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

Mastering Lunate Dislocation: A Case for FRCS Success

23 Apr 2026 89 min read 139 Views
Lunate Dislocation: A Case Presentation for FRCS (Tr & Orth) Oral Examination

Key Takeaway

In this comprehensive guide, we discuss everything you need to know about Mastering Lunate Dislocation: A Case for FRCS Success. A volar lunate dislocation involves significant wrist injury, presenting as a specific dislocation a case where the lunate bone displaces volarly. The capitate typically remains articulated with the radius. Radiographic assessment reveals characteristic findings like carpal malalignment, interrupted Gilula’s lines, and the lunate appearing 'wedge'-shaped, requiring further imaging for confirmation.

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Question 1

A 35-year-old male presents to the emergency department after a fall onto an outstretched hand (FOOSH) with the wrist hyperextended and ulnarly deviated. Radiographs demonstrate the lunate remaining in articulation with the distal radius, but the capitate is dorsally dislocated, and all other carpal bones are displaced dorsally relative to the lunate. The lunate appears to have lost its articulation with the capitate. Which of the following best describes this injury pattern?





Explanation

The description of the lunate remaining articulated with the radius while the capitate and other carpal bones are displaced dorsally relative to the lunate is the classic definition of a perilunate dislocation. In a true lunate dislocation, the lunate itself dislocates volarly, losing articulation with both the radius and the capitate, often appearing like a 'spilled teacup' on lateral radiographs. Scapholunate dissociation is a ligamentous injury without gross carpal dislocation. Trans-scaphoid perilunate dislocation is a specific type of perilunate dislocation involving a scaphoid fracture, which is not mentioned here. Radial styloid avulsion is a fracture, not a carpal dislocation pattern.

Question 2

Which carpal bone is most commonly affected by avascular necrosis following a lunate dislocation?





Explanation

The lunate is most susceptible to avascular necrosis (Kienböck's disease) after a lunate dislocation or perilunate dislocation due to its precarious blood supply. The lunate receives its blood supply primarily from two dorsal and two volar vessels, forming an intraosseous network. Dislocation can disrupt these vessels, leading to ischemia and subsequent avascular necrosis. While other carpal bones can suffer from vascular compromise, the lunate's anatomy makes it particularly vulnerable in this context.

Question 3

On a true lateral radiograph of the wrist, a lunate dislocation is characterized by:





Explanation

A lunate dislocation on a true lateral radiograph is classically described as the lunate losing its normal articulation with the distal radius and rotating volarly, often appearing like a 'spilled teacup'. Option A describes a perilunate dislocation. Option B describes the lunate's appearance on an AP view in a perilunate dislocation or due to rotation. Option D is incorrect as lunate dislocation involves significant disruption of carpal alignment. Option E is characteristic of scapholunate dissociation, which can be part of a perilunate injury but not the defining feature of a lunate dislocation itself.

Question 4

A patient presents with acute wrist pain, swelling, and paresthesias in the thumb, index, middle, and radial half of the ring finger after a high-energy fall. Examination reveals a tense median nerve compression. What is the most appropriate initial management step for a suspected lunate dislocation in this scenario?





Explanation

Acute median nerve compression in the setting of a lunate dislocation is a surgical emergency. The initial management should be prompt closed reduction under conscious sedation or regional anesthesia to decompress the median nerve and attempt to restore carpal alignment. This is often the first step before considering open reduction. While operative exploration may be necessary if closed reduction fails or if instability persists, it's not the absolute initial step unless reduction is impossible. A splint alone won't address the nerve compression. MRI and neurophysiologic studies, while useful for planning definitive care, are not initial emergency interventions for acute nerve compression.

Question 5

What is the Mayfield classification system primarily used to describe in the context of carpal injuries?





Explanation

The Mayfield classification system describes the progressive stages of perilunate instability and dislocation. It outlines a sequential pattern of ligamentous disruption around the lunate, starting from scapholunate dissociation (Stage I), progressing to capitolunate dislocation (Stage II), triquetrolunate disruption (Stage III), and ultimately lunate dislocation (Stage IV), where the lunate itself displaces volarly. It is not used for Kienböck's disease, distal radius fractures, TFCC tears, or ulnar impaction.

Question 6

Which ligament is typically the first to fail in the Mayfield Stage I pattern of perilunate instability?





Explanation

Mayfield Stage I involves disruption of the scapholunate interosseous ligament (SLIL), leading to scapholunate dissociation. This is the initial step in the progressive arc of perilunate instability. Subsequent stages involve further ligamentous disruptions around the carpus. The other ligaments mentioned become involved in later stages or are not the primary initial failure point in this specific classification system.

Question 7

Following successful closed reduction of a lunate dislocation, which imaging modality is typically recommended to assess for associated occult carpal fractures or persistent instability?





Explanation

A CT scan is highly recommended after closed reduction of a lunate or perilunate dislocation. It provides excellent bony detail to identify occult carpal fractures (e.g., scaphoid, triquetrum, radial styloid) that may not be evident on plain radiographs, assess the accuracy of reduction, and identify any remaining carpal malalignment. Ultrasound is not ideal for deep carpal bone assessment. Bone scintigraphy is for metabolic activity, not acute injury detail. EMG is for nerve function. While radiographs are essential, they often miss subtle but critical bony injuries in this complex region.

Question 8

What is the primary goal of surgical management for chronic, irreducible lunate dislocations?





Explanation

For chronic, irreducible lunate dislocations, the primary goal of surgical management shifts from complete anatomical restoration (which is often impossible) to pain relief and the creation of a stable, functional wrist. This may involve salvage procedures like proximal row carpectomy or wrist arthrodesis. Full range of motion is rarely achievable in chronic cases. Ulnar nerve decompression is not typically the primary issue with lunate dislocation (median nerve is more common). Preventing Kienböck's in the unaffected wrist is irrelevant. Immediate return to high-impact activities is unrealistic and often contraindicated.

Question 9

A patient presents 3 weeks after a FOOSH injury with persistent wrist pain, stiffness, and weakness. Initial radiographs at an outside facility were reported as normal. Current radiographs show a 'spilled teacup' sign on the lateral view and a 'piece of pie' sign on the AP view. What is the most likely diagnosis?





Explanation

The 'spilled teacup' sign on a lateral view (volar displacement and rotation of the lunate) and the 'piece of pie' sign on the AP view (lunate appears triangular due to rotation) are pathognomonic for a lunate dislocation. The scenario suggests a missed diagnosis, which is common if initial radiographs are suboptimal or misread. The other options do not present with these specific radiographic findings.

Question 10

Which of the following ligaments is crucial for maintaining the stability of the proximal carpal row and is often injured in perilunate dislocations?





Explanation

The scapholunate interosseous ligament (SLIL) is a critical stabilizer of the proximal carpal row, particularly between the scaphoid and lunate. Its rupture is the initiating event in Mayfield Stage I perilunate instability and is often involved in more severe perilunate and lunate dislocations. The dorsal radiocarpal and radioscaphocapitate ligaments are also important but the SLIL is key for proximal row integrity. The ulnocarpal complex is important for ulnar-sided stability. The transverse carpal ligament forms the roof of the carpal tunnel.

Question 11

When performing an open reduction of a perilunate or lunate dislocation, a combined dorsal and volar approach is often favored. What is the primary advantage of the volar approach in this context?





Explanation

The volar approach is crucial for decompressing the median nerve, which is frequently compressed by the volarly displaced lunate or edematous tissues in lunate dislocations. It also allows direct access for the repair of the crucial volar ligaments, such as the radioscaphocapitate and long radiolunate ligaments, which are often torn. The dorsal approach is better for visualizing and reducing dorsally displaced carpal bones and repairing dorsal ligaments. Thus, a combined approach addresses both aspects.

Question 12

What is the typical timeframe within which closed reduction and percutaneous pinning are most likely to be successful for a lunate or perilunate dislocation?





Explanation

Closed reduction and percutaneous pinning are generally most successful if performed within 1 week of injury. Beyond this timeframe, soft tissue swelling, adhesions, and muscle spasm make closed reduction increasingly difficult, and the chances of successful anatomical reduction diminish significantly, often necessitating open reduction. While 24 hours is ideal, up to a week is generally considered the window for attempts at closed reduction before considering open options.

Question 13

A patient undergoes open reduction and internal fixation (ORIF) for a perilunate dislocation. Post-operatively, serial radiographs are obtained. Which finding on follow-up imaging would raise the most concern for inadequate reduction or impending carpal collapse?





Explanation

A normal scapholunate angle is typically between 30-60 degrees. An increase to 70 degrees (or more) indicates persistent scapholunate dissociation and dorsal intercalated segmental instability (DISI), which is a significant concern for inadequate reduction, persistent instability, and future carpal collapse (SNAC wrist). K-wires are expected post-ORIF. Mild swelling is common. A capitolunate angle of 15 degrees is within the normal range (typically <30 degrees). Mild joint space narrowing may indicate pre-existing arthritis or post-traumatic changes, but an increased scapholunate angle is a more acute indicator of instability in this context.

Question 14

Which of the following associated injuries is most frequently found in conjunction with a perilunate dislocation, particularly in high-energy trauma?





Explanation

A scaphoid fracture is the most common associated bony injury with perilunate dislocations, leading to a 'trans-scaphoid perilunate dislocation'. This injury occurs when the force of the dislocation propagates through the scaphoid bone instead of rupturing the scapholunate ligament alone. It's important to specifically look for this given its high incidence and implications for treatment.

Question 15

What is the primary vascular supply to the lunate that is at risk during a lunate dislocation?





Explanation

The lunate receives its blood supply from branches of both the radial and ulnar arteries, which form dorsal and volar arterial networks that penetrate the bone. This dual supply makes it susceptible to avascular necrosis when these networks are disrupted, which is common in dislocations where the lunate's ligamentous attachments (and thus vascular pedicles) are torn. Options A and B are partially correct but do not encompass the full, dual supply. Interosseous arteries contribute distally but are not the primary direct supply to the lunate itself in this context.

Question 16

A 40-year-old construction worker sustained a lunate dislocation 8 weeks ago. He now presents with persistent pain, stiffness, and signs of median nerve compression despite an attempted closed reduction at an outside facility. Radiographs confirm irreducible volar displacement of the lunate. What surgical approach would be most appropriate at this stage?





Explanation

For a subacute (8 weeks) and irreducible lunate dislocation with persistent median nerve symptoms, a combined dorsal and volar approach is typically indicated. The volar approach allows for median nerve decompression and volar ligament repair/reconstruction. The dorsal approach is crucial for achieving anatomical reduction of the lunate, especially when it's volarly dislocated, and for addressing dorsal ligamentous injuries. Proximal row carpectomy or wrist arthrodesis are salvage procedures usually reserved for chronic cases with significant arthrosis or failed ligament repair, not necessarily as the primary approach for a subacute irreducible dislocation, unless salvage is the only option due to extensive damage.

Question 17

Which of the following is NOT a typical radiographic sign of a lunate dislocation?





Explanation

In a lunate dislocation, the lunate loses its normal articulation with the distal radius and displaces volarly. Therefore, the lunate will NOT appear to articulate normally with the distal radius on any view; it will be displaced. The other options are classic signs: 'spilled teacup' (volar displacement/rotation of lunate), 'piece of pie' (lunate appears triangular on AP due to rotation), increased scapholunate interval (often associated, as it's a progression from perilunate), and loss of carpal row parallelism, indicating disruption of normal alignment.

Question 18

What is the primary mechanism by which median nerve neuropathy occurs in acute lunate dislocations?





Explanation

The most common mechanism of median nerve neuropathy in acute lunate dislocations is compression. The lunate dislocates volarly and rotates, falling directly into the carpal tunnel. This, combined with significant soft tissue edema and hemorrhage, dramatically increases pressure within the unyielding carpal tunnel, leading to acute compression of the median nerve. Direct transection is rare, stretching is less common, and ischemic injury is less likely the primary cause compared to direct compression.

Question 19

After open reduction and internal fixation of a perilunate dislocation, what is the recommended minimum duration of immobilization in a cast?





Explanation

Following ORIF of a perilunate or lunate dislocation, immobilization in a cast (typically forearm-based or long-arm, depending on stability and surgeon preference) is recommended for 6-8 weeks. This allows sufficient time for initial ligamentous healing and fibrous stabilization around the reduced carpal bones. Premature mobilization can lead to loss of reduction and recurrent instability. After 6-8 weeks, K-wires are typically removed, and a controlled rehabilitation program begins.

Question 20

Which of the following indicates a successful closed reduction of a lunate dislocation on a lateral radiograph?





Explanation

A successful reduction of a lunate dislocation is indicated when the lunate, capitate, and distal radius are aligned in a single column on a lateral radiograph. This demonstrates the restoration of normal carpal alignment and articulation. Options A, B, D describe various forms of malalignment. A persistent 'piece of pie' sign indicates residual rotation of the lunate, suggesting incomplete reduction or a perilunate variant.

Question 21

Which of the following factors significantly increases the likelihood of a lunate dislocation requiring open reduction and internal fixation rather than successful closed reduction?





Explanation

An associated scaphoid fracture (trans-scaphoid perilunate dislocation) significantly complicates closed reduction. The presence of a fracture fragment prevents smooth reduction and often requires open reduction to stabilize the fracture and repair associated ligaments, even if initial closed reduction of the dislocation seems possible. The other options generally favor successful closed reduction or are less of a contraindication to closed reduction attempts.

Question 22

What is the term for chronic carpal instability characterized by progressive degeneration of the scaphoid, lunate, and radius articulation, often a sequela of an untreated or inadequately treated scapholunate dissociation or perilunate injury?





Explanation

SLAC wrist (Scapholunate Advanced Collapse) is a specific pattern of degenerative arthritis that results from chronic scapholunate dissociation or perilunate instability. It progresses through stages, starting with arthritis between the scaphoid and radial styloid, then progressing to the entire radioscaphoid joint, and eventually affecting the capitolunate joint, with relative sparing of the radiolunate joint until late stages. Kienböck's disease is avascular necrosis of the lunate, De Quervain's is tenosynovitis, TFCC tear is a cartilaginous injury, and a ganglion cyst is a soft tissue mass.

Question 23

A patient presents with a chronic lunate dislocation (over 3 months old) and severe wrist pain, significantly impacting activities of daily living. Radiographs show marked degenerative changes. Which of the following salvage procedures is generally considered in such a case?





Explanation

For chronic lunate dislocations with significant degenerative changes and pain, a proximal row carpectomy (PRC) is a common salvage procedure. PRC involves excising the scaphoid, lunate, and triquetrum, allowing the capitate to articulate directly with the distal radius. This provides pain relief and preserves a functional range of motion when reconstructive options are no longer viable. Ligament repair is unsuitable for chronic cases with arthritis. Limited arthrodesis might be considered for specific types of instability but PRC is more commonly chosen for diffuse degeneration post-dislocation. Wrist arthrodesis is a more extensive salvage with complete loss of motion. Radial shortening is for ulnar-negative variance. Excision of the lunate alone is not a standard procedure for chronic dislocation and would lead to collapse.

Question 24

In the context of carpal instability, what does 'DISI' stand for and what is its characteristic radiographic appearance?





Explanation

DISI stands for Dorsal Intercalated Segmental Instability. It is characterized by a dorsal tilt or extension of the lunate (seen as an increased scapholunate angle >60 degrees and an increased capitolunate angle >30 degrees on a lateral radiograph). This pattern is commonly associated with scapholunate ligament disruption. Volar tilt of the lunate (VISI) is associated with lunotriquetral ligament disruption.

Question 25

When attempting closed reduction of an acute lunate dislocation, what is the initial maneuver typically employed after achieving adequate anesthesia?





Explanation

The classic maneuver for reducing a lunate dislocation involves applying longitudinal traction to the hand, hyperextending the wrist to disengage or 'unlock' the lunate from under the capitate, then applying direct volar pressure over the lunate while simultaneously flexing the wrist to push the lunate back into its radial fossa. This sequence is critical for successful reduction. Direct volar pressure alone or hyperflexion initially would be ineffective or even counterproductive.

Question 26

What is the primary role of K-wire fixation after open reduction of a lunate or perilunate dislocation?





Explanation

K-wires (Kirschner wires) are used to provide temporary internal fixation and maintain the reduction of the carpal bones and the repaired ligaments. They act as internal splints, holding the carpus in the anatomically reduced position while the soft tissues (ligaments and capsule) heal. They do not provide definitive bony union (unless used for a specific fracture), compress articular fragments, stimulate bone growth, or directly prevent nerve compression (though successful reduction indirectly aids nerve decompression).

Question 27

Which of the following physical examination findings is most indicative of acute median nerve compression in a patient with a wrist injury?





Explanation

Paresthesias and numbness in the median nerve distribution (thumb, index, middle, and radial half of the ring finger) are the classic signs of acute median nerve compression, such as that caused by a lunate dislocation. Pain with wrist extension might indicate tendonitis or extensor injury. Dorsal swelling is non-specific. Loss of sensation in the small finger suggests ulnar nerve involvement. Crepitus with forearm rotation points to distal radioulnar joint (DRUJ) injury or fracture.

Question 28

When evaluating a lateral wrist radiograph, what normal alignment feature, when disrupted, suggests a perilunate or lunate dislocation?





Explanation

On a true lateral wrist radiograph, the radius, lunate, and capitate should appear collinear, forming a continuous 'column.' Disruption of this collinear relationship, particularly the lunate displacing volarly or the capitate displacing dorsally relative to the lunate, is a hallmark of lunate or perilunate dislocations. Gilula's lines are assessed on an AP view to evaluate carpal alignment. Radial styloid-scaphoid articulation and pisiform-triquetrum articulation are important but not the primary indicator on a lateral for this specific injury. Ulnar variance relates to distal radius and ulna length.

Question 29

A patient with a chronic, untreated lunate dislocation presents with severe pain and functional limitation. Surgical options are being discussed. What is a significant contraindication for performing a proximal row carpectomy (PRC) in this scenario?





Explanation

Significant chondral damage to the capitate head or the lunate fossa of the distal radius is a major contraindication for a proximal row carpectomy (PRC). For a PRC to be successful, the articulating surfaces of the capitate (which will then articulate with the radius) and the lunate fossa of the distal radius must have relatively preserved cartilage. If these surfaces are already severely arthritic, a PRC will likely lead to continued pain and poor outcomes, making wrist arthrodesis a more appropriate salvage procedure. Other options are generally not contraindications.

Question 30

What is the most likely long-term complication if a lunate dislocation is missed or inadequately treated?





Explanation

SLAC wrist (Scapholunate Advanced Collapse) is the most likely and debilitating long-term complication of missed or inadequately treated lunate or perilunate dislocations, particularly those involving scapholunate ligament injury. The chronic instability leads to abnormal mechanics and progressive degenerative arthritis. While carpal tunnel syndrome can be an acute complication, SLAC wrist describes the chronic arthritic degeneration. Other options are less directly linked as a primary long-term complication of a missed lunate dislocation.

Question 31

During open reduction of a lunate dislocation, which carpal bone is typically reduced first to help re-establish carpal alignment?





Explanation

When performing open reduction of a lunate dislocation, the lunate itself is usually reduced first. The goal is to bring the lunate back into its anatomical position within the lunate fossa of the radius. Once the lunate is reduced and provisionally stabilized (often with K-wires), the rest of the carpus (especially the capitate and scaphoid) can then be reduced around it, restoring the crucial radiolunate and capitolunate articulations. Attempting to reduce other bones first without the lunate in place is generally less effective.

Question 32

A 28-year-old male sustains a dorsal perilunate dislocation. After successful closed reduction, what is the next most critical step in management to ensure optimal outcome and prevent recurrence?





Explanation

Dorsal perilunate dislocations, even if successfully reduced closed, are highly unstable due to extensive ligamentous disruption. The next critical step is almost always surgical stabilization with K-wires and ligament repair (ORIF) to maintain the reduction and allow for proper ligamentous healing. Without surgical stabilization, the risk of redislocation and chronic instability (leading to SLAC wrist) is very high. Immediate motion is contraindicated. A short arm cast alone is insufficient for stabilization of such an unstable injury.

Question 33

Which type of carpal instability is characterized by a volar tilt of the lunate on a lateral radiograph and is typically associated with a lunotriquetral ligament injury?





Explanation

VISI (Volar Intercalated Segmental Instability) is characterized by a volar tilt or flexion of the lunate on a lateral radiograph. This pattern is typically associated with disruption of the lunotriquetral interosseous ligament (LTIL). DISI is a dorsal tilt of the lunate, associated with SLIL injury. SNAC and SLAC are patterns of degenerative arthritis. Radial intercalated segmental instability is not a recognized term.

Question 34

What anatomical structure provides the most substantial extrinsic volar support to the lunate, often injured in lunate dislocations?





Explanation

The radioscaphocapitate ligament (also known as the 'long radiolunate ligament' or 'arcuate ligament') is a strong extrinsic volar ligament that originates from the radius and inserts onto the scaphoid, capitate, and lunate. It is a critical stabilizer of the scaphoid and lunate and is frequently torn in perilunate and lunate dislocations. The dorsal radiocarpal ligament is dorsal. The ulnolunate ligament is on the ulnar side. The TFCC stabilizes the DRUJ and ulnar carpus. The ECU tendon is an extrinsic muscle tendon.

Question 35

A patient presents with persistent wrist pain and weakness 6 months after a successful closed reduction of a lunate dislocation. Clinical examination reveals mild tenderness over the dorsal wrist and a positive Watson (scaphoid shift) test. Radiographs show a persistently widened scapholunate interval. What is the most likely diagnosis?





Explanation

A persistently widened scapholunate interval on radiographs and a positive Watson test are pathognomonic for chronic scapholunate dissociation and instability, often a sequela of an inadequately healed perilunate injury or a missed ligamentous injury after reduction. While Kienböck's is avascular necrosis of the lunate, and De Quervain's is tenosynovitis, they do not present with these specific radiographic and clinical signs. DRUJ instability would involve ulnar-sided pain and specific DRUJ tests. A ganglion cyst is a soft tissue mass.

Question 36

When assessing carpal alignment on an AP radiograph, what normal 'arc' should be present, and its disruption indicates carpal instability?





Explanation

Gilula's three arcs are three smooth, continuous lines that should be present on a normal AP radiograph of the wrist. Arc I outlines the proximal convexities of the scaphoid, lunate, and triquetrum. Arc II outlines the distal concavities of the same bones. Arc III outlines the proximal convexities of the capitate and hamate. Disruption of any of these arcs indicates carpal malalignment or instability. The other options are not specific to assessing intercarpal alignment in this manner.

Question 37

Which surgical technique for lunate or perilunate dislocation repair involves advancing a portion of the dorsal radiocarpal ligament to augment the repair of the scapholunate ligament?





Explanation

The Blatt capsulodesis, also known as dorsal capsulodesis, is a surgical technique used to stabilize the scapholunate joint, often in chronic scapholunate dissociation following perilunate injuries. It involves creating a flap from the dorsal radiocarpal ligament and attaching it to the dorsal aspect of the scaphoid and lunate to restrict excessive scaphoid flexion. The Brunelli procedure uses a flexor carpi radialis (FCR) slip. Rappaport and Ramon's tenodesis are not standard terms for this approach. Watson scaphoidectomy is part of a SLAC wrist salvage.

Question 38

What is the critical differentiating factor between a dorsal perilunate dislocation and a dorsal trans-scaphoid perilunate dislocation?





Explanation

The critical differentiating factor is the presence of an associated scaphoid fracture. In a dorsal perilunate dislocation, the entire carpus (excluding the lunate) displaces dorsally, and the scapholunate ligament typically ruptures. In a dorsal trans-scaphoid perilunate dislocation, the scaphoid fractures instead of the scapholunate ligament tearing, and the fracture fragments displace along with the rest of the carpus. This has significant implications for surgical management.

Question 39

In the context of carpal injury imaging, what specific view is often most helpful in demonstrating a subtle scapholunate dissociation?





Explanation

A clenched-fist AP view (or radial deviation view) is often crucial for unmasking a subtle scapholunate dissociation. By making a fist, the extensor carpi radialis longus and brevis contract, pulling the scaphoid proximally and radially. If the scapholunate ligament is torn, this maneuver can exaggerate the scapholunate gap ('Terry Thomas sign') and reveal dynamic instability that might not be visible on standard views. The scaphoid view is good for scaphoid fractures. Ulnar deviation may close the gap.

Question 40

What is the typical presentation of a patient with an untreated chronic lunate dislocation after several months or years?





Explanation

Untreated chronic lunate dislocations inevitably lead to progressive wrist pain, stiffness, weakness, and the development of degenerative arthritis (SLAC wrist). The chronic malalignment causes abnormal loading patterns and articular cartilage damage. Acute, severe pain usually subsides after the acute phase, but chronic, escalating pain replaces it. Spontaneous resolution is highly unlikely. DRUJ pain and ulnar nerve symptoms are not the primary, most common long-term sequelae of a lunate dislocation.

Question 41

Which diagnostic finding on plain radiographs would necessitate an immediate surgical consultation in a patient with a wrist injury?





Explanation

A lunate dislocation, especially when associated with median nerve paresthesias, constitutes a surgical emergency. The nerve compression requires urgent reduction (closed or open) to prevent irreversible damage. While other fractures mentioned may require surgical consideration, they typically do not demand the same immediate emergent surgical intervention as an acute lunate dislocation with nerve compromise.

Question 42

In the context of lunate dislocation, what is the significance of the capitolunate angle?





Explanation

The capitolunate angle is measured on a true lateral radiograph and indicates the relationship between the longitudinal axes of the capitate and the lunate. Normally, this angle should be less than 30 degrees. An increased capitolunate angle (>30 degrees) suggests disruption of the normal sagittal alignment of the midcarpal joint, commonly seen in DISI (lunate dorsiflexed) or VISI (lunate volaflexed). It directly reflects sagittal plane alignment, unlike the other options.

Question 43

A patient sustained an acute dorsal perilunate dislocation with an associated scaphoid waist fracture (trans-scaphoid perilunate dislocation). After open reduction and internal fixation, what is a specific challenge related to the scaphoid fracture component?





Explanation

Trans-scaphoid perilunate dislocations carry a high incidence of scaphoid nonunion or avascular necrosis (AVN) of the proximal pole of the scaphoid. The scaphoid's blood supply enters predominantly distally and dorsally. A waist fracture can disrupt this supply, especially to the proximal pole. This complicates healing and necessitates meticulous fixation and often bone grafting. Ulnar nerve compression is less common than median nerve compression. Bone quality is not necessarily poor. Associated ligamentous injuries can and should be repaired. Kienböck's in the contralateral wrist is unrelated.

Question 44

Which specific K-wire configuration is commonly used to stabilize the scapholunate articulation after reduction of a perilunate dislocation?





Explanation

To stabilize the scapholunate articulation and maintain the reduction of the lunate within the carpal rows, K-wires are typically placed from the scaphoid into the lunate, and from the capitate into the lunate. This 'sandwich' fixation helps to maintain the critical relationship of the lunate with both the scaphoid and the capitate, preventing both scapholunate dissociation and capitolunate instability. Pinning from the radius to the lunate is also often done to stabilize the radiolunate articulation, but the question specifically asks about scapholunate. Other options are for different joints or stability patterns.

Question 45

What is the most common direction of displacement for the lunate in a true lunate dislocation?





Explanation

In a true lunate dislocation, the lunate almost universally dislocates volarly into the carpal tunnel, losing its articulation with both the distal radius and the capitate. This is in contrast to a perilunate dislocation where the lunate remains in place, and the rest of the carpus displaces dorsally around it.

Question 46

Which clinical sign, if present, would indicate a high probability of successful closed reduction of a lunate dislocation, even before confirmation with radiographs?





Explanation

An audible 'clunk' or 'thud' during the reduction maneuver, coupled with immediate and significant relief of median nerve symptoms (if present), is a strong clinical indicator of successful closed reduction of a lunate dislocation. This suggests the lunate has popped back into its anatomical position, decompressing the nerve. The other options suggest either an unsuccessful reduction or complications.

Question 47

Regarding the Mayfield classification, what event signifies the transition from Stage III to Stage IV, resulting in a true lunate dislocation?





Explanation

Mayfield Stage IV, a true lunate dislocation, occurs when the entire perilunate arc of instability is completed. This means the lunate loses its final articulation, the radiolunate articulation, allowing it to displace volarly. Stage I is scapholunate, Stage II is capitolunate, Stage III is triquetrolunate. The final stage is the disruption of the radiolunate ligament, leading to the lunate's volar displacement.

Question 48

After open reduction and internal fixation of a perilunate dislocation, what is the most important component of the initial rehabilitation phase (post-immobilization)?





Explanation

Following the immobilization period (typically 6-8 weeks) after ORIF of a perilunate dislocation, the initial rehabilitation phase should focus on gentle, active and active-assisted range of motion exercises within protected arcs. The goal is to gradually restore motion without stressing the healing ligaments or risking redislocation. Aggressive stretching, high-resistance exercises, or immediate return to sports would jeopardize the repair. Complete avoidance of motion would lead to severe stiffness.

Question 49

A patient presents with persistent wrist pain and difficulty with grip strength 1 year after a lunate dislocation was managed with closed reduction and casting. Radiographs now show sclerosis and collapse of the lunate with associated radial shortening. What is the most likely diagnosis?





Explanation

Sclerosis and collapse of the lunate with associated radial shortening (due to the collapsed lunate) after a lunate dislocation is characteristic of Kienböck's disease, specifically post-traumatic avascular necrosis of the lunate. Lunate dislocation can disrupt the lunate's precarious blood supply, leading to AVN. While other complications are possible, this specific constellation of findings points to Kienböck's disease. Carpal tunnel syndrome could be present but doesn't explain the bone changes.

Question 50

Which of the following describes the 'Signet Ring Sign' on an AP wrist radiograph in the context of carpal instability?





Explanation

The 'Signet Ring Sign' on an AP wrist radiograph refers to a foreshortened, rounded, and often sclerotic appearance of the scaphoid. This occurs when the scaphoid is abnormally flexed (due to scapholunate ligament disruption), causing its distal pole to overlap the proximal pole, giving it the appearance of a signet ring. This is a classic sign of scapholunate dissociation and dorsal intercalated segmental instability (DISI).

Question 51

What is the approximate incidence of median nerve compression in acute lunate dislocations?





Explanation

Median nerve compression symptoms occur in a significant number of acute lunate dislocations, with reported incidences ranging from 25% to over 50%. The volarly displaced lunate directly impinges on the nerve within the unyielding carpal tunnel, making it a common and urgent concern requiring prompt reduction.

Question 52

When planning an open reduction of a lunate dislocation, what is the preferred incision for optimal exposure of the volar aspect of the wrist and the median nerve?





Explanation

For volar exposure to decompress the median nerve and repair volar ligaments in a lunate dislocation, a longitudinal incision, typically a modified carpal tunnel incision, is often preferred. It usually starts in the palm, slightly radial to the thenar crease (to avoid injuring the recurrent motor branch of the median nerve), and extends proximally across the wrist crease towards the distal forearm. This provides good visualization while minimizing potential for neurovascular injury. A zig-zag incision across the wrist crease is often used for carpal tunnel release but needs careful extension for dislocation. Dorsal incision is for dorsal structures. Ulnar or transverse incisions are not suitable for primary volar exposure.

Question 53

In the context of carpal kinematics, which of the following best describes the normal movement of the lunate during radial deviation of the wrist?





Explanation

During normal radial deviation of the wrist, the lunate extends (dorsiflexes) and translates ulnarly. Conversely, during ulnar deviation, the lunate flexes (volarflexes) and translates radially. This complex kinematic pattern is essential for normal wrist motion and is disrupted in carpal instability. This understanding is crucial for appreciating the mechanics behind perilunate and lunate dislocations.

Question 54

Which factor, when present in a patient with a lunate dislocation, may make closed reduction more challenging due to soft tissue interposition?





Explanation

Chronic dislocations (generally >3 weeks) become significantly more challenging to reduce closed due to the development of adhesions, fibrosis, muscle spasm, and swelling around the dislocated carpal bones, leading to soft tissue interposition that physically blocks reduction. While high-energy injury can cause more complex trauma, the chronicity itself is the primary factor for soft tissue interposition. Ligamentous laxity might theoretically make reduction easier, but also less stable post-reduction. Ulnar styloid fracture is bony, not soft tissue interposition. Absence of nerve symptoms doesn't affect mechanical reduction difficulty.

Question 55

What type of carpal instability results from the failure of the lunotriquetral ligament?





Explanation

Failure of the lunotriquetral ligament (LTIL) leads to Volar Intercalated Segmental Instability (VISI). In VISI, the lunate takes on a volaflexed posture (volar tilt) due to the loss of its dorsal connection to the triquetrum. This often results in an increased capitolunate angle, with the capitate extending dorsally relative to the lunate. DISI results from scapholunate ligament failure, leading to dorsal tilt of the lunate.

Question 56

When considering the long-term prognosis of a successfully treated lunate or perilunate dislocation, what is the most significant determinant of functional outcome?





Explanation

The most significant determinant of long-term functional outcome in lunate or perilunate dislocations is the success of anatomical reduction and stable fixation of all components (bones and ligaments). Meticulous restoration of carpal alignment and stability is crucial to prevent chronic instability, progressive arthritis (SLAC wrist), and functional deficits. While other factors play a role, anatomical reduction is paramount. Pre-existing arthritis is a contraindication to reconstructive surgery and points to salvage. Duration of cast and prophylactic antibiotics are important but secondary to achieving stable anatomical reduction.

Question 57

Which view on a wrist radiograph is best for evaluating Gilula's lines?





Explanation

Gilula's lines, which are used to assess the smooth curvilinear alignment of the proximal and distal carpal rows, are best evaluated on a standard AP (Anteroposterior) view of the wrist. Disruption of these lines indicates carpal instability or dislocation.

Question 58

A patient is undergoing open reduction and internal fixation of a perilunate dislocation. During the procedure, the dorsal aspect of the scapholunate interosseous ligament is found to be avulsed from the lunate. What specific suture technique is commonly used to repair this type of ligamentous injury?





Explanation

When a ligament, such as the scapholunate interosseous ligament, is avulsed from its bony insertion (e.g., from the lunate), transosseous sutures are typically used. This involves drilling small holes through the bone (lunate in this case) and passing the sutures through the avulsed ligament, then through the bone, to re-anchor the ligament securely to its anatomical insertion. Simple interrupted sutures to the capsule or bridging sutures are generally insufficient for reattaching a ligament avulsed from bone. Horizontal mattress is a general technique, but transosseous specifically addresses avulsion from bone.

Question 59

Following reduction of a perilunate dislocation, what specific finding on CT scan would confirm adequate reduction and good prognosis, assuming no associated fractures?





Explanation

Adequate reduction of a perilunate dislocation means that the carpal bones are restored to their anatomical relationships. A CT scan confirming smooth articulation between the lunate and radius (radiocarpal joint), and the lunate and capitate (midcarpal joint), indicates proper alignment and a good reduction. A 3mm scapholunate interval is borderline to abnormal (typically <2mm or <3mm for dynamic instability). A capitolunate angle of 45 degrees indicates persistent DISI or VISI and is not adequate. Residual volar tilt of the lunate indicates VISI and inadequate reduction. Slight widening of the midcarpal joint indicates persistent instability.

Question 60

What is the primary role of wrist arthrodesis in the management of lunate dislocation?





Explanation

Wrist arthrodesis (fusion) is a salvage procedure typically reserved for severe, chronic, painful, and unmanageable carpal instability or arthritis resulting from long-standing lunate/perilunate dislocations, failed reconstructive surgeries, or advanced SLAC/SNAC wrist. It aims to eliminate pain by fusing the wrist bones, sacrificing all motion. It does not preserve motion, is not for acute nerve compression (though it can indirectly alleviate chronic nerve symptoms), nor is it a primary treatment for Kienböck's without dislocation, and it certainly does not facilitate a quicker return to high-impact sports due to complete loss of motion.

Question 61

Which of the following describes the anatomical position of the lunate relative to the capitate in a dorsal perilunate dislocation?





Explanation

In a dorsal perilunate dislocation, the lunate maintains its articulation with the distal radius, but the capitate (and the rest of the carpus) dislocates dorsally relative to the lunate. Therefore, the capitate is displaced dorsally relative to the lunate. If the lunate itself displaces volarly, it is a true lunate dislocation. Understanding this relationship is fundamental to differentiating these injuries.

Question 62

What is the earliest reliable indicator of potential avascular necrosis of the lunate on plain radiographs after a lunate dislocation?





Explanation

The earliest reliable radiographic indicator of avascular necrosis (AVN) of the lunate (Kienböck's disease) is increased density or sclerosis of the lunate. This is due to ischemic bone death, followed by new bone formation and trabecular thickening, which makes the bone appear denser on radiographs. Subchondral collapse is a later stage. Decreased signal intensity on T1-weighted MRI is a more sensitive and earlier indicator than X-ray, but the question specifies plain radiographs. Increased radiolucency would be rare in AVN and increased joint space is not a direct sign of AVN itself.

Question 63

In an acute lunate dislocation, the interval between the lunate and the scaphoid on an AP radiograph is often widened. What is the typical measurement that indicates significant scapholunate dissociation?





Explanation

A scapholunate interval (SL gap) greater than 3 mm on an AP radiograph is generally considered indicative of significant scapholunate dissociation, often referred to as the 'Terry Thomas sign.' Normal is typically 2 mm or less, though some consider 3 mm borderline. A dynamic study, like a clenched-fist view, can accentuate a subtle widening.

Question 64

Which of the following ligaments is considered the 'keystone' of carpal stability?





Explanation

While several ligaments contribute to carpal stability, the scapholunate interosseous ligament (SLIL) is often referred to as the 'keystone' or most critical intrinsic stabilizer of the proximal carpal row. Its integrity is fundamental to preventing carpal collapse and progressive instability (DISI, SLAC wrist). Damage to the SLIL is the initiating event in Mayfield Stage I perilunate instability and is central to the pathophysiology of perilunate and lunate dislocations.

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