CHAPTER 8 Meniscal Transplantation

Nicole A. Friel, Mark A. Slabaugh, Brian J. Cole

Surgical treatment of meniscus lesions has changed significantly over time. Meniscal tears were traditionally treated with meniscal excision, but it became understood that loss of the meniscus alters the biologic and biomechanical environment of the knee.¹^,² The resulting degenerative changes in the involved compartment led us away from meniscus removal and toward meniscus preservation. Partial meniscectomy and meniscus repair procedures have become the standard of care. For patients for whom meniscal preservation is not an option, meniscal allograft transplantation can be done for a select subset of patients who have become symptomatic from their meniscal deficiency. This offers restoration of anatomic and biomechanical function.

With the advent of meniscal transplantation procedures, several techniques have evolved, including separate bone plugs on the anterior and posterior horns as well as bone bridges (keyhole, trough, dovetail, and bridge in slot variations). The bone bridge is almost always used for the lateral meniscus because of the close proximity between the anterior and posterior horns. The medial meniscus can be anchored with either plugs or a bridge, because the anatomy of the anterior horn is variable and the plugs may allow for minor modifications. We prefer the bridge in slot technique for lateral and medial menisci for a number of reasons, including its simplicity and secure bony fixation, ability to perform concomitant procedures easily, and the ability to maintain the native anterior and posterior meniscal horn attachments.

ANATOMY

The menisci are semilunar-shaped fibrocartilaginous structures that function in shock absorption,³ load transmission,⁴^–⁶ secondary mechanical stability,⁷^,⁸ joint lubrication,⁹ and nutrition.¹⁰ Circumferentially oriented collagen fibers provide resistance to hoop stresses whereas radially oriented fibers hold the circumferential fibers together and provide resistance to shear.¹¹^,¹² The anterior and posterior horns attach to bone by interdigitating collagen fibers oriented to transmit load and shear optimally from the meniscus to the tibia.¹³

The menisci are composed of 74% water,¹⁴ allowing for optimization in force transmission. The lateral meniscus carries 70% of the lateral compartment load, compared with 50% by the medial meniscus.⁶^,¹⁵ The menisci transmit 50% of the joint load when in knee extension and 90% when the knee is in flexion.⁶^,¹⁵ Loss of the meniscus, therefore, increases the load on the articular cartilage surfaces and facilitates the development of early degenerative changes. Loss of just 16% to 35% of the meniscal tissue can lead to a 350% increase in contact forces.⁴ Clinical studies support meniscus preservation, because a greater size of meniscal resection is associated with a poor clinical outcome.¹⁶^–¹⁹

PATIENT EVALUATION

History

Eliciting a thorough history is especially important because causative factors, associated injuries, and prior treatments can all affect the treatment plan. Often, patients report a specific knee injury with subsequent surgical treatment consisting of meniscectomy or meniscal repair. Patients usually describe a period of pain relief following the surgery but, over time, joint line pain and activity-related swelling ensue. Recent operative reports or photographs are useful to rule out arthritic changes, which would otherwise contraindicate meniscal transplantation. In a setting in which recent information is unavailable regarding the anatomy and pathology in the knee (e.g., from a recent arthroscopy), it might be prudent to consider a diagnostic arthroscopy to provide updated information for proper surgical planning.

Physical Examination

Examination often reveals full range of motion. Depending on recent activity, a joint effusion may be present. Joint line or femoral condyle tenderness is occasionally found. A thorough physical examination is essential to reveal malalignment, ligament deficiency, or articular cartilage lesions that would modify the treatment plan. These findings need to be addressed, either as a concurrent or staged procedure.

Diagnostic Imaging

A complete set of radiographs must be obtained to evaluate limb alignment and the degree of joint space narrowing and secondary osteoarthritic changes caused by a prior meniscectomy. In addition, a magnification marker or quarter should be placed on the cassette at the level of the joint line on two orthogonal views for meniscal sizing. Views include weight-bearing anteroposterior (AP) in full extension, weight-bearing posteroanterior (PA) in 45-degree-flexion, non–weight-bearing 45-degree-flexion, axial view of the patellofemoral joint, and a long leg mechanical axis view.

Magnetic resonance imaging (MRI) is usually reserved for challenging cases when certain questions are left unanswered. The extent of meniscectomy, status of the articular cartilage, and degree of subchondral edema in the involved compartment can all be assessed by MRI.

TREATMENT

Indications and Contraindications

The success of meniscal transplantation depends on careful selection of the ideal candidate. Typically, patients are relatively young (younger than 50 years) and often present with a history of prior total or subtotal meniscectomy with persistent pain localized to the meniscus-deficient compartment. The knee joint must be stable or stabilized and have normal alignment, with intact articular surfaces (grade I or II). Any grade III or IV lesions should be focal and require concomitant treatment.

Although not absolute contraindications, chondral defects, malalignment, or ligamentous instability all require consideration for concurrent or staged procedures to ensure that all joint pathology is addressed. In the past, full-thickness chondral defects were considered a contraindication; however, cartilage degeneration is not a significant risk factor for meniscal allograft failure.²⁰ Outcomes of many concurrent procedures, including meniscal transplantation with concurrent autologous chondrocyte implantation (ACI)²¹^,²² and osteochondral allograft³² have shown excellent results in the carefully selected patient.

Concurrent or staged corrective osteotomy is indicated for patients with deviation toward the involved compartment. Axial malalignment can exert abnormal pressure on the newly placed graft, which can lead to loosening, overload, degeneration, and failure.²³^–²⁵

Anterior cruciate ligament (ACL)–deficient patients who have had a prior medial meniscectomy may benefit from concomitant ACL reconstruction (ACLR) and meniscal transplantation. Many studies have shown that meniscectomized ACL-deficient knees lead to worsening degenerative changes. The more aggressive approach of combination ACLR and meniscal transplantation has good long-term follow-up as opposed to untreated (left alone) knees. In addition, the posterior horn of the medial meniscus is an important secondary stabilizer to anterior translation and may be important in preventing secondary “stretch” of the ACL reconstructed knee.⁷^,²⁶^–²⁸

Contraindications for meniscal transplantation include diffuse arthritic changes, squaring or flattening of the femoral condyle or tibial plateau, significant osteophyte formation in the involved compartment, tibiofemoral subluxation, inflammatory arthritis, synovial disease, previous joint infection, skeletal immaturity, or marked obesity.

Conservative Management

Patients who have had a prior meniscectomy should have a trial of conservative treatment before consideration of operative measures. Activity modifications, anti-inflammatory medications, and occasionally injections can be recommended to help determine which patients can function without surgical intervention. More aggressive management of the relatively young patient following lateral meniscectomy might be considered, especially in female athletes with slight valgus who are at significant risk for the development of progressive lateral compartment arthritis.²⁹

PEARLS& PITFALLS

• Patient selection for operative intervention is crucial. Patients must be able to understand the indications, activity limitations, and possible outcomes.

• Patients who are overweight or have unrealistic expectations regarding excessive postoperative function need to realize that the longevity of the meniscal graft is negatively affected by these two variables.

The success of meniscal transplantation is dependent on careful size matching of the meniscus allograft to the native meniscus. Meniscal allografts are compartment- and size-specific. Anteroposterior and lateral preoperative radiographs with sizing markers are important for meniscal sizing (Figs. 8-1 and 8-2). Allograft sizing is of significant importance, because oversized meniscal allografts lead to greater forces across the articular cartilage.³⁰ On the other hand, undersized allografts result in greater forces seen by the meniscal tissue.³⁰ The meniscus width is determined on the AP radiograph by measuring from the edge of the ipsilateral tibial spine to the edge of the tibial plateau. Meniscal length is determined on the lateral radiograph as determined by the AP dimension of the ipsilateral tibial plateau. These measurements, after correction for magnification, are multiplied by 0.8 for medial and 0.7 for lateral meniscus. Other methods using height and weight have been proposed, but are not routinely used.³¹^,³²