A Radiographic Analysis of Proximal Humeral Anatomy in Patients with Primary Glenohumeral Arthritis and Implications for Press-Fit Stem Length

While short stems in total shoulder arthroplasty (TSA) preserve bone stock and facilitate revision surgery, they have been associated with higher rates of malalignment and loosening in some cases compared to standard length stems. The purpose of this study was to analyze the intramedullary canal in progressive increments distal to the greater tuberosity to provide anatomic information about the optimal length of press-fit short stems for alignment and stability in TSA. We hypothesized that the humeral canal diameter will remain variable for the first 50 to 75 mm distal to the greater tuberosity and will become consistent thereafter. A retrospective review of 99 consecutive patients undergoing TSA with CT scans was performed. Intramedullary anterior-posterior (AP) and medial-lateral (ML) width as well as diameter were analyzed on two-dimensional computed tomography following multiplanar reconstruction. Measurements were taken at consistent distances distal to the greater tuberosity (GT). The transition point was measured at the proximal level of the humerus where endosteal borders of the medial and lateral cortices became parallel. The mean transition point was 73 mm from the GT (range: 53 to 109 mm). ML and AP widths became consistent 80 mm distal to the GT. IM diameter became consistent after 90 mm distal to the GT and a stem length of 90 mm extended past the transition point in 91.9% of cases. In TSA, a humeral stem length of 90 mm is required to predictably reach points at which the humeral canal becomes cylindrical and consistent in diameter. This information may aid data-driven decisions on humeral stem length during press-fit fixation, assuring consistency of alignment and implant stability, while maintaining ease of revision associated with a short stem implant. Level of evidence: III

Reverse total shoulder arthroplasty

AIMS

This systematic review asked which patterns of complications are associated with the three reverse total shoulder arthroplasty (RTSA) prosthetic designs, as classified by Routman et al, in patients undergoing RTSA for the management of cuff tear arthropathy, massive cuff tear, osteoarthritis, and rheumatoid arthritis. The three implant design philosophies investigated were medial glenoid/medial humerus (MGMH), medial glenoid/lateral humerus (MGLH), and lateral glenoid/medial humerus (LGMH).

METHODS

A systematic review of the literature was performed via a search of MEDLINE and Embase. Two reviewers extracted data on complication occurrence and patient-reported outcome measures (PROMs). Meta-analysis was conducted on the reported proportion of complications, weighted by sample size, and PROMs were pooled using the reported standardized mean difference (SMD). Quality of methodology was assessed using Wylde's non-summative four-point system. The study was registered with PROSPERO (CRD42020193041).

RESULTS

A total of 42 studies met the inclusion and exclusion criteria. Rates of scapular notching were found to be significantly higher in MGMH implants (52% (95% confidence interval (CI) 40 to 63)) compared with MGLH ((18% (95% CI 6 to 34)) and LGMH (12% (95% CI 3 to 26)). Higher rates of glenoid loosening were seen in MGMH implants (6% (95% CI 3 to 10)) than in MGLH implants (0% (95% CI 0 to 2)). However, strength of evidence for this finding was low. No significant differences were identified in any other complication, and there were no significant differences observed in PROMs between implant philosophies.

CONCLUSION

This systematic review has found significant improvement in PROMS and low complication rates across the implant philosophies studied. Scapular notching was the only complication found definitely to have significantly higher prevalence with the MGMH implant design. Cite this article: Bone Joint J 2021;103-B(5):813-821.

Primary reverse shoulder replacement with a short stem: A systematic literature review

Background

Total shoulder arthroplasty implant designs have continued to evolve over the years. One recent change has been the shortening of the humeral component to preserve bone stock and to facilitate revision surgery. Despite promising clinical results, radiographic bone adaptions occur frequently in short-stem total shoulder arthroplasty, and limited data exist on short-stem reverse shoulder arthroplasty (RSA). The purpose of this systematic review was to provide an overview about the functional and radiographic outcomes after an uncemented short-stem RSA, as well as identify areas of clinical importance that are underreported in the current literature.

Methods

A systematic review of the literature was performed in accordance with the PRISMA guidelines using PubMed, Cochrane Central Register of Controlled Trials, and EMBASE. Clinical outcome studies reporting on short-stem RSA outcomes with evidence level I-IV were included. Demographics, clinical and radiological outcomes, as well as complications and revision data were systematically analyzed and described.

Results

Ten studies, published between 2014 and 2019, reporting on 555 shoulders with a mean follow-up of 32 months (range, 20-99.6 months) met the inclusion criteria. For all studies cuff tear arthropathy was the main indication for RSA (36%), followed by primary osteoarthritis (20%). Clinical outcome was reported in nine of ten studies, with range of motion improving in all studies. Six of the seven studies that used the Constant score (CS) demonstrated significant improvement (27.9 points to 69.3 points in weighted means). All studies reported on radiographic changes and bone adaptions. Among these, scapular notching was the most commonly observed (60 out of 327 cases, 18%) but without any described implication on clinical outcomes. No stem loosening was recorded at any final follow-up. A total of 63 complications (12.9%) were reported, with scapula fractures being the most commonly reported complication. Revision surgery was necessary in 24 cases (4.9%).

Conclusion

Good clinical results, comparable with long-stem RSAs, are reported at short-term follow-up for short-stem RSAs. Humeral bone adaptions occur frequently but aseptic stem loosening is not a matter of concern at short-term follow-up. An area of clinical importance that is under-reported is the relation between filling ratio and stem alignment in short-stem RSA.

Subsidence of Uncemented Short Stems in Reverse Shoulder Arthroplasty-A Multicenter Study

BACKGROUND

The radiological phenomenon of subsidence following the implantation of uncemented short-stem reverse prostheses (USSP) has not yet been described. The purpose of this study was to describe the rate and potential risk factors for subsidence. We hypothesized that subsidence may be a frequent finding and that a subsidence of >5 mm (mm) is associated with an inferior clinical outcome.

METHODS

A total of 139 patients with an average age of 73 ± 9 years were included. The clinical and radiological outcome was evaluated at a minimum follow-up (FU) of 12 months.

RESULTS

No humeral component loosening was present at a mean FU of 18 (range, 12-51) months. Mean Constant Score (CS) and Subjective Shoulder Value (SSV) improved significantly from 34.3 ± 18.0 points and 37.0 ± 19.5% preoperatively to 72.2 ± 13.4 points and 80.3 ± 16.5% at final FU (p < 0.001). The average subsidence of the USSP was 1.4 ± 3.7 mm. Subsidence of >5 mm was present in 15 patients (11%). No association between a subsidence >5 mm and CS or SSV was found (p = 0.456, p = 0.527). However, a subsidence of >5 mm resulted in lower strength at final FU (p = 0.022). Complications occurred in six cases (4.2%), and the revision rate was 3.5% (five cases).

CONCLUSIONS

Although subsidence of USSP is a frequent radiographic finding it is not associated with loosening of the component or a decrease in the clinical outcome at short term FU.

LEVEL OF EVIDENCE

Level 4, retrospective study.

Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties?

BACKGROUND

Shorter humeral stems were developed to improve bone preservation, vascularity and osteointegration in reverse total shoulder arthroplasty (RSA). While some studies examined the relationship between canal filling and radiographic changes, none evaluated the association between stem alignment and canal fill ratio (CFR).

HYPOTHESIS

The hypothesis was that stem misalignment after RSA would be associated with lower CFR.

PATIENTS AND METHODS

The authors retrospectively reviewed immediate postoperative radiographs of 157 patients, comprising 56 men (36%), who underwent RSA with a short uncemented stem with neck shaft angle (NSA) default of 145°. The parameters included postoperative NSA and metaphyseal CFR, both measured with excellent inter-observer agreement. Uni- and multivariable linear regressions were performed to determine associations between postoperative NSA and 5 variables (CFR, gender, age, BMI, and surgical approach).

RESULTS

Postoperative NSA was 149°±8°, exceeding 5° of varus in 15 shoulders (9%) and 5° of valgus in 60 shoulders (38%), and CFR was 58%±8%. CFR was lower in shoulders with varus stem alignment (54%±6%) than shoulders with neutral stem alignment (59%±8%, p=0.033). Multivariable regression revealed that postoperative NSA increased with age (beta: 0.20; p=0.008), was higher for shoulders operated with the subscapularis- and deltoid-sparing approach (beta: 3.82; p=0.040) but lower for men (beta: -4.14; p=0.002).

CONCLUSIONS

Stem misalignment exceeded 5° in 47% of the shoulders. Women, older age, and subscapularis- and deltoid-sparing approach are associated with greater risks of valgus stem positioning, while lower CFR seems to be associated with greater risks of varus stem positioning.

LEVEL OF EVIDENCE

IV; case series.

Does proximal porous coating in short-stem humeral arthroplasty reduce stress shielding?

CONTEXT

Short-stem humeral designs in shoulder arthroplasty have been introduced recently. A retrospective cohort study was conducted to determine if newer proximal porous titanium coating in humeral short stems produced clinical and radiologic improvements.

METHOD

Short-stem humeral implants (Tornier Ascend, Wright Medical) were used in 46 anatomical total shoulder replacements from October 2012 to December 2015. Clinical and radiologic measures were analyzed at one- and two-year follow-up.

RESULTS

Nineteen shoulders received earlier grit blasted stems (Ascend Monolithic), and 27 shoulders received the later stems with proximal titanium porous coating (Ascend Flex). At two-year follow-up, radiographic changes and stress shielding were similar. Medial cortical thinning were more frequently observed in Monolithic (18 of 19) compared to Flex stems (19 of 27) on the PA films, though this was not statistically significant (P = 0.061). Clinical outcome scores improved regardless of the stem type used and independent of the radiologic adaptations on plain films. One participant with the Ascend Flex developed glenoid component failure and rotator cuff tear and was subsequently revised.

DISCUSSION

Clinical and radiological outcomes are similar in both short-stem designs. Proximal titanium porous coating may reduce medial calcar cortical thinning but it does not prevent it.

KEY MESSAGE

When compared to similarly designed uncoated grit-blasted stems, proximally porous coated humeral short stems produced similar clinical and radiological results. The proximal titanium porous coating may reduce medial cortical thinning.

Influence of uncemented humeral stem proximal geometry on stress distributions and torsional stability following total shoulder arthroplasty

Background

While surgeons tend to implant larger stems to improve torsional stability, numerous studies demonstrated that increasing humeral stem diameter could exacerbate stress-shielding and lead to bone resorption. We aimed to determine the influence of humeral stem proximal geometry on stress distributions and torsional stability following total shoulder arthroplasty.

Methods

Preoperative computed tomography scans were acquired from 5 patients and processed to form 3-dimensional models of the proximal humerus. Computer models of 3 generic implants were created based on three designs: predominantly oval, semi-angular, and predominantly angular. All stems shared identical head geometry and differed only in the proximal metaphyseal area. Finite element analyses were performed, with the humerus rigidly constrained distally, and loaded to simulate the joint reaction force. Implant torsional stability and proximal bone stress distributions were assessed for the three different stem designs with three sizes: oversized (stem making contact with the cortical diaphysis), normosized (one increment smaller) and undersized (two increments smaller).

Results

Considering the normosized stems, the angular design increased the physiologic bone stresses at the proximal section by 39–42%, while the oval and semi-angular designs reduced them by 5–9% and 8–13%, respectively. The oval design exhibited a median rotation of 2.1°, while the semi-angular and angular designs exhibited median rotations of 1.8°.

Conclusion

The semi-angular stem granted an adequate compromise between physiologic stress distributed by the oval stem and torsional stability of the angular stem. Surgeons should be aware of the various benefits and drawbacks of the different humeral stem designs to ensure adequate torsional stability and physiologic loading.