# Compartment Syndrome: Pathophysiology, Diagnosis, and Fasciotomy

## Introduction

Compartment syndrome arises when the pressure within a closed fascial compartment increases to a level that impairs tissue perfusion, ultimately causing ischemia and tissue necrosis. In vascular surgery, this condition most frequently occurs following reperfusion of an acutely ischemic limb, prolonged ischemia times, or venous outflow obstruction. Rapid identification and timely fasciotomy are critical to prevent irreversible damage to muscles and nerves.

## Pathophysiology

### The Ischemia-Reperfusion Cascade

Acute arterial occlusion initiates tissue ischemia and cellular injury. When blood flow is restored, reperfusion triggers a complex inflammatory response characterized by the release of oxygen free radicals, activation of neutrophils, and secretion of cytokines. This inflammatory milieu damages the endothelium, increasing capillary permeability and leading to interstitial edema. Since the fascial compartments are non-compliant, the resulting edema raises intracompartmental pressure. Once this pressure surpasses capillary perfusion pressure—typically around 25 to 30 mmHg—a vicious cycle ensues: ischemia causes more edema, which further elevates pressure and worsens ischemia.

### Critical Pressure Thresholds

Under normal conditions, compartment pressures range from 0 to 8 mmHg. Capillary blood flow becomes compromised when compartment pressure exceeds 20 mmHg. Muscle necrosis begins when pressures remain above 30 mmHg for more than 6 to 8 hours. Many diagnostic protocols use the delta pressure, defined as the difference between diastolic blood pressure and compartment pressure; a delta pressure less than 30 mmHg is considered diagnostic of compartment syndrome. Sustained elevated pressures can cause complete muscle necrosis within as little as six hours.

| Parameter | Value | Clinical Significance |
|-----------|-------|----------------------|
| Normal compartment pressure | 0–8 mmHg | Baseline; no intervention needed |
| Capillary perfusion compromised | >20 mmHg | Early warning; close monitoring required |
| Absolute pressure threshold | >30 mmHg | Fasciotomy indicated |
| Delta pressure (diastolic − compartment) | <30 mmHg | Diagnostic of compartment syndrome |
| Time to irreversible muscle necrosis | 6–8 hours at >30 mmHg | Defines urgency of intervention |

### Risk Factors in Vascular Surgery

Several factors increase the risk of compartment syndrome in vascular surgery. Acute limb ischemia with ischemia times exceeding six hours is a major risk. Procedures such as embolectomy and thrombectomy, as well as reperfusion after aortic surgery, can precipitate the condition. Combined arterial and venous injuries, massive fluid resuscitation, prolonged limb compression (for example, in the lithotomy position), and anticoagulation therapy—which raises the risk of compartment hemorrhage—also contribute to its development.

![Cross-sectional anatomy of the lower leg showing four fascial compartments](images/lower-leg-compartments-anatomy.jpg)

## Diagnosis

### Clinical Presentation - The "Six Ps"

The clinical diagnosis of compartment syndrome is guided by the "Six Ps." The earliest and most reliable sign is pain that is out of proportion to the clinical situation and worsens with passive stretch of the affected muscles. On examination, the involved compartment feels tense and swollen. Paresthesias indicate nerve ischemia within the compartment, while paralysis is a late sign reflecting advanced muscle and nerve damage. Pallor may or may not be present, and pulses can remain intact despite compartment syndrome. Pulselessness is a very late finding, and the presence of palpable pulses does not exclude the diagnosis.

### Compartment Pressure Measurement

When clinical assessment is inconclusive, especially in patients who are obtunded, sedated, or neurologically impaired, compartment pressure measurement is essential. This is performed using a Stryker needle or an arterial line transducer inserted directly into the compartment. In the lower leg, all four compartments—anterior, lateral, superficial posterior, and deep posterior—should be measured. An absolute compartment pressure greater than 30 mmHg or a delta pressure less than 30 mmHg indicates the need for fasciotomy.

### Laboratory Findings

Laboratory markers support the diagnosis and help monitor complications. Elevated creatine kinase (CK) levels, often exceeding 10,000 U/L, indicate muscle injury. Myoglobinuria manifests as dark urine and a positive urine dipstick for blood without red blood cells on microscopy. Rhabdomyolysis can also cause hyperkalemia, metabolic acidosis, and elevated lactate levels. Monitoring for acute kidney injury is crucial, as myoglobin can obstruct renal tubules.

## Four-Compartment Fasciotomy of the Lower Leg

### Two-Incision Technique (Standard)

The standard approach to decompress all four compartments of the lower leg involves two incisions. The lateral incision is made along a line extending from the fibular head to the lateral malleolus. After incising the skin and subcutaneous tissue, the lateral intermuscular septum is exposed. The fascia anterior to this septum is incised to release the anterior compartment, while the fascia posterior to the septum is incised to decompress the lateral compartment. Careful identification and protection of the superficial peroneal nerve, which crosses the lateral compartment, are essential.

The medial incision is placed approximately 2 cm posterior to the medial tibial border to avoid injury to the saphenous vein and nerve. The fascia overlying the gastrocnemius and soleus muscles is incised to release the superficial posterior compartment. To decompress the deep posterior compartment, the soleus muscle is detached from the medial tibial border, and the deep fascia is incised; this compartment is the most commonly missed during fasciotomy. The posterior tibial neurovascular bundle must be identified and protected throughout the procedure.

### Single-Incision Technique

An alternative single-incision technique involves a lateral incision combined with fibulectomy, allowing access to all four compartments. This method is less commonly used due to higher morbidity and is typically reserved for specific cases such as combined fracture management.

![Two-incision four-compartment fasciotomy technique with lateral and medial approaches](images/fasciotomy-two-incision-technique.jpg)

### Fasciotomy Principles

Fasciotomy incisions should extend the full length of the compartment to ensure adequate decompression, as insufficient incision length is the most frequent cause of failed fasciotomy. Any nonviable muscle—characterized by dark color, lack of contractility, and absence of bleeding—should be debrided. The wounds are left open and managed with negative pressure wound therapy or moist dressings. Delayed primary closure, skin grafting, or healing by secondary intention is planned for 48 to 72 hours postoperatively.

## Upper Extremity Compartment Syndrome

Although less common, compartment syndrome can occur in the upper extremity, particularly after brachial artery embolectomy or prolonged ischemia. The forearm contains three compartments: volar, dorsal, and mobile wad. The volar compartment is released through a curvilinear incision extending from the antecubital fossa to the carpal tunnel. Additionally, the hand's interosseous and thenar/hypothenar compartments may require decompression.

## Postoperative Management

Postoperative care involves aggressive intravenous fluid resuscitation to maintain urine output above 200 mL per hour in cases of rhabdomyolysis. Alkalinization of the urine with intravenous sodium bicarbonate helps reduce myoglobin precipitation within the renal tubules. Serial monitoring of serum potassium, creatinine, and creatine kinase is necessary. Calcium administration should be avoided in hyperkalemia associated with rhabdomyolysis, as it may exacerbate muscle injury. Wound closure is delayed for 48 to 72 hours, using vessel loops for gradual approximation or split-thickness skin grafting as needed.

![Fasciotomy wound managed with negative pressure wound therapy before delayed closure](images/fasciotomy-npwt-closure.jpg)

## Key Clinical Pearls

Compartment syndrome remains primarily a clinical diagnosis, and fasciotomy should not be delayed while awaiting pressure measurements if classic signs are present. Pain that is disproportionate to the injury and worsened by passive stretch is the earliest and most reliable indicator. The deep posterior compartment is the most commonly missed during fasciotomy, so all four compartments must always be released. The presence of palpable pedal pulses does not exclude compartment syndrome. When ischemia time exceeds six hours before revascularization, prophylactic fasciotomy should be strongly considered to prevent irreversible damage.

## References

1. Defined, Defined, et al. "Compartment syndrome of the lower extremity after vascular surgery." *J Vasc Surg*. 2015;61(4):1033-1040.  
2. Defined, Defined, et al. "Diagnosis and treatment of acute extremity compartment syndrome." *Lancet*. 2015;386(10000):1299-1310.  
3. Defined, Defined, et al. "Fasciotomy technique and wound management after reperfusion injury." *Semin Vasc Surg*. 2009;22(1):36-44.  
4. Defined, Defined, et al. "Rhabdomyolysis and acute kidney injury." *N Engl J Med*. 2009;361(1):62-72.