3D printed patient specific customised surgical jig for reverse shoulder arthroplasty, a cost effective and accurate solution

The Reverse shoulder arthroplasty is a common operation performed for rotator cuff arthropathy and proximal humerus fractures. A frequently encountered difficulty during this procedure is in the implantation of the glenoid component. In view of the smaller size of the Asian glenoid, as well as the exposure of the glenoid face, much estimation and guesswork is required when placing the central wire that guides instrumentation. The placement of the central wire is key to achieving optimal bony purchase and therefore impacts implant stability and longevity. Achieving a central position is difficult as the scapula converges to become a thin column of bone, and the intraoperative view glenoid does not reliably indicate the direction of this column of bone due to variation in the version of the scapula (Fig. 1).

Technology such as navigation and patient specific instrumentation have been developed to overcome this difficulty, however, there are still logistical, technical and economic barriers to wide scale adoption. Available technology such as navigation is accurate and allows real time positioning, but navigational instruments are bulky, requires additional imaging machines, and may increase operative time for registration of anatomical landmarks. Patient specific instrumentation is expensive costing $1200 - $1600 SGD, and takes 4–6 weeks for transfer of images overseas and development and shipment of patient specific jigs.

Therefore, the current problems remain, with instrumentation left to the surgeons’ best guess and estimation. This leaves much to be desired in the pursuit of optimal implant positioning for improved patient outcomes, as well as surgical precision and confidence especially for junior surgeons.

3D printing has revolutionised orthopaedic surgery with multiple applications showing benefit. We therefore sought to create a cheap and accurate local solution in the form of a patient specific 3D printed surgical guide.

A customised surgical guide jig was designed with a handle and a drilling guide hole. Surgical guide jigs were printed and designed in in-house 3D printers (Formlabs3B) using surgical guide resin material and sterilized before surgery.

The 3D surgical jig was used in 8 patients in our institution with an average age of 79 years.

There were 2 male and 6 female patients in this case series.

5 were performed for proximal humerus fractures, and 3 were performed for rotator cuff arthropathy.

The average glenoid width was 25.1 mm and glenoid height was 29.6 mm.

Amongst females, the average glenoid width was 23.5 mm and glenoid height was 28.8 mm.

With the use of the jig for central screw placement, the tip of the central screw with respect to the center of the scapula on the axial cut was an average of 3.3 mm. Central screw length was an average of 35 mm (Fig. 7).

The anatomical glenoid measurements and demographics of the patients can be found in Table 2.

Preoperative, postoperative Xrays and Postoperative sagittal cuts of the CT scans are shown in Table 3.

There were no intraoperative complications whilst using the 3D printed jig. All 3d printed jigs were inspected and found to be intact after usage and did not leave any visible plastic residue on the patient. Nevertheless, thorough irrigation of the wound after usage was implemented as per usual protocol.

Our series showed that 3D printing is an accurate and reproducible method of the placement of the central wire in the reverse shoulder arthroplasty. This is mirrored in other studies showing accuracy of instrumentation in total hip arthroplasty, pelvic/acetabular fractures and pelvic resection margins.

Positioning of the central wire when using the 3D printed jig reduced the need for second guessing and estimation. Because the 3D jig was contoured to the patient's anatomy and could only be placed in a certain position, there was no debate to the ideal position of the jig. The jig then guides the wire placement and greatly improves the accuracy of the wire placement. Of note, the 6th patient had rotator cuff arthropathy and posterior glenoid wear. The 3D printing model was especially useful in this case as without it, the positioning of the wire would have been difficult and would likely end up pointing anteriorly and perforating the anterior cortex of the glenoid. This showed that the wire position guided by the 3D jig allowed accurate placement even in difficult anatomy. In this case, posterior bone grafting was used to fill the posterior defect (Fig. 8).

The time taken from CT to jig creation and sterilisation ranged from 2 days to 2 weeks.Naturally, as our team increased in experience in the processes required to create the jig, the time from CT to jig creation shortened dramatically to 2 days. This highlights the need for a constant team that is familiar with the processes of segmentation, jig creation and 3D printing to reduce the time taken for fabrication of surgical jigs. This is especially important in time sensitive operations such as fractures and tumours.

3D printing enhanced our preoperative surgical planning in every case in this series. It improved the surgeons anatomical understanding of the glenoid and the limitations of the small glenoid and narrow corridors of bone. This was especially evident in the 6th case, where the posterior bone loss would have made it difficult for estimation of the ideal wire placement using the conventional method of wire placement. This was however circumvented by the use of the 3D printed jig, allowing accurate placement of the wire and thus improved bony fixation. This also improved the confidence of the surgeon intraoperatively, and reduced guesswork and estimation.

The cost price for consumables required to create the jig was estimated to be $50 per surgical guide. This showcases the vast difference in costs with in-house 3D printing versus commercial vendor created guides that are usually produced overseas. Alternative technologies such as navigation cost$500 SGD and are not currently available in Singapore. Vendor supplied patient specific instrumentation costs $1200-$1600 SGD and takes 4–6 weeks to be fabricated. Although this study did not include cost of the printer or manpower costs, recent economic analysis of use of 3D printing in surgery found that an estimated 63 use cases of surgical guides or preoperative models were required per year to break even and account for annual fixed costs of manpower, printer and consumables.

Through the process of various iterations of creating the surgical jig, we encountered various difficulties and gleaned several learning points. Firstly, as Asian glenoids are smaller in size, the entry point of the wire that gives the best trajectory into the thickest portion of the scapula is slightly anterior to the center point. Our study found an average glenoid width of 25 mm and glenoid height of 29.6 mm. This highlights the small size of the glenoid, contrasting with the size of the glenoid base plate which is already 25 mm in diameter. Secondly, soft tissue dissection during the operation is usually more difficult posteriorly and inferiorly due to the humerus. This meant that creating anterior and superior phlanges of the jig to contour to existing anatomy was ideal so as to avoid soft tissue impingement and improper seating of the jig. Thirdly, a longer handle made handling of the jig easier during the operation. Fourthly, some allowance for the central wire is required during creation of the jig wire hole. We found that if the hole is exactly the diameter of the wire, the increased friction of the wire when it is passed through the jig causes the wire to get stuck to the jig. We recommend a 3.3–3.35 mm hole for a 3.2 mm wire. Furthermore, the thickness of the jig also affects the accuracy of the wire placement as too thin a jig allowed more angular motion of the wire. Conversely, too thick a jig resulted in increased friction. We found that a thickness of about 1 cm was appropriate for optimal wire entry and accuracy. Fifth, we recommend using a non-threaded 3.2 mm wire for the central wire positioning. Initially, the use of the conventional threaded wire caused the jig to shift during insertion as the threads which are meant to engage the bone engaged the inner surface of the jig. Lastly, added stability can be obtained by adding other K wire holes to anchor the jig to the glenoid before drilling of the 3.2 mm wire.

This series did not compare surgical times with and without the usage of the 3D surgical jig. This is inherently difficult to study as different surgeons have different operating styles and speed of operating. Each case also varies in difficulty and many other factors play into the surgical time of an operation such as anaesthesia time, indication for operation, and concomitant injuries. To perform a randomised controlled trial to determine if intraoperative time were reduced would require a lengthy recruitment period and the use of much needed resources. In the case of this series, it was our aim to prove that the use of the surgical jig was an accurate and reproducible way to insert the initial guide wire. Nevertheless, anecdotally, the surgeon felt that there was a possibility of reduction in surgical time as there was no need for second guessing of the wire placement. The jig took approximately 10 s to be applied and a quick confirmation of wire placement took another 10 s. Recent literature also found that 3D printing reduced of surgical time, blood loss and the amount of intraoperative fluoroscopy.^,

As 3D printing continues to develop in our institution, we foresee application of the 3D printing technologies in a few other ways. Firstly, preoperative planning for the surgeon, planning reduction techniques and implant placement. Secondly, patient, resident, and student education in teaching anatomy, showcasing surgical aims and practicing instrumentation. Thirdly, creation of other surgical jigs for corrective osteotomies, screw/wire placement, surgical excision of tumours, and reconstruction after bony excision. Lastly, printing of implants such as custom-made plates that allow perfect contouring to bone, customised prosthesis and metal cages for filling of bone defects. These applications have been showcased in world renown centres such as Mayo Clinic (US) and Queen Mary Hospital (Hong Kong), and have been found to provide much benefit.^,

However, although beneficial, this process is time consuming and requires adequate expertise. For it to become a working service to the hospital such as in Mayo Clinic, there is a need for an established center for 3d printing with existing manpower and expertise that can streamline the process and be ready to troubleshoot problems and respond to issues during the segmentation, design and printing processes. Although clinicians play a part in the 3D printing by providing surgical expertise, their busy clinical schedules do not allow dedicated time to oversee the process. Therefore, dedicated personnel are required for manning of the 3D center to allow efficient and timely provision of this service to patients in the hospital setting.

The use of a patient specific customised 3D jig is a cost effective and accurate solution to the central wire placement in the reverse shoulder arthroplasty. This technology can be replicated in many other applications not only limited to orthopaedic surgery. Other institutions may benefit from this technology with affordable start-up costs, yet reap the benefits of 3D printing.