Abstract
Background
The association between size of ganglia or type of ganglia (intra-articular or extra-articular) and meniscal tears or severity of the osteoarthritis (OA) is not evaluated.
Purpose
To evaluate the prevalence, size, and location of intra- and extra-capsular ganglia at the gastrocnemius origin and to assess their associations with meniscal injury and grades of OA.
Material and Methods
This study included 301 consecutive patients who had knee pain and had undergone magnetic resonance imaging (MRI) of the knee. We evaluated presence of ganglia at the gastrocnemius muscle origin site and diagnosed whether it was an intra-capsular located or mixed-capsular located (intra-capsular and extra-capsular) and then measured the diameter of each ganglion. After two weeks, we evaluated whether articular cartilage injury existed. The presence of a meniscal tear was also recorded.
Results
A total of 186 patients (93%) had intra- and extra-capsular ganglia. Intra-capsular ganglia were found in 183 cases (91%) and mixed-capsular ganglia were found in 16 cases (8%). In cases with intra- and extra-capsular ganglia, more meniscal tears were found (P = 0.029). Intra-capsular ganglia showed more meniscal tears (P = 0.021). Intra-capsular ganglia were more likely to have high-grade OA (P = 0.043). Patients who had a meniscal tear displayed larger-sized ganglia, especially of the intra-capsular type (P = 0.044).
Conclusion
Patients with intra- and extra-capsular ganglia, especially of the intra-capsular type, are more likely to have meniscal injury and more severe OA. Patients with a meniscal tear or OA are more likely to have larger intra- and extra-capsular ganglia, especially of the intra-capsular type.
Introduction
A ganglion cyst is a non-malignant cystic mass that occurs in association with musculoskeletal structures. Ganglion cysts are sometimes simply referred to as ganglia or a ganglion. The etiology of ganglion cysts is unclear and generally thought to result from myxoid degeneration of the connective tissue associated with joint capsules, ligaments, tendon sheaths, bursae, or bone (1). Ganglion cysts occur more commonly in young women and usually around the hand (2). They are sometimes identified around the knee joint and are found at intra- or extra-articular areas. A ganglion of the knee joint capsule is a different pathology from a joint recess or popliteal cyst (3,4). Numerous workers have described intra-articular ganglia relating to the anterior cruciate ligament, posterior cruciate ligament, Hoffa fat pad, and the menisci (5). The association of ganglia around the posterior capsule of the knee joint and meniscal tears or osteoarthritis (OA) is currently unknown. Recently, Park et al. (4) reported that high-grade OA was associated with extra-capsular type ganglia. However, they did not evaluate the association between the size of ganglia or type of ganglia (intra-articular or extra-articular) and meniscal tears or the severity of the OA.
The aim of the present study was to evaluate the prevalence, size, and location of intra- and extra-capsular ganglia at the gastrocnemius and to assess their associations with meniscal tears and the grades of OA.
Material and Methods
Case selection
The institutional review board of our hospital approved this study and waived its patient consent requirements due to the retrospective design. We retrospectively evaluated 301 consecutive patients who had knee pain and had undergone magnetic resonance imaging (MRI) of the knee from April 2019 to August 2019. Exclusion criteria were previous knee surgery (eight cases), ligament tear (44 cases), extreme age distribution (too young [<30 years, 28 cases] or too old [>80 years, four cases]), fractures (five cases), and infectious arthritis (three cases). Finally, a total of 196 MRI examinations from 187 patients were included (nine patients underwent MRI of both knees). The study group consisted of 77 men and 110 women (mean age = 51.32 ± 12.28 years, age range = 30–79 years).
MRI parameters
We used a 3-T MRI machine (Achieva; Philips, Best, The Netherlands) and an eight-channel (SENSE technique), phased-array, knee-dedicated coil. The detailed parameters for each MRI sequence are described in Table 1.
MRI sequences and parameters.
FS, fat saturation; FSE, fast spin echo; MRI, magnetic resonance imaging; PD, proton density; TE, echo time; TR, repetition time.
Image analysis
MRI image interpretation was performed by two experienced musculoskeletal radiologists (fellowship-trained musculoskeletal radiologists with 18 and 10 years of experience, respectively) by consensus. First, they evaluated the presence of ganglia at the gastrocnemius muscle origin site and diagnosed whether it was intra-capsular lesion or mixed-capsular lesion (intra-capsular lesion and extra-capsular lesion), and then they measured the maximal diameter of each ganglia. The maximum transverse and vertical length of ganglion cysts were measured in axial images and the maximum height was measured in sagittal images. Then, the mean diameters of the ganglia were calculated. The measurements of the intra-capsular portions and extra-capsular portions were made independently. The presence of a meniscal tear was also recorded. A meniscal tear was diagnosed when an MRI signal change was seen in the meniscus and/or the presence of morphological changes such as radial tears, flap tears, or bucket handle tears existed (4,6). OA was graded from 0 to 4 using the MR grading system of OA of the knee joint proposed by Park et al. (Table 2) (7). We have used this grading system since 2014 in our daily reporting process. The physicians are satisfied with the reporting format and say the grading system is fairly consistent with clinical outcomes.
Proposed MR grading system of OA of the knee joint (Park grading system (7)).*
*Cartilage grade – Noyes classification. If the lesion with each cartilage grade does not have additional findings, the lesion corresponds to one grade lower state. Meniscal injury grade – Stoller et al. grade.
BME, bone marrow edema; MR, magnetic resonance; OA, osteoarthritis.
Statistical analysis
We used the Pearson chi-square test to analyze the association between the presence of intra- and extra-capsular ganglia and the presence of a meniscal tear. We analyzed the correlation between the presence of intra- and extra-capsular ganglia and the grade of OA of the femorotibial joint with the Cochran–Armitage test. The correlation between the mean size of the intra- and extra-capsular ganglia and the presence of a meniscal tear was analyzed using a Student's t-test. Statistical analysis was performed using PASW software version 18.0 (IBM Corp., Armonk, NY, USA). A value of P ≤ 0.05 was considered to be statistically significant.
Results
Among the 201 patients, 186 (93%) had intra- and extra-capsular ganglia (Table 3). Intra-capsular (suspected hydrops) ganglia were found in 183 cases (91%) (Fig 1) and mixed-capsular ganglia were found in 16 cases (8%) (Fig 2). The incidences according to the presence of a meniscal tear are described in Table 3. There were only three cases with extra-capsular ganglia. There were 141 intra- and extra-capsular ganglia (75.8%, 139 intra- and mixed-capsular cases and two extra-capsular cases) in the medial femoral condyle and 45 intra- and extra-capsular ganglia (24.2%, 44 intra and mixed-capsular cases and one extra-capsular case) in the lateral femoral condyle. In the cases with intra- and extra-capsular ganglia, more meniscal tears were found (P = 0.029) (Table 3). Although the patients who had intra-capsular ganglia showed more meniscal tears (P = 0.021), the patients who had mixed-capsular ganglia did not show a difference in the incidence of meniscal tear (P = 0.343). The incidences of each OA grade according to the type of ganglia are described in Table 4. Patients with intra-capsular ganglia were more likely to have high-grade OA (Park grade ≥2) compared with the other groups (P = 0.043). Table 5 shows the correlation between the meniscal tear and the size of each ganglion. The patients who had a meniscal tear showed larger ganglia, especially of the intra-capsular type (P = 0.044). Table 6 shows the correlation between the presence of OA and the size of each ganglion. The patients who had OA (Park grade ≥1) showed larger ganglia, especially of the intra-capsular type (P = 0.049).
Intra-capsular ganglion cyst at the gastrocnemius in a 55-year-old woman. (a) PD fat saturation sagittal MR image (TR/TE = 4300/30 ms) shows an intra-capsular ganglion cyst (arrow, mean size = 8.68 mm) in the medial femoral condylar area. (b) T2W fat saturation coronal MR image (TR/TE = 5000/65 ms) shows chondral lesions (thick arrow) and bone marrow edema (thin arrow) in the medial femoral condyle, suggesting osteoarthritis. (c) T2W fat saturation coronal MR image (TR/TE = 5000/65) shows a horizontal tear of the medial meniscus (arrow). MR, magnetic resonance; PD, proton density; TE, echo time; TR, repetition time; T2W, T2-weighted.
Mixed-capsular ganglia at the gastrocnemius in a 54-year-old woman. (a) PD fat saturation sagittal MR image (TR/TE = 4300/30 ms) shows an extra-capsular ganglion cyst (arrow, mean size = 11.02 mm) in the medial femoral condylar area. (b) PD fat saturation sagittal MR image (TR/TE = 4300/30 ms) shows another intra-capsular ganglion cyst (arrow, mean size = 12.04 mm) in the medial femoral condylar area. (c) PD fat saturation sagittal MR image (TR/TE = 4300/30 ms) in the other section shows a chondral lesion in the lateral femoral condyle, suggesting osteoarthritis MR grade I. (d) T2W fat saturation coronal MR image (TR/TE = 5000/65 ms) shows an oblique tear of the lateral meniscus (arrow). MR, magnetic resonance; PD, proton density; TE, echo time; TR, repetition time; T2W, T2-weighted.
Meniscal tears according to presence of intra- and extra-capsular ganglia.
Values are given as n (%).
OA grades according to presence of intra- and extra-capsular ganglia.
Values are given as n (%). OA grades are based on the Park grading system (7).
OA, osteoarthritis.
The size of intra- and extra-capsular ganglia according to the presence of meniscal tears.
The size of mixed-capsular ganglia refers to the extra-capsular portions.
The size of intra- and extra-capsular ganglia according to presence of OA.
The size of mixed-capsular ganglia refers to the extra-capsular portions.
OA, osteoarthritis.
Discussion
Park et al. (4) reported 39 (39%) cases of extra-capsular ganglia, 63 (63%) cases of intra-capsular ganglia, and 27 (27%) cases with no ganglia among 100 knee MRI scans. Among them, 70 (70%) intra- and extra-capsular ganglia and 21 (21%) extra-capsular ganglia were reported in the medial portion of the knee, as well as 32 (32%) intra- and extra-capsular ganglia and 18 (18%) extra-capsular ganglia in the lateral portion of the knee (4). Here, intra- and extra-capsular ganglia included the intra-capsular type and extra-capsular type.
In the present study, the incidence of intra- and extra-capsular ganglia and no ganglia among the total of 201 cases of MRI was 91.0% (183 cases) and 7.5% (15 cases), respectively. The incidence of patients with ganglia in our study is much higher than that of Park's study. This discrepancy may be due to the different classification of whether the intra-capsular ganglion (posteriorly located hydrops) is true ganglia or not. Age composition of the study groups may be another cause of this discrepancy. The study group of the previous report included patients aged 18–30 years, but our group did not. This may mean that older patients have more intra- and extra-capsular ganglion cysts. We found a female predominance of the intra- and extra-capsular ganglion cysts (female:male ratio = 3:2); however, Park et al. did not report the sex ratio of the lesions (4). Another explanation of this discrepancy is confusion of the definition of the intra-capsular ganglion. There are anatomical joint recesses above the posterior femoral condyle (3,4). This prominent recess filled with joint effusion can be confused with intra-capsular ganglion.
We found at least three times more medial side lesions than lateral (76% vs. 24%). The previous study also reported a higher incidence of ganglia in the medial portion of the knee. The higher frequency may be related to the different degree of loading between the medial and lateral locations, as repetitive loading has been proposed as a possible etiology, much like in OA (4).
Although the origin of ganglia has not been fully elucidated, it has been hypothesized that they originate from leakage of synovial fluid from the joint, from mucoid degeneration of the adjacent extra-articular connective tissue, or mucin secretion by the mesenchymal cells (8). Some authors have suggested the capsular rent theory for the origin of ganglia (8). They have postulated that joint loading may lead to rent in the joint capsule and allow leakage of synovial fluid into the peri-articular tissue. Another theory suggests that stretching of the joint capsule or ligaments would stimulate mucin production; this mucin would eventually be encapsulated to form ganglia (9). Joint abnormalities caused by chronic degenerative disease may result in altered biomechanics and aggravation of joint loading, with subsequent progression to cyst formation (8).
A ganglion cyst can be divided into intra-capsular ganglia and mixed (extra-capsular alone or extra-capsular with intra-capsular ganglia) (10). Table 3 suggests that patients with intra- and extra-capsular ganglia or intra-capsular ganglia had a significantly higher incidence of meniscus tear (56% vs. 27% and 56% vs. 28%; P < 0.05) whereas the patients who had mixed-capsular ganglia showed similar incidence (65% vs. 53%; P > 0.05).
Patients with a meniscal tear showed larger intra-capsular ganglia (Table 5). Furthermore, patients with intra-capsular ganglia showed a higher incidence of advanced osteoarthritis (grade > 2) (Table 6). The patients who had OA also showed larger intra-capsular ganglia. Although the differences are sub-millimeters, they are clinically relevant as the percent ratio of size differences is up to 10% (10% in meniscal tear and 9% in advanced OA). This raises the hypothesis that the presence and size of intra-capsular ganglia may be an indicator of the presence and/or grade of meniscal tear and OA. If we assume that there is progression from intra-capsular ganglia to mixed-capsular ganglia, it seems that there would be more meniscal tears and OA with mixed-capsular ganglia. However, our study showed conflicting results. It is also thus a bit surprising that the mean size of the intra-capsular ganglia is higher than the mixed-capsular ganglia. The exact cause is difficult to determine, and a simple passage of time may not be able to explain more frequent meniscal tears and OA in the intra-capsular ganglia group.
The present study has some limitations. First, the patients who were enrolled had variable symptoms; therefore, the results of this study might not represent general incidence. Second, histopathological confirmation of the lesion was not performed. Third, the correlation with clinical symptoms was not evaluated. Fourth, we diagnosed and measured the ganglia in consensus by two radiologists. There may be a joint recess mimicking a ganglion; we needed an unequivocal diagnosis of the ganglion with consensus evaluation by two experienced radiologists.
In conclusion, patients with intra- and extra-capsular ganglia, especially the intra-capsular type, are more likely to have meniscal injury and more severe OA. In addition, patients with a meniscal tear or OA are likely to have larger intra- and extra-capsular ganglia, especially the intra-capsular type.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
