Indications and Contraindications
A comprehensive examination is conducted to assess gait, range of motion, tibiofemoral pain and crepitus, muscle strength, and ligament stability. Tibiofemoral joint-line tenderness is the primary indicator of a meniscal tear. Other clinical signs include pain on forced flexion, obvious meniscal displacement during joint compression, a lack of full extension, and a positive McMurray test.
Radiography should include a lateral view at 30° of flexion, a patellofemoral axial view, and a weight-bearing posteroanterior view at 45° of flexion. Full-length standing hip-knee-ankle weight-bearing radiographs are used as indicated to quantify varus or valgus malalignment. Magnetic resonance imaging may be done with a proton-density-weighted, high-resolution, fast-spin-echo sequence to determine the status of the articular cartilage and the menisci.
The indications and contraindications for meniscal repair are shown in Table I. Active patients in their second, third, or fourth decade of life are excellent candidates. Unstable red-white tears longer than 10 to 12 mm in the middle third of the meniscus should be considered for repair. The meniscal tissue should appear nearly normal, without secondary tears or fragmentation. The tear must be reducible at the time of arthroscopy, with adequate tear-site apposition. Patients must agree to comply with the postoperative rehabilitation program and avoid strenuous activities and deep knee flexion for four to six months.
Older, sedentary patients or those unwilling to comply with the postoperative rehabilitation protocol are treated with partial meniscectomy. Repair of inner-third white-white tears is not recommended. Middle-third white-white tears are repaired only when there is extension into this region from a red-red or red-white tear (a large flap tear). Repair is not appropriate for chronic degenerative tears, partial tears, or stable longitudinal tears <10 mm in length.
Operative Techniques
Complications and deteriorating results have been reported following the use of all-inside meniscal fixation devices17-22, which have inferior failure, stiffness, and displacement properties compared with vertical sutures23,24. The lack of prospective, randomized Level-I clinical studies precludes definitive recommendations regarding the various devices that are currently available22,25. Therefore, this article focuses on suture repair techniques and outcomes. The operative procedure has been described in detail by us elsewhere15.
A 30° arthroscope is used for standard intra-articular evaluation. A 70° arthroscope inserted through the notch allows visualization of the posterior peripheral meniscal attachment. The inside-out repair technique requires an accessory 3-cm posteromedial (Fig. 1) or posterolateral (Fig. 2) incision for safe suture retrieval. This exposure protects the neurovascular structures during suture retrieval and knot tying. The approach is performed under tourniquet control with the surgeon seated and using a headlight and the sterile prepared foot placed in the surgeon's lap. A popliteal retractor (Stryker, Kalamazoo, Michigan) is used to protect the popliteal neurovascular structures (Fig. 3).
The 30° arthroscope is placed through the anteromedial portal for repairs of the medial meniscus and through the anterolateral portal for repairs of tears of the posterior third of the lateral meniscus. The meniscal tear is first carefully inspected to determine that good-quality meniscal tissue remains. The superior and inferior synovial attachments of the meniscus are rasped, and the tear edges are débrided to remove loose fragments. Often, there are remaining meniscal fragments at the outer meniscal tear region that require débridement to obtain a good perpendicular meniscal bed for suture fixation.
A single-barrel curved or straight cannula (Richard Wolf Medical Instruments, Vernon Hills, Illinois) is placed in the opposite portal for suture advancement. Curved cannulae are used to direct suture needles away from the midline neurovascular structures. After anatomic reduction of the tear edges, multiple vertical divergent sutures are advanced, retrieved through the accessory posterior incision, and tied directly to the posterior aspect of the capsule. The first vertical sutures are placed at the superior border of the meniscal tear to reduce the meniscus and prevent superior migration when inferior sutures are placed. Sutures are placed every 3 to 5 mm along the tear edges in both a superior and an inferior plane. The close interval between the sutures is required to maintain tear-site reduction during the prolonged time needed for the healing of these avascular repairs. The repair is performed with multiple number-2-0 braided polyester nonabsorbable sutures (Ticron [Davis and Geck, Danbury, Connecticut] or Ethibond [Ethicon, Somerville, New Jersey]) on double-loaded 10-in (25.4-cm) needles.
For tears in the middle third of the meniscus, sutures are passed through the opposite portal with use of a 60° curved suture passer. The skin is undermined for suture retrieval. Tears in the anterior third are managed with a small skin incision, dissection down to the anterior meniscal attachment, and an outside-in repair.
A double-stacked technique is used for single longitudinal tears (Fig. 4). Superior (femoral surface) sutures are placed first to reduce the meniscus to its bed, and inferior (tibial surface) sutures are then placed to approximate the inferior portion of the tear. The same technique is used for double longitudinal tears in which the outer tear is near the meniscocapsular junction and the inner tear is near the red-white junction (Fig. 5). The peripheral tear is repaired first, followed by the central tear, which is repaired with vertical divergent sutures that span both tear sites (Fig. 6).
Radial tears that extend to the outer third of the meniscus and the periphery of the meniscal attachment may be repaired. Horizontal sutures are used to reduce these tears anatomically and are placed at 2 to 4-mm intervals. Three or four sutures are placed superiorly, and one or two sutures are placed inferiorly. The inner tear is repaired first, after which the peripheral tear is repaired (Fig. 7). Repair of a flap tear is indicated when the tear extends to the red-white junction or the periphery. Flap tears are managed by first repairing the radial component with horizontal sutures and then repairing the longitudinal component (Fig. 8).
Strategies to Augment Healing
Experimental studies have demonstrated that avascular meniscal tears do not heal spontaneously26-29. Therefore, techniques to promote a healing response are considered essential in the management of these injuries. A fibrin clot has been used, with varying success, by some authors29-31 in order to provide a reparative scaffold that supplies growth factors to promote chemotaxis, cell proliferation, and matrix synthesis to the tear site. Another technique is trephination, in which radially oriented channels to the peripheral vascular supply are created to encourage vascular and cell migration to the tear site. Again, reports on healing after this technique have demonstrated variable outcomes. For instance, Scott et al.32 reported an increase in the overall rate of healing of both medial and lateral menisci from 54.8% to 64% after the introduction of a technique involving dissection of the parameniscal synovial membrane. Zhang et al.33 reported a rerupture rate of only 5% in a group of thirty-six patients who had undergone suture repair as well as trephination.
Rasping of the vascularized parameniscal synovium promotes an injury response to assist healing. A few studies have demonstrated that, following the use of this technique, synovial cells migrate to the site of an avascular meniscal tear26,34 and result in superior healing compared with that following the use of a fibrin clot31. In a clinical study of the results of eighty-one inside-out repairs with parameniscal synovial rasping for tears with a 3 to 5-mm rim, Henning et al.35 reported a failure rate of only 9%. Rasping of the meniscal surface has been shown to induce expression of cytokines such as interleukin-1a, platelet-derived growth factor, and transforming growth factor-ß136. The expression of these chemotactic and mitogenic factors may facilitate meniscal healing.
Cell-based therapy involves transfer of tissue-engineered cells seeded onto scaffolds to augment healing. One study37 showed that implantation of an allogenic meniscal scaffold seeded with autologous articular chondrocytes along with a repair in a porcine model resulted in gross and histologic evidence of healing in all specimens. In contrast, no healing was seen in three control groups: one treated with a scaffold with repair, one treated with a repair alone, and one treated with no repair. In another study38, autologous and allogenic chondrocytes were seeded onto a bioabsorbable mesh to treat avascular porcine meniscal lesions; there was complete or partial healing in all animals, whereas there was no healing with repair alone or no treatment. Mesenchymal stem cells are appealing because of their potentially unlimited supply and ability to differentiate into specific therapeutic cell types39,40. Steinert et al.40 genetically modified bovine meniscal and mesenchymal stem cells to produce transforming growth factor-ß1. The cells were inserted by means of a scaffold into explanted avascular meniscal repair sites. Both cells types resulted in cell proliferation, increased synthesis of proteoglycan and collagen, and histologic evidence of healing.
Growth factors promote cell maturation, differentiation, and proliferation and hold promise for healing of avascular tears. In a sheep model, meniscal fibrochondrocytes from the avascular region responded to basic fibroblast growth factor by proliferating and creating new extracellular matrix41. DNA formation increased sevenfold, and protein synthesis increased fifteenfold. Other authors have identified transforming growth factor-ß1 as being effective at stimulating extracellular matrix production by rabbit meniscal fibrochondrocytes42.
The use of platelet-rich plasma as a healing adjunct has recently generated interest. Platelet-rich plasma contains a multitude of growth factors in physiologic proportions, which may be better than the use of isolated growth factors. Platelet-rich plasma may stimulate chemotaxis, cell proliferation, and angiogenesis. Ishida et al.43 reported that platelet-rich plasma improved healing of avascular meniscal defects, as determined on the basis of histologic criteria, in a rabbit model. Furthermore, in vitro analysis revealed enhanced extracellular matrix synthesis and proliferative behavior with platelet-rich plasma. Not all growth factors have been successful at promoting meniscal healing44,45. The ideal growth factor or combination of factors, dosage, and delivery mechanism as well as the potential side effects require further study.
Postoperative Rehabilitation
The rehabilitation program following repair of complex and avascular meniscal tears is summarized in the Appendix46. Immediate knee motion from 0° to 90° is permitted. The goal is a range of motion of 0° to 90° by seven to ten days, 120° by three to four weeks, and 135° by five to six weeks. Protected, partial weight-bearing for four weeks is recommended, with up to six weeks of toe-touch weight-bearing when the patient had a radial tear. No squatting or deep flexion activities are permitted for four to six months, and running, jumping, and cutting are restricted for six months.
Clinical Outcomes
Several prospective studies have documented our experience with inside-out avascular meniscal repair, which we began performing in 1983. The first investigation included sixty-six patients who underwent a concomitant meniscal repair and anterior cruciate ligament reconstruction, followed by arthroscopy six to twenty-five months postoperatively47. There was a total of seventy-nine meniscal repairs; fifty-one were done for tears located in the outer third of the meniscus, and twenty-eight were done for complex tears that extended into the middle third. Follow-up arthroscopy was indicated for symptoms related to either tibial hardware or tibiofemoral joint pain. A surgeon who had not been involved in the care of the patients reviewed the arthroscopic videotapes and operative records.
Of the repaired tears located in the outer third of the meniscus, 94% were classified as completely healed; 4%, as partially healed; and 2%, as failed. Of the repaired tears in the middle third, 54% were classified as completely healed; 32%, as partially healed; and 14%, as failed. The use of immediate knee motion and early weight-bearing was not deleterious to the healing of the meniscal repairs. This was one of the first investigations to demonstrate that repair of meniscal tears that either are located in the outer third or extend into the middle third have a satisfactory rate of healing when the procedure is warranted on clinical grounds.
In our next prospective study, we determined the clinical outcomes of treatment of 198 meniscal tears (in 177 patients) that extended into the middle third of the meniscus or that had a rim width of =4 mm48. Either a clinical examination at a minimum of two years postoperatively or follow-up arthroscopy was necessary for inclusion in the study. One hundred and twenty-six (71%) of the patients underwent anterior cruciate ligament reconstruction either with the meniscal repair (ninety-six patients) or at a mean of twenty-two weeks after the repair (thirty patients).
The overall rate of reoperations due to tibiofemoral symptoms was 20% (thirty-nine meniscal repairs). All patients who had tibiofemoral pain underwent follow-up arthroscopy. The reoperation rates according to the type of tear are shown in Table II. The limited number of meniscal tears in the individual classification categories prevented us from drawing specific conclusions regarding the outcome for each tear pattern.
The effect of six factors on healing rates of meniscal repairs was evaluated in the study48 (Table III). The rates of healing were significantly affected by three factors: the tibiofemoral compartment of the meniscal repair (with the healing rate being higher after the lateral meniscal repairs than after the medial meniscal repairs), the time from the repair to the follow-up arthroscopy (with the patients evaluated twelve months or less postoperatively having a higher healing rate than those evaluated more than twelve months postoperatively), and the presence of tibiofemoral symptoms at the time of follow-up (with asymptomatic patients having a higher healing rate than symptomatic patients). The results of this investigation support a recommendation of repair of meniscal tears that extend into the middle third of the meniscus, especially in patients in their third or fourth decade of life and in competitive athletes. The reoperation rate in the study should not be interpreted as the rate of meniscal healing.
We performed a third prospective study to determine the outcome of meniscal tears that extended into the avascular region in patients forty years of age or older49. Thirty of thirty-one consecutive meniscal repairs in twenty-nine patients were followed with either a clinical examination or arthroscopy. Anterior cruciate ligament reconstruction was performed at the time of the meniscal repair in twenty-one patients (72%).
There were no tibiofemoral joint symptoms and no need for additional surgery at the time of follow-up after twenty-six meniscal repairs (87%). We did not find the tibiofemoral compartment of the meniscal repair, the chronicity of the injury, concomitant anterior cruciate ligament reconstruction, or the condition of the articular cartilage to have a significant association with the presence of tibiofemoral pain at the time of follow-up or the need for a meniscal resection. There were no infections, knee motion problems, cases of saphenous neuritis, or other major complications. This study demonstrated that repair of complex tears in older adults is feasible, and that the majority of patients do not have tibiofemoral joint symptoms at an average of three years postoperatively.
In a fourth prospective study, we evaluated the results of seventy-one of seventy-four consecutive meniscal repairs (a 96% follow-up rate) that had been done in fifty-eight patients (sixty-four knees) under the age of twenty years50. Fifty-four knees (84%) were in patients who had reached skeletal maturity. Forty-three meniscal repairs (61%) in thirty-six knees were performed concurrently with an anterior cruciate ligament reconstruction, and fourteen meniscal repairs (20%) in eleven knees were done at a mean of thirty-four weeks prior to an anterior cruciate ligament reconstruction. All patients who had an anterior cruciate ligament reconstruction were skeletally mature. The initial follow-up evaluation, at a mean of fifty-one months postoperatively, showed no tibiofemoral symptoms or failure requiring resection after fifty-three (75%) of the seventy-one meniscal repairs.
From this study50, a subgroup of twenty-nine meniscal repairs of single longitudinal tears that extended into the avascular zone underwent further evaluation. Clinical evaluation was conducted in nineteen cases (at a mean of 16.8 ± 3.3 years postoperatively), magnetic resonance imaging was done in seventeen (at a mean of 17.2 years), and weight-bearing posteroanterior radiographs were made in twenty-two (at a mean of 16.8 ± 3.2 years). The results were determined with two validated knee-rating systems and the assessment of radiographs and medical records by independent physicians and researchers. A 3-T magnetic resonance imaging scanner with cartilage-sensitive pulse sequences, including T2 mapping, was used to study cartilage degeneration and repair site characteristics. Eighteen (62%) of the twenty-nine meniscal repairs were successful, with retention of a meniscus that appeared to be functional. Six repairs required meniscal resection, two knees demonstrated loss of joint space on radiographs, and three repairs failed according to magnetic resonance imaging criteria. There were no significant differences between the short and long-term results in terms of the mean scores for pain, swelling, and jumping; the patient's grade of the overall knee condition; or the overall Cincinnati knee rating score.
The results of this long-term evaluation50 support the recommendation of repair of simple or complex meniscal tears that extend into the avascular zone when the appropriate indications are present. This recommendation is particularly appropriate for young active individuals in whom removal of a meniscal tear that extends into the middle avascular region would result in major loss of meniscal function and an increased risk of future joint arthritis. Advanced magnetic resonance imaging and weight-bearing posteroanterior radiographs are essential to determine the actual failure rate and chondroprotective effects of meniscal repairs.
A summary of the clinical outcomes of meniscal repair in a variety of other, recently published investigations is provided in a table in the Appendix20,21,51-66. The majority of these studies focused on vertical meniscal suture repair techniques; few authors reported on the outcome of horizontal suture repair or all-inside fixators. The rates of failure of vertical and horizontal suture repairs vary greatly, as do correlations with the side of the meniscal tear, concurrent anterior cruciate ligament reconstruction, the location of the meniscal tear, and patient age and sex.
Investigations of newer all-inside suture systems such as the RAPIDLOC (DePuy Mitek, Raynham, Massachusetts), MaxFire Meniscal Repair Device (Biomet, Warsaw, Indiana), and FAST-FIX (Acufex, Smith and Nephew Endoscopy, Andover, Massachusetts) have demonstrated acceptable failure rates of between 9% and 13%51,52,58,60,66-68. However, longer-term follow-up of the results associated with these systems is required to ensure that the rate of failure does not increase with time. In addition, we believe that the use of only two or three sutures, as practiced with all-inside suture systems, provides inadequate stabilization and is inferior to the use of multiple vertical divergent sutures.
Complications and deteriorating results were reported following the early use of all-inside fixation devices17-21,67. Lee and Diduch17 reported an increasing rate of failure with time in twenty-eight patients who had undergone meniscal repair with the Meniscus Arrow (Bionx Implants, Blue Bell, Pennsylvania) and a concomitant anterior cruciate ligament reconstruction. The initial success rate of 90.6% reported at a mean of 2.3 years postoperatively decreased to 71.4% at 6.6 years. Complications with this device, such as chondral damage, cyst formation, chronic effusions, joint irritation, synovitis, and device breakage and migration into the extra-articular soft tissues, have been reported by several authors18-20,69-74.
The question of whether meniscal repair is effective in preventing joint deterioration remains unanswered. However, the well-documented irreparable joint damage and the poor results of long-term clinical studies following partial and total meniscectomy indicate that preservation of meniscal tissue is paramount for long-term joint function. It is our opinion that the gold-standard technique is a meticulous inside-out repair with multiple vertical divergent sutures and an accessory posteromedial or posterolateral approach to tie the sutures directly posterior to the meniscus attachment. We consider meniscal repair to be as important as, if not more important than, an anterior cruciate ligament reconstruction with regard to the long-term knee function of patients who sustain these concomitant injuries. Often, a complex meniscal repair will take as long as an anterior cruciate ligament reconstruction, and the surgeon should prepare for sufficient time when planning the operative procedure.
We disagree with the approach of leaving a meniscal tear that is longer than 10 to 12 mm untreated at the time of anterior cruciate ligament reconstruction. To use a conservative approach and hope for healing may risk further tearing and subsequent loss of meniscal function. Once a meniscectomy has been performed in a young patient, there are few additional options. It is unfortunate that many patients requiring meniscal transplantation had ineffective original treatment of the meniscal tear; either a large tear was not treated or was repaired with too few sutures or with fixators that provided only limited stability, or a major tear that extended into the middle avascular region was removed when it could have been repaired.
A fibrin clot technique was not used in our studies47-50, as the clot would have interfered with the exact millimeter-to-millimeter reduction and fixation at the meniscal tear site with the suture technique that was performed. In the future, tissue engineering may increase the success rates of meniscal repairs of tears that extend into the avascular region75-79. Cell-based therapy involving use of meniscal fibrochondrocytes, articular chondrocytes, or mesenchymal stem cells seeded onto scaffolds offers promise80,81, as does the introduction of growth factors into the repair site.
Concepts
Although many meniscal tears are repairable, as previously discussed, not all torn menisci are salvageable, especially if considerable tissue damage has occurred. The goal of transplantation of human menisci is to restore the load-bearing function of the meniscus, decrease symptoms, and provide chondroprotective effects82-86. Even though the procedure was first described more than twenty-five years ago87, it remains in an evolving state with an unpredictable and often undesirable long-term outcome. Clinical studies have shown that meniscal transplantation decreases tibiofemoral joint pain in the short term. However, in our experience, most meniscal transplants gradually deteriorate, tear, or shrink, thereby losing the ability to provide function. Therefore, the current goal is to provide short-term benefits to the patient until a superior meniscal transplant is clinically available.
Indications and Contraindications
The clinical evaluation of a candidate for meniscal transplantation is the same as that described for a candidate for meniscal repair. The indications and contraindications for this procedure are shown in Table IV. The optimal candidate is a patient under the age of fifty who has had a total meniscectomy, has pain with daily activities, and demonstrates early deterioration of the articular cartilage in the involved tibiofemoral compartment. There should be no radiographic evidence of advanced arthritis in the tibiofemoral joint. At least 2 mm of tibiofemoral joint space should be visible on the 45° weight-bearing posteroanterior radiograph88. Arthroscopic examination confirms that a patient is a suitable candidate for meniscal transplantation. Normal axial alignment and a stable joint are required. The body mass index must be within the normal range.
Advanced knee joint arthritis with flattening of the femoral condyle, concavity of the tibial plateau, and osteophytes that prevent anatomic seating of the meniscal transplant are contraindications. Untreated lower-limb malalignment and knee joint instability are associated with poor outcomes of meniscal transplantation. Preexisting knee arthrofibrosis, severe lower-limb muscular atrophy, and a history of joint infection with subsequent arthritis are all contraindications. Symptomatic noteworthy deterioration of the patellofemoral articular cartilage (exposure of subchondral bone) and obesity (a body mass index of >30 kg/m2) are also contraindications.
Transplant Sizing
We use the radiographic criteria for sizing of meniscal transplants established by Pollard et al.89, and we avoid secondary sterilization with irradiation. The medial meniscal transplant cannot be oversized in its medial-to-lateral dimension, as this would prevent use of the slot technique and the preferable bone-bridge transplant technique, which maintains the native geometry of the implant. In addition, the medial meniscus may have a thin or narrow anterior-third attachment distal to the tibial joint surface, which is not acceptable. The lateral meniscus may have a diminutive (8 to 10-mm) middle-third anatomic configuration, which also is not suitable for transplantation. The transplant is inspected before the patient is anesthetized, and preoperative planning involves advising the patient that, in rare instances, the transplant may not be suitable and thus may prevent the operative procedure from commencing.
Operative Management
Transplantation of the Lateral Meniscus
The operative technique has been described in detail elsewhere90,91. 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. A meniscal bed of 3 mm is retained when possible. The meniscal bed and the adjacent synovium are rasped in an attempt to aid in revascularization.
A limited 3-cm lateral arthrotomy is performed just adjacent to the patellar tendon and is preferred over an all-arthroscopic technique. A second 3-cm incision is made posterolaterally, and the approach is the same as that used for a repair of the lateral meniscus, as already described. An appropriately sized popliteal retractor is placed directly behind the lateral meniscus bed and anterior to the lateral head of the gastrocnemius.
The width of the transplant is determined. A template, made out of aluminum foil, of the transplant's width and length is cut and is inserted into the lateral compartment to determine the proper placement of the bone slot. This sizing step is important to ensure that no lateral overhang (extrusion) of the meniscal body is produced by placing the bone slot too far laterally. A rectangular bone slot is prepared at the anterior and posterior meniscal tibial attachment sites to match the dimensions of the prepared transplant.
The tibial bone slot is 1 to 2 mm wider than the transplant to facilitate implantation. A tibial slot sizing guide is used to check the length and depth. A sizing block confirms that the transplant bone bridge is of the correct width and depth.
Use of a dovetail technique, which has the advantage of providing additional stability to the fixation at the tibial bone portion of the transplant, may also be considered. This procedure entails cutting a trapezoidal bone block that includes a more narrow 7-mm bone bridge. This procedure requires additional time to prepare the transplant.
The transplant is inserted into the slot (Fig. 9), and the bone portion of the graft is seated against a retained posterior bone buttress at the tibia to achieve correct anterior-to-posterior placement of the attachment sites. A vertical suture in the posterior aspect of the meniscal body is passed posteriorly to provide tension and facilitate placement of the transplant. The knee is flexed, extended, and rotated to confirm that the placement of the transplant is correct. Sutures are placed into the anterior one-third of the meniscus, attaching it to the prepared meniscal rim under direct visualization.
Two number-2-0 nonabsorbable sutures passed retrograde into the tibial slot over the central bone bridge (before passage of the transplant) hold the transplant securely in the tibial slot and are tied over a tibial post. The arthrotomy site is closed, and the inside-out meniscal repair is completed with multiple vertical divergent sutures, which are placed first superiorly to reduce the meniscus and then inferiorly in the outer one-third of the transplant. Sutures are not placed in the middle and inner thirds to avoid weakening the transplant, which has limited healing capability in those regions (Fig. 10).
Transplantation of the Medial Meniscus
A 4-cm anteromedial skin incision is made adjacent to the patellar tendon for the anterior arthrotomy and a second 3-cm vertical incision is made posteromedially, in a manner similar to that described for inside-out meniscal repairs. A meniscal retractor is placed in the interval anterior to the gastrocnemius tendon and directly posterior to the meniscal bed and the posterior aspect of the capsule. The two approaches are performed with the tourniquet inflated to 275 mm Hg. The approaches usually require less than fifteen minutes; otherwise, the tourniquet is not used.
The goal of the operative procedure is to transplant the medial meniscus and bone attachments into the normal anterior and posterior attachments and to suture the transplant to maintain the desired position in the knee joint. An aluminum foil template of the medial meniscus transplant is measured according to its anterior-posterior and medial-lateral dimensions and is inserted through the anterior arthrotomy site to measure the medial tibial plateau.
It is verified that the anterior and posterior meniscal attachment locations are at the anatomically correct sites. The central bone-bridge technique removes 4 to 6 mm of the medial intercondylar tubercle. If the transplant is suitable and no medial tibial overhang is present, then the central bone-bridge technique is our preference. If the transplant needs to be adjusted and tensioned to fit to the medial tibial plateau, then the two-tunnel technique is selected. This sizing step is critical to obtain proper placement of the medial meniscal transplant into the host tibia. In some knees, the central slot technique is not possible because of a sizing problem that results in excessive medial displacement of the meniscal body or that compromises the tibial attachment of the anterior cruciate ligament.
Central Bone-Bridge Technique for Transplantation of the Medial Meniscus
The meniscal transplant is prepared with use of either a rectangular or a dovetail technique. A reference slot is first made on the tibial plateau in the anteroposterior direction. A guide pin is positioned in the slot, inferiorly on the tibia, and a cannulated drill-bit is placed over the pin to drill a tunnel. Osteotomes and chisels are then used to prepare the tibial slot. The anterior cruciate ligament attachment is located directly lateral to the tibial slot, and no more than 2 mm of its attachment should be compromised. The final tibial slot is 8 to 9 mm in width and 10 mm in depth. A rasp is used to smooth the slot to allow insertion of the transplant's central bone bridge.
A vertical suture is placed through the posterior meniscal horn and advanced through the capsule to exit through the posteromedial incision. The meniscus is passed through the arthrotomy site into the knee, with tension placed on the posterior suture to facilitate the proper positioning of the meniscus in the knee joint. The position of the central bone bridge is adjusted in the anterior-posterior direction to be anatomically correct relative to the femoral condyle. The knee is moved through flexion and extension and tibial rotation to align the transplant. Occasionally, there is an osteophyte on the anterior portion of the medial tibial plateau that must be resected to avoid compression of the meniscal transplant.
The suture fixation of the meniscal transplant is the same as that described for the lateral meniscus transplant (Fig. 11).
Two-Tunnel Technique for Transplantation of the Medial Meniscus
If it is determined that the central bone-bridge technique cannot be used, the surgeon must prepare separate anterior and posterior bone attachments for the meniscal transplant that will be secured to the normal anatomic attachment sites. We do not recommend using a meniscal implant from which one or both bone plugs have been removed, leaving only a soft-tissue graft without bone fixation, as this compromises fixation at the anatomic attachment sites and meniscal extrusion is usually the end result. The transplant is prepared with a posterior bone plug 8 mm in diameter and 12 mm in length. The anterior bone attachment is 12 mm in width, length, and depth. Two number-2-0 nonabsorbable sutures are passed retrograde through each bone attachment, with two additional locking sutures placed in the meniscus adjacent to the bone attachment for secure fixation.
The anteromedial and posteromedial approaches are performed as described. A guidewire is placed adjacent to the tibial tubercle and is directed to the anatomic posterior meniscal attachment. A tibial tunnel is drilled over the guidewire to a diameter of 9 mm. The bone tunnel edges are chamfered and slightly enlarged with a curet to allow easier passage of the graft into the tibial tunnel. A limited medial femoral condyle notchplasty is usually required. At least 8 mm of opening adjacent to the posterior cruciate ligament and medial femoral condyle is required to pass the posterior bone attachment of the graft. Rarely, a subperiosteal release of the long fibers of the tibial attachment of the distal part of the medial collateral ligament (with later suture anchor repair) is required to open the medial aspect of the tibiofemoral joint sufficiently.
The graft is passed through the anteromedial arthrotomy site. The surgeon is seated with a headlight in place, and the patient's knee is flexed 90°. A guidewire is passed retrograde through the tibial tunnel, and the sutures attached to the posterior bone plug are retrieved. A second suture is placed in the posterior horn and is passed inside out through the posteromedial approach to guide the meniscus.
The knee is flexed 20° under a maximum valgus load to facilitate passage of the posterior bone plug with the meniscal body suture held by an assistant. A nerve hook or other blunt instrument is used to gently assist the passage of the graft. With direct visualization, it is possible to confirm appropriate passage of the meniscal graft and positioning into the medial tibiofemoral compartment. Care is taken to not advance the posterior part of the meniscal body too far into the tibial tunnel and to seat only the osseous portion of the graft in order to not shorten the overall circumference of the meniscal graft.
The posterior meniscal bone attachment sutures are tied over the tibial post to provide tension to the posterior bone attachment. One or two sutures are passed to secure the posterior horn. The knee is flexed and extended to assess meniscal fit and displacement. The optimal location for the anterior meniscal bone attachment is identified to restore proper meniscal position and prevent medial overhang of the transplant. The knee is placed in full extension, and the position of the transplant is verified as being correct.
A 12-mm rectangular bone attachment is fashioned in the tibia to correspond to the anterior bone plug of the meniscal graft. A 4-mm bone tunnel is placed at the base of this bone slot to exit at the anterior aspect of the tibia just proximal to the posterior bone tunnel. The sutures are passed through the bone tunnel, and the anterior horn is seated. Full knee flexion and extension are again performed to determine proper graft placement and fit. Tension is applied to the anterior bone sutures, which are not tied at this point but are used to maintain tension in the graft during the inside-out suture repair. This meticulous seating of the meniscal transplant under circumferential tension with bone attachments for both the anterior and the posterior horn is believed to be crucial for an effective weight-bearing position and function of the meniscus.
The anterior arthrotomy site is closed, and the suture cannula is inserted into the lateral portal for the meniscal repair. The meniscal repair is performed in an inside-out fashion, starting with the posterior horn, with use of multiple vertical divergent sutures of number-2-0 nonabsorbable material both superiorly and inferiorly and constant tensioning of the meniscus from posterior to anterior to establish circumferential tension.
Alternative techniques such as use of meniscal fixators are not recommended, as these devices lessen the ability to precisely secure and restore tension to the meniscal transplant. Finally, the anterior arthrotomy site is opened and final tensioning and fixation of the anterior horn bone attachment are performed. Additional sutures are required to secure, under direct vision, the most anterior one-third of the meniscus to the capsular attachments (Fig. 12).
Clinical Outcomes
We conducted two prospective clinical investigations of ninety-six fresh-frozen irradiated92 and forty consecutive cryopreserved82 medial and lateral meniscal transplants. The follow-up rate was 100% in both of these prospective studies.
In the first investigation, we analyzed the outcomes after implantation of a total of ninety-six consecutive irradiated meniscal transplants in eighty-two patients92. Twenty-eight menisci in twenty-seven patients required early arthroscopic resection because of a lack of healing at a mean of ten months postoperatively. These twenty-eight menisci were included in the overall failure rate. Additionally, one patient died of causes unrelated to the knee condition prior to the two-year follow-up point. This left sixty-seven menisci (fifty-seven medial and ten lateral) in fifty-four patients, who all returned for follow-up at a mean of forty-four months (range, twenty-two to 111 months) postoperatively.
The meniscal transplant failure rate was 6% (one) of eighteen knees with normal or only mild arthritis as seen on magnetic resonance imaging, 45% (fourteen) of thirty-one knees with moderate arthritis, and 80% (twelve) of fifteen knees with advanced arthritis (p < 0.001). (Magnetic resonance imaging was not performed on three knees.)
Independent examiners conducted histologic evaluations of the twenty-eight meniscal allografts that had failed early. There was no evidence of a cellular reaction suggestive of a rejection phenomenon in any of the tissues examined. The specimens consistently demonstrated minimal, if any, cellular repopulation of any portion of the meniscus. The predominant cell type was a fibrocyte. Remodeling with abnormal collagen orientation was found in six specimens. The remodeling phenomenon resulted in a loss of the normal surface radial collagen architecture and a loss of the normal circumferential fibers within the meniscal substance. In essence, the tissue represented a fibrous tissue interposition arthroplasty with little to no remaining true meniscus properties.
It is not known if low-dose irradiation (2.0 to 2.5 Mrad [20,000 to 25,000 Gy]) affects the failure rate of meniscal transplantation. This study92 suggested that patients with advanced arthritis and alterations in joint geometry (a major tibial concavity and femoral condyle flattening) with exposed bone surfaces over the majority of the tibiofemoral compartment are not candidates for meniscal transplantation.
In the second prospective study, designed to avoid graft irradiation, a total of forty cryopreserved meniscal transplants were implanted in thirty-eight patients, who were then followed for a mean of forty months (range, twenty-four to sixty-nine months) postoperatively82. There were twenty male and eighteen female patients whose mean age at surgery was thirty years. At the time of the lateral meniscus transplant, a concurrent osteochondral autograft transfer of the lateral femoral condyle was done in thirteen knees to treat a full-thickness articular cartilage defect. Knee ligament reconstruction was done before the meniscal transplant in four knees and at the same time as the transplant in four knees.
Twenty-nine meniscal transplants (73%) were analyzed with magnetic resonance imaging at an average of thirty-five months (range, twelve to sixty-seven months) postoperatively. Independent orthopaedic surgeons who were blinded with regard to patient information reviewed these images, measuring the height, width, and displacement of the transplant during full or partial weight-bearing conditions93. A system for the classification of meniscal transplant characteristics was developed on the basis of the findings on magnetic resonance imaging, clinical examination, follow-up arthroscopy (when performed), and tibiofemoral symptoms.
Before the surgery, thirty patients (79%) had moderate-to-severe pain with daily activities, but only four (11%) had pain with daily activities at the time of follow-up. All patients had had preoperative pain in the tibiofemoral compartment in which the meniscectomy was performed, but at the time of follow-up twenty-seven knees (68%) had no tibiofemoral compartment pain and thirteen (33%) were improved and had only mild pain. Thirty-four patients (89%) stated that the condition of the knee had improved. Preoperatively, only one patient was able to participate in sports without problems. At the time of follow-up, twenty-nine patients (76%) were participating in light low-impact sports without problems and one patient was participating with symptoms, against advice.
One patient had signs of a meniscal transplant tear at the time of follow-up. One patient had tibiofemoral joint line pain and increased palpable crepitation compared with the findings of the preoperative examination. All patients had a normal range of knee motion.
Five patients had follow-up arthroscopy because of symptoms related to the transplant. A tear in the periphery of the meniscal transplant, at the capsular junction, was successfully repaired in three patients, and small tears in the transplant were resected in two patients. None of these patients had additional symptoms. One other patient had a total knee replacement thirty-five months following the meniscal transplant because of unresolved knee pain.
The mean displacement of the twenty-nine meniscal transplants examined with magnetic resonance imaging was 2.2 ± 1.5 mm (range, 0 to 5 mm) in the coronal plane. In the sagittal plane, the mean displacement of the posterior horn of the transplants was 1.1 ± 2.0 mm (range, 0 to 9 mm) and the mean displacement of the anterior horn was 1.2 ± 1.7 mm (range, 0 to 6 mm). Intrameniscal signal intensity was normal in one case, was grade 1 in thirteen cases, was grade 2 in eleven, was grade 3 in three, and could not be evaluated in one.
There was a correlation between the arthritis rating on magnetic resonance imaging and the transplant characteristics. Of the sixteen transplants in knees with mild arthritis, ten had normal characteristics and six had altered characteristics. Of the twelve transplants in knees with moderate arthritis, three had normal characteristics, four had altered characteristics, and five failed.
Studies of cryopreserved meniscal transplants conducted by others have revealed a failure rate of approximately 30%. Stollsteimer et al.94 followed twenty-three patients for thirteen to sixty-nine months after implantation of a cryopreserved meniscal transplant. Eight patients (35%) required a second operation because of meniscal symptoms five to twenty-eight months postoperatively. Although good pain relief was obtained in eighteen knees, magnetic resonance imaging in twelve knees showed some shrinkage of the transplants, which were an average of 63% of the size of the contralateral normal menisci.
Rath et al.95 reported the results two to eight years following implantation of twenty-two cryopreserved meniscal transplants. A concomitant anterior cruciate ligament reconstruction was done in eleven of the eighteen patients. Eight menisci (36%) failed and were removed at an average of thirty-one months after implantation. Histologic analysis of the torn transplants demonstrated a >50% reduction in the number of meniscal fibrochondrocytes at the periphery compared with the number in the torn native menisci. Even so, all patients except one had significant improvements in outcome scores (p < 0.0001). Hommen et al.96 reported a ten-year survival rate of only 45% nine to thirteen years following implantation of twenty cryopreserved meniscal transplants. The failures were identified on the basis of low Lysholm scores (<65 points), no reduction in pain, findings on magnetic resonance imaging, and second-look arthroscopy data.
Van Arkel et al.97 reported the results of nineteen cryopreserved meniscal transplants followed for fourteen to fifty-five months postoperatively with magnetic resonance imaging, arthroscopy, and clinical examination. Sixteen transplants were successful, and three failed as indicated by clinical findings. However, magnetic resonance imaging criteria revealed eight failures, as four transplants had severe shrinkage and four had moderate shrinkage. None of the transplants were in a normal position; eleven showed partial extrusion, six demonstrated extrusion, and two had a bucket-handle-like appearance. The authors did not provide details on the surgical technique, including whether attachment of the anterior and posterior horns was performed.
To our knowledge, two survival analyses of meniscal transplantation have been published. Van Arkel and de Boer98 conducted such an analysis of sixty-three consecutive cryopreserved meniscal transplants followed for four to 126 months postoperatively. Persistent pain or mechanical damage (a detached or torn transplant) was used to determine transplant failure. The cumulative ten-year survival rates of lateral transplants, medial transplants, and combined transplants in the same knee were 76%, 50%, and 67%, respectively. Lateral transplants failed at an average of fifty-three months after implantation, and medial transplants failed at an average of twenty-five months.
Verdonk et al.84 performed a follow-up study of 100 fresh meniscal transplants at a mean of 7.2 years postoperatively. The failure rate was 28% for medial meniscus transplants (mean time to failure, 6.0 ± 8.8 years) and 16% for lateral meniscus transplants (mean time to failure, 4.8 ± 2.8 years). The average cumulative survival time (11.6 years) was identical for the medial and lateral transplants. The cumulative survival rates at ten years were 74.2% for the medial transplants and 69.8% for the lateral transplants. Medial meniscus transplants done concurrently with a high tibial osteotomy had a higher cumulative survival rate of 83.3% at ten years.
Postoperative alterations in the signal intensity of meniscal transplants on magnetic resonance imaging have been frequently reported94,97,99,100. Potter et al.99 evaluated twenty-nine meniscal transplants with magnetic resonance imaging and clinical examination three to forty-one months postoperatively. Increased signal intensity was detected in the posterior horn in fifteen knees, and peripheral displacement at the body was noted in eleven; all of these knees had moderate or severe chondral degeneration. Histologic analysis demonstrated peripheral cellular repopulation but a central core that was acellular or hypocellular with evidence of disorganized collagen fibers. Knees with mild chondral degeneration had no abnormalities noted in the meniscal transplant and demonstrated clinical results that were superior to those with severe chondral degeneration.
Verdonk et al.101 followed thirty-eight patients with a total of thirty-nine fresh meniscal allografts for ten to 14.8 years postoperatively. Standing posteroanterior radiographs of thirty-two knees made at the time of follow-up revealed no further decrease in the tibiofemoral joint space in thirteen knees (41%), a grade-1 decrease in eleven (34%), a grade-2 decrease in seven (22%), and a grade-3 decrease in one (3%). Magnetic resonance imaging was performed on seventeen knees and revealed partial extrusion of the transplant in twelve of them. Grade-3 signal intensity was noted in seven transplants at one year and in ten transplants at the final follow-up evaluation. The authors concluded that the operation had a potentially chondroprotective effect on the basis of the absence of additional joint space narrowing in 41% of the cases.
In conclusion, meniscal transplantation is acceptable for younger patients, especially those who have symptoms with daily activities as there are few if any other available treatment options for such patients. The short-term results have shown that the majority of patients have improved knee function and relief of pain. However, whether this operation provides a chondroprotective effect remains unknown. For this reason, meniscal transplantation is not recommended after meniscectomy in asymptomatic patients. Rather, patients should be followed yearly and magnetic resonance imaging of the articular cartilage to detect early deterioration should be performed before substantial symptoms occur in order to provide a relative indication for a meniscal transplant procedure. The long-term outcome appears to be eventual deterioration, degeneration, and loss of function. Patients should be advised that the procedure has only short-term benefits and, in the long term, additional surgery will likely be required. On the basis of our experience, we believe it reasonable to consider a second meniscal transplant procedure after the first transplant has undergone the expected deterioration and symptoms have returned.
There are several areas in which advances may improve the success rates of meniscal transplantation. These include issues related to transplant remodeling; collagen fiber restoration to resist tensile, compressive, and shear forces; changes in the transplant collagen matrix with altered material and structural properties; cellular repopulation and function with regard to maintaining transplant homeostasis; and the use of fresh transplants with viable cells and meniscal scaffolds.