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Failure of Meniscus Allograft Transplantation
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Failure of Meniscus Allograft Transplantation Eric D Haunschild BS , Ron Gilat MD , Kelechi Okoroha MD , Brian J. Cole MD, MBA PII: DOI: Reference:
S1060-1872(19)30087-5 https://doi.org/10.1016/j.otsm.2019.150713 YOTSM 150713
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Operative Techniques in Sports Medicine
Please cite this article as: Eric D Haunschild BS , Ron Gilat MD , Kelechi Okoroha MD , Brian J. Cole MD, MBA , Failure of Meniscus Allograft Transplantation, Operative Techniques in Sports Medicine (2019), doi: https://doi.org/10.1016/j.otsm.2019.150713
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Failure of Meniscus Allograft Transplantation Eric D Haunschild BS1, Ron Gilat MD1, Kelechi Okoroha MD1, Brian J Cole MD, MBA1
1
Midwest Orthopedics at Rush University, Rush University Medical Center, Chicago, IL
Corresponding Author: Brian J. Cole MD, MBA 1611 West Harrison Street Chicago, Illinois 60612 (708) 505-8941 [email protected]
Abstract: Meniscus allograft transplantation (MAT) has emerged as an acceptable surgical therapy in relieving pain and restoring function in young patients with symptomatic meniscal deficiency without severe osteoarthritis. Despite its early success, at long-term follow-up MAT has been associated with significant rates of graft failure, requiring repeat interventions and often progression to arthroplasty. In select patients who previously benefited from a primary MAT and have an identified, treatable cause of failure, revision meniscus allograft transplantation (RMAT) may be considered. Careful identification and treatment of concomitant pathologies known to cause failure, including ligamentous instability, cartilage injury and limb malalignment, should be addressed at the time of revision surgery. Acute tears should be assessed for whether they are amenable to repair or replacement with a new graft is required. The
author’s preferred approach is to perform the bone-slot technique for both primary and revision cases. Literature on outcomes following RMAT are limited but favorable, with higher failure rates than primary MAT but significant functional outcome improvement in most patients.
Introduction In a select population of young patients with functional loss of the meniscus or prior (sub-)total meniscectomy, and without severe osteoarthritis, meniscal allograft transplantation (MAT) may be indicated. MAT has emerged as a viable technique to decrease pain and preserve knee function. Although not definitively proven, the surgery may have joint preserving potential by decreasing the progression of osteoarthritis in these select patients. However, long-term failures of MAT are not uncommon, with incidence of failure ranging from 10-29%.1-3 While some symptomatic patients undergo debridement only of the failed transplant or arthroplasty when indicated, in select otherwise healthy patients who experienced substantial clinical benefit from their primary MAT, revision meniscus allograft transplantation (RMAT) may be considered.
Epidemiology Incidence and risk factors for failure of MAT have been well reported in the published literature, with often discordant findings. In a recent analysis of failures at a mean of 59 months after MAT, McCormick et al.4 found a 4.7% incidence of failure requiring RMAT or conversion to arthroplasty. Thirty-two percent of patients required secondary surgery, with a majority undergoing isolated arthroscopic debridement. However, those patients that did require secondary surgery within two years after MAT had a significantly higher risk of requiring future arthroplasty (odds ratio: 8.4). Zaffagnini and
collegues evaluated a case series of 147 patients at a mean of four years after soft tissue only MAT and found a surgical failure rate of 5%. Notably, there was no significant differences in failure associated with medial or lateral transplants, isolated or combined MAT, patient age, or patient BMI.5 Similarly an investigation of 230 MATs in a physically active military population found a surgical failure rate of 5.7% at a mean or 2.14 years after surgery. In this study concomitant ligament or realignment procedures were identified as significant risk factors for failure.6 These findings are supported by a recent investigation of 40 patients receiving MAT with concomitant ACL reconstruction, which identified a 20% failure rate at mean 7.3 years after surgery, similarly suggesting the need for concomitant ACL reconstruction as a predictor of MAT failure.7 Several analyses have investigated concomitant cartilage degeneration and its impact on failure of MAT. Lee and associates evaluated 222 patients receiving MAT at five years following surgery and categorized patients by International Cartilage Repair Society (ICRS) grade of cartilage injury. The authors found that patients with high grade bipolar degeneration had significantly lower MAT graft survival rate (62.2%) than patients with high-grade unipolar (90.3%) or low-grade unipolar (93.3%) defects.8 Another recent case series of 125 patients at five years after MAT analyzed graft survival in patients with partial-thickness, unipolar full-thickness, and bipolar full-thickness articular cartilage defects. With failure defined as needing graft removal, RMAT, or arthroplasty, failure rates with bipolar full thickness defects (29.6%) were greater than those with unipolar full-thickness (11.1%) and partial thickness (2.9%) defects.9 A systematic review of six trials assessing outcome at a mean of three years after surgery in patients receiving MAT with concomitant cartilage repair or restoration procedures found that four of the six trials demonstrated equivalent functional outcomes to isolated MAT, with the last two reporting inferior outcomes in those patients receiving concomitant procedures.10 The aggregate failure rate was 12%, with 85% of failures attributable to the MAT procedure. These findings
suggest that MAT with concomitant cartilage procedures produces similar outcomes and failure rates to what has been reported in isolated MAT procedures.
Mechanisms of Meniscal Allograft Failure MAT failure is commonly classified into early and late failure with several different etiologies of graft failure previously identified. A cause of both early and late failure in bony MAT is delayed union or nonunion of the graft bone block to the recipient bone trough. Researchers have suggested that ligamentous injury or malalignment of the knee can lead to non-union of the graft. de Boer and colleagues suggested this mechanism for MAT failure when evaluating a case series of 24 patients who underwent medial MAT. Their study identified varus malalignment in two patients and deficient cruciate ligaments in another case of failed meniscal allografts. When reviewing immunohistochemical reactions, key proliferation markers were localized near areas of microvascular supply whereas in critical areas of the knee, focal areas of degeneration were noted with no surrounding proliferation markers. The authors suggested that non-union may be caused by vascularization deficiencies, and that ligamentous instability or mechanical malalignment may alter contact pressures endured by the meniscus. This ultimately could lead to altered vascularization patterns of the meniscus and ultimate failure of healing.11 Another prevalent etiology of MAT failure is acute trauma to the transplanted knee resulting in graft rupture. This can occur in the immediate post-operative period due to premature strenuous activity or at any point after surgery due to excessive forces, analogous to native meniscus injury. Following trauma, patients should be carefully evaluated to assess if the graft tear is amenable to simple debridement, repair, or if a new graft is needed. In addition, any concomitant injuries sustained during
the trauma should be assessed and considered in the context of altered biomechanical forces that may affect MAT survival as described above.11 Since the introduction of MAT, there have been concerns of the immunogenicity of meniscal allografts. However, concerns have not been validated in the literature, with only a single case report showing arthroscopic and histologic evidence of acute immune-mediated rejection at ten weeks after MAT.12 In addition to the above mentioned mechanisms of failure, there are many changes to the transplanted graft that occur over time which can lead to gradual failure. As in native meniscus tissue, over time meniscus allografts undergo repetitive stress leading to degenerative changes to the graft. These degenerative changes when subjected to continued shearing forces may result in significant symptoms, as well as progress to functional failure of the MAT. Another well-identified time-dependent morphologic change unique to meniscus allografts is graft shrinkage, which has been demonstrated to develop and progress following MAT.13-15 However, the effect of these changes is unclear, with multiple investigations reporting no significant effect of the extent of shrinkage on clinical outcome.16-18 Further investigations are needed to assess the clinical significance of changes to graft morphology as it pertains to clinical or surgical failure requiring revision surgery.
Operative Considerations to Optimize Outcomes Following MAT
Graft Sizing A critical preoperative consideration for MAT is sizing of the meniscus allograft. Meniscus allografts are both size and compartment-specific, with incorrect sizing resulting in altered joint
mechanics. Specifically, oversized grafts lead to greater forces on the articular cartilage while undersized grafts result in increased forces on the graft itself.19 These altered mechanics may result in early degenerative changes and subsequent failure of the grafts, ultimately requiring RMAT or arthroplasty. Once particular consequence of mismatch is graft extrusion, a known cause for graft failure and a relative indication for RMAT.20,21 To minimize mismatch of grafts, we utilize the sizing method described by Pollard et al.22 Briefly, standard AP and lateral knee radiographs are measured to obtain graft measurements within 10% of error. On AP films, measurement of the distance between the tibial eminence to the periphery of the tibial plateau, corresponds to the coronal width of the medial or lateral meniscus. On lateral radiographs, the anterior to posterior (AP) length of the graft is measured as 80 percent of the AP length of the tibial plateau for the medial meniscus and 70 percent of the AP length of the tibial plateau for the lateral meniscus. A modification to the Pollard sizing method has been described by Yoon et al, using the measurements and applying them to a mathematical model providing more precise sizing.23
Graft Fixation Technique Several techniques have been proposed for fixation of the anterior and posterior roots of the meniscus allograft. MAT fixation techniques are commonly categorized as either osseous fixation (using either a bone-plug or bone-bridge technique) or soft-tissue fixation (which includes passing sutures through tibial tunnels or simple fixation with peripheral sutures). Fixation technique should be carefully scrutinized as isolated soft tissue fixation has been associated with slightly inferior biomechanical outcomes when compared to osseous fixation.24-26 For this reason, the senior author utilizes bony fixation, more specifically using a bone bridge, during primary MAT and RMAT. However, to date there is
no literature identifying clear differences in functional outcomes following either osseous or soft tissue fixation.27
Graft Preservation Technique Since the introduction of MAT, several types of preservation techniques have been utilized: fresh, fresh-frozen, cryopreserved, and lyophilized grafts. Of these, fresh-frozen grafts remain the most widely used in practice today. Lyophilized grafts have been found to have significantly greater morphologic changes and poorer long-term outcomes when compared to fresh-frozen grafts.28 Comparative trials on cryopreserved versus fresh-frozen grafts remain limited in both MAT and RMAT at this time, with recent evidence showing modest decreases in graft shrinkage in fresh-frozen grafts as compared to cryopreserved grafts.29 In both primary and revision MAT cases, we prefer to use freshfrozen grafts due to their established efficacy, ease of processing, lower immunogenicity, and lower cost.4,7
Concomitant Surgery In addition to the considerations outlined above, careful assessment of ligamentous integrity and distal alignment of the affected limb should be completed prior to primary meniscus transplant. In early outcome studies, knees with significant ligamentous instability or limb malalignment were associated with greater rates of MAT failures, with the authors proposing that these factors hindered vascularization and healing of grafts.30,31 If ligamentous injury or distal malalignment are identified, these pathologies should be addressed with either a staged or concomitant procedure as indicated.
Pre-operative Evaluation As when considering primary MAT, it is essential to complete a thorough history and physical exam when assessing patients for RMAT. Consensus criteria have yet to be determined for surgical considerations specific to RMAT, but many of the criteria employed by the senior author are similar to those for MAT. That is, patients should be young and physically active with focal symptoms attributable to meniscal deficiency. Chondral defects or progression of arthritic change to the joint should be assessed, as patients with significant arthritic changes to the joint are more likely to fail. Investigation and evaluation of any concomitant injuries should be assessed with visual inspection, limb alignment assessment, range-of-motion, palpation, and ligamentous and meniscal testing. Patients will often have focal pain and swelling to palpation, worsened with activity, as well as mechanical symptoms in the affected knee. At minimum, a bilateral long-leg weight-bearing radiographic series and unilateral knee MRI should be obtained to assess for extrusion or tears of the meniscus allograft as well as evidence of other joint pathologies and limb alignment. Second-look arthroscopy should also be performed on a case-by-case basis prior to a revision procedure to directly visualize extent of graft union and injury, as these can be key considerations when planning revision procedures (Figure 1). Another key consideration independent of clinical or radiographic criteria is the degree to which the patient improved following their initial MAT. RMAT requires a lengthy and involved rehabilitation process with a high risk of being unable to return to prior level of activity. Patients who experienced minimal to no improvement following MAT are unlikely to experience a significant benefit with RMAT and should probably explore other treatment options.
Operative Considerations for RMAT
An acute traumatic meniscal allograft tear should be addressed in a timely fashion. Meniscocapsular detachment due to failure of the graft to heal can result in a bucket-handle or a longitudinal tear, which can sometimes be successfully treated with repair of the allograft. Radial and flap tears are less likely to allow repair and may require arthroscopic debridement or graft replacement, dependent on morphology and depth. Root-tears may or may not be amendable for repair according to the tear location and the method applied for fixation during the primary surgery. Soft-tissue or bone plug root tears may be repaired in the same tunnel technique used in the primary surgery. If slot technique was used, a root tear is theoretically less likely to occur, but if does happen, can be repaired using a tunnel or an anchor. Acute tears that are not suitable for repair and cases with biologic degeneration of the graft require RMAT with a new graft. The technique used to secure the new graft is generally independent of the technique used for the primary surgery. Some authors advocate using the bone plug technique.32 However, we prefer the use of the slot technique previously described33-36 and summarized as follows both for primary and revision cases, as this allows for secure bone fixation and ease in performing any concomitant osteotomy or ligamentous reconstruction at the time of RMAT. Patients should be placed supine with a standard thigh holder and tourniquet before being draped in a sterile fashion. The procedure should then begin with diagnostic arthroscopy to evaluate for concomitant ligamentous or chondral pathology. The meniscus should be examined to visualize if the initial allograft is amenable to simple debridement or repair. If simple debridement or repair are not feasible, and an RMAT is elected, the remaining initial allograft should be debrided to a stable rim of peripheral meniscus tissue with anterior and posterior horn insertion sites maintained. Following arthroscopy, surgical exposure should be obtained with an anterior longitudinal incision and mini-arthrotomy in line with the anterior and posterior horn insertion sites. Arthrotomy can
be performed either adjacent to or through the patellar tendon based upon surgeon preference. Depending on whether a medial or lateral transplant is being performed, an accessory posterolateral or posteromedial incision should be made approximately one-third above and two-thirds below the joint line to permit inside-out repair of the meniscus following graft insertion. Attention is then made to creating the tibial slot. This should be completed by using electrocautery to make a line connecting the anterior and posterior horn insertions and using a 4.5millimeter burr to create an initial slot along this line. A guide wire is then inserted distal and parallel to the initial slot, which is then overreamed using an 7-8 millimeter cannulated reamer. A box cutter is then used to create the final tibial slot, measuring approximately 8 millimeters wide and 10 millimeters deep. The tunnel should then be smoothed out using a rasp prior to graft insertion. The graft can be prepared at any point during the case once thawed. A bone bridge is created, 10 millimeters deep and 7 millimeters wide, from the tibial plateau attached to the thawed graft (Figure 2A). The bone bridge is purposefully undersized to allow for ease of insertion into the slot following graft preparation. Any bone posterior to the posterior meniscal horn attachment should be removed, and any bone anterior to the anterior meniscal horn attachment should be preserved to maintain graft integrity during graft passage. Lastly, a single vertical mattress traction stitch should be placed at the junction of the posterior and middle-third of the graft. A passing wire is guided into the accessory incision and out the anterior arthrotomy. The traction stitch suture ends are then inserted into the passing wire, which is then pulled back through the accessory incision (Figure 2B). The prepared allograft is then passed into the tibial slot. Under direct visualization, the bone bridge is advanced into the tibial slot and secured with a single interference screw. Attention is then placed to the meniscus, which is repaired to the joint capsule using inside-out vertical mattress sutures (Figure 2C). Generally, 8-10 sutures are required for repair.
There are several considerations that relate to the cause of failure of the primary MAT, which may affect the surgical technique of RMAT. Any graft extrusion should be identified in postoperative MRI and/or during second look arthroscopy. A common cause of extrusion is malposition of the tunnels or slot (for example: lateral malposition of a lateral MAT).37 Operative treatment should be based on a case by case basis, but may include tunnel or slot repositioning, anchor fixation of the body of the meniscus to the tibia and graft replacement with appropriate graft sizing. If a concomitant pathology is detected it should be addressed accordingly during RMAT; an ACL tear should be reconstructed, malalignment should be addressed with a high tibial osteotomy (HTO) or a distal femoral osteotomy (DFO), and an osteochondral lesion should be addressed with an appropriate cartilage restoration procedure. In general, any concomitant osteotomy or cartilage procedure should be performed after RMAT, as passing the graft requires significant stress to the knee that may compromise these procedures. For concomitant ACL reconstruction, the senior author prefers to use a modified bridge-in-slot technique previously described.38 Following arthroscopy and both meniscus and ACL graft preparation, the next operative steps are to prepare the femoral tunnel for ACL graft passage and to create the tibial slot for meniscus graft fixation. The ACL tibial tunnel is then drilled as obliquely as possible to minimize any effect on slot placement of the MAT. Then, the ACL graft should be passed and fixed on the femoral side prior to introducing, fixing, and repairing the meniscus graft. Following secure fixation of the meniscus graft, tibial fixation of the ACL graft is performed.
Rehabilitation
Evidence-based criteria for rehabilitation after RMAT have not been defined. In cases of RMAT using the bridge in slot technique, the senior author employs the same rehabilitation protocol as in patients following MAT. Patients are placed in a hinged knee brace and are allowed initial partial weightbearing while the brace is locked in full-extension. Immediately following surgery, non-weight-bearing range-of-motion-to 90 degrees of flexion is permissible. At six to eight weeks after surgery, full weightbearing can be advanced as tolerated with initiation of range-of-motion and strengthening exercises. Bracing is discontinued at eight weeks, at which point closed kinetic chain strengthening and neuromuscular proprioception exercises can progress as tolerated. At approximately 20 weeks after surgery, patients can advance to sport-specific drills and running, assuming that all earlier rehabilitation milestones have been met.
Outcomes of Revision MAT Published literature on the outcomes of RMAT are limited. In a small case series of patients undergoing RMAT with a bridge-in-slot technique, Yanke et al.39 assessed clinical outcome at mean 3.83 years after RMAT. Average time to RMAT was 3.45 years after the initial MAT procedure. Clinical outcome findings were promising, with significant improvements in IKDC and KOOS outcome scores as well as no significant progression of radiographic or Outerbridge grading. Seven out of eight patients who completed final follow-up reported that they would undergo the surgery again. One patient out of the original 11 patient cohort underwent arthroplasty in the follow-up time period. In addition to the small cohort, this study was limited by several patients with differing concomitant procedures, limiting the generalizability of the outcomes of this cohort to a greater population of patients with failed MAT. Lee et al.40 analyzed a similar sized cohort of lateral RMAT using bone blocks and a keyhole tibial slot technique in 9 patients. Three patients had a repeat failure of their RMAT in the first year after
surgery, all due to bucket-handle displacement of the graft. A further two patients had insufficient healing on MRI follow-up without failure. However, all six patients who did not experience treatment failure had significant outcome improvements on IKDC and Lysholm measures at a mean 29.2 months follow-up. These findings suggest that RMAT can be an effective treatment but has inferior short-term graft survival rates compared to MAT.
Case Report of Revision MAT Recently a 21-year-old female was treated by the senior author with a revision MAT. The patient suffered from chronic medial knee pain and had undergone three medial meniscectomies at ages 15, 16, and 17, each of which provided little relief. At age 20 the patient underwent a medial MAT using the bridge-in-slot technique41 without perioperative complications and excellent apposition and anatomic fit of the transplant. Following surgery, the patient reported improved pain and swelling and was progressing with rehabilitation well until approximately 6 months after surgery, when she gradually developed medial joint space pain and localized swelling, with MRI at that time showing evidence of meniscal extrusion (Figure 3A-C). At nine months after primary MAT, the patient underwent diagnostic arthroscopy, which showed an unstable and irreparable fragment of transplanted meniscus that was excised from the midbody to posterior horn. After stabilization, approximately 50% of the original graft was found to be compromised, but there was no concomitant articular cartilage damage. Despite arthroscopic stabilization and conservative management with physical therapy and corticosteroid injection, the patient was unable to return to prior level of physical activity and experienced worsening pain with performing activities of daily living. At this point, given her young age and otherwise healthy knee, the patient was recommended to undergo revision MAT.
At one year after primary MAT, the patient underwent revision MAT with excision of the remaining primary allograft and transplantation of a new allograft utilizing the same bridge-in-slot technique utilized in the first MAT procedure. At final follow-up four months after revision MAT, the patient was symptom free and progressing through rehabilitation without difficulty.
Case Report: MAT Repair A 21-year old male professional baseball player underwent both a primary lateral MAT and MAT repair by the senior author. Previously, at age 19, the patient had undergone a lateral meniscectomy for a tear suffered while playing baseball and had relief for approximately one month before suffering recurrent pain and inability to return to sport. At age 20 the patient underwent primary lateral MAT to alleviate his persistent symptoms, using a bridge-in-slot technique for graft fixation. The patient went through routine post-surgical rehabilitation without difficulty and successfully returned to professional baseball. However, approximately one year after surgery the patient suffered a traumatic knee injury while sliding into a base with immediate mechanical symptoms. The patient underwent knee arthroscopy, which confirmed a tear of the transplanted lateral meniscus just anterior and posterior to the popliteal hiatus. The tear was amenable to suture repair, which was completed with passage of eight sutures with subsequent excellent apposition to the periphery. At that time, concomitant microfracture of the intercondylar notch and injection of four milliliters of PRP were performed. Following repair of the transplanted meniscus, the patient was able to return to prior level of play and remains playing professional baseball at a higher level of play than prior to his surgeries, at nine years after MAT repair.
Conclusion: In select patients with an initial functional improvement following MAT prior to subsequent failure, RMAT may be indicated to alleviate pain and perhaps delay progression of osteoarthritis. The indications and optimal surgical technique for RMAT have yet to be determined, but our preference is to use a bridge-in-slot technique and address all other pathologies as indicated. Following rehabilitation, preliminary outcomes of RMAT are encouraging, with improved functional outcomes in short-term follow-up. While promising, published literature on RMAT is limited, with future studies needed to assess surgical indications, outcomes, and techniques.
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journal of arthroscopic & related surgery : official publication of the Arthroscopy Association of North America and the International Arthroscopy Association. 2014;30(12):1602-1608. Lee BS, Bin SI, Kim JM, Kim WK, Kim JH. Revision Meniscal Allograft Transplantation in the Lateral Compartment: Disparate MRI and Clinical Outcomes During the Early Postoperative Period. The American journal of sports medicine. 2016;44(11):2884-2891. Kaplan DJ, Glait SA, Ryan WE, Jr., et al. Meniscal Allograft Transplantation Made Simple: Bridge and Slot Technique. Arthroscopy techniques. 2017;6(6):e2129-e2135.
Medial Femoral Condyle
Medial Meniscus
Tibial Plateau
Figure 1: Arthroscopic probing of a meniscal allograft tear following primary meniscal allograft transplantation (red arrow).
Figure 2A-C: Operative technique for a medial meniscus RMAT. A. Sizing of meniscus allograft prior to preparing bone bridge. B. Preparing to insert the meniscus allograft in to the knee. Traction stitch on graft passed through to the postero-medial capsule using a passing wire prior to graft insertion through arthrotomy. C. Suture management following repair of allograft using the inside-out technique. Additional all-inside sutures are used as necessary.
Figure 3A-C: Preoperative MRI prior to RMAT. A. Medial-Sagittal view showing anterior displacement of the anterior horn accompanied by bone marrow edema in the medial femoral condyle and its counterpart on the anterior edge of the medial tibial plateau. The posterior horn is deformed and partially missing. (red arrow). B. Axial imaging demonstrating significant morphologic changes and irregularity of the original meniscus allograft (red arrows). C. Coronal imaging showing significant graft extrusion of the meniscus allograft (red arrow).
Failure of Meniscus Allograft Transplantation Eric D Haunschild BS , Ron Gilat MD , Kelechi Okoroha MD , Brian J. Cole MD, MBA PII: DOI: Reference:
S1060-1872(19)30087-5 https://doi.org/10.1016/j.otsm.2019.150713 YOTSM 150713
To appear in:
Operative Techniques in Sports Medicine
Please cite this article as: Eric D Haunschild BS , Ron Gilat MD , Kelechi Okoroha MD , Brian J. Cole MD, MBA , Failure of Meniscus Allograft Transplantation, Operative Techniques in Sports Medicine (2019), doi: https://doi.org/10.1016/j.otsm.2019.150713
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Failure of Meniscus Allograft Transplantation Eric D Haunschild BS1, Ron Gilat MD1, Kelechi Okoroha MD1, Brian J Cole MD, MBA1
1
Midwest Orthopedics at Rush University, Rush University Medical Center, Chicago, IL
Corresponding Author: Brian J. Cole MD, MBA 1611 West Harrison Street Chicago, Illinois 60612 (708) 505-8941 [email protected]
Abstract: Meniscus allograft transplantation (MAT) has emerged as an acceptable surgical therapy in relieving pain and restoring function in young patients with symptomatic meniscal deficiency without severe osteoarthritis. Despite its early success, at long-term follow-up MAT has been associated with significant rates of graft failure, requiring repeat interventions and often progression to arthroplasty. In select patients who previously benefited from a primary MAT and have an identified, treatable cause of failure, revision meniscus allograft transplantation (RMAT) may be considered. Careful identification and treatment of concomitant pathologies known to cause failure, including ligamentous instability, cartilage injury and limb malalignment, should be addressed at the time of revision surgery. Acute tears should be assessed for whether they are amenable to repair or replacement with a new graft is required. The
author’s preferred approach is to perform the bone-slot technique for both primary and revision cases. Literature on outcomes following RMAT are limited but favorable, with higher failure rates than primary MAT but significant functional outcome improvement in most patients.
Introduction In a select population of young patients with functional loss of the meniscus or prior (sub-)total meniscectomy, and without severe osteoarthritis, meniscal allograft transplantation (MAT) may be indicated. MAT has emerged as a viable technique to decrease pain and preserve knee function. Although not definitively proven, the surgery may have joint preserving potential by decreasing the progression of osteoarthritis in these select patients. However, long-term failures of MAT are not uncommon, with incidence of failure ranging from 10-29%.1-3 While some symptomatic patients undergo debridement only of the failed transplant or arthroplasty when indicated, in select otherwise healthy patients who experienced substantial clinical benefit from their primary MAT, revision meniscus allograft transplantation (RMAT) may be considered.
Epidemiology Incidence and risk factors for failure of MAT have been well reported in the published literature, with often discordant findings. In a recent analysis of failures at a mean of 59 months after MAT, McCormick et al.4 found a 4.7% incidence of failure requiring RMAT or conversion to arthroplasty. Thirty-two percent of patients required secondary surgery, with a majority undergoing isolated arthroscopic debridement. However, those patients that did require secondary surgery within two years after MAT had a significantly higher risk of requiring future arthroplasty (odds ratio: 8.4). Zaffagnini and
collegues evaluated a case series of 147 patients at a mean of four years after soft tissue only MAT and found a surgical failure rate of 5%. Notably, there was no significant differences in failure associated with medial or lateral transplants, isolated or combined MAT, patient age, or patient BMI.5 Similarly an investigation of 230 MATs in a physically active military population found a surgical failure rate of 5.7% at a mean or 2.14 years after surgery. In this study concomitant ligament or realignment procedures were identified as significant risk factors for failure.6 These findings are supported by a recent investigation of 40 patients receiving MAT with concomitant ACL reconstruction, which identified a 20% failure rate at mean 7.3 years after surgery, similarly suggesting the need for concomitant ACL reconstruction as a predictor of MAT failure.7 Several analyses have investigated concomitant cartilage degeneration and its impact on failure of MAT. Lee and associates evaluated 222 patients receiving MAT at five years following surgery and categorized patients by International Cartilage Repair Society (ICRS) grade of cartilage injury. The authors found that patients with high grade bipolar degeneration had significantly lower MAT graft survival rate (62.2%) than patients with high-grade unipolar (90.3%) or low-grade unipolar (93.3%) defects.8 Another recent case series of 125 patients at five years after MAT analyzed graft survival in patients with partial-thickness, unipolar full-thickness, and bipolar full-thickness articular cartilage defects. With failure defined as needing graft removal, RMAT, or arthroplasty, failure rates with bipolar full thickness defects (29.6%) were greater than those with unipolar full-thickness (11.1%) and partial thickness (2.9%) defects.9 A systematic review of six trials assessing outcome at a mean of three years after surgery in patients receiving MAT with concomitant cartilage repair or restoration procedures found that four of the six trials demonstrated equivalent functional outcomes to isolated MAT, with the last two reporting inferior outcomes in those patients receiving concomitant procedures.10 The aggregate failure rate was 12%, with 85% of failures attributable to the MAT procedure. These findings
suggest that MAT with concomitant cartilage procedures produces similar outcomes and failure rates to what has been reported in isolated MAT procedures.
Mechanisms of Meniscal Allograft Failure MAT failure is commonly classified into early and late failure with several different etiologies of graft failure previously identified. A cause of both early and late failure in bony MAT is delayed union or nonunion of the graft bone block to the recipient bone trough. Researchers have suggested that ligamentous injury or malalignment of the knee can lead to non-union of the graft. de Boer and colleagues suggested this mechanism for MAT failure when evaluating a case series of 24 patients who underwent medial MAT. Their study identified varus malalignment in two patients and deficient cruciate ligaments in another case of failed meniscal allografts. When reviewing immunohistochemical reactions, key proliferation markers were localized near areas of microvascular supply whereas in critical areas of the knee, focal areas of degeneration were noted with no surrounding proliferation markers. The authors suggested that non-union may be caused by vascularization deficiencies, and that ligamentous instability or mechanical malalignment may alter contact pressures endured by the meniscus. This ultimately could lead to altered vascularization patterns of the meniscus and ultimate failure of healing.11 Another prevalent etiology of MAT failure is acute trauma to the transplanted knee resulting in graft rupture. This can occur in the immediate post-operative period due to premature strenuous activity or at any point after surgery due to excessive forces, analogous to native meniscus injury. Following trauma, patients should be carefully evaluated to assess if the graft tear is amenable to simple debridement, repair, or if a new graft is needed. In addition, any concomitant injuries sustained during
the trauma should be assessed and considered in the context of altered biomechanical forces that may affect MAT survival as described above.11 Since the introduction of MAT, there have been concerns of the immunogenicity of meniscal allografts. However, concerns have not been validated in the literature, with only a single case report showing arthroscopic and histologic evidence of acute immune-mediated rejection at ten weeks after MAT.12 In addition to the above mentioned mechanisms of failure, there are many changes to the transplanted graft that occur over time which can lead to gradual failure. As in native meniscus tissue, over time meniscus allografts undergo repetitive stress leading to degenerative changes to the graft. These degenerative changes when subjected to continued shearing forces may result in significant symptoms, as well as progress to functional failure of the MAT. Another well-identified time-dependent morphologic change unique to meniscus allografts is graft shrinkage, which has been demonstrated to develop and progress following MAT.13-15 However, the effect of these changes is unclear, with multiple investigations reporting no significant effect of the extent of shrinkage on clinical outcome.16-18 Further investigations are needed to assess the clinical significance of changes to graft morphology as it pertains to clinical or surgical failure requiring revision surgery.
Operative Considerations to Optimize Outcomes Following MAT
Graft Sizing A critical preoperative consideration for MAT is sizing of the meniscus allograft. Meniscus allografts are both size and compartment-specific, with incorrect sizing resulting in altered joint
mechanics. Specifically, oversized grafts lead to greater forces on the articular cartilage while undersized grafts result in increased forces on the graft itself.19 These altered mechanics may result in early degenerative changes and subsequent failure of the grafts, ultimately requiring RMAT or arthroplasty. Once particular consequence of mismatch is graft extrusion, a known cause for graft failure and a relative indication for RMAT.20,21 To minimize mismatch of grafts, we utilize the sizing method described by Pollard et al.22 Briefly, standard AP and lateral knee radiographs are measured to obtain graft measurements within 10% of error. On AP films, measurement of the distance between the tibial eminence to the periphery of the tibial plateau, corresponds to the coronal width of the medial or lateral meniscus. On lateral radiographs, the anterior to posterior (AP) length of the graft is measured as 80 percent of the AP length of the tibial plateau for the medial meniscus and 70 percent of the AP length of the tibial plateau for the lateral meniscus. A modification to the Pollard sizing method has been described by Yoon et al, using the measurements and applying them to a mathematical model providing more precise sizing.23
Graft Fixation Technique Several techniques have been proposed for fixation of the anterior and posterior roots of the meniscus allograft. MAT fixation techniques are commonly categorized as either osseous fixation (using either a bone-plug or bone-bridge technique) or soft-tissue fixation (which includes passing sutures through tibial tunnels or simple fixation with peripheral sutures). Fixation technique should be carefully scrutinized as isolated soft tissue fixation has been associated with slightly inferior biomechanical outcomes when compared to osseous fixation.24-26 For this reason, the senior author utilizes bony fixation, more specifically using a bone bridge, during primary MAT and RMAT. However, to date there is
no literature identifying clear differences in functional outcomes following either osseous or soft tissue fixation.27
Graft Preservation Technique Since the introduction of MAT, several types of preservation techniques have been utilized: fresh, fresh-frozen, cryopreserved, and lyophilized grafts. Of these, fresh-frozen grafts remain the most widely used in practice today. Lyophilized grafts have been found to have significantly greater morphologic changes and poorer long-term outcomes when compared to fresh-frozen grafts.28 Comparative trials on cryopreserved versus fresh-frozen grafts remain limited in both MAT and RMAT at this time, with recent evidence showing modest decreases in graft shrinkage in fresh-frozen grafts as compared to cryopreserved grafts.29 In both primary and revision MAT cases, we prefer to use freshfrozen grafts due to their established efficacy, ease of processing, lower immunogenicity, and lower cost.4,7
Concomitant Surgery In addition to the considerations outlined above, careful assessment of ligamentous integrity and distal alignment of the affected limb should be completed prior to primary meniscus transplant. In early outcome studies, knees with significant ligamentous instability or limb malalignment were associated with greater rates of MAT failures, with the authors proposing that these factors hindered vascularization and healing of grafts.30,31 If ligamentous injury or distal malalignment are identified, these pathologies should be addressed with either a staged or concomitant procedure as indicated.
Pre-operative Evaluation As when considering primary MAT, it is essential to complete a thorough history and physical exam when assessing patients for RMAT. Consensus criteria have yet to be determined for surgical considerations specific to RMAT, but many of the criteria employed by the senior author are similar to those for MAT. That is, patients should be young and physically active with focal symptoms attributable to meniscal deficiency. Chondral defects or progression of arthritic change to the joint should be assessed, as patients with significant arthritic changes to the joint are more likely to fail. Investigation and evaluation of any concomitant injuries should be assessed with visual inspection, limb alignment assessment, range-of-motion, palpation, and ligamentous and meniscal testing. Patients will often have focal pain and swelling to palpation, worsened with activity, as well as mechanical symptoms in the affected knee. At minimum, a bilateral long-leg weight-bearing radiographic series and unilateral knee MRI should be obtained to assess for extrusion or tears of the meniscus allograft as well as evidence of other joint pathologies and limb alignment. Second-look arthroscopy should also be performed on a case-by-case basis prior to a revision procedure to directly visualize extent of graft union and injury, as these can be key considerations when planning revision procedures (Figure 1). Another key consideration independent of clinical or radiographic criteria is the degree to which the patient improved following their initial MAT. RMAT requires a lengthy and involved rehabilitation process with a high risk of being unable to return to prior level of activity. Patients who experienced minimal to no improvement following MAT are unlikely to experience a significant benefit with RMAT and should probably explore other treatment options.
Operative Considerations for RMAT
An acute traumatic meniscal allograft tear should be addressed in a timely fashion. Meniscocapsular detachment due to failure of the graft to heal can result in a bucket-handle or a longitudinal tear, which can sometimes be successfully treated with repair of the allograft. Radial and flap tears are less likely to allow repair and may require arthroscopic debridement or graft replacement, dependent on morphology and depth. Root-tears may or may not be amendable for repair according to the tear location and the method applied for fixation during the primary surgery. Soft-tissue or bone plug root tears may be repaired in the same tunnel technique used in the primary surgery. If slot technique was used, a root tear is theoretically less likely to occur, but if does happen, can be repaired using a tunnel or an anchor. Acute tears that are not suitable for repair and cases with biologic degeneration of the graft require RMAT with a new graft. The technique used to secure the new graft is generally independent of the technique used for the primary surgery. Some authors advocate using the bone plug technique.32 However, we prefer the use of the slot technique previously described33-36 and summarized as follows both for primary and revision cases, as this allows for secure bone fixation and ease in performing any concomitant osteotomy or ligamentous reconstruction at the time of RMAT. Patients should be placed supine with a standard thigh holder and tourniquet before being draped in a sterile fashion. The procedure should then begin with diagnostic arthroscopy to evaluate for concomitant ligamentous or chondral pathology. The meniscus should be examined to visualize if the initial allograft is amenable to simple debridement or repair. If simple debridement or repair are not feasible, and an RMAT is elected, the remaining initial allograft should be debrided to a stable rim of peripheral meniscus tissue with anterior and posterior horn insertion sites maintained. Following arthroscopy, surgical exposure should be obtained with an anterior longitudinal incision and mini-arthrotomy in line with the anterior and posterior horn insertion sites. Arthrotomy can
be performed either adjacent to or through the patellar tendon based upon surgeon preference. Depending on whether a medial or lateral transplant is being performed, an accessory posterolateral or posteromedial incision should be made approximately one-third above and two-thirds below the joint line to permit inside-out repair of the meniscus following graft insertion. Attention is then made to creating the tibial slot. This should be completed by using electrocautery to make a line connecting the anterior and posterior horn insertions and using a 4.5millimeter burr to create an initial slot along this line. A guide wire is then inserted distal and parallel to the initial slot, which is then overreamed using an 7-8 millimeter cannulated reamer. A box cutter is then used to create the final tibial slot, measuring approximately 8 millimeters wide and 10 millimeters deep. The tunnel should then be smoothed out using a rasp prior to graft insertion. The graft can be prepared at any point during the case once thawed. A bone bridge is created, 10 millimeters deep and 7 millimeters wide, from the tibial plateau attached to the thawed graft (Figure 2A). The bone bridge is purposefully undersized to allow for ease of insertion into the slot following graft preparation. Any bone posterior to the posterior meniscal horn attachment should be removed, and any bone anterior to the anterior meniscal horn attachment should be preserved to maintain graft integrity during graft passage. Lastly, a single vertical mattress traction stitch should be placed at the junction of the posterior and middle-third of the graft. A passing wire is guided into the accessory incision and out the anterior arthrotomy. The traction stitch suture ends are then inserted into the passing wire, which is then pulled back through the accessory incision (Figure 2B). The prepared allograft is then passed into the tibial slot. Under direct visualization, the bone bridge is advanced into the tibial slot and secured with a single interference screw. Attention is then placed to the meniscus, which is repaired to the joint capsule using inside-out vertical mattress sutures (Figure 2C). Generally, 8-10 sutures are required for repair.
There are several considerations that relate to the cause of failure of the primary MAT, which may affect the surgical technique of RMAT. Any graft extrusion should be identified in postoperative MRI and/or during second look arthroscopy. A common cause of extrusion is malposition of the tunnels or slot (for example: lateral malposition of a lateral MAT).37 Operative treatment should be based on a case by case basis, but may include tunnel or slot repositioning, anchor fixation of the body of the meniscus to the tibia and graft replacement with appropriate graft sizing. If a concomitant pathology is detected it should be addressed accordingly during RMAT; an ACL tear should be reconstructed, malalignment should be addressed with a high tibial osteotomy (HTO) or a distal femoral osteotomy (DFO), and an osteochondral lesion should be addressed with an appropriate cartilage restoration procedure. In general, any concomitant osteotomy or cartilage procedure should be performed after RMAT, as passing the graft requires significant stress to the knee that may compromise these procedures. For concomitant ACL reconstruction, the senior author prefers to use a modified bridge-in-slot technique previously described.38 Following arthroscopy and both meniscus and ACL graft preparation, the next operative steps are to prepare the femoral tunnel for ACL graft passage and to create the tibial slot for meniscus graft fixation. The ACL tibial tunnel is then drilled as obliquely as possible to minimize any effect on slot placement of the MAT. Then, the ACL graft should be passed and fixed on the femoral side prior to introducing, fixing, and repairing the meniscus graft. Following secure fixation of the meniscus graft, tibial fixation of the ACL graft is performed.
Rehabilitation
Evidence-based criteria for rehabilitation after RMAT have not been defined. In cases of RMAT using the bridge in slot technique, the senior author employs the same rehabilitation protocol as in patients following MAT. Patients are placed in a hinged knee brace and are allowed initial partial weightbearing while the brace is locked in full-extension. Immediately following surgery, non-weight-bearing range-of-motion-to 90 degrees of flexion is permissible. At six to eight weeks after surgery, full weightbearing can be advanced as tolerated with initiation of range-of-motion and strengthening exercises. Bracing is discontinued at eight weeks, at which point closed kinetic chain strengthening and neuromuscular proprioception exercises can progress as tolerated. At approximately 20 weeks after surgery, patients can advance to sport-specific drills and running, assuming that all earlier rehabilitation milestones have been met.
Outcomes of Revision MAT Published literature on the outcomes of RMAT are limited. In a small case series of patients undergoing RMAT with a bridge-in-slot technique, Yanke et al.39 assessed clinical outcome at mean 3.83 years after RMAT. Average time to RMAT was 3.45 years after the initial MAT procedure. Clinical outcome findings were promising, with significant improvements in IKDC and KOOS outcome scores as well as no significant progression of radiographic or Outerbridge grading. Seven out of eight patients who completed final follow-up reported that they would undergo the surgery again. One patient out of the original 11 patient cohort underwent arthroplasty in the follow-up time period. In addition to the small cohort, this study was limited by several patients with differing concomitant procedures, limiting the generalizability of the outcomes of this cohort to a greater population of patients with failed MAT. Lee et al.40 analyzed a similar sized cohort of lateral RMAT using bone blocks and a keyhole tibial slot technique in 9 patients. Three patients had a repeat failure of their RMAT in the first year after
surgery, all due to bucket-handle displacement of the graft. A further two patients had insufficient healing on MRI follow-up without failure. However, all six patients who did not experience treatment failure had significant outcome improvements on IKDC and Lysholm measures at a mean 29.2 months follow-up. These findings suggest that RMAT can be an effective treatment but has inferior short-term graft survival rates compared to MAT.
Case Report of Revision MAT Recently a 21-year-old female was treated by the senior author with a revision MAT. The patient suffered from chronic medial knee pain and had undergone three medial meniscectomies at ages 15, 16, and 17, each of which provided little relief. At age 20 the patient underwent a medial MAT using the bridge-in-slot technique41 without perioperative complications and excellent apposition and anatomic fit of the transplant. Following surgery, the patient reported improved pain and swelling and was progressing with rehabilitation well until approximately 6 months after surgery, when she gradually developed medial joint space pain and localized swelling, with MRI at that time showing evidence of meniscal extrusion (Figure 3A-C). At nine months after primary MAT, the patient underwent diagnostic arthroscopy, which showed an unstable and irreparable fragment of transplanted meniscus that was excised from the midbody to posterior horn. After stabilization, approximately 50% of the original graft was found to be compromised, but there was no concomitant articular cartilage damage. Despite arthroscopic stabilization and conservative management with physical therapy and corticosteroid injection, the patient was unable to return to prior level of physical activity and experienced worsening pain with performing activities of daily living. At this point, given her young age and otherwise healthy knee, the patient was recommended to undergo revision MAT.
At one year after primary MAT, the patient underwent revision MAT with excision of the remaining primary allograft and transplantation of a new allograft utilizing the same bridge-in-slot technique utilized in the first MAT procedure. At final follow-up four months after revision MAT, the patient was symptom free and progressing through rehabilitation without difficulty.
Case Report: MAT Repair A 21-year old male professional baseball player underwent both a primary lateral MAT and MAT repair by the senior author. Previously, at age 19, the patient had undergone a lateral meniscectomy for a tear suffered while playing baseball and had relief for approximately one month before suffering recurrent pain and inability to return to sport. At age 20 the patient underwent primary lateral MAT to alleviate his persistent symptoms, using a bridge-in-slot technique for graft fixation. The patient went through routine post-surgical rehabilitation without difficulty and successfully returned to professional baseball. However, approximately one year after surgery the patient suffered a traumatic knee injury while sliding into a base with immediate mechanical symptoms. The patient underwent knee arthroscopy, which confirmed a tear of the transplanted lateral meniscus just anterior and posterior to the popliteal hiatus. The tear was amenable to suture repair, which was completed with passage of eight sutures with subsequent excellent apposition to the periphery. At that time, concomitant microfracture of the intercondylar notch and injection of four milliliters of PRP were performed. Following repair of the transplanted meniscus, the patient was able to return to prior level of play and remains playing professional baseball at a higher level of play than prior to his surgeries, at nine years after MAT repair.
Conclusion: In select patients with an initial functional improvement following MAT prior to subsequent failure, RMAT may be indicated to alleviate pain and perhaps delay progression of osteoarthritis. The indications and optimal surgical technique for RMAT have yet to be determined, but our preference is to use a bridge-in-slot technique and address all other pathologies as indicated. Following rehabilitation, preliminary outcomes of RMAT are encouraging, with improved functional outcomes in short-term follow-up. While promising, published literature on RMAT is limited, with future studies needed to assess surgical indications, outcomes, and techniques.
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Medial Femoral Condyle
Medial Meniscus
Tibial Plateau
Figure 1: Arthroscopic probing of a meniscal allograft tear following primary meniscal allograft transplantation (red arrow).
Figure 2A-C: Operative technique for a medial meniscus RMAT. A. Sizing of meniscus allograft prior to preparing bone bridge. B. Preparing to insert the meniscus allograft in to the knee. Traction stitch on graft passed through to the postero-medial capsule using a passing wire prior to graft insertion through arthrotomy. C. Suture management following repair of allograft using the inside-out technique. Additional all-inside sutures are used as necessary.
Figure 3A-C: Preoperative MRI prior to RMAT. A. Medial-Sagittal view showing anterior displacement of the anterior horn accompanied by bone marrow edema in the medial femoral condyle and its counterpart on the anterior edge of the medial tibial plateau. The posterior horn is deformed and partially missing. (red arrow). B. Axial imaging demonstrating significant morphologic changes and irregularity of the original meniscus allograft (red arrows). C. Coronal imaging showing significant graft extrusion of the meniscus allograft (red arrow).