Introduction
Humeral shaft fractures generally necessitate surgical intervention due to the significant complication rates associated with conservative management, although conservative treatment may be considered in cases of minimally displaced fractures or among elderly patients [1-3].
Distal third fractures constitute 16% of humeral shaft fractures and standard intramedullary nailing is challenging in these fractures due to the small size of distal fragments. Consequently, open reduction and internal fixation (ORIF) with a plate is a treatment of choice [4,5].
For ORIF with a plate of humerus diaphyseal fractures, the surgical approach depends on the fracture location. Commonly, proximal humeral fractures are approached anteriorly, midshaft fractures are approached anterolaterally, posteriorly, or posterolaterally, and distal diaphyseal fractures are approached posteriorly or posterolaterally [3,5,6]. Recent studies have reported favorable outcomes with anterior plating for distal third humeral shaft fractures, although the optimal surgical approach is still debatable [7-11].
Posterior plating through a posterior approach is prevalent but is risky. The procedure frequently requires interaction with the radial nerve, thus risking nerve adhesion and iatrogenic injury due to the nerve’s limited mobility. Moreover, radial nerve adhesion complicates implant removal and increases the risk of nerve damage [3,4,7]. This approach also often involves significant iatrogenic injury to the triceps muscle resulting in prolonged recovery times and increased postoperative pain. Additionally, discomfort is caused by skin protrusion in the posterolateral aspect of the elbow [6,9,12]. Alternatives such as anterolateral and lateral approaches with anterior or dual plating have been explored [6,7]. The anterolateral approach can be performed without encountering the radial nerve. However, due to the proximity of the coronoid fossa, it has the disadvantage of potentially limiting the number of screws that can be fixed to the distal bone fragment [6,9,13]. Taking into consideration the various pros and cons, a reasonable option for one-third of humerus shaft fractures with small distal fragments would be using the posterior approach in which a plate is applied to the posterior side where tensile forces act, to allow for sufficient screw fixation. However, based on the author’s experience, we believe that a sufficiently stable fixation can be achieved through anterior plating. Previous studies have reported on the use of dual plates or alternative types of plates and have documented the effectiveness of anterior plating for a single fracture type [6-8].
We aimed to assess if stable fixation using anterior plating can be used in distal third humeral shaft fractures based on preoperative radiological standards.
Methods
Ethics statement: This is a retrospective case series approved by the Institutional Review Board of Samsung Medical Center (No. SMC 2024-05-058). Written informed consent was obtained from the patients for the publication of this report including all clinical images.
1. Patient selection
We included patients who underwent surgical treatment for distal third humeral shaft fractures at Samsung Medical Center between 2019 and 2023. Distal third humeral shaft fractures were defined when the center of the fracture line was in the distal third of the humeral diaphysis. We excluded cases with pathological fractures and periprosthetic fractures. Additionally, cases in which follow-up was not possible for less than 6 months were excluded. During the study period, 22 patients with distal third humeral shaft fractures had surgery, of which 18 were treated using the anterior approach. In four patients, the distance from the proximal margin of the coronoid fossa to the point where a cortex width of at least 10 mm (near and far) could be secured was found to be less than 50 mm. As a result, stable fixation with three screws could not be achieved, and posterior plating was performed.
2. Surgical procedure
Under general anesthesia, the patient’s arm was positioned on the table in a supine position and covered with orthopedic drapes. All surgeries were performed by a single-hand surgeon with over 10 years of experience. A skin incision was made along the lateral border of the biceps brachii followed by identification of the intermuscular space between the biceps and brachialis. After retracting the biceps brachii muscle to the ulnar side, the brachialis was then split to expose the humerus and fracture site. In cases of fractures with a wedge fragment, care was taken to preserve the attached soft tissue to each fragment. Anatomical reduction was achieved using reduction clamps and lag screw fixation was performed when feasible. We identified and marked the most proximal region of the distal bone fragment where a cortical width of at least 10 mm could be achieved. The plate was then provisionally applied, taking care to avoid encroachment on the coronoid fossa, to assess the feasibility of securing at least three screws. Both the metaphyseal and locking compression plates (LCPs) have a width of 11 mm. By strategically positioning these plates slightly off-center over the area with the 10-mm cortical width, we were able to minimize plate protrusion. The plate was positioned perpendicular to the midline of the distal humerus anteromedial or anterolateral border and the locking screw was fixed in the direction perpendicular to the border. Subsequently, If the plate floated above the bone contour, plate bending was performed. However, in most cases, bending was not necessary. As a neutralization plate, only locking screws were ultimately fixed in the plate holes. Metaphyseal locking or LCPs were used (DePuy Synthes, West Chester, PA, USA). After fixation, the skin was sutured, a compression dressing was applied, and a long arm splint was placed. At 1 to 2 weeks after surgery, the splint was changed to a thermoplastic brace and range of motion (ROM) exercises were initiated.
3. Data collection
We reviewed patient charts to collect basic information, postoperative ROM, and details about the types and numbers of plates and screws used during surgery, and any postoperative complications. Preoperative radiographs provided data on fracture morphology (spiral, oblique, and comminuted) and the distribution of the distal fragment’s fracture line which was measured from the proximal margin of the coronoid fossa to the most distal and proximal points of the fracture line (Fig. 1). Using preoperative computed tomography (CT) scans, we established a reference point on the axial view of the distal fragment where both the near and far cortices identified a width of at least 10 mm, measured along a line parallel to the humerus central plane. From this most proximal point, we measured the length to the proximal margin of the coronoid fossa on the coronal view (Fig. 2). The 10-mm cortical width threshold was empirically set by the author, drawing on the AO reference, which suggests that the distance for lag screw fixation should approximate the screw head diameter. This value was adapted based on the author’s clinical experience to ensure secure fixation. We evaluated postoperative radiographs for the number of cortical fixations in the distal fragment, fracture union, and callus formation (Table 1).
Results
During the study period, a total of 25 patients with distal one-third humeral shaft fractures underwent surgery. About two patients were excluded due to pathological fractures or periprosthetic fractures and one patient was excluded due to lack of follow-up. A total of 22 patients were enrolled, and the mean follow-up period was 13.61 months (range, 6–28 months). Among the 22 patients, four patients were treated with posterior fixation using a posterior approach, and 18 patients underwent anterior fixation using an anterior approach. Data for the 22 patients who received an operation are presented in Table 2. The mean age of the patients was 36 years (range, 14–85 years) and comprised of 15 male and seven female patients. The most common form of injury was due to a fall, and the majority (77.2%) had simple spiral or simple wedge fractures.
Radiographic measurements who received anterior fixation are shown in Table 3. The distance from the proximal margin of the coronoid fossa to the most distal part of the distal fragment was 33 mm (range, 4–50 mm), and the distance to the most proximal part from the proximal margin of the coronoid fossa was 107 mm (range, 57–145 mm). The distance on CT scans where both cortices could be fixed was 61 mm (range, 36–96 mm). The distal fracture fragment had an average of 7.9 cortices (range, 6–10 cortices) fixed. Lag screws measuring 3.5 and 2.7 mm were fixed in 17 out of 18 patients who underwent anterior plating, with an average of 2.4 screws (range, 1–4 screws) per patient (Figure 3, 4).
All patients achieved bone union within 12 weeks (range, 12.69±2.43 weeks) postoperatively. One patient had preoperative radial nerve palsy necessitating radial nerve exploration during surgery, which resulted in complete recovery. Within 3 months postoperatively, all patients achieved a ROM equivalent to the contralateral side, and there were no complications such as nerve palsy, delayed union, or nonunion.
Discussion
The objective of our study was to analyze distal humeral diaphysis fractures exhibiting a fracture pattern characterized by long spiral fractures accompanied by large butterfly fragments. Our analysis showed that radiographs indicated an average distance of 33±11 mm from the distal margin of the distal fragment to the proximal margin of the coronoid fossa, whereas CT scans indicated a mean length of 61±30 mm suitable for stable fixation of both near and far cortices, using a 10-mm width criterion. We found that stable fixation could be achieved through anterior plating, with an average of 7.9±1.5 cortices secured within the distal fragment.
The threshold of 10 mm was determined for the following reasons: The screw needs to be fixed close to the apex of the fracture fragment. Although there is no precise reference for this, the principle was derived from the AO reference, which states that when fixing a lag screw, the minimal distance to the fracture line must be equal to the diameter of the screw head. The author arbitrarily set this criterion based on this principle. Since the function here is not that of a lag screw, instead of using the 3.5-mm screw head size, a distance of about 10 mm (which is three times the screw diameter) was typically found to provide secure fixation. Therefore, this criterion was established based on the author’s clinical experience and judgment.
Most distal one-third humerus fractures occur in relatively young patients during activities such as arm wrestling or falling on an outstretched arm, owing to the sudden torsional force, bending force, and axial compression. These fractures often present as long spiral fractures with butterfly fragments [1,2]. Due to the extension of the fracture line close to the elbow, securing more than three screws in the distal fragment is challenging. To ensure stability, at least six cortical fixations are necessary. Kobayashi et al. [14] suggested sufficient fixation with one lag screw and four cortical fixations. These fractures are often sufficiently large to allow stabilization using a lag screw. Even when the distal fragment is small and the beak is thin and long, stable fixation can be achieved if a 3.5- or 4.5-mm screw can be inserted into the most proximal part with a width less than 10 mm. If a length of 50 mm is secured from this point to the proximal margin of the coronoid fossa, fixation with more than six cortices can be achieved using three holes in the plate. In the case of a metaphyseal LCP, four 3.5-mm screws and one 4.5-mm cortical screw can be fixed within this length, and an LCP can accommodate three 4.5-mm cortical or 5.0-mm locking screws (Fig. 5). The metaphyseal plate and LCP have a narrow width of approximately 11 mm, and being straight plates, they allow for flexible application. Even when dealing with a small distal fragment or a long, thin beak, the plates can be positioned towards the medial or lateral column, facilitating secure fixation while avoiding the coronoid fossa.
In this study, adequate fixation was achieved using the anterior approach in 18 out of 22 patients (81.8%) with distal humeral shaft fractures. These fractures were predominantly spiral or oblique, allowing for sufficient lag screw fixation. Although the fracture line extended distally up to 33 mm from the coronoid fossa, adequate fixation was confirmed up to 61 mm on CT scans.
Distal humeral fracture surgical procedures include anterior, anterolateral, and posterior approaches. The anterior approach involves a longitudinal split of the brachialis, whereas the anterolateral approach borders the biceps brachii and brachialis medially and brachioradialis laterally. Posterior approaches can be divided into triceps splitting and triceps sparing (reflecting) techniques [4,5,12]. The anterolateral approach allows for exposure of the entire humerus without radial nerve exploration and facilitates the use of minimally invasive techniques. However, it poses challenges due to the convex surface of the humerus and limitations in distal screw purchase near the coronoid fossa [2-5,12].
To overcome the difficulty of anterior screw fixation, a reversed proximal humeral internal locking system plate (PHILOS; DePuy Synthes, Paoli, PA, USA) has been introduced with promising results. A recent biomechanical study compared the extra-articular distal humerus plate with the PHILOS plate (Depuy Synthes) and reported similar stability with the PHILOS plate achieving four distal screws and the posterior plate achieving five screws [9,10]. The design of the PHILOS plate, with nine locking screw holes over a 45-mm length, provides sufficient fixation even in small distal fragments.
The PHILOS plate is designed to fit the contour of the greater tuberosity of the proximal humerus resulting in a wider and more convex proximal portion. This characteristic makes it difficult to adjust the position of the plate and it can be relatively bulky (Fig. 6). In the intraoperative field, the plate may obscure the near cortex of the fracture line that extends medially and distally and the fixed angle locking system limits the ability to insert screws at angles other than those predetermined by the plate. In addition to these points, even when fixing the same number of four screws, there are issues with stress distribution due to the short working length and the intersecting directions of the screws. Taking these factors into account, a straight plate allows for more flexible positioning along the fracture line, either medially or laterally. This enables continuous intraoperative visualization of the near cortex and facilitates precise placement of screws. The thickness of the 3.5/4.5/5.0 LCP is 4.2 mm which is thicker than the 3.7 mm PHILOS plate and provides greater mechanical strength. Unlike the PHILOS plate which only accommodates 3.5 mm screws, the 3.5/4.5/5.0 LCP can use 4.5- and 5.0-mm screws. Therefore, theoretically, it can offer stronger fixation when securing the same number of locking screws.
In distal one-third fractures, surgeons are most concerned about the radial nerve. Radial nerve palsy occurs in approximately 7% to 17% of humeral shaft fractures [15-17]. In cases where nerve entrapment is suspected such as with Holstein–Lewis fractures, severely displaced fractures caused by high-energy trauma, and open fractures, proactive primary radial nerve exploration could be a better option [7,18]. However, there is ongoing debate regarding intraoperative radial nerve exploration in cases of radial nerve palsy associated with low-energy trauma or partial radial nerve palsy. Recent studies have reported that no significant difference was noted in the recovery of radial nerve palsy regardless of whether primary nerve exploration is done [15-17,19,20]. Ostermann et al. [21] reported that in cases of low-grade radial nerve palsy, trauma mechanism, fracture type, fracture location, and treatment modality do not influence the timing of radial nerve recovery. In contrast, a systematic review by Hegeman et al. [22] indicated that the group undergoing exploration and subsequent neurolysis had a higher complete recovery rate compared to the group without exploration. No study has specifically focused on primary radial nerve palsy in low-energy distal one-third humerus shaft fractures; however, the fracture patterns described in this study are mostly due to low-energy trauma. Even if nerve injury or entrapment occurs, it is likely to happen at the distal intermuscular septum, making it possible to explore using an anterolateral approach. If the radial nerve is explored, it can be extended to the lateral column of the elbow which enables lateral plating along with dual plating that can be conducted with anterior plating. Lee et al. [13] introduced the advantages of dual plating in distal third humerus fractures, which include the ability to use a smaller incision and relatively shorter plating.
Secondary radial nerve palsy occurring intraoperatively or postoperatively is one of the most troublesome complications associated with humerus shaft fracture surgery. Some surgeons prefer the posterior approach which allows direct visualization of the radial nerve, and others opt for the anterolateral approach which enables safe reflection of the brachialis muscle. However, the posterior approach may increase the risk of iatrogenic radial nerve injury due to limited nerve mobility and the need to place the plate beneath the nerve. Shon et al. [23] reported in a systematic review that the posterior approach resulted in significantly higher rates of iatrogenic radial nerve injury compared to the anterolateral approach and had an odds ratio of 2.72. Shimamoto et al. [11] found that in distal one-third humerus fractures, iatrogenic radial nerve injury occurred in 0 out of 20 cases with anterior plating and in four out of 30 cases with posterior plating. Anterior plating through the anterolateral approach can also result in iatrogenic palsy. This is particularly due to the potential risk of injuring the radial nerve as it passes through the spiral groove on the posterior aspect of the humerus during the placement of proximal screws. In our practice, we perform preoperative magnetic resonance imaging to assess radial nerve injuries and to determine their course, ensuring the safe positioning of the proximal screws during surgery. In this study, one patient presented with radial nerve injury at the time of injury. In this patient, we performed dissection up to the distal portion of the spiral groove to confirm the continuity of the radial nerve, and we observed recovery 3 months postoperatively. Additionally, no other patients experienced postoperative radial nerve palsy.
This study has several limitations. First, it is a retrospective study and did not include a control group. Second, the sample size was small because of which the efficacy of anterior plating through the anterolateral approach used in this study could not be demonstrated. Third, heterogeneity in the results was observed because we used two different types of plates. Fourth, since we did not use comminuted fracture types, the stability of the plates as bridging plates could not be evaluated. Future biomechanical studies are needed to assess the stability of the LCP application method for distal one-third humerus fractures. Additionally, larger sample size studies are necessary to clarify the efficacy of anterior plating with LCP.
Conclusion
Our study showed that in distal third humeral fractures, stable fixation can be achieved using an anterior straight plate if a length of 50 mm from the proximal margin of the coronoid fossa is secured even if the distal fragment is small, where both the near and far cortices have a width of at least 10 mm at the most proximal portion of the fracture line.
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