Session I - Upper Extremity

Fractures of the Olecranon: A Biomechanical Study of the Joint Stresses Comparing Two Methods of Treatment

David E. Ede, MD; Berton R. Moed, MD; Thomas D. Brown, PhD,Wayne State University, Detroit, MI

Purpose: To evaluate the effect of two types of olecranon fracture treatment, open reduction and internal fixation (ORIF) and fragment excision, on humero-ulnar joint stress.

Methods: Eight matched pairs of fresh frozen cadaveric upper extremities were thawed and then stripped of skin, muscular and neurovascular tissue. The lateral collateral ligament was sectioned to provide access to the elbow joint surfaces. The medial joint structures were left intact. The proximal aspect of the humeri were potted in PVC tubing using polymethylmethacrylate. The elbows were then placed in a testing jig after the method of Fyfe et al.¹ with the triceps tendon secured to the jig to maintain 90^o of elbow flexion. The intraarticular pressures were measured using a pressure-sensitive film (Pressensor, Inteque Resources Co., Fort Lee, New Jersey) after application of a 0.15-kg/cm extension torque (0.835 kg at 18cm). Pretreatment normal peak pressures were recorded. Pressensor has been previously used within the elbow joint in the attempt to define the contact area of the humero-ulnar joint. However, it was found to be unsatisfactory due to the inability to have it conform to the contour of the joint surfaces. Therefore, different geometric designs for application of the Pressensor were first evaluated. This led to the development of a polygonal design which was protected from the joint by packaging them in a polyurethane film coated with a glue spray. Colormetric analysis was performed using the scale provided by the manufacturer. Peak pressures were determined (measured as kgf/cm²) for the medial and lateral surfaces of both the proximal and distal facets. This method was used for all subsequent pressure samples.

A 50 percent olecranon osteotomy was then performed simulating a fracture, and each pair of elbows was randomized into two treatment groups: ORIF (using a tension-band wiring technique) and fragment excision. Joint pressures were remeasured. A two-tailed paired t-test was used for statistical analysis.

Results: Evaluation of the pretreatment normals revealed that the peak pressures were fairly evenly distributed between the proximal and distal olecranon facets. Following osteotomy, it was found that, overall, the peak pressures were higher in the excision group. Comparing the posttreatment, experimental group to its pretreatment (normal) counterpart for pressures in the distal medial and distal lateral facets, it was found that the peak pressures were significantly higher for the fragment excision group (p=0.005 and p=0.0008, respectively), but were not significantly different in the ORIF group (p=0.55 and p=0.15, respectively). For the proximal medial and proximal lateral facets in the ORIF group, again, there was no difference (p=0.42 and p=0.83, respectively). In the fragment excision group, no comparison could be made because these facets had been removed by the excision. However, there was load sharing noted between the triceps tendon and the humeral articulation which showed no statistical difference from the pretreatment normals (p=0.20 and p=0.57).

Discussion & Conclusion: Displaced fractures of the olecranon are usually treated by ORIF with fragment excision reserved as a salvage procedure. However, attention has recently been focused on excision as a primary form of treatment due to reported claims of comparable clinical results as well as studies noting significant complications, such as infection, loss of fixation and painful hardware, associated with ORIF. Based on the findings of this study, ORIF restores the normal biomechanics of the elbow joint, while fragment excision abnormally elevates the joint stresses. These elevated joint stresses may, over time, contribute to the development of elbow pain and osteoarthrosis. Therefore, ORIF should continue to be the regarded as the treatment of choice for displaced fractures of the olecranon.

1. Fyfe IS, Mossad MM, Holdsworth BJ: Methods of fixation of olecranon fractures: An experimental mechanical study. JBJS, 67B:367-372, 1985.