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1. List the major bones (or groups of bones) in the upper limbs and describe which joints they form.

The basic organization of the upper and lower limb bones are similar with a single bone in the most proximal segment (humerus & femur), 2 bones in the intermediate segment (radius/ulna & tibia/fibula), and numerous smaller bones associated with the wrist/hand and ankle/foot.

Terminology reminder (to help throughout MSK!):

Proximal: towards trunk or point of origin

Distal: away from trunk or point of origin

Pectoral Girdle

The pectoral girdle is composed of the clavicle (collarbone) and scapula (shoulder blade), and serves to connect the upper limb to the trunk (axial skeleton). The clavicle articulates with the sternum (sternoclavicular joint) and the scapula (acromioclavicular/AC joint). The scapula also articulates with the humerus at the glenohumeral (shoulder) joint.

Arm

The bone of the arm is the humerus, which is the longest bone of the upper limb. This bone will distally articulate with both the

• Ulna (humero-ulnar/elbow joint), and 

• Radius (humeroradial joint).

Forearm

There are two bones of the forearm: the medial ulna and lateral radius. The ulna plays the larger role in the humero-ulnar (elbow) joint, whereas it is the radius that articulates with the proximal row of carpal bones to form the radiocarpal (wrist) joint. The ulna and radius also articulate with one another in three separate joints: 

• Proximal & distal radio-ulnar joints and the 

• Intermediate interosseous joint, which connects the diaphyses of these bones.

Carpals

There are 8 carpal bones per upper limb, located in approximately the wrist region, and these are organized into a proximal row (4) and distal (row). Most of the proximal row articulates with the radius to form the radiocarpal (wrist) joint. The distal row articulates with metacarpals at the carpometacarpal (CMC) joints. 

The carpals will articulate with one another at intercarpal joints. The scaphoid bone, located in the lateral most portion of the proximal row is the most frequently fractured carpal bone, and due to a tenuous blood supply, there may be avascular necrosis here.

Metacarpals

There are 5 metacarpals, numbered 1-5. The first metacarpal is lateral (think anatomical position) and is associated with the 1st digit, or thumb. The metacarpals will articulate with the distal row of carpal bones at the carpometacarpal joints, and the proximal phalanges at the metacarpophalangeal (MP/MCP) joints.

Phalanges

There are 14 phalanges: 5 proximal; 4 intermediate (there is not an intermediate phalange in the 1st digit); 5 distal. The proximal phalanges will articulate with the metacarpals at the metacarpophalangeal (MP/MCP) joints, and the intermediate phalanges at the proximal interphalangeal (PIP) joints. The intermediate phalanges will articulate with the distal phalanges at the distal interphalangeal (DIP) joints. In the first digit, the joint between the proximal and distal phalanges is just referred to as the interphalangeal joint.

2. List the major bones (or groups of bones) in the lower limbs and describe which joints they form.

The basic organization of the upper and lower limb bones are similar with a single bone in the most proximal segment (humerus & femur), 2 bones in the intermediate segment (radius/ulna & tibia/fibula), and numerous smaller bones associated with the wrist/hand and ankle/foot.

Pelvic Girdle

The pelvic girdle is composed of the 2 coxal (hip) bones and the sacrum. These bones will articulate at the sacro-iliac (SI) joints. The coxal bones will articulate with one another at the pubic symphysis, an anterior cartilaginous joint. The coxal bones will articulate at the acetabulum to the head of the femur at the hip joint.

Thigh

The bone of the thigh region is the femur, and this is the longest bone in the body. This bone will articulate proximally with the coxal bone at the hip joint, and distally with the tibia and patella at the knee joint.

Leg

There are two bones of the leg: the medial and weight-bearing tibia & the lateral fibula. The tibia articulates with the femur at the knee joint, and with the talus at the talocrural (ankle) joint. The fibula also articulates with the talus at the talocrural (ankle) joint. Similar to what occurs in the forearm, the tibia and fibula articulate with each other in 3 locations (proximal, intermediate, and distal) at tibiofibular joints.

Tarsals

There are 7 tarsals per lower limb (one less than the carpals, but significantly larger bones). The talus is more superiorly oriented and articulates with the tibia and fibula at the talocrural (ankle) joint. The calcaneus (‘heel bone’) is the largest tarsal bone, and is located inferior to the talus, forming the subtalar joint. The 4 of the other tarsal bones articulate with the metatarsals at the tarsometatarsal joints.

Metatarsals

There are 5 metatarsals, numbered 1-5. The first metatarsal is medial, and is associated with the great/big toe. The metatarsals articulate with the tarsal bones at the tarsometatarsal joints, and with the proximal phalanges at the metatarsophalangeal (MP/MTP) joints. 

Phalanges

There are 14 phalanges: 5 proximal; 4 intermediate (there is not an intermediate phalange in the 1st digit); 5 distal. The proximal phalanges will articulate with the metatarsals at the metatarsophalangeal (MP/MTP) joints, and the intermediate phalanges at the proximal interphalangeal (PIP) joints. The intermediate phalanges will articulate with the distal phalanges at the distal interphalangeal (DIP) joints. In the first digit, the joint between the proximal and distal phalanges is just referred to as the interphalangeal joint.

3. Describe the structure and composition of synovial joints, in addition to common accessory structures of synovial joints.

Synovial joints are articulations between bones that are connected via an articular capsule, rather than a continuous sheet of connective tissue (which is what occurs with fibrous and cartilaginous joints). This organization allows for free movement at these joints. Most joints of the body are synovial joints, particularly in the appendicular skeleton.

All synovial joints have:

• Articular (synovial) capsule: this is what actually attaches the bones

  • Two parts of the capsule: an outer fibrous layer and the inner synovial membrane, which secretes synovial fluid

    • Synovial fluid is important in reducing friction, nourishing structures and removing wastes within the joint. It typically has a slightly viscous and slippery composition

  • In certain regions, tendons and ligaments can replace portions of the capsule

• Articular (synovial) cavity: ‘space’ (although it is rarely much real space) between articulating bones and articular capsule

• Articular cartilage: covers the ends of articulating bones; does not connect the bones

  • Hyaline cartilage; mostly avascular and slow to heal

While not considered part of the 3 main structures of a synovial joint, ligaments are found in association with most synovial joints. Ligaments are connective tissues that connect bone to bone. Ligaments can be a thickening of the outer portion of the articular capsule or completely separated from the capsule. Both ligaments and tendons (connects muscle to bone) play important roles in the structural integrity of joints.

Many of the more complex synovial joints will have accessory structures that play various roles in protection support, etc.

Labra, articular discs, and menisci are all composed of fibrocartilage predominantly and have slightly different compositions and functions. Labra are typically associated with ball and socket joints and form a lip around the socket portion to provide a better fit for the ball portion of the joint. Articular discs can be complete or incomplete and can serve to divide an articular cavity into 2 components or as a shock absorber. Menisci are similar in function to the labra, but are typically incomplete.

Bursae are sac-like structures (very similar in composition to a synovial capsule with synovial fluid) that are often associated with synovial joints, particularly in areas with increased friction. Specialized bursae surrounding long tendons are often referred to as tendon sheaths. Inflammation of a bursa is referred to as bursitis.

4. Describe the contents and composition of muscle compartments and the role fascia plays in musculoskeletal anatomy.

Muscle compartments are groups of muscles that share similar neurovascular supply and actions enveloped in deep fascia. They are separated from other compartments by comparatively thick layers of deep fascia, referred to as intermuscular septa, which also often attach to bone.

The deep fascia of the limbs have many functions, but of particular importance is resistance of excessive muscle expansion during contraction. This allows the muscles to compress the veins, and assist venous valves in directing blood flow towards the heart. This also allows more efficient actions to occur within a muscle group.

Escaped blood, suppuration caused by an infection, or other factors can lead to increased pressure within these relatively unyielding compartments leading to compartment syndrome. This can lead to entrapment or compression of structures within. The anterior leg compartment is particularly susceptible to this type of syndrome, but can occur at any compartment.

Arm (brachium)

• Anterior (flexor) compartment

• Posterior (extensor) compartment

• These muscles move the elbow joints primarily.

Forearm (antebrachium)

• Anterior (flexor/pronator) compartment

• Posterior (extensor/supinator) compartment

• These muscles move the radio-ulnar, radiocarpal (wrist), and varying joints of the hand - depending on specific muscle.

Hand

• Thenar compartment - thumb (1st digit); lateral

• Hypothenar compartment - pinky (5th digit); medial

• Deeper compartments

  • These muscles are located within and affect movements of the joints of the hand.

The subclavian a. supplies the root of the neck structures and small portions of the shoulder region. This artery will continue as the axillary a. at the lateral margin of the 1st rib.

The axillary a. will supply shoulder muscles, and will continue as the brachial a. at the inferior margin of the teres major m.

The brachial a. will supply the arm compartments, and will bifurcate into the radial a. & ulnar a. in the cubital fossa.

The radial a. will supply lateral portions of the anterior forearm compartment and portions of the hand, being the major contributor to the deep palmar arch but also a portion to the superficial palmar arch.

The ulnar a. will supply medial & deep portions of the anterior forearm compartment, the posterior compartment of the forearm, and portions of the hand, being the major contributor to the superficial palmar arch but also a portion to the deep palmar arch. There are variable anastomoses with the arches.

Venous drainage

The veins of the upper limb may be loosely categorized as either superficial or deep, with the major (largest) veins of the upper limbs being superficial.

Superficial veins

The superficial hand and forearm are drained laterally (thumb-side) by the cephalic v., and medially by the basilic v. The cephalic and basilic vv. course through the subcutaneous layer, often met with small tributaries. Blood from the cephalic v. may be shunted to the basilic v. from a frequently present median cubital v., which can be used for venipuncture (any superficial vein can be used for venipuncture).

Deep veins

Deep veins are typically accompanying veins (venae comitantes) of arteries (radial vv., ulnar vv., brachial vv., etc.). Deep veins, therefore, follow a very similar pattern of the arteries that they accompany. Most deep veins of the upper limb return to either the basilic v., or its direct continuation the axillary v.

Returning blood to the heart:

The basilic v. (superficial) meets the brachial vv. (deep) to form the axillary v. at the inferior margin of the teres major m. The axillary v. becomes the subclavian v. at the lateral margin of the 1st rib. 

Innervation of the Upper Limb

While we will explore the innervation of the upper limb in more granular detail in upcoming sessions as we discuss the specific muscle compartments, it should be noted here that the upper limb receives almost all somatic afferent and efferent fibers from branches of the brachial plexus. A large portion of the shoulder region receives cutaneous (somatic afferent) innervation from branches of the cervical plexus, while portions of the axilla (armpit) and posterior arm are innervated by the intercostobrachial n. (derived from T2 - so not typically the brachial plexus). Postganglionic sympathetic fibers also travel with branches of these plexuses that serve roles in vasoconstriction and initiating secretion of sweat. There are no parasympathetic fibers associated with the upper limb.

Lymphatic drainage

Upper limb lymphatics fall into two categories: superficial (which follow veins) and deep (which follow arteries).

Lymph from the upper limb ultimately channels into the axillary group of nodes: humeral (lateral), central, apical, subscapular, & (delto)pectoral.

7. Locate the main muscle groups and muscle compartments of the lower limb.

The lower limb consists of four major areas that can be further subdivided into compartments/regions. Each of these segments is conceptually divided into regions/muscle compartments for more precise description.

The lower limb is specialized for bipedal locomotion; however, there are notable similarities between the upper and lower limbs.

Proximal Hip

• Gluteal region: located in posterior proximal hip

  • Move the hip joint

Thigh

• Anterior compartment

  • Move the hip and knee joints

• Medial (adductor) compartment

  • Move the hip joint

• Posterior compartment

  • Move the hip and knee joints

Leg

• Anterior (extensor) compartment

• Lateral compartment

• Posterior compartments

• These compartments primarily move the talocrural (ankle) joint and many joints of the foot

Foot

• Plantar region: sole of foot

• Dorsal region

• These muscles are located within and affect movements of the joints of the foot.

The femoral artery travels through the femoral triangle (will be discussed in another learning objective) and through the thigh. It, with its major branch, the deep artery of thigh, will supply muscles of the thigh.

As it nears the knee, it passes through a hiatus in an adductor muscle to relocate on the posterior surface of the distal femur. At this adductor hiatus and proximal popliteal fossa region, the femoral artery will change its name to the popliteal a., which will supply primarily regions and components of the knee joint.

The popliteal a. continues through the popliteal fossa to enter the leg. As it does, it splits into the anterior tibial a. and the posterior tibial a.

The anterior tibial artery will travel anterior to the interosseous membrane to supply the muscles of the anterior compartment of the leg. As this artery passes across the dorsal ankle, its name will change to the dorsalis pedis a.

The posterior tibial artery (and its branches) will travel posterior the interosseous membrane to supply muscles of the posterior and lateral compartments of the leg. It will course posterior to the medial malleolus, and at the calcaneus, will split into the medial plantar a. and lateral plantar a.

The dorsalis pedis a. and medial & lateral plantar aa. will supply the muscles and structures of the foot.

Venous drainage

The veins in the lower limbs have numerous valves to allow for proper directional flow (towards the heart), working against gravitational pull.

Veins are divided into superficial (located in subcutaneous tissue) and deep (accompanying veins - accompanying arteries). Superficial veins of the lower limbs always drain into deep veins by means of sometimes prominent perforating veins.

Superficial veins

There are two main superficial veins of the lower limbs:

• Great saphenous vein: runs along the medial portion of the lower limb throughout its length; drains into the femoral v.

• Small (short;lesser) saphenous vein: located in posterior leg; drains into the popliteal v.

Deep veins

Deep veins of the lower limb accompany arteries and often have similar names. These are the major (largest) veins of the lower limb. These veins (which are often paired - venae comitantes) are often packaged with arteries within a vascular sheath.

Competency of valves are vital in directing blood flow in the proper direction. If competency has been compromised (potentially due to rotation or over-dilation), veins may become varicose. Varicose veins present as a dilated vein with valves that do not close - allowing some blood to flow away from the heart.

Deep vein thrombosis (DVT) can occur in one or more deep veins typically after a period of venous stasis or stagnation, that may occur due to a multitude of reasons, such as inactivity of muscles and insufficiency of the musculovenous pump. A thrombus formed from a DVT may break away from the vein and travel to the lungs → pulmonary (thrombo)embolism.

Innervation of the Lower Limb

While we will explore the innervation of the lower limb in more granular detail in upcoming sessions as we discuss the specific muscle compartments, let’s discuss the major plexuses that will serve this region.

The anterior and medial compartments of the thigh are innervated by branches of the lumbar plexus. There is a small amount of cutaneous innervation distal to the thigh from lumbar plexus branches.

All other regions of the lower limb, including the gluteal region, are innervated by branches of the sacral plexus, primarily branches of the sciatic n.

Postganglionic sympathetic fibers also travel with branches of these plexuses that serve roles in vasoconstriction and initiating secretion of sweat. There are no parasympathetic fibers associated with the lower limb.

Lymphatic drainage

Similar to the upper limb, there are superficial and deep lymphatic vessels associated with the lower limbs. The superficial lymph vessels tend to drain to the superficial inguinal lymph nodes, while the deep vessels will drain to the deep inguinal lymph nodes. The superficial inguinal nodes drain into the deep inguinal nodes at the femoral triangle. 

9. List the boundaries and describe the contents of the femoral triangle.

The femoral triangle is a landmark located in the superomedial portion of the thigh.

The boundaries of the femoral triangle are:

• Superior: inguinal ligament

• Lateral: sartorius m.

• Medial: adductor longus m.

• Deep: Iliopsoas & pectineus mm.

Femoral neurovasculature lie in this triangular space as they enter/exit the lower limb. The relationship of the neurovascular structures is important when accessing the vasculature. 

The structures are organized in the following way from medial to lateral:

• Femoral canal (with deep inguinal lymph nodes), Femoral Vein, Femoral Artery, Femoral Nerve (VAN)

The femoral arterial pulse is palpable and from there one can understand the location of other structures in this region, such as in femoral vein cannulation.

A femoral sheath, formed by fascia, will surround the femoral artery, femoral vein, and the femoral canal (a short region containing connective tissues and lymphatics). 

The base of the femoral canal is the femoral ring, which is the typical site of a femoral hernia.