and if large diameter head balls are used. Dislocations occurring between three months and five years after insertion usually occur due to malposition of the components, or dysfunction of nearby muscles. Risk factors of late dislocation (after five years) mainly include: Female sex Younger age Previous subluxation without complete dislocation Previous trauma Substantial weight loss Recent onset or progression of dementia or a neurological disorder Malposition of the cup Liner wear, particularly when it allows head movement of more than 2 mm within the cup compared to its original position Prosthesis loosening with migration Surgeons who perform more operations tend to have fewer dislocations. An anterior approach seems to lower dislocation rates when small diameter heads are used, but that benefit has not been shown when compared to modern posterior incisions with the use of larger diameter heads. The use of larger diameter head size in itself decreases dislocation risk, even though this correlation is only found in head sizes up to 28 mm: larger heads do not result in a statistically significant decrease in dislocation rate. Keeping the leg out of certain positions during the first few months after surgery further reduces risk. Infection Infection is one of the most common causes for revision of a total hip replacement. The incidence of infection in primary hip replacement is 1% or less in the United States. Risk factors for infection include obesity, diabetes, smoking, immunosuppressive medications or diseases, and history of infection. Limb length inequality Most adults have a limb length inequality of 0–2 cm which causes no deficits. It is common for people to sense a larger limb length inequality after total hip replacement. Sometimes the leg seems long immediately after surgery when in fact both are equal length. An arthritic hip can develop contractures that make the leg behave as if it is short. When these are relieved with replacement surgery and normal motion and function are restored, the body feels that the limb is now longer than it was. This feeling usually subsides by six months after surgery as the body adjusts to the new hip joint. The cause of this feeling is variable, and usually related to abductor muscle weakness, pelvic obliquity, and minor lengthening of the hip during surgery (<1 cm) to achieve stability and restore the joint to pre-arthritic mechanics. If the limb length difference remains bothersome to the patient more than six months