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Meniscal Root Tears: Current Concepts

Robinson JR, Jermin PJ

Volume 1 | Issue 2 | Aug – Nov 2016 | Page 35-46.


Author: Robinson JR[1], Jermin PJ[1].

[1] Avon Orthopaedic Centre Bristol, UK.

Address of Correspondence

Mr James Robinson, MB BS, MRCS, FRCS(Orth) MS
Avon Orthopaedic Centre, Bristol, UK
Email: info@KneeSpecialists.co.uk


Abstract

The menisci provide tibio-femoral joint congruity, stabilisation, shock absorption and proprioception. These functions are reliant on firm attachment to the tibial plateau at the meniscal roots. Meniscal root tears result in similar biomechanical consequences to total meniscectomy, but they remain easy to miss clinically and radiological evaluation may be unreliable. Different repair techniques are becoming more reproducible and laboratory studies have shown that the load bearing function of the menisci may, following adequate repair, be returned to approximate that of the intact knee. Whilst techniques continue to evolve, a lengthy period of protective post-operative rehabilitation remains necessary. It is hypothesized that restoration of the ability of the meniscus to dissipate load through the distribution of hoop stresses is projective of adjacent hyaline cartilage and the development of degenerate joint disease. subsequent progressive joint failure that may occur if they are left untreated.
Keywords: Meniscal Root Tear, Meniscal repair.


Introduction

The vital role meniscal integrity plays in the function of a healthy knee is well understood. As a result surgical treatment of meniscal tears has progressed. Previously, open total meniscectomy was performed for meniscal tears, however, the 132 fold increase in the rate of knee replacement that resulted condemned the technique to the annals of history (1). The treatment of meniscal tears now emphasises meniscal preservation when possible, with studies showing a reduction in osteoarthritis following meniscal repair as compared to tear resection (2). It has been demonstrated that tears of the meniscal root attachments de-function the effected meniscus and result in similar biomechanical consequences to total meniscectomy (3). Whilst the significance of meniscal root tears has long been recognised, it is only in the last decade that surgical techniques have evolved to allow the routine management of these lesions, aimed at improving symptoms and avoiding subsequent progressive joint failure that may occur if they are left untreated.

Meniscal Anatomy & Function
The menisci are 2 semi-lunar, fibrocartilage structures that surround the weight bearing surface of the medial and lateral tibial plateau (Fig. 1). They are wedge-shaped in cross section and crescent shaped in the axial plane. They are composed of 3 segments: an anterior horn/root, a body, and a posterior horn/root.(4,5). The medial meniscus is an asymmetric shaped structure, firmly attached to the joint capsule at its periphery (with, for example, the deep medial collateral ligament having both menisco-femoral and menisco-tibial fibres), thus rendering it relatively immobile and more prone to injury. The lateral meniscus is a much more symmetrical, incomplete O-shape and is less firmly attached making it a much more mobile structure to accommodate the increase in antero-posterior translation that occurs in the lateral compartment (during knee flexion, the lateral meniscus moves posteriorly by approximately 19mm, compared to only 4 mm for the medial meniscus (6)). Although the volumes of both menisci may be relatively similar, the lateral meniscus covers a significantly larger area of the tibial plateau than the medial meniscus (59% +/-6.8% vs 50% +/-5.5%) (7). The superior surfaces of both menisci are concave and thus congruent with the convex femoral articulation. The inferior surfaces are relatively flat, allowing them to effectively articulate with the tibial plateau (8,9).  Each meniscus is composed of an interlacing network of collagen fibres, proteoglycans and glycoproteins. They are composed of approximately 75% water, 20% type I collagen, and 5% of other substances including proteoglycans, elastin and type II collagen (10,11). In a study examining bovine menisci, Andrews et al. (12) found that the ultra-stucture of the meniscus transitioned from highly aligned, longitudinally orientated collagenous fibres in the outer rim to a woven, less aligned structure in the inner meniscus. They found that the outer meniscus closely resembled a ligamentous structure, whereas the inner meniscus more closely resembled hyaline cartilage. The role of the menisci is to provide tibio-femoral joint congruity, stabilisation, shock absorption and proprioception (9). They are essential for joint preservation (1,2). As the knee is loaded, joint compression acts to extrude the menisci in a radial direction towards the periphery of the joint. “Hoop stress” in the circumferential collagen bundles resist this meniscal extrusion (5,9,10,11). Two types of fascicle organisation are seen – braided and woven (12). Braided structures result in increased stiffness with increased deformation owing to increasing friction. This organisation is well suited to the circumferential hoop stresses that the meniscus is exposed to during loading. The woven structure is commonly used to withstand compressive loads; it converts compressive forces into tensile forces. The distribution of hoop stresses by the circumferential fibres helps to transmit even axial loads across the joint surfaces and approximately 50-70% of the total weight transmitted through either compartment is transmitted through each individual meniscus (13). This dissipation of load is protective of the adjacent hyaline cartilage, but is completely reliant on firm attachment of the menisci to the tibial plateau. The anterior and posterior horns of each meniscus are securely anchored to the tibial inter-condylar region by strong ligamentous-like root attachments. The anterior root attachments have relatively simple, planar insertions into the tibial plateau while the posterior roots have complex 3 dimensional insertions. (9,12,14) Knowledge of the anatomy of the meniscal root attachments is essential when considering repair as anatomic root repairs restore cartilage contact areas and minimise peak cartilage contact pressures better than non-anatomic root repair (15). The meniscal roots have three parts: the ligamentous mid-substance (root ligament), the transitional zone between the root ligament and meniscal body, and the bony insertion of the root ligament at the tibial plateau. (16) The transitional zone between the root ligament and the meniscus is considered to be the weakest link of the meniscus root (16) and this may explain the common finding of radial tears in the position particularly in degenerate menisci. The roots are very well vascularised, comparable to the red-red zone of the meniscus(16).

Medial Meniscus Anterior Root Attachment
The anatomy of the anterior medial meniscus root attachment is variable with 4 different types described by Berlet & Fowler (17). In 59% of knees the meniscus attached to the flat portion of the intercondylar region of the tibial plateau (Type 1). In 24% of knees the meniscus attached on the downward slope of the medial articular plateau towards the anterior intercondylar area (Type 2). In 15% of knees the root attached on the anterior slope of the medial tibial plateau (Type 3). In 3% the meniscus was only anchored by the peripheral coronary ligament with no direct attachment to the tibial plateau (Type 4). The anterior horn root attachment was associated with the fibres of anteromedial bundle of the ACL in 59% of knees. The anterior intermeniscal ligament (AIML) has been found to connect the anterior horns of both menisci in around 46% of knees although in 26% of knees it has been shown to run from the anterior horn of the medial meniscus to the lateral aspect of the joint capsule, anterior to the lateral meniscus. The significance of the intermeniscal ligament is unclear (18). Poh et al. (19) sectioned the AIML and found no change in the tibio-femoral contact mechanics. The authors concluded that the anterior root attachments result in the menisci distributing loads independently of one-another. In a separate study, however, Paci et al (20) sectioned the AIML and did notice significantly raised contact pressures within the medial compartment of the knee. As its role remains uncertain, it would seem reasonable to preserve and protect it during surgery if possible.

Medial Meniscus Posterior Root Attachment
Johannsen et al. (21) reported that position of the medial meniscus posterior horn root attachment was a mean distance of 3.5mm lateral to the medial tibial plateau articular cartilage inflection point and 8.2mm anterior to the most superior position of the PCL attachment site and a mean distance of 9.6mm posterior and 0.7mm lateral to the apex of the medial tibial eminence. Adjacent to the attachment of the posterior root are what some surgeons term the “shiny white fibres” (Fig. 2). These are easily recognisable and appear distinct to the root attachment although are continuous with the main posterior root attachment. Whilst not part of the central root attachment, it has been demonstrated that these supplementary ‘shiny white’ fibres significantly contribute to the biomechanical properties of the native meniscal root(16).

figure-1-and-2

Lateral Meniscal Anterior Root Attachment
This attaches just anterior to the lateral tibial eminence and and is intimately related to the tibial attachment of the ACL (Fig. 3a) . Zantop (22) et al reported that the centre of the anteromedial (AM) bundle of the ACL was, on average, 5.2mm medial and 2.7mm posterior to the lateral anterior root; while the posterolateral (PL) bundle was 11.2mm posterior and 4.1mm medial to the anterior root. Various studies have noted that the anterior horn of the lateral meniscus attaches to the ACL in all knees, sharing approximately 60% of their attachment sites (9,22,23,24,25). The lateral meniscal anterior root attachment is smaller than the medial meniscal anterior root, with average footprints of 44.5 mm2 and 93 mm2 respectively. The proximity of the lateral meniscus anterior root attachment to the ACL tibial attachment means that an ACL reconstruction tunnel placed postero-lateral in the ACL tibial attachment site may significantly weaken or disrupt the LM anterior root attachment (15).

Lateral Meniscal Posterior Root Attachment
The lateral meniscus posterior root attachment is posteromedial to the lateral tibial eminence apex, medial to the lateral articular cartilage edge, anterior to the PCL tibial attachment and anterolateral to the medial meniscus posterior root attachment. (9,25,26). Johannsen et al (21) also reported the centre of the lateral meniscal posterior root to be an area 4.3mm medial and 1.5mm posterior to the lateral tibial eminence (Fig. 3b) . Three different attachment patterns have been described (16). In 76% of cases, two insertion sites were found with the predominant component attaching to the intertubercular area with anterior extension into the medial tubercle and the minor component attaching to the posterior slope of the lateral tibial tubercle. In the remaining 24%, there was a solitary insertion site to either the inter tubercular area or the posterior slope of the lateral tubercle.

figure-3a-and-3b

Pathology & Epidemiology
The principle mechanical function of the menisci is to convert compressive loads into hoop stresses and relies on their firm attachment to the tibial plateau. Thus, when the meniscus root is torn, there is no restraint to the peripheral distortion of the menisci and meniscal extrusion occurs. The biomechanical consequences are of a decreased contact surface between the tibia and femur and supra-physiological cartilage contact pressures, analogous to a total meniscectomy (3) (Fig. 4). In a normal knee, peak articular cartilage contact pressures are on average, 3841 kPa. In the context of a medial meniscal posterior root tear, this can rise to 5084 kPa. The contact area falls from an average of 594mm2 in the normal knee to 474mm2 when there is a tear of the medial meniscal posterior root (27). It has been demonstrated that contact pressures and contact areas may be normalised following meniscus root repair. (3,28,29,30) The sequence of joint failure is thought to be: a root tear occurs, this results in greater meniscal displacement and gap formation at the root avulsion site when compressive loads are placed across the knee. Over time the meniscus extrudes as a result of unopposed radial forces. This leads to a combination of altered knee biomechanics and significant increases in articular cartilage contact pressures within that compartment resulting in degeneration and osteoarthritis (31).

figure-4

Anterior Meniscal Root Tears
Tears of the anterior roots are uncommon (11,32,33,34,35,36) but importantly, the anterior root attachment may be disrupted or weakened by iatrogenic injury (misplaced anterior cruciate ligament reconstruction tunnels and intra medullary tibial nailing entry sites being examples (15,37)). Medial Meniscal Posterior Root Tears. It is estimated that injury to the medial meniscus posterior root attachment may be present in 10-21% of arthroscopic meniscal repairs or meniscectomies (38,39,40). The true incidence may be higher owing to the limitations of current MRI to diagnose these tears. In addition the root attachment may not be routinely visualised by some surgeons who undertake knee arthroscopy. Increased age, female sex, raised BMI and varus alignment have all been associated with a higher incidence of medial root tears (38,39,40). Medial meniscus posterior root attachment tears are often more chronic and degenerate in nature, and may not be associated with an acute event.

Lateral Meniscus Posterior Root Tears
It has been suggested that the increased mobility of the lateral meniscus, results in the lateral meniscal root attachments being subjected to less stress than the medial side.(33,40,41). However the lateral meniscus is known to be an important restraint to the pivot shift (42) and injury to the lateral meniscus is implicated as a cause of the high grade pivot shift (43,44) Tears of the lateral posterior root have been observed in 7-9.8% of patients with an ACL rupture (45,46). The risk factors for tears here are largely unknown, associations with sporting activity and pivot-contact sports have been noted. (47,48) (Figure 5)

figure-5

Diagnosis
Clinical Presentation
Clinical diagnosis of meniscal root tears remains challenging. The signs and symptoms that commonly manifest with typical meniscal tears may not be present with meniscal root tears. Patients may present with joint line tenderness but without mechanical symptoms. Lee et al (49) found that in their series of 21 patients with medial meniscus posterior root attachment tears, only 14.3% and 9.5% of their patients, respectively, complained of locking and giving way. Most patients with a medial root tear do not recall a specific event leading to their pain (50). On examination, the most commonly encountered signs are posterior knee pain with deep flexion (66.7%) and joint line tenderness (31.9%). McMurray’s test may be positive in 57.1% and an effusion present in only 14.3% of patients (49). Seil et al (51) described a novel test for medial meniscal posterior root avulsions: the patient was fully relaxed and the knee in extension; during varus stress testing, the anteromedial joint line was palpated and meniscal extrusion was reproduced. Extrusion disappeared when the leg was brought into normal alignment. The reliability of this test, however, is currently unclear and we have not found it to be particularly useful.
figure-6-and-7-final

Diagnostic Imaging
In addition to the difficulties of clinical diagnosis, accurate radiological diagnosis is heavily reliant on imaging quality and the expertise of the reporting radiologist. In a study of 67 patients with arthroscopy proven posterior medial meniscal root tears, only 72.9% were detected by pre-operative MRI scanning, the remaining patients showed degeneration and /or fluid accumulation at the posterior horn without a visible tear(40). The posterior root of the medial meniscus may be best visualised on 2 consecutive T2 coronal MRI images as a band of fibrocartilage anchoring the posterior horn to the tibial plateau (Fig. 6). Meniscal root tears may be difficult to visualise directly and the relatively small size of the meniscal roots means that tears may be missed by standard 2 mm MRI sections. The presence of medial meniscal extrusion has been described as having a high correlation with the presence of a posterior root tear (Fig. 7) Meniscal extrusion is defined as partial or total displacement of the meniscus from the tibial articular cartilage. (52,53) More than 3mm of meniscal extrusion, on mid-coronal imaging, has been shown to lead to articular cartilage degeneration and is associated with complex meniscal tear patterns and tears of the posterior roots (53,54). Not all cases of meniscal extrusion, however, are a result of root tears. Magee (55) hypothesised that there may be a group of patients who stretch their meniscal roots, leading to extrusion but without a frank tear. Meniscal extrusion is less common in lateral tears for a number of reasons.

figure-8-and-9

The lateral compartment is subject to lower contact pressures than the medial side and hence lateral extrusion is less likely to occur. In addition to this, the lateral posterior root has further anchorage from meniscofemoral ligaments. They provide additional restraint to extrusion with a reported rate of 14% lateral meniscal extrusion if they are intact (56). If the meniscofemoral ligaments are not present or torn, in the setting of a posterior root tear, the extrusion rate of the lateral meniscus quadruples and approaches that of the medial meniscus. Another surrogate sign of a root tear is a ‘ghost sign.’ (Fig. 8) On a sagittal MRI cut, both the anterior and posterior horns should be visible. If the anterior horn is present but the posterior one is not, it is termed a ‘ghost meniscus.’ This finding is highly suggestive of a root tear and will often be found in tandem with extrusion on the coronal cuts (54,57). We have also found that the axial T2 weighted sequence to be useful for identifying meniscal root tears, particularly radial tears adjacent to the meniscal root. (Fig. 9). Tibial bone marrow oedema may be noted adjacent to the root attachment in acute meniscal root avulsion (Fig. 10). Bone marrow oedema, seen more peripherally in tibia, or affecting the medial femoral condyle may develop as the result of overload within the compartment, as a result of loss of meniscal function following a medial root tear (Fig. 11)

figure-10

Arthroscopic Assessment of the meniscal root attachments.
Due to the difficulties of accurate clinical and radiological diagnosis, the gold standard for determining the presence of a meniscus root tear remains arthroscopic assessment (55).

figure-11

Placement of the anterolateral arthroscopy portal high and adjacent to the patella tendon facilitates viewing of the medial meniscus posterior horn root attachment with the arthroscope placed in the intercondylar notch, adjacent to the PCL (Fig. 12). Sometimes soft tissue (synovium and fat) overlying the PCL may need to be removed with either shaver or radio-frequency ablation device to improve the view of the posterior root attachment of the medial meniscus (Figure 13). The senior author has not found a “reverse notch plasty” (as described by some authors (58)) to be necessary, however, a medial collateral pie crusting is almost always required for medial posterior horn root repair.

figure-12

Classification
The most commonly used classification system for posterior root tears is the LaPrade classification (Figure 14) (59). This is an anatomic classification system: Type 1 (7% of tears) are partial thickness, stable root tears. Type 2 (68% of tears) are complete tears within 9mm of the root attachment; this is further subdivided into 2A, 2B & 2C, located 0-3, 3-6 & 6-9mm respectively from the root attachment.

figure-13-and-14

Type 3 (6% tears) are a bucket handle tear with complete root detachment. Type 4 (8% tears) are complex oblique tears with complete root detachments extending into the root attachment. Type 5 (8%) are bony avulsion of the root. This classification is purely anatomical and does not offer a guide to treatment or prognosis. West et al. classified lateral meniscus root tears associated with an acute ACL injury. Three types of tear were identified at arthroscopic assessment: Type 1 were root avulsions. Type II were isolated radial split tears within one centimetre from the root insertion. Type 3 were complete root tears with radial and longitudinal elements (60). Another classification has also been described relating to the integrity of the menisco-femoral ligaments (MFL): Type 1 tears are avulsions of the root. Type 2 are radial tears of the lateral meniscus posterior horn with an intact meniscofemoral ligament. Type 3 is complete detachment of the posterior meniscus horn (61). Again these classifications are descriptive and do not, yet, guide treatment or prognosis, although it is suggested that lateral meniscus posterior root tears, in which the meniscofemoral ligament remain intact, may not require treatment.

figure-15

Treatment
There are three treatment categories for meniscal root tears: non-operative, partial meniscectomy and meniscal repair. Historically, the first two options have dominated. Non-operative treatment of these injuries still has a role. In poor surgical candidates (multiple co-morbidities, advanced age or significant underlying degenerative joint disease) an initial trial of non-operative treatment remains an appropriate first line treatment. When considering surgery, particularly when repairing these tears, it is important to appreciate any coronal plane malalignment that may be present in the patient. For example: repairing, and not offloading, a posterior medial root tear in a patient with significant genu varum, may be at higher risk of failure unless a concomitant corrective osteotomy was undertaken to offload the compartment and the repair (Fig. 15)

Non-Operative Treatment
Non-operative treatment fails to address the abnormal biomechanical environment that these tears create, and may lead to progressive osteoarthritis (62). In certain groups of patients (elderly, the obese, poor surgical candidates, or patients with advanced underlying degenerative joint disease) non-operative treatment may be reasonable. Symptomatic treatment with NSAIDs (oral or topical), activity modification and offloading braces may alleviate the joint pain associated with root tears. Initial bone marrow oedema as a result of the changed loading in the compartment may settle.

Operative Treatment
Meniscectomy
Historically, partial or total meniscectomies have been performed for root tears, typically providing short-term symptomatic relief with unknown long term consequences. An recent retrospective study of 58 patients with medial meniscal root tears who underwent either meniscectomy or root repair reported that while both treatments significantly improved subjective outcome scores (Lysholm & IKDC scores, p < 0.05), the repair group had more improvement and less progression of arthritis at mean follow up at 4 years (30). For patients with chronic root tears and symptomatic grade 3 or 4 chondral lesions who fail non-operative treatment partial meniscectomy remains the treatment of choice. If resecting a root tear, care must be employed not to debride the whole footprint otherwise a functionally meniscectomised knee will be created. Advantages of partial meniscectomy over repair are decreased operative time, less taxing post op recovery regime and an earlier return to sports / activities.

Meniscal Root Repair
Meniscal root tear repair may provide symptomatic relief and reduce abnormal articular cartilage loads implicated in the development of degenerative joint disease. Indications for meniscal repair are expanding but at present the main indications for root repair are: (1) acute traumatic root tears in patients with no underlying arthritis, with the aim of preventing the development of arthritis & (2) chronic, symptomatic root tears in young/middle aged patients without significant pre-existing arthritis (23,63). Lateral meniscus tears are most commonly associated with ACL tears and should be repaired concomitantly. Medially there are usually two distinct injury patterns – acute & chronic. An acute tear is often associated with the multi-ligamentous injured knee, particularly a complete MCL tear where the meniscocapsular ligaments are intact but the meniscus is avulsed from the root (63). In this setting there is a clear indication for meniscal root repair to prevent progressive joint failure. Conversely, chronic injuries are much more insidious in nature and have been reported to result in rapid ipsilateral compartment cartilage degeneration if undetected (63). The treating surgeon must distinguish if the tear is causative or resultant from the arthritis, which can be a difficult distinction to make. If there are only early chondral changes on imaging with evidence of a root tear and meniscal extrusion, repair would be indicated to prevent progression of arthritis. The two most common methods of meniscal root repair are: transosseous suture repairs and suture anchor repairs. It is important to note that non-anatomical meniscal root repair has a substantial deleterious effect on meniscal function (64).

Suture Anchor Technique
This technique has a theoretical advantage that it does not involve drilling a tibial tunnel, which may be useful in the presence of concomitant ligamental reconstruction. It uses “all-inside” fixation, and avoids the need for a distal fixation which potentially places abrasive forces on the sutures used. The shorter menisco-suture construct may reduce micro-motion at the repair site (65) The technique does, however, require the placement of a posterior arthroscopic portal. The technique described by Engelsohn et al (66) used an accessory posteromedial portal. The repairs were tensioned using standard arthroscopic knot tying techniques from the anteromedial portal. The authors stated that in a ligamentously stable knee, the accessory (high PM) portal was necessary to achieve appropriate anchor placement. Others have reported a similar technique for repair of posterior medial root tears, with placement of high PM portal, approximately 4cm above the joint line and posterior to the medial femoral condyle, with insertion of a double-loaded metal suture anchor and suture passage using a suture hook and a shuttle suture(67).

Transosseous Tunnel Suture Repair
There have been several variants of this technique described (10,68,69,70,71). The advantage of transosseous repair is that a posteromedial arthroscopy portal is frequently not required. As with all cortical suspensory fixation methods, there has been concern about a ‘bungee effect,’ with transosseous tunnel meniscal root repair, and resultant micro-motion at the repair site as a result of the long menisco-suture construct. Feucht et al (65) found that transosseous root repair resulted in 2.2mm +/- 0.5 mm of displacement under cyclical loading in a porcine model compared with 1.3 mm +/- 0.3 mm with suture anchor repair. However, although associated with less micro-motion the technique of placing a suture anchor in a small space while achieving accurate reduction of the tear and preserving the native articular cartilage is technically challenging. Yung et al (67) reported that the suture anchor may loosen and protrude into the joint over time. LaPrade advocates the use of two tibial tunnels for repairs of radial tears of the medial meniscus, siting less gaping after cyclical loading in laboratory conditions, and also significantly stronger ultimate failure loads. (72) We have found that trans-osseous repair allows accurate tear reduction and may also enhance meniscal healing due to the effect of the trans-tibial drilling, with stem cells from the bone marrow entering the intra-articular space (65). It is the senior author’s (JRR) preferred technique of fixation: a standard arthroscopy is performed via anteromedial and anterolateral portals. An accessory anteromedial portal may also be used. In medial repairs, a ‘MCL pie-crusting’ is almost always required to gain sufficient access to the tear and posterior root attachment side (Figure 16 a and b) . This technique has been shown to increase the medial joint opening by 3-4 mm (73,74) and does not result in long term valgus laxity or adverse clinical outcomes (75).  The tear is identified and the root attachment repair site is debrided using an RF wand, /shaver / curette to remove scar tissue down to bone to improve healing. Using arthroscopic graspers, the meniscus is pulled towards the attachment site to ensure that the tear may be reduced (Figure 16 c) .Particularly in chronic cases is may be necessary to mobilise the torn meniscus by freeing it from a scar tissue adherence to the the posterior capsule. This may be achieved with arthroscopic scissors and / or RF wand. With the root attachment site prepared and the tear mobilised, a tip aimer is introduced through the antero-medial portal. We utilise an standard ACL tip aimer for lateral meniscus root repairs (Accufex, Smith and Nephew, Andover MA). For medial meniscus posterior horn repairs, however, we use the labral repair attachment for the Accufex aimer which is flat and more easily positioned at the posterior horn root attachment site without injuring articular cartilage (Figure 16d). Tip aimers specific for meniscus root repair are commercially available. A 2.7mm passing pin is drilled to the meniscus root attachment site and then over drilled with a 4.5mm cannulated drill. The drill is left in situ and loop of No1 nylon passing suture passed up the drill with a suture passer, grasped and retrieved through the anteromedial portal (Figure 16e).  An 8 mm arthroscopic cannula is placed into the AM portal facilitate suture management and passage. A suture passing device may then be used to pass suture or tape across the meniscus (Figure 16f). The senior author prefers the FirstPass ST device (Smith and Nephew, Andover, MA) as it may be used to pass 2 mm tape (UltraTape, Smith and Nephew, Andover, MA) directly across the meniscus (Figure 16 g). 2 tapes are normal used (Figure 16h) although sometime 3, particularly if there are vertical splits exist in the meniscus (more common with chronic tears and it is necessary to have tape on both sides of the vertical split). For medial meniscus posterior horn root repairs in tight knees, despite an MCL pie crust, access for the suture passing device may be difficult and risk articular cartilage injury. In this situation a 70 degree suture passer (eg AcuPass, Smith and Nephew, Andover, MA) may be used to pass a loop of nylon across the meniscus and this then is used to shuttle the tape across the meniscus. Once passed through the meniscus, the tapes are individually passed down the trans-osseous tunnel. Reduction of the tear is then performed under direct vision (Figure 16 i) by pulling on the tapes which are then tied over a post screw and washer of a button at the external aperture of the trans-osseous tibial tunnel creating a suspensory fixation. In vitro studies have suggested that the use of two parallel tunnels may reduce displacement of the repair (76). Different suture repair techniques have been trailed in the laboratory. Knopf et al. (77) showed that a simple number 2 suture repair using 2 sutures had the lowest pull out strength (Mean approx 60N load to failure). More complex suture patterns (loop suture and modified Kessler) improved pull out strength, however more complex suture patterns are prone to creep and subsequent displacement of the repair. The use of tape improves the pressure distribution on the meniscus and pull out strength (Robinson et al. unpublished data).

figure-16

Postoperative Rehabilitation
It is important to note that no fixation method is able to restore the strength of the native root attachments. Improved healing rates have been shown in studies where patients were kept non-weight bearing for more than 8 weeks (10,30,48). A slow, conservative post-operative rehabilitation is therefore recommended (77). Most authors advocate full leg extension in either a cast or knee brace (30,32,48,68) for 2 weeks after repair. We allow flexion after this, however this is limited in order minimise stress on the repair to 0-90 degrees for medial meniscal root repairs and 0-70 degrees for lateral (because of the increased antero-posterior excursion in the lateral compartment with knee flexion (78). No loaded flexion greater than 90 degrees or twisting is allowed for 3 months post-op. Return to full activities or sports is generally achieved at 5-6 months post-operatively.

Clinical Outcomes
Studies reporting the outcomes following meniscal root repair are generally limited to case-series or cohort studies. It is perhaps unsurprising that the results are somewhat conflicting (48,65,67,79,80,81) given that the indications for meniscal root repair techniques have evolved and that several different surgical techniques are described.  All clinical studies report improvement in subjective outcomes measures at 2-3 years after repair (48,49,67,79,80). Structural outcomes evaluated with MRI or second look arthroscopy have produced conflicting results. Kim et al (50) reported reduced (improved) extrusion following both trans osseous tunnel and suture anchor type repair techniques, but Jung et al (79) found no change in meniscal extrusion after suture anchor repair. Moon et al (80) reported increased meniscal extrusion following the trans-osseous suture technique however, the patient population included people with severe osteoarthritis and a relatively high age (59 years), the poor results may have been attributable to these patient factors, both of which are are considered by some to be contra-indications to meniscal root repair. However other authors (R LaPrade, personal communication 2016) have not shown worse results related to patient age, given the absence of significant arthritic change.  Lee et al (49) performed second look arthroscopies in 10 patients who had under gone trans-osseous repair, they found healing in all patients 2 years after repair. Conversely, Seo et al (79) performed second look arthroscopies in 11 patients and found that none had complete healing at 1 year post-operatively. However, 82% of these patients, had chronic meniscal root tears, perceived as having a poorer healing capabilities (76,79). Importantly, the timing of the introduction of weight bearing postoperatively appears to have an important role in the success of healing of the meniscus root repair. Studies in which where weight bearing was allowed prior 6 weeks showed poorer healing rated compared with those in which the introduction of weight-bearing was delayed until to 8 weeks post-operatively (49,50,67).

Conclusions
Meniscus root repair is technically demanding with a steep learning curve. However, techniques are becoming more reproducible and straightforward, particularly as instrumentation to facilitate the procedure has improved and continues to evolve. The basis of treatment is founded upon sound biomechanics principles that have been robustly demonstrated in laboratory studies and the clinical finding that root injuries can lead to rapid joint failure. Meniscus root repair demonstrably improves the meniscal function of load transmission, rendering biomechanics close to the intact state. The objective is to slow or prevent joint deterioration yet, established osteoarthritis would appear to a be a contra-indication to repair. Whilst there are studies showing improvements in patient outcomes following meniscal root repair the impact on delaying the progression of osteoarthritic change remains to be unequivocally demonstrated and it would be wise for enthusiasm in this regard to be moderated until further studies have reported longer-term outcomes.


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How to Cite this article:. Robinson JR and Jermin PJ. Meniscal Root Tears: Current Concepts. Asian Journal of Arthroscopy  Aug – Nov 2016;1(2):35-46.

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All-Inside Meniscus Repair

William M Weiss, F. Alan Barber

Volume 1 | Issue 2 | Aug – Nov 2016 | Page 8-13


Author: William M Weiss[1], F. Alan Barber[2]

[1] Texas Tech University Health Sciences Center El Paso, Texas.
[2[ Plano Orthopedic Sports Medicine and Spine Center Plano, Texas.

Address of Correspondence

Dr William M Weiss
Texas Tech University Health Sciences Center Department of Orthopedic Surgery and Rehabilitation 4801 Alberta Avenue El Paso, Texas 79902.
E-mail: william.m.weiss@ttuhsc.edu


Abstract

 Meniscal surgery has undergone a considerable shift in goals over the last century. While early meniscal surgery consisted of mostly total meniscectomy, recognition of the importance of this structure resulted in a shift to partial meniscectomy, and then to repair in appropriate patients. The over-reaching goal is now the preservation of meniscal tissue to minimize the risk of osteoarthritis, particularly in the young athlete. Technologic advances in arthroscopy and instrumentation have allowed the development of minimally invasive techniques, which decrease the risks associated with open surgery. While no meniscal repair technique has been demonstrated to be superior in its outcomes, the all-inside technique requires no accessory incisions and minimizes the risk to posterior structures. While the early all-inside implants have been shown to risk chondral damage, the literature demonstrates that newer suture-based implants do not share these complications, and result in the healing of appropriate tears.
Key Words: All-inside, Meniscal tear, Meniscal repair, Chondral injury.


Introduction

The first open meniscal repair was performed in 1885 [1], though resection has been more common. With the advent of arthroscopy, minimally invasive techniques replaced open repairs, and provided better access to difficult areas while minimizing surgical risks. The inside-out suture repair was initially the described, and continues to be used with excellent results [2]. The outside-in repair was developed later to decrease risk of injury to posterior neurovascular structures [3]. In recent years, advances in instrument and implant technology have allowed the development of all-inside repair techniques. These rely on specialized implants, but avoid additional incisions, decreasing risk to posterior neurovascular elements, and reducing surgical times [4]. The purpose of this review is to examine the evolution of the all-inside meniscal repair technique, with outcomes and complications.

Meniscus Anatomy, Function, And Healing:
The menisci are crescent shaped fibrocartilaginous structures situated in both the medial and lateral compartments of the knee, between the femur and tibia. Each meniscus has an anterior and posterior horn, and is attached to the tibia by the anterior and posterior meniscal roots and to the peripheral capsule by the coronary ligaments. They are triangular in cross section, conforming to both the distal femur and proximal tibia. This conformity effectively deepens the articular surfaces of the knee, providing shock absorption and contributing to stability, particularly with injury to stabilizing ligaments. This also increases the surface area for load distribution to the articular cartilage, decreasing contact stresses by converting vertical compression stresses to radially oriented hoop stresses [5, 6]. By maintaining space in the joint, the meniscus improves diffusion of synovial fluid, and provides nutrition and lubrication to the cartilage. The healing capacity of the meniscus is determined primarily by blood supply, as it is largely avascular and does not typically heal spontaneously. The meniscus is divided into zones in accordance with blood supply and healing capacity. The peripheral third (within 3 mm of the meniscosynovial junction) is well vascularized, as the blood supply enters the here [7]. This zone is referred to as red-red, and is mostly likely to heal. The inner third (over 5 mm from the meniscosynovial junction) receives no vascular supply, is called the white-white zone, and is least likely to heal. The middle zone, called red-white (between 3 to 5 mm from the meniscosynovial junction), has some vascularity [7, 8]. Red-red zone tears are commonly repaired in appropriate patients, while repairs of red-white zone tears are less likely to heal.  Meniscal tear characteristics also influence healing potential. Longitudinal vertical tears (including bucket handle tears and meniscocapsular tears) have the capacity to heal with repair, while degenerative or complex (multi-planar), radial, horizontal, or flap tears are much less likely. Larger and less stable meniscal tears have higher failure rates, as have those repaired more than 8 weeks from injury [9]. Lateral compartment tears are also more likely to heal than those occurring medially [9]. This may be due to increased blood supply to the posterior horn of the lateral meniscus.

Meniscal Repair Technique
To overcome the inherent physiologic challenges of meniscal repair, the environment and technique must be optimized. Factors controlled by the surgeon include tissue preparation, the stability of fixation, knee stability and leg alignment, and post-operative rehabilitation. Preparation should include rasping of the tear, and the perimeniscal synovium. This stimulates the healing response [10], and can allow healing of isolated stable tears without fixation, particularly with concomitant ACL reconstruction [10,11]. Some advocate trephination to create vascular access channels, which may contribute to fibrovascular healing of avascular areas [12]. The addition of fibrin clot [13, 14], platelet-rich fibrin matrix [15], and collagen matrix with bone marrow [16] have been demonstrated to aid healing. Meniscal repair with associated ACL reconstruction improves healing, possibly by increasing blood in the joint, while lack of ACL function practically assures failure from stresses on the repair [17, 18]. ACL deficiency increased the failure rates of meniscal repair from 5% to 46% [19], demonstrating the importance of stability. Normal knee alignment also is required for successful meniscus repair outcomes. Forces within the knee, and through the meniscus, during normal gait can reach four times body weight and present significant challenges to fixation [20]. However, during unloaded knee motion the meniscus experiences only compressive forces [21, 22]. Therefore, fixation should maintain tissue approximation and neutralize sheer stresses. For suture-based repairs, vertically oriented non-absorbable sutures are considered the gold-standard, because of load to failure [23]. This configuration encircles the strong circumferential fibers, maximizing strength. Meniscus repairs are weak at the scar after 12 weeks 24, and visual evidence of healing at second-look arthroscopy has been seen at up to four months [25].

Surgical Technique Of Meniscus Fixation:
Arthroscopic techniques are the preferred method for meniscal repair; however no consensus exists as to the best technique. The most common indication for all-inside repair is tears of the posterior horn, as risk to neurovascular structures is decreased. All-inside repairs require less surgical time than other methods [26]. However, all-inside repairs do require an intact meniscal rim, highly specialized instruments, and implants. All-inside meniscal repair devices have progressed from rigid implants to current adjustable suture-based devices. Earlier versions of all-inside devices are no longer widely used or recommended. The adjustable suture-based all-inside devices are the state of the art.

Self-Adjusting Suture Containing Implants
The current generation of all-inside devices use ultra-high molecular weight polyethylene (UHMWPE) containing suture to connect typically non-absorbable poly ether-ether-ketone (PEEK) anchors. The suture is pre-tied, typically with a sliding and self-locking knot. Insertion instruments require only standard anterior portals, and often use a disposable cannula or a skid to aid passage. The meniscus repair device is inserted through the inner meniscus fragment to a pre-determined depth of the peripheral rim, often guided by the cannula. Once both anchors are deployed, the sliding-locking knot is cinched to compress the tear. This adjustability allows appropriate tensioning for reduction and healing, and the option to place horizontal, oblique, or vertical configurations.

figure-1-2-and-3

The FasT-Fix (Smith & Nephew, Andover, MA) was the first adjustable suture-based device (Fig. 1). It consisted of two 5 mm anchors, made of either poly L lactic acid (PLLA, absorbable) or polyacetal (nonabsorbable) connected by No. 0 non-absorbable braided polyester suture. The anchors are delivered by an instrument that is either straight or angled 22°. Once both anchors span the tear, the pre-tied sliding-locking knot is tensioned using a knot pusher/suture cutter. The original design was modified to become the Ultra Fast-Fix by reconfiguring the needle to facilitate insertion, and replacing the suture with a stronger No. 0 UHMWPE UltraBraid. The current iteration is the FasT-Fix 360 (Fig. 2), in which the anchors have been reconfigured to PEEK with an arrow design, and the suture is now No. 2-0 UltraBraid.

The RapidLoc (Mitek, Raynham, MA) was an adjustable suture-based device, consisting of a PLLA “backstop” and a PLLA or polydioxanone (PDS) “top hat”, connected by either a No. 2-0 absorbable Panacryl or non-absorbable braided polyester suture (Fig. 3). The “backstop” anchor was placed across the tear to be extra-capsular, and the pre-tied sliding knot and “top hat” was then advanced, compressing the tear. The instrument included straight, 12° and 27° angled needles.

The OmniSpan (Mitek, Raynham, MA) replaced the RapidLoc, and uses a loop of No. 0 OrthoCord (55% PDS and 45% UHMWPE) suture between two PEEK anchors (Fig. 4). The sliding-locking knot is outside the loop, reinforcing the first anchor, and forming a double suture repair without a knot on the articular surface. Both loops of the repair are tightened concurrently, allowing equal tension. This device allows sutures to be placed in both horizontal and vertical mattress fashion.

figure-4-and-5

The Meniscal Cinch (Arthrex, Naples, FL) has undergone incremental improvements since its inception (Fig. 5). The device is inserted with a 15° curved “gun” containing two separate trocar needles. It has an adjustable depth limiter on the handle, which is most commonly used at 18 mm. Each needle is loaded with a tubular PEEK anchor, and connected with a No. 2-0 FiberWire composed of UHMWPE and braided polyester (Arthrex Inc, Naples FL). The system includes a blue plastic “shoehorn” cannula to facilitate insertion, which is 6 mm in diameter and requires a large portal. The instrument allows placement of a vertical mattress stitch, secured with a pre-tied sliding-locking knot. After insertion, the first needle is removed and handed off. The second needle is “clicked” into position, and then a second device is inserted. Once both devices are deployed, the suture is gently pulled at the handle to tension the repair. A disposable knot pusher/suture cutter is provided.

The Sequent meniscal repair device (ConMed Linvatec, Largo, FL) utilizes No. 0 Hi-Fi (braided UHMWPE) suture with up to seven PEEK anchors measuring 1.3 mm in diameter and 5.1 mm long (Fig. 6). Each anchor is placed individually through the meniscus, with a straight or 15° curved instrument, and deployed on the extra-capsular surface. The suture is then tensioned to set the anchor into the tissue, and additional anchors can then be placed with the same device. A minimum of 3 anchors must be inserted to complete the repair, although more can be used to create an all-inside continuous stitch. This allows numerous stitch configurations, from continuous to interrupted stitches, and vertical or horizontal mattresses. This is the only device that can place multiple stitches without removal from within the joint. However, the technique is demanding, and practice in the laboratory prior to use is advised. The set includes a side-loading disposable suture cutter for use at completion.

figure-6-7-and-8

The MaxFire MarXmen (Biomet Sports Medicine, Warsaw, Indiana) is an self-adjusting all-inside all-suture implant with No. 0 MaxBraid PE (UHMWPE) and two braided polyester sleeves serving as anchors (Fig. 7). It is similar to the JuggerKnot all-suture anchor in design and function, but modified for the meniscus. The instrument uses a needle (straight or curved) to insert the suture and two polyester anchors through the meniscus. The sliding-locking knot allows tensioning, and devices can be placed in either a horizontal or vertical mattress fashion.

The CrossFix meniscal repair system (Cayenne Medical, Scottsdale, AZ) passes a No. 0 Force Fiber (UHMWPE) suture through two parallel 15 gauge hollow needles (straight or curved 12°, Fig. 8). Once the needles penetrate the meniscus, crossing the tear, a small shuttle passes the suture from one needle to the other on the extra-capsular surface. As the needles are withdrawn, a 3 mm horizontal mattress suture is left, and a pre-tied sliding Weston knot is advanced to secure the reduction. Additional arthroscopic knots can be added as reinforcement, if desired.

The AS (all suture) Repair device (Covidien, Minneapolis, MN) is similar to the CrossFix in design and function (Fig. 9). While the two needles are the same size, the AS repair device has conical solid needles with a polymer coat (NuCoat) to facilitate penetration. The instrument can be straight or curved 15°, and passes a No. 2-0 UHMWPE suture using a similar shuttle needle, but uses a modified Tennessee slider knot with two half hitches to secure the repair. Both instruments result in a 3 mm wide horizontal mattress, with a knot on the meniscal surface that risks chondral injury. Due to the instrument dimensions, only horizontal mattress sutures are possible. Conceptually, this newest generation of all-inside suture based devices allows improved reduction, tissue compression, and stability compared to previous iterations. The overall goal of all-inside meniscal repair devices is to decrease complications seen with the earlier generations, and promote healing. However, these devices can generate significant tension which may be detrimental, leading to implant failure. Few investigations regarding outcomes and complications of these adjustable all-inside suture implants are available in the literature.

figure-9

Results Of All-inside Meniscal Repair:
Arthroscopic meniscal repair methods have similar outcomes to open methods, with the gold standard inside-out suture repair having a success rate of 82% [17, 27], and outside-in suture repairs having success rates as high as 87% [28]. The original suture-based all-inside technique described by Morgan reported good results, but without any long term follow-up [29]. Early devices which rely on arthroscopic knot tying demonstrate up to 90% success initially, but this declines to 81% at 1 year [30].

Suture based implants have good strength, and are biomechanically equivalent to the gold standard vertical mattress sutures [31,32]. However, as this is the latest generation of all-inside devices, there is little long term outcome data available. The RapidLoc has demonstrated success rates of 86 to 91% [33, 34, 35], but there are reported failure rates of 35% [36] with complications reminiscent of rigid devices [37]. Longer term follow-up of these devices shows re-operation rates of 48% [38]. The FasT-Fix has also shown success rates from 82 to 92% [39,40], but with limited reports of complications. All-Inside devices have been demonstrated to have greater failure strength than inside out alternatives in the repair of radial meniscal tears [41].

Comparison Of Meniscal Repair Devices: Author’s preferred technique:
A human cadaver knee based comparison of several all-inside meniscus repair devices was carried out by the senior author to compare the technical ease, reproducibility, and consistency of using these devices in human meniscus tissue. A needle penetration depth limited to 18mm was found to be anatomically safe. Curved needles effectively reached the posterior horn with minimal articular cartilage injury. However, significant differences were observed in the technical ease, reproducibility, and consistency of all these devices. The FastFix 360 and OmniSpan were easiest to insert, least likely to excoriate articular cartilage, and most consistent in performance. Yet, the OmniSpan did not have any knot or device on the surface to later damage the articular cartilage. Based upon this data the author’s preferred technique uses the OmniSpan. The control provided by the gun allows for better positioning of the implants and decreased articular cartilage damage. Prototypes of the next generation of OmniSpan (the TrueSpan) perform even better but await clinical experience to confirm our expectations of superior performance.

Complications
All-inside meniscus repair has all the known risks and potential complications of knee arthroscopy. These occur in approximately 1% of patients, and include neurovascular injury, infection, and thrombophlebitis [42]. While neurovascular injuries are likely the most common complication of knee arthroscopy, when compared to other meniscal repair techniques the risk of this complication with all-inside repairs is decreased. Neurologic injury rates as low as 2% have been reported for all-inside techniques, in comparison to 9% for inside-out repairs [43]. The development of the all-inside technique was primarily to eliminate the need for accessory incisions and suture passing that are responsible for most of the neurovascular risk, so that repairs in the posterior horn can be done more safely. Injury to the saphenous nerve is most frequent, but as it is a sensory nerve this is often of little consequence [44]. Peroneal nerve palsy and popliteal artery pseudoaneurysm have also been reported 45, as have cases of cyst formation and synovitis [46, 47]. Complications associated with the adjustable-suture based current generation of all-inside devices include over penetration of the implant, loss of fixation, inadequate tension, and problems with implant deployment [48,49]. An overall complication rate for all-inside repair of 19% has been reported comparable to the gold standard [43]. The RapidLoc has caused cartilage injury in limited reports [50,37], and cadaveric studies have demonstrated placement of these implants may be challenging, but the significance of this is unclear [48,49]. Complications of all-inside repair can be minimized with detailed knowledge of anatomy, proper portal placement, measurement of meniscal depth, and placement of the indicated implant in an appropriate and secure manner.

Rehabilitation:
Post-operative rehabilitation following meniscus repair is highly variable between surgeons, with little consensus in the literature. Early knee motion is thought to be advantageous, as prolonged immobilization is known to lead to stiffness, atrophy, and impaired healing of the meniscus [51]. However, higher degrees of knee flexion cause considerable posterior translation of the femoral condyles, which increases forces within the meniscus and may stress repairs [52]. Weight-bearing can help reduce and stabilize longitudinal (bucket-handle) meniscus tears due to radially directed hoop-stresses [22], but loads with knee flexion cause increasing shear forces in the meniscus. These forces are increased almost four times with the combination of weight-bearing and flexion to 90 degrees [52].  Based on this information, weight-bearing in full extension poses little risk to repairs of longitudinal meniscal tears, and may aid with reduction and healing. However, for radial or meniscal root tear repairs (which are challenging with limited success), weight bearing is not advisable since circumferential fibers are not intact and the tear will be distracted. Accelerated rehabilitation programs designed to return patients to sport earlier have been described [53, 54], permitting early full weight bearing and unrestricted knee motion. The only limitations on return to sport in accelerated programs are the resolution of postoperative effusion, and return of full motion. Thus far, results of accelerated programs have shown return to sport without re-injury or complications. Meniscal repair in the setting of ACL reconstruction presents unique challenges. There is no evidence to support slowing ACL rehabilitation for an associated meniscal repair, and with the increased stability of new adjustable suture-based devices there is less reason to do so 55. The author’s current protocol for modern all-inside devices allows immediate range of motion from 0 to 90 degrees, immediate full weight bearing, early closed-chain strengthening, flexibility and endurance training. After 2 months, full flexion is allowed, and full return sport is permitted once the knee has no effusion, has regained full extension, and demonstrates flexion to greater than 135°.

Conclusions
Advances in arthroscopy and instrumentation technology have made all-inside meniscal repair popular and effective in appropriate meniscal tears. While no arthroscopic method has proven to have superior outcomes in the literature, all-inside methods are indicated for posterior horn meniscal tears to minimize the risk to neurovascular structures. The adjustable suture-based designs have so far demonstrated improved versatility and outcomes comparable to other methods. The versatility of these implants also allows their use in meniscal repairs that are not repairable by other methods, promoting the preservation of meniscal tissue when possible.


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How to Cite this article:. Weiss WM, Barber FA. All-Inside Meniscus Repair. Asian Journal of Arthroscopy  Aug – Nov 2016;1(2):8-13.

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