Posterior meniscal root tears: a case report and update of current concepts
W.A. van der Wal1,3 S.J. Maresch2,3 1Orthopaedic surgeon, Department of Orthopaedic Surgery, ZGV, Ede, The Netherlands 2Radiologist, Department of Radiology, ZGV, Ede, The Netherlands 3Sports Valley High Performance Medical Center, ZGV, Ede, The Netherlands Corresponding author: W.A. van der Wal: wavanderwal@me.com
Introduction: posterior meniscal root tears used to be an underexposed injury due to lack of awareness and a poor understanding of the importance of the meniscal root for a normal knee function. Purpose: to present a case and overview of recent literature. The content of this paper can be used to write an addition to the Dutch knee arthroscopy guideline in which posterior meniscal root tears are not mentioned. Patient and intervention: a 23-year-old patient sustained a traumatic injury of the right knee while playing soccer. An MRI-scan identified an ACL-rupture, a vertical rupture of the posterior horn of the medial meniscus, and a posterior root tear of the lateral meniscus. The patient underwent an ACL-reconstruction and repair of both the medial meniscal tear and the lateral meniscal posterior root tear. Outcome: twelve months postoperatively, the patient has fully recovered and returned to play at his pre-injury level. Conclusion: it is important to recognize and treat posterior meniscal root tears. Meniscal root repairs have been reported to improve clinical outcomes and decrease the risk of early degenerative changes.
Introduction Both the medial and lateral menisci have a stout attachment at their very anterior and posterior aspects, which are called the root attachments. These root attachments are important because they hold the meniscus in place, provide stability to the circumferential hoop fibers of the meniscus, and prevent meniscal extrusion. Anterior root tears are rare. The anterior medial root is at risk during intramedullary tibial nailing and the anterior lateral root is at risk with non-anatomic placement of the tibial tunnel during ACL-reconstruction. In recent years, scientific interest towards posterior meniscal root tears has increased. In an anatomy study it was reported that the medial meniscal posterior root is located 8 mm anteromedial from the margin of the PCL, and 1 cm posterior to the apex of the medial tibial eminence. The lateral meniscal posterior root inserted over a broader area 4 mm medial and 1.5 mm posterior to the lateral tibial eminence apex, and 10.1 mm anterior to the PCL margin (figure 1).1 A posterior meniscal root tear is defined as a radial tear within 9 mm of the root bony attachment or a bony avulsion injury.2 Multiple classification schemes have been proposed to characterize posterior meniscal root tears. The classification scheme of LaPrade et al divides posterior root tears into five subtypes (figure 2).2 Posterior meniscal root tears cause significant alterations in tibiofemoral contact pressure, and consequently may lead to premature degenerative osteoarthritis. In a biomechanical study it was reported that a tear of the posterior root of the medial meniscus increases contact pressures similar to a total meniscectomy.2,3 There is increasing evidence that both medial and lateral posterior meniscal root tears need to be repaired in symptomatic patients without significant osteoarthritis.4 Two thirds of posterior meniscal root tears concern the medial meniscus, one third the lateral meniscus. Medial and lateral posterior meniscal root tears differ in clinical presentation and patient demographics. Medial meniscal posterior root tears usually affect middle-aged individuals, tend to occur in isolation and are more common in female patients. Up to 21,5% of medial meniscal posterior horn tears may be root tears.5 Lateral meniscal posterior root tears usually affect younger athletes who commonly have concurrent ACL tears.5,6 In a recent large case-control study the incidence of lateral meniscal posterior root tears in the ACL injured knee was 6,6%.4,6 In an ACL deficient knee, the lateral meniscal posterior root plays an important role in stabilizing the knee in both anterior tibial translation and during pivoting activities, and has been reported to act as primary stabilizer for internal rotation at higher flexion angles.7 Therefore, a root repair should be performed concurrently with an ACL reconstruction to avoid persistent instability and increased forces on the ACL graft.7 The clinical diagnosis is challenging and often limited due to aspecific symptoms, underestimating the incidence of a posterior meniscal root tear. MRI is the primary diagnostic tool for meniscal root tears. The specificity and sensitivity have been described as moderate to good.8-10 Some root tears may not be identified until arthroscopy.
We present a case of an ACL tear combined with a medial meniscal posterior horn tear and lateral meniscal posterior root tear and an update of current concepts on diagnostics and treatment of posterior meniscal root tears.
Figure 1. Medial and lateral meniscal posterior root attachments relevant anatomy (right knee). (A) superior view and (B) posterior view. ACL, anterior cruciate ligament bundle attachments; LPRA, lateral meniscus posterior root attachment; LTE, lateral tibial eminence; MPRA, medial meniscus posterior root attachment; MTE, medial tibial eminence; PCL, posterior cruciate ligament bundle attachments; SWF, shiny white fibers of posterior horn of medial meniscus (re-printed with permission Am J Sports Med 2012 40(10): 2345 Johannsen AM et al).
Figure 2. Meniscal root tear classification system in five different groups based on tear morphology. All meniscal tears are shown as medial meniscal posterior root tears for consistency in this illustration. The 5 tear patterns are classified based on morphology: partial stable root tear (type 1), complete radial tear within 9 mm from the bony root attachment (type 2), bucket-handle tear with complete root detachment (type 3), complex oblique or longitudinal tear with complete root detachment (type 4), and bony avulsion fracture of the root attachment (type 5) (re-printed with permission Am J Sports Med 2015 43(2): 365 LaPrade CM et al)
Patient A 23-year-old patient presented with pain and swelling in the right knee, three weeks after a valgus rotational trauma while playing soccer. At physical examination there was moderate effusion of the knee and patient allowed a range of motion of 110-5-0. There was tenderness over the medial and lateral joint spaces. The MCL and LCL showed no increased laxity. There was a grade 2 Lachman test and a grade 2 pivot shift. Dial test in 30 and 90 degrees and PCL tests showed no abnormalities. Meniscal provocation tests (McMurray and Thessaly) were negative. Intervention Weightbearing AP and lateral radiographs showed no abnormalities besides signs of knee joint effusion. An MRI-scan (Philips Ingenia 1.5 T MRI system, Best, the Netherlands, with a dedicated 16-channel knee coil) confirmed the suspected ACL tear with corresponding bone bruising pattern. An oblique tear of the posterior horn of the medial meniscus was described as well as a posterior root tear of the lateral meniscus. The PCL, MCL and LCL were intact, and no chondral defects were detected (figure 3). Patient was referred to a physiotherapist for pre-operative training. Knee extension and flexion muscle strength was evaluated two weeks pre-operatively with a Biodex Multi-Joint System 4 (Biodex, Shirley, New York). Eight weeks post-trauma he underwent arthroscopic surgery. There was a vertical tear in the posterior horn of the medial meniscus which was repaired with an all-inside suture (Fast-fix 360, Smith&Nephew, Watford, England). There was a complete grade 2 tear (according to LaPrade et al) of the posterior root of the lateral meniscus (figure 4) which was repaired using a two tunnel transtibial pull-out technique. Two tape sutures were positioned in the posterior root using an all-inside device (Smith&Nephew). An all-inside ACL-reconstruction using a semi-tendinosis quadrupled autograft was performed (Arthrex, Naples, Florida, USA). Patient was discharged on the same day. Figure 5 shows the postoperative X-ray. The early rehabilitation timeline was as described by Mueller et al; weightbearing was not allowed for 6 weeks with an allowed range of motion of 0 – 90 degrees. After six weeks weightbearing was progressed to full in three weeks’ time and full range of motion was allowed.11 Further rehabilitation was performed in accordance with the evidence statement ACL rehabilitation of the Royal Dutch Physiotherapy Association (KNGF).
Figure 3. MRI PD + FS coronal view (A) with arrow pointing to lateral meniscus posterior root tear and PD sagittal view (B) with arrow pointing to lateral meniscus posterior root tear and line at intact meniscofemoral ligament of Wrisberg.
Figure 4. Arthroscopic view from anterolateral portal, after removal of ACL remnants, with probe identifying the lateral meniscus posterior root tear.
Figure 5. Postoperative anterior-posterior (A) and lateral (B) X-ray after ACL all-inside reconstruction and transtibial pull-out lateral meniscus posterior root repair.
Comparison & Relevant literature A search on Pubmed was conducted to review recent literature (2005 – 2020) on posterior meniscal root tears. The search terms ‘meniscal root (tear)’, ‘meniscal root (repair)’ and ‘meniscus root’ were used, and a selection of recent laboratory, case series, commentary, and review studies were chosen in order to present an overview of current concepts on diagnostics and treatment. In the Dutch knee arthroscopy guideline meniscal root tears are not mentioned so this paper could be used to write an addition to this guideline. The majority of cases of medial posterior root tears occur in degenerative knees without a specific injury event, or after minor trauma as squatting.12 Known risk factors for a medial posterior root tear are increased age, varus alignment, high BMI, and female sex.13 Furthermore, a possible role of posterior medial meniscal root injury in the aetiology of spontaneous osteonecrosis of the knee (SONK) has been described.14 In a large series of patients undergoing ACL reconstruction, participation in contact sports and the presence of a concomitant medial meniscal tear were found to be independent risk factors for a lateral posterior meniscal root tear.6 Physical examination may be unreliable since symptoms from posterior meniscal root tears tend to present differently compared to meniscal body or horn tear symptoms. Patients may or may not have heard an associated ‘pop’. It may be difficult to elicit pain from patients with passive range of motion; deep flexion, especially under load, as in squatting, may be helpful in identifying a posterior root tear in particular. McMurray’s test has poor sensitivity.15 Because of the complementary biomechanical relationship of the lateral meniscus root and ACL, a 3+ Lachman and 3+ pivot shift test during physical examination should raise suspicion for a combined ACL and lateral meniscus posterior root tear.4 MRI direct findings of a meniscal root tear are in the axial plane a (marching) cleft perpendicular to the meniscus (= radial tear), in the coronal plane a vertical linear defect (truncated triangle), in the sagittal plane a ghost meniscus sign (absence of a normal meniscus)4,10,12,16 and a giraffe neck sign.17 Tears of the root can be manifested by the standard meniscus tear criteria; ‘2 slice touch’ rule, meniscal distortion or intrameniscal signal that extends to the surface of the meniscus.9 The highest sensitivity (77%) and specificity (73%) are reached when assessed in three planes on the specific locations with fluid- and non-fluid sensitive sequences.4 An indirect MRI finding is meniscal extrusion (>3 mm) which is less common in lateral than in a medial root tear.9,10,12,16 Association findings of a root tear are insertional posterior medial meniscus root osseous changes (focal bone marrow oedema or cyst like changes beneath the insertion), regional synovitis, osteoarthritis, insufficiency fracture and cruciate ligament degeneration.16 Posterior root tears of the lateral meniscus can be difficult to assess on MRI for multiple reasons8,9 which should be mentioned in the report to alert the surgeon for evaluation.9 The gold standard to confirm the presence of a meniscal root tear is arthroscopy. The posterior roots can be visualized using standard anterolateral and anteromedial portals. The integrity of the roots can be tested using a probe. Accessory anterolateral and anteromedial portals can be made as needed. Some surgeons prefer a drive through intercondylar notch view or the usage of accessory posteromedial or posterolateral portals. In the past most patients with root injuries were treated non-operatively or with a partial meniscectomy. In older patients, poor surgical candidates or patients with advanced arthritis non-operative treatment can still be the best treatment of choice. Patients with symptomatic tears (mechanical symptoms) who have failed non-operative treatment can benefit from partial or subtotal meniscectomy.
There are two main indications for a meniscal root repair: 1. acute, traumatic tears in patients without chondral damage, in order to relieve symptoms and prevent the development of arthritis in the future; 2. chronic symptomatic root tears in young or middle-aged patients without significant pre-existing degenerative changes in the ipsilateral compartment. Often the acute tears are posterior lateral tears associated with an ACL injury, and the root should be repaired during ACL-reconstruction. Increased knee instability due to lateral meniscal root deficiency may contribute to increased functional limitations in patients and potentially to increased loads on ACL reconstruction grafts.4 A combination of lateral meniscal root avulsion and deficient meniscofemoral ligaments leads to increased contact pressure in the lateral compartment. Concurrent ACL reconstruction and lateral meniscal root repair restore mean contact pressure and area to the intact state, slowing down the development of lateral compartment arthritis.18 An acute medial root tear can be associated with multi-ligamentous knee injury with a complete MCL tear in which meniscocapsular ligaments are intact, but the meniscus is avulsed at the root. A meniscal treatment algorithm is presented in figure 6.12 The two most described techniques for arthroscopic meniscal root repair are a suture anchor repair and a transtibial suture repair. In the suture anchor technique, described for medial posterior root tears, an anchor is inserted at the anatomic footprint through a high posteromedial portal and the root is reattached with two vertical sutures.19 The transtibial repair technique is probably the most used technique and multiple variations have been described.20 The footprint is decorticated using a curette and sutures are passed through the meniscal root usually using an all-inside device. One or two tibial tunnels are drilled, and the sutures are retrieved and tied over a bone bridge, post, or button (figure 7). Clinical outcome studies have shown that meniscal root repairs improve subjective patient outcomes, and that root repair can slow down the progression of osteoarthritis.21,22
Bijschrift 6: Treatment decision making for meniscal root tears.
Bijschrift 7: Transtibial pull-out repair technique of a medial meniscal posterior root tear using two transtibial bone tunnels (re-printed with permission Am J Sports Med 2015 43(4): 901 LaPrade CM et al)
Outcome Six and twelve months postoperatively knee extension and flexion muscle strength were evaluated with a Biodex System 4 Dynamometer. At 12 months there was a side-to-side difference in knee extension and flexion muscle strength of less than 10% both measured at 60 and at 180 degrees per second. Patient was able to resume playing soccer without complaints and played his first match twelve months after surgery. Recommendations Historically meniscal root tears were left untreated or treated with a partial meniscectomy. Multiple studies have shown this leads to increased contact pressures on articular cartilage and possible rapid development of osteoarthritis. In patients with little or no degenerative changes a repair of meniscal root tears should be considered. Although no long-term randomized controlled studies have been published to date, current evidence shows meniscal root repairs lead to high satisfaction rates, superior outcomes to arthroscopic meniscectomy for root tears, and potentially slowing or halting progression of arthritis. Disclosure The authors have nothing to disclose.
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