A Closer Look At Lateral Talar Process Fractures With Snowboarding Injuries
- Volume 22 - Issue 2 - February 2009
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In relation to this study, further research examined the effect of excision of a 1 cm3 fragment from the LTP to the ankle and subtalar joints9 The results indicated that there was no instability at the ankle or at the subtalar joint upon removal of the fragment after comparing non-stressed and stressed measurements.
Examining Possible Etiologies Of LTP Fractures
What exactly is the mechanism of LTP injuries? Many years of study have gone into identifying and determining appropriate ways of treating what was initially a very rare occurrence until the introduction of snowboarding.1,10
Historically, Hawkins described the mechanism of injury as dorsiflexion of the ankle associated with inversion.11 Reinforcing this statement, Huson described the posterior talar and calcaneal facets as congruous in stance. 12
However, upon inversion of the STJ, the talus rotates or shifts laterally with the posterior aspect of the lateral process of the talus abutting against the posterior articular process of the calcaneus. A dorsiflexory force initiated at this incongruous position would ultimately cause a fracture of the lateral process.
This is distinct from what researchers earlier thought of as an avulsion fracture caused by the tension on the lateral talocalcaneal ligament. Hawkins indicated that anatomical dissections have proven that the lateral talocalcaneal ligament is nothing more than a thickening of the lateral aspect of the STJ capsule, and an LTP fracture is not associated with STJ dislocation with rupture of this ligament.11 With this concept and theory, recent literature has expanded the understanding of a true LTP fracture and the mechanism of injury.
In 2001, Boon, et al., recognized that axial loads on a dorsiflexed position of the ankle while being inverted may be a cause of the injury. 13 However, they continued to hypothesize that there may be an external rotational component. Due to the high number of nonunions and malunions with inadequately treated LTP injuries, researchers thought that “the rotatory and hinge movements of the talocrural and STJ are at a higher risk for avascular necrosis.” 13
They obtained 10 fresh cadaveric ankles with an average age of 79 years. Researchers induced lateral talar process fractures under specific loading conditions. They placed four out of 10 specimens in 20 degrees of dorsiflexion and 10 degrees of inversion with axial loading only. There were no LTP fractures induced in this group. The group that experienced lateral rotation (external) of 20 degrees sustained LTP fractures.
The minimum load was 2200 N while the maximum load was 8900 N. Researchers thought the variation in loading forces was due to the conditions of the specimens themselves.
Do The Boots Contribute To These Injuries?
With these results, Boon, et al., noted that it is unclear whether boot design has an effect on injury outcomes.13
With this in mind, researchers assessed three types of boots. Kirkpatrick, et al., indicated that 77.3 percent of snowboarders used soft boots, 8.5 percent of patients used hybrid boots and 14.1 percent used hard boots. 1 Soft boot wearing was more predictive of soft tissue ankle sprains and non-talar fractures as opposed to hard boots. They found that hybrid boots stabilize against ankle sprains better than soft boots and also significantly reduce the number of LTP fractures. According to Kirkpatrick and colleagues, there was a significant increase in the presence of LTP fractures with the use of hard boots.1
However, Boon, et al., theorizes that given the fixed position of the foot when it is placed in a hard boot, it would be unlikely that the hindfoot would be subjected to inversion and dorsiflexion in the first place.13 Therefore, they suggested an alternate mechanism of the injury to the LTP: external rotation with dorsiflexion and inversion.