Meniscal allograft transplantation: Dovetail technique

OVERVIEW

Chapter synopsis

Meniscal allografts have been shown to provide subjective benefits in symptomatic patients after meniscectomy. Various surgical techniques have been described, but basic science studies have shown that maintenance of the horn attachments with bone may provide superior biomechanical function. The dovetail technique is a method that provides not only a bone bridge but also a press-fit fixation.

Important points

Patients should be symptomatic or have radiographic evidence of stress reaction of the involved compartment.
Because of the higher failure rate in knees with advanced arthritis and the limited supply of grafts, meniscal allografts should not be considered a substitute for arthroplasty.
Any additional pathology (e.g., anterior cruciate ligament deficiency, malalignment) must be corrected to improve success.

Clinical/surgical pearls

Make sure the working portal is straight in line with the meniscal horn attachments. Any obliquity in the channel may result in a non-anatomic graft position.
If concerned of proper graft size, initially place a suture in the posterior aspect then middle segment before fixation of the anterior aspect. The anterior horn is more amenable to adjusting placement.
If no meniscal rim is remaining, initial fixation with all-inside sutures should be used with caution. With only the capsule to secure the graft, the sutures can entrap the capsule and limit full extension or extrude the graft.
The graft-bone channel must match the height of the tibial plateau. If too high, the bone will impede reduction of the graft into the knee and limit knee extension. If the graft-bone is recessed in the channel, it can pull the graft more midline and prevent sufficient graft at the outer border to suture. Slivers of bone can be packed in the channel base to raise the height.

Clinical/surgical pitfalls

While the graft-host healing is rarely a problem, attention to detail for an anatomic graft placement is vital to have a functioning graft.

Introduction

The meniscus provides many important functions of the knee, and it is of little debate that the meniscus-deficient knee is susceptible to altered biomechanics, instability, and degeneration. With the known increased risk of developing arthritis following meniscectomy, meniscal allografts have been studied as a promising substitute. While durability and the ability to prevent or to delay arthritis are still debated, studies have shown that patients commonly have less pain and improved function after meniscus transplantation. However, the indications are narrow, and the procedure is technically challenging.

Many surgical methods have been described for meniscal allograft transplantation. They are typically classified into two broad categories on the basis of securing the meniscus at its root’s attachment sites with bone or without bone (soft tissue only). Although bone fixation techniques are more difficult, basic science and biomechanical studies have shown that bone fixation may more closely replicate normal meniscus function. While some studies report no difference in early functional outcomes, long term follow-up has found a lower rate of graft extrusion and less progression of joint space narrowing when secured with bone.

Several methods of bone fixation of the horns have been described with bone plugs, bone trough, and dovetail techniques normally used. The authors’ preference is the dovetail technique for lateral meniscus transplantation and bone plugs for medial meniscus transplantation. The rationale for the medial side takes into consideration that the distance between the anterior and posterior horns is typically 2.5 to 3 cm, with a highly variable anterior attachment site. By having the horns separate (i.e., two separate bone plugs), it enables placement of the plugs to match the native meniscus insertion sites. Because the anterior and posterior horns of the native lateral meniscus are usually only 1 cm apart, two bone tunnels have the risk of tunnel convergence and compromised fixation. As a result, a bone bridge between the horns is recommended on the lateral side, with the dovetail technique enabling press-fit fixation.

Preoperative considerations

History

Not all patients develop symptomatic degenerative changes after meniscectomy. Therefore, prophylactic replacement of the meniscus is not recommended. In addition, with the supply of meniscus allografts limited to only a few thousand a year, candidates need to be selected wisely. There is a general agreement that the first consideration for meniscal allograft transplantation is a symptomatic patient in whom it is confirmed that the majority of the meniscus has been excised. In addition, surgery should only be performed if a patient has failed all conservative treatment measures, such as activity modification, weight loss, bracing, injections, and oral anti-inflammatory medications.

Signs and symptoms

The typical signs and symptoms for appropriate candidates are as follows:

Symptoms are localized to the involved compartment
Discomfort is commonly present with activities of daily living and enhanced with activity
Joint effusions may occur and are typically activity related

Physical examination

Possible candidates typically have minimal physical findings beyond joint line tenderness and, at most, mild joint effusions. A thorough physical exam is important to identify findings that may preclude surgical candidacy:

Evidence of diffuse arthritis: palpable osteophytes, decreased range of motion, marked crepitus
Ligamentous instability (needs to be corrected before or at the time of implantation)
Limb alignment (if mechanical axis is through the involved compartment, may need realignment)
Morbid obesity
Other limb or back abnormalities

Imaging

Radiography

Include a magnification marker for reference in graft sizing.

Weight-bearing 45-degree posteroanterior view
Weight-bearing anteroposterior view in full extension
Non–weight-bearing 45-degree lateral view
Axial view of the patellofemoral joint
Full-length view of limb for mechanical axis evaluation

Other modalities

Magnetic resonance imaging (MRI) is commonly performed if there is a question regarding the degree of meniscectomy, associated pathologic change, and to evaluate bone stress reaction.

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