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Meniscal Allograft Transplantation Abstract Meniscal allograft transplantation is a reasonable treatment option for the young patient with symptomatic meniscal deficiency. Although clinical results are promising, in most studies only mixed procedures have been performed, with short- or medium-term follow-up. Important potential prognostic factors include patient selection, severity of degenerative changes, limb stability and alignment, graft sizing and processing methods, graft placement, and graft fixation. The use of meniscal allograft transplantation should be considered a salvage operation for the difficult clinical dilemma of meniscal deficiency in young patients. Nonetheless, in carefully selected patients, this procedure can predictably relieve compartmental symptoms, and, in conjunction with anterior cruciate ligament reconstruction, restore knee stability. In addition, the partial restoration of meniscal function provided by this procedure may slow the degenerative arthritic process. I njury to the menisci of the knee can lead to alteration in the stability and biomechanics of involved joints. Meniscal injuries may alter the transmission of loads across the knee joint or may destabilize the knee, especially when injuries are sustained in conjunction with anterior cruciate ligament (ACL) injury. Such injuries may lead to clinical and radiographic articular cartilage changes. Meniscus repair or partial meniscectomy are common procedures that attempt to preserve meniscal functions, which include load transmission, proprioception, joint lubrication, and stability. However, with large tears that require partial or total meniscal excision, preservation of the meniscus sometimes is impossible. Meniscal deficiency may in turn lead to progressive dete- rioration of the articular cartilage, with resultant radiographic joint space narrowing. Meniscal allograft transplantation is a surgical option for select patients with symptomatic meniscal deficiency. Often this deficiency is addressed in conjunction with concomitant injuries, the most common being tears of the ACL. A number of basic science as well as clinical studies have helped clarify the role of the variables that may contribute to successful meniscal transplantation. These factors include patient selection, surgical technique, graft sizing and preservation, graft fixation, and graft placement. Anatomy and Function The menisci are fibrocartilaginous structures consisting of coarse cartilage bundles circumferentially ar- ranged to disperse compressive load and radially resist shear. 1 Water ac- counts for 70% of meniscal compo- sition; collagen (90% of it type I) Jon K. Sekiya, MD Christopher I. Ellingson, MD Dr. Sekiya is Assistant Professor, University of Pittsburgh Medical Center, Center for Sports Medicine, Pittsburgh, PA. Dr. Ellingson is Lieutenant Commander, Medical Corps, United States Navy, Bone and Joint/Sports Medicine Institute, Department of Orthopaedic Surgery, Naval Medical Center Portsmouth, Portsmouth, VA. The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government. None of the following authors or the departments with which they are affiliated has received anything of value from or owns stock in a commercial company or institution related directly or indirectly to the subject of this article: Dr. Sekiya and Dr. Ellingson. Reprint requests: Dr. Sekiya, University of Pittsburgh Medical Center, Center for Sports Medicine, 3200 S Water Street, Pittsburgh, PA 15203. J Am Acad Orthop Surg 2006;14:164- 17 4 Copyright 2006 by the American Academy of Orthopaedic Surgeons. 164 Journal of the American Academy of Orthopaedic Surgeons makes up 60% to 70% of the dry weight. 2 Trapped by negatively charged glycosaminoglycans, water in the menisci provides resistance to compressive loads, and two types of fibrochondrocytes synthesize the fibrocartilaginous matrix. At birth, the entire meniscus is vascular, but by adulthood, only the outer 10% to 30% of vascularity remains, with blood supplied via the perimeniscal capillary plexus off the superior and inferior medial and lateral genicular arteries. 3,4 Postulated to have mech- anoreceptive proprioceptive function, 5 type I and II nerve endings are found at the horn insertions in the outer portions. Both menisci are C-shaped and attach to the tibia via bony attachments to the tibial plateau; a discoid variant of the lateral meniscus is found in 3.5% to 5% of patients. 6 The surface area of the anterior tibial bony attachment of the medial meniscus is 61 mm 2 ; the posterior attachment is anterior to the insertion of the posterior cruciate ligament. 7 Covering a larger portion of the tibial articular surface, the lateral meniscus is semicircular, with the anterior horn attaching adjacent to the ACL and the posterior horn attaching behind the intracondylar eminence. 3 With knee flexion, average excursions of the menisci are 5.2 mm for the medial and 11 mm for the lateral. 8 A primary function of the menisci is load sharing, which is accomplished through improving knee con- gruency and increasing joint contact area. The medial and lateral menisci transmit 50% and 70% of their compartmental loads, respectively. Me- dial meniscectomy decreases contact area 50% to 70% and increases contact stress 100%, 3 whereas lateral meniscectomy decreases contact area 40% to 50% but dramatically increases contact stress 200% to 300% secondary to the relative convex surface of the medial tibial plateau. 3 Another function of the menisci involves their viscoelastic properties, which aid in shock absorption; meniscectomy has been reported to decrease the shock absorption capa- bilities of the knee by 20%. 9 The medial meniscus also acts as a secondary restraint to anterior tibial translation in the ACL-deficient knee; therefore, medial meniscectomy in the ACL-deficient knee increases tibial translation by 58% at 90°. 3 The posterior horn of the medial meniscus is especially important in contributing to joint stability. 10 Meniscal Allograft Preservation The four main methods of preserving allografts are fresh, cryopreserved, fresh-frozen (deep-frozen), and freeze-dried. In accordance with standards established by The Amer- ican Association of T issue Banks for donor suitability and testing, 11 menisci are harvested under strict asep- tic conditions within 12 hours of cold ischemic time. They may be harvested with or without bone plugs and a small synovial rim for atraumatic handling of the allograft. 11 The allografts are then pro- cessed according to the preservation method. Fresh grafts, maintained at 4°C in lactated Ringer solution, can be stored for up to 7 days only. Such limited time for graft sizing and se- rologic testing presents logistical dif- ficulties and limits the use of fresh grafts in clinical practice. Further, these grafts have not been shown to improve efficacy in vivo. Cryopreserved allografts main- tain a cell viability of 10% to 40% by use of controlled freezing in a glycerol-containing medium (ie, cryoprotectant). The expense and difficulty of this technique has limited its use, especially given the un- certainty of donor-cell viability. Me- niscal allografts are invaded by host cells as early as 4 weeks after transplantation. 12 Fresh-frozen allograft preservation, in which allografts are stored at approximately −80°C, is a simpler and less expensive method than cryopreservation. Although fresh- frozen allografts lack donor-cell viability, the lack of viability has not affected allograft survival and meniscal transplant outcomes. The use and demand for fresh-frozen meniscal allografts is increasing. Freeze-drying (lyophilization) involves the dehydration of allografts during freezing in a vacuum. The allografts are then thawed and rehy- drated before transplantation. Al- though this method allows for indefinite storage, it also produces alterations in the biomechanical properties and the size of the allografts. Today, freeze-drying has fallen out of use and is not recommended. Means for secondary sterilization of allografts are available but also are not recommended; two examples are ethylene oxide and gamma ir radia- tion. The use of ethylene oxide has been linked to soft-tissue synovitis caused by its by-products. 13 Expo- sure to >2.5 mRad of gamma radia- tion negatively affects the mechanical properties of collagen-containing tissues. 14 Because >3 mRad of gamma irradiation is needed to eliminate human immunodeficiency virus DNA in allograft tissue, the use of gamma irradiation in the sterilization of meniscal allografts is not recommended. In addition, according to one series, 15 poor clinical results may be associated with gamma irradiation of the meniscal allograft. Meniscal allografts are not type cross-matched with the recipient; 16 therefore, occasionally an immune system inflammatory response oc- curs. An immunologic study by Ro- deo et al 17 identified class I and II human leukocyte antigens on frozen meniscal allografts. The authors evaluated 28 meniscal allografts (25 patients); all were deep frozen and nonirradiated. Nine of ten samples that underwent immunohistochem- ical analysis contained immunoreac- tive cells, but no frank evidence of immunologic rejection was seen. In Jon K. Sekiya, MD, and Christopher I. Ellingson, MD Volume 14, Number 3, March 2006 165 general, although histology scoring was improved in menisci with no immune response, there was no difference in clinical outcome between the two groups. However, the effect of an immune system inflammatory response is clinically unknown. A prospective study to evaluate the re- lationship between inflammatory response and meniscal allograft rejection or function is warranted. 16 Preclinical Evidence of Meniscal Allograft Healing Function In vitro and animal model studies have advanced the understanding of meniscal function, allograft selection, and the technical consider- ations of meniscal transplantation. In 14 cryopreserved medial meniscal allografts performed in a canine model, Arnoczky et al 18 showed that grafts healed to the capsule by fi- brovascular scar and retained their normal gross appearance. Histologic examination at 3 months revealed cellular distribution and metabolic activity comparable with those of controls. Medial meniscal transplantation using autograft, fresh allograft, or cryopreserved allograft were compared in a goat model. 19 Evaluation at 6 months revealed little histologic difference between implanted menisci and controls. In addition, the allografts had nearly normal peripheral vascularity, although transplanted menisci were reported to have slightly decreased proteoglycan content with increased water content. In another study, the use of a vascularized synovial flap accelerated re- vascularization of allograft menisci in rabbits. 20 No significant difference was found between cryopreserved and fresh-frozen allografts in goats, with nearly complete remodeling of both types of allografts at 6 and 12 months. 21 Using DNA analysis, Debeer et al 22 reported the nearly complete repopulation of cryopreserved meniscal allograft tissue by host cells in allograft remodeling in a human recipient 1 year after transplantation. A cadaveric biomechanical study on meniscal allografts demonstrated improved contact areas and decreased contact pressures after lateral meniscus allograft replacement. 23 This study demonstrated the impor- tance of securing both the anterior and posterior horns of meniscal allografts. With both horns released, contact pressures with allografts were equal to contact pressures in knees after total meniscectomy. Huang et al 24 recently reinforced findings that show improved contact pressures in meniscectomized knees after meniscal transplantation. However, the efficacy of meniscal transplantation in slowing degenerative changes has not consistently been demonstrated. In a study of a rabbit model reported by Cummins et al, 25 transplants performed immediately or at 3 months after medial meniscectomy showed a slowing in the progression of degenerative changes. Regardless of the timing of transplantation, groups receiving a transplant had fewer degenerative changes compared with meniscectomized controls. Yet Aagaard et al 26 showed improved prevention of articular cartilage degeneration in sheep with meniscal allograft transplants performed immediately compared with 3 months after meniscectomy. However, Rijk et al 27 found no significant difference with reference to subsequent degeneration between meniscectomized rabbit knees and those undergoing immediate or de- layed (6 weeks) meniscal transplantation. Similarly, using a sheep model, Edwards et al 28 found no difference among total meniscectomy, meniscal autograft, or meniscal allograft groups with respect to degenerative changes seen at an average of 21 months postoperatively. In another study, Rijk and Van Noorden 29 showed significantly (P ≤ 0.005) more shrinkage in meniscal allografts implanted 6 weeks after meniscectomy compared with those implanted immediately after meniscectomy in a rabbit model. Interest- ingly, the cellular content and histology of implanted menisci did not differ significantly between the two groups. Experimental and clinical studies are needed to evaluate the effect that shrinkage may have on long-term meniscal allograft properties and function. Indications and Preoperative Evaluation Surgery for the meniscus- deficient knee should be considered only after exhausting all nonsurgical measures. Nonsurgical treatment of patients who have undergone meniscectomy includes using unloading braces, encouraging nonimpact activities and exercises, and initiating pharmacologic measures. When these therapies fail to provide relief of symptoms or to prevent progression of joint space narrowing, meniscal transplantation may be considered in select patients. The exception to nonsurgical therapy may be concomitant ACL and medial meniscus deficiency with significant anteromedial rotatory instability. In this situation, earlier intervention of an ACL combined with medial meniscal transplantation may improve stability, ACL graft survival, and eventual clinical outcome. 10,30-33 Meniscal transplantation is indi- cated in patients aged <40 years with an absent or nonfunctioning meniscus. The upper limit is 50 years for patients who are highly active with only limited arthritis and who are not good candidates for arthroplasty. These patients have pain localized to the affected compartment with activities of daily living or sports, normal mechanical alignment, and Outer- bridge grade I or II articular changes. Contraindications include knee instability or marked varus/valgus malalignment, unless these issues can be addressed concurrently. Varus/valgus malalignment is de- Meniscal Allograft Transplantation 166 Journal of the American Academy of Orthopaedic Surgeons fined as asymmetry ≥2° to 4° compared with the contralateral knee or as the weight-bearing line on long-leg alignment radiographs falling into the affected meniscus-deficient compartment. Additional contraindications to meniscal transplantation are age >50 years, osteophytes indicating bony architectural changes, or Out- erbridge grade IV articular changes (unless focal defects are addressed concomitantly with osteochondral allograft transplantation or autolo- gous chondrocyte implantation). Preoperative physical examination should include inspection of stance, gait, and squat and of prior incisions about the knee. Examina- tion includes joint-line palpation, McMurray’s test, knee range of motion, presence of effusion, muscle strength, and assessment of ligamen- tous instability. Radiographic studies include weight-bearing 45° flexion posteroanterior, Merchant, and non–weight-bearing lateral views using magnification markers. Long-leg alignment radiographs also should be obtained in order to objectively evaluate lower extremity mechanical alignment. Magnetic resonance imaging (MRI) provides information regarding the subchondral bone, menisci, and hyaline cartilage. When previous arthroscopic images are un- clear or are not available, diagnostic arthroscopy can accurately define the extent of meniscectomy and degree of arthrosis. Although sizing and matching of meniscal allografts to recipient knees is critical, the tolerance of size mismatch in knees undergoing meniscal transplantation is not known. Sizing of allografts is done using MRI, computed tomography, or plain radiographs, or by making direct measurements. In patients with a prior meniscectomy, the contralateral knee may be used for sizing. In a study measuring patient knees, however, Johnson et al 34 reported variability in meniscal size between opposite knees. The consistent rela- tionship between meniscal size and landmarks in plain radiographs reported by Pollard et al 35 often is used by tissue banks for allograft sizing. Although comparison of MRI scans to plain radiographs showed that MRI is slightly more accurate at sizing allografts, only 35% of menisci measured with MRI came to within 2 mm of the actual size. 36 Carpenter et al 37 compared MRI scans with computed tomography scans and plain radiographs for meniscal allograft sizing and found that MRI consistently underestimated the anteroposterior and mediolateral sizes of both the medial and lateral menisci; however, MRI was more accurate in estimating meniscal height. The authors concluded that computed tomography and plain radiog- raphy are more useful in allograft sizing but that MRI measurements may improve as experience is gained. McDermott et al 38 measured the menisci in 22 pairs of cadaveric knees and found that the average medial and lateral meniscal lengths were 45.7 mm and 35.7 mm, respectively. Additionally, the authors measured the meniscal circumfer- ence, meniscal body width, and overall meniscal width, then corre- lated these measurements with radiographic sizing of the tibial plateaus. By using measurements of the length and width of the medial and lateral tibial plateaus, meniscal size was predicted with a mean error rate of 5%. 38 Huang et al 39 evaluated the cross- sectional parameters of lateral meniscal allografts compared with native lateral menisci in cadaveric knees and found increased contact pressures when allografts did not match native menisci. The greatest predictor of differences in contact pressures was the difference found in the width of the menisci. The authors therefore postulated that protocols used to select allografts should focus on cross-sectional parameters to match the native meniscus, particularly width. Surgical Technique Isolated Meniscal Transplant Surgical Technique Garrett 40 initially used an open technique for medial meniscal transplantation, with takedown of the medial collateral ligament with a piece of bone off the medial femur. The graft was placed under direct visualization, and subsequent repair of the medial collateral ligament was performed with a screw and washer. This technique is no longer used because of the amount of soft-tissue trauma that occures to the medial stabilizing structures of the knee. Once the patient is anesthetized, meniscal allograft transplantation begins with an examination to evaluate range of motion and ligamen- tous instability. 31,41-43 Meniscal deficiency and the condition of the articular cartilage are determined arthroscopically. The involved meniscus posterior horn and body are débrided to a 1- to 2-mm synovial rim, leaving a vascular source to aid in graft healing. Graft passage and fixation are achieved through a small medial or lateral parapatellar arthrotomy as well as an accessory posteromedial arthrotomy or posterolateral incision (for medial or lateral meniscal transplantation, respectively) (Figure 1). Lateral meniscus grafts are fashioned with a bone bridge, whereas medial grafts are fashioned with bone plugs (Fig- ure 2). Fixation of both horns is critical for proper function 23 and can be accomplished through a two-bone plug technique, 44 through a bone bridge in a trough 41,42,45 keyhole for the lateral meniscus, with no bone block, 23,46,47 or with suture fixation. 48 For a medial transplantation, the anterior and posterior bone plugs are pulled into their respective tunnels placed at the native meniscal insertion sites. For a lateral transplantation, the bone bridge is placed into a bone trough at the anatomic posi- Jon K. Sekiya, MD, and Christopher I. Ellingson, MD Volume 14, Number 3, March 2006 167 tions of the anterior and posterior horns of the lateral meniscus. With either technique, the bone fixation is secured using a no. 2 braided suture. Anatomic placement of meniscal allografts is essential for proper distribution of contact pressures. Sekaran et al 49 found that nonanatomic placement of medial meniscus posterior horn tunnels ≥5 mm medially and ≥5 mm posteriorly caused a notable shift in the centroid of contact pres- sure and increased contact pressures. Allograft fixation is then achieved by suturing to the native meniscus rim with an inside-out technique, starting at the posterolateral or posteromedial corner to the midbody to establish position and fit. A no. 2-0 braided polyester suture on long nee- dles can be used for the inside-out arthroscopic technique. The anterior to midbody meniscal allograft rim is fixed using a no. 0 Ethibond (Ethi- con, Somerville, NJ) suture placed through the parapatellar arthrotomy. A femoral distractor on the affected knee compartment can assist with graft passage, arthroscopic visualization (especially of the posterior horn), and graft fixation (Figure 3). Additional techniques for lateral meniscal allograft transplantation include modifications to the bone- bridge-and-trough technique that ac- tually lock in the lateral meniscal allograft, thereby providing additional stability to the meniscal horn fixation. One popular method includes the keyhole technique, 50 which uses a guide and drill to create a round bone trough that then narrows at the surface of the tibial plateau (Figure 4). This allows the bone bridge to Figure 2 Medial meniscal allograft fashioned with bone plugs attached to the anterior (white arrow) and posterior (black arrow) horns. Preplaced sutures are fixed to the posterior horn of the medial meniscal allograft (arrowhead). ACL = anterior cruciate ligament Figure 3 A femoral distractor can assist with graft passage, posterior horn visualization, and suture fixation. Figure 1 A, Medial meniscal allograft transplantation with anterior (large arrow) and posterior (small arrow) bone plugs through transosseous tunnels. A combination of arthroscopically and open placed sutures fix the meniscal allograft to the peripheral rim. B, Lateral meniscal allograft transplantation using a bone bridge. The bone bridge is secured in the tibial trough (large arrow) using transosseous sutures (small arrow). A combination of arthroscopically and open placed sutures fix the meniscal allograft to the peripheral rim. Meniscal Allograft Transplantation 168 Journal of the American Academy of Orthopaedic Surgeons lock into the tibial bone trough, providing additional stability to the construct. Other similar methods exist, including the “dovetail” technique. Although suture fixation attached to bone plugs or a bone bridge is usually sufficient for a secure graft healing, clinically these techniques offer additional methods for meniscal horn fixation stability. Others have recommended suture attachment without bone for meniscal allograft anterior and posterior horn fixation. 48 This technique uses a circumferential osseocancellous trough combined with transosseous tibial tunnel fixation of the meniscal allograft horns (Figure 5). Recently, the popularity of the bone-bridge-and-trough technique has been expanded for use in medial meniscal allografts. Preserving the circumferential hoop stresses and secure fixation of the anterior and posterior horns of the meniscal allograft are attractive reasons for using this technique; however, we caution against its use because of the potential for problems resulting from the position of the medial meniscus posterior horn, which is directly in line behind the ACL tibial attachment 34 (Figure 6). To position this trough without disrupting the ACL attachment, the tendency may be to medi- alize the bone trough location, thereby altering movement of the anatomic location of the posterior and/or anterior horn attachments. This nonanatomic positioning may then significantly alter the biomechanical properties of the transplanted meniscus. 49 However, this may not be a serious issue in the patient undergoing a combined medial meniscus transplant and ACL reconstruction, which allows the ACL tunnel to be drilled following anatomic bone bridge placement. Combined Meniscal Transplantation With Anterior Cruciate Ligament Reconstruction Meniscal transplantation combined with ACL reconstruction is performed in knees with ACL insuf- ficiency and symptomatic meniscal deficiency. Standard femoral and tibial tunnels are drilled and prepared before meniscal allograft insertion, and the procedure is performed as previously described. 30,31,41,42 The use of patellar tendon allograft decreases associated donor-site morbidity in this complex knee reconstruction. T ibial tunnel drilling requires special care because this tunnel often en- croaches on the bone trough for the meniscus. 41 To circumvent this prob- lem, the ACL graft passage and femoral fixation should be done before placing the lateral meniscal allograft Figure 4 Keyhole technique for lateral meniscal allograft transplantation. A, Lateral meniscal allograft fashioned using the keyhole technique. Note that the deeper portion of the bone bridge (large arrow) for the meniscal allograft is fashioned larger than the superficial portion (small arrow), which is matched to the corresponding recipient in the lateral tibia (B). This allows the lateral meniscal allograft to “lock” into the tibial attachment. (Panel A adapted with permission from Cryolife, Marietta, GA.) Figure 5 Osseocancellous trough technique for meniscal allograft fixation. The circumferential trough is created medially on the peripheral tibial plateau and on the anterior and posterior horn meniscal attachments using an arthroscopic shaver. The anterior and posterior horns of the meniscal allograft are secured to their attachments using transosseous suture fixation and arthroscopically placed inside-out sutures around the peripheral rim. (Adapted with permission from Boss A, Klimkiewicz J, Fu FH: Technical innovation: Creation of a peripheral vascularized trough to enhance healing in cryopreserved meniscal allograft reconstruction. Knee Surg Sports Traumatol Arthrosc 2000;8:159-162.) Jon K. Sekiya, MD, and Christopher I. Ellingson, MD Volume 14, Number 3, March 2006 169 bone bridge. The meniscal allograft is then fixed, as previously described. For medial meniscal allograft transplantation, placement and drilling of the posterior bone plug tunnel is fa- cilitated by passing the ACL graft after the meniscal allograft is secured. In both the medial and lateral allograft procedures, tibial ACL allograft fixation is performed after meniscal allograft placement and fixation. Postoperative Care There is no clear consensus concern- ing rehabilitation protocols for patients who have undergone meniscal allograft transplantation; this is a result, in part, of the lack of scientific studies on the topic. In general, weight-bearing and range-of-motion limitations typically are imposed in a fashion similar to that of a major meniscal repair, until meniscal allograft healing has occurred (usually by 8 to 12 weeks) (Figure 7). A concomitant ACL reconstruction, when performed, also affects the rehabilitation protocol, with motion emphasized to prevent arthrofibrosis. 51 Full hyperextension symmetrical to the contralateral normal extremity typically is the goal in the first few weeks. Full weight bearing and flexion beyond 90° usually is allowed after 6 to 12 weeks postoperatively. V igorous, high-impact activities gen- erally are discouraged indefinitely. Fritz et al 52 protect meniscal transplants for the first 4 weeks using a hinged range-of-motion brace at 0 to 90°. Kohn et al 51 use pro- longed epidural anesthesia to facili- tate postoperative continuous pas- sive motion until 0 to 90° is achieved. Fritz et al 52 allow patients to partially bear weight for the first week, with the brace locked in full extension to avoid shear, whereas Kohn et al 51 keep patients non– weight bearing for 3 weeks. Both groups advance weight bearing and discontinue crutches at 4 to 6 weeks for cases in which the patient has 90° to 100° of knee flexion, full knee extension, and minimal or absent swelling, and is able to walk without a bent-knee gait. At 6 weeks, closed chain exercises are started at 0 to 45°, progressing to 75°. Patients may return to sedentary work at 1 week, strenuous work at 3 to 4 months, low-impact exercises at 8 weeks, and running after 4 to 5 months. Al- though light or moderate sports are allowed at 6 to 9 months, strenuous sports are not recommended. Results Milachowski et al 53 performed the first isolated meniscal allograft transplant in 1984; the authors reported the results of 6 fresh-frozen (deep-frozen) and 16 freeze-dried allografts in 20 patients with a 14- month follow-up evaluation, including a second-look arthroscopy (Table 1, available at http:// jaaos.org/cgi/content/full/14/3/164/ DC1). Although fresh-frozen allografts were more likely to have an improved clinical appearance, both graft types showed a decrease in size, and neither showed signs of inflam- mation or rejection. Reaction at the synovial joint was more pronounced in the lyophilized group, as was graft shrinkage. The authors concluded that, overall, the fresh-frozen allografts showed better results, although the failure rates were comparable between the two groups. Garrett 40 presented results in 43 patients with a 2- to 7-year follow-up. Secondary procedures were performed in most of the patients, with 24 concomitant ACL reconstructions, 13 osteotomies, and 11 osteochondral allografts. Sixteen fresh and 27 cryopreserved grafts were used. Second-look arthroscopy was performed in 28 patients, with 20 grafts found to be intact. The main factor in failure was the degree of arthritis in the knees. Two failures occurred in 32 patients with Outerbridge grade III chondromalacia; 6 failures occurred in 11 patients with grade IV chondromalacia. Graft type did not appear to affect outcome. Figure 6 Anterior cruciate ligament insertion site (colored with ink) is in line with the medial meniscus anterior and posterior horns. A, Medial meniscus allograft flipped over laterally showing the medial extent of the anterior and posterior meniscus attachments. B, Medial meniscus allograft left in situ showing the lateral extent of the anterior and posterior meniscus attachments. Meniscal Allograft Transplantation 170 Journal of the American Academy of Orthopaedic Surgeons van Arkel and de Boer, 54 in 1995, reported the results of 23 cryopreserved allografts at 2- to 5-year follow-up. There were 20 clinical successes and 3 failures requiring graft removal. The authors considered the failures to be secondary to uncorrected alignment. No immune response was noted in the failures. Cameron and Saha 55 performed allograft transplantation of 67 fresh- frozen irradiated grafts in 63 patients. Osteotomies were performed in 34 patients; the average medial compartment varus was 7.1°, and average lateral compartment valgus, 5.9°. Mean follow-up was 31 months, and the success rate using the Lysholm knee rating scale was 87%. The authors emphasized that limb alignment is important in the outcome of meniscal transplantations and recommended the need for further research to determine whether the meniscal allograft or realignment procedure was more important in achieving pain relief. In eight patients who had had prior un- successful realignment procedures, insertion of the meniscal allograft resulted in one excellent, four very good, and three good results. A prospective study comparing realignment with and without meniscal allograft would help determine whether it was the realignment with or without the meniscal transplant, or both, that was responsible for improved outcomes. Carter 56 had favorable outcomes in 45 of 46 patients evaluated at an average of 2.9 years. Three grafts partially failed, and one graft complete- ly failed, requiring three partial meniscectomies and one total meniscectomy. These failures were at- tributed to patient selection in two cases, technical error in one, and noncompliance in one. Internation- al Knee Documentation Committee (IKDC) scores revealed that all but the patient with complete graft failure had improvement in pain. Second-look arthroscopy in 38 patients showed healing at the meniscal capsular repair site. MRI was not useful in evaluating graft integrity because no correlation was found between abnormal signal intensity and second-look arthroscopies that revealed no abnormalities. Noyes and Barber-Westin 15 reported results of 96 meniscal allografts perfor med in 82 patients. Fresh-frozen grafts exposed to 2.5 mRad of gamma irradiation were used. Most grafts were fixed only at the posterior horn; no grafts were secured by both the anterior and posterior horns. Twenty-nine of the 96 grafts failed within 24 months, requiring removal; these were not included in the follow-up. Of the 67 meniscal transplants evaluated at 2 to 5 years, 27 failed. Overall results for all 96 allograft transplantations were 9% healed, 31% partially healed, 58% failed, and 2% lost to follow-up. A correlation between arthritic changes and meniscal healing was observed. Stollsteimer et al 57 reported results of 23 allografts in 22 patients followed for an average of 40 months. All allografts were nonirradiated and cryopreserved; surgery was arthroscopically assisted with implantation using a bone plug technique. Postop- erative joint space narrowing measured radiographically averaged 0.88 mm. Bilateral knee MRI was performed in 12 patients. All patients improved clinically, as measured at final follow-up with Tegner, L ysholm, and IKDC scores. In addition, allograft size was noted to have shrunk to an average of 63% of the normal contralateral side; the significance of the observed allograft shrinkage is not known. Figure 7 Arthroscopic images of healing of a medial meniscal allograft 4 months after transplantation. A, Suture fixation of medial meniscal allograft using arthroscopically placed, vertical mattress, inside-out sutures (arrow). B, Healed posterior horn that is stable with arthroscopic probing (arrow). C, Restoration of normal contour of the junction of the midbody and posterior horn (arrow). D, Healed midbody peripheral rim verified by direct arthroscopic visualization and probing (arrow). FC = femoral condyle, M = meniscus, TP = tibial plateau Jon K. Sekiya, MD, and Christopher I. Ellingson, MD Volume 14, Number 3, March 2006 171 All 18 patients evaluated by Rath et al 58 an average of 5.4 years after meniscal allograft transplantation had a marked decrease in pain and improvement in function. No joint space narrowing was observed on 45° posteroanterior weight-bearing radiographs; however, 8 of 22 allografts tore during the study period (5 as a result of trauma). After initial positive outcomes, these allograft failures required six partial and two total meniscectomies secondary to mechanical symptoms. Excised allografts were examined histological- ly and found to have reduced cellu- larity and cytokine expression compared with controls. Two patients, both requiring total meniscectomy after failure, requested reimplantation secondary to return of symptoms after the removal of allograft menisci; these two patients were included in the study from time of reimplantation. It is postulated that allograft menisci have a reduced functionality secondary to repopulation with fewer cells, as measured by this decrease in growth factor production. Verdonk 59 found a notable difference in preoperative and postoperative pain scores, with 87% of postoperative patients stating that they would undergo transplantation again. There were no significant differences between isolated medial or lateral meniscus transplants. Wirthetal 60 reported the long- term results of 23 meniscal transplantations with simultaneous ACL reconstructions, measured an average of 3 and 14 years postoperatively. Seventeen lyophilized and six deep- frozen grafts were used. Although MRI and arthroscopy demonstrated a reduction in the size of lyophilized grafts, all patients improved in Lysholm scores. Deep-frozen meniscal allograft patients did better in both objective and subjective results compared with lyophilized allograft patients. van Arkel and de Boer 61 recently evaluated 63 meniscal allografts in 57 patients at an average follow-up of 60 months. Thirty-four patients had isolated lateral meniscal transplantation, 17 had isolated medial meniscal transplantation, and 6 had combined transplantation. Preoperative instability secondary to ACL deficiency or meniscectomy was present in 21 patients; postoperative stability was achieved in 11 of these patients. Al- lograft failure, measured by persis- tent pain or mechanical failure, occurred in 13 transplantations (5 lateral, 7 medial, and 1 medial and lateral). The cumulative survival rate of lateral, medial, and combined allografts was 76%, 50%, and 67%, respectively. Rupture of the ACL had a significant (P = 0.003) negative correlation with successful medial meniscal transplantation. Additionally, lateral meniscal transplantations did significantly (P = 0.004) better than medial transplantations clinically. Biomechanical function and anatomic differences likely explain this difference. Medial meniscal allograft survival should improve with con- current ACL reconstruction in the ACL-deficient knee. Yoldas et al 42 evaluated 31 patients with meniscal transplants, twenty of which were combined with ACL reconstructions, with a minimum 2-year follow-up. Thirty of the 31 patients had a normal or nearly normal rating according to IKDC knee function and activity level. Nineteen of the knees that underwent combined meniscal transplant and ACL reconstruction were normal or nearly normal according to IKDC stability testing. The average single-leg hop and vertical jump was 85% that of the contralateral limb. No progressive joint space narrowing was seen on radiographic examination. Sekiya et al 62 evaluated 25 patients who underwent isolated lateral meniscal transplantation at an average follow-up of 3.3 years. Bony fixation of the allograft was performed in 17 patients; 8 patients had suture fixation of the anterior and posterior horns of the meniscal allograft. In these patients, 79% had normal or nearly normal scores according to IKDC knee function, activity level, and overall subjective ratings. Medical Outcomes Study 36-Item Short Form (SF-36) physical and mental component summary scores revealed that transplant recip- ients performed at higher levels than age- and sex-matched population controls. The average scores for the single-leg hop and vertical jump test were 91% and 85%, respectively, of the contralateral limb. There was no joint space narrowing seen over time on radiographic examination. In addition, radiographic preoperative and postoperative joint space measurements of the involved lateral compartment were significantly (P ≤ 0.05) associated with mean lower subjective assessment, symptoms, sports activity score, Lysholm score, and final IKDC rating at latest follow-up. Finally, patients treated with the bony technique had significantly (P ≤ 0.05) better range of motion, according to IKDC criteria, at latest follow-up compared with the suture fixation group. Sekiya et al 31 also evaluated 28 patients who underwent combined meniscal transplantation with ACL reconstruction (average follow-up, 2.8 years). Of these patients, 86% to 90% had normal or nearly normal scores, according to IKDC overall subjective and symptoms assessment. Combined ACL and meniscal transplantation patients scored at higher levels on SF-36 physical and mental component summary scores than did age- and sex-matched popu- lations. Ninety percent of the patients also had normal or nearly normal scores by Lachman’s scoring system and pivot-shift testing. KT- 1000 testing at both 20 lb and at maximum manual demonstrated an average of 1.5 mm of increased anterior translation compared with the normal contralateral knee. No joint space narrowing was seen over time on radiographic examination. 31 Meniscal Allograft Transplantation 17 2 Journal of the American Academy of Orthopaedic Surgeons Recently, Graf et al 30 retrospec- tively reviewed nine patients who had undergone combined medial meniscal transplantation and ACL reconstruction (minimum follow-up, 8.5 years; average follow-up, 9.7 years). One allograft was removed because of the presence of a presumed low-grade infection. Seven of eight patients had normal or nearly normal IKDC scores while remaining at their preoperative radiographic score levels without progression. Six of eight patients were extremely pleased with their knee function and were highly active in recreational sports. Six of eight patients also had normal or nearly normal scores, according to IKDC functional testing. Finally, all eight patients stated that they would recommend the procedure to a friend and would undergo the procedure again, given similar circumstances. 30 Summary Meniscal transplantation continues to evolve as a treatment for difficult meniscal injuries that necessitate partial or total meniscectomy. Initial clinical results are promising, but long-term clinical outcomes remain to be established. Important surgical factors include patient selection, limb stability and alignment, graft sizing, graft placement, and graft fixation. Currently, meniscal allograft transplantation should be considered a salvage operation for symptomatic meniscal deficiency in the young patient. Nonetheless, with careful patient selection, this procedure can predictably relieve compartmental pain and restore knee stability (for medial meniscal transplantation) when associated with combined ACL reconstruction. In addition, meniscal allograft transplantation may partially restore native meniscal function, as is seen with slowing of the degenerative ar thritic process in transplanted meniscus-deficient knee compartments. References Evidence-based Medicine: Studies referenced are primarily case-control reports of meniscal allografts (level III). There are no prospective, ran- domized studies on this topic to date (level I, II studies). Citation numbers printed in bold type indicate references published within the past 5 years. 1. Beaupre A, Choukroun R, Guidouin R, Garneau R, Gerardin H, Cardou A: Knee menisci: Correlation between microstructure and biomechanics. Clin Orthop Relat Res 1986;208:72- 75. 2. McDevitt CA, Webber RJ: The ultra- structure and biochemistry of meniscal cartilage. Clin Orthop Relat Res 1990;252:8-18. 3. Greis PE, Bardana DD, Holmstrom MC, Burks RT: Meniscal injury: I. Ba- sic science and evaluation. JAm Acad Orthop Surg 2002;10:168-176. 4. Arnoczky SP, Warren RF: Microvas- culature of the human meniscus. Am J Sports Med 1982;10:90-95. 5. Dye SF, Vaupel GL, Dye CC: Con- scious neurosensor y mapping of the internal structures of thehuman knee without intraarticular anesthesia. Am J Sports Med 1998;26:773-777. 6. Vandermeer RD, Cunningham FK: Arthroscopic treatment of the discoid lateral meniscus: Results of long- term follow-up. Arthroscopy 1989;5: 101-109. 7. Johnson DL, Swenson TM, Livesay GA, Aizawa H, Fu FH, Harner CD: Insertion-site anatomy of the human menisci: Gross, arthroscopic, and to- pographical anatomyas abasis forme- niscal transplantation. Arthroscopy 1995;11:386-394. 8. Thompson WO, Thaete FL, Fu FH, Dye SF: Tibial meniscal dynamics using three-dimensional reconstruction of magnetic resonance images. Am J Sports Med 1991;19:210-216. 9. Voloshin AS, Wosk J: Shock absorption of meniscectomized and painful knees: A comparative in-vivo study. J Biomed Eng 1983;5:157-161. 10. Levy IM, Torzilli PA, Warren RF: The effect of medial meniscectomy on anterior posterior motion of the knee. J Bone Joint Surg Am 1982;64:883- 887. 11. Verdonk R, Kohn D: Harvest and con- servation of meniscal allografts. Scand J Med Sci Sports 1999;9:158- 159. 12. Jackson DW, Whelan J, Simon TM: Cell survival after transplantation of fresh meniscal allografts: DNA probe analysis in a goat model. Am J Sports Med 1993;21:540-549. 13. Jackson DW, Windler GE, Simon TM: Intra-articular reaction associated with use of freeze-dried, ethylene oxide-sterilized bone-patella tendon- bone allografts in the reconstruction of the anterior cruciate ligament. Am J Sports Med 1990;18:1-11. 14. Yahia L, Zukor D: Irradiated meniscal allotransplants of rabbits: Study ofthe mechanical properties at six months postoperation. Acta Orthop Belg 1994;60:210-215. 15. Noyes FR, Barber-Westin SD: Irradiat- ed meniscus allografts in the human knee: A two to five year follow-up. Orthop Trans 1989;19:417. 16. Goble EM, Kohn D, Verdonk R, Kane M: Meniscal substitutes – human experience. Scand J Med Sci Sports 1999;9:146-157. 17. Rodeo SA, Senevirante A, Suzuki K, Felker K, Wickiewicz TL, Warren RF: Histological analysis of human meniscal allografts. J Bone Joint Surg Am 2000;82:1071-1082. 18. Arnoczky SP, McDevitt CA, Schmidt MB, Mow VC, Warren RF: The effect of cryopreservation in canine menisci: A biomechanical morphologic and biomechanical evaluation. J Orthop Res 1988;6:1-12. 19. Jackson DW, McDevitt CA, Simon TM, Arnoczky SP, Atwell EA, Silvino NJ: Meniscal transplantation using fresh and cryopreserved allografts: An experimental study in goats. Am J Sports Med 1992;20:644-656. 20. Yamazaki K, Tachibana Y: Vascular- ized synovial flap promoting regener- ation of the cryopreserved meniscal allograft: Experimental study in rabbits. J Orthop Sci 2003;8:62-68. 21. Fabbriciani C, Lucania L, Milano G, Schiavone Panni A, Evangelisti M: Meniscal allografts:Cryopreservation vs. deep-frozen techniques. An experimental study in goats. Knee Surg Sports Traumatol Arthrosc 1997;5: 124-134. 22. Debeer P, Decorte R,Delvaux S, Belle- mans J: DNA analysis of a transplanted cryopreserved meniscal allograft. Arthroscopy 2000;16:71-75. 23. Paletta GA Jr, Manning T, Snell E, Parker R, Bergfeld J: The effect of allograft meniscal replacement on intraarticular contactarea and pressures in the human knee: A biomechanical study. Am J Sports Med 1997;25:692- 698. Jon K. Sekiya, MD, and Christopher I. Ellingson, MD Volume 14, Number 3, March 2006 17 3

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