Pelvic Girdle and Leg Joints: Anatomy and Function
Joints of the Pelvic Girdle
1. Sacroiliac Joint
The sacroiliac joint connects the sacrum to the ilium (part of the hip bone). The articular surfaces are the auricular surfaces of the sacrum and ilium. It is stabilized by ligaments and a joint capsule. This cartilaginous joint has limited mobility, allowing for slight gliding movements. It facilitates nutation (inferior end of the sacrum moves posteriorly) and counternutation (inferior end of the sacrum moves anteriorly). The axis of movement is horizontal, and these movements are more pronounced in women. The sacroiliac joint is crucial for distributing weight from the ischial spine or the femoral heads.
2. Pubic Symphysis
The pubic symphysis is a cartilaginous joint that joins the innominate bones at the anterior midline of the pelvic girdle. It is an amphiarthrosis, meaning it allows very little movement.
Joints of the Lower Limb
1. Hip Joint (Coxofemoral Joint)
The hip joint connects the femur to the coxal bone (hip bone). It is a highly mobile ball-and-socket joint, allowing for a wide range of motion, including flexion-extension, internal and external rotation, abduction, adduction, and circumduction (a combination of these movements). The articular surfaces are the head of the femur and the acetabulum (hip socket). The joint is secured by the joint capsule and the iliofemoral, pubofemoral, ischiofemoral, and round ligaments of the femoral head.
2. Knee Joint
The knee joint connects the femur to the tibia and patella (kneecap). The articular surfaces include:
- Distal end of the femur: trochlea and condyles
- Proximal end of the tibia: tibial plateaus
- Patella
The knee joint is stabilized by the joint capsule and the following ligaments: anterior, posterior, and lateral (internal and external) ligaments, as well as the anterior and posterior cruciate ligaments.
Menisci: These are fibrocartilaginous structures inserted into the tibia and the joint capsule. They enhance joint congruency, improve mobility, and help absorb pressure. The knee is a hinge joint that primarily allows for flexion (heel towards the buttocks) and extension (limited, especially after flexion). Rotation is also possible when the knee is flexed.
3. Superior Tibiofibular Joint
The superior tibiofibular joint is located between the tibia and fibula. The articular surfaces are on the tibia and fibula, and the joint is stabilized by the joint capsule and the anterior and posterior tibiofibular ligaments. It is an arthrodial joint (gliding joint) with subtle movements.
4. Inferior Tibiofibular Joint
The inferior tibiofibular joint is a syndesmosis (fibrous joint) with an interosseous membrane providing some flexibility. The articular surfaces are on the tibia and fibula, and the joint is reinforced by the anterior, posterior, and interosseous ligaments. The fibula exhibits a slight gliding motion on the tibia during dorsiflexion of the foot.
5. Ankle Joint (Talocrural Joint)
The talocrural joint involves the tibia, fibula, and talus (ankle bone). It primarily allows for dorsiflexion and plantarflexion, occurring around a transverse axis passing through the malleoli (bony prominences on either side of the ankle). Abduction-adduction (around a longitudinal axis) and pronation-supination (around an anteroposterior axis) also occur.
Tarsal Joints
1. Subtalar Joint
The subtalar joint is located between the talus and calcaneus (heel bone). It consists of two distinct articulations: anterior and posterior. It is an arthrodial joint (gliding joint) that contributes to pronation and supination.
2. Chopart’s Joint (Midtarsal Joint)
Chopart’s joint connects the calcaneus to the cuboid and the talus to the navicular. It comprises two joints: the calcaneocuboid and talonavicular joints. This joint allows for twisting movements of the foot: inversion (adduction + supination + extension) and eversion (pronation + abduction + flexion).