1. General Principles & Basic Science MCQs

DISCUSSION: The major risk of performing a high tibial osteotomy is neurovascular injury. The new version of the high tibial osteotomy makes a transverse osteotomy at the level of the tibial tubercle. The osteotome is protected by the oblique belly of the popliteus muscle. The popliteal artery and vein and tibial nerve all lie posterior to the muscle. The soleus muscle originates below this level.

Rising from a seated position on a chair on the affected leg has been shown to create the highest contact pressure within the hip, even higher than full weight-bearing during walking.Limiting activities that create high contact pressures is important in situations such as after internal fixation of an acetabular fracture. Full weight bearing during a normal gait cycle is often considered too much contact pressure and considered a risk for early failure of fixation. During the postoperative period weight bearing and activities are limited to prevent this. It has been shown that the highest contact pressures, even higher than normal walking, are seen when rising from a chair on the affected leg.Brand et al. analyzed joint reactive forces in patients walking with and without a cane. Compared to age matched controls they estimate that using a cane decreases the contact pressure in the hip to about 60% of normal.Hodge et al. looked at data from an implanted hip prosthesis with pressure sensors. They found that some activities common to the early rehabilitative period, such as using a bed pan and performing isometric exercises about the hip, can create pressure approaching those of normal walking. The highest pressures recorded were when rising from a chair.Incorrect answers:

This patient has septic prepatellar bursitis. Padding, cold therapy, compression, nonsteroidal anti-inflammatory drugs, and aspiration are thought to be acceptable treatments for aseptic prepatellar bursitis; they have little role in septic bursitis. Antibiotics along with aspiration or placement of a percutaneous drain have been associated with success in some cases of septic prepatellar bursitis, but the standard treatment is complete bursectomy with systemic antibiotics.

DISCUSSION:Highly cross-linked polyethylene makes material resistant to adhesive wear. Abrasive wear from third bodies  does  not  decrease  wear.  The  fatigue  strength  of  such  material  is  inferior  to  that  of  traditional polyethylene, and its resistance to creep is the same, if not lower, than that of traditional polyethylene.

DISCUSSION: An isotropic material is one that has similar mechanical properties regardless of the orientation of the material. Examples of isotropic materials include metals, plastics, and methacrylate. Most biologic tissues are anisotropic, meaning their mechanical properties alter depending on the materials’ orientation to the applied stress. REFERENCE: Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2007, pp 58-59.

Anabolic steroids have many effects on the body. Increased muscle mass occurs specifically through increased production of messenger RNA. HDL levels usually decrease but do not affect muscle. Also, steroids act to change the effects of cortisol to decrease catabolism.

The ankle-brachial index (ABI) of left and right limbs are 0.78 and 0.96 respectively. CT angiography (or conventional angiography) of the left lower extremity is indicated because of abnormal ABI <0.9. It is sufficient to observe the right lower extremity (ABI >0.9).Injury to the popliteal artery is present in 10-40% of knee dislocations (KD). ABI<0.9 has sensitivity of 87% and specificity of 97% for the diagnosis of arterial disruption. Delayed recognition of an occlusive injury (>8 hours) is likely to result in above knee amputation.Stannard et al. examined the role of selective arteriography based on serial physical examination. They found arterial injury in 7% (9 out of 134 knees), and abnormal physical findings in 10 patients, with only 1 false positive. They recommend arteriography for patients with decreased pulses, color or temperature, expanding knee hematoma, or an abnormal physical examination prior to presentation in the emergency department.Mills et al. reviewed the value of ABI for diagnosing arterial injury after knee dislocation. They found that of the 29% with ABI <0.9, all required surgery for arterial injury. Of the remaining patients with ABI >0.9, none had vascular injury. They concluded ABI >0.9 has negative predictive value of 100%.Nicandri et al. reviewed an algorithm for selective angiography. They recommend the following: (1) Intact pulses and ABI >0.9, observation for 24 hours. (2) Asymmetric pulses or ABI <0.9, arteriogram. (3) Hard signs of vascular injury (absent distal pulses, distal ischemia, active hemorrhage, expanding pulsatile hematoma), surgical exploration.Figure A is a table showing systolic pressure readings at different sites. To calculate the ABI, the highest measured arterial pressure in the ankle or foot is divided by the higher brachial arterial pressure from both upper extremities.Incorrect Answers:

The genitofemoral nerve and the sympathetic plexus consistently lie on the ventral surface of the psoas muscle. The ilioinguinal and iliohypogastric nerves are the most superior branches of the lumbar plexus and emerge along the upper lateral border of the psoas muscle traveling toward the quadratus lumborum. Both the obturator and femoral nerves are deep and lateral to the psoas muscle.

Type I collagen fibers are most responsible for the tensile strength of a peripheral nerve. Type I collagen is the most abundant collagen of the human body which forms large, eosinophilic fibers known as collagen fibers. It is present in scar tissue, the end product when tissue heals by repair, as well as tendons, ligaments, the endomysium of myofibrils, the organic part of bone, the dermis, the dentin and organ capsules.

Antifungals such as amphotericin and nystatin bind to sterols in the cell membrane and disrupt its integrity, allowing diffusion of macromolecules and causing cell death. Sulfonamides and trimethopim mimic the metabolite substrate and block synthesis of metabolites such as folic acid. Rifampin inhibits bacterial RNA polymerase, blocking synthesis of RNA. Tetracycline, chloramphenicol, and clindamycin bind to ribosomes and block bacterial growth by inhibiting protein synthesis.

These diseases cause demyelinated regions of the axon and thus have a higher capacitance and lower membrane resistance (opposite of normal) and thus affects an action potential’s saltatory propagation. When an action potential is propagate down a myelinated axon and reaches a demyelinated region its conduction becomes slowed or may even stop. This loss of conduction had effects on behavior.

The obturator internus originates on the obturator membrane and adjacent bone, including the quadrilateral plate, and exits the lesser sciatic notch to insert on the posterior medial greater trochanter.

Integrins are groups of molecules essential for osteoclast attachment to the bone surface. Specifically, aVß3 is a type of integrin found on osteoclasts that attaches to bone by coupling with vitronectin.

Knowledge of intermuscular and internervous planes allows safe exposures throughout the body. The posterior (Thompson) approach to the proximal forearm uses the interval between the extensor carpi radialis brevis and extensor digitorum communis. The anterior (Henry) approach to the proximal forearm uses the interval between the brachioradialis and the flexor carpi radialis.

TNF, IL1 and IL-6 receptor blockade helps to slow/arrest bone erosion in RA and is also effective in reducing synovitis.Cytokines TNF, IL-1 and IL-6 are key players in RA. TNF stimulates migration of osteoclast precursors from the bone marrow into the periphery, and stimulates expression of surface receptors to facilitate differentiation. In the joint, M-CSF and RANKL stimulate differentiation towards osteoclasts. Final differentiation into bone-resorbing osteoclasts is achieved following contact with the bone surface.Schett et al. reviewed bone erosions in RA. They state that the main triggers of bone erosion are synovitis, RANKL, and anti-citrullinated protein antibodies. In RA, there is an abundance of osteoclasts in bone erosions, but a paucity of mature osteoblasts, suggesting the presence of molecules that block osteoblast differentiation.Ideguchi et al. investigated whether repair of erosions occurs in patients with rheumatoid arthritis (RA) treated with conventional disease-modifying anti-rheumatic drugs (DMARDs). They detected repair of erosions in 10.7% of RA patients treated with DMARDs. They recommend the use of DMARDs to reduce disease activity and thus reduce erosions.Illustration A shows the action of antirheumatic drugs on osteoclast differentiation and bone erosion.

DISCUSSION: This patient has cellulitis, which is typically caused by group A Streptococcus or Staphylococcus. The patient’s lack of improvement with first-line antibiotics is concerning for methicillin-resistant Staphylococcus aureus (MRSA) infection. MRSA cellulitis is becoming more prevalent in young athletes, and a high index of suspicion is required to provide appropriate intervention during this aggressive disease process. The diagnosis is typically made clinically without the use of cultures. Oral trimethoprim-sulfamethoxazole (a sulfonamide-class drug) double strength twice daily for 10 to 14 days or doxycycline (a tetracycline-class drug) 100 mg twice daily for 10 to 14 days are recommended for first-line treatment of suspected MRSA cellulitis. There is no indication to proceed with irrigation and debridement; however, if the patient develops a soft-tissue abscess or the underlying joint becomes involved, this would be an appropriate intervention. Switching the athlete to an IV cephalosporin (cefazolin) is not likely to be effective against the presumed resistant bacteria. Ciprofloxacin (a fluoroquinolone-class drug) is effective against many bacteria, but not MRSA. The current recommendation for wrestlers with cellulitis is that return to competition be allowed after 72 hours of antibiotic treatment if there has been no extension of the cellulitis for 48 hours, the lesion can be covered, and there is no drainage from the lesion. The other responses are not current recommendations for return to competition.

DISCUSSIONFor many years, it was believed that large particles incited the histiocytic response. It is now well established that submicron-size particles stimulate this response.

DISCUSSION: The diagnosis is severe osteoporosis because this patient's T-score is lower than -2.5 on DEXA scan and her fragility fracture involves the T12 vertebra. Osteoporosis may be associated with polymorphisms of the COL1A1 gene. EXT1 is associated with multiple hereditary exostoses, and translocation X:18 is associated with synovial sarcoma. The gene p53 is associated with Li-Fraumeni syndrome and osteosarcoma. RECOMMENDED READINGS: Masoodi TA, Alsaif MA, Al Shammari SA, Alhamdan AA. Evaluation and identification of damaged single nucleotide polymorphisms in COL1A1 gene involved in osteoporosis. Arch Med Sci. 2013 Oct 31;9(5):899-905. Kurt-Sirin O, Yilmaz-Aydogan H, Uyar M, Seyhan MF, Isbir T, Can A. Combined effects of collagen type I alpha1 (COL1A1) Sp1 polymorphism and osteoporosis risk factors on bone mineral density in Turkish postmenopausal women. Gene. 2014 May 1;540(2):226-31.

DISCUSSION: Certain medical procedures involving blood are specifically prohibited in the belief system of a Jehovah’s Witness whereas others are not doctrinally prohibited. For procedures where there is no specific doctrinal prohibition, a Jehovah’s Witness should obtain the details from medical personnel and make his or her own decision. Transfusions of allogeneic whole blood or its constituents or preoperative donated autologous blood are prohibited. Other procedures, while not doctrinally prohibited, are not promoted such as hemodilution, intraoperative cell salvage, use of a heart-lung machine, dialysis, epidural blood patch, plasmapheresis, white blood cell scans (labeling or tagging of removed blood returned to the patient), platelet gel, erythropoietin, or blood substitutes. The patient should not be given blood. Plasma expanders should be used first to restore hemodynamic stability. Cell saver blood from an open wound is not recommended nor would there likely be enough from an open tibial fracture to salvage. The patient’s family may be expressing their own beliefs rather than the patient’s beliefs and it would be better to ask the patient when he or she is more alert to determine what procedures they would allow. A consult with the ethics committee will unnecessarily delay an intervention that should restore hemodynamic stability. REFERENCES: Jimenez R, Lewis VO (eds): Culturally Competent Care Guidebook. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2007. Jehovah’s Witnesses Official Web Site: Medical Care and Blood, 2008, http://www.watchtower.org/e/medical_care_and_blood.htm

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.