Adult humeral shaft fractures are a commonly encountered orthopedic condition, historically managed conservatively through the application of hanging casts or U-slabs [1-3]. Surgical intervention, such as plating or nailing, has traditionally been reserved for cases with fracture displacement or risk factors that may impede successful conservative treatment [4].

The optimal approach to surgical management of humeral shaft fractures remains a subject of ongoing debate, balancing the imperative of achieving anatomical reduction with the preservation of soft tissues. The primary treatment objectives include prompt restoration of upper limb function and successful fracture healing. Open reduction and internal fixation (ORIF) utilizing plates and screws have long been considered the gold standard due to their comparatively lower complication rates and shorter time to union in contrast to intramedullary nailing [5-7].

However, concerns surrounding soft tissue dissection inherent to ORIF have prompted the development of less invasive techniques, allowing for indirect reduction and bridge plating of the humerus. Initial reports have demonstrated favorable healing rates, satisfactory alignment, and infrequent complications associated with this approach [8-11]. Therefore, in this prospective study, we sought to evaluate the clinical, radiographic, and functional outcomes of anterior bridge plating utilizing the minimally invasive plate osteosynthesis (MIPO) technique for the treatment of humeral shaft fractures. The study encompassed a minimum follow-up duration of one year, enabling a comprehensive assessment of the efficacy of this surgical modality.

This study was approved by the Institutional Review Board of Dayanand Medical College and Hospital Ludhiana (No. BFUHS/2k12/p-TH/1043) after taking written consent from the patients. This prospective cohort study was undertaken at Dayanand Medical College and Hospital in India and enrolled a total of 43 patients who underwent anterior bridge plating utilizing the MIPO technique from January 2016 to January 2017. The inclusion criteria were patients between 25 and 65 years of age presenting with closed, displaced diaphyseal fractures of the humerus. Prior to surgery, informed consent was obtained from all participants. Patients with open fractures, concurrent neurovascular injury, or a history of infection in the humerus or elbow were excluded from the study. The exclusion of open fractures was due to the increased risk of infection and complications, which could confound the outcomes specific to the MIPO technique. Open fractures are associated with higher infection rates and may require additional surgical interventions, making them less suitable for a minimally invasive approach like MIPO. Furthermore, cases with previous infection were excluded to prevent potential biases related to compromised bone healing or persistent infection risk, which could adversely affect the outcomes of the surgical procedure and the study's validity.

Among the 43 patients initially enrolled, one patient experienced a sudden cardiac event, likely myocardial infarction, approximately 2 and a half months after sustaining the humeral fracture. Additionally, two patients were lost to follow-up. Consequently, complete follow-up data for evaluation and analysis were available for 40 patients. All of these fractures were treated using an anterior locking compression plate inserted via the MIPO technique.

Of the 40 patients included in the final analysis, 31 were male and nine were female, with a mean age of 48.18 years (range, 25–65 years). The fractures were classified according to the AO classification system, as summarized in Table 1. It is noteworthy that more than half of the fractures (25 fractures) affected the non-dominant hand among the participants in this study.

The AO classification system was utilized to categorize the fractures based on their anatomical characteristics. Among the patients included in this study, the majority of fractures fell under the BII category, accounting for 42.5% of the cases. Fractures categorized as AI, AII, AIII, BI, CII, and CIII were also observed in varying proportions. No fractures were classified as BIII or CI in this patient cohort.

The patient population exhibited a notable prevalence of multiple fractures, with only seven patients presenting with an isolated humeral shaft fracture. The distribution of associated injuries among the patients is presented in Table 2, providing a comprehensive overview of the injury patterns observed in our series. Upon admission, all patients underwent a thorough evaluation, including neurovascular assessment and Advanced Trauma Life Support examination, in the emergency department. Postoperative, the functional outcome of the affected upper extremity was assessed using the University of California at Los Angeles (UCLA) score for shoulder function and the Mayo Elbow performance score.

Within our patient cohort, nine individuals exhibited blunt trauma chest injuries, while seven had fractures in the shaft of the femur. Additionally, six patients had fractures involving the distal end of the radius and phalanx, while five patients sustained tibia and fibula fractures or clavicle fractures. Only one patient presented with a fracture involving both bones of the forearm.

Among the 40 patients enrolled in this study, a total of nine fractures affected the non-dominant upper limb. All patients sustained injuries as a result of road traffic accidents. In our series, fracture union was observed in 38 cases, accounting for a success rate of 95%. However, two fractures failed to achieve union within the 6-month follow-up period and necessitated a secondary bone grafting procedure to facilitate union.

Among the 38 patients who experienced fracture union, the radiographic assessment revealed that three fractures (7.5%) achieved union in less than 12 weeks, 33 fractures (82.5%) achieved union between 12 and 16 weeks, and two fractures (5%) required more than 16 weeks to achieve union (Fig. 3). The average length of incision in our study proximal was 2.8 cm (2–3 cm) and distally was 3.1 cm (range, 2.5–3.5 cm) which was believed to have cosmetically appropriate outcomes with our patients.

When evaluating final functional outcomes of the shoulder, an excellent result was observed in 33 patients (82.5%), while seven patients (17.5%) demonstrated good shoulder function, as determined by the UCLA score. Regarding the final assessment of elbow function, 31 patients (77.5%) achieved an excellent outcome, six patients (15%) achieved a good outcome, two patients (5%) attained a fair outcome, and one patient (2.5%) with concurrent fractures of both forearm bones exhibited a poor outcome.

It is worth noting that a considerable proportion of the cases included in this study involved polytrauma (33 patients), and some patients presented with additional fractures in the same upper limb as the humeral shaft fracture under investigation. We believe that the presence of such concomitant fractures in the affected upper limb may have introduced some complexity to the final clinical analysis.

The mean side-to-side differences for shoulder abduction, external rotation, internal rotation, and forward elevation were 4.1º, 3.5º, 4.8º, and 5.2º, respectively (Table 3). These differences in ROM between the operated and nonoperated sides were found to be statistically significant (P<0.001). However, despite the statistical significance, no clinically meaningful differences were identified in the overall subjective outcomes assessed using the questionnaire.

Adult humeral shaft fractures are prevalent, constituting 3% of all orthopedic injuries, and imposing a substantial societal burden [12]. While conservative management has traditionally been considered the "gold standard" for humeral fractures, there has been a global trend among orthopedic surgeons towards a preference for surgical intervention in adult humeral diaphyseal fractures. This shift can be attributed to the changing dynamics of society, where individuals are increasingly engaged in demanding occupations and patients require expedited return to work. As a result, the acceptance of conservative treatment for humeral shaft fractures has decreased, leading to an increased preference for surgical intervention in managing these fractures. Operative treatment is a viable option for adult humeral shaft fractures that are amenable to conservative management. The two primary methods of operative fixation for these fractures are intramedullary nailing and compression plating. Although external fixation plays a role in polytrauma or as a temporary stabilizer, its use for definitive management is limited and not recommended due to the risk of pin tract infection [13].

Despite the availability of various surgical techniques, none are devoid of risks and complications. Interlocking nailing is preferred for comminuted, segmental, and pathological fractures, while plating is preferred when radial nerve exploration is necessary [6,14]. Antegrade interlocking nails can lead to impairment of shoulder function due to the impingement caused by proximal migration of the nail, violation of the rotator cuff, and adhesive capsulitis [7,15,16]. This problem can be minimized by using a retrograde technique, although it carries a risk of elbow movement restriction and fracture at the insertion point [16,17]. Conventional plating techniques involve an extensive surgical approach for open reduction of such fractures, and common concerns in plating patients include infection, nonunion, radial nerve palsy, and elbow stiffness [7,16-18].

Literature reports healing rates ranging from 88% to 100% for ORIF of humerus diaphyseal fractures [6-8,14,15,19-22]. Adequate fracture reduction is consistently reported, with malunion occurring in less than 5% of cases [6,7,19,20]. However, iatrogenic radial nerve injuries have been reported in up to 31% of cases, and infections have been reported in approximately 3%–7% of cases, with some studies reporting infections in 21% of fractures [7,8,14,15,17-21]. Extensive soft tissue dissection and wide radial nerve exposure associated with ORIF may be potential risk factors for these complications. Furthermore, bone grafting is frequently required to achieve high union rates, with reported frequencies ranging from 0% to 49% in the literature [6,7,19-21].

Intramedullary techniques have raised concerns regarding restricted shoulder movements and the risk of delayed union [5-7,16-18]. Although reaming may facilitate bone healing, nonunion has been reported in 0%–9% of cases, and complications such as splitting or bursting of the shaft can occur during retrograde nail insertion [23-27]. However, these complications can be minimized by avoiding levering or forceful manipulation and carefully advancing the nail with axial turning movements. Iatrogenic fractures of the humeral shaft occur in approximately 0%–5.8% of cases treated with nailing [26].

The MIPO technique for plating humeral shaft fractures has gained popularity due to its preservation of the blood supply compared to the open plating technique, which requires periosteal stripping [8,28]. The advantages of the MIPO technique include higher union rates, less soft tissue dissection, decreased need for bone grafting, and faster functional recovery [8,28]. Several studies on MIPO of humerus shaft fractures have reported healing rates of 100% for closed fractures and between 90% and 100% for open fractures [8-11]. Infection rates after MIPO range from 0% to 17% in closed fractures and from 0% to 7% in studies including open fractures [8-11]. The healing rate of 94% reported in our study supports MIPO as an effective surgical option for humeral shaft fractures. Compared to other studies employing both MIPO and conventional plating techniques, our study's union rates are consistent with the upper range of reported outcomes. Similar studies by An et al. [8] and Jiang et al. [9] report union rates between 90% and 100% for MIPO, similar to our 95% success rate. No superficial or deep infections attributed to closed fractures were encountered in our series, which can be attributed to the use of strict aseptic conditions in the operating room and perioperative antibiotics in accordance with the literature. We encountered two cases of nonunion attributed to smoking; both individuals were active smokers and did not discontinue smoking even after surgery. To address this issue, the patients were provided with counseling regarding the detrimental effects of smoking on fracture healing and were strongly advised to quit smoking. Subsequently, both patients underwent bone grafting without the need for hardware removal, and the fractures successfully achieved union within 4 months following the secondary procedure. The literature revealed a consistent association between smoking and delayed fracture healing, increased risk of nonunion, and poorer overall outcomes, as smoking affects blood flow and oxygenation, alters osteoblasts activity, and, moreover, inhibits growth factor production leading to delayed union [29-31].

In terms of elbow ROM, our study found an average ROM of 116°, similar to the results reported by Jiang et al. [9] and Pospula and Abu Noor [11]. Most studies on MIPO in humeral shaft fractures have reported average elbow ROM ranging from 128° to 134° [8-11]. Furthermore, MIPO consistently results in elbow ROM above 100°, which is the minimum value required for normal elbow function [8-11,32]. In our series, two patients had a final coronal angulation of at least 10°. Although the humerus can tolerate coronal angulations of up to 20° before becoming functionally limiting, our results indicate the technical complexity of achieving anatomical alignment using a minimally invasive approach.

To ensure adequate fracture alignment, we focused on three aspects: (1) achieving adequate abduction of the upper extremity during surgery to avoid varus malalignment, (2) maintaining 30° of elbow flexion with longitudinal traction of the arm to prevent flexion-extension malalignment, and (3) obtaining intraoperative images in anteroposterior, lateral, and oblique views using an image intensifier machine. No iatrogenic radial nerve injuries occurred in our series, which can be attributed to blunt dissection, careful retraction, gentle handling of soft tissues, and the absence of Homann's retractors, consistent with most studies. Only one case of iatrogenic radial nerve palsy following the MIPO technique has been reported in a series of humeral shaft fractures by Pospula and Abu Noor [11].

One of the challenges of anterior humeral bridge plating using the MIPO technique is achieving adequate fracture reduction. Unlike conventional ORIF, which allows direct visualization of the fracture and temporary stabilization with bone clamps, MIPO requires indirect reduction techniques and closed fracture manipulation during plate fixation. Despite these challenges, malunion rates for anterior bridge plating range from 0% to 3%, similar to those reported for ORIF [8-11].

The use of locking or simple cortical screws in anterior humeral bridge plating remains a topic of discussion. Currently, there is no conclusive study in the literature supporting either option. However, we believe that locking screws might excessively stiffen the construct, increasing the risk of non-union [33,34]. In our cases, we used locking screws in four patients (10%) with poor bone quality, as we were concerned about the potential backing out of cortical screws. This area could be further investigated to compare the results of anterior humeral bridge plating with cortical and locking screws.

There are several limitations to our study. First, we did not have a control group for comparison, and the follow-up rate was less than 100%, which may have introduced bias. However, the primary objective of our study was to evaluate the functional outcome of anterior humeral bridge plating in humeral shaft fractures. Second, the postoperative calculation of humeral malrotation was not accurately determined as no postoperative computed tomography scans were performed. However, intraoperative reduction with good clinical alignment of the upper limb was visually confirmed based on the criteria by Krettek et al. [35] and validated by a senior trauma surgeon with extensive experience in orthopedic trauma surgery. Finally, the potential risk of secondary shoulder arthritis due to inadvertent malrotation during surgery, as reported by Wang et al. [36], would require a longer follow-up period to determine the exact incidence and could be explored in future studies.

Anterior humeral bridge plating using the MIPO technique has shown favorable outcomes in terms of high union rates, minimal disruption to the soft tissue envelope, improved cosmesis, and rapid and satisfactory functional recovery in patients with humeral shaft fractures. Based on our findings, we highly recommend this approach as an effective treatment option. However, it is important to note that the procedure is complex and entails a steep learning curve for optimal results.