Radial head fractures with associated elbow injuries are common and the identification of these concomitant injuries is essential for determinant of treatment and outcome. It has been well known that the complete articular radial head fractures (mason III) are always with a high rate of associated elbow injuries[14, 17], while the rate in partial articular radial head fractures is unclear. In the present study, the rate of partial articular radial head fractures with associated injuries was 58.6%. Similar high rates has been documented by van Riet et al[12] (50%), Couture A, et al[18] (70%) and Itamura J et al [19] (92%), while great differences were observed in previous literatures, and some authors reported a low rates ranging 7.5%~12.2%[20–22]. The wide discrepancies were result of different sensitivity of assessment as well as study design. In our series, all concomitant associated elbow injuries with radial head fractures were identified by CT scan and intraoperative evaluation, which could minimize the risk of missed diagnosis. Given the high incidence of this damage, our data highlights the importance of being vigilant to associated injuries, especially in the case of CT scan being not available.
Many methods were used to investigate the morphology of the radial head, including caliper ruler, plain X-rays, CT, MRI and computer aided design (CAD) software[16, 23–26]. However, due to small number of subjects or non-precise measurement, different results were reported. In order to make an accurate measurement, we used a three-dimensional CT model to analysis the radial head fracture characteristics based on MIMINCS software. The widely used MIMICS software utilizes a consistent algorithm for bone identification (on CT slides), which could minimize the judgment or bias. Its advantages include easiness to use and accurate modeling function, which could provide more detailed information of periarticular fractures than CT scans, especially when CT scans are underwent in a nonstandard position in emergency room. The satisfactory intraobserver and interobserver reliability indicated that the measured parameters were reasonable. Besides, the average diameter of radial head in our study was 20.3 mm compared to 20.5 mm in the report of Mahaisavariya B [15], in which the radial head morphology was evaluated with a reverse engineering.
The most important finding of our study was that the large fragment located in anteromedial quadrant of radial head was correlation with concomitant elbow injuries. In the current study, the large fragment in the anteromedial quarter of radial head was correlated with more than 6-fold of concomitate associated injuries than that of anterolateral quarter. Given the lack of investigations addressing this factor, our finding may be more special relevant. The mechanism of fall on the outstretched hand can produce a variety of fracture patters in elbow joint. In a biomedically study [27], Amis and Miller reported that different angles of elbow flexion in the impaction injuries could cause different type of elbow fractures (e.g. distal humerus fractures, radial head fractures, coronoid fractures and olecranon fractures). Radial head fractures occurred in the range of 0° to 80 ° flexion, distal humeral fractures in the range 115° to 145°, coronoid fractures in the arc of 0° to 35° flexion and always combination with radial head fractures. In another cadaveric study, Fitzpatrick M J et al[28] proved that the rotation of forearm during axial load was the primary determinant of elbow fracture-dislocation pattern. When the forearm was in pronation, axial force often caused terrible triad injuries while the isolated elbow dislocation without fractures usually occurred in supination. The different location of radial head large fragment in patients with and without concomitant associated injuries maybe caused by different position of forearm and elbow during the accidents. In other words, the patients with associated elbow injures may have a more supinated forearm and extended elbow during a fall. Unfortunately, it is difficult for patients to recall the accurate position of forearm and elbow during a fall because the accident usually happens rapidly. Further biomechanical studies are needed to verify our assumed mechanism. The advantage of having information on location of large fragment is that it would remind the physicians to be aware of associated injuries which maybe the potential causes of elbow instability and a miss diagnosis would result in significant morbidity.
The current study also supports that the comminuted fracture pattern and separated fragments of radial head are correlation to concomitant associated injuries of elbow. In the present study, the comminuted fracture pattern was more than 7-fold increase to concomitate associated injuries while nearly 5-fold increase in case of separated fragments being present. The results of this study were consistent with previous publication[12, 14, 29]. In a retrospective study, Liu G et al[29] reported 17 of 20 patients with comminuted partial radial head fractures were associated with dislocation and fractures of the elbow and all patients needed operative treatment. Based on radiographic observation Rineer CA, et al [14] reported loss of cortical contact were 21-fold increase at risk of concomitant associated elbow injures than those of cortical contact. The elbow is relatively stable due to its bony structure. Therefore, a tremendous force is required to break out the joint. The comminuted fracture or obviously displaced fragments mean that the joint should be subjected to a serious injury. It is well known that the higher the force, the more likely to cause complex elbow fracture or dislocation.
On the contrary, the results of our study showed that radial head fracture size was not associated with the concomitant injuries of the elbow. For the stability of elbow, the ligaments are more important than the radial head and the radial head was the secondary elbow stabilizer[2, 30]. In a biomechanical study, Beingessner et al [31] investigated the association between radial head fracture size and elbow stability with intact and disrupted ligaments. In their study, radial head fractures were simulated in eight unpreserved cadaveric elbow joints by sequential removing 30° up to 120° wedges from the anterolateral radial head, and the elbow stability was determined by measuring the valgus angulation and ulna external rotation relative to the humerus. They found that the size of radial head fracture was not significantly associated with elbow stability during active elbow motion. In our series, the average radial head fracture size in the group with concomitant associated injuries was 41.9% compared to 38.3% in group with no associated injuries. In a similar study[3], Capo et al reported the average radial head size was 42.7% in the dislocation group while 42.3% in the remained reduced group. Besides, in the present study, no evidence has been found to support the arc of the fragment were correlation to the associated injuries with radial head fracture. A prior study[3] had reported that a higher arc of fracture was a predictor of concomitant associated injuries. In our study, the similar result was found with a bivariant analysis, but when other potential factors were controlled, the arc of radial head fracture was no longer associated with concomitant associated injuries. Nevertheless, it is difficult to compare our study with prior publication. For example, the present study included more patients with isolated partial radial head fracture compared to previous studies. These findings in our study suggest that it is unreliable using the size and arc of radial head fracture to decide the presence of concomitant associated injuries.
There are several limitations in this study in addition to the respectively nature. Firstly, we could not utilize the uninjured radial head to determine the surface area and the estimated surface area basing on the πr2 formula would result in some bias. Secondly, due to the difficulty of measuring distance in a 3D radial head model, we did not use the displacement of fragment as a marker to evaluate the concomitant associated injuries. Thirdly, as the most prominent area of biceps tuberosity is broad and variable, choosing it as a measurement standard may have biased our result.
Nevertheless, to the best of our knowledge, the current study is the largest and comprehensive investigation of fracture pattern characteristics and associated elbow injures in partial articular radial head fractures with CT scan. A total of 70 patients and 10 variables that could be correlation with the concomitant associated injuries were analyzed. The results of our study will be hopefully helpful for the treating surgeons in the initial consultation and operative decision-making.