Introduction

At a minimum 12 years follow-up the Authors performed a matched paired study between 2 groups: Bi-Unicompartimental (femoro-tibial) versus Total Knee Replacements, both navigated, they hypothesised that Bi-UKR guarantees a clinical score and patient satisfaction at least similar to TKR without differences in survivorship.

The objective of this paper is to demonstrate the difference in post-operative complication rates between Computer-assisted surgery (CAS) and conventional techniques in spine surgery. Several studies have shown that the accuracy of pedicle screw placement significantly improves with use of CAS. Yet, few studies have compared the incidence of post-operative complications between CAS and conventional techniques.

The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database was used to identify patients that underwent posterior lumbar fusion from 2011 to 2013. Multivariate analysis was conducted to demonstrate the difference in post-operative complication rates between CAS and conventional techniques in spine surgery.

Out of 15,222 patients, 14,382 (95.1%) were operated with conventional techniques and 740 (4.90%) were operated with CAS. Multivariate analysis showed that patients in the CAS group had less odds to experience adverse events post-operatively (OR 0.57, P <0.001).

This paper examined the complications in lumbar spinal surgery with or without the use of CAS. These results suggest that CAS may provide a safer technique for implant placement in lumbar fusion surgeries.

Introduction. This study aims to evaluate the effect of using different types of fixator on the quality of callus and complications during distraction osteogenesis in patients with achondroplasia. Materials and Methods. Forty-nine achondroplasia patients with a minimum follow-up of 36 months who underwent limb lengthening between 2005 and 2017 with external fixator only were included. Thirty-three of the patients underwent lengthening using classical Ilizarov frame, while spatial frame used for sixteen. Regenerate quality is evaluated according to the Li classification on the X-ray taken one month after the end of the distraction. Complications were noted in the follow-up period. Results. The mean age at the time of surgery was 8,6 years. The mean external fixation index (EFI) was 34,3 and 30,1 day/cm for spatial frame and Ilizarov frame respectively. Mean follow-up period of 161,62 months and mean fixator period of 257 days. Amount of lengthening was 7,2 cm for Ilizarov frame, and 7,5 cm for spatial frame. Rate of callus with good morphological quality seen at consolidation was 72,4% and 50% for Ilizarov and spatial frames respectively. Two groups show similar results of complication rates in terms of pin site infection, premature fibular consolidation, regenerate fracture, plastic deformation, knee contracture. However fibular nonunion rates were higher for Ilizarov-type fixator. Conclusions. Although spatial frame with computer assistance brings easier follow-up for deformity correction, Ilizarov-type external fixator show slightly higher rates of good quality callus during consolidation for patients with achondroplasia

Introduction. Stryker computer navigation system has been used for total knee arthroplasty (TKA) procedures since October 2008 at the Russian Ilizarov Scientific Centre for Restorative Traumatology and Orthopaedics. Material and methods. There have been 126 computer assisted TKA that accounted for 11.5 % of primary TKA within this period (1096 procedures). Arthritis of the knee joints with evident pain syndrome was an indication to TKA surgery. Arthritis of the knee joint of 27 patients (21.4 %) was accompanied by femoral deformity of various etiology with debris found in the medullary canal in several cases. The rest 99 patients (78.6 %) were regular cases of primary TKA. Results. We compared the results of correction of lower limb biomechanical axis with TKA employing navigation and without computer assistance. Regular TKA procedures showed no substantial difference in the correction of biomechanical axis. Complete correction using computer navigation was achieved in 85 % of the cases versus 79 % of the patients without navigation. The deformity up to 3° developed in 14 % of navigated cases and in 17 % of the cases without computer assistance. An error of deformity correction was 3–5° in 4 % of the cases without computer navigation. Those were cases of challenging primary TKA. So the advantages of computer navigation have become evident with greater deformities, and in the cases when intramedullary guide can hardly be used due to severe deformities in the femoral metaphysis and diaphysis, after several operative procedures of osteosynthesis with deformed, obliterating bone marrow canal or presence of debris. Complete correction using computer navigation was achieved in 85.2 % cases versus 42.8 % patients without navigation. Postoperative varus of 2° was observed in 14.8 % cases (valgus or varus deformity of 3° developed in 28.6 % of the cases without computer assistance). Conclusion. What is better: special instrumentation or navigation?. Current instrumentation can provide regular mechanical control of the limb axis and is based on the principles of intramedullary, extramedullary and even double guide placement. Image-free navigation and standard surgical techniques can equally be used for simple cases of primary TKA. Same landmarks are used. These landmarks are determined by a surgeon quite subjectively and can lead to inadequate usage of special instrumentation and computer navigation. However, computer navigation should be used in the cases when intramedullary guide can hardly be used, not desirable or possible. Special instrumentation can fail in setting a valgus angle needed with extraarticular femoral deformity. Navigation allows determining rotation more precisely in the cases when posterior femoral condyles contour (posttraumatic condition, hypoplastic condyles) is distorted. Assessment of ligament balance can be rather subjective when special instrumentation is used. Application of computer navigation is helpful for measurements of flexion and extension gaps sixe and regularity. Computer navigation is contraindicated for contractures and ankyloses of the hip joint. For the rest of the cases the choice of instrumentation is a surgeon's decision

INTRODUCTION. Unicompartmental knee arthroplasty (UKA) is considered a highly successful procedure. However, complications and revisions may still occur, and some may be related to the operative technique. Computer assistance has been suggested to improve the accuracy of implantation of a UKA. The present study was designed to evaluate the long-term (more than 10 years) results of an UKA which was routinely implanted with help of a non-image based navigation system. MATERIAL AND METHODS. All patients operated on between 2004 and 2005 for implantation of a navigated UKA were included. Usual demographic and peri-operative items have been record. All patients were prospectively followed with clinical and radiological examination. All patients were contacted after the 10 year follow-up for repeat clinical and radiological examination (KSS, Oxford knee questionnaire and knee plain X-rays). Patients who did not return were interviewed by phone call. For patients lost of follow-up, family or general practitioner was contacted to obtain relevant information about prosthesis survival. Survival curve was plotted according to Kaplan-Meier. RESULTS. 57 UKAs were implanted during the study time-frame. Final follow-up (including death or revision) was obtained for 50 cases (88%). Clinical status after 10 years was obtained for 45 cases (80%). 4 prosthetic revisions were performed for mechanical reasons during the follow- up time (7%). The 10 year survival rate was 94%. No component was considered loose at the final radiographic evaluation. No polyethylene wear was detected at the final radiographic evaluation. DISCUSSION. This study confirms our initial hypothesis, namely quite satisfactory results of a navigated implanted UKA after more than 10 years. Navigation, whose precision is no longer to be demonstrated, probably contributed to the quality of the results. A more consistent anatomical reconstruction and ligamentous balance of the knee should lead to more consistent survival of the UKA. However, superiority of navigated UKA in comparison to conventional implanted UKA is difficult to prove because of the subtle differences expected in mostly underpowered studies. Longer term follow-up may be required

INTRODUCTION. Total knee arthroplasty (TKA) is considered a highly successful procedure. Survival rates of more than 90% after 10 years are generally reported. However, complications and revisions may still occur for many reasons, and some of them may be related to the operative technique. Computer assistance has been suggested to improve the accuracy of implantation of a TKA (Jenny 2005). Short term results are still controversial (Roberts 2015). However, few long term results have been documented (Song 2016). The present study was designed to evaluate the long-term (more than 10 years) results of a TKA which was routinely implanted with help of a non-image based navigation system. The 5- to 8-year of this specific TKA has already been documented (Jenny 2013). The hypothesis of this study will be that the 10 year survival rate of this TKA will be improved in comparison to historical papers when analyzing survival rates and knee function as evaluated by the Knee Society Score (KSS). MATERIAL AND METHODS. All patients operated on between 2001 and 2004 for implantation of a navigated TKA were eligible for this study. Usual demographic and peri-operative items have been record. All patients were prospectively followed with clinical and radiological examination. All patients were contacted after the 10 year follow-up for repeat clinical and radiological examination (KSS, Oxford knee questionnaire and knee plain X-rays). Patients who did not return were interviewed by phone call. For patients lost of follow-up, family or general practitioner was contacted to obtain relevant information about prosthesis survival. Survival curve was plotted according to Kaplan-Meier. RESULTS. 247 TKAs were implanted during the study time-frame. 225 cases had an optimal lower limb axis (HKA angle between 177° and 183°) after TKA (91%). Final follow-up (including death or revision) was obtained for 200 cases (81%). Clinical status after 10 years was obtained for 146 cases (59%) (KSS, 102 cases – Oxford questionnaire, 146 cases – radiologic evaluation, 94 cases). 4 prosthetic revisions were performed for mechanical reasons during the follow-up time (1%). The 10 year survival rate was 98%. The mean KSS was 188 points. The mean Oxford score was 55 points. No component was considered loose at the final radiographic evaluation. No polyethylene wear was detected at the final radiographic evaluation. DISCUSSION. This study confirms our initial hypothesis, namely quite satisfactory results of navigated implanted TKA after more than 10 years. Navigation, whose precision is no longer to be demonstrated, probably contributed to the quality of the results. A more consistent anatomical reconstruction and ligamentous balance of the knee should lead to more consistent survival of the TKA. Other authors did observe similar results (Baumbach 2016). However, superiority of navigated TKA in comparison to conventional implanted TKA is difficult to prove because of the subtle differences expected in mostly underpowered studies. Longer term follow-up may be required

Despite many new methods with preoperative or intra-operative assistance to improve the accuracy of leg alignment, traditional intramedullary (IM) method of bone cutting is still the most commonly used. Traditional TKR using IM guide has more outliers comparing to new computer aided methods, especially in bowing femur which is more prevalent in Asian population. And IM guide could not be used when there is a medullary bony pathology. Avoiding entrance of medullary cavity has been proposed as one of criteria of minimally invasive TKA. We have designed an extramedullary (EM) guide for the distal femoral bone cutting with millimeter to millimeter increment which is compatible with all posterior referencing instrumentation systems. With mechanical line as the guide line on long leg X-ray film taking with the knee and foot facing anteriorly, the amount of distal femoral bone cutting was measured and recorded on computer screen pre-operatively. During surgery, distal femoral cutting was performed using the EM cutting jig for coronal alignment adjustment tool and anterior femoral cortex and a guide post as sagittal alignment guide. We retrogratively compared the post-operation long leg X-ray film of two hundreds patients using IM or EM guides, the mechanical alignment of femoral components were measured in coronal and sagittal planes. The results showed no significant difference in distribution and the ratio of outliers. However, if the bowing of femur is more than 8 degree, the outlier is more in the IM group. We have applied this technique in 8 patients having medullary pathology including plates or nails in femur. All patients got good post-operative limb alignment without the needs of computer assistance device during surgery. In conclusion, the technique is easy and the instrument is simple. The operative time was not prolonged; the medullary cavity was not entered and compatible with the principle of MIS technique. In case of medullary cavity is obstructed, it is cost-effective by using our EM guide comparing to other methods such as CAOS or PSI

Recently, several preliminary reports have been issued on the application of computer assistance to bone tumour surgery. Surgical navigation systems can apply three-dimensional images such as CT and MR images to intraoperative visualization. Although CT is better at describing cortical bone status, MRI is considered the best method for defining the extent of marrow involvement for bone tumours and for planning surgical resection in bone tumour surgery. There have been a few reports on the application of MR imaging to navigation-assisted bone tumour surgery through CT–MR image fusion. However, the CT–MRI fusion technique requires additional costs and exposure of the patient to radiation from the preoperative CT, as well as additional time for image fusion. Above all, the image fusion process is a kind of registration (image to image registration) that inevitably leads to registration error. Herein we describe a new method for the direct application of MR images to navigation-assisted bone tumour surgery as an alternative to CT–MRI fusion. Six patients with an orthopaedic malignancy were employed for this method during navigation-assisted tumour resection. Resorbable pin placement and rapid 3-dimensional spoiled gradient echo sequences made the direct application of MR images to computer-assisted bone tumour surgery without CT–MR image fusion possible. A paired-point registration technique was employed for patient-image registration in all patients. It took 20 min on average to set up the navigation (range 15 to 25 minutes). The mean registration error was 0.98 mm (range 0.4 to 1.7 mm). On histologic examination, distances from tumours to resection margins were in accord with preoperative plans. Mean duration of follow-up was 25.8 months (range 18 to 32 months). No patient had a local recurrence or distant metastasis at the last follow-up. Direct patient-to-MRI registration is a very useful method for bone tumour surgery, permitting the application of MR images to intraoperative visualization without any additional costs or exposure of the patient to radiation from the preoperative CT scan

While double-bundle anterior cruciate ligament (ACL) reconstruction attempts to recreate the two-bundle anatomy of the native ACL, recent research also indicates that double-bundle reconstruction more closely reproduces the biomechanical properties of the ACL and restores the rotatory and sagittal stability to the level of the intact knee that was not attainable with anatomic single-bundle reconstruction. Though double-bundle reconstruction provides these potential biomechanical benefits, it poses a significant challenge to the surgeon who must attempt to accurately place twice as many tunnels while avoiding tunnel convergence compared to single-bundle reconstruction. In addition, previous work has shown that tunnel malpositioning may cause grafts that fail to reproduce the native biomechanics of the ACL, increase graft tension in deep knee flexion, increase anterior tibial translation, and produce lower IKDC (International Knee Documentation Committee) scores. We hypothesise that experienced surgeons without the use of computer-assisted navigation will place tunnels on the tibial plateau and lateral femoral condyle that more closely emulate the locations of the native anteromedial (AM) and posterolateral (PL) ACL bundles than inexperienced surgeons with the use of computer-assisted navigation. A novice surgeon group comprised of three medical students each performed double-bundle ACL reconstruction using passive computer-assisted navigation on a total of eleven cadaver knees. Their individual results were compared to three experienced orthopaedic surgeons each performing the identical procedure without the use of computer-assisted navigation on a total of nine cadaver knees. There were no significant differences in placement of either the AM or PL tunnels on the tibial plateau between novice surgeons using computer-assisted navigation and experienced surgeons without the use of computer navigation. On the lateral femoral condyle, novice surgeons placed the AM and PL tunnels significantly more anterior along Blumensaat's line on average compared to experienced surgeons. Both groups placed femoral AM and PL tunnels anterior to previously described AM and PL bundle positions. Novice surgeons utilizing computer-assisted navigation and experienced surgeons without computer assistance place the AM and PL tunnels on the tibial side with no significant difference. On the lateral femoral condyle, novice surgeons utilising computer-assisted navigation place tunnels significantly anterior along Blumensaat's line compared to experienced surgeons without the use of computer navigation

Primary malignant bone tumor often requires a surgical treatment to remove the tumor and sometimes restore the anatomy using a frozen allograft. During the removal, there is a need for a highest possible accuracy to obtain a wide safe margin from the bone tumour. In case of reconstruction using a bone allograft, an intimate and precise contact at each host-graft junction must be obtained (Enneking 2001). The conventional freehand technique does not guarantee a wide safe margin nor a satisfying reconstruction (Cartiaux 2008). The emergence of navigation systems has procured a significant improvement in accuracy (Cartiaux 2010). However, their use implies some constraints that overcome their benefits, specifically for long bones. Patient-specific cutting guides become now available for a clinical use and drastically simplify the intra-operative set-up. We present the use of pre-operative assistances to produce patient-specific cutting guides for tumor resection and allograft adjustment. We also report their use in the operative room. We have developed technical tools to assist the surgeon during both pre-operative planning and surgery. First, the tumor extension is delineated on MRI images. These MRI images are then merged with Computed Tomography scans of the patient. The tumor and the CTscan are loaded in custom software that enables the surgeon to define target (desired) cutting planes around the tumor (Paul 2009) including a user-defined safe margin. Finally, cutting guides are designed on the virtual model of the patient as a mould of the bone surface surrounding the tumor, materialising the desired cutting planes. When required, a massive bone allograft is selected by comparing shapes of the considered patient's bone and available allografts. The resection planes are transferred onto the selected allograft and a second guide is designed for the allograft cutting. The virtually-designed cutting guides are then manufactured by a rapid prototyping machine using biocompatible material. This procedure has been used to excise a local recurrence of a tibial sarcoma and reconstruct the anatomy using a frozen tibial allograft. The pre-operative planning using virtual models of the patient's bone, tumor and the available allografts enabled the surgeon to localise the tumor, define the desired cutting planes and select the optimal allograft. Patient- and allograft-specific guides have been designed and manufactured. A stable and accurate positioning of guide onto the patient's tibia was made easier thanks to the plate formerly put in place during the previous surgery. An accurate positioning of the allograft cutting guide has been obtained thanks to its design. The obtained reconstruction was optimal with a adjusted allograft that was perfectly fitting the bone defect. The leg alignment was also optimally restored. Computer assistances for tumor surgery are progressively appearing. We have presented at CAOS 2010 an optical navigation system for tumor resection in the pelvis that was promising. However, such a tool is not well adapted for long bones. We have used patient-specific guides on a clinical case to assess the feasibility of the technique and check its accuracy in the resection and reconstruction. The surgeon has benefited from the 3D planning to define his strategy. He had the opportunity to select the optimal transplant for his patient and plan the same cuttings for the allograft and the patient. During the surgery, guide positioning was straightforward and accurate. The bone cuttings were very easy to perform. The use of custom guides decreases the operating time when compared to the conventional procedure since there is no need for measurements between cutting trajectories and anatomical landmarks. Furthermore, the same cutting planes were performed around the tumor and onto the allograft to obtain a transplant that optimally fills the defect. We recommend the use of such an intra-operative assistance for tumor surgery

Pertrochanteric femoral fractures are common and intramedullary nailing with a proximal femoral nail (PFNA®) is an accepted method for the surgical treatment. Accurate guide wire and subsequent hardware placement in the femoral neck is believed to be essential in order to avoid mechanical failure. Malpositioned implants may lead to rotational or angular malalignment or “cut out” in the femoral neck. Hip and knee arthritis might be a potential long-term consequence. The conventional technique might require multiple guidewire passes, and relies heavily on fluoroscopy. A computer-assisted surgical planning and navigation system based on 2D-fluoroscopy was developed in-house as an intraoperative guidance system for navigated guide wire placement in the femoral neck and head. To support the image acquisition process, the surgeon is supported by a so-called “zero-dose C-arm navigation” module. This tool enables a virtual radiation-free preview of the X-ray images of the femoral neck and head. The aim of this study was to compare PFNA® insertion using this system to conventional implantation technique. We hypothesised that guide wire and subsequent implant placement using our software decreases radiation exposure to the minimum of two images and reduces the number of drilling attempts. Furthermore, accuracy of implant placement in comparison to the conventional method might be improved and operation time shortened. We used 24 identical intact left femoral Sawbones® to simulate reduced pertrochanteric femoral fractures. First, we performed placement of the PFNA® into 12 Sawbones using the conventional fluoroscopic technique (group 1). Secondly, we performed placement of the PFNA® into 12 Sawbones guided by the computer-assisted surgical planning software (group 2). In each group, we first performed open and secondly minimal-invasive intramedullary nailing in six sawbones each. For minimal-invasive guide wire placement, a surgical drape imitated soft tissue coverage. Conventional and navigated technique used a C-arm fluoroscope (Siemens IsoC 3D®, Erlangen, Germany) in conventional 2D mode. Guidewire and subsequent blade placement in the femoral neck was evaluated. We documented: 1: the number of fluoroscopic images; 2: the total number of drilling attempts; 3: implant placement accuracy (3.1. Tip apex distance (TAD); 3.2. visible penetrations of the femoral neck and head; 3.3. blade-corticalis bone distance in the anteroposterior and lateral plane) and the 4: operation time. The number of fluoroscopic single shots taken to achieve an acceptable PFNA®-blade position was reduced significantly with computer-assistance by 71.5% (p<0.001) in the open and by 72,4% (p<0.001) in the minimally invasive technique. In each operation two X-rays for final documentation were taken. The average number of drilling attempts for the computer-guided system was significantly (p<0.05) less than that of the conventional technique in the minimally invasive procedure. The average number of drilling attempts showed no difference between the computer-assisted and conventional techniques in the open procedure. Accuracy of implant placement showed no difference between the computer-assisted and the conventional group. Computer assistance significantly increased the mean operation time for fixation of pertrochanteric femoral fractures with a PFNA® by 79.8% (p<0.001) in the open technique and by 54.4% (p<0.001) in the minimally invasive technique. Use of our computer-guided system for fixation of pertrochanteric femoral fractures by a PFNA® decreases the number of fluoroscopic single shots and of suboptimal guide wire passes while maintaining blade placement accuracy that is equivalent to the conventional technique. Computer-assisted surgery with our system increases the operation time and has just been tested in non-fractured sawbones. Although these results are promising, additional studies including fractured sawbones and cadaver models with extension of the navigation process to all steps of PFNA® introduction and with the goal of reducing the operation time are indispensable before integration of this navigation system into the clinical workflow

INTRODUCTION. In computer-aided total knee arthroplasty (TKA), surgical navigation systems (SNS) allow accurate tibio-femoral joint (TFJ) prosthesis implantation only. Unfortunately, TKA alters also normal patello-femoral joint (PFJ) functioning. Particularly, without patellar resurfacing, PFJ kinematics is influenced by TFJ implantation; with resurfacing, this is further affected by patellar implantation. Patellar resurfacing is performed only by visual inspections and a simple calliper, i.e. without computer assistance. Patellar resurfacing and motion via patient-specific bone morphology had been assessed successfully in-vitro and in-vivo in pilot studies aimed at including these evaluations in traditional navigated TKA. The aim of this study was to report the current experiences in-vivo in two patient cohorts during TKA with patellar resurfacing. MATERIALS AND METHODS. Twenty patients with knee gonarthrosis were divided in two cohorts of ten subjects each and implanted with as many fixed-bearing posterior-stabilised prostheses (NRG® and Triathlon®, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. Fifteen patients were implanted; five patients of the Triathlon cohort are awaiting hospital admission. TKAs were performed using two SNS (Stryker®-Leibinger, Freiburg-Germany). In addition to the traditional knee SNS (KSNS), the novel procedure implies the use of the patellar SNS (PSNS) equipped with a specially-designed patellar tracker. Standard navigated procedures for intact TFJ survey were performed using KSNS. These were performed also with PSNS together intact PFJ survey. Standard navigated procedures for TFJ implantation were performed using KSNS. During patellar resurfacing, the patellar cutting jig was fixed at the desired position with a plane probe into the saw-blade slot; PSNS captured tracker data to calculate bone cut level/orientation. After sawing, resection accuracy was assessed using a plane probe. TFJ/PFJ kinematics were captured with all three trial components in place for possible adjustments, and after final component cementing. A calliper and pre/post-TKA X-rays were used to check for patellar thickness/alignment. RESULTS. This protocol was performed successfully in TKAs, resulting in 30 min longer TKA. Final lower limb misalignment was within 0.5°, resurfaced patella was 0.4±1.2 mm thinner than the native, and patellar cut was 0.4°±4.1° laterally tilted. Final PFJ kinematics was taken within the reference normality in both series. PFJ flexion, tilt and medio-lateral shift range were 66.9°±8.5° (minimum÷maximum, 15.6°÷82.5°), 8.0°±3.1° (−5.3°÷2.8°), and 5.3±2.0 mm (−5.5÷0.2 mm), respectively. Significant (p<0.005) correlations were found between the internal/external rotation of the femoral component and PFJ tilt (R. 2. =0.41), and between the mechanical axis on the sagittal plane and PFJ flexion (R. 2. =0.44) and antero-posterior shift (R. 2. =0.45). Patellar implantation parameters were confirmed by X-ray inspections. Discrepancies in thickness up to 5 mm were observed between SNS- and calliper-based measurements. CONCLUSIONS. These results support relevance/efficacy of patellar tracking in in-vivo navigated TKA and may contribute to a more comprehensive assessment of the original whole knee, i.e. including also PFJ. Patellar preparation would be supported for suitable component positioning in case of resurfacing, but, conceptually, also in not-resurfacing if SNS does not reveal PFJ abnormalities., Using this procedure in the future, TFJ/PFJ abnormalities can be corrected intra-operatively by more cautious bone cut preparation and prosthetic positioning on the femur, tibia and patella

During total knee replacement (TKR), surgical navigation systems (SNS) allow accurate prosthesis component implantation by tracking the tibio-femoral joint (TFJ) kinematics in the original articulation at the beginning of the operation, after relevant trial components implantation, and, ultimately, after final component implantation and cementation. It is known that TKR also alters normal patello-femoral joint (PFJ) kinematics resulting frequently in PFJ disorders and TKR failure. More importantly, patellar tracking in case of resurfacing is further affected by patellar bone preparation and relevant component positioning. The traditional technique used to perform patellar resurfacing, even in navigated TKR, is based only on visual inspection of the patellar articular aspect for clamping patellar cutting jig and on a simple calliper to check for patellar thickness before and after bone cut, and, thus, without any computer assistance. Even though the inclusion in in-vivo navigated TKR of a procedure for supporting also patellar resurfacing based on patient-specific bone morphology seems fundamental, this have been completely disregarded till now, whose efficacy being assessed only in-vitro. This procedure has been developed, together with relevant software and surgical instrumentation, as an extension of current SNS, i.e. TKR is navigated, at the same time measuring the effects of every surgical action on PFJ kinematics. The aim of this study was to report on the first in-vivo experiences during TKR with patellar resurfacing. Four patients affected by primary gonarthrosis were implanted with a fixed bearing posterior-stabilised prosthesis (NRG, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. All TKR were performed by means of two SNS (Stryker®-Leibinger, Freiburg, Germany) with the standard femoral/tibial trackers, the pointer, and a specially-designed patellar tracker. The novel procedure for patellar tracking was approved by the local ethical committee; the patients gave informed consent prior the surgery. This procedure implies the use of a second system, i.e. the patellar SNS (PSNS), with dedicated software for supporting patellar resurfacing and relative data processing/storing, in addition to the traditional knee SNS (KSNS). TFJ anatomical survey and kinematics data are shared between the two. Before surgery, both systems were initialised and the patellar tracker was assembled with a sterile procedure by shaping a metal grid mounted with three markers to be tracked by PSNS only. The additional patellar-resection-plane and patellar-cut-verification probes were instrumented with a standard tracker and a relevant reference frame was defined on these by digitisation with PSNS. Afterwards, the procedures for standard navigation were performed to calculate preoperative joint deformities and TFJ kinematics. The anatomical survey was performed also with PSNS, with relevant patellar anatomical reference frame definition and PFJ kinematics assessment according to a recent proposal. Standard procedures for femoral and tibial component implantation, and TFJ kinematics assessment were then performed by using relevant trial components. Afterwards, the procedure for patellar resection begun. Once the surgeon had arranged and fixed the patellar cutting jig at the desired position, the patellar-resection-plane probe was inserted into the slot for the saw blade. With this in place, the PSNS captured tracker data to calculate the planned level of patellar bone cut and the patellar cut orientation. Then the cut was executed, and the accuracy of this actual bone cut was assessed by means of the patellar-cut-verification probe. The trial patellar component was positioned, and, with all three trial components in place, TFJ and PFJ kinematics were assessed. Possible adjustments in component positioning could still be performed, until both kinematics were satisfactory. Finally, final components were implanted and cemented, and final TFJ and PFJ kinematics were acquired. A sterile calliper and pre- and post-implantation lower limb X-rays were used to check for the patellar thickness and final lower limb alignment. The novel surgical technique was performed successfully in all four cases without complication, resulting in 30 min longer TKR. The final lower limb alignment was within 0.5°, the resurfaced patella was 0.4±1.3 mm thinner than in the native, the patellar cut was 1.5°±3.0° laterally tilted. PFJ kinematics was taken within the reference normality. The patella implantation parameters were confirmed also by X-ray inspection; discrepancies in thickness up to 5 mm were observed between SNS- and calliper-based measurements. At the present experimental phase, a second separate PSNS was utilised not to affect the standard navigated TKR. The results reported support relevance, feasibility and efficacy of patellar tracking and PFJ kinematics assessment in in-vivo navigated TKR. The encouraging in-vivo results may lay ground for the design of a future clinical patella navigation system the surgeon could use to perform a more comprehensive assessment of the original whole knee anatomy and kinematics, i.e. including also PFJ. Patellar bone preparation would be supported for suitable patellar component positioning in case of resurfacing but, conceptually, also in not resurfacing if patellar anatomy and tracking assessment by SNS reveals no abnormality. After suitable adjustment and further tests, in the future if this procedure will be routinely applied during navigated TKR, abnormalities at both TFJ and PFJ can be corrected intra-operatively by more cautious bone cut preparation on the femur, tibia and also patella, in case of resurfacing, and by correct prosthetic component positioning

Introduction. Valgus knee deformity is associated especially with differences in anatomy between medial and lateral femoral condyles. Vertically smaller lateral condyle and more distally located medial condyle cause valgus deformity in extension. The anteroposterior dimensions of both condyles influence the knee axis in flexion. In a „true“ valgus knee there is a mismatch between both condyles in both the vertical and anteroposterior dimensions, the lateral condyle is generally smaller. In a „false“ valgus knee there is no mismatch between anteroposterior dimensions of both condyles, the knee axis changes from valgus into varus with increased degree of flexion and lateral soft tissue structures are that's why not so contracted as in „true“ valgus knee deformity, where the knee stays in valgus deviation during the whole range of motion. The aim of the study was to preoperatively identify and analyse patterns of passive movement of osteoarthritic valgus knees with imageless navigation system to optimise surgical approach and intra-operative tissue handling during subsequent total knee replacement (TKR) surgery. Material and Methods. TKR were prospectively performed in 50 valgus knees. Cases with severe bony destruction and enormous soft tissue laxity were excluded from the study. The kinematic navigation system used was OrthoPilot® (Aesculap, Tuttlingen, Germany). It is designed to produce a numerical output of varus/valgus deviation of the knee against the degree of flexion. Before skin incision for TKR surgery, active markers were attached percutaneusly to the femur and the tibia with bicortical screws to create two ‘rigid bodies’. After the registration process the kinematic analysis was performed by passive movement of the knee. The mechanical axis was recorded at 0°, 30°, 60°, 90°, and 120° of flexion. The valgus deformity persistent through the whole range of motion was called „true“ and the valgus deformity passing into varus with flexion was called „false“. In „true“ valgus knees the lateral approach according to Keblish was used, in „false“ valgus knees we used standard medial parapatellar approach. Results. The pre-operative valgus deformity in extension ranged from 13° to 4° (mean 7,8°). We observed „true“ valgus type deformity during passive range of movement in 34 cases (68 %) and „false“ type of kinematics in 16 cases (32 %). The average value of valgus deviation in extension in „true“ group was 7,9° (range, 13° to 4°) and in „false“ group 7,5° (range, 9° to 6°), without statistically significant difference. In the „true“ valgus deviation group the value of deformity gradually decreased with flexion in all cases. The mean difference between axis deviation in 0° and 120° of flexion was 5,5° (range, 10° to 1°) in this group. In the „false“ valgus group the varus deviation was observed either already in 60° of flexion or in most cases in 90° of flexion. The mean difference between axis deviation in 0° and 120° of flexion in this group was much more significant – 12,0° (range, 14° to 10°) – there was statistically significant difference between both groups. The mean time necessary for data collection before surgery was 6 minutes (range, 4 to 11 minutes); afterwards, tha navigation was used for TKR implantation. No complications were observed regarding to the navigation usage. Subsequently correct soft tissue balance was achieved in all TKRs using this method. Conclusions. Computer navigation assistance can easily and fast help to identify the character of valgus deformity („true“ or „false“) just before skin incision. In „true“ valgus deviation lateral structures (iliotibial band, vastus lateralis tendon, lateral collateral ligament, and the popliteus muscle) are tight and lateral approach according to Keblish may be necessary for appropriate release and soft tissue balancing during TKR surgery. Mostly used standard medial parapatellar approach is always sufficient in „false“ valgus knees. Computer navigation can help surgeon to choose the appropriate parapatellar approach (medial or lateral) just before the surgery without significant time lost