Subject population:
First 25 subjects undergoing knee MRI at our hospital who satisfied the following inclusion criteria were prospectively studied:
a) Subjects in whom ACL injury has been diagnosed on MRI
b) It is a self-reported non-contact ACL injury
c) Those who are willing to participate in the study and
d) Those who sign our institutional review board - approved informed consent.
Following exclusion criteria were used:
a) History of trauma to the soft tissue of the lower extremity requiring surgical repair/reconstruction (excluding ACL tears)
b) Meniscectomy of greater than one-fourth of the meniscus and
c) Fracture of lower extremity bones requiring internal fixation.
Also,
another 25 control subjects with normal or non-injured ACL who match the above selected subjects in gender,
age,
weight,
height,
and ethnicity were invited to participate in the study.
Static and dynamic ultrasound study of the normal knees of all 50 subjects was performed to measure maximum diameter of ACL near tibial insertion site.
The sonographer was blinded as to the status of the subject being examined.
Agreement between the sonographers was studied.
In addition to the main objectives,
correlation between diameter of ACL and weight,
height,
and age of the subject was also studied.
We did one to one matching between the injured subjects and the matched controls for height,
weight,
gender and ethnicity and achieved similar mean between groups for age.
Each injured subject and the matched control had the same gender and ethnicity.
The control subjects were chosen in such a way that the disparity between heights of each and every ACL-injured subject and the matched control was less than 5 centimeters and the disparity between weights of each and every ACL-injured subject and the matched control was less than 3 kilograms.
The average difference between the heights of control and injured subjects was within 1 cm (170.7 cm vs 171.2 cm) and the average difference between the weights of control and injured subjects was within 1.5 kg (78.7 kg vs 80.2 kg).
No statistically significant disparity was observed amongst the ACL-injured and control groups for age (P=0.890),
height (P=0.768),
weight (P=0.685),
and gender (P=1.00) based on statistical analysis using an unpaired Student t test and Chi-square tests [ Table 1 ].
The study was approved by our institutional research ethics committee.
Ultrasound-Based Diameter Calculation
Only tibial part of ACL could be examined by ultrasound.
Maximum diameter of ACL near tibial insertion site was measured by static and dynamic ultrasound (Siemens,
Munich,
Germany) study using high frequency (7-9 MHz) linear transducer with the subject's knee in 90 degree flexion in supine position.
While examining the ACLs,
we asked the subjects to internally or externally rotate their leg to perform the dynamic ultrasound examination.
The linear high frequency ultrasound probe was placed on the subject’s skin inferior to patella such that its long axis is parallel to that of the ACL.
This was achieved by rotating the superior part of the probe externally by 30 degrees [ Fig. 1 ].
The ACL was visualized as a thick linear hypoechoic band like structure inserted approximately 11 mm caudal to the tibial plateau and intercondylar eminence [ Fig. 1 ].
The maximum diameter of ACL near tibial insertion site was measured for 25 opposite,
normal or unaffected knees of persons who suffered noncontact injury to ACL and for 25 controls matched for weight,
height,
gender,
and age.
Each ACL was measured separately by two radiologists who were blinded to the status of the subject (injured or control group).
Interobserver variation was calculated.
Average of the two measurements was considered for statistical analysis.
We applied stepwise multiple regression to the statistical data to assess the disparity in the diameter of ACL between injured and control groups.
During this analysis weight,
height,
age,
and gender were deemed to be potential covariates.
Validation of Ultrasound-Based Diameter Calculation
MRI is considered a gold standard for in vivo ACL diameter measurement.
We used MRI studies of 10 knees of 10 control subjects for validating the ultrasound-based ACL diameter (near tibial insertion site) measurement performed in this study.
MRI examinations were performed using a GE Signa 1.5T system.
Sagittal 3D-SPGR MRI images with voxel size of 0.055 × 0.055 × 0.15 cm were obtained.
The MRI examination was performed on one randomly chosen knee of each of the control subjects.
The subject was placed in supine position with knee in 90 degree flexion to mimic the position during ultrasound study.
Maximum antero-posterior diameter of each ACL (near tibial insertion site) was measured by two radiologists independently.
Interobserver variation was measured.
Average of the two measurements was compared with average of maximum ACL diameter estimated by ultrasound.
Sample size
No similar studies in literature.
No formal sample size calculation.
Total of 50 subjects/knees
- 25 ACL-injured subjects
- 25 non-injured matched controls.
Statistical analysis
- Descriptive statistics.
- Chi-square test/Fisher’s exact test.
- Unpaired t-test/Mann Whitney U test.
- Paired t-test.
- Intra-class correlation coefficient (ICC).
- Bland-Altman plots.
- Pearson’s correlation coefficients.
- Stepwise multiple regression.
- PASW Statistics (v19.0,
SPSS Inc.)