Forearm Compartment Syndrome

Etiology

The most common causes include:

1. Trauma is, by far, the most common cause. Within the trauma spectrum, fractures of the midshaft radius and/or ulna, distal radius fractures, or supracondylar humerus fractures are the most common causes in children. Other types of trauma include crush injuries, contusions, or gunshot wounds to the forearm.
2. Tight casts, dressings, or external wrappings
3. Extravasation of intravenous fluids/infusions[4][5]
4. Burns
5. Bleeding disorders
6. Post-ischemic swelling
7. Arterial injuries[6]
8. Intensive use of muscles during exercise, seizures, eclampsia, tetany
9. Intravenous drug administration
10. Anticoagulation therapy increases the risk of compartment syndrome in patients who sustain an injury to their forearm.[7]
11. Rare causes such as snake bites or carbon monoxide intoxication[8]

Epidemiology

Compartment syndrome in the forearm is most commonly seen after trauma associated with fractures, crush injuries, head injuries, and burns.[9] The National Trauma Data Bank (U.S.A.) reveals 1.22% of forearm fractures and 3.79% of tibial fracture patients underwent fasciotomy for compartment syndrome.[7] Young patients with a mean age of 32 years in males and a mean of 44 years in females are likely to be affected, while the overall incidence of acute compartment syndromes is 3.1 per 100000 population per year in the western world.[10] Incidence is increased in men compared to women with a ratio of 10 to 1.

Pathophysiology

There is more than one theory to describe the pathophysiology of compartment syndrome.[11] Among them, the common factor tends to be anoxia at the cellular level following a cascade of events.[12] The increased pressure within the osseofascial compartment affects the venous return system, which results in decreased arterial pressure and an increase in venous pressure. This leads to a shift in the interstitial and cellular osmolality, creating a vicious cycle of cellular anoxia, leading to chemical mediators further increasing capillary permeability.

Vascularisation in the middle of the muscle belly is more affected, and that is when muscle degeneration occurs. Muscles centered around the anterior interosseous artery are the most commonly affected, particularly FPL and FDP. In the acute stage, nerves are involved because of ischemia, and in later stages, damage occurs due to entrapment of nerves in the fibrous tissue. Muscles can retain the electrical response for up to 3 hours. They can tolerate ischemia for up to 4 hours, and irreversible damage occurs at 8 hours. Nerves can conduct impulses for up to 1 hour. They can survive up to 4 hours (neuropraxia), and at 8 hours, irreversible damage occurs.[7]

When sustained vascular compromise occurs, the muscle undergoes necrosis, fibrosis, and contracture. Associated nerve damage causes further muscle dysfunction, sensory deficits, and may result in chronic pain. The result is a dysfunctional muscle compartment with local and distant manifestations that depend on the compartment involved and the degree of muscle contracture and nerve damage.[1]

History and Physical

Compartment syndrome of the forearm is primarily a clinical diagnosis. Patients often present within a few hours of the inciting event, sometimes even within 48 hours. They present with a swollen, tense, tender forearm with overlying skin that is often pink. Pain that is out of proportion to the injury is the pathognomonic sign, especially on passive stretching of the fingers. Pain is usually not relieved by rest, analgesia, or anti-inflammatory medication. Pain can, however, disappear in late stages or presentations or chronic compartment syndrome. A few patients who present a few hours after the onset of compartment syndrome present with hemorrhagic blisters in addition to the above mentioned.

Sensory deficits or paresthesias are usually signs of nerve ischemia in the affected compartment and can be present. Paralysis is often a late sign.

Radial and ulnar pulses are usually intact, given the systolic arterial pressure (around 120 mmHg) usually exceeds the pressure within the involved compartment. The absence of pulses is usually a late finding, and amputations are considered when there is a significant amount of ischaemic tissue death.

In children, anxiety associated with increasing analgesic requirements is a reliable indicator of compartment syndrome.[13]

Be aware pain can sometimes be difficult to assess or be absent if there is nerve damage, in polytrauma patients, a patient who is unconscious or sedated, and in children or patients who have had some form of regional nerve blocks for pain relief.[1][14]

Evaluation

Using a combination of clinical diagnosis and intracompartmental pressure measurements increases both the sensitivity and specificity of diagnosing the forearm compartment syndrome.[15]

Measurements of the affected compartment can be done using a transducer connected to a catheter inserted 5 cm into the forearm's affected area. Normal intracompartmental pressures vary between 0 to 8 mmHg, and critical pressure is considered anything above 30 mmHg.

A pressure higher than 30 mmHg of the patient's diastolic blood pressure (delta p) is associated with compartment syndrome, and fasciotomy is indicated in that case. The delta p (delta pressure) is the difference between the patient's diastolic blood pressure and the compartment pressure. A delta p of less than 30 mmHg strongly suggests acute compartment syndrome.

Compartment pressure measurements are indicated in polytrauma patients, patients not alert or unreliable, or with inconclusive physical examination findings. Positive clinical findings should prompt urgent surgical intervention without the need for compartment measurements.[1]

Other investigations to aid diagnosis include forearm radiographs or MRI scans of the forearm (mainly in chronic compartment syndrome rather than acute settings).

Treatment / Management

Patients with suspected acute compartment syndrome of the forearm should be assessed following the advanced trauma life support principles and managed in a multidisciplinary approach. A senior review must be done as soon as possible after the patient has arrived in the emergency department. First steps can be taken on initial assessment such as oxygen administration, elevating the arm in a sling, splitting or removing a tight cast or dressing, ensuring the patient is normotensive as hypotension reduces perfusion pressure and causes further tissue injury. The definitive treatment of acute compartment syndrome is a surgical intervention in the form of urgent forearm compartment fasciotomies.[1][16]

Surgical intervention is performed under general anesthetic. The fasciotomy approaches are volar and dorsal. The volar incision starts just radial to FCU at the wrist and extends proximally to the medial epicondyle. The fascia over the deep muscle compartment needs to be dissected. This approach decompresses the anterior compartment and the posterior compartment as well. The incision can extend distally also to release the carpal tunnel. The dorsal incision starts 2 cm distal to the lateral epicondyle toward the midline of the wrist. It decompresses the mobile wad of Henry and the posterior compartment. Usually, the wounds are left open and covered in sterile dressings, and the patient will require a second look intervention at 48 to 72 hours. During the second look procedure, the dead muscle tissue needs to be debrided, and delayed primary closure of the wounds can be attempted. If the operating team cannot close the wounds, a negative pressure dressing should be considered, followed at a later stage by split-thickness skin grafting.[17][13]

Differential Diagnosis

Patients with spreading cellulitis can present with pain, swelling, and redness over the forearm. In such scenarios, the cellulitis might be spreading from the hand (distal to proximal) or the arm or olecranon. There might be a history of trauma/penetrating injury/insect bites that precipitated the cellulitis. The forearm compartments remain soft and passive stretch of muscles dodo not tend to cause excruciating pain as it does in compartment syndrome with a firm to palpate compartments.

Prognosis

The most important prognostic value in patients with acute compartment syndrome of the forearm is the time to diagnosis and fasciotomy. Reports suggest a rate of fasciotomy between 2% to 24% in acute compartment syndrome patients. This is mainly due to uncertainties in diagnosing this condition. The timing of the diagnosis and immediate surgical intervention is critical and limb saving. Delayed diagnosis can have devastating consequences on the patient. Prognosis varies from full recovery to amputation depending on the time of presentation, symptoms at presentation (absent pulses, as well as paralysis of the affected limb, are signs associated with late presentations), time to diagnosis, and surgical intervention.[1]

Complications

Failure to relieve the pressure in time can lead to tissue death in the affected compartment.

The most common complication is Volkmann ischemic contracture, an irreversible muscle contracture in the forearm, wrist, and hand resulting from muscle damage and necrosis. Patients usually present with particular clinical features, including elbow flexion, forearm pronation, wrist flexion, thumb adduction, metacarpophalangeal joints extension, and interphalangeal joints flexion. Volkmann contracture can be classified using the Tsuge classification into mild (when only finger flexor muscles are affected), moderate (when wrist and finger flexors are affected), and severe (when wrist, finger flexors, and extensors are all affected). Treatment options for this condition range from dynamic splinting to excision of necrotic tissue and tendon transfers.[17]

Other complications include nerve damage, gangrene, chronic regional pain syndrome, and rhabdomyolysis, potentially leading to kidney failure. Rhabdomyolysis has been reported in up to 23% of cases diagnosed with acute compartment syndrome in general. Rhabdomyolysis presents clinically as a triad of symptoms, including muscle stiffness, muscle pain (particularly back pain), and poor urine output or dark-colored urine.[14][18]