[Conventional radiology of osteoporosis and radiographic absorptiometry]

Comparative anatomical measurements of osseous structures in the ovine and human knee

The ovine stifle has been increasingly used as a large animal model for the human knee. Still, comparative anatomical measurements of the knee in sheep and humans are missing. Thus, the purpose of this study was to describe and measure the osseous anatomy of the ovine stifle in comparison to the human knee. Twenty-four stifles of skeletal-mature merino-sheep and 24 human cadaver knees were obtained and distances between selected anatomical structures of the distal femur, the proximal tibia, and the patella were measured digitally and documented. Based on these, intercondylar ratio, tibial aspect ratio, patella aspect ratio and the cortical index were calculated. Regarding epicondylar width, lateral condylar width, medial condylar width and the tibial dimensions, the ovine stifle can be considered as a human knee scaled down by one third. However, sheep have a smaller trochlear width and a narrower femoral intercondylar notch than humans resulting in lower relative values for intercondylar width and intercondylar height. The distal femur's cortical index is the same in both species. In contrast, sheep have a massive bone stock below their tibial plateau and a proximal tibial shaft with remarkably thick cortical bone. The ovine stifle can be regarded as a useful model for the human knee. However, future studies should consider the differences in the femoral intercondylar notch width, the patellofemoral joint's biomechanics and the proximal tibia's cortical bone stock.

Bone quality measured by the radiogrammetric parameter "cortical index" and reoperations after locking plate osteosynthesis in patients sustaining proximal humerus fractures

AIM

To analyse the radiogrammetric parameter "cortical index" (CI) and its predictive value for proximal humerus fractures. Furthermore, to investigate the reoperations and the cause of reoperations after locking plate osteosynthesis of displaced proximal humerus fractures.

PATIENTS AND METHODS

113 consecutive patients (73 women and 40 men) with a median age of 66 years (range 18-100 years) were included in this study. The median follow-up time in our database was 4.7 years (range 45-72 months). For a comparative matched-group analysis of the CI, patients with a fall on the shoulder without fracture were selected. Demographic data and all reoperations were recorded after median 58 months postoperatively. The CI was measured at the proximal humeral diaphysis.

RESULTS

The CI showed to be significant lower in the fracture group (mean 0.28) when compared to the matched group (mean 0.47, p < 0.01). 39% patients underwent a reoperation within 40 months postoperatively. 24% were reoperated within the first 12 months postoperatively, and 15% were reoperated after 12 months or later. The reoperation was independent of bone quality (p = 0.85).

CONCLUSIONS

The risk for reoperation is independent of the CI even though the CI may be a predictor for proximal humerus fracture. Younger patients should be aware that surgical treatment of proximal humerus fractures might be a two-stage surgery. Regular follow-up visits for older patients during the first postoperative year must be assured.

Mechanical behavior of screws in normal and osteoporotic bone

Fracture fixation in severe osteoporotic bone by means of implants that rely on screw anchorage is still a clinical problem. So far, a sufficiently accurate prediction of the holding capacity of screws as a function of local bone morphology has not been obtained. In this study the ultimate pullout loads of screws in the epi-, meta-, and diaphyseal regions of human tibiae were correlated to the cortical thicknesses and cancellous bone mineral densities at the screw axes determined from QCT densitometric data. Stepwise multiple linear regression showed that in regions with cortical thicknesses below 1.5 mm, cancellous density determined the ultimate pullout load (R2 = 0.85, p < 0.001), while in regions with cortices above 1.5 mm, cortical thickness alone significantly influenced the holding capacity of a screw (R2 = 0.90, p < 0.001). The findings of this study provide a basis for a bone morphology-related pre-operative estimation of the holding capacity of screws, which could help to improve their proper application in osteoporotic bone.