When someone gets a hip replaced, it's not uncommon for that leg to subsequently be a little longer or shorter than it was before. Thanks to a new system developed by German scientists, however, that may soon no longer be the case.

Ordinarily, if an artificial hip changes leg-length by less than a centimeter, the body is able to adapt. If the change in length is much more than that, however, it can lead to posture problems. These can in turn cause back pain, unless corrective shoe lifts are used to make up the difference.

Hopefully things won't reach that point, though, if the new technology comes into common use.

Created by a team at the Fraunhofer Institute for Machine Tools and Forming Technology, it begins with the surgeon temporarily attaching a plastic box to the patient's shin as they're lying on their back on the operating table, prior to surgery. The surgeon then lifts their leg up by the heel, rotating the leg upward. As they do so, a 3D camera tracks its arc relative to the hip, by following optical markers on the box. This provides a linked computer with rotational measurements of the leg, which indicate how far the shin moves from the hip throughout the leg's range of motion.

The patient's hip is then surgically replaced with an artificial one that's unique to the system. Before that artificial hip is secured permanently in place, the surgeon once again lifts the leg up. If the computer/camera system notes that the rotational measurements are different than they were before the surgery, a sliding screw which connects the artificial hip's femoral stem and acetabular cup (its "ball and socket") can be adjusted to tweak the implant's length accordingly.

Should the length discrepancy be too great to be corrected by that screw, a longer or shorter stem and/or cup can simply be selected. That's not too likely to be necessary, however, as custom software advises the surgeon on what size to select in the first place, based on patient X-rays and the rotational measurements (see image above). In any case, once the new measurements match the old ones, the implant can be secured and the surgery completed.

Although the system is still currently in the testing phase, the scientists hope that it will be ready for clinical use within two years.

Source: Fraunhofer

View gallery - 2 images