Long bone fracture reduction and deformity correction using the hexapod external fixator with a new method: a feasible study and preliminary results

The Clinical Application of Double Taylor Spatial Frame in Segmental Tibial Fracture

OBJECTIVES

Multi-planar external fixation has been used for the management of segmental tibial fractures with severe soft tissue injuries. However, fewer specialized studies have been reported. The primary aim of this study was to describe our experience of treating fractures of this type using the Taylor Spatial Frame and Ilizarov external fixation methods.

METHODS

We retrospectively analyzed 33 patients with segmental tibial fracture treated at our institution between January 2016 and December 2020. The patients were divided into double Taylor Spatial Frame (D-TSF) and Ilizarov groups based on the external fixation structure. Baseline demographic data included sex, age, injury side and cause, open or closed fracture, time from injury to surgery, complications, and external frame removal and fracture healing time. The hip-knee-ankle angle (HKA) was measured from preoperative, immediate postoperative, and final follow-up full-length X-rays of bilateral lower limbs. We determined the degree of deviation in the HKA by calculating the difference between the measured angle and the ideal value of 180°; the absolute value was used to assess recovery of the lower limb force line. At the final follow-up, Johner-Wruhs tibial fracture outcome criteria (J-W TFOC) were used to classify the postoperative function of the affected limb as excellent, good, moderate, or poor. Count data were analyzed with the chi-square test or Fisher's exact test; the Mann-Whitney U test was used for rank data.

RESULTS

No statistically significant differences were observed between the two groups in terms of sex, age, side of injury, cause of injury, closed or open fracture, or time between injury and surgery, which indicates that the groups were comparable (p > 0.05). A statistically significant difference was observed in external frame removal and fracture healing time between the D-TSF and Ilizarov groups (36.24 ± 8.34 vs 45.42 ± 10.21 weeks, p = 0.009; 33.33 ± 8.21 vs 42.00 ± 9.78 weeks, p = 0.011). The Johner-Wruhs criteria were used to assess the function of the affected limb, the D-TSF group performed better in correcting the lower limb force line than the Ilizarov group. A statistically significant difference in terms of excellent ratings was observed between the two groups (18/2/1/0 vs 5/5/1/1, p = 0.010). Postoperative follow-up X-rays demonstrated a significant improvement in the HKA in both groups immediately after surgery and at the final follow-up compared to the angle before surgery. At the final follow-up, a statistically significant difference was observed in the degree of deviation in the HKA between the two groups (1.58° ± 0.84° vs 2.37° ± 1.00°, p = 0.023).

CONCLUSION

The D-TSF treatment is associated with minimal secondary damage to soft tissue, a straightforward and minimally invasive procedure, multiplanar stable fracture fixation, and optimization of fracture alignment and lower limb force lines, therefore, it is highly effective therapeutic option for segmental tibial fracture.

Accuracy of the hexapod external fixator in treating tibial angular deformities with or without limb length discrepancy: a retrospective study

OBJECTIVE

Hexapod external fixator systems allow simultaneous deformity correction in multiple planes as well as limb lengthening. The aim of this study is to evaluate the accuracy of a hexapod frame (smart correction frame) in different types of tibial deformities requiring correction with or without lengthening.

METHODS

A total of 54 tibial angular deformities and limb length discrepancies operated with a hexapod frame between January 2015 and January 2021 were classified into four groups: "Group A ( n  = 13): only lengthening," "Group B ( n  = 14): lengthening and uniplanar correction," "Group C ( n  = 16): only uniplanar correction," and "Group D ( n  = 11): biplanar correction." The accuracy of angular deformity correction/lengthening was calculated by dividing the actual correction/lengthening achieved after frame removal by the preoperative planned lengthening/correction.

RESULTS

The lengthening accuracy in Group A and Group B was 96.3 ± 7.1% and 95.7 ± 5.9%, respectively ( P  = 0.685). The angular deformity correction accuracy was 85.1 ± 9.9% for Group B, 85.2 ± 13.9% for Group C, and 80.2 ± 18.4% for Group D ( P  = 0.852). A revision program was performed in six cases (1 in Group B, 1 in Group C, and 4 in Group D) for full correction of the deformities.

CONCLUSION

The accuracy of tibial lengthening is high with the hexapod frame and is minimally affected by simultaneous deformity correction; however, the accuracy of angular correction slightly reduces as the deformity becomes more complex. Surgeons should be aware that reprogramming may be required after complex deformity correction.

Robot-patient registration for optical tracker-free robotic fracture reduction surgery

BACKGROUND AND OBJECTIVE

Image-guided robotic surgery for fracture reduction is a medical procedure in which surgeons control a surgical robot to align the fractured bones by using a navigation system that shows the rotation and distance of bone movement. In such robotic surgeries, it is necessary to estimate the relationship between the robot and patient (bone), a task known as robot-patient registration, to realize the navigation. Through the registration, a fracture state in real-world can be simulated in virtual space of the navigation system.

METHODS

This paper proposes an approach to realize robot-patient registration for an optical-tracker-free robotic fracture-reduction system. Instead of the optical tracker which is a three-dimensional position localizer, X-ray images are used to realize the robot-patient registration, combining the relationship of both the robot and patient with regards to C-arm. The proposed method consists of two steps of registration, where initial registration is followed by refined registration which adopts particle swarm optimization with the minimum cross-reprojection error based on bidirectional X-ray images. To address the unrecognizable features due to interference between the robot and bone, we also developed attachable robot features. The allocated robot features could be clearly extracted from the X-ray images, and precise registration could be realized through the particle swarm optimization.

RESULTS

The proposed method was evaluated in phantom and ex-vivo experiments involving a caprine cadaver. For the phantom experiments, the average translational and rotational errors were 1.88 mm and 2.45°, respectively, and the corresponding errors in the ex vivo experiments were 2.64 mm and 3.32° The results demonstrated the effectiveness of the proposed robot-patient registration.

CONCLUSIONS

The proposed method enable to estimate the three-dimensional relationship between fractured bones in real-world by using only two-dimensional images, and the relationship is accurately simulated in virtual reality for the navigation. Therefore, a reduction procedure for successful treatment of bone fractures in image-guided robotic surgery can be expected with the aid of the proposed registration method.