Lag screw fixation

While dislocations and ligament injuries are common throughout the hand, they are most common at the proximal interphalangeal (PIP) joint.
The spectrum of these injuries ranges from minor stretching (sprains) to complete disruptions of the ligaments.

Dislocations of the PIP joint are classified according to the direction of displacement of the middle phalanx. They can be palmar, dorsal, lateral, or lateral rotatory.

The collateral ligament usually tears at one of two locations:
a) at its attachment to the proximal phalanx
b) at its attachment to the volar plate and middle phalanx.
Often, these injuries are accompanied by a partial lesion of the volar plate.

Lateral subluxation can be accompanied by a condylar fracture, or a plateau fracture (either as an avulsion fracture, or as an impaction fracture).

Avulsion fractures are the result of side-to-side (coronal) forces acting on the finger, putting the collateral ligament under sudden tension. The ligament is usually stronger than the bone, causing the ligament to avulse a fragment of bone at its insertion.
Avulsion fractures result in marked joint instability.
If the fracture is not displaced, nonoperative treatment is usually indicated (buddy taping to the adjacent finger). Displaced fractures, however, must be internally fixed.

Only avulsion fractures with large fragments can be treated with lag screws.

Animation of the injury mechanism

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

For this procedure a midaxial approach to the PIP joint is normally used.

In cases of associated dislocation, start by reducing the dislocation.
Apply traction to the finger, with the PIP joint in slight flexion, to relax the flexor tendons and the lateral band.

Then, maintaining the traction, deviate the finger laterally...

...and rotate towards the contralateral side.

In the majority of cases, the collateral ligament regains its natural anatomical position after reduction.

Reduction is achieved by pulling the finger laterally, in the direction opposite to the forces that created the fracture, and into PIP flexion, as necessary, to approximate the fragment. The avulsed fragment is pushed into place by the surgeon’s thumb.

In displaced fractures, open reduction is often necessary after preparation of a gliding hole (see later).
A small pointed reduction forceps will be used gently to reduce the fracture from palmar to dorsal and from proximal to distal. The application of excessive force can result in fragmentation.

Note
Anatomical reduction is important to prevent chronic instability or posttraumatic degenerative joint disease.

The maximal permitted diameter of the screw head is one third of the diameter of the avulsed fragment.
Screw length needs to be adequate for the screw to penetrate and purchase in the opposite cortex.

Laterally deviate the phalanx in the opposite direction to gain maximal visualization of the joint (open book).
Evaluate the fracture geometry and determine the ideal position of the gliding hole (perpendicular to the fracture plane, and through the center of the fragment).

The risk of this procedure is the additional dissection and potential resulting devascularization, which can jeopardize fracture healing.

The avulsed fragment is now reduced anatomically, and held with a pointed reduction forceps, or a dental pick, as previously discussed.

There are two options to prepare the gliding hole and the threaded hole:

1) Gliding hole first
Drill the gliding hole in the near cortex. Ensure perfect fracture reduction and then insert a drill guide. Drill the threaded hole in the far (trans) cortex through the drill guide.
This method ensures that the threaded hole is perfectly in line with the gliding 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 gliding 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 gliding 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.

Insert the lag screw and tighten it. The screw should just penetrate the opposite cortex.
Check under image intensification. Reduction must be anatomical.

In cases where the avulsed fragment is so small that the screw length is not sufficient to reach the far cortex, the fixation can be strengthened by adding a figure-of-eight wire loop, passing beneath the ligament insertion into the fragment.
The wire loop is also a good choice if the achieved compression is not sufficient for other reasons.

Protect the digit with buddy strapping to the adjacent finger, to neutralize lateral forces on the finger.

While the patient is in bed, use pillows to keep the hand elevated above the level of the heart to reduce swelling.

See the patient 5 days and 10 days after surgery.

The patient can begin active motion (flexion and extension) immediately after surgery.

For ambulant patients, put the arm in a sling and elevate to heart level.

Instruct the patient to lift the hand regularly overhead, in order to mobilize the shoulder and elbow joints.

The implants may need to be removed in cases of soft-tissue irritation.

In case of joint stiffness, or tendon adhesion’s restricting finger movement, tenolysis, or arthrolysis become necessary. In these circumstances, take the opportunity to remove the implants.