Paper 35: Preoperative Predictors of Arthroscopic Partial Meniscectomy: The APM Index Score

OBJECTIVES: Meniscal tears are one of the most common knee conditions treated by orthopaedic surgeons. Patients who do not respond to conservative management are often offered arthroscopic partial meniscectomy (APM). Clinical care of these patients could be enhanced by a scoring system that uses preoperative factors to predict the likelihood of pain relief following APM. The purpose of this study is to create an index score based on easily available preoperative risk factors to predict favorable outcomes following APM. METHODS: We performed a retrospective review of prospectively collected data from a consecutive cohort of patients from a single surgeon in an outpatient setting. Patients were included in the study if they had a meniscal tear, failed nonoperative treatment measures, and completed preoperative patient reported outcome questionnaires. We defined clinical improvement as achieving a score of ≥ 90 at one-year postoperatively or an improvement of 10 points in the KOOS pain subscale (the minimal clinically important difference (MCID)). We used multivariable logistic regression models to identify factors associated with clinical improvement and created a scoring system by assigning points to each variable proportional to its regression coefficient. RESULTS: 468 patients who underwent APM between August 2012 and October 2020 were included in this study. The mean age was 49 [SD=10.4, range 19-81], 58% were female, 88% were white, and 79% were overweight or obese. 84% of subjects met our criteria for clinical improvement. In the multivariable model, longer symptom duration, higher Kellegren-Lawrence (KL) grade, and higher pre-treatment KOOS pain score were associated with lower likelihood of clinical improvement one-year postoperatively. The adjusted odds ratios are shown in Table 1. Based on the regression coefficients from the model, those with KL grade 0 were assigned 2 points and all other factors (pre-treatment KOOS pain score ≤ 60, symptom duration ≤ 6 months, and KL grade 1 or 2) were assigned 1 point (Table 1). The scoring algorithm performed well with higher total scores predicting a higher likelihood of achieving clinical improvement: 40% for total score 0, 68% for score 1, 80% for score 2, 89% for score 3, and 96% for score 4 (Figure 1). We also examined a scoring system that did not include pre-treatment KOOS pain score since it might not be readily available in a clinical setting. In this abbreviated model, those with KL score 0 or 1 and those with symptom duration < 3 months were assigned 2 points; those with KL score 2 or symptom duration 3-6 months were assigned 1 point (Table 1). The likelihood of achieving clinical improvement ranged from 66% among those with score 0 to 90% among those with score 3 or 4 (Figure 1). CONCLUSIONS: The results of this study serve to create a screening tool that may help to identify patients who would benefit from APM intervention. Further research should validate the index an an independent sample. We note that the index does not compare the benefits of undergoing APM versus other nonoperative treatments, but it can help the physician to engage in the shared decision-making process with patients regarding the possible benefits of undergoing APM.