Fast, robust, and accurate monocular peer-to-peer tracking for surgical navigation.

PURPOSE: This work presents a new monocular peer-to-peer tracking concept overcoming the distinction between tracking tools and tracked tools for optical navigation systems. A marker model concept based on marker triplets combined with a fast and robust algorithm for assigning image feature points to the corresponding markers of the tracker is introduced. Also included is a new and fast algorithm for pose estimation. METHODS: A peer-to-peer tracker consists of seven markers, which can be tracked by other peers, and one camera which is used to track the position and orientation of other peers. The special marker layout enables a fast and robust algorithm for assigning image feature points to the correct markers. The iterative pose estimation algorithm is based on point-to-line matching with Lagrange-Newton optimization and does not rely on initial guesses. Uniformly distributed quaternions in 4D (the vertices of a hexacosichora) are used as starting points and always provide the global minimum. RESULTS: Experiments have shown that the marker assignment algorithm robustly assigns image feature points to the correct markers even under challenging conditions. The pose estimation algorithm works fast, robustly and always finds the correct pose of the trackers. Image processing, marker assignment, and pose estimation for two trackers are handled in less than 18 ms on an Intel i7-6700 desktop computer at 3.4 GHz. CONCLUSION: The new peer-to-peer tracking concept is a valuable approach to a decentralized navigation system that offers more freedom in the operating room while providing accurate, fast, and robust results.

Computer aided planning of orthopaedic surgeries: the definition of generic planning steps for bone removal procedures.

PURPOSE: An increasing number of orthopaedic surgeons are using computer aided planning tools for bone removal applications. The aim of the study was to consolidate a set of generic functions to be used for a 3D computer assisted planning or simulation. METHODS: A limited subset of 30 surgical procedures was analyzed and verified in 243 surgical procedures of a surgical atlas. Fourteen generic functions to be used in 3D computer assisted planning and simulations were extracted. RESULTS: Our results showed that the average procedure comprises 14 ± 10 (SD) steps with ten different generic planning steps and four generic bone removal steps. CONCLUSIONS: In conclusion, the study shows that with a limited number of 14 planning functions it is possible to perform 243 surgical procedures out of Campbell's Operative Orthopedics atlas. The results may be used as a basis for versatile generic intraoperative planning software.

How deep can straight instruments be inserted into the femoral canal: a simulation study based on cadaveric femora.

Determining how deep instruments can be inserted into the femoral canal without touching adjacent structures is a fundamental necessity for navigating instruments in primary and revision total hip arthroplasty. The aim of the study was to determine the reachable depth of a straight instrument inserted into the femur canal during primary and revision total hip arthroplasty. Based on the three-dimensional data of twenty-six femurs, obtained from a CT scan, the insertion depth of a virtual, straight instrument was accessed by a simulation. The effect of the diameter of the virtual instrument and the extension of the osteotomy were evaluated. Without extending the osteotomy, 100% of the femoral canal was reachable to a depth of 5.1-6.3 cm for instruments with a diameter of 10 mm. The depth was measured from the lower edge of the osteotomy. A maximum lateral extension of the osteotomy by 1 cm enlarges the access to a depth of 8.8 cm. The results provide a theoretical basis for the limitations of guiding instruments used for the preparation of the femoral canal. Bone preserving methods need the development of angulated instruments to reach deep areas in the femoral canal.

The use of time-of-flight camera for navigating robots in computer-aided surgery: monitoring the soft tissue envelope of minimally invasive hip approach in a cadaver study.

BACKGROUND: Time-of-flight (TOF) cameras can guide surgical robots or provide soft tissue information for augmented reality in the medical field. In this study, a method to automatically track the soft tissue envelope of a minimally invasive hip approach in a cadaver study is described. METHODS: An algorithm for the TOF camera was developed and 30 measurements on 8 surgical situs (direct anterior approach) were carried out. The results were compared to a manual measurement of the soft tissue envelope. RESULTS: The TOF camera showed an overall recognition rate of the soft tissue envelope of 75%. On comparing the results from the algorithm with the manual measurements, a significant difference was found (P > .005). CONCLUSIONS: In this preliminary study, we have presented a method for automatically recognizing the soft tissue envelope of the surgical field in a real-time application. Further improvements could result in a robotic navigation device for minimally invasive hip surgery.

Hemispheric cups do not reproduce acetabular rim morphology.

BACKGROUND: Iliopsoas impingement is a recurrent complication following THA, caused by muscle friction against a protrusive prosthetic cup.This study was designed to quantify the dimensional variations in acetabular rim profiles, with particular regard to the iliopubic valley, in order to suggest means to prevent iliopsoas impingement. MATERIAL AND METHODS: 34 cadaver pelvises were analyzed using a hip navigation system. The morphometric data were processed to plot profiles of all acetabular rims with particular regard to the shape and depth of the psoas valley. RESULTS: The acetabular rim is an asymmetric succession of 3 peaks and 3 troughs. The psoas valley is a salient feature in most pelvises and there is only a weak correlation between its depth (mean 3.8 mm, SD 2.0) and acetabular diameter, anteversion, or inclination. INTERPRETATION: It would be difficult to obviate the anterior overlap of the acetabulum using a hemispheric cup, a fortiori in certain morphotypes, without compromising range of motion or risk of dislocation. The solution for prevention of iliopsoas impingement would be to adapt cup design to acetabular anatomy, which may require different implants for the right and left sides, and hence a doubled inventory.