Digital mucous cysts develop in the distal interphalangeal joint. They show a few diagnostic problems.
They appear in adult people in the form of a small, cold, firm mass, covered with a transparent layer at the dorsal joint level.
When observing the skin, some cysts are not apparent, it is only known they are there because of a nail groove at the base of the cyst. This deformation may appear before the transparent sac. Cystic lesions are located in the proximal ungual recessus compressing the matrix, thus creating this groove.
In most cases, these cysts are adjacent to the DIP joint by means of a lining.
DIP joint arthrosis is related in 75% of the cases and explains the appearance of the skin lesion.
Average age for this pathology is around 60, more frequent among women. The three first fingers are most commonly affected, particularly the middle finger.
In most cases the injury is painless. Patients resort to consultation due to the appearance and enlargement of the cyst. Grooving of the nail is present in 30% of the cases.
Fistulisation of the cyst is not rare; whether it is performed spontaneously or therapeutically, its major risk is bacteria contamination and arthritis, as the cyst is adjacent to the joint.
Strict Anterior/Posterior standard radiographs will show joint impingement in 15% of the cases. The anterior view will show presence of osthephytes, in around 40% of the cases, even in the anterior view, joint dislocation can be observed in certain cases. These signs are directly associated with the arhtosic process.
The literature has described various treatments such as abstention, aspiration, injections, CO2 snow, radiotherapy, etc. However, surgery has been studied in a precise manner.
Surgical protocol should be meticulous and broad in order to avoid recurrence.
full skin-cyst excision 
excision of dorsal joint osteophytes 
excision of the pathological joint capsule. The delicate extensor tendon region should be protected 
Joint lavage and intra-joint synovectomy. 
Coverage of skin substance loss through complete skin grafting or rotation local flap.
Scarring requires 2-3 weeks and the cosmetic result is achieved in 3 months.
In order for the surgical treatment to be effective, it should be broad. However, the extensor should be protected to prevent the distal phalanx from dropping, which can naturally happen if the osteophytes are bulky. Recurrence risk is around 2%, thanks to this treatment.
Arthritis will keep evolving and the joint pruning performed in the per-operative period does not have any influence in the degenerative joint injuries. Therefore, progressive stiffness of the finger is not related to surgery.
