Don’t Get All Hyper!

One of the most challenging aspects of anatomy for new students is the specialized terminology. We use these terms so we can communicate effectively. But, achieving this goal requires a shared understanding of standard terms and their meanings.

Last fall, there was a robust discussion on HAPS-L about defining “hyperextension”. In general, the contributors agree that extension increases the angle between segments of a common joint. But, defining hyperextension was trickier.

Some sources define hyperextension by the angle of the joint. However, there is disagreement over whether the “neutral” (normal anatomic) position should be designated as 180° or 0°. Furthermore, in some joints, extension normally exceeds the neutral position. So, an arbitrary limit based on the angle between adjoining bones will be difficult to apply universally.

Another option is to use the basic definition of extension as movement relative to normal anatomic position without reference to specific angles. While this is more practical, it makes the definition of hyperextension more complex. For example, the metatarsophalangeal, talocrural, and acetabulofemoral joints all normally extend past NAP.

At a minimum, the definition is in the name:  ‘hyper’ means ‘beyond’ or ‘over’, so generally, it is extension beyond the normal range of motion. However, even that definition has its own difficulties. Consider for example the degree of back or hip extension in this contortionist…

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…this range of motion is far beyond what any of us would consider normal (or even desirable), but it is quite within the “normal” range for individuals trained for this activity.

Less extreme examples of “enhanced” extension can occur in cases of general ligamentous laxity and or of variations in joint surfaces that result in being able to extend (and in some cases, flex or rotate) beyond the range we have defined as normal. Elite athletes and other performers may often produce movements that exceed the textbook descriptions of “normal” ranges of motion.

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After teaching A&P within and among several programs and majors, I have found that different disciplines often “flavor” terminology to highlight the issues most relevant to their professional concerns. For example, students of athletic performance or rehabilitation are concerned with the potential or actual injuries that often occur with hyperextension. However, even though hyperextension can cause injuries, as the examples above indicate, injury is not always the result.

The one element that all definitions have in common is that hyperextension is extending beyond the normal ROM. So, if we agree that this concept is essential to the general definition, we have a minimal standard of reference in the commonality in how the concept is expressed. Borrowing a page from C.S. Lewis, let’s call this “mere hyperextension”.

For “mere hyperextension”, we take the literal meanings of the prefix and root: hyper means “above” or “beyond” and “extension” is the movement of the joint in a way that increases the angle between structures on opposite sides of the joint. Thus, hyperextension would be extension beyond the usual anatomic range of motion.


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Andrew Petto recently retired as Distinguished Lecturer Emeritus from the University of Wisconsin–Milwaukee where he taught anatomy and physiology beginning in 2004. He began teaching human anatomy and physiology (to mortuary students) in 1989, and has since taught A&P to massage therapists, dancers, physical therapists, nurses, and herds of undergraduates at UWM, His PhD is in Biological Anthropology (comparative functional morphology) with post-doctoral studies in primate behavioral biology at Harvard Medical School (NERPRC) and in primate ecology in the Department of Anthropology at UW-Madison, supplemented by graduate studies in curriculum and instruction at Drexel University. His latest book, Human Structure and Function—an interactive textbook for students outside the sciences—was published by Tophat in 2017. His next book, Humans, is a collaboration with Alice Beck Kehoe of an introductory textbook on our species

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