Meniscal allograft transplantation and scaffolds: a narrative review

Introduction

The menisci are crescent-shaped fibrocartilaginous structures situated between the femoral condyles and tibial plateau in the medial and lateral compartments of the knee. These structures are essential for distributing load, absorbing shock, enhancing joint stability, and facilitating joint lubrication and proprioception (1,2). Meniscal tears represent the most common intra-articular knee injury, with an estimated incidence ranging from 60 to 70 per 100,000 persons annually (3,4). Although meniscal preservation is prioritized, partial meniscectomy remains the most frequently performed meniscal procedure in the United States (5). However, the removal of meniscal tissue alters knee biomechanics by reducing contact area and increasing contact stress, ultimately accelerating cartilage degeneration and increasing the risk of early-onset osteoarthritis (6).

To address meniscal deficiency, meniscal allograft transplantation (MAT) and meniscal scaffolding have emerged as biologic and synthetic reconstructive options aimed at restoring joint biomechanics, improving function, and delaying further joint degeneration (7-9). Despite promising outcomes in pain relief and function, MAT remains underutilized in clinical practice (4). The reported incidence in the United States ranges from 0.12 to 0.24 per 100,000 persons, with only marginal increases over the past decade (10).

In contrast, for patients with symptomatic segmental meniscal deficiency following partial meniscectomy, meniscal scaffolds have gained traction as a restorative option when a stable peripheral rim and intact ligamentous structures are preserved. These scaffolds are designed to act as a porous framework that allows native cells to infiltrate to promote tissue regeneration, with the goal of restoring meniscal function and preserving joint integrity (8,11,12). Biologic implants, such as the collagen meniscus implant (CMI) and synthetic scaffolds (Actifit), have demonstrated potential in clinical use; however, their effectiveness is limited to cases where a functional meniscal rim remains intact (13). More recently, scaffolds such as MeniscoFix™, a collagen-hyaluronan infused, fiber-reinforced, three-dimensional (3D)-printed polymeric implant, have been developed to support both soft tissue and bony integration (12).

This chapter will review current literature on MAT and meniscal scaffolding, including advances in implant technologies and clinical outcomes. We present this article in accordance with the Narrative Review reporting checklist (available at https://aoj.amegroups.com/article/view/10.21037/aoj-2025-1-88/rc).

Methods

A narrative review of the current literature on MAT and meniscal scaffolds was conducted (Table 1). Key studies were identified through a comprehensive search of PubMed, MEDLINE, and the Cochrane Database of Systematic Reviews on April 30, 2025, using the search terms “meniscal allograft transplantation” OR “meniscal scaffolding”. Articles published between January 1992 and April 2025 were considered. Eligible studies included peer-reviewed articles written in English, Spanish, or Portuguese related to MAT and scaffolds. Given the limited availability of long-term clinical data for meniscal scaffolds, relevant preclinical studies were also included. Study selection was performed independently by two authors (G.A.E. and E.H.), with discrepancies resolved through discussion with the senior author (R.M.F.).

Patient evaluation

A thorough clinical history and diagnostic workup are critical in identifying candidates for meniscal restoration via MAT or meniscal scaffolding. Patients typically report a history of subtotal or total meniscectomy followed by a symptom-free interval and subsequent pain localized to the affected compartment. This discomfort is often activity-dependent, presenting as joint line pain, swelling, or catching sensations (13,14).

On physical examination, most candidates exhibit a stable knee with a full range of motion. Specific findings, such as medial or lateral joint line tenderness, mechanical symptoms, and effusion, support a diagnosis of meniscal deficiency. It is essential to assess for coronal alignment abnormalities, as uncorrected varus or valgus deformities may predispose to graft/implant overload or failure. In medial MAT cases, varus alignment affecting the medial compartment may necessitate a concurrent valgus-producing high tibial osteotomy (HTO) or distal femoral osteotomy (DFO) to offload the graft (15). Similarly, in lateral MAT cases, valgus alignment affecting the lateral compartment may necessitate a concurrent varus-producing DFO or HTO, pending where the malalignment is occurring, to offload the graft. For scaffolds, eligibility often requires mild or no malalignment, generally within ±5°, and the absence of ligamentous instability (14). If instability is present, particularly following an anterior cruciate ligament (ACL) injury, concomitant stabilization may be performed during scaffold implantation or MAT (14).

Radiographs of the knee, including standard anteroposterior (AP), lateral, Rosenberg, and axial patellofemoral views, play a pivotal role in identifying degenerative changes and help rule out advanced osteoarthritis [Outerbridge grade IV or Kellgren-Lawrence (KL) grades III–IV]. Magnetic resonance imaging (MRI) is essential for evaluating residual meniscal tissue, cartilage status, and bone marrow edema suggestive of compartment overload (16,17). For scaffolds, MRI also ensures that the peripheral rim and horns remain intact, a crucial criterion for implant stability and ingrowth (13). In cases with prior ACL reconstruction (ACLR), special attention must be given to tibial tunnel position, especially when using the bridge-in-slot technique, to avoid interference with the meniscal root insertion (18). Ultimately, both MAT and scaffold candidates exhibit clinical and imaging features suggestive of meniscal insufficiency but differ slightly in anatomical requirements, age distribution, and tolerance for concomitant joint pathology.

Indications and contraindications

Proper patient selection remains essential in determining suitability for MAT and scaffold-based implants. Although both techniques aim to address symptomatic meniscal deficiency, they are indicated for distinct patterns of meniscal loss and are not interchangeable. A comparative overview of indications, contraindications, and clinical considerations for MAT and meniscal scaffolding is provided in Table 2, highlighting their complementary roles within the meniscal reconstruction treatment algorithm.

MAT

Indications

MAT is primarily indicated for symptomatic meniscal deficiency in patients younger than 55 years of age who have a well-aligned and stable knee without significant cartilage damage (18-21). Suitable candidates typically experience localized pain in the affected compartment and are willing and able to follow a structured rehabilitation protocol. Although traditionally performed in younger individuals, recent data suggest a growing trend toward offering MAT to patients even over 55 years (22).

MAT may be performed as an isolated procedure or in conjunction with corrective interventions when additional pathologies contribute to abnormal joint mechanics. Concomitant ACLR is commonly performed in patients with ligamentous insufficiency to restore overall knee stability and optimize the mechanical environment for graft function (23). Similarly, MAT may be combined with cartilage restoration techniques to address focal chondral defects, with multiple studies demonstrating improved clinical outcomes when biomechanical overload is corrected at the time of transplantation (24).

Contraindications

Contraindications include asymptomatic patients, those with moderate to severe osteoarthritis (KL grade III or IV), diffuse Outerbridge grade IV chondral damage, skeletal immaturity, a history of or active joint infection, inflammatory arthritis, and a body mass index (BMI) greater than 30 kg/m² (25-27). Other relative contraindications include recent corticosteroid use, arthrofibrosis, and muscular atrophy (20).

Meniscal scaffolding

Indications

Meniscal scaffolds are indicated for symptomatic patients with segmental meniscal deficiency following partial meniscectomy, provided that a stable peripheral meniscal rim and intact ligamentous structures are preserved. Unlike MAT, scaffolds are not intended for subtotal or total meniscal deficiency, where MAT remains the reconstructive option (28,29). Candidates are typically skeletally mature patients between 16 and 50 years of age with well-aligned or surgically correctable knees and no more than mild to moderate cartilage injury (30-32).

Contraindications

Contraindications for scaffolds include unstable knee joints, malalignment exceeding 5° in varus or valgus, Outerbridge or International Cartilage Repair Society (ICRS) grade IV lesions, and the absence of a supportive meniscal rim (33). Additional exclusion criteria include autoimmune disorders, systemic infections, collagen or polyurethane (PU) allergy, BMI greater than 35 kg/m², and pregnancy. Although scaffolds are frequently used in isolation, they may also be performed alongside procedures such as ACLR or HTO to restore joint biomechanics (33,34).

Available and emerging meniscal scaffolds

A variety of scaffold designs have been developed, broadly categorized as natural or synthetic, and typically implemented as cell-free constructs that rely on host-mediated tissue ingrowth. Table 3 summarizes the characteristics of currently available and emerging meniscal scaffolds.

CMI

Various designs and materials have been explored in the development of meniscal scaffolds, which are broadly classified as natural or synthetic. Natural scaffolds may be either cell-free or cell-containing (35). The only natural scaffold approved by both the Food and Drug Administration (FDA) and the European Union (EU) is the CMI (Stryker), a porous scaffold made of ~97% fibrillar type I collagen from bovine Achilles cell-free scaffold (35). Its cross-linked matrix provides strength and control resorption rate while being completely resorbable over time, demonstrating biocompatibility with no signs of cytotoxicity or carcinogenicity (12,14,28,36).

Other single-component scaffolds under investigation include decellularized autologous supraspinatus tendon, autologous meniscal fragments, porcine small intestine submucosa, and silk fibroin; additionally, composite constructs using extracellular matrix-based biomaterials (including blends of meniscal extracellular matrix with tendon-derived matrices) have also been explored (11,28,37).

Actifit

Actifit is a cell-free scaffold composed of PU and polycaprolactone (PCL), approved in Europe, Korea, Mexico, and recently by the FDA (37,38). Introduced in 2011 by Orteq Bioengineering (London, UK), it is a PU alternative to collagen scaffolds, featuring a biphasic polymer blend for meniscal regeneration. It comprises 80% biodegradable polyester soft segments for mechanical strength (38). The scaffold degrades gradually through hydrolysis of polyester bonds, providing structural support during early tissue regeneration (15,38). Long-term outcome data for Actifit remain limited, and mechanistic investigations of scaffold integration continue to rely largely on in vitro and animal models (39,40).

MeniscoFix™

MeniscoFix™ is a fiber-reinforced, collagen-hyaluronan-infused 3D-printed scaffold created by NovoPedics for total meniscus replacement. It uses resorbable polymer and features a 3D-printed architecture of circumferential and radial filaments to mimic the native meniscus structure. Preclinical studies in sheep have reported the induction of functional neomeniscus tissue that could potentially prevent catastrophic joint damage. However, no clinical trials in humans have been initiated to date (41,42).

Biomechanics

Multiple studies have reported that meniscal scaffolds restore tibiofemoral contact mechanics and demonstrate the ability to decrease contact pressure after implantation similar to meniscus allografts (43-45). However, the long-term chondroprotective effect of these treatments is still unclear. Neither CMI nor Actifit has demonstrated a clear advantage over partial meniscectomy, and data from the 20-year follow-up of CMI indicate no radiographic superiority or chondroprotective effect (46).

Pre-operative considerations

When a patient is a candidate for MAT, coordination with a tissue bank is crucial for proper graft availability, size preparation, and preservation to meet the patient’s specific requirements to optimize surgical outcomes. Although MAT is well established and widely performed in select countries outside the United States, including Italy, Spain, and the United Kingdom, the availability of appropriately sized allografts and access to specialized tissue banking infrastructure remain limited in many other regions worldwide (47). As a result, fewer countries outside the United States have established local tissue banks, and they also face limited legal authority regarding the use of donor grafts, which restricts the usage of MAT. In this context, alternative meniscal substitutes gain prominence (48).

Allograft sizing and matching

Accurate sizing of the meniscal allograft begins with proper assessment of the recipient compartment, a critical step in achieving optimal fit and function. One of the most applied radiographic techniques is the Pollard method (Figure 1), which employs AP and lateral radiographs to correlate soft tissue dimensions with bony landmarks. This method calculates meniscal width from the apex of the tibial eminence to the outer margin of the tibial metaphysis on the AP view. Length is estimated from the sagittal view, approximately 80% of the tibial plateau for the medial meniscus and 70% for the lateral meniscus (49). However, this method is not without limitations; studies have shown an average sizing error of 7.8%, with greater inaccuracy for the lateral meniscus (50).

Figure 1 Pollard method. AP and lateral knee radiographs demonstrating measurement technique for allograft sizing. (A) Meniscal width on AP radiographs is measured from the apex of the tibial eminence to the margin of the tibial metaphysis for both the medial and lateral menisci, respectively. (B) Lateral radiograph of the knee. The sagittal tibial plateau length is represented by the black arrow. The medial meniscus length is approximately 80% of the total sagittal length and the lateral meniscus length is 70% of the total sagittal length. AP, anteroposterior.

Recent advancements favor the use of MRI-based contralateral sizing, which directly measures the unaffected meniscus in the opposite knee. This approach has shown greater reliability and reduced variability compared to radiographic estimation. MRI avoids the projectional distortion seen in radiographs and capitalizes on the anatomical symmetry between right and left knees (51-53). Kaleka et al. (54) endorse contralateral MRI as the most accurate approach, though Pollard’s method remains an acceptable option for medial meniscus graft sizing.

For lateral meniscal sizing, Yoon’s radiographic method is commonly used to estimate graft length by measuring the tibial plateau on calibrated AP and lateral radiographs, with lateral meniscal length approximated as a defined percentage of the tibial plateau dimension (50). In contrast, Van Thiel’s anthropometric formula estimates meniscal width using patient-specific variables such as height, weight, and sex to predict graft dimensions (55). Nevertheless, anthropometric models often exceed the 10% error threshold deemed clinically acceptable, prompting recent literature to support Yoon’s technique as the only viable alternative when MRI is unavailable, especially for lateral sizing (56-58). Additional methods, including computed tomography (CT)-based assessments and emerging techniques incorporating meniscal height, have also been explored, though evidence remains preliminary and lacks long-term validation (59-61).

The importance of precise sizing cannot be overstated. Undersized grafts may lead to improper contact with the femoral condyle, increasing joint stress and the risk of graft failure. Conversely, oversized grafts are more susceptible to extrusion due to inadequate compressive engagement (62). A slight oversizing is generally preferred, particularly when using soft-tissue techniques, as these allow intraoperative trimming and greater adaptability to anatomic variability (18).

An MRI-based 3D contralateral meniscus segmentation can also be utilized for allograft or scaffold sizing, as the intra-individual 3D shapes of the left and right menisci are very similar and can serve as a template for the contralateral side (63). Similar to MAT, selecting the appropriately sized scaffold requires the patient’s anthropometric data, radiographs, CT scans, or MRI images to apply the same formulas and estimations.

Allograft processing

Current meniscal allograft preservation focuses on fresh-frozen (irradiated or non-irradiated) and fresh/viable grafts, while cryopreserved options are used more sparingly (64). Standard procurement involves harvesting grafts within 24 hours postmortem, typically from donors under 45 years of age (27). Lyophilized grafts, once considered viable, have been phased out due to adverse alterations in tissue properties such as significant size reduction, tissue shrinkage, and compromised tensile strength (65,66).

Fresh allografts are favored for their retention of viable chondrocytes, which contribute to preserving the extracellular matrix and overall biomechanical integrity. Although this viability offers theoretical benefits, animal models indicate rapid host cell repopulation—sometimes within a week—mitigating the long-term relevance of donor cell viability (67,68). These grafts are stored in nutrient media for 2–4 weeks, but the narrow storage window complicates logistics, limits thorough disease screening, and prohibits terminal sterilization, raising concerns about pathogen transmission (69).

In contrast, fresh-frozen grafts are more widely used due to logistical convenience. These grafts undergo an initial 4-week freeze for serologic testing, then are thawed, soaked in antibiotics, and re-frozen at −80 ℃ for long-term storage for up to 5 years (69,70). While practical, fresh-frozen grafts have shown limited cellular viability, minor shrinkage, altered collagen architecture, and reduced biological integration in in-vivo studies, direct implications for clinical outcomes are still under debate (71,72). Non-irradiated grafts are generally preferred, as gamma irradiation has been associated with diminished mechanical strength, which novel supercritical carbon dioxide sterilization aims to address (73,74).

Comparative outcomes remain inconclusive. A study evaluating 14 fresh allografts vs. 13 fresh-frozen allografts showed functional improvements in favor of the fresh group; however, variables such as additional procedures [e.g., meniscotibial ligament reconstruction and osteochondral allografts (OCAs)] complicated direct comparison (75). Other investigations have reported no significant difference in graft longevity or clinical efficacy (76).

Cryopreservation, which involves dehydrating cells and using cryoprotectants before freezing at −196 ℃, enables graft storage for up to a decade (70). These grafts may better preserve structural and mechanical integrity, though they have drawbacks—significant fibrochondrocyte apoptosis has been observed (77,78). Literature comparing fresh-frozen and cryopreserved grafts is mixed: while some studies suggest lower shrinkage and reduced failure rates with fresh-frozen grafts, others find that cryopreserved grafts better retain elasticity and tensile resilience (79). In the absence of definitive clinical consensus, surgeon preference and availability often drive the selection. Notably, at the 2015 International Meniscus Reconstruction Experts Forum, 68% of surgeons favored fresh-frozen, non-irradiated grafts, 14% chose fresh/viable grafts, and fewer than 10% selected cryopreserved or irradiated options (9).

Scaffold preparation

Meniscal scaffold sterilization processes must preserve both structural and biochemical properties to ensure the intended functions post-sterilization without compromising polymer characteristics. Classic sterilization methods, such as ethylene oxide (EtO) and gamma irradiation, can damage scaffold properties due to their vulnerable chemical structure. While EtO maintains biocompatibility, it compromises dimensions, structure, and mechanical integrity, making it unsuitable. Biodegradable scaffolds are particularly sensitive due to their chemical properties (80,81). Freeze-drying is a gentle sterilization method, but it lacks full efficacy on its own. It is often combined with methods such as gamma irradiation or EtO to enhance its antimicrobial effectiveness (82). Recent studies have demonstrated that electron beam irradiation can sterilize scaffolds without compromising their mechanical properties or in vivo function. Unlike traditional methods, it may even enhance tensile strength, making it a recommended sterilization technique that has been successfully used in ACL human trials (80,83).

Donor-recipient matching considerations

Accurate donor-recipient matching is a critical component of MAT and extends beyond graft size and preservation method. While graft sizing remains the primary determinant of biomechanical restoration, emerging evidence suggests that biologic matching factors may also influence outcomes. Specifically, donor-recipient sex mismatch has been associated with inferior graft survivorship and patient-reported outcomes (PROs) compared with sex-matched allografts (84).

Surgical technique

A variety of surgical strategies have been developed for MAT and meniscal scaffolding, each with specific technical demands and anatomical considerations.

MAT techniques

Three primary MAT fixation strategies are most commonly reported in the literature: bone bridge-in-slot, bone plug, and all–soft tissue fixation techniques (26,85). These approaches differ primarily in how the anterior and posterior meniscal roots are secured to the tibia, which may influence graft positioning, extrusion, and load transmission.

Bone bridge techniques maintain the native relationship between the anterior and posterior roots and are most frequently applied in lateral MAT, where the close proximity of the roots favors a single bony construct (26). Bone plug techniques provide independent bony fixation of each root and are more commonly used in medial MAT, particularly when avoidance of tunnel convergence or compatibility with concomitant osteotomy is desired (85). All-soft tissue techniques eliminate bony fixation altogether and instead rely on transosseous sutures or anchors, offering technical simplicity but raising concerns regarding graft extrusion and altered contact mechanics (86).

Comparative biomechanical and clinical studies have demonstrated no consistent superiority of one technique over another in terms of PROs, graft survivorship, or extrusion when appropriately indicated (87). While some meta-analyses suggest lower reoperation or extrusion rates with bony fixation methods, recent comparative cohort studies and systematic reviews report similar functional outcomes across fixation strategies, highlighting the influence of patient selection, alignment correction, and concomitant procedures rather than fixation method alone (86-90).

MAT is also associated with a notable learning curve. Longitudinal data from high-volume surgeons demonstrate reductions in graft extrusion and technical complications with increased procedural experience, underscoring the role of surgeon familiarity rather than technique selection alone in optimizing outcomes (91).

Meniscal scaffolds

Meniscal scaffolds are implanted using suture-based fixation to the native meniscal rim and are fundamentally dependent on the presence of a stable, vascularized peripheral rim. Fixation strategies are conceptually similar across scaffold types and typically involve inside-out, outside-in, or all-inside suturing techniques to promote stability and facilitate tissue ingrowth (92). Current evidence does not demonstrate clinically meaningful differences in outcomes attributable to specific fixation configurations, and scaffold survivorship appears primarily related to biological integration rather than mechanical fixation strategy (92,93).

Outcomes

MAT

A growing body of evidence has investigated outcomes associated with MAT, examining factors such as functional recovery, graft longevity, and radiographic progression. Across these studies, patients consistently demonstrate clinically meaningful improvements in PROs, often exceeding the minimal clinically important difference (MCID) (94). Reported survivorship rates remain encouraging, reaching 80.9% at a mean follow-up of 5.4 years (20), 73.5% at 10 years, and 60.3% at 15 years (Table 4) (95). Along with improving symptoms, MAT has been associated with a delay in the onset of osteoarthritis by approximately 10.5 years postoperatively (96).

In a systematic review of 24 medial MAT studies, Leite et al. comparatively evaluated bone plug (n=235), bone bridge (n=55), and soft-tissue fixation (n=38), reporting similar clinical outcomes and graft extrusion, with no association found between extrusion and functional scores (97). This aligns with other level 2 studies’ findings of no significant clinical differences between bone bridge and soft-tissue techniques (89,90). Although a systematic review by Ow reported higher reoperation rates for bone bridge (32.6%) and soft tissue (13.4%) compared to bone plug fixation (5.1%), recent comparative data by Bhattacharyya [2023] challenge this trend, suggesting variability across cohorts (86,90). Overall, reoperation rates are 15–33% for bone bridge, 15–27% for soft tissue, and 1.6–20% for bone plug techniques. Similarly, graft failure rates vary by technique: 7.5–17.4% for bone bridge, 1.8–18% for soft tissue, and 3.6–25% for bone plug, within 5 years postoperatively (90,98-103).

In cases of isolated MAT, long-term outcomes have shown significant improvements in pain reduction and functional recovery. Saltzman et al. found that increased bone marrow lesion size correlated with worse postoperative pain scores. Despite this, graft survival rates remained high with 95% at 2 years and 87% at 5 years, with 27.5% of revision surgery (23). Vundelinckx et al. observed stable improvement in Knee Injury and Osteoarthritis Outcomes Score (KOOS), Lysholm, and Tegner scores up to 12.7 years postoperatively, despite a mild reduction in joint space width (103). Lee et al. reported stable joint space and PROs despite MRI revealing allograft shrinkage (103,104).

Return to sports (RTS)

Athletes, particularly those involved in high-impact or pivoting sports, face an increased risk of meniscal injuries and often encounter pressure to RTS quickly to minimize downtime. The decision to RTS following MAT presents a nuanced clinical challenge: balancing graft integrity with the physical demands of competitive activity. Systematic reviews reveal wide variability in RTS rates (20–92%) and graft survival (45–98.9%) within 7.6 to 16.9 months postoperatively (104-107).

Notably, professional athletes often demonstrate higher graft survivorship but lower RTS rates compared with younger or recreational cohorts (108). In contrast, younger athletes (<25 years) report higher RTS rates (77–92%), whereas older athletes show lower rates of return to pre-injury performance, underscoring the influence of age and competitive demands on RTS expectations after MAT (109).

MAT with concomitant procedures

MAT is often performed in conjunction with other interventions (e.g., ACLR, HTO, and OCA), generally leading to favorable outcomes (Table 4) (25).

MAT plus ACLR

ACLR is the most frequently performed concurrent procedure with MAT, as it simultaneously addresses both meniscal deficiency and ligamentous instability, contributing to improved knee stability and overall function (110,111). In a study by Saltzman et al. involving 40 patients over a 5.7-year follow-up, substantial gains were observed in KOOS, International Knee Documentation Committee (IKDC), and Western Ontario and McMaster Universities Arthritis Index (WOMAC) scores. Approximately 50% of patients returned to sports within 9.1 months, and graft survival rates exceeded 80% (23).

MAT plus HTO

The integration of HTO with MAT remains a debated topic, particularly given that axial malalignment has traditionally been viewed as a potential contraindication for MAT. In a 2024 study by Grassi et al., outcomes were analyzed in 110 patients—55 undergoing combined medial meniscus allograft transplantation (MMAT) and HTO, and 55 receiving MMAT alone—over a follow-up period of up to 8 years. Both cohorts experienced significant improvements in Visual Analog Scale (VAS) pain, Lysholm, Tegner, and KOOS scores, with no notable differences in clinical outcomes between the groups. However, the MMAT + HTO cohort exhibited a higher failure rate (9.1%) compared to the isolated MMAT group (1.8%), though this was not statistically significant (P=0.093). These findings suggest that although correct malalignment does not preclude MMAT, it may modestly increase the risk of failure (112).

MAT plus OCA

MAT is often paired with OCA to address additional focal chondral lesions. In a cohort of 48 patients, Getgood et al. reported significant postoperative gains in IKDC and Knee Society Function (KS-F) scores. However, 54.2% of patients required subsequent surgical intervention. Five-year graft survival rates were 78% for MAT and 73% for OCA, decreasing slightly to 69% and 68% at the 10-year mark. While outcomes for combined MAT and OCA procedures with more advanced osteoarthritis or bipolar tibiofemoral involvement experienced less favorable results, underscoring the advantages of timely surgical intervention (113). Similarly, a study by Frank et al. involving 100 patients (n=50 per group) found no significant differences in reoperation rates, graft failure, PROs, or complication rates between those undergoing isolated OCA and those undergoing combined OCA and MAT (114).

Meniscal scaffolds

Clinical outcomes and survivorship of meniscal scaffolds have been reported primarily for the CMI and the PU-based Actifit scaffold. Both implants demonstrate meaningful improvements in pain and function, with acceptable mid- to long-term survival when appropriately indicated (115).

For CMI, reported implant survival ranges from 93–96% at 2 years, 85–97% at 5 years, 80–91% at 10 years, 64–88% at 10–15 years, and up to 88% at 20 years for medial implantation (92,116-120). Implant location appears to influence durability, with higher 10-year survival for medial scaffolds (90.4%) compared with lateral scaffolds (77.4%) (115).

Actifit scaffolds demonstrate comparable survivorship. Five-year survival rates range from 66.7–87.9% for medial implantation and 53.8–86.9% for lateral implantation, with overall reported survival of 64–96% at 2 years, 62.2–87.6% at 5 years, and approximately 77% at 10 years (31,115,121-123). In a multicenter European study, Toanen et al. found no statistically significant differences in survivorship or PROs between medial and lateral Actifit implants at 5-year follow-up (121).

Direct comparisons between CMI and Actifit suggest similar clinical performance. A 10-year comparative cohort study and two systematic reviews found no significant differences in pain relief, functional scores, or activity levels between the two scaffold types, and no clear evidence favoring one implant over the other (115,124). As such, implant selection is often guided by availability, surgeon experience, and regulatory considerations rather than demonstrated superiority.

Outcomes following isolated scaffold implantation appear more favorable than when scaffolds are combined with additional procedures. Isolated CMI implantation has demonstrated 10-year survival rates of approximately 94%, compared with 68% when performed concomitantly with procedures such as ACLR, HTO, or cartilage restoration (120,125). However, other studies report no significant differences in PROs between isolated and combined procedures, and the impact of concomitant surgery on complication rates and revision risk remains debated (96,104,126). When performed alongside MAT or alignment correction, these combined procedures aim to address underlying biomechanical contributors to joint degeneration rather than directly enhance scaffold survivorship.

Across both scaffold types, long-term follow-up demonstrates sustained improvements in VAS, KOOS, and IKDC scores, despite imaging findings of scaffold shrinkage, resorption, or joint space narrowing (127,128). Inferior outcomes have been associated with advanced cartilage degeneration and longer intervals between meniscectomy and scaffold implantation (125,129). Conversely, patients aged ≥45 years have been reported to demonstrate lower postoperative pain scores, likely reflecting lower activity demands rather than superior functional recovery (129). A small number of studies reported minimal or no improvement in select outcome measures, which may be attributable to limited sample sizes (122,130). To date, no studies have evaluated meniscal scaffold outcomes relative to the MCID or longitudinal osteoarthritis progression.

Meniscal scaffolds with concomitant procedures

Scaffolds plus ACLR

Pereira et al. (5-year follow-up, n=20) reported that simultaneous ACLR with an Actifit for partial meniscus replacement yields favorable clinical outcomes, showing significant improvements in PROs. MRI findings reveal inconsistent scaffold integration and a slight decline in scores between the 2- and 5-year marks, despite high patient satisfaction and an 87% survival rate (131). Interestingly, Toanen et al. found no significant difference in outcomes at 2 years between isolated Actifit (n = 87); however, by 5 years, the ACLR patients (n=27) showed slightly better results in VAS, Lysholm, and KOOS scores (121). Bulgheroni et al. (9.6-year follow-up, n=17) reported significant clinical improvement with CMI on Lysholm, VAS, Tegner, and IKDC for the treatment of chronic or acute medial meniscus tears, with less knee laxity reported in the acute group (116).

Scaffolds plus HTO

In contrast to the clinical differences observed with Actifit ACLR, Toanen et al. found no statistically significant differences in clinical outcomes between the Actifit + HTO group (n=22) and the control group (n=92) at the 2- or 5-year time points (121). Comparing medial CMI combined with HTO vs. HTO alone, Linke et al. (2-year follow-up, n=39) found only minor, non-significant differences in Lysholm, IKDC, and pain scores between the groups in favor of CMI with HTO (93).

Conclusions

Both MAT and meniscal scaffolds have the potential to improve clinical outcomes in patients with symptomatic post-meniscectomy syndrome; however, they serve distinct and complementary roles rather than representing competing treatment options. Meniscal scaffolds are indicated for segmental meniscal defects following partial meniscectomy in the presence of an intact peripheral rim, whereas MAT is reserved for subtotal or total meniscal deficiency. Success of these procedures requires careful patient selection and precise preoperative planning and surgical execution. Mid- to long-term outcomes of both MAT and scaffolds demonstrate satisfactory functional outcomes and graft survival when performed in isolation or concomitantly with other procedures such as ACLR, HTO, or OCA, while return to sport rates are varied. It is of major importance that future research focuses on optimizing fixation methods and finding the optimal treatment strategy for specific patient groups. New techniques for partial and total meniscal replacement continue to evolve and will be followed with interest.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Annals of Joint for the series “The Medial Knee at Risk”. The article has undergone external peer review.

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://aoj.amegroups.com/article/view/10.21037/aoj-2025-1-88/rc

Peer Review File: Available at https://aoj.amegroups.com/article/view/10.21037/aoj-2025-1-88/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aoj.amegroups.com/article/view/10.21037/aoj-2025-1-88/coif). The series “The Medial Knee at Risk” was commissioned by the editorial office without any funding or sponsorship. R.M.F. reports a relationship serving on the boards of AOSSM education committee and Journal of Shoulder and Elbow Surgery editorial board. She received consulting or advisory fees from Arthrex and JRF Ortho, fellowship support from Stryker and Smith and Nephew, and royalties from Elsevier. She is an unpaid consultant for Bodycad USA Corp. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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