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Difficulty: HardEpidemiologic Study Designs

Sports medicine researchers are investigating the long-term risk of developing early-onset osteoarthritis of the knee following anterior cruciate ligament (ACL) reconstruction. They access a national surgical database to identify 5,400 amateur athletes who underwent primary ACL reconstruction between 2005 and 2010. They also identify 10,800 matched amateur athletes who were treated for non-ligamentous knee sprains during the same period. The research team then links these surgical and clinical records to a national outpatient health registry spanning from 2005 through 2026 to ascertain how many individuals in each group were subsequently assigned diagnostic codes for knee osteoarthritis. Which of the following accurately identifies the study design used in this investigation and its primary measure of association?

  1. Retrospective cohort study; relative riskAnswer
  2. B
    Case-control study; odds ratio
  3. C
    Prospective cohort study; relative risk
  4. D
    Nested case-control study; odds ratio
  5. E
    Cross-sectional study; prevalence ratio

Answer

Retrospective cohort study; relative risk
The study design described is a retrospective cohort study. The defining characteristic of any cohort study is the sampling strategy: subjects are grouped based on their exposure status (in this case, ACL reconstruction versus non-ligamentous knee sprain). The defining characteristic of a retrospective cohort study is its temporality: the exposure and the outcomes have already occurred by the time the investigation begins, and the researchers rely on historical data to track the cohort forward in time to determine the incidence of the outcome (osteoarthritis). Because cohort studies directly measure the incidence of disease in exposed and unexposed groups, the appropriate primary measure of association is relative risk (risk ratio).

Step-by-Step Solution

1
Analyze the sampling strategy used to define the study groups.
The researchers grouped the subjects based on their exposure status (ACL reconstruction versus non-ligamentous sprain).
Grouping subjects by exposure prior to determining the outcome is the fundamental characteristic of a cohort design, differentiating it from case-control studies which group by outcome.
2
Determine the temporal relationship between the study initiation and the events.
Both the exposure (2005-2010) and the outcome tracking (up to 2026) occurred in the past relative to the researchers' analysis, utilizing historical databases.
Following an exposed group forward in historical time using existing records defines a retrospective cohort study.
3
Identify the standard statistical measure for this design.
Relative risk (or risk ratio).
Cohort studies measure disease incidence over time, allowing for the direct calculation of relative risk by comparing the incidence in the exposed group to the incidence in the unexposed group.

Key Concept

Retrospective cohort studies group subjects by historical exposure status and track them longitudinally via existing records to determine outcome incidence, utilizing relative risk to measure the association.
Estimated Time:1m 15s
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Epidemiologic Study Designs

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