Physeal fractures: Salter–Harris, growth arrest and the transitional fractures of the ankle

The physis

The physis is a disc of cartilage between the epiphysis and the metaphysis. Its zones are arranged from the epiphyseal side towards the metaphysis, and each has a different job and a different mechanical strength.

Resting (reserve) zone

Scattered chondrocytes in abundant matrix, next to the epiphysis. Stores nutrients and supplies cells to the zone below.

Proliferative zone

Chondrocytes divide and stack into columns. This is where longitudinal growth is generated; achondroplasia is a defect of this zone.

Hypertrophic zone

Cells enlarge, then die as the matrix around them calcifies (the zone of provisional calcification). It has the least matrix and is mechanically the weakest. Rickets is a failure of provisional calcification, and slipped capital femoral epiphysis occurs through this zone.

Metaphysis

Vascular invasion lays down primary spongiosa on the calcified cartilage. Osteomyelitis and scurvy are metaphyseal diseases.

Around the edge, the groove of Ranvier supplies cells for growth in width and the perichondral ring of LaCroix gives mechanical support. The germinal layer is nourished from the epiphyseal side, so where the epiphysis is entirely intra-articular (the proximal femur and the proximal radius), separation can cut off its blood supply.

The Salter–Harris classification

What predicts growth disturbance

• Type. Types III, IV and V are more likely to cause arrest than I and II, but the type is not the whole story.
• Which physis. The undulating distal femoral and proximal tibial physes interlock with the metaphysis, so a fracture shears across the ridges and damages germinal cells; arrest is common after distal femoral physeal fractures, even type II injuries. These physes also contribute most of the growth of the lower limb, so arrest costs more length: growth happens near the knee and away from the elbow.
• Age. A younger child has more growth to lose, but also more capacity to remodel.
• Energy and displacement. High-energy, comminuted and widely displaced fractures fare worse.
• Treatment. Repeated or late forceful manipulation and threaded implants across the physis can cause arrest themselves.

Remodelling is greatest close to the physis, in the plane of movement of the nearest joint, and in younger children. Rotational malunion does not remodel.

Managing physeal fractures

• Types I and II. Gentle closed reduction early, then a cast. In young children some residual angulation in the plane of joint movement can be accepted because it will remodel. If the fracture is unstable, smooth Kirschner wires may cross the physis.
• Types III and IV. Anatomical reduction of the joint surface and the physis, often open. Screws are placed parallel to the physis, within the epiphysis or the metaphysis, without crossing it.
• Follow-up. Fractures at high risk of arrest are followed with radiographs until normal growth is confirmed. A Park–Harris growth arrest line that runs parallel to the physis is reassuring; one that converges towards the physis points to a bar.

Physeal bars

A bony bridge across the physis tethers growth. A central bar causes shortening and a tented physis; a peripheral bar causes angular deformity. MRI or CT maps its size and position. Langenskiöld’s criteria for bar resection with interposition of fat or cement are a bar involving less than half of the physis in a child with at least two years of growth remaining. Otherwise the arrest is completed by epiphysiodesis (with contralateral epiphysiodesis if the length discrepancy would be significant), and deformity or shortening is corrected by osteotomy or lengthening.

Transitional fractures of the distal tibia

In adolescence the distal tibial physis closes over about 18 months, starting centrally, then medially and finally laterally. While the anterolateral part is still open, external rotation injuries produce two characteristic fractures.

• Tillaux fracture. A Salter–Harris III fracture of the anterolateral epiphysis, avulsed by the anterior inferior tibiofibular ligament.
• Triplane fracture. A Salter–Harris IV pattern in three planes: sagittal through the epiphysis, axial through the physis and coronal through the metaphysis. It may have two, three or four parts.
• Imaging and treatment. CT defines the fragments. Articular displacement of more than about 2 mm after closed reduction is an indication for open or percutaneous reduction and fixation.
• Little remaining growth. Because the physis is already closing, growth arrest is less of a concern than joint congruity.

In younger children, a Salter–Harris III or IV fracture of the medial malleolus is different: a bar can form across the open medial physis and cause progressive varus deformity, so these need anatomical reduction and careful follow-up.

Sites that need respect

Distal femur

High risk of growth arrest after any type. Hyperextension injuries that displace the epiphysis anteriorly endanger the popliteal vessels.

Proximal tibia

The popliteal artery is tethered near the trifurcation and can be injured by posterior displacement of the metaphysis; watch for compartment syndrome.

Proximal humerus

Contributes most of the growth of the humerus and remodels remarkably, so considerable displacement can be accepted in younger children.

Distal radius

The commonest site of physeal fracture and very forgiving. Avoid late remanipulation.