Oh, dear. So, your finger is starting to look bent? 

This position is known as a Boutonniere deformity (boo-ton-e-air), where the PIP joint becomes fixed in flexion and the DIP joint becomes hyperextended. The various muscles and their tendons which act upon the fingers work in perfect equilibrium, balancing the forces which act to pull into flexion or extension.

Disruption to this equilibrium results in changes in posture, movement and function. Injury can result from an open wound (eg by glass, a blade or a grinder) or a closed wound such as a dislocation, involuntary forced flexion of the joint beyond its range or blunt trauma.

 boutonniere

(Image courtesy of www.merckmanuals.com)

This deformity is the result of injury to the central slip of the extensor tendon mechanism, which is responsible for straightening the joints of the finger. The central slip is the middle segment of the tendon when it branches into three segments. The middle segment attaches to the base of the middle phalanx and extends the PIP joint. The outer two segments are referred to as the lateral bands, and their role is to switch between extension of the DIP joint and assisting in flexion of the PIP joint.  

 centralslip

(Image courtesy of www.jaaos.org)

Without your central slip tendon to counteract the pull of flexion, the PIP joint flexes and the lateral bands drift down towards the palm, further assisting flexion. They begin to tighten on either side, like a horse‚Äôs reins, tightening the DIP joint and making it hard for the DIP joint to flex.  When this position is prolonged, a tough ligament around the DIP joint known as the oblique retinacular ligament becomes increasingly tight. Over time, the DIP joint struggles to flex as the resistance increases from the lateral bands and from the tightening ligament. This is when the deformity is quite rigid and unable to be corrected passively.

How will we fix it?

The deformity can be managed conservatively by therapy or sometimes will require surgery. Therapy uses static and dynamic splints and exercises to regain length in the tight ligament and tendons, to restore normal flexion of the DIP joint and extension of the PIP joint. Once full extension of the finger is restored, then a period of immobilisation in full extension using a thermoplastic splint may be required to allow the central slip to heal.

In some cases, conservative treatment is insufficient and surgery is required to repair the central slip tendon. If you require surgery, then splinting and therapy will still be necessary.

Your therapist will also work with you on restoring movement, strength and normal function of your hand. 

How do you prevent it?

Seeing a hand therapist early after injury is paramount to preventing a fixed deformity in your finger.