A 35-year-old woman presents with progressive vision loss and severe headache. MRI shows cavernous sinus thrombosis with extension into the superior ophthalmic vein. Blood cultures grow Staphylococcus aureus. History reveals she had squeezed a facial pustule near her upper lip 5 days prior. Evaluate the anatomical explanation and risk stratification for this complication.
Q2
A 52-year-old diabetic man undergoes emergent fasciotomy for compartment syndrome of the right leg following a tibia-fibula fracture. Intraoperatively, the anterior compartment muscles appear dusky and do not contract with stimulation. The lateral compartment muscles appear viable. Deep posterior compartment shows borderline viability with weak contraction. Superficial posterior compartment is clearly viable. Synthesize a management plan that optimizes limb salvage while minimizing morbidity.
Q3
A 29-year-old man sustains a gunshot wound to the medial upper arm. He presents with inability to flex his elbow and loss of sensation over the lateral forearm. Angiography shows intact brachial artery, but compartment pressures in the anterior arm compartment are 55 mmHg. His blood pressure is 90/60 mmHg after resuscitation. Evaluate the optimal surgical approach considering all clinical factors.
Q4
A 67-year-old man develops severe abdominal pain 3 days after elective sigmoid colectomy. CT shows fluid tracking along the left psoas muscle and into the left thigh anterior compartment. No bowel perforation is identified, but there is concern for an anastomotic leak. Analyze the fascial anatomy to determine the most likely pathway of fluid spread from the retroperitoneum to the thigh.
Q5
A 42-year-old injection drug user presents with fever, dysphagia, and neck swelling. CT shows a multiloculated abscess in the retropharyngeal space with air-fluid levels extending into the posterior mediastinum to the level of T6. Despite the inferior extent, the abscess has not spread to the anterior mediastinum. Analyze the fascial anatomy to explain this pattern of spread.
Q6
A 38-year-old woman presents with progressive difficulty swallowing and a neck mass. CT shows a 4 cm mass in the retropharyngeal space extending from the skull base to T2 vertebral level. The mass displaces the carotid sheath laterally. Analysis of the fascial anatomy reveals the mass is contained between two fascial layers. Which fascial boundaries define this space?
Q7
A 55-year-old man undergoes axillary lymph node dissection for melanoma. Postoperatively, he develops arm swelling and is found to have a fluid collection. Aspiration reveals milky fluid with triglyceride level of 250 mg/dL. The surgeon explains this complication relates to injury of structures within a specific fascial compartment. Which fascial space contains the structure most likely injured?
Q8
A 32-year-old motorcyclist sustains a tibial fracture. Eight hours post-injury, he develops severe pain in his lower leg unresponsive to morphine, with pain on passive toe dorsiflexion. Dorsalis pedis and posterior tibial pulses are palpable. Compartment pressures measure 45 mmHg in the anterior compartment and 42 mmHg in the lateral compartment. His blood pressure is 110/70 mmHg. Apply compartment syndrome criteria to determine the appropriate management.
Q9
A 45-year-old diabetic woman develops necrotizing fasciitis of the perineum following a perirectal abscess. During surgical debridement, the surgeon needs to understand the extent of potential spread. The infection has violated Colles' fascia. To which anatomical locations can this infection most readily spread?
Q10
A 28-year-old construction worker presents to the emergency department with severe pain and swelling of his right forearm following a crush injury 6 hours ago. On examination, the forearm is tense and tender, with pain on passive finger extension. Radial pulse is present but weak. Capillary refill is 4 seconds. Which compartment is most likely affected based on the clinical presentation?
Fascial compartments US Medical PG Practice Questions and MCQs
Question 1: A 35-year-old woman presents with progressive vision loss and severe headache. MRI shows cavernous sinus thrombosis with extension into the superior ophthalmic vein. Blood cultures grow Staphylococcus aureus. History reveals she had squeezed a facial pustule near her upper lip 5 days prior. Evaluate the anatomical explanation and risk stratification for this complication.
A. Direct lymphatic spread from facial infection due to rich subcutaneous lymphatic network
B. Valveless facial venous system allowing retrograde flow from danger triangle to cavernous sinus (Correct Answer)
C. Contiguous spread through cribriform plate from nasal cavity involvement
D. Hematogenous seeding via internal jugular vein and sigmoid sinus
E. Extension through pterygoid venous plexus communicating with middle meningeal vein
Explanation: ***Valveless facial venous system allowing retrograde flow from danger triangle to cavernous sinus***
- The **danger triangle of the face** (perioral and nasal areas) contains **valveless veins**, which allows blood to flow in a **retrograde** direction toward the intracranial space.
- Infections in this region can spread via the **angular vein** into the **superior ophthalmic vein**, directly reaching the **cavernous sinus** and causing septic thrombosis.
*Direct lymphatic spread from facial infection due to rich subcutaneous lymphatic network*
- While the face has a rich **lymphatic network**, lymphatic drainage typically leads to **submandibular or cervical lymph nodes**, not the cavernous sinus.
- Cavernous sinus thrombosis is a **vascular complication** specifically involving the **venous system**, not the lymphatic system.
*Contiguous spread through cribriform plate from nasal cavity involvement*
- The **cribriform plate** is a route for infections to enter the **subarachnoid space**, primarily leading to **meningitis** or brain abscesses.
- It does not serve as the primary anatomical conduit for superficial facial infections to localize within the **cavernous sinus**.
*Hematogenous seeding via internal jugular vein and sigmoid sinus*
- The **internal jugular vein** and **sigmoid sinus** represent the **outflow tract** away from the brain; flow to the cavernous sinus through this route would be highly atypical.
- Bacterial seeding via this route would usually imply **systemic bacteremia** or infection in the **mastoid air cells**, rather than a localized facial pustule.
*Extension through pterygoid venous plexus communicating with middle meningeal vein*
- The **pterygoid venous plexus** can communicate with the cavernous sinus, but it primarily drains the **infratemporal fossa** and deep face, not the superficial upper lip.
- The **middle meningeal vein** drains into the pterygoid plexus or sphenoparietal sinus and is not the classic path for **danger triangle** infections.
Question 2: A 52-year-old diabetic man undergoes emergent fasciotomy for compartment syndrome of the right leg following a tibia-fibula fracture. Intraoperatively, the anterior compartment muscles appear dusky and do not contract with stimulation. The lateral compartment muscles appear viable. Deep posterior compartment shows borderline viability with weak contraction. Superficial posterior compartment is clearly viable. Synthesize a management plan that optimizes limb salvage while minimizing morbidity.
A. Debride anterior compartment only, leave wounds open, second look in 48 hours for other compartments
B. Debride all nonviable muscle, preserve borderline tissue, second look in 24 hours (Correct Answer)
C. Complete debridement of anterior and deep posterior compartments with immediate wound closure
D. Below-knee amputation given extent of muscle necrosis and diabetes
E. Hyperbaric oxygen therapy for 48 hours before deciding on debridement versus amputation
Explanation: ***Debride all nonviable muscle, preserve borderline tissue, second look in 24 hours***
- Immediate **debridement** of non-contractile, dusky muscle is crucial to prevent **myoglobinuria**, metabolic acidosis, and **acute kidney injury**.
- Marginal tissue should be preserved during the initial surgery to maximize potential **limb salvage**, necessitating a **mandatory second-look** procedure within 24-48 hours.
*Debride anterior compartment only, leave wounds open, second look in 48 hours for other compartments*
- Leaving known nonviable muscle in the anterior compartment for 48 hours increases the risk of **secondary infection** and systemic inflammatory response syndrome.
- Re-exploration should be performed sooner (24 hours) when multiple compartments show **borderline viability** to ensure timely intervention.
*Complete debridement of anterior and deep posterior compartments with immediate wound closure*
- **Immediate wound closure** is strictly contraindicated in compartment syndrome as it can cause a recurrence of increased pressure and facilitates **anaerobic infection**.
- Over-debridement of the **deep posterior compartment** before its viability is definitively determined could result in unnecessary loss of **plantarflexion** and sensation.
*Below-knee amputation given extent of muscle necrosis and diabetes*
- **Amputation** is premature as the lateral and superficial posterior compartments are viable, providing a foundation for a **functional limb**.
- While **diabetes** may complicate healing, it is not an absolute indication for primary amputation in the setting of salvageable muscle groups.
*Hyperbaric oxygen therapy for 48 hours before deciding on debridement versus amputation*
- Delaying surgical **debridement** of necrotic tissue to pursue **HBO therapy** is dangerous and allows for the progression of sepsis and muscle breakdown.
- HBO therapy is an **adjunct**, not a replacement for mechanical decompression and removal of dead tissue in **acute compartment syndrome**.
Question 3: A 29-year-old man sustains a gunshot wound to the medial upper arm. He presents with inability to flex his elbow and loss of sensation over the lateral forearm. Angiography shows intact brachial artery, but compartment pressures in the anterior arm compartment are 55 mmHg. His blood pressure is 90/60 mmHg after resuscitation. Evaluate the optimal surgical approach considering all clinical factors.
A. Immediate fasciotomy of anterior compartment with nerve exploration and vascular repair
B. Fasciotomy of both anterior and posterior compartments with primary nerve repair
C. Further resuscitation to MAP >65, then fasciotomy with delayed nerve repair
D. Emergent fasciotomy, debridement, and temporary vascular shunt placement
E. Complete neurovascular exploration with definitive repair and compartment release (Correct Answer)
Explanation: ***Complete neurovascular exploration with definitive repair and compartment release***
- The patient exhibits clinical and objective signs of **acute compartment syndrome** (pressure 55 mmHg) and **musculocutaneous nerve** injury, requiring emergency surgical intervention.
- A total assessment is necessary because the **gunshot wound** trajectory near the medial arm risks occult damage to the **neurovascular bundle** despite initial angiographic findings.
*Immediate fasciotomy of anterior compartment with nerve exploration and vascular repair*
- While an anterior fasciotomy is vital, focusing solely on the anterior compartment may be insufficient if the high-energy trauma caused **posterior compartment** injury.
- **Vascular repair** is not indicated at this stage as angiography has already confirmed the **brachial artery** is intact.
*Fasciotomy of both anterior and posterior compartments with primary nerve repair*
- Primary nerve repair is often contraindicated in **high-velocity gunshot wounds** due to the "zone of injury" and potential for further tissue debridement needs.
- While dual-compartment release is thorough, the emphasis on **primary repair** in an unstable, potentially contaminated trauma setting is surgically premature.
*Further resuscitation to MAP >65, then fasciotomy with delayed nerve repair*
- While hemodynamic stability is important, the **Delta pressure** (60 - 55 = 5 mmHg) is critically low, meaning any delay in fasciotomy will lead to **muscle necrosis**.
- Resuscitation should occur **concurrently** with surgical preparation rather than as a prerequisite that delays limb-saving decompression.
*Emergent fasciotomy, debridement, and temporary vascular shunt placement*
- The use of a **temporary vascular shunt** is reserved for patients with confirmed arterial transection to maintain distal perfusion during damage control.
- Since the **brachial artery** is intact per angiography, shunting is unnecessary and adds pointless risk and operative time.
Question 4: A 67-year-old man develops severe abdominal pain 3 days after elective sigmoid colectomy. CT shows fluid tracking along the left psoas muscle and into the left thigh anterior compartment. No bowel perforation is identified, but there is concern for an anastomotic leak. Analyze the fascial anatomy to determine the most likely pathway of fluid spread from the retroperitoneum to the thigh.
A. Direct extension through the inguinal canal following the spermatic cord
B. Tracking along psoas muscle through femoral triangle via femoral sheath
C. Spread through obturator foramen along obturator neurovascular bundle
D. Extension along iliacus fascia through muscular lacuna beneath inguinal ligament (Correct Answer)
E. Dissection through transversalis fascia into preperitoneal space and anterior abdominal wall
Explanation: ***Extension along iliacus fascia through muscular lacuna beneath inguinal ligament***
- The **iliacus fascia** and **psoas fascia** create a continuous sheath that provides a direct anatomical pathway for retroperitoneal fluid to descend into the **anterior thigh**.
- This fluid collection passes deep to the **inguinal ligament** via the **muscular lacuna**, which contains the **psoas major**, **iliacus**, and the **femoral nerve**.
*Direct extension through the inguinal canal following the spermatic cord*
- The **inguinal canal** is an oblique passage in the **anterior abdominal wall**, not a primary conduit for **retroperitoneal** fluid tracking from the psoas muscle.
- Fluid in this canal would typically lead to **scrotal swelling** or a mass in the **inguinal region** rather than tracking into the anterior thigh compartment.
*Tracking along psoas muscle through femoral triangle via femoral sheath*
- The **femoral sheath** is an extension of the **transversalis** and **iliac fasciae** that surrounds the femoral vessels, but it is distinct from the muscular compartment containing the psoas.
- While the psoas muscle enters the **femoral triangle**, the sheath primarily contains the **femoral artery, vein, and canal**, not the muscle itself.
*Spread through obturator foramen along obturator neurovascular bundle*
- The **obturator foramen** serves as a pathway for structures to move from the **lesser pelvis** into the **medial (adductor) compartment** of the thigh.
- Fluid tracking here would be located more medially and would not typically track from the high **retroperitoneal psoas region** into the anterior compartment.
*Dissection through transversalis fascia into preperitoneal space and anterior abdominal wall*
- The **transversalis fascia** provides a barrier between the abdominal muscles and the **peritoneum**; fluid tracking here would stay in the **anterior abdominal wall**.
- This pathway does not provide a direct descent into the **thigh** and would not explain fluid tracking specifically along the **psoas muscle**.
Question 5: A 42-year-old injection drug user presents with fever, dysphagia, and neck swelling. CT shows a multiloculated abscess in the retropharyngeal space with air-fluid levels extending into the posterior mediastinum to the level of T6. Despite the inferior extent, the abscess has not spread to the anterior mediastinum. Analyze the fascial anatomy to explain this pattern of spread.
A. The danger space between alar and prevertebral fascia allows posterior but not anterior spread (Correct Answer)
B. The buccopharyngeal fascia extends to diaphragm blocking anterior spread
C. The prevertebral fascia prevents anterior spread into mediastinum
D. The alar fascia fuses with the pericardium preventing anterior extension
E. The investing layer of deep cervical fascia diverts infection posteriorly
Explanation: ***The danger space between alar and prevertebral fascia allows posterior but not anterior spread***
- The **danger space** is a potential space located between the **alar fascia** anteriorly and the **prevertebral fascia** posteriorly, providing a low-resistance pathway for infection to spread from the skull base to the **diaphragm**.
- Because this space is positioned behind the **visceral compartments** and is bounded by the fusion of fascial layers laterally, it anatomically directs the descent of a **retropharyngeal abscess** into the **posterior mediastinum** while isolating it from the anterior mediastinum.
*The prevertebral fascia prevents anterior spread into mediastinum*
- The **prevertebral fascia** forms the posterior boundary of the danger space; while it prevents spread into the **vertebral bodies**, it does not explain why the infection is restricted from the **anterior mediastinum**.
- This fascia continues down to the **coccyx**, meaning it helps facilitate deep vertical spread rather than serving as a transverse barrier to anterior compartments.
*The alar fascia fuses with the pericardium preventing anterior extension*
- The **alar fascia** actually ends and fuses with the **buccopharyngeal fascia** at the level of **T2**; it does not extend further to fuse with the **pericardium**.
- The **pretracheal fascia** is the layer that blends with the fibrous pericardium, and it is located much more anteriorly in the neck.
*The buccopharyngeal fascia extends to diaphragm blocking anterior spread*
- The **buccopharyngeal fascia** (the posterior part of the visceral fascia) only extends inferiorly to the level of the **superior mediastinum** (around T2-T4) where it blends with the esophagus.
- It forms the anterior wall of the **retropharyngeal space** and cannot block spread to the diaphragm as it does not reach that far inferiorly.
*The investing layer of deep cervical fascia diverts infection posteriorly*
- The **investing fascia** is the most superficial layer of deep cervical fascia, surrounding the **sternocleidomastoid** and trapezius muscles.
- It typically limits spread to the **anterior or posterior triangles** of the neck and does not communicate with the deep **retropharyngeal** or **danger spaces** involved in mediastinitis.
Question 6: A 38-year-old woman presents with progressive difficulty swallowing and a neck mass. CT shows a 4 cm mass in the retropharyngeal space extending from the skull base to T2 vertebral level. The mass displaces the carotid sheath laterally. Analysis of the fascial anatomy reveals the mass is contained between two fascial layers. Which fascial boundaries define this space?
A. Between visceral fascia anteriorly and prevertebral fascia posteriorly
B. Between investing layer of deep fascia and prevertebral fascia
C. Between buccopharyngeal fascia anteriorly and alar fascia posteriorly (Correct Answer)
D. Between superficial cervical fascia and prevertebral fascia
E. Between alar fascia anteriorly and prevertebral fascia posteriorly
Explanation: ***Between buccopharyngeal fascia anteriorly and alar fascia posteriorly***
- The **retropharyngeal space** is bounded anteriorly by the **buccopharyngeal fascia** (covering the pharyngeal constrictors) and posteriorly by the **alar fascia**.
- This space extends from the **base of the skull** to the **superior mediastinum** (approximately T2 level), which matches the clinical presentation of this mass.
*Between superficial cervical fascia and prevertebral fascia*
- The **superficial cervical fascia** is the subcutaneous layer containing the platysma; it does not form the boundary of the deep skeletal/visceral spaces of the neck.
- This area is too superficial to contain a mass that displaces the **carotid sheath** laterally from a retropharyngeal location.
*Between visceral fascia anteriorly and prevertebral fascia posteriorly*
- This describes a broad area incorporating several distinct spaces; the **visceral fascia** (pretracheal) is located anterior to the trachea and esophagus.
- It does not properly define the **retropharyngeal space** which is critical for understanding the path between the pharynx and the vertebral column.
*Between investing layer of deep fascia and prevertebral fascia*
- The **investing layer** surrounds the entire neck like a collar, covering the trapezius and sternocleidomastoid muscles.
- It is not at the correct anatomical depth to define the specific compartment where the mass is located between the **pharynx** and the **spine**.
*Between alar fascia anteriorly and prevertebral fascia posteriorly*
- These layers define the **"danger space,"** which extends from the skull base all the way to the **diaphragm**.
- While the mass in the question reaches T2, the standard description of the **retropharyngeal space** (containing the retropharyngeal nodes) is between the buccopharyngeal and alar fasciae.
Question 7: A 55-year-old man undergoes axillary lymph node dissection for melanoma. Postoperatively, he develops arm swelling and is found to have a fluid collection. Aspiration reveals milky fluid with triglyceride level of 250 mg/dL. The surgeon explains this complication relates to injury of structures within a specific fascial compartment. Which fascial space contains the structure most likely injured?
A. Axillary space deep to clavipectoral fascia (Correct Answer)
B. Retropectoral space behind pectoralis major
C. Superficial fascia between skin and pectoralis major
D. Space between pectoralis major and minor muscles
E. Intermuscular space between deltoid and pectoralis
Explanation: ***Axillary space deep to clavipectoral fascia***
- The patient has a **chylous leak** (milky fluid with **triglycerides >110 mg/dL**), caused by injury to the **thoracic duct** or right lymphatic duct where they enter the venous system at the base of the axilla/neck.
- The **axillary space** is enclosed by the **clavipectoral fascia**, which contains major neurovascular structures and terminal lymphatic trunks that are susceptible to injury during **axillary lymph node dissection**.
*Superficial fascia between skin and pectoralis major*
- This layer contains primarily **subcutaneous fat** and cutaneous nerves, not the major lymphatic trunks responsible for chylous fluid.
- Injury here would result in a **seroma** (clear fluid) or hematoma, rather than high-triglyceride **chyle**.
*Space between pectoralis major and minor muscles*
- This is known as the **interpectoral space** (containing Rotter's nodes), but it does not house the main thoracic duct termination.
- While lymph nodes are present here, a leak from these nodes would not typically produce the milky, high-triglyceride fluid characteristic of a **ductal injury**.
*Retropectoral space behind pectoralis major*
- This space is primarily occupied by the **pectoralis minor** and loose connective tissue, serving as a landmark during surgery.
- Injury in this specific plane usually involves **pectoral nerves** or vessels rather than the central **cisterna chyli** derivatives or thoracic duct.
*Intermuscular space between deltoid and pectoralis*
- This describes the **deltopectoral groove**, which contains the **cephalic vein** and the deltoid branch of the thoracoacromial artery.
- This area is lateral to the main axillary lymph node stations and does not contain the lymphatic anatomy associated with **chylous complications**.
Question 8: A 32-year-old motorcyclist sustains a tibial fracture. Eight hours post-injury, he develops severe pain in his lower leg unresponsive to morphine, with pain on passive toe dorsiflexion. Dorsalis pedis and posterior tibial pulses are palpable. Compartment pressures measure 45 mmHg in the anterior compartment and 42 mmHg in the lateral compartment. His blood pressure is 110/70 mmHg. Apply compartment syndrome criteria to determine the appropriate management.
A. Immediate four-compartment fasciotomy (Correct Answer)
B. Fasciotomy of anterior compartment only
C. Continue observation with serial examinations every 2 hours
D. Elevate leg above heart level and apply ice
E. Mannitol infusion and repeat pressure measurements in 1 hour
Explanation: ***Immediate four-compartment fasciotomy***
- The patient exhibits **pain out of proportion** to the injury and **pain on passive toe dorsiflexion**, which are the most sensitive clinical indicators for **Acute Compartment Syndrome (ACS)**.
- A **compartment pressure >30 mmHg** or a **Delta pressure** (Diastolic BP minus Compartment Pressure) of **≤30 mmHg** (70 - 45 = 25 mmHg in this case) confirms the need for emergent **surgical decompression**.
*Continue observation with serial examinations every 2 hours*
- Observation is inappropriate given that the patient's **compartment pressures** already exceed the surgical threshold and clinical symptoms are progressing.
- Delaying surgery risks irreversible **ischemic necrosis** of muscles and nerves, which can occur within **4 to 6 hours**.
*Elevate leg above heart level and apply ice*
- **Elevation** of the limb is strictly contraindicated in ACS as it decreases **arterial perfusion pressure**, further compromising tissue oxygenation.
- Ice can cause **vasoconstriction**, which exacerbates the **ischemic insult** already occurring within the high-pressure compartments.
*Fasciotomy of anterior compartment only*
- Although the anterior compartment is the most commonly affected, ACS in the lower leg requires a **four-compartment fasciotomy** to ensure all potential zones of pressure are released.
- Releasing only one compartment can lead to **missed syndrome** in the other three compartments (lateral, superficial posterior, and deep posterior), leading to permanent disability.
*Mannitol infusion and repeat pressure measurements in 1 hour*
- **Mannitol** may be used in specific crush injuries but is not a substitute for mechanical decompression when **intracompartmental pressures** are significantly elevated.
- Repeating measurements in an hour causes a dangerous delay in treatment for a patient who already meets the diagnostic criteria for **immediate surgical intervention**.
Question 9: A 45-year-old diabetic woman develops necrotizing fasciitis of the perineum following a perirectal abscess. During surgical debridement, the surgeon needs to understand the extent of potential spread. The infection has violated Colles' fascia. To which anatomical locations can this infection most readily spread?
A. Ischiorectal fossa and gluteal region
B. Medial thighs and popliteal fossa
C. Anterior abdominal wall and medial thighs
D. Scrotum/labia, penis, and anterior abdominal wall (Correct Answer)
E. Retroperitoneal space and pelvis
Explanation: ***Scrotum/labia, penis, and anterior abdominal wall***
- **Colles' fascia** is the deep layer of the superficial perineal fascia and is continuous with the **Dartos fascia** of the scrotum/labia and the **Scarpa's fascia** of the anterior abdominal wall.
- Because these layers form a continuous compartment, infections like **Fournier’s gangrene** travel easily along these planes but are blocked from entering the thighs by the attachment to the **fascia lata**.
*Anterior abdominal wall and medial thighs*
- While the infection can spread to the **anterior abdominal wall**, it is restricted from spreading to the **medial thighs**.
- This is due to the firm attachment of **Colles' fascia** to the **fascia lata** (deep fascia of the thigh) just distal to the **inguinal ligament**.
*Ischiorectal fossa and gluteal region*
- **Colles' fascia** attaches posteriorly to the **perineal body** and the margin of the **perineal membrane**, which prevents the spread of fluid or infection into the **anal triangle** or **ischiorectal fossa**.
- The **gluteal region** is separated from these superficial compartments by dense deep fascia and the bony attachments of the **sacrotuberous ligaments**.
*Medial thighs and popliteal fossa*
- As noted, the **fascia lata** attachment prevents any superficial perineal infection from descending into the **thigh**.
- The **popliteal fossa** is located much further distally and is anatomically isolated from the superficial perineal pouch by multiple fascial and muscular layers.
*Retroperitoneal space and pelvis*
- The **perineal membrane** and the **pelvic diaphragm** (levator ani muscle) act as robust physical barriers that prevent the upward spread of superficial infections into the **pelvic cavity**.
- Spread to the **retroperitoneum** would require a breach of the deep pelvic fascia or a different source of infection, such as a perforated viscus, rather than a violation of **Colles' fascia**.
Question 10: A 28-year-old construction worker presents to the emergency department with severe pain and swelling of his right forearm following a crush injury 6 hours ago. On examination, the forearm is tense and tender, with pain on passive finger extension. Radial pulse is present but weak. Capillary refill is 4 seconds. Which compartment is most likely affected based on the clinical presentation?
A. Anterior (volar) compartment (Correct Answer)
B. Mobile wad compartment
C. Superficial posterior compartment
D. Deep posterior compartment
E. Thenar compartment
Explanation: ***Anterior (volar) compartment***
- The **anterior (flexor) compartment** contains the finger and wrist flexors; therefore, **pain on passive finger extension** is the most sensitive and earliest clinical sign of compartment syndrome in this space.
- Following a **crush injury**, increased pressure in this compartment compromises the **median and ulnar nerves** and leads to the tense, tender forearm swelling and **delayed capillary refill** observed.
*Superficial posterior compartment*
- This compartment contains the **extensors of the wrist and fingers**; involvement would characteristically result in **pain on passive finger flexion**, not extension.
- It is less commonly the primary site for initial compartment syndrome symptoms compared to the more confined and muscular volar space.
*Deep posterior compartment*
- This space houses muscles primarily responsible for **thumb abduction and extension** (e.g., abductor pollicis longus); isolated pressure here would not cause global volar tension.
- While it can be affected, it would not typically present with the classic **pain on passive extension of all fingers** seen in volar involvement.
*Mobile wad compartment*
- This lateral compartment contains the **brachioradialis** and radial wrist extensors; pressure here would result in pain during **passive wrist flexion and ulnar deviation**.
- It is a distinct anatomical space from the anterior compartment and is less likely to be the sole cause of the neurovascular signs and finger involvement described.
*Thenar compartment*
- The **thenar compartment** is located in the palm of the hand and contains muscles for thumb opposition; it is not located in the **forearm** where the injury occurred.
- Involvement here would cause localized thumb pain and weakness but would not result in the **radial pulse compromise** or generalized forearm tension noted.
