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Constraint and Nonconstraint of Foot and Lower Extremity Joints

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Jan 31, 2015.

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    One of the ideas not much discussed regarding joint motion in the foot and lower extremity is the idea of joint constraint. Antony Huson (see illustration below) has previously discussed the constraint and non-constraint mechanisms of the foot in his classic chapter "Functional Anatomy of the Foot":

    Huson was not the first to discuss the concepts of joint "constraint" and "nonconstraint". Many previous scientific articles on joint implant design use the terms "constrained", "nonconstrained" and "unconstrained" to describe the mechanical characteristics of joint implant design. When a joint implant is "constrained", it is designed to move along a relatively stationary axis of motion regardless of the direction of the external force acting across that joint. When a joint implant is "unconstrained", it is designed to move along multiple axes of motion giving it some freedom to "wobble" (i.e. rotate and translate in different planes) which will depend on the magnitude and direction of the external force acting across the joint. I believe that the way forward for us to better understand the biomechanics of the foot and lower extremity is to better appreciate the concepts of "joint constraint".

    No joint functions along a single, solitary axis of motion like a set of door hinges. All joints of the human body will rotate across multiple axes of motion, with some joints being more "constrained" by their internal structures (i.e. ligaments, articular surfaces) which "guide" the joint through a range of motion along a relatively stable bundle of axes of motion, while other joints being "unconstrained", allowing motion in multiple body planes along widely varying axes of motion that are dependent largely on the magnitude, direction and point of application of external loading forces acting on the foot and the internal loading forces from the ligaments, tendons and muscles acting on the foot.

    For example, which of these foot joints is most constrained?

    Ankle joint
    Subtalar joint
    Talo-navicular joint
    Calcaneo-cuboid joint

    My guess is that the order from most constrained joint to least constrained joint is as follows:

    Most Constrained
    Subtalar joint
    Ankle joint
    Calcaneo-cuboid joint
    Talo-navicular joint
    Least Constrained

    In other words, when an external loading force is applied from any direction across any of the above joints, which of these joints will tend to move along the least widely divergent bundle of joint axes? The subtalar joint is by far the most tightly constrained due to its tight bundle of ligaments within the sinus tarsi and the talo-navicular joint, with its "ball and socket" design, is likely the least constrained of these joints since it will basically allow rotation about nearly any axis of motion which is dependent on the external forces acting on the foot and the internal forces from the extrinsic and intrinsic muscles of the foot.

    Unfortunately, these considerations are rarely mentioned within the foot and lower extremity biomechanics literature. However, these are important central concepts that will allow us all to better understand the kinematics and kinetics of the foot and lower extremity.
  2. I'd have the calcaneocuboid ahead of the ankle in terms of constraint. There's a lot of slop in that ankle mortice.
  3. I did have problems with ordering of the CCJ and ankle joint. I guess total range of motion plays in as a factor here with the ankle joint having the larger range of motion than the CCJ but with the CCJ having a smaller range of motion but without the gliding constrained motion of the ankle joint. Something new and interesting to think about...I like that!:drinks
  4. dottiekat

    dottiekat Member

    Student pod so I'm very basic on my knowledge
    If STJ is surrounded by ligaments, held in a ball and socket type structure and influenced by external forces which have the power to pronated and supinate the structure is it not more un-constrained?
    apols for my inferior question :-/
  5. Dottiekat:

    As a student, you would get more replies to your request if you provided us your name and where you are studying podiatry.

    In answer to your question, the subtalar joint (STJ) it not a "ball and socket" type joint, such as the shoulder or hip joint. Rather the STJ, due to its very strong and short internal ligaments located deep within the sinus tarsi area, allow the talus and calcaneus to rotate relative to each other along a fairly narrowly defined axis (i.e. STJ axis). These short and strong ligaments include the cervical ligament, which is the strongest ligament of the talo-calcaneal joint, and the interosseous talo-calcaneal ligament. Other smaller ligaments also make contributions to STJ stability within the sinus tarsi. Therefore, because of these tight, strong ligaments within the sinus tarsi and the complex joint shapes of the articular facets of the talo-calcaneal joint, the STJ is probably the most tightly constrained joint of the human lower extremity.

    Now, let's talk more about constrained and nonconstrained joints. As an example of a constrained axis of rotation, get up, find and inspect the nearest door, which generally will have three hinges oriented with a vertical axis which allows the door to open and close along this vertical axis. Now, press on this door with your hand from a multitude of directions. What happens? Does the door ever rotate about any axis other than the vertical axis which is defined by the three door hinges? No. These door hinges are an example of very tightly constrained axis of rotation since, regardless of the direction of the external force acting on the door, motion of the door will occur basically about a single axis of rotation.

    Now, for another example, go ahead and sit back down and with your left hand, push on your relaxed right hand in a multitude of directions (i.e. from medial, from lateral, from palmar and from volar) to cause motion about your right wrist joint. What happens? Does the wrist joint move about just one axis of rotation, or does it instead move around a multitude of axes of rotation, with the location and direction of the axis of rotation being dependent on the direction of the external force from your other hand?

    The wrist joint is an example of a relatively nonconstrained (unconstrained) joint where the direction of external force application will cause a large change in the location and direction of the joint axis that occurs. [Remember, motion or two objects relative to each other determines their axis of rotation. Joint axes are not fixed in space and do not necessarily determine how motion will occur about any joint.] The midtarsal joint of the foot is a relatively nonconstrained joint, especially when compared to the STJ, with the ankle joint being relatively intermediate in level of constraint between the STJ and ankle joint.

    Hope this helps with your question about joint constraint and nonconstraint:drinks
  6. dottiekat

    dottiekat Member

    Thanks Kevin

    I'm studying Podiatry at University of East London - I'm second year and we just started doing more indepth biomechanics this year.

    I've just joined the site so apols for my poor etiquette.

    Regards Katrina
  7. efuller

    efuller MVP

    In addition to Kevin's excellent answer: A good read is Cahil DR. The Anatomy and Function of the Contents of the Human Tarsal Sinus and Canal. Anat. Rec. 153 p1-18. 1965. This paper describes how the posterior facet and anterior and middle facets of the talocalcaneal joint can "constrain" motion around a single axis. (To be more precise a bundle of axes) It also describes the ligaments quite well.

    Then there is Ganley's two unit tarsus concept: There is the talus and the rest of the foot and the rest of the foot deforms around the talus. Those words helped me when I was a student.

    The two unit tarsus cocept is also interesting when talking about constrained motion. Motion at the STJ may necessarily cause motion of the CC and TN joints. When I first saw the title of the thread, and the mention of Huson, I thought the discussion was going to go in that direction.

  8. efuller

    efuller MVP

    Actually there is a lot of slop in the talocalcaneal joint. We just don't have a stress inversion x-ray to see that is there.
    J Orthop Res. 1988;6(5):749-57.
    Predicting talocalcaneal joint orientations from talocalcaneal/talocrural joint orientations.
    Engsberg JR1, Grimston SK, Wackwitz JH.

    I read that over 20 years ago, so I hope that's the correct site. That paper was discussed in Winter's paper on determining the STJ axis with motion analysis tools. Winter said that when the joint is loaded, it will have a fixed axis. However, if you grab a calcaneus and move it relative to a talus, you will get some slop because those ligaments will stretch. So, in our discussion of constraint of motion we have to consider how the compression of gravity and ground reaction force will increase the input force needed to cause some motions that would be easily found in an unloaded foot.

  9. No worries, Katrina. Good luck with your studies. I'll be taking a short vacation in London (what a great city!) with my lovely wife this June, before I lecture in Manchester for the 2015 Biomechanics Summer School. It's very smart of you to come onto this site and pick our brains. I just wish I had Podiatry Arena when I was a podiatry student.:drinks
  10. Good point, Eric. It is likely that the midtarsal joint is also much more constrained when the plantar foot is loaded by ground reaction force
  11. efuller

    efuller MVP

    I was thinking there would be much more constraint in the ankle and STJ when weight bearing as the joint surfaces would be compressed together. In the midtarsal joint, when weight bearing, the forces are tending to cause the joint surfaces to separate. When the joint surfaces are compressed together it will be harder to get motion of one side of the joint surface, while the other side stays in contact. For example the a-p view of the ankle with a stress lateral x-ray. One side of the joint is separated and the other side of the joint is still in contact. To have this happen weight bearing, the foot has to be inverted enough that the center of pressure from ground reaction force is quite far medial relative to the center of pressure of the tibia talus joint. When that happens, there will be a large inversion moment at the ankle joint.

  12. Trevor Prior

    Trevor Prior Active Member

    When I did my post grad degree back in the 80's, Huson was well referred to, in particular his work on ligament direction guiding motion and joint axes. I agree with all that has been written previously but suspect the degree of constraint / non constraint between the respective joints probably varies between individuals. Thus, if we took the ankle and CCJ, in some it may be the CCJ and others the AKJ.

    I have a great video of someone who has had an STJ fusion yet the rearfoot has relatively good inversion eversion due to motion at the ankle. I have seen a few STJ fusions over the years and generally, the rearfoot motion is very restricted. This particular patient commented that he had expected to experience more stiffness than he had and is a good example of the variation we see and what makes analysing and managing foot function so complex.
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