Biomechanical considerations on shoulder joint prosthesis implantation

The biomechanical goals of prosthetic reconstruction of the shoulder are to restore the normal anatomy and range of motion, and to recreate the normal soft tissue balance of the static and dynamic stabilizers of the glenohumeral joint. An unconstrained prosthesis design best reproduces the physiological articulation and original anatomy of the shoulder. Humeral head components have been recently developed, which are adaptable to the variable anatomy of the proximal humerus (third generation design). A precise reconstruction of the three dimensional structure of the proximal humerus may lead to an improved functional outcome. However, there is still a lack of biomechanical data to support this concept. The optimal design of the glenoid component remains a challenge for future research. Specific issues including the choice of biomaterials, the optimum shape, radius of curvature, surface area of the articulation, component height and stem design remain under investigation. Although the prosthetic design represents an important factor in the success of glenohumeral arthroplasty, the surgical reconstruction of the soft tissues to recreate the normal soft tissue balance as well as postoperative rehabilitation determine the functional outcome.     

Stemless shoulder prosthesis versus conventional anatomic shoulder prosthesis in patients with osteoarthritis

Background

The stemless shoulder prosthesis is a new concept in shoulder arthroplasty. To date, only a few studies have investigated the results of this prosthesis. The aim of this study was to investigate the clinical and radiological midterm results of this implant in comparison with a standard anatomic stemmed shoulder prosthesis.

Materials and methods

The Constant score, the DASH score, the active range of motion (abduction, anteversion, external rotation), and the radiological results were examined in 82 patients with primary osteoarthritis of the shoulder treated with either the Total Evolutive Shoulder System^® (Biomed, France) stemless shoulder prosthesis or the Affinis^® (Mathys, Switzerland) stemmed shoulder prosthesis to detect possible differences in the functional outcome and to evaluate radiological properties of the implants. Patients were examined before and 32 ± 4 months after surgery.

Results

There was no significant difference in the Constant scores of the groups treated with the stemless shoulder prosthesis (65.0 ± 11.0 points) and the stemmed shoulder prosthesis (73.2 ± 11.3 points; P = 0.162). The estimated blood loss (P = 0.026) and the mean operative time (P = 0.002) were significantly lower in the group with the stemless shoulder prosthesis.

Conclusions

The use of the stemless shoulder prosthesis yielded good results which, in a mid-term follow-up, were comparable with those provided by a standard anatomic shoulder prosthesis. Further investigations are needed regarding the long-term performance of this prosthesis.     

Penile prosthesis implantation

The development of effective systemic therapy for the treatment of erectile dysfunction has resulted in a significant increase in the number of men presenting for treatment. Not all men with erectile dysfunction will respond to systemic therapy; those who fail may be candidates for penile prosthesis implantation if second and third lines of treatment also fail or are rejected by the patient and his partner. Penile prosthesis implantation continues to play a role in the treatment of erectile dysfunction. There is a potential for the number of penile prosthesis implantation procedures to actually increase. The ideal penile prosthesis is a three-piece inflatable device that permits good penile flaccidity and increases in size and becomes rigid with inflation.     

Fixation of the reversed shoulder prosthesis

The last decade has seen an increased interest in reversed shoulder prostheses. Success rates with these designs have been varied, with initial performance marred by failures resulting from improper implant alignment and an emerging engineering understanding. Competitor products to the well-documented Grammont design have yielded increasingly high success rates. Understanding the relationships between implant design, surgical procedure, and clinical outcome is important so that current results can be improved upon. This study considers the performance of 3 different reversed shoulder designs from the perspective of osseointegration, with the results broadly validated through comparison with experimental data. Finite element modeling was used to clarify the relationships between lateral offset of the center of rotation, screw insertion angle, screw length, screw diameter, bone material quality, and the potential for interdigitation of the supporting bone onto the reversed prosthesis. The results indicate that screw length, insertion angle, and diameter, when maximized, allow the least relative motion between the implant and underlying bone. When the bone is stiffer, the relative motion of the implant is lower. In almost all scenarios modeled, the interface micromotion was small enough to suggest that the glenoid was stable enough to encourage bone ingrowth across the majority of the bone-implant interfaces.     

The superolateral approach for shoulder prosthesis

We describe a superolateral approach to the shoulder for implantation of total shoulder prostheses or humeral prostheses. The advantages of this approach include preservation of the supraspinatus tendon and an excellent exposure of the posterior part of the glenoid cavity. We illustrate this approach with three clinical examples: total shoulder arthroplasty with reconstruction of the posterior part of the glenoid using a screwed autograft for central degeneration with posterior wear of the glenoid, intermediate arthroplasty for excentric degeneration with irreparable rotator cuff tears, and simple humeral arthroplasty with bone suture of the tuberosities for cephalotuberosity fracture.     

Computed tomography evaluation of shoulder prosthesis retroversion

Computed tomography (CT) allows calculation of anatomic and prosthetic humeral head retroversion. The purpose of this study was to demonstrate how the retroversion angle measured by CT scan varied with changes in arm position in the CT scan reference system. A trigonometric analysis shows that the measured retroversion angle decreases when the arm is in extension and increases when it is in flexion, compared with the true retroversion angle determined perioperatively. For the same degree of flexion, or extension, the error of measurement is greater when the initial true retroversion is low. A shoulder prosthesis with 20 degrees of true head retroversion was radiologically scanned with different degrees of flexion, extension, and abduction. The results validate the theoretical analysis. Trigonometric formulas are proposed to correct the retroversion angle measured by CT scan.     

Partial prosthesis of the shoulder joint--personal experience

Hemiarthroplasty of the shoulder is a treatment of choice for severe types of proximal humeral fractures. From 2001 to 2003, 8 hemiarthroplasties were performed at the University Clinic for Orthopaedic Surgery and Traumatology, Clinical Center Novi Sad. The aim of this study was to retrospectively assess functional outcomes of those patients. By determing the factors that affected the outcome, we would try to improve results of future patients.     

Evolution of the reverse total shoulder prosthesis

Over the last decade, reverse total shoulder arthroplasty has gained significant popularity due to its ability to address difficult reconstructive shoulder problems that could not be adequately treated in the past. The concept of the reverse shoulder prosthesis was introduced in the 1970s, but the initial attempts were associated with high complication and implant failure rates. The pioneering work of Paul Grammont (shifting the center of rotation medially and distally) and the development of the DELTA prosthesis have been fundamental to all subsequent reverse shoulder arthroplasty systems. These semiconstrained prostheses utilize the deltoid to improve function and stability of the shoulder joint by coupling a convex glenoid with a concave humeral component. Modern generations of reverse shoulder prosthesis continue to evolve on the fundamentals of Grammont. Though results of these new prosthesis demonstrate promising outcomes, many controversies and challenges continue to be refined. An historical review of the evolution of reverse shoulder arthroplasty is presented, as well as the currently expanding indications for its application.     

Mechanical complications of total shoulder inverted prosthesis

Our series of inverted prosthesis included 5 patients with a mean age of 73 +/- 6 years. In 4 cases, the implant was performed as a surgical revision. The follow up was 81 +/- 15 months. Three shoulders were pain free whereas two caused a dull pain after a free interval due to mechanical complications. The mean active elevation was 72 degrees while external rotation was - 2 degrees. The adjusted Constant score passed from 32 to 60. In case of complications, the score dropped to 32. Mechanical complications were important with in one case, an unscrening of the glenosphere and in two cases, a loosening of the glenoid prosthesis. This last and major complication occurred 6 years after surgery and was promoted by the occurrence of a progressive bone erosion in the scapula. This gap represented an attempt to accomodate the medial part of the humeral prosthesis under the scapula when the arm is at rest or in adduction. The concept of an inverted prosthesis is attractive and this implant remains one of the options in cuff-tear arthropathy. Our results were not as good as those reported by others but most of ours patients had been already operated before. The occurrence of an osseous gap on pilar of scapula may lead to failure of this prosthesis. This gap remains a threath as it can progress and as such warrants a design alteration of the prosthesis.     

Contemporary aspects of penile prosthesis implantation

PURPOSE: Erectile dysfunction today has a number of effective treatment options. This review was undertaken to examine the contemporary role of penile prosthesis implantation in the treatment of this disorder. MATERIALS AND METHODS: A MEDLINE search was performed on the topic of penile prostheses and implants. Current literature was reviewed with regard to types of penile implants, issues related to prosthesis implantation, results, and patient/partner satisfaction. RESULTS: Mechanical failure rates for early penile prostheses, especially the inflatable type, were unacceptably high. Advances in both prosthesis design and implantation techniques have resulted in increased device survival with 5-year actuarial survival rates free of mechanical failure ranging from 86.2 to 93.6%. Recent reviews of implant recipients show 83 and 85% satisfaction and for partners 70 and 76% satisfaction. CONCLUSIONS: When systemic therapy for erectile dysfunction fails, men have a variety of other options to choose from. Penile prosthesis implantation is an option that is feasible for nearly every man with this disorder. Current device survival rates and patient and partner satisfaction rates are high.     

Current status of penile prosthesis implantation

Today most men with erectile dysfunction (ED) can be effectively treated with less invasive means than penile prosthesis implantation. Nevertheless, there remain men who do not respond to simple treatments such as systemic medication and who either do not respond to or reject intermediate treatment such as penile injection therapy. For these men, penile prosthesis implantation remains a reasonable option. This review discusses types of penile prostheses, how to choose among prosthesis types, key features of implant techniques, infection management, penile reconstruction related to prosthesis implantation, and patient and partner satisfaction.     

The inverse prosthesis as a revision prosthesis in failures of shoulder hemiarthroplasty

The authors describe their series of seven cases of complications and failures of shoulder hemiarthroplasty that were submitted to revision surgery involving an inverse prosthesis. This prosthesis has for some time now been indicated in elderly patients with arthropathy caused by rupture of the cuff. In our cases this prosthesis was implanted in patients who had undergone shoulder hemiarthroplasty for fracture and for arthrosis. The Constant score was used for pre- and postoperative evaluation. Results at mid-term, from 2 to 4 years, indicate evident improvement in Constant score that rose from a mean of 23.14 preoperatively to a mean of 49.14 postoperatively. Despite the limited follow-up the authors suggest the use of the inverse prosthesis as an effective alternative solution in shoulder arthroplasty revision surgery.