, Francois Lintz2, Cesar de Cesar Netto3, Alexej Barg4, Arne Burssens5 and Scott Ellis6
Keywords
ImagingWeight bearing CTSyndesmotic injuryDeltoid ligament injuryIntroduction
Injury to the distal tibiofibular syndesmosis is common and appears in up to 20% of patients with an ankle sprain or ankle fracture [1–3]. If not treated appropriately, long-lasting disabilities like chronic pain, instability, and ankle joint osteoarthritis may occur [2, 4, 5]. Injury can occur to any of the four main components of the distal tibiofibular syndesmosis: the anterior inferior tibiofibular ligament (AITFL), interosseous membrane (IOM), posterior inferior tibiofibular ligament (PITFL), and transverse tibiofibular ligament (TTFL) [2, 3, 6]. Additionally, a deltoid ligament injury is also frequently present in patients with syndesmotic injury [7].
While pronounced injuries can be reliably assessed using conventional radiographs, the diagnosis of incomplete injuries, especially in the absence of a fracture (e.g., high ankle sprain), is difficult [8–11]. In addition, measurements on conventional radiographs do not reliably reflect the injury pattern, which limits the general utility of conventional radiographs in assessing the distal tibiofibular syndesmosis [12]. Correlating findings in magnetic resonance imaging (MRI) with patient complaints can prove challenging [3]. Therefore, an accurate imaging modality to assess patients with incomplete injuries to the distal tibiofibular syndesmosis is desirable.
With the introduction of weight-bearing CT scans, detailed assessment of foot and ankle disorders under load-bearing conditions became possible [13–15]. However, the impact of load on two-dimensional (2D) measurements performed on axial CT images to assess the integrity of the distal tibiofibular syndesmosis is debated [16, 17]. The purpose of this cadaver study was to assess the influence of weight on the assessment of incomplete and more complete syndesmotic injuries using 2D measurements on axial CT images. We hypothesized that weight would significantly impact on the assessment of both incomplete and more complete injuries to the distal tibiofibular syndesmosis.
Methods
Data Source
Seven pairs of male cadavers (tibia plateau to toe-tip) were included (mean age 62 ± 7 [range 52–70] years; mean weight 84.9 ± 15.3 [range 65.8–104.8] kg; mean body mass index (BMI) 26.8 ± 5.0 [range 19.7–32.5] kg/m2). Inclusion criteria were 20–70 years of age and a BMI of less than 35 kg/m2. Exclusion criteria were a history of any foot and ankle injuries or a history of surgery of the foot and ankle.
Experimental Setting
First, intact ankles (native) were scanned. Second, one specimen from each pair underwent AITFL transection (Condition 1A), while the contralateral underwent deltoid transection (Condition 1B). Third, the lesions were reversed on the same specimens, and the remaining intact deltoid ligament or AITFL was transected in each ankle (Condition 2). Finally, the interosseous membrane (IOM) was transected in all ankles (Condition 3). Conditions 1A and 1B were considered to mimic incomplete injuries, while Conditions 2 and 3 were considered to mimic more complete injuries. For each condition, non-weight-bearing, half-bodyweight (42.5 kg), and full-bodyweight (85 kg) CT scans were taken. Loading levels were determined from the average of specimen donor anthropometrics. Preconditioning of the specimen was performed by statically loading the frame with 42.5 kg and 85 kg for 2 minutes each before the experiments were performed.
Measurements for interobserver agreement calculation were done by a fellowship-trained orthopedic surgeon and a research analyst. For calculation of the intraobserver agreement, measurements were performed two times with an interval of 3 weeks by a fellowship-trained orthopedic surgeon. Each observer completed a computer-based training before measurements were performed.
Imaging and Measurements
Statistical Analysis
Intraclass correlation (ICC) was used to quantify the agreement of measurements between and within observers. Estimates and 95% confidence intervals (CI) were calculated for each type of measurement. Interobserver agreement was modeled with a two-way random effect model of absolute agreement with a single measurement per observation. Intraobserver agreement was modeled with a two-way mixed effect model of consistency with a single measurement per observation. Agreement was rated as excellent with an ICC >0.75; good with an ICC = 0.61–0.75; fair with an ICC = 0.4–0.6; and poor with an ICC <0.4 [16].
Linear mixed effect models were fit for responses. Cadaver, treated as a random effect, and foot, (left or right) treated as a fixed effect, were included in all models in addition to the variables presented lateral in the tables. Models were fit for subsets of the data (with given weight or condition constant) and estimates and 95% CI are given for differing levels of condition or weight. Confidence intervals were calculated using a Tukey adjustment for multiple comparisons within each model. Significance was determined based on a P-value of less than 0.05 after the Tukey adjustment. All calculations were done in R 3.4.1, specifically using package psych and ImerTest.
Results
Agreement of computed tomography scans assessed by intraclass correlation (ICC) [1]
Interobserver: ICC(2,1) Estimate (95% CI) |
Level of agreement |
Intraobserver: ICC(3,1) Estimate (95% CI) |
Level of agreement | |
---|---|---|---|---|
Angle 1 |
0.39 (0.12, 0.60) |
Poor |
0.51 (0.27, 0.69) |
Fair |
Angle 2 |
0.44 (−0.08, 0.74) |
Fair |
0.67 (0.48, 0.80) |
Good |
ATFD |
0.54 (0.30, 0.71) |
Fair |
0.58 (0.35, 0.74) |
Fair |
AFT |
0.65 (0.45, 0.79) |
Good |
0.61∗ (0.39, 0.76) |
Good |
MFT |
0.65 (0.45, 0.79) |
Good |
0.71∗ (0.53, 0.82) |
Good |
PFT |
0.53 (0.29, 0.70) |
Fair |
0.54 (0.30, 0.71) |
Fair |
TFCS |
0.61 (0.74, 0.97) |
Good |
0.79 (0.89, 0.97) |
Excellent |
TFO |
0.57 (0.53, 0.98) |
Fair |
0.94 (0.97, 0.99) |
Excellent |
Influence of load on computed tomography measurements across all tested conditions (difference between weight application in millimeters [mm]) [1]
Mean (SD; mm) |
Estimate (95% CI) | |||
---|---|---|---|---|
Non-weight-bearing |
Half-bodyweight | |||
Angle 1 |
Non-weight-bearing |
−13.3 (5.8) |
– |
– |
Half-bodyweight |
−13.4 (5.3) |
0.0 (−1.8, 1.8) |
– | |
Full-bodyweight |
−13.8 (5.4) |
−0.5 (−2.2, 1.3) |
−0.4 (−2.2, 1.4) | |
Angle 2 |
Non-weight-bearing |
10.3 (7.5) |
– |
– |
Half-bodyweight |
10.8 (7.9) |
0.5 (−0.8, 1.8) |
– | |
Full-bodyweight |
11.1 (7.4) |
0.8 (−0.5, 2.1) |
0.3 (−1.0, 1.6) | |
ATFD |
Non-weight-bearing |
4.6 (1.0) |
– |
– |
Half-bodyweight |
4.7 (1.3) |
0.1 (−0.4, 0.5) |
– | |
Full-bodyweight |
4.5 (1.0) |
−0.1 (−0.5, 0.3) |
−0.2 (−0.6, 0.3) | |
AFT |
Non-weight-bearing |
2.3 (1.6) |
– |
– |
Half-bodyweight |
2.1 (1.5) |
−0.1 (−0.6, 0.3) |
– | |
Full-bodyweight |
1.0 (1.5) |
−0.3 (−0.7, 0.2) |
−0.2 (−0.6, 0.3) | |
MFT |
Non-weight-bearing |
9.3 (1.5) |
– |
– |
Half-bodyweight |
9.4 (1.4) |
0.1 (−0.3, 0.6) |
– | |
Full-bodyweight |
9.7 (1.4) |
0.4 (−0.1, 0.8) |
0.3 (−0.2, 0.7) | |
PFT |
Non-Weight-bearing |
8.1 (1.2) |
– |
– |
Half-bodyweight |
7.9 (1.1) |
−0.1 (−0.5, 0.3) |
– | |
Full-bodyweight |
7.6 (1.1) |
−0.4∗ (0.8, −0.0) |
−0.3 (−0.7, 0.1) | |
TFCS |
Non-Weight-bearing |
4.5 (1.6) |
– |
– |
Half-bodyweight |
4.7 (1.5) |
0.2 (−0.2, 0.5) |
– | |
Full-bodyweight |
4.7 (1.5) |
0.1 (−0.3, 0.5) |
−0.1 (−0.4, 0.3) | |
TFO |
Non-Weight-bearing |
6.2 (1.5) |
– |
– |
Half-bodyweight |
6.1 (1.5) |
−0.1 (−0.7, 0.4) |
– | |
Full-bodyweight |
6.2 (1.4) |
0.0 (−0.5, 0.5) |
0.1 (−0.4, 0.7) |