Juvenile bone and joint diseases: large dogs, rear legs; and small dogs (Proceedings)

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Juvenile bone and joint diseases: large dogs, rear legs; and small dogs (Proceedings)

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Aug 01, 2011

JBJD's of large dogs, rear legs

Osteochondritis Dissecans (OCD) Hock

Pathogenesis



OCD of the hock occurred bilaterally in 42% of the reported cases. The lateral trochlear ridge is involved in 25% of the cases and the medial trochlear ridge in 75% of the cases. Lesions tend to be very large and most commonly are located at the proximal or central aspects of the medial trochlear ridge. Multiple OCD lesions per joint has been reported in 3 dogs. In addition, subchondral bone cyst similar to those reported in man and horses has been reported in one dog. OCD of the hock accounts for 9% of all canine OCD reported to the VMDB.

Signalment

Age at presentation ranges from 4 months to 4 years, with less than year old being most common. Rottweiler's have accounted for 41% of the reported cases. Males account for 50% of the reported cases.

History

Lameness is often subtle with an insidious onset. Several months between initial lameness and presentation to a veterinarian is common.

Clinical exam

Marked hyperextension of the tarsus is common. Swelling of the periarticular tissues and distention of the joint is common, unlike OCD of other joints. Additional findings may include decreased range of flexion, valgus deformity of the tarsus and pain at full flexion and/or extension.

Ancillary exam(s)

Imaging of the OCD lesion of a tarsus can be difficult, and requires excellent technique and "skyling" of the lesion. In addition, lateral trochlear ridge lesions might be missed due to superimposition of the calcaneous in dorsoplantar radiographs. Therefore, several radiographic projections are recommended to visualize the OCD lesion(s). A D45° L-P1MO projection skylines the medial trochlear ridge while the D45° M-P1LO projection skylines the lateral trochlear ridge. Flexion of the tarsal joint to an angle 10° -15° from the X-ray beam removes the superimposition of the calcaneous to better visualize the central portion of the lateral trochlear ridge, but not the proximal part of the lateral trochlear ridge. Widening of the medial tibiotarsal joint space due to flattening of the medial trochlear ridge is an early and progressive radiographic sign. Additional radiographic changes suggestive of OCD of the tarsus include osteophyte formation, and soft tissue swelling. Lameness might be minimal despite severe DJD changes radiographically.

Treatment(s)

The benefit of surgery over conservative treatment of OCD of the tarsus is debatable. In one report of 11 dogs (17 joints), with a follow up time of 16-79 months, the authors reported no difference between operated and un-operated joints based on clinical examination by two veterinarians (one blinded to treatment method) and radiographs. In contrast, a different study stated that surgery is usually successful if it is performed prior to the onset of debilitating osteoarthritis, reporting good to fair results 10 months after surgery, but poor results with conservative therapy. Numerous other authors state surgery is preferred over conservative treatment. OCD lesions of the tarsus tend to be quite large and their removal produces a significant defect and instability of the joint. Maintaining the OCD cartilage flap in situ is preferable to removal of the flap IF it can be stabilized and healing promoted. Attachment of an OCD flap with autogenous bone plugs, lag screw or Kirschner wires has been reported, but the lack of significant subchondral bone with the flap often makes this difficult or impossible. Drilling of an attached flap to create vascular access channels is common in man. The use of N-Butyl 2-Cyanoacrylate for stabilization of tarsal OCD lesions has been reported in 3 dogs that resulted in a 30-40° loss of range of motion but no progression of DJD radiographically and no lameness at 9, 13 and 16 months after surgery. The author has used forage to create vascular access points of fixation with fair to good results, dependant on existing DJD. Surgical technique is probably important to the outcome. Approaches include transaction of the collateral ligament, malleolar osteotomy or combined approaches dorsal and plantar to the collateral ligament without transaction of a collateral ligament or osteotomy. Most lesions can be adequately exposed without osteotomy or desmotomy thus avoiding the additional morbidity of these procedures. Surgery of an asymptomatic joint is questionable.

Prognosis/Client Education

Prognosis of OCD of the tarsus is guarded, but depends on many factors. Minimal curettage is important to minimize joint instability. Additional factors that affect prognosis include unilateral versus bilateral joint involvement, size of the OCD lesion, surgical approach and the duration between onset of clinical signs and treatment (severity of DJD at the time of treatment). Postoperative lameness might be minimal despite progressive and or severe DJD radiographically.