Chronic knee pain is a prevalent health problem of middle and old age.1 It has been found to be significantly associated with lower quality of life and is a major public health issue.2–4 Effective prevention and early treatment of knee pain at these ages has a major influence on healthy aging in the population.5 In the younger population, knee pain can have many possible causes, with medial plica syndrome always mentioned in the differential diagnosis6; in contrast, osteoarthritis (OA) is regarded as the most common cause of knee pain in middle-aged and older people in addition to trauma-related conditions, such as meniscus and/or ligament injury, crystal-induced inflammatory arthropathy, and rheumatoid arthritis.7,8 Therefore, the issue of knee pain during middle and old age has always been intermingled with OA in the literature.1–3,7,9,10
Although OA is the most common concomitant diagnosis of the patients with knee pain in this age group, the etiology and mechanism of the pain have yet to be fully understood. Many studies have been conducted to investigate the origin of pain in the OA knee,11–16 and they have reached the consensus that it is multifactorial, including psychosocial factors, mechanical factors (eg, misalignment, valgus-varus laxity, body mass index, and abnormal gait), subchondral bone abnormalities (eg, denuded subchondral bone and bone marrow lesions), and synovitis. Within these factors, synovitis has recently been increasingly recognized as an important feature of the pathophysiology of the OA knee.17 It was not only proven to be strongly correlated with knee pain severity18,19 but also considered a predictive factor of subsequent advanced chondropathy in the OA knee.20 Therefore, synovitis treatment must be considered when treating OA knee pain.21
The mediopatellar plica is a fold in the synovium that represents an embryologic remnant in the development of the knee's synovial cavity.22,23 Although the prevalence of medial plica ranges widely, from 22% to 95%,24–26 it is generally agreed that this structure can produce knee pain and can be successfully treated by arthroscopic resection in the event that it becomes inflamed, thickened, and/or less elastic.27–29 In a review of the literature, it appears to be only recognized as one of the main causes of knee pain in adolescents or young adults.23,25–30 With the exception of a small number of case reports,31 few studies have specified this well-known structure in their descriptions with regard to its presentation or clinical manifestation in older populations. Recent studies32–36 that investigated the chronological evolution of medial plicae disclosed that medial plica was more commonly found in patients with OA knees and that the severity of the degeneration was positively correlated with the severity of the medial plica and the patient age. According to these studies, the abrasion from repeated friction between the medial plica and the facing medial femoral condyle during daily activities would increase the severity of the pathologic change in the medial plica and give rise to clinical symptoms such as synovitis and pain. Surgical eradication of this abrasion could cure most patients’ pain and even decelerate or halt the degenerative process in their knees.37,38 However, there is no study in the literature that has focused on the clinical presentation of medial plicae in middle-aged and older individuals.
In this study, the prevalence and clinical manifestations of medial plica-related medial abrasion syndrome (MAS) in a population of middle-aged and older patients suffering from chronic knee pain were prospectively investigated. This syndrome was evaluated and defined by its clinical manifestations, including predisposing factors, symptoms, signs, radiographic manifestations, and arthroscopic findings. The clinical outcome of pain relief by arthroscopic medial release (AMR)37 for this syndrome was also investigated. We postulated that this syndrome would be a common cause of knee pain in this age group and could be effectively treated using AMR.
MATERIALS AND METHODS
From March to August 2007, 176 consecutive patients >40 years, with a total of 243 knees that had received arthroscopic surgery at our institute by the first author, were included in this prospective study. All these patients were referred from other institutions with a given clinical diagnosis and had been treated conservatively, including physical therapy and medication, for >1 year. For the 67 bilateral cases, each knee was evaluated as an individual case.
The predisposing factors and presenting symptoms were questioned and recorded by a nursing specialist for each knee. The presenting physical signs of each knee were evaluated by the first author. During the history taking and physical examination, special attention was paid to the medial plica-related items that are described in the next subsections.
The presentation of a single episode of injury, such as knee buckling when it was suddenly bent, direct blunt injury over the anterior-medial aspect of the knee, or unexpected twisting of the knee (eg, change of position when kneeling).
Having a history of repeated bending (such as squatting, kneeling, climbing stairs, hiking on slopes, climbing mountains, or bicycling) for either occupational or recreational reasons or of prolonged bending (such as driving or taking any transportation vehicle for a long distance) of the involved knee.
The pain was always described as a deep, throbbing, or sharp ache that would intensify when climbing stairs, sitting with the knees flexed for long periods of time, rising from a sitting position, or extending the knee against resistance. Night pain and difficulty finding a suitable sleep position were also common complaints. Some patients pointed to the anterior-medial aspect of the knee when providing the location of the pain.
A feeling or hearing of clicks or crepitus when the involved knee was flexed or extended after prolonged sitting, possibly accompanied by pain.
Snapping or Locking
A feeling of buckling or a sense of insecurity or pseudolocking in a particular position, which mostly occurs when the knee is partially bent while bearing weight. Occasionally, locking occurs when a patient stands up to walk after sitting or lying down for a long period of time. The knee will unlock after standing for a few minutes.
Precise tender area over the region between the inferior-medial margin of the lower pole of the patella and the ridge of the medial femoral condyle.
A palpable band with snapping or crepitation over the tender area mentioned earlier.
All procedures were performed under either spinal or general anesthesia. During arthroscopic examination, special focus was placed on the presentation of the medial plica and the chondral lesions in the knee as clues for medial abrasion (see Supplemental Video, http://links.lww.com/MD/A247, which demonstrates the medial abrasion phenomenon). The size and appearance of the medial plicae and the location and severity of the cartilaginous degeneration over the medial femoral condyle facing the medial plica were inspected and recorded according to Lyu and Hsu classification.34 The cartilaginous degeneration over the medial, lateral, and patellofemoral compartments was recorded based on the Outerbridge classification.39 To investigate the relationship between the severity of the degeneration in different parts of the knee and that of the plical lesion, an arbitrary scoring system was defined to represent the severity of the cartilaginous degeneration on the medial femoral condyle facing the medial plica, medial compartment, lateral compartment, patellofemoral joint, and the whole knee, as shown in Table 1.
For patients with a medial plica, AMR37 was performed to remove the tissue occupying the space over the inferomedial region of the patella, including the ligamentum mucosum, fibrotic or inflamed synovium, capsule, and distal part of the medial plica. The tight and obliterated medial facet of the patellofemoral joint (Fig. 1A) was released by medial retinaculotomy (Fig. 1B). The adequacy of the medial release was checked by pushing the tip of the scope under the patella and verifying if the previously tightly closed medial patellofemoral joint space could be easily opened and the medial retinaculum was clearly visible when the knee was fully extended (Fig. 1C). For patients with a meniscus tear, a partial meniscectomy was performed only when there was evidence of impingement. No reconstruction was performed for knees with ligament injury.
For patients who received AMR, suction drain was used for 24 hours. The involved limb was protected by an elastic bandage for 1 week. Full range of motion and free ambulation were allowed as tolerated. The patient was discharged the day after the operation. Home exercise programs, including active range of motion and quadriceps setting, were emphasized.
Follow-Up and Evaluation of Outcomes
Regular follow-up was undertaken monthly for 6 months. Thereafter, patients returned yearly for outcome evaluation. Of the 176 patients with 243 knees at the beginning of the study, 169 patients with 232 knees completed the 3-year follow-up study. The follow-up rates were 96% of the patients or 95.5% of the knees studied.
The pain domain of the Knee Society scoring system (KSS) was used to evaluate the pain preoperatively on the day before surgery and postoperatively on the last clinic visit. The score ranges from 0 to 50 points, with 50 points indicating no pain and 0 point indicating severe pain.40 In addition, subjective satisfaction was assessed by asking patients using the criteria we developed for this study as follows: excellent, free of symptoms and no limitation in activities; good, greatly improved, occasional pain without pain medication, and normal activities; fair, same as preoperative condition and no improvement; and poor, has received or considered further operative treatment. The outcome was regarded as satisfactory if the subjective satisfaction was rated as “excellent” or “good.” The inquiry of subjective satisfaction ratings and evaluation of KSS scores were conducted by 2 different nursing specialists. In bilateral cases, each knee was evaluated separately.
This study was approved by the Research Ethics Committee of the Buddhist Dalin Tzu Chi General Hospital, which is certified by the Department of Health in Taiwan (IRB Approval Number: B09704022). Informed consent forms were obtained from all the patients who participated in this study.
The data and normality of data distribution were validated, and nonparametric analysis was used in this study. All values are presented as medians and ranges. Comparisons were made using the Kruskal–Wallis test to detect differences in the patients’ age distribution and the type and severity of the medial plica in each grade of OA. Comparison of the preoperative and postoperative Knee Society pain scores was performed using the Wilcoxon signed-rank test. The difference between categorical variables was tested with Pearson χ2 test. A P value less than 0.05 was considered to be statistically significant. SPSS version 15 (SPSS Inc., Chicago, IL) was used to analyze the data.
The median age of the patient cohort was 63 years (range, 41–82 years old). Of the 169 patients, 139 (82%) were female.
The age distribution and the prevalence of medial plica found in each subgroup of patients by diagnosis are shown in Table 2. OA was the most common clinical diagnosis (205/232, 88.4%). All the patients with the diagnosis of meniscus tear and ligament injury had received previous arthroscopic surgery at other hospitals. The prevalence of medial plica in the full study was 95%, and there was no significant difference between the genders.
The sensitivity and specificity of each parameter regarding the predisposing factors, symptoms, and signs for the diagnosis of medial plica-related MAS are shown in Table 3. Overuse, of some variety, was the most common response to inquiries regarding disease history. Nevertheless, having a history of knee injury was a more specific predisposing factor for MAS. The main complaint of the patients with MAS was pain localized over the anteromedial aspects of their knees. They would also describe episodes of crepitus, catching or snapping when performing specific activities when bending the knee was required. Although the sensitivity of pain and crepitus was high, the specificity of these symptoms was low and not reliable for the diagnosis of MAS. The most sensitive and specific test during the physical examination was the reproducible local tenderness over the inferior-medial margin of the lower pole of the patella and the ridge of the medial condyle. The finding of a palpable band, although not common, was another specific finding for the diagnosis of MAS. Although effusion occasionally occurred and represented acute inflammation, its sensitivity and specificity were also low.
Varying degrees of the roentgenographic manifestation of MAS, including joint space narrowing, spur formation, subchondral sclerosis, and cystic formation, were observed in the axial view (Merchant view) of the patellofemoral joint, as shown in Fig. 2. However, in the early stage of this syndrome, using this special view to make a diagnosis is difficult due to the commonly concurrent lateral deviation or compression of the patella.
For the knees with a medial plica, the age distribution of the different types of medial plica for each grade of severity is summarized in Table 4. The median age of each type and each grade of medial plica were statisticlly different (P < 0.001) after comparing each group using the Kruskal–Wallis test.
For the patients who had received previous arthroscopic surgery for meniscus tear (N = 11) or ligament injury (N = 8), marked fibrotic change in the medial plica was common. No further operation was mandated for the menisci or ligaments of these patients.
After adequate synovectomy and releasing of the inferomedial area of the patella and medial gutter, 2 distinct foci of cartilaginous lesions described by Lyu and Hsu34 could be found on the edge and anterior part of the medial femoral condyle (Fig. 3). They were called “hidden lesions” because on most occasions, due to either synovitis or tightness of the joint space, these lesions were easily overlooked during routine arthroscopic examination. Only after adequate medial release did they become visible (Fig. 4). The appearance of these focal cartilaginous lesions was unique and different from what has been described in the classical arthroscopic classification of cartilaginous lesions. These lesions could be classified into 5 stages by Lyu and Hsu as shown in Fig. 5.34 The severity of cartilaginous degeneration in individual locations represented by the arbitrary scoring system shown in Table 1 is summarized in Table 5. We found that the severity of degeneration in each individual location and in the whole knee were negatively correlated with the size and positively correlated with the severity of the medial plica.
As shown in Tables 6 and 7, the subjective satisfaction rating of the patients suffering from MAS who received AMR was 85.5%, and their Knee Society pain scores improved from 8 (range, 4–28) to 50 (range, 30–50). After comparing their satisfaction rates, we found no significant difference between male (85%) and female (85.6%) patients (P = 0.928) (Tables 8 and 9). The improvement in the scores was significant for all grades of plica lesions and for each category of diagnosis. Satisfactory outcomes were obtained for all patients with the diagnosis of “meniscus tear or ligament injury, received previous arthroscopic surgery.”
The most important finding of this study was the discovery of a high prevalence (95%) of medial plica in a cohort of middle-aged and older individuals who suffered from chronic knee pain. OA was the most common concomitant clinical diagnosis. Medial plica-related MAS, which affected most of these patients, was found to have characteristic clinical manifestations. Symptoms of pain and crepitus in motion and local tenderness found during physical examination were the most sensitive parameters for the diagnosis. History of a single knee injury, local tenderness, and a palpable band as identified during physical examination were the most specific parameters for the diagnosis. Various degrees of distinctive radiographic and arthroscopic findings associated with this syndrome were also elucidated. Most of the patients with this syndrome could be successfully treated using AMR, yielding a satisfaction rate of 85.5% after a 3-year follow-up.
In a nationally representative cross-sectional survey in the United States, 18.1% of men and 23.5% of women aged ≥60 years reported knee pain.2 The prevalence of knee pain among South Koreans >50 years was reported to be 46.2%.41 In another study investigating chronic knee pain in 892 participants >40 years of age, OA was found to be the most common diagnosis (85%).6 Our study also found OA to be the most common diagnosis (88.4%) in knees that had received arthroscopy for debilitating pain in the same age group.
Because knee pain is the most disturbing symptom of the OA knee, it has been scrupulously investigated. Nonetheless, the origin and mechanism of the pain have not yet been definitively clarified. Many studies12,42–45 have been conducted that focused on the relationship between radiographic manifestations and OA knee pain in which the pain was found to be associated with bone marrow lesions, effusion, and synovitis, suggesting that these features may indicate the origin of the knee pain. The relationship between specific tissue lesions and pain severity in persons with OA knees has also been investigated. One of the sources of OA knee pain is believed to be local chronic inflammation of the knee joints, which involves the production of various inflammatory cytokines in the synovial membrane.46,47 In recent studies, synovitis has been noted to be an important factor in OA knee pain.13,16,21,48,49 Our findings and the favorable AMR outcomes verified that the repeated friction or impingement between the tight, fibrotic, and hypertrophied medial plica and the adjacent medial femoral condyle in patients with MAS could have given rise to chronic synovitis in the anteromedial compartment and thus might explain the characteristic presentation of the chronic knee pain in these patients.
The prevalence of medial plica is quite variable23–26 according to the literature and was recently reported to be higher in OA knees.34,36 In this cohort of middle-aged and older individuals who were predominantly affected by OA knee pain, we also found a high prevalence (95%) of medial plica. To the best of our knowledge, no previous studies have been conducted that demonstrate medial plica-related MAS in this age group. Our patients’ clinical manifestations, including predisposing factors, symptoms, and signs, were similar to those reported by others in younger populations.23,27,30,50 Our description of the radiographic manifestations of MAS in the present study is the first in the literature. However, because of the intermingling of the commonly concurrent lateral deviation or compression of the patella, early detection of MAS is difficult by conventional radiographic evaluation, including the axial view. Further investigation using a more precise modality, such as magnetic resonance imaging, might be valuable for the early detection of this syndrome. The findings of our arthroscopic evaluations were consistent with those of the previous studies34,51 and provided more insight into the chronological evolution of the medial plica. We propose that the repeated abrasion between the medial plica and the facing medial femoral condyle in daily activities will increase the severity of the pathologic changes in the medial plica and simultaneously decrease its size due to wear. Meanwhile, degenerative cartilaginous lesions on the facing medial femoral condyle will also increase in severity. These findings suggest that MAS might play a role in the pathogenesis of medial compartment OA of the knee, a possibility that warrants further investigation.
Although it is agreed that medial plica syndrome can be successfully treated by arthroscopic resection,27–29 the success rates vary.23 Concerns have been proposed about the more disabling and painful arthroscopic resection scar and about less-successful results in older patients.50 In middle and old age, the chronological evolution of the medial plica could make it difficult to view during arthroscopic examinations. In addition, the related pathologic condition of the medial capsule might become unmanageable by simple resection of the medial plica. To our understanding, there was no literature that focused on this issue except for one study that investigated the promising outcomes of performing AMR for medial plica-related medial abrasion in OA knee patients.37 The main rationale for this AMR was to eradicate the friction or impingement between the pathologic medial plica and the adjacent medial femoral condyle32–34 by resecting the plica and releasing the fibrotic medial joint capsule and retinaculum. The beneficial effect of releasing retinaculum bands has also been verified and reported by Yilmaz et al.52 The effect of AMR was validated by a recent study35 that investigated interleukin-1β (IL-1β) mRNA and matrix metalloproteinase-3 (MMP-3) mRNA expressions in the medial plica isolated from patients with different stages of medial compartment OA of the knee. According to this study, the repeated abrasions of the medial plica triggered IL-1β production and enhanced the expression of MMP-3. Therefore, removal of a pathologic medial plica and its related inflamed structures by AMR can effectively relieve symptoms37 or even modify the disease process of OA in the knee, according to a recent study.38 Our outcomes also indicated that AMR is a useful modality for treating MAS in middle-aged and older patients. It reduced their pain and satisfied the majority of them.
There were some limitations of this study. Although a high prevalence of MAS was found in this cohort, because of the limited number of patients, statistically valuable information about the prevalence of MAS in each subgroup of patients with different diagnoses could not be obtained. Moreover, because OA was the main diagnosis of patients with knee pain in this study and AMR for their MAS satisfied most of them, further study with a sufficient number of patients in 2 different groups—those with and without knee OA—is warranted to clarify whether to consider MAS the main cause of OA knee pain. Furthermore, radiographic evaluation, such as magnetic resonance imaging, might be helpful for acquiring additional information about this syndrome for its early diagnosis. More precise radiographic outcome evaluation is also mandatory, especially in the case of OA knees. These shortcomings in our investigation warrant further studies.
In conclusion, we found that medial plica-related MAS in middle and old age was a common clinical condition. We defined this syndrome by investigating its clinical presentations, including predisposing factors, symptoms, signs, radiographic manifestations, and arthroscopic findings, and determined that it was a common cause of knee pain in this age group; we recommend that MAS be taken into consideration during the differential diagnosis and postulate that MAS can be effectively treated using AMR. In addition, our findings of the coincidence of knee OA and MAS and the encouraging outcomes by treating them using AMR might assist in identifying a target for treatment of this common disease.
1. Andersen RE, Crespo CJ, Ling SM, et al. Prevalence of significant knee pain among older Americans: results from the Third National Health and Nutrition Examination Survey. J Am Geriatr Soc
2. Muraki S, Akune T, Oka H, et al. Impact of knee and low back pain on health-related quality of life in Japanese women: the Research on Osteoarthritis Against Disability (ROAD). Mod Rheumatol
3. Fernandez-Lopez JC, Laffon A, Blanco FJ, et al. Prevalence, risk factors, and impact of knee pain suggesting osteoarthritis in Spain. Clin Exp Rheumatol
4. Fransen M, Su S, et al. A longitudinal study of knee pain in older men: Concord Health and Ageing in Men Project. Age Ageing
5. Jinks C, Jordan K, Croft P. Osteoarthritis as a public health problem: the impact of developing knee pain on physical function in adults living in the community: (KNEST 3). Rheumatology (Oxford)
6. Calmbach WL, Hutchens M. Evaluation of patients presenting with knee pain: Part II. Differential diagnosis. Am Fam Phys
7. Doherty M, Hawkey C, Goulder M, et al. A randomised controlled trial of ibuprofen, paracetamol or a combination tablet of ibuprofen/paracetamol in community-derived people with knee pain. Ann Rheum Dis
8. Yasuda K. Knee pain in the aged: pathomechanism, diagnosis, and treatment of osteoarthritis of the knee. Hokkaido Igaku Zasshi
9. Muraki S, Oka H, Akune T, et al. Prevalence of radiographic knee osteoarthritis and its association with knee pain in the elderly of Japanese population-based cohorts: the ROAD study. Osteoarthritis Cartilage
10. Nguyen US, Zhang Y, Zhu Y, et al. Increasing prevalence of knee pain and symptomatic knee osteoarthritis: survey and cohort data. Ann Intern Med
11. Zifchock RA, Kirane Y, Hillstrom H. Are joint structure and function related to medial knee OA pain? A pilot study. Clin Orthop Relat Res
12. Yusuf E, Kortekaas MC, Watt I, et al. Do knee abnormalities visualised on MRI explain knee pain in knee osteoarthritis? A systematic review. Ann Rheum Dis
13. Wenham CY, Conaghan PG. Imaging the painful osteoarthritic knee joint: what have we learned? Nat Clin Pract Rheumatol
14. Moisio K, Eckstein F, Chmiel JS, et al. Denuded subchondral bone and knee pain in persons with knee osteoarthritis. Arthritis Rheum
15. Miura H, Takasugi S, Kawano T, et al. Varus-valgus laxity correlates with pain in osteoarthritis of the knee. Knee
16. Lo GH, McAlindon TE, Niu J, et al. Bone marrow lesions and joint effusion are strongly and independently associated with weight-bearing pain in knee osteoarthritis: data from the osteoarthritis initiative. Osteoarthritis Cartilage
17. Hayashi D, Roemer FW, Katur A, et al. Imaging of synovitis in osteoarthritis: current status and outlook. Semin Arthritis Rheum
18. Baker K, Grainger A, Niu J, et al. Relation of synovitis to knee pain using contrast-enhanced MRIs. Ann Rheum Dis
19. Zhang Y, Nevitt M, Niu J, et al. Fluctuation of knee pain and changes in bone marrow lesions, effusions, and synovitis on magnetic resonance imaging. Arthritis Rheum
20. Ayral X, Pickering EH, Woodworth TG, et al. Synovitis: a potential predictive factor of structural progression of medial tibiofemoral knee osteoarthritis: results of a 1 year longitudinal arthroscopic study in 422 patients. Osteoarthritis Cartilage
21. Hill CL, Hunter DJ, Niu J, et al. Synovitis detected on magnetic resonance imaging and its relation to pain and cartilage loss in knee osteoarthritis. Ann Rheum Dis
22. Ogata S, Uhthoff HK. The development of synovial plicae in human knee joints: an embryologic study. Arthroscopy
23. Dupont JY. Synovial plicae of the knee. Controversies and review. Clin Sports Med
24. Gurbuz H, Calpur OU, Ozcan M, et al. The synovial plicae in the knee joint. Saudi Med J
25. Blok A, Weiss W, Dolata T, et al. Medial synovial plica. Ortop Traumatol Rehabil
26. Nakayama A, Sugita T, Aizawa T, et al. Incidence of medial plica in 3,889 knee joints in the Japanese population. Arthroscopy
27. Bellary SS, Lynch G, Housman B, et al. Medial plica syndrome: a review of the literature. Clin Anat
28. Dorchak JD, Barrack RL, Kneisl JS, et al. Arthroscopic treatment of symptomatic synovial plica of the knee. Long-term followup. Am J Sports Med
29. Jackson RW, Marshall DJ, Fujisawa Y. The pathologic medical shelf. Orthop Clin North Am
30. Irha E, Vrdoljak J. Medial synovial plica syndrome of the knee: a diagnostic pitfall in adolescent athletes. J Pediatr Orthop B
31. Mine T, Ihara K, Kawamura H, et al. Shelf syndrome of the knee in elderly people: a report of three cases. J Orthop Surg (Hong Kong)
32. Lyu SR. Relationship of medial plica and medial femoral condyle during flexion. Clin Biomech (Bristol, Avon)
33. Lyu SR, Tzeng JE, Kuo CY, et al. Mechanical strength of mediopatellar plica-the influence of its fiber content. Clin Biomech (Bristol, Avon)
34. Lyu SR, Hsu CC. Medial plicae and degeneration of the medial femoral condyle. Arthroscopy
35. Wang HS, Kuo PY, Yang CC, et al. Matrix metalloprotease-3 expression in the medial plica and pannus-like tissue in knees from patients with medial compartment osteoarthritis. Histopathology
36. Lyu SR, Chiang JK, Tseng CE. Medial plica in patients with knee osteoarthritis: a histomorphological study. Knee Surg Sports Traumatol Arthrosc
37. Lyu SR. Arthroscopic medial release for medial compartment osteoarthritis of the knee: the result of a single surgeon series with a minimum follow-up of four years. J Bone Joint Surg Br
38. Lyu SR, Hsu CC, Lin CW. Arthroscopic cartilage regeneration facilitating procedure for osteoarthritic knee. BMC Musculoskelet Disord
39. Cameron ML, Briggs KK, Steadman JR. Reproducibility and reliability of the outerbridge classification for grading chondral lesions of the knee arthroscopically. Am J Sports Med
40. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res
41. Kim IJ, Kim HA, Seo YI, et al. Prevalence of knee pain and its influence on quality of life and physical function in the Korean elderly population: a community based cross-sectional study. J Korean Med Sci
42. Felson DT, Chaisson CE, Hill CL, et al. The association of bone marrow lesions with pain in knee osteoarthritis. Ann Intern Med
43. Sowers MF, Hayes C, Jamadar D, et al. Magnetic resonance-detected subchondral bone marrow and cartilage defect characteristics associated with pain and X-ray-defined knee osteoarthritis. Osteoarthritis Cartilage
44. Barker K, Lamb SE, Toye F, et al. Association between radiographic joint space narrowing, function, pain and muscle power in severe osteoarthritis of the knee. Clin Rehabil
45. Hayes CW, Jamadar DA, Welch GW, et al. Osteoarthritis of the knee: comparison of MR imaging findings with radiographic severity measurements and pain in middle-aged women. Radiology
46. Torres L, Dunlop DD, Peterfy C, et al. The relationship between specific tissue lesions and pain severity in persons with knee osteoarthritis. Osteoarthritis Cartilage
47. Orita S, Koshi T, Mitsuka T, et al. Associations between proinflammatory cytokines in the synovial fluid and radiographic grading and pain-related scores in 47 consecutive patients with osteoarthritis of the knee. BMC Musculoskelet Disord
48. de Miguel Mendieta E, Cobo Ibanez T, Uson Jaeger J, et al. Clinical and ultrasonographic findings related to knee pain in osteoarthritis. Osteoarthritis Cartilage
49. Ikeuchi M, Takahashi T, Tani T. Localized synovial hypertrophy in the anteromedial compartment of the osteoarthritic knee. Arthroscopy
50. Griffith CJ, Laprade RF. Medial plica irritation: diagnosis and treatment. Curr Rev Musculoskelet Med
51. Christoforakis JJ, Sanchez-Ballester J, Hunt N, et al. Synovial shelves of the knee: association with chondral lesions. Knee Surg Sports Traumatol Arthrosc
52. Yilmaz C, Golpinar A, Vurucu A, et al. Retinacular band excision improves outcome in treatment of plica syndrome. Int Orthop
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