Angular Limb Deformities

Dane Tatarniuk, DVMJune 26th, 2013

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

ALD Etiology

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

Periosteal Stripping

• Tarsal Valgus– Either cranial or caudal to

the lateral digital extensor tendon

– Periosteum of tibia is thicker than that of the radius

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

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

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 / 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)

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

• 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)

• 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

• Blinded radiographic measurement of ALDs

• No difference between stripped limbs and controlled limbs from 30 days to 1 year of age

• 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

• 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

• 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

• 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

• 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

• 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

• 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

Questions?