Canal preparation for prosthetic radial head replacement: rasping versus reaming

Indications and Clinical Results of Radial Head Replacement: Has Anything Changed?

Radial head fractures are common injuries comprising 1/3 of the fractures about the elbow. As a secondary valgus stabilizer of the elbow, radial head fractures can compromise elbow stability leading to long-term pain, dysfunction, and degenerative change. Furthermore, radial head fractures can be accompanied by associated injuries including ligamentous lesions that can further exacerbate elbow instability, leading to long-term sequelae. As fixation principles and technology have evolved, so has the ability to render surgical treatment for these fractures. In general, minimally displaced and some displaced fractures may be treated nonoperatively with early motion. Fractures with a block to rotation and displaced fragments with 3 or fewer fragments may be treated with open reduction and internal fixation. Comminuted fractures or those with greater than 3 fragments may be successfully treated with radial head replacement. Associated elbow instability will also influence treatment decisions.

Stem Length and Neck Resection on Fixation Strength of Press-Fit Radial Head Prosthesis: An In Vitro Model

PURPOSE

Various radial head prosthesis designs are currently in use. Few studies compare different prosthetic designs. We hypothesized that increasing a cementless implant stem's length would reduce stem-bone micromotion, with both short and long neck cuts. We also hypothesized that a minimum stem length might be required for the initial fixation strength of a press-fit implant.

METHODS

In 16 fresh-frozen cadaveric elbows (8 pairs), the radial head and neck were cut either 10 or 21 mm below the top of the head. Modular cementless stems were inserted and sequentially lengthened in 5-mm increments. Micromotion under eccentric loading was tested after each incremental change.

RESULTS

Incremental lengthening of the prosthetic stem and the amount of neck resection (10-mm cut vs 21-mm cut) both had a significant effect on micromotion. After a 10-mm radial head-neck resection, we observed a significant decrease in micromotion with stem lengths of 25 mm or greater, whereas with 21 mm of neck resection there was no further reduction in micromotion with increased stem length. These differences can be explained, at least in part, by the concept of the cantilever quotient: the ratio of the head-neck length outside the bone to the total length of the implant.

CONCLUSIONS

The length of the stem affects the initial stability of press-fit radial head prostheses when the level of head and neck resection is at the minimum (ie, 10 mm) for currently available prosthetic designs. At this resection level, stems 25 mm or greater had significantly higher initial stability, but all stem lengths tested had mean micromotion values within the threshold for bone ingrowth.

CLINICAL RELEVANCE

The length of a radial head prosthetic stem affects the initial stability of press-fit radial head prostheses when the level of head and neck resection is at the minimum (ie, 10 mm) for currently available prosthetic designs.