Physeal Fractures in Small Animals

Figure 1 Physeal fractures can occur in any juvenile animal, even with little trauma, because the physis is weaker than the adjacent bone and ligaments. Orthogonal radiographs of any painful joint should be performed. Oblique projections, radiographs of the limb in different positions, and radiographs of the contralateral limb for comparison can all aid in the diagnosis of a physeal fracture. Shown here are lateral stifle radiographs from an 8-month-old mixed breed dog that presented for acute onset of lameness in the left pelvic limb after he slipped earlier that evening; pain was localized to the left stifle. Notice the open physes of the proximal tibia and distal femur, which are normal for a dog of this age. There is physeal separation and cranial displacement of the proximal epiphysis in the left tibia, and a greenstick fracture of the left fibula (arrows).

Figure 2 Physeal fractures can also occur secondary to major trauma. It is important to stabilize the trauma patient and evaluate the entire set of thoracic and orthopedic radiographs for the presence of concurrent injuries. This 7-month-old Mastiff was in a vehicular accident and sustained bilateral capital physeal fractures (arrows), an avulsion physeal fracture of the right greater trochanter (arrow), a left ilial body fracture (arrow), a left acetabular fracture (arrow), and pubic and ischial fractures.

Figure 3 Bone heals very quickly in immature animals, and a physeal fracture that is not quickly identified and treated will heal on its own; in most cases, this leads to a malunion or angular limb deformity, which can significantly affect clinical function. These radiographs show an 11-month-old Labrador retriever that sustained an undiagnosed physeal fracture of the proximolateral tibial physis, resulting in partial physeal closure (arrows) and a substantial valgus deformity.

Figure 4 The Salter-Harris classification method was first described in the human literature in 1963. Its scale of I–V is based on prognosis and the fracture’s anatomic location: the higher the number, less favorable the prognosis. This scheme, however, does not consider other factors that affect prognosis in small animals, such as the specific bone, the location within the bone, and the patient’s age and remaining growth potential.

Figure 5 A Salter-Harris Type I fracture involves separation through the physis. Fractures frequently occur through the hypertrophic zone of the physis, and therefore growth may still occur from the injured physis if the germinal layer of cells has not been damaged during the injury or surgery. This fracture most commonly occurs in the proximal femur, namely the capital physis (arrows, left), typically in juvenile cats and dogs as well as male cats up to 2–3 years of age. If a capital physeal fracture occurs in a patient younger than 6–7 months of age, damage to the blood supply or direct physeal trauma may cause cessation of growth from the capital physis, resulting in a dysplastic hip (shown in the bone specimen on the right).

Figure 6 On the ventrodorsal radiographic projection of the pelvis (left), hip extension may cause reduction of the capital physeal fracture and obscure the diagnosis. Accurate diagnosis can be facilitated with a “frog leg” or flexed hip ventrodorsal radiographic projection of the pelvis (right), which distracts the fracture fragments and makes the physeal separation more identifiable. The dog in the radiographs above has a right capital physeal fracture (arrows).

Figure 7 A Salter-Harris Type II fracture involves bone separation through the physis and metaphysis, most commonly occurring in the distal femur. The radiographs show a Salter-Harris Type II fracture of the proximal tibial physis (arrows) and a short oblique fracture of the fibula (arrow) in a 10-month-old mixed breed dog.

Figure 8 A Salter-Harris Type III fracture involves separation through the physis and epiphysis, and typically occurs in puppies 2–4 months of age; it is most commonly seen in the distal humerus, though it is uncommon in dogs. In these post-operative radiographs of a 3.5-month-old Saint Bernard, a Salter-Harris Type III fracture of the medial femoral condyle was identified (arrows). The patient was immediately re-operated and the physeal fracture was repaired with a screw placed in lag fashion and an anti-rotational Kirschner wire. Note that the screw does not cross the physis; this is to avoid interference with growth potential.

Figure 9 A Salter-Harris Type IV fracture involves separation through the metaphysis, the physis, and the epiphysis. This fracture (arrows) most commonly occurs in the distal humerus, specifically the lateral portion of the humeral condyle, in puppies that jump down from high locations. As the high load is transferred up the radius, excessive force is put on the lateral portion of the humeral condyle, resulting in a fracture.

Figure 10 A Salter-Harris Type V fracture is a crushing injury to the physis. The conical shape of the distal ulnar physis predisposes this location to injury, which often results in necrosis of the germinal cells in the resting zone and permanent cessation of growth. Depending on the patient’s age and remaining growth potential, this may lead to limb shortening, and, in the case of the antebrachium, angular limb deformities or elbow incongruity. Shown above is the clinical appearance and radiographs of an 11-month-old Cairn terrier that developed a valgus deformity and external torsion of the antebrachium secondary to premature closure of the right distal ulnar growth plate.

Figure 11 If a Salter-Harris Type V fracture of the distal ulnar physis is identified early, a distal partial ulnar ostectomy can prevent the formation of angular or torsional deformities by allowing the radius to continue to grow linearly in an unrestricted fashion. If premature closure of the distal ulnar physis has resulted in elbow incongruity (arrows, left), a proximal oblique ulnar osteotomy can restore the elbow joint congruity (right). Note the gap at the osteotomy site that occurred when the proximal ulnar bone segment shifted proximally, resulting in improvement in joint congruity.

Figure 12 Careful surgical technique is important when repairing physeal fractures, as excessive dissection may damage the epiphyseal or metaphyseal blood vessels, and use of reduction forceps or retractors in the physis may damage the germinal cell layer. Anatomic reduction is imperative to maintain the potential for longitudinal growth and for restoration of articular surfaces. The above radiographs show the classic repair of a Salter-Harris Type IV fracture of the lateral portion of the humeral condyle, which involves a screw placed in lag fashion to provide interfragmentary compression and a K-wire placed in the lateral epicondylar ridge to prevent rotation of the fracture fragment.

Figure 13 Smooth pins (ideally, parallel or angled at or near 90° relative to the physis) are often used to repair physeal fractures because they cause minimal trauma and allow continued growth of the physis. The radiographs of a kitten above show a Salter-Harris Type II fracture of the distal femur, which was repaired with 2 dynamic intramedullary pins.

Figure 14 Bridging the physis with screws, bone plates, pin and tension-band fixation, or external fixation devices is not advised unless the patient is very near skeletal maturity, as this will result in closure of the growth plate. If they are used in very young patients, they should be removed 2–3 weeks postoperatively. These radiographs show a Salter-Harris Type I fracture of the tibial tuberosity (A) in a 5-month-old dog that was stabilized with a pin and tension-band repair (B). The owner did not return for re-evaluation until 10 weeks postoperatively. Radiographs at that time revealed that the physis of the tibial tuberosity had closed, while the physis of the tibial plateau continued to grow (C). This patient also sustained an apical fracture of the patella, which was managed conservatively.

Figure 15 The prognosis of physeal fractures is best if the fracture is quickly identified and repaired with reduction and rigid fixation. If the fracture involves the articular surface, some degree of osteoarthritis can be expected over time. The prognosis is guarded for chronic fractures, fractures with marginal or unstable repairs, and for patients with significant growth potential remaining. The radiographs above of a 1-year-old Mastiff were taken six months following repair of Salter-Harris Type I fractures of the right greater trochanter and capital physis. Both fractures were repaired with smooth Kirschner wires. The fractures have healed, and there are no signs of osteoarthritis in the hip joint at this time. Clinical function was excellent.