• The function of the menisci in load transmission across the tibiofemoral joint is well established.

• Meniscal deficiency leads to increased articular cartilage contact stress, which predisposes to progressive joint degeneration.

• Numerous clinical studies demonstrate the relationship between meniscal deficiency and progressive articular cartilage degeneration.

• The lateral meniscus plays a greater role in load transmission in the lateral compartment than does the medial meniscus in the medial compartment.¹

• Medial meniscus transmits 50% of compartment load.

• Lateral meniscus transmits 70% of compartment load.

• The menisci transmit 50% of load in extension, 85% of load in flexion.²

• Degenerative changes typically progress more rapidly in the lateral compartment following lateral meniscectomy than in the medial compartment following medial meniscectomy.

• There is a subgroup of patients in whom degenerative changes can proceed very rapidly following lateral meniscectomy.

• This occurs most commonly in adolescent females.

• Valgus alignment may play a role.

• More rapid progression of degenerative changes likely occurs in younger patients due to acute meniscal loss following traumatic injury, in contrast to patients in whom a degenerative tear develops gradually over time, thus allowing the joint to accommodate to the gradual loss of meniscal function.

• The menisci also play a role in knee stability.

• The lateral meniscus has a role in controlling lateral compartment translations during the pivot shift in the anterior cruciate ligament (ACL)-deficient knee.³

• Specific tear patterns in the lateral compartment that may require subtotal meniscectomy:

• Bucket-handle tear.

• Radial tear that extends to the capsule. This tear pattern typically occurs at the junction of the anterior horn and mid-third of the meniscus and almost exclusively occurs in the lateral compartment.

• Pain and swelling are the typical symptoms following meniscal loss.

• Concomitant lateral meniscal transplantation should be considered during revision ACL reconstruction in patients with prior lateral meniscectomy to replace the role of the lateral meniscus as a secondary stabilizer.

• Extensive, full-thickness cartilage loss on the lateral femoral condyle or lateral tibial plateau.

• In contrast, a focal chondral lesion may be appropriate for concomitant cartilage repair/resurfacing.

• The threshold for acceptable size and location of a cartilage defect that can still allow meniscal transplantation is unknown.

• Erosive cartilage loss on the posterior margin of the lateral tibial plateau is harder to treat and may be considered a relative contraindication.

• Remodeling of the architecture of the lateral femoral condyle, with flattening, is a contraindication.

• A valgus mechanical axis, with the weight-bearing line displaced lateral to the lateral tibial spine, should be corrected with concomitant or prior realignment osteotomy.

• Patients usually are asymptomatic in the early time period following meniscectomy; however, given the well-established natural history of lateral meniscal deficiency in young patients, the question often arises about doing early lateral meniscal transplantation to prevent progressive degenerative changes.

• The rationale for early or “prophylactic” transplantation is to prevent the known morbid sequelae of lateral meniscectomy.

• Because the results of meniscal transplantation are superior when performed in the setting of minimal chondral degeneration, a case can be made for early transplantation.

• I recommend monitoring of these knees with serial physical examinations and surveillance MRIs. If a patient develops an effusion, or MRI scan begins to demonstrate progressive degenerative changes, then a case can be made for transplantation, even in the absence of overt symptoms.

• Quantitative MRI using measurement of T2 relaxation time (as a measure of collagen organization) and T1rho (as a measure of proteoglycan content) may be helpful to monitor for development of cartilage changes before such changes are evident on standard morphologic MRI.

• In the future, sensitive serum and synovial fluid biomarkers may allow early detection before development of structural changes in MRI.

• Careful history and examination

• Understanding of the patient’s goals and expectations

• Review of prior operative reports

• Careful physical examination with particular attention to standing alignment, prior incisions, presence of an effusion, range of motion, ligament stability, and presence of joint line tenderness

• Standing (weight-bearing) radiographs, including posterior-anterior view in flexion to show posterior aspect of the joint

• Long films from hip to ankle to measure mechanical axis

• MRI to evaluate articular cartilage, subchondral bone architecture, remaining meniscus, and status of medial and patellofemoral compartments (Fig. 39-1)

• Graft is sized relative to bony dimensions.

• Tissue banks generally use plain radiographs to measure length and width of the tibial plateau.

• MRI also can be used for measurement of length and width of the tibial plateau.

• If the tissue bank supplies the meniscus with no attached bone, there are formulae to allow prediction of meniscal dimensions.⁴

• Meniscal “width” on anterior-posterior (AP) radiograph

▪ Respective midpoint of tibial eminence to bony periphery

▪ 1:1 ratio

• Meniscal “length” on lateral radiograph

▪ Medial = 80% of sagittal diameter of plateau

▪ Lateral = 70% of sagittal diameter of plateau

• The tolerance of the compartment for meniscal size mismatch is not known.

• Undersized grafts should be avoided because of the potential difficulty in achieving anatomic bone attachment of the horns centrally and reaching the capsular periphery.

• Biomechanical studies demonstrate superior graft fixation strength with bone fixation compared to sutures alone attached to the horns.⁵

• Options for bone fixation are individual bone plugs attached to the anterior and posterior horns or a common bone slot that connects both anterior and posterior horns (“keyhole” technique) (Fig. 39-2).

• The advantage of a common bone slot is that it maintains the anatomic relationship between the anterior and posterior horns and their attachment sites to bone.

• A potential pitfall with the bone-slot technique is that the slot may be made too much into the lateral compartment in an effort to avoid injury to the ACL in making the central slot.

• An advantage of individual bone plugs attached to the anterior and posterior horns is that these can be placed anterior and posterior to the ACL, allowing anatomic placement.

• Secure suture fixation of the graft to the capsule is critical; the posterolateral capsule is looser than the medial side.

• Native lateral meniscus is more mobile than the medial meniscus.

• Standard anteromedial and anterolateral viewing portals are established.

• The medial portal should be placed a bit higher to allow instruments through this portal to pass over the intercondylar eminence to work in the lateral compartment.

• The knee is placed in the “figure-four” position, at 90 degrees of flexion with varus stress to open the lateral compartment.

• The lateral compartment normally has more opening than the medial side, so there typically is ample working room with varus stress.

• In a tight lateral compartment, “pie crusting” of the iliotibial band and/or lateral capsule can be done with an 18-gauge spinal needle from outside-in, although this is rarely required.

• The capsular rim is prepared with a standard shaver. A small remnant of the red zone of the native meniscus (2-3 mm) can be left to suture into (Fig. 39-3).

• A standard ACL vector guide is used for tunnel placement (Fig. 39-4).

• I recommend 9-mm tunnels.

• A blind-ended tunnel can be created for the posterior horn with a RetroDrill (Arthrex Inc., Naples, FL) (Fig. 39-5).