Is there a Goldilocks age for TJA? Should patients endure the pain just a little bit longer until they reach the age of 60? Alternatively, should patients hurry up and get their joint replaced before they get too old? Like everything in medicine, a pure numeric threshold is just artifice, and patient specific factors must drive clinical decisions. Yet broader trends help to inform decisions and so we examine the impact of age on TJA.
Older patients (>80 years old).
Patients > 80 years old achieve improved pain and improved function similar to patients in their 60s and 70s. One study looked at people in their 90s and found that they too improved significantly with pain and function after TKA, and therefore, age alone should not prevent people from getting a surgery that can improve quality of life [1, 2].
Yet it is seen that older patients are more likely to have other medical conditions (including atrial fibrillation, high blood pressure etc) that can complicate recovery. There are reports of higher complication rates after surgery due to these medical conditions. One study suggested that the risk of death after surgery was 3x higher, the risk of MI or other cardiac complication was 2.5x higher, and the risk of pneumonia was 3.5x higher.  Another study looking 1 year mortality risk saw 5% in 90 year olds, 3% in 80 year olds and 0.8% in younger patients (not all of this is attributed to the surgery because the overall mortality rate for all 90 year olds is 12% at 1 year...which is actually higher than those undergoing surgery probably because those cleared for surgery are healthier) [4, 5]. This significant increased risk is important to remember because a hip and knee replacement surgery is life-improving but not life-saving and therefore patients need to know that the surgery can be considerable more life-threatening in patients older than 80 [6, 7].
The length of hospitalization is also longer (3.4 days for 90s, 3.3 days for 80s, and 2.8 days for < 80).
Younger Patients (<55 years old)
The average age for a joint replacement is about 70 years old. But < 55 is the vastest growing group undergoing TJA. In 2007 only 6% of TKAs were performed in patients under 50 years old .
The etiology for TJA in young patients is significantly different than in the elderly. The incidence of primary osteoarthritis is less common, with over 50% presenting for other reasons such as AVN, post-traumatic arthritis (30% of cases in TKA), and inflammatory arthritis, which at baseline are all associated with higher complication rates.
In TKA, many studies suggest good mid-term (5-10 yr) survival of 95-99% . Yet other studies suggest the mid-term (7 year) revision rate is higher than average, about 8%, most commonly due to aspetic loosening and deep infection   . Survivorship appears lower than the overall TKA population, and the rate of early aspetic loosening may be 4x higher. The Australian registry reported 12% revision rate at 10 years for patients with TKA under 55 yo. The Kaiser registry showed 2x higher revision rate in younger patients .
In THA, mid-term (10 year) survivorship, for cementless implants using highly crosslinked poly, appears equivalent to older THA population [14, 15], with wear rates of 0.02 mm/yr. Long-term revision rate (18 year avg) in patients under 50 yo was about 80%, with 95% survival of the femoral component and 85% survival of the acetabular component   . These figures reflect survival using contemporary cementless implants, while survival rates of cemented/older designs appears notably inferior . Some studies report accelerated poly wear rates of 0.2 mm/yr (due to increased activity) , while other studies have looked at activity levels in THA under 50 yo and found activity level (1.2 millino gait cycles/yr) and wear rates (0.1mm/yr) comparable to older counterparts .
The higher revision rate may be predisposed due to the underlying cause for TJA, such as posttraumatic arthritis. Others argue that younger patients are more active and thus place greater demands on the implants, accelerating the wear. However, studies have shown that young patients are not uniformly more active, and that there is significant variability among young patients[21, 22]. In THA about 37% returned to recreational sports (impact activity), yet for TKA only 10% returned to such activities. Furthermore, in THA, the use of HXLPE has reduced wear to levels similar to average population age.
It appears that at 10 years after UKA in patients under 60 years old, 90% survival compared with 96% in people over 60 years old .
One issue is that younger patients have higher expectations than older patients , appear more sensitive to residual symptoms , and found that age is the most important preoperative characteristic that predicts postop patient-reported outcomes .
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