Canine Congenital Musculoskeletal Disorders Study Guide

Overview and Clinical Importance

Congenital musculoskeletal disorders represent a significant category of developmental orthopedic diseases in dogs commonly tested on the NAVLE. This guide covers two high-yield conditions: Legg-Calve-Perthes disease (LCPD) and osteochondrosis/osteochondritis dissecans (OCD). Both affect young, growing dogs but have distinct breed predispositions, presentations, and treatments.

Part 1: Legg-Calve-Perthes Disease (LCPD)

Definition and Synonyms

Legg-Calve-Perthes disease is a primary, idiopathic, noninflammatory degeneration of the femoral head and neck associated with ischemia and avascular necrosis of bone. Synonyms: Aseptic necrosis of the femoral head, Avascular necrosis of the femoral head, Perthes disease, Coxa plana.

Etiology and Pathophysiology

The exact cause is unknown, but a hereditary component is strongly suspected (autosomal recessive in Manchester Terriers and Toy Poodles).

Pathogenic Sequence

• Vascular insult: Interruption of blood supply to femoral head epiphysis
• Ischemic necrosis: Death of osteocytes and bone matrix
• Structural weakening: Loss of bone integrity
• Collapse: Femoral head deformation under weight-bearing
• Secondary osteoarthritis: DJD due to incongruent joint surfaces

Signalment and Breed Predisposition

High-Risk Breeds

Yorkshire Terrier, West Highland White Terrier (33x higher risk), Miniature Pinscher, Toy/Miniature Poodle, Chihuahua, Manchester Terrier, Pomeranian, Cairn Terrier, Jack Russell Terrier, Dachshund, Bichon Frise, Lhasa Apso, Pug.

Board Tip - Memory Aid: "LCPD = Little Canine Perthes Disease" - Remember LCPD affects LITTLE dogs, unlike OCD which affects large breeds!

Clinical Signs

• Early: Irritability, reluctance to jump, mild intermittent lameness
• Intermediate: Progressive hindlimb lameness worsening over 2-3 months
• Advanced: Non-weight bearing lameness, severe muscle atrophy, limb shortening

Physical Examination Findings

• Pain on hip extension and abduction (especially with internal rotation)
• Decreased range of motion
• Thigh muscle atrophy (develops within 2 weeks of onset)
• Crepitus in advanced cases
• Negative Ortolani sign (differentiates from hip dysplasia)

Radiographic Findings

Treatment

Femoral Head and Neck Ostectomy (FHO) - Treatment of Choice

FHO removes the diseased femoral head and neck, eliminating bone-on-bone contact and the source of pain. A fibrous pseudoarthrosis (false joint) forms between femur and acetabulum.

Part 2: Osteochondrosis and Osteochondritis Dissecans (OCD)

Definitions

Osteochondrosis (OC): Abnormal endochondral ossification in articular-epiphyseal cartilage of growing animals resulting in abnormally thickened cartilage.

Osteochondritis Dissecans (OCD): When abnormal cartilage fissures, cracks, and forms a flap that may partially or completely separate from underlying bone.

Etiology

Multifactorial disease: Genetics (strong hereditary component), rapid growth, excess nutrition (especially CALCIUM), trauma, hormonal imbalances, and ischemia all contribute.

Signalment

Board Tip - Memory Aid: "OCD = Obviously Chunky Dogs" - OCD affects large/giant breeds, opposite of LCPD!

Anatomic Locations

Clinical Signs

• Gradual onset lameness worsening with exercise, improving with rest
• Stiffness after rest ("start-up" lameness)
• Joint effusion, reduced ROM, muscle atrophy
• Pain on joint manipulation

Radiographic Findings

• Flattening of articular surface (most consistent finding)
• Subchondral defect (radiolucent crater)
• Calcified flap/fragment ("joint mouse")
• Sclerosis at defect margins

Treatment

Surgery is indicated for most OCD cases. Conservative management only for dogs less than 6 months with minimal signs and no radiographic changes.

Arthroscopy is the gold standard: Minimally invasive flap removal, debridement of lesion bed, subchondral bone forage (microfracture) to stimulate fibrocartilage formation.

LCPD vs. OCD: Key Differences