Arthroscopic Approaches to the Palmar Aspect of the Equine Carpus

JONATHAN CHEETHAM, VetMB and ALAN J. NIXON, BVSc, MS, Diplomate ACVS

Objective—To identify sites for arthroscopic access to the palmar aspects of the antebrachiocarpal(AC) and middle carpal (MC) joints, and describe visible carpal bone surfaces for each approach.Study Design—Prospective experimental study.Animals—Equine carpi: 16 cadavers, 8 live horses.Methods—A latex model was used to identify possible sites for arthroscopic access to the palmaraspects of the AC and MC joints. Carpi (n¼ 24) were examined arthroscopically and arthroscopicaccess sites and visible carpal bone surfaces were described.Results—Arthroscopic approaches and instrument portals were developed for the medial and lat-eral aspects of the palmar pouches of the AC andMC joints. The palmar surface of the radial carpalbone and radius, and the dorsal articular surfaces of the accessory carpal bone, could be viewedusing palmar approaches to the AC joint. The palmar aspect of the radial, third and second carpalbones (medially) and ulnar and fourth carpal bones (laterally) could be observed using a palmarapproach to the MC joint.Conclusions—Arthroscopic access, using separate medial and lateral portals to the AC and MCjoints, allowed assessment of portions of the caudodistal radius, the palmar surfaces of the radial,ulnar, second, third and fourth carpal bones, and the dorsal aspect of the accessory carpal bone.Clinical Relevance—Arthroscopic approaches to the palmar aspect of the carpus could be used toremove fracture fragments, and to assess the medial palmar intercarpal ligaments.r Copyright 2006 by The American College of Veterinary Surgeons

INTRODUCTION

OSTEOCHONDRAL CHIP fracture of the dorsalperimeter of the carpal bones is a common injury in

racehorses.1 Discrete fracture of any of the palmar carpalbone surfaces can also occur2,3; however, this injury ap-pears less common than dorsal fragmentation. Similarlyarthroscopic approaches to the dorsal aspects of theequine carpal bones are well described.1,2 There are fewreports of removal of fracture fragments from the palmaraspects of the carpal bones.2–6

Anatomically detailed descriptions of the palmarpouches of the individual joints of the carpus are limit-ed.7 Most describe a well-formed palmar pouch, for bothantebrachiocarpal (AC) and middle carpal (MC) joints,with variable out pouchings, to accommodate the artic-ulation with the accessory carpal bone. More complete

surgical or anatomic descriptions of arthroscopic accessto the palmar surfaces of the carpal bones were notfound. Fractures of the palmar surfaces of the carpalbones are not common in horses but arise with sufficientfrequency to warrant development of techniques for sur-gical exploration. Our purpose was to develop approach-es to the palmar aspect of the carpus and describe thevisible carpal bone surfaces.

MATERIALS AND METHODS

Anatomic Models

A latex model was created to clarify the anatomy of thepalmar pouches of the equine carpus. Yellow latex (40mL;DAP Dynaflex 230, DAP Inc., Baltimore, MD and yellowpigment # 07354, Polysciences Inc., Warrington, PA) was in-jected through a dorsal stab incision into the right AC joint of

Presented at the American College of Veterinary Surgeons Symposium, Denver, CO, October 2004.

Address reprint requests to Alan J. Nixon, BVSc, MS, Department of Clinical Sciences, College of Veterinary Medicine, Cornell

University, Ithaca, NY 14853. E-mail: ajn1@cornell.edu.

Submitted August 2005; Accepted December 2005

From the Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY.

r Copyright 2006 by The American College of Veterinary Surgeons

0161-3499/06

doi:10.1111/j.1532-950X.2006.00141.x

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Veterinary Surgery

35:227–231, 2006

a cadaveric carpus, retrieved from a 450kg Thoroughbredgelding. Red latex (40mL; DAP Dynaflex 230, DAP Inc., andred pigment # 07350, Polysciences Inc.) was injected similarlyinto the MC joint. The soft tissues were removed by boiling indilute sodium hydroxide, the bones bleached in 3% sodiumperoxide, and the latex replaced in a correct anatomic ar-rangement. This model was used to identify potential sites forarthroscopic access. Anatomic dissection was performed onfour cadaver carpi to identify the proximity of neurovascularstructures to the pouches identified on the latex models.

Arthroscopic Access

Sixteen limbs from 8 equine cadavers and both carpi of 4anesthetized horses were used to establish suitable ar-throscopic portals for access to the palmar aspects of theAC and MC joints. The anesthetized horses were 3–4-yearsold and weighed 440–460kg. Anesthetized horses were posi-tioned in dorsal recumbency and the palmar aspects of thecarpi aseptically prepared and draped; cadaver carpi wereprepared similarly. The carpus was placed in 20–301 flexionand the joint to be examined arthroscopically was distendedwith 25–30mL lactated Ringer’s solution using dorsal land-marks. Visible and palpable palmar outpouchings of the ACand MC joints were selected and a 5mm incision madethrough the skin and joint capsule with a #15 scalpel blade. A4mm 301 oblique forward viewing video-arthroscope (Dyo-nics, Smith & Nephew, Andover, MA) coupled to a 3-chipdigital video camera (Dyonics) was used. Photographic andvideo documentation of visible surfaces was digitally recordedon a combination capture unit (SDC-Pro 2, Stryker Endos-copy, Santa Clara, CA). Four cadaveric carpi were subse-quently dissected to examine the proximity of periarticularligaments and neurovascular structures.

RESULTS

Latex Model

The model identified 3 distensible pouches on the pal-marolateral aspect of the AC joint separated by variousattachments of the accessory carpal bone to the radiusand the proximal row of carpal bones. A single pouchwas identified on the medial aspect of the AC joint,and the medial and lateral aspects of the MC joint(Figs 1 and 2).

Arthroscopic Technique

Positioning the limb with the carpus in 20–301 flexionimproved entry to the palmar pouches. The joints weredistended with lactated Ringer’s solution, using dorsallandmarks,2 before insertion of the arthroscope into thepalmar cul-de-sacs. Five millimeter stab incisions wereused for arthroscopic and instrument portals throughout.If difficulty was experienced when attempting to enter apalmar pouch, the degree of carpal flexion was adjusted

slightly to facilitate access. A lower fluid pressure wasused compared with that routinely used during dorsalcarpal arthroscopy, and the fluid flow was off until cor-rect positioning was confirmed, because this resulted inless subcutaneous fluid accumulation.

AC Joint

Medial Approach. The arthroscope was inserted,through a stab incision palmar to the medial collateralligament at the level of the distal radius and in the palmarregion of the palmar pouch (Fig 3). Care was taken toangle the arthroscope sleeve dorsally to avoid iatrogenicdamage to the medial palmar vein and flexor carpi ra-dialis tendon, or inadvertent entry into the carpal canal.This approach provided good access to the voluminouspalmaromedial pouch of this joint. The medial junctionof the palmar surfaces of the radius and the radial carpalbone provided a landmark for orientation (Fig 4A).Moving laterally, it was possible to identify the entirepalmar articulation of the radius with the radial carpalbone (Fig 4B). Moving the arthroscope proximally withinthe pouch enabled identification of the attachment of thethick joint capsule to the caudal radius (Fig 4C). If in-strumentation was required, the arthroscopic portal was

Fig 1. Palmaromedial view of latex model showing medial

palmar pouches of antebrachiocarpal joint and middle carpal

joint. The model is positioned upside down to reflect a horse in

dorsal recumbency.

228 PALMAR ARTHROSCOPY OF THE EQUINE CARPUS

positioned proximally and palmarly in the pouch to allowinsertion of a second portal distally and medially. Thispouch was bounded laterally by the thick palmar radio-carpal ligament, prohibiting access to the palmar aspectof the intermediate carpal bone.Lateral Approach. The latex model identified 3 lateralpouches to the AC joint distributed around the ligament-ous and capsular attachments to the accessory carpalbone (Fig 2). The most proximal pouch was the largest ofthese, and was entered with a stab incision, centeredover the area of palpable distension proximal to theaccessory carpal bone and accessorioulnar ligament, atthe level of the physeal remnant of the distal radius.The arthroscopic portal was made in the most proximalpart of this out-pouching, leaving the area immediatelyproximal to the accessory carpal bone available forinstrument access (Fig 5). The arthroscope initially en-tered a proximolateral voluminous palmar pouch, andwas then redirected distodorsally to view the proximalconcave articulation of the dorsal aspect of the accessorycarpal bone with the radius (Fig 6A). It was not generallypossible to view the palmaroproximal aspect of theintermediate carpal bone.

The middle pouch was located in the triangle formedby the distocaudal radius, the accessoriocarpoulnar lig-ament and the accessorioulnar ligament. Arthroscopicaccess was extremely restricted; however, it was possible

to obtain a limited view of the ulnar carpal bone and itsarticulation with the distal convex surface of the acces-sory carpal bone (Fig 6B).

The most distal pouch identified on the latex modelcould not be entered with a 4mm arthroscope and wasnot explored.

Fig 2. Palmarolateral view of latex model showing lateral

palmar pouches of antebrachiocarpal joint and middle carpal

joint. The model is positioned upside down to reflect a horse in

dorsal recumbency.

Fig 3. Illustration of palmaromedial approach to ante-

brachiocarpal joint. Additional landmarks indicate middle car-

pal joint approach for insertion of arthroscope (o) and

instrument (x).

Fig 4. Anatomic specimen for medial approach to ante-

brachiocarpal joint: medial (A) and central (B) portions of

articulation between radius and radial carpal bone and

proximomedial attachment of joint capsule (C).

229CHEETHAM AND NIXON

MC Joint

Medial Approach. The palmaromedial pouch was en-tered at the center of the palpable distension just caudalto the medial collateral ligament. The arthroscope wasinserted through a 5mm skin incision in a 451 palmaro-medial to dorsolateral direction and was directed ap-

proximately 201 distally (Fig 3). Once in the pouch, thearthroscope was redirected distally and it was possible toidentify the insertion of the medial palmar intercarpalligament (MPICL) on the palmarolateral aspect of thesecond carpal bone and the palmaromedial aspect of thethird carpal bone (Fig 7A). The arthroscope was thenredirected dorsally to view the palmar articulation of thesecond carpal bone with the radial carpal bone and thepalmar bundles of the MPICL (Fig 7B). If an instrument

Fig 5. Illustration of palmarolateral approach to middle

carpal joint with landmarks for antebrachiocarpal joint ap-

proach for insertion of arthroscope (o) and instrument (x).

Fig 6. Composite showing arthroscopic images for lateral

approaches to antebrachiocarpal joint: (A). Proximal ap-

proach—concave articulation of the dorsal aspect of the ac-

cessory carpal bone with the radius. (B). Distal approach—

articulation of ulnar carpal bone with distal convex surface of

accessory carpal bone.

Fig 7. Composite showing arthroscopic images for medial

approach to middle carpal joint. (A) Articulation of second

carpal bone with radial carpal bone and palmar bundles of

MPICL. (B) Attachment of medial palmar intercarpal liga-

ment (MPICL) onto second and third carpal bones.

Fig 8. Composite showing arthroscopic images for lateral

approach to middle carpal joint. (A) rounded distolateral cor-

ner of fourth carpal bone. (B) articulation of ulnar carpal bone

with fourth carpal bone. (C) sharp distolateral corner of ulna

carpal bone.

230 PALMAR ARTHROSCOPY OF THE EQUINE CARPUS

portal was required it was placed, with the aid of a pre-placed 18G needle, but generally lateral and in the sametransverse plane, as the arthroscope portal.Lateral Approach. This pouch was clearly palpable afterdistention and was entered through a skin incision 10–15mm palmar to the lateral collateral ligament and be-tween the accessoriocarpoulnar ligament and the access-orioquartal ligament (Fig 5). Once in the pouch thearthroscope was redirected dorsally to view the palm-arodistal protrusion of the ulnar carpal bone and its ar-ticulation with the sloping palmaroproximal aspect of thefourth carpal bone (Fig 8). If an instrument portal wasrequired, it was placed lateral, and in the same transverseplane, as the arthroscopy portal. It was not possible toview the lateral palmar intercarpal ligament or the pal-marolateral aspect of third carpal bone.

Complications. Peri-portal subcutaneous fluid accu-mulation occurred in most of the arthroscopic proceduresperformed; however, it only limited the duration of ar-throscopic access in one. The proximity of instrumentand arthroscopic portals in the MC joint made triangu-lation and manipulation within the joint difficult. Syno-vial proliferation often necessitated the use of amotorized synovial resector to improve exposure. Accesswas obtained to the appropriate pouch in all cases. Noperiarticular neurovascular structures were damaged dur-ing arthroscopy of the palmar carpal pouches in the 4carpi that were dissected after arthroscopic exploration.Inadvertent entry to the carpal flexor sheath occasionallyoccurred when attempting to enter the palmarolateralpouch of the AC joint. This was corrected by carefullyredirecting the arthroscope more dorsally.

DISCUSSION

Five separate and independent arthroscopic approach-es were developed to examine the palmar aspect of theequine carpus. The medial and lateral approaches to thepalmar aspect of the AC joint provided good access tothe medial third and lateral aspect of the distocaudal ra-dius, the whole of the palmar surface of the radial carpalbone and the proximal articulation of the accessory car-pal bone. The addition of an instrument portal wasstraightforward in these pouches and was assisted byneedle insertion before skin incision. The middle ap-proach to the palmarolateral aspect of the AC joint pro-vided very limited access, and the distal pouch could notbe explored.

The approaches to the palmar aspect of the MC jointwere more difficult; however, with practice and theknowledge gained from the latex model and the previous

anatomic dissections, the palmarolateral and palmaro-medial approaches were consistently achieved. Neverthe-less, it was common to make several attempts to locatethe arthroscope correctly within the joint. Using theseapproaches it was possible to view portions of the palmarsurfaces of the radial, second and third carpal bones, andthe palmar bundles of the MPICL (medial approach),and portions of the palmar surfaces of the ulna andfourth carpal bones (lateral approach).

It was not possible to view the palmaroproximal as-pect of the intermediate carpal bone, the palmarolateralaspect of the third carpal bone or the lateral palmar in-tercarpal ligament. The palmar bundles of the MPICLwere clearly identified using the medial approach to theMC joint, however, instrument access was more difficultthan using a standard dorsal approach with maximalflexion of the joint.

These techniques could be used for removal of fracturefragments from the caudomedial aspect of the radius andthe palmar surfaces of the radial, ulnar, second, third andfourth carpal bones and the dorsal aspect of the accessorycarpal bone. They could also be used to evaluate thepalmar bundles of the MPICL, and to retrieve fracturefragments or broken instruments resulting from a previ-ous dorsal arthroscopy.

We describe development of arthroscopic portals tothe palmar aspect of the AC and MC joints. These ap-proaches have been used on a number of clinical cases,and with experience, provide access for identification andremoval of osteochondral fragments from the radius andradial, accessory, ulna and fourth carpal bones.

REFERENCES

1. McIlwraith CW, Yovich JV, Martin GS: Arthroscopic sur-

gery for the treatment of osteochondral chip fractures in

the equine carpus. J Am Vet Med Assoc 191:531–540, 1987

2. McIlwraith CW, Nixon AJ, Wright IM, Boening J: Diag-

nostic and Surgical Arthroscopy in the horse (ed 3). Lon-

don, UK, Mosby-Elsevier, 2005

3. Wilke M, Nixon AJ, Malark J, et al: Fracture of the palmar

aspect of the carpal bones in horses: 10 cases (1984–2000). J

Am Vet Med Assoc 219:801–804, 2001

4. Hurtig MB, Fretz PB: Arthroscopic landmarks of the equine

carpus. J Am Vet Med Assoc 189:1314–1321, 1986

5. McIlwraith CW: Fractures of the carpus, in Nixon AJ (ed):

Equine Fracture Repair. Philadelphia, PA, Saunders, 1996,

pp 208–220

6. Dabareiner RM, Sullins KE, Bradley W: Removal of a frag-

ment from the palmar aspect of the intermediate carpal

bone in a horse. J Am Vet Med Assoc 203:553–555, 1993

7. Dyce KM, Sack WO, Wensing CJG: The forelimb of the

horse, in Textbook of Veterinary Anatomy. Philadelphia,

PA, Saunders, 1996, 582pp

231CHEETHAM AND NIXON