Femur, Knee, Ankle

Femur  

The femur is the longest and heaviest bone in the body.  It is the most proximal bone of the leg in vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles, and amphibians.  The femur transmits body weight from the hip bone to the tibia when a person is standing.  Its length is approximately one quarter of a person’s height.   The femur consists of a shaft and two ends: proximal/superior and inferior/distal.   The head and the neck of the femur are a part of the superior end.  The neck of the femur is trapezoidal in shape.  Its skinnier end connects with the head of the femur and its thicker base is continuous with the shaft.

The femur is commonly fractured.  The neck of the femur is the most frequently fractured.  It is the narrowest and weakest portion of the bone.  The femoral neck of people younger than 40 is usually strong, and when fractures do occur, it’s usually due to high energy impacts.  Femoral neck fractures are most common in individuals older than 60, especially women because their femoral necks are more often weak due to osteoporosis.   One example, a transcervical fracture, occurs at the middle of the femoral neck and usually occurs as a result of indirect trauma like stumbling or stepping down hard off of a curb or step.   Fractures of the femoral neck cause lateral rotation of the lower limb and they often disrupt the blood supply to the head of the femur.  

Knee

                The Knee joint is the largest and most superficial joint.  It joins the thigh with the leg and consists of two articulations: one between the femur and tibia, and one between the femur and patella.  It is a hinge type of synovial joint and allows for flexion and extension.  The hinge movements are combined with gliding, rolling, and rotation about a vertical axis.    The strength of the knee joint depends on two things: the strength and actions of the surrounding muscles and their tendons, and the ligaments that connect the femur and tibia.  Knee joint injuries are common because the knee is a low-placed, mobile, weight-bearing joint, serving as a fulcrum between two long levers.

                Ligament sprains are the most common knee injuries in contact sports.  They occur when a force is applied against the knee and the foot cannot move; usually the knee is flexed and the foot is fixed on the floor.  The anterior cruciate ligament (ACL) serves as a pivot for rotary movements of the knee and is taut during flexion.  Hyperextension and severe force directed anteriorly against the femur with the knee semi-flexed may tear the ACL.  Tears commonly occur in the middle of the ligament.

Ankle   

                The ankle joint is a hinge type joint.  The ankle joint occurs where the tibia and fibula meet the talus.  The ankle is reinforced laterally by the lateral ligament. The lateral ligament is composed of the anterior talofibular ligament, posterior talofibular ligament, and calcaneofibular ligament.  The ankle is reinforced medially by the medial ligament. The medial ligament is made of the tibionavicular part, the tibiocalcaneal part, the anterior tibotalar part, and the posterior tibiotalar part.  The main movements of the ankle are dorsi-flexion and plantar flexion of the foot. 

                The ankle is the most frequently injured major joint in the body.  The most common ankle injury is an ankle sprain.  Ankle sprains occur when ligaments or fibers tear.  Most ankle sprains are inversion injuries and occur when the foot is forcibly inverted.  These involve twisting of the joint when the foot is flat.  Lateral ligament sprains are also common.  The lateral ligament is weaker than the medial ligament.  The lateral ligament sprain usually occurs in sports that include running and jumping.

Sources:
Clinically Oriented Anatomy
 en.wikipedia.org/wiki/Femur
en.wikipedia.org/wiki/Ankle