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.

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.