Effects of clustered drill holes on the breaking strength of the equine third metacarpal bone.

This research studied the influence of clustered drill holes on the breaking strength of horse third metacarpal bones (found in the leg of the horse), discovering that the drilled holes acted as stress concentrators and reduced the stress required to break the bone.

Objective and Methodology

• The research aimed to understand the effects of clustered drill holes on the breaking strength of equine third metacarpal bones, typically known as the cannon bone in horses. Breaking strength denotes the amount of stress that can be endured before the failure of a material – in this case, the horse’s metacarpal bone.
• Researchers conducted in-vitro tests on these bones sourced from 39 horses ranging from 2 to 7 years old.
• The tests utilized a palmarodorsal 3-point bending technique. This method is a specific type of structural testing where a load is applied at a central point between two support points.

Treatment and Control Groups

• Four types of treatments were examined. Two sets of drill hole sizes (2.7mm and 3.5mm) were tested in clusters of either a 4-hole or 7-hole pattern.
• These clusters were made in the dorsal cortex (the outer side) of the distal diaphysis (the portion between the end and center of a long bone) of the left third metacarpal bone of the horses.
• As a control group, right third metacarpi (bones of the horse’s leg) were left undrilled.

Findings

• The research concluded that the drilled holes acted as stress concentrators. Stress concentration refers to a location in a material (or bone, in this case) experiencing a significantly higher rate of stress compared to its surroundings.
• As a result of this stress concentration, the bones with drilled holes needed less stress to fail or break, which significantly (P less than 0.05) decreased the breaking strength of the bones. Here, ‘P’ refers to the p-value, a statistical measure used to determine if the observed results are statistically significant. A P value of less than 0.05 is usually considered significant.
• Despite this, the differences in breaking strength among the different treatment groups were not statistically important. This means that the size and pattern of the drilled hole clusters did not significantly affect the breaking strength of the bones.