Compartment Syndrome of the Forearm and Hand: Anatomy, Etiology, and Surgical Management

INTRODUCTION TO UPPER EXTREMITY COMPARTMENT SYNDROME

Acute compartment syndrome (ACS) of the upper extremity represents a catastrophic orthopedic emergency characterized by elevated interstitial pressure within a closed osteofascial space. This elevated pressure compromises microvascular perfusion, leading to a destructive cycle of tissue ischemia, cellular hypoxia, and progressive edema. If left untreated, or if surgical decompression is delayed, the irreversible necrosis of muscle and nerve tissue culminates in Volkmann’s ischemic contracture—a devastating condition characterized by severe fibrotic deformity, neurologic profound deficit, and a functionless limb.

For the orthopedic surgeon, a profound understanding of the complex compartmental anatomy of the forearm and hand is the foundation of both accurate diagnosis and effective surgical decompression. The upper extremity possesses a highly intricate fascial architecture, and failure to release even a single involved compartment can result in permanent morbidity.

SURGICAL ANATOMY OF THE FOREARM COMPARTMENTS

The forearm is anatomically divided into four distinct, yet interconnected, osteofascial compartments. These compartments are defined by the radius, the ulna, the interosseous membrane, and the investing antebrachial fascia.

1. The Superficial Volar Compartment

The superficial volar (anterior) compartment is the most frequently involved space in forearm compartment syndrome. It contains the primary flexors of the wrist and the superficial flexors of the digits.
* Muscular Contents: Pronator teres, flexor carpi radialis (FCR), palmaris longus (PL), flexor carpi ulnaris (FCU), and flexor digitorum superficialis (FDS).
* Neurovascular Elements: The ulnar nerve and artery run deep to the FCU, while the median nerve courses between the two heads of the pronator teres and deep to the FDS.

2. The Deep Volar Compartment

Situated deep to the superficial volar compartment and directly anterior to the radius, ulna, and interosseous membrane, the deep volar compartment is a critical space that can occasionally be involved in isolation.
* Muscular Contents: Flexor digitorum profundus (FDP), flexor pollicis longus (FPL), and pronator quadratus.
* Neurovascular Elements: The anterior interosseous nerve (AIN) and anterior interosseous artery course along the interosseous membrane.

Clinical Pearl: Clinically differentiating isolated involvement of the deep volar compartment from combined superficial and deep involvement is notoriously difficult. However, severe pain with passive extension of the distal phalanx of the thumb (stretching the FPL) or the distal phalanges of the digits (stretching the FDP) in the absence of pain during wrist extension strongly suggests isolated deep volar compartment ischemia.

3. The Dorsal Compartment

The dorsal (posterior) compartment contains the extensor musculature of the wrist and digits. While less commonly involved as an isolated entity compared to the volar compartments, it is frequently affected in severe crush injuries or high-energy trauma.
* Muscular Contents: Extensor digitorum communis (EDC), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), supinator, abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and extensor indicis proprius (EIP).
* Neurovascular Elements: The posterior interosseous nerve (PIN) and posterior interosseous artery.

4. The Mobile Wad of Henry

Located on the anterolateral aspect of the forearm, the mobile wad is a distinct fascial compartment that must be evaluated independently during any forearm decompression.
* Muscular Contents: Brachioradialis, extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB).
* Neurovascular Elements: The superficial branch of the radial nerve courses deep to the brachioradialis.

SURGICAL ANATOMY OF THE HAND COMPARTMENTS

The fascial anatomy of the hand is highly compartmentalized, making it uniquely susceptible to localized ischemic events. Unlike the forearm, where multiple muscles share a single large fascial envelope, the hand contains numerous small, tightly invested spaces. Injection dissection studies, notably those by Halpern and Mochizuki, have definitively mapped these distinct compartments.

The Interosseous Compartments

There are seven distinct interosseous compartments in the hand. Each interosseous muscle is surrounded by a tough, unyielding investing fascial layer.
* Dorsal Interossei: Four separate compartments containing the dorsal interosseous muscles (responsible for digit abduction).
* Volar Interossei: Three separate compartments containing the volar interosseous muscles (responsible for digit adduction).

The Intrinsic Muscle Compartments

• The Thenar Compartment: Contains the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.
• The Hypothenar Compartment: Contains the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi.
• The Adductor Compartment: A distinct, deep compartment containing the adductor pollicis muscle.

The Digital Compartments

The digits themselves possess a highly constrained fascial architecture. The neurovascular bundles of each digit are strictly compartmentalized by Cleland’s and Grayson’s ligaments and surrounding fascial layers. This micro-compartmentalization makes the digital nerves and vessels highly vulnerable to excessive localized swelling, which can rapidly lead to digital ischemia.

Surgical Warning: When performing fasciotomies of the hand, releasing the dorsal interossei does not decompress the volar interossei or the adductor pollicis. Each of the 10 distinct intrinsic compartments must be individually addressed if global hand compartment syndrome is suspected.

ETIOLOGY AND EPIDEMIOLOGY

The etiology of upper extremity compartment syndrome is diverse, encompassing traumatic, iatrogenic, medical, and environmental causes. The unifying pathophysiological mechanism is an increase in compartmental volume or a decrease in compartmental size, leading to critical tissue ischemia.

Traumatic Etiologies

Fractures and soft tissue crush injuries are the most common precipitants of forearm compartment syndrome.
* Fracture-Related ACS: Elliott and Johnstone demonstrated that 18% of forearm compartment syndromes were directly caused by fractures. While isolated distal radial fractures are rarely associated with compartment syndrome (incidence of approximately 0.3%), the presence of an ipsilateral elbow injury dramatically alters the risk profile. An ipsilateral elbow injury combined with a distal radius fracture results in forearm compartment syndrome in up to 15% of patients, likely due to massive energy transfer, extensive soft tissue stripping, and compromised venous outflow.
* Soft Tissue Injuries: Soft tissue injuries without underlying fractures account for a significant portion of cases (23%, per Elliott and Johnstone). Crush injuries, in particular, cause massive muscle maceration and subsequent edema that rapidly overwhelms the fascial envelope.

Pediatric Considerations

The epidemiology of pediatric forearm compartment syndrome has evolved. Historically, supracondylar humeral fractures were considered the most frequent cause of forearm compartment syndrome in children, primarily due to brachial artery compromise or massive antecubital swelling.
However, contemporary data from Grottkau et al. revealed a paradigm shift: pediatric forearm fractures are now significantly more commonly associated with compartment syndrome than supracondylar fractures (74% vs. 15%). Furthermore, the increasing use of elastic stable intramedullary nailing (ESIN) for pediatric forearm fractures has introduced a new iatrogenic risk factor, with multiple reports documenting compartment syndrome following intramedullary fixation, likely secondary to pressurized intramedullary reaming and hematoma extravasation.

Non-Traumatic and Systemic Causes

• Coagulopathies: Internal bleeding, particularly in patients with hemophilia or those on aggressive anticoagulant therapy, can rapidly fill a compartment following trivial trauma.
• Prolonged External Compression: Often seen in obtunded patients (e.g., drug overdose, prolonged surgical positioning), leading to "crush syndrome" and rhabdomyolysis.
• Vascular/Iatrogenic: Intraarterial injections of illicit drugs or sclerosing agents cause severe vasospasm and endothelial damage. Arterial line complications can also precipitate ACS.
• Environmental: Circumferential full-thickness burns (requiring escharotomy) and snake bites (venom-induced capillary leak) are well-documented triggers.
• Infections: Severe necrotizing fasciitis or deep space abscesses can increase compartmental pressures to ischemic thresholds.

PATHOPHYSIOLOGY AND BIOMECHANICS OF ISCHEMIA

Compartment syndrome is driven by the ischemia-edema cycle. Normal capillary perfusion pressure is approximately 20 to 30 mm Hg. When interstitial pressure within a closed fascial compartment rises, it first collapses the thin-walled venules. This venous outflow obstruction leads to venous hypertension, which subsequently increases capillary hydrostatic pressure.

The increased hydrostatic pressure forces fluid into the interstitial space, further elevating compartmental pressure. Once the interstitial pressure exceeds the capillary perfusion pressure, capillary blood flow ceases. It is critical to understand that arterial inflow continues until the compartment pressure equals systolic blood pressure; therefore, distal pulses remain palpable until the very late, irreversible stages of the syndrome.

Pitfall: Relying on the absence of a radial or ulnar pulse to diagnose forearm compartment syndrome is a dangerous clinical error. Pulselessness is a sign of arterial occlusion or terminal compartment syndrome. The diagnosis must be made based on the "Delta P" (Diastolic Blood Pressure minus Compartment Pressure). A Delta P of less than 30 mm Hg is an absolute indication for emergent fasciotomy.

SURGICAL MANAGEMENT: FASCIOTOMY TECHNIQUES

The definitive treatment for acute compartment syndrome is emergent surgical fasciotomy. The goal is the complete, unhindered release of all involved fascial envelopes.

Indications and Positioning

• Indications: Unequivocal clinical signs (pain out of proportion, severe pain with passive stretch, tense compartments) or a Delta P < 30 mm Hg in an obtunded or polytraumatized patient.
• Positioning: The patient is positioned supine with the arm extended on a hand table. A tourniquet should be applied but not inflated unless massive, uncontrollable hemorrhage is encountered, as tourniquet ischemia confounds the assessment of muscle viability.

Forearm Fasciotomy: The Volar Approach

The volar approach is the workhorse of forearm decompression, designed to release the superficial volar, deep volar, and mobile wad compartments. The extended Henry approach or the MacKenzie curvilinear incision is utilized.

1. Incision: Begin proximal to the antecubital fossa, medial to the biceps tendon. Extend the incision distally in a curvilinear fashion across the volar forearm.
2. Wrist Extension: As the incision approaches the wrist, curve it ulnarward to avoid crossing the wrist flexion crease at a right angle (preventing future flexion contractures) and to protect the palmar cutaneous branch of the median nerve.
3. Carpal Tunnel Release: Extend the incision into the palm, staying in line with the fourth ray, and completely divide the transverse carpal ligament to decompress the median nerve.
4. Fascial Release: Divide the antebrachial fascia longitudinally.
5. Lacertus Fibrosus: Proximally, the lacertus fibrosus (bicipital aponeurosis) must be completely divided to decompress the proximal median nerve and brachial artery.
6. Deep Compartment Access: Retract the superficial flexors (FCR, FCU, FDS) to expose the deep compartment (FDP, FPL). The fascia overlying these deep muscles must be incised.
7. Epimysiotomy: If the muscle bellies remain tight after fascial release, a careful epimysiotomy (scoring the muscle envelope) should be performed.
8. Mobile Wad: Identify the mobile wad laterally and release its investing fascia through the same volar incision by undermining the skin flap radially.

Forearm Fasciotomy: The Dorsal Approach

If the dorsal compartment remains tense after volar decompression, a separate dorsal incision is mandatory.
1. Incision: Make a longitudinal incision from the lateral epicondyle directed toward the midline of the wrist (Lister's tubercle).
2. Fascial Release: Incise the dorsal antebrachial fascia, taking care to identify and protect the extensor retinaculum distally unless the distal tendons are specifically tethered.
3. Deep Exploration: Ensure the fascia over the deep extensors (APL, EPB, EPL) is adequately released.

Hand Fasciotomy Approaches

Decompression of the hand requires meticulous attention to the 10 intrinsic compartments.

1. Dorsal Interosseous Incisions: Two longitudinal dorsal incisions are made. The first is placed over the second metacarpal (allowing access to the 1st and 2nd dorsal interossei). The second is placed over the fourth metacarpal (allowing access to the 3rd and 4th dorsal interossei).
2. Volar Interosseous and Adductor Release: Through the index metacarpal incision, blunt dissection is carried volar to the metacarpal to release the volar interossei and the adductor pollicis compartment.
3. Thenar and Hypothenar Incisions: Separate longitudinal incisions are made along the glabrous border of the thenar and hypothenar eminences to release their respective fascial envelopes.
4. Digital Fasciotomy: If the digits are involved, mid-axial incisions are made along the non-contact borders of the fingers (ulnar side of index/middle, radial side of ring/small) to release the digital fascial compartments.

POSTOPERATIVE PROTOCOLS AND WOUND MANAGEMENT

Following successful fasciotomy, the wounds must never be closed primarily. The massive tissue edema that follows reperfusion requires the wounds to remain open to prevent recurrent compartment syndrome.

• Wound Coverage: Negative Pressure Wound Therapy (NPWT / Wound VAC) is the gold standard for postoperative management. It manages exudate, reduces interstitial edema, and assists in gradual wound edge approximation. Alternatively, the "shoelace" technique using vessel loops interlaced through skin staples can provide dynamic, gradual closure.
• Second Look: A mandatory return to the operating room is scheduled for 48 to 72 hours post-decompression for wound irrigation, debridement of any newly demarcated necrotic muscle, and assessment for closure.
• Definitive Closure: Delayed primary closure is achieved when edema subsides (typically 5-7 days). If the skin edges cannot be approximated without tension, split-thickness skin grafting (STSG) is required.
• Rehabilitation: Immediate postoperative splinting in a functional position (wrist extended 20 degrees, MCP joints flexed 70 degrees, IP joints fully extended) is critical to prevent contractures. Early passive and active range of motion exercises are initiated as soon as clinically tolerated to ensure optimal functional recovery of the upper extremity.