8.14 Meniscal injury and management

In the past, scant regard was paid to these collagenous structures, and almost any patient with a symptomatic knee, whatever their age, would have them totally removed through an arthrotomy with a Smillie knife.

Over time a more conservative surgical approach has evolved as surgeons have realized that menisci actually have an important role in knee function and that meniscectomized knees inevitably progress to accelerated osteoarthrosis. Arthroscopy has revolutionized the management of meniscal injury, allowing minimal resection or repair, with minimal morbidity and an extremely low complication rate.

The menisci are semilunar in plan view, wedge-shaped in cross-section, and consist predominately of type 1 collagen, although types II, III, V, and VI are present in small amounts. Type II fibres are more prominent on the surface layers. They are attached circumferentially to the capsule and at either end to the tibial surface by strong ligaments (Figure 8.14.1). In addition, the posterior horn of the lateral meniscus has two ligaments (Wrisberg and Humphrey) which pass either side of the posterior cruciate ligament to the medial femoral condyle.

The predominant orientation of collagen bundles is circumferential, with a small number of radially orientated ‘tie’ fibres. When load is applied, the orientation of the fibres, with the meniscus fixed at either end, allows the generation of ‘hoop stresses’ and this in turn absorbs load across the joint. In the medial compartment the meniscus absorbs 40% of the load across the tibiofemoral joint and the lateral compartment 60% due to its higher relative surface area.

This becomes even more important when the anatomy of the tibial plateau on either side of the joint is taken into account. In the medial compartment the medial tibial plateau is concave and in the lateral compartment, convex. The consequences of loss of a meniscus are therefore much more severe on the lateral side of the joint, where without the meniscus there is almost point contact between the articular surfaces. The high contact stresses that this creates can lead to the rapid development of wear.

‘Dynamic’ magnetic resonance imaging (MRI) studies have shown that the medial meniscus is static during flexion and extension making the posterior horn vulnerable to tearing in extremes of flexion. The lateral meniscus, however, is extremely mobile during flexion and extension, virtually coming off the back of the lateral tibial plateau during full flexion.

The only common developmental variation is the discoid meniscus which almost exclusively occurs on the lateral side (Figure 8.14.2) and has a prevalence of approximately 5%. This can produce symptoms at a very young age.

In the younger patient the typical history of injury is of a weight-bearing, twisting injury. Pain is localized to the affected joint line. Swelling usually occurs slowly overnight and often settles in a few days.

In non-sporting situations, patients with occupations that involve working with the knees in full flexion such as electricians, plumbers, etc., are prone to tearing the posterior horn of the medial meniscus.

In the more chronic situation, there is recurrent pain localized to the affected joint line and intermittent swelling.

Chronic meniscal injuries usually produce a degree of quadriceps wasting. There may be subtle losses of either terminal extension or flexion. It is important to look for a small effusion as this may confirm intra-articular pathology. There may be joint line tenderness and a positive McMurray’s test.

Plain x-rays (anteroposterior weight bearing, intercondylar and lateral) are useful, where early degenerative change may be identified and will exclude a number of other pathologies. Degenerative tears of the medial meniscus can produce narrowing of the posteromedial joint space on the intercondylar view.

MRI is only indicated where the diagnosis is in doubt after history, examination, and plain x-rays. MRI is neither 100% sensitive nor specific for either medial or lateral meniscal pathology and may completely miss a reduced peripheral bucket handle tear. It also has a false positive rate, especially in patients over the age of 40 where there is almost always a degenerate signal in the posterior horn of the medial meniscus which is difficult to distinguish from a degenerate tear.

MRI diagnosis should always be taken in conjunction with history and examination before subjecting the patient to surgery.

Early compartment wear and small chondral lesions of the femoral or tibial surfaces can produce symptoms very similar to that of a meniscal tear and these may not be picked up on MRI scanning.

On the medial side of the joint, a medial plica and injury to the deep part of the medial collateral ligament (Figure 8.14.3) may also produce a clinical picture that is difficult to differentiate from a meniscal tear and these are also unlikely to be diagnosed on MRI.

Flap tears (Figure 8.14.4) tend to produce intermittent symptoms, with a feeling of catching and clicking. If in the middle third of the meniscus the patient may be able to feel something ‘pop out’ at the joint line. (If the lump always appears at the same site it will be a flap tear and not a loose body.)

Occasionally the flap will tuck itself underneath the rim of the meniscus—these tears often produce a fairly constant and quite significant pain. At arthroscopy there is a rounded appearance to the edge of the meniscus and the offending fragment can be retrieved into the joint with an arthroscopic probe, before resection.

These tears may present with a locked knee or produce intermittent symptoms of true locking. A locked knee due to a torn meniscus presents with an inability to fully extend the knee with pain localized to the site of the pathology. Locking in full extension tends to be produced by patellofemoral pathology.

In the acute situation peripheral bucket handle tears may produce a haemarthrosis.

Once locked, the knee may spontaneously ‘clunk’ back into extension or, as patients learn how to unlock the knee, by hyperflexing and rotating the joint.

Horizontal cleavage tears (Figure 8.14.5) can act like flap valves allowing synovial fluid to be forced out of the joint during knee flexion and then not allowing it to return. This produces a meniscal cyst, classically seen on the lateral side. Meniscal cysts are not uncommon on the medial side but are less visible because of the broad medial collateral ligament.

Symptoms are of a chronic aching pain localized over the cyst, often worse at night. On the lateral side, a bony hard cyst may be found, localized to the joint line and, most pronounced at 45 degrees of flexion.

Almost invariably on the lateral side, there is a small radial tear at the junction of middle and anterior thirds with a horizontal cleavage behind it, leading into the cyst.

Degenerate type tears are usually complex with a combination of flap and horizontal cleavage patterns. Sometimes initial inspection may appear relatively normal but there may be an inferior partial thickness tear which then leads in to a horizontal cleavage component.

On the medial side with degenerate posterior horn tears, there may be limitation of flexion and difficulty with squatting. Patients often also complain of pain at night when sleeping on their side with the knees placed together.

There are some tears that do not require treatment. Partial thickness or short (less than 5mm) full thickness split tears that are stable and small radial tears can safely be left, particularly if they are asymptomatic.

The majority of symptomatic meniscal tears are treated by arthroscopic resection of the damaged portion of the meniscus leaving as much normal tissue as possible. This results in a speedy resolution of symptoms with minimal morbidity.

Portal placement is critical in making resection technically easier. For a lateral meniscal tear an anterolateral portal for the arthroscope and a medial portal in the middle of the ‘soft spot’, with the knee in the ‘figure 4’ position, for the instruments, allows ready access to most of the meniscus. Slightly extending the knee makes surgery to the anterior horn easier.

On the medial side, an anterolateral portal and a low medial portal just over the anterior horn allows access to the posteromedial aspect of the joint. This is aided by a side post at mid-thigh and a strong assistant (or a leg holder) to open out the joint which can sometimes be very tight. Surgery to the anterior third may be aided by swapping the arthroscope to the medial portal and arthroscopic tools to the lateral.

A variety of sharp specialist tools with upbiters, sidebiters, and arthroscopic shavers are essential to provide speedy, low-morbidity surgery, without damage to the surrounding articular cartilage.

In degenerate tears of the posterior horn of the medial meniscus, where there is virtually always a horizontal cleavage component, it is important to remove the inferior leaf of the horizontal cleavage to prevent recurrence of symptoms.

In the absence of associated pathology, recovery to full activity takes on average 4–6 weeks on the medial and 6–8 weeks on the lateral side following resection of a meniscal tear.

It was King who first observed that menisci have a limited and peripheral blood supply and that meniscal tears could heal, but only when they involved the peripheral third of the meniscus. This work was expanded by Arnoszky and Warren and their work led to the development of a variety of techniques for repairing appropriate meniscal tears rather than just excising them.

The current techniques of repair are either inside–outside (passing suture needles through the meniscus and out through a separate lateral or medial incision) if the tear involves the anterior two-thirds of the meniscus, or inside–inside with a ‘stapling’ device if the tear involves the posterior horn. Devices available include bioabsorbable darts, arrows, and screws as well as devices that use preknotted sutures. It is important to mix superior and inferior surface sutures to prevent the meniscus rucking up.

In an intact knee, a bucket handle tear involving the periphery of the meniscus with bleeding on both sides of the repair (‘red on red’), healing rates are in the region of 66% (Figure 8.14.6).

Rates of healing decrease if the tear is more than 4 weeks old, the peripheral rim width is greater than 4mm, or the patient is over 40 years of age. Rates of healing are better if the repair is done in conjunction with anterior cruciate ligament reconstruction.

Rehabilitation after repair is controversial with a range of protocols recommended from non-weight bearing and restricted range of motion, to full weight bearing with no restriction of range of movement or limitation of activity. Early full weight bearing and motion do not seem to be detrimental to healing rates, although limiting knee flexion to 90 degrees for 6 weeks and only returning to sport at 12 weeks seems a sensible approach.

As the consequences of this common injury have become recognized, the challenge has been to find a solution that will prevent premature degenerative change occurring, lessen patients’ symptoms (predominately pain), and improve function. This has largely been on two fronts.

Clinical trials of the use of collagen scaffolds sutured into the meniscal defect with the aim of allowing healing to occur were carried out in the early 1990s. Despite promising initial and even medium-term results, this technique has not gained widespread acceptance.

Future developments may include implantation of patients’ fibrocytes into the synthetic collagen matrix, the use of growth factors, and tissue manipulation with gene therapy.

Another key development has been the development of meniscal transplantation, where a suitably sized meniscal allograft is either sutured to a meniscal rim, or is transplanted with a bone bock and ligaments at either end and fixed into a suitably prepared bed.

The experience in both Europe and the USA has been encouraging with satisfactory early to medium-term results in reducing patient symptoms. Long-term results still remain uncertain, however, as does the best technique for preservation, sizing, and implantation.