Written Examination Part III (Essay) 1998

Written Examination Part III (Essay) 1998 - Lower Limb and Thorax

Structural Basis of Medical Practice -- Gross Anatomy

The Pennsylvania State University College of Medicine

Note: This guide indicates key points to address in answering the question. This is not the "answer."

Review the boundaries (6 in number), structures entering and leaving, and the lymphatic drainage of the popliteal fossa, and state the relationships of these structures within the fossa. (12 pts.)

General comments

posterior to knee, diamond shaped, fat filled, passage of key structures to the lower limb

Superior boundary - apex of diamond formed by semimembranosus and semitendinosus

sciatic n. - enters from posterior thigh deep to hamstrings, divides into tibial (medial) and common peroneal (lateral) nn.

Superior lateral boundary - biceps femoris

superior lateral genicular a.v. - leaves popliteal fossa femur at lateral femoral epicondyle superior to origin of gastrocnemius

Superior medial boundary - semitendinosus and semimembranosus

superior medial genicular a.v. - leaves popliteal fossa at medial femoral epicondyle superior to adductor tubercle

Inferior lateral boundary - lateral head of gastrocnemius

inferior lateral genicular a.v. - leaves popliteal fossa crossing posterior surface of popliteus fascia and arcuate ligament, deep to head of gastrocnemius
common peroneal n. - leaves popliteal posterior to lateral head gastrocnemius

Inferior medial boundary - medial head of gastrocnemius

inferior medial genicular a.v. - leaves popliteal fossa posterior surface of tibia near the plateau, deep to head of gastrocnemius

Inferior boundary - apex of diamond formed by convergence of the two heads of gastrocnemius

posterior tibial a.v. - leaves popliteal fossa deep to the heads of origin of soleus
sural aa. - leaves popliteal fossa by entering the bellies of gastrocnemius
branches of tibial n. to the gastrocnemius

Posterior boundary - popliteal fascia (deep fascia), tranisition from fascia lata to crural fascia

medial and lateral sural nn. - branches for tibial and common peroneal nn.
short saphenous v. - pierces popliteal fascia to enter the popliteal v.

Anterior boundary - femur, joint capsule, oblique popliteal lig., arcuate lig., popliteus m.

popliteal a.v. - enter through adductor hiatus (superior medial anterior in the fossa) as continuation of the femoral vessels.
middle genicular a. leaves popliteal fossa through the posterior aspect of the joint capsule

Relations within the fossa - superficial to deep: sciatic n and branches, femoral v., femoral a.
Lymphatic drainage - popliteal lymph nodes

superficial drainage of leg along channels enter popliteal fossa along with the lesser saphenous v.
deep drainage of leg enters popliteal fossa along with posterior tibial vessels
lymph from popliteal fossa ascend along femoral vessels to deep inquinal nodes

Review the bones, articulations, ligaments, muscles, and fascial specializations that contribute to the stability of the hip joint. State when and why the hip joint is maximally stabilized. (10pts)

General comments

This hip joint is a synovial "ball and socket" joint

Bones and articulations

head of femur (ball fits into the acetabulum (socket)
depth of acetabulum is increased by labrum, labrum overlies the transverse acetabulum ligament at the acetabular notch
acetabular notch bridged by the transverse acetabular lig
articular cartilage on head of femur and on lunate surface of acetabular fossa
ligamentum teres attaches to acetabular fossa near transverse acetabular ligament

Ligaments - capsular thickenings

pubofemoral - from pectin line to intertrochanteric line, resists abduction
iliofemoral - from anterior inferior iliac spine (deep to rectus femoris straight head) to intertrochanteric line and lessor trochanter (Y-ligament)

fibers spiral anterior from medial to lateral - resist extension and shorten on extension to stabilize joint

ischiofemoral - from ischium to greater trochanter and intertrochanteric line, resists hyperextension and flexion

Muscles - all muscles that cross the joint contribute to stabilization

anterior group - flexors: iliopsoas adds major support, rectus femoris, sartorius
medial group - all of the adductors
posterior group - extensors: the hamstrings
gluteal region - rotators and abductors: the five short lateral rotators, gluteus maximus, medius, and minimus, tensor fascia lata
fascial specialization - iliotibial tract

The hip joint is maximally stable during extension as is the case during quiet standing. The line of gravity falls behind the axis causing to hip to extend. Capsular thickenings (aforementioned ligaments) spiral from posterior to anterior and from medial on the pelvic girdle to lateral on the femur. As the ligaments tighten the capsule shortens similar to twisting a wet towel. This forces the head of the femur deep securely into the acetabular fossa.

Discuss the medial longitudinal arch and indicate your understanding of the bones, ligaments, muscles, and fascial specializations. Relate your anatomical explanations to clinical problems, particularly a loss of senstaion in the plantar aspect of the foot, and complaints of cold feet. (10 pts)

Bones - calcaneus, head of talus, navicular, cuneiforms, and first 3 metatarsals - labeled drawing was helpful (with discussion)

talocalcaneonavicular joint has the head of the talus of as the "keystone" wedged between the calcaneus and navicular
spring ligament is the floor of the talocalcaneonavicular joint and acts as a "staple" to hold the navicular to the calcaneus

Spring ligament - plantar calcaneonavicular ligament

maintains the head of talus at the peak of the medial longitudinal arch
stretching of this ligament allows the navicular bone to move away from the calcaneus -- the talus would fall

Additional "staples"

minor support by long and short plantar
tendinous insertions of tibialis posterior, tibialis anterior, peroneus longus
note: peroneus longus is a tie beam for the transverse arch, a vertical support for the lateral longitudinal arch, and a staple for the medial longitudinal arch

"Tie beam" support - structures serving to approximate the bones of the arch

intrinsic mm - adductor hallucis oblique head, flexor hallucis, abductor hallucis, flexor digitorum brevis, quadratus plantae, lumbricals
extrinsic mm - flexor hallucis longus is key, tibialis posterior, flexor digitorum longus
fascia - plantar aponeurosis and skin

Vertical support - "suspension"

tibialis anterior

Sensory disturbance and cold feet

A fallen medial arch indicates failure of the spring ligament to approximate the navicular bone to the calcaneus. As a result, the head of the talus moves inferiorly into the region traversed by the medial and lateral plantar vessels and nerves. Compression of these structures accounts for the clinical observations

A patient leans to the right during swing phase of the left leg. The previous day this patient received an intragluteal injection into the upper medial quadrant. Using your knowledge of the nerves, muscles, relationshiops and function of the gluteal region, provide an explanation for these clinical findings. (8 pts)

General Comments: The upper medial quadrant injection put the superior gluteal nerve at risk. Disruption of gate is largely due to dropping of the pelvic girdle opposite ot the injury. When the lower limb opposite to the injury is raised (swing phase) the pelvis sags to that side. Normally, gluteus minimus and gluteus medius pull downward on the pelvic girdle opposite to the limb in swing phase. This keeps raises the opposite side upward during swing phase. This demonstrates a reversal of origin and insertion. In this case, opposite of embyologic origin and insertion, the gluteus minimus and medius mm are viewed as arising from the femur (greater trochanter) and inserting upon the ilium. In order to restore the line of gravity, the patient leans to the side of injury. The resulting gate is known as Trendelenberg's gate (gluteal waddle).
Relations of upper medial quadrant - superficial is gluteus maximus

Superior to inferior - superior gluteal n.a.v., piriformis (emerging from greater sciatic foramen)

Relations of lower medial quadrant - piriformis, inferior gluteal n.a.v., sciatic n. posterior femoral cutaneous n. pudendal n and internal pudendal a.v. (emerging from greater sciatic foramen) superior gemellus, obturator internus, inferior gemellus, quadratus femoris
Relations and innervations of superior gluteal n.

enters gluteal region superior to piriformis and courses laterally between gluteus medius and minimus to reach tensor fascia lata

Abductors of the hip - provide fixation of the pelvic girdle

gluteus minimus - ileum to superior greater trochater (deepest of gluteal mm)
gluteus medius - ileum to superior greater trochanter - posterior to gluteus minimus
tensor fascia lata - anterior superior iliac spine to iliotibial tract (lateral side of superior fibular and surrounding area)

Why inject in upper lateral quadrant?

This region is far removed from the sciatic nerve. The superior gluteal nerve traverses the upper lateral quadrant. However the nerve is ramfied by this time. Thus, an injection could not damage the superior gluteal nerve in total. The worse case would be to hit the branch to the tensor fascia lata.

What are the structural entities that support the function of the right ventricle? (8 pts)

General comments: The right ventricle is "C" shaped relative to the more circular left venticle. Wall thickness is about 1/3 that of the left ventrical. This reflects differences in the distribution of the pulmorary artery (lungs) and the aorta (entire body). The ventrical is lined by endocardium.
Tricuspid valve (right atrioventricular valve)

3 cusps - anterior, posterior, and septal, prevent retrograde flow from ventricle to atrium
chordae tendinae - cord like structures attaching the cusps to the papillary mm,
papilary mm. - anterior, posterior, and septal, each papillary mm excerts control over more than one cusp

prevent eversion of valve cusps

Trabeculae carnea - muscular ridges of the right ventricle

septomarginal trabeculae - arising from the interventricular septum and extending to anterior papillary m., carries purkinje fibers

Interventricular septum - separates the right and left ventricles

membranous portion - superior near pulmonary trunk
AV bundle - part of the heart conduction system

Conus arteriosus (infundibulum) - smooth "neck of funnel" leading toward the pulmonary valve
Pulmonary valve - 3 cusps, lunules, nodules

prevent retrograde flow from the pulmonary trunk into the right ventrical

Define the posterior mediastinum and discuss the contents (nerves, vasculature, viscera, lymphatics) in the posterior mediastinum. Provide an understanding of the relationship of the structures within the posterior mediastinum. (8 pts)

Boundaries

superior - line from T4 toward jugular notch (only that part of line posterior to middle mediastinum)
inferior - diaphram posterior to middle mediastinum down to T12
lateral - fibrous layer of mediastinal parietal pleura
anterior - posterior to middle mediastinum
posterior - lateral aspects of vertebral bodies (includes sympathetic trunk)
medial - the middle of the posterior midiastinum is also midsaggital, ie, a medial boundary does not exist

Structures from deep to superficial

right intercostal aa. - immediately deep to azygos system and sympathetic trunk
azygos system - azygos v. and hemiazygos v., cross anterior vertetral bodies superficial to right intercostal aa and deep to splanchnic nn.
thoracic sympathetic trunk - immediately superficial to intercostal vessels
splanchnic nerves - coursing inferior medial and anterior from sympathetic trunk ganglia
thoracic duct - superficial to azygos v. between esophagus and aorta, deviates to the left in superior region
esophagus and esophageal plexus - deviates to the right superiorly and left inferiorly
aorta - left of vertebral bodies and esophagus
vagus n. - enters posterior to root of lung
bifurcation of trachea - immediately superior to esophagus in superior region
deep cardiac plexus and nerves - anterior to tracheal bifurcation

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The Structural Basis of Medical Practice