Ring Avulsion Injury

Mechanism. A ring snags on a hook, fence or machinery as the person falls or jumps. The ring transmits a sudden axial traction to the finger and degloves the soft-tissue sleeve from the bone.

The spectrum. Depending on the force, the injury ranges from a circumferential soft-tissue injury with preserved perfusion, through circulatory compromise with the artery and/or vein avulsed, to complete degloving (the 'squirrel-cage' or 'glove' avulsion) or frank amputation. The bone often fails distally, around the DIP joint, while the PIP joint and FDS insertion remain, which is an important prognostic point.

The skin lies. The visible wound may be a simple circumferential laceration, but the traction has stretched and torn the arteries, veins and nerves over a long segment. The zone of vascular injury is far more extensive than it appears.

Urbaniak classification. The injury is graded by the Urbaniak classification, with the Kay modification below, to guide treatment. The Urbaniak grade turns on the circulation of the digit:

• Class I - circulation adequate, with a circumferential soft-tissue injury
• Class II - circulation inadequate, from arterial and/or venous compromise
• Class III - complete degloving or complete amputation

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Kay's modification adds two things Urbaniak does not flag, both prognostic: an associated bone or joint injury (class III) and the FDS level of a complete amputation (class IV).

• Class I - circulation adequate, with or without skeletal injury
• Class II - inadequate circulation without bone or joint injury, subdivided IIa (arterial inadequate) and IIv (venous inadequate)
• Class III - inadequate circulation with an associated fracture or joint injury, likewise subdivided by arterial or venous compromise; a more severe, less favourable group
• Class IV - complete amputation, subdivided by the level relative to the FDS insertion

Why the FDS level matters. Amputation distal to the FDS insertion, with the FDS preserved, carries a far better functional prognosis than amputation proximal to it. This FDS-level split is the prognostic heart of the classification.

Preserving an Amputated or Devascularised Part

Getting this wrong at the referring hospital forecloses the reconstruction before the hand surgeon sees the patient, and it is asked in vivas precisely because it is so often done badly.

1. Wrap the part in saline-moistened gauze.
2. Seal it in a plastic bag.
3. Place the sealed bag in ice water.

What must not happen. The part must not touch ice directly and never dry ice, which freezes and destroys the tissue. It must not be left soaking in water or saline, which macerates it. And it must not travel separately: the part and the patient are transferred together to the replantation centre.

Alongside the part. Resuscitate and assess for other injuries, give tetanus prophylaxis and antibiotics, radiograph the hand and the amputated part, keep the patient nil by mouth, and photograph the injury before dressing it.

The Ischaemia Clock

A digit contains no muscle bulk, which is why it tolerates ischaemia far better than an amputation through the palm or forearm. It is also why a delayed presentation is not by itself a reason to abandon a finger.

Class I. Clean and repair the soft tissue, fix any fracture, and repair tendons and nerves as needed. No microvascular repair is required.

Class II. Urgent microvascular revascularisation of the artery, and of the vein where needed. Because the injury is extended, the vessels are debrided to healthy ends and bridged with interposition vein grafts, as described under the repair sequence below. Nerves are repaired and soft-tissue cover (flap or graft) is provided as required.

Class III and complete amputation. Replantation is weighed against completion amputation on the factors below.

Replant or Amputate

What favours replantation. These factors predict a good result, and replantation is more worthwhile when they are present:

• An intact PIP joint and FDS (amputation distal to the FDS insertion)
• A lower Urbaniak or Kay class
• A clean digit and wound
• Short, acceptable ischaemia time
• A non-smoker
• A patient who accepts, and is able to commit to, a long rehabilitation

What favours amputation. Where those favourable factors are absent, a well-fashioned completion (revision) amputation restores quick, reliable function. Severe contamination, prolonged warm ischaemia, heavy smoking and a single insensate border or index digit all favour amputation.

The shared decision. The choice is shared with the patient and weighs hand dominance, occupation, the specific digit, cosmetic wishes and rehabilitation capacity. A stiff, insensate, cold-intolerant salvaged digit, especially a single index or border finger, is often bypassed by the patient and can impair overall hand use. A completion amputation giving quick, reliable, pain-free function may then be the better functional result.

The Repair Sequence, and How Avulsion Changes It

The order. Repair follows the standard replantation sequence, BEFANV: Bone, Extensor, Flexor, Artery, Nerve, Vein. Working from the stable platform outwards means no later repair is made under tension, and bone is shortened as required to let the soft-tissue and vessel repairs sit tension-free.

The veins. After about 10-15 minutes of arterial perfusion the dorsal veins engorge and become identifiable. The aim is two veins for every artery repaired, with the skin closed loosely so the closure itself does not strangle the venous outflow.

Both sides of the circulation are avulsed. In an avulsion the dorsal veins are stripped over the same long segment as the digital arteries, so vein grafts are frequently needed on the venous side too. The requirement is usually remembered only for the artery.

Debride until the vessel is normal, then debride further. The intima is damaged well beyond the visibly injured segment. Debride back to healthy intima and bridge the gap with an interposition vein graft for a tension-free anastomosis. The classic errors are resecting too little and then anastomosing damaged intima, or resecting adequately and then pulling the ends together under tension instead of grafting the gap.

Tag every structure before repairing anything. In a degloved, retracted, blood-filled field the commonest cause of failure is a cut end that cannot be found again when it is needed.

Keeping It Alive: Monitoring and Salvage

What is observed. Monitoring a replanted or revascularised digit is a defined observation, not a general instruction. Colour, capillary refill, pulp turgor, temperature and the Doppler signal are checked hourly for the first 24-48 hours, then every 2-4 hours. A temperature difference of more than 2 degrees from an adjacent normal digit is a useful adjunct, and an implantable Doppler probe gives continuous monitoring where available.

Read the colour. The two failures look different:

• Arterial occlusion - a pale, cool digit with sluggish refill and no Doppler signal
• Venous congestion - a blue, swollen, tense digit with brisk refill that bleeds dark blood on pin-prick; the commoner early problem, and especially so after an avulsion because the venous repair is the more precarious one

Environment and drugs. Keep the patient warm, well hydrated and pain-free, because cold, hypovolaemia and pain all cause vasospasm. Enforce absolute abstinence from nicotine and caffeine, elevate the hand, and give aspirin 75-150 mg daily for 2-4 weeks with thromboprophylaxis as indicated.

Salvaging the congested digit. Loosen tight dressings and remove constricting sutures first. Then use medicinal leeches, or remove the nail plate and apply heparin-soaked gauze to encourage controlled bleeding, so-called chemical leeching. Patients on leech therapy need antibiotic cover against Aeromonas hydrophila and monitoring of haemoglobin.

A low threshold to return to theatre. Deterioration that does not respond promptly to these measures is an indication to re-explore, and the salvage rate falls with every hour of delay.

Outcomes by class. Total active motion and two-point discrimination deteriorate progressively from class I to II to III, as in the cited systematic-review figures. Class I does best, class II does well with revascularisation, and class III results are variable, with selected replants doing well when the PIP joint and FDS are intact.

Counselling. Even a successful replant is commonly cold intolerant. Counsel patients that even a salvaged finger may end up stiff, cold-intolerant or partly insensate.