Anatomical vs. functional compartments of the forearm

While there are only three anatomical forearm compartments (flexor, extensor, lateral), the flexor compartment is functionally composed of superficial and deep sub-compartments, divided by a second fascial layer. In treating compartment syndrome, both compartments must be decompressed surgically. The lateral compartment (Henry’s mobile wad) is rarely affected by compartment syndrome.

Technique

Positioning and preparation: Supine positioning with arm board. Tourniquet not inflated.

Flexor compartment: Incision is marked from the ulnar border of flexor carpi ulnaris at the wrist, extending up towards the medial epicondyle. The hook of hamate can be palpated to identify the distal insertion of FCU, and care should be taken to avoid injury to the ulnar nerve and artery distally, where they are most superficial. The fascia overlying FCU should be incised to the length of the incision —finishing 2cm distal to the epicondyle— decompressing the superficial flexor compartment.

Following this, bluntly dissect the plane between FCU (to the ulnar side) and FDS (radially), taking care to avoid damaging the ulnar neurovascular bundle within this plane. Identify and incise the second fascial layer overlying flexor digitorum profundus to decompress the deep flexor compartment.

Extensor and lateral compartments: Incision is marked from the mid-line of the dorsal wrist towards the lateral epicondyle. Incise the overlying fascia —finishing 2cm distal to the epicondyle— to decompress the extensor compartment.

Within the extensor compartment, identify and bluntly develop the plane between extensor digitorum and extensor carpi radialis brevis. This allows for medial retraction of extensor digitorum, so the lateral compartment fascia can be released. Ensure to progress proximally towards the lateral supracondylar ridge of the distal humerus.

Viability assessment: Once each compartment has been released, tissue viability should be assessed. Healthy muscles will appear red/pink, will bleed on pin-prick and contract when stimulated by diathermy. Muscles that are pale/grey, oedematous and unresponsive are likely non-viable. However, they should be re-assessed at 48-hour intervals and debrided only once clearly declared non-viable.

While neurological injury is difficult to ascertain intra-operatively, vascular assessment of pulses and distal perfusion should be performed.

Closure: Following thorough irrigation, the fasciotomy incisions should each be left open with negative-pressure dressing coverage. The patient will need to return for re-look debridement at 48-hour intervals.

Final closure should be delayed until non-viable muscle has declared and been debrided, and tissue status has stabilised. Delayed primary closure is preferred, but reconstructive grafting may be required.