Lateral Discoid meniscus
Discoid Meniscus
Every knee has a medial and lateral meniscus which are C-shaped pieces of fibrocartilage that absorb stress and act as cushions between the bones at the knee. At birth, the meniscus is not C-shaped, but discoid (round like a discus).
With growth and walking, the discoid meniscus evolves into its normal C-shape. In some children, the lateral meniscus continues to stay discoid with growth.
- Incidence
- present in 3-5% of population
- location
- usually lateral meniscus involved
- 25% bilateral
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Treatment
Traditionally, the treatment of choice for symptomatic stable or unstable discoid lateral meniscus was open total meniscectomy. The residual meniscal tissue that had been left after partial meniscectomy was considered abnormal and was, therefore, supposed to be resected as well [9, 15, 24, 25]. The menisci serve as load distributors and shock absorbers and play a role in joint stability as well as in synovial fluid distribution and cartilage nutrition. Better understanding and documentation of the importance of the menisci to normal articular function has led to preservation of stable meniscal tissue as part of treatment planning.
Partial meniscectomy of normal shaped menisci, was shown to increase the contact stresses in proportion to the amount of removed meniscus [49]. Following total meniscectomy, the contact area was decreased by 75% while contact stresses increased by 235% [49]. The lack of normal meniscal fibrocartilage arrangement in discoid menisci types 1 and 2 may play a roll in load changes after partial meniscectomy of lateral discoid meniscus, but no data supporting it has yet been published. A meniscus-deficient knee carries a high risk of early cartilage degeneration and early degenerative changes. Total meniscectomy of a non-discoid meniscus often leads to osteoarthritis [50–54]. Bearing in mind the detrimental effect of meniscectomy on the knee’s function, the goal in treatment planning should be preservation of meniscal tissue.
Incidentally found discoid lateral meniscus with no symptoms or physical signs should not be treated surgically. A periodic follow-up for exclusion of symptoms and a physical examination enables early detection of any deterioration and appropriate treatment planning.
Snapping knee with no other symptoms and no radiographic signs of accompanying articular lesions can be followed-up and then treated should it become symptomatic. A patient may become symptomatic due to instability of the meniscus, a new tear of the ill-defined meniscus, or as the result of accompanying findings, such as osteochondral lesions to the lateral joint compartment.
Arthroscopic partial meniscectomy (saucerization) is the treatment of choice for symptomatic stable, complete, or incomplete discoid lateral meniscus [8, 30, 55]. The width of the remaining peripheral rim is an important feature to consider when meniscectomy is performed. Most authors agree that the width of the remaining peripheral rim should be between 5 mm and 8 mm to prevent impingement and instability of the remaining part of a discoid lateral meniscus that may lead to future secondary meniscal tear [55, 56]. If a meniscal tear is present, partial central meniscectomy in conjunction with suture repair of the peripheral tear can be effective treatment [57] (Fig. 3a–c).
The reparability of the lateral discoid meniscus cannot be reliably predicted from imaging studies, even MRI [58], and can best be decided on intraoperatively. Klingele et al. [59] reported that 28.1% of arthroscopically evaluated discoid lateral menisci had peripheral rim instability; therefore, the planning and preparation of surgery should include anticipation of a possible need for meniscal stabilization by suturing.
Motoric and radio frequency tools are used for meniscal reshaping. When meniscal instability is found clinically or arthroscopically, stabilization of the meniscus should be considered providing that the meniscal tissue quality allows it. We usually use an inside-out technique for meniscal suturing and use the all-inside meniscal devices for augmentation.
Type-III unstable lateral discoid menisci can be reattached to the posterior capsule and complete meniscectomy should be condemned.
Finally, despite technical improvements in arthroscopic surgery, arthroscopic procedures for treatment of discoid meniscus are considered technically difficult due to the abnormal size, height, and quality of the discoid meniscus [28, 30].
Treatment outcome
Meniscectomy of the lateral meniscus harbors a detrimental effect on the lateral knee. A retrospective review of patients who underwent arthroscopic partial lateral meniscectomy for lateral meniscus tears demonstrated that early results for partial lateral meniscectomy could be quite good, but that significant deterioration of functional results and decreased activity level can be anticipated [60]. The results of total or near-total meniscectomy of non-discoid meniscus in pediatric patients are poor, with the risk of early arthrosis [52, 53].
There has been a trend toward choosing meniscal preservation procedures for treating discoid lateral meniscus. Aichroth et al. [28] reviewed 52 children with 62 discoid lateral menisci and an average follow-up of 5.5 years. The children’s average age at operation was 10.5 years and the mean delay in diagnosis was 24 months. Of knees with symptomatic torn discoid menisci, 48 underwent open total lateral meniscectomy, 6 had arthroscopic partial meniscectomy, and 8 with intact discoid menisci were left alone. The reported outcomes were 37% of the knees with excellent results, 47% with good results, 16% with fair results, and no poor results. Early degenerative changes were seen in the lateral compartment in three knees of older patients (over 16 years of age) with a follow-up period of 11, 13, and 18 years after total meniscectomy. The authors concluded that arthroscopic partial meniscectomy should be recommended only when the posterior attachment of the discoid meniscus is stable and that total meniscectomy is indicated for the Wrisberg-ligament type of discoid meniscus with posterior instability.
Washington et al. [61] reported good or excellent results in 13 of 18 knees of patients with a mean age of 17 years (8–28 years). Radiographs of 9 knees (8 patients with a mean age of 15 years; 7–26 years) showed evidence of slight narrowing of the joint space in only 3 of them.
Raber et al. [62] reviewed the results of total meniscectomies performed in 17 knees (14 children) for discoid lateral meniscus at a mean follow-up of 19.8 years (range 12.5–26.0 years). They found that 10 of these knees had clinical symptoms of osteoarthrosis. Plain radiographs were available for 15 knees and 10 showed osteoarthritic changes.
Aglietti et al. [63] reported 10-year follow-up results of arthroscopic meniscectomies for symptomatic discoid lateral menisci in 17 adolescents. They found no correlation between the type of meniscectomy (partial or total) and the clinical and radiographic results. Development of radiographic changes, such as minor osteophytes in the lateral compartment of 8 knees and less than 50% narrowing of the lateral joint space, was found in 11 knees. The reported clinical results were excellent or good in 16 of their 17 patients.
It should be emphasized that excellent or good clinical reports after a 10-year follow-up in this age group calls for a critical appraisal. The follow-up period puts those patients in their mid-to late twenties. In the face of the reported high incidence of ominous premature radiographic arthritic changes in this and the other series, a longer follow-up period is needed.
Currently, the indications and results of treatment options, such as meniscal transplantation for knees with a history of discoid lateral meniscectomies and meniscectomy, have not yet been conclusively defined. There is some experience in performing allograft meniscal transplantation for those cases but no reports have appeared in the literature thus far. Heightened awareness of the clinician to the possibility of discoid meniscus, its variable presentations and complications, and management considerations may improve therapeutic outcome.
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