A typical site for metacarpal base fractures is the fifth metacarpal. Most of these fractures are comminuted and impacted, and are often associated with carpo-metacarpal fracture dislocations. Additional dorsal shearing fractures of the hamate may be present. These fractures are usually fixed with plates, or K-wires in the case of small fragments, and may need bone grafting.
CT scans are very helpful to determine the number, size and position of the fragments.
Depending on the fracture geometry, simpler fractures can be treated with lag screws (e.g. extensor carpi ulnaris tendon avulsion fractures), or with T-, Y- or L-shaped plates.
Dislocation of the 4th metacarpal
Fractures of the fifth metacarpal base may be associated with a carpo-metacarpal dislocation of the fourth ray. In that case, the fourth metacarpal is reduced first and usually stabilized with transfixion K-wires. Occasionally, there is a subluxation of the 3rd metacarpal, or even the 2nd metacarpal, and any combination of additional fractures can be seen.
Apply axial traction on the finger, either manually or with a finger trap. A small external fixator can be used, with K-wires inserted into the hamate and the distal metacarpal, preliminarily to fix the reduction. Capsulotomy is needed to check the reduction of the articular fragments if the joint capsule is not already ruptured.
Use a dental, pick, a periosteal elevator, or small K-wires to reduce the fragments. Insert small K-wires for preliminary fixation of these articular fragments. Occasionally, these K-wires are inserted percutaneously; make sure not to injure the dorsal sensory branch of the ulnar nerve. In case of a bone defect, bone graft from the distal radius is used to fill the void. Check reduction using image intensification. If the hamate is uninjured, its articular surface can be used as a template for restoring the articular surface of the metacarpal base.
Check rotational alignment
Turn the hand over and flex the fingers passively to check for correct rotational alignment. The image on the right shows rotational malalignment of the middle finger (“scissoring”).
Accompanying hamate fracture
In the case of a shearing fracture of the hamate, reduce this fragment first and fix it with a lag screw.
4. Plate preparation
Depending on fragment size, a 2.0 mm, or, more frequently, a 1.5 mm plate is used. T-, L- or Y-shaped plates can be used and the choice depends on the geometry of the fracture. At least 2 screws should be inserted into the diaphyseal fragment.
Contouring of the plate
The plate must be contoured exactly to fit the surface of the metacarpal, including any necessary twisting.
Apply the plate
Position the plate exactly so that the articular fragments can be fixed using screws through the proximal plate holes. Often, it is not possible to insert a screw into each fragment. Small fragments should be supported by adjacent large fragments, or bone graft. Be careful to ensure that the screws do not perforate the joint surface.
Buttress small fragments
If necessary, small K-wires can be inserted transversely just deep to the subchondral cortical bone, in order to buttress these small fragments.
Drill for first screw
Begin fixation with the most critical articular fragment. Drill carefully in order not to displace the fragments. Measure for the length of the screw.
Insert first screw
Insert the first screw without completely tightening it. Confirm the reduction and correct screw position using image intensification.
Fix plate to diaphysis
With the first screw in place, align the plate along the shaft. Usually, the plate is now fixed to the diaphyseal fragment with one screw through its most distal hole. Tighten this screw.
Insert second proximal screw
Drill the second main articular fragment. Avoid penetration of the joint surface and interference with the first screw. Measure screw length with a depth gauge. Insert the screw and alternately tighten the two screws in the articular fragments
If additional large metaphyseal fragments need fixation, insert screws through the plate, or insert an independent lag screw. If needed, use additional bone graft to fill any defect.
Insert second diaphyseal screw
Insert the second and, if possible, a third screw into the diaphyseal fragment and tighten them.
When the fixation is completed, remove the external fixator and K-wires, other than those needed to buttress small articular fragments.
6. Complex fragmentation
Bridging fixation with ExFix
If fixation can not be performed with screws and plates, stabilization can be achieved with an external fixator bridging the fracture zone from the hamate to the metacarpal. This allows for the restoration of correct length and rotational alignment.
Bridging fixation with internal fixator
This can also be performed using a bridging plate as an internal fixator with screws inserted into the hamate and the diaphysis of the metacarpal. The plate is removed when the fracture has completely healed after about 4 months.
7. 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.