AAOS Anatomy Board Review (Set 2): Upper, Lower Extremity & Spine MCQs | 2008 Exam Prep

The MRI scans show a paralabral cyst, which is most commonly associated with labral tears. Compression of the suprascapular nerve results in weakness of the supraspinatus and/or infraspinatus depending on the level of compression. Piatt BE, Hawkins RJ, Fritz RC, et al: Clinical evaluation and treatment of spinoglenoid notch ganglion cysts. J Shoulder Elbow Surg 2002;11:600-604.

Knowledge of intermuscular and internervous planes allows safe exposures throughout the body. The posterior (Thompson) approach to the proximal forearm uses the interval between the extensor carpi radialis brevis and extensor digitorum communis. The anterior (Henry) approach to the proximal forearm uses the interval between the brachioradialis and the flexor carpi radialis. Spinner M: Injuries to the Major Branches of Peripheral Nerves of the Forearm, ed 2. Philadelphia, PA, WB Saunders, 1978, pp 66-77.

Popliteal artery injury during total knee arthroplasty is relatively rare. Knee flexion, the position that occurs during most of the arthroplasty procedure, allows the popliteal vessels to fall posteriorly, further away from harm. Anatomically, the popliteal artery lies anterior to the popliteal vein and 9 mm posterior to the posterior aspect of the tibial plateau in 90 degrees of flexion. Barrack RL, Booth RE Jr, Lonner JH, et al (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, p 151.

The radiograph reveals diffuse osteopenia and areas in the proximal femora that are moth-eaten in appearance. The extent of the marrow-replacing process is evident on the MRI scans, which reveal signal abnormality throughout the entire pelvis and both proximal femora. This represents a marrow-packing process, of which multiple myeloma is the best choice. This diagnosis is also supported by the anemia noted on the patient's history. Metastatic carcinoma and lymphoma also may have a similar presentation.

All of the muscles are innervated by the peroneal nerve with the exception of the tibialis posterior which is innervated by the tibial nerve. Tibialis posterior function is best tested with resistance to plantar flexion and inversion.

The structure shown is the exiting nerve root at the L3-4 disk, which is the right L3 root.

Proximal row carpectomy is a salvage wrist procedure that yields a surprisingly stable construct. This has been attributed to two factors: 1) the congruency of the head of the capitate in the lunate fossa (this articulation is less congruent than the native lunate/lunate fossa relationship, but surprisingly stable), and 2) preservation of the radioscaphocapitate ligament, the most radial of the palmar extrinsic ligaments, which prevents ulnar subluxation after proximal row carpectomy.

The radiographs reveal a predominantly lytic, destructive lesion of the distal femur, although there is a hint of some blastic change as well. The lesion has violated the cortex, and there is mineralization outside the cortex laterally. The lateral radiograph suggests a soft-tissue density. These aggressive changes on radiographs in this age group are strongly suggestive of osteosarcoma. Sanders TG, Parsons TW: Radiographic imaging of musculoskeletal neoplasia. Cancer Control 2001;8:221-231.

The ligaments shown are the components of the lateral collateral ligament complex, and the structure indicated by the letter "A" is the radial collateral ligament. The lateral ulnar collateral ligament is the structure indicated by the letter "C" and the annular ligament is indicated by the letter "B." The transverse ligament is a component of the medial collateral ligament complex. Morrey BF: Anatomy of the elbow joint, in Morrey BF (ed): The Elbow and Its Disorders. Philadelphia, PA, WB Saunders, 1993, p 30.

The MRI scans show a displaced bucket-handle medial meniscus tear that can be visualized on coronal, sagittal, and axial views. The sagittal view shows the typical "double posterior cruciate ligament sign," in which the low-signal bucket-handle fragment parallels the normal low-signal posterior cruciate ligament. The coronal and axial images both show the displaced medial meniscus in the notch. Sanders TG, Miller MD: A systematic approach to magnetic resonance imaging interpretation of sports medicine injuries of the knee. Am J Sports Med 2005;33:131-148.

The radiograph reveals bilateral severe acetabular protrusio. The bone scan and history confirm involvement of multiple joints, including the knees and the hindfoot. Although the first four choices can all cause the acetabular protrusio, the associated multiple joint involvement suggests the diagnosis of rheumatoid arthritis. Arthrokatadysis, or primary protrusio acetabuli, is often associated with osteomalacia but not other joint disease. Developmental dysplasia is a common cause of bilateral hip pathology but does not have acetabular protrusio. Resnick D: Diagnosis of Bone and Joint Disorders, ed 3. Philadelphia, PA, WB Saunders, 1995, pp 956-957. Wheeless' Textbook of Orthopaedics: Acetabular Protrusio. www.wheelessonline.com/ortho/acetabular_protrusio

At the level of tibial bone resection in total knee arthroplasty, the common peroneal nerve lies superficial to the lateral head of the gastrocnemius and is therefore protected by this structure. In an MRI study of 60 knees, the mean distance from the bony posterolateral corner of the tibia to the nerve was 1.49 cm, with no distance less than 0.9 cm. The distance from the bone to nerve was greater in larger legs. Clarke HD, Schwartz JB, Math KR, et al: Anatomic risk of peroneal nerve injury with the "pie crust" technique for valgus release in total knee arthroplasty. J Arthroplasty 2004;19:40-44.

The images show a complex, lobular lesion of the thigh that has signal characteristics that follow fat. The size of the lesion, the areas of stranding within the mass, along with mild uptake on the gadolinium sequences and the mild edema within the lesion on the T2-weighted image make liposarcoma the most likely diagnosis and simple intramuscular lipoma far less likely. All other diagnoses listed would not follow fat characteristics shown on the MRI sequences.

The arrows in the figure show the deep branch of the ulnar nerve (more radial) and the superficial branch of the ulnar nerve within Guyon's canal. Guyon's canal is approximately 4 cm long beginning at the proximal extent of the transverse carpal ligament and ends at the aponeurotic arch of the hypothenar muscles. Many structures comprise the boundaries of Guyon's canal. The floor, for example, consists of the transverse carpal ligament, the pisohamate and pisometacarpal ligaments, and the opponens digiti minimi. Within Guyon's canal, the ulnar nerve bifurcates into the superficial and deep branches. The ulnar artery is immediately adjacent and radial to the ulnar nerve. The median nerve is visualized within the carpal tunnel, and the palmar cutaneous branch is more radial to Guyon's canal and volar to the carpal tunnel. The radial and ulnar digital nerves to the little finger are branches off of the superficial branch of the ulnar nerve distal to its emergence from Guyon's canal. The ulnar artery is the round structure located radial to the branches of the ulnar nerve within Guyon's canal. Adjacent to the ulnar artery are two small veins. The dorsal cutaneous branch of the ulnar nerve branches from the ulnar nerve in the distal forearm, well proximal to Guyon's canal. The common digital artery to the fourth web branches from the superficial palmar arch distal to Guyon's canal. The hook of the hamate is clearly seen in the figure, orienting the observer to the ulnar side of the wrist. Gross MS, Gelberman RH: The anatomy of the distal ulnar tunnel. Clin Orthop Relat Res 1985;196:238-247.

These radiographs are dominated by the subsidence of the femoral component. There is also evidence of polyethylene wear and femoral osteolysis in the region of the greater trochanter. There is no evidence of proximal (calcar) stress shielding, and there is a thick distal pedestal. Engh and associates defined two major signs of osseointegration - the absence of radiolucent lines around the porous-surfaced portion of the implant and new bone bridging the gap between the endosteal surface and the porous portion of the implant. Implant migration indicates failure of ingrowth. Osteolysis is a periprosthetic loss of bone secondary to particulate debris and it is often clinically silent unless it is accompanied by pathologic fracture. It is often globular. Acetabular loosening is based on radiolucent lines and implant migration. The current radiographs demonstrate subsidence of the stem with pedestal formation. Engh CA, Massin P, Suthers KE: Roentgenographic assessment of biologic fixation of porous-surface femoral components. Clin Orthop Relat Res 1990;257:107-128.

Flexor tenosynovitis of the thumb flexor tendon sheath can spread proximally and form an abscess within the thenar space of the palm. The flexor pollicis longus tendon does not pass through the central space of the palm or the hypothenar space of the palm. The flexor pollicis longus tendon does pass through the carpal tunnel, but this is not a palmar space. The three palmar spaces include the hypothenar space, the thenar space, and the central space. The posterior adductor space would likely only be involved secondarily after spread from a thenar space infection. Hollinshead W: Anatomy for Surgeons: The Back and Limbs, ed 3. Philadelphia, PA, Harper and Row, 1982, vol 3, pp 478-479.

The appropriate placement of the anterolateral portal provides access to the lateral gutter of the joint while avoiding the superficial peroneal nerve. The safest location for the portal is approximately 4 mm lateral to the peroneus tertius tendon, the closest of the tendons listed to the anterolateral portal. Because the superficial peroneal nerve location is variable, attempts to visualize, palpate, or transilluminate the nerve are mandatory.

The radiograph reveals a metaphyseal lesion with some stippled mineralization suggesting a chondroid tumor. The bone scan shows increased uptake, beyond what is expected for a simple enchondroma, and beyond the limits of the lesion. The MRI sequences shows a lobular lesion on the T1- and T2-weighted (bright on the T2 sequence) images with inhomogeneous uptake of gadolinium; both findings are typical for a chondroid lesion. The history of pain, the positive bone scan, the age of the patient, the size of the lesion, and the central location (enostotic) of the lesion all suggest a malignant cartilage tumor. The images are not consistent with the other diagnoses. In particular, plasmacytoma is more uniformly bright on T2-weighted images and often has a negative bone scan. Menendez LR (ed): Orthopaedic Knowledge Update: Musculoskeletal Tumors. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 187-194.

The rotator cuff interval is located between the supraspinatus and subscapularis and the biceps tendon is deep to the interval. It is a triangular area where the base is the coracoid process and the apex is the transverse humeral ligament at the biceps sulcus. Closure or tightening of this area is often helpful in patients with shoulder instability. Conversely, this area is often contracted in patients with adhesive capsulitis and may need to be released. Selecky MT, Tibone JE, Yang BY, et al: Glenohumeral joint translation after arthroscopic thermal capsuloplasty of the rotator interval. J Shoulder Elbow Surg 2003;12:139-143.

Branches of the medial antebrachial cutaneous nerve can often be identified during routine ulnar nerve surgery crossing the medial aspect of the elbow. It should be preserved to avoid development of painful paresthesias.

Os acromiale represents a failure of fusion of the anterior acromial apophysis and has been reported in approximately 8% of the population. Patients with a symptomatic os acromiale often report impingement-type symptoms with pain over the superior acromion, especially with overhead activities or sleeping. When nonsurgical management is unsuccessful, surgical options include excision, open reduction and internal fixation, and arthroscopic decompression. Kurtz CA, Humble BJ, Rodosky MW, et al: Symptomatic os acromiale. J Am Acad Orthop Surg 2006;14:12-19.

The dorsomedial cutaneous nerve of the hallux, which is a distal branch of the superficial peroneal nerve, supplies sensation to the skin on the dorsal and medial half of the hallux and may be injured during a chevron bunionectomy. Injury to the nerve leads to particularly painful neuromas that directly impinge on the shoe. For this reason, direct medial approaches are typically preferred for access to the medial aspect of the metatarsophalangeal joint.

The radiograph shows enlargement of the bone, coarse trabeculation, a blastic appearance, and thickening of the cortex, revealing the classic appearance of Paget's disease in the sclerotic phase, the most common presentation. While lymphoma may present as a blastic lesion, it will not have the same enlargement, coarse trabeculation of bone, and the significant sclerosis seen here. Menendez LR (ed): Orthopaedic Knowledge Update: Musculoskeletal Tumors. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 211-215.

The sciatic nerve is formed by the roots of the lumbosacral plexus. It exits the pelvis through the greater sciatic notch and appears in the buttock anterior to the piriformus. From that point, the sciatic nerve passes posteriorly over the superior gemellus, obturator internus, inferior gemellus, and quadratus femoris before it passes deep to the biceps femoris. The tendon of the obturator internus passes through the lesser sciatic notch. Hoppenfeld S, deBoer P: Surgical Exposures in Orthopaedics: The Anatomic Approach. Philadelphia, PA, JB Lippincott, 1984, p 347. Anderson JE: Grant's Atlas of Anatomy, ed 7. Baltimore, MD, Lippincott Williams & Wilkins, 1978, pp 4-34, 4-36.

The femoral nerve is the most lateral structure in the anterior neurovascular bundle. The femoral artery and vein lie medial to the nerve. Retractors placed in the anterior acetabular lip should be safe, although neurapraxia of the femoral nerve may occur if retraction is prolonged or forceful leading to quadriceps weakness. The femoral artery and nerve are well protected by the interposed psoas muscle. Damage to the lateral femoral cutaneous nerve, causing numbness over the anterolateral thigh, can occur while developing the interval between the tensor fascia latae and sartorious in the anterior (Smith-Petersen) approach but less likely in the Watson-Jones approach. Superior gluteal injury and accompanying abductor insufficiency may occur during excessive splitting of the glutei during the direct lateral (Hardinge) approach. Foot drop secondary to sciatic injury is more common with a posterior exposure or posterior retractor placement. Hoppenfeld S, deBoer P: Surgical Exposures in Orthopaedics: The Anatomic Approach. Philadelphia, PA, JB Lippincott, 1984, p 325.