Trauma&Anatomy Flashcards
Which metacarpals articulate with the hamate bone?
The hamate articulates with the 4th and 5th metacarpals, forming a saddle-shaped joint with the 5th and a flatter joint with the 4th, providing ulnar-sided hand stability.
Which anatomical structures significantly influence displacement of fractures at the base of the 5th metacarpal?
The intrinsic hypothenar muscles (abductor digiti minimi, flexor digiti minimi) and the **extensor carpi ulnaris (ECU) **tendon insertion primarily influence fracture displacement.
Is the flexor carpi ulnaris tendon a primary deforming force in 5th carpometacarpal fractures?
No, the flexor carpi ulnaris tendon inserts on the pisiform and does not significantly influence fracture displacement at the 5th CMC joint.
Describe a common mechanism causing dorsal avulsion fractures of the hamate.
Axial loading combined with flexion or rotational forces applied to the fifth metacarpal typically cause avulsion fractures at ligament attachments on the dorsal hamate.
Which injury pattern is commonly associated with dorsal avulsion fractures of the hamate?
They frequently occur alongside dislocations or subluxations of the 5th carpometacarpal joint.
What is the preferred imaging modality for accurately assessing complex hamate and CMC joint fractures?
Computed tomography (CT) imaging is preferred due to superior visualization of fracture patterns, small fragments, and articular involvement.
Which additional imaging modality should be used when ligamentous injury at the 5th CMC joint is suspected?
Magnetic resonance imaging (MRI) is recommended to evaluate ligament integrity and soft tissue involvement.
How should displaced fractures of the 5th CMC joint without significant comminution typically be managed?
Closed reduction with percutaneous Kirschner wire (K-wire) fixation is the recommended minimally invasive and stable treatment.
Why is proper placement of Kirschner wires crucial in managing 5th CMC joint fractures?
Proper K-wire placement ensures fracture stability by adequately engaging both metacarpal and carpal bones, preventing secondary displacement.
What complications arise from untreated dorsal avulsion fractures of the hamate?
Persistent instability, chronic pain, and reduced grip strength commonly result from untreated avulsion fractures.
What clinical findings indicate a hamate fracture?
Pain in the hypothenar eminence, exacerbated by palpation or resisted finger flexion, indicates a likely hamate fracture.
Which X-ray view enhances visualization of suspected injuries to the 5th CMC joint?
A 30-degree pronated oblique view significantly improves visualization of the 5th CMC joint.
What is meant by a ‘reverse Bennett fracture’?
A reverse Bennett fracture refers to a fracture-dislocation of the 5th metacarpal base, analogous to the thumb’s Bennett fracture, often requiring similar management.
What typical symptoms suggest a hamate body fracture?
Ulnar wrist pain, swelling, tenderness, and exacerbation of symptoms with gripping or ulnar deviation movements suggest a hamate body fracture.
Why is early mobilization critical after K-wire fixation of a 5th CMC joint fracture?
Early mobilization prevents joint stiffness and facilitates functional recovery, provided fracture stability is maintained.
What is the anatomical and functional distinction of the 5th CMC joint compared to the 2nd and 3rd?
The saddle-shaped articulation of the 5th CMC joint allows greater mobility and hand cupping movements, unlike the rigid 2nd and 3rd CMC joints.
How should an acute dislocation of the 5th CMC joint be reduced?
Reduction involves longitudinal traction and direct manual pressure over the base of the metacarpal, followed by splinting or fixation if unstable.
Which ligamentous structures are most commonly injured during dorsal dislocation of the 5th CMC joint?
Dorsal CMC ligaments, responsible for resisting dorsal displacement, are typically injured or ruptured in these dislocations.
Which metacarpals are more prone to instability when fractured, and why?
The first (thumb) and fifth (little finger) metacarpals are more prone to instability due to their border position, greater mobility at the CMC joints, and reduced support from intermetacarpal ligaments. Deforming forces from muscles like the abductor pollicis longus (first) and extensor carpi ulnaris (fifth) exacerbate displacement.
What anatomical structures primarily prevent displacement in metacarpal shaft fractures?
Intermetacarpal ligaments and intrinsic muscles stabilize central metacarpals (second to fourth). Border metacarpals (first and fifth) lack bilateral support, increasing their displacement risk.
How does the anatomical structure of the 2nd and 3rd CMC joints contribute to their stability?
The 2nd and 3rd CMC joints are stabilized by saw-tooth articular surfaces and strong ligaments (flexor carpi radialis anteriorly, extensor carpi radialis longus and brevis posteriorly), making them rigid and resistant to displacement.
What is the effect of the cam-shaped metacarpal head on MCP joint stability?
The cam-shaped metacarpal head makes collateral ligaments lax in extension and taut in flexion, enhancing stability during grip and pinch while allowing mobility in extension.
What is the typical angulation pattern seen in metacarpal shaft fractures, and what causes it?
Apex dorsal angulation occurs due to volar pull from interosseous muscles on the distal fragment, bending the fracture dorsally. This is a consistent biomechanical pattern in transverse fractures.
What role do interosseous muscles play in the deformity of transverse metacarpal fractures?
Interosseous muscles flex the MCP joint, pulling the distal fragment volarward, resulting in apex dorsal angulation, a key deformity in transverse fractures.
What is the relationship between apex dorsal angulation and shortening in metacarpal fractures?
Each 2.4° of apex dorsal angulation correlates with approximately 1mm of shortening, aiding in assessing fracture severity and functional impact.
What is the optimal finger position for assessing malrotation in metacarpal fractures, and why?
Flexion (e.g., making a fist) is optimal because it tightens collateral ligaments via the cam-shaped metacarpal head, revealing malalignment as fingertips deviate from pointing toward the scaphoid tubercle.
How does malrotation of metacarpal fractures manifest clinically at the fingertips?
**10° of metacarpal malrotation **causes about 2cm of fingertip overlap or underlap, impacting cosmetics and function due to amplified distal effects.
What radiographic views are optimal for evaluating metacarpal fractures?
PA/AP, lateral, and oblique views are ideal. Semi-pronation obliques assess index/middle metacarpals, semi-supination obliques evaluate ring/small metacarpals, and Brewerton views (65° MCP flexion) examine metacarpal heads.
What is the most valid method for measuring metacarpal shortening?
The Shortening Absolute Value (SH-Abs) method compares the fractured metacarpal’s length on AP view to the contralateral side, providing a precise shortening measurement.
How much apex dorsal angulation is acceptable in metacarpal shaft fractures of the index and middle fingers?
Angulation exceeding 10° requires reduction due to limited CMC joint mobility, which restricts compensation in these rigid digits.
How much apex dorsal angulation is acceptable in metacarpal shaft fractures of the ring and small fingers?
*** Ring finger tolerates up to 30°,
* small finger up to 40-50°, **
due to greater CMC joint mobility (10-15° for ring, 20-30° for small), allowing functional adaptation.
What are the indications for surgical treatment of metacarpal shaft fractures?
Surgery is indicated for angulation beyond acceptable limits
>10° index/middle,
>30-40° ring/small,
rotational malalignment, open fractures, multiple fractures, or inability to fully extend the MCP joint post-block.
What is the recommended treatment approach for small finger metacarpal neck fractures with significant angulation?
Nonoperative treatment is effective even up to 70° angulation, with studies showing comparable or better outcomes than surgery due to preserved motion and healing capacity.
What surgical fixation method shows superior outcomes for fifth metacarpal neck fractures?
Antegrade intramedullary fixation (bouquet method) outperforms crossed pins or transverse pinning, offering better MCP joint motion and total active range.
What is a potential complication of improper immobilization in metacarpal shaft fractures, and how can it be prevented?
Intrinsic muscle contracture, leading to clawing, can result from improper immobilization.
Prevention involves MCP flexion at 70-90° (intrinsic-plus position) and early motion to maintain muscle length.
What is pseudoclawing, and how does it relate to metacarpal fractures?
Pseudoclawing is PIP extensor lag from MCP hyperextension compensating for angulation or shortening, reducing force to the PIP joint and impairing extension.
Is nonunion common in metacarpal shaft fractures, and what are the main risk factors?
Nonunion is rare due to robust blood supply. Risk factors include infection, inadequate immobilization, soft tissue damage, and patient factors like smoking, not fracture pattern.
What is the relationship between metacarpal shortening and extensor lag?
Each 2mm of shortening causes about 7° of MCP extensor lag, as it disrupts the extensor mechanism linked to the metacarpal head via sagittal bands.
What anatomical structures primarily stabilize the thumb MCP joint?
Volar plate and collateral ligaments (radial and ulnar).
What is the role of the sesamoid bones in the thumb MCP joint?
They are embedded in the tendons of the flexor pollicis brevis and adductor pollicis, aiding in joint stability and function.
What is the typical mechanism of injury for a dorsal MCP dislocation of the thumb?
Hyperextension or axial loading, such as a fall onto an outstretched hand.
What is the initial management approach for most dorsal MCP dislocations of the thumb?
Closed reduction under local anesthesia, as most dislocations can be managed without surgery.
Describe the optimal closed reduction maneuver for simple dorsal thumb MCP dislocations.
Hyperextension of the MCP joint followed by gentle volar-directed pressure on the proximal phalanx base, then flexion of the joint; this relaxes entrapped structures facilitating reduction.
Why is simple longitudinal traction not the preferred reduction maneuver for dorsal thumb MCP dislocations?
Because longitudinal traction alone tightens entrapped volar structures around the metacarpal neck, potentially worsening the deformity.
What anatomical structure is most commonly disrupted in dorsal thumb MCP dislocations, leading to irreducibility?
The volar plate is most commonly disrupted and interposed, causing irreducibility. Collateral ligament avulsions are less common.
Which anatomical structures typically become entrapped in complex irreducible dorsal thumb MCP dislocations?
The volar plate, sesamoid bones, and occasionally flexor pollicis longus tendon become entrapped behind the metacarpal head, blocking closed reduction.
What role do sesamoid bones play in complex dorsal thumb MCP dislocations?
Sesamoids may become entrapped between joint surfaces (‘locked thumb’) or sustain fractures during injury or reduction attempts, complicating management.
What radiographic finding strongly indicates a complex irreducible dorsal thumb MCP dislocation?
Interposition of sesamoid bones visible on radiographs strongly suggests a complex irreducible dislocation requiring surgical intervention.
What imaging modality is most useful for diagnosing associated sesamoid fractures in thumb MCP dislocations?
Ultrasound or CT scan, as they detect small fractures not visible on plain X-rays.
What is a potential associated injury with dorsal MCP dislocations of the thumb?
Sesamoid bone fractures, which can complicate management and recovery.
After reducing a dorsal thumb MCP dislocation, why is dynamic testing essential?
Dynamic testing assesses joint stability through controlled movements, identifying subtle instabilities not seen on static imaging alone, guiding further management such as immobilization or surgery.
After successful reduction of a thumb MCP dislocation, what is the typical immobilization period?
2-3 weeks in a thumb spica splint, followed by progressive mobilization.
What is the most appropriate management for a Seymour fracture in a child presenting with a flexed fingertip and nail bed injury?
Open reduction, nail bed repair, and Kirschner wire fixation. This is required because Seymour fractures are open physeal fractures with potential nail bed interposition, necessitating debridement and stabilization to prevent infection and deformity.
Why does the fingertip remain flexed in a Seymour fracture?
Due to the terminal extensor tendon inserting on the proximal dorsal epiphysis and the flexor digitorum profundus on the metaphysis distal to the fracture, causing a flexion imbalance. This reflects the fracture’s physeal disruption.
How can a Seymour fracture be differentiated from a jersey finger on examination?
Seymour fracture presents with a flexed fingertip, visible proximal nail plate, and subungual hematoma, indicating an open fracture, while jersey finger shows DIP extension due to flexor tendon avulsion. This distinction is critical for diagnosis.
Which structures most commonly block reduction in an irreducible dorsal MCP dislocation of the index finger?
Lumbrical muscle radially and flexor tendons ulnarly. These taut structures form a noose around the metacarpal neck, preventing reduction, unlike the volar plate alone.
Why is traction alone insufficient to reduce an irreducible dorsal MCP dislocation?
Taut medial and lateral structures, such as lumbricals and flexor tendons, encircle the metacarpal neck, resisting traction. This requires open intervention beyond simple traction.
Which digit is most frequently affected by dorsal MCP dislocations?
Index finger, followed by the little finger. This reflects the common injury pattern due to forced hyperextension, as seen in clinical practice.
What is the most appropriate management for a type IV mallet injury with >30% articular surface involvement?
Closed reduction and longitudinal pin fixation. This restores articular congruity and reduces subluxation, preventing osteoarthritis, as most cases can be managed closed.
Why is pin fixation preferred over splinting for a type IV mallet injury with a large articular fragment?
The large fragment causes distal phalanx subluxation, requiring stabilization beyond splinting to maintain reduction and prevent joint degeneration.
What is the most appropriate management for a thumb UCL avulsion with a palpable mass?
Open reduction and internal fixation. A Stener lesion involves UCL retraction with adductor aponeurosis interposition, preventing healing without surgical restoration.
Why does immobilization fail in a Stener lesion?
The interposed adductor aponeurosis prevents UCL contact with its avulsion site, leading to chronic instability. Surgical repair is necessary to restore anatomy.
What surgical steps are key in repairing a Stener lesion?
Debridement, division of adductor aponeurosis, and UCL anchoring to the proximal phalanx. This re-establishes ligament continuity, followed by protection with a K-wire and cast.
Why is dynamic traction effective for PIP fracture-dislocations?
Distraction reduces the fracture and restores joint anatomy via ligamentotaxis, while allowing movement to minimize stiffness, unlike rigid fixation.
How does dynamic traction differ from extension splinting in PIP injury management?
Dynamic traction uses distraction for unstable fractures, whereas extension splinting stabilizes simpler avulsions like central slip injuries, without addressing joint instability.
What finding in a fifth metacarpal neck fracture most likely requires surgical intervention?
Malrotation. It causes scissoring, impairing function, unlike angulation, which the fifth digit tolerates up to 70 degrees due to CMC mobility.
