The main finding in this study was that variation in standardised surgery rates ranged from almost none to tenfold across the six orthopedic procedures in publicly funded Norwegian hospitals between 2012 and 2016. The variation was very high (SCV > 10) for arthroscopy for degenerative knee disease for patients 50 years and older, moderate (SCV 3–5) for the decompression procedures for lumbar disc herniation and lumbar spinal stenosis, and low (SCV < 3) for arthroplasty for osteoarthritis of the knee or hip, and surgical treatment for hip fracture.
The rates for arthroscopy for degenerative knee disease decreased markedly in all hospital referral areas. This indicates that practice is being adapted to recommendations in new guidelines (24). Persisting variation in arthroscopy rates might suggests, however, that different areas are adapting asynchronously. A similar pattern of decrease has been reported in other European countries, as well as in the US (5, 25, 26).
We observed that higher rates of arthroscopy for degenerative knee disease had a weak association to more orthopedic surgeons and a larger proportion of the population living in rural areas. The reason for this is unknown and may relate to local practice differences, availability of services or specific lifestyle demands.
Studies from Ireland, Korea and the UK (5, 7, 27) report an increase in knee arthroplasty with deprivation. Rates for knee and hip arthroplasty have also been associated with numbers of surgeons, hospital capacity (7, 27, 28), and socioeconomic factors (28, 29). Our findings align with those reported by de Pina et al. (9) and Mäkelä et al. (30), who found no association with supply or socioeconomic factors. The relatively low variation in arthroplasty for osteoarthritis of the hip is similar to that seen in Finland, where variation decreased from threefold in 1998 to 1.9-fold in 2005 (30).
As surgical treatment of a hip fracture is considered both effective and necessary, we did not expect to find any association with supply or demand related factors. The small amount of variation in hip fracture surgery is in line with other reports (5, 31, 32) and variation is generally considered to reflect the relatively small differences in incidence.
Variation in spine surgery procedures, similar to that found in the current study, has been observed both internationally and in Norway (3, 5, 33), and is related to more uncertainty about the effectiveness of the procedures (34). Bederman et al. (33) found that higher rates were associated with lower income, but found no association with supply of physicians. The number of hospitals was negatively associated with spine surgery rates in Ireland (5). We found no notable association between spine surgery rates and the area-level supply or demand related factors analysed in our study.
Strengths and weaknesses
The main strength of this study is the availability of nationwide data on orthopedic procedures performed at publicly funded hospitals, which gives a comprehensive picture of variation in public healthcare.
While the majority of orthopedic surgery, and all hip fracture surgery, in Norway is performed in publicly funded hospitals, the proportion of private providers range from 12 to 30 percent (arthroscopy for degenerative knee disease 19 of 64, decompression for lumbar disc herniation and lumbar spinal stenosis 10 of 43, arthroplasty for osteoarthritis of the knee 9 of 60, and arthroplasty for osteoarthritis of the hip 7 of 60 hospitals). Most private hospitals perform both publicly funded and privately funded treatment, but report only publicly funded activity to the NPR. Accordingly, absence of data on privately funded activity is a limitation in our analysis, as the data does not reflect all activity. For some of the studied procedures, private activity has been reported to increase variation (4, 16). Further, the number of hospitals is a crude measure as it does not account for differences in hospital capacity.
Conservative treatment is an important option for many orthopedic conditions. While this is generally acknowledged, the lack of uniformity in conservative care in the Norwegian public health care system might be a driver of variation in surgery rates. It is a limitation that we could not account for this, due to the availability of data.
The number of surgeons includes practicing surgeons nationwide, but remains a rough estimate as surgeons’ area of residence might not always coincide with the area in which they work, especially in the larger capitol area. Furthermore, we have not included the varying number of surgeons in training, who independently perform some of the included procedures in many hospitals. The proportion of surgeons in training varies between geographical areas, but we did not have access to these data. Finally, some surgeons are not permanently employed, but contracted through staffing agencies. Data quantifying this are not available, either.
It is a limitation of the study design that data on demand-related factors were available on area, and not individual, level. This precludes us from exploring variation in surgery rates in light of demand in the patient groups involved. Hence, the analysis of associations between surgery rates and demand-related factors only gives rough estimates of this relationship. Nevertheless, geographic variation research conducted at a national level, using area-level units of analysis while crude, is important in signalling potential inequality and treatment underuse or overuse (35, 36).
The associations found in our study between area-level demand and supply-related factors and surgery rates were weak. We might assume that the included orthopedic surgery rates are not notably associated with regional numbers of hospitals or surgeons, or with income, education, unemployment, health level (estimated by mortality as a proxy) or with urbanization. This could be a result of longstanding efforts in Scandinavia to facilitate equity by universal health care and tax paid education.
On the other hand, one could argue that area-level factors reflecting demand are not detailed enough to detect the associations that may exist between socioeconomic factors and surgery rates. To further explore this, qualitative analyses and more detailed multilevel analyses including individual-level data of factors known to influence surgery rates are needed. This is being explored in two ongoing Norwegian studies on geographic variation in hip and knee arthroplasty and lumbar spine surgery, using mixed methods design consisting of multilevel analyses on registry data and qualitative data collection from focus groups (general practitioners) and individual interviews (patients and surgeons).
While sociodemographics and healthcare supply do not seem to explain variation in common orthopedic procedures based on our findings, we acknowledge that there are more factors known to impact utilization of health care. These include differences in preferences among surgeons, the effect of shared decision-making, as well as capacity and structural aspects of the health care system (6, 8, 11, 37, 38, 39).