Does shape and size of the stems affect the stress-shielding around press-fit radial head arthroplasty?

Abstract

Aims It has been hypothesized that proximal radial neck resorption (PRNR) following press-fit radial head arthroplasty (RHA) is due to stress-shielding. We compared two different press-fit stems by means of radiographs to investigate whether the shape and size of the stems are correlated with the degree of PRNR. Methods The radiographs of 52 RHAs were analyzed both at 14 days postoperatively and after two years. A cylindrical stem and a conical stem were implanted in 22 patients (group 1) and 30 patients (group 2), respectively. The PRNR was measured in the four quadrants of the radial neck and the degree of stem filling was calculated by analyzing the ratio between the prosthetic stem diameter (PSD) and the medullary canal diameter (MCD) at the proximal portion of the stem (level A), halfway along the stem length (level B), and distally at the stem tip (level C). Results Overall, 50 of the 52 patients displayed PRNR. The mean PRNR observed was 3.9 mm (0 to 7.4). The degree of endomedullary stem filling at levels A, B, and C was 96%, 90%, and 68% in group 1, and 96%, 72%, and 57%, in group 2, with differences being significant at levels B (p < 0.001) and C (p < 0.001). No significant correlations emerged between the severity of PRNR and the three stem/canal ratios either within each group or between the groups. Conclusion PRNR in press-fit RHA appears to be independent of the shape and size of the stems. Other causes besides stem design should be investigated to explain completely this phenomenon. Cite this article: Bone Joint J 2021;103-B(3):530–535.

Assessment of progression and clinical relevance of stress-shielding around press-fit radial head arthroplasty

“…These observations suggest that the aetiology of PRNR may be multifactorial, as has been suggested previously. 7 In our opinion, damage to vascularization in the radial neck during surgery may represent one of these causes.…”

“…Few studies have been published on PRNR after RHA. 6,7,13 Chanlalit et al 6 radiologically evaluated 26 patients with different types of RHA and found that 65% displayed PRNR after a mean follow-up of 33 months, with no significant differences between stems that were cemented or press-fitted, had a curved or straight stem, or were smooth or rough. Moreover, the authors observed that PRNR started between the first and the 15th month after surgery and did not progress markedly beyond 26 months.…”

“…In 2021, Giannicola et al 7 performed a study in which they compared two radial head implants to assess whether the shape and the size of the stems affected PRNR. The degree of resorption in the four quadrants of the radial neck of a bipolar implant with a conical stem and an anatomical implant with a cylindrical stem were analyzed.…”

“…Other radiographs were obtained annually thereafter until final follow-up. The following radiological views were used to evaluate the four quadrants of the radial neck in all the patients, as described by Chanlalit et al 6 and Giannicola et al: 7 standard anteroposterior (AP) view (elbow in full extension with the forearm supinated) and standard lateral (L) view (elbow flexed at 90° with forearm supinated). The radiographs were also obtained in neutral or pronated rotation in both the AP and L views in patients with rotatory stiffness, and in the AP view with the beam perpendicular to the forearm in patients with elbow stiffness affecting extension.…”

“…Only one other recent study has focused on this phenomenon by comparing a cylindrical and an anatomical press-fit stem: the shape and size of the stems did not significantly affect the degree of proximal radial neck resorption (PRNR). 7 No other studies have investigated this phenomenon and many aspects remain unclear.…”