4. DISTAL PHALANX
4.1. Fracture- dislocations of the DIPJ
(A) Dorsal Avulsion
The typical injury is the mallet injury. If there is less than 20% of the dorsal articular surface avulsed, these are almost always stable and can simply be treated with a mallet splint worn full time for 6 weeks and part time for 2 weeks. For late presenters they should have the splint on full time for 8 weeks and part time for 2 weeks. PIP joint movement must be encouraged in this period and therefore proper use of the splint shown to the patient. Frequently the commercially available splints must be shortened to achieve this, especially for the little finger. Daily washing with the finger held straight is important. Local massage over the dorsum of the DIP joint may reduce the risk of localised CRPS 1 which delays a good outcome although it typically resolves.
If there is more than 20% dorsal avulsion there is a risk of volar subluxation of the main fracture fragment. True lateral radiographs need to be taken and repeated for three weeks from injury as late subluxation can occur. This is easily missed on the usual rather oblique radiographs. If there is volar subluxation of the main fracture fragment (most of the distal phalanx) of 1-2 mm this needs to be reduced and held. Under local anaesthetic a 1.1 mm K-wire is passed carefully along the middle of the distal phalanx attempting to exit the base through the main fragment of the articular surface. This can be difficult to achieve. If the wire passes though the fracture line the dorsal fragment may displace a little but unless marked this gives acceptable results. The distal phalanx is reduced and the wire passed into the middle phalanx.
The K-wire always needs protection with a splint or plaster for 4 weeks, and at some time between 4 and 5 weeks the wire is removed and the joint mobilised. They will probably have a mild extensor lag long term and a dorsal bony prominence.
If the joint is not reduced it may dislocate volarly giving little option for late treatment other than fusion.
Some surgeons advocate use of a second wire to reduce the dorsal fragment. This gives better radiographs but does not seem to affect the outcome. We tend not to add the second wire as it simply adds complexity. Open reduction and fixation is associated with very high complication rates in most published series and should be avoided.
(B) Volar Avulsion
This is an avulsion of the insertion of the FDP tendon and needs to be reduced open via a volar Brunner incision and held with a pull through suture or small bone anchor(s). Occasionally with a very large fragment a single screw can be used. This is a complicated operation and requires a reasonably experienced Surgeon. They will then need a physiotherapy-supervised controlled active mobilisation protocol as for the standard flexor tendon repair with dorsal protection for 6 weeks full time, 6 weeks part time
(C) Comminuted intra-articular (Pilon or fracture dislocation)
This is similar to the Pilon fractures/fracture dislocations of the PIPJ and treatments are the same.
4.2. Distal Phalanx - Shaft
These are common injuries typically as simple transverse fractures or comminuted crush fractures.
This can be from a fall, but often follow a direct blow. There may be a little displacement, but typically it is not off-ended. A little displacement is normally accepted and early mobilisation encouraged. If there is off-ending of the distal fracture fragment this is unstable and there may be interposed soft tissue, which would result in a non-union. This fracture can be reduced and held with a 1.1 mm K-wire along the length of the distal phalanx. If there is quite a small proximal fragment then it may be necessary to cross the DIP joint. This should not be done lightly, as wires at this level seem to have amongst the highest incidence of pin track sepsis, which can then cause DIP joint infection. The commonest fracture with a small proximal fragment is the Seymour fracture through the physis in a child. It is important to open the fracture site to ensure no soft tissue is interposed. The overlying sterile nail matrix will have been torn and should be repaired with absorbable sutures. We use 6/0 Vicryl rapide.
This is essentially a soft tissue injury and should be addressed as such. The patients therefore require elevation, early mobilisation and desensitisation. They should be warned that there may be bone union with some displacement, or even a fibrous non-union but this is not typically a functional problem. Occasionally there will be a bone spike which may need removal late on as they do not resorb. There may be occasional symptomatic non-union which requires late excision of the small fracture fragment. Neither of these risks should typically encourage the surgeon to operate, as the early operative risks are greater and late treatment typically with excision under local anaesthetic is relatively simple and safe. Cold intolerance is almost inevitable and patients should be warned of this.