A three-dimensional measurement approach for the morphology of the femoral head

Abstract

The hip joint is one of the most frequent sites of osteoarthritis. Advances in diagnosis and clinical treatment have progressed dramatically in the last few decades; however, there are limitations associated with the lack of reliable measures for quantifying hip joint morphology. Current diagnostic measures of the hip are performed with pre-determined measures, typically lengths and angles, on 2D radiographic planes. The current measurement techniques do not utilize the inherent 3D nature of CT and MR imaging and do not necessarily quantify the relevant clinical pathologies. A valid and reliable measurement modality that measures the surface geometry of the femoral head is necessary for early diagnosis and treatment of hip disease. The purpose of this study was to establish a method to quantify femoral head morphology using a three-dimensional model. A novel measurement approach was applied to 45 cadaveric femurs (23 right; 22 left; nine female, 17 male) and their digitally reconstructed 3D CT models. The mean difference between the cadaveric and digital measures was -2.04 mm with 95% confidence limits (CI) of 13.67 mm and -17.75 mm, respectively. The digital measurement approach was found to have excellent intraobserver reliability (ICC = 0.99, CI 0.98-0.99) and interobserver reliability (ICC = 0.98, CI 0.93-0.99). This valid and reliable novel digital measurement approach enables quantification of the 3D surface geometry of the femoral head and is able to measure individual variations and potentially detect abnormalities. This method may be used to assist future studies to establish valid diagnostic measurements for femoral head and head-neck junction pathologies.

Keywords: Mimics; cadaveric; hip joint; morphology; morphometrics; reliability; three-dimensional; validity.

Figure 1

Measurement of the femoral cadaveric specimens. (a) Establishment of the 0° angle marker. (b) Linear surface measurement of the femoral head from the centre of the fovea marker to the point where the convexity of the femoral head meets the concavity of the femoral neck using suture string. (c) Projected lines representing the 12 angle markers radiating from the centre of the fovea every 30°.

Figure 2

Measurement of the femoral digital models. (a) Establishment of the centre of the fovea and the 0° angle marker. (b) Creation of the angle template on a 2D plane. (c) Measurement of the femoral head from the centre of the fovea marker to the point where the convexity of the femoral head meets with the concavity of the femoral neck. Measurements are taken at each of the 12 angle markers.

Figure 3

Polar graphs of intraobserver reliability measurements of femoral head surface. The 12 axes represent the 12° points where the measurements were taken (n = 45). The mean measurement (mm ± SD) for each degree point is plotted for the first and second measures recorded by observer 1. (a) Mean cadaveric first and second measurements. (b) Mean digital first and second measurements.

Figure 4

Bland–Altman plot of intraobserver variability (n = 45) of the (a) femoral cadaveric measures (bias = 0.94 ± 5.16 mm) and (b) femoral digital measures (bias = −0.72 ± 5.30 mm). The x-axis plots the mean measurement between observations, recorded by observer 1, against the difference between the measures (mm) on the y-axis (first measure − second measure).

Figure 5

Polar graphs of interobserver reliability measurements of the femoral head (n = 18). The 12 axes represent the 12° points where the measurements were taken and the mean measurement (mm ± SD) for each degree point is plotted for both observers. (a) Cadaveric measures for observer 1 (C.M.) and observer 2 (J.T.). (b) Digital measures for observer 1 (C.M.) and observer 2 (J.T.).

Figure 6

Bland–Altman Plot of interobserver variability (n = 18) of the (a) femoral cadaveric measures (bias = −2.60 ± 5.33 mm) and (b) femoral digital measures (bias = 1.82 ± 9.47 mm). The x-axis plots the mean measurement between observations against the difference between the measures (mm) on the y-axis [first observer (C.M.) − second observer (J.T.)].

Figure 7

Polar graph of mean femoral cadaveric and digital measurements (mm ± SD) (n = 45). The 12 axes represent the degree (°) points (see Fig. 1c) identifying measurement position. Mean measurements for each degree point are plotted for the cadaveric and digital measures.

Figure 8

Bland–Altman plot of the difference between the femoral cadaveric measurements and the femoral digital measurements (n = 45; bias = −2.04 ± 8.00 mm). The x-axis plots the mean of two measurements against the difference between the measurement modalities (cadaveric − digital) on the y-axis.