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Angular Limb Deformities in Horses

Angular Limb Deformities in Horses

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  • Carpal and tarsal bones ossify within the 2-3 weeks prior to birth.
  • Congenital vs. acquired – before or after birth,

Angular limb deformity Angular limb deformity Presentation Transcript

  • Angular Limb DeformitiesDane Tatarniuk, DVMJune 26th, 2013
  • Angular Limb DeformityCauses:(1) Uneven elongation of the physis(2) Abnormal development of carpal ortarsal bones(3) Ligamentous laxity• Valgus = Deviation towards the lateral plane• Varus = Deviation towards the medial plane• A deviation, either in the lateral or medial direction, inthe frontal plane of the limb• Best viewed from the cranial/dorsal aspect of limb
  • Bone Development• Bone requires pre-existing connective tissuematrix to develop• Bone formation(1) Intramembranous ossification• Primitive connective tissue• Flat bones of skull and mandible(2) Endochondral ossification• Pre-existing cartilage is converted to bone• Appendicular bones, axial skeletal bones, pelvis(3) Ectopic ossification• Connective tissue not normally converted to bone ossifies
  • Endochondral Ossification• Mesenchymal stem cellsdifferentiate intochondrocytes– Hyaline cartilage laid out as atemplate of the bone to beformed– Matrix composed of type 2collagen• Soft, flexible• Different centers ofossification arise– Diaphysis• Primary center– Epiphysis• Secondary center
  • Endochondral Ossification• Ossification centers characterized byenlargement of chondrocytes– Glycoprotein accumulates intracellular,cytoplasm becomes vacuolated• Lacunae expands– Potential space within cartilage matrixcontaining osteocytes• Calcium phosphate accumulates oncartilage matrix
  • Endochondral Ossification• Cartilage calcifies and hypertrophiedchondrocytes undergo apoptosis– Within interior of the cartilage model• Perichondrium is activated– Cells lining the cartilage model that develops intoperiosteum– Blood vessels extend in, bring osteoprogenitor cells• Become osteoblasts• Osteoblasts concentrate on surface of calcifiedcartilage– Deposit bone matrix
  • Endochondral Ossification• Bone & cartilage matrix mineralizes– Collagen fibers (in combo with glycoproteins,chondroitin sulfate) act as catalyst– Transforms calcium & phosphate into solid mineraldeposit on collagen fibers
  • Endochondral Ossification• Primary vs. Secondary Centers(1) Epiphyseal ossification center does not replaceall of epiphyseal cartilage• Becomes articular cartilage(2) Transverse disk of epiphyseal cartilage remainsbetween epiphysis & diaphysis• Growth plate, or physis
  • Growth in Length• Chondrocytes within thephysis arrange incolumns running parallel– Columns separated bythin cartilage strips• Cells of growth platearrange in specific layersto promote growth inlength
  • Growth in Length• Zone of Rest– Normal hyaline cartilage• Zone of Proliferation– Farthest to diaphysis– Chondrocytes dividing• Zone of Maturation /Hypertrophy– Enlargement of chondrocytes• Zone of Calcification– Chondrocytes die– Matrix begins to calcify• Zone of Ossification– Osteoprogenitor cells invade– Osteoblasts calcify matrix alongcalcified cartilage
  • Growth in Length• Zone of Proliferationadvances growth plateaway from diaphysis• Osteoclasts convertprimary spongiosa to truebone at diaphyseal side ofgrowth plate• Net result– Growth plate remains samelength while the length ofbone continues to grow
  • Growth in Length• Once bone has reached mature length,proliferation of cartilage cells slows to halt• Replacement of cartilage with bone atdiaphyseal side of physis continues• Eventually, entire physis is replaced by bone– Growth plate closes– Trabeculae of epiphyses and diaphysis iscontinuous
  • Wolff’s Law• Healthy bone adapts tophysiologic load which is applied– Change in external state andinternal architecture– Principle of bone remodelling• If loading increases, bone willremodel to become stronger toresist that load• If load decreases, bone willbecome weaker as a response
  • Physeal Growth• Cells in the physis that are loaded more, growfaster• Cells in the physis that are loaded less, growslower• This response continues, ideally, so that thebone grows in length to compensate forwhere the majority of the load is imparted• Dynamic (physiologic) loading is beneficial– Loading is intermittent
  • Static Compression• Static (pathological) compression is detrimental– Cells in the physis are loaded to far and growthretarded– If compression is uniform, limb remains straight butshorter than its potential growth– If compression is not uniform, limb will deviate towardsthe more compressed side of the physis• Effects of static compression (Farnum 2000)– Prolonged rate of DNA synthesis during proliferation– Reduction of chondrocyte kinetic parameters
  • Physeal Growth Plate Closure• All physis within long bones are under influenceof timed physeal growth• Physis within the same bone or between differentbones will close at different times
  • Growth Plate Closure• The distal radial physis is open for up to 2years– Majority of growth occurs by 6 months• Evaluate once/month for first 6 months– Thereafter, slow growth up to 1-2 years– Treatment intervention often performed after 3months– Final closure occurs at mean of 24.7 months (Fretz1984)
  • Growth Plate Closure• The distal metacarpal/tarsal physis is openfor up to 3 months– Majority of growth occurs by 2 months– Treatment intervention at 4 to 8 weeks– Require much quicker evaluation early on in life• Evaluate once/week from birth to 6 weeks of life• Majority of distal tibial physis growth occursby 4 months
  • ALD Etiology
  • D.O.D. Incidence• Retrospective study (McIlwraith)– Developmental Orthopedic Disorder in 193 of 1711 TBfoals• D.O.D. = ALD, flexoral deformity, OCD, physitis, juvenilearthritis, wobblers– 156 of 193 involved physis (72.9% of cases)• 92 of 193 = A.L.D.• 64 of 193 = physitis– Peak incidence occurred between weanling & end ofDecember– 11.3% of D.O.D cases required treatment intervention
  • ALD Incidence• Prevalence:– ALDs requiring intervention = 4.7% (Wolhfender 2009)• Carpal valgus more than carpal varus• Fetlock varus more than fetlock valgus• Hock valgus more than hock varus• Carpal valgus can be a normal deformity in theyoung foals– Many will correct as the foal ages and chest widens– Up to 5° carpal valgus considered normal (Bramlage1990) until age of weanling
  • Indication for ALD Intervention• Economic impact– Thoroughbred & Standardbred industry– Sales price influenced by conformation of horse• Discipline– Most horses can compensate for mild to moderateALDs if low level work is goal– Racing• Less tolerance for variation from ideal conformation• Cost of poor performance or reduced sales price outweighscost of surgery– Show Horses• Conformation often judged to place one horse over anotherin a class
  • Not all ALDs are bad• One conformational fault may be negated byanother conformational fault• Example:– Off-set knee, where-in distal limb at radio-carpaljoint appears displaced laterally relative to radius• Creates increased loading of medial aspect of carpus– In this case, a carpal valgus would be beneficial as itwould increase loading on the lateral aspect of thecarpus
  • Diagnostics• Visual Exam– Rotation of the limb can skew theappearance of angularity• ie, standing in front of foal thefetlock often appears to be valgus.when in front of limb, fetlock isfound to truly be straight or varuswith external rotation of entire limb(toe out conformation)– Line up in front of the limb, notthe foal– Corrects as the chest widens andpushes elbows outwards
  • Diagnostics• Flexion of Limb– Helps decrease influence of rotation of limb– Flex the joint wherein angular deformity is suspect• Improves visual assessment of whether ALD truly exists– Valuable when multiple joint ALDs are present insame limb• ie, both fetlock varus and carpal valgus– Lateral to medial flexion can help determine if ALDcan be manually straightened• Carpal/tarsal bone or ligamentous instability
  • Diagnostics• Active Movement Exam– Watch the foal at the walk– Excessive, exaggeratedmovement of the joint mayindicate ligamentous laxity– Watch for winging or paddlingmovement of the joint ofinterest during the walk
  • Diagnostics• Radiographic Exam– Dorsal-Palmar/Plantar• +/- Lateral– Sufficient radiographic image of longbone on either side of suspect joint• To mid-diaphysis– Near perfect positioning throughmidline of sagittal plane• Measurement– Draw lines down the sagittal plane ofboth bones– Where the lines intersect is where theALD originates• Concurrent exam for physitis,cuboidal bone pathology, etc.
  • Therapy• Need to determine why the ALD exists– Laxity vs. cubodial bone vs. physeal growth disparity• Ligamentous laxity & normal ossification– Gradual increase in exercise to strengthen musclesand soft tissues• Abnormal ossification– Stall rest to prevent osteoarthritis, further damage tocuboidal bone– Application of splint to maintain limb in normalvertical axis (without angulation)• Do not incorporate toe in splint, to help strengthen peri-articular soft tissues
  • Therapy• Correction without intervention– Using the principles of dynamic loading of physealgrowth• Concave side of physis will grow faster than convex side• Foals will self correct the angulation when given acontrolled exercise pattern– Requirements• Physeal growth is responding dynamic, not static,compressive forces• An acceptable amount of physeal growth potentialremains
  • Farrier Therapeutics• Helps maintain normal dynamic compressive forces• Rasp/lower either the lateral or medial aspect of the limb• Varus deformity- Trim the medial aspect of the limb- Distributes more dynamic forces onthe medial, or convex, aspect of thephysis- Dynamic forces stimulate growthalong the convex side of the ALD• Valgus deformity- Trim the lateral aspect of the limb- Distributes dynamic forces on thelateral, or convex, aspect of the physis
  • Farrier Therapeutics• Hoof wall extensions– Either on lateral or medialaspect– “Dalric” glue-on shoes• Valgus deformity– Requires a medial extension• Varus deformity– Requires a lateral extension
  • Surgical Therapy• Indications for surgical intervention(1) Deformity too severe to correct by normalgrowth(2) Deformity that is correcting too slowly by normalgrowth to achieve ideal conformation before thegrowth plate closes(3) Deformity that creates a secondaryconformation abnormality or a secondary injuryin the limb• Requires growth potential at growth plate
  • Periosteal Stripping• “Hemi-circumferential periosteal transection”• Theory:– Periosteum is opposing force to normal physealgrowth of bone when static compression has occurred• Procedure:– Transection of periosteum on the slower growing sideof physis (concave aspect)– ‘Growth Acceleration’• Lower risk of complications• Field procedure
  • Periosteal Stripping• Carpal valgus– 3 cm vertical skin incision between common &lateral digital extensor tendon• Start from point 5 cm proximal to distal physis of radiusand continue proximally– Incise down to periosteum– Blunt dissect subcutaneous tissue and tendonsfrom periosteum– Curved scalpel blade (#12) to transect theperiosteum• Severs rete carpi volaris = bleeding• Periosteum transected in an inverted T fashion– Elevate the two triangular flaps using periostealelevators– If rudimentary ulna is ossified, remove withrongeurs (tether)– Routine closure subcutaneous tissue & skin
  • Periosteal Stripping• Fetlock varus– Similar procedure– Distal-most aspect ofmetaphysis of MC3/MT3, onmedial aspect– Be careful not to enterpalmar/plantar out-pouch offetlock joint– Periosteum of MC3/MT3 ismuch thinner compared toradius
  • Periosteal Stripping• Tarsal Valgus– Either cranial or caudal tothe lateral digital extensortendon– Periosteum of tibia isthicker than that of theradius
  • Periosteal Stripping• ‘Bench Knees’– Result of two opposingALDs• Valgus deformity from distalradius• Varus deformity of proximalthird of MC3– Limb appears straight– If noted in first 2 months oflife, can be treated withstripping over total lengthof MC3 using an I-shapedincision
  • Transphyseal Screw & Wire• Described in 1977• ‘Growth Retardation’– Applied to the convex side to bridge the physis• Two 4.5mm screw implants placed through stabincisions– Not completely tightened• Tissue between stab incisions is elevated withhemostat• 18 gauge wire loop placed around screw heads infigure-8 pattern– Twist wire over proximal screw head for bettercosmetic result• Tighten screw heads• Closure of subcutaneous tissue & skin routinely
  • Transphyseal Screw• Described in 2004• ‘Growth Retardation’– Placed on convex aspect of ALD• Advantages– Cosmetic– Less implant placed– Simpler surgical technique• Technique– Place cortical screw through metaphysis,across physis, into epiphysis– 4.5mm screw in distal radius / tibial physis– 3.5mm screw in distal MC3/MT3 physis
  • Transphyseal Screw• Less common use in distal radial / tibialphysis– More prone to physitis• Metaphyseal collapse– Weak internal architecture of themetaphysis due to inflammation• Collapses when the bone cannot supportnormal weight any longer– Very acute change in angulation of thelimb– Accompanied by pain and increasedlameness– Can occur delayed, after the screw hasbeen removed (up to 5 months after)
  • Implant Removal• Careful observation of the limb on a weeklybasis– Consensus between veterinarian, owner, trainerthat the limb has corrected adequately• Removal of implants– Standing, sedated or short-term general anesthesia– Identify screw head, stab incision• Can use radiographs for assistance– Remove screw, careful not to strip or break thescrew upon removal
  • • 199 TB foals that had periosteal transection• Racing records compared to 1017 siblings• Evaluated starting status, -2/-3/-4 yr old starts, earnings,earnings/start, starts percentile ranking order• Distal metacarpal/metatarsal HCPT– Fewer 2-year-old starts (1.09 vs 2.19)– Did not have a significantly different SPR or lower startingpercentage, vs. controls• Distal radial HCPT– Lower starting percentage (48 vs 55%)– Fewer 2-year-old starts (1.22 vs 1.70)– Lower SPR (32.53 vs 53.32)
  • • 10 healthy foals, prospective study• Study design:– At 30 days, transphyseal bridge implants placed laterally– Implants removed at 90 days or when 15 degrees angulationachieved– Same time, periosteal transection performed on concave aspectof limb– Sham surgery performed on control limb– Confined to small pens– Feet were rasped once/week to maintain lateral-medial balance– D.P. radiographs taken at 0, 2, 4, 6, 8, 48 weeks post-stripping
  • • Blinded radiographicmeasurement of ALDs• No difference betweenstripped limbs andcontrolled limbs from 30days to 1 year of age
  • • Soft tissue swelling that developed at the site ofperiosteal transection gave visual appearance of astraighter conformation– However radiographic measurement revealed no significantdifference in angulation• Critics of the paper will note that:– ALDs were induced by uneven physeal compression, and notfrom physeal trauma– 15 degrees angulation– Controlled prospective clinical trial performed in artificiallyinduced ALDs, not naturally occurring cases
  • • Screw & tension band loop wire technique vs. singletransphyseal screw in distal radius• Age range 261 – 457 days• n = 568 yearlings– S & W = 253– S.T.S. = 315• Mean age at surgery 383 days (S.T.S.) vs. 368 days (S & W)• S.T.S. left in for a significantly shorter amount of time (mean= 38 days vs. 54 days S & W)• No difference between gender, limb, lateral/medialplacement• Complications identified by any horse that required repeatx-rays following implant insertion
  • • Physitis and metaphyseal collapse occurred moreoften with S.T.S.• No difference in complication rate for seroma, infection,and over-correction between the two techniques
  • • Evaluated gender, surgery, screw removal date, surgicalsite, appearance, limb(s) affected, ALD type, ALDdegree deviation– Compared to siblings who did not undergo surgery• 53 varus carpi– Mean age for placement of T.S. was 398 days– Mean varus angularity was 3.1 degrees– Mean days till screw removal was 39 days– 6 horses developed cosmetic blemish at surgical site• Results– No statistical difference in yearling sales price– No significant effect of STS was seen on ability to start orwin a race
  • • Impression was that physitis (seen in older yearlings)indicated physis still open• Believe that S.T.S. induced changes quicker due toimmediate static compression• Screw & Wires have lag phase where limb has to grow toinduce further compressive forces• In a few limbs, screw was removed when limb wasdetermined to be perfectly straight and the limbcontinued to straighten past the desired angle• Therefore advocate removal of screw at 90 – 95% ofdesired angle
  • • Radial shock wave generator– 3 bar, 15 Hz, 2000 cylces performed weekly– Application to the convex aspect of the limb– All of the limbs straightened between 15 and 76days• Mean 25 days– No mechanism of action proposed
  • • 5 month, 52kg, male donkey• Chronic healing SH type 2 fracture ofproximal radius & transverse fractureof ulna– 30 degree acquired valgus deformity• Transverse osteotomy 3cm distal tooriginal fracture• Adjustable hinged external ringfixator• Applied 1mm distraction per day• 48 days post-op– Removed fixator• 76 days post-op– Bony callus at osteotomy site– Correction of valgus deformity
  • Questions?