Progression of radiographic hip osteoarthritis over eight years in a community sample of elderly white women

Authors


Abstract

Objective

To describe progression over 8 years in a community-based sample of elderly women with radiographic findings of hip osteoarthritis (RHOA) with or without hip pain.

Methods

Baseline and followup anteroposterior pelvic radiographs were obtained at a mean ± SD 8.3 ± 0.4 years of followup in women age ≥65 years at the baseline examination of the Study of Osteoporotic Fractures. We evaluated progression in 936 hips of 745 women with one or more baseline findings of RHOA: summary OA grade ≥2, minimum joint space (MJS) ≤1.5 mm, definite femoral or acetabular osteophytes, definite superolateral joint space narrowing (JSN), or moderate or worse superomedial JSN. We separately examined progression in hips with an MJS between 1.5 mm and 2.5 mm. Hip pain and lower extremity disability were assessed by questionnaire and examination. Measures of progression included an increase in summary grade of radiographic findings, increase in total osteophyte score, decrease in MJS of ≥0.5 mm, total hip replacement (THR), and increase in lower extremity disability score. Odds ratios (ORs) and 95% confidence intervals (95% CIs) for baseline radiographic predictors of progression were estimated using general estimating equations.

Results

During followup, 12.9% of women with baseline RHOA underwent THR, and 22.8% had substantial worsening of lower extremity disability, while 64.6% of hips with RHOA showed radiographic progression or were replaced. Progression was greater by all measures in the 37% of hips and 47% of women with both RHOA and hip pain at baseline. Of hips with pain, 23.6% progressed to THR compared with 2.7% of hips without pain (OR 8.1 [95% CI 4.2, 15.4], P < 0.001), and MJS decreased ≥0.5 mm in 53.7% of hips with pain compared with 30.7% of hips without pain (OR 1.9 [95% CI 1.4, 2.6], P < 0.001). Women with hip pain were more likely to have worsened lower extremity disability (29.3% versus 17.6%; OR 1.8 [95% CI 1.2, 2.8], P = 0.0053). Hips with an MJS >1.5 mm and ≤2.5 mm (n = 1,868) had primarily superomedial narrowing and comparatively low rates of progression that did not differ by hip pain. Femoral osteophytes, superolateral JSN, and subchondral bone changes were independent predictors of progression.

Conclusion

Among women recruited from the community, radiographic and clinical progression was greater in those with symptomatic RHOA, but still substantially less frequent than previously reported for hip OA patients in clinical settings. Asymptomatic RHOA and hips with an isolated finding of mild JSN (MJS of 1.5 mm to 2.5 mm) were unlikely to progress over 8 years.

Hip and knee osteoarthritis (OA) are both major causes of disability in elderly populations (1–3). However, compared with knee OA (4, 5), there are far fewer studies of the natural history and risk factors for progression of hip OA, and there are no studies of progression of hip OA from community-based radiographic surveys. Such studies are important for identifying those at greatest risk for development of clinically significant disease and disability and for the discovery of factors that may slow progression.

Studies of hip OA patients referred to hospital-based physicians demonstrate a rapid rate of progression in both radiographic and clinical disease. Dougados et al studied 506 patients with clinical hip OA who participated in a randomized controlled trial of diacerein. They found that a decline in minimum joint space (MJS) of >0.5 mm occurred in 22% of these patients and a total hip replacement (THR) was needed and performed in 6% within 12 months (6). By 36 months, this type of progression had occurred in 42% and 21% of patients, respectively. Ledingham et al studied hip OA patients referred to a hospital rheumatology and orthopedic clinic and found that two-thirds of them had radiographic worsening and 47% had a THR over a median of 20 months of followup (7). Danielsson performed a long-term followup of 117 of 168 patients diagnosed as having hip OA at a hospital orthopedic clinic in Sweden from 1950 to 1954. After 10 years, 28% had undergone hip surgery and two-thirds of unoperated hips had progressed radiographically (8).

Estimates of the prevalence of radiographic hip OA in the general population of Caucasian adults age ≥55 years range from 5% to 25% (1–3). A large proportion of persons from the community with radiographic hip OA do not report hip pain (9), and it is not known whether the high rate of hip OA progression seen in clinic patients also occurs in persons with radiographic hip OA identified from community surveys. Hip pain is the primary reason that patients with hip OA seek medical care (6, 7). Clinic patients with hip OA may have more severe structural and symptomatic disease, worse ability to cope with their symptoms or functional limitations, or greater financial resources to obtain treatment (6, 7).

The objectives of this study were 1) to describe radiographic and clinical progression during 8 years of followup in a community-based sample of elderly women with radiographic findings of hip OA (RHOA) with and without the presence of hip pain, and 2) to identify baseline radiographic characteristics associated with an increased risk of progression.

PATIENTS AND METHODS

Subjects.

Subjects were participants in the Study of Osteoporotic Fractures (SOF), a multicenter cohort study initiated in 1986 to determine risk factors for osteoporotic fractures in elderly postmenopausal women (10). Participants were all age ≥65 years at baseline and were recruited between September 1986 and October 1988 from population-based listings in 4 metropolitan areas of the US (10). Nonwhite women were excluded from the original cohort because of their low incidence of hip fracture, as were women who were nonambulatory or who had undergone bilateral hip replacement (10). An 8-year followup radiograph (mean ± SD 8.3 ± 0.4 years of followup) was obtained in 5,928 women (61% of the original 9,704 subjects in the study and 73% of the surviving subjects). Four hundred sixty-seven subjects who were unable to attend the clinic visit had a followup radiograph performed using portable equipment at their places of residence (11). Subjects with a diagnosis of rheumatoid arthritis, Paget's disease, or prior hip fracture or hip surgery were excluded from this analysis (11–13).

Radiography and interpretation.

At the baseline visit and followup visit, a supine anteroposterior radiograph of the pelvis was obtained using the same protocol. The subjects' feet were placed at 15–30 degrees of internal rotation, the central ray was centered on the symphysis pubis, and a 101-cm focal film distance at 70–80 kV (peak) was used.

Radiographs were assessed for individual radiographic features of hip OA using atlas photographs to improve the reliability of the readings (12, 13). Each radiograph was rated for joint space narrowing (JSN) in the superomedial and superolateral hip joint areas, and for osteophytes in 4 locations: the lateral femoral, lateral acetabular, medial femoral, and medial acetabular areas. JSN was graded on a scale of 0–4 and osteophytes were graded on a scale of 0–3 in each location. Osteophyte scores in all 4 locations were summed for a total score (range 0–12). Subchondral cysts, sclerosis, and femoral head deformity were scored 0 for absent and 1 for present. Using a caliper and reticule, we measured to 0.1 mm the MJS from the acetabular roof to the femoral head according to the method of Lequesne (14). The limit of MJS measurement in the medial direction was either 45 degrees from perpendicular or to where the bright line of the acetabular roof was no longer visible, whichever was less in the medial direction.

Pairs of radiographs were initially read and measured side-by-side by one primary reader (NEL) who was blinded to the order of the films by masking identifying information and randomly assigning the order of films (11). Based on the initial reading, all pairs of radiographs with either definite osteophytes or definite narrowing (score ≥2) in any location were evaluated together by 2 readers (NEL and MCH) to reach a consensus score. A total of 21% of the film pairs underwent a consensus reading.

Interrater reliability for the radiograph readings assessed on a random sample of 178 film pairs was excellent for MJS <1.5 mm (κ = 0.95) and definite JSN in any location (κ = 0.91) and very good for definite osteophytes in any location (κ = 0.71) and summary grade ≥2 (κ = 0.65) (12, 15). The mean ± SD decrease in MJS in hips imaged by portable radiography was greater than that in hips imaged in radiography suites (−0.25 ± 0.43 mm versus −0.15 ± 0.37 mm; P < 0.001).

Definitions of radiographic hip OA and radiographic progression.

A summary grade of 0–4 (modified Croft grade) was assigned to each hip based on individual radiographic features (13, 15, 16). Grade 0 was a normal hip. Grade 1 indicated the presence of possible (feature grade 1) JSN or osteophytes only, or isolated definite JSN or isolated definite osteophytes (feature score ≥2 in any location) without other findings. Grade 2 required the presence of either definite JSN or definite osteophytes plus at least 1 of the other 5 features. Grade 3 required the presence of either definite osteophytes or JSN plus at least 2 other features. Grade 4 hips met the criteria for grade 3 plus deformity.

Hips and subjects were considered to have baseline RHOA and were included in this analysis if any of the following 5 criteria were present: a summary grade ≥2, an MJS of ≤1.5 mm, JSN superolaterally grade ≥2 or superomedially grade ≥3, or definite osteophytes in any location (17). Hips that did not meet any of these criteria but that had an MJS >1.5 mm and ≤2.5 mm were considered to have possible radiographic OA (17–19). To describe the pattern of JSN, we classified hips with equal grades of superomedial and superolateral JSN as having “concentric” narrowing, hips with superomedial JSN score greater than superolateral JSN score as having “superomedial” narrowing, and hips with superolateral JSN score greater than superomedial JSN score as having “superolateral” narrowing.

A hip was classified as having progressed radiographically if any of the following occurred between baseline and followup: a decrease in MJS of ≥0.5 mm for hips with a baseline MJS ≥0.5 mm (6, 18), an increase of ≥1 in summary grade, or an increase of ≥2 in total osteophyte score. To account for changes in MJS in hips that underwent THR prior to the followup radiograph, we assigned an MJS change of −1.0 mm for hips with baseline MJS ≥1 mm, based on reported studies on loss of joint space in the 12 months preceding THR (19, 20). For hips with a baseline MJS ≥0.5 mm and <1 mm that underwent THR, the imputed decline in MJS was equal to the baseline MJS.

Assessment of symptomatic hip OA and disability.

Hip pain was assessed by questionnaire and defined as hip pain “on most days for at least one month” in the past year at every visit (19). In addition, at visit 2, a physical examination was performed to detect the presence of hip pain with passive internal rotation of the hip. A hip was considered painful if it was positive by either method. Symptomatic RHOA was defined as hip pain and radiographic changes of OA in the same hip.

A measure of lower extremity disability (adopted from the Supplement on Aging to the 1984 National Health Interview Survey) administered at the baseline, year 4, and year 8 followup visits assessed the level of difficulty (scored 0 for none, 1 for some, 2 for much, and 3 for unable) in performing 5 daily activities (score range 0–15) (21). Activities included walking 2–3 blocks on level ground, climbing 10 steps without stopping, preparing meals, performing heavy housework, and shopping. The internal consistency of the disability index as applied in our cohort was satisfactory (22). We calculated the change in the total disability score between baseline and the 8-year followup visit. For women who had a THR prior to the 4-year followup visit (n = 56), we did not calculate a change in disability score. If a subject had a THR after the 4-year followup visit, we calculated a change score between baseline and the 4-year followup visit.

We obtained medical records for women who reported undergoing a THR during followup. After review of the hospital discharge abstract and operative record, women were classified as having had a THR for hip OA if the abstract/record stated that the treatment was for OA or degenerative joint disease of the hip with no mention of osteonecrosis, hip fracture, or a failed prosthesis (19). Twenty-eight women who did not have a followup radiograph had a THR for OA during the study and were included in analyses of this end point.

Other measurements.

All study participants completed a self-administered questionnaire at baseline that assessed age, self-reported health status, current medication use including nonsteroidal antiinflammatory drugs (NSAIDs), and whether a physician had ever told the participant that she had arthritis. Height was measured using a wall-mounted Harpenden stadiometer (Holtain, Dyfed, UK), and weight was measured with a balance-beam scale (10, 11). Calcaneal bone mineral density (BMD) was measured at the baseline examination using single-photon absorptiometry (Osteoanalyzer; Siemens-Osteon, Wahiawa, HI). The protocols for these measurements in the SOF have been well described elsewhere (10, 11, 15).

Statistical analysis.

For statistical analysis, we included only women with RHOA in at least 1 hip at their baseline visit. We compared the distributions of demographic variables, body composition, and lower extremity disability status between subjects with RHOA with hip pain and those with RHOA and no hip pain at baseline and tested for differences with t-tests for continuous measures and chi-square tests for dichotomous measures. Logistic regression was used to estimate the adjusted odds ratios (ORs) for predictors of dichotomous measures of progression. Linear regression was used for continuous measures of change that included changes in the MJS and lower extremity disability scores. General estimating equations using SAS software (SAS Institute, Cary, NC) were used to adjust for the correlation between a subject's right and left hips when calculating 95% confidence intervals (95% CIs) and P values in hip-specific analyses. Analyses of the association of baseline hip pain with progression were adjusted for age, weight, height, estrogen use, calcaneal BMD, health status, and baseline radiographic severity using the sum total of all individual radiographic feature scores.

RESULTS

Among the 5,928 women with baseline and followup hip radiographs, 936 hips in 745 women (12.6% of women) had RHOA at baseline. Four hundred sixty hips with baseline RHOA (49%) met >1 of the 5 radiographic criteria for OA. Most of the remaining hips that met only a single definition qualified on the basis of a definite osteophyte (285 of 476), and nearly all of these (n = 224) had acetabular but not femoral osteophytes.

Just under half (46.5%) of the women with RHOA at baseline reported hip pain “on most days for at least one month” during the previous year. Women with symptomatic hip OA (RHOA and hip pain) at the baseline visit were younger, heavier, and had more lower extremity disability than those without hip pain (Table 1). Seventy percent of women with symptomatic hip OA reported that they were taking NSAIDs regularly or had been told by a doctor that they had “arthritis,” compared with 46% of women with RHOA and no hip pain.

Table 1. Baseline characteristics of 745 subjects with radiographic findings of hip osteoarthritis (OA), by hip pain status*
 All subjects with hip OA (n = 745)Baseline hip pain
Present (n = 347)Absent (n = 396)
  • *

    Baseline radiographic findings include any of the following: summary grade ≥2, minimum joint space ≤1.5 mm, joint space narrowing (JSN) superolaterally grade ≥2 or superomedially grade ≥3, osteophyte score ≥2. A summary grade of 0–4 (modified Croft grade) was assigned to each hip based on individual radiographic features. Grade 0 = normal hip; grade 1 = possible (feature grade 1) JSN or osteophytes only, or isolated definite JSN or isolated definite osteophytes (feature score ≥2 in any location) without other findings; grade 2 = either definite JSN or definite osteophytes plus at least 1 of the other 5 features; grade 3 = either definite osteophytes or JSN plus at least 2 other features; grade 4 = criteria for grade 3 plus deformity. ERT = estrogen replacement therapy.

  • Subjects either reported having had hip pain most days in 1 month during the past year or hip pain during a hip joint range-of-motion examination. Two subjects had missing values for hip pain.

  • P < 0.05 versus the group with no hip pain.

Demographic   
 Age, mean ± SD years71.8 ± 5.271.3 ± 4.772.2 ± 5.5
 Weight, mean ± SD kg68.4 ± 11.870.2 ± 12.566.8 ± 11.0
 Height, mean ± SD cm159.4 ± 5.9159.7 ± 5.8159.1 ± 6.0
 Current ERT use, %12.613.411.9
 Walk >1 block daily, %49.049.053.3
Disability score (range 0–15), %   
 % with score ≥134.844.726.0
 % with score ≥49.713.85.8
Radiographic findings, no. (%)   
 In 1 hip552 (74.1)253 (72.9)299 (75.5)
 In both hips191 (25.6)94 (27.1)97 (24.5)

After a mean of 8.3 years of followup, nearly two-thirds of women, and just over half of the hips, with RHOA had progressed radiographically, and ∼1 in 10 hips had been replaced (Table 2). A woman's risk of progression was not related to the number of hips involved at baseline. The mean ± SD change in MJS after 8.3 years in all hips with RHOA was 0.41 ± 0.59 mm. A decrease in MJS of ≥0.5 mm occurred in 38% of hips, but this dropped to 32% when hips that underwent a THR were excluded.

Table 2. Subjects and hips meeting the criteria for progression of hip osteoarthritis (OA) during 8.3 years of followup*
Baseline radiographic hip OATHR for OAIncrease in summary grade ≥1Decrease in MJS ≥0.5 mmIncrease in osteophyte score ≥2Any radiographic progression or THR
  • *

    Values are the number (%).

  • For hips with total hip replacement (THR) and baseline minimum joint space (MJS) ≥1 mm, we imputed the changes in MJS to be −1 mm. For hips with THR and baseline MJS <1 mm, the change in MJS is equal to the baseline MJS.

  • Subjects were considered to have had progression if either hip with baseline radiographic OA met criteria for progression.

Subjects with radiographic hip OA (n = 745)96 (12.9)272 (36.5)343 (46.0)230 (30.9)481 (64.6)
 Unilateral OA (n = 554)67 (12.1)204 (36.8)254 (45.8)155 (28.0)356 (64.3)
 Bilateral OA (n = 191)29 (15.2)68 (35.6)89 (46.6)75 (39.3)125 (65.4)
Hips with radiographic OA (n = 936)97 (10.4)192 (20.5)353 (37.7)202 (21.6)483 (51.6)

For THR and all radiographic measures, the risk of progression was significantly greater in hips with pain at baseline compared with hips without pain, even after adjusting for the severity of baseline radiographic findings of OA, age, weight, and other covariates (Table 3). For example, THR was performed in 23.6% of OA hips with baseline pain and only 2.7% of OA hips without pain at baseline (OR 8.1 [95% CI 4.2, 15.4], P < 0.001). An increase in total osteophyte score of ≥2 was seen in 34.0% of painful hips compared with 20.3% of hips without pain (OR 2.0 [95% CI 1.4, 2.9], P = 0.0004). The mean decrease in MJS during the 8-year study was 0.50 mm in painful hips compared with 0.35 mm in hips without pain at baseline (P = 0.0345). A decrease in MJS of ≥0.5 mm occurred in 53.7% of painful hips compared with 30.7% of hips without pain (OR 1.9 [95% CI 1.4, 2.6], P < 0.001). When hips undergoing THR during the study were excluded, the risk of a decline in MJS remained higher in painful hips (OR 1.4 [95% CI 1.0, 2.0], P = 0.048).

Table 3. Progression of hip OA by baseline hip pain status*
 Radiographic hip OARisk of progression in hips with pain vs. hips without pain, OR (95% CI), P
Without pain (n = 591)With pain (n = 343)
  • *

    OR = odds ratio; 95% CI = 95% confidence interval (see Table 2 for other definitions).

  • Hip-based regressions were adjusted for baseline age, weight, height, estrogen use, calcaneal bone mineral density, health status, and baseline radiographic severity.

  • Excludes 97 hips undergoing THR.

  • §

    Beta coefficient calculated instead of OR.

  • Excludes 49 hips with MJS <0.5 mm at baseline.

  • #

    “Any radiographic progression” includes increase in summary grade ≥1, decrease in MJS ≥0.5 mm, or increase in osteophyte score ≥2.

THR for OA, % progressing2.723.68.1 (4.2, 15.4), <0.001
Increase in summary grade ≥1, % progressing20.229.81.5 (1.0, 2.1), 0.0401
Decrease in MJS, mean ± SD mm−0.35 ± 0.55−0.50 ± 0.63−0.09 (−0.18, −0.07), 0.0345§
Decrease in MJS ≥0.5 mm, % progressing30.753.71.9 (1.4, 2.6), <0.001
Increase in osteophyte score ≥2, % progressing20.334.02.0 (1.4, 2.9), 0.0004
Any radiographic progression or THR, % progressing#43.565.91.98 (1.5, 2.7), <0.001

Worsening of lower extremity disability occurred in 22.8% of women with RHOA overall and was significantly more frequent (29.3%) in women with symptomatic RHOA at baseline than in those with asymptomatic OA (17.6%) (Table 4). Of women with painful hip OA, nearly 1 in 2 had an increase in disability or underwent THR, a risk of clinical worsening that was 3-fold greater than that in women without painful RHOA at baseline. In contrast, only 11.8% of these women had an improvement in disability score of ≥4 points (data not shown).

Table 4. Progression of lower extremity disability in subjects with and those without hip pain at baseline*
 Radiographic hip OARisk of progression in hips with pain vs. hips without pain, OR (95% CI), P
Without pain (n = 396)With pain (n = 301)
  • *

    Excludes 56 subjects undergoing THR before the visit 3 date for whom change in disability could not be calculated. See Tables 2 and 3 for definitions.

  • Subjects in this group had radiographic findings of OA and hip pain in the same hip, in 1 or both hips. Forty-six subjects had hip pain but not in the same hip with radiographic OA. They were analyzed as a separate group, but results are not shown.

  • Person-based regressions were adjusted for baseline age, weight, height, estrogen use, calcaneal bone mineral density, health status, baseline disability score, and baseline radiographic severity.

  • §

    Change in disability scores ranges from −15 to 15.

  • Beta coefficient calculated instead of OR.

Change in disability score, mean ± SD§1.5 ± 3.12.2 ± 3.50.64 (0.14, 1.13), 0.0125
Disability score change ≥4, % progressing17.629.31.82 (1.19, 2.77), 0.0053
Disability score change ≥4 or THR, % progressing20.147.82.93 (2.01, 4.27), <0.001

Table 5 shows the relationship of baseline radiographic features with the risk of THR and radiographic progression. The presence of definite femoral osteophytes was associated with a significantly increased risk of progression by all measures. In contrast, hips with only acetabular osteophytes progressed at a rate similar to those with no osteophytes. Hips without any osteophytes (“atrophic OA”) did not have a higher risk of progression. A superolateral pattern of JSN was associated with greater risks of progression to THR and decrease in MJS. Compared with hips without JSN, hips with a concentric or a superomedial pattern of JSN were also more likely to progress to THR, but to a much lesser degree than hips with superolateral JSN. The presence of a superomedial pattern of JSN was inversely related to progression of osteophytes. Subchondral bone abnormalities (cysts and sclerosis) at baseline were associated with increased risks of THR and decline in MJS. Hips with sclerosis were also more likely to have an increase in osteophytes.

Table 5. Baseline radiographic features and progression of hip OA during 8.3 years of followup*
Baseline radiographic feature% of hipsOR (95% CI)
THRIncrease in summary grade ≥1Decrease in MJS ≥0.5 mmIncrease in osteophyte score ≥2Any radiographic progression or THR
  • *

    JSN = joint space narrowing (see Tables 2 and 3 for other definitions).

  • Excludes 97 hips undergoing THR.

  • Excludes 49 hips with MJS <0.5 mm at baseline.

  • §

    Cut point for osteophyte score ≥2 in each location.

  • Reference groups have score of 0 for osteophytes and JSN. Models include dummy variables for possible osteophytes and JSN (grade 1).

Osteophytes      
 Acetabular and femoral§11.15.1 (2.2, 11.9)2.1 (1.0, 4.3)1.9 (1.1, 3.2)1.4 (0.7, 2.9)2.5 (1.4, 4.6)
 Femoral only21.62.6 (1.2, 5.8)3.1 (1.6, 5.8)2.5 (1.5, 4.0)3.7 (2.0, 6.6)4.9 (3.0, 8.1)
 Acetabular only32.91.0 (0.4, 2.9)1.1 (0.6, 2.3)1.2 (0.7, 2.1)1.1 (0.6, 2.2)1.3 (0.8, 2.2)
 None24.01.0 (referent)1.0 (referent)1.0 (referent)1.0 (referent)1.0 (referent)
JSN      
 Concentric6.85.1 (1.8, 14.6)0.5 (0.2, 1.1)1.4 (0.7, 2.9)0.5 (0.2, 1.1)0.7 (0.3, 1.5)
 Superolateral7.69.2 (3.8, 22.5)0.5 (0.2, 1.1)2.2 (1.4, 4.0)1.1 (0.5, 2.2)1.9 (1.0, 3.6)
 Superomedial44.03.0 (1.4, 6.3)0.6 (0.3, 0.9)1.2 (0.8, 1.8)0.5 (0.3, 0.8)0.7 (0.5, 1.2)
 None41.61.0 (referent)1.0 (referent)1.0 (referent)1.0 (referent)1.0 (referent)
Cysts      
 ≥110.53.8 (2.1, 7.1)0.6 (0.3, 1.0)2.8 (1.7, 4.8)1.3 (0.9, 1.7)1.8 (1.0, 3.3)
 089.51.0 (referent)1.0 (referent)1.0 (referent)1.0 (referent)1.0 (referent)
Sclerosis      
 ≥139.73.5 (1.8, 6.8)1.2 (0.9, 1.8)3.4 (2.5, 4.8)3.5 (2.3, 5.3)3.7 (2.6, 5.2)
 060.31.0 (referent)1.0 (referent)1.0 (referent)1.0 (referent)1.0 (referent)

A large number of hips in this sample (n = 2,178) had an MJS >1.5 mm and ≤2.5 mm, and most of these (n = 1,868) had no other baseline findings of RHOA as defined above. Approximately 21% of hips with an MJS between 1.5 mm and 2.5 mm and no other findings were painful at baseline, about the same as the 23% of hips with an MJS >2.5 mm. The vast majority of these hips (83%) had mild superomedial JSN (grade 2) and no or minimal superolateral JSN (grade 0 or 1). The risk of progression in these hips was substantially less than in hips without pain that met the criteria for RHOA (Tables 3 and 6). Only 0.5% progressed to THR, and the mean total loss of joint space over 8 years was 0.14 mm, 60% less than the mean loss of joint space in hips with baseline RHOA but no pain. In addition, there was no evidence that radiographic progression or THR in this group of mildly narrowed hips with no other radiographic findings was related to baseline hip pain (Table 6). A 4-point worsening in disability score occurred in 16.6% of women with mildly narrowed hips overall, but was more likely to occur (in 24.9%; P < 0.001) if a woman had hip pain.

Table 6. Progression of hip OA by baseline hip pain status, for hips with baseline MJS >1.5 mm and ≤2.5 mm*
 Hips with baseline MJS >1.5 mm and ≤2.5 mmRisk of progression in hips with pain vs. hips without pain, OR (95% CI), P
Without pain (n = 1,473)With pain (n = 395)
  • *

    Does not include 310 hips with MJS >1.5 mm and ≤2.5 mm that also had other radiographic findings, including summary grade ≥2, joint space narrowing superolaterally grade ≥2 or superomedially grade ≥3, and osteophyte score ≥2. NA = not available (too few cases of THR in the subgroup for regression analysis) (see Tables 2 and 3 for other definitions).

  • Hip-based logistic and linear regressions were adjusted for baseline age, weight, height, estrogen use, calcaneal bone mineral density, health status, and baseline radiographic severity.

  • Excludes 4 hips undergoing THR during followup.

  • §

    Beta coefficient calculated instead of OR.

  • Excludes 49 hips with MJS <0.5 mm at baseline.

THR for OA, % progressing0.10.5NA
Increase in summary grade ≥1, % progressing7.77.71.1 (0.7, 1.6), 0.8236
Decrease in MJS, mean ± SD mm−0.13 ± 0.33−0.14 ± 0.34−0.01 (−0.05, 0.03), 0.6871§
Decrease in MJS ≥0.5 mm, % progressing11.011.91.1 (0.8, 1.6), 0.5513
Increase in osteophyte score ≥2, % progressing3.95.61.6 (0.9, 2.7), 0.0823
Any radiographic progression or THR, % progressing16.817.71.1 (0.8, 1.5), 0.4305

DISCUSSION

The prevalence of RHOA in this community-based sample of white women age ≥65 years was substantial (>12%). Approximately half of these women had significant hip pain at baseline, defined as “pain on most days for at least one month” over the previous year. During 8 years of followup, 10% of hips with baseline RHOA were replaced, another 40% progressed radiographically, and approximately one-fourth of women with RHOA experienced a worsening of physical disability involving the lower extremities.

The risk of structural or disability progression was much higher in women with symptomatic hip OA at baseline. The presence of pain at baseline in hips with RHOA was a strong predictor of subsequent total joint replacement, worsening of lower extremity disability, and radiographic progression. The more rapid radiographic progression in painful hips was independent of the baseline severity of radiographic disease, and the reasons for this association deserve further investigation. However, even in painful hips, the risk of radiographic and clinical progression in our cohort was substantially less than has been reported previously for hip OA patients in clinical settings. Moreover, hips with an MJS between 1.5 mm and 2.5 mm, a mildly narrowed joint space that is sometimes included in the definition of prevalent RHOA, but no other radiographic findings had a very low risk of progression even when hip pain was present. These findings have important implications for defining radiographic hip OA, for understanding its natural course, and for targeting interventions to lessen its impact.

Although our definition of symptomatic hip OA was consistent with the American College of Rheumatology clinical and radiographic classification criteria for hip OA (23), the likelihood that these women recruited from the community would have progressive disease was much lower than has been observed in patients being treated for hip OA. Approximately 1 in 4 women with symptomatic RHOA at baseline underwent THR over an 8-year period. In contrast, in previous hospital outpatient series, 20–50% of patients with hip OA underwent THR after only 2–3 years of followup (6, 7, 24). The mean JSN in hips with symptomatic OA after 8 years in our study was 0.50 mm. In contrast, Dougados et al found a mean joint space loss of 0.69 mm after only 3 years in the placebo-treated patients in the randomized controlled trial of diacerein (25). Our finding is similar to those in studies of knee OA, in which the annual joint space loss in population-based samples is substantially less than that observed in patients from clinical cohorts or recruited for clinical trials (26). This slower rate of progression in community-based samples suggests that interventions designed to slow the development of hip OA in this group may need to target individuals with an increased risk of progression, even among those with hip pain and radiographic findings.

Because there is no single universally accepted definition of RHOA for use in population studies, we used several different radiographic criteria to identify hips with OA at baseline, including criteria based solely on JSN and others based on a combination of radiographic features (16). We used ≤1.5 mm as the value for hip MJS that defined OA. An MJS ≤2.5 mm has also been used to define hip OA in epidemiologic studies (16, 27–29). The use of a 2.5-mm MJS cut point was originally validated for hip OA in men, but the mean MJS in Caucasian women is 0.3–0.5 mm less than that in Caucasian men (27, 30). Methods for selecting gender-specific cut points for MJS using trimmed means and SDs of normal values (31) suggest an MJS cut point of ≤1.7 mm to define hip OA in Caucasian women (32), close to the criterion used in the present study as well as in several other studies (30, 32).

Furthermore, had we used a 2.5-mm hip MJS cut point to define OA, this would have profoundly altered our findings. In these elderly women, we identified a large subgroup of hips with possible RHOA defined by an MJS between 1.5 mm and 2.5 mm, but without any of the other radiographic findings used to define OA in our study. These hips overwhelmingly had grade 2 JSN in a superomedial direction. Radiographic progression and THR were much less common in these hips with isolated superomedial narrowing, even when hip pain was present, compared with hips we classified as having RHOA. This suggests the potential for a high degree of misclassification for prevalent RHOA in elderly white women when an MJS ≤2.5 mm is used by itself, and supports the use of a more stringent cut point for MJS in this group. An alternative approach, also used in our study, is to require a greater degree of JSN in the superomedial direction than in the superolateral direction to define OA. In our study, 50% of hips with an MJS between 1.5 mm and 2.5 mm and narrowing in a superolateral direction had other radiographic findings that classified them as OA hips, compared with only 12% of hips with an MJS between 1.5 mm and 2.5 mm and narrowing in a superomedial direction.

Finally, it is also possible that a high frequency of isolated, mild superomedial narrowing is specific to our method for measuring hip MJS, since the medial boundary for a measurement of MJS may differ across studies and investigators. However, we limited the region in which MJS could be defined in the medial direction to ∼45 degrees from perpendicular or to where the bright line of the acetabular roof was no longer visible, whichever was less medial. The prevalence of isolated, mild superomedial narrowing may be sensitive to how the limits of the medial region are defined, and other approaches may yield different results. The clinical significance and etiology of this radiographic finding and whether there are subsets of these hips that show greater progression need further investigation.

Our findings regarding baseline radiographic predictors of progression conflict with two observations from previous studies. First, we found that hips with definite femoral osteophytes had a substantially increased risk of radiographic progression and THR, even after adjusting for the presence of other radiographic features. This is in contrast to Danielsson's classic study, which suggested that hips with osteophytes but without JSN or subchondral bone changes did not progress radiographically or clinically (8). However, that study did not distinguish femoral from acetabular osteophytes. In our study, acetabular osteophytes were not even weakly associated with progression but were present without other radiographic findings in 23% of hips with RHOA compared with only 5% with femoral osteophytes. While this contrast in risk of progression by osteophyte location may suggest differences in biology, it seems equally possible that the assessment of acetabular osteophytes is prone to error and misclassification since it is often difficult to distinguish them from normal anatomy. Our finding that femoral osteophytes, even when isolated, are strong predictors of progression suggests that their presence alone may be a valid radiographic marker of hip OA.

Second, hips with minimal or no osteophytosis in our study did not progress more rapidly than hips with osteophytes. Further, in a result similar to our findings for femoral osteophytes, the presence of subchondral sclerosis was associated with an increased risk of radiographic progression and THR. Thus, our findings are not consistent with the notion that there is more rapid progression in hips with an “atrophic bone response” as suggested in a previous study of hip OA patients (7).

Consistent with results of two other studies (6, 7), we found that a superolateral pattern of joint space loss carried an especially high risk of progression to THR and further loss of joint space. Hips with concentric and superomedial patterns were also more likely to progress to THR compared with hips with insignificant JSN, although less so than hips with a superolateral pattern. Interestingly, hips with the superomedial and concentric patterns were also much less likely to have further development of osteophytes, suggesting that these patterns of narrowing may be linked to a decreased bone response. The strong associations with progression found for femoral osteophytes, JSN and its location, and subchondral bone sclerosis suggest that these features may be useful in identifying more rapid progressors appropriate for interventions in community-based samples of subjects with hip OA.

Our results provide a clear indication of the substantial long-term health impact of painful hip OA in women identified with this condition from the community. A significant increase in disability or THR occurred in almost one-half of women with symptomatic hip OA at baseline. The risk of worsened lower extremity disability was substantially increased in those with hip pain at baseline, even after adjusting for the severity of radiographic OA and other covariates. This is consistent with findings of other studies suggesting that joint symptoms are an important mediator of disability resulting from structural damage in the joint with OA (33).

Our study has several noteworthy strengths. It is the first study of progression among persons with hip OA identified from a community-based radiographic survey, and it is the largest longitudinal radiographic study of hip OA. The followup was long enough and the sample size large enough to observe important radiographic and clinical progression in a large number of hips despite the relatively slow development of these changes in OA. We used a spectrum of outcomes to assess progression of hip OA, including radiographic measures of MJS width, individual radiographic features, and a summary grade of radiographic OA, as well as THR for OA and worsening of lower extremity disability. We read hip radiographs paired by subject but blinded to order, a technique that may increase precision in measurement of change in joint space (34).

Our study also has several limitations. Because of the long followup period and advanced age of the subjects at baseline, ∼40% of women died or were unable to return for a followup radiograph. However, we used portable equipment to obtain radiographs at the residences of women who were unable to return for clinic visits, and we asked all women who were unable to return for clinic visits about THR and disability as part of self-administered questionnaires and/or during periodic postcard and telephone contacts. Because many women underwent THR before the followup radiograph, we imputed a change in MJS for these replaced hips using data on mean declines in MJS in the year prior to joint replacement (19, 24, 25). This may result in overestimating the decline in joint space in these hips. In addition, our use of portable x-ray equipment for some of the followup radiographs may have added to error in the measurement of MJS, since it is more difficult to standardize the x-ray view with this equipment. We did not obtain a measurement of hip pain severity that could be used to assess change in pain as an outcome. Also, we observed very little progression in the group with only superomedial JSN of 1.5–2.5 mm. Our results may not apply to men, to women age <65 years, or to nonwhites.

In summary, in this community-based sample of elderly white women, >12% had radiographic hip OA at the start of the study. Radiographic progression over 8 years was substantially greater in the nearly one-half of these women who had hip pain at baseline. Worsening of disability occurred or a THR was performed in approximately half of the women with symptomatic hip OA, a risk 3 times greater than for those with asymptomatic radiographic hip OA. However, even women with symptomatic hip OA in this community-based sample had rates of progression well below those observed in studies of clinic- or hospital-based samples of hip OA patients. In addition to hip pain, baseline radiographic findings that predicted more rapid radiographic and clinical progression included the presence of femoral osteophytes, subchondral bone sclerosis, and superolateral or concentric JSN, while hips without pain and those with an MJS of 1.5–2.5 mm and no other radiographic findings were least likely to progress. Community-based interventions to slow the progression of hip OA will need to target subgroups of patients with radiographic hip OA with the greatest likelihood of progression.

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