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What is the relevance of the tip-apex distance as a predictor of lag screw cut-out?

Goffin JM, Jenkins PJ, Ramaesh R, Pankaj P, Simpson AH - PLoS ONE (2013)

Bottom Line: Using a simple mathematical formulation, the relationship between the position of the lag screw tip (relevant to both intramedullary and extramedullary devices) and the concept of tip-apex distance (TAD) was derived.In order to visualize better this concept, the locus of points having the same TAD was plotted and the dependence of TAD on the location of the lag screw tip was also reported.It was shown that TAD should be adjusted for the size of the femoral head (a variable which varies a lot according to the sex of the patient) while no correlation was found between TAD and bone morphometry indices obtained from micro-CT data (BV/TV and Tb.Th).

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedic Surgery, The University of Edinburgh, Edinburgh, United Kingdom.

ABSTRACT
Using a simple mathematical formulation, the relationship between the position of the lag screw tip (relevant to both intramedullary and extramedullary devices) and the concept of tip-apex distance (TAD) was derived. TAD is widely used in operating theaters as a surgical guideline in relation to the fixation of trochanteric fractures, and in clinical studies as a predictor of lag screw cut-out. In order to visualize better this concept, the locus of points having the same TAD was plotted and the dependence of TAD on the location of the lag screw tip was also reported. It was shown that TAD should be adjusted for the size of the femoral head (a variable which varies a lot according to the sex of the patient) while no correlation was found between TAD and bone morphometry indices obtained from micro-CT data (BV/TV and Tb.Th). Therefore, these results seem to suggest that TAD lacks mechanical justification and that predictors which are based on mechanical properties, such as bone density, should be investigated further.

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Related in: MedlinePlus

Relationship between micro-CT data and TAD.Tip-apex distance (TAD in mm), ratio of bone volume to total volume (BV/TV in %) as well as trabecular thickness (Tb.Th in mm) were represented for 18 cubic regions of interest (ROI) in planes 1 and 2, as depicted in Figure 1.
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pone-0071195-g007: Relationship between micro-CT data and TAD.Tip-apex distance (TAD in mm), ratio of bone volume to total volume (BV/TV in %) as well as trabecular thickness (Tb.Th in mm) were represented for 18 cubic regions of interest (ROI) in planes 1 and 2, as depicted in Figure 1.

Mentions: Finally, taking advantage of micro-CT scan data of femoral heads, the relationship between bone properties and TAD was assessed and reported in Figure 7. In particular, the following bone morphometry indices were considered: BV/TV (bone volume over total volume in percent) and Tb.Th (trabecular thickness in mm). There was no correlation between TAD and BV/TV (r = 0.17, p = 0.49) or TAD and Tb. Th. (r = −0.03, p = 0.89).


What is the relevance of the tip-apex distance as a predictor of lag screw cut-out?

Goffin JM, Jenkins PJ, Ramaesh R, Pankaj P, Simpson AH - PLoS ONE (2013)

Relationship between micro-CT data and TAD.Tip-apex distance (TAD in mm), ratio of bone volume to total volume (BV/TV in %) as well as trabecular thickness (Tb.Th in mm) were represented for 18 cubic regions of interest (ROI) in planes 1 and 2, as depicted in Figure 1.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756032&req=5

pone-0071195-g007: Relationship between micro-CT data and TAD.Tip-apex distance (TAD in mm), ratio of bone volume to total volume (BV/TV in %) as well as trabecular thickness (Tb.Th in mm) were represented for 18 cubic regions of interest (ROI) in planes 1 and 2, as depicted in Figure 1.
Mentions: Finally, taking advantage of micro-CT scan data of femoral heads, the relationship between bone properties and TAD was assessed and reported in Figure 7. In particular, the following bone morphometry indices were considered: BV/TV (bone volume over total volume in percent) and Tb.Th (trabecular thickness in mm). There was no correlation between TAD and BV/TV (r = 0.17, p = 0.49) or TAD and Tb. Th. (r = −0.03, p = 0.89).

Bottom Line: Using a simple mathematical formulation, the relationship between the position of the lag screw tip (relevant to both intramedullary and extramedullary devices) and the concept of tip-apex distance (TAD) was derived.In order to visualize better this concept, the locus of points having the same TAD was plotted and the dependence of TAD on the location of the lag screw tip was also reported.It was shown that TAD should be adjusted for the size of the femoral head (a variable which varies a lot according to the sex of the patient) while no correlation was found between TAD and bone morphometry indices obtained from micro-CT data (BV/TV and Tb.Th).

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedic Surgery, The University of Edinburgh, Edinburgh, United Kingdom.

ABSTRACT
Using a simple mathematical formulation, the relationship between the position of the lag screw tip (relevant to both intramedullary and extramedullary devices) and the concept of tip-apex distance (TAD) was derived. TAD is widely used in operating theaters as a surgical guideline in relation to the fixation of trochanteric fractures, and in clinical studies as a predictor of lag screw cut-out. In order to visualize better this concept, the locus of points having the same TAD was plotted and the dependence of TAD on the location of the lag screw tip was also reported. It was shown that TAD should be adjusted for the size of the femoral head (a variable which varies a lot according to the sex of the patient) while no correlation was found between TAD and bone morphometry indices obtained from micro-CT data (BV/TV and Tb.Th). Therefore, these results seem to suggest that TAD lacks mechanical justification and that predictors which are based on mechanical properties, such as bone density, should be investigated further.

Show MeSH
Related in: MedlinePlus