Meniscal tears can be either traumatic or degenerative in nature. Meniscal tears are uncommon in persons under 10 years of age, but become increasingly common during and after adolescence. Degenerative tears can be found in as much as 60% of the population over age 65. The majority of these tears, however, are asymptomatic and occur in association with degenerative joint disease. The changing patterns of meniscal injury with chronological age most likely correlate with normal alterations in collagen fiber orientation with aging, as well as increasing intrasubstance degeneration.
The majority of meniscal tears affect the medial meniscus and tend to involve the posterior horn. Meniscal tears are either partial or full thickness and stable or unstable. An unstable tear is one where the entire tear or a portion thereof can be displaced into the joint space. There it may become trapped, causing pain by traction at the meniscocapsular junction. It may be responsible for symptoms of catching, locking, and effusion.
Meniscal injuries can be further classified based on their tear patterns (Figure 7). A vertical or longitudinal tear occurs in line with the circumferential fibers of the meniscus (Figure 8). If long enough, this tear is known as a bucket-handle tear. At arthroscopy, the bucket-handle tear may be seen as being attached anteriorly and posteriorly. Alternatively, it may be detached at either end or transected in the middle with unstable anterior and posterior flaps. A bucket-handle tear may displace into the intercondylar notch, where it may cause true locking of the knee joint.
Diagram of meniscal tear patterns: (A) Vertical or longitudinal (Bucket-handle), (B) Flap or Oblique, (C) Radial or Transverse, (D) Horizontal, (E) Complex degenerative. (Reprinted with permission.)
Hinkin DT. Arthroscopic partial meniscectomy. In: Balderston RA, Miller MD, eds. Operative Techniques in Orthopaedics. Philadelphia, Pa: WB Saunders; 1995:30, Figure 1.
Oblique tears are also known as flap or parrot beak tears and are perhaps the most common (Figure 9). These occur generally at the junction of the posterior and middle thirds.
Radial tears occur in a similar location. They extend from the inner free margin toward the periphery (Figure 10). If such a tear reaches the periphery, it transects the meniscus and renders the hoop stress-distributing capacities of the meniscus useless. Such a tear is the functional equivalent of a total meniscectomy.
Horizontal cleavage tears usually occur in older individuals. They extend from the inner free margin peripherally to the intrameniscal substance where myxoid degeneration may be present. These tears divide the meniscus into superior and inferior flaps, either of which may be unstable (Figure 11).
Complex degenerative tears occur in older patients. Osteoarthritic changes may be visible on plain radiographs, and chondromalacia of the articular surfaces is commonly encountered. The tears occur in multiple planes (Figure 12).
Treatment of meniscal tears includes simple observation, meniscectomy, and meniscal repair. Tears that are stable, < 1 cm in length, and that do not cause significant mechanical symptoms may be treated with simple observation. Those tears that are unstable and contribute to mechanical symptoms are treated with operative intervention. As early as 1936, King drew several important conclusions based on studies of dogs. He showed that a tear within the substance of the meniscus in all likelihood would never heal, but that a tear through the periphery of the meniscus may heal.
Total meniscectomy was advocated as recently as 1971 for meniscal pathology. With the advent of the arthroscope, as well as the recognition of the importance of the menisci to knee function and load transmission, the role of partial meniscectomy has become much more viable.
Patients with tears that are unstable, occur in the inner two thirds of the meniscal substance, and cause mechanical symptoms are candidates for partial meniscectomy. Metcalf[26,30] has outlined principles for partial meniscectomy, which include removing all unstable fragments, contouring the meniscus to a relatively smooth, stable rim, and avoiding obtaining a perfectly smooth rim. He advocated switching portals in order to adequately assess the meniscal contour and favored frequent use of a probe to provide tactile feedback. He also noted that the meniscocapsular junction should be protected. Both motorized and hand instruments should be used.
The indications for meniscal repair continue to evolve. Factors affecting success include tear age, location and pattern, age of the patient, as well as any associated injuries. Tears amenable to repair include unstable tears > 1 cm in length and occurring in the outer 20% to 30% toward the periphery, or in the so-called red-red zone.[31,32] Those tears occurring more toward the junction of the red-white zone may also heal, and the decision to repair should be made based on the clinician's judgment. Ideal candidates for repair are vertical, longitudinal tears occurring within 3 mm of the peripheral rim.
The knee should also be ACL-stable or stabilized. The prognosis for a meniscal repair decreases in the ACL-deficient knee, as the meniscus is required to play an increased role in restricting anterior posterior translation, thus placing the repaired tissue at risk. Success rates for meniscal repair average approximately 70% to 80% in most series. Repairs performed in conjunction with an ACL reconstruction, however, offer a greater success rate, on the order of 90%.[31,32,33,34,35,36,37,38,39]
Both open and arthroscopically assisted meniscal repair techniques have been described. Open meniscal repair offers the advantage of better preparation of the tear site. However, only the most peripheral of tears in the red-red zone are amenable to this technique because of exposure and accessibility. Long-term follow-up of open meniscal repairs has revealed success rates ranging from 84% to 100%.
Arthroscopically assisted meniscal repairs have been described as inside-out, outside-in, and all-inside techniques. Henning[36,37] first described the inside-out technique of arthroscopic meniscal repair. Inside-out techniques utilize zone-specific cannulas to pass sutures through the joint and across the tear. The sutures are swaged onto flexible needles. A small posterior joint line incision is used to retrieve the sutures and tie directly on the capsule. The use of a posterior retractor, such as a gynecologic speculum, is vital in order to protect the posterior neurovascular structures.
The outside-in techniques have been described by Warren and Morgan and Casscells. Outside-in techniques involve passing sutures percutaneously through spinal needles at the joint line across the tear, and then retrieving the sutures intra-articularly. Mulberry knots can then be tied on the intra-articular free ends of the suture. A small incision is then made at the joint line, where the protruding suture ends are retrieved and tied directly on the capsule. An alternative technique is to retrieve the intra-articular portion of the suture with another pass across the tear using a wire snare and tying the suture back on itself on the capsule. This technique eliminates the need for Mulberry knots. A potential disadvantage of the outside-in technique is difficulty in reducing the tear and opposing the edges while passing the sutures.
The all-inside technique was traditionally used to perform repairs of the far posterior horns, where a posterior accessory portal is used, along with passing a suture with a suture hook device.[40,41] The suture would then be tied intra-articularly. More recently, technologic advances have brought about a number of implantable anchors, arrows, screws, and staples that facilitate meniscal repair without the need for accessory incisions or portals. These devices can be found of permanent, as well as absorbable materials. Although the pullout strength of some of these devices has been shown to approximate those of mattress sutures in cadaveric studies,[42,43] there have been no long-term clinical studies that compare them to more traditional repair techniques (Figure 13).
Essential principles of meniscal repair include preparing the tear with a rasp or abrader, establishment of a hemarthrosis or use of a fibrin clot, and the presence or establishment of a stable knee.[31,32,36,38,40]
Postoperative rehabilitation of the knee is controversial. Factors to consider include the nature of the tear, the stability of the repair, and the presence of a stable knee. If the repair is performed in conjunction with an ACL reconstruction, many surgeons do not deviate from their postoperative ACL rehabilitation protocol. If the meniscal repair is performed as an isolated procedure, it is reasonable to limit either range of motion, weight bearing or both. It seems reasonable to permit a range of motion from 0 to 90 degrees, as well as full weight bearing in a brace locked at 0 degrees extension for 6 weeks. Return to sports can be anticipated within 4 to 6 months.
The complication rate of meniscal repair approaches 2% and is most commonly neurovascularly related. An awareness of the saphenous nerve and its infrapatellar branch on the medial side, as well as the peroneal nerve on the lateral side, is paramount.
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