Medical devices and/or lead extensions having fixation structures with retained portions providing medical lead fixation

A medical system, comprising:

• a medical device having a stimulation circuit and a header block, the header block having a bore with an engagement surface and a plurality of electrical connectors within the bore that are electrically coupled to the stimulation circuit;
• the medical device further comprising:
• a fixation structure mechanically engaged with the engagement surface of the header block, the fixation structure including a grip portion and a deformable portion that is retained by the grip portion and is constrained by the header block, the deformable portion providing a compression force in a radial direction of the bore when a force is applied from the grip portion to the deformable portion;
• and
• a medical lead having a lead body surrounding electrical conductors, the lead body having a proximal region positioned within the bore of the header block, the proximal region having a plurality of contacts that engage corresponding electrical connectors in the bore and engage the conductors within the lead body, the deformable portion of the fixation structure being compressed into contact with a portion of the proximal region of the medical lead to fix the medical lead within the bore.