Biomechanical comparison of stemless humeral components in total shoulder arthroplasty

BackgroundThe purpose of this study was to compare initial fixation strength between various stemless and stemmed humeral components and to correlate implant fixation strength with bone mineral density (BMD).MethodsFive humeral stem designs were investigated: Stemless-A (four hollow fins), Stemless-B (central body, three solid fins), Stemless-C (central screw, peripheral rim-fit), Short stem (50 mm), and Standard stem (130 mm). Fifty cadaveric human humerii were obtained and divided into five groups. BMD within the humeral head was determined for all samples. The mean BMD was similar between groups. The 25 samples with the lowest and highest BMDs were categorized as “Low” and “High,” respectively, with a BMD threshold of 0.35 g/cm², creating BMD subgroups. After implantation, each sample underwent a standardized biomechanical testing protocol, with axial loading followed by torsional loading. Sensors attached to the specimen recorded micromotion throughout testing. Axial loading consisted of cyclic loading for 100 cycles at 3 peak forces (220, 520, and 820 N). Torsional loading consisted of 100 cycles of internal/external rotation at 0.1 Hz at 6 peak torques, or until failure (±2.5, 5, 7.5, 10, 12.5, and 15 Nm). Failure was defined as the torque at which any bone fracture, implant detachment from anchor/stem, or an excess of 50° internal/external rotation occurred. Groups and BMD subgroups were compared.ResultsAt maximal axial loading, Stemless-B demonstrated greater micromotion (540 μm) than Stemless-C (192 μm) (P = .003). Stemless-B and Stemless-A (387 μm) also had greater micromotion than Short stem (118 μm, P < .001, P = .03) and Standard stem (85 μm, P < .001, P = .01). When comparing low-BMD samples at maximal axial loading, these differences were accentuated, but comparison of high-BMD samples showed no significant differences between groups. Torsional testing demonstrated that Standard stem failed at greater torque (7.2 Nm) than Stemless-B (2.3 Nm, P < .001), Stemless-A (1.9 Nm, P < .001), and Stemless-C (3.9 Nm, P = .01). When comparing torsional testing results of low-BMD samples, both Standard stem and Short stem failed at greater torque than Stemless-B (P = .02, P = .003) and Stemless-A (P = .03, P = .004) but failed at a similar torque to Stemless-C. Torsional testing of high-BMD samples showed that Standard stem failed at a greater torque than all stemless designs.ConclusionStemless humeral implants should be used with caution in low-BMD settings (<0.35 g/cm²). A central screw and peripheral rim-fit stemless anchor design demonstrated greater fixation strength at low BMD when compared with other designs, while all stemless designs performed similarly at high BMD.Level of evidenceBasic Science Study; Cadaveric Study     

Difference in clinical outcome between total shoulder arthroplasty and reverse shoulder arthroplasty used in hemiarthroplasty revision surgery

Introduction:The increase of shoulder replacements will lead to a higher revision rate of shoulder arthroplasties. The aim of this study is to evaluate the clinical results of revision surgery performed in our hospital, distinguish the differences in clinical outcome according to revision indication and differences between total shoulder arthroplasty (TSA) and reverse shoulder arthroplasty (RSA) in hemiarthroplasty (HA) revision surgery.Results:From July 1994 to July 2008, 39 patients (40 shoulders) underwent revision arthroplasty. Of 19 patients (19 shoulders) we obtained a complete follow-up. The mean age at revision surgery 69 ± 10 years (range: 46-83) and the mean follow-up 41 ± 31 months (range: 10-113). In 7 cases TSA was used for revision when the cuff was intact, 12 times RSA was performed. The indications for the revision were glenoid erosion (n = 4), humeral component malposition (n = 2), cuff-pathology (n = 12) and infection (n = 1). Postoperative constant score 51.7 ± 11.4 for TSA and 31.1 ± 18.7 for RSA (P = 0.008). The DASH was 48.3 ± 25.1 and 68.7 ± 17.5, respectively (P = 0.09). DSST showed 6 ± 4 and 4 ± 4 (P = 0.414). OSS 41.3 ± 10.1 and 28.1 ± 10.3 (P = 0.017). SF-36 43.3 ± 22.1 and 24.5 ± 12.8 (P = 0.072). Four shoulders (21%) presented four complications.Conclusions:In this study, revision surgery showed poor to reasonable postoperative results and better clinical outcome for TSA. When a revision after HA was needed, and the soft-tissue component of the shoulder was intact, a TSA proved to be a preferable solution.     

5Effects of numeral component design on total shoulder arthroplasty

The last decade has brought exciting new ideas into the field of shoulder arthroplasty. This is particularly true withrespect to our understanding of humeral anatomy and how this relates to component design. Anatomic studies have informed the implant industry and surgeons alike leading to new implants and surgical techniques that better conform to normal anatomy. Proximal humeral anatomy is extremely variable. Radius of curvature varies from 20 to 30 mm, head shaft angle from 30° to 50°, offset is variable in 3 dimensions, and retroversion ranges from 0° to 50°. Equally variable are the prosthetic systems available for humeral replacement and the surgical techniques with which they are implanted. A modern approach to shoulder arthroplasty must incorporate an understanding of this variability to effectively reconstruct the anatomy of any particular patient. Available biomechanical information shows that displacing the position of the humeral articular surface by as little as 4 to 5 mm has significant consequences. Increasing the thickness by this amount tensions the overlying soft tissues and rotator cuff decreasing glenohumeral range of motion and introducing aberrant translations of the head on the glenoid. Shifting the articular surface similarly tensions corresponding aspects of the rotator cuff and may result in impingement ox the tuberosities on the glenoid rim, Exact replication of the patient's anatomy is probably not necessary, but staying within the stated limits is highly desirable. Cemented components facilitate this goal by allowing some adjustment of the prosthetic position within the cement mantle. Press-fit components that allow anatomic reconstruction have a significantly greater challenge.     

Uncemented femoral revision arthroplasty using the modular revision prosthesis MRP-TITAN revision stem

Objective  Restoration of a painless hip joint capable of bearing weight by uncemented implantation of a rotationally stable, modular revision stem anchored in the diaphysis. Indications  Prosthetic stem loosening with osteolytic bone defects (defect classification types I–III according to Paprosky), material failure with broken prosthesis, sub-and/or periprosthetic femoral fractures, and tumors. Contraindication  Extensive osteolysis preventing diaphyseal anchorage of the prosthetic stem. Surgical technique  Transgluteal approach to the hip joint. Removal of the loose prosthetic stem and, if cemented, the bone cement as well. Excision of intramedullary granulation tissue. Reaming of the medullary cavity with flexible reaming shafts and formfit, uncemented implantation of the star-shaped modular revision stem with diaphyseal press-fit. If there is extensive loss of metaphyseal bone stock, augmentation with autogenous-allogenic bone should be performed. Postoperative management  Mobilization on two underarm crutches from the 1st postoperative day. Removal of the Redon drains after 48 hours. Partial loading with 20 kg for 6 weeks postoperatively. If plain radiographs show unchanged seating of the prosthesis after 6 weeks, loading can be increased by 10 kg per week until full weight bearing is achieved; thrombosis prophylaxis is continued throughout. Radiologic checkups will be done after 3, 6, and 12 months. After that, the patient should be checked annually. Results  Forty-five patients (N = 48 prostheses) with an average age of 67.2 years (min/max: 42.4–87.4 years) were investigated. The average implantation time of the Modular revision prosthesis MRP-TITAN revision stem was 4.7 years (min/max: 1.0–9.0 years). The Harris hip score for Paprosky bone defect types I–III had increased from 25.6 preoperatively to 71.4 postoperatively at the time of the final follow-up (p ³ 0.05). Extensively defective bone was diagnosed preoperatively in 32 patients (¹Paprosky IIB). Plain radiographs showed stable anchorage without migration in 44 patients. In one case, the stem (implantation time 2.36 years) was replaced due to increasing axial subsidence (¹5 mm). Good integration of bone graft with subsequent defect regeneration was seen in all patients with bone trans-plant (N = 30). Postoperative dislocation occurred in six patients and required closed reduction in four cases. Open reduction was performed in two patients, whereby the external rotation angle of the prosthetic neck was corrected without dismantling the distally anchored prosthetic stem components. The mechanical failure rate over the follow-up period of 9 years was 1 out of the 48 prospectively investigated prostheses. The rate of survival according to Kaplan-Meier was 97%.     

Short stem shoulder replacement

Context:

It is agreed that it is important to anatomically reproduce the proximal humeral anatomy when performing a prosthetic shoulder replacement. This can be difficult with a long stemmed prosthesis, in particular if there is little relationship of the metaphysis to the humeral shaft. The ‘short stem’ prosthesis can deal with this problem.

Aims:

A prospective study assessed the results of total shoulder arthroplasty using a short stem humeral prosthesis, a ceramic humeral head, and a pegged cemented polyethylene glenoid.

Materials and methods:

Patients with primary shoulder osteoarthritis were recruited into this prospective trial and pre-operatively had the ASES, Constant, SPADI, and DASH scores recorded. The patients were clinically reviewed at the two weeks, eight weeks, one year, and two year mark with completion of a data form. Radiological evaluation was at the eight week, one year and two year follow-up. At the one and two year follow-up the satisfaction rating, the range of passive and active motion, Constant, ASES, SPADI, DASH and pain results were recorded and analysed with SPPS 20.

Results:

During the study period 97 short stem, ceramic head total shoulder replacements were carried out. At the time of follow-up 12 were two years from operation and 38 one year from operation. Active elevation was overall mean 160 degrees. Constant scores were 76 at 1 year, and 86 at 2 years, ASES 88 and 93, and satisfaction 96% and 98% respectively at one and 2 year follow up. There were no problems during insertion of the humeral prosthesis, or any radiolucent lines or movement of the prosthesis on later radiographs.

Conclusion:

The short stem prosthesis had no complications, and on follow up radiographs good bone fixation. These fairly short term clinical results were overall good.