Limbs

**NOTE only the LONG HEAD of TRICEP extends to the scapula & works on shoulder joint**

Injuries to the upper roots of the brachial plexus (C5 and C6) are the most common types of injuries--resulting in a condition known as Erb-Duchenne Palsy. It affects especially the suprascapular, axillary, and musculocutaneous nerves, which causes paralysis of the rotator cuff muscles, biceps, brachialis, coracobrachialis, and deltoid. It also knocks out the upper and lower subscapular nerves, denervating subscapularis and teres major. It knocks out most of the lateral pectoral nerve, but the majority of pect major is innervated by medial pectoral nerve, so it is only weakened. After this injury, the upper limb hangs limply, medially rotated by an unopposed latissimus and pectoralis major muscles, and pronated due to a loss of biceps. So, the limb is constantly adducted and medially rotated. However, the limb can no longer be abducted because both supraspinatus, which initiates abduction, and deltoid, which allows for complete abduction, have been denervated.

As far as extension and flexion go: Extension occurs through the actions of the triceps which is innervated by the radial nerve. This nerve should still be intact. Flexion of the arm is not totally lost if biceps brachii and coracobrachialis are denervated, because pectoralis major is not completely lost.

note: location of how subclavian artery transitions from axilla--> brachial--> once it passes teres major

Axillary- deltoid
Radial- all posterior muscles
Ulnar- hand, flexor carpi ulnaris, medial half of flexor digitorum profundus

In the clinic
Imaging the blood supply to the upper limb
When there is clinical evidence of vascular compromise to the upper limb, or vessels are needed to form an arteriovenous fistula (which is necessary for renal dialysis), imaging is required to assess the vessels.
Ultrasound is a useful tool for carrying out a noninvasive assessment of the vessels of the upper limb from the third part of the subclavian artery to the deep and superficial palmar arteries. Blood flow can be quantified and anatomical variants can be noted.
Angiography is carried out in certain cases. The femoral artery is punctured below the inguinal ligament and a long catheter is placed through the iliac arteries and around the arch of the aorta to enter either the left subclavian artery or the brachiocephalic trunk and then the right subclavian artery. Radiopaque contrast agents are injected into the vessel and radiographs are obtained as the contrast agents pass first through the arteries, then the capillaries, and finally the veins.

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In the clinic
Trauma to the arteries of the upper limb
The arterial supply to the upper limb is particularly susceptible to trauma in places where it is relatively fixed or in a subcutaneous position.
Fracture of rib I
As the subclavian artery passes out of the neck and into the axilla, it is fixed in position by the surrounding muscles to the superior surface of rib I. A rapid deceleration injury involving upper thoracic trauma may cause a first rib fracture, which may significantly compromise the distal part of the subclavian artery or the first part of the axillary artery. Fortunately, there are anastomotic connections between branches of the subclavian artery and the axillary artery, which form a network around the scapula and proximal end of the humerus; therefore, even with complete vessel transection, the arm is rarely rendered completely ischemic (ischemia is poor blood supply to an organ or a limb).
Anterior dislocation of the humeral head
Anterior dislocation of the humeral head may compress the axillary artery resulting in vessel occlusion. This is unlikely to render the upper limb completely ischemic, but it may be necessary to surgically reconstruct the axillary artery to obtain pain-free function. Importantly, the axillary artery is intimately related to the brachial plexus, which may be damaged at the time of anterior dislocation.

In the clinic
Subclavian pinch-off syndrome
There are a number of routes through which central venous access may be obtained. The "subclavian route" and the jugular routes are commonly used by clinicians. The subclavian route is a misnomer that remains the preferred term in clinical practice. In fact, most clinicians enter the first part of the axillary vein.
There are a number of patients that undergo catheterization of the subclavian vein/axillary vein. Entering the subclavian vein/axillary vein is a relatively straightforward technique. The clavicle is identified and a sharp needle is placed in the infraclavicular region aiming superomedially. When venous blood is aspirated, access has been obtained. This route is popular for long-term venous access, such as Hickman lines, and for shorter-term access where multiple-lumen catheters are inserted (e.g., intensive care unit). The subclavian vein/axillary vein is also the preferred site for insertion of pacemaker wires. There is, however, a preferred point of entry into the vein to prevent complications. The vein should be punctured in the midclavicular line or lateral to this line. The reason for this puncture site is the course of the vein and its relationship to other structures. The vein passes anterior to the artery, superior to the first rib and inferior to the clavicle as it courses through the thoracic inlet. Beneath the clavicle is situated the subclavius muscle. Should the puncture of the vein enter where the subclavius muscle is related to the axillary vein, the catheter or wire may become kinked at this point. Moreover, the constant contraction and relaxation of this muscle will induce fatigue in the line and wire, which may ultimately lead to fracture. A fractured pacemaker wire or a rupture in a chemotherapy catheter can have severe consequences for the patient.

** at cervical level, spinal nerve corresponds to INFERIOR disc level of the vertebrae, but since there are 8 spinal chords with only 7 vertebrae, once you hit T1 vertebrae, the spinal nerve leave out T1/T2 foramen

Endochondral (indirect ossification)
i. Occurs by ossification and eventual replacement of hyaline cartilage
ii. Steps
1. Embryonic mesenchymal condensation; differentiate into chondrocytes
2. Small hyaline cartilage molecule = analgen
3. Extracellular matrix calcifies (chondrolcalcin) this forms a “subperiosteal bone collar”
a. So this means that this process is dependent upon intramembranous ossification to begin ossification
4. Diffusion of nutrients to cartilage tissue is interrupted
5. Chondrocytes undergo hypertrophy until they burst
6. Cartilage undergoes degeneration-creates a cavity
7. Blood vessels appear at this site of degenerating cartilage (Angiogenic Inhibiting Factor removed!)
a. This is known as a periosteal bud bringing osteoprogenitor cells, bone marrow cells, and osteoclasts
8. Degenerating cartilage is resorbed (removed by chondroclasts) but leaves collagen matrix behind
9. Pervascular mesenchymal cells become osteogenic (BMP or Osteogenin)
10. Osteoblasts deposit osteoid remnants on collagen
11. Osteoid becomes mineralized (osteonectin and osteocalcin).
a. THIS IS PRIMARY ENDOCHONDRAL BONE
12. The space created by cartilage resorption is now the primary marrow cavity
13. Primary endochondral bone is soon resorbed by osteoclasts and chondroclasts
14. New or secondary (adult) bone is laid in ways similar to intramembranous development and the resultant marrow space is now called a secondary (adult) marrow cavity.
iii. While these series of events occur near the site of endochondral ossification center, cartilage tissue further away from this center continues to proliferate, grow interstitially (CGF, Growth Hormone) and add to the endochondral cartilage model.
iv. Diaphysis is the primary ossification center.

ii. Steps:
1. Mesenchymal cells aggregate
2. Blood vessels appear in this aggregate
3. Ostegenicity is invoked and osteoblast are formed
4. Osteoblasts secrete osteoid which soon mineralizes
5. Matrix lamellae are formed and these fuse to form trabeculae and spicules
6. Trabeculae interweave to form spongy bone, or go on to form the elaborate compact bone architecture

There are 3 key tissues that come together to form the limb: (1) Somatopleuric lateral plate
mesoderm forms bones, tendons, ligaments and vasculature, (2) somites form muscle and (3) neural
crest cells form pigment cells and Schwann cells. Remember that somites differentiate into four types,
the hypomere comes from myotome and hypomere is what forms the muscles of the limbs. As groups
of muscles diverge from hypomere, their motor innervation will follow, which results in complicated
plexuses of nerves that supply our limbs.

The length of time cells spend in the progress zone determines if they will form proximal or distal components of the limb

Damage to ulnar nerve.
• Injury usually occurs at four places:
1. Posterior to medial epicondyle of humerus (trauma).
2. Cubital tunnel formed by tendinous arch connecting humeral and ulnar heads of the
flexor carpi ulnaris (OT Hazard).
3. At the wrist (trauma).
4. At the hand (cyclist’s palsy).
• Injury may result in extensive motor and sensory loss to the hand with accompanying impaired
power of adduction.
• On flexing wrist joint, hand is drawn to radial side by FCR in absence of balance provided by
FCU.
• Patients are likely to have difficulty making a fist due to paralysis of intrinsic hand muscles.
• MP joints become hyperextended, cannot flex 4th & 5th digits at DIP.
• Cannot extend IP when trying to straighten fingers.

Neurological examination of the legs
Some of the commonest conditions that affect the legs are peripheral neuropathy (particularly associated with diabetes mellitus), lumbar nerve root lesions (associated with pathology of the intervertebral discs), fibular nerve palsy, and spastic paraparesis.
Look for muscle wasting-loss of muscle mass may indicate loss of or reduced innervation.
Test the power in muscle groups-hip flexion (L1, L2-iliopsoas-straight leg raise); knee flexion (L5 to S2-hamstrings-the patient tries to bend the knee while the examiner applies force to the leg to hold the knee in extension); knee extension (L3, L4-quadriceps femoris-the patient attempts to keep the leg straight while the examiner applies a force to the leg to flex the knee joint); ankle plantarflexion (S1, S2-the patient pushes the foot down while the examiner applies a force to the plantar surface of the foot to dorsiflex the ankle joint); ankle dorsiflexion (L4, L5-the patient pulls the foot upward while the examiner applies a force to the dorsal aspect of the foot to plantarflex the ankle joint).
Examine knee and ankle reflexes-a tap with a tendon hammer on the patella ligament (tendon) tests reflexes at the L3-L4 spinal levels and tapping the calcaneal tendon tests reflexes at the S1-S2 spinal levels.
Assess status of general sensory input to lumbar and upper sacral spinal cord levels-test light touch, pin prick, and vibration sense at dermatomes in the lower limb.

GENU VARUS= Bow legged, like cowboy (ya dang varmit!!)

Femoral L2 to L4 All muscles in the anterior compartment of thigh; in the abdomen, also gives rise to branches that supply iliacus and pectineus Skin over the anterior thigh, anteromedial knee, medial side of the leg, and the medial side of the foot

Obturator L2 to L4 All muscles in the medial compartment of thigh (except pectineus and the part of adductor magnus attached to the ischium); also innervates obturator externus Skin over upper medial aspect of thigh

Sciatic L4 to S3 All muscles in the posterior compartment of thigh and the part of adductor magnus attached to the ischium; all muscles in the leg and foot Skin over lateral side of leg and foot, and over the sole and dorsal surface of foot

The common fibular nerve originates from the sciatic nerve in the posterior compartment of thigh or in the popliteal fossa (Fig. 6.87A), and follows the medial margin of the biceps femoris tendon over the lateral head of the gastrocnemius muscle and toward the fibula. Here it gives origin to two cutaneous branches, which descend in the leg:
the sural communicating nerve, which joins the sural branch of the tibial nerve and contributes to innervation of skin over the lower posterolateral side of the leg;
the lateral sural cutaneous nerve, which innervates skin over the upper lateral leg.
The common fibular nerve continues around the neck of the fibula and enters the lateral compartment by passing between the attachments of the fibularis longus muscle to the head and shaft of fibula. Here the common fibular nerve divides into its two terminal branches:
the superficial fibular nerve;
the deep fibular nerve.

four muscles in the ANTERIOR COMPARTMENT of the leg-the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius (Fig. 6.88 and Table 6.9). Collectively they dorsiflex the foot at the ankle joint, extend the toes, and invert the foot. All are innervated by the deep fibular nerve,

Fibularis longus Upper lateral surface of fibula, head of fibula, and occasionally the lateral tibial condyle Undersurface of lateral sides of distal end of medial cuneiform and base of metatarsal I Superficial fibular nerve [L5, S1, S2] Eversion and plantarflexion of foot; supports arches of foot
Fibularis brevis Lower two-thirds of lateral surface of shaft of fibula Lateral tubercle at base of metatarsal V Superficial fibular nerve [L5, S1, S2] Eversion of foot

AVN= death of bone & cartilage

MOST COMMONLY INVOLVED:
Femoral head
Lunate
Talus
Proximal Scaphoid
Humeral Head
Vertebral Body

I already tore this one

Periodicity - mechanism is governed by oscillators that involve the hairy gene (a
pair-rule gene of drosophila) or related genes. Hairy expression is very dynamic -
moves back and forth along the unsegmented paraxial mesoderm every 90 minutes in
the mouse. As it recedes caudally a small amount is left where a new somite will bud
off. While the targets of the hairy transcription factor are unknown, they may include
ephrins and their receptors.

Initially the cells of the somites are pluripotential; however, as development proceeds
different regions of the somites become committed to a particular fate due to factors secreted
by the surrounding tissues. At the end of week 4 as the somites become polymorphous, the
gap junctions break apart, and the cells migrate throughout the embryo. These regions of
the dissolving somite include:
1. Sclerotome - ventral-medial portion of the somite which is induced by the factor sonic
hedgehog (Shh) that is secreted by the notochord and the ventral portion of the neural
tube. It will give rise to the chondrocytes of the vertebral column.
2. Dermatome - dorsal portion of the somite, which is induced by neurotrophin 3 (NT-3)
secreted by the dorsal region of the neural tube, gives rise to the dermal connective
tissue of the dorsal skin (other cells are responsible for the dermis in other portions of
the body). Antibodies to NT-3 inhibit the formation of the dermis.
3. Epimere - small dorsal-medial part of the myotomes, which is induced by members of
the Wnt family secreted by the apical region of the neural tube. It will give rise to the
muscles of the back.
4. Hypomere - dorsal-lateral part of the myotomes, which is induced by Bone
morphogenic protein-4 (BMP4) and perhaps FGF5 secreted by the lateral mesoderm.
There is another factor secreted by the neural tube that inhibits the effects of BMP4 so
that it acts only on the most lateral cells of the somite. These cells give rise to the
muscles on the lateral and ventral body wall in the thorax and abdomen.
B. Sclerotome - represents the ventro-medial section of the somites. It is the first to dissociate
from the somite and migrate. The cells migrate medially and ventrally (to surround the
notochord) and dorsally (to surround the neural tube). They differentiate into fibroblasts
(connective tissue), and chondroblasts (cartilage). Ultimately, they form the vertebral
column.
C. Dermomyotome - what remains of the somite after the sclerotome migration. This is further
divided into the two regions (Fig. 12):
1. Dermatome – the dorsal section – mesenchymal cells that migrate under the surface
ectoderm to form the subcutaneous tissue.
2. Myotome – located between the sclerotome and the dermatome. The cells transform
into spindle-shaped cells that migrate away. These cells form all of the voluntary
skeletal muscle in the trunk of the body from the neck down, as well as the muscles of
the limbs. The myotome consists of two divisions:
a. Epimere – small section of myotome cells which differentiate into the skeletal
muscles along the back (posture, etc.).
b. HYPOMERE- larger section of myotome which migrates around rest of the body (front, sides, etc.) gives rise to intercostal muscles, abdominal obliques, and rectus abdominus)