Anatomical and Surgical Risk Factors Affecting the Internal Mechanical Conditions in the Transtibial Residuum

Transtibial amputation (TTA) patients face ongoing morphological changes in their residual limb. The residuum volume changes due to weight gain or loss, diurnal edema, and muscle atrophy. Consequently, the TTA prosthetic-user is fitted with a new prosthetic socket approximately every four years. Despite new innovations in socket and liner materials and design, contemporary prosthetics are not yet equipped to confront these changes. The TTA residual limb is therefore subjected to high superficial and internal stresses which may cause injury. Appending the hazardous condition of natural volume change of the residuum is the initial geometrical state of the truncated bones. The primary surgical considerations in TTA are the tibial length, the bevelment of the distal end of the tibia and the location of the surgical scar. These risk factors may significantly affect the well being of the TTA residuum. Previous studies assumed that the criteria for a well-fitted socket were low interface stresses. However, while interface stress measurements may help prevent superficial skin damage, knowledge of the internal stress distribution can prevent the formation of deep tissue injury (DTI) [1]. While superficial pressure ulcers are visually detected, DTI is concealed under the skin and spreads to its surroundings in the soft tissues of the residuum. If this latent wound is ignored, the skin will rupture to reveal a massive injury to skin, fat and muscle tissues, clinically termed as a type IV pressure ulcer. Our purpose was to evaluate the effect of the following risk factors on the internal mechanical condition of the TTA residuum: shorter tibial lengths (thicker muscle flap tissue), milder tibial end bevelments, different mechanical properties of the muscle flap (simulating both variance between patients or flaccid versus contracted muscle) and superficial scarring in inferior and anterior locations on the skin.