|Year : 2022 | Volume
| Issue : 3 | Page : 310-317
Microscopic structural changes in osteoarthritic menisci of the human knee joint
Sanjay Kumar Yadav1, Veereshkumar S Shirol1, Ramesh Chavan2, Shilpa M Bhimalli1
1 Department of Anatomy, J. N. Medical College, KAHER, Belgaum, Karnataka, India
2 Department of Pathology, J. N. Medical College, KAHER, Belgaum, Karnataka, India
|Date of Submission||20-May-2022|
|Date of Acceptance||18-Jul-2022|
|Date of Web Publication||27-Dec-2022|
Mr. Sanjay Kumar Yadav
Department of Anatomy, J. N. Medical College, KAHER, Belgaum - 590 010, Karnataka,
Source of Support: None, Conflict of Interest: None
Background: Osteoarthritis (OA) is a degenerative joint disease for which there is currently no cure. It is characterized by degeneration of articular cartilage and changes in other joint tissues, including subchondral (substance) bone and menisci. It is one of the leading causes of chronic disability. Patients affected by this disease experience pain and loss of function. OA can be caused by a variety of factors, including diet, injury, stress, and genetic abnormalities. However, the molecular mechanisms driving the disease onset and progression are not fully understood. Therefore, this study is undertaken to estimate a large number of human OA menisci for microscopical structural changes in osteoarthritic menisci by histological techniques. Materials and Methods: Medial and lateral osteoarthritic menisci were collected from 110 human knee joints. After collecting the meniscal samples were stored in 10% formalin for 3–5 days. For each meniscus, three separate (anterior, middle, and posterior) parts were processed. The menisci were sectioned in two places vertically at 45° and 135° angles relative to the sagittal plane. After that, each part was sectioned along the horizontal plane from the inner border to the outer border. Then, tissues were fixed in 10% buffered formalin for 24 h. Tissue samples were brought in for routine tissue processing and studied for histological stain with hematoxylin and eosin (H and E) and Alcian blue pH 2.5, to find surface integrity, cellularity, fibrous organization and collagen orientation, and mucoid degeneration. Results: Meniscal degeneration begins with the tissue material rather than the surface. Tissue fibrillation and tears were first observed at the inner border, spread over time to the articular surface of the meniscus, and progressed to complete destruction or loss of meniscal tissue. The left side knee menisci have more OA than the right side. OA cases were more common in both legs, in the age group 60–69 years. Women and Hindus have higher OA cases than men and other religions, respectively. Nonvegetarian and physically inactive individuals were more susceptible to OA, and B +ve and O +ve were more prone to OA than other blood groups. Conclusion: Significant cellular and matrix differences were observed in the meniscus during degeneration. These findings may contribute to further understanding of knee OA and the search for biological treatments. OA was associated with religions, family history, dietary habits, exercise, blood types, and age groups. Hence, there is a need for a program on the care of dietary habits and physical activities for reducing the progression of OA.
Keywords: Histological structural, human knee joint, menisci, osteoarthritic
|How to cite this article:|
Yadav SK, Shirol VS, Chavan R, Bhimalli SM. Microscopic structural changes in osteoarthritic menisci of the human knee joint. J Sci Soc 2022;49:310-7
| Introduction|| |
The meniscus is a complex fibrocartilaginous tissue that is critical in the knee joint for shock absorption, load distribution, stability, and protection of articular cartilage. Each knee has two menisci: i.e., (i) medial meniscus and (ii) lateral meniscus. The medial meniscus is semicircular and significantly wider posteriorly than anteriorly. However, the lateral meniscus is almost round and roughly uniform in width from anterior to posterior. It occupies a larger portion of the articular surface (80%) than the medial meniscus (60%) and is more mobile.
The developing meniscus is very cellular and vascular. As the fetus continues to develop, the cell structure of the meniscus gradually decreases, accompanied by an increase in the content of collagen arranged in a circumference. In adulthood, only peripheral 10%–30% of menisci have a blood supply. In a normally aligned knee, approximately 70% of the load is conducted through the medial tibiofemoral compartment and 30% through the lateral compartment.
Osteoarthritis (OA) is a degenerative joint disease, for which there is currently no cure. It is characterized by degeneration of articular cartilage and changes in other joint tissues, including subchondral bone and menisci. The knee meniscus plays an important role in the complex biomechanics of the knee joint. Meniscal injury, partial or total meniscectomy, or meniscal degeneration are thought to contribute to the development or progression of knee OA. Most of what is known about microstructural changes in the OA meniscus comes from animal studies. This study was conducted to understand human meniscus changes caused by knee OA. Osteoarthritic menisci may exhibit changes in surface integrity, cellularity, fibrous organization, and collagen orientation, which could be interpreted as cellular and structural evidence for the development of knee OA.
OA is one of the leading causes of chronic disability. OA most commonly affects middle-aged and older adults, although younger adults may be affected by injury or overuse. Patients affected by this disease experience pain and loss of function. OA can be caused by a variety of factors, including diet, injury, stress, and genetic abnormalities. However, the molecular mechanisms driving disease onset and progression are not fully understood. Therefore, a study was conducted to examine the microscopical structural changes in the OA meniscus by histological technique.
| Materials and Methods|| |
Medial and lateral osteoarthritic menisci were collected from 110 human knee joints of both sexes, 65 women and 45 men, aged 50–84 years. These menisci specimens were collected from consecutive OA patients who undergo total knee joint replacement surgery, and who have undergone lower limb amputation surgery from the Orthopedics department unit of KLES Dr. Prabhakar Kore Hospital and Medical Research Centre, Belagavi, Karnataka, India. Patients were excluded in case of any malignancy in the menisci or torn menisci and injuries to the menisci. Ethical clearance was obtained by the KAHER'S, Ethics Committee on human subjects. After collecting the meniscal samples were stored in 10% formalin for 3–5 days. After that menisci were cut in a standardized way. For each meniscus, three separate (anterior, middle, and posterior) parts were processed. The menisci were sectioned in two places vertically at 45° and 135° angles relative to the sagittal plane. After that, each part was sectioned along the horizontal plane from the inner border to the outer border. Then, tissue of medial and lateral meniscal samples was fixed in 10% buffered formalin for 24 h. Tissue samples were brought in for routine tissue processing and studied for histological stain with H and E and Alcian blue pH 2.5.
Histological processing and staining
Tissue samples of the medial and lateral menisci were taken and routinely processed in the histology laboratory. After fixation, dehydrated with graded alcohol, then cleared with xylene and infiltrated with paraffin. Tissue was embedded with paraffin and blocks were prepared. After that using the rotatory microtome, 5 μm sections were cut from each region of the medial and lateral menisci and stained with H and E to assess surface integrity, cellularity, fibrous organization, and collagen alignment. Alcian blue pH 2.5 stain was applied for the evaluation of mucoid degeneration.
Histological staining techniques were used to stain the following parts of the menisci of both legs.
For left knee joint
- Left leg medial meniscus anterior part (LMA)
- Left leg medial meniscus middle part (LMM)
- Left leg medial meniscus posterior part (LMP)
- Left leg lateral meniscus anterior part (LLA)
- Left leg lateral meniscus middle part (LLM)
- Left leg lateral meniscus posterior part (LLP).
For right knee joint
- Right leg medial meniscus anterior part (RMA)
- Right leg medial meniscus middle part (RMM)
- Right leg medial meniscus posterior part (RMP)
- Right leg lateral meniscus anterior part (RLA)
- Right leg lateral meniscus middle part (RLM)
- Right leg lateral meniscus posterior part (RLP).
Development of histological scoring/grading system
The scoring system reported in this study was developed after reviewing slides from patients of different ages with OA. For the histological evaluation of the meniscus, criteria were selected that were significantly associated with major changes by age and disease [Table 1]. These criteria include: (i) characteristics of the tissue surface (smoothness or degree of fibrillation, indentations, and undulations); (ii) cellularity (normal, hypercellular, hypocellular, and acellular); (iii) organization of the collagen matrix and fibers including hyalinization, cyst formation, chipping, and tears; (iv) intensity of Alcian blue pH 2.5 staining for mucoid degeneration. After evaluating each category, a total score was calculated. Grade 1 represents normal tissue with scores ranging from 0 to 3, Grade 2 indicates mild degeneration with scores ranging from 4 to 6, Grade 3 indicates a moderately degenerated tissue score of 7–9, and Grade 4 represents the severe degeneration scores ranging from 10 to 12.
For the histological evaluation of meniscus specimens, degeneration grade was assessed by the “C. Pauli” microscopic grading system.
- The range of possible total scores was 0–12 was converted into four grades G1 = 0–3, G2 = 4–6, G3 = 7–9, and G4 = 10–12
- G1 – represents – Normal
- G2 – represents – Mild degeneration
- G3 – represents – Moderate degeneration
- G4 – represents – Severe degeneration
- All images were captured with an Olympus BX-41 microscope equipped with Gryphax software elements. (U-TV1X-2) T7 Tokyo, Japan.
Validation of the grading systems
To validate the microscopic grading system proposed in this study, 110 pairs of menisci (lateral and medial) from the left and right legs, of which the lateral and medial each had three distinct sections (anterior, middle, and posterior), so the total number of slides 660 were graded by Pathologist of KAHER'S, J. N. Medical College, Belagavi.
Descriptive statistics were used to generate histological scores and distributions to summarize mild, moderate, and severe meniscal OA. A nonparametric method (Chi-square test) was used to see the association between the sides and OA. Furthermore, there is a 5% significance level. Analyses were performed using MS Excel and SPSS version 22 (IBM, Bangalore, Karnataka, India).
| Results|| |
Analysis of Osteoarthritis menisci
Microscopic evaluation of menisci from osteoarthritic knee joints (Grade II, III, and IV) revealed fibrocartilaginous disruption. The degenerated extracellular matrix shows fine fibrillation and loss of structure, the fusion of the spaces occupied by the cells of the meniscus and matrix. Great variability in cell distribution was observed with hypercellular, hypocellular, and acellular areas, as well as areas containing large and abundant cell groups. Clusters of abnormal cells were found near the surface of the meniscus, typically associated with a worn area [Figure 1]. Variability was observed in the intensity pattern of mucoid degeneration with light and moderate staining areas.
Histological assessment of meniscus in LMA
Histological evaluation of the left leg medial meniscus (LMA) of the anterior part is shown in [Figure 1], where (1) Indicates bands of degenerative changes, (2) Degenerated extracellular matrix substance (mucoid) is observed, (3) Diffuse hypercellularity with inflammation is observed, and (4) Separation of fibrocartilage with organized collagen fibers.
Histological assessment of meniscus in LMM
Histologic evaluation of the meniscus in the middle medial meniscus (LMM) of the left leg is shown in [Figure 1], where (1) indicates moderate abrasion, fraying and waviness, few indentations, and few clefts, (2) the disorganized cellular pattern showed hypocellular to acellular areas and cell clusters, and (3) indicates the presence of degenerated extracellular matrix; most of the collagen fibers appear unorganized.
Histological assessment of meniscus in LMP
[Figure 1] shows the histological evaluation of the meniscus in the left leg medial meniscus posterior part (LMP), where (1) indicates moderate-to-severe abrasion with a tear, (2) diffuse hypercellularity is seen, and (3) fibrocartilage separation in the presence of disorganized collagen fibers.
Histological assessment of meniscus in LLA
[Figure 1] discloses histological assessment of meniscus in left leg lateral meniscus anterior part (LLA), where 1 indicates slight abrasion and wrinkle, 2 indicates diffuse hypercellularity, and 3-indicates loose and degenerative changes.
Histological assessment of meniscus in LLM
[Figure 1] reveals a histological assessment of meniscus in the left leg lateral meniscus middle part (LLM), where 1 represents a slightly worn and undulating surface, 2 represents a normal distribution of cells; cells appear to be more arranged between fibers, and 3 degenerated extracellular matrix substance and collagen fibers are unorganized.
Histological assessment of meniscus in LLP
[Figure 1] shows a histological assessment of the meniscus in the left leg lateral meniscus posterior part (LLP), where 1 indicates severe abrasion, tear, and disruption, 2 depicts diffuse hypercellularity with clusters of cells, and 3-Fibrocartilage dissociation (edema, mucosal degeneration, cystic fissures, and disjointed collagen fibers.
Alcian blue at pH 2.5 staining intensity
LMA, LMP, LLA, and LLP showed slight staining intensity to Alcian blue 2.5, with a score of 1, while LMM and LLM showed moderate staining intensity for Alcian blue 2.5 scored as 2 [Figure 2].
[Figure 3] shows the distribution of OA menisci percentage on the side of the legs. Approximately 51% of people have left leg OA and 49% in the right legs. Among 110 OA patients, about 59% and 41% of OA problems are in females and males, respectively [Figure 4].
|Figure 4: OA menisci by sex, religion, family history, and vegetarian food. OA: Osteoarthritis|
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OA are varying by age and side, as shown in [Figure 5]. Minimum case of OA was found in 50–59 and 70+ years, whereas OA cases were higher in the age group 60–69 years in both left and right side legs.
Sex, religions, family history, and vegetarian food
The distribution of OA in this series is shown in [Figure 4]. In the gender group, women have a higher incidence of OA than men, i.e., (59% of women and 41% of men). Among religions, Hindus get a more percentage of OA, than other religions (Muslims and Christians), (57% Hindu, 41% Muslim, and 2% Christian). Of these, 64% had no family history of OA, while 36% had a family history of OA. Whereas for dietary habits, nonvegetarians (71%) were more susceptible to OA than vegetarians (29%).
Among different types of physical activity, i.e., (moderate, active, light, medium, and inactive), inactive people were more affected by OA (52.7%). In the blood group distribution, people with B +ve (30.9%) and O +ve (35.5%) blood types are more susceptible to OA than other blood types. In terms of age group distribution, people aged 60–69 were more susceptible to OA than other age groups [Figure 6].
|Figure 6: Menisci by exercise, the blood group, and age group. OA: Osteoarthritis|
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[Table 2] reveals the histological grade distribution of the OA meniscus on the sides of the leg and its medial and lateral meniscal parts. In this study, 110 medial and lateral menisci were observed in the anterior, middle, and posterior parts. About 51% of the left OA meniscus and 49% of the right OA meniscus were observed [Figure 3]. The study showed 8.9% mild, 76.8% moderate, and 14.3% severe OA in the left leg medial meniscus anterior part (LMA), whereas 1.8% mild, 92.9% moderate, and 5.4% severe OA in LMM. In LMP, mild, moderate, and severe OA are 14.3, 75% and 10.7%, respectively [Table 2].
|Table 2: Osteoarthritis menisci by side of legs and parts of medial menisci|
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Left leg lateral meniscus anterior part (LLA) had 8.9% mild, 85.7% moderate, and 5.4% severe OA. However, LLM had 12.5% mild, 76.8% moderate, and 10.7% severe OA, whereas LLP had 12.5% mild, 83.9% moderate, and 3.6% severe OA [Table 3].
|Table 3: Osteoarthritis menisci by side of legs and parts of lateral menisci|
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Right leg medial meniscus anterior part (RMA) had 3.7% mild, 79.6% moderate, and 16.7% severe OA, whereas RMM had 1.9% mild, 90.7% moderate, and 7.4% severe OA. Similarly, RMP had 1.9% mild, 81.5% moderate, and 16.7% severe OA [Table 2]. The right leg lateral meniscus anterior part (RLA) showed 98.1% moderate and 1.9% severe OA. Similarly, RLM had mild (7.4%), moderate (81.5%), and severe (11.1%) OA. However, RLP was 1.9% mild, 87.0% moderate, and 11.1% severe OA [Table 3]. The posterior part of the medial menisci of both legs is significantly associated with OA [Table 2], whereas, the anterior and posterior parts of the lateral menisci have a significant association (P < 0.05) [Table 3].
| Discussion|| |
Menisci are complex fibrocartilaginous tissues. Several disruption and loss of articular fibrocartilage is the structural hallmark of OA. The menisci play an important role in both tibiofemoral compartments through load distribution and shock absorption. Microscopic analysis revealed a strong association between degenerated meniscus and OA.,,,, Microscopic degeneration is a nearly constant finding in middle-aged and older patients and is common in both the lateral and medial menisci. In elderly participants with uniform degeneration of the matrix and collagen, other factors may contribute to severe meniscal tears. Meniscal degeneration is a complication of OA. However, inaccessible meniscal injuries can also lead to OA. The mechanistic relationship between meniscus injury and knee OA is not fully understood. Experimental animal models are used to study meniscal changes during OA development. Several authors have also described human meniscus degeneration.,,,, but most grading systems for the meniscus are based on MRI. However, this study provides a more systematic assessment of aging and OA meniscal changes at the microscopic level and validates more details about the severity of OA through a grading system.
Histological analysis (H and E staining) of the medial meniscus in the posterior part of the left and right legs observed moderate-to-severe abrasion, and tore on the surface, diffuse cellularity, fibrocartilage separation, the presence of disorganized collagen fibers, and rarely mucoid degeneration. In the lateral meniscus of both legs, there were slight abrasions and folds on the surface, diffuse cellularity, and loose fibers with degenerative changes observed in the anterior part, while in the posterior part of the lateral meniscus were seen severe abrasion, tearing, and destruction on the surface, diffuse hypercellularity with a cluster of cell and fibrocartilage dissociation, and broken collagen fibers. In another study, the examination of articular cartilage in a human knee with OA and found that histological analysis (H and E staining) of cartilage from an OA donor showed joint swelling and edema and horizontal splitting cracks or flaps. The surface becomes dull and irregular and has minimal healing capacity. Moderate OA cartilage showed structural changes, including a reduction in superficial and medial cartilage thickness. The collagen network structure was damaged, resulting in reduced cartilage thickness. Chondrocytes can no longer maintain their repair activity, and cartilage tissue was subsequently lost. In severe OA cartilage surface, fissures were deep, cells in the peripheral zone disappear, and clonal, intermediate, and circular zones lack cells that were not arranged in the columns. The slight changes are detected in the cartilage surface, which is no longer smooth, and the subchondral bone shows fibrillation. In other studies on animals, in the rabbit OA model, cell density in the meniscus increased or decreased depending on the area, and clusters of cells were frequently found in degenerated areas., However, these changes were not evident in the human OA meniscus.,
In different parts of the meniscus of both legs, the medial meniscus had mild (14.3% on left and 1.9% on right), moderate (75.0% on left and 81.5% on right), and severe (10.7 on left and 16.7% on right) OA in the posterior part, shown significant at 5% level. While the lateral menisci in anterior and posterior part menisci were significant at the 5% level. In other studies of human OA menisci, histological changes in the anterior part segment of the OA meniscus were moderate. Furthermore, in other studies conducted on human menisci, in moderate or severe OA, there was severe matrix destruction in one or more meniscal regions. The posterior part was most often affected microscopically. Biomechanically, during knee flexion, the femoral condyles roll back onto the tibial plateau and more force is transmitted to the posterior portion of the meniscus, usually subluxing the posterior part of the lateral meniscus during deep flexion.,,, On the other hand, the anterior part is always less affected. This suggests that the anterior part may be more resistant to degeneration or that the anterior part is subject to less damaging biomechanical stress. On macroscopic and histopathological examination, the inner borders of the medial and lateral menisci tend to degenerate.
Apart from this, in the current study, the left leg has more OA than the right leg. OA cases in both left and right legs were higher in the 60–69 years of age group. While another study described, that the chance of developing OA increases with age by previously injured joint overload, joint misalignment, and obesity can all contribute to the development of OA. Age-related changes observed in the cells and extracellular matrix of joint tissue may increase the susceptibility of older adults to OA. Other risk factors for OA also exist. OA is characterized by an imbalance between catabolic and anabolic activity in the joints, and aging may contribute to this imbalance. Aging chondrocytes respond poorly to growth factor stimulation and are unable to maintain articular cartilage homeostasis. Chondrocyte loss due to increased susceptibility to cell death also appears to be important.
This study shows OA is associated with gender, religion, family history, dietary habits, exercise, blood type, and age groups in India. However, in the previous study, OA was not correlated with religion, family history, food pattern, exercise, and blood groups.,,,,,,,,,,,,,,,,, The study found that across gender groups, women (59%) had more OA than men (41%), because risk factors for OA in women, as in men, are many like anatomical differences, obesity, previous trauma, genetic disorder, and hormonal issues. Menopausal women often gain weight, and increased joint stress leads to increase OA in women. Anatomically, women's hips are wider than men's. The angle formed by the hip bone being wider than the knee puts more stress on the outside of the knee. This “knock-kneed” posture, even mild, leads to OA in some women over time. Anatomical differences between males and females that play a role include a narrower femur, thinner patella, greater quadriceps angle, and differences in tibial condyle size.
The present study shows Hindus (57%) had higher rates of OA than Muslim religion (41%), whereas another study found the same that Muslims have a lower prevalence of OA than Hindus of the same race but with different religious practices. The Muslim way of praying since childhood, forcing the knees into deep flexion, may stretch the soft tissue surrounding the knee and decrease stiffness and contact pressure of the articular cartilage, and in family history, 64% had no family history of OA. While other studies described that, people inherit an increased risk of developing OA. This predisposition can be passed down from generation to generation in families, but the pattern of inheritance is unknown. In the first cross-sectional comparison, the author reported a higher prevalence and severity of cartilage defects in the offspring. While the longitudinal study suggested that not only genetic but knee cartilage loss, changes in cartilage defects, and decreased physical performance all play a role in the development of knee OA, this is likely polygenic but reflects a shared environment. The authors concluded that offspring with a family history of knee OA have an increased risk of knee pain independent of structural factors, suggesting that genetic factors may be involved in the OA.
Nonvegetarians (71%) were more susceptible to OA than vegetarians. According to Chang Xu et al., western unhealthy dietary patterns that include French fries, red and processed meats, poultry, refined grains, sugar-sweetened beverages foods, and pizza, were associated with increased radiographic and symptomatic knee OA progression, whereas adherence to promoting a healthy, prudent diet that includes fruits, vegetables, beans, fish, and whole grains were associated with decreased radiographic and symptomatic Knee OA progression in longitudinal cohorts of men and women.
The study also showed that people who did not participate in physical activity were more likely to be affected by OA (52.7%). Other studies were concluded that physical activity increased the risk of OA if it was a part of sports activity that continually exposed normal joints to a high level of impact or torsional loading, and also if the activity consisted of sport that could lead to injury to supporting structures such as ligaments, tendons, and menisci. There is overwhelming evidence that mild-to-moderate physical activity does not cause or accelerate knee OA; in fact, exercise prevents its onset and is clearly effective in treating and managing OA-related pain and functional decline. According to modern literature, regular mild-to-moderate physical activity has preventive and therapeutic effects in patients with knee OA.,
In this study, B +ve (30.9%) and O +ve (35.5%) blood types are more susceptible to OA than people with other blood groups. Whereas another study found that the AB blood group is a risk factor for primary knee joint OA independent of age and gender. Blood group-related LeY antigen may play a role in the association between AB blood group and primary knee OA. Despite rigorous methodology, the inherent limitations of retrospective studies are unavoidable.
Prospective cohort studies should confirm the findings of this study.
| Conclusion|| |
Degeneration of the meniscus begins in the substance of the tissue rather than the surface. Tissue fibrillation and tears are first observed at the inner border, spread over time to the articular surface of the meniscus, and progress to complete destruction or loss of meniscus tissue. OA menisci in both legs were significantly associated with medial menisci of the posterior part (P < 0.05), while lateral meniscus of the anterior and posterior parts was significantly associated with OA menisci. The left leg knee menisci have more OA prevalent than the right leg knee menisci. OA cases are more in both legs in the 60–69 years of age group. The OA cases are more in women and Hindus than in men and other religions, respectively. Nonvegetarians and not physically active are more likely to be affected by OA. Moreover in blood groups, B +ve and O +ve are more susceptible to OA than other blood groups. The findings of this study may help the physicians, clinicians, and policy planners to have programs on the care of dietary habits and physical activities for reducing the progression of OA.
The authors would like to thank Mr. Mahantesh B. Ilkal for his assistance regarding histological experiments. In addition, the department of the orthopedics unit, KLES Dr. Prabhakar Kore Hospital, and Medical Research Centre are also acknowledged for their cooperation.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3]