2.21 Developmental Abnormalities of Bones

What are examples of developmental bone abnormalities?

1. Angular limb deformity (ALD)

2. Physitis

3. Physeal fractures (Salter-Harris fractures)

4. Defects of the spine

5. Digit malformation

6. Rickets

What is an angular limb deformity (ALD)?

A skeletal defect where a portion of the limb is bent inward or outward at an abnormal angle from the midline of the body.

Which direction does valgus bend the limb?

Inward/medial.

Which direction does varus bend the limb?

Outward/lateral.

Which limb deformity is more common in newborn foals, valgus or varus?

Valgus. Often grow out of it.

Which ALD is more severe?

Varus.

Which joints are most commonly affected by angular limb deformities?

Carpus, and sometimes tarsus and fetlocks.

What types of factors may cause ALD?

• Perinatal factors

• Developmental factors

What are the common perinatal factors contributing to angular limb deformities?

Premature birth, twin pregnancy, placentitis, perinatal soft tissue trauma, and poorly calcified bone.

What are the developmental factors contributing to angular limb deformities?

Unbalanced nutrition, excessive exercise, trauma, inappropriate growth, and hypothyroid hormone deficiency.

What are the clinical signs of angular limb deformities?

Presence of valgus or varus, swelling, lameness, and excessive wearing of the hoof on the medial or lateral side.

How is angular limb deformity diagnosed?

Clinical signs, degree of deviation, and X-ray.

What is the conservative treatment for mild angular limb deformities in young foals?

Stall rest, splints, cast, corrective hoof trimming, and glue-on shoes with outside or inside extensions.

What type of dalric shoes are used for valgus vs. varus?

• Valgus: medial extensions

• Varus: lateral extensions

What is the surgical treatment for severe angular limb deformities in older foals?

• Valgus: Enhance growth on lateral side (needle into growth plate).

• Varus: Hoof extension and screw into lateral side to enhance growth on the medial side.

What are more invasive surgical methods for treatment of ALD?

Periosteal stripping of radius, transphyseal bridging, transphyseal screw placement, corrective osteotomy or ostectomy

What is the prognosis for severe angular limb deformities?

Poor without treatment, but favourable with early detection and proper surgery.

What is the average age of physeal fusion for the distal radius in horses?

6-9 months.

What is the average age of physeal fusion for the distal femur in horses?

24-30 months.

What is physitis?

Inflammation and swelling of a growth plate (physis).

Which growth plates are more commonly affected by physitis at which ages?

• Nursing foals: P1

• Post-weaning: Radius (also, metacarpus/metatarsus)

What are the common causes of physitis?

Trauma, overfeeding (grow too fast), obesity, mineral imbalances, and genetic predisposition, Salter-Harris fractures.

What is the pathological result of physitis?

Disturbance of endochondral ossification.

What are the clinical signs of physitis?

Swelling at the physis, varying lameness, and choppy gait.

How is physitis diagnosed?

X-ray, calcium:phosphorus ratio (1:1), and increased alkaline phosphatase (ALP).

How is physitis treated?

Reduce food intake, limit exercise, correct diet imbalances, and provide box rest with soft bedding.

What are the types of Salter-Harris fractures?

• I: Straight across

• II: Above

• III: Lower

• IV: Through Everything

• V: cRush

What is the most common type of physeal fracture in foals?

Salter-Harris type II fracture.

What is the pathological result of physeal fractures?

Disruption of the bone in growth plate.

What is the treatment of physeal fractures?

 Important to use a locking technique - Locking compression plate (for long bones) + lag screws + cast. (metal plates and screws on each side of the bone).

What are defects of the spine?

• Scoliosis: S-shaped spine.

• Lordosis: Sway-back /downward curved spine.

• Kyphosis: Upward curving of the spine.

• Synostosis: fusion of a vertebra with the next vertebra

How common are defects of the spine?

Uncommon.

What is digit malformation?

2nd or 4th splint bone develops into a complete lower limb and foot.

Which is rickets?

Rare. Nutritional deficiency of vitamin D. Results in metaphyseal flaring and bowing of extremities.

What age are radial fractures more common?

4 months.

What age are cannon bone fractures more common?

18 months.

Which joints are most affected by ALD?

• Front: carpal joint with radius

• Hind: tarsal/hock with tibia.

What is the prognosis of cuboidal bone malformation?

Bad. No real treatment as is due to prematurity.