The hip is a ball and socket joint. It is a round ball (femoral head) in a perfectly matched cup (acetabulum) with the apposing surfaces covered by a smooth, rubbery cartilage surface.

The critical parts to a hip include the cartilage, the labrum, and the muscles and tendons that surround the hip.

The labrum is a fibrous ring around the rim of acetabulum. The labrum and the cartilage work together to distribute a thin layer of lubricating synovial fluid between the ball and socket. This fluid is like oil in a car motor. The hip needs proper function of all of these elements to prevent degeneration of the articular surface cartilage.

Arthritis is the loss of the articular cartilage with resulting pain, deformity, and inflammation. The apposing surfaces become rough and misshaped. The bone will develop cysts (cavities) and spurs (bone growth at the joint margin) and with complete loss of cartilage, the two boney surfaces beneath will begin to rub. The deformity and pain leads to loss of range of motion of the hip.

There are many causes of hip arthritis. The most common include:

OsteoArthritis (OA): Most commonly used term, but the precise mechanism of OA is not completely understood and many other forms of arthritis are probably lumped into OA unwittingly. A good analogy would be your hair turning grey as you get older. The cells that make and sustain the cartilage just stop reproducing. The cartilage wears out and goes away.

Trauma: Trauma to the hip can consist of small unappreciated damage and crush injuries of the cartilage itself from minor falls, to major fractures and dislocations of the hip that change the congruency of the joint. Over time these injuries can lead to death and further damage of the cartilage resulting in arthritis.

Infection: Viral and bacterial infections of the hip joint can destroy the joint surface. This is likely secondary to the profound inflammatory response that occurs with the body's attempt to fight the infectious agent.

Autoimmune diseases/Inflammatory arthropathy: This type of arthritis is secondary to an inappropriate attack by the body's immune system on itself. Rheumatoid Arthritis is a common example, though there are many others. The end result is painful inflammation and destruction of the cartilage with inflammatory tissue or cells.

Dysplasia: Subtle deformity of the hip, usually present at birth, will lead to damage of the cartilage over time. Like a tire on a wheel that isn't correctly aligned, the ball doesn't fit well into the socket. The cartilage is not properly lubricated and the pressure on it is excessive. There is a wide spectrum of dysplasia from very mild to severe. It is likely present in people who present with arthritis or hip pain at younger ages.

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The diagnosis can be confusing, as there is overlap between spine disease, tendonitis, bursitis, labral disease, and primary hip arthritis. I frequently see patients from and refer patients to my spine or pain management colleagues as we work together to try to obtain the correct diagnosis. Sometimes its easy, sometimes its not, and it can be more than one thing.

Common hip arthritis:

-Localized to the groin, inside of the thigh and even the knee

-Not usually low back, buttock, back or side of the thigh.

-Pain can be intermittent and very sharp, or dull and continuous.

-Made worse with activity and activities that require increased motion of the hip or impact.

-Commonly includes difficulty with getting comfortable for sleep and frequent waking from sleep.

-Pain on initiation of daily activity, that may get somewhat better with motion.

-Difficulty with motions that require high hip flexion, like tying shoes or placing socks.

-Mechanical clicking or grinding sounds with hip movement.