Our Orfit blog shares information and instructions in matching our thermoplastic materials to orthotic designs.
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Today, we focus on the “Stack” or “Mallet Finger” Orthosis.
A mallet finger develops when there has been disruption of the terminal slip extensor tendon to the digital phalanx (zone I), causing an inability to actively extend the distal interphalangeal joint (DIP).
The mechanism of injury can be sudden forceful flexion of the extended fingertip or blunt trauma to the dorsum of the finger. The injury can even result in a variable-sized bone avulsion from the distal phalanx or fracture through an open epiphysis.
How are mallet finger injuries classified (Doyle’s Classification of Mallet Finger Injuries)?
- Type 1: closed rupture of tendon insertion
- Type 2: Open injury with tendon laceration
- Type 3: Open injury with deep abrasion with loss of skin, subcutaneous tissue and tendon substance
- Type 4A: trans-epiphyseal plate fracture in children
- Type 4B: avulsion fracture of the distal phalanx involving 20-30% of articular surface
- Type 4C: fracture >50% with palmar subluxation of the distal phalanx
How are Mallet injuries treated in the clinic?
The main purpose of the mallet finger splint treatment is to hold the DIP finger joint in passive (hyper) extension so that healing of the injured tissue takes place. The splint should allow functional flexion of the proximal interphalangeal Joint (PIP). Extension of the joint is maintained by means of a lever arm system. This orthotic treatment aims to promote safe healing of the tendon, without the formation of adhesions, resulting in a strong tendon that is able to pull through its full excursion.
In practice, the patient may end up with a splinting regime of continuous (24/7) immobilization during 6-8 weeks, if necessary followed by 4-6 weeks of night splinting. Careful mobilization can be started after the 6-8 weeks immobilization period.
This long duration is needed because the short lever arm of the Extensor Digitorum Communis (EDC) tendon dictates full pull through of the EDC for the last few degrees of finger extension. Therefore there is no tolerance for even the slightest stretching out of the healed tissue.
When issuing a removable splint, it is of utmost importance to instruct the patient that the DIP joint must be maintained in extension at all times, even during wound care or daily hygiene.
*The following points are important and need to be considered:
- The DIP joint should be held in maximum comfortable extension or in slight hyperextension (0° -15°) if tolerated. Over-extension could pose a risk as many patients show blanching of the pulpa with even as little as 15° hyperextension. Ischemia will most likely develop after some weeks. Therefore the immobilization into extension without pulpa-blanching is only possible when the angle is no greater than half the maximum passive hyperextension.
- The splint should allow near full PIP joint flexion.
*Please note that the dorsum of the DIP joint is an area where pressure easily becomes a problem!
An easy method to fabricate a classic “stack” or “mallet” splint is to make a dorsally closed cylinder around the distal and middle phalanx and cut out the excessive material around the nail.
The most suitable Orfit sheet material to fabricate this splint design is Orfit Classic 1.6mm micro perforated. The stickiness of the material helps to create a thin and neat- looking dorsal and permanently bonded seam. The micro perforation style provides proper ventilation.
Orficast Thermoplastic Tape is also an excellent material for this splint and requires very little preparation or pattern making. Cut a strip of Orficast (20cm) and activate in hot water of minimum 65°C. Dry slightly to remove the excessive hot water and fold the material double lengthwise and press both layers together firmly. Stretch the activated material slightly to make the middle of the strip a little bit thinner. Pose the thinnest and middle part of the strip on the fingertip starting right under the nail. Stretch both ends of the strip proximally while crossing one end over the other covering the dorsal part of the distal and middle phalanx and leaving the nail uncovered. The DIP joint can be positioned between 0-15° degrees of (hyper) extension. Smooth all of the Orficast layers together. When sufficiently hardened, remove the splint and trim all sharp edges, corners and any excessive material away. The patient should be able to slide this splint on and off the involved finger, while maintaining continuous DIP extension. Keep the splint in place by adding an adhesive strapping tape or an velcro tape.