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Loss of sensation of the medial side of the leg denotes injury to the saphenous nerve. It is a branch of the posterior division of the femoral nerve.

The saphenous nerve is the largest cutaneous branch of the femoral nerve.

It arises from the posterior division of the femoral nerve. In the femoral triangle, it lies lateral to the femoral artery. It then enters the adductor canal where it crosses anterior to the femoral artery to lie medial to it. It leaves the adductor canal by piercing the fascia lata between the gracilis and sartorius and supplies the skin over the patella.

It then descends along the medial border of the tibia along with the long saphenous vein and supplies the skin on the medial side of the knee leg and foot as far as up to the first metatarsophalangeal joint.

The images given below show the cutaneous innervation of the lower limb.

The anterior division of the obturator nerve does not innervate the adductor magnus. It is supplied by the posterior division of the obturator nerve.

The obturator nerve arises from the anterior division of the ventral rami of L2-L4. Near the obturator foramen, it divides into anterior and posterior branches.

• Anterior division supplies pectineus, adductor longus, adductor brevis, and gracilis
• Posterior division supplies adductor magnus, obturator externus. It also supplies adductor brevis if the muscle is not supplied by the anterior division

The image given below shows the course of the obturator nerve.

The sciatic nerve does not innervate the muscles of the gluteal region.

It is the largest nerve of the body and is made up of L4 to S3 spinal nerves of the sacral plexus. It leaves the pelvis through the greater sciatic foramen, inferior to the piriformis. It descends in the posterior thigh and divides into the tibial and common peroneal nerves proximal to the knee joint.

The tibial component of the sciatic nerve supplies:

• Semimembranosus
• Semitendinosus
• Ischial part of adductor magnus
• Long head of biceps femoris

The common fibular component of the sciatic nerve supplies a short head of the biceps femoris. The images given below shows the course of the Sciatic nerve.

The given clinical scenario is suggestive of left superior gluteal nerve injury.

The patient shows characteristic lurching gait/ Trendelenburg's gait (positive Trendelenburg's sign), which is seen in paralysis of gluteus medius and gluteus minimus muscles. These muscles are supplied by the superior gluteal nerve.

When the leg on one side is lifted off the ground, the gluteus medius and minimus muscles, on the opposite supported side, exert traction on the hip bone by acting from the femur. This action results in the slight raising of the pelvis on the unsupported side, which helps maintain the trunk in the upright position.

When the gluteus medius and minimus are paralyzed, the pelvis sinks down on the unsupported

(normal) side, when the patient tries to stand on the affected limb.

In the given case, when the patient lifts up his right leg and tries to stand on the left leg, his right pelvis tilts down. This shows that the left side abduction mechanism is paralyzed and the right side is normal. Hence, the left superior gluteal nerve injury is present in this case.

The image given below shows the Trendelenberg test.

Note: Inferior gluteal nerve supplies the gluteus maximus muscle.

The nerve affected in this patient is the common fibular nerve (common peroneal nerve). It is derived from the dorsal branches of the L4 - L5 and S1 - S2 ventral rami.

The sciatic nerve divides into the tibial nerve and the common fibular nerve.

The common fibular nerve runs obliquely along the lateral side of the popliteal fossa to the fibular head. It lies between the biceps femoris and lateral head of the gastrocnemius. It then curves laterally around the neck of the fibula, where it is most commonly injured (e.g., due to a tight plaster cast).

It gets divided into superficial and deep fibular nerves. Injury to the common peroneal nerve will lead to:

• Weakness of dorsiflexion of foot or foot drop
• Loss of eversion
• Loss of extension of toes
• Sensory loss
• Anterior and lateral side of the leg
• Dorsum of the foot including the medial side of the great toe

The images given below show the common peroneal nerve course and the sensory area supplied.

Note: Ankle reflex is preserved in common peroneal nerve palsy.

Peroneus longus is innervated by the superficial peroneal nerve. The rest of the muscles mentioned above are innervated by the deep peroneal nerve.

The anterior compartment of the leg is supplied by the deep peroneal nerve. It consists of:

• Tibialis anterior
• Extensor hallucis longus
• Extensor digitorum longus
• Peroneus tertius

The lateral compartment of leg is supplied by the superficial peroneal nerve. It consists of peroneus longus and peroneus brevis.

The posterior compartment of leg is supplied by the tibial nerve. It consists of

• Gastrocnemius
• Soleus
• Plantaris
• Popliteus
• Flexor hallucis longus
• Flexor digitorum longus
• Tibialis posterior

Morton’s neuroma may occur due to the entrapment of branches of the medial plantar nerve.

It is the most common form of nerve entrapment in the foot. It is due to the entrapment of the 3rd common digital nerve which is a branch of the medial plantar nerve.

The medial plantar nerve can also be compressed at the Knot of Henry. It is the point where the tendon of flexor hallucis longus passes deep to the tendon of flexor digitorum longus to reach the medial side of the sole of the foot.

The image given below shows the Morton's neuroma.

Baxter’s nerve is a branch of the lateral plantar nerve.

Clinical significance: Compression of Baxter's nerve by the deep fascia that covers abductor hallucis is implicated to be a possible cause of chronic heel pain and plantar fasciitis.

The deep circumflex iliac artery is a branch of the external iliac artery, not the femoral artery.

The femoral artery is the continuation of the external iliac artery. It starts behind the inguinal ligament midway between the anterior superior iliac spine and pubic symphysis.

It descends in the thigh anteromedially in the femoral triangle and passes through the adductor canal. It exits the adductor canal by passing through adductor hiatus, to reach the popliteal fossa and becomes the popliteal artery.

Branches of the femoral artery given below:

• Superficial epigastric artery
• Superficial circumflex iliac artery
• Superficial external pudendal artery
• Deep external pudendal arteries
• Muscular branches
• Profunda femoris artery
• Descending genicular artery

The superior gluteal artery does not contribute to the formation of cruciate anastomosis.

Cruciate anastomosis lies at the level of the lesser trochanter and is formed by:

• Transverse branches of medial and lateral circumflex femoral arteries
• Descending branch of the inferior gluteal artery
• Ascending branch of the first perforating artery

The image given below shows the anastomosis around the hip joint.

Note: Traumatic insults to the lower extremity (fractures, stab wounds, or gunshot wounds) can result in blood loss. It is important for the clinician to understand the arterial anastomoses in the affected area so that bleeding can be appropriately managed and exsanguination can be avoided.

Kanavel's sign is suggestive of tenosynovitis.

Clinically, it can distinguish infectious tenosynovitis from superficial or localized abcess. Kanavel's sign has the following effects -

• Tenderness over affected tendon
• Fusiform swelling over affected tendon
• The affected finger is in slight flexion
• Pain on passive extension of the affected finger

The given image shows an infection, paronychia, of the middle finger. It can spread into the mid-palmar space.

Infections of the:

• Ring and middle finger spread into the mid-palmar space
• Index finger to thenar space
• Little finger spread to ulnar bursa and mid palmar space.

The 1st lumbrical is not a content of the mid-palmar space.

The 1st lumbrical is related to the FDP (flexor digitorum profundus) tendon of the index

(2nd finger). Thus, it lies in the thenar space.

The 2nd, 3rd, and 4th lumbricals are related to the FDP of the middle (3rd finger), ring (4th finger), and little (5th finger) respectively. Thus, they lie in the mid-palmar space.

The given image shows an infection of the pulp space of the finger or whitlow. It requires incision and drainage because when neglected, whitlow can lead to necrosis of the distal 4/5th of the terminal phalanx. It does not cause necrosis of the entire phalanx because the proximal

1/5th escapes as in this part the artery does not cross the fibrous septa.

The pulp space of fingers contains subcutaneous fat arranged in tight compartments. These compartments are formed by fibrous septa extending from the skin to the periosteum of the terminal phalanx.

Whitlow or pulp space infections are treated by a lateral incision and drainage. Its complications are:

• Ischemic necrosis of the distal 4/5th of terminal phalanx due to vessel occlusion.
• Osteomyelitis
• Flexor tenosynovitis
• Septic arthritis of DIP (distal interphalangeal joint)

The nipple is supplied by the anterior branch of the lateral cutaneous branch of T4 (4th intercostal nerve).

The breast is innervated by anterior and lateral branches of the 4th to 6th intercostal nerves (sensory and sympathetic efferent).

The breast (mammary gland) is a modified sweat gland. It lies on the deep pectoral fascia overlying the pectoralis major muscle. It is supplied by the internal thoracic artery, lateral thoracic artery, and lateral branches of posterior intercostal arteries.

The axillary tail of Spence is the axillary process of the mammary gland. It passes through the foramen of Langer.

Foramen of Langer is an opening in the deep fascia through which the superolateral quadrant is prolonged towards the axilla. It lies along the inferolateral edge of the pectoralis major and may extend through the deep fascia up to the apex of the axilla.

The blood supply of the breast does not include the axillary artery. The blood supply of the breast: 4 major sources

Artery

Lateral thoracicartery

Medial mammary branches o finternal thoracicartery

Area suppli ed

Lateral Medial

Artery Area suppli

ed

Pectoral branches of theacro miothoracicandSuperior thor acicarteries

2ndto 4thposterior intercosta larteries

Superior

Base

The veins of the breast correspond with the arteries, draining into the axillary and internal thoracic veins.

Note: The left internal mammary artery (left internal thoracic artery) is the preferred vessel for coronary artery bypass grafting (CABG) because it has superior short- and long-term patency rates compared to saphenous vein grafts.

Alveolar epithelium is cuboidal in the resting phase, and columnar during lactation.

The fibrous stroma forms septa (suspensory ligaments of Cooper) which anchor the skin and gland to the pectoral fascia. It forms the major part of the gland but is absent beneath the areola and nipple.

In the development of breasts, the thoracic ectodermal ingrowths branch into 15–20 solid buds of ectoderm that will become the lactiferous ducts and their associated lobes of alveoli in the fully formed.

Contraction of myoepitheliocytes facilitates the passage of the milk along the ducts. The lactiferous ducts are arranged in a radial fashion and converge towards the nipple and form lactiferous sinuses.

Mammary gland cells secrete milk protein casein by merocrine secretion. Milk lipid is secreted by apocrine secretion.

Types of glands:

• Exocrine
• Endocrine

Exocrine glands: The secretions are initially packaged into membrane-bound vesicles. These are then conveyed to the cell surface.

• Merocrine: It is the most common type. Vesicles fuse with the plasma membrane and secrete on the surface. e.g. sweat glands, protein in mammary gland, pancreas, salivary gland.
• Apocrine: Apical portion is pinched off for secretion. e.g. milk fat in the mammary gland, atypical sweat glands, ceruminous glands, glands of Moll.
• Holocrine: Entire gland disintegrates to liberate secretion. e.g. sebaceous gland.
• Eccrine: Active transportation from plasma as exudate. E.g., previously sweat gland was eccrine, now moved under merocrine.

Endocrine glands: Direct secretion into connective tissue interstitium and then into the circulation.

Lymphatics from the upper outer quadrant of the breast drain first into the anterior axillary lymph nodes (sentinel nodes).

A sentinel node is the first lymph node that receives lymphatic drainage from the tumor. It is identified so that it can be removed during the surgery. The lymph node is sent for histopathological analysis to detect metastasis.

The axillary nodes receive more than 75 of the lymph from the breast.

Surgical classification of nodes:

Nodes are described in relation to pectoralis minor:

• Level 1 (Low nodes) - below pectoralis minor
• Level 2 (Middle nodes) - behind the muscle
• Level 3 (Apical/upper nodes) - between the upper border of the pectoralis minor and the lower border of the clavicle

There may be nodes between pectoralis minor and major; this interpectoral group of nodes is also known as Rotter’s nodes.

The given image shows the peau d'orange appearance of the breast. It occurs due to the blockade of sub-dermal lymphatics. It is one of the most conspicuous signs of breast cancer.

The lymphatic blockade gives rise to edema in the breast. However, the swelling is restricted wherever the skin is tethered to the ligaments of Cooper. This deepens the openings of the sweat glands and hair follicles, giving rise to the typical orange peel appearance.

The given clinical scenario is suggestive of Horner's or Bernard-Horner's syndrome. It can be caused by the lesion of the white ramus of T1.

Horner's syndrome is characterized by a constricted pupil (miosis), drooping of the upper eyelid (ptosis), and an absence of sweating of the face (anhidrosis). It occurs due to the disruption of the sympathetic nerve supply.

In the autonomic nervous system, the sympathetic plexus is thoracolumbar and the parasympathetic plexus is craniosacral.

The sympathetic plexus is formed along the side of the spinal cord by white ramus inflow

(preganglionic nerve fibers) and gray ramus outflow (postganglionic) and it extends from T1-L2.

In Horner's syndrome, since the sympathetic inflow is disrupted, the white ramus of the spinal cord is affected as shown below.

The difference between the sympathetic and parasympathetic ganglions are tabulated below.

Location

Pre-ganglionic fibers Post-ganglionic fibers

Sympathetic ganglions

Closer to the spinal cord Short

Long

Parasympathetic ganglio ns

Closer to the organ Long

Short

Arterial supply to brachial plexus is from branches of subclavian and vertebral arteries, and not from carotid arteries.

The upper/superior trunk of the brachial plexus gives two branches:

• Suprascapular nerve (C5, C6)
• Nerve to the subclavius (C5, C6)

Radial nerve (C5, C6, C7, C8, T1) is the largest branch of the brachial plexus. It originates as the terminal branch of the posterior cord of the plexus.

Brachial plexus variations can be 2 types:

• C4 pre-fixed brachial plexus
• T2 post-fixed brachial plexus

The thoracodorsal nerve would be anesthetized in the infraclavicular nerve block as it is an infraclavicular branch of the brachial plexus. It arises from the posterior cord (C6-C8).

Branches of the brachial plexus that arise from the roots and trunk are supraclavicular branches. They include:

• Dorsal scapular nerve (C5)
• Long thoracic nerve of Bell (C5-C7)
• Suprascapular nerve (C5, C6)
• Nerve to Subclavius (C5, C6)

All the other branches of the brachial plexus that arise from the cords are infraclavicular branches.

In the given clinical scenario, upper cervical trunk injury causes Erb's or Erb-Duchene palsy. This palsy involves adduction and medial rotation at the shoulder, and not abduction.

The most common cause of Erb's palsy is the undue separation of head and neck i.e. fall on shoulder and birth injuries. The stretching causes damage to the upper trunk (C5, C6). Hence, the affected nerves include:

• Suprascapular nerve
• Axillary nerve
• Musculocutaneous nerve
• Radial nerve

Erb's palsy has a typical presentation of a policeman's tip or waiter's tip hand deformity. It includes the following features:

• Arm is adducted and medially rotated at the shoulder joint
• Elbow joint is extended
• Radioulnar joint is pronated
• Sensory loss along the outer aspect of the arm

The given image below shows classic deformity seen in Erb's palsy.