Children's hip fractures have historically had a bad prognosis. Accurate stable fixation has been one of the factors identified to improve the outcome.
Stable fractures have a better prognosis than displaced fractures.
The main problems have been avascular necrosis (AVN) due to disruption of the blood supply, nonunion and malunion due to unstable fixation.
The objective is timely fixation without disruption of the blood supply.
Note: Care must be taken to rule out slipped capital femoral epiphysis (SCFE). Fractures can be distinguished from SCFE by a detailed history supplemented by appropriate x-ray examination and assessment; in unclear situations, an MRI is indicated.
2.0, 2.5, or 3.0 mm K-wires can be selected, depending upon the size of the child.
Larger K-wire sizes are preferred for stability.
Threaded K-wires also increase stability.
Typically, two K-wires separated vertically are inserted. This configuration may be more suitable in smaller bones.
An alternative is three K-wires used in an apex-distal, triangular configuration, with the lower central K-wire abutting the calcar.
Inserting a single central K-wire does not provide rotational stability.
2. Patient preparation and approaches
Depending on the approach, the patient may be placed either supine or lateral.
For this procedure the following approaches may be used:
A K-wire is inserted through the lateral cortex of the femur just above the level of the lesser trochanter and advanced to the fracture line.
Pitfall: Secondary subtrochanteric fractures may occur if K-wires are inserted with an entry point distal to the level of the lesser trochanter.
The femoral neck is manipulated gently into position, usually by traction in the line of the femoral neck using a bone hook.
If necessary, manipulation of the femoral head is achieved using a small K-wire, inserted into the femoral head, as a joystick.
Gentle reduction maneuvers are essential, in order to prevent secondary damage to the femoral head blood supply.
When acceptable reduction has been obtained, the first K-wire is advanced across the fracture and into the femoral head. Overpenetration into the hip joint must be avoided.
Additional wires are inserted under x-ray control, using image intensification.
The K-wire positions are confirmed on AP and lateral x-ray images, using image intensification.
If using a standard radiolucent table, the K-wire fixation is generally stable enough to allow a “frog” lateral view.
The K-wires are repositioned if necessary.
Images at multiple angles are used to confirm that the K-wires do not penetrate into the hip joint.
Pitfall: K-wire penetration can occur, especially with eccentrically placed wires, even if not apparent on standard AP or lateral x-rays.
Typically, 5 mm of epiphyseal bone/cartilage should remain between the wire tip and joint surface.
Dynamic, real-time image intensification, with a full range of internal and external rotation at different degrees of flexion, is useful to see how close the K-wire-tip is to the joint surface of the head.
Observing an approach/withdrawal of the K-wire tip helps in judging its position. Some surgeons supplement this examination with 3-D image intensification for confirmation.
Arthrography is useful to confirm correct wire placement in the younger patient.
The K-wires can be bent, cut short, and left beneath the fascia lata.
The K-wires are usually removed with a short secondary procedure, once the fracture is healed.
5. Hip spica
Because K-wire fixation is less stable, and only indicated for younger children, a hip spica cast is generally used to supplement the fixation.