One-fourth of all ankle trauma involve injury to the syndesmotic ankle complex, which may lead to syndesmotic instability and/or posttraumatic ankle osteoarthritis in the long term if left untreated. The diagnosis of these injuries still poses a deceitful challenge, as MRI scans lack physiologic weightbearing and plain weightbearing radiographs are subject to beam rotation and lack 3D information. Weightbearing cone-beam CT (WBCT) overcomes these challenges by imaging both ankles during bipedal stance, but ongoingdebate remains whether these should be taken under weightbearing conditions and/or during application of external rotation stress. The aim of this study is study therefore to compare both conditions in the assessment of syndesmotic ankle injuries using WBCT imaging combined with 3D measurement techniques.

In this retrospective study, 21 patients with an acute ankle injury were analyzed using a WBCT. Patients with confirmed syndesmotic ligament injury on MRI were included, while fracture associated syndesmotic injuries were excluded. WBCT imaging was performed in weightbearing and combined weightbearing-external rotation. In the latter, the patient was asked to internally rotate the shin until pain (VAS>8/10) or a maximal range of motion was encountered. 3D models were developed from the CT slices, whereafter. The following 3D measurements were calculated using a custom-made Matlab® script; Anterior tibiofibular distance (AFTD), Alpha angle, posterior Tibiofibular distance (PFTD) and Talar rotation (TR) in comparison to the contralateral non-injured ankle.

The difference in neutral-stressed Alpha angle and AFTD were significant between patients with a syndesmotic ankle lesion and contralateral control (P=0.046 and P=0.039, respectively). There was no significant difference in neutral-stressed PFTD and TR angle.

Combined weightbearing-external rotation during CT scanning revealed an increased AFTD in patients with syndesmotic ligament injuries. Based on this study, application of external rotation during WBCT scans could enhance the diagnostic accuracy of subtle syndesmotic instability.

Intra-articular cartilage pressure distribution in the knee joint is critical in the understanding of osteoarthritis. Combining personalized statistical modeling of the morphological characteristics with discrete element modeling enables patient-specific predictions of the pressure on the tibial plateau. However, modeling of the meniscus during gait is complicated by the dynamic nature of the structure. Nevertheless, the position of the meniscus has a substantial impact on intra-articular stress distribution. Therefore, the focus of this presentation will be on how modeling of meniscal movement during knee flexion improves insight in general meniscal kinematics for the use in tibiofemoral stress distribution calculations.

Several emerging reports suggest an important involvement of the hindfoot alignment in the outcome of knee osteotomy. At present, studies lack a comprehensive overview. Therefore, we aimed to systematically review all biomechanical and clinical studies investigating the role of the hindfoot alignment in the setting of osteotomies around the knee.

A systematic literature search was conducted on multiple databases combining “knee osteotomy” and “hindfoot/ankle alignment” search terms. Articles were screened and included according to the PRISMA guidelines. A quality assessment was conducted using the Quality Appraisal for Cadaveric Studies (QUACS) - and modified methodologic index for non-randomized studies (MINORS) scales.

Three cadaveric, fourteen retrospective cohort and two case-control studies were eligible for review. Biomechanical hindfoot characteristics were positively affected (n=4), except in rigid subtalar joint (n=1) or talar tilt (n=1) deformity. Patient symptoms and/or radiographic alignment at the level of the hindfoot did also improve after knee osteotomy (n=13), except in case of a small pre-operative lateral distal tibia- and hip knee ankle (HKA) angulation or in case of a large HKA correction (>14.5°). Additionally, a pre-existent hindfoot deformity (>15.9°) was associated with undercorrection of lower limb alignment following knee osteotomy. The mean QUACS score was 61.3% (range: 46–69%) and mean MINORS score was 9.2 out of 16 (range 6–12) for non-comparative and 16.5 out of 24 (range 15–18) for comparative studies.

Osteotomies performed to correct knee deformity have also an impact on biomechanical and clinical outcomes of the hindfoot. In general, these are reported to be beneficial, but several parameters were identified that are associated with newly onset – or deterioration of hindfoot symptoms following knee osteotomy. Further prospective studies are warranted to assess how diagnostic and therapeutic algorithms based on the identified criteria could be implemented to optimize the overall outcome of knee osteotomy.

Remark: Aline Van Oevelen and Arne Burssens contributed equally to this work

The incisura fibularis (IF) provides intrinsic stability to the ankle joint complex by interlocking the distal tibia and fibula. Despite a high frequency of ligamentous ankle injuries, scant attention has been given to the morphology of the IF morphology incisura fibularis in the onset and development of these lesions. Therefore, we systematically reviewed the relation between ligamentous ankle disorders and the morphometrics of the IF.

A systematic literature search was conducted on following databases: PubMed, Embase and Web of Science. Search terms consisted of ‘ankle trauma’, ‘ankle injury’, ‘ankle sprain’, ‘ankle fracture’, ‘tibiofibular’, ‘fibular notch’, ‘fibular incisura’, ‘incisura fibularis’, ‘morphometric analysis’, ‘ankle syndesmosis’, ‘syndesmotic stability’. The evaluation instrument developed by Hawker et al. was used to assess the quality of the selected studies. This protocol was performed according to the PRISMA guidelines and is registered on PROSPERO (CRD42021282862).

Nineteen studies were included and consisted of prospective cohort (n=1), retrospective comparative (n=10), and observational (n=8) study design. Comparative studies have found certain morphological characteristics in patients with ankle instability. Several studies (n=5) have correlated a shallow IF depth with a higher incidence of ankle injury. A significant difference has also been found concerning the incisura height and angle (n=3): a shorter incisura and more obtuse angle have been noted in patients with ankle sprains. The mean Hawker score was 28 out of 36 (range=24-31).

A shallower IF is associated with ligamentous ankle lesions and might be due to a lower osseous resistance against tibiofibular displacement. However, these results should be interpreted in light of moderate methodological quality and should always be correlated with clinical findings. Further prospective studies are needed to further assess the relation between the incisura morphometrics and ligamentous disorders of the ankle joint.

Keywords: ankle instability, ankle injury, incisura fibularis, fibular notch, tibiofibular morphometrics, ankle syndesmosis

Introduction and Objective

The human body is designed to walk in an efficient way. As energy can be stored in elastic structures, it is no surprise that the strongest elastic structure of the human body, the iliofemoral ligament (IFL), is located in the lower limb. Numerous popular surgical hip interventions, however, affect the structural integrity of the hip capsule and there is a growing evidence that surgical repair of the capsule improves the surgical outcome. Though, the exact contribution of the iliofemoral ligament in energy efficient hip function remains unelucidated. Therefore, the objective of this study was to evaluate the influence of the IFL on energy efficient ambulation.

Introduction and Objective

Forced external rotation is hypothesized as the key mechanism of syndesmotic ankle injuries. This complex trauma pattern ruptures the syndesmotic ligaments and induces a three-dimensional deviation from the normal distal tibiofibular joint configuration. However, current diagnostic imaging modalities are impeded by a two-dimensional assessment, without taking into account ligamentous stabilizers. Therefore, our aim is two-fold: (1) to construct an articulated statistical shape model of the normal ankle with inclusion of ligamentous morphometry and (2) to apply this model in the assessment of a clinical cohort of patients with syndesmotic ankle injuries.

Syndesmotic ankle injuries are present in one fourth of all ankle trauma and may lead to chronic syndesmotic instability as well as posttraumatic ankle osteoarthritis. The main challenge remains distinguishing them from other types of ankle trauma. Currently, the patient's injured and non-injured ankles are compared using plain radiographs to determine pathology. However, these try to quantify 3D displacement using 2D measurements techniques and it is unknown to what extent the 3D configuration of the normal ankle syndesmosis is symmetrical.

We aimed to assess the 3D symmetry of the normal ankle syndesmosis between the right and left side in a non- and weightbearing CT.

In this retrospective comparative cohort study, patients with a bilateral non-weightbearing CT (NWBCT; N=28; Mean age=44, SD=17.4) and weight-bearing CT (WBCT; N=33; Mean age=48 years; SD=16.3) were analyzed. Consecutive patients were included between January 2016 and December 2018 when having a bilateral non-weightbearing or weightbearing CT of the foot and ankle. Exclusion criteria were the presence of hindfoot pathology and age less than 18 years or greather than 75 years. CT images were segmented to obtain 3D models. Computer Aided Design (CAD) operations were used to fit the left ankle on top of the right ankle. The outermost point of the apex of the lateral malleolus (AML), anterior tubercle (ATF) and posterior tubercle (PTF) were computed. The difference in the coordinates attached to these anatomical landmarks of the left distal fibula in the ankle syndesmosis with respect to right were used to quantify symmetry. A Cartesian coordinate system was defined based on the tibia to obtain the direction of differences in all six degrees of freedom. Statistical analysis was performed using the Mann-Whitney U test to allow comparison between measurements from a NWBCT and WBCT. Reference values were determined for each 3D measurement in a NWBCT and WBCT based on their 2SD. The highest difference in translation could be detected in the anterior-posterior direction (Mean AP_NWBCT= −0.01mm; 2SD=3.43/Mean AP_WBCT=−0.1mm; 2SD=2.3) and amongst rotations in the external direction (Mean AP_NWBCT=−0.3°; 2SD=6.7/Mean AP_WBCT=-0,2°; 2SD=5.2). None of these differences were statistically significant in the normal ankle syndesmosis when obtained from a NWBCT compared to a WBCT (P>0.05).

This study provides references values concerning the 3D symmetry of the normal ankle syndesmosis in weightbearing and non-weightbearing CT-scans. These novel data contribute relevantly to previous 2D radiographic quantifications. In clinical practice they will aid in distinguishing if a patient with a syndesmotic ankle lesion differs from normal variance in syndesmotic ankle symmetry.

High ankle sprains (HAS) cause subtle lesions in the syndesmotic ligaments of the distal tibiofibular joint (DTFJ). Current intrinsic anatomical parameters of the DTFJ are determined based on 2D imaging and uncertainty remains whether they differ in a HAS patients. The aim of this study is therefore two-fold: radiographic parameters will be determined in 3D and compared in a healthy vs sprained group. Ten patients with a mean age of 42,56 (SD = 15,38) that sustained a HAS and twenty-five control subjects with a mean age of 47,44 (SD = 6,55) were retrospectively included. The slices obtained from CT analysis were segmented to have a 3D reconstruction. The following DTFJ anatomical parameters were computed using CAD software: incisura width, incisura depth, incisura length, incisura angle, and incisura-tibia ratio. The mean incisura depth in the sprained group was 3,93mm (SD = 0,80) compared to 4,76 mm (SD = 1,09) in the control group, which showed a significant difference (P < 0.05). The mean incisura length in the group of patients with HAS was 30,81 mm (SD = 3,17) compared to 36,10mm (SD = 5,27) in the control group which showed a significant difference (P < 0.05). The other DTFJ anatomical parameters showed no significant difference. This study shows a significant difference in both incisura depth and incisura length between HAS patients and control subjects. These parameters could be used to identify potential anatomical intrinsic risk factors in sustaining a HAS.