ABOS Part I Orthopaedic Review: Mallet Finger & Skier's Thumb Diagnosis, Management & Treatment | Part 21589

Correct Answer: C

The patient's presentation of a 'jammed' finger, inability to actively extend the DIP joint, a resting flexion deformity, and full passive extension, coupled with normal radiographs, is classic for a soft tissue mallet finger. According to the Doyle classification, this is a Type I injury, which involves a soft tissue avulsion of the terminal extensor tendon from its insertion on the distal phalanx without significant bony involvement. The case explicitly states that Type I is the primary focus of the review and that the vast majority of acute soft tissue mallet injuries are successfully managed non-operatively. The core principle of non-operative management is continuous immobilization of the DIP joint in full extension or slight hyperextension (0-10 degrees) for a prolonged period, typically 6 to 8 weeks, followed by a gradual weaning phase. The PIP joint should be left free to allow full range of motion.

Option A is incorrect because Type II involves a bony avulsion fracture of less than 30% of the articular surface, and surgical repair is not the initial management for an acute Type I injury.

Option B is incorrect because Type III involves a bony avulsion fracture of more than 30% of the articular surface, often with subluxation, which is not present here.

Option D is incorrect because Type IV is an epiphyseal fracture in children (Salter-Harris type I or II), which is not applicable to a 38-year-old adult.

Option E is incorrect because immediate active and passive DIP joint flexion would disrupt the healing tendon and lead to failure of treatment. Continuous immobilization is paramount during the initial healing phase.

Correct Answer: D

The case explicitly states that in a soft tissue mallet injury (Type I), the terminal extensor tendon is ruptured from its insertion, disrupting the extensor moment arm at the DIP joint. This disruption leaves the DIP joint extension unopposed, and the powerful pull of the flexor digitorum profundus (FDP) tendon, which inserts on the volar aspect of the distal phalanx, creates the characteristic flexion deformity. The FDP is the sole flexor of the DIP joint.

Option A (Extensor Digitorum Communis) is an extrinsic extensor, but its terminal tendon is what is disrupted, leading to the deformity, not causing it.

Option B (Central slip of the extensor mechanism) primarily extends the PIP joint and is typically intact in a pure soft tissue mallet finger. Its overactivity can contribute to a swan neck deformity, but it does not cause DIP flexion.

Option C (Flexor Digitorum Superficialis) inserts on the middle phalanx and primarily flexes the PIP joint, not the DIP joint.

Option E (Lumbrical muscles) are intrinsic muscles that contribute to MCP joint flexion and PIP/DIP extension, but they are not the primary cause of the DIP flexion deformity in a mallet finger.

Correct Answer: C

The 'Surgical Anatomy & Biomechanics' section clearly identifies the Triangular Ligament as a crucial supporting structure. It states: 'Located dorsally, it stabilizes the lateral bands, preventing their volar subluxation and maintaining their position for efficient DIP joint extension.'

Option A (Volar plate) is a ligamentous structure on the volar aspect of the joint that prevents hyperextension, but it is not involved in stabilizing the dorsal extensor mechanism.

Option B (Annular pulleys) are part of the flexor tendon sheath system, crucial for maintaining the mechanical advantage of the flexor tendons, not the extensor mechanism.

Option D (Sagittal bands) are located at the MCP joint level and stabilize the extensor digitorum communis tendon over the MCP joint, not the DIP joint.

Option E (Transverse retinacular ligament) is mentioned as influencing joint movement and preventing dorsal migration of the lateral bands, but the triangular ligament is specifically highlighted for preventing volar subluxation and maintaining position for efficient DIP extension.

Correct Answer: C

The 'Indications & Contraindications' section explicitly lists 'Failed Non-Operative Management: Persistent extensor lag of more than 15-20 degrees after an adequate course of continuous splinting (typically 8 weeks, followed by night splinting)' as a primary indication for surgical management. This patient fits this criterion, having a 20-degree lag after an attempted 8-week splinting course (albeit with poor compliance).

Option A (Acute presentation within 4-6 weeks of injury) is an indication for non-operative management, not surgical.

Option B (Patient compliance with continuous splinting) is a factor for successful non-operative management, not an indication for surgery.

Option D (Absence of secondary deformity like a fixed swan neck) would typically favor non-operative management if the injury is acute and correctable, or it means the surgery would be less complex if performed for other reasons. The presence of a fixed swan neck, however, would be an indication for surgery.

Option E (Minimal initial extensor lag) would typically favor non-operative management.

Correct Answer: C

The 'Pre-Operative Planning & Patient Positioning' section, under 'Imaging,' states: 'Plain Radiographs: Standard AP, lateral, and oblique views of the affected digit are mandatory. These are crucial to rule out bony avulsion fractures (Doyle Type II, III, IV), DIP joint subluxation, and pre-existing arthritis. A true lateral view is essential to accurately assess the joint alignment and presence of bony avulsion.'

Option A (MRI) is generally not indicated for routine soft tissue mallet finger. It may be considered in very chronic, complex cases but is not mandatory for initial evaluation.

Option B (CT scan) is not mentioned as a mandatory initial imaging study for mallet finger. It might be used for complex bony avulsions but not for initial soft tissue mallet evaluation.

Option D (Ultrasound) can visualize tendons but is not considered mandatory for initial evaluation and may not reliably rule out small bony avulsions or subluxation as effectively as radiographs.

Option E (Bone scan) is a nuclear medicine study used for detecting bone pathology like stress fractures, infections, or tumors, and is not indicated for routine mallet finger evaluation.

Correct Answer: C

The 'Internal Fixation (K-wire)' section states: 'After the tendon repair, transarticular K-wire fixation of the DIP joint is almost always performed to protect the repair and maintain the joint in the desired position during healing.' It further specifies: 'The DIP joint is gently placed in full extension or slight hyperextension (0-10 degrees).' The image clearly depicts a K-wire traversing the DIP joint, holding it in extension.

Option A is incorrect because the K-wire is not primarily for dynamic compression or bone healing in a soft tissue injury. Its role is static immobilization.

Option B is incorrect because the K-wire prevents active range of motion at the DIP joint, which is crucial to protect the healing tendon. Early active motion is contraindicated.

Option D is incorrect because while over-extension should be avoided to prevent volar plate injury, the primary purpose of the K-wire is not to prevent this specific injury during rehabilitation, but rather to immobilize the joint for tendon healing.

Option E is incorrect because the K-wire immobilizes the joint and tendon, which can actually contribute to stiffness if not managed properly in rehabilitation. It does not facilitate tendon gliding or prevent adhesions directly.

Correct Answer: B

The 'Detailed Surgical Approach / Technique' section, under 'Repair Technique,' describes 'Tendon-to-Bone Reattachment (Direct Repair)' as the most common technique for acute and subacute mallets, involving drill holes or suture anchors. For chronic injuries, it states: 'For chronic injuries with significant retraction and scar tissue, direct reattachment may lead to excessive tension. The tendon may be advanced distally and reattached to the distal phalanx as described above.' This directly addresses the scenario of significant retraction and a short distal stump, where advancement and reattachment to the bone are necessary.

Option A (Direct tendon-to-tendon repair) is typically used when a sufficient distal tendon stump remains, which is rare in Type I mallet injuries, especially chronic ones with a 'very short distal stump.' It's more common for lacerations.

Option C (Primary DIP joint arthrodesis) is a salvage procedure for severe, irreparable damage with significant functional impairment, not a primary repair technique for a chronic mallet finger, especially in an athlete.

Option D (Central slip tenotomy) would weaken PIP extension and is not a technique for repairing a mallet finger; it might be considered in severe swan neck deformities but not as a primary mallet repair.

Option E (Lateral band reconstruction without addressing the terminal tendon) is incomplete and would not restore DIP extension. Lateral band involvement may be addressed in chronic cases, but the primary issue is the terminal extensor tendon.

Correct Answer: C

The 'Post-Operative Rehabilitation Protocols' section, under 'Phase 1: Immobilization (Weeks 0-6),' explicitly states for DIP Joint Immobilization: 'Crucial Principle: Absolutely no active or passive DIP joint flexion is permitted. The patient must be meticulously educated on this, particularly for activities of daily living.' This is the most critical instruction to protect the healing tendon repair.

Option A is incorrect because active DIP flexion would directly stress and likely rupture the healing tendon.

Option B is incorrect because passive DIP extension is already maintained by the K-wire/splint, and passive flexion is contraindicated.

Option D is incorrect because light resistive exercises for DIP extension are typically introduced much later, in Phase 3 (Weeks 12+), after the tendon has had significant time to heal.

Option E is incorrect because K-wires should only be removed by a medical professional, typically at 6 weeks post-operatively, not by the patient at home due to discomfort, as this could lead to complications like infection or re-injury.

Correct Answer: C

The 'Complications & Management' section identifies 'Extensor Lag / Re-rupture' as the 'Most common (5-20%), higher in chronic cases' and 'the most common reason for unsatisfactory outcomes.' For salvage strategies, it states: 'For persistent, functionally significant lag, revision surgery may be considered. Options include repeat direct repair, tendon advancement (if proximal tissue allows), tenodesis (using a portion of the lateral band or a small palmaris longus graft), or, in cases of severe, irreparable damage with significant functional impairment, DIP joint arthrodesis (fusion) in a functional position (typically 10-15 degrees of flexion).'

Option A (Infection) is a complication, but its incidence is low (1-5%), and aggressive physical therapy is not the primary salvage for infection.

Option B (Stiffness / Loss of Motion) is common, but early active DIP flexion is contraindicated and would worsen the outcome, not salvage it.

Option D (Nail Deformity) is often cosmetic and not typically salvaged with nerve release/neurolysis, which is for nerve irritation/neuroma.

Option E (Skin Necrosis) is low incidence (1-3%), and prolonged splinting is not a salvage for skin necrosis; it requires wound care, debridement, or skin grafting.

Correct Answer: B

The 'Indications & Contraindications' section, under 'Operative Indications,' lists 'Open Mallet Injuries: Lacerations over the DIP joint with extensor tendon disruption, which require surgical debridement and primary repair to prevent infection and facilitate healing.' The 'Summary of Key Literature / Guidelines' further reinforces this: 'Acute open mallet finger lacerations require surgical debridement and primary repair, irrespective of the degree of lag, to prevent infection and restore tendon integrity.'

Option A is incorrect because open injuries carry a high risk of infection and require surgical intervention, unlike most closed injuries.

Option C is incorrect because while swan neck deformity is a potential secondary complication, the immediate priority for an open injury is infection prevention and primary tendon repair.

Option D is incorrect because MRI is generally not indicated for routine mallet finger, and for an acute open injury, surgical exploration and repair are more urgent than advanced imaging.

Option E is incorrect because DIP joint arthrodesis is a salvage procedure for severe, irreparable cases, not the preferred initial treatment for an acute open mallet finger, especially in a young, active patient.

Correct Answer: C

The case explicitly states, 'When the metacarpophalangeal joint is in extension during the traumatic event, the accessory ulnar collateral ligament and volar plate bear the initial stress. However, as the joint is forced into flexion and abduction, the proper ulnar collateral ligament becomes the primary restraint and subsequently fails.' This accurately describes the sequential failure of the ulnar collateral ligament complex in a Skier's Thumb injury.

Option A is incorrect because the proper UCL is the primary restraint in flexion, not extension, and the accessory UCL bears initial stress in extension.

Option B is incorrect because while the volar plate contributes to stability in extension, it is not the primary restraint in both positions, nor does it typically fail before the entire UCL complex in this specific mechanism.

Option D is incorrect because the adductor pollicis aponeurosis is a muscular aponeurosis, not a primary ligamentous restraint, and its interposition (Stener lesion) occurs after the UCL rupture, not as a primary failure leading to it.

Option E is incorrect because a forced abduction injury primarily stresses the ulnar collateral ligament, not the radial collateral ligament, which resists varus forces.

Correct Answer: C

The case explicitly states, 'During palpation of the ulnar joint line, a distinct, firm, highly tender, pea-sized mass was appreciated proximally and ulnarly to the metacarpophalangeal joint line. This palpable mass is the pathognomonic clinical hallmark of a Stener lesion. It represents the avulsed, retracted distal end of the ulnar collateral ligament that has displaced superficial to the proximal edge of the adductor pollicis aponeurosis.' This interposition prevents healing and necessitates surgical intervention.

Option A is incorrect because a partial tear would not typically present with a palpable, retracted mass, and would likely have a firm endpoint on stress testing.

Option B is incorrect because while an avulsion fracture can occur, the description of a 'pea-sized mass' refers to soft tissue (the ligament stump), and radiographs would be needed to confirm a bony avulsion, which were negative in this case.

Option D is incorrect because a ganglion cyst is typically a chronic, non-traumatic finding, and while it can be firm, it would not be acutely tender in this context or pathognomonic for an acute ligamentous injury.

Option E is incorrect because a flexor pollicis longus tendon rupture would present with an inability to flex the IP joint and a different palpable mass location, not specifically at the MCP joint ulnar aspect.

Correct Answer: C

The case states, 'The absolute angulation exceeding 35 degrees, combined with a side-to-side difference greater than 15 degrees, provided definitive clinical evidence of a complete, full-thickness rupture of the proper ulnar collateral ligament.' The finding of 40 degrees of valgus angulation in 30 degrees of flexion, with a side-to-side difference of 30 degrees (40 vs 10), and a soft endpoint, unequivocally indicates a complete rupture. Testing in 30 degrees of flexion specifically isolates the proper ulnar collateral ligament.

Options A and B are incorrect because partial sprains (Grade I or II) would typically present with less laxity (often <30 degrees) and, crucially, a firm endpoint, indicating some intact ligamentous fibers.

Option D is incorrect because an isolated accessory UCL injury would primarily manifest as instability in extension, not gross instability in 30 degrees of flexion where the proper UCL is the primary restraint.

Option E is incorrect because a volar plate avulsion primarily causes hyperextension instability, and while it can be part of a complex injury, the gross valgus instability in flexion points directly to UCL failure.

Correct Answer: C

The case explicitly states under 'Clinical Pearls and Pitfalls': 'Local Anesthesia is Mandatory: Attempting to grade laxity in an acutely injured, unanesthetized thumb is highly unreliable due to involuntary muscle guarding by the adductor pollicis. A local intra-articular or digital block is essential for an accurate physical examination.' This is a crucial step for accurate diagnosis.

Option A is incorrect because while testing in extension is part of the assessment, the '30-Degree Flexion Rule' is critical for isolating the proper UCL, which is often the primary injury. Testing only in extension may yield a false negative if the volar plate and accessory ligament are intact.

Option B is incorrect because the case states, 'in the modern clinical setting, stress radiography is largely contraindicated when a Stener lesion is suspected clinically' due to the risk of iatrogenic Stener lesion formation or conversion of a partial to a complete tear.

Option D is incorrect because the case advises, 'Palpation Precedes Stress: Always palpate the ulnar joint line for a Stener lesion before applying valgus stress. Forceful stress testing of a non-displaced complete tear can iatrogenically displace the ligament superficial to the aponeurosis, converting a potentially non-operative injury into an operative one.'

Option E is incorrect because the interphalangeal joint's motion does not significantly confound MCP joint stress testing, and its immobilization is not a standard or critical step for this specific assessment.

Correct Answer: C

The case explicitly describes the MRI findings: 'Crucially, the MRI demonstrated the classic yo yo on a string sign. The torn, retracted ulnar collateral ligament stump appeared as a balled-up, nodular mass of low signal intensity (the 'yo-yo') resting superficial and proximal to the low-signal band of the adductor pollicis aponeurosis (the 'string'). This confirmed the presence of a Stener lesion.' This is the pathognomonic MRI sign for a Stener lesion.

Option A is incorrect because plain radiographs already ruled out a bony avulsion, and the 'yo-yo on a string' sign specifically refers to soft tissue interposition.

Option B is incorrect because this describes a partial sprain (Grade I or II), not a complete rupture with retraction and aponeurotic interposition.

Option D is incorrect because this describes a radial collateral ligament injury, which is on the opposite side of the joint and has a different mechanism and clinical presentation.

Option E is incorrect because while an intra-articular hematoma is expected with acute trauma, it does not represent the 'yo-yo on a string' sign, which specifically identifies the displaced ligament stump and aponeurosis.

Correct Answer: C

The case clearly states, 'In this patient's case, the clinical examination demonstrating gross valgus instability lacking a firm endpoint, combined with the palpable mass and definitive MRI evidence of a Stener lesion, served as absolute indications for operative intervention.' The Stener lesion creates a mechanical barrier to healing, making non-operative management futile. Open surgical repair with suture anchor fixation is the standard of care for acute, complete UCL ruptures with a Stener lesion.

Option A is incorrect because non-operative management is strictly reserved for partial tears or non-displaced bony avulsions, not for complete ruptures with a Stener lesion where spontaneous healing is impossible.

Option B is incorrect because the diagnosis is highly probable clinically and definitively confirmed by MRI, making a second opinion for diagnosis unnecessary and delaying definitive treatment.

Option D is incorrect because percutaneous pinning is typically used for fractures or dislocations requiring temporary stabilization, not for direct ligamentous repair in the presence of a Stener lesion which requires open reduction.

Option E is incorrect because corticosteroid injections are contraindicated in acute ligamentous injuries, especially ruptures, as they can impair healing and increase the risk of further damage. They are also not a definitive treatment for mechanical instability.

Correct Answer: C

The case explicitly highlights this surgical pitfall: 'Radial Sensory Nerve Injury: The dorsal sensory branches of the radial nerve are highly variable and course directly through the surgical field. Meticulous blunt dissection and gentle retraction are critical. A postoperative neuroma in this location is often debilitating.' These branches are superficial and easily injured during the initial approach to the ulnar aspect of the thumb MCP joint.

Option A is incorrect because the flexor pollicis longus tendon is on the volar aspect of the thumb and is not typically encountered or at risk with an ulnar approach to the MCP joint.

Option B is incorrect because the radial artery is more proximally located in the wrist (anatomic snuffbox) and not directly in the superficial surgical field for a thumb MCP ulnar collateral ligament repair.

Option D is incorrect because the ulnar nerve is located on the ulnar side of the hand and wrist, but its sensory branches to the thumb are not typically in the immediate superficial field of a thumb MCP ulnar approach.

Option E is incorrect because the extensor pollicis brevis tendon is on the dorsal-radial aspect of the thumb and while it is part of the extensor mechanism, the dorsal sensory radial nerve branches are more superficial and at higher risk during the initial skin incision.

Correct Answer: B

The case outlines the acute immobilization phase: 'The patient is instructed to maintain strict elevation of the operative extremity above the level of the heart to mitigate swelling. Active range of motion of the shoulder, elbow, and non-involved digits is strongly encouraged to prevent stiffness and promote venous return. The interphalangeal joint of the involved thumb must be actively flexed and extended multiple times daily to prevent tethering of the flexor pollicis longus tendon.'

Option A is incorrect because active abduction would place direct stress on the healing UCL repair and is strictly contraindicated in the early phase.

Option C is incorrect because passive valgus stress testing would risk disrupting the fresh repair and is not part of the early rehabilitation protocol.

Option D is incorrect because the splint is typically removed by a therapist at the 2-week mark, and strict immobilization is crucial for protection during the initial healing phase.

Option E is incorrect because progressive strengthening exercises are initiated much later, typically at 6 weeks postoperatively, after initial ligament-to-bone healing has occurred.

Correct Answer: C

The case discusses the classification of UCL injuries by chronicity: 'Acute injuries (typically <3 weeks old) are amenable to direct primary repair. Chronic injuries (>3-4 weeks old) often present with retracted, scarred, and attenuated ligamentous tissue that is inadequate for primary repair, necessitating complex ligamentous reconstruction using autograft (e.g., palmaris longus or plantaris tendon).' A 6-month-old injury with significant retraction and scarring falls squarely into the chronic category, requiring reconstruction.

Option A is incorrect because direct primary repair is reserved for acute injuries where the ligament tissue is healthy and can be reapproximated to its footprint. In chronic cases, the tissue is often too attenuated or scarred.

Option B is incorrect because non-operative management is ineffective for complete ruptures, especially chronic ones with gross instability, and would lead to persistent pain and dysfunction.

Option D is incorrect because percutaneous pinning is a temporary fixation method and does not address the underlying ligamentous deficiency in chronic instability.

Option E is incorrect because while arthrodesis provides stability, it sacrifices motion and is typically reserved as a salvage procedure for severe, painful, degenerative arthritis or failed reconstructions, not as a primary treatment for chronic instability in an otherwise healthy joint.

Correct Answer: C

The case describes this step: 'Using a small curette and a fine surgical burr, the cortical bone at the footprint was decorticated to expose bleeding cancellous bone. This crucial step stimulates the local inflammatory cascade and provides marrow-derived osteoprogenitor cells to enhance ligament-to-bone healing.' This is a fundamental principle in orthopedic surgery to promote robust soft tissue-to-bone healing.

Option A is incorrect because while anchor placement is important, decortication's primary role is biological, not purely mechanical for anchor purchase, which is achieved by proper anchor design and insertion technique.

Option B is incorrect because debridement of frayed ligament edges is done on the ligament itself, not by decorticating the bone. Decortication is about preparing the bone for healing, not removing tissue.

Option D is incorrect because decortication does not primarily decompress the joint space; that is achieved by proper reduction and irrigation. It also doesn't directly prevent stiffness.

Option E is incorrect because suture anchors are used for fixation, not direct suture passage through the bone in this context. Decortication is not for easier suture passage.