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.
If cannulated screws are not available, modification of this technique allows standard screws to be inserted.
If the child is too small for screw fixation, 2.0, 2.5, or 3.0 mm K-wires can be selected, depending on the size of the child.
Larger K-wire sizes are preferred for stability. Threaded K-wires also increase stability.
Typically, two screws (or K-wires) separated vertically are inserted. This configuration may be more suitable in smaller bones.
An alternative is three screws (or K-wires) used in an apex-distal, triangular configuration, with the lower central screw (or K-wire) abutting the calcar.
Inserting a single central screw (or K-wire) does not provide rotational stability and is, therefore, less applicable for fractures, even though it is a common choice for SCFE.
Pitfall: Secondary subtrochanteric fractures may occur if screws are inserted below the level of the lesser trochanter.
Guide wire insertion
Under image intensification, the first guide wire is inserted through the lateral cortex above the lesser trochanter, just above the calcar and into the center of the inferior half of the femoral head.
A wire can be placed along the anterior surface of the femoral neck as an indication of the anteversion.
Additional guide wires are inserted under image intensification, according to the two, or three, screw configuration chosen.
The 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 wires are repositioned if necessary.
Images at multiple angles are used to confirm that the K-wires do not penetrate into the hip joint.
3. K-wire fixation alone
If K-wire fixation alone is used, the K-wires are cut and bent, leaving them deep to fascia lata.
The stab incisions are enlarged to allow for screw insertion. The incision is deepened down to bone by spreading the tissues with an artery forceps or blunt scissors.
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 K-wires are overdrilled, through a soft tissue protector, with an appropriate sized cannulated drill bit.
Intermittent screening with an image intensifier is recommended to ensure that the guidewire does not penetrate into the hip joint as the drill advances.
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 joint.
Typically, 5 mm of epiphyseal bone/cartilage should remain between screw-tip and joint surface. Three, or four, threads lying within the epiphysis provides adequate fixation.
Pitfall: Screw penetration can occur, especially with eccentrically placed screws, even if not apparent on AP or lateral x-rays.
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 screw-tip is to the joint surface of the head.
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
The guide wires are removed, once the full complement of screws has been shown to be ideally positioned.
Forces through the hip are less with toe-touch weight bearing than with no weight bearing. Therefore, toe-touch is normally recommended for initial mobilization. This needs to be taught to children by a physiotherapist.
Range of movement
Range-of-movement exercises should start in the immediate postoperative period to prevent stiffness. Surgeons should indicate if any extremes of movement are forbidden.
Having started with toe-touch weight bearing, children progress to partial weight bearing and then to full weight bearing according to their age and the predicted rate of healing of their fracture. Even older adolescents should be fully weight bearing without aids at three months.
Swimming can be allowed as soon as partial weight bearing is permitted. Contact sports should be avoided for at least six months.
X-rays are generally taken immediately after the surgery and at 6 and 12 weeks.
Implants that cross the physis should be removed if there is significant growth remaining. The fracture should be healed and consolidated prior to removal (see Healing times).
Implants in young children should always be removed to prevent them from being covered by bony overgrowth.