Sonographic Diagnosis of Exostoses of theCaudal Distal Radius

Johanna M. Reimer, VMD, Diplomate ACVIM

Ultrasonographic evaluation of the caudal distal radius for exostoses in horses of any age and breed withpalmar pericarpal pain is warranted since radiographs may be negative. Author’s address: Roodand Riddle Equine Hospital, PO Box 12070, Lexington, Kentucky 40580-2070; email: jreimer@roodandriddle.com. © 2010 AAEP.

1. Introduction

Exostoses of the caudal perimeter of the distal ra-dius resulting in lameness accompanied by intermit-tent effusion of the carpal synovial sheath have beendescribed. Such exostoses are categorized as eithersolitary osteochondromas, which are typically lo-cated 2–4 cm proximal to the physeal scar, or phy-seal remnant spikes, which originate directly overthe physeal scar. Osteochondromas typically affectyoung horses, whereas physeal remnant spikes mayaffect older horses as well. Radiography has beenroutinely used for the detection of these exostoses.Radiographic recognition of small physeal remnantspikes can be more difficult because of superimposi-tion over the physeal scar, and some osteochondro-mas are small and difficult to detect. However, notall exostoses are clinically important.1,2

Arthroscopic removal of clinically important exos-toses is the treatment of choice.1–3 The procedurecan also be used to examine the carpal sheath inwhich an exostosis is not radiographically apparentbut lameness has been isolated to the carpal syno-vial sheath. Sonographic detection of distal radialbone spikes and osteochondromas has been men-tioned in the literature, but the procedure and sono-

graphic features were not described in detail.1–3

Ultrasonography can be used to diagnose exostosesthat are not radiographically apparent as well as aidin determining their significance by imaging theirextension into the carpal sheath and/or associatedstructures.1

The purposes of this paper are to describe thesonographic appearance and location of clinicallyimportant caudal radial exostoses, highlight the im-portance of using ultrasonography to identify exos-toses that are not evident radiographically, andincrease awareness of caudal distal radial exostosesas a potential cause of lameness in the absence ofcarpal sheath effusion.

2. Materials and Methods

Horses in which a diagnosis of a caudal radial exos-tosis was made and an ultrasound study of the car-pal synovial sheath was performed before diagnosiswere included in the study. A diagnosis was madeeither by the sonographic demonstration of a clearlydemarcated bone spike or large exostosis into thecarpal sheath accompanied by synovial effusion inthe proximal aspect of the sheath or at the time ofsurgery. The procedure for sonographic evaluationof the carpal synovial sheath was performed as de-

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NOTES

scribed in the literature using a 7- or 8-MHz lineararray transducer4 and was amended to include eval-uation of the surface of the caudomedial distal ra-dius in transverse and sagittal planes from the mostproximal visible extent of the superior check liga-ment to the level of the physeal scar. The ultra-sound beam was fanned across the surface of the

radius in a sagittal plane to enable evaluation of asmuch of the surface of the palmar radius as possible.The locations of any exostoses in relation to thesuperior check ligament, deep flexor muscle, and/orphyseal scar were noted.

3. Results

Fourteen cases of caudal radial exostoses in whichan ultrasound study was performed before diagnosiswere identified between 2001 and January 2010.All horses were Thoroughbreds, ranging in age from2 to 4 yr. Thirteen of the horses presented for mildto moderate effusion of the carpal sheath. Three ofthese horses had recurrent effusion after a transientresponse to intrathecal corticosteroids and hyal-uronic acid. Mild lameness present in two otherhorses was isolated to the carpal sheath by intrathe-cal infiltration of local anesthetic. One horse withno effusion in the carpal sheath was examined todetermine the cause of a 4- to 5-degree lameness (ona scale of 1–5) that had been abolished with peri-neural anesthesia of the median and ulnar nerves.

An exostosis protruding into the carpal sheathwas identified at the time of the ultrasound exami-nation in 12 of 14 horses (Figs. 1–4). Retrospectivescrutiny of the sonograms of one horse in which thediagnosis was confirmed during arthroscopy re-vealed a spike-shaped exostosis that was poorly de-lineated and partially obscured by the deep digitalflexor muscle. The majority (11 of 13) of exostosesidentified with ultrasound in this study were spur-or spike-like projections. Two horses had largeknobby protrusions into the carpal sheath that weresubsequently readily identifiable radiographicallyand typical in appearance for most osteochondro-mas. Ten exostoses were discovered in a locationencompassing the superior check ligament and thedeep flexor muscle 2–4 cm above the physeal scar.Exostoses were discovered at the level of, or in closeproximity to, the physeal scar in three horses.Grossly visible tearing of the superior check liga-

Š

Fig. 1. (A) Sagittal view of a distal radial exostosis (arrow)immediately proximal to the physeal scar in a 4-yr-old Thorough-bred broodmare with 5/5 lameness of 3 wk in duration. Theexostosis was discovered during the sonographic evaluation ofthe carpal region after lameness was abolished with median andulnar perineural anesthesia. The exostosis was not evidentradiographically, and there was no effusion in the carpalsheath. Excision of the exostosis was curative. Proximal is tothe right. (B) Sonogram obtained slightly more abaxial to theimage in A, showing the fibers of a small accessory head ofthe deep digital flexor tendon (between arrows) hooked over theexostosis. The involved tendon was located immediately dorsalto the superior check ligament and found to attach to the pal-mar surface of the deep flexor tendon distally. This tendon doesnot seem to be present in all horses as far as the author candetermine. The severity of lameness was likely attributable tothe “snagging” of this tendon by the spur and not a result oftenosynovitis.

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ment associated with the exostosis was present intwo horses, impingement without gross fiber tearingof the superior check ligament was identified sono-graphically in three horses (Figs. 3 and 4), and im-

Fig. 2. (A) Sagittal image of the distal medial radius show-ing a small exostosis (arrow) just proximal to the edge of thephyseal scar in a 2-yr-old Thoroughbred colt presented formoderate synovial effusion of the carpal sheath. The horsewas sound at the time of the examination. Radiographs werenegative. Note that the exostosis is similar in appearance tothat affecting the horse depicted in Figure 1, but the clinicalpresentation of each case was remarkably different. Theexostosis in this case was located just slightly more axiallyand slightly more proximally than Figure 1. The exostosisillustrated here impinged on the abaxial edge of the deepdigital flexor tendon as determined by ultrasonography andwas confirmed during arthroscopic removal of the exostosis.Proximal is to the right. MA, median artery; SC, superiorcheck ligament. (B) Transverse view of the exostosis. Lat-eral is to the right. Notice the exostosis protruding betweenthe superior check ligament (SC) and the deep digital flexormuscle (DD). SD, superficial digital flexor tendon. Dorsal isto the right.

Fig. 3. (A) Sagittal image of a 6-mm-long exostosis (arrow) of thedistal radius of a 2-yr-old Thoroughbred with intermittent lame-ness associated with recurrent carpal sheath effusion. SC, su-perior check ligament. Proximal is to the right. (B) Transverseimage of the exostosis showing impingement on the superiorcheck ligament. SC, superior check ligament; arrow, exostosis.

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pingement into the deep flexor tendon or anaccessory tendon (Fig. 1B) was identified in fivehorses during the ultrasound examination. The re-maining exostoses protruded into the carpal sheathand were surrounded by synovial fluid. One horsehad tearing of the deep flexor tendon into the prox-imal palmar metacarpal region.

Radiographs were obtained in 13 of 14 cases andconsidered diagnostic in five cases. One horse withrecurrent carpal sheath synovitis and in which ra-diography and ultrasonography were negative un-derwent magnetic resonance imaging, at which timean exostosis was identified.

Thirteen horses underwent arthroscopic removalof the exostoses, and one horse was lost to follow-up.Surgery reports were available for 12 of the horses,and all described damage to a tendinous structureopposite the exostosis.

4. Discussion

The results of this report illustrate the value ofultrasonography for the detection of clinically im-portant exostoses of the caudal distal radius in

horses. The majority of these exostoses were notdetected with radiography. It was also a vital toolin the diagnosis of a physeal remnant spike thatresulted in severe lameness in the absence of carpalsheath effusion. The exostosis in this case was atthe medial edge of the carpal sheath and envelopedby an accessory tendon. This may have not onlycontributed to the profound lameness in this horsebut also limited the development of synovitis. Inlight of this recent case, the author now incorporatesa cursory evaluation of the surface of the caudaldistal radius into the ultrasound evaluation ofhorses with lameness suspected to be originatingfrom the proximal metacarpal region or palmar car-pus as well as those with carpal synovial sheatheffusion. Sonographic evaluation of the proximallateral aspect of the carpal sheath may be informa-tive, even in the absence of palpable abnormalitiesor synovial abnormalities in the metacarpal region.

Although the horses of this report were relativelyyoung (2–4 yr of age), lameness resulting from phy-seal remnant exostoses has been confirmed in horsesfrom 3 to 12 yr of age, with an average age of 6 yr.2

All horses in this report were Thoroughbreds, whichis reflective of our hospital population. Physealremnant exostoses were identified in Thorough-breds, Warmbloods, and mixed breed in a previousreport.2 Ultrasonographic evaluation of the caudaldistal radius for exostoses in horses of any age andbreed with palmar peri-carpal pain and negative orequivocal radiographs may be warranted. Intra-thecal local anesthesia can be used to confirm thesignificance of any sonographic findings. It is im-portant for sonographers to familiarize themselveswith the varied appearance of the caudal distal ra-dius in sound limbs to avoid the potential for false-positive diagnoses, because some exostoses may notbe clinically important.2

References1. McIlwraith CW. Osteochondromas and physeal remnant

spikes in the carpal canal, in Proceedings. 12th AnnualAmerican College of Veterinary Surgeons Symposium 2002;168–169.

2. Nixon AJ, Schachter BL, Pool RR. Exostoses of the caudalperimeter of the radial physis as a cause of carpal synovialsheath tenosynovitis and lameness in horses: 10 cases(1999–2003). J Am Med Vet Assoc 2004;224:264–270.

3. Stashak TS. Lameness: the forearm (antebrachium). In:Stashak TS, ed. Adams’ lameness in horses, 5th ed. Philadel-phia, PA: Lippincott Williams & Wilkins, 2002;864–867.

4. Denoix JM, Busoni V. Ultrasonographic anatomy of the ac-cessory ligament of the superficial digital flexor tendon inhorses. Equine Vet J 1999;3:186–191.

Fig. 4. Transverse image of an exostosis impinging on the supe-rior check ligament in a 2-yr-old Thoroughbred filly with recur-rent effusion in the carpal sheath. Dorsal is to the right. SC,superior check ligament.

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