Meniscal ossicle with associated tear of the posterior root

Posted By Rita Cruz
Meniscal ossicle with associated tear of the posterior root

Gender, Age

Male, 29

Diagnosis

Meniscal ossicle with associated tear of the posterior root

History

A 29-year-old man presents with knee pain after a bicycle fall 10 days prior, with occasional locking feeling.

Findings

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 and bone contusions on both posterior tibial plateau.

Discussion

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 vascularization 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 important to prevent early osteoarthritis and cartilage lesions [2-4]. 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. TREATMENT 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. DIFFERENTIAL DIAGNOSIS Ossified intraarticular loose body Chondrocalcinosis Osteochondritis dissecans Avulsion fracture (posterior meniscal root, posterior cruciate ligament, semimembranosus tendon)

Pearls

-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.

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