DIAGNOSIS FOCUS

DIAGNOSIS OF MENISCAL INJURY TO THE KNEE

By Dr Philip Batty, MRCGP, Dip.Sp.Med

The clinical diagnosis of injuries to the knee is a subject of considerable debate and research. The knee is the largest artic- ulating joint in the body and lacks inher- ent stability, such that it relies on soft tissues to provide stability. These soft tis- sues are subjected to large forces and are therefore prone to injury. In the sport sce- nario, the frequency of injury to the knee is considered to be in the range of 15 to 30% of all injuries but variations occur between sport and the sexes.

Ten to 15% of adults in the community report knee symptoms, which results in 3 to 5% of consultations with general prac- titioners (1) and subsequent referrals for imaging or specialist intervention. Careful history and examination can assist in determining whether there is a local mus- culoskeletal problem, especially a torn meniscus or ligamentous structure, and whether operative or non-operative inter- vention is required. A torn meniscus or ligament can cause significant pain and disability and, particularly in the athlete, expeditious repair may be necessary.

Musculoskeletal conditions are common and costly, but doctors receive little train- ing in musculoskeletal medicine (2), which can lead to sub-optimal treatment.

Anatomical review It is necessary to be aware of the anatomy of the knee in order to understand the injuries that can occur around the joint. The knee is a modified hinge joint with a large range of movement. The stability is provided by soft tissue structures such as the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), the medial collateral ligament (MCL) and the lateral collateral ligament (LCL), the menisci, the capsule and the muscles. The long lever arm forces acting across the knee, together with a lack of superficial ‘padding’ make the knee susceptible to injury.

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The cruciate ligaments The ligaments passively limit the movement of the joint. The ACL and PCL limit anterior and posterior motion of the tibia on the femur respectively. An ACL injury therefore leads to abnormal forward motion of the tibial plateau. This also leads to relative internal rotation of the tibia during the ter- minal part of extension. Symptomatically patients may describe a sensation that the knee is weak or giving way. This may occur when walking, but frequently is more apparent when twisting or turning. A lack of stability is also a frequent symptom because of the ACL’s role in proprioception.

An isolated tear of the PCL allows the tibial plateau to move posteriorly. There may be no associated symptoms although knee buckling can occur, especially when pivoting.

Facts about meniscal fibrocartilage ● Semi-lunar, crescenteric shaped struc- tures attached to tibial plateau ● Wedge-shaped with thin free edge on inner margin ● Surface flat inferiorly and concave superior surface ● Provides surface for transmission 50% of axial forces across knee (3) ● The menisci increase joint stability, assist nutrition, lubrication and shock absorption for articular cartilage (4)

The menisci The lateral meniscus is larger than the medial meniscus and less firmly adherent to the tibia, resulting in greater mobility. The medial meniscus is firmly attached to the joint capsule and medial collateral lig- ament, and is relatively immobile with greater force transmission and suscepti-