The Hip Joint and Its Structure

The Hip Joint

• Cartilage's coefficient of friction is significantly lower than that of ice (0.002 - 0.01 compared to 0.2- 0.5).
• The acetabulum is deepened by the fibrocartilaginous acetabular labrum.
• The labrum is attached to the bony rim and the transverse ligament.

Ligaments of the Hip Joint

• The pubofemoral ligament resists hip extension, adduction, and abduction, situated anteriorly.
• The ischiofemoral ligament resists hip abduction and extension, situated posteriorly.
• The ligament of the head of femur (ligamentum teres) has no role in stability despite attaching to the fovea.
• The ligamentum teres forms a synovial membrane tube for blood vessels and is absent in adults.

Hip Stability

• The gluteal muscles are crucial for hip stability.
• The gluteus maximus is a powerful extensor, laterally rotating the thigh.
• The gluteus medius and minimus are important for abduction and medial rotation of the thigh.

Tensor Fascia Lata and Iliotibial Band

• The tensor fascia latae (TFL) helps with hip flexion, abduction, and medial rotation.
• The TFL inserts into the iliotibial tract, which is a strong membranous fascia and attaches to the lateral condyle of the tibia.

Hip Flexors

• The rectus femoris flexes the hip joint and extends the knee joint.
• The iliacus flexes the thigh.
• The iliopsoas group consists of three muscles (iliacus, psoas minor, and psoas major) that share a common insertion and are powerful hip flexors.

Adductors

• The adductor brevis, adductor longus, and adductor magnus all adduct the thigh.
• They have different origins and insertions, but are all innervated by the obturator nerve, except the adductor magnus which also receives innervation from the tibial portion of the sciatic nerve.

Piriformis

• The piriformis laterally rotates and abducts the thigh.
• Depending on hip position, it can also medially rotate the thigh.

Hamstrings

• The hamstrings originate at the ischial tuberosity (except the short head of the biceps femoris).
• The biceps femoris has long and short heads, and both flex the knee; the long head also extends the hip.
• The semimembranosus and semitendinosus flex the knee, extend the hip, and slightly medially rotate.

Bi-Articular Muscles

• The rectus femoris, sartorius, and gracilis are bi-articular muscles that work at both the hip and knee joints.
• The sartorius flexes, abducts, and laterally rotates the hip joint.
• The gracilis adducts the hip joint and flexes the knee.