Written Examination August 26, 2010: Part IV Essay - Answer Guide

Medial Region of Ankle - August 26, 2010

A 25 year old male is the unrestrained driver of a motor vehicle involved in a high speed head on collision. His feet are impacted into the floor. X-rays of the right ankle taken in the Emergency Department reveal a displaced fracture of the calcaneus through the attachments of the calcaneofibular and tibiocalcaneal ligaments. As a 2nd year resident, you are asked to: Review structures related to the medial region of the ankle. Include bones, muscles, fascia, retinacula, innervation, articulation and movements, medial longitudinal arch, as well their anatomic relationship. Also discuss the effects on foot movement(s) and gait. (12 pts)

Explicit Statement of Structures at Risk

  • Skin
  • Flexor retinaculum (Tom, Dick, and a very Nervous Harry)
    • tibialis posterior tendon
    • flexor digitorum longus
    • posterior tibial artery and vein - superficial to sustentaculum tali
      • medial and lateral plantar arteries
      • medial calcaneal artery
    • tibial nerve
      • lateral and plantar branches
      • medial calcaneal nerve
    • flexor hallucis longus tendon
    • synovial tendon sheaths
  • deltoid ligament - anterior tibiotalar, posterior tibiotalar, tibiocalcaneal, and tibionavicular ligaments are components
  • abductor hallucis
  • medial malleolus of tibia
  • talus bone
  • calcaneus bone
  • navicular bone
  • plantar calcaneonavicular ligament (spring ligament)
  • talocrural joint
  • talocalcaneonavicular joint
  • subtalar joint

Bones, Joints, Articulations and Movements

  • medial malleolus of tibia
  • calcaneus
  • talus
  • sustentaculum tali
  • talocrural joint - flexion and extension of ankle, most stable in extension (dorsiflexion)
  • talocalcaneonavicular joint - eversion
  • subtalar joint - eversion

Muscles, Movements, and Gait

  • flexor digitorum longus - flexion of the DIP, PIP, MP, and ankle
  • flexor hallucis longus - flexion of the IP, MP, and ankle
  • abductor hallucis - abduction of the great toe
  • tibialis posterior - flexion and inversion of the ankle
  • mechanical damage to the region is expected to compromise inversion and lead to an everted foot
  • nerve damage to the medial and lateral planter nerves will affect push off due to weakened intrinsic muscles of the sole of the foot

Fasciae, Retinaculae, and Ligaments

  • flexor retinaculum - supports flexor digitorum longus and flexor hallucis longus, synovial sheaths
  • synovial tendon sheaths
  • deltoid ligaments and named parts - resists eversion
  • plantar calcaneonavicular ligament - supports the medial longitudinal arch

Vasculature and Lymphatic Drainage

  • medial branches of malleolar anastomosis for arteries and veins
    • anterior medial malleolar artery
    • posterior medial malleolar artery
    • medial tarsal artery
    • medial calcaneal artery
  • great saphenous vein crosses anterior to medial malleolus
  • superficial lymphatic drainage primarily follows the great saphenous vein toward superficial inguinal nodes
  • deep lymphatic drainage is toward popliteal nodes

Innervation

  • tibial nerve
  • medial plantar nerve - abductor hallucis, flexor digitorum brevis, the flexor hallucis brevis, and the first Lumbrical
  • lateral plantar nerve - the rest of intrinsic muscles
  • cutaneous innervation by medial calcaneal nerve
  • cutaneous innervation by saphenous nerve

Medial Longitudinal Arch

  • Bones
    • calcaneus, head of talus, navicular, cuneiform bones, and first 3 metatarsals (heads of) - 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 approximate the navicular to the calcaneus
  • Ligaments
    • 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; if stretched, the talus falls
    • deltoid ligament
    • minor support by long and short plantar
  • Muscles
    • Suspends the arch
      • tibialis posterior - suspends the arch
      • tibialis anterior - suspends the arch
      • extensor hallucis longus - suspends the arch
    • Staples the arch
      • peroneus longus - tendinous insertions staple the arch
        • 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
      • tibialis posterior - tendinous insertions staple the arch
      • tibialis anterior - tendinous insertions staple the arch
    • "Tie beam" support - structures serving to approximate the bones of the arch
      • intrinsic mm - adductor hallucis oblique head, flexor hallucis longus, abductor hallucis, flexor digitorum brevis, quadratus plantae, lumbricals
      • extrinsic mm - flexor hallucis longus is key, tibialis posterior, flexor digitorum longus
      • fascia - plantar aponeurosis and septa
      • skin
  • Fascial Specializations
    • fascia - plantar aponeurosis and septa
    • skin
  • Neural and Vascular Relationships
    • Tibial nerve and posterior tibial artery elaborate medial and lateral plantar arteries and nerves
    • Medial and lateral plantar nerves and vessels pass deep to abductor hallucis to enter plantar region
    • Lateral planter nerve and vessels pass superior to flexor hallucis brevis and inferior to quadratus plantae to reach lateral aspect of sole.
  • Consequences of Damage
    • 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 inferior into the region traversed by the medial and lateral plantar vessels and nerves. Compression of these structures could lead to cold feet (poor circulation) and paresthesias (compressed nerves).

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Mechanics of Breathing and the Thoracic Cage - August 26, 2010

A 66 year old male is admitted to the general medicine ward service with respiratory failure that requires mechanical ventilation. In discussing the case, it is unclear if it is due to a disease process affecting the muscles of respiration or the nerves that innervate the various mechanisms involved in breathing. In order to understand which structure may be the cause of his respiratory failure your attending physician asks you to: Discuss the mechanics of breathing, focusing on explaining the basic movements (including joints) of the thoracic cage and expansion of the lung in respiration. (12 pts)

Ribs, Joints, and Respiratory Movement

  • Ribs
    • True ribs: 1-7
    • False ribs: 8-10
    • Floating ribs: 11-12
  • Joints
    • costovertebral - synovial
      • between head of the rib and the same numbered vertebral body, the superior vertebral body, and the intervertebral disc
      • radiate ligaments
    • costotransverse - synovial
      • between tubercle of rib and same numbered transverse process
      • costotransverse ligaments
    • sternochondral - synovial
      • between sternum and chondral cartilages
      • radiate ligaments
    • interchondral - synovial
      • between chondral cartilages
    • costochondral - fibrous (Gray's contends that movement does not occur here)
  • Anterior posterior movement
    • pump handle for true ribs
    • cupped tubercle of transverse process results in pump handle of upper ribs
    • costovertebral, costochondral and sternochondral joints involved
    • The pump-handle movement of respiration refers to the movements of the upper 6 ribs during breathing. During inspiration there is an increase in the anterior-posterior diameter of the thorax. The sternum moves superiorly and anteriorly in accord with rib movements occurring at the costovertebral, costotransverse, costochondral, and sternochondral joints. Relative to the lower ribs, the costotransverse joint articulation at the transverse process is cupped and accommodates the tubercle of the rib. This articulation permits the rib to rotate on a transverse axis. A slight downward movement at the head of the rib is amplified distally at the sternum. This movement is transferred to the sternum by the costochondral and sternochondral joints. The result is that the sternum raises on inspiration much like the raising of a pump-handle when drawing water from the depths of a well
  • Transverse Movement
    • bucket handle for false ribs
    • planar tubercle of transverse process permits an outward sliding of the rib and results in bucket handle of lower ribs
    • costovertebral, interchondral, costochondral and sternochondral joints involved
  • Vertical Movement
    • diaphragmatic
    • phrenic n., pericardiacophrenic vessels, ant. post. intercostal vessels
    • Upon diaphragmatic contraction the height of the diaphragmatic dome drops to increase the vertical extent of the thoracic cavity.
    • Intercostal muscles hold the thoracic wall rigid and thereby increase the effectiveness of diaphragmatic movement.
  • Lung Movement
    • capillary effect, negative pressure, etc.
    • pneumothorax - air enters and breaks capillary effect, loss of negative pressure, the lung collapses

General Comments. (Optional)

  • The vasculature supply to the thoracic wall travels within the neurovascular plane defined superficially by the internal intercostal muscles and membrane (posterior) and deeply by the subcostal (posterior), innermost intercostal (intermediate), and transversus thoracis (anterior) muscles. The intercostal veins, arteries, and nerves are located inferior to the costal groove of the superior rib defining an intercostal space. From superior to inferior is vein, artery, nerve. Posterior, lateral, and anterior branches of the intercostal vessels and nerves leave the neurovascular plane to supply superficial regions of the thoracic wall. The lateral branches further divide into posterior and anterior branches whereas the anterior branches further divide into medial and lateral branches.

Collateral circulation and structure (Optional)

  • The bulk of the anterior vasculature has the subclavian arteries and brachiocephalic veins as the parent vessels whereas the bulk of the posterior vasculature has the descending aorta (first two intercostal spaces excepted) and azygous system as the parent vessels. The anterior and posterior vasculatures anastomose within the thoracic wall. Thus, the aortic arch can deliver blood directly to the descending aorta or indirectly to the descending aorta by way of the anterior vasculature (subclavian to internal thoracic to anterior intercostals to posterior intercostals to descending). See below.
  • Borders
    • anterior - sternum (manubrium, body, xiphoid process), chondral cartilages
    • posterior - vertebral bodies
    • lateral - ribs proper
    • superior - thoracic inlets
    • inferior - thoracic outlet
  • Vertebral projections
    • sternal notch - T3
    • sternal angle - T4
    • xiphisternal junction - T9
    • inferior extent of costal margin - L3
  • Fascial layers at midaxillary line
    1. skin
    2. tela subcutanea
    3. external intercostal
    4. internal intercostal
    5. neurovascular plane (van)
    6. innermost intercostal
    7. endothoracic fascia
    8. fibrous layer parietal costopleura
    9. serous layer of parietal costopleura
  • Intercostal muscles - superficial to deep
    • External intercostals - anterior membrane, downward "V"
    • Internal intercostals - posterior membrane upward "V", superficial to neurovascular plane
    • Innermost intercostals - posterior as subcostals, anterior as transversus thoracis, deep to neurovascular plane
  • Innervations
    • Motor innervations by intercostal nerves and posterior rami of spinal nerves T1-11
    • Cutaneous innervation described above in General Comments
      • Skin overlying xiphoid process is by spinal nerve T8
    • Autonomic innervation follows intercostal nerves
      • preganglionic cell bodies in IMLCC T1-11, postganglionic cell bodies in thoracic sympathetic trunk ganglia
  • Arteries
    • Posterior intercostal spaces
      • 1-2 Supreme (highest) thoracic artery from costocervical trunk of subclavian artery
      • 3-11 Posterior intercostal arteries from the descending aorta
    • Anterior intercostal spaces
      • 1-6 - Internal thoracic artery from subclavian artery
      • 7-9 - Musculophrenic artery from internal thoracic artery
      • 10-11 - Superior epigastric from internal thoracic artery
  • Veins
    • Right posterior intercostal spaces
      • 1 - Supreme (highest) intercostal vein from brachiocephalic vein
      • 2-4 - superior intercostal vein from arch of the azygous vein
      • 5-11 - Posterior intercostal veins from azygous vein
    • Left posterior intercostal spaces
      • 1 - Supreme (highest) intercostal vein from brachiocephalic vein
      • 2-4 - superior intercostal vein from accessory hemiazygous vein, or brachiocephalic vein, or coronary sinus
      • 5-11 - Posterior intercostal veins from hemiazygous vein
    • Anterior intercostal spaces
      • 1-6 - Internal thoracic vein
      • 7-9 - Musculophrenic vein
      • 10-11 - Superior epigastric vein

Lymphatic Drainage (Optional)

  • Laterally, lymph drainage from the anterior thoracic wall (breast) is into groups of axillary nodes. Most of this drainage is into the pectoral nodes located along pectoral branches of the thoracoacromial vessels. Pectoral nodes drain into the apical nodes located near the apex of the axilla. On the left, the axillary nodes give rise to the subclavian lymphatic trunk. This vessel commonly drains into the thoracic duct and then the angle of internal jugular. The right subclavian duct often drains directly into the venous system. Apical nodes also have drainages into cervical and supraclavicular nodes. Metastatic disease in these nodes is especially difficult to remove.
  • The medial aspect of the breast is drained by intercostal vessels into parasternal nodes. Parasternal and paratracheal drainages combine to form the bronchomediastinal lymph trunks. Drainage continues into the right lymphatic duct on the right and the thoracic duct on the left.
  • The breast is also drained by subcutaneous vessels. These vessels have a wide distribution ranging from the cervical region to the inguinal region and crossing the midline. If the deeper lymph channels are blocked, as may be the case with cancer, subcutaneous drainage may greatly increase and widely disperse cancerous cells.
  • axillary notes receive 75% of lymphatic drainage
    • pectoral nodes - lateral border of pectoralis major
    • apical nodes - beneath the clavicle
    • supraclavicular nodes
    • cervical nodes
  • parasternal nodes
    • along the internal thoracic artery
  • subcutaneous lymphatics
    • distribute to wide area if deep lymphatics are blocked (e.g. cancer)
  • intercostal nodes
    • along the azygous veins in the posterior mediastinum
    • drain posterior intercostal spaces
    • left intercostal nodes may drain directly into thoracic duct
    • right intercostal nodes may find their way to the right lymphatic duct
  • left/right differences
    • right side into right (subclavian) lymph duct
    • left side into thoracic duct and left subclavian v.
  • Summary.
    • Laterally, lymph drainage from the breast is into groups of axillary nodes. Most of this drainage is into the pectoral nodes located along pectoral branches of the thoracoacromial vessels. Pectoral nodes drain into the apical nodes located near the apex of the axilla. On the left, the axillary nodes give rise to the subclavian lymphatic trunk. This vessel commonly drains into the thoracic duct and then the angle of internal jugular. The right subclavian duct often drains directly into the venous system. Apical nodes also have drainages into cervical and supraclavicular nodes. Metastatic disease in these nodes is especially difficult to remove.
  • The medial aspect of the breast is drained by intercostal vessels into parasternal nodes. Parasternal and paratracheal drainages combine to form the bronchomediastinal lymph trunks. Drainage continues into the right lymphatic duct on the right and the thoracic duct on the left.
  • The breast is also drained by subcutaneous vessels. These vessels have a wide distribution ranging from the cervical region to the inguinal region and crossing the midline. If the deeper lymph channels are blocked, as may be the case with cancer, subcutaneous drainage may greatly increase and widely disperse cancerous cells.
  • Posterior intercostal spaces drain into intercostal nodes located in the posterior mediastinum.

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Knee Joint - August 26, 2010

An 18 year old football player is tackled during a football game. He falls to the ground holding his left knee. When reviewing the video replay of the tackle, it is noted that he was struck on the posterior lateral aspect of the knee. On exam, he has "a positive anterior drawer sign" (forward sliding of tibia) and tenderness and laxity (relaxation/looseness) of the medial joint space of the knee when valgus (bending/twisting) stress is placed on it. 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

  • Synovial hinge joint between the femoral and tibial condyles.
  • Tibial plateau is cupped by the medial and lateral menisci.
  • Femoral condyles - shape
  • Tibial condyles - shape
  • Patella articulates anteriorly as a sesamoid bone in the quadriceps tendon.
  • Articular cartilage
  • Superior tibiofibular joint - synovial plane joint

Ligaments

  • 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 tendon
    • From lateral femoral epicondyle to the head of the fibula
    • resists adduction of tibia
  • Popliteofibular ligament
    • from popliteus tendon to head of fibula
    • resists adduction of tibia
  • Anterior cruciate ligament
    • from lateral posterior femoral condyle to anterior aspect of tibial intercondylar eminence.
    • resists forward displacement of the tibia.
    • Alar fold
  • Posterior cruciate ligament
    • from posterior medial femoral condyle to posterior aspect of tibial intercondylar eminence.
    • resists posterior displacement of tibia
    • Alar fold
  • Oblique popliteal and arcuate ligaments strengthen the posterior joint capsule.
    • Semimembranosus
    • Popliteus
  • Coronary, transverse genicular, and meniscofemoral ligaments secure the menisci.
    • Tibial plateau

Cavities and bursae

  • Synovial joint cavity
    • attaches to edges of menisci - articular surface is intrasynovial
    • Alar folds anterior to anterior crucial ligament - posterior limit of midsagittal synovial cavity
    • reflections of the synovial membrane along the intercondylar fossa - cruciate ligaments are extrasynovial.
    • continuous with suprapatellar bursa (quadriceps bursa)
      • Articularis genu
  • prepatellar bursa
    • bursitis
  • infrapatellar bursa
    • Superficial and deep
  • Joint Capsule
    • ligaments making up the capsule (above)
    • intercondylar area is extrasynovial
    • popliteus tendon within cavity
    • patellar retinaculum
    • patellar and quadriceps tendon

Muscles, Movements and Limitations of Movement

  • 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, and sartorius.
    • 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, semitendinosus, gracilis, and sartorius.
    • innervation by tibial nerve, tibial portion sciatic, obturator, and femoral nerves respectively.
    • 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 ligaments.
  • Fascial Specializations
    • patellar retinaculum
    • iliotibial tract
    • investing fascia

Vascular Supply - Genicular Anastomosis

  • Superior and inferior, medial and lateral genicular arteries, and middle genicular from the popliteal artery.
    • Middle genicular artery and intercondylar space
  • 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
  • Accompanying veins

Lymphatic Supply

  • popliteal nodes - receive superficial and deep drainages
  • Infections of the lateral foot may cause swelling of popliteal nodes that, in turn, disrupts the contents of the popliteal fossa.

Innervation (Hilton's Law)

  • small branches of the femoral, obturator, and sciatic, and tibial nerves pierce the joint capsule.

"Screw Home"

  • 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 femur.
  • This medial rotation torques the joint capsule and its ligamentous specializations (medial and later collateral ligaments). 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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Comments

 

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-- LorenEvey - 30 Aug 2010

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Topic revision: r1 - 31 Aug 2010, UnknownUser
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