Biomechanical in-vitro study to evaluate different osteosynthesis methods in comminuted intraarticular olecranon fractures

Status:

completed 01/2012

Aims:

Fractures of the olecranon are common injuries to the elbow joint. This in-vitro biomechanical study aimed to evaluate a modified one-third tubular hook plate osteosynthesis in comparison to tension band wiring and anatomically preformed plate osteosynthesis in multifragmentary olecranon fractures.

Activities/Methods:

Bone mineral density (BMD) of 32 fresh-frozen human proximal ulna specimens were measured by pQCT and three groups consisting of ten specimens with comparable BMD’s were formed. A Schatzker type D olecranon fracture was simulated by osteotomies and fixation were performed by the use of tension band wiring, hook plate osteosynthesis and anatomical preformed, optional angular-stable plate osteosynthesis. Biomechanical testing under static and dynamic loading conditions with infrared motion tracking has been carried out.

Additionally, biomechanical behavior of human specimens and artificial bones (synbone and sawbone) has been compared.

Results:

Radiology: Measuring bone mineral density (BMD) at the olecranon, no correlation between specimens’ age and BMD was detectable. Male specimens presented significant higher BMD values compared with female ones (p=0.025). There was no significant difference between left and right bones.

Biomechanics I: No significant differences for stiffness (p=0.141) and settling in loaded and unloaded conditions(p=0.400, p=0.166) were found comparing tension band wiring (TBW), hook-plate osteosynthesis and LCP hook-plate osteosynthesis in simulated 30° elbow flexion. Similar results were found for 90° flexion (stiffness p=0.281, settling loaded p=0.278 and unloaded p=0.171). One specimen in the TBW and one in the hook plate group presented settling more than 2mm in loaded conditions in 30° elbow flexion and were rated as failed. This observation was not significant (p=0.58). In unloaded conditions, two specimens of the hook plate group presented with settling more than 2mm these findings were insignificant as well (p=0.11).

Biomechanics II: In 30° flexion human specimens had significant lower stiffness values than Synbone (p=0.021) and Sawbone (p=0.000) specimens. Settling in loaded and unloaded conditions was significant greater in human bone than in Synbone (p=0.001, p=0.002) and Sawbone (p=0.019, p=0.000). Comparing Synbones and Sawbones, no significant differences were found. One human specimen failed due to settling more than 2mm in loaded and two in unloaded conditions. These findings were also insignificant. In 90° flexion human specimens also had significant lower stiffness values than Synbone (p=0.024) and Sawbone (p=0.013) specimens. Settling in loaded as well as unloaded conditions was significant greater in human bones compared with Synbone (p=0.001, p=0.000) and Sawbones (p=0.004, p=0.004). Comparing Synbones and Sawbones, no significant differences were found.

Discussion and conclusion: With regard to BMD measurement we found a wide range of BMD values in the evaluated specimens. In order to avoid influenced biomechanical results due to BMD heterogeneous groups, future studies should consider BMD measurement for group consistency. Also in clinical studies comparable groups considering sex distribution are mandatory as we found significant differences between male and female individuals. In the part biomechanics I we found comparable biomechanical behavior between TBW, hook-plate and LCP hook-plate osteosynthesis in simulated comminuted olecranon fractures. Under clinical considerations the hook-plate has the edge over TBW considering the eliminated risk for wire migration and skin perforation and over LCP hook-plate osteosynthesis with respect to implant costs. Prospective clinical trials are needed to proof the lower incidence of complications when using the one-third tubular hook-plate technique. Comparing human and artificial bones, we found significant differences in all evaluated parameters. Thereby we were able to proof that studies performed with different specimens are limited comparable, at best. Whether fresh frozen human or artificial bones simulate in-vivo conditions best is unknown. Based on our biomechanical results, availability and ethical aspects human as well as artificial bone have pros and cons.

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