Case Report

Carpal arthrodesis using a minimally invasive approach andlocking compression plates: Three casesO. Brandenberger†‡, F. Rossignol‡*, S. Bartke§, T. Van Bergen¶ and A. Vitte†

†Clinique V�et�erinaire de Grosbois, Boissy St Leger; ‡Clinique Equine de l’Ecole Nationale V�et�erinaire de MaisonsAlfort, Maisons Alfort, France; §Tier€arztliche Praxis f€ur Pferde, Warendorf-Milte, Germany; and ¶Department of Surgeryand Anesthesiology of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.*Corresponding author email: fabricerossignol94@orange.fr.

Keywords: horse; carpal arthrodesis; minimal invasive; carpal instability; locking compression plate

SummaryThree horses with carpal instability due to comminutedsecond carpal bone fractures (Cases 1 and 3), fracture of thehead of the second metacarpal bone (Case 1) orcomminuted fractures of the fourth carpal bone, ulnar andintermediate carpal bones (Case 2) were treated byminimally invasive approach for partial (Cases 1 and 3) orpancarpal (Case 2) joint arthrodesis, using lockingcompression plates. The joint cartilage was removed byeither an arthroscopic approach (middle carpal joint andantebrachiocarpal joint) or a percutaneous drilling technique(carpometacarpal joint). Two or 3 locking compression plateswere contoured to the dorsolateral, dorsomedial anddorsoaxial aspects of the carpal joints using a custom-madetunnelling tool and a minimally invasive tunnelling technique,and the screws were positioned through stab incisions. Allcases recovered well, were lame free at the walk, were ableto trot and gallop and could be used for leisure and pastureactivities (partial carpal arthrodesis) and breeding (pancarpalarthrodesis). Post-operative x-rays showed progressive jointfusion after 12 months (Case 1), 5 months (Case 2) and10 months (Case 3). Case 2 with a pancarpal arthrodesisshowed a mechanical lameness at the walk due to theinability to flex the carpus. Carpal flexion aftercarpometacarpal and middle carpal arthrodesis in Case 1was calculated to be 42.6° and 44° in Case 3.

Introduction

Comminuted or displaced fractures of the carpal bones arenot common in horses and are often associated with majorcarpal instability (Auer and Lischer 2012). If accurateanatomical reconstruction of the fractured bone isimpossible, the only treatment to restore weightbearing andto prevent deformity, severe osteoarthritis or opposite forelimblaminitis is joint arthrodesis. Two types of carpal arthrodesishave been described (Barr 1994; Carpenter et al. 2008; Auerand Lischer 2012). If one of the 3 carpal joints(carpometacarpal [CMC], middle carpal [MC] joint orantebrachial carpal [ABC] joint) or 2 (CMC and MC) areinvolved then partial carpal arthrodesis is appropriate. Forpartial joint arthrodesis, the CMC joint alone, the MC andCMC joint together, and the ABC joint alone can be fused.Range of movement after partial carpal arthrodesis is limitedto the non-used joint (e.g. after ABC joint arthrodesis therange of flexion depends on the range of flexion of the MCjoint) (Tulloch et al. 2015). However, if both MC and ABC

joints are affected, pan-carpal arthrodesis is recommendedwith complete loss of joint movement (McIlwraith et al. 2015;Tulloch et al. 2015). In high motion joints such as themetacarpophalangeal or ABC joints, arthrodesis is essentiallya salvage procedure, the aim being to allow comfortablelocomotion at pasture or to save the animal for breedingpurposes. According to Lewis (2001), the long-term prognosisfor salvage was good (81%) but complications includedimplant failure and contralateral laminitis. The standardapproach is a slightly curved incision over the dorsal aspectof the distal radius (in the case of a pancarpal arthrodesisor partial ABC joint arthrodesis), carpus and proximalmetacarpus (Barr 1994; Carpenter et al. 2008; Auer andLischer 2012). Carpenter et al. (2008) described use of one 16-hole and one 14-hole large fragment locking compressionplates (LCPs) for pancarpal arthrodesis, with a single 40 cmlong vertical skin incision made on the dorsal aspect of thelimb. The main disadvantages of a large incision include thehigher exposure to contamination and the difficulties forclosure of the incision, especially over one or more voluminousosteosynthesis plates. Minimally invasive plate fixation, keepingthe skin over the plate intact and making small incisions overthe plate holes to allow screw insertion, was described byJames and Richardson in 2006, who employed this minimallyinvasive technique in 22 cases of incomplete distal thirdmetacarpal/metatarsal condylar fractures, and 6 fetlock and4 pastern arthrodeses (James and Richardson 2006). Here, wereport our experiences with a minimally invasive approach forpartial and pan-carpal arthrodesis, in which either 2 or 3 LCPwere applied in 3 horses.

Case histories

Case 1A 10-year-old Warmblood gelding was referred to the clinicwith a radiographic diagnosis of an acute, displacedcomminuted fracture of the second carpal bone (C2) andhead of second metcaparpal bone (MCII) of the right frontlimb of unknown cause. The horse was referred immediatelyafter injury with a large Robert Jones full leg bandage and acaudally-applied splint.

Case 2A 10-year-old Arabian mare was referred due to the suddenoccurrence of severe left forelimb lameness during anendurance race. The referring veterinarian diagnosedmultiple fractures of the proximal row of carpal bones based

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on radiographs, applied a Robert Jones full leg bandage with2 full-length wooden splints on the lateral and caudal aspectsto stabilise the limb, and administered 4.4 mg/kg bwtphenylbutazone i.v. prior to immediate referral.

Case 3A 10-month-old French Standardbred colt was found lame onpasture, was diagnosed with a comminuted fractured C2based on radiographs, and immediately referred with aRobert Jones full leg bandage with a palmar splint.

Clinical and radiographic findings

Case 1The gelding had a severe lameness apparent at the walkand rested the limb on the tip of the hoof (grade 5/5American Association of Equine Practitioners [AAEP; Swanson1984]) with a moderately swollen medial aspect of thecarpus that was painful to flexion. Lateromedial (LM),dorsopalmar (DP), dorsomedial–palmarolateral oblique(DMPLO) and dorsolateral-palmaromedial oblique (DLPMO)radiographic projections showed a displaced sagittal C2fracture and an oblique, displaced articular fracture ofproximal MCII. The medial fragment of C2 showed markedmedial dislocation, with several small fragments and pinpointmineral opacities in/around the fracture gap, and soft tissueswelling on the medial aspect of the carpus.

Case 2The mare was nearly nonweightbearing on the left forelimbdue to carpal instability that resulted in a valgus deviation ofthe limb at the carpus (grade 5/5 AAEP [Swanson 1984]).Effusion and oedema of the soft carpal tissues was apparentand flexion of the carpus caused pain and obviouscrepitation. Radiographs (DP, DLPMO and DMPLO) showedsevere multiple, comminuted and displaced fractures of theulnar, intermediate, and fourth carpal bones (C4) with carpusvalgus, caused by collapse of the lateral aspect of MC andABC joints. Numerous small fragments were visible on thelateral aspect of the carpus (Fig 1).

Case 3The colt was lame at the walk, with an exaggerated headand neck nod (grade 4/5 AAEP [Swanson 1984]), flexion ofthe carpus elicited a pain response, and swelling wasapparent on the lateral aspect. Radiographs (LM, DP, DMPLOand DLPMO) showed a comminuted markedly displacedfracture of the medial border of C2, and thickening of theperiarticular soft tissues.

Surgical details

Case 1After premedication with sodium penicillin (Penicilline G,Panpharma, Luitr�e, France, 22,000 iu/kg bwt. i.v.), gentamicin(Forticine, Vetoquinol, Lure, France, 6.6 mg/kg bwt. i.v.) andphenylbutazone (Phenylarthrite, Vetoquinol, Lure, France,4.4 mg/kg bwt. i.v.) and sedation with acepromazine(Calmivet, Vetoquinol, Lure, France, 0.05 mg/kg bwt. i.v.),detomidine (Detogesic, Zoetis France SAS, Paris, France,0.04 mg/kg bwt. i.v.) and morphine (Morphine Lavoisier; CDMLavoisier, Paris, France, 1 mg/kg bwt. i.v.) the gelding wasinduced with ketamine (Ketamidor, Richter Pharma AG, Wels,Austria, 2.2 mg/kg bwt. i.v.) and diazepam (Valium; RocheSAS, Boulogne-Billancourt, France, 0.02 mg/kg bwt. i.v.) andpositioned in left lateral recumbency. General anaesthesiawas maintained with isoflurane (Isoflo, Zoetis France SAS, Paris,France) in oxygen and air in a semiclosed ventilating system,combined with a detomidine constant rate infusion (0.04 mg/kg bwt/h). Aseptic preparation of the right front limb from thecoronary band to the elbow, was done in preparation for apartial carpal arthrodesis of the MC and CMC joints.Arthroscopy was performed on the MC joint using a lateralapproach and a medially-positioned instrument portal. Thevisible articular cartilage was removed with a manual curettefor debridement of the medial aspect of the joint.Subsequently the position of the arthroscope and the curettewere switched in the portal sites so the cartilage on thelateral aspect of the joint could be visualised and curetted.After debridement down to the subchondral bone, acancellous bone graft (approximately 4 mL) was aseptically

a) b) c)

Fig 1: Preoperative radiographs of left carpus of Case 2. (a) dorsolateral-palmaromedial oblique projection, (b) dorsopalmarprojection, (c) dorsomedial–palmarolateral oblique projection: severe multiple, comminuted and displaced fracture of the ulnar, theintermediate, and the fourth carpal bones (arrows).

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2 Minimally invasive carpal arthrodesis

collected from the ileal wing and injected into the MC jointthrough the lateral and medial arthroscopy portals using 3 mLsyringes with their tips cut off. The portals were then closed ina routine manner and the fluoroscope positioned in alateromedial direction. Debridement of the CMC jointcartilage was achieved using a drilling technique throughstab incisions. A 4.5 mm drill bit was inserted approximately2.5 cm laterally, dorsolaterally and dorsomedially and thedrilling was performed with a fanning technique (3 horizontaldirections for each insertion point) under fluoroscopicguidance. A longitudinal 3-4 cm skin incision was made onthe lateral aspect of the proximal third of the thirdmetacarpal bone (MCIII), after which a custom-madetunnelling tool/plate-passer (James and Richardson 2006) wasinserted under the skin (under fluoroscopic guidance) tocreate a subcutaneous tunnel in direct apposition to theperiosteum. The tunnelling tool was pushed over the thinfibrous CMC joint capsule and under the thick joint capsuleof the MC joint by pressing its tip against the distal aspect ofthe capsule, incising it through the skin and gliding the toolunder the capsule and under the synovial membrane(Supplementary Item 1). This was performed to be able toplace the plate close to the bone surface and createstability as the distance between the plate and the bonewas reduced and therefore allowing to anchor the carpalbones with angled nonlocking cortical screws. A similarincision was made on the proximal aspect of the MC jointcapsule to allow the tool to exit. A 7-hole narrow LCP platewas suitably contoured with radiographic control using aplate-bending press (Synthes). After verifying the appropriateplacement by fluoroscopy and radiography, stab incisionswere made through the most proximal and most distal holesof the plate after palpation of the depression of the platehole. LCP drill guides were inserted and radiographic andfluoroscopic images were again obtained before drilling holesin the MCIII and intermediate carpal bone, and inserting thelocking head screws (LHS) while pressing the plate firmlyagainst the bone. A 4.5 mm cortical screw was placed in theintermediate carpal bone using an angle in order to avoidentering the articulation between the intermediate carpalbone and the third carpal bone. An LHS was placed in thethird carpal bone, the remaining 3 distal holes were filled with2 LHS and a 4.5 mm cortical screw inserted using stabincisions in the McIII. This procedure was repeated on themedial side using a 7-hole broad LCP plate. The mostproximal hole was filled with a LHS inserted in the radialcarpal bone, the second proximal hole was a LHS insertedthe third carpal bone and the third most proximal hole wasfilled with a 4.5 mm cortical screw inserted in the third carpalbone. Three LHS and one 4.5 mm cortical screw wereanchored in the MCIII (Fig 2). The skin incisions were closed ina single layer using 1 USP monofilament polyamid (Ethilon).1 Afull limb fibreglass cast was applied and a head and tail ropesystem used to assist recovery, which was uneventful.Anaesthesia time was 5 h and surgical time was 3.25 h.

Case 2Premedication, sedation, induction and maintenance ofgeneral anaesthesia were similar to Case 1. The mare wasplaced in dorsal recumbency, with the limb attached to anelectrical winch. This positioning allowed a good alignmentof the limb in extension and radiographic control of theposition of the limb and the plates was easy to achieve

from all directions. General anaesthesia was maintained asdescribed for Case 1. The limb was aseptically preparedand draped for a pancarpal arthrodesis. The MC and ABCjoint were debrided using arthroscpy, the CMC joint wasdebrided with the drilling technique as described for Case 1.An arthroscopic motorised shaver device (Arthrex Shaverwith Oval FlushCut 8 Flute, 5.5 mm, 13 cm, Ref AR 8550FOE)2

was used to facilitate articular cartilage debridement in theMC and ABC joint. Cancellous bone graft (approximately6 mL) was collected from the sternum due to the position ofthe horse in dorsal recumbency. A technique described byRichardson et al. (1986) was used; briefly, a 7 cm incisionwas performed approximately 20 cm cranial to the xyphoid,the pectoral muscle was elevated and after removing theventral cartilage of the underlying forth and fifth sternebrae,the cancellous bone was removed using a large curetteand was injected into MC and ABC joint through thearthroscopy portals similar to Case 1. First, a 12-hole, 5.5 mmbroad LCP plate was placed dorsolaterally by tunnellingand using radiographic control. The plate was placed underthe MC and ABC joint capsule through stab incisions similarto Case 1. Five 5.0 mm LHS screws were anchored in thedistal radius, one LHS was anchored in the radial,intermediate and ulnar carpal bone, one 4.5 mm corticalscrew placed in lag fashion across the plate and thefractured C4 through stab incisions, and 3 LHS wereanchored in the MCIII. A second, 13-hole, broad 4.5 mmplate was placed dorso-medially and was stabilised with 4LHS in the distal radius and 4 LHS anchored in the MCIII(Figs 3 and 4). Again the plate was placed under the MCand ABC joint capsule. The skin was closed using acombination of skin sutures (same as Case 1) and skinstaples. Full limb fibreglass cast application and assistedrecovery was as described for Case 1. Total anaesthesiatime was 5 h and total surgery time 3.5 h.

ADPOSTOP

a) b)

ADPOSTOP

Fig 2: Case 1: Partial arthrodesis of the middle carpal andcarpometacarpal joints with 2 plates (one 7-hole broad lockingcompression plate dorsomedially and one 7-hole narrow lockingcompression plate dorsolaterally) 24 h post-operative radiographs.(a) Lateromedial projection, (b) DP projection. carpometacarpal[CMC], middle carpal [MC] joint or antebrachial carpal.

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O. Brandenberger et al. 3

Case 3Premedication, sedation, induction and maintenance ofgeneral anaesthesia were as described for Case 1. The horsewas placed in right lateral recumbency and prepared forpartial arthrodesis of MC and CMC joints. Cartilagedebridement of MC and CMC joints was achieved as inCase 2. Cancellous bone graft (approximately 4 mL) wascollected from the ileal wing and inserted through thearthroscopy portals of the MC joint. Three LCP plates wereapplied using the same minimally invasive technique underfluoroscopic and radiographic control. The decision to place

3 plates instead of 2 was made to allow placement of morescrews into both rows of the carpal bones in order to addstability to the construct (D. Richardson, personalcommunication, 2014). The plates were placed in adorsolateral (6-hole, narrow 4.5 mm), dorsomedial (7-holenarrow 4.5 mm) and axial (6-hole broad 4.5 mm) position andstabilised using a combination of 5.0 LHS and 4.5 mm corticalscrews. The proximal holes of all 3 plates were filled with LHSthat anchored the proximal row of the carpal bones. Thesecond most proximal holes of the dorsolateral anddorsomedial plate were filled with a 4.5 mm cortical screwthat was angled proximally in order to anchor the proximalrow of the carpal bones. The third, fourth most proximal andthe most distal holes of the axial plate were filled with 4.5 mmcortical screw at slight angles in order to avoid contact withthe LHS of the dorsolateral and dorsomedial plates (Fig 5).Skin closure, full limb fibreglass cast application and assistedrecovery was as described for Case 1. Total anaesthesia timewas 4.5 h and total surgery time 3 h.

Post-surgical management and outcome

Case 1The gelding was fully weightbearing directly after surgery.Treatment with sodium penicillin (Penicilline G, 22,000 iu/kgbwt. i.v.) and gentamicin (Forticine, 6.6 mg/kg bwt. i.v.) wascontinued for 5 days. Phenylbutazone (Phenylarthrite, 2.2 mg/kg bwt. i.v.) was given for 5 days and then dose wasreduced to 1.1 mg/kg bwt. i.v.) for another 10 days. The castwas removed standing 2 weeks after surgery and the skinsutures were removed at the same time. A sleeve (tube) castfrom proximal antebrachium to distal metacarpus wasapplied for 4.5 weeks to maintain the carpus in an extendedposition. A Robert Jones bandage was applied for 2 moreweeks. The horse was turned out on a large paddock4 months after surgery. Radiographs taken 8 months aftersurgery showed thickening of the periarticular tissues

a) b) c)

Fig 4: Case 2: pancarpal arthrodesis with 2 plates (one 12-hole, 5.5 mm broad locking compression plate and one 13-hole, 4.5 mmbroad locking compression plate) 36 h post-operative radiographs. (a) Lateromedial projection, (b) dorsopalmar projection, (c)dorsomedial–palmarolateral oblique projection.

Fig 3: Plate fixation using the locking compression plate drillguides through stab incisions.

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4 Minimally invasive carpal arthrodesis

(swelling), more pronounced dorsally. The LM projectionshowed bony fusion of the MC joint and new periosteal boneformation around the proximal part of the plates. Recurrentinflammation of the soft tissues on the dorsal aspect of thecarpus resulted in episodes of lameness and a subclinicalinfection without drainage was suspected. It was decided toremove the plates under general anaesthesia. No signs of pusor liquid around the plates were found intraoperatively andthe bacterial swab cultures of the plates were negative.Control radiographs immediately after plate removal showedankylosis of the MC joint with periarticular bone (osteophytes)dorsally and medially and marked narrowing of the CMCjoint space with periarticular bone formation (Fig 6). A fulllimb cast was applied for recovery and then replaced with aRobert Jones bandage that was left in place for 15 days untilremoval of the sutures. The horse was kept in the box foranother 15 days and was then hand walked for one month.Then the horse had hydrotherapic rehabilitation with an ovalwater horse walker (System Voncini)3 during a period of2.5 months. The first week, the horse was trained for 5 min/day, then the time of training was progressively increased to20 min/day during the next 3 weeks. Twelve months after theinitial surgical operation, examination by the authors revealedthat the horse was not lame at the walk and showed a 2/5AAEP lameness at the trot on a straight line. The owner wasadvised to use the horse as a leisure horse (ridden trot andlight gallop). Today, 3 years after surgery, the owner reportedthat the horse is used as a leisure riding horse and a video ofthe horse showed that it was lame free at the walk and atthe trot on a straight line. Carpal flexion is pain free and themaximal angle between the radius and the MCIII wascalculated from a picture at 42.6° (Tulloch et al. 2015).

Case 2The mare was fully weightbearing immediately after surgery.Antimicrobial treatment was continued for 10 days.Phenylbutazone (Phenylarthrite, 2.2 mg/kg bwt. i.v.) wasgiven for 8 days. As for Case 1, the cast was removed2 weeks after surgery and, at the same time, the skin suturesand staples were removed and a sleeve cast was applied.The sleeve cast was replaced by a modified Robert Jones fulllimb bandage 1.5 months after surgery (4 weeks after itsapplication) and the mare was discharged from the clinic9 weeks after surgery. The bandage was kept for anothermonth and was changed once a week.

A clinical examination 3 months after surgery revealedgrade 2/5 AAEP lameness (Swanson 1984) at the walk and 3/5 at the trot with an abnormal gait due to the mechanicalstiffness of the carpus. The radiographic evaluation at5 months revealed ankylosis of the MC and ABC joints andthinning of the CMC joint, periarticular bone formation(osteophytes) of all 3 joints (more pronounced laterally) withmild thickening of the periarticular tissues (Fig 7). Nine monthsafter surgery, the referring veterinarian reported, that thepainful part of the lameness had disappeared and a 2/5AAEP lameness at the trot remained due to the mechanicalstiffness; the mare still showed an altered gait but was able tolie down and get up and could gallop in the paddock.

Case 3As in Cases 1 and 2, the colt was comfortable in the castafter surgery and the antimicrobial treatment was continuedfor 5 days and anti-inflammatory medication were continuedas in Case 2. Two weeks after surgery, the cast and sutureswere removed standing and a sleeve cast was applied. Thecolt was discharged 15 days after surgery, the owner being

a) b)

A

Fig 5: Case 3: partial carpal arthrodesis of the middle carpal andcarpometacarpal joints with 3 plates (lateral 6-hole narrowlocking compression plate [LCP], medial 7-hole narrow LCP andsagittal 6-hole broad LCP), 24 h post-operative radiographs. (a)dorsolateral-palmaromedial oblique projection, (b) dorsopalmarprojection.

AD

a) b)

AD

Fig 6: Case 1: Partial arthrodesis of the middle carpal andcarpometacarpal joints with 2 plates, 8 months post-operativeradiographs immediately after removal of the plates. (a)Lateromedial projection, (b) dorsopalmar projection. Bonyankylosis of the MC, with severe periarticular bone osteophytes,more pronounced dorsally and medially. Severe thinning of thecarpometacarpal joint space, with marked periarticular boneosteophytes.

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O. Brandenberger et al. 5

instructed to keep the colt in the box for 1 month, have thecast removed after this time and then let the horse on asmall paddock for 1 month. Two and a half months aftersurgery, the colt was turned out in pasture. Radiographicexamination 3 months post-operatively showed beginning ofbony ankylosis of the MC and CMC with mild periarticularbone formation. The DMPLO views showed healing of thefracture line in the C2 and partial fusion of the bone with thehead of the proximal MCII. Ten months after surgery, a videoof the horse showed that it was sound at walk and trot andwas kept in pasture. Radiographs revealed ankylosis of theMC joint and marked thinning of the CMC joint. Carpalflexion was calculated from a picture at 44° (Tulloch et al.2015).

Discussion

We report a minimally invasive technique for partial andpancarpal arthrodesis using LCP in 3 horses. In all 3 cases,complete debridement of the visually apparent cartilage inthe MC (Cases 1, 2 and 3), and the ABC (Case 2), wasachieved with curettes and motorised (shaver) burrs, using astandard arthroscopy approach. Motorised burrs should beused with caution, specifically for cartilage removal, to avoidinadvertent or excessive bone trimming leading todestabilisation of the bones. James and Richardson (2006)described arthroscopic debridement of the cartilage, in acase of metacarpophalangeal/metatarsophalangealarthrodesis, as having the advantage of being thorough andaccurate, but the disadvantage of requiring significantlymore time. In our cases, arthroscopic debridement wascompleted quickly due to the arthroscopically noncomplexappearance of the MC and ABC joints. The arthroscope andthe instruments were switched so that all visually apparent

cartilage could be removed. We believe that, with the helpof a motorised shaver tool, arthroscopic debridement forcarpal arthrodesis can be completed within an acceptabletime. An alternative minimally invasive debridementtechnique is to drill the cartilage with a 5.5 mm drill bitinserted through several stab incisions. James and Richardson(2006) reported using this technique for minimally invasivemetacarpophalangeal/metatarsophalangeal and proximalinterphalangeal joint arthrodesis. This procedure is quick butthere is a possibility of incomplete cartilage removal. Webelieve that with the drilling technique there is a definite riskof incomplete cartilage removal, particularly in the MC andABC joint, (due to the different small bones, articular stepsand difficult fluoroscopic assessment). However, we did usedrilling to debride the rigid CMC joint. We used a horizontalfanning technique through 3 incisions and this resulted inradiographically visible bony fusion in all 3 cases. Use of thedrilling technique for treatment of CMC osteoarthritis isestablished and was evaluated on 12 client horses by Barberet al. (2009). It has also been used by Carpenter et al. (2008)for the CMC joint during a pancarpal arthrodesis procedure.

A minimally invasive approach was used to apply theplates. We made small skin incisions at the distal or proximalend of the plate and passed a custom-made tunnelling toolunder the skin and under the joint capsule to create asubcapsular, intrasynovial path for the plate. We then passedthe plate and applied screws through small skin incisions atthe level of the plate holes. The minimally invasive principle ofbone plate fixation was described by James and Richardson(2006) in a case series of 32 horses with lower limb injuries. Asingle plate was applied in all these cases, whereas 2 or 3plates were minimally invasively applied in our cases. Thisadded the difficulty of having to place the screws of oneplate without them interfering with the screws of the otherplate(s). In Cases 1 and 3, this step was facilitated byfluoroscopic image intensification, which also reduced theneed for numerous radiographs. Fluoroscopy was notavailable for Case 2 and radiological exposure for thesurgical team was probably higher than if an open approachhad been used. One advantage of the minimally invasiveapproach is the ease of skin closure. Skin closure can bechallenging with an open approach, where 2 or even 3plates are placed, and can require tension-relieving sutures(Carpenter et al. 2008) or even relief incisions. These were notnecessary in our cases and we were able to close all incisionswith simple skin sutures and/or staples. This easier closure ofthe incision might help to reduce surgery time. However, thetime taken to close the incisions was not recorded for any ofthe cases and would not be easy to compare with otherreports due to the small number of cases published. Thetension due to the subcutaneous plates was distributed overthe many small incisions and this facilitated healing of the skinincisions. In all 3 cases, incisional healing was excellent, rapid,without dehiscence or secondary healing, and the finaloutcome was cosmetically appealing.

LCPs were applied in all our cases. These plates wereinitially described by Levine and Richardson (2007), in a caseseries of fracture repair and distal limb arthrodesis in 31horses. They suggested the major advantage of such LCPswas the increased stability. The comfort of the horses aftersurgery in our report was good, and no loosened implants orscrews were observed, confirming the stability of theconstructs. Another advantage of LCPs cited by Levine and

a) b)

Fig 7: Case 2: pancarpal arthrodesis with 2 plates, 5 monthpost-operative radiographs. (a) Lateromedial projection, (b)dorsopalmar projection. Bony ankylosis of the middle carpal joint.Thinning of the antebrachial carpal and carpometacarpal jointspaces. Periarticular osteophytes of the antebrachial carpal,middle carpal and carpometacarpal joints, more pronouncedlaterally.

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Richardson (2007) was the reduced need for accurateanatomical plate contouring. Plate contouring, however, wasconsidered necessary in our cases as the small carpal boneswere fixed to the plate with 4.5 mm cortical screws in neutralor lag fashion. We used cortical screws in order to anchor asmuch of the small carpal bones as possible so as to increasestability. The application of cortical screws in a plate in anoncontact way could lead to screw loosening. Contouringthe plates proved challenging, as the minimally invasiveapproach did not allow direct visualisation of the bonecontours. Several radiographs or fluoroscopic imageintensification were required for this step. The number ofradiographic of fluoroscopic images is likely to be smaller inan open approach, pointing out a disadvantage of theminimal invasive approach. A third advantage of LCPmentioned by Levine and Richardson (2007) was that thethreaded drill guides were helpful when drilling and applyingthe screws through small incisions. We add that thesethreaded drill guides made it possible to determine theposition of the intended screw on radiographs and helped tohold the plate in place during insertion of the first LHS screw.We agree with Levine and Richardson’s comment that theuse of self-tapping LHS screws eliminates the time-consumingstep of tapping predrilled holes and would reduce surgerytime. LCP and LHS implants have the disadvantage of beingexpensive, and our 3 cases of carpal arthrodesis eachrequired 2 or 3 plates, leading to higher costs compared tothe dynamic compression plate system.

Reported complications after carpal arthrodesis includesupporting limb lameness, and infections of the incision andimplant (Auer and Lischer 2012). The minimal invasiveapproach for carpal arthrodesis might have reduced the riskfor infection in our cases. Minimally invasive plate fixation inhorses reduces the tissue exposed to contamination andkeeps the soft tissue envelope more intact than theconventional open approach (James and Richardson2006). In their publication, James and Richardsoncompared 10 minimally invasive metacarpophalangeal/metatarsophalangeal and proximal interphalangeal jointarthrodeses with 15 treated by conventional open approach.Only 4 of the 10 minimally invasive arthrodeses becameinfected, compared with 12 out of the 15 treated by openapproach. There was no significant difference between thesegroups; however, a tendency is visible and the authorssuggested that the minimally invasive arthrodesis techniquemay reduce morbidity and mortality of these procedures(James and Richardson 2006). For both partial and pancarpalarthrodesis, the incision required with the conventionalapproach is very long (up to 40 cm) (Carpenter et al. 2008)and therefore prone to postoperative infection. We report ourexperience of carpal arthrodesis using a minimal invasiveapproach in 3 cases and no infection occurred in this smallsample group. However, we suspected a chronic infection inCase 1 and removed the plates 8 months after surgery. Thebacteriological sample of the surgical site and plates werenegative and an inflammatory irritation or instability mighthave been the cause of the intermittent discomfort. Thehorse was comfortable after the removal of the plates. Webelieve that using the minimal invasive approach for carpalarthrodesis reduces this risk, because of less tissue beingexposed to contamination, less soft tissue trauma, tissuehandling and tissue dehydration (James and Richardson2006).

We found that the horses with the partial carpalarthrodesis (CMC and MC joints) had a nonpainful flexionwith remaining angles of 42.6° and 44°, 3 years (Case 1) and10 months (Case 3) after surgery, respectively. The remainingcarpal flexion was calculated by Tulloch et al. (2015) in anex vivo model to be 43 � 7.6° after MC/CMC arthrodesis. Theauthors speculated that this would allow a horse to be usedat a trot or slow canter and the outcome of our casessupports their statement, as both Cases 1 and 3 could trotand gallop without signs of lameness and Case 1 was usedas a leisure riding horse. Pancarpal arthrodesis is known to bea salvage procedure. The mare in our study showed gaitchanges due to the stiffness of the limb but was able to trotand gallop and could fulfil the intended use as a breedingmare.

The minimally invasive LCP plate fixation techniqueseems to be well suited for partial and pancarpal jointarthrodesis. Disadvantages include the greater radiologicalexposure, due to the multiple control radiographs requiredto correctly apply the plates and screws. Surgery time is notnecessarily shorter than with the standard open approachtechnique. The main advantages of the minimally invasiveapproach are easier closure and the lower exposure tocontamination.

Authors’ declaration of interests

No conflicts of interest have been declared.

Ethical animal research

No experimental animals were included in the study.

Authorship

F. Rossignol performed all surgeries and contributed to thepreparation of the manuscript. O. Brandenberger assisted inone surgery and wrote the manuscript. S. Bartke, T. VanBergen and A. Vitte all assisted in one surgery. All authorshave approved the final version of the manuscript.

Manufacturers' addresses1Ethicon, Issy Les Moulineaux, France.2Arthrex, Lezennes, France.3Kraft, Kraft Horse Walker, Frankenhardt-Hornhardt, Germany.

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Supporting information

Additional Supporting Information may be found in the onlineversion of this article at the publisher’s website:

Supplementary Item 1: Minimal invasive plate application forcarpal arthrodesis.

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