Angular Limb Deformities in Horses

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

2. Angular Limb Deformity
Causes:
(1) Uneven elongation of the physis
(2) Abnormal development of carpal or
tarsal 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, 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 after 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
• Less tolerance for variation from ideal conformation
• Cost of poor performance or reduced sales price outweighs
cost of surgery
– Show Horses
• Conformation 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
(1) Deformity too severe to correct by normal
growth
(2) Deformity that is correcting too slowly by normal
growth to achieve ideal conformation before the
growth plate closes
(3) 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
• 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)

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
– Correction of valgus deformity

52. Questions?