What is the Difference Between Hip and Pelvis

The main difference between hip and pelvis is that hip is the area at the top and the side of the thigh, beside the pelvis. But, the pelvis is the lower part of the torso. Furthermore, the ball and socket synovial joint of the hip is formed by an articulation between the pelvic acetabulum and the head of the femur. But, the bone structure of the pelvis is posteriorly made up by the sacrum and the coccyx, and laterally and anteriorly by a pair of hip bones, which include  ilium, ischium, and pubis.  

In brief, hip and pelvis are two anatomical structures, which make up the lower part of the torso; the trunk of the body of humans and other bipeds and quadrupeds. Furthermore, the main function of both structures is to bear the weight of the body when sitting and standing, transferring the weight from the upper axial skeleton to the lower appendicular skeleton. 

Key Areas Covered 

1. What is Hip
     – Definition, Anatomy, Function
2. What is the Pelvis
     – Definition, Anatomy, Function
3. What are the Similarities Between Hip and Pelvis
     – Outline of Common Features
4. What is the Difference Between Hip and Pelvis
     – Comparison of Key Differences

Key Terms 

Acetabulum, Appendicular Skeleton, Hip, Ilium, Ischium, Pelvis, Pubis

What is Hip 

The hip is either an anatomical region or a joint, occurring laterally on each side of the pelvis. As a region, hip occurs laterally and anterior to the gluteal region, inferiorly to the iliac crest, and overlying the greater trochanter of the femur or the thigh bone. Also, the projecting region of the hip is mainly formed by the greater trochanter of the femur.

Anatomy

Looking at the joint, it refers to the acetabulofemoral joint, which is a ball and socket joint between the head of the femur and the acetabulum of the pelvis. Here, the acetabulum is the socket of the hip bone into which the head of the femur fits. Hence, the hip joint allows the free rotation of the femur. Moreover, there are two types of ligaments, which take part in the formation of the hip joint; intracapsular and extracapsular ligaments. Basically, the ligament of the head of the femur is intracapsular. And, the three main extracapsular ligaments include the iliofemoral and the pubofemoral ligaments, which are anterior. The third extracapsular ligament is the ischiofemoral ligament, which is posterior.

Figure 1: Hip Joint – Anatomy

Function

Normally, in quadrupeds, including both amphibians and reptiles, the femur extends horizontally as they carry their upper body parallel to the ground. Therefore, this does not permit great resistance to gravity. On the contrary, bipeds, such as humans and other mammals, have vertically dropping femur from the hip joint, permitting to hold itself off the ground and leading to specializations for running and leaping. In any case, the main function of the hip joint is to transfer the weight of the upper part of the body towards the appendicular skeleton or to the legs. 

What is the Pelvis 

The pelvis is the lower part of the trunk of vertebrates, occurring between the abdomen and the upper parts of the thighs.

Anatomy

The bony structure of the pelvis is posteriorly made up of the sacrum and the coccyx. But, the anterior and lateral regions of the bony pelvis are made up of a pair of hip bones. Here, the hip bone consists of thee bones; the ilium, ischium, and the pubis. Further, these three bones join together by the triradiate cartilage during childhood. Ultimately, they fuse together into a single bone after puberty. So, in brief, the sacrum and the coccyx belong to the axial skeleton while the three hip bones belong to the appendicular skeleton. 

Figure 2: The Pelvis – Anatomy

Furthermore, the ligaments that take part in the assembly of the pelvis include sacrospinous and the sacrotuberous ligaments, which are posterior. And, the other ligaments are the iliolumbar, anterior sacroiliac, and pubic symphysis, and they are anterior, in exception to the ligaments in the hip joint.

Function

The pelvic cavity is the body cavity surrounded by the pelvis. Primarily, it contains the reproductive organs, bladder, and rectum. Therefore, the pelvis is responsible for protecting the above organs. Consequently, the female pelvis is larger and broader than the male pelvis. But, the male pelvis is taller than the female pelvis. Else ways, the pelvis bears the weight of the upper body when sitting and standing. Also, it transfers the weight towards the legs through the hip joint. 

Similarities Between Hip and Pelvis  

• Hip and pelvis are two anatomical structures, which occur at the lower part of the torso.  
• The bone structure of them belongs to the appendicular skeleton of humans and other bipeds and quadrupeds.  
• Also,  both of their function is to bear the weight of the upper part of the body while transferring the weight from the upper axial skeleton to the lower appendicular skeleton.  
• Both hip and pelvis fractures are serious and painful injuries, which require quick-care orthopedic injury treatment in order to prevent permanent damage to the bone or surrounding soft tissues.   

Difference Between Hip and Pelvis 

Definition 

Hip refers to the laterally projecting region of each side of the lower or posterior part of the trunk formed by the lateral parts of the pelvis and the upper part of the femur together with the fleshy parts covering them. On the other hand, pelvis refers to the large bony frame near the base of the spine to which the hindlimbs or legs are attached in humans and other bipeds and quadrupeds. 

Significance 

The hip forms a projection in the lateral part of the pelvis along with the upper thigh bone on each side of the body. While the pelvis forms the lower part of the torso between the abdomen and the upper thighs. 

Anatomy 

The hip is a ball and socket synovial joint, formed by an articulation between the pelvic acetabulum and the head of the femur. Meanwhile, the bone structure of the pelvis is posteriorly made up by the sacrum and the coccyx and laterally and anteriorly by a pair of hip bones;  ilium, ischium, and pubis. 

Ligaments 

The types of ligaments take part in the formation of the hip joint include the iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament, and the ligament of the head of the fumer. Meanwhile, the ligaments in the pelvis include the sacrospinous, sacrotuberous, iliolumbar, anterior sacroiliac ligaments, and the pubic symphysis. 

Function 

Hip connects the upper thighs to the pelvis, facilitating the transfer of the weight of the body from the upper axial skeleton to the lower appendicular skeleton, while pelvis forms a basin-shaped ring of bones, which bears the weight of the upper part of the body when standing and sitting. 

Type of Fractures 

Hip fractures occur by an injury to the upper part of the femur, which may involve the femoral head, the femoral neck or the trochanter, while pelvic fractures occur by an injury to any of the large butterfly-shaped group of bones–the ilium, ischium, and pubis–located at the base of the spine.  

Causes of Fractures 

Hip fractures mainly occur due to the low bone density and as a result of a fall, while pelvic fractures frequently occur due to traumatic injuries from car accidents and as a result of a fall from a significant height. 

Conclusion 

The hip is the region of the lower part of each side of the pelvis. Basically, the upper parts of the thigh bones connect to the pelvis. Structurally, it is a type of ball and socket synovial joint. Also, the heads of the thigh bones articulate to the acetabulum of the pelvis. Functionally, the main function of the hip is to transfer the weight of the upper part of the body towards the legs. On the other hand, the pelvis is the lower part of the torso. It occurs in the body of humans and other bipeds and quadrupeds. Generally, the pelvic girdle is formed posteriorly by the sacrum and coccyx and anteriorly and laterally by a pair of hip bones; ilium, ischium, and pubis. Functionally, the pelvis bears the weight of the upper part of the body. In summing up all that we discussed here, the main difference between hip and pelvis is the anatomy, function, and the type of fractures.  

References:

1. Jones, Oliver. “The Hip Joint.” TeachMeAnatomy, 19 Jan. 2019, Available Here.
2. Bengochea, Kim. “Pelvis.” Kenhub, Kenhub, 27 Jan. 2020, Available Here.
3. Zamorano, Tony. “Hip & Pelvic Fractures.” Go to Ortho, Go To Ortho, 1 Feb. 2019, Available Here.

Image Courtesy:

1. “916 Hip Joint” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia   
2. “817 Ligaments of Pelvis” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia