The current systematic review and meta-analysis aims to evaluate the factors that affect union rates following fixation of osteochondritis dissecans of the knees. The systematic review was conducted using the keywords “knee” and “osteochondritis dissecans” or “osteochondral lesion” via a search through PubMed and Cochrane Library. All original human studies that reported on factors affecting union rates following fixation of osteochondritis dissecans of the knees were included. Nineteen studies with 512 knees were included. The union rates following surgical fixation of osteochondritis dissecans was 88% (95% confidence interval [CI]: 85–91%). Stability of the osteochondritis dissecans intraoperatively was the most important factor in affecting the union rates (pooled relative risk: 1.20; 95% CI: 1.07–1.36). No other risk factors, including skeletal maturity, gender of patients, location of osteochondritis dissecans, size of osteochondritis dissecans, open versus arthroscopic surgery, and number of fixation devices used affected the union rates following surgical fixation of osteochondritis dissecans. Surgical fixation of osteochondritis dissecans provided good union rates in majority of the patients, and stability of the osteochondritis dissecans intraoperatively was the most important factor in affecting the union rates.