What is an ossicle in the knee?

What is an Ossicle in the Knee?

An ossicle in the knee is a small bone or bone fragment that can occur either as an accessory bone (developmental variant), a sequela of prior injury (such as avulsion fractures or chronic stress), or as an unusual finding within meniscal tissue.

Types and Origins of Knee Ossicles

Developmental/Traumatic Ossicles

• Osgood-Schlatter-related ossicles are the most common type, appearing as bone fragments near or at the tibial tuberosity, representing either sequelae of apophysitis or normal variants in ossification 1, 2.
• These ossicles typically form after repetitive traction injury during adolescence when the patellar tendon insertion becomes inflamed, leading to bone fragmentation that may persist into adulthood 1.
• Avulsion fractures can create small osseous fragments, such as those seen along the medial patellar margin following patellar dislocation, or Segond fractures from lateral capsular avulsion 3.
• Ossicles may occasionally be separated from the anterior tibia by a prolongation of the knee joint space, representing either post-traumatic or developmental variants 2.

Meniscal Ossicles

• Meniscal ossicles are rare findings consisting of cortical or cancellous bone tissue with central viable marrow surrounded by meniscal cartilage 4.
• These typically occur within the substance of the meniscus (most commonly the medial meniscus posterior horn) and present with symptoms of catching, giving way, or intermittent discomfort 4.
• They must be distinguished from intra-articular loose bodies on imaging and clinical evaluation 4, 5.

Clinical Significance

Symptomatic Presentations

• Chronic pain is the primary concern, particularly in Osgood-Schlatter disease where persistent ossicles can cause pain with kneeling or physical activity despite skeletal maturity 1.
• Meniscal ossicles may cause mechanical symptoms including catching, locking, or giving way, and can be associated with degenerative changes in the adjacent articular cartilage 4.
• Large or intra-articular ossicles associated with Osgood-Schlatter disease, though rare, can protrude into the knee joint and cause significant symptoms 6.

Asymptomatic Findings

• Many ossicles, particularly those related to old Osgood-Schlatter disease, remain asymptomatic and represent incidental radiographic findings 2.
• The presence of an ossicle does not automatically indicate it is the pain source; clinical correlation is essential 3.

Diagnostic Approach

Initial Imaging

• Plain radiographs are the appropriate first-line imaging study to identify ossicles, assess their location, and evaluate for associated findings 3.
• Small osseous fragments along the medial patellar margin on axial knee radiographs suggest prior patellar dislocation 3.

Advanced Imaging When Indicated

• MRI without IV contrast is the preferred next study when radiographs show an ossicle but the clinical picture requires further characterization of associated soft tissue injury 3.
• MRI can assess the integrity of ligaments (such as the medial patellofemoral ligament), define cartilage injury extent, identify loose bodies, and evaluate conditions like Osgood-Schlatter or Sinding-Larsen-Johansson syndrome 3.
• CT without IV contrast may be useful to confirm prior osseous injury or evaluate patellofemoral anatomy in specific clinical contexts 3.

Management Considerations

Conservative Management

• Most ossicles, particularly those from Osgood-Schlatter disease, respond to activity modification and symptom management 1.
• The primary goal is reduction of pain and swelling, with physical activity limitation until symptoms resolve 1.

Surgical Indications

• Persistent pain with kneeling due to an ossicle that does not respond to conservative measures (typically several months of treatment) is the indication for surgical excision 1.
• Surgical treatment involves removal of the ossicle, surrounding bursa, and any bony prominence 1.
• Meniscal ossicles causing mechanical symptoms may require arthroscopic excision, which can range from partial to subtotal meniscectomy depending on the extent of involvement 4, 6.

Common Pitfalls

• Do not assume all ossicles are symptomatic—correlation with clinical examination and patient symptoms is mandatory before attributing pain to an incidental ossicle 3, 2.
• Distinguish meniscal ossicles from loose bodies—meniscal ossicles are embedded within meniscal tissue, while loose bodies are free-floating intra-articular fragments 4.
• Evaluate for associated pathology—ossicles may be markers of prior significant injury (such as ACL tears with avulsion fragments) that require comprehensive assessment 3.