Elbow Dysplasia in Skeletal Pathobiology

• Radiography of developmental disorders focuses on radiographic findings instead of pathophysiology.
• Review common OCD findings in any species and recognize the radiographic appearance of OCD by joint and species.
• Also review the different presentations of elbow dysplasia in dogs.

Osteochondrosis (OC) and Osteochondritis Dissecans (OCD)

• Key radiographic findings, regardless of species or joint, include a concave or irregular defect associated with the affected articular surface, representing chondromalacia.
• Sclerosis shows as increased soft tissue opacity surrounding or under the cartilaginous defect.
• Fragments of cartilage result from cracking in the weak cartilage.
  • Non-mineralized flaps require arthrography for detection
• Soft tissue swelling/synovial effusion is a possible radiographic finding.
• The most common radiographic finding is the cartilaginous defect or irregularities associated with the articular surface.
• "Flap" shape can be misleading, varying from thin to rounded/irregular when mineralized.
  • Detection of non-mineralized flaps in the shoulder requires arthrogram.

Osteochondrosis (OC)

• OC lesions do not necessarily cause lameness.
• OCD lesions are more likely to cause lameness.
• Joint defects without pain commonly result from OC lesions.
• In horses, flattening of the articular surface and subchondral bone in the ridges of the trochlea of the talus may be observed without pain.
• Retained cartilaginous core occurs because endochondral ossification extends into the metaphysis and physis of the bone (seen in dogs).

Joints Affected by OCD in Dogs

• Radiographic findings include concave defects, radiopaque halos of sclerotic subchondral bone, and mineralized flaps (some remain non-visible as cartilaginous tissue).
• Mineralization of flaps varies in size and shape, ranging from faint linear opacity to rounded joint bodies.

Joints Affected by OCD in Horses

• Radiographic abnormalities for stifle OCD are similar to those in small animals.
• Common abnormalities include irregular or concave defects on the articular surfaces of the ridges of the trochlea of the femur or the femoral condyles.
  • Flaps may or may not be mineralized.
• The most common site is the middle third of the lateral ridge of the trochlea of the femur
• Possible involvement of the articular surface of the patella and the tibial plateau.
• "Subchondral cyst-like" lesions which can present in the medial or lateral femoral condyle, are used in equine radiography to describe OCD lesions associated with the femoral condyles.
• The use of the term DIRT (Distal Intermediate Ridge of the cochlea of the Tibia) refers to OCD in the distal tibia by Equine practitioners.
• OCD lesions may affect the lateral and medial ridges of the tibial cochlea, the medial and lateral ridges of the trochlea of the talus, and even the tibial malleoli, and tarso crural joint space.
• OCD fragments can be found distally due to gravity and the anatomy of the tarso crural joint space.

OCD of the Fetlock Joint

• Associated with joint bodies on the proximal palmar aspect of P1.
• Joint bodies are sometimes considered avulsion fragments from trauma.
• OCD is more common in the dorsal aspect of the sagittal ridge and the condyles of the metacarpus or metatarsus.
• OC/OCD lesions can technically affect any area undergoing endochondral ossification in most of the larger joints in animals.
• Potential affection of intervertebral disc spaces.
• Radiographic diagnosis relies on recognizing abnormal radiographic findings rather than memorizing common sites.

Elbow Dysplasia Radiographic Facts

• Dysplasia includes fragmented medial coronoid process of the ulna, OCD of the humeral condyle, and ununited anconeal process.
• Other considerations: ununited humeral condyle, ununited medial epicondyle, and non-specific elbow malformation (incongruity) that result in DJD; fragmented medial coronoid process of the ulna is the most common presentation of the elbow dysplasia complex.
• The fragment from the medial coronoid process is often not seen.
• Craniocaudal view: used to differentiate between diseases, displays the humeral condyle and coronoid process best
• Earliest sign of DJD of the elbow(according to OFA): periarticular new bone formation.
  • OFA registry utilizes a flexed lateral view for this reason.
• Sclerosis of the ulnar semilunar notch :often over-diagnosed.
• The anconeal process normally fuses at 4-6 months.
• Severe DJD makes it difficult to differentiate a true OCD lesion of the humeral condyle from subchondral erosion and loss of cartilage (kissing lesion).

Elbow Anatomy Landmarks

• Composed of the medial and lateral epicondyles, the humeral condyle, and the medical coronoid process.
• The ulna contains the anconeal process, ulnar trochlear notch, and the medial coronoid process.
• DP landmarks consist of the medial coronoid process, head of the radius, humeral condyle and humeral epicondyles
• Other key features include the capitulum and the fovea.

Elbow Dysplasia

• Elbow dysplasia includes three original diseases: ununited anconeal, fragmented coronoid, and OCD humeral condyle.
• Three additional diseases that are now included are: ununited humeral condyle, ununited medial epicondyle, and non-specific elbow malformation which is incongruency.
• Elbow dysplasia describes abnormal conformation of the elbow joint.
• It is a developmental disease affecting immature patients with varying degrees of lameness.

Ununited Anconeal

• A normal elbow X ray is contrasted with one showing ununited anconeal.
• Ununited anconeal process appears as a free triangular fragment.
• The anconeal process is normally a separate center of ossification.
• It usually fuses around four to six months of age.
• Abnormal shape of the ulnar notch may predispose to a patient to ununited anconeal process.
• The undue stress from the abnormal shape of the ulnar notch results in failure of the process to unite.
• Remodeling of the separate anconeal process can occur if the condition has been present for a while.

Fragmented Coronoid Findings

• DJD, finding a fragment is unusual.
• Periarticular new bone formation at the anconeal process and radial head.
• Sclerosis of the semilunar notch.
• This is the most common potential diagnosis for elbow DJD.
• Fragmented coronoid presents irregularity to the medial coronoid process
• The fragment is usually detached.
• Degenerative joint disease (DJD) is the end result.
• Findings for DJD include periarticular new bone formation associated with the cranial aspect of the radial head.
  • This results in some irregularities and thickening of the radial head.
• Periarticular new bone formation is also associated with the proximal border of the anconeal process, causing the landmark to become irregular and thickened.
• There is increased sclerosis of the semilunar notch.

Fragmented Medial Coronoid Process of the Ulna

• On an X ray, it appears as a small, detached piece of bone on the medial aspect of the coronoid process.
• The medial coronoid process may appear blunted and irregular.

OCD Lesions

• Signs to look for include: concave or irregular defect at the articular surface, a radiopaque halo surrounding the defect, a joint body, and soft tissue swelling.

OC: Osteochondrosis

• It results from failure of endochondral ossification.
• The persistent cartilage surface becomes weak.
• Cracks develop under pressure, resulting in osteochondritis dissecans-OCD.
• This process results in flaps of cartilage that may or may not detach.
• The place where the flaps originate is the defect.
• A radiopaque halo surrounding the defect is sclerosis, indicating weak and inflamed bone.

OCD Defects

• Appearance includes mineralized flaps, and sclerosis.
• Defects are distinct from the bone.
• Defects can be highlighted by an orange line.
• Sclerosis is highlighted by pink shading.
• A mineralized flap can be highlighted with yellow fill.
• *United humeral condyle is only diagnosed following a fracture
  • Fracture borders are smooth and blunted even shortly after clinical signs of lameness.
  • A traumatic event can cause the separate ossification centers of the humeral condyle to fall apart if they never fuse.

Elbow Study Views

• The standard elbow study involves two views: lateral and cranial-caudal.
• In the lateral view, the anconial process and medial coronoid process of the ulna are partially obscured.
• Eliminating the radius and humerus in the lateral view allows better visualization of the anconial process, the semilunar trochlear notch, and the medial coronoid process of the ulna.
• Bone abnormalities in the ulnar notch may lead to different presentations of elbow dysplasia.
  • Examples are a tight notch causing anconeal process issues or a wide notch causing joint looseness.
• Adding the radius back can make the medial coronoid process more difficult to see.
• Adding the humerus obscures most structures.
  • The anconial process is obscured by the medial and lateral humeral epicondyles.
• The medial epicondyle is the largest anatomical protuberance, featuring a 90-degree bend.
• The lateral humeral epicondyle has a more curved border.
• The Orthopedic Foundation for Animals (OFA) recommends a flexed lateral view to detect early elbow dysplasia changes.
• DP landmarks consist of the medial coronoid process, head of the radius, humeral condyle and humeral epicondyles
• The medial humeral epicondyle is seen on the craniocaudal view of the elbow.
• The head of the radius is projected towards the lateral aspect in the craniocaudal view.
• In the antebrachium, the radius is lateral proximally but medial distally.
• The capitulum articulates with the head of the radius.
• The humeral fovea contacts the ulna.

Osteochondritis Dissecans (OCD) Lesions on Radiographs

• Three key things to look for:
  • Irregular defects at the articular surfaces of the cartilage.
  • Radiopaque halos surrounding the defect, which are areas of sclerosis of the subchondral bone.
  • A joint body.
• Soft tissue swelling surrounding the joint space may or may not be seen.
• In a lateral view of an immature patient's shoulder joint, look for a concave defect associated with the caudal aspect of the humeral head and faintly defined halo surrounding the defect.
• Arthrograms, which involve placing positive contrast material inside the joint space, are not commonly performed nowadays.
  • In an arthrogram, the filling defect represents the cartilaginous flap.
• The cartilaginous flap is only visible if mineralized or by use of contrast

Osteochondrosis Pathophysiology

• Osteochondrosis (OC) involves failure of endochondral ossification, resulting in an area of cartilage that remains cartilage but is weak and prone to cracks.
• Osteochondritis dissecans (OCD) is a crack in the weak cartilage that results in a flap of cartilage, which can be attached or detached.
• The concave defect is the place where the flap originates.
• Cartilage is radiolucent
• Fissure- crack
• Sometimes the cartilaginous flap will mineralize (joint body) and other times it will not (requires arthrogram to see it).
• Cartilage is translucent

Radiographic Signs of Osteochondritis dissecans

• Sclerosis is weak, inflamed bone, is typically adjacent to the cartilaginous defect.
• In equine stifle radiographs, a cyst-like lesion (lucent defect surrounded by a sclerotic halo).
• In equine radiology, OCD fragments may be seen near the intermediate ridge of the cochlea of the tibia, the medial ridge of the cochlea of the tibia, or caudal to the ridges of the trochlea of the talus.
• In canine tarsocrural joints, look for a mineralized OCD fragment associated with a defect of the subchondral bone, sclerosis of the malleolus of the tibia, and soft tissue swelling.
• OCD without a mineralized fragment can be seen in the region of the medial aspect of the humeral condyle.