What is the maximum knee flexion contracture that can be accommodated with a traditional transtibial PTB socket?

The traditional patellar tendon-bearing (PTB) socket design for transtibial prostheses generally accommodates a maximum knee flexion contracture of approximately 25 degrees. This limitation is primarily due to the structural and functional considerations of the PTB socket. When the contracture exceeds this threshold, it can significantly affect the alignment and function of the prosthesis, including loading on the residual limb and the user's gait mechanics.

The PTB socket is shaped to provide support to the patellar tendon while ensuring that the limb is well-distributed under load. As the knee flexion contracture increases beyond 25 degrees, it becomes increasingly challenging to maintain proper alignment and functionality. Beyond this point, adjustments in the socket design or prosthetic alignments would be necessary to accommodate the altered biomechanics effectively. Thus, the design of the PTB socket is optimized for contractures up to 25 degrees, making this the maximum recognized limit in traditional applications.