AAOS & ABOS Anatomy MCQs (Set 2): Musculoskeletal, Neuro, & Regional Topography for Board Review

The radiograph shows a fabella, a sesamoid bone that is usually found within the tendon of the lateral head of the gastrocnemius. It can be confused with a loose body on radiographs. It occurs in 18% of patients and is often bilateral. Anderson JE (ed): Grant's Atlas of Anatomy, ed 7. Baltimore, MD, Williams & Wilkins, 1978, pp 4-69.

Talar compression syndrome is also known as os trigonum syndrome or posterior ankle impingement syndrome and occurs in activities involving extreme ankle plantar flexion. It involves pinching of the posterior talus (os trigonum or posterior process of the talus) between the calcaneus and tibia. The flexor hallucis longus also may be impinged. The other structures are not commonly injured in this syndrome. Brodsky AE, Khalil MA: Talar compression syndrome. Am J Sports Med 1986;14:472-476. Wredmark T, Carlstedt CA, Bauer H, Saartok T: Os trigonum syndrome: A clinical entity in ballet dancers. Foot Ankle 1991;11:404-406.

The femoral nerve enters the thigh behind the inguinal ligament, lying on the surface of the iliopsoas muscle lateral to the femoral artery and vein. The nerve divides into numerous muscular and cutaneous branches in the femoral triangle. The first motor branch (sometimes two branches) is to the sartorius. There is a variable branch to the pectineus. Subsequent branches go to the rectus femoris and then the vastus muscles in variable order. The last motor branch is to the articularis genu. The muscular branches can be injured in anterior approaches to the hip, especially the middle window of the ilioinguinal approach. Hollinshead WH: Textbook of Anatomy, ed 3. Hagerstown, MD, Harper and Row, 1974, p 404.

Pacinian corpuscles are nerve endings that provide the perception of pressure.

Ecchymosis on the medial side of the ankle is distributed in the posterior tibialis tendon sheath location, posterior to the medial malleolus, and extending inferiorly to the tendon's attachment on the navicular. MRI is the imaging study of choice to determine the extent of tendon damage. MRI will also help assess the deltoid ligament. Bone scans and CT are helpful in identifying osteochondral fractures and occult fractures; however, these studies are not indicated for this patient. Peroneal tendons are located lateral on the ankle. Arthroscopy of the ankle joint would not be helpful in assessing the posterior tibial tendons. Lutter LD, Mizel MS, Pfeffer GB (eds): Orthopaedic Knowledge Update: Foot and Ankle. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1994, pp 307-317.

The anterior cruciate ligament can be visualized on an axial MRI scan as a low-signal structure lying in the lateral aspect of the intercondylar notch. Visualization in multiple planes increases the accuracy of MRI to view the anterior cruciate ligament. The posterior cruciate ligament and ligament of Wrisberg are located on the medial wall of the notch. The ligamentum mucosum is anterior to the notch, and the popliteus tendon is posterior to the lateral femoral condyle. Resnick D, Kang HS (eds): Internal Derangements of Joints: Emphasis on MR Imaging. Philadelphia, PA, WB Saunders, 1997, pp 675-699.

Cutaneous sensation to the buttock is provided by the superior, middle, and inferior cluneal nerves. The superior cluneal nerves are the lateral branches of the dorsal rami of the upper three lumbar nerves and penetrate deep fascia just proximal to the iliac crest. They pass distally to the skin of the buttock and will be injured if the exposure extends more than 8 cm anterolateral to the posterior superior iliac spine. The lateral femoral cutaneous nerve can be injured in an anterior ilium bone graft. The superior gluteal nerve or even the sciatic nerve can be injured if bone is removed from the sciatic notch or dissection is not kept subperiosteal; however, the rate of injury is far less than cluneal nerve injury. The L5 and S1 nerve roots are anterior and can be injured if the inner table bone is harvested and the dissection is not kept subperiosteal or is too medial; however, the rate of injury still is far less than cluneal nerve injury. Hoppenfeld S, deBoer P: Surgical Exposures in Orthopaedics: The Anatomic Approach. Philadelphia, PA, JB Lippincott, 1984, pp 295-297. Hollinshead WH: Textbook of Anatomy, ed 3. Hagerstown, MD, Harper and Row, 1974, p 379. Last RJ: Anatomy: Regional and Applied, ed 6. London, England, Churchill Livingstone, 1978, p 23.

The radiograph shows widening between the scaphoid and lunate. The normal variance is up to 5 mm. Although several ligaments may be torn, the scapholunate interosseous ligament must be torn for this widening to occur. Cooney WP, Linscheid RL, Dobyns JH: The Wrist: Diagnosis and Operative Treatment. St Louis, MO, Mosby-Year Book, 1998, vol 1, pp 503-506.

The popliteal tendon arises from the posterior aspect of the tibia and courses through the knee joint through the popliteus hiatus of the lateral meniscus before attaching on the lateral femur anterior to the lateral collateral ligament. It is the only tendon in the knee joint that can be viewed directly on arthroscopy. Kimura M, Shirakura K, Hasegawa A, Kobayashi Y, Udagawa E: Anatomy and pathophysiology of the popliteal tendon area in the lateral meniscus: 1. Arthroscopic and anatomical investigation. Arthroscopy 1992;8:419-423.

The motorized shaver is adjacent to the acetabular labrum, which is torn. The femoral head and acetabulum are normal in appearance. Neither the fat pad nor a loose body is identified.

While it is possible to damage any of these structures, unrecognized intraoperative laceration without adequate coagulation of the superior lateral geniculate artery is common. This can result in significant postoperative hemarthrosis and a return to surgery when bleeding cannot be controlled. Cash JD, Hughston JC: Treatment of acute patella dislocation. Am J Sports Med 1988;16:244-249.

The radiographs show posterior instability caused by an absent posterior cruciate ligament. The tibia is significantly displaced posteriorly with respect to the femur. This can be demonstrated with a lateral radiograph obtained with the knee in flexion. The anterior cruciate ligament has been resected but is not responsible for the instability shown.

Nonbloody effusions that are greater than 1 mL are readily detected by MRI. They appear black on T1-weighted images and white on T2-weighted images. A sanguinous effusion is seen as white on T1-weighted images and black on T2-weighted images. Resnick D, Kang HS: Synovial joints, in Resnick D, Kang HS (eds): Internal Derangements of Joints: Emphasis on MR Imaging. Philadelphia, PA, WB Saunders, 1997, pp 49-53.

The projection of the sacroiliac joint on the outer surface of the ilium should be well understood to avoid violation of the joint during bone graft harvesting and to help in insertion of the screw across the joint. The sacroiliac joint has superior and inferior limbs. The average lengths of the superior and inferior limbs are 4.4 cm and 5.6 cm, respectively. The average width of each limb is 2.0 cm. The average distance from the longitudinal axis of the superior limb to the posterior superior iliac spine is 5.5 cm. The average longitudinal axis of the inferior limb is 1.2 cm superior to the inferior margin of the posterior inferior iliac spine. The average angle between the two axes is 93 degrees. Figure 21c most closely shows the projection of the sacroiliac joint on the outer table of the ilium. Waldrop JT, Ebraheim NA, Yeasting RA, Jackson WT: The location of the sacroiliac joint on the outer table of the posterior ilium. J Orthop Trauma 1993;7:510-513.

From birth until the age of 4 years, the primary blood supply to the femoral head is from the medial and lateral circumflex arteries that traverse the femoral neck. After the age of 4 years, the contribution of the lateral femoral circumflex artery, which traverses the anterior portion of the femoral neck, becomes negligible. The posterosuperior and posteroinferior retinacular vessels, branches of the medial femoral circumflex artery, become the primary blood supply to the epiphysis. The contribution of the artery of the ligamentum teres is minimal after the age of 4 years. Hughes LO, Beaty JH: Fractures of the head and neck of the femur in children. J Bone Joint Surg Am 1994;76:283-292.

It is critical for graft isometry and knee stability that the femoral tunnel be placed as far posterior as possible on the lateral femoral condyle. Superiorly, the graft should be at the one o'clock position on the left knee. Resident's ridge is a false posterior shelf that often seems like the extreme posterior cortex. Abnormal tunnel placement results in a variety of complications, including an unstable knee, early graft failure, and joint stiffness. Johnson RJ, Beynnon BD, Nichols CE, Renstrom PA: The treatment of injuries of the anterior cruciate ligament. J Bone Joint Surg Am 1992;74:140-151.

In the Smith-Petersen approach to the hip, dissection is carried out between the tensor fascia lata laterally (supplied by the superior gluteal nerve) and the sartorius and rectus femoris medially (both supplied by the femoral nerve). Crenshaw AH Jr: Surgical techniques and approaches, in Canale ST (ed): Campbell's Operative Orthopaedics, ed 9. St Louis, MO, Mosby-Year Book, 1998, vol 1, pp 82-85.

From proximal to distal, the brachial plexus is divided into roots, trunks, divisions, and cords before forming specific peripheral nerve branches. The structure marked Q is called the posterior cord because it lies posterior to the axially artery at the level of the cords. Its terminal branches are the upper subscapular (V), thoracodorsal (W), lower subscapular (X), axillary (F), and radial (G) nerves. Anderson JE (ed): Grant's Atlas of Anatomy, ed 7. Baltimore, MD, Williams and Wilkins, 1978, pp 6-24.

On T1-weighted images, the posterior cruciate ligament is a low-signal (black) structure that courses from the posterior aspect of the tibia to the medial femoral condyle. The posterior cruciate ligament can appear as arcuate, U-shaped, or kinked. The other structures have similar signal but different anatomic locations. Gross ML, Grover JS, Bassett LW, Seeger LL, Finerman GA: Magnetic resonance imaging of the posterior cruciate ligament: Clinical use to improve diagnostic accuracy. Am J Sports Med 1992;20:732-737.

Chronic anterior inferior tibiofibular ligament sprains can lead to thickening and synovitis that catches or impinges dorsiflexion; patients often note painful clicking with dorsiflexion eversion. The other structures are not affected by this injury. Hopkinson WJ, St Pierre P, Ryan JB, Wheeler JH: Syndesmosis sprains of the ankle. Foot Ankle 1990;10:325-330. Amendola A: Controversies in diagnosis and management of syndesmosis injuries of the ankle. Foot Ankle 1992;13:44-50. Baxter DE: The Foot and Ankle in Sports. St Louis, MO, Mosby-Year Book, 1995, p 30.

The modified Brostrom lateral ankle ligament stabilization procedure uses the remnants of the anterior talofibular and the calcaneofibular ligaments, supplemented by the inferior retinaculum and the transferred talocalcaneal ligament to stabilize the lateral ankle. Chrisman and associates described the use of one half of the peroneus brevis. Watson-Jones and Evans used the entire peroneus brevis. The peroneus longus has been taken by mistake. The plantaris has been used in triligamentous reconstruction. Gould N, Seligson D, Gassman J: Early and late repair of lateral ligament of the ankle. Foot Ankle 1980;1:84-89. Hamilton WG, Thompson FM, Snow SW: The modified Brostrom procedure for lateral ankle instability. Foot Ankle 1993;14:1-7. Chrisman OD, Snook GA: Reconstruction of lateral ligament tears of the ankle: An experimental study and clinical evaluation of seven patients treated by a new modification of the Elmslie procedure. J Bone Joint Surg Am 1969;51:904-912. Evans DL: Recurrent instability of the ankle: My method of surgical treatment. Proc R Soc Med 1953;46:343. Watson-Jones R: Fractures and Joint Injuries, ed 3. Baltimore, MD, Williams and Wilkins, 1946, p 234.

The axillary nerve lies within millimeters of the anterior inferior capsule. The inferior capsule is of varying thickness, and thermal energy used in shortening the ligament can cause damage to the sensory fibers of the axillary nerve. Clinically, this is manifested as a burnt skin sensation in the axillary nerve distribution area. The motor branch of the axillary nerve is usually spared. The suprascapular nerve and the radial nerve are far from the shrinkage zone. The musculocutaneous nerve, frequently at risk with open procedures, lies well anterior. Fanton GS: Arthroscopic electrothermal surgery of the shoulder. Op Tech Sports Med 1998;6:157-160.

The MRI scan shows a ganglion cyst in the region of the spinoglenoid notch. These are difficult to diagnose clinically but are readily apparent on MRI. They usually cause compression of the suprascapular nerve and weakness of the infraspinatus and supraspinatus muscles. Resnick D, Kang HS (eds): Internal Derangements of Joints: Emphasis on MR Imaging. Philadelphia, PA, WB Saunders, 1997, pp 306-309.

Recurrent posterolateral rotatory instability of the elbow is difficult to diagnose. Such instability can be demonstrated only by the lateral pivot-shift test. The cause for this condition is laxity of the ulnar part of the lateral collateral ligament, which allows a transient rotatory subluxation of the ulnohumeral joint and a secondary dislocation of the radiohumeral joint. The annular ligament remains intact, so the radioulnar joint does not dislocate. Treatment consists of surgical reconstruction of the lax ulnar part of the lateral collateral ligament. The anterior band is the most important part of the medial collateral which is lax in valgus instability of the elbow. Morrey BF: Acute and chronic instability of the elbow. J Am Acad Orthop Surg 1996;4:117-128.

The line labeled 6 points to the A2 pulley. This structure is the condensation of the digital flexor tendon sheath corresponding to the proximal aspect of the proximal phalanx. Grayson's ligament is volar to the digital nerve and artery. Cleland's ligament is dorsal to the digital nerve and artery. The sagittal band anchors the extensor tendons over the metacarpophalangeal joints. The triangular ligament connects the lateral bands just proximal to the terminal tendon inserting onto the base of the distal phalanx. Hollinshead WH: Anatomy for Surgeons: The Back and Limbs, ed 3. Philadelphia, PA, Harper and Row, 1982, p 467.