How reliable is MRI to diagnose ACL (anterior cruciate ligament rupture)?

Question

at the end of January 2019, I had an accident while skiing and was diagnosed shortly after with ACL (Anterior cruciate ligament rupture). The diagnosis was confirmed by 4 different doctors who all are very experienced with MRI scans. All of them told me right away, by looking at the scans, that it is completely ruptured. 6,5 weeks later I underwent surgery and the doctor found my cruciate ligaments to be intact. He did the Lachman-test which turned out to be negative. A small part of my cruciate ligament was, in fact, loose and he removed it (I saw that in real time on the screen). He told me this happens very rarely and I should be really happy which I am.

But I am wondering what is going on. As far as I know, the cruciate ligament cannot grow back together. My symptoms after the accident aligned perfectly though with the diagnosis of being left with the posterior cruciate ligament only.

Can anybody provide some insightful input?

Answer 1

Nothing is more helpful than a comprehensive physical examination by an expert and the clinical course of the disease, for ruling out the ACL rupture. Evidence supports that

The accuracy of the clinical examination and MRI evaluation was equal for diagnosing meniscal tears and ACL ruptures

[reference]. Moreover,

the Lachman test has great efficacy in ruling out a diagnosis of ACL rupture because of the lowest negative likelihood ratios [reference]

Notice that, MRI is associated with higher false-positive rates, if performed suddenly after trauma or in patients with prior knee trauma. All mild soft injuries may show some signal contacting after trauma.