Table 2.

Results for patient-reported outcome measures (PROM)

Author	Journal	Year	Number	Age (years)	Result
No difference
Sveikata [33]	Geriatr Orthop Surg Rehabil	2017	314	< 75, ≥ 75	Post operation 1 year: no difference in pain (P = 0.592), stiffness (P = 0.729), or function (P = 0.082) according to WOMAC and SF-12 physical (P = 0.082) and mental (P = 0.559) health score
Escobar [31]	J Eval Clin Pract	2017	492		No difference between minimal clinically important difference (MCID)/patient acceptable symptom state (PASS) (P = 0.5)
Lizaur-Utrilla [35]	Knee Surg Sport Traumatol Arthrosc	2016	≤ 55: 61 60–70: 61	≤ 55, 60–70	Post operation 5 years, there were no significant differences between groups in KSS knee or function, WOMAC pain or function, or SF-12 physical or mental. However, there were better results in younger patients for KSS function (P = 0.018), WOMAC function (P = 0.028), SF-12-physical (P = 0.001) and SF-12-mental (P = 0.035), although clinically relevant
Maempel [40]	Acta Orthop	2015	3144	< 75, 75–80, > 80	Post operation 5 years: all groups showed similar substantial improvements in AKS, which were maintained (all P < 0.001)
Kuo [44]	J Orthop Surg Res	2014	1024	< 80, ≥80	Both groups (≥ 80, < 80) had improved in the KSS (≥ 80: 86, < 80: 88), KSFS (≥ 80: 87, < 80: 89), WOMAC (≥ 80: 15.0, < 80: 14.6) scores
Hamilton [47]	BMJ Open	2013	4709		Median age of satisfied group is 70.3 and unsatisfied group is 70.0 (P = 0.829)
Kennedy [48]	Clin Orthop Rel Res	2013	≥80: 438 < 80: 2754	< 80, ≥80	There was no difference in pain scores at 3, 5, and 10 years between the ≥ 80 years group and < 80 years group. The KSS was comparable between groups at year 5, but the KSFS was lower in the octogenarians
William [50]	Bone Joint J	2013	2456	< 55 55–64, 65–74, 75–84, ≥ 85	Postoperative scores were comparable across age groups, but a linear trend for greater postoperative improvement in OKS and EQ-5D was seen with decreasing age (P < 0.033)
Clement [53]	Bone Joint J	2011	677	< 80, ≥ 80	Post operation 1 year: no significant difference was observed between the groups in the mean improvement in OKS (95% CI − 0.65 to 2.94, P = 0.16)
Difference
Pitta [25]	J Arthroplast	2019	3693		For the KOOS pain, KOOS activity, and LEAS outcomes, the divergence point occurred at age 68 years. For the KOOS symptom outcomes, the divergence point occurred at age 70 years.
Elmallah [34]	J Knee Surg	2016	278	< 55, 55–74, > 74	For KSS objective, patiemts 75 years and older had the highest mean score at final follow up (97 points). In KSS function, the < 55-years group had highest scores at 2-year (90 vs. 87 vs. 75 points) and 5-year follow up (96 vs. 88 vs. 72 points). For SF-36 and LEAS, the cohorts 75 years and older had the lowest mean scores at various time points. In the mental component, those < 55 years had the lowest scores postoperatively
Older better
Townsend [29]	J Knee Surg	2018	356	< 50, 50–59, 60–69, 70–79, > 79	Postoperative WOMAC and overall, pain, and function OKS significantly differed among the age groups (P  < 0.05), with patients younger than 60 years reporting the worst scores in the postoperative time period. Older patients reported better preoperative overall, pain, and function scores and greater post-TKA outcomes than younger patients
Merle-Vincent [54]	Joint Bone Spine	2011	264	≤ 70, > 70,	Age older than 70 years at surgery was associated with a higher satisfaction rate (odds ratio of age ≥ 70 years is 3.9 [1.1–14.3]; P = 0.038)
Younger better
Murphy [14]	Bone Joint J	2018	2838	< 80, ≥ 80	SF-12 PCS, coefficient of ≥ 80-group is − 4.46 (− 6.18, − 2.73), P < 0.001
KJ Oh [26]	Aging Clin Exp Res	2018	79	65–70, ≥ 80	The octogenarian patient group had significantly inferior outcomes for WOMAC and SF-36 score compared to the sexagenarian patient group (P = 0.009 and P = 0.022, respectively)
Naylor [28]	Arthritis Care Res	2018	1289		Post operation 3 years: younger age (P = 0.0018) was significantly associated with regular physical activity
Razak [36]	J Bone Joint Surg Am	2016	3062		Younger age KSS predicted a good outcome at 5 years (OKS: OR of age is 2.66 (2.61–2.71), SF-36 PCS: OR of age is 2.64 (2.59–2.67))
Singh [57]	Osteoarthr Cartil	2010	7139	61–70, 71–80, > 80	Significantly predictors of overall moderate–severe activity limitation 2-years post-TKA was age 71–80 (OR: 2.1 [1.5, 2.8]) and age > 80 (OR: 4.1 [2.7, 6.1]) vs, age ≤ 60 years, and 5 years post-TKA was age 71–80 (OR: 2.4 [1.7, 3.5]) and age > 80 (OR: 4.7 [2.8, 7.9]) vs. age ≤ 60 years
Extreme age
Extreme old age
Skinner [37]	Ann R Coll Surg Eng	2016	67	70–79, 90–99	For preoperative OKS no significant difference between nonagenarians and control group
Extreme young age
Lange [27]	J Arthroplast	2018	1058	18–55, 65–75	Distribution of satisfaction responses was shifted toward greater satisfaction in older patients (P < 0.001). Younger patients reported greater knee-related dysfunction and higher activity levels preoperatively and postoperatively (P = 0.0002)
Haynes [32]	Knee	2017	≤ 55: 82 65–75: 85	≤55, 65–75	The younger patient cohort reported substantially lower preoperative clinical outcome scores. WOMAC pain (12.1 points, P < 0.01), and WOMAC physical function. (6.9 points, P < 0.01) improvement was noted; however, WOMAC pain score remained lower among the younger patient cohort
Clement [19]	Arch Arthop Trauma Surg	2018	2589	< 55, 55 ≤	The younger age group was twice as likely to be dissatisfied with their overall outcome and pain relief, with only 83% and 85% being satisfied compared to 92% and 91% in the older age group, respectively

KSS Knee Society Score, WOMAC Western Ontario and McMaster Osteoarthritis Index, KSFS Knee Society Function Score, OKS Oxford Knee Score, OR odds ratio, SF Short Form, PCS Physical Component Score, AKS American Knee Society, LEAS Lower Extremity Activity Scale, ADL activities of daily living, TKA total knee arthroplasty