Tomographic evaluation of Hill-Sachs lesions: is there a correlation between different methods of measurement?

BACKGROUND: Several methods are currently available to evaluate and quantify the glenoid or humeral bone loss; however, none is universally accepted, particularly in the case of Hill-Sachs (HS) lesions. PURPOSE: To establish whether there is correlation among different methods of measuring HS lesions, and to investigate the correlation between glenoid bone loss and the various HS lesion measurements and to assess the inter-observer reliability of such measurements. MATERIAL AND METHODS: We assessed computed tomography (CT) or arthro-CT scans taken from individuals with recurrent anterior glenohumeral dislocation. The scans were independently assessed by two examiners. The parameters assessed were as follows: HS lesion width and depth on the axial and coronal planes, articular arc loss on the axial plane, and percentage of glenoid bone loss on the sagittal plane. RESULTS: Scans from 50 shoulders were assessed. The percentage of articular arc loss and HS lesion width on the axial plane were the only measurements that exhibited strong correlation (r = 0.83; P < 0.001). The values of the correlation coefficient corresponding to HS lesion depth on the coronal plane were the lowest. Most of the measurements exhibited moderate correlation. The inter-examiner reliability was good relative to all measurements except for HS lesion width and depth on the coronal plane, for which it was moderate. CONCLUSION: The measurements of articular arc loss and HS lesion width on the axial plane exhibited strong correlation. The inter-examiner reliability relative to articular arc loss, HS lesion width and depth on the axial plane, and glenoid bone loss was good.

Number of pegs influence focal stress distributions and micromotion in glenoid implants: a finite element study.

The present study was conducted to compare the stability of four commercially available implants by investigating the focal stress distributions and relative micromotion using finite element analysis. Variations in the numbers of pegs between the implant designs were tested. A load of 750 N was applied at three different glenoid positions (SA: superior-anterior; SP: superior-posterior; C: central) to mimic off-center and central loadings during activities of daily living. Focal stress distributions and relative micromotion were measured using Marc Mentat software. The results demonstrated that by increasing the number of pegs from two to five, the total focal stress volumes exceeding 5 MPa, reflecting the stress critical volume (SCV) as the threshold for occurrence of cement microfractures, decreased from 8.41 to 5.21 % in the SA position and from 9.59 to 6.69 % in the SP position. However, in the C position, this change in peg number increased the SCV from 1.37 to 5.86 %. Meanwhile, micromotion appeared to remain within 19-25 µm irrespective of the number of pegs used. In conclusion, four-peg glenoid implants provide the best configuration because they had lower SCV values compared with lesser-peg implants, preserved more bone stock, and reduced PMMA cement usage compared with five-peg implants.

Bone remodelling around a cementless glenoid component.

Post-operative change in the mechanical loading of bone may trigger its (mechanically induced) adaptation and hamper the mechanical stability of prostheses. This is especially important in cementless components, where the final fixation is achieved by the bone itself. The aim of this study is, first, to gain insight into the bone remodelling process around a cementless glenoid component, and second, to compare the possible bone adaptation when the implant is assumed to be fully bonded (best case scenario) or completely loose (worst case scenario). 3D finite element models of a scapula with and without a cementless glenoid component were created. 3D geometry of the scapula, material properties, and several physiological loading conditions were acquired from or estimated for a specific cadaver. Update of the bone density after implantation was done according to a node-based bone remodelling scheme. Strain energy density for different loading conditions was evaluated, weighted according to their frequencies in activities of daily life and used as a mechanical stimulus for bone adaptation. The average bone density in the glenoid increased after implantation. However, local bone resorption was significant in some regions next to the bone-implant interface, regardless of the interface condition (bonded or loose). The amount of bone resorption was determined by the condition imposed to the interface, being slightly larger when the interface was loose. An ideal screw, e.g. in which material fatigue was not considered, was enough to keep the interface micromotions small and constant during the entire bone adaptation simulation.