Yield Strength Testing in Human Cadaver Nasal Septal Cartilage and L-Strut Constructs

Abstract

IMPORTANCE To our knowledge, yield strength testing in human nasal septal cartilage has not been reported to date. An understanding of the basic mechanics of the nasal septum may help surgeons decide how much of an L-strut to preserve and how much grafting is needed. OBJECTIVES To determine the factors correlated with yield strength of the cartilaginous nasal septum and to explore the association between L-strut width and thickness in determining yield strength. DESIGN, SETTING, AND PARTICIPANTS In an anatomy laboratory, yield strength of rectangular pieces of fresh cadaver nasal septal cartilage was measured, and regression was performed to identify the factors correlated with yield strength. To measure yield strength in L-shaped models, 4 bonded paper L-struts models were constructed for every possible combination of the width and thickness, for a total of 240 models. Mathematical modeling using the resultant data with trend lines and surface fitting was performed to quantify the associations among L-strut width, thickness, and yield strength. The study dates were November 1, 2015, to April 1, 2016. MAIN OUTCOMES AND MEASURES The factors correlated with nasal cartilage yield strength and the associations among L-strut width, thickness, and yield strength in L-shaped models. RESULTS Among 95 cartilage pieces from 12 human cadavers (mean [SD] age, 67.7 [12.6] years) and 240 constructed L-strut models, L-strut thickness was the only factor correlated with nasal septal cartilage yield strength (coefficient for thickness, 5.54; 95% CI, 4.08-7.00; P < .001), with an adjusted R 2 correlation coefficient of 0.37. The mean (SD) yield strength R 2 varied with L-strut thickness exponentially (0.93 [0.06]) for set widths, and it varied with L-strut width linearly (0.82 [0.11]) or logarithmically (0.85 [0.17]) for set thicknesses. A 3-dimensional surface model of yield strength with L-strut width and thickness as variables was created using a 2-dimensional gaussian function (adjusted R 2 = 0.94). Estimated yield strengths were generated from the model to allow determination of the desired yield strength with different permutations of L-strut width and thickness. CONCLUSIONS AND RELEVANCE In this study of human cadaver nasal septal cartilage, L-strut thickness was significantly associated with yield strength. In a bonded paper L-strut model, L-strut thickness had a more important role in determining yield strength than L-strut width. Surgeons should consider the thickness of potential L-struts when determining the amount of cartilaginous septum to harvest and graft. LEVEL OF EVIDENCE NA.

Toward tissue-engineering of nasal cartilages

“…The L-strut, named in reference to its shape, is the remaining intact region of the septum after submucous resection during septoplasty or graft harvesting ( Figure 1). To avoid nasal collapse, it is widely accepted that the minimum widths of the caudal and dorsal arms of the L-strut need to be 10 mm [95]. However, it has been shown that thickness of the L-strut has a greater impact on L-strut yield strength [25,95].…”

“…To avoid nasal collapse, it is widely accepted that the minimum widths of the caudal and dorsal arms of the L-strut need to be 10 mm [95]. However, it has been shown that thickness of the L-strut has a greater impact on L-strut yield strength [25,95]. Despite its importance, thickness is rarely taken into account in L-strut mechanical strength modeling due to the complexity of accounting for both dimensions during rhinoplasty.…”

Redefining the nasal septal L‐strut: A quantitative analysis of septal arcs and angles

“…Because the thickness of the septum has been shown to be greatest adjacent to the septal base and most narrow in the central portion of the septum and near the ASP, the nasal septum adjacent to the ASP is afflicted with both decreased L‐strut width as well as with a thin depth. As prior research has shown, changing the anatomical constructs of L‐struts affects its underlying strength as compared to the unaltered septa . As such, the C‐strut concept informs the surgeon, during creation of the cartilage cuts, to arc the incisions posteriorly in a curvilinear fashion, paralleling the natural caudal and dorsal arc to ensure adequate strut width and maximal cartilage harvest.…”

“…As prior research has shown, changing the anatomical constructs of L-struts affects its underlying strength as compared to the unaltered septa. 2,10,12,13 As such, the C-strut concept informs the surgeon, during creation of the cartilage cuts, to arc the incisions posteriorly in a curvilinear fashion, paralleling the natural caudal and dorsal arc to ensure adequate strut width and maximal cartilage harvest. For example, a surgeon working within the L-strut paradigm may adequately estimate the strut width from the ASP but continue a linear cartilage cut that does not adequately provide enough distance from the PCSP.…”

The Creation of an Average 3D Model of the Human Cartilaginous Nasal Septum and Its Biomimetic Applications

“…Since septal shape shows significant variability between individuals, these studies may not be representative of the general patient population [6]. Furthermore, while studies have focused on the width of the dorsal and caudal struts, Liu et al showed that thickness is a more important determinant of overall L-strut strength [15].…”