DOUBLE WALL BELOW KNEE PROSTHESIS WITH REMOVABLE KNEE BRACE

Mei Fong, PT; Jon Allen,CP(c); Alberta Children's Hospital, Alberta Artificial Limb, Calgary, Alberta, Canada


The patient is a highly active, demanding 15-year-old boy with a heavy build. He has congenital partial absence of the tibia and fibula bilaterally. This has left him with very short below knee type residual limbs with knee instability.

Fitting problems

Figure 1

Over the past four years, he has had recurring pain on his left tibial tubercle and right prepatellar bursa areas. Upon examination, these areas are very tender to touch and heavily calloused. Due to discomfort in and frequent breakdown of his previous prostheses and liners he has not been wearing any prostheses and instead has been relying on his wheelchair and walking on his knees. The latter only serves to further aggravate his knees, which were inflamed and make prosthetic fitting increasingly difficult.

The patient needed prostheses with all of the following characteristics:

  1. A socket designed to remove specific weight bearing on the patellar tendon area
  2. A comfortable form of knee stabilization
  3. Good suspension that will still distribute the forces over the entire limb
  4. The prostheses needed to be strong, durable and light

 

Figure 2

Until now the best answer to this system has been below knee specific weight-bearing sockets with exoskeletal finishes and incorporated thigh lacer. The suspension of these was with thermoplasticelastomer (TPE) style liner systems with pin attachment.

Creative solution

Figure 3

A total surface bearing socket design with liner technology was developed, which helps to unload the socket and distributes some of the forces to the thigh, much like a thigh corset. Consequently the same degree of pressure is exerted on soft tissues and bony regions over a larger area, above and below the knee joint.

The double wall socket design, originally designed by Tec Interface Systems, allows the wearer to use a cushion liner with a suction sleeve and socket. This provides positive suspension while limiting force transmission to the residual limb. The suction socket then fits into an external socket, and is secured in place by using a clutch lock mechanism. The addition of a removable knee brace to the double wall below knee prosthesis, provides an element of stability to the wearer's knee joint, as well as a means to absorb forces and pressure, that would normally be transferred directly to the amputee's residual limb. Since the knee brace is easily removable by the amputee, it can be worn only when needed and is easily replaced if damaged.

Figure 4

Figure 5

Results

Since he received this type of prostheses, his pain on the right pre patellar bursa and the left tibial tubercle has resolved with reduction in callous buildup He is back on his feet and resumed his active routines.

Please direct correspondence to Mei Fong.