1986 Elbow incongruity and de-velopmental elbow diseases in the dog: PartI. Journal of the American Animal HospitalAssociation 22: 711–724

48. Wind A P 1993 Elbow dysplasia. In Slatter D(ed.) Textbook of small animal surgery (2ndedn). W B Saunders, Philadelphia: 1966–1977

49. Wind A P, Doval J 1994 Guide to radiographicinterpretation of the canine elbow joint.Institute for Genetic Control in Animals,University of California, Davis

50. Wind P, Packard M E 1986 Elbow incongru-ity and developmental elbow diseases inthe dog: Part II. Journal of the AmericanAnimal Hospital Association 22: 725–735

54 0038-2809 Tydskr.S.Afr.vet.Ver. (1998) 69(2): 43–54