carpal and tarsal fractures in dogs and cats
Injuries to the carpal and tarsal joints are common in performance dogs. These joints act as shock absorbers during weight bearing and are prone to injury due to their anatomic complexity and lack of muscular support. It is this complexity that creates a diagnostic problem for many veterinarians, and many carpal and tarsal injuries, particularly those that go undiagnosed or untreated, can result in an increased risk of osteoarthritis and potential long-term lameness.
Cause of carpal and tarsal fractures in dogs and cats
Carpal and tarsal injuries can result from either acute traumatic events or activities that cause sudden repetitive sprains to the joints’ supportive structures. Possible modes of injury include hyperextension (the most common type seen in agility dogs), hyperflexion with rotation, varus (inside of the limb) or valgus (outside of the limb) injuries, degeneration of ligaments in some breeds (Collies and Shelties), and certain immune-mediated diseases such as rheumatoid arthritis.
How does a veterinarian diagnose carpal or tarsal fractures in dogs and cats?
Diagnosing mild carpal and tarsal injuries can be difficult, but is possible using a combination of physical examination and imaging techniques. Dogs with carpal or tarsal injuries can present with either acute (sudden) or chronic (slowly progressive) lameness of varying degrees depending on the severity of the injury as shown inFigure 3. Palpation of the affected joint may reveal soft tissue swelling, discomfort, crepitus (crunching on manipulation), decreased range of motion, or instability when stressed (either in extension, flexion, varus or valgus, internal or external rotation). Palpation of the nonaffected joint on the opposite limb can be helpful in determining normal from abnormal motion.
X-rays can be taken to evaluate the type and severity of injury as seen in Figure 4.Although you cannot see ligamentous structures on x-rays, you can see bone fractures, luxations (dislocations or misalignments), and abnormal opening of a joint when stressed (extension, flexion, varus or valgus), which can help determine ligament integrity. Chronic or repetitive injuries may have bone spurs where ligaments attach, and those will also show up in an x-ray.
Fluoroscopy, which is performed in “real time,” takes an x-ray movie while you put the joint through its range of motion. It can show excessive openings of the joint spaces or abnormal gliding (subluxation) in carpal and tarsal injuries. When available, fluoroscopy is preferred over “stress” x-rays to evaluate carpal or tarsal joint motion during manipulation. If there is carpal or tarsal pain without x-ray abnormalities, an MRI (magnetic resonance imaging) or arthroscopy can be useful in diagnosing minor ligament sprains.
Carpal and Tarsal fracture considerations
- If your dog or cat has a fractured carpal or tarsal injury, the animal may walk plantigrade on the limb or may be non-weight bearing.
- Pain, swelling, and crepitus are present in the affected limb.
- Anatomic reduction and rigid fixation are necessary for optimal outcome in animals with intra-articular fractures of tarsus.
- Conservative treatment with casts or splints is not effective.
- External coaptation is also not appropriate for calcaneal fractures because bandaging or splint application is ineffective in countering tensile forces produced by the Achilles muscle-tendon unit.
- With calcaneal fractures, the pull of the gastrocnemius muscle must be resisted with a tension band wire, lag screws, or a plate.
- Articular fractures of the talus must be anatomically reduced and rigidly stabilized for optimal outcome.
Types of carpal and tarsal fractures in dogs and cats
Carpal and tarsal injuries can be classified into sprains, luxations, fractures, or a combination of the three. Sprains are the most common injuries in performance dogs, and sprains to the carpal and tarsal joints are the most likely to go undiagnosed. A sprain is an injury to a ligament that can occur in the midportion of the ligament or at its attachment to bone. Sprains are graded by severity. Grade 1 sprains are mild and described as an overstretching of the ligament, without a tear or loss of function. Grade 2 sprains are moderate in severity and are described as a partial tear. The general continuity of the ligament is intact though its strength is significantly reduced. Grade 3 sprains are severe and involve complete disruption or tearing of the ligament, resulting in joint instability. Since ligaments have a poor blood supply and require the formation and organization of collagen (scar tissue) for their repair, ligament healing times can be quite lengthy. Ligaments only regain about 60% of their original strength after one year. If a gap forms or is present at the junction of the ligament ends during healing, permanent ligament elongation and subsequent instability may result, even if an intact ligament reforms.
Luxation, or dislocation, involves the disruption of multiple ligaments and the joint capsule. In the carpus, the antebrachiocarpal joint is the most common site of luxation due to its increased range of motion and its conformation. In the tarsus, however, the intertarsal joints are commonly affected due to the relative lack of bone interdigitation of these joints compared to the tibiotarsal joint, which serves as an inherent joint stabilizer.
Common fractures associated with carpal and tarsal injuries in performance dogs include the attachment sites for the collateral ligaments (avulsion fractures) or bone fractures due to compression or shear forces. Fractures at these sites result in joint instability when stressed on palpation or during weight bearing. Another fracture site is the accessory carpal bone in the front limb, where the flexor carpi ulnaris tendon attaches. A hyperextension injury can result in fracture of the accessory carpal bone where the tendon attaches, as well as damage to the palmar (underside) ligaments. Similarly, in the hind limb, fractures of the calcaneus (heel bone) can occur.
Indications that carpal or tarsal fracture surgery is needed
Internal fixation is used for simple or comminuted metacarpal/metatarsal bone fractures or in patients with three or four fractured bones. In multiple bone fractures, the fixation can be used for all fractured bones or for metacarpal/metatarsal bones 3 and 4 only, i.e. weight-bearing toes.
Options for fixation include plating or wiring (rarely performed), traditional IM pinning, IM pinning by distraction and the most recent technique, the SPIDER external fixator.
The three pinning techniques include:
1. Traditional intramedullary pinning
In this technique, the pins are placed in a retrograde fashion. Pins are first placed into the distal bone segment. The pins exit at the metacarpophalangeal or metatarsophalangeal joint. Then the pins are driven into the proximal segment of the fractured bone.
Once proper placement has been achieved, the pins are bent and cut short near the knuckles.
2. Impaled (IM) pinning by distraction
This older technique has been recently revived by Degasperi et al.* The two bone fragments are distracted and “impaled” onto a short pin. This is easier to do in cats than in dogs, presumably because of increased flexibility of the feline paw.
The distraction or “dowel” technique is next to impossible in some dogs. Care should be taken not to break or crush the bone during distraction, especially in young patients.
3. SPIDER external fixator
A new technique nicknamed a SPIDER (for secured pin intramedullary dorsal epoxy resin), the device combines IM pins with an external skeletal fixator, which means that we do not need a splint.
In the case of fractures of all four toes (metacarpals or metatarsals), four IM pins are placed as in the traditional IM technique described above. The pins are bent dorsally but not cut short. One or two additional pins are placed transversally across the carpus or the tarsus, and bent dorsally. The ends of all converging pins are encased in bone cement (polymethyl methacrylate) or acrylic.
Which procedure to use depends on the dog, the type of fracture, and other individualized patient factors. For example, some patients simply will not allow their owners to clean the pin tracts. Some owners are mentally incapable of looking at the SPIDER external fixator, let alone clean the pin tracts. The proper surgical method for you and your dog should be decided after asking your veterinary surgeon what your treatment options are.