Ian,
The IF for 2007 is calculated as:
A = the number of times articles published in the journal in 2005-6 were cited in indexed journals during 2007
B = the number of "citable items" (articles, reviews, proceedings or notes, excluding editorials and letters-to-the-Editor) published in 2005-6
2007 IF= A/B
Only two foot-related journal are tracked by Thomson ISI (the company that "owns" the IF), and their 2007 IFs are:
JAPMA: 0.407
Foot and Ankle International: 0.956
The new journal, Journal of Foot and Ankle Research, doesn't yet have an IF as it hasn't been published for a long enough period of time.
IFs are a seriously flawed measure of journal quality, influence or impact. There have been several papers which discuss this, the best being by Per Seglen in the BMJ (link). The key flaws of the IF are as follows (taken from Seglen):
Journal impact factors are not statistically representative of individual journal articles
Journal impact factors correlate poorly with actual citations of individual articles
Authors use many criteria other than impact when submitting to journals
Citations to "non-citable" items are erroneously included in the database
Self citations are not corrected for
Review articles are heavily cited and inflate the impact factor of journals
Long articles collect many citations and give high journal impact factors
Short publication lag allows many short term journal self citations and gives a high journal impact factor
Citations in the national language of the journal are preferred by the journal's authors
Selective journal self citation: articles tend to preferentially cite other articles in the same journal
Coverage of the database is not complete
Books are not included in the database as a source for citations
Database has an English language bias
Database is dominated by American publications
Journal set in database may vary from year to year
Impact factor is a function of the number of references per article in the research field
Research fields with literature that rapidly becomes obsolete are favoured
Impact factor depends on dynamics (expansion or contraction) of the research field
Small research fields tend to lack journals with high impact
Relations between fields (clinical v basic research, for example) strongly determine the journal impact factor
Citation rate of article determines journal impact, but not vice versa
Despite these flaws, researchers will probably still aim for so-called "high-impact" journals until a better system of ranking them is developed.