Chapter 8: Skeletal System: Appendicular Skeleton PDF

# Chapter 8: Skeletal System: Appendicular Skeleton ## 8.3 The Pelvis - The pelvic girdle is formed by the two hip bones, the sacrum, and the coccyx. - The hip bones, also known as the *coxal*, *innominate*, or *hip* bones, are each a single bone that develops as a fusion of three separate bones...

# Chapter 8: Skeletal System: Appendicular Skeleton ## 8.3 The Pelvis - The pelvic girdle is formed by the two hip bones, the sacrum, and the coccyx. - The hip bones, also known as the *coxal*, *innominate*, or *hip* bones, are each a single bone that develops as a fusion of three separate bones in the fetus: *ilium*, *pubis*, and *ischium*. - The ilium, the largest of the three bones, contributes to the formation of the *acetabulum*, the socket that receives the head of the femur. - The pubis, the anterior most bone, joins with the pubis of the opposite side on the midline to form the *pubic symphysis*. - The ischium, the posterior most bone, contributes to the *acetabulum* and forms the *ischial tuberosity*, the bony prominence that bears the weight of the body when sitting. ### 8.3.1 Pelvic Girdle - The pelvic girdle is a basin-shaped structure that provides support for the weight of the upper body, attachment for numerous muscles, and protection of the internal organs - The pelvic girdle is made up of the two hip bones, the sacrum, and the coccyx. - The hip bones are joined anteriorly at the *pubic symphysis* and posteriorly to the sacrum at the *sacroiliac joints*. ### 8.3.2 Hip Bone - The hip bone is a single bone formed by the fusion of the *ilium*, *pubis* and *ischium*. - The bones are usually fused by 17-23 years old, but can still be seen as separate in younger adults. #### Ilium - The *ilium* is the largest of the three hip bones. - The upper part of the bone is called the *ala*, and the lower part is called the *body*. - The *iliac crest* is the superior border of the ilium, which serves as a site for muscle attachment. - The *anterior superior iliac spine* is the anterior end of the iliac crest, which is an important landmark in the pelvic region. - The *anterior inferior iliac spine* is located just inferior to the superior iliac spine, and is also a site for muscle attachment. - The *posterior superior iliac spine* is located at the posterior end of the iliac crest, and is an important landmark for the pelvic region. - The *posterior inferior iliac spine* is located just inferior to the posterior superior iliac spine, and is also a site for muscle attachment. - The *greater sciatic notch* is a large indentation on the posterior surface of the ilium which provides passage for the sciatic nerve and other vessels. - The *iliac fossa*is a smooth, concave surface on the medial surface of the ilium, provides a site for muscle attachment. - The *auricular surface* is a rough, oval-shaped surface which allows for articulation with the sacrum. - The *arcuate line* curves inferiorly from the auricular surface. - The *gluteal lines* are three curved lines on the lateral surface of the ilium. These lines serve as sites of attachment for the gluteal muscles. #### Pubis - The *pubis* is the inferior most bone of the hip, located in the anterior part of the pelvis - It is divided into a superior *rami* and an inferior *rami* - The *superior rami* fuses with the iliac body above the *acetabulum*. - The *inferior rami* forms part of the *obturator foramen*. - The *pubic crest* is a thick ridge on the superior surface of the pubis. - The *pubic tubercle*, a small projection at the lateral end of the pubic crest marks the start of the *pectineal line*. - The *pubic symphysis* is a cartilaginous joint that connects the two pubic bones. #### Ischium - The *ischium* is the posteriorly located bone that forms the inferior side of the pelvic girdle. - The *body of the ischium* is a thick, roughened portion of the bone which connects with the *ilium* and *pubis*. - The *ischial spine* is the superior portion of the ischium, an important landmark in the pelvic region. - The *lesser sciatic notch* is located inferior and medial to the ischial spine. - The *ischial tuberosity* is another important landmark, sitting inferior to the spine. This rough projection serves as the point of support when sitting. ### 8.3.3 Pelvis Major and Pelvis Minor - The *pelvis* is divided into two portions by a line called the *pelvic brim*. - The pelvis major (false pelvis) is the portion superior to the pelvic brim. It comprises the iliac fossae, and the space between the *iliac crests*. - The pelvis minor (true pelvis) is the portion inferior to the pelvic brim. The pelvis minor contains the pelvic organs, including the bladder, rectum, and the reproductive organs. - The pelvic minor has an opening called the *pelvic inlet* at the superior end, the *pelvic floor*, and a bony opening called the *pelvic outlet* at the inferior end. #### **Pelvic Brim** The pelvic brim is a curved line formed by the following landmarks: - The promontory of the sacrum - The arcuate line of the ilium - The pectineal line of the pubis - The superior edge of the pubic symphysis #### **Pelvic Outlet** The pelvic outlet is a more complex structure consisting of. The pelvic outlet is the space inferior to the pelvic inlet bounded by: - The tip of the coccyx - The ischial tuberosities - The inferior margin of the pubic symphysis ### **8.3.4 Differences between Male and Female Pelvis** - The female pelvis is wider and shallower than the male pelvis. - The pelvic inlet in the female pelvis is oval, while the pelvic inlet in the male pelvis is heart shaped. - The subpubic angle is greater in the female pelvis (greater than 90 degrees), but less than 90 degrees in males. ### **Pelvimetry** - *Pelvimetry* is the measurement of the pelvic inlet and outlet. It is important for obstetricians to know the dimensions of the pelvis in order to determine if the fetus can pass through the birth canal. ## 8.6 Lower Limb - The lower limb consists of the femur, tibia, fibula, patella, tarsals, metatarsals, and phalanges. - The femur is the largest bone in the body and forms the skeletal framework of the thigh. - The tibia forms the skeletal framework of the shin. - The fibula is a smaller bone located on the lateral aspect of the leg. It provides stability and attachment for muscles but does not bear weight. - The patella (kneecap) is a small, triangular bone located in front of the knee joint and articulates with the femur. - The tarsals are 7 bones, composed of the talus, calcaneus, navicular, cuboid, and the medial, intermediate, and lateral cuneiforms. - The metatarsals form the skeletal framework of the foot. - The phalanges are the bones of the toes. ### 8.6.1 Femur - The femur is the largest bone in the body. - The proximal end of the femur is comprised of: - *Head*: Articulates with the *acetabulum* of the hip bone, forming the hip joint. - *Neck*: Connects the head to the shaft. - *Greater trochanter*: Serves as a site for muscle attachment. - *Lesser trochanter*: Serves as a site for muscle attachment. - *Intertrochanteric crest*: A ridge that runs between the greater and lesser trochanters. - The shaft, or *diaphysis* is long and cylindrical. - It has a prominent medial *linea aspera* and a *lateral lip*. - It has also a *medial lip*, which attaches to the intermuscular septum. - It also has a *pectineal line* above the *linea aspera*, which serves as a site for muscle attachment. - The distal end of the femur consists of: - *Medial condyle*: Articulates with the medial condyle of the tibia. - *Lateral condyle*: Articulates with the lateral condyle of the tibia. - *Intercondylar fossa*: A depression between the condyles which houses the anterior cruciate ligament. - *Medial epicondyle*. - *Lateral epicondyle*. - *Adductor tubercle*: A small prominence on the medial epicondyle that serves as a site for muscle attachment. - *Patellar surface*: A smooth, slightly convex surface that articulates with the patella. ### 8.6.2 Patella - The *patella* is a sesamoid bone. - It is embedded in the tendon of the *quadriceps femoris muscle*. - It is a protective structure for the knee joint. - The *patella* helps to increase the leverage of the *quadriceps femoris muscle* during knee extension. ### 8.6.3 Tibia - The *tibia* is the medial bone in the lower leg. - The *tibial plateau*: Composed of the medial and lateral *condyles*, which articulate with the femoral condyles. This articulation forms the knee joint. - *Intercondylar eminence* is the bony protrusion in between the *tibial condyles*, it serves as an attachment point for the cruciate ligaments. - *Tibial tuberosity*: A bony projection on the anterior surface of the tibia, where the patellar ligament attaches. - *Soles* or *tibial shaft*: It is the main part of the bone. - *Medial malleolus*: It is a bony prominence on the medial side of the distal end of the tibia. - The *medial malleolus* articulates with the talus bone of the foot, forming the ankle joint. - *Fibular notch*: A small depression that articulates with the *fibula*. ### 8.6.4 Fibula - The fibula is the lateral bone of the lower leg. It does not bear weight. - *Head*: Articulates with the lateral condyle of the tibia, forms the *proximal tibiofibular joint*. - *Shaft*: It is the main part of the fibula. - *Lateral malleolus*: It is a bony prominence on the lateral side of the distal end of the fibula. - The *lateral malleolus* articulates with the talus bone of the foot, forming the ankle joint. ### 8.6.5 Foot - The foot is divided into three regions: the *tarsus*, the *metatarsus*, and the *phalanges*. - The *tarsus* is the proximal part of the foot and consists of 7 bones: - *Talus*: Articulates with the tibia and fibula to form the ankle joint. - *Calcaneus*: The largest bone in the foot, which forms the heel. - *Navicular*: Located on the medial side of the foot and articulates with the talus. - *Cuboid*: Articulates with the calcaneus and the fourth and fifth metatarsals. - *Cuneiforms*: There are three cuneiform bones: medial, intermediate, and lateral. Articulate with the navicular and metatarsals. - The *metatarsus* is the middle part of the foot and consists of 5 bones: - They are numbered I to V from the medial to lateral sides. - *Metatarsals* articulate proximally with tarsals and distally with the phalanges to form the metatarsophalangeal joint. - The *phalanges* are the bones of the toes. - Each toe (except the big toe) has 3 phalanges, while the big toe has 2. - The *phalanges* are named as *proximal*, *middle*, and *distal*. - *Phalanges* are named I to V from the big toe to the little toe. ### 8.6.6 Foot Arches - The foot has three arches, the *medial longitudinal arch*, the *lateral longitudinal arch*, and the *transverse arch*. - The arches provide support and help to absorb shocks while walking. - **Medial Longitudinal Arch:** - It is the highest of the three arches in the foot. - It is supported by the talus, navicular, cuneiforms, and three medial metatarsals. - **Lateral Longitudinal Arch:** - It is a lower arch than the medial longitudinal arch. - It is supported by the calcaneus, cuboid, and the fourth and fifth metatarsals. - **Transverse Arch:** - It is formed across the foot by the arrangement of the tarsal bones and the metatarsals. ### 8.6.6 Foot Disorders - **Flat Foot:** - This condition is characterized by a loss of the medial longitudinal arch. - The cause of flatfoot can be a weakened arch support, congenital, or trauma. - **Metatarsalgia:** - In metatarsalgia, a metatarsal bone becomes irritated, causing pain under the second, third or fourth toe in the ball of the foot. - The causes of metatarsalgia can be due to high heels, overuse, improper footwear, or tight muscles in the foot. - **Pes Planus:** - This condition, also known as flatfoot, is mainly a result of the collapse of the medial longitudinal arch. - The cause is a weakening of the muscles and ligaments that support the arch. - **Hallux Valgus:** - This condition, also known as bunion, is a deformity of the big toe, in which the big toe drifts outward and pushes against the second toe. - The cause is usually genetic, but it can also be caused by ill-fitting shoes or excessive weight. ### 8.6.7 Foot Problems - **Foot pain:** The most common foot problem, due to various causes, like plantar fasciitis, bunions, hammertoe or nerve entrapment. - **Bunions:** This a bone deformity where the big toe is bent toward the second toe, causing pain and inflammation. - **Hammertoe:** A second toe bent or curled toward the ground, causing pain and discomfort. - **Plantar fasciitis:** Inflammation of the plantar fascia, a thick band of tissue that runs along the bottom of the foot, resulting in pain and stiffness. - **Heel pain:** Can be the result of plantar faciitis, Achilles tendonitis, or a bone spur. ### 8.6.8 Ankle Disorders - **Ankle sprain:** Occurs when the ligaments that support the ankle joint are stretched or torn. - **Ankle fracture:** Occurs when one or more bones in the ankle joint are broken. - **Achilles tendinitis:** Inflammation of the Achilles tendon, which connects the calf muscle to the heel bone. - **Tendonitis:** Inflammation of any tendon in the ankle or foot. 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