Issue: November 2020
Source/Disclosures
Source:

Ahn JH, et al. Arthrosc. 2015;doi:10.1016/j.arthro.2014.12.012.

Disclosures: Erdman reports she is a committee member for the Orthopaedic Trauma Association. Bolia, Mason and Weber report no relevant financial disclosures. The authors would like to acknowledge The Cappo Family Research Fund.
November 16, 2020
8 min read
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An 11-year-old girl with painful mechanical symptoms in her knee

Issue: November 2020
Source/Disclosures
Source:

Ahn JH, et al. Arthrosc. 2015;doi:10.1016/j.arthro.2014.12.012.

Disclosures: Erdman reports she is a committee member for the Orthopaedic Trauma Association. Bolia, Mason and Weber report no relevant financial disclosures. The authors would like to acknowledge The Cappo Family Research Fund.
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A previously healthy 11-year-old girl presented to the orthopedic clinic with a 6-month history of “popping” when she bends her right knee. This mechanical symptom worsened with time.

The “popping” was associated with pain and swelling that prevented her from playing soccer. She had no history of discreet trauma but reported multiple knee buckling episodes of the knee.

Doctor Name, MD
Travis Frantz
Doctor Name, MD
Ian Savage-Elliott

Physical exam revealed no malalignment, minimal knee effusion and tenderness along the lateral joint line. She had full range of motion (0° to 130°); however, there was a visible and palpable snapping on the lateral side of the knee (Video). Her ligamentous exam was stable throughout and she had a positive McMurray sign. Radiographs of the knee showed open physes, normal alignment, subtle widening of the lateral joint space and a “squared off” appearance of the lateral tibial plateau. She underwent MRI, which demonstrated findings consistent with a lateral discoid meniscus (Figure 1).

1. Anteroposterior (AP) radiographs of the bilateral knees show widened lateral joint space and cupping of the lateral tibial plateau in the right knee, suggestive of a discoid meniscus (a). Coronal (b) and sagittal MR images (c) of the right knee demonstrate a diffusely enlarged lateral meniscus that extends to the intercondylar region with bridging of the anterior and posterior horns and intrameniscal signal that shows there is mucinous degeneration.

Source: Alexander E. Weber, MD

What treatment options are available for this patient with discoid meniscus?

See answer below

Nonoperative management, meniscectomy, saucerization or meniscal repair

The patient completed a course of physical therapy and, after no significant improvement in symptoms, she underwent arthroscopic surgery to address her discoid meniscus. The video presented shows the knee examination under anesthesia in the OR. The lateral meniscus was saucerized and contoured using arthroscopic biters and shavers. The anterior and posterior roots were firmly attached, but the body of the meniscus was pathologically mobile. Using an outside-in approach, the body of the meniscus was stabilized to the joint capsule. The outside-in approach utilizes two percutaneous spinal needles to place vertical mattress stitches in the meniscus. A small incision is made to tie the vertical mattress stitches over the joint capsule. On intraoperative physical exam, there was no reproducible snapping with flexion of the knee as there was preoperatively. At 2 months postoperatively, the patient was progressing well with physical therapy and denied any recurrent mechanical symptoms, which was confirmed by the intraoperative findings and procedures performed (Figure 2).

2. Arthroscopic images show a lateral discoid meniscus (a), highly mobile and unstable tissue with intact anterior and posterior roots (b), the status after saucerization (c), the passing of the outside-in meniscal repair sutures (d), and restoration of normal lateral meniscus contour and stability (e).

Discussion

A discoid meniscus is a congenital variant involving abnormal morphology, increased size and potential instability of the meniscus. Discoid menisci typically involve the lateral compartment of the knee with an estimated incidence of 3% to 5% in the United States population. The incidence of bilateral discoid lateral meniscus has been reported to be about 20%. In some cases, discoid meniscus remains asymptomatic until adulthood. Discoid menisci are more prone to tearing due to abnormal anatomy, including decreased and disorganized collagen fibers and mucoid degeneration resulting in reduced tissue quality, abnormal vascularity, a larger and thicker size leading to impingement between the tibial and femoral surfaces, and occasionally a lack of normal meniscal-capsular attachments. In 1969, Masaki Watanabe, MD, classified different types of discoid menisci based on arthroscopic appearance and stability. Type 1 discoid menisci are stable and complete, meaning these cover the entire tibial plateau. Type 2 discoid menisci are stable and partial, meaning these cover up to 80% of the tibial plateau. The type 3 classification is given to discoid menisci that are unstable, otherwise known as the Watanabe variant. This type demonstrates an instability to arthroscopic probing due to the lack of any posterior meniscotibial attachments. The only posterior stability conferred on type 3 menisci are to the meniscofemoral ligament of Wrisberg.

Diagnosis of a discoid meniscus is based on clinical presentation and imaging findings. Patients often first present during childhood or adolescence for complaints of a snapping knee. This is caused by the deficiency of posterior attachments and resultant hypermobility of the lateral meniscus at the posterior horn, causing the discoid meniscus to displace into the intercondylar notch during knee extension. Patients may also complain of lack of terminal extension and pain in the involved compartment, especially when presenting with a concomitant meniscal tear. On physical exam, positive findings of the involved knee compartment may include joint line tenderness, a lateral joint line bulge, swelling and a positive McMurray test. Radiographs may be normal or they can show some pathognomonic signs of a discoid meniscus. These signs are squaring of the lateral femoral condyle, cupping of the lateral tibial plateau, lateral joint space widening and/or a hypoplastic lateral tibial spine. On MRI, diagnosis of a discoid meniscus is conferred with a transverse meniscal diameter greater than 15 mm on coronal view or when is there is continuity of the anterior and posterior horns noted on at least three consecutive 5-mm cuts on the sagittal view (also known as the bow-tie sign). Notably, in the study by Mininder S. Kocher, MD, MPH, and colleagues, physical exam was shown to be more sensitive for the diagnosis of discoid meniscus compared with MRI (89% sensitivity for physical exam vs. 39% for MRI).

Treatment options

After the diagnosis of a discoid meniscus is made, treatment may consist of nonoperative and operative management with different surgical options available. Asymptomatic patients or patients with painless knee snapping and preserved range of motion can be managed nonoperatively with observation. On the other hand, patients who complain of pain and/or loss of motion should undergo surgical intervention, especially when nonoperative treatment fails to improve their symptoms. Physical therapy may include knee range of motion exercises, strength training, manual therapy, functional training and gain training. Surgical options include meniscectomy, meniscal repair and saucerization. In the past, total meniscectomy was the mainstay of treatment for symptomatic discoid meniscus. In follow-up studies, however, this surgical method has been shown to lead to accelerated degenerative changes in the knee. D.A. Räber and colleagues looked at outcomes 20 years after total meniscectomy for discoid lateral meniscus in children. Of the 17 knees examined, 10 showed clinical and radiographic signs of osteoarthrosis compared with the contralateral, uninvolved knee. Additionally, the work done by M.E. Baratz and colleagues on cadaveric models showed total meniscectomy leads to a 75% decrease in tibiofemoral contact area and a 235% increase in peak contact stresses, further highlighting the importance of preserving the meniscus to optimize force transmission and chondroprotection in the knee.

Due to the association of degenerative changes after total meniscectomy, preferred treatment for a symptomatic discoid meniscus now includes arthroscopic saucerization with or without meniscal repair as needed. The goal of saucerization is to remove the symptomatic excess meniscal tissue while preserving the meniscal rim, thus keeping intact the biomechanical advantages of the meniscus on joint load transmission. Meniscal repair, especially of detached peripheral rims, helps to stabilize the remaining meniscus and reduce hypermobility. All-inside, inside-out and outside-in techniques may be employed for meniscal repair depending on surgeon preference and tear characteristics. Care should be taken to not remove too much meniscal tissue, with an intact peripheral rim of approximately 6 mm to 8 mm usually recommended. Internal horizontal cleavage tears are commonly seen in the peripheral rim due to impaired tissue quality of the discoid meniscus. These tears can be treated with excision of one leaflet or repair, depending on size and stability. In terms of postoperative rehabilitation, saucerization alone does not require any period of restricted weight-bearing. If combined with meniscal repair, weight-bearing should be protected usually for 6 weeks postoperatively to protect the repair. A hinged knee brace is usually used with range of motion progressed gradually. Return to sports can begin after full knee motion and strength in the involved extremity have returned.

Outcomes of aucerization, repair

Outcomes after saucerization and repair of symptomatic discoid meniscus show positive results. In a study by Tahir Ogut, MD, and colleagues, out of 11 knees treated with saucerization, they found nine patients to have excellent and two patients to have good results after a mean of 4.5 years of follow-up. They also noted that none of the patients exhibited signs of degenerative changes on radiographs at final follow-up. In a study by Jin Hwan Ahn, MD, and colleagues with 10 years of follow-up, fewer patients treated with saucerization progressed to show degenerative changes (23%) compared with meniscectomy (88%). The addition of meniscal repair with saucerization for instability and/or tear has also shown favorable results. Cordelia W. Carter, MD, and colleagues found no statistically significant difference in outcome measures in their cohort of 57 symptomatic discoid menisci treated with saucerization alone or with repair. Patients previously treated with meniscectomy for symptomatic discoid meniscus may progress to consideration for meniscal allograft transplantation. Results by Kyoung Ho Yoon, MD, and colleagues showed no difference in outcome scores, such as for pain and activity, at final follow-up after meniscal transplantation for meniscectomy of symptomatic discoid vs. non-discoid menisci. Saucerization and repair for discoid meniscus provides the best chance for symptomatic relief and joint preservation; however, if this approach is not feasible, such as due to a complex and irreparable tear of the discoid meniscus, then total meniscectomy with future transplantation remains a viable option. Further studies with long-term follow-up are needed to elucidate the effect of saucerization and repair on the risk of progression to osteoarthrosis.