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Closed fracture reduction can be a challenging task. Robot-assisted reduction of the femur is a newly developed technique that could minimize potential complications and pitfalls associated with fracture reduction and fixation. We conducted an experimental study using 11 human cadaver femora with intact soft tissues. We compared robot-assisted fracture reduction using 3D visualization with manual reduction, using 2D fluoroscopy. The main outcome measure was the accuracy of reduction. The manual reductions were done by an experienced orthopedic trauma surgeon, whereas the robot-assisted reductions were done by surgeons of different experience. The robot-assisted group showed significantly less postreduction malalignment (p < 0.05) for internal/external rotation (2.9° vs. 8.4°) and for varus/valgus alignment (1.1° vs. 2.5°). However, the reduction time was significantly (p < 0.01) longer (6:14 min vs. 2:16 min). The higher precision associated with robot-assisted fracture reduction makes this technique attractive and further research and development worthwhile. In particular, less experienced surgeons may benefit from this new technique. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1240–1244, 2010
Closed reduction and minimally invasive stabilization techniques help preserve the biologic environment of fractures, leading to enhanced union rates and decreased infection rates.1–4 However, closed reduction can be technically demanding. Three main problems exist: (1) manipulation of the fragments without exposing the fracture site; (2) assessment of the correct reduction; and (3) temporary stabilization.5, 6 These problems are especially evident in femoral shaft fractures. The thick muscle envelope leads to high counteracting forces and torques, and the central position of the shaft makes direct manipulation of the fragments difficult.7–9 In addition, 2D fluoroscopy provides suboptimal radiographic visualization with regards to the precision of reduction, particularly considering the tubular shape of the femoral shaft. Even intramedullary nails, which can be used as self-aligning implants, cause malalignment, especially rotationally.4, 10–13
New devices and techniques have recently been developed to support fracture reduction. From devices like the AO femoral distractor, development has lead to the implementation of navigation systems to aid the surgeon, for example, by enhanced visualization.7, 14–21 But navigation does not solve the precise manipulation of the bone fragments and their retention in the reduced position until fitting the fracture fixation device. A robot application may be expedient.
The implementation of a robotic system into the process of fracture reduction meets two challenges. It facilitates the assessment of the fracture by intelligent and interactive visualization and enables intuitive fracture manipulation. Further, the robots' ability of rigid fracture retention after reduction coincides with temporary fixation.
The idea of robot-assisted fracture reduction was first described in 1995 by Bouazza-Marouf et al.22 Ten years later the first experiments using synthetic composite bones were presented23 demonstrating robot-assisted fracture reduction to be highly accurate and to require less radiation. A subsequent study on human cadavers showed a decreased radiation time. Nevertheless the reduction accuracy could not be improved significantly compared to the manual reduction.24 Reduction control in the first study was facilitated by two orthogonal cameras, whereas in the second study a 2D image intensifier was used. These findings demonstrated that visualization is a crucial factor in achieving accurate results. Since the cameras only showed a surface image of the fragments, we postulate that a significant improvement of the final fracture alignment by 3D fragment visualization is one element of the robotic setup. Further setup elements like the ability of rigid retention and the feedback of forces at the fracture site contribute to this improvement.
The purpose of our study was to compare manual fracture reduction using 2D fluoroscopy with robot-assisted reduction using 3D fracture visualization software. The focus of imaging was on the fracture site. Because of the limited scanning volume (12 × 12 cm2) of intraoperative 3D fluoroscopy, it was impossible to represent the entire femur. A recent publication emphasized the importance of natural forms of human communication in a human/machine interface, described as “AHMI—Advanced Human Machine Interface.”25 To meet one of the demands of natural human environmental perception, we chose to implement an interactive 3D surface model.
The revolutionary aspect of this method is that a (limited) virtual direct view of the fracture site is used to align the entire femur, disregarding the proximal and distal aspects of the bone. This contrasts with the conventional method, paying less attention to the fracture site rather than to axes, length, and rotation of the femur. We hypothesized that robot-assisted fracture reduction with 3D visualization would be more accurate and faster than the conventional method and that a homogenous result among the operating surgeons would be achieved.
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This study had several limitations. We chose cadavers embalmed in formalin because of their availability and logistic advantages. Nonembalmed cadavers or living patients might show different characteristics during reduction. However, thus far no study has compared the reduction of differently fixed cadavers or living patients. In our study, the trauma surgeon rated the reduction in the cadavers somewhat easier than reduction of femoral shaft fractures in patients. Only type A and B fractures were presented in this study. Type C fractures, in which no contact between the proximal and distal segments exists, might not profit from 3D visualization. Only one surgeon performed the manual reduction, whereas four different surgeons performed the robotic-assisted reduction. However, we do not expect a more accurate manual fracture reduction, considering data from clinical studies.10, 11, 13
The reduction time in the robot-assisted group was much longer than expected. Although all reductions were successfully performed, the load limit (a recommended nominal load of 60 N and a maximum load of 110 N) of the robot was frequently outrun. When this maximum load was reached, evasive action was necessary to lower the counteracting forces and proceed with reduction; this was the main time-consuming step. Increasing the maximal load capacity would have put the bone, soft-tissues, and the equipment at a higher risk of damage. Measurements of intraoperative forces during fracture reduction showed peak values of >400 N,8 almost four times the load capacity of our robot. Graham et al.,28 using simulation software to represent the complex biological system of bone–muscle interaction of the fractured femur, found forces that rose up to 428 N in a midshaft-fracture, equivalent to in vivo measurements.
The robotic reduction was slower, but more accurate than manual reduction. The above-mentioned study8 did not measure the minimum forces necessary to reduce the fracture, but rather the peak forces that occurred during successful reduction. A principal objective of a robotic application is to obtain low peak forces, almost at the level of the minimal forces during the entire reduction process. Reduced peak forces and precise movements might lower iatrogenic soft-tissue trauma reached by intelligent reduction paths with respect to the anatomical and biomechanical attributes of the soft-tissue envelope. The robot-controlling computer in our setup displayed the forces in a real-time bar diagram, so the surgeon could continuously reevaluate his strategy of reduction and find the ideal path.
The use of a 3D fluoroscope is controversial. We integrated it into the experiment to generate a surface-visualized virtual model, which then could be manipulated intuitively. To enhance the man–machine interface and to obtain the most information from a limited scanning range of ∼12 cm3 at the fracture site, a 3D visualization was implemented.
Robot-assisted fracture reduction is a new topic in orthopedic trauma care. Thus far, only experimental studies by a few groups have been published.23–25, 28–32 Improved precision of reduction is the most discussed objective. Although precision was significantly improved with the robot, malalignment after manual reduction was more than satisfactory. Clinical studies showed higher values of malalignment than those found in our study.7, 14, 16, 33 All of the manual reductions were performed by an experienced trauma surgeon, whereas all robot-assisted fracture reductions were done by surgeons of lesser experience. Experienced surgeons may not profit as much as younger or inexperienced surgeons from robot-assisted reduction. We can also speculate that the younger surgeons are more acquainted with 3D computer animations and telemanipulators and that their acceptance of such new technologies might be higher.
Several critical points need to be addressed prior to practical implementation of robot-assisted fracture reduction. Patient safety remains the first priority. As mentioned above, higher maximum robotic loads increase the risk of damage to bone and soft-tissues. We used a software controlled load cell. In case of software problems the pneumatic safeguard stopped the controller whenever the critical force (i.e., torque) was exceeded.
Ergonomic considerations are important. Placing a device like a serial robot into an OR results in loss of space. Either the system can be setup in a large enough operating theatre or compromises must be made. In particular, keeping sterility is a requirement. The robotic system developed by Graham et al. uses a parallel robotic configuration. The payload to weight (and size) ratio of a parallel system is higher than that of a serial system, which is advantageous considering ergonomics and sterility.25
Financial aspects must also be considered. To avoid increasing time in the operating room, the duration of setup and reduction must be about the same as with conventional procedures. Purchasing and maintenance costs of the robotic system must be weighed against the benefit of increased precision and therefore potentially fewer revision surgeries. Also, the presence of an assistant surgeon might not be necessary when using a robot. Nevertheless, it might be economically unreasonable for hospitals to purchase a robot system exclusively for the reduction of shaft fractures.
Robot-assisted reduction is a new attempt to improve the precision of postreduction alignment. The precision is significantly higher compared to the conventional technique. Before this technique can be applied to patient care, however, further research is necessary, especially on its applicability and safety issues. However, the increased accuracy of fracture reduction makes this new robotic reduction technique an attractive, especially to less experienced surgeons.