1. General Principles & Basic Science MCQs

DISCUSSION: Chondrocytes are obtained from cartilage harvested from non-weight-bearing areas of the knee. The extracellular matrix is digested, and the chondrocytes are expanded for later transplantation. Cells implanted into a defect are secured with a flap of periosteum. Cells are expanded to obtain 20 to 50 times the original number of cells to transplant at a cell density of 3x10^7 cells/mL. There is a direct relationship between cell number and biosynthetic activity. Osteochondral lesions of up to 8 mm may be treated with autologous transplant alone; larger depth lesions should be bone grafted at the time of harvest. Mesenchymal stem cells differentiate easily into fibrous tissue, bone, and fat; conversion of mesenchymal stem cells into cartilage in vitro currently is difficult to accomplish. Goldberg and Caplan, however, were able to obtain cartilage repair using mesenchymal stem cells transplanted into defects in rabbits in vivo. In animal studies, fluorescent-labeled cells persist for at least 14 weeks, integrate with the surrounding normal margins, and become part of the repaired tissue replete with sulfated proteoglycans and type II collagen.

DISCUSSION: It is appropriate for orthopaedic surgeons to have relationships with industry as long as the relationship is for the good of the patient and no “quid pro quo” intent exists. A grant to cover registration at a CME event is appropriate but travel and hotel for a spouse is not. For orthopaedists who are faculty at a meeting sponsored by industry, it is appropriate for travel and expenses to be covered for that faculty member. Care must be exercised that the faculty member contributes in an amount appropriate for the expenses paid. The faculty member must ensure that information presented is unbiased and based on reasonable data and opinion. Consulting agreements should spell out specifically the duties of the agreement and payment should be appropriate for the time spent. There should be a defined work product for the consulting. Agreements that are thinly veiled payments for use of a company’s products must be avoided. In all cases, the agreements must stand up to public scrutiny. Restricted grants for specific industry-sponsored programs aimed at residents are not appropriate. Unrestricted grants intended for attendance at approved CME courses are appropriate. Dinners at which information is presented about topics that can aid in patient care are appropriate as long as the expense is reasonable ($100 or less/person) and the guest list includes individuals who can use the information in a patient case. Clearly a “premium” dinner for office staff to review new surgical instrumentation would not pass this test. REFERENCE: Opinions on ethics and professionalism, in Guide to The Ethical Practice of Orthopaedic Surgery, ed 6. American Academy of Orthopaedic Surgeons, Rosemont, IL, 2006, pp 38-42.

DISCUSSION: Highly cross-linked polyethylene has gained widespread acceptance for joint arthroplasty components because of reported experimental and early clinical accounts of significant reductions in wear. Cross-linking is increased by imparting additional energy into the polymer (above that conventionally used for sterilization). The thermal treatments after cross-linking stabilize the material against oxidative degradation by quenching free radicals and also reduce the elastic modulus. One disadvantage of the increased cross-linking is a reduction in toughness that makes the polyethylene more susceptible to crack initiation and propagation. The reduced toughness raises concerns for gross component fracture and fracture at stress concentrations that can arise with the locking mechanisms used to secure polyethylene inserts into metallic backings. Nonconsolidated polyethylene particles have been associated with increased subsurface density secondary to oxidative degradation in conventional polyethylene implants. The quenching of free radicals by thermal treatment in highly cross-linked polyethylene should prevent this problem. REFERENCES: Collier JP, Currier BH, Kennedy FE, et al: Comparison of cross-linked polyethylene materials for orthopaedic applications. Clin Orthop 2003;414:289-304. 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, pp 203-208. Wright TM, Maher SA: Biomaterials, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

Question.9 . A 42-year-old woman has the injury shown in Figures 78a and 78b. The decision to treat the ulnar styloid surgically is based upon which finding?Patient ageDisplacement of the radius fractureDisplacement of the ulnar styloid fracturePosition of the ulnar styloid after open reduction and internal fixation of the radiusStability of the distal radioulnar joint after open reduction and internal fixation of the radius

DISCUSSION: The distal femoral epiphysis grows approximately 1 cm per year and in boys, growth ceases at approximately age 16 years. Therefore, the patient’s limb-length discrepancy at maturity would be 12 cm (9 cm of remaining growth plus the 3-cm discrepancy he has from the previous surgery).

DISCUSSIONThe structures at risk are the anterior tibial artery and deep peroneal nerve in the anterior compartment, superficial peroneal nerve in the lateral compartment, sural nerve in the superficial posterior compartment, and posterior tibial nerve and posterior tibial and peroneal arteries and veins in the deep posterior compartment.

The goal in the initial phase of shoulder rehabilitation is to improve flexibility, reestablish baseline dynamic stability, normalize muscle balance, and restore proprioception. In the advanced strengthening and final phase, the goals are to initiate aggressive strengthening drills, enhance power and endurance, perform functional drills, and to gradually initiate throwing activities.

DISCUSSION: Clerical error leading to acute hemolysis and even death occurs in 1:12,000 to 1:50,000 transfusions. Bacterial contamination leading to sepsis/shock occurs in 1:1 million transfusions. HIV transmission is approximately 1:500,000 transfusions and hepatitis C is 1:103,000 transfusions. Anaphylactic reactions occur in 1:150,000 transfusions. REFERENCES: Aubuchon JP, Birkmeyer JD, Busch MP: Safety of the blood supply in the United States: Opportunities and controversies. Ann Intern Med 1997;127:904-909. Popovsky MA, Whitaker B, Arnold NL: Severe outcomes of allogeneic and autologous blood donation: Frequency and characterization. Transfusion 1995;35:734-737.

DISCUSSION: The inferior gluteal nerve supplies the gluteus maximus muscle. The superior gluteal nerve supplies the gluteus medius, gluteus minimus, and tensor fascia lata muscles. The femoral nerve supplies the quadriceps, sartorius, and pectineus muscles. The pudendal nerve is primarily a sensory nerve. REFERENCE: Last RJ: Anatomy: Regional and Applied, ed 6. London, England, Churchill Livingstone, 1978, pp 146-147.

Gentamicin and the aminoglycosides (i.e., streptomycin, tobramycin, amikacin, and neomycin) work by binding to the 30S ribosome subunit, leading to the misreading of mRNA. This misreading results in the synthesis of abnormal peptides that accumulate intracellularly and eventually lead to cell death. These antibiotics are bactericidal. Cephalosporins, vancomycin, and penicillins interfere with cell wall synthesis by inhibiting the transpeptidase enzyme. Polymyxin, nystatin, and amphotericin increase cell membrane permeability by disrupting the functional integrity of the cell membrane. The quinolones inhibit the enzyme DNA gyrase. Lastly, metronidazole forms oxygen radicals that are toxic to anaerobic organisms because they lack the protective enzymes, superoxide dismutase and catalase.

Because the radiographs reveal poor regenerate bone, especially anteriorly and laterally, the first step in management is to slow the distraction rate. If this does not solve the problem, temporary reversal of the distraction, or “accordionization,” can be used to induce a greater healing response. Maintaining the same distraction rate will further impair regenerate formation and delay healing. Bone grafting should be reserved as an option if decreasing the distraction rate or alternating a week of compression with a week of distraction fails to improve the callus formation. Repeat corticotomy is performed in patients with premature consolidation.

Although this is a randomized controlled study, there is substantial crossover between the treatment groups, evaluation could not be blinded (radiographs) and was performed by one of the surgeons, and follow-up was moderate. According to Oxford Group criteria, this would be a Level II study.

BMP proteins, which are part of the larger transforming growth factor-beta superfamily, 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 is a 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. β-catenin is an intracellular molecule that plays a key role in the Wnt signaling pathway.

Femoral nerve is located in the anterior neurovascular bundle which does not lie between the gluteus medius minimus. Obturator arises from lumbar plexus supplies and runs with the adductor muscles. Inferior gluteal runs with the posterior neurovascular bundle which do not lie between these muscles. The lateral femoral cutaneous arises inferior and medial to the ASIS which is anterior and medial to this area as well.The direct lateral approach (Transgluteal approach). No true intervenous plane (“split the fibers” of the gluteus medius “distal to the point where the superior gluteal nerve supplies the muscle”). “Do not (split) more than 3 cm above the upper boarder of the trochanter.”

Factor Ia is fibrin. The enzyme that breaks down fibrin is plasmin. Tranexamic acid (TXA) is an antifibrinolytic that prevents the activation of plasmin from the inactive zymogen plasminogen.Tranexamic acid competitively inhibits the activation of plasminogen to plasmin by binding to specific sites on both plasminogen and plasmin. Tranexamic acid has roughly eight times the antifibrinolytic activity of an older analogue, e-aminocaproic acid. It is used during joint replacement surgery to reduce blood loss and the need for transfusion.Watts et al. review strategies for minimizing blood loss and transfusion. They recommend 1g of TXA prior to incision, and 1g at wound closure. They also recommend giving fluids for symptoms of anemia, rather than transfusion, as even high risk patients do well with sufficient intravascular volume even with low hemoglobin levels.Imai et al. evaluated TXA in 107 patients undergoing THA. They found that intraoperative blood loss after preoperative TXA administration was lower than both control and postoperative TXA administration groups. They recommend using 1 g of TXA 10 minutes before surgery and 6 hours after the first administration to best reduce blood loss during THA.Gillette et al. retrospectively reviewed 2046 patients receiving TXA for THA or TKA together with either aspirin, warfarin or dalteparin. They found that the rates of symptomatic DVT (0.35%, 0.15%, and 0.52%, respectively) and nonfatal PE were similar (0.17%, 0.43%, and 0.26%, respectively) for the 3 drugs respectively. They recommend TXA to decrease blood loss and transfusion.Illustration A shows the role of tranexamic acid in the fibrinolytic cycle and theclotting cascade.Incorrect Answers:

DISCUSSION: Synovial tissue is composed of vascularized connective tissue that lacks a basement membrane. Two cell types (type A and type B) are present: type B cells produce synovial fluid. Synovial fluid is made of hyaluronic acid and lubricin, proteinases, and collagenases. It is an ultrafiltrate of blood plasma added to fluid produced by the synovial membrane. It does not contain erythrocytes, clotting factors, or hemoglobin. It lubricates articular cartilage and provides nourishment via diffusion. Synovial fluid exhibits non-Newtonian flow characteristics. The viscosity coefficient is not a constant, the fluid is not linearly viscous, and its viscosity increases as the shear rate decreases.

The most common nerve injury associated with dislocation of the shoulder involves the axillary nerve. This is typically a stretch injury, or neurapraxia, that occurs with anterior displacement of the humeral head out of the glenoid. The suspected diagnosis can be confirmed with neurodiagnostic testing after the first 2 to 3 weeks. A gradual return to normal function is the expected result, though mild deficits may remain. A neurotmetic injury, in which there is complete disruption of the entire nerve, would show no return of function. This type of injury is more likely associated with a penetrating injury, a laceration secondary to a fracture fragment, or occasionally with a direct blow of sufficient force.

DISCUSSION: Bisphosphonates are stable analogues of pyrophosphate that have a strong affinity for bone hydroxyapatite; these agents inhibit bone resorption by reducing the recruitment and activity of osteoclasts and increasing apoptosis. Bone formed while patients are receiving bisphosphonate treatment is histologically normal. Bisphosphonates have been shown to be effective in decreasing pathologic fractures, bone pain, and the need for radiation therapy in patients with multiple myeloma and metastatic carcinoma to bone. The most effective method of administration is via monthly intravenous infusion. Osteonecrosis of the mandible is sometimes a complication of this treatment. REFERENCES: Gass M, Dawson-Hughes B: Preventing osteoporosis-related fractures: An overview. Am J Med 2006;119:S3-S11. 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, pp 226-227.

DISCUSSION: The medial sural arteries vascularize the gastrocnemius, plantaris, and soleus muscles proximally. These arteries arise from the popliteal artery. If this artery is not adequately mobilized, a gastrocnemius soleus flap can be devascularized.