The Pelvic Girdle Consists Of Two

The Pelvic Girdle Consists of Two: A Deep Dive into Pelvic Anatomy and Function

The human body is a marvel of engineering, and at its core lies the skeletal system, providing structure, support, and protection. Within this system, the pelvic girdle stands out as a crucial structure, playing a vital role in locomotion, weight bearing, and organ protection. Understanding its composition and function is critical for appreciating the complexities of human biomechanics and overall health. This article will delve into the details of the pelvic girdle, exploring its two main components, their intricate articulation, and the significance of this structure in various aspects of human life.

The Two Bones of the Pelvic Girdle: A Closer Look

The pelvic girdle, also known as the bony pelvis, isn't a single bone but a complex arrangement of three bones fused together: the two hip bones (ossa coxae or innominate bones) and the sacrum. While the sacrum forms a crucial part of the pelvic girdle, this article will primarily focus on the two innominate bones that are frequently referred to as the two bones comprising the pelvic girdle. Each innominate bone itself is formed by the fusion of three separate bones during development: the ilium, the ischium, and the pubis. These three bones fuse together in a region called the acetabulum, which is the socket that articulates with the head of the femur (thigh bone), forming the hip joint.

1. The Ilium: The Superior Wing

The ilium is the largest of the three bones that make up the hip bone. It's a large, wing-shaped bone that forms the superior portion of the hip. Its most prominent feature is the iliac crest, a thick, curved ridge that can be easily palpated on the lateral aspect of the hip. The iliac crest serves as an important landmark for both anatomical studies and clinical procedures. The ilium also has several other significant features:

• Iliac fossa: A concave surface on the internal aspect of the ilium, providing attachment points for several important muscles.
• Greater sciatic notch: A large notch located on the posterior aspect of the ilium, allowing passage of the sciatic nerve.
• Auricular surface: An articular surface on the medial aspect of the ilium, articulating with the sacrum to form the sacroiliac joint. This joint plays a pivotal role in transferring weight from the upper body to the lower limbs.
• Anterior superior iliac spine (ASIS) and Anterior inferior iliac spine (AIIS): Important bony landmarks used for muscle attachments and palpation.
• Posterior superior iliac spine (PSIS) and Posterior inferior iliac spine (PIIS): Similar to the anterior spines, these serve as crucial attachment points for various muscles and ligaments.

2. The Ischium: The Inferior and Posterior Support

The ischium is located inferior and posterior to the ilium. It contributes significantly to the weight-bearing capacity of the pelvis. Key features of the ischium include:

• Ischial tuberosity: A roughened, prominent bony projection that bears the weight of the body when seated. It's a crucial attachment point for several hamstring muscles.
• Ischial spine: A sharp projection that contributes to the formation of the greater and lesser sciatic notches.
• Ischial ramus: This forms part of the inferior aspect of the hip bone and contributes to the formation of the obturator foramen (a large opening in the hip bone).

3. The Pubis: The Anterior Bridge

The pubis is the anterior portion of the hip bone, forming the anterior part of the pelvic girdle. Its key features include:

• Pubic symphysis: This is a cartilaginous joint where the two pubic bones meet in the midline of the body. It allows a slight degree of movement, particularly during childbirth.
• Superior and inferior pubic rami: These form the superior and inferior borders of the pubis. They meet at the pubic symphysis and contribute to the formation of the obturator foramen.
• Pubic tubercle: A bony prominence located at the lateral end of the pubic crest.

The Pelvic Girdle: Beyond the Two Innominate Bones

While the innominate bones form the foundational structure, understanding the pelvic girdle requires acknowledging the crucial role played by the sacrum and coccyx. The sacrum, a triangular bone formed by the fusion of five sacral vertebrae, articulates with the ilium at the sacroiliac joints. This articulation is crucial for weight transfer and stability. The coccyx, or tailbone, is a small, rudimentary bone located inferior to the sacrum. Its function is less significant, providing minor support for pelvic floor structures.

The Significance of the Pelvic Girdle

The pelvic girdle's unique structure contributes significantly to several crucial bodily functions:

1. Weight Bearing and Locomotion:

The pelvis acts as the central bridge between the upper and lower body, transmitting weight from the spine to the lower extremities. Its strong structure and sturdy articulations with the femur allow for efficient locomotion, whether walking, running, or jumping. The shape and alignment of the pelvic girdle heavily influence gait and posture.

2. Protection of Internal Organs:

The bony pelvis provides vital protection for several essential organs, including:

• Urinary bladder: Protected by the anterior and inferior aspects of the pelvis.
• Reproductive organs: The female reproductive organs (uterus, ovaries, fallopian tubes) are housed within the pelvic cavity. The male reproductive organs (prostate gland, seminal vesicles) are also supported by the pelvic structures.
• Part of the gastrointestinal tract: The terminal parts of the large intestine are located within the pelvis.
• Part of the nervous system: Important nerves and blood vessels pass through the pelvic region.

3. Childbirth:

The female pelvis undergoes significant changes during pregnancy and childbirth. The ligaments and joints of the pelvis become more flexible, allowing for expansion to accommodate the growing fetus and facilitate passage during delivery. The shape and size of the pelvic inlet and outlet are critical factors in determining the ease of childbirth.

4. Muscle Attachment:

Numerous muscles attach to the pelvic girdle. These muscles play key roles in locomotion, posture, and other bodily functions. They include:

• Gluteal muscles: Major extensors of the hip.
• Hamstring muscles: Extensors of the hip and flexors of the knee.
• Hip adductors: Adduct the thigh.
• Abdominal muscles: Contribute to core stability and support.
• Pelvic floor muscles: Support pelvic organs and aid in continence.

Pelvic Girdle Injuries and Conditions:

The pelvic girdle, due to its weight-bearing and central role in locomotion, is susceptible to various injuries and conditions:

• Fractures: Pelvic fractures can range from simple to complex, depending on the severity and location of the fracture.
• Sacroiliac joint dysfunction: This condition involves pain and dysfunction in the sacroiliac joint.
• Pelvic instability: A condition characterized by excessive movement at the sacroiliac joints or pubic symphysis.
• Osteoarthritis: Degenerative joint disease that can affect the sacroiliac joints and hip joints.
• Pelvic inflammatory disease (PID): An infection of the female reproductive organs.

Conclusion: The Foundation of Movement and Stability

The pelvic girdle, composed of two innominate bones (each a fusion of ilium, ischium, and pubis), along with the sacrum and coccyx, is a cornerstone of the human musculoskeletal system. Its intricate structure, comprising various bony landmarks, joints, and muscle attachments, ensures its multifaceted roles in weight bearing, locomotion, organ protection, and childbirth. Understanding its anatomy and function is paramount for healthcare professionals, athletes, and anyone seeking to optimize their physical health and performance. Further research and continued study of the pelvic girdle will undoubtedly reveal more about its complexities and its critical role in human health and well-being. The detailed understanding of this crucial region is vital for early diagnosis, effective treatment, and the prevention of various health issues that may arise.