Material properties of trabecular bone structures

Abstract

The transplantation of human allograft for restoration and filling of cortical bone defects is well known. Our aim was an experimental investigation of the mechanical stability of the often used femoral head spongiosa depending on the caliber and extent of the allograft. To evaluate the orientation of the trabecular structures of the femoral head and relate this data to its mechanical properties, morphometric studies were combined with mechanical tests of cancellous bone specimens. The mechanical examination of the allograft was done following the compression test according to DIN 50106. We examined 36 human unfixed hip joint spongiosa cylinders with a height of 11 mm and a diameter of 24 mm. We took three specimens from each femoral head. We compressed the allograft at a constant velocity of 0.017 mm/sec. We calculated the maximum compression strength, the yield point and the Young's modulus. We also examined 12 parallelepipedic specimens with (17 x 17 x 51 mm) for morphometric analysis and loading in the direction of the primary compressive group (PCG), as well as perpendicular loading and at an angle of 45 degrees. We found divergent mechanical stabilities. None of the femoral heads showed comparable compressive strength. There was no position dependency of the strength of the samples. No relation between optical appearance and strength was found. We found a value for the lower compressive strength, which can be used for calculation as a basic value for safe constructions. Furthermore we tested the well known dependence of strength on the direction of the trabecular structure. We found a strong relationship between strength and load direction on the preferred direction of the trabecular structure. The sole recommendation resulting from our investigations is to rely on the lowest compressive strength for all preoperative planning. Relying on higher compressive strength by using the theoretical predicted areas of higher strength is hazardous since we found no correlation between position of sampling and strength. The size of our samples is important, because of the fact that different sizes of the samples might cause different failure mechanisms in the samples. The preparation of the femoral head spongiosa should be done according to the primary compressive group of the trabecular structure.

Mechanical testing of cancellous bone from the femoral head: Experimental errors due to off-axis measurements

“…The results found in the present study are in disagreement with those reported by Birnbaum et al (2001). This disagreement could be explained by the fact that in their study the specimens were tested along an axis set considering the local anatomy of the proximal femur.…”

“…There is only one experimental study (Birnbaum et al, 2001) that can be compared with the present one. The results found in the present study are in disagreement with those reported by Birnbaum et al (2001).…”

“…This disagreement could be explained by the fact that in their study the specimens were tested along an axis set considering the local anatomy of the proximal femur. At a later check Birnbaum et al (2001) found that this axis did not correspond to the MTD, which is used in this study to set the testing direction. Additionally, the experimental procedure and specimen size used were different.…”

“…To the authors' knowledge, only one experimental study (Birnbaum et al, 2001) has been done to evaluate the effect of testing cancellous bone off-axis. Birnbaum et al (2001) found no significant difference between the maximum compressive strength, when testing the cancellous bone of the femoral head extracted along the postulated primary compressive group, which was identified on the basis of the local anatomy of the femur, and at an off-axis angle of 451. There is thus a disagreement between theoretical predictions and experimental results about the importance of testing cancellous bone in the MTD.…”

Function-Orientated Structural Analysis of the Proximal Human Femur

“…In this study, a completely different approach to inferring a force distribution pattern on the human proximal femur has been applied: since the internal trabecular system of bone tissue aligns with the principal stresses, a widely accepted concept [Pauwels, 1954;Rydell, 1973;Osborne et al, 1980;Fyhrie and Carter, 1986;Kerr et al, 1986;Biewener et al, 1996;Cody et al, 1996;Smit et al, 1997;Turner et al, 1997;Uchiyama et al, 1999;Birnbaum et al, 2001;Gomberg et al, 2003;Ruimerman et al, 2003;Kinney et al, 2005], analysis of this internal bone structure may help to clarify the direction of forces acting on bone tissue. In this way, bone itself can serve as a record of its biomechanical history [Carter et al, 1989] and can provide a basis to examine which of the two biomechanical models in question reflects the physiologic situation most appropriately.…”