Radiocapitellar stability: the effect of soft tissue integrity on bipolar versus monopolar radial head prostheses

Introduction: Radiocapitellar stability depends, in part, on concavity-compression mechanics. This study was conducted to examine the effects of the soft tissues on radiocapitellar stability with radial head prostheses. Hypothesis: Monopolar radial head implants are more effective in stabilizing the radiocapitellar joint than bipolar radial head prostheses, with the soft tissues intact or repaired. Materials and methods: Twelve fresh frozen elbow specimens were used to evaluate radiocapitellar stability with monopolar and bipolar radial heads. The study variables focused on varying soft tissue conditions and examined the mean peak subluxation forces put forth by each prosthesis design. Results: With the soft tissues intact, the mean peak force resisting posterior subluxation depended significantly on the radial head used (P = .03). Peak force was greatest for the native radial head (32 +/- 7 N) and least with the bipolar prosthesis (12 +/- 3 N), with the monopolar prosthesis falling in between (21 +/- 4 N). The presence of soft tissues significantly affected the bipolar implant's ability to resist subluxation, though it did not significantly impact the native or monopolar radial heads. Discussion: This study reveals the dependence of radiocapitellar stability on soft tissue integrity, particularly for bipolar prostheses. Overall, monopolar prostheses have a better capacity to resist radiocapitellar subluxation. Conclusion: From a biomechanical perspective, the enhancement of elbow stability with a monopolar radial head prosthesis is superior to that with a bipolar design. This is especially true when the integrity of the soft tissues has been compromised, such as in trauma. Level of evidence: Basic Science Biomechanical Laboratory Study. (C) 2011 Journal of Shoulder and Elbow Surgery Board of Trustees.