Thursday, May 31, 2012

Effects of Load-Bearing in Cerebral Palsy: Bones

The intent of this post is two-fold: 1) to discuss and explore a very relevant, critical, yet controversial subject of dicussion within Cerebral Palsy (CP) (and other disorders of movement and posture)...2) to link previous posts together with this one to shape a formulate the overall narrative. As always, my overall intention is not to discredit any particular school of thought, strategy, or central philosophy...rather to bring the realities of the mechanical challenegs (and consequences) that accompany CP to the forefront so that specific, goal-oriented strategies can be formulated. It should be clear that these strategies are case specific and therefore need to be evaluated with it´s own set of standards.

This first installment will focus on the direct effect of load-bearing (weight-bearing) on the bones. However, before any in-depth discussion begins, I should define what load-bearing means within the context of this post. To be very specific, load bearing is: exposing an architectural system to structural load or stress. Therefore, in the human organism this is very clearly achived in either a seated or standing position.

The benefits of load bearing or weight bearing in the healthy person are quite obvious and straightforward...the ground force reaction promotes to development of growing bones and contributes to the development of healthy bone density. Although this is very true, the fundamental mistake that is quite often made is that this statement is imported to the CP community. Why is this a mistake? This statement assumes that the transmission of ground force reaction is efficient and therefore travels to the relevant load bearing structures throughout the disorders of movement and posture (CP, for example), force transmission is extremely disrupted and inefficient. This disruption leads to improper stress distribution, accessory and compensatory activation of skeletal muscle, overuse and fatigue syndromes, as well as structural deterioration. To be very clear: mechanical forces in the CP individual DO NOT travel in a manner that facilitates healthy growth and development.

I doubt any responsible professional would debate this fact...however, a fundamental question is therefore raised: if this is an understandable fact, why is there such a rush to implement "standing" protocols? This is a glaring contradiction that generally goes unseen, but certainly exists...and therefore needs to be addressed.

In order to address this delicate topic intelligently and responsibly, we need to dissect the effects of load bearing into some fundamental component parts: the effect on the bony skeleton itself and the effect on the soft tissue. The effects on the system as a whole are actually greater than the sum of the component parts, but far more complex...therefore a basic understanding of the component parts should give some clarity on the potential "biomechanical tax" that is paid when weight bearing is aggressively promoted.

MECHANOTRANSDUCTION IN BONES: If the term Mechanotransduction is new to you, i would refer you to my previous post titled "Mechanotransduction: Response to Manual Therapy". However, to summarize the concept, it is the cellular response to mechanical forces or loads. The precise mechanism in which bones sense mechanical stimulii is still largely being researched, however the concept of cellular mechanotransduction in the bones is widely accepted as a likely mechanism. With respect to the skeleton, there is an integration of the understanding of the connective tissue memebrane of the bone (periosteum), cellular tensegrity, and the effects of mechanotransduction on the nucleus of the osteoblast. Effectively, mechanical stress and deformation that is load-induced activates a change in the genetic program of the bone (gene transcription). Mechanical information is relayed from the bone to the gene by a succession of long-term deformation and changes in conformation. If the stresses applied to the bone are not distributed properly, skeletal growth and absorption are disrupted...which leads to eventual bony deformation and therefore impaired function.

Although this is a common understanding in the field of cellular biochemistry, it doesnt seem to reach the professional "masses" to be applied responsibly in rehabilitative protocols. Given this knowledge, it becomes clear that consistent, intensive, and aggressive strategies geared towards standing protocols (standers, for example) is potentially costly when you consider the "biomechanical tax" to be paid in the long-term. Although bony misalignment is a reality in the CP individual, load bearing and exposing an altered structural "scaffold" to loads exacerbates the deterioration of structural integrity.

Although significant, this is only part of the overall perspective. The effects of load bearing with respect to the soft-tissue will be the subject of the second load-bearing post. Hopefully both or either will stimulate some analytical thought on the subject and consequenty result in more informed and effective strategies.



  1. Thanks for making load bearing easier to understand...this concept is one which I intuitively believed. PT's were anxious to get Adam in a stander right after his near drown. A collapsed core, weakened myofascia and an hour plus upright in a stander equals scoliosis thanks to the effects of gravity's downward pull...just so much common sense that evades people.

  2. This is very timely for us and great information. Just recently, I have notice that Mitchell's feet/ankles are very pronated and his arches in his feet are gone. This is leading to sores on his bony projections when he wears shoes. I also learned that he is standing more in the prone stander to participate fully in class. I have to resort to getting him AFOs to prevent any more damage. So weight bearing may not be the best for him.

  3. Excellent post. Thank you. I appreciate the clarity and organization of thought. It certainly makes the subject of weight-bearing in relation to bone development easier to digest and further solidifies our decision to postpone weight bearing until Emma's structure is restored. It also gives me the tools I need to discuss this topic more intelligently with therapists and other professionals. Thanks again.

  4. Gavin, what a great post, we'll I couldn't agree with you more, but we ended up having a trade off. Oatie was becoming agoraphobic, afraid of people, becoming more antisocial and just plain afraid of anything outside the home from being in his wheels, whereas before this happened he would be the one to be the life and soul of a party. His immaturity gap Vs his age was increasing greatly too as he didn't have any independence at all either.

    So we gave into the walker, which has turned his world right around, it also gave him the confidence to ride his new adaptive bike where as if he was afraid of the outside he wouldn't do that either.

    In his Walker, he tends to "toe walk" which he doesn't do if he walks unaided... so we make him walk slower so he walks as you or I would. So we limit his use of the Walker and always have a pair of wheels handy lol! But he's back to being a super sociable jolly soul again, so we just keep on Machining him and rolling him as much as possible.

    1. Greetings! Thanks so much for your comment! I always welcome any and every form of comment / critique...mainly because it stimulates intelligent debate on important issues. I should mention that I agree with your strategy 100%. My post typically consider the mechanical aspects purely...however the SOCIAL AND COGNITIVE components are just as important. The unfortunate reality is that walkers are aggresively used exclusively for the physical ¨rehabiliation¨ of the child...which has definite mechanical consequences if used improperly. However, using them to contribute to a childs social and cognitive development is an excellent rationale...and one that I completely agree with! It isnt the ¨tool¨ per se, rather the intent (or intended outcome) that needs to be considered. Therefore, your particular rationale, thought process, and strategy is absolutely great! I really like to hear stories like this. Very, very good sounds like you have some great perspective on the big picture! Thanks again for reading and I hope you continue to keep reading. If you think it would help, please recommend the blog to others as well. All the best! -Gavin-

  5. I'm not sure what-weight bearing exercizes are. Could someone provide a link to a video or diagram showing what it entails? Thank you.

    1. Greetings Alex. Weight bearing exercises are quite simply activities that involve mechanical loading of the person onto the feet / legs. To be precise, within the context of this CP related post, weight-bearing is the use of standers, standing frames, and extends into the use of orthopedic braces to facilitate weight-bearing exercises. To put it simply, it is the act of standing a person with CP (and other disorders of movement) with the intention of contributing to some potential improvement in walking performance. If you Google "standers" or "standing frame" you will get quite alot of images and examples. The main message is not to "demonize" these tools...rather to highlight the "biomechanical tax" that is incurred when they are implemented. It is a far better situation to know and understand all of the "hidden taxes" involved as opposed to getting an unexpected surprise later on down the road. Further, the concept of load-bearing isnt restricted to refers to load-bearing in any form. People who are mildly affected (and therefore are mobile and ambulatory) will experience the same phenomenon...but to a lesser extent. Therefore, load-bearing (or weight-bearing) is a characteristic in comes in many forms.

      I hope this has proved helpful....and please feel free to communicate more if you have any other questions or require any further enhancement!