PATHOPHYSIOLOGY AND BIOMECHANICS OF ACUTE COMPARTMENT SYNDROME

Acute compartment syndrome (ACS) of the upper extremity represents a catastrophic orthopaedic emergency characterized by elevated tissue pressure within a closed osteofascial space. This elevated pressure compromises the arteriovenous pressure gradient, leading to a collapse of the microcirculation, subsequent tissue hypoxia, and ultimately, irreversible myoneural necrosis.

The biomechanical cascade of ACS is driven by the unyielding nature of the fascial envelopes surrounding the forearm and hand musculature. When intracompartmental volume increases—whether due to hemorrhage from a supracondylar or distal radius fracture, severe soft tissue crush injury, or reperfusion edema—the inelastic fascia restricts expansion. As interstitial pressure rises above the venous outflow pressure, venous congestion occurs, further exacerbating the pressure rise. Once the interstitial pressure approaches the diastolic blood pressure, capillary perfusion ceases.

Surgical Warning: The Myth of the Palpable Pulse
A palpable radial or ulnar pulse does not rule out acute compartment syndrome. Capillary perfusion ceases long before the intracompartmental pressure exceeds systolic arterial pressure. The presence of a pulse in a tense, swollen forearm should never provide false reassurance.

If left untreated, the ischemic cascade results in muscle infarction, fibrotic replacement, and the devastating clinical entity known as Volkmann’s ischemic contracture, characterized by severe flexion deformities of the wrist and digits, alongside profound neurologic deficits.

DIAGNOSTIC PRINCIPLES AND PRESSURE THRESHOLDS

The diagnosis of ACS is primarily clinical, classically described by the "6 Ps": Pain out of proportion to the injury, Pallor, Paresthesias, Pulselessness, Paralysis, and Poikilothermia. However, pain with passive stretch of the involved compartment's musculature remains the most sensitive and reliable early clinical indicator.

In scenarios where the clinical picture is equivocal, or in patients who are obtunded, intubated, or uncooperative, objective measurement of intracompartmental pressures using a hand-held monitoring device (e.g., Stryker Intra-Compartmental Pressure Monitor) is mandatory.

The Delta Pressure Concept

Modern orthopaedic practice relies heavily on the "Delta Pressure" ($\Delta$P) concept rather than an absolute pressure threshold. Impending tissue ischemia occurs when the tissue pressure reaches between 30 mm Hg and 20 mm Hg below the diastolic blood pressure.

• $\Delta$P = Diastolic Blood Pressure - Compartment Pressure

Fasciotomy is strictly indicated under the following parameters:
1. Normotensive Patients: Positive clinical findings combined with compartment pressures greater than 30 mm Hg, especially when the duration of increased pressure is unknown or exceeds 8 hours.
2. Unconscious/Uncooperative Patients: An absolute compartment pressure greater than 30 mm Hg, or a $\Delta$P of less than 30 mm Hg.
3. Hypotensive Patients: A lower absolute pressure threshold is required. Fasciotomy is indicated if the compartment pressure is greater than 20 mm Hg, as the diminished diastolic pressure narrows the perfusion gradient.

Clinical Pearl: The Golden Rule of Compartment Syndrome
As a general rule, when in doubt, the compartment should be released. If a fasciotomy proves later to have been unnecessary, the result is merely a scar. However, if a fasciotomy should have been performed but was delayed or omitted, the result is catastrophic loss of muscle tissue, permanent disability, and potential limb loss. Delay in diagnosis remains the single most important determining factor of poor outcomes.

Normal function is regained in approximately 68% of patients when fasciotomy is performed within 12 hours from the onset of compartment syndrome. Compartment pressures should be aggressively monitored in young patients with high-energy injuries to the forearm diaphysis or distal radius, or in patients with significant soft tissue injuries complicated by a bleeding diathesis.

TECHNIQUES FOR MEASURING COMPARTMENT PRESSURES

Accurate measurement requires meticulous technique and a thorough understanding of upper extremity cross-sectional anatomy. A hand-held monitoring device is utilized, ensuring the system is properly zeroed at the level of the compartment being measured.

Measuring Forearm Compartments

The forearm consists of three primary compartments: Volar (superficial and deep), Dorsal, and the Mobile Wad.

• Volar Compartment: Insert the needle into the volar muscle mass. Confirm placement by observing a pressure spike during passive extension of the wrist and digits.
• Dorsal Compartment: Insert the needle into the dorsal musculature to a depth of approximately 2 cm. Confirm accurate placement by applying external compression to the dorsal compartment or by performing passive flexion of the wrist, which should elicit a transient rise in the pressure reading.
• Mobile Wad: Identify the radial-most portion of the forearm (comprising the brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis). Insert the needle perpendicular to the skin to a depth of 1.0 to 1.5 cm. A rise in pressure is identified by external compression or passive flexion of the wrist.

Measuring Hand Compartments

The hand contains 10 distinct fascial compartments: four dorsal interosseous, three volar interosseous, the thenar, the hypothenar, and the adductor pollicis. Pressure measurements are not obtained from the digits but at the site of maximal swelling within these specific compartments. Evaluate the compartments individually. If a single compartment pressure is elevated, surgical release of all hand compartments and the carpal tunnel is mandated.

• Dorsal Interosseous Compartments: Insert the needle through the dorsal skin of the hand, exactly 1 cm proximal to the metacarpal head, advancing until it rests within the muscle belly. To accurately judge depth, it is highly recommended to place identifiable marks on the needle at 1.0, 1.5, and 2.0 cm.
• Adductor Pollicis Compartment: Insert the needle on the radial side of the second metacarpal, directing it into the substance of the thumb-index web space.
• Thenar and Hypothenar Spaces: Insert the needle at the junction of the glabrous (palmar) and nonglabrous (dorsal) skin over the maximal bulk of the respective muscle compartment. Advance the needle at least 5 mm below the enveloping fascia to ensure accurate pressure assessment.

SURGICAL ANATOMY OF THE UPPER EXTREMITY COMPARTMENTS

A comprehensive understanding of the fascial boundaries is prerequisite for an effective release.

The Forearm

• Superficial Volar Compartment: Contains the pronator teres, flexor carpi radialis (FCR), palmaris longus (PL), flexor carpi ulnaris (FCU), and flexor digitorum superficialis (FDS).
• Deep Volar Compartment: Contains the flexor digitorum profundus (FDP), flexor pollicis longus (FPL), and pronator quadratus. This compartment is most frequently involved and most commonly inadequately released.
• Dorsal Compartment: Contains the extensor digitorum communis (EDC), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and extensor indicis proprius (EIP).
• Mobile Wad: Contains the brachioradialis, ECRL, and ECRB.

PREOPERATIVE PLANNING AND POSITIONING

• Anesthesia: General anesthesia is preferred. Regional anesthesia (e.g., supraclavicular or axillary blocks) is strictly contraindicated in the setting of impending or suspected ACS, as it will mask the cardinal symptom of breakthrough pain and obscure ongoing ischemic changes.
• Positioning: The patient is positioned supine with the affected arm extended on a radiolucent hand table.
• Tourniquet: A sterile tourniquet may be applied but should not be inflated unless catastrophic hemorrhage is encountered. Inflating a tourniquet exacerbates ischemia and prevents the surgeon from assessing muscle viability and tissue perfusion during the release.

SURGICAL TECHNIQUE: FOREARM FASCIOTOMY

The gold standard for forearm compartment syndrome is a comprehensive volar and dorsal release.

The Volar Approach (McConnell / Henry Combined Exposure)

1. Incision: Make a volar curvilinear incision similar to McConnell’s combined exposure of the median and ulnar neurovascular bundles, as originally described by Henry. Begin proximally, medial to the biceps tendon. Cross the elbow flexion crease at an oblique angle to prevent future flexion contractures. Carry the incision distally along the volar forearm, curving toward the ulnar aspect of the wrist. Extend the incision into the palm to allow for a complete carpal tunnel release, strictly avoiding crossing the wrist flexion crease at a right angle.
2. Proximal Release: Identify and divide the lacertus fibrosus (bicipital aponeurosis) proximally. Evacuate any underlying hematoma.
3. Vascular Assessment: In patients with a suspected brachial artery injury (e.g., associated with a supracondylar humerus fracture), expose the brachial artery and determine whether there is free, pulsatile blood flow. If flow is unsatisfactory, perform an arteriotomy or remove the adventitia to expose any underlying clot, spasm, or intimal tear. Resect the damaged segment if necessary, and perform a primary anastomosis or interpose a reversed saphenous vein graft.
4. Superficial Compartment Release: Release the superficial volar compartment throughout its entire length using open scissors, meticulously freeing the fascia over the superficial compartment muscles (FCR, PL, FCU, FDS).
5. Deep Compartment Release: This is the most critical step. Identify the flexor carpi ulnaris (FCU). Retract the FCU and its underlying ulnar neurovascular bundle medially (ulnarly). Simultaneously, retract the flexor digitorum superficialis (FDS) and the median nerve laterally (radially). This interval exposes the flexor digitorum profundus (FDP) residing in its deep compartment.
6. Epimysiotomy: Check to see if the overlying fascia or epimysium of the FDP is tight. Incise it longitudinally under direct vision.
   • Muscle Viability Check: If the muscle appears gray, dusky, or non-contractile, the prognosis for recovery may be poor. However, borderline muscle may still be viable and should be allowed to perfuse. Do not perform aggressive debridement of questionable muscle during the index procedure; wait for a second-look operation at 48 hours.
7. Distal Release and Carpal Tunnel: Continue the dissection distally by incising the transverse carpal ligament along the ulnar border of the palmaris longus tendon and median nerve, fully decompressing the carpal tunnel.
8. Median Nerve Decompression: In cases presenting with median nerve palsy or severe paresthesias, trace and observe the median nerve along the entire zone of injury. Ensure it is not severed, contused, or entrapped between the ulnar and humeral heads of the pronator teres. If entrapment is identified, a partial pronator tenotomy is necessary to fully liberate the nerve.
9. Fracture Management: In a patient with a concomitant supracondylar fracture or distal radius fracture, reduce the fracture and stabilize it (e.g., pinning with Kirschner wires or external fixation) to control bleeding and restore skeletal stability, which aids in soft tissue resting tension.

Pitfall: Incomplete Deep Compartment Release
The most common error in forearm fasciotomy is failing to adequately release the deep volar compartment. The FDP and FPL are highly susceptible to ischemia. The surgeon must actively seek the interval between the FCU and FDS to visualize and release the deep fascia.

The Dorsal Approach

While the volar incision decompresses the superficial and deep volar compartments, the dorsal fascia must also be addressed if dorsal pressures remain elevated.
1. Incision: Make a straight longitudinal incision over the dorsal forearm, starting 3-4 cm distal to the lateral epicondyle and extending toward the midline of the wrist.
2. Fascial Release: The dorsal forearm fascia is released through the interval between the extensor carpi radialis brevis (ECRB) and the extensor digitorum communis (EDC).
3. Mobile Wad: The mobile wad can often be accessed and released through the volar incision by undermining radially, or through the dorsal incision. Ensure the fascia overlying the brachioradialis and ECRL/ECRB is completely incised.

SURGICAL TECHNIQUE: HAND FASCIOTOMY

When hand compartment pressures are elevated, all compartments must be released.

1. Dorsal Interosseous Release: Make two longitudinal dorsal incisions. The first is placed over the second metacarpal to access the first and second dorsal interossei. The second is placed over the fourth metacarpal to access the third and fourth dorsal interossei. Blunt dissection is used to sweep along the radial and ulnar borders of the metacarpals to release the volar interossei.
2. Adductor Pollicis Release: The adductor pollicis can be released through the first dorsal incision by dissecting bluntly into the first web space, taking care to protect the radial artery as it dives between the two heads of the first dorsal interosseous muscle.
3. Thenar Release: Make a longitudinal incision along the radial border of the first metacarpal at the junction of the glabrous and nonglabrous skin. Release the thenar fascia.
4. Hypothenar Release: Make a longitudinal incision along the ulnar border of the fifth metacarpal, again at the glabrous/nonglabrous junction, and release the hypothenar fascia.

POSTOPERATIVE PROTOCOL AND WOUND MANAGEMENT

The management of the fasciotomy wound is as critical as the release itself.

1. No Primary Closure: Under no circumstances should the skin be closed at the time of the index procedure. Anticipate secondary closure or skin grafting at a later date.
2. Nerve Protection: If the median nerve is exposed within the distal forearm, it must not be left to desiccate. Suture the distal radial-based forearm flap loosely over the nerve to provide soft tissue coverage and prevent necrosis.
3. Dressings: Apply sterile, non-adherent dressings. Negative Pressure Wound Therapy (NPWT / VAC dressing) is highly recommended. NPWT set at -75 to -125 mm Hg continuous pressure helps manage profound exudate, reduces interstitial edema, and promotes the formation of healthy granulation tissue.
4. Splinting: The limb should be splinted in a functional position: wrist in 20-30 degrees of extension, metacarpophalangeal (MCP) joints in 70-90 degrees of flexion, and interphalangeal (IP) joints in full extension.
5. Second-Look Surgery: A mandatory return to the operating room is scheduled for 48 to 72 hours postoperatively. During this stage, any definitively necrotic muscle is debrided.
6. Definitive Closure: Once the edema has subsided (typically 5 to 10 days post-injury), the wounds may be managed with delayed primary closure using vessel loops (shoelace technique) or covered with a split-thickness skin graft (STSG).

COMPLICATIONS

Failure to adhere to strict diagnostic thresholds and meticulous surgical technique can result in severe complications. Missed ACS leads to Volkmann's ischemic contracture, necessitating complex salvage procedures such as infarct excision, neurolysis, and free functioning muscle transfers (e.g., gracilis transfer). Iatrogenic complications during fasciotomy include injury to the superficial sensory branch of the radial nerve, the palmar cutaneous branch of the median nerve, and incomplete release of the deep volar compartment. Strict adherence to the anatomical intervals described above minimizes these risks and ensures optimal functional recovery.

📚 Medical References

• forearm compartment syndrome, Clin Orthop Relat Res 134:225, 1978.
• Goldie BS, Jones NF, Jupiter JB: Recurrent compartment syndrome and Volkmann contracture associated with