1. General Principles & Basic Science MCQs

DISCUSSION: The brachialis muscle typically receives dual innervation. The major portion is innervated by the musculocutaneous nerve. Its inferolateral portion is innervated by the radial nerve. The others listed have single innervation. The anterior approach to the humerus, which requires splitting of the brachialis, capitalizes on this dual innervation. REFERENCE: Mahakkanukrauh P, Somsarp V: Dual innervation of the brachialis muscle. Clin Anat 2002;15:206-209.

DISCUSSION: 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. REFERENCES: Anderson JE (ed): Grant’s Atlas of Anatomy, ed 7. Baltimore, MD, Williams & Wilkins, 1978, pp 4-69. Weissman BNW, Sledge CB (ed): Orthopaedic Radiology. Philadelphia, PA, WB Saunders, 1986, p 514.

DISCUSSION: Hypophosphatemic rickets is an inherited disorder that is transmitted by a unique sex-linked dominant gene. Therefore, if a male patient has a female offspring, his affected X chromosome will be transmitted and all of his female children will have hypophosphatemic rickets. All male offspring of a male patient will be unaffected. All offspring of a female patient have a 50% chance of having the disorder. Understanding the inheritance of hypophosphatemic rickets facilitates early diagnosis and early treatment. Medical treatment with phosphorus and some types of vitamin D (most authors recommend calcitriol) improves, but does not fully correct, the mineralization defect in hypophosphatemic rickets. However, if medical treatment is begun before the child begins walking, the growth plate is then adequately protected and a bowleg deformity will most likely be prevented.

Tendons consist of mainly type I collagen (95%); a small amount of collagen types III, V, VI; and proteoglycans (< 5%). Proteoglycans have highly charged glycosaminoglycan side chains that attract water and help keep tendons well hydrated. Decorin is the most common proteoglycan in tendons and has been shown to bind to collagen. Tenascin-C is a glycoprotein upregulated in tendinopathy.

TGF-beta 1 stimulates the synthesis of extracellular matrix (ECM) and causes synovial proliferation and fibrosis.TGF-beta is the most thoroughly investigated member of the TGF-beta superfamily. This group includes TGF-beta1, BMP-2, and BMP-7. Besides the above activities, TGF-beta1 also stimulates chondrocyte synthetic activity and decreases the catabolic activity of IL-1.Fortier et al. reviewed the role of growth factors in cartilage repair and modificationof osteoarthritis. They found that members of the TGF-beta superfamily, FGF family, IGF1, and PDGF have all been investigated as possible treatment augments in the management of chondral injuries and early arthritis. They concluded that more research was necessary before routine application.Illustration A shows a summary of the different growth factors and their effects on cartilage.Incorrect Answers:

Osteoclasts resorb bone. Osteoclasts are derived from monocytes and macrophages that fuse to form multinucleated cells in response to receptor activator of nuclear factor kappa B (RANKL) and macrophage colony stimulating factor (MCSF). Osteoclasts attach to bone surfaces through a specific cell attachment receptor called an integrin (avβ3 or vitronectin receptor). The ruffled border refers to multiple invaginations of plasma membrane against the bone matrix surface. Lysosomes move to the ruffled border of osteoclasts and discharge lysosomal enzymes into the resorption region. These enzymes include cathepsin K, matrix metalloproteinase, and carbonic anhydrase (CA II).

The direct anterior (Smith-Petersen) approach utilizes a true internervous plane. Superficial dissection occurs between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep interval is between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

The sciatic nerve lies posterior to the external rotators. Retractors placed deep and posterior to the acetabulum, especially without the protection of the reflected external rotators, place the sciatic nerve at direct risk of compression or laceration.

DISCUSSION: The terminal branch of the posterior interosseous nerve is contained in the fourth dorsal compartment. The contents of the various dorsal wrist compartments are as follows: 1st Compartment: Abductor pollicis longus, extensor pollicis brevis; 2nd Compartment: Extensor carpi radialis brevis, extensor carpi radialis longus; 3rd Compartment: Extensor pollicis longus; 4th Compartment: Extensor digitorum communis, extensor indicis proprius, posterior interosseous nerve; 5th Compartment: Extensor digiti minimi; 6th Compartment: Extensor carpi ulnaris. The extensor indicis proprius is also contained in the fourth dorsal compartment. The extensor digiti minimi is located in the fifth dorsal compartment. The extensor carpi radialis brevis is located in the second dorsal compartment. The extensor pollicis longus is located in the third dorsal compartment, and the abductor pollicis longus is located in the first dorsal compartment. REFERENCES: Hoppenfeld S, deBoer P: Surgical Exposures in Orthopaedics, ed 2. Philadelphia, PA, Lippincott-Raven, 1994, pp 150-151. Netter F: The Ciba Collection of Medical Illustrations: The Musculoskeletal System, Part 1: Anatomy, Physiology and Metabolic Disorders. West Caldwell, NJ, Ciba-Geigy Corporation, 1987, vol 8, p 60.

DISCUSSION: The saphenous nerve is located on the posterior medial aspect of the knee and must be protected when performing an inside-out repair of the medial meniscus. The peroneal nerve is most at risk with lateral meniscal repairs. The other structures usually are not at risk with meniscal repair. REFERENCES: Cannon WD Jr, Morgan CD: Meniscal repair: Arthroscopic repair techniques. Instr Course Lect 1994;43:77-96. Scott GA, Jolly BL, Henning CE: Combined posterior incision and arthroscopic intra-articular repair of the meniscus: An examination of factors affecting healing. J Bone Joint Surg Am 1986;68:847-861.

Rejecting the null hypothesis when it is true is an example of a type-I error.Type-I errors, to put it simply, detect an effect that is not present. In contrast, a type-II error fails to detect an effect that is present. In simple studies, the rate of a type-I error is denoted by a (alpha). For a 95% confidence level, the value of alpha is 0.05. This means that there is a 5% probability that we will reject a true null hypothesis.Illustration A shows the difference between type-I and type-II errors. Incorrect Answers;not technically considered "errors," but instead are variables that properly constructed studies attempt to avoid. Answer 4: Variance is an estimate of the variability of each individual data point from the mean.

DISCUSSION: The indications for high tibial valgus osteotomy include a physiologically young age, arthritis confined to the medial compartment, 10 to 15 degrees of varus alignment on weight-bearing radiographs, a preoperative arc of motion of at least 90 degrees, flexion contracture of less than 15 degrees, and a motivated, compliant patient. Contraindications include lateral compartment narrowing of the articular cartilage, lateral tibial subluxation of greater than 1 cm, medial compartment bone loss, ligamentous instability, and inflammatory arthritis. REFERENCES: Naudie D, Bourne RB, Rorabeck CH, Bourne TT: The Insall Award: Survivorship of the high tibial valgus osteotomy. A 10- to 22-year followup study. Clin Orthop 1999;367:18-27. Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 255-264.

The radiograph reveals densities within the articular cartilage of the knee commonly referred to as chondrocalcinosis. The term chondrocalcinosis refers to the presence of calcium-containing crystals detected as radiodensities in cartilage. Calcium-containing crystals other than calcium pyrophosphate dihydrate may also deposit in articular cartilage and menisci, producing both radiographically detectable densities in cartilage and joint inflammation or degeneration. Hemochromatosis, alkaptonuria (ochronosis), and Wilson’s disease are characterized by cellular deposition of iron, calcium, and copper ions, respectively, into various tissues including articular cartilage and can give this appearance. Septic arthritis does not usually cause chondrocalcinosis.

In patients with radial nerve injuries with closed humeral fractures, it has been reported that 85% to 95% spontaneously recover. Based on this premise, most surgeons favor expectant management of these injuries. Even if there is no evidence of recovery at 6 weeks, repeat electromyography at 12 weeks is advocated. If there are no clinical or electromyographic signs of recovery at 6 months, exploration is recommended.

Communication failures are the leading cause of wrong side surgeries, medication errors and diagnostic delays.Poor communication sets up environments in which medical errors can take place. Per the Joint Commission, medical errors may be the among the top 10 causes of death in the United States. Establishing open lines of communication is critical to reduce the risk of error and enhance patient safety.Gandhi et al. designed a framework to study missed or delayed diagnoses and their causes. The most significant factors contributing to errors were poor handoffs, failures in judgment, failures in memory and failures in knowledge.O’Daniel et al. review the importance of professional communication and collaborative team efforts. They note that patient safety is at risk when poor communication is in place. The leading cause for medication errors, treatment delays and wrong-site surgeries is communication failure.Illustration A shows the leading causes of death in the United States. This includes “preventable errors” as a cause.Incorrect Answers:

The other foils in this answer would be both unethical and would be a violation of “anti-dumping” laws. This would further open the physician, hospital and staff to possible litigation.

EXPLANATION: CRPS 2 develops after nerve injury, whereas CRPS 1 occurs without nerve injury. The diagnostic criteria are otherwise the same for the 2 conditions. A 3-phase bone scan can be helpful; a pattern of increased uptake in all 3 phases, and particularly diffuse periarticular uptake in and around the joints of the affected extremity during the delayed phase, is considered typical of CRPS, especially during the first 6 months; however, it is not specific enough to be used as a diagnostic criteria. Unfortunately, the pathophysiological mechanisms underlying CRPS remain unclear, and, as such, no standard diagnostic test for CRPS exists. There are 3 major sets of diagnostic criteria for CRPS: the International Association for the Study of Pain (IASP) criteria, the Budapest Research Criteria, and the Veldman criteria. According to IASP, CRPS type 1 involves an initiating noxious event or a cause of immobilization; continuing pain/allodynia/hyperalgesia for which the pain is disproportionate to any known inciting event; evidence of edema, changes in skin blood flow, or abnormal pseudomotor activity in the region of pain; and exclusion of the diagnosis by the existence of other conditions that would otherwise account for the degree of pain and dysfunction. CRPS type 2 is a syndrome that develops after nerve injury, contends IASP. Spontaneous pain or allodynia/hyperalgesia occurs and is not necessarily limited to the territory of the injured nerve; there is or has been evidence of edema, a skin blood flow abnormality, or abnormal sudomotor activity in the region of pain since the inciting event; and the diagnosis is excluded by the existence of conditions that would otherwise account for the degree of pain and dysfunction.

A 35-year-old man reports ulnar sided wrist pain. Radiographs show ulnar positive variance with cystic changes in the ulnar head and lunate. His body mass index (BMI) is 22, and he has had a 1.5-pack-per-day smoking history for the past 10 years. He undergoes an oblique ulnar shortening osteotomy with volar placement of the plate. Nine months after surgery, he reports continued pain, and radiographs reveal a nonunion. Of the factors cited for this patient, which has been shown to most likely increase the risk of nonunion?

When erythromycin is taken concomitantly with digoxin, carbamazapine, cyclosporine, oral anticoagulants and theophylline, it can increase their blood levels. Erythromycin has no significant effect in the blood levels of the other listed agents. (Clindamycin enhances neuromuscular blocking effects and amphoterecin B may cause digoxin toxicity.)