Fractures and luxations of the hind limb (Proceedings)
Fractures of the femur and tibia occur commonly and are often a result of vehicular trauma. Animals are assessed for soft tissue injuries as described for pelvic fractures. The pelvis is carefully evaluated for injury because concurrent pelvic and femur fractures are common. Substantial hemorrhage can accompany diaphyseal femur fractures, resulting in a tense painful swelling contained by the fascia lata and deep connective tissues of the thigh. It is helpful to place a drain in these cases at the time of surgery to decrease pressure within the fascial compartment. Deep pain perception is evaluated in all animals with femoral fractures by pinching the lateral digits to assess the integrity of the sciatic nerve. There should be a flexor withdrawal as a response to a toe pinch. Reduced sensation or reduced flexor withdrawal can occur as a result of contusion to the nerve. Any positive sensation or withdrawal reflex means that nerve continuity is present. These cases typically return to full function neurologically within 3 weeks. Complete absence of sensation or withdrawal can mean severance of a nerve or can be a temporary conduction disturbance (neuropraxia).
The tibia has less soft tissue covering than the femur so open fractures are more common. Open fractures are treated by clipping hair, copious lavage of the wound with sterile saline and application of a sterile contact layer followed by soft padded bandage or splint. Tibial fractures are amenable to closed or semiclosed surgical stabilization with an external fixator.
Subluxation injuries of the tarsocrural joint occur as a result of medial or lateral collateral ligament rupture. Malleolar fractures also destabilize the collateral ligaments because the malleoli serve as the origin of the medial and lateral collateral ligaments. Valgus angulation indicates medial collateral ligament rupture and varus angulation indicates lateral collateral ligament rupture. Shearing wounds occur when an animal is hit by a car with the leg held in an abducted position. The medial tissues of the tarsus are abraded or sheared by contact and dragging on pavement. These are highly contaminated wounds that require copious lavage under anesthesia and daily bandage changes to allow contraction and re-epithelialization of soft tissues. Collateral ligament injury is always present with shearing wounds. The malleoli protrude above the level of the tibial shaft so are vulnerable to being completely removed with this injury.Specific Fractures
Proximal femur fractures
Anatomy: the proximal end (metaphysis-epiphysis) is composed of the femoral head and neck, the greater, lesser, and third trochanters, and the subtrochanteric area. The greater trochanter is the insertion for the middle and deep gluteal muscles, the lesser trochanter is the insertion for the iliopsoas muscle and the third trochanter is the insertion for the superficial gluteal muscle. The femoral head and most of the neck are enclosed by the joint capsule.
Capital physeal fractures: This is a Salter Harris type I fracture through the proximal physis of the femur. This is the most common fracture of the proximal femur in dogs. The proximal physis is responsible for all of the length of the femoral neck and for 25 % of the longitudinal growth of the femur. Closure of the femoral capital physis occurs between 6 and 9 months of age in most dogs and between 7 and 10 months of age in cats. Premature closure of the femoral capital physis occurs consistently after trauma and causes some degree of shortening of the femoral neck and the overall femoral length. The severity depends on the animal's age. By 5 months of age, 80 % of the growth of femoral head and neck is completed. Animals 5 months of age or younger are at great risk of developing a dysplastic hip with this injury. Animals of this age are better served by having a femoral head and neck ostectomy (FHO) to treat this injury as opposed to a fracture repair.
Bilateral femoral capital physeal separations, unrelated to overt trauma, have been reported in overweight, castrated male cats that are older than 12 months. This condition has been described as feline physeal dysplasia syndrome. Obesity and early castration are speculated to play a role in the pathogenesis of the condition. The fractures are treated the same way in cats as they are in dogs.
Surgical stabilization of capital physeal fractures: The surgical approach is a craniolateral approach to the hip joint. This is the same approach that is used to perform an FHO. The fracture is reduced and then stabilized with approximately 3 k-wires extending from the trochanter and subtrochanteric region into the femoral head. The K-wires are placed parallel to one another. The k-wires must not extend through the articular cartilage and into the joint.
Healing is generally good with surgical repair done very soon after injury. The prognosis is influenced by the age of the animal. Those animals less than 5 months of age have a greater chance of malformation and degeneration of the hip.
Postoperative radiographs: An "apple core" appearance to the femoral neck is common after this surgery and is not problematic. This remodeling is associated with hypervascularity of the femoral neck during evascularization of the femoral epiphysis.