Functional analysis on the treatment of torn discoid lateral meniscus

The Knee 18 (2011) 369–372

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The Knee

Functional analysis on the treatment of torn discoid lateral meniscus To Wong, Ching-Jen Wang ⁎ Department of Orthopaedic Surgery, Chang Gung Memorial Hospital – Kaohsiung Medical Center, Chang Gung University College of Medicine, Kaohsiung, Taiwan

a r t i c l e

i n f o

Article history: Received 7 January 2010 Received in revised form 18 June 2010 Accepted 4 July 2010 Keywords: Discoid meniscus Functional outcome Arthroscopy

a b s t r a c t The purpose of this study is to evaluate the functional outcome on the treatment of torn discoid lateral meniscus. Thirty-two torn discoid lateral meniscuses in 29 patients were retrospectively reviewed. There were 13 males and 16 females with a mean age of 31.3 ± 17.0. The age distribution were 24% in pediatric age (b 11 years old), 38%in young adult under 25 years and 38% in 25 years and older. Subjective symptoms included pain in 63%, popping and snapping in 56%, locking in 41%, givingway in 17%; and objective signs included decreased knee motion in 16%. Partial lateral menisectomy and saucerization were performed in 18 knees (56%), meniscus repairs were done in eight knee (25% ) and subtotal lateral menisectomy in six knees (19%). At an average follow up of 52.5 ± 25.9 months (24-96 months). The results showed 84% good to excellent, 16% fair, and none poor. No significant difference was noted on the outcomes of different treatment methods. The age of symptom onset and the time of operation correlated with the IKDC and Tenger score. (p b 0.001). Our data showed symptomatic torn discoid lateral meniscus may manifest at any age from childhood to adult. The first manifestation of symptom before age 11 year old was observed in only 24%. Therefore, discoid lateral meniscus should not be considered a childhood disease. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Discoid meniscus is a variation of fibrocartilaginous structure of the knee which was first reported by Young in 1889. It is discoid in shape rather than semilunar. This atavistic anomaly almost solely occurs on lateral side.[1] Discoid lateral meniscus is grossly thicker and has poor vascularity than the normal meniscus. The ultrastructures of discoid meniscus differ from the normal meniscus with a decrease in the number of collagen fibers and heterogeneous courses of collagen fibers [2]. The prevalence of discoid meniscus is between 0.4% and 20%. It is rare in Caucasian [3,4] but more common in Asian . [3,5,6]. Common symptoms of discoid lateral menisci include pain, popping and snapping, locking, and decreased knee extension [7,8]. The diagnosis of discoid lateral meniscus is made by clinical symptoms with high index of suspicion. The symptoms are annoying, but non-disabling in most cases. Radiographs of the knee are usually unremarkable. Magnetic resonance imaging and arthroscopy are the best tools for the diagnosis. The commonly used classification was proposed by Watanabe et al in 1978 [9]. There are three types of discoid lateral meniscus including complete, incomplete and Wrisberg type with instability caused by deficient posterior tibial

⁎ Corresponding author. Department of Orthopaedic Surgery, Section of Sports Medicine, Chang Gung Memorial Hospital Kaohsiung Medical Center, 123, Ta-Pei Rd., Niao-Sung Hsiang, Kaohsiung Hsien, Taiwan. Tel.: + 886 7 7317123x8003; fax: + 886 7 7318762. E-mail address: [email protected] (C.-J. Wang). 0968-0160/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2010.07.002

attachments. Previous literatures suggested this abnormality is most symptomatic in the pediatric age group [10,11]. However, an incidental finding of torn discoid lateral meniscus is often encountered during arthroscopy for symptomatic knee in adult. In this study, we retrospectively analyzed the functional outcome of management for symptomatic torn discoid lateral meniscus at our hospital in the past ten years. 2. Patients and Methods Between November 1995 and November 2005, 32 discoid lateral menisci were diagnosed in 29 patients among 1994 arthroscopy procedures at our institution. Patients characteristic and clinical history were retrospective reviewed. There were 13 (44.8%) male, 16 (55.2%) females with an average age of 31.3 ± 17.0 years ( range 6 to 64 years ) (Table 1). Fifteen menisci occurred on right knee and 11 on left knee. Three had bilateral knee involvement. The discoid lateral meniscus was arthroscopically classified according Watanabe classification including complete, incomplete and Wrisberg type at the time of arthroscopy surgery. The associated injuries included five torn medial meniscus, two anterior cruciate ligment tear resulting from traffic accident and one osteochondritis dessicans in the lateral femoral condyle. Conservative treatments including knee brace, physiotherapy and exercise program etc were first suggested to all cases. Surgical intervention was indicated in patients with failure to conservative treatment for three clinical visits within 3 months or patients with mechanical symptoms such as locked knee. Stability of the injured

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Table Table 11 Age distribution Age distribution of of 29 29 patients patients with with Discoid Discoid Meniscus. Meniscus.

Table 2 Demographic and Surgical Procedure for 29 patient with Discoid Lateral Meniscus.

meniscus was determined intraoperatively. Arthroscopic partial lateral meniscectomy and saucerization was performed in 18 torn but stable lateral menisi. Saucerization and repair of lateral meniscus were performed in eight unstable peripheral tears of the lateral meniscus. All inside repair using meniscus arrows (DePuy Mitek, Massachusetts, United States) was used to stabilize the peripheral tear of the lateral meniscus. Subtotal lateral meniscectomy was done in six cases with complex tears of the lateral meniscus. Approximately two third of meniscus was excised with intact peripheral rim. The concomitant surgeries included five partial medial meniscectomy, two anterior cruciate ligament reconstruction and one osteochondral allograft implantation for osteochondritis dessicans of the lateral femoral condyle. Postoperatively immediate weight-bearing and knee range-ofmotion exercise and quadriceps and hamstring exercise were allowed in those with partial meniscectomy and saucerization. However, nonweight-bearing for 4 to 6 weeks on the affected leg was suggested to those with meniscal repair or subtotal lateral meniscectomy. The evaluations included functional score, Lysholm-II knee scoring system, International Knee Documentation Committee ( IKDC) [12] and Tegner activity score of the knee. 2.1. Statistical analysis Patient demographics were analyzed using Pearson's chi-square test. The correlation between function outcome and factor determination was performed using Spearman correlation test and ANOVA. The difference on functional outcome between different treatment methods and the medical status were analyzed using an independent sample t-test and Mann-Whitney U test. A p-value of less than 0.05 was considered to be significant.

Case no

Gender

Side

Age

Symptoms and signs

Type

Surgery procedure

1 2 3 4 5 6 7

F M F M M M F

R R R L L R B

6 6 8 9 9 10 11

L P,S,L L P,S,G,D P,S P,S L

8 9 10 11 12 13 14 15

F M F M M F F M

L L R L L R R B

20 21 21 25 26 27 28 36

L P,S P,S,G P,S,L P,S L,G P,S,G P,S

16 17 18 19 20

M M F F F

R R L L B

37 37 40 41 41

P,S,D L P,S P,S,L P

21 22 23 24 25 26 27 28 29

F F F M F F F M M

R R R R R L L R L

42 43 44 46 50 51 51 59 64

P,S L P,S,D P,S L L,G,D P,S P P,S,D

W C C C C C C C C C C C C C C I I C C C C C C C C C C C W I C C

subtotal PM PM subtotal PM subtotal R R R PM PM R PM R subtotal PM PM subtotal R PM R PM PM PM PM subtotal PM PM R PM PM PM

Commitant surgery

ACL, MM

MM,OCD ACL

MM

MM MM

Symptom and sign: P:pain;S:popping and snapping;L:locking;G:givingway;D:decrease knee extension; Type: C: complete; I: incomplete; W: Wrisberg-type; Procedure: PM: partial lateral menisceotomy and saucerization; R: meniscus repairs; Subtotal: subtotal lateral menisectomy: Commitant surgery: MM: torn medial meniscus; ACL: anterior crucitated ligament tear; OCD: osteochondritis dessican.

3. Result Of the 32 discoid lateral menisci, 27 (84.4%) were complete discoid lateral menisci, three (9.4%) incomplete and two (6.3%) Wrisberg-type. Meniscus instability was noted in 31.3% (10 of 32). Only 9.4% (three of 32) of the knees had a history of trauma. Surgical treatment included partial menisectomy and saucerization in 56% (18 of 32), meniscus repairs in 25% ( 8 of 32 ) and subtotal lateral menisectomy in 19% ( 6 of 32 ) (Table 2). At an average follow-up of 64.5 ± 25.9 months (range, 36-108 months), the results were good to excellent in 84.3%( 27 of 32 ), 15.6%(5 of 32) fair and none poor. The mean IKDC score was 71.7 ± 12.4 (range 41.3 to 86.2 points). 79.3% (23 of 29) patients had Tegner activity score from 5 to 7. Two cases (6%) developed decreased flexion of the knee less than 115 degree. Re-tear rate was clinically noted in 16% (5 of 32) of the knees and all were in adulthood beyond 37 year-old (Table 4) (Case no. 16, 20, 23, 25, 27). The functional outcomes of the subgroups of different surgical approaches were compared, and no significant difference on the functional outcomes was observed (Table 3). However, there was a negative correlation between the age at the time of treatment and the functional outcome, including IKDC and Tenger activity score.

Table 3 Functional outcome of different surgical procedure.

Partial lateral menisceotomy and saucerization (n = 15) Meniscus repairs (n = 8) Subtotal lateral menisectomy (n = 6) p- value between surgical group §

Lysholm-II knee score

Mean IKDC score

Tegner activity score

VAS pain score (0-10)

92.2 ± 7.0 (80 - 100) 93.3 ± 5.0 (86 - 100) 89.8 ± 12.3 (71.0 - 100) 0.721

72.6 ± 12.1 (48.2 – 86.2) 73.0 ± 11.5 (56.3 - 85) 70.4 ± 16.0 (41.3 - 82.7) 0.922

5 (4 - 7) 5 (4 - 6) 5 (3 - 6) 0.428

0.6 ± 0.1(0 - 3) 0.5 ± 0.8(0 - 2) 0.5 ± 0.5(0 - 1) 0.952

§ ANOVA analysis between surgical techniques. No Post Hoc Test performed as p-value N 0.05. A p-value b 0.05 is considered to be significant.

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our study. Radiographs of the knee are usually unremarkable except degenerative changes. Magnetic resonance image (MRI) provides the best information in establishing the diagnosis of discoid lateral meniscus and the associated tear. The transverse diameter, relative structure mobility and abnormal cartilage signal were discussed on MRI diagnosis of discoid meniscus. [13] Arthroscopy provides prudent information in the confirmation of discoid lateral meniscus. Arthroscopy provides direct visualization on the morphology, classification and determination of instability of discoid lateral meniscus [14–16]. The treatment of choice for discoid lateral meniscus begins with conservative treatments, including knee brace, physiotherapy and exercise program. NSAID are usually ineffective [17]. Surgical management is indicated in patients with failure to conservative treatments or patients with mechanical symptom such as locked knee. Historically, total menisectomy was the surgery of choice. However, total meniscectomy was associated with development of degenerative changes of the knee in long term. [18] Currently, arthroscopic partial meniscectomy with saucerization and repair of unstable meniscus is considered the gold standard procedure.[19,20]. In 1989, Vandermmer and Cunningham reported 55% excellent result after saucerization and repair of discoid lateral meniscus at 54 months follow-up. [21] Similar results were reported elsewhere. [3,22–24] .On long-term result, Washington reported 72% good to excellent in 17 year follow up.[7] Other long-term satisfactory results were documented in the literature[19,25]. Re-tear of discoid lateral meniscus was about 6.5%12% [21,26]. In our series, 78% good to excellent result was obtained at an average follow up of 6 years. The re-tear rate was 15.6% and all are in adulthood. Five patients had retear of the meniscus with manifestations of clinical symptoms including pain and locking. All patients with retear of the meniscus were older population. High rate of meniscus tear and degenerative lesion in discoid meniscus may be attributed to disorganization of the circular collagen fiber system. [27]. Furthermore, degenerative change with a decrease in the

Table 4 Comparision of functional outcome between the retear group and non retear group. Age (range) Lysholm-II Mean IKDC Tegner VAS pain knee score score activity score (0 - 10) score Re-tear group(n = 5) Non re-tear group (n = 24) p-value

44.6 ± 5.9 (37 – 51) 28.6 ± 17.3 (6 - 64) 0.05

88.5 ± 9.2

61.3±19.3

5

1 ± 0.8

92.6 ± 7.5

74.0±10.4

6

0.5 ± 0.8

0.022

0.028

0.001

0.188

371

A p-value b0.05 is considered to be significant.

(p b 0.001). (Table 5). We further compared the difference in functional outcome between the subgroups of varus and valgus knee according to anatomical axis. Significant difference was found in IKDC and Tenger activity scores, but not in LysholmII knee score and pain score. No significant correlation was noted between the degrees of anatomical axis and the functional score. (Table 6).

4. Discussion The etiology of discoid meniscus is still debated [1]. The symptoms may occur at any age from childhood to adult with or without a history of trauma. Previous literature suggested this abnormality is most symptomatic in pediatric age group [10,11]. However, in our clinical practice, incidental finding of torn discoid lateral meniscus is not uncommon in arthroscopy for symptomatic knee. More than one third of our cases(38%) had the symptom occurred at age 25 year and older. Therefore, discoid meniscus is not necessary a disease manifested in childhood. Diagnosis of discoid lateral meniscus was made by clinical symptoms with high index of suspicion. The symptoms are annoying but non-disabling in most cases. History of trauma occurred in 9.4% in

Table 5 Correlation of functional outcome with the age at operation. Type of Discoid menscus Lysholm-II knee score Mean IKDC score Tegner activity score VAS pain score (0 - 10) Partial lateral meniscectomy and saucerization (n = 15) Incomplete (n = 2) Complete (n = 13) p-value* Age # Correlation Coefficient p-value Meniscus repairs (n = 8) Complete (n = 7) Wrisberg-type (n = 1) p-value···· Age # Correlation Coefficient p-value Subtotal lateral menisectomy (n = 6) Complete (n = 5) Wrisberg-type (n = 1) p-value···· Age # Correlation Coefficient p-value

S S

S

92.5 ± 3.5 92.2 ± 7.5 0.951 0.172 0.556 93.6 ± 5.3 91.0 0.825 -0.406 0.425 87.8 ± 12.6 100 0.228 -0.412 0.417

71.2 ± 13 72.9 ± 12.5 0.865 0.547 0.043 75.1 ± 10.7 58.6 0.825 -0.771 0.072 68.0 ± 16.6 82.7 0.137 -0.899 0.015

5 5 0.905 0.740 0.002 5 5 0.633 -0.648 0.164 4 6 0.120 -0.820 .046

1 ± 1.4 0.5 ± 1.0 0.557 0.363 0.201 0.6 ± 0.8 0 0.450 0.439 0.383 0.6 ± 0.5 0 0.317 0.293 0.573

# Spearman correlation test * Independent sample t-test···· Mann-Whitney U test; A p-value b0.05 is considered to be significant.

Table 6 Comparision of functional outcome between the varus knee group and valgus knee group.

Varus knee group (n = 13) Valgus knee group (n = 19) p-value Correlation between anatomical axis and functional score # p-value

Age (range)

Degree of anatomical axis

Lysholm-II knee score

Mean IKDC score

Tegner activity score

VAS pain score (0 - 10)

39.6 ± 11.9 (20 - 59) 26.3 ± 17.9 (6 - 64) 0.037

6.0 ± 2.5 (2 - 10) 7.6 ± 2.9 (4 - 15) 0.127

90.2 ± 6.3 92.9 ± 8.5 0.408 0.118

65.4 ± 13.3 76.5 ± 9.9 0.016 -0.37

5 5 0.039 -0.53

0.8 ± 0.9 0.4 ± 0.8 0.18 -0.80

# Spearman correlation test ; A p-value b 0.05 is considered to be significant.

0.54

0.85

0.79

0.68

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cellularity of the meniscus beyond the age of 40 increase the risk of retear and poor functional outcome.[28]. In our study, discoid menicus in valgus knee had significant better functional score than those with varus alignment. However, more varus knee was noted in the older patients (p = 0.037), and no difference in pain score may support the hypothesis. Okazaki found that outcome of surgical treatment for older patients may deteriorate because the development of degenerative changes of the knee in adulthood [29]. A negative correlation of the functional outcome was noted with the age at the time of operation. More than half of our cases underwent surgical treatment before 25 years of age and all achieved full knee extension except one with flexion limitation. “All-inside” meniscus arrows were used for repair of unstable meniscus, and subtotal meniscectomy for complex tear that was irrepairable. Better functional outcome were observed in the groups with partial meniscectomy and meniscus repair than the subtotal meniscectomy group, but no statistical significant account for this difference. Degenerative change after subtotal meniscectomy may worsen the clinical outcome. However, the age at the time of treatment can affect the treatment outcome. 5. Conclusion In this study, we found symptomatic discoid lateral meniscus occurred at any age from childhood to adult. Satisfactory result was found at up to 6 years follow-up, and the prognosis is better if surgery was performed in younger age. 6. Conflict of interest statement No external funding from a commercial party was received for this project. The authors declared that they did not receive any honoraria or consultancy fee for the writing of this papers. The authors further declaimed no conflict of interest in term of stock or option ownerships from any company. References [1] Le Minor JM. Comparative morphology of the lateral meniscus of the knee in primates. J Anat 1990;170:161–71. [2] Atay OA, Pekmezci M, Doral MN, Sargon MF, Ayvaz M, Johnson DL. Discoid meniscus: an ultrastructural study with transmission electron microscopy. Am J Sports Med 2007;35(3):475–8. [3] Ikeuchi H. Arthroscopic treatment of the discoid lateral meniscus. Technique and long-term results. Clin Orthop Relat Res 1982;167:19–28. [4] Nathan PA, Cole SC. Discoid meniscus. A clinical and pathologic study. Clin Orthop Relat Res 1969;64:107–13.

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