Radial head reconstruction in elbow fracture-dislocation: monopolar or bipolar prosthesis?

Abstract

Background: Monopolar and bipolar radial head prosthetic arthroplasties have been used successfully to treat elbow fracture-dislocation with unsalvageable radial head fractures. The relative stability of these two designs in different clinical situations is a topic of ongoing investigation.

Questions/purposes: We tested the effects of monopolar and bipolar fixed-neck prosthetic radial head implants on improvement in elbow coronal and axial plane laxity in a terrible triad biomechanical model that accounted for lateral collateral ligament integrity and the presence of a transverse coronoid fracture.

Methods: Kinematic data were collected on six fresh-frozen cadaveric upper extremities tested with passive motion throughout the flexion arc. Varus and valgus gravity stress were applied with the wrist in neutral position. A lateral collateral ligament reconstruction was simulated. We assessed instability after radial head resection and reconstruction with either a monopolar or bipolar implant in the presence of a transversely fractured (Regan and Morrey Type 2) or fixed coronoid process.

Results: With collateral ligament integrity, no difference was detected, with the numbers available, in valgus laxity between implants under valgus stress (p = 1.0). Laxity improvement with each prosthesis was higher when the coronoid was fractured (mean ± SD: monopolar: 7.4° ± 1.6°, p < 0.001; bipolar: 6.4° ± 1.6°, p = 0.003) than when it was fixed (monopolar: 4.0° ± 1.6°, p = 0.02; bipolar: 4.2° ± 1.6°, p = 0.01). With the numbers available, there was no difference in external rotation laxity between implants under valgus stress (p = 1.0). The greatest stabilizing effect of the prostheses occurred when the coronoid was fractured (monopolar: 3.3° ± 1.2°, p = 0.15; bipolar: 3.3° ± 1.2°, p = 0.17). Radial head arthroplasty offered no substantial stability under varus stress for varus or internal rotation laxity.

Conclusions: In our terrible triad cadaveric model, coronoid fixation was effective in improving varus laxity with a monopolar or bipolar prosthesis in place. Also, both types of prostheses were effective in improving valgus and external rotation laxity to the elbow, regardless of coronoid status. With collateral ligaments reconstructed, no large kinematic differences were noted between implants regardless of the varus-valgus position or whether the coronoid was fractured or fixed.

Clinical relevance: The data from our cadaveric model support the use of either implant type in terrible triad injuries if the collateral ligaments are intact or reconstructed.

Fig. 1

The bipolar implant may be converted to a monopolar prosthesis by eliminating the motion at the articulation.

Fig. 2

Visual and fluoroscopic inspection of the ulnohumeral joint resulted in accurate implant placement, as demonstrated by final complete dissection of each specimen at the conclusion of the experimental protocol.

Fig. 3

Valgus ulnohumeral laxity is improved with use of either a monopolar or bipolar prosthesis.

Fig. 4

External rotation ulnohumeral laxity is improved with radial head arthroplasty. Only very small differences were seen between monopolar and bipolar implants.

Fig. 5

The dominant effect of coronoid fracture fixation on varus laxity is demonstrated, with little effect seen for radial head prosthetic implant.

Fig. 6

The effect of coronoid fracture fixation is seen by comparing solid with dashed lines. Little effect is seen on internal rotation laxity with either radial head prosthesis.