Background

The use of Computed Tomography (CT) as a medical imaging tool has widespread applications in the field of knee surgery. Surgeons use a CT scan in a conventional way during the pre-operative stage, to plan the position of the femoral component in the horizontal plane. In the post-operative stage, the use of a CT scan is a routine tool in the evaluation of failed TKA as rotational malalignment of the femoral component has been determined as a cause of poor clinical outcome after TKA.

Eligible patients were randomly allocated to PMI or standard intramedullary jigs. Smith and Nephew's patient specific cutting blocks (Visionaire) were used for PMI. Postoperative component positioning was investigated using the ‘Perth CT protocol’. Deviation of more than 3° from the recommended position was regarded as an outlier. Exact Mann-Whitney U test was used to compare component positioning and difference in proportion of outliers was calculated using Chi Squared analysis.

Fifty-five knees were enrolled in the standard instrumentation group and fifty-two knees in the PMI group.

Coronal femoral alignment was 0.7 ± 1.9° (standard) vs 0.5 ± 1.6° (PMI) (P=0.33). Outliers 9.4% vs 7.4% (P=0.71). Coronal tibial alignment was 0.4 ± 1.5° (standard) vs 0.6 ± 1.4° (PMI) (P=0.56). Outliers 1.9% vs 1.9% (P=0.99). Sagittal femoral alignment was 0.6 ± 1.5° (standard) vs 1.3 ± 1.9° (PMI) (P=0.07). Outliers 3.8% vs 13.2% (P=0.09). Tibial slope was 1.7 ± 1.9 ° (standard) vs 1.8 ± 2.7° (PMI) (P=0.88). Outliers 13.2% vs 24.1% (P=0.15). External rotation of femoral component was 0.6 ± 1.4° (standard) vs 0.2 ± 1.8° (PMI) (P=0.14). Outliers: 3.8% vs 5.6% (P=0.66).

Compared to standard intramedullary jigs, patient matched instrumentation does not improve component positioning or reduce alignment outliers.

Introduction:

Recently there has been interest in an alternative method of aligning a total knee arthroplasty (TKA) referred to as kinematic alignment. The theoretical appeal of this method is that alignment of each patient's knee can be individualized through the use of preoperative imaging and computer software, with the goal of achieving pre-arthritic alignment through restoration of the axes of rotation of each particular knee. Clinical studies have evaluated the outcomes of this new alignment technique, but to date there have been no randomized controlled trials comparing kinematic alignment to mechanical alignment. This randomized controlled trial was conducted to compare kinematically aligned and mechanically aligned TKA outcomes of knee pain, function and motion at two years' post-op, along with a comparison of limb, knee, and implant alignment of the two methods.

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.

Most discussions of alignment after TKA focus on defining “malalignment”; the prefix mal- is derived from Latin and refers to bad, abnormal or defective and thus by definition malalignment is bad, abnormal or defective alignment. No one then wants a “malaligned” knee. The intellectually curious, however, might switch the focus to the other end of the spectrum and ask what does an ideally aligned knee look like in 2015? Is there really one simple target value for alignment in all patients undergoing TKA? Is that target broad (zero +/−3 degrees mechanical axis) or is it a narrow target in which a penalty, in regard to durability or function, is incurred as soon as you deviate even 1 degree? Is that ideal target the same if we are evaluating the functional performance of the TKA versus the durability of the TKA or could there be 2 different targets, one that maximises function and one that maximises durability? Is that target adequately described by a single 2-dimensional value (varus/valgus alignment in the frontal plane) as measured on a static radiograph? Is that value the same if the patient has a fixed pelvic obliquity, a varus thrust in the contralateral knee or an abnormal foot progression angle?. It is revealing to ask “do we understand TKA alignment better in 2015 than in 1979…?” Maybe not. We allowed ourselves over the past 2 decades to be intellectually complacent in regard to questions of ideal alignment after TKA. The constraints on accuracy imposed by our standard total knee instruments and the constraints on assessment imposed by 2-dimensional radiographs made broad, simple targets like a mechanical axis +/− 3 degrees reasonable starting points yet we have not further worked to verify if we can do better. It is naïve to think that the complex motion at the knee occurring in 6-dimensions over time can be reduced to a single static target value like a neutral mechanical axis and have strong predictive value in regard to the success or failure of an individual TKA. We assessed 399 knees of 3 different modern cemented designs at 15 years and found that factors other than alignment were more important than alignment in determining the 15-year survival. Until more precise alignment targets can be identified for individual patients or sub-groups of patients then a neutral mechanical axis remains a reasonable surgical goal. However, the traditional description of TKA alignment as a dichotomous variable (aligned versus malaligned) defined around the broad, generic target value of 0 +/− 3 degrees relative to the mechanical axis is of little practical value in predicting the durability or function of modern TKA

THA: Approaches and Recovery; THA: Instability and Spinal Deformity; Revision for THA Instability: Dual Mobility Cups; Removal of Infected THA: Risk Factors for Complications; Tribocorrosion: Incidence in the Symptomatic THA; THA: Outcomes and Education Levels; THA: Satisfaction levels and Residual Symptoms; THA: Expectations and LOS; TKA: Kneeling and Recreation Expectations; TKA: Alignment and Long Term Survival; Patello-Femoral Arthroplasty vs TKA; Unicompartmental Knee Arthroplasty and Age; Wound Treatments and Sepsis in TJA; TKA: Managing Sepsis With I & D; Chronic Salvage in TKA: When is Enough Enough?; Revision TKA: Single Component Revision

Introduction. Computed tomography (CT) based preoperative planning provides useful information for severe TKA and revision TKA cases, such as the amount of augmentation, length of stem extension and component alignment, to achieve correct alignment and joint line. In this study, we evaluated TKA alignment performed with CT preoperative planning. Materials and Methods. 7 primary TKAs for severe deformity and 3 revision TKAs were included. CT preoperative planning was performed with JIGEN (LEXI, Japan). Constrained condylar prosthesis (LCCK, Zimmer) were used in all case. For femoral component, axial alignment was decided by controlled IM rod insertion to femoral canal. Rotational alignment was decided according to anterior cortex that usually was not compromised. For tibial component, axial alignment was set to perpendicular to tibial mechanical axis. Coverage and joint line level were carefully decided. The amount of bone resection of bilateral distal and posterior femoral condyle and proximal tibia was measured, respectively. Stem extension length and offset were selected according to components position and canal filling. Amount of augmentation was also estimated bilateral distal and posterior femoral condyle, respectively. Postoperative component alignment was evaluated three-dimensionally with Knee-CAS (LEXI, Japan). Results. All femoral and tibial components were implanted within 5°in coronal and sagittal plane. All knees showed mechanical alignment within 5 degree from neutral. One of 10 TKAs needed femoral component size down, and two of 20 stems needed size change

No, Neutral mechanical axis has never been regarded as “necessary” to the success of TKA. In fact it has never been established as “ideal” with published data. Tibial femoral alignment after TKA is important, but it is also an issue that we do not understand completely. Neutral mechanical alignment refers to the relationship between the mechanical axes of the femur and tibia as shown on full length radiographs. “Neutral” means that these axes are collinear, i.e. that a line may be drawn from the center of the hip to the center of the ankle and it will intersect the center of the knee joint. The allure of the “straight line” has led many surgeons to regard a neutral mechanical axis as “perfection” for TKA surgery, but indeed, it is not the usual “normal” alignment for most human knees, nor is it the target for many conventional knee replacements. The “neutral mechanical axis” represents OVERCORRECTION for most knees. Moreland demonstrated in 1987 that few human knee joints are naturally aligned “in neutral”, but with the line from center of hip to center of ankle passing through the medial compartment. This tendency to relative varus mechanical axis in most human knees was corroborated by Bellemans et al in 2012. They substituted the word “constitutional varus” for what would otherwise be known as “normal alignment”. In general, patients with pathologic or significant varus alignment, whose arthroplasties have been performed competently, are at greatest risk for failure by wear, osteolysis and loosening. This is the prototypical failure mechanism that pre-occupied the surgeons responsible for making knee arthroplasty successful in the 1970s. The first paper to identify varus TKA alignment and failure due to loosening was Lotke and Ecker in 1977. They worked from short radiographs and ushered in an era of careful attention to valgus TKA alignment-not neutral alignment. Correction of varus deformity combined with ligament balancing was probably responsible for making condylar type knee arthroplasties work durably in the early days. Full length radiographs, used by Kennedy and White in 1987 to study alignment in unicompartmental arthroplasties, provide a more sophisticated method of evaluating knee alignment. These studies must be aligned with correct rotation to be valid. Computerised navigation was probably responsible for some surgeon's dedication to the neutral mechanical axis. The study of Parratte et al from Mayo has received much attention and argued that a neutral mechanical axis did NOT improve success rates at 15 years. It should be noted that these TKA's were expertly performed and even the less well-aligned cases were not “excessively” malaligned. This study does not state that alignment is irrelevant to the success of TKA, but rather that a range of alignments (with stability) might be expected to produce a durable arthroplasty. Concurrent with these developments has been an interest in “under-correcting” knee deformity or allowing osseous anatomy (with compensation for cartilage loss) guide component position. In truth, it is inaccurate to describe conventional “align and balance” techniques as necessarily seeking a neutral mechanical axis. Most classical alignment techniques do, however, alter the angle of component position from the original articular surface angles and theoretically may not function as well with the native soft tissue environment. Surgeons who would align the TKA identically to the arthritic knee may credit previous generations with improving the technology such that this is a possibility. If every patient is to be aligned with this technique, however, this suggests that soft tissue pathology does not exist. As with all complex issues, glib answers are to be avoided and deep analysis is appropriate

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. To test whether there are differences in postoperative mechanical and component alignment, and in functional results, between conventional, navigated and patient-specific total knee arthroplasties in a low-volume centre?. MATERIAL AND METHODS. Retrospective cohort study of 391 patients who received conventional, navigated or patient- specific primary cemented TKA in a low-volume hospital. RESULTS. The risk of mechanical alignment outliers was 89% lower in the navigated group compared to the conventional TKA group. There was a 63% lower risk of femoral component malalignment and a 66% lower risk of tibial component malalignment in the navigated group. No significant reduction in the risk of malalignment was seen in the patient-specific group. Total WOMAC and Oxford scores were no different between the three techniques. The patient-specific group reported better WOMAC pain scores. PSI TKA was 33% more expensive than conventional TKA and 28% more expensive than Navigated TKA. DISCUSSION. Navigated TKA improved alignment, but neither navigated nor patient-specific TKA improved functional outcomes. Patient-specific TKA was more expensive, with little additional benefit. Clinical relevance: The routine use of patient-specific instrumentation in low-volume centers is not supported by the currently available data

Summary sentence. The bowing of the femur defines a curvature plane to which the proximal and distal femoral anatomic landmarks have a predictable interrelationship. This plane can be a helpful adjunct for computer navigation to define the pre-operative, non-diseased anatomy of the femur and more particularly the rotational alignment of the femoral component in total knee arthroplasty (TKA). Background and aims. There is very limited knowledge with regards to the sagittal curvature -or bowing- of the femur. It was our aim (1) to determine the most accurate assessment technique to define the femoral bowing, (2) to define the relationships of the curvature plane relative to proximal and distal anatomic landmarks and (3) to assess the position of femoral components of a TKA relative to the femoral bowing. Materials and methods. Four independent algorithms were developed and tested on 3D models of 18 cadaveric femora. A sensitivity study showed that a bisector-based method supplied the most stable results. In order to verify if the curvature plane can be used for TKA alignment, the anteversion angle was determined relative to this plane and compared with anteversion angles defined using the coronal plane. Results. The average curvature of the cadaveric femora was 895.85 mm (SD = 184.53 mm). The mean anteversion angle calculated along the projected mechanical or anatomical axis in the coronal plane were 8.2+/−5.2° and 7.6+/− 4.8°. These angles calculated along the projected mechanical or anatomical axis in the curvature plane were 8.2+/−5.2° and 5.2+/−4.8° respectively (p>0.05). Assessment of the component placement relative to the mechanical axis showed that in the coronal plane, an average deviation of 1.84° was measured. In the sagital plane, the average deviation from the mechanical axis was 2.01°. The components were placed in 1 to 2° of extension relative to the femoral bowing. Discussion. A new and stable algorithm was successfully developed to determine the curvature of the femoral shaft. This curvature was comparable to 2 previously reported curvatures. Our study also demonstrates a predictable interrelationship between the femoral shaft curvature on one side and the rotation of the distal femur on the other side. This finding is of great interest in view of a recent trend amongst knee surgeons to aim at anatomical restoration of the patient's original anatomy. Patient matched cutting blocks as well as patient specific implants are today increasingly considered in daily practice in an attempt to restore the patient's natural anatomy and biomechanics. Computational methods to reverse engineer the pre-diseased status of the knee joint regarding its anatomy and orientation are therefore of great importance. The findings from our study suggest that the femoral shaft's curvature is a helpful adjunct to this. Furthermore, abnormal rotational alignment of an axially malaligned component can be assessed accurately with this new reference plane. However, further research on implementing this algorithm and this plane into clinical practice is mandatory. However, further research on implementing this into clinical practice is required

Introduction. Proper total knee arthroplasty balancing relies on accurate component positioning and alignment as well as soft tissue tensioning. Technology for cutting guide alignment has evolved from the “free hand” technique in the 1970's, to traditional intra/extra medullary rods in the 1980's and 1990's, to computer navigated surgery in the 2000's, and finally to patient specific custom cutting blocks in the 2010's. The latest technique is a modification to conventional computer navigation assisted surgery using Brainlab's Dash™ TKA/THA software platform that runs as an application on an Apple IPod held by the surgeon in a sterile pouch in the operative field. The handheld IPod touch screen allows the surgeon to control all aspects of the navigation interface without needing the assistance of an observer to manually run the software. In addition, the surgeon is able to always focus on the operative field while ‘navigating’ without looking up at a remote image monitor. This study represents a prospective analysis of the first 30 U.S. TKA cases performed using the newly commercially released Dash™ software using an IPod during surgery. Methods. Thirty consecutive primary total knee arthroplasty procedures were performed using the Dash™ software (Brainlab) and an IPod touch (Apple). A cemented Genesis II (Smith Nephew) posterior stabilized implant was used in all cases. Femoral and tibial sensor arrays were placed in meta-diaphyseal regions for bone registration. We recorded the time spent to set up the arrays, time for bony registration, time to navigate the cutting guides, and the tourniquet time. After all bone cuts were completed, the tibial cut was manually measured with an intramedullary angle check instrument to assess the planned zero degree posterior slope and neutral varus/valgus coronal alignment. Final femoral and tibial component alignment and orientation was measured on standing long axis AP and lateral radiographs. Measurements from the Dash™ alignment group were compared to 30 consecutive surgeries using the author's traditional technique of intramedullary cutting block alignment (control group). Results. In the initial 6 surgeries conducted, total navigation time exceeded 20 minutes reflecting the learning curve. In the remaining computer navigation group cases, average time for array set up was 3 minutes, average time for bony registration was 3 minutes, average time for navigating the cutting guides was 12 minutes, and average tourniquet time was 53 minutes. In the control group, the average tourniquet time was 44 minutes. There was no statistically significant difference in component alignment between the two groups when measuring distal femoral valgus angle, posterior condylar offset, femoral flexion/extension angle, tibial slope angle, or tibial varus/valgus angle. Conclusions. Total knee arthroplasty using computer navigation and an IPod interface with Dash™ software is as accurate when compared to a traditional intramedullary TKA alignment technique. Only an additional average time of 9 minutes (after initial learning curve) using Dash™ navigation was needed. Further studies will compare these alignment techniques to extramedullary alignment and custom patient specific cutting block procedures

Background:. For the past four decades controversy surrounds the decision to retain or sacrifice the posterior cruciate ligament during a total knee arthroplasty. To our knowledge no study has been done to describe the effect of releasing the PCL on the range of motion of the knee. Study design:. Case series. Methods:. Computer navigation data (Brainlab) was obtained intra-operatively from thirty patients at total knee arthroplasty. Coronal alignment, maximal passive knee extension and maximal passive flexion was captured before and after release of the PCL. Results:. Releasing the posterior cruciate ligament led to an increase in maximal extension in all patients (av 3,6°) and a decrease in coronal deformity in 63%. The surprising finding was an increase in maximal knee flexion (av 5°, range 0 to 10°.) The increase in maximal flexion was statistically significant. Conclusion:. Sacrificing the posterior cruciate ligament alters the kinematics of the knee and the resultant increase in knee flexion might explain why cruciate sacrificing total knee arthroplasty has superior flexion compared to cruciate retaining designs

Introduction. For nearly 58% of total knee arthroplasty (TKA) revisions, the reason for revision is exacerbated by component malalignment. Proper TKA component alignment is critical to functional outcomes/device longevity. Several methods exist for orthopedic surgeons to validate their cuts, however, each has its limitations. This study developed/validated an accurate, low-cost, easy to implement first-principles method for calculating 2D (sagittal/frontal plane) tibial tray orientation using a triaxial gyroscope rigidly affixed to the tibial plateau of a simulated leg jig and validated 2D tibial tray orientation in a human cadaveric model. Methods. An initial simulation assessed error in the sagittal/frontal planes associated with all geometric assumptions over a range of positions (±10°, ±10°, and −3°/0°/+3° in the sagittal, frontal, and transverse planes, respectively). Benchtop experiments (total positions - TP, clinically relevant repeated measures - RM, novice user - NU) were completed using a triaxial gyroscope rigidly affixed to and aligned with the tibial tray of the fully adjustable leg-simulation jig. Finally, two human cadaveric experiments were completed. A similar triaxial gyroscope was mounted to the tibial tray of a fresh frozen human cadaver to validate sagittal and frontal plane tibial tray orientation. In cadaveric experiment one, three unique frontal plane shims were utilized to measure changes in frontal plane angle. In cadaveric experiment two, measurements using the proprosed gyroscopic method were compared with computer navigation at a series of positions. For all experiments, one rotation of the leg was completed and gyroscopic data was processed through a custom analysis algorithm. Results. Mathematical simulations showed that over the range of tested orientations, error from our geometric assumptions would be less than 1° and 0.2° in the sagittal and frontal planes, respectively. Results of all bench-top experiments are shown in Figure 1. The average angular error during the TP experiment (black bars) was 1.09°±0.80° and 0.60°±0.46° in the sagittal/frontal planes. The average angular error during the RM experiment (white bars) in the sagittal/frontal planes was 0.27°±0.25° and 0.30°±0.23°. The average angular error from the NU experiment (grey bars) in the sagittal/frontal planes was 1.50°±1.57° and 0.82°±0.77°. During cadaveric experiment one (Figure 2), computed frontal plane angles were 2.83°±0.98°, −1.67°±1.99°, and −4.33°±0.53° after placing distinct 2° lateral, 2° medial, and 4° medial shims. Finally, the average angular error from cadaveric experiment two (Figure 3) over all positions was 1.73°±1.12° and 1.56°±1.45° in the sagittal and frontal planes, respectively. Discussion. Despite the high frequency of TKA procedures, a significant number fail and need to be revised for improper component alignment. This study showed through a first-principles approach that surgeons can assess 2D orientation of the tibial component intraoperatively with 1° of accuracy with a single triaxial gyroscope rigidly affixed to the tibial plateau. Moreover, this study showed through the use of a cadaveric model that surgeons could assess 2D alignment of the tibial component with a gyroscope rigidly affixed to the tibial plateau. To our knowledge, this is first method to offer true 2D tibial tray orientation assessment using only a single triaxial gyroscope

Introduction. Total Knee Replacement (TKR) alignment measured intra-operatively with Navigation has been shown to differ from that observed in long leg radiographs (Deep 2011). Potential explanations for this discrepancy may be the effect of weight bearing or the dynamic contributions of soft tissue loads. Method. A validated, 3D, dynamic patient specific musculoskeletal model was used to analyse 85 post-operative CT scans using a common implant design. Differences in coronal and axial plane tibio-femoral alignment in three separate scenarios were measured:. Unloaded as measured in a post-op CT. Unloaded, with femoral and tibial components set aligned to each other. Weight bearing with the extensor mechanism engaged. Scenario number two illustrates the tibio-femoral alignment when the femoral component sits congruently on the tibia with no soft tissue acting whereas scenario three is progression of scenario number two with weight applied and all ligaments are active. Two tailed paired students t-test were used to determine significant differences in the means of absolute difference of axial and coronal alignments. Results. The mean coronal alignment were 1.7° ± 2.1° varus (range, −3.0° to 7.0°), 0.8° ± 2.0° varus (range, −3.7° to 4.8°), 0.4° ± 2.0° varus (range, −3.9° to 5.1°) for unloaded, unloaded with implants set aligned and weight bearing scenarios respectively. The mean of absolute difference in coronal alignment between the unloaded and weight bearing scenario was 1.8° ± 1.5° (range 0.0° to 5.9°). The mean axial alignment were 6.8° ± 5.5° external rotation (ER) (range, 20.0° ER to 11.0° internal rotation (IR)), 5.2° ± 6.1° ER (range, 24.8° ER to 12.6° IR), 7.1° ± 5.5° ER (range, 20.7° ER to 6.8° IR) for unloaded, unloaded with implants set to congruency and weight bearing scenarios respectively. The mean of absolute difference in axial alignment between the unloaded and weight bearing scenario was 2.8° ± 2.0° (range 0.1° to 8.8°). Statistically significant absolute differences in coronal and axial alignments were found. Conclusions. ‘Correct’ alignment has long been considered and important predictor of longevity and function following TKR surgery (Sikorski 2008). However, recent reports have challenged these long held beliefs. One possible reason is that these alignments are measured in static condition, not in a functional position where soft tissue is active. This study showed that knee joint alignment changes significantly between unloaded and loaded scenarios. This suggest that static, unloaded measurements do not represent functional alignment. Thus, tibio-femoral alignment measured from unloaded condition may not describe a ‘correct’ alignment for a particular patient. Further work should focus on dynamic and functional descriptions of component and/or limb alignment

Introduction. In total knee arthroplasty, the alignment of leg depends on the alignment of the component. In unicompartmental knee arthroplasty, it is determined by the thickness of the implant relative to the bone excised mostly. After initial scepticism, UKA is increasingly accepted as a reliable procedure for unicompartmental knee osteoarthritis with the improvements in implant design, surgical technique and appropriate patient selection. Recently, computer assisted UKA is helpful in accuracy and less invasive procedure. But, fixed bearing or mobile bearing in UKA is still controversy. We compared the early clinical and radiological results of robot-assisted unicompartmental knee arthroplasty using a fixed bearing design versus a mobile type bearing design. Materials and Methods. A data set of 50 cases of isolated compartmental degenerative disease that underwent robot-assisted UKA using a fixed bearing design were compared to a data set of 50 cases using a mobile bearing type design. The operations were performed by one-senior author with the same robot system. The clinical evaluations included the Knee Society Score (knee score, functional score) and postoperative complications. The radiological evaluations was assessed by 3-foot standing radiographs using the technique of Kennedy and White to determine the mechanical axis and femoro-tibial angle for knee alignment. Operative factors were evaluated including length of skin incision, operation time, blood loss, hospital stay and intraoperative complications. Results. There were no statistically significant differences in operation time, skin incision size, blood loss and hospital stay. (p > 0.05) There were no significant differences in Knee Society Scores at last follow up. An average preoperative femorotibial alignment was varus alignment of −1° in both groups. Postoperative patients with fixed-bearing implants had an average +2.1° valgus and the patients with mobile bearing implants had +5.4° valgus in femorotibial alignment, which was different.(p<0.05) There was one case of medial tibia plateau fracture in fixed bearing group in 3 months postoperatively. And there were one case of liner dislocation with unstable knee in 6 weeks postoperatively and one case of femoral component loosening in 1 year postoperatively in mobile bearing group. There was no intraoperative complication. The average preoperative knee score was 45.8, which improved to 89.5 in fixed bearing group and 46.5, which improved to 91.2 in mobile bearing group at last followup. The average preoperative function score was 62.4 which improved to 86.5 in fixed bearing group and 60.7 which improved to 88.2 in mobile bearing group at last followup. Conclusion. In ourearly experience, two types of bearing of robot-assisted UKA groups showed no statistical differences in clinical assessment but there was statistical difference in postoperative radiological corrected alignment. But in aspect of early complications, we think that mobile bearing seems to be requiring more attention in surgery