Arthroscopy: The Journal of Arthroscopic and Related Surgery 7(2):241-243 Published by Raven Press, Ltd. 0 1591 Arthroscopy Association of North America

Case Report

The Meniscal Ossicle: The Consequence Meniscal Avulsion

of a

Eugene E. Berg, M.D.

Summary: A case is presented in which an ossicle was evaluated acutely. Arthroscopy disclosed a tibia1 osteochondral fracture avulsed by the posterior attachment of the medial meniscus. Treatment was conservative with a good clinical result. Key Words: Meniscal ossicleMenisca1 avulsion. -

shift test result was negative, even with the thigh abducted and the leg externally rotated. X-ray films revealed an apparent fracture adjacent to the medial tibia1 eminence posteriorly (Fig. 1). Both cruciate ligaments were normal to arthroscopic visualization and to probing. The lateral meniscus was intact. The posterior horn of the medial meniscus was attached to a tibia1 osteochondral avulsion fracture. A small peripheral tear extended into the posterior meniscus and was considered stable. Neither the meniscus nor its attached tibial fragment could be displaced by nerve-hook manipulation. The osteochondral tibia1 plateau avulsion fracture/meniscus complex was easily reduced when valgus stress was relaxed and the knee was placed in slight flexion (Fig. 2). Thus, the patient was treated in a flexed knee immobilizer, and was non-weight-bearing for 3 weeks. After 3 additional weeks of progressive weight-bearing, the immobilizer was discontinued. Two-and-a-half months after injury, the patient resumed working. A follow-up telephone communication disclosed no subsequent locking, giving way, knee pain, or recurrent swelling.

Meniscal ossicles are reported to be rare in humans. These ossified structures embedded in the meniscus are easily distinguished from degenerative meniscal calcification associated with calcium pyrophosphate deposition disease (l), but may be confused with a loose body (2-5). Meniscal ossicles are usually unilateral and localized to the posterior horn of the medial meniscus (2-6). Theories of etiology include metaplastic ossification (l), traumatic avulsion (2,7), or that the ossicle represents a normative sesamoid bone (35).

CASE REPORT A 27-year-old tree surgeon fell 10 ft while descending from a tree. A valgus injury to both the right knee and ankle was sustained. Physical examination disclosed an effusion that yielded 60 ml of blood. The knee was tender over the medial joint line and was stable to valgus stress in 0 and 25” of knee flexion. The Lachman test was slightly increased when compared with the unaffected side but had a firm endpoint. With the patient under general anesthesia, the asymmetry in the Lachman maneuver was again appreciated; however, the pivot

DISCUSSION

From the Department of Orthopaedic Surgery, University of South Carolina School of Medicine, Columbia, South Carolina, U.S.A. Address correspondence and reprint requests to Dr. E. E. Berg, Department of Orthopaedic Surgery, University of South

Published reports of meniscal ossicles suggest that they are a rare condition. Their origin and natural history are uncertain. In rodents they are commonly found in the anterior horn (2,4,7).

Carolina School of Medicine, Two Richland Medical Park, Suite 404, Columbia, SC 29203, U.S.A.

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E. E. BERG

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FIG. 1. Anteroposterior x-ray film of the right knee depicts a small fleck of bone (arrow) adjacent to the medial tibia1 eminence.

The anatomy of the medial meniscal bony attachment has been poorly defined. The medial meniscus is the more stable meniscus and exhibits half as much anterior-posterior motion as the lateral meniscus does over the full arc of knee flexion (8,9). The lateral meniscus, which is more mobile, has a well-delineated posterior ligamentous attachment via the meniscofemoral ligaments of Wrisberg and/ or Humphry. The medial meniscus has no such meniscofemoral ligamentous counterpart.

The meniscofemoral and meniscotibial capsular ligaments are loose structures that form perimeniscal recesses and accommodate torsion, flexion, and hoop stresses (8,9). The semimembranosus tendon sends one of its five slips to insert on the posterior medial meniscus (8). Magnetic resonance imaging has disclosed avulsion fracture of the semimembranosus tendon in two older patients who both had associated anterior cruciate ligament injuries (IO). The semimembranosus lesion is more anteriorly located than described in this report. The fact that the posterior horn of the medial meniscus avulsed an osteochondral fragment of tibia1 plateau indirectly supports the notion that there is a significant posterior medial meniscotibial attachment. Recent reports of experimental meniscal transplantation work also suggest that anterior and posterior meniscal horns may have bony tibia1 insertion (11,12). Because the fracture could be reduced under arthroscopic visualization, it was elected to treat this lesion nonoperatively. The natural history of this fracture is unclear. Some reports state that meniscal ossicles are or become symptomatic and require surgical excision (2,4,5,7). Glass et al. noted the ossicle to be an incidental, asymptomatic finding that could be mistaken for a loose body (3). Preliminary short-term follow-up in this case has suggested that the lesion became asymptomatic. CONCLUSION A case is described in which a small intraarticular fracture adjacent to the tibia1 eminence was caused by posterior horn, medial meniscotibial avulsion. This report speculates that this traumatic lesion is the etiology of meniscal ossicles and suggests that the posterior horn of the medial meniscus may have a more complex ligamentous relationship to the tibia than has been appreciated. REFERENCES 1. Weaver JB. Calcification and ossification

of the menisci. J

Bone Joint Surg [Am] 1942;24:87%32.

FIG. 2. Arthroscopic view of the posterior horn, medial meniscus with attached tibial bony avulsion fracture. The MFC (medial femoral condyle) is above, and the nerve probe (arrows) is on the meniscus with hemorrhagic fronds hanging from the avulsed tibial osteochondral fracture. The tibia1 eminence (TE) is seen below, left.

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2. Conforty B, Lotem M. Ossicles in human menisci: report of two cases. Clin Orthop 1979;144:272-5. 3. Glass RS, Barnes WB, Kells DU, Thomas S, Campbell C. Ossicles of knee menisci. Reports of seven cases. Clin Orthop 1975;111:163-71. 4. Mariani PP. Puddu G. Meniscal ossicle. A case report. Am J Sports Med 1981;9:392-3.

5. Rosen IE. Unusual intrameniscal lunulae. Three case reports. J Bone Joint Surg [Am] 1958;40:925-8. 6. Richmond J, Samo RC. Post trauma intracapsular bone frag-

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ments: association with men&al tears. AJR 1988;150:15960. Symeonides PP, Ioannides G. Ossicles of knee menisci. Report of three cases. JBoneJoinr Surg [Am] 1972;54:1288-92. Brantiaan OC. Voshell AF. The mechanics of the ligaments and menisci of the knee joint. J Bone Joint S&g [Am] 1941;23:44-66. Galeazzi R. Clinical and experimental study of lesions of the semilunar cartilages of the knee joint. J Bone Joint Surg [Am] 1927;9:515-23. Yao L, Lee JK. Avulsion of the posteromedial tibial plateau

by the semimembranosus tendon: diagnosis with MR imaging. Radiology 1989; 172:513-4. 11. Duval P, Yahia H, Zukor D, Rubins I, Drouin G. Effects of irradiation on the mechanical properties of knee meniscal grafts. In: Transactions of the 36th Annual Meeting, Orthopaedic Research Society. 19!90;15:218. 12. Jackson DW, McDevitt CA, Atwell EA. Arnoczky

SP, Simon TM. Meniscal transplantation using fresh and cryopreserved allografts-an experimental study in goats. Trunsaclions of the 36th Annual Meeting, Orthopaedic Research Sociery.

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Arthroscopy. Vol. 7, No. 2, 1991

The meniscal ossicle: the consequence of a meniscal avulsion.

A case is presented in which an ossicle was evaluated acutely. Arthroscopy disclosed a tibial osteochondral fracture avulsed by the posterior attachme...
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