Introduction: Shoulder arthroplasty in rheumatoid patients gives satisfactory pain relief and some recovery of motion. Long term complications are however frequent, such as loosening of the glenoid and rotatorcuff insufficiency. Proximal migration (PM) might be related to both these conditions, and is assumed to lead to deterioration in function and recurrence of pain.

Goal: Aim of this study was to evaluate the occurrence and identify risk factors for proximal migration after shoulder arthroplasty in a rheumatoid population.

Methods and patients: Data of 102 patients (FU 5.8 yrs) treated with a shoulder arthroplasty for rheumatoid gleno-humeral disease was analysed. Requirements were at least 3 years of follow–up and 3 follow-up moments. At each visit clinical scores and standardised radiographs were performed prospectively. Rotator-cuff status was scored per-operatively. For quantification of PM a validated measurement technique - The Spina Humeral centre method- was used. A significant decrease of the subacromial space was defined as more than two times the standard deviation of the measurement accuracy (3.65 mm).

Results: In 25 of 77 cases PM was present. PM commenced in two separate patterns, determined by the time-frame that passed before PM commenced. Early PM started directly during postoperative rehabilitation within the first two postoperative years, late PM after two years. This allowed group formation according to migration pattern; patients with no PM (PMnone), patients with late PM (PMlate) and those with early PM (PMearly). Age was higher in the PMearly group. Rotator cuff tears were more frequent and more severe in the PM groups. The ROM improved postoperatively in the PMnone and PMlate group, with deterioration of the latter in time. The HSS clinical outcome score improved in all groups.

Quality of rotator cuff repair did not alter PM outcome. PM did not occur more frequently in hemi-artho-plasty compared to total shoulder arthroplasty. A more upward oriented glenoid was observed in the PMearly and PMlate groups.

A changed kinematic elbow axis can cause early loosening of elbow endoprostheses and can decrease the functional outcome. Therefore, these prostheses and their alignment tools are designed to reconstruct normal joint kinematics. We investigated whether it is possible to reconstruct the pre-operative kinematic axis of the elbow when an iBP^™ elbow endoprosthesis (Biomet) has been placed.

The calibrated Flock of Birds® electromagnetic tracking device registered controlled passive elbow flexion of ten embalmed upper extremities. The pre-operative kinematic elbow axes were established using helical axes.

Results were expressed in the humeral coordinate system defined by the glenohumeral joint rotation centre and the lateral and medial epicondyle of the humerus. The glenohumeral joint rotation centre was determined using a regression method. The senior author implanted the iBP^™ elbow endoprosthesis using standard instrumentation for humeral component alignment. The post-operative kinematic axes were then calculated. A Student’s t-test was performed to compare the pre- and post-operative axes.

No significant differences were found in the direction of the kinematic elbow axes before and after surgery, indicating no alteration in the valgus/varus angle or change in longitudinal rotation of the ulna with respect to the humerus. However, the axis was located significantly more distal (mean difference 7.0 mm, p = 0.004) after surgery. The ventral-dorsal location of the kinematic axis was not significantly different (p = 0.748) after surgery, but there was some variation in individual axes. The iBP^™ Elbow System enables the reconstruction of the direction of the pre-operative kinematic elbow axis. While the exact position of the pre-operative axis could not be reproduced in vitro, the kinematic axis of the elbow is expected to be less distal in vivo as a result of the extensive destruction of the rheumatoid elbow. Individually adjustable alignment tools might enable more precise reconstruction.

The incidence of loosening of a cemented glenoid component in total shoulder arthroplasty, detected by means of radiolucent lines or positional shift of the component on true antero-posterior radiographs, has been reported to be between 0% to 44%. These numbers depend on the criteria used for loosening and on the length of follow-up. Radiolucent lines are however difficult to detect and to interpret, because of the mobility of the shoulder girdle and the obliquity of the glenoid, which hinder standardisation of radiographs. After review of radiolucencies around cemented glenoid components with a mean follow-up of 5. 3 years in 48 patients we found progressive changes to be present predominantly at the inferior pole of the component. This may hold a clue for the mechanism behind loosening of this implant. Since loosening is generally defined as a complete radiolucent line around the glenoid component and is difficult to assess as a result of the oblique orientation of the glenoid, an underestimation of the loosening rate using radiological data was suspected. Therefore a pilot study using Roentgen Stereophotogrammatric Analysis (RSA) was performed.

In five patients an additional analysis of glenoid component loosening using digital Roentgen Stereophotogrammetric Analysis (RSA) was performed. The relative motion of the glenoid component with respect to the scapula was assessed and the length of this translation vector was used to represent migration. Loosening was defined as a migration of the component, exceeding the pessimistic estimate of the accuracy of RSA 0. 3 mm for this study. After three years of follow-up, three out of five glenoid components had loosened (1. 2 – 5. 5 mm migration). In only one patient with a gross loosened glenoid, the radiological signs were consistent with the RSA findings. It was concluded that when traditional radiographs are used for assessment of early loosening, the loosening rate is underestimated. We recommend that RSA be used for this.

The radiographs of sixty-four patients with seventy humeral head replacements were reviewed for signs of stress shielding. Forty-nine were implanted for rheumatoid arthritis, twenty-one for osteoarthritis. The radiographic follow-up averaged 5. 3 years. Measurements of cortex thickness were performed in four regions along the stem of the implant and the differences between the post-operative radiograph and radiograph at follow-up were calculated. The size of the stem in relation to the diameter of the humerus was calculated using validated measures, resulting in the relative stem size.

A reduction of 1.6 millimeters or more was considered to be a significant reduction, because this lay outside of the calculated 95% normal range for the group as a whole. In six patients (9%) a significant reduction, in cortical thickness was observed in the proximal lateral region of the humeral stem. Five of these had rheumatoid arthritis and one osteoarthritis. In the stress shielding group the relative stem size was found to be significantly higher (p=0. 013) than in the non-stress shielding group (0. 58 versus 0. 48). Osteoporosis, especially present in rheumatoid arthritis, could well be a risk factor. It was concluded that stress shielding is a long-term complication of shoulder arthroplasty and that the relative stem size is an important factor in its genesis. These resorptive processes may lead to a higher risk of failure of the implant and gives an increased risk for mid-stem fractures, due to cantilever loading. It is also desirable to preserve the proximal bone stock, considering the difficulties that arise when, for whatever reason, revision of the implant is necessary.

The incidence of loosening of a cemented glenoid componentin total shoulder arthroplasty, detected by means of radiolucent lines or positional shift of the component on true anteroposterior radiographs, has been reported to be between 0% and 44%. Radiolucent lines are, however, difficult to detect and to interpret because of the mobility of the shoulder girdle and the obliquity of the glenoid which hinder standardisation of radiographs. We examined radiolucencies around cemented glenoid components in 48 patients, with a mean follow-up of 5.3 years, and found progressive changes to be present predominantly at the inferior pole of the component. This may hold a clue for the mechanism of loosening of this implant.

In five patients we performed an additional analysis of loosening of the glenoid component using digital roentgen stereophotogrammetric analysis (RSA). After three years, three of the five implants had loosened (migration 1.2 to 5.5 mm). In only one, with gross loosening, were the radiological signs consistent with the RSA findings.

When traditional radiographs are used for assessment, the rate of early loosening is underestimated. We recommend that RSA be used for this.