Digital mucous cysts (DMCs) are a common presentation to primary care and unfortunately for many, the underlying diagnosis is not appreciated, thus delaying referral to a hand surgery service.
Clinical features
DMCs are essentially ganglions arising from the distal inter-phalangeal joints (DIPJ) of the fingers or thumb and it is thought that the aetiology is an underlying osteoarthritic joint.
DMCs are typically localised to one side of the midline over the dorsal aspect of the distal phalanx of the digit between the DIPJ and the nail cuticle edge. They normally have the typical appearance of a cyst and can almost look like a well-demarcated fluid filled blister (see image below).
The finger is marked prior to the surgical technique clearly demonstrating the cyst and the proposed rotational flap
As the cyst is fluid filled, the size may vary considerably allowing it to be distinguished from a Heberden’s nodule. It is not uncommon for patients to report spontaneous rupture of these cysts with a clear viscous discharge similar in appearance to a fast-acting adhesive.
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The lesion may cause local pressure to the adjacent nail bed and this can result in a longitudinal groove or split in the nail. Movement of the DIPJ may also be reduced and painful indicating the presence of an underlying degenerative joint.
DMCs are more common in women and are most often seen in the fifth to seventh decades of life.1 Patients normally present to the primary care team concerned about the cosmetic appearance of the lesion, but they can also have associated pain and may present with recurrent infections if the cysts discharge or if the patients perform needle punctures.
Pain may be secondary to the local pressure from the cyst or from the underlying degenerative joint.
Non-operative management
These approaches are commonly practised in the primary care setting and include compression (which bursts the cyst), aspiration, cortisone injection, subcutaneous de-roofing or even local resection.
Referrals to dermatology are common where techniques, such as liquid nitrogen therapy or a carbon dioxide laser, may be utilised. These techniques, unfortunately, have a variable and sometimes high recurrence rate.2 Furthermore, repeated aspirations or ruptures increase the risk of infection seeding into the DIPJ and subsequent septic arthritis of the joint.
Operative management
Observation of the DMC is an accepted treatment option in many cases as the cysts sometimes disappear spontaneously after a few months. Indications for surgery may include recurrent discharge, nail abnormalities and thinning of the overlying skin, but the commonest reason is due to cosmesis as patients are unhappy with the appearance of their finger.
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This may also affect their employment if they are in direct contact with customers. Pain is a relative indication for operative treatment as patients are warned that cyst excision may not provide complete pain relief due to the presence of the underlying osteoarthritic joint.
It was previously accepted that the only definitive surgical management for DMCs was DIPJ arthrodesis. While this technique is undoubtedly successful, it is not indicated for a joint with minimal pain and only slight reduction in movement.
To enable complete excision, the cyst needs to be removed together with overlying skin and underlying joint capsule.3,4 Very small cysts may be excised in an ellipse to allow direct skin closure, but a common cause for recurrence is failure to excise enough skin due to concerns of wound closure.
For larger cysts or to decrease risk of recurrence, various skin incisions have been proposed including local rotation or advancement flaps which provide coverage for excised or thinned skin overlying the cyst.4
In our unit, all DMCs are excised and the skin defect covered using a local rotation flap extended to the level of the proximal inter-phalangeal joint (see image top). This minimises the risk of recurrence and also of wound problems from stretching skin too tightly. The procedure is performed under local anaesthesia using a digital tourniquet so even patients with significant medical comorbidities are eligible.
We have recently performed a retrospective review of all surgical cases performed by the senior author in the past 10 years using the above technique. In a cohort of more than 60 patients with a minimum postoperative follow-up of six months, we identified only one case of cyst recurrence.
Summary
DMCs are a common presentation to the primary care setting and numerous conservative treatment methods are utilised. Most, however, have an unacceptable recurrence rate and we recommend that patients are referred promptly to the local hand service for formal cyst excision and coverage using a local rotation flap.
- Mr Johnson is a specialty registrar in orthopaedic surgery and Mr Cox a consultant hand and orthopaedic surgeon in the Raigmore Hospital Hand Unit, Inverness, Scotland
References
1. Dodge LD, Brown RL, Niebauer JJ et al. The treatment of mucous cysts: long-term follow-up in sixty-two cases. J Hand Surg Am 1984; 9: 901-4.
2. Nelson CL, Sawmiller S, Phalen GS. Ganglions of the wrist and hand. J Bone Joint Surg Am 1972; 54: 1459-64.
3. Shin EK, Jupiter JB. Flap advancement coverage after excision of large mucous cysts. Curr Orthop Pract 2008; 19(3): 276-9.
4. Kleinert HE, Kutz JE, Fishman JH et al. Etiology and treatment of the so-called mucous cyst of the finger. J Bone Joint Surg Am 1972; 54: 1455-8.
