The knee joint contains two C-shaped pieces of cartilage called menisci, which act as cushions between the thigh bone (femur) and the shin bone (tibia). These structures help distribute forces across the knee evenly and contribute to joint stability. A discoid meniscus is an abnormally shaped meniscus, differing from the typical crescent or C-shape, which can affect the knee’s normal mechanics and function.
Understanding Lateral Discoid Meniscus
A lateral discoid meniscus is a meniscus on the outer side of the knee that is shaped more like a disc or oval than the usual crescent. This condition is a congenital anomaly, meaning it is present from birth due to abnormal meniscal development. The tissue often has a less organized fiber structure than a normal meniscus, making it more susceptible to tearing.
There are different types of discoid menisci, categorized by their shape and attachments. The complete type covers a significant portion of the shin bone, appearing largely disc-shaped. An incomplete discoid meniscus is wider and thicker than a normal meniscus but retains some crescent shape. The Wrisberg ligament type lacks a normal meniscal attachment, leading to increased instability. Their abnormal shape and thickness increase susceptibility to injury and tearing, even without trauma.
Recognizing the Signs
Many individuals with a discoid meniscus may not experience symptoms, with the knee adapting to the anatomical variation. However, symptoms often emerge when the discoid tissue wears down, tears, or becomes unstable. This can happen gradually due to regular use or be triggered by specific activities.
Common symptoms include:
Pain and tenderness, often on the outside of the knee, which can be sharp during high-intensity activities like running, jumping, pivoting, or twisting.
A popping or clicking sensation within the knee.
Stiffness or inflammation.
Limited range of motion.
A feeling that the knee is unstable or “giving out.”
A catching or locking sensation when attempting to fully bend or straighten the knee.
Diagnosis and Treatment Approaches
Diagnosis begins with a physical examination. A healthcare provider assesses the knee’s motion, strength, flexibility, and checks for tenderness or swelling. Specific tests, such as the McMurray test, may be performed, where the knee is bent and rotated to elicit clicking or pain, indicating meniscal issues.
Imaging techniques confirm the diagnosis. X-rays may show indirect signs, such as a widened joint space, but do not directly visualize the meniscus. Magnetic Resonance Imaging (MRI) is the definitive diagnostic tool, providing detailed images of the meniscus, its abnormal shape, and any associated tears. MRI can also help assess for peripheral detachment, which influences surgical planning.
Treatment varies depending on symptoms. Asymptomatic individuals typically do not require surgery and may be managed with periodic follow-up. For those with mild symptoms without a tear, non-surgical options include:
Rest
Applying ice to reduce swelling
Physical therapy to strengthen surrounding muscles and improve knee mechanics
Over-the-counter pain medications to manage discomfort
When a discoid meniscus causes persistent symptoms, especially with a tear, surgery is often recommended. Arthroscopic surgery is the standard procedure, involving small incisions through which a surgeon inserts a camera and specialized instruments to work within the knee joint. The goal is to preserve as much healthy meniscal tissue as possible while addressing the abnormal shape or tear; this often involves a partial meniscectomy, removing the abnormal or torn portion to reshape it into a more normal crescent-like form. If there is a peripheral detachment, a meniscal repair may be performed to stabilize the tissue. Total meniscectomy, removing the entire meniscus, is rarely performed due to the increased risk of future degenerative arthritis.
Recovery and Long-Term Outlook
Recovery following surgery typically involves a structured rehabilitation program. Physical therapy plays a significant role in restoring knee function and strength. Initially, the focus is on managing pain and swelling, followed by exercises to regain full range of motion.
The time frame for returning to normal activities varies, but many patients resume daily routines within a few weeks after arthroscopic reshaping. If a meniscal repair was performed, the recovery period might be longer, potentially requiring crutches for several weeks to limit weight-bearing and a hinged knee brace to protect the healing tissue. The long-term outlook depends on the extent of the original condition and the amount of meniscal tissue preserved during surgery. While many experience good outcomes, there is potential for future issues like osteoarthritis, particularly if a significant portion of the meniscus was removed. Continued follow-up with a provider can help monitor knee health and address any emerging concerns.