Broadening the Search

Because the returns from a PubMed search are characteristically larger than you want, it is difficult to appreciate that the search might need to be broadened. But very often the literalness of the computer system defeats your intentions. We have seen that many times in the other parts of this workshop

• collateral ligament is not the same as collateral ligaments
• non union is not the same as Fractures, Ununited or pseudarthrosis
• Gustillo is not the same as Gustilo
• Wrist fracture is not the same as distal radius fracture or Colles' fracture

So while it may be obvious that you have to narrow the search, you may need to give special consideration to whether you should broaden it first.

How to find out that you need a wider search

Are you using a synonym?

Almost always you are. There are so many ways to describe medical conditions with more or less precision

• avascular necrosis/osteonecrosis/aseptic necrosis
• Hip, femoral neck, intertrochanteric, acetabulum
• arthritis ( & 57 varieties thereof) !
• frature/crack/break

If you are using a synonym then you will need to put ALL the synonyms into the system to make sure that you have caught everything you need. This is difficult because we each tend to use the terms we are familiar with and may not think of the terms other people use. Much better to use a MeSH term.

Is your term a MeSH term?

To find out check "Details" (after you have run the search)

On the PubMed page enter Avascular Necrosis and click on Go then Click on Details
In the text box note that Avascular Necrosis is not referred to as a MeSH term

You could try other synonyms but the systematic way to do it is to use the MeSH Browser.

To the left of the PubMed page under PubMed Services click on the link to MeSH Browser
Enter the words Avascular Necrosis and click Go
This is the way PubMed describes the nature and function of MeSH terminology	MeSH is NLM's controlled vocabulary used for indexing articles in PubMed. MeSH terminology provides a consistent way to retrieve information that may use different terminology for the same concepts.

Avascular necrosis is not a MeSH term as we found out before. However, MeSH offers a number of terms which are close. Select Bone Avascular Necrosis and click on "Browse this term"

The site will now show you which is the real MeSH term for this concept and give a definition to make sure this is what you are looking for.

Scroll down to see the MeSH tree of terms that are related to  Osteonecrosis. Note that it appears under 2 disease categories Musculoskeletal Diseases (arrow) and Pathological Conditions. There is some redundancy in the system to allow you to find a subject from different angles. Note also that Osteonecrosis is not a terminal "twig" but has branches and twigs related to the femoral head below it. By default any search for osteonecrosis will be "exploded" and include all subsequent twigs.

Scroll back up again and click on the Add link to add the term to the Search. When you start using the MeSH Browser the Search is empty so take the AND (default) operator

You will see in the dialog box that the search term now is Osteonecrosis[MESH] which means that PubMed will search for all articles that have been indexed under that term, all the subheadings of that term and all the terms that come after it in the tree.

As a result this search will net you a very large number of articles. More importantly, because you have used a MeSH term for the search you can be reasonably sure it is as broad as you could want. Note that this process did offer you a chance to define your search a bit more narrowly and still remain comprehensive. If your topic of interest was Legg-Perthes Disease or AVN of the femoral head you could have picked one of those out of the MeSH tree and searched exclusively but comprehensively for that.

Broadening the Search using Boolean OR

The Boolean term OR allows you to broaden the search. If you think you know all the synonyms likely to be used you can try this. The word OR must be in upper case, otherwise it will be ignored.

A search for Osteonecrosis OR avascular necrosis OR aseptic necrosis yielded 7730 citations. Looking at the papers which appear in this collection but not in the Osteonecrosis[mesh] collection shows that AVN was a peripheral issue in most of these papers. There are also some which haven't been indexed yet.

Broadening, using Boolean terms is perhaps more useful when you are dealing with a much more defined situation.

Run the following searches

Search String	Outcome
Intrafocal pinning	12
Kapandji pinning	26
Intrafocal pinning OR Kapandji pinning	28

So although most authors attribute the intrafocal pinning technique to its originator and many describe the technique as Intrafocal (Kapandji) pinning there are 2 papers which only refer to "intrafocal".

MeSH terminology is much too coarsely granular to help in this situation.

Summary

• Learn to use MeSH teminology if you want to be more sure that your search is inclusive

• Further broadening with OR can be used if you know all the synonyms

• where the MeSH system doesn't cover the topic in fine enough detail using OR to broaden the search is the best way.

Myles Clough mylesclough@shaw.ca
Clinical Instructor, Department of Orthopaedics, University of British Columbia
B.C. Canada
Feedback, Comments and Questions welcome.