ABOS Part 1 Shoulder & Elbow MCQs - Advanced Board Prep

Correct Answer: A

The standard Grammont-style reverse total shoulder arthroplasty (rTSA) biomechanically functions by medializing and inferiorizing the center of rotation of the glenohumeral joint. While inferiorization recruits more deltoid fibers and increases its moment arm for forward elevation, the medialization of the center of rotation significantly decreases the resting tension and the moment arm of the posterior rotator cuff (infraspinatus and teres minor). This biomechanical disadvantage often results in decreased active external rotation, a common clinical finding post-rTSA, especially if the posterior cuff is already compromised or absent. Newer lateralized rTSA designs attempt to restore this tension to improve external rotation. Options B, C, and D incorrectly describe the biomechanical shifts of a Grammont prosthesis. Option E is a technical error but not the primary inherent design reason for this specific, predictable deficit.

Correct Answer: C

In extension-type supracondylar humerus fractures, the direction of displacement of the distal fragment dictates which structures are at risk from the sharp proximal fragment. When the distal fragment is displaced posterolaterally, the proximal fragment is driven anteromedially. This anteromedial spike puts the median nerve (specifically its anterior interosseous nerve branch) and the brachial artery at the highest risk of injury. Conversely, if the distal fragment is displaced posteromedially (the most common pattern), the proximal fragment is driven anterolaterally, putting the radial nerve at risk. The ulnar nerve is most commonly injured in flexion-type supracondylar fractures or iatrogenically during medial pin placement for fixation.

Correct Answer: C

This patient's history of a prior dislocation and symptoms of the elbow "giving out" when pushing up from a chair (which applies an axial load, valgus stress, and supination to the elbow) are classic for posterolateral rotatory instability (PLRI). PLRI is caused by insufficiency of the lateral ulnar collateral ligament (LUCL). The most specific physical examination test for PLRI is the lateral pivot-shift test of the elbow (or the posterolateral rotatory apprehension test). The moving valgus stress test and milking maneuver evaluate the medial ulnar collateral ligament (MUCL) for valgus instability. The hook test is used to diagnose distal biceps tendon ruptures. Tinel's sign evaluates for cubital tunnel syndrome.

Correct Answer: C

The Latarjet procedure provides stability through a "triple effect": 1) the bony augmentation of the anterior glenoid defect, 2) the dynamic "sling effect" of the conjoint tendon (short head of biceps and coracobrachialis), and 3) the repair of the capsule to the stump of the coracoacromial ligament. To achieve the sling effect, the coracoid and conjoint tendon are passed through a horizontal split made in the subscapularis muscle (typically between its superior two-thirds and inferior one-third). When the arm is abducted and externally rotated (the position of vulnerability), the conjoint tendon acts as a dynamic sling across the anterior-inferior capsule, preventing anterior translation of the humeral head.

Correct Answer: B

Hertel et al. described specific radiographic criteria that are highly predictive of ischemia and subsequent avascular necrosis (AVN) of the humeral head following proximal humerus fractures. The most critical predictors of ischemia are: 1) a short calcar segment (metaphyseal head extension < 8 mm), 2) disruption of the medial hinge (> 2 mm of displacement), and 3) an anatomic neck fracture pattern. A medial hinge disruption > 2 mm indicates severe displacement that likely tears the critical ascending branch of the anterior humeral circumflex artery and the intraosseous anastomoses from the posterior humeral circumflex artery. A calcar length of 12 mm (Option A) is protective against AVN. Tuberosity displacement and surgical neck angulation alone are less predictive of AVN than the integrity of the medial hinge and calcar.

Correct Answer: C

The patient's presentation of lost digit extension at the MCP joints with preserved, radially deviated wrist extension is the classic clinical picture of a posterior interosseous nerve (PIN) palsy. The PIN innervates the extensor digitorum communis, extensor indicis proprius, extensor digiti minimi, extensor carpi ulnaris (ECU), and the thumb extensors. Because the extensor carpi radialis longus (ECRL) is innervated by the radial nerve proximal to the PIN branch, wrist extension is preserved but deviates radially due to the loss of the ECU. During a two-incision distal biceps repair, the PIN is at significant risk during the posterolateral exposure of the radial tuberosity if the forearm is not kept in maximal pronation. Pronation moves the PIN anteriorly and safely away from the surgical field.

Correct Answer: C

The coracoclavicular (CC) ligaments consist of the conoid and trapezoid ligaments. Anatomically, the conoid ligament is located posteromedial to the trapezoid ligament. Biomechanically, the conoid ligament is cone-shaped and serves as the primary restraint to superior translation of the clavicle relative to the acromion. The trapezoid ligament is located anterolateral to the conoid, is broader, and serves as the primary restraint to axial compression of the AC joint (resisting the acromion being driven medially under the clavicle). Understanding this specific anatomy is critical for anatomical CC ligament reconstruction techniques.

Correct Answer: D

Medial epicondyle fractures in pediatric and adolescent patients are common. The absolute indications for surgical intervention (ORIF) are an open fracture and incarceration of the medial epicondyle fragment within the elbow joint (which blocks motion and damages articular cartilage). Relative indications, which are highly debated in the literature, include displacement > 5-15 mm, ulnar nerve dysfunction (especially if progressive or severe), and high-demand athletic status (e.g., throwing athletes or gymnasts who require profound valgus stability). However, incarceration within the joint is universally recognized as an absolute indication for surgery.

Correct Answer: B

Adhesive capsulitis (frozen shoulder) is fundamentally a fibrotic disease process of the glenohumeral joint capsule, particularly affecting the rotator interval and anterior capsule. Histologically, it is characterized by a dense proliferation of fibroblasts and myofibroblasts, leading to excessive type III collagen deposition and subsequent capsular contracture. The primary cytokine driving this profibrotic cascade is Transforming Growth Factor-beta (TGF-β), along with Platelet-Derived Growth Factor (PDGF). It is not primarily an acute inflammatory process (neutrophils/IL-1), a bone resorptive process (osteoclasts/RANKL), or a cartilage degenerative process (chondrocytes/MMP-13).

Correct Answer: B

The Bryan and Morrey classification describes fractures of the capitellum. A Type I fracture (Hahn-Steinthal) involves a large osseous piece of the capitellum, often including a portion of the lateral trochlea. A Type II fracture (Kocher-Lorenz) is a shear fracture involving primarily the articular cartilage with very little subchondral bone, often referred to as an "uncapping" of the capitellum. A Type III fracture (Broberg-Morrey) is a severely comminuted fracture of the capitellum. A Type IV fracture (McKee modification) is a coronal shear fracture that includes the capitellum and the majority of the trochlea. The vignette specifically describes the classic Kocher-Lorenz (Type II) pattern.

Correct Answer: B

Scapular notching is a well-documented complication unique to reverse total shoulder arthroplasty (rTSA), occurring when the medial aspect of the humeral component impinges against the inferior scapular neck during arm adduction. To minimize this risk, the current biomechanical consensus recommends placing the metaglene (baseplate) flush with or slightly overhanging the inferior glenoid rim, and utilizing an inferior tilt (typically 10 to 20 degrees). Superior placement of the metaglene fails to clear the inferior scapular pillar, leading to early impingement and subsequent mechanical wear (notching) of the bone. Inferior tilt (Option A) and lateralization (Option D) are actually techniques used to prevent notching. Retroversion (Option C) primarily affects anterior-posterior stability, and oversizing the glenosphere (Option E) generally increases the offset, which can also help reduce notching rather than cause it.

Correct Answer: B

The management of a "pink, pulseless" hand in the setting of a displaced pediatric supracondylar humerus fracture is a classic orthopedic emergency scenario. The absence of a palpable pulse is often due to kinking, spasm, or tethering of the brachial artery over the proximal fracture fragment, rather than a complete transection. Because the hand remains pink and well-perfused (indicating adequate collateral circulation), the immediate next step is urgent closed reduction and percutaneous pinning (CRPP) in the operating room. Reduction relieves the tension on the neurovascular bundle, and the pulse often returns. If the hand were "white and pulseless" (ischemic), urgent reduction is still the first step, but if it remains ischemic after reduction, open vascular exploration is mandated. Delaying reduction for advanced imaging (CT angiogram or Doppler) in a pink, pulseless hand is contraindicated as it delays definitive treatment. Skeletal traction is a historical treatment rarely used today for this indication.

Correct Answer: B

Hertel et al. described specific radiographic criteria that are highly predictive of humeral head ischemia and subsequent avascular necrosis (AVN) following proximal humerus fractures. The most critical predictors include a short metaphyseal head extension (calcar length) of less than 8 mm, disruption of the medial periosteal hinge, and an anatomic neck fracture pattern. A calcar length of <8 mm indicates that the fracture has occurred very close to the articular surface, severely compromising the ascending branch of the anterior humeral circumflex artery and the intraosseous anastomoses from the posterior humeral circumflex artery. While tuberosity displacement and angulation are important for overall fracture classification (e.g., Neer criteria) and functional outcomes, the specific measurement of the posteromedial calcar segment is the strongest independent predictor of AVN.

Correct Answer: B

The standard surgical protocol for treating a Terrible Triad injury of the elbow follows a "deep to superficial" and "inside-out" approach to systematically restore stability. The accepted sequence is: 1) Fixation of the coronoid process (or repair of the anterior capsule if the fragment is too small), which restores the anterior buttress. 2) Fixation or replacement of the radial head, which restores the anterior and valgus buttress. 3) Repair of the lateral ulnar collateral ligament (LUCL) complex, which restores posterolateral rotatory stability. The medial ulnar collateral ligament (MUCL) is typically only repaired if the elbow remains unstable in extension after the first three steps have been completed. Repairing the LUCL first would restrict access to the deeper intra-articular structures (coronoid and radial head).

Correct Answer: C

The Rockwood classification categorizes AC joint injuries based on the degree and direction of displacement and the involved anatomical structures. A Type III injury involves rupture of both the AC and CC (conoid and trapezoid) ligaments, resulting in 25-100% superior displacement, but the deltotrapezial fascia remains largely intact. A Type V injury is a more severe variant characterized by >100% (often 100-300%) superior displacement of the clavicle. This extreme displacement is only possible because, in addition to the AC and CC ligament ruptures, there is extensive stripping and disruption of the deltotrapezial fascia from the distal clavicle. Type IV is posterior displacement into the trapezius. Type VI is inferior displacement under the coracoid.

Correct Answer: B

Lateral epicondylitis ("tennis elbow") is clinically termed an "-itis," but histologically it is a degenerative tendinopathy rather than an acute inflammatory process. The classic histological description, coined by Nirschl, is "angiofibroblastic hyperplasia" or "angiofibroblastic tendinosis." This is characterized by disorganized, immature collagen fibers, an absence of acute inflammatory cells (like polymorphonuclear leukocytes), an increase in ground substance, and prominent neovascularization (fibroblastic and vascular response). This degenerative tissue fails to heal properly due to repetitive microtrauma. Therefore, options suggesting acute inflammation, granulomas, or normal healthy tendon are incorrect.

Correct Answer: C

The ulnar nerve can be compressed at several distinct anatomical sites around the elbow. From proximal to distal, these include the Arcade of Struthers, the medial intermuscular septum, the medial epicondyle, Osborne's ligament (the fascial band connecting the humeral and ulnar heads of the flexor carpi ulnaris), and the deep flexor-pronator aponeurosis. Among these, Osborne's ligament is the most common site of entrapment in idiopathic cubital tunnel syndrome. The anconeus epitrochlearis is an anomalous muscle present in a minority of the population that can cause compression, but it is not the most common overall cause.

Correct Answer: D

The biceps brachii is a powerful flexor of the elbow, but its primary and most powerful biomechanical role is as a supinator of the forearm, especially when the elbow is flexed. If a complete distal biceps tendon rupture is left untreated, the brachialis muscle can largely compensate for elbow flexion, resulting in a relatively modest loss of flexion strength (typically around 30%). However, there is no muscle that can fully compensate for the loss of the biceps in supination. Consequently, patients managed non-operatively experience a significant and permanent loss of forearm supination strength, typically ranging from 40% to 50%, along with a decrease in supination endurance.

Correct Answer: B

The patient presents with isolated weakness and atrophy of the infraspinatus muscle, which is innervated by the suprascapular nerve. The suprascapular nerve passes through the suprascapular notch (where it innervates the supraspinatus) and then courses around the base of the scapular spine through the spinoglenoid notch to innervate the infraspinatus. Compression at the suprascapular notch (e.g., by the transverse scapular ligament) typically causes weakness in BOTH the supraspinatus and infraspinatus. Compression at the spinoglenoid notch (often due to a paralabral cyst associated with a posterior labral tear in overhead athletes) results in isolated infraspinatus weakness, as the motor branches to the supraspinatus have already branched off proximally. The quadrilateral space contains the axillary nerve.

Correct Answer: B

Osteochondritis dissecans (OCD) of the capitellum is typically seen in adolescent athletes involved in repetitive overhead or upper-extremity weight-bearing sports, such as gymnastics and baseball pitching. The primary biomechanical driver is repetitive valgus stress across the elbow joint. This valgus stress creates tension on the medial structures (e.g., MUCL) but simultaneously causes severe lateral compression forces across the radiocapitellar joint. This repetitive, excessive compressive loading leads to focal ischemia, microfracture, and eventual avascular necrosis of the vulnerable subchondral bone of the capitellum, resulting in OCD and potential loose body formation.

Correct Answer: B

The fundamental biomechanical principle of the reverse total shoulder arthroplasty (rTSA), originally designed by Paul Grammont, is the medialization and inferiorization of the glenohumeral center of rotation. By moving the center of rotation medially, the moment arm of the deltoid muscle is significantly increased, which enhances its mechanical advantage and allows it to elevate the arm even in the absence of a functional rotator cuff. Inferiorizing the center of rotation tensions the deltoid, further optimizing its length-tension relationship and increasing its compressive force across the joint, which aids in stability. The rTSA does not restore the native anatomic center of rotation (Option C); it intentionally alters it. Medialization actually increases the risk of scapular notching (Option E), which is why modern designs often incorporate lateralized glenospheres or eccentric glenospheres to mitigate this, though the primary biomechanical driver remains deltoid optimization. Compressive forces are increased, not decreased, to provide stability (Option D).

Correct Answer: C

During the Latarjet procedure, the coracoid process (with the attached conjoint tendon—short head of the biceps and coracobrachialis) is transferred to the anterior glenoid. The musculocutaneous nerve typically enters the coracobrachialis muscle approximately 3 to 8 cm distal to the tip of the coracoid process. When retracting the conjoint tendon medially to expose the anterior glenoid and subscapularis, aggressive or deep retractor placement can stretch or directly compress the musculocutaneous nerve. The axillary nerve (Option A) is at risk inferiorly during capsular release and glenoid preparation. The suprascapular nerve (Option B) is posterior and superior, not typically at risk during the anterior coracoid transfer. The radial nerve (Option D) is posterior to the humerus. The long thoracic nerve (Option E) is medial on the chest wall.

Correct Answer: B

In extension-type supracondylar humerus fractures, the direction of displacement of the distal fragment dictates which structures are at risk from the sharp proximal fragment. When the distal fragment is displaced posteromedially, the proximal fragment is driven anterolaterally. This anterolateral spike puts the radial nerve at the highest risk of injury. A radial nerve injury would present as an inability to extend the wrist and the metacarpophalangeal (MCP) joints of the fingers (Option B). Conversely, if the distal fragment is displaced posterolaterally, the proximal fragment is driven anteromedially, putting the median nerve (specifically the anterior interosseous nerve, AIN) at risk. AIN injury presents as an inability to flex the IP joint of the thumb and DIP joint of the index finger (the "OK" sign) (Option A). Options C, D, and E describe ulnar nerve deficits, which are more commonly associated with flexion-type supracondylar fractures or iatrogenic injury during medial pin placement.

Correct Answer: B

The patient's history and symptoms are classic for posterolateral rotatory instability (PLRI) of the elbow, which results from insufficiency of the lateral ulnar collateral ligament (LUCL). The most appropriate provocative test is the lateral pivot-shift test of the elbow. This test is performed with the patient supine and the arm overhead. The examiner applies a combination of supination, valgus stress, and an axial load while slowly flexing the elbow from a fully extended position. This maneuver causes the radial head to subluxate posterolaterally. As flexion continues past approximately 40 degrees, the triceps and brachialis pull the joint back into a reduced position, often with a palpable or audible "clunk." Pronation and varus stress (Option A) do not recreate the posterolateral subluxation mechanism. Valgus stress with pronation (Option C) tests the medial collateral ligament.

Correct Answer: C

A direct tendon insertion (enthesis), such as the rotator cuff footprint, consists of four distinct histological zones that transition mechanical stress from the compliant tendon to the rigid bone. From superficial to deep, these zones are: 1) Tendon (parallel collagen fibers), 2) Uncalcified fibrocartilage, 3) Calcified fibrocartilage, and 4) Bone. The "tidemark" is a distinct basophilic line that separates the uncalcified fibrocartilage from the calcified fibrocartilage. Therefore, the zone immediately superficial to the tidemark is the uncalcified fibrocartilage. Understanding this anatomy is crucial because surgical repair often results in healing via a fibrovascular scar rather than regeneration of this complex 4-zone enthesis, which contributes to the risk of re-tear.

Correct Answer: C

The characteristic displacement of a midshaft clavicle fracture is dictated by the muscular attachments on the clavicle. The proximal (medial) fragment is pulled superiorly and posteriorly by the unopposed action of the sternocleidomastoid (SCM) muscle. The distal (lateral) fragment is displaced inferiorly by the weight of the arm and the pull of the deltoid muscle, and it is pulled medially by the pectoralis major and latissimus dorsi muscles, leading to shortening of the shoulder girdle. The trapezius attaches to the distal third of the clavicle and does not cause the superior displacement of the proximal fragment. The subclavius lies inferior to the clavicle and depresses it.

Correct Answer: C

The posterior interosseous nerve (PIN), a motor branch of the radial nerve, is at significant risk during the anterior single-incision approach for distal biceps repair, particularly if retractors are placed blindly or aggressively around the radial neck. The PIN innervates the extensor digitorum communis (EDC), extensor carpi ulnaris (ECU), and other extensors. Injury results in the inability to extend the fingers at the MCP joints. Wrist extension is preserved but occurs with radial deviation because the extensor carpi radialis longus (ECRL) is innervated by the radial nerve proper, proximal to the PIN branch, while the ECU (innervated by the PIN) is paralyzed. The lateral antebrachial cutaneous nerve (LABCN) is the most commonly injured sensory nerve in this approach, but it would cause sensory deficits in the lateral forearm, not motor weakness. Median and AIN injuries would affect volar forearm flexors.

Correct Answer: D

The Walch classification describes glenoid morphology in primary glenohumeral osteoarthritis.
- Type A glenoids have a centered humeral head (A1 = minor erosion, A2 = major central erosion).
- Type B glenoids have posterior subluxation of the humeral head. B1 features posterior subluxation without significant bony erosion. B2 is the classic "biconcave" glenoid with posterior wear, retroversion, and posterior subluxation.
- Type C glenoids are dysplastic with severe retroversion (>25 degrees) regardless of humeral head subluxation.
The description of a biconcave glenoid with posterior subluxation perfectly matches a Walch Type B2 glenoid. Addressing the retroversion and posterior wear in a B2 glenoid is a critical and challenging aspect of total shoulder arthroplasty to prevent early component loosening.

Correct Answer: C

Osborne's ligament (or the cubital tunnel retinaculum) is the fascial band that bridges the humeral and ulnar heads of the flexor carpi ulnaris (FCU) muscle. It forms the roof of the cubital tunnel and is a primary site of ulnar nerve compression at the elbow. The Arcade of Struthers (Option A) is a fascial band extending from the medial head of the triceps to the medial intermuscular septum, located approximately 8 cm proximal to the medial epicondyle, and is another potential site of ulnar nerve compression. The Ligament of Struthers (Option B) is an anomalous structure associated with a supracondylar process that can compress the median nerve. The Lacertus fibrosus (Option D) is the bicipital aponeurosis, which can compress the median nerve. The Arcade of Frohse (Option E) is the proximal edge of the superficial head of the supinator, a common site of posterior interosseous nerve (PIN) compression.

Correct Answer: B

Historically, the anterior humeral circumflex artery (AHCA), specifically its ascending anterolateral branch running in the bicipital groove, was considered the primary blood supply to the humeral head. However, more recent quantitative anatomical studies (e.g., by Hettrich et al.) have demonstrated that the posterior humeral circumflex artery (PHCA) provides the majority (up to 64%) of the blood supply to the humeral head. The PHCA gives off the arcuate artery, which enters the posteromedial aspect of the proximal humerus and perfuses the articular segment. Disruption of the posteromedial hinge in proximal humerus fractures significantly compromises this blood supply, increasing the risk of avascular necrosis (AVN).

Correct Answer: B (Quadrangular space)

The primary blood supply to the articular segment of the humeral head is the posterior humeral circumflex artery (specifically its arcuate branch), which provides the majority of the intraosseous vascularity. The posterior humeral circumflex artery travels through the quadrangular space along with the axillary nerve. The boundaries of the quadrangular space are the teres minor (superior), teres major (inferior), long head of the triceps (medial), and the surgical neck of the humerus (lateral). Disruption of this vessel in displaced 3- and 4-part fractures significantly increases the risk of avascular necrosis (AVN). The triangular space contains the circumflex scapular artery. The triangular interval contains the radial nerve and profunda brachii artery. The rotator interval contains the coracohumeral ligament, superior glenohumeral ligament, and long head of the biceps tendon.

Correct Answer: B (Inability to extend the wrist and digits)

In extension-type supracondylar humerus fractures, the direction of distal fragment displacement dictates which neurovascular structures are at greatest risk due to the relative position of the proximal fragment spike. When the distal fragment displaces posteromedially, the sharp proximal fragment is driven anterolaterally. The radial nerve is located anterolaterally in the distal arm and is therefore the most commonly injured nerve in this specific displacement pattern, leading to an inability to extend the wrist and digits. Conversely, if the distal fragment displaces posterolaterally, the proximal fragment is driven anteromedially, placing the anterior interosseous nerve (AIN) and median nerve at risk (leading to an inability to flex the IP joint of the thumb and DIP of the index finger). Ulnar nerve injuries (numbness in the small finger, weak thumb adduction) are more commonly associated with flexion-type supracondylar fractures or iatrogenic injury during medial pinning.

Correct Answer: C (Lateralization of the center of rotation)

Scapular notching in rTSA occurs when the medial aspect of the humeral polyethylene liner impinges against the inferior scapular neck during arm adduction. The traditional Grammont-style rTSA inherently medializes and inferiorizes the center of rotation to maximize the deltoid moment arm. However, this profound medialization brings the humeral component closer to the scapular neck, increasing the risk of notching. To combat this, modern techniques utilize lateralization of the center of rotation (either via a bony increased-offset [BIO-RSA] or a metallic lateralized glenosphere/baseplate). Lateralizing the glenosphere pushes the humerus away from the scapula, increasing the impingement-free range of motion in adduction. Superior translation exacerbates notching. Medialization is the primary cause of notching. Retroversion affects anterior/posterior stability, not inferior notching. Decreasing the neck-shaft angle (e.g., from 155 to 135 degrees) actually helps reduce notching, but lateralization of the glenosphere is a primary glenoid-sided strategy.

Correct Answer: C (Supinator crest of the ulna)

The patient's clinical presentation (clicking, giving way when pushing off a chair) and a positive pivot-shift test are pathognomonic for posterolateral rotatory instability (PLRI) of the elbow. PLRI is caused by insufficiency of the lateral ulnar collateral ligament (LUCL). The LUCL is the primary restraint to varus and posterolateral rotatory forces. Anatomically, the LUCL originates from the lateral epicondyle of the humerus, blends with the annular ligament, and inserts onto the supinator crest of the proximal ulna. It does not insert on the radial neck, coronoid process (which is the insertion for the anterior bundle of the MUCL), or the olecranon.

Correct Answer: A (Short head of the biceps and coracobrachialis)

The Latarjet procedure involves transferring the coracoid process, along with its attached conjoint tendon, to the anterior-inferior glenoid neck. The "triple blocking" effect consists of: 1) a bony block from the transferred coracoid, 2) a dynamic "sling effect" from the conjoint tendon, and 3) capsular repair (often using the coracoacromial ligament stump). The conjoint tendon is composed of the short head of the biceps brachii and the coracobrachialis. When the arm is placed in the vulnerable position of abduction and external rotation, these muscles contract and act as a dynamic sling across the anterior-inferior capsule, preventing anterior translation of the humeral head. The pectoralis minor inserts on the medial aspect of the coracoid and is typically released during the procedure. The long head of the biceps originates from the supraglenoid tubercle.

Correct Answer: C (Arcade of Frohse)

This patient's presentation is classic for radial tunnel syndrome, which involves compression of the posterior interosseous nerve (PIN), a motor branch of the radial nerve. Symptoms include deep aching pain in the proximal lateral forearm, tenderness distal to the lateral epicondyle (unlike lateral epicondylitis, where tenderness is directly over the epicondyle), and pain with resisted supination. Because the PIN is a motor nerve, there are no sensory deficits. The most common site of PIN compression within the radial tunnel is the Arcade of Frohse, which is the proximal fibrous edge of the superficial head of the supinator muscle. The Arcade of Struthers and Osborne's fascia are associated with ulnar nerve compression (cubital tunnel). The Ligament of Struthers and Lacertus fibrosus (bicipital aponeurosis) are associated with median nerve compression (pronator syndrome).

Correct Answer: B (Subclavian vein)

During ORIF of midshaft clavicle fractures, plunging drills or screws pose a significant risk to the underlying neurovascular structures. Directly posterior to the medial and middle thirds of the clavicle lies the subclavian vein, which is the most anterior and medial structure in the neurovascular bundle at this level. It is separated from the posterior cortex of the clavicle only by the thin subclavius muscle and fascia. The subclavian artery and the trunks of the brachial plexus lie posterior and slightly superior to the vein. The suprascapular nerve branches off the superior trunk further laterally. The axillary artery is the continuation of the subclavian artery distal to the lateral border of the first rib. The phrenic nerve lies on the anterior scalene muscle, deeper and more medial.

Correct Answer: A (Repair the medial ulnar collateral ligament (MUCL))

The standard surgical algorithm for a Terrible Triad injury (elbow dislocation, radial head fracture, coronoid fracture) proceeds from deep to superficial and lateral to medial. The steps are: 1) Address the coronoid (fix if Type II/III; Type I tip avulsions are often anterior capsule avulsions and can be left or suture-lassoed if unstable), 2) Address the radial head (fix or replace), 3) Repair the lateral collateral ligament complex (LUCL). After these steps, the elbow is taken through a range of motion to assess stability. If the elbow remains unstable in extension (meaning it subluxates or dislocates), the next step in the algorithm is to address the medial side by repairing the medial ulnar collateral ligament (MUCL). If the elbow remains unstable even after MUCL repair, a hinged external fixator is applied. Fixing a Type I coronoid tip with a screw is technically difficult and often unnecessary if the capsule is repaired. Resecting the coronoid would worsen instability.

Correct Answer: B (Coracohumeral ligament and superior glenohumeral ligament)

This patient has classic adhesive capsulitis (frozen shoulder), which is strongly associated with diabetes. The hallmark physical exam finding is a significant loss of passive external rotation with the arm at the side. The anatomical structures that primarily restrict external rotation when the arm is adducted (at the side) are the components of the rotator interval: the coracohumeral ligament (CHL) and the superior glenohumeral ligament (SGHL). Pathologically, adhesive capsulitis involves profound fibroblastic proliferation, inflammation, and contracture of these specific structures, leading to the characteristic clinical deficit. The middle glenohumeral ligament restricts external rotation at 45 degrees of abduction. The inferior glenohumeral ligament (anterior band) restricts external rotation at 90 degrees of abduction. The posterior band of the IGHL restricts internal rotation.

Correct Answer: B (Diminished resistance to valgus torque)

The medial epicondyle serves as the origin for the flexor-pronator mass and the medial ulnar collateral ligament (MUCL). During the late cocking and early acceleration phases of throwing, the elbow is subjected to tremendous valgus stress. The MUCL is the primary static stabilizer against this valgus torque, and the flexor-pronator mass provides dynamic stabilization. An avulsion fracture of the medial epicondyle compromises both of these structures. If it progresses to a symptomatic nonunion, the medial side of the elbow becomes incompetent, leading to a diminished resistance to valgus torque, medial elbow instability, and pain during throwing. Varus torque is resisted by the lateral collateral ligament complex. Extension is controlled by the triceps (olecranon insertion). Supination is controlled by the biceps and supinator.

Correct Answer: Superior tilt of the glenosphere.

Scapular notching is a well-recognized complication unique to reverse total shoulder arthroplasty (rTSA). It occurs due to mechanical impingement of the medial edge of the humeral polyethylene liner against the inferior scapular neck during arm adduction and internal rotation. To minimize this risk, biomechanical principles dictate that the glenosphere should be placed with a neutral version and approximately 10 to 20 degrees of inferior tilt. Superior tilt of the glenosphere moves the center of rotation superiorly, decreasing the clearance between the humeral component and the scapular pillar, thereby significantly increasing the risk and severity of scapular notching. Using a larger diameter glenosphere or lateralizing the center of rotation actually helps decrease the risk of notching by increasing the impingement-free range of motion.

Correct Answer: Spontaneous resolution and reossification with rest and activity modification.

This clinical presentation is classic for Panner's disease, an osteochondrosis of the capitellum. It typically affects children between 5 and 10 years of age, often those involved in repetitive overhead or upper extremity weight-bearing sports (like gymnastics or baseball). Radiographically, it presents as diffuse sclerosis and fragmentation of the capitellar ossification center. Crucially, Panner's disease is a self-limiting condition of avascular necrosis followed by revascularization and reossification. The natural history is excellent, with spontaneous resolution expected over several months to a few years. Treatment consists of rest, activity modification, and symptomatic management. This must be differentiated from osteochondritis dissecans (OCD) of the capitellum, which typically occurs in older children/adolescents (12-16 years), presents with focal lesions, and carries a higher risk of loose body formation and long-term arthritic changes.

Correct Answer: Spinoglenoid notch.

The patient presents with isolated weakness and atrophy of the infraspinatus muscle, indicating an entrapment of the suprascapular nerve at the spinoglenoid notch. The suprascapular nerve branches off the upper trunk of the brachial plexus, passes through the suprascapular notch (under the transverse scapular ligament) where it innervates the supraspinatus muscle. It then courses around the base of the scapular spine through the spinoglenoid notch to innervate the infraspinatus. Compression at the suprascapular notch would result in weakness of both the supraspinatus (abduction) and infraspinatus (external rotation). Compression at the spinoglenoid notch, often seen in overhead athletes due to repetitive stretching or paralabral cysts, results in isolated infraspinatus weakness. The quadrilateral space contains the axillary nerve; the spiral groove contains the radial nerve; the cubital tunnel contains the ulnar nerve.

Correct Answer: Arcuate branch of the posterior humeral circumflex artery.

Historically, the ascending branch of the anterior humeral circumflex artery (the anterolateral branch) was thought to be the primary blood supply to the humeral head. However, modern anatomical and perfusion studies (such as those by Brooks et al. and Hettrich et al.) have demonstrated that the posterior humeral circumflex artery, specifically via its arcuate branch, provides the majority (up to 64%) of the blood supply to the articular segment of the humeral head. In displaced 3- and 4-part proximal humerus fractures, especially those involving the anatomic neck or with significant medial hinge disruption, this posterior supply is severely compromised, leading to a high rate of avascular necrosis. The circumflex scapular and thoracoacromial arteries do not provide primary intraosseous supply to the humeral head.

Correct Answer: Repair the lateral ulnar collateral ligament (LUCL) complex.

The 'Terrible Triad' of the elbow consists of a posterior elbow dislocation, a radial head fracture, and a coronoid fracture. The standard surgical algorithm for restoring stability proceeds from deep to superficial, typically starting with the coronoid (anterior stabilization), followed by the radial head (lateral column bony stabilization). After these bony structures are addressed, the lateral collateral ligament complex (specifically the LUCL), which is invariably torn in this injury pattern (usually avulsed from the lateral epicondyle), must be repaired. If the elbow remains unstable in extension and supination after coronoid and radial head fixation, the LUCL is the primary deficient restraint. Repairing the MUCL is only indicated if the elbow remains unstable in extension and pronation after the coronoid, radial head, and LUCL have all been securely fixed. A hinged external fixator is a salvage option if stability cannot be achieved after all ligamentous repairs. Upsizing the radial head can lead to overstuffing, causing capitellar wear and stiffness.

Correct Answer: Medial and posterior.

The coracoclavicular (CC) ligaments are the primary restraints to superior and posterior translation of the clavicle relative to the acromion. They consist of two distinct bands: the conoid and the trapezoid. The conoid ligament is the more medial and posterior of the two. It originates from the posteromedial base of the coracoid process and inserts onto the conoid tubercle on the posteromedial undersurface of the distal clavicle. The trapezoid ligament is located lateral and anterior to the conoid. It originates from the superior aspect of the coracoid process and inserts onto the trapezoid line on the anterolateral undersurface of the distal clavicle. Understanding this spatial relationship is critical for anatomical CC ligament reconstruction techniques.

Correct Answer: Lateral antebrachial cutaneous (LABC) nerve.

The lateral antebrachial cutaneous (LABC) nerve is the terminal sensory branch of the musculocutaneous nerve. It exits the deep fascia lateral to the biceps tendon in the distal arm and courses superficially over the brachioradialis to supply sensation to the lateral forearm. During a single-incision anterior approach for distal biceps repair, the LABC nerve is highly vulnerable to traction injury from lateral retractors. Injury results in sensory deficits along the lateral forearm, as described in the vignette. The posterior interosseous nerve (PIN) is a motor nerve at risk during the deep dissection (especially if retractors are placed blindly around the radial neck) or during a two-incision approach, but injury would cause weakness in finger/thumb extension, not isolated sensory loss. The superficial radial nerve is further distal and deep to the brachioradialis in this region.

Correct Answer: Late cocking / maximal external rotation.

Internal impingement (posterosuperior impingement) is a pathological condition commonly seen in overhead athletes, particularly baseball pitchers. It occurs when the arm is placed in extreme abduction and maximal external rotation—the classic position of the 'late cocking' phase of throwing. In this position, the articular surface of the posterior rotator cuff (supraspinatus and infraspinatus) becomes pinched between the greater tuberosity of the humerus and the posterosuperior glenoid rim and labrum. Over time, this repetitive microtrauma leads to articular-sided rotator cuff tears (like PASTA lesions) and posterosuperior labral fraying or tears. The acceleration phase involves rapid internal rotation, and the follow-through phase involves deceleration and cross-body adduction, neither of which produces this specific posterosuperior pinch.

Correct Answer: Inhibition of the differentiation of mesenchymal stem cells into osteoprogenitor cells.

Radiation therapy is a highly effective prophylactic measure against heterotopic ossification (HO) following trauma or surgery. Its primary mechanism of action is the inhibition of rapidly dividing cells. Specifically, low-dose radiation targets pluripotential mesenchymal stem cells in the surrounding soft tissues, preventing their proliferation and subsequent differentiation into osteoprogenitor cells and osteoblasts. Because it targets the early differentiation phase, radiation must be administered shortly before or within 24 to 72 hours after surgery, before the mesenchymal cells have committed to the osteoblastic lineage. It does not destroy mature bone (hydroxyapatite), nor does it primarily target mature osteoblasts or osteoclasts. While NSAIDs (like indomethacin) work by inhibiting prostaglandins (which also play a role in osteogenic differentiation), radiation directly halts the cellular differentiation cascade.

Correct Answer: Teres minor.

The axillary nerve is the most commonly injured nerve during an anterior glenohumeral dislocation due to traction as it courses inferiorly to the joint capsule. It exits the axilla to reach the posterior shoulder and innervate the deltoid and teres minor by passing through the quadrilateral space. A thorough understanding of this anatomy is crucial for both diagnosis and surgical approaches (e.g., posterior approach to the shoulder). The borders of the quadrilateral space are: Superiorly: Teres minor (and the inferior margin of the subscapularis/capsule more anteriorly); Inferiorly: Teres major; Medially: Long head of the triceps brachii; Laterally: Surgical neck of the humerus. Therefore, the teres minor forms the superior border.

The Latarjet procedure provides stability through three main mechanisms. The most significant stabilizing factor in the abducted and externally rotated position is the 'sling effect' of the conjoint tendon compressing the inferior subscapularis and anterior capsule.

In the setting of significant anterior glenoid bone loss (>20-25%), soft tissue stabilization alone has unacceptably high failure rates. The Latarjet procedure provides a triple blocking effect (bone, sling, and capsule) to definitively restore stability in these high-risk patients.

Subscapularis failure after anatomic TSA typically presents with increased passive external rotation, weak internal rotation, and positive lift-off or belly-press tests. It is a recognized complication related to the takedown and repair of the tendon during the standard deltopectoral approach.

A lateralized glenosphere in rTSA increases the lateral offset, thereby decreasing the risk of inferior scapular notching caused by the humeral component impacting the scapular neck. However, lateralization may increase shear forces at the glenoid baseplate-bone interface.

The standard surgical sequence for a terrible triad injury involves a deep-to-superficial approach: fixing the coronoid first (anterior stability), addressing the radial head (lateral column), and finally repairing the lateral ulnar collateral ligament (LUCL) to restore posterolateral stability.

The two-incision technique for distal biceps repair is associated with a higher risk of heterotopic ossification and radioulnar synostosis due to subperiosteal dissection along the ulna. Conversely, the single-incision approach carries a higher risk of lateral antebrachial cutaneous nerve and PIN injuries.

Hertel established that a metaphyseal head extension (calcar length) of less than 8 mm, disruption of the medial hinge, and an anatomic neck fracture are the strongest predictors of humeral head ischemia following proximal humerus fractures.

The Arcade of Struthers is a fascial band extending from the medial intermuscular septum to the medial head of the triceps, located about 8 cm proximal to the medial epicondyle. It is a known site of ulnar nerve compression, especially after anterior transposition.

For reverse Hill-Sachs lesions involving 20-40% of the articular surface, transferring the lesser tuberosity with the attached subscapularis tendon into the defect (modified McLaughlin procedure) effectively prevents engagement and restores stability. Arthroplasty is reserved for older patients or defects >40%.

The anterior bundle of the MUCL is the primary restraint to valgus stress at the elbow during throwing. It originates on the anterior undersurface of the medial epicondyle and inserts on the sublime tubercle of the anteromedial coronoid facet.

ORIF of completely displaced midshaft clavicle fractures with >2 cm of shortening significantly decreases the rate of nonunion and symptomatic malunion compared to non-operative treatment. However, ORIF carries a higher overall reoperation rate, largely due to symptomatic hardware removal.

The Latarjet procedure provides stability primarily through the dynamic sling effect of the conjoined tendon on the lower subscapularis and anteroinferior capsule. This effect is most pronounced when the arm is in the vulnerable abducted and externally rotated position. The bony block and capsular repair play secondary stabilizing roles.

Hertel identified specific radiographic predictors for humeral head ischemia, with a metaphyseal head extension (calcar length) of less than 8 mm being a highly reliable predictor of avascular necrosis. An intact medial hinge and anatomical neck fractures are also critical determinants in assessing the vascular viability of the humeral head.

In a terrible triad injury, if the elbow remains unstable after addressing the coronoid, radial head, and LUCL, the MCL should be repaired to restore medial column stability. Hinged external fixation is generally reserved for cases where instability persists despite repair of all essential osseous and ligamentous stabilizers.

Paralabral cysts at the spinoglenoid notch typically arise from a one-way valve effect caused by a posterior or posterosuperior labral tear. These cysts selectively compress the suprascapular nerve after it has already innervated the supraspinatus, leading to isolated infraspinatus atrophy and external rotation weakness.

Subscapularis failure after an aTSA classically presents with a sudden "pop", weakness in internal rotation (positive belly-press/lift-off tests), and increased passive external rotation. It is a severe complication that compromises anterior stability, often necessitating surgical repair or revision to a reverse total shoulder arthroplasty.

The Posterior Interosseous Nerve (PIN) is at high risk of injury during single-incision distal biceps repairs, particularly when drilling the posterior radius for suspensory cortical button fixation. The PIN wraps around the radial neck within the supinator and can be directly transected by an over-penetrating drill bit.

Spinal accessory nerve injury denervates the trapezius muscle, leading to lateral scapular winging characterized by downward rotation and lateral translation. This typically occurs iatrogenically after surgical procedures in the posterior triangle of the neck.

The extended lateral approach provides excellent direct visualization of the anterior articular surface of the capitellum and lateral trochlea, which is strictly required for accurate reduction of coronal shear fractures. Olecranon osteotomies provide excellent posterior visualization but poor access to the anterior articular surface.

Complete displacement (>100%) and significant shortening (historically >2 cm) are strong absolute or relative indications for operative fixation of midshaft clavicle fractures. Current literature supports fixation for completely displaced fractures to decrease nonunion rates and improve early functional recovery compared to non-operative treatment.

In the native anatomy of the coracoclavicular ligaments, the conoid ligament footprint is located posteromedially on the conoid tubercle, approximately 45 mm from the distal clavicle. The trapezoid ligament footprint is located more anterolaterally, approximately 25 mm from the distal clavicle.