Prosthetic shoulder arthroplasty, part 1

Question: Given the expanding indications for prosthetic shoulder arthroplasty, what challenges and controversies remain?

Issue: October 2016

ByJonathan C. Levy, MD

BySamer S. Hasan, MD, PhD

Expanding indications of RSA may further advance prosthetic shoulder arthroplasty

The utilization of shoulder arthroplasty continues to increase, as shoulders have consistently been the fastest-growing segment of the arthroplasty market. A larger active arthritic patient population combined with numerous reports of the durability and reliability of shoulder arthroplasty has resulted in this sustained exponential growth. However, possibly the single most influential reason for this growth has been the introduction of the reverse shoulder replacement. Reproducible outcomes with decreased complication rates continue to be observed and expansion of indications has since resulted.

Shoulder arthroplasty was traditionally reserved for end-stage arthropathy. Those cases with associated irreparable rotator cuff tears were managed using hemiarthroplasty and had “limited goals” expectations. With reverse shoulder arthroplasty (RSA), the framework of defining patient expectations has changed. Improvements in both pain and function have been observed consistently for many of the challenging indications for arthroplasty and even for cases of rotator cuff insufficiency without arthritis.

As the learning curve for this new procedure has evolved — both in terms of surgical technique and implant technology — the confidence in RSA has expanded. Cases that would traditionally be managed with anatomic arthroplasties with less predictable results are now often being managed with RSA; these include patients with osteoarthritis and repairable rotator cuff tears, osteoarthritis patients with severe static instability and posterior wear, patients with thin rotator cuff tendons and/or atrophied rotator cuff muscles and elderly patients with osteoarthritis. The use of RSA in these scenarios remains controversial, as no study to date has compared the outcomes of RSA to total shoulder arthroplasty (TSA) in those patient populations.

Challenges remain

Certainly, challenges remain for both anatomic and RSA. For anatomic TSA, glenoid loosening remains one of the most common long-term complications. With multiple studies demonstrating patients with loose glenoids reporting worse outcomes, the goal of improving glenoid fixation has been universal. Multiple methods of improving glenoid fixation have been developed to enhance fixation: press-fit pegs with improved fixation; metal-hybrid glenoid components with the potential to create long-term bonds between the implant and glenoid bone; and components that require minimal use of cement with hopes of osseous integration. However, if glenoid loosening can be overcome, glenoid wear will likely become the next problem. In an effort to limit glenoid wear, improvements in polyethylene previously used in hip and knee arthroplasty have been applied to glenoid components, including highly cross-linked polyethylene and vitamin E polyethylene components.

Another controversy in anatomic TSA relates to the proper management of patients with glenoid retroversion, posterior wear and posterior subluxation, often referred to as the Walch B2 glenoid. Concerns relate to reports of higher rates of glenoid loosening and worse outcomes in this subset of patients. Surgical techniques and implant alternatives have been utilized in an attempt to improve these results. Included in these methods are the use of augmented glenoids, posterior-bone graft, partial correction of glenoid version by reaming the anterior glenoid and RSA. Only with comparative studies will this controversy be answered. Many of these methods are being studied in this patient population.

Common complications

After the introduction of the RSA, there were numerous concerns regarding how complications could be managed. Most of these concerns have been subdued, as most common complications have found manageable solutions. Early glenoid baseplate failures seen in earlier designs are now rare with improved understanding of surgical technique and modifications in implant designs. When glenoid baseplate failures do occur, revisions have been successful for the most part. The same can be said for RSA instability and humeral periprosthetic fractures. Postoperative neuropraxia associated with RSA over-lengthening which typically resolve with time.

Possibly the greatest unsolved RSA complication remains acromion and scapular stress fractures. While osteoporosis has been shown to increase the relative risk of these fractures by two-fold, no other risk factor has been identified to help surgeons avoid this complication. Most patients who sustain acromion stress fractures maintain improvements from their preoperative level of pain and function, yet many continue to have disabling pain with no predictable or reliable solution. Efforts at better understanding how to avoid these postoperative fractures and selection of optimal treatments will facilitate management of this complication.

With the expanding indications of RSA, the justification for this trend will be defined by long-term success. Will outcomes following RSA outperform those following TSA? Will RSA complications continue to be successfully managed? Answers to these questions with long-term follow-up will help define the popularity of RSA.

References:
Buckingham BP, et al. J Shoulder Elbow Surg. 2005;doi:10.1016/j.jse.2004.10.008.
Carpenter SR, et al. Curr Rev Musculoskelet Med. 2016;doi:10.1007/s12178-016-9319-x.
Hendel MD, et al. Am J Orthop (Belle Mead NJ). 2016;45(4):220-227.
Khatib O, et al. J Shoulder Elbow Surg. 2015;doi:10.1016/j.jse.2015.05.038.
Levy JC, et al. J Bone Joint Surg Am. 2013;doi:10.2106/JBJS.K.01516.
Noyes MP, et al. J Shoulder Elbow Surg. 2015; doi: 10.1016/j.jse.2015.02.018.
Teusink MJ, et al. J Shoulder Elbow Surg. 2014;doi:10.1016/j.jse.2013.09.010.

For more information:
Jonathan C. Levy, MD, is chief of orthopedics at Holy Cross Hospital, program director at Holy Cross Shoulder and Elbow Fellowship, medical director at Holy Cross Orthopedic Research Institute and an Orthopedics Today Editorial Board member. He can be reached at Holy Cross Hospital, 5597 N. Dixie Hwy., Oakland Park, FL 33334; email: jonlevy123@yahoo.com.

Disclosure: Levy reports he is a paid consultant for and receives royalties from DJO Global.

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Evolution of surgical techniques should minimize complications

Prosthetic shoulder arthroplasty is growing exponentially in the United States and abroad at a rate that exceeds the growth of total knee arthroplasty.

Samer S. Hasan, MD, PhD — Samer S. Hasan

The number of prosthetic shoulder arthroplasties performed in the United States has increased from less than 14,000 in 1993 to 72,000 in 2013; that number likely approached 100,000 in 2015. The principal catalyst for this domestic growth was the introduction of RSA in 2003. RSA has revolutionized the treatment of cuff tear arthropathy, massive rotator cuff tears with pseudoparalysis, proximal humerus fractures and failed prosthetic shoulder arthroplasties.

However, other factors have also contributed to this trend. Young orthopedic surgeons are exposed to prosthetic shoulder arthroplasty during residency training and many gain additional training during fellowship training in shoulder and elbow surgery, upper extremity or sports medicine, so they are comfortable performing prosthetic shoulder arthroplasty in practice. In addition, patient expectations are evolving with many elderly patients unaccepting of shoulder pain, stiffness and dysfunction that when conservative treatment fails for shoulder arthritis, these patients embrace prosthetic shoulder arthroplasty and prospects of improved shoulder comfort and function.

Due to studies demonstrating durable clinical results in older patients clearly superior to those of salvage alternatives, such as glenohumeral arthrodesis, young patients with advanced shoulder arthritis are also being considered for prosthetic shoulder arthroplasty.

New techniques, technologies

In recent years, new techniques and technologies for prosthetic shoulder arthroplasty have emerged in addition to RSA, which have helped address previously unmet needs. Despite the expanding indications in prosthetic shoulder arthroplasty, many controversies and challenges remain, which include optimizing surgical technique to minimize complications, refining the precision of component implantation to restore shoulder anatomy and function and enhancing implant durability and adaptability as prosthetic shoulder arthroplasty is performed in younger and more active patients. Precise indications for various types of prosthetic shoulder arthroplasty are evolving and risks and benefits need to be evaluated both with respect to each other, as well as to emerging non-prosthetic techniques and alternatives, such as superior capsular reconstruction and novel tendon transfers for irreparable rotator cuff tears and arthroscopic and biologic interventions for shoulder arthritis.

Exposure of the glenohumeral joint during anatomic shoulder arthroplasty is most commonly achieved by performing a subscapularis tenotomy or peel though a deltopectoral approach. However, many surgeons currently favor lesser tuberosity osteotomy to promote bone-to-bone healing and facilitate monitoring of that healing postoperatively. Although several studies have demonstrated superior repair integrity and/or subscapularis function following lesser tuberosity osteotomy, others have not, and irrespective of repair technique concerns remain about the alarmingly high incidence of subscapularis muscle atrophy, which is most likely a neurogenic phenomenon.

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New subscapularis-preserving approaches have been developed to circumvent concerns about tendon healing and muscle atrophy; these include exposures through the rotator interval inferior to the subscapularis and arthroscopic-assisted techniques. However, these strategies have a steep learning curve, require specialized instrumentation and have limitations, especially with respect to resecting inferior humeral osteophytes and exposure for glenoid preparation. In addition, careful patient selection appears to be critical, so these techniques may not generalize to most surgeons and their patients.

Complications

Prosthetic joint infection is a potentially catastrophic complication, and therefore, efforts to prevent this infection during prosthetic shoulder arthroplasty are critically important. One challenge unique to prosthetic shoulder arthroplasty in comparison to other joint arthroplasties is infection frequently caused by Propionibacterium acnes, a commensal and indolent organism that can lead to frequent false-positive and false-negative cultures inhibiting our ability to make an accurate diagnosis.

Although there is widespread agreement regarding certain strategies for preventing prosthetic joint infection, such as using chlorhexidine during surgical preparation and discarding the skin knife after incision, other strategies remain controversial, such as using antibiotic-impregnated cement or applying antibiotics powder to the wound prior to closure. With the lack of consensus on prevention, there is no consensus definition on infection after prosthetic shoulder arthroplasty, diagnosis and treatment. Strategies, including assays of joint fluid biomarkers, may help diagnose shoulder prosthetic joint infection.

Restoring normal glenohumeral joint anatomy and normal shoulder kinematics and function is a goal of prosthetic shoulder arthroplasty, but can be difficult in cases of severe glenoid retroversion. In particular, patients with Walch B2 glenoid deformity and the recent recognition of B3 glenoid deformity present a significant treatment challenge. Historically, biconcave glenoid wear patterns have been addressed at surgery by asymmetric reaming to correct or partly correct glenoid version. However, this strategy removes a substantial amount of glenoid subchondral bone leading to several undesirable consequences, such as increased risk of glenoid implant peg perforation and subsidence, and a medialized joint center, which decreases rotator cuff muscle tension and function. This is often confounded by the fact that patients with these glenoid wear patterns are often young, active men who have high expectations for strength recovery and implant durability.

New strategies, implants

New strategies are available to address severe glenoid deformity. New glenoid implants, such as the Global Steptech (DePuy Synthes) and the Augmented Equinoxe (Exactech), with an asymmetrical backside that are either sloped or stepped have been developed to address asymmetrical glenoid wear patterns. Short- and mid-term results are promising, but glenoid preparation can be difficult and requires the removal of a considerable amount of glenoid bone.

Another strategy is to abandon anatomic shoulder arthroplasty in favor of RSA, which may be easier to implant in a glenoid with deficient bone stock or residual retroversion as bone grafting to resolve the defect and fixing the metal glenoid baseplate without cement has been shown to be highly successful. However, high-level studies comparing these two strategies are lacking and concerns remain about the durability of RSA in young, active patients because of the paucity of long-term outcomes studies in this population.

The difficulty of addressing severe glenoid deformity has highlighted the marked imprecision in correcting glenoid version based on intraoperative assessment and 2-D imaging. One method to improve surgical precision is the use of computer-aided navigation, which has been used in other joints, such as the hip, knee and only in limited fashion in the shoulder. Overall, this technique appears to be too unwieldy to be used efficiently and consistently.

Preoperative planning

Preoperative planning using advanced imaging improves the precision of prosthetic implantation. Currently available software for several implant systems allows interactive virtual surgical planning for both anatomic and reverse total shoulder replacement. In addition, advances in 3-D printing have enabled the development of custom or patient-specific instrumentation or guides based on processed CT imaging to establish the location and orientation of the glenoid centerline prior to reaming in order to correct glenoid deformity. Implant manufacturers offer patient-specific instrumentation systems, such as PSI (ZimmerBiomet), Match Point System (DJO Global) and others.

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Several studies into advanced preoperative planning have demonstrated both utility and improved precision in correcting glenoid version. However, there is considerable debate on which surgeon should use it and when. Moreover, patient-specific instrumentation does not substitute for careful and thorough soft-tissue releases that maximize glenoid exposure, which may not be helpful for a less experienced surgeon. Conversely, high-volume shoulder replacement surgeons may struggle with justifying the added expense and operative time except for the most challenging cases. Overall, post-processing of advanced imaging, virtual surgical planning and patient-specific guides add to the cost of prosthetic shoulder arthroplasty that these strategies may prove to be difficult to justify unless used selectively.

Robotic surgery has revolutionized certain surgical subspecialties and is commonly used during unicompartmental knee arthroplasty and certain total hip arthroplasties. However, glenohumeral joint anatomy presently precludes robotic shoulder surgery, but that may change in the future.

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For more information:
Samer S. Hasan, MD, PhD, is an orthopaedic surgeon at MercyHealth Cincinnati SportsMedicine & Orthopaedic Center, chairman of the Department of Surgery, The Jewish Hospital – MercyHealth, volunteer instructor at the Department of Orthopaedic Surgery, University of Cincinnati and Orthopedics Today Editorial Board Member. He can be reached at MercyHealth Cincinnati SportsMedicine & Orthopaedic Center, 10663 Montgomery Road, Cincinnati, OH 45242; email: s1663h@yahoo.com.

Disclosure: Hasan reports he is a paid consultant for DJO Global.