The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA, the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered ‘alignment outliers’ in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients’ own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients’ own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal

Introduction. In major orthopaedic departments, typically several total knee systems are used. Each system requires several sets of instruments, each set with many trays of complicated and expensive parts. The logistics and costs of maintainance are considerable. Our overall goal is to investigate the feasibility of autoclavable single-use 3D printed instruments made from a polymeric material, used for any type of total knee design. The procedure will be standardized and adjustments easy to implement. Each set will be packaged individually, and used for a single case. There are many aspects to this study; in this part, the aims are to identify suitable materials for autoclavability and strength, and then to compare the accuracy of a novel design of 3D printed tibial cutting guide with a current metallic guide. Methods. Test samples were designed to simulate shapes in current instruments, such as mating pegs and holes, threaded screws, and slotted blocks. Each set was produced in biocompatible materials, ABS-M30i, VeroClear (MED610), Ultem1010, and Nylon 12. Each part was laser scanned, and then imaged virtually using a reverse engineering software (GeoMagic). Manual measurements of key dimensions were also made using calipers. The parts were autoclaved using a standardized protocol, 30 minutes at 250° F. All parts were re-scanned and measured to determine any changes in dimensions. To test for strength and abrasion resistance, the slotted blocks were pinned to sawbones model tibias, and an oscillating saw used to cut through the slot. A compact 3D printed tibial cutting guide was then designed which fitted to the proximal tibia and allowed varus-valgus, tibial slope and height adjustments. A small laser attached to the guide projected to a target at the ankle. Tests were made on 20 sawbones, and compared with 20 with a standard metal cutting guide. Digitization was used to measure the angles of the cuts. Results. Prior to autoclaving, the mating parts of all parts were congruent, except for Nylon 12 which had processing debris in slots and screw threads. The ABS-M30i shapes became grossly deformed after autoclaving. The other materials experienced only small changes in dimensions without loss of overall shape, but the slot of the Nylon 12 block was stenotic, 1.4 mm compared to 0.9 mm before autoclaving. In saw blade testing, the VeroClear block fractured through the corner of the slot, while the Nylon 12 block deformed due to heating. The Ultem1010 block produced a small amount of debris, but maintained its shape without any structural damage. In the tests of the tibial cutting guide the 3D printed laser-guided tibial cutting guide resulted in a mean absolute error of 1.72°±1.31° and 1.19°±0.93°, for the tibial slope and varus-valgus respectively. For the conventional guides, these values were 3.78°±1.98° and 2.33°±0.98°, respectively. These measurements were found to be statistically significant with p values of 0.004 and 0.001, respectively. Conclusions. Thus far, apart from patient specific cutting guides and trial components, 3D printing has had limited applications in total knee surgery. As cost containment remains prominent, the use of 3D printing to produce standardized instruments may become viable. These instruments would not require pre-op planning such as CT or MRI, yet allow patient-specific angular settings. Our results indicated that Ultem1010 is a promising material, while a novel tibial cutting guide showed higher accuracy than standard, as well as being quicker to use. These initial tests indicated the viability of 3D printed instruments, but further work will include design and evaluation of the other cutting guides, manufacturing logistics such as in-house or company- based, and economics

Introduction and Aims. Sensor technology is seeing increased utility in joint arthroplasty, guiding surgeons in assessing the soft tissue envelope intra-operatively (OrthoSensor, FL, USA). Meanwhile, surgical navigation systems are also transforming, with the recent introduction of inertial measurement unit (IMU) based systems no longer requiring optical trackers and infrared camera systems in the operating room (i.e. OrthAlign, CA, USA). Both approaches have now been combined by embedding an IMU into an intercompartmental load sensor. As a result, the alignment of the tibial varus/valgus cut is now measured concurrently with the mediolateral tibiofemoral contact load magnitudes and locations. The wireless sensor is geometrically identical to the tibial insert trial and is placed on the tibial cutting plane after completing the proximal tibial cut. Subsequently, the knee is moved through a simple calibration maneuver, rotating the tibia around the heel. As a result, the sensor provides a direct assessment of the obtained tibial varus/valgus alignment. This study presents the validation of this measurement. Method. In an in-vitro setting, sensor-based alignment measurements were repeated for several simulated conditions. First, the tibia was cut in near-neutral alignment as guided by a traditional, marker-based surgical navigation system (Stryker, MI, USA). Subsequently, the sensor was inserted and a minimum of five repeated sensor measurements were performed. Following these measurements, a 3D printed shim was inserted between the sensor and the tibial cutting plane, introducing an additional 2 or 4 degrees of varus or valgus, with the measurements then being repeated. Again, for each condition, a minimum of five sensor measurements were performed. Following completion of the tests, a computed tomography (CT) scan of the tibia was obtained and reconstructed using open source software (3DSlicer). Results. By identifying anatomic landmarks on the 3D reconstructed tibia and fibula, the actual tibial coronal alignment of 0.43° valgus was obtained (Figure 1a), in close agreement with the one degree valgus alignment reported by the optical navigation system. Both reference values match well with the 1.16° valgus (SD: 0.91°) calculated by the IMU- based sensor system. When introducing the shims, the sensor consistently predicts the relative angular changes, with a maximum relative difference between the expected and measured condition of 1.29°. For each condition, the standard deviation remained small, with values ranging from 0.27° to 0.60° based on at least five repeated measures (Figure 1b). Conclusion. In conclusion, this paper demonstrates that sensor technology can be used to evaluate tibial coronal alignment, with an accuracy in line with available 3D measurement systems. The authors recognize however the need for further validation, currently being undertaken

Background:. Varus or Valgus malpositioning of tibial prosthetic components in total knee replacement (TKR) surgery may lead to early failure due to increased polyethelene wear, soft tissue imbalancing, aseptic loosening and eventually revision surgery. Therefore, the clinical success of total knee arthroplasty (TKA) correlates with good component alignment. Conventional methods of coronal tibial alignment result in an acceptable range of prosthetic alignment in relation to the anatomical axis (tibial tangent angle). The measurement ranges from 90° ± 3°, but literature quotes that there is up to 27% of cases with coronal tibial alignment deviation of greater than 3°. Many studies show that the use of conventional intramedullary rod alignment versus extramedullary rod alignment gives similar results. The tibial alignment and overall prosthetic alignment in TKA has improved remarkably by using computerized navigation assisted surgery (CAS), with tibial tangent angle of 90° ± 3 in up to 97% of cases. However, the success of accurate tibial and femoral alignment depends on the surgeon and the data fed to the computer. Also long term results on survival rates of TKR using CAS is still pending. It is clear that assessing tibial alignment (ie. anatomical axis) with whatever method used faces challenges which will affect the tibial bony cuts and the final tibial tangent angle. To achieve a 90° tibial cut in relation to the anatomical axis we made use of fluoroscopy intra-operatively to assess the anatomical axis of the tibia and the correct alignment of the tibial cutting block. Methods:. TKR's were performed on 36 consecutive patients over a 4 month period. The aim was to assess the coronal tibial alignment of the tibial component intra-operatively using fuloroscopy. A conventional manual extramedullary alignment rod with its tibial cutting block was used and the final positioning was confirmed with an image intensifier. The tibial cutting block must be at 90° to the anatomical axis of the tibia. The rest of the TKR procedures were performed as routinely described. Post-operative radiographs were taken on the same day as the surgery and again at six week follow up visit when the tibial tangent angle was measured. Results:. The coronal tibial angulation was consistent at 0° in 32 knees with a 1°–2° deviation in 4 knees. Conclusion:. We conclude that the use of fluoroscopy intra-operatively can improve the tibial component alignment and thus decrease the cumulative errors which have significant and dramatic effects on the function and the longevity of the total knee prosthesis

INTRODUCTION. The alignment of components in total knee arthroplasty (TKA) is perceived to be one of the most influential factors in determining the long-term outcomes. A contemporary debate exists regarding the choice of the alignment method. As a vast majority of the surgeons support the basis of the mechanical alignment philosophy (MA), others believe in the concept of anatomical alignment theory (AA) to closely match the anatomy of the femur and the tibia of the native knee [1]. This study was intended to evaluate the accuracy of achieving a planned tibial resection target using either the MA or AA methods. Materials and Methods. Five healthy cadaveric knees (tibia and foot only) were studied. Four surgeons were independently asked to position a tibial cutting block (without pinning) using conventional extramedullary mechanical instrumentation (Exactech LPI instrumentation, Gainesville, FL, USA). Surgeons were asked to target a predefined proximal tibial cut according to MA (Varus= 0°, posterior slope= 3°, resection level= 10 mm) or to AA (Varus= 3°, posterior slope= 6°, resection level= 9 mm). Once the surgeon expressed satisfaction with the achieved position of the tibial cutting block, the planned resection was recorded using an imageless guidance system (ExactechGPS. ®. , Blue-Ortho, Grenoble, FR). Surgeons completed at least three positioning trial for each alignment method on each cadaver. The accuracy and outliers (deviated more than 2°/mm from the target [2]) of resection planning were compared between the MA and AA methods. Statistical significance was defined as p< 0.05. Results. The signed deviations were significantly greater for the AA method than the MA method for both the varus/valgus and the posterior tibial slope parameters (Table 1). A significant increase of the percentage of outliers for the varus/valgus parameter was observed in the AA (43.6%) method compared to the MA (8.9%) method (Table 2). Regardless the type of method, the surgeons tended to place the cutting block with less varus than expected per the plan. Discussion. While only focusing on the tibial resection planning, the findings of this study coincide with previous studies reporting that conventional instruments can achieve satisfactory lower limb alignment (within ± 3° of varus/valgus relative to mechanical axis) in 60% to 80% of the cases [3–4]. This study also highlights the difficulty of reproducing resection parameters associated with the AA method using conventional instrumentation. Notably, it was observed that in more than 40% of the cases, the deviation from the targeted value in the coronal plane was higher than 2°; which may impact clinical outcomes. Based on these findings, advanced technologies, such as computer navigation, may be of particular use to proponents of the AA method to assist in reducing deviations from planned resections

Introduction. The conventional bone resection technique in TKA is recognized as less accurate than computer-assisted surgery (CAS) and patient-matched instrumentation (PMI). However, these systems are not available to all surgeons performing TKAs. Furthermore, it was recently reported that PMI accuracy is not always better than that of the conventional bone resection technique. As such, most surgeons use the conventional technique for distal femur and proximal tibia resection, and efforts to improve bone resection accuracy with conventional technique are necessary. Here, we examined intraoperative X-rays after bone resection of the distal femur and proximal tibia with conventional bone resection technique. If the cutting angle was not good and the difference from preoperative planning was over 3º, we considered re-cutting the bone to correct the angle. Methods. We investigated 117 knees in this study. The cutting angle of the distal femur was preoperatively determined by whole-length femoral X-ray. The conventional technique with an intramedullary guide system was used for distal femoral perpendicular resection to the mechanical axis. Proximal tibial cutting was performed perpendicular to the tibial shaft with an extramedullary guide system. The cutting angles of the distal femur and proximal tibia were estimated by intraoperative X-ray with the lower limb in extension position. When the cutting angle was over 3º different from the preoperatively planned angle, re-cutting of distal femur or proximal tibia was considered. Results. On the intraoperative X-ray, the average femoral cutting angle difference from preoperative planning was 0.1º (SD: 2.6º) and the average tibial cutting angle was 1.1º varus (SD: 1.8º). Over 3º and 5º outlier cases were observed in 15 knees and 5 knees on the femoral side and in 15 knees and 3 knees on the tibial side respectively. Cutting angle correction was performed in 18 knees on the distal femur and 17 knees on the proximal tibia. On the postoperative X-ray, over 3º and 5º outliers were observed in 16 knees and only 1 knee on the femoral side and in 11 knees and no cases on the tibial side respectively. Cases with outliers over 3º were not different between intra- and postoperative estimation; however, the number of over 5º outliers was decreased from 8 knees (6.8%) to 1 knee (0.9%) including both the femoral and tibial sides (p < 0.05, Chi-square test). Discussion. Precise bone cutting technique is important for TKA; however, the bone resection accuracy of the conventional technique is far from satisfactory. CAS, PMI, and portable navigation have been developed for precise bone resection in TKA. However, these new technologies involve additional cost and have not been clearly shown to improve accuracy. Most surgeons currently use the conventional technique, and we think it is possible to improve bone resection accuracy with the conventional technique in TKA. Our method is simple and requires just one intraoperative X-ray. This is cost-effective and can be performed by most surgeons. Our results indicate that a single intraoperative X-ray can reduce the number of excessive bone resection angle outliers in TKA

Purpose. Total knee replacement is the one of the most performed surgeries. However, patient's satisfaction rate is around 70–90 % only. The sacrifice of cruciate ligament might be the main reason, especially in young and active patients. ACL stabilizes the knee by countering the anterior displacing and pivoting force, absorbs the shock and provides proprioception of the knee. However, CR knees has been plagued by injury of PCL during the surgery and preservation of the ACL is a demanding technique. Stiffness is more common comparing to PS designed knee. To insert a tibial baseplate with PE is usually thicker than 8 mm comparing to 2–4 mm of removed tibial bone. The stuffing of joint space may put undue tension on preserved ACL and PCL. Modern designed BCR has been pushed onto market with more sophisticated design and instrumentation. However, early results showed high early loosening rate. Failure to bring the tibia forward during cementing may be the main cause. The bone island where ACL footprint locates is frequently weak, intraoperative fracture happens frequently. A new design was developed by controlled elevation and reattachment of the ACL footprint to meet all the challenges. Method. A new tibial baseplate with a keel was designed. The central part of the baseplate accommodates elevated bony island with ACL footprint. The fenestrations at the central part is designed for reattachment of bony island under proper tension with heavy sutures and fixed at anterior edge of the baseplate in suture bridge fashion and also for autograft to promote bony healing after reattachment. The suture bridge method has been used by arthroscopists for ACL avulsion fracture without the need of immobilization. The elevation of bony island release the tension in the ACL which come from stuffing of baseplate and PE insert and greatly facilitate cementing of the baseplate. The keel improve the weakness of traditional U shape design of BCR knees. Instead of keeping the bony island intact by separately cutting the medial and lateral tibial plateau in BCR knees in the past, we choose to saw the tibial plateau in one stroke as in PS knees, then removes the two condyles. The bony island includes the footprint both ACL and PCL. The central part of tibial baseplate will push the bony island upward which release the undue tension in the cruciate ligaments. Summary. We proposed a new solution for the kinematic conflict in the present bi-cruciate knee designs by elevation and re- attachment of bony island with ACL footprint at the same time simplify the ACL preservation. The simple tibial cutting procedure also facilitate the process. The technique protects PCL from injury during tibial bone cutting in CR knees. We believe the new BCR design has the potential to replace CR knee in term of function and longevity in the future

BACKGROUND. We conducted this study to determine if the pre-surgical patient specific instrumented planning based on Computed tomography scans can accurately predict each of the femoral and tibial resections. The technique helps in optimization of component positioning and hence overall alignment thereby reducing errors. This makes it less invasive, more efficient and cost effective. The surgical plan in combination with the cutting guides determine the resection thickness, component size, femoral rotation and femoral and tibial component alignment. Several clinical studies have shown that PSI is safe, accurate and reproducible in primary TKA. Accurate preparation of the femoral and tibial surfaces will determine alignment and component positioning and this in turn reflects on function and longevity. METHODS. The study was conducted prospectively between May 2016 and December 2017 in our institution. Patients admitted over a period of these twenty months were included in the study. Patients with primary or secondary osteoarthritis (OA) and inflammatory arthritis who were suitable to undergo patient-specific TKA were included in the study. Patients with conventional instrumented TKR and those with significant deformities requiring constrain including valgus or varus of greater than 20 degrees with incompetent lateral or medial collateral ligaments were excluded from the study along with revisions of partial knee to TKA using PSI blocks. Prophecy® Preoperative Navigation 3D printed Guides were used for the Evolution Medial Pivot knee replacement system (. Microport Orthopaedics (Arlington, TN 38002, USA)). in all cases. The operating surgeon measured all the resections made (4 femoral and 2 tibial) using vernier calipers intraoperatively. These measurements were then compared with the preoperative CT predicted bone resection surgical planning. The senior author (IN) also designed markings on the tibial cutting blocks to improve accurate placement on the tibia and further markings on the femoral cutting blocks to ensure accurate positioning and rotational alignment improving accuracy of the cuts and femoral rotation. Further markings by senior surgeon (IN) on the pre-operative plans included tibial rotational plans in relation to the tibial tubercle. RESULTS. A total of 3618 readings were calculated from 201 knees (105 right and 96 left). There were 112 females and 76 males, and the average age was 67.72 years (44 to 90 years) and average BMI 32.3 (25.1 to 42.3). The surgical time ranged from 46 to 102 minutes with a mean operating time of 62 minutes. All Femoral and Tibial blocks sat accurately on the bony surfaces before being pinned. 94% of all collected resection readings were below the error margin of ≤1.5 mm of which 90% showed resection error of ≤1mm. Mean error of different resections were ≤0.60 mm (P ≤ 0.0001). In 24% of measurements there were no errors or deviations from the templated resection (0.0 mm). CONCLUSION. The 3D printed cutting blocks with slots for jigs accurately predict bone resections in PSI total knee arthroplasty which would directly affect component positioning and hence longevity and function

Patients presenting with arthrosis following high tibial osteotomy (HTO) pose a technical challenge to the surgeon. Slight overcorrection during osteotomy sometimes results in persisting medial unicompartmental arthrosis, but with a valgus knee. A medial UKA is desirable, but will result in further valgus deformity, while a TKA in someone with deformity but intact cruciates may be a disappointment as it is technically challenging. The problem is similar to that of patients with a femoral malunion and arthrosis. The surgeon has to choose where to make the correction. An ‘all inside’ approach is perhaps the simplest. However, this often means extensive release of ligaments to enable ‘balancing’ of the joint, with significant compromise of the soft tissues and reduced range of motion as a consequence. As patients having HTO in the first place are relatively high demand, we have explored a more conservative option, based upon our experience with patient matched guides. We have been performing combined deformity correction and conservative arthroplasty for 5 years, using PSI developed in the MSk Lab. We have now adapted this approach to the failed HTO. By reversing the osteotomy, closing the opening wedge, or opening the closing wedge, we can restore the obliquity of the joint, and preserve the cruciate ligaments. Technique: CT based plans are used, combined with static imaging and on occasion gait data. Planning software is then used to undertake the arthroplasty, and corrective osteotomy. In the planning software, both tibial and femoral sides of the UKA are performed with minimal bone resection. The tibial osteotomy is then reversed to restore joint line obliquity. The placing of osteotomy, and the angling and positioning in relation to the tibial component are crucial. This is more important in the opening of a closing wedge, where the bone but is close to the keel cut. The tibial component is then readjusted to the final ‘Cartier’ angle. Patient guides are then made. These include a tibial cutting guide which locates both the osteotomy and the arthroplasty. At operation, the bone cuts for the arthroplasty are made first, so that these cuts are not performed on stressed bone. The cuts are not in the classical alignment as they are based upon deformed bone so the use of patient specific guides is a real help. The corrective osteotomy is then performed. If a closing wedge is being opened, then a further fibular osteotomy is needed, while the closing of an opening wedge is an easier undertaking. Six cases of corrective osteotomy and partial knee replacement are presented. In all cases, the cruciates have been preserved, together with normal patello-femoral joints. Patient satisfaction is high, because the deformity has been addressed, restoring body image. Gait characteristics are those of UKA, as the ACL has been preserved and joint line obliquity restored

INTRODUCTION. While multiple factors contribute to the variability of prosthesis placement during total knee arthroplasty (TKA), the accuracy of the surgeon's resection planning (positioning of the cutting block) is arguably the most critical. One may postulate that proper training, including enabling the surgeon to passively receive quantitative feedback on the cutting block position, may help him/her improve resection accuracy. The purpose of this study was to test the hypothesis that passive reception of feedback on cutting block position improves the accuracy of the successive TKA resection planning. Materials and Methods. Five cadaveric knees (tibia and foot only) were studied. After arthrotomy, the tracker of an imageless navigation system (ExactechGPS. ®. , Blue-Ortho, Grenoble, FR) was attached to the tibia. A navigated TKA procedure was initiated starting with registration of anatomical landmarks. Four surgeons then positioned the tibial cutting block (without pinning) on each knee using standard extramedullary mechanical instruments. The planned target resection was neutral varus/valgus, 3° posterior slope, and 10mm resection depth referencing the lateral plateau. Each surgeon performed 3 planning trials on each of the 5 knees, removing the cutting block between attempts. The planned resections were measured using an instrumented checker provided with the navigation system, referencing the cutting block. Surgeons were informed of the resection parameters measured by the navigation system after each planning trial. The deviations in resection parameters between the resection target and the cutting block position were calculated for each planning trial. The effect of receiving passive feedback on the accuracy of successive placement of the cutting block was assessed by comparing the deviations between each surgeon's 3 trials on the same cadaver (paired-t test). Statistical significance was defined as p<0.05. Results. For all 3 trials in each of the 5 knees, the planned resections tended to be more valgus, and had more posterior slope and a larger resection depth compared to the resection target (Fig. 1). The average magnitudes of the deviations ranged from 0.8° to 1.3° for alignment parameters, and 0.8 to 1.2 mm for resection depth (Fig. 2). No significant differences were observed across the 3 planning trials for any of the resection parameters (N.S.). Discussion. This study rejected the hypothesis that passive feedback improves the accuracy of successive tibial resection planning during TKA. This may be due to disconnect between feedback reception and subsequent resection planning. A possible solution to inaccuracies in resection planning may be intraoperative information exchange between the surgeon and the measurement tool, such as a navigated surgery, which has been proven to offer excellent resection accuracy [1]. In addition, compared to previous studies on resection variability based on the actual bony resection [1,2], which reflects the accumulated errors from all the potential sources, this study improved the understanding of surgical variability specifically during the planning phase of the tibial resection. The data from this study may benefit the improvement of instrument design or surgical techniques to assist more accurate TKA resections

Clinical success of total knee arthroplasty is correlated with correct orientation of the components. Controversy remains in the orthopaedic community as to whether the intramedullary or extramedullary tibial alignment guide is more accurate in the tibial cut. Is there any difference between intramedullary and extramedullary jigs to achieve better accuracy of the tibial components in total knee replacements?. A retrospective study done on 100 patients during the time period 2007 to 2010. The 100 knee replacements were done by the same surgeon, where 50 patients had the intramedullary tibial alignment guide and the other 50 had the extramedullary one. The tibiofemoral angle was measured pre-operatively as well as post operatively, the tibial alignment angle was measured post operatively then the results were statistically analysed using the SPSS. There was no significant difference between both groups regarding the tibial alignment angles. Both techniques proved accurate in producing an acceptable post operative tibial component alignment angle. We recommend orthopaedic surgeons choose either technique knowing that accuracy levels are similar. The debate between intramedullary and extramedullary tibial cutting jigs/guides/ devices continues and most orthopaedic surgeons will use their preferred technique and will continue to achieve good post operative results as we have found in our centre. Our study is rare due to the fact we have a single surgeon performing both techniques, therefore controlling for any surgical experience or operating technique differences

Aims

Mid-level constraint designs for total knee arthroplasty (TKA) are intended to reduce coronal plane laxity. Our aims were to compare kinematics and ligament forces of the Zimmer Biomet Persona posterior-stabilized (PS) and mid-level designs in the coronal, sagittal, and axial planes under loads simulating clinical exams of the knee in a cadaver model.

The ligament balance as well as the alignment is essential for successful total knee arthroplasty (TKA). However it is usually assessed and adjusted only at 0? and 90?. In order to evaluate the ligament balance at the other angles we have used a navigation system. Twenty-one patients underwent posterior stabilised mobile bearing TKA using a CT-based navigation system were included in this study. Immediately post-operation and still under anaesthesia, varus and valgus stresses were applied on operated knees manually at 0?, 30?, 60?, 90? and 120?. The ligament balance was calculated based on the angles under varus and valgus stress displayed on the navigation screen, presenting a relationship between the femoral and tibial cutting planes. The mean ligament balance angle at 0?, 30?, 60?, 90? and 120? were −2? ± 3.6?, −5.8? ± 7.9?, 5.0? ± 6.9?, −1.3? ± 5.4?, 7.9? ± 7.2?, respectively. At 0? and 90? balance was well adjusted, however in the other angles, it was quite varied. At 30? and 120?, the lateral side was loose, on the other hand, medial side was looser at 60? knee flexion angle. The good balance at 0? and 90? is understandable because the balance is assessed and adjusted in these angles. Regarding the other angles, the 30? and 120? results corresponded with previous studies; however, the 60? results did not correlate. Although the reason is unknown, it must be aware the mid-flexion and deep flexion instability is quite common. Further investigations about the impact on clinical outcomes of such instabilities and how to adjust them if they are critical are needed

Aims

This study aimed to identify the effect of anatomical tibial component (ATC) design on load distribution in the periprosthetic tibial bone of Koreans using finite element analysis (FEA).

The aim of this study was to evaluate the rotational axis of the tibia and the association of its axis to tibial coronal alignment after TKR. TKRs were performed using navigated mobile bearing system (40 knees), conventional mobile bearing (48 knees) and conventional fixed bearing (40 knees) and preoperative and postoperative CT scans were assessed using 3D image reconstruction-analysis program. The tibial AP axis which was defined as the line connecting the middle of the PCL and the medial edge of the patellar tendon attachment was measured relative to the AP axis of distal femur preoperatively and postoperatively, as well as the coronal angle of the tibia and posterior slope. The tibial coronal alignments in navigation, postoperative plain radiograph and CT were compared. The AP axis of the tibia was in 2.10° internally rotated position relative to the AP axis of the femur preoperatively and 3.54° postoperatively (range, 19.5° internal rotation to 16.8° external rotation). The coronal angle of the tibia was 0.46° varus on plain radiograph, 0.72° varus on CT, 0.37° valgus in navigation (p=0.005). Posterior slope was 2.53° on plain radiograph and 0.67° in navigation (p< 0.001). There was no correlation between postoperative rotational position of the tibia relative to the femur and the difference in the tibial coronal angle between navigation data and CT. The proposed anteroposterior axis of the tibia centered between 0 to 5 degrees internally rotated position relative to the femur but showed wide range of deviation. The rotation angle of the tibial cutting in navigated TKR did not influence on the postoperative measurement discrepancy between navigation and CT

Introduction. Regarding TKA, patient specific cutting guides (PSCG), which have the same fitting surface with patient's bones or cartilages and uniquely specify the resection plane by fitting guides with bones, have been developed to assist easy, low cost and accurate surgery. They have already been used clinically in Europe and the USA. However little has been reported on clinical positioning accuracy of PSCG. Generally, the methods of making PSCG can be divided into 3 methods; construct 3D bone models with Magnetic Resonance (MR) images, construct 3D bone models with Computed Tomography (CT) images, and the last is to construct 3D bone models with both MR and CT images. In the present study, PSCG were made based on 3D bone models with CT images, examined the positioning accuracy with fresh-frozen cadavers. Materials and Methods. Two fresh-frozen cadavers with four knees were scanned by CT. Image processing software for 3D design (Mimics Ver. 14, Marialise Inc.) was used to construct 3D bone model by image thresholding. We designed femoral cutting guides and tibial cutting guides by CAD software (NX 5.0, Siemens PLM Software Co.). CT free navigation system (VectorVision Knee, BrainLab, Inc.) was used to measure positioning error. Average absolute value of positioning error for each PSCG was derived. Results. The average absolute value of positioning error in femoral PSCG was 1.5±0.8° for varus/valgus, 2.3±1.9° for extension/flexion, 1.2±1.8 mm for bone resection. The stability of femoral PSCG was satisfactory. The average absolute value of positioning error in tibial PSCG was 4.3±2.5° for varus/valgus, 5.2±3.3° for anterior slope/posterior slope, 2.6±1.1 mm for bone resection. The stability of tibial PSCG was not sufficient. Discussion. PSCG of the present study were made based on CT images, mainly designed to be fit with cortex, keeping away from cartilage or osteophytes. The fitting surfaces of distal femoral PSCG covered anterior femoral cortex. Also, the fitting surface of tibial PSCG fit to anterior medial cortex of horizontal tibial tuberosity. The average absolute value of positioning error by tibial PSCG varied widely. The main cause for this was their contacts with patellar tendon. Lateral sides of PSCG were contacted with patella tendon near the tibial tuberosity, they were pushed medially. Positioning accuracy of the femoral PSCG is thought to be enough for clinical application

In order to enhance the acceptance of computer assisted surgery in joint replacement, a development-cooperation with BrainLAB, Germany was set up to develop a user-friendly handheld navigation device. A sterile draped Apple® IPod-Touch which is placed into a hardcover cradle, is used as navigation monitor and touchscreen control. Different instruments, such as navigation-pointer are attached to the cradle. In addition the workflows for TKR and THR procedures have been optimised. Therefore the main focus for TKR is navigation of femoral and tibial resection as well as leg alignment control. For the THR the system enables an intraoperative control of leg-length and femoral-offset measurement in comparison with the preoperative situation. Each step of the procedure is supported by video animations of the specific navigation workflow. Between September and December 2010 the first clinical study on the usability in TKR and THR was performed for 20 cases using a prototype system. The study was approved by the local ethic committee and the “German Federal Institute for Drugs and Medical Devices (BfArM)”. Special interest was taken to the aspects of usability and the necessary time periods for specific steps of the procedure. Usability was measured for specific time periods of the procedure assessment of the usability of the surgical team. In addition postoperative x-rays were evaluated for implant position, leg alignment for TKR and hip joint geometry for THR cases. Throughout the study for each assigned patient the procedure could be performed as planned. Several design inputs were identified for further improvement of the final system. Therefore time measurements of the first five cases were excluded. For the TKR cases the registration process of the last 5 cases was less than 3 minutes. The interval for the tibial resection was between 3 and 7 minutes (aligning tibial cutting block – end of tibial verification). The interval for the distal femur resection was between 7 and 11 minutes (aligning femoral cutting block – end of femoral verification). All 10 Patients showed a final leg alignment on the postoperative standing x-ray within the save-zone of +/− 3° from neutral alignment. For the THR cases the preoperative registration period including the femoral head resection and acetabular registration was between 7 and 12 Minutes. Each final measurement of the hip geometry was done in less than 2 minutes. The evaluation of the pelvic ap-x-ray pre- and postoperative showed equivalent measurements of the new hip geometry compared with the intraoperative measured values. No specific complications occurred throughout the study. In conclusion the BrainLAB–DASH-System has shown a high grade of usability and very short learning curve within this first clinical study. The use of a standard Apple® IPod-touch as a user interface seems to enhance the acceptance of the navigation technique. Equivalent precision compared to standard navigation systems have been demonstrated

Introduction. In total knee arthroplasty extramedullary tibial guides could not to be as accurate as requested in obtaining proper alignment perpendicular to the mechanical axis. The aim of this study was to determine the accuracy of an accelerometer-based system (KneeAlign 2; OrthAlign Inc, Aliso Viejo, California) as evaluated by post-op X-rays analysis. Methods. Between March 2012 and May 2012 thirty consecutive patients with primary gonarthrosis were selected for unilateral total knee arthroplasty (TKA) using a handheld surgical navigation system to perform the tibial resection. Navigation procedure: The entire system is provisionally secured to the tibia using a spring placed around the leg and is fixed to the proximal aspect of the tibia using 2-headed pins. Before fixing the system proximally, an aiming arm is used to align the top of the device with the anterior cruciate ligament footprint and the medial one third of the tibial tubercle. Distally, a footplate connected to the tibial jig is used to keep the EM jig a set distance off of the tibial surface. A gyrometer within the navigation unit is then able to calculate the posterior slope of the tibial jig. Subsequent anatomical landmarkings of both the lateral and medial malleoli are identified using the distal aspect of the EM jig to establish the tibia's mechanical axis. Similarly, the gyrometer within the navigation unit is able to calculate the varus or valgus alignment of the tibial jig relative to the tibia's established mechanical axis. Once anatomical registration has been performed, the tibial cutting block is placed at the proximal aspect of the device, and real-time feedback is provided by the navigation unit to the surgeon, who is then able to set the cutting block's varus/valgus and posterior slope alignment before performing the tibial resection. Postoperatively, standing anteroposterior hip-to-ankle radiographs and lateral knee-to-ankle radiographs were performed to determine the varus/valgus alignment and the posterior slope of the tibial components relative to the mechanical axis in both the coronal and sagittal planes. The difference between the intraoperative reading of the tibial varus/valgus alignment and posterior slope provided by the system was compared to the radiographic measurements obtained postoperatively for each respective case. Differences were analysed via standard t test. The critical level of significance was set at P <0.05. Results. Intraoperatively, the average reading provided by the system with regard to varus/valgus alignment before performing the tibial resection was 0.3° ± 0.3° relative to the mechanical axis and 5.4° ± 0.9° in the sagittal plane. The average tibial component alignment postoperatively in the knees with was 0.6° ± 0.3° in the coronal plane (P=0.07) and 4.7° ± 0.9° in the sagittal plane (P=0.07). In no case a difference > 2° from the planned resection was detected in both coronal and sagittal plane. Conclusions. The handheld surgical navigation system combines the accuracy of computer-assisted surgery systems with the ease of use and familiarity of conventional instrument. The system might improve the accuracy of the tibial resection and subsequent tibial component alignment in TKA

To make rectangular flexion and extension gap is an important goal in total knee arthroplasty (TKA). The purpose of this study was to determine the AP and rotational position of the femora component to obtain rectangular flexion with reference to the anatomical landmarks. One hundred and twenty seven varus osteoarthritic knees (87 patients) undergoing TKA from June 2004 to March 2006 were included (72 women and 15 men, mean age 74.4 years). All operations were performed with Vanguard PS, Biomet (Warsaw, IN U.S.A.). The position of femoral component was determined using a modified Ranawat block (Equiflex. ™. ) to obtain the rectangular flexion gap equal to extension gap. This instrument uses the balanced soft tissue sleeve in extension as a guide to create a balanced flexion gap. The flexion gap asymmetry after TKA was evaluated as the angle between the posterior condylar axis (PCA) and the tibial cutting line (TCL) by axial radiography of the distal femur. (. Tokuhara et. al., . JBJS. (88-B), . 2006. ). Briefly, axial radiography of the distal femur of flexed knee was obtained with a 1.5kg distraction force in ankle joint. This technique led to clear visualization of the asymmetry of the flexion gap. Femoral component rotation was evaluated using pre- and post-operative axial radiography of the distal femur (. Kanekasu et. al., . CORR. (434), . 2005. ). Condylar twist angle (CTA) is the angle between the CEA and the PCA. The rotational position femoral component relative to the PCA was calculated by subtracting post-operative CTA from pre-operative CTA. In addition, the thicknesses of resected bone from the lateral and medial posterior femoral condyles were measured. The asymmetry of the flexion gap was 1.6±2.4° with slight laxity in the lateral side. The average amount of external rotation of the femoral component relative PCA was on 6.2 ±2.5°. The thickness of resected bone from the posterior lateral and medial condyles were 4.7 ± 2.1 mm and 8.6 ±2.1 mm respectively. The results of this study have shown that, for a well-balanced flexion gap, femoral component should be excessively rotated by 3 degrees compared to current recommendation (Parallel to SEA) As for the AP position, the average amount of medial bone resection is equal to the implant thickness (9 mm). This information is useful for the modification of measured resection technique to obtain rectangular flexion gap