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Fig 1

Fig. 1

Graphic displaying an example of each type of meniscal root tear as described by the LaPrade classification system. A Type 2A tear is depicted as an example for a Type 2 tear. Reproduced with permission from LaPrade et al.12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Fig 2

Fig. 2

Increased signal on magnetic resonance imaging resulting from posterior meniscal root injury (white arrow).

Fig 3

Fig. 3

Sagittal magnetic resonance imaging demonstrating the “ghost sign,” where the normal signal for the posterior meniscal root is absent (dotted outline).

Fig 4

Fig. 4

Coronal magnetic resonance imaging demonstrating significant medial meniscal extrusion (white arrow and dashed lines).

Fig 5

Fig. 5

Axial magnetic resonance imaging demonstrating lateral meniscal root tear (white arrow).

Fig 6

Fig. 6

Arthroscopic probing of meniscal root revealing a lateral meniscal tear.

Fig 7

Fig. 7

Medial meniscal root repaired with a side-to-side technique.

Fig 8

Fig. 8

Normal position for a surgical button (white arrow) over the anterior transtibial tunnel aperture for root repair (left) compared with a modified transtibial position marked by the surgical button (white arrow) following proximal tibial osteotomy (right).

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Abstract

Recent interest has uncovered the importance of understanding meniscal root anatomy, its effect on biomechanics of the knee joint, and appropriate treatment modalities. Meniscal root tears may account for up to one-fifth of all meniscal tears and have downstream consequences that can be as severe as total meniscectomy due to the unique force-dispersing properties of the meniscus. Meniscal biomechanics rely heavily upon the integrity of root attachments, and this historically overlooked etiology of knee pain and early onset osteoarthritis plays a vital role in maintaining the longevity of the knee joint. As meniscal root pathology becomes more commonly known and clinically assessed, an understanding of classifications, repair methods, and indications is important for surgeons.

Introduction

Historically overlooked as an etiology of knee pain and early onset osteoarthritis (OA), the meniscal root plays a vital role in maintaining the longevity of the knee joint.1x1Steineman, B.D., LaPrade, R.F., Santangelo, K.S., Warner, B.T., Goodrich, L.R., and Haut Donahue, T.L. Early osteoarthritis after untreated anterior meniscal root tears: an in vivo animal study. Orthop J Sports Med. 2017; 5: 2325967117702452https://doi.org/10.1177/2325967117702452

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,2x2Floyd, E.R., Rodriguez, A.N., Falaas, K.L. et al. The natural history of medial meniscal root tears: a biomechanical and clinical case perspective. Front Bioeng Biotechnol. 2021; 9: 744065https://doi.org/10.3389/fbioe.2021.744065

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Reported to affect nearly 100,000 patients annually, meniscal root tears (MRTs) account for up to 10% to 21% of all meniscal tears and have been labeled as a “silent epidemic” due to their widespread underdiagnosis and the rapid progression of untreated injuries to OA.3x3LaPrade, R.F., Floyd, E.R., Carlson, G.B., Moatshe, G., Chahla, J., and Monson, J.K. Meniscal root tears: solving the silent epidemic. J Arthrosc Surg Sports Med. 2021; 2: 47–57https://doi.org/10.25259/jassm_55_2020

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, 4x4LaPrade, C.M., Jansson, K.S., Dornan, G., Smith, S.D., Wijdicks, C.A., and LaPrade, R.F. Altered tibiofemoral contact mechanics due to lateral meniscus posterior horn root avulsions and radial tears can be restored with in situ pull-out suture repairs. J Bone Joint Surg Am. 2014; 96: 471–479https://doi.org/10.2106/JBJS.L.01252

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, 5x5Cinque, M.E., DePhillipo, N.N., Moatshe, G. et al. Clinical outcomes of inside-out meniscal repair according to anatomic zone of the meniscal tear. Orthop J Sports Med. 2019; 7: 2325967119860806https://doi.org/10.1177/2325967119860806

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, 6x6Bonasia, D.E., Pellegrino, P., D'Amelio, A., Cottino, U., and Rossi, R. Meniscal root tear repair: why, when and how?. Orthop Rev (Pavia). 2015; 7: 5792https://doi.org/10.4081/or.2015.5792

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Demographic differences have been reported for types of MRTs, with young male patients more likely to present with lateral MRTs, often in the setting of multiple ligament knee injuries, knee trauma, or concomitant anterior cruciate ligament (ACL) tears.7x7Cinque, M.E., Chahla, J., Moatshe, G., Faucett, S.C., Krych, A.J., and LaPrade, R.F. Meniscal root tears: a silent epidemic. Br J Sports Med. 2018; 52: 872–876https://doi.org/10.1136/bjsports-2017-098942

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Medial MRTs often occur via a low-energy mechanism and are more common in older patients with higher body mass index (BMI) and existing degenerative changes in the knee.8x8Brophy, R.H., Wojahn, R.D., Lillegraven, O., and Lamplot, J.D. Outcomes of arthroscopic posterior medial meniscus root repair: association with body mass index. J Am Acad Orthop Surg. 2019; 27: 104–111https://doi.org/10.5435/jaaos-D-17-00065

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,9x9Krych, A.J., Bernard, C.D., Kennedy, N.I. et al. Medial versus lateral meniscus root tears: is there a difference in injury presentation, treatment decisions, and surgical repair outcomes?. Arthroscopy. 2020; 36: 1135–1141https://doi.org/10.1016/j.arthro.2019.11.098

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An MRT is defined as a complete bony or soft tissue avulsion of the root attachment or a radial tear that occurs within 1 cm of the meniscal root attachment.10x10Matheny, L.M., Ockuly, A.C., Steadman, J.R., and LaPrade, R.F. Posterior meniscus root tears: associated pathologies to assist as diagnostic tools. Knee Surg Sports Traumatol Arthrosc. 2015; 23: 3127–3131https://doi.org/10.1007/s00167-014-3073-7

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, 11x11LaPrade, R.F., Padalecki, J.R., Jansson, K. et al. Biomechanical consequences of a complete radial tear adjacent to the medial meniscus posterior root attachment site. Orthop J Sports Med. 2014; 2: 699–707https://doi.org/10.1177/2325967114s00004

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, 12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Recent studies have recognized the extent to which MRTs disrupt the native biomechanical role of the meniscus.4x4LaPrade, C.M., Jansson, K.S., Dornan, G., Smith, S.D., Wijdicks, C.A., and LaPrade, R.F. Altered tibiofemoral contact mechanics due to lateral meniscus posterior horn root avulsions and radial tears can be restored with in situ pull-out suture repairs. J Bone Joint Surg Am. 2014; 96: 471–479https://doi.org/10.2106/JBJS.L.01252

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| Google ScholarSee all References
,10x10Matheny, L.M., Ockuly, A.C., Steadman, J.R., and LaPrade, R.F. Posterior meniscus root tears: associated pathologies to assist as diagnostic tools. Knee Surg Sports Traumatol Arthrosc. 2015; 23: 3127–3131https://doi.org/10.1007/s00167-014-3073-7

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,13x13Kennedy, N.I., Michalski, M.P., Engebretsen, L., and LaPrade, R.F. Iatrogenic meniscus posterior root injury following reconstruction of the posterior cruciate ligament: a report of three cases. JBJS Case Connect. 2014; 4: e20https://doi.org/10.2106/JBJS.CC.M.00175

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, 14x14Griffith, C.J., LaPrade, R.F., Fritts, H.M., and Morgan, P.M. Posterior root avulsion fracture of the medial meniscus in an adolescent female patient with surgical reattachment. Am J Sports Med. 2008; 36: 789–792https://doi.org/10.1177/0363546507308195

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, 15x15Padalecki, J.R., Jansson, K.S., Smith, S.D. et al. Biomechanical consequences of a complete radial tear adjacent to the medial meniscus posterior root attachment site: in situ pull-out repair restores derangement of joint mechanics. Am J Sports Med. 2014; 42: 699–707https://doi.org/10.1177/0363546513499314

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Meniscal root integrity is critical for the conversion of axial tibiofemoral loads into hoop stresses.2x2Floyd, E.R., Rodriguez, A.N., Falaas, K.L. et al. The natural history of medial meniscal root tears: a biomechanical and clinical case perspective. Front Bioeng Biotechnol. 2021; 9: 744065https://doi.org/10.3389/fbioe.2021.744065

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| Google ScholarSee all References
,12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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,16x16Allaire, R., Muriuki, M., Gilbertson, L., and Harner, C.D. Biomechanical consequences of a tear of the posterior root of the medial meniscus. Similar to total meniscectomy. J Bone Joint Surg Am. 2008; 90: 1922–1931https://doi.org/10.2106/JBJS.G.00748

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A root avulsion alters the tibiofemoral load distribution across the tibial plateau because of meniscal extrusion, which increases the pressure on the articular cartilage. Past biomechanical studies have demonstrated changes in area and contact pressures across the tibiofemoral joint following an MRT are comparable with a meniscal deficient state.16x16Allaire, R., Muriuki, M., Gilbertson, L., and Harner, C.D. Biomechanical consequences of a tear of the posterior root of the medial meniscus. Similar to total meniscectomy. J Bone Joint Surg Am. 2008; 90: 1922–1931https://doi.org/10.2106/JBJS.G.00748

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These altered tibiofemoral loads have been shown to intensify degenerative changes in the knee joint.9x9Krych, A.J., Bernard, C.D., Kennedy, N.I. et al. Medial versus lateral meniscus root tears: is there a difference in injury presentation, treatment decisions, and surgical repair outcomes?. Arthroscopy. 2020; 36: 1135–1141https://doi.org/10.1016/j.arthro.2019.11.098

Abstract | Full Text | Full Text PDF | PubMed | Scopus (27)
| Google ScholarSee all References
,17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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Past literature has reported a strong association between MRTs and progression to knee OA,1x1Steineman, B.D., LaPrade, R.F., Santangelo, K.S., Warner, B.T., Goodrich, L.R., and Haut Donahue, T.L. Early osteoarthritis after untreated anterior meniscal root tears: an in vivo animal study. Orthop J Sports Med. 2017; 5: 2325967117702452https://doi.org/10.1177/2325967117702452

Crossref | PubMed | Scopus (19)
| Google ScholarSee all References
,7x7Cinque, M.E., Chahla, J., Moatshe, G., Faucett, S.C., Krych, A.J., and LaPrade, R.F. Meniscal root tears: a silent epidemic. Br J Sports Med. 2018; 52: 872–876https://doi.org/10.1136/bjsports-2017-098942

Crossref | PubMed | Scopus (28)
| Google ScholarSee all References
,17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,18x18Choi, E.S. and Park, S.J. Clinical evaluation of the root tear of the posterior horn of the medial meniscus in total knee arthroplasty for osteoarthritis. Knee Surg Relat Res. 2015; 27: 90–94https://doi.org/10.5792/ksrr.2015.27.2.90

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and MRTs often occur in the fourth or fifth decade of life. Early detection is crucial to restore native knee joint loading and for the prevention of articular cartilage degeneration.3x3LaPrade, R.F., Floyd, E.R., Carlson, G.B., Moatshe, G., Chahla, J., and Monson, J.K. Meniscal root tears: solving the silent epidemic. J Arthrosc Surg Sports Med. 2021; 2: 47–57https://doi.org/10.25259/jassm_55_2020

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| Google ScholarSee all References
,7x7Cinque, M.E., Chahla, J., Moatshe, G., Faucett, S.C., Krych, A.J., and LaPrade, R.F. Meniscal root tears: a silent epidemic. Br J Sports Med. 2018; 52: 872–876https://doi.org/10.1136/bjsports-2017-098942

Crossref | PubMed | Scopus (28)
| Google ScholarSee all References
,17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,19x19Packer, J.D. and Rodeo, S.A. Meniscal allograft transplantation. Clin Sports Med. 2009; 28: 259–283https://doi.org/10.1016/j.csm.2008.10.011

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For decades, meniscectomy was the standard treatment following meniscal injury, and continues to be widely utilized. However, given the significant risk of progression to OA, treatment by meniscectomy has come under scrutiny and current research emphasizes meniscus preservation with anatomically oriented meniscal root repair techniques.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,20x20Ro, K.H., Kim, J.H., Heo, J.W., and Lee, D.H. Clinical and radiological outcomes of meniscal repair versus partial meniscectomy for medial meniscus root tears: a systematic review and meta-analysis. Orthop J Sports Med. 2020; 8: 2325967120962078https://doi.org/10.1177/2325967120962078

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This article will review the anatomy and biomechanics of the meniscus root attachments, with diagnostic and surgical treatment pearls, and discuss the current state of MRT repairs and salvage techniques.

Anatomy/biomechanics

Meniscus anatomy: Structure is function

The medial and lateral menisci form 2 C-shaped borders filling the triangular space between the tibial and femoral articular cartilage surfaces and the joint capsule. The meniscus itself is roughly the shape of a collapsed triangle on cross section, with a broad, vascular outside body which thins to a less vascular and then ultimately avascular apical ridge between chondral surfaces. This unique space-filling shape leads to increased joint-surface contact area.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,23x23Laprade, R.F., Floyd, E.R., Carlson, G.B., Moatshe, G., Chahla, J., and Monson, J.K. Meniscal root tears: solving the silent epidemic. J Arthrosc Surg Sports Med. 2020; 2: 47–57https://doi.org/10.25259/JASSM_55_2020

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The lateral meniscus is smaller and more circular with its anterior and posterior roots nearly meeting at the lateral intercondylar eminence. Both anterior and posterior medial meniscal roots lie peripheral to the lateral root insertions, forming more of a horseshoe or C shape.

The medial meniscus, perhaps due to the greater percentage of weightbearing through the medial femoral and tibial pillars, is more rigidly attached to the tibia and the surrounding capsule, and therefore, less mobile. The medial meniscus therefore provides a certain measure of stability for the femoral condyle on the tibia—a sort of shallow, rounded cup holder. The lateral meniscus in comparison has more laxity allowing a small amount of anteroposterior glide along the tibial surface so as to better move with the lateral femoral condyle during natural axial rotation about the tibiofemoral joint. Much of the posterior horn of the lateral meniscus lacks meniscocapsular attachments, thereby allowing this increased mobility. However, the meniscofemoral ligaments, which course from the medial most extent of the posterior horn to their attachment sites in the femoral notch both anterior and posterior to the bundles of the Posterior cruciate ligament (PCL), both confer notable stability namely to internal rotation and anterior translational forces.

While the meniscocapsular attachments and meniscofemoral ligaments are both important for meniscal stability, the most biomechanically important connections are the meniscal root attachments.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,22x22Aspden, R.M., Yarker, Y.E., and Hukins, W.L. Collagen orientations in the meniscus of the knee joint. J Anat. 1985; 140: 371–380

PubMed
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,23x23Laprade, R.F., Floyd, E.R., Carlson, G.B., Moatshe, G., Chahla, J., and Monson, J.K. Meniscal root tears: solving the silent epidemic. J Arthrosc Surg Sports Med. 2020; 2: 47–57https://doi.org/10.25259/JASSM_55_2020

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Furthermore, meniscal root integrity is crucial to meniscal function as a whole, because the disruption of these anchoring sites releases the circular tension holding the meniscus between the tibiofemoral cartilages.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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The resulting axial compression through the tibiofemoral joint then pushes the meniscus out of the articular joint space, thereby diminishing the ability of the meniscus to adequately disperse axial tibiofemoral joint forces.

Biomechanics, stability, and sequalae

Foundational studies examining the biomechanical and structural characteristics of the menisci have established their critical role in modulating force transmission across the tibiofemoral articulation.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,21x21Bhatia, S., LaPrade, C.M., Ellman, M.B., and LaPrade, R.F. Meniscal root tears: significance, diagnosis, and treatment. Am J Sports Med. 2014; 42: 3016–3030https://doi.org/10.1177/0363546514524162

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,22x22Aspden, R.M., Yarker, Y.E., and Hukins, W.L. Collagen orientations in the meniscus of the knee joint. J Anat. 1985; 140: 371–380

PubMed
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Classically, the meniscus has been likened to a “shock absorber” in the knee.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,23x23Laprade, R.F., Floyd, E.R., Carlson, G.B., Moatshe, G., Chahla, J., and Monson, J.K. Meniscal root tears: solving the silent epidemic. J Arthrosc Surg Sports Med. 2020; 2: 47–57https://doi.org/10.25259/JASSM_55_2020

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It functions in this capacity by converting axial compressive loads into radial tangential “hoop stresses.”17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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| Google ScholarSee all References
,22x22Aspden, R.M., Yarker, Y.E., and Hukins, W.L. Collagen orientations in the meniscus of the knee joint. J Anat. 1985; 140: 371–380

PubMed
| Google ScholarSee all References
In doing so, the menisci reduce the total compressive forces experienced by the chondral cartilage of the tibial plateau and femoral condyles.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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| Google ScholarSee all References
,22x22Aspden, R.M., Yarker, Y.E., and Hukins, W.L. Collagen orientations in the meniscus of the knee joint. J Anat. 1985; 140: 371–380

PubMed
| Google ScholarSee all References
Furthermore, by increasing the contact surface area of the tibiofemoral articulation, the menisci function to spread compressive loads over a larger surface area, thereby avoiding the phenomenon of “point loading.” This dispersion of axial compressive loads across the knee helps to provide long-term protective effects to chondral surfaces and prevent progression of osteoarthritic changes.1x1Steineman, B.D., LaPrade, R.F., Santangelo, K.S., Warner, B.T., Goodrich, L.R., and Haut Donahue, T.L. Early osteoarthritis after untreated anterior meniscal root tears: an in vivo animal study. Orthop J Sports Med. 2017; 5: 2325967117702452https://doi.org/10.1177/2325967117702452

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In addition, the loss of stability caused by root tears leads to increased instability and motion across the tibiofemoral articulation, which puts increased strain on stabilizing ligaments such as the ACL.24x24Samuelsen, B.T., Aman, Z.S., Kennedy, M.I. et al. Posterior medial meniscus root tears potentiate the effect of increased tibial slope on anterior cruciate ligament graft forces. Am J Sports Med. 2020; 48: 334–340https://doi.org/10.1177/0363546519889628

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It may also be that increased motion due to instability inferred by meniscal root pathology changes the biomechanics of the tibiofemoral joint to an extent that expedites the joint degradation sustained.

Pathology discussing diagnosis

LaPrade classification of meniscal root tears

The term MRT is used to describe damage occurring to one of the meniscal attachment sites within 1 cm from the meniscal root insertion.1x1Steineman, B.D., LaPrade, R.F., Santangelo, K.S., Warner, B.T., Goodrich, L.R., and Haut Donahue, T.L. Early osteoarthritis after untreated anterior meniscal root tears: an in vivo animal study. Orthop J Sports Med. 2017; 5: 2325967117702452https://doi.org/10.1177/2325967117702452

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,17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

Crossref | PubMed | Scopus (3)
| Google ScholarSee all References
,23x23Laprade, R.F., Floyd, E.R., Carlson, G.B., Moatshe, G., Chahla, J., and Monson, J.K. Meniscal root tears: solving the silent epidemic. J Arthrosc Surg Sports Med. 2020; 2: 47–57https://doi.org/10.25259/JASSM_55_2020

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Meniscal root tears can manifest in a variety of ways, necessitating the use of an appropriate classification system. The LaPrade classification for MRTs classifies MRTs based on the location and quality of the tear.12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Unlike other proposed systems for classifying MRTs, the LaPrade classification for MRTs applies to both the anterior and posterior roots and separates tears into 5 types (Fig. 1).12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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,17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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Type 1 describes an isolated, stable partial tear of the meniscal root.12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Type 2 describes a complete radial tear of the meniscal root and contains 3 subtypes which differ based on their location along the meniscal root relative to the center of the root insertion; Type 2A occurs at less than 3 mm from the center of the root attachment, Type 2B occurs from 3 to 6 mm from the center of the root attachment site, Type 2C occurs from 6 to 9 mm from the center of the root attachment site.12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Type 3 describes an MRT with a concomitant longitudinal/circumferential tear (commonly referred to as a “bucket handle” tear).12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Type 4 describes an oblique tear of the meniscus that extends into the meniscal root resulting in complete root detachment.12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Finally, Type 5 describes the case of a complete bony avulsion fracture of the root from its attachment to the tibial plateau.12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Fig 1 Opens large image

Fig. 1

Graphic displaying an example of each type of meniscal root tear as described by the LaPrade classification system. A Type 2A tear is depicted as an example for a Type 2 tear. Reproduced with permission from LaPrade et al.12x12LaPrade, C.M., James, E.W., Cram, T.R., Feagin, J.A., Engebretsen, L., and LaPrade, R.F. Meniscal root tears: a classification system based on tear morphology. Am J Sports Med. 2015; 43: 363–369https://doi.org/10.1177/0363546514559684

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Extrusion and nonanatomic repair

Many studies have shown that the meniscus-deficient knee (eg, patients treated with meniscectomy or hemi-meniscectomy) almost always consistently and rapidly progresses to OA.1x1Steineman, B.D., LaPrade, R.F., Santangelo, K.S., Warner, B.T., Goodrich, L.R., and Haut Donahue, T.L. Early osteoarthritis after untreated anterior meniscal root tears: an in vivo animal study. Orthop J Sports Med. 2017; 5: 2325967117702452https://doi.org/10.1177/2325967117702452

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,25x25LaPrade, R.F. Not your father's (or mother's) meniscus surgery. Minn Med. 2007; : 41–43

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Furthermore, biomechanical models have shown the meniscal root-deficient knee to be biomechanically equivalent to the meniscectomized knee, and therefore, pose a similarly significant risk of progression to fulminant OA.16x16Allaire, R., Muriuki, M., Gilbertson, L., and Harner, C.D. Biomechanical consequences of a tear of the posterior root of the medial meniscus. Similar to total meniscectomy. J Bone Joint Surg Am. 2008; 90: 1922–1931https://doi.org/10.2106/JBJS.G.00748

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,17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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Studies have further demonstrated that nonanatomic repair of an MRT functions biomechanically similar to leaving the root left untreated and thereby would have significant long-term degenerative effects.26x26LaPrade, C.M., Foad, A., Smith, S.D. et al. Biomechanical consequences of a nonanatomic posterior medial meniscal root repair. Am J Sports Med. 2015; 43: 912–920https://doi.org/10.1177/0363546514566191

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,27x27Steineman, B.D., LaPrade, R.F., and Haut Donahue, T.L. Nonanatomic placement of posteromedial meniscal root repairs: a finite element study. J Biomech Eng. 2020; 142: 081004https://doi.org/10.1115/1.4045893

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This is because the chondroprotective functions of the menisci are ultimately dependent upon their attachment to their respective anatomic root attachment sites.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,21x21Bhatia, S., LaPrade, C.M., Ellman, M.B., and LaPrade, R.F. Meniscal root tears: significance, diagnosis, and treatment. Am J Sports Med. 2014; 42: 3016–3030https://doi.org/10.1177/0363546514524162

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,28x28Pache, S., Aman, Z.S., Kennedy, M. et al. Meniscal root tears: current concepts review. Arch Bone Jt Surg. 2018; 6: 250–259

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When the native menisci experience axial compressive forces, they are placed into circular traction.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,22x22Aspden, R.M., Yarker, Y.E., and Hukins, W.L. Collagen orientations in the meniscus of the knee joint. J Anat. 1985; 140: 371–380

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,28x28Pache, S., Aman, Z.S., Kennedy, M. et al. Meniscal root tears: current concepts review. Arch Bone Jt Surg. 2018; 6: 250–259

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However, when the MRTs are compromised, the meniscus is unable to retain circular traction, and instead, extrudes out of the joint space.17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,21x21Bhatia, S., LaPrade, C.M., Ellman, M.B., and LaPrade, R.F. Meniscal root tears: significance, diagnosis, and treatment. Am J Sports Med. 2014; 42: 3016–3030https://doi.org/10.1177/0363546514524162

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,28x28Pache, S., Aman, Z.S., Kennedy, M. et al. Meniscal root tears: current concepts review. Arch Bone Jt Surg. 2018; 6: 250–259

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As a result, the meniscus is unable to disperse axial compressive loads, and point loading occurs.15x15Padalecki, J.R., Jansson, K.S., Smith, S.D. et al. Biomechanical consequences of a complete radial tear adjacent to the medial meniscus posterior root attachment site: in situ pull-out repair restores derangement of joint mechanics. Am J Sports Med. 2014; 42: 699–707https://doi.org/10.1177/0363546513499314

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Point loading results in a phenomenon described previously as spontaneous osteonecrosis of the knee (SONK, now thought to be more appropriately referred to as “subchondral insufficiency fracture,” or SIFK), which is one of the identifiable signs of an MRT that can be found on magnetic resonance imaging (MRI).17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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,29x29Hussain, Z.B., Chahla, J., Mandelbaum, B.R., Gomoll, A.H., and LaPrade, R.F. The role of meniscal tears in spontaneous osteonecrosis of the knee: a systematic review of suspected etiology and a call to revisit nomenclature. Am J Sports Med. 2019; 47: 501–507https://doi.org/10.1177/0363546517743734

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Therefore, strategies to minimize meniscal extrusion following meniscal root repair have also become an area of great focus.29x29Hussain, Z.B., Chahla, J., Mandelbaum, B.R., Gomoll, A.H., and LaPrade, R.F. The role of meniscal tears in spontaneous osteonecrosis of the knee: a systematic review of suspected etiology and a call to revisit nomenclature. Am J Sports Med. 2019; 47: 501–507https://doi.org/10.1177/0363546517743734

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, 30x30Dean, R.S., DePhillipo, N.N., Monson, J.K., and LaPrade, R.F. Peripheral stabilization suture to address meniscal extrusion in a revision meniscal root repair: surgical technique and rehabilitation protocol. Arthrosc Tech. 2020; 9: e1211–e1218https://doi.org/10.1016/j.eats.2020.04.022

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, 31x31Daney, B.T., Aman, Z.S., Krob, J.J. et al. Utilization of transtibial centralization suture best minimizes extrusion and restores tibiofemoral contact mechanics for anatomic medial meniscal root repairs in a cadaveric model. Am J Sports Med. 2019; 47: 1591–1600https://doi.org/10.1177/0363546519844250

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Diagnostic pearls

Due to the acceleration of joint degeneration caused by MRTs, early diagnosis and prompt treatment is paramount for good outcomes. The clinical diagnosis begins with a detailed patient history and physical examination, and while certain radiographic findings may raise clinical suspicion, the gold standard for diagnosis is ultimately MRI and arthroscopy. Regarding the notoriety of MRTs as missed diagnoses, high clinical suspicion is required for the diagnosis, and clinician understanding of etiology and diagnostic signs is crucial.

History and physical examination

The difficulty of diagnosing MRTs stems in part from the lack of similarity to injury of the meniscal body. It has been reported, for example, that only 10% to 15% of patients with medial posterior root tears exhibit signs of knee locking or giving way.32x32Lee, D.W., Ha, J.K., and Kim, J.G. Medial meniscus posterior root tear: a comprehensive review. Knee Surg Relat Res. 2014; 26: 125–134https://doi.org/10.5792/ksrr.2014.26.3.125

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Indeed, similar to the majority of chronic meniscal injuries in older populations, up to 70% of patients cannot recall a direct inciting injury.33x33Kim, J.H., Chung, J.H., Lee, D.H., Lee, Y.S., Kim, J.R., and Ryu, K.J. Arthroscopic suture anchor repair versus pullout suture repair in posterior root tear of the medial meniscus: a prospective comparison study. Arthroscopy. 2011; 27: 1644–1653https://doi.org/10.1016/j.arthro.2011.06.033

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When present, the mechanism of injury may lead to clinical suspicion of a root tear, such as a rotatory blow to a flexed knee which is assumed to be a common etiology. The presence of an ACL injury should also prompt examination for an MRT, most commonly in the lateral posterior root. Lateral meniscus root tears have been reported to have an incidence rate ranging from 2.65% to 16% in ACL injuries.34x34Magosch, A., Mouton, C., Nührenbörger, C., and Seil, R. Medial meniscus ramp and lateral meniscus posterior root lesions are present in more than a third of primary and revision ACL reconstructions. Knee Surg Sports Traumatol Arthrosc. 2021; 29: 3059–3067https://doi.org/10.1007/s00167-020-06352-3

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Physical examination is also limited in diagnostic utility, with some combination of pain with deep flexion (for posterior root tears), palpable meniscal extrusion, and a positive McMurray's test being present in only 50% to 60% of patients.36x36James, E., Cinque, M., Chahla, J., and LaPrade, R. An evidence-based approach to the diagnosis and treatment of meniscal root tears. Min Ortop Traumatol. 2017; 68https://doi.org/10.23736/S0394-3410.17.03805-X

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Physician gestalt after history and physical should direct further diagnostic imaging.

Imaging

Plain film radiographs including Rosenberg view are commonly obtained in orthopedic clinics; these images are less helpful for characterizing type of meniscal pathology and instead more helpful with inferring chronicity and severity of degenerative changes. Because root tears are structurally comparable to meniscal deficiency, the onset of rapid arthritic changes and increased Kellgren-Lawrence scores, particularly in young patients, should provoke investigation for MRTs. Long leg standing films should be acquired to assess coronal alignment as well. More recent literature has demonstrated that varus malalignment of >5° is associated with slightly decreased outcome scores compared with neutral alignment.37x37Ridley, T.J., Ruzbarsky, J.J., Dornan, G.J. et al. Minimum 2-year clinical outcomes of medial meniscus root tears in relation to coronal alignment. Am J Sports Med. 2022; 50: 1254–1260https://doi.org/10.1177/03635465221080167

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However, patients still have low failure rate and good improvements in outcome scores with varus alignment following meniscal root repair. Furthermore, concomitant osteotomy in this population was associated with significantly worse outcomes and therefore is no longer recommended in this patient cohort.

MRI is the most reliable noninvasive test for MRTs. Although in the past, studies had demonstrated specificity as low as 70%,38x38Ozkoc, G., Circi, E., Gonc, U., Irgit, K., Pourbagher, A., and Tandogan, R.N. Radial tears in the root of the posterior horn of the medial meniscus. Knee Surg Sports Traumatol Arthrosc. 2008; 16: 849–854https://doi.org/10.1007/s00167-008-0569-z

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the literature now reports recent diagnostic advances have improved predictive values to over 90%.39x39De Smet, A.A. and Mukherjee, R. Clinical, MRI, and arthroscopic findings associated with failure to diagnose a lateral meniscal tear on knee MRI. AJR Am J Roentgenol. 2008; 190: 22–26https://doi.org/10.2214/ajr.07.2611

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, 40x40LaPrade, R.F., Ho, C.P., James, E., Crespo, B., LaPrade, C.M., and Matheny, L.M. Diagnostic accuracy of 3.0 T magnetic resonance imaging for the detection of meniscus posterior root pathology. Knee Surg Sports Traumatol Arthrosc. 2015; 23: 152–157https://doi.org/10.1007/s00167-014-3395-5

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, 41x41Choi, S.H., Bae, S., Ji, S.K., and Chang, M.J. The MRI findings of meniscal root tear of the medial meniscus: emphasis on coronal, sagittal and axial images. Knee Surg Sports Traumatol Arthrosc. 2012; 20: 2098–2103https://doi.org/10.1007/s00167-011-1794-4

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Signs of MRTs on MRI include increased signal resulting from fluid collection near the meniscal roots (Fig. 2), the ghost sign (sagittal cuts on which the meniscus is not identifiable in its normal position, Fig. 3), and coronal views showing meniscal extrusion greater than 3 mm from the tibial articular cartilage (Fig. 4).17x17Banovetz, M.T., Roethke, L.C., Rodriguez, A.N., and LaPrade, R.F. Meniscal root tears: a decade of research on their relevant anatomy, biomechanics, diagnosis, and treatment. Arch Bone Jt Surg. 2022; 10: 366–380https://doi.org/10.22038/ABJS.2021.60054.2958

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Axial cuts can similarly be quite telling and representative of an MRT if the imaging cuts demonstrated have a good on-profile view of the root attachment (Fig. 5). Associated SONK, a misnomer more properly replaced with SIFK, is bony edema of the femoral condyles or tibial plateau thought to be caused by increased point-loading due to lack of meniscal support. This is another MRI finding that, in the absence of obvious causes, should prompt further investigation of an MRT.28x28Pache, S., Aman, Z.S., Kennedy, M. et al. Meniscal root tears: current concepts review. Arch Bone Jt Surg. 2018; 6: 250–259

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Fig 2 Opens large image

Fig. 2

Increased signal on magnetic resonance imaging