Observational Study of the Distribution and
Diversity of Interventional Pain Procedures
Among Hospitals in the State of Iowa
Authors: Dexter Franklin 
Published: February 2021

Background: Critical access hospitals represent 61% of hospitals in the rural United States, and
68% of hospitals in Iowa. The role of small hospitals, such as critical access hospitals, in providing
interventional chronic pain procedures is unknown.
Objectives: We evaluated whether: a) the diversity of interventional pain procedures offered by
hospitals is related to their size and is attributable principally to lumbosacral epidural injections; b)
critical access hospitals contribute substantively to the count and diversity of pain procedures; and
c) whether most interventional pain procedures performed at hospitals’ facilities are performed by
relatively few proceduralists or by the cumulative activity of many clinicians.
Study Design: This research involved an observational cohort design with a sample size of n =
283,940 interventional pain procedures.
Setting: Data were collected from hospital-owned facilities in the state of Iowa from July 2012
through September 2017.
Methods: The diversity of types of interventional pain procedures performed statewide was
quantified in terms of the relative proportions of procedures at each hospital using the Herfindahl
index. Bilinear weighted least squares regression quantified the relationship between the inverse
of the Herfindahl and the percentage of procedures that were lumbar or caudal epidural. Kendall
tau concordances quantified the relationship between counts of interventional pain procedures and
hospital size. Using a blinded version of the National Provider Identifier of the clinician with primary
responsibility for performing the principal procedure of the ambulatory visit, we calculated the
percentage shares of interventional pain procedures performed by the 1% and 5% of proceduralists
who performed the most procedures.
Results: The diversity of types of procedures substantively differentiated among hospitals.
Heterogeneity among hospitals in the proportion of procedures that were lumbar or caudal
epidural injections substantively contributed to the heterogeneity among hospitals (P < .001).
Hospitals performing more procedures tended to have greater diversity of types of procedures
(P < .001). However, the strength of the concordance was small (Kendall τb
= 0.332), showing
substantial heterogeneity among hospitals. The 82 critical access hospitals statewide cumulatively
accounted for 23.9% of interventional pain procedures. The critical access hospitals’ procedures
were mostly (67.7%) lumbar or caudal epidural injections (P < .001), greater than the 48.9% of
the other 41 hospitals (P < .001). Procedures were concentrated among proceduralists. The 1.0%
of the proceduralists performing the most procedures performed 64.8% of procedures. The 5.0%
of proceduralists performing the most procedures performed 87.7% of procedures.
Limitations: The data are procedures were performed in hospital-owned facilities of Iowa.
Conclusions: Although busier pain programs, based on procedures per week, generally
performed more types of procedures, the variability was so large that the number of procedures
a pain program performs per week cannot validly be used to infer the diversity of the hospital’s
pain medicine practice. Hospitals with pain medicine programs that lack diversity in the types of procedures performed may provide limited options for patients and be susceptible to changes in payment for individual procedures.
Relatively few proceduralists performed the vast majority of the procedures.
Key words: Critical access hospitals, Herfindahl, interventional pain procedures, managerial epidemiology, pain medicine, state
outpatient procedure database, lumbar epidural