To What Extent Is Severe Osteoarthritis Preventable?

Occupational and Non-Occupational Risk Factors for Knee and Hip Osteoarthritis

Tea Kontio; Markku Heliövaara; Eira Viikari-Juntura; Svetlana Solovieva


Rheumatology. 2020;59(12):3869-3877. 

In This Article


Hospital Discharge Register

The National Hospital Discharge Register is held by The National Institute for Health and Welfare in Finland, and it contains all in- and outpatient visits with their diagnostic codes. It is a previously known reliable source of information (1). We only used the in-patient data with the appropriate diagnostic codes.

ICD Codes for Hospitalization Due to Knee and Hip Injuries

The following ICD codes were used to identify major injury of the knee prior to baseline and during follow-up: 724.10, 821.21, 821.31, 821.91, 822.00 – 822.90, 823.00, 823.10 and 823.90, 836.00 – 836.91, 844.00 (ICD-8); 7170A – 7179X, 8360A, 8361A and 8362A, 8212A – 8213X, 8220A – 8221A, 8230A and 8231A, 8363A – 8366B, 8440A – 8449X (ICD-9); M23.0 – M23.9 and S83.2; S72.4, S82.0 and S82.1; S83.0 and S83.1; S83.3 – S83.7 (ICD-10).

The following ICD codes were used to identify hip injury: 808.00, 808.10, 808.90, 820.00–820.03, 820.10–820.12, 821.00, 821.10, 821.21 and 821.31 (ICD-8); 8080A, 8081A, 820, 821, 9350A and 8351A (ICD-9); S72.0-S72.9. S73, S77, S32.4 and S32.7 (ICD-10).

Calculation of Population Attributable Fractions

We calculated the population attributable fraction (PAF) to estimate the proportion of new cases of hospitalizations due to knee or hip OA that could be attributed to prior injury, BMI and cumulative workload. For a dichotomous risk factor (prior injury) we used the following formula: PAF= p(RR-1)/(p(RR-1)+1), where p denotes the prevalence of the risk factor in the population and RR denotes the relative risk of hospitalizations due to knee or hip OA associated with the risk factor. For a risk factor with more than two categories (BMI and composite cumulative workload) we used the following formula:

where pi is the proportion of population at exposure level i, RRi is the relative risk at exposure level i and n is the number of exposure levels.

After the calculation of PAF for each risk factor of interest, we calculated the overall PAF using the sum formula [22]: PAFoverall= 1- (1-PAF1)(1-PAF2) …. (1-PAFn).

Sensitivity Analysis

Of the 4187 persons (90.2% of the study population) who participated in the clinical examination at baseline, 53 (1.3%) had prevalent knee or hip OA diagnosed by a physician during the clinical examination. We carried out a sensitivity analysis to examine, whether the presence of knee or hip OA at baseline affected the observed associations. For this, we repeated the main analyses excluding persons with prevalent knee or hip OA at baseline.

Clinical Diagnosis of OA at Baseline

The diagnosis of OA was based on clinical examination by specially trained physicians according to a standardized written protocol. The clinical examination included estimations of limitations in the range of motion, tenderness, deformations, joint effusion and stability of the knee joint. The diagnosis was based on symptoms and findings. To validate the clinical diagnosis of knee OA, radiographs were taken for a subsample of participants; the agreement between clinical and radiological diagnosis using the Kellgren and Lawrence grading scale was moderate (2).

The clinical examination for hip OA included moderate or slight restrictions in extension, inner rotation or outer rotation, especially if combined with tenderness associated with movement and typical symptoms (3). This diagnosis has not been validated.

Results of the sensitivity analysis. When persons with prevalent knee or hip OA at baseline were excluded, all observed associations remained similar to those found in the total study population (Table S3).


  1. Sund R, Nurmi-Luthje I, Luthje P, Tanninen S, Narinen A, Keskimaki I. Comparing properties of audit data and routinely collected register data in case of performance assessment of hip fracture treatment in Finland. Methods of information in medicine. 2007;46(5):558–66.

  2. Toivanen AT, Arokoski JP, Manninen PS, Heliovaara M, Haara MM, Tyrvainen E, et al. Agreement between clinical and radiological methods of diagnosing knee osteoarthritis. Scandinavian journal of rheumatology. 2007;36(1):58–63.

  3. Kaila-Kangas L. Musculoskeletal disorders and diseases in Finland : Results of the Health 2000 Survey: National Institute for Health and Welfare; 2007 [Available from: