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Stemless and short stem humeral components in shoulder arthroplasty.

Shoulder arthroplasty design has undergone continuous evolution since the original monoblock design of Neer. Current humeral stem designs are frequently modular, to allow for intraoperative decisions made by the surgeon to dictate the final sizing of the device based on individual patient variables. However, even with maximum stem modularity in its current form, there are still situations of metadiaphyseal deformity that make using a stemmed device very difficult. In addition, while loosening of a humeral stem in the absence of infection is uncommon, other stem-related problems do exist in shoulder arthroplasty. Stem related issues can be divided into intraoperative and postoperative problems. In response to these clinical issues and industry market-related challenges, there has been a period of rapid growth of short stem and stemless devices for humeral-sided arthroplasty. We will review the literature available on these different designs.

Historically, humeral stems have progressed from monoblock components designed for cemented fixation to modular coated devices for press-fit application. Intraoperative complications associated with the use of a stem include humeral shaft fracture during preparation, insertion, or removal; difficulty removing a well-fixed stem either because of aggressive coating or because of cement fixation during revision surgery necessitating humeral shaft osteotomy; and malalignment of the metadiaphyseal portion of the humerus requiring tuberosity osteotomy in cases of post-traumatic deformity. (1,2) The natural offset from the intramedullary axis of the humerus and the center of rotation of the humeral head can lead some surgeons using stemmed devices to malposition the humeral head as well, resulting in altered joint kinematics and rotator cuff dysfunction. Problems that surgeons encounter after insertion of a stemmed device include proximal bone loss from stress shielding, postoperative periprosthetic fractures, osteolysis from polyethylene debris, and prosthetic loosening.

Additionally, the rapid growth of stemless devices has been driven by market factors. Specifically, manufacturers with only third generation shoulder prostheses, as opposed to fourth generation prostheses, are unable to completely reproduce the proximal humeral anatomy. This is most obvious in the inability of these prostheses to accurately reproduce a patient's humeral neck angle in a continuous manner: third generation systems attempt to reproduce neck angle in a costly manner by providing multiple stemmed devices at defined neck angles that may or may not correspond to the patient's actual humeral neck anatomy or to that of the osteotomy. Stemless devices are less expensive from an inventory perspective because of the reduced modularity, as they do not require different neck angles and require a smaller scope to reproduce the anatomy without concern for intramedullary canal size, which commonly varies between 7 mm to 17 mm in diameter.

Short Stem Review

The uncemented short stem prosthesis is a bone preserving design, and if the short stem is a platform or convertible design, it also has the potential to have a simplified revision option to or from anatomic and reverse shoulder arthroplasty. Stable proximal fixation of the short stem prosthesis is typically achieved by compaction of metaphyseal cancellous bone.

No mid-term or long-term follow-up is currently published for short stem devices. After 2 years of follow-up, 44 Aequalis Ascend patients demonstrated improvement in Constant and pain scores with few complications and exhibited clinical results comparable to those of established prosthetic systems. (3) A radiographic assessment showed 13.6% of cases with slight stress shielding at the medial cortex, but no stem subsidence was found. (3) Similarly, the Biomet Comprehensive "mini" stem (83 mm length) underwent a retrospective study with 44 patients who underwent a primary rTSA. (4) At a mean follow-up of 27 months, pain was rated as mild or none in 97.7% of shoulders, patients had improved range of motion and improved Neer scores with 95.4% being excellent or satisfactory, and there was no radiological evidence of loosening of the humeral stem in any patient. (4)

Stemless Design Review

Stemless designs completely avoid diaphyseal instrumentation and fixation and resect the humeral head at the anatomic neck. Designs for fixation range from threaded central cages to larger coated metaphyseal derotational fins with or without a collar that can sit on the cut surface of the humeral head. These devices are ideally suited for younger patients in which revision can be expected in the future in order to preserve bone stock and also for deformity cases where even short stem devices would not be useful without a realigning tuberosity osteotomy. Because of the anatomic neck osteotomy utilized by stemless devices, the humeral head resection allows for easier exposure to resurface the glenoid, as compared to humeral head resurfacing, though it is less bone preserving.

While stemless devices remove less overall bone than stemmed devices, they likely remove more metaphyseal bone as that bone is exclusively relied upon for fixation. As some stemless devices do not permit the use of both aTSA and rTSA, these devices may need to be removed at revision to a rTSA. Given that more metaphyseal bone is likely removed, it is important to recognize that the fixation in revision surgery may be compromised by the use of a stemless device at the primary surgery.

The TESS device was first reported in 2010 to improve range of motion, as well as Constant, WOOS, and DASH scores. (5) Intraoperative fractures did occur during the early learning curve while inserting this device, none of which were recognized at the time of surgery and all of which healed uneventfully. (5) In comparative studies against the Neer II and Bigliani-Flatow devices, the TESS fared well and had similar outcomes for osteoarthritis. (6) In a comparison to patients with a stemmed device, Mathys Affinis and TESS stemless patients had less blood loss and a shorter operative time. (1)

The Biomet Nano device is the next generation of the TESS device with a 6-armed corolla that impacts into the metaphysis and mates with the head via a screw-in Morse taper device. It has been designed as a platform stem, allowing both anatomic and reverse arthroplasty from the same metaphyseal fixation. This device has been in use in Canada for some time and is currently under FDA evaluation for use in the USA, however, no clinical outcomes have been published.

Habermeyer and coworkers recently reported on the use of 233 stemless Arthrex Eclipse implants with an average follow up of 23 months. (7) Improvements in the Constant score with only one case of loosening was found. However, periprosthetic fractures were not eliminated by the use of a stemless device. A more recent study from this group with longer follow-up (mean: 72 months) continued to support the use of the device; however, there was a 9% revision rate and a 12.8% complication rate. (8)

Finally, the Tornier Simpliciti and Zimmer Sidus implants both feature coated derotational fins with a collar. The Tornier Simpliciti recently gained 510k clearance with clinical data, and the Zimmer device is currently under investigation by the FDA, both have been sold in Europe for several years.

Conclusion

As a result of the recognition of their clinical utility, stemless and short-stemmed humeral-sided devices are available and traditional longer-stemmed devices may see a decrease in usage. Short-term clinical follow-up studies have shown not only absence of failure with these newer shorter and stemless designs but also equivalence in terms of early outcomes compared to traditional stemmed devices with the benefits of shorter operative time, less blood loss, and the potential to reduce stress shielding, and periprosthetic fractures. However, none of these devices have documented long-term clinical follow-up, the ease of revision is relatively undocumented, and the stress transfer relationship with metaphyseal bone is unknown. For these reasons, longer-term clinical follow-up is necessary to confirm these promising initial experiences and demonstrate that these short-term results hold-up over time.

Conflict of Interest Statement

Howard Routman, D.O., is a consultant for Exactech, Inc., Gainesville, Florida. Lisa Becks, M.S., and Christopher P. Roche, M.S., M.B.A., are an employees of Exactech, Inc., Gainesville, Florida.

References

(1.) Berth A, Pap G. Stemless shoulder prosthesis versus conventional anatomic shoulder prosthesis in patients with osteoarthritis: a comparison of the functional outcome after a minimum of two years follow-up. J Orthop Traumatol. 2013 Mar; 14(1):31-7.

(2.) Churchill RS. Stemless shoulder arthroplasty: current status. J Shoulder Elbow Surg. 2014 Sep; 23(9):1409-14.

(3.) Schnetzke M, Coda S, Walch G, Loew M. Clinical and radiological results of a cementless short stem shoulder prosthesis at a minimum follow-up of two years. Int Orthop. 2015 Jul; 39(7):1351-7.

(4.) Giuseffi SA, Streubel P, Sperling J, Sanchez-Sotelo J. Shortstem uncemented primary reverse shoulder arthroplasty. Bone Joint J. 2014 Apr; 96-B(4):526-9.

(5.) Huguet D, DeClercq G, Rio B, et al. Results of a new stemless shoulder prosthesis: Radiologic proof of maintained fixation and stability after a minimum of three years' follow-up. J Shoulder Elbow Surg. 2010 Sep; 19(6):847-52.

(6.) Razmjou H, Holtby R, Christakis M, et al. Impact of prosthetic design on clinical and radiologic outcomes of total shoulder arthroplasty: a prospective study. J Shoulder Elbow Surg. 2013 Feb; 22(2):206-14.

(7.) Brunner UH, Fruth M, Ruckl K, et al. Die schaftfreie EclipseProthese: Indikation und mittelfristige Ergebnisse. Obere Extremitat. 2012; 7(1):22-8.

(8.) Habermeyer P, Lichtenberg S, Tauber M, Magosch P. Midterm results of stemless shoulder arthroplasty: a prospective study. J Shoulder Elbow Surg. 2015; Sep; 24(9):1463-72.

Howard D. Routman, D.O., Lisa Becks, M.S., and Christopher P. Roche, M.S., M.B.A.

Howard D. Routman, D.O., Atlantis Orthopaedics, Palm Beach Gardens, Florida. Lisa Becks, M.S., and Christopher P. Roche, M.S., M.B.A., Exactech, Inc., Gainesville, Florida. Correspondence: Howard D. Routman, D.O., F.A.O.A.O., Atlantis Orthopedics, 130 JFK Drive, Suite 201, Atlantis, Florida 33462; hdr@floridashoulder.com.
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Author:Routman, Howard D.; Becks, Lisa; Roche, Christopher P.
Publication:Bulletin of the NYU Hospital for Joint Diseases
Article Type:Report
Date:Oct 1, 2015
Words:1621
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