1.PASTERNARTHRODESISDane Tatarniuk, DVM

2. SIGNALMENT Presenting complaint: Chronic left forelimb lameness 20 years old Percheron / Quarter horse Mare Current use: Retired 3. HISTORY Chronic left forelimb lameness First noted October of 2011, attended by DVM #1 Recommendations: Rest, NSAIDs Lameness did not improve, slowly worsened. Evaluated by DVM #2 in April of 2012. Diagnosed straight sesamoidean desmitis by ultrasound. Recommendations: Rest, NSAIDs, Stem cell therapy (offered but not performed) Has not responded to rest/NSAID therapy; progressively hasworsened 4. PHYSICAL & LAMENESS EXAM Bright, alert, responsive Vital parameters within normal limits Passive Exam Atrophy of left pectoral muscle Marked left front soft tissue swelling, from fetlock distally to hoof capsule Hoof tester = negative Active Exam Lame at the walk on hard surface (Grade 4/5 - left front) 5. RADIOGRAPHS: JULY 30, 2012 6. DIAGNOSTICS - RADIOGRAPHS Palmer subluxation of left frontproximal inter-phalangeal joint Proximal phalanx osteophytes Dorsal, medial, lateral aspects Middle phalanx osteophytes Proximal-dorsal Decreased trabeculationdiffusely Dis-use osteopenia 7. PASTERN ANATOMY Low motion, high load joint Proximal phalanx bone (P1) Wider proximal vs. distal Distal aspect shaped with two condyles; separated by shallow axial groove Palpable tubercles on lateral/medial sides for origin of pastern collateralligaments Middle phalanx bone (P2) Half as long as P1 Both extremities equal width Proximal surface hollowed by axial ridge Proximal collateral tubercles Proximal-palmer border has smooth fibrocartilage Enlarges articular surface; site of insertion for ligaments 8. PASTERN ANATOMY Pastern (Proximal Inter-phalangeal) Joint Restricted low motion joint Paired axial & abaxial ligaments Origin: Palmer-distal P1 Insertion: Palmer-proximal P2 Straight sesamoidean ligament Origin: Base of proximal sesamoid bones Insertion: Fibrocartilage of palmer P2 Joint Capsule Dorsal and palmer pouch Pouches are smaller (compared to that of fetlock) 9. PASTERN ANATOMY Pastern (Proximal Inter-phalangeal) Joint Common digital extensor tendon Limited attachment on dorsal surface of P1 & P2 Superficial digital flexor tendon Attaches to distal tubercles of P1 & fibrocartilage ofP2 Interosseus muscle / suspensory ligament Insertion: Abaxial surface of proximal sesamoid bones Extensor branch: Extends dorsally to joincommon digital extensor tendon Distal digital annular ligament Origin: medial and lateral P1 Sling for palmer pastern ligaments Insertion: Palmer aspect of P111 10. DIAGNOSTICS - ULTRASOUND Ultrasound exam: Rupture of straight sesamoidean ligamentAdams Lameness, p348 -349 11. TREATMENT OPTIONS Non-surgical management: Electrical stimulation External coaptation with confinement Monoiodoacetate Ethyl alcohol Laser without implants Rarely successful remaining cartilage within joint Surgical management: Trans-articular lag screws Dorsal plate Combination dorsal plate & trans-articular lag screws 12. PASTERN ARTHRODESIS Plate / Lag Screw Combination Axial plate with two abaxial lag screws Biomechanical advantage Compression across entire joint Tensile forces induced at palmer aspect of joint by the plate neutralized by two oblique trans-articular lag screws Plate provides dorsal compression Commonly 3-hole or 4-hole dynamic compression plate Locking compression plate would be most novel ($) Some reports of two plates, T-plates, Y-plate, spoon plates Combine plate with two 5.5 screws placed in lag fashion (current standard) 13. PASTERN ARTHRODESIS Lag Technique Only Two or three tran-sarticular screws Parallel or diverging 4.5mm screws more likely to fail compared to 5.5mm screws Two 5.5mm screws similar strength compared to three 5.5mm screws Can be placed using a minimally-invasive (stab incision) approach Drawback: Minimal compression of dorsal surface Discomfort from excessive bone formation impinging on extensortendon and / or coffin joint 14. SURGICAL TECHNIQUE Inverted T incision Distal to metacarpal(tarsal)-phalangeal joint Ends 2cm proximal to coronary band Horizontal incision extends 4cm on either side of midline Dissect through subcutaneous tissue to commondigital extensor tendon Two triangular skin incisions dissected free andretracted back Transect the CDE tendon with inverted V incision Level of insertion of branches of suspensory apparatus Remove any bony proliferation, present on dorsal AOsurface Chisel & mallet 15. SURGICAL TECHNIQUE Transect joint capsule lateral/medial collateral ligaments dorsally Remove cartilage with curet, both articular surfaces Changes the radii of two opposing bones Reduces radius of proximal phalanx Increases radius of middle phalanx End result: Increased contact between opposing bones If not performed, cyclic screw failure can occur Can place cancellous bone between Osteostixis of both subchondral bone plates 2.5mm drill bit, 0.5cm apart 16. SURGICAL TECHNIQUE Extend foot - close pastern joint to normalanatomic position Place plate on dorsal surface Contour plate to bone, increase contact Two holes overlying distal proximal phalanx One hole overlying proximal middle phalanx Avoid extensor process, distal sesamoid bone Place two plate screws Proximal & distal Drill 4.0 mm thread hole perpendicular to phalanx Neutral & loading 17. SURGICAL TECHNIQUE Drill 5.5 mm glide hole for trans-articularscrew Middle phalanx wider than proximal; diverge screw Dorso-axial to palmaro(plantaro)-abaxial Enter joint halfway between dorsal & palmer(plantar)cortices Countersink used to create depression forscrew head Thread hole for trans-articular lag screwdrilled, tapped, and screwedLag Technique 4.5 Cortex Screw5.5 Cortex ScrewGliding Hole 4.5 mm 5.5 mmThread Hole3.2 mm 4.0 mmScrew Tap4.5 mm 5.5 mm 18. SURGICAL TECHNIQUE Tighten trans-articular screws, followed by tightening two bone platescrews Place final proximal bone plate screw in routine fashion Closure of CDE tendon, simple continuous, absorbable suture Skin closed using non-absorbable suture or staples 19. CAST PLACEMENT Objectives: Placed to protect fixation in recovery Support healing of soft tissue structures Provide addition fixation / stabilization of the joint Placement: Foam cast padding Stockinet Synthetic cast material Sets in 5 minutes, allows weight bearing in 30 minutes Permeable, yet still resistant to water 3-4 rolls circumferentially with 50% overlap 1-2 rolls in dorsal-palmer direction Methyl-methacrylate on solar surface 20. POST OPERATIVE CARE tube omeprazole, SID, PO Phenylbutazone Varies depending on comfort level Mostly - 1 gram phenylbutazone, BID, PO Occasionally 2 grams phenylbutazone in AM, 1 gram in PM, PO Twice daily physical examinations Check cast / check bandage splint Q6hr Monitor weight bearing, up/down Q1hr 21. POST OPERATIVE CARE Recheck radiographs taken on August 8th, 2012 7 days post-op Noted bending of trans-articular lag screws Recovery Largest force applied 22. POST OPERATIVE CARE First cast change on August 28th, 2012 Under general anesthesia Sutures removed from incision Appeared healthy Cast sores Moderate cast sore noted on the palmer fetlock Mild, superficial sore on the dorsal proximal cannon bone Silver sulfadiazine applied prior to second cast placement Recovery from anesthesia unremarkable Recheck radiographs no change in screw bending 23. CAST MANAGEMENT Cast Sores Dorsal-Proximal aspect of metacarpus / metatarsus III Compression at breakover or cast loosening Palmer / plantar aspect of fetlock; abaxial sesamoid Pressure applied during stance / load phase Signs Decreased weight bearing Suppuration through cast (flies) Swelling above cast Increased heat on palpation May necessitate early cast removal Other cast complications Breakage, osteopenia, joint stiffness, tendon laxity 24. POST OPERATIVE CARE September 7th, 2012 36 days post op Cast removal Cleaned wounds Bandaged leg Placed PCV splint Dorsal aspect Hoof wall to carpus 25. POST OPERATIVE CARE Recheck radiographs onSeptember 9, 2012 38 days post-op Noted mild to moderatehyperextension of the coffin joint Bending of screws static Intact No indication of infection Evidence of bony proliferation Joint fusion 26. OUTCOME Tuesday, September 25th 8 weeks out from surgery (54 days) Recheck radiographs revealed no further changes in implants Noted negative coffin bone angle EDSS shoes placed by farrier + trim Currently doing bandage with splint q12hr and bandage without splint q12hr 27. REHABILITATION Confine horse to stall rest Minimum 3 months Hand-walking is sometimes considered at 6 weeks post-op Small paddock turn-out following stall rest Additional 3 months Return to exercise / intended use Considered at 6 months post-op, in most cases Time from surgery to return to use ranges from 6 to 12 months 28. PROGNOSIS Success rates, forelimbs: 50 to 86% Success rates, hindlimbs: 80 to 95% Combining studies, overall success rate is 78% Complications reduce prognosis Post-operative pain Cast sores Incisional infections Implant infections Construct failure Distal inter-phalangeal joint pathology Support limb laminitis 29. LITERATURE Proximal interphalangeal joint arthrodesis using a combinationplate-screw technique in 53 horses. Knox et al. 2006 47% osteoarthritis 21% joint luxation 13% subchondral bone cysts 11% fractures 60% had 3 hole DCP, 32% had 4 hole DCP 93% wore cast for 14 days or less, only one cast applied 11% experienced cast sores on dorsal MC3/MT3 & back of fetlock Median hospitalization duration 25 days 30. LITERATURE Knox et al, continued. 87% used for intended use 81% forelimb 95% hindlimb 18% developed implant infections Enterbacter, Streptococcus, Staphylococcus, Pseudomonas 7% had implants removed PIP joint degeneration pre-op not predictive of post-op success Early cast removal: shorter hospitalization, improved comfort; butincreased cyclic load on implants 31. LITERATURE A Technique for Laser-Facilitated Equine Pastern ArthrodesisUsing Parallel Screws Inserted in Lag Fashion. Watts et al,2010. Sample size = 7 joints Diode laser, 2000 J of energy to joint 3 parallel 5.5mm lag screws Lag screws placed using stab incisions (minimally invasive) Bandage or bandage casts for 3 weeks Turn-out by 3 months Results: at 6 months 5 horses sound 4 horses with radiographic evidence of joint fusion 5 horses returned to intended use 2 horses with lameness / did not return to previous use 32. LITERATURE Watts et al, continued. Laser vaporization of synovial fluid, chondrocyte death Heating collagen contraction, joint capsule shrinking Decrease nerve innervation Decreased cost, decreased post-operative pain 1 horse had soft tissue necrosis at site of needle-laser insertion More dorsal peri-articular bone formation Further investigations: Histopathology of cartilage / ankylosis after laser Determine optimal laser dose 33. LITERATURE Minimally invasive plate fixation of lower limb injury in horses: 32cases James et. al, 2006 Articular cartilage removed using 5.5mm drill bit Stab incision to place tran-sarticular lag screws Small incision made over mid-P1, 3 cm length, proximal aspect ofsite Plate passing device Subtendinous tunnel created Plate (4 hole DCP) placed and aligned using fluoroscopicguidance Bone plate screws placed through stab incisions 34. LITERATURE James et al., continued. 5 joints treated for PIP arthrodesis All hindlimbs treated All 5 returned to previous function Decreases post-op pain, decreases post-operative hospitalization Maintaining soft tissue envelope decreases risk of infection Decreased exposure to OR air, surgical field contamination Increased tissue handling & tissue dehydration decreases tissue immunity Doubling of infection rate with each hour of surgery Less complete cartilage destruction? 35. LITERATURE Arthrodesis of the Equine Proximal Interphalangeal Joint: Abiomechanical comparison of two parallel headless, tapered,variable-pitched, titanium compression screws and two parallel5.5 mm stainless-steel cortical screws Wolker et al., 2009. Cadaver limbs, 10 each group 3-point bending materials-testing machine Force applied in dorsal-palmer direction Measured maximal bending moment at time of failure & composite stiffness No biomechanical difference between two screw types 1 horse in tapered group had failure at screws Rest in study failed at bone, not screw 36. LITERATURE Wolker et al., continued. Suggestion that tapered, headless screws: Are more biocompatible Decrease soft tissue irritation Increased bone-screw interface = increased fatigue resistance Titanium screws may be less inflammatory than stainless steel Tapered screws have continuous variable thread pitch alonglength Provides only 2mm compression Thought is that tapered screws would decrease dorsalproliferation seen with lag screw fixation (by itself) Need clinical study 37. LITERATURE Ethyl alcohol for chemical arthrodesis of the proximalinterphalangeal joint. Caston. 2010 AAEP. Abstract only Clinical cases of diagnosed pastern osteoarthritis Results: 19 out of 21 horses returned to intended use Not all cases had radiographic examination confirming joint fusion Average time till return to work was 8 months Each horse had multiple injections (minimum of 3 per horse) 3 horses had mild, transient complications what type not defined in abstract Suggestion that if surgical fusion is not an option, this may be analternative, more affordable technique 38. LITERATURE A limited surgical approach for pastern arthrodesis in horses withsevere osteoarthritis Jones et al., 2009. Retrospective of 12 pastern joints fused Joint was not dis-articulated Cartilage was not debrided Applied bone plate and trans-articular screws in standard fashion Results: Identified shorter hospitalization time & shorter surgical time Determined that 92% of cases decreased one grade of lameness 73% of owners would elect to do procedure again Poor retrospective 39. LITERATURE Distal limb cast sores in horses: Risk factors and early detectionusing thermography Levet et al., 2009. Prospective analysis: 70 horses Superficial dermal sore / deep dermal sore / full thickness sore Thermography prior to cast removal at coolest site, dorsal cannon bone, andpalmer/plantar fetlock Results: 80% had superficial dermal sore 34% had deep dermal sore 1% had full thickness sore No influence of type of injury, clipped skin, Incidence increased with duration of cast and age of horse 40. LITERATURE Levet et al., continued. Cosmetic blemish 5% - alopecia, leukotrichia, or scar Thermography Detects surface temperature via measuring infra-red radiation Performed in 35 cases Severity of sores associated with increasing temperature Measuring difference between location and coolest part of cast Cut off values for probable superficial dermal sore = 2.3 C difference Cut off value for probable deep dermal sore = 4.3 C difference 41. REFERENCES Auer JA: Arthrodesis techniques, in Auer JA, Stick JA (eds): Equine Surgery (ed 4).Philadelphia, PA, WB Saunders, 2006, pp 10731086 Johnson JE: Ringbone: treatment by ankylosis. Proc Am Assoc Equine Pract 20:6780, 1974 Knox, P.M. and Watkins, J.P. (2006) Proximal interphalangeal joint arthrodesis using acombination plate-screw technique in 53 horses (1994-2003). Equine vet. J. 38, 538-542. MacLellan, K., Crawford, W.H. and MacDonald, D.G. (2001) Proximal interphalangeal jointarthrodesis in 34 horses using two parallel 5.5-mm cortical bone screws. Vet. Surg. 30, 454-459. Read EK, Chandler D, Wilson DG: Arthrodesis of the equine proximal interphalangeal joint: amechanical comparison of 2 parallel 5.5 mm cortical screws and 3 parallel 5.5 mm corticalscrews. Vet Surg 34:142147, 2005 Schaer, T.P., Bramlage, L.R., Embertson, R.M. and Hance, S. (2001) Proximal interphalangealarthrodesis in 22 horses. Equine vet. J. 33, 360-365. Stashak TS: The Pastern, in Stashak TS (ed): Adams Lame- ness in Horses (ed 5).Philadelphia, PA, Lippincott, Wil- liams & Wilkins, 2002, pp 733741 Watt BC, Edwards RB, Markel MD, et al: Arthrodesis of the equine proximal interphalangealjoint: a biomechanical comparison of three 4.5mm and two 5.5mm cortical screws. Vet Surg30:287294, 2001