CORR Insights®: What Regions of the Distal Clavicle Have the Greatest Bone Mineral Density and Cortical Thickness? A Cadaveric Study

Where Are We Now?

Approximately 200,000 clavicle fractures, representing 2.6% to 5% of all total fractures, are reported each year, with approximately 85% of these fractures occurring in the middle one-third of the clavicle, and 15% to 21% occurring in the distal third [4-8]. Current treatment options for distal-third clavicle fractures include non-surgical management for Neer Type I, III, and IV patterns and operative treatment including superior locked plating or hook plating for Neer Type II and V patterns. Difficulties with non-unions for the Neer Type V pattern remain a concern since these fractures include comminution and the forces across this portion of the clavicle (due to the weight of the arm) make secure fixation difficult.

Recent biomechanical studies have focused on the middle-third of the clavicle and have either concentrated on the external geometry or the intramedullary canal [1, 2]. The findings from these studies can help the clinician, as well as medical device manufacturers, by identifying areas of the clavicle that can withstand higher forces or that may need special attention for their lack of density. This is analogous to the findings of Spross and colleagues [9] for proximal humerus fractures where they found a correlation between increases in bone mineral density and a more stable fracture fixation. In the current study, Chen and colleagues [3] found higher bone mineral densities and cortical thicknesses in the areas of the conoid tubercle and intertubercle space.

Knowing this, medical device companies may want to design fracture plates that have screw trajectories that allow for bi-cortical fixation into these areas without exiting the bone, thus giving the clinician the option to locate screws along these two areas to increase the chances of a stable fixation.

Where Do We Need To Go?

Although the current study concentrated on the distal clavicle [3], questions still remain regarding how the middle and proximal areas of the clavicle differ in densities and cortical thicknesses. Current studies available for bone density of the clavicle are unfortunately limited to either the whole clavicle [7] or relatively large sections of the clavicle [4, 5] and don’t give the detail necessary for better clinical or manufacturer recommendations. In addition to knowing the areas of increased densities and thicknesses, it would be helpful to know how these areas correlate with the forces that the clavicle sees so that manufacturers can develop devices that can better deal with these forces. Another question that arises from this study is how the densities and thicknesses vary with age and sex. Many of the current clavicle fixation devices are designed to cover a large percentage of the population without considering specific variances found in the population.

How Do We Get There?

Future studies should elaborate on the findings of the current study; in particular, I would hope to see more studies in cadavers with larger sample sizes, more diverse ages, and studies that include balanced representation of both sexes. In addition to these descriptive studies, biomechanical studies should be performed that include both mechanical and computational models. Although these types of studies are resource intensive, biomechanical studies can be performed to validate the finite element models, which can in turn be used to test different fixation techniques and implant geometries. The biomechanical studies should replicate the physiologic loading pattern of the clavicle since many of the current studies test clavicles in three or four-point bending and torsionally along the axis of the clavicle which may or may not be relevant to how the clavicle is loaded.