Medical devices include fixation structures that include retained portions that provide medical lead fixation within the medical devices. Lead extensions include fixation structures that include retained portions that provide medical lead fixation within the lead extensions. A grip that a clinician may grasp and manipulate is engaged with a nose structure of a header block of the medical device or a connector block of a lead extension and manipulation of the grip causes compression of a deformable structure to ultimately create fixation of the lead or lead extension within the header block or the lead within the extension connector block. The deformable structure may be the retained portion of the fixation structure or alternatively may be separate from the fixation structure.