Introduction: Intraoperative visualisation of anatomic joint line reduction and hardware placement is techniqually demanding, twodimensional c-arm imaging do not always allow acute decision making about remaining articular steps and hardware misplacement. Postoperatively identification of these failures may need extensive revison surgery and is costly. The new mobile Iso-C3D imaging device provides intraoperative multiplanar reconstructions, consequently immediate decision making becomes possible.

Materials and Methods: 250 different joint fractures were intraoperatively scanned with the Iso-C3D (ankle fractures; forefoot, calcaneus; pilon tibiale; tibia plateaus; wrists; spine; pelvic fractures). Multiplanar reconstructions were obtained from 100 fluoroscopic images the Iso-C-3D provides during one automatic scan protocol. Decisions about remaining articular steps and implant misplacements were compared with the knowledge of conventional c-arm images which were done before. If necessary directly intraoperative corrections were performed.

Results: In 43 clinical cases (17%) a direct intraoperative correction resulted in implant change (8%) or correction of reduction (9%), caused by articular steps > 2mm, screw or k-wire misplacement. In all those cases conventional c-arm images did not reveal the significant step or misplacement, correction decision were all based on the Iso-C3D imaging in those cases. In other (9%) significant steps or misplacements were identified in c-arm images and confirmed with the Iso-C3D images.

Discussion: With the new intraoperative three dimensional imaging device a direct introperative idenfication of remaining intraarticular steps and implant misplacements becomes possible. Missed steps and misplacements can be avoided and reduction of operative revison rates might result.

Introduction: Image based navigation is able to increase precision and reduce intraoperative radiation time in drilling procedures in orthopeadic trauma indications. Due to specific anatomic conditions and necessary adequate fluoroscopic visualizing, specific indications need intraoperative 3-D fluoroscopy based navigation modalities. This kind of navigation has already been successfully used in several orthopaedic interventions. The complex anatomic structure of the scaphoid, the suggested minimal invasiveness and misplacement rates of the screws make 2-D based fluoroscopic navigation impossible. Missing options for a stable reference marker fixation at the scaphoid or carpus did not allow an intraoperative registration for the navigation. We report about the development of an adequate non invasive fixation technique of the reference marker for navigated interventions and the first implementation of 3-D fluoroscopy based scaphoid screws.

Materials and method: Fixation of the reference marker was achieved by immobilisation of the complete hand and forearm in maximum dorsal extension of the wrist. We used a completely new developed radiolucent hand fixation device (HFD) fixed nonivasively to the carpus and a conventional navigation system (Brainlab, Germany) in combination with 3-D fluoroscopic imaging (Iso-C, Siemens, Germany).

Tests were done on 10 intact specimen and the process included the initial drilling and final placement of an osteosynthetic screw. Postoperative placement was controlled with a 3-D scan. Results concerning a defined optimal screw positioning and drill failures attempts were done by another independent surgeon.

Results: All 3-D scans were done without complications. The multiplanar reconstructions allowed a proper visualisation of the scaphoid in all cases. No additional movement of the fixed extremity occurred during the operation. No registration failures were detected. An optimally defined screw placement in the scaphoid was achieved in 9 cases. Two repeated drill attempts were necessary in one case, another case needed three drill attempts. The scaphoid was never perforated.

Discussion: Our development of a new immobilizing device for the complete hand and forearm allows proper use of 3-D fluoroscopy based navigation at the scaphoid including a placement of an osteosynthetic screw. Further movements of the hand or fingers are intraoperatively only possible after the definite drill placement has been performed.

The 3-D imaging modality allows a direct control of the reduction and screw placement intraoperatively. Our tests did not include simulated fracture conditions, a general use of our new technique can now only be implemented to non displaced fracture types, while clinical and further laboratory tests have to improve our findings for all types of scaphoid fractures.

Introduction: The main purpose of this study was to analyze the accuracy of conventional versus navigated open wedge corrective osteotomies of the proximal tibia. Furthermore, the intraoperative radiation dosage and the time of the operative procedure of both groups were compared.

Methods: 20 legs of 11 fresh cadaver (9 male, 2 female, age 35–71 years) were randomly assigned to conventional open wedge high tibial osteotomy (HTO) (n=10) or navigated open wedge HTO (n=10). Two legs had to be excluded because of pre-existing knee injuries. The aim of all corrective operations was to align the mechanical axis to pass through 80% of the tibial plateau (80% Fujisawa line), regardless of the preexisting alignment. The intraoperative mechanical axis was evaluated either by the cable technique for conventional HTO, or by a navigation module for navigated HTO (Medivision, Oberdorf/Switzerland). An angle fixed implant with interlocking screws (Tomofix, Mathys, Bettlach/Switzerland) was used to minimize postoperative loss of correction. Postoperatively, CT-scans were performed and the Fujisawaline and MPTA measured with a computer software for deformity analysis (Med-iCAD) The main outcome parameter was the accuracy of the correction, which was measured by the Fujisawa line. Secondary outcome parameters were the intraoperative radiation measured by the dose area product and the time of the operative procedure. For statistical analysis the standard deviation (S.D.) was calculated and the paired t-test applied.

Results: After conventional HTO, the mechanical axis was intersecting the Fujisawa line at 72.1% of the tibial plateau (range 60.4–82.4%, S.D. 7.2%). In contrast, after navigated HTO the tibia plateau was passed through 79.7% (range 75.5–85.8%, S.D. 3.3%). Thus, the accuracy of the correction was significantly higher after navigated HTO (p=0.020). In addition, the standard deviation of the corrections was significantly lower after navigated HTO (p=0.012). The medial proximal tibia angle (MPTA) increased 7.9° (range: 4.7–12.1°) after conventional HTO and 9.1° (range: 4.6–12.6°) after navigated HTO. The average dose area products of the conventional HTO (49.5 cGy/cm2, range 36.0–81.2 cGy/cm2) and navigated HTO (42.8 cGy/cm2, range 28.3–58.1 cGy/cm2) were comparable (p=0.231). However, navigated HTO elongated the operation time significantly (navigated HTO: 82 min, range 55–98 min; conventional HTO: 59 min, range 47–73 min) (p< 0.001).

Conclusion: Continuous three-dimensional imaging of the axis and of intraoperative tools with the a navigation module significantly improves the accuracy of open wedge osteotomies of the proximal tibia. Prospective clinical studies will show whether the results of this cadaver study can be transferred to the regular clinical use.

Introduction: Movement of the limb during computer aided arthroplasty may cause soft tissue impingement on the reference marker(RM) and consequently alter the spatial relationship between RM and bone with resulting inaccuracies in navigation. The purpose of this study was to investigate the effect of different degrees of soft tissue dissection on the stability of reference markers during limb movement.

Methods: The stability of both one- and two-pin RM systems inserted using three different levels of soft-tissue dissection was analysed in relation to a super-stable RM in fresh cadaver lower limbs. The spatial relationship of the two RMs was analysed using the VectorVision^® system (BrainLAB, Germany) during multiple repetitions of four predefined limb movements. All tests were done with RMs inserted in both the distal-anterior femur and distal-lateral femur.

Results: Analysis of movements of the test RM in relation to the super-stable RM showed that rotations of less than 0.15^o and translations of less than 0.4mm occurred in most test combinations. The combination that showed the greatest instability was when a stab incision was used to insert a pin in the distal/lateral femur (translation 0.73mm+/−0.05, rotation 0.25^o+/− 0.05)(p< 0.001). This instability occurred in both single and double pin RMs(p=0.21).

Conclusions: RM pins can be placed in the anterior distal femur through simple stab incisions without resulting in significant soft tissue impingement during limb movement. If pins are placed in the lateral distal femur through stab incisions, impingement may occur from the fascia lata. Release of the fascia lata 1cm either side of the pin prevents significant impingement. Wide skin incision is unnecessary in any location.

Movement of the limb during computer aided arthroplasty may cause soft tissue impingement on the reference marker(RM) and consequently alter the spatial relationship between RM and bone with resulting inaccuracies in navigation. The purpose of this study was to investigate the effect of different degrees of soft tissue dissection on the stability of reference markers during limb movement.

The stability of both one- and two-pin RM systems inserted using three different levels of soft-tissue dissection was analysed in relation to a super-stable RM in fresh cadaver lower limbs. The spatial relationship of the two RMs was analysed using the VectorVision® system (BrainLAB, Germany) during multiple repetitions of four predefined limb movements. All tests were done with RMs inserted in both the distal-anterior femur and distal-lateral femur.

Analysis of movements of the test RM in relation to the super-stable RM showed that rotations of less than 0.15o and translations of less than 0.4mm occurred in most test combinations. The combination that showed the greatest instability was when a stab incision was used to insert a pin in the distal/lateral femur (translation 0.73mm+/− 0.05, rotation 0.25o+/− 0.05)(p< 0.001). This instability occurred in both single and double pin RMs(p=0.21).

RM pins can be placed in the anterior distal femur through simple stab incisions without resulting in significant soft tissue impingement during limb movement. If pins are placed in the lateral distal femur through stab incisions, impingement may occur from the fascia lata. Release of the fascia lata 1cm either side of the pin prevents significant impingement. Wide skin incision is unnecessary in any location.

In computer assisted orthopaedic surgery, rigid fixation of the Reference Marker (RM) system is essential for reliable computer guidance. A minimum shift of the RM can lead to substantial registration errors and inaccuracies in the navigation process. Various types of RM systems are available but there is little information regarding the relative stabilities of these systems. The aim of this study was to test the rotational stability of three commonly used RM systems.

One hundred and thirty Synbones and 15 cadavers were used to test the rotational stability of three different RM systems (Schanz’ screw, Brain-Lab MIRA and Stryker adjustment system). Using a specially developed testing device, the peak torque sustained by each RM system was assessed in various anatomical sites.

Comparison of means for Synbone showed that the BrainLab MIRATM system was the most stable (mean peak torque 5.60+/− 1.21 Nm) followed by the Stryker systemTM (2.53+/− 0.53 Nm) and the Schanz screw(0.77+/− 0.39 Nm)(p< 0.01). The order of stability in relation to anatomical site was femoral shaft, distal femur, tibial shaft, proximal tibia, anterior superior iliac spine, iliac crest and talus. Results from the cadaver experiments showed similar results. Bi-cortical fixation was superior to mono-cortical fixation in the femur(p< 0.01) but not the tibia(p=0.22).

The RM system is the vital link between bone and computer and as such the stability of the RM is paramount to the accuracy of the navigation process. In choosing RM systems for computer navigated surgery surgeons should be aware of their relative stability. Anatomical site of RM placement also affect the stability. Mono-cortical fixation is generally less stable than bi-cortical.

The aim of this pilot study was to evaluate the accuracy of two different methods of navigated retrograde drilling of talar lesions. Artificial osteochondral talar lesions were created in 14 cadaver lower limbs. Two methods of navigated drilling were evaluated by one examiner. Navigated Iso-C^3D was used in seven cadavers and 2D fluoroscopy-based navigation in the remaining seven. Of 14 talar lesions, 12 were successfully targeted by navigated drilling. In both cases of inaccurate targeting the 2D fluoroscopy-based navigation was used, missing lesions by 3 mm and 5 mm, respectively. The mean radiation time was increased using Iso-C^3D navigation (23 s; 22 to 24) compared with 2D fluoroscopy-based navigation (14 s, 11 to 17).

Tibial rotation and translation provide important stability parameters after ACL reconstruction. An accurate tool for a combined pre- intra- and postoperative stability measurement is not in clinical use so far. Navigation of the drill canals for the ACL placement and evaluation of possible impingement problems has been introduced for some years already, while measurement of the tibial translation and rotation is only available for a short time and only available for a few navigation modules. Navigation provides an accuracy of 1mm/1°, therefore navigated measurement of tibial rotation and translation were evaluated in this study with a new developed mechanical device and directly compared to conventional measurement techniques.

Accuracy of navigation was compared with the KT1000 for the anterior-posterior (AP) translation and to a new developed goniometer tool concerning the rotational range of motion. Comparative tests included plastic whole leg models and specimens. Tests were repeated with intact and dissected ACL′s. A conventional navigation system (Vector Vision, Brainlab, Germany) was used in all cases. This included software developed for fluoroscopy based navigated ACL reconstruction. The following knee kinematics were detectable with the navigation system: Flexion/Extension degrees of the knee joint (°); AP translation of the tibia in relation to the femur (mm); Axial tibial rotation relative to the femur (°).

Validation of Navigation: first neutral tibial rotation was defined and marked in the knee joint in neutral position. All rotational measurements were done with a new developed goniometer tool and compared to the navigated technique. Then the knee was rotated externally until 45° (maximum) and internally 45° (maximum), by single 2.5° steps. These measurements were repeated in 0°, 30°, 60° and 80° knee flexion. All tests were repeated three times and performed by 3 different observers. A total of 1296 measurements were done. Measurements of the tibial translation were compared with the KT 1000 for the specimen testing.

Results revealed: accurate navigated measurement of tibial rotation in plastic and specimen models; variation of absolute AP translation values between KT1000 and navigation; variation of the AP translation corresponding to the ACL condition; increased range of total tibial rotation after dissecting the ACL compared to the intact ligament.

Restoration of the rotational stability and limiting of the AP translation is necessary to provide normal knee kinematics after ACL reconstructions. Intraoperative measurements of these stability parameters are demanding and so far not established with navigation systems or conventionally. As our results show, navigation offers an accurate technique for measurement of the AP translation and rotation of the knee with intact and dissected ACL’s under laboratory conditions. General use in the evaluation of a successful ACL reconstruction becomes possible intraoperative and might be reproducible for further measurements. Clinical studies are needed to improve our results.

Anatomic reduction and appropriate implant placement is essential for optimal treatment of intraarticular tibial plateau fractures. Standard intraoperative fluoroscopy provides limited visualization of the reduction and hardware placement compared with pre- or postoperative 3-D imaging modalities. As such, post-operative computer tomography (CT) has become a common procedure to evaluate the quality of the reduction and fixation. The Iso-C3D provides 3-D intraoperatively imaging to dynamically assess the surgical reduction and fixation at different anatomic regions. We report on our first 19 clinical tibial plateau fractures scanned intra-operatively with the Iso-C 3D.

Between January and November 2003, 19 intraarticular tibia plateau fractures were scanned intraoperatively with the Iso-C3D (Siemens, Germany). No formal selection criteria were utilised except for the presence of a tibial plateau fracture. Operative procedures included 14 cases of open reduction internal fixation and 5 cases of internal fixation with arthroscopic assisted reduction.

Imaging Technique: All patients were positioned on full-carbon tables for the operative procedure. After initial operative reduction and fixation, conventional two-dimensional fluoroscopic imaging was performed using standard AP and lateral projections. These images were evaluated by the operating surgeon; if the reduction and fixation was judged to be appropriate, Iso-C3D imaging was initiated

In 21% (n=4) of all cases an immediate revision of the operative procedure was performed after Iso-C3D imaging. These revisions were not deemed necessary with conventional fluoroscopy alone. In two cases, significant intra-articular incongruencies (greater than two millimetres) were noted. Additionally, in two cases, implant mal-position was detected. All patients had a postoperative CT scan. All CT scans confirmed the intraoperative Iso-C imaging, no further additional articular incongruencies or malpositioned implants were identified. When compared to conventional C-arm images, the Iso-C 3D scans demonstrated improved ability to identify the articular malreduction and implant mal-position in all cases.

We have demonstrated that the Iso-C3D provides reliable intraoperative evaluation of reduction and hardware placement compared to traditional CT scans for tibial plateau fractures. In addition, clinically relevant intra-operative information was gained with its use in this study. In four (21%) cases, the operative treatment was modified due to the use of the multiplanar imaging modality. On average, 10 minutes of additional operative time was required for the use of Iso-C3D scanning and the evaluation of the images. Further prospective clinical studies are needed to improve our findings.