These fractures involve acute failure of the physis, which is usually the result of high energy trauma. Accordingly, the risk of avascular necrosis is high and a gentle anatomical reduction with stable internal fixation is required to provide the best prognosis.
6.5, 7.0, or 7.3 mm cannulated screws are used for adolescents.
4.0, or 4.5 mm cannulated screws may be selected for younger children. Be aware that these screws are considerably weaker and prone to breakage if used in too heavy a child.
Typically, two screws separated vertically are inserted. This configuration may be more suitable in smaller bones.
An alternative is three screws used in an apex-distal, triangular configuration, with the lower central screw abutting the calcar.
Inserting a single central screw does not provide rotational stability and is, therefore, less applicable for fractures, even though it is a common choice for slipped capital femoral epiphysis (SCFE).
Pitfall: Secondary subtrochanteric fractures may occur if screws are inserted below the level of the lesser trochanter.
2. Patient preparation and approaches
Depending on the approach, the patient may be placed either supine or lateral.
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 epiphysis, as a joystick.
Gentle reduction maneuvers are emphasized in order to prevent secondary damage to the femoral head blood supply.
Guide wire insertion
When anatomical reduction is obtained, the first wire is advanced across the fracture and into the femoral head. Penetration into the hip joint should be avoided.
Additional wires are inserted under image intensifier control, according to the two- or three-screw configuration chosen.
The guide wire positions are confirmed on AP and lateral x-rays.
If using a standard radiolucent table, the K-wire fixation is generally stable enough to allow a “frog” lateral view.
The wires are repositioned if necessary.
Images at multiple angles are used to confirm that the guide wires do not penetrate into the hip joint.
Measuring screw length
A depth gauge is used to measure screw length.
If a dedicated cannula/depth gauge set is not available, then a K-wire, of the same length as that inserted, is placed onto the lateral cortex adjacent to the inserted wire, and the difference measured to determine the screw length.
Drilling screw holes
The wires are overdrilled with the appropriately sized cannulated drill bit.
Adolescents in particular have very dense strong bone in the metaphysis near the growth plate and predrilling is recommended.
If cannulated screws are not available, then guide wires should be removed one at a time and an appropriate drill used.
Two or three cannulated screws are then inserted over the guide wires.
Note: Fully-threaded cannulated screws are easier to remove later.
Image intensification is used to confirm that the screw tip does not penetrate into the cartilage or the joint.
Typically, 5 mm of epiphyseal bone/cartilage should remain between the screw tip and joint surface. Three or four threads crossing the physis provides adequate fixation.
Pitfall: Screw penetration can occur, especially with eccentrically placed screws, even if not apparent on standard AP or lateral x-rays.
Real-time, dynamic image intensification, through a full range of internal and external rotation, and at different degrees of flexion, is useful to confirm the distance between the screw tip and the joint space.
Observing an approach/withdrawal of the screw 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 and screw placement in the younger patient.
Guide wire removal
Guide wires are removed.
5. Hip spica
If solid fixation has been obtained with screws, and the patient/family can reliably comply with toe-touch weigh bearing, then a cast is not necessary.
For patients below 5 years of age, a hip spica cast can be used if desired.