96 



H. Wagner 



siAN vessels are recanalized across the fracture line, producing immediately mature 

 lamellar bone In concentric layers. 



This phenomenon led to the opinion, that the reduction of bone fragments in cases 

 of internal fixation is so perfectly possible, that no tissue from the periosteum and 



the endosteum can invade the bone 

 fissure and the healing is maintained by 

 the Haversian vessels alone. 



This explanation is not satisfactory, 

 because we find a primary ossification 

 also in cases of rigid fixation without 

 anatomical reduction. Other factors, 

 mechanical ones, must therefore be re- 

 sponsible for this phenomenon. 



In a further experiment we cut into 

 the femoral shaft of the dog small 

 transverse saw-slots of 60 micron width, 

 without opening the medullary cavity. 

 A number of the slots were closed to 

 the periosteum with a wire-suture (hemi- 

 cerclage), the other ones were left upon 

 (Fig. 3). Twenty-three days later we see 

 a primary ossification and a recanali- 

 zation of the Haversian vessels, with- 

 out any difference between the two 

 groups. 



Now we modified the experiment: 

 we cut the saw-slot deep into the mar- 

 rowcavity until we got a slight move- 

 ment in the slot when bending the bone. 

 We now expected to find, under the 

 influence of discontinuous pressure and 

 traction, a chondro-fibrotic callus for- 



^^ ~*****^Jfl ^___^i.,i — - mation. "We actually found bone re- 



^/^' |ni ^.,.«— »-«*«"i^" sorption and chondrofibrotic callus, as 



^^Hbaas^V-Tfte. - ^m' we expected, but the expermient gave 



us an additional result, which we had 

 not expected namely, at the ends of the 

 slot there appeared also a primary ossi- 

 fication (Fig. 4). 



This finding can be explained by 



the rate of motion in the bone-gap: in 



the centre of the slot, where the amplitude of movement is high, we find bone 



resorption and chondro-fibrotic callus, at the ends of the slot, where the amplitude is 



low, almost zero, there appears a primary ossification. 



These biomechanic relations are of great practical importance in bone surgery: the 

 primary stability of metal implantation is the basic condition for the rigid fixation of 

 bone fragments. The primary instability leads to bone resorption and delayed healing. 



Fig. 3. Transverse saw-scciiDii m the U'ini>r.il sliatt c 

 the dog, without opening the marrow-cavity. After 2 

 days recanalisation of Haversian vessels, without an 

 difference, whether the bone defect was closed by hem 

 cerclage or not 



