THE SURGEON’S DUTIES
how can surgeons better replicate the
COR and the Iannotti Circle?
In my last post, I presented information that lays out the importance of restoration of both the COR and the Iannotti circle in anatomic shoulder replacement. Related metrics, but separate. And both are likely important for optimizing outcomes of replacement.
What does the surgeon control?
Four elements impact the position of the humeral head. Surgeons have control of these elements, and use of the tools presented here can lead to better execution of the surgery. Understanding them is critical to our job. Ignoring these elements is unwarranted and ill advised. Allow me to develop the thoughts. I’m open to debate and discussion.
The following sections describe the crucial elements to consider:
- Humeral neck cut
- Selection of stemmed/stemless component
- Virtual pre-operative planning
- Guided neck cut (in development)
Humeral Neck Cut
It may seem simple: use a guide and make a cut. After-all, if a guide is provided, it must mean that it works.
If used properly, it can work. But they are cumbersome, and they often lead the surgeon into a “conservative cut” that leaves behind too much neck.
Unfortunately, this sawbones model isn’t what is seen at surgery.
Osteophyte and surrounding soft tissue obscure visualization of the anatomic neck. More often than not, surgeons will make a “conservative” cut superiorly in an effort to protect the rotator cuff.
Inferior osteophyte may lead the surgeon to make a varus cut if they fail to remove the osteophyte prior to making the cut.
As shown in our SAFE study, high humeral heads were present in 2/3 of patients who were dissatisfied with the outcome of their shoulder replacement.1
Cumbersome cutting guides may contribute to this error
Making a free hand cut after complete resection of osteophyte is my preferred method make an appropriate cut. Additionally, careful pre-operative planning of the resection height aids in execution of the cut (more below).
Selection of Stemmed vs Stemless Design
The use of a stem may theoretically drive the position of the humeral head into malposition. This relates not only to the head height, but also the varus/valgus inclination as well as the offset of the head from the humeral canal. Avoiding use of a stem may lead the surgeon to better replicate COR and the Iannotti circle.
High stems are commonly seen. This may relate to surgeons trying to “fill” the canal with the device, similar to the feel of a total hip stem. Incomplete seating of the device can result, as seen in the above image.
Additionally, varus malposition was described in a 2005 paper.2 Varus positioning is an easy error to make. Varus stems shift the COR. A stemless device’s COR is not driven by a poor stem position.
The fixed neck angle on most stemmed implants may lead to improper shift of COR in 20% of the population, as shown in a JBJS study from 2009.3 Most stemmed implants do not allow the surgeon to control inclination of the device. Stemless devices are not constrained by this limitation.
Normal humeral heads are offset from the canal. Eccentric heads were made to attempt to address this issue, but errors in positioning can still occur from improper stem placement. Stemless devices are not limited by this canal/head linkage.
Stemless devices should theoretically eliminate variables of varus/valgus, head shaft offset, and height/depth of stem insertion.
As always, we should look to the literature for data. Being relatively novel technology, we don’t have much to guide us. The existing studies are somewhat conflicting.
The first paper was published in 2021.4 A comparison of the COR of stemmed vs stemless devices showed better restoration of the neck/shaft inclination with stemless devices, but no improvement in the COR. Some technical issues may have contributed to the conclusion, as this included photo shows a humeral head that lies outside of the Iannotti circle.
A second paper in 2021 again showed no difference in COR. However, outliers were more common in the stemless group (more varus position in the stemless group).5 An issue with the neck cut was highlighted by this included image.
A third paper clearly showed improvement in restoration of COR with stemless devices.6 Stemless devices were within 2.1 mm of the native COR, vs 2.7 mm for stemmed implants. More importantly, the number of outliers (>4 mm shift in COR) decreased from 17% to 3% with use of stemless implants.
Definitive conclusions about the restoration of COR and Iannotti circle with stemmed vs stemless devices cannot be made at this time. An accurate neck cut and selection of appropriate head size does seem important if surgeons choose to use a stemless device.
Virtual Pre-op Planning
How can the surgeon make an accurate neck cut and select an appropriate humeral head size? If these are critical element with use of stemless device, and I think they are based on the available data, we should use available technology to help us to better execute the surgery and restore COR.
The first study to look at this issue in 2021 did not show improved replication of COR or the Iannotti circle with use of virtual planning.7 Clearly, errors in neck cut continued to contribute to errors in COR, as 65% of the shoulder shifted > 3 mm. Planning alone did not seem to help. The authors suggest that use of a guide may improve execution of the neck cut.
I have recently collaborated with several peers to conduct an interesting study that was recently submitted for publication. Our data demonstrates improvement in restoration with COR using virtual planning. We anticipate seeing this data in print in 2024.
Guided neck cut/AR technology
Shoulder surgeons are on the cusp of being able to routinely utilize AR technology to guide the neck cut. It is vital that we demonstrate improvement in restoration of both the COR and the Iannotti circle. We all understand that value is determined by seeing improvements in outcome related to increase in cost. AR will definitely increase cost.
Outcomes will be measured radiographically. I anticipate this data will come. We also need to demonstrate improvements in clinical outcomes and longevity. This will be a large undertaking, and will require long term follow-up.
Summary
In an effort to better replicate COR and the Iannotti circle, surgeons control several factors. A proper neck cut seems imperative. Use of a stemless device can eliminate many of the variables that can cause errors with use of a stemmed implant. However, it relies on a proper neck cut to do so. Virtual planning and guided execution of the neck cut offer great promise. Gathering long term data to prove its value is essential. This pathway is one of the most enticing aspects of being a shoulder surgeon in the next, and likely last, decade of my surgical practice.
References
- Franta AK, Lenters TR, Mounce D, Neradilek B, Matsen FA 3rd. The complex characteristics of 282 unsatisfactory shoulder arthroplasties. J Shoulder Elbow Surg. 2007 Sep-Oct;16(5):555-62. doi: 10.1016/j.jse.2006.11.004. Epub 2007 May 16. PMID: 17509905. ↩︎
- Iannotti JP, Spencer EE, Winter U, Deffenbaugh D, Williams G. Prosthetic positioning in total shoulder arthroplasty. J Shoulder Elbow Surg. 2005 Jan-Feb;14(1 Suppl S):111S-121S. doi: 10.1016/j.jse.2004.09.026. PMID: 15726070. ↩︎
- Jeong J, Bryan J, Iannotti JP. Effect of a variable prosthetic neck-shaft angle and the surgical technique on replication of normal humeral anatomy. J Bone Joint Surg Am. 2009 Aug;91(8):1932-41. doi: 10.2106/JBJS.H.00729. PMID: 19651952. ↩︎
- Pinto MC, Archie AT, Mosher ZA, Ransom EF, McGwin G, Fehringer EV, Brabston EW 3rd, Ponce BA. Radiographic restoration of native anatomy: a comparison between stemmed and stemless shoulder arthroplasty. J Shoulder Elbow Surg. 2019 Aug;28(8):1595-1600. doi: 10.1016/j.jse.2019.01.015. Epub 2019 Apr 11. PMID: 30982698. ↩︎
- Cox RM, Sholder D, Stoll L, Abboud JA, Williams GR Jr, Ramsey ML, Lazarus MD, Horneff JG 3rd. Radiographic humeral head restoration after total shoulder arthroplasty: does the stem make a difference? J Shoulder Elbow Surg. 2021 Jan;30(1):51-56. doi: 10.1016/j.jse.2020.04.014. Epub 2020 Jun 9. PMID: 32713669. ↩︎
- Sears BW, Creighton RA, Denard PJ, Griffin JW, Lichtenberg S, Lederman ES, Werner BC. Stemless components lead to improved radiographic restoration of humeral head anatomy compared with short-stemmed components in total shoulder arthroplasty. J Shoulder Elbow Surg. 2023 Feb;32(2):240-246. doi: 10.1016/j.jse.2022.07.024. Epub 2022 Sep 15. PMID: 36115615. ↩︎
- Grubhofer F, Muniz Martinez AR, Haberli J, Selig ME, Ernstbrunner L, Price MD, Warner JJP. Does computerized CT-based 3D planning of the humeral head cut help to restore the anatomy of the proximal humerus after stemless total shoulder arthroplasty? J Shoulder Elbow Surg. 2021 Jun;30(6):e309-e316. doi: 10.1016/j.jse.2020.08.045. Epub 2020 Sep 17. PMID: 32950671. ↩︎
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