Hypermobile meniscus manifests as abnormal kinematics that can cause knee joint pain, resulting in pain without substantial meniscus tear1. Although this phenomenon is common on the lateral meniscus2,3, as far as we know there are no reports of a battery of the diagnosis and surgical treatment of the medial meniscus is available in the English-language literature. Here, we report a rare case of hypermobile medial meniscus without substantial meniscus tear, diagnosed by arthroscopy and treated by meniscal suture.
The patient was informed that data concerning the case would be submitted for publication, and he provided consent.
A 21-year-old college soccer player (height: 174.0 cm, weight: 64.2 kg, body mass index: 21.2 kg/cm2) visited our clinic because he had experienced frequent left knee pain when he landed, turned, and made an inside-kick to pass the ball with his left leg. In his early teenage years, he had experienced a contact valgus forced to the left knee, which is speculated to have resulted in a medial collateral ligament injury. However, previous medical evaluations did not identify a substantial knee injury. After this injury, he occasionally experienced medial knee pain when he played soccer and especially when he kicked the ball off the inside of the foot. The medial knee pain prevented him from continuing to play when he was a college athlete. We examined his knee but no medial joint space tenderness nor any joint effusion was found. The range of motion of the knee was normal. A Lachman's test and Pivot shift test both proved negative. Also, valgus stress tests both at the 0° and the 30° extension were negative. The McMurray test for meniscus-related injury4 returned negative results, whereas the Steinman test5,6 in the valgus and external rotated position was positive. Radiograph findings were normal, and magnetic resonance imaging (MRI) did not show any medial structural abnormality (Figs. 1-A and 1-B).
Figs. 1-A and 1-B Preoperative MRI. PDWI coronal and T2WI sagittal MRIs showed no meniscus tear or ligament injuries. Preoperative MRIs proved it as a normal medial meniscus. MRI = magnetic resonance imaging, PDWI = proton-density weighted imaging.
We started with comprehensive conservative treatment, including rest from soccer, and physical therapy focused on the quadriceps muscle strength. However, these treatments proved ineffective. Four months after his first visit, an arthroscopy examination and possible surgical treatment was scheduled.
The arthroscopy showed no ligament or cartilage damage, as well as no medial joint widening when we applied valgus knee stress. The medial meniscal surface was smooth, and the arthroscopic probe found no apparent tear. However, there was loosened, scar-like tissue between the peripheral middle to anterior segment of the medial meniscus and the anteromedial capsule (Fig. 2). The anterior segment of the medial meniscus was easy to slide into the intercondylar eminence or the center of the tibial plateau, and the loosened scar tissue between the capsule and peripheral rim of medial meniscus was stretched out using a probe withdrawal maneuver (Figs. 3-A through 3-C). From the arthroscopic findings, we assumed that a meniscocapsular or meniscofemoral abnormal lesion had stretched out and it caused the hypermobility of the medial meniscus without substantial tear and so developed the medial side pain.
Figs. 3-A through 3-C Arthroscopic view of hypermobile medial meniscus in the left knee. Arthroscopic investigation showed no substantial tear of the medial meniscus. However, the outer margin of the peripheral rim of the meniscus was filled with loosened tissue in a concave shape (Fig. 3-A). The medial meniscus was easily drawn to the center of the knee joint with a probe and impinged into the femorotibial joint surface, confirming the stretched meniscocapsular lesion (Fig. 3-B). In the reduction position, the capsule and meniscus complex component appear normal (Fig. 3-C).
To restrain excessive hypermobility of the medial meniscus, after meniscal rasping on the abnormal meniscocapsular site, we tightened the anteromedial segment of the medial meniscus to the joint capsule using an inside-to-outside suture technique with 5 stitches of 2-0 braided threads (Fig. 4). Then the abnormal movement of the medial meniscus had diminished.
Immediately after surgery, the preoperative positive Steinman test then became negative. Also, an immediate improvement in the range of motion, full weight-bearing, and ability to walk without braces was noted. Two months after surgery, his full range of motion was restored. Three months after surgery, the patient started jogging and then performing agile movements, and he resumed playing soccer 4 months after surgery. Six months after surgery, he played soccer games without any sensation of pain, only experiencing a feeling of muscle weakness. Eight months after surgery, the patient was completely free of any symptoms. One year after surgery, he continued to play soccer at the preinjury level. His Lysholm score7 improved from 90 points presurgery to 100 points 6 months and 12 months postsurgery. T2-weighted MRI examination showed that the presurgery high-intensity fat imposing on the meniscocapsular area in the anterior segment of the meniscus had changed to a low intensity of somewhat firm tissue 4 months after surgery (Figs. 5-A and 5-B). X-ray photograph 1 year after surgery showed normal findings (Figs. 6-A and 6-B).
Figs. 5-A and 5-B Preoperative and postoperative T2-weighted magnetic resonance imaging. The presurgery high-intensity area between the capsule and outer rim of the peripheral meniscus (Fig. 5-A) turned into a low intensity area 4 months postsurgery (Fig. 5-B), implying the fatty imposed hypermobility loose tissue had changed into firm connective tissue (surrounded by a yellow circle).
Figs. 6-A and 6-B Postoperative X-ray. Plain X-ray examination showed normal knee findings 1 year after surgery.
As far as we know, only 1 piece of literature from PubMed Central is available that has mentioned hypermobile medial meniscus6. However, that report described a snapping meniscus with anterior horn injury, whereas our report treated the meniscus hypermobility without snapping and without substantial meniscus tear7. In our case, the patient asserted that he had experienced medial collateral injury in his younger years and conservative treatment had diminished his valgus knee instability. However, we inferred that there was a possibility of damage to his meniscofemoral or meniscocapsular because of the medial ligament structure injury he sustained while playing soccer. In sports activities involving cutting or pivoting maneuvers, the meniscocapsular tissue is surrendered under repeated tensile stress, which may have resulted in a subtle medial capsular injury8. We hypothesized that in this case, a previous medial collateral ligament injury was involved in both his superficial and deep ligament layers. After the superficial medial collateral ligament had healed enough to regain valgus stability of the knee, the deep medial collateral ligament, that controls meniscus stability by attaching to the peripheral meniscus, had remained unstable. At the same time, because the meniscocapsular portion was well vascularized, the simultaneous irregular healing process at this site induced hypermobile medial meniscus without MRI abnormality9,10. We also assumed that the pathokinematics of hypermobility at the meniscocapsular portion was related to preoperative negative McMurray and positive Steinman testing. Because the McMurray test maneuver is usually examined in a bent knee position, and if there is no substantial meniscal tear, the test might not apply stress at the meniscofemoral site. However, the Steinman test can apply external and valgus stress in a closely extended knee position so that this maneuver can enforce tensile strain at the meniscocapsular lesion. Then the Steinman test could induce the medial meniscus hypermobility and cause pain at the medial knee joint when the meniscocapsular is loosened after a deep medial collateral ligament chronic injury. Moreover, there was only indirect correlative evidence between hypermobility meniscus and the patient's medial side knee pain because repair of the hypermobile medial meniscus led to improvement in symptoms. However, since the Steinman test had turned negative without inducible pain immediately after the meniscus suture, the hypermobility must be the main reason of the patient's medial knee pain.
The ordinal preoperative radiographic examination hardly detects the hypermobile abnormal meniscocapsular lesion. Rubin et al. reported that meniscocapsular separation was difficult to detect by MRI, with a positive predictive value of only 9%11. In our case, only intraoperative arthroscopic findings could investigate the meniscocapsular lesion and the abnormal movement of the medial meniscus. Therefore, an arthroscopy diagnosis is the only pragmatically authentic method currently available. A dynamic MRI may be useful to diagnose such pathology, however, it is not widely available.
Several options of treatment strategies for meniscal hypermobility have been reported12-16. A case series of meniscal hypermobility demonstrated the efficacy of the suture technique for small meniscal tears involving meniscocapsular separations16. In that report, 5 of the 6 patients returned to their previous level of sports performance after meniscus suture. It can be concluded that the meniscus preserving and stabilization by suture technique was the key aspect resulting in a positive clinical outcome. We also treated our case by the suture technique stabilizing the anterior meniscus to the capsule. Although the second-look arthroscopy was not performed to confirm whether its stability was maintained, the postoperative MRI showed decreasing high T2-weighted sequence signals in the fat imposing loosened area in the meniscal suture site, which implied the preoperative loose extended tissue area had changed into a firm connective tissue area.
In conclusion, a careful arthroscopic inspection is essential for the diagnosis of hypermobile medial meniscus. We can conclude that suture of the meniscocapsular portion is an optimal surgical treatment for this rare phenomenon.
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