Shoulder prostheses treating cuff tear arthropathy: a comparative biomechanical study

Morphology of the scapula relative to the reverse shoulder prosthesis

PURPOSE

To analyse the morphology of the scapula relative to the reverse shoulder prosthesis.

METHODS

Scapulas of 46 women and 27 men aged 16 to 84 (mean, 53) years with proximal humeral fractures (n=52) or recurrent antero-inferior instability (n=21) were assessed using 3-dimensional computed tomography (CT). For comparison, 108 cadaveric scapulas with unknown epidemiology were assessed using a goniometer and a caliper. The length of the glenoid neck, the angle between the glenoid surface and the upper posterior column of the scapula, and the angles between the major craneocaudal glenoid axis and (1) the base of the coracoid process and (2) the upper posterior column of the scapula were assessed.

RESULTS

The length of the glenoid neck was classified into short and long. In the respective CT and cadaveric groups, the anterior glenoid neck was short in 42% and 18% of scapulas and long in 58% and 82%, whereas the posterior glenoid neck was short in 34% and 60% of scapulas and long in 66% and 40%. The angle between the glenoid surface and the upper posterior column of the scapula was classified into types I (50-52 degrees) and II (62-64 degrees). In the respective CT and cadaveric groups, 61% and 71% of scapulas were type I and 39% and 29% were type II. All differences between groups were significant. The mean angles between the major craneocaudal glenoid axis and (1) the base of the coracoid process and (2) the upper posterior column of the scapula were 18 and 8 degrees, respectively.

CONCLUSION

Because of variations in scapular morphology, individualised adjustment is needed for reverse shoulder prostheses. Three-dimensional CT is valuable in preoperative planning.

Biomechanical evaluation of different designs of glenospheres in the SMR reverse total shoulder prosthesis: range of motion and risk of scapular notching

BACKGROUND

Reverse total shoulder arthroplasty is a treatment option for cuff tear arthropathy. Scapular notching remains a concern. This biomechanical study compared the range-of-motion in different designs of glenospheres and hence the relative risk of scapular notching.

METHOD

A precision coordinate device was used to investigate four different designs of glenospheres (SMR prosthesis); 36 mm concentric (Standard), 36 mm eccentric, 44 mm concentric, and 44 mm eccentric glenospheres. The centre of rotation in each design was first established. The position of the humeral prosthesis was recorded in the plane of the scapula to compare the degree of adduction and the total range-of-motion.

RESULTS

Eccentric glenospheres were found to improve range-of-motion by allowing a higher degree of adduction. Larger diameter glenospheres were found to improve range-of-motion by increasing adduction and abduction. Compared to the 36 mm concentric (standard) glenosphere, the 36 mm eccentric glenosphere improved adduction by 14.5 degrees, the 44 mm concentric glenosphere improved adduction by 11.6 degrees, the 44 mm eccentric glenosphere improved adduction by 17.7 degrees.

CONCLUSION

Eccentric glenospheres with a center-of-rotation placed more inferiorly were shown to improve adduction. This design may reduce the clinical incidence of scapular notching.

Primary stability in reversed-anatomy glenoid components

Reversed-anatomy shoulder replacement is advocated for patients with poor rotator cuff condition, for whom an anatomical reconstruction would provide little or no stability. Modern generations of this concept appear to be performing well in the short-term to midterm clinical follow-up. These designs are almost always non-cemented, requiring a high degree of primary stability to encourage bone on-growth and so to establish long-term fixation. Six different inverse-anatomy glenoid implants, currently on the market and encompassing a broad range of geometrical differences, were compared on the basis of their ability to impart primary stability through the minimization of interface micromotions. Fixing screws were only included in the supero-inferior direction in appropriate implants and were always inclined at the steepest available angle possible during surgery (up to a maximum of 30°). The extent of predicted bony on-growth was, of course, highly dependent on the threshold for interface micromotion. In some instances an additional 30 per cent of the interface was predicted to promote bone on-growth when the threshold was raised from 20 μm to 50 μm. With maximum thresholds of micromotion for bone on-growth set to 30 μm, the Zimmer Anatomical device was found to be the most stable of the series of the six designs tested herein, achieving an additional 3 per cent (by surface area) of bone on-growth above the closest peer product (Biomet Verso). When this threshold was raised to 50 μm, the Biomet Verso design was most stable (3 per cent above the second-most stable design, the Zimmer Anatomical). Peak micromotions were not a good indicator of the predicted area of bone on-growth and could lead to some misinterpretation of the implant's overall performance. All but one of the implants tested herein provided primary stability sufficient to resist motions in excess of 150 μm at the interface.

The biomechanics of reverse anatomy shoulder replacement--a modelling study

BACKGROUND

Reverse anatomy shoulder prostheses, in which a partial sphere is attached to the scapula and a socket to the humerus, have become popular for the treatment of arthritic shoulders with severe rotator cuff arthropathy. While they have been in relatively common use, their biomechanical aspects have not been fully investigated.

METHODS

This study uses an adaptation of a 3D biomechanical shoulder model to describe the DELTA reverse prosthetic shoulder geometry and to investigate its properties. The muscle configuration was modified to represent the pathology and joint contact forces were computed for standardised activities.The model also uses a contact detect algorithm to record the impingement of the prosthesis with the scapula.

FINDINGS

Results showed that the reverse design increases the deltoid function compensating for the dysfunctional rotator cuff muscles by providing sufficient moment arm (increased by 42%) to elevate the arm. It also restores joint stability by reversing the envelope of the joint contact forces and reacting to the increased shear forces. Despite these advantages, the model also confirms impingement and predicts bone notches from the contact of the prosthesis with the scapula border. Results indicate that optimised fixation and design alterations can reduce the problem but is difficult to eliminate it without compromising the joint stability.

INTERPRETATION

The study provides a deep understanding of the function of the reverse designs highlighting their advantages in irreparable rotator cuff arthropathy but also the associated problems that compromise their use. Despite the limitations results indicate that reverse designs can be optimised to provide maximum functionality.

An evaluation of the relationships between reverse shoulder design parameters and range of motion, impingement, and stability

BACKGROUND

The purpose of this study was to evaluate the role of reverse shoulder design parameters on performance.

METHODS

A computer analysis was conducted on the Grammont reverse shoulder to quantify the effect of varying design parameters on functional measurements during humeral abduction/adduction. To demonstrate the application of these relationships, a novel prosthesis was designed.

RESULTS

The Grammont reverse shoulder impinged inferiorly and superiorly on the glenoid at 31 degrees and 95 degrees of humeral abduction with an average jump distance of 10 mm. Several linear relationships were identified. The proposed 38 mm, 42 mm, and 46 mm reverse shoulder designs impinged inferiorly and superiorly on the glenoid at 7.3 degrees/87.5 degrees, 1 degrees/87.5 degrees, and 0 degrees/89.3 degrees of humeral abduction with an average jump distance of 11.7 mm, 13.5 mm, and 14.1 mm, respectively.

CONCLUSIONS

The results of this study demonstrate that subtle changes in design parameters can minimize inferior glenoid impingement and offer potential for dramatic functional improvements in ROM (39%) and jump distance (36%).

Treatment of comminuted fractures of the proximal humerus in elderly patients with the Delta III reverse shoulder prosthesis

OBJECTIVES

To evaluate clinical and radiologic results after implantation of the Delta III reverse shoulder prosthesis in elderly patients with comminuted fractures of the proximal humerus.

DESIGN

Prospective, single-center-based cohort study.

SETTING

Level II Trauma Center.

PATIENTS

Patients undergoing insertion of Delta III reverse shoulder prosthesis for the treatment of comminuted fractures of the proximal humerus between July 2002 and December 2004.

INTERVENTION

Surgery with the Delta III reverse shoulder prosthesis through a juxta-acromial approach.

MAIN OUTCOME MEASURES

Duration of surgery, x-ray evaluation by Nerot's Score, complications, and functional outcome based on the Constant Score, the modified American Shoulder and Elbow Surgeons Score, the Disabilities of the Arm, Shoulder and Hand Score, and the 36-item short-form health survey (SF-36) Score.

RESULTS

Twenty patients (14 females, 6 males) with a mean age of 74.85 +/- 5.73 years were included into the study followed up for 33.29 +/- 9.6 months. The average range of motion was for abduction 112.5 +/- 38.19 degrees and for anterior elevation 122.67 +/- 32.84 degrees. The mean Constant Score was 67.85 +/- 13.56. The mean Disabilities of the Arm, Shoulder and Hand Score was 46.85 +/- 15.68, and the mean modified American Shoulder and Elbow Surgeons Score was 68 +/- 11.83. The Physical Component Scale of the SF-36 was 38 +/- 11.94. The Mental Component Scale of the SF-36 score was 52.59 +/- 10.92. Operations were performed 10.05 +/- 8.78 days (3-41) after trauma, and the average operation time was 75.7 +/- 18.11 minutes.

CONCLUSIONS

The good functional outcome and the short intervention time in our present study and not needing a sufficient rotator cuff for implementation purposes suggest the use of the Delta III reverse shoulder prosthesis as a treatment option for elderly patients with comminuted fractures of the proximal humerus.

Cadaveric and three-dimensional computed tomography study of the morphology of the scapula with reference to reversed shoulder prosthesis

Purpose

The purpose of this study is to analyze the morphology of the scapula with reference to the glenoid component implantation in reversed shoulder prosthesis, in order to improve primary fixation of the component.

Methods

Seventy-three 3-dimensional computed tomography of the scapula and 108 scapular dry specimens were analyzed to determine the anterior and posterior length of the glenoid neck, the angle between the glenoid surface and the upper posterior column of the scapula and the angle between the major craneo-caudal glenoid axis and the base of the coracoid process and the upper posterior column.

Results

The anterior and posterior length of glenoid neck was classified into two groups named "short-neck" and "long-neck" with significant differences between them. The angle between the glenoid surface and the upper posterior column of the scapula was also classified into two different types: type I (mean 50°–52°) and type II (mean 62,50°–64°), with significant differences between them (p < 0,001). The angle between the major craneo-caudal glenoid axis and the base of the coracoid process averaged 18,25° while the angle with the upper posterior column of the scapula averaged 8°.

Conclusion

Scapular morphological variability advices for individual adjustments of glenoid component implantation in reversed total shoulder prosthesis. Three-dimensional computed tomography of the scapula constitutes an important tool when planning reversed prostheses implantation.

Simulated joint and muscle forces in reversed and anatomic shoulder prostheses

Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0 degrees to 150 degrees of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90 degrees of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it. This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.

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.

Consequences of scapular anatomy for reversed total shoulder arthroplasty

The reverse total shoulder prosthesis provides successful functional outcome in many patients with rotator cuff tear arthropathy. However, scapular notching, a direct consequence of mechanical impingement between the humeral prosthesis and the glenoid, remains a major concern. We presumed a better knowledge of the anatomy of the scapula would enable design or placement modifications to minimize this phenomenon. After establishing a uniform spatial reference system using easy locatable surgical reference points and planes, we analyzed 200 dry bony scapulae and defined the glenoid and infraglenoid anatomy relative to the reference system. The bony rim of the two inferior quadrants of the glenoid forms a semicircle the center of which can be used perioperatively as an easy locatable bony reference point. The infraglenoid tubercle varies in width and length, and can interfere with the humeral part of the reverse prosthesis, creating scapular notching. To avoid notching, we suggest using a convex base plate with a smaller radius than currently used, placing it as low as possible with a 42-mm glenosphere eccentrically assembled to create a posterior offset. If prosthetic overhang cannot be obtained, we suggest removing part of the infraglenoid tubercle.

Prosthetic component relationship of the reverse Delta III total shoulder prosthesis in the transverse plane of the body

The Delta III (DePuy International Ltd, Leeds, UK) reverse total shoulder prosthesis has provided a successful functional outcome in cuff tear arthropathy (CTA); however, internal and external rotation remain compromised. Positioning of the prosthetic components in the transverse plane has theoretically been suggested to affect rotation. Twenty-seven patients who received a Delta III reversed total shoulder prosthesis for CTA were analyzed (mean follow-up, 43 months) using standard radiographs and computed tomography. The position of the prosthetic components and the possible influence of scapular rotation was analyzed using a uniform spatial reference system using axes in reference to the sagittal or coronal plane. We assessed impingement of the humeral component on the glenoid neck in neutral and internal rotation. An increase in the anterior divergence of the glenoid and humeral prosthetic components correlates with an increase in radiologically measured internal rotation (r = 0.932, P < .001). The uniformity of the reference system used seems to allow accurate positioning of the components intraoperatively and can be useful for analysis of the prosthetic component relationship postoperatively.

Grammont inverted prosthesis for the treatment of cuff tear arthropathy: a 6-year follow-up study

This study evaluated mid-term functional results of the Grammont inverted prosthesis for the treatment of shoulder osteoarthritis associated with massive cuff rupture. Twenty-eight patients with a minimum of 6 years of follow-up were evaluated. Clinical evaluation was performed on all patients preoperatively and at follow-up using the Constant score. Radiologic assessment included radiographs and magnetic resonance imaging preoperatively and radiographs at follow-up. Constant score improved from 27.4 preoperatively to 64.6 postoperatively. The inverted prosthesis is attractive and remains one of the options for treating cuff tear arthropathy. However, glenoid loosening remains a serious problem.

Latissimus dorsi transfer to restore external rotation with reverse shoulder arthroplasty: a biomechanical study

In patients with pseudoparesis of the shoulder resulting from irreparable rotator cuff tears, reverse shoulder arthroplasty (RSA) can restore active elevation, but external rotation remains less predictable. Latissimus dorsi transfer (LDT) has been shown to be effective in restoring external rotation in patients with posterosuperior tears of the rotator cuff. The aim of this study is to determine the capacity of the LDT to restore external rotation in combination with RSA and to investigate the mechanical advantage produced by 3 different insertion sites. A biomechanical model was created using a reverse total shoulder prosthesis with 3 different transfer insertions. Moment arms were measured for 2 static positions and 1 motion of the humerus. The moment arm analysis showed that LDT can improve active external rotation in the setting of a reverse prosthesis. An insertion site on the posterior side of the greater tuberosity (adjacent to the teres minor insertion) produced a greater external rotation moment arm.

Contribution of the reverse endoprosthesis to glenohumeral kinematics

After placement of a reverse shoulder endoprosthesis, range of motion is usually still compromised. To what extent this occurs from limitation in motion of the reverse endoprosthesis is, however, unclear. We measured the motion pattern of 16 patients (18 shoulders) during three active and passive range of motion tasks using a six degree-of-freedom electromagnetic tracking device. Despite rotator cuff deficiencies, glenohumeral elevation contributed roughly two-thirds of the total thoracohumeral elevation, which is comparable to healthy subjects. However, patients could not actively use the full range of motion provided by the prosthesis. Although we found considerable interindividual differences in shoulder kinematics, the limitation in glenohumeral range of motion appears related to a lack of generated muscle force and not the design of the prosthesis.

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.

[Bipolar shoulder prosthesis for rheumatoid arthritis with irreparable rotator cuff tear: results after 5 years' follow-up]

PURPOSE OF THE STUDY

The goal of this study was to assess the clinical and radiological outcome of bipolar shoulder prosthesis in twelve shoulders with rheumatoid arthritis (RA) and irreparable rotator cuff tears.

MATERIAL AND METHODS

The follow-up was more than five years (range 2-9 years). In addition, in order to investigate the effect of rheumatoid arthritis on outcome, results were compared with ten bipolar shoulder prostheses implanted for osteoarthritis with massive rotator cuff tears.

RESULTS

The mean preoperative Constant score was 16.9 points with 2.6 points for pain, 4.2 points for activity, 9.5 points for motion and 0.6 points for force. The preoperative active motion was 63.8 degrees for forward flexion, 45 degrees for abduction and 12 degrees for active external rotation. At last follow-up, the average Constant score was 39.4 points with 10.7 points for pain, 10.8 points for activity, 13.8 points for motion and 4.1 points for force. Regarding the active motion, mean forward flexion was 83.7 degrees, 70.4 degrees for abduction and 29.1 degrees for external rotation. The complication rate was low, mainly superior migration due to infraspinatus tear and glenoid wear. Satisfactory deltoid arm level was achieved in all patients and no loosening was observed. Preoperative and postoperative scores of the rheumatoid group were not significantly different from the arthritis group (p<0.001).

DISCUSSION

Our findings suggest that bipolar shoulder prosthesis provides a viable replacement alternative in RA combined with massive rotator cuff tear with a low rate of complication. Bipolar shoulder prosthesis demonstrates no clear superiority over conventional hemiarthroplasty regarding improved motion and glenoid wear. In addition, no significant difference with arthritis was observed (p<0.05), assuming that outcome depends principally on the preoperative condition of the rotator cuff.

CONCLUSION

Some massive tears involving the subscapularis tendon can lead to anterior recurrence after bipolar shoulder prosthesis. They might be a limit to the procedure and require a reversed shoulder prosthesis or a glenohumeral arthrodesis.

Radiologic assessment of reverse shoulder arthroplasty

The reverse shoulder prosthesis was approved for clinical use in the United States in March 2004. This new prosthesis reverses the normal ball-and-socket relationship of the shoulder joint. As a result of replacement of the glenoid component with a ball and of the humeral head with a socket, the center of rotation is moved distally and medially, allowing more control of shoulder motion by the deltoid muscle. This improved geometric configuration allows shoulder reconstruction in patients who have irreparable rotator cuff damage with secondary arthropathy, pain, and "pseudoparalysis" (ie, inability to lift the arm above the horizontal). Patients experience a significant improvement in range of motion and markedly decreased pain after undergoing reverse shoulder arthroplasty; however, the procedure is associated with a relatively high rate of complications, including dislocation, infection, loosening, malpositioning of the glenoid component or fixation screws, disassembly of the humeral component, periprosthetic fracture, and inferior glenoid impingement leading to scapular erosion. Therefore, it is important that the radiologist be familiar with the normal and abnormal imaging appearances of this new prosthesis.

Management of shoulder hemiarthroplasty in a patient with rheumatoid arthritis

STUDY DESIGN

Case report.

BACKGROUND

Rehabilitation after shoulder hemiarthroplasty for rotator cuff tear arthropathy (RCTA) represents a significant challenge to physical therapists. Limited goals have been defined for this patient population and include no pain or slight pain at rest, moderate pain with vigorous activity, shoulder external rotation active range of motion (AROM) greater than 20 degrees, and shoulder abduction AROM greater than 90 degrees.

CASE DESCRIPTION

The patient was a 60-year-old female elementary school teacher with functional class III adult-onset rheumatoid arthritis, who came to physical therapy 2 weeks after undergoing a hemiarthroplasty for RCTA of the right shoulder. Physical therapy included 33 treatment sessions involving 4 to 11 exercises each session. All sessions were performed under the direct supervision of a physical therapist utilizing specially designed equipment. Physical therapy emphasized early active assisted elevation range of motion (ROM), graded progressive exercise, and functional training. All exercises were performed in a pain-free ROM or a ROM that did not increase shoulder pain.

OUTCOMES

Following physical therapy, subjective pain scale at rest was 0/10 and during vigorous activity 1/10 to 2/10. Shoulder AROM was normal and shoulder rotation and elevation strength was good. There was a significant improvement in shoulder proprioception and the patient demonstrated a negative belly press test for subscapularis muscle integrity. Additionally, the patient's score on the self-report section of the American Shoulder and Elbow Surgeons Assessment Form increased from 0% at the initial examination to 70% at discharge.

DISCUSSION

Despite limited expectations, this patient achieved normal shoulder ROM and near normal shoulder strength after 14 weeks of physical therapy. Overall, an early, aggressive, progressively graded exercise program appears to be a safe and effective form of treatment after shoulder hemiarthroplasty for RCTA.