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. 2021 Jan 20;23:150–154. doi: 10.1016/j.jor.2021.01.003

Mid-term outcomes of anterior cruciate ligament reconstruction across age groups: A national database study☆

McKayla Kelly 1,∗, Justin Turcotte 1, Dimitri Thomas 1, Benjamin Petre 1, Christina Morganti 1, James York 1, Daniel Redziniak 1
PMCID: PMC7843512  PMID: 33551608

Abstract

Background

The purpose of this study was to examine the impact of age on complication risk after anterior cruciate ligament reconstruction.

Methods

The TriNetX research database was retrospectively queried for patients undergoing primary arthroscopic ACL reconstruction. Univariate logistic regression was performed to evaluate the risk of complication by age group.

Results

A total of 21,449 patients were included in the study. Patients ≥61 years old demonstrated significantly higher rates of repeat reconstruction. Rates of postoperative opioid related disorders and surgical site infection varied by age.

Conclusion

For patients undergoing ACL reconstruction, increasing age is associated with increased risk of developing opioid related disorders, and repeat reconstruction.

Keywords: anterior Cruciate ligament, ACL, Reconstruction, Aging athlete

1. Introduction

The anterior cruciate ligament (ACL) stabilizes the knee joint during movement, specifically protecting against anterior translation of the tibia on the femur and providing rotational stability by preventing internal rotation of the tibia.26 Injury or rupture of the ACL is fairly common, afflicting approximately 250,000 Americans each year.25 Injury and rupture occur when excessive tensile strength is placed on the ligament. The estimated maximum tensile strength of the ACL is 1725 ± 270 N while the force exerted during most vigorous activities exceeds this amount.25 Many studies have investigated ACL rupture treatment and recovery in young athletes (<30 years old); however, fewer studies have explored the outcomes for older patients undergoing similar treatment.7,15,20,24 In recent years, people aged 45–70 years old have adopted a more active lifestyle, increasing the risk of associated injury.29,35 In a New Zealand national population-based study, adults aged 45 years or older accounted for approximately 20% of sports related knee ligament injuries and roughly 50% of all knee ligament injuries.23 Despite the increasing prevalence of knee ligament injuries among the active aging population, controversy remains regarding the appropriate treatment for these patients.35 Some studies have shown positive outcomes associated with non-operative treatment for patients older than 40 years.8,14 However, more recent studies found that ACL reconstruction results in improved knee stability, function, and patient satisfaction scores in both young and older patient populations.3,23,29 The healing process changes as aging occurs,28,35 making it important to evaluate patient outcomes within multiple age groups to determine the best course of treatment. The purpose of this study is to examine the impact of age on risk of complications after ACL reconstruction.

2. Methods

The following study was deemed exempt from institutional review board review by the institution's clinical research committee. The TriNetX research database was retrospectively queried as of June 19, 2020. TriNetX is a health research network that includes longitudinal data from 35 healthcare organizations and includes over 54 million patients.32 All queries were developed using current procedural terminology (CPT) and international classification of disease 10th edition (ICD-10) codes. Diagnoses using ICD-9 coding were converted to ICD-10 codes using the general equivalence mapping (GEMS) methodology.1

All patients undergoing primary arthroscopic ACL reconstruction before June 19, 2017 were included to allow for three years of postoperative follow up. Patients with a documented prior ACL reconstruction were excluded. The study population was stratified into the following age groups at the time of surgery: ≤ 30 years old (yo.), 31–40 yo., 41–50 yo., 51–60 yo., and ≥61 yo. All outcomes were measured during the postoperative day 30 to 3-year time point. The 30-day postoperative window was not included to eliminate the effect of minor postoperative complications not requiring longer-term treatment. All study outcomes were defined by CPT code based on documented provider judgment. The primary endpoint of the study was a repeat ACL reconstruction surgery (CPT Code 29,888) within the 3-year postoperative period. Secondary outcomes assessed included common post-operative complications such as rates of surgical site infection (ICD-10 code T81.4), knee stiffness (ICD-10 Code M25.66) and opioid related disorders (ICD-10 Codes in the F11 category) not present prior to surgery. These outcomes were selected based on their clinical significance and potential to negatively affect long-term physical function and quality of life. Although surgical site infection following ACL reconstruction is relatively uncommon it is an important marker to consider given the serious possible long term complications resulting from this early post-operative outcome which include graft failure, arthrofibrosis, and articular cartilage loss.21 Knee stiffness is a more common post-operative complication manifesting in a decreased range of motion which can be attributed to poor graft position, cyclops lesions, or arthrofibrosis.33 Regardless of the specific cause of this knee stiffness, patients suffering from this affliction experience significant pain that can negatively impact patient satisfaction. Opioid related disorder in this study included documented opioid abuse, opioid dependence, and opioid use unspecified. In previous studies preoperative and prolonged post-operative opioid use have been associated with worse outcomes following orthopedic surgical procedures.2,12,27 The definitions of all surgical procedures, comorbidities, and outcomes are presented in the Appendix.

Univariate statistical analysis was performed to evaluate differences in comorbidity burden and outcomes between groups. Chi-square testing with post-hoc pairwise Bonferonni corrected comparison of proportions using the z-test was conducted. Univariate logistic regression was then performed to evaluate the risk of primary and secondary outcome occurrence in each age group in comparison to the control group of patients ≤30 years old. All statistical analysis was performed in SPSS version 26 (IBM, Armonk, NY). Statistical significance was assessed at P < 0.05.

2.1. About TriNetX

TriNetX is a “global health research network that optimizes clinical research and enables discoveries through the generation of real-world evidence.“32 This large research database includes input from 35 healthcare organizations and over 54 million patients. Most participating institutions contribute retrospective data 7 years or older. Variables captured include demographics, medications, lab values, diagnoses (all mapped to ICD-10 coding), and procedures (ICD-10 PCS and CPT). Statistical analysis is performed within the analytics platform using parallel R and Python queries triangulated to maximize test accuracy.32 HIPAA (Health Insurance Portability and Accountability Act) compliant electronic health record (EHR) data is collected from participating health care organizations who submit structured and unstructured data elements. TriNetX is a federated network and received a waiver from Western Institutional Review Board as the only data received includes aggregated counts and statistical summaries of de-identified information. No protected health information is exchanged in retrospective analyses.

3. Results

A total of 21,449 patients were included in the study. Across age groups, statistically significant differences in gender (overall % female = 40.5), race (overall % white = 70.5), and the prevalence of osteoarthritis (overall = 6.0%), primary hypertension (overall = 5.0%), metabolic disorders (overall = 3.9%), diabetes mellitus (overall = 1.2%), and heart disease (overall = 1.9%) were observed (all p < 0.001). Each comorbidity increased in prevalence with advancing age (Table 1). Despite these differences, we elected not to control for age, race, or comorbidity burden when comparing outcomes between groups, as these factors are clinically relevant differences that may influence outcomes between these heterogeneous populations.

Table 1.

Patient demographics and comorbidities by age group.

Patient Characteristic – % ≤30 years
N = 14,199		 31–40 years
N = 3990		 41–50 years
N = 2347		 51–60 years
N = 777		 ≥61 years
N = 136		 All Patients
N = 20,628		 χ2 P-Value
Female 40.3a 36.4b 55.0c 50.8c 50.0a,c 40.5 <0.001
White 66.4a 74.5b 81.8c 87.9d 86.8d 70.5 <0.001
Osteoarthritis 2.3a 9.4b 15.4c 24.8d 30.1d 6.0 <0.001
Primary Hypertension 1.3a 7.7b 15.0c 23.6d 30.9d 5.0 <0.001
Metabolic Disorders 1.2a 5.0b 11.2c 19.7d 30.9e 3.9 <0.001
Diabetes Mellitus 0.4a 1.6b 3.2c 5.0c 7.4c 1.2 <0.001
Heart Disease 1.0a 2.4b 4.4c 7.1d 10.3d 1.9 <0.001
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χ2 P-Value <0.05 in bold.

Statistically significant post-hoc bonferonni adjusted pairwise z-test of proportions between age groups denoted by different subscript lettering (ie. a,b = significant difference; b,b = no significant difference, etc.).

The overall rate of repeat ACL reconstruction within three-years postoperatively was 1.4%. Statistically significant differences in repeat ACL reconstruction rates were observed across groups (p < 0.001). In comparing differences between groups using Bonferroni adjusted pairwise z-tests of proportions, patients ≤30 years old (repeat ACL reconstruction rate: 1.7%) demonstrated significantly higher rates of repeat ACLR than patients in the 31–40 (0.6%) and 41–50 (0.6%) age groups, similar rates to the 51–60 group (1.3%), and lower rates than the ≥61 group (7.4%). The overall rate of surgical site infection was 0.6%, with statistically significant differences occurring between age groups (p = 0.040); rates ranged from 0.0% in the ≥61 group to 1.3% in the 51–60 group. Although statistically different, no clinically significant trends were observed. No statistically significant differences in rates of postoperative knee stiffness were observed, with an overall prevalence of 6.4% in the population. Postoperative opioid related disorders occurred in 0.4% of patients overall and followed a positive correlation with increasing age. Significantly lower rates of opioid related disorders were observed in the ≤30 group (0.1%) when compared to the 31–40 (0.5%), 41–50 (0.9%) and 51–60 (1.4%) groups, which were all statistically equivalent. Patients ≥61 years old demonstrated significantly higher rates of opioid related disorders than all other age groups (7.4%) (Table 2).

Table 2.

Thirty-day to three-year patient outcomes by age group.

Patient Characteristic – % ≤30 years
N = 13,680		 31–40 years
N = 3870		 41–50 years
N = 2248		 51–60 years
N = 741		 ≥61 years
N = 136		 All Patients
N = 20,675		 χ2 P-Value
Repeat ACL Reconstruction 1.7a 0.6b 0.6b 1.3a,b 7.4c 1.4 <0.001
Surgical Site Infection 0.5a 0.7a,b 0.7a,b 1.3b 0.0a,b 0.6 0.040
Stiff Knee 6.3a 6.6a 6.6a 7.7a 7.4a 6.4 0.524
Opioid Related Disorders 0.1a 0.5b 0.9b 1.4b 7.4c 0.4 <0.001
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χ2 P-Value <0.05 in bold.

Statistically significant post-hoc bonferonni adjusted pairwise z-test of proportions between age groups denoted by different subscript lettering (ie. a,b = significant difference; b,b = no significant difference).

The risk of occurrence of the various outcomes was then assessed using univariate logistic regression to compare each age group with patients ≤30 years old. A summary of age groups at double the risk of each outcome (OR ≥ 2.0, p < 0.05) is presented with all results included in Table 3. In comparison to the ≤30 group, patients ≥61 had 4.621 times higher odds of repeat ACL reconstruction, while patients ages 51–60 had 2.585 times higher odds of surgical site infection. The odds of developing opioid related disorders increased with age, from an odds ratio of 3.559 in the 31–40 group to 57.005 in the ≥61 group (all p < 0.001).

Table 3.

Univariate logistic regression comparing risk of complications to patients ≤30 Years old.

Patient Characteristic 31–40 years
 41–50 years
 51–60 years
 ≥61 years
OR (95% CI) P-Value OR (95% CI) P-Value OR (95% CI) P-Value OR (95% CI) P-Value
Repeat ACL Reconstruction 0.379 (0.250–0.573) <0.001 0.365 (0.212–0.627) <0.001 0.796 (0.421–1.507) 0.484 4.621 (2.396–8.913) <0.001
Surgical Site Infection 1.328 (0.852–2.070) 0.210 1.355 (0.787–2.333) 0.274 2.585 (1.329–5.031) 0.005 0.000 (N/A) 0.996
Stiff Knee 1.066 (0.923–1.231) 0.387 1.056 (0.923–1.231) 0.555 1.248 (0.945–1.650) 0.119 1.189 (0.622–2.272) 0.600
Opioid Related Disorders 3.559 (1.882–6.728) <0.001 6.161 (3.257–11.655) <0.001 9.866 (4.571–21.295) <0.001 57.005 (25.987–125.048) <0.001
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P-Value <0.05 in bold.

4. Discussion

The rise in physical activity level and sports involvement among the aging population is accompanied by an increase in the number of ACL injuries and reconstructions in adults aged >40 years.28 Patients with knee ligament injuries can undergo surgical reconstruction or non-operative treatment to improve both knee pain and stability, however, there remains debate about the effectiveness of surgical reconstruction in older patients. Wierer et al. conducted a prospective study of 59 patients with an isolated ACL tear who underwent reconstruction within 48 h from injury comparing outcomes for patients 18–40 years old with 40–60 years old.34 The researchers focused on functional outcomes documented via several questionnaires including the Lysholm score, visual analogue scale for pain (VAS), and Tegner activity level. There were no significant differences in Lysholm score or VAS score between the age groups. Both age groups returned to their pre-injury activity level following recovery from reconstruction. Although the current study design precluded the evaluation of functional outcomes, the findings of similar rates of knee stiffness align with Wierer et al.’s observation of similar Lysholm scores across age groups, which include the symptoms of limp, locking, instability, pain, swelling, stair climbing and squatting.

A strength of the current study is the evaluation of the prevalence of postoperative opioid related disorders. A positive correlation between increasing age and the risk of developing opioid related disorders with significant increases in risk occurring at each increased age interval was shown. The odds of increased opioid related disorders, which ranged from over 3.5 times in the 31–40 yo. population to 57 times in the ≥61 yo. population are notable, and this trend requires further investigation. A potential explanation for this observation is higher levels of chronic pain, rather than acute postoperative pain, leading to higher rates of opioid related disorders in older patients. Although we controlled for opioid related disorders prior to surgery, we were unable to account for differences in chronic pain or history of opioid use. According to Chau et al., the use of opiates is growing in older adults due to the prevalence of chronic pain.11 The high level of chronic pain experienced by this patient population places them at risk for long term use of opioids which can develop into opioid dependence or possibly opioid abuse. Physiological changes that occur naturally during aging such as impaired metabolism, excretion, and physical reserve can lead to an increased occurrence of harmful side effects such as respiratory depression, highlighting the need to minimize narcotic use in older patients.30 In contrast to the current findings, multiple studies have found no difference or lower postoperative opioid consumption in older patients undergoing various orthopedic surgical procedures.29,34 However, in light of the ongoing opioid epidemic and known risk for addiction, the current findings highlight the need to remain vigilant in identifying patients at risk for development of opioid related disorders after ACLR and to maximize the use of multimodal analgesia protocols rather than opioids for postoperative pain management across all age groups.

In alignment with other studies, we observed that patients ≥61 years are at increased risk for repeat ACL reconstruction. Csintalan et al. analyzed 14,522 patients enrolled in an ACL reconstruction registry to evaluate the risk factors associated with reoperations. Patient age ≥ 26 years, was associated with a higher risk of reoperation following ACL reconstruction.16 Similarly, we found patients ≥61 had 4.621 times higher odds of repeat ACL reconstruction compared to those ≤30 years old. The increased risk for reoperation after initial ACL reconstruction may be due to the change in the healing process that occurs with aging.28 Mesenchymal stem cells provide vascular/hematopoietic support to the ACL in addition to helping with cartilage formation; over time the number of these cells decreases, potentially adversely affecting postoperative healing.28 In addition, age related decreases in growth factor receptors causes decreased cellular metabolism, stunted collagen production, and a reduction in apoptotic rate.13 Collagen fiber disorientation, ligament sheath inflammation, and increased degeneration are also apparent in histological examinations of ACLs of patients older than 40 years of age.9,22 While patients ≥61 years of age experienced significantly higher rates of repeat ACL reconstruction than younger patients, the overall rate of repeat surgery observed in the current study was lower than previously reported (13.1%–26.7%).18,31

The American Academy of Orthopedic Surgeons (AAOS) Clinical Practice Guidelines presents an evidence-based approach to managing patients with an ACL injury. Surgical reconstruction is recommended for active patients age 18–35 years, however there are few evidence-based data available for the treatment of ACL injury in patients older than 40 years. Activity level may be a more important factor than age to consider patients for surgical reconstruction. Active adults who are involved in sports or work in jobs that require pivoting, turning, or heavy manual labor should be considered appropriate surgical candidates. Patients with knee instability also have a high risk of secondary knee injury and should be considered for surgical reconstruction.10 In addition, debate remains surrounding the best type of graft to use in elderly patients. Bone-patellar tendon-bone (BPTB) autograft has widely been used in patients older than 40 years.4,6,17 Barrett et al. conducted a cohort study with 63 patients over the age of 40 in an effort to determine the superior graft choice for this patient population, either allograft or autograft. BPTB allograft allowed patients to return to sport activities quicker, however, this graft type also had a higher incidence of failure and increased laxity. In comparison, BPTB autografts appeared to be a tighter graft with a lower incidence of failure in this patient population.4 Unfortunately, due to the nature of the administrative database used in this study we were unable to determine graft type for each patient.

Nonoperative treatment options remain a viable alternative to surgery for patients with an ACL injury. Frobell et al. conducted a randomized, controlled trial with 121 adults who sustained an acute ACL injury, and compared outcomes for those undergoing nonoperative treatment versus surgical intervention.19 The non-operative treatment included structured rehabilitation with the option of later ACL reconstruction if needed; the surgical intervention included early ACL reconstruction with structured rehabilitation. The absolute change in the mean Knee Injury and Osteoarthritis Outcome Score (KOOS) from baseline to 2 years was 39.4 for the nonoperative treatment cohort and 39.2 for those who underwent early reconstruction. There were no significant differences in all five KOOS subscales, the Medical Outcomes Study 36 Item Short-Form Health Survey, or the Tegner Activity Scale score. Overall early surgical intervention was not superior to nonoperative treatment; however, this study did not analyze the impact of age on outcomes. All of the patients included in this study were active adults aged 18–35 years. Ciccotti et al. retrospectively reviewed middle aged patients (40–60 years) who had an ACL rupture treated with aggressive non-operative treatment.14 Of the 30 patients examined, 83% of these patients achieved a satisfactory outcome with guided rehabilitation and modified activity. Outcomes were recorded using the Lysholm scale, Lachman test, pivot shift test, MRI results, and anterior-posterior laxity as measured by a KT-1000 arthrometer. Based on the findings of these previous studies, non-operative treatment is a viable option for patients with ACL injury regardless of age.

The use of a large multisite administrative database poses several limitations in this study. First, the TriNetX database relies on de-identified coded data which has been previously demonstrated to have suboptimal validity.5 In this study specifically, the ambiguity of CPT codes contributes to the lack of validity of coding. The CPT code for revision and primary ACL reconstruction do not specify laterality leading to difficulty when deciphering between revision surgery and contralateral primary ACL reconstruction. In addition, we were unable to determine the mechanism of injury, indication for reconstruction, and lifestyle specifics such as preoperative fitness or activity level. We could not identify or exclude patients with a multi-ligamentous injury. Since ACL reconstruction is not common among patients older than 61 there is a possibility this population had more severe injuries (multi-ligamentous) which could impact the rate of postoperative complications. Second, there is potential that patients sought follow up care at institutions not participating in the database after their initial surgery, therefore making it possible that overall rates of the various outcomes are underreported. Third, based on our national database study design, we were unable to control for aspects of ACL reconstruction that can significantly impact postoperative outcomes including graft type, concomitant procedures, and rehabilitation protocols. Despite these limitations, we suggest our findings add value to the relatively limited evidence evaluating outcomes of ACL reconstruction in older patients. The trends observed across this large, national sample may help guide endpoints to be evaluated using more granular procedure-specific registries or future prospective trials.

5. Conclusions

For patients undergoing ACL reconstruction, increasing age is associated with increased risk of developing opioid related disorders, and repeat ACL reconstruction for patients ≥61 years. Overall complication rates were low; however, given these findings, appropriate patient selection is key to ensuring successful surgical outcomes in older patients undergoing ACL reconstruction.

Declaration of competing interest

No declared conflicts of interest. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Footnotes

☆

All work performed at Anne Arundel Medical Center.

Appendix 1. Coding definitions

Surgical Procedures CPT and ICD-10 Code Definitions
Arthroscopically aided anterior cruciate ligament repair/augmentation or reconstruction 29,888, excluding patients with prior history of 29,888
Comorbidities (Diagnosis present up to 1 year prior to surgery)
Osteoarthritis M15-M19
Essential (primary) hypertension I10
Metabolic disorders E70-E88
Diabetes mellitus E08-E13
Heart disease I30–I52
Outcomes (Diagnosis or procedure present 1 month to 3 years after surgery)
Repeat ACLR 29,888 (Arthroscopically aided anterior cruciate ligament repair/augmentation or reconstruction)
Surgical Site Infection T81.4 (infection following a procedure)
Opioid related disorders F11 (opioid abuse, opioid dependence, opioid use [unspecified])
Stiff knee M25.66 (Stiffness of knee, not elsewhere classified)
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