Analysis of reverse total shoulder joint forces and glenoid fixation

Reverse total shoulder arthroplasty (rTSA) implants are intended to restore stability and function to shoulders with rotator cuff deficiency. The implant consists of a glenosphere projecting from a glenoid baseplate and articulating in a socket at the proximal end of a humeral component. Despite the demonstrated clinical efficacy, little information is available regarding the joint forces about this construct and the stability of the glenoid component against these forces. Our hypotheses were that the joint forces about the rTSA were comparable to that about a normal shoulder joint, and that the micromotion between the baseplate and the scapula against these loads would be sufficiently low to induce bone ingrowth. To investigate this, a custom testing rig was constructed to simulate active shoulder elevation in fresh-frozen shoulder specimens. The forces about the rTSA were calculated and found to include compressive and shear forces up to 0.7 and 0.4 BW, respectively. In contrast to a normal shoulder, where the joint forces peak at 90° of abduction, forces about the rTSA were highest at about 60° of abduction. These forces were then applied in cyclic loading conditions to the glenoid baseplate, and the micromotion of the implant relative to the bone was measured in the four quadrants of the component. For two different rTSA designs (DePuy Delta III? and Encore RSP?) and in the entire range of the fixation testing, the cyclical micromotions were always less than 62 μm. Thus, under loading conditions similar to physiological shoulder elevation, micromotion of the glenoid component was sufficiently low and within previously published limits to induce bone ingrowth.     

Pain and function in eight hundred and fifty nine patients comparing shoulder hemiprostheses, resurfacing prostheses, reversed total and conventional total prostheses

Purpose

Functional results of reversed total prostheses (RTP) have—to a very limited degree—been compared with those of other shoulder prosthesis types. The aim of our study was to compare results of four different types of shoulder prostheses in terms of function, pain, and quality of life (QoL).

Methods

Questionnaires were completed by 859 patients with shoulder prostheses registered in the Norwegian Arthroplasty Register. Patients with osteoarthritis (OA), rheumatoid arthritis (RA), or fracture sequela (FS) were included. Symptoms and function were assessed using the Oxford Shoulder Score (OSS, scale 0–48), and the EuroQoL-5D (EQ-5D) was used to assess QoL.

Results

Best functional results were obtained using conventional total prostheses (TPs) and RTPs —mean OSS improvement 18 and 16 units, respectively, vs 11 with hemiprostheses (HPs). For patients with OA, TPs performed best; for those with RA and FS, RTPs performed best; and those with HPs had the worst results in all diagnostic groups. The greatest improvement in QoL was seen in patients with TPs and RTPs.

Conclusions

Conventional TPs provide the best improvement in pain, function and QoL in OA patients; RTPs are superior in patients with RA and FS.     

Preservation of the shoulder joint by the use of a hybrid-spacer after septic loosening of a reversed total shoulder joint arthroplasty: a case report

Infections of a total joint replacement (TJR) of the shoulder are rare complications. After revision surgery, the incidence rises dramatically. If infection occurs, it leads to a loss of function and may be devastating to the joint. Treatment options range from single- to multiple-staged revision programs, permanent resection arthroplasty or exarticulation. In this case, a reversed shoulder endoprosthesis, which was implanted after multiple revisions of a TJR due to a posttraumatic omarthrosis and rotator cuff insufficiency, got infected. A hybrid-spacer, made of a humeral nail and a custom-made PMMA spacer forming the humeral head, was used during the revision program. After two operations, clinical and paraclinical signs turned back to normal. The patient felt well and was satisfied with the result of the therapy. The hybrid-spacer was then left in situ as a definitive solution with a satisfying range of motion. This case report shows that a hybrid-spacer can be helpful in the treatment of an infected shoulder TJR.     

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.     

Differences in shoulder muscle activity between patients with generalized joint laxity and normal controls

The aim of the present study was to analyze shoulder muscle activity in patients with generalized joint laxity and shoulder instability and to compare it with muscle activity recorded in healthy subjects from an earlier study. Electromyographic (EMG) activity was recorded from eight shoulder muscles in six patients using surface and intramuscular fine-wire electrodes. Recordings were made from the subscapularis, supraspinatus, infraspinatus, pectoralis major (sternoclavicular part), the anterior, middle, and posterior parts of the deltoid, and the latissimus dorsi. The EMG signal was low-pass filtered, full-wave rectified, and time-average. Normalization of the EMG allowed interindividual and intraindividual comparisons. During abduction and flexion, muscle activity in the anterior and middle parts of the deltoid was significantly decreased in the patients, and during internal rotation activity in the subscapularis was increased. As in healthy subjects, patients showed simultaneous activity in both those muscles producing the movement and in the antagonistic muscles. The altered muscle activity observed in patients with generalized joint laxity provides (1) a basis for understanding the mechanism of their shoulder instability and (2) the rationale for a physical training program for these patients.     

Degenerative changes of the deltoid muscle have impact on clinical outcome after reversed total shoulder arthroplasty

Introduction  

Despite a high complication rate, subjective and objective results of reversed shoulder arthroplasty for severe rotator cuff lesions associated with osteoarthritis, fracture sequelae, or revision of hemiarthroplasty are favorable. However, whether the changes in biomechanics of the joint may lead to structural changes in the remaining rotator cuff and the deltoid muscle, and may thereby alter the clinical result, has rarely been described. This study investigates the context between postoperative fatty infiltration of the remaining rotator cuff and the deltoid muscle, and the clinical outcome after reversed shoulder arthroplasty.     

Bone mineral density of the shoulder joint in frozen shoulder

The purpose of this study was to evaluate the osteopenia in several parts of the shoulder joint in a series of individuals suffering from frozen shoulder and to elucidate the pathogenesis. The bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DEXA). In 30 cases of frozen shoulder, 16 men and 14 women, BMD of the head of the humerus, greater tubercle of the humerus, surgical neck of the humerus, and neck of the scapula was evaluated. The average age of the male patients was 58.4 years and of the women, 59.5 years. At the neck of the scapula, there were no significant differences in any of the cases. However, there was a marked decrease in BMD at the proximal end of the humerus on the affected side of women. In contrast, men showed no significant difference between the affected and unaffected shoulders, suggesting that the degree of osteopenia remains low compared with women. Although frozen shoulder is a disease which may occur in both men and women, the loss of bone was conspicuous only in women. This may be due to the involvement of female hormones in alterations of bone in frozen shoulder, as in cases of osteoporosis, in addition to the originally low bone density in women. The degree of osteopenia of the proximal humerus with frozen shoulder was not correlated with the duration of the disease, range of motion of the shoulder joint, or patient's age.     

The shoulder joint in chronic polyarthritis

In patients with rheumatoid arthritis, shoulder problems are very common. In the present study, 96 of 105 patients, i.e., 91%, reported shoulder problems. Thirty-one percent of the patients had such severe shoulder disability that they considered it to be their main rheumatic problem. With increasing duration of the rheumatic shoulder disease, there are progressive destructive changes and a decrease in the range of motion and functional capacity even with conservative treatment, indicating that intervention with surgical procedures may be warranted. In the early effusive stages of rheumatic shoulder disease, radiological synovectomy with beta-emitting radionuclides may be indicated. In proliferative synovitis, surgical synovectomy gives good pain relief and increased shoulder mobility and function. In shoulders with more advanced painful shoulder arthropathy, shoulder replacement is gaining in popularity. However, it is mandatory that candidates must be selected very carefully for shoulder replacement and in patients with severe fibrotic capsulitis, muscular atrophy or mutilation with severe loss of bone, the results after shoulder replacement surgery are often less successful.