Computer-assisted percutaneous scaphoid fixation: concepts and evolution

Ultrasound-Based Registration for the Computer-Assisted Navigated Percutaneous Scaphoid Fixation

An ultrasound (US)-based computer-assisted approach has the potential to improve the accuracy and precision of screw placement for the percutaneous fixation of scaphoid fractures and also reduce the radiation dose for patient and clinical staff. Therefore, a surgical plan based on preoperative diagnostic computed tomography (CT) is registered with intraoperative US images, enabling a navigated percutaneous fracture fixation. However, approaches published so far rely on semimanual methods for intraoperative registration and are limited by long computation times. To address these challenges, we propose the employment of deep learning-based methods for US segmentation and registration in order to achieve a fast and fully automated yet robust registration process. For validation of the proposed US-based approach, we first provide a comparison of methods for segmentation and registration, assess their contribution to the overall error throughout our pipeline, and, finally, evaluate navigated screw placement in an in vitro study on 3-D printed carpal phantoms. Successful screw placement has been achieved for all ten screws, with deviations from the planned axis of 1.0 ± 0.6 and 0.7 ± 0.3 mm at the distal and proximal pole, respectively. The complete automation and total duration of about 12 s also allow seamless integration of our approach into the surgical workflow.

Three-Dimensional Printed Targeting Device for Scaphoid Fracture Fixation

Background: Percutaneous guide wire insertion for scaphoid screw fixation can be challenging and often requires multiple attempts with significant radiation exposure to the surgical team. A 3-dimensional (3D) printed targeting device has the potential to reduce procedure time and intraoperative radiation exposure. Methods: Our targeting device protocol included a preprocedure computed tomography (CT) scan of a casted cadaver wrist, followed by 3D printing of a customized targeting guide. In a comparison trial, seven orthopedic surgery residents performed percutaneous scaphoid guide wire insertion on different cadaver specimens by both freehand technique and using our targeting device. Radiation exposure and procedure times were compared. All specimens underwent postprocedure CT to assess Kirschner wire (K-wire) accuracy, determined by central third placement. Pre- and postprocedure CT scans from the targeting device group were co-registered to compare planned and actual K-wire trajectories. Results: Using the freehand technique, mean fluoroscopy time was 120 seconds (standard deviation: ±53 seconds) generating 2.45 milligray of radiation. Average procedure time was 21 minutes with a mean of 6.4 (range: 3-9) insertion attempts. A single insertion attempt was made using the targeting device with an average procedure time of 30 seconds and no fluoroscopy exposure. Four K-wires were placed within the central scaphoid in both groups. Using the targeting device, average linear deviation from the planned trajectory was 2.1 mm, while the maximum linear deviation was 3.75 mm. Conclusion: When compared to freehand scaphoid guide wire insertion, our targeting device provides similar accuracy while significantly reducing intraoperative radiation exposure and procedure time.

Computer-assisted Surgery for Scaphoid Fracture

The computer-assisted surgery (CAS) has significantly improved the accuracy, reliability and outcomes of traumatic, spinal, nerve surgery and many other operations with a less invasive way. The application of CAS for scaphoid fractures remains experimental. The related studies are scanty and most of them are cadaver researches. Some intrinsic defects from the registration procedure, scan and immobilization of limbs may inevitably result in deviations. Some deviations become more obvious with operations of small bones (such as scaphoid) although they are acceptable for spine and other orthopedic surgeries. We reviewed the current literatures on the applications of CAS for scaphoid operation and summarized technical principles, scan and registration methods, immobilization of limbs and their outcomes. On the basis of the data, we analyzed the limitations of this technique and envisioned its future development.

Scaphoid screw fixation perpendicular to the fracture plane: Comparing volar and dorsal approaches

INTRODUCTION

To percutaneously fixate a midwaist scaphoid fracture, both volar and dorsal approaches are considered valid options although they may have different screw insertion angles relative to the scaphoid fracture plane influencing fixation stability. In this virtual simulation study, we investigated the accessibility of placing a screw perpendicularly to the fracture plane in transverse and horizontal oblique scaphoid midwaist fracture models and compared standard volar and dorsal approaches.

MATERIAL AND METHODS

Computed tomography scans of 38 healthy wrists were used to obtain virtual 3-dimensional wrist models in flexion and extension. In case the trapezium in volar approach or the distal radius in dorsal approach obstructed the screw axis perpendicular to the fracture plane, an alternative non-obstructed screw axis was chosen as close as possible to the perpendicular axis. The deviation angle between the best possible non-obstructed screw placement and true perpendicular screw placement was quantified.

RESULTS

For transverse fractures, the average deviation angle (±standard deviation) was 8° (±5°) in volar approach, and 0° (±0°) in dorsal approach. For horizontal oblique fractures, these angles were 40° (±6°) and 14° (±8°), respectively.

DISCUSSION

In our simulations, compared to the volar approach, the dorsal approach provided the most precise screw placement perpendicular to the fracture plane, with the largest differences for horizontal oblique fractures. When taken in addition to screw purchase, thread engagement and protrusion risk, information about screw orientation may help surgeons in deciding between percutaneous approaches in scaphoid surgery on which there is currently no consensus.

LEVEL OF EVIDENCE

N/A.

Scaphoid screw placement under minimal radiation exposure

BACKGROUND

Percutaneous scaphoid fixation through either a volar or dorsal approach has the advantage of minor soft tissue damage compared with ORIF, and faster fracture union compared with conservative treatment. However, this technique demands highly intraoperative reliance on X-ray control, including increased radiation exposure and all associated side effects.

PURPOSE

To test the possibility and efficacy of volar percutaneous scaphoid screw placement under minimalradiation exposure.

METHODS

The sample included 20 hands (seven left, 13 right) from human adult cadavers. For this study, the utilised wrists were assumed to have non-displaced scaphoid fractures. Using a percutaneous approach, a 2-mm Kirschner wire (K-wire) was advanced to the distal pole of the scaphoid and placed in a 45° horizontal and vertical angle under monitoring with the C-arm. The K-wire was inserted blindly alongside the estimated length of the scaphoid. Following K-wire insertion, four X-rays were taken to depict K-wire positioning and to assess positioning alongside the axis of the scaphoid and K-wire protrusion. The rating scale comprised 1 (good), 2 (moderate) or 3 (poor).

RESULTS

All tested radiographic views were evaluated with a median of 2 points (moderate position) regardingplacement alongside the scaphoid axis.

CONCLUSION

Our results indicate that percutaneous scaphoid fixation with the guide wire placed in a 45° horizontal and vertical angle enables primary moderate positioning, which may lead to quicker adjustment to the ideal position and a decrease of radiation exposure.

Percutaneous Screw Fixation for Scaphoid Fractures

Treatment of nondisplaced scaphoid waist fractures has evolved from conventional cast immobilization to percutaneous screw insertion. This study assessed clinical and radiologic outcomes of volar percutaneous screw fixation for 15 type B2 scaphoid fractures (according to the Herbert and Fisher classification). All patients were followed for an average of 33 months (range, 6-50 months). All fractures achieved radiographic union at an average of 57 days (range, 35-70 days), requiring no additional procedures. None of the patients showed radiographic signs of osteoarthritis, osteonecrosis of the scaphoid, or hardware-related complications. For scaphoid waist fractures without collapse, percutaneous screw fixation provided satisfactory results with a high rate of union, early return of function, and minimal complications. [Orthopedics. 2017; 40(4):e729-e734.].

Operative Treatment of Acute Scaphoid Fractures

Optimal treatment of acute scaphoid fractures is a necessary goal for many reasons. One is that the scaphoid is the most commonly fractured carpal bone. Another is that a missed diagnosis of an acute scaphoid fracture leads to the more challenging situation of a delayed union, non-union and risk for premature radiocarpal arthrosis. Because the scaphoid has an inherent risk for nonunion due to its the tenuous blood supply, timely diagnosis and appropriate treatment are considered critical to achieving acceptable results and to avoiding the consequences of failed union.

Intraoperative 3-dimensional imaging of scaphoid fracture reduction and fixation

INTRODUCTION

We examined the clinical benefit of two intraoperative three-dimensional imaging modalities for reduction and fixation of scaphoid fractures.

HYPOTHESIS

Our hypothesis was that three dimensional imaging will aid in operative care in comparison with standard fluoroscopy.

METHODS

In 25 consecutive patients treated for fractures, after satisfactory reduction and fixation was obtained with a single Kirschner wire using fluoroscopy, intraoperative three-dimensional visualization was performed. The quality of fracture reduction, wire position and extrusion of the wire were examined.

RESULTS

In two of the 25 cases, after three-dimensional visualization, malreduction of the fracture was seen and the reduction revised. Artifact and the dependency on technologist performance, limited the use of these modalities to locate the wire accurately.

DISCUSSION

Diagnosis of malreduction of a scaphoid fracture is possible with 3-dimensional modalities. Utilization of these systems is still limited by technical factors.