Ankle joint classification: Merrill's says hinge, Bontrager's says saddle
Key takeaways
- Merrill's 15th edition and StatPearls call the ankle a hinge joint.
- Bontrager's 9th edition calls it a saddle joint.
- ARRT says it avoids content where resources have conflicting perspectives.
- The tibia, fibula and talus form the joint in every source we opened.
Sources disagree on this one, and we won’t pretend otherwise. The two positioning textbooks we read split: Merrill’s calls the ankle a hinge joint, and Bontrager’s calls it a saddle joint. StatPearls, an encyclopedia, also says hinge. We can’t tell you which label the ARRT® Radiography exam would use.
Which sources say hinge, and which say saddle?
| Source | Ankle joint type |
|---|---|
| Merrill’s Atlas, 15th ed. (2023) | Hinge (ginglymus), listed with the elbow and knee |
| StatPearls, Ankle Joint (2023) | Hinged synovial joint |
| Bontrager’s Textbook, 9th ed. (2018) | Saddle (sellar), noting that earlier references used ginglymus |
Bontrager’s says earlier references classed the ankle as a ginglymus, and that current references classify it as a saddle joint. Merrill’s is the later of the two books we read, and it still says hinge. We read those editions only, so check the edition your program uses.
Our foot, ankle and calcaneus chapter and positioning fundamentals chapter give both labels.
What should you do for the registry exam?
ARRT’s content specifications say it “avoids content when there are multiple resources with conflicting perspectives.” Neither the 2022 nor the 2027 outline lists a joint type for the ankle. That may make a hinge-or-saddle question less likely, but that is our inference, and ARRT doesn’t say what it tests fact by fact.
Our practical advice is to learn both labels and know who uses each. If your program’s textbook or instructor picks one, use it in that course. The wider joint types are in our positioning fundamentals chapter.
What isn’t in dispute?
The tibia, fibula and talus form the joint. The medial malleolus, lateral malleolus and tibial plafond form the mortise, and the talus sits inside it.
Both textbooks tie the positioning to that shape. For the AP mortise projection, rotate the whole leg internally 15 to 20 degrees. Bontrager’s and Merrill’s also agree that the first carpometacarpal joint of the thumb is a saddle joint, so that joint isn’t in dispute.
Our Procedures guide covers the ankle series with the rest of the limb. To test yourself, try the extremity practice questions.
Frequently asked questions
Is the ankle a hinge or saddle joint?
Sources conflict. Merrill's 15th edition and StatPearls say hinge. Bontrager's 9th edition says saddle.
Which answer should I use on the ARRT exam?
We can't say, because ARRT's outlines don't list joint classifications. ARRT says it avoids content where resources conflict. Learn both labels and check what your program's textbook uses.
What bones form the ankle joint?
The tibia, the fibula and the talus. The two malleoli and the tibial plafond form the mortise that holds the talus.
Sources
Found an error? Email [email protected] with the page and the source.
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