Introduction

The aim of this study was to quantitatively analyze the amount coronal plane laxity in mid-flexion that occurs with a loose extension gap in TKA. In the setting of a loose extension gap, we hypothesized that although full extension is achieved, a loose extension gap will ultimately lead to increased varus and/or valgus laxity throughout mid flexion.

Long-term implant survivorship in total knee arthroplasty (TKA) depends on the alignment of the tibial and femoral components, as well as on the mechanical alignment of the leg. Computer navigation improves component and limb alignment in TKA compared to the manual technique. However, its use is often associated with an increase in surgical time. We aimed to evaluate the use of adjustable cutting blocks (ACB) in navigated TKA. We hypothesised that the use of ACB would (1) improve tibial and femoral component positioning; (2) improve postoperative mechanical leg alignment; and (3) decrease tourniquet time, when compared to conventional cutting blocks (CCB).

This was a retrospective cohort study of 94 navigated primary TKA. Patients were classified into two groups according to whether the surgery had been performed using ACB or CCB. There were sixty-four patients in the CCB group and 30 patients in the ACB group. Charts were reviewed to obtain the following data: age, gender, body mass index (BMI), tourniquet time and operated side. Pre- and postoperative standing full-leg radiographs and lateral radiographs were reviewed.

Mean coronal femoral alignment for the CCB group was 0.8® varus (SD = 1.95®) and for the ACB group it was 1.1® varus (SD = 1.5®) (P = 0.12). Mean coronal tibial alignment for the CCB group was 0.1® valgus (SD = 1.3®) and for the ACB group it was 0.5® varus (SD = 1.01) (P = 0.15). Sagittal tibial alignment was a mean 0.5® of anterior slope (SD = 2.9®) for the CCB group and 0.7® anterior slope (SD = 2.5®) for the ACB group (P = 0.38).

Preoperatively, the CCB group had a mean mechanical alignment of 1.8® varus (SD = 9.6®), while the ACB group had a mean 1.8® varus (SD = 9.37®) (P = 0.88). After surgery, mechanical leg alignment for the CCB group improved to a mean 0.7® varus (SD = 2.7®) (P = 0.0001), while the ACB group improved to 1.8® varus (SD = 1.7®) (P<0.0001). There was significantly less variability in postoperative mechanical alignment in the ACB group (P = 0.0091).

Mean tourniquet time for the CCB group was 91 minutes (SD = 17.7 minutes). The ACB group a mean tourniquet time of 76 minutes (SD = 16.7 minutes) (P = 0.01). In the multiple linear regression model, the use of an ACB reduced tourniquet time by 16.8 minutes (P = 0.001).

Adjustable cutting blocks for TKA significantly reduced postoperative mechanical alignment variability and tourniquet time compared to conventional navigated instrumentation, while providing equal or better component alignment.

Controversies about the management of injuries to the soft tissue structures of the posteromedial corner of the knee and the contribution of such peripheral structures on rotational stability of the knee are of increasing interest and currently remain inadequately characterised. The posterior oblique ligament (POL) is a fibrous extension off the distal aspect of the semimembranosus that blends with and reinforces the posteromedial aspect of the joint capsule. The POL is reported to be a primary restraint to internal rotation and a secondary restraint to valgus translation and external rotation. Although its role as a static stabiliser to the medial knee has been previously described, the effect of the posterior oblique ligament (POL) injuries on tibiofemoral stability during Lachman and pivot shift examination in the setting of ACL injury is unknown.

The objective of this study was to quantify the magnitude of tibiofemoral translation during the Lachman and pivot shift tests after serial sectioning of the ACL and POL.

Eight knees were used for this study. Ligamentous constraints were sequentially sectioned in the following order: ACL first, followed by the POL. Navigated mechanised pivot shift and Lachman examinations were performed before and after each structure was sectioned, and tibiofemoral translation was recorded.

Lachman test: There was a mean 6.0 mm of lateral compartment translation in the intact knee (SD = 3.3 mm). After sectioning the ACL, translation increased to 13.8 mm (SD = 4.6; P<0.05). There was a nonsignificant 0.7 mm increase in translation after sectioning the POL (mean = 14.5 mm; SD = 3.9 P>0.05).

Mechanised pivot shift: Mean lateral compartment translation in the intact knee was −1.2 mm (SD = 3.2 mm). Sectioning the ACL caused an increase in anterior tibial translation (mean = 6.7 mm; SD = 3.0 mm; P<0.05). No significant change in translation was seen after sectioning the POL (mean = 7.0 mm, SD = 4.0 mm; P>0.05).

Sectioning the POL did not significantly alter tibiofemoral translation in the ACL deficient knee during the Lachman and pivot shift tests. This study brings into question whether injuries to the POL require reconstruction in conjunction with ACL reconstruction. More studies are needed to further characterise the role of the injured POL in knee stability and its clinical relevance in the ACL deficient and reconstructed knee.

Injuries to the posterior cruciate ligament (PCL) and the posterolateral corner (PLC) of the knee remain a challenging orthopaedic problem. Studies evaluating PCL and PLC reconstruction have failed to demonstrate a strong correlation between the degree of knee laxity as measured by uniplanar testing and subjective outcome or patient satisfaction. The effect that changing the magnitude of posterior tibial slope has on multiplanar, rotational stability of the PCL-deficient knee has yet to be determined. We aimed to evaluate the effect that changes in posterior tibial slope would have on static and dynamic stability of the PCL-PLC deficient knee.

Ten knees were used for this study. Navigated posterior drawer and standardised reverse mechanised pivot shift maneuvers were performed in the intact knee and after sectioning the PCL, the lateral collateral ligament (LCL), the popliteofibular ligament (PFL) and the popliteus muscle tendon (POP). Navigated high tibial osteotomy (HTO) was performed to obtain the desired change in tibial plateau slope (+5® or −5® from native slope). We then repeated the posterior drawer and the reverse mechanised pivot shift test for each of the two altered slope conditions.

Mean posterior tibial translation during the posterior drawer in the intact knee was 1.4 mm (SD = 0.48 mm). In the PCL-PLC deficient knee, posterior tibial translation increased to 18 mm (SD = 5.7 mm) (P < 0.001). Increasing the amount of posterior tibial slope by 5® reduced posterior tibial translation to 12 mm (SD = 4.7 mm) (P < 0.01). Decreasing the amount of posterior slope by 5® compared to the native knee, increased posterior tibial translation to 21 mm (SD = 6.8 mm) (P < 0.01). There was a significant negative correlation between the magnitude of tibial plateau slope and the magnitude of the reverse pivot shift (R2 = 0.71; P < 0.0001).

Mean posterior tibial translation during the reverse mechanised pivot shift test in the intact knee was 7.8 mm (SD = 2.8 mm). In the PCL-PLC deficient knee, posterior tibial translation increased to 26 mm (SD = 5.6 mm) (P < 0.001). Increasing the amount of posterior tibial slope by 5® reduced posterior tibial translation to 21 mm (SD = 6.7 mm) (P < 0.01). Decreasing the amount of posterior slope by 5® compared to the native knee, increased posterior tibial translation to 34 mm (SD = 8.2 mm) (P < 0.01). There was a significant negative correlation between the magnitude of tibial plateau slope and the magnitude of the reverse pivot shift (R2 = 0.72; P < 0.0001).

Decreasing the magnitude of posterior slope of the tibial plateau resulted in an increase in the magnitude of posterior tibial translation during the posterior drawer and the reverse mechanised pivot shift test in the PCL-PLC deficient knee. Conversely, increasing the slope of the tibial plateau reduced the amount of posterior tibial translation during the posterior drawer and the reverse mechanised pivot shift test. However, the effect of the increase in slope was not sufficient to reduce posterior tibial translation to levels similar to those of the intact knee.

Accurate and reliable registration of the ankle center is a necessary requirement in computer-assisted TKR. There is debate among surgeons over which registration procedure more accurately reflects the true center of the ankle joint. The aim of this study was to compare two different ankle registration landmarks on radiographs and determine how much they differed from the anatomic center of the talus in the frontal plane. Specifically, we asked what the average deviation in tibial mechanical axis registration would be when registering the ankle center using: A) the extreme medial and lateral points; and B) the most distal points, of the respective malleoli. A second question was whether or not BMI had any significant effect on mechanical axis registration error.

We reviewed the preoperative hip-to-ankle radiographs of 40 patients who underwent navigated TKR at our institution. The patient cohort was composed of 32 females and 7 males, with a mean age of 69 years (range, 45–84 years) and a mean BMI of 29.9 (range, 14.7–43.3). All radiographs were stored in and reviewed using PACS.

No clinically significant divergence from the anatomic center of the ankle was seen when using the Extremes Midpoint technique (mean divergence = 0.2® lateral; SD = 0.5®; 95% CI = −0.3®, −0.1®) or the Distal Midpoint technique (mean divergence = 0.2® lateral; SD = 0.6®; 95% CI = −0.39®, 0®). The mean difference between both techniques was 0.02® (SD = 0.3®; 95% CI = −0.1®, 0.1®; P = 0.68). BMI had no significant effect on the divergence from the true ankle center for either the Extremes Midpoint (R² = 0.002; P = 0.78) or the Distal Midpoint techniques (R² = 0.004; P = 0.90).(Figure 2)

The center of the ankle, as determined by using the Extremes Midpoint technique, lied 1.1 mm (SD = 2.6 mm; 95% CI = −1.9 mm to −0.3 mm) from the anatomic axis of the tibia. When determined using the Distal Midpoint technique, the center of the ankle lied 1.7 mm (SD = 2.3 mm; 95% CI = −2.5 mm to −0.98 mm) from the anatomic axis. Although statistically significant (P = 0.028), this difference was not clinically relevant (<3 mm). BMI had no significant effect on these differences (R² = 0.07; P = 0.11; R² = 0.02, P = 0.38).(Figure 3)

There is no significant difference between ankle registration using the Extremes Midpoint or the Distal Midpoint techniques and the anatomic center of the ankle. Patients' BMI does not seem to affect the registration of the ankle center with either technique.

Over the last two decades, anatomic anterior cruciate ligament (ACL) reconstructions have gained popularity, while the use of extraarticular reconstructions has decreased. However, the biomechanical rationale behind the lateral extraarticular sling has not been adequately studied. By understanding its effect on knee stability, it may be possible to identify specific situations in which lateral extraarticular tenodesis may be advantageous. The primary objective of this study was to quantify the ability of a lateral extraarticular sling to restore native kinematics to the ACL deficient knee, with and without combined intraarticular anatomic ACL reconstruction. Additionally, we aimed to characterise the isometry of four possible femoral tunnel positions for the lateral extraarticular sling.

Eight fresh frozen hip-to-toe cadavers were used in this study. Navigated Lachman and mechanised pivot shift examinations were performed on ACL itact and deficient knees. Three reconstruction strategies were evaluated: Single bundle anatomic intraarticular ACL reconstruction, Lateral extraarticular sling, Combined intraarticular ACL reconstruction and lateral extraarticular sling. After all stability tests were completed, we quantified the isometry of four possible femoral tunnel positions for the lateral extraarticular sling using the Surgetics navigation system. A single tibial tunnel position was identified and digitised over Gerdy's tubercle. Four possible graft positions were identified on the lateral femoral condyle: the top of the lateral collateral ligament (LCL); the top of the septum; the ideal tunnel position, as defined by the navigation system's own algorithm; and the actual tunnel position used during testing, described in the literature as the intersection of the linear projections of the LCL and the septum over the lateral femoral condyle. For each of the four tunnel positions, the knee was cycled from 0 to 90® of flexion and fiber length was recorded at 30® intervals, therefore quantiying the magnitude of anisometry for each tunnel position.

Stability testing: Sectioning of the ACL resulted in an increase in Lachman (15mm, p = 0.01) and mechanised pivot shift examination (6.75mm, p = 0.04) in all specimens compared with the intact knee. Anatomic intraarticular ACL reconstruction restored the Lachman (6.7mm, p = 3.76) and pivot shift (−3.5mm, p = 0.85) to the intact state. With lateral extraarticular sling alone, there was a trend towards increased anterior translation with the Lachman test (9.2mm, p = 0.50). This reconstruction restored the pivot shift to the intact state. (1.25mm, p = 0.73). Combined intraarticular and extraarticular reconstruction restored the Lachman (6.2mm, p = 2.11) and pivot shift (−3.75mm, p = 0.41) to the intact state. There was no significant difference between intraarticular alone and combined intraarticular and extraarticular reconstruction. (p = 1.88)

Isometry: The ideal tunnel position calculated by the navigation system was identified over the lateral femoral condyle, beneath the mid-portion of the LCL. The anisometry for the ideal tunnel position was significantly lower (5.9mm; SD = 1.8mm; P<0.05) than the anisometry of the actual graft position (14.9mm; SD = 4mm), the top of the LCL (13.9mm; SD = 4.3mm) and the top of the septum (12mm; SD = 2.4mm).

In the isolated acute ACL deficient knee, the addition of a lateral extraarticular sling to anatomic intraarticular ACL reconstruction provides little biomechanical advantage and is not routinely recommended. Isolated lateral extraarticular sling does control the pivot shift, and may be an option in the revision setting or in the lower demand patient with functional instability. Additionally, the location of the femoral tunnel traditionally used results in a significantly more anisometric graft than the navigation's system mathematical ideal location. However, the location of this ideal tunnel placement lies beneath mid-portion of the fibers of the LCL, which would not be clinically feasible.

Controversies about the management of injuries to the soft tissue structures of the posteromedial corner of the knee and the contribution of such peripheral structures on rotational stability of the knee are of increasing interest and currently remain inadequately characterised. The posterior oblique ligament (POL) is a fibrous extension off the distal aspect of the semimembranosus that blends with and reinforces the posteromedial aspect of the joint capsule. The POL is reported to be a primary restraint to internal rotation and a secondary restraint to valgus translation and external rotation. Although its role as a static stabiliser to the medial knee has been previously described, the effect of the posterior oblique ligament (POL) injuries on tibiofemoral stability during Lachman and pivot shift examination in the setting of ACL injury is unknown.

The objective of this study was to quantify the magnitude of tibiofemoral translation during the Lachman and pivot shift tests after serial sectioning of the ACL and POL.

Eight knees were used for this study. Ligamentous constraints were sequentially sectioned in the following order: ACL first, followed by the POL. Navigated mechanised pivot shift and Lachman examinations were performed before and after each structure was sectioned, and tibiofemoral translation was recorded.

Lachman test: There was a mean 6.0 mm of lateral compartment translation in the intact knee (SD = 3.3 mm). After sectioning the ACL, translation increased to 13.8 mm (SD = 4.6; P<0.05). There was a nonsignificant 0.7 mm increase in translation after sectioning the POL (mean = 14.5 mm; SD = 3.9 P>0.05).

Mechanised pivot shift: Mean lateral compartment translation in the intact knee was −1.2 mm (SD = 3.2 mm). Sectioning the ACL caused an increase in anterior tibial translation (mean = 6.7 mm; SD = 3.0 mm; P<0.05). No significant change in translation was seen after sectioning the POL (mean = 7.0 mm, SD = 4.0 mm; P>0.05).

Sectioning the POL did not significantly alter tibiofemoral translation in the ACL deficient knee during the Lachman and pivot shift tests. This study brings into question whether injuries to the POL require reconstruction in conjunction with ACL reconstruction. More studies are needed to further characterise the role of the injured POL in knee stability and its clinical relevance in the ACL deficient and reconstructed knee.

Unicompartmental knee replacement (UKR) has good outcomes for the treatment of compartmental osteoarthritis of the knee. Mechanical alignment overcorrection is associated with early failure of the femoral and tibial components. Preoperative mechanical alignment is the most important predictor of postoperative alignment. However, most studies do not take into consideration the magnitude of preoperative deformity when reporting on mechanical alignment outcomes after UKR.

We aimed to determine the magnitude of postoperative mechanical alignment achieved based on the magnitude of preoperative alignment; and to compare the number of cases of overcorrection into valgus to historical data.

This was a radiographic review of patients who underwent robotic medial UKR by a single surgeon between 2007 and 2011. Two examiners measured pre- and postoperative mechanical alignment for all patients on long-leg radiographs. Patients were classified into three groups of preoperative mechanical alignment: mild varus (0–5®); moderate varus (5–10®); and severe varus (>10®). Patients with valgus alignment (<0®) were excluded. Linear regression was used to estimate the magnitude of postoperative alignment for each group, adjusting for age, BMI, gender, side, implant type, and polyethylene thickness.

89 patients were included. Mean preoperative alignment was 7.3® varus (95% CI = 6.6®–8®; range, 0.1–15® varus). Mean postoperative alignment was 2.8® varus (95% CI = 1.9®–3.8®; range, 1.4® valgus–9.7® varus). There was a significant difference in postoperative mechanical alignment between the three groups (Table 1) (P<0.05). Four overcorrections (4.5%) were detected, all under 1.5® valgus. This percentage of overcorrection was significantly better than previous conventional UKR reports (mean = 12.6%; P = 0.04).

The magnitude of postoperative alignment in medial UKR depends on the severity of the preoperative deformity. Reports on radiographic outcomes of UKR should be stratified by the magnitude of preoperative alignment. The risk of overcorrection is reduced when using robotic assistance compared to using the conventional manual technique.

Aims/Hypothesis

The aims of this study were: 1) to quantitatively analyse the amount of knee extension that is achieved with +2mm incremental increases in the amount of distal femoral bone that is resected during TKA in the setting of a flexion contracture, 2) to quantify the amount of coronal plane laxity that occurs with each 2mm increase in the amount of distal femur resected. In the setting of a soft tissue flexion contracture, we hypothesized that although resecting more distal femur will reliably improve maximal knee extension, it will ultimately lead to increased varus and/or valgus laxity throughout mid-flexion.

Purpose

Our aim was to compare the passive kinematics and coronal plane stability throughout flexion in the native and the replaced knee, using three different TKA designs: posterior stabilized (PS), bi-cruciate substituting (BCS), and ultracongruent (UC). Our hypotheses were: 1.) a guided motion knee replacement (BCS) offers the closest replication of native knee kinematics in terms of femoral rollback 2.) the replaced knee will be significantly more stable in the coronal plane than the native knee; 3.) No difference exists in coronal plane stability between the 3 implants/designs throughout flexion.

INTRODUCTION

Allograft reconstruction after resection of primary bone sarcomas has a non-union rate of approximately 20%. Achieving a wide surface area of contact between host and allograft bone is one of the most important factors to help reduce the non-union rate. We developed a novel technique of haptic robot-assisted surgery to reconstruct bone defects left after primary bone sarcoma resection with structural allograft.

Unicompartmental knee arthroplasty (UKA) is an increasingly attractive and clinically successful treatment for individuals with isolated medial compartment disease who demand high levels of function. A major challenge with UKA is to place the components accurately so they are mechanically harmonious with the retained joint surfaces, ligaments and capsule. Misalignment of UKA components compromises clinical outcomes and implant longevity. Cobb et al. (JBJS-Br 2006) showed that robot-assisted placement of UKA components was more accurate than traditional techniques, and subsequently that the clinical outcomes were improved. Cobb’s method, however, employed rigid intraoperative stabilization of the bones in a stereotactic frame, which is impractical for routine clinical use. Robotic systems have now advanced to include dynamic bone tracking technologies so that rigid fixation is no longer required. The question is -Do these robotic systems with dynamic bone tracking provide the same accuracy advantages demonstrated with robotic systems with rigidly fixed bones? We compared robot-assisted and traditionally instrumented UKA in six bilateral pairs of cadaver specimens. In all knees, a CT-based preoperative plan was performed to determine the ideal positions and orientations for the implant components. Traditional manual instruments were utilized with a tissue-sparing approach to implant one knee of each pair. A haptic robotic system acting as a virtual cutting guide was used to perform the robot-assisted UKA, again with a tissue-sparing approach. Postoperative CT scans were obtained from all knees, and the 3D placement errors were quantified using 3D-to-3D registration of implant and bone models to the reconstructed CT volumes.

The magnitudes of femoral implant orientation error were significantly smaller for the robot-assisted implants compared to traditionally implanted components (4° vs 11°, p< 0.001), but the magnitudes of femoral placement error did not reach significance (3mm vs. 5mm, p=0.056). The magnitudes of tibial implant placement error were not significantly different (4mm vs. 5mm and 7° vs. 7°, p> 0.05).

Well-placed UKA implants can provide durable and excellent functional results, which is an increasingly attractive option for young and active patients with severe compartmental osteoarthritis who wish not to have or to delay a total knee replacement.

Previous studies have demonstrated significant improvement in implant placement accuracy and clinical results with robot-assisted surgery using rigid bone fixation. This study demonstrates it is possible to achieve significant accuracy improvements with robot-assisted techniques allowing free bone movement. Additional larger trials will be required to determine if these differences are realized in clinical populations.

Measurement of precision in positioning multiple autologous osteochondral transplantation in comparison to the conventional free hand technique.

The articular surfaces of 6 cadaveric condyles (medial – lateral) were used. The knee was referenced by a navigation system (Praxim). The pins carrying the navigation detectors were positioned to the femur and to the tibia. The grafts were taken from the donor side (measurement I) with the special instrument which carried the navigation detectors. The recipient site was prepared and the donor osteochondral grafts were forwarded to the articular surface (II). The same procedure took place without navigation. The articular surface congruity was measured with the probe (measurement III)

The angle of the recipient plug removal (measurement I) with the navigation technique was 3,27° (SD 2,05°; 0°–9°). The conventional technique showed 10,73° (SD 4,96°; 2°–17°). For the recipient plug placement (measurement II) under navigated control a mean angle of 3,6° (SD 1,96°; 1°–9°) was shown, the conventional technique showed results with a mean angle of 10,6° (SD 4,41°; 3°–17°). The mean depth (measurements III) under navigated control was 0,25mm (SD 0,19mm; 0mm–0,6mm). With conventional technique the mean depth was 0,55mm (SD 0,28mm; 0,2mm –1,1mm).

The application of navigation showed that complications like diverging of the grafts leading to breakage or loosening as well as depth mismatch which can lead to grafts sitting over or under the articular surface can be avoided providing better results in comparison to the free hand procedure

Background: Navigation allows for determination of the mechanical axis of the lower extremity. We evaluated the intra- and inter-observer reliability with an image-free navigation system and determined the accuracy of the navigation system to monitor changes in lower limb alignment as compared to alignment measured with a novel 3D CT method.

Methods: A total of 13 cadaver legs were used to evaluate the intra- and inter-observer registration reliability by three observers. Navigated HTOs were then performed on all legs and pre/postoperative values of the varus-valgus angles were recorded. Data were compared to equivalent measures obtained by 3D CT using intra-class correlation coefficients (ICCs).

Results: The ICCs for intra-observer varus-valgus reliability ranged from 0.756 to 0.922, inter-observer reliability was 0.644. ICCs for navigation-CT comparison were 0.784 for varus-valgus angle (pre-op), 0.846 (postop) and 0.873 (delta). Maximum differences in navigation-CT measurements in varus-valgus angle (delta) were 4.5° for all trials. There was poor reliability and accuracy in the axial plane (tibial rotation) as well as fair reliability and accuracy in the sagittal plane (tibial slope).

Conclusion: Image-free navigation is reliable for dynamic monitoring of coronal leg alignment but shows relevant limitations in determination of sagittal and axial plane alignment.

Background: Correct ligament balance is a critical factor in both cruciate retaining and substituting total knee arthroplasty (TKA). Due to a lack in current tools, however, little data exists on gap kinematics with the patella is in its anatomical position and with the ligaments tensed. The objective of this study was to quantify the effects of the patellar position and PCL resection on gap kinematics when constant tension is applied to the medial and lateral compartments.

Methods: A novel computer-controlled tensioner was used to measure the medial and lateral gaps in 10 normal knee specimens throughout a full range of motion. Gaps were measured medially and laterally using constant applied forces of 50N, 75N and 100N per side. Gap data were acquired at 0°, 30°, 60°, 90°, 120° of flexion. The test was performed with the patella everted and reduced, and with the PCL intact and resected.

Results: At 90° of flexion:

the mean medial gap was 1.5–2.5mm smaller than the mean lateral gap for all scenarios and forces tested (p< 0.05);

During knee flexion from 30° to 90°, the PCL tended to squeeze the medial compartment by 1–2mm (p< 0.05). Increasing the force from 50N to 100N per side resulted in a mean gap increase of 0.5mm throughout the range of flexion.

Conclusions: Measurement of gap kinematics with a computer-controlled tensioner and a completely reduced patella is feasible. Everting the patella and resecting the PCL both have significant effects on flexion gap balance and symmetry. Knees which are balanced with the patella everted may be post-operatively 1–3mm more lax in flexion than planned. Retaining the PCL may result in asymmetric tightening of the medial gap from 30° to 90°.

Background: Arthroscopic femoral osteoplasties might cause prolonged operative times, restricted intraop-erative overview or insufficient localisation of surgical tools. Computer assisted techniques should improve the precision with an overall accuracy is within 1mm/1°. An automated navigated registration process matching preoperative CT data and intraoperative fluoroscopy, should allow for non-invasive registration for FAI surgery. We evaluated the general precision (I) of the CT and fluoroscopic matching process and (II) the precision of identifying the defined osseous lesions in various anatomical areas.

Material and Methods: Three cadavers (6 hip joints) utilizing a conventional navigation system were used. Before preoperative CT scans, defined osseous lesion (0.5x0.5mm) in the femoral neck, head neck junction, head region were created under fluoroscopic control. Following reference marker fixation, two fluoroscopic images (12 inch c-arm) with 30° angle differences of the hip joint were taken. Automated segmentation including CT-fluoro image fusion by the navigation system enabled a noninvasive registration process Precision of registration process was tested with a straight navigated pointer (1mm tip) trough a lateral arthroscopic portal, during virtual contact to the bone, without arthroscopic control After arthroscopic view was enabled the in vivo distance of pointer tip to bone was measured (I). In vivo real distances between inserted navigated shaver and osseous lesions was done over an anterior hip arthrotomy. Under navigated control, blinded to the situ, placement in the lesions should be done. Distances between shaver tip and osseous lesions were measured with a caliper (II).

Results: The precision for registration (I) was within 0.9mm within the femoral neck (SD 0.24mm; 0.6–1.3mm); 1.2 mm (SD 0.33mm; 0.8–2.0mm) (p> 0.05) for the head neck junction; 2.9 mm (SD 0.57mm; 1.8–3.7mm) for the femoral head (p< 0.001 respectively p< 0.001) Mean offset of the navigated shaver to the lesions (II) was 0.93 mm (SD 0.65mm; 0–2mm). Within the femoral neck a mean accuracy of 0.6mm (SD 0.59mm; 0–1.4mm), the head neck junction 0.8 mm (SD 0.78mm; 0.1–1.5mm), the femoral head 1.3 mm (SD 0.50mm; 0.6–1.7mm) was found (p> 0.05; p> 0.05; p> 0.05).

Conclusion: A combined CT-fluoroscopy matching procedure allows for a reproducible noninvasive registration process for navigated FAI surgery. Precision of the registration process itself is more accurate at the femoral neck and head-neck junction than at the femoral head area. However a navigated identification of osseous lesions was possible within 1mm deviations in all regions.

Background: A navigated 8 in 1 femoral cutting guide for TKA that does not require primary fixation or intramedullary guides was developed. The hypothesis of our study were twofold: 1) the navigation system allows for precise alignment and adjustment of a new femoral 8 in 1 cutting guide with negligible variance in the initially planned vs. achieved implant position; 2) resulting femoral cuts are very accurate without relevant cutting errors.

Material and Methods: We demonstrate our approach with the Universal Knee Instrument (UKI, Precimed Inc. USA), a versatile 8 in 1 TKA guide designed to perform all femoral cuts with a single jig. We integrated an array of “adjustable constraints” into the UKI by machining four threaded holes directly through the template. Adaptation to a navigation system has been performed by integrating the adjustable constraints protocol on the open platform Surgetics Station (PRAXIM-medivision, France), which uses image-free BoneMorphing technology. Based on navigated bone morphing the required preadjustment of the guide was done mechanically, with depth control by mini screws. Testings on 10 cadavers compared the planned vs. achieved positions of the jig before, after fixation, final implant position and planned vs. achieved cutting procedures.

Results: Results revealed for valgus/varus deviations before fixation −0.1°±0.7°, after 0.0°±0.8° (p=0.51), final implant position 0.9°±1.7° (p=0.93). For flexion before fixation −0.3°±1.3° after −0.3°±1.8° (p=0.44), final position 2.9°±2.5° (p=0.65). Distal cut height before fixation 0.0°±0.4°, after 0.1°±0.3° (p=0.61), final position 0.3°±1.0° (p=0.1). Axial rotation before −0.3°±1.1°, after fixation 0.2°±1.4° (p=0.57), final implant position 0.8°±2.7° (p=0.89). Anterior-posterior positions before fixation 0.7°±1.4°, after 1.0°±1.6° (p=0.27), final position 3.4°±1.3° (p=0.13). Highest deviations in the planned vs. actual cut position was found for the posterior cut −3.1°±2.4° in sagittal and anterior cut 0.8°±1.9° in the coronal plane. The highest mean errors in the final implant position where on the order of 3 degrees/mm in flexion and anterior-posterior positioning.

Conclusion: A novel ‘CAS-enabled 8 in 1 jig’ has been developed and validated. The system allows for direct execution of a complex, multi-planar CAS plan with single navigated device. The instrumentation is considerably simplified and eliminates the problems associated with sequential jigs.

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.

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.