Scintigraphic changes of osteoarthritis: An analysis of findings during routine bone scans to evaluate the incidence in an Indian population.

AIMS: The reported prevalence of osteoarthritis (OA) varies according to the method that is used to detect it. X-rays are commonly used in the diagnosis of OA. However, marked osteoarthritic damage must be present to detect characteristic changes with radiologic imaging. Our intention was to evaluate bone scans (1) he occurrence of such changes, (2) he incidence of OA (single or multiple joints) in the general population (a mixture of urban and rural) who were asymptomatic. Data on OA incidence in India is sketchy and sparse as against more detailed information obtained from USA and European nations. Also, clinical rheumatologists are not well-versed with the potential application of bone scans in the management of arthritides.
MATERIALS AND METHODS: Two hundred and eighty nine planar images of routine bone scans were randomly evaluated by two trained nuclear medicine physicians. The ages of the patients ranged from 20 to over 80 years.
RESULTS: It is observed that as the age increases, the incidence of joint involvement increases. However, it is worth noting that even in the age group of 20-40 years, as many as 34% of asymptomatic persons have involvement of the joints. In this age group, as the manifestation is probably in the inception stage, there is a tendency for single joint involvement as against multiple joints seen in the older age groups. Another point to note is that the incidence of joint involvement was not affected by weight. In our patient population, gross obesity was not seen. The predominant joints involved are the knees and hips, followed by the shoulders and ankles. Females show a higher incidence than males. Some patients would be having only a single site or multiple site involvement. This observation is important as in a single, simple test whole body survey gives more information with low radiation burden.
CONCLUSION: Scintigraphic prevalence of OA is higher than reported in US, Europe, and Asia as this test is more sensitive in detecting early changes as compared to radiological changes. These findings on scintigraphy in asymptomatic cases have not been described to the best of our knowledge. Epidemiological demography in published reports is based on clinical or radiological changes observed in single joints which are predominantly symptomatic and multiple joint involvement is rarely recorded. The sensitivity of scintigraphy to show early changes in bone homeostasis and remodeling needs to be exploited.

INTRODUCTION

Incidental detection of arthritic changes on a bone scan is a common finding which is often not reported and considered to be of little importance in the clinical context of the study. In the present analysis, we were curious to assess the incidence of changes in the joints observed on scans which were performed for skeletal metastasis, non-specific bone pains, and other benign bone diseases.

The reported prevalence of osteoarthritis(OA) varies according to the method that is used to detect it. X-rays are commonly used in the diagnosis of OA. However, marked OA damage must be present to detect characteristic changes with radiologic imaging. More subtle damage may not be observed using this technique. Radiographic changes are seen in over half of all people older than age 65 with OA of the knee. In contrast, data obtained from autopsy studies indicate that there is almost universal evidence of OA damage in people aged 65 and over.

Our intention was to evaluate

The occurrence of such changes,

The incidence of OA (single or multiple joints) in the general population (a mixture of urban and rural) who were asymptomatic and

To identify whether the data would be of utility in enhancing the applicability of bone scans in clinical setting of OA.

Data on OA incidence in India sketchy and sparse as against more detailed information obtained from USA and European nations. Also, clinical rheumatologists are not well-versed with the potential application of bone scans in the management of arthritides.

MATERIALS AND METHODS

Two hundred and eighty nine planar images of bone scans were randomly evaluated by two trained nuclear medicine physicians. These scans were done in the majority of patients to exclude skeletal metastases and benign bone diseases.

The ages of the patients ranged from 20 to over 80 years. Patients generally did not volunteer having pain in the joints. patients, when questioned regarding pain, some did say there was mild/moderate pain in the knee or shoulder but none were disabled by the pain and were not on any drugs for the pain.

The following criteria were used to assess the involvement of joints. In general, the intensity of uptake was considerably more than the adjacent bone. No attempt was made to quantify the intensity of the uptake [Figures 1–3].

Figure 1

Scintigraphic appearance of the knees

Figure 3

Scintigraphic osteoarthritis changes in the ankle and small joints

Uptake of tracer in the knee joints

Medial tibia-point-like, tramline, extended.

Medial femur-point-like, tramline, extended.

Lateral tibia-point-like, tramline, extended.

Lateral femur-point-like, tramline, extended.

Patella-point-like, tramline, extended.

Femoral trochlea-point-like, tramline, extended.

Bone uptake in sub-chondral lesion.

Bone uptake in osteophyte.

Bone uptake in cartilage defect.

Narrowing of the joint space.

Scintigraphic images observed in the hip joints

Little, if any, increase in uptake around the hip joint.

Moderate increase in uptake in the weight-bearing area in the upper part of the acetabulum.

Moderate increase in uptake in both the weight-bearing (The line below is a continuation of the sentence) area and the medial side of the hip joint in the lower part of the acetabulum.

Marked increase in uptake in the upper half of the femoral head.

Marked increase in uptake throughout the joint.

Narrowing of the joint space.

Scintigraphic changes seen in the shoulder joint

Mild increase of uptake in the joint.

Moderate increase in uptake in the upper or lower margins of the glenoid.

Moderate/marked increase of uptake in the humeral head.

Marked increase in the whole joint.

Reduction of joint space.

Scintigraphy changes in the ankle joint

Medial tibial–point-like, tramline or extended.

Lateral tibial–point-like, tramline, extended.

Lateral fibular–point-like, tramline, extended.

Sub-chondral-tibial.

Increased uptake in the talus.

Small joints of the hands and feet

Increased uptake in the metacarpo/metatarso-phalangeal joints.

Increased uptake in the inter-phalangeal joints.

Radiography of affected joints has been important in establishing the diagnosis of OA. The American College of Rheumatology has developed the following criteria for classification of the disease.[1-3]

ForOA of the knee, the presence of knee pain and radiographic osteophytes and at least one of the following: Age greater than 50 years, morning stiffness lasting less than 30 min, and crepitus on motion.

For OA of the hip, the presence of hip pain and at least two of the following: Erythrocyte sedimentation rate of less than 20 mm/h, radiographic femoral or acetabular osteophytes, and radiographic joint-space narrowing.

Radiological studies were not frequently performed in our group of patients and there was no correlation of radiological and scintigraphy studies in the data.

RESULTS

Analysis of data was done of the 289 bone scans as follows:

It is observed that as the age increases, the incidence of joint involvement increases. However, it is worth noting that even in the age group of 20-40 years, as many as 34% of asymptomatic persons have involvement of the joints. In this age group, as the manifestation is probably in the inception stage, there is a tendency for single joint site involvement as against multiple joints seen in the older age groups [Figures 4 and 5].

Figure 4

The distribution of joint involvement according to age and weight

Figure 5

The incidence of osteoarthritis in overweight and normal weight individuals. There were 35 individuals (M/F 6/29) in the overweight category and 40 (M/F 12/28) in the normal weight group

Another point to note is that the incidence of joint involvement was not affected by weight. In our patient population, gross obesity was not seen.

Table 1 shows that the incidence of joint involvement increases with age. Females had a higher incidence in all age groups.

Table 1

Analysis of scintigraphy changes in the various joints

The predominant joints involved are the knees and hips, followed by the shoulders and ankles. Some patients would be having only a single site or multiple site involvement. The intent of the Table 1 is to show the incidence of a particular joint involvement.

There were no grossly obese patients in our study. No difference in incidence was seen between those who were mild to moderately overweight and those with normal weight.

DISCUSSION

OA is an enigmatic condition which remains poorly understood. It can be regarded as a mixture of damage to a joint and the reaction pattern induced by that damage.[4-6]

The pathological processes taking place include cartilage destruction, sub-chondral bone changes, and a variable degree of synovial reaction. The outcome of OA is variable and can include extensive changes in the anatomy of the joint, pain (particularly on joint use), and disability resulting from pain, loss of joint movement and stability, and other changes.

The visible outcomes tend to appear and change slowly, with a time course of many years. The combination of heterogeneity, slow change, and an absence of any way of measuring the disease processes makes it a difficult disease to investigate.

Over the past 20 years, understanding of the disease process known as OA has grown substantially. OA is not a single disease entity. Rather, it is a group of overlapping diseases characterized by damage to and focal loss of cartilage as well as hypertrophic changes (osteophytes) in adjacent sub-chondral bone.[78]

The pathologic changes in OA result from an imbalance of tissue turnover within the joint (cartilage, bone, synovial membrane, and capsule). Metabolically active cartilage undergoes degeneration when the normal balance of degradation and repair is disrupted.

OA is thought primarily to be a disease of the articular cartilage. Changes also occur in the bone beneath the cartilage and it is not known where the first areas of abnormality are. The water content of the remaining proteoglycans increases, and they become swollen, resulting in a softening of cartilage and reduced resistance to pressure and shear forces.[9-18] Matrix depletion occurs when the response to excessive mechanical forces is inadequate or when there is an age-related loss of ability to respond to normal joint forces. Thus, risk factors for OA include anything that reduces the reparative ability of articular tissues or increases the loading forces on these tissues. Several cytokines, such as IL-1-beta and transforming growth factor-beta, proteases (the most important of which is matrix metalloprotease), and nitric oxide synthetase all appear to be essential for cartilage degradation in the pathogenesis of OA.[151718]

One view of OA is that a stiffening of the underlying bone results in bone which is no longer a good shock absorber for the cartilage. This may result from repetitive micro fractures in the bone.[1617]

It is proposed that the biomechanics of the joint are perturbed by the loss of tension from the ligament following trauma, leading to remodeling of the sub-chondral bone.

Osteoarthrosis is a physiologic imbalance, a “joint failure” similar to “heart failure,” in which mechanical factors play a role. Stiffening of the sub-chondral bone also can effect joint conformation, which involves deformation of articular cartilage and bone to create maximum contact areas under load.[19-24] Both acute traumatic stress and repetitive stress to the joint are risk factors for OA.[24] Persons who are overweight have a markedly increased risk of knee OA and a slightly increased risk of hip OA.

Muscle weakness can result from OA and contribute to its progression. Quadriceps muscle weakness is directly correlated with pain and disability in patients with knee OA.[25]

Genetic factors strongly contribute to the risk of OA.[21-23]

Scintigraphic[26-29] changes have been used as a means of assessing the disease process in a population of patients with chronic OA of the knee joints and hip joints. Radiographic changes for comparison fulfilled the American Rheumatism Association criteria. Most had joint space narrowing and sub-chondral bone changes in symptomatic knees and hips; these signs are generally regarded as the cardinal features of OA.

The patients evaluated varied from those with the minimum evidence of OA to severe joint damage resulting in the need for drugs and walking aids.

The radiographs showed the expected dominance of the medial and patellofemoral compartment changes, lateral disease being much less common.

The finding that osteophytosis without joint space narrowing is common in the lateral compartment when other compartments have evidence of cartilage damage was a new observation in the study. It may indicate a reaction to abnormal stresses on the lateral compartment consequent on medial compartment disease.

It has been known for many years that bone scanning agents can localize to osteoarthritic joints. Experimental studies in animal models have shown that the isotope is taken up in areas of active sub-chondral bone and in growing osteophytes.[29]

Previous work in human OA has shown that the technique may be of predictive value in hand disease, and that scintigraphy is a sensitive way of detecting disease at the knee joint.

Different patterns of scan activity in OA have been described.[2627] A variety of different patterns of isotope uptake can be differentiated inOA of the knee and hip [Figures 1 and 2].

Figure 2 (a-e)

Scintigraphic changes in hip joint

A few knees[2627] had radiographic evidence of OA without any scan abnormality, however, and several compartments had scintigraphic changes only. This indicates that scintigraphy provides a different type of information to that present on the radiograph.

The attempted correlation of scintigraphic, clinical, and radiographic abnormalities provides some clues to the possible significance of the different patterns of isotope retention. The common linear tramline or joint line pattern of uptake correlates well with sub-chondral sclerosis. It seems likely, therefore, that this represents active bone formation in OA.

There is some evidence that this pattern is also associated with active osteophyte formation as seen by magnetic resonance imaging,[28-31] suggesting that it may detect growing (rather than mature) osteophyte in addition to remodeling of sub-chondral bone.

The less common extended pattern of isotope uptake in sub-chondral bone was associated with more severe radiographic damage and may be indicative of advanced changes or active disease progression. The generalized pattern of uptake may be of most clinical significance. Early generalized isotope retention reflects abnormal perfusion and is sensitive to intra-articular steroids. It would therefore appear to reflect an inflammatory component of the disease.

In order to assess the predictive value of scintigraphy in the progression of the disease, a 5-year-study period of 120 knees (60 patients) were analyzed radiographically.[32-35] 12% had progressive disease. Of 32 knees with severe scan abnormalities, (88%) showed progression, whereas none of the 55 knees with no scan abnormality at entry progressed. Pain severity predicted a subsequent operation, but age, sex, symptom duration, and obesity had no predictive value. Scintigraphy predicts subsequent loss of joint space in patients with established OA of the knee joint.

Prevalence and incidence are different measures of a occurrence. The “prevalence” of a condition means the number of people who currently have the condition, whereas “incidence” refers to the annual number of people who have a case of the condition. These two measures are very different. A chronic incurable disease like diabetes can have a low incidence but high prevalence, because the prevalence is the cumulative sum of past year incidence rates. A short-duration curable condition (next line is a continuation of the sentence) such as the common cold can have a high incidence but low prevalence, because many people get a cold each year, but few people actually have a cold at any given time (so prevalence is low and is not a very useful statistic.[1-3]

OA is the most prevalent form of arthritis in the United States, affecting more than 70% of adults between 55 and 78 years old. Women are affected more than men. Hip OA is more common in Western populations, suggesting that race and environmental factors may also be important. The incidence of symptomatic knee OA is 1% per year, with a radiographic incidence of 2% per year. The rate of radiographic progression has been estimated at about 4% per year.[36-42]

Reported incidence (European Commission of Health and Consumer Protection Directorate C, Public Health and Risk Assessment and National Health Examination Survey 1960-1962, National health and examination survey (NHANES) 1 1971-1975 and Framingham study 1983-1985) of OA of the knee and hip joints as evaluated by radiological or clinical criteria varies from country to country. Incidence of hip joint involvement was 0.9-3.1/100,000 in Bulgaria, 19-35 in UK, 5.8-22 in Czechoslovakia, 2.6-24.6 in Switzerland, 150-296 in Sweden, and 35 in USA.

Incidence of knee joint involvement/100,000 was 5.8-7.8 in Bulgaria, 7.5-34.8 in UK, 7.5-21 in Netherlands, 9-37 in Checoslovakia, 3-26 in Germany, 489-700 in Finland, 31-105 in Sweden, and 35-2000 in USA. Age group of the subjects varied from 35 to 93 years.[36-42]

Prevalence of OA in Asian populations[43] is shown in figures given below. Data will vary as different criteria of the study were used in different countries for analysis. Data points were in some studies not available and hence this does not suggest absence of the disease [Figures 6–13].

Figure 6

Incidence of osteoarthritis knee joints in China

Figure 13

Incidence of osteoarthritis of hip joints in Asian population

Incidence of osteoarthritis of knees in Bangladesh

Incidence of osteoarthritis of the knees in Pakistan

Incidence of osteoarthritis in knees in India. Ur-urban, Ru-rural. M-male, F-female

Incidence of osteoarthritis (OA) of knees in Philippines. Painful joints were predominant in the rural population as also OA increasing with age

Incidence of osteoarthritis of the knees in Vietnam

Incidence of osteoarthritis of the knees in Malaysia

Incidence was reported on clinical and radiological features. Urban and rural population was differentiated as the occupation of the two varied widely and could have different risk factors. It can be seen that the incidence of OA is low while pain is the predominant feature.

There was no significant difference in the presence of pain in the rural, and urban rich and poor. OA was higher in females as compared to males in all the above categories.

The urban population had a higher incidence of pain especially in females in the age group of 55-65 years. OA was not recorded by radiological criteria but on presence of pain.

The incidence of pain in urban female was the highest while the incidence of OA was highest in mixed population.

Painful joints were predominant in the rural population as also OA increasing with age.

The study shows a higher incidence of pain and OA in urban females above 65 years. As in all the figures above, the incidence of OA is far lower than the incidence of pain.

Indian females had a higher incidence of and OA as compared to Malay and then the Chinese.

The incidence of pain in hip joint was higher in the Bangladesh and Vietnam, especially, in the elderly urban population while the incidence of OA is low in general in Asians as compared to the European and American population.

Although OA is worldwide in distribution, geographic and ethnic differences have been reported. For example, the prevalence of hand and knee OA is similar among Europeans and Americans. There is greater variation in the distribution of hip OA with markedly lower rates in African Blacks, Asian Indians, and Hong Kong Chinese. It has been suggested that the lower rates detected among these populations may be due to lower rates of congenital or developmental abnormalities and in some cultures, the common use of squatting postures, which force the hip through extreme ranges of motion.[34-36] The rate of radiographic progression has been estimated at about 4% per year.[34]

Our study shows the incidence of OA as defined on scintigraphy in a random selection of persons. Scintigraphy changes have been present in young people below 40 years of age in as many as 34% of cases with predominant involvement of the knee joints. As age advances, a larger percentage of persons show scintigraphy changes. Our study also shows less frequent involvement of the small joints of the hands as opposed to that reported in literature.

Scintigraphic prevalence of OA is higher than reported in US, Europe, and Asia as this test is more sensitive in detecting early changes as compared to radiological changes.

These findings on scintigraphy in asymptomatic cases have not been described to the best of our knowledge. Epidemiological demography in published reports is based on clinical or radiological changes observed in single joints which are predominantly symptomatic and multiple joint involvements are rarely recorded. The advantage of scintigraphy lies in ability to survey the whole body and identify joints involved in a simple and single operation. The sensitivity of scintigraphy to show early changes in bone homeostasis and remodeling needs to be exploited.

Scintigraphy hence is a good technique to

Establish the prevalence of OA in the general population using sensitive techniques such as bone scans

To identify persons with joint changes

To systematically follow-up annually asymptomatic persons to keep track of progression of the disease and

To assess the effect of various drugs in the management of OA.