Developmental Elbow Disease (DED)
Pathophysiology, Diagnostics, and Medial Coronoid Disease (MCD)
The Paradigm Shift: From ED to DED
Historically, "Elbow Dysplasia" (ED) was utilized as an umbrella term encompassing four distinct conditions: Ununited Anconeal Process (UAP), Osteochondritis Dissecans (OCD) of the humeral condyle, Fragmented Medial Coronoid Process (FMCP), and joint incongruity.
Modern veterinary orthopaedics has largely abandoned this blanket terminology in favour of Developmental Elbow Disease (DED). This shift acknowledges that these conditions are not always isolated entities but are frequently interconnected manifestations of underlying biomechanical and developmental abnormalities—most notably, radioulnar incongruity (RUI) and trochlear notch dysplasia.
Similarly, the term "Fragmented Medial Coronoid Process" (FMCP) has been superseded by Medial Coronoid Disease (MCD). This reflects the clinical reality that the medial coronoid process does not simply "fragment" spontaneously. Instead, it undergoes a spectrum of disease ranging from microcracking and chondromalacia to complete fragmentation, driven by chronic mechanical overload.
Pathophysiology of MCD & RUI
The canine elbow is a highly complex hinge joint requiring perfect articulation between the humerus, radius, and ulna. DED predominantly affects large and giant breed dogs, with a strong genetic predisposition.
The prevailing theory for the pathogenesis of MCD is biomechanical overload of the medial compartment. This overload is typically driven by two primary forms of asynchronous growth:
- Radioulnar Incongruity (RUI): If the radius is shorter than the ulna (a "short radius"), the humeral condyle places disproportionate, supraphysiologic weight-bearing forces directly onto the medial coronoid process of the ulna. Over time, this leads to subchondral bone fatigue, microfractures, and eventually, gross fragmentation.
- Trochlear Notch Dysplasia: An elliptical or abnormally shaped trochlear notch creates a "wedging" effect. As the humerus is forced into a poorly fitted notch, it places immense sheer stress on the anconeal process and the medial coronoid process.
Furthermore, dynamic incongruity—driven by the rotational pull of the biceps and brachialis muscles during the gait cycle—can exacerbate rotational conflict at the radioulnar articulation, further stressing the medial coronoid.
Advanced Diagnostics: The Superiority of CT
While orthogonal radiography remains a useful initial screening tool for assessing secondary osteophytosis and gross incongruity, it is woefully inadequate for the definitive diagnosis of early MCD.
The Limitations of Radiography
Superimposition of the radial head over the medial coronoid makes identifying non-displaced fissures or micro-fragmentation nearly impossible on standard 2D views. Up to 50% of dogs with arthroscopically confirmed MCD have "normal" looking coronoids on standard radiographs.
Computed Tomography (CT)
CT is the gold standard for non-invasive evaluation of the canine elbow. It provides multi-planar reconstructions essential for identifying radioulnar incongruity (down to <1mm accuracy), subchondral sclerosis, focal radiolucency, and early fissures of the medial coronoid process.
Surgical Interventions
The surgical management of DED is highly patient-specific, depending heavily on the age of the dog, the degree of articular cartilage damage (Outerbridge scoring), and the presence of RUI.
1. Arthroscopic Debridement & Subtotal Coronoid Ostectomy (SCO)
Arthroscopy offers superior magnification and illumination for evaluating the joint. Treatment of MCD typically involves the arthroscopic removal of the fragmented bone and debridement of diseased cartilage. In cases of diffuse coronoid microcracking, a Subtotal Coronoid Ostectomy (SCO) may be performed to remove the entire diseased portion of the medial coronoid, leaving a bleeding subchondral bone bed to form fibrocartilage.
2. Biceps Ulnar Release Procedure (BURP)
In patients where dynamic rotational incongruity is suspected, transection of the ulnar insertion of the biceps brachii tendon (BURP) reduces the rotational force placed on the medial coronoid process during the stance phase, relieving chronic mechanical overload.
3. Load-Shifting Osteotomies (PAUL & Proximal Ulnar Osteotomy)
In cases of severe medial compartment disease where conservative debridement is insufficient, procedures like the Proximal Abducting Ulnar Osteotomy (PAUL) or a sliding proximal ulnar osteotomy may be employed. These biomechanically shift the weight-bearing axis laterally, offloading the diseased medial compartment onto the relatively healthier lateral compartment.
Note: Despite surgical intervention, DED is a progressive disease. All surgical modalities must be coupled with rigorous, lifelong multimodal osteoarthritis management (NSAIDs, weight control, and physiotherapy).
Selected Literature & References
- Fitzpatrick, N., et al. (2009). "Radioulnar incongruence in dogs with medial coronoid disease: technique and results of measurement using computed tomography." Veterinary Surgery. (Establishing CT as the gold standard for evaluating RUI).
- Michelsen, J. (2013). "Canine elbow dysplasia: Aetiopathogenesis and current treatment recommendations." The Veterinary Journal. (Comprehensive review on the shift toward the DED/MCD nomenclature and biomechanical overload theories).
- Vezzoni, A., et al. (2014). "Arthroscopic findings in 182 elbows with medial coronoid disease." Veterinary Surgery. (Detailing the varying spectrums of MCD pathology visible only via arthroscopy).
- Kramer, A., et al. (2006). "Comparison of radiography and computed tomography for the diagnosis of elbow dysplasia in dogs." Veterinary Record. (Highlighting the high false-negative rate of standard 2D radiography in early DED).
- Moores, A.P., et al. (2008). "Clinical outcome of dogs treated with the Proximal Abducting Ulnar Osteotomy (PAUL)." Veterinary and Comparative Orthopaedics and Traumatology. (Evaluating load-shifting outcomes in end-stage medial compartment disease).