Literature Talk 2

Effect of Full-Length Carbon Fiber Insoles on Lower Limb Kinetics in Patients With Midfoot Osteoarthritis. A Pilot Study (Am J Phys Med Rehabil 2018)

Taeim Yi, MD, Jung Hyun Kim, PT, Mooyeon Oh-Park, MD, and Ji Hye Hwang, MD, PhD

Another study on Arthritis and Carbon plated insoles. But this time on midfoot arthritis. It is an important concept to try to get around because of the potential impacts it can have for many patients and also the complexity of managing the pathology. Still research has been pretty mixed on this and there is a growing sense that there is a need for more directed randomized controlled trials on the use of insoles for foot arthritis.

Theory Behind

The goal in reducing pain in the midfoot comes from the reduction of compression of the midfoot joints; namely the Tarso-metatarsal joints and naviculo-cuneiform joints. To break that down even further, we are trying to reduce excessive movements of the joint which would be mainly limiting the dorsiflexion of the joints at toe-off. Some of these excessive movements have been attributed to a hypermobile 1st ray that contributes to the additional compression at the midfoot joints.

The use of the carbon plated insole here does 2 things which is to stabilize the midfoot joints to prevent any excessive movements, presumably to stiffen up the joint and also to help in sagittal plane propulsion, where the insole has a slight rocker and toe-spring to reduce the need for metatarsal dorsiflexion on toe-off.

Pilot Study Critique

There are some things that the study could have shed more light on

1. They did not have a calculation of required study population size to give a clinically relevant outcome.

2. There wasn’t a threshold for a clinical relevant outcome. The statistical tests were focused on finding the significance in difference in VAS.

3. Statistical test felt a little off. It is hard to know whether the test was suited for the data because I was trying to figure out why the authors had to use the Wilcoxon signed-rank test. My only guess is that there were just too few data points for it to confidently be normal in distribution. I would have to look at more EMG and GRF force studies to see what the differences are in statistical analysis.

This made the results hard to really take into account because of the above flaws.

There were also methodological issues that mired the study

1. There was no standardized qualification of midfoot osteoarthritis. They were diagnosed to have midfoot OA through clinical presentation and history rather than with any radiographic justification to it. The classification of mild or moderate midfoot was also based on pain scores rather than through radiographic imaging. Which seemed rather odd as pain is not the most objective of criterias around.
2. There was no effort to introduce any forms of blinding or randomisation.
3. The diagrams were not the best and I had to really try to guess the units of what was being compared. One thing that still confuses me is whether there was a comparison made with mild midfoot OA and controls without the use of the insoles and whether statistical analysis was done. The results seem to point that there was but there was no actual diagram or table to show that they did.

However, I did like the use of the diagrams to showcase the insoles, and the insole description was detailed. Also with the use of standardized footwear.

Results Reported

It was really messy but roughly what the pilot study found was that

1. The use of insoles by healthy controls led to a decrease in the total ground reaction force and significant increase in time under the loading phase
2. This reported reduction of ground reaction force was consistent with the other groups studied
3. The EMG activities of the Gastrocnemius and soleus were also significantly increased during the push off phase with insoles compared with walking without the insoles in the midfoot arthritis group
4. EMG Activity of the tibialis anterior was decreased
5. The VAS score was reduced in the patients who were classified as moderate OA

The patients did not bring it home or use the insoles for a follow up period. It was a single controlled lab experiment.

My thoughts

The paper was a little all over the place with their theories in explaining the results. They did not give a clear explanation of why ground reaction force was reduced. They did try to explain why the EMG activities were increased and attributed it to the concomitant contraction of muscles in midfoot OA patients to increase stability of the foot as compared to healthy controls. However, I doubt whether they have clearly demonstrated this in their statistical analysis. Also, they did not explain why possibly gastrocnemius and soleus were elevated. There was probably an indirect inference being made to explain why the tibialis anterior was reduced and this was because that the tibialis anterior did not need to work as hard as the insole was able to stiffen up the midfoot. The VAS score was then explained by the theory that was put off before.

Well, not a really well done pilot study. I think the thing we can get out of this study was that there is possibly a reduction in symptoms of arthritic midfoot patients with the use of insoles although there is a high risk of bias here due to how the methodology was.

Off the top of my head, a possible explanation why there is a reduction of Ground reaction force from using the insoles might be due to limb stiffness due to contacting a harder surface. Where similar studies in the use of firmer midsoles have seen a decrease in ground reaction force than softer insoles. (Of course there is the problem of force frequencies as presented by Malisoux).

It is possible that the tibialis anterior fires less due to the carbon fiber insole stabilizing the midfoot. However, I am curious how it does not fire more to control the foot when it goes into swing (The study does not include those values)

The increase in the calf complex muscles might be due to the carbon insoles being a disturbance to the calcaneal rocker due to the construct of the insole. The foot has to get past that initial height in the rear of the insole so I would imagine that there could be a concentric increase to get past that portion of the insole to capitalize on the forefoot rocker.

Conclusion

This made my head hurt but I’ll have to look for more of such studies and also understand the biomechanics and muscle activities of patients with midfoot OA.