This retrospective multi-centre study reports the radiographic characteristics of RHA and a revision rate surgery of 10,5% at two-year follow-up. The comparison between groups shown that patients who underwent annular ligament repair, as associated surgical procedure, have a significant statistical difference, in term of RHA survival.
The RHA is indicated in un-reconstructible Mason type III and IV and in those elbow injuries where the radial head, as a secondary stabilizer, becomes essential. No guidelines have been published yet to suggest which prosthetic model is the most suitable depending on the diagnosis or which design is the most suitable.
Different kinds of stem can be implanted, such as loose-fit, press-fit and cemented stems; monopolar and bipolar designs are also available as well as spherical or anatomical heads. There are no studies demonstrating the superiority of a model on the others, but many report how the correct size (such as diameter and height of the head) is determinant for final outcome [18,19]. Some authors prefer bipolar prosthesis because it better restore the tracking with the capitellum; other authors are convinced of monopolar design superiority because of the construct stability [16,20]. However, bipolar implants have some peculiar risks, such as components dissociation and polyethylene osteolysis. Our study compared only press-fit and loose-fit stems and we did not find one to be superior to the other, although we did not analyse functional outcomes but only radiographic results.
A mean 10% removal/revision rate is reported in literature and it occurs within two years from primary surgery on average; the main causes are aseptic loosening of the implant and pain [5]. Pain is a symptom, not the cause and it might be explained by many reasons. O’Driscoll and Herald suggested that proximal forearm pain in patients with press-fit RHA is a strong symptomatic loosening indicator, even in absence of radiographic loosening signs [21]. Moreover, this study revealed that intentionally loose-fit positioned prostheses failed earlier, if compared to press-fit implants (failure occurs after an average of 17 and 53 months, respectively).
Other causes of removal/revision implant are stiffness with heterotopic ossifications, impingement associated with overstuffing and persistent clinical instability [12,20,22].
It has been shown that the minimum follow-up required to fully evaluate the complications after RHA is 39 months [23]. Viveen et al., in a recent systematic review, revealed that the most frequent causes of RHA failure are symptomatic aseptic loosening (30%), stiffness (20%) and persistent pain (17%), they also reported that failure occurred after 34 months on average [20].
The results of our study are in line with those of the literature; we report a revision/removal rate of 10,5% and an average time to failure of 24 months; our main failure causes are aseptic loosening and implant overstuffing.
VanRiet et al. showed that the timing of RHA positioning is the main factor influencing the appearance of osteolysis of the capitellum; prostheses implanted 6 months after the initial trauma are associated with clear radiographic signs of erosion [22]. In our study, most patients do not have or have slight signs of bone resorption of the capitellum: this happened probably because all the prostheses have been placed in acute; however, it has been confirmed in our study, that those who show a serious compromised capitellum have overstuffing.
Aseptic loosening is a frequent problem: radiolucencies around the stem are typical in zones one and seven and seem to occur mostly early after implantation, generally between the first and fifteenth post-operative months. Subcollar resorption could affect both press-fit and loose-fit stem, but it is often reported with press-fit prostheses and seems to be stationary after one or two years, without progression and without clinical symptoms [24].
An innovative datum that emerged from our study, is the importance of ligament reconstruction time related to RHA, in particular the execution or not of some type of surgical procedures on the lateral, medial collateral ligament and on the annular ligament. In literature, although there are several studies that underscore the importance of ligament repair, only few focus on the relation with RHA [5,6,22]. Hackl et al in their multi-center retrospective analysis of 466 cases, showed that one of the most common causes of revision was instability; they found 170 unstable elbows, 65 of them had stage II to III posterolateral rotatory instability, 38 valgus instability, 28 multidirectional instability, 19 varus posteromedial rotatory instability, nine longitudinal forearm instability, nine persisting elbow dislocation and two proximal radioulnar instability [7]. They also highlighted that instability is directly related to the severity of the initial trauma, especially in case of Mason type IV fractures, terrible-triad injuries and Monteggia-like injuries. Delclaux et al described that instability is related to LCL complex failure most of the times; only lateral ligaments suture with a radial head prosthesis can restore elbow stability close to normal [8]. Elbow stability can be influenced also by the type of prosthesis: monopolar prostheses have shown to better restore stability than bipolar prostheses [9,25].
In our study, we assessed the type of radial head fracture according to Mason’s classification: in Mason type IV, due to elbow dislocation, LCL should always be repaired or at least tested; in Mason type III, LCL repair might not be performed in condition of a proven joint stability. The MCL repair depends on initial traumatic mechanism, whereas the annular ligament should always be sutured as it is damaged by the fracture or by the surgical access. From our data it clearly emerges that if ligament time is not performed, the removal/revision rate is higher; however, only the correlation with annular ligament suture was statistically significant; in fact, annular ligament is essential to ensure normal prosthesis-capitellum tracking. Wapler et al found that when RHA is used, MCL tears, that occurs with severe radial head trauma, can heal even if it is not directly repaired; according to them it seems justified to restore the elbow’s stability with a RHA without repairing the MCL surgically [26].
Our study has several weaknesses: firstly, it is retrospective and no clinical evaluation was performed: this prevented us from analyzing the correlation between the revision/removal rate and the presence of pain. Secondly, despite it is a multi-centric study, it includes very heterogenous cases with a wide range of diagnosis, several prostheses models and different surgeons. Furthermore, the ligament repair data could be underestimated since surgeons might have them omitted from surgery’s reports (too predictable to be mentioned).
Further studies are required to demonstrate the importance of ligamentous component during radial head replacement. Since registers for other joints prosthesis already exist, in order to encourage next studies, we recommend the creation of a regional/national RHA register.