Connor, Yong, M.S./OMS II¹; Logan, Morrison, D.O./Orthopedic Surgery Resident²; Tristan, Brunet, B.S./OMS IV¹; Alexis, Rondinelli, M.S./OMS II¹; Rachel, Palet, M.S./OMS III³; Geoffrey, McCullen, MD/Orthopedic Surgeon^1
1University of New England College of Osteopathic Medicine
²Community Memorial Health System
³University of North Texas Health Science Center

Abstract

Meniscus allograft transplantation (MAT) is an established treatment for symptomatic meniscal deficiency, providing pain relief, functional improvement, and the potential to delay joint degeneration. Despite generally favorable outcomes, heterogeneity in how “failure” is defined across the literature limits comparability and clinical interpretation. This narrative review evaluated reported definitions of MAT failure to identify common criteria and propose a more standardized framework. A PubMed and grey literature search identified 25 studies published within the past 12 years that reported clinical outcomes of MAT and explicitly defined failure. While all studies included at least one criterion, no two definitions were identical. Most definitions relied on surgical endpoints such as reoperation, graft removal, or conversion to total knee arthroplasty, whereas relatively few incorporated patient-reported outcome measures (PROMs). Among PROM-based definitions, a Lysholm score <65 was most frequently cited. Ten of 25 Identified articles used this threshold while seven articles also included KOOS scores and six articles also included IKDC scores. MAT consistently improved outcomes such as IKDC, KOOS, and Lysholm scores, with 10-year survivorship ranging from 60–90% and greater durability in younger, less arthritic patients. Revision cohorts demonstrated higher failure rates than primary MAT, and concomitant procedures—including ACL reconstruction, cartilage restoration, and osteotomy—were shown to influence survivorship. These findings highlight the disconnect between surgical and clinical definitions of failure, which may overlook patient dissatisfaction despite technically successful procedures. A practical and comprehensive definition that incorporates both reoperation and PROM thresholds, such as a Lysholm score <65, would improve consistency in research reporting, enhance clinical counseling, and refine understanding of MAT’s role in delaying or preventing arthroplasty.

Keywords: Meniscus allograft transplantation, survivorship, patient-reported outcomes, graft failure.

Introduction
Meniscus allograft transplantation ( MAT) is a surgical option for younger, active patients with symptomatic meniscal deficiency seeking to delay arthroplasty (TKA). MAT offers a biomechanically restorative alternative that can relieve pain, restore function, and delay degenerative changes following irreparable meniscal loss (13,14). Since its introduction in the 1980s, MAT has demonstrated potential benefits in improving quality of life and slowing osteoarthritis progression. However, interpretation of these outcomes remains challenging due to the absence of a universally accepted definition of MAT failure.

Long-term studies have shown that MAT can preserve knee function and postpone arthroplasty when indicated. Van der Wal et al reported meaningful improvements in patient-reported outcome measures (PROMs) despite prior surgery, while Phillips et al observed nearly 80% graft survival at 10 years with improved pain and activity levels (13,20). Short-term outcomes have also been encouraging, particularly when supported by structured rehabilitation protocols (17). Nevertheless, inconsistent definitions of failure limit comparability and generalizability across studies, which complicates clinical decision-making.

MAT techniques such as bone plug, bridge-in-slot, and soft-tissue fixation continue to evolve, yet no single approach has demonstrated clear superiority (13,14). Advancements in graft preservation and rehabilitation may contribute to improved outcomes, but complications—including extrusion, infection, and cartilage injury—remain a concern and may necessitate additional procedures such as ACL reconstruction or osteotomy (20,21). Importantly, complications such as graft shrinkage or extrusion do not always correlate with patient dissatisfaction or poor clinical outcomes (6). Patient-specific variables, including malalignment and comorbidities, further influence results and complicate assessment of surgical success (2,18).

Currently, MAT failure is defined variably across the literature, including criteria such as graft revision, conversion to arthroplasty, radiographic abnormalities, or PROM thresholds (7,9). Liu et al noted that imaging findings alone are insufficient, as graft abnormalities do not always correlate with symptoms or functional limitations (9). A comprehensive definition that incorporates surgical, radiographic, and functional outcomes is needed to standardize reporting and interpretation (12). Across included studies, we identified five recurring elements in failure definitions: conversion to arthroplasty, graft removal, revision MAT, any reoperation, and PROM thresholds. This review synthesizes the literature on MAT failure, focusing on revision rates, graft survival, and PROMs, to guide future research and clinical decision-making.

 Methods
A literature review was conducted to characterize the definitions of failure used in studies on meniscus allograft transplantation. Eligible articles were published in English within the past 12 years and included original clinical data related to MAT outcomes. Studies were included if they addressed MAT failure using clinical, surgical, or patient-reported outcome measure definitions The search was performed using PubMed only. Search terms included: “meniscus,” “meniscus allograft transplant,” “knee,” “failure,” “success,” and “outcomes.” Filters were applied to limit results to English-language publications within the past 12 years. Titles and abstracts were screened independently by two reviewers (CY and TB). Full-text review was conducted for articles meeting inclusion criteria. Any discrepancies were resolved through discussion. No automation tools or AI-assisted screening methods were used. The primary outcome of interest was the definition of failure used in each study. Collected data included study design, definitions of failure, type of failure criteria, and PROMs used. Studies were categorized based on whether they defined failure by surgical endpoints, PROM thresholds, or a combination of both. Where available, specific PROM thresholds used to define failure were recorded.

Results
A total of 25 articles met inclusion criteria, each documenting outcomes following meniscus allograft transplantation. All studies provided at least one definition of MAT failure; however, no two studies used identical criteria. Of these, 18 reported both PROMs and surgical data related to revision procedures. Despite this, consistent or synonymous definitions of failure were not identified, underscoring variability in both surgical and clinical failure parameters.

Eight studies collected and analyzed PROMs but did not incorporate them into their failure definition. For example, Parkinson et al defined failure strictly as “complete removal of the allograft, revision, or conversion to joint replacement” while also collecting KOOS and IKDC scores, without including specific thresholds in their criteria (11). This highlights a disconnect between outcome measurement and failure definition.

Twelve studies defined failure using only surgical criteria. For instance, McCormick et al described failure as requiring arthroplasty or allograft revision within 2 years, reporting that 59% of patients underwent arthroscopic debridement and 4.7% underwent revision or TKA during this period (10). Similarly, Cvetanovich et al defined failure as requiring TKA, unicompartmental knee arthroplasty (UKA), or total meniscectomy, reporting a 13.8% failure rate (3). Limiting failure to surgical endpoints may exclude clinically relevant interventions, such as partial meniscectomies or debridement, particularly important in younger, more active patients.

Thirteen studies incorporated both surgical and clinical definitions of failure. PROMs most commonly included KOOS, IKDC, and Lysholm scores. Anatomic failure, such as meniscal tears exceeding 50%, was often reported separately from clinical failure. For example, one study reported that only 3.7% of patients had both anatomic and clinical failure, defined as a significant meniscal tear with a Lysholm score <65 (15). Song et al also noted that anatomic failure did not necessarily correspond with poor clinical outcomes or need for reoperation, as patients often reported improved quality of life and satisfaction despite graft abnormalities (15).

PROM thresholds varied, but the Lysholm score <65 was the most frequently applied clinical criterion. Ten of the 25 articles used this threshold, sometimes alongside KOOS. The frequent use of Lysholm demonstrates its perceived value in capturing knee instability and functional impairment. The inclusion of PROMs alongside surgical outcomes provides a more comprehensive definition of MAT failure, integrating both anatomical and patient-centered perspectives.

Discussion
Defining failure in meniscus allograft transplantation remains complex and is influenced by multiple factors affecting knee stability, graft health, and long-term outcomes. Across the literature, definitions vary widely, limiting comparability between studies and hindering the development of standardized treatment guidelines.

A major limitation in developing an inclusive definition of MAT failure is variability in patient-specific factors, including age, prior injuries, athletic activity, and postoperative rehabilitation protocols. Additional influences include ligamentous insufficiency, malalignment, and cartilage status, all of which complicate outcome assessment. Age is frequently cited as a prognostic factor, with worse outcomes generally associated with increasing age. However, findings are inconsistent. Zaffagnini et al compared outcomes of MAT in patients older than 50 years versus those younger than 30 and reported inferior results in the older cohort, potentially due to cartilage quality and reduced healing capacity (23). In contrast, Kim et al found no significant difference in failure rates by age or cartilage status in a cohort undergoing primary isolated lateral MAT (5). Although younger age is generally associated with improved outcomes (19), no universal age threshold exists. The International Meniscus Reconstruction Experts Forum (IMReF) consensus statement similarly notes the absence of standardized age-based candidacy criteria (4).

Cartilage status, often graded using the Outerbridge classification, is another key determinant. MAT is typically contraindicated in advanced osteoarthritis or Outerbridge grade III–IV damage across multiple compartments. Still, some evidence suggests benefit in patients with focal or bipolar lesions when MAT is performed with cartilage restoration. Lee et al reported effectiveness in patients with bipolar lesions but greater graft survival in those with unipolar lesions (8). Bloch et al likewise found higher-grade cartilage damage associated with reduced survivorship compared to mild or moderate degeneration (1).

Prior surgical history and concomitant pathology also impact outcomes. Zaffagnini et al demonstrated that MAT combined with ACL reconstruction yielded superior functional and pain scores compared with isolated MAT (24). These findings highlight the importance of optimizing the joint environment—through alignment correction, ligament stabilization, and cartilage preservation—before or during MAT.

Postoperative rehabilitation protocols further contribute to heterogeneity. While many guidelines recommend progression to full weight-bearing by 6 weeks and achieving >90° of motion by that time, protocols vary substantially. Some advocate earlier range of motion, though supporting evidence is limited. Return-to-sport timelines are commonly cited at 6–12 months (22), but long-term graft durability under high-load conditions remains uncertain.

MAT is temporizing; durability varies with alignment, cartilage status, compartment, and activity. Many patients ultimately undergo arthroplasty, but MAT can delay progression in appropriately selected cases. MAT does not eliminate the need for future arthroplasty but may delay progression of osteoarthritis by reducing bone-on-bone contact. The procedure provides chondroprotective effects and allows patients to regain function before ultimately requiring TKA (16). Therefore, MAT failure should be defined not by the inevitability of future replacement, but by premature graft loss or functional decline.

Incorporating both surgical and clinical outcomes is essential. Surgical endpoints provide objective evidence of graft failure, while PROMs capture patient-centered outcomes such as pain relief, activity level, and overall satisfaction. Ignoring either dimension narrows applicability and risks underrepresenting clinically meaningful failures.

Taken together, these variables underscore the challenge of standardizing MAT failure definitions. Patient variability, surgical technique, cartilage status, rehabilitation strategy, and reporting methods all contribute to heterogeneity. A unified definition incorporating both surgical and clinical endpoints, with attention to graft integrity, patient symptoms, and return to function, will improve the comparability of MAT research and optimize patient selection and treatment planning.

With performing a narrative review, there is limitation on assessment of bias. Although our article search methods were done systematically, a formal risk-of-bias assessment was not completed, leaving the potential for our data to not be reliably replicable in future studies. While acknowledging these limitations, performing this narrative review allows a direct approach of bringing together multiple aspects of what has already been found to be effective guidelines toward identifying MAT failures. Analysis of the identified articles with a broad lens view helps potentially identify overlooked criteria that should be implemented in a better synthesized definition.

Conclusion
This review highlights the substantial variability in how failure is defined in the meniscus allograft transplantation literature. While many studies define failure through graft removal or conversion to total knee arthroplasty, patient-reported outcome measures are often underutilized or inconsistently applied. This disconnect may overlook patients who remain dissatisfied despite technically successful procedures and contributes to inconsistent perceptions of MAT outcomes. Our analysis found that the most frequently cited definitions of failure were the need for reoperation and a Lysholm score <65. These criteria provide a practical framework that incorporates both surgical and patient-centered outcomes, allowing application across diverse patient populations. We therefore propose that future studies when recording MAT failure report any reoperation—including TKA, graft removal, or revision—or a Lysholm Knee Score <65, in a tiered fashion that distinguishes major and minor reoperations. Failure should be at least assessed at the 12 and 24 month mark using: Tier 1 surgical failure defined as conversion to arthroplasty (TKA/UKA) or complete graft removal; Tier 2 surgical failure defined as revision MAT or subtotal meniscectomy removing more than 50% of the graft; and PROM failure defined as Lysholm <65 or failure to achieve a Patient Acceptable Symptom State on IKDC or KOOS Sports/Pain Any Tier 1 event constitutes failure. A Tier 2 event constitutes failure if accompanied by PROM failure at the same or subsequent assessment. Isolated arthroscopic debridement without PROM failure should not be classified as failure but should be reported as an adverse event. Although MAT is not a definitive treatment, its long-term success should be assessed using a consistent, multidimensional approach. Establishing a standardized definition of failure will improve comparability of research, enhance clinical counseling, and refine understanding of MAT’s role in delaying or preventing joint arthroplasty.

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