1. Introduction
Clavicle fractures account for 2% to 5% of all adult fractures and are particularly common within shoulder girdle fractures, which comprise 35% to 44% of such injuries [
1,
2,
3,
4]. Traditionally, clavicle fractures were treated nonoperatively with figure-of-eight bandages, even in cases with substantial displacement. This approach was supported by early studies indicating nonunion rates of less than 1% with conservative treatment and relatively high nonunion rates following operative treatment [
5,
6,
7]. However, recent studies report several complications of conservative treatment such as shortening, malunion, limitation of motion of the shoulder joint, and poor patient satisfaction due to long period of motion restriction. These studies suggest operative treatment, which provides firm internal fixation, resulting in an early recovery of the range of motion.
The human clavicle is highly variable within any given population. It is a double-curved, S-shaped, three-dimensional structure with complex morphology. Variations exist not only in its length and diameter but also in its cross-sectional shape and the degree of bowing. Differences are observed between males and females and even between the left and right clavicle in the same individual. This indicates significant personal deviation in clavicle anatomy [
8,
9,
10,
11].
Surgical treatments for clavicle fractures include interfragmentary screw fixation, cerclage wiring, intramedullary fixation, and plate fixation [
12,
13,
14,
15]. Plate fixation provides rigid fixation, allowing for early mobilization [
16,
17]. It is particularly preferred in displaced comminuted fractures where soft tissues impede fracture reduction. Plate fixation also offers firm stabilization through cortical bone compression and resistance to torque. One meta-analysis study reported that plate fixation reduced the nonunion rate from 15.1% to 2.2% [
18]. However, due to the unique anatomic diversity, clavicle fractures are still challenging injuries to shoulder surgeons.
Pre-contoured anatomical plates were introduced to address these challenges by fitting the natural shape of the clavicle. The original purposes of the pre-contoured plates are to shorten operation time by eliminating the step of contouring the plate at the time of surgery, reducing the possibility of malreduction resulting in malunion afterwards, and preventing skin protrusion by improper fitting of the plate. However, surgeons often find that these plates do not perfectly conform to the clavicle’s unique anatomy, necessitating additional manipulation and bending during surgery.
The application of 3D printing technology in medicine has significantly advanced over recent decades [
19,
20,
21,
22]. In orthopedics, 3D printing is used for creating anatomical models primarily for surgical planning, as well as for producing surgical guides and custom implants. Surgical guides and custom implants created with 3D printing technology have become widely used and continue to develop rapidly [
8,
23,
24,
25]. These custom implants and guides offer advantages such as reduced surgical time, improved clinical outcomes, and decreased radiation exposure [
26].
The aim of this study is to evaluate the conformity of pre-contoured anatomical plates to the human clavicle and to analyze the variations in clavicle shape and length between individuals using 3D-printed clavicle models. Our hypothesis was that, due to the significant anatomic variance in human clavicles, the three widely used commercially available pre-contoured anatomical plates would show a range of conformity with the actual human clavicle.
4. Discussion
By using 3D-printed models, this study demonstrated significant individual differences in anatomic clavicle morphology. The pre-contoured clavicle plates showed low conformity and high variance among individuals. Additionally, the lateral distance between the distal end of the clavicle and the plate was not consistent, making it difficult to suggest an objectively optimal position. This study also identified the potential for a medial gap, which, if too large, could result in malreduction, necessitating additional bending. Furthermore, the possibility of overhang was observed, which could make it difficult to use the distal screw holes if the overhang is significant.
Superior clavicle plating, which is commonly chosen, carries risks such as underlying neurovascular injury, prominent skin protrusion, or hypertrophic scarring. To address these issues and accommodate the complex 3D anatomy of the human clavicle, a distal clavicle anatomical pre-contoured plate was developed. This plate aims to shorten operation time by eliminating the need for additional bending during surgery and reducing the risk of infection associated with plate repositioning. If the plate does not anatomically contour to the bone precisely, it can lead to nonunion or malunion of the fracture. Additionally, skin protrusion caused by an imperfectly contoured plate may result in discomfort and cosmetic problems, potentially requiring further surgery for plate removal.
Numerous studies have reported good clinical outcomes using pre-contoured plates. Fleming et al. [
27] reported a 100% union rate and excellent return of function, with no mandatory need for removal. High union rates with good clinical outcomes and low complication rates were reported using superior locking pre-contoured plates in patients with distal clavicle fractures in a study by Andersen et al. [
28]. Chandrasenan et al. [
29] revealed that pre-contoured anatomical plates are fit to the actual clavicle and shorten the operation time. Additionally, their high mechanical strength decreases the likelihood of metal breakage. VanBeek et al. [
30] reported that plates with low profiles and beveled edges help prevent skin protrusion, thereby reducing the necessity for plate removal.
However, despite these advantages, pre-contoured plates often do not fit the clavicle perfectly. This misfit is due to the complex anatomical features of the human clavicle and individual variations. A cadaveric study by Andermahr et al. [
31] which analyzed the length, diameter, and curvature of 196 embalmed and 10 fresh human clavicles, revealed significant anatomical variations among individuals. When comparing sexes, male clavicles were found to be longer, thicker, and to have a greater curvature than female clavicles. Consistent with previous studies, the length of the clavicle differed significantly between men and women in this study.
In terms of the conformity between pre-contoured plates and human clavicle models, this study revealed significant discrepancies, particularly with larger gaps observed in shorter clavicles. These findings align with the study by Huang et al. [
32]. which identified the apex of the superior bow on the lateral aspect of the clavicle as a challenging fit for pre-contoured plates. Furthermore, unlike in men, pre-contoured plates did not conform well in white women. Unlike our study, which analyzed Asian clavicle models, Huang et al.’s research focused on the pre-contoured Acumed Locking Clavicle, a design optimized for the medial three-fifths of the clavicular shaft. Their study employed a two-dimensional analysis using digital image software (Adobe Photoshop). Malhas et al. [
8] suggested that smaller clavicles, commonly found in women, benefit more from plating systems with various plate shapes. Most anatomical studies have been conducted on Western populations, including white and black individuals, and the design of pre-contoured plates typically reflects these populations’ anatomical data. In contrast, our study used 3D models of Asian clavicles, which led to larger gaps and greater discrepancies in plate conformity.
Most anatomical studies on the human clavicle have been cadaveric or based on imaging software, such as Photoshop or 3D virtual reconstruction medical software using CT data [
32,
33]. Particularly, assessing the contact and compatibility of pre-contoured plates with the clavicle in simulation studies can be challenging, especially concerning screw fixation, because the contact situation may change after compression from screw fixation. This study is significant because it used actual clavicle models created with 3D printing technology instead of relying solely on image-based simulations. By using these actual models, it is possible to replicate the real conditions of plate fixation. Additionally, a bone clamp was used in this study to simulate the compression of the plate via screw fixation, providing a more accurate representation of the clinical scenario.
Over the past decade, 3D printing technology has been widely adopted in medicine. Particularly in orthopedics, it has been actively applied to implant design and the creation of surgical guides [
34,
35,
36]. Prebending the pre-contoured clavicle plate prior to surgery and using the prebent plate during the operation can potentially shorten the operation time and is especially beneficial when employing the minimally invasive plate osteosynthesis (MIPO) technique. Kim et al. [
3] demonstrated that preoperative prebending of pre-contoured plates, compared to intraoperative bending, resulted in better anatomical reduction and shorter surgery times in patients with mid-shaft clavicle fractures. Additionally, another study by Kim et al. [
37] utilized 3D-printed clavicle models to improve the fitting of pre-contoured plates in comminuted fractures, which facilitated minimally invasive procedures and enhanced fracture healing.
The current study had multiple limitations. First, the plating and measurement were performed by a senior surgeon, whose subjectivity may have influenced the process. Although the surgeon has extensive experience with clavicle fractures, the surgical concept and perspective of a single individual could have impacted the objectivity of this study. However, efforts were made to ensure objectivity by using clamping to replicate the plate and clavicle mismatch encountered during actual surgeries. The experience of a seasoned senior surgeon was utilized to enhance the reliability of the measurements. Second, only the vertical and horizontal lengths between the clavicle model and the pre-contoured plate were measured and analyzed. Due to the use of 3D-printed models, three-dimensional measurements such as rotational or angular assessments were not conducted. Third, the Meshmixer software was used for smoothing to address step-off artifacts in the reconstructed model. However, differences or variations were not verified using specific features. The authors minimized the smoothing process to modify only the step-off artifacts and preserve the original structure. Fourth, only three products from the anatomical distal clavicle plate system were evaluated. Different results might be obtained with other products. Nevertheless, this study is significant because it focused on pre-contoured anatomical distal clavicle plate systems, in contrast to previous studies that analyzed plates suitable for the mid-shaft or medial three-fifths of the clavicle [
29,
30,
32,
33]. Fifth, the sample size was relatively small, with only 30 cases, which may limit the generalizability to the entire population. However, the clavicle lengths of both men and women in this study followed a normal distribution, with 100% post hoc power [
38].