Abstract
Background:
Anterior cruciate ligament (ACL) injuries can be treated with or without ACL reconstruction (ACLR), and more high-quality studies evaluating outcomes after the different treatment courses are needed. The purpose of the present study was to describe and compare 5-year clinical, functional, and physical activity outcomes for patients who followed our decision-making and treatment algorithm and chose (1) early ACLR with preoperative and postoperative rehabilitation, (2) delayed ACLR with preoperative and postoperative rehabilitation, or (3) progressive rehabilitation alone. Early ACLR was defined as that performed ≤6 months after the preoperative rehabilitation program, and late ACLR was defined as that performed >6 months after the preoperative rehabilitation program.
Methods:
We included 276 patients from a prospective cohort study. The patients had been active in jumping, pivoting, and cutting sports before the injury and sustained a unilateral ACL injury without substantial concomitant knee injuries. The patients chose their treatment through a shared decision-making process. At 5 years, we assessed the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF), Knee injury and Osteoarthritis Outcome Score (KOOS), Marx Activity Rating Scale, sports participation, quadriceps muscle strength, single-legged hop performance, and new ipsilateral and contralateral knee injuries.
Results:
The 5-year follow-up rate was 80%. At 5 years, 64% of the patients had undergone early ACLR, 11% had undergone delayed ACLR, and 25% had had progressive rehabilitation alone. Understandably, the choices that participants made differed by age, concomitant injuries, symptoms, and predominantly level-I versus level-II preinjury activity level. There were no significant differences in any clinical, functional, or physical activity outcomes among the treatment groups. Across treatment groups, 95% to 100% of patients were still active in some kind of sports and 65% to 88% had IKDC-SKF and KOOS scores above the threshold for a patient acceptable symptom state.
Conclusions:
Patients with ACL injury who were active in jumping, pivoting, and cutting sports prior to injury; who had no substantial concomitant knee injuries; and who followed our decision-making and treatment algorithm had good 5-year knee function and high sport participation rates. Three of 4 patients had undergone ACLR within 5 years. There were no significant differences in any outcomes among patients treated with early ACLR, delayed ACLR, or progressive rehabilitation alone.
Level of Evidence:
Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.
Anterior cruciate ligament (ACL) injuries can be managed with or without ACL reconstruction (ACLR)1–3. The existing literature is sparse but generally has not demonstrated superior outcomes of ACLR compared with progressive rehabilitation alone4–10.
Comparing outcomes after ACLR and progressive rehabilitation alone involves important challenges. First, the population of patients with ACL injuries is highly heterogeneous, and some patients do better with rehabilitation alone than others11. Consequently, treatment does not fit into a one-size-fits-all paradigm. Second, surgery is only one part of a treatment course; patient education, high-quality rehabilitation, surgical indications, and timing of treatment are also important12. Therefore, we need to move beyond relying only on randomized controlled trials (RCTs) evaluating the effect of single treatment components to inform clinical practice. An evaluation of a clinical treatment algorithm including shared decision-making based on patients’ needs, expectations, and function is also needed.
The Delaware-Oslo ACL Cohort Study is a longitudinal cohort study of patients who had been active in jumping, pivoting, and cutting sports before injury and who had no substantial concomitant knee injuries. Before participating in an informed shared decision-making process with their physical therapists and orthopaedic surgeons, all patients underwent a 5-week preoperative rehabilitation program with progressive neuromuscular and strength training followed by clinical testing13. Patients were advised on treatment choice on the basis of dynamic instability, knee function, and intention to return to level-I sports. Achievement of good knee function after the preoperative rehabilitation was the main patient-reported reason for choosing progressive rehabilitation alone14. Regardless of treatment choice, all patients underwent progressive rehabilitation guided by functional testing11,14.
Based on subgroups of the present cohort, we previously reported (1) large improvement in knee function after preoperative rehabilitation13 and argued that knee function should be emphasized in treatment choices15, (2) that a number of factors are prognostic for successful outcome16,17, (3) that coper classification may change after preoperative rehabilitation and affect 2-year outcomes18,19, (4) that 2-year outcomes after progressive rehabilitation alone are equivalent to those after ACLR14, and (5) that 2-year outcomes in our surgically treated patients are superior to those after usual care in the United States20 and Norway21. We have yet to report the long-term clinical, functional, physical activity, and radiographic22 outcomes for the whole cohort.
The purpose of the present study was to describe and compare the 5-year clinical, functional, and physical activity outcomes for patients who had gone through our decision-making and treatment algorithm and had chosen either (1) early ACLR with preoperative and postoperative rehabilitation, (2) delayed ACLR with preoperative and postoperative rehabilitation, or (3) progressive rehabilitation alone. Early ACLR was defined as that performed ≤6 months after the preoperative rehabilitation program, and late ACLR was defined as that performed >6 months after the preoperative rehabilitation program.
Materials and Methods
Patients
Three hundred athletes were consecutively enrolled into this prospective cohort study from the University of Delaware, Newark, Delaware, United States, or the Norwegian Sports Medicine Clinic, Oslo, Norway, between 2006 and 2012. Complete unilateral ACL injury and concomitant injuries were verified with magnetic resonance imaging (MRI), and increased anterior knee joint laxity was measured with a KT1000 arthrometer (MEDmetric Corporation). The inclusion criteria were an age between 13 and 60 years and preinjury participation in level-I or II sports ≥2 times/week (Table I)11,23. We excluded patients with current or previous ipsilateral or contralateral knee injuries, those with concomitant grade-III ligament injury, those with full-thickness articular cartilage damage or fracture, and those who were unable to attend preoperative rehabilitation. All patients had to have resolution of acute impairments (have no or minimal pain or effusion during or after plyometric activities) before inclusion in the study (within 3 months after injury [Oslo] or within 7 months after injury [Delaware]). If not, they were excluded (for example, patients with symptomatic meniscal injuries). Patients with obviously repairable menisci on MRI such as bucket-handle tears with locked knees were also excluded and were referred to an orthopaedic surgeon. Among the original 300 patients, 24 had had a previous ACLR and came to our clinics with a graft rupture; those patients were excluded from the present study. Hence, the present study included 276 patients (142 from Oslo and 134 from Delaware) with a first-time ACL injury.
TABLE I.
| Level | Sports Activity | Example of Sports |
|---|---|---|
| I | Jumping, cutting, pivoting | Soccer, football, handball, basketball, floorball |
| II | Lateral movements, less pivoting than level I | Tennis, squash, alpine skiing, snowboarding, gymnastics, baseball, softball |
| III | Straight-ahead activities, no jumping or pivoting | Running, cross-country skiing, weightlifting |
| IV | Sedentary |
We obtained written informed consent or assent with parental consent and approvals from the Regional Committee for Medical and Health Research Ethics of Norway and the University of Delaware institutional review board.
Treatment Algorithm
After impairment resolution (mean, 59 days after injury) and inclusion in the study, all patients participated in a 5-week (10-session) preoperative rehabilitation program consisting of progressive neuromuscular and strength training exercises as described by Eitzen et al.13. The patients received education, including information about treatment alternatives, before they underwent functional testing and made their treatment choice in consultation with their orthopaedic surgeons and physical therapists. We were more likely to recommend ACLR to patients experiencing dynamic knee instability24 after preoperative rehabilitation and those who intended to return to level-I sports. Achieving good knee function after rehabilitation was the main patient-reported reason for choosing progressive rehabilitation alone14. Despite recommendations, 34% of the patients who chose progressive rehabilitation alone intended to return to level-I sports14. Delayed ACLR was indicated for patients with dynamic knee instability24 or if they changed their minds about the treatment choice that they had made.
Several experienced (and, in the United States, subspecialty-certified) sports orthopaedic surgeons performed the ACLRs, and graft choices were shared decisions. Bone-patellar tendon-bone autografts (21.5%), single-bundle or double-bundle hamstring autografts (51.5%), or allografts (27%) were used. Postoperative rehabilitation consisted of 3 phases and was individually adjusted for concomitant injuries, graft type, and knee function. The acute postoperative phase (phase 1) addressed swelling, range of motion, and atrophy. The milestones of the rehabilitation phase (phase 2) were to achieve a muscle strength and hop performance limb symmetry index (LSI) of ≥80%. In the return-to-sport phase (phase 3), participation in sports-specific training gradually increased and the milestones were a strength and hop LSI of ≥90%. Patients who did not undergo ACLR typically continued progressive rehabilitation for 3 to 4 months with the same phases.
Data Collection
At 5 years after completion of preoperative rehabilitation or after ACLR, patients completed the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF)25–28 and Knee injury and Osteoarthritis Outcome Score (KOOS)29,30. The KOOS consists of 5 subscales: pain, other symptoms, function in daily living, function in sport and recreation (Sport/Rec), and knee-related quality of life (QoL)30. The minimum clinically important change (MCIC) is 11.5 points for the IKDC-SKF27, 12.1 points for KOOS Sport/Rec, and 18.3 points for KOOS QoL31.
We assessed quadriceps strength with use of the peak torque from maximum isometric contraction (3 repetitions) or from concentric isokinetic testing (4 trial repetitions and 5 test repetitions) with use of electromechanical dynamometers (Kin-Com; DJO Global)32. We tested the uninjured leg first. The isometric test (Delaware) was performed with hips and knees in 90° of flexion. The isokinetic test (Oslo) was performed at 60°/second between 90° of flexion and full extension (Biodex6000; Biodex Medical Systems).
Four single-legged hop tests were performed in the following order: (1) the single hop for distance, (2) the crossover hop for distance, (3) the triple hop for distance, and (4) the 6-m timed hop16,17,33. We tested the uninjured leg first. One practice trial was performed before we recorded 2 trials, from which the mean score was calculated. During the first 3 hop tests, we considered trials valid if the final landing was stable (without touching the floor or walls with the other foot or hands or performing additional hops).
We assessed new ipsilateral and contralateral knee injuries with clinical examination, including arthrometer measurements. The diagnosis was verified with MRI and/or during surgery if indicated.
We recorded sports participation with use of the question, “What sports or exercise are you participating in now?” and graded the most knee-demanding sport from I to IV (Table I). Frequency of participation in sports involving running, pivoting, cutting, and deceleration was assessed with use of the Marx Activity Rating Scale34.
Data Management and Statistical Analysis
As previously noted, we classified ACLRs performed ≤6 months after the preoperative rehabilitation program as early and those performed >6 months as delayed.
We reported muscle strength and single-legged hop performance with the LSI (i.e., the performance of the involved limb as a percentage of the performance of the contralateral limb). The rate of new ipsilateral or contralateral knee injuries was calculated among those who attended either the 2-year or 5-year follow-up. In addition to calculating the mean and standard deviation, we classified patients as above or below the top 15th normative percentile25 for age and sex-matched subjects with healthy knees for the IKDC-SKF and above or below the patient acceptable symptom state (PASS) threshold for the IKDC-SKF, KOOS Sport/Rec, and KOOS QoL35.
Sample-size estimation showed that we needed 25 patients in each group to detect a between-group difference in IKDC-SKF scores larger than the MCIC of 11.5 points27 with an estimated standard deviation of 1214 with an alpha level of 0.017 and 80% power.
Most continuous outcome measures were skewed according to the Kolmogorov-Smirnov test, but, because of the high number of participants, and after inspection of histograms and skewness, we concluded that they were close enough to a normal distribution to use parametric tests36. We assessed group differences with 1-way analysis of variance (ANOVA) tests (continuous variables) and with chi-square tests or Fisher exact tests (categorical variables)37. Because we aimed to evaluate outcomes in the 3 treatment groups following our treatment algorithm, and because this is not an effect study, we performed unadjusted analyses.
Results
Of the 276 patients included in this study, 54 (20%, including 19 [13%] from the Oslo group and 35 [26%] from the Delaware group) were lost to 5-year follow-up. Of those, 14 patients (5% of the cohort) had been managed nonoperatively at the time of the latest follow-up but we were unable to ascertain whether they had had a subsequent operation (Fig. 1). More patients completed the patient-reported outcome measures (PROMs) (72% to 80%) than the clinical/functional tests (59% to 70%). Patients who were lost to follow-up (n = 54) were younger (mean difference, 3.8 years [95% confidence interval (CI), 0.9 to 6.7 years]; p = 0.010) and had a higher body mass index at inclusion (mean difference, 2.2 kg/m2 [95% CI, 0.7 to 2.2 kg/m2]; p = 0.004) than those who attended follow-up.
Fig. 1.
Patient flowchart.
Among the patients with ascertained treatment status at 5 years (95% of the cohort), 167 (64%) had undergone early ACLR, 30 (11%) had had delayed ACLR, and 65 (25%) had had progressive rehabilitation alone. Accordingly, 30 (32%) of the 95 patients who initially chose rehabilitation alone ended up with delayed ACLR (19 patients had surgery between 6 and 12 months after inclusion, 7 patients between 12 and 24 months, and 4 patients at >24 months). The patients who chose progressive rehabilitation alone were significantly older, less likely to participate in level-I sports preinjury, and less likely to have concomitant injuries to the medial meniscus compared with those who underwent early or delayed ACLR (Table II). The meniscal procedures that were performed during ACLR were either excisions (26%), repairs (56%), or trephination/rasping (18%).
TABLE II.
Descriptive Characteristics at Inclusion
| Early ACLR (N = 167) | Delayed ACLR (N = 30) | Progressive Rehabilitation Alone (N = 65) | P Value | |
|---|---|---|---|---|
| Inclusion site (Oslo/Delaware) | 48%/52% | 70%/30% | 54%/46% | 0.078 |
| Age* (yr) | 24.7 ± 8.7 | 24.4 ± 9.4 | 31.9 ± 10.9 | <0.001 |
| Female sex (no. of patients) | 76 (46%) | 9 (30%) | 36 (55%) | 0.067 |
| Body mass index* (kg/m2) | 24.6 ± 4.0 | 24.4 ± 4.6 | 24.3 ± 3.2 | 0.838 |
| Preinjury sports participation (no. of patients) | <0.001 | |||
| Level-I | 129 (77%) | 25 (83%) | 30 (46%) | |
| Level-II | 38 (23%) | 5 (17%) | 35 (54%) | |
| Concomitant injuries† (no. of patients) | ||||
| Medial meniscus | 45 (27%) | 8 (27%) | 7 (11%) | 0.027 |
| Lateral meniscus | 34 (20%) | 7 (23%) | 6 (9%) | 0.100 |
| Cartilage | 12 (7%) | 5 (17%) | 5 (8%) | 0.220 |
| Medial collateral ligament (grade I or II) | 39 (23%) | 6 (20%) | 11 (17%) | 0.552 |
| Lateral collateral ligament (grade I or II) | 3 (2%) | 1 (3%) | 4 (6%) | 0.194 |
| Meniscal surgery at time of ACLR (no. of patients) | 69 (41%) | 12 (40%) | NA‡ | 0.893 |
The values are given as the mean and the standard deviation.
Number of patients diagnosed with the injury with use of MRI at the time of inclusion.
NA = Not applicable.
Five-Year Clinical, Functional, and Physical Activity Outcomes
There were no significant differences in any clinical, functional, or physical activity outcomes between the 3 treatment groups (Table III) (see also Appendix).
TABLE III.
Five-Year Outcomes*
| Early ACLR | Delayed ACLR | Progressive Rehabilitation Alone | P Value | |
|---|---|---|---|---|
| Time from injury to 5-year follow-up† (n = 222) (yr) | 5.5 ± 0.5 | 6.1 ± 0.6 | 5.4 ± 0.5 | <0.001 |
| IKDC-SKF† (n = 222) (points) | 89 ± 12 | 85 ± 15 | 87 ± 13 | 0.308 |
| KOOS† (points) | ||||
| Pain (n = 220) | 94 ± 9 | 90 ± 12 | 94 ± 9 | 0.213 |
| Symptoms (n = 220) | 89 ± 13 | 86 ± 15 | 92 ± 13 | 0.156 |
| Activities of daily living (n = 220) | 98 ± 7 | 97 ± 6 | 97 ± 5 | 0.860 |
| Sport/Rec (n = 219) | 89 ± 17 | 81 ± 22 | 87 ± 21 | 0.209 |
| QoL (n = 219) | 80 ± 21 | 70 ± 19 | 78 ± 19 | 0.083 |
| Quadriceps muscle strength: limb symmetry index† (n = 193) | 97% ± 12% | 93% ± 16% | 101% ± 21% | 0.111 |
| Single-legged hop tests: limb symmetry index† | ||||
| Single hop for distance (n = 166) | 99% ± 10% | 97% ± 8% | 101% ± 9% | 0.203 |
| Crossover hop for distance (n = 162) | 99% ± 9% | 95% ± 8% | 99% ± 9% | 0.329 |
| Triple hop for distance (n = 162) | 99% ± 8% | 97% ± 6% | 100% ± 7% | 0.471 |
| 6-meter timed hop (n = 163) | 99% ± 7% | 97% ± 6% | 99% ± 7% | 0.408 |
| New knee injuries, ipsilateral (no. of patients) | ||||
| Graft rupture | 19 (12%) of 153 | 5 (19%) of 27 | NA | 0.368 |
| Meniscus | 11 (7%) of 153 | 3 (11%) of 27 | 5 (8%) of 65 | 0.721 |
| Cartilage | 2 (1%) of 153 | 1 (4%) of 27 | 0 (0%) of 65 | 0.315 |
| MCL/LCL | 4 (3%) of 153 | 0 (0%) of 27 | 0 (0%) of 65 | 0.575 |
| PCL | 1 (1%) of 153 | 0 (0%) of 27 | 0 (0%) of 65 | 1.000 |
| New knee injuries, contralateral (no. of patients) | ||||
| ACL rupture | 12 (8%) of 153 | 0 (0%) of 27 | 4 (6%) of 65 | 0.399 |
| Meniscus | 2 (1%) of 153 | 0 (0%) of 27 | 3 (5%) of 65 | 0.211 |
| Cartilage | 0 (0%) of 153 | 0 (0%) of 27 | 1 (2%) of 65 | 0.376 |
| MCL/LCL | 0 (0%) of 153 | 0 (0%) of 27 | 0 (0%) of 65 | |
| PCL | 0 (0%) of 153 | 0 (0%) of 27 | 0 (0%) of 65 | |
| Sports participation (no. of patients) | 0.140 | |||
| Level-I | 47 (35%) of 135 | 4 (17.5%) of 23 | 16 (25%) of 64 | |
| Level-II | 36 (27%) of 135 | 4 (17.5%) of 23 | 20 (31%) of 64 | |
| Level-III | 45 (33%) of 135 | 15 (65%) of 23 | 26 (41%) of 64 | |
| Level-IV | 7 (5%) of 135 | 0 (0%) of 23 | 2 (3%) of 64 | |
| Returned to preinjury sports participation (no. of patients) | 64 (47%) of 135 | 6 (26%) of 23 | 30 (47%) of 64 | 0.159 |
| Marx activity rating scale* (n = 199) | 8 ± 4 | 8 ± 4 | 7 ± 4 | 0.314 |
IKDC-SKF = International Knee Documentation Committee Subjective Knee Form, KOOS = Knee injury and Osteoarthritis Outcome Score, MCL = medial collateral ligament, LCL = lateral collateral ligament, PCL = posterior cruciate ligament, ACL = anterior cruciate ligament, and NA = not applicable.
The values are given as the mean and the standard deviation.
Figure 2 shows the percentages with IKDC-SKF scores above/below the top 15th percentile25 and IKDC-SKF, KOOS Sport/Rec, and KOOS QoL scores above/below the PASS threshold35. The percentages were similar across treatment groups (p = 0.144 to 0.520).
Fig. 2.
Bar graphs showing the percentage of patients in each treatment group with IKDC-SKF scores above the 15th percentile and IKDC-SKF, KOOS Sport/Rec, and KOOS QoL scores above the PASS threshold.
Discussion
Among patients in this prospective cohort study who followed our decision-making and treatment algorithm, 64% chose early ACLR, 11% chose delayed ACLR, and 25% chose progressive rehabilitation alone. Regardless of treatment, most patients in our cohort achieved good 5-year outcomes: between 65% and 88% had IKDC-SKF, KOOS Sport/Rec, and KOOS QoL scores above the PASS threshold35, and nearly all patients still participated in some kind of sports. There were no significant differences in any outcomes among the 3 treatment groups. Except for new meniscal injuries, there was a tendency toward worse outcomes for the patients who underwent delayed ACLR. It is important to bear in mind that the reasoning for surgery was different for delayed ACLR compared with early ACLR, which may affect the outcomes.
Because the present study is not an effect study, and because we aimed to describe and compare outcomes in the 3 treatment groups following our treatment algorithm, we performed unadjusted analyses. Differences in characteristics between treatment groups likely played a role in who chose which treatments. Specifically, those who chose rehabilitation alone were older, more likely to have participated in level-II sports before the injury, and less likely to have concomitant meniscal injuries compared with the 2 ACLR groups. Those patients reported good function after preoperative rehabilitation as the reason for their treatment choice, whereas delayed ACLR was indicated for those with dynamic instability14.
Comparisons with Other Studies
Others have also found similar outcomes between patients managed with ACLR and those managed with progressive rehabilitation alone4,5,7,9,38. However, the present cohort study is unique as it evaluated the outcomes of a specific shared decision-making and treatment algorithm wherein all patients participated in a preoperative rehabilitation program.
The surgically treated patients in our cohort had better 2-year outcomes than those who receive usual care (matched patients in the Norwegian National Knee Ligament Registry and the Multicenter Orthopaedic Outcomes Network [MOON] cohort)20,21. These findings were attributed to the extended preoperative and high-quality postoperative rehabilitation in our cohort20,21. The 5-year IKDC-SKF score for all patients managed with ACLR in our cohort (the early and delayed ACLR groups combined) was still superior to the 6-year score for the MOON cohort (median, 93 versus 77)39, whereas the KOOS Sport/Rec and QoL scores were superior to the 5-year outcomes of primary ACLR in the Swedish National Anterior Cruciate Ligament Register (mean, 88 versus 69 points for KOOS Sport/Rec and 78 versus 66 for KOOS QoL)40. The differences between the cohorts exceed the MCIC for both the IKDC-SKF and KOOS Sport/Rec scores27,31.
The rates of secondary ipsilateral and contralateral ACL injuries have been reported to be at least 3% to 8% in previous studies38,41,42. Our rates of contralateral ACL injuries in all groups (0% to 8%) and graft ruptures in the early ACLR group (12%) correspond with those rates. The graft rupture rate was higher among patients with delayed ACLR (19%), although it did not significantly differ from that among patients with early ACLR. Our rate of new ipsilateral meniscal injuries (7% to 11%) was low compared with those in previous studies (5% to 52%)43, and, importantly, we found no differences among treatment groups.
Strengths and Limitations
Compared with RCTs, the external validity of our study is high because our treatment algorithm is in line with current practice clinical recommendations12. However, the external validity is limited to patients who are active in jumping, pivoting, or cutting sports preinjury without substantial concomitant injuries and who have resolution of acute impairments within 3 to 7 months after injury. Our high follow-up rate for PROMs (80%) is an important strength of a 5-year follow-up study.
Because the delayed ACLR group was small, the 95% CIs for the mean differences in IKDC-SKF, KOOS Sport/Rec, and KOOS QoL scores between this treatment group and the 2 other groups were wide. As 95% CIs included the MCIC for these instruments (see Appendix), we cannot exclude the existence of clinically meaningful differences.
Clinical Implications
Our results have important implications for clinical practice. First, progressive rehabilitation alone is a viable solution for some patients, and clinicians should communicate the possibility of living an active life with good knee function without surgery. Second, as the 5-year outcomes of our cohort exceeded those commonly reported in the literature39,40, we advocate the use of our decision-making and treatment algorithm in clinical practice.
Implications for Future Research
An exceedingly small number of our cohort had IKDC-SKF and KOOS scores below the PASS threshold that represents poor knee function and patient satisfaction. Further research is needed to understand how these patients differ from other patients and to predict who will benefit the most from each treatment strategy. Recent studies have started this important work11,19,44.
Conclusions
Patients with ACL injuries who had been active in jumping, pivoting, and cutting sports prior to injury; who had no substantial concomitant knee injuries; and who followed our decision-making and treatment algorithm had good 5-year knee function and high sport participation rates. Within 5 years, 64% had chosen early ACLR, 11% had chosen delayed ACLR, and 25% had chosen progressive rehabilitation alone. There were no significant differences in any outcomes among the 3 treatment groups. Understandably, the choices that participants made differed by age, concomitant injuries, symptoms, and predominantly level-I versus level-II preinjury activity level. We believe that progressive neuromuscular and strength training rehabilitation as a preoperative rehabilitation program, and patient education and clinical testing as part of an informed shared decision-making process, should be the gold standard for treating patients with ACL injury.
Supplementary Material
Acknowledgments
Funding: NIH
Disclosure: The Delaware-Oslo ACL Cohort study is funded by the National Institutes of Health, grant R37HD37985. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJS/G500).
We thank all of the participating patients in our cohort. We thank the Norwegian Sports Medicine Clinic (NIMI) and University of Delaware Physical Therapy Clinic for providing facilities for clinical testing, and those who assisted with data collection: Martha Callahan, Håvard Moksnes, Ingrid Eitzen, Annika Storevold, Ida Svege, Espen Selboskar, Ben Clarsen, Karin Rydevik, Marte Lund, Kristine Roberg Hytten, Andrew Lynch, David Logerstedt, Airelle Giordano, Angela Smith, Matthew Failla, and Elizabeth Wellsandt. We also thank James Alesi for organizing our database and Morten W. Fagerland for statistical advice.
Footnotes
Appendix
Supporting material provided by the authors is posted with the online version of this article as a data supplement at jbjs.org (http://links.lww.com/JBJS/G501).
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