Lower extremity anatomy
Hip region
The hip region comprises two bony structures- the acetabulum and femur.
The normal angle of inclination is 115-125 degrees (the angle formed between the femoral neck and femoral shaft) - if the angle is >125 degrees, then referred to as coxa valga; if the angle is <115 degrees, then referred to as coxa vara. Femoral neck angle is positioned anteriorly at a 10-15 degree angle; excessive anterior rotation >25 degrees is anteversion, and excessive posterior rotation <10 degrees is retroversion.
The primary movements of the hip are:
- Hip flexion/extension
- Hip external rotation/internal rotation
- Hip abduction/adduction
The hip joint is a stable synovial joint due to the bony anatomy and strength of ligaments, capsule, and labrum.
- Capsule encloses the entire joint
- Labrum
- Attached to the acetabulum and serves to deepen the structure to allow for greater articulation
- Ligaments
- Iliofemoral
- Two bands that originate at the anterior inferior iliac spine (AIIS), run medially to the distal intertrochanteric line, and laterally to the proximal aspect of the intertrochanteric line
- Both bands tighten with extension and external rotation; the superior band tightens with adduction; the inferior band tightens with abduction
- Pubofemoral
- Band tightens with extension, external rotation, and abduction
- Ischiofemoral
- Band tightens with medial rotation, abduction, and extension
- Iliofemoral
Other pertinent structures of the hip joint are:
- Inguinal ligament - forms a tunnel for vital arteries, veins, and nerves in the lower extremity
- Bursae - act as fluid-filled sacs that provide cushioning and friction reduction between tendons, joints, muscles, and bone
Knee region
The knee region is composed of four bones: the femur, tibia, fibula, and patella.
These bony structures then form three joints: tibiofemoral, patellofemoral, and proximal tibiofibular joint.
The primary movements of the knee that are aided by the three joints of the knee are:
- Knee flexion/extension
- Knee (tibial) internal/external rotation - available only when the knee is flexed; in the last degrees of extension the tibia externally rotates on the femur (the femur internally rotates on the fixed tibia in weight bearing) to lock the knee, called the screw-home mechanism
Other pertinent structures of the knee joint are:
- Capsule
- Tibiofemoral capsule covers the distal femur and proximal tibia- posteriorly divided into medial and lateral sections, anterior cut-out for the patella
- Proximal tibiofibular capsule is continuous with the knee 10% of the time
- Ligaments
- Tibiofemoral and patellofemoral joints
- Medial collateral ligament
- Tightened in extension; slackened in flexion
- Resists valgus forces and external rotation of the tibia
- Lateral collateral ligament
- Tightened in extension; slackened in flexion
- Prevents external rotation and provides stability against varus forces
- Anterior cruciate ligament
- Prevents anterior displacement of the tibia on the femur and provides rotational stability
- Posterior cruciate ligament
- Prevents posterior displacement of the tibia on the femur
- Medial collateral ligament
- Proximal tibiofibular joint ligaments
- Anterior tibiofibular ligament
- Reinforces anterior capsule
- Posterior tibiofibular
- Reinforces the posterior capsule
- Anterior tibiofibular ligament
- Tibiofemoral and patellofemoral joints
- Menisci
- Function
- Deepen the fossa of the tibia
- Increased congruency of the tibia and femur
- Reduces friction between joints during movement
- Improves weight distribution
- Provides shock absorption and lubrication to the knee
- Provide stability to the tibiofemoral joint
- Lateral meniscus
- Outer side of joint
- Attached to the popliteus and the joint capsule
- Stabilizes the knee against lateral rotation and tibial rotation
- Medial meniscus
- Inner side of joint
- Attached to the medial collateral ligament and joint capsule
- Stabilizes the knee against medial rotation and tibial translation
- Function
- Bursae - also present in the knee joint (see hip region above for their function)
Foot and ankle region
The ankle/foot joint is composed of four major articulations, which include the talocrural, subtalar, metatarsophalangeal, and interphalangeal joints.
The primary movements of the foot/ankle joint are:
- Ankle plantarflexion/dorsiflexion
- Ankle inversion/eversion
Other pertinent structures of the ankle/foot joint are:
- Capsule
- Provides stability to the joints of the ankle/foot
- Ligaments
- Talocrural joint
- The medial collateral ligament (Deltoid ligament) has deep and superficial fibers
- Lateral collateral ligament: Anterior talofibular, calcaneofibular, posterior talofibular
- Syndesmosis tibiofibular joint (high ankle ligaments)
- Anterior inferior tibiofibular ligament
- Posterior inferior tibiofibular ligament
- Metatarsophalangeal joint
- Plantar ligaments
- Collateral ligaments
- Interphalangeal joint
- Plantar ligament
- Collateral ligament
- Talocrural joint
- Plantar fascia
- Collagen fibers connecting from the medial calcaneus to the phalanges
- Fascia tightens during dorsiflexion- leads to supination and inversion
- Bursae - also present in the ankle/foot joint (see hip region above for their function)