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Category: Sports; Trauma Introduction/Purpose: Syndesmotic ankle injuries are present in one-fourth of all ankle trauma and may lead to syndesmotic instability or posttraumatic ankle osteoarthirtis on the long term. At present, they continue to impose a diagnostic dilemma our clinical practice. While magnetic resonance imaging lacks application of load to the ankle joint, plain weightbearing radiographs are skewed by superposition of the osseous structures. The recent advent of weightbearing cone-beam CT (WBCT) overcomes these drawbacks by imaging both ankles during bipedal stance. However, it remains debated whether syndesmotic ankle injuries should be imaged under weightbearing conditions and/or during application of external rotation. Therefore, we aimed to implement both weightbearing and external rotation in the assessment of syndesmotic ankle injuries using WBCT imaging combined with 3D measurement techniques. Methods: In this retrospective study, patients with an acute syndesmotic ankle injury were analyzed using a WBCT (N= 21; Age= 31.64±14.07 years old). Inclusion criteria were an MRI confirmed syndesmotic ligament injury imaged by a WBCT of the ankle during weightbearing and combined weightbearing-external rotation. Exclusion criteria consisted of fracture associated syndesmotic injuries. For the external rotation protocol, the patient was asked to internally rotate the shin while ensuring that the foot remained firmly plantigrade until pain (Visual Analogue Scale > 8/10) or a maximal range of motion was reached. 3D models were generated from the CT slices. Tibiofibular displacement and Talar Rotation were quantified by automated 3D measurements using a custom-made Matlab® script; Anterior Tibiofibular distance (ATFD), Alpha angle, posterior Tibiofibular distance (PTFD) and Talar rotation (TR) angle in comparison to the contralateral non-injured ankle. Results: The difference in neutral-stressed Alpha angle and ATFD showed a significant difference between patients with a syndesmotic ankle lesion and contralateral control (P = 0.046 and P = 0.039, respectively). The difference in neutral-stressed PTFD and TR angle did not show a significant difference between patients with a syndesmotic ankle lesion and healthy ankles (P = 0.492; P = 0.152, respectively). Conclusion: Application of combined weightbearing-external rotation reveals an increased ATFD in patients with syndesmotic ligament injuries (Figure 1). This study provides the first insights based on 3D measurements to support the potential relevance of applying external rotation during WBCT imaging. In clinical practice, this could enhance the current diagnostic accuracy of subtle syndesmotic instability in a non-invasive manner. However, future studies are required to determine cut-off values that may indicate the amount of displacement that might lead to chronic instability and require a certain type of treatment strategy.

Category: Ankle; Trauma Introduction/Purpose: Approximately 10-15% of posterior malleolar fractures (PMFs) are "small shell," extra-articular fragments. Current classification systems present difficulties to perform a uniform typification of PMFs and contain no consensus on whether they should be fixed. Anatomical studies have identified two distinct components of the posterior inferior tibiofibular ligament (PITFL); the superficial band is thought to be more important than its deep counterpart in imparting syndesmotic stability. However, the involvement of one or both bands of the PITFL by small shell PMFs has not been evaluated so far. Hence, we conducted this study to perform 3D mapping of small shell PMFs and to determine whether surgeons should fix these routinely. Methods: Ankle fracture patients with a ‘small shell’ PMF (Haraguchi 3/Mason 1/Bartoníček 1 or 2) were included. Demographics, radiological features, treatment, and outcomes were recorded. 3D models of the fractured tibiae were generated from CT scans and superimposed on a statistical shape model of the right tibia, which served as a template. Fracture lines along with footprints of superficial and deep PITFL were marked on the template. 3D fracture heat maps were generated. Size of the fracture fragments and involvement of the superficial and deep PITFL footprints were quantified using a custom MATLAB script (Figure 1). Sparing of the footprint was defined as an overlap of < 1% between the fracture line and the footprint areas. Odds ratios (OR) with 95% confidence intervals (CI) were determined to determine which variables correlated with sparing of the PITFL footprint; P-values of < 0.05 were considered significant. Results: Thirty-nine patients were included. The superficial PITFL footprint was spared in 15 (38%), deep PITFL in 10 (26%), and both in 4 cases (10%). Males and Weber C fractures had a higher likelihood of sparing the superficial and deep PITFL footprints, respectively (P = 0.04). Supination external rotation (SER) patterns were less likely to demonstrate syndesmotic widening if either PITFL footprint was spared. Direct fixation of the PMF was done in 1 case; syndesmotic fixation in 25 cases and in 14 cases, no syndesmotic fixation was done. Of these, 11 were SER injuries where stability was achieved after fixation of medial and lateral malleoli. In 1 SER and pronation external rotation (PER) injury case, the syndesmosis was stable after fixation of a large Chaput fragment. Conclusion: This study demonstrated that 48% of small shell PMFs spare either the superficial or deep footprint of the PITFL; in 10% both PITFL footprints were spared. Hence, 58 % of small-shell PMFs may not benefit from direct fixation. Additionally, SER injuries with small shell PMFs that spare either PITFL footprint may not demonstrate radiographic instability and may not need direct or indirect fixation after addressing other components of the ankle fracture. However, given the fact that syndesmotic stability is not dictated by the PITFL alone, it remains prudent to stress the syndesmosis per-operatively to determine if syndesmotic fixation is needed.

Category: Hindfoot; Sports Introduction/Purpose: The use of a dorsal closing wedge calcaneal osteotomy (DCWCO) in the treatment of insertional Achilles tendinopathy (IAT) has recently gained popularity. The anatomical changes imposed by the osteotomy are believed to improve both the biological and mechanical processes involved in IAT. However, the impact of shortening the Achilles leverage arm after DCWCO and the full impact of DCWCO on foot anatomy and function is not well understood. This study aimed to examine the effects of DCWCO on the 3D alignment and biomechanics of the foot and ankle in IAT patients through simulated models of DCWCO. The hypothesis was that DCWCO would significantly impact foot alignment and decrease gastrocsoleus lever arm. Methods: Six weightbearing ankle CTs of patients with IAT were identified from the clinical database. Bone segmentation was performed and DCWCOs were conducted in standardized planes with six variations, resulting in a total of 36 foot models. Two plantar osteotomy starting points were defined as 1-cm anterior (posterior osteotomy) and 2-cm anterior (anterior osteotomy) to the most plantar point of calcaneus. The osteotomies were extended to dorsal surface at 1-cm anterior to posterosuperior calcaneus with 6, 10, or 14-mm wedges anteriorly. After the osteotomies, the posterior part of the calcaneus was rotated around the plantar starting point until proper bone contact was achieved. Achilles reconstruction was also performed using pre-defined Achilles insertion points. All models were then transferred to a MATLAB-based algorithm for automated measurements. These measurements included talocalcaneal, calcaneal pitch, Böhler, and Achilles tendon sagittal angles, Achilles moment arm, Achilles- posterosuperior calcaneus distance, and difference in soleus-Achilles length. Results: Anteriorly placed osteotomy caused more significant decrease in the Böhler angle (p < 0.001). Evaluation of the posteriorly placed osteotomy separately showed no significant decrease in the Böhler angle for patients with more than 30- degrees of preoperative Böhler angle (p=0.26). However, patients with a preoperative Böhler angle less than 30-degrees showed a significant decrease, approaching values close to 5-degrees (p=0.004). Gastrocsoleus moment arm decrease was found to be 2-3% by using force/moment equation. The change in the distance between Achilles tendon and the posterosuperior calcaneus was similar between anterior and posterior osteotomies, with less than 3-mm in a 6-mm wedge and more than 5-mm in a 10-mm wedge osteotomy. The calculations showed that ankle dorsiflexion can increase by one degree for each mm of resection. Conclusion: An anteriorly placed starting point for a DCWCO can negatively affect foot alignment and offer limited benefits for Achilles decompression. If the preoperative Böhler angle is less than 30, a DCWCO can significantly decrease the Böhler angle, potentially putting the subtalar joint at risk for arthritis by increasing the load as reported by some finite element studies. The maximum decrease in gastrocsoleus power is less than 3%, which may be clinically insignificant. A posterior starting point with 10- mm wedge can be adequate to move Haglund around 5-mm anteriorly and can move Achilles insertion 10-mm superiorly to decrease tension.

Category: Trauma; Ankle Introduction/Purpose: Weber-B ankle fractures represent an increasingly common injury world-wide, and the decision for operative fixation often hinges on the stability and congruency of the ankle. While tibiotalar displacement is typically evaluated using the medial clear space on plain radiographs, this method remains prone to inaccuracy because of x-ray beam rotation and manual measurement errors. Furthermore, the influence of these fractures on the mechanical environment of the ankle remains unknown. The recent advent of weightbearing cone-beam CT (WBCT) overcomes these drawbacks by imaging during bipedal stance, allowing a 3D anatomical and mechanical analysis. Therefore, the aim of this study was to analyze the 3D mortise displacement and contact mechanics in weber B ankle fractures by use of WBCT in comparison to their healthy contralateral side. Methods: In this retrospective study, our ankle trauma database was searched for Weber-B ankle fractures imaged by bilateral WBCT imaging between 2015 and 2022. Exclusion criteria consisted of metal or motion artifacts, presence of ankle osteoarthritis, and an age less than 18 years or more than 75 years. Segmentation into 3D models of bone was performed semi-automatically, while personalized cartilage layers were modeled based on a previously validated methodology. Bilateral ankle models were imported in custom-made Matlab® script for an automated anatomical and mechanical analysis. 3D mortise congruency was evaluated by use of following parameters: fibular length, talocrural angle, distance mapping of the medial gutter and tibiofibular clear space distance mapping. Contact mechanics were evaluated by the mean and maximum contact stress of the tibia and talus, as well as the contact area (Figure 1). A student’s T-test was performed to investigate the difference between the fractured and healthy side. Results: Thirty-two patients, with mean age 38.50 years (SD = 15.81 ) and weight 79.12 kg (SD = 16,24), were confirmed eligible for analysis. Statistical analysis revealed that there were no significant differences for all anatomical parameters (P > 0.05). The mean contact stress of the fractured and healthy side was 2.10 (SD = 0.42) MPa and 2.10 (SD = 0,41) MPa, respectively, whereas the maximum stress was 7.67 MPa (SD = 1.55) and 7,47 MPa (SD = 1,67), respectively. No statistical significant differences were found between all mechanical parameters (P > 0.05). Conclusion: This study demonstrates that contact mechanics are not affected in Weber-B fractures with a congruent mortise. Therefore, non-operative treatment could be considered, as there will theoretically be no increased risk for the patients to develop posttraumatic osteoarthritis in the long term. In clinical practice, WBCT could prove useful to determine the 3D anatomical and mechanical environment of ankle fractures and guide patients towards (non-) operative treatment. However, further studies should focus on the minimal clinical important difference/rehabilitation factors associated with mortise malalignment based on concomitant contact stress increase, which would warrant and identify which cases need surgical reduction.

Category: Hindfoot; Ankle Introduction/Purpose: Several emerging reports suggest an important involvement of the hindfoot alignment in the outcome of knee osteotomy. At present these studies are scattered across the literature and 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. Methods: A systematic literature search was conducted on following databases: Pubmed, EMBASE, Cochrane Library and Web of Science. Search terms consisted of 'knee osteotomy' combined with 'hindfoot/ankle alignment'. Inclusion criteria were all English language studies analyzing the association between knee osteotomy and hindfoot alignment comprising biomechanical or clinical outcomes. Exclusion criteria consisted of knee osteotomy performed in conjunction with total knee arthroplasty and level V studies. A quality assessment was conducted using the Quality Appraisal for Cadaveric Studies (QUACS) - and modified methodologic index for non-randomized studies (MINORS) scales. This protocol was performed according to the PRISMA guidelines and registered on PROSPERO (CRD42021277189). Results: Eighteen studies were confirmed eligible and consisted of a cadaveric (n=3) -, retrospective cohort (n=14) - and case- control (n=2) study design. Following knee osteotomy, biomechanical hindfoot characteristics were also positively affected (n=4), except in rigid subtalar joint (n=1) or talar tilt (n=1) deformity. Patient symptoms and/or radiographic alignment (Fig. 1a) at the level of the hindfoot did also improve after knee osteotomy (n=13). However this did not apply in case of a small pre-operative lateral distal tibia- and hip knee ankle (HKA) angulation (Fig. 1b) 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. Conclusion: 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. These results should be interpreted in light of the moderate methodological quality of the included studies. Therefore, 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 in relation to the foot and ankle.

Category: Trauma; Ankle Introduction/Purpose: Forced external rotation is hypothesized as the key mechanism of syndesmotic ankle injuries, inducing a three-dimensional deviation from the normal distal tibiofibular joint alignment. These lesions, especially when subtle, present a deceitful diagnostic challenge. Current diagnostic imaging modalities are impeded by a two-dimensional assessment, without considering ligamentous stabilizers. Accurate diagnosis of syndesmotic lesions should involve 3D weightbearing osseous imaging in combination with - preferably automated- inclusion of patient-specific ligamentous information. Therefore, our aim is two-fold: (1) to construct a three-dimensional articulated statistical shape model of the normal distal tibiofibular joint with inclusion of ligamentous morphometry and (2) to detect differences in predicted syndesmotic ligament length of patients with syndesmotic lesions with respect to normative data. Methods: Training data comprised non-weightbearing CT scans from asymptomatic controls (N= 76, Mean age 63 +/- 19 years), weightbearing CT scans from patients with syndesmotic ankle injury (N = 13, Mean Age 35 +/- 15 years) and their weightbearing healthy contralateral side (N = 13). CT scan segmentation was used to generate 3D bone models in the control and patient group. All ankles were aligned based on the tibia. Path and length of the syndesmotic ligaments were predicted using a discrete element model, wrapped around bony contours. Statistical shape model evaluation was based on accuracy, generalization and compactness. The predicted ligament length in patients with syndesmotic lesions was compared to healthy controls by use of two-tailed Two- Sample student's t-test. Results: Our presented skeletal shape model described the training data with an accuracy of 0.23 +/- 0.028 mm. Mean prediction accuracy of ligament insertions was 0.53 +/- 0.12 mm. Mean length of the Anterior inferior tibiofibular ligament was 12.26 +- 1.89mm for the control cases, 12.32 +- 1.58 mm for the contralateral cases and 14.13 +- 1.48 mm for the cases with syndesmotic lesions. Statistically significant differences were found between the latter two (95% CI [ 0.323.29], p = 0.017) There was a significant correlation between presence of syndesmotic injury and the positional alignment between the distal tibia and fibula (r = 0.873, p < 0,001). Conclusion: Statistical shape modelling combined with patient-specific ligament wrapping techniques can facilitate the diagnostic workup of syndesmotic ankle lesions under weightbearing conditions. In doing so, an increased anterior tibiofibular distance was detected, corresponding to an 'anterior open-book injury' of the ankle syndesmosis as a result of anterior inferior tibiofibular ligament elongation/rupture (Figure 1).

Category: Ankle; Ankle Arthritis; Hindfoot Introduction/Purpose: While correction of varus alignment at the level of the ankle joint has been investigated extensively after supramalleolar osteotomy (SMOT), the effect on the hindfoot alignment remains unclear. This can be attributed to the limitations of former 2-dimensional radiographic measurements used to quantify the complex 3-dimensional subtalar joint alignment. Therefore, we aimed to determine both the ankle and subtalar joint alignment before and after SMOT using a weightbearing CT and autogenerated 3-dimensional measurements. Methods: Twenty-seven patients with a mean age of 53 years (SD=10.1; range=25-73) were retrospectively analyzed in a pre- post study design using weightbearing CT images. Inclusion criteria were correction of ankle varus deformity by either an opening wedge (N=19) or dome osteotomy (N=8). Exclusion criteria consisted of an additional inframalleolar bony correction, i.e. calcaneal osteotomy or subtalar arthrodesis. Corresponding three-dimensional bone models were reconstructed to compute the autogenerated measurements: tibial anterior surface (TAS) -, tibiotalar surface (TTS)-, talar tilt (TT) - and talocalcaneal (TC) angle. Results: The pre-operative (TAS=86.9°, SD=4.9; TTS=79.8°, SD=5.6; TT=8.8°, SD=4.3) radiographic parameters of the ankle joint alignment improved significantly compared to the post-operative parameters (TAS=92.4°, SD=4.9; TTS=87.1°, SD=6.3; TT=5.1°, SD=2.7; P

Category: Ankle Arthritis; Hindfoot Introduction/Purpose: Dome shaped supramalleolar osteotomies are a well-established treatment option for correcting ankle deformity. However, the procedure remains technically demanding and is limited by a two-dimensional (2-D) radiographic planning of a three-dimensional (3-D) deformity. Therefore, we implemented a weight-bearing CT-scan (WBCT) to plan a 3-D deformity correction using patient specific guides. Methods: A 3-D guided dome shaped supramalleolar osteotomy was performed to correct ankle varus deformity in a cohort of 5 patients with a mean age of 53,8 years (range: 47-58). WBCT images were obtained to generate 3-D models, which enabled a deformity correction using patient specific guides. These technical steps are outlined and associated with a retrospective analysis of the clinical outcome using the EFAS score, Foot and Ankle Outcome Score (FAOS) and Visual Analog Pain scale (VAS). Radiographic assessment was performed using the tibial anterior surface angle (TAS), tibiotalar angle (TTS), talar-tilt angle (TTA), hindfoot angle (HA), tibial lateral surface angle (TLS) and tibial rotation angle (TRA). Results: The mean follow-up was 40,8 months (range 8-65) and all patients showed improvements in the EFAS score, FAOS and VAS (p < 0.05). A 3-month postoperative WBCT confirmed healing of the osteotomy site and radiographic improvement of the TAS, TTS and HA (p0.05). Conclusion: Dome shaped supramalleolar osteotomies using 3-D printed guides designed on WBCT, are a valuable option in correcting ankle varus deformity and mitigates the technical drawbacks of free-hand osteotomies.

Category: Hindfoot; Midfoot/Forefoot; Other Introduction/Purpose: In progressive collapsing foot deformity (PCFD), hind- and midfoot deformities are paramount. However, an accurate assessment thereof, using weightbearing radiography, remains challenging. Automated three-dimensional (3D) measurements derived from weightbearing computed tomography (WBCT) scans may provide a more accurate approach for deformity assessment. In this study, automated 3D measurements based on WBCT were compared to two-dimensional (2D) measurements performed on weightbearing radiographs. Furthermore, it was investigated whether various stages of PCFD could be identified using automated 3D measurements. Methods: Twenty patients treated at our institution with either a flexible (N=10) or rigid (N=10) PCFD were identified, retrospectively analyzed and compared to a control group of thirty healthy individuals. Four angles and two distances measured on weightbearing radiographs were compared to the automated 3D measurements derived from WBCT scans. Results: In 5 out of 6 variables, the reliability of the measurements derived from weightbearing radiographs was lower than the automated measurements that derived from WBCT scans. The automated 3D measurements showed: the talar tilt in the ankle mortise was more valgus in patients with a rigid PCFD when compared to patients with a flexible PCFD; medial facet subluxation was present in all but one patient; patients with a sinus tarsi impingement evidenced a higher overlap between the talus and calcaneus (12.4+-2.6 mm) compared to patients without impingement (7.8+-3.9 mm; P=0.020). Conclusion: A higher reliability of automated 3D measurements derived from WBCT scans, was evident for most variables when compared to measurements based on weightbearing radiographs. Besides being less prone to errors, automated 3D measurements may provide more reliable information regarding the hind- and midfoot alignment in patients with PCFD. Future studies may show to what extent 3D measurements could contribute to current diagnostic algorithms and treatment concepts of patients with PCFD.

Category: Ankle Introduction/Purpose: Syndesmotic ankle injuries are challenging to diagnose, since current 2D imaging techniques try to quantify a 3D displacement. Therefore, our aim was two-fold: to determine displacement of sequential syndesmotic ankle injuries under various amounts of load using a 3D weightbearing CT (WBCT) and to assess the relation with current 2D imaging. Methods: Seven paired male cadaver specimens were included (tibia plateau to toe-tip) and mounted into a custom-built frame. WBCT scans were obtained after different patterns of load (0 kg or 85 kg) were combined with torque (0 Nm or 10 Nm external rotation). These conditions were repeated after each ligament condition: intact ligaments, sequential sectioning of the anterior inferior tibiofibular ligament (AITFL), deltoid ligament (DL), and interosseous membrane (IOM). CT images were segmented to obtain 3D models. These allowed quantification of displacement based on the position of computed anatomical landmarks in reference to the intact position of the fibula. A correlation analysis was performed between the 2D and 3D measurements. Results: The effect of torque caused significant displacements in all directions (P0.05). Weight caused a significant lateral (mean=-1.4 mm, SD=1.5) and posterior translation (mean=-0.6 mm, SD=1.8). The highest displacement consisted of external rotation (mean=-9.4°, SD=6.5) and posterior translation (mean=6.1 mm, SD=2.3) after IOL sectioning combined with torque (Fig. 1). Pearson correlation coefficients were moderate (range 0.31-0.51, P

Category: Hindfoot Introduction/Purpose: An adult-acquired flatfoot deformity is a three-dimensional (3D) condition characterized by a loss of the medial longitudinal arch, valgus alignment of the hindfoot, and abduction of the midfoot. When conservative measures are not sufficient, a medializing calcaneal osteotomy (MCO) is frequently performed to correct the deformity, but there is lack of data on the associated three-dimensional variables defining the final correction. A possible reason for this shortcoming could be the current image-based analyses, mainly performed on bi-dimensional radiographs. These are hampered by errors in 3D rotations and superimposition of bony structures. The aim of this study was therefore to assess the correlation between the preoperative hindfoot valgus deformity and calcaneal osteotomy angle and the postoperative calcaneal displacement by use of weightbearing CT (WBCT). Methods: Weight-bearing CT scans obtained pre- and post-operatively were analyzed for sixteen patients with a mean age of 49.4 years (range: 18-66 years). Indication for surgery was adult-acquired flat foot deformity stage II. Based on the WBCT images, pre- and post-operative 3D bone morphological models of the tibia, talus, calcaneus, and the second metatarsal were created, on which anatomical bony landmarks were computationally identified to define a Foot Anatomical reference Frame (FAF). This FAF was used to measure valgus deformity pre- and post-operatively, inclination of the osteotomy plane, and displacement of the calcaneus (Fig. 1). Linear regression was conducted to assess the relationship between these measurements. Results: On average, the hindfoot valgus changed from 13.1° (±4.6) preoperatively to 5.7° (±4.3) postoperatively. A mean inferior displacement of 3.2 mm (±1.3) was observed along the osteotomy with a mean inclination angle of 54.6° (±5.6), 80.5° (±10.7), - 13.7° (±15.7) in the axial, sagittal and coronal planes, respectively. A statistically significant positive relationship (P < .05, R2 = 0.6) was found between the preoperative valgus, the axial osteotomy inclination, and the inferior displacement. Conclusion: This study shows that the degree of preoperative valgus of the hindfoot and the axial osteotomy angle are predictive factors for the amount of postoperative plantar displacement of the calcaneus. These findings contrast the general recommendation of performing a 90° calcaneal osteotomy angle, i.e. perpendicular to the lateral calcaneal wall in every patient. The obtained factors should be taken into account when performing a MCO and could be integrated in a computer-based pre- operative planning.

Category: Hindfoot, Trauma Introduction/Purpose: Accurate assessment of subtalar joint stability is difficult. Weightbearing CT (WBCT) scans have increased in popularity among foot and ankle surgeons as it offers an accurate representation of hindfoot joint alignment under weightbearing conditions. However, the clinical utility of this imaging modality to diagnose subtalar joint instability has yet to be investigated. The purpose of this study was to assess the impact of load and torque application on the assessment of subtalar joint instability when using WBCT scans. We hypothesized that load and torque application would improve the ability to identify subtalar joint instability. Methods: Fourteen paired male cadavers (tibial plateau to toe-tip) were included. A radiolucent frame held specimens in a plantigrade position while non-weightbearing and weightbearing CT scans (with and without torque application) were taken. First, intact ankles (Native) were scanned. Second, one specimen from each pair underwent interosseous talo-calcaneal ligament (ITCL) transection (Condition 1A), while the contralateral underwent calcaneo-fibular ligament (CFL) transection (Condition 1B). Third, the lesions were reversed on the same specimens and the remaining intact ITCL or CFL was transected (Condition 2). Finally, the deltoid ligament was transected in all ankles (Condition 3). Two radiographic measurements were performed on the level of the ankle joint (talar tilt [TT], anterior talar translation [ATT]), while the subtalar tilt (STT) was measured at the anterior, middle, and posterior plane of the subtalar joint. Inter- and intra-observer agreement calculations were additionally performed. Results: Weight did not impact most measurements, while the majority of measurements differed significantly within each condition after torque application. Measurements performed at the level of the subtalar joint were more reliable and better predictors for subtalar joint instability compared to measurements performed at the level of the ankle joint. Discrete ITFL, combined ITFL/ CFL, and combined ITFL/ CFL/ deltoid ligament injuries had significantly different STT values than native ankles (Figure 1). Conclusion: Measurements to assess the stability of the subtalar joint should primarily be performed at the level of the subtalar joint rather than at the level of the ankle joint when using WBCT scans. Torque application is crucial for identifying subtalar joint instability, while the application of load should be avoided. Future clinical studies will therefore face substantial technical challenges should they attempt to determine the clinical utility of WBCT scans for assessment of subtalar joint instability.

Category: Hindfoot Introduction/Purpose: Patients with a hindfoot deformity pose a particular challenge when performing a total knee arthroplasty (TKA). This could be attributed to the lack of insights concerning hindfoot alignment outcome. Our objective was to perform a systematic review of the literature to investigate the influence of TKA on hindfoot alignment and vice-versa. Methods: This systematic review was performed in accordance to PRISMA guidelines; the original protocol is registered on PROSPERO (ID: 106980). The following electronic databases were searched to identify capable studies: Pubmed, EMBASE, Web of Science, Google Scholar, and Cochrane Library. To ensure the quality of the review, a quality assessment was performed according to the MINORS criteria. The mean MINORS score was 9.5 (range 7-12) and concurred with a good quality of the obtained studies. Results: Sixteen identified articles met the review criteria: six prospective cohort studies, nine retrospective studies, and one case-control study. Five articles reporting on clinical outcomes were identified; a pre-operative hindfoot deformity negatively influenced TKP outcome (N=4) or demonstrated no influence (N=1). Thirteen articles reporting on radiographic outcomes were identified. Five studies reported a significant improvement (P < 0.05) of hindfoot alignment after TKA, two studies demonstrated improvement limited to valgus hindfeet, seven studies observed a significant (P < 0.05) correlation between knee and hindfoot alignment, and two studies reported the association between hindfoot OA in patients undergoing TKA. Two studies reporting biomechanical outcomes were identified; these reported a shift of the weighbearing axis after TKA as a result of the remaining hindfoot deformity. Conclusion: TKA can improve the alignment of valgus hindfeet, but improvement was less pronounced in varus hindfeet. Furthermore, a worse clinical outcome is expected after TKA in patients with concomitant ankle OA. A remaining hindfoot deformity shifts the weightbearing axis, which could shorten the survival of the total knee prosthesis.

Category: Hindfoot Introduction/Purpose: The exact relationship between different types of hindfoot deformities and the full leg alignment is currently unclear. Therefore, our aim is to assess hindfoot alignment on a weight-bearing CT (WBCT) and its association with the full leg radiographic alignment. Methods: A retrospective analysis was performed on a study population of 109 patients (mean age of 53 years ± 14.49) with a varus or valgus hindfoot deformity and the presence or absence of ankle osteoarthritis (OA) based on the Takakura classification. The mechanical hindfoot - (mHA) and subtalar vertical angle (SVA) were determined on WBCT, while the mechanical tiba – (mTA) and mechanical tibiofemoral angle (mTFA) were measured on full leg radiographs. Results: In patients with ankle OA, a hindfoot valgus deformity was associated with a significantly higher mean varus alignment of the knee (mTFA = -1.8°±2.1; mTAx= -4.3°±1.9) compared to a valgus alignment of the knee (mTFA = 0.3°±2.6; mTAx= -1.4°±2.2; P 0.05). Conclusion: A valgus hindfoot deformity demonstrated a higher varus alignment of the knee when compared to patients with a hindfoot varus deformity, if ankle OA was present. The subtalar joint did not attain an overall compensatory correction towards the hindfoot deformity as opposed to a compensatory orientation of the tibia alignment. In clinical practice, these findings could improve the current understanding of both joint preserving as well as joint replacing procedures of the hindfoot and the knee.

Category: Radiolography Introduction/Purpose: Weight-bearing CT (WBCT) has been proven to allow for more precise and valid measurement of bone position than conventional weight-bearing radiographs (R) and conventional CT without weight-bearing (CT). Time spent for image acquisition has been shown to be lower for WBCT than for R and CT. Radiation dose for WBCT has been shown to be lower for WBCT than for CT. A WBCT device (PedCAT, Curvebeam, Warrington, PA, USA) had been brought on line July 1, 2013 in the first author´s foot and ankle department. The purpose of this study was to assess the benefit of using WBCT instead of R and/or CT in a foot and ankle center regarding time spent for image acquisition, radiation dose, disturbances, and cost effectiveness. Methods: All patients who obtained WBCT (PedCAT)from July 1, 2013 until September 30, 2018 were included in the study. Age, sex, primary pathology were analyzed. The time spent for image acquisition (T) was calculated based on an analysis of previous study as follows: R (bilateral feet dorsoplantar and lateral, metatarsal head skyline view), 902 seconds; CT (bilateral feet and ankle), 415 seconds; WBCT (bilateral), 207 seconds. Radiation dose (RD) per patient was calculated based on previous phantom measurements as follows: R, 1.4 uSv; CT, 25 uSv; WBCT 4.2 uSv1. For analysis cost effectiveness, device cost, reimbursement and working time cost of radiology technicians were taken into consideration within the local circumstances. All parameters were compared between the time period using WBCT (yearly average) with the parameters from 2012, i.e. before availability of WBCT. Results: 10,087 WBCT scans were obtained in 4,702 patients (4,702 (47%) before treatment; 5,385 (53%) follow-up; mean age, 52.0; 40% male). Primary pathologies were forefoot deformities (n=916 (20%) and ankle instability/cartilage defect (n=534 (13%)), and hindfoot deformity (n=480 (10%)). 1,940 WBCT scans were obtained on average yearly, and 10.4 CTs (WBCT group). In 2012, 1,850 R and 254 CTs were obtained (R(+CT) group). Yearly RD was 4.4 uSv for WBCT group and 4.8 uSv for R(+CT) group (difference 0.4 uSv decrease with WBCT 8%, p

Category: Hindfoot Introduction/Purpose: An adult acquired flat foot (AAFD) is a complex 3D deformity. A medializing calcaneal osteotomy (MCO) is a surgical procedure frequently performed to correct the valgus alignment of the hindfoot in a stage II AAFD, when conservative measurements fail. However currently little is known on its accurate influence regarding the hindfoot alignment (HA). The aim is therefore to assess the influence of a MCO on the 3D HA using computer aided software analysis of the images retrieved from a weightbearing cone beam CT (WBCT). Methods: Twelve patients with a mean age of 49,4 years (range 18-67yrs) were prospectively included in a pre-post study design. Indications for surgical correction by a MCO with a solitary translation consisted of an AAFD stage II (N=10) and a posttraumatic valgus deformity (N=2). Fixation of the osteotomy was performed by a step-plate or double screw. WBCT was obtained pre- and post-operative. Images were subsequently segmented to allow a HA calculation in 3D(HA3D) by an angle between the anatomical tibia axis and the axis connecting the computed inferior calcaneuspoint and the centroid of the talus in the coronal plane based on a Cartesian coordinatesystem(Fig 1A, C). The tibia in the HA3D was separately assessed by the anatomical tibia axis (TAx 3D) and the axis to determine the tibial rotation(TR 3D) in the axial plane by connecting the computed most outer point of the anterior and posterior tubercle of the incisura fibularis(Fig 2A, D). Results: The mean medial translation of the calcaneal osteotomy during surgery was 5.72 mm (SD = 3.9). The mean HA3D pre-operatively equaled 18.21 degrees of valgus (SD = 6.6) and post-operatively 9.31 degrees of valgus (SD = 6.18). The Paired Student’s t-test showed a significant correction of 8.89 degrees (95%CI [5.99, 11.80], P

Category: Midfoot/Forefoot Introduction/Purpose: Surgical planning based on angular measurements obtained on conventional radiographs is challenging due to perspective distortion and operator bias. Novel weightbearing CT (WBCT) three-dimensional (3D) measurements using coordinate systems may represent a more reliable and accurate evaluation of this 3D deformity. The objective of this study was to compare the M1-M2 intermetatarsal angle (IMA) obtained manually on WBCT digitally reconstructed 2D radiographs versus a set of coordinates from the full 3D dataset, in patients with hallux valgus (HV) deformity and in healthy controls. We hypothesised that the 3D measurements would be more reliably obtained, demonstrating different values when compared to 2D radiographic measurements. Methods: In this multicenter retrospective comparative study, 83 feet that underwent WBCT of the foot were included (41 HV: mean age 59, 81% female, 42 controls: mean age 52, 80% female). Datasets were analysed by three independent trained foot and ankle surgeons using the same protocol. Coordinates in three planes (x, y, z) of four different landmark points were harvested: center of the heads and midpoint of the proximal metaphysis of the 1st and 2nd metatarsal. The IMA measurements were then performed in reconstructed radiographic images (DRR-IMA). The data collected was then analyzed by a single 4th independent and blinded investigator who calculated the 3D angle (3D-IMA) and its projection on the weightbearing plane (2D-IMA). Intra-observer realiability was assessed by Pearson/Spearman’s correlation. Intermethod correlation was evaluated by intraclass correlation coefficient (ICC). Mean values for measures were comparared by One-way ANOVA. P-values of less than 0.05 were considered significant. Results: Intraobserver reliability was excellent for radiographic DRR-IMA (0.95) and 3D coordinates assessment (0.99). Intermethod correlation between the three different imaging modalities (DDR, 2D and 3D), considering bias and interactions, were respectively 0.71 and 0.51 in control and HV patients. IMA measurements were found to be similar when measured in DRR, 2D and 3D WBCT images, for both controls and HV patients. Mean values and confidence intervals (CI) for controls were 8.8 degrees (CI, 7.9-9.7) in DDR images, 9.8 degrees (CI, 8.7-10.9) in 2D images and 10.6 degrees (CI, 9.5-11.8) in 3D images. When compared to controls, HV patients demonstraded significantly increased IMA (p

Category: Other Introduction/Purpose: Weight-bearing CT (WBCT) has been proven to allow for more precise and valid measurement of bone position than conventional weight-bearing radiographs (R) and conventional CT without weight-bearing (CT). Time spent for image acquisition has been shown to be lower for WBCT than for R and CT2. Radiation dose for WBCT has been shown to be lower for WBCT than for CT. A WBCT device (PedCAT, Curvebeam, Warrington, PA, USA) had been brought on line July 1, 2013 in the first author´s foot and ankle department. The purpose of this study was to assess the benefit of using WBCT instead of R and/or CT in a foot and ankle center regarding time spent for image acquisition, radiation dose, disturbances, and cost effectiveness. Methods: All patients who obtained WBCT July 1, 2013 until December 31, 2017 were included in the study. Age, sex and primary pathology were analyzed. The time spent for image acquisition (T) was calculated based on an analysis of a previous study as follows: R (bilateral feet dorsoplantar and lateral, metatarsal head skyline view), 902 seconds; CT (bilateral feet and ankle), 415 seconds; WBCT (bilateral), 207 seconds. Radiation dose (RD) per patient was calculated based on previous phantom measurements as follows: R, 1.4 uSV; CT, 25 uSv; WBCT 4.2 uSv. For analysis of cost effectiveness device cost, reimbursement and working time cost of radiology technicians were taken into consideration within the local circumstances. All parameters were compared between the time period using WBCT (yearly average) with the parameters from 2012, i.e. before availability of WBCT. Results: 8,129 WBCT scans were obtained in 3,874 patients (3,874 (48%) preoperatively, 4,255 (52%) follow-up; mean age, 52.2; 39% male). Primary pathologies were forefoot deformities (n=728 (19%) and ankle osteoarthritis/cartilage defect (n=412 (11%)). 1,804 WBCT scans were obtained on average yearly, and 10 CTs (WBCT group). In 2012, 1,750 R and 250 CTs were obtained (R(+CT) group). Yearly RD was 4.3 uSv for WBCT group and 5.0 uSv for R(+CT) group (difference 0.6 uSv decrease with WBCT 13%, p

Category: Hindfoot Introduction/Purpose: Hindfoot and knee coronal alignments have shown to be related in previous literature suggesting that there might be some degree of compensation between the two. However, previous studies have focused on the effects of knee surgery on hindfoot alignment, not on the preoperative relationship. Recent 3D weight bearing imaging technology may help to investigate this. The objective of this study was to analyse the preoperative relationships between knee and hindfoot coronal alignments using bilateral weight bearing CT (WBCT) and biplanar low dose radiography (BLDR). We hypothesized that hindfoot valgus and varus respectively compensates knee varus and valgus. Methods: Relevant ethical approval was obtained for this retrospective comparative level 3 study including 124 limbs in 62 patients (32 female, 30 male), mean age 56 (23-84). Mean BMI was 27 (20-38). Cases included had been referred continuously according to diagnostic protocols in our institution, for a combined WBCT and BLDR investigation. Age, gender and BMI were recorded. Cases with a history of trauma or surgery, which may have caused a change in lower limb alignment, were excluded. Hindfoot alignment was measured using a semi automatic software (TALAS, Curvebeam, Warrington PA, USA) and given as Foot Ankle Offset (FAO). Knee alignment was measured using the EOS platform (EOS Imaging, Paris, France) and given as HKA. Distribution and demographics of hindfoot alignment in the varus and valgus knee groups were studied. Correlations were investigated using linear regression and Bland and Altman plots. Results: Incidence of Varus hindfeet was 15.8% in the Valgus knee group and 25.5% in the Varus knee group but the difference was not significant (p=0.82). Bland and Altman plots did not yield any additional result. No linear correlation was found between hindfoot and knee coronal alignments in the study population. Conclusion: Our results do not confirm prior findings regarding compensatory valgus in varus knees, and do not confirm the hypothesis according to which linear compensatory mechanisms may relate knee and hindfoot alignments. In practice, these results suggest that in cases where knee and hindfoot misalignments are associated, the causes for each should be analyzed independently before any assumption is made as to hypothetical interactions. Furthermore, subsequent studies are warranted to investigate whether other kinds of non-linear correlations way be found in selected populations.

Category: Ankle Introduction/Purpose: Syndesmotic lesions of the ankle have shown to be challenging injuries towards diagnosis and surgical treatment. This could be mainly attributed to the limitations of 2D imaging, which make it difficult to accurately determine the extent of the lesion and to verify if peroperatively an anatomical reduction is achieved of the distal tibiofibular congruence. The aim of this study is therefore to develop a reproducible method to quantify the displacement in a syndesmotic ankle lesion in all six degrees of freedom based on 3D imaging. Methods: Eighteen patients were retrospectively included having a unilateral syndesmotic lesion. N=12 sustained a high ankle sprain and a bilateral weightbearing conebeam CT was obtained because of positive clinical syndesmotic tests. N=6 presented with a fracture associated syndesmotic lesion and were imaged by a bilateral non-weightbearing CT. The non-affected ankle was used as a template after being mirrored and matched on the contralateral ankle containing a syndesmotic lesion (Fig 1A-B). The distal fibula was marked by computer calculation of the most outer point of the anterior tubercle, posterior tubercle and apex malleolis lateralis. The change of these points towards the unaffected fibular position was used to quantify the syndesmotic lesion (Fig 1C). A control group of seven patients (N=7) was used to analyse if these changes differed from the normal variation in tibio-fibular congruency (Fig 1D). Results: The main findings consisted of a statistical significant difference in the mean mediolateral diastasis of both the sprained group (M = 1.60 mm, SD=1.02) and the fracture group (M = 1.69 mm, SD=0.62) compared to the control group (P