The medial meniscus is the most easily injured of the menisci. Differences in the anatomical attachments of the medial meniscus compared to the lateral, mean that the medial meniscus becomes distorted during combined flexion and rotation movements in a manner not experienced on the lateral side.
Mechanism of Injury
Medial meniscal injuries are usually considered as either traumatic or degenerative. Whilst degenerate tears may present with a gradual history of increasing symptoms, traumatic injuries will usually occur suddenly as the knee is straightened and rotated from a bent position against resistance. This may occur as a single event during a sporting activity, or during a period of unaccustomed squatting such as laying flooring or playing with children. The most commonly injured area is the posterior horn.
Presentation
The exact presentation of a medial meniscal injury will vary according to the morphology of the tear sustained. Meniscal tears can be simply divided into vertical longitudinal, vertical radial, horizontal or complex. Symptoms that a meniscal tear may present with include:
Locking: The inability to straighten the affected knee to the same extent as the other side. Crucially, this is due to a mechanical block and whilst pain may be a feature, it is not the sole reason the knee is unable to extend. This presentation is caused by a bucket handle tear (an unstable vertical longitudinal tear) of the meniscus moving out of position creating the mechanical block to movement.
Pain: This is characteristically intermittent in nature and associated with activities such as stair climbing or running. Patients will often complain of an inability to squat fully. Patients will also exhibit tenderness along the joint line of the affected knee.
Swelling: In large peripheral tears, the injury may be associated with a post-traumatic effusion. More commonly, the irritation caused by the damaged meniscus causes recurrent effusions associated with exacerbation of the symptoms. Another form of swelling is the localized meniscal cyst caused by a complex meniscal tear acting as a flap valve to synovial fluid leading to the gradual formation of a parameniscal cyst that may be apparent clinically.
Clicking: Patients will often complain of, and sometimes be able to reproduce clicking. This is a palpable demonstration of the ongoing damage that is being caused by the displaced meniscal fragment. The description patients find most easy to understand is of a broken tooth within a gearbox jamming the machinery.
Investigation
Ultrasound
Very rarely indicated. MRI is the preferred investigation for this pathology.
X-ray
This is useful in the assessment of additional knee pathology, such as osteoarthritis that may impact on the prognostic information given to the patient.
C.T.
Not usually indicated as a first line investigation for the assessment of knee pain.
M.R.I.
This is the most useful investigation for cases where diagnostic doubt exists. It is highly sensitive and specific but it is important to remember that both false negatives and positives do occur.
Treatment
Conservative
In cases where a meniscal injury is associated with degenerative change within the knee, it may be difficult to ascertain which pathology is causing the majority of the symptoms. In such cases, an intervention may not relieve all symptoms or may lead to a perceived deterioration in knee function.
Arthroscopic excision
This is the most commonly performed treatment option and provides an excellent, long term symptom relief for the majority of patients. Although the majority of patients will experience improvement within a few weeks of surgery, some may require longer periods due to extensive quadriceps atrophy or other intra-articular pathology.
Arthroscopic repair
In certain specific cases, the meniscus may be able to be repaired. The limited application for meniscal repair is due to the poor blood supply found within the majority of the meniscus meaning only the outer 25% has viable healing potential. It is an important consideration for many patients that a meniscal repair will necessitate a much prolonged period of rehabilitation when compared to a simple excision.
