Is Hypermobility Limited To Just The First Ray?

In my last two blog posts, I discussed twisted plate orthotics. This is an orthotic theory and technique that surprisingly few podiatrists seem to use or be aware of. The primary reason I use a twisted plate orthosis is to address dorsal flexibility (hypermobility for those who prefer the term) of the fifth ray. Accordingly, I would like to discuss a simple way to evaluate the fifth ray to determine if there is flexibility one needs to address by utilizing a twisted plate modification or a lateral forefoot wedge modification.

In 2013, Bates and colleagues discussed the assumption that the lateral column of human feet evolved to be relatively stiff in comparison to that of apes.¹ Employing pressure mapping, the authors said the idea of a difference in stiffness between humans and apes at the lateral column is false. While the researchers did find plenty of humans with relatively stiff or essentially inflexible lateral columns of their feet, they also noted that many humans had very movable and much more flexible lateral columns than originally thought. The researchers also found that there are many species of apes that have significantly more stiff lateral columns that are much more in common with humans.¹

Other work done by Nester, Lundberg and their respective teams showed there is approximately double the amount of motion between the fourth and fifth metatarsals and the cuboid as there is between the first metatarsal and the medial cuneiform.^2,3 In regard to the measure of comparison between the medial and lateral columns, Nester and colleagues wrote that there is about one-third greater motion of the medial column, from the talus to the first metatarsal, as there is of the lateral column, from the calcaneus to the fourth and fifth metatarsals.²

The takeaway from these articles is that we as lower extremity specialists need to realize that many of our patients have quite a bit of flexibility built into the lateral columns of their feet. The only way to know who has this flexibility and how much is to evaluate the motion that may or may not be there.

In the picture above, you can see the fifth ray (yellow line), which is about three to four mm above the level of the third metatarsal head (red line). Nester states that the fourth and fifth metatarsals tend to move as a unit as do the first through third metatarsals.² I disagree with him on that latter point in that I find that the first ray tends to move significantly more dorsally and somewhat plantarly in comparison to the second ray. 

Regardless, the point I wish to make is that in general, the second and third metatarsals are almost always stable in comparison to the first, fourth and fifth metatarsals. Therefore, you can compare dorsal motion of the fifth ray to the third metatarsal and the first ray dorsal motion to the second metatarsal.  

To compare and measure the amount of difference in the dorsal motion (or dorsal excursion) of the fifth ray, you can put your right thumb under the third MPJ and your left thumb (as shown in the picture) under the fifth MPJ. Then as you dorsiflex the fifth ray to resistance, you can make a comparison of the distance between your two thumbs in millimeters. Keep in mind that one should keep the foot in subtalar joint (STJ) neutral throughout this measurement.

At this point, you now have an idea of how much actual dorsal motion or excursion the lateral column has available during gait. The importance of this is that in many feet, if the lateral excursion is high, say higher than three mm, this can keep the foot from resupinating in a timely manner in late midstance and into propulsion. The increased excursion of the lateral column allows the foot to stay pronated as the foot enters propulsion and delays the ability of the foot to resupinate.

To combat an issue like this, you can add a forefoot wedge under the fifth ray. That will eat up the available dorsal excursion range of motion and allow the foot to move its center of force in a much more timely manner from the lateral aspect toward the first MPJ, helping to resupinate the foot during late midstance and into propulsion. I know that some practitioners prefer to add a pad or wedge under the cuboid to combat issues like I have described here. That is, of course, not unreasonable but in my experience, using a wedge under the more distal aspect of the lateral column has a more pronounced effect as I have examined the use of both modifications with the use of in-shoe pressure.

Finally, I usually find that the measure of this dorsal excursion of the fifth ray is often the exact amount needed in millimeters to wedge the lateral column in most of my orthotic prescriptions. I have also found that patients with zero to two mm of dorsal excursion often do not need any valgus wedging at all. Additionally, those with zero mm of dorsal excursion or less should probably never have a wedge modification to their orthotic devices. In fact, I see a lot of high-level athletes with previous fifth metatarsal fractures who have minimal to no motion in their fifth ray. These athletes are at risk of reinjury if we do not offload this area of the lateral column or drastically decrease the stiffness of their orthotic device.

In conclusion, we really need to measure the lateral column for dorsal excursion. In my opinion, this is a key factor in optimizing the timing of the proper effect of custom foot orthotics for our patients. Hopefully, you will consider utilizing this technique yourself. If you have questions, please let me know.

Dr. Williams is a Past President and Fellow of the American Academy of Podiatric Sports Medicine. He is the Director of Breakthrough Sports Performance, LLC in Chicago. Dr. Williams has disclosed that is the Medical Director for Go 4-D and a consultant for HP FitStation.

References

1. Bates KT, Collins D, Savage R, et al. The evolution of compliance in the human lateral mid-foot. Proc R Soc B. 2013;280(1769):20131818.
2. Nester CJ, Liu AM, Ward E, et al. In vitro study of foot kinematics using a dynamic walking cadaver model. J Biomech. 2007;40(9):1927–1937. 
3. Lundgren P, Nester C, Liu A, et al. Invasive in vivo measurement of rear-, mid- and forefoot motion during walking. Gait Posture. 2008;28(1):93–100.