1. General Principles & Basic Science MCQs

DISCUSSION: The modified posterior approach with elevation of the medial and lateral heads of the triceps can provide exposure of 94% of the humeral shaft. The traditional posterior triceps-splitting approach exposes 55% of the humeral shaft. REFERENCES: DeFranco MJ, Lawton JN: Radial nerve injuries associated with humeral fractures. J Hand Surg Am 2006;31:655-663. Gerwin M, Hotchkiss RN, Weiland AJ: Alternative operative exposure of the posterior aspect of the humeral diaphysis with reference to the radial nerve. J Bone Joint Surg Am 1996;78:1690-1695.

DISCUSSION: Alendronate is a second-generation bisphosphonate, and it can cause epigastric distress in up to 30% of patients. This side effect can be minimized by gradually building up to therapeutic doses over a period of 4 to 8 weeks. REFERENCES: Marshall JK, Rainsford KD, James C, et al: A randomized controlled trial to assess alendronate-associated injury of the upper gastrointestinal tract. Aliment Pharmacol Ther 2000;14:1451-1457. Lane JM, Sandhu HS: Osteoporosis of the spine, in Garfin SR, Vaccaro AR (eds): Orthopaedic Knowledge Update: Spine. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1997, pp 227-234.

Bone is a composite of both inorganic and organic material. The inorganic component of bone comprises 60% to 70% of the tissue, water accounts for 5% to 8%, and the organic matrix makes up the remainder. Collagen accounts for 90% of the organic component and thus 20% to 25% of bone weight. Collagen accounts for the flexibility of bone. The inorganic component of bone is made primarily of calcium and phosphorous, in the analogue of hydroxyapatite, and other ions including sodium, magnesium, and carbonate.

Plastic deformation of viscoelastic tissues represents deformation of the soft tissues to the point of failure. The lining up of collagen fibers would be in the “toe region” of the curve, which, in the case of the FSU, would be mainly in the neutral zone. Elastin is a minor contributor to the composition of the ligaments and would be protected by the stiffer collagen fibers. The transition between flexion and extension occurs in the neutral zone, and reversible elongation occurs in the elastic zone.

Johnell et al. demonstrated that lower BMD is a significant risk factor for osteoporotic fractures in both men and women. The other options provided in the source text are either incorrect or represent distractors.

Etanercept is a molecule consisting of the Fc portion of IgG fused to the extracellular domain of the p76 human TNF-α receptor. It is soluble and binds TNF-α. Infliximab is the monoclonal antibody that binds TNF-α. IL-1 receptor antagonists are still in development. Leflunomide is a drug that inhibits pyrimidine synthesis and is similar to methotrexate as an antimetabolite.

DISCUSSION: According to the 2008 AAOS Clinical Practice Guideline, Treatment of Osteoarthritis of the Knee (Nonarthroplasty), level 1 evidence confirms that weight loss and exercise benefit patients with knee osteoarthritis. The other responses have either inclusive evidence (a valgus-directing brace) or no evidence to support their use (glucosamine 1,500 mg/day and chondroitin sulfate 800 mg/day as well as arthroscopic debridement and lavage).

DISCUSSION: The initial signs and symptoms of acute hematogenous osteomyelitis vary widely but usually include fever, bone pain, and impaired use of the involved extremity. In lower extremity infections, the child may limp or refuse to walk. Examination often reveals bone tenderness. In more advanced cases, erythema, warmth, and swelling may be present. The WBC and neutrophil counts are not always elevated, but the erythrocyte sedimentation rate will be abnormal in more than 90% of patients. When the infection is diagnosed early, before a subperiosteal abscess has formed, antibiotics alone may be adequate to treat the infection. This patient has a more advanced infection, however, with the MRI scan revealing a subperiosteal abscess that was confirmed by aspiration. When an abscess is present, surgical drainage is generally indicated to remove devitalized tissue and to enhance the efficacy of the antibiotics. Further studies, such as bone or indium scans, are not necessary and will delay definitive treatment.

A football player injures his knee when he is tackled and falls awkwardly. He does not note any discreet “pop,” but pain prevents him from returning to the game. An effusion is noted the following day and an MRI scan is ordered. Selected images are shown in Figures 1 through 3. Based on these images, physical examination findings likely include

DISCUSSION: In the 2004 ACCP guidelines, there were three prophylactic regimens that received a grade 1A favorable recommendation. These included low-molecular-weight heparin, warfarin, or fondaparinux, as long as they are used for at least 10 days. If warfarin is used, the target INR should be 2.0 to 3.0, according to the guidelines. Pneumatic compression sleeves have gained popularity in the orthopaedic community but have not received a grade 1A rating from the ACCP at this time. Use of aspirin by itself is discouraged by the ACCP. REFERENCE: Geerts WH, Pineo GF, Heit JA, et al: Prevention of venous thromboembolism: The seventh ACCP Conference on antithrombotic and thrombolytic therapy. Chest 2004;126:338S-400S.

DISCUSSIONCertain anticoagulants are associated with an increased risk for wound complications. Two studies showed an increase in postsurgical bleeding and wound drainage following use of LMWH. Other investigators have associated use of anticoagulants such as LMWH with an increased incidence of persistent wound drainage and subsequent infection. Current evidence does not support a significant difference in complication rates with and without the use of wound drains or a tourniquet. Regional anesthesia has been associated with less blood loss than general anesthesia and is not associated with a difference in wound complication incidence.

The differential diagnosis of genu varum includes physiologic genu varum, Blount's disease, skeletal dysplasia, and metabolic bone disease. Children with Blount's disease are generally in the 95th percentile for height and weight, and usually multiple family members are not affected. The radiographs show widening of the physis and metaphyseal flaring. In Blount's disease, the characteristic radiographic changes involve only the tibia, and at this age, most commonly show beaking of the medial metaphysis. Skeletal dysplasias, such as chondrometaphyseal dysplasia, are associated with short stature, and the radiographic changes are similar to those seen here. However, laboratory studies in these children will be within normal limits. Children with chronic renal disease will often be of short stature, and the radiographic findings are again similar to those shown here. However, BUN and creatinine levels are elevated and phosphate levels are elevated rather than decreased in children with renal disease. The absence of dietary deficiencies and positive family history rules out vitamin D-deficient rickets. There are four types of vitamin D-resistant rickets: failure of production of 1,25-dihydroxy vitamin D, phosphate diabetes (hypophosphatemic rickets), end organ insensitivity to vitamin D, and renal tubular acidosis. All types of vitamin D-resistant rickets are resistant to treatment with physiologic doses of vitamin D. The patient’s clinical picture, family history, laboratory studies, and radiographs are most consistent with hypophosphatemic rickets. This entity is inherited as a sex-linked dominant trait.

The corona mortis, or "crown of death," is a common anatomic variant that consists of an anastomosis between the obturator and the external iliac or inferior epigastric arteries or veins. Its reported incidence is over 80%. It is located behind the superior pubic ramus at a variable distance from the symphysis pubis (3 cm to 9 cm). It is at risk during surgical approaches to the anterior pelvic ring. If accidentally cut, the vessel can retract making control of hemorrhage difficult.

The patient has diastrophic dysplasia. Affected individuals have rhizomelic short stature, cauliflower ears, severe joint contractures (especially knees and hips), hitchhiker’s thumb, and a cleft palate. The most common foot abnormality is a rigid equinovarus deformity. Surgical results are poorer than those for idiopathic clubfeet and often require bony procedures or talectomy.

Aggrecan's primary function in the intervertebral disc is to maintain water content.Aggrecan, the most abundant proteoglycan within the intervertebral disk, is a hydrophillic molecule which helps attract and maintain water within the disc. This is important to maintain compressive strength. Early in life aggrecan has a high percentage of chondroitin sulfate chains. With aging this gradually changes to higher percentage of keratin sulfate. Other proteoglycans include decorin and versican. Decorin is believed to regulate cell cycles and influence fibrillogensis. Versican is a large extra-cellular matrix proteoglycan involved in cell adhesion and migration.Roughley et al. provide a review of biologic changes within the intervertebral disc during development, maturation, and degeneration. They note that aggrecan works to maintain water content within the disc, thus improving its compressive strength. Aggrecan content decreases with age leading to a loss of compressive strength.Illustration A shows the structure of aggrecan.Incorrect answers:

Osteogenesis imperfecta (OI) is a genetically determined disorder of type I collagen synthesis that is characterized by bone fragility. This patient has had three fractures of the long bones by age 2 years, with the last one occurring after relatively minor trauma. The patient’s history and clinical features are consistent with a diagnosis of Sillence type IA OI. Cells from individuals with type I OI largely demonstrate a quantitative defect of type I collagen; they synthesize and secrete about half the normal amount of type I procollagen.

Closed kinetic chain exercises are used early in the rehabilitation process. The distal segment is fixed, and an axial load is applied which provides glenohumeral compression and reduces the demand on the rotator cuff. These exercises stimulate co-contractions of the scapular and rotator cuff muscles, load scapular stabilizers, and facilitate active motion. Facilitated active motion exercises use proximal segment motion to stimulate and facilitate motion in the target tissue. These exercises are often performed in diagonal movements. Resistive active motion exercises are used later in the rehabilitation process. These are typically open kinetic chain exercises that involve active glenohumeral motion with extrinsic loads such as weights or exercise tubing. During the later stages of upper extremity rehabilitation, plyometrics are added. These exercises help to prepare the athlete for return to sport. When performed at slower speeds, these exercises emphasize stabilization and control. As the speeds increase, muscles begin to work in the stretch-shortening sequence associated with sports participation.

PVL is a cytotoxin that defines CA-MRSA and is not typical of hospital-acquired MRSA. PVL has the ability to lyse white blood cells and cause tissue necrosis, allowing for rapid progression of abscess formation. Beta-lactamase is an enzyme that breaks the beta-lactam bond of penicillin and is present in most strains of Staphylococcus aureus today. Synthetic penicillins such as methicillin are resistant to the effects of beta-lactamase. MRSA and CA-MRSA carry the mecA gene, which encodes a penicillin-binding protein with a very low affinity for beta-lactam antibiotics, resulting in methicillin resistance. SCCmec mobile genetic units carry the mecA gene with additional genetic elements that together yield the multidrug-resistant strains found in healthcare environments. SCCmec type IV is specific to CA-MRSA and lacks these additional genetic elements, resulting in less multidrug resistance.

DOMS is primarily associated with eccentric exercise because fiber lengthening occurs during muscle contraction. Muscle injury occurs very early during eccentric exercise, with structural disruption of the cytoskeleton. A significant increase in creatine kinase levels occurs 24 to 48 hours after exercise and may peak between 3 to 6 days after exercise. All other choices are not strongly associated with delayed muscle soreness.

The anterior portal for hip arthroscopy is approximately 6 cm distal to the anterior superior iliac spine, penetrating the muscle belly of the sartorius and the rectus femoris before entering through the anterior capsule. The lateral femoral cutaneous nerve is divided into three or more branches at the level of this portal and may be injured during portal placement. The femoral nerve and artery are more medial and at less risk. The superior gluteal and sciatic nerves are posterior and not at risk with an anterior portal.