gms | German Medical Science

Objectives: Absolute stability for primary fracture healing requires interfragmentary compression. In daily practice, compression pressure distribution or force are not measured [1]. Brink et al. 2013 showed that compressive forces were not sufficiently achieved in transverse olecranon fractures fixated by tension band wiring [2]. Wähnert et al. 2013 proved strong effects of relaxation of interfragmentary compression within the first hours in a low-density artificial (osteoporotic) bone model and suggest augmentation to attenuate this effect [3]. We hypothesize that compression can be controlled using different standard compression techniques such as a compression plate or an interfragmentary lag screw. Furthermore, we hypothesize that loss of interfragmentary compression through relaxation within one hour can be attenuated by auxiliary fixation such as a neutralization plate.

Methods: Ovine femora and humeri (total N=12, 6 each) were equally separated into two groups: First group (1) received a 45 degree oblique osteotomy at mid-diaphysis and was fixated using a 3.5mm lag screw and a locking compression plate (3.5mm LCP, DePuy Synthes) as neutralization plate. Second group (2) received a transverse osteotomy and was fixated using a compression plate (LCP) with eccentric placement of first 2 screws (of 6 cortical screws, (Figure 1 [Fig. 1])). Interfragmentary pressure was recorded using a Tekscan 5033 sensor.

Results and conclusion: Initial median interfragmentary compression forces in group 1 (25%/75% quartile) were 57 N (52 N/104 N), and in group 2 median forces were 37 N (23 N/ 61 N), p>0.05 (Mann-Whitney U-test). Median loss of compression over time were 3.1% in group 1 and 1.1% in group 2 within one hour (Figure 1 [Fig. 1]), p>0.05). A long term measurement of more than 12 hours of an exemplary sample from group 1 resulted in a force reduction of 5.9%.

Different individual compression levels were achieved, not significantly influenced by the method of fixation. With a lag screw, we could not monitor the whole area between the fragments, thus the resulting compression forces might even be higher in group 1 than reported. Relaxation of compression was minimal in our set-up with stiff ovine bones. However, we could confirm that lag screws placed outside of the plate before further screws (locking or non-locking) for fracture fixation may help to maintain interfragmentary compression [4] with low variation of compression force in sufficient bone quality, although additional functional loads remain to be added.