1. General Principles & Basic Science MCQs

DISCUSSION: The patient has the typical history and presentation of transient synovitis of the hip, a condition that is more common in children age 2 to 5 years but which may affect children up to 12 years.  The discomfort typically is noted on awakening, and the child will refuse to walk.  Later in the day, the pain commonly improves and the child can walk but will have a limp.  Mild to moderate restriction of hip abduction is the most sensitive range-of-motion restriction.  The extent of the evaluation for transient synovitis depends on the intensity and duration of symptoms.  Because she has been afebrile for the past 24 hours, observation is the management of choice.  In the differential diagnosis of suspected transient synovitis, septic arthritis of the hip is the primary disorder to exclude.  Osteomyelitis of the proximal femur also should be considered.  In most patients, clinical examination will differentiate of these disorders to a reasonable certainty.  Plain radiographs are normal in the early stage of an infectious process.  Ultrasonography shows increased fluid in the hip joint in both transient synovitis and septic arthritis.  MRI can differentiate the two conditions; however, this test would require general anesthesia and is not required in most patients in this age group.  If a child with transient synovitis has a concurrent infectious process such as an upper respiratory tract infection or otitis media, the temperature will most likely be elevated.  In this situation, a full evaluation for an infectious process and initiation of IV antibiotics should be considered.  This would include radiographs, CBC count, erythrocyte sedimentation rate, blood cultures, aspiration of the hip joint, and IV antibiotics.REFERENCES: Del Beccaro MA, Champoux AN, Bockers T, Mendelman PM: Septic arthritis versus transient synovitis of the hip: The value of screening laboratory tests.  Annals Emerg Med 1992;21:1418-1422.Kehl DK: Developmental coxa vara, transient synovitis, and idiopathic chondrolysis of the hip, in Morrissy RT, Weinstein SL (eds): Lovell and Winter’s Pediatric Orthopaedics, ed 5.  Philadelphia, PA, Lippincott Williams and Wilkins, 2001, pp 1035-1058.

Brown-Séquard syndrome is most commonly seen after penetrating injuries to the spinal cord and results in ipsilateral loss of motor function and contralateral loss of pain and temperature sensation. Patients with central cord syndrome have greater weakness in the upper extremities than in the lower extremities. Loss of proprioception is typically seen in patients with posterior cord syndrome.

DISCUSSION: The plantar-medial cutaneous nerve is at risk with the surgical approach to the medial sesamoid.  It is found directly underlying an incision made at the junction of the glabrous skin of the hallux and must be identified before the approach can proceed.  Transection will result in a painful neuroma that impinges on the plantar-medial surface of the toe and cause problems with shoe wear.  The only other structure that lies near the surgical field is the abductor hallucis tendon which lies dorsal to the incision.REFERENCE: Sarrafian SK: Anatomy of the Foot and Ankle, Descriptive, Topographic, Functional, ed 2.  Philadelphia, PA, JB Lippincott, 1993, p 377.

DISCUSSION:A high hip center is not recommended for Crowe type IV hips because of the lack of acetabular bone and altered hip biomechanics. An anatomic center is a better option but necessitates a technique to address the tight  soft-tissue  envelope.  A  trochanteric  osteotomy  with  progressive  femoral  shortening  has  been described but can be prone to trochanter nonunion. Iliofemoral lengthening prior to surgery has been described  but  may  not  be  tolerated  by  all  patients.  A  shortening  subtrochanteric  osteotomy  avoids trochanter nonunion and allows adjustment of femoral anteversion. Fixation of the osteotomy can include a stem with distal rotational control, plate fixation, a step versus oblique cut, or strut grafts.

DISCUSSION: Gaucher’s disease is characterized by macrophage accumulation of glucocerebroside that is caused by a deficiency of lysosomal enzyme glucocerebrosidase. It is an autosomal-recessive trait and is most commonly found in Ashkenazi Jews. Orthopaedic surgeons see patients with Gaucher’s disease usually because of osteonecrosis of the hip. Calcium pyrophosphate is associated with pseudogout. Hydroxyproline is a breakdown product of collagen and is found in high levels in patients with Paget’s disease. Homogentisic acid is associated with ochronosis (alkaptonuria).

Hyaluronic acid (HA) is abundant in cartilage and synovial fluid and is thought to be integral to joint lubrication, although its role is not clearly understood. HA binds to lubricin, a glycoprotein, creating a cross-linked network. Boundary lubrication occurs when the fluid film has been depleted and the contacting bearing surfaces are separated only by a boundary lubricant of molecular thickness, which prevents excessive bearing friction and wear. In articular cartilage, this monolayer of glycoprotein is adsorbed on each of the opposing articular surfaces. Friction experiments in a porcine model have shown that with compression, HA diffuses out of the cartilage and becomes physically trapped and constricted by the collagen network at the interface. This in effect creates a "boundary lubricant." Vitronectin is a glycoprotein similar in the N and C terminal to lubricin. It does not bind to HA. Aggrecan is the second-most-common protein by dry weight of cartilage extracellular matrix. Aggrecan interacts with HA and link proteins to create a proteoglycan aggregate that attracts water to cartilage and gives the tissue its viscoelastic properties. Chondroitin sulfate contributes to matrix proteoglycan structure rather than boundary lubrication.

The mass or volume of a muscle is proportional to its work capacity, and the fiber length of a muscle is proportional to its potential excursion. By dividing the fiber length into the volume of each muscle, the cross-sectional area of the muscle is determined.The concept of physiologic cross section of a muscle from Weber and Fick, identifies the critical importance of the cross sectional area of all the fibers of a muscle as proportional to maximum tension. (Relationship between muscle size and muscle strength).

Muscle force during isometric contractions (muscle not allowed to shorten) varies with starting length. If the length is too long, the sarcomeres generate little or no active tension. If a muscle is overstretched during certain surgical procedures, then the patient may generate less than 30% maximal force. The force-velocity relationship describes isotonic (constant load) conditions.

In a review of the practical applications of antibiotic-loaded bone cement for the treatment of infected total joint arthroplasties, Hanssen and Spangehl described commercially available antibiotic-loaded bone cement as low-dose antibiotic cements. These cements generally contained 0.5 g of either tobramycin or gentamicin per 40 g of cement. They are indicated for use in prophylaxis and not for treatment of infected total joint arthroplasties. High-dose antibiotic-loaded bone cements are described as those containing greater than 1.0 g of antibiotic per 40 g of cement. Effective elution levels have been documented with 3.6 g tobramycin and 1.0 g vancomycin per 40 g of bone cement. This was documented by Penner and associates. Furthermore, it was shown that the combination of the two antibiotics in the bone cement improved the elution of both antibiotics.

DISCUSSION: The ascending branch of the lateral femoral circumflex artery crosses the gap between the tensor fascia lata and the sartorius and must be identified and ligated or coagulated. The other vessels are out of the field of dissection. REFERENCES: 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 312. Hoppenfeld S, deBoer P: Surgical Exposures in Orthopaedics: The Anatomic Approach. Philadelphia, PA, JB Lippincott, 1984, p 304.

Which of the following statements about the lateral femoral cutaneous nerve is true? It courses under the inguinal ligament.

The meniscofemoral ligaments connect the posterior horn of the lateral meniscus to the intercondylar wall of the medial femoral condyle. The ligament of Humphrey (arrow) passes anterior to the posterior cruciate ligament, whereas the ligament of Wrisberg passes posterior to the posterior cruciate ligament.

The mechanism by which bisphosphonates act is by inhibiting osteoclasts. One mechanism of bisphosphonates is to cause osteoclast apoptosis. Another mechanism of bisphosphonates is to disrupt the cytoskeleton of osteoclasts, resulting in loss of the ruffled border. The uncoupling of bone resorption and bone formation with decreased bone resorption results in increased bone mineralization. This translates into fewer fractures in patients with osteogenesis imperfecta and improved quality of life.

DISCUSSION: Because the man is only recently removed from his injury and is judged capable of returning to work with some restrictions, the term that best describes his work status is temporary partial disability. REFERENCE: Beaty JH (ed): Orthopaedic Knowledge Update 6. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 131-137.

DISCUSSION: The radiograph reveals severe intestinal dilatation, which has occurred as the result of acute colonic pseudo-obstruction and is associated with excessive narcotic administration following total joint arthroplasty. Anesthetic type, antibiotic administration, and warfarin have not been associated with this obstruction. Electrolyte imbalances such as hypokalemia have been associated with postsurgical acute colonic pseudo-obstruction.

In a postganglionic injury to the brachial plexus, the rhomboid muscle, innervated by the dorsal scapular nerve, would still be expected to function. This is a useful clinical sign that the brachial plexus lesion is postganglionic as opposed to preganglionic. The musculocutaneous, axillary, and suprascapular nerves are all located distal to Erb’s point (the most common location of an upper nerve root brachial plexus injury), and all contain fibers from the C5 and C6 nerve roots. Therefore, these nerves are not expected to function normally following a postganglionic C5 and C6 nerve root injury.

This is prospective cohort study with Level-II evidence.Level of evidence provides guidance to the study quality. It is used to assess therapeutic studies (as with this question), prognostic studies, diagnostic studies and economic or decision models. When determining the level of evidence, readers must critically appraise the study question, treatment, intervention and outcomes of the study design. Level-II therapeutic studies consist of well-designed prospective cohort studies, poor-quality randomized controlled trials (follow-up less than 80%) and systematic review of Level-II studies or non-homogenous Level-I studies.Wright et al. provided an excellent summary of clinical research study level of evidence. This has been provided as Illustration A.Illustration A shows a chart of level of evidence. There is a column for each type of study which corresponds to a row that outlines the level of evidence based on studydesign.Incorrect Answers:Low serum phosphate and normal calcium levels are found in what common etiology of hereditary rickets?X-linked hypophosphatemicVitamin D-dependent, type IVitamin D-dependent, type IIAutosomal dominant hypophosphatemicJansen's metaphyseal chondrodysplasiaLow serum phosphate and normal calcium levels are found in X-linked hypophosphatemic rickets.X-linked hypophosphatemic rickets is the most common form of hereditary rickets. It is an X-linked dominant disorder which has been linked to the PHEX gene. Laboratory findingsof this disorder include low serum phosphate, normal serum calcium and 25 hydroxycholecalciferol levels, and inappropriately low 1,25-dihydroxyvitamin D3.Carpenter et al. showed hypophosphatemic rickets was initially referred to as “vitamin D resistant rickets” due to its lack of response to therapeutic vitamin D. Current treatment with activated vitamin D metabolites (calcitriol oralfacalcidol) and phosphate salts have been shown to help with this condition.Illustration A shows an insufficiency fracture of the proximal tibia in an adult patient with X-linked hypophosphatemic rickets. A stress fracture on the medial tibia may be a presenting feature of untreated disease.Incorrect Answers:receptor (PTHR1).A healthy patient undergoes routine pre-operative laboratory testing and is found to have a leukocyte count of 1.5 × 10(9) cells/L. When the historical records are examined, this is found to be the patients base-line level over a period of years. Which of the following statements is most likely to be true:The patient is at a significantly higher risk of surgical infectionThe patient is more likely to be of African than of European descentThe patient is more likely to be of European than of Middle Eastern descentThe patient is more likely to be a non-athlete than an athleteThe patient is more likely to be female than maleThe clinical presentation is consistent with Benign Ethnic Neutropenia, a condition in which a patient has chronic, benign, inborn and lifelong absolute neutrophl count below population mean. This condition is found in the U.S. to be most common in African- Americans, some groups of Middle Eastern patients, males, children under 5 years old, and athletes compared to non- athletes.A standardized level at present for abnormally low absolute neutrophil count (ANC) is below 1.5 x 10(9) cells/L, however this may not have clinical or scientific relevance as a cutoff point, particularly in the affected Ethnic groups. Fewer than 1% of all populations have absolute neutrophil count < 1.0 X 10(9) cells/L. Most patients in the affected ethnic groups with low ANC and no associated history or symptoms are not expected to have any increased risk of infection or adverse effect. Smoking was also associated with higher leukocyte and neutrophil counts but proportionately lower increase in African-American patients. One hypothesis for the increased prevalence of B.E.N. in patients of African descent is a theorized evolutionary protection against malaria, thoughit remains unclear if this is causal or just correlative.Haddy et al. provide an excellent scientific review of B.E.N. and emphasize the importance of recognizing this most common form of neutropenia.Eichner et al. review B.E.N. in the setting of sports medicine and state the relative increase of these lab findings in athletes vs non-athletes.Hsieh et al. provide an extensive cross-sectional population study focused on the prevalence of Benign Ethnic Neutropenia in the U.S. They reviewed 25,222 participants in the National Health and Nutrition Examination Survey 1yr ofage or older from 1999-2004, and detail the association of this condition with age, sex, ethnicity, and smoking status.Denic et al. analyzed neutrophil count in a healthy Arab population in the U.A.E. and found low neutrophil counts in this population with a distribution suggestive, but not definitively, of an autosomal dominant inheritance. They also discuss the hypothesized association of B.E.N. and malaria infection.Incorrect answers:

A muscle's response to injury can be divided into 4 phases: necrosis, inflammation, repair, and fibrosis. Muscle fibrosis occurs at the same time as muscle regeneration and has been shown to involve TGF-ß1. IGF-1 and bFGF are important trophic factors in muscle regeneration. Bone morphogenetic protein has several functions including bone and cartilage regeneration.