TJA is a great surgery for allowing people to return to daily activities. But what about activities beyond grocery shopping, visiting friends and family and going for walks. Surgeons have looked into the activities their patients return to, and the incidence of complications to make some recommendations about how active you can be after surgery. The Baby Boomer Generation is the most active elderly population in history. Many remain extremely active into their 70s and 80s, playing golf, tennis, swimming and hiking.
Lets look at the risks of these activities and the current recommendations made by the Knee Society and the American Hip Society.  The concern for over-activity is the risk of accelerated wear of the joint replacement, as well as risk of falls and subsequent prosethesis loosening or periprosthetic fracture[2, 3].
It appears that preop function plays an important role in determining postoperative return to sport. 
GOLF. About 1-8% of people that get a hip replacement actively play golf. In areas like Florida and Arizona this number is probably much higher. Golf is considered a low impact sport on the hips and is therefore allowed after hip replacement by 99% of orthopedic surgeons. To date, there are no published reports of acute hip prosthesis loosening, or hip dislocation during golf. X-rays of a swing in people with and without a hip replacement show very similar motion within the hip (which is great, because it means that your handicap won't change too much). Similarly there are no significant adverse events reported in TKA after golf.
It is important to note however, that golf is a more demanding sport than many people give it credit for. The golf swing places a high torque on the lower back and hip, and some doctors remain concerned that this repetitive force, over many years, could lead to the hip replacement wearing out prematurely.
A recent study looked at x-rays of people with hip replacements while swinging their golf club. During a normal golf swing (these people had time to warm up, and had no complaints of pain while swing the club), over 1/3 showed signs that the ball and socket of the hip replacement were improperly bumping into each other (this is called impingement). This has some orthopedic surgeons concerned that this could lead to premature wearing out of the replacement or it could cause a hip dislocation, although there is no evidence to date that suggests this minor bumping during activities is significant. The impingement was seen in people where the socket was positioned in more anteversion, and the people had a swing that produced more hip external rotation.
TENNIS. High impact and therefore generally discouraged by orthopedic surgeons. Studies on hip and knee replacement in people that played competitive tennis showed significant improvement in pain relief and court mobility after the joint replacement. So a hip or knee replacement will let you get back to playing tennis, however, there is the concern that a fall could cause significant damage to the affected joint or overuse could lead to premature failure of the joint replacement.
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