Lecture 14: Pelvic Girdle and Legs

Sexual Dimorphisms in the pelvis

Female is larger and broader across pelvic opening; male is narrower A broader pubic angle (inferior angle between pubic bones) in females compared to males Less curvature of the sacrum/coccyx in females; in males, arcs into pelvic Ilium is broader laterally, project less upward in females versus males.

Lower Leg

Tibia (thick, medial) Fibula (fine, lateral) Patella

Pubic symphysis (amphiarthrosis)

- The two pubic bones are joined together through a fibrocartilage disk and strengthened through accessory ligaments. function: to act as a shock absorber. example: During pregnancy the gap between the two pubic bones widens, as much as doubling, to allow hypermobility of the pelvic girdle during the birthing process. In some cases, complete separation (diastasis) of the joint occurs during delivery

Tibial and Fibular Collateral Ligaments (supporting ligament)

- also called medial and lateral collateral ligaments, respectively, these are extracapsular (outside of the joint capsule) ligaments that tighten only when the knee is fully extended, whereupon they stabilize the joint.

knee joint

- joins the lower leg to the thigh and, together with the hip and ankle joints, supports the weight of the body. - largest joint in the human body. - a synovial hinge joint with a tremendous amount of movement (more than any other joint in the lower body) - lacks the large muscles and ligaments that strengthen the hip joint. - weaker than the hip joint, allow some rotational movement in addition to flexion and extension

Acetabulofemoral joint (hip joint)

- similar to the articulation between the humerus and scapula, the hip joint is a classic ball-and-socket joint that functions to attach the legs to the pelvic girdle

Sacro-iliac (SI) joint

- the posterior and medial aspects of the ilium articulate with the sacrum in an incredibly strong synovial joint. - This joint has a limited amount of movement and functions predominantly as a shock absorber and to transfer forces from the legs to the spine. - During pregnancy (and to a lesser degree during menstruation), female hormones cause the ligamentous support of this joint to weaken in preparation for the birthing process. This can predispose women to arthritis in this joints - the more children, the higher the risk factor.

Patellar ligament and patellar retinaculae (supporting ligament)

- the tendons of the quadriceps complex pass across the anterior surface of the knee and join with the patellar ligament below the patella. The patella is a large sesamoid bone that forms within the quadriceps tendon. The patellar ligament connects the patella to the tibia, and is stabilized on either side by the patellar retinaculae. The patellar ligament is important because it stabilizes the anterior surface of the tibiofemoral joint where there is no joint capsule

Anterior/Posterior Cruciate Ligaments (ACL/PCL)

- these are intracapsular ligaments that attach the intercondylar region of the tibia to the condyles of the femur. They are named based on where they originate on the tibia - they actually cross one another as they insert on the femoral condyles (crucialis is latin for "cross"). These are very important for limiting anterior/posterior shifting of the tibiofemoral joint. They are also important for "locking the knees", as we'll discuss below. The ACL is particularly important for limiting anterior/lateral movement of the tibia relative to the femur. The PCL limits the ability of the tibia to shift posteriorly and medially relative to the femur.

Lateral longitudinal arch

- this arch bears most of the body weight while standing and initially while walking/running. Comprised of calcaneus, cuboid, and the fifth metatarsal and supported by the plantar fascia - a sheet-like structure consisting of dense, regular connective tissue that extends from the calcaneus to the proximal phalanges of the toes

knee joint made up of two joints

- tibiofemoral joint (between the lateral/medial condyles of the femur and the lateral/medial condyles of the tibia) - patellofemoral joint (between the patella and the intercondylar fossa of the femur).

Iliotibial tract

The knee is also stabilized laterally by the iliotibial tract (IT Band). The iliotibial tract shifts slightly anteriorly during knee extension and slightly posteriorly during knee flexion. In this way it helps to stabilize the lateral aspect of the knee during walking/running.

Joint Capsule

a complete arrangement of ligaments, cartilages and tendons. To withstand the immense vertical stresses placed on the knee, the articular surfaces of the tibia and femur are separated by a pair of fibrocartilage pads, the medial and lateral menisci

menisci have the following functions

a. Increase the surface area of the tibiofemoral joint b. Cushion against shocks/stress c. Change shape as the joint moves to continue supporting the articulation d. Provide some lateral stability (to limit lateral/medial rotation)

Stability of acetabulofemoral joint relies on 5 structural elements

a. The articular capsule is particularly strong, contributing greatly to the stability of the joint. b. The joint capsule is surrounded by several superficial ligaments that help stabilize the joint while simultaneously aiding joint movement. The three largest are: i. Iliofemoral ligament (posterior) ii. Ischiofemoral ligament (posterior) iii. Pubofemoral ligament (anterior) c. The depth of the acetabulum is increased through a ring of fibrocartilage called the acetabular labrum - similar to the glenoid labrum in the shoulder joint. A fat pad within the acetabular fossa acts as a shock absorber. d. On the outside of the labrum is a ring-like ligament that extends to the head of the femur. This ligamentum capitis femoris (or ligamentum teres) is an important stabilizing factor that limits the tendency of the head of the femur to move away from the acetabulum during some joint movements. It relaxes, however, when you cross your leg in front of your hip (adduction), facilitating movement in this direction. e. The muscles and tendons of the hip joint help further stabilize the joint.

pelvic girdle

consists of the paired hip bones, or coxal bones. Each hip bone began embryologically as three separate bones: the ilium, ischium and pubis. These three bones fuse during development in a process that may last until age 25. All three bones of each coxa come together at the acetabulum - the site where the head of the femur articulates with the pelvis.

what is the pelvic girdle comprised of?

major bony portion of the bony pelvis, which consists of the two hip bones, the sacrum and the coccyx. The bony pelvis functions to (1) support soft organs in the pelvic region, and (2) connects the trunk and legs, and (3) balances the trunk for bipedal locomotion. It is considerably more broad and shallow in humans and other partially bipedal organisms compared with quadrupeds

Transverse arch

this arch extends across the inferior aspects of the metatarsals and distal tarsals. It results from the change in curvature between the lateral and medial longitudinal arches

Medial longitudinal arch

this is the distinct "arch" of the foot familiar to most people. It is considerably more flexible than the lateral longitudinal arch and prevents compression of nerves/blood vessels against the substrate, as well as providing flexibility while walking. Body weight shifts from the lateral to medial longitudinal arch during ambulation. Comprised of talus, navicular bone, medial cuneiform and metatarsals 1-2

Popliteal ligaments

this pair of ligaments are also extracapsular and support the posterior aspect of the joint. They extend between the femur and the heads of the tibia and fibula