Biomechanical relevance of glenoid component positioning in the reverse Delta III total shoulder prosthesis

The presence of a notch at the inferior part of the scapular neck is a common radiographic finding in patients treated with a reverse Delta III shoulder prosthesis. It is thought that this notch is a result of mechanical contact between the polyethylene cup of the humeral implant and the inferior glenoid pole during adduction of the arm. This in vitro study assessed the effect of glenoid component positioning on glenohumeral range of motion in 8 shoulder specimens. Four different positions of the glenosphere were tested: glenosphere centered on the glenoid, leaving the inferior glenoid rim uncovered (configuration A); glenosphere flush with the inferior glenoid rim (configuration B); glenosphere extending beyond the inferior glenoid rim (configuration C); and glenosphere tilted downward 15 degrees (configuration D). The respective mean adduction and abduction angles in the scapular plane were -25 degrees and 67 degrees for configuration A, -14 degrees and 68 degrees for configuration B, -1 degrees and 81 degrees for configuration C, and -9 degrees and 75 degrees for configuration D. Placing the glenosphere distally (test configuration C) significantly improved adduction and abduction angles compared with all other test configurations (P < .001).     

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.     

Prosthetic overhang is the most effective way to prevent scapular conflict in a reverse total shoulder prosthesis

Background and purpose?Controversies still exist about whether there is any effect of operative approach on survival of hip prostheses. We compared long-term survival of primary total hip arthroplasties in a welldefined study population from a national prospective population-based registry with regard to the three most commonly used surgical approaches.

Methods?We assessed prosthesis survival according to surgical approach (the lateral with or without trochanteric osteotomy, and the posterolateral) for 19,304 Charnley and 6,002 Exeter total hip arthroplasties performed from 1987 to 2004.

Results?For Charnley total hip arthroplasties, lateral approach with trochanteric osteotomy had a lower probability of revision than lateral approach without trochanteric osteotomy (RR = 0.6, 95% CI: 0.5–0.8). The lower revision rate was due to fewer revisions for aseptic loosening and dislocation. The differences had declined in the latest time period (1995–2004). We observed no differences between lateral approach without trochanteric osteotomy and posterolateral approach, except that there were more revisions due to dislocation in the posterolateral approach group (RR = 1.9, 95%CI: 1.1–3.2). No statistically significant differences were observed for Exeter total hip arthroplasties.

Interpretation?For Charnley prostheses, the lateral approach with trochanteric osteotomy gave a reduced revision risk compared to the other approaches, which was due to fewer revisions for dislocation, and in the first time period also fewer revisions due to aseptic loosening.     

Optimal positioning of the humeral component in the reverse shoulder prosthesis

Introduction

Total reverse shoulder arthroplasty is becoming more and more the standard therapeutic practice for glenohumeral arthropathy with massive lesions of the rotator cuff. The biomechanical principle of this prosthesis is represented by the reversion of the normal anatomy of the shoulder joint. This non-anatomical prosthesis leads to a medialization of the rotation centre of the glenohumeral joint and also to a distalization of the humeral head. All that causes a deltoid tension increasing so allowing a larger abduction of the arm. Main complications of the reverse shoulder prosthesis are due to the joint instability, the scapular notching and the wear of the polyethylene insert.

Purpose

The main goal of the present work is to study the effect of the positioning of the humeral component on the intrinsic stability of the reverse shoulder prosthesis. In particular, through finite element method simulations, the variation of the stability ratio of the shoulder joint has been calculated for both vertical and horizontal dislocating loads depending on the humeral stem version angle. Moreover, in order to estimate the wear of the polyethylene cup, some analyses have been developed to calculate the pressures on the polyethylene insert.

Results

The obtained results demonstrate the dislocation of a shoulder prosthesis and the wear of the polyethylene insert can be prevented or limited by conveniently varying the version angle of the humeral component.     

Predictors of scapular notching in patients managed with the Delta III reverse total shoulder replacement

BACKGROUND: The reverse Delta III shoulder prosthesis can relieve pain and restore function in patients with cuff tear arthropathy. The most frequently reported radiographic complication is inferior scapular notching. The purpose of the present study was to evaluate the clinical relevance of notching and to determine the anatomic and radiographic parameters that predispose to its occurrence. METHODS: Seventy-seven consecutive shoulders in seventy-six patients with an irreparable rotator cuff deficiency were managed with a reverse Delta III shoulder arthroplasty and were followed clinically and radiographically for a minimum of twenty-four months. The effects of cranial-caudal glenoid component positioning and the prosthesis-scapular neck angle on the development of inferior scapular notching and clinical outcome were assessed. RESULTS: All shoulders that had development of notching did so in the first fourteen months. Of the seventy-seven shoulders that were studied, thirty-four (44%) had inferior scapular notching, twenty-three (30%) had posterior notching, and six (8%) had anterior notching. Osteophytes along the inferior part of the scapula occurred in twenty-one (27%) of the seventy-seven shoulders. The angle between the glenosphere and the scapular neck (r = 0.667) as well as the craniocaudal position of the glenosphere (r = 0.654) were highly correlated with inferior notching (p < 0.001). A notching index was calculated with use of the height of implantation of the glenosphere and the postoperative prosthesis-scapular neck angle. This allowed prediction of the occurrence of notching with a sensitivity of 91% and specificity of 88%. The height of implantation of the glenosphere had approximately an eight times greater influence on inferior notching than the prosthesis-scapular neck angle did. Inferior scapular notching was associated with a significantly poorer clinical outcome. CONCLUSIONS: Inferior scapular notching after reverse total shoulder arthroplasty adversely affects the intermediate-term clinical outcome. It can be prevented by optimal positioning of the glenoid component.     

The reverse shoulder prosthesis (Delta III) in acute shoulder fractures: technical considerations with respect to stability

The reverse shoulder prosthesis reverses the relationship between the scapular and humeral component, resulting in a mechanical advantage as the deltoid muscle is able to compensate for the rotator cuff deficiency. Based on this mechanical advantage, the reverse shoulder prosthesis has become an accepted alternative for the treatment of complex proximal humeral fractures. The purpose of this article is to discuss technical considerations related to stability in the use of the reverse shoulder prosthesis in acute shoulder fractures, based on clinical experience.     

Glenohumeral relationship in the transverse plane of the body

Reconstruction of a normal glenohumeral relationship is desirable for a successful arthroplasty. Double-contrast computed tomography was performed on 49 healthy shoulders in young volunteers. For creation of a uniform spatial reference system, the subjects were positioned in a thoracobrachial orthosis with the arm adducted in the coronal plane and the forearm flexed in the sagittal plane, and they were examined in dorsal recumbency. The classical anatomic angles were measured, and the anatomic axes were determined and quantified as angles to the coronal plane. When the axis of the glenoid was correlated to the axis of the humeral head, a mean of 8.5 degrees divergence in a clear Gaussian distribution was found. This contrasts with the variability of the version of the humeral head and of the glenoid and offers a useful guideline in difficult prosthetic surgery of the shoulder in which normal anatomic landmarks are lost because of arthritic or traumatic deformity.     

Delta III reverse-ball-and-socket total shoulder prosthesis for acute complex fractures of the proximal humerus in elderly population

Background

The Delta III semi-constrained reverse-ball-and-socket total shoulder prosthesis works only with an intact deltoid muscle. Our purpose is to evaluate the results in a consecutive series of acute complex fractures of the proximal humerus in elderly population with a poor bone quality when the main problem is to obtain a reliable and efficient re-fixation of the tubercles with classical orthopaedic devices.

Methods

From 1993 to 2005, 36 Delta III were implanted, 27 three-part, and four-part displacements and nine fracture-dislocations, in 3 males for 33 females, for 16 dominant sides, with an average age of 75 years. The surgery was realized under general anaesthesia, in semi-sitting position, by an antero-lateral approach with retroversion of the humeral-cemented stem of 20° to 0°. Post-operative physiotherapy was not always realizable.

Results

The results were estimated with the clinical Constant scoring system, AP and lateral view X-rays. Twenty-five cases were reviewed because nine were deceased and two moved out. At a mean follow-up of 71 months, the Constant score was 59 points for a contra-lateral shoulder evaluated at 81. The results were good in respect of pain (14.1), activity (14.3), strength (14.1), anterior elevation (7.5), abduction (6.5), but very poor for external (1.1), and internal (1.4) rotations. The radiographs showed: one aseptic glenoid loosening at 12-year follow-up with surgical revision, 14 inferior scapular notching (seven stages 1, five stages 2, one stage 3, one stage 4), 14 inferior spurs stable after emergence without clinical repercussion, four medial and two lateral proximal humeral bone loose, and two medial humeral lucent lines.

Conclusions

For acute complex fractures of the proximal humerus, in elderly population with poor bone quality, when an efficient and reliable re-fixation of the tubercles is difficult or impossible, the Delta III prosthesis is a possible alternative with good functional outcome except rotations but with a lot of worrying inferior scapular notching.     

Analysis of a retrieved delta III total shoulder prosthesis

A reversed Delta III total shoulder prosthesis was retrieved post-mortem, eight months after implantation. A significant notch was evident at the inferior pole of the scapular neck which extended beyond the inferior fixation screw. This bone loss was associated with a corresponding, erosive defect of the polyethylene cup. Histological examination revealed a chronic foreign-body reaction in the joint capsule. There were, however, no histological signs of loosening of the glenoid base plate and the stability of the prosthetic articulation was only slightly reduced by the eroded rim of the cup.     

Treatment of painful pseudoparesis due to irreparable rotator cuff dysfunction with the Delta III reverse-ball-and-socket total shoulder prosthesis

BACKGROUND: The Delta III reverse-ball-and-socket total shoulder implant is designed to restore overhead shoulder function in the presence of irreparable rotator cuff deficiency by using the intact deltoid muscle and the stability provided by the prosthetic design. Our purpose was to evaluate the clinical and radiographic results of this arthroplasty in a consecutive series of shoulders with painful pseudoparesis due to irreversible loss of rotator cuff function. METHODS: Fifty-eight consecutive patients with moderate-to-severe shoulder pain and active anterior elevation of <90 degrees due to an irreparable rotator cuff tear were treated with a Delta III total shoulder replacement at an average age of sixty-eight years. Seventeen of the procedures were the primary treatment for the shoulder, and forty-one were revisions. The patients were examined clinically and radiographically after an average duration of follow-up of thirty-eight months. RESULTS: On the average, the subjective shoulder value increased from 18% preoperatively to 56% postoperatively (p < 0.0001); the relative Constant score, from 29% to 64% (p < 0.0001); the Constant score for pain, from 5.2 to 10.5 points (p < 0.0001); active anterior elevation, from 42 degrees to 100 degrees (p < 0.0001); and active abduction, from 43 degrees to 90 degrees (p < 0.0001). The patients for whom the implantation of the Delta III prosthesis was the primary procedure and those who had had previous surgery showed similar amounts of improvement. The total complication rate, including all minor complications, was 50%, and the reoperation rate was 33%. Of the seventeen primary operations, 47% (eight) were associated with a complication and 18% (three) were followed by a reoperation. Of the forty-one revisions, 51% (twenty-one) were associated with a complication and 39% (sixteen) were followed by a reoperation. Subjective results and satisfaction rates were not influenced by complications or reoperations when the prosthesis had been retained. CONCLUSIONS: Total shoulder arthroplasty with the Delta III prosthesis is a salvage procedure for severe shoulder dysfunction caused by an irreparable rotator cuff tear associated with other glenohumeral lesions. Complications were frequent following both primary and revision procedures, but they rarely affected the final outcome. The procedure has a substantial potential to improve the condition of patients with severe shoulder dysfunction, at least in the short term.     

Prosthetic design considerations in total shoulder arthroplasty

Total shoulder replacements should, as far as possible, be designed after normal anatomy. A small mismatch in curvature between the humeral head and glenoid surfaces may reduce edge loading when the humerus translates on the glenoid, but may increase contact stresses caused by point loading. Modularity increases sizing options but decreases head size for a given soft-tissue space and introduces the risk of component dissociation. Releases and soft-tissue balancing at surgery, and rehabilitation afterwards, are more important than the type of glenohumeral prosthesis implanted.     

Factors affecting fixation of the glenoid component of a reverse total shoulder prothesis

The semiconstrained design of the reverse arthroplasty allows loads from the humerus to challenge the fixation of the glenoid component to the scapula. We examined some of the factors affecting the quality of glenoid screw fixation, including the density of the material into which the screws are placed, the purchase of individual screws, and the direction of loading in relation to screw placement. Loads were applied by the humeral component to glenoid components with different conditions of fixation. The load to failure for each set of conditions was measured and compared statistically. Load to failure was less when the glenoid component was fixed to material of lesser density. Each screw contributed to the quality of fixation; the screw nearest the point of load application made the largest contribution. Load to failure was less when the load was colinear with a line through the nonlocking holes in the base plate compared to colinear with a line through the locking holes. In performing a reverse total shoulder, surgeons should emphasize secure intraosseous placement of the fixation screws in the best quality bone available. The placement of the inferior screw appears to be the most critical.