Paper 62: Predictors of Return to Activity at 2 Years After Anterior Cruciate Ligament Reconstruction Among Patients with High Baseline Pre-Injury Marx Activity Level

Abstract

Objectives:

Multiple authors have observed that preinjury activity level is a strong predictor of activity level after anterior cruciate ligament (ACL) reconstruction (ACLR.) However, among subjects with a relatively high baseline activity level, predictors for a successful return to preinjury activity level after ACLR remain poorly understood. The purpose of this study was to employ multivariable modeling to identify predictors of return to preinjury level of activity after ACLR among patients with high pre- injury activity scores (Marx activity scores 12-16) that have been prospectively enrolled in the Multicenter Orthopaedic Outcomes Network (MOON) cohort. We hypothesized that age, gender, preoperative activity level, and concurrent articular cartilage injuries would predict return to baseline, preinjury activity level 2 years after ACLR.

Methods:

All unilateral ACL reconstructions from 2002-2008 enrolled in the MOON cohort performed in subjects with baseline preinjury Marx activity scores ranging from 12 to 16 were evaluated with specific focus on return to preinjury activity level at 2 years postoperative. Continuous variables such as age, BMI, education level, baseline Short Form-36 mental component survey (MCS), baseline Marx activity were summarized using median and interquartile ranges. Categorical variables such as sex, race, smoking status, reconstruction type (primary/revision), graft type etc. were displayed using counts and percentages. The primary outcome of interest was return to activity, which was defined as a raw difference of ≥ -2 between Marx activity score at 2-year minus baseline Marx activity. This means that anyone who had a ≥ -2 difference in Marx activity was considered returned to activity; otherwise, he/she was not considered able to return to activity. To identify predictors and possible risk factors contributing to return to activity, a multivariable logistic regression model was built. Multivariable modeling was performed to identify risk factors for subjects’ inability to return to baseline, preinjury activity level. The relative importance of each predictor was ranked according to the increase in Akaike information criterion (AIC) upon removal from the full model; the importance rankings are presented in descending order; only positive values are presented in the graphs. AIC quantifies the amount of information explained by the covariates, while penalizing variables for the number of degrees of freedom they use. An AIC-increase 2 indicated that the given variable contributed to a statistically better model.

Results:

There were 1188 patients with 2-year follow up that met the inclusion criteria. The two year follow-up for MARX activity was 82.7 % (1188/1437.) The cohort was comprised of 714 males (60.1%) and 474(39.9%) females. The median age of the cohort was 22 years (25^th; 75^th interquartile range: 18.0 years; 31.2 years) (Table 1.) Six hundred and forty two (54%) of subjects reported a MARX activity of 16. Overall, 466 (39.2%) subjects were able to return to activity, while 722 subjects (60.7%) were not able to return to activity (Table 2.) Female gender, smoking at the time of ACLR, lower education level, lower SF-36 Mental Component Score (MCS), and higher Marx activity scores were not predictive of a subject’s inability to return to baseline, preinjury activity level (Figure 1.) For example, for baseline Marx activity score, after controlling for other variables, the odds of returning to high activity for a subject with a baseline Marx activity score of 16 (the third quartile of baseline Marx activity score of this cohort) was 32% lower compared to a subject with a baseline Marx activity score of 12 (the first quartile of baseline Marx activity score) (OR = 0.68 (0.5, 0.93), P = 0.016). Stated differently, the higher the baseline Marx activity score that a person reported at the time of enrollment, the less likely he/she was to return to a relatively high preinjury activity level. Graft type, revision ACLR, the presence of medial and/or lateral meniscal pathology, history of meniscal surgery, the presence of articular cartilage pathology, history of articular cartilage treatment, or the presence of high-grade knee laxity were not predictive of a subject’s ability to return to baseline, preinjury activity level.

Conclusions:

There are several noteworthy findings of the current study. First, only 39.2% of highly active subjects in this cohort were able to return to same high level of activity at 2 years post ACLR. Second, according to predictive modeling considering all variables of interest, female gender, positive smoking status, lower education level, lower SF-36 MCS, and higher baseline Marx activity scale were all risk factors predictive for the inability to return to preinjury activity level. Furthermore, the interaction between subjects’ age and education level resulted in a variable effect of the likelihood for returning to activity: more highly educated patients at the extremes of age were more likely to return to activity than similarly educated patients in the middle range of ages (22-32 years.) Thus, our hypothesis was only partially proven as the presence of articular cartilage and/or meniscal injuries with or without treatment did not predict a lower likelihood of subjects’ returning to activity nor did a higher baseline, preinjury Marx activity level. In fact, the opposite was true with a lower baseline, preinjury activity level predicting return to activity. To our knowledge, this is the largest cohort comprised of subjects with objectively defined high baseline, preinjury activity level analyzed with multivariable predictive modeling to identify risk factors for an inability to return to high activity at 2 years post ACLR.