Surgical techniques for knee meniscus tears have evolved considerably over recent decades to improve patient outcomes. Unfortunately, the vast majority of meniscus tears are not suitable for repair, and arthroscopic partial meniscectomy remains the best option for patients with symptomatic tears.
Arthroscopic partial meniscectomy is an outpatient procedure that can be performed under various types of anesthesia, including general anesthesia, spinal anesthesia, or regional anesthesia with or without sedation. In most cases, non-surgical treatment is the foundation of initial care before any surgical intervention is considered. This conservative approach typically includes ice, nonsteroidal anti-inflammatory drugs (NSAIDs) when not contraindicated, physical therapy, activity modification, and possibly an intra-articular steroid injection.
The patient is positioned supine on the operating table. A leg holder or a post is used during the procedure to apply valgus and varus stress.
Several anesthesia options are available for a meniscectomy, although spinal anesthesia or general anesthesia are generally preferred.
The foot of the table can be extended or lowered. If the foot is not lowered and a leg holder is used, it is important to position the leg holder so that the hip is flexed to 30 degrees. This keeps the knee free and provides easy access for arthroscopic instruments.
A routine knee arthroscopy can be performed without a tourniquet. This is facilitated by distending the joint with a local anesthetic containing epinephrine before placing the portals. Infiltrating the portal sites with local anesthetic and epinephrine also makes tourniquet-free knee arthroscopy easier.
There are several possible portals for arthroscopic meniscectomy. A vertical portal is placed just lateral to the proximal patellar tendon for the arthroscope, and a relatively low, oblique anteromedial portal is used for instrumentation.
The anterolateral portal should be developed with the knee flexed to at least 50 degrees to protect the articular surfaces. After penetrating the capsule and synovium with a blunt obturator, the knee is extended to help position the sheath in the suprapatellar pouch. Using a spinal needle to locate the anteromedial portal while visualizing from the anterolateral portal is often beneficial for optimizing portal placement.
The surgeon should be prepared to use several other portals as needed. Specifically, posteromedial or posterolateral portals can be helpful for removing a retained meniscus fragment that has migrated into the posterior compartment. These must be developed with the knee flexed to 90 degrees. Protecting neurovascular structures is of utmost importance when establishing and using either of these portals.
The posterolateral portal must always be developed well anterior to the biceps tendon to avoid the peroneal nerve. These portals are safest to develop by first using a spinal needle for localization. Placing the cannula with a blunt obturator through the capsule should be done under direct visualization of the capsule.
The arthroscope is introduced into the knee through the standard anterolateral portal using a blunt obturator. When using a pump, a distension pressure of only 30 to 40 mm Hg is typically required. A complete diagnostic examination should be performed at the beginning of every arthroscopic knee surgery.
Next, the anteromedial portal is established as described earlier, and the arthroscopic probe is introduced to examine the menisci. The medial meniscus should first be inspected superiorly and inferiorly to identify any tear areas and determine the length and width of any tear. Tear stability and proximity to the peripheral blood supply should be assessed, as these are important factors in the treatment decision.
The cruciate ligaments should be examined after the medial compartment, and again, palpation is necessary not only to assess anatomy but also tension. Finally, the lateral compartment is inspected in the figure-four position. Rotating the 30-degree scope allows the posterior, middle, and anterior horns of the lateral meniscus to be visualized in sequence. The offset should be directed posteriorly to view the posterior horn, then carefully rotated as inspection progresses laterally and anteriorly. Again, defining the extent and anatomy of the tear is the first step.
The classic arthroscopic surgical technique for resecting unstable longitudinal, flap, and parrot-beak tears is called the cut-and-avulse technique. In this technique, cutting or biting instruments are used to nearly completely detach the large unstable fragment from the remaining meniscus. Leaving a few fibers intact prevents a free fragment from forming and floating away. This large fragment is then grasped with a grasper and avulsed, typically through repeated rolling motions that increase stress on the small remaining attachment area.
Several tear patterns have been described in the medial meniscus. The most common are vertical longitudinal, horizontal cleavage, flap or parrot-beak, radial, and complex tears. Complex tears involve at least two of the other tear patterns. Tears can also be categorized by their etiology (traumatic or degenerative).
The goal of any meniscus resection is to remove the unstable and damaged meniscal tissue while preserving as much normal or near-normal meniscus as reasonably possible. The edges of the tear resection must be carefully tapered so that no sharp transitions remain at the resection margin.
The first step in any meniscus resection is to define the tear anatomy. If the tear cannot be adequately visualized using a post or leg holder and valgus stress, a relaxation technique involving needling of the medial collateral ligament (MCL) can be useful. This can be done through the joint with an 18-gauge spinal needle or percutaneously with a 1.5-inch needle, holding the bevel perpendicular to the MCL fibers. Several perforations of the MCL are made directly above the meniscus. Gentle, then progressively firmer, valgus stress is applied until the MCL opens enough for visualization. This step is crucial to prevent damage to the articular cartilage during meniscectomy. This is only necessary when insufficient space exists to visualize and instrument the meniscus without release.
Vertical longitudinal tears typically occur in the posterior horn and can extend along the circumferential fibers of the meniscus toward the middle and anterior portions. Adequate valgus stress must be applied to facilitate visualization. External rotation of the leg can also help visualization by bringing the posterior tibia and the attached medial meniscus forward relative to the femoral condyle. When making the first cut, attention is typically directed to the posterolateral extent of the tear. Using scissors or a knife, the most lateral attachment of the unstable segment is divided, leaving only a few fibers. Attention is then directed to the most medial or anterior location of the tear, which should be completely released using a biter that tapers into the axilla of the tear. The released portion of the meniscus can then be grasped and avulsed, typically with repeated rolling motions. A small motorized shaver (3 to 4 mm) is then used to suction any debris from the release and subsequently smooth and contour the remaining meniscus.
If the vertical longitudinal tear extends too far anteriorly to properly begin the taper from the anteromedial portal, the anterior release is more easily accomplished with the arthroscope in the anteromedial portal and the cutting instrument in the anterolateral portal. When a vertical longitudinal tear extends from the posterior horn forward to the middle or anterior portion of the meniscus, it can be called a bucket-handle tear and may displace, causing the knee to lock. The easiest way to resect a locked bucket-handle tear is to reposition it through valgus stress and use a blunt obturator to manipulate it back into a reduced position. In a tight joint with a long-standing displaced segment, reduction of the displaced segment may not be possible. Using the described needling technique to release the MCL can facilitate reduction.
Flap tears of the posterior and middle portions of the medial meniscus are relatively common. They can arise from a small vertical longitudinal tear that has propagated through the free edge of the meniscus. The resection technique for flap tears is identical to that of a vertical longitudinal tear, except that with the preferred cut-and-avulse technique, there is only one attachment site that should not be completely cut. Tapering the resection edges is crucial. Flap tears tend to occur more centrally than vertical longitudinal tears and are therefore located in relatively softer, less dense meniscal tissue, meaning they can often be removed simply with a shaver.
Horizontal cleavage tears typically occur in the older population and are more of a degenerative tear pattern. They typically involve central degeneration within the meniscus that propagates to the undersurface through rotational shear. They frequently cause pain but rarely mechanical symptoms. Typically, these tears are resected with a punch. Since the smaller leaflet is usually the inferior one, this should be preferentially removed. It is also technically easier to access, as the superior surface of the meniscus in a horizontal cleavage tends to slide behind the condyle. The leaflet to be removed must be resected to the point where no pathological movement remains between it and the remaining leaflet.
Complex tears result from a tear pattern involving multiple planes. They occur more frequently in older patients where the meniscal tissue is already somewhat abnormal. The meniscus should be probed and assessed before resection to identify the tear pattern as accurately as possible. Flap tears and vertical longitudinal tears are resected using the techniques described earlier. It is important to ensure that no flap remains folded under the meniscus. This is typically the case when a flap is located beneath the surface in the middle portion of the meniscus.
The figure-four position facilitates visualization and instrumentation of the lateral compartment. If a lateral meniscus tear is anticipated, it is beneficial to place the anteromedial portal slightly higher to ease the transition over the tibial spine for instrumenting the lateral meniscus. If the portal is too low to achieve this readily, the skin can be retracted slightly proximally and a new capsular portal can be made, allowing easy instrumentation of the lateral compartment.
Unlike posterior horn medial meniscus tears, a vertical longitudinal tear in the posterior horn of the lateral meniscus can be asymptomatic. These should be probed and evaluated. If they can be subluxated anteriorly under the condyle, they present a problem for recurrent symptoms. Shelbourne and Heinrich showed that if the tears are stable and located behind the popliteus hiatus, they rarely cause symptoms and can be left in place.
The cut-and-avulse technique remains suitable for lateral meniscus resections. Since the arthroscope is typically in the anterolateral position to visualize a lateral meniscus tear, the more anterior axilla of the tear can be easily addressed from this scope position, and the resection instruments are introduced through the anteromedial portal. It is technically difficult to release the posterior axilla of a vertical longitudinal tear in the lateral meniscus when the anterior cruciate ligament is intact, as the ACL blocks access to this area when instruments are used through the anteromedial portal. In this case, it is optimal to switch portals, placing the arthroscope medially and the instruments laterally, to allow for an appropriate tapered release.
Flap tears of the lateral meniscus commonly have a flap attached to the posterior bony attachment of the meniscus. This is often associated with a cruciate ligament tear, and care must be taken to ensure that the bony attachment of the remaining meniscus remains intact. For small tears, resection is not necessary. If they are large and could potentially cause mechanical symptoms, a resection should be performed.
Horizontal tears are less common in the lateral meniscus than on the medial side. These are a degenerative tear pattern, and resection should be based on removing the smaller leaflet, as is done on the medial side.
Radial tears are common in the lateral meniscus. They are typically located in the middle portion or slightly anterior to the middle. If they extend to the meniscosynovial junction within the vascular zone of the meniscus, the deeper portions can be repaired with a complex repair. If they are located entirely within the thin middle portion of the meniscus, a resection should be performed. The anterior leaflet can be created using instruments introduced through the anteromedial portal with a side biter. The posterior leaflet can be created using a standard biter through the same portal. Shaving is appropriate to remove any frayed edges that might propagate.
Meniscal cysts are more commonly associated with lateral meniscus tears than with medial tears. They are typically identified with a degenerative meniscus tear and usually arise from a tear just anterior to the middle meniscus. They present as a relatively firm, rubbery nodule that can be painful and may transilluminate. They are easily identified on MRI. The degenerative torn portion of the meniscus should be resected, and then it is appropriate to enter the cyst with a small shaver (3.0 to 3.5 mm). The opening of this cyst should be widened sufficiently so that it does not reform.
A discoid meniscus should not be resected unless it is causing mechanical symptoms. If the tear breaks through to the superior surface, it can be easily visualized. If the tear runs entirely horizontally within the meniscal body or penetrates inferiorly, it can be difficult to detect. Resection of a discoid meniscus should be carefully contoured to try to create as normal a meniscus as possible.
Immediate postoperative pain from a partial meniscectomy is minimal due to the use of additional local anesthesia in the portal areas and possibly within the joint. The incisions can be closed in several ways. Cryotherapy can be helpful for reducing swelling in the postoperative period. Early range-of-motion exercises, quadriceps sets, and straight-leg raises are appropriate for maintaining quadriceps tone.
Deep vein thrombophlebitis (DVT) can occur after a routine meniscectomy, although it is rare. It is appropriate to take steps to minimize this risk. Using elastic compression stockings is a mechanical means to reduce the risk of DVT. Chemoprophylaxis with 325 mg of aspirin once or twice daily for several weeks after knee arthroscopy is also reasonable.
At the first postoperative visit, careful attention should be paid to any signs of DVT. Referral to a physical therapist is considered for selected patients to restore strength and function. Physical therapy after arthroscopic meniscectomy is not required if patients are able to perform exercises on their own.
