Intramedullary K-wire fixation is mainly used in subcapital fractures of the metacarpals, especially the fifth metacarpal (“Boxer’s fracture”). With this technique, impairment of tendon gliding over a distally placed implant on the bone is avoided.
For this procedure the following approaches may be used:
For the 5th metacarpal, the entry point is dorsoulnar at the metacarpal base, without damaging the carpo-metacarpal joint and respecting the insertion of the extensor carpi ulnaris tendon. Check under image intensification. For the other metacarpals the entry point is dorsally at the metacarpal base. Care must be taken that the protruding ends of the K-wires will not interfere with the gliding of the extensor tendons.
Opening the cortex
The dorsoulnar cortex is opened with a 2 mm drill bit. Drilling is first done perpendicularly to the bone surface, so that the drill does not accidentally slip off the bone. A drill sleeve has to be used to protect the dorsal sensory branch of the ulnar nerve, or the extensor tendons.
Preparing the entry portal
Tilt the drill by approximately 60 degrees so that it enters the intramedullary canal at as obtuse an angle as possible. Do not drill through the opposite cortex. The drill hole is then enlarged with a 2.7 mm, or 3.2 mm, drill bit, or a burr, in this oblique direction.
Pre-bending the K-wires
Two or three K-wires of 1 mm, or 1.25 mm, diameter have to be inserted with the blunt tip first, to reduce the risk of perforating the thin cortex of the metacarpal head. They are bent in the following way: The distal tip is bent upwards with pliers by about 20 degrees. About 2 cm further, the wire is bent in the same direction by not more than 10 degrees. At a point where the wire is slightly longer than the metacarpal into which it will be inserted, the proximal end of the wire is bent through 90 degrees in the same plane. This way, the direction of the insertion can always be controlled. To avoid injury, the sharp end of the wire is bent over.
Two wires are inserted manually into the medullary canal and advanced into the diaphysis without reaching the fracture zone. The bent tip should point in a palmar direction.
The fracture is preliminarily reduced by flexing the MP and PIP joints to 90 degrees, and using the proximal phalanx to push up the metacarpal head (Jahss maneuver).
Advance and rotate K-wires
The wires are now advanced manually, or with a hammer, across the fracture zone into the head. The correct position is checked using image intensification. Make sure not to perforate the thin cortex. The K-wires are then rotated so that the bent tips are pointing dorsally and diverging in slightly different directions (dorso-radial and dorso-ulnar). Ideally, the blunt tips lie underneath the dorsal cortex of the head.
This allows for a 3 point fixation which increases the stability of the construct and prevents the K-wires from backing out proximally. The K-wires are then bent at the level of the entry portal and cut.
5. Postoperative splint
A removable splint is applied at the end of the operation, with the hand in an intrinsic plus (Edinburgh) position.
While the patient is in bed, use pillows to keep the hand elevated above the level of the heart to reduce swelling.
For ambulating patients, put the arm in a sling and elevate to heart level.
Instruct the patient to regularly lift his hand above the head in order to mobilize the shoulder and elbow joints and to reduce swelling.
See patient after 2 days for changing of the dressing. After 10-12 days remove the sutures and confirm with x-rays that no secondary displacement has occurred.
At that time, active mobilization is started, supervised by a physical therapist. The splint is continued.
Additional x-rays are taken 6 weeks after internal fixation. Usually the K-wires can then be removed.