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Abstract

Medial meniscus extrusion (MME) is the displacement of the meniscus beyond the edge of the medial tibial plateau. Proposed etiologies for MME include biologic degeneration of meniscal tissue, the result of a medial meniscus posterior root tear (MMPRT), and the failure of the meniscotibial ligament. Standard MMPRT repairs do not address this MME, as it often persists or worsens postoperatively, even with successful root healing. New techniques, such as centralization sutures, have been developed to supplement the standard MMPRT repair technique. Systematic reviews and randomized controlled trials confirm that the addition of a centralization suture significantly reduces MME, improves joint contact pressures, and enhances patient-reported outcomes. Even though postoperative extrusion still exists after centralization suture use, likely due to the degenerative nature of the meniscus, this represents a shift towards improved knee joint preservation. Continuing progress in this field requires standardization of measurement and diagnosis, establishing the minimal clinically important difference of postoperative extrusion for a successful MMPRT repair, and long-term clinical evidence. This narrative review will explore current understanding of MME, current treatment options, and topics to guide future research.

Keywords

Meniscus extrusion medial meniscus posterior root repair centralization suture

Introduction

Medial meniscus extrusion (MME) is defined as the displacement of the medial meniscus beyond the outer margin of the medial tibial plateau, shown in Figure 1.¹ While a small degree of extrusion can be physiologic under an axial load, a displacement of greater than 3 mm as measured on non-weightbearing MRI is considered pathological.^2,3

Figure 1.

Meniscal extrusion (d) demonstrating a reference line drawn based only on the position of the tibial plateau. Reprinted from Farivar et al. with permission from AJSM, Volume 51, Issue 12. Published 10/2023.

MME has mainly been considered a consequence of a medial meniscus posterior root tear (MMPRT), as extrusion signified that the circumferential fibers were biomechanically inactive. In a healthy knee, the circumferential fibers convert axial forces into circumferential tensile stresses to distribute load across the tibial plateau and shield the underlying articular cartilage from excessive peak contact pressures. In a MMPRT, the damaged posterior meniscal root is unable to generate hoop stress, rendering it similar to a “functional total meniscectomy,” leaving the articular cartilage exposed to peak contact pressures.^4,5 The paradox of this pathology is that MME has been reported prior to a MMPRT, persisting or possibly worsening after a successful anatomic MMPRT repair, or in cases of early cartilage degeneration and osteophyte formation without root disruption^1,6,7 Thus, MME may not be merely a sign of injury, but a dynamic process rooted in the failure of the entire knee joint.⁸ MMPRTs and MME are now seen as an important independent risk factor for osteoarthritis (OA), and the clinical approach to knee joint preservation is evolving as the association between extrusion and meniscal health is further explored.²

This narrative review will discuss (1) the evolving understanding of meniscal extrusion pathophysiology, (2) current treatment options for MMPRT and MME, and (3) future areas of research need to be explored. In accordance with the Scale for the Assessment of narrative review articles principles for narrative reviews, we predefined the aim of the narrative review and conducted a structure search using PubMed/MEDLINE to find original articles published between January 2005 and December 2025. The search was based on but not limited to terms such as “meniscal extrusion,” “meniscus root tear,” “medial meniscus root repair,” “transtibial pull-out,” “suture anchor,” “centralization,” “meniscotibial ligament,” “medial meniscus MRI,” “meniscus weight-bearing/upright MRI,” “medial meniscus ultrasound,” “medial meniscus physical therapy,” “postoperative protocol,” “medial meniscus extrusion MCID,” and “biologic meniscal healing.” Of the qualifying articles, we included randomized control trials, prospective/retrospective cohorts, systematic reviews, meta-analyses, consensus statements/guidelines, and biomechanical investigations relevant to MME as these studies provide the most robust data. Studies excluded included those not in English, insufficient outcome data, or not relevant to MME/MMPRTs. The novelty of this narrative review is that it addresses the current evidence of MME and reframes the discussion from current knowledge to possible solutions for MME.⁹

Pathophysiology

Current emerging data questions whether meniscal extrusion is the inciting event or the final consequence of a MMPRT. This shift in perspective comes from a 2020 case series by Krych et al. in which all patients reportedly demonstrated disruption of the meniscotibial ligament (MTL) and meniscal extrusion prior to the subsequent diagnosis of an MMPRT.¹⁰ This finding challenges the conventional view that MME is a consequence of a MMPRT, and suggests that failure of the secondary meniscal stabilizers may initiate a cascade that culminates to a MMPRT.⁸ Using this new frame for meniscus pathophysiology, Krych et al. offered a rationale for why root repair alone may be insufficient in controlling meniscus extrusion. In the same study, meniscal extrusion increased from 3.3 to 5.5 mm at the time the MMPRT was identified on MRI.¹⁰ This finding theorizes that stress on the MTL leads to a degenerative dysfunction in its ability to stabilize the meniscus. With the peripheral stabilizer compromised, the meniscus begins to displace radially. This extrusion concentrates biomechanical forces onto the posterior root attachment, which eventually fails under the overloading tension, resulting in a complete tear.⁸

This clinical finding is supported by a biomechanical study by Doan et al., which found that the creation of an isolated MTL tear resulted in significant meniscal extrusion.¹¹ Extrusion further increased with a MMPRT, which in turn caused an increase in the medial compartment pressures.¹¹ It should be noted that MTL tears did not initially alter medial compartment contact mechanics, a finding that seems contradictory to the association of MME and OA.¹¹ This discrepancy may be explained by the circumferential fibers being still intact, allowing for the meniscus to maintain axial load distribution in a static testing environment. Doan et al. results were from a cadaveric study which do not account for dynamic forces, cyclic loading, and the progressive biologic degeneration seen in native knees. As a result, it was theorized that the primary role of the MTL is to act as a peripheral tether to keep the meniscus centered.¹¹ Extrusion from MTL injury was theorized to a piece of a broader pathophysiologic process, with additional factors such as MMPRT and chronic tissue degeneration, that cumulate to cause the contact pressure dependent osteoarthritic changes.

Emerging evidence suggests that MME may continue to worsen even after successful MMPRT repair, supporting a cumulative degenerative theory of failure. Krych reported that despite a 98% meniscal healing rate on postoperative MRI, mean extrusion increased from 1.9 to 2.6 mm at roughly six months follow-up after a transtibial medial root repair.¹ Within this study, a cohort of 10 patients had a postoperative MRI at a mean of 16 days, prior to weightbearing on the MMPRT repair. There was a reported increased extrusion of 0.36 mm within this short timeframe, but this value was not significant (p = 0.23).¹ Kawada et al. reported a significant progression (3.63–4.59 mm) of MME at one year postoperatively, even in patients with healed MMPRTs confirmed by second-look arthroscopy.¹² With the highest level of evidence, Tollefson's randomized control trial reported that medial meniscal extrusion significantly increased in 96.2% of patients at six months postoperatively compared to their preoperative measurements. Figure 2 shows preoperative and postoperative measurements of MME giving a visual representation of persistent, postoperative extrusion.⁶

Figure 2.

Representative coronal fat-suppressed turbo spin echo images showing (A, C) preoperative and (B, D) postoperative medial meniscal extrusion measurements in left knees. Patients underwent double-tunnel transtibial root repair (A, B) with and (C, D) without a centralization suture. Meniscal extrusion was measured between two parallel lines along the Z-axis of the images: one at the peripheral margins of the medial tibial plateau and one at the outermost edge of the medial meniscal body at the level of the medial collateral ligament. Decreased extrusion is depicted postoperatively in (B) a patient with a centralization suture compared to (D) a patient without a centralization suture. Reprinted from Tollefson et al. with permission from AJSM, Volume 53, Issue 12. Published 10/2025.

Regardless of the pathophysiologic sequence of extrusion and root tears, MME association with knee OA has been clearly defined. Using T2 mapping MRI, Hada et al. showed that MME was strongly associated with medial tibial osteophyte distance, in patients with early-stage OA without MMPRT.⁷ A meta-analysis by Fong et al. reported that patients with existing OA were 3.86 times more likely to have major MME (defined as > 3 mm) compared to patients without OA.¹³ Chung et al. 2021 conducted a long-term study with a minimum 10-year follow-up, reporting that an increase in postoperative MME of more than 0.7 mm following a root repair was a predictor for clinical failure, defined as an ultimate conversion to a total knee arthroplasty.¹⁴ This clinical evidence points to MME as a global degenerative pathology, calling for advancements in the surgical approaches aimed at treating MME and MMPRTs.¹³

Where are we with meniscal extrusion treatment

The current standard of care for MMPRTs and MME is an anatomic transtibial pull-out technique, which involves passing sutures through the torn meniscal root and channeling them through bone tunnels drilled from the anterior aspect of the tibia to the medial meniscus posterior root's native attachment site.¹⁵ The sutures are tensioned and secured with a cortical button on the anterior aspect of the tibia.⁴ Studies have demonstrated that nonanatomic placement of the MMPRT repair, even off by a margin as small as 5 mm, fails to restore normal joint contact mechanics and is functionally equivalent to leaving the root tear untreated.⁴ However, even a perfectly anatomic root repair does not necessarily resolve the broader biomechanical issue of meniscal extrusion, which behaves somewhat independently of tunnel accuracy. The distinction becomes evident when reviewing postoperative outcomes.

A meta-analysis by Perry et al. investigated outcomes following MMPRT repair and highlighted a distinct disconnect between patient symptoms and the underlying mechanical state of their knees.¹⁶ Despite persistent meniscus extrusion following repair, patient reported improved Lysholm, Knee Osteoarthritis Outcome Score (KOOS), and International Knee Documentation Committee (IKDC) scores and only 5.9% of patients had progression of OA, measured by the Kellgren-Lawrence scale.¹⁶ This proposes a critical question: how do surgeons balance the worsening radiographic data of extrusion with the successful clinical data of patient satisfaction?

This disconnect has been addressed by commentary on a second-look arthroscopy study that reported a healed MMPRT repair that demonstrates laxity during arthroscopy is biomechanically nonfunctional and leads to the same osteoarthritic progression as a failed repair.¹⁷ Although an intact meniscus initially protects the articular cartilage and provides pain relief, tissue laxity allows for further extrusion over time. A cadaveric study by Steineman et al. stated that repairs are subject to loosening under cyclic loading simulating postoperative rehabilitation.¹⁸ The extrusion in this study was due to the enlargement of the suture holes in the meniscus. Repetitive stress and friction during cyclic testing allowed the sutures to effectively saw into the meniscal tissue. It is important to note that no specimens in this study experienced failure of the MMPRT repair. As extrusion worsens, joint mechanics further deteriorate, contributing to the progression of OA.^17,19 Many experts believe that the phenomenon of an intact but lax meniscus may explain why patients often experience symptom improvement after MMPRT repair, followed by recurrent or progressive symptoms over time.¹⁹ MME has been recognized as biomechanically important, but it remains uncertain whether radiographic improvements should outweigh patients reported outcomes as a predictor of joint preservation. In practice, postoperative decision making should balance radiographic extrusion with positive patient outcomes, with caution against overtreating isolated radiographic extrusion in a clinically improving patient. Long-term studies examining patient outcomes, extrusion trajectories, and OA progression are needed to determine when MME should be prioritized as a target of clinical management.

With the transtibial pull-out technique coming under question, alternative techniques, such as suture anchor techniques, have gained interest as biomechanical data and early clinical data appear promising. Recent biomechanical studies have shown that suture anchor repairs may exhibit less displacement under cyclic loading, better contact mechanics and compartment pressures, and improved healing on post-operative MRI.^20,21 Rebuttal against this innovation states that outcomes are highly dependent on suture construct design and deployment within a limited posterior space, implant prominence within the articular space, and that most proposed gain is related to biomechanical data with limit clinic data showing minimal to no improvement in patient reported outcomes.^20–22 Even with disadvantages described as greater displacement from meniscus-suture interface and morbidity of tunnel drilling, advantages such as reproducibility, diminished articular footprint, ability to target the native footprint for anatomic fixation, robust cortical fixation, and biological healing potential given marrow stimulation are reasons why the transtibial repairs has remained the standard of care.^15,22

Given the growing evidence that a transtibial MMPRT repair is not sufficient by itself to preserve the articular cartilage of the knee joint, several techniques have been developed to augment the repair. A meniscal centralization suture, also referred to as a peripheral stabilization suture, is a technique that secures the extruded meniscus back to the tibial plateau during root repair surgery.²³ This highlights the function of the MTL as a secondary peripheral stabilizer. A centralization suture involves the placement of one or more all-suture anchors at the periphery of the tibial plateau.²⁴ Sutures from these anchors are passed through the meniscus and tensioned to reduce the extruded meniscus to an anatomic position.²⁵ Centralization was originally described for the lateral meniscus, but has since been successfully adapted as a possible augment to address MME.²⁶ There are two primary approaches of centralization sutures: posteromedial anchoring and posteromedial tibial pullout technique.

Posteromedial anchoring involves mobilizing the MTLs and then placing one to three knotless all-inside suture anchors in the rim of the tibial plateau. An all-inside meniscus repair device is used to place vertical mattress sutures through the outer rim of the extruded meniscus, through the capsule and MTL which tethers the repair stitch to the MTL without piercing the meniscus. The theoretical advantage of securing the MTL rather than suturing the meniscus body is that native anteroposterior motion of the meniscus in flexion and extension is maintained without potentially iatrogenically over-constraining the meniscus. Also, by avoiding meniscal body perforation, circumferential fibers are not disrupted, preserving a native environment for optimal hoop stress biomechanics. When tensioning the sutures, the meniscus is pulled back to its native position within the margin of the tibial plateau, reducing extrusion and centralizing it on the articular surface.^8,24,27

In the posteromedial tibial pullout technique, sutures are passed through the posteromedial corner of the meniscus, before exiting through a tibial tunnel as shown in Figure 3. Figure 3 illustrates literature that states there are techniques where the same transtibial tunnel as the MMPRT repair can be used, or a new tunnel can be created 15 mm medial to the root insertion, or at the midpoint between the posterior root attachment and the posterior border of the MCL.³ Regardless, the sutures are secured to the anteromedial tibial surface.³

Figure 3.

(A) Axial and (B) anterior posterior views of an anatomic medial meniscal root repair technique with centralization suture in a right knee. Figure illustrates the difference in a one tunnel versus two tunnel centralization suture technique. ACL: anterior cruciate ligament; PCL: posterior cruciate ligament. Reprint from Daney et al. with permission from AJSM, Volume 47, Issue 7. Published 06/2019.

A systematic review found that the posteromedial anchoring technique demonstrated a significant reduction in medial meniscal extrusion (mean difference range of −1.2 to −0.2 mm) within studies when comparing preoperative-to-postoperative changes in extrusion data. Posteromedial anchoring also showed more consistent improvements in extrusion compared to posteromedial transtibial pullout repair and isolated MMPRT repairs when indirectly compared with other studies. The same review found that the posteromedial tibial pullout technique had conflicting results, with some studies showing no benefit and others even reporting an increase in postoperative extrusion (mean difference range of −0.50 to +1.46 mm).³

The ideal number and location of tibial anchors for centralization sutures have yet to be determined. One biomechanical study using porcine tissue reported that three sutures significantly reduced extrusion compared to two sutures.²⁴ These sutures were placed 10 mm anterior to the posterior border of the medial collateral ligament.²⁴ A separate porcine study reported that a suture placed at the apex of the posterior horn was most effective at reducing extrusion.²⁸ In another porcine model conducted by Boksh et al., they reported that using two suture tapes reduced extrusion and improved joint mechanics compared to suture anchors.²⁷ Daney et al. investigated the location of a centralization suture placed at the midpoint between the root attachment and the posterior border of the MCL. They reported no significant biomechanical differences found between the anatomic MMPRT repair and anatomic MMPRT repair with centralization state; however, the centralization suture did help reduce MME and contact mechanics in the nonanatomic repair model, which simulated a chronically extruded meniscus.²⁸

Lastly, there is an ongoing debate regarding the most durable suture configuration for a MMPRT repair. Biomechanical studies have compared various constructs, including the modified Mason-Allen, two simple stitches, locking-loop stitches, and vertical mattress sutures, to evaluate which suture pattern offers the highest strength with minimal MME.^4,29 While the data is mixed on which provides the best results, optimizing suture materials, configurations, and fixation methods are needed to minimize MMPRT repair loosening as simulated rehabilitation studies show that loosening is unrecoverable with addition rehabilitation.^19,29,30

Overall, the clinical outcomes suggest that a MMPRT repair with a centralization suture offers promising results. A case series with a mean follow-up of two years reported improvement in patient-reported outcomes including the Visual Analog Scale, KOOS jr., and the IKDC, indicating improvements in pain, function, and overall satisfaction. Three patients out of 25 obtained an MRI around five months postoperative: two for acute pain and one for research purposes. This provided radiographic evidence that supported centralization can improve MME and patient outcome scores. The three patients showed an average extrusion of 1.6 mm postoperatively compared to 3.3 mm preoperatively.³¹ There was no evidence of degenerative changes on postoperative radiographs of 23 out of 25 of the patients. None of the patients required revision meniscus surgery or TKA conversion within the two years follow-up timeframe.

A systematic review and meta-analysis reported that meniscal centralization sutures significantly reduced MME (p < 0.00001) and restored MME to levels similar to the native knee from 0 to 90 degrees of flexion. Tibiofemoral contact pressure was reduced (3.2–5.0 times closer to the native biomechanics compared to MMPRT) and load sharing contact area was improved following a centralization suture. The clinical data reveal improved KOOS, Lysholm, and IKDC scores. Lastly centralization sutures had few complications with preserved ROM, joint space, and varus deformity with medial compartment disease.^27,28

Tollefson et al. conducted a randomized control trial with 26 patients that found the addition of a centralization suture to MMPRT repair resulted in significantly decreased postoperative extrusion at six months postoperatively compared to MMPRT repair alone. While the augmentation did not completely prevent extrusion, it reduced the progression of MME by over 50%.⁶ This study included patients with high BMI and varus malalignment, excluding extreme malignment at the surgeon's discretion, which are known risk factors for increasing medial compartment pressures promoting postoperative extrusion. In patients with residual varus, MMPRT repair with centralization may limit postoperative extrusion progression, but it may not eliminate it because the underlying coronal plane imbalance continues to bias the meniscus toward extrusion. Therefore, individual patient risk factors should be considered when interpreting extrusion outcomes after centralization. The authors attempted to protect the MMPRT repair and centralization suture by using an unloading bracing postoperatively to decrease medial compartment forces and limit MME in patients with varus deformity.⁶ To summarize, centralization sutures has been shown to reduce extrusion, improve contact mechanics and functional outcomes, preserve knee range of motion, and play a role in joint space preservation in early stages of OA.^6,27,28

Nonetheless, even perfect anatomical MMPRT repairs with a centralization suture have not been shown to prevent all postoperative extrusion, begging the question, Is there something wrong with the tissue itself? Tollefson et al. hypothesized that continued extrusion may be related to poor quality of the meniscal tissue itself. Increased T2 values on high powered MRIs may be signs of increased meniscus volume, which could be a result of collagen matrix disorganization. It's plausible that this degenerative swollen tissue lacks the ability to resist extrusion, even after re-anchoring the root.⁶ Table 1 recaps the key findings within this section.

Table 1.

MMPRT repair versus MMPRT repair + centralization.

	MMPRT repair	MMPRT repair + centralization
Postoperative MME	> 96% patient have increased postoperative extrusion	Persistent postoperative extrusion but <50% compared to MMPRT repair without centralization
Biomechanical results	Strong construct, but subject to loosening with suture hole enlargement under cyclic loading	Tibiofemoral contact pressure was reduced (3.2–5.0 times closer to the native biomechanics compared to MMPRT. Extrusion decreased by 50% compared to isolated MMPRT repair
Limitations	Root healing and symptom improvement may occur despite worsening MME; Uncertainty with long-term joint preservation	Postoperative extrusion may persist due to degenerative meniscal tissue even with centralization suture.

Comparison of MMPRT repair performed with and without a meniscal centralization suture. The figure summarizes key differences in postoperative extrusion, biomechanical results, and key limitations.

MME: medial meniscal extrusion; MMPRT: medial meniscus posterior root tear.

How can we solve meniscus extrusion

Given the fact that patients report significant clinical improvement despite worsened extrusion after MMPRT, we must define what a successful MMPRT repair is.^13,16 The first step in doing so is standardizing imaging and the measurement of extrusion so the data may be conglomerated and analyzed.

MRI is the current gold standard for identifying and measuring meniscus extrusion, with more than 95% of members of the Meniscus International Network (MenIN) favoring MRI as their primary imaging modality.^2,30,32 However, a systematic review by Farivar et al. highlighted significant heterogeneity in the literature regarding how extrusion is classified.³³ To classify as pathologic or physiologic, MME is measured using a coronal MRI scan from a medial structure to the peripheral border of the extruded meniscus. The review identified primary medial coronal landmarks used for measurement: the MCL (38%, most common), the midpoint of the anterior-posterior length of the medial meniscus (23% of studies), and the middle of the medial femoral condyle (19%).³³ The pathologic threshold of >3 mm of MME is not universally agreed upon as some experts prefer a threshold of 4 mm. Svensson et al. found that a general population had an average of 2.7 mm of extrusion in knees without radiographic signs of OA.³⁴ This meant that using 3 mm as “pathologic” for extrusion may be over labeling knees as degenerative without clinical or radiographic evidence. By raising the threshold to 4 mm, the sensitivity remained acceptable while specificity improved, resulting in a better overall ability to distinguish knees with degenerative changes from those without.^33,34 This lack of consensus in measurement and pathologic classification complicates direct comparison between studies.

A growing body of evidence suggests that classifying MME by millimeters measured on an MRI may be an oversimplification.³⁰ Extrusion varies with position and weight-bearing status, therefore, static imaging may not fully capture the dynamic behavior of the meniscus. Unloaded knees that were deemed “healthy” showed extrusion ranges from 0.7 to 1.1 mm.^35–37 Under an axial load, a “healthy” knee extrudes an additional 0.8–1.2 mm compared to baseline extrusion.^35–37 In pathologic states, such as MMPRT or mucoid degeneration, baseline and loaded states often report a higher values.^35–37 In Daney et al., they reported no difference in extrusion in every repair state (anatomic/nonanatomic, with or without centralization) in a unloaded knee in full extension, suggesting that axial stress and higher degrees of flexion may be required to evaluate MME. This was further supported in their study when maximal amount of meniscal extrusion was observed when the knee was loaded at 90 degrees of flexion.³² Patient-specific factors must be accounted for as well, as higher patient BMI has been shown to significantly increase the difference of extrusion on weightbearing ultrasound compared to supine imaging.³⁵ Lastly, there is a phenomenon known as the “dead meniscus sign” which may be seen on ultrasound where the meniscus is maximally extruded and dynamic extrusion may fail to occur with weightbearing.³⁰ Given these considerations, alternative imaging modalities and combined imaging may be better suited to identify extrusion due to the meniscus's dynamic nature. Notably a dynamic ultrasound study performed while walking found that MME was greater in osteoarthritic knees than in healthy controls, and in dynamic images compared to static weightbearing images.^38,39 Ultrasound offers excellent sensitivity (>90%) and specificity (>70%) for detecting meniscal extrusion and its dynamic cost-effective nature makes it a promising screening tool.¹⁰ Ultrasound can be followed by MRI for confirmation of extrusion, as well as to identify concomitant pathologies such as MMPRT or chondral lesions.³⁰ CT scan may also be an option when MRI is not available.³⁰

In addition to standardizing imaging modalities and measurement techniques, we must determine the minimal clinically important difference (MCID) for extrusion reduction in order to define a successful MMPRT repair. The MCID is the smallest change in a specific patient-reported outcome that a patient perceives as beneficial. Although hypothetical, establishing a MCID would help determine how much reduction is necessary to produce meaningful improvements for patients and could help guide surgeons in selecting interventions most likely to yield clinical benefits. It may also help explain why patients feel clinical benefit despite persistent extrusion if they have achieved the MCID.

In regard to patients, the clinical evidence strongly suggests a case-by-case approach to managing MME and MMPRT repair. To be set up for success, clear patient indications and contraindications must be defined. Patients with the best prognosis typically present with minimal pre-existing OA (Kellgren-Lawrence grade I-II) and minimal varus alignment.^10,31 A MMPRT repair with a centralization suture is most effective with minimizing meniscus extrusion when the articular cartilage and overall joint environment are relatively preserved.^24,32 The most significant negative predictor for long-term success is a preoperative mechanical varus alignment greater than 5 degrees as a significant long-term risk factor for conversion to total knee arthroplasty.¹⁴ In such cases, addressing the MMPRT without correcting the underlying malalignment may be insufficient to stop degenerative extrusion.¹⁶ Patients with greater than 5 degrees of varus have been excluded from centralization suture studies as academic opinions often consider a high tibial osteotomy to correct the malalignment, unloading the medial compartment, limiting chronic degeneration in younger patients.^2,14 Other treatments, such as the use of medial unloader braces in these often older patients with MMPRTs, has also been proposed to protect a MMPRT repair in patients with varus alignment. In these cases, the braces are used preoperatively to allow patients to get used to wearing the medial unloader brace and then used postoperatively starting with weight bearing at 6 weeks and worn for all weight bearing activities until at least four months postoperatively. Additionally, a higher BMI is an established risk factor for the development of MMPRTs as it places increased mechanical stress on the post-surgical repair construct, contributing to poorer outcomes.^30,33 Lastly, delaying surgical intervention may have a negative impact on outcomes as well. A 2024 study by Krych et al. found that a longer duration of nonoperative treatment correlated with higher postoperative pain levels, with optimal surgical timeline within 13 weeks of symptom onset.³¹

Beyond patient selection, several modifiable factors play a crucial role in the ultimate structural and clinical success of the repair. A 2023 study by Kawada et al. identified a direct link between quadriceps function and the structural stability of the repair. The researchers found that greater postoperative quadriceps strength was significantly correlated with less progression of medial meniscal extrusion and better KOOS scores.¹² This is clinically significant as it can be objectively targeted as a modifiable risk factor in physical therapy.

Rehabilitation protocols can be highly varied and lack standardization, especially when factoring in new techniques such as a centralization suture.^2,27 This is particularly concerning given the biomechanical evidence showing that early or improper weightbearing can cause unrecoverable loosening and failure of the repair construct.^12,40 A postoperative protocol, as described by Monson et al., states nonweightbearing for 6 weeks, with protected range of motion less than 90 degrees for 2 weeks, and then graduated weightbearing and range of motion increases as the patient progresses. This approach allows for biological healing of the MMPRT, limiting postoperative stiffness, and protecting the repair construct.⁴⁰

Addressing the poor intrinsic healing capacity of the meniscus is a critical frontier. Biological augmentation strategies, such as platelet-rich plasma, fibrin clots, marrow venting, and degradable implants aim to create a more favorable environment for tissue healing and regeneration. While there are biological theories behind these procedures, these modalities have failed to translate into high-level clinical evidence, with human trials yielding mixed results.^41,42 Tissue level investigational research will be needed to address the gaps of biologic meniscal healing.

Despite increasing interest in meniscus extrusion, high-quality evidence to guide repair strategies remains limited, specifically randomized controlled trials. The Tollefson et al. randomized control trial provided critical data comparing root repair with and without a centralization suture showed that centralization significantly diminishes the postoperative increase in extrusion.⁶ More studies like this are required to continue to advance the field.

As seen with Daney et al., cadaveric studies at time zero may report similar findings to standard MMPRT repair and MMPRT repair plus a centralization suture, but may not totally represent how the repair acts in clinical settings after withstanding thousands of loading cycles during postoperative rehabilitation.³² The primary goal of a root repair is preventing long-term OA, yet most studies are limited to short-term follow-up roughly around two years of data.^3,27 Future studies should attempt to elucidate the optimal meniscus extrusion method and to investigate long-term durability of such repairs.^32,35 Lastly, heterogeneity in extrusion measurement methods complicates cross-study comparisons. To overcome this, establishment of large, standardized, multi-center patient registries are essential to track outcomes over 5- to 10-year periods.^3,27 Future studies should also evaluate outcomes of combined root repair, centralization sutures, and MTL techniques as no study to date has investigated a comprehensive, multi-tissue stabilization strategy that addresses the meniscus root, the MTL, and the meniscus capsule.

As a narrative review, this article is limited by potential selection bias and decreased reproducibility due to no strictly predefined protocol. The currently available evidence regarding centralization techniques, biomechanical rationale, and clinical outcomes originates from a limited number of high-volume research groups. While this reflects expertise in the field, it introduces the possibility of confirmation or publication bias.

Conclusions

The understanding of meniscus extrusion has evolved drastically over the past decade. Once viewed as a consequence of MMPRTs, meniscus extrusion is now recognized as an early step in the degenerative process. Evidence shows that a standard MMPRT repair can heal the posterior attachment but may be insufficient to correct the extrusion that can predispose to long-term joint failure. With evidence suggesting that a difference of less than 1 mm of postoperative extrusion may be the difference between a successful repair and progression towards a total knee arthroplasty, surgical augments to specifically address extrusion should be explored. Meniscus centralization sutures appear to be a promising technique with early clinical and radiographic data showing that this combined approach, standard transtibial MMPRT repair plus a centralization suture, could successfully reduce extrusion, improve patient-reported outcomes, and decrease the progression of OA at short-term follow-up. This combined approach may represent a shift in the management of MMPRT, from isolated repairs to comprehensive restoration.

Footnotes

ORCID iDs

Tyler R Ehrke

Taidhgin J Keel

Grace E Guerin

Benjiman J Wilebski

Luke V Tollefson

Robert F LaPrade

Author contributions

Ehrke T., Guerin G., and Keel T. drafted the manuscript. Wilebski B. reviewed the manuscript and provided preliminary revisions. Tollefson L. and LaPrade R. provided senior review, critical revisions, and final approval of the manuscript. All authors reviewed and approved the final submitted version.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: R.F.L. is a consultant for Ossur, Smith & Nephew, and Responsive Arthroscopy; receives royalties from Ossur, Smith & Nephew, Elsevier, and Arthrex; receives research grants from Ossur, Smith & Nephew, Arthroscopy Association of North America (AANA), and AOSSM; is on committees for International Society of Arthroscopy, Knee Surgery and Orthopedic Sports Medicine, AANA, and AOSSM; is on the editorial board for The American Journal of Sports Medicine, Journal of Experimental Orthopedics, Knee Surgery, Sports Traumatology, Arthroscopy, Journal of Knee Surgery, Journal of Orthopedic & Sports Physical Therapy, and Operative Techniques in Sports Medicine; and receives educational support from Foundation Medical.

Data availability statement

No new data was generated in support of this study. All data presented in this narrative review was derived from previously published articles cited in the manuscript.

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Meniscus extrusion after a medial meniscus root repair: Where we are and how can we solve it?

Abstract

Keywords

Introduction

Pathophysiology

Where are we with meniscal extrusion treatment

How can we solve meniscus extrusion

Conclusions

Footnotes

ORCID iDs

Author contributions

Funding

Declaration of Conflicting Interests

Data availability statement

References