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35 (); 37-42
doi:
10.1016/j.jor.2022.10.009

Outcomes of different stem sizes in shoulder arthroplasty

,
Aberdeen Upper Limb Unit, Department of Trauma and Orthopaedics, Woodend Hospital, NHS Grampian , Aberdeen, UK

∗Corresponding author: Rohan Bidwai. rbidwai@gmail.com

Received: , Accepted: ,
Professor P K Surendran Memorial Education Foundation
Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Abstract

The successive refinement in implant design and operative technique alongwith improved understanding has resulted in increased incidence of total shoulder arthroplasty (TSA). Simultaneously, the indications of TSA have widened and include a range of shoulder pathologies.

Using the keywords and relevant literature, we have described an overview of the different stem sizes used in shoulder arthroplasty. Relevant description of clinical and radiological outcome is done with regards to different stem sizes.

There are plethora of shoulder replacement systems, based on unique philosophy and having their own advantages and disadvantages. Additionally, the rise in ageing population had increased the need for revision TSA, thereby necessitating the judicious choice of implant at primary TSA. We further present the role of cemented and uncemented humeral stems and discuss the findings of finite element analysis. The choice of humeral stem size and use of cemented or uncemented stems have been reported to affect the clinical and radiological outcomes.

Keywords

Finite element analysis
Humeral stem
Implant design
Cemented fixation
Proximal humerus
Shoulder arthroplasty
Uncemented fixation
1

1 Introduction

Total shoulder arthroplasty (TSA) is an established surgical procedure for a spectrum of shoulder disorders including inflammatory arthritis, osteoarthritis (OA), rotator cuff arthropathy, irreparable rotator cuff tear, complex proximal humerus fractures and avascular necrosis of the humeral head.1 The first shoulder replacement was performed in 1893 by Jules Emile Pean.2 The modern era of shoulder arthroplasty was ushered in 1955, when Charles Neer pioneered hemi-arthroplasty for proximal humeral fractures.3 In 1975, Neer further presented favourable patient satisfaction following shoulder arthroplasty (SA) for glenohumeral OA.4 In the following years, improved understanding of biomechanics and several design changes led to the development of the Grammont reverse TSA, for elderly patients with rotator cuff tear arthropathy.5 In the last decade, wider acceptance of SA has almost tripled its annual incidence rates.6,7 Additionally, shoulder arthroplasty is the third most common joint replacement procedure performed in the United States.1 In this article, we describe various types of humeral stem designs and evaluate the outcomes associated with different stem sizes in SA. We further present the role of cemented and uncemented humeral stems and discuss the findings of finite element analysis.

2

2 Various stem designs

Since its inception, the stem design in SA has witnessed drastic changes. The initial design introduced by Neer consisted of a monoblock stem and a polyethylene glenoid prosthesis with a radius of curvature corresponding to the humeral head. This design was reported to provide effective pain relief and substantial improvement in movement and function of shoulder joint in patients with glenohumeral OA. The subsequently introduced design incorporated modularity between the head and the implant stem, permitting better flexibility, creating a customised implant for an individual patient, with a superior adjustment into the soft tissue around the shoulder.8

These earlier stem designs used cement to stabilise the humeral component, with promising findings documented over decades. With the arrival of newer stem designs, uncemented (press-fit) fixation have gained wider acceptance due to several advantages, including simple revision surgery, reduced surgical duration, preservation of bone stock and enduring secure prosthetic fit. However, uncemented prostheses maybe susceptible to particular complications, including intraoperative fractures. Additionally, cemented prostheses provide better reduction in axial and rotational micromotion than uncemented prostheses.9

Traditionally, the length of majority of the stems was decided arbitrarily so as to cover the upper half to third of the humeral shaft. Standard-stems have shown excellence performance and survival.10 However, use of small stems, rather than comparatively long-stems, is associated with several benefits including prevention of stress shielding, comparatively easy revision and no hindrance for implantation of an ipsilateral total elbow arthroplasty. An initial effort to prevent stem use was introduction of resurfacing arthroplasty. Cementless surface replacement arthroplasty has advantage of being bone preserving and maintaining the native anatomy. Copeland resurfacing hemiarthroplasty has been a popular design which was first introduced in 1979 as surface implant with a central peg supported by screw (Mark I,3 M, UK). In 1990, further development of design led to a modern fluted taper fit prosthesis and this did not have a screw (Mark II, Zimmer, Swindon, UK). To promote biological fixation, hydroxyapatite coating was added for the subsequent design in 1993 (Mark III, Biomet Merck, Swindon, UK).11 One of the essential prerequisites was predominate involvement of humeral head and maintenance of atleast 60% of humeral head. The designer group have shown excellent outcomes, high satisfaction rate (81.2%) and survival rate of 97% at 5 years and 11 years in case series on population with age less than 50 years.12 Subsequent studies done at independent centres have shown variable results but they do demonstrate high satisfaction rates in patients when offered for Osteoarthritis. Dekker et al.13 in their study involving consecutive series of 279 Copeland resurfacing done over 14 years period have demonstrated 5-year survival rate of 90% in OA group while the Rotator cuff tear group has shown poor outcome with 5 year survival rate of 55%. Even with the rise in popularity of anatomic and reverse shoulder arthroplasty (RSA) in recent times, resurfacing arthroplasty can be a reasonable option in patients with osteoarthritis over 65 years of age with good bone stock and in the absence of cuff tear.13

3

3 Stem designs: standard stem vs short stem vs stemless prostheses

For SA, the available humeral stems include standard-stem, short-stem, stemless and resurfacing implants. Stem is responsible for load transfer from joint to bone; hence, the success of an implant can be influenced by design and stem type. Traditionally, the standard-stem has been considered as a benchmark against which performance of other variants have been tested and analysed. As per the study by Razfar et al., the stem length for standard-stem, short-stem and stemless are around 100 mm, 50 mm and 25 mm, respectively14(Figs. 1–3).

Stemless humeral implant.
Fig. 1 Stemless humeral implant.
Short stem humeral implant.
Fig. 2 Short stem humeral implant.
Standard stem.
Fig. 3 Standard stem.

Current literature suggests that SA results in substantially improved clinical outcomes and range of motion (ROM).15–17 Notwithstanding, the overall promising clinical outcomes, use of standard-stem is associated with several intra-operative (peri-prosthetic fractures, false route and malpositioning) and post-operative complications (stem loosening, migration or disassembly, bone loss, stress-shielding, stem fracture, peri-prosthetic fracture, polyethylene residues and others).18When a standard stem is employed, use of a cemented long-stem prostheses or extensive bone ingrowth make it cumbersome to remove the fixed components during revision surgery and can result in bone loss.19,20 Thus, these group of patients generally require extra procedures including osteotomy of the proximal humerus.20

Over the past 10 years, to enhance the outcome and lessen the complications, several modifications have been incorporated, on both glenoid and humeral components of SA.21 One such modification was to decrease the length of the stem, to conserve bone stock and lessen or eradicate some of the longer-stem related complications.22–25 The purpose of designing the long- and short-stem prosthesis was to hold the implant by employing pressure to the humeral shaft and compressing the cancellous bone of the proximal metaphysis, respectively.26 Shorter-stems are reported to generate humeral stresses that more firmly resemble the intact stress distribution in the proximal cortical bone, which may result in enhanced implant survival and decreased rates of peri-prosthetic fracture.14 Thus, unlike long-stem prosthesis, short-stem prosthesis can decrease the proximal humeral stress-shielding.26 Additionally, it has been demonstrated that compared to the larger sized short-stem prosthesis (one with larger diameter), the smaller sized short-stem prosthesis results in bone stresses that are nearly identical to the intact state at various sites beneath the humeral head resection. Similarly, the smaller sized short-stem prosthesis leads to a significantly lesser proportion of expected bone resorption, thereby resulting in decreased stress-shielding.27

In 2004, Biomet Inc. introduced the first stemless SA, also termed canal-sparing SA.22 Currently, various anatomic stemless protheses are available in the market. By fixing the prosthesis on the humeral metaphysis, they decrease the chances of stem-related complications. By promoting enhanced prosthesis positioning on the proximal humerus, they re-established the centre of rotation (CoR) with enhanced glenohumeral kinematics.28,29 With stemless implants, revision surgeries are relatively easy while preserving bone quality.30 Their indications are identical to those of anatomical stemmed implants, the benefits include preserving humeral bone stock, restoring patient anatomy (humeral head diameter, humeral shaft angle and lateralisation) and less complications during component removal for revision SA.28,31,32 Other benefits include having sufficient access for implantation of a glenoid component,33 role in proximal humerus malunion,34 easy revision,35 decreased surgical duration and reduced blood loss.33,36 These numerous advantages have raised the popularity of the stemless prostheses and the current trend of NJR reflects this finding.37 However, in certain scenarios of poor bone stock including insufficient metaphyseal bone stock, metabolic bone disease, bone cyst and avascular necrosis, the stemless design would be contraindicated.12,33,38 A traditional stemmed prostheses is anchored on a much stiffer cortical bone, while a stemless implant is fixed within cancellous bone.39 Thus, the stemless protheses may be at a higher risk of loosening and instability.

4

4 Clinical outcome: cemented-vs uncemented-stem prostheses

With improved implant position and version, issues related to abnormal anatomy can be overcome by cemented stems.40 By permitting impregnation with antibiotics, they decrease the risk of peri-prosthetic infection.41 Long-term follow-up studies have demonstrated their superiority over uncemented-stems in terms of better quality of life and enhanced forward flexion.40 Irrespective of stem length, comparison of cemented- and uncemented-stems suggested additional requirement of revision surgery with uncemented-stems. However, it was observed to be a result of glenoid-associated problems rather than the humeral-associated issues.40 It is further observed that cementing may lead to superior distribution of stress to cortical bone and decrease proximal stress-shielding. However, it is associated with certain untoward effects including bone stock loss from reaming, more cumbersome revision due to cement removal and cement toxicity. For stem fixation, cement pressurisation is critical. With shorter stemmed prostheses, pressurisation may be more challenging due to termination of the stem tip at the broad metaphyseal-diaphyseal junction.42

In the last 2 decades, uncemented fixation for humeral stems has gained significant popularity. It is now the most common type of fixation across North America.7 Uncemented implants have the potential for long-term survival while maintaining adequate bone stock. These can be advantageous as opposed to cemented stems which demonstrate bone resorption in long-term.43,44 Operating time is reduced and cement specific complications like embolisation and transient hypotension are also avoided.40 Despite these advantages, there have been some concerns such as radiolucency,45 medial stress-shielding,46 osteopenia in the medial cortex47 and spot welds in the lateral cortex.48 Medial stress shielding as noted in study by Schnetzke et al.46 can predispose to late periprosthetic fractures. In a systematic review by Phadnis et al., intraoperative fractures were more common during implantation of uncemented implants.49 These findings highlight the importance of exact press-fit technique to avoid it. Though cemented and uncemented stems have equivalent long-term clinical outcomes, the rise in the incidence of uncemented stems can be attributed to the potential advantages.

In a propensity score-matched analysis, Werthel et al. demonstrated that both cemented- and uncemented-stems have a long-term (20-years) survival of >90%.50 In a retrospective study, Salesky et al. evaluated intra- or post-operative outcomes in patients undergoing revision SA and concluded that cemented or uncemented stems during primary SA showed comparable requirement of intra-operative humeral osteotomy, surgical time, post-operative complication rates and humeral lucencies.51 In a recent meta-analysis, Uy et al. concluded that cemented- and uncemented-stems have identical short-to mid-term revision rates.9

In patients undergoing RSA, an early systematic review by Phadnis et al. concluded that uncemented stems provide comparable functional outcome and superior complication profile.49 In a retrospective analysis involving patients with proximal humeral fracture, Patel et al. suggested equivalent radiographic outcomes in patients who underwent cemented and uncemented RSA.52 In another retrospective study with long-term follow-up (mean 9.5 years), Mazaleyrat et al. demonstrated equivalent outcomes scores with cemented and uncemented RSA, though the active shoulder ROM was significantly worse with the uncemented group. This finding could be ascribed to more commonly observed tuberosity resorption in uncemented group.53 Thus, available evidence demonstrates comparable clinical outcomes between cemented and uncemented stem.

5

5 Radiographic restoration of anatomy: stemmed vs stemless prostheses

The stemmed and stemless TSA are suggested to differ in terms of reconstruction of the glenohumeral relationship. As described above, stemmed implants are fixed in humeral diaphysis, and the glenohumeral relationship is decided by the alignment within the humeral shaft and the head position.54 This has been taken into consideration in the newer designs, however, in patients with abnormal diaphyseal anatomy, recreation of anatomic relationship could lead to difficulties. As stemless prostheses are fixed on metaphysis, the glenohumeral relationship is not determined by the relationship of the humeral head with the diaphysis.54–56 This leads to restoration benefit, critical for anatomic balance of the shoulder and reconstruction of the rotator cuff muscles lever arms.57,58 This in turn results in a favourable long-term reconstruction of physiological movement and pain-relief through maintenance of the CoR and sufficient tightening of the surrounding soft tissues.59

In a large series of stemless TSA using Affinis Short (Mathys Ltd, Bettlach, Switzerland), Chawla et al. reported excellent reconstruction of geometry by analysing deviation of CoR, humeral head diameter, humeral head height and neck shaft angle.60 In an observational study involving patients who underwent stemless SA, von Engelhardt et al. reported an excellent clinical outcome and a precise reconstruction of the joint (lateral glenohumeral offset, humeral offset, acromiohumeral distance, neck shaft angle and height of CoR).61 Additionally, in a retrospective study, Flurin et al. concluded that enhanced anatomic restoration with stemless prostheses leads to superior long-term clinical outcomes.62 In another retrospective study, Cavinatto et al. examined the precision of anatomic restoration with various humeral designs and observed significantly better percentage of prostheses overhang and reconstruction of humeral head height with stemless elliptical design than stemmed and stemless spherical designs. Thus, the stemless elliptical implant resulted in closer reconstruction of the geometry.63

Available evidence suggests contradictory findings related to radiographic anatomic reconstruction by these prostheses. In a retrospective cohort study, Pinto et al. observed no significant differences between the stemmed and stemless prostheses in terms of anatomic reconstruction index and humeral parameters (head centring, head height, diameter, lateral and medial offset). However, stemless prostheses demonstrated significantly enhanced reconstruction of the humeral neck angle.64 Similarly, in a prospective randomised trial, Uschok et al. demonstrated no significant differences between the stemless and standard stem prostheses in terms of the lateral offset, medial offset and change in the inclination angle.65 Contrarily, in a retrospective review, Cox et al. compared standard-stem, short-stem and stemless prostheses and reported no significant difference between them in terms of reconstruction of acceptable humeral head height and CoR. Compared to the stemmed prostheses, stemless prostheses were significantly more likely to be placed in varus. Thus, anatomic reconstruction of humeral parameters was observed to a significantly lesser extent with the stemless than the stemmed prostheses.66 Further randomised prospective studies are required to justify these contrary findings.

6

6 Clinical outcomes: stemmed vs stemless shoulder prostheses

In a mid-term analysis, McMillan et al. demonstrated excellent clinical survivorship of stemless TSA using Affinis short implants.67 The proposed advantages of stemless SA such as avoiding stem-related complications and preserving bone stock are particularly favourable to patients and surgeons, provided that the absence of a stem does not confer an increased risk of implant instability and therefore, impaired survivorship. Available meta-analysis suggests no significant difference between stemmed and stemless prostheses except the fact that stemless TSA results in significantly shortened surgical time and reduced blood loss following surgery. Peng et al. reported no significant differences between stemmed and stemless prostheses in terms of short-to mid-term Constant score (CS), pain score, daily routine activities, strength, satisfactory clinical outcomes, post-operative ROM and maximal active ROM.68 Similarly, Wei et al. reported equivalent short- and mid-term effects of stemmed and stemless TSA, but stemless TSA resulted in reduced duration of surgery and decreased the intraoperative blood loss.69 Liu et al. concluded that both stemmed and stemless anatomic TSA had equivalent complication rates and functional outcomes, however stemless prostheses resulted in significantly reduced surgical time and blood loss.70 Recently, Shin et al. compared complication rates and clinical outcomes of conventional stemmed and stemless implants. Though the post-operative CS and complication rates did not differ between the two, post-operative ROM was significantly higher with stemless implants.26 In another recent meta-analysis, Willems et al. observed that both stemmed and stemless implants had equivalent short- and medium-term clinical outcomes, complications and revision rates. However, stemless implants had lower intra-operative fracture rates and radiologic abnormalities around them.71 Though the short- and medium-term outcomes and patient satisfaction are comparable with both prothesis, long-term outcomes need to compare in future studies.

Evolution of Reverse polarity SA have demonstrated a similar trend like the anatomic variant. Humeral diaphyseal stem in RSA has been at the centre of various intraoperative and postoperative complications. Uncemented stemless metaphyseal implants have been developed to address this and these involve minimal bone cut. Verso shoulder [Innovative Design Orthopaedics, London, UK (formerly Biomet, UK)] and the TESS reverse shoulder (Biomet, France) have been in clinical use since 2005. The Verso Shoulder humeral implant loads into the metaphyseal region, has a press fit construct and the combined implant angle is 145. Glenoid baseplate is fixed by a hydroxyapatite coated central tapered screw and 2 additional screws.72 The designer group have demonstrated excellent restoration of shoulder function, high satisfaction scores, improvement in range of motion in midterm follow up up to 7 years.73 Similarly, Beck et al. have shown comparable clinical and radiographical outcome of TESS Stemless RSA as compared to its stemmed counterparts. Survivorship was 93.1% at 101 months.74 Encouraging results of Stemless metaphyseal TSA have been also shown by Virani et al. in the context of clinical and radiological parameters at a mean follow up of 78 months.75 These advantage of bone preservation and comparable outcomes could explain the rise in popularity in recent times of the Stemless RSA.

7

7 Finite element (FE) analysis

Elimination of proximal trabecular bone was proposed to enhance load bearing capability, cement-cortical contact and longer prostheses survival of cemented femoral components.76 Various FE studies involving arthroplasty have demonstrated effects of cementing technique and prostheses (design and positioning) on cement and bone stresses.77,78

Though the most common factor leading to revisions and complications following a primary TSA is the failure of the glenoid component,79 peri-prosthetic fractures or loosening around the stem are occasionally reported.80,81 Nagels et al. observed that stem size directly affects the zones and extent of humeral stress-shielding,82 which could thus result in peripheral bone resorption.14,80 At 7–8 years follow-up, 40–60% short uncemented-stems show proximal humeral stress-shielding signs.83,84 Compared to the weight-bearing hip joint, muscles around the shoulder joint transfer load more proximally, thus contributing to the stimulus based higher sensitivity of humeral metaphysis than the femoral metaphysis.80 To decrease these complications and assist revision if required, manufacturers have designed shortened humeral stems and stemless humeral heads.14,80 In a FE analysis, Razfar et al. reported that short stems could decrease the proximal humeral stress-shielding.14 Thus, it is necessary to amend humeral stem size and proximal geometry to restrict stress-shielding as well as provide sufficient implant stability with osteointegration.

8

8 Conclusion

In the contemporary world, stemless humeral prostheses are being increasingly used as compared to their stemmed counterparts. This is mainly due to several advantages associated with stemless design including significantly shorter duration of surgery, reduced blood loss and ease of revision, while maintaining equivalent clinical outcomes. Additionally, they permit excellent restoration of anatomy and are devoid of the problems associated with stemmed implants. Stress-shielding is an issue associated with uncemented stems and short-stems filling the canal to a lesser extent reduces the risk of stress-shielding. However, it is worthwhile to understand the importance of stemmed prosthesis and having those in the armamentarium of Shoulder Surgeons.

Similarly, in the light of above data (reduced operating time, prevention of cement complications), uncemented humeral stem fixation is gaining popularity. Though cemented stems have shown equivalent long-term outcomes, they have additional benefit of antibiotics impregnation in the settings of infection.

Funding/sponsorship

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors”

Informed consent (Patient/guardian)

Not Applicable.

Institutional ethical committee approval

Not applicable.

CRediT authorship contribution statement

Rohan Bidwai: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. Kapil Kumar: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.

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