The Ankle Joint(s)

Anatomy, Evolution and Function

Outline

• Anatomy

– The ankle: 3 joints in 1

• Evolution

– Mammalian evolution

– The ape-like condition

• Function

– Comparing apes and humans

– Fossil inferences

Inferior Tibiofibular Joint

• Involves only the bottom ends of the tibia and fibula.

• Tibia and fibula are unfused at their top and bottom articulations.

• A ligamentous syndesmosis allows some flexibility at the bottom articulation.

AITFL and PITFL, anterior and posterior inferior tibiofibular ligaments; IM, interosseous membrane; TrTFL, transverse tibiofibular ligament. (Tsao, 2010)

Talocrural Joint

• The ankle ‘proper’ allows for plantarflexion and dorsiflexion only (raising and lowering of the foot).

• It is the main interaction of the leg with the tarsal bones of the foot.

• The only weight-bearing interaction is between the tibial plafond and the trochlea of the talus.

Huei-Ming, 2004.

Soft Tissues - Ligaments

• A complex of 4 ligaments attaches the tibia to the tarsals.

• These are known collectively as the deltoid ligament.

• The lateral ligaments attaching the fibula to the tarsals are more distinct from one another.

Both: Stern, 2003. Essentials of Gross Anatomy.

Soft Tissues - Muscles

• The tibialis anterior (left) is the prime dorsiflexor (raises foot) at the talocrural joint.

• The gastrocnemius and the soleus inserting into the Achilles tendon (bottom right) are the prime plantarflexors (go on tiptoes).

Above: Duke Universty School of Medicine, 2011 Right: Avenue Clinic, 2014.

Sub-talar (talocalcaneal) joint

• Consists of 3 largely distinct articular surfaces.

• The anterior & middle, and posterior articular surfaces act as counter-rotating screws.

Above: Stern, 2003. Essentials of Gross Anatomy. Right: Harcourt-Smith, 2002.

Soft Tissues - Muscles

• Inversion (sole toward the body’s midline) and eversion (sole outwards) occurs around the subtalar axis (right).

• Tibialis anterior is the main invertor.

• The fibularis/peroneal muscles (below) act as the principal evertors.

Above: Lewis, 1980b. Right: Barraclough, 2014.

Evolution of the Ankle Joints

• Pre-mammalian (therapsid) condition. – Talus lay next to, as opposed

to on top of, the calcaneus.

– There was a major weight-bearing joint between fibula and calcaneus.

– More similar to a modern primate wrist with cartilage menisci (m) between bones (right).

Top: Calcaneofibular articulation in an alligator (Online Biology Library). Bottom: Wrist joint of common chimpanzee (Lewis, 1970).

Evolution of the Ankle Joints

• Mammalian condition

– Talus shifts superiorly to rest on top of the calcaneus.

– Portions of the menisci are are replaced by tibiocalcaneal and posterior tibiotalar ligaments in the tree shrew.

– The talus assumes a trochlear morphology

– Medial trochlear surface becomes distinct from the superior trochlear surface.

Evolution of the Ankle Joints

• Ape condition

– Fibula and calcaneus no longer articulate.

– Modified medial and lateral talar articular surfaces for the malleoli.

Comparative Functional Anatomy - Talocrural joint

• Lateral trochlear border is far longer front-to-back than the medial border in apes (right).

• In humans, the medial border is relatively higher, meaning the trochlea has a more horizontal surface. It is steeply angled in apes.

Right tali of male gorilla(top) (Lewis, 1980) and modern human (bottom) (Latimer et al., 1987).

Comparative Functional Anatomy - Talocrural joint

• The orientation of the distal tibial articular surface (talar angle; right) affects bipedal efficiency.

• Trochlear morphology (previous slide) further contributes to an exaggerated outwards-arcing path of the tibia in bipedal locomotion (right).

Talar angle (top) and path in bipedal locomotion (bottom in chimp (left) and human (right) (DeSilva, 2009; Aiello & Dean, 1990).

Comparative Functional Anatomy - Talocrural joint

• The medial malleolar facet of the talus is cupped anteriorly (top right, far side).

• The lateral malleolar facet of the talus flares inferiorly and laterally top right, near side).

• Medial malleolus is more robust in apes than in humans.

Orientation of the lateral malleolar facet in a common chimpanzee (left) and a modern human (right) (Aiello & Dean, 1990).

Left talus of a gibbon showing specialised morphology of malleolar facets (Latimer et al., 1987).

Comparative Functional Anatomy - Talocrural joint

• Fibular talar facet is inferiorly orientated in apes (arrows, right).

• Trochlear surface is highly convex front-to-back.

• Increased front-to-back wedging (bottom right, near side) in the chimp exaggerates the screwing motion of talus on calcaneus.

Illustrating left tali of common chimpanzee (left) and anatomically modern human (right) (DeSilva, 2009).

Orientation of the lateral malleolar facet in a common chimpanzee (left) and a modern human (right) (Aiello & Dean, 1990).

Comparative Functional Anatomy - Sub-talar joint

• The posterior and anterior sub-talar joints act as counter-rotating screws.

• The axis of the sub-talar joint runs at an oblique angle to the foot (arrow).

• Talus screws the calcaneus forward into the more distal tarsal bones.

Diagram of a saki monkey right foot in eversion (left) and inversion (right) (Lewis, 1980c).

Comparative Functional Anatomy - Sub-talar joint

• In non-human primates:

– Relatively large-angled articular surfaces allow a great range of inversion/eversion (far right).

– The foot is in a stable inverted configuration for grasping a vertical branch or other support.

Diagram of a saki monkey right foot in eversion (left) and inversion (right) (Lewis, 1980c).

Comparative Functional Anatomy - Sub-talar joint

• Sustentaculum tali (bears the anterior and middle sub-talar joint facets; arrow) is more prominent in humans. (Sadly this picture is from the wrong side to see it properly).

• The calcaneal tuberosity is greatly enlarged in humans relative to apes (bracket; more later). Calcanei of a common chimpanzee (top) and a human (bottom)

(Lewis, 1983).

Comparative Functional Morphology - Sub-talar joint

• Sub-talar axis is more vertically orientated in humans than apes.

• Talus screws downwards, causing the calcaneus to rotate (far right).

• The foot is now in a stable configuration for weight-bearing.

• Smaller-angled articular surfaces limit the range of inversion/eversion.

Showing orientation of the sub-talar axis of a human foot in early (left) and middle (right) stance phase (Lewis, 1980c).

Comparative Functional Anatomy - Soft tissues

• Plantarflexor (gastrocnemius & soleus)

muscle mass is relatively greater in

humans than apes.

• The Achilles tendon is longer and more

robust in humans than in apes (right).

• A well-developed enthesis organ is present

in the human heel ( bottom right).

– The bursa protects the tendon from friction

on the calcaneus.

– The Sharpey’s fibres increase the strength

of the tendon’s insertion.

• (If the Achilles tendon comes away from the

bone, it usually takes some bone with it!)

© J. R. Lumbard, 2014

© Penas, 2013.

Comparative Functional Anatomy - The Hominins • 2-million-year-old

fossils from East and South Africa (D & E) both show an ape-like talus and a human-like rest of foot.

• A key adaptation to bipedality is closer alignment of the sub-talar axis with the long axis of the foot (B is a modern human).

Orientation of the sub-talar axis in: A, Neanderthal; B, modern human; C, composite Dmanisi foot; D, OH8; E, Stw573. (Pontzer et al., 2010).

Comaparative Functional Anatomy - The Hominins • The angle of the distal

tibial articular surface is a useful proxy for a bipedal gait.

• It is possible to infer this angle from an isolated talus using wedging angles discussed earlier.

• A whole range of hominins from between 4 and 1.5 million years ago show more similarity to modern humans than to African apes.

Talocrural joints (posterior aspect) of: Left, Australopithecus afarensis; middle, common chimpanzee; right, gorilla (Latimer et al., 1987).

Comparing the talar angle between a modern human (left) and a generalised African ape (right) (Aiello & Dean, 1990).

Comaparative Functional Anatomy - The Hominins: Soft tissues

• 2-million-year-old hominin A. sediba appears to have had a bursa. Compare human and sediba (*, top right & bottom left).

• The Neanderthal calcaneal tuberosity (bottom right) is relatively longer than in modern humans.

• This would have biased the Achilles tendon lever action to producing powerful movements, rather than faster movements of the foot as in modern humans.

Lateral calcaneus of a common chimpanzee (top left); human (top right); Australopithecus sediba (bottom left); A. afarensis (bottom right) (Zipfel et al., 2011).

Summary

• Three separate joints help to produce a complex suite of movements.

• These include movements in the distal foot.

• Bony anatomy can be used to infer soft tissue anatomy and locomotor mode.

Image References

Aiello, L. & Dean, C., 1990. An introduction to human evolutionary anatomy, London: Acade.

Avenue Clinic, 2014. Achilles Problems. St peter Port: Guernsey. Available from: avenueclinic.co.uk. [Accessed: 27/02/2014].

Barnett, C.H. & Napier, J.R., 1953. The rotatory mobility of the fibula in eutherian mammals. Journal of anatomy, 87(1), pp.11–21.

Barraclough, M. 2014. Ask The Trainer. Available from: www.askthetrainer.com. [Accessed: 27/02/2014].

DeSilva, J.M., 2009. Functional morphology of the ankle and the likelihood of climbing in early hominins. Proceedings of the National Academy of Sciences of the United States of America, 106(16), pp.6567–72.

Duke University School of Medicine, 2011. Anatomy Learning Resources. Durham: North Carolina. Available from: https://web.duke.edu. [Accessed: 27/02/2014].

Harcourt-Smith, W., 2002. FORM AND FUNCTION IN THE HOMINOID TARSAL. University College London.

Huei-Ming, C. 2004. The Ankle Complex. College of Medicine, National Taiwan University: Taiwan. Available from: www.pt.ntu.edu.tw. [Accessed: 27/02/2014].

Latimer, B., Ohman, J.C. & Lovejoy, C.O., 1987. Talocrural joint in African hominoids: implications for Australopithecus afarensis. American journal of physical anthropology, 74(2), pp.155–75.

Leland, YT. 2010. MRI Web Clinic – July 2010 High ankle sprains. United Surgical Partners International; PLLC: Addison, Texas. Available from: www.radsource.us. [Accessed: 27/02/2014].

Lewis, O., 1983. The evolutionary emergence and refinement of the mammalian pattern of foot architecture. Journal of anatomy, 137, pp.21–45.

Lewis, O.J., 1980a. The joints of the evolving foot. Part II. The intrinsic joints. Journal of anatomy, 130(Pt 4), pp.833–57.

Lewis, O.J., 1980b. The joints of the evolving foot. Part III. The fossil evidence. Journal of anatomy, 131(Pt 2), pp.275–98.

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skeletal system of theGalago senegalensis. Primates, 12, pp.313–321. Wikimedia Commons, 2014. Retrieved from:

http://upload.wikimedia.org/wikipedia/commons/4/4d/Gray270.png. [Accessed: 27/02/14].

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