Meniscal damage to the knee

An update by Sam Oussedik and Fares Haddad

The menisci are two crescent-shaped pieces of cartilage present in both knees, one in the medial tibiofemoral compartment – the medial meniscus – and the other in the lateral tibiofemoral compartment – the lateral meniscus. Together these structures act in four different ways to improve knee function:

*They transmit load across the joint. In extension, this is up to 50% of axial load; in flexion it increases to 90%

*They improve joint congruency or stability

*They increase the contact surface area of tibia and femur, helping to spread axial load across a greater area of articular cartilage

*They help to circulate synovial fluid around the knee(1).

To carry out these functions, the menisci have a complex structure. They are composed of a specialised type of fibrocartilage the high water content of which allows them to resist the forces they must withstand. They have a limited healing potential. Their blood supply only reaches the outermost 10% to 30% of each meniscus; within this region tears may heal. More centrally placed tears have very little chance of healing. Meniscal injuries are relatively common, with the medial meniscus most often injured. The posterior part of the medial meniscus also supplements the anterior cruciate ligament (ACL) in restraining anterior tibial translation, helping to stop the tibia from sliding forwards against the femur. This puts the meniscus at risk from injury in any trauma that disrupts the anterior cruciate ligament. It also means that anterior cruciate ligament deficiency can lead to tears in the meniscus. More commonly, the menisci are damaged from a twisting injury to the knee, with the foot usually anchored on the ground. These traumatic injuries should be differentiated from degenerative tears, which occur in an older age group, although sometimes in patients as young as their late 20s, often in association with early degenerative changes in the knee.

Typically a client with a traumatic meniscal tear will have a history of recent trauma, swelling of the knee, and a restricted range of motion. If there is a ‘bucket-handle’ tear, where a mobile segment of torn meniscus can lodge in the joint, the client may feel frequent locking of the knee, or the inability to fully extend. More frequently symptoms may simply be of discomfort over one side of the knee, particularly in deep flexion. The client may not be able to kneel or squat, and may not ‘trust’ that knee. Joint line tenderness is a common feature and restricted range of motion may be the result of effusion or mechanical block by a mobile segment of meniscus. Pain is elicited on deep squatting.

McMurray’s test is diagnostic: the knee is placed into full flexion and the tibia is internally and externally rotated as the knee is brought into extension. This test is positive if pain is elicited in the presence of a palpable or audible clicking.

Meniscal injuries can be diagnosed on magnetic resonance imaging (MRI), but this is not necessary for the isolated injury, although it may yield valuable information if a more complex injury is suspected. Arthroscopy is also diagnostic, with direct visualisation of the injury. However, clinical diagnosis is preferable prior to any procedure being undertaken.

Meniscal Tear Management

Non-operative Meniscal Tear

While a relatively asymptomatic client with low functional demands may do very well with non-operative management, where the tear is symptomatic or the patient has a high functional demand, an orthopaedic surgeon should assess the case for a possible operation.

Symptomatic tears may result in further damage to the articular surfaces of the femur and tibia. The added stress on the torn meniscus associated with greater sporting activity may also result in degeneration of the torn segment, such that meniscal repair may not be possible. Early assessment is therefore required, before secondary damage is caused.

Non-operative management is usually reserved for those patients with few or no symptoms who are able to carry out a full range of physical activities. This group is usually made up of older patients with degenerative tears in the presence of significant degenerate changes in the knee. Physiotherapy helps to regain range of motion and strengthen muscle groups. This is also an important part of postoperative management.

If there is doubt and the patient has a combination, for example, of patellofemoral pain and a borderline meniscal pathology, clinically and on MRI, non-operative treatment of the patellofemoral symptoms and knee Meniscal damage to the knee An update by Sam Oussedik and Fares Haddad control may sometimes be sufficient to keep symptoms at bay. Careful review is necessary.

Operative Meniscal Tear

Patients with recurrent mechanical symptoms and/or significant pain require operative management. Nowadays this means an arthroscopy. Depending on the location of the tear, several options are available. Partial meniscectomy is indicated for those tears which are degenerate, or outside the vascularised zone. During this procedure, specialised instruments are introduced through an arthroscopy portal to remove the torn piece of cartilage, leaving a stable rim of tissue behind. The least possible amount of tissue is removed, so as to leave behind the largest amount of healthy, stable tissue to continue protecting the articular cartilage from increased stress.

In those tears that lie within the vascularised zone, repair can be attempted by fixing the damaged part to the meniscus behind it and the joint capsule. Tears repaired at the time of cruciate ligament reconstruction have a better prognosis. We believe this is related to the fact that these are traumatic tears in healthy menisci with good healing potential rather than degenerate ‘predetermined’ tears, which have poor healing potential.

Results for meniscal repair are very good, especially when carried out during ACL reconstruction. Boyd and Myers(2) estimate a re-tear rate of less than 10%. The long-term effects on articular cartilage are not yet well understood, but we believe that meniscal preservation offers the best hope of avoiding further damage. In functional terms, most patients will recover all but the final(3) degrees of flexion, which is inconsequential for most sporting needs. It is important that the patient is pre-warned about this likelihood.

Shelbourne et al(4) looked at rehabilitation following isolated meniscal repair. They found that an accelerated programme, allowing a full range of motion and weight bearing as tolerated, had similar results in terms of meniscal healing to a more conventional restrictive regime.

Meniscal Tears: New developments

While peripheral meniscal tears may be amenable to repair, those within the avascular zone have traditionally had to be cut out. Tissue engineering techniques are being developed to address this problem. One possible solution is to deliver cells to a tear together with the specific growth factors necessary for repair to take place. So far animal work has focused on discovering which materials are needed to effect a repair. This type of approach may well yield clinically significantresults in the not too distant future. Meniscal transplant is an option for the treatment of severe meniscal damage.

Indications for this form of treatment vary among researchers. Some believe that persistent pain in a compartment that has lost its meniscus is good enough to attempt implantation; others argue some degree of chondral damage is a prerequisite. Preserved meniscal tissue from cadavers is used. As yet results for this are mixed(5); associated problems include: the availability of meniscal tissue for graft, its preservation, possible transfer of disease, shaping of the graft and potential immunological reactions to it. In trying to overcome some of these concerns, attention has turned to alternative sources of graft material. One such alternative is the use of bovine-derived collagen. However, in order for tissue ingrowth to occur, a rim of the patient’s own meniscus must be present. Again, results for this technique are rather poor(3).

The purpose of all of these procedures should be to prevent chondral damage while restoring knee function. As yet this has proved to be a difficult target to attain. No research published to date shows such results. This has led some to believe that the procedure itself may be to blame for some of the chondral damage seen. Work is therefore focusing on more minimally invasive techniques to implant material.

References

1. Alford JW, Cole BJ ‘Cartilage restoration part I: basic science, historical perspective, patient evaluation, and treatment options’ Am J Sports Med2005 Feb; 33(2):295-306

2.Boyd KT, Myers PT ‘Meniscus preservation; rationale, repair techniques and results’ The Knee2003; 10:1-11

3. Stone KR, Steadman JR, et al ‘Regeneration of meniscal cartilage with use of a collagen scaffold. Analysis of preliminary data’ J Bone Joint Surg (Am)1997; 79:1770-7

4. Shelbourne KD, Patel DV, et al ‘Rehabilitation after meniscal repair’ Clin Sports Med’ 1996 Jul; 15(3):595-612

5. Rijk PC ‘Meniscal allograft transplantation – part I: background, results, graft selection and preservation, and surgical considerations’ Arthroscopy2004 Sep; 20(7):728-43