[Computer-assisted surgical planning. 3-D software for the PC]

Three-dimensional computed tomographic angular measurements of the canine tibia using a bone-centered coordinate system

Introduction

Canine tibial alignment is determined by two-dimensional angular measurements, and tibial torsion is challenging. Aim of the study was the development and evaluation of a CT technique to measure canine tibial varus and torsion angles independent from positioning and truly three-dimensional.

Materials and methods

A bone-centered 3D cartesian coordinate system was introduced into the CT-scans of canine tibiae and aligned with the anatomical planes of the bone based on osseous reference points. Tibial torsion, and varus (or valgus) angles were calculated based on geometric definition of projection planes with VoXim® medical imaging software using 3D coordinates of the reference points. To test accuracy of the tibial torsion angle measurements, CT scans of a tibial torsion model were performed in 12 different hinge rotation setups ranging from the normal anatomical situation up to +/ 90° and compared to goniometer measurements. Independency of tibial positioning on the CT scanner table was evaluated in 20 normal canine tibiae that were scanned in a position parallel to the z-axis and two additional off-angle double oblique positions having 15° and 45° deviation in direction of the x- and y-axes. Angular measurements in oblique positions were compared with the normal parallel position by subtraction. Precision was tested using clinical CT scans of 34 canine patients with a clinical diagnosis of patellar luxation.

Results

Accuracy testing in the tibial torsional deformity model revealed a difference of 0.2° demonstrated by Passing-Bablok analysis and Bland-Altman-Plots. Testing for independency from tibial positioning resulted in mean differences less than 1.3°. Precision testing in clinical patients resulted in coefficients of variation for repeated measurements of 2.35% (intraobserver agreement) and 0.60% (interobserver agreement) for the tibial torsion angle, and 2.70% (intraobserver agreement) and 0.97% (interobserver agreement) for the tibial varus (or valgus) angle.

Discussion

The technique is lacking determination of bone deformities in the sagittal plane, and demonstration of accuracy in severe complex bone deformities in multiple planes.In conclusion, we developed a method to measure canine tibial torsional and varus or valgus deformities, that calculates in 3D space, and we demonstrated its accuracy in a torsional deformity model, and its precision in CT data of clinical patients.

Introduction of a bone-centered three-dimensional coordinate system enables computed tomographic canine femoral angle measurements independent of positioning

Introduction

Measurement of torsional deformities and varus alignment in the canine femur is clinically and surgically important but difficult. Computed tomography (CT) generates true three-dimensional (3D) information and is used to overcome the limitations of radiography. The 3D CT images can be rotated freely, but the final view for angle measurements remains a subjective variable decision, especially in severe and complex angular and torsional deformities. The aim of this study was the development of a technique to measure femoral angles in a truly three-dimensional way, independent of femoral positioning.

Methods

To be able to set reference points in any image and at arbitrary positions of the CT series, the 3D coordinates of the reference points were used for mathematical calculation of the angle measurements using the 3D medical imaging Software VoXim^®. Anatomical reference points were described in multiplanar reconstructions and volume rendering CT. A 3D bone-centered coordinate system was introduced and aligned with the anatomical planes of the femur. For torsion angle measurements, the transverse projection plane was mathematically defined by orthogonality to the longitudinal diaphyseal axis. For varus angle measurements, the dorsal plane was defined by a femoral retrocondylar axis. Independence positioning was tested by comparison of angle measurement results in repeated scans of 13 femur bones in different parallel and two double oblique (15/45°) positions in the gantry. Femoralvarus (or valgus), neck version (torsion), and inclination angles were measured, each in two variations.

Results

Resulting mean differences ranged between -0.9° and 1.3° for all six determined types of angles and in a difference of <1° for 17 out of 18 comparisons by subtraction of the mean angles between different positions, with one outlier of 1.3°. Intra- and inter-observer agreements determined by repeated measurements resulted in coefficients of variation for repeated measurements between 0.2 and 13.5%.

Discussion

The introduction of a bone-centered 3D coordinate system and mathematical definition of projection planes enabled 3D CT measurements of canine femoral varus and neck version and inclination angles. Agreement between angular measurements results of bones scanned in different positions on the CT table demonstrated that the technique is independent of femoral positioning.

Computer aided surgery in foot and ankle: applications and perspectives

PURPOSE

At the beginning of the twenty-first century, the computer has supplemented the possibilities of orthopaedic surgery. This article analyses the feasibility and potential clinical benefit of intraoperative three-dimensional imaging (3D), computer assisted surgery (CAS) and intraoperative pedography (IP) in foot and ankle surgery.

METHODS

The feasibility, accuracy and clinical benefit of 3D, CAS and IP were analysed in ongoing experimental and prospective studies at the institution in which the inventor of IP and principal user of 3D and CAS in foot and ankle surgery operates.

RESULTS

Three dimensional imaging: In approximately one third of the cases, reduction/correction and/or implant position was corrected after intraoperative 3D scan during the same procedure in different prospective, consecutive, non-controlled studies (Level III). CAS: CAS guidance for the correction of deformities of the ankle, hindfoot and midfoot/tarsometatarsal (TMT) joint provided higher accuracy, a faster correction process and better scores at a minimum follow-up of two years in comparison without CAS guidance in a single-centre matched-pair follow-up study (Level II). IP: Additional use of IP as the only difference between two groups with correction and/or arthrodesis at foot and/or ankle led to improved clinical outcome scores at a mean of two years follow-up in a prospective randomised controlled study (Level I).

CONCLUSIONS

Three dimensional imaging provides important information which could not be obtained from two-dimensional C-arm alone. The benefit of CAS is high when improved accuracy may lead to an improved clinical outcome. Intraoperative pedography is useful when intraoperative biomechanical assessment may lead to an immediate improvement of the achieved surgical result.

[Computer-assisted surgery-(CAS-)guided correction arthrodesis of the subtalar joint]

OBJECTIVE

Restoration of a stable and plantigrade foot in deformities at the hindfoot and concomitant degenerative changes at the subtalar joint.

INDICATIONS

Deformities at the hindfoot and concomitant degenerative changes at the subtalar joint.

CONTRAINDICATIONS

Active local infection or relevant vascular insufficiency.

SURGICAL TECHNIQUE

Prone position and posterolateral approach to the subtalar joint. Placement of dynamic reference bases in talus and calcaneus through stab incisions. Two-dimensional image acquisition for navigation. Definition of the axes of talus and calcaneus, and of the extent of correction. Exposure of the subtalar joint and removal of remaining cartilage. Computer- assisted surgery-(CAS-)guided correction and transfixation of the corrected position with two 2.5-mm Kirschner wires. Transplantation of autologous cancellous and cortical bone, if necessary. Three-dimensional (3-D) image acquisition for analysis of the accuracy of the correction and planning of the drillings for the screws. CAS-guided drilling and insertion of the screws. 3-D image acquisition for analysis of the accuracy of the correction implant position. Wound closure in layers.

POSTOPERATIVE MANAGEMENT

15 kg partial weight bearing in an orthosis (e.g. Vacuped TM, OPED Inc., Valley, Germany) for 6 weeks, followed by full weight bearing in a stable standard shoe.

RESULTS

From September 1, 2006 to August 31, 2008, 26 correction arthrodeses were performed. The accuracy was assessed by intraoperative 3-D imaging. All achieved angles/translations were within a maximum deviation of 2°/2 mm when compared to the planned correction. Complications that were associated with CAS were not observed. In all 25 cases that completed 2-year follow-up, timely fusion was registered.

[Computer-assisted surgery-(CAS-) guided correction arthrodesis of the ankle joint]

OBJECTIVE

Restoration of a stable and plantigrade foot in deformities at the ankle and concomitant degenerative changes at the ankle joint.

INDICATIONS

Deformities at the ankle and concomitant degenerative changes at the ankle joint.

CONTRAINDICATIONS

Active local infection or relevant vascular insufficiency.

SURGICAL TECHNIQUE

Supine position and anterior approach to the ankle joint. Placement of dynamic reference bases (DRBs) in tibia and talus. Two-dimensional (2-D) image acquisition for navigation. Definition of axes of tibia and talus, and of the extent of correction. Exposition of the ankle joint and removal of remaining cartilage. Computer-assisted surgery-(CAS-) guided correction and transfixation of the corrected position with two 2.5-mm Kirschner wires. Transplantation of autologous cancellous and cortical bone, if necessary. 3-D image acquisition for analysis of the accuracy of the correction and planning of the drillings for the four screws (two parallel from anterolateral, one from posteromedial from the tibia, and one from lateral from the fibula). CAS-guided drilling and insertion of the screws. 3-D image acquisition for analysis of the accuracy of the correction and implant position. Layerwise closure.

POSTOPERATIVE MANAGEMENT

Partial weight bearing with 15 kg in an orthosis for 6 weeks, followed by full weight bearing in a stable standard shoe.

RESULTS

From September 1, 2006 to August 31, 2008, 24 correction ankle arthrodeses were performed. The accuracy was assessed by intraoperative 3-D imaging. All achieved angles/ translations were within a maximum deviation of 2 degrees /2 mm when compared to the planned correction. Complications that were associated with CAS were not observed. In all 20 patients that completed follow-up so far, a timely fusion was registered.

Computer Assisted Surgery (CAS) guided arthrodesis of the foot and ankle: an analysis of accuracy in 100 cases

BACKGROUND

Computer Assisted Surgery (CAS) has shown the potential to increase the accuracy of surgical procedures in different fields of orthopedic surgery. The clinical experiences of 100 cases with CAS guided arthrodeses were evaluated.

MATERIALS AND METHODS

Two navigation systems were used (VectorVision/Navivision, Brainlab). Patients with unilateral foot and/or ankle correction arthrodesis from January 1st, 2005 to March 31st, 2008 were included. The correction was planned on the basis of clinical findings, radiographs and computer tomography. Time spent, accuracy, and problems that occurred with CAS guidance were analyzed. The accuracy was assessed by intraoperative three-dimensional imaging with ISO-C 3D or ARCADIS-3D (Siemens). The deviation from the achieved correction in comparison with the planned correction was analyzed.

RESULTS

One hundred patients were included (ankle, n = 19; subtalar, n = 23; ankle and subtalar, n = 12; midfoot/tarsometatarsal (TMT), n = 28, others, n = 18). The average time needed for preparation was 356 seconds (5 minutes, 56 seconds) (range, 4 to 30 minutes), the correction took an average of 28 (range, 12 to 140) seconds. The CAS system encountered malfunctions in 3 procedures (3%). In the remaining cases, all the achieved corrections were within a maximum deviation of 2 degrees/mm when compared to the planned correction (p < 0.05).

CONCLUSION

With CAS guidance for the correction of deformities of the foot and ankle, a surgeon can achieve a high degree of accuracy with a rapid correction. The high accuracy may lead to improved clinical outcomes.

[Subtalar arthrodesis with calcaneal osteotomy]

The amount of postraumatic deformities of the calcaneus after fracture is classified in 5 types (Type I-V). The bony situation includes in the simple group A malunions, in group B the more demanding nonunions and in Group C the worst cases with additional aseptic or septic necrosis of parts of the calcaneus. For type I with posttraumatic arthritis of the subtalar joint and without malalignement, an in situ-arthrodesis is suitable. Type II, with an additional varus- or valgus hind foot deformity, but especially in type III with additional loss of height and dorsal tilting of the talus a bone block distraction arthrodesis is required. Type IV includes, additionally to the pathology of type I to type III, a lateral translation of the calcaneus. This indirectly causes a severe hind foot valgus and an abutment of the posterior facet towards the lateral malleolus. This type needs osteotomy of the calcaneus through the old fracture surfaces, performed using a bilateral approach. Type V is very rare but the most difficult one for reconstructive surgery because the talus is additionally tilted out of the ankle joint. Therefore, in addition to the bilateral approach and calcaneal osteotomy, an anteromedian approach to the ankle joint is necessary. The surgical procedure in group A (malunion) is more or less the same like in group B (nonunion). Group C (aseptic / septic osteonecrosis) needs a preliminary radical necrectomy in a two stage reconstructive procedure.

[Computer-assisted operational planning for pediatric abdominal surgery. 3D-visualized MRI with volume rendering]

Exact surgical planning is necessary for complex operations of pathological changes in anatomical structures of the pediatric abdomen. 3D visualization and computer-assisted operational planning based on CT data are being increasingly used for difficult operations in adults. To minimize radiation exposure and for better soft tissue contrast, sonography and MRI are the preferred diagnostic methods in pediatric patients. Because of manifold difficulties 3D visualization of these MRI data has not been realized so far, even though the field of embryonal malformations and tumors could benefit from this.A newly developed and modified raycasting-based powerful 3D volume rendering software (VG Studio Max 1.2) for the planning of pediatric abdominal surgery is presented. With the help of specifically developed algorithms, a useful surgical planning system is demonstrated. Thanks to the easy handling and high-quality visualization with enormous gain of information, the presented system is now an established part of routine surgical planning.

Mathematical model for pre-operative planning of linear and closing-wedge metatarsal osteotomies for the correction of hallux valgus

First-metatarsal osteotomy is performed for an abnormal intermetatarsal angle and severe hallux valgus deformity. The metatarsal head is slid along the osteotomy and fixed with a Kirschner wire to achieve angular and linear realignment with respect to the other metatarsals. When reduction of joint subluxation is also sought, a bone wedge is removed. A mathematical model and a corresponding computer-based tool were developed for pre-operative planning of the optimum surgical solution. Standard intermetatarsal angle correction, head-to-sesamoids re-alignment, joint subluxation reduction and metatarsal length adjustment were all pursued. A standard pre-surgical dorso-plantar radiograph of the patient, with an additional metal ball for calculation of X-ray magnification, was necessary to analyse the original and final geometrical configurations. For the first time, expected bone loss and wire diameter were also considered. The angles of bone cuts and the amount of sliding along these cuts were calculated by the model according to the surgical goal. All the resulting geometrical parameters, both in the pre- and planned post- operative configuration, were provided in graphical and tabular form. In a change from former qualitative analysis of radiograms, the surgeon can now enter the operating theatre with a detailed plan of the goal to be achieved.

Calcaneus fractures: facts, controversies and recent developments

The management of calcaneus fractures and their associated soft tissue injuries are challenging tasks for the surgeon. Open reduction and stable internal fixation with a lateral plate and without joint transfixation has been established as a standard therapy for displaced intra-articular fractures with good to excellent results in two-thirds to three-quarters of cases in larger clinical series. Bone grafting appears not useful in the vast majority of cases. Anatomical reduction of joint congruity and the overall shape of the calcaneus are important prognostic factors. The quality of joint reduction should be reliably proven intra-operatively either with Brodén views, high-resolution fluoroscopy or open subtalar arthroscopy. Treatment results are adversely affected by open fractures, delayed reduction after more than 14 days and individual risk factors such as high body mass index and smoking. The extended lateral approach respects the neurovascular supply to the heel and allows a good exposure of the fractured lateral wall, and the subtalar and calcaneocuboid joints in most fractures. In selected fracture patterns percutaneous screw fixation, possibly with arthroscopic control, is a good alternative. Open fractures, compartment syndrome and fractures with severe soft tissue compromise are treated as emergency cases. Early, stable soft tissue coverage appears promising in treating complex open fractures. The benefits of newly developed plate designs and subtalar arthrolysis at the time of hardware removal remains to be proven in further studies. Calcaneal malunions after conservative therapy of displaced fractures are disabling conditions that can be treated successfully with a staged protocol according to the type of deformity. Treatment options include lateral wall decompression, subtalar in situ, or corrective, arthrodesis and calcaneal osteotomy along the former fracture line.