Reverse total shoulder arthroplasty (RTSA) is known to improve the functional outcome of patients with cuff tear arthropathy. Most patients after RTSA report good clinical scores and pain reduction as well as recovery of range of motion [1,2]. In addition, owing to advances in surgical techniques and devices, decreasing complication rates are reported [3].

However, the RTSA procedure remains technically challenging and results in a number of complications such as scapular notching, early loosening, instability, and poor function [4,5]. In particular, these complications are associated with glenoid component malpositioning, especially superior tilt of the glenoid component [6]. Variable scapular anatomy, glenoid bone loss, and joint stiffness contribute to difficulty in proper positioning of the glenoid component [7]. Abnormal glenoid morphology is observed in about 40% of patients requiring RTSA, making it unfeasible to place the glenoid component along the anatomic center line in these patients [8,9].

Preoperative planning with 3-dimensional (3D) imaging and patient-specific instrumentation (PSI) helps in resolving problems that might occur in total knee replacement [10,11], and these techniques have recently been introduced in shoulder arthroplasty to overcome the problems of glenoid deformity and bone loss. Patient-specific guides (PSGs) have been suggested to improve the accuracy and reproducibility of the positioning of components in RTSA [7,12].

Considering the above rationales, numerous studies have been initiated for PSG, particularly cadaver studies [7,13]. Although most patients with rotator cuff arthropathy have abnormalities of the glenoid [8,9], cadavers with standardized glenoid (with no defect or deformity lesion) can be worked on, and has the advantage of allowing to check for actual reproducibility.

This study aimed to assess whether the use of our novel PSG, constructed using a 3D technique, in RTSA would allow accurate and reliable implantation of the glenoid and humeral components.

This study is a prospective randomized clinical trial designed to test the hypothesis that applying PSGs with 3D reconstruction technique is superior to conventional surgical techniques for the placement of glenoid and humerus components in cadaveric shoulders. The SDs of superoinferior offset, anteroposterior offset, inclination, and version were lower in the PSG group than in the conventional group, indicating that the use of PSG is more consistent than the conventional method in positioning the glenoid component. Furthermore, the humeral stem canal center angle in the humeral component was significantly lower in the PSG group (p=0.009). The humeral stem in the PSG group was precisely located at the center of the medullary canal of the humerus, compared with the conventional group.

The RTSA procedure is technically challenging and is reported to be associated with instability, early loosening, scapular notching, and poor function, especially due to glenoid component malpositioning [4,5,17-19]. Errors in inclination angle are known to impart the greatest probability for clinical failure in total shoulder arthroplasty (TSA) [20]. Similarly, in RTSA, errors in inclination need to be avoided due to increased scapular notching and component loosening [21].

However, it is more difficult to control the version and slope, especially if the original articular surface is not aligned neutrally owing to wear or abnormal shape; thus, accuracy and reproducibility are dependent on the surgeon’s skills and interpretation of the position and shape of the scapula.

To solve these problems, some authors used computer-assisted navigation to improve the accuracy of glenoid component positioning and wear correction [22,23]. However, navigated systems often require large and expensive equipment for implementation, thereby increasing the operating time by 20%, and conferring additional cost to the procedure [24,25].

As an alternative method to overcome this problem, PSGs created using the 3D reconstruction technique enable preoperative planning with automatic software. Moreover, the use of PSG provides accurate and reproducible positioning and orientation of the glenoid and humeral components in RTSA. Early cadaver studies on TSA and RTSA have reported the accuracy and reproducibility of PSI. Levy et al. [7] reported the accuracy of PSI in positioning the glenoid baseplate in RTSA. They reported that the translational accuracy of the starting point for the guide pin averaged 1.2 ± 0.7 mm, whereas the accuracy of the inferior inclination was 1.2° ± 1.2° and that of the glenoid version was 2.6° ± 1.7°. Their study concluded that PSGs were highly accurate in reproducing the starting point, inclination, and version set on preoperative guides. Walch et al. [26] also showed a good correlation between preoperative planning and the achieved position of the guide pin in an in vitro study on the use of PSI for glenoid component placement in TSA. They reported a mean entry point position error of 1.05 ± 0.31 mm, a mean inclination error of 1.42° ± 1.37°, and a mean version error of 1.64° ± 1.01°.

In an in vivo study, Gauci et al. [27] reported that the mean error of the glenoid component in PSI was lower than that of the glenoid component and the preoperative planning value in anatomical TSA. The mean error in the accuracy of the entry point was -0.1 ± 1.4 mm in the horizontal plane and 0.8 ± 1.3 mm in the vertical plane. The mean error in the orientation of the glenoid component was 3.4° ± 5.1° for version and 1.8° ± 5.3° for inclination. In a series of 10 consecutive patients who underwent TSA and RTSA with PSI, Suero et al. [25] also reported that PSI enables adjusting the position of the glenoid component and screws.

However, in a recent study, Lau and Keith [28] claimed that PSI was not as successful as it appeared in previous studies. They produced PSGs that permitted 0° glenoid inclination and version in TSA, and 10° inferior inclination in RTSA. For the TSA group, the mean version was measured at 8° ± 10° retroversion and 1° ± 4° inclination. For the RTSA group, the mean version was 10° ± 10° retroversion and -1° ± 5° inclination. They demonstrated that the use of PSGs does not automatically allow flawless glenoid component positioning. We designed PSGs for accurate implant positioning by applying 3D CT and automatic software, and showed good consistency in cadavers. However, it is unknown whether our PSG will show good results in vivo.

The most important aspect in the implantation of a humeral component in shoulder arthroplasty is to set the correct entry point at the center of the humeral canal. Failure to set the correct entry point results in malalignment, such as varus of the humeral component, which in turn leads to long-term implant failure. Another important aspect of the humeral component is that neck cutting should be precise and should match the version and inclination of the patient’s own humeral anatomical neck. If the retroversion becomes larger or smaller, the external rotation and internal rotation may be restricted [29,30]. As per our understanding, there are few reports on implantation of humeral components using PSG. We designed a humeral PSG to improve the humeral stem alignment, and our results indicate better stem alignment than the conventional method. However, the PSG system only provides a helpful anatomical guideline of the humeral canal for surgeons, and does not replace the comprehensive understanding of the complex anatomy of the proximal humeral.

The current study is meaningful in being a level I clinical trial using cadavers to evaluate this technique in RTSA. However, there are some limitations to our technique and study, which are consistent with the precautions required when applying PSI in RTSA. First, creating a PSG depends on a precisely defined preoperative plan using the accurate 3D model of the patient’s scapula. Although accurate 3D models of the scapula and humerus need to be separated from the surrounding soft tissue, this could prove difficult owing to cartilage loss, severe bone defect, calcification, stiffness, and previous fractures. Second, a stable fit and precise positioning of the PSI guide to the glenoid rim is dependent on exposure after sufficient removal of the soft tissue around the joint surface; thus, there is a possibility of damage to important structures and subsequent complications. Third, this study lacks analysis of other variables such as screw position. The guidelines for glenoid positioning, which consider the peripheral screws used and the patient’s bone quality, are currently unclear. In this study, version and tilt were used as neutral values, but this was not true for all cadavers. More research is required to investigate the ideal glenoid positioning for maximum functionality and mechanical stability.

Compared to the standard conventional surgical techniques, the use of PSGs with a 3D reconstruction technique reduces variability in the positioning of glenoid and humerus components and prevents extreme position errors in RTSA. However, although application of PSG adds to the preoperative planning time, the surgeon’s intuition remains important. The clinical effects, costs, and long-term effects of this technology require further cost-benefit analysis and clinical research.