AAOS Orthopedic Anatomy MCQs: Upper Extremity & Hip

Question 1

Figure 42 is a transverse MRI scan of the left shoulder. The arrow points to which of the following structures?

Explanation

The figure shows an axial image of the shoulder immediately inferior to the coracoid process. The subscapularis tendon, which can be traced from the myotendinous junction, is torn and detached from its lesser tuberosity attachment on the humerus. Lateral to the lesser tuberosity, the bicipital groove is empty. The arrow points to the subluxated biceps tendon. Superficial fibers of the subscapularis tendon are contiguous with the biceps retinaculum, which covers the bicipital groove and hold the biceps tendon in place. The vast majority of subscapularis tendon tears result in disruption of the biceps retinaculum with resultant subluxation of the tendon. Resnick D, Kang HS (eds): Internal Derangement of Joints: Emphasis on MR Imaging. Philadelphia, PA, WB Saunders, 1997, pp 308-317.

Question 2

Within the menisci, the majority of the large collagen fiber bundles are oriented in what configuration?

Explanation

The majority of large collagen fibers within the menisci are oriented circumferentially. It is these fibers that develop the hoop stress with compressive loading of the menisci. Most meniscal tears are longitudinal and occur between these circumferential fibers. Mow VC, et al: Structure and function relationships of the menisci of the knee, in Mow VC, Arnoczky SP, Jackson DW (eds): Knee Meniscus: Basic and Clinical Foundations. New York, NY, Raven Press, 1992, pp 37-57.

Question 3

For halo traction, what is the preferred site for anterior pin placement?

Explanation

The safe zone for anterior halo pin insertion is marked laterally by the anterior border of the temporalis muscle (to avoid penetration of this muscle and relative thin cortex of the skull). Medially, the pin should be placed 4.5 cm lateral to the midline to avoid injury to the supraorbital nerve or the frontal sinus. The safe area is marked superiorly by the head equator to avoid cephalad migration of the pin and inferiorly by the supraorbital ridge to prevent displacement or penetration into the orbit.

Question 4

A 12-year-old boy has had progressive pain and flatfeet for the past year. Pain is increased with weight-bearing activities. Examination reveals that subtalar motion is absent. On standing, the patient has obvious hindfoot valgus and loss of the normal arch bilaterally. Plain radiographs are shown in Figures 43a through 43c, and a CT scan is shown in Figure 43d. What is the most likely diagnosis?

Explanation

The axial views show fusion of the talus and calcaneus at the medial facet (talocalcaneal coalition). Peroneal spastic flatfoot is a descriptive term applying to the symptoms of painful flatfoot associated with apparent peroneal spasm and is sometimes caused by tarsal coalition; however, this is not the most appropriate diagnosis for this patient. Flexible flatfoot with a short Achilles tendon often causes symptoms similar to the ones listed above, but subtalar motion should be normal. A diagnosis of calcaneonavicular coalition can be made based on plain oblique views of the foot but is not seen in these views. Posterior tibial tendon dysfunction in the absence of other pathology is uncommon in children. Vincent KA: Tarsal coalition and painful flatfoot. J Am Acad Orthop Surg 1998;6:274-281.

Question 5

When performing ankle arthroscopy through the anterolateral portal, what anatomic structure is at greatest risk?

Explanation

The superficial branch of the peroneal nerve travels subcutaneously anterior to the lateral malleolus at the ankle. It can be easily damaged by deep penetration of the knife blade when making this portal or when passing shavers in and out of the portal. Anesthesia or dysesthesia from laceration or neuroma formation can cause significant postoperative morbidity. The anterior tibialis tendon, anterior tibial artery, and the deep peroneal nerve are located much more anterior and central on the ankle. The sural nerve is posterior lateral to the ankle and is not at risk from this portal. Ferkel RD, Heath DD, Guhl JF: Neurological complications of ankle arthroscopy. Arthroscopy 1996;12:200-208.

Question 6

Figure 44 shows the AP radiograph of the hip of a patient who underwent screw fixation of the acetabulum. Which of the following structures is at least risk for injury during screw placement in the acetabular component?

Explanation

Acetabular screws are inserted to supplement fixation. The acetabular component can be divided into four quadrants. Anatomic studies have shown that screws placed in the anterior superior and anterior inferior quadrants of the cup may injure the external iliac vein and obturator artery, respectively. Posterior superior and posterior inferior placement (in screws greater than 25 mm) may injure the sciatic nerve or the superior gluteal artery. The common iliac artery is proximal to the acetabulum and is at least risk for injury from acetabular screw placement.

Question 7

Figure 45 shows the lateral radiograph of a 19-year-old swimmer who has had back pain for the past 2 months. What is the most likely diagnosis?

Explanation

The patient has a pars interarticularis defect of L5 without apparent listhesis. The other diagnoses are not present. Papanicolaou N, Wilkinson RH, Emmans JB, Treves S, Micheli LJ: Bone scintigraphy and radiography in young athletes with low back pain. Am J Roentgenol 1985;145:1039-1044.

Question 8

Figure 46 shows the AP radiograph of a patient with right shoulder pain. What is the most likely diagnosis?

Explanation

Posttraumatic osteolysis of the distal portion of the clavicle is a condition that can be a complication of acute or repetitive trauma. The distal end of the clavicle is frayed and resorbed. Resorption may occur after weeks or months. The end of the clavicle may reconstitute over a period of months, or the acromioclavicular joint may remain widened. The differential diagnosis for distal clavicular erosion also includes rheumatoid arthritis, hyperparathyroidism, neoplastic destruction, cleidocranial dysplasia, and pyknodysostosis. Acutely, a type 2 acromioclavicular joint injury does not result in erosion or resorption of the clavicle. Periosteal sleeve injuries radiographically mimic acromioclavicular joint dislocation. Rickets occurs only in childhood.

Question 9

The main arterial supply to the humeral head is provided by which of the following arteries?

Explanation

The main arterial supply to the humeral head is provided by the ascending branch of the anterior humeral circumflex artery and its intraosseous continuation, the arcuate artery. There are significant intraosseous anastomoses between the arcuate artery, the posterior humeral circumflex artery through vessels entering the posteromedial aspect of the proximal humerus, the metaphyseal vessels, and the vessels of the greater and lesser tuberosities. Four-part fractures and dissection during exposure affect perfusion of the humeral head. Brooks CH, Revell WJ, Heatley FW: Vascularity of the humeral head after proximal humeral fractures: An anatomical cadaver study. J Bone Joint Surg Br 1993;75:132-136.

Question 10

Figure 47 shows a transverse MRI scan of a patient's left shoulder. The findings reveal which of the following abnormalities?

Explanation

The MRI scan shows a defect in the posterior aspect of the humeral head, commonly referred to as a Hill-Sachs lesion. This is an impaction fracture of the humeral head that occurs during anterior shoulder dislocation. The abnormality on this image is an irregularity of the posterior humeral head; the humeral head otherwise has a homogenous appearance. The coracoid, subscapularis, and posterior labrum are normal. Griffin LY (ed): Orthopaedic Knowledge Update: Sports Medicine. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1994, pp 47-63.

Question 11

An 18-year-old man sustains an injury to the right brachial plexus after falling off his bicycle. Examination reveals no rhomboideus major or minor muscle function. This finding most likely indicates a preganglionic injury to which of the following nerve roots?

Explanation

The rhomboideus major and minor muscles are innervated by the dorsal scapular nerve, which is supplied entirely by the C5 nerve root. The dorsal scapular nerve arises just distal to the dorsal root ganglion of the C5 nerve root. A functioning rhomboid muscle indicates that an injury involving C5 nerve root fibers must be postganglionic or distal to the C5 dorsal root ganglion. Woodburne RT, Crelin ES, Kaplan FS, Dingle RV (eds): The Ciba Collection of Medical Illustrations. Summit, NJ, Ciba-Geigy Corporation, 1987, vol 8, pp 23-28.

Question 12

A 53-year-old man with a history of severe left hip pain has a significant limp that is the result of a 5-cm limb-length discrepancy. An AP radiograph is shown in Figure 48. The underlying etiology is most likely related to a history of

Explanation

Radiographic abnormalities such as coxa magna, coxa breva secondary to growth arrest, and coxa plana and acetabular deformities are associated with healed Legg-Calve-Perthes disease. Femoral heads that were flat yet congruent with the acetabulum are at risk for disabling arthritis in the sixth decade of life in 50% of these untreated patients. As the normal ball-and-socket joint deforms to a flattened cylinder, the hip loses abduction and rotation capability, while retaining flexion and extension potential. If the femoral head is flat and is not concentric with the acetabulum, early severe arthritis occurs. Hinge abduction and anterior impingement are known sequelae of a flat, incongruent femoral head.

Question 13

Where does the median nerve pass in the proximal forearm?

Explanation

The median nerve passes through the pronator teres and deep to the flexor digitorum superficialis. The ulnar artery passes deep to both. Anderson JE (ed): Grant's Atlas of Anatomy, ed 7. Baltimore, MD, Williams and Wilkins, 1978, pp 6-55.

Question 14

The vascularity of the digital flexor tendons is significantly richer in what cross-sectional region?

Explanation

The vascularity of the dorsal portion of the digital flexor tendons is considerably richer than the volar portion. The other regions are not preferentially more vascular. Hunter JM, Scheider LH, Makin EJ (eds): Tendon Surgery in the Hand. St Louis, MO, Mosby, 1987, pp 91-99.

Question 15

Figures 49a and 49b show MRI scans of the shoulder. What is the most likely diagnosis?

Explanation

The supraspinatus tendon shows clear detachment and retraction from its greater tuberosity attachment by the absence of the normal dark subacromial signal extending to the attachment on the greater tuberosity. There is no anterior inferior glenoid labral detachment that usually is seen in a Bankart lesion. The acromioclavicular joint shows no evidence of separation. The humeral head is migrated cranially, indicating a chronic rotator cuff tear. Iannotti JP, Zlatkin MB, Esterhai JL, Kressel HY, Dalinka MK, Spindler KP: Magnetic resonance imaging of the shoulder: Sensitivity, specificity, and predictive value. J Bone Joint Surg Am 1991;73:17-29. Seeger LL, Gold RH, Bassett LW, Ellman H: Shoulder impingement syndrome: MR findings in 53 shoulders. Am J Roentgenol 1988;150:343-347.

Question 16

A fracture of the radial head is surgically exposed using a posterolateral approach to the elbow. Once the radial head is exposed, how should the arm be positioned to best protect the posterior interosseous nerve from injury?

Explanation

As long as the dissection stays proximal to the annular ligament, the posterior interosseous nerve is not at risk for injury. However, to ensure that the nerve is as far removed from the surgical field as possible, the forearm should be placed in pronation. Forearm supination of any degree will bring the nerve toward the surgical field. A neutral position of the forearm or elbow extension with wrist extension will not protect the posterior interosseous nerve. Hoppenfeld S, deBoer P: Surgical Exposures in Orthopaedics: The Anatomic Approach, ed 2. Philadelphia, PA, Lippincott-Raven, 1992, p 100.

Question 17

Figure 50 shows the MRI scan of a 20-year-old female college soccer player with knee pain. What is the most likely diagnosis?

Explanation

The MRI scan shows an acute complete tear of the posterior cruciate ligament. No evidence is seen of a quadriceps tendon rupture, a tibia fracture, or a bone contusion. Beaty JH (ed): Orthopaedic Knowledge Update 6. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 533-557.

Question 18

The tibiofibular overlap used to diagnose syndesmotic diastasis on an AP view is most commonly measured between the

Explanation

The tibiofibular overlap is measured between the medial border of the fibula and the lateral border of the anterior tibial tubercle. Plain radiographic assessment of the distal tibiofibular syndesmosis requires AP and mortise views. The following criteria have been used as the normal limits in adults: a talocrural angle of + or - 83 degrees with up to 5 degrees of normal difference between both sides, a medial clear space of less than 4 mm, a talar tilt of less than 2 mm, a tibiofibular clear space of less than 5 mm, a tibiofibular overlap of greater than or equal to 0 mm, and a talar subluxation that is a subjective assessment of congruity of the tibial articular surface and the talar dome; any incongruity is abnormal. It has been recommended to obtain the first three measurements on the mortise view and the other three on the AP view. Wuest TK: Injuries to the distal lower extremity syndesmosis. J Am Acad Orthop Surg 1997;5:172-181.

Question 19

Figures 51a and 51b show subluxation of the

Explanation

The extensor carpi ulnaris tendon is shown subluxated from its tunnel at the ulnar head; this requires disruption of the tendon's subsheath. Rowland SA: Acute traumatic subluxation of the extensor carpi ulnaris tendon at the wrist. J Hand Surg Am 1986;11:809-811.

Question 20

The so-called high ankle sprain from an external rotation mechanism of injury typically involves injury to which of the following structures?

Explanation

Ankle sprains most commonly involve injury to the lateral collateral ligaments of the ankle (anterior talofibular, posterior talofibular, and calcaneofibular) from an inversion mechanism of injury. A different entity has been more recently described that involves an external rotation mechanism of injury that widens the ankle mortise and disrupts the anterior inferior tibiofibular ligament. Deltoid ligament and extensor retinaculum injuries do occur, although infrequently, and involve eversion and extreme plantar flexion mechanisms, respectively. Last RJ: Anatomy: Regional and Applied, ed 6. London, England, Churchill Livingstone, 1978, p 182. Kaye RA: Stabilization of ankle syndesmosis injuries with a syndesmosis screw. Foot Ankle 1989;9:290-293. Baxter DE: The Foot and Ankle in Sports. St Louis, MO, Mosby-Year Book, 1995, p 30.

Question 21

In the first dorsal compartment of the wrist, what tendon most frequently contains multiple slips?

Explanation

The first extensor compartment of the wrist typically contains a single extensor pollicis brevis tendon and the abductor pollicis longus tendon that nearly always has multiple tendon slips. The extensor pollicis brevis tendon is frequently found to be separated from the slips of the abductor pollicis longus tendon by an intracompartmental septum. During surgery, this septum must be divided to complete the release of the compartment. Jackson WT, Viegas SF, Coon TM, Stimpson KD, Frogameni AD, Simpson JM: Anatomical variations in the first extensor compartment of the wrist: A clinical and anatomical study. J Bone Joint Surg Am 1986;68:923-926.

Question 22

The preferred surgical approach to the elbow of a child with an irreducible type III supracondylar distal humerus fracture and pulseless extremity is through which of the following muscle intervals?

Explanation

In a type III supracondylar distal humerus fracture of the elbow, the brachial artery can become incarcerated, yielding a pulseless extremity. In this situation, closed reduction may not be effective; therefore, open management is often necessary. The preferred surgical approach to the brachial artery and to this fracture is the anterior approach to the cubital fossa. The lacertus fibrosis is incised, and the dissection is carried out between the brachialis (musculocutaneous nerve) and the pronator teres (median nerve), mobilizing the brachial artery. Once the brachial artery is mobilized, the anterior elbow joint capsule may be exposed. The interval between the brachialis and the biceps describes the anterolateral approach to the elbow more commonly used for exposure of the proximal aspect of the posterior interosseous nerve. The dissection interval between the brachioradialis and the pronator teres describes the proximal extent of the anterior approach to the radius. Tubiana R, McCullough CJ, Masquelet AC: An Atlas of Surgical Exposures of the Upper Extremity. Philadelphia, PA, JB Lippincott, 1990, p 115.

Question 23

A 48-year-old man has recurrent right knee pain. Figure 52a shows the sagittal proton density T2-weighted MRI scan, and Figure 52b shows the sagittal T2-weighted MRI scan at the same level. The arrow is pointing to a

Explanation

Meniscal tears have many configurations and locations. The normal medial meniscus has a bow-tie configuration on the two most medial consecutive sagittal views. Toward the center of the joint the anterior and posterior horns have a triangular shape. These images show an abnormal intra-articular low-signal structure located anterior to the intact posterior cruciate ligament. This most likely represents a torn and displaced posterior horn of the medial meniscus, sometimes called "double PCL sign". A popliteal cyst and ligaments of Wrisberg and Humphry are not visible on these figures. Helms CA: MR image of the knee, in Fundamentals of Skeletal Radiology, ed 2. Philadelphia, PA, WB Saunders, 1995, pp 172-191.

Question 24

Figure 53 shows a thoracolumbar specimen as viewed from posterior to anterior following removal of all posterior elements. Which of the following structures does the red string pass under?

Explanation

The string passes under the ligamentum flavum as it runs from the posterior aspect of the vertebra above to the inferior aspect of the vertebra below in the sagittal midline. This is an important structure in diskectomy and in posterior approaches to the thoracolumbar spine and neural elements. It is rarely visualized in its entirety because typical exposures provide only a limited view.

Question 25

A 5-year-old girl sustained a comminuted Salter-Harris type IV fracture of the left distal tibia 2 years ago. The AP radiograph shown in Figure 54a reveals a growth arrest and a 1.4-cm limb-length discrepancy. The ankle is in approximately 20 degrees of varus. Figure 54b shows a coronal reconstruction image of the distal tibial physis, and Figure 54c shows a sagittal reconstruction image of the same area. On the sagittal reconstruction image, the bar extends from the 9-mm mark to the 24-mm mark in 3-mm increments. On the coronal image, the bar extends from the 9-mm mark to the 24-mm mark, also in 3-mm increments. A map of the physeal bar based on these measurements is shown in Figure 54d. Initial treatment should consist of

Explanation

Mapping of a physeal bar from biplane polytomography or CT helps to identify lesions that should be treated surgically and aids in planning the surgical approach and resection. Criteria for surgical excision are at least 2 years of longitudinal growth remaining and involvement of no more than 50% of the physis. Osteotomy is required if angular deformity is greater than 20 degrees. Although this physeal bar is large, it is slightly less than 50% of the total area of the physis. Limb lengthening in this case should be reserved for failure of bar resection. Physiodesis of the opposite distal tibia at this age would result in disproportionate shortening of both tibiae. Carlson WO, Wenger DR: A mapping method to prepare for surgical excision of a partial physeal arrest. J Pediatr Orthop 1984;4:232-238.

Question 26

A 35-year-old male sustains a posterior shoulder dislocation. Post-reduction, he has isolated weakness of the deltoid and teres minor. The injured nerve exits the axilla through a space bounded by which of the following structures?

Explanation

The axillary nerve and posterior humeral circumflex artery pass through the quadrangular space. This space is bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the surgical neck of the humerus.

Question 27

During an anterior intrapelvic (modified Stoppa) approach to the acetabulum, brisk arterial bleeding is encountered near the superior pubic ramus. This bleeding most likely originates from an anomalous anastomosis between the obturator vessels and which of the following?

Explanation

The "corona mortis" is an anatomical variant vascular connection between the obturator system and the external iliac or inferior epigastric system. It is located on the posterior aspect of the superior pubic ramus and is at high risk during anterior intrapelvic approaches.

Question 28

When placing screws into the acetabulum during total hip arthroplasty, the "safe zone" that provides optimal bone stock while minimizing the risk of neurovascular injury is located in which quadrant?

Explanation

The posterior-superior quadrant is considered the safe zone for acetabular screw placement. It offers excellent bone stock and minimizes the risk of penetrating injury to the external iliac vessels and the obturator nerve.

Question 29

The rotator interval of the shoulder is a distinct anatomical space containing the long head of the biceps and the coracohumeral ligament. Which of the following structures forms the superior border of this interval?

Explanation

The rotator interval is bounded superiorly by the anterior margin of the supraspinatus tendon. It is bounded inferiorly by the superior margin of the subscapularis tendon and medially by the base of the coracoid process.

Question 30

In a 6-year-old child, the predominant blood supply to the proximal femoral epiphysis is derived from branches of which of the following vessels?

Explanation

The medial femoral circumflex artery, specifically its lateral epiphyseal branches, is the predominant blood supply to the femoral head in pediatric and adult populations. The contribution from the artery of the ligamentum teres is variable and relatively insignificant.

Question 31

During the classic ilioinguinal approach to the pelvis, the middle window is accessed to treat anterior column fractures. Which structures define the medial and lateral borders of this middle window?

Explanation

The middle window of the ilioinguinal approach is accessed between the iliopsoas/femoral nerve (bound by the iliopectineal fascia) laterally and the external iliac vessels medially.

Question 32

The ulnar nerve is compressed at the elbow in a 45-year-old patient. During surgical release of the cubital tunnel, the surgeon must divide the fascial roof of the tunnel. What structure forms this roof?

Explanation

The roof of the cubital tunnel is formed by Osborne's ligament, a fascial band connecting the two heads of the flexor carpi ulnaris. The floor is formed by the medial collateral ligament and joint capsule.

Question 33

A surgeon is performing a posterior approach to the humerus. To identify the radial nerve, she explores the triangular interval. This interval is bounded by the long head of the triceps, the teres major, and which of the following structures?

Explanation

The triangular interval is bounded superiorly by the teres major, medially by the long head of the triceps, and laterally by the lateral head of the triceps or humeral shaft. It contains the radial nerve and the profunda brachii artery.

Question 34

During a posterior approach to the hip, the short external rotators are tenotomized. Which of the following muscles inserts on the medial aspect of the greater trochanter, immediately superior to the superior gemellus?

Explanation

The piriformis tendon inserts on the superior/medial aspect of the greater trochanter, immediately superior to the conjoined tendon of the superior gemellus, obturator internus, and inferior gemellus.

Question 35

A rock climber presents with a "bowstringing" deformity of the right ring finger following a sudden pop. Rupture of which pair of flexor tendon pulleys is most commonly responsible for clinically significant bowstringing?

Explanation

The A2 and A4 pulleys are the most critical biomechanical components of the flexor pulley system. Rupture of these two pulleys results in significant tendon bowstringing and loss of mechanical efficiency.

Question 36

A cyclist presents with numbness in the little finger and weakness in finger abduction. Entrapment is suspected in Guyon's canal. Which structures form the floor of Guyon's canal?

Explanation

The floor of Guyon's canal is formed by the transverse carpal ligament and the pisohamate ligament. The roof is formed by the volar carpal ligament and palmaris brevis.

Question 37

A volleyball player presents with isolated weakness of external rotation of the shoulder. Atrophy is noted only in the infraspinatus fossa. The suprascapular nerve is likely entrapped at which anatomical location?

Explanation

Entrapment of the suprascapular nerve at the spinoglenoid notch affects only the infraspinatus muscle. Entrapment at the more proximal suprascapular notch would affect both the supraspinatus and infraspinatus muscles.

Question 38

When planning repair of a torn abductor tendon of the hip, the surgeon must identify the distinct insertion footprints. The gluteus medius inserts primarily on which aspect of the greater trochanter?

Explanation

The gluteus medius inserts broadly on the lateral and superoposterior facets of the greater trochanter. The gluteus minimus has a more anterior insertion on the anterior facet.

Question 39

A patient sustains a displaced scaphoid waist fracture. The high risk of proximal pole avascular necrosis is due to the retrograde blood supply originating from branches of which artery?

Explanation

The major blood supply to the scaphoid is derived from dorsal branches of the radial artery. These vessels enter the scaphoid at its distal pole and flow in a retrograde direction to supply the proximal pole.

Question 40

During a volar approach to the proximal radius (Henry approach), the radial nerve is at risk when exposing the proximal third of the shaft. To safely mobilize the supinator muscle and protect the posterior interosseous nerve, the forearm should be placed in what position?

Explanation

Placing the forearm in full supination displaces the posterior interosseous nerve laterally, away from the surgical field during the volar (Henry) approach to the proximal radius.

Question 41

Following a severe pelvic ring fracture, a patient experiences loss of perineal sensation and sphincter dysfunction. The injured nerve normally exits the pelvis through the greater sciatic foramen and re-enters the perineum through which structure?

Explanation

The pudendal nerve exits the pelvis through the greater sciatic foramen to pass posterior to the sacrospinous ligament. It then re-enters the perineum via the lesser sciatic foramen to supply the perineum and external sphincters.

Question 42

A patient exhibits an inability to make an "OK" sign, demonstrating weakness in flexing the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Which muscle is typically NOT innervated by the affected nerve?

Explanation

The anterior interosseous nerve (AIN) innervates the flexor pollicis longus, pronator quadratus, and the radial half of the flexor digitorum profundus. The flexor digitorum superficialis is innervated by the main branch of the median nerve, not the AIN.

Question 43

A patient suffers a traction injury to the upper trunk of the brachial plexus (Erb's palsy). Which of the following nerves branches directly from the roots of the brachial plexus and may remain intact depending on the exact level of the lesion?

Explanation

The dorsal scapular nerve (C5) and the long thoracic nerve (C5-C7) arise directly from the roots of the brachial plexus. The suprascapular nerve branches more distally from the upper trunk.

Question 44

The triangular fibrocartilage complex (TFCC) is the primary stabilizer of the distal radioulnar joint. Which portion of the articular disc has the best potential for healing after repair due to its rich vascularity?

Explanation

The peripheral 10-20% of the TFCC, specifically its ulnar attachment, is well-vascularized by branches of the ulnar artery and anterior interosseous artery. This periphery has an excellent capacity to heal after surgical repair, whereas the central portion is avascular.

Question 45

A traumatic laceration to the mid-palm involves the superficial palmar arch. This structure is formed primarily by the continuation of the ulnar artery and is typically completed by a branch from which of the following?

Explanation

The superficial palmar arch is formed predominantly by the distal continuation of the ulnar artery. It is usually completed radially by joining the superficial palmar branch of the radial artery.

Question 46

A 35-year-old man undergoes a deltopectoral approach for open reduction and internal fixation of a proximal humerus fracture. During the procedure, a vessel passing through the quadrangular space with the axillary nerve is inadvertently injured. Which of the following arteries is most likely affected?

Explanation

The quadrangular space transmits the axillary nerve and the posterior circumflex humeral artery. The boundaries are the teres minor (superior), teres major (inferior), long head of triceps (medial), and humerus (lateral).

Question 47

During an anterior (Smith-Petersen) approach to the hip for an open reduction of a developmental dysplasia of the hip, the surgeon utilizes a true internervous plane. This superficial plane is developed between muscles innervated by which two nerves?

Explanation

The superficial internervous plane for the Smith-Petersen approach is between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The deep plane lies between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 48

A 28-year-old carpenter suffers a deep laceration to the base of his thenar eminence. He subsequently presents with an inability to perform palmar abduction of the thumb, but thumb interphalangeal joint flexion is preserved. Which of the following muscles is paralyzed due to this isolated nerve injury?

Explanation

The recurrent motor branch of the median nerve supplies the thenar muscles: abductor pollicis brevis, opponens pollicis, and the superficial head of the flexor pollicis brevis. Palmar abduction is the primary function of the abductor pollicis brevis.

Question 49

During an ilioinguinal approach to the pelvis for an anterior column acetabular fracture, massive hemorrhage occurs from a torn vessel lying over the superior pubic ramus, approximately 5 cm from the symphysis. This bleeding is most likely originating from the 'corona mortis', which is an anastomosis between the external iliac system and which of the following?

Explanation

The corona mortis is a critical vascular anastomosis between the external iliac system (usually the inferior epigastric artery/vein) and the internal iliac system (obturator artery/vein). It crosses the superior pubic ramus and is highly vulnerable during anterior pelvic ring surgery.

Question 50

An orthopaedic surgeon evaluates an MRI of the shoulder for a suspected biceps pathology. The radiologist notes an abnormality within the rotator interval. Which of the following structures is considered a normal anatomic component or boundary of this specific space?

Explanation

The rotator interval is a triangular anatomic space defined by the subscapularis anteriorly, supraspinatus superiorly, and the base of the coracoid medially. Its contents include the long head of the biceps tendon, the superior glenohumeral ligament, and the coracohumeral ligament.

Question 51

A patient develops weakness in thumb and finger extension following open reduction and internal fixation of a proximal third radius fracture utilizing an anterior (Henry) approach. Sensation on the dorsum of the hand remains fully intact. The injured nerve typically enters the forearm and passes between the two heads of which muscle?

Explanation

The posterior interosseous nerve (PIN) is a pure motor branch of the radial nerve that can be injured during the Henry approach to the proximal radius. It passes into the extensor compartment between the superficial and deep heads of the supinator muscle at the Arcade of Frohse.

Question 52

A 45-year-old woman complains of painful numbness and paresthesias over the anterolateral aspect of her thigh three months after an anterior iliac crest bone graft harvest. The nerve most likely injured typically exits the pelvis in which anatomical location relative to the anterior superior iliac spine (ASIS)?

Explanation

The lateral femoral cutaneous nerve (LFCN) provides sensory innervation to the anterolateral thigh and is at risk during anterior iliac crest grafting. It typically courses medial and inferior to the ASIS, passing under or through the inguinal ligament.

Question 53

The unique vascular anatomy of the lunate predisposes it to Kienböck's disease. In the majority of the population, what is the anatomical pattern of the extraosseous arterial supply to the lunate?

Explanation

Approximately 80% of lunates have consistent dorsal and volar arterial networks that enter the bone and anastomose intraosseously in a Y-, I-, or X-pattern. The remaining 20% have only a single volar supply, placing them at higher risk for avascular necrosis.

Question 54

A patient with neglected suppurative tenosynovitis of the small finger presents with a 'horseshoe abscess' spreading into the thumb. The purulence has tracked proximally into the deep fascial space of the distal volar forearm. This space is known as:

Explanation

Parona's space is the deep fascial space in the distal volar forearm, located between the pronator quadratus fascia and the flexor digitorum profundus tendons. Infections from the radial and ulnar bursae can communicate proximally into this space.

Question 55

During a total hip arthroplasty using a posterior approach, the surgeon carefully identifies the sciatic nerve. In roughly 10-15% of the population, a common anatomic variation exists concerning the relationship of the sciatic nerve to the piriformis muscle. Which of the following describes this most frequent variant?

Explanation

The standard anatomy (85%) has the undivided sciatic nerve exiting below the piriformis. The most common variant (10-15%) involves a split nerve where the common peroneal division pierces the piriformis while the tibial division passes inferiorly.

Question 56

A 52-year-old woman presents with isolated medial scapular winging that is significantly accentuated when she pushes against a wall with her arms forward. She has a history of an axillary lymph node dissection. Injury to which of the following nerves is the primary cause of her deficit?

Explanation

Medial scapular winging is classically caused by serratus anterior muscle paralysis due to long thoracic nerve injury. Lateral winging is typically caused by trapezius paralysis secondary to spinal accessory nerve injury.

Question 57

A 21-year-old collegiate baseball pitcher undergoes an ulnar collateral ligament (UCL) reconstruction. The primary medial restraint to valgus stress of the elbow, which is targeted for reconstruction, has its distal insertion on which of the following anatomic structures?

Explanation

The anterior bundle of the UCL is the primary restraint to valgus stress at the elbow from 30 to 120 degrees of flexion. It originates on the anteroinferior medial epicondyle and inserts on the sublime tubercle of the coronoid process of the ulna.

Question 58

When evaluating pediatric hip vascularity to understand the risk of avascular necrosis in Legg-Calvé-Perthes disease, which of the following vessels provides the predominant blood supply to the capital femoral epiphysis in a 6-year-old child?

Explanation

Between ages 3 and 10, the growth plate acts as a barrier to metaphyseal vessels, and the artery of the ligamentum teres is not yet a significant contributor. The primary blood supply to the capital femoral epiphysis is via the lateral epiphyseal branches of the medial femoral circumflex artery (MFCA).

Question 59

A professional rock climber presents with a 'bowstringing' deformity of his middle finger flexor tendons after feeling a loud pop during a difficult hold. To maintain proper flexor tendon biomechanics and prevent bowstringing, which two annular pulleys are considered the most critical to preserve or reconstruct?

Explanation

The A2 (proximal phalanx) and A4 (middle phalanx) pulleys are the most biomechanically important annular pulleys in the flexor tendon sheath. Their disruption leads to clinically significant bowstringing and loss of flexor excursion.

Question 60

During acetabular component fixation in a total hip arthroplasty, the surgeon defines the safe zones based on Wasielewski's quadrant system, using a line from the ASIS through the center of the acetabulum and a perpendicular line at the center. Placing a screw in the anterosuperior quadrant places which structure at highest risk?

Explanation

In the quadrant system for acetabular screw placement, the anterosuperior quadrant contains the external iliac vessels. The anteroinferior contains the obturator neurovascular bundle, while the posterosuperior and posteroinferior are considered the safe zones.

Question 61

During a dorsal surgical approach to the wrist for scaphoid fixation, Lister's tubercle is identified as a critical bony landmark. The tendon that uses Lister's tubercle as a mechanical pulley is found in which extensor compartment of the wrist?

Explanation

The extensor pollicis longus (EPL) tendon resides alone in the third extensor compartment. It hooks around the ulnar aspect of Lister's tubercle (dorsal tubercle of the radius), which acts as a pulley to change its line of pull toward the thumb.

Question 62

A 31-year-old elite volleyball attacker presents with isolated weakness in shoulder external rotation. Abduction strength is normal, and there is visible atrophy of the infraspinatus without supraspinatus involvement. An MRI reveals a paralabral cyst compressing a nerve. At which precise anatomical location is the compression occurring?

Explanation

The suprascapular nerve innervates the supraspinatus before passing through the spinoglenoid notch to innervate the infraspinatus. A cyst at the spinoglenoid notch selectively compresses the distal branches, resulting in isolated infraspinatus atrophy and external rotation weakness.

Question 63

A trauma surgeon is performing posterior pelvic ring fixation for a vertically unstable sacral fracture. During dissection near the greater sciatic notch, the surgeon must be mindful of the ligament that defines the inferior border of the greater sciatic foramen. Which ligament is this?

Explanation

The sacrospinous ligament runs from the sacrum to the ischial spine, dividing the greater and lesser sciatic notches into the greater and lesser sciatic foramina. It serves as the inferior boundary of the greater sciatic foramen.

Question 64

A 48-year-old mechanic undergoes an in situ decompression of the ulnar nerve for advanced cubital tunnel syndrome. During the release, the primary compressive fascial structure forming the roof of the cubital tunnel between the medial epicondyle and the olecranon must be divided. This structure is known as:

Explanation

Osborne's ligament (or the cubital tunnel retinaculum) forms the roof of the cubital tunnel, bridging the two heads of the flexor carpi ulnaris from the medial epicondyle to the olecranon. Division of this ligament is the key step in in situ ulnar nerve decompression.

Question 65

A patient sustains a highly comminuted rami fracture with extension into the obturator canal. On physical examination, there is weakness in hip adduction and an area of numbness over the medial aspect of the middle third of the thigh. The injured nerve directly innervates which of the following muscles?

Explanation

The obturator nerve passes through the obturator canal and innervates the medial compartment of the thigh, which includes the adductor longus, brevis, magnus, obturator externus, and gracilis. It also provides sensation to the medial aspect of the middle thigh.

Question 66

An injury to the posterior cord of the brachial plexus would result in weakness of all of the following muscles EXCEPT:

Explanation

The posterior cord innervates the deltoid, latissimus dorsi, subscapularis, and the extensors of the arm and forearm. The pectoralis major is innervated by the medial and lateral pectoral nerves, which arise from the medial and lateral cords respectively.

Question 67

During an anterior (deltopectoral) approach to the shoulder, the cephalic vein is identified as a landmark. What is the internervous plane utilized in this surgical approach?

Explanation

The deltopectoral approach utilizes the internervous plane between the deltoid (axillary nerve) and the pectoralis major (medial and lateral pectoral nerves). The cephalic vein typically lies within this interval and is usually retracted laterally.

Question 68

In repairing a posterior column acetabular fracture via a Kocher-Langenbeck approach, the surgeon must identify and protect the primary blood supply to the adult femoral head. Which of the following arteries provides this primary supply?

Explanation

The deep branch of the medial femoral circumflex artery (MFCA) is the primary blood supply to the adult femoral head. It courses anterior to the superior gemellus and obturator internus, making it vulnerable during posterior approaches.

Question 69

A 25-year-old bodybuilder presents with posterior shoulder pain and deltoid weakness. MRI reveals a paralabral cyst compressing a structure within the quadrangular space. Which of the following defines the inferior border of this space?

Explanation

The quadrangular space contains the axillary nerve and posterior circumflex humeral artery. Its borders are the teres minor (superior), teres major (inferior), long head of the triceps (medial), and surgical neck of the humerus (lateral).

Question 70

An orthopedic trauma surgeon is performing an anterior intrapelvic (Stoppa) approach. To avoid life-threatening hemorrhage, caution is taken around the corona mortis. This structure represents an anastomosis between which two vascular systems?

Explanation

The corona mortis is a vascular anastomosis between the obturator and the external iliac or inferior epigastric vessels. It crosses the superior pubic ramus and is at high risk of injury during anterior intrapelvic exposures.

Question 71

During open reduction and internal fixation of a middle-third humeral shaft fracture via a posterior approach, the radial nerve is identified. At what approximate distance proximal to the lateral epicondyle does the radial nerve pierce the lateral intermuscular septum?

Explanation

The radial nerve runs in the spiral groove and pieces the lateral intermuscular septum to enter the anterior compartment approximately 10 cm proximal to the lateral epicondyle. This is a critical landmark during humeral fracture fixation.

Question 72

A 60-year-old woman exhibits a prominent Trendelenburg gait post-total hip arthroplasty via a direct lateral (Hardinge) approach. Injury to which nerve is the most likely cause, and what are its contributing nerve roots?

Explanation

The superior gluteal nerve (L4, L5, S1) innervates the gluteus medius, gluteus minimus, and tensor fasciae latae. Injury during a direct lateral approach leads to abductor weakness and a positive Trendelenburg sign.

Question 73

A 45-year-old cyclist complains of little finger numbness and hand weakness. Examination localizes compression to Guyon's canal. Which structure forms the floor of this anatomical space?

Explanation

The floor of Guyon's canal is primarily formed by the transverse carpal ligament (flexor retinaculum) and the pisohamate ligament. The roof is formed by the volar carpal ligament (palmar carpal ligament).

Question 74

During a posterior approach to the shoulder, the quadrilateral space is identified to locate the axillary nerve and posterior circumflex humeral artery. Which muscle serves as the inferior border of this anatomical space?

Explanation

The quadrilateral space is bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the surgical neck of the humerus.

Question 75

A patient undergoes surgical fixation of an anterior column acetabular fracture via the ilioinguinal approach. Significant hemorrhage is encountered when dissecting over the superior pubic ramus. Which anatomical variant is most likely injured?

Explanation

The corona mortis is a venous or arterial anastomosis between the external iliac and obturator systems. It is located approximately 5 to 6 cm from the symphysis pubis on the posterior aspect of the superior pubic ramus.

Question 76

A 35-year-old male presents with posterolateral rotatory instability (PLRI) of the elbow following a dislocation. Which of the following describes the origin and insertion of the primary ligamentous restraint involved in this condition?

Explanation

The lateral ulnar collateral ligament (LUCL) is the primary restraint to PLRI of the elbow. It originates on the lateral epicondyle and inserts distally on the supinator crest of the ulna.

Question 77

To preserve the primary blood supply to the adult femoral head during a posterior approach to the hip, which anatomical structure protects the main arterial contribution before it enters the joint capsule?

Explanation

The medial femoral circumflex artery (MFCA) provides the primary blood supply to the adult femoral head. The deep branch of the MFCA runs anterior to the quadratus femoris and is protected by the obturator externus muscle.

Question 78

A patient presents with numbness in the radial 3.5 digits and aching pain in the proximal forearm. Sensation over the thenar eminence is decreased. Electrodiagnostic studies suggest a proximal median nerve compression. Which of the following structures is the most likely site of entrapment?

Explanation

Sensory loss over the thenar eminence indicates compression proximal to the carpal tunnel, as the palmar cutaneous branch arises proximal to the transverse carpal ligament. Entrapment sites for pronator syndrome include the Ligament of Struthers, lacertus fibrosus, and the two heads of the pronator teres.

Question 79

During a surgical approach to the greater sciatic notch, the surgeon notes an anatomical variation where a portion of the sciatic nerve pierces the piriformis muscle. Which specific nerve division is most commonly involved in this variant?

Explanation

In approximately 10% of the population, the sciatic nerve separates early, with the common peroneal division piercing through the piriformis muscle. The tibial division typically exits below the piriformis.

Question 80

When repairing a flexor tendon laceration in Zone II of the hand, preserving the intricate pulley system is critical. Which two pulleys are considered the most biomechanically essential to prevent bowstringing of the flexor tendons?

Explanation

The A2 and A4 pulleys are the most critical for maintaining the mechanical advantage of the flexor tendons and preventing bowstringing. The A2 pulley is located over the proximal phalanx, and the A4 pulley is located over the middle phalanx.

Question 81

The surgical safe zone for the placement of a lateral portal in hip arthroscopy or pins in the proximal femur is determined by the course of the superior gluteal nerve. On average, how far proximal to the tip of the greater trochanter does the superior gluteal nerve course?

Explanation

The superior gluteal nerve courses approximately 3 to 5 cm proximal to the tip of the greater trochanter. Dissection or pin placement proximal to this zone risks denervation of the gluteus medius, gluteus minimus, and tensor fasciae latae.

Question 82

In a massive rotator cuff tear involving the subscapularis and supraspinatus, the biceps tendon is noted to be unstable. Which anatomical structures form the medial and lateral borders of the rotator interval that typically stabilize the long head of the biceps?

Explanation

The rotator interval is bounded superiorly/laterally by the supraspinatus and inferiorly/medially by the subscapularis. It contains the coracohumeral ligament, superior glenohumeral ligament, and the long head of the biceps tendon.

Question 83

A patient with an Essex-Lopresti injury has longitudinal radioulnar dissociation. Which component of the interosseous membrane (IOM) of the forearm provides the greatest longitudinal stability and must be considered during reconstruction?

Explanation

The central band of the interosseous membrane is the thickest and most crucial component for longitudinal stability of the forearm. It originates proximally on the radius and courses distally and ulnarly to insert on the ulna.

Question 84

A patient presents with winging of the scapula characterized by medial translation of the inferior pole during active wall push-ups. Which nerve is most likely injured, and what is its segmental origin?

Explanation

Medial winging of the scapula is caused by paralysis of the serratus anterior, which is innervated by the long thoracic nerve (roots C5, C6, C7). Lateral winging is typically associated with spinal accessory nerve (trapezius) injury.

Question 85

A 65-year-old female experiences isolated rupture of the flexor pollicis longus (FPL) tendon following a volar plate fixation for a distal radius fracture. Which anatomical landmark on the distal radius is most commonly associated with FPL tendon attrition in this setting?

Explanation

The "watershed line" is a critical volar bony landmark on the distal radius. Placement of a volar plate distal to this line significantly increases the risk of flexor tendon irritation and subsequent rupture, most commonly the FPL.

Question 86

The pudendal nerve is at risk during certain pelvic fracture fixations and ischial spine procedures. Through which anatomical sequence does the pudendal nerve course to reach the perineum?

Explanation

The pudendal nerve exits the pelvis through the greater sciatic foramen inferior to the piriformis muscle. It then crosses posterior to the sacrospinous ligament and re-enters the perineum via the lesser sciatic foramen to enter Alcock's canal.

Question 87

A 28-year-old overhead athlete presents with poorly localized posterior shoulder pain and paresthesias over the lateral deltoid. MRI shows isolated atrophy of the teres minor muscle. Which of the following anatomic boundaries define the space where the affected nerve is most likely compressed?

Explanation

The patient has quadrilateral space syndrome, compressing the axillary nerve. The quadrilateral space is bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the surgical neck of the humerus.

Question 88

During an anterior intrapelvic (modified Stoppa) approach to fix an acetabular fracture, brisk arterial bleeding is encountered just posterior to the superior pubic ramus. This vessel, known as the corona mortis, typically represents an anastomosis between the obturator vessels and which of the following?

Explanation

The corona mortis is an anastomotic vascular connection between the obturator system (internal iliac) and the external iliac or inferior epigastric systems. It is located on the posterior aspect of the superior pubic ramus and must be carefully ligated during anterior intrapelvic approaches.

Question 89

A 45-year-old mechanic complains of lateral forearm pain and weakness in extending the fingers at the metacarpophalangeal joints, but examination reveals normal wrist extension with radial deviation. Which of the following anatomic structures is the most common site of compression for the affected nerve?

Explanation

The patient has Posterior Interosseous Nerve (PIN) syndrome, causing finger extension weakness with preserved radial wrist extension (ECRL is supplied by the radial nerve proper). The most common site of PIN compression is the Arcade of Frohse, the proximal fibrous edge of the supinator muscle.

Question 90

A patient presents with a severe Trendelenburg gait following a direct lateral (Hardinge) approach for a total hip arthroplasty. To avoid iatrogenic denervation of the anterior portion of the abductor musculature, the proximal split of the gluteus medius should be limited to what maximum distance proximal to the tip of the greater trochanter?

Explanation

The superior gluteal nerve supplies the gluteus medius, minimus, and tensor fasciae latae. To prevent denervation during a direct lateral approach, the split in the gluteus medius should not extend more than 5 cm proximal to the tip of the greater trochanter.

Question 91

A 22-year-old man sustains a scaphoid waist fracture. The high risk of avascular necrosis of the proximal pole is primarily due to its tenuous retrograde blood supply. The predominant arterial supply to the proximal pole of the scaphoid enters through which of the following areas?

Explanation

The scaphoid relies on a retrograde blood supply, with 70% to 80% of the blood entering via the dorsal ridge from branches of the radial artery. Fractures at the waist interrupt this blood flow, placing the proximal pole at high risk for avascular necrosis.

Question 92

During a posterior approach to the hip for arthroplasty, extreme external rotation of the femur prior to capsulotomy can put the deep branch of the medial circumflex femoral artery (MCFA) at risk. This critical vessel, which provides the main blood supply to the femoral head, courses between which two muscles prior to piercing the capsule?

Explanation

The deep branch of the medial circumflex femoral artery (MCFA) courses posterior to the obturator externus and passes between the inferior border of the inferior gemellus and the superior border of the quadratus femoris. Protecting this interval is essential to preserve the blood supply to the femoral head.

Question 93

A 30-year-old volleyball player complains of vague posterior shoulder pain and isolated weakness in external rotation. Examination reveals profound atrophy of the infraspinatus but normal bulk and strength of the supraspinatus. Entrapment of the involved nerve is most likely caused by a paralabral cyst located at which of the following anatomic structures?

Explanation

The suprascapular nerve innervates the supraspinatus and then passes through the spinoglenoid notch to innervate the infraspinatus. Compression at the spinoglenoid notch (often by a paralabral cyst) causes isolated infraspinatus weakness, whereas compression at the suprascapular notch affects both muscles.

Orthopedic Board Review Set 675: 100 MCQs for ABOS, OITE, FRCS – Hip Focus

AAOS Orthopedic Anatomy MCQs (Set 4): Upper Extremity & Pelvic Hip Review

Key Takeaway

AAOS Orthopedic Anatomy MCQs (Set 4): Upper Extremity & Pelvic Hip Review

Chapter Index