Lag screw fixation

These common fractures are usually best treated with lag screws.

A minimum of two screws must be used, which necessitates that the length of the fracture zone be at least twice the diameter of the metacarpal bone. In case of a shorter fracture line, a single lag screw and a protection plate must be used.

AO teaching video: Metacarpal IV—Long spiral fracture—Fixation with two 2.0 mm lag screws

For this procedure the following approaches may be used:

• Dorsal approach to metacarpals
• Dorsal approach to 2nd metacarpal
• Dorsal approach to 5th metacarpal

To determine the exact geometry of the fracture and correct placement of the screws, it may be helpful to open the fracture plane by exerting traction and rotation on the finger.
The fracture may be cleared of interposed soft tissues; if necessary, the fracture site can be irrigated for better visualization.

Traction is exerted by an assistant while the surgeon reduces the fracture using pressure from a periosteal elevator, or a dental pick.

Hold the reduction with one, or two, pointed reduction forceps and confirm using image intensification. Make sure that the reduction forceps does not conflict with the planned screw positions.
It is essential to confirm that the apex of each fracture fragment has been properly reduced.

Turn the hand over and passively flex the fingers to check for correct rotational alignment.
The image on the right shows rotational malalignment of the middle finger (“scissoring”).

Lag screws should be inserted perpendicularly to the fracture plane. Tightening a screw that is not perpendicular to the fracture plane risks fracture displacement.

Be sure to insert the screws as lag screws, with a glide hole in the near (cis) cortex, and a thread hole in the far (trans) cortex.
Inserting a screw, across a fracture plane, that is threaded in both cortices (position screw) will hold the fragment apart and apply no interfragmentary compression.

Each lag screw must be inserted perpendicularly to the fracture plane.
In spiral fractures, the result is that the screws follow a helical disposition.

If the fracture length permits, 3 lag screws should be inserted. Generally, they should be inserted at equal intervals.

If the fragment is too short to allow for the insertion of 3 screws, use 2 screws, but recognize that this is a less stable construct. If in doubt, add a protection plate.

The screws should not converge to one point on the far cortex, as this may weaken the fixation if the holes are too close to each other, or fissuring occurs when the screws are tightened. Such convergence will only occur if there is a failure to insert the screws perpendicular to the fracture plane.

Often there are short fissure lines that are not apparent on the x-rays. Check for these under direct vision and make sure that the screws are not inserted through these fissure lines.

Do not insert screws too close to the fracture. A minimal distance from the fracture line, equal to the screw head diameter, must be observed.

There are two options to prepare the glide hole and the thread hole:
1) Glide hole first
Drill the glide hole in the near cortex. Check perfect fracture reduction and then insert a drill guide. Drill the thread hole in the far (trans) cortex through the drill guide.
This method ensures that the thread hole is perfectly in line with the glide hole.
This is the preferred method.

2) Thread hole first
Drill a hole through both cortices, using the drill for the thread hole. Then use the corresponding larger drill bit to overdrill the near cortex to create the glide hole.
This technique is useful for small fragments. The disadvantage, however, is that the holes may not be centered in relation to each other.
Pearl
If the near cortex is tapped prior to overdrilling for the glide hole, eccentric passage of the second drill is less likely. This can be achieved by inserting the chosen self-tapping screw through the near (cis) cortex and then removing it. The drill will now follow exactly the threaded axis.

Make sure that the drill bit for the glide hole does not reach and damage the far cortex as the purchase of the screw will be compromised.

2) Thread hole first
Drill a hole through both cortices, using the drill for the thread hole. Then use the corresponding larger drill bit to overdrill the near cortex to create the glide hole.
This technique is useful for small fragments. The disadvantage, however, is that the holes may not be centered in relation to each other.
Pearl
If the near cortex is tapped prior to overdrilling for the glide hole, eccentric passage of the second drill is less likely. This can be achieved by inserting the chosen self-tapping screw through the near (cis) cortex and then removing it. The drill will now follow exactly the threaded axis.

Do not advance the countersink too deeply into the cortex: the cortical thickness will determine the depth of countersinking. Excess penetration risks break-through of the screw head when tightened and loss of fixation. Countersinking is, therefore, done by hand and not with a power tool.

Avoid countersinking in the metaphyseal regions as the cortex is very thin.

When measuring for screw length in oblique drill holes, the measurement to the acute angle is different from the measurement to the obtuse angle. This problem increases with the degree of obliquity.
Always measure both angles and use the longer measurement. However, keep in mind that too long a screw can protrude to the extent that it puts the soft tissues at risk.

Ensure that a screw of the correct length is used.
-Too short screws do not have enough threads to engage the far cortex properly. This problem increases when self-tapping screws are used due to the geometry of their tips.
-Too long screws endanger the soft tissues, especially tendons and neurovascular structures. With self-tapping screws, the sharp cutting flutes are especially dangerous, and great care has to be taken that the flutes do not protrude beyond the cortical surface.

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.