Lag screw fixation

Fractures of the diaphysis can be transverse, oblique, spiral, or comminuted.
Treatment of long oblique and spiral fractures is similar. The difference is in the screw insertion in relation to the fracture plane, which is strictly single in the long oblique fractures. In the spiral fractures, the fracture plane is helical and, therefore, each screw is inserted in a slightly different direction.
Indirect reduction is achieved by traction and digital manipulation. Usually, these fractures are unstable.
There are two possibilities to treat this fracture: closed reduction with percutaneous pin/screw fixation, or ORIF with lag screws.
Other indications for ORIF are open fractures, or soft-tissue lacerations.

The decision whether a compression plate or a protection plate is used in oblique fractures depends on the length of the fracture line. In a long fracture, fixation with 2, or more, lag screws is usually sufficient, and no protection plate is necessary.
A good rule is the following:
The fracture line (B) should be at least twice the length of the diameter of the phalangeal diaphysis (A), i.e. B >= 2A.

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 the following approaches may be used:

• Midaxial approach to the proximal phalanx
• Dorsal approach to the phalangeal metaphysis (after Pratt)

Reduction can be achieved by traction and lateral pressure exerted by the surgeon.
In this fracture pattern, stable closed reduction is an exception.
If the fracture reduction appears stable, and nonoperative treatment is being considered, it is essential to confirm reduction under image intensification.

Rotate the finger, open the fracture, and irrigate the fracture zone for good direct visualization.
Determine the exact geometry of the fracture. This is very important for later screw placement.

Direct reduction is necessary when the fracture can not be reduced by traction and lateral manipulation, or the reduction is unstable.
When indirect reduction is not possible, this is usually due to interposition of parts of the extensor apparatus.
It is wise to use magnifying loupes in order to be able to identify any additional fracture lines.
Gently use pointed reduction forceps to reduce the fracture anatomically.
Beware: excessive pressure may cause fracture comminution.

Check reduction under image intensification. It is mandatory to confirm that the apex of each fracture fragment has been properly reduced, otherwise, malrotation may result.

Provisionally hold the reduction with either 2 K-wires, or 1 K-wire and a reduction forceps.

At this stage, after provisional fixation, it is advisable to check the alignment and rotational correction by moving the finger through a range of motion.
Rotational alignment can only be judged with the fingers in a degree of flexion, and never in full extension. Malrotation may manifest itself by overlap of the flexed finger over its neighbor. Subtle rotational malalignments can often be judged by tilting of the leading edge of the fingernail, when the fingers are viewed end-on.
If the patient is conscious and the regional anesthesia still allows active movement, the patient can be asked to extend and flex the finger.
Any malrotation is corrected by direct manipulation and later fixed.

Under general anesthesia, the tenodesis effect is used, the surgeon fully flexing the wrist to produce extension of the fingers, and fully extending the wrist to cause flexion of the fingers.

Alternatively, the surgeon can exert pressure against the muscle bellies of the proximal forearm to cause passive flexion of the fingers.

If the screws are not perpendicular to the fracture plane, screw tightening may lead to fracture displacement.

If possible, 3 lag screws should be inserted. As a general rule, they should be inserted at equal intervals.
Do not insert a screw too closely to the apex of each fracture fragment, as this may cause comminution.
It is wise to use magnification loupes throughout the procedure to avoid inserting screws through incomplete fissures.

If the fragment is too short to allow for insertion of 3 screws, use 2 screws, equally spaced.

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 cortex properly. This problem increases when self-tapping screws are used due to the geometry of their tip.
• Too long screws endanger the soft tissues, especially tendons and neurovascular structures. With self-tapping screws, the cutting flutes are especially dangerous, and great care has to be taken that the flutes do not protrude beyond the cortical surface.

There are two important reasons for countersinking:

1. The risk of soft-tissue irritation is greatly reduced by ensuring that the the screw head protrudes only minimally from the bone surface.
2. Countersinking ensures that the screw head has a maximal contact area with the bone, distributing the forces from the screw head more widely and more biodynamically than an unsunk head.

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) Threaded hole first
Drill a hole through both cortices, using the drill for the threaded 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.

Use a 1.5 mm (1.3 mm) drill bit, carefully drill a gliding hole for the first screw in the near (cis) cortex. Excessive pressure may cause fracture comminution.
In case three screws are planned, drill for the middle screw first.

Insert a drill guide and drill a 1.1 mm thread hole in the far (trans) cortex. When perforating the far cortex, be careful not to injure the soft tissues.

Using a drill guide not only preserves the soft tissues and ensures ideal centering of the threaded hole, but also helps to prevent the drill from breaking, due to excessively oblique insertion.

Countersink the gliding hole in order to reduce contact pressure and prevent the screw head from being too prominent. This should never be undertaken using a power tool.

Use a depth gauge to measure for screw length. In case of an oblique drill hole, be sure to measure to the obtuse angle of the cortex.

Insert the first lag screw. If the fragment is large enough for three screws, carefully tighten this screw now. Be sure to engage the far cortex, but beware of soft-tissue injury that might be caused by a screw’s protruding too far.
The fracture is now compressed.

If the fragment is too short for three screws, do not tighten the first screw, and prepare for the second screw in a similar fashion. Insert the second screw.
It is important to tighten the two screws alternately, so as not to displace the fracture reduction.

In case a peripheral screw has to be inserted close to the apex of a fragment, use 1.3 mm screws. Keep in mind that the minimal distance to the fracture line must be equal to the diameter of the screw head.

Prepare for the remaining screws in the same fashion as for the first.
Insert the screws and carefully tighten them alternately.
Confirm fixation under image intensification.

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

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

See patient after 5 days and 10 days of surgery.

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.