The three-dimensional (3D) correction of glenoid erosion is critical to the long-term success of total shoulder replacement (TSR). In order to characterise the 3D morphology of eroded glenoid surfaces, we looked for a set of morphological parameters useful for TSR planning. We defined a scapular coordinates system based on non-eroded bony landmarks. The maximum glenoid version was measured and specified in 3D by its orientation angle. Medialisation was considered relative to the spino-glenoid notch. We analysed regular CT scans of 19 normal (N) and 86 osteoarthritic (OA) scapulae. When the maximum version of OA shoulders was higher than 10°, the orientation was not only posterior, but extended in postero-superior (35%), postero-inferior (6%) and anterior sectors (4%). The medialisation of the glenoid was higher in OA than normal shoulders. The orientation angle of maximum version appeared as a critical parameter to specify the glenoid shape in 3D. It will be very useful in planning the best position for the glenoid in TSR.

Cite this article: Bone Joint J 2014;96-B:513–18.

Wear of polyethylene is associated with aseptic loosening of orthopaedic implants and has been observed in hip and knee prostheses and anatomical implants for the shoulder. The reversed shoulder prostheses have not been assessed as yet. We investigated the volumetric polyethylene wear of the reversed and anatomical Aequalis shoulder prostheses using a mathematical musculoskeletal model. Movement and joint stability were achieved by EMG-controlled activation of the muscles. A non-constant wear factor was considered. Simulated activities of daily living were estimated from in vivo recorded data.

After one year of use, the volumetric wear was 8.4 mm³ for the anatomical prosthesis, but 44.6 mm³ for the reversed version. For the anatomical prosthesis the predictions for contact pressure and wear were consistent with biomechanical and clinical data. The abrasive wear of the polyethylene in reversed prostheses should not be underestimated, and further analysis, both experimental and clinical, is required.

Introduction: Locking plates and screws have been developed to increase stability of internal fixation in osteoporotic bone. The anatomic design should also facilitate the fracture’s reduction in complex cases.

The aim of this study was analyse the results of locking plates used for fractures of the proximal humerus and to look for specific complications.

Method: Forty four patients (mean age 60; 28 males and 16 females) were treated with a locking plate (Philos, Synthes-Sratec Medical, Switzerland) for trauma of the proximal humerus. There were fourteen 2-part (32%), ten 3-part (23%), ten valgus impacted 4-part (23%), 3 classical 4-part (7%) fractures and 7 non-unions (15%). Five patients presented an associated gleno-humeral dislocation. Patients were reviewed clinically and radiologically at a mean follow-up of 21 months (6–42). A particular attention was paid to the occurrence of specific complications.

Results: A deep infection occurred in two patients (4,5%); two others lost the reduction (4,5%), and one broke his plate (2,3%). We observed 9 cases (20,5%) of avascular necrosis. Six patients (13,6%) had an impaction of the fracture with secondary intraarticular protrusion of the locked screws, which induced a secondary glenoid wear. The impaction sometimes occurred even without any evidence of AVN. Protrusion of screws were more frequent in elderly patients or in cases of non-union. Revision surgery (18 operations) was performed in 16 patients (36%) : 9 isolated material removal; 3 revisions for loss of reduction and malposition of the plate; 2 debridement including implantation of a cement spacer with antibiotics; 4 arthroplasties (2 hemi and 2 total shoulder prostheses).

Conclusions: Proximal humerus locking plates and screws, designed to improve stability in osteoporotic bone, may have specific complications. They do not prevent fracture’s impaction, resulting in an intraarticular protrusion of the locked screws, which may induce a severe secondary wear of the glenoid. This phenomenon could be due to the direction of the forces and stresses applied on the humeral head, which is mainly parallel to the screws and not perpendicular to them. Accordingly, patients operated on with proximal humerus locking plates should be regularly controlled. In case of progressive humeral head impaction, the material should be removed before it damages the glenoid.

Introduction. Quantification of daily upper-limb activity is a key determinant in evaluation of shoulder surgery. For a number of shoulder diseases, problem in performing daily activities have been expressed in terms of upper-limb usage and non-usage. Many instruments measure upper-limb movement but do not focus on the differentiations between the use of left or right shoulder. Several methods have been used to measure it using only accelerometers, pressure sensors or video-based analysis. However, there is no standard or widely used objective measure for upper-limb movement. We report here on an objective method to measure the movement of upper-limb and we examined the use of 3D accelerometers and 3D gyroscopes for that purpose.

Methods. We studied 8 subjects with unilateral pathological shoulder (8 rotator cuff disease: 53 years old ± 8) and compared them to 18 control subjects (10 right handed, 8 left handed: 32 years old ± 8, younger than the patient group to be almost sure they don_t have any unrecognized shoulder pathology). The Simple Shoulder Test (SST) and Disabilities of the Arm and Shoulder Score (DASH) questionnaires were completed by each subject.

Two modules with 3 miniature capacitive gyroscopes and 3 miniature accelerometers were fixed by a patch on the dorsal side of the distal humerus, and one module with 3 gyroscopes and 3 accelerometers were fixed on the thorax. The subject wore the system during one day (8 hours), at home or wherever he/she went. We used a technique based on the 3D acceleration and the 3D angular velocities from the modules attached on the humerus.

Results. As expected, we observed that for the stand and sit postures the right side is more used than the left side for a healthy right-handed person(idem on the left side for a healthy left-handed person). Subjects used their dominant upper-limb 18% more than the non-dominant upper-limb. The measurements on patients in daily life have shown that the patient has used more his non affected and non dominant side during daily activity if the dominant side = affected shoulder. If the dominant side ≠ affected shoulder, the difference can be showed only during walking period.

Discussion-Conclusion. The technique developed and used allowed the quantification of the difference between dominant and non dominant side, affected and unaffected upper-limb activity. These results were encouraging for future evaluation of patients with shoulder injuries, before and after surgery. The feasibility and patient acceptability of the method using body fixed sensors for ambulatory evaluation of upper limbs kinematics was shown.

Introduction. Arthritis of the glenohumeral joint is usually associated with erosion and flattening of the articular surfaces. The aim of this study was to evaluate the influence of the articular flattening on the joint reaction forces and the humeral head translations during abduction and rotation.

Method. Analysis was conducted with a 3D finite element model of the shoulder, including the scapula, the humerus and 6 muscles: middle, anterior and posterior deltoid, supraspinatus, subscapularis, and infraspinatus. Both the glenoid and humeral head were eroded to artificially reproduce the flattening of an arthritic joint. Two situations were studied:

1) an intact joint with a radius of curvature of 24mm for the humeral head and 26mm for the glenoid;

Movements of external rotation (0–45°) and abduction (0–150°) were performed by muscles’ activation. Contact forces caused by muscles wrapping on bony surfaces were accounted for. Joints forces, glenohumeral contact point locations and humeral head translations were calculated for the intact and eroded joint.

Results: For the eroded joint, articular forces were up to seven times higher during rotation and five times higher during abduction. For the intact joint, the glenohumeral contact point and humeral head remained centred. On the other hand, for the eroded joint, eccentric contact points with large antero-posterior and supero-inferior humeral head translations were observed. Animated views showed that this fact was clearly related to the rocking-horse effect.

Conclusions: This study showed that flattening of the glenohumeral joint due to osteoarthritis increases dramatically the articular forces and humeral head translations. This phenomenon is by itself responsible for progression of the joint’s erosion and flattening and acts as a vicious cycle. It also partly explains the reduced range of motion observed clinically. Accordingly, to limit the risks of rocking-horse effect after shoulder arthroplasty, the joint’s reconstruction should restore a natural articular radius of curvature, with a centre of rotation in the middle of the humeral head.

Introduction: Despite a multitude of reports detailing the management of infected hips and knees with or without arthroplasty, only little information is available on how to deal with infected shoulders. Besides primary haematogenous infection, the increasing number of surgical procedures (infiltration, arthroscopy, ORIF, total- or hemi arthroplasty) confront the orthopaedic surgeon increasingly with this devastating complication. Our goal is to present our experience with the use of a cement spacer in the treatment of infected shoulder joints.

Material and Methods: Between 1995 and 2005 9 patients were diagnosed with deep shoulder infection. The study includes 5 women and 4 men. The mean age at the time of diagnosis of the infection was 65 years (range, 51–78 years). Only 2 patient had had no prior surgery of the shoulder. 5 patients had an infection of a shoulder arthroplasty and 2 patients had been treated with ORIF for fracture.

All of the patients underwent resection the humeral head or retrieval of the arthroplasty with large debridement followed by implantation of an antibiotic impregnated polymethyl methacrylate spacer. After a mean duration of two months of antibiotics and after normalisation of the CRP a delayed reimplantation of a prosthesis was performed in 6 patients. One patient is awaiting arthroplasty, while two patients are satisfied with the functional result obtained with the spacer and do not want further surgery.

Results: None of the patients developed recurrent infection at an average follow-up time of 36 months. Shoulder function was judged objectively and subjectively to be at least satisfactory in all of the patients.

Conclusions: Staged treatment of infected shoulders using antibiotic impregnated polymethyl methacrylate spacers showed in our small group of patients, good and reproducible results. The individually moulded and fitted spacer filling the joint cavity and restoring the normal anatomy of the shoulder after joint debridement makes secondary procedures much easier. In the cases of exchange prosthetic reconstruction no recurrent infection has been experienced and all of the patients have substantial pain relief and an adequate shoulder function. Based on this experience the authors think that staged treatment and the use of a cement spacer in infected shoulder joints is a valid approach.

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° to 150° 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° 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.

Purpose: The causes of glenoid loosening are multifactorial (implant design, surgical technique, bone properties, soft tissue properties). This biomechanical study was conducted to evaluate the consequences of two clinical problems often encountered in shoulder arthroplasty: subscapular tension and glenoid retroversion.

Material and methods: We developed a 3D model of the shoulder including the rotator cuff. A total prosthesis was implanted by digital modellisation. The humeral prosthesis imitated the adaptable third-generation implants, with a stem and a portion of a metal sphere, were used to achieve anatomic reconstruction of the proximal humerus. The polyethylene glenoid, cemented to bone, had a central stem and a flat base. Two subscapular tension (normal and twice normal) and two glenoid positions (0° and 20° retroversion) were tested. External rotation (0–40°) and internal rotation (0–60°) were simulated. We calculated displacement of the glenohumeral contact point, joint forces and contact pressures, interosseous glenoid stress, and micromovement of the bone-cement-implant interfaces.

Results: Subscapular tension produced increased forces and joint pressures, associated with moderate posterior translation of the glenohumeral contact point. Retroversion induced more marked posterior displacement of the contact point, leading to significantly higher intraosseous glenoid stress and micromovements at the interfaces. The association of subscapular tension and glenoid retroversion produced important concentration of stress forces in the posterior part of the glenoid and increased all the micromovements.

Discussion: Subscapular tension and retroversion of the glenoid implant have significant biomechanical effects which can favour glenoid loosening. Correction of these two parameters must be carefully controlled during shoulder arthroplasty.