Abstract
Introduction Magnetic resonance imaging (MRI) is important in non-invasive evaluation of osseous and soft-tissue structures in the post-traumatic knee. However, it is sometimes impossible to determine if a focus of high signal intensity in the meniscus is confined to the substance, or extends to involve the joint surface. This is a critical differentiation as the latter represents menisci tears that can be found and treated arthroscopically, whereas the former represents degradation, intra-substance tears or normal variants not amenable to arthroscopic intervention.
The aim of this study was to investigate occurrence of altered signal intensity in the posterior horn of the medial meniscus and correlate with arthroscopic findings.
Materials and Methods 64 patients with suspected post-traumatic internal derangement of the knee who underwent MRI prior to arthroscopy were evaluated. All patients initially had MR imaging of the symptomatic knee using a standard protocol in a Siemens Symphony 1.5 Tesle Magnetom. MR images were then interpreted and reported by 2 radiologists experienced in MR and skeletal radiology. Meniscal tears were graded according to the system validated by Lotysch. A Grade 3 signal was considered unequivocal evidence of a meniscal tear. Equivocal tears (Grade 2/3 signal) were diagnosed if it was unclear if there was a small portion of normal intact meniscal tissue between a linear high signal in the meniscus and the articular surface abutting the meniscus.
Arthroscopy was subsequently performed by senior surgeons aware of the MR findings within 2 weeks of imaging.
Patients were re-assessed clinically and evaluated functionally at a mean follow-up time of 5 months. Radiographic, arthroscopic and clinical results were then correlated and evaluated.
Results There were 48 males and 16 females in the group, with a mean age of 28.2 years.. Tears of the posterior horn of the medial meniscus were reported on MRI unequivocally (Grade 3 signal) in 18 patients and equivocally (Grade 2/3 signal) in 10 patients. Subsequent arthroscopic correlation revealed 16 tears (89%) in the unequivocal group and only one tear (10%) in the equivocal group.
Discusion The finding that only 10% of patients with an equivocal tear in the posterior horn of the medial meniscus on MRI were subsequently found to have a tear on arthroscopy would suggest that early arthroscopic intervention is not warranted in these cases. We suggest that unless symptoms persist over the course of 3 to 6 months, or if a more compelling symptom complex develops, only then should arthroscopic evaluation be considered.
Conclusion Equivocal tears on MRI of the posterior horn of the medial meniscus have a low rate of arthroscopically detected tears and a trial of conservative therapy may be prudent in such cases.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
