Physeal fractures in immature animals: part 2 – spine and hindlimbs

Part one of this article (VT46.08) discussed the principles of physeal fracture stabilisation and specific physeal fractures of the bones of the forelimb. Part two will discuss physeal fractures of the bones of the spine and hindlimb.

Spinal fractures

The primary centres of ossification within the vertebral bodies have usually fused by birth to ensure the neural arch is complete. The vertebral end plates have physes at either end (cranially and caudally) to allow longitudinal growth of the spine and these usually ossify by around 11 months of age.

Trauma can lead to end plate fractures and treatment is dependent on the neurological status of the animal, the degree of cord compression and the owners’ finances. If no deep pain sensation is in the limbs caudal to the fracture site then euthanasia is often recommended since chances of recovery are minimal.

If surgery is indicated then referral for advanced imaging is usually advised to accurately assess the fractures using CT and/or the integrity and degree of compression of the spinal cord with MRI. A human classification system adapted for veterinary use discusses the three compartments that contribute to spinal stability: the dorsal compartment consists of the dorsal spinous processes and ligaments, the vertebral laminae, articular processes and vertebral pedicles.

The middle compartment is difficult to assess without a CT scan, but consists of the dorsal longitudinal ligament, annulus fibrosis and vertebral body. The ventral compartment includes the ventral vertebral body, the lateral and ventral aspects of the annulus fibrosis, the nucleus pulposus and the ventral longitudinal ligament.

If only one of the three compartments is compromised then conservative treatment with a splint can be attempted. If two or three are compromised then surgical stabilisation is advised.

Pelvic fractures

The pelvis consists of multiple growth plates that have variable times to fusion, with the acetabulum usually fused by  3 to 4 months, while the tuber ischii take up to 10 months.

Since one of the principles of pelvic fracture repair is that surgery is indicated to restore the weight-bearing axis, physeal pelvic fractures involving the ilium or ischium may not require surgery, since they do not contribute to this axis.

However, acetabular fractures will require surgery. Since the fractures are articular then rigid internal fixation is indicated, which is usually performed using plate and screws or pins and poly(methyl methacrylate). This will result in premature physeal fusion.

However, since this growth plate closes early, it is unlikely to be of any consequence for the animal.

Should an incongruity between the femoral head and acetabulum occur with secondary luxation, subluxation or degenerative joint disease then salvage surgeries, such as femoral head and neck excision or total hip replacement arthroplasty, could be considered.

An example of a Salter-Harris type one acetabular physeal fracture in a kitten is shown in Figure 1.

Femur fractures

The proximal femur consists of two separate physes – the femoral head (or capital physis), which usually fuses by 10.5 months in the dog and 8 months in the cat, and the greater trochanter, which fuses around 10.5 months in the dog and 7.5 months in the cat. The distal condyle of the femur has a single physis that usually closes by 11 months in the dog and 15 months in the cat.

Although these are the average published ages of physeal closure, it should be remembered dog breed/size will impact on these timings and, particularly for cats, neutering status. For example, femoral head capital physeal fractures can be as late as two years of age in neutered male cats since the sex hormones, particularly oestrogen, are required for physeal fusion.

Proximal femoral physes

Avulsion of the greater trochanter can occur due to the distractive force of the gluteal muscle insertion resulting in a Salter-Harris type one fracture. Since this is an avulsion fracture, stabilisation is preferred using pins and tension band wire or potentially a lag screw.

Even in young animals, the extent of growth occurring from this physis is minimal, so premature closure should not result in any long-term consequence for the dog or cat. In a very young animal, preservation of physeal growth can be attempted by repairing using parallel Kirschner wires (K-wires) or cross pins, but this may not be sufficiently robust to counteract the distractive force.

Capital physeal fractures are relatively common and usually have a Salter-Harris type one configuration, although type three fractures can also be observed.

Some of these fractures can be minimally displaced and difficult to appreciate on radiographs alone, but without stabilisation, can lead to degenerative joint disease due to the instability associated with them.

Several stabilisation methods have been reported. The authors’ preferred method is to place parallel K-wires retrograde from the physis, down the femoral neck to exit the lateral cortex and pull these through from the far side so the points lie just below the physis.

Next, the fracture is reduced and the pins are advanced medially a short distance so they sit within the femoral head. This method is particularly useful when the teres ligament is intact (Figure 2). Alternative methods are a lag screw placed from lateral into the femoral head or a lag screw placed from the articular surface from the fovea capitus and countersunk below the articular cartilage.

The latter method was associated with a high failure rate in one report and cannot be recommended¹.

Distal femoral physis

Distal femoral physeal fractures are usually Salter-Harris type one or type two, although intracondylar fractures can also occur, converting the fracture into a Salter-Harris type three or type four.

In general, stabilisation consists of open reduction and crossed K-wires or Rush-type pins to hold the condyle in place. For optimal mechanical strength, the pins should cross each other proximal to the physis (Figure 3).

A common problem encountered with these fractures is inaccurate reduction; usually an under-reduction. Reduction can be aided by drilling a small hole in the femur just proximal to the patella groove to gain better grip with pointed reduction forceps to prevent them slipping distally and damaging the articular cartilage of the patella groove.

If the reduction is not satisfactory, there can be excessive laxity in the quadriceps mechanism, which can result in patella luxation.

In cases that have sustained considerable trauma, prophylactic 90/90 flexion bandaging or passive range of motion exercises should be encouraged as early as possible to try to limit the risk of developing quadriceps contracture. For the Salter-Harris type three or type four fractures, a transcondylar screw is also placed in addition to the cross or Rush-type pins. This is usually reverse drilled from the fracture surface outwards to ensure the screw is placed within the centre of the femoral condyle.

The screw can be placed in a lag or positional fashion. Care should be taken if placing lag screws in immature bone as it is particularly soft so a washer should be used to dissipate the load over a larger surface area and the surgeon should take care not to overtighten the screw.

Tibia and fibula fractures

The proximal tibia consists of two separate physes – the tibial plateau and the tibial tuberosity, on which the patella ligament inserts. The plateau usually fuses by 11 months in dogs.

The tibial tuberosity fuses to the tibial plateau somewhat earlier in dogs at around 5 months to 8 months before the whole tibial epiphysis fuses to the metaphyseal bone.

In cats, both fuse at the same time – around 15 months of age. An additional physis at the distal tibia usually closes by 10.5 months in dogs and cats.

The proximal fibula fuses around 10 months in dogs and 13 months in cats, whereas the distal malleolar physis closes at 9.5 months in dogs and 12 months in cats.

Proximal tibial physes

Usually, fractures consist of either a Salter-Harris type one fracture of the tibial tuberosity alone or in combination with the tibial plateau. The latter can also occur as a Salter-Harris type two configuration as a small piece of tibial metaphysis can fracture off with the plateau.

Due to the distractive forces of the patella ligament on the tibial tuberosity apophysis, stabilisation is usually performed with a pin(s) and tension band wire in a similar method as used for tibial tuberosity transposition for patella luxation surgery.

Two pins are driven through the tuberosity, starting just above the insertion of the patella ligament in a slightly distomedial direction until the far cortex is breached. The pins are then bent over and cut off so a small hook is present.

The tension band wire is applied through a small hole drilled in the tibial diaphysis and passed around the pins under the patella ligament to avoid the wire causing damage to the ligament as it is tightened (Figure 4).

For fractures that also involve the tibial plateau, either the tibial tuberosity alone is stabilised with a pin and tension band wire as described previously.

In some cases, additional cross pins are placed laterally and medially to further stabilise the proximal tibia. Some of these fractures can occur with minimal displacement and may heal with conservative treatment.

However, the concern with conservative treatment – or those stabilised with surgery, but with damage to the caudal aspect of the plateau – is that as the animal grows an excessively steep tibial plateau angle can develop. This, in turn, can predispose the dog to rupture of the cranial cruciate ligament.

A corrective osteotomy can be performed in these cases, such as a cranial tibial wedge ostectomy or tibial plateau levelling osteotomy, in the same way as used for management of cruciate disease.

Distal tibia and fibula physis

The distal tibia can sustain Salter-Harris type one or type two fractures in combination with a distal fibula physeal fracture of Salter-Harris type one.

These are usually repaired with cross pins through the malleoli or Rush-type pins. If a single malleolar fracture occurs, this can be a source of hock instability and even lead to luxation. In this case, reduction followed by pin and tension band wire (due to the distractive forces of the collateral ligaments) should be used to stabilise the hock.

Alternatively, the hock can be immobilised using a transarticular external skeletal fixator to prevent movement and allow the fracture time to heal (Figure 5).

It is important the external fixator is not left on too long or the range of motion of the hock may never return to normal.

Tarsus fractures

Although uncommon, Salter-Harris type one fractures of the calcaneus have been described. Due to the insertion of the common calcaneal tendon, these are avulsion fractures and should be repaired with pins and tension band wire.

Although this wire will span the physis, restriction of longitudinal growth of this bone is unlikely to be of any clinical consequence to the dog.

It is advised the pins are placed as laterally and medially as possible and that the tension band wire is placed against the bone and under the superficial digital flexor tendon.

Metatarsal and metacarpal fractures

Fractures of the base or the head of the metacarpals or metatarsal can be observed, often in combination with diaphyseal fractures of the same or adjacent bones (Figure 6). For the physeal fracture, fixation with cross pins is usually sufficient although the other fractures may need an alternative means of stabilisation.

If the fractures involve digits three or four then internal fixation is recommended. However, given the young age of patients with physeal fractures, conservative management may be successful with external coaptation if surgery is not an option (Figure 6).

• Physeal fractures in immature cats and dogs: part 1 – forelimbs