[Muscles of the below-knee amputees]

Abstract

Objective: The objective of this article is to review anatomical, histological and physiological muscle changes following below-knee amputation.

Materials and methods: We searched the PubMed and Reedoc databases for studies evaluating modifications of the below-knee stump and changes over time in its anatomy, volume and histology. We also looked at postamputation modifications in gait and balance.

Results: Below-knee amputees show muscular atrophy on both the amputated side and nonamputated side, with fewer and smaller muscle fibres (particularly slow-twitch fibres). This amyotrophy varies in magnitude and distribution and can reach about 25% for the quadriceps (predominantly on the medial side), but is nonsignificant for the hamstrings. This amyotrophy results from the anatomical consequences of the surgical act. The loss of one or more of a muscle's insertions or reimplantation into a nonphysiological site prompts greater atrophy. Changes in muscle activation patterns also lead to atrophy. The hamstrings replace the triceps as the main muscles for propulsion and the remaining stump muscles contract so as to ensure a good fit with the prosthesis. The below-knee amputee must adapt to a new muscular state: gait symmetry is altered, energy expenditure for walking is higher and training is needed in order to achieve optimal balance control.