1. General Principles & Basic Science MCQs

The demonstration in Video 92 shows the tendons of the semitendinosus and gracilis muscles. They insert on the tibia deep to the sartorial fascia. The semimembranosus inserts more proximal and posterior on the tibia. RECOMMENDED READINGS: Babb JR, Detterline AJ, Noyes FR. AAOS Orthopaedic Video Theater. The Key to the Knee: A Layer-by-Layer Video Demonstration of Medial and Anterior Anatomy. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2009. Hoppenfeld S, deBoer P. Surgical Exposures in Orthopedics. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2003:493-568.

DISCUSSION: Kinematic analysis of both menisci demonstrates anterior movement with extension and posterior movement with flexion. The lateral meniscus has more mobility than the medial meniscus because of less soft-tissue attachments. REFERENCES: Insall JN, Scott WN (eds): Surgery of the Knee, ed 3. New York, NY, Churchill Livingstone, 2001, vol 1, p 474. Thompson WO, Thaete FL, Fu FH, et al: Tibial meniscal dynamics using 3D reconstructions of MR images, in Proceedings of the Orthopaedic Research Society 1990;389. Vaccaro AR (ed): Orthopaedic Knowledge Update 8. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2005, pp 15-28.

DISCUSSION: The latissimus dorsi inserts on the humerus metaphysis between the pectoralis major (posterior) and teres major (anterior). Teres minor inserts on the base of the greater tuberosity. Pectoralis minor does not insert on the humerus. REFERENCES: Williams PL, Warwick R, Dyson M, Bannister LH: Neurology, in Gray’s Anatomy, ed 37. Edinburgh, Scotland, Churchill Livingstone, 1989, pp 1131-1132. Last RJ: Anatomy: Regional and Applied, ed 6. London, England, Churchill Livingstone, 1978, pp 131-132.

DISCUSSION: Rheumatoid arthritis (RA) is a complex multisystem disorder. It has been suggested that patients with RA have an impaired capacity to control infection with Epstein-Barr virus. Epstein-Barr virus has oncogenic potential and is implicated in the development of some lymphomas. Recent publications provide evidence for an altered Epstein-Barr virus-host balance in patients with RA who have a relatively high Epstein-Barr virus load. Large epidemiologic studies confirm that lymphoma is more likely to develop in patients with RA than in the general population. The overall risk of development of lymphoma has not risen with the increased use of methotrexate or biologic agents. Histologic analysis reveals that most lymphomas in patients with RA are diffuse large B cell lymphomas, a form of non-Hodgkin lymphoma. Epstein-Barr virus is detected in a proportion of these. Patients with RA do not have prevalence for infection with any of the other mentioned viruses. REFERENCES: Callan MF: Epstein-Barr virus, arthritis, and the development of lymphoma in arthritis patients. Curr Opin Rheumatol 2004;16:399-405. Baecklund E, Sundstrom C, Ekbom A, et al: Lymphoma subtypes in patients with rheumatoid arthritis: Increased proportion of diffuse large B cell lymphoma. Arthritis Rheum 2003;48:1543-1550.

The radiograph shows multiple wide physes, consistent with a diagnosis of rickets. A low serum phosphorous level and an elevated alkaline phosphatase level are the hallmarks in diagnosing familial hypophosphatemic Vitamin D-resistant rickets. Serum calcium is usually normal or low normal. This disease is inherited as an X-linked dominant trait and usually presents at age 18 to 24 months. The disease results from a poorly defined problem with renal phosphate transport in which normal dietary intake of vitamin D is insufficient to achieve normal bone mineralization. Renal tubular dysfunction is associated with urinary phosphate wasting. Treatment involves oral phosphate supplementation, which can cause hypocalcemia and secondary hyperparathyroidism. To prevent associated problems, high doses of Vitamin D are administered. While obtaining a scanogram may be clinically indicated in an associated limb-length discrepancy, and subsequent corrective surgery may be indicated, either of these choices would not be the first course of action. An orthosis may slow the progression of genu varum in this disorder but is less important than establishing the correct diagnosis to begin pharmacologic treatment. This amount of varum and tibial bowing far exceeds the normal limits of physiologic genu varum. Skeletal dysplasias usually are not associated with abnormal laboratory values.

Treatment should consist of relative protection for 10 to 14 days followed by early range of motion and gentle closed-chain quadriceps strengthening. Isolated grade 1 and grade 2 posterior cruciate ligament injuries can be successfully managed nonsurgically. Progression to global knee strengthening can begin 4 to 6 weeks after the injury, with return to functional activity when full range of motion and strength is established. Plyometric exercises involve rapid alteration of contraction and loading of a muscle and should not be used in the early rehabilitation of a ligament injury of the knee because it risks further injury to the ligament. Hamstring strengthening should be avoided until the ligament has healed (4 to 6 weeks) because the posterior force on the tibia will stress the injured posterior cruciate ligament. Immobilization may be used for a short time to allow swelling and pain to subside, but early range of motion is preferred to avoid unnecessary stiffness following the stable injury.

Biglycan and versican are two of the small proteoglycans in cartilage. Biglycan plays a role in molecular association between cartilage and other molecules. Versican is more associated with the cell surface and plays multiple roles. Aggrecan has a longer core protein with multiple keratin sulfate and chondroitin sulfate chains. The molecular weight is around 1,000,000. Aggrecan aggregates on hyaluronic acid with link proteins. Aggrecan can associate with 50 times its weight in water. The resulting swelling pressure is retained by 20% by type II collagen. This results in the physiologic properties of articular cartilage. Type IX collage plays a role in matrix molecule association with type II collagen.

Open chain exercises of the lower extremity are defined as "The foot is mobile, and motion at the knee joint occurs independent of motion at the hip and ankle joints, as opposed to closed chain exercises in which the foot is fixed and motion at the knee joint is accompanied by motion at the hip and ankle joints in a predictable manner.

Experimental models of late-stage arthritis in animals demonstrated lower compressive modulus, higher permeability, and higher water content. There is proteoglycan loss within the matrix. A significant and progressive decrease in the tensile and shear modulus has been observed.

DISCUSSION: Passive glycation of articular cartilage occurs over decades. One of the consequences of this glycation appears to be the stiffening of collagen. This phenomenon appears to be associated with an increased collagen degradation and development of osteoarthrosis. Passive glycation also results in a relatively yellow appearance. Passive glycation does not directly influence chondrocyte proliferation. REFERENCES: DeGroot J, Verzijl N, Wenting-van Wijk MJ, et al: Accumulation of advanced glycation end products as a molecular mechanism for aging as a risk factor in osteoarthritis. Arthritis Rheum 2004;50:1207-1215. Chen AC, Temple MM, Ng DM, et al: Induction of advanced glycation end products and alterations of the tensile properties of articular cartilage. Arthritis Rheum 2002;46:3212-3217.

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).

Answering this question requires understanding of two important biomechanics concepts. First, because neither the object being held in the hand nor the body is moving and, hence, their accelerations are zero, the problem is one of static equilibrium in which the sum of the moments acting on the body is zero. Second, a moment is the action of a force that causes an object to rotate about any point away from its line of action. The magnitude of the moment is the magnitude of the force multiplied by the perpendicular distance between the line of action and the point (often called the moment arm or lever arm). In this problem, two forces are causing moments about the elbow. The magnitude of the moment caused by the object in the hand is 5 N times 30 cm or 150 N-cm. To maintain equilibrium, the moment caused by the biceps force must also have a magnitude of 150 N-cm. Its moment arm is 2 cm, so the magnitude of the biceps force is 150 N-cm divided by 2 cm, which equals 75 N. In general, functional loads such as the object are always at a mechanical advantage (i.e., have a longer moment arm) over the muscle. Therefore, muscles must generate large forces to overcome the moments caused by even small functional loads.

Rheumatoid factor is present in 80% to 90% of adult patients with rheumatoid arthritis. Although rheumatoid factor is very sensitive, it is not very specific. Antinuclear antibodies (ANA) can be detected in 30% to 40% of patients with rheumatoid arthritis.

BMP proteins, which are part of the larger transforming growth factor-beta super family, bind to serine/threonine receptors on the cell surface. This binding causes phosphorylation of SMAD proteins, which in turn forms a complex that enters the nucleus and initiates the transcription of several genes involved in osteoblastic differentiation. Adenylate cyclase isa transmembrane protein that acts intracellularly to activate the G protein pathways. Myc is a proto-oncogene that encodes for a transcription factor involved in numerous cell- activation pathways, but is not directly phosphorylated by BMP receptor.ß-catenin is an intracellular molecule that plays a key role in the Wnt signaling pathway. This pathway is also involved in osteoblastic differentiation, but differs in target proteins within the cell.A 45-year-old previously healthy woman has experienced weakness and fatigability for 2 months. She states she feels best in the morning, but tires easily with exertion. If she sits and rests her strength improves, but she easily tires with each activity. When her fatigue is most severe, she has double vision. Physical examination ispositive for ptosis with upward gaze after 20 seconds. When she holds her arms out straight she shows good initial strength, but rapidly decreasing strength with time. What is the pathologic cause of her muscle weakness?Ig antibodies at the neuromuscular (NM) junctionDecreased release of acetylcholine at the NM junctionDecrease in myelin sheath of axonal nerves with loss of NM junctionAbsence of dystrophin with excess calcium at sarcolemmaThe patient has myasthenia gravis, which has its onset in middle age and causes progressive weakness because of the loss of acetylcholine receptors secondary to autoimmune antibodies at the NM junction. Rest periods allow uptake of acetylcholine and initial strength, but easy fatigability. Treatment is aimed at immunomodulation; acetyl cholinesterase inhibitors often coupled with thymectomy can control symptoms.Decreased release of acetylcholine at the NM junction is the effect of a nondepolarizing drug or toxin botulinum. Patients with muscular dystrophy lack dystrophin that acts at the sarcolemma to regulate calcium channels, and onset of this condition occurs at a younger age. The decrease in myelin indicates Charcot-Marie-Tooth disease and isoften seen with long axon degeneration, such as in the feet and lower legs.You are studying a single continuous variable after administration of a defined treatment intervention. Your statistician informs you the data are not normally distributed. What is the best test to analyze the data?Analysis of variance (ANOVA)Regression analysisStudent t testMann-Whitney U testThe Mann-Whitney U test is used when data are nonparametric, meaning either not normally distributed or variances are not equal among groups. Both the Student t test and ANOVA are used with parametric, normally distributed data. A regression analysis is astatistical model that allows for control of potentially confounding variables. It is used to assess the relationship between a dependent variable and (usually) multiple independent variables.Which of the following is the mechanism of action of aspirin?Inhibition of vitamin K-dependent carboxylationInhibition of factor Xa through antithrombin bindingBinding of cyclooxygenase (COX)-1 and COX-2Direct thrombin inhibitionGlycoprotein IIIb agonist bindingAspirin works by the irreversible binding of cycloxygenase (COX). This effect inhibits platelet generation of thromboxane A2, resulting in an antithrombotic effect. In addition, there is a decrease in the level of prostaglandin production due to the COX-1 binding.Aspirin's effects and respective mechanisms of action vary with dose:Low doses (typically 75 to 81 mg/day) are sufficient to irreversibly acetylate serine 530 of cyclooxygenase (COX)-1. This effect inhibits platelet generation of thromboxane A2, resulting in an antithrombotic effect.FOR ALL MCQS CLICK THE LINK ORTHOMCQ BANKIntermediate doses (650 mg to 4 g/day) inhibit COX-1 and COX-2, blocking prostaglandin (PG) production, and have analgesic and antipyretic effects. Illustration A shows the mechanism of action of aspirin.InCORRECT Answers: 1,2,4,5: Aspirin does not have any of these mechanisms of action.A study is proposed in which 2 groups of patients are randomized to treatment with bisphosphonates or placebo. This is an example of what study type?Crossover design trialParallel design trialCohort studyCase seriesIn a parallel design trial, participants are randomized to 2 or more groups, each of which receives a different treatment or intervention. For example, Group A receives the drug and Group B receives the placebo. This type ofdesign allows for comparison between groups. In a crossover design clinical trial, both groups receive both interventions over a defined time period. For example, Groups A and B both receive the drug as well as the placebo. This allows for within-participant comparisons. In a cohort study, patient groups are followed over time on the basis of having or not having received an exposure. Cohort studies are not randomized. In a case series, patients often receive a particular treatment and the outcomes are then examined.An otherwise healthy 50-year-old man who is a smoker undergoes a posterior spine fusion with instrumentation for spondylolisthesis. What can the patient do to minimize his risk for pseudarthrosis?Increase calcium and vitamin D intakeAvoid all nonsteroidal anti-inflammatory drugs (NSAIDs)Maintain smoking cessationEngage in early physical therapy to strengthen the trunk musculatureSmoking is the biggest risk factor for nonunion and should be strictly avoided. NSAIDs interfere with bone healing, but not as strongly as smoking. Early mobilization would potentially stress the construct, inducing movement that leads to nonunion. Without history of calcium and vitamin D deficiency, increasing intake would not decrease the risk of nonunion.When making a comparison to autograft incorporation, the inflammatory process in allograft tissue anterior cruciate ligament (ACL) reconstructionoccurs earlier.occurs later.is prolonged.is shortened.Compared to similar autograft, allograft tissue demonstrates a prolonged inflammatory response, slower rate of biological incorporation and remodeling, and a higher proportion of large-diameter collagen fibrils. Native ACL insertsinto bone through a transition of 4 distinct zones: tendon, unmineralized fibrocartilage, mineralized fibrocartilage, and bone. This transition is not reproduced with tendon grafts, which instead heal with interposed fibrovascular scar at the graft-tunnel interface. The scar rapidly remodels to form perpendicular fibers resembling Sharpey fibers and, eventually, mature bone growth into the outer portion of the graft. The intra- articular portion of allograft undergoes an initial phase of necrosis followed by repopulation by host synovial cells into the acellular collagen scaffold.Revascularization and maturation complete the ligamentization of graft tissue.A researcher decides she wants to look at the current total number of patients who have methicillin-resistantStaphylococcus aureus(MRSA) infections in a hospital on 1 particular day. What is the researcher measuring?Correlation coefficient of MRSAPrevalence of MRSAIncidence of MRSARelative risk of MRSAThe prevalence of a disease is a measure of the number of cases of a disease at or during a specific time point or time period. In this case, the researcher wants to know the prevalence of disease on a given day. Incidence measures new cases of a disease or event per unit of time. Correlation coefficient is a measure of how 2 things correlate with one another, while relative risk is a statistical outcome that is often used in case-control or cohort studies to provide a measure of the risk of a particular disease occurring when a certain exposure has already occurred.A 48-year-old man who is scheduled to undergo total knee replacement has an X-linked clotting disorder that leads to abnormal bleeding and recurrent, spontaneous hemarthrosis. Before undergoing surgery, he should have replacement therapy ofprotein C and S.vitamin K.von Willebrand factor.factor VIII.Hemophilia A is an X-linked recessive deficiency of factor VIII that can lead to significant bleeding problems including recurrent spontaneous hemarthroses that can lead to synovitis and joint destruction. von Willebrand disease is a lack of von Willebrand factor that leads to decreased platelet aggregation; more commonly patients have mucosal bleeding and not hemarthroses. Vitamin K deficiency is not hereditary; it is typically attributable to inadequate dietary intake, malabsorption, and loss of storage sites from hepatocellular disease. Protein C and S deficiencies are autosomal-dominant diseases that lead to thrombosis, not bleeding, as protein C and S shut off thrombin formation.What is the recommended optimal timing of presurgical antibiotic administration to prevent infection in patients undergoing total joint replacement surgery?Within 1 hour before incisionWithin 2 hours before incisionImmediately after incisionWithin 1 hour after incisionThe current recommendation for antibiotic prophylaxis for major orthopaedic surgical procedures is to administer intravenous antibiotics within 1 hour of surgical incision. Redosing of antibiotics should occur 3 to 4 hours after the initial dose for procedures that extend beyond 3 to 4 hours. Little evidence supports postsurgical antibiotic use beyond 24 hours. As you move beyond 1 hour from time of administration of antibiotics, risk for infection increases and rates of bacterial cell death decline. It is not acceptable toadminister presurgical antibiotics after incision.Bacterial resistance to antibiotics in biofilm is an example ofavoidance.decreased susceptibility.inactivation.mutation.CORRECT answer: 1Three basic mechanisms of antibiotic resistance have been identified: avoidance, decreased susceptibility, and inactivation. Biofilm formation is a classic example of avoidance, whereby the biofilm creates a physical barrier to the antibiotic. Bacteria can decrease their susceptibility to antibiotics by mutating the antibiotic target or generating a mechanism to inactivate the antibiotic. Biofilm formation develops when a sufficient mass of bacteria forms on a surface. The cell-to-cell signaling becomes sufficient to activate transcription of genes needed for biofilm formation in a process known as quorum sensing. Once the bacteria produce a mature biofilm, they enter a greatly reduced or stationary phase of growth. Lastly, high-shearenvironments seem to stimulate biofilm production.A patient with Paget disease who is intolerant of bisphosphonates is given calcitonin. What is the mechanism of action of calcitonin?Promotes reabsorption of phosphate in the renal tubulesInterferes with osteoclast maturationInterferes with intestinal absorption of calciumUpregulates osteoblast formationCalcitonin is a hormone that reduces serum calcium concentration by directly interfering with osteoclast maturation via receptors. Calcitonin inhibits phosphate reabsorption and decreases calcium reabsorption in the kidneys. By attenuating cartilage breakdown and stimulating cartilage formation via inhibitory pathways of matrix metalloproteinases, calcitonin also has achondro-protective effect on articular cartilage. Calcitonin has no major effects on intestinal absorption of calcium, but may aid in small-bowel secretion of sodium, potassium, chloride, and water. Calcitonin also has no receptor effect on osteoblasts.A cartilage water content increase is the hallmark of whichosteoarthritis stage?PrearthritisEarlyLateTerminalThe first stage of osteoarthritis is marked by an increase in water content secondary to disruption of the matrix framework. This is followed by an increase in chondrocyte anabolic and catabolic activity in response to tissue damage. Wnt-induced signal protein 1 increases chondrocyte protease expression. Failure to restore tissue balance ultimately leads to continued destruction and osteoarthritis. One hallmark of osteoarthritic cartilage is a reduced repair mechanism attributable to decreased chondrocyte response to growth factor stimulation (transforming growth factor-alpha and insulin-like growth factor-1).Mitochondrial dysfunction and increased production of reactive oxygen species may promote cell senescence, a progressive slowing of cellular activity. Microscopic evidence of cartilage degeneration begins with fibrillation of the superficial and transition zones, followed by disruption of the tidemark by subchondral blood vessels and eventual subchondral bone remodeling. This process ultimately leads to cartilage degradation with decreased water content in the late and terminal phases of osteoarthritis.What is the plasma half-life of warfarin?1 to 2 hours4 to 6 hours12 to 18 hours36 to 42 hoursWarfarin, which is dosed daily, can take 72 to 96 hours to reach therapeutic levels. It has a plasma half-life of 36 to 42 hours. Low-molecular heparins have a plasma half-life of 4 to 5 hours, and fondaparinux has a half-life of 17 to 21 hours. Warfarin will not affect the International Normalized Ratio (INR) until 2 to 3 days after it is given. Patients on chronic warfarin therapy shouldhave treatment stopped 3 to 5 days before elective surgery to allow the INR to normalize.A 70-year-old woman with a body mass index (BMI) of 34 and a history of hypercholesterolemia has elected to undergo total hip arthroplasty. Her son recently learned he has Factor V Leiden following an episode of pulmonary embolism. What are this patient's risk factors for thromboembolic disease?Type of surgery, age, and BMIType of surgery, hypercholesterolemia, and ageAge, BMI, and hypercholesterolemiaBMI, type of surgery, and hypercholesterolemiaRisk stratification is one of the most critical clinical evaluations before undergoing total joint arthroplasty. Many factors have been identified to increase risk for venous thromboembolism (VTE). The major factors include previous VTE, obesity, type of surgery (such as total joint arthroplasty), hypercoagulable states, myocardial infarction, congestive heart failure, family history of VTE, and hormonal replacement therapy.Hypercholesterolemia is not a risk factor for thromboembolic disease.DNA replication occurs during which phase of the cell cycle?MSRG1G2The cell cycle consists of four distinct phases: initial growth (G1), DNA replication/synthesis (S), a gap (G2), and mitosis (M) (see illustration).The G1 and G2 phases of the cell cycle represent the “gaps” or growth phases in the cell cycle that occur between DNA synthesis and mitosis. G0 cells are in a stable state and have not entered the cell cycle. During the S phase, the DNA is synthesized and replicated. During the M phase or mitosis, all genetic material divides into two daughter cells.The cells are diploid (2N) in the G0 and G1 phases. The cells become tetraploid (4N) at the end of S and for the entire G2 phases. There is no R phase in the cell cycle.What antithrombotic agent is a selective factor I0a inhibitor?WarfarinLow-molecular-weight heparinRivaroxabanAspirinRivaroxaban is a selective factor I0a inhibitor. Aspirin is a cyclooxygenase inhibitor. Low-molecular-weight heparin is a nonspecific anticoagulant. Warfarin is a vitamin K antagonist and reduces production of clotting factors II, VII, IX, and X.A 68-year-old woman had advanced right knee arthritis and total knee replacement was planned. She learned she had primary biliary cirrhosis at age 41 and now has advancing liver failure. Preoperative coagulation tests show a baseline International Normalized Ratio (INR) of 1.36. Appropriate methods to prevent thromboembolicdisease as recommended by the 2011 AAOS Clinical Practice Guideline,Preventing Venous Thromboembolic Disease in Patients Undergoing Elective Hip and KneeArthroplasty, includeuse of mechanical prophylaxis (eg, pneumatic calf compressors) while in the hospital.oral warfarin with a goal INR between 2.0 and 3.0.low-dose warfarin for 3 weeks postsurgically beginning 48 hours after surgery.no prophylaxis because this patient already is partially anticoagulated secondary to her liver disease.The 2011 AAOS Clinical Practice Guideline,Preventing Venous Thromboembolic Disease in Patients Undergoing Elective Hip and Knee Arthroplasty, recommends the use of mechanical prophylaxis for patients at increased riskfor bleeding (including those with liver disease or hemophilia). This recommendation is the consensus of the workgroup that established these guidelines because there was insufficient evidence to justify a stronger recommendation in this clinical scenario. The other responses use no prophylaxis or pharmacological prophylaxis. Pharmacological prophylaxis is not recommended in patients who are at increased risk for bleeding.The pharmacokinetics of which deep venous thrombosis (DVT) prophylactic agent are affected by liver function and dietary intake?DalteparinWarfarinFondaparinuxEnoxaparinWarfarin is an oral vitamin K antagonist that is rapidly absorbed from the gastrointestinal tract. It accumulates in the liver, where it is metabolized and excreted. The pharmacokinetics of warfarin can be affected by certain drugs or disease states that influence liver function. Fondaparinux is a synthetic factor Xa inhibitor that is eliminated through the kidneys. Both Dalteparin and Enoxaparin are low-molecular-weight heparins that activate antithrombin and inhibit factors Xa and IIa. Like Fondaparinux, they are eliminated through the kidneys and should be used with caution in patients with kidney disease.What infection-control measure has been shown to have the most notable impact in reducing surgical-site infections?Intravenous antibiotic administration within 1 hour of surgical incisionScreening and decolonization of patients colonized with methicillin-resistantStaphylococcus aureusHorizontal laminar flowUse of enclosed body exhaust suitsTimely administration of prophylactic antibiotics is the most important factor shown to decrease surgical-site infections. The use of horizontal laminar flow and body exhaust suits has not been shown to significantly affect infection rates.The resistance to pullout of a screw in osteoporotic bone is increased by all of the following EXCEPT?Placement parallel to the trabecular patternPurchase in cortical boneUse of a fixed angle (locking screw construct)Tapping prior to screw placementAugmentation with polymethylmethacrylateOf the options listed, tapping prior to screw placement is the only variable that does not increase the pullout strength of a screw in osteoporotic bone.Cornell reviews internal fixation in osteoporotic bone. According to this article, the quality of the bone is the primary determinant of the holding power of an individual screw. Other factors that increase the pullout strength include fixation in cortical bone (cortical bone has greater mineral density and, therefore, greater resistance to screw pullout than trabecular bone), screws placed parallel to the trabecular pattern, and screw fixation augmented with PMMA. The addition of a locking plate will also increase the resistance to failure by creating a fixed angle construct. Tapping prior to placement of the screw has not been shown to increase resistance to pullout, on the contrary studies have shownthis decreases resistance to pullout.Turner et al examined the holding strength of small and large diameter screws in healthy bovine and diseased human bone. They found the screw diameter, trabecular orientation of the bone, and mineral content of the bone all affect the holding strength. A larger diameter screw, parallel placement to the trabecular pattern, and purchase in bone with a higher density all increase the holding strength.Gigantism affects which region of the growth plate labeled in Figure A?ABCDEGigantism, like achondroplasia, affects the proliferative zone (Region C of Figure A) of the growth plate. In Figure A, Region A is the epiphysis, Region B is the resting zone, Region D is the hypertrophic zone, and Region E is the metaphysis. Illustration A is another depiction of the physis which is labeled. Gigantism is typically caused by a pituitary adenoma which over secretes growth hormone. Its effect on the proliferative zone results in bone overgrowth and excessive height and limb length. Acromegaly may also becaused by a pituitary adenoma that over secretes growth hormone, but has its effect once the physis has closed.Plain radiographs do not provide an accurate assessment of bone mineral density (BMD) until what percentage of mineral has been lost?

Because of the previously transferred bone block of coracoid and short arm flexors, the musculocutaneous nerve often scars along the anteroinferior glenohumeral capsule. Mobilization of this tissue places the nerve at greatest risk. The axillary nerve is also potentially at risk, but this is nonspecific to prior surgery, particularly the Bristow procedure.

In a parallel design trial, participants are randomized to 2 or more groups, each of which receives a different treatment or intervention. For example, Group A receives the drug and Group B receives the placebo. This type of design allows for comparison between groups. In a crossover design clinical trial, both groups receive both interventions over a defined time period. For example, Groups A and B both receive the drug as well as the placebo. This allows for within-participant comparisons. In a cohort study, patient groups are followed over time on the basis of having or not having received an exposure. Cohort studies are not randomized. In a case series, patients often receive a particular treatment and the outcomes are then examined.

DISCUSSION: Necrotizing fasciitis (NF) results in the death of the body's soft tissue. It is a severe disease of sudden onset that spreads rapidly. Symptoms include red or purple skin in the affected area, with severe pain, fever, and vomiting. The most commonly affected areas are the limbs and perineum. Early diagnosis is difficult as the disease often looks like a simple superficial skin infection in the early stages. While a number of laboratory and imaging modalities can raise the suspicion for necrotizing fasciitis, the gold standard for diagnosis is a surgical exploration in the setting of high suspicion. When in doubt, a small "keyhole" incision can be made into the affected tissue. If a finger easily separates the tissue along the fascial plane, the diagnosis is confirmed and an extensive debridement should be performed. The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score can be utilized to risk stratify people who have signs of cellulitis and determine the likelihood of necrotizing fasciitis being present. It uses six serologic measures, including C-reactive protein, total white blood cell count, hemoglobin, sodium, creatinine, and glucose. Polymicrobial synergistic infection was the most common cause of necrotizing fasciitis (48 patients; 53.9%) with streptococci and enterobacteriaceae being the most common isolates. Group-A streptococcus was the most common cause of monomicrobial necrotizing fasciitis. The most common associated comorbidity was diabetes mellitus (63 patients; 70.8%).

Transcranial motor-evoked potentials provide the most specific early indicator of an intraoperative spinal cord injury. Somatosensory-evoked potentials are routinely used but do not have the sensitivity and specificity of motor-evoked potentials. EMG evaluations are routinely used for root evaluation following pedicle screw placement. BAERs are typically used in monitoring brain surgery.

DISCUSSION: A flexion contracture of the elbow is commonly seen in hemiplegic patients following cerebrovascular accidents. Spasticity and myostatic contracture of the joint are both causative factors. In patients with a flexion deformity of less than 90 degrees, musculocutaneous neurectomy is recommended, followed by serial casting to treat any residual deformity. At 9 months after injury, physical therapy will not significantly improve motion. Nerve blocks may be used in the early stages of recovery to facilitate therapy and serial casting. REFERENCE: Waters RL, Keenan ME: Surgical treatment of the upper extremity after stroke, in Chapman MW (ed): Operative Orthopedics. Philadelphia, PA, JB Lippincott, 1988, vol 2, pp 1449-1450.