A 29-year-old man presents with left knee pain after a bicycle fall 10 days prior, with occasional locking feeling and knee instability.
Radiographs showed a millimetric ossification projected over the posteromedial articular space of the knee.
Magnetic resonance imaging (MRI) revealed an intrasubstance ossification of the posterior root of the medial meniscus, as well as a tear of the posterior root. Moreover, there was a complete rupture of the anterior cruciate ligament and bone contusions on both posterior tibial plateaux due to the trauma mechanism.
BACKGROUND
A meniscal ossicle (ossification within the substance of the meniscus) is a rare entity, with a reported incidence of 0.15% in a study of 1287 consecutive MRI examinations [1].
Histologically it is composed of trabecular and lamellar bone containing bone marrow, surrounded by cartilage within the meniscus [2].
By far the most frequent location is the posterior root or horn of the medial meniscus. This is presumably due to two factors, the first being the strong posteromedial tibial attachment of the medial meniscus rendering it less mobile and more vulnerable to lesions, and the second being the abundant vascularisation of this area which facilitates heterotopic ossification of injured meniscal tissue.
Several pathophysiologic hypotheses have been proposed. Metaplasia and heterotopic ossification secondary to trauma (single or repetitive microtrauma) is currently favoured [3].
CLINICAL PERSPECTIVE
A meniscal ossicle can be an incidental asymptomatic finding, but is usually associated with intermittent pain and can be accompanied by an effusion. Mechanical locking (as in cases of intraarticular loose body) is uncommon but may occur, and radiographic confusion with a loose body is frequent.
There is a high likelihood of associated meniscal tears near the ossicle, particularly in the posterior root [3]. Detection and management of associated meniscal injuries, as well as differentiation from a loose body that requires removal, is crucial to prevent early osteoarthritis and cartilage lesions [2-4].
In our patient the locking could have been caused by the ossicle or the meniscal root tear.
IMAGING PERSPECTIVE
MRI is the modality of choice for conclusively diagnosing meniscal ossicles and depicting concurrent intraarticular pathology that may influence management.
The key finding is a well-defined structure with signal intensity identical to normal bone marrow within the substance of the meniscus.
OUTCOME
Asymptomatic patients without associated injuries are managed conservatively. Non-operative treatment is also recommended for non-surgical candidates and those with advanced osteoarthrosis [5].
Arthroscopic removal and meniscal repair is the treatment of choice, and was proposed to our patient along with anterior cruciate ligament reconstruction.
TAKE-HOME MESSAGES / TEACHING POINTS
A meniscal ossicle is commonly confused with a loose intraarticular body. MRI can conclusively make the diagnosis and depict associated lesions, avoiding unnecessary arthroscopy exploration in asymptomatic patients.
The presence of a meniscal ossicle should prompt the radiologist to perform a careful meniscal tear search, especially near the posterior root.
Written informed patient consent for publication has been obtained.
[1] Schnarkowski P, Tirman PFJ, Fuchigami KD, Crues JV, Butler MG, Genant HK (1995) Meniscal ossicle: radiographic and MR imaging findings. Radiology 196:47-50 (PMID: 7784586)
[2] Prabhudesai V, Richards PJ (2003) Radiological appearance as a meniscal ossicle develops: a case report and review of literature. Injury 34:378–38 (PMID: 12719169)
[3] Mohankumar R, Palisch A, Khan W, White LM, Morrison WB (2014) Meniscal ossicle: posttraumatic origin and association with posterior meniscal root tears. AJR 203:1040–1046 (PMID: 25341143)
[4] Rohilla S, Yadav RK, Singh R, Devgan A, Dhaulakhandi DB (2009) Meniscal ossicle. J Orthopaed Traumatol 10:143–145 (PMID: 19590936)
[5] Cinque ME, Chahla J, Moatshe G, Faucett SC, Krych AJ, LaPradeet RF (2018) Meniscal root tears: a silent epidemic. Br J Sports Med 52(13):872-876 (PMID: 29574455)
| URL: | https://www.eurorad.org/case/16545 |
| DOI: | 10.35100/eurorad/case.16545 |
| ISSN: | 1563-4086 |
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