Metacarpal head fractures may be simple, but are often multifragmentary. The degree of displacement and the number of fragments may be difficult to judge on standard x-rays. CT scans can be helpful in these situations.
The fractures can usually be treated with screw fixation. If the fragments are sufficiently large, screws are inserted in an antegrade manner, without perforating the articular cartilage. In smaller fragments, retrograde fixation has to be performed, and the screws are inserted through the articular cartilage. Care must be taken to bury the screw head underneath the cartilage. As an alternative to standard screws, small headless screws can be used if the fragment is sufficiently thick. In severely impacted fractures, bone graft, harvested from the distal radius, may be necessary.
The articular fragments are manipulated using a dental pick, small K-wires, or a small periosteal elevator. Small K-wires can also be used for preliminary fixation. Depending on fracture configuration, pointed forceps may be useful for reduction.
In impacted fractures, the articular surface is reduced, and the bony defect under the fragments is filled with bone graft from the distal radius. This also helps to keep the fragments in place when the screw fixation is performed.
Anatomical reduction is mandatory
Anatomical reduction of the joint surface must be checked under direct view and image intensification. Maximally flex the MP joint in order to gain a view of the palmar aspect of the metacarpal head.
4. Large fragment fixation - antegrade
If the fragments are large enough to allow sufficient purchase, antegrade screws are preferred, in order not to penetrate the joint surface. Drilling must be performed very carefully in order not to perforate the articular cartilage. If necessary, drilling is performed under image intensification. Drill at low speed and without exerting pressure. Make sure that the screws do not conflict with the collateral ligament. As the screws do not engage the opposite cortex, they are inserted as position screws, i.e. they are threaded in both fragments.
If the fragments extend to the metaphyseal region, bicortical lag screws can be used.
Measure for length
Measure for correct screw length using the appropriate depth gauge. When measuring, be careful not to displace the reduced fragments. If a position screw is planned, choose a slightly shorter screw length than measured to avoid fragment displacement. Countersinking is only performed when the entry point of the screw is in the diaphyseal region.
Carefully insert the screw without displacing the reduced fragments. Confirm using image intensification. Insert additional screws in a similar manner.
5. Small fragment fixation - retrograde
Small fragments are best stabilized with retrograde screws that are inserted through the articular cartilage. Choose the smallest possible screw diameter to minimize the damage to the joint surface. Headless screws – if available in very small sizes – have the advantage that they can be inserted deeper into the fragment without protruding. Depending on the fracture configuration and available screw lengths, the opposite cortex may be engaged. Standard screws are usually inserted as position screws.
Drilling and measuring
Drill carefully in order not to displace the fragments. Measure for correct screw length with a depth gauge. When measuring, be careful not to displace the reduced fragments.
Countersinking the articular cartilage
When standard (headed) screws are used, the cartilage is countersunk to facilitate burial of the screw head. Be careful not to injure the thin subchondral cortex.
Carefully insert the screw without displacing the reduced fragments. Make sure that the screw head is buried in the articular cartilage and does not protrude into the joint. Insert additional screws using a similar technique.
6. Postoperative splint
A removable splint may be applied at the end of the operation, with the hand in an intrinsic plus (Edinburgh) position. In compliant patients with stable internal fixation the splint can be removed after any swelling has receded. It may be worn at night for a longer period as this may increase patient comfort.
While the patient is in bed, use pillows to keep the hand elevated above the level of the heart, in order to reduce swelling.
For ambulant patients, put the arm in a sling and elevate to heart level.
Instruct the patient to lift his hand regularly above the head, in order to mobilize the shoulder and elbow joints.
See the patient after 2 days for a dressing change. After 10-12 days, remove the sutures and confirm radiologically that no secondary displacement has occurred. Additional x-rays are taken 4 weeks after internal fixation. Usually, the fracture line will still be visible. X-rays are repeated after 8 weeks to assess union. Strengthening exercises and manual work are allowed according to clinical and radiological evidence of bone healing.
As pain and swelling recede, early, active, controlled digital range of motion exercises gently progress. The importance of mobilization must be emphasized to the patient and rehabilitation should be supervised by a physical therapist.