INDICATIONS

The meniscus provides important functions in the human knee, including load bearing, shock absorption, stability, and joint nutrition, that are vital for the integrity of the articular cartilage. Although many meniscus tears can be successfully repaired, including complex tears that extend into the central avascular region,^52,53 not all are salvageable, especially if considerable tissue damage has occurred. Transplantation of human menisci is hypothesized to restore partial load-bearing meniscus function, decrease patient symptoms, and provide some chondroprotective effects.^{10,25,37,63,70} However, the procedure remains in an evolving state, as investigations of tissue-processing, secondary sterilization, and long-term function continue to evaluate its effectiveness. Clinical studies have shown that meniscus transplantation decreases tibiofemoral joint pain in the short term. However, long-term investigations report that most transplants gradually deteriorate, tear, or shrink in size, thereby losing the ability to provide function, as is described later. Accordingly, the goal is to provide short-term benefits until a more suitable meniscus transplant is clinically available. At best, the transplant provides only partial function, and therefore, strenuous sports and high-impact activities are not advised postoperatively even though many younger patients have the desire to return to unrestricted athletics. Education of the patient and family is required so that all understand and accept these current limitations of the procedure.

The optimal candidate is a patient under the age of 50 who has had a total meniscectomy, has pain that limits daily activities, and demonstrates early articular cartilage deterioration in the involved tibiofemoral compartment. There should be no radiographic evidence of advanced tibiofemoral joint arthritis. At least 2 mm of tibiofemoral joint space should be visible on 45° weight-bearing posteroanterior (PA) radiographs.⁵⁰ Arthroscopic examination performed prior to meniscus transplantation confirms that the patient is a suitable candidate. In the most advanced cases, there should be no or only minimal bone exposed on tibiofemoral surfaces. Few treatment options are available for these individuals, especially those younger than 30 years of age, and the goal in the short-term is to decrease pain, increase knee function, allow pain-free activities of daily living, and delay the onset of tibiofemoral arthritis. Normal axial alignment and a stable joint are required. The body mass index (BMI) must be within normal range.

CONTRAINDICATIONS

Patients who have had a meniscectomy are evaluated with 45° PA weight-bearing radiographs and magnetic resonance imaging (MRI)^45,46 to determine the status of the joint, articular cartilage, and subchondral bone edema. Advanced knee joint arthritis with flattening of the femoral condyle, concavity of the tibial plateau, and osteophytes that prevent anatomic seating of the meniscus transplant are contraindications. Clinical studies have shown poor results and high failure rates in knees with this amount of joint damage.^19,35,46,60

Untreated lower limb malalignment is associated with failed meniscus transplantation^8,12,64,65; therefore, the patient must be willing to first undergo a corrective osteotomy. Axial correction is recommended in knees in which the weight-bearing line is less than 45% (varus) or greater than 55% (valgus), representing a 2° to 3° change from normal alignment. Uncorrected knee joint instability, especially anterior cruciate ligament (ACL) deficiency, is also associated with poor outcomes after meniscus transplantation.⁶⁴ Patients must undergo concurrent or staged ACL reconstruction to restore normal stability to protect the meniscus transplant.

Preexisting knee arthrofibrosis, significant lower limb muscular atrophy, and a history of prior joint infection with subsequent arthritis are all contraindications for this operation. Symptomatic noteworthy patellofemoral articular cartilage deterioration (subchondral bone exposure) and obesity (BMI > 30) are also contraindications.

Prophylactic meniscus transplantation after total meniscectomy is not recommended in asymptomatic patients who do not have articular cartilage deterioration because long-term predictable success rates for transplants are not available. In addition, the operative procedure does carry a slight risk for complications that could make the patient’s condition worse.

The clinical problem is often encountered involving patients younger than 30 years of age who have undergone meniscectomy years ago, do not have articular cartilage damage, and are asymptomatic. Clinical studies show that eventual deterioration of the meniscectomized tibiofemoral compartment will most likely occur. These patients are advised that there is no optimal or predictable operative procedure to replace meniscus function and that they should decrease or refrain from participating in high-impact, strenuous activities. There are sensitive and accurate MRI cartilage techniques to determine the status of the articular cartilage in the meniscectomized compartment.^44,45 When early but definite articular cartilage damage is detected, it can be logically assumed that the joint deterioration will continue over time and the opportunity exists to perform meniscus transplantation. This still represents a difficult choice for the patient in terms of undergoing surgery before the onset of major joint symptoms. In addition, the transplant may not function and further arthroscopic surgery may be required to remove the tissue. Most patients who develop early cartilage damage in the meniscectomized compartment complain of pain with strenuous athletic activities, but not with recreational or daily activities. These patients are not truly asymptomatic and desire to lessen the risk of further joint deterioration to the level at which it will affect lower intensity activities. Patient education and a conservative approach to recommendation of transplantation are important until a more dependable transplant is available.

The presence of a full-thickness femoral condylar defect with bone exposure is a relative contraindication to meniscus transplantation. Concurrent articular cartilage restorative procedures (such as osteochondral grafts or autologous chondrocyte implantation) can be successfully performed with meniscus transplantation^18,38 and expand the indications to include knees with these lesions.

CLINICAL BIOMECHANICS

Effect Fixation and Location of Meniscus Transplants

The method of fixation of meniscus transplants to the surrounding tissues is believed to be paramount in subsequent load-bearing function and chondroprotective effects. The goal is to reproduce the normal attachment sites, allowing lateral and medial transplants to remain in their anatomic location and move normally throughout knee motion.^47,68 The use of a transplant with bone for fixation incorporated with either a central bone bridge or a two-tunnel technique (as described later in this chapter) is, in the authors’ opinion, required to obtain these goals. Soft tissue meniscus transplants, without bone fixation, are not recommended. Although soft tissue transplants are far easier to prepare and implant surgically, scientific data are inadequate to support that the soft tissue ends of the meniscus implant will heal and provide the circumferential tension in the meniscus that is required for function (Fig. 29-1).

FIGURE 29-1 Visual inspection of meniscus allograft prior to implantation.

The importance of securing the anterior and posterior horns of an LMT was documented by Chen and colleagues,⁹ who investigated a variety of surgical methods for meniscus implantation. Using an autograft cadaver model, the study revealed that a transplant that had either a bony bridge or bone plug fixation of both horns produced contact area, peak contact pressure, and average central pressure results similar to those of an intact meniscus. Procedures in which either only one horn was secured or neither horn was secured demonstrated a loss of mechanical function and subsequent expected benefit of the transplant.

Alhalki and coworkers¹ compared three fixation methods of medial meniscus autografts in cadaver knees to determine which method restored tibial contact mechanics closest to normal. The experimental design tested bone plug fixation alone, bone plug fixation combined with peripheral suturing of the transplant to the native rim, and suturing of the horns through bone tunnels combined with peripheral suturing of the transplant to the native rim. The study revealed that bone plug fixation produced contact mechanics closest to normal; however, the maximum pressure was significantly greater than that in the intact knee. There was no benefit in adding peripheral sutures to the bone plug fixation model. Importantly, fixation with sutures only did not restore normal contact mechanics and was not recommended by the investigators.

Verma and associates⁷² measured medial compartment peak pressure, mean pressure, and contact area in eight cadaver knees to determine whether a difference existed between medial meniscus transplants (MMTs) implanted with a bone plug technique and those with a bone trough technique. The data indicated no difference between the two techniques for all three variables, which were restored to values similar to those measured in the intact knees. The authors cited clinical advantages with the trough technique for both medial and lateral meniscus transplantation.

The effect of variations in placement of the posterior horn attachment of an MMT were investigated by Sekaran and colleagues.⁵⁶ Using a cadaver autograft model, the posterior horn tunnel was placed either in its anatomic position or 5 mm medial or 5 mm posterior to the anatomic location. The study showed that placing the posterior horn tunnel 5 mm medial to its anatomic position caused an increase in normalized maximum pressure, a posterior shift in the location of the centroid of the contact area, and an increase in the normalized mean pressure. Placing the posterior horn tunnel 5 mm posterior was not as detrimental; however, this location resulted in a significant shift in the centroid of contact area. The authors concluded that surgeons should place the posterior horn tunnel as close to its anatomic position as possible, with a tolerance limit of less than 5 mm medial and 5 mm posterior to this location.

CLINICAL EVALUATION

A thorough history is taken that includes assessment of prior operative records and current symptoms and functional limitations. A comprehensive knee examination is performed that includes assessment of knee flexion and extension, patellofemoral indices, tibiofemoral pain and crepitus, muscle strength, and gait abnormalities. The appropriate clinical tests for the ACL, posterior cruciate ligament (PCL), medial, and posterolateral structures are performed.

MRI is obtained using proton-density–weighted, high-resolution, fast-spin-echo sequences^45,46 to determine the status of the articular cartilage and prior meniscectomized tibiofemoral compartment. Radiographs include AP, lateral at 30° of knee flexion, weight-bearing PA at 45° of knee flexion, and patellofemoral axial views. Axial lower limb alignment is measured using double-limb standing hip-knee-ankle weight-bearing radiographs¹⁶ in knees that demonstrate varus or valgus alignment.

Patients complete questionnaires and are interviewed for the assessment of symptoms, functional limitations, sports and occupational activity levels, and patient perception of the overall knee condition according to the Cincinnati Knee Rating System (CKRS).⁴

PREOPERATIVE PLANNING

Meniscus transplants are obtained from tissue banks accredited by the American Association of Tissue Banks (AATB) and inspected by the U.S. Food and Drug Administration (FDA), in which serologic testing meets or exceeds the standards of these organizations.⁶⁷ Importantly, donor selection criteria may vary between tissue banks and the surgeon should understand the specific criteria used by the bank chosen to supply the transplant.

A variety of sterilization techniques have been described for meniscus transplants, including none (fresh-frozen), irradiated, cryopreserved, and proprietary chemical techniques. To date, no scientific data exist to select one type of graft processing method over another. Some authors⁸ advocate combined secondary sterilization using low-dose irradiation (1–2 Mrads) and chemical agents.

Surgeons should be aware that so-called sterilization processes may not prevent contamination and do not guarantee a sterile graft. The authors recommend that grafts be selected that have undergone some form of sterilization to decrease the risk of bacterial infection. Prophylactic antibiotics are administered intravenously before surgery, and patients are carefully monitored postoperatively for any signs of infection. The implications of different processing techniques on graft sterility and donor selection issues, allograft harvesting techniques, and disease testing are beyond the scope of this chapter and have been discussed in detail by others.^5,10,67

Although there is no standard protocol at present, AP and lateral radiographs are used to obtain approximate width and length measurements for the meniscus transplant.⁴³ A number of studies have been performed to determine the appropriate sizing method for meniscus transplants.^15,21,58,61 Shaffer and coworkers⁵⁸ found no difference between AP radiographs and MRI in terms of accuracy in measuring actual meniscus width and length. With accuracy defined as no more than a 2-mm difference between actual meniscus dimensions in cadaver specimens and that measured on the films, the accuracy rates were 33% for AP radiographs and 37% for MRI. Stone and associates⁶¹ suggested that recipient height, weight, and gender be considered as important matching criteria when selecting meniscus transplants. These investigators measured meniscus and tibial plateau dimensions in 111 patients using MRI and correlated the dimensions with the patients’ height, weight, BMI, and gender. Height correlated well with total tibial plateau width (R = 0.7194), and females generally had smaller meniscus dimensions than males. In addition, patients with a BMI greater than 25 had larger meniscus dimensions than patients with a lower BMI at any given height.

Donahue and colleagues¹⁵ developed an algorithm for meniscus transplant sizing based on MRI measurements. The authors recommended that tissue banks follow the algorithm, which involves a series of six steps. These include making four transverse and six cross-sectional measurements for each transplant in the bank’s inventory using a three-dimensional coordinate digitizing system, obtaining MRI of the recipient’s uninjured knee and measuring nine parameters for the medial or lateral meniscus, and performing a series of calculations to determine the best match.

The problem still exists that even though an approximate size can be determined preoperatively, in many knees the tibiofemoral joint has undergone degenerative changes that produce subtle alterations in joint geometry leading to permanent alterations in the normal surface stress distribution of the joint surface.⁷ A meniscus transplant does not have the ability to restore the native or normal state of the meniscectomized compartment. Future studies are required to determine the effect of subtle size and shape mismatch of the transplant on retaining articular cartilage functional properties. A chondroprotective effect of meniscus transplants has yet to be proved. This involves sophisticated questions regarding the chondrocyte function, cartilage collagen, and glycosaminoglycan homeostasis and resultant biomechanical properties.

It is preferred that the tissue bank provides a digital photograph of the transplant selected for the patient before surgery. A metric ruler is placed adjacent to the transplant in the photograph to ensure that the specimen is of adequate size and width. Certain medial menisci may have a hypoplastic anterior horn that is narrow, inserting distal to the medial tibial surface (type III⁶), and are not acceptable for implantation. The middle third of a medial or lateral meniscus may be 8 to 10 mm in width and suitable only for small patients. The lateral meniscus may have reduced anterior-to-posterior length, less than that calculated on the sagittal radiograph, and not be suitable for implantation.

Judgment is required at surgery when the meniscus bone bridge technique is performed, which requires good size matching to prevent medial or lateral meniscus extrusion. The authors prefer to take the added time to use a bone bridge or bone plug technique (bone-meniscus-bone implant), which does require a good geometric and anatomic fit. Alternative techniques are available in which the meniscus is sutured in place without bone plugs, which is not recommended.

The patient is advised that the transplant will be inspected in the operating room before the induction of anesthesia. It is rare that the operative procedure cannot be performed as planned; however, there is always the chance that the transplant will not meet the desired criteria.

Knees with associated varus osseous malalignment require a staged corrective osteotomy prior to the meniscus transplant procedure. Knees with ligament deficiency require a staged ligament reconstruction. Some studies have advocated concurrent ACL reconstruction and meniscus transplantation.^20,57,77 The normal ACL tibial attachment site and the ACL tibial graft tunnel may compromise meniscus transplant tibial fixation. This may occur when the slot technique to be described is selected in patients whose central tibial intercondylar region is not wide enough to accommodate both the meniscus transplant slot and the ACL tibial graft tunnel. Because it is not possible in these knees to use the central slot technique, a two-tunnel procedure is selected for the MMT.

INTRAOPERATIVE EVALUATION

MMTs are not prepared until the surgeon determines whether the central bone bridge technique (which is preferred) or the two-tunnel technique (separate anterior and posterior bone attachments and tunnels) will be performed, as is described later.

LMTs are prepared before the operative procedure to determine the depth and width required for the tibial slot for the central bone bridge technique. The central bone portion of the LMT incorporates the anterior and posterior meniscal attachments and usually measures 8 mm in width in smaller patients and 9 mm in larger patients. The posterior 8 to 10 mm of tibia bone bridge that protrudes beyond the posterior horn attachment is removed to produce a buttress against the prepared bone slots in the host knee. Commercially available (Stryker Endoscopy Co., Kalamazoo, MI, and Cryolife Inc., Kennesaw, GA) sizing blocks and channel cutters are helpful for appropriate sizing, as is described later.

All knee ligament subluxation tests should be performed after the induction of anesthesia in both the injured and the contralateral limbs. The amounts of increased anterior tibial translation, posterior tibial translation, lateral and medial joint opening, and external tibial rotation should be documented. A thorough arthroscopic examination should be conducted, documenting articular cartilage surface abnormalities³⁹ and the condition of the menisci.

OPERATIVE TECHNIQUE: LMT

The patient is placed in a supine position on the operating room table with a tourniquet applied with a leg holder, and the table adjusted to allow 90° of knee flexion. The opposite lower extremity is placed in a thigh-high elastic stocking and is padded to maintain mild hip flexion to decrease tension on the femoral nerve. After examination under anesthesia, diagnostic arthroscopy confirms the preoperative diagnosis and articular cartilage changes. A meniscus bed of 3 mm is retained when possible, except at the popliteal tendon region where the native meniscus rim is removed. The meniscus bed and adjacent synovium are rasped to aid in revascularization of the transplant.

Critical Points INTRAOPERATIVE EVALUATION

• Inspect transplant prior to administration of anesthesia.

• Medial meniscus transplant: Choose either central bone bridge or two-tunnel technique.

• Lateral meniscus transplant: Prepare implant to determine depth and width required for tibial slot.

• Repeat all knee ligament subluxation tests under anesthesia, both injured and contralateral limbs.

• Rate all articular cartilage surfaces for abnormalities

Normal.

Grade 1, softening.

Grade 2A, fissuring & fragmentation < 50% depth of the articular surface.

Grade 2B, fissuring & fragmentation > 50% depth of the articular surface.

Grade 3, subchondral bone exposed.

The tourniquet is inflated for only the two initial operative approaches. A limited 3-cm lateral arthrotomy is made just adjacent to the patellar tendon. Although arthroscopic techniques are available to prepare the tibial slot, the limited arthrotomy provides superior visualization and avoids incising into the patellar tendon, which must be displaced medially to properly place the tibial slot. A common mistake involves placing the central tibial slot lateral to the normal attachment of the anterior horn of the lateral meniscus.

A second 3-cm posterolateral incision is made just behind the fibular collateral ligament (FCL; Fig. 29-2), similar to that described in Chapter 28, Meniscus Tears: Diagnosis, Repair Techniques, and Clinical Outcomes, for inside-out lateral meniscus repairs.^29,53 The interval between the short head of the biceps muscle and the iliotibial band is identified and incised. The lateral head of the gastrocnemius is gently dissected with Metzenbaum scissors off the posterior capsule at the joint line just above the fibular head. Care is taken at this point because dissection that extends too far proximal to the joint line would enter the joint capsule. If this occurs, a capsular repair is required to maintain joint integrity during the inside-out meniscal repair procedure.

FIGURE 29-2 A, Site of the posterolateral incision for a lateral meniscus transplant. B, Incision site in the interval between the posterior edge of the iliotibial band and the anterior edge of the biceps tendon. C, The interval between the lateral gastrocnemius and the posterolateral capsule is opened bluntly, just proximal to the fibular head, avoiding entering the joint capsule proximally.

The inferior lateral geniculate artery, in close proximity, is identified and preserved. The space between the posterolateral capsule and the lateral head of the gastrocnemius is further developed bluntly. An appropriately sized popliteal retractor is placed directly behind the lateral meniscus bed and anterior to the lateral gastrocnemius muscle.

The width of the transplant is determined. A template made out of aluminum foil of the transplant’s width and length is cut and inserted into the lateral compartment to determine the proper placement of the bone slot. This sizing step is important to ensure that there is no lateral overhang (extrusion) of the meniscal body produced by placing the bone slot too far laterally. If there is a mismatch that results in lateral extrusion, the procedure may be converted from the bone bridge technique to one using two separate bone plugs and bone tunnels. The posterior bone plug is located directly at the lateral meniscus attachment. The anterior bone plug is placed more medially by a few millimeters to prevent lateral extrusion. The use of the bone bridge technique does require adequate size matching, and judgment is required at surgery in using the central bridge or separate bone plug technique. This same concept applies to MMTs. A rectangular bone slot is prepared at the anterior and posterior meniscus tibial attachment sites to match the dimensions of the prepared transplant.

The sequence of steps to prepare the lateral tibial slot is shown in Figure 29-3. The tibial bone slot is 1 to 2 mm wider than the transplant to facilitate implantation. The anterior and posterior horns of the transplant are placed into their normal attachment locations, adjacent to the ACL. It is important to note that a prior ACL reconstruction in which the tibial tunnel was placed in a lateral position may produce a technical problem in creating the tibial slot.

FIGURE 29-3 A, Tibial slot technique for lateral meniscus transplantation. The technique is shown for the lateral meniscus. An arthroscopically assisted technique or minilateral arthrotomy may be used in this procedure. The authors prefer the miniarthrotomy because it offers superior visualization and avoids incising the patellar tendon. Establish a line connecting the center of the anterior and posterior horn attachments using an electrocautery device. In the mini–open arthrotomy, a template of the meniscus coronal width is used to verify the medial-to-lateral width of the transplant to move the slot appropriately to prevent tibial overhang of the transplant. B, A burr removes the tibial spine and creates a 4-mm straight anterior-to-posterior reference slot along the plane of the tibial slope. C, This calibrated guide pin sits flush with the articular cartilage. D, The drill guide uses a guide pin that has been marked with a laser to set the depth of a second guide pin, allowing a drill to ream 5 mm less to retain the posterior portion of the tibial slot. E–G, The 8-mm drill bit with a collar at the defined depth is used, followed by use of a box cutter to create a rectangular slot of the desired depth and width. H, The lateral meniscus transplant with the central bone bridge technique is ready to be placed into the tibial slot.

(A–H, Reprinted with permission from Noyes, F. R.; Barber-Westin, S. D.; Rankin, M.: Meniscal transplantation in symptomatic patients less than fifty years old: surgical technique. J Bone Joint Surg Am 87[suppl 1{pt 2}]:149–165, 2005.)

A starter chisel and finishing chisels provide an alternative technique to create and fashion the tibial slot to its final depth and width (Fig. 29-4A