Influence of ankle joint position on angles and distances of the ankle mortise using intraoperative cone beam CT: A cadaveric study

Validity of the Center-Center Method for the Syndesmotic Fixation Axis Compared to the Transsyndesmotic Axis

BACKGROUND

Placement of clamp forceps along the transsyndesmotic (TS) axis reduces the risk of iatrogenic syndesmotic malreduction during ankle fracture surgery with tibiofibular diastasis. This study aimed to measure the difference between the TS axis and the axis determined by an intraoperative fluoroscopic technique using the center-center (CC) method. We also compared the values obtained when the CC method was performed at different heights from the tibial plafond.

METHODS

We evaluated the computed tomography scans of 150 patients with normal syndesmosis. The CC method was simulated using digitally reconstructed radiographs. The TS and CC axes were projected onto an axial computed tomographic image linked to digitally reconstructed radiography. The angle between the two axes (interaxis angle) and the distance between the intersection of these axes and the medial tibial cortex (interaxis distance) were measured. The procedures were performed 0, 10, and 20 mm proximal to the tibial plafond, and the measurements were compared among the different heights using a 1-way repeated-measures analysis of variance.

RESULTS

The TS axis was found to be externally rotated to the CC axis, with an interaxis angle of 8.5 degrees (SD, 6.8 degrees). The interaxis angle increased from 1.9 degrees at a height of 0 mm to a greater angle at higher heights (P < .001). The overall interaxis distance was 7.7 (SD, 6.3) mm, increasing from 2.0 mm at a height of 0 mm to a greater distance at higher heights (P < .001).

CONCLUSION

The TS axis was externally rotated relative to the CC axis, and the difference between the 2 axes was greater when the CC method was performed on the higher heights from the tibial plafond. To clamp the syndesmosis along the TS axis, the CC method should be applied close to the ankle joint.

LEVEL OF EVIDENCE

Level IV, case series.

Detection of fibular rotational changes in cone beam CT: experimental study in a specimen model

Background

In syndesmotic injuries, incorrect reduction leads to early arthrosis of the ankle joint. Being able to analyze the reduction result is therefore crucial for obtaining an anatomical reduction. Several studies that assess fibular rotation in the incisura have already been published. The aim of the study was to validate measurement methods that use cone beam computed tomography imaging to detect rotational malpositions of the fibula in a standardized specimen model.

Methods

An artificial Maisonneuve injury was created on 16 pairs of fresh-frozen lower legs. Using a stable instrument, rotational malpositions of 5, 10, and 15° internal and external rotation were generated. For each malposition of the fibula, a cone beam computed tomography scan was performed. Subsequently, the malpositions were measured and statistically evaluated with t-tests using two measuring methods: angle (γ) at 10 mm proximal to the tibial joint line and the angle (δ) at 6 mm distal to the talar joint line.

Results

Rotational malpositions of ≥ 10° could be reliably displayed in the 3D images using the measuring method with angle δ. For angle γ significant results could only be displayed for an external rotation malposition of 15°.

Conclusions

Clinically relevant rotational malpositions of the fibula in comparison with an uninjured contralateral side can be reliably detected using intraoperative 3D imaging with a C-arm cone beam computed tomography. This may allow surgeons to achieve better reduction of fibular malpositions in the incisura tibiofibularis.

Are SER-II Ankle Fractures Anatomic? Computed Tomography Demonstrates Mortise Malalignment in the Setting of Apparently Normal Radiographs

BACKGROUND

Ankle fracture treatment is predicated on minimal displacement, leading to abnormal joint contact area. The purpose of this investigation is to determine whether computed tomography (CT) detects subtle mortise malalignment undetectable by x-ray in supination-external rotation-II (SER-II) injuries.

METHODS

A total of 24 patients with SER-II injuries, as demonstrated by negative gravity stress radiography, were included. Medial clear space (MCS) measurements were performed on bilateral ankle x-rays (injured and contralateral, uninjured side) at several time points as well as bilateral non-weight-bearing CT performed once clinical and radiographic healing was demonstrated (mean = 66 days post injury, range = 61-105 days). Statistical analyses examined differences in measurements between both sides.

RESULTS

Final x-rays demonstrated no differences between normal and injured ankle MCS (P = .441). However, CT coronal/axial MCS measurements were different (P < .05). CT coronal MCS measured wider by a mean difference of 0.67 mm (P < .001).

CONCLUSION

There is a high incidence of subtle mortise malalignment in SER-II ankle fractures, as demonstrated by CT, which is undetectable when assessed by plain radiographs. Although clinical outcomes are yet unknown, there are important implications of the finding of confirmed, subtle mortise malalignment in SER-II injuries and the limitations of x-ray to detect it.

LEVEL OF EVIDENCE

Level III.

Computer-assisted contralateral side comparison of the ankle joint using flat panel technology

PURPOSE

Reduction and osteosynthesis of ankle fractures is a challenging surgical procedure when it comes to the verification of the reduction result. Evaluation is conducted using intra-operative imaging of the injured ankle and depends on the expertise of the surgeon. Studies suggest that intra-individual variance of the ankle bone shape and pose is considerably lower than the inter-individual variance. It stands to reason that the information gain from the healthy contralateral side can help to improve the evaluation.

METHOD

In this paper, an assistance system is proposed that provides a side-to-side view of the two ankle joints for visual comparison and instant evaluation using only one 3D C-arm image. Two convolutional neural networks (CNN) are employed to extract the relevant image regions and pose information of each ankle so that they can be aligned with each other. A first U-Net uses a sliding window to predict the location of each ankle. The standard plane estimation is formulated as segmentation problem so that a second U-Net predicts the three viewing planes for alignment.

RESULTS

Experiments were conducted to assess the accuracy of the individual steps on 218 unilateral ankle datasets as well as the overall performance on 7 bilateral ankle datasets. The experiments on unilateral ankles yield a median position-to-plane error of [Formula: see text] mm and a median angular error between 2.98[Formula: see text] and 3.71[Formula: see text] for the plane normals.

CONCLUSION

Standard plane estimation via segmentation outperforms direct pose regression. Furthermore, the complete pipeline was evaluated including ankle detection and subsequent plane estimation on bilateral datasets. The proposed pipeline enables a direct contralateral side comparison without additional radiation. This has the potential to ease and improve the intra-operative evaluation for the surgeons in the future and reduce the need for revision surgery.

Validation of radiological reduction criteria with intraoperative cone beam CT in unstable syndesmotic injuries

Purpose

Acute unstable syndesmotic lesions are regularly treated with closed or open reduction and fixation with either a positioning screw or tight rope. Conventional fluoroscopy is limited to identify a malreduction of the ankle mortise. The aim of the study was to validate the reduction criteria of intraoperative cone beam CT in unstable syndesmotic injuries by analyzing the clinical outcome.

Methods

Acute unstable syndesmotic injuries were treated with a positioning screw fixation, and the reduction in the ankle mortise was evaluated with intraoperative cone beam CT. The patients were grouped postoperatively according to the radiological reduction criteria in the intraoperative 3D images. The reduction criteria were unknown to the surgeons. Malreduction was assumed if one or more reduction criteria were not fulfilled.

Results

Seventy-three of the 127 patients could be included in the study (follow-up rate 57.5%). For 41 patients (56.2%), a radiological optimal reduction was achieved (Group 1), and in 32 patients (43.8%) a radiological adverse reduction was found (Group 2). Group 1 scored significantly higher in the Olerud/Molander score (92.44 ± 10.73 vs. 65.47 ± 28.77) (p = 0.003), revealed a significantly higher range of motion (ROM) (53.44 vs. 24.17°) (p = 0.001) and a significantly reduced Kellgren/Lawrence osteoarthritis score (1.24 vs. 1.79) (p = 0.029). The linear regression analysis revealed a correlation for the two groups with the values scored in the Olerud/Molander score (p < 0.01).

Conclusion

The reduction criteria in intraoperative cone beam CT applied to unstable syndesmotic injuries could be validated. Patients with an anatomic reduced acute unstable syndesmotic injury according to the criteria have a significantly better clinical outcome.

Influence of syndesmotic injuries and posterior malleolar ankle fractures on fibula position in the ankle joint: a cadaveric study

PURPOSE

The aim of this study was to identify to what extent a dissection of the syndesmosis and an avulsed posterior edge of the tibia can change the tibiofibular diastasis and fibular rotation.

METHODS

Three-dimensional scans with a mobile C-arm of 22 cadaver legs were taken of the intact fibula, after dissection of the anterior part of the syndesmosis and the interosseous membrane, osteotomy of the posterior malleolus, and osteosynthesis. The tibiofibular diastasis as well as the angle of fibular rotation was identified in the four steps and the means compared to each other using a t test for paired samples.

RESULTS

The distinction between the intact fibula vs. the osteotomy of the posterior tibia was 0.082 ± 0.332 mm for the tibiofibular distance in the incisura tibiofibularis (p 0.261) and 0.046 ± 0.486 degrees for the angle of the fibular rotation (p 0.665).

CONCLUSION

Neither the dissection of the syndesmosis nor the osteotomy of the posterior malleolus significantly influenced the position of the fibula in the incisura tibiofibularis in the cadaveric model. However, in the nonweight-bearing situation, a lesion of the syndesmotic complex might not be evident in intraoperative three-dimensional imaging.