Intra-articular distal humerus fractures are uncommon injuries, with a reported incidence of 5.7 to 8.3 per 100,00 people per year [1,2]. These fractures are challenging to treat and often require surgical intervention. In younger patients with good bone quality and higher functional demands, the preferred surgical option is open reduction and internal fixation (ORIF). Studies have shown that the functional outcome after fixation of intra-articular fractures is directly related to the quality of reduction, especially the joint surface [3,4].

The recreation of three-dimensional (3D)-printed models of fractured bone from computed tomography (CT) data could be beneficial for preoperative planning of complex cases. To improve visualization of the fracture with conventional imaging modalities, 3D models allow a better sense of the fracture fragments and manipulation needed prior to the actual surgery. Such models also allow creation of patient-specific custom implants that better suit individual anatomy [5].

Despite these benefits, 3D printing is not routinely used in preoperative evaluation and surgical planning of distal humerus fractures. It is unclear if application of 3D printing will significantly improve functional outcomes. Hence, we conducted this systematic review and meta-analysis to answer the following questions: (1) Does the application of 3D-printed models of distal humerus fractures lead to quicker surgeries, with a reduction in need for fluoroscopy? (2) Do these surgeries result in less blood loss compared with conventional methods? (3) Is the complication rate lower for surgeries operated with 3D printing assistance, and do they have a better overall functional outcome?

We hypothesized that 3D printing would lead to quicker surgeries with less use of fluoroscopy and fewer complications, potentially improving final clinical outcomes. This research draws a detailed comparison of cases operated using 3D-printed models with those performed using conventional techniques to offer better evidence in favor or against this technology. To the best of our knowledge, there have been no previous systematic reviews on this topic.

Because this is a systematic review article and we did not process individual patient data, ethics approval was not deemed necessary.

Distal humerus fractures present distinct challenges for the treating surgeon owing to their complex anatomy, soft tissue injuries, and excessive load on the implants. Inadequate reduction of joint surface leads to inferior functional outcomes. Therefore, proper preoperative planning is crucial, and use of 3D-printed models could play an important role in managing these fractures.

Our systematic review revealed that application of 3D printing-assisted surgery produced significantly better outcomes than conventional methods in terms of quicker procedures with less intraoperative blood loss. Patients who underwent surgery with 3D printing also had a lower rate of perioperative complications and better overall functional outcomes than conventional surgery patients, but this difference was not statistically significance. Similar results have been reported in studies focusing on other intra-articular and complex injuries such as tibial plateau fractures, pilon fractures, pelvic-acetabular fractures, proximal humerus fractures, and revision total hip arthroplasty [11-16].

The group with 3D-printed models consistently demonstrated reduced surgical duration. Nevertheless, a more comprehensive assessment is necessary to determine the clinical significance of these time savings. Prolonged operating time is directly linked to the incidence of perioperative complications [17]. Although the difference in complication rate among the two the groups did not reach statistical significance, the significant reduction in surgical duration due to 3D printing-assisted surgery could potentially decrease the incidence of complications, especially infections. The significant decrease in blood loss with the help of this technique could also play a role in reducing postoperative anemia-related complications.

In the articles assessed in this review, 3D printing was primarily used for preoperative planning, wherein 3D-printed models are physical replicas that demonstrate the fracture's distinct morphology and allow the surgeon to carry out simulated reduction maneuvers. These models could be used to plan the ideal surgical approach and the direction of screws, for implant selection and positioning, and to determine the requirements for bone grafts. This technique could greatly help amateur surgeons in their surgical planning of multi-fragmentary articular fracture patterns (AO type C3).

Despite the various benefits, this technique does have some drawbacks. The added costs involved in preparing the 3D models are generally passed on to the patients, increasing their economic burden. According to Yang et al. [9], the cost of printing a 3D model was only U.S. $ 2–3; however, this does not account for the capital required to set up the printing facility, which requires expensive instruments likely beyond the budget of low-volume clinics. Complex 3D models require time for preparation and printing, limiting their application in emergency cases or open fractures. These limitations notwithstanding, because setting up a 3D printer is a one-time investment, and since this technique may be applied to other areas such as fractures of the proximal humerus, pelvis/acetabulum, and in arthroplasty cases, we recommend 3D printing facilities for centers that have sufficient capital and caseloads.

This meta-analysis also has a few limitations. Because a primary outcome was not defined, the potential for type-I and type-II errors is inflated. The included studies did not report a sufficiently long follow-up to account for long-term complications such as secondary osteoarthritis. The relatively small overall sample size could also explain why some results did not reach statistical significance. The lack of blinding of participants and personnel in most studies may have also led to bias. Yang et al. [9] and Zheng et al. [10] provided data on blood loss, but Shuang et al. [8] did not, which restricts the potential for a comprehensive pooled analysis. Due to the limited number of studies and their potentially diverse contexts, the findings may not be universally applicable.

Despite these limitations, there are several strengths to this review. To the best of our knowledge, this is the first meta-analysis evaluating the utility of 3D printing in the fixation of distal humerus fractures. We strictly followed a pre-defined study protocol. All the included studies were randomized controlled trials, giving rise to the best quality of synthesized evidence. There was uniformity in reporting the outcomes between all the studies.

Application of 3D printing assistance in distal humerus fractures—especially AO type 13C3, multi-fragmentary, complete articular fractures—leads to significantly shorter operating times and less blood loss, indirectly reducing the risk of infection. This technique could also potentially improve the reduction quality and postoperative functional outcomes, but more high-quality studies are required to generate sufficient evidence.