L. De Wilde

One-stage revision for patients with a chronically infected reverse total shoulder replacement

We retrospectively reviewed 11 consecutive patients with an infected reverse shoulder prosthesis. Patients were assessed clinically and radiologically, and standard laboratory tests were carried out. Peroperative samples showed Propionbacterium acnes in seven, coagulase-negative Staphylococcus in five, methicillin-resistant staphylococcus aureus in one and Escherichia coli in one. Two multibacterial and nine monobacterial infections were seen. Post-operatively, patients were treated with intravenous cefazolin for at least three days and in all antibiotic therapy was given for at least three months. Severe pain (3 of 11) or severe limitation of function (3 of 11) are not necessarily seen. A fistula was present in eight, but function was not affected. All but one patient were considered free of infection after one-stage revision at a median follow-up of 24 months, and without antibiotic treatment for a minimum of six months. One patient had a persistent infection despite a second staged revision, but is now free of infection with a spacer. Complications included posterior dislocation in one, haematoma in one and a clavicular fracture in one. At the most recent follow-up the median post-operative Constant-Murley score was 55, 6% adjusted for age, gender and dominance. A one-stage revision arthroplasty reduces the cost and duration of treatment. It is reliable in eradicating infection and good functional outcomes can be achieved.

Consequences of deltoid muscle elongation on deltoid muscle performance: a computerised study

BACKGROUND The deltoid muscle plays an important role in normal shoulder function. Knowledge of the position of the glenohumeral rotational centre and of the deltoid muscle length is essential to understand optimal placement of a total shoulder prosthesis. OBJECTIVE This study is designed to analyse the effect of deltoid muscle elongation on shoulder joint function. DESIGN A three-dimensional model of the glenohumeral joint with deltoid muscle analysis in the scapular plane. METHODS A geometrical three-dimensional ball-and-socket model of the shoulder joint was developed. From dry bones, the position of the origins and insertions of the three parts of the deltoid muscle relative to the calculated centre of rotation of the humeral head was defined. The position and the direction of the muscle force working lines relative to this humeral centre were calculated using former measurements and CT-data of the deltoid. Muscle length-tension data were applied to obtain angle-force relationships. The model was used to calculate the angle-force relationships, the moment arm and the moment of the deltoid muscle components for successive arm elevation angles in the scapular plane. These data were compared to those of a theoretical situation assuming a 10% elongation of the muscle. RESULTS Muscle angle-force curves show a more favourable slope after moderate (10%) deltoid muscle elongation. Elongating the muscle by changing the distance between the humeral rotation point and the deltoid insertion along the humeral axis does not affect moment arms. The moments of the deltoid muscle forces themselves, however, seem more adapted to elevation in the scapular plane. The deltoid maximal moment exceeds the arm-weight moment by about 40% instead of being approximately equal, and that the maximum is situated around 100 degrees of elevation. CONCLUSIONS From a biomechanical point of view, stretching the deltoid muscle by 10% seems to result in a significantly more favourable position in case of shoulder elevation at 90 degrees of abduction in the scapular plane in a centred glenohumeral joint. RELEVANCE This model suggests that a 10% elongation of the deltoid muscle, the most important shoulder abductor, improves its ability to elevate the arm. If properly implemented, this observation can be very important in the treatment and early rehabilitation of rotator-cuff-insufficient shoulders treated by a specific total shoulder replacement design.

Parameters influencing glenoid loosening

ABSTRACT Introduction: There is a lack of organization in existing studies on the outcome and complications of total shoulder arthroplasty. As a result, it is difficult to gain substantial evidence regarding the rate and risk factors for the occurrence of glenoid loosening which remains the most common cause of prosthetic failure. To improve the quality of future studies, an agreement should exist on definitions of glenoid loosening and on the potential risk factors. Areas covered: Reviewing the literature, loosening can be defined as the appearance of radiolucent lines, radiological loosening, clinical loosening and revision as the end stage. Three different categories of influencing parameters can be distinguished: implant related, patient related and surgeon related. Expert commentary: The aim of this review is to organize the available knowledge on glenoid failure, as well as to describe the gaps so that it will constructively contribute to the debate on how to prevent glenoid failure in the anatomic total shoulder arthroplasty.

Improving the surface properties of an UHMWPE shoulder implant with an atmospheric pressure plasma jet

Insufficient glenoid fixation is one of the main reasons for failure in total shoulder arthroplasty. This is predominantly caused by the inert nature of the ultra-high molecular weight polyethylene (UHMWPE) used in the glenoid component of the implant, which makes it difficult to adhesively bind to bone cement or bone. Previous studies have shown that this adhesion can be ameliorated by changing the surface chemistry using plasma technology. An atmospheric pressure plasma jet is used to treat UHMWPE substrates and to modify their surface chemistry. The modifications are investigated using several surface analysis techniques. The adhesion with bone cement is assessed using pull-out tests while osteoblast adhesion and proliferation is also tested making use of several cell viability assays. Additionally, the treated samples are put in simulated body fluid and the resulting calcium phosphate (CaP) deposition is evaluated as a measure of the in vitro bioactivity of the samples. The results show that the plasma modifications result in incorporation of oxygen in the surface, which leads to a significant improved adhesion to bone cement, an enhanced osteoblast proliferation and a more pronounced CaP deposition. The plasma-treated surfaces are therefore promising to act as a shoulder implant.

Defining the shortest path in wrapping algorithms for musculoskeletal modeling

In musculoskeletal modeling, many muscles cannot be represented as straight lines from origin to insertion because the bony and musculotendinous morphology of neighboring structures causes them to wrap. Most of these passive structures can adequately be described as simple geometric shapes like spheres and cylinders. A technique for describing smooth muscle paths around multiple obstacles has been developed for modeling use. Until now obstacle-set methods have combined the path of single structures. This does not analytically define the shortest path around multiple objects (Charlton and Johnson, 2001). In this study a method is presented to select the shortest muscle path between origin and insertion from all possible smooth paths between these two points. As an example for multiple obstacle wrapping the deltoid muscle was chosen.

The history of shoulder arthroplasty

Abstract: Shoulder arthroplasty is currently an established treatment for any type of osteoarthritis. It can provide reliable pain relief and, if biomechanical and anatomical considerations are taken into account pre- and postoperatively, it can provide an improved to almost normal function of the shoulder. These results last on the longer term and provide a relevan improvement of the quality of life. Depending on the indication an anatomical or a reverse polarity shoulder arthroplasty can be indicated. In general, the anatomical prosthesis needs a normal rotator cuff function whereas the reversed prosthesis only needs a well-functioning deltoid. This chapter discusses the biomechanical specificities and indications of each type of shoulder prosthesis.

Estimating muscle fibre paths: a new method

The prevalence of omarthrosis, possible necessitating joint replacement, varies from 2.5% at the age of 50 years up to more than 10% at the age of 80 years. Due to individual variations in shoulder anatomy, the outcome of such surgery is often difficult to predict. To date optimum prosthetic configuration and technique are not yet defined. Moreover it is known that even small differences in operative prosthetic positioning importantly affect the final functionality (de Leest et al. 1996). As biomechanical models become more commonly used in pre operative planning there is a need to include detailed morphometric information including muscle pennation angles and 3 dimensional fibre paths accurately. To accomplish this some methods have been developed in the past, but these methods only captured a number of discrete points along the muscle fibre (Kaptein and van der Helm 2004). We propose a new technique that allows obtaining accurately origins, insertions and full paths of the muscle fibres. This information is to be used in conjunction with detailed 3D reconstructions of all bones involved in shoulder movement to create individualized shoulder models.

Motion capturing devices for assessment of upper limb kinematics: a comparative study

The influence of biomechanical research on orthopaedic practice has expanded in the last few years. Unlike the biomechanics of the lower limb, little is known yet about the biomechanics of the glenohumeral joint. Upper extremity kinematics can give insight into function after shoulder arthroplasty. Data on ranges of motion related to the performance of a selection of activities of daily living can aid the clinician in evaluating the outcome of the shoulder and elbow arthroplasties. For the assessment of complex movement of the glenohumeral joint, a 3D motion-capturing device is required. Several different types of devices are available; the most commonly used are optical systems. Alternative devices include electromagnetic systems, ultrasound systems, electrogoniometers. This study compares three different systems for assessment of upper limb kinematics.

Biomechanics in cuff tear arthropathy

In rotator cuff deficiency, shoulder function often is impaired, ranging from weakness to frank pseudoparalysis. The progression to cuff-tear arthropathy can be followed radiographically through stepwise progression of characteristic changes. (Hamada et al. 1990) Typical radiographic findings include: a reduction of the acromiohumeral distance, acromial and humeral head erosion, spur formation, periarticular osteopenia, joint narrowing and medialization of the humeral head. Because joint function, moment arms, muscle lengths and wrapping angles depend on the position of muscle insertions and origins relative to the joint centre, both humeral head ascension and medialization determine the function of the diseased shoulder and are therefore useful for a biomechanical classification purpose and for surgical decision making. We investigated to what extent humeral head ascension and medialization contribute to the clinically observed functional loss in cuff tear arthropathy and how they influence mechanics when both are present.