The most common condition that calls for hip and knee surgery, either independently or together, is arthritis. Arthritis can do irreparable damage to a joint by allowing it to move in ways it is not designed to, and when the joint wears out to the point that is causes severe or chronic pain, hip and knee surgery may be called for. These surgeries are rarely conducted at the same time, as recovering from both hip and knee surgery can be quite painful and debilitating. Most people have one surgery at a time, though both joints may need the surgery at some point.
Arthritis is a degenerative condition that involves the breakdown of the ligaments that hold the joint together, as well as cartilage within the joint. As those ligaments and cartilage wear out or break down, swelling and inflammation is common, and the joint is allowed to move in ways it would not otherwise move. Bones can grind against each other, forming painful bone deformities. The joint may begin to press against nerves, or it may cause bursitis or other painful conditions. Hip and knee surgery are usually reserved for only the most severe cases of arthritis and may require a total replacement of the joint. Over 100 types of arthritis exist, and some may be less severe than others, so more than one doctor's consultation may be in order before a decision to replace the joint is made.
Ligament tears will very often require hip and knee surgery as well. The knee ligaments can be damaged fairly easily, especially during athletic activity. The most commonly damaged ligament in the knee is the Anterior Cruciate Ligament, or ACL. An ACL tear does not necessarily require surgery to fix, but in very severe cases, a surgery will more than likely be necessary. The mobility of the joint after surgery may suffer, and the athlete may be more susceptible to injury once the ACL has been damaged and repaired.
Fractures can lead to hip and knee surgery in more severe cases. Fractures occur when the bones of the joints or other parts of the body endure a stress that the muscles and bones are not designed to handle. This stress can lead to small cracks in the bone, known as fractures. The severity of the fracture will dictate whether surgery is necessary; small fractures such as stress fractures do not usually require a surgery, but more severe fractures — especially compound fractures, in which the bone punctures through the skin — will require a surgery to repair the injury.