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Management of discoid lateral meniscus tears: Observations in 34 knees
Management of Discoid Lateral Meniscus Tears: Observations in 34 Knees ¨ . Ahmet Atay, M.D., M. Nedim Doral, M.D., Gu¨rsel Leblebiciog˘lu, M.D., Onur Tetik, M.D., O ¨ stu¨n Aydıngo¨z, M.D. and U
Purpose: The goal of this study was to evaluate arthroscopic partial resection of discoid lateral meniscus tears with an emphasis on radiographic evidence of degenerative changes after this procedure. Type of Study: Retrospective clinical study. Methods: Of 41 patients with an arthroscopic diagnosis of discoid meniscus over an 8-year period, 34 symptomatic lateral discoid meniscus tears in 33 patients were analyzed at an average follow-up of 5.6 years. The average age at operation was 19.8 years and most patients had vague and intermittent symptoms that caused delay in clinical diagnosis. Results: Eight patients were lost to follow-up and were excluded from the study. Magnetic resonance imaging, performed in 12 cases, and arthroscopy in all of these patients provided the precise diagnosis. All of the knees with symptomatic torn discoid menisci underwent arthroscopic partial meniscectomy. Only 1 Watanabe Wrisberg ligament type of discoid meniscus with posterior instability was totally meniscected. Based on Ikeuchi’s grading, 39% of the knees had an excellent result, 46% had a good result, and 15% had a fair result; none of the results was poor. Conclusions: At an average 5-year follow-up, partial meniscectomy in patients with a Watanabe complete or incomplete discoid meniscus showed 85% good or excellent clinical results. However, a significant percentage of patients show femoral condyle flattening on radiography. Key Words: Discoid lateral meniscus—Meniscectomy—Arthroscopy—Magnetic resonance imaging.
D
iscoid meniscus denotes an abnormality in which the cartilaginous meniscus of the knee is disk shaped and usually of increased thickness, implying greater coverage of the tibia. The first account of this condition was in 1889 when Young1 reported on 2 cases of lateral discoid menisci in a cadaveric specimen. The reported prevalence of discoid meniscus varies between 0.4% and 17%, depending on the method of investigation, selection criteria, and the patient population.2-6 The vague and intermittent symptoms associated with this anomaly can cause
From the Departments of Orthopaedics and Traumatology (O.A.A., M.N.D., G.L., O.T) and Radiology (U.A.), Hacettepe University Medical Center, Ankara, Turkey. ¨ . Ahmet Atay, Address correspondence and reprint requests to O M.D., Department of Orthopaedics and Traumatology, Hacettepe University Medical Center, 06100 Ankara, Turkey. E-mail: [email protected] © 2003 by the Arthroscopy Association of North America 0749-8063/03/1904-3118$30.00/0 doi:10.1053/jars.2003.50038
346
difficulty and delay the diagnosis. Precise diagnosis has become possible using magnetic resonance imaging (MRI) and arthroscopy. In the past, failure of conservative treatment has led to the open total resection of the anomalous structure,7-9 but recently the advantages and the improvement that arthroscopy has offered widened its application and permitted more accurate diagnosis and treatment of the lesion.3,10,11 Recent biomechanical studies of knee function have revealed the importance of the menisci, and partial, instead of total, resection of a torn meniscus has been advised.12-14 This paper reports our experience in performing partial resections of the discoid meniscus, with an overview of the indications for the surgery, the technique, and the advantages. Moreover, radiographic changes representing joint degeneration after partial meniscectomy for discoid meniscus tears have not been previously analyzed. Our hypothesis was that partial meniscectomy for meniscal tears in patients with discoid me-
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 4 (April), 2003: pp 346-352
DISCOID LATERAL MENISCUS TEARS niscus results in good clinical results but shows radiographic evidence of degenerative changes. METHODS A review of operative records in our department from 1990 to 1998 indicated that 41 patients consecutively received an arthroscopic diagnosis of discoid meniscus. Eight of these patients (19.5%) could not be contacted for follow-up. Therefore, 33 patients (34 knees) were available for evaluation and follow-up using clinical and operative records and physical examination. Details of clinical signs and symptoms, intraoperative findings, and radiographs and MRIs were obtained from the archives and medical records. Review of the patients’ medical records allowed determination of the presenting complaint in the affected knee, as well as the duration of symptoms and presence or absence of an acute precipitating injury. Any significant history of locking, catching, clicking, or other mechanical symptoms, pain, or effusion was noted. Initial complete knee examinations were performed recording range of motion, joint alignment, and presence or absence of effusion, patellofemoral and tibiofemoral joint line tenderness, patellar subluxation, ligament stability, and meniscal symptoms. Routine standing anteroposterior and lateral radiographs were taken, and 12 patients (36%; 6 men and 6 women; 9 right and 3 left knees) also underwent MRI examinations with 1.5-T and 0.5-T systems. Surgical arthroscopic treatment was recommended for symptomatic discoid menisci only when conservative methods of treatment (resting, plus nonsteroidal anti-inflammatory drugs in adults) had failed. Therefore, it was restricted to patients with repeated or persistent locking, a block to extension, or severe pain. In symptomatic patients with MRI findings of a torn discoid meniscus, conservative treatment was deferred. The arthroscopic procedure was performed by 2 surgeons (M.N.D., O.A.A.) under general anesthesia, and a calibrated pneumatic tourniquet was used routinely (tourniquet time was never applied for more than 90 minutes). The patient was placed in the supine position, with hip slightly flexed, abducted, and externally rotated and with the knee flexed 60° to 90°. This position permitted the application of varus stress to widen the lateral compartment. The surgical arthroscope was 4 mm in diameter and had a 30° foreoblique view. Two anterior portals were used for surgical instruments and 1 medial suprapatellar portal for
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drainage. Careful probing was performed to identify the type of meniscus and the shape of any tear, and to measure the intact part of the rim. Each discoid meniscus was classified by using the system of Watanabe et al.,15 which is based on the degree of coverage of the tibial plateau and stability (complete, incomplete, or Wrisberg type [absent or abnormal posterior tibial attachment]). Tears of the discoid meniscus, when present, were classified with respect to the location, type, and pattern of instability. The specific technique for partial meniscectomy depends on the tear configuration. The surgical goal was removal of the central and torn portions of the discoid meniscus with preservation of a stable peripheral rim as much as possible. This procedure was indicated when the discoid meniscus showed only slight degeneration (because it could represent an intrasubstance lesion) or a tear. The transformation of discoid meniscus into a semilunar structure involved 2 steps. The first was removal of the central portion of the discoid meniscus. In complete types, because of the size of the meniscus (which is often soft and torn) and limited space for instrumentation, a resection should be performed using basket forceps. Central meniscectomy is begun at the free edge of the meniscus by cutting from back to front while changing the optic portal. The 3-way technique, in which the arthroscope is introduced through the patellar tendon, was used in only 8 cases. Using this technique made it possible to perform a central lateral monoblock meniscectomy. The meniscus was incised through the tear using a small scissor. The anterior insertion and healthy anterior part were left untouched, and by pulling the central part towards the intercondylar fossa, we could complete partial resection of the central and posterior parts of the meniscus. The posterior insertion of the meniscus was also left intact. Arthroscopic treatment of incomplete discoid meniscus tears is easier and quite similar to partial meniscectomies performed for a nondiscoid lateral meniscus tear. The second step was to taper the remaining rim of the meniscus to allow a more uniform distribution of forces between the tibia and femur. This was performed with the motorized shaver. All patients were discharged within a few hours of surgery with an elastic bandage around the knee. They were allowed full weight bearing and were asked to perform active knee motion without resistance. Follow-up physical examination was performed by the operating surgeons and consisted of a full evaluation of the operative knee with specific emphasis on mechanical symptoms, range of motion, joint line tender-
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ness, and gait. Special attention was directed to the lateral compartment, but other abnormalities were recorded as well. Radiographically evident osteoarthrosis was graded with the use of Ahlback’s16 criteria, which include femoral condylar flattening, joint space narrowing, and osteophyte formation, with the contralateral knee used as a control. Postoperative radiographs were obtained in full extension of the knee. Of the 32 knees evaluated using the contralateral knee as a control (1 patient had bilateral discoid menisci with tears), no statistically significant difference was found when comparing Ahlback changes of joint space narrowing and osteophyte formation (P ⫽ 1). However, a statistically significant difference was found between groups in the comparison of the femoral condylar flattening (P ⫽ .00349) (Fisher exact test; P values of ⱕ .05 were considered to be statistically significant). The clinical results were determined with the scale of Ikeuchi.3 An excellent result indicates no limitation of motion, clicking, noise, or pain; a good result indicates occasional slight pain, but no other symptoms associated with motion; a fair result indicates slight pain, clicking, or noise with motion as well as limitation of motion; and a poor result indicates pain at rest as well as with motion, and limitation of motion. RESULTS The follow-up interval for 33 available patients (34 knees) ranged from 2 years and 7 months to 8 years and 9 months (mean, 5 years and 6 months). We operated on 21 right and 13 left knees and 1 of the patients had bilateral lesions. There were 19 men and 14 women, and the ages at operation ranged from 11 to 45 years (mean, 19.8 years). The duration of symptoms before surgery ranged from 3 to 36 months (mean, 13 months). Pain was present in all patients and referable to the anterolateral side in the majority of the cases. The signs included a locking knee in 11 patients (32%), effusion in 9 (27%), and the classic clunk had been noted in 12 (35%) knees (Table 1). The lateral femoral tibial space
TABLE 1. Symptoms and Signs of the 33 Patients Pain Effusion Clunk Locked knee
33 (100%) 9 (27%) 12 (35%) 11 (32%)
TABLE 2. MRI Features of 12 Discoid Lateral Menisci Horizontal cleavage tear Radial tear Complex degenerated tear Horizontal cleavage tear plus radial tear Horizontal cleavage tear with peripheral tears Bucket-handle tear
4* 2* 2† 2 1 1
*Parameniscal cysts accompanied the discoid lateral menisci in one case in each of these categories. †Osteochondral injury with surrounding bone marrow edema was present in lateral tibial plateau in one of these cases.
enlargement could not be found in any of the knees, and early degenerative changes were seen in the lateral compartment in only 5 knees at the preoperative radiographic examination.16 The discoid menisci were grouped into 3 types according to the classification of Watanabe et al.15: 26 (77%) were classified as complete, 7 (21%) as incomplete, and 1 (2%) as Wrisberg type. In each knee, a tear was detected on arthroscopic examination, although some were not readily identifiable during routine arthroscopic examination, even with probing (in such cases, the incision made on the discoid meniscus in the light of the MRI suggestion of an intrasubstance tear actually revealed a tear). The shape of the tear in the complete-type lesions was longitudinal in 4 (15%), horizontal cleavage in 17 (66%), buckethandle in 2 (8%), and complex degenerated in 3 (11%). Of the 7 knees that had an incomplete-type lesion, 4 (57%) had a radial tear, 2 (29%) had a longitudinal tear, and 1 (14%) had a complex degenerated tear. The only Wrisberg-type meniscus had a complex degenerated tear. This was in a 20-year-old man who presented with pain and locking episodes of 1 year duration; he was followed up for 3 years and 2 months. Neither medial discoid menisci nor associated tears were found. On all 12 patients who underwent MRI examination, the lateral menisci was of the discoid type. Table 2 summarizes the MRI findings. Based on the coverage of the tibial articular surface, 6 of the discoid menisci were classified as incomplete type on MRI and the other 6 as complete type. This classification was confirmed using arthroscopy in all patients. Horizontal cleavage tears were the most common finding on MRI. All tears diagnosed on MRI were confirmed using arthroscopy (Figs 1 and 2). Thirty-three central partial meniscectomies and 1 total meniscectomy were performed on lateral discoid menisci. All complete and incomplete discoid meniscus tears were treated by partial meniscectomy. The
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FIGURE 1. (A) Sagittal T1-weighted MRI depicts a radial tear in the anterior portion of the body of a discoid lateral meniscus. (B) Arthroscopy confirmed this finding.
hypermobile Wrisberg-type discoid meniscus tear with no posterior capsule attachment was treated using total meniscectomy. In 1 of the knees, MRI and arthroscopy showed rapid secondary degenerative changes of the adjacent articular cartilage and bone, especially of the tibial surface, showing the possible adverse effects of the symptomatic discoid meniscus on the joint.13,17 We rated the clinical results using Ikeuchi’s grading system; 13 (39%) of the knees had an excellent result,
16 (46%) had good results, and 5 (15%) had fair results. The patient with the Wrisberg-type discoid meniscus tear had a good Ikeuchi grade, and radiographically he displayed lateral femoral flattening on radiography. None of the knees had a poor result. DISCUSSION The classical explanation for the discoid lateral meniscus is the persistence of the initial embryonic
FIGURE 2. (A) Sagittal proton-density MRI shows a horizontal cleavage tear in a discoid lateral meniscus. (B) Arthroscopy confirmed this finding after partial removal of the central portion of the discoid meniscus.
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FIGURE 3. (A) Complete type of discoid lateral menisci without tear on the femoral side as seen in arthroscopy. (B) A horizontal cleavage tear was seen after partial removal of the central portion of discoid meniscus. (C) Residual meniscus is seen in arthroscopy after completion of the partial resection procedure.
arrangement.6 Despite the fact that there is no accepted embryological explanation for discoid menisci, most people think they are congenital.18,19 Kaplan18 speculated that discoid menisci may be caused by abnormal motion of the menisci. Comparative data favor a phylogenetic origin, but a universally accepted explanation of the discoid lateral meniscus has not yet been developed.19 A discoid lateral meniscus is more common than a discoid medial meniscus and causes symptoms primarily in children and adolescents.9,10 In the present study, tears of the discoid lateral menisci, especially the complete and incomplete types, occurred in patients at any age, which agrees with some reports in the literature.2,3,20-22 Pain is the predominant symptom in the majority of the cases,23,24 and this was also true for our study group. However, on examination, the classic clunk so characteristic of the discoid meniscus was elicited in only 12 (35%) of our cases and exclusively in children. Radiographs do not play a significant role in the diagnosis of lateral discoid meniscus. In our series, none of the knees displayed the classic lateral joint space widening that previous researchers have described.2,25 Magnetic resonance imaging can accurately show a discoid meniscus26 and reveal a tear.27,28 Its positive predictive value for diagnosing discoid lateral menisci has been reported as 92%; however, the same value for diagnosing tears of these abnormal menisci was low (57%).28 A study by Ryu et al.28 involving 77 knees with MRI findings of lateral discoid meniscus tear stated that the most common type of discoid lateral meniscal tear was peripheral tear with horizontal tears. However, our study of 12 knees with discoid lateral menisci showed that horizontal cleavage tears
were the most common type of tear in these abnormal menisci. Moreover, the positive (as well as negative) predictive value of MRI in diagnosing the presence and type of tears in discoid menisci was 100% in our study, although the number of cases with MRI examinations is quite limited as compared with Ryu et al.’s28 work. We believe that in the evaluation of symptomatic patients (those with persistent knee pain and episodes of locking) MRI should be routinely used. The classic statement by Smillie6 that horizontal cleavage is the most frequent type of discoid meniscus tear may be true for complete discoid meniscus tears. However, some authors reported that longitudinal tears are predominant in most knees in children.3,10,29,30 In this series, we found that 66% of complete discoid meniscus tears were horizontal cleavage. Although we performed arthroscopy, no abnormality was usually apparent on the femoral surface of the complete type of meniscus (Fig 3A). Probe palpation of the femoral surface of the discoid meniscus, however, could show a slight sagittal irregularity. The meniscus was incised along the line of irregularity, and the tear could be seen within its structure (Figs 3B and 3C). In some cases, lesions were not detected even using a probe. Therefore, it was difficult to identify intrasubstance pathology using arthroscopy alone. If MRI was not available, we would hesitate to excise menisci. Hamada et al.27 reported on the usefulness of MRI in evaluating intrasubstance tears in symptomatic stable discoid menisci. We also believe that MRI could be more helpful in tears that arose on the undersurface or in the midsubstance of the menisci. Conversely, in the incomplete discoid menisci, 57% of the tears were radial and all of the tears were easily
DISCOID LATERAL MENISCUS TEARS noticed in arthroscopy. We also easily noted 1 unstable discoid meniscus, which had a degenerated complex tear in arthroscopy. Many surgical procedures have been used for partial meniscectomy, such as open excision, piecemeal arthroscopic excision, morcellation excision, semiarthroscopic excision, and 1-piece excision.3,13,31,32 In the present study, we performed piecemeal arthroscopic partial excision in most of the cases. Despite the reports stating that this technique could be more aggressive and more dangerous to the normal cartilage and tissue of the joint, we believe it to be the best technique when the meniscus restricts the space available for manipulating the surgical instruments and the scope because of the size and thickness of the discoid meniscus. This is especially true in the complete type.3,32 We agree with other researchers that loose bodies can be produced and that this method requires a long operating time because of the time taken to avoid creating cartilage lesions while manipulating instruments.3,10,13,25,31,32 We performed 1-piece excision in 8 knees similar to Kim’s32 description. In addition, by using the patellar tendon portal, we could pull the resected part for helping the cutting instruments while changing scope portals. The width of the rim of the remaining meniscus has been reported to measure between 3 and 8 mm.10,30-32 In our study, although it depended on the type of the meniscus and the shape and extent of the tear, the horizontal thickness of the remainder of the menisci was not more than 8 mm in any case. In addition, no patients complained of pain due to the impingement of the femoral condyle against the rim of meniscus. Total meniscectomy of a lateral nondiscoid meniscus often leads to osteoarthritis.33 According to the literature, children who have a discoid meniscus are not prone to osteoarthrotic changes.10,30 Hayashi et al.10 reported that the axial alignment of the extensor mechanism and the pliability of immature tissue might allow adaptation of the knee to the stresses of activity. They reviewed 53 discoid menisci treated by arthroscopic partial or total lateral meniscectomy and found no degenerative changes at an average follow-up of 31.2 months. This was not true for discoid menisci in adults, and mild degenerative changes were seen in partial meniscectomy knees in our series. It might be due to the composition of our study group, whose average age was 19.8, and our average follow-up of 5 years and 6 months, older and longer than the other series reported in the literature.2-4,10,13,14,25,27 For all its ability to reconstruct an otherwise abnormal meniscus, partial
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meniscectomy, which has been advised to avoid progressive degeneration of the cartilage of the joint, is not necessarily a benign procedure. It has been shown that the arrangement of the collagen fibers in a discoid meniscus differs from the arrangement in the normal meniscus and this, by itself, can be an underlying factor for the joint cartilage degeneration.13 We did not find any association between the radiographic changes and the clinical outcome. The result of partial meniscectomy was rated as excellent or good in 84% of the cases in our series, similar to the reports in the literature.10,13,23,25,29-31,34 Even though some authors recommend complete or subtotal meniscectomy as a better alternative to partial meniscectomy (because of a higher rate of reoperation in partial meniscectomies), we did not have to perform any second-look arthroscopy because of retear of the abnormal meniscus rim.3,35 Generally, the discoid meniscus is not symptomatic unless a tear has occurred.36 However, the discovery of such an anomaly can also be made during arthroscopy performed for other purposes. In such instances, discoid menisci should not be treated, even with partial resection. Partial resection should only be performed when clear meniscal symptoms exist. Still, some doubts about the long-term results of the partial resection procedure persist. However, we believe that partial meniscectomy has the important advantage of leaving a rim of meniscus, which has a biomechanical function. Nevertheless, although arthroscopic partial meniscectomy is effective and useful, it is difficult and requires an experienced surgeon. In conclusion, at an average of 5 years’ follow-up, partial meniscectomy in patients with a Watanabe complete or incomplete type of discoid meniscus showed 85% good or excellent clinical results. However, a significant percentage of femoral condyle flattening was seen on radiographs. REFERENCES 1. Young RB. The external semilunar cartilage as a complete disc: Memoirs and memoranda in anatomy. London: Williams and Nortage, 1889. 2. Dichault SC, DeLee JC. The discoid lateral meniscus syndrome. J Bone Joint Surg Am 1982;64:1068-1073. 3. Ikeuchi H. Arthroscopic treatment of lateral discoid meniscus: Technique and long-term results. Clin Orthop 1982;167:19-28. 4. Jeannopoulos CL. Observation of discoid menisci. J Bone Joint Surg Am 1950;32:649-652. 5. Noble J. Lesions of the menisci: Autopsy incidence in adults less than fifty-five years old. J Bone Joint Surg Am 1977;59: 480-483. 6. Smillie IS. The congenital discoid meniscus. J Bone Joint Surg Br 1948;30:671-682.
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7. Kobayashi A, Uezaki N, Mitsuyasu M. Discoid meniscus of the knee joint. Clin Orthop 1975;10:10-24. 8. Raber DA, Friederich NF, Hefti F. Discoid lateral meniscus in children. J Bone Joint Surg Am 1998;80:1579-1586. 9. Washington ER, Root L, Liener UC. Discoid lateral meniscus in children. J Bone Joint Surg Am 1995;77:1357-1361. 10. Hayashi KL, Yamaga H, Ida K, et al. Arthroscopic meniscectomy for discoid lateral meniscus in children. J Bone and Joint Surg Am 1989;78:1495-1500. 11. Kim SJ, Lee YT, Choi CH, et al. A partially duplicated discoid lateral meniscus. Arthroscopy 1998;14:518-521. 12. Cargill AOR, Jackson JP. Bucket-handle tear of the medial meniscus. J Bone Joint Surg Am 1976;58:248-251. 13. Fujikawa K, Iseki F, Mikura Y. Partial resection of the discoid meniscus in the child’s knee. J Bone Joint Surg Br 1981;63: 391-395. 14. McGinty JB, Geuss LF, Marvin RA. Partial or total meniscectomy. J Bone Joint Surg Am 1977;59:763-766. 15. Watanabe M, Takeda S, Kieuchi H. Atlas of arthroscopy. ed 3. Tokyo: Igakushoin, 1979;88. 16. Ahlback S. Osteoarthrosis of the knee. A radiographic investigation. Acta Radiol 1968;277:7-72 (suppl). 17. Hall FM. Arthrography of the discoid lateral meniscus. AJR Am J Roentgenol 1977;128:993-1002. 18. Kaplan EB. Discoid lateral meniscus of the knee joint: Nature, mechanism, and operative treatment. J Bone Joint Surg Am 1957;39:77-87. 19. Le Minor JM. Comparative morphology of the lateral meniscus of the in primates. J Anat 1990;170:161-171. 20. Albertsson M, Gillquist J. Discoid lateral menisci: A report of 29 cases. Arthroscopy 1988;4:211-214. 21. Berson BL, Herman G. Torn discoid menisci of the knee in adults: Four case reports. J Bone Joint Surg Am 1979;61:303304. 22. Corso SJ, Bochner RM. Bilateral discoid lateral meniscus in the seventh decade: A case report. Am J Knee Surg 1990;3: 139-142.
23. Aichroth PM, Patel DV, Marx CL. Congenital discoid lateral meniscus in children. J Bone Joint Surg Br 1991;73:932-936. ¨ A, Doral MN, Aksoy MC, et al. Arthroscopic partial 24. Atay O resection of the discoid meniscus in children. Turk J Pediatr 1997;39:505-510. 25. Bellier G, Dupont JY, Larrain M, et al. Lateral discoid menisci in children. Arthroscopy 1989;5:52-56. 26. Silverman JM, Mink JH, Deutsch AL. Discoid menisci of the knee: MR imaging appearance. Radiology 1989;173:351-354. 27. Hamada M, Shino K, Kawano K, et al. Usefulness of magnetic resonance imaging for detecting intrasubstance tear and/or degeneration of lateral discoid meniscus. Arthroscopy 1994; 10:645-653. 28. Ryu KN, Kim IS, Kim EJ, et al. MR imaging of tears of discoid lateral menisci. AJR Am J Roentgenol 1998;171:963967. 29. Pellaci P, Montanari G, Prosperi P, et al. Lateral discoid meniscus: Treatment and results. Arthroscopy 1992;8:526530. 30. Vandermeer RD, Cunningham K. Arthroscopic treatment of the lateral discoid menicus: Results of long term follow-up. Arthroscopy 1989;5:101-109. 31. Dimakopoulus P, Patel D. Partial excision of discoid meniscus. Acta Orthop Scand 1989;60:40-41. 32. Kim SJ, Yoo JH, Kim HK. Arthroscopic one-piece excision technique for the treatment of symptomatic lateral discoid meniscus. Arthroscopy 1996;12:752-755. 33. Manzione M, Pizzutillo PD, Peoples AB, Schweizer PA. Meniscectomy in children: A long term follow-up study. Am J Sports Med 1983;11:111-115. 34. Fritschy D, Gonseth D. Discoid lateral meniscus. Int Orthop 1991;15:145-147. 35. Sugawara O, Miyatsu M, Yamashita I. Problems with repeated arthroscopic surgery in the discoid meniscus. Arthroscopy 1991;7:68-71. 36. Clark CR, Ogden JA. Development of the menisci of the human knee joint. J Bone Joint Surg Am 1983;65:538-547.
Purpose: The goal of this study was to evaluate arthroscopic partial resection of discoid lateral meniscus tears with an emphasis on radiographic evidence of degenerative changes after this procedure. Type of Study: Retrospective clinical study. Methods: Of 41 patients with an arthroscopic diagnosis of discoid meniscus over an 8-year period, 34 symptomatic lateral discoid meniscus tears in 33 patients were analyzed at an average follow-up of 5.6 years. The average age at operation was 19.8 years and most patients had vague and intermittent symptoms that caused delay in clinical diagnosis. Results: Eight patients were lost to follow-up and were excluded from the study. Magnetic resonance imaging, performed in 12 cases, and arthroscopy in all of these patients provided the precise diagnosis. All of the knees with symptomatic torn discoid menisci underwent arthroscopic partial meniscectomy. Only 1 Watanabe Wrisberg ligament type of discoid meniscus with posterior instability was totally meniscected. Based on Ikeuchi’s grading, 39% of the knees had an excellent result, 46% had a good result, and 15% had a fair result; none of the results was poor. Conclusions: At an average 5-year follow-up, partial meniscectomy in patients with a Watanabe complete or incomplete discoid meniscus showed 85% good or excellent clinical results. However, a significant percentage of patients show femoral condyle flattening on radiography. Key Words: Discoid lateral meniscus—Meniscectomy—Arthroscopy—Magnetic resonance imaging.
D
iscoid meniscus denotes an abnormality in which the cartilaginous meniscus of the knee is disk shaped and usually of increased thickness, implying greater coverage of the tibia. The first account of this condition was in 1889 when Young1 reported on 2 cases of lateral discoid menisci in a cadaveric specimen. The reported prevalence of discoid meniscus varies between 0.4% and 17%, depending on the method of investigation, selection criteria, and the patient population.2-6 The vague and intermittent symptoms associated with this anomaly can cause
From the Departments of Orthopaedics and Traumatology (O.A.A., M.N.D., G.L., O.T) and Radiology (U.A.), Hacettepe University Medical Center, Ankara, Turkey. ¨ . Ahmet Atay, Address correspondence and reprint requests to O M.D., Department of Orthopaedics and Traumatology, Hacettepe University Medical Center, 06100 Ankara, Turkey. E-mail: [email protected] © 2003 by the Arthroscopy Association of North America 0749-8063/03/1904-3118$30.00/0 doi:10.1053/jars.2003.50038
346
difficulty and delay the diagnosis. Precise diagnosis has become possible using magnetic resonance imaging (MRI) and arthroscopy. In the past, failure of conservative treatment has led to the open total resection of the anomalous structure,7-9 but recently the advantages and the improvement that arthroscopy has offered widened its application and permitted more accurate diagnosis and treatment of the lesion.3,10,11 Recent biomechanical studies of knee function have revealed the importance of the menisci, and partial, instead of total, resection of a torn meniscus has been advised.12-14 This paper reports our experience in performing partial resections of the discoid meniscus, with an overview of the indications for the surgery, the technique, and the advantages. Moreover, radiographic changes representing joint degeneration after partial meniscectomy for discoid meniscus tears have not been previously analyzed. Our hypothesis was that partial meniscectomy for meniscal tears in patients with discoid me-
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 4 (April), 2003: pp 346-352
DISCOID LATERAL MENISCUS TEARS niscus results in good clinical results but shows radiographic evidence of degenerative changes. METHODS A review of operative records in our department from 1990 to 1998 indicated that 41 patients consecutively received an arthroscopic diagnosis of discoid meniscus. Eight of these patients (19.5%) could not be contacted for follow-up. Therefore, 33 patients (34 knees) were available for evaluation and follow-up using clinical and operative records and physical examination. Details of clinical signs and symptoms, intraoperative findings, and radiographs and MRIs were obtained from the archives and medical records. Review of the patients’ medical records allowed determination of the presenting complaint in the affected knee, as well as the duration of symptoms and presence or absence of an acute precipitating injury. Any significant history of locking, catching, clicking, or other mechanical symptoms, pain, or effusion was noted. Initial complete knee examinations were performed recording range of motion, joint alignment, and presence or absence of effusion, patellofemoral and tibiofemoral joint line tenderness, patellar subluxation, ligament stability, and meniscal symptoms. Routine standing anteroposterior and lateral radiographs were taken, and 12 patients (36%; 6 men and 6 women; 9 right and 3 left knees) also underwent MRI examinations with 1.5-T and 0.5-T systems. Surgical arthroscopic treatment was recommended for symptomatic discoid menisci only when conservative methods of treatment (resting, plus nonsteroidal anti-inflammatory drugs in adults) had failed. Therefore, it was restricted to patients with repeated or persistent locking, a block to extension, or severe pain. In symptomatic patients with MRI findings of a torn discoid meniscus, conservative treatment was deferred. The arthroscopic procedure was performed by 2 surgeons (M.N.D., O.A.A.) under general anesthesia, and a calibrated pneumatic tourniquet was used routinely (tourniquet time was never applied for more than 90 minutes). The patient was placed in the supine position, with hip slightly flexed, abducted, and externally rotated and with the knee flexed 60° to 90°. This position permitted the application of varus stress to widen the lateral compartment. The surgical arthroscope was 4 mm in diameter and had a 30° foreoblique view. Two anterior portals were used for surgical instruments and 1 medial suprapatellar portal for
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drainage. Careful probing was performed to identify the type of meniscus and the shape of any tear, and to measure the intact part of the rim. Each discoid meniscus was classified by using the system of Watanabe et al.,15 which is based on the degree of coverage of the tibial plateau and stability (complete, incomplete, or Wrisberg type [absent or abnormal posterior tibial attachment]). Tears of the discoid meniscus, when present, were classified with respect to the location, type, and pattern of instability. The specific technique for partial meniscectomy depends on the tear configuration. The surgical goal was removal of the central and torn portions of the discoid meniscus with preservation of a stable peripheral rim as much as possible. This procedure was indicated when the discoid meniscus showed only slight degeneration (because it could represent an intrasubstance lesion) or a tear. The transformation of discoid meniscus into a semilunar structure involved 2 steps. The first was removal of the central portion of the discoid meniscus. In complete types, because of the size of the meniscus (which is often soft and torn) and limited space for instrumentation, a resection should be performed using basket forceps. Central meniscectomy is begun at the free edge of the meniscus by cutting from back to front while changing the optic portal. The 3-way technique, in which the arthroscope is introduced through the patellar tendon, was used in only 8 cases. Using this technique made it possible to perform a central lateral monoblock meniscectomy. The meniscus was incised through the tear using a small scissor. The anterior insertion and healthy anterior part were left untouched, and by pulling the central part towards the intercondylar fossa, we could complete partial resection of the central and posterior parts of the meniscus. The posterior insertion of the meniscus was also left intact. Arthroscopic treatment of incomplete discoid meniscus tears is easier and quite similar to partial meniscectomies performed for a nondiscoid lateral meniscus tear. The second step was to taper the remaining rim of the meniscus to allow a more uniform distribution of forces between the tibia and femur. This was performed with the motorized shaver. All patients were discharged within a few hours of surgery with an elastic bandage around the knee. They were allowed full weight bearing and were asked to perform active knee motion without resistance. Follow-up physical examination was performed by the operating surgeons and consisted of a full evaluation of the operative knee with specific emphasis on mechanical symptoms, range of motion, joint line tender-
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ness, and gait. Special attention was directed to the lateral compartment, but other abnormalities were recorded as well. Radiographically evident osteoarthrosis was graded with the use of Ahlback’s16 criteria, which include femoral condylar flattening, joint space narrowing, and osteophyte formation, with the contralateral knee used as a control. Postoperative radiographs were obtained in full extension of the knee. Of the 32 knees evaluated using the contralateral knee as a control (1 patient had bilateral discoid menisci with tears), no statistically significant difference was found when comparing Ahlback changes of joint space narrowing and osteophyte formation (P ⫽ 1). However, a statistically significant difference was found between groups in the comparison of the femoral condylar flattening (P ⫽ .00349) (Fisher exact test; P values of ⱕ .05 were considered to be statistically significant). The clinical results were determined with the scale of Ikeuchi.3 An excellent result indicates no limitation of motion, clicking, noise, or pain; a good result indicates occasional slight pain, but no other symptoms associated with motion; a fair result indicates slight pain, clicking, or noise with motion as well as limitation of motion; and a poor result indicates pain at rest as well as with motion, and limitation of motion. RESULTS The follow-up interval for 33 available patients (34 knees) ranged from 2 years and 7 months to 8 years and 9 months (mean, 5 years and 6 months). We operated on 21 right and 13 left knees and 1 of the patients had bilateral lesions. There were 19 men and 14 women, and the ages at operation ranged from 11 to 45 years (mean, 19.8 years). The duration of symptoms before surgery ranged from 3 to 36 months (mean, 13 months). Pain was present in all patients and referable to the anterolateral side in the majority of the cases. The signs included a locking knee in 11 patients (32%), effusion in 9 (27%), and the classic clunk had been noted in 12 (35%) knees (Table 1). The lateral femoral tibial space
TABLE 1. Symptoms and Signs of the 33 Patients Pain Effusion Clunk Locked knee
33 (100%) 9 (27%) 12 (35%) 11 (32%)
TABLE 2. MRI Features of 12 Discoid Lateral Menisci Horizontal cleavage tear Radial tear Complex degenerated tear Horizontal cleavage tear plus radial tear Horizontal cleavage tear with peripheral tears Bucket-handle tear
4* 2* 2† 2 1 1
*Parameniscal cysts accompanied the discoid lateral menisci in one case in each of these categories. †Osteochondral injury with surrounding bone marrow edema was present in lateral tibial plateau in one of these cases.
enlargement could not be found in any of the knees, and early degenerative changes were seen in the lateral compartment in only 5 knees at the preoperative radiographic examination.16 The discoid menisci were grouped into 3 types according to the classification of Watanabe et al.15: 26 (77%) were classified as complete, 7 (21%) as incomplete, and 1 (2%) as Wrisberg type. In each knee, a tear was detected on arthroscopic examination, although some were not readily identifiable during routine arthroscopic examination, even with probing (in such cases, the incision made on the discoid meniscus in the light of the MRI suggestion of an intrasubstance tear actually revealed a tear). The shape of the tear in the complete-type lesions was longitudinal in 4 (15%), horizontal cleavage in 17 (66%), buckethandle in 2 (8%), and complex degenerated in 3 (11%). Of the 7 knees that had an incomplete-type lesion, 4 (57%) had a radial tear, 2 (29%) had a longitudinal tear, and 1 (14%) had a complex degenerated tear. The only Wrisberg-type meniscus had a complex degenerated tear. This was in a 20-year-old man who presented with pain and locking episodes of 1 year duration; he was followed up for 3 years and 2 months. Neither medial discoid menisci nor associated tears were found. On all 12 patients who underwent MRI examination, the lateral menisci was of the discoid type. Table 2 summarizes the MRI findings. Based on the coverage of the tibial articular surface, 6 of the discoid menisci were classified as incomplete type on MRI and the other 6 as complete type. This classification was confirmed using arthroscopy in all patients. Horizontal cleavage tears were the most common finding on MRI. All tears diagnosed on MRI were confirmed using arthroscopy (Figs 1 and 2). Thirty-three central partial meniscectomies and 1 total meniscectomy were performed on lateral discoid menisci. All complete and incomplete discoid meniscus tears were treated by partial meniscectomy. The
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FIGURE 1. (A) Sagittal T1-weighted MRI depicts a radial tear in the anterior portion of the body of a discoid lateral meniscus. (B) Arthroscopy confirmed this finding.
hypermobile Wrisberg-type discoid meniscus tear with no posterior capsule attachment was treated using total meniscectomy. In 1 of the knees, MRI and arthroscopy showed rapid secondary degenerative changes of the adjacent articular cartilage and bone, especially of the tibial surface, showing the possible adverse effects of the symptomatic discoid meniscus on the joint.13,17 We rated the clinical results using Ikeuchi’s grading system; 13 (39%) of the knees had an excellent result,
16 (46%) had good results, and 5 (15%) had fair results. The patient with the Wrisberg-type discoid meniscus tear had a good Ikeuchi grade, and radiographically he displayed lateral femoral flattening on radiography. None of the knees had a poor result. DISCUSSION The classical explanation for the discoid lateral meniscus is the persistence of the initial embryonic
FIGURE 2. (A) Sagittal proton-density MRI shows a horizontal cleavage tear in a discoid lateral meniscus. (B) Arthroscopy confirmed this finding after partial removal of the central portion of the discoid meniscus.
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FIGURE 3. (A) Complete type of discoid lateral menisci without tear on the femoral side as seen in arthroscopy. (B) A horizontal cleavage tear was seen after partial removal of the central portion of discoid meniscus. (C) Residual meniscus is seen in arthroscopy after completion of the partial resection procedure.
arrangement.6 Despite the fact that there is no accepted embryological explanation for discoid menisci, most people think they are congenital.18,19 Kaplan18 speculated that discoid menisci may be caused by abnormal motion of the menisci. Comparative data favor a phylogenetic origin, but a universally accepted explanation of the discoid lateral meniscus has not yet been developed.19 A discoid lateral meniscus is more common than a discoid medial meniscus and causes symptoms primarily in children and adolescents.9,10 In the present study, tears of the discoid lateral menisci, especially the complete and incomplete types, occurred in patients at any age, which agrees with some reports in the literature.2,3,20-22 Pain is the predominant symptom in the majority of the cases,23,24 and this was also true for our study group. However, on examination, the classic clunk so characteristic of the discoid meniscus was elicited in only 12 (35%) of our cases and exclusively in children. Radiographs do not play a significant role in the diagnosis of lateral discoid meniscus. In our series, none of the knees displayed the classic lateral joint space widening that previous researchers have described.2,25 Magnetic resonance imaging can accurately show a discoid meniscus26 and reveal a tear.27,28 Its positive predictive value for diagnosing discoid lateral menisci has been reported as 92%; however, the same value for diagnosing tears of these abnormal menisci was low (57%).28 A study by Ryu et al.28 involving 77 knees with MRI findings of lateral discoid meniscus tear stated that the most common type of discoid lateral meniscal tear was peripheral tear with horizontal tears. However, our study of 12 knees with discoid lateral menisci showed that horizontal cleavage tears
were the most common type of tear in these abnormal menisci. Moreover, the positive (as well as negative) predictive value of MRI in diagnosing the presence and type of tears in discoid menisci was 100% in our study, although the number of cases with MRI examinations is quite limited as compared with Ryu et al.’s28 work. We believe that in the evaluation of symptomatic patients (those with persistent knee pain and episodes of locking) MRI should be routinely used. The classic statement by Smillie6 that horizontal cleavage is the most frequent type of discoid meniscus tear may be true for complete discoid meniscus tears. However, some authors reported that longitudinal tears are predominant in most knees in children.3,10,29,30 In this series, we found that 66% of complete discoid meniscus tears were horizontal cleavage. Although we performed arthroscopy, no abnormality was usually apparent on the femoral surface of the complete type of meniscus (Fig 3A). Probe palpation of the femoral surface of the discoid meniscus, however, could show a slight sagittal irregularity. The meniscus was incised along the line of irregularity, and the tear could be seen within its structure (Figs 3B and 3C). In some cases, lesions were not detected even using a probe. Therefore, it was difficult to identify intrasubstance pathology using arthroscopy alone. If MRI was not available, we would hesitate to excise menisci. Hamada et al.27 reported on the usefulness of MRI in evaluating intrasubstance tears in symptomatic stable discoid menisci. We also believe that MRI could be more helpful in tears that arose on the undersurface or in the midsubstance of the menisci. Conversely, in the incomplete discoid menisci, 57% of the tears were radial and all of the tears were easily
DISCOID LATERAL MENISCUS TEARS noticed in arthroscopy. We also easily noted 1 unstable discoid meniscus, which had a degenerated complex tear in arthroscopy. Many surgical procedures have been used for partial meniscectomy, such as open excision, piecemeal arthroscopic excision, morcellation excision, semiarthroscopic excision, and 1-piece excision.3,13,31,32 In the present study, we performed piecemeal arthroscopic partial excision in most of the cases. Despite the reports stating that this technique could be more aggressive and more dangerous to the normal cartilage and tissue of the joint, we believe it to be the best technique when the meniscus restricts the space available for manipulating the surgical instruments and the scope because of the size and thickness of the discoid meniscus. This is especially true in the complete type.3,32 We agree with other researchers that loose bodies can be produced and that this method requires a long operating time because of the time taken to avoid creating cartilage lesions while manipulating instruments.3,10,13,25,31,32 We performed 1-piece excision in 8 knees similar to Kim’s32 description. In addition, by using the patellar tendon portal, we could pull the resected part for helping the cutting instruments while changing scope portals. The width of the rim of the remaining meniscus has been reported to measure between 3 and 8 mm.10,30-32 In our study, although it depended on the type of the meniscus and the shape and extent of the tear, the horizontal thickness of the remainder of the menisci was not more than 8 mm in any case. In addition, no patients complained of pain due to the impingement of the femoral condyle against the rim of meniscus. Total meniscectomy of a lateral nondiscoid meniscus often leads to osteoarthritis.33 According to the literature, children who have a discoid meniscus are not prone to osteoarthrotic changes.10,30 Hayashi et al.10 reported that the axial alignment of the extensor mechanism and the pliability of immature tissue might allow adaptation of the knee to the stresses of activity. They reviewed 53 discoid menisci treated by arthroscopic partial or total lateral meniscectomy and found no degenerative changes at an average follow-up of 31.2 months. This was not true for discoid menisci in adults, and mild degenerative changes were seen in partial meniscectomy knees in our series. It might be due to the composition of our study group, whose average age was 19.8, and our average follow-up of 5 years and 6 months, older and longer than the other series reported in the literature.2-4,10,13,14,25,27 For all its ability to reconstruct an otherwise abnormal meniscus, partial
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meniscectomy, which has been advised to avoid progressive degeneration of the cartilage of the joint, is not necessarily a benign procedure. It has been shown that the arrangement of the collagen fibers in a discoid meniscus differs from the arrangement in the normal meniscus and this, by itself, can be an underlying factor for the joint cartilage degeneration.13 We did not find any association between the radiographic changes and the clinical outcome. The result of partial meniscectomy was rated as excellent or good in 84% of the cases in our series, similar to the reports in the literature.10,13,23,25,29-31,34 Even though some authors recommend complete or subtotal meniscectomy as a better alternative to partial meniscectomy (because of a higher rate of reoperation in partial meniscectomies), we did not have to perform any second-look arthroscopy because of retear of the abnormal meniscus rim.3,35 Generally, the discoid meniscus is not symptomatic unless a tear has occurred.36 However, the discovery of such an anomaly can also be made during arthroscopy performed for other purposes. In such instances, discoid menisci should not be treated, even with partial resection. Partial resection should only be performed when clear meniscal symptoms exist. Still, some doubts about the long-term results of the partial resection procedure persist. However, we believe that partial meniscectomy has the important advantage of leaving a rim of meniscus, which has a biomechanical function. Nevertheless, although arthroscopic partial meniscectomy is effective and useful, it is difficult and requires an experienced surgeon. In conclusion, at an average of 5 years’ follow-up, partial meniscectomy in patients with a Watanabe complete or incomplete type of discoid meniscus showed 85% good or excellent clinical results. However, a significant percentage of femoral condyle flattening was seen on radiographs. REFERENCES 1. Young RB. The external semilunar cartilage as a complete disc: Memoirs and memoranda in anatomy. London: Williams and Nortage, 1889. 2. Dichault SC, DeLee JC. The discoid lateral meniscus syndrome. J Bone Joint Surg Am 1982;64:1068-1073. 3. Ikeuchi H. Arthroscopic treatment of lateral discoid meniscus: Technique and long-term results. Clin Orthop 1982;167:19-28. 4. Jeannopoulos CL. Observation of discoid menisci. J Bone Joint Surg Am 1950;32:649-652. 5. Noble J. Lesions of the menisci: Autopsy incidence in adults less than fifty-five years old. J Bone Joint Surg Am 1977;59: 480-483. 6. Smillie IS. The congenital discoid meniscus. J Bone Joint Surg Br 1948;30:671-682.
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