Abstract
Background:
At 2 to 3 years after anterior cruciate ligament reconstruction (ACLR), the relationship between known modifiable osteoarthritis (OA) risk factors and recurrent knee injury is unknown. This study aimed to determine the odds of new or recurrent traumatic knee injury in a cohort of young female athletes with ACLR 2 to 3 years postsurgery compared with healthy control participants. Secondary objectives were to explore the relationships of moderate and vigorous physical activity (MVPA) and body mass index (BMI) with knee injury, and to document self-reported MVPA satisfaction and beliefs about OA.
Study Design:
Prospective cohort.
Level of Evidence:
Level 2.
Methods:
A total of 51 female athletes with unilateral ACLR 1 to 2 years previously and 51 age and sport-matched control participants underwent assessment of MVPA (GT3X accelerometers) and BMI. One year later, participants self-reported knee injuries. Bivariable conditional logistic regression explored the association between knee injury, MVPA, and BMI in each group (injury/control).
Results:
At 1-year follow-up (n = 101), 19.6% of the injured cohort and 6.0% of control participants sustained a new or recurrent knee injury. The odds of knee injury for the injury group increased 7-fold over controls [odds ratio (OR) = 7.00 (95% CI = 0.86, 56.90)], although this was not statistically significant. The OR for MVPA was 0.98 (95% CI = 0.93, 1.03) and BMI was OR = 1.24 (95% CI = 0.85, 1.82). Half (56.0%) of injury participants and 66% of controls were satisfied with their MVPA; 81.6% of injury participants believed they had increased knee OA risk compared with someone who had never had a knee injury.
Conclusion:
In the 2 to 3 years after ACLR, 1 in 5 young female athletes had a new or recurrent knee injury. Based on the point estimate, injured participants were more likely to suffer a traumatic knee injury than matched control participants. MVPA and BMI were not associated with increased odds of knee injury.
Clinical Relevance:
Clinicians should be encouraged to have in-depth conversations with female athletes with previous ACLR regarding enjoyable and sustainable MVPA participation to promote long-term joint health.
Keywords: ACL reconstruction, recurrent injury, physical activity, knee osteoarthritis, body mass index
Anterior cruciate ligament (ACL) tears are among the most common and dreaded injuries for young female athletes. 22 Around 1 in 20 female athletes engaging in pivoting sports such as soccer and basketball sustain ACL injuries annually, which is approximately 3 times the rate of their male counterparts. 27 Short-term burdens include high pain and psychological distress, reduced quality of life, 21 and large societal costs [$13,000 per ACL reconstruction (ACLR)]. 16 In the longer term, female athletes with previous ACL injury have 4 to 6 times greater risk of knee osteoarthritis (OA), 26 and over twice the risk of needing a total joint replacement within 15 years as compared with their uninjured peers. 1 Maintaining a healthy body weight and engaging in regular moderate and vigorous physical activity (MVPA) are key strategies for secondary prevention of OA. 38
Obesity is one of the most established risk factors for the development of knee OA, contributing through both systemic 36 and mechanical 15 mechanisms. The lifetime risk of OA increases with higher body mass index (BMI), leading to two-thirds of obese adults developing symptomatic disease. 23 Whereas the body of evidence surrounding physical inactivity as a risk factor for knee OA is less established, findings from a landmark cadaveric study indicate altered lifestyles (included reduced physical activity [PA]) associated with the postindustrial era may have contributed to a doubling of knee OA prevalence since the mid-20th century. 35 Muscle function and proprioception impairments, a consequence of physical inactivity, are associated with knee pain and development of knee OA. 28 Given the greatly increased risk of OA development in an ACL injury population, obesity and MVPA are key areas to generate greater in-depth knowledge.
Sport participation is one key mode to achieve MVPA. However, returning to sport after ACLR has been found to greatly increase risk of recurrent knee injury, 37 and sustaining a second knee injury then further increases the likelihood of OA. 12 Meta-analysis has found that 1 in 4 young athletes sustain a graft rupture or contralateral ACL tear. 40 At 5 years, those with revision ACL surgery have lower scores across all 5 Knee injury and Osteoarthritis Outcome Score (KOOS) subscales, compared with those who had a single ACLR. 17 At 6 years, 60% have knee OA. 12 Increased pain and symptoms, reduced quality of life, and early onset OA are a grim reality for many of those suffering recurrent ACL injuries.
Both MVPA participation and obesity have previously not been examined as risk factors for new or recurrent knee injury in this population, despite their strong links to long-term joint health. Further, little is known about the satisfaction of young female athletes with their MVPA participation or their perceptions about OA risk in the intermediate term after ACLR.
The primary purpose of this study was to determine the risk of new or recurrent traumatic knee injury in a cohort of young female athletes with primary unilateral ACLR and age- and sport-matched knee healthy control participants at 2 to 3 years post-ACLR. The secondary purposes included to explore the relationships of MVPA and BMI with traumatic knee injury and described young female MVPA satisfaction and their beliefs about knee OA risk.
Methods
Participants
This study was conducted in a cohort of 102 female youths and young adults aged 15 to 23 years: 51 had undergone ACLR in the previous 2 to 3 years (injury group) and 51 had no previous knee injury (control group) and were matched by age and sport background. Ethical approval was given by the University of British Columbia Behavioural Research Ethics Board (H16-01938). A detailed description of participant inclusion and exclusion criteria, recruitment, and full data collection procedures has been published previously. 9 Briefly, female participants were aged 14 to 22 years at recruitment, and either had unilateral ACLR for a sport-related knee injury in the previous 1 to 2 years (injury group) or no previous knee injury (control group). Control participants were matched by age (date of birth within 1 year) and previous sport (primary sport and competitive level) to each injury participant. Injury participants were recruited from Orthopaedic Surgeons in the province of British Columbia, as well as through study information distributed by collaborators. Control participants were identified by each injury girl as previous teammates at the time of knee injury or by study collaborators.
Data Collection
Each participant attended a single inperson data collection session between October 2016 and September 2017. A set of study-specific questions and patient-reported outcome measures were collected including the KOOS 29 and Tegnar Activity Scale. 30 Anthropometric measurements were made using a medical scale (seca model 869) (weight to the nearest 0.1 kg) and stadiometer (seca model 217) (height to the nearest 0.1 cm) to calculate BMI (kg/m2). For descriptive purposes, BMI was categorized using percentiles based on US reference data for adolescents, 4 and by accepted adults standards for participants older than 19 years. 11 To maximize the use of available data for analysis, BMI was kept as a continuous variable in the regression model.
MVPA participation was measured using a triaxial Actigraph GT3X accelerometer (Actigraph). Participants were instructed to wear the device for 13 days for all waking hours. A valid day consisted of a minimum of 10 hours of wear time,20,34 and participants needed a minimum of 4 valid days (with 1 weekend day) to be included in the analyes.7,8 Monitor nonwear time and total wear time were estimated and validated using reccommendations by Choi et al 5 . The digitalized acceleration signal was converted into 1-minute epochs with an activity count for each epoch. During data reduction, PA was classified into minutes of light, moderate, and vigorious PA based on validated cut points (light, 100-2019 counts; moderate, 2020-5998 counts; vigorous, >5999 counts). 34 Meeting Canadian Physical Activity guidelines (adults aged 18 years and older should accumulate 150 minutes per week of MVPA; youth younger than 18 years should do 60 minutes per day of MVPA) was examined descriptively, and participants were assigned to groups dichotomized as yes (meeting the guidelines) or no (not meeting the guidelines).32,33 Weekly PA was calculated as the mean number of minutes per day for each participant, multiplied by 7 to account for the varied number of valid days among participants. A full detailed description of the protocol for accelerometer fit, weartime requirements and validation, adherence strategies, and data processing has been published previously. 9
At 1 year after the main data collection, all participants were emailed follow-up questions using Research Electronic Data Capture (REDCap). 14 These questions were in a variety of formats including yes or no, open text, and multiple choice. Participants were asked to self-report any new or recurrent knee injuries (including non-ACL injuries) within the past year, their return-to-sport status, satisfaction with current MVPA, and belief about OA risk. To comprehensively capture any knee injuries, the exact wording to the follow-up question was: “Have you had any knee injuries since your original participation in this study 1 year ago?” with response choices “yes or no.” Participants who answered yes, were then asked to describe the knee injury in an open text box. As per consensus statement, 2 return to sports was divided into 3 levels: “returned to participation:” modified training/practicing; “returned to play:” engaged in sport, but not at preinjury level; or “returned to performance:” performing at or above preinjury level. Satisfaction with current MVPA was measured with a 5-point scale varying from 1 (not at all satisfied) to 5 (very satisfied). To evaluate perceived future OA risk, participants in the injury group were asked: “In 10 years, what do you believe is your risk of knee OA compared with someone who has never had a knee injury,” whereas control group participants were asked: “In 10 years, what do you believe is your risk of knee OA compared with someone who had a previous knee injury.” Participants had the following check box response choices: decreased risk, no increased risk, slightly increased risk, or significantly increased risk.
Analysis
Data were summarized descriptively using means with standard deviations for continuous variables and frequency with percentages for categorical variables. Differences in baseline exposure variables between injury and control groups have been examined previously. 9 Bivariable conditional logistic regression was used to explore the association between new or recurrent knee injury or no knee injury (outcome) and group (injury or control), MVPA participation (continuous variable), and BMI (continuous variable). A multivariable model was not feasible due to the relatively low number of “events” in the outcome. All statistical analyses were performed using SAS version 9.4 (SAS Institute). In the case of missing data, the participant and their match were removed from that specific analysis.
Results
Participant recruitment is outlined in Figure 1. ACLR group (n = 51) characteristics (eg, injured structures, mechanism of injury) from the main data collection are outlined in Table 1. Table 2 summarizes participant characteristics and patient reported outcome measures from main data collection for the full sample (n = 102). At mean 1.07 (SD = 0.12) years, 101 (99.0%) participants completed the online follow-up questions (Table 3). In the previous year, 10 (19.6%) and 3 (6.0%) participants from the injury and control groups, respectively, sustained a new or recurrent knee injury. Injuries reported included ACL tear, meniscus lesion, medial collateral ligament tear, and patellar dislocation (Table 3).
Figure 1.
Participant recruitment and data collection.
Modified from Ezzat et al. 9
Table 1.
ACLR group characteristics from main data collection (n = 51) a
| n (%) | |
|---|---|
| Injured structures | |
| ACL | 51 (100.0) |
| MCL | 2 (2.9) |
| Lateral meniscus | 15 (29.4) |
| Medial meniscus | 12 (23.5) |
| Mechanism of injury | |
| Noncontact | 31 (63.3) |
| Contact | 18 (36.7) |
| Time since surgery, y; median (range) | 1.1 (1.0-2.0) |
| Time since injury, y; median (range) | 1.7 (1.1-7.3) |
| RTS, yes | 28 (54.9) |
| Performance level | 14 (50.0) |
| Time after surgery RTS, mo; median (range) | 12.0 (3.5-22.0) |
Adapted from Ezzat et al. 9 ACL, anterior cruciate ligament; ACLR, anterior cruciate ligament reconstruction; MCL, medial collateral ligament; RTS, return to sport
Table 2.
Participant characteristics and exposure variables (injury, BMI, MVPA) for ACLR and control groups from main data collection (n = 102) a
| Variable | Injury (n = 51) |
Control (n = 51) |
|---|---|---|
| Age, y; median (range) | 18 (15-22) | 18 (15-22) |
| Height, cm; mean (SD) | 166.0 (6.4) | 165.1 (5.7) |
| Weight, kg; mean (SD) | 64.0 (10.4) | 61.6 (7.7) |
| BMI (kg/m2); mean (SD) | 23.3 (3.9) | 22.6 (2.5) |
| BMI classification, n (%) | ||
| Underweight | 1 (1.96) | 0 |
| Normal | 39 (76.5) | 43 (84.3) |
| Overweight | 7 (13.7) | 8 (15.7) |
| Obese | 4 (7.8) | 0 |
| KOOS | ||
| Symptoms | 85.7 (32.1, 100) | 96.4 (67.9, 100) d |
| Pain | 91.7 (66.7, 100) | 100 (80.6, 100) d |
| ADL | 98.5 (82.4, 100) | 100 (91.2, 100) d |
| Sport/rec | 85 (50.0, 100) | 100 (80.0, 100) d |
| QoL | 62.5 (6.25, 93.8) | 100 (68.8, 100) d |
| Tegner Activity Scale, median (range) | 7 (1-10) | 9 (2-10) |
| PAG, yes; n (%) b | 23 (46.0) | 31 (60.8) |
| MVPA, mean minutes per day c | 38.8 (8.1-108.9) | 41.8 (11.6-158.7) |
Adapted from Ezzat et al. 9 ACL, anterior cruciate ligament; BMI, body mass index; MCL, medial collateral ligament; MVPA, moderate and vigorous physical activity; PAG, physical activity guidelines; QoL, quality of life; RTS, return to sport.
n = 49; n = 50 injury group.
Values for participants with valid days (n = 50, injury group; n = 51, control group).
Mean matched pair difference 95% CI does not include the null value of zero.
Table 3.
Participant characteristics and injury outcome details for ACLR and control groups at 1-year follow-up (n = 101)
| Variable | Injured n = 51 |
Control n = 50 a |
|---|---|---|
| Time since main data collection, years; mean (SD) | 1.08 (0.89) | 1.07 (0.12) |
| New or recurrent knee injury, yes; n (%) | 10 (19.6) | 3 (6.0) |
| Injured side, ipsilateral; n (%) | 7 (70.0) | NA |
| Injured structures; n (%) | ||
| ACL | 2 (20.0) | 0 |
| Meniscus | 2 (20.0) | 0 |
| Concurrent ACL and meniscus | 3 (30.0) | 0 |
| Other ligament | 2 (20.0) | 2 (66.7) |
| Patellar dislocation | 1 (10.0) | 1 (33.3) |
| RTS, yes; n (%) | 34 (66.7) | NA |
| Performance level, n (%) | 19 (37.3) | |
| Reasons for not RTS; n, (%) | ||
| Not given clearance by PT or surgeon | 1 (5.9) | |
| Poor knee function or pain | 1 (5.9) | |
| Chose other sports | 1 (5.9) | |
| New interests or commitments | 10 (58.8) | |
| Other | 4 (23.5) | |
| Satisfied with PA participation b | ||
| Not at all | 5 (10.0) | 1 (2.0) |
| Not really | 4 (8.0) | 5 (10.0) |
| Undecided | 13 (26.0) | 11 (22.0) |
| Satisfied | 19 (38.0) | 24 (48.0) |
| Very satisfied | 9 (18.0) | 9 (18.0) |
| Belief about your OA risk in 10 years c | ||
| Decreased risk | 3 (6.1) | 19 (38.8) |
| No difference in risk | 6 (12.2) | 29 (59.2) |
| Slightly increased risk | 25 (51.0) | 1 (2.0) |
| Highly increased risk | 15 (30.6) | 0 |
One participant lost to follow-up. ACL, anterior cruciate ligament; OA, osteoarthritis; PA, physical activity; PT, physiotherapy; RTS, return to sport.
n = 50 injury group.
n = 49 per group.
In the injury group, 66.7% reported having returned to sport (at any level), whereas 37.3% stated they had returned to the same level or higher than before their ACL injury. Regarding satisfaction with PA participation, 56.0% of those in the injury group reported being satisfied or very satisfied, compared with 66.0% of the control participants. Among the injury group participants, nearly one-third (30.6%) and over one-half (51.0%) of participants believed they were at highly or slightly increased OA risk in 10 years compared with someone without a previous knee injury, respectively. Conversely, in the control group, 38.8% of participants believed they had decreased OA risk compared with someone with a previous knee injury.
Bivariable conditional logistic regression did not find statistically significant odds of increased new or recurrent knee injury for the injury group (odds ratio [OR] = 7.0; 95% CI = 0.86, 56.90), amount of MVPA participation (OR = 0.98; 95% CI = 0.93, 1.03), or higher BMI (OR = 1.24; 95% CI = 0.85,1.82).
Discussion
This study revealed key aspects about new or recurrent knee injury, satisfaction with MVPA, and beliefs about OA in young female athletes at 2 to 3 years subsequent to ACLR, as well as in their uninjured peers. The injury group had 7-fold increased odds of sustaining a recurrent knee injury; although this is clinically relevant, this finding was not statistically significant potentially due to the small sample size. The injury group sustained 5 ACL injuries over the 1-year period, while there were none in the control group. This aligns with previous studies that report 5 to 6 times increased risk of a second ACL injury compared with a first-time ACL injury. 24 While the rate of recurrent ACL injury seems greatest in the 2 years directly after surgery, the current study at 2 to 3 years after ACLR still found an incidence proportion of 19.6% or nearly 1 in 5 (vs control group, 6%).
The amount of objectively measured MVPA was not a risk factor for new or recurrent knee injury. Given the immense importance of PA to overall health across all body systems, including joint health, this finding should encourage clinicians to expand their conversations with patients beyond return to sport, to discuss different options for obtaining MVPA post-ACLR. For example, PAs that can be performed outside of structured context, such as jogging or cycling are more likely to continue into adulthood than team sports. 18 Further, as they progress through adolescence, youth and young adults often change sports due to lack of available sport opportunities, changing interests, 31 or evolving athletic identity, 10 thus returning to their same preinjury sport may not align with their lifestyle priorities. In the current study, only 37% of female athletes in the injury group reported returning to their preinjury level of sport performance, with the primary reason for not returning reported as due to “new interests or commitments.” Somewhat troubling is that only 56% and 66% of participants in the injury and control groups, respectively, were satisfied with their current MVPA participation, which warrants further investigation. Given that establishing high levels of PA in adolescence and young adulthood is predictive of maintaining this healthy activity levels later in life, clinicians should take time to help individuals post-ACLR to find enjoyable and sustainable forms of PA instead of emphasizing return to sport.
The results of the current study suggest that an elevated BMI may not be an important risk factor for recurrent injury. However, given the other negative health consequences associated with obesity, it is concerning that BMI does appear to increase during the postoperative period in adolescents after ACLR.13,19 MacAlpine et al 19 reported median percentile BMI increases of 2.63 points at 2 years postsurgery among patients who were considered normal weight at the time of their ACLR. Other longer-term studies have reported that higher BMI is related to negative health outcomes 3 to 10 years after knee injury, 39 and being overweight or obese is related to worse knee joint outcomes related to OA in the short and long term.6,25
When asked about their beliefs regarding future knee OA, over 80% in the injury group responded they were at increased risk, while nearly 40% in the control group responded they were at decreased risk compared with someone with a previous knee injury. These results align with patient beliefs about knee OA after ACLR in adults (mean age, 32.1 years) where Bennell et al 3 reported that 70% rated themselves as being at greater risk of OA compared with their healthy peers. Similarly, previous qualitative interviews with 20 young adults 3 to 10 years after knee injury found that participants had a sense of acceptance of their knee injury and their increased likelihood of OA. 10 These studies, taken together with the current work, underscore that there is a high level of awareness that having a previous knee injury increases risk of future OA. Clinicians should focus on evidence-based patient education on modifiable OA risk factors and motivational interviewing strategies to mitigate future OA risk.
The strengths of this study include the novel matched pair cohort design involving young, active women. The prospectively collected exposure variables of objectively measured MVPA participation and BMI, as a proxy for overweight and obese, have not previously been explored as increasing odds of new or recurrent knee injury. The excellent response rate at 1-year follow-up (99%) improves the external validity and generalizability of the results. The limitations of this work are the small sample size and consequently low number of “events” resulting in large 95% CI. Therefore, this study may be underpowered to detect the true strength of the relationships between the exposure variables and new or recurrent injury, and the results are preliminary. However, point estimates do highlight a clinically meaningful difference in injury rates between those with past ACLR and healthy matched controls, and new or recurrent injury rates are comparable with other research up to 2 years or beyond 3 years after ACLR.24,37 Given the paucity of studies that have examined new or recurrent knee injury during 2 to 3 years after surgery and the relationships between MVPA or BMI and knee injury, this work should be considered as a starting point for others in the field.
In conclusion, over this 1-year period, nearly 1 in 5 sustained a knee injury in the ACLR group, compared with just over 1 in 20 in the control group. This highlights that the period spanning 2 to 3 years post-ACLR remains an exceptionally high-risk time for new or recurrent knee injuries in young female athletes. Neither MVPA nor BMI significantly increased the odds of new or recurrent knee injury. While these results should be interpreted cautiously, they can be considered encouraging by suggesting that female adolescents can engage in MVPA without increasing their odds of new or recurrent knee injury.
Acknowledgments
Thanks go to the participants for contributing their time and experiences to this study.
Footnotes
The following author declared potential conflicts of interest: A.M.E. has received an Evidence to Innovation seed grant from BC Children’s Hospital Research, a Child and Family Research Institute graduate scholarship from the British Columbia Children’s Hospital Research Institute, and a doctoral award from the Canadian Child Health Clinician Scientist Program.
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