Aim. The aim of this study is to evaluate the effect of three-dimensional (3D) simulation with 3D planning software ZedKnee® (ZK) in total knee arthroplasty (TKA). Materials and methods. The participants in this study were all TKA patients whose operations were simulated by using ZK. The alignment of all components was evaluated with the ZK valuation software in postoperative computer tomography. Thirty patients (43 knees) met the inclusion criteria. 6 patients were male and 24 patients were female. The mean age of the 30 patients was 72 years old. Diagnoses for surgery were: osteoarthritis- 40 knees, rheumatoid arthritis- 2 knees and osteonecrosis- 1 knee. TKA was performed using the measured resection technique. The distal femur axis where the intramedullary rod would be inserted was drawn manually on the 3D image. Then, the angle between the distal femoral axis and the mechanical axis was measured. The rotational angles of the femoral components were determined from the automatically calculated angle between the posterior condylar axis and the surgical epicondylar axis (SEA) by using ZK. The ZK data used during the operation was the posterior condylar angle, the angle between the distal femoral axis and the mechanical axis and implant size. Results. The angle in coronal plane between the 3D mechanical axis and the distal femoral axis in preoperative planning ranged between 3 degrees and 11 degrees, mean 6.7 (SD 2.2) degrees. The postoperative femoral component alignment was on average 0.7 (SD 1.3) degrees in varus. Outlier of more than 3 degrees in coronal alignment was recognized in 3 cases (7%). The mean posterior condylar angle in preoperative planning was 3.8 (SD 1) degrees. The postoperative femoral component alignment was on average 1.5 (SD 1.6) degrees in external rotation to surgical epicondylar axis. Outlier of more than 3 degrees in rotational alignment was recognized in 6 cases (14%). The concordance rate between the preoperative planning size and the intraoperative selective size was 91%. Discussion. Some errors may be observed in the preoperative TKA X-ray planning, because of the rotational position of the femur while having the X-ray taken or angle of the X-ray beam. Kanekasu et al reported the measurement of the condylar twist angle during the X-ray and it was relatively correct compared with the measurement during CT. Max 1.9 degrees error occurred in the measurements using X-rays. It appeared that preoperative planning using CTs was more accurate than using X-rays. Conclusion. Femoral components with 3D simulation using ZK were fixed perpendicularly against the mechanical axis and parallel to the surgical epicondylar axis with high accuracy. We considered that the ZK 3D simulation in TKA is useful for the accurate alignment of femoral components

Purpose:. The use of computer navigation has been shown to improve the accuracy of femoral component placement compared to conventional instrumentation in hip resurfacing. Whether exposure to computer navigation improves accuracy when the procedure is subsequently performed with conventional instrumentation without navigation has not been explored. We examinedwhether femoral component alignment utilizing a conventional jig improves following experience with the use of imageless computer navigation for hip resurfacing. Methods:. Between December 2004 and December 2008, 213 consecutive hip resurfacings were performed by a single surgeon. The first 17 (Cohort 1) and the last 9 (Cohort 2) hip resurfacings were performed using a conventional guidewire alignment jig. In 187 cases the femoral component was implanted using the imageless computer navigation. Cohorts 1 and 2 were compared for femoral component alignment accuracy. Results:. All components in Cohort 2 achieved the position determined by the pre-operative plan. The mean deviation of the stem-shaft angle (SSA) from the pre-operatively planned target position was 2.2 degrees (SD, 2.2°, 95% CI, 0.8°, 3.7°) in Cohort 2 and 5.6 degrees (SD, 4.3°, 95% CI, 3.6°, 7.6°) in Cohort 1 (p = 0.01). Four implants in Cohort 1 were positioned at least 10 degrees varus compared to the target SSA position and another four were retroverted. Conclusions:. Femoral component placement utilizing conventional instrumentation may be more accurate following experience using imageless computer navigation

Introduction

There is many reports about complications with a resurfacing total hip arthroplasty (RHA). One of the most common complications is the femoral neck fracture. A notch and malalignment were risk factors for this. For an accurate implanting the femoral component in RHA, we performed 3D template and made a patient specific template (PST) using 3D printer and applied this technique for a clinical usage. We report a preliminary early result using this novel technique.

Purpose

Proper positioning of the components of a knee prosthesis for obtaining post-operative knee joint alignment is vital to obtain good and long term performance of a knee replacement. Although the reasons for failure of knee arthroplasty have not been studied in depth, the few studies that have been published claim that as much as 25% of knee replacement failures are related to malpositioning or malalignment [x].

The use of patient-matched cutting blocks is a recent development in orthopaedics. In contrast to the standard cutting blocks, they are designed to fit the individual anatomy based on 3D medical images. Thus, landmarks and reference axes can be identified with higher accuracy and precision. Moreover, stable positioning of the blocks with respect to the defined axes is easier to achieve. Both may contribute to better alignment of the components.

The objective of this study was to check the accuracy of femoral component orientation in a cadaver study using specimen-matched cutting blocks in six specimens; first for a bi-compartmental replacement, and then for a tri-compartmental replacement in the same specimen.

The iASSIST system is a portable, accelerometer base with electronic navigation used for total knee arthroplasty (TKA) which guides the surgeon to align and validate bone resection during the surgical procedure. The purpose of this study was to compare the radiological outcome between accelerometer base iASSIST system and the conventional system. Method. A prospective study between two group of 36 patients (50 TKA) of primary osteoarthritis of the knee who underwent TKA using iASSIST ™ or conventional method (25 TKA in each group) from January 2018 to December 2019. A single surgeon performs all operations with the same instrumentation and same surgical approach. Pre-operative and postoperative management protocol are same for both groups. All patients had standardized scanogram (full leg radiogram) performed post operatively to determine mechanical axis of lower limb, femoral and tibial component alignment. Result. There was no significant difference between the 2 groups for Age, Gender, Body mass index, Laterality and Preoperative mechanical axis(p>0.05). There was no difference in proportion of outliers for mechanical axis (p=0.91), Coronal femoral component alignment angle (p=0.08), Coronal tibial component alignment angle (p=1.0). The mean duration of surgery, postoperative drop in Hb, number of blood transfusion didn't show significant difference between 2 groups (p>0.05). Conclusion. Our study concludes that despite being a useful guidance tool during TKA, iASSIST does not show any difference in limb alignment (mechanical axis), Tibial and femoral component alignment when compared with the conventional method

INTRODUCTION. To obtain appropriate joint gap and soft tissue balance, and to correct the lower limb alignment are important factor to achieve success of total knee arthroplasty (TKA). A variety of computer-assisted navigation systems have been developed to implant the component accurately during TKA. Although, the effects of the navigation system on the joint gap and soft tissue balance are unclear. The purpose of the present study was to investigate the influence of accelerometer-based portable navigation system on the intraoperative joint gap and soft tissue balance. METHODS. Between March 2014 and March 2015, 36 consecutive primary TKAs were performed using a mobile-bearing posterior stabilized (PS) TKA (Vanguard RP; Biomet) for varus osteoarthritis. Of the 36 knees, 26 knees using the accelerometer-based portable computer navigation system (KneeAlign2; OrthAlign) (N group), and 10 knees using conventional alignment guide (femur side; intramedullary rod, tibia side; extramedullary guide) (C group). The intraoperative joint gap and soft tissue balance were measured using tensor device throughout a full range of motion (0°, 30°, 45°, 60°, 90°, 120°and full flexion) at 120N of distraction force. The postoperative component coronal alignment was measured with standing anteroposterior hip-to-ankle radiographs. RESULTS. The mean joint gaps at each flexion angle were maintained constant in N group, and there was a tendency of the joint gap at midflexion ranges to increase in C group. The joint gaps at 30°and 45°of flexion angle in C group were significantly larger than that of in N group. The mean soft tissue balance at 0°of flexion was significantly varus in N group than that of in C group. Postoperatively, in N group, the mean femoral component alignment was valgus 0.1°± 1.3°(range, varus 2°- valgus 3°), the mean tibial component alignment was valgus 1.1°± 1.7°(range, varus 1°- valgus 3°) to the coronal mechanical axis. In C group, the mean femoral component alignment was varus 2.3°± 1.9°(range, varus 6°- valgus 1°), the mean tibial component alignment was valgus 2.0°± 1.3°(range, 0°- valgus 5°) to the coronal mechanical axis. There was statistically significant difference in femoral component alignment, there was no statistically significant difference in tibial component alignment. DISCUSSION AND CONCLUSION. The present study demonstrated that navigation-assisted TKA was prevented the joint gaps from increasing at 30°and 45°of flexion. However, it was difficult to achieve soft tissue balance at extension. In conventional TKA, the femoral component alignment was usually varus. In contrast, accelerometer-based portable navigation system is superior to implant the femoral component accurately. However, there were several cases that femoral component alignment is valgus because of a variation in the accuracy of this navigation system. Surgeons should be aware of difficulty to accomplish all of appropriate joint gap and soft tissue balance, and lower limb alignment in navigation-assisted TKA

INTRODUCTION. Although the most commonly used method of femoral component alignment in total knee arthroplasty (TKA) is an intramedullary (IM) guides, this method demonstrated a limited degree of accuracy. The purpose of this study was to assess whether a portable, accelerometer-based surgical navigation system (Knee Align 2 system; Orth Align, Inc, Aliso Viejo, Calif) improve accuracy of the post-operative radiographic femoral component alignment compared to conventional IM alignment guide. MATERIALS & METHODS. Since February 2014, 44 consecutive patients (39 female, 5 male) with primary arthritis of the knee were enrolled in this prospective, randomized controlled study. 24 patients underwent TKA (Vanguard RP or PS, Biomet Japan) using the navigation device for the distal femoral resection (Navigated Group), and 20 patients with conventional femoral IM alignment guide. The proximal tibial resection was performed using an extramedullary guide. All the operation was performed by a single senior surgeon (YK) with the same gap balancing technique except for the use of the navigation system for the femur. Accuracy of femoral implant positioning was evaluated on 2 weeks postoperative standing anteroposterior (AP) hip to ankle radiographs. RESUTS. In the navigated group, 100% of patients had an alignment within 90 ± 3° to the femoral mechanical axis in the coronal plane, versus 90.0% in the IM guides cohort (Fig). The mean absolute difference between the intraoperative goal and the postoperative alignment was 0.79 ± 1.0° in the Knee Align 2 cohort, and 1.72 ± 1.6° in the IM guides cohort (P < 0.05). There was a difference in the standard deviations observed for the navigated cases and the conventional cases when femoral component position was considered. There were no technique specific complications associated with the navigation system. DISCUSSION & CONCLUSION. The distal femoral resection has been the main source of error as for the neutral mechanical axis because of the difficulty in visualization and detection of the center of the femoral head. The results in the current study have shown that a portable, accelerometer-based navigation device (Knee Align 2 system) significantly decreases outliers in femoral component alignment compared to conventional IM alignment guides in TKA

Introduction. Robotics have been applied to total knee arthroplasty (TKA) to improve surgical precision in component placement and joint function restoration. The purpose of this study was to evaluate prosthetic component alignment in robotic arm-assisted (RA)-TKA performed with functional alignment and intraoperative fine-tuning, aiming for symmetric medial and lateral gaps in flexion/extension. It was hypothesized that functionally aligned RA-TKA the femoral and tibial cuts would be performed in line with the preoperative joint line orientation. Methods. Between September 2018 and January 2020, 81 RA cruciate retaining (CR) and posterior stabilized (PS) TKAs were performed at a single center. Preoperative radiographs were obtained, and measures were performed according to Paley's. Preoperatively, cuts were planned based on radiographic epiphyseal anatomies and respecting ±3° boundaries from neutral coronal alignment. Intraoperatively, the tibial and femoral cuts were modified based on the individual soft tissue-guided fine-tuning, aiming for symmetric medial and lateral gaps in flexion/extension. Robotic data were recorded. Results. A total of 56 RA-TKAs performed on varus knees were taken into account. On average, the tibial component was placed at 1.9° varus (SD 0.7) and 3.3° (SD 1.0) in the coronal and sagittal planes, respectively. The average femoral component alignment, based on the soft tissue tensioning with spoons, resulted as follows: 0.7° varus (SD 1.7) in the coronal plane and 1.8° (SD 2.1) of external rotation relative to surgical transepicondylar axis in the transverse plane. A statistically significant linear direct relationship was demonstrated between radiographic epiphyseal femoral and tibial coronal alignment and femoral (r=0.3, p<0.05) and tibial (r=0.3, p<0.01) coronal cuts, resepctively. Conclusion. Functionally aligned RA-TKA performed in varus knees, aiming for ligaments’ preservation and balanced flexion/extension gaps, provided joint line respecting femoral and tibial cuts on the coronal plane

Background:. Appropriate positioning of total knee arthroplasty (TKA) components is a key concern of surgeons. Post-operative varus alignment has been associated with poorer clinical outcome scores and increased failure rates. However, obtaining neutral alignment can be challenging in cases with significant pre-operative varus deformity. Questions:. 1) In patients with pre-operative varus deformities, does residual post-operative varus limb alignment lead to increased revision rates or poorer outcome scores compared to correction to neutral alignment? 2) Does placing the tibial component in varus alignment lead to increased revision rates and poorer outcome scores? 3) Does femoral component alignment affect revision rates and outcome scores? 4) Do these findings change in patients with at least 10 degrees of varus alignment pre-operatively?. Patients and Methods:. 553 patients undergoing TKA for varus osteoarthritis were identified from a prospective database. Patients were divided into those with residual post-operative varus and those with neutral post-operative alignment. Revision rates and clinical outcome scores were compared between the two groups. Revision rates and outcome scores were also assessed based on post-operative component alignment. The analysis was repeated in a subgroup of patients with at least 10 degrees of pre-operative varus. Results:. At a mean follow-up of 5.7 years (range: 2 to 19.8 years), residual varus deformity did not yield significantly increased revision rates or poorer outcome scores. Varus tibial component alignment and valgus femoral component alignment were associated with poorer outcome scores. Results were similar in the significant varus subgroup. Conclusions:. Residual post-operative varus deformity after TKA does not yield poorer clinical results in patients with pre-operative varus deformities, providing tibial component varus is avoided

Purpose. The purpose of this study is to investigate the relationship between the angles made by the reference axes on the computerized tomography (CT) images and comparison of the knee alignment between healthy young adults and patients who is scheduled to have total knee arthroplasty. Materials and Methods. This study was conducted in 102 patients with osteoarthritis of knee joint who underwent preoperative computerized tomography (CT). The control group included 50 patients having no arthritis who underwent CT of knee. Axial CT image of the distal femur were used to measure the angles among the the anteroposterior (AP) axis, the posterior condylar axis (PCA), clinical transepicondylar axis (cTEA) and the surgical transepicondylar axis (sTEA). Then, the differences in amounts of rotation between normal and osteoarthritic knee was evaluated. Results. The mean angle between cTEA and PCA in the osteoarthritis group was 5.0°±2.2, whereas that in the control group was 5.5°±2.0. The mean angle between cTEA and sTEA in the osteoarthritis group was 3.7°±0.8, whereas that in the control group was 4.3°±0.6. The mean angle between AP axis and PCA in the osteoarthritic group was 93.25°±2.0, whereas in the control group was 96.3°±1.9. There was significant differences in angles between AP axis and PCA. But, no significant difference was seen in angles between cTEA and PCA, cTEA and sTEA in two groups. Conclusion. In result of this study, the angle between cTEA and PCA showed an average external rotation of 5.0° in osteoarthritic group. More external rotation was needed for the femoral component alignment than 3° recommended in usual total knee arthroplasty. The angle between AP axis and PCA is decreased in osteoarthritic knee compared with normal knee. But, osteoarthritic change of knee joint had no significant effect on the relationships of other axes

BACKGROUND. Computer navigation system offers an inherent advantage to surgeons improving the surgical technique of total knee arthroplasty (TKA) in that it provides constant visual and numerical feedback throughout the procedure. On this basis, this study was designed to explore the chronologic change of surgical outcomes in TKA by a single surgeon with experience of over 50 Imageless navigation-assisted TKA procedures before. METHODS. Surgical outcomes were analyzed in 295 consecutive total knee arthroplasties treated in period 1 (2011.1–2012.12) in which both navigation (53 knees, P1-NAVI) and conventional technique (106 knees, P1-CON) were used and in period 2 (2013.1–2013.12) in which conventional technique (136 knees, P2-CON) was only used. The study parameters were implantation accuracy, clinical outcome, operation time and complications. Coronal femoral component and tibial component angle, and hip–knee–ankle mechanical axis alignment were evaluated. Results. A statistically significant superior result was achieved in final mechanical axis and coronal tibial component angle during P1-NAVI to P1-CON (p=0.00 and p=0.047). However, comparisons between P1-NAVI and P2-CON did not reveal the statistical significant differences in mechanical axis (p=0.08). Additionally during P2-CON, the result of mechanical axis alignment was superior to P1-CON (p=0.009). However, a statistically significant inferior result in coronal tibial component angle during P2-CON was shown in comparison with P1-NAVI (p=0.00) as well as P1-CON (p=0.02). In terms of coronal femoral component alignment, the statistically inferior result during P1-CON was shown in comparison with P1-NAVI (p=0.00) as well as P2-CON (p=0.01). There was no statistically significant differences between P1-NAVI and P2-CON (P=0.08). A statistically significant increase in operating time was found in P1-NAVI compared to P1-CON as well as P2-CON (p=0.01, p=0.00). Additionally, P1-CON has shown the increased operating time compared to P2-CON (p=0.02). There was no statistically significant differences in complications between P1-NAVI and P1-CON. However, the overall number of complication was decreased from period 1 (P1) to period 2 (P2). Conclusions. After stop using imageless navigation system, the mechanical axis and frontal femoral component angle was well maintained. But, surgeon could not maintain the coronal tibial component alignment. The operating time and number of complications were decreased over time. Based on this single surgeon's chronologic change of surgical outcomes, the continuing use for real time feedback such like navigation is needed to maintain the consistency of TKA

Arthrofibrosis remains a dominant post-operative complication and reason for returning to the OR following total knee arthroplasty. Trauma induced by ligament releases during TKA soft tissue balancing and soft tissue imbalance are thought to be contributing factors to arthrofibrosis, which is commonly treated by manipulation under anesthesia (MUA). We hypothesized that a robotic-assisted ligament balancing technique where the femoral component position is planned in 3D based on ligament gap data would result in lower MUA rates than a measured resection technique where the implants are planned based solely on boney alignment data and ligaments are released afterwards to achieve balance. We also aimed to determine the degree of mechanical axis deviation from neutral that resulted from the ligament balancing technique. Methods. We retrospectively reviewed 301 consecutive primary TKA cases performed by a single surgeon. The first 102 consecutive cases were performed with a femur-first measured resection technique using computer navigation. The femoral component was positioned in neutral mechanical alignment and at 3° of external rotation relative to the posterior condylar axis. The tibia was resected perpendicular to the mechanical axis and ligaments were released as required until the soft tissues were sufficiently balanced. The subsequent 199 consecutive cases were performed with a tibia-first ligament balancing technique using a robotic-assisted TKA system. The tibia was resected perpendicular to the mechanical axis, and the relative positions of the femur and tibia were recorded in extension and flexion by inserting a spacer block of appropriate height in the medial and lateral compartments. The position, rotation, and size of the femoral component was then planned in all planes such that the ligament gaps were symmetric and balanced to within 1mm (Figure 1). Bone resection values were used to define acceptable limits of implant rotation: Femoral component alignment was adjusted to within 2° of varus or valgus, and within 0–3° of external rotation relative to the posterior condyles. Component flexion, anteroposterior and proximal-distal positioning were also adjusted to achieve balance in the sagittal plane. A robotic-assisted femoral cutting guide was then used to resect the femur according to the plan (Figure 2). CPT billing codes were reviewed to determine how many patients in each group underwent post-operative MUA. Post-operative mechanical alignment was measured in a subset of 50 consecutive patients in the ligament balancing group on standing long-leg radiographs by an independent observer. Results. Post-operative MUA rates were significantly lower in the ligament balancing group (0.5%; 1/199) than in the measured resection group (3.9%; 4/102), p=0.051. 91.3% (42/46) of knees were within 3° and 100% (46/46) were within 4° of neutral alignment to the mechanical axis post-operatively in the ligament balancing group. Conclusions. Gap driven femoral based planning in TKA resulted in a significantly lower post-operative manipulation rate than in the measured resection approach, while maintaining acceptable overall alignment to the mechanical axis

Introduction. Total Knee Arthroplasty (TKA) is an established procedure for relieving patients of pain and functional degradation associated with end-stage osteoarthritis of the knee. Historically, alignment of components in TKA has focused on a ‘reconstructive’ approach neutral to the mechanical axes of the femur and tibia coupled with ligament balancing to achieve a balanced state. More recently, Howell et al. have proposed an alternate approach to TKA alignment, called kinematic alignment. (Howell, 2012) This approach seeks to position the implants to reproduce underlying, pre-disease state femoral condylar and tibial plateau morphology, and in doing is ‘restorative’ of the patients underlying knee kinematic behaviour rather than ‘reconstructive’. While some promising early clinical results have been reported at the RCT level (Dosset, 2014), in vivo comparisons of the kinematic outcome achieved at patient specific levels with the two alignment techniques remain an impossibility. The aim of this research is to develop and report preliminary findings of a means of simulating both alignment techniques on a number of patients. Method. In 20 TKR subjects, 3D geometry of the patient was reconstructed from preoperative CT scans, which were then used to define a patient specific soft tissue attachment model. The knees were then modelled passing through a 0 to 140 degree flexion cycle post TKR under each alignment technique. A multi-radius CR knee design has been used to model the TKA under each alignment paradigm. Kinematic measurements of femoral rollback, internal to external rotation, coronal plane joint torque, patella shear force and varus-valgus angulation are reported at 5, 30, 60, 90 and 120 degrees of flexion. Student's paired 2 sample t-tests are used to determine significant differences in means of the kinematic variables. Results. The mean femoral component alignment to the femoral mechanical axis was 3.3° ± 2.2° valgus and 2.3° ± 1.6° internal to the surgical transepicondylar axis in the kinematically aligned models. The mean tibial component alignment to the tibial mechanical axis was 3.5° ± 2.4° varus and 7.6° ± 6.5° internal to Insall's tibial anterior-posterior axis. The mechanically aligned model sims were all neutral to both axes. As a result of the relative match in femoral valgus & tibial varus component angulation, mean long leg varus at 5° degrees through 60° is not significantly different from the mechanically aligned knees, though with much higher variance in the kinematically aligned group. Statistically significant differences were observed at 90 and 120 degrees, where the long leg angle is dictated by posterior condylar contact on the femur rather than distal. Other statistically significant differences in mean results were observed, notably for coronal plain joint torque (at 5° and 30°, mechanical alignment higher). Discussion. Kinematic aligned TKR is conceptually a very different operation to mechanically aligned TKR, targeting different biomechanical goals. While evidence exists for improved clinical results in patients at a broad level, simulation tools at a patient specific level are a platform that, with development, could distinguish between patients benefiting most from a restorative or a reconstructive approach to their surgery

Introduction. Minimally invasive Computer Assisted Total Knee Arthroplasty (MICATKA) has benefits of reduced blood loss, shorter hospital stay, improved post-operative quadriceps function and enhanced post-operative recovery. Our study looked into these factors to compare if there was a significant difference when compared to conventional Computer Assisted Total Knee Arthroplasty (CATKA). Objective. Compare radiological and clinical outcomes of MICATKA and CATKA at a minimum of 5 years. Methods. 40 patients who underwent MICATKA were compared with 40 patients having conventional CATKA. Component positioning was assessed radiographically with AP long leg standing views. Knee Society Scores, length of stay and recovery of straight leg raise was also recorded pre-operatively and at 6-monthes and then yearly until 5 year follow up. Results. Pre-operative Knee Society Scores showed no significant difference between the two groups. Post operatively the mean femoral component alignment was 89.7 degrees for MICATKA and 90.2 for CATKA. The mean tibial component alignment was 89.7 degrees for both. Knees Society Scores in the short term (6, 12, 18 and 24 months) were statistically better in the MICATKA (p<000.1) group. Straight leg raise was achieved by day one in 93% of the MICATKA compared to only 30% of the CATKA. Length of stay for MICATKA was a mean of 3.25 days with CATKA a mean of 6 days. At five years there was no significant difference in the MICATKA and CATKA in Knee Society Scores and there were two revisions in the MICATKA group and one in the CATKA group. Conclusions. MICATKA have significantly better outcomes in the immediate short-term compared to CATKA. In the medium term these differences are not significant and similar outcomes can be achieved when performing CATKA in both clinical and radiographic assessments

Introduction. Patellofemoral (PF) complications are among the most frequently observed adverse events after total knee arthroplasty (TKA). It has been reported that PF complications after TKA include decreasing knee range of motion, anterior knee pain, quadriceps and patellar-tendon rupture, patellar subluxation, and partial abrasion and loosening of the patellar component. Although recent improvements in surgical technique and prosthetic design have decreased these complications, the percentage of patients who have a revision TKA for PF complications still ranged up to 6.6% to 12%. For the present study, we hypothesized that the alignment of the femoral component is correlated with PF contact stress. The purpose of this study was to investigate the relationship between femoral component alignment and PF contact stress in vivo, using a pressure sensor in patients who had favorable extension-flexion gap balance during TKA. Methods. Thirty knees with medial compartment osteoarthritis that underwent posterior stabilized mobile-bearing TKA using identical prostheses (PFC Sigma RPF; Depuy, Warsaw, IN, USA) by a single surgeon (TM) with modified gap technique under a computed tomography (CT)-based navigation system (Vector Vision 1.61; Brain Lab, Heimstetten, Germany) were evaluated. PF contact stress was measured intraoperatively and compared with the alignment of the femoral component including intraoperative navigation data concerning medial shift of the patella and lateral tilt of the patella, postoperative coronal femoral component angle (alpha angle), postoperative sagittal femoral component angle (gamma angle), postoperative condylar twist angle (CTA), postoperative lateral condylar lift-off angle, and postoperative mechanical femoral component angle (mFCA). In addition, postoperative Insall-Salvati ratio (I-S ratio) was measured by dividing the length of patellar tendon by the greatest diagonal length of the patella. Results. Maximum PF stress was 2.4 ± 1.9 MPa, medial shift of the patella was 2.6 ± 1.5 mm, and lateral tilt of the patella was 8.5 ± 4.2 degrees. The PF contact stress was not correlated sagittal and coronal alignment of the femoral component and patella tracking, whereas rotational alignment of the femoral component was negatively correlated with the PF contact stress (r = −0.718, p < 0.01). Discussion and conclusion. Multiple regression analysis shows that PF contact stress correlates with CTA, I-S ratio positively correlates with PF contact stress in Spearman correlation analysis. The results of the present study showed a negative correlation between maximum stress in the PF joint and CTA. It has been reported that excessive external rotation increases the medial flexion gap, leading to symptomatic flexion instability of the femoral component. In addition, external rotation of the femoral component can cause relative medialization of the trochlear groove during flexion, resulting in anterior knee pain. Therefore, we should carefully decide the proper rotational alignment of the femoral component. It has been reported that PF contact stress in a normal knee was from 2.1 to 2.9 MPa in a cadaveric study. In the present study, patients with rotational alignment of the femoral component after TKA between 1.2° and 2.2° internally rotated from CEA had PF contact stress in this normal range

Introduction. A large number of total knee arthroplasty (TKA) patients, particularly in Japan, India and the Middle East, exhibit anatomy with substantial proximal tibial torsion. Alignment of the tibial components with the standard anterior-posterior (A-P) axis of the tibia can result in excessive external rotation of the tibial components with respect to femoral component alignment. This in turn influences patellofemoral (PF) mechanics and forces required by the extensor mechanism. The purpose of the current study was to determine if a rotating-platform (RP) TKA design with an anatomic patellar component reduced compromise to the patellar tendon, quadriceps muscles and PF mechanics when compared to a fixed-bearing (FB) design with a standard dome-shaped patellar component. Methods. A dynamic three-dimensional finite element model of the knee joint was developed and used to simulate a deep knee bend in a patient with excessive external tibial torsion (Figure 1). Detailed description of the model has been previously published [1]. The model included femur, tibia and patellar bones, TKA components, patellar ligament, quadriceps muscles, PF ligaments, and nine primary ligaments spanning the TF joint. The model was virtually implanted with two contemporary TKA designs; a FB design with domed patella, and a RP design with anatomic patella. The FB design was implanted in two different alignment conditions; alignment to the tibial A-P axis, and optimal alignment for bone coverage. Four different loading conditions (varying internal-external (I-E) torque and A-P force) were applied to the model to simulate physiological loads during a deep knee bend. Quadriceps muscle force, patellar tendon force, and PF and TF joint forces were compared between designs. Results. The RP design demonstrated consistently lower medial-lateral (M-L) force at the PF joint than the FB design, with greater differences between designs in later flexion once the patella was engaged in the sulcus groove; root-mean-square (RMS) differences in M-L force averaged 50 N less in the RP design throughout the flexion cycle, and 70 N less after 45° flexion (Figure 2). The FB design aligned for optimal bone coverage demonstrated 15% higher M-L forces than the FB design aligned with the tibial A-P axis. RMS load required by the quadriceps muscle was 60 N lower with the RP design than the FB design throughout the cycle (Figure 2). Discussion. Comparing a RP design with an anatomic patellar component and a FB design with a domed patellar component, the RP design demonstrated lower M-L PF joint and soft-tissue extensor mechanism forces. Differences were more pronounced under conditions of high I-E torque where the RP design accommodated large relative TF rotation. Differences in FB alignment resulted in substantially different PF M-L forces; when the FB component was mal-aligned with respect to the tibial A-P axis (and the line-of-action of the patellar tendon) the resulting M-L PF force was increased. The RP design reduced the demands on the extensor mechanism and loads on the PF joint and facilitated better coverage of the resected tibial bone surface

Introduction:. Alignment of the initial femoral guidewire is critical in avoiding technical errors that may increase the risk of failure of the femoral component. A novel alternative to conventional instrumentation for femoral guidewire insertion is a computed tomography (CT) based alignment guide. The aim of this study was to assess the accuracy of femoral component alignment using a CT-based, patient specific femoral alignment guide. Methods:. Between March 2010 and January 2011, 25 hip resurfacings utilizing a CT-based femoral alignment guide were performed by three surgeons experienced in hip resurfacing. Stem-shaft angle (SSA) accuracy was assessed using minimum 6 week post-operative digital radiographs. A benchside study was also conducted utilizing six pairs of cadaveric femora. Each pair was divided randomly between a group utilizing firstly a conventional lateral pin jig followed by computer navigation and a group utilizing a CT-based custom jig. Guidewire placement accuracy for each alignment method was assessed using AP and lateral radiographs. Results:. In the clinical series, the post-operative SSA differed from the planned SSA by a mean of 1.3° (SD 4.8, range −9–14). The final SSA measured within ± 5° of the planned SSA in 20 of 24 cases (83%). There was no significant difference between surgeons in post-operative SSA accuracy (p = 0.697). In the benchside study, the custom jig (mean error 6.4°, SD 2.9) provided a comparable level of accuracy to that of the conventional jig (mean error 5.5°, SD 3.6, p = 0.851). Guidewire version using the custom jig (mean error 1.0°, SD 0.4) was comparable to computer navigation (mean error 3.9°, SD 2.1, p = 0.101) and was superior to the conventional jig (mean error 5.6°, SD 2.9, p = 0.008). Conclusion:. CT-based, patient specific guidewire alignment jigs provide a satisfactory level of accuracy for alignment of the femoral component. A custom guidewire alignment jig is comparable to computer navigation and may be a better alternative to conventional instrumentation for placement of the initial femoral guidewire in hip resurfacing. Accuracy results of the device approach those previously established for imageless computer navigation in hip resurfacing (1)

Minimally invasive total knee arthroplasty is growing in popularity. It appears to reduce blood loss, reduce hospital stay, improve post-operative quadriceps function and shorten post-operative recovery. We show our experience of minimally invasive TKA with a computer navigation system. The first series compared forty MICA TKA and forty conventional computer assisted total knee arthroplasties (CATKA). Component positioning was assessed radiographically with long leg Maquet views. Knee Society Scores (KSS) were recorded pre-operatively and at 6, 12, 18 months. Length of stay and recovery of straight leg raise was also recorded. A second series of fifty MICATKA patients were assessed post-operatively for component alignment using long leg Maquet views. Twenty-two of these patients had assessment of femoral rotation using CT. In the first series pre-operative KSS showed no significant difference between the two groups. Post-operatively the mean femoral component alignment was 89.7 degrees for MICATKA and 90.2 for CATKA. The mean tibial component alignment was 89.7 degrees for both. KSS at 6, 12, 18 months were statistically better in the MICATKA (p<000.1). Straight leg raise was achieved by day one in 93% of the MICATKA compared to 30% of the CATKA. Length of stay for MICATKA was a mean of 3.25 days with CATKA a mean of 6 days. In the second series the mean femoral component varus/valgus angle was 89.98 degrees, the mean tibial component varus/valgus angle was 89.91 degrees and the mean femoral component rotation was 0.6 degrees of external rotation. MICATKA is a safe procedure with reproducible results. Alignment is equivalent to CATKA. It gives statistically significant improvement in KSS compared to the open procedure. The length of stay and time to straight leg raise are also reduced. At 2 years follow-up we have seen no revisions and no evidence of loosening radiographically

Introduction. Computer assisted surgery (CAS) systems have been shown to improve alignment accuracy in total knee arthroplasty (TKA), yet concerns regarding increased costs, operative times, pin sites, and the learning curve associated with CAS techniques have limited its widespread acceptance. The purpose of this study was to compare the alignment accuracy of an accelerometer-based, portable navigation device (KneeAlignÒ 2) to a large console, imageless CAS system (AchieveCAS). Our hypothesis is that no significant difference in alignment accuracy will be appreciated between the portable, accelerometer-based system, and the large-console, imageless navigation system. Methods. 62 consecutive patients, and a total of 80 knees, received a posterior cruciate substituting TKA using the Achieve CAS computer navigation system. Subsequently, 65 consecutive patients, and a total of 80 knees, received a posterior cruciate substituting TKA using the KneeAlignÒ 2 to perform both the distal femoral and proximal tibial resections (femoral guide seen in Figure 1, and tibial guide seen in Figure 2). Postoperatively, standing AP hip-to-ankle radiographs were obtained for each patient, from which the lower extremity mechanical axis, tibial component varus/valgus mechanical alignment, and femoral component varus/valgus mechanical alignment were digitally measured. Each measurement was performed by two, blinded independent observers, and interclass correlation for each measurement was calculated. All procedures were performed using a thigh pneumatic tourniquet, and the total tourniquet time for each procedure was recorded. Results. In the KneeAlignÒ 2 cohort, 92.5% of patients had an alignment within 3° of a neutral mechanical axis (vs. 86.3% with AchieveCAS, p<0.01), 96.2% had a tibial component alignment within 2° of perpendicular to the tibial mechanical axis (vs. 97.5% with AchieveCAS, p=0.8), and 94.9% had a femoral component alignment within 2° of perpendicular to the femoral mechanical axis (vs. 92.5% with AchieveCAS, p<0.01). The mean tourniquet time in the KneeAlignÒ 2 cohort was 48.1 + 10.2 minutes, versus 54.1 + 10.5 in the AchieveCAS cohort (p<0.01). The interclass correlation coefficient for measurement of the postoperative tibial alignment was 0.92, for femoral alignment was 0.85, and for overall lower extremity alignment was 0.94. Conclusion. Accelerometer-based, portable navigation can provide the same degree of alignment accuracy as large console, imageless CAS system in TKA, while also decreasing operative times. The KneeAlignÒ 2 successfully combines the benefits and accuracy of large-console, CAS systems, while avoiding the use of extra pin sites, decreasing operative times, and providing a level of familiarity with conventional alignment methods

INTRODUCTION. Unicompartmental knee arthroplasty (UKA) can achieve excellent clinical and functional results for patients suffering from single compartment osteoarthritis. However, UKA is considered to be more technically challenging to perform, and malalignment of the implant components has been shown to significantly contribute to UKA failures. The purpose of this investigation was to determine the clinically realized accuracy of UKA component placement using surgical navigation and dynamically referenced tactile-robotics. METHODS. Pre-op CT, post-op CT, and surgical plan were available for 22 knees out of the first 45 procedures performed using a new tactile-guided robotic system. 3D component placement accuracy was assessed by comparing the pre-operative plan with the post-operative implant placement (desired versus actual). Bone and implant models were obtained from postoperative CT scans taken immediately following the surgery. A 3D to 3D iterative closest point registration procedure was performed and the measured implant position was directly compared to the preoperative plan. Errors were assessed as single axis root-mean-square (RMS) entities. RESULTS. Femoral component RMS placement errors averaged 1.4 mm/2.6° along any single axis. Tibial component RMS placement errors averaged 1.18 mm/2.14° along any single axis. CONCLUSION. Using traditional manual instruments, Cobb et al. found average RMS errors of 2.20mm/5.48°. Using the robotic approach with bones fixed, Cobb et al. reported RMS errors of 1.11 mm/2.5°, directly comparable to our results with bones moving freely during surgery. Varus/valgus femoral component alignment and posterior tilt of the tibial component are within the accepted range to prevent excessive edge loading, leading to tibial plateau collapse and/or excessive wear. Dynamically-referenced tactile robotics provide a new tool to accurately prepare bone with minimally invasive approaches. Our results suggest excellent UKA implant placement accuracy can be achieved, comparable to that demonstrated for statically referenced tactile robotics. The patients were the first group from a single surgeon using this technique, suggesting good implant alignment is achieved in what normally would be considered a learning phase. Finally, these patients were treated with the first approved version of this new tool, suggesting further refinement of this robotic technology will enhance the accuracy and usability of this tool