CORR Insights®: Fracture of the Anteromedial Facet of the Coronoid Is More Common Than Previously Thought in Combined Fractures of the Coronoid and Radial Head

Where Are We Now?

Elbow fracture-dislocations are complex injuries. An incomplete understanding of how associated fractures and ligament injuries affect the direction of elbow instability can lead to recurrent or residual instability after operative treatment.

To help recognize the resulting elbow instability, common combinations of fractures and ligament injuries are often categorized into two large groups with distinct surgical treatments [6]. The first group is posterolateral rotatory instability or the terrible triad injury, defined classically as a radial head fracture, lateral ulnar collateral ligament injury, and coronoid tip fracture. These injuries are typically approached laterally to address the radial head and lateral ulnar collateral ligament. The small coronoid fragment is visualized through the lateral approach and fixated with suture or retrograde screws through the dorsal ulna for fixation. The second group is varus posteromedial instability, which classically results from an anteromedial or basal coronoid fracture with relatively infrequent radial head involvement. The coronoid fractures associated with varus posteromedial instability are large enough to compromise the coronoid’s role as a buttress against posteromedial and posterior displacement of the ulna. These injuries are typically approached medially because a medial approach offers more direct visualization, reduction, and robust fixation (such as a buttress plate) than can be achieved through a lateral approach. Distinguishing between varus posteromedial instability and posterolateral rotatory instability helps avoid the pitfall of inadequately treating an anteromedial coronoid fracture through the limitations of a lateral approach, which can risk residual posteromedial instability.

The results from de Klerk et al. [1], published in this issue of Clinical Orthopaedics and Related Research®, show us that these two injury patterns coexist more frequently than was previously thought, and we should therefore (continue to) seek basal or anteromedial fragment extension even in the setting of a radial head fracture. This is best identified with CT coronal plane reconstructions in the plane of the coronoid and, ideally, through three-dimensional reconstructions with digital humeral subtraction. In addition to avoiding residual varus posteromedial instability, preoperative identification of anteromedial involvement and the potential need for a medial approach have practical advantages for the surgeon, including patient positioning (supine versus lateral decubitus for a posterior incision) and a more accurate prediction of case duration and preparation of implants (that is, buttress plate). Overall, the results of de Klerk et al. [1] remind us to not be too hasty in assessing coronoid fragment size in the setting of a radial head fracture, and they can help with surgical planning.

Where Do We Need To Go?

We need to better understand whether addressing coronoid fragments with anteromedial rim and tip involvement through a lateral approach—alongside a technically well-executed radial head treatment and lateral ulnar collateral ligament repair—is associated with posteromedial failure. There is consensus that tip fractures can be treated adequately through a lateral approach (or may not even need fixation) [3, 4, 7] and that basal fractures are better treated medially. The need for clarity applies to medium-sized fragments between these two extremes, such as the 24% of fractures with anteromedial rim and tip involvement [1] (O’Driscoll Type 2, Subtype 2). Biomechanical data on this topic have suggested that lateral repair can help compensate for some but not all varus/valgus instability with these fragments [8], but clinical data are needed to better guide management.

A related question to be answered is how much better we resolve instability when we use a medial approach to treat fragments involving the tip and anteromedial rim rather than using a lateral approach to fix the fragments. If a fragment is large enough that a medial approach can achieve anterograde (volar to dorsal) screw fixation or have significant surface area in contact with a buttress plate, the effort and morbidity of a medial approach seem justified by the increased rigidity of those constructs compared with what could be achieved laterally. This difference in rigidity has been shown biomechanically for O’Driscoll Type 2, Subtype 3 fractures [5]. By contrast, there are some fragments that involve the anteromedial rim but are too small for independent screw fixation or to meaningfully buttress with a plate; for these, perhaps a medial approach does not provide enough “bang for our buck.”

The answers to these two questions would be helpful in understanding whether the anteromedial rim involvement we see on preoperative imaging justifies planning for a medial approach.

How Do We Get There?

Multiple technical and rehabilitation factors make it hard to clinically study whether anteromedial rim involvement addressed through a lateral approach is likely to result in residual posteromedial instability. For example, there may be variability in the strength of coronoid fixation achieved through a lateral approach, and the fixation may be more likely to fail in the setting of an overstuffed radial head, an incompetent lateral ulnar collateral ligament, or a rehabilitation protocol allowing early terminal extension. Nevertheless, I believe we can get some answers by focusing on the treatment of combined radial head and coronoid fractures involving the anteromedial rim.

One place to start is by retrospectively assessing the outcomes of the 24% of patients in this CORR® study [1] who had O’Driscoll Type 2, Subtype 2 (anteromedial rim and tip) fractures. Did fractures addressed through a lateral approach have an unacceptably high risk of recurrent instability? Did fractures approached medially fare better?

Another way of looking at the data from this study is that the frequency of anteromedial rim involvement seems higher than most surgeons’ frequency of performing a medial approach and postoperative instability. Perhaps this suggests that our status quo of laterally approached coronoid fixation is enough and anteromedial rim involvement does not universally necessitate a medial approach.

I suspect we will never fully be able to know before surgery whether the patient will benefit from a medial approach for fragments involving the anteromedial rim and tip. Fortunately, studies like this one in CORR [1] remind us of this possibility, even with injuries that look like a classic terrible triad at first glance. We can continue to rely on intraoperative stability testing for residual posteromedial instability after completing the lateral work to help us make the final decision.

Read This Next

• This instructional course lecture text teaches the classic elbow fracture-dislocation injury patterns and introduces the O’Driscoll classification for coronoid fractures [6].

• In this retrospective study of 67 fixated coronoid fractures, the authors found a low frequency of anteromedial facet involvement with terrible triad injuries and a high rate of varus posteromedial instability even with small fragments involving the anteromedial facet [2].

• This biomechanical study examines the effect of various coronoid fracture morphologies on varus and valgus stability in both the lateral ulnar collateral ligament–deficient and lateral ulnar collateral ligament–repaired state. It demonstrates that the lateral repair can compensate for some anteromedial rim involvement, but maybe not enough with larger fragments [8].