Floating Elbow

Compartment syndrome: what "a high index of suspicion" actually means

Telling a candidate to be vigilant is not an answer. The examinable content is how you make the diagnosis and what you do about it.

In the child, the classic five Ps are useless. Pain, pallor, paraesthesia, paralysis and pulselessness are late signs, and pulselessness is often absent altogether - compartment pressure rises well above capillary filling pressure long before it occludes a major artery, so a palpable pulse never excludes the diagnosis. The early signs in a child are the three A's: increasing Analgesia requirement (the most useful single sign - a child needing escalating opioid after fixation is declaring itself), Anxiety and Agitation. Add to those pain on passive extension of the fingers, a tense, swollen forearm, and pain disproportionate to the injury.

Measure when the clinical picture is unreliable - the obtunded, intubated, very young or regionally blocked patient. The threshold is a delta P of less than 30 mmHg, that is, the diastolic blood pressure minus the measured compartment pressure. An absolute pressure alone is misleading in a hypotensive patient, which is why the differential is used. Measure in the compartment nearest the fracture and in the deep volar compartment, which is where the pressure is highest and where flexor digitorum profundus dies.

Fasciotomy is the treatment and it is time-critical. For the forearm this means a volar release through an extended Henry-type or curved ulnar-based incision, decompressing the superficial and - crucially - the deep flexor compartment, combined with a carpal tunnel release, and a separate dorsal incision for the extensor and mobile wad compartments if they remain tight after volar release. Leave the wounds open, re-look at 48 hours, and close or graft when swelling permits. Note that a regional block can mask the developing syndrome, which is a real argument against dense regional anaesthesia in exactly this injury.

The pulseless hand: pink is not the same as white

A pulseless hand comes in two forms, and they are managed differently.

• The white (or dusky), pulseless hand is an unperfused hand - cool, pale, sluggish or absent capillary refill. This is limb-threatening ischaemia. Reduce and stabilise the fracture immediately, and if perfusion does not return at once, explore the brachial artery with vascular surgical support. Do not observe it.
• The pink, pulseless hand is perfused but without a palpable radial pulse - warm, pink, with capillary refill, presumably supported by collateral flow. This is the genuinely contested one. After reduction and fixation the reasonable position is admission and close serial observation by an experienced team, with documented perfusion checks; but persistent pulselessness, any deterioration, or an inability to observe reliably should prompt vascular assessment and exploration rather than indefinite watching. The concern is not the missing pulse itself but the occult ischaemia and the developing compartment syndrome behind it, and there is a well-recognised subgroup whose collateral flow proves inadequate. A pink pulseless hand with rising analgesia requirement or a tense forearm is a compartment syndrome until proven otherwise, not a reassuring sign.

Choosing the implants, and one position that must be avoided

In the child. The supracondylar fracture is stabilised with percutaneous K-wires - two or three lateral entry wires, or crossed wires accepting the ulnar nerve risk of the medial pin. The point specific to the floating elbow is that the forearm fracture must also be stabilised rather than treated in a cast as it might be in isolation: leaving it to a cast both fails to abolish the flail segment and requires a circumferential dressing over a maximally swelling limb. Fix it by flexible intramedullary nails, K-wires or a plate depending on level and age.

Do not immobilise the elbow in hyperflexion. Flexion beyond about 90 degrees markedly raises compartment pressure and reduces brachial artery flow, and in a limb already at high risk this is how an avoidable Volkmann's contracture is produced. This is precisely why the supracondylar fracture is pinned rather than held reduced by hyperflexion in a cast, and why the post-operative splint sits in less than 90 degrees with the dressing loose and split.

In the adult. Both fractures are usually plated. For the humerus, plate fixation is generally preferred to intramedullary nailing in this setting: it gives rotational control, permits direct reduction and, where the fracture is distal or intra-articular, is the only option - while an antegrade nail adds shoulder morbidity and controls rotation less well in a limb where the forearm is also unstable. Nailing remains reasonable for a segmental or pathological midshaft fracture, or in the polytrauma patient where speed and soft-tissue preservation dominate. The radial nerve must be identified or deliberately protected with a distal-third humeral fracture and again at plate removal. For the forearm, restore radial bow and length with plate fixation of both bones - malunion here costs pronation and supination, which is the function the patient will actually notice.