Lower Limb and Thorax Written Examination Part III- August 31, 2001
The College of Medicine of The Pennsylvania State University
Note: This is an outline of items to discuss -- NOT the "Answer"
[ The Structural Basis of Medical Practice ]
Table of Contents
- Review the lymphatic drainage of the lung. (5 pts)
- Review the anatomy of the posterior thigh. (10 pts)
- Review the anatomy of the piriformis m. and the superior gluteal n.. (10 pts)
- Review the anatomy of the posterior nediastinum. (10 pts)
- Review the fascial barriers separating the pericardial cavity from the pleural cavity. (5 pts)
- Review the anatomy and function of the knee joint. (12 pts)
1. Review the lymphatic drainage of the lung. (5 pts)
Clinical note - Large paratracheal nodes may compress lung (middle lobe syndrome)
- Pulmonary nodes of each lung drain toward bronchopulmonary nodes
- Bronchopulmonary nodes drain into tracheobronchial nodes
- Join drainage from parasternal nodes to form bronchomediastinal lymph trunks
- Bronchomediastinal trunks drain into the subclavian vv.
- Possible right and left lung differences
- Right into right lymphatic duct - bracheocephalic v.
- Left into thoracic duct - bracheocephalic v.
Clinical note - Adhesions of visceral and parietal pleura introduces alternative drainage patterns.
2. Discuss the anatomy of the posterior compartment of the thigh,
including function, boundaries, relationships, innervations, and vascularization, along with a
definition of the hamstring muscles. (10 pts)
- The hamstring muscles, arising from the ischial tuberosity and inserting on the tibia, are biarticulate.
Thus, they act at both the hip (extension) and the knee (flexion). Semimembranosus and semitendinosus are
medial rotators of the knee. Biceps femoris is a lateral rotator at the knee.
- The short head of the biceps, a hybrid muscle, crosses one joint -- the knee joint. It is a flexor and a
lateral rotator of the knee.
- The posterior adductor magnum crosses one joint -- the hip joint. It is an extensor of the hip.
- Anterior: adductor magnus, femur, vastus lateralis, lateral and medial intermuscular septa
- Posterior: fascia lata
- Lateral: fascia lata, lateral intermuscular septum
- Medial: fascia lata, medial intermuscular septum
- Superior: Gluteal fold
- Inferior: axis of the knee joint (includes superior aspect of popliteal fossa)
- Relationships (see boundaries)
- Deepest in the posterior compartment is the adductor magnus. Perforating arteries pierce the adductor magnus
medial to this muscle's insertion along the linea aspera of the femur. The most posterior fibers of adductor
magnus extend to the adductor tubercle of the medial femoral epicondyle. The adductor hiatus results from a
discontinuity of insertion along the inferior aspect of the linea aspera.
- The semimembranosus and semitendinosus course downward from the ischial tuberosity. Both muscles deviate to the
medial side. Semitendinosus crosses posterior to the knee and then turns anterior to insert with the pes anserinus.
Semimembranosus is closely applied to the anterior (deep) surface of semitendinosus. It crosses posterior to the
knee and inserts on the postero-medial aspect of the medial tibial condyle.
- The long-head of the biceps courses downward from the ischial tuberosity and deviates to the lateral side as it
approaches the knee. The tendon of insertion crosses posterior to the knee and inserts on the postero-lateral
aspect of the lateral tibial condyle and on the head of the fibula. The short-head of the biceps arises from the
middle third of the femur and joins the long-head in the lower one-third of the thigh.
- The sciatic nerve enters the posterior thigh from the gluteal region passing on the anterior (deep) surface
of the inferior free edge of the gluteus maximus. It lies lateral to the ischial tuberosity and is applied to the
posterior surface of the adductor magnus (medial to femur). The sciatic nerve courses downward between biceps
femoris and adductor magnus. At the inferior 1/3 of the thigh the sciatic nerve deviates medially as the
biceps deviates laterally. In the superior aspect of the popliteal fossa the sciatic nerve branches into the
common peroneal nerve and the tibial nerve.
- The posterior femoral cutaneous nerve of the thigh follows the medial posterior aspect of the sciatic nerve.
- The hamstring muscles and the posterior adductor magnus are innervated by the tibial portion of the sciatic nerve.
These branches occur in the gluteal region and in the superior thigh. They branch from the medial side of the sciatic nerve.
The short head of the biceps receives a lateral branch of the sciatic nerve derived from the peroneal portion.
- The posterior cutaneous nerve of the thigh sends branches posteriorly that pierce the fascia lata to provide cutaneous
innervation to the posterior aspect of the thigh as far inferiorly as the lower reaches of the popliteal region.
- The upper 1/3 of the posterior compartment receives vascular supply from the inferior gluteal, medial and lateral circumflex,
and 1st perforating vessels. The sciatic nerve receives the arteria commitans nervi ischiadici from the inferior gluteal vessels.
This vessel is subsequently augmented by the perforating vessels and branches of the popliteal vessels.
- The middle 1/3 of the thigh receives the perforating vessels from the profunda femoral vessels. These 4-6 vessels perforate
the insertions of the adductor magnus along the medial border of the femur.
- The lower 1/3 of the posterior compartment receives
vascular from the popliteal vessels in addition to the lower perforating vessels.
- Definition of the hamstrings
- The hamstring muscles: 1) arise from the ischial tuberosity, 2) are biarticulate (cross two joints), and 3) are innervated by
the tibial portion of the sciatic nerve.
- They are the semimembranosus, semitendinosus, and long-head of the biceps femoris
3. Discuss the anatomical relationships of the piriformis muscle. Furthermore,
describe the course of the superior gluteal nerve in the gluteal region, and the functional deficits and compensations(s)
resulting from injury. (10 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 to 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
- Relations of piriformis - superficial is gluteus maximus
Relations and innervations of superior gluteal n.
- Piriformis enters the gluteal region by way of the greater sciatic foramen). It inserts upon the supero-posterior greater trochanter.
- Superior - superior gluteal n.a.v., gluteus medius, gluteus minimus
- Inferior - inferior gluteal n.a.v., sciatic nerve, superior gemellus (obturator internus, inferior gemellus, quadratus femoris)
- Anterior - sciatic nerve, posterior cutaneous nerve of the thigh, gluteus minimus, pudendal nerve, internal pudendal vessels
- Posterior - gluteus maximus, gluteus medius
- Lateral - greater trochanter of femur, tensor fascia lata
- Medial - sacrum, pelvic cavity, pudendal nerve, internal pudendal vessels
Abductors (and medial rotators) of the hip - provide fixation of the pelvic girdle
- enters gluteal region superior to piriformis and courses laterally between gluteus medius and minimus to reach tensor fascia lata
Why inject in upper lateral quadrant?
- gluteus minimus - ileum to superior greater trochanter (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 head and surrounding area)
- This region is far removed from the sciatic nerve. The superior gluteal nerve traverses the upper lateral quadrant. However the nerve is
ramified 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.
4. Define the posterior mediastinum and discuss its contents. (10 pts)
- superior - line from T4 toward jugular notch (only that part of line posterior to middle mediastinum)
- inferior - diaphragm 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 mediastinum is also midsaggital, i.e., a medial boundary does not exist
- right intercostal aa. - immediately deep to azygos system and sympathetic trunk
- azygos system - azygos v. and hemiazygos v., cross anterior vertebral bodies superficial to right intercostal aa and deep to splanchnic nn.
- thoracic sympathetic trunk - immediately superficial (lateral) to intercostal vessels
- splanchnic nerves - coursing inferior medial and anterior from sympathetic trunk ganglia
- ramus communican - branching posterior from sympathetic trunk ganglia and connecting to spinal nerve at intervertebral foramen
- 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
5. Discuss the fascial barrier separating the pericardial
cavity from the pleural cavity. What structures would be vulnerable to damage in this area? (5 pts)
An infection of the pericardial cavity could erode fascial layers gaining access to the pleural cavity. Beginning within the
pericardial cavity proceeding laterally, these layers are:
- serous parietal pericardium
- fibrous pericardium
- endothoracic fascia - the phrenic nerve and the pericardiacophrenic vessels are vulnerable within this fascia
- fibrous layer of mediastinal parietal pleura
- serous layer of parietal mediastinal pleura
6. Discuss the anatomy of the knee joint. Include bones, cartilage, ligaments, muscles, bursa, vascular supply,
innervation, stabilization, center of gravity, and locking/unlocking of the knee joint. (12 pts)
Bones and Articulations (x pts)
ligaments (x pts)
Synovial hinge joint between the femoral and tibial condyles.
Tibial plateau is cupped by the medial and lateral menisci.
Patella articulates anteriorly as a sesamoid bone in the quadriceps tendon.
Cavities and bursae (x pts)
Medial collateral ligament (attached to medial meniscus).
medial femoral epicondyle to the medial tibial condyle.
resists abduction of tibia.
Lateral collateral ligament (interval between lateral meniscus and ligament
transmits popliteus m.
From lateral femoral epicondyle to the head of the fibula
resists adduction of tibia.
Anterior cruciate ligament
from lateral posterior femoral condyle to anterior aspect of tibial intercondyler
resists forward displacement of the tibia.
Posterior cruciate ligament.
from posterior medial femoral condyle to posterior aspect of tibial intercondyler
resists posterior displacement of tibia.
Oblique popliteal and arcuate ligaments strengthen the posterior joint
coronary, transverse genicular, and meniscofemoral ligaments secure the
Capsular joint cavity (x pts)
Synovial joint cavity
attaches to edges of menisci - articular surface is intrasynovial
Alar folds anterior to anterior crucial ligament - posterior limit
of midsaggital synovial cavity
reflections of the synovial membrane along the intercondylar fossa - cruciate
ligaments are extrasynovial.
continuous with suprapatellar bursa (quadriceps bursa)
Muscles, Movements and limitations of movement (x pts)
ligaments making up the capsule (above)
intercondylar area is extrasynovial
popliteus tendon within cavity
Fascial Specializatons (x pts)
Primarily flexion and extension (hinge joint).
Some rotation (30-40 degrees) is possible when the knee is flexed.
Flexion is primarily by the hamstrings, short head of biceps, gracilis,
innervated by tibial portion sciatic, peroneal portion sciatic, obturator,
and femoral nerves respectively.
minor flexion by popliteus, gastrocnemius, and plantaris.
flexion is limited by quadriceps, cruciate ligaments, and by opposing soft
tissues (calf and thigh).
Extension is primarily by the quadriceps and tensor fascia lata.
innervation by femoral nerve and superior gluteal nerve.
extension is limited by hamstrings, cruciate ligaments, collateral ligaments,
posterior joint capsule.
Medial rotation of tibia is primarily by popliteus, semitendonosus, gracilis,
innervation by tibial nerve, tibial portion sciatic, obturator, and femoral
limitation of movement by collateral ligaments
Lateral rotation of tibia is primarily by biceps femoris.
innervation by tibial and peroneal portions of sciatic nerve.
limitation of movements by collateral ligaments.
Abduction and adduction is limited by the medial and lateral collateral
vascular supply (x pts)
Innervation (Hilton's Law) (x pts)
Superior and inferior, medial and lateral genicular arteries, and middle
genicular from the popliteal artery.
descending genicular artery from femoral artery and descending branch from
lateral femoral circumflex artery
Fibular circumflex artery, and anterior and posterior tibial recurrent
arteries from the anterior and posterior tibial artery
"Screw Home" (x pts)
small branches of the femoral, obturator, and sciatic, and tibial nerves
pierce the joint capsule.
Consider when the knee is extended with the foot planted on the ground.
In this case, the tibia is fixed by virtue of the planted foot. Thus, rotation
of the knee occurs as movement of the femur. The femur rotates medially
as the knee "locks" in extension. The lateral femoral condyle is smaller
than the medial femoral condyle. As the knee is extended the smaller condyle
moves through its arc before the medial condyle. Thus, movement stops at
the lateral condyle while the femoral medial condyle continues to move
further posteriorly. This movement results in a medial rotation of the
This medial rotation torques the joint capsule and it's ligamentus specializations
(medial and later collateral ligs). The "twisting" of the capsular
ligaments causes the region to tighten. This firmly approximates the femoral
condyles to the tibial plateau and "locks" the knee. The femur "screws"
medially onto the tibial plateau due to the larger medial condyle and the
twisting of the capsular ligaments. On extension, the knee goes through
a "screw home" rotation that results in "close packing."
The final medial rotation of the femur is driven by the line of gravity
moving anterior to the axis of the knee joint. Thus, locking the
knee is driven by gravity. Unlocking the knee requires muscular involvement.
The popliteus, having lateral superior to medial inferior attachments,
posterior to the axis of the knee, can to lateral rotate the femur
(reverse origin and insertion) and, thus, unlock the knee joint.
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