The biomechanical effect of prosthetic design on radiocapitellar stability in a terrible triad model

Abstract

Objectives: The integrity of elbow soft tissues affects radiocapitellar joint stability in the presence of bipolar radial head (RH) prostheses. This study examined the effect on radiocapitellar stability of monopolar designs versus bipolar RH prostheses in an elbow model with a surgically controlled terrible triad injury.

Methods: In each of 8 fresh-frozen elbow specimens (4 male and 4 female), a terrible triad fracture dislocation was created through soft tissue releases, coronoid fracture, and RH resection. Radiocapitellar stability was recorded under the following 3 sets of conditions: (1) surgical control (native RH), (2) RH replacement (circular monopolar or bipolar), (3) replacement with alternate circular RH not used in condition 2, and (4) replacement with the anatomic RH.

Results: The type of RH used significantly impacted the mean peak force required to resist posterior subluxation (p = 0.0001). The mean peak subluxation force of the bipolar prosthesis (1 ± 1 N) was significantly less than both the anatomic (16 ± 1 N) and nonanatomic circular (12 ± 1 N) implants (p = 0.0002). The peak subluxation force of the native RH (18 ± 2 N) was not different than the anatomic implant (p = 0.09) but was greater than the nonanatomic circular design (p = 0.0006).

Conclusions: Monopolar RHs confer greater radiocapitellar stability than bipolar implants in the setting of terrible triad injuries. Of the 2 monopolar designs tested, the anatomic design provided more stability than the non-anatomic RH prosthesis.