Carpal Hyperextension

Introduction

Canine carpal hyperextension is caused by a third degree sprain of the carpus. It is most commonly seen in large, young dogs after trauma (such as jumping from a height), but it can also be seen secondary to degeneration in older dogs.

Generally, traumatic injury causes damage and disruption to the palmar fibrocartillage and ligaments (including the two accessory carpal-metacarpal ligaments) of the carpal joint. It can occur unilaterally or bilaterally.

Clinical Signs

The dog will present with lameness and hyperextension of the carpus when weightbearing. The severity of hyperextension depends on the level of damage. On physical exam, periarticular thickening is normally apparent. Effusions and pain may be present, especially if the condition is chronic.

Diagnosis

After taking dorsopalmar and lateral radiographs of the affected limb, stressed radiographs are needed to identify the location of the damage and to assess the level of instability and ligament disruption. These can normally be taken standing, with the dog weightbearing on the affected limb. As the cause of carpal hyperextension is normally traumatic, the limb should be thoroughly assessed for any other damage that may have occurred - particularly to the proximal metacarpal bones and collateral ligaments.

Treatment

Due to the severity of ligament damage resting the dog will not be curative. Therefore pancarpal arthrodesis is the treatment of choice for this condition.

The first stage of the surgery is the debridement of the articular cartillage on the joint surfaces. Secondly, cancellous bone is collected from a distant site and implanted in the surgical site. Finally, a specific pancarpal arthrodesis bone plate (ideal), medial bone plate or external skeletal fixator is used to fix the joint in position. Complete immobilisation of the joint is necessary for successful surgery, and external coaption may be used as an extra method of immobilisation. It is important to arthrodese the joint in the normal weightbearing position (approximately 170° dorsal) to minimise lameness post operatively.

Partial carpal arthrodesis can be performed if damage and instability is limited to the intracarpal and carpometacarpal joint. This does preserve some joint movement but the surgery is less successful and associated with the development on degenerative joint disease.

Complications of the surgery include malunion or non-union of the joint, implant failure, incorrect arthodesis angle, fracture, wound breakdown and infection.

Prognosis

The prognosis is good. The limb compensates for the lack of carpal movement, resulting in minor functional gait abnormality once the animal has recovered from surgery.

Carpal Hyperextension Learning Resources
Flashcards Test your knowledge using flashcard type questions	Small Animal Orthopaedics Q&A 02

References

Dyce, J (1996) Arthrodesis in the dog In Practice 1996;18:267-279

Lewis, DD & Parker, RB & Bloomberg, MS (1998) Self-Assessment Colour Review Small Animal Orthopaedics Manson

Roch, S & Gemmill, T (2009) Orthopaedic conditions of the metacarpus, metatarsus and digits in the dog In Practice 2009 31: 484-494

Whitelock, R (2001) Conditions of the carpus in the dog In Practice 2001 23: 2-13

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