Pain in the hip joint or acetabulofemoral joint is very common among both men and women across the world. Women tend to suffer more from hip pain than the men.(1) There can be various causes for the pain in the hip joint but before we cover the medical conditions that can cause hip joint pain, let us first try understanding the anatomy and the function of the hip joint or acetabulofemoral joint.
Anatomy of Hip Joint or Acetabulofemoral Joint and Its Function
Hip joint is also known as Acetabulofemoral joint. Hip joint is a synovial joint. Hip joint comprises of articulation of head of the femur and an acetabulum socket of pelvic bone. Inner surface of acetabulum and head of femur are covered with cartilage to allow smooth rotation of head of femur within the socket of pelvic bone known as acetabulum.
What Is An Acetabulum?
Acetabulum is a lateral part of pelvis and shapes as a hollow cup, which holds head of the femur bone. Acetabulum is a cup shape socket, which is a part of the pelvic bone.(2)
What Is Head of Femur?
Femur is a long bone that lies between pelvis and knee. Head of femur is a proximal (cephalic end) part of femur bone that rests within acetabulum.(3) Head of femur is round bony structure attached to acetabulum socket by a strong ligament.
What Is The Function of Hip Joint or Acetabulofemoral Joint?
Functions of The Hip Joint or Acetabulofemoral Joint are:
- Hip Joint or Acetabulofemoral Joint supports the weight of the body in both static (e. g. standing) and dynamic (e. g. walking or running) postures
- Maintains balance in standing position
- Hip Joint or Acetabulofemoral Joint assists ambulation or mobility
- Moves leg forward (flexion) and backward (extension)
- Hip Joint or Acetabulofemoral Joint rotates leg outward (external rotation) and inward (internal rotation)
What Can Cause Hip Joint Pain or Acetabulofemoral Joint Pain?
Hip joint pain is caused by hip joint disease and referred pain to the hip.
Inflammatory Joint Disease That Can Cause Hip Joint Pain or Acetabulofemoral Joint Pain
- Osteoarthritis of Hip
- Rheumatoid Arthritis of Hip
- Psoriatic Arthritis of Hip
- Juvenile Rheumatoid Arthritis of Hip
Why Does Inflammatory Joint Disease Cause Hip Joint Pain or Acetabulofemoral Joint?
Inflammatory joint disease causes inflammation of synovial membrane and cartilage, which are covering the bones of head of femur and acetabulum. Inflammation releases certain irritants that stimulates pain receptors and induces pain1. Chronic pain caused by inflammatory joint disease is a nociceptive pain and responds to anti-inflammatory medications such as Motrin and Naproxen.
Infection of The Hip Joint that Can Cause Hip Joint Pain or Acetabulofemoral Joint Pain
- Septic Arthritis of Hip
What Is Hip Joint Infection or Acetabulofemoral Joint Infection?
Infection is caused by colonization of bacteria, viruses, parasites and fungus within different organs including joints. Hip joint or Acetabulofemoral joint is mostly affected by bacterial infection. Infected hip joint or Acetabulofemoral joint is known as septic hip joint arthritis.
Why Is Hip Joint or Acetabulofemoral Joint Infection Painful?
Infected hip joint or Acetabulofemoral joint is extremely painful. Pain in the hips in initial stage is caused by continuous irritation of pain receptors and nerve fibers by nerve irritants, dead cells, and metabolites. Infection of the hip joint or Acetabulofemoral joint causes abscess or pus. Pus contains chemical irritants, dead cells and toxic metabolites. In the later stage, the hip joint becomes necrotic and joint is often filled with pus and blood. Hip necrosis occurs because of lack of blood supply to bones, cartilages, and synovial membrane1. Hip joint necrosis causes joint dislocation and fracture of hip joint resulting in severe pain. Fluid such as abscess or blood in joint causes pain by producing severe pressure over pain receptors.
Injuries That Can Cause Hip Joint Pain or Acetabulofemoral Joint Pain
- Hip Fracture
- Hip Joint Dislocation or Acetabulofemoral Joint Dislocation
Why Hip Joint Fracture or Acetabulofemoral Joint Fracture or Dislocation Results in Severe Intractable Pain in Hips?
Hip joint fracture involves fracture of pelvis, acetabulum, head of femur, or neck of femur. Dislocation often results following tear of ligaments and cartilages supporting hip joint. Immediately following fracture and dislocation of hip joint, pain is extremely severe. Pain following hip joint fracture or dislocations are divided as initial pain and delayed pain.
What Causes Initial Hip Joint Pain or Acetabulofemoral Joint Pain After Fracture or Dislocation?
Following Abnormalities Causes Initial Hip Joint Pain After Fracture or Dislocation:
- Soft tissues tear such as muscles, ligaments and synovial membrane can cause hip pain.
- Inflammation of the soft tissue like muscles, ligaments, and synovial membrane surrounding hip joint can also cause hip joint pain or Acetabulofemoral joint pain.
- Fracture of cartilages resulting in release of irritants resulting in pain following stimulation of pain receptors.
- Blood clots within the joint and around the joint stretching the joint and soft tissue.
- Irritations of the pain receptors located over periosteum (covering of the bones), ligaments, synovial membrane, and cartilages.
Following Abnormalities Causes Delayed Hip Joint Pain or Delayed Acetabulofemoral Joint Pain:
- Inflammation of the soft tissue and cartilages supporting joint.
- Infection within joint or surrounding tissue.
- Inability to stand or sustain the weight.
- Ligament and muscles stiffness.
Diseases That Can Cause Hip Joint Pain or Acetabulofemoral Joint Pain
- Avascular Necrosis
- Bone Cancer and Metastasis
Why Does Osteoporosis Cause Severe Hip Joint Pain or Acetabulofemoral Joint Pain?
Osteoporosis causes bones to be brittle and weak. Osteoporosis itself often is not painful but osteoporosis causes fracture of neck of femur, which results in severe intractable hip joint pain.
How Does Avascular Necrosis Cause Hip Joint Pain or Acetabulofemoral Joint Pain?
Avascular necrosis is a bone disease that results from lack of blood supply. Lack of blood supply is often secondary to vasoconstriction, dehydration, and interruption of blood vessels following fracture. Long-term use of corticosteroids and alcohol consumption also causes avascular necrosis. Avascular necrosis is mostly observed (69 % cases or more) involving hip joint2.
Initial pain is mild to moderate and pain is observed during ambulation or following pressure on the affected bone. Initial pain is caused by lack of blood supply resulting in irritation of the pain receptors located over covering of bones known as periosteum. Later avascular necrose bone fractures and pain becomes extremely severe. Avascular necrosis of hip joint causes joint collapse resulting in severe pain with any movement of leg2.
Why Does Hip Joint Cancer or Metastasis Cause Severe Hip Joint Pain or Acetabulofemoral Joint Pain?
Hip joint cancer is rare but cancer metastasis of hip joint is often seen in colon or lung cancer. Initial pain is secondary to irritation of pain receptors during initial phase of growth and normal tissue encroachment by cancer tissue3.Later, as cancer tissue expands the pain is secondary to pressure over the nerves or secondary fracture of hip joint.
Inflammation of Soft Tissue Surrounding The Hip Joint That Can Cause Hip Joint Pain or Acetabulofemoral Joint Pain
- Hip Bursitis
- Hip Tendinitis
- Hip Muscle Strain
Which Soft Tissues Surround The Hip Joint or Acetabulofemoral Joint?
Hip joint is surrounded by tendon, ligament and muscle. Tendons are the tough bands of fibrous tissue. Tendons are continuation of the tapering muscle tissue on both end muscles. Tendon holds to the bones with firm grips, so muscles can contract and relax without shifting its position around the bones and joint.
What Are The Functions of Hip Joint Ligament or Acetabulofemoral Joint Ligament?
Ligaments around hip joint are tough band of fibrous tissue with several anatomical functions as follows-
- Muscle Ligaments- Ligaments of skeletal muscles are band of fibrous tissue like tendon situated between muscle and bones. A ligament anchor several muscles around the hip joint and stabilizes the hip joint.
- Joint Ligaments- Two bones forming the joints are firmly held together by ligaments attached to proximal and distal bones of the joint. Strong and short length of ligament prevents joint dislocation.
- Capsular ligaments – Synovial joint capsules are supported by capsular ligaments and provides joint stability.
Why Does Soft Tissue Inflammation Cause Hip Joint Pain?
Inflammation of soft tissue produces several chemicals such as prostaglandin, bradykinin and thrombin, which irritate pain receptors and nerve fibers resulting in nociceptive pain. In later stage continuous inflammation induces hypersensitivity of nerve receptors and nerve fibers. Hypersensitive receptors and nerve fibers when stimulated produce neuropathic pain.
What are the Causes of Referred Pain to the Hip Joint or Acetabulofemoral Joint?
Referred pain is the pain felt at distant or different location than the site where pain is induced. Referred hip joint pain or acetabulofemoral joint pain is often associated with normal hip joint. Radiological studies and other investigations is mostly normal in-patient suffering with referred hip joint pain.
Causes of Referred Hip Joint Pain or Referred Acetabulofemoral Joint Pain Are As Follows-
- Lumbar disk herniation may pinch nerve in spinal canal or nerve foramina resulting in severe radicular pain, which may be felt as referred pain over hip joint.
- Facet joint hypertrophy or arthritis may cause referred pain in hip joint
- Sciatica pain is often felt in lower leg and may be associated with referred hip joint pain.
- Cauda equina pain is caused by spinal stenosis and in most of the cases causes hip joint pain with urinary and fecal incontinence.
- Spinal stenosis causes severe pressure on lumbar and sciatic nerves in spinal canal resulting in gluteal and hip referred pain.
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