Quantifying Meniscal Extrusion Using Ultrasound in the Setting of Concomitant Cadaveric Knee Lesions: Part I: The Medial Meniscotibial Ligament and Posterior Medial Meniscal Root

A single root repair and centralisation tunnel best restores tibiofemoral contact mechanics and extrusion following a medial meniscus posterior root tear: An in vitro biomechanical study

PURPOSE

To evaluate what tunnel combination, with respect to anatomical transtibial pull-through root repair (ATPR) and transtibial centralisation (TTC), best restores tibiofemoral contact mechanics and meniscal extrusion following a medial meniscus posterior root tear (MMPRT).

METHODS

Meniscal extrusion and contact mechanics were measured using two-dimensional imaging and pressure films in 10 porcine knee joints. The posterior root was tested under six states: (1) intact; (2) MMPRT; (3) one tunnel ATPR and one tunnel TTC (1-ATPR + 1-TTC); (4) two tunnel ATPR and one tunnel TTC (2-ATPR + 1-TTC); (5) 1-ATPR + 2-TTC; and (6) 2-ATPR + 2-TTC. The testing protocol loaded knees with 200-N axial compression at 4 flexion angles (30°, 45°, 60° and 90°). At each angle and state, meniscal extrusion was measured as the difference in its position under load to that of the unloaded condition in the intact state. Contact area and pressure were recorded for all states at all angles and were analysed using a MATLAB programme.

RESULTS

MME was significantly reduced with both the 1-ATPR + 2-TTC and 2-ATPR + 2-TTC tunnels in comparison to the 1-ATPR + 1-TTC and 2-ATPR + 1-TTC tunnels at 60° and 90° (p < 0.05). The intact meniscus and 1-ATPR + 1-TTC technique had higher contact area at 60° (p = 0.01 and 0.04, respectively) and lower contact pressure at 90° (p = 0.01 and 0.04, respectively) compared to the 2-ATPR + 2-TTC technique. Otherwise, all tunnel combinations were similar to one another for contact mechanics and restored the loading profile to that of an intact meniscus (p > 0.05).

CONCLUSION

When there are concerns of extrusion following a MMPRT, a combination of one centralisation and one root repair tunnel may provide better biomechanical properties compared to the addition of extra tunnels.

LEVEL OF EVIDENCE

Not applicable (laboratory study).

Arthroscopic Centralization of the Extruded Meniscus With Posterior Root Tear: A Technique Using Meniscotibial Ligament Fixation

Meniscal root tears have been shown to significantly impact tibiofemoral mechanics and contribute to accelerated development of osteoarthritis. A common finding in conjunction with a meniscal root tear is extrusion of the meniscus. Meniscal extrusion is an independent risk factor for tibiofemoral cartilage loss and the progression of osteoarthritis. Meniscus centralization was first introduced to directly address extrusion alongside root repair techniques. To date, reported techniques for meniscus centralization generally involve anchoring the meniscus directly to the tibia in some fashion, which can limit the normal anatomic motion of the meniscus. We present a technique for meniscus centralization that aims to maintain natural meniscal motion by utilizing the meniscotibial ligaments.

Medial Meniscotibial Ligament Deficiency Increases Medial Meniscus Extrusion and Posterior Root Forces

BACKGROUND

There is growing evidence that medial meniscotibial ligament (MTL) deficiency and medial meniscus extrusion may precede the development of some medial meniscus posterior root (MMPR) tears. However, no study has investigated the biomechanical consequences of MTL deficiency on the MMPR.

HYPOTHESIS

(1) MTL deficiency leads to increased medial meniscus extrusion, (2) increased medial meniscus extrusion is correlated with increased compression and shear forces at the MMPR, and (3) MTL repair restores medial meniscus extrusion and MMPR forces to native levels.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fifteen pairs of fresh-frozen cadaveric knees were tested. Specimens were organized into 3 groups according to a balanced incomplete block design: (1) native, (2) MTL deficiency, and (3) MTL repair. For the MTL deficiency group, a 3-cm deficiency in the MTL was developed under direct arthroscopic visualization. Specimens in the MTL repair group underwent a 2-anchor repair that compressed the joint capsule to the proximal tibia. All specimens were biomechanically tested in full extension with a tensile testing machine. The specimens underwent cyclic loading for 10,000 cycles at 1 Hz and compression of 20 to 500 N, with a 500-N compressive force applied for 30 seconds after the 0th, 100th, 1000th, and 10,000th cycles. Ultrasound was used to measure medial meniscus extrusion. Shear and compressive forces at the MMPR were measured with a 3-axis sensor installed inferior to the MMPR tibial attachment.

RESULTS

Medial meniscus extrusion was significantly increased in the MTL deficiency group compared with the native group (0th: 1.6 ± 0.1 mm vs 1.2 ± 0.1 mm, P < .05; 100th: 2.2 ± 0.2 mm vs 1.5 ± 0.2 mm, P < .05; 1000th: 2.8 ± 0.2 mm vs 1.8 ± 0.2 mm, P < .05; 10,000th: 3.5 ± 0.3 mm vs 2.1 ± 0.2 mm, P < .05). Compression root force was significantly increased in the MTL deficiency group compared with the native group at all cyclic loading points (0th: 21.7 ± 12.8 N vs 13.6 ± 2.4 N, P < .05; 100th: 18.9 ± 11.0 N vs 12.1 ± 7.5 N, P < .05; 1000th: 16.5 ± 9.9 N vs 11.2 ± 7.5 N, P < .05; 10,000th: 12.6 ± 8.6 N vs 9.0 ± 6.9 N, P < .05). Root shear force was significantly increased in the MTL deficiency group compared with the native group at the 0th (17.5 ± 2.5 N vs 13.6 ± 2.4 N, P < .001) and 100th (16.2 ± 2.6 N vs 12.1 ± 2.2 N, P < .001) cycles. Medial meniscus extrusion, root shear force, and compression root force of the MTL repair group were not significantly different from the native group for all cyclic loading points.

CONCLUSION

Medial MTL deficiency led to increased medial meniscus extrusion as well as greater compression and shear forces at the MMPR compared with the intact and repaired MTL states, suggesting that MTL deficiency may predispose the MMPR to injury in a cadaveric model.

CLINICAL RELEVANCE

MTL deficiency predisposes one to medial meniscus extrusion and MMPR tears. Subsequently, MTL repair can potentially correct medial meniscus extrusion and normalize forces at the MMPR.

Deep medial collateral ligament plays a stabilising role under degenerative medial meniscus root tears

PURPOSE

Several posterior medial meniscal root (PMMR) repair techniques have been developed to restore the load-bearing function of the meniscus and reduce extrusion. The medial meniscotibial ligament (MMTL) has been shown to play a significant role in meniscal stability. This study evaluates the stabilising function of the MMTL by directly influencing the force exerted on the PMMR during weight-bearing and valgus motion of the knee. Our aim is to investigate whether loss of MMTL integrity is a determining factor in PMMR subluxation.

METHODS

Using a 3D model of the knee with parameters from experimental studies, compressive and valgus loading scenarios were simulated using the finite element method to analyse the mechanical response of different knee structures. To investigate the correlation between the integrity of the MMTL and the force acting on the PMMR, different degrees and types of injuries to both structures were modelled for comparison with the healthy joint, providing insights into their importance in preventing or correcting extrusion.

RESULTS

During compressive loading, tears in the MMTL and PMMR result in a 5.8% and 30.9% increase in meniscal extrusion, respectively, while a combined injury results in a 43.9% increase, indicating that the MMTL provides a secondary constraint against extrusion. Moreover, the importance of the MMTL in restraining extrusion becomes more pronounced as the PMMR weakens, as is typical in degenerative tears. Finally, during valgus motion, the MMTL prevents separation of the meniscus from the tibial plateau and reduces strain/stress on the PMMR.

CONCLUSION

The integrity of the MMTL plays a crucial role in reducing meniscal extrusion and PMMR overload, particularly when the root is affected by degenerative tears. Therefore, surgical repair of the MMTL can improve meniscal function, potentially reducing the risk of osteoarthritis and should be considered as a better treatment strategy for PMMR tears.

LEVEL OF EVIDENCE

Level III.

Meniscal extrusion: Proposal for a novel qualitative classification

Meniscal extrusion (ME), defined as the radial displacement of the meniscal body outside the margins of the tibial plateau, has been seen as an independent and relevant predictor of intra-articular knee degeneration. Nonetheless, available classifications for ME are exclusively quantitative assessments not considering the context in which extrusion is identified. Indeed, ME can be the result of several different conditions spanning from acute tears to chronic degeneration and its definition cannot be only dependent on the numeric calculation of the radial displacement of the meniscal body. Furthermore, growing evidence supports the existence of a paraphysiological ME resulting from joint loading, limb malalignment, anatomical abnormalities of the meniscal attachments to the femur and tibia or a nonpathological finding after meniscal allograft transplantation. It is therefore clear that an exclusively quantitative assessment of ME cannot be sufficient since this condition can develop in such different clinical scenarios. For this reason, a novel qualitative classification for ME is proposed, differentiating between three distinct conditions: a paraphysiological ME, a pathological ME and ME related to degenerative conditions. Furthermore, a comprehensive review of the present literature has been conducted to report the most relevant and updated evidence on the topic highlighting the difference in the clinical management of each different category.

Level of Evidence

Not applicable.

Arthroscopic meniscal posterior root repair combined with centralization reduces medial menicus extrusion associated with posterior root tears: One-year clinical outcomes

PURPOSE

This study aimed to assess the short-term clinical efficacy of combining posterior meniscal root repair with meniscal centralization technology in the treatment of medial meniscus posterior root tears (MMPRTs) and notable meniscus extrusion.

METHODS

In this retrospective analysis, patients aged 43-76 years with only chronic posterior root tears of the medial meniscus and notable extrusion were followed up for 12-14 months.

INCLUSION CRITERIA

(1) persistent medial knee joint pain affecting daily life, presenting with joint space tenderness; (2) showing the ineffectiveness of conservative treatment for a minimum of 3 months; conservative treatment includes non-invasive methods such as nonsteroidal anti-inflammatory drugs, physical therapy and massage, but does not include intra-articular injections. (3) Kellgren-Lawrence Grades 0-II osteoarthritis (OA) of the knee joint; and (4) diagnosis of a posterior root tear of the medial meniscus with notable meniscus extrusion confirmed through knee-joint plain magnetic resonance imaging (MRI) scans, where coronal image revealed a meniscus body extrusion of ≥3 mm.

EXCLUSION CRITERIA

(1) Kellgren-Lawrence Grades III-IV OA in the knee joint; (2) presence of knee joint infection or other structural damage to the knee joint; (3) history of previous knee joint surgery; (4) demonstrating joint instability or abnormal lower-limb alignment (varus deformity >5°); and (5) presence of severe mental illness, coagulation disorders, or other serious medical conditions. The Lysholms score, the Hospital for Special Surgery (HSS) knee score, the visual analogue scale (VAS) score and meniscal extrusion values were evaluated before and after surgery in 23 patients through a comparative analysis.

RESULTS

The results of the follow-up conducted 12-14 months post-operatively indicated a significant improvement in the patients' conditions. In particular, the Lysholms scores (preoperative: 50.9 ± 10.2; 1-year post-surgery: 72.0 ± 8.4), HSS knee scores (preoperative: 45.9 ± 10.6; 1-year post-surgery: 79.1 ± 11.1) and VAS scores (preoperative: 4.0 ± 1.1; 1-year post-surgery: 0.9 ± 0.7) exhibited notable enhancements. Furthermore, compared to the preoperative values, the degree of meniscus extrusion measured by coronal MRI of the knee joint significantly improved post-operatively (preoperative: 3.7 ± 0.8 mm; 1-year post-surgery: 2.2 ± 0.6 mm). These findings all yielded a p < 0.05, signifying statistical significance.

CONCLUSION

In patients with chronic MMPRTs and notable extrusion, a combination of posterior meniscal root repair and centralization technology can effectively restore meniscus function and rectify the medial meniscus displacement, resulting in favourable short-term clinical outcomes.

LEVEL OF EVIDENCE

Level IV.

Diagnosis and Treatment Strategies of Meniscus Root Tears: A Scoping Review

Background

Meniscus root tears comprise 10% to 21% of all meniscal tears. These tears alter knee biomechanics, elevating contact pressure, akin to a meniscectomy. Consequently, they are linked to advanced joint degeneration and cartilage damage in the affected compartment.

Purpose

To systematically evaluate and relate the current literature describing the diagnosis and treatment strategies for meniscus root tears.

Study Design

Scoping review; Level of evidence, 4.

Methods

This review was conducted following the guidelines of the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) extension for scoping reviews. Inclusion criteria encompassed English-language clinical and preclinical research, technical notes, and narrative reviews on meniscus root tears. Exclusion criteria were studies on patellar tendon rupture, studies on medial patellofemoral ligament rupture with additional knee joint ligament injuries, studies of patients <16 years old, and studies involving open fractures. The data were summarized using a descriptive analysis and a thematic analysis.

Results

After 1425 articles were identified, 461 studies were included; 17% (n = 78) were case reports or case series, 15% (n = 71) were technical notes, 9% (n = 41) addressed aspects of diagnosis, 7% (n = 32 ) were narrative reviews, and 5% (n = 21) were systematic reviews or meta-analyses. Studies presenting original data comprised 57% (n = 262) of all included studies, and 97% of the studies were of evidence levels 3 to 5. Contributions were mainly from the United States (n = 123; 27%), Republic of Korea (n = 102; 22%), and Japan (n = 99; 21%). Many studies (n = 216; 47%) focused on the treatment and outcomes of meniscus root tears. A significant chronological surge in the quantity of studies addressing the diagnosis and treatment of meniscus root tears was evident, particularly over the past 3 years. Consensus was found regarding the definition of meniscus root tears, the advantages of early repair, and postoperative rehabilitation protocols. The variations in surgical techniques and operative strategies created the greatest amount of contention, along with clinical assessment and imaging modalities.

Conclusion

High-level evidence studies for diagnosing and managing meniscus root tears were scarce. A consensus has yet to be reached regarding the role of concomitant osteotomy, comparison of repair techniques, the use of a centralization stitch, patient factors affecting outcomes, and long-term outcomes of nonoperative management.

Arthroscopic Belt Capsulodesis Using a Knotless Soft Suture Anchor for Extruded Medial Meniscus

In recent years, degenerative meniscal lesions have received increasing attention as an etiologic factor of knee osteoarthritis. Among various relevant factors, medial meniscal extrusion has been shown to be an independent predictor of the onset and progression of knee osteoarthritis. Therefore, surgical reduction of the extruded medial meniscus to restore meniscal function is key to preventing osteoarthritis of the knee. The arthroscopic centralization technique using knotless anchors has been developed and refined to reduce meniscal extrusion in the posteromedial region of the knee. Although a short-term study has reported favorable outcomes, the technique presents some pitfalls and can be technically challenging. This article describes the rationale and procedure for arthroscopic belt capsulodesis using 2 knotless anchors for reduction of medial meniscal extrusion. The reported procedure is technically simple and efficiently reduces meniscal extrusion by repairing the meniscotibial capsule, and it may be useful in the prevention of osteoarthritic progression.

More than 3 mm of preoperative medial meniscal extrusion is identified as a key risk factor for varus progression in limb alignment after arthroscopic repair of medial meniscus posterior root tear

PURPOSE

To investigate the risk factors for varus progression after arthroscopic medial meniscal posterior root tear (MMPRT) repair and to compare the clinical outcomes between two groups: one with more varus progression and the other with less varus progression.

METHODS

Patients who underwent isolated arthroscopic repair of MMPRT between 2015 and 2020 were enroled, and 2-year follow-up data were collected. Participants were categorized into two groups based on preoperative values of the weight-bearing line (WBL) ratio: group A with <5.9% increase and group B with ≥5.9% increase. Various factors, including demographic features and radiological findings, were analysed and compared between the two groups. Intra-meniscal signal intensity, meniscal healing, medial meniscal extrusion (MME), and articular cartilage grade were assessed preoperatively and 1-year postoperatively using coronal magnetic resonance imaging.

RESULTS

The final cohort consisted of 34 patients in group A and 46 in group B, with a mean age of 55.8 ± 11.2 and 59.8 ± 6.6 years, respectively. Preoperative WBL ratio and cartilage lesions in the medial compartment did not differ between the groups. Preoperative MME were significantly lower in group A than those in group B (2.6 ± 0.6 mm in group A and 3.5 ± 0.7 mm in group B, p < 0.05). Patient-reported outcomes at the 2-year follow-up did not differ between the two groups (n. s.). In a logistic analysis, the odds ratio of MME was 2.1 (p < 0.05), and the cutoff value of MME was 3.02 mm.

CONCLUSION

Preoperative MME is a risk factor for varus progression. However, no differences in patient-reported outcomes were observed at 2-year follow-up, even in the group with greater varus progression.

LEVEL OF EVIDENCE

Level IV.

Incomplete Histologic Healing and Diminished Biomechanical Strength of Meniscus-Bone Interface After Medial Meniscus Posterior Root Transosseous Repair in a Goat Model

PURPOSE

To enhance the understanding of histologic healing after repairing medial meniscal posterior root tears (MMPRTs) at an early stage, utilizing a goat model.

METHODS

Eighteen adult goats, totaling 36 knee joints, were allocated into 3 groups (n = 12): sham group (Sham), root tear group (RT), and root tear with transosseous suture group (RTS). At 12- and 24-week intervals postsurgery, all the knees were harvested for imaging, macroscopic, histologic, and biomechanical assessments.

RESULTS

The intact root served as a meniscus-bone interface that connected the tibial and circular fibers of the meniscus with a bony insertion and a root-meniscus transition. A direct fibrous connection was displayed at the bony insertion proximal to the synovium in the RTS group, while the remaining regions of the root displayed indirect fibrous healing. The healing in the RT group was disjointed and reminiscent of scar tissue. The RTS group exhibited a more pronounced coronal extrusion compared to the Sham group (0.42 ± 0.09 vs 0.19 ± 0.02, P = .0012) but was improved relative to that of the RT group (0.49 ± 0.02, P = .0028). The failure load and stiffness of the RTS group were notably higher than those of the RT group, with a strength of 42.67% and a stiffness of 83.75% of the intact root. All the samples ruptured at the root-meniscus transitions.

CONCLUSIONS

The incomplete healing may be attributed to the histologic factors underlying the low healing rate and persistent medial meniscal extrusion. Notably, the region attached to the posterior cruciate ligament exhibited superior healing compared to other regions of the bony insertion in the repaired group. Conversely, the root-meniscus transition displayed discontinuity, representing a mechanical weakness in the healing process.

CLINICAL RELEVANCE

Modifications of bone tunnel positioning and suture placement could be undertaken in subsequent studies to enhance the healing of the root-meniscus transition.

In vivo movement interrelationships among the medial meniscus, joint capsule, and semimembranosus during tibial rotation

The meniscal position within the knee is critical to maintain normal knee function. The joint capsule might dynamically coordinate the medial meniscus (MM) by transmitting a semimembranosus action. However, their interrelationships in vivo are unclear. We aimed to determine relationships among the MM, joint capsule, and semimembranosus during passive tibial external-internal and isometric tibial internal rotation at the medial and posteromedial knees of 10 healthy individuals in vivo using ultrasound. We analyzed images of the MM and joint capsule locations at the medial and posteromedial knee and the velocity waveform similarity of each structure during rotational tasks. Both isometric internal rotation with semimembranosus action and passive tibial external rotation displaced the MM inward at the medial knee. The MM and joint capsule during these MM displacements coordinately moved with more than moderate cross-correlation coefficients (passive external and isometric internal rotations, ≥ 0.54 and ≥ 0.90, respectively). The movements of the MM and joint capsule to the semimembranosus during isometric internal rotation also coordinated with moderate cross-correlation coefficients (≥ 0.62). Therefore, the joint capsule might dynamically coordinate the MM by transmitting semimembranosus action. Whether increased tibial internal rotation or semimembranosus shortening causes MM extrusion awaits further investigation.

High Tibial Osteotomy Alone Does Not Decrease Medial Meniscus Extrusion in the Setting of Medial Meniscus Posterior Root Tear: A Cadaveric Study

PURPOSE

To investigate whether inducing valgus alignment and shifting the load laterally through high tibial osteotomy (HTO) alone decreases the extent of medial meniscus extrusion (MME) in the setting of medial meniscus posterior root tear (MMPRT) using ultrasound evaluation.

METHODS

Eight fresh-frozen human cadaveric knee specimens were tested using a 6-degree-of-freedom robotic testing system and ultrasound. Each specimen was tested in 5 conditions: (1) intact, (2) MMPRT, (3) medial meniscus repair (MMR), (4) combined medial open-wedge HTO + MMR, and (5) HTO + MMPRT. Measurements were obtained over the medial collateral ligament (central image) and posterior to the medial collateral ligament (posterior image) with a 250-N axial load at 0°, 30°, and 90° of knee flexion. Statistical analysis was performed using a 2-factor repeated-measures analysis of variance.

RESULTS

MME was significantly greater in HTO + MMPRT (0°: 2.44 ± 0.41 mm, 30°: 2.47 ± 0.37 mm, 90°: 2.41 ± 0.28 mm) than HTO + MMR in central images (mean difference +0.83 mm, P < .001). No significant difference was found between HTO + MMPRT and MMPRT in MME. MMR had significantly less MME than MMPRT (mean difference -0.58 mm, P < .001, posterior image at 0° and central image at 90°, P = .002). HTO + MMR showed significantly less MME than MMR alone at 30° and 90° of knee flexion in the central image (30°: -0.38 ± 0.05 mm, 90°: -0.45 ± 0.06 mm, P < .001) and 90° of knee flexion in the posterior image (-0.38 ± 0.08 mm, P = .004).

CONCLUSIONS

HTO alone did not decrease MME in the setting of MMPRT, while MMR alone decreased MME after MMPRT. Additionally, HTO + MMR decreased MME after MMPRT compared to MMR alone, although the clinical significance was uncertain.

CLINICAL RELEVANCE

The findings of this study provide clinicians with valuable insights for improving MME. HTO alone does not decrease MME in cases of MMPRT.

Meniscal extrusion consensus statement: A collaborative survey within the Meniscus International Network (MenIN) Study Group

PURPOSE

The purpose of the present study was to perform a survey administered to members of the Meniscus International Network (MenIN) Study Group, seeking to delineate the most contentious aspects of meniscal extrusion classification and provide a foundation for new, more comprehensive definitions and treatments for these pathologies.

METHODS

MenIN Study Group is a group of international experts treating and performing research on meniscus pathology and treatment. All MenIN Study Group members were asked to complete a survey aimed at establishing criteria for the optimal classification system for meniscal extrusion. Data obtained from the completed questionnaires were transferred into a spreadsheet and then analysed. All responses are presented as counts, percentages or means.

RESULTS

Forty-seven (85.5%) MenIN Study Group members completed the survey and were included in this analysis. Key aspects recommended for inclusion in a comprehensive classification system for meniscal extrusion included laterality (93.6%), anatomical location (76.6%), patient age (76.6%), body mass index (BMI) (68.1%) and aetiology (68.1%). For classifying meniscal extrusion, 53.2% considered the distance in millimetres from the tibial plateau's outer margin as the most reliable measurement technique on imaging. Preferences for imaging modalities varied, with 44.7% favouring weight-bearing magnetic resonance imaging (MRI) and 36.2% opting for weight-bearing ultrasound due to its greater availability. Respondents advocated for a classification system addressing stability or progression of meniscal extrusion (66%), reducibility (53.2%), potential progression of knee osteoarthritis (OA) (83%), influencing treatment approaches (83%), a gradation system (83%), consideration of dynamic factors (66%), association with clinical outcomes and prognosis (76.6%) and investigation around centralization procedures (57.4%).

CONCLUSIONS

In conclusion, the findings of this survey shed light on the global perspectives regarding meniscal extrusion classification. It was generally felt that a new classification of extrusion measured on MRI scans at the mid-tibial plateau should be developed, which considers factors such as laterality, anatomical location, age, BMI and aetiology. Additionally, the results support the integration of dynamic factors and clinical outcomes in MRI-based classifications to inform treatment approaches.

LEVEL OF EVIDENCE

Level IV.

Measuring Technique for Meniscal Extrusion Using Ultrasound in the Setting of Posterior Medial Meniscal Root Tears

Meniscal extrusion (ME) is a valuable, noninvasive diagnostic tool for meniscus pathology. In addition, ultrasound can allow for instant results in the office. However, ME is a fragile metric in the degree of millimeters. The inconsistent techniques used by different authors in the literature and the additional operator variability that ultrasound technology introduces make it important a systematic approach is used. The purpose of this study is to propose a reproducible technique. The current authors recommend having the patient in (1) 30° of knee flexion while weight-bearing, (2) capturing the image at the posterior border of the medial collateral ligament, (3) using a reference line parallel to the articular margin of the tibia, and (4) measuring ME at the coronal midpoint of the outermost edge of the meniscus.

Figure-4 Patient Positioning Increases Medial Meniscus Extrusion on Ultrasound in Patients With Posterior Medial Meniscus Root Tears of the Knee

Purpose

To compare the degree of medial meniscal extrusion (MME) between knees with medial meniscus posterior root tear (MMPRT) and degenerative tears of the medial meniscus using ultrasonography (US) in different limb positions and to identify the findings characteristic of MMPRT.

Methods

The study group comprised 25 subjects with MMPRT (group RT), 25 subjects with degenerative medial meniscal tears (group D), and 25 knees with no abnormalities of the medial meniscus (MM) on magnetic resonance imaging (MRI) (group C) whose age was ≥40 years. MME was evaluated using US in the supine, figure-4, feet-dangling, and standing positions. The MME was evaluated by the actual measurement values and the relative values to the MME in the supine position. The differences in the MME among the 3 groups in each limb position were analyzed using one-way analysis of variance. P < .05 was considered significant.

Results

The actual MME values were largest in group RT in all 4 limb positions. When changing the limb position from the supine to the figure-4, the actual MME increased from 3.8 ± 0.8 mm to 5.5 ± 1.3 mm in group RT, whereas it decreased from 3.4 ± 1.1 mm to 1.8 ± 1.2 mm in group D, showing the most significant difference in MME of the figure-4 position between the 2 groups (P < .001). In group RT, 88% of knees had the maximum MME in the figure-4 position. In group D, 60% of knees had the maximum MME in the standing position and only 2 knees (8%) had the maximum MME in the figure-4 position.

Conclusions

The increase in MME from the supine to the figure-4 position was a characteristic finding of MMPRT but not degenerative tears.

Level of Evidence

Level III, case-control study.

Editorial Commentary: Traumatic and Atraumatic Meniscal Root Injuries Can Occur Both Medially and Laterally: No Rule Without Exceptions!

It took a long time for meniscal root injuries to slowly gain scientific and clinical attention some 40 years after the first arthroscopic meniscal resection. Medial root injuries are mostly degenerative in nature and often are associated with obesity and varus deformity. However, lateral root injuries are more commonly traumatic in origin and are associated with anterior cruciate ligament injuries. But, there is no rule without an exception. Laterally, there are isolated root injuries without anterior cruciate ligament involvement and also nontraumatic root injuries that can be associated with a valgus leg axis. Traumatic medial root injuries, on the other hand, occur in the context of knee dislocations. Therefore, the therapeutic concepts should not be based strictly on the localization medial or lateral but on the etiology, traumatic and not traumatic. Even though it has been shown that many patients benefit from refixation of the meniscus root, it seems sensible to search for the etiology of nontraumatic root injuries and to integrate this into the therapeutic concept (e.g., additional osteotomy to correct the varus or valgus deformity). However, the degenerative changes in the relevant compartment must also be taken into account. Recent biomechanical results on the influence of the meniscotibial (medial) or meniscofemoral (lateral) ligaments on extrusion are also relevant with regard to the success of root refixation. These results can provide the rationale for carrying out additional centralization.