At four years after surgery, the right stemless component (below left) shows localized absence of bone beneath the inferior aspect of the humeral head (green arrow).
At four years after surgery, the left short stemmed component (below right) shows reduced bone density proximal to the diaphysis into which the component has been tightly inserted (black arrows). The red arrows show the localized osteopenia of the lateral humerus while the yellow arrows show the absence of bone medially.
As pointed out in a prior post, with stemmed implants loads applied to the humeral head are distributed by the stem to the humeral diaphysis. However, with the stemless humeral arthroplasty, loads applied to the prosthetic humeral head are distributed to the humeral metaphysis (blue rectangle), bypassing the humeral cortex unless there is contact between the head and humeral neck cut (red arrows). The degree of cortical loading is a function of implant design and surgical technique.
In this post we'll take a closer look at what's been published about stress shielding and adaptive changes after stemless humeral arthroplasty. There's a lot here so you may want to skip to the Comment at the bottom to see a summary.
Computer model studies
Comparison of proximal humeral bone stresses between stemless, short stem, and standard stem length: a finite element analysis used finite element analysis to investigate the effect of humeral component length on stresses in the proximal humerus. The authors found that cortical bone stresses in the most proximal slice for the standard and short stem models were significantly reduced compared with the intact and stemless models. These reductions persisted in the second cortical slice for the standard stem compared with the intact, stemless, and short models. They concluded that reducing stem length produced humeral stresses that more closely matched the intact stress distribution in proximal cortical bone. Opposing trends presented in the proximal trabecular bone, probably because of differences in load transfer when shorter stems are used.
The effect of stemless humeral component fixation feature design on bone stress and strain response: a finite element analysis analyzed the effect of several different humeral component fixation design features
The implant–bone contact area was greatest for peripheral, followed by central and boundary-crossing designs. All implants elicited similar bone stress variations, which were greatest 0 to 5 mm beneath the resection and laterally. The simulated potential cortical response was also similar for all implants, with the greatest simulated resorbing potential 0 to 15 mm beneath the resection, and very little expected remodeling. Differences between implants were most prominent within the simulated potential trabecular response, with the central implants having the least bone volume percentage expected to resorb.
Bone adaptation impact of stemless shoulder implants: a computational analysis used a computer model to explore the influence of 5 stemless designs on bone adaptation of the humerus (Eclipse, Global Icon, SMR, Simpliciti, and Sidus stemless systems). For the designs not possessing a collar that covers the entire resected surface of the humerus, conditions of contact and no contact were simulated between the humeral head components and the bone surface.
The bone adaptation process was evaluated by comparing differences in bone density between the implanted models and the intact model of the humerus.
The Eclipse-based design was associated with the largest bone mass loss, whereas the SMR based design caused the least. When contact was simulated between the resected bone surface and the humeral head components of the SMR-, Simpliciti-, and Sidus-based designs and, bone resorption increased.
The bone adaptation process was evaluated by comparing differences in bone density between the implanted models and the intact model of the humerus.
The Eclipse-based design was associated with the largest bone mass loss, whereas the SMR based design caused the least. When contact was simulated between the resected bone surface and the humeral head components of the SMR-, Simpliciti-, and Sidus-based designs and, bone resorption increased.
The authors concluded that when considering the bone adaptation process, the results suggest that the SMR-based implant presents the best performance and that contact between the humeral head component and the resected bone surface should be avoided.
Clinical studies
Notably, the clinical papers reviewed below show a wide spread in assessment methods and in the reported rates of stress shielding in the humerus after stemless arthroplasty.
Clinical and radiographic outcomes of the Simpliciti canal-sparing shoulder arthroplasty system: a prospective two-year multicenter study. evaluated 147 patients with glenohumeral arthritis treated with the Simpliciti total shoulder system at two year followup.
There was no reported evidence of migration, subsidence, osteolysis, or loosening of the humeral components.
Radiological changes do not influence clinical mid-term outcome in stemlesshumeral head replacements with hollow screw fixation: a prospective radiological and clinical evaluation used the Eclipse shoulder prosthesis 73 patients, 37% of which had localized bone loss.
Mid-term results with an anatomic stemless shoulder prosthesis in patients with primary osteoarthritis evaluated 38 patients at an average of 37 months after insertion of a TESS stemless shoulder prosthesis. No signs of stress shielding were noted.
Results of a new stemless shoulder prosthesis: Radiologic proof of maintained fixation and stability after a minimum of three years’ follow-up reported 36 months followup in 63 patients having the TESS stemless shoulder prosthesis; no stress shielding was reported.
The authors of Short-term radiographic analysis of a stemless humeral component for anatomic total shoulder arthroplasty reported the two year radiographic outcomes for 54 patients receiving the Equinoxe Stemless. Stress shielding was observed in 4 patients (7%) with the medial calcar being the most common location of stress shielding. Three of the 4 patients had evidence of partial resorption while 1 patient (25%) had evidence of complete resorption.
Proximal humeral bone loss in stemless shoulder arthroplasty: potential factors influencing bone loss and a new classification system. found that women patients were more likely to experience bone loss after stemless arthroplasty with the Affinis Short Stemless Anatomic Shoulder Prosthesis. Shown below are anteroposterior radiographs demonstrate bone loss grades at the proximal humerus. Grade 0: no bone loss, grade I: bone loss with rounding off of the medial calcar, grade II: bone loss with the corner of the metallic fin at the medial calcar exposed, and grade III: bone loss up to the central stem at the medial calcar. Arrows indicate areas of bone loss.
The SPECT/CT data suggested that the primary osseointegration of the stemless shoulder prosthesis was almost completed 3 months after implantation.
There was no reported evidence of migration, subsidence, osteolysis, or loosening of the humeral components.
Another study of the Simpliciti was Early fixation of the humeral component in stemless total shoulder arthroplasty which used radiostereometric analysis radiographs obtained in 24 patients at one day, six weeks, six months, one year, and two years postoperatively. At two years, median translation along the x-, y-, and z-axis was -0.12 mm, -0.17 mm,, and 0.09 mm. Median rotation around the x-, y-, and z-axis was 0.12°, -0.98°, and 0.09°. Overall, 20 prostheses stabilized within 12 months postoperatively. Four cases had continuous shift in position.
The authors of Stress shielding following stemless anatomic total shoulder arthroplasty found that with the Sidus stemless component, 41% of shoulders demonstrated stress shielding at 2 years postoperatively. 7% demonstrated severe stress shielding with 6 occurring along the medial calcar (red arrow).
The authors of Screw fixation in stemless shoulder arthroplasty for the treatment of primary osteoarthritis leads to less osteolysis when compared to impaction fixation compared their results with the Eclipse Shoulder Prosthesis
The authors of Screw fixation in stemless shoulder arthroplasty for the treatment of primary osteoarthritis leads to less osteolysis when compared to impaction fixation compared their results with the Eclipse Shoulder Prosthesis
to their results with the Sidus Stem-free Shoulder System
they found no osteolysis of the medial calcar at a mean of 42 months in 18 patients having the Eclipse; however with the Sidus, osteolysis of the medial calcar was present in seven of the 21 patients at a mean of 36 months after surgery (see above).
Results for the Eclipse implant were reported in Midterm results of stemless shoulder arthroplasty: a prospective study for 78 patients at a minimum follow-up of 5 years. Bone mineral density was reduced in 34.9% of the older population.
they found no osteolysis of the medial calcar at a mean of 42 months in 18 patients having the Eclipse; however with the Sidus, osteolysis of the medial calcar was present in seven of the 21 patients at a mean of 36 months after surgery (see above).
Results for the Eclipse implant were reported in Midterm results of stemless shoulder arthroplasty: a prospective study for 78 patients at a minimum follow-up of 5 years. Bone mineral density was reduced in 34.9% of the older population.
Nine-year outcome after anatomic stemless shoulder prosthesis: clinical and radiologic results presented results for 49 patients receiving the Eclipse shoulder prosthesis at mean of 9 years. Localized lowering of bone density was seen in 29% of the patients.
Radiological changes do not influence clinical mid-term outcome in stemlesshumeral head replacements with hollow screw fixation: a prospective radiological and clinical evaluation used the Eclipse shoulder prosthesis 73 patients, 37% of which had localized bone loss.
Survival of stemless humeral head replacement in anatomic shoulder arthroplasty: a prospective study reported outcomes for 75 patients having the Eclipse shoulder prosthesis with a mean followup of 126 months. Stress shielding around the humeral component was not detected.
Mid-term results with an anatomic stemless shoulder prosthesis in patients with primary osteoarthritis evaluated 38 patients at an average of 37 months after insertion of a TESS stemless shoulder prosthesis. No signs of stress shielding were noted.
The authors of Short-term radiographic analysis of a stemless humeral component for anatomic total shoulder arthroplasty reported the two year radiographic outcomes for 54 patients receiving the Equinoxe Stemless. Stress shielding was observed in 4 patients (7%) with the medial calcar being the most common location of stress shielding. Three of the 4 patients had evidence of partial resorption while 1 patient (25%) had evidence of complete resorption.
Proximal humeral bone loss in stemless shoulder arthroplasty: potential factors influencing bone loss and a new classification system. found that women patients were more likely to experience bone loss after stemless arthroplasty with the Affinis Short Stemless Anatomic Shoulder Prosthesis. Shown below are anteroposterior radiographs demonstrate bone loss grades at the proximal humerus. Grade 0: no bone loss, grade I: bone loss with rounding off of the medial calcar, grade II: bone loss with the corner of the metallic fin at the medial calcar exposed, and grade III: bone loss up to the central stem at the medial calcar. Arrows indicate areas of bone loss.
At a median of 85 months after surgery the bone loss was as shown in the table below.
SPECT/CT demonstrates the osseointegrative response of a stemless shoulder prosthesis. considered the metaphyseal bone metabolic activity in 28 patients after insertion of the Affinis Short.
The SPECT/CT data suggested that the primary osseointegration of the stemless shoulder prosthesis was almost completed 3 months after implantation.
Reliability of stemless shoulder arthroplasty in rheumatoid arthritis:observation of early lysis around the humeral component compared outcomes for the Affinis Short in 35 patients with RA to 35 patients with osteoarthritis.The proportion of progressive proximal humeral bone loss after TSA was 33% in the RA group and 13% in the control group. Two examples of severe bone loss are shown below.
Impact of humeral stem length on calcar resorption in anatomic total shoulder arthroplasty was a retrospective review of TSA patients treated with three different-length humeral implants (canal-sparing, short, and standard-length designs). Patients were matched 1:1:1 based on both gender and age (±4 years), resulting in 40 patients per cohort. The canal-sparing implant was the Enovis CS Edge. At 3 months, calcar resorption was observed in 20% of the canal sparing cohort, while the short and standard designs demonstrated resorption in 55% and 52.5%, respectively. At 12 months, calcar resorption was seen in 65% of the canal-sparing design, while both the short and standard designs had a 77.5% rate of resorption. The severity of calcar resorption for the canal-sparing cohort was significantly lower at all time points when compared to the short stem.
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).