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Discoid meniscus
DISCOID MENISCUS DAVID C. NEUSCHWANDER, MD
The discoid meniscus is an uncommon but not remote meniscal anomaly. Watanabe classified discoid menisci into three types: complete, incomplete, and Wrisberg-ligament type. These menisci vary in size, shape, presence of a posterior meniscal attachment, and mode of presentation. The complete and incomplete types are usually incidental arthroscopic findings unless they present with symptoms of an associated meniscal tear. The Wrisberg variant presents with the snapping knee syndrome, with visible, and often audible dunking with flexion and extension of the knee. The complete and incomplete types should be left alone unless there is an associated meniscal tear, in which case a saucerization procedure should be performed. The Wrisberg variant should have attachment of its hypermobile posterior horn. KEY WORDS: meniscus, discoid meniscus, meniscectomy
The discoid meniscus is an interesting meniscal anomaly. It presents more commonly in the lateral compartment, but it can also occur medially. There has been controversy in the literature with regard to its etiology, presentation, and treatment. It is important to distinguish the complete and incomplete discoid menisci from the so-called Wrisbergligament type. These menisci vary in size, shape, presence of a posterior meniscal attachment, and mode of presentation. The complete and incomplete types vary in their extent of tibial plateau coverage. They are usually asymptomatic incidental arthroscopic findings unless associated with a meniscal tear. These menisci are both discshaped, with a normal posterior meniscal attachment, and display no abnormal motion of their posterior horns with flexion or extension of the knee. In the literature, the snapping knee syndrome has been attributed generally to all discoid menisci, but more appropriately should be reserved for the so-called Wrisbergligament type. 1 This anomaly is relatively normal in shape, has absence of a posterior meniscal attachment, and is unassociated with trauma. 1-3 This usually presents in younger individuals with a popping sound with flexion and extension of the knee that is caused by abnormal meniscal motion because of lack of the posterior meniscal attachment. The snapping knee syndrome symptoms usually occur intermittently, and the patient usually presents w h e n the popping becomes more consistent and symptomatic. The size and shape of the Wrisberg-ligament type meniscus has been variably described in the literature. In most cases, it has been reported to be normal or hypertrophic in its posterior horn, but without a discoid
From the Department of Orthopedic Surgery, University of Pittsburgh School of Medicine, Pittsburgh, PA. Address reprint requests to David C. Neuschwander, MD, Department of Orthopedic Surgery, University of Pittsburgh School of Medicine, 2550 Mosside Boulevard, Suite 405, Monroeville, PA 15146. Copyright © 1995 by W. B. Saunders Company 1048-6666/95/0501-0011$05.00/0
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shape. 1-4 In our experience, the Wrisberg variant does not have a discoid shape, and therefore, we have described this as the lateral meniscal variant with absence of the posterior coronary ligament. 2'5
HISTORY The discoid lateral meniscus was first described by Young in 1887, 6 but it was not until 1910 that Krois attributed the snapping knee syndrome to this anomaly. 7 The first discoid medial meniscus was reported by Watson-Jones in 1930. s Smillie was the first to acquire extensive clinical experience, describing 29 cases in 1948. 9 He attributed this anomaly to an atavistic phenomenon with persistence of a disc-shaped meniscus arrested at different stages of embryonic development. He classified the discoid menisci into three types: primitive, intermediate, and infantile. Kaplan performed cadaveric dissections, embryologic studies, and dissection at operation of six discoid menisci, and he reported this in 1957. ~° His study took exception with Smillie's theory. His anatomic studies of the human fetus showed that neither the lateral nor medial meniscus assumed a discoid shape during any stage of development. Kaplan's dissections in animals and in six clinical cases showed that the posterior horn of the lateral meniscus was not attached to the tibial plateau. Rather, it had an attachment to the lateral aspect of the medial femoral condyle by a meniscofemoral ligament, the ligament of Wrisberg. He was of the opinion that hypermobile, normally shaped menisci became discoid as a result of abnormal meniscal motion from lack of a posterior capsular attachment. Kaplan noted that the Wrisberg ligament pulled the lateral meniscus into the intercondylar notch during extension, and he believed that this abnormal mediolateral motion led to hypertrophy of the meniscus and its resulting discoid shape (Fig 1). Clark and Ogden 11 noted more developmental variation of the lateral than the medial meniscus and also corroborated Kaplan's findings. They dissected 548 knees be-
Operative Techniques in Orthopaedics, Vol 5, No 1 (January), 1995: pp 78-87
Knee E x t e n d e d
Me
Knee Flexed
lteral niscus scold)
meR
Fig 1. Diagram of the Wrisberg lateral meniscus being pulled into the intercondylar notch with extension by the ligament of Wrisberg. With flexion, the lateral meniscus is pulled laterally by the coronary ligament and popliteal tendon.
tween 14 weeks gestation and 14 years of age and found no evidence of a disc-shaped meniscus during any stage of development. Smillie's and Kaplan's theories have flaws that cannot be substantiated. Smillie's theory is not explainable by embryologic studies that do not demonstrate a discshaped meniscus ~,t any stage of development. Kaplan's theory does not explain the more common discoid lateral meniscus, in which the meniscus has a normal meniscotibial attachment, nor does this theory explain the existence of a discoid medial meniscus. A congenital theory has also been proposed, with isolated reports of occurrence in twins and familial transmission. 12,13
CLASSIFICATION Smillie devised the first classification system based on his theory that the discoid meniscus resulted from an arrest of the meniscus at various stages of embryologic development. Kaplan described only the Wrisberg-ligament type in his embryologic and cadaveric studies and six clinical cases. Watanabe performed the first arthroscopic surgery in 1962 and subsequently described the classification of discoid lateral menisci based on their arthroscopic appearance. 4 He described three different types of discoid meniscus: complete, incomplete, and Wrisberg-ligament type (Fig 2). The complete and incomplete types differ in the amount of lateral plateau coverage by a disc-shaped meniscus with a normal posterior meniscal attachment. The Wrisberg-ligament type was described as being fairly normal in size and shape but lacking a posterior meniscal attachment, except the ligament of Wrisberg. Hall 14 subsequently developed a classification based on the arthrographic appearance of the discoid lateral meniscus; however, the Watanabe classification is the most universally recognized and used by clinicians. Dickhaut and DeLee~ refined the clinical presentation of the complete and incomplete types as compared with the Wrisberg-ligament type. They reported that the complete and incomplete types were usually asymptomDISCOID MENISCUS
Fig 2. Diagram of Watanabe's classification of a discoid lateral meniscus: (A) incomplete; (B) complete; and (C) Wrisberg-ligament variant. There is a normal posterior coronary ligament in the complete and incomplete types; this ligament is missing in the Wrisberg type. The size and shape of the Wrisberg type are fairly normal. (Reprinted with permission. 2)
atic unless associated with a meniscal tear. They reported that the Wrisberg-ligament type was more commonly associated with the snapping knee and had a fairly normal meniscal shape with the exception of hypertrophy of the posterior horn of the lateral meniscus in six cases. 1 With other investigators, 3A we also agree that the Wrisberg type has a relatively normal shape, and therefore, we call this entity the lateral meniscal variant with absence of the posterior coronary ligament, to distinguish it from a true discoid meniscus. 2
INCIDENCE After a thorough literature review, it is difficult to determine accurate incidence rates of the discoid lateral meniscus and the Wrisberg-ligament variant. Early studies used meniscectomy specimens obtained from arthrotomy and had reported rates between 2.4% and 4.2%. 9As These studies did not include the Wrisberg type because this variant would not be recognized because it was not abnormal in shape, but had absence of the posterior meniscal attachment. Arthroscopic studies more accurately depict actual rates. However, the indications for arthroscopy have varied among studies presenting incidence rates. There has been a significant difference between the rates reported in the Japanese and Korean populations compared with other parts of the world. 1'4'16-2° Watanabe's arthroscopic study reported a 26% incidence of discoid lateral meniscus and 3.1% incidence of Wrisberg-ligament type 79
in arthroscopies that were performed in knees in which internal derangement was suspected. 4 Ikeuchi 17 had a 16.6% incidence rate of discoid lateral meniscus with no Wrisberg-ligament types over a 20-year period. Seong reported a 15% incidence of discoid lateral meniscus and no Wrisberg-ligament types in a study of 236 Korean patients who underwent arthroscopy because of variable symptoms attributable to the meniscus or other structures of the knee. Interestingly, Seong et al also conducted an autopsy study, in which they dissected 124 Korean adult knees and found an 8.1% incidence of discoid lateral meniscus and no cases of the Wrisbergligament type, despite having a posterior menisofemoral ligament (Wrisberg ligament) present in 95.2% of the specimens. Dickhaut and DeLee reported a 5% incidence of the complete type (no incompletes) and 2% incidence of the Wrisberg-ligament type in 347 knees that underwent arthroscopy for suspected meniscal abnormality. Between 1979 and 1986, Albertson and Gillquist reviewed 7,056 arthroscopies performed at their clinic for all indications and had a 0.4% rate of discoid lateral meniscus, with none of the Wrisberg-ligament type. 21 Similarly, low rates have been reported in the Swiss, Italian, and other United States studies, with reported incidence rates of 0.9%, 3.5%, and 1.5%, respectively. 19"22"23 Our study of 3,468 knee arthroscopies for all indications had a 0.8% rate of discoid lateral meniscus and 0.2% rates of the Wrisberg-ligament variant. 2 Some of the differences between studies may be because of the inclusion criteria, but it seems that the discoid meniscus is more common in the Japanese and Korean populations than the rest of the world. 4'16-18 It is also interesting that no cases of the Wrisberg-ligament type were reported in two large Japanese and one Korean study, especially in light of the relatively high incidence of Wrisberg ligaments in the Korean autopsy study. 16-18 The incidence of discoid medial meniscus has been reported to vary from 0% to 0.3% in different studies. 19"24 Only the complete and incomplete types of medial menisci have been reported, and a Wrisberg ligament variant has not been identified.
CLINICAL PRESENTATION Dickhaut and DeLee 1 described the complete and incomplete types of discoid lateral meniscus as clinically presenting much differently than the Wrisberg type. The classic snapping knee syndrome presents most commonly in children and adolescents with the Wrisbergligament type. Complete and incomplete types usually are incidental findings at the time of arthroscopy for other reasons. If the complete and incomplete types have a tear of their meniscal substance, the clinical signs and symptoms are similar to that of any other meniscal tear, and these tears usually tend to present in adults. Figure 3 shows a case of an incomplete discoid lateral meniscus with a tear extending almost to the periphery. It must be remembered that the Wrisberg-ligament variant usually presents at a younger age, and it is more difficult to elicit a history and perform a consistent phys80
Fig 3. Arthroscopic appearance of an incomplete discoid lateral meniscus with a tear that extends almost to the peripheral edge of the meniscus,
ical examination on a child or adolescent compared with an adult. 25 The early presenting symptoms with children are often vague and inconclusive, and a high index of suspicion must always be maintained. Dickhaut and DeLee had 12 patients with complete discoid lateral menisci visualized at arthroscopy. Preoperatively, two patients had lateral joint line tenderness on examination. These two, along with one other patient, had a tear of the complete type of discoid lateral meniscus. None of the other nine patients had signs or symptoms preoperatively, and the complete discoid meniscus was an incidental arthroscopic finding. Patients with a complete or incomplete discoid meniscus with associated tear may have a history of trauma and most commonly present with pain and clicking as the most common presenting symptoms. Lateral joint line tenderness, clicking, and effusion are the most common physical signs of a complete or incomplete lateral meniscus associated with a tear.15 The age at presentation of complete and incomplete types tends to be somewhat older than with the Wrisberg type. In most studies of complete and incomplete types, the average age is between 24 and 34 y e a r s .1' '2 18 •21 •22 However, these can occur at any age, and Corso presented a report of a 64-year-old patient with sequentially occurring bilaterally symptomatic discoid lateral meniscus l e s i o n s . 26"27 The incidence of bilaterality of the complete and incomplete types is difficult to ascertain because the discoid meniscus is often asymptomatic. Bellier 28 reported a 20.2% bilaterality verified by arthrogram or arthroscopy, whereas Nathan is reported a 10% incidence, and most studies report less than 10% incidence of bilaterality. 17'18'21 We treated one patient w h o had a complete discoid lateral meniscus with tear in one knee and a lateral meniscal variant with absence of the posterior coronary ligament in the contralateral knee. 2 All patients with the Wrisberg-ligament type reported thus far have had the classic snapping knee syndrome. 1-3 DAVID C. NEUSCHWANDER
They have presented with the complaint of lateral compartment pain, an audible clunk with flexion and extension of the knee, and absence of any history of trauma. Repetitive t r a u m a may play some as yet indeterminate role in the presentation of this abnormality. 2 An audible or visible clunk occurs near the end of terminal extension. The clunk is an audible sound that is associated with a visible adjustment of the knee. We concur with Woods, that the lateral side of the knee adjusts with flexion and extension of the knee. 2"3 In our experience, the patient's clunk developed gradually, and he or she did not seek orthopaedic medical attention until it was associated with pain and beginning to occur with almost every range of motion of the knee. Our patients had an average age of 26 years, with four patients between 11 and 13 years of age, and three patients between 40 and 50 years, a Our patients differed from others reported in the literature, who were all equal[ to or less than 16 years of age. ~'3 Radiographic findings that have been reported in association with discoid lateral meniscus have included a squared-off appearance of the lateral femoral condyle; widened lateral tibiofemoral joint space; cupping of the lateral aspect of the tibial plateau articular surface; a high fibular head; and hypoplasia of the lateral intercondylar spine, a6'ag'3° However, these findings are uncommon. Of 12 patients with complete lateral discoid menisci, Dickhaut and DeLee reported three patients with widening of the lateral joint and two patients with cupping of the lateral tibial plateau. Aichroth reviewed 62 discoid menisci and treated five patients with a widened tibiofemoral lateral joint space and three patients with lateral tibial plateau cupping. 31 Interestingly, he also noted that seven knees had an associated osteochondritis dissecans of the lateral femoral condyle, and four had ossification defects affecting the lateral femoral condyle. In Bellier's study, there were five patients who had an increased tibiofernoral space resulting from lateral and inferior obliquity of the lateral tibial plateau, and two patients who had bhmting of the lateral tibial eminence, as Silverman 32 reported that the discoid meniscus can be diagnosed by magnetic resonance imaging if three continuous 5-ram sagittal sections demonstrate continuity of the anterior and posterior horns of the meniscus. No case of a Wrisberg-type meniscus has shown characteristic radiographic changesJ '2 The Wrisberg-ligament type lateral meniscus, or lateral meniscus variant 'with absence of the posterior coronary ligament, has a very recognizable clinical examination. Once this audible and visible adjustment of the knee has been observed by the examiner, it is not an easily forgotten part of the clinical acumen. However, there are other differential diagnostic entities that can cause snapping around the knee in a child or adolescent, including subluxation or dislocation of the patellofemoral joint, snapping of the tendons around the knee, congenital subluxation of the proximal tibiofibular joint, osteochondritis dissecans, and chondrornalacia of the patella. Discoid medial menisci are much less common than discoid lateral menisci. 19'24 Of his 10,000 knee meniscectomy cases, Srnillie found only seven cases of discoid medial meniscus. 33 Most patients with discoid medial DISCOID MENISCUS
Fig 4. The probe near the intercondylar eminence has been placed beneath the hypertrophic inner border of a complete discoid lateral meniscus.
menisci present because they have an associated meniscal tear, and they present with symptoms like any other meniscal tear. Initially, symptomatic discoid medial menisci were thought to occur only in children and adolescents. More recently, a comparable incidence has been described in adults. 26"34"35 In Dickason's series, 65% of the patients became symptomatic w h e n they were older than 18 years of ageJ 9 Radiographically, widening of the medial tibiofemoral cartilage space and proximal mediotibial epiphyseal collapse have been reported36"37; however, these are rare findings.
ARTHROSCOPIC EVALUATION The customary systematic evaluation of the knee joint should be undertaken arthroscopicalIy. This should include visualization and probing of the anterior and pos-
Fig 5. Same case as Fig 4, in which the rest of the lateral compartment is covered by the discoid lateral meniscus,
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terior cruciate ligaments in addition to the medial and lateral menisci. If the free inner edge of the meniscus cannot be easily visualized, the surgeon may be dealing with a discoid lateral meniscus. Visualization should then be directed centrally in the area of the tibial eminence (Figs 4 to 6), where a complete discoid lateral meniscus may be recognized. The meniscus should be visualized and probed while observing meniscal motion with flexion and extension of the knee. An attempt at probing the inferior attachment of the posterior horn should be performed, but this is often very difficult because of the increased thickness of the discoid meniscus. The probe should also be used to pull on the superior aspect of the posterior horn of the lateral meniscus to evaluate the integrity of the posterior horn attachment. The posteromedial and posterolateral compartments should be visualized through the intercondylar notch, and an accessory portal for posteromedial or posterolateral direct visualization should be used w h e n deemed necessary. The lateral meniscal variant with absence of the posterior coronary ligament may or may not have slight (1 to 2 ram) increased plateau coverage and hypertrophy of its posterior horn. However, it is not discoid in shape. It can be distinguished from a lateral meniscal tear by the following: its smooth, rounded border of the meniscus; the absence of any plane of cleavage indicating prior continuity of the meniscus and a posterior capsule (Fig 7); the absence of synovial hypertrophy; and the absence of attachment of the coronary ligament to its usual site just anterior to the popliteus tendon. There has been some variance in opinion with regard to the Wrisberg-ligament type and whether its posterior horn subluxes anteriorly with flexion or extension of the knee. Kaplan 1° is of the opinion that the meniscus subluxated in extension by being displaced into the intercondylar notch by its attachment to the ligament of Wrisberg. He stated that with each knee flexion, the lateral meniscus was pulled laterally by the coronary ligament and the popliteal tendon. Dickhaut and DeLee 1 noted
Fig 6. A different case example of a complete discoid lateral meniscus draping over the tibial eminence. Note the apparent difference in the thickness of the meniscal edge as compared with Fig 4. 82
Fig 7. Direct visualization of the posterolateral portion of the meniscal variant with absence of the posterior coronary ligament via an accessory posterolateral portal, The probe has been introduced through the anteromedial portal and through the intercondylar notch to lie around the posterior horn of the lateral meniscus, Note the smooth, rounded border of the meniscus and the absence of any posterior meniscal attachment.
hypermobility with flexion and extension of the knee, but did not detail w h i c h position c a u s e d subluxation. Woods and Whelan 3 found that the meniscus was reduced in extension and subluxated anteriorly with knee flexion. Woods and Whelan 3 visualized arthroscopically that the meniscus "was seen to roll up in the front of the lateral compartment with knee flexion" (Fig 8). As the knee extended, the rolled meniscus reduced at 10° to 20 ° of knee flexion (Fig 9). Our experience with six cases of the lateral meniscal variant with absence of the posterior coronary ligament showed that the posterior horn subluxated anteriorly in three cases with flexion and in three cases with extension. 2 Figure 10 shows the arthroscopic view of the posterior horn of the lateral meniscus subluxated anteriorly.
A
B
C
D
Fig 8. Rolling up of the lateral meniscus with knee flexion. (Reprinted with permissiona). DAVID C. NEUSCHWANDER
A
B
Fig 9, Reduction of the meniscus 10 ° to 20 ° as the knee is extended, (Reprinted with permission2),
Fig 11. Slightly hypertrophic posterior horn of the lateral meniscus with absence of the posterior coronary ligament in extension.
Fig 10. Anterior subluxation of the posterior horn and the lateral meniscal variant with absence of the posterior coronary ligament with knee flexion.
Extension resulted in reduction of the posterior horn of the lateral meniscus (Fig 11). The reason for this difference is unclear, but it may in some way be related to the fact that the ligament of Wrisberg (posterior meniscofemoral ligament) and a ligament of H u m p h r e y (anterior meniscofemoral ligament) are not consistently present. Their presence has been variably reported as 70% to 100%.37-39 In one study, 70% of the specimens had either a ligament of Wrisberg or a ligament of Humphrey; however, both ligaments were absent in 30% of the cases. 38
TREATMENT Recommended treatment depends on the type of meniscus that is visualized and probed at the time of arthroscopy. Possibilities Lnclude: (1) complete or incomplete discoid meniscus without tear; (2) complete or incomplete discoid meniscus with tear; and (3) Wrisberg-ligament DISCOID MENISCUS
type (ie, lateral meniscal variant with absence of the posterior coronary ligament). A medial meniscus counterpart without a posterior coronary ligament attachment has not been reported. The intact complete or incomplete meniscus should not be violated at the time of arthroscopy (after an exhaustive search for a tear), and the patient should be followed-up clinically. Dickhaut and DeLee 1 were the first to followup on a group of patients with the incidental finding of a discoid lateral meniscus. None of their patients had symptoms attributable to discoid lateral meniscus with an average follow-up at 23 months. Sugawara 4° had 6.5% rearthroscopy rate in patients who initially had saucerization for a previously intact discoid lateral menisci. Five of these cases had a tear of the saucerized rim of the lateral meniscus. The recommended procedure for the complete and incomplete discoid meniscus with a tear is an arthroscopic central partial meniscectomy, or so-called saucerization procedure. This has evolved from the previously reco m m e n d e d open lateral meniscectomy technique; 1°'15 however, no long-term studies substantiate that the partial meniscectomy is superior. In fact, Ikeuchi's study 17 had better results in the group treated by total meniscectomy than those treated with partial meniscectomy with short-term follow-up. However, the r e c o m m e n d e d treatment has evolved based on the accumulated knowledge of the many functions of the meniscus. 41-44 The long-term results after total lateral discoid meniscectomy in children have not been good. The longestterm study was conducted by Kurosaka, with a 20- to 26-year follow-up for total menisectomy for discoid lateral meniscus. 45 Kurosaka reported subjectively good longterm results in greater than 90% of the patients; however, 70% showed moderate-to-severe radiographic changes. Vavaren also reported unsatisfactory results. 46 8;3
Abdon also reported a long-term follow-up of total meniscectomy in children, with an average follow up of 16.8 years. 47 Many of these surgeries were for posttraumatic and meniscal conditions, and there were only 10 cases of total meniscectomy for discoid lateral menisci. Overall, 74% of the patients were pleased with their surgical outcome, but there were only 52% to 58% objectively satisfactory results according to the two scoring systems used. Range of motion was significantly decreased after open lateral meniscectomy, and minor instabilities and major instabilities were noted in 45% and 15% of the patients, respectively. Grade I gonarthrosis was present in 39% of the operated knees, and grades II and III changes in 9%. Also, meniscectomy for a normally shaped meniscus with tear has resulted in a high percentage of unsatisfactory results, especially in children. 40,48,49 As previously noted, central partial meniscectomy or saucerization techniques for the symptomatic complete or incomplete discoid meniscus with tears have been recommended. 1,20,21,50,51 The literature has variably reported the most common tear types. Smillie reported the most common type as a horizontal cleavage tear in the adult population. Hyashi 16 reported the most common type as a longitudinal tear in the posterior segment of middle segment. However, these tears can be of almost any type, including radial, bucket-handle, or complex. It is technically difficult to perform the saucerization procedure because of the confined working space within the compartment. Hyashi recommends that the meniscus be contoured to a 6-mm rim for an incomplete discoid to avoid subsequent tear of the saucerized rim.16 The difference between the complete and incomplete types is because of the increased thickness of the peripheral rim in the complete type as compared with the incomplete. Vandeermeer51 reported a rearthroscopy rate of 28% with discoid lateral menisci in dealing with retears of the peripheral rim and other subtle abnormalities that may have not been initially appreciated and that progressed to tears.
extension maneuver. The popliteal tendon should be evaluated, as should the ligament of Wrisberg, if present. Visualization of the posterior horn of the lateral meniscus should be achieved through the intercondylar notch, and an accessory posterolateral portal should be used to evaluate any questionable posterior meniscal attachment (Fig 12). The saucerization technique for the complete or incomplete lateral meniscus can be performed in either a onepiece or piecemeal fashion. One-piece excision can be a very difficult and often frustrating arthroscopic experience. This technique is performed by sequentially incising the anterior, middle, and posterior segments of the lateral meniscus (Fig 13). Next, the posterior attachment, and finally the anterior horn attachment can be released, and the saucerized meniscus can be removed with a grasper. The middle and posterior segments can be cut with angled scissors, and the anterior horn can be incised using arthroscopic scissors or a meniscal blade (Beaver 6600 optimatic blade, R. Beaver, Inc, Waltham, MA). It may be necessary to change the working and visualization portals w h e n performing this saucerization procedure. Arthroscopic piecemeal saucerization usually is less technically difficult to perform, especially in the case of a very hypertrophic complete discoid lateral meniscus. The anterior portion can be removed with the meniscal blade or a side-cutting basket punch. Removal of the anterior portion allows more working space for approach to the middle and subsequently the posterior horns. Curved, straight, and any angled instrumentation can be used for contouring the remaining meniscus to a wellcontoured stable rim.
SAUCERIZATION PROCEDURE FOR COMPLETE AND INCOMPLETE LATERAL DISCOID MENISCUS WITH TEAR We use a commercially available thigh-holding device and a well-trained assistant to provide constant and consistent varus stress with the leg internally rotated to gain maximal lateral joint opening for the arthroscopic procedure. Varying degrees of knee flexion can be attempted to obtain the best visualization of the lateral compartment and room for manipulating instruments. Initially, a systematic approach to the knee arthroscopy should be performed, as previously discussed. Visualization and probing of the meniscus should be performed, noting meniscal mobility and any evidence of a meniscal tear. The posterior horn of the lateral meniscus should be visualized with flexion and extension of the knee, and anterior subluxation of the posterior horn should be attempted with the probe during this flexion-
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Fig 12. Smooth, rounded border of the posterior horn of the lateral meniscal variant with absence of the posterior coronary ligament as visualized via direct posterolateral portal.
DAVID C. NEUSCHWANDER
Fig 13. One-piece excision of a discoid lateral meniscus as described by Hyashi: (1) initial incision of anterior segment of the meniscus; (2) extension of the incision to the middle and posterior segments; (3) release of posterior horn; and (4) release of anterior insertion and subsequent removal with grasper,
LATERAL MENISCAL VARIANT WITH ABSENCE OF POSTERIOR CORONARY LIGAMENT WRISBERG TYPE The Wrisberg-ligament type, or lateral meniscal variant with absence of the posterior coronary ligament, has traditionally been treated by total meniscectomy. Dickhaut and DeLee reported six patients with this type. Four of these patients had an associated vertical tear of the hypermobile posterior horn. They performed an arthroscopic total lateral m e n i s c e c t o m y in all six cases. 1 Rosenberg et al were the first to describe one case of an arthroscopic attachment for the Wrisberg type rather than total meniscectomy, s2 Neuschwander et al published the first series of patients with posterior horn meniscal attachment for the lateral meniscal variant with absence of the posterior coronary ligament with acceptable shortterm results. 2 This series used arthroscopic techniques similar to a more customary lateral meniscal repair. 2 Routine systematic arthroscopic inspection is performed, documenting the absence of posterior meniscal attachment and posterior horn instability by probing with flexion and extension of the knee. Direct posterolateral visualization via an accessory portal is performed to show the absence of any cleavage plane of previous continuity. The meniscus is visualized for evidence of hypertrophy and probed for any meniscal substance tear. T h r o u g h a posterolateral incision, with identification and protection of the peroneal nerve and retraction of the biceps tendon inferi0rly, the meniscus is reduced if displaced. Sutures are placed through the meniscus arthroscopically, and u n d e r direct vision, are passed through the posterolateral capsule (inside-out technique). Nonabsorbable sutures that have been commercially swaged onto the needles and arthroscopically positioned are used. Cannula are placed through the anteromedial
DISCOID MENISCUS
and anterolateral portals for suturing the meniscus to the capsule (whichever is appropriate for the portion of the meniscus that was being sutured). The sutures are tied over the capsule, and the incision is closed. 2 Postoperatively, the knee is immobilized for 3 to 4 weeks at the angle of flexion at which the least tension was present in the suture line. The patients remain non-weightbearing for an additional 4 weeks, during which time range-of-motion exercises and a quadriceps rehabilitation program are instituted.
RESULTS OF TREATMENT As noted previously, total lateral meniscectomy for discoid lateral meniscus showed promising short-term results, but longer4erm follow-up studies showed results to be less encouraging. 45"46 Very few contemporary studies have been conducted of partial lateral meniscectomy (saucerization) for discoid lateral meniscus. Bellier observed 19 children who underwent arthroscopic partial meniscectomy and had a 94% excellent result rate, with a maximum follow-up of 3 years. 2s Longer-term followup studies with more patients will be necessary to document the efficacy of this procedure. Vandermeer has described poor prognostic indicators in dealing with the discoid lateral meniscus. These indicators include evidence of degenerative changes at index arthroscopy, female gender, and age greater than 30 years. 51 Dickason reported that all patients in their study group, with the exception of one with a dislocating patella, returned to full activity without symptoms after treatment for discoid medial meniscus. 19 Neuschwander et al have the only substantiated group of patients followed-up after posterior meniscal attachment for a lateral meniscal variant with absence of the posterior coronary
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TABLE 1. Anomalies of the Lateral Meniscus
Appearance Symptoms Mobility Posterior meniscotibial attachment Age at presentation Method of treatment
Discoid
Lateral Meniscal Variant With Absence of the Posterior Coronary Ligament
Disc-shaped Rarely, unless torn Normal Present Varies Incidental, none; tear, saucerization
Mildly hypertrophic When hypermobile Hypermobile posterior horn Absent Varies Posterior meniscocapsular attachment
ligament. 2 T h e y t r e a t e d six p a t i e n t s w i t h p o s t e r i o r h o r n a t t a c h m e n t , a n d o n e p a t i e n t w h o h a d a partial m e n i s c e c t o m y for a c o m p l e x tear of t h e h y p e r m o b i l e p o s t e r i o r h o r n . T h e r e w e r e f o u r excellent, o n e g o o d , a n d o n e fair s h o r t - t e r m r e s u l t s , w i t h a n a v e r a g e f o l l o w u p of 32 m o n t h s in t h e p o s t e r i o r - h o r n a t t a c h m e n t g r o u p . I n b o t h p a t i e n t s w i t h l e s s - t h a n - e x c e l l e n t results, d e g e n e r a t i v e c h a n g e s w e r e n o t e d at the i n d e x a r t h r o s c o p i c p r o c e d u r e .
SUMMARY A discoid m e n i s c u s is a n u n c o m m o n a r t h r o s c o p i c finding. It is difficult to d i a g n o s e clinically, w i t h t h e exception of the W r i s b e r g - l i g a m e n t t y p e (lateral m e n i s c a l varia n t w i t h a b s e n c e of t h e p o s t e r i o r c o r o n a r y ligament), w h i c h p r e s e n t s w i t h t h e classic s n a p p i n g k n e e s y n d r o m e . C o m p l e t e a n d i n c o m p l e t e t y p e s are m o r e difficult to dia g n o s e p r e o p e r a t i v e l y ; h o w e v e r , t h e y s h o u l d be c o n s i d e r e d in t h e case of a y o u n g p a t i e n t w i t h m e c h a n i c a l s y m p t o m s , m e c h a n i c a l s y m p t o m s w i t h n o h i s t o r y of t r a u m a , or a discoid lesion in the contralateral knee. 51 T h e discoid m e n i s c u s a n d lateral m e n i s c a l v a r i a n t w i t h a b s e n c e of the p o s t e r i o r c o r o n a r y l i g a m e n t c a n p r e s e n t in c h i l d h o o d , a d o l e s c e n c e , or a d u l t h o o d (Table 1). T h e art h r o s c o p i s t s h o u l d k n o w h o w to deal w i t h t h e discoid lateral m e n i s c u s w h e n it is f o u n d arthroscopically. This d e p e n d s o n t h o r o u g h v i s u a l i z a t i o n a n d p r o b i n g of the m e n i s c u s at t h e time of a r t h r o s c o p y , in a d d i t i o n to evalu a t i o n w i t h flexion a n d e x t e n s i o n of the knee. A n incidental d i s c o i d m e n i s c u s w i t h o u t a tear s h o u l d be left alone. S a u c e r i z a t i o n to a w e l l - c o n t o u r e d stable rim of a p p r o x i m a t e l y 6 m m s h o u l d be p e r f o r m e d in t h e case of c o m p l e t e d i s c o i d m e n i s c u s w i t h a tear, a n d saucerization to a n 8 - m m r i m s h o u l d be a c h i e v e d for a n inc o m p l e t e discoid. A t t a c h m e n t of t h e h y p e r m o b i l e p o s terior h o r n s h o u l d be p e r f o r m e d for the lateral m e n i s c a l v a r i a n t w i t h a b s e n c e of the p o s t e r i o r c o r o n a r y l i g a m e n t .
REFERENCES 1. Dickhaut SC, DeLee JC: The discoid lateral-meniscus syndrome. J Bone Joint Surg [AM] 64:1068-1073, 1982 2. Neuschwander DC, Drez D, Finney TP: Lateral meniscal variant with absence of the posterior coronary ligament. J Bone Joint Surg [Am] 74:1186-1190, 1992 3. Woods GW, Whelan JM: Discoid meniscus. Clin Sports Med 9:695706, 1990 4. Watanabe M: Arthroscopy of the knee joint, in Helfet AJ (ed): Disorders of the Knee. Philadelphia, PA, Lippincott, 1974, p 45 5. Neuschwander DC: Discoid lateral meniscus, in Fu FA, Harner CD, Vince KG (eds): Knee Surgery (in press) 6. Young RB: The external semilunar cartilage as a complete disc, in 86
Cleland J, Mackay JY, Young RB (eds): Memoirs and Memoranda in Anatomy. London, England, Williams & Norgate, 1889, p 179 7. Kroiss F: Die Verletzungen der Kniegelenkoszwischenknorpel und ihrer Verbindungen. Beitr Klin Chir 66:598-801, 1910 8. Watson-Jones R: Specimen of internal semilunar cartilage as a complete disc. Proc R Soc Lond 23:588, 1930 9. Smillie IS: The congenital discoid meniscus. J Bone Joint Surg [Br] 30:671-682, 1948 10. Kaplan EB: Discoid lateral meniscus of the knee joint: Nature, mechanism, and operative treatment. J Bone Joint Surg [Am] 39:77-87, 1957 11. Clarke CR, Ogden JA: Development of the menisci in the human knee joint. J Bone Joint Surg [Am] 65:538-547, 1983 12. Gebhart MC, Rosenthal RK: Bilateral lateal discoid meniscus in identical twins. J Bone Joint Surg [Am] 61:1110-1111, 1979 13. Dashefsky JH: Discoid lateral meniscus in three members of a family: Case reports. J Bone Joint Surg [Am] 53:1208-1210, 1971 14. Hall FM: Arthrography of the discoid lateral meniscus. Am J Roentgenol 218:993-1002, 1977 15. Nathan PA, Cole SC: Discoid meniscus: A clinical and pathological study. Clin Orthop 64:107-113, 1969 16. Hayashi LK, Yamaga H, Ida K, et al: Arthroscopic meniscectomy for discoid lateral meniscus in children. J Bone Joint Surg [Am] 70:14951500, 1988 17. Ikeuchi H: Arthroscopic treatment of the discoid lateral meniscus: Technique and long-term results. Clin Orthop 167:19-28, 1982 18. Seong SC, Park MJ: Analysis of the discoid meniscus in Koreans. Orthopedics 15:61-65, 1992 19. Dickason JM, Del Pizzo W, Blazina ME, et al: A series of ten discoid medial menisci. Clin Orthop 168:75-79, 1982 20. Fujikawa K, Iseki F, Mikura Y: Partial resection of the discoid lateral meniscus in the child's knee. J Bone Joint Surg [Br] 63:391-395, 1981 21. Albertsson M, Gillquist J: Discoid lateral menisci: A report of 29 cases. Arthroscopy 4:211-214, 1988 22. Fritschy D, Gonseth D: Discoid lateral meniscus. Int Orthop 15:145147, 1991 23. Pellacci F, Stilli S, Pignatti G: Arthroscopic surgical technique in the treatment of lesions of the discoid meniscus. Ital J Orthop Traumatol 14:357-362, 1988 24. Johnson RG, Simmons EH: Discoid medial meniscus. Clin Orthop 167:176-179, 1982 25. Morrissy RT, Eubanks RG, Park JP, et ah Arthroscopy of the knee in children. Clin Orthop 162:103-107, 1982 26. Berson BL, Hermann G: Torn discoid menisci of the knee in adults: Four case reports. J Bone Joint Surg [Am] 61:303-304, 1979 27. Corso SJ, Bochner RM: Bilateral discoid lateral meniscus in the seventh decade: A case report, Am J Knee Surg 3:139-142, 1990 28. Bellier G, Dont J, Larrain M, et ah Lateral discoid menisci in children. Arthroscopy 5:52-56, 1989 29. Engber WE, Mikelson MR: Cupping of the lateral tibial plateau associated with a discoid meniscus. Orthopedics 4:904-906, 1981 30. Haveson SB, Rein Bh Lateral discoid meniscus of the knee: Arthroscopic diagnosis. Am J Roentgenol Rad Ther Nuc Med 109:581-585, 1970 31. Aichroth PM, Patel DV, Marx CL: Congenital discoid lateral meniscus in children. A followup study and evolution of management. J Bone Joint Surg [Br] 73:932-936, 1991 32. Silverman JM, Mink JH, Deutsch AL: Discoid menisci of the knee: MR imaging appearance radiology. 173:351-354, 1989 33. Smillie IS: Injuries to the knee joint (ed 4). Edinburgh, Churchill Livingstone, 1970 DAVID C. NEUSCHWANDER
34. Riachi E, Phares A: An unusual deformity of the medial semilunar cartilage. J Bone Joint Surg [Br] 45:146, 1963 35. Richmond DA: Two cases of discoid medial cartilage. J Bone Joint Surg [Br] 40:268, 1958 36. Cave EF, Staples OS: Congenital discoid meniscus. Am J Surg 54:371-376, 1941 37. Weiner B, Rosenberg N: Discoid medial meniscus: Association with bone changes in the tibia. J Bone Joint Surg [Am] 56:171-173, 1974 38. Girgis FG, Marshall JL, AL Monajem ARS: The cruciate ligaments of the knee joint: Anatomical, functional and experimental analysis. Clin Ortop 106:216-231, 1975 39. Heller L, Langman J: The menisco-femoral ligaments of the human knee. J Bone Joint Surg [Br] 46:307-313, 1964 40. Sugawara O, Miyatsu M, Yamashita I, et al: Problems with repeated arthroscopic surgery on the discoid meniscus. Arthroscopy 7:68-71, 1991 41. Kettelkamp DB, Jacobs AW: Tibiofemoral contact area: Determination and implications. J Bone Joint Surg [Am] 54:349-356, 1972 42. Seedhom BB: Transmission of the load in the knee joint with special reference to the role of the menisci. I. Anatomy, analysis and apparatus. Eng Med 8:207-219, 1979 43. Seedhom BB, Hargreaves DJ: Transmission of the load in the knee joint with special reference to the role of the menisci. II. Experimental results, discussion and conclusion. Eng Med 8:228-330, 1979
DISCOID MENISCUS
44. Walker PS, Erkman J: The role of the menisci in force transmission across the knee. Clin Orthop 109:184-192, 1975 45. Kurosaka M, Yoshiya S, Ohno O, et al. Lateral discoid meniscectomy: A 20-year followup. Presented at the American Academy of Orthopaedic Surgery Meeting, San Francisco, CA, January 1987 46. Vahvanen V, Aalto K: Meniscectomy in children. Acta Orthop Scand 50:791-795, 1979 47. Abdon P, Turner MS, Petterson H, et al: A long-term follow-up study of total meniscectomy in children. Clin Orthop 257:166-170, 1990 48. Medlar RC, Mandiberg JJ, Lyne ED: Meniscectomies in children: Report of long-term results (mean, 8.3 years). Am J Sports Med 8:87-92, 1980 49. Zaman M, Leonard MA: Meniscectomy in children: Results in 59 knees. Injury 12:425-428, 1981 50. Hanks GA, DeClaire JH, Handal JA, et al: Arthroscopic partial meniscectomy for a discoid lateral meniscus tear in a child: Case report and review of the literature. Am J Knee Surg 2:175-179, 1989 51. Vandermeer RD, Cunningham FK: Arthroscopic treatment of the discoid lateral meniscus: Results of long-term follow-up. Arthroscopy 5:101-109, 1989 52. Rosenberg TD, Paulos LE, Parker RD, et ah Discoid symptomatic Wrisberg-ligament type. Arthroscopy 3:277-282, 1987
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The discoid meniscus is an uncommon but not remote meniscal anomaly. Watanabe classified discoid menisci into three types: complete, incomplete, and Wrisberg-ligament type. These menisci vary in size, shape, presence of a posterior meniscal attachment, and mode of presentation. The complete and incomplete types are usually incidental arthroscopic findings unless they present with symptoms of an associated meniscal tear. The Wrisberg variant presents with the snapping knee syndrome, with visible, and often audible dunking with flexion and extension of the knee. The complete and incomplete types should be left alone unless there is an associated meniscal tear, in which case a saucerization procedure should be performed. The Wrisberg variant should have attachment of its hypermobile posterior horn. KEY WORDS: meniscus, discoid meniscus, meniscectomy
The discoid meniscus is an interesting meniscal anomaly. It presents more commonly in the lateral compartment, but it can also occur medially. There has been controversy in the literature with regard to its etiology, presentation, and treatment. It is important to distinguish the complete and incomplete discoid menisci from the so-called Wrisbergligament type. These menisci vary in size, shape, presence of a posterior meniscal attachment, and mode of presentation. The complete and incomplete types vary in their extent of tibial plateau coverage. They are usually asymptomatic incidental arthroscopic findings unless associated with a meniscal tear. These menisci are both discshaped, with a normal posterior meniscal attachment, and display no abnormal motion of their posterior horns with flexion or extension of the knee. In the literature, the snapping knee syndrome has been attributed generally to all discoid menisci, but more appropriately should be reserved for the so-called Wrisbergligament type. 1 This anomaly is relatively normal in shape, has absence of a posterior meniscal attachment, and is unassociated with trauma. 1-3 This usually presents in younger individuals with a popping sound with flexion and extension of the knee that is caused by abnormal meniscal motion because of lack of the posterior meniscal attachment. The snapping knee syndrome symptoms usually occur intermittently, and the patient usually presents w h e n the popping becomes more consistent and symptomatic. The size and shape of the Wrisberg-ligament type meniscus has been variably described in the literature. In most cases, it has been reported to be normal or hypertrophic in its posterior horn, but without a discoid
From the Department of Orthopedic Surgery, University of Pittsburgh School of Medicine, Pittsburgh, PA. Address reprint requests to David C. Neuschwander, MD, Department of Orthopedic Surgery, University of Pittsburgh School of Medicine, 2550 Mosside Boulevard, Suite 405, Monroeville, PA 15146. Copyright © 1995 by W. B. Saunders Company 1048-6666/95/0501-0011$05.00/0
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shape. 1-4 In our experience, the Wrisberg variant does not have a discoid shape, and therefore, we have described this as the lateral meniscal variant with absence of the posterior coronary ligament. 2'5
HISTORY The discoid lateral meniscus was first described by Young in 1887, 6 but it was not until 1910 that Krois attributed the snapping knee syndrome to this anomaly. 7 The first discoid medial meniscus was reported by Watson-Jones in 1930. s Smillie was the first to acquire extensive clinical experience, describing 29 cases in 1948. 9 He attributed this anomaly to an atavistic phenomenon with persistence of a disc-shaped meniscus arrested at different stages of embryonic development. He classified the discoid menisci into three types: primitive, intermediate, and infantile. Kaplan performed cadaveric dissections, embryologic studies, and dissection at operation of six discoid menisci, and he reported this in 1957. ~° His study took exception with Smillie's theory. His anatomic studies of the human fetus showed that neither the lateral nor medial meniscus assumed a discoid shape during any stage of development. Kaplan's dissections in animals and in six clinical cases showed that the posterior horn of the lateral meniscus was not attached to the tibial plateau. Rather, it had an attachment to the lateral aspect of the medial femoral condyle by a meniscofemoral ligament, the ligament of Wrisberg. He was of the opinion that hypermobile, normally shaped menisci became discoid as a result of abnormal meniscal motion from lack of a posterior capsular attachment. Kaplan noted that the Wrisberg ligament pulled the lateral meniscus into the intercondylar notch during extension, and he believed that this abnormal mediolateral motion led to hypertrophy of the meniscus and its resulting discoid shape (Fig 1). Clark and Ogden 11 noted more developmental variation of the lateral than the medial meniscus and also corroborated Kaplan's findings. They dissected 548 knees be-
Operative Techniques in Orthopaedics, Vol 5, No 1 (January), 1995: pp 78-87
Knee E x t e n d e d
Me
Knee Flexed
lteral niscus scold)
meR
Fig 1. Diagram of the Wrisberg lateral meniscus being pulled into the intercondylar notch with extension by the ligament of Wrisberg. With flexion, the lateral meniscus is pulled laterally by the coronary ligament and popliteal tendon.
tween 14 weeks gestation and 14 years of age and found no evidence of a disc-shaped meniscus during any stage of development. Smillie's and Kaplan's theories have flaws that cannot be substantiated. Smillie's theory is not explainable by embryologic studies that do not demonstrate a discshaped meniscus ~,t any stage of development. Kaplan's theory does not explain the more common discoid lateral meniscus, in which the meniscus has a normal meniscotibial attachment, nor does this theory explain the existence of a discoid medial meniscus. A congenital theory has also been proposed, with isolated reports of occurrence in twins and familial transmission. 12,13
CLASSIFICATION Smillie devised the first classification system based on his theory that the discoid meniscus resulted from an arrest of the meniscus at various stages of embryologic development. Kaplan described only the Wrisberg-ligament type in his embryologic and cadaveric studies and six clinical cases. Watanabe performed the first arthroscopic surgery in 1962 and subsequently described the classification of discoid lateral menisci based on their arthroscopic appearance. 4 He described three different types of discoid meniscus: complete, incomplete, and Wrisberg-ligament type (Fig 2). The complete and incomplete types differ in the amount of lateral plateau coverage by a disc-shaped meniscus with a normal posterior meniscal attachment. The Wrisberg-ligament type was described as being fairly normal in size and shape but lacking a posterior meniscal attachment, except the ligament of Wrisberg. Hall 14 subsequently developed a classification based on the arthrographic appearance of the discoid lateral meniscus; however, the Watanabe classification is the most universally recognized and used by clinicians. Dickhaut and DeLee~ refined the clinical presentation of the complete and incomplete types as compared with the Wrisberg-ligament type. They reported that the complete and incomplete types were usually asymptomDISCOID MENISCUS
Fig 2. Diagram of Watanabe's classification of a discoid lateral meniscus: (A) incomplete; (B) complete; and (C) Wrisberg-ligament variant. There is a normal posterior coronary ligament in the complete and incomplete types; this ligament is missing in the Wrisberg type. The size and shape of the Wrisberg type are fairly normal. (Reprinted with permission. 2)
atic unless associated with a meniscal tear. They reported that the Wrisberg-ligament type was more commonly associated with the snapping knee and had a fairly normal meniscal shape with the exception of hypertrophy of the posterior horn of the lateral meniscus in six cases. 1 With other investigators, 3A we also agree that the Wrisberg type has a relatively normal shape, and therefore, we call this entity the lateral meniscal variant with absence of the posterior coronary ligament, to distinguish it from a true discoid meniscus. 2
INCIDENCE After a thorough literature review, it is difficult to determine accurate incidence rates of the discoid lateral meniscus and the Wrisberg-ligament variant. Early studies used meniscectomy specimens obtained from arthrotomy and had reported rates between 2.4% and 4.2%. 9As These studies did not include the Wrisberg type because this variant would not be recognized because it was not abnormal in shape, but had absence of the posterior meniscal attachment. Arthroscopic studies more accurately depict actual rates. However, the indications for arthroscopy have varied among studies presenting incidence rates. There has been a significant difference between the rates reported in the Japanese and Korean populations compared with other parts of the world. 1'4'16-2° Watanabe's arthroscopic study reported a 26% incidence of discoid lateral meniscus and 3.1% incidence of Wrisberg-ligament type 79
in arthroscopies that were performed in knees in which internal derangement was suspected. 4 Ikeuchi 17 had a 16.6% incidence rate of discoid lateral meniscus with no Wrisberg-ligament types over a 20-year period. Seong reported a 15% incidence of discoid lateral meniscus and no Wrisberg-ligament types in a study of 236 Korean patients who underwent arthroscopy because of variable symptoms attributable to the meniscus or other structures of the knee. Interestingly, Seong et al also conducted an autopsy study, in which they dissected 124 Korean adult knees and found an 8.1% incidence of discoid lateral meniscus and no cases of the Wrisbergligament type, despite having a posterior menisofemoral ligament (Wrisberg ligament) present in 95.2% of the specimens. Dickhaut and DeLee reported a 5% incidence of the complete type (no incompletes) and 2% incidence of the Wrisberg-ligament type in 347 knees that underwent arthroscopy for suspected meniscal abnormality. Between 1979 and 1986, Albertson and Gillquist reviewed 7,056 arthroscopies performed at their clinic for all indications and had a 0.4% rate of discoid lateral meniscus, with none of the Wrisberg-ligament type. 21 Similarly, low rates have been reported in the Swiss, Italian, and other United States studies, with reported incidence rates of 0.9%, 3.5%, and 1.5%, respectively. 19"22"23 Our study of 3,468 knee arthroscopies for all indications had a 0.8% rate of discoid lateral meniscus and 0.2% rates of the Wrisberg-ligament variant. 2 Some of the differences between studies may be because of the inclusion criteria, but it seems that the discoid meniscus is more common in the Japanese and Korean populations than the rest of the world. 4'16-18 It is also interesting that no cases of the Wrisberg-ligament type were reported in two large Japanese and one Korean study, especially in light of the relatively high incidence of Wrisberg ligaments in the Korean autopsy study. 16-18 The incidence of discoid medial meniscus has been reported to vary from 0% to 0.3% in different studies. 19"24 Only the complete and incomplete types of medial menisci have been reported, and a Wrisberg ligament variant has not been identified.
CLINICAL PRESENTATION Dickhaut and DeLee 1 described the complete and incomplete types of discoid lateral meniscus as clinically presenting much differently than the Wrisberg type. The classic snapping knee syndrome presents most commonly in children and adolescents with the Wrisbergligament type. Complete and incomplete types usually are incidental findings at the time of arthroscopy for other reasons. If the complete and incomplete types have a tear of their meniscal substance, the clinical signs and symptoms are similar to that of any other meniscal tear, and these tears usually tend to present in adults. Figure 3 shows a case of an incomplete discoid lateral meniscus with a tear extending almost to the periphery. It must be remembered that the Wrisberg-ligament variant usually presents at a younger age, and it is more difficult to elicit a history and perform a consistent phys80
Fig 3. Arthroscopic appearance of an incomplete discoid lateral meniscus with a tear that extends almost to the peripheral edge of the meniscus,
ical examination on a child or adolescent compared with an adult. 25 The early presenting symptoms with children are often vague and inconclusive, and a high index of suspicion must always be maintained. Dickhaut and DeLee had 12 patients with complete discoid lateral menisci visualized at arthroscopy. Preoperatively, two patients had lateral joint line tenderness on examination. These two, along with one other patient, had a tear of the complete type of discoid lateral meniscus. None of the other nine patients had signs or symptoms preoperatively, and the complete discoid meniscus was an incidental arthroscopic finding. Patients with a complete or incomplete discoid meniscus with associated tear may have a history of trauma and most commonly present with pain and clicking as the most common presenting symptoms. Lateral joint line tenderness, clicking, and effusion are the most common physical signs of a complete or incomplete lateral meniscus associated with a tear.15 The age at presentation of complete and incomplete types tends to be somewhat older than with the Wrisberg type. In most studies of complete and incomplete types, the average age is between 24 and 34 y e a r s .1' '2 18 •21 •22 However, these can occur at any age, and Corso presented a report of a 64-year-old patient with sequentially occurring bilaterally symptomatic discoid lateral meniscus l e s i o n s . 26"27 The incidence of bilaterality of the complete and incomplete types is difficult to ascertain because the discoid meniscus is often asymptomatic. Bellier 28 reported a 20.2% bilaterality verified by arthrogram or arthroscopy, whereas Nathan is reported a 10% incidence, and most studies report less than 10% incidence of bilaterality. 17'18'21 We treated one patient w h o had a complete discoid lateral meniscus with tear in one knee and a lateral meniscal variant with absence of the posterior coronary ligament in the contralateral knee. 2 All patients with the Wrisberg-ligament type reported thus far have had the classic snapping knee syndrome. 1-3 DAVID C. NEUSCHWANDER
They have presented with the complaint of lateral compartment pain, an audible clunk with flexion and extension of the knee, and absence of any history of trauma. Repetitive t r a u m a may play some as yet indeterminate role in the presentation of this abnormality. 2 An audible or visible clunk occurs near the end of terminal extension. The clunk is an audible sound that is associated with a visible adjustment of the knee. We concur with Woods, that the lateral side of the knee adjusts with flexion and extension of the knee. 2"3 In our experience, the patient's clunk developed gradually, and he or she did not seek orthopaedic medical attention until it was associated with pain and beginning to occur with almost every range of motion of the knee. Our patients had an average age of 26 years, with four patients between 11 and 13 years of age, and three patients between 40 and 50 years, a Our patients differed from others reported in the literature, who were all equal[ to or less than 16 years of age. ~'3 Radiographic findings that have been reported in association with discoid lateral meniscus have included a squared-off appearance of the lateral femoral condyle; widened lateral tibiofemoral joint space; cupping of the lateral aspect of the tibial plateau articular surface; a high fibular head; and hypoplasia of the lateral intercondylar spine, a6'ag'3° However, these findings are uncommon. Of 12 patients with complete lateral discoid menisci, Dickhaut and DeLee reported three patients with widening of the lateral joint and two patients with cupping of the lateral tibial plateau. Aichroth reviewed 62 discoid menisci and treated five patients with a widened tibiofemoral lateral joint space and three patients with lateral tibial plateau cupping. 31 Interestingly, he also noted that seven knees had an associated osteochondritis dissecans of the lateral femoral condyle, and four had ossification defects affecting the lateral femoral condyle. In Bellier's study, there were five patients who had an increased tibiofernoral space resulting from lateral and inferior obliquity of the lateral tibial plateau, and two patients who had bhmting of the lateral tibial eminence, as Silverman 32 reported that the discoid meniscus can be diagnosed by magnetic resonance imaging if three continuous 5-ram sagittal sections demonstrate continuity of the anterior and posterior horns of the meniscus. No case of a Wrisberg-type meniscus has shown characteristic radiographic changesJ '2 The Wrisberg-ligament type lateral meniscus, or lateral meniscus variant 'with absence of the posterior coronary ligament, has a very recognizable clinical examination. Once this audible and visible adjustment of the knee has been observed by the examiner, it is not an easily forgotten part of the clinical acumen. However, there are other differential diagnostic entities that can cause snapping around the knee in a child or adolescent, including subluxation or dislocation of the patellofemoral joint, snapping of the tendons around the knee, congenital subluxation of the proximal tibiofibular joint, osteochondritis dissecans, and chondrornalacia of the patella. Discoid medial menisci are much less common than discoid lateral menisci. 19'24 Of his 10,000 knee meniscectomy cases, Srnillie found only seven cases of discoid medial meniscus. 33 Most patients with discoid medial DISCOID MENISCUS
Fig 4. The probe near the intercondylar eminence has been placed beneath the hypertrophic inner border of a complete discoid lateral meniscus.
menisci present because they have an associated meniscal tear, and they present with symptoms like any other meniscal tear. Initially, symptomatic discoid medial menisci were thought to occur only in children and adolescents. More recently, a comparable incidence has been described in adults. 26"34"35 In Dickason's series, 65% of the patients became symptomatic w h e n they were older than 18 years of ageJ 9 Radiographically, widening of the medial tibiofemoral cartilage space and proximal mediotibial epiphyseal collapse have been reported36"37; however, these are rare findings.
ARTHROSCOPIC EVALUATION The customary systematic evaluation of the knee joint should be undertaken arthroscopicalIy. This should include visualization and probing of the anterior and pos-
Fig 5. Same case as Fig 4, in which the rest of the lateral compartment is covered by the discoid lateral meniscus,
81
terior cruciate ligaments in addition to the medial and lateral menisci. If the free inner edge of the meniscus cannot be easily visualized, the surgeon may be dealing with a discoid lateral meniscus. Visualization should then be directed centrally in the area of the tibial eminence (Figs 4 to 6), where a complete discoid lateral meniscus may be recognized. The meniscus should be visualized and probed while observing meniscal motion with flexion and extension of the knee. An attempt at probing the inferior attachment of the posterior horn should be performed, but this is often very difficult because of the increased thickness of the discoid meniscus. The probe should also be used to pull on the superior aspect of the posterior horn of the lateral meniscus to evaluate the integrity of the posterior horn attachment. The posteromedial and posterolateral compartments should be visualized through the intercondylar notch, and an accessory portal for posteromedial or posterolateral direct visualization should be used w h e n deemed necessary. The lateral meniscal variant with absence of the posterior coronary ligament may or may not have slight (1 to 2 ram) increased plateau coverage and hypertrophy of its posterior horn. However, it is not discoid in shape. It can be distinguished from a lateral meniscal tear by the following: its smooth, rounded border of the meniscus; the absence of any plane of cleavage indicating prior continuity of the meniscus and a posterior capsule (Fig 7); the absence of synovial hypertrophy; and the absence of attachment of the coronary ligament to its usual site just anterior to the popliteus tendon. There has been some variance in opinion with regard to the Wrisberg-ligament type and whether its posterior horn subluxes anteriorly with flexion or extension of the knee. Kaplan 1° is of the opinion that the meniscus subluxated in extension by being displaced into the intercondylar notch by its attachment to the ligament of Wrisberg. He stated that with each knee flexion, the lateral meniscus was pulled laterally by the coronary ligament and the popliteal tendon. Dickhaut and DeLee 1 noted
Fig 6. A different case example of a complete discoid lateral meniscus draping over the tibial eminence. Note the apparent difference in the thickness of the meniscal edge as compared with Fig 4. 82
Fig 7. Direct visualization of the posterolateral portion of the meniscal variant with absence of the posterior coronary ligament via an accessory posterolateral portal, The probe has been introduced through the anteromedial portal and through the intercondylar notch to lie around the posterior horn of the lateral meniscus, Note the smooth, rounded border of the meniscus and the absence of any posterior meniscal attachment.
hypermobility with flexion and extension of the knee, but did not detail w h i c h position c a u s e d subluxation. Woods and Whelan 3 found that the meniscus was reduced in extension and subluxated anteriorly with knee flexion. Woods and Whelan 3 visualized arthroscopically that the meniscus "was seen to roll up in the front of the lateral compartment with knee flexion" (Fig 8). As the knee extended, the rolled meniscus reduced at 10° to 20 ° of knee flexion (Fig 9). Our experience with six cases of the lateral meniscal variant with absence of the posterior coronary ligament showed that the posterior horn subluxated anteriorly in three cases with flexion and in three cases with extension. 2 Figure 10 shows the arthroscopic view of the posterior horn of the lateral meniscus subluxated anteriorly.
A
B
C
D
Fig 8. Rolling up of the lateral meniscus with knee flexion. (Reprinted with permissiona). DAVID C. NEUSCHWANDER
A
B
Fig 9, Reduction of the meniscus 10 ° to 20 ° as the knee is extended, (Reprinted with permission2),
Fig 11. Slightly hypertrophic posterior horn of the lateral meniscus with absence of the posterior coronary ligament in extension.
Fig 10. Anterior subluxation of the posterior horn and the lateral meniscal variant with absence of the posterior coronary ligament with knee flexion.
Extension resulted in reduction of the posterior horn of the lateral meniscus (Fig 11). The reason for this difference is unclear, but it may in some way be related to the fact that the ligament of Wrisberg (posterior meniscofemoral ligament) and a ligament of H u m p h r e y (anterior meniscofemoral ligament) are not consistently present. Their presence has been variably reported as 70% to 100%.37-39 In one study, 70% of the specimens had either a ligament of Wrisberg or a ligament of Humphrey; however, both ligaments were absent in 30% of the cases. 38
TREATMENT Recommended treatment depends on the type of meniscus that is visualized and probed at the time of arthroscopy. Possibilities Lnclude: (1) complete or incomplete discoid meniscus without tear; (2) complete or incomplete discoid meniscus with tear; and (3) Wrisberg-ligament DISCOID MENISCUS
type (ie, lateral meniscal variant with absence of the posterior coronary ligament). A medial meniscus counterpart without a posterior coronary ligament attachment has not been reported. The intact complete or incomplete meniscus should not be violated at the time of arthroscopy (after an exhaustive search for a tear), and the patient should be followed-up clinically. Dickhaut and DeLee 1 were the first to followup on a group of patients with the incidental finding of a discoid lateral meniscus. None of their patients had symptoms attributable to discoid lateral meniscus with an average follow-up at 23 months. Sugawara 4° had 6.5% rearthroscopy rate in patients who initially had saucerization for a previously intact discoid lateral menisci. Five of these cases had a tear of the saucerized rim of the lateral meniscus. The recommended procedure for the complete and incomplete discoid meniscus with a tear is an arthroscopic central partial meniscectomy, or so-called saucerization procedure. This has evolved from the previously reco m m e n d e d open lateral meniscectomy technique; 1°'15 however, no long-term studies substantiate that the partial meniscectomy is superior. In fact, Ikeuchi's study 17 had better results in the group treated by total meniscectomy than those treated with partial meniscectomy with short-term follow-up. However, the r e c o m m e n d e d treatment has evolved based on the accumulated knowledge of the many functions of the meniscus. 41-44 The long-term results after total lateral discoid meniscectomy in children have not been good. The longestterm study was conducted by Kurosaka, with a 20- to 26-year follow-up for total menisectomy for discoid lateral meniscus. 45 Kurosaka reported subjectively good longterm results in greater than 90% of the patients; however, 70% showed moderate-to-severe radiographic changes. Vavaren also reported unsatisfactory results. 46 8;3
Abdon also reported a long-term follow-up of total meniscectomy in children, with an average follow up of 16.8 years. 47 Many of these surgeries were for posttraumatic and meniscal conditions, and there were only 10 cases of total meniscectomy for discoid lateral menisci. Overall, 74% of the patients were pleased with their surgical outcome, but there were only 52% to 58% objectively satisfactory results according to the two scoring systems used. Range of motion was significantly decreased after open lateral meniscectomy, and minor instabilities and major instabilities were noted in 45% and 15% of the patients, respectively. Grade I gonarthrosis was present in 39% of the operated knees, and grades II and III changes in 9%. Also, meniscectomy for a normally shaped meniscus with tear has resulted in a high percentage of unsatisfactory results, especially in children. 40,48,49 As previously noted, central partial meniscectomy or saucerization techniques for the symptomatic complete or incomplete discoid meniscus with tears have been recommended. 1,20,21,50,51 The literature has variably reported the most common tear types. Smillie reported the most common type as a horizontal cleavage tear in the adult population. Hyashi 16 reported the most common type as a longitudinal tear in the posterior segment of middle segment. However, these tears can be of almost any type, including radial, bucket-handle, or complex. It is technically difficult to perform the saucerization procedure because of the confined working space within the compartment. Hyashi recommends that the meniscus be contoured to a 6-mm rim for an incomplete discoid to avoid subsequent tear of the saucerized rim.16 The difference between the complete and incomplete types is because of the increased thickness of the peripheral rim in the complete type as compared with the incomplete. Vandeermeer51 reported a rearthroscopy rate of 28% with discoid lateral menisci in dealing with retears of the peripheral rim and other subtle abnormalities that may have not been initially appreciated and that progressed to tears.
extension maneuver. The popliteal tendon should be evaluated, as should the ligament of Wrisberg, if present. Visualization of the posterior horn of the lateral meniscus should be achieved through the intercondylar notch, and an accessory posterolateral portal should be used to evaluate any questionable posterior meniscal attachment (Fig 12). The saucerization technique for the complete or incomplete lateral meniscus can be performed in either a onepiece or piecemeal fashion. One-piece excision can be a very difficult and often frustrating arthroscopic experience. This technique is performed by sequentially incising the anterior, middle, and posterior segments of the lateral meniscus (Fig 13). Next, the posterior attachment, and finally the anterior horn attachment can be released, and the saucerized meniscus can be removed with a grasper. The middle and posterior segments can be cut with angled scissors, and the anterior horn can be incised using arthroscopic scissors or a meniscal blade (Beaver 6600 optimatic blade, R. Beaver, Inc, Waltham, MA). It may be necessary to change the working and visualization portals w h e n performing this saucerization procedure. Arthroscopic piecemeal saucerization usually is less technically difficult to perform, especially in the case of a very hypertrophic complete discoid lateral meniscus. The anterior portion can be removed with the meniscal blade or a side-cutting basket punch. Removal of the anterior portion allows more working space for approach to the middle and subsequently the posterior horns. Curved, straight, and any angled instrumentation can be used for contouring the remaining meniscus to a wellcontoured stable rim.
SAUCERIZATION PROCEDURE FOR COMPLETE AND INCOMPLETE LATERAL DISCOID MENISCUS WITH TEAR We use a commercially available thigh-holding device and a well-trained assistant to provide constant and consistent varus stress with the leg internally rotated to gain maximal lateral joint opening for the arthroscopic procedure. Varying degrees of knee flexion can be attempted to obtain the best visualization of the lateral compartment and room for manipulating instruments. Initially, a systematic approach to the knee arthroscopy should be performed, as previously discussed. Visualization and probing of the meniscus should be performed, noting meniscal mobility and any evidence of a meniscal tear. The posterior horn of the lateral meniscus should be visualized with flexion and extension of the knee, and anterior subluxation of the posterior horn should be attempted with the probe during this flexion-
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Fig 12. Smooth, rounded border of the posterior horn of the lateral meniscal variant with absence of the posterior coronary ligament as visualized via direct posterolateral portal.
DAVID C. NEUSCHWANDER
Fig 13. One-piece excision of a discoid lateral meniscus as described by Hyashi: (1) initial incision of anterior segment of the meniscus; (2) extension of the incision to the middle and posterior segments; (3) release of posterior horn; and (4) release of anterior insertion and subsequent removal with grasper,
LATERAL MENISCAL VARIANT WITH ABSENCE OF POSTERIOR CORONARY LIGAMENT WRISBERG TYPE The Wrisberg-ligament type, or lateral meniscal variant with absence of the posterior coronary ligament, has traditionally been treated by total meniscectomy. Dickhaut and DeLee reported six patients with this type. Four of these patients had an associated vertical tear of the hypermobile posterior horn. They performed an arthroscopic total lateral m e n i s c e c t o m y in all six cases. 1 Rosenberg et al were the first to describe one case of an arthroscopic attachment for the Wrisberg type rather than total meniscectomy, s2 Neuschwander et al published the first series of patients with posterior horn meniscal attachment for the lateral meniscal variant with absence of the posterior coronary ligament with acceptable shortterm results. 2 This series used arthroscopic techniques similar to a more customary lateral meniscal repair. 2 Routine systematic arthroscopic inspection is performed, documenting the absence of posterior meniscal attachment and posterior horn instability by probing with flexion and extension of the knee. Direct posterolateral visualization via an accessory portal is performed to show the absence of any cleavage plane of previous continuity. The meniscus is visualized for evidence of hypertrophy and probed for any meniscal substance tear. T h r o u g h a posterolateral incision, with identification and protection of the peroneal nerve and retraction of the biceps tendon inferi0rly, the meniscus is reduced if displaced. Sutures are placed through the meniscus arthroscopically, and u n d e r direct vision, are passed through the posterolateral capsule (inside-out technique). Nonabsorbable sutures that have been commercially swaged onto the needles and arthroscopically positioned are used. Cannula are placed through the anteromedial
DISCOID MENISCUS
and anterolateral portals for suturing the meniscus to the capsule (whichever is appropriate for the portion of the meniscus that was being sutured). The sutures are tied over the capsule, and the incision is closed. 2 Postoperatively, the knee is immobilized for 3 to 4 weeks at the angle of flexion at which the least tension was present in the suture line. The patients remain non-weightbearing for an additional 4 weeks, during which time range-of-motion exercises and a quadriceps rehabilitation program are instituted.
RESULTS OF TREATMENT As noted previously, total lateral meniscectomy for discoid lateral meniscus showed promising short-term results, but longer4erm follow-up studies showed results to be less encouraging. 45"46 Very few contemporary studies have been conducted of partial lateral meniscectomy (saucerization) for discoid lateral meniscus. Bellier observed 19 children who underwent arthroscopic partial meniscectomy and had a 94% excellent result rate, with a maximum follow-up of 3 years. 2s Longer-term followup studies with more patients will be necessary to document the efficacy of this procedure. Vandermeer has described poor prognostic indicators in dealing with the discoid lateral meniscus. These indicators include evidence of degenerative changes at index arthroscopy, female gender, and age greater than 30 years. 51 Dickason reported that all patients in their study group, with the exception of one with a dislocating patella, returned to full activity without symptoms after treatment for discoid medial meniscus. 19 Neuschwander et al have the only substantiated group of patients followed-up after posterior meniscal attachment for a lateral meniscal variant with absence of the posterior coronary
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TABLE 1. Anomalies of the Lateral Meniscus
Appearance Symptoms Mobility Posterior meniscotibial attachment Age at presentation Method of treatment
Discoid
Lateral Meniscal Variant With Absence of the Posterior Coronary Ligament
Disc-shaped Rarely, unless torn Normal Present Varies Incidental, none; tear, saucerization
Mildly hypertrophic When hypermobile Hypermobile posterior horn Absent Varies Posterior meniscocapsular attachment
ligament. 2 T h e y t r e a t e d six p a t i e n t s w i t h p o s t e r i o r h o r n a t t a c h m e n t , a n d o n e p a t i e n t w h o h a d a partial m e n i s c e c t o m y for a c o m p l e x tear of t h e h y p e r m o b i l e p o s t e r i o r h o r n . T h e r e w e r e f o u r excellent, o n e g o o d , a n d o n e fair s h o r t - t e r m r e s u l t s , w i t h a n a v e r a g e f o l l o w u p of 32 m o n t h s in t h e p o s t e r i o r - h o r n a t t a c h m e n t g r o u p . I n b o t h p a t i e n t s w i t h l e s s - t h a n - e x c e l l e n t results, d e g e n e r a t i v e c h a n g e s w e r e n o t e d at the i n d e x a r t h r o s c o p i c p r o c e d u r e .
SUMMARY A discoid m e n i s c u s is a n u n c o m m o n a r t h r o s c o p i c finding. It is difficult to d i a g n o s e clinically, w i t h t h e exception of the W r i s b e r g - l i g a m e n t t y p e (lateral m e n i s c a l varia n t w i t h a b s e n c e of t h e p o s t e r i o r c o r o n a r y ligament), w h i c h p r e s e n t s w i t h t h e classic s n a p p i n g k n e e s y n d r o m e . C o m p l e t e a n d i n c o m p l e t e t y p e s are m o r e difficult to dia g n o s e p r e o p e r a t i v e l y ; h o w e v e r , t h e y s h o u l d be c o n s i d e r e d in t h e case of a y o u n g p a t i e n t w i t h m e c h a n i c a l s y m p t o m s , m e c h a n i c a l s y m p t o m s w i t h n o h i s t o r y of t r a u m a , or a discoid lesion in the contralateral knee. 51 T h e discoid m e n i s c u s a n d lateral m e n i s c a l v a r i a n t w i t h a b s e n c e of the p o s t e r i o r c o r o n a r y l i g a m e n t c a n p r e s e n t in c h i l d h o o d , a d o l e s c e n c e , or a d u l t h o o d (Table 1). T h e art h r o s c o p i s t s h o u l d k n o w h o w to deal w i t h t h e discoid lateral m e n i s c u s w h e n it is f o u n d arthroscopically. This d e p e n d s o n t h o r o u g h v i s u a l i z a t i o n a n d p r o b i n g of the m e n i s c u s at t h e time of a r t h r o s c o p y , in a d d i t i o n to evalu a t i o n w i t h flexion a n d e x t e n s i o n of the knee. A n incidental d i s c o i d m e n i s c u s w i t h o u t a tear s h o u l d be left alone. S a u c e r i z a t i o n to a w e l l - c o n t o u r e d stable rim of a p p r o x i m a t e l y 6 m m s h o u l d be p e r f o r m e d in t h e case of c o m p l e t e d i s c o i d m e n i s c u s w i t h a tear, a n d saucerization to a n 8 - m m r i m s h o u l d be a c h i e v e d for a n inc o m p l e t e discoid. A t t a c h m e n t of t h e h y p e r m o b i l e p o s terior h o r n s h o u l d be p e r f o r m e d for the lateral m e n i s c a l v a r i a n t w i t h a b s e n c e of the p o s t e r i o r c o r o n a r y l i g a m e n t .
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