Injuries to the anterolateral ligament are observed more frequently compared to lesions to the deep iliotibial tract (Kaplan fibers) in anterior cruciate ligamant deficient knees using magnetic resonance imaging

MRI data of 91 consecutive sujects, out of those 25 children, with clinical and radiological diagnosed ACL rupture were retrospectively reviewed focusing on the accuracy of detection and potential injuries to the ALL or dITT. All diagnoses were made by sports-medicine trained orthopaedic surgeons and two musculosceletal radiologists, respectively. Prior to inclusion an in depth clinical history was obtained and medical records were checked for previous knee injuries or surgeries. Patients were excluded in case of metallic material such as screws or plates around the knee, motion artifacts or different MRI protocols.

All MRIs were obtained using an identical protocol. Patients were examined in supine position with extended knees using a dedicated 15-channel knee coil. The following sequences were used for the 3.0 T Scanner (Avanto/Skyra, Siemens, Erlangen, Germany): coronal T1-weighted images (TE 10/13, TR 696/522, SL 3 mm); coronal PD-weighted images with fat-saturation (TE 40/38, TR 4100/3230, SL 3 mm); sagittal PD-weighted images with fat-saturation (TE 39/38, TR 3000/3710, SL 3 mm) and axial PD-weighted images with fat-saturation (TE 31/37, TR 3010/3100, SL 3.5/3 mm). Two trained and certified musculoskeletal radiologists (HB, KC) with dedicated MRI experience analyzed coronal, sagittal and axial MRI sets of all patients using the imaging viewer Impax EE (Agfa Health Care N.V., Mortsel, Belgium). Before the start of the analysis, a specialist in the field of anterolateral knee anatomy lectured and briefed both radiologists in a private cadaver dissection classe All relevant lateral and anterolateral structures of the knee were dissected and studied.

Both radiologist were blinded to the clinical findings of the patients. Each radiologist performed the analysis twice with an interval in between greater than 2 weeks. For ALL diagnostic, a low-signal ligamentous structure originating from the postero-proximal region of the lateral femoral epicondyle, running in an anterodistal direction deep to the ITT, crossing the lateral collateral ligament in the proximal third and inserting on the anterlateral tibia between Gerdy’s tubercle and the fibular head, was searched. For the diagnostic of the dITT an extraarticular, low-signal band structure connecting the ITT to the proximal ridge of the distal femur was scouted. Detailed definition of both structures as well as diagnostic criteria for MRI identification are reported in Table 1.

Each radiologiest categorized both structures first as either visible or non visible and subsequentely as intact, partial or complete injured. A complete ALL or dITT lesion was diagnosed in case of discontinued fibers in combination with intra- or peri-ligamentous edema. A partial ruptur was defined as an alteration of the normal fiber contiguity but without a clear ligament disruption. Abnormal intraligamentous signal and surrounding periligamentous edema may be present in partial ligament ruptures. In case an ALL injury was diagnosed, further subspecification in proximal- (above meniscus level) and distal- (below meniscus level) intraligamentous lesions as well as tibial avulsion fractures (Segond type) were made. For ITT lesions, a further subclassification in (a) proximal lesions of the deep ITT (Kaplan fiber complex) or (b) lesions to the COL of the ITT [20, 29, 34, 49] was conducted. The COL was defined according to previous recommendations as deep fibers running from the region of the Kaplan fiber complex to the anterolateral tibia [9, 20, 29, 34, 49]. After data analysis and inter-and intra-observer calculation, discrepant radiological findings were reviewed, discussed and a consensus was found between both radiologists. The results of the consensus are reported in the result section and Table 3.

Descriptive statistics and statistical analysis were performed using SPSS v. 22 (IBM Corp.). Cohen’s Kappa and 95% confidence intervals (95% CI) were determined as a measure of inter- and intra-observer reproducibility. A value of 0.70 for Cohen’s Kappa was considered as threshold for substantial reproducibility [27]. Sample size considerations were based on power analysis for a Pearson correlation as an approximation for the Cohen’s Kappa coefficient. Power analysis for Cohen’s Kappa was not available in common power analysis software packages. An observed correlation coefficient of 0.83 in a sample of 60 cases was sufficient to demonstrate exceedance of the 0.70 threshold with alpha = 0.05 and beta = 0.20 (one-sided). Power analysis was done with G*Power 3.1.9.2 [8]. The following scale of measurement agreement was applied: 0–0.2, slight; 0.21–0.4, fair; 0.41–0.6, moderate; 0.61–0.8, substantial; 0.81–1, almost perfect [27].

In 77 (84.6%) of all patients the ALL was visible. The deep femoral attachments of the dITT (Kaplan fiber complex) were identified in 75 (82.4%) of the cases. The COL of the ITT was not seen in any patient. For further subclassification in adult and pediatric patients see Table 3.

An injury to the ALL as seen in 45 (58.5%) of the patients. Out of those were 17 (22.1%) complete- and 28 (36.4%) partial ALL tears, respectively. In none of the cases a tibial avulsion (Segond lesion) was detected. An lesion to the dITT was visualized in 16 (21.3%) of the patients with six (8.0%) beeing complete and 10 (13.3%) beeing partial ruptures. Combined injuries of both the ALL and the dITT was reported in nine (12.7%) patients. For further subclassification in adult and pediatric patients see Table 2. Examples of intact and ruptured structures are presented in Figs. 1, 2 and 3.

Detailed inter- and intra-observer data are presented in Table 4. Overall inter-observer agreement was high with calculated Cohen’s Kappa values of 0.95 (95% CI 0.89–1.00) for proximal ALL injuries, 0.91 (95% CI 0.82–0.99) for distal ALL lesions and 0.94 (95% CI 0.86–1.00) for ruptures of the Kaplan fiber complex. The COL was not visible in any patients. For each of the investigated parameters absolute agreement between the observers was at least 94.0%. Calculated intra-observer reliability values were 0.95 (95% CI 0.89–1.00) for proximal ALL lesions, 0.93 (95% CI 0.85–1.00) for distal ALL lesions and 0.94 (95% CI 0.87–1.00) for lesions of the Kaplan fibers complex. For each of the investigated parameters absolute agreement between the two time points was at least 0.95.