Meniscus injuries

Introduction

The menisci are important structures in the knee that function as shock absorbers and bushings to improve the congruency of the knee (Figure 1). Previously it was common to excise them when they were torn. More recently however techniques have been developed o repair them arthroscopically illustrating the recognition it now enjoys as an important structure of the knee.

Anatomy

The menisci are C-shaped structures sitting on the tibial plateau. They are attached to the capsule on their outside and to the tibiain the front and back (Figure 1). They are well supplied by a plexus of arteries, veins and nerves. The blood supply is richest at the edges (the red zone) and poor towards the centre (white zone). Consequently the periphery heals better than the centre.

Figure 1. The knee is surrounded by a plexus of vessels (red-artery, blue-vein, yellow nerves). Any one of these can get injured in the process of meniscal repairs (left panel). The menisci function as bushings or bumpers around the edges of the knee to improve shock absorbency and congruency (right, top). The blood supply to the knee is marked by an inner dis-vascular third (while zone, w), an outer vascular third (red zone, r) and the intervening red-white (rw) zone.

Evaluation

Clinical evaluation is the best indicator of a meniscal tear. Patients with meniscal tears usually have pain on the line of the joint. Some may have locking or the inability to straighten the knee in a springy way. Based on these symptoms alone an arthroscope may be warranted. Some patients may however need an MRI to be assured that an operation is necessary. This can be a double edged sword however as false negative scans (ie. the scans are read as normal when in fact there is a tear) are not infrequent. When in doubt the clinical evaluation takes precedence over the MRI (Figure 2).

Figure 2. The typical MRI views to evaluate a meniscal tear are the coronal (upper row) and saggittal sections. On the coronal sections one can readitly determine menisco-capsular (red zone tears). The saggittal sections show the anterior and posterior sections of the menisci as two triaangles or bow-tie.

Surgery

Meniscal tears are usually managed arthroscopically in this day. This involves the creation of two portals usually but sometimes in difficult locations addition portals may be necessary. Two types of repairs are described. In all-in repairs, the tear is visualised and secured with with some kind of suture anchor completely arthroscopically. In my practice this is feasible in ninety-five percent of the time. Very occasionally an inside out technique is performed where the sutures are deployed arthroscopically but tied in plain site on the outside. This runs the risk of snagging one of the sensory nerves described above. Injuring the nerve in this way can be painful but it is rarely necessary to have repeat surgery to undo the knots. When the tears are ragged or in the white zone (Figure 3a and b)they are best trimmed back to a normal contour of the meniscus. If however, they are in the red or red-white zone they can be repaired with good likelihood of healing (Figure 3c and d).

Figure 3. Depending on how the tears appear, different treatments are advocated. Raggedy tears (a) are best trimmed back to a stable edge. White zone tears are best trimmed back to a stable edge as they heal poorly if repaired due to poor blood supply. Red zone (d) and red-white tears should be repaired although the latter hav a lower healing rate.

Conclusions

Meniscal repairs are simple procedures that can be done expediently with minimal complications and good expectation of recovery. Post-operatively, patients should be appropriately rehabilitated but should expect to return to sport by 3 months.

Figure 4 (video). A video demonstrating the technique of medial meniscus tear repair using an "all in" technique.

Figure 5 (video). A video demonstrating the technique of medial meniscus tear repair in the anterior horn. This is a very rare occurrence in less than 5% of cases.