Comparison of Arthroscopic and Open Assessment of Size and Grade of Cartilage Defects of the Knee

PurposeThe purpose of our study was to compare arthroscopic versus open measurement of cartilage defects and determination of defect grade according to the International Cartilage Repair Society (ICRS) classification.MethodsArthroscopic determination of defect size and grade according to the ICRS classification of 450 focal cartilage defects in 407 patients who underwent autologous chondrocyte implantation was compared with definite findings at the time of open knee surgery. Results were analyzed based on defect location, defect size, and experience of the treating surgeon.ResultsOpen evaluation of all cartilage defects showed a mean size of 4.54 ± 2.11 cm2, whereas arthroscopic determination resulted in a significantly larger mean defect size of 5.69 ± 1.81 cm2 (P < .001, r = 0.757). This observation was found in all subgroups concerning defect location and experience of the treating surgeon (P < .001). Overestimation was pronounced among inexperienced surgeons (all P < .01) and in smaller defects (P < .01). Concerning grading of the defect according to the ICRS classification, there was a consensus in 80.9% of the cases when arthroscopic grading was compared with open grading. No differences were found based on defect location or experience of the treating surgeon (P > .05).ConclusionsAlthough a high correlation was found between arthroscopic and open evaluation of the cartilage defect size, there is a significant overestimation of the cartilage defect size during arthroscopy. This observation is independent of defect location. Smaller defects and inexperienced surgeons are factors that make an overestimation of defect size more likely. Arthroscopic detection and estimation of the full-thickness cartilage defects according to the ICRS classification seem reliable.Level of EvidenceLevel IV, therapeutic case series.