|Year : 2015 | Volume
| Issue : 1 | Page : 155-156
Painful knee: Is the anterior cruciate ligament torn?
Chandrashekhar A Sohoni
Department of Radiology, NM Medical, Pune, Maharashtra, India
|Date of Web Publication||13-Apr-2015|
Dr. Chandrashekhar A Sohoni
Department of Radiology, NM Medical, Pune, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Sohoni CA. Painful knee: Is the anterior cruciate ligament torn?. Arch Med Health Sci 2015;3:155-6
A 50-year-old man presented with right-knee pain after having suffered a twisting injury to the knee joint while walking 2 weeks ago. On examination, no obvious peri-articular swelling was noted. The range of motion was normal; however, there was pain on flexion. Except for the Lachmann's test which was equivocal, there were no other signs of instability. No tenderness was seen along medial joint line. Magnetic resonance imaging (MRI) revealed diffuse thickening of anterior cruciate ligament (ACL) with abnormal hyperintense signal and intervening normal hypointense fibres on T2 weighted (T2W) and proton density fat saturated (PDFS) sequences [Figure 1]. The ACL showed intermediate signal on T1 weighted (T1W) sequence. The alignment of the ligament was normal. This appearance of the ACL was reported to be due to mucoid degeneration rather than a tear. However, still suspecting a partial tear of ACL due to persistent pain and signal abnormality on MRI, a diagnostic arthroscopy was performed which conclusively ruled out ACL tear.
|Figure 1: The ACL shows diffuse thickening and abnormal hyperintense signal with intervening normal hypointense fi bres on (a) T2W and (b) PDFS sequences – the classic "Celery stalk" appearance. The ACL shows intermediate signal on (c) T1W sequence|
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The exact etiology of mucoid degeneration of ACL is unknown, although hypothesized possibilities include aging, and congenital or acquired entrapment of synovial tissue between ACL fibres.  The typical MRI appearance resembling a "Celery stalk" is due to deposition of glycosaminoglycans among collagen bundles.  ACL degeneration may present with posterior knee pain that is exacerbated by flexion, and/or painful limitation of movements.  In the absence of any other lesion, it is possible that the knee pain in our patient was due to mucoid degeneration of ACL. The injury was probably incidental.
Mucoid degeneration of ACL may be confused with a ligament tear on MRI, particularly when ACL injury is clinically suspected.  The history of antecedent trauma, equivocal Lachmann's test and persistent knee pain prompted diagnostic arthroscopy for ACL evaluation in our patient, despite the accurate pre-operative MRI diagnosis. This case reiterates the value of MRI in making a specific diagnosis in case of soft-tissue lesions of the knee.
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