Arguably the largest impact on TSA preoperative patient care as the result of advanced technology is the development of 3D preoperative planning software. Recent literature shows that the mere exercise of going through the thought process of preoperative planning in 3D leads to better accuracy in surgical placement of the final glenoid implant.¹,²,³,⁴,⁵ Such software has evolved rapidly in recent years and continues to be a major area of focus for development. This type of software is now widely available from most orthopedic implant manufacturers, which allows the surgeon to virtually perform a TSA procedure and place the glenoid and humeral implants in 3D space with millimeter and degree precision (FIGURE 52.1). All current systems allow for planning and adjustment of glenoid component positioning in the scapula, and some systems allow for templating the humeral component as well as manipulation of the bones in 3D space which can provide a basic biomechanical assessment of the effect of the type and position of the implants chosen.

At the time of writing, all commercially available software is CT-based and is constructed solely on the bony anatomy of a patient. Future advancements in imaging modalities will include visualization of the soft tissues around the shoulder, allowing for further evaluation and assessment by the surgeon beyond the bony structures. This could be accomplished through improvements in any of three currently available imaging modalities. The first improvement can be through advancements in CT scan imaging, where dual-energy CT or image postprocessing can enhance the visual acuity of soft tissue structures.⁶,⁷ The second can be through improvements in MRI, which traditionally is an imaging modality more suited for soft tissue visualization. Advancements and availability of high-resolution MRI with a small image slice thickness will need to be made more readily available to replace the current standard of care for shoulder arthroplasty imaging, which is a CT scan.⁸ A combination of imaging modalities may also be used, but due to the cost and logistic challenges of patients having more than one preoperative scan (both CT and MRI), one imaging modality will need to rise above the other as the better solution to visualize both bony and soft tissue anatomy. Although high-resolution CT is currently more readily available, MRI has the advantage of no radiation exposure for the patient as
well as higher resolution of soft tissue anatomy due to the different weighting abilities of the scanner detectors. The third imaging modality improvement could be with ultrasound, which technically has the highest spatial resolution of these three imaging modalities. However, challenges in beam penetration through the entirety of the shoulder, a lower signal-to-noise ratio, and variations in operator technique all present technical challenges that will need to be overcome before ultrasound can be adopted to produce a high-resolution 3D model of the shoulder.⁹

When a patient with metal implants in the shoulder is scanned with any of these imaging modalities, metal artifact is generated, distorting the image and limiting the efficacy of these scans in this clinical situation. Metal artifact reduction (MAR) techniques will continue to improve over time, especially as 3D imaging becomes more prevalent in orthopedics¹⁰,¹¹ (FIGURE 52.2). Although 2D biplanar x-ray imaging is a fourth imaging modality that has shown some promise in other total joint applications, this imaging technique does not have the local accuracy that CT imaging does for the shoulder, especially with regards to the local accuracy needed for accurate resolution of the glenoid and glenoid vault.

Once the soft tissue structures are incorporated into preoperative planning software, full assessment and optimization of the biomechanics of the joint can be performed. For an anatomic total shoulder arthroplasty (ATSA), it is well established in the literature that reproducing the anatomy is correlated with positive clinical outcomes.¹²,¹³ This includes reproduction of the native humeral head and restoration of the joint line, reconstruction of the glenoid anatomy with a properly positioned glenoid component, and proper tensioning of the rotator cuff.¹⁴,¹⁵,¹⁶,¹⁷ All of these parameters can currently be preoperatively planned, but limited information is provided to the user on what the optimal targets are and how to quantify them. Regarding glenoid component positioning, current literature shows there has yet to be a consensus on the proper way to plan for an individual patient. Not only is there high variability in planning the same patient among different surgeons but also high variability in planning the same patient at different times by the same surgeons.¹⁸,¹⁹ This lack of consensus will ultimately be settled by controlling for individual variables with long-term clinical outcome studies. Additionally, as computing power, imaging inputs, and shoulder-specific knowledge all increase, preoperative planning software will evolve to include a more patient-specific biomechanical analysis, which a process that is currently time-consuming and traditionally only available with statistical shape models (SSM)
in a research setting.²⁰,²¹ The customization and specificity provided by looking at the patient’s native joint offsets, muscle tensioning, comorbidities, and other patient-specific parameters will empower surgeons to optimize implant type and position based on not only established means but also on what is best for a particular patient.

The greatest area for improvement in optimizing soft tissue tensioning in TSA resides in reverse total shoulder arthroplasty (RTSA), as tensioning parameters are not only patient-specific but are also more greatly influenced by implant parameters due to the non-anatomic reproduction of the joint in RTSA. Different implant systems and manufacturers use a variety of parameters to adjust the medialization and lateralization of the glenoid and humeral components, amount of distalization of the humeral components, and overall tension of the joint.²²,²³,²⁴,²⁵,²⁶ A certain amount of glenoid/humeral lateralization for one patient may not be ideal for another, and vice versa. For example, a lateralized glenosphere may tension the deltoid more but could cause complications in an osteoporotic patient with a thinner acromion.²⁷,²⁸ However, determining the optimal tension of a RTSA will not only be influenced by offsets that create the most efficient moment arms but also by the efficiency, tensioning, and function of the individual muscles involved.²²,²⁹,³⁰,³¹ Future preoperative planning software that incorporates soft tissue data will be able to factor in the influence of these parameters and determine what may be optimal for a particular patient.

Another area of improvement involving soft tissues is quantifying the amount of fatty infiltration and volume of the muscle bodies.³² Specifically, being able to quantify the percentage of fatty infiltration of the rotator cuff and deltoid muscles will help surgeons discern if and how functional the muscles are before surgery, potentially aiding in the decision-making process to determine if a RTSA is preferred in a patient with an intact
but potentially nonfunctioning rotator cuff.³³,³⁴ This will benefit both ATSA and RTSA, as it will help surgeons determine the condition of specific muscles, their strength potential, how well they are functioning, and how their role will affect the greater biomechanics of the shoulder complex once other parameters are modified.

Lastly, there will be advancements in how the preoperative planning software user interface is delivered to and used by the surgeon. Traditional systems use software on a 2D computer screen or tablet, but future systems will evolve toward a mixed reality, augmented reality (AR), or immersive virtual reality environment.³⁵ These systems give the surgeon the ability to virtually perform the surgery in a digital environment that mimics the operating room (OR), often giving tactile, haptic feedback on surgical movements and providing valuable information on not only the optimal plan for the case but how to perform the procedure in a stepwise fashion (FIGURE 52.3). This may influence a surgeon’s preoperative plan in TSA; for example, in a scenario where a significantly retroverted glenoid implant is planned and then changed as a result of realizing challenging glenoid exposure with such retroversion during the virtual case. Such applications also have potential to aid in medical training by providing a safe, low-cost environment for physicians to practice in a virtual environment, where specific movements and procedures could be repeated until mastery is achieved.

As advancements in 3D printing continue to decrease cost and logistical challenges associated with traditional manufacturing techniques, the ability to machine implants and instruments on-demand and potentially even in a hospital or an OR environment will develop. Patient-specific instrumentation has been a popular application of 3D printing in TSA, but recent literature has shown mixed results with currently available techniques.⁴,³⁶ In addition, ordering imaging and custom instrumentation in advance of a procedure sometimes presents issues with lead times and available resources. With the ability to customize instrumentation on-site for a procedure, exact drill/saw guides and jigs can be created after surgical exposure of the bony landmarks, accommodating for variance in surgical approach and any change in the patient’s anatomy since the time of imaging. This will also enable a surgeon to pivot to a different treatment if needed by adjusting the custom instrumentation accordingly in real-time.

3D printing patient-specific implants and instruments on-demand will also greatly reduce the inventory needed for a TSA, as many manufacturer-specific instruments will no longer be needed to successfully perform the case. The large inventory of different sizes and types of implants required to be available for a specific case will no longer be necessary as only one implant will be produced for each case. This has the potential to reduce both OR time and the total cost of the procedure while also increasing surgeon confidence in the preoperatively planned and selected implant.

In addition to instrumentation, on-site 3D printing will allow surgeons to address complex anatomy at the time of surgery. Custom implants are traditionally reserved for severe deformities when a standard off-the-shelf product will not suffice. Improvements in 3D printing and reductions in manufacturing costs will bring mass customization to all patients. A risk with current 3D printed custom implants is having the implant not fit the patient at the time of surgery either due to further degeneration of the patient’s anatomy since the time of preoperative imaging or because of inaccurate implant construction from the imaging. On-site 3D printing could allow a more precise implant to be created to fit the patient’s anatomy after exposure and could more easily accommodate for intraoperative variables that are difficult to predict such as change in bony geometry due to fracture or tumor removal. It will also improve the patient experience in the healthcare system and potentially reduce the overall length of the treatment regimen. The patient could be scanned, have implants and instruments printed, and the case performed all within the same institution (FIGURE 52.4).

Another application of advanced technology in the intraoperative domain is through smart instruments. A smart instrument can be defined as any tool that is traditionally purely mechanical in nature but is augmented by electronic components to provide additional information or guidance to the user. One such instrument is a device to define the soft tissue tension in the shoulder. This would be clinically beneficial in both ATSA and RTSA but may have more utility in RTSA as proper tension is usually a technique that is “experience based”. Thus far, targets for optimal tensioning have yet to be quantified, but the effects of improper tension are well documented.³⁷,³⁸,³⁹,⁴⁰ An electromechanical humeral liner trial for RTSA that provides surgeons with the tension of the reduced RTSA construct in pounds and the point of contact of the load has recently been developed and is currently in early stages of clinical use (FIGURE 52.5). This has the potential to allow surgeons to define the optimal tension for a particular patient and vary the implant type and offsets accordingly. Research shows that RTSA tension is indeed patient-specific and does have a direct impact on range of motion (ROM).⁴¹ It will be important to evaluate the stability and tension of the joint throughout a dynamic ROM assessment and not just a static load assessment in one position (FIGURE 52.6). The effect of procedural differences such as subscapularis repair will also likely change the joint tension and biomechanics throughout the various ranges of motion. This type of tension measuring device will also be useful in ATSA and could help surgeons determine when to upsize or downsize the humeral head or when additional capsular releases or imbrication procedures are needed. Due to size constraints, the humeral head trials are the more likely location for the load sensors instead of the smaller glenoid components. A future application of such tensioning devices may be an automatically detecting and self-expanding trial implant or tensioning instrument to simplify the trialing process and more efficiently establish the proper tension for the ROM assessment portion of the procedure. Combined with recommendations from clinical outcomes, a patient’s unique biomechanics may be assessed real-time in the OR, providing the surgeon the opportunity to adjust implant type and position based on direct assessment rather than only preoperative imaging. Other smart instrument applications could be sensors used on the muscles themselves to determine individual muscle tension, strain, activation, and efficiency.

In addition, a common challenge in ATSA is determining if humeral bone has sufficient density and structure to support the use of a variety of press-fit implants that all load the bone in different ways (standard stem, short stem, stemless, or resurfacing humeral implant).⁴²,⁴³,⁴⁴ Assessments of the humeral bone are traditionally qualitative and rely on surgeon feel and judgment intraoperatively. An instrument with sensors could apply a local load to an area of the bone and provide feedback to the surgeon on thresholds for bone quality and what the anticipated fixation of different types of implants would be to assist in optimal humeral implant selection.

Intraoperative navigation provides additional patient and instrument positional information to the surgeon in real-time to help guide more precise and accurate placement of the instruments and implants during the procedure.⁴⁵,⁴⁶ This can be a tremendous benefit in TSA, where incisions are limited, and exposure of the glenohumeral joint can be challenging.⁴⁷ On the scapular side, the smaller bony anatomy of the glenoid provides a relatively small target for the glenoid implants, which can be difficult to orient properly even for experienced surgeons.⁴⁸ The detrimental impact of glenoid implant malposition is well documented in ATSA, potentially leading to early loosening.⁴⁹,⁵⁰,⁵¹,⁵²,⁵³,⁵⁴ In RTSA, implant malposition can not only cause early loosening but can adversely affect stability and ROM and result in complications such as scapular notching and dislocation.²²,³¹,³⁷,³⁸,⁵⁵,⁵⁶,⁵⁷,⁵⁸,⁵⁹,⁶⁰

Conventional navigation employs the use of a camera tracking system and registration algorithm to orient the patient’s physical anatomic structures to a virtual model from either preoperative imaging in image-based navigation or an SSM representing the anatomic structure in imageless navigation. Such systems provide feedback to the surgeon by overlaying the surgical tools on the patient imaging displayed on a screen as is common
in stereotaxic neurosurgery procedures or on a digital 3D rendering of the patient’s anatomic structure represented by an SSM. These systems require the creation of a local coordinate system to orient the patient to the imaging or SSM. This typically requires a surgeon to attach either an active (usually infrared light-emitting diode) or passive (infrared reflective) tracker to the patient’s bone and then perform a registration algorithm to orient the imaging to the patient’s body. This is typically performed manually via a handheld probe by touching specific structures on the patient as prompted by the navigation interface. However, this technique
can be prone to user error if the precise instructions are not followed or if the patient’s physical structures do not match the imaging. Additional trackers are then placed onto calibrated surgical instruments to orient the system.⁶¹ This entire procedure can be time consuming, often requires troubleshooting, and can be frustrating to the surgeon.