1. General Principles & Basic Science MCQs

DISCUSSION: If a Cobb elevator is directed caudally while stripping the periosteum over the iliac wing, it will encounter the sciatic notch. Although this puts the sciatic nerve at risk, the first structure encountered is the superior gluteal artery. Because it is tethered at the superior edge of the notch, it is very vulnerable to injury and can then retract inside the pelvis, making it difficult to obtain hemostasis. The inferior gluteal artery exits the sciatic notch below the piriformis and is more protected. The cluneal nerves are at risk only if the incision extends too anteriorly, and the sacroiliac joint can be entered while harvesting the graft.

The most important muscle adaptation resulting from endurance training is an increase in capillary density. Increased capillary density improves blood and nutrient delivery and elimination of metabolic waste. Increased recruitment of motor units, hyperplasia, and hypertrophy are all adaptations that occur with resistance training or strength training. There is no significant change in glycolytic enzyme activity.

DISCUSSION: Risk factors can suggest the existence of osteoporosis. However, definitive testing, based on the use of bone densitometry measurements, uses the T score in which an average score is taken from a normal population of young women. The presence of increased osteoid in lamellar bone is seen in osteomalacia but not osteoporosis. The presence of fractures is evidence of a risk factor for osteoporosis and can predict future fractures, but it does not definitively confirm the diagnosis. The Singh index is a radiographic finding that is not as accurate as bone mineral density scores.

Children with JRA frequently have valgus in association with hypervascularity because of chronic inflammation. This is normally caused by overgrowth of the medial femoral epiphysis. Staple hemiepiphyseodesis, if done early, can reverse the deformity. Osteotomy is usually unnecessary at this age, and there is a risk of stiffness of the knee following the procedure. Synovectomy may be helpful but will not prevent or correct a deformity.

The largest arterial contribution to the patella will enter at the distal (inferior) pole of the patella, with the dominant artery entering inferomedially.The arterial blood supply to the patella is made up of branches of six main arteries: the descending genicular, the superior medial and lateral genicular, the inferior medial and lateral genicular, and the anterior genicular. Several of these branches contribute to the anastomotic network that surround the patella. From the ring, there are two main interosseous blood supply systems to enter the patella, known as the midpatellar and polar vessel systems. The distal pole of the patella is considered to be the largest arterial contribution to the peripatellar ring and the polar vessel system.Lazaro et al. used twenty matched pairs of fresh-frozen cadaveric knees to isolate the dominant blood supply to the patella. After cannulating the superficial femoral artery, anterior tibialis artery, and posterior tibialis artery and performing magnetic resonance imaging, they found that the largest arterial contribution to the patella entered at the inferior pole in 100% of the specimens. In sixteen specimens (80%), the dominant artery entered the medial aspect of the distal pole. In three specimens (15%), it entered the lateral aspect of the distal pole.Illustation A shows the arterial supply system to the patella. The dominant arterial supply enters at the distal (inferior) pole of the patella, with the dominant geniculate arteries entering inferomedially (labelled with a green star). Illustration B shows an anatomical illustration of the patellar blood supply. Note the dominant distal pole blood supply (arrow).Incorrect Answers:

DISCUSSIONKnowledge of the basic nomenclature of antibiotic use is important to effectively treat patients and communicate with colleagues. The effectiveness of an antimicrobial against an infecting organism is measured by the MIC, which refers to the concentration needed to prevent growth of a microorganism on culture medium, and MBC, which is the smallest concentration of the antibiotic necessary to kill the microorganism in culture. Typically, an antibiotic is considered bactericidal if the MBC is no more than 4 times the MIC. The spectrum of antimicrobial coverage refers to an agent’s effectiveness against a range of bacteria. An antibiogram refers to the tabulation of prevalence of different bacteria in a specific setting or specific patient population. Antibiotic susceptibility and resistance refers to the bacteria’s ability to be affected or unaffected by a given antibiotic.

EXPLANATION: The patient developed a large bone defect after undergoing multiple débridements for an open fracture. The most appropriate graft in this setting is a vascularized bone graft. Considering the length of the defect, a free vascularized fibular graft would be a suitable graft. The indications for a vascularized bone graft include infection, inadequate vascularity of the surrounding tissues, bone defects larger than 6 centimeters, and previous failed bone grafts. The osteocytes survive in the vascularized graft, allowing primary bone healing and thereby limiting a loss of graft strength. In contrast, nonvascularized bone graft heals by creeping substitution with a loss of its initial strength. Calcium sulfate pellets and calcium phosphate cement are synthetic bone substitutes with osteoconductive properties. Their role in fracture healing is limited. Demineralized bone matrix is the matrix remaining after allograft undergoes decalcification processing. These products alone would not be optimal in the treatment of such a large bone defect.

DISCUSSION: Iliotibial band friction syndrome is one of the most common causes of lateral knee pain in runners. It is caused by increased friction between the iliotibial band and the lateral femoral condyle because of increased tension on the lateral structures. It may be caused by a prominence of the lateral epicondyle or a malalignment of the lower extremity in the runner, including genu varum, tibia vara, heel varus and forefoot supination, or compensating pronation. These structural characteristics can couple with relative muscle imbalance and lead to an altered running gait, enhancing friction between the lateral femoral condyle and the iliotibial band. Management is usually nonsurgical, including stretching of the iliotibial band and strengthening of the hip abductor muscles, with occasional use of cortisone injections or iontophoresis. REFERENCES: Noble CA: The treatment of iliotibial band friction syndrome. Br J Sports Med 1979;13:51-54. James SL: Running injuries to the knee. J Am Acad Orthop Surg 1995;3:309-318. James SL, Jones DV: Biomechanical aspects of distance running, in Cavanagh PR (ed): Biomechanics of Distance Running. Champaign, IL, Human Kinetic Books, 1990, pp 249-269.

Although previous theories on acetabuIar wear implicated fatigue cracking and delamination which is a major mode of polywear in knees, the primary mechanism of wear of polyethylene acetabular components has been shown to be adhesion and abrasion. In an analysis of 128 componenets retrieved at autopsy or revision surgery, wear appeared to occur mostly at the surface of the components and to be due to large strain plastic deformation and orientation of the surface layers into fibrils that subsequently ruptured during multidirectional motion. It was also shown conclusively that 32 mm displayed significantly more wear (volumetric wear) than with either 22 or 26/28 mm heads ( 1 mm increase in size increased volumetric wear by 10%). The wear at the articulating surface was characterized by highly worn polished areas superiorly and less worn areas inferiorly separated by a ridge. Abrasion was very common, occurring after adhesion and plastic deformation of poly fibrils, and abrasion secondary to third body wear. As well, wear rates decreased with longer survival of components, indicating a "wearing in" phenomenon, arguing against oxidative and fatigue wear. Crevice corrossion = occurs in fatigue cracks with low 02 tension (under screw heads,etc.) Oscillatorry fretting = cyclical outer surface abrading from small movements. Fatigue and delamination = predominant in total knees, where stresses are maximum just below the surface of the poly, causing fatigue over time with susequent delamination. In contrast, hip wear occurs primarily at the surface of the poly.

DISCUSSION: Inflammation, overload, or decreased matrix production may lead to cartilage degeneration. During the second stage of articular cartilage degeneration with osteoarthritis, there is increased chondrocyte activity with proliferation and increased production of extracellular matrix. At the same time, there is an increase in catabolic activity with removal of damaged matrix to facilitate matrix remodeling. Chondrocyte repair response decreases with aging. Matrix degradation includes decreased proteoglycan production, less aggregation, and shorter glycosaminoglycan chains.REFERENCE: Buckwalter JA, Mankin HJ, Grodzinsky AJ: Articular cartilage and osteoarthritis. Instr Course Lect 2005;54:465-480.

Use of teriparatide in association with fracture fixation promotes healing because these fractures are associated with delayed healing. The other responses are not associated with healing of these fractures.

Localized PVNS is a variant of the disease process where the synovial proliferation occurs in one area and usually presents as a discrete mass. It has been effectively treated with complete excision. This may be performed arthroscopically or with arthrotomy. Complete synovectomy and radiation therapy are unnecessary to eradicate the localized form of PVNS.

The radiograph demonstrates thickened trabeculae and thickened cortices in the left proximal femur compared to the right, and the bone scan shows increased uptake in this area. The MRI scans show thickened trabeculae with normal marrow signal. These findings are diagnostic of Paget’s disease. Medical treatment, including bisphosphonates and calcitonin, is indicated for painful bone lesions.

The radial nerve is 4 to 7 mm from the anterolateral portal, which is placed 1 cm anterior and 3 cm proximal to the lateral epicondyle. The posterior interosseous nerve can lie 1 to 14 mm from the portal site.

Significant extopic bone formation results from a combination of initial trauma to the gluteal muscle mass and surgical exposure of the lateral surface of the pelvis. Extensile (extended iliofemoral or triradiate) approaches are associated with the highest incidence of ectopic bone formation, whereas the ilioinguinal approach is rarely associated with this complication. Many of the fractures described in this chapter require a posterolateral or extensile approach in order to achieve acceptable fracture reduction. When these approaches must be used, local measures may be helpful in reducing the incidence of heterotopic ossification. Debridement of devitalized muscle, particularly the gluteus minimus, has been shown to limit the extent of ectopic bone formation.Prevention:incision choice: ilioinguinal if possibleradiationindocin (give pepcid with it)

DISCUSSION: Although there are several bursae in the posterior portion of the knee, the most prevalent one with a connection to the knee joint is the one in the interval between the semimembranosus and the medial head of the gastrocnemius muscle. The popliteus muscle and posterior cruciate ligament, the posterior cruciate ligament and lateral gastrocnemius muscle, and the medial gastrocnemius muscle and posterior cruciate ligament are all too lateral and uncommon. The semitendinosus and medial head of the gastrocnemius muscles do not come in contact in the posterior aspect of the knee. REFERENCES: Resnick D: Diagnosis of Bone and Joint Disorders, ed 3. Philadelphia, PA, WB Saunders, 1995, p 379. Justis EJ Jr: Nontraumatic disorders, in Crenshaw AH (ed): Campbell’s Operative Orthopaedics, ed 7. Philadelphia, PA, Lippincott, 1987, vol 3, p 2257.

DISCUSSIONVancomycin and tobramycin do not produce systemic toxicity in doses as high as 10.5 grams of vancomycin and 12.5 grams of tobramycin per 40 mg of PMMA.RECOMMENDED READINGSHake ME, Young H, Hak DJ, Stahel PF, Hammerberg EM, Mauffrey C. Local antibiotic therapy strategies in orthopaedic trauma: Practical tips and tricks and review of the literature. Injury. 2015 Aug;46(8):1447-56. doi: 10.1016/j.injury.2015.05.008. Epub 2015 May 14. Review. PubMed PMID: 26007616.View Abstract at PubMedSpringer BD, Lee GC, Osmon D, Haidukewych GJ, Hanssen AD, Jacofsky DJ. Systemic safety of high-dose antibiotic-loaded cement spacers after resection of an infected total knee arthroplasty. Clin Orthop Relat Res. 2004 Oct;(427):47-51. PubMed PMID: 15552135.View Abstract at PubMedCLINICAL SITUATION FOR QUESTIONS 84 THROUGH 86Figure 84 is the noncontrast MR image obtained at 2 weeks postinjury for a 52-year-old man who was injured after falling from a ladder. His arm is caught in an abducted, externally rotatedposition. There is no sense of dislocation. Initial radiograph findings are normal. The radiologic review reads “Probable superior labral anterior to posterior (SLAP) tear.”

Understanding collagen orientation is important to understand articular cartilage damage and disease. Articular cartilage acts as a fiber-reinforced composite matrix able to withstand and distribute physiologic loads without mechanical failure. Collagen fibers form a complex framework with a distinctive cross-sectional architecture. The superficial zone is characterized by collagen fibers oriented parallel to the joint surface and a relatively low concentration of proteoglycans. The transitional zone is characterized by larger diameter collagen fibers oriented in a more random manner, with a higher concentration of proteoglycans. The deep zone has the largest collagen fibers with a vertical arrangement. It has the highest proteoglycan concentration. Calcification of the matrix is seen in the zone of calcified cartilage.

Posterior capsule stretching is performed in the cross-chest and behind the back positions. Stretching in internal rotation in the abducted shoulder will further stretch the posterior capsule. Wide grip stretch, and anterior capsule and strengthening exercises will not necessarily stretch the capsule.