Osteoarthritis is the most common form of arthritis, frequently it occurs in weightbearing joints mainly knees and hips. The ends of the bones are lined with a smooth surface called cartilage. Cartilage acts as a shock absorber, providing gliding surfaces between bones.
With osteoarthritis this smooth surface may become rough or wear away completely, causing inflamation, pain and restricted motion.
Ostoarthritis is usually a slowly degenerative disease in which cartilage gradually wears away.
It may also develop after an injury to the joint in which damage to the cartilage can lead to accelerated wear of the joint surfaces.

Symptoms of osteoarthritis of the hip are discomfort and pain, if the condition gets worse the joint gets stiff and inflammated.
You may loose joint mobility and start to limp.

Osteoarthritis (OA) of the hip is caracterised by groin pain.

OA of the knee creates difficulties raising from chairs and climbing stairs.

Initial treatment of OA of the hip and knee begins with non-operative treatment giving antiinflammatory medication (NSAID). Injections (cortisone, hyaluronic acid) are available.
When non-operative treatment fails surgical options are considered.
In later stages a total joint replacement may be neccessary.

more info OA of the hip
more info OA of the knee (total and unicompartmental replacement)