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At Issue: Prosthetic shoulder arthroplasty, part 2
Question: With the introduction of new and novel implant designs for use in anatomic and reverse TSA, how might these influence technological advances?
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Emerging technological advances pave way for future patient care
Although total reverse shoulder arthroplasty is performed more frequently than anatomic total shoulder arthroplasty in the United States and abroad, reverse shoulder arthroplasty is not typically indicated for patients with shoulder arthritis and an intact rotator cuff.
Moreover, the incidence of rotator cuff insufficiency increases with age, and many patients with an intact rotator cuff who undergo anatomic shoulder arthroplasty will eventually develop a rotator cuff tear. Although silent, these rotator cuff tears can become symptomatic and require treatment.
In addition, some patients develop symptomatic subscapularis failure shortly after surgery, but unless this is recognized and treated promptly, the tear may be irreparable at revision surgery.
In these situations, conversion from anatomic shoulder arthroplasty to reverse shoulder arthroplasty becomes necessary. Historically, this has required the removal of the well-fixed humeral stem and cemented polyethylene glenoid components. While extracting a press-fit stem with limited or without proximal coating can be straightforward, some cases can be difficult.
Hemiarthroplasties performed in an osteopenic bone or for fracture may be implanted with cement. Extracting well-fixed cemented stems introduces difficulty and potential for great morbidity. The removal of existing implants adds surgical risk, time and cost, as well as additional costs of new implants.
Convertible stems, implant systems
The need to convert from anatomic shoulder arthroplasty to reverse shoulder arthroplasty (RSA) and the cost and challenges of removing well-fixed components has motivated the development of platform systems that employ convertible modular humeral implants. This may enable the anatomic humeral head component to be exchanged for a reverse shoulder socket, while leaving the well-fixed humeral stem in place. On the glenoid side, there has been some renewed interest in metal-backed implants. The metal backing serves as a baseplate, and the polyethylene glenoid can be replaced with a glenosphere that affixes to that baseplate.
The concept of convertibility is desirable, but several barriers to its widespread acceptance remain. Compared with anatomic stems, some reverse stems sit lower within the humeral metaphysis to accommodate an inlayed socket. Moreover, the inclination angles for anatomic shoulder arthroplasty and RSA may be different.
These differences can be addressed by various adapters or by using a modular humeral component composed of separate stem and body components. At revision surgery, the longer body of an anatomic shoulder arthroplasty can be replaced by a shorter body that accepts an inlay RSA shell and socket, while retaining the same distal stem. However, increased modularity introduces increased opportunity for implant failure at various interfaces.
On the glenoid side, the polyethylene implant for an anatomic shoulder arthroplasty is inserted in neutral inclination, but for RSA, slight inferior tilt may be desirable. Furthermore, metal-backed glenoids in anatomic shoulder arthroplasty have suffered from high rates of early failure and historically inferior results because the overall glenoid construct is too thick or the polyethylene component is too thin.
Short stems, stemless designs
Early humeral stems were long implants that were designed for diaphyseal fit and fill. However, modern stems obtain metaphyseal fit because of the refined instrumentation for humeral bone preparation, as well as textured and/or hydroxyapatite proximal coating.
Consequently, long stems are unnecessary, and the current trend favors shorter stems. These have certain advantages in cases of humeral deformity, such as fracture malunion, and in cases of ipsilateral elbow surgery. Although these are often touted as bone-conserving, short-stem implants require as much bone removal and bone preparation as longer stems. Humeral loosening is rare with conventional humeral stems. Newer short stems will need to demonstrate similar results and low revision rates.
Recently, several implant manufacturers have taken this trend a step further with the development of stemless humeral implants, such as the Simpliciti Shoulder System (Wright Medical Group) and Eclipse Shoulder Arthroplasty System (Arthrex). These are similar to conventional implants in that these replace the resected humeral head. However, instead of employing a stem that is inserted into the diaphysis for stability and fixation, these devices rely solely on metaphyseal fixation and use cages or other fixation methods. Stemless designs have enjoyed widespread use in Europe for several years, and more recently, the Simpliciti Shoulder System has been approved for use in the United States.
Alternative bearings
Glenoid implant durability is the weak link during anatomic shoulder arthroplasty and although this relates mainly to glenoid implant loosening, there has been concerns over glenoid polyethylene wear and osteolysis. Polyethylene wear is also a concern in RSA because wear and osteolysis may contribute to scapular notching.
Vitamin E-infused polyethylene has demonstrated decreased wear in hip and knee studies. However, the clinical benefit of this remains unknown and it may be several more years before this is clinically established.
Humeral heads and glenospheres are typically manufactured from a cobalt-chrome alloy, which contains nickel. Patients with a documented nickel allergy can undergo prosthetic shoulder arthroplasty, employing a titanium humeral head or glenosphere, which are nickel-free components.
Other alternative bearings offer the promise of superior wear and biocompatibility, but remain unavailable in the United States. Ceramic glenospheres have been developed and are in use in Europe. However, ceramic is a brittle material, especially for the hip, so concerns have been raised regarding its durability.
Pyrolytic carbon or pyrocarbonate is a material similar to graphite that has a long history of use in wrist implants and more recently, for radial head and interphalengeal joint implants. One advantage of this material is that it articulates well with and causes less damage to cartilage, so it may be useful for humeral head replacement or hemiarthroplasty design. Pyrocarbonate is brittle, which complicates fabrication and limits its applications.
Future patient care
Novel implant designs, convertibility and alternative bearings, such as pyrocarbonate, offer hope for younger patients considering prosthetic shoulder arthroplasty because these advancements improve implant durability and facilitate revision. More refined surgical planning and advanced imaging has led to improved surgical precision and deformity correction, but indications for patient-specific guides are evolving.
Surgical techniques are being refined to optimize subscapularis management, prevent prosthetic joint infection and avoid other complications. The expectation is that well-designed, high-level studies of these emerging techniques and technologies will translate into evidence-based recommendations to help guide the care of our patients in the future.
- References:
- Boileau P, et al. J Shoulder Elbow Surg. 2002;doi:10.1067/mse.2002.125807.
- Carpenter SR, et al. Curr Rev Musculoskelet Med. 2016;doi:10.1007/s12178-016-9319-x.
- Churchill RS. J Shoulder Elbow Surg. 2014;doi:10.1016/j.jse.2014.05.005.
- Churchill RS, et al. Curr Rev Musculoskelet Med. 2016;10.1007/s12178-016-9320-4.
- Churchill RS, et al. J Bone Joint Surg Am. 2016;doi:10.2106/JBJS.15.00181.
- Cuff D, et al. J Shoulder Elbow Surg. 2011;doi:10.1016/j.jse.2010.10.026.
- Gutiérrez S, et al. J Bone Joint Surg Am. 2008;doi:10.2106/JBJS.H.00012.
- Habermeyer P, et al. J Shoulder Elbow Surg. 2015;doi:10.1016/j.jse.2015.02.023.
- Harmer L, et al. Curr Rev Musculoskelet Med. 2016;doi:10.1007/s12178-016-9313-3.
- Jackson JD, et al. J Shoulder Elbow Surg. 2010;doi:10.1016/j.jse.2010.04.001.
- Ives EP, et al. J Clin Ultrasound. 2013;doi:10.1002/jcu.21980.
- Levy DM, et al. Int J Shoulder Surg. 2016;doi:10.4103/0973-6042.180720.
- Morwood MP, et al. J Shoulder Elbow Surg. 2015;doi:10.1016/j.jse.2015.01.015.
- Oral E, et al. Int Orthop. 2011;doi:10.1007/s00264-010-1161-y.
- Sahota S, et al. J Shoulder Elbow Surg. 2014;doi:10.1016/j.jse.2014.02.004.
- Schairer WW, et al. J Shoulder Elbow Surg. 2015;doi:10.1016/j.jse.2014.08.026.
- Sher JS, et al. J Bone Joint Surg Am. 1995;77(1):10-15.
- Tashjian RZ. Clin Sports Med. 2012;doi:10.1016/j.csm.2012.07.001.
- Taunton MJ, et al. J Bone Joint Surg Am. 2008;doi:10.2106/JBJS.G.00966.
- Wagner ER, et al. Clin Orthop Relat Res. 2015;10.1007/s11999-015-4448-x.
- Werner BC, et al. Curr Rev Musculoskelet Med. 2016;doi:http://dx.doi.org/10.1007/s12178-016-9317-z.
- Wieser K, et al. Clin Orthop Relat Res. 2015;doi:10.1007/s11999-014-3985-z.
- For more information:
- Samer S. Hasan, MD, PhD, is an orthopaedic surgeon at MercyHealth Cincinnati Sports Medicine & 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.
Innovation in prosthetic systems offers improved outcomes in shoulder arthroplasty
Future technological advances in shoulder arthroplasty must answer challenges in three major areas: reproducibility; adaptability; and revisability. To date, improvements in prosthetic systems have resulted in an increase in the volume of shoulder arthroplasties in the world, the number of physicians performing the operation and an expansion of indications for the procedure to include cases with greater soft tissue and bony deficiency.
Although innovation has progressed more slowly in shoulder arthroplasty compared to hip arthroplasty and knee arthroplasty, it has been steady since the procedure gained popularity in the 1970s.
Reproducibility
“The worst thing you can do for some people is to give them too many choices,” my mentor, Louis U. Bigliani, MD, used to say. While prosthetic systems must strive to deal with variability in anatomy, the decision-making process during surgery must be relatively straightforward and reproducible. Computer-assisted navigation systems, such as those pioneered by Joseph P. Iannotti, MD, PhD, are in its early stages, but are helpful in allowing careful preoperative planning with regard to prosthetic sizing and placement. These systems are helpful in allowing visualization of bony deformity and can be used to develop patient-specific instrumentation.
Current techniques in shoulder arthroplasty depend too much on “eyeballing,” especially on the glenoid side. Even in the hands of experienced surgeons, deformity correction and implant placement are not as accurate or ideal when performed free-hand compared to when utilizing a guide system. Computer-assisted navigation in its current form is expensive and time-consuming, and progress in this area must include improvement in both of these issues.
The expansion of 3-D printer availability may have a big impact in allowing physicians to routinely create models of their patients’ shoulders and drilling guides, which will make this technology more practical. When the art of shoulder arthroplasty is replaced by science, the procedure will become more reproducible.
Adaptability
The first shoulder implant systems had few component options, and the surgeon often had to work hard to adapt the patient to the implant with less than optimal results. The so-called “third generation” of shoulder prostheses, pioneered by Gilles Walch, MD, was designed around a better understanding of proximal humeral anatomy.
Newer stemless humeral components have allowed surgeons to reliably situate the humeral head in the face of significant proximal humeral deformity, as seen in cases of post-traumatic malunions. Results are comparable to stemmed implants, while preserving proximal humeral bone stock. These components are being used successfully in standard cases of glenohumeral arthritis.
Glenoid deformity remains a challenge, and the most common method of dealing with typical posteroinferior glenoid wear is to “take down the high side.” This often leads to a loss of subchondral bone and may be associated with earlier implant loosening and failure. Newer posteriorly augmented glenoid components are now available and allow preservation of subchondral bone. The effectiveness and durability of glenoid components will require scrutiny in the years to come.
Revisability
Shoulder arthroplasty revision offers unique challenges that have resulted in outcomes inferior to those seen in revision hip arthroplasty. Humeral bone quality is often compromised, and removal of a well-fixed humeral stem often leads to significant damage to the bone and its surrounding soft tissues.
Convertible stems have limited the need for stem extraction, as long as these were placed correctly at the index procedure. Stemless components are easily revisable without significant bone injury. The trend toward shorter stems has resulted in greater preservation of humeral bone stock without significant issues of stem loosening. Glenoid bone loss in the face of component loosening remains a challenge, and new tools for preoperative planning with 3-D CT scans and custom components are now being tested.
Cases of severe bone loss may require some type of augmentation with either a metal screw-in component or bony and metal-backed screw-in component. Longer term studies will be required to determine the durability of these constructs.
There is no doubt that reverse total shoulder has revolutionized our ability to revise failed prostheses in the face of bony or soft tissue deficiency, and further investigation into the optimization of component design and positioning is ongoing.
The future of shoulder arthroplasty is bright with significant innovation in component systems that allow us to offer this treatment to a greater variety of patients with improvements in functional results and longevity. As more surgeons perform this surgery, design teams should focus on issues of reproducibility, adaptability and revisability.
- References:
- Boileau P, et al. J Bone Joint Surg Br. 1997;79(5):857-865.
- Churchill RS, et al. J Bone Joint Surg Am. 2016;doi: 10.2106/JBJS.15.00181.
- Iannotti J, et al. J Bone Joint Surg Am. 2014;doi: 10.2106/JBJS.L.01346.
- Karelse A, et al. J Shoulder Elbow Surg. 2014;doi: 10.1016/j.jse.2013.11.023.
- Neer CS. Clin Orthop Relat Res. 1982;(170):189-195.
- For more information:
- Xavier A. Duralde, MD, can be reached at Peachtree Orthopedics, 2045 Peachtree Rd., Ste. 600, Atlanta, GA 30309; email: mhooton@pocatlanta.com.
Disclosure: Duralde reports he has no relevant financial disclosures.
A note from the editors
Click here to read part 1 of this At Issue discussion.