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Incidence of Bilateral Discoid Lateral Meniscus in An Asian Population: An Arthroscopic Assessment of Contralateral Knees
Incidence of Bilateral Discoid Lateral Meniscus in An Asian Population: An Arthroscopic Assessment of Contralateral Knees Ji-Hoon Bae, M.D., Hong-Chul Lim, M.D., Dae-Hee Hwang, M.D., Jae-Kwang Song, M.D., Jun-Sung Byun, M.D., and Kyung-Wook Nha, M.D.
Purpose: To investigate the incidence of bilateral discoid lateral meniscus (DLM) and to evaluate the arthroscopic features of lateral meniscus in asymptomatic contralateral knees in an Asian population who presented with symptomatic DLMs. Methods: This study prospectively enrolled 52 consecutive patients who underwent arthroscopic procedures for symptomatic DLMs (31 complete and 21 incomplete) and who consented to the examination of the contralateral knee at the time of arthroscopy. Types of DLMs and of meniscus tears were assessed by use of arthroscopic findings. Preoperative and postoperative functional outcomes were evaluated with Lysholm and Tegner activity scores. Results: Arthroscopic examinations showed 21 complete DLMs, 19 incomplete DLMs, 11 normal lateral menisci, and 1 ring-shaped lateral meniscus in contralateral knees. The incidence of bilateral DLM in our study population was 79% (41 of 52 contralateral knees). Furthermore, 65% of patients (34 pairs of knees) had the same DLM types. In addition, 3 pairs of knees with complete DLMs had menisci of different thicknesses. DLM tears were observed in 2 contralateral knees (1 radial and 1 longitudinal) and were treated by partial central meniscectomy. Conclusions: This study provides evidence of the high prevalence of bilateral DLM in an Asian population. Level of Evidence: Level I, testing of previously developed diagnostic criteria in a series of consecutive patients.
D
iscoid lateral meniscus (DLM) is a well-known anatomic variant of clinical importance because it may be prone to intrasubstance degeneration and tears, although most surgeons agree that asymptomatic DLMs do not require surgical treatment.1-3 Early studies showed that DLMs are more prone to mechanical stresses and tears than normal lateral me-
From the Department of Orthopaedic Surgery, Inje University, Ilsanpaik Hospital (J-H.B., D-H.H., J-K.S., K-W.N.), Ilsan; Department of Orthopaedic Surgery, Korea University, Ansan Hospital (J-H.B., J-S.B.), Ansan; and Department of Orthopaedic Surgery, Korea University, Guro Hospital (H-C.L.), Seoul, South Korea. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received May 11, 2011; accepted December 2, 2011. Address correspondence to Kyung-Wook Nha, M.D., Ph.D., Department of Orthopaedic Surgery, Inje University, Ilsanpaik Hospital, 2240 Daehwadong, Ilsanseogu, Goyangsi, Gyeonggido, 411706, South Korea. E-mail: [email protected] © 2012 by the Arthroscopy Association of North America 0749-8063/11292/$36.00 doi:10.1016/j.arthro.2011.12.003
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nisci because they are thicker and have less vasculature, which often lacks peripheral attachments.4-9 Frequently, patients with a DLM tear or their family members question the likelihood of a DLM in the contralateral knee. However, few epidemiologic data are available on the incidence of bilateral DLM. The incidence of bilateral DLM has been reported to range from 5% to 20%.9-14 However, the true incidence of bilateral DLM may be underestimated because in most patients, the contralateral knees are asymptomatic. In a recent magnetic resonance imaging (MRI) study, it was found that DLM commonly occurs bilaterally.15 However, although MRI is a valuable noninvasive diagnostic tool, it sometimes provides inadequate details of DLM tear morphology (type, shape, and thickness).16,17 We designed this study to determine the incidence of bilateral DLM and to document and compare DLM shapes in pairs of knees. On the basis of the findings of a recent report,15 we hypothesized that (1) the incidence of bilateral DLM is higher than previously
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 28, No 7 (July), 2012: pp 936-941
BILATERAL DISCOID LATERAL MENISCUS reported and (2) the shapes of lateral menisci are similar in paired knees. METHODS Study Design and Subjects Institutional review board approval was obtained before this prospective investigation, and all patients provided written informed consent before participating in the study. Each patient was asked to allow us to examine the contralateral asymptomatic knee at the time of symptomatic knee surgery, and those who agreed were included. We enrolled 52 patients (Korean) from September 2004 to December 2009. There were 21 female and 31 male patients with a mean age of 25.4 ⫾ 14.5 years.
937
alyzed, because a previous study showed that a high fibular head and a widened lateral tibiofemoral joint space are statistically associated with the presence of a DLM. A fibular head height was defined as the distance from the imaginary tibial joint line to the tip of the fibular head. The lateral tibiofemoral joint space was defined as the distance from the imaginary tibial joint line to the lateral femoral condylar joint line at its midportion. A fibular head height of less than 13 mm and a lateral tibiofemoral joint space greater than 5 mm were deemed positive findings.15,20 The measurement was recorded to the nearest one-tenth of millimeter by use of a digitized picture archiving and communication system (STARPACS; Infinitt Healthcare, Seoul, South Korea), and the magnification factor was corrected automatically in the program. Symptomatic and contralateral knees were compared with respect to these 2 parameters.
Preoperative MRI in Symptomatic Knees Preoperatively, DLMs were confirmed by use of 1.5-T MRI scans in the symptomatic knees of all patients. MRI criteria for a DLM include 3 or more successive sagittal slices with continuity between the anterior and posterior meniscal horns or a transverse meniscal diameter of greater than 15 mm or greater than 20% of the tibial width on transverse images.7,18 All of the magnetic resonance images were reviewed by an independent musculoskeletal radiologist. The morphologic types of DLMs were determined by the Watanabe classification as follows: complete, incomplete, or Wrisberg type, which is described as a normal-shaped meniscus lacking a posterior coronary ligament attachment with an anomalous attachment to the meniscofemoral ligament of Wrisberg.13 In addition, we differentiated ring-shaped meniscus as the fourth type of DLM.19 The potential presence of intra-articular pathology, such as a meniscal tear, ligament injury, or chondral lesion, was carefully examined. DLM tear patterns were classified as horizontal, longitudinal, bucket handle, radial, and complex. MRI was not performed in contralateral asymptomatic knees. Plain Radiographs Standard plain radiographs of both knees were taken, including anteroposterior view with weight bearing, lateral view at 30° of knee flexion, Merchant view, and both tibia tunnel views. Characteristic radiographic findings were evaluated as described by Kim et al.20 Of the several parameters, lateral tibiofemoral joint space and fibular head height were an-
Arthroscopic Examination We examined the contralateral knee arthroscopically at the time of symptomatic knee surgery, because this would provide more accurate morphologic information on menisci with tears at lower cost than MRI, despite its invasive nature. All arthroscopies were performed by 1 of 2 authors (J-H.B. or K-W.N.). Symptomatic knees were first examined systematically through an anterolateral portal to detect evidence of coexistent pathologies. The meniscus was carefully probed to determine the type of discoid, as well as its thickness, and tear extent. Discoid menisci were classified based on morphology as described earlier and peripheral rim stability (stable or unstable).21,22 DLM tear patterns were classified as simple horizontal, complicated horizontal, longitudinal, bucket handle, radial, or complex.23 If the main component of a tear was horizontal whereas another component was combined, the tear was defined as a complicated horizontal tear, and a complex tear was defined as a combination of 2 major tear components (except a horizontal tear) or as a combination of 3 or more major tear components including a horizontal tear. Associated meniscal tears were treated by partial meniscectomy leaving a 6- to 8-mm intact peripheral rim of meniscal tissue. After meniscectomy, pathologic instability was treated by meniscal repair to the capsule. After arthroscopic procedures had been conducted on symptomatic knees, contralateral knees were examined to determine the morphologies of contralateral menisci. Patients treated by partial meniscectomy alone were allowed immediate weight bearing. Physical therapy
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was instituted at 2 weeks postoperatively, and a gradual return to sports was started at approximately 8 weeks. Patients who underwent meniscal repair in addition to meniscectomy were allowed partial weight bearing with a hinged knee brace, and range of motion was gradually increased to 0° to 90° by weeks 6 to 8. Patients returned to sports activities at 3 to 4 months after surgery. Preoperative and postoperative functional outcomes were evaluated by use of Lysholm scores and Tegner activity scores.
TABLE 1.
Tear Types in Symptomatic Knees Type of Discoid Meniscus
Tear Type
Complete
Incomplete
Total
Simple horizontal Complicated horizontal Longitudinal Bucket handle Radial Complex
19 8 2 2 1 1
7 5 2 2 2 1
26 13 4 4 3 2
Statistical Analysis Preoperative and postoperative Lysholm scores and Tegner activity scores were analyzed by the Wilcoxon signed rank test. The paired t test was used to compare right and left knees with respect to lateral tibiofemoral joint space and fibular head height. The KruskalWallis test was used to compare lateral tibiofemoral joint spaces and heights of fibular heads in the normal, incomplete, and complete discoid groups. Cohen analysis was used to determine levels of interobserver agreement. Values were interpreted as follows according to the classification of Landis and Koch24: no agreement, less than 0; slight agreement, 0 to 0.20; fair agreement, 0.21 to 0.40; moderate agreement, 0.41 to 0.60; substantial agreement, 0.61 to 0.80; and almost perfect agreement, 0.81 to 1. All statistical analyses were performed with SPSS software, version 12.0 (SPSS, Chicago, IL). Statistical significance was accepted for P ⬍ .05. RESULTS Symptomatic Knees Most patients presented with symptoms and signs of a meniscus tear. Pain was the predominant symptom, and lateral tibiofemoral joint line tenderness predominated. On plain radiographs, a high fibular head was seen in 6 knees (12%) and a widened tibiofemoral joint space in 9 (17%). None of the knees had both of these findings. Preoperative MRI scans showed 29 complete and 19 incomplete DLMs. In 4 knees DLM type could not be clearly determined because a torn lateral meniscus had displaced to the intercondylar notch. DLM tears were present in all knees (Table 1). Chondral lesions were found in 4 affected knees, but no ligament injuries were observed. At arthroscopy, DLMs were classified as complete in 31 knees and incomplete in 21. Of the 4 knees not typed by MRI, 2 were of the complete type and 2 were
of the incomplete type. There was no Wrisberg type. A simple horizontal cleavage tear was the most common type of tear encountered (Table 1). In addition, a stable osteochondral lesion of the lateral femoral condyle was found in 1 knee. All the patients were treated by partial central (42 knees) or subtotal (10 knees) meniscectomy. Two patients underwent meniscal repairs after partial central meniscectomy because of an unstable peripheral rim. Antegrade subchondral drilling was performed in 1 knee with an osteochondral lesion of the lateral femoral condyle. At a mean follow-up of 30 ⫾ 5.6 months (range, 22 to 42 months), all patients were asymptomatic with respect to tibiofemoral joint symptoms and did not require further surgery. No knee motion problems, infections, or other complications occurred. The mean Lysholm knee score of 55 ⫾ 4.3 preoperatively improved significantly to 91 ⫾ 3.4 postoperatively (P ⬍ .05), and the median Tegner activity score of 2 preoperatively improved significantly to 5 (P ⬍ .05). No degenerative changes were observed on the plain radiographs at a mean follow-up of 30 months. Contralateral (Asymptomatic) Knees Three patients complained of a painless, audible snap during knee range of motion, especially near terminal extension. However, no treatment was undertaken because there were no meniscal tears or intra-articular pathologies. On plain radiographs, no statistical differences were found between ipsilateral and contralateral knees with respect to lateral tibiofemoral joint space or fibular head height. A high fibular head (6 knees [12%]) and a widened tibiofemoral joint space (9 knees [17%]) were observed in some patients with symptomatic knees. Analysis showed significant and substantial agreement ( ⫽ 0.650). No significant differences were observed between normal, incomplete, and complete discoid types
BILATERAL DISCOID LATERAL MENISCUS TABLE 2.
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Height of Fibular Head and Lateral Tibiofemoral Joint Space Normal Meniscus* (n ⫽ 11)
Incomplete Discoid (n ⫽ 40)
Complete Discoid (n ⫽ 52)
P Value
14.2 ⫾ 1.2 4.2 ⫾ 1.2
13.2 ⫾ 1.2 5.2 ⫾ 1.2
12.2 ⫾ 1.2 6.2 ⫾ 1.2
Not significant Not significant
Fibular head Lateral tibiofemoral joint space
*Crescent-shaped meniscus that covers one-third to one-half of articular surface of corresponding tibial plateau.
in terms of lateral tibiofemoral joint space or fibular head height (Table 2). Arthroscopic examinations showed 21 complete DLMs, 19 incomplete DLMs, 11 normal lateral menisci, and 1 ring-shaped lateral meniscus. The incidence of bilateral DLM in the study population was 79% (41 of 52 contralateral knees). Furthermore, 65% of patients (34 pairs of knees) had the same DLM type (Table 3, Fig 1), and 3 pairs of knees with a complete DLM type had lower DLM thicknesses in contralateral knees. A DLM tear was observed in 2 knees (1 radial and 1 longitudinal), and they were treated with partial meniscectomy. At a mean follow-up of 30 ⫾ 5.6 months, the mean Lysholm knee score was 92 ⫾ 2.6 and the median Tegner activity score was 5. DISCUSSION This study shows that bilateral DLM is more common than previously reported. Recent studies also support a high incidence of bilateral DLM. Ahn et al.15 investigated contralateral knees by MRI in 33 patients who underwent arthroscopic surgery for a symptomatic DLM and found that 97% of patients had bilateral DLM. These findings will help inform patients with a symptomatic DLM regarding the probability of a DLM in the contralateral knee. The true incidence of bilateral DLM is likely to be higher than TABLE 3.
Types of Lateral Menisci in Same Patients
Symptomatic Knee C C C IC IC IC C
Contralateral Knee
No. of Patients
C IC N C IC N Ring shaped*
19 4 7 2 15 4 1
Abbreviations: C, complete discoid lateral meniscus; IC, incomplete discoid lateral meniscus; N, normal crescent-shaped lateral meniscus. *Circular-shaped lateral meniscus with central perforation.19,25-27
previously reported because the majority of previous studies have been conducted on symptomatic knees.9 The findings of this study allow Asian patients with a symptomatic DLM to be better informed about the probability of a DLM in the contralateral knee. Similarities between lateral menisci in bilateral knees have been reported previously.15,28 Kato et al.28 analyzed 602 knees in 306 cadavers and found that the shapes of lateral menisci were similar bilaterally. In addition, in an MRI study,29 88% of 33 patients were found to have same-shaped menisci in both knees. In our study we found that 65% of patients with DLMs had the same shape in both knees. However, interestingly, we found that 3 pairs of knees with a complete DLM had lateral menisci with different thicknesses. It has been reported that plain radiography provides supplementary diagnostic information,9,15,20 but our findings do not support the suggestion that radiographs contribute to preoperative screening assessments or to the diagnosis of DLM without associated tears. The findings suggestive of a DLM include a widened lateral joint space, squaring of the lateral femoral condyle, cupping of the lateral tibial plateau, hypoplasia of the lateral tibial eminence, and elevation of the fibular head. In this study we analyzed only 2 plain radiography parameters that have been statistically associated with the presence of a DLM, namely, fibular head height and widening of the lateral tibiofemoral joint space.20 However, we found that these parameters were not significantly different for normalshaped menisci, incomplete DLMs, and complete DLMs. Two knees with a normal lateral meniscus had a widened lateral tibiofemoral joint space. In addition, all had no significantly different radiographic findings between right and left knees, including 11 patients who had a DLM in the symptomatic knee and a normal lateral meniscus in the contralateral knee. The predictive value of plain radiographs to determine the presence of DLM may still be questionable. An intact DLM is commonly encountered as an incidental finding during arthroscopy or MRI and does not necessarily require treatment.1-3 However, it is not known in what proportion of patients left untreated
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FIGURE 1.
Complete DLM in symptomatic knee and incomplete DLM in contralateral knee.
will a tear or degeneration within the meniscus eventually develop. Presumably, the shape, thickness, structural weakness, poor vascularity, and abnormal mobility of a DLM make it biomechanically weak and prone to tears,4 and recently, this has been borne out by several recent reports.15,28,30,31 In our study 2 DLM tears were incidentally found in the contralateral knees during arthroscopy. More recently, degenerative changes have been reported in adult patients with a DLM tear who were either asymptomatic or became symptomatic when middle aged.29 These reports caution that clinicians should take into account the propensity for degeneration and tear development when a DLM is incidentally detected by MRI or arthroscopy and that treatment should be considered. In addition, we recommend that bilateral DLM should be suspected in patients with a symptomatic DLM and that the contralateral knee should be examined for any clinical or radiologic evidence of a DLM. However, it remains to be determined whether MRI or arthroscopy is required in both knees of suspected DLM patients. The strength of this study was that arthroscopy allowed more accurate assessments to be made of the shapes of DLMs in contralateral knees, even though it is an invasive procedure. In addition, data were collected from a consecutive series of patients. However, the study also has its limitations. In particular, the study cohort was relatively small and subjects were Asian (Korean), and thus our findings cannot be extrapolated to other ethnic groups. Second, because intrasubstance degeneration or tears in DLMs could not be detected at arthroscopy, our findings do not address the true prevalence of DLM pathology in contralateral asymptomatic knees.
CONCLUSIONS This study provides evidence of the high prevalence of bilateral DLM in an Asian population. Acknowledgment: The authors give special thanks to all the patients who participated in this study.
REFERENCES 1. Adachi N, Ochi M, Uchio Y, Kuriwaka M, Shinomiya R. Torn discoid lateral meniscus treated using partial central meniscectomy and suture of the peripheral tear. Arthroscopy 2004;20: 536-542. 2. Atay OA, Doral MN, Leblebiciog˘lu G, Tetik O, Aydingöz U. Management of discoid lateral meniscus tears: Observations in 34 knees. Arthroscopy 2003;19:346-352. 3. Good CR, Green DW, Griffith MH, Valen AW, Widmann RF, Rodeo SA. Arthroscopic treatment of symptomatic discoid meniscus in children: Classification, technique, and results. Arthroscopy 2007;23:157-163. 4. Clark CR, Ogden JA. Development of the menisci of the human knee joint. Morphological changes and their potential role in childhood meniscal injury. J Bone Joint Surg Am 1983;65:538-547. 5. Rosenberg TD, Paulos LE, Parker RD, Harner CD, Gurley WD. Discoid lateral meniscus: Case report of arthroscopic attachment of a symptomatic Wrisberg-ligament type. Arthroscopy 1987;3:277-282. 6. Woods GW, Whelan JM. Discoid meniscus. Clin Sports Med 1990;9:695-706. 7. Kocher MS, Klingele K, Rassman SO. Meniscal disorders: Normal, discoid, and cysts. Orthop Clin North Am 2003;34: 329-340. 8. Auge WK II, Kaeding CC. Bilateral discoid medial menisci with extensive intrasubstance cleavage tears: MRI and arthroscopic correlation. Arthroscopy 1994;10:313-318. 9. Rao SK, Rao PS. Clinical, radiologic and arthroscopic assessment and treatment of bilateral discoid lateral meniscus. Knee Surg Sports Traumatol Arthrosc 2007;15:597-601.
BILATERAL DISCOID LATERAL MENISCUS 10. Aichroth PM, Patel DV, Marx CL. Congenital discoid lateral meniscus in children. A follow-up study and evolution of management. J Bone Joint Surg Br 1991;73:932-936. 11. Bellier G, Dupont JY, Larrain M, Caudron C, Carlioz H. Lateral discoid menisci in children. Arthroscopy 1989;5:52-56. 12. Pellacci F, Montanari G, Prosperi P, Galli G, Celli V. Lateral discoid meniscus: Treatment and results. Arthroscopy 1992;8: 526-530. 13. Ikeuchi H. Arthroscopic treatment of the discoid lateral meniscus. Technique and long-term results. Clin Orthop Relat Res 1982:19-28. 14. Dickhaut SC, DeLee JC. The discoid lateral-meniscus syndrome. J Bone Joint Surg Am 1982;64:1068-1073. 15. Ahn JH, Lee SH, Yoo JC, Lee HJ, Lee JS. Bilateral discoid lateral meniscus in knees: Evaluation of the contralateral knee in patients with symptomatic discoid lateral meniscus. Arthroscopy 2010;26:1348-1356. 16. Yue BW, Gupta AK, Moorman CT III, Garrett WE, Helms CA. Wrisberg variant of the discoid lateral meniscus with flipped meniscal fragments simulating bucket-handle tear: MRI and arthroscopic correlation. Skeletal Radiol 2011;40:1089-1094. 17. Kim YG, Ihn JC, Park SK, Kyung HS. An arthroscopic analysis of lateral meniscal variants and a comparison with MRI findings. Knee Surg Sports Traumatol Arthrosc 2006;14:20-26. 18. Silverman JM, Mink JH, Deutsch AL. Discoid menisci of the knee: MR imaging appearance. Radiology 1989;173:351-354. 19. Monllau JC, León A, Cugat R, Ballester J. Ring-shaped lateral meniscus. Arthroscopy 1998;14:502-504. 20. Kim SJ, Moon SH, Shin SJ. Radiographic knee dimensions in discoid lateral meniscus: Comparison with normal control. Arthroscopy 2000;16:511-516.
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21. Jordan MR. Lateral meniscal variants: Evaluation and treatment. J Am Acad Orthop Surg 1996;4:191-200. 22. Andrish JT. Meniscal injuries in children and adolescents: Diagnosis and management. J Am Acad Orthop Surg 1996;4: 231-237. 23. Bin SI, Kim JC, Kim JM, Park SS, Han YK. Correlation between type of discoid lateral menisci and tear pattern. Knee Surg Sports Traumatol Arthrosc 2002;10:218-222. 24. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33:159-174. 25. Pandey V, Dinesh KV, Acharya KK, Rao PS. Ring meniscus mistaken for incomplete discoid meniscus: A case report and review of literature. Knee Surg Sports Traumatol Arthrosc 2010;18:543-545. 26. Arnold MP, Van Kampen A. Symptomatic ring-shaped lateral meniscus. Arthroscopy 2000;16:852-854. 27. Kim SJ, Jeon CH, Koh CH. A ring-shaped lateral meniscus. Arthroscopy 1995;11:738-739. 28. Kato Y, Oshida M, Aizawa S, Saito A, Ryu J. Discoid lateral menisci in Japanese cadaver knees. Mod Rheumatol 2004;14: 154-159. 29. Ahn JH, Choi SH, Lee YS, et al. Symptomatic torn discoid lateral meniscus in adults. Knee Surg Sports Traumatol Arthrosc 2011;19:158-164. 30. Nawata K, Teshima R, Ohno M, Takita T, Otuki K. Discoid lateral menisci in older patients. A radiographic study of 21 cases. Int Orthop 1999;23:232-235. 31. Rohren EM, Kosarek FJ, Helms CA. Discoid lateral meniscus and the frequency of meniscal tears. Skeletal Radiol 2001;30: 316-320.
Purpose: To investigate the incidence of bilateral discoid lateral meniscus (DLM) and to evaluate the arthroscopic features of lateral meniscus in asymptomatic contralateral knees in an Asian population who presented with symptomatic DLMs. Methods: This study prospectively enrolled 52 consecutive patients who underwent arthroscopic procedures for symptomatic DLMs (31 complete and 21 incomplete) and who consented to the examination of the contralateral knee at the time of arthroscopy. Types of DLMs and of meniscus tears were assessed by use of arthroscopic findings. Preoperative and postoperative functional outcomes were evaluated with Lysholm and Tegner activity scores. Results: Arthroscopic examinations showed 21 complete DLMs, 19 incomplete DLMs, 11 normal lateral menisci, and 1 ring-shaped lateral meniscus in contralateral knees. The incidence of bilateral DLM in our study population was 79% (41 of 52 contralateral knees). Furthermore, 65% of patients (34 pairs of knees) had the same DLM types. In addition, 3 pairs of knees with complete DLMs had menisci of different thicknesses. DLM tears were observed in 2 contralateral knees (1 radial and 1 longitudinal) and were treated by partial central meniscectomy. Conclusions: This study provides evidence of the high prevalence of bilateral DLM in an Asian population. Level of Evidence: Level I, testing of previously developed diagnostic criteria in a series of consecutive patients.
D
iscoid lateral meniscus (DLM) is a well-known anatomic variant of clinical importance because it may be prone to intrasubstance degeneration and tears, although most surgeons agree that asymptomatic DLMs do not require surgical treatment.1-3 Early studies showed that DLMs are more prone to mechanical stresses and tears than normal lateral me-
From the Department of Orthopaedic Surgery, Inje University, Ilsanpaik Hospital (J-H.B., D-H.H., J-K.S., K-W.N.), Ilsan; Department of Orthopaedic Surgery, Korea University, Ansan Hospital (J-H.B., J-S.B.), Ansan; and Department of Orthopaedic Surgery, Korea University, Guro Hospital (H-C.L.), Seoul, South Korea. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received May 11, 2011; accepted December 2, 2011. Address correspondence to Kyung-Wook Nha, M.D., Ph.D., Department of Orthopaedic Surgery, Inje University, Ilsanpaik Hospital, 2240 Daehwadong, Ilsanseogu, Goyangsi, Gyeonggido, 411706, South Korea. E-mail: [email protected] © 2012 by the Arthroscopy Association of North America 0749-8063/11292/$36.00 doi:10.1016/j.arthro.2011.12.003
936
nisci because they are thicker and have less vasculature, which often lacks peripheral attachments.4-9 Frequently, patients with a DLM tear or their family members question the likelihood of a DLM in the contralateral knee. However, few epidemiologic data are available on the incidence of bilateral DLM. The incidence of bilateral DLM has been reported to range from 5% to 20%.9-14 However, the true incidence of bilateral DLM may be underestimated because in most patients, the contralateral knees are asymptomatic. In a recent magnetic resonance imaging (MRI) study, it was found that DLM commonly occurs bilaterally.15 However, although MRI is a valuable noninvasive diagnostic tool, it sometimes provides inadequate details of DLM tear morphology (type, shape, and thickness).16,17 We designed this study to determine the incidence of bilateral DLM and to document and compare DLM shapes in pairs of knees. On the basis of the findings of a recent report,15 we hypothesized that (1) the incidence of bilateral DLM is higher than previously
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 28, No 7 (July), 2012: pp 936-941
BILATERAL DISCOID LATERAL MENISCUS reported and (2) the shapes of lateral menisci are similar in paired knees. METHODS Study Design and Subjects Institutional review board approval was obtained before this prospective investigation, and all patients provided written informed consent before participating in the study. Each patient was asked to allow us to examine the contralateral asymptomatic knee at the time of symptomatic knee surgery, and those who agreed were included. We enrolled 52 patients (Korean) from September 2004 to December 2009. There were 21 female and 31 male patients with a mean age of 25.4 ⫾ 14.5 years.
937
alyzed, because a previous study showed that a high fibular head and a widened lateral tibiofemoral joint space are statistically associated with the presence of a DLM. A fibular head height was defined as the distance from the imaginary tibial joint line to the tip of the fibular head. The lateral tibiofemoral joint space was defined as the distance from the imaginary tibial joint line to the lateral femoral condylar joint line at its midportion. A fibular head height of less than 13 mm and a lateral tibiofemoral joint space greater than 5 mm were deemed positive findings.15,20 The measurement was recorded to the nearest one-tenth of millimeter by use of a digitized picture archiving and communication system (STARPACS; Infinitt Healthcare, Seoul, South Korea), and the magnification factor was corrected automatically in the program. Symptomatic and contralateral knees were compared with respect to these 2 parameters.
Preoperative MRI in Symptomatic Knees Preoperatively, DLMs were confirmed by use of 1.5-T MRI scans in the symptomatic knees of all patients. MRI criteria for a DLM include 3 or more successive sagittal slices with continuity between the anterior and posterior meniscal horns or a transverse meniscal diameter of greater than 15 mm or greater than 20% of the tibial width on transverse images.7,18 All of the magnetic resonance images were reviewed by an independent musculoskeletal radiologist. The morphologic types of DLMs were determined by the Watanabe classification as follows: complete, incomplete, or Wrisberg type, which is described as a normal-shaped meniscus lacking a posterior coronary ligament attachment with an anomalous attachment to the meniscofemoral ligament of Wrisberg.13 In addition, we differentiated ring-shaped meniscus as the fourth type of DLM.19 The potential presence of intra-articular pathology, such as a meniscal tear, ligament injury, or chondral lesion, was carefully examined. DLM tear patterns were classified as horizontal, longitudinal, bucket handle, radial, and complex. MRI was not performed in contralateral asymptomatic knees. Plain Radiographs Standard plain radiographs of both knees were taken, including anteroposterior view with weight bearing, lateral view at 30° of knee flexion, Merchant view, and both tibia tunnel views. Characteristic radiographic findings were evaluated as described by Kim et al.20 Of the several parameters, lateral tibiofemoral joint space and fibular head height were an-
Arthroscopic Examination We examined the contralateral knee arthroscopically at the time of symptomatic knee surgery, because this would provide more accurate morphologic information on menisci with tears at lower cost than MRI, despite its invasive nature. All arthroscopies were performed by 1 of 2 authors (J-H.B. or K-W.N.). Symptomatic knees were first examined systematically through an anterolateral portal to detect evidence of coexistent pathologies. The meniscus was carefully probed to determine the type of discoid, as well as its thickness, and tear extent. Discoid menisci were classified based on morphology as described earlier and peripheral rim stability (stable or unstable).21,22 DLM tear patterns were classified as simple horizontal, complicated horizontal, longitudinal, bucket handle, radial, or complex.23 If the main component of a tear was horizontal whereas another component was combined, the tear was defined as a complicated horizontal tear, and a complex tear was defined as a combination of 2 major tear components (except a horizontal tear) or as a combination of 3 or more major tear components including a horizontal tear. Associated meniscal tears were treated by partial meniscectomy leaving a 6- to 8-mm intact peripheral rim of meniscal tissue. After meniscectomy, pathologic instability was treated by meniscal repair to the capsule. After arthroscopic procedures had been conducted on symptomatic knees, contralateral knees were examined to determine the morphologies of contralateral menisci. Patients treated by partial meniscectomy alone were allowed immediate weight bearing. Physical therapy
938
J-H. BAE ET AL.
was instituted at 2 weeks postoperatively, and a gradual return to sports was started at approximately 8 weeks. Patients who underwent meniscal repair in addition to meniscectomy were allowed partial weight bearing with a hinged knee brace, and range of motion was gradually increased to 0° to 90° by weeks 6 to 8. Patients returned to sports activities at 3 to 4 months after surgery. Preoperative and postoperative functional outcomes were evaluated by use of Lysholm scores and Tegner activity scores.
TABLE 1.
Tear Types in Symptomatic Knees Type of Discoid Meniscus
Tear Type
Complete
Incomplete
Total
Simple horizontal Complicated horizontal Longitudinal Bucket handle Radial Complex
19 8 2 2 1 1
7 5 2 2 2 1
26 13 4 4 3 2
Statistical Analysis Preoperative and postoperative Lysholm scores and Tegner activity scores were analyzed by the Wilcoxon signed rank test. The paired t test was used to compare right and left knees with respect to lateral tibiofemoral joint space and fibular head height. The KruskalWallis test was used to compare lateral tibiofemoral joint spaces and heights of fibular heads in the normal, incomplete, and complete discoid groups. Cohen analysis was used to determine levels of interobserver agreement. Values were interpreted as follows according to the classification of Landis and Koch24: no agreement, less than 0; slight agreement, 0 to 0.20; fair agreement, 0.21 to 0.40; moderate agreement, 0.41 to 0.60; substantial agreement, 0.61 to 0.80; and almost perfect agreement, 0.81 to 1. All statistical analyses were performed with SPSS software, version 12.0 (SPSS, Chicago, IL). Statistical significance was accepted for P ⬍ .05. RESULTS Symptomatic Knees Most patients presented with symptoms and signs of a meniscus tear. Pain was the predominant symptom, and lateral tibiofemoral joint line tenderness predominated. On plain radiographs, a high fibular head was seen in 6 knees (12%) and a widened tibiofemoral joint space in 9 (17%). None of the knees had both of these findings. Preoperative MRI scans showed 29 complete and 19 incomplete DLMs. In 4 knees DLM type could not be clearly determined because a torn lateral meniscus had displaced to the intercondylar notch. DLM tears were present in all knees (Table 1). Chondral lesions were found in 4 affected knees, but no ligament injuries were observed. At arthroscopy, DLMs were classified as complete in 31 knees and incomplete in 21. Of the 4 knees not typed by MRI, 2 were of the complete type and 2 were
of the incomplete type. There was no Wrisberg type. A simple horizontal cleavage tear was the most common type of tear encountered (Table 1). In addition, a stable osteochondral lesion of the lateral femoral condyle was found in 1 knee. All the patients were treated by partial central (42 knees) or subtotal (10 knees) meniscectomy. Two patients underwent meniscal repairs after partial central meniscectomy because of an unstable peripheral rim. Antegrade subchondral drilling was performed in 1 knee with an osteochondral lesion of the lateral femoral condyle. At a mean follow-up of 30 ⫾ 5.6 months (range, 22 to 42 months), all patients were asymptomatic with respect to tibiofemoral joint symptoms and did not require further surgery. No knee motion problems, infections, or other complications occurred. The mean Lysholm knee score of 55 ⫾ 4.3 preoperatively improved significantly to 91 ⫾ 3.4 postoperatively (P ⬍ .05), and the median Tegner activity score of 2 preoperatively improved significantly to 5 (P ⬍ .05). No degenerative changes were observed on the plain radiographs at a mean follow-up of 30 months. Contralateral (Asymptomatic) Knees Three patients complained of a painless, audible snap during knee range of motion, especially near terminal extension. However, no treatment was undertaken because there were no meniscal tears or intra-articular pathologies. On plain radiographs, no statistical differences were found between ipsilateral and contralateral knees with respect to lateral tibiofemoral joint space or fibular head height. A high fibular head (6 knees [12%]) and a widened tibiofemoral joint space (9 knees [17%]) were observed in some patients with symptomatic knees. Analysis showed significant and substantial agreement ( ⫽ 0.650). No significant differences were observed between normal, incomplete, and complete discoid types
BILATERAL DISCOID LATERAL MENISCUS TABLE 2.
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Height of Fibular Head and Lateral Tibiofemoral Joint Space Normal Meniscus* (n ⫽ 11)
Incomplete Discoid (n ⫽ 40)
Complete Discoid (n ⫽ 52)
P Value
14.2 ⫾ 1.2 4.2 ⫾ 1.2
13.2 ⫾ 1.2 5.2 ⫾ 1.2
12.2 ⫾ 1.2 6.2 ⫾ 1.2
Not significant Not significant
Fibular head Lateral tibiofemoral joint space
*Crescent-shaped meniscus that covers one-third to one-half of articular surface of corresponding tibial plateau.
in terms of lateral tibiofemoral joint space or fibular head height (Table 2). Arthroscopic examinations showed 21 complete DLMs, 19 incomplete DLMs, 11 normal lateral menisci, and 1 ring-shaped lateral meniscus. The incidence of bilateral DLM in the study population was 79% (41 of 52 contralateral knees). Furthermore, 65% of patients (34 pairs of knees) had the same DLM type (Table 3, Fig 1), and 3 pairs of knees with a complete DLM type had lower DLM thicknesses in contralateral knees. A DLM tear was observed in 2 knees (1 radial and 1 longitudinal), and they were treated with partial meniscectomy. At a mean follow-up of 30 ⫾ 5.6 months, the mean Lysholm knee score was 92 ⫾ 2.6 and the median Tegner activity score was 5. DISCUSSION This study shows that bilateral DLM is more common than previously reported. Recent studies also support a high incidence of bilateral DLM. Ahn et al.15 investigated contralateral knees by MRI in 33 patients who underwent arthroscopic surgery for a symptomatic DLM and found that 97% of patients had bilateral DLM. These findings will help inform patients with a symptomatic DLM regarding the probability of a DLM in the contralateral knee. The true incidence of bilateral DLM is likely to be higher than TABLE 3.
Types of Lateral Menisci in Same Patients
Symptomatic Knee C C C IC IC IC C
Contralateral Knee
No. of Patients
C IC N C IC N Ring shaped*
19 4 7 2 15 4 1
Abbreviations: C, complete discoid lateral meniscus; IC, incomplete discoid lateral meniscus; N, normal crescent-shaped lateral meniscus. *Circular-shaped lateral meniscus with central perforation.19,25-27
previously reported because the majority of previous studies have been conducted on symptomatic knees.9 The findings of this study allow Asian patients with a symptomatic DLM to be better informed about the probability of a DLM in the contralateral knee. Similarities between lateral menisci in bilateral knees have been reported previously.15,28 Kato et al.28 analyzed 602 knees in 306 cadavers and found that the shapes of lateral menisci were similar bilaterally. In addition, in an MRI study,29 88% of 33 patients were found to have same-shaped menisci in both knees. In our study we found that 65% of patients with DLMs had the same shape in both knees. However, interestingly, we found that 3 pairs of knees with a complete DLM had lateral menisci with different thicknesses. It has been reported that plain radiography provides supplementary diagnostic information,9,15,20 but our findings do not support the suggestion that radiographs contribute to preoperative screening assessments or to the diagnosis of DLM without associated tears. The findings suggestive of a DLM include a widened lateral joint space, squaring of the lateral femoral condyle, cupping of the lateral tibial plateau, hypoplasia of the lateral tibial eminence, and elevation of the fibular head. In this study we analyzed only 2 plain radiography parameters that have been statistically associated with the presence of a DLM, namely, fibular head height and widening of the lateral tibiofemoral joint space.20 However, we found that these parameters were not significantly different for normalshaped menisci, incomplete DLMs, and complete DLMs. Two knees with a normal lateral meniscus had a widened lateral tibiofemoral joint space. In addition, all had no significantly different radiographic findings between right and left knees, including 11 patients who had a DLM in the symptomatic knee and a normal lateral meniscus in the contralateral knee. The predictive value of plain radiographs to determine the presence of DLM may still be questionable. An intact DLM is commonly encountered as an incidental finding during arthroscopy or MRI and does not necessarily require treatment.1-3 However, it is not known in what proportion of patients left untreated
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FIGURE 1.
Complete DLM in symptomatic knee and incomplete DLM in contralateral knee.
will a tear or degeneration within the meniscus eventually develop. Presumably, the shape, thickness, structural weakness, poor vascularity, and abnormal mobility of a DLM make it biomechanically weak and prone to tears,4 and recently, this has been borne out by several recent reports.15,28,30,31 In our study 2 DLM tears were incidentally found in the contralateral knees during arthroscopy. More recently, degenerative changes have been reported in adult patients with a DLM tear who were either asymptomatic or became symptomatic when middle aged.29 These reports caution that clinicians should take into account the propensity for degeneration and tear development when a DLM is incidentally detected by MRI or arthroscopy and that treatment should be considered. In addition, we recommend that bilateral DLM should be suspected in patients with a symptomatic DLM and that the contralateral knee should be examined for any clinical or radiologic evidence of a DLM. However, it remains to be determined whether MRI or arthroscopy is required in both knees of suspected DLM patients. The strength of this study was that arthroscopy allowed more accurate assessments to be made of the shapes of DLMs in contralateral knees, even though it is an invasive procedure. In addition, data were collected from a consecutive series of patients. However, the study also has its limitations. In particular, the study cohort was relatively small and subjects were Asian (Korean), and thus our findings cannot be extrapolated to other ethnic groups. Second, because intrasubstance degeneration or tears in DLMs could not be detected at arthroscopy, our findings do not address the true prevalence of DLM pathology in contralateral asymptomatic knees.
CONCLUSIONS This study provides evidence of the high prevalence of bilateral DLM in an Asian population. Acknowledgment: The authors give special thanks to all the patients who participated in this study.
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