Radiological evaluation before and after treatment with an osseointegrated bone-anchor following major limb amputation-a guide for radiologists.

Osseointegrated implants have been developed to allow direct skeletal fixation of a prosthesis as an alternative to traditional socket-fitted prostheses for patients who have suffered from a major limb amputation. The implants contribute to improvements in functional outcome and quality of life and radiological evaluation plays a crucial role in pre- and post-operative assessment. This article acts as a guide for radiologists who may be tasked with providing the radiological information required by surgeons and prosthetists. We also look at the radiological appearances of complications that may arise in patients treated with an osseointegrated implant. Plain X-rays are used to screen patients who wish to undergo treatment. Limb-length X-rays are then used to measure the length of any residual bone, and comparisons can be made with the normal side (if present). From this, decisions about the likely size of the implant and the need for further amputation can be made. CT scans enable accurate assessment of the medullary cavity and cortical thickness. Post-operatively, plain X-rays form the mainstay of the routine monitoring of the bone-implant interface. Potential complications include infection, aseptic loosening, mechanical fracture of the implant and periprosthetic fracture. Infection and aseptic loosening can be seen as a lucency at the bone-implant interface which (if left untreated) can lead to loss of the implant. Implant and periprosthetic fractures are radiographically obvious. Radiologists involved in the care of patients undergoing treatment with an osseointegrated implant should become familiar with the imaging requirements so they can contribute to optimal patient outcomes.

Poor judgment of distance between nociceptive stimuli.

Although pain is traditionally assumed to be poorly localized, recent work indicates that spatial acuity for nociception is surprisingly high. Here we investigated whether the nervous system can also accurately estimate the distance between two nociceptive stimuli. Estimating distance implies a metric representation of spatial relations, a property that underlies abilities such as perceiving the size of external objects. We presented pairs of simultaneous nociceptive or non-nociceptive somatosensory stimuli, and asked participants to judge the distance between them. Judgments of distance between nociceptive stimuli were much worse than judgments of distance between non-nociceptive tactile stimuli, even on skin regions where spatial acuity for nociception exceeded spatial acuity for touch. Control experiments ruled out explanations based on inaccurate localization of double nociceptive stimuli. Thus, the nervous system poorly represents the distance between two nociceptive stimuli. The dissociation between high spatial acuity and poor distance judgment in the nociceptive system may reflect a specialization for computing accurate spatial representations useful to protect the body, rather than to perceive the size of external objects.