1. General Principles & Basic Science MCQs

Of the materials listed titanium (100GPa) has an elastic modulus closest to cortical bone (approximately 18GPa) as well as cancellous bone (approximately 2GPa).Titanium is a material that is light, highly ductile, strong and corrosion resistant. However, titanium has poor wear resistance and is notch sensitive. It is commonly used as an orthopaedic implant materials because it has torsional and axial stiffness (moduli) that most closely mimics bone. Young’s modulus is constant and different for each material and represents the material's ability to maintain shape under external loading.Rho et al found that the average Young's modulus for trabecular bone measured ultrasonically and mechanically was 14.8 GPa (S.D. 1.4) and 10.4 (S.D. 3.5), respectively. The average Young's modulus of microspecimens of cortical bone measured ultrasonically and mechanically was 20.7 GPa (S.D. 1.9) and 18.6 GPa (S.D. 3.5), respectively.Illustration A depicts a stress vs. strain curve. The slope of the line in the elastic zone represents the Young Modulus of Elasticity.Incorrect Answers:

DISCUSSION: As a side effect of treatment, phenytoin induces osteomalacia, or rickets, in growing children, through interference with metabolism of vitamin D.  Oral supplementation of vitamin D can minimize this effect in patients who are undergoing prolonged treatment with phenytoin.REFERENCE: Chung S, Ahn C: Effects of anti-epileptic drug therapy on bone mineral density in ambulatory epileptic children.  Brain Dev 1994;16:382-385.

DISCUSSION: Following a radial nerve neurapraxia above the elbow, muscle recovery can be expected in a predictable pattern.  Although variations will occur, the return of function or reinnervation usually occurs in the following order:  brachioradialis, extensor carpi radialis longus, supinator, extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum comminus, extensor digiti minimi, extensor indicis proprious, extensor pollicis longus, abductor pollicis longus, and extensor pollicis brevis.REFERENCES: Netter F: The Ciba Collection of Medical Illustrations: The Musculoskeletal System.  Part 1, Anatomy, Physiology and Metabolic Disorders.  West Caldwell, NJ,Ciba-Geigy, 1991, vol 8, p 53.Hollinshead WH: Anatomy for Surgeons: The Back and Limbs, ed 3.  Philadelphia, PA,Harper and Row, 1982, vol 3, pp 428-429.

DISCUSSION: Adductor myodesis is critical for optimal outcome after transfemoral amputation. Pinzur et al. emphasize that when the adductors are not anchored to bone, the hip abductors are able to act unopposed, producing a dynamic flexion-abduction deformity. This deformity prepositions the femur in an orientation that is not conducive to efficient walking. The retracted adductor muscles lead to a poorly cushioning soft-tissue envelope, further complicating prosthetic fitting. Preservation of a functional adductor magnus helps to maintain the muscle balance between the adductors and abductors by allowing the adductor magnus to maintain its power and retain the mechanical advantage for positioning the femur. Preservation is best accomplished with a myodesis.

Ligaments are viscoelastic, meaning that their deformation under load depends not only on the magnitude of the load but also on the rate of loading. Under higher load rates (faster loading), natural ligaments are stiffer and stronger. Therefore, it is important in such an experiment to apply a loading rate that is physiologically relevant, ie, that represents typical or worst case activities. Creep refers to deformation of a viscoelastic material over time under constant load. Stress relaxation refers to a decrease in stress over time under a constant displacement.

r the medial 1/3The picture shows a laterally subluxed and a relatively-externally rotated patella on a femoral component. The question tells us that the femoral component is internally rotated and the tibial component is perfectly placed. If we know that the femoral component should be externallyrotated about 3 degrees, we know that in this patient, that’s where the problem is. So, we don’t have to do anything to the quads, tubercle or tibial component. We need to revise the femur. Besides, a lateral retinacular release may damage the lateral geniculates; since this patient most likely had a medial arthrotomy, this may devascularize the patella and lead to patellar AVN. A lateral retinacular release will not address the malpositioned components )back to this question next question

The findings in this patient are classic for septic arthritis. If confirmed by aspiration, urgent debridement of the joint is required to help prevent long-term sequela of septic arthritis. IV antibiotics alone are not an appropriate treatment for septic arthritis of the hip. Additional prolonged work-up with rheumatology, Western Blot, and MRI would most likely delay the prompt surgical treatment of septic arthritis of the hip.(SBQ13PE.61) Mutations in genes COL1A1/COL1A2 are responsible for the clinical manifestations of:Review TopicMarfan's syndromeOsteopetrosisOsteogenesis imperfectaAchondroplasiaMultiple Epiphyseal DysplasiaOsteogenesis imperfecta is caused by mutations in type I collagen genes COL1A1 or COL1A2 in 85% of cases.Pathological manifestions of osteogenesis imperfecta (OI) occur because of abnormal type 1collagen . Clinical manifestations include multiple fractures, blue sclera, and scoliosis. The genes responsible for normal collagen synthesis are COL1A1/COL1A2 and many mutations have been characterized which result in OI. Quantitative collagen defects result in a milder phenotype whereas qualitative collagen defects result in more severe clinical manifestations.Zeitlin et al. reviewed osteogenesis imperfecta. They report that bone fragility in OI stems from decreased bone mass, disturbed organization of bone tissue, and altered bone geometry (size and shape). They found that cyclical intravenous pamidronate administration reduces bone pain and fracture incidence while increasing bone density and level of ambulation with minimal side effects.Burnei et al. review the diagnosis and treatment of OI. They report that medical treatment with bisphosphonates, even in patients younger than age 2 years, have become widely accepted in the symptomatic treatment of OI. They report alendronate has proven to beneficially decrease fracture frequency while improving vertebral bone density and quality of life.Illustration A shows the Sillence Classification of Osteogenesis Imperfecta. Incorrect Answers:

DISCUSSION: C-reactive protein declines rapidly as the clinical picture improves.  Failure of the C-reactive protein to decline after 48 to 72 hours of treatment should indicate that treatment may need to be altered.  Blood culture is positive only 50% of the time and will be negative soon after antibiotics are administered, even if treatment is not progressing satisfactorily.  WBC count is highly variable and poorly correlated with treatment.  The ESR rises rapidly but declines too slowly to guide treatment.  Radiographic findings may not change but can take up to 2 weeks to show changes.REFERENCE: Unidia-Kallio L, et al:  Serum c-reactive protein, ESR and WBC in acute hematogenous osteomyelitis in children.  Pediatrics 1994;93:59-62.

This patient presents with symptoms and findings highly suspicious for super- imposed septic arthritis and gout. This patient is likely going to need to go to the operating room for emergent I&D (not listed as an answer choice). Because cultures have already been obtained, the most appropriate next step in management would be to begin empiric intravenous antibiotics.While the incidence of superimposed gout and septic arthritis is low (~1.5%),it is reported. In the presence of crystals on aspiration, one should not rule out the possibility of septic arthritis. If there are other risk factors for infection, or the synovial WBC count is high (greater than 50,000), then empiric antibiotics should be initiated immediately after cultures are obtained. If the patient has other evidence supporting septic arthritis (positive Gram stain, purulence), emergent I&D is indicated. Even if the initial suspicion is lower, if they havenot respond to antibiotics after 24-48 hours they should undergo I&D.Shah et al. investigated 265 crystal-positive joint aspirates in a 7-year retrospective study. They found the incidence of concomitant septic arthritis and crystal disease was 1.5% (4 cases including 2 knees, 1 hip, 1 ankle). All 4 patients that had superimposed infection had a WBC of > 50,000. They concluded that the presence of crystals in the synovial fluid cannotconclusively rule out a septic joint.Schuind et al. described a case report of concomitant septic arthritis and gout of the wrist. They found that cultures were positive for Staphylococcus aureus while pathological examination revealed aggregated crystals of monosodium urate.Figure A shows tense, erythematous swelling of the right knee. Figure B is a table showing synovial fluid analysis with elevated WBC and PMN cell count characteristic of septic arthritis. Figure C shows needle-shaped negatively birefringent crystals on polarizing microscopy. Illustration A shows the synovial fluid characteristics in different disease conditions.Incorrect Answers:An 82-year-old osteoporotic woman undergoes total hip arthroplasty for osteoarthritis. During implant trialing, a crack is heard. Intraoperative fluoroscopy reveals a long, spiral fracture of the distal femur. The fracture is reduced and fixed with an anatomic locking plate. The rest of the total hip arthroplasty proceeds uneventfully. Following surgery the surgeon has a meeting with the family and apologizes and provides full disclosure, accepts responsibility, provides a detailed explanation as to what happened, and gives reassurance that steps will be taken to prevent recurrences. This communication approach will most likelyLead to lower patient satisfaction ratesLead to higher patient satisfaction ratesLead to higher likelihood the patient will take legal action against surgeonLead to higher likelihood the patient will change physiciansPrevent any legal actionThe surgeon has provided all the elements of good communication with the patient and family. His actions will lead to improved patient satisfaction, compared to nondisclosure and attempting to push or shirk responsibility.In the event of a medical error or adverse event, effective communication with the patient and family is necessary. Effective communication should comprise:an apology, full disclosure (an explanation of what happened), accepting responsibility, and corrective steps that will be taken to prevent recurrence.While accepting responsibility is integral to the explanation process, it is different from accepting blame.Mazor et al. found patients would more likely change physicians and seek legal advice in situations with a life-threatening outcome where physicians chosenon-disclosure. They recommend full disclosure, acceptance of responsibility, an apology, detailed explanations, and assurances that steps will be taken to prevent recurrences will result in positive outcomes in terms of patient satisfaction, trust, and emotional response.MacDonald et al. addressed medical errors in an editorial. Besides full disclosure, they feel that an apology is necessary. This includes an acknowledgement of the event and one’s role in the event, and a genuine expression of regret. Apology laws exist to to reduce concerns about legal implications of disclosure and apology.Incorrect Answers:The acquired immune response mediated by the interaction between the T cell receptor and major histocompatibility complex requires which of the following first steps?Antigen phagocytosis by T cellsAntigen processing and presentation to T cellsAntigen recognition by natural killer T cellsAntigen proliferation by polymerase chain reactionT cell disulfide bond cleavage and enzymatic processingThe process of antigen processing and presentation is the first step of the acquired immune response. This is performed by the so called antigen presentation cells (APC) of which B cells and dentritic cells are two examples. The APC breaks down the protein antigen in a multitude of enzymatic reactions and presents key peptide sequences via the major histocompatibility complex(MHC) receptors. Once presented on the surface of the APC, the T-cell receptor recognizes the MHC/antigen complex leading to T-cell activation. At no point in this process are antigens phagocytosed by T cells. Natural killer T cells are involved in this sequence, but not for antigen processing and presentation. Polymerase chain reaction is a laboratory tool used to amplify nucleic acid. Finally, disulfide bond cleavage is a step involved in the APCs antigen processing reaction and does not occur in T cells.All of the following are true regarding a physician responding to a formal written complaint by a patient EXCEPT:Complaint should be taken seriouslyWritten response by the physician is requiredPhysician mandated to retain an attorney to address the formal complaintPatient should be supplied with contact information for the institution's patient representative departmentLaw mandates that the physician respond to the formal complaintIt is important for the surgeon to know how to manage a formal complaint. An attorney is not required to assist on behalf of the physician when addressing a formal complaint. All complaints must be taken seriously and the physician is required by law to respond to all formal complaints in writing. Verbalresponses to formal, written complaints are not sufficient. If a patient is filing a formal complaint it is advisable that the patient be supplied with contact information for the institution's patient representative department.What laboratory findings would you expect to find in a patient newly diagnosed with renal osteodystrophy?Decreased PTH secretion, hypophosphatemia, and hypocalcemiaIncreased PTH secretion, hyperphosphatemia, and hypocalcemiaDecreased PTH secretion, hypophosphatemia, and hypercalcemiaIncreased PTH secretion, hyperphosphatemia, and hypercalcemiaHypophosphatemia and hypocalcemiaRenal osteodystrophy is characterized by bone mineralization deficiency due to the electrolyte and endocrine abnormalities associated with chronic kidney disease. The pathogenesis of renal osteodystrophy is multifactorial. Hypocalcemia occurs due to the inability of the damaged kidney to convert vitamin D3 into its active form, calcitriol. The hypocalcemia and lack of phosphate excretion by the damaged kidney causes hyperparathyroidism and secondary hyperphosphatemia.Loss of function in the 25(OH) vitamin D1-alpha hydroxylase gene causes which of the following diseases?HyperphosphatemiaVitamin D resistant ricketsHereditary Vitamin D dependant rickets type IHereditary Vitamin D dependant rickets type IIHypophosphatemic ricketsLoss of function mutations in the 25 (OH) vitamin D hydroxylase gene cause hereditary vitamin D dependant rickets type I. Hereditary vitamin D dependant rickets type II is caused by a defect in intracellular receptor for 1,25-(OH)2- vitamin D3. Both forms ofhereditary vitamin D dependent rickets show decreased serum calcium/phosphorous, elevated alkaline phosphatase/PTH,but type I has a decrease in the 1,25(OH)2 vitamin D and type II shows a increase in 1,25(OH)2 vitamin D. Vitamin D resistant rickets (Familial Hypophosphatemic Rickets) is caused by a large deletion in the PHEX gene and results in low serum phosphorous, elevated alkaline phosphatase, and normal calcium. Hyperphosphatemia can be caused by mutation in the GALNT3 gene and results in elevated serum phosphate and decreased PTH/calcium.Kato et al. describe the molecular physiology of vitamin D metabolism and the recognized gene mutations associated with various clinical manifestations of mutations in vitamin D homeostasis.Figure A is a radiograph taken after an open reduction and internal fixation of a periprosthetic distal femur fracture. With this type of hybrid locked plate fixation, what is the difference between screw A and screw B?Screw A can assist in fracture reduction while screw B provides a fixed angle supportScrew A provides improved axial stiffness while screw B provides a fixed angle supportScrew A can be used to reduce the plate to bone while screw B can be used to lag fracture fragments togetherScrew A provides a fixed angle support while screw B can be used to reduce the plate to the boneScrew A can be used to lag fracture fragments together and screw B increases the plate bone frictional stabilityLocking screws provide a fixed angle support and can improve fixation in osteoporotic bone while nonlocking screws can be used to reduce the plate to the bone, lag fracture fragments together and increase the plate bone frictional stability. "Hybrid" locked plate fixation utilizes both screw types in order to assist with difficult fracture fixation such as when there is a short metaphyseal segment and osteoporotic bone.Zura et al discusses the biomechanical and biological advantages offered by locked plate fixation.Using levels of evidence in research studies, which of the following represents a level II study?Retrospective case control studyProspective cohort studyCase report of 3 patients with the same diseaseHigh-quality randomized prospective clinical trialThe opinion of a review panel at the annual AAOS meetingLevel II Evidence includes prospective cohort studies. There are 5 levels of evidence in clinical research. Level I includes randomized clinical trials. Level II includes prospective cohort studies. Level III includes case control studies AND retrospective cohort studies. Level IV includes case series. Level V evidence includes expert opinion, case reports, and personal observation. The cited reference by Bernstein et al is an excellent review of Evidence Based Medicine (EBM) and describes the 5 step process of making medical decisions based on the available, and often limited, evidence. These steps include: 1) Formulate answerable questions. 2) Gather the evidence. 3) Appraise the evidence. 4) Implement the evidence. 5) Evaluate the process. The reference by Spindler et al is another review article that discusses the different levels of evidence for different study types.All of the following are true regarding the assessment of bone mineral density EXCEPT?Bone mineral density loss is not apparent on standard radiographs until 30% to 40% of mineral is lostDual energy x-ray absorbtiometry (DEXA) is only able to measure mineralization of the axial skeletonSingle photon absorbtiometry allows for the analysis of bone mineralization in the appendicular skeleton aloneQuantitative computed tomography (QCT) is associated with 10 times the radiation of a DEXA scanMRI allows for accurate discrimination of normal bone from osteopenic boneswithout exposing the patient to ionizing radiationDual energy x-ray absorbtiometry (DEXA) scans allow for accurate assessment of bone mineralization in both the axial and appendicular skeleton.Over the last decade, DEXA has become a safe, cost-effective and reliable method to quantify bone mineral density. The World Health Organization (WHO) has adopted DEXA derived BMD measurements to define normal bone, osteopenia, and osteoporosis in the adult and paediatric population. The typical DEXA analysis therefore reports a Z-score, which is the number of standard deviations (SDs) that a patient's BMD is above or below the mean value for persons of the patient's age and sex. The T score is the number of SDs the patient's BMD is either above or below the mean value for young patients of the same gender.Tortolani et al. provide an overview of the techniques used to assess bone mineral density, the pathophysiology of osteopenia, and the evaluation and treatment options for the general pediatric population as well as for patients with specific pediatric disorders. The authors encouraged orthopaedic surgeons to understand the problems of osteopenia in both otherwise healthy children and children with chronic disorders.Binkovitz & Henwood provide a review of DEXA technique and interpretation with emphasis on the considerations unique to pediatrics. They found that changes in bone size over time, as occurs in normal pediatric development, confound DXA interpretation. This is one of the major limitations in the use of pediatric DXA. However, attempts to correct for or to circumvent this limitation have been proposed and show promise in improving DXA interpretation andour understanding of bone physiology.T-score according to the World Health Organization (WHO): A T- score of -1.0 or above is normal bone density.A T-score between -1.0 and -2.5 means you have low bone density or osteopenia.A T-score of -2.5 or below is a diagnosis of osteoporosis.Incorrect Answers:A mother brings her 4-year-old daughter to your clinic for evaluation of knocked knees and short stature. On exam, the patient ambulates with a circumduction gait pattern and frequently falls. Plain radiographs are displayed in Figure A. Laboratory data is obtained and notable for calcium 9.1 mg/dL (RR 8.5-

DISCUSSION: An MRI scan is both highly sensitive and specific for the evaluation of osteonecrosis.  The measurement of increased intraosseous pressure can be technically difficult and the results have been variable.  Plain radiographs can be normal early in the progression of osteonecrosis of the femoral head.  The technetium Tc 99m bone scan is a very sensitive test.  However, it is not specific; increased uptake can be noted in patients with arthritis, neoplastic disease, fracture, or sepsis.  In addition, because of bilaterality, the frequency of false-negative scans is relatively high.REFERENCES: Steinberg ME: Early diagnosis, evaluation, and staging of osteonecrosis, in Jackson DW (ed): Instructional Course Lectures 43.  Rosemont, IL, American Academy of Orthopaedic Surgeons, 1994, pp 513-518.Glickstein MF, Burk DL Jr, Schiebler ML, et al: Avascular necrosis versus other diseases of the hip: Sensitivity of MR imaging.  Radiology 1988;169:213-215.

Water content is increased early in the OA cartilage and is associated with the loss of proteoglycan and an increase in the collagen/proteoglycan ratio. Collagen synthesis is increased, but the majority of the material synthesized is Type II, not Type I collagen. Type I collagen increases slightly, particularly in the osteophyte region.Chondrocytes in OA are much more metabolically active than those of normal cartilage. Studies reveal measuring the levels of utilization on sulfate and H-glucosamine informing components of cartilage matrix. The amount of DNA also rises in OA cartilage most noticeable at the articular chondrocyte.The synthesis of hyaluronate increases. Recent data suggests 1) hyaluronate that is synthesized is abnormal and, hence, does not allow aggregation; or 2) The excess synthesis is a response to a rapid degradation of synthesized product. This is in light of the fact that synthesis increases, yet concentration of hyaluronate decreases.The correct answer is that proteoglycan content decreases. The synthesis of proteoglycan increases in OA, but due to the increased rate of breakdown of proteoglycan there is a net result of lowered proteoglycan content.

DISCUSSION: The most likely diagnosis is acute osteomyelitis.  She may also have a septic wrist; however, the lytic lesion in the distal radius has the typical presentation and radiographic appearance of metaphyseal osteomyelitis.  In this area of sluggish vascular flow, low oxygen tension, and low pH, bacterial seeding is common and is the usual origin of metaphyseal osteomyelitis.  Leukemia and Ewing’s sarcoma can present as a lytic lesion with an elevated erythrocyte sedimentation rate, but they are much less common than osteomyelitis and are less focal and more destructive in appearance.  Nonossifying fibroma is typically metaphyseal and eccentric; however, it is well circumscribed and uncommon in the upper extremity.  Eosinophilic granuloma does not typically present with inflammatory indicies.REFERENCES: Dormans JP, Drummond DS: Pediatric hematogenous osteomyelitis: New trends in presentation, diagnosis and treatment.  J Am Acad Orthop Surg 1994;2:333-341.Song KM, Sloboda JF: Acute hematogenous osteomyelitis in children.  J Am Acad Orthop Surg 2001;9:166-175.

DISCUSSION: The pedigree documents involvement of male offspring only, and it also shows transmission through an uninvolved female carrier.  This inheritance pattern is most consistent with a x-linked recessive inheritance.  It would be inconsistent with a dominant inheritance pattern unless there was incomplete penetrance.  Autosomal-recessive inheritance would be possible only if the family member labeled II.F was also a carrier of the same gene; however, this is unlikely.  Mitochondrial inheritance is possible, but as with autosomal patterns, mitochondrial inheritance normally affects both male and female offspring.  It is transmitted only through the maternal line.REFERENCE: Gelehrter TD, Collins FS: Principles of Medical Genetics.  Baltimore, Md, Williams & Wilkins, 1990, pp 27-45.

DISCUSSION: Chronic dislocation of the patella is occasionally seen in patients with Down syndrome.  In early childhood, patellar realignment may restore stability of the patellae.  In later childhood, bony changes in the patellar groove interfere with stability, even if surgical realignment is performed.  Realignment can also lead to increased knee pain postoperatively.  In asymptomatic patients who are able to extend their knees, continued observation is the management of choice.REFERENCES: Dugdale TW, Renshaw TS: Instability of the patellofemoral joint in Down syndrome.  J Bone Joint Surg Am 1986;68:405-413.Mendez AA, Keret D, MacEwen GD: Treatment of patellofemoral instability in Down’s syndrome.  Clin Orthop 1988;234:148-158.

DISCUSSION: BotulinumA toxin acts by interfering with presynaptic acetylcholine release at cholinergic nerve terminals without destroying nerve endings, nerve terminals, or neuromuscular junctions. Thus, the toxin blocks neuromuscular control and functionally denervates the muscle.

EXPLANATION:The lateral cord of the brachial plexus gives off the lateral pectoral nerve, the musculocutaneous nerve, and then contributes to the median nerve. The patient has had recovery of function of these components except for the musculocutaneous nerve. The musculocutaneous nerve innervates the biceps and the brachialis, which provide elbow flexion. To restore motor function, a nerve transfer would have to providereinnervation of the biceps and brachialis.

Angiotensin II receptor blockade (e.g. losartan) administered after injury has been shown to improve muscle regeneration and decrease fibrosis in normal skeletal muscle.Skeletal muscle undergoes a natural process of healing and regeneration after injury. The formation of fibrous tissue in place of normal muscle is also part of this process. However, fibrous tissue in place of muscle can predispose the area to re-injury and impaired function. Administration of angiotensin II receptor blockade medications (e.g. losartan) after skeletal muscle injury has been shown to decrease the apoptotic cascade response and the formation of fibrous tissue. The mechanism of benefit is thought to be associated with blockade of insulin-like growth factor.Terada et al. looked at the affect of platelet-rich plasma (PRP) and losartan on muscle healing after contusion injuries. They showed that PRP plus losartan combinationtherapy improved overall skeletal muscle healing by enhancing angiogenesis and follistatin expression as well as reducing the expression of phosphorylated Smad2/3 and the development of fibrosis.Bedair et al. used a rat model to investigate the effect of angiotensin receptor blockade on muscle fibrosis after injury. They found that angiotensin receptor blockade therapy significantly reduced fibrosis and led to an increase in the number of regenerating myofibers in acutely injured skeletal muscle.Incorrect

Intra-articular distal humerus fractures are best approached through a posterior elbow approach, including an olecranon chevron osteotomy to clearly visualize the reduction of the articular surface. The other stated approaches will not provide sufficient visualization of the joint surface to allow stable reduction. A closed reduction and screw fixation will not offer optimal fracture stability.

DISCUSSION: A knock-out mouse to the Vitamin D receptor would cause loss of vitamin D function, resulting in rickets. Renal failure would not occur; although Vitamin D is converted from 25 (OH) D to 1,25 (OH) D in the kidney, the active hormone acts on the gut and bone.  Osteopetrosis can be seen as the phenotype for the c fos knock-out mouse; the Jansen-type metaphyseal dysplasia phenotype results from overactivation of the PTH/PTHrp receptor.  Although compensatory hyperparathyroidism would occur, excessive PTH would not be able to rescue the skeletal loss and instead phosphoturia and phosphotasia would result.REFERENCES: Glowacki J, Hurwitz S, Thornhill TS, et al: Osteoporosis and vitamin-D deficiency among postmenopausal women with osteoarthritis undergoing total hip arthroplasty.  J Bone Joint Surg Am 2003;85:2371-2377.Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2.  Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, p 51.