Abstract
Background:
Total knee arthroplasty (TKA) in younger patients is relatively uncommon.
Methods:
The PearlDiver M165Ortho data set was used to identify TKA patients aged 15 to 45 years. Primary diagnoses associated with surgery were categorized into the following groups: primary osteoarthritis (OA), posttraumatic arthritis (PTOA), rheumatoid arthritis (RA), and osteonecrosis. Ninety-day adverse events and readmissions and 10-year periprosthetic fractures, loosening, stiffness, revisions, and prosthetic joint infection (PJI) were determined. Independent predictors of adverse outcomes were identified by using multivariable analysis, and Kaplan-Meier survival analysis for 10-year revisions was performed.
Results:
A total of 26,566 TKA patients aged 15 to 45 years were identified. Among this cohort, the diagnosis associated with surgery was OA for 22,900 (86.2%), PTOA for 1648 (6.2%), RA for 1438 (5.4%), and osteonecrosis for 580 (2.2%). For the entire study cohort, 90-day adverse events were noted for 11.1% and readmissions for 7.4%. The 10-year periprosthetic fracture rate was 0.2%, aseptic loosening rate was 3.6%, stiffness rate was 26.9%, revision rate was 7.9%, and PJI rate was 5.7%. Diagnosis associated with surgery was not predictive of 90-day outcomes or 10-year adverse periprosthetic fracture, aseptic loosening, stiffness, or revisions. On Kaplan-Meier analysis, survival was clinically similar across all diagnosis groups, ranging from 86.2% to 89.7% at 10 years.
Conclusion:
Young TKA patients experience relatively low 90-day adverse events and readmissions and long-term complications regardless of diagnosis associated with surgery. Implant survival is similarly to what is observed in older TKA.
Total knee arthroplasty (TKA) is one of the most frequently performed and successful procedures in all of orthopaedics.1 Although most commonly indicated for older adults with end-stage knee osteoarthritis, TKA is sometimes performed in younger patients for the management of alterative underlying pathologies, including early-onset idiopathic osteoarthritis (OA), posttraumatic arthritis (PTOA), rheumatoid arthritis (RA), and osteonecrosis.2 Because TKA technology and techniques continue to evolve and improve, more young patients with end-stage knee pathology are being considered for this procedure.1
Relatively sparse literature exists exploring primary diagnoses associated with surgery and outcomes of TKA in the younger population. Existing studies evaluating “young” patients with TKA generally evaluate patients younger than 65 years on aggregate, which—although still an important demographic—misses the opportunity to evaluate very young patients undergoing TKA. For example, one study which analyzed the National Hospital Discharge Survey (NHDS) database between 2001 and 2010 identified 33,066 TKA patients younger than 65 years, with a mean age of 56.4 years.3 This study reported no differences in the rates of acute medical adverse events postoperatively between TKA patients younger than and older than 65 years—but did not evaluate long-term outcomes.3
Another single-institution study of 31 TKA patients younger than 65 (average age 52.6) years evaluated long-term outcomes, reporting a 13-year survival of 89.7% with no difference in survival rate by diagnosis associated with surgery.4 A 1998 single-institution study of 54 TKA patients with an average age of 43 years reported outstanding patient outcomes, with 99% survival at 10 years and 95% survival at 15 years postoperatively, with notable improvements in functional outcomes and low acute postoperative complication rates.5 The youngest cohort of TKA patients to date was published in 2012, including 33 TKA patients with an average age of 36 years.2 This study was limited to a 4-year follow-up period, with implant survival at this end point being 97%.2 Overall, this study reported low postoperative complication and revision rates and notable improvement in functional outcomes among young TKA.2
Previous literature in this space has several strengths. As institutional retrospective reviews, these studies were able to capture detailed surgical indications, as well as radiographic and functional outcomes. Furthermore, individual patients could be observed to ensure more robust follow-up. However, these existing studies have several limitations. For one, they capture relatively small numbers of patients and are limited to outcome metrics that can be assessed based on statistical power. Furthermore, many are limited to single institutions, introducing variations or biases in surgical technique, implants, and outcomes that may differ from the overall landscape of TKA in the United States. In addition, these studies generally do not capture very young patients with TKA, with most designating all TKA patients younger than 65 years on aggregate as “young.” Thus, there is a missed opportunity to evaluate diagnoses associated with and outcomes of TKA specifically in the late adolescent/young adult period, constituting a rare but important demographic of patients.
This study used PearlDiver M165Ortho data set to characterize the primary associate diagnoses, postoperative complications, and 10-year survival to revision surgery among patients with TKA aged 15 to 45 years. This national study provides an analysis of the largest sample of young TKA patients to date. The large number of patients captured provides insight into the overall trends in care and outcomes of the young TKA patients. Furthermore, this work builds on the growing trend of using large national databases to better understand relatively rarer patient population, providing trends and findings that would be unattainable through institutional studies.6–13
Methods
Database and Cohort
This study used the 2010 to 2023 PearlDiver M165Ortho database (Colorado Springs, Colorado)—a Health Insurance Portability and Accountability Act (HIPAA)-compliant national billings claims data set containing health information on more than 165 million orthopaedic patients in the United States. This database contains patients across all payer types and sites of care in the United States. This database is well-established for TKA studies.8,14,15 PearlDiver data is deidentified and aggregated at the user level; thus, our institutional review board (IRB) determined studies using this database exempt from review.
First occurrences of primary or conversion TKAs in the database were identified by CPT codes 27447 and same day occurrence of 27447 and 27132. Age 45 years was chosen as the upper limit for “young” TKA patients in this study because this was approximately two standard deviations below the average age of TKA patients in the data set (66.18 ± 10.6 years old, Figure 1). Fifteen years old was designated as the lower limit for TKA patients in this study. Patients with a diagnosis of malignancy or infection on the day of TKA were excluded from the study cohort. To ensure long-term outcome assessment, only patients with at least one documented healthcare interaction in each of the 10 years after their index TKA were included in the final cohort. This approach ensures that included patients remained active in the healthcare system more than the full 10-year study period, thereby mitigating the risk of loss to follow-up. Patients without activity across the 10-year interval were excluded to reduce survivorship and attrition bias. Activity was defined as any inpatient, outpatient, or procedural claim within the administrative database.
Figure 1.
Graph showing percentage of total knee arthroplasty (TKA) patients each year of age among all TKA patients in database. Figure does not include TKA patients aged 70 years or older, who comprised 40% of all TKA patients in the database; however, the average age of a TKA patient in the database does account for this group.
Primary Diagnoses Associated With Surgery and Cohort Demographics
Using the PearlDiver diagnosis track system, the primary diagnosis associated with TKA among patients in the study cohort was identified by International Classification of Disease (ICD) 9 and 10 diagnosis codes. This yielded approximately 250 individual diagnosis codes which were manually grouped into diagnosis associated with surgery categories: primary osteoarthritis (OA), posttraumatic arthritis (PTOA), rheumatoid arthritis (RA), and osteonecrosis.
Patients in the study cohort were then sorted by diagnosis associated with surgery. Demographics were determined both for the overall study cohort and for patients in each diagnosis subgroup, including age, sex, and Elixhauser Comorbidity Index (ECI, a longitudinal measure of patient comorbidity burden generated using ICD codes).16
A total of 1,660,909 TKA patients were initially abstracted from the database. The average ± standard deviation age of this population was 66.18 ± 10.6 years. Isolating the analysis to TKA patients aged 15 to 45 years with activity in the database for at least 10 years postoperatively resulted in 26,566 patients in the final study cohort. The average age of the cohort was 41.02 ± 5.66 years, with a sex distribution of 17,944 (67.5%) women and 8622 (32.5%) men. As measured by ECI, the average comorbidity burden of the study cohort was 4.19 ± 3.20.
Postoperative Outcomes
ICD codes were then used to identify 90-day postoperative adverse events, as previously described.9,10,12,17–19 Adverse events were sorted into categories, including serious adverse events (sepsis, surgical site infection, venous thromboembolism [VTE], and myocardial infarction), minor adverse events (urinary tract infection, transfusion, pneumonia, wound complication [wound dehiscence or hematoma], acute kidney injury, and pancreatitis), and any adverse events (aggregate serious adverse events or minor adverse events). Categorization was based on the immediate threat to life or limb posed by each complication. Although alternative classifications such as local versus systemic complications exist, we used a severity-based framework to support outcome comparisons. Ninety-day readmissions were also determined using the PearlDiver readmission function.
Longer-term outcomes including 10-year periprosthetic fracture, aseptic loosening, stiffness, revisions, and prosthetic joint infections (PJI) were similarly categorized by ICD codes. Ten-year revision surgeries were captured by CPT codes 27486, 27487, and 27488.
Data Analysis
Univariable analysis was performed to compare the incidence of 90-day adverse events and readmissions, 10-year periprosthetic fractures, aseptic loosening, stiffness, revisions, and PJI between the diagnosis associated with surgery subgroups. Analysis of variance (ANOVA) was used to evaluate differences in the incidence of postoperative complications between groups.
Multivariate logistic regression models including patient age, ECI, sex, and diagnosis associated with surgery were then performed to determine the odds ratios (OR) and 95% confidence intervals (CIs) of experiencing 90-day adverse events or readmissions, 10-year periprosthetic fracture, aseptic loosening, stiffness, revision surgery, and PJI regarding a referent value within each variable included in the model.
Kaplan-Meier survival analysis was performed to compare 10-year survival to revision surgery between the diagnosis associated with surgery cohorts of young TKA patients. Log-rank analysis was performed to evaluate for statistically significant differences in 10-year survival between each diagnosis associated with surgery subgroup regarding the osteoarthritis cohort.
All statistical analyses were performed using the in-built PearlDiver system. Statistical significance was designated as P < 0.05. PRISM-9 (GraphPad Software, San Diego, CA) and Microsoft Excel (Microsoft Corporation, Redmond, WA) were used to create all figures.
Results
Study Cohorts
Regarding primary diagnoses associated with surgery, 22,900 (86.2%) had surgery for OA, 1,648 (6.2%) had surgery for PTOA, 1,438 (5.4%) for RA, and 580 (2.2%) for osteonecrosis. The percentage of patients with OA as their primary diagnosis associated with TKA increased with age: among patients aged 15 to 24, 160 (60.2%) had surgery for OA; among those aged 25 to 34, 1,375 (70.4%) had surgery for OA; among those aged 35 to 45, 21,365 (87.8%) had surgery for OA. Table 1 depicts demographics of the total study cohort and for each diagnosis associated with surgery group. Figure 2 shows the percent of TKA patients in each age bracket stratified by diagnosis associated with surgery.
Table 1.
Demographics of Patients Aged 15 to 45 Years Who Underwent Total Knee Arthroplasty
| Primary Diagnosis Associated With TKA | Total | Primary Osteoarthritis | Posttraumatic | Rheumatoid Arthritis | Osteonecrosis |
| N | 26,566 (100%) | 22,900 (86.2%) | 1648 (6.2%) | 1438 (5.4%) | 580 (2.2%) |
| Age (mean ± SD) | 41.02 ± 5.66 | 41.4 ± 4.07 | 40.2 ± 4.79 | 39.22 ± 5.70 | 36.09 ± 7.09 |
| 15-24 | 266 (1%) | 160 (0.7%) | 18 (1.1%) | 39 (2.7%) | 49 (8.4%) |
| 25-34 | 1953 (7.4%) | 1375 (6.0%) | 194 (11.8%) | 226 (15.7%) | 158 (27.2%) |
| 35-45 | 24,347 (91.6%) | 21,365 (93.3%) | 1436 (87.1%) | 1173 (81.6%) | 373 (64.3%) |
| Sex | |||||
| Women | 17,944 (67.5%) | 15,565 (68.0%) | 823 (49.9%) | 1174 (81.6%) | 382 (65.9%) |
| Men | 8622 (32.5%) | 7335 (32.0%) | 825 (50.1%) | 264 (18.4%) | 198 (34.1%) |
| ECI (mean ± SD) | 4.19 ± 3.20 | 3.71 ± 2.12 | 3.68 ± 3.13 | 4.77 ± 3.29 | 5.63 ± 4.27 |
Figure 2.
Graph showing percentage of total knee arthroplasty patients in each age bracket stratified by primary diagnosis associated with surgery.
Incidence of Adverse Events
The incidence of 90-day adverse events and readmissions are represented in Table 2. Of the 26,566 patients in the total study cohort, 2,945 (11.1%) experienced any 90-day adverse event. Split by diagnoses associated with surgery, the incidence of 90-day adverse events ranged from 10.9% for patients with OA to 16.7% for patients with osteonecrosis. In total, 1,952 patients (7.4%) of the total study cohort experienced 90-day readmission. Stratified by diagnoses associated with surgery, readmissions ranged from 7.2% for patients with PTOA to 12.2% for patients with osteonecrosis.
Table 2.
Incidence of 90-Day Adverse Events and Readmissions After Total Knee Arthroplasty Among Patients Aged 15 to 45 Years
| Primary Diagnosis Associated With TKA | Total (N = 26,566) | Primary Osteoarthritis (N = 22,900) | Posttraumatic (N = 1648) | Rheumatoid Arthritis (N = 1438) | Osteonecrosis (N = 580) | P |
| 90-day any adverse events | 2945 (11.1%) | 2494 (10.9%) | 189 (11.5%) | 165 (12.6%) | 97 (16.7%) | <0.0001 |
| 90-day serious adverse events | 1370 (5.2%) | 1221 (5.3%) | 89 (5.4%) | 58 (4.4%) | 52 (9.0%) | <0.0001 |
| Sepsis | 167 (0.6%) | 128 (0.6%) | 13 (0.8%) | 16 (1.1%) | <11 | |
| Surgical site infection | 495 (1.9%) | 405 (1.8%) | 42 (2.5%) | 34 (2.4%) | 14 (2.4%) | |
| VTE* | 841 (3.2%) | 717 (3.1%) | 40 (2.4%) | 54 (3.8%) | 30 (5.2%) | |
| Myocardial infarction | 58 (0.2%) | 28 (0.1%) | <11 | <11 | <11 | |
| 90-day minor adverse events | 1912 (7.2%) | 1584 (6.9%) | 129 (7.8%) | 133 (10.1%) | 66 (11.4%) | <0.0001 |
| Urinary tract infection | 625 (2.4%) | 539 (2.4%) | 28 (1.7%) | 35 (2.4%) | 23 (4.0%) | |
| Transfusion | 426 (1.6%) | 356 (1.6%) | 18 (1.1%) | 37 (2.6%) | 15 (2.6%) | |
| Pneumonia | 269 (1.0%) | 207 (0.9%) | 18 (1.1%) | 19 (1.3%) | 15 (2.6%) | |
| Wound complication* | 580 (2.2%) | 452 (2.0%) | 66 (4.0%) | 45 (3.1%) | 17 (2.9%) | |
| Acute kidney injury | 229 (0.9%) | 189 (0.8%) | 15 (0.9%) | 15 (1.0%) | <11 | |
| Pancreatitis | 63 (0.2%) | 33 (0.1%) | <11 | <11 | <11 | |
| 90-day readmissions | 1952 (7.4%) | 1589 (6.9%) | 118 (7.2%) | 174 (12.1%) | 71 (12.2%) | <0.0001 |
Bold text indicates P < 0.05.
Table 3 shows the results of multivariate logistic regression analysis for predictors of 90-day adverse events and readmissions controlling for patient age, ECI, sex, and diagnosis associated with surgery.
Table 3.
Multivariate Analysis of Odds of 90-Day Complications After Total Knee Arthroplasty in Patients Aged 15 to 45 Years
| N = 26,566 | Adverse Events | Readmissions | ||
| OR (95% CI) | P | OR (95% CI) | P | |
| Age | ||||
| 35-45 (referent) | ||||
| 25-34 | 1.34 (0.88-2.15) | 0.6610 | 1.37 (0.85-2.30) | 0.2241 |
| 15-24 | 1.49 (0.95-2.22) | 0.0676 | 1.85 (1.14-2.86) | 0.0096 |
| ECI (per 2-point increase) | 1.28 (1.25-1.31) | <0.0001 | 1.23 (1.20-1.27) | <0.0001 |
| Sex | ||||
| Women (referent) | ||||
| Men | 0.87 (0.79-0.96) | 0.0039 | 1.12 (1.03-1.25) | 0.0393 |
| Primary diagnosis | ||||
| Osteoarthritis (referent) | ||||
| Rheumatoid | 0.81 (0.45-1.35) | 0.4493 | 0.77 (0.36-1.43) | 0.4486 |
| Osteonecrosis | 1.02 (0.61-1.62) | 0.9471 | 0.76 (0.37-1.38) | 0.4019 |
| Posttraumatic | 0.86 (0.64-1.13) | 0.3002 | 0.60 (0.39-0.88) | 0.0171 |
Bold text indicates P < 0.05.
Greater comorbidity burden as measured by ECI was the only positive predictor of 90-day adverse events (per two-point increase, OR 1.28, P < 0.0001), whereas men were slightly protected (relative to women, OR 0.87, P = 0.0039). Younger age was the strongest predictor of 90-day readmissions (relative to age 35 to 45, age 15 to 24 OR 1.85, P = 0.0096) distantly followed by being a man (relative to women, OR 1.12, P = 0.0393). Diagnosis associated with surgery did not predict the odds of 90-day adverse events or readmissions.
Ten-year periprosthetic fractures, aseptic loosening, stiffness, revisions, and PJI for the total study cohort and each diagnosis associated with surgery subcohort are shown in Table 4. Ten-year periprosthetic fracture was experienced by 53 (0.2%) patients in the total study cohort, 49 of these patients fall under the OA diagnosis subgroup. In total, 946 patients (3.6%) of the total study cohort experienced aseptic loosening, with minimal variation by diagnosis associated with surgery: ranging from 3.2% to 3.6%. Ten-year stiffness was noted for 7,149 (26.9%) patients in the total study cohort, with rates ranging from 26.7% of patients with OA to 29.2% of patients with PTOA. Ten-year revisions were noted for 2,087 (7.9%) of the overall study cohort, with rates ranging from 7.8% for patients with OA and RA to 9.1% for patients with osteonecrosis. In total, 1,503 (5.7%) of the 26,566 patients in the total study cohort experienced PJI in the 10 years postoperatively, ranging from 5.3% of patients with osteoarthritis to 8.3% of patients with osteonecrosis.
Table 4.
Incidence of Long-Term Complications After Total Knee Arthroplasty Among Patients Aged 15 to 45 Years
| Primary Diagnosis Associated With TKA | Total (N = 26,566) | Primary Osteoarthritis (N = 22,900) | Posttraumatic (N = 1648) | Rheumatoid Arthritis (N = 1438) | Osteonecrosis (N = 580) | P |
| 10-year prosthetic joint infection | 1503 (5.7%) | 1219 (5.3%) | 126 (7.6%) | 110 (7.6%) | 48 (8.3%) | <0.0001 |
| 10-year periprosthetic fracture | 53 (0.2%) | 49 (0.2%) | <11 | <11 | <11 | <0.0001 |
| 10-year loosening | 946 (3.6%) | 829 (3.6%) | 52 (3.2%) | 46 (3.2%) | 19 (3.3%) | <0.0001 |
| 10-year stiffness | 7149 (26.9%) | 6106 (26.7%) | 481 (29.2%) | 404 (28.1%) | 158 (27.2%) | <0.0001 |
| 10-year revisions | 2087 (7.9%) | 1782 (7.8%) | 140 (8.5%) | 112 (7.8%) | 53 (9.1%) | <0.0001 |
Bold text indicates P < 0.05.
Table 5 shows the results of multivariate logistic regression analysis for predictors of 10-year periprosthetic fracture, aseptic loosening, stiffness, revision surgery, and PJI controlling for patient age, ECI, sex, and diagnosis associated with surgery. Notably, age, ECI, and diagnosis associated with surgery did not predict the odds of experiencing 10-year periprosthetic fracture, aseptic loosening, stiffness, or revision surgery. Age was a strong predictor of PJI (relative to age group 35 to 45, age 25 to 34 OR 1.31, P < 0.0001, age 15 to 24 OR 1.75, P < 0.0001). Men were at a greater risk of PJI (relative to women, OR 1.62, P < 0.0001) and a less prominent predictor of aseptic loosening (relative to women, OR 1.17, P = 0.0384) and revision surgery (OR 1.11, P = 0.0413). Conversely, men had lower odds of developing stiffness (OR 0.86, P < 0.0001). Sex did not influence the odds of periprosthetic fracture.
Table 5.
Multivariate Analysis of Odds of 10-Year Complications After Total Knee Arthroplasty in Patients Aged 15 to 45 Years
| N = 25,566 | Periprosthetic Fracture | Loosening | Stiffness | Revisions | Prosthetic Joint Infection | |||||
| OR (95% CI) | P | OR (95% CI) | P | OR (95% CI) | P | OR (95% CI) | P | OR (95% CI) | P | |
| Age | ||||||||||
| 35–45 (referent) | ||||||||||
| 25–34 | 2.38 (0.47-12.50) | 0.3011 | 0.36 (0.09-1.47) | 0.1540 | 0.76 (0.53-1.09) | 0.1394 | 1.07 (0.65-1.75) | 0.2707 | 1.31 (1.26-1.35) | <0.0001 |
| 15–24 | 4.17 (0.94-16.67) | 0.0598 | 0.29 (0.07-1.15) | 0.0776 | 0.83 (0.58-1.15) | 0.2687 | 1.41 (0.88-2.27) | 0.1496 | 1.76 (1.04-2.81) | <0.0001 |
| ECI (per 2-point increase) | 0.84 (0.68-1.03) | 0.0913 | 0.98 (0.93-1.02) | 0.3346 | 0.98 (0.96-1.00) | 0.0644 | 1.05 (1.02-1.08) | 0.002 | 1.14 (1.10-1.18) | <0.0001 |
| Sex | ||||||||||
| Women (referent) | ||||||||||
| Men | 0.76 (0.41-1.39) | 0.3668 | 1.17 (1.01-1.35) | 0.0384 | 0.86 (0.81-0.92) | <0.0001 | 1.11 (1.01-1.23) | 0.0413 | 1.62 (1.44-1.82) | <0.0001 |
| Primary diagnosis | ||||||||||
| Osteoarthritis (referent) | ||||||||||
| Rheumatoid | 4.29 (0.68-14.81) | 0.0521 | 0.58 (0.14-1.54) | 0.3519 | 1.14 (0.80-1.60) | 0.4524 | 0.97 (0.53-1.75) | 0.9162 | 1.08 (0.51-2.02) | 0.8160 |
| Osteonecrosis | 2.87 (0.16-14.02) | 0.3077 | 0.66 (0.16-1.75) | 0.4771 | 0.80 (0.53-1.19) | 0.2859 | 0.84 (0.44-1.61) | 0.6043 | 1.07 (0.52-1.96) | 0.8432 |
| Posttraumatic | 0.79 (0.04-3.64) | 0.8168 | 0.66 (0.37-1.08) | 0.1245 | 1.13 (0.94-1.36) | 0.1812 | 0.99 (0.73-1.35) | 0.9401 | 1.32 (0.94-1.79) | 0.0898 |
Bold text indicates P < 0.05.
Survival to Revision Surgery
The results of Kaplan-Meier analysis for 10-year survival to revision surgery after TKA stratified by diagnosis associated with surgery are shown in Figure 3. Relative to the OA diagnosis group, implant survival was statistically lower for patients with osteonecrosis (P = 0.0063) but clinically similar at 10 years for all groups: OA (89.7%), RA (89.3%), PTOA (88.5%), osteonecrosis (86.2%).
Figure 3.
Kaplan-Meier curves showing 10-year survival to revision surgery after total knee arthroplasty among patients aged 15 to 45 years stratified by primary diagnosis associated with surgery.
Discussion
Although most TKAs are performed in older patients, the proportion performed in younger patients is increasing.3,20,21 Young patients with TKA face unique challenges, such as developmental or traumatic abnormalities which can make the surgeries more complicated, and active lifestyles can contribute to higher rates of loosening and wear postoperatively.4,22,23 Data are sparse on the short-term and long-term outcomes for young patients undergoing TKA, with existing studies being limited by small sample sizes or relatively older “young” populations.2,24–27 To address this gap in the literature, this study used a national administrative database to identify 26,566 young TKA patients, aged 15 to 45 years at the time of surgery and further characterized the diagnoses associated with surgery, adverse events, and implant survival among this cohort.
Consistent with previous estimates, young patients accounted for a small percentage, less than 1%, of all TKA patients.25 When this cohort was stratified into three age subgroups (15 to 24, 25 to 34, 35 to 45), diagnosis associated with surgery was found to vary by age. Primary OA was an increasingly common diagnosis associated with surgery among the older subgroups, which is a reasonable observation given the well-known association between osteoarthritis and age.28 Osteonecrosis, PTOA, and RA were more common diagnoses among the younger subgroups.
Overall, approximately 11% of patients experienced a 90-day adverse event, with minor adverse events being more common than serious adverse events. Ninety-day readmission rates were also modest, at approximately 7%. These findings are similar to previous estimates of readmission rates in older TKA patients.29,30 On multivariate analysis, patients in the 15 to 24 cohort were more likely to be readmitted than those in the 35 to 45 cohort. It is possible that this youngest cohort had more advanced pathology at baseline, making surgery more complicated and contributing to more challenging recoveries.23 Notably, there were no differences in adverse events or readmissions by diagnosis associated with surgery.
Joint stiffness was by far the most prevalent 10-year adverse event evaluated in this study, affecting approximately 25% of patients. This is lower than the estimated 41% of young TKA patients experiencing postoperative stiffness reported by Parvizi et al,31 but higher than previously reported rates of stiffness in older TKA patients—reported between 4 and 6%.32–34 However, it is possible that these differences reflect differences in methodology—the administrative coding may be incomplete, and patients may be more likely to report the symptom when asked directly through survey. On multivariate analysis, men had lower odds of postoperative stiffness compared with women, consistent with previous studies.33,35,36 The reasons for this are likely multifactorial and cannot be clearly delineated based on the results of this study.
Reassuringly, the incidence of more serious 10-year adverse events was low, with less than 1% of patients experiencing periprosthetic fracture and less than 3% experiencing implant loosening. On multivariate analysis, men had higher rates of loosening. Periprosthetic fracture rates at 10 years in geriatric patients have been previously reported at 1.2 to 1.4%.37 Long-term aseptic loosening rates have not been reported in the geriatric TKA population. Again, the reasons underlying this finding are likely multifactorial and cannot be clearly determined based on the results of this study. Notably, none of the aforementioned 10-year complications varied by age, ECI, or diagnosis associated with surgery.
Ten-year survival to revision surgery was high, at approximately 92% for the total study cohort—identical to previously reported 10-year survival to revision surgery in geriatric TKA patients.38 In a systematic review of TKA patients younger than 55 years, Keeney et al.24 reported a 10-year implant survival rate of 90.6 to 99%, which is consistent with this study. In an 18-year analysis of 103 knees, Diduch et al.39 reported a similar survival rate of 94% with highly positive long-term functional outcome scores. It has been previously reported that men have a higher lifetime risk of revision TKA compared with women, with sex differences being the largest among younger patients.22 In this study, men and higher ECI patients were associated with increased odds of revision surgery on multivariate analysis, but the effect size was small. In primary diagnosis associated with surgery, no differences existed in survival among patients with PTOA, RA, and primary OA, which is consistent with the literature.4
PJI is a rare, but highly morbid, complication after total joint arthroplasty. This study found the incidence of 10-year PJI was just more than 5%, which aligns with infection rates reported for older patients.40 On multivariate analysis, patients in the 25 to 34 and 15 to 24 age cohorts had a notably higher odds of PJI compared with patients in the 35 to 45 cohort. Younger age has previously been associated with a higher risk of revision for PJI after TKA; however, the reason for this finding remains unclear.41,42 Young patients undergoing TKA likely represent a unique population with greater underlying health conditions, thereby increasing the risk of infection. Men and higher ECI patients were also associated with increased odds of periprosthetic joint infection, consistent with previous reports.42,43 Although age and sex are not modifiable characteristics, efforts to lessen patient comorbidity burden before surgery may help decrease infection risk postoperatively.
As with all administrative database studies, this study has some limitations. First, we could not extract specific indications for surgery from the database but were rather limited to primary diagnoses associated with surgery as a proxy. Although this is not a perfect solution, primary diagnoses associated with surgery can provide a general understanding of primary reasons for surgery—the number of patients identified in this study allow for meaningful inferences regarding patterns of care. Second, the accuracy of the analysis relies on the accuracy of the diagnosis and procedure coding—with previous literature highlighting the overdiagnosis of primary OA as the diagnosis associated with surgery for young patients undergoing TKA.44
In addition, although previous knee procedures can be identified using CPT codes, laterality modifiers—although present in some cases—are inconsistently coded and therefore unreliable for determining whether procedures were performed on the same knee as the subsequent TKA. To avoid introducing misclassification bias, we did not include surgical history as a covariate in our analysis. Similarly, although immunosuppressive diagnoses and medications can be identified through ICD and pharmacy codes, the database does not provide information on dosage, treatment duration, or clinical context. As such, we were unable to assess the degree of individual immune compromise, and immune status was not included as an independent variable in our models.
Furthermore, in the absence of radiographic data, the relationship between preoperative disease burden and postoperative outcomes could not be explored in this study. We also could not examine patient-reported functional outcomes, such as KSS or WOMAC scores.45 Last, by requiring a minimum of 10 years of healthcare activity after surgery, we ensured long-term follow-up for the study cohort. However, this criterion inherently excludes patients lost to follow-up within that period, potentially introducing attrition bias. If patients who underwent revision TKA were more likely to lose insurance coverage, migrate between plans not captured in PearlDiver, or die, then our analysis may underestimate the true long-term revision rate. That said, given our large sample size, the inclusion of only patients with repeated database presence more than a decade offers a reasonable and conservative estimate of survivorship within a real-world, continuously monitored cohort. As a result, the reported 10-year revision rate should be interpreted as applicable to patients with continuous healthcare engagement.
Overall, this study found relatively reassuring rates of 90-day adverse events and readmissions, 10-year periprosthetic fracture, loosening, revisions, and PJI among a large cohort of young patients with TKA. These complications were generally more common among patients with higher comorbidity burdens at the time of surgery but similar across the different diagnoses associated with surgery. Younger age did increase the risk of readmissions and PJI; however, long-term outcomes were reassuringly unaffected by patient age. Building on this work, future research should examine implant outcomes beyond 10 years, and as revisions become necessary, evaluate patient outcomes after these subsequent procedures.
Footnotes
Grauer serves as Editor-in-Chief of the North American Spine Society Journal (NASSJ). None of the following authors or any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this article: Ratnasamy, Kaszuba, Maloy, Vasavada, Vasudevan, and Rubin.
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