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Evaluation of medial meniscus tears and meniscal stability: Weight-bearing MRI vs arthroscopy
European Journal of Radiology 82 (2013) 633–639
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European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Evaluation of medial meniscus tears and meniscal stability: Weight-bearing MRI vs arthroscopy Antonio Barile a,∗ , Laura Conti a , Giuseppe Lanni a , Vittorio Calvisi b , Carlo Masciocchi a a b
Department of Radiology, University of L’Aquila, S. Salvatore Hospital, Coppito, L’Aquila, Italy Department of Orthopaedic Surgery, University of L’Aquila, Coppito, L’Aquila, Italy
a r t i c l e
i n f o
Article history: Received 6 April 2012 Received in revised form 17 September 2012 Accepted 9 October 2012 Keywords: Medial meniscus Tears Weight-bearing MRI
a b s t r a c t To assess the role of dedicated low-field standard and weight-bearing MRI in the evaluation of stable or unstable tears of medial meniscus in comparison with arthroscopy. Our series included 1750 knee MRI scans performed with a high-field MRI scanner from July 2010 to August 2011. We retrospectively reviewed and analyzed 20 MRI exams of normal knee and 57 MRI exams of knee with clinical evidence of tears of the medial meniscus. In the same session, after conventional 1.5 T and “dedicated” 0.25 T supine MRI exam, the patients underwent weight-bearing examination with the same dedicated MRI unit. In all cases sagittal and coronal PD-W were used. All patients underwent arthroscopy 18–25 days after the weight-bearing MRI. In the first group, no statistically significant anatomical modifications of shape, intensity and position of the medial meniscus between standard 1.5 T, dedicated supine and upright MRI were observed. In group A, the images acquired in the supine position (dedicated and 1.5 T MRI) documented in 21 cases a traumatic tear (group 2A) and in 36 cases a degenerative tear (group 2B). In group 2A, weight-bearing MRI showed presence of unstable tear a degenerative unstable meniscal tear only in 19 out of 36 cases. In group 2B, weight-bearing MRI showed only in 9 out 21 cases. Arthroscopy confirmed weight-bearing MRI diagnosis in all cases. This new approach to meniscus pathology gives an important contribution to a better management of a diagnostic–therapeutic approach in which standard MRI has not played a key role, so far. © 2012 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Meniscal diseases are commonly studied by means of MRI which allows [1–3], evaluation of meniscal injuries with high precision, showing 93% sensitivity and 88% specificity [4]. For a diagnosis of meniscal tear to be confirmed through MRI, some criteria must be fulfilled, among which the extension of the hyperintense intrameniscal signal on short echo-time sequences to one of the two joint surfaces. However, in the clinical practice, a MR-confirmed meniscal alteration not associated with a surgically treatable condition may occur. For this reason, several methods have been used in order to discriminate between symptomatic and asymptomatic meniscal injuries, thus introducing the notion of “meniscal stability”. So far, the meniscal stability has been evaluated only through arthroscopic methods [5], since the orthopaedic surgeon can decide
∗ Corresponding author at: Department of Radiology, University of L’Aquila, S. Salvatore Hospital, Coppito, 67100 L’Aquila, Italy. Tel.: +39 0862 414258; fax: +39 0862 311277. E-mail addresses: [email protected] (A. Barile), [email protected] (L. Conti), [email protected] (G. Lanni), [email protected] (C. Masciocchi). 0720-048X/$ – see front matter © 2012 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejrad.2012.10.018
whether to resect or to repair the meniscus, by considering only the stability degree of the lesion [5–9]. Our study tried to identify a new approach for the analysis of meniscal pathologies, by taking into account the dynamic features of meniscal injuries and, mainly, by considering the possibility of evaluating meniscal alterations through dedicated low magnetic field MR devices, which allow both standard and upright examinations. Our study was aimed at determining prospectively whether weight-bearing MRI can provide precise information concerning stability or instability of meniscal lesions, to help the orthopaedic surgeon in planning the surgical intervention. 2. Materials and methods 2.1. Patient selection criteria Our series included 1750 knee MRI scans performed with a highfield MRI scanner (1.5 T General Electric Signa Horizon) from July 2010 to August 2011. Every scan was performed using a dedicated coil. On the basis of MRI diagnoses, our series was divided into two groups. The first included 12 male and 8 female patients, whose age ranged from 18 to 52 years (mean 36.5), who came under our
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observation with a clinical diagnosis of anterior knee pain with neither prior history of trauma nor lesions and/or ligament and meniscus instability. The second group included 33 male and 24 female patients, aged from 18 to 54 (mean 37.5 years) who came under our observation with a clinical suspicion of medial meniscus injury, previously diagnosed by an orthopaedic surgeon and then documented by high-field MRI. In accordance with the declaration of Helsinky and the Institutional Review Board, after informed consent, the selected series (57 knee MR exams) underwent a dedicated musculoskeletal MRI lowfield study. The patients with grade 1 and 2 degenerative meniscal lesions, traumatic radial meniscal tears, bucket-handle meniscus tear or with ligament affections were excluded from our study, while our 57 patients were divided on the basis of their injury: 36 degenerative lesions, including grade 3 injuries (group 2A), and 21 traumatic tears (group 2B), including longitudinal tear and traumatic meniscocapsular separation. 2.2. 1.5 T MRI Knee MRI protocol employed sagittal proton density-weighted scans (PD, TE = 13.5 ms, TR = 1800), coronal spin echo T1-weighted images (SE; TE = 20 ms; TR = 400), axial fast spin echo T2-weighted scans (FSE TE = 180 ms; TR = 3200) and coronal STIR sequences (TE = 20 ms; TR = 2500). The field of view (FOV) was 16–18 cm, matrix 256 × 256, 4 mm slice thickness, 0.4 mm gap, NEX = 2. The total duration of MR examination was about 30 min. 2.3. Dedicated MRI (0.25 T G-scan Esaote) We performed standard MR examinations of the knee using an Esaote G-scan dedicated MR unit and obtained upright weightbearing MRI examinations rotating the table of about 82◦ . The knee MRI protocol in clinostatism employed sagittal FSE sequences T2- (TE = 125 ms and TR = 3100) and PD-weighted (TE = 28 ms and TR = 800), coronal X-BONE (TE = 14–28 ms and TR = 860) and axial turbo multi-echo (TME; TE = 28 ms and TR = 2930). Weight-bearing MRI the protocol employed sagittal T2(FSE; TE = 125 ms and TR = 3100) and PD-weighted (SE; TE = 28 ms and TR = 800) sequences, as well as coronal X-BONE sequences (TE = 14–28 and TR = 860). The field of view (FOV) was 16–18 cm, matrix 256 × 184, 4 mm slice thickness, 0.4 mm gap, NEX = 2. The total duration of MR examination was about 40 min (30 min for standard MR plus 10 min for weight-bearing MRI exam). 2.4. Stability/instability evaluation of medial meniscus injuries The evaluation of MR exam was performed separately by two experienced musculoskeletal radiologists (AB and LC). Problematic cases (in number of 5) were discussed together to accomplish a common diagnosis. The measurements to assess the meniscal stability/instability were taken on both sagittal and coronal scan planes passing through the posterior horn of the medial meniscus. Medial meniscus anatomy and load-induced physiological variations were evaluated by measuring 4 parameters: 1. meniscal morphology, scored through a three-point Likert scale (0 = regular, 1 = slightly irregular, 2 = irregular); 2. intrameniscal signal analysis, scored through a five-point Likert scale (0 = homogeneous, 1 = slightly non-homogeneous,
non-homogeneous, 3 = non-homogeneous, 2 = rather 4 = strongly non-homogeneous); 3. the assessment of meniscal extrusion on a coronal plane (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau); 4. the assessment of meniscal extrusion on a sagittal plane (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau). Analyzing standard MR examinations of grade 3 meniscal degenerations (A and B), longitudinal lesions and traumatic meniscocapsular separation, we evaluated: 1. medial meniscus morphology and signal intensity, thus making a basic diagnosis; 2. the assessment of meniscal extrusion (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau); Employing the weight-bearing MR we evaluated: 1. meniscal morphology and signal intensity load-induced variations, scored on a five-point Likert scale (0 = no alterations; 1 = slight alteration of injury and signal; 2 = noticeable alteration of lesion morphology and signal intensity; 3 = remarkable alteration of lesion morphology and signal intensity; 4 = meniscal fragments); 2. meniscal extrusion increase on a coronal plane (measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau). Moreover, in cases of traumatic meniscocapsular separation, meniscal stability/instability was evaluated on sagittal scanning planes, by measuring the increase of the gap between meniscus and capsule. 2.5. Arthroscopy All the patients belonging to the second group (2A and 2B) underwent arthroscopic surgery 18–25 days after the weightbearing MRI examination. 3. Results 3.1. Anatomy and physiological load-induced modifications: evaluations and results Medial meniscus scans acquired in the supine position by using both the 1.5 T and the 0.25 T-dedicated low-field MR standard in supine position, showed a homogeneous intensity of intrameniscal signal and a regular meniscal morphology, both on sagittal and coronal planes, in the first group of patients. No significant differences were found between information obtained with the 1.5 T MR system and those provided by the dedicated magnet. After a 82◦ table rotation, MRI examinations allowed evaluation of the physiological variations of the signal under physiological load, as well as of the medial meniscal position and morphology. Morphology, intrameniscal signal and measurements of the grade of medial meniscal extrusion, evaluated on both sagittal and coronal planes, did not show statistically significant differences (Fig. 1 and Table 1).
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(eleven grade 3A-lesions (Fig. 2) and eight grade 3B-lesions (Fig. 3)) (Table 2). Neither false positives nor false negatives were found. 3.3. Traumatic meniscal tears: evaluation and results High-field MRI scan identified 21 traumatic tears (group 2B) including 6 traumatic meniscocapsular separation and 15 longitudinal tears of the medial meniscus posterior horn. In every patient, weight-bearing MRI confirmed the high-field MRI diagnosis. Upright MRI showed meniscal instability in 9 out of 21 cases (3 meniscocapsular separation (Fig. 4) and 6 longitudinal tears (Fig. 5)) (Table 3). Neither false positives nor false negatives were found. 3.4. Arthroscopy: results Arthroscopy confirmed in every case the diagnosis obtained by weight-bearing MRI (19 degenerative unstable lesions, 9 traumatic unstable lesions). 4. Discussion and conclusion
Fig. 1. Anatomy of the medial meniscus with dedicated low-field standard and upright-MRI. (A) Sagittal scan plane PD-weighted in the supine position. (B) Coronal scan plane GE-weighted in the supine position. (C) Sagittal scan plane PD-weighted in orthostatic position. (D) Coronal scan plane GE-weighted in orthostatic position. Both morphology and signal intensity of medial meniscus do not change during the passage from a clinostatic to an orthostatic position.
3.2. Degenerative meniscal tears: evaluation and results High-field MR examinations of group 2A revealed 21 linear signal alterations (grade 3A) and 15 globular degenerative signal alterations (grade 3B). In order to evaluate degenerative meniscal injuries, we used a widely accepted, four-grade classification, as the most cited and reproducible by MRI, based on intrameniscal signal and evaluated on sagittal plane. The coronal plane was used to measure the meniscal extrusion grade. The dedicated MRI exam carried out in clinostatism confirmed in every patient the high-field MRI diagnosis. 2A-group MR examination under physiological load identified unstable meniscal tears in 19 out of 36 cases belonging to the second group Table 1 Physiological anatomy and modifications of the load. Parameters
Standard MR
Weight-bearing MR
Intrameniscal signal (Likert scale) Meniscal morphology (Likert scale) Meniscal extrusion (sagittal)a Meniscal extrusion (coronal)b
Homogeneous Regular Absent Absent
Homogeneous Regular Absent Absent
a The assessment of meniscal extrusion on a sagittal plane (by measuring meniscal portion which was out of a plane passing through the outer edge of medial femoral condyle and the outer edge of the medial tibial plateau). b The assessment of meniscal extrusion on a coronal plane (by measuring meniscal portion which was out of a plane passing through the outer edge of medial femoral condyle and the outer edge of the medial tibial plateau).
the the the the
The meniscus is a crucial component of the knee complex biomechanical system, and a critical element in dispersing loads, in increasing the contact area and allowing an even distribution of weight through the articular surfaces. Moreover, menisci deepen the articular surfaces of the otherwise relatively flat tibial plateau, thus providing the adaptation between the relatively round femoral condyles and the flat tibial joint surfaces. The meniscus increase congruity between the rounded femoral condyles and the flattened surfaces of the tibial plateau. The meniscus also promotes load distribution and joint lubrification. The posterior horn of the meniscus has a strong attachment to the tibia near the tibial spine, known as the meniscal root. The posterior horn of the medial meniscus moves minimally during knee flexion. This strong attachment of the posterior horn of the medial meniscus contributes to an increased frequency of tears in this region. Being firmly attached to the tibial plateau through the meniscal root, near the posterior tibial spine, and having little possibility of movement during knee flexion, the posterior horn of the medial meniscus is particularly vulnerable to damage, which can lead both to a degeneration and to an injury in this area. On a normal condition, both morphology and signal intensity of the meniscus do not change during the passage from supine and upright position; furthermore, on the sagittal scan plane, the posterior horn of the medial meniscus always maintains its relationship with the tibial plateau (Fig. 1). The possible meniscal damage, together with the resulting alteration of flexion function, may modify the load distribution model, thus contributing to knee instability. The main MRI criterion to diagnose a meniscal tear is the increased intrameniscal signal intensity of short echo-time sequences (TE) extended to a joint surface. However, an increased meniscal signal intensity is not enough to diagnose a meniscal tear, being this diagnosis more accurate when observed in two or more contiguous images, or when detected on sagittal as well as on coronal planes. The second criterion to diagnose a meniscal tear is the alteration of the normal morphology without previous surgery. Stoller et al. first suggested a classification system based on four MRI meniscal signal variations. Mesgarzadeh et al. further extended the meniscal tears classification up to eight types. However, a common classification system has not been accepted, yet.
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Fig. 2. Unstable degeneration (tear type 3) of the medial meniscus posterior horn. (A) Sagittal scan plane PD-weighted in the supine position with dedicated low-field MRI shows type 3 degeneration tear of the posterior horn of the medial meniscus. (B) Sagittal scan plane PD-weighted in the orthostatic position with low-field upright-MRI confirms type 3 degeneration tear and suggests an unstable lesion well depicting a posterior shift of the horn: see lines in (A) and (B). (C) Arthroscopy confirms unstable type 3 degenerative tear of the medial meniscus.
Fig. 3. Stable degeneration (tear type 3) of the medial meniscus posterior horn. (A) MRI sagittal scan plane PD-weighted using 1.5 T unit and (B) sagittal scan plane PDweighted in the supine position with dedicated low-field MRI; type 3 degeneration tear of the medial meniscus posterior horn is well documented in both images. (C) Sagittal scan plane PD-weighted in the orthostatic position with low-field upright-MRI; note the absence of significative modification of the meniscus with respect to clinostatic examination. (D) Arthroscopy confirms stable type 3 degeneration tear of the medial meniscus.
In our study, we adopted a widely accepted classification system, which is based on four grades of meniscal alteration: grade 0 = normal meniscus, with homogeneous low signal of the entire meniscus; grade 1 = increased intrameniscal signal limited to a clearly localized globular focus not extended to a joint surface; grade 2 = increased linear wedge-shape intrameniscal signal not extending to the joint surface; grade 3 = real meniscal tear, increased linear (3A group) or globular (3B group) intrameniscal signal alteration that reaches the upper or lower articular surface; grade 4 describes a torn and fragmented meniscus. It is worth noting that this classification system is based on signal intensity, and that only grade 3 indicates a meniscal injury [10–12].
Another important criterion to evaluate meniscus instability is the presence of meniscal extrusion, or the medial displacement of the medial meniscus beyond the tibial margin. According to many studies, this seems to result from a remarkable degeneration of the meniscus circumferential fibres, with the subsequent loss of the ability to resist hoop strain. Moreover, the degeneration of the circumferential fibres reduces the meniscus ability to distribute the load, thus causing joint cartilage degeneration. A medial meniscus extrusion higher than 3 mm has been associated with degenerative meniscal diseases, to radial, complex, horizontal meniscal tears and mainly to tears involving meniscal root, with subsequent loss of meniscal stability [13–16].
Fig. 4. Unstable traumatic meniscocapsular separation of the medial meniscus posterior horn. (A) Sagittal scan plane PD-weighted with 1.5 T MRI and (B) sagittal scan plane PD-weighted in the supine position with dedicated low-field MRI well documented the lesion. (C) Sagittal scan plane PD-weighted in the orthostatic position with low-field upright-MRI showing an increased space between the meniscus and capsule (see lines in (B) and (C)) indicates an unstable lesion. (D) Arthroscopy confirms unstable meniscocapsular separation of the medial meniscus posterior horn.
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Table 2 Meniscal degeneration. Cases
Standard MR
Weight-bearing MR
Results
Arthroscopy
– – – – 3 mm 2.5 mm – – – 1.8 mm 2.3 mm – – – 2 mm 3.3 mm 2.7 mm – 2.5 mm – –
Stable Stable Unstable Stable Unstable Unstable Stable Unstable Stable Unstable Unstable Stable Stable Stable Unstable Unstable Unstable Stable Unstable Unstable Stable
– – 1.8 mm – 2.2 mm – – 3 mm 2.6 mm – – 3.2 mm – – –
Stable Stable Unstable Stable Unstable Unstable Stable Unstable Unstable Stable Unstable Unstable Unstable Stable Stable
Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed
Morphology and intensity of signal
Meniscal extrusiona (mm)
Modification morphology and intensity of signal (Likert scale)
Increase meniscal extrusiona (mm)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A
No No No No Yes (1.2 mm) Yes (0.8 mm) No No No Yes (0.3 mm) Yes (1 mm) No No No No Yes (0.8 mm) Yes (1 mm) No Yes (0.7 mm) No No
0 0 3–4 0–1 4 3–4 0 3 0–1 3 4 0 0–1 0–1 3–4 4 3–4 0 3–4 3–4 0
22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B
No No No No Yes (0.4 mm) No No Yes (1.2 mm) Yes (0.6 mm) No No Yes (1 mm) No No No
0 0 2 0 3–4 3–4 0 4 3 0 3–4 4 3 0 3–4
a The assessment of meniscal extrusion on a coronal plane (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau).
In our experience, weight-bearing MRI always depicted unstable lesions. In these cases, during the passage from supine and upright position, a modification of the meniscal morphology was constantly present, resulting in a posterior subluxation of the posterior horn of the medial meniscus. This phenomenon can be well appreciated on sagittal scan planes in which the posterior horn of the medial
meniscus loses its congruity with the tibial plateau (Fig. 2). Otherwise, morphological modifications and posterior subluxation of the posterior horn of the medial meniscus, were not present in stable lesions (Fig. 3). Traumatic meniscal injuries are described on the basis of their different morphology: they can have longitudinal, horizontal,
Fig. 5. Unstable longitudinal traumatic tear of the medial meniscus posterior horn. (A) Sagittal scan plane PD-weighted in the supine position with dedicated low-field MRI shows the longitudinal tear of the free edge of the posterior horn of the medial meniscus. (B) Sagittal scan plane PD-weighted in the orthostatic position with low-field upright-MRI shows the increased intrameniscal extension of the lesion to the articular surface (arrow). (C) Arthroscopy confirms unstable traumatic tear of the medial meniscus with the presence of flap.
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Table 3 Meniscal traumatic tears. Cases
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 5 6
Standard MR
Weight-bearing MR
Results
Arthroscopy
– – – – 2 mm – – 1.7 mm – – – – – 0.4 mm –
Stable Unstable Stable Stable Unstable Unstable Stable Unstable Stable Stable Stable Unstable Stable Unstable Stable
Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed
0
Expansion of space between meniscus and capsule (mm) 1.2
Unstable
Confirmed
0
1.4
Unstable
Confirmed
0
–
Stable
Confirmed
0
0.8
Unstable
Confirmed
0
–
Stable
Confirmed
0
–
Stable
Confirmed
Morphology and intensity of signal
Meniscal extrusiona (mm)
Modification morphology and intensity of signal (Likert scale)
Increase meniscal extrusion coronal** (mm)
Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear
No No No No Si (1 mm) No No Si (0.8 mm) No No No No No No No
0 3 0–1 0 3–4 3 0 2 0–1 0 0 3–4 0 3 0–1 Modification morphology and intensity of signal (Likert scale)
Traumatic meniscocapsular separation Traumatic meniscocapsular separation Traumatic meniscocapsular separation Traumatic meniscocapsular separation Traumatic meniscocapsular separation Traumatic meniscocapsular separation
a The assessment of meniscal extrusion on a coronal plane (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau).
radial, complex, bucket-handle patterns. For this reason they have different clinical and surgical implications. Usually, longitudinal and oblique tears can be repaired, while horizontal, radial and complex lesions are frequently hard to fix through a simple meniscal repair and need either partial meniscectomy or complete meniscectomy [17,18]. Therefore, in this study these injuries have been excluded. In our experience, all cases of unstable meniscocapsular separations, unlike stable ones, presented an increase of meniscocapsular distance on sagittal scan planes (Fig. 4). In unstable traumatic longitudinal tears of the posterior horn of the medial meniscus, weight-bearing MRI depicted in all cases an increase of the tear-related intrameniscal high signal intensity, sometimes allowing a better identification of small flaps of the free edge (Fig. 5). The absence of false positives and false negatives in this study is probably due to two main reasons: an extremely careful and targeted patient selection and the potentials of weight-bearing MRI which really allows to determine the stability/instability of a meniscal tear. Moreover, the targeted patient series and consequently the restricted number of patients, who underwent weight-bearing MRI exam, finds its explanation in the accurate clinical selection. Indeed, all these patients were preliminarily clinically evaluated by an orthopaedic group posing a precise diagnostic question in view of a possible surgical treatment. The good match between weight-bearing MRI and arthroscopy in diagnosing both degenerative and traumatic tears shows that a stable/unstable lesion can be easily detected on sagittal scan planes; moreover, in clinical practise, this result can be obtained
by additional 10 min to the standard MR examination that do not discomfort to the patient. The decision of surgery is based mainly on clinical data, lesion morphology, size and location detectable on standard MRI scans [19,20]. Orthopaedic surgery is currently mostly conservative: in fact, during a meniscus repair or a meniscus removal intervention, the most common goal is to preserve as much meniscal tissue as possible, in order to reduce subsequent degenerative alterations [20]. In our experience, only some kind of injuries were associated with instability, and could benefit from surgery. Although meniscal stability/instability has been evaluated through arthroscopic investigation, our study highlighted the diagnostic usefulness of weight-bearing MRI, which allowed us to evaluate the biomechanical stress caused by a physiological load, thus making a latent instability of the meniscus reliably evident. This was possible through an in vivo, non invasive reproduction of how a biomechanical stress results on a joint with a medial meniscal tear. Upright MRI allows to record every load-induced physiological variations, thus showing both the meniscal tear stability and a latent instability, making it possible to correctly guide the orthopaedic surgeon towards a conservative treatment, meniscal repair or rather towards a partial meniscectomy. Moreover, this new diagnostic instrument allows to recognize the stability of a meniscal tear, thus avoiding the damages deriving from arthroscopic investigations, as well as allowing a spontaneous healing of the injury. This new approach to meniscal pathologies help in the diagnostic and therapeutic.
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However, in spite of the excellent results, we firmly believe that further studies are needed on a larger series of patients, possibly in a multicentric study. Conflict of interest There is no conflict of interest. References [1] Barile A, Masciocchi C, Mastantuono M, Passariello R, Satragno L. The use of “dedicated” MRI system in the evaluation of knee joint diseases. Clinical MRI 1995;5(2):79–82. [2] Masciocchi C, Barile A, Satragno L. Muscoloskeletal MRI: dedicated systems. European Radiology 2000;10:250–5. [3] Barile A, Iannessi F, Masciocchi C. New developments in “dedicated” MRI the joints: the E-scan, technical and clinical considerations. Clinical MRI 2000;10(2):39–41. [4] Anderson MW. MR imaging of the meniscus. Radiologic Clinics of North America 2002;40:1081–94. [5] Kim SB, Ha JK, Lee SW, et al. Medial meniscus root tear refixation: comparison of clinical, radiologic, and arthroscopic findings with medial meniscectomy. The Journal of Arthroscopic and Related Surgery 2011;27(3):346–54. [6] DeHaven KE. Decision-making factors in the treatment of meniscus lesions. Clinical Orthopaedics and Related Research 1990;252:49–54. [7] Vedi V, Williams A, Tennant SJ, Spouse E, Hunt DM, Gedroyc WM. Meniscal movement: an in-vivo study using dynamic MRI. Journal of Bone and Joint Surgery British Volume 1999;81:37–41. [8] Koenig JH, Ranawat AS, Umans HR, et al. Meniscal root tears: diagnosis and treatment. The Journal of Arthroscopic and Related Surgery 2009;25(9):1025–32.
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European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Evaluation of medial meniscus tears and meniscal stability: Weight-bearing MRI vs arthroscopy Antonio Barile a,∗ , Laura Conti a , Giuseppe Lanni a , Vittorio Calvisi b , Carlo Masciocchi a a b
Department of Radiology, University of L’Aquila, S. Salvatore Hospital, Coppito, L’Aquila, Italy Department of Orthopaedic Surgery, University of L’Aquila, Coppito, L’Aquila, Italy
a r t i c l e
i n f o
Article history: Received 6 April 2012 Received in revised form 17 September 2012 Accepted 9 October 2012 Keywords: Medial meniscus Tears Weight-bearing MRI
a b s t r a c t To assess the role of dedicated low-field standard and weight-bearing MRI in the evaluation of stable or unstable tears of medial meniscus in comparison with arthroscopy. Our series included 1750 knee MRI scans performed with a high-field MRI scanner from July 2010 to August 2011. We retrospectively reviewed and analyzed 20 MRI exams of normal knee and 57 MRI exams of knee with clinical evidence of tears of the medial meniscus. In the same session, after conventional 1.5 T and “dedicated” 0.25 T supine MRI exam, the patients underwent weight-bearing examination with the same dedicated MRI unit. In all cases sagittal and coronal PD-W were used. All patients underwent arthroscopy 18–25 days after the weight-bearing MRI. In the first group, no statistically significant anatomical modifications of shape, intensity and position of the medial meniscus between standard 1.5 T, dedicated supine and upright MRI were observed. In group A, the images acquired in the supine position (dedicated and 1.5 T MRI) documented in 21 cases a traumatic tear (group 2A) and in 36 cases a degenerative tear (group 2B). In group 2A, weight-bearing MRI showed presence of unstable tear a degenerative unstable meniscal tear only in 19 out of 36 cases. In group 2B, weight-bearing MRI showed only in 9 out 21 cases. Arthroscopy confirmed weight-bearing MRI diagnosis in all cases. This new approach to meniscus pathology gives an important contribution to a better management of a diagnostic–therapeutic approach in which standard MRI has not played a key role, so far. © 2012 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Meniscal diseases are commonly studied by means of MRI which allows [1–3], evaluation of meniscal injuries with high precision, showing 93% sensitivity and 88% specificity [4]. For a diagnosis of meniscal tear to be confirmed through MRI, some criteria must be fulfilled, among which the extension of the hyperintense intrameniscal signal on short echo-time sequences to one of the two joint surfaces. However, in the clinical practice, a MR-confirmed meniscal alteration not associated with a surgically treatable condition may occur. For this reason, several methods have been used in order to discriminate between symptomatic and asymptomatic meniscal injuries, thus introducing the notion of “meniscal stability”. So far, the meniscal stability has been evaluated only through arthroscopic methods [5], since the orthopaedic surgeon can decide
∗ Corresponding author at: Department of Radiology, University of L’Aquila, S. Salvatore Hospital, Coppito, 67100 L’Aquila, Italy. Tel.: +39 0862 414258; fax: +39 0862 311277. E-mail addresses: [email protected] (A. Barile), [email protected] (L. Conti), [email protected] (G. Lanni), [email protected] (C. Masciocchi). 0720-048X/$ – see front matter © 2012 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejrad.2012.10.018
whether to resect or to repair the meniscus, by considering only the stability degree of the lesion [5–9]. Our study tried to identify a new approach for the analysis of meniscal pathologies, by taking into account the dynamic features of meniscal injuries and, mainly, by considering the possibility of evaluating meniscal alterations through dedicated low magnetic field MR devices, which allow both standard and upright examinations. Our study was aimed at determining prospectively whether weight-bearing MRI can provide precise information concerning stability or instability of meniscal lesions, to help the orthopaedic surgeon in planning the surgical intervention. 2. Materials and methods 2.1. Patient selection criteria Our series included 1750 knee MRI scans performed with a highfield MRI scanner (1.5 T General Electric Signa Horizon) from July 2010 to August 2011. Every scan was performed using a dedicated coil. On the basis of MRI diagnoses, our series was divided into two groups. The first included 12 male and 8 female patients, whose age ranged from 18 to 52 years (mean 36.5), who came under our
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observation with a clinical diagnosis of anterior knee pain with neither prior history of trauma nor lesions and/or ligament and meniscus instability. The second group included 33 male and 24 female patients, aged from 18 to 54 (mean 37.5 years) who came under our observation with a clinical suspicion of medial meniscus injury, previously diagnosed by an orthopaedic surgeon and then documented by high-field MRI. In accordance with the declaration of Helsinky and the Institutional Review Board, after informed consent, the selected series (57 knee MR exams) underwent a dedicated musculoskeletal MRI lowfield study. The patients with grade 1 and 2 degenerative meniscal lesions, traumatic radial meniscal tears, bucket-handle meniscus tear or with ligament affections were excluded from our study, while our 57 patients were divided on the basis of their injury: 36 degenerative lesions, including grade 3 injuries (group 2A), and 21 traumatic tears (group 2B), including longitudinal tear and traumatic meniscocapsular separation. 2.2. 1.5 T MRI Knee MRI protocol employed sagittal proton density-weighted scans (PD, TE = 13.5 ms, TR = 1800), coronal spin echo T1-weighted images (SE; TE = 20 ms; TR = 400), axial fast spin echo T2-weighted scans (FSE TE = 180 ms; TR = 3200) and coronal STIR sequences (TE = 20 ms; TR = 2500). The field of view (FOV) was 16–18 cm, matrix 256 × 256, 4 mm slice thickness, 0.4 mm gap, NEX = 2. The total duration of MR examination was about 30 min. 2.3. Dedicated MRI (0.25 T G-scan Esaote) We performed standard MR examinations of the knee using an Esaote G-scan dedicated MR unit and obtained upright weightbearing MRI examinations rotating the table of about 82◦ . The knee MRI protocol in clinostatism employed sagittal FSE sequences T2- (TE = 125 ms and TR = 3100) and PD-weighted (TE = 28 ms and TR = 800), coronal X-BONE (TE = 14–28 ms and TR = 860) and axial turbo multi-echo (TME; TE = 28 ms and TR = 2930). Weight-bearing MRI the protocol employed sagittal T2(FSE; TE = 125 ms and TR = 3100) and PD-weighted (SE; TE = 28 ms and TR = 800) sequences, as well as coronal X-BONE sequences (TE = 14–28 and TR = 860). The field of view (FOV) was 16–18 cm, matrix 256 × 184, 4 mm slice thickness, 0.4 mm gap, NEX = 2. The total duration of MR examination was about 40 min (30 min for standard MR plus 10 min for weight-bearing MRI exam). 2.4. Stability/instability evaluation of medial meniscus injuries The evaluation of MR exam was performed separately by two experienced musculoskeletal radiologists (AB and LC). Problematic cases (in number of 5) were discussed together to accomplish a common diagnosis. The measurements to assess the meniscal stability/instability were taken on both sagittal and coronal scan planes passing through the posterior horn of the medial meniscus. Medial meniscus anatomy and load-induced physiological variations were evaluated by measuring 4 parameters: 1. meniscal morphology, scored through a three-point Likert scale (0 = regular, 1 = slightly irregular, 2 = irregular); 2. intrameniscal signal analysis, scored through a five-point Likert scale (0 = homogeneous, 1 = slightly non-homogeneous,
non-homogeneous, 3 = non-homogeneous, 2 = rather 4 = strongly non-homogeneous); 3. the assessment of meniscal extrusion on a coronal plane (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau); 4. the assessment of meniscal extrusion on a sagittal plane (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau). Analyzing standard MR examinations of grade 3 meniscal degenerations (A and B), longitudinal lesions and traumatic meniscocapsular separation, we evaluated: 1. medial meniscus morphology and signal intensity, thus making a basic diagnosis; 2. the assessment of meniscal extrusion (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau); Employing the weight-bearing MR we evaluated: 1. meniscal morphology and signal intensity load-induced variations, scored on a five-point Likert scale (0 = no alterations; 1 = slight alteration of injury and signal; 2 = noticeable alteration of lesion morphology and signal intensity; 3 = remarkable alteration of lesion morphology and signal intensity; 4 = meniscal fragments); 2. meniscal extrusion increase on a coronal plane (measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau). Moreover, in cases of traumatic meniscocapsular separation, meniscal stability/instability was evaluated on sagittal scanning planes, by measuring the increase of the gap between meniscus and capsule. 2.5. Arthroscopy All the patients belonging to the second group (2A and 2B) underwent arthroscopic surgery 18–25 days after the weightbearing MRI examination. 3. Results 3.1. Anatomy and physiological load-induced modifications: evaluations and results Medial meniscus scans acquired in the supine position by using both the 1.5 T and the 0.25 T-dedicated low-field MR standard in supine position, showed a homogeneous intensity of intrameniscal signal and a regular meniscal morphology, both on sagittal and coronal planes, in the first group of patients. No significant differences were found between information obtained with the 1.5 T MR system and those provided by the dedicated magnet. After a 82◦ table rotation, MRI examinations allowed evaluation of the physiological variations of the signal under physiological load, as well as of the medial meniscal position and morphology. Morphology, intrameniscal signal and measurements of the grade of medial meniscal extrusion, evaluated on both sagittal and coronal planes, did not show statistically significant differences (Fig. 1 and Table 1).
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(eleven grade 3A-lesions (Fig. 2) and eight grade 3B-lesions (Fig. 3)) (Table 2). Neither false positives nor false negatives were found. 3.3. Traumatic meniscal tears: evaluation and results High-field MRI scan identified 21 traumatic tears (group 2B) including 6 traumatic meniscocapsular separation and 15 longitudinal tears of the medial meniscus posterior horn. In every patient, weight-bearing MRI confirmed the high-field MRI diagnosis. Upright MRI showed meniscal instability in 9 out of 21 cases (3 meniscocapsular separation (Fig. 4) and 6 longitudinal tears (Fig. 5)) (Table 3). Neither false positives nor false negatives were found. 3.4. Arthroscopy: results Arthroscopy confirmed in every case the diagnosis obtained by weight-bearing MRI (19 degenerative unstable lesions, 9 traumatic unstable lesions). 4. Discussion and conclusion
Fig. 1. Anatomy of the medial meniscus with dedicated low-field standard and upright-MRI. (A) Sagittal scan plane PD-weighted in the supine position. (B) Coronal scan plane GE-weighted in the supine position. (C) Sagittal scan plane PD-weighted in orthostatic position. (D) Coronal scan plane GE-weighted in orthostatic position. Both morphology and signal intensity of medial meniscus do not change during the passage from a clinostatic to an orthostatic position.
3.2. Degenerative meniscal tears: evaluation and results High-field MR examinations of group 2A revealed 21 linear signal alterations (grade 3A) and 15 globular degenerative signal alterations (grade 3B). In order to evaluate degenerative meniscal injuries, we used a widely accepted, four-grade classification, as the most cited and reproducible by MRI, based on intrameniscal signal and evaluated on sagittal plane. The coronal plane was used to measure the meniscal extrusion grade. The dedicated MRI exam carried out in clinostatism confirmed in every patient the high-field MRI diagnosis. 2A-group MR examination under physiological load identified unstable meniscal tears in 19 out of 36 cases belonging to the second group Table 1 Physiological anatomy and modifications of the load. Parameters
Standard MR
Weight-bearing MR
Intrameniscal signal (Likert scale) Meniscal morphology (Likert scale) Meniscal extrusion (sagittal)a Meniscal extrusion (coronal)b
Homogeneous Regular Absent Absent
Homogeneous Regular Absent Absent
a The assessment of meniscal extrusion on a sagittal plane (by measuring meniscal portion which was out of a plane passing through the outer edge of medial femoral condyle and the outer edge of the medial tibial plateau). b The assessment of meniscal extrusion on a coronal plane (by measuring meniscal portion which was out of a plane passing through the outer edge of medial femoral condyle and the outer edge of the medial tibial plateau).
the the the the
The meniscus is a crucial component of the knee complex biomechanical system, and a critical element in dispersing loads, in increasing the contact area and allowing an even distribution of weight through the articular surfaces. Moreover, menisci deepen the articular surfaces of the otherwise relatively flat tibial plateau, thus providing the adaptation between the relatively round femoral condyles and the flat tibial joint surfaces. The meniscus increase congruity between the rounded femoral condyles and the flattened surfaces of the tibial plateau. The meniscus also promotes load distribution and joint lubrification. The posterior horn of the meniscus has a strong attachment to the tibia near the tibial spine, known as the meniscal root. The posterior horn of the medial meniscus moves minimally during knee flexion. This strong attachment of the posterior horn of the medial meniscus contributes to an increased frequency of tears in this region. Being firmly attached to the tibial plateau through the meniscal root, near the posterior tibial spine, and having little possibility of movement during knee flexion, the posterior horn of the medial meniscus is particularly vulnerable to damage, which can lead both to a degeneration and to an injury in this area. On a normal condition, both morphology and signal intensity of the meniscus do not change during the passage from supine and upright position; furthermore, on the sagittal scan plane, the posterior horn of the medial meniscus always maintains its relationship with the tibial plateau (Fig. 1). The possible meniscal damage, together with the resulting alteration of flexion function, may modify the load distribution model, thus contributing to knee instability. The main MRI criterion to diagnose a meniscal tear is the increased intrameniscal signal intensity of short echo-time sequences (TE) extended to a joint surface. However, an increased meniscal signal intensity is not enough to diagnose a meniscal tear, being this diagnosis more accurate when observed in two or more contiguous images, or when detected on sagittal as well as on coronal planes. The second criterion to diagnose a meniscal tear is the alteration of the normal morphology without previous surgery. Stoller et al. first suggested a classification system based on four MRI meniscal signal variations. Mesgarzadeh et al. further extended the meniscal tears classification up to eight types. However, a common classification system has not been accepted, yet.
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Fig. 2. Unstable degeneration (tear type 3) of the medial meniscus posterior horn. (A) Sagittal scan plane PD-weighted in the supine position with dedicated low-field MRI shows type 3 degeneration tear of the posterior horn of the medial meniscus. (B) Sagittal scan plane PD-weighted in the orthostatic position with low-field upright-MRI confirms type 3 degeneration tear and suggests an unstable lesion well depicting a posterior shift of the horn: see lines in (A) and (B). (C) Arthroscopy confirms unstable type 3 degenerative tear of the medial meniscus.
Fig. 3. Stable degeneration (tear type 3) of the medial meniscus posterior horn. (A) MRI sagittal scan plane PD-weighted using 1.5 T unit and (B) sagittal scan plane PDweighted in the supine position with dedicated low-field MRI; type 3 degeneration tear of the medial meniscus posterior horn is well documented in both images. (C) Sagittal scan plane PD-weighted in the orthostatic position with low-field upright-MRI; note the absence of significative modification of the meniscus with respect to clinostatic examination. (D) Arthroscopy confirms stable type 3 degeneration tear of the medial meniscus.
In our study, we adopted a widely accepted classification system, which is based on four grades of meniscal alteration: grade 0 = normal meniscus, with homogeneous low signal of the entire meniscus; grade 1 = increased intrameniscal signal limited to a clearly localized globular focus not extended to a joint surface; grade 2 = increased linear wedge-shape intrameniscal signal not extending to the joint surface; grade 3 = real meniscal tear, increased linear (3A group) or globular (3B group) intrameniscal signal alteration that reaches the upper or lower articular surface; grade 4 describes a torn and fragmented meniscus. It is worth noting that this classification system is based on signal intensity, and that only grade 3 indicates a meniscal injury [10–12].
Another important criterion to evaluate meniscus instability is the presence of meniscal extrusion, or the medial displacement of the medial meniscus beyond the tibial margin. According to many studies, this seems to result from a remarkable degeneration of the meniscus circumferential fibres, with the subsequent loss of the ability to resist hoop strain. Moreover, the degeneration of the circumferential fibres reduces the meniscus ability to distribute the load, thus causing joint cartilage degeneration. A medial meniscus extrusion higher than 3 mm has been associated with degenerative meniscal diseases, to radial, complex, horizontal meniscal tears and mainly to tears involving meniscal root, with subsequent loss of meniscal stability [13–16].
Fig. 4. Unstable traumatic meniscocapsular separation of the medial meniscus posterior horn. (A) Sagittal scan plane PD-weighted with 1.5 T MRI and (B) sagittal scan plane PD-weighted in the supine position with dedicated low-field MRI well documented the lesion. (C) Sagittal scan plane PD-weighted in the orthostatic position with low-field upright-MRI showing an increased space between the meniscus and capsule (see lines in (B) and (C)) indicates an unstable lesion. (D) Arthroscopy confirms unstable meniscocapsular separation of the medial meniscus posterior horn.
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Table 2 Meniscal degeneration. Cases
Standard MR
Weight-bearing MR
Results
Arthroscopy
– – – – 3 mm 2.5 mm – – – 1.8 mm 2.3 mm – – – 2 mm 3.3 mm 2.7 mm – 2.5 mm – –
Stable Stable Unstable Stable Unstable Unstable Stable Unstable Stable Unstable Unstable Stable Stable Stable Unstable Unstable Unstable Stable Unstable Unstable Stable
– – 1.8 mm – 2.2 mm – – 3 mm 2.6 mm – – 3.2 mm – – –
Stable Stable Unstable Stable Unstable Unstable Stable Unstable Unstable Stable Unstable Unstable Unstable Stable Stable
Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed
Morphology and intensity of signal
Meniscal extrusiona (mm)
Modification morphology and intensity of signal (Likert scale)
Increase meniscal extrusiona (mm)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A Grade 3A
No No No No Yes (1.2 mm) Yes (0.8 mm) No No No Yes (0.3 mm) Yes (1 mm) No No No No Yes (0.8 mm) Yes (1 mm) No Yes (0.7 mm) No No
0 0 3–4 0–1 4 3–4 0 3 0–1 3 4 0 0–1 0–1 3–4 4 3–4 0 3–4 3–4 0
22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B Grade 3B
No No No No Yes (0.4 mm) No No Yes (1.2 mm) Yes (0.6 mm) No No Yes (1 mm) No No No
0 0 2 0 3–4 3–4 0 4 3 0 3–4 4 3 0 3–4
a The assessment of meniscal extrusion on a coronal plane (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau).
In our experience, weight-bearing MRI always depicted unstable lesions. In these cases, during the passage from supine and upright position, a modification of the meniscal morphology was constantly present, resulting in a posterior subluxation of the posterior horn of the medial meniscus. This phenomenon can be well appreciated on sagittal scan planes in which the posterior horn of the medial
meniscus loses its congruity with the tibial plateau (Fig. 2). Otherwise, morphological modifications and posterior subluxation of the posterior horn of the medial meniscus, were not present in stable lesions (Fig. 3). Traumatic meniscal injuries are described on the basis of their different morphology: they can have longitudinal, horizontal,
Fig. 5. Unstable longitudinal traumatic tear of the medial meniscus posterior horn. (A) Sagittal scan plane PD-weighted in the supine position with dedicated low-field MRI shows the longitudinal tear of the free edge of the posterior horn of the medial meniscus. (B) Sagittal scan plane PD-weighted in the orthostatic position with low-field upright-MRI shows the increased intrameniscal extension of the lesion to the articular surface (arrow). (C) Arthroscopy confirms unstable traumatic tear of the medial meniscus with the presence of flap.
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Table 3 Meniscal traumatic tears. Cases
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 5 6
Standard MR
Weight-bearing MR
Results
Arthroscopy
– – – – 2 mm – – 1.7 mm – – – – – 0.4 mm –
Stable Unstable Stable Stable Unstable Unstable Stable Unstable Stable Stable Stable Unstable Stable Unstable Stable
Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed Confirmed
0
Expansion of space between meniscus and capsule (mm) 1.2
Unstable
Confirmed
0
1.4
Unstable
Confirmed
0
–
Stable
Confirmed
0
0.8
Unstable
Confirmed
0
–
Stable
Confirmed
0
–
Stable
Confirmed
Morphology and intensity of signal
Meniscal extrusiona (mm)
Modification morphology and intensity of signal (Likert scale)
Increase meniscal extrusion coronal** (mm)
Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear Horizontal tear
No No No No Si (1 mm) No No Si (0.8 mm) No No No No No No No
0 3 0–1 0 3–4 3 0 2 0–1 0 0 3–4 0 3 0–1 Modification morphology and intensity of signal (Likert scale)
Traumatic meniscocapsular separation Traumatic meniscocapsular separation Traumatic meniscocapsular separation Traumatic meniscocapsular separation Traumatic meniscocapsular separation Traumatic meniscocapsular separation
a The assessment of meniscal extrusion on a coronal plane (by measuring the meniscal portion which was out of a plane passing through the outer edge of the medial femoral condyle and the outer edge of the medial tibial plateau).
radial, complex, bucket-handle patterns. For this reason they have different clinical and surgical implications. Usually, longitudinal and oblique tears can be repaired, while horizontal, radial and complex lesions are frequently hard to fix through a simple meniscal repair and need either partial meniscectomy or complete meniscectomy [17,18]. Therefore, in this study these injuries have been excluded. In our experience, all cases of unstable meniscocapsular separations, unlike stable ones, presented an increase of meniscocapsular distance on sagittal scan planes (Fig. 4). In unstable traumatic longitudinal tears of the posterior horn of the medial meniscus, weight-bearing MRI depicted in all cases an increase of the tear-related intrameniscal high signal intensity, sometimes allowing a better identification of small flaps of the free edge (Fig. 5). The absence of false positives and false negatives in this study is probably due to two main reasons: an extremely careful and targeted patient selection and the potentials of weight-bearing MRI which really allows to determine the stability/instability of a meniscal tear. Moreover, the targeted patient series and consequently the restricted number of patients, who underwent weight-bearing MRI exam, finds its explanation in the accurate clinical selection. Indeed, all these patients were preliminarily clinically evaluated by an orthopaedic group posing a precise diagnostic question in view of a possible surgical treatment. The good match between weight-bearing MRI and arthroscopy in diagnosing both degenerative and traumatic tears shows that a stable/unstable lesion can be easily detected on sagittal scan planes; moreover, in clinical practise, this result can be obtained
by additional 10 min to the standard MR examination that do not discomfort to the patient. The decision of surgery is based mainly on clinical data, lesion morphology, size and location detectable on standard MRI scans [19,20]. Orthopaedic surgery is currently mostly conservative: in fact, during a meniscus repair or a meniscus removal intervention, the most common goal is to preserve as much meniscal tissue as possible, in order to reduce subsequent degenerative alterations [20]. In our experience, only some kind of injuries were associated with instability, and could benefit from surgery. Although meniscal stability/instability has been evaluated through arthroscopic investigation, our study highlighted the diagnostic usefulness of weight-bearing MRI, which allowed us to evaluate the biomechanical stress caused by a physiological load, thus making a latent instability of the meniscus reliably evident. This was possible through an in vivo, non invasive reproduction of how a biomechanical stress results on a joint with a medial meniscal tear. Upright MRI allows to record every load-induced physiological variations, thus showing both the meniscal tear stability and a latent instability, making it possible to correctly guide the orthopaedic surgeon towards a conservative treatment, meniscal repair or rather towards a partial meniscectomy. Moreover, this new diagnostic instrument allows to recognize the stability of a meniscal tear, thus avoiding the damages deriving from arthroscopic investigations, as well as allowing a spontaneous healing of the injury. This new approach to meniscal pathologies help in the diagnostic and therapeutic.
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