Category: Biomechanics

by Richard Blake DPM MS

A Review

Most biomechanics texts are very dense. They are filled with theory, formulas, definitions and diagrams. They often have little to directly link them to patient diagnosis and care. This book is different. Practical Biomechanics is as it says, “practical” and straight forward. It is not dependent on long discussions of joint axes or theory. In fact, I’d call it theory agnostic.

But what it does is give you insight into the thinking of someone who has mastered clinical biomechanics. Dr. Blake gives advice on how to approach the injured patient, what factors to look at, and how he approaches problems. He discusses “Occam’s razor” and the “rule of three”. Occam’s razor is a manner of looking for the simplest explanation for what is causing a problem. And the rule of three is Dr. Blake’s idea that there are often more than one factor that needs to be looked at in determining what led to a specific problem.

The book is written with a conversational tone. It has been said that a book is a conversation between the author and the reader. But that is not often said about a book on biomechanics. Perhaps years back, Galileo attempted to model a dialogue while reviewing models, in his “Dialogue Concerning the Two Chief World Systems”. Dr. Blake’s book is easier to follow and there are no arguments about what model to follow.

The book reviews much straight forward thinking. It talks to you and then poses questions. The questions are an important part of the book. Most are not quite standard knowledge. But the answers to the questions and explanations are at the end of the text. They add to your learning how Dr. Blake thinks about the analysis and treatment of the patient.

This is the first book in what is conceived as a four part series. The second book is expected in the fall. The others will follow. If you are a student or a practitioner, this is a book you’ll want to read. It is not a self-help book.

A two part interview was recently conducted over Zoom. I participated in the second part of the interview:

Richard Blake in conversation with Ben Pearl and Steve Pribut

And the first part of the interview was conducted by Ben Pearl of Fit Foot U:

Richard Blake interviewed by Ben Pearl

Special Topic: Orthotic Modifications for Over Supinated Feet

In most cases I am not designing a foot to correct a “foot type” but to provide a solution for a specific clinical problem. While having a high arched, over supinated, under pronated foot may predispose to certain problems other “foot types” can have many of the same problems.

Some problems that can occur and are related to supination movements (or even “moments”) include:

•  chronic and repeated ankle sprains
•  peroneus brevis tendinopathy
•  peroneus longus tendinopathy
•  cuboid stress fractures
• 4th and 5th metatarsal stress fractures
• 5th metatarsal base or midshaft fractures
• lateral leg pain (peroneal muscle group)

In many instances with problems like these, immobilization may be necessary for a time. Wobble board training should be incorporated into rehabilitative programs. The purpose of the wobble board training is to have the neuromuscular system adapt the peroneal muscles to performing repetitive firing for stabilization. The angles that the wobble board makes with the ground and the motion and angular relationships that it engenders in your ankle and leg are ideal to training the peroneals to fire appropriately.

The wobble board assists in training muscle strength, balance, and improving joint position sense. There is nothing that beats this 3 in 1 training.

For patients who do not have a dramatic Pes Cavus foot there are a few specific corrections I include in the orthotic:

• Accurate cast of the foot.
  I do not want a 2D pressure scan. I want to hold the foot in neutral subtalar joint position. And I want to plantar flex the first ray by either light dorsal pressure over the first metatarsal or by slight dorsiflexion of the great toe during the casting.
• Minimal cast correction.
  I want the cast to reflect the shape of the foot to mirror it so that when I want to alter forces, they will be altered by the shape and adjustments to the orthotic. I want the forces distributed through a large surface area and need conformity between the shape of the foot and the shape of the orthotic.
• No lateral bevel.
  This resists over supination directly. It is like an outrigger on a boat. It also changes moments of force going into the foot.
• 3 degree lateral forefoot wedge.
  This is often used to prevent over supination of the foot after the heel as left the ground or as weight is transferred towards the forefoot.

These are often my starting steps to deal with the problems listed above when they are resistent to treatment.

For a Pes Cavus, high arched, over supinated foot podiatrist Richard Blake, DPM has put a great video on line. It details his 8 steps to deal with this foot type using specially customized orthotics. The modifications made for this problem are not found in over the counter orthotics. And many specialists do not see enough patients with high arches to be adept at treating the problems associated with this foot type. It is important to find a physician that has experience with sports medicine, high arch feet, and biomechanics.
The Blake 8 Steps (only slightly modified) follow:

First an accurate cast is required as described above.

A) Rounding of the lateral border of the cast or via CAD/CAM to have the orthotic better grip the foot.
B) Lateral Kirby Skive. Often 2 to 4 mm.
C) Deep Heel Cup – up to 25 mm.
D) Extended lateral heel cup or “lateral flange”
E) Eliminate “medial heel grind off” and/or add No Lateral Bevel in rearfoot posting instructions.
F) Lateral arch fill to add more surface contact area
G) Narrower orthotic (sometimes) to limit any antipronatory forces. (note: some will go for wide or nomal width for increased stability and contact)
H) Forefoot modifications such as lateral wedge

Dr. Blake reviews these modifications in a 9 minute video on YouTube: https://www.youtube.com/watch?v=hMhrTmWXfDA

This video is well worth watching for anyone who needs the modifications or anyone who is planning to incorporate them into a patient’s orthotics.

Note: Images Courtesy of ProLab Orthotics

High Arches can make you feel like you are heading for your own personal apocalypse. Turn it down and listen to Arch Enemy with some heavy metal:

Or if you feel like stepping out, you can go retro with John Mayall’s Bluesbreakers:

The current issue of Medicine and Science in Sports and Exercise (MSSE) has a study which indicates that the frontal plane force vector of the limb is directed more medially (toward the midline of the body) in those who have sufferred tibail stress fractures. The magnitude of forces in the control group were the same as those in the group that had sufferred injury. The conclusion of the authors was that the direction of the forces may be a contributor in the development of tibial stress fractures. This add a specific biomechanical risk factor for tibial stress fractures.

Within a narrow to medium range of normal this may be very significant. At greater deviations from normal, such as with severe genu valgum or varum (knock kneed or bow legged), my guess is that the forces will be too far away from the affected area to matter. So one day another study, with more extremes will have a different result than the current one. Study design and sample populations play a large role in study results.

Studies have already demonstrated the efficacy of the Pneumatic Walker in aiding and speeding healing of tibial stress fractures. Excessive pronation plays a role in overload of the medial muscles of the leg and also will shift the force vectors medially. Well designed custom foot orthotics should effectively shift the vector laterally and could be useful in preventing recurrence. No one factor alone though should be considered enough. Bone density, calcium and Vitamin D needs, and training must be evaluated.

Already, the warnings are in for avoiding too much, too soon and to allow your body, and your bones to adapt to the stresses you want to place them under. Increase your training slowly, gradually, and carefully and make certain to drop back every 2-3 weeks while increasing the training volume (and load).

References:

External Frontal Plane Loads May Be Associated with Tibial Stress Fracture.
Medicine & Science in Sports & Exercise. 40(9):1669-1674, September 2008.
CREABY, MARK W. 1,2; DIXON, SHARON J. 2

Clinical Biomechanics  Volume 19, Issue 1, January 2004, Pages 71-77
The role of selected extrinsic foot muscles during running
Kristian M. O’Connor and Joseph Hamill

Effect of Inverted Orthoses on Lower-Extremity Mechanics in Runners.
Medicine & Science in Sports & Exercise. 35(12):2060-2068, December 2003.
WILLIAMS , DORSEY S. III 1; MCCLAY DAVIS, IRENE 2 3; BAITCH, STEPHEN P. 4