Chapter 57

Allograft Meniscus Transplantation

Dovetail Technique

Thomas R. Carter

Chapter Synopsis

• Meniscal allografts have been shown to provide subjective benefit in knees that have undergone meniscectomy. Various surgical techniques have been described, but basic science studies have shown that maintenance of the horn attachments with bone provides superior 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.

• Rule out other possible causes of the patient’s pain when considering candidates.

• 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 [ACL] deficiency) must be corrected to improve success.

• An osteotomy should be done when the mechanical axis passes through the involved compartment, but typically only to the opposite tibial spine rather than to the extent required for an arthritic knee.

Clinical and Surgical Pearls

• Proper placement of the arthroscopic portals has a major effect on allowing complete visualization of the posterior horn, as well as ensuring that the channel is a straight line between the two meniscus attachments. The contralateral portal is made first and hugs the patellar tendon. A spinal needle is used to ensure straight alignment before the ipsilateral portal is made. Any obliquity on the ipsilateral side can result in improper channel alignment.

• On occasion, the graft has a tendency to be pulled outward when it is sutured. Placement of the initial few sutures in horizontal fashion on the superior aspect of the meniscus can aid in maintaining proper position.

• If the meniscus excision left no meniscal rim, all-inside sutures should be used with caution. With only the capsule to secure the graft, they tend to entrap the capsule and limit full extension or result in the meniscus being pulled outward during the repair.

• It is important to have the graft-bone channel match the height of the tibial plateau. If it is too high, the bone will impinge above on the femoral condyle and make reduction into the knee difficult and also limit knee motion. If the graft-bone is recessed in the channel, it can pull the meniscus down into the channel and as a result not allow sufficient graft at the outer border to suture. In such a case the graft is removed, and slivers from the cut bone are packed at the channel base to raise the height.

• If the bone is inserted too far into the channel, a threaded K-wire can be drilled into the end to remove the graft. If the channel preparation does not result in a press-fit, a bioscrew can be used along the side of the bone to secure it.

Clinical and Surgical Pitfalls

• Although it is technically easier to implant the meniscus without bone, basic science studies show that horn attachments secured by bone better replicate the normal meniscus.

• Whereas a graft typically heals well in the host, great attention to detail for an anatomic placement of the graft is needed to provide greater function.

The meniscus performs many functions for the well-being of the knee, including load bearing, joint stability, and congruency. With so many roles in maintaining normal knee function, it is of little debate that excision results in an increased risk of arthritis. Unfortunately, the ideal replacement for the meniscus has yet to be discovered. At present, meniscal allografts have served as the most successful substitute. Whereas the durability and the ability to prevent or to delay arthritis are questioned, studies have shown that patients typically have less pain and improved function after meniscus implantation. 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 attachment sites with bone or without bone. Although bone fixation techniques are more difficult, several basic science studies have shown that they more closely replicate normal meniscus stress force protection. Although a few clinical studies report no difference in outcome when bone fixation is not used, until comparative long-term studies have been completed, bone fixation methods are recommended.

Within the bone fixation category, several techniques are used. These include bone plugs, the keyhole method, the slot technique, and the dovetail technique. Each has its pros and cons. I prefer the dovetail technique for the lateral meniscus and bone plugs for the medial meniscus. 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. Having the horns separate (i.e., two separate bone plugs) enables placement of the bone plugs to match the native meniscus insertion sites. Because the anterior and posterior horns of the native lateral meniscus are usually only a centimeter apart, the presence of two bone tunnels in such close proximity would create a great risk that the tunnels would converge and compromise fixation. As a result, a bone bridge between the horns is recommended on the lateral side. The dovetail method enables not only preparation of the channel under direct observation but also a press-fit fixation.

Preoperative Considerations

History

Not all patients who have undergone meniscectomy go on to develop arthritis, and with the supply of meniscus limited to only a few thousand per year, candidates need to be selected wisely. Treatment may be considered simply as a preventative measure although the patient has no symptoms and only limited meniscectomy. At present there is general agreement that the first considerations for meniscal allograft are a history of the patient being symptomatic and confirmation that the majority of the meniscus has been excised.

Typical History

The typical history for appropriate candidates is as follows:

• Symptoms are localized to the involved compartment.

• Discomfort is commonly present with activities of daily living and enhanced activity.

• Joint effusions may occur and are commonly activity related.

Physical Examination

Possible candidates typically have minimal physical findings beyond joint line tenderness and, at most, mild joint effusions.

More often, patients have findings that may preclude surgical candidacy, such as the following:

• 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 malalignment (if mechanical axis is through 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 is performed if there is a question of degree of meniscectomy or associated pathologic change or to evaluate bone stress reaction.

Historically, bone scans can be performed if there is a question of reactive changes in the joint and if localized only to the involved knee compartment. However, magnetic resonance scans are just as useful for this purpose and have superseded the use of bone scans.

Indications and Contraindications

The ideal candidate is a patient who has had a prior meniscectomy in an otherwise normal knee and experiences pain localized to the involved compartment. The degree of articular cartilage damage is slight and is found only in the affected side. The knee is without ligament laxity, and the limb alignment is similar to that of the contralateral leg.

However such ideal patients are few. Consideration may be given to patients with grade III chondrosis but not diffuse knee involvement. Patients with grade IV chondromalacia are not candidates, unless there is a localized defect that can be corrected with joint repair or restoration-type procedures. Associated pathologic processes, such as ligament instability and limb malalignment, provided correction can be performed, do not exclude patients.

Contraindications are advanced arthrosis of the involved compartment and diffuse knee joint chondrosis. Comorbidities that are not correctable are exclusion criteria. Obesity, inflammatory arthropathy, and avascular necrosis are also contraindications. Unrealistic expectations of the patient should also be taken into consideration (the knee will not be returned to normal).

Surgical Planning

Concomitant Procedures

Ligament instability and contained chondral defects are addressed at the time of the meniscus implantation. Controversy exists as to whether limb realignment should be performed any time the mechanical axis passes through the involved compartment or only if there is a measurable difference between the two legs. I typically will perform an osteotomy when the comparative mechanical axis of the lower extremities shows more than 2 to 3 degrees toward the involved side consistent with the degeneration of the joint. Apart from this debate, limb realignment procedures are usually performed when the meniscus is implanted.

If both osteotomy and ligament reconstructions are necessary, it is common to stage the procedures because of concerns regarding tunnel or screw overlap and associated adequate fixation. My preference is to perform the osteotomy first, then after healing perform the meniscus and ligament reconstructions.

Allograft Sizing

Various methods have been used for sizing of meniscal allografts to match the host. Although magnetic resonance images and computed tomographic scans can be used, plain radiographs are the most common means. Anteroposterior and lateral views are obtained with a magnification marker placed at the level of the joint line. Any obliquity or rotation that may affect measurement of the tibial plateau is not acceptable. Regardless of the method of sizing the graft, it is prudent for the treating surgeon to verify the size match.

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