COMPARTMENT SYNDROME

Compartment syndromes develop when the pressure in closed compartment (such as the four compartments of the leg, the anterior or posterior compartment of the thigh, or the three compartments of the forearm) rises to the point that the microvascular circulation of the muscles and nerves in the compartment are compromised.


Pathophysiology

Compartment syndromes develop when the pressure in closed compartment rises to the point that the microvascular circulation of the muscles and nerves in the compartment are compromised.

Normal compartmental pressure is 0 to 10 mmHg. When the tissue pressure rises to between 10 mm Hg and 30 mm Hg of the diastolic pressure, the perfusion of both muscle and nerve is compromised and ischemia occurs.

Important things to remember:

1. With complete ischemia, muscle remains viable for up to 3 to 4 hours without irreversible damage.
1. At 6 to 8 hours of complete ischemia, there is variable recovery.
2. More than 8 hours of complete ischemia causes irreversible muscle injury.
1. Peripheral nerves show conduction changes after 1 hour of total ischemia, the neurons and supporting structures can sustain up to 4 hours of total ischemia with a reversible injury pattern (neuropraxia - conduction defect with Wallerian degeneration).


Presentation

Patients with compartment syndrome present with severe pain that is out of proportion to their injury. The evaluation of patients is difficult and deceiving as the clinical picture can be variable. The amount of pain must be assessed carefully, and assessments should be made at multiple times, ideally by the same individual or with carefully documented progress notes. Pain is often intense, and patients with a fully evolved compartment syndrome have difficulty lying quietly - most resist the clinician palpating the leg.

The key historical finding is extreme pain. Therefore, clinicians must be extremely careful not to over medicate a patient with analgesics because medications mask the compartment syndrome.


Physical Examination

5 steps of examination:

Step 1. Visually inspect the involved limb. Does the limb appear swollen? With marked swelling, the limb will often have a circular appearance and the skin may be taut and shiny without wrinkles.

Step 2. Palpate each compartment. Is there extreme pain with palpation? Is the compartment soft or hard?

Step 3. Test motor function and grade on a scale of one to five. First ask the patient to flex and extend the digits of the involved joint. This test checks if the involved muscles move easily through the compartment. If the patient can easily flex and extend, then swelling in the compartment is probably not severe. Next, test the muscle group and grade the strength.

Step 4. Passively flex and extend the digits or joint, assessing for pain. Extreme pain on passive flexion and extension is a sign of impending compartment syndrome. The tissue pressure in the compartment has risen to the point that there is severe pain with excursion of the muscle and tendons throughout the compartment.

Step 5. Test sensory nerve function by assessing sensibility of the nerves that travel through the compartment. The ability of the patient to feel light touch should be checked first and compared from side to side. If light touch cannot be felt, then one should measure the ability of the patient to detect pin prick. One should also assess for paresthesias and dysesthesias.


Assessment and Decision-Making

After examining the patient, the clinician must decide whether the patient has: 1) no evidence of a compartment syndrome, 2) a possible or probable compartment syndrome, or a 3) definite compartment syndrome.

No evidence of a compartment syndrome
In this scenario, the patient does not have pain out of proportion to injury; the involved compartment is soft, or, if swollen, the amount of swelling is in proportion to the injury; and palpation of the compartment does not produce intense pain. Motor function is normal and any weakness noted should be within the limits one would expect for normal pain and weakness secondary to the injury.


Possible or probable compartment syndrome
In this scenario, the clinician is unsure whether the patient has elevated tissue pressure, which may indicate a compartment syndrome. The patient may have any combination of pain out of proportion to injury, a tense or painful compartment, loss of motor function or sensation, or pain on passive stretch of the muscle of the compartment. To determine whether there are elevated pressures within the compartment, the clinician must measure the pressures within the compartment. Once the compartment pressures have been measured, the clinician then compares the pressures to the diastolic pressure and makes a decision as to whether a compartment syndrome is present.


Definite compartment syndrome

A definite compartment syndrome is present when the patient has severe pain out of proportion to injury, severe pain on passive stretch of the compartment and tenseness.There may be loss of neurologic function (motor or sensory changes).

The patient should be scheduled for immediate fasciotomy of the involved limb. Compartment pressures are measured to confirm the clinician's diagnosis. The pressure measurements are performed either at the bedside or in the operating room.


Tissue Pressure Measurement

Several instruments are used to measure tissue pressure. One may use a manometer, which is an electronic device such as is available in the intensive care unit, or a custom application such as the Stryker tissue pressure measurement device.

When measuring tissue pressure in a patient with a tibial fracture, the measurement should be done at the level of the fracture.


Indications for fasciotomy

The indications for fasciotomy have varied in the literature. Some authors have recommended an absolute tissue pressure measurement, while others have advocated determining the gradient by comparing the tissue pressure to either the diastolic pressure or the mean arterial pressure. The diastolic pressure is most commonly used because one does not have to do a calculation to determine mean arterial pressure (mean arterial pressure is the diastolic pressure plus one third of the difference between the systolic and diastolic pressures).

An important point to remember is that basic science studies have shown that normal muscle perfusion remains intact with tissue pressures within 10 mm Hg of the diastolic pressure. With injured muscle, the threshold decreases to within 20 mm Hg of the diastolic pressure. With this basic science knowledge, many authors now recommend fasciotomy when the tissue pressure is within 30 mm Hg of the diastolic pressure.


References

* Heckman MM, Whitesides TE Jr, Grewe SR, Judd RL, Miller M, Lawrence JH 3rd. Histologic determination of the ischemic threshold of muscle in the canine compartment syndrome model. J Orthop Trauma. 1993; 7:199-210.

* Heppenstall RB, Sapega AA, Scott R, Shenton D, Park YS, Maris J, Chance B. The compartment syndrome: An experimental and clinical study of muscular energy metabolism using phosphorus nuclear magnetic resonance spectroscopy. Clin Orthop. 1988; 226:138-155.

* Heppenstall RB, Scott R, Sapega A, Park YS, Chance B. A comparative study of the tolerance of skeletal muscle to ischemia: Tourniquet application compared with acute compartment syndrome. J Bone Joint Surg Am. 1986; 68:820-828.

* Whitesides TE, Heckman MM. Acute compartment syndrome: Update on diagnosis and treatment. J Am Acad Orthop Surg. 1996; 4:209-218.

* Whitesides TE. Compartment syndromes and the role of fasciotomy, its parameters and techniques. Instr Course Lect. 1977; 26:179-196.