Medial meniscal posterior root tear – A current concept review

Anatomy

The anterior and posterior horns of both the medial and lateral menisci are anchored by four meniscal roots [Figure 1]. These include the anterior root attachments of the medial and lateral menisci and the posterior root attachments of the medial and lateral meniscus. Each of these attachments includes a core group of fibers and additional connecting fibers.

Close

Figure 1:

The top surface of the tibia depicting the attachment of the roots of the menisci. MPRA: Medial posterior root attachment, LPRA: Lateral posterior root attachment, LARA: Lateral anterior root attachment, MARA: Medial anterior root attachment, ACL: Anterior cruciate ligament, MTE: Medial tibial eminence, LTE: Lateral tibial eminence.

Export to PPT

The distances from the attachment points of meniscal roots to landmarks such as the lateral tibial eminence (LTE) and medial tibial eminence (MTE) have been established through research on cadavers. They are crucial for correctly repairing meniscal roots. Repairing meniscal roots in a way that does not follow the natural anatomy often leads to outcomes similar to removing the meniscus entirely, increasing the risk of osteoarthritis (OA).

Hence, it is crucial to have a comprehensive grasp of the anatomy of the meniscal root to ensure proper repositioning of the menisci. At times, accomplishing this requires extensive use of arthroscopic tools or similar instruments, particularly when the menisci have become attached in an unnatural location to the adjacent tissue.

Biomechanics and significance of meniscal root

The meniscus’s role is essential in knee biomechanics, its integrity depends on secure root attachments, which prevent displacement during movement. Detachment disrupts knee function similar to total meniscectomy. Medial meniscal root tears resemble subtotal meniscectomy, leading to increased contact pressures and reduced area.

Prevalence

Advancements in imaging methods have led to increased recognition of meniscal root tears and greater awareness among clinicians. The incidence of meniscal root tears has been reported to account for 10–21% of all meniscal tears, representing a substantial portion of meniscus-related issues.^[1]

Incidence rates vary with age and activity levels. Although they can occur in all age groups, older adults often experience degenerative root tears. At the same time, younger individuals may suffer traumatic injuries during sports or activities involving sudden pivoting or twisting motions.^[13] An increased risk of medial root tears has been linked to female sex, increasing age, an elevated body mass index, and a decrease in sports activity levels.^[15]

Etiology

These injuries can occur due to traumatic events or more commonly in degenerative knees, with minor movements like squatting also contributing to tears.^[16] Among the meniscal roots, the MPRA is particularly susceptible, with an incidence ranging from 10% to 21% of medial meniscus tears.^[15] Notably, about 70–80% of individuals diagnosed with SPONK have associated medial meniscus posterior root tears, suggesting a correlation between the tear and this syndrome.

1. Trauma: Meniscal root tears can be caused by acute trauma, such as twisting or hyperextension of the knee joint, primarily during sports or accidents.

2. Degeneration: Chronic degenerative changes in the meniscus predispose it to tears, particularly at the root attachment site. Aging, repetitive stress, and underlying conditions like OA significantly contribute to this process.

Predisposing factors

Anatomic variations in meniscal root anatomy, such as root attachment angle or size discrepancies, may increase susceptibility to tears. Abnormalities in knee biomechanics, such as altered joint loading patterns or malalignment, can exert excessive stress on the meniscal root, making it more vulnerable to injury. Genetic factors may play a role in predisposing individuals to meniscal root tears, although specific genetic markers remain to be elucidated.^[17] Certain systemic conditions such as rheumatoid arthritis or metabolic disorders may weaken the meniscus and contribute to root tears.^[18]

Physical examination

During a physical examination, commonly observed indicators include posterior knee discomfort during deep flexion and sensitivity along the joint line.^[20] McMurray testing yielded positive results in only 57.1% of cases, while effusion was evident in merely 14.3%.^[19] A new varus stress examination helped identify the avulsion of the posterior root of the medial meniscus. In this examination, the patient should be completely relaxed with the knee extended. When conducting the varus stress test, meniscal extrusion can be detected through palpation along the anteromedial joint line. The extrusion diminishes on restoring the knee to its normal alignment.^[21] Despite limited data to provide quantitative sensitivity or specificity, they advocated for its utility in diagnosis and clinical monitoring.^[21]

Imaging

The preferred imaging technique for diagnosing meniscal root tears and associated pathologies is MRI, which has high reported sensitivity and specificity, particularly with T2-weighted sequences [Figure 3]. Key MRI signs suggestive of root tears include root discontinuity, extrusion, and the ghost sign, which together enhance diagnostic accuracy. Extrusions larger than 3 mm on mid-coronal imaging have a strong correlation with degenerative changes, highlighting their importance for diagnosis.^[22]

Close

Figure 3:

Fast spin echo T2-weighted fat suppression images (a) sagittal section shows the oblique tear of the posterior horn of the medial meniscus extending into the root attachment (left arrow) and (b) coronal image with a change in signal intensity (right arrow).

Export to PPT

While challenges persist in visualizing the posterior medial meniscus root on MRI, efforts are focused on improving detection methods. Differentiating true medial meniscal root tears from other tear types is vital for determining appropriate treatment strategies. In addition, standard MRI protocols can detect lateral meniscal root tears, but the accuracy of MRI in identifying these tears has not been fully determined.

Non-operative treatment

The approach to meniscal root tear management is determined by the severity of the injury, the timing of surgical intervention for the injury, and the clinical status of the articular surface area. Surgery aims to restore normal articular load and knee joint motion, hence delaying the onset of OA. As a result, surgical management is usually not suggested for individuals with extensive and advanced cartilage degradation; however, it could be taken into account for individuals with specific cartilage deficiencies to help relieve symptoms.

The recommended approach is to avoid surgery for individuals with major additional health issues and advanced OA (Kellgren–Lawrence grade ≥3) as shown on radiographs. Patients in this category may find relief from symptoms using pain relievers and an off-loader brace that unloads the medial compartment. If non-operative treatment fails and patients progress to knee OA, partial or total knee replacement may be considered as a further option.

Meniscectomy

Meniscectomy has been linked to a greater likelihood of developing arthritis when compared to non-surgical treatment, while meniscal root repair has been an economically efficient procedure. Non-surgical treatment or meniscectomy for meniscal root tears may lead to unfavorable clinical results and require a transition to total knee arthroplasty, as suggested by various studies. Meniscal removal is now seldom recommended, except in cases of degenerative tears that are advanced or cause significant physical symptoms for the patient, despite the expected arthritic progression.

Root repair

Anatomic repair-transtibial pull-out repair

The method outlined includes sutures being passed through the meniscus root, brought back through tunnels created in the proximal tibia, and then anchored across an attachment, button, or anterior tibia bone bridge [Figure 4]. There are various variations in meniscal suture configurations, including two basic sutures, the horizontal mattress stitch, modified Mason-Allen (MMA), and two customized loop stitches. Studies have shown that two simple sutures minimize root displacement, exhibit higher stiffness, and supposedly show no significant variance from the more complex MMA suture. The anatomical footprint can be better replicated and biological healing can be improved through the use of single-tunnel and double-tunnel techniques.^[24] Fixation with a button is preferred because it is less intrusive and provides a reduced risk of soft-tissue damage than screw and washer fixation. This technique aims to provide stability and function with minimal complications and maximize the healing process.

Close

Figure 4:

Transtibial pull-out repair of a medial meniscal posterior root tear in a right knee.

Export to PPT

Non-anatomical root repair (all inside suture repair technique)

The evaluation of a tear in the posterior root of the medial meniscus involves the use of a probe inserted through an anteromedial portal. If the exposure of the posterior root of the medial meniscus is obstructed and if there is tightness in the medial compartment, an outside-in percutaneous release of the medial collateral ligament will be performed. Medial meniscus posterior root fixation will be done in a cerclage fashion superiorly and inferiorly to the capsular margins. There will be two vertical mattress sutures used to secure the posterior root tear of the medial meniscus through the anteromedial portal.

To avoid over-penetration, which may lead to neurovascular injury, the depth penetration is limited to 12–14 mm to prevent over-penetration to the posterior joint capsule. Thorough probing medial meniscus tightness ensured with posterior capsular attachment in cerclage configurations. A procedure will be carried out to vent the bone marrow in the intercondylar notch to enhance healing, through the introduction of bone marrow elements, such as mesenchymal stem cells, to migrate to the surface of the damaged cartilage. A hinged knee brace will be applied for the post-operative course. A proposed algorithm is presented in Table 1 for managing medial meniscal root tears.

Table 1: Management algorithm for medial meniscal root tear.

MMPRTs: Medial meniscus posterior root tears; K-L grading: Kellgren and lawrence grading

Post-operative rehabilitation

The operated knee will be restrained in a brace with the knee extended for 4 weeks. The patient will be allowed closed chain range of motion exercises. Active or passive range of motion will be allowed up to 90° starting on day 1 for 6 weeks. The patient will be kept non-weight bearing for four weeks followed by partial weight bearing with progression to complete weight bearing and a full range of motion by 8–10 weeks post-surgery. After the surgery, deep squatting and strenuous activity like running will be allowed at 4 months and 6 months, respectively.

To optimize conditions for healing after meniscal root repair, patients undergo a carefully structured rehabilitation protocol.

The rehabilitation program aims to promote healing while gradually restoring mobility and strength. Deep knee flexion exercises are integrated into the regimen to enhance flexibility and functionality.^[25]

Outcomes

As per treatment protocols, meniscal root tears have evolved significantly. Recent literature-based analysis has shown debatable outcomes following non-operative management versus operative management including meniscectomy and repair. Until 2005, there was a consistent increase in publications; from 2005 to 2022, there was an almost fourfold increase.^[26]

The transtibial pullout technique is reported to effectively restore knee joint motion in the vast majority of individuals when repairing meniscal root tear injuries. LaPrade et al. undertook a study that included 45 knees. They noted improvements in Lysholm scores and observed no substantial variations in operational result ratings between patients younger than 50 and those aged 50 and above.^[27]

Ozkoc et al.^[15] defined the clinical outcomes of patients who underwent partial meniscectomy, with a Level 4 retrospective study (67 patients, 56.7 months), comparing post-operative MRI and surgical outcomes. The clinical results were evaluated by Kellgren–Lawrence grading, Lysholm scoring, and radiological investigations which revealed that the average Lysholm score increased from 53 to 67. Pre-operative Kellgren–Lawrence Grade 2 (range 0–3) raised to 3 (range 2–4). Hence, they concluded that the arthroscopic partial meniscectomy for posterior root medial meniscus tears reduces symptoms but does not stop the progression of OA. Kim et al.^[28] investigated the outcomes of patients in two groups (28 with partial meniscectomy and 30 with arthroscopic transtibial pullout repair) and found that arthroscopic transtibial pullout surgery produced improved functional and radiological outcomes. The repair group achieved significantly higher International Knee Documentation Committee (IKDC) and Lysholm scores, with less joint space narrowing and less advancement to Kellgren–Lawrence grading.

Surgical repair, particularly a transtibial tunnel pull-out technique, has yielded excellent outcomes, ensuring anatomical reduction and fixation on the anterior tibia.^[29]

Jung et al.^[30] investigated the subjective and objective outcomes of all inside root repair of a posterior root medial meniscus tear in 21 knees over a 24–48-month period. Clinical evaluation was performed utilizing tenderness over the joint line, the McMurray test, and radiographic examinations. They concluded that no patients experienced joint line discomfort, effusion, or a positive McMurray test result after surgery. Significant improvements were observed in both Tegner activity level and Lysholm scores. The average medial meniscus extrusion was 3.9 mm preoperatively and 3.5 mm postoperatively (P > 0.05). Choi et al.^[31] proposed an arthroscopic all-inside approach to maintain the structural vitality and biomechanics of the meniscus instead of resorting to meniscectomy. A curette is used to remove the attachment of the posterior horn.

The posteromedial portal had two fiber wires and a metal anchor inserted through it. An anatomic insertion of the posterior meniscus root was done using a polydioxanone suture.

Zhu et al.^[32] in the study discussed a new arthroscopic repair technique for individuals more than 45–50-year-old patients with tears in the posterior root of the medial meniscus and assessed the outcomes of this procedure throughout 3–6 months of follow-up. The mean Lysholm score improved significantly, the median Tegner activity score improved, and the mean IKDC score improved.

As previously mentioned, research in the literature has shown that meniscal root tears are better treated with a variety of repair techniques than meniscectomy, provided that the root tear is amenable to repair. Stem cells and other biological treatments, such as platelet-rich plasma (PRP), are utilized to enhance the healing process for tears.^[33] Meniscal root tear repair may be a viable option to improve objective and subjective outcomes in clinical and radiological settings.