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Orthopedic Board Prep: Interactive Viva Exam Practice for Trauma & Surgical Cases

FRCS Oral Exam Trauma Case: Master Perilunate Dislocation

23 Apr 2026 90 min read 168 Views
Gilula's Lines

Key Takeaway

Discover the latest medical recommendations for FRCS Oral Exam Trauma Case: Master Perilunate Dislocation. A common trauma case for FRCS involves perilunate dislocation, characterized by dorsal dislocation of the capitate and distal carpal row, with the lunate remaining in the radial lunate fossa. Diagnosis includes examining radiographs for gingival line disruption and utilizing Gilula's lines—three distinct curves assessing wrist alignment. Emergency management typically requires prompt reduction of this significant injury.

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Question 1

A 35-year-old male presents after a fall onto an outstretched hand (FOOSH) with the wrist in hyperextension and ulnar deviation. Radiographs reveal a complete dorsal dislocation of the capitate and other carpals relative to the lunate, which remains articulated with the radius. What is the most common direction of carpal displacement in a typical perilunate dislocation?





Explanation

Perilunate dislocations are typically classified by the displacement of the carpus relative to the lunate. In the vast majority of cases, the carpus dislocates dorsally while the lunate maintains its articulation with the radius. A true lunate dislocation, often referred to as a 'spilled teacup' sign on a lateral radiograph, involves the lunate displacing volarly, but this is a sequel to a perilunate injury, not the initial perilunate displacement itself.

Question 2

A trauma series radiograph of the wrist is performed for a patient suspected of a perilunate injury. On the lateral view, what is the key radiographic finding that indicates a perilunate dislocation (as opposed to a lunate dislocation)?





Explanation

On a true lateral radiograph, the hallmark of a perilunate dislocation is the loss of the normal collinear relationship between the radius, lunate, and capitate, specifically the capitate dislocating dorsally relative to the lunate. The lunate maintains its articulation with the radial facet. A lunate appearing triangular and volar-displaced (the 'spilled teacup' sign) is characteristic of a lunate dislocation, which often represents the final stage of a trans-scaphoperilunate injury where the lunate dislocates volarly. Widened scapholunate interval and disruption of Gilula's lines are primarily seen on the PA view, while a scaphoid fracture is an associated injury, not the defining radiographic feature of the dislocation itself.

Question 3

A 40-year-old construction worker presents with acute wrist pain and marked swelling after falling from a ladder. Clinical examination reveals numbness and paresthesias in the thumb, index, and middle fingers, along with weakness of thumb abduction. Which of the following is the most likely cause of these neurological symptoms in the context of an acute perilunate dislocation?





Explanation

Median nerve compression is a common and critical complication of acute perilunate dislocations, occurring in up to 30-50% of cases. The dislocated carpus, particularly the capitate, and often the associated soft tissue swelling, directly compress the median nerve within the confined space of the carpal tunnel. The symptoms described (numbness/paresthesias in thumb, index, middle fingers, and weakness of thumb abduction via abductor pollicis brevis) are classic for median nerve compression. Early recognition and reduction are crucial to prevent permanent nerve damage. Radial and ulnar nerve involvement are far less common with this specific injury pattern, and brachial plexus or anterior interosseous nerve injuries are unlikely to present solely with these wrist-level symptoms.

Question 4

What is the most frequently associated carpal bone fracture seen in conjunction with a perilunate dislocation?





Explanation

The scaphoid is the most commonly fractured carpal bone in association with perilunate dislocations, occurring in approximately 50-70% of cases. This combination is often referred to as a trans-scaphoid perilunate dislocation. The mechanism involves the carpus 'peeling off' the lunate, and as the forces increase, the scaphoid is loaded in such a way that it fractures, typically through its waist. Other carpal fractures can occur but are less common than a scaphoid fracture in this setting.

Question 5

Following an acute perilunate dislocation, what is the initial management priority after patient stabilization and pain control?





Explanation

The immediate priority for an acute perilunate dislocation, after addressing life-threatening injuries and achieving patient stability and adequate analgesia, is prompt closed reduction. This should ideally be performed as soon as possible, often under conscious sedation or general anesthesia, to decompress the median nerve, restore carpal alignment, and reduce the risk of avascular necrosis of the lunate. While often not definitive treatment, it is a critical temporizing measure. MRI is useful for surgical planning but not an acute priority over reduction. Open reduction and internal fixation is often indicated but usually follows a failed closed reduction or is part of a planned definitive surgical approach, not the absolute first step. A sugar tong splint without reduction is inadequate and harmful. Physiotherapy begins after stabilization.

Question 6

Which ligament is considered the 'key' to carpal stability and is most commonly injured in the initial stages of a perilunate dislocation, according to Mayfield's progressive perilunar instability classification?





Explanation

According to Mayfield's progressive perilunar instability classification, the scapholunate interosseous ligament (SLIL) is the 'key' ligament involved in the initial stages (Stage I) of perilunate instability. Injury to the SLIL allows for dissociation between the scaphoid and lunate, which is the precursor to further carpal displacement. Subsequent stages involve disruption of the radiolunate, capitolunate, and finally the lunotriquetral ligaments or a complete lunate dislocation.

Question 7

A patient undergoes closed reduction of an acute perilunate dislocation. Post-reduction radiographs demonstrate reasonable carpal alignment, but the scapholunate interval remains widened. What is the most appropriate next step in management?





Explanation

Persistent widening of the scapholunate interval post-reduction, even with apparent general carpal alignment, indicates a persistent scapholunate dissociation and significant ligamentous injury. This instability necessitates surgical intervention, typically open reduction and internal fixation (ORIF) with ligament repair or reconstruction (e.g., K-wire stabilization of the scapholunate joint and repair of the dorsal capsular ligaments) to achieve stable anatomical reduction and prevent long-term instability and arthritis. Discharge, observation, or immediate physiotherapy are inappropriate and would lead to poor outcomes. MRI might be done pre-operatively, but the clinical decision is clear.

Question 8

What is the primary role of an urgent CT scan of the wrist in the initial assessment of a suspected perilunate dislocation, especially after initial plain radiographs?





Explanation

While plain radiographs provide the initial diagnosis, a CT scan is invaluable in the acute setting of a perilunate dislocation, particularly if surgical intervention is planned. Its primary role is to precisely identify and characterize any associated fractures (e.g., scaphoid, capitate, triquetrum, radial styloid) that may not be clearly visible on plain films, and to confirm the exact alignment of the carpal bones. This information is crucial for surgical planning. MRI is better for ligamentous integrity and vascularity, and median nerve compression is a clinical diagnosis confirmed by nerve studies if necessary.

Question 9

A 28-year-old female presents with a chronic, unreduced perilunate dislocation sustained 6 months prior. She complains of persistent pain, stiffness, and weakness. What is the most appropriate definitive management strategy for a chronic perilunate dislocation?





Explanation

Chronic, unreduced perilunate dislocations (typically defined as older than 6-8 weeks) often lead to significant pain, stiffness, and degenerative changes, making anatomical reduction difficult and often impossible without significant bony or soft tissue releases. In these cases, the goal shifts from anatomical reduction and primary ligament repair to salvage procedures. Options include proximal row carpectomy (PRC) if the articular cartilage of the lunate fossa and capitate head is preserved, or wrist arthrodesis (fusion) for severe degenerative changes or when PRC is not feasible. Simple closed reduction, arthroscopy, observation, or splinting are inadequate for long-standing dislocations with established pathology.

Question 10

What is a potential long-term complication of a perilunate dislocation, even after successful reduction and stabilization, particularly if scaphoid avascular necrosis occurs?





Explanation

While lunate AVN is a risk, a more direct consequence of an untreated or complicated trans-scaphoid perilunate dislocation is Scaphoid Nonunion Advanced Collapse (SNAC) wrist. If the scaphoid is fractured and fails to unite (nonunion), the altered mechanics of the wrist lead to progressive collapse and arthritis, starting in the radioscaphoid joint. Lunate AVN (Kienböck's) is a risk for the lunate itself, but SNAC is directly related to scaphoid fracture nonunion in the context of the overall carpal derangement. Carpal tunnel syndrome can be an acute complication but often resolves with reduction, though chronic cases can persist. Malunion of the distal radius and ulnar impaction are less directly related to the specific pathology of perilunate dislocation.

Question 11

During open reduction and internal fixation of a perilunate dislocation, which surgical approach provides the best exposure for dorsal ligament repair and reduction of dorsal carpal displacement?





Explanation

The dorsal approach to the wrist, typically between the third (extensor pollicis longus) and fourth (extensor digitorum communis and indicis proprius) extensor compartments, provides excellent exposure for visualization of the dorsal carpal ligaments, the scapholunate joint, and for reduction of dorsally dislocated carpal bones. It allows for repair of the dorsal scapholunate ligament and placement of K-wires to stabilize the scapholunate and capitolunate joints. A volar approach is primarily for addressing median nerve compression or for certain lunate dislocations, but less ideal for primary dorsal ligament repair. Other approaches are less suitable for the primary dorsal instability.

Question 12

A patient with a perilunate dislocation presents with profound median nerve symptoms. After urgent closed reduction, the symptoms persist without improvement. What is the most appropriate next step?





Explanation

Persistent profound median nerve symptoms after successful closed reduction of a perilunate dislocation necessitate urgent carpal tunnel release. While some transient symptoms may improve with reduction, persistent or worsening signs of nerve compression suggest ongoing impingement, potentially by soft tissue swelling, hematoma, or even incarcerated ligaments/bone fragments within the carpal tunnel. Delaying decompression risks permanent median nerve damage. Waiting or non-surgical treatments are inappropriate in this acute, symptomatic scenario. Repeating reduction could cause further harm if the nerve is already compressed. Cervical spine imaging is not indicated for acute wrist-level median nerve symptoms.

Question 13

Which of the following describes a Stage III perilunate instability according to Mayfield's classification?





Explanation

Mayfield's classification describes progressive carpal instability in a four-stage sequence: Stage I involves rupture of the scapholunate interosseous ligament. Stage II progresses to disruption of the capitolunate relationship (often with capitohamate involvement as the capitate displaces dorsally). Stage III involves additional disruption of the lunotriquetral interosseous ligament, allowing for further rotational instability. Stage IV represents a complete dislocation of the lunate volarly into the carpal tunnel, which is the final stage of the continuum and is technically a lunate dislocation following a perilunate injury.

Question 14

In a trans-scaphoid perilunate dislocation, after open reduction and K-wire stabilization of the scapholunate and capitolunate joints, what is the most critical aspect for surgical repair of the scaphoid fracture?





Explanation

For a trans-scaphoid perilunate dislocation, once carpal alignment is restored and stabilized (often with K-wires), the scaphoid fracture requires anatomical reduction and rigid internal fixation. The gold standard for scaphoid waist fractures is a headless compression screw, which provides stable fixation, allows for early rehabilitation (relative to cast alone), and minimizes the risk of nonunion and subsequent SNAC wrist. External fixation, bone grafting (unless there's significant bone loss), simple capsular repair, or serial casting alone are generally not sufficient for this complex injury pattern.

Question 15

What is the primary goal of K-wire stabilization following open reduction of a perilunate dislocation?





Explanation

K-wire stabilization, typically involving wires across the scapholunate and capitolunate joints, serves to temporarily maintain the anatomical reduction of the carpal bones and protect the repaired or reconstructed ligaments while they heal. It provides a stable environment for soft tissue healing, preventing redislocation. It does not provide rigid fixation for immediate weight-bearing, directly affect median nerve compression (though reduction helps), or primarily stimulate bone healing or enhance lunate blood supply. These wires are usually removed at 8-12 weeks.

Question 16

Which radiographic sign on the PA wrist view is most indicative of scapholunate dissociation, often seen accompanying perilunate dislocations?





Explanation

The 'Terry Thomas sign' refers to a widened scapholunate interval, typically >3mm (or >2mm when compared to the contralateral wrist), on the PA radiograph. This gap indicates dissociation between the scaphoid and lunate, a hallmark of scapholunate ligament injury, which is almost universally present in perilunate dislocations. Positive/negative ulnar variance, lunate sclerosis (Kienböck's), and DRUJ incongruity are different pathologies or signs.

Question 17

After surgical repair of a perilunate dislocation, what is the recommended typical duration for K-wire removal?





Explanation

K-wires used to stabilize carpal alignment following perilunate dislocation repair are typically removed at 8-12 weeks post-operatively. This timeframe allows sufficient healing of the repaired ligaments and dorsal capsule. Earlier removal risks redislocation due to inadequate healing, while leaving them in longer increases the risk of pin track infection and stiffness. The exact timing can vary slightly based on surgeon preference and the specific injury/repair.

Question 18

What is the critical distinction between a perilunate dislocation and a lunate dislocation on a lateral wrist radiograph?





Explanation

On a lateral wrist radiograph, the defining difference is the relationship of the lunate to the radius. In a perilunate dislocation, the lunate maintains its articulation with the distal radius, while the capitate and the rest of the carpus dislocate dorsally. In a lunate dislocation, the lunate itself dislocates volarly into the carpal tunnel, losing its articulation with both the radius and the capitate (which then aligns with the radius). The 'spilled teacup' sign refers to the volar-tilted and dislocated lunate in a lunate dislocation.

Question 19

Which intrinsic carpal ligament plays a crucial role in preventing dorsal intercalated segmental instability (DISI) deformities?





Explanation

The scapholunate interosseous ligament (SLIL) is critical for preventing dorsal intercalated segmental instability (DISI) deformities. When the SLIL is disrupted, the scaphoid flexes volarly, and the lunate extends dorsally (due to the pull of the triquetrum via the intact lunotriquetral ligament and extrinsic ligaments), leading to the characteristic DISI posture. Conversely, lunotriquetral ligament injury leads to volar intercalated segmental instability (VISI).

Question 20

A patient with a perilunate dislocation is successfully reduced and stabilized. Which of the following is an expected post-operative limitation or complication, even with optimal management?





Explanation

Even with successful reduction and optimal surgical management, perilunate dislocations are severe injuries. Patients often experience some degree of persistent wrist stiffness, reduced range of motion, and decreased grip strength in the long term. While excellent results can be achieved, complete restoration of pre-injury function is rare. The risk of future wrist osteoarthritis remains high due to articular cartilage damage and altered carpal mechanics. Permanent median nerve palsy is a complication if not addressed, but not an expected outcome with optimal care. Immediate return to activities is unrealistic.

Question 21

What is the preferred method for assessing the alignment and stability of the scaphoid and lunate post-operatively, particularly regarding dynamic instability?





Explanation

While static PA and lateral radiographs are standard, stress radiographs, particularly a clenched-fist PA view, are often used to dynamically assess scapholunate stability post-operatively or in cases of suspected instability. This view can exaggerate any widening of the scapholunate interval (Terry Thomas sign) if instability persists. EMG is for nerve function, ultrasound has limited utility for deep carpal instability, and bone scan is for metabolic activity or inflammation. CT/MRI can assess static alignment and ligament integrity but not dynamic instability as effectively as stress radiographs.

Question 22

Which muscle tendon is typically retracted dorsally to gain access to the dorsal wrist capsule during a dorsal approach for perilunate dislocation repair?





Explanation

In a dorsal approach to the wrist for perilunate dislocation, the interval between the third (extensor pollicis longus) and fourth (extensor digitorum communis and indicis proprius) extensor compartments is commonly utilized. The extensor pollicis longus (EPL) tendon (within the 3rd compartment) is typically retracted radially, and the common digital extensors (within the 4th compartment) are retracted ulnarly, or the fourth compartment is incised and its contents retracted. The EPL is the muscle most commonly identified and retracted to define this interval for exposing the dorsal wrist capsule.

Question 23

The concept of 'lesser arc injury' versus 'greater arc injury' in carpal trauma refers to:





Explanation

The 'greater arc' of the carpus refers to the bony structures that form the periphery (scaphoid, trapezium, trapezoid, capitate, hamate, triquetrum). A 'greater arc injury' typically involves carpal bone fractures (e.g., trans-scaphoid, trans-capitate, trans-triquetral) in addition to ligamentous disruption. The 'lesser arc' refers to the intrinsic intercarpal ligaments (scapholunate, lunotriquetral). A 'lesser arc injury' involves only ligamentous disruption without carpal fractures, which is less common in severe dislocations. Thus, it's about whether the injury path includes fractures or just ligaments around the lunate.

Question 24

A patient has a chronic perilunate dislocation with significant degenerative changes noted on radiographs, including radioscaphoid arthritis and collapse. The lunate fossa of the radius appears relatively preserved. Which salvage procedure might be considered?





Explanation

For chronic perilunate dislocations with established degenerative changes, especially radioscaphoid arthritis, but with a preserved lunate fossa, a Proximal Row Carpectomy (PRC) can be a viable salvage option. PRC involves excising the scaphoid, lunate, and triquetrum, allowing the capitate to articulate directly with the lunate fossa of the radius. This provides pain relief and preserves a good range of motion, provided the capitate head and lunate fossa are healthy. Four-corner fusion (fusion of capitate, hamate, triquetrum, lunate) is an alternative but also involves removing the scaphoid, leaving the lunate, and fusing it to other carpals – it leads to less motion than PRC but can be more stable. Total wrist arthroplasty is generally reserved for inflammatory arthritis or very low demand patients. Arthroscopy and STT fusion are not appropriate for advanced degenerative changes from a perilunate dislocation.

Question 25

What is the typical sequence of ligamentous disruption in a progressive perilunar instability, as described by Mayfield?





Explanation

Mayfield's classification describes progressive failure of ligaments from radial to ulnar in a perilunar injury. Stage I: Scapholunate interosseous ligament and volar radioscaphocapitate ligament rupture. Stage II: Dorsal capitolunate ligament and sometimes other volar ligaments rupture, leading to capitolunate dissociation. Stage III: Lunotriquetral interosseous ligament ruptures. Stage IV: Complete lunate dislocation volarly. Therefore, the sequence is generally Scapholunate, then Capitolunate (implying dorsal radiocarpal), then Lunotriquetral.

Question 26

A 50-year-old male with an acute perilunate dislocation reports a 'pop' in his wrist. Which of the following findings on physical examination, in addition to pain and swelling, would be most concerning for a potential complication requiring immediate intervention?





Explanation

Loss of sensation in the thumb, index, and middle fingers (median nerve distribution) is a critical finding indicating significant median nerve compression. This complication can lead to permanent nerve damage if not promptly addressed by reduction (and surgical decompression if symptoms persist after reduction). While the other findings are expected with a severe wrist injury, median nerve compromise carries the highest risk of immediate long-term morbidity and dictates urgent management. Intact capillary refill is a positive sign, indicating adequate perfusion, not a concern.

Question 27

Which of the following statements regarding the stability of a reduced perilunate dislocation is MOST accurate?





Explanation

Perilunate dislocations involve extensive disruption of the intrinsic and extrinsic carpal ligaments. Even after successful closed reduction, the carpus remains inherently unstable due to this significant ligamentous damage. This instability often necessitates surgical stabilization (e.g., K-wire fixation and ligament repair/reconstruction) to maintain anatomical alignment and allow for proper ligamentous healing. Closed reduction alone typically leads to redislocation or chronic instability, and physiotherapy cannot compensate for the structural loss.

Question 28

What imaging modality is most sensitive for assessing the integrity of the scapholunate interosseous ligament and detecting subtle carpal instability patterns after reduction?





Explanation

Magnetic Resonance Imaging (MRI), especially with arthrography (MRA), is the most sensitive imaging modality for directly visualizing and assessing the integrity of the intrinsic carpal ligaments, such as the scapholunate interosseous ligament. It can detect subtle tears and provide detailed information about soft tissue injury and early degenerative changes not visible on plain radiographs or CT. CT is excellent for bony detail and alignment, but less sensitive for ligaments. Ultrasound and bone scintigraphy have limited roles in this specific assessment.

Question 29

Which of the following is considered a relative contraindication to attempting closed reduction of an acute perilunate dislocation?





Explanation

An open fracture or significant skin compromise overlying the wrist joint is a relative contraindication to closed reduction attempts, especially if it could convert a closed injury to an open one through excessive manipulation, or if there's a risk of introducing infection. While median nerve palsy and swelling are common, they are indications for urgent reduction rather than contraindications. Older age or an associated undisplaced radial styloid fracture do not preclude careful closed reduction.

Question 30

What is the primary vector of force leading to a perilunate dislocation according to biomechanical studies?





Explanation

The typical mechanism of injury for a perilunate dislocation involves a fall onto an outstretched hand (FOOSH) with the wrist in forced hyperextension, ulnar deviation, and often an element of intercarpal supination. This combination of forces causes the carpus to dorsally 'peel off' the lunate, leading to the progressive ligamentous disruption characteristic of a perilunate injury. Other force vectors are less common for this specific injury pattern.

Question 31

In the context of perilunate instability, what is the significance of the 'ring sign' on a PA wrist radiograph?





Explanation

The 'ring sign' (or 'signet ring sign') is seen on a PA radiograph when the scaphoid bone is rotated into flexion. This flexion creates a superimposition of its distal pole on its body, making the distal pole appear as a dense ring. This sign is indicative of rotary subluxation of the scaphoid, which occurs due to disruption of the scapholunate interosseous ligament, a key component of perilunate instability. It does not directly indicate AVN, scaphoid fracture (though often co-occurs), lunotriquetral widening, or triquetral fracture.

Question 32

When performing open reduction and internal fixation for a perilunate dislocation, after reducing the carpus, which anatomical structure is most commonly targeted for primary repair or augmentation to restore dorsal carpal stability?





Explanation

While volar ligaments are often ruptured, the dorsal approach allows for direct repair of the dorsal radiocarpal ligaments, particularly the dorsal intercarpal ligament and the dorsal scapholunate ligament. These ligaments are crucial for dorsal carpal stability and are typically extensively disrupted in perilunate dislocations. Their repair or augmentation, along with K-wire stabilization, is essential to prevent recurrent dorsal subluxation. The TFCC primarily stabilizes the DRUJ. Volar ligaments are also important but typically addressed via a separate volar approach or indirectly.

Question 33

Post-operatively, what is the recommended position for wrist immobilization after surgical repair of a perilunate dislocation?





Explanation

Following surgical repair of a perilunate dislocation, the wrist is typically immobilized in a neutral position or slight flexion (around 10-20 degrees) and slight ulnar deviation. This position helps to maintain the reduction, reduce tension on the repaired dorsal ligaments, and keep the scaphoid in a more favorable position for healing, minimizing the tendency for scaphoid flexion. Extreme positions should be avoided.

Question 34

What factor is most strongly associated with a higher likelihood of failure following surgical repair of perilunate dislocations?





Explanation

Delay in surgical intervention, particularly beyond 6 weeks (often considered chronic), is strongly associated with a higher likelihood of surgical failure, residual pain, stiffness, and the development of degenerative arthritis. With chronicity, soft tissues contract, articular cartilage may be damaged, and reduction becomes more challenging, often requiring salvage procedures rather than primary repair. Acute presentation and K-wire stabilization improve outcomes, and patient age or absence of scaphoid fracture are less dominant factors for failure compared to chronicity.

Question 35

Which of the following describes the anatomical defect in a 'trans-radial styloid perilunate dislocation'?





Explanation

A 'trans-radial styloid perilunate dislocation' refers to a perilunate dislocation that is associated with a fracture of the radial styloid process. The force vector typically involves a radial component, causing the radial styloid to avulse or fracture as the carpus displaces. This is a common associated bony injury and falls under the 'greater arc' injury pattern when combined with the ligamentous disruption.

Question 36

In the classification of carpal instability, what does the acronym 'DISI' stand for?





Explanation

DISI stands for Dorsal Intercalated Segmental Instability. It is a common pattern of carpal collapse seen after scapholunate ligament injury, where the scaphoid flexes volarly, and the lunate extends dorsally, causing the lunate to appear dorsally tilted on a lateral radiograph. The opposing pattern, VISI (Volar Intercalated Segmental Instability), is caused by lunotriquetral ligament injury.

Question 37

What is the typical management for a perilunate dislocation in a young, active patient presenting acutely (within hours to days) without significant associated fractures or neurovascular compromise?





Explanation

For young, active patients with acute perilunate dislocations, particularly when there is no significant neurovascular compromise after initial reduction, open reduction and internal fixation (ORIF) with primary ligament repair and K-wire stabilization is the preferred definitive treatment. This approach aims to restore anatomical alignment, reconstruct or repair the torn ligaments, and prevent long-term instability and osteoarthritis. While closed reduction is an urgent first step, it is rarely definitive for long-term stability due to the extensive ligamentous damage. Other options are either inadequate or too extreme for an acute presentation.

Question 38

Which structure contributes significantly to the blood supply of the lunate and is at risk during severe lunate displacement or manipulation?





Explanation

The blood supply to the lunate is somewhat precarious and arises primarily from small intraosseous vessels that enter through its volar and dorsal capsules, fed by branches of the radial and ulnar arteries (specifically the radial recurrent, anterior and posterior carpal arches, and sometimes the deep palmar arch). These capsular attachments are often disrupted during severe dislocations, increasing the risk of avascular necrosis (Kienböck's disease). The deep and superficial palmar arches are more macro-level structures, and the interosseous arteries supply forearm muscles and other carpal bones more directly.

Question 39

A patient is undergoing open reduction for a chronic perilunate dislocation. The surgeon observes significant contracture of the dorsal wrist capsule and ligaments. What intraoperative maneuver might be necessary to achieve reduction?





Explanation

In chronic perilunate dislocations, contracture of the volar wrist capsule and ligaments is a common impediment to reduction, especially of the dorsally displaced carpus. A volar capsular release, typically through a separate volar incision, may be necessary to allow the carpus to be reduced volarly and regain its articulation with the lunate. Dorsal capsulodesis is a stabilization procedure, not a release to aid reduction. Distraction osteogenesis or excisions are typically not needed to simply achieve reduction unless part of a salvage procedure. Proximal row carpectomy is a salvage, not a reduction, procedure.

Question 40

In a complete lunate dislocation (Stage IV Mayfield), the lunate typically displaces in which direction?





Explanation

In a complete lunate dislocation (Mayfield Stage IV), the lunate itself dislocates volarly into the carpal tunnel, typically after the entire carpus has dislocated dorsally and then the lunate is 'pushed out' volarly. This is often associated with significant median nerve compression. Perilunate dislocation is when the carpus dislocates dorsally around the lunate, which maintains its radiolunate articulation.

Question 41

What is the primary purpose of a 'holding suture' or 'repair' of the dorsal wrist capsule/ligaments after reduction of a perilunate dislocation?





Explanation

Repair of the dorsal wrist capsule and ligaments (e.g., dorsal intercarpal, dorsal scapholunate ligaments) is a critical step after reducing a perilunate dislocation. These structures are essential for providing dorsal stability to the carpus and preventing recurrent dorsal displacement or subluxation. This soft tissue repair, often augmented with K-wires, is paramount for a stable construct. It does not primarily address nerve compression (which is from the dislocation itself), provide rigid bony fixation (which comes from K-wires or screws), or directly alter wrist extension/flexion beyond restoring normal anatomy.

Question 42

Which patient factor is most likely to negatively impact the long-term functional outcome after a perilunate dislocation, even with appropriate surgical management?





Explanation

A high-energy mechanism of injury generally correlates with more severe soft tissue and cartilaginous damage, leading to a poorer prognosis regardless of the surgical outcome. The energy involved can cause more extensive ligamentous tears, articular cartilage contusions, and greater initial displacement, making anatomical reduction more challenging and increasing the long-term risk of post-traumatic arthritis and stiffness. While pre-existing arthritis is a confounder, high energy is an intrinsic factor of the injury itself.

Question 43

What is the primary goal of early wrist mobilization after K-wire removal and cast discontinuation in a surgically treated perilunate dislocation?





Explanation

The primary goal of early, controlled wrist mobilization after K-wire removal and cast discontinuation is to regain wrist range of motion and prevent post-operative stiffness, which is a common and challenging complication after severe wrist trauma. While strengthening is also important, it comes after regaining motion. Preventing AVN or accelerating bone healing are not primary goals of early mobilization at this stage.

Question 44

Which of the following describes a key finding of a chronic perilunate instability on a lateral radiograph, even if not fully dislocated?





Explanation

Chronic perilunate instability often manifests as a Dorsal Intercalated Segmental Instability (DISI) deformity. On a lateral radiograph, this is characterized by the lunate being extended dorsally (tilted backward) and the scaphoid being flexed volarly, creating an increased capitolunate and radiolunate angle. This abnormal alignment results from the disruption of the scapholunate ligament, which normally couples the scaphoid and lunate movements. Other options are either incorrect or not specific to perilunate instability.

Question 45

When performing closed reduction of a perilunate dislocation, what is the crucial final maneuver after traction and counter-traction?





Explanation

After applying longitudinal traction and counter-traction to disimpact the carpus, the crucial final maneuver for closed reduction of a dorsally dislocated perilunate injury involves direct pressure applied volarly to the dorsally displaced capitate, combined with acute volar flexion of the wrist. This maneuver guides the capitate back into articulation with the lunate. The wrist is then typically brought into a neutral or slightly flexed position for temporary immobilization.

Question 46

What is the typical time frame considered for a perilunate dislocation to be classified as 'chronic' versus 'acute'?





Explanation

Perilunate dislocations are generally considered 'acute' if treated within 6 to 8 weeks of injury. Beyond this timeframe, they are typically classified as 'chronic'. The distinction is critical because chronic dislocations often involve significant soft tissue contracture, articular cartilage damage, and established degenerative changes, making anatomical reduction much more challenging, and often necessitating salvage procedures rather than primary ligament repair.

Question 47

Which of the following ligaments is considered an 'extrinsic' carpal ligament?





Explanation

Extrinsic carpal ligaments connect the carpal bones to the radius or ulna, while intrinsic ligaments connect carpal bones to each other within the carpus. The Radioscaphocapitate ligament is a strong volar extrinsic ligament, connecting the radius to the scaphoid and capitate. The scapholunate and lunotriquetral interosseous ligaments are intrinsic. Capitalunate and scaphotrapezial are also intrinsic intercarpal ligaments.

Question 48

Which specific view on plain radiographs is most critical for evaluating the alignment of the lunate and capitate in the sagittal plane?





Explanation

The lateral view of the wrist is absolutely critical for evaluating the alignment of the lunate and capitate (and radius) in the sagittal plane. This view allows for assessment of the radiolunate and capitolunate angles, and identification of loss of collinearity or the 'spilled teacup' sign, which are hallmarks of perilunate and lunate dislocations, respectively. Other views provide different perspectives or focus on specific bones.

Question 49

What is the most common presenting complaint of a patient with a chronic, untreated perilunate dislocation?





Explanation

A chronic, untreated perilunate dislocation typically presents with progressive dull aching pain, significant wrist stiffness, and weakness. While acute dislocations cause severe pain, chronic conditions evolve into a pattern of chronic discomfort and functional limitation, often with established post-traumatic arthritis. Complete inability to move is less common than severe restriction. Median nerve symptoms can persist but are often not the only complaint.

Question 50

A patient is diagnosed with a trans-scaphoid perilunate dislocation. What is a key consideration when planning the surgical approach for this combined injury?





Explanation

For a trans-scaphoid perilunate dislocation, optimal management often requires both volar and dorsal approaches. The volar approach allows for débridement of the carpal tunnel, reduction of any volar lunate displacement, and repair of volar ligaments. The dorsal approach allows for reduction of the dorsally dislocated carpus, internal fixation of the scaphoid fracture (if it's a dorsal approach for scaphoid), and repair of the dorsal capsuloligamentous structures. While some surgeons may attempt a single approach for simpler cases, complex trans-scaphoid injuries often benefit from dual access. Avoiding K-wires is incorrect, and both bony fixation and ligament repair are critical.

Question 51

Which of the following is an accepted technique for primary repair of the scapholunate interosseous ligament during open surgery?





Explanation

Suture anchor repair, where the torn ends of the scapholunate interosseous ligament (SLIL) are reattached to the scaphoid and lunate using suture anchors, is an accepted technique for primary repair of acute SLIL tears during open surgery for perilunate dislocations. This directly addresses the ligamentous instability. Excision or leaving it unrepaired is not appropriate for primary repair. Dynamic splinting is not a repair technique. Grafting with fascia lata is a reconstruction technique, typically used for chronic cases or failed primary repairs, not primary repair itself.

Question 52

What is the reported incidence of median nerve compromise in acute perilunate dislocations?





Explanation

Median nerve compromise is a well-known and relatively common complication in acute perilunate dislocations, with reported incidences ranging from 30% to 50%. The acute displacement of the carpus, particularly the capitate, into the carpal tunnel, along with associated swelling and hemorrhage, directly compresses the median nerve. Prompt reduction is crucial to alleviate this compression.

Question 53

What is the potential consequence of untreated or missed perilunate dislocation in terms of long-term wrist function?





Explanation

Untreated or missed perilunate dislocations inevitably lead to progressive carpal collapse, chronic pain, significant stiffness, and debilitating post-traumatic osteoarthritis. The severe disruption of carpal alignment and ligamentous integrity results in abnormal joint mechanics that rapidly degenerate the articular cartilage. There is no spontaneous full recovery, and long-term functional impairment is the norm.

Question 54

Which of the following describes a key element of post-operative rehabilitation for a surgically treated perilunate dislocation, after immobilization period?





Explanation

Post-operative rehabilitation for a surgically treated perilunate dislocation, after the period of immobilization (typically K-wire removal and cast discontinuation), involves a carefully structured program of progressive controlled active and passive range of motion exercises. This is followed by gradual strengthening exercises once adequate motion and ligament healing are confirmed. Immediate full weight-bearing, passive-only motion, or complete avoidance of movement are incorrect and would lead to poor outcomes or excessive stiffness.

Question 55

When assessing a lateral radiograph for perilunate stability, what is the normal radiolunate angle?





Explanation

On a true lateral radiograph, the normal lunate has a slight volar tilt, meaning the long axis of the lunate should be collinear with the long axis of the radius, with a radiolunate angle typically between 0 and -10 degrees (representing slight volar tilt of the lunate relative to the radius). A dorsal tilt of the lunate (positive angle) is indicative of a DISI deformity, often seen in scapholunate dissociation. A volar tilt >30 degrees is seen in VISI deformity.

Question 56

What is the typical K-wire configuration used for scapholunate stabilization after perilunate reduction?





Explanation

The typical K-wire configuration for scapholunate stabilization after reduction of a perilunate dislocation involves two wires: one K-wire placed from the scaphoid into the lunate to stabilize the scapholunate joint, and another K-wire placed from the lunate into the capitate to maintain the capitolunate alignment. This construct provides a stable environment for ligament healing and prevents redislocation. Other options are incorrect or represent different stabilization strategies.

Question 57

Which complication is unique to injuries involving the lunate, such as perilunate dislocation, due to its somewhat tenuous blood supply?





Explanation

Kienböck's disease, or avascular necrosis (AVN) of the lunate, is a specific and severe complication unique to injuries or conditions affecting the lunate bone. Due to its unique and often tenuous blood supply, which can be disrupted by significant trauma like a perilunate dislocation, the lunate is prone to AVN, leading to collapse and subsequent degenerative arthritis. While other options are possible complications of wrist trauma, Kienböck's specifically relates to the lunate's vascularity.

Question 58

Which nerve is at highest risk of iatrogenic injury during a dorsal approach to the wrist for perilunate dislocation repair?





Explanation

During a dorsal approach to the wrist, particularly when dissecting radially or near the first and second extensor compartments, the superficial radial nerve (a sensory branch of the radial nerve) is at highest risk of iatrogenic injury. This nerve courses subcutaneously and can be easily damaged, leading to sensory deficits or painful neuromas. The median and ulnar nerves are volar, and the radial nerve proper and posterior interosseous nerve are deeper and less vulnerable in a standard dorsal wrist approach.

Question 59

What is the most appropriate initial splinting technique following a successful closed reduction of an acute perilunate dislocation?





Explanation

Following a successful closed reduction of an acute perilunate dislocation, the wrist should be immobilized in a long arm sugar tong splint. This provides rigid immobilization of the wrist, prevents pronation/supination (which can affect carpal stability), and helps to maintain the reduction. A short arm splint is insufficient as it does not control forearm rotation. A circumferential cast without padding risks compartment syndrome in an acute injury. A wrist wrap provides inadequate immobilization.

Question 60

If a chronic perilunate dislocation is left untreated, what is the most likely long-term degenerative pattern that will develop?





Explanation

Untreated chronic perilunate dislocations lead to progressive carpal collapse and arthritis, most commonly in the pattern of Scapholunate Advanced Collapse (SLAC) wrist. If a scaphoid fracture is also present and untreated (trans-scaphoid perilunate), it can progress to Scaphoid Nonunion Advanced Collapse (SNAC) wrist. Both SLAC and SNAC patterns involve progressive osteoarthritis of the radiocarpal and midcarpal joints due to the altered biomechanics and instability caused by the initial injury and subsequent collapse. These are the most common and severe degenerative sequelae.

Question 61

A 30-year-old patient undergoes ORIF for a trans-scaphoid perilunate dislocation. Post-operatively, K-wires are placed across the scapholunate and capitolunate joints. What is the approximate period of time the K-wires are typically left in place before removal?





Explanation

K-wires are typically left in place for approximately 8-12 weeks after surgical repair of perilunate dislocations. This duration allows for sufficient healing of the repaired ligaments and the scaphoid fracture (if present). Removing them too early risks redislocation or nonunion, while leaving them in too long increases the risk of infection, pin tract problems, and prolonged stiffness. After removal, a period of protected motion and strengthening follows.

Question 62

Which carpal bone is considered the 'intercalated segment' and has no direct tendon attachments, making its position dependent on surrounding ligaments?





Explanation

The lunate is considered the 'intercalated segment' of the carpus. It is unique in that it has no direct muscular or tendinous attachments; its position and motion are entirely dictated by the tension and integrity of the surrounding intrinsic and extrinsic ligaments that connect it to the scaphoid, triquetrum, radius, and capitate. This makes it particularly vulnerable to instability and displacement when these ligaments are injured, as seen in perilunate dislocations.

Question 63

What diagnostic imaging is considered the gold standard for defining bony anatomy and displacement in a complex carpal fracture-dislocation like a perilunate injury?





Explanation

While plain X-rays are the initial diagnostic tool and lateral views are crucial, a CT scan with 3D reconstructions is considered the gold standard for precisely defining the complex bony anatomy, articular congruity, and any associated fractures (e.g., scaphoid, capitate, triquetrum) in a complex carpal fracture-dislocation like a perilunate injury. It offers superior detail compared to X-rays and better bony resolution than MRI. MRI is superior for soft tissue/ligamentous injury.

Question 64

Which of the following is NOT a recognized component of a 'lesser arc' carpal injury?





Explanation

A 'lesser arc injury' refers to perilunate instability patterns that involve only ligamentous disruptions, primarily of the intrinsic intercarpal ligaments (scapholunate, lunotriquetral, and related extrinsic ligaments like radiolunate and capitolunate). A 'greater arc injury' involves a combination of ligamentous disruption and associated carpal bone fractures. Therefore, a fracture of the waist of the scaphoid is a component of a 'greater arc' injury, not a 'lesser arc' injury.

Question 65

In the context of surgical repair of perilunate dislocation, what is the purpose of temporary wrist arthrodesis (e.g., with an external fixator) in select severe cases?





Explanation

In very severe or comminuted perilunate fracture-dislocations, or cases with extensive soft tissue damage, temporary wrist arthrodesis, often achieved with an external fixator, can be used to provide prolonged, rigid immobilization. This protects extensive ligamentous and bony repairs, allows soft tissues to heal, and prevents collapse or redislocation, especially in highly unstable situations where K-wires alone might be deemed insufficient. It is a more robust form of immobilization, not a substitute for internal fixation or a means to facilitate early motion.

Previous ChapterMastering Lunate Dislocation: A Case for FRCS Success
Dr. Mohammed Hutaif
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Prof. Dr. Mohammed Hutaif
Consultant Orthopedic & Spine Surgeon
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