Angular limb deformity

Angular Limb Deformities in Horses

1. Angular Limb Deformities Dane Tatarniuk, DVM June 26 th , 2013

2. Angular Limb Deformity Causes: Uneven elongation of the physis Abnormal development of carpal or tarsal bones Ligamentous laxity Valgus = Deviation towards the lateral plane Varus = Deviation towards the medial plane A deviation, either in the lateral or medial direction, in the frontal plane of the limb Best viewed from the cranial/dorsal aspect of limb

3. Bone Development Bone requires pre-existing connective tissue matrix 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

4. Endochondral Ossification Mesenchymal stem cells differentiate into chondrocytes Hyaline cartilage laid out as a template of the bone to be formed Matrix composed of type 2 collagen Soft, flexible Different centers of ossification arise Diaphysis Primary center Epiphysis Secondary center

5. Endochondral Ossification Ossification centers characterized by enlargement of chondrocytes Glycoprotein accumulates intracellular, cytoplasm becomes vacuolated Lacunae expands Potential space within cartilage matrix containing osteocytes Calcium phosphate accumulates on cartilage matrix

6. Endochondral Ossification Cartilage calcifies and hypertrophied chondrocytes undergo apoptosis Within interior of the cartilage model Perichondrium is activated Cells lining the cartilage model that develops into periosteum Blood vessels extend in, bring osteoprogenitor cells Become osteoblasts Osteoblasts concentrate on surface of calcified cartilage Deposit bone matrix

7. Endochondral Ossification Bone & cartilage matrix mineralizes Collagen fibers (in combo with glycoproteins, chondroitin sulfate) act as catalyst Transforms calcium & phosphate into solid mineral deposit on collagen fibers

8. Endochondral Ossification Primary vs. Secondary Centers (1) Epiphyseal ossification center does not replace all of epiphyseal cartilage Becomes articular cartilage (2) Transverse disk of epiphyseal cartilage remains between epiphysis & diaphysis Growth plate, or physis

9. Growth in Length Chondrocytes within the physis arrange in columns running parallel Columns separated by thin cartilage strips Cells of growth plate arrange in specific layers to promote growth in length

10. 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 along calcified cartilage

11. Growth in Length Zone of Proliferation advances growth plate away from diaphysis Osteoclasts convert primary spongiosa to true bone at diaphyseal side of growth plate Net result Growth plate remains same length while the length of bone continues to grow

12. Growth in Length Once bone has reached mature length, proliferation of cartilage cells slows to halt Replacement of cartilage with bone at diaphyseal side of physis continues Eventually, entire physis is replaced by bone Growth plate closes Trabeculae of epiphyses and diaphysis is continuous

13. Wolff’s Law Healthy bone adapts to physiologic load which is applied Change in external state and internal architecture Principle of bone remodelling If loading increases, bone will remodel to become stronger to resist that load If load decreases, bone will become weaker as a response

14. Physeal Growth Cells in the physis that are loaded more, grow faster Cells in the physis that are loaded less, grow slower This response continues, ideally, so that the bone grows in length to compensate for where the majority of the load is imparted Dynamic ( physiologic ) loading is beneficial Loading is intermittent

15. Static Compression Static ( pathological ) compression is detrimental Cells in the physis are loaded to far and growth retarded If compression is uniform, limb remains straight but shorter than its potential growth If compression is not uniform, limb will deviate towards the more compressed side of the physis Effects of static compression ( Farnum 2000) Prolonged rate of DNA synthesis during proliferation Reduction of chondrocyte kinetic parameters

16. Physeal Growth Plate Closure All physis within long bones are under influence of timed physeal growth Physis within the same bone or between different bones will close at different times

17. Growth Plate Closure The distal radial physis is open for up to 2 years 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 a fter 3 months Final closure occurs at mean of 24.7 months ( Fretz 1984)

18. Growth Plate Closure The distal metacarpal/tarsal physis is open for 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 occurs by 4 months

19. ALD Etiology

20. D.O.D. Incidence Retrospective study (McIlwraith) Developmental Orthopedic Disorder in 193 of 1711 TB foals D.O.D. = ALD, flexoral deformity, OCD, physitis, juvenile arthritis, 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 of December 11.3% of D.O.D cases required treatment intervention

21. 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 the young foals Many will correct as the foal ages and chest widens Up to 5° carpal valgus considered normal ( Bramlage 1990) until age of weanling

22. Indication for ALD Intervention Economic impact Thoroughbred & Standardbred industry Sales price influenced by conformation of horse Discipline Most horses can compensate for mild to moderate ALDs if low level work is goal Racing L ess tolerance for variation from ideal conformation Cost of poor performance or reduced sales price outweighs cost of surgery Show Horses C onformation often judged to place one horse over another in a class

23. Not all ALDs are bad One conformational fault may be negated by another conformational fault Example: Off-set knee, where-in distal limb at radio-carpal joint appears displaced laterally relative to radius Creates increased loading of medial aspect of carpus In this case, a carpal valgus would be beneficial as it would increase loading on the lateral aspect of the carpus

24. Diagnostics Visual Exam Rotation of the limb can skew the appearance of angularity ie, standing in front of foal the fetlock often appears to be valgus. when in front of limb, fetlock is found to truly be straight or varus with external rotation of entire limb (toe out conformation) Line up in front of the limb, not the foal Corrects as the chest widens and pushes elbows outwards

25. 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 in same limb ie, both fetlock varus and carpal valgus Lateral to medial flexion can help determine if ALD can be manually straightened Carpal/tarsal bone or ligamentous instability

26. Diagnostics Active Movement Exam Watch the foal at the walk Excessive, exaggerated movement of the joint may indicate ligamentous laxity Watch for winging or paddling movement of the joint of interest during the walk

27. Diagnostics Radiographic Exam Dorsal-Palmar/Plantar +/- Lateral Sufficient radiographic image of long bone on either side of suspect joint To mid-diaphysis Near perfect positioning through midline of sagittal plane Measurement Draw lines down the sagittal plane of both bones Where the lines intersect is where the ALD originates Concurrent exam for physitis, cuboidal bone pathology, etc.

28. 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 muscles and soft tissues Abnormal ossification Stall rest to prevent osteoarthritis, further damage to cuboidal bone Application of splint to maintain limb in normal vertical axis (without angulation) Do not incorporate toe in splint, to help strengthen peri-articular soft tissues

29. Therapy Correction without intervention Using the principles of dynamic loading of physeal growth Concave side of physis will grow faster than convex side Foals will self correct the angulation when given a controlled exercise pattern Requirements Physeal growth is responding dynamic, not static, compressive forces An acceptable amount of physeal growth potential remains

30. 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 on the medial, or convex, aspect of the physis Dynamic forces stimulate growth along the convex side of the ALD Valgus deformity Trim the lateral aspect of the limb Distributes dynamic forces on the lateral, or convex, aspect of the physis

31. Farrier Therapeutics Hoof wall extensions Either on lateral or medial aspect “ Dalric ” glue-on shoes Valgus deformity Requires a medial extension Varus deformity Requires a lateral extension

32. Surgical Therapy Indications for surgical intervention Deformity too severe to correct by normal growth Deformity that is correcting too slowly by normal growth to achieve ideal conformation before the growth plate closes Deformity that creates a secondary conformation abnormality or a secondary injury in the limb Requires growth potential at growth plate

33. Periosteal Stripping “Hemi-circumferential periosteal transection” Theory: Periosteum is opposing force to normal physeal growth of bone when static compression has occurred Procedure: Transection of periosteum on the slower growing side of physis (concave aspect) ‘Growth Acceleration’ Lower risk of complications Field procedure

34. 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 radius and continue proximally Incise down to periosteum Blunt dissect subcutaneous tissue and tendons from periosteum Curved scalpel blade (#12) to transect the periosteum Severs rete carpi volaris = bleeding Periosteum transected in an inverted T fashion Elevate the two triangular flaps using periosteal elevators If rudimentary ulna is ossified, remove with rongeurs (tether) Routine closure subcutaneous tissue & skin

35. Periosteal Stripping Fetlock varus Similar procedure Distal-most aspect of metaphysis of MC3/MT3, on medial aspect Be careful not to enter palmar/plantar out-pouch of fetlock joint Periosteum of MC3/MT3 is much thinner compared to radius

36. Periosteal Stripping Tarsal Valgus Either cranial or caudal to the lateral digital extensor tendon Periosteum of tibia is thicker than that of the radius

37. Periosteal Stripping ‘Bench Knees’ Result of two opposing ALDs Valgus deformity from distal radius Varus deformity of proximal third of MC3 Limb appears straight If noted in first 2 months of life, can be treated with stripping over total length of MC3 using an I-shaped incision

38. Transphyseal Screw & Wire Described in 1977 ‘Growth Retardation’ Applied to the convex side to bridge the physis Two 4.5mm screw implants placed through stab incisions Not completely tightened Tissue between stab incisions is elevated with hemostat 18 gauge wire loop placed around screw heads in figure-8 pattern Twist wire over proximal screw head for better cosmetic result Tighten screw heads Closure of subcutaneous tissue & skin routinely

39. 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

40. Transphyseal Screw Less common use in distal radial / tibial physis More prone to physitis Metaphyseal collapse Weak internal architecture of the metaphysis due to inflammation Collapses when the bone cannot support normal weight any longer Very acute change in angulation of the limb Accompanied by pain and increased lameness Can occur delayed, after the screw has been removed (up to 5 months after)

41. Implant Removal Careful observation of the limb on a weekly basis Consensus between veterinarian, owner, trainer that 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 the screw upon removal

42. 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 starting percentage, vs. controls D istal 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 )

43. 10 healthy foals, prospective study Study design: At 30 days, transphyseal bridge implants placed laterally Implants removed at 90 days or when 15 degrees angulation achieved Same time, periosteal transection performed on concave aspect of 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

44. Blinded radiographic measurement of ALDs No difference between stripped limbs and controlled limbs from 30 days to 1 year of age

45. Soft tissue swelling that developed at the site of periosteal transection gave visual appearance of a straighter conformation However radiographic measurement revealed no significant difference in angulation Critics of the paper will note that: ALDs were induced by uneven physeal compression, and not from physeal trauma 15 degrees angulation Controlled prospective clinical trial performed in artificially induced ALDs, not naturally occurring cases

46. Screw & tension band loop wire technique vs. single transphyseal 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/medial placement Complications identified by any horse that required repeat x-rays following implant insertion

47. Physitis and metaphyseal collapse occurred more often with S.T.S . No difference in complication rate for seroma , infection, and over-correction between the two techniques

48. Evaluated gender, surgery, screw removal date, surgical site, appearance, limb(s) affected, ALD type, ALD degree 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 or win a race

49. Impression was that physitis (seen in older yearlings) indicated physis still open Believe that S.T.S. induced changes quicker due to immediate static compression Screw & Wires have lag phase where limb has to grow to induce further compressive forces In a few limbs, screw was removed when limb was determined to be perfectly straight and the limb continued to straighten past the desired angle Therefore advocate removal of screw at 90 – 95% of desired angle

50. 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 76 days Mean 25 days No mechanism of action proposed

51. 5 month, 52kg, male donkey Chronic healing SH type 2 fracture of proximal radius & transverse fracture of ulna 30 degree acquired valgus deformity Transverse osteotomy 3cm distal to original fracture Adjustable hinged external ring fixator Applied 1mm distraction per day 48 days post-op Removed fixator 76 days post-op Bony callus at osteotomy site C orrection of valgus deformity

52. Questions?