6. THUMB PHALANGES
6.1. Proximal Phalanx Base (Ligament Injuries)
Essentially these are avulsion injuries of the collateral ligaments.
(a) Radial collateral ligament
If they are stable and there is a small bony fragment they should simply be mobilised. If they are unstable, they can be held in plaster. Because there is no overlying tendon as for the Stener lesion on the ulnar side, these can typically be held just in a thumb spica POP. The thumb should be held in a little bit of radial deviation and slight flexion at the MP joint for 4 weeks, with mobilisation thereafter. We typically immobilise the thumb and then discharge the patient with removal of the POP in the plaster room and no formal medical follow-up.
(b) Ulnar collateral ligament
If there is a small bony avulsion with only limited displacement, then these have been shown to do well held in POP with a little flexion and ulnar deviation for 4 weeks. It is however necessary to check for stability for rarely there is a combination of bony avulsion and soft tissue rupture with a Stener lesion. If there is no bony avulsion it must be assumed that there is a Stener lesion (interposition of the adductor pollicis aponeurosis between the ruptured ends of the UCL, preventing healing) if there is significant opening of the joint. In that case surgery must be recommended. This is undertaken via a dorso-ulnar longitudinal curved incision, avoiding the radial nerve branches, a longitudinal incision through the adductor hood, finding the avulsion and simply replacing it. There are various methods for holding that in place, including bone anchors or pull through sutures. The key is to place the ligament in the correct place and either hold it rigidly or hold the MP joint reduced with a single 1.1mm K-wire across it.
6.2. Thumb Proximal Phalanx Base (Intra-articular)
As for the finger PIP joints the patterns are Pilon fractures or fracture dislocations (fracture dislocations are rare).
a. Pilon fractures
Pilon fractures follow falls or missed catches with end on force through the proximal phalanx. They are well treated with dynamic external fixators. There are often larger fracture fragments so we often supplement the dynamic external fixator with some percutaneous 1.1 mm K-wires and sometimes even supplemental bone grafting through a limited incision. Some surgeons would favour open reduction and fixation with plates/screws. This is feasible for thumb Pilon fractures where there are larger fragments but not in the fingers. Again we have been very pleased with the results with dynamic external fixation and we do not open these fractures. Even with supplemental K-wires early movement is possible with the dynamic external fixator. The wires need to be left in for 4-5 weeks. The uninjured joints, especially the IP joint needs to be mobilised actively with physio supervision.
b. Fracture dislocations
These are rare. As for PIP joint fracture dislocations (see section …….) small volar or dorsal bone fragments can be ignored although dorsal avulsions of the insertion of the EPB tendon can lead to a secondary boutonnière deformity. Significant bone avulsions (> 2-3 mm) should have the MP joint splinted in extension for 6 weeks. If there is residual MP joint subluxation this should be reduced and can typically be held with a single 1.1 mm K-wire for 4-5 weeks with POP support. If there were an insufficient main dorsal fragment this would almost certainly be a Pilon fracture (see above)
6.3. Thumb Proximal Phalanx – Shaft
As for the fingers the patterns are transverse, short oblique, long oblique or spiral.
These injuries seem uncommon and can largely be treated as for the fingers, but are easier to hold in most instances, thus a moulded plaster may suffice. There are however occasions where there will be quite a lot of comminution in the mid shaft of the proximal phalanx, related to a direct blow and this will be longitudinally unstable. This is an indication for a static external fixator. This can be performed with 2 K-wires proximally and distally to maintain rotational control, and held with devices on either side, typically cement (See section 3.2, p……..).
The thumb in particular is vulnerable to a massive crush injury involving both the proximal and distal phalanges. There is typically a burst injury of the skin. Internal fixation is very difficult. The best indication is when the skin is so damaged as to need a skin flap and hence the bones will be exposed. In most cases this is not necessary and external fixation possibly with supplemental K-wires should hold the fracture out to length and allow soft tissue healing. Bone graft is likely to be necessary either immediately or as a delayed primary procedure typically around 4 weeks post injury when the wounds have healed but there is little soft tissue contracture. We recommend rigid fixation and bone grafting with a view to early mobilisation.. The aim of treatment is to maintain alignment out to length anticipating that the thumb will be very stiff long-term. Provided CMC joint movement is maintained good functional should be achieved.
In children Salter Harris II fractures of the base may require manipulation if grossly angulated and cosmetically apparent. There is considerable potential for remodelling and the prognosis is excellent.
6.4. Thumb Proximal Phalanx- Distal
The patterns are the same as for the middle phalanges of the fingers and the treatment is the same. As the bones are larger, it is a little easier. Because of the importance of the thumb, one is if anything slightly more exacting in demands for reduction at the IP joint level.
6.5. Thumb Distal Phalanx
Patterns and management are as for the DIP joints of the fingers