Foot Structure and Shims

by Michal Tonetti

In the ideal foot structure for ankle and knee stability, the first and second metatarsal bones (behind the first two toes) are the same length. The heel, ankle, knee, and second toe should line up for all of the muscles to have the appropriate mechanical advantage. When not interfered with by abnormal bones and other twisting forces from above, feet with this structure support the ankle and knee joints without effort. Dr. Brian Rothbart identified the foot structure in which the first metatarsal is short (primus metatarsus supinatus) due to incomplete unwinding of the ankle bone in the gestational period. This creates dangerous ankle (hyperpronation) and knee instability (twisting in while knee bending) which causes tension and postural strain throughout the body. Well over half of us have this instability.

After years of teaching myself to twist my feet for knee stability I was pleased to find the work of Dr Rothbart, the leading researcher in the field of using proprioceptive stimulus under the first metatarsal head, in the Journal of Bodywork and Movement Therapies. A proprioceptive stimulus is a post (shim) that simply stops the downward movement of the first bone to effortlessly synchronize the contraction of the arch support muscles to stabilize the ankle and knee joints before they twist in.

Professor Rothbart was adamant, when I talked with him, that without advanced training or the supervision of someone with advanced training, the risk of too much or too little stimulus and having trouble and a bad experience is too high. If you have the means to work with Dr. Rothbart, it is my opinion that is the surest route to get the results you are after. He has developed software to measure all of the bones and angles and has developed a step by step protocol for his therapy. Dr. Rothbart can be found online and is available for consultation, professional measurement and fitting, and professional training in Rothbart Proprioceptive Therapy.

Here is my take on it. You have to pay attention. If you cannot work with Dr. Rothbart; any health professional should know, or know how to find out, what neutral heels, ankles, and knees looks like. I ordered measuring wedges and premade insoles online at mortonfoot.com; I did ok with the 3.5 millimeter model but I did not like having the stimulus under my big toe so I worked with my shoemaker to customize shorter shims for me. Three millimeter shims under my first metatarsal head works beautifully to allow me to relax my feet without my knees twisting in while I walk, dance, and play hacky-sack. An added benefit has been more foot strength while barefoot as well. The stimulus is used under the forward end of the first bone behind the big toe. The short first bone is normally twisted with the inside edge high (supinated). This means that the stimulus is wedge shaped, thicker on the inside edge and tapering down, so there is no shim under the second bone of the ball of the foot behind the second toe. The shape and strength (height) of the stimulus has to be correct for the foot; too much can actually be dangerous, and too little does not solve the problems. Too much stimulus, too soon can overwhelm the body’s ability to adapt, inflame the foot and misalign the knee. The foot, lower leg, and the whole body above need time to adjust. It can take months to build up the foot and leg strength but the improvements can last for life. I think it is safer to err on the side of too little and you can always add more height later. The diving and sinking movement pattern presented in the video, Making Peace With Gravity will facilitate the process of reshaping the muscular web to support all of the bones in neutral alignment. Start with minutes a day of proprioceptive stimulus (shims under short bones) till you are sure that your body is adapting properly; add more time only when you are sure that you are not hurting yourself. You should be able to really relax your foot muscles while walking and dancing without knee wobble. The proof is in your joint alignment and ability to relax in movement.

I have seen numerous people get more stability using prefab insoles or custom shims; but two friends had a hard time. One needed four or five millimeters but in my inexperience I gave her six mm. Without a careful break in period, too much stimulus too soon made her feet hurt and through her balance off. This happened a couple years ago and she is finally almost open to giving it a try with the correct stimulus and break in period. Another friend put six mm in his work boots with no break in period and when his feet started hurting, he thought that the pain was normal. By the time his feet were very inflamed months later, he took out the insoles; the stimulus “did not work” for him. Now he is changing his walking pattern (eliminating toeing out and heel striking), his feet are healing up and we will give it another try soon.

In order to find the right height for the shim, you need to determine how far off the ground the first bone is when all the joints are neutral. To find neutral put more weight on your left foot to work with the right one. With the ball and heel on the ground and knee bent a little, slowly and gently twist your right knee in and then out a couple times and come to rest with your knee straight over the middle of your foot, aiming down the second toe. When the heel and ankle joints are balanced and neutral, see if the first bone behind the big toe is on the ground. Press down with that bone and see if the knee twists in. If the knee tracks straight, pushing down with the first metatarsal head while relaxing the foot, you are not a candidate for proprioceptive stimulus. If the first bone is short and the knee twists in, place successively taller wedges under that bone till you can press down with the short bone with your knee tracking straight instead of twisting in. Make sure the second bone is on the ground; measure the height of the wedge at the inside edge with the knee and ankle neutral. Say the height of the wedge is ten millimeters or one centimeter; the height of the shim would be about one third the height of the bone with the heel and ankle and knee neutral or three millimeters. A fifteen millimeter deficit will require about a five millimeter shim but I would start with four millimeters and see if that is enough. Use the smallest stimulus you can get away with while still getting results (feet relaxed and knees tracking straight over the feet).