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.

Femoral neck fractures

Surgical repair of femoral neck fractures: Multiple (usually 3) parallel K-wires as described for capital physeal fractures.

Prognosis of surgery: Good. Functional recovery is expected in most animals in which a stable repair is achieved.

Cats: There is a specific form of pathological fracture of the femoral neck that occurs in male cats younger than 2 years of age called metaphyseal osteopathy. This can present as bilateral femoral neck fractures that may have a history of chronic progressive lameness prior to the actual fracture. This is treated with bilateral FHOs.

Femoral Diaphyseal Fractures

Fracture stabilization

Transverse and short oblique: dynamic compression plate (DCP plate), interlocking nail, or intramedullary pin (IM pin) and Type I external fixator.

Long oblique/spiral: IM pin and full cerclage wire, bone plate.

Comminuted: Interlocking nail (excellent option in most cases), buttress plate, plate-pin combination, or IM pin and type I external fixator.

Technique for IM pin placement

IM pins can be placed in retrograde fashion by entering the fracture site and directing the pin towards the trochanteric fossa of the proximal fragment. The proximal fracture fragment must be held in adduction and extension to direct the pin away from the sciatic nerve. The pin must be cut very short so that it does not extend above the greater trochanter. The pin should sit in the lateral trochanteric fossa—so that it is right up against the greater trochanter.

In most dogs, the conformation of the distal femur is such that the passage of a pin results in the distal end of the pin being directed cranially towards the trochlear groove. If possible, the distal segment of the femur is positioned slightly cranially ("overreduced") to seat the pin in the more caudally in the femoral condyle. In cats, the femur is straighter, and a pin can easily be seated in the metaphyseal-epiphyseal cancellous bone without overreducing.

The pin should occupy approximately 70% of the marrow cavity. Pins do not control rotation or compressive forces so must be accompanied by ancillary fixation. If the obliquity is great enough, pins are paired with cerclage wires. In short oblique or comminuted fractures, pins are paired with a type I external fixator. An older technique for IM pinning is to use stack pins. It was believed that inserting multiple pins in the femoral canal would provide control of rotation. This has been disproven. In a retrospective study stack pinning had a 50 % complication rate.

It has been shown that a single pin combined with a two-pin type I external fixator

provided greater resistance to rotation than the use of three or more IM pins.

Interlocking nail

The interlocking nail is a very useful implant for femur fractures especially comminuted. Placement has to be normograde with this system. The most stable system is achieved with 2 screws proximally and 2 distally.

Plate Fixation

The most commonly used type of plate in veterinary surgery is the DCP plate. Compression is applied by loading the screw hole eccentrically. This is done for transverse fractures only. Otherwise, the plate is either neutralization or a buttress plate. Lengthening plates have no screw holes in the middle and are designed for spanning or buttressing the area of the fracture. Plates can be used along with an IM pin in a "plate and rod" combination. The plate complements the pin by resisting rotation and compression and the pin reduces bone plate strain in bending, thus preventing fatigue failure of the plate. In this case, a pin is chosen to fill only 30 to 40 % of the marrow cavity to leave room for screws.

External Skeletal Fixation

The proximity of the abdominal wall and the bulk of the muscles around the femur limit the use of external fixators to type I. A type I fixator can be paired with an intramedullary pin as mentioned above. Additionally, the pin can be "tied in" to the external fixator to further control rotational forces. To do this, the IM pin exits the skin above the greater trochanter and is secured to the external fixator connecting bar using a clamp.

Clamp rod internal fixation (VetFix)

This is a new technique that stabilizes long bone fractures by contouring a rod to fit the bone, sliding clamps onto the rod, and securing the rod with screws that go through the clamps. This fixation can be used on a variety of fractures.

Specific Complications of Diaphyseal Femur Fractures

a. Nonunion: inadequate fixation.

b. Quadriceps contracture: this is a preventable problem. It occurs most commonly in younger dogs that have had surgical manipulation of the distal diaphysis and metaphysis of the femur. Abundant callus adheres the quadriceps muscles to the periarticular area of the stifle joint and restricts motion. Once it happens it is essentially irreversible. Clients must be instructed to flex and extend the knee joint 10 to 15 times twice daily for the first 4 weeks postoperatively. Have clients demonstrate this for you in the exam room before you send them home to make sure they understand how to do it.

c. Loss of femoral length: The femur can lose up to 20 % of its length without causing a problem. The affected knee is extended a bit more and the opposite knee is flexed.

d. Sciatic nerve injuries: most often a result of IM pinning. The pin sits in the medial versus the lateral aspect of the trochanteric fossa and it is too long. Signs may occur 2 to 3 weeks after surgery due to fibrovascular proliferative response around the pin that secondarily compresses the nerve.

Distal femoral fractures

1. Anatomy: The condyles of the femur are offset caudally from the long axis of the bone. The distal femoral physis is an irregular W shape. The distal physis contributes 65 % to 75 % of the longitudinal growth of the femur in dogs. The most rapid growth period is between 3 and 5 months of age; 80% of the growth occurs by 5 months of age.

2. Physeal fractures

Fractures through the distal femoral physis are usually Salter Harris type II injuries. These are the most common distal femoral injuries in dogs. The epiphysis (distal piece) displaces caudally because of the pull of the gastrocnemius, semi-m and semi-t muscles. These fractures should be operated on as soon as possible to facilitate reduction. The fractures are stabilized using normograde cross pin placement.

a. Technique for cross-pinning: Once the fracture is reduced, small Steinmann pins are placed in normograde fashion. The first pin is placed at in the lateral condyle. The point of insertion is just cranial to the tendon of origin of the long digital extensor muscle. The pin crosses the fracture line and exits the cortical bone of the medial distal femoral shaft. The second pin is placed medially, at the same level as the first pin, and exits the cortical bone of the lateral distal femoral shaft. The pins should cross above the fracture site not right at the fracture site. The pins can be countersunk below the surface of the cartilage using a pin setter (pin setter kit available from Securos).

b. Prognosis: very good.

Diaphyseal Tibial Fractures

1. General: Most fractures of the tibia include the fibula, although the fibula is frequently ignored in treatment unless the stability of the hock is jeopardized. Preoperative treatment: careful cleaning of any open wounds and application of a Robert Jones bandage to decrease swelling and improve patient comfort.

Type of repair dictated by the fracture configuration.

a. Spiral and long oblique can be repaired nicely with IM pin and full cerclage wire.

1. Landmark for normograde pinning: Medial side of the tibial plateau between the medial collateral ligament and the patellar tendon. If difficulty is encountered while placing the pin, move down a pin size and start the pin a little more cranially closer to the patellar tendon).

2. Do not retrograde an IM pin in the tibia.

b. Comminuted tibial fractures: Well-suited for external fixation or pin-plate combination.