Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Differences in the Observed Rate of Hip Fracture in Male and Female Patients Diagnosed with Osteoarthritis or Ankylosing Spondylitis Compared with the Expected Based on the General Population Seeking Health Care.

Englund2,  Martin, Franklin3,  Jonas, Petersson1,  Ingemar F.

Lund University Hosp, Lund, Sweden
Musculoskeletal Sciences, Department of Orthopedics, Clinical Sciences Lund, Lund University, Lund, Sweden
University Hospital, Akureyri, Iceland

Background:

There are conflicting reports of the association between hip osteoarthritis (OA) and hip fracture, and little is known of the association between knee OA or ankylosing spondylitis (AS) and hip fracture.

Objective:

To study the rate of hip fracture in male and female OA and AS patients compared with the general population seeking health care.

Methods:

Cohort design; Sweden has publicly funded health care with all in- and outpatient health care consultations registered by the patient's personal identifier. We studied residents aged >=20 yrs of southern Sweden by 1 Jan 2004 who consulted a physician at least once the following 4 calendar years (n=761,210 of total adult population n=879,624), thus being captured with diagnostic codes in the Skane Health Care Register (SHCR). We identified all residents with an ICD-10 code given by a physician for: hip OA (M16), n=11,901, mean age 69.6 yrs, 57.1% women; knee OA (M17), n=23,866, mean age 66.3 yrs, 58.8% women; AS (M45), n=1374, mean age 53.1 yrs, 39.8% women. To obtain observed hip fracture rates we calculated the person-time for each individual, from the day of his/her first OA or AS diagnosis within the study period until the day of first hip fracture (ICD-10 codes: S72.0, S72.1, or S72.2) or until another censoring event (death, relocation, or end of study period by cross-referencing with the population register). The person-time for each subject in the general population aged >=20 yrs seeking health care (n=761,210, the background population) started to count by his/her first diagnostic code (any ICD-10 code) in the SHCR within the period until first hip fracture or another censoring event (in an identical fashion as for OA and AS patients). We then calculated the standardized fracture-rate ratio (SFR) by dividing the observed rate of hip fracture in OA or AS patients by their expected rate (based on the age- and gender-specific rates in the background population). Thus, a SFR >1 equals an increased rate of hip fracture and <1 equals a reduced rate of hip fracture compared with the background population. In a sensitivity analysis for estimates in OA patients, we excluded all residents (in both the OA cohort and the background population) being registered with total hip replacement within the study period.

Results:

In female knee OA patients the hip fracture rate was significantly reduced by about 20%, but not in men. No significant SFRs were found for hip OA patients, neither men nor women (Figure). In AS we found the SFR increased by about 70% for both men an women. However, due to the relatively rare AS diagnosis and low number of fractures observed, the 95% CIs were large and included one (the SFR for men and women combined was 1.68, 95 % CI 0.94, 2.77).

Figure. Standardized hip fracture-rate ratio (SFR) in male (•) and female ([cir]) hip and knee OA patients. The ratio is obtained by dividing the observed fracture rate among OA patients divided by their expected rate based on the hip fracture rate in the background population. In the second set of estimates in each graph subjects with total hip replacement (THR) within the study period are excluded. Error bars are 95% confidence intervals.

Conclusion:

In a comprehensive population-based dataset over 4 years, we observed a 20% decreased rate of hip fracture in female knee OA patients compared to the expected, while there was an 70% increased rate in AS patients.

To cite this abstract, please use the following information:
Englund, Martin, Franklin, Jonas, Petersson, Ingemar F.; Differences in the Observed Rate of Hip Fracture in Male and Female Patients Diagnosed with Osteoarthritis or Ankylosing Spondylitis Compared with the Expected Based on the General Population Seeking Health Care. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :963
DOI: 10.1002/art.28730

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