Predictors of activity level 2 years after anterior cruciate ligament reconstruction (ACLR): a Multicenter Orthopaedic Outcomes Network (MOON) ACLR cohort study

Abstract

Objective: The study was conducted to quantify activity level 2 years after anterior cruciate ligament reconstruction and identify explanatory variables measured at baseline (demographics, concomitant meniscal/articular cartilage injuries and their treatment) associated with activity level at short-term follow-up (2 years).

Study design: Cohort study; Level of evidence, 2.

Methods: In 2002, the Multicenter Orthopaedic Outcomes Network (MOON) consortium began enrolling patients undergoing anterior cruciate ligament reconstruction at 6 recruitment sites. The current study reports 2-year follow-up of patients enrolled in 2002. Participants completed a series of validated, patient-oriented questionnaires that included activity level assessment. Measurement of intra-articular pathology, techniques of anterior cruciate ligament reconstruction, and secondary procedures were recorded at baseline by participating surgeons. Multivariable proportional odds ordinal logistic regression was used to assess predictors of activity level after adjusting for baseline patient characteristics. Interquartile range (IQR) odds ratios (ORs) are given for continuous variables. The fitted model that used ORs to specify predicted probabilities of exceeding any activity level was translated into predicted mean activity level.

Results: Of the 446 patients who underwent unilateral anterior cruciate ligament reconstruction, follow-up was obtained on 393 (88%). Male patients comprise 56% of the cohort, with a median age of 23 years. The median and IQR International Knee Documentation Committee subjective score was 53 (range, 40-65) preoperatively and increased to 84 (range, 74-92) 2 years postoperatively. Median and IQR activity level was 12 (range, 8-16) at baseline, and declined to 9 (range, 3-13) at follow-up. The proportion of participants returning to the same or higher level of activity 2 years after anterior cruciate ligament reconstruction was 45%. After controlling for other baseline factors such as age, marital and student status, contralateral knee status, sport and competition level, and articular cartilage/meniscal injuries, factors associated with higher activity levels at 2 years were higher baseline activity (IQROR = 3.84; 95% confidence interval [CI], 1.98-7.43; P < .0001) and lower baseline body mass index (IQROR = 1.37; 95% CI, 1.04-1.82; P = .027). The following baseline factors were associated with lower activity: female sex (OR = 0.60; 95% CI, 0.39-0.91; P = .015), smoking within 6 months prior to surgery (OR = 0.55; 95% CI, 0.33-0.92; P = 0.023), and revision anterior cruciate ligament reconstruction (OR = 0.41; 95% CI, 0.20-0.83; P = .014). Factors presumably related to functional status of the knee such as the condition of the articular cartilage and menisci, as well as normalcy of the contralateral knee, were not predictive of activity level at 2 years.

Conclusion: (1) Evaluation of posttreatment activity levels should control for patients' preoperative activity because this is a strong predictor of future activity. (2) Assuming physical activity is an important component of a healthy person, investigation of potential interventions to improve future activity could target modifiable exposures such as weight. (3) Further evaluation is needed to explore the association of sex and revision surgery on activity level following anterior cruciate ligament reconstruction.

Figure 1

Flow diagram – 2002 Multicenter ACLR Cohort.

Figure 2

KOOS Profile with 0.95 Confidence Limits comparing baseline (t0) and 2 year (t2) scores for pain, symptoms, ADL function, sports & recreation, and knee-related quality of life subscales.

Figure 3

Summary plot of key predictors of Marx activity level at 2 years adjusted for all variables in the final model. Vertical black tics indicate the log odds ratio (for continuous predictors the IQROR is given), which can be read off the top horizontal axis, surrounded by the 95% confidence intervals in grey that should not overlap the vertical dashed line indicating zero if there is a statistically significant effect. For example, the effect of lowering BMI from its third quartile (28) to its first quartile (22) is to raise the mean two-year activity score by 1.4 points (95%CI=1.04–1.82), while those injured in soccer have a mean two-year activity score 2.8 points higher than subjects with non-sport injuries (95%CI= 1.3–5.7).

Figure 4

Nomogram for the model predicting Marx activity level 2 years after ACLR. Use the top line to get points for each individual predictor listed in the left hand column. Manually sum these points, and then transfer the sum to the total points axis to determine the corresponding Predicted Activity Score on the bottom line of the nomogram.