Essentials of Orthopedic Surgery, third edition / 14-Answers to Questions

Answers to Questions

Chapter 1

1-1. Answer: c

Osteoporosis results from net bone resorption. Therefore, there is net loss of bone. There is no change in the standard mineral to matrix ratio. Cortical diameter increases and bone mineral density (BMD) by dual-energy X-ray absorptiometry (DEXA) decreases.

1-2. Answer: e

Paget’s is a disease of typically older males and results from increased bone turnover. Bone formation and bone resorption both increase.

1-3. Answer: d

The mechanical properties of bone depend largely on its unique integrated lamellar structure. Apatite is the primary mineral and the collagen is type I. (Remember, the word ONE is found in BONE.)

1-4. Answer: a

Without doubt, the common denominator in these and other similar diseases is muscle imbalance. This imbalance results in abnormal agonist– antagonist relationships, leading to joint contractures, fixed deformities, subluxation, and dislocation. In cerebral palsy (CP), the imbalance is spastic muscle versus more spastic muscle, in spina bifida the imbalance is largely weak muscle versus absent muscle, and in polio the imbalance is absent and weak muscle versus normal muscle. Nevertheless, the net result is the same: muscle imbalance.

1-5. Answer: c

Vitamin C deprivation causes the condition known as scurvy. Dilantin is toxic to liver microsomes, hence blocking normal pathways of vitamin D metabolism.

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506 Answers to Questions

1-6. Answer: e

All are typical characteristics of hyaline cartilage.

1-7. Answer: b

Achondroplasia is an abnormality of the proliferating zone of the physis resulting primarily in short stature. Typically, these individuals have bowlegs, kyphotic spines, and are of normal intelligence.

1-8. Answer: e

Rheumatoid arthritis is a synovial disease characterized by hyperemia and hyperplasia of the synovium. There is NO repair attempt made; hence, all the changes around the joint are atrophic. Vascular hyperemia is the mechanism of resorption on both sides of the joint.

1-9. Answer: a

Gout produces typically focal changes around the joints as a result of the deposition of urate.

1-10. Answer: b

Polio does NOT affect the sensory nerves. It is purely a motor neuropathy; therefore, neuropathic joints are not seen.

1-11. Answer: e

All are typical of avascular necrosis (AVN). The talus, proximal femur, and scaphoid all have a retrograde blood flow, making them vulnerable to AVN.

1-12. Answer: c

Collagen is a linear protein molecule that is highly cross-linked at multiple sites in the triple helix called tropocollagen. Both cell populations can synthesize the molecule despite the fact that the amino acid sequence is different. Type I collagen is found in bone and type II collagen in cartilage. The primary mechanical role of collagen is to provide tensile strength to the tissue.

Chapter 2

2-1. Answer: e

Twisting-type forces, which cause torsional loading to bone, produce spiral fractures. These fractures appear as an oblique fracture in both anteroposterior and lateral radiographs.

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2-2. Answer: b

Axonotmesis is an anatomic disruption of the axon in its intact sheath. In neuropraxia, the nerve is anatomically intact and physiologically nonfunctional. Neurotmesis is an anatomic disruption of the nerve itself (axons and sheath).

2-3. Answer: b

In the metabolic phase of fracture healing, the soft callous is reworked by a number of specific cellular elements to produce a firm, hard callous satisfactory for meeting the mechanical demands placed upon the fracture in the early phase. This process usually begins 4 to 6 weeks after the injury.

2-4. Answer: h

All the above answers are documented complications of fractures. See the chapter for more detail.

2-5. Answer: c

Midshaft radius and ulna fractures, or “both bone forearm fractures,” require anatomic reduction and rigid fixation to allow early range of motion and less stiffness. The remaining fractures can all be treated conservatively and nonsurgically, with reasonable expectation for regaining excellent function of the extremity.

2-6. Answer: b

The middle column includes the posterior half of the vertebral body and the posterior longitudinal ligament. The anterior column includes the anterior half of the vertebral body and the anterior longitudinal ligament. The posterior column includes the pedicles and the lamina (see Figure 2-15).

2-7. Answer: c

An open fracture of the pelvis with injury to the bowel and the urogenital system still carries with it a mortality rate of 50%. Great care in evaluating the patient is essential. A rectal and vaginal examination is required to assure that the fracture is not open through those soft tissue structures.

2-8. Answer: c

These fractures occur through an area below the lesser trochanter and do not heal quite as rapidly as the intertrochanteric injuries. In the younger population, subtrochanteric fractures usually follow the severe trauma of motor vehicle accidents. In the elderly, they are caused by severe osteoporosis or a pathologic process in the subtrochanteric area.

508 Answers to Questions

2-9. Answer: c

This injury is the result of very severe trauma. True dislocation of the knee is a very serious injury notable for producing arterial damage to the popliteal vessels. The popliteal artery is fixed anatomically at the level of the proximal tibia by the interosseous membrane and, therefore, is placed at great risk when the knee dislocates.

2-10. Answer: d

All displaced ankle fractures should be treated surgically.

Chapter 3

3-1. Answer: c

The involucrum refers to an area of new or reactive bone growth around a sequestrum or focus of necrotic bone.

3-2. Answer: d

Staphylococcus aureus is by far and away the most common organism found in pediatric osteomyelitis.

3-3. Answer: b

Plain radiographs rarely demonstrate evidence of changes within the bone until 10 days to 2 weeks.

3-4. Answer: b

Staphylococcus aureus is the most common isolate from an adult septic joint.

3-5. Answer: c

It is the phenotypic alterations in the bacteria encased in the slime layer that most directly renders the antibiotic resistance.

3-6. Answer: a

Hematogenous inoculation is the most common cause of osteomyelitis in the pediatric population.

3-7. Answer: d

All the above are known risk factors for the development of a septic arthritis.

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3-8. Answer: b

Soft tissue swelling is the earliest radiographic change that may be evident on plain films; this is particularly important in the distal aspect of the extremities where these soft tissue changes may be readily detectable.

3-9. Answer: d

In general, wounds associated with open fractures should be carefully inspected and then dressed in preparation for an emergent operative debridement. There is little or no reason to obtain predebridement cultures.

3-10. Answer: c

This would be considered a grade 1 open fracture. It is recommended that a first-generation cephalosporin alone be used in this setting.

Chapter 4

4-1. Answer: d

Both answers a and b describe benign or benign aggressive bone tumors, and answer c describes sarcomas of the soft tissues. Osteosarcoma and Ewing’s sarcoma are the two most commonly diagnosed primary bone sarcomas in patients less than 30 years of age.

4-2. Answer: a

Sarcomas tend to grow in a centripetal manner and push and compress the surrounding tissues. This tendency is important in that limb-sparing surgeries can typically take place due to this “buffer zone” with few or any malignant cells noted. It is very rare for sarcomas to be found in adjacent lymph nodes.

4-3. Answer: d

A large open biopsy can cause contamination of the surrounding soft tissues, making a limb-sparing procedure impossible. Although staging studies are crucial in diagnosing a sarcoma, one should always perform a core biopsy under CT guidance if there is a question of malignancy. Multiple cores are usually obtained and provide an accurate diagnosis in more than 95% of all patients.

4-4. Answer: d

Any and all of these characteristics can be displayed by an osteosarcoma.

510 Answers to Questions

4-5. Answer: a

The distal femur, proximal tibia, and proximal humerus are the most common anatomic sites, in descending order. Tumors arising in the proximal femur and pelvis are less common. The spine is the most common site of metastatic carcinomas, usually after the age of 40 years.

4-6. Answer: d

Each of these diagnoses is seen in older adults; they are commonly found in the flat bone of the pelvis and may result in a pathologic fracture.

4-7. Answer: b

Batson’s plexus is a venous system (plexus) surrounding the spine (vertebral bodies) and arises from the abdominal and thoracic cavity structures. There are no valves within this system, thus permitting blood carrying tumor cells to travel ‘backward’ away from the heart during valsalva type of breathing and seed the spine. This is thought to be the primary physical mechanism for carcinoma metastases to the spine. The brachial plexus is the correct name for the answer given in a.

4-8. Answer: d

Benign bone tumors do not metastasize but often require treatment for all the reasons in answers a–c; for example, benign UCBS often present with a fracture, osteoid osteomas are always painful and require removal, and cartilage tumors as well as GCTS may become malignant.

4-9. Answer: d

Surgery, chemotherapy, and radiation therapy are all utilized for highgrade soft tissue sarcomas. Surgery and radiation therapy given postoperatively are almost always required. Chemotherapy, either preoperative (called induction chemotherapy) or postoperative, is recommended for high-grade soft tissue sarcomas that are more than 5 cm in size and are deep, that is, occurring below the deep fascia.

4-10. Answer: b

A lipoma characteristically appears homogeneous and bright on T1 sequence on an MRI. The signal looks identical to the surrounding subcutaneous fat, whereas most sarcomas are dark on T1 and bright on T2.

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Chapter 5

5-1. Answer: b

Most are hereditary and are characterized by generalized skeletal abnormalities. The face is commonly involved, and typically there is genu varum or genu valgum.

5-2. Answer: d

It is multifactorial with environment and genetics playing a role. The reason that the left hip is much more frequently involved is the subject of speculation.

5-3. Answer: a

The child’s periosteum has an inner cambial or osteogenic layer. The structure is of great mechanical significance as a dense fibrous membrane usually assisting in fracture reduction and maintenance.

5-4. Answer: e

Achondroplasia is a physeal dysplasia with the proliferating zone being most affected.

5-5. Answer: b

Slipped capital femoral epiphysis (SCFE) is common in obese adolescents, presenting as a painful limp. It is classified based on the ability of the child to bear weight on the limb: stable or unstable (cannot bear weight).

5-6. Answer: d

Avascular necrosis (AVN) of the femoral head is the definition of Perthes’ and a complication of the other two.

5-7. Answer: d

Because of the ligamentous laxity, typical in these children, the arch collapses and they have flatfeet.

5-8. Answer: a

Fracture of the parietal bone is the most common skull fracture and rarely indicates battery. Rather, suspicion should be raised if the fracture is not typical: frontal, temporal, etc.

5-9. Answer: e

Osteolysis of the metaphysis is a radiographic hallmark of leukemia.

512 Answers to Questions

5-10. Answer: c

A Trendelenburg gait results from putting the Trendelenburg sign into motion. The Trendelenburg sign is caused by either weakness of the abductor muscles or shortening of the lever arm over which they act. When the patient is asked to stand on the affected side, because of inability to stabilize the pelvis the iliac crest on the contralateral side is seen to drop. Put into motion, the child throws the upper body over the affected hip to prevent falling.

5-11. Answer: 3

Displacement alone is the most forgiving, especially in the younger age groups.

5-12. Answer: e

The Pavlik harness has become the worldwide standard for the management of developmental dysplasia of the hip (DDH) in infants. If, however, the position is extreme (especially in abduction), avascular necrosis can occur. Overall, the device is capable of normalizing the hip in about 90% of affected.

Chapter 6

6-1. Answer: c

Type I collagen is the major constituent of tendon, comprising 86% of its dry weight. It is the high concentration of collagen in combination with its parallel orientation that gives it high tensile strength.

6-2. Answer: d

Dancing is most commonly associated with an overuse of the flexor hallicus longus tendon. This is a classic finding specific to this activity. Other tendonopathies are sport specific and can be found in Table 6-1.

6-3. Answer: d

A grade III ligamentous injury is best characterized by complete ligamentous rupture without any structural integrity remaining. A common example is that of a complete rupture of the anterior cruciate ligament that results in increased translation of the tibia to anteriorly directed force.

6-4. Answer: b

Muscular strains most commonly occur with passive stretching and lengthening that occur during eccentric muscular contractions.

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6-5. Answer: a

The proteoglycan component of articular cartilage makes it most effective in resisting compression across a joint.

6-6. Answer: e

The meniscus has a poor blood supply, limited largely to the peripheral one-third of its structure. The potential for meniscal tears to heal is based primarily on the location of the tear as well as the morphology. Tears best associated with potential to heal with repair are red–red longitudinal tears of the meniscus.

6-7. Answer: c

Injury patterns in sports medicine are best described as either microtraumatic or macrotraumatic. Microtraumatic injuries include overuse injuries. Of those injuries listed, the only injury not caused by a single episode of trauma is a stress fracture of the hip.

6-8. Answer: b

Achilles tendonitis represents an overuse injury. Initial management of all overuse injury involves activity modification; this is an essential component to management of all entities that involve an overuse component. Often, this requires cessation of the sport in question.

6-9. Answer: d

At their attachments to bone, the transition from ligament to bone occurs gradually in a series of distinct phases. These phase range from ligament to fibrocartilage, from fibrocartilage to mineralized fibrocartilage, and from mineralized fibrocartilage to bone. The size of each zone varies from ligament to ligament and is related to its structural properties. Collagen fibers, known as Sharpey’s fibers, run in continuity throughout this zone of transition and have an important role in securing the ligament to bone.

6-10. Answer: a

Collagen chains are linked together to form fibrils that in turn are bound together by a proteoglycan matrix to form a fascicle, the primary unit in tendon structure. Fascicles in turn are bound by the endotenon, a layer of elastin-containing loose connective tissue that supports the blood, lymphatic, and neural supply to the tendon unit. It is the endotenon that is contiguous with both the muscle fibers and the periosteum at the musculotendinous and tendo-osseous junctions, respectively.

514 Answers to Questions

Chapter 7

7-1. Answer: e

Any or all of the above may be seen in a patient with cervical myelopathy. Abnormality of gait, particularly a broad-based and shuffling gait, is the hallmark abnormality of cervical myelopathy, but any of the above can be seen.

7-2. Answer: c

The triceps reflex is innovated by C7, and a diminished triceps reflex would be seen in a C7 radiculopathy.

7-3. Answer: a

Cervical myelopathy results in upper motor neuron findings for spasticity including hyperreflexia of the lower extremities, up-going toes, and, depending on the level of the spinal cord compression, hyperactivity in the upper extremities.

7-4. Answer: a

Spondylosis of the cervical (or lumbar) spine includes disk degeneration. The first and most striking finding in disk degeneration is a decrease in water content of the nucleus pulposus. All the other abnormalities are indeed seen in cervical and lumbar spondylosis.

7-5. Answer: d

In a relatively healthy, middle-aged patient, the presence of cervical myelopathy represents a fairly clear-cut indication for surgical treatment. The presence of chronic severe axial neck pain is usually treated nonoperatively. Patients with a herniated disk, even with evidence of radiculopathy, are usually treated nonoperatively, and that is certainly the first line of treatment in most cases.

7-6. Answer: a

All the above patterns of instability, including mixed patterns involving C1–C2, the occipitocervical junction, and the subaxial spine can be seen. Instability at C1–C2, however, is the most common pattern of instability seen.

7-7. Answer: d

It has been estimated that between 60% and 80% of adults in the United States will have at least one episode of significant low back pain in their lifetime.