Introduction

The characteristic malformation on the fingertip that resembles a hammer or mallet is known as mallet finger. As the finger is angled against the natural physiology of a finger, this deformity prevents the finger from straightening. Participating in sports like basketball or netball regularly causes physical stress to the fingers, which results in this deformity since the fingertips are frequently struck with force. The swan neck deformity, which is more severe than the mallet finger and results in poor finger function, can develop from untreated mallet finger. It causes the fingertip to resemble a swan’s neck. After reading this article, you should have a better understanding of how both conditions develop and how to prevent them. 

Finger and tendon involvement

The extension of the fingers and wrists is connected to a complex network of extensor tendons in the hand. There are intrinsic and extrinsic tendons in the extensor tendon system, but let's first define a tendon before delving into the specifics of the two. Tendons act as connectors between bones and muscles. Made of tough fibrous tissue found all over the body, they play a key role in enabling movement. Since the tendon tissue is located near the muscle and contains contractile fibres, which are involved in shortening and producing force within muscle cells, the muscle influences the tendon's activity, which in turn influences how the muscles work.¹

The intrinsic tendon

All of the hand's muscles include intrinsic tendons, which regulate motor function. These include the hypothenar muscles, which control the little finger, and the thenar muscles, which control the thumb.

Lumbricals interossei

In order to perform complex hand movements, such as pinching or typing, these four muscles cooperate to flex the metacarpophalangeal (MCP) joints and extend the interphalangeal (IP) joints.² These muscles allow the knuckles to bend while keeping the fingers straight. This is useful when typing and holding small objects.

The extensor tendon

The hand's extensor tendon system is a sophisticated network that extends from the forearm to the wrist and fingers. Two lateral bands and a centre slip comprise the extensor action. While the lateral bands move along each side of the finger and unite to create the terminal extensor tendon, which inserts into the distal phalanx and extends the DIP joint, the central slip attaches to the base of the middle phalanx, helping to straighten the proximal interphalangeal (PIP) joint.

By extending the DIP joint, the terminal extensor tendon helps to straighten the fingertip.⁴ It enters the dorsal crest, which is the dorsal base of the distal phalanx. This tendon is the final segment of the finger's extensor mechanism.⁵ The extensor tendons are like pull-cords that straighten your fingers, right down to the fingertip.

Muscle-tendon balance

The strength of the muscles and the mechanical characteristics of the tendons must be balanced for the tendons to transfer force efficiently and guarantee movement. If the muscles become stronger, however, the tendons do not adapt to this, causing strain on the tendon, which can induce an injury. Research indicates that muscles and tendons do not adapt at the same rate, which leads to an imbalance in the tendons and muscles that frequently occurs in persons who exercise intensely without taking breaks, resulting in rapid muscle growth.⁶

What is a mallet finger?

Let's imagine this: A ball striking the tips of the finger violently during a baseball game can cause the extended fingertip to flex forcefully. This is a common cause of mallet finger. The extensor tendon, which is responsible for straightening the fingertips, is impacted, making it difficult to extend the finger's last joint and giving it a limp appearance.⁷ Injury to the fingertips may result inInjury to the fingertips may result in a soft tissue mallet injury if it causes a rip in the tendon itself. If the bone is separated from the tendon, known as an avulsion fracture, it will cause a bony mallet.  

Without affecting the bone, tendinous mallet finger happens when the terminal extensor tendon tears at its insertion on the dorsal base of the distal phalanx. It is typically brought on by an abrupt force applied to an extended DIP joint, which results in an imbalance in extensor forces and, if ignored, can result in permanent deformity.

An avulsion injury known as bony mallet finger occurs when the extensor tendon pulls a piece of bone away from the distal phalanx during a violent impact, usually a ball striking the fingertip. The extensor mechanism is interfered with, and joint instability may result as the tendon stays intact but separates from the bone fragment.

Development of swan neck deformity

Eventually, a swan neck deformity may develop if the mallet finger is not treated or is not well managed. This is marked by the fingertip joint (DIP) bending downward, the middle finger joint (PIP) bending further backwards than it should, and a small bend in the joint where the finger meets the hand (MCP).⁸ The tip droops, the middle joint bends the wrong way, and the base joint curves slightly. Swan neck deformity results from an imbalance in the finger's extensor mechanism, which can be brought on by trauma to the extensor mechanism, tightening of the extensor tendons at the Tightness at PIP joint, reduced function of the terminal extensor tendon at the fingertip, or ongoing inflammation, such as rheumatoid arthritis, that weakens the tendons can all contribute. In short, any issue that interferes with the mechanism that straightens the finger can lead to swan neck deformity. It can gradually deteriorate hand function if treatment is not received.

Either the tightness or overpull of the extensor mechanism on the proximal phalanx, or the lack of the extension mechanism at the distal phalanx, causes the deformity. The loss of the extensor tendon at the distal phalanx may be the first step, eventually leading to the distinctive bent shape. In other words, the deformity usually starts with tendon loss at the fingertip, then works its way up the finger.

One of the following may cause damage to the terminal tendon:

• A severe injury to the extensor mechanism (closed avulsion) caused by a direct strike to an extended finger 
• Weakening of the extensor tendon subluxation due to rheumatoid arthritis or other inflammatory disease
• Weakness from persistent inflammation at the DIP joint⁹

Excess tension in the central slip, along with stiffness in the small hand muscles, can result in the PIP joint bending backwards more than normal. Rheumatoid arthritis, severe brain injury, stroke, or just intrinsic tightness may be the cause of this. The hyperextension observed at the PIP joint and swan neck deformity are also caused by laxity of the volar plate. Overall, swan neck deformity happens when the finger’s straightening system is thrown off balance from injury, disease, or ligament looseness, causing the tip to droop and the middle joint to bend backwards.

Prevention 

Given that mallet finger is frequently caused while participating in sports, wearing finger splints and protective clothing, as well as generally being aware of your fingers, can help prevent chronic mallet finger. The severity of the mallet finger determines the course of treatment. The most popular treatment is splinting, which involves limiting the DIP joint's range of motion for six to eight weeks. Surgical procedures such as pinning involve inserting pins through the skin into the bone to hold the shattered fragments in place while the bone heals. Once the bone has healed, the pins are removed.

Hand therapy is usually the treatment for swan neck deformities if interventions are not implemented in a timely manner. This includes splinting and passive stretching to improve the mobility and flexibility of the PIP and DIP joints. Although stretching and running can improve mobility, surgery is probably not going to be necessary to restore the finger to its original state.

Patients are still able to move their PIP joint normally in the early stages of swan neck deformity.⁹ Surgery in these situations frequently attempts to restore the support that the volar plate typically provides. FDS tenodesis is a popular technique that aids in preventing the PIP joint from overextending. However, if the lateral bands are already slack, this won't correct the mallet finger deformity on its own. If the anatomy is still healthy, a lateral band tenodesis may be utilised in these situations to address both problems. In addition to soft tissue procedures, joint fusion or replacement may be required in advanced cases if there is joint damage (arthrosis). They may also need joint replacement (arthroplasty) if the MCP joints are also affected.

Summary 

Mallet finger, which is frequently brought on by a hard impact during sports, is an injury in which the terminal extensor tendon is damaged, causing the fingertip to droop. It may involve a bone avulsion or a tendinous tear. A swan neck deformity, in which the fingertip droops and the middle joint bends backwards, may result from it if treatment is not received. An imbalance in the finger's extensor system, which can be brought on by trauma, joint laxity, or inflammatory diseases such as rheumatoid arthritis, causes this deformity.

Muscle and tendon balance is essential for finger mobility. When muscles grow stronger more quickly than tendons can adjust, the risk of tendon injury increases. Splints and finger protection during activities are examples of prevention. Complications can be avoided with early surgery or splinting treatment. Treatment for swan neck deformities can include hand therapy or tenodesis, and in severe cases, surgical options such as joint fusion or joint replacement may be required.

The key to maintaining hand function is early treatment.