This is a single-center observational cross-sectional study. Normal magnetic resonance imaging (MRI) scans (as reported by a senior radiologist) performed for patients with suspected knee ligamentous injury were used for analysis after our hospital's ethical committee's approval. Adult patients between 18 and 60 years were included. Knees where the MRI shows signs of osteoarthritis, gross bony, or cartilaginous defects were excluded. MRI of 100 males and 100 females were used for this study.
Imaging technique:
A Siemens 1.5 Tesla magnet (Siemens, Erlangen, Germany) and a knee joint surface coil were used for examination. Images were taken at an intervening interval of 0.3 mm and a thickness of 3 mm. To obtain an axial image parallel to knee joints, scans were performed while the patient was lying supine, and the knee was fully extended, keeping the patella towards the ceiling. The obtained images were processed via the local picture archiving and collecting system (PACS) used in our hospital, and the PACS software (Paxera Ultima 360) was used to do the measurements. To ensure the accuracy of the measurements, two of the authors measured each of the endpoints independently, and the average of both measurements was used for final analysis. Measurements were performed as follows:
A- Distal Femoral (f) measurement (Fig.1):
The trans-epicondylar axis (TEA) was first drawn as a line connecting the apexes of the medial and lateral femoral epicondyles in the widest axial cut of the distal femur (which contains the epicondyles) (Fig.1a) (17). The distal femoral measurements were done in the axial cut 9 mm above the most distal point of the medial femoral condyle to mimic the distal femoral cut in TKA as follows:
1) The femoral mediolateral (fML) length: was measured as the longest line connecting the medial and the lateral dimensions parallel to the trans-epicondylar axis (Fig.1b).
2) The femoral anteroposterior (fAP) length: according to Kim et al. (16), there is no significant difference between Lateral femoral anteroposterior (fAP) length and the fAP length so we considered the former as the AP femoral length. As the highest and the lowest points of the lateral distal femoral condyles (LDFC) could not be visualized in the same axial cut, so, we draw a line tangential to the lowest point of the lateral femoral condyle and parallel to the TEA in the corresponding axial cut (Line 1) (Fig.1c). We reproduced line 1 in the axial cut that contains the highest point of the LDFC, and a second line tangential to the highest point and parallel to the TEA was drawn (Line 2). The vertical distance between Line 1 and Line 2 represents the fAP length (Fig.1d).
3) The distal femur's aspect ratio (AR) was then calculated as (fML/fAP).
B- Proximal Tibial (t) measurement (Fig.2):
The femoral TEA was reproduced in the tibial cuts. The proximal tibial measurements were performed in the axial cuts 8-9 mm distal to the joint surface (3 slices from the joint surface) as follows:
1) The tibial mediolateral (tML) length: it was measured as the longest mediolateral line (which is parallel to the TEA) in the axial cuts of the proximal tibia (17, 25, 26).
2) The tibial anteroposterior (tAP) length: at the same level of the cuts, it was measured as the length of a line drawn perpendicular to the tML through the midpoint of the axial cut (17, 20, 25).
3) The tibial AR was calculated as (tML/tAP).
Anthropometric measurements of males and females from the current study were compared to detect gender differences in the Egyptian population. These values were then compared with corresponding values for other ethnic groups and with geometric values for modern TKA implants and knee prostheses that are commonly used in Egypt.
Seven implant types were used for comparison. NexGen (Zimmer), PFC-Sigma (DePuy, J & J), Scorpio PS (Stryker), Genesis 2, Journey 2, and Anthem (Smith & Nephew), and Freedom (Maxx Health). The first three implants are widely used in our country. Scatter graphs were plotted with the patient size and the best possible implant size for all the implants.
Statistical analysis:
Data were verified, coded by the researchers, and analyzed using SPSS (IBM_SPSS. Statistical Package for Social Science. Ver.21. Standard version. Copyright © SPSS Inc., 2011-2012. NY, USA. 2012.). Descriptive statistics: Means, standard deviations, and ranges were calculated. Intraclass Correlation Coefficient (ICC) was used to test the inter-rater reliability (ICC > 0.5 is considered acceptable, > 0.6 moderate, > 0.7 good, > 0.8 High and > 0.9 Excellent). Test of significances: for continuous variables, a one-sample t-test was used to compare the mean of the study parameters against each of the other studies' single mean. Independent t-test analysis was carried out to compare the means of normally distributed data, while the Mann-Whitney U test was calculated to test the median differences of the data that do not follow a normal distribution. A p-value ≤ 0.05 was considered significant.