BACKGROUND: The optimal degree of conformity between the glenoid and humeral components in total shoulder arthroplasty for best performance and durability is still a matter of debate. The main aim... Show moreBACKGROUND: The optimal degree of conformity between the glenoid and humeral components in total shoulder arthroplasty for best performance and durability is still a matter of debate. The main aim of this study is to evaluate the influence of joint conformity on the bone-implant interface micromotions in a cementless glenoid implant. MATERIALS AND METHODS: Polyethylene inlays with different degrees of conformity (radial mismatch of 0, 2, 4, and 6 mm) were mounted on a cementless metal back and then implanted in a bone substitute. These glenoid components were loaded by a prosthetic humeral head during a force-controlled experiment. Normal-to-interface micromotions and bone substitute deformations were measured at different points of the interface. Rim displacement and humeral head translation were also measured. A finite element (FE) model of the experiments was implemented to estimate the normal- and tangent-to-interface micromotions in the entire bone-implant interface. RESULTS: All measured variables increased with less-conforming PE inlays. Normal-to-interface micromotions were significantly larger (P < .05) when the radial mismatch was 6 mm compared with the fully conforming inlay. The FE model was in agreement and complemented the experimental results. FE model-predicted interface micromotions were already significantly larger when the radial mismatch was equal to 4 mm. DISCUSSION: In a force-controlled experiment with a cementless glenoid component, a non-conforming PE inlay allows larger interface micromotions than a conforming inlay, reaching a magnitude that may hamper local bone ingrowth in this type of component. This is mainly because of the larger humeral head translation that boosts the effects of the so-called rocking-horse phenomenon. Show less
Purpose Segmentation of rheumatoid joints from CT images is a complicated task. The pathological state of the joint results in a non-uniform density of the bone tissue, with holes and... Show morePurpose Segmentation of rheumatoid joints from CT images is a complicated task. The pathological state of the joint results in a non-uniform density of the bone tissue, with holes and irregularities complicating the segmentation process. For the specific case of the shoulder joint, existing segmentation techniques often fail and lead to poor results. This paper describes a novel method for the segmentation of these joints. Methods Given a rough surface model of the shoulder, a loop that encircles the joint is extracted by calculating the minimum curvature of the surface model. The intersection points of this loop with the separate CT-slices are connected by means of a path search algorithm. Inaccurate sections are corrected by iteratively applying a Hough transform to the segmentation result. Results As a qualitative measure we calculated the Dice coefficient and Hausdorff distances of the automatic segmentations and expert manual segmentations of CT-scans of ten severely deteriorated shoulder joints. For the humerus and scapula the median Dice coefficient was 98.9% with an interquartile range (IQR) of 95.8-99.4 and 98.5% (IQR 98.3-99.2%), respectively. The median Hausdorff distances were 3.06 mm (IQR 2.30-4.14) and 3.92 mm (IQR 1.96 5.92 mm), respectively. Conclusion The routine satisfies the criterion of our particular application to accurately segment the shoulder joint in under 2 min. We conclude that combining surface curvature, limited user interaction and iterative refinement via a Hough transform forms a satisfactory approach for the segmentation of severely damaged arthritic shoulder joints. Show less
BACKGROUND: In massive rotator cuff tears a teres major (TMj) tendon transfer to the insertion of the supraspinatus (SSp) reverses its adduction moment arm into abduction which is supposed to be an... Show moreBACKGROUND: In massive rotator cuff tears a teres major (TMj) tendon transfer to the insertion of the supraspinatus (SSp) reverses its adduction moment arm into abduction which is supposed to be an adequate salvage procedure. Analysis of muscle function to find biomechanical ground of such success is scarce. METHODS: We compared pre- and postoperative clinical outcome of TMj transfer, i.e. Range of Motion, pain, Constant Shoulder scores and arm force. TMj activation was evaluated in 14 patients suffering massive cuff tears using activation ratios to describe the desired 'in-phase' and undesired 'out-of-phase' contribution to the external arm moment. Additionally, we analyzed activation of the latissimus dorsi (LD) and the medial part of the deltoids (DE). The activation ratios were compared to controls and TMj activation ratios were related to clinical outcome. FINDINGS: TMj tendon transfer improved arm function. Pre-operatively, we observed 'out-of-phase'abduction activation of TMj and LD. After transfer patients activated TMj according to its new anatomical position. 'Out-of-phase' LD abduction activation persisted. The clinical improvements coincided with changes in activation ratio of TMj. INTERPRETATION: 'Out-of-phase' TMj adductor activation is associated with compromised arm function in patients with irreparable cuff tears. After transfer, TMj is activated in correspondence with its new anatomical function, which was supportive for the improved arm function. Show less
Background: In massive rotator cuff tears a teres major (TMj) tendon transfer to the insertion of the supraspinatus (SSp) reverses its adduction moment arm into abduction which is supposed to be an... Show moreBackground: In massive rotator cuff tears a teres major (TMj) tendon transfer to the insertion of the supraspinatus (SSp) reverses its adduction moment arm into abduction which is supposed to be an adequate salvage procedure. Analysis of muscle function to find biomechanical ground of such success is scarce. Methods: We compared pre- and postoperative clinical outcome of TMj transfer, i.e. Range of Motion, pain, Constant Shoulder scores and arm force. TMj activation was evaluated in 14 patients suffering massive cuff tears using activation ratios to describe the desired 'in-phase' and undesired 'out-of-phase' contribution to the external arm moment. Additionally, we analyzed activation of the latissimus dorsi (LD) and the medial part of the deltoids (DE). The activation ratios were compared to controls and TMj activation ratios were related to clinical outcome. Findings: TMj tendon transfer improved arm function. Pre-operatively, we observed 'out-of-phase' abduction activation of TMj and LD. After transfer patients activated TMj according to its new anatomical position. 'Out-of-phase' LD abduction activation persisted. The clinical improvements coincided with changes in activation ratio of TMj. Interpretation: 'Out-of-phase' TMj adductor activation is associated with compromised arm function in patients with irreparable cuff tears. After transfer, TMj is activated in correspondence with its new anatomical function, which was supportive for the improved arm function. (C) 2009 Elsevier Ltd. All rights reserved. Show less
