Authors of section

Authors

Renato Fricker, Matej Kastelec, Fiesky Nuñez, Terry Axelrod

Executive Editor

Chris Colton

Open all credits

Lag screw fixation

1. Principles

Anatomy

The distal phalanx is divided into three anatomical parts: most proximally, the metaphysis, followed by the diaphysis (“shaft”), and finally the ungual tuberosity (“tuft”).
The base of the distal phalanx has a prominent dorsal crest at the insertion of the extensor tendon. The tendon is also adherent to the distal interphalangeal (DIP) joint capsule.
On the palmar surface is the insertion of the flexor digitorum profundus tendon. This is also adherent to the volar plate.
The flexor tendon inserts into the whole width of the base of the distal phalanx.
The volar plate is very flexible, allowing hyperextension of the DIP joint and pulp-to-pulp pinch.

The vascularity of the extensor tendons is more precarious than that of the flexor tendons. This prolongs extensor tendon healing time.

The distal phalanx is divided into three anatomical parts: most proximally, the metaphysis, followed by the diaphysis ...

Diagnosis

Discontinuities of the extensor insertion are often referred to as “mallet injury” or “baseball finger”. They can be purely tendinous, or bony avulsion fractures.
Diagnosis is based on

  1. The clinical history of the trauma
  2. Deformity, pain and swelling located in the dorsal aspect of the DIP joint
  3. Inability actively and fully to extend the DIP joint
  4. X-rays

AP and true lateral x-rays of the DIP joint are necessary for the diagnosis of fracture avulsions.
Low-energy radiographs, as used to visualize soft tissues, can be useful in identifying small flakes of bone.

Discontinuities of the extensor insertion are often referred to as “mallet injury” or “baseball finger”.

Flexion injury

The commonest cause of these injuries is forcible flexion of the actively extended DIP joint, as when stubbing a straight finger against resistance.

The commonest cause of these injuries is forcible flexion of the actively extended DIP joint, as when stubbing a straight ...

Axial compression injury

Occasionally, the injury is the result of an axial overload of the terminal segment of the finger, causing joint impaction and a dorsal marginal fracture, which is retracted by the pull of the extensor tendon.

Occasionally, the injury is the result of an axial overload of the terminal segment of the finger, causing joint impaction ...

Fracture subluxation of DIP joint

An obliquely orientated axial compression force sometimes results in a dorsal marginal fracture, involving approximately half the articular surface, and can disrupt the collateral ligaments.

An obliquely orientated axial compression force sometimes results in a dorsal marginal fracture, involving approximately ...

In such instances the pull of the flexor digitorum profundus results in palmar subluxation of the distal phalanx.
This injury represents a strong indication for ORIF.

In such instances the pull of the flexor digitorum profundus results in palmar subluxation of the distal phalanx.

Spectrum of injury – partial disruption

These injuries may be complete disruptions or partial disruptions.
The nature of the disruption may be either a tear of the tendon insertion without fracture, or a bony avulsion of the tendon from the dorsum of the base of the distal phalanx, the bony fragment being of variable size.

In incomplete tendon injuries the resulting extension lag is no greater than 30 degrees. The patient retains a partial ability actively to extend the DIP joint.

These injuries may be complete disruptions or partial disruptions.

In complete disruption of extensor mechanism, the patient is unable actively to extend the DIP joint.
The flexor digitorum profundus exerts a flexion deforming force onto the distal phalanx, partly counterbalanced by the intact oblique retinacular ligaments and the collateral ligaments.

In complete disruption of extensor mechanism, the patient is unable actively to extend the DIP joint.

A similar clinical picture is presented by bony avulsion of the extensor mechanism at its insertion. The dorsal avulsion fracture is of variable size.

A similar clinical picture is presented by bony avulsion of the extensor mechanism at its insertion.

Swan-neck deformity
In some patients, elasticity of the ligaments and a lax PIP joint can result in swan-neck deformity, because after disruption of the extensor mechanism at the DIP joint, all extensor forces are concentrated on the PIP joint.

In some patients, elasticity of the ligaments and a lax PIP joint can result in swan-neck deformity, because after ...

Nonoperative treatment (splinting)

Nonoperative treatment can produce excellent results, with near-normal range of motion, due to bone remodelling, even in the presence of persisting fragment displacement.
Nonoperative treatment is based on immobilization of the DIP joint in extension, leaving the PIP joint free.

Duration of immobilization
The DIP joint should be immobilized in extension for 8 weeks. It must be impressed on the patient that splintage should be uninterrupted during this period.
It must be kept in mind that the vascularity of this area is precarious, even in healthy patients, and healing is slow. Any shorter period of immobilization risks re-rupture. Joint stiffness is unusual after these injuries.

Result
Frequently, patients may complain of a dorsal prominence, and of loss of the last 10-20 degrees of extension of the DIP joint. Dorsal tenderness rarely persists for more than a month or so after removal of the splint.

Nonoperative treatment can produce excellent results, with near-normal range of motion, due to bone remodelling, even in the...

Dorsal splint vs palmar splint

Using a dorsal splint has the advantage of leaving the patient with the ability to pinch while the digit is immobilized.
However, proponents of palmar splintage argue that the palmar aspect is better cushioned than the dorsal and thereby can tolerate the splint better.

Proponents of palmar splintage argue that the palmar aspect is better cushioned than the dorsal and thereby can tolerate the...

Contoured custom thermoplastic splint

The advantage of a custom thermoplastic splint is that it is better adapted to the shape of the finger, and easier to change.

The advantage of a custom thermoplastic splint is that it is better adapted to the shape of the finger, and easier to change.

Cleaning

Instruct the patient to keep the finger in extension by pinching it with the thumb when the splint is taken off for cleaning.
Flexing the finger may delay the healing process.

Instruct the patient to keep the finger in extension by pinching it with the thumb when the splint is taken off for cleaning.

Pitfalls of nonoperative treatment

Hyperextension of the DIP joint
Do not attempt to immobilize the joint in hyperextension. This can compromise the precarious vascularization of the skin of the dorsal aspect of the joint and might provoke ischaemia and possible necrosis.

Immobilization of the PIP joint
Do not immobilize the PIP joint as this may result in flexion contraction of the joint.

lag screw fixation

2. Operative treatment: caveat

Inexperienced handling of this area may harm the germinative matrix of the nail and cause permanent deformity. Consider that nonoperative treatment is almost always a viable alternative in these fractures, often with comparable results. Operative treatment should only be attempted by experienced hand surgeons, in selected cases.

Absolute indications for surgical intervention are:

  • Open fractures
  • Palmar subluxation of the DIP joint

It is wise always to use magnifying loupes in these surgical procedures.

These injuries may be complete disruptions or partial disruptions.

3. Approach

For this procedure a dorsal approach to the DIP joint is normally used.

lag screw fixation

4. Reduction

Clean the fracture side

Flex the DIP joint. In order to gain better visualization of the fracture, use a syringe to clean out blood clots with a jet of water.
Often the degree of comminution is not apparent from the x-rays, and can only be determined under direct vision.
Use a dental pick to carefully free interposed tissues, and to remove blood clots and other debris.

In order to gain better visualization of the fracture, use a syringe to clean out blood clots with a jet of

Reduce the fracture

Extend the DIP joint. Put manual pressure on the palmar side of the distal phalanx.
Now complete the reduction with help of a dental pick.

Complete the reduction with help of a dental pick.

5. Drilling

Choosing screw size

The maximal permitted diameter of the screw is one third of the diameter of the avulsed fragment.
Screw length needs to be adequate for the screw to penetrate the opposite cortex.
Most commonly, a 1.0 mm screw is used. 1.3 mm screws can also be used for large fragments.

The maximal permitted diameter of the screw is one third of the diameter of the avulsed fragment.

Pitfall: causing comminution

Be very careful when drilling. When not drilling gently, comminution of the fragments may be caused.

Drill a gliding hole
Maintaining the reduction with a drill guide, drill a gliding hole using a 1.0 mm drill bit for a 1.0 mm screw.

Be very careful when drilling. When not drilling gently, comminution of the fragments may be caused.

Drill thread hole

Now use a corresponding drill bit to drill a thread hole into the opposite fragment, penetrating the far (trans) cortex.

Use a depth gauge to measure for accurate screw length.

Now use a corresponding drill bit to drill a thread hole into the opposite fragment, penetrating the far (trans) cortex.

Pitfall: Oblique measuring

When measuring for screw length in oblique drill holes, the measurement for the far cortex may be different from the measurement for the near cortex. This problem increases with the degree of obliquity.
Always measure both cortices and use the longer measurement. Keep in mind that a too long, protruding screw puts the soft tissues at risk.

The measurement for the far cortex may be different from the measurement for the near cortex. This problem increases with ...

6. Lag screw fixation

Screw insertion

Insert a self-tapping lag screw and tighten it. The screw should penetrate the opposite cortex.

The screw should penetrate the opposite cortex.

Drilling

Check under image intensification. Reduction must be anatomical.

Check under image intensification. Reduction must be anatomical.

Pitfall: Overtightening the screw

Be careful not to overtighten the screw as this may result in comminution of the fragment.

Be careful not to overtighten the screw as this may result in comminution of the fragment.

Option in large fragments: 2nd screw

In very large fragments, a second screw can be added to improve stability.

In very large fragments, a second screw can be added to improve stability.

Pitfall: palmar subluxation

If the collateral ligament and the volar plate are ruptured, palmar subluxation usually persists.

In such a case, the DIP joint needs to be immobilized with a K-wire.

If the collateral ligament and the volar plate are ruptured, palmar subluxation usually persists.

7. Aftertreatment

Aftertreatment depends on the size of the fragment, the quality of the bone, and the stability gained by the fixation.

The DIP joint is immobilized in extension in a palmar splint, leaving the PIP joint free.
PIP joint movement is encouraged immediately to avoid extensor tendon adhesion.
A Coban bandage to reduce swelling is recommended.

If the fixation is strong enough, the patient is encouraged to take off the splint 2-3 times daily, and to commence with gentle active exercises.

k wire fixation

Functional exercises

After 3 weeks, the splint is removed, and unrestricted active flexion and extension is permitted.
Passive motion is only permitted after 4 weeks.

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.
Mobilization of the PIP and MCP joints are encouraged from the very beginning.

k wire fixation

Implant removal

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