Objective To investigate the pathological features and their clinical significances in knee joints of middle-aged and elderly patients with knee pain. Methods A prospective sequential study was carried out on over-40-year-old patients undergoing arthroscopy due to knee pain in our department from January to December 2012. All cases were identified to be suffering from cartilage lesion (grade Ⅳ) by arthroscopy. Those with severe synovitis and needing synovectomy were excluded. Gender, age, affected side, body mass index (BMI) and Lysholm scores were recorded preoperatively. The joint surfaces where cartilage lesion (grade Ⅳ) existed on, medial/lateral meniscus tears, loose bodies, and anterior cruciate ligament (ACL) and/or posterior cruciate ligament (PCL) rupture were noted intraoperatively. All above items were statistically analyzed; and there was statistical significance when P＜0.05. Results There were 161 cases enrolled in the cohort. There were 31 males and 130 females (80.7%), with an age of (62.98±7.93) years, BMI of (26.39±3.41)kg/m2, and preoperative Lysholm scores of (45.34±15.65). For articular surface with grade Ⅳ cartilage degenerative lesion, patellofemoral compartment accounted for 88.8%, medial compartment for 57.8%, and lateral compartment for 24.8%. In the cohort, there were 70.8% patients suffering from medial meniscus tear, and 25.5% having lateral tear. In addition, the percentage of loose bodies, old ACL rupture and old PCL rupture were 47.8%, 3.7%, and 0.6%, respectively. Statistical analysis indicated that gender (P＝0.006), age (P＝0.040) and cartilage lesions (grade Ⅳ) on medial femoral condyle (MFC) (P＝0.032) were correlated with preoperative Lysholm scores. Medial meniscus tear (P＝0.002, r＝0.246) and grade Ⅳ cartilage lesion on medial femoral condyle (MFC) (P＝0.004, r＝0.223) had positive correlation with BMI. Conclusion In this cohort of knee pain patients with degenerative changes, cartilage lesion on patellofemoral compartment is the most common, while, old ACL/PCL ruptures are the least. Besides the cartilage degenerative lesion, the medial meniscus tear is probably one of the key factors that aggravate knee pain. Female, older-aged and suffering from grade Ⅳ cartilage lesion on MFC usually have lower preoperative Lysholm scores and more worse symptoms. The patients with higher BMI have high risk of medial meniscus tear and grade Ⅳ cartilage on MFC.