[AMP-L] Transtibial Bursas and Socket Interface

[Wayne Renardson]

>From Mr. Donnie Priest via OANDP-L with permission:

Dear Todd, Justin, et al.

IDEAS ON THE BURSA

I should start by saying that I am not a doctor and have no desire to be.
However, I would like to put my two cents worth to foster some
discussion about bursas and the amputee.  However, I am an amputee and
prosthetist, and have a structural/functionalist logical style.

I have had three bursas. Each time they were the symptom that
highlighted a bone spur (I was a growing child).  I was able to have
modifications done to the prosthesis to accommodate the bursa, but
ultimately had surgeries (after x-rays) to remove the bone spurs. However,
not every bursa is a sign of a bone spur…but it was in my case.

In light of recent posts I would like to point out that the prosthetic 
socket interface with regard to the residual limb should be considered 
more of a fibrous joint than a solid, non-moving interface. In the 
BKamputee during knee contraction, the gastroc-soleus complex 
compresses and the tibia/fibula move posterior in the socket.  This can 
be seen in a plastic check socket, and a gap may form at the anterior 
tibia in many socket situations.  In the AK amputee the need for 
posting of the femur demonstrates the femur also moves posteriorly as 
the hamstring muscle group compresses. Thus, due to the movement of the 
bones inside the socket, the socket to residual limb interface should 
be considered to have characteristics similar to a fibrous joint.  

With this movement a shear force occurs, and the skin adheres by friction to
the socket interface as the bone moves in comparison to the
surrounding muscle tissue.  It appears from the recent posts and my very
limited research that a bursa will form as the body’s mechanism to limit
the friction with regard to shear forces. Thus not only the amount of
movement is important, but also the friction of the interface materials and
the load carried through the area. Specifically, for a bursa on the distal
tibia, the greater the end bearing, the higher the friction becomes.

Further, certain socket types allow for a lower frictional resistance 
with regard to the deformation of the soft tissues and movement of the 
bones inside the socket. From my personal experience (although more 
research is necessary in this area) I believe that a locking gel liner 
increases the friction of the residual limb with regard to its ability 
to deform under amputee pathologic gait. However there is also a 
benefit to this, such as a longer lever arm, and less movement inside 
the socket. Every amputee is different, and one needs to evaluate the 
person to determine what system is best for their lifestyle.  

Further, the internal characteristics likely play a major role in the 
formation of bursas. I would appreciate a trained medical doctor to 
elaborate on this.  I am under the impression that a nicely beveled 
bone allows for and easier movement through the soft tissues since the 
soft tissues deform during ambulation. I also believe the healing 
process after the surgery varies from person to person and thus the 
smoothness of the cut bones will vary. I had an excellent surgeon and I 
obtained my bursas many years after my surgery but attributed that to 
growth since I was an adolescent at the time of my amputation. I also 
do not know how the body heals after an amputation and if the loading 
effects of end-bearing (total contact) walking can re-stimulate bone 
formation.  

>From my limited reseach, life, and prosthetic experience, the bursa 
formation is a compounding issue. In order to limit the friction, the 
body creates more fluid (volume).  However, by creating more volume in 
a confined area (the prosthetic socket), the friction is increased (not 
decreased). Thus, with more friction, the body creates a bigger bursa 
and it often cannot heal because the cause is not fixed. In order to 
fix the cause, the friction and shear need to be limited. This can be 
done both prosthetically, surgically, chemically, by changing one’s 
lifestyle (walking), and likely in other ways I am forgetting.  

Prosthetically, I would suggest the person see their prosthetist to 
limit the shear or frictional force by socket shape, interface type, 
suspension type, or loading characteristics.  I am not a doctor, so I 
would refer the person to a doctor about internal and chemical changes. 
As to ones lifestyle, that is for the person to decide given full 
knowledge of the situation.   

This is my two cents worth about bursas.  I hope that it fosters 
discussion and leads to a better understanding of both the socket 
interface and the physiology as to why a bursa may occur.  I would 
appreciate any opinions, especially to the concept that a prosthetic 
socket to residual limb interface should be considered a joint rather 
than a rigid body.  

Ideally one wants a rigid body for weight transfer, and a movable joint 
for shock absorption…with the individual balance achieved based upon 
the characteristics of the person using the prosthetic and his or her 
lifestyle and basis for happiness.  

Sincerely,

Donnie Priest
<donniepriest at HOTMAIL.COM>