The aim of this study is to assess the discrepancy between weight bearing long leg radiographs and supine MRI alignment. There is currently increasing interest in the use of MRI to assess knee alignment and develop custom made cutting blocks utilising this data. However in almost all units MRI scans are performed supine and it is recognised that knee alignment can alter with weight bearing. 46 patients underwent MRI scans as pre-operative planning for Biomet signature total knee replacement and the measure of varus or valgus deformity on MRI was obtained from the plan produced by Biomet Signature software system. 41 of these patients had long leg weight bearing radiographs performed. 33 of these radiographs were amenable to measuring the knee alignment on the picture archiving and communication system (PACS). These measurements were performed by two assessors and inter-observer reliability was satisfactory. There was a significant difference between the alignment as measured on supine MRI compared with weight bearing long leg films. In knee arthroplasty one of the aims is to correct the biomechanical axis of the knee and one of the appeals of custom made cutting blocks is that this can be achieved more easily. However it is important to realise that alignment is not a static value and thus correcting supine alignment may not necessarily result in correction of weight bearing alignment

The gold standard for measuring knee alignment is the lower limb mechanical axis. This is traditionally assessed by weight-bearing full length lower limb X-rays (LLX). CT scanograms (CTS) are however, becoming increasingly popular in view of lower radiation exposure, speed and supine positioning. We assessed the correlation and reproducibility of knee joint coronal alignment using these two imaging modalities. LLX and CTS images were obtained in 24 knees with degenerate joint disease or failed TKR. Hip to ankle mechanical alignment were measured using the PACS software. Coronal knee alignment was assessed from the centre of the knee, measuring the valgus/varus angle relative to the mechanical axis. Measurements were made by two orthopaedic surgeons (Research Fellow and Consultant) on two separate occasions. The mean alignment angles measured by observers 1 and 2 on CTS were 180.29° (SD 6.04) and 180.71° (SD 6.13) respectively, while on LLX were 181.04° (SD7.58) and 181.04° (SD 7.72). The measurements between the two observers were highly correlated for both the CTS (r = 0.97, p < 0.001) and the LLX (r = 0.99, p < 0.001). The angles measured on CTS and LLX were highly correlated (r = 0.826, p < 0.001) with high degree of internal consistency (ICC = 0.804). Malalignment of greater than 5° was seen in 19% of the CTS and 35% of the LLX. There was good correlation between CT scanogram and weight-bearing X-ray measurements in normally-aligned knees. However, as expected, in the malaligned lower limb, the influence of weight-bearing is critical which demonstrates the significance of weight-bearing X-rays

Identifying and restoring alignment is a primary aim of total knee arthroplasty (TKA). In the coronal plane, the pre-pathological hip knee angle can be predicted using an arithmetic method (aHKA) by measuring the medial proximal tibial angle (MPTA) and lateral distal femoral angle (aHKA=MPTA - LDFA). The aHKA is shown to be predictive of coronal alignment prior to the onset of osteoarthritis; a useful guide when considering a non-mechanically aligned TKA. The aim of this study is to investigate the intra- and inter-observer accuracy of aHKA measurements on long leg standing radiographs (LLR) and preoperative Mako CT planning scans (CTs).

Sixty-eight patients who underwent TKA from 2020–2021 with pre-operative LLR and CTs were included. Three observers (Surgeon, Fellow, Registrar) measured the LDFA and MPTA on LLR and CT independently on three separate occasions, to determine aHKA. Statistical analysis was undertaken with Bland-Altman test and coefficient of repeatability.

An average intra-observer measurement error of 3.5° on LLR and 1.73° on CTs for MPTA was detected. Inter-observer errors were 2.74° on LLR and 1.28° on CTs. For LDFA, average intra-observer measurement error was 2.93° on LLR and 2.3° on CTs, with inter-observer errors of 2.31° on LLR and 1.92° on CTs. Average aHKA intra-observer error was 4.8° on LLR and 2.82° on CTs. Inter-observer error of 3.56° for LLR and 2.0° on CTs was measured.

The aHKA is reproducible on both LLR and CT. CT measurements are more reproducible both between and within observers. The difference between measurements using LLR and CT is small and hence these two can be considered interchangeable. CT may obviate the need for LLRs and may overcome difficulties associated with positioning, rotation, body habitus and flexion contractures when assessing coronal alignment.

Background. There are limited previous findings detailed biomechanical properties following implantation with mechanical and kinematic alignment method in robotic total knee arthroplasty (TKA) during walking. The purpose of this study was to compare clinical and radiological outcomes between two groups and gait analysis of kinematic, and kinetic parameters during walking to identify difference between two alignment method in robotic total knee arthroplasty. Methods. Sixty patients were randomly assigned to undergo robotic-assisted TKA using either the mechanical (30 patients) or the kinematic (30 patients) alignment method. Clinical outcomes including varus and valgus laxities, ROM, HSS, KSS and WOMAC scores and radiological outcomes were evaluated. And ten age and gender matched patients of each group underwent gait analysis (Optic gait analysis system composed with 12 camera system and four force plate integrated) at minimum 5 years post-surgery. We evaluated parameters including knee varus moment and knee varus force, and find out the difference between two groups. Results. The mean follow up duration of both group was 8.1 years (mechanical method) and 8.0 years (kinematic method). Clinical outcome between two groups showed no significant difference in ROM, HSS, WOMAC, KSS pain score at last follow up. Varus and valgus laxity assessments showed no significant inter-group difference. We could not find any significant difference in mechanical alignment of the lower limb and perioperative complicatoin. In gait analysis, no significant spatiotemporal, kinematic or kinetic parameter differences including knee varus moment (mechanical=0.33, kinematic=0.16 P0.5) and knee varus force (mechanical=0.34, kinematic=0.37 P0.5) were observed between mechanical and kinematic groups. Conclusions. The results of this study show that mechanical and kinematic alignment method provide comparable clinical and radiological outcomes after robotic total knee arthroplasty in average 8 years follow-up. And no functional difference were found between two knee alignment methods during walking

Background. There are limited previous findings detailed biomechanical properties following implantation with mechanical and kinematic alignment method in robotic total knee arthroplasty (TKA) during walking. The purpose of this study was to compare clinical and radiological outcomes between two groups and gait analysis of kinematic, and kinetic parameters during walking to identify difference between two alignment method in robotic total knee arthroplasty. Methods. Sixty patients were randomly assigned to undergo robotic-assisted TKA using either the mechanical (30 patients) or the kinematic (30 patients) alignment method. Clinical outcomes including varus and valgus laxities, ROM, HSS, KSS and WOMAC scores and radiological outcomes were evaluated. And ten age and gender matched patients of each group underwent gait analysis (Optic gait analysis system composed with 12 camera system and four force plate integrated) at minimum 5 years post-surgery. We evaluated parameters including knee varus moment and knee varus force, and find out the difference between two groups. Results. The mean follow up duration of both groups was 8.1 years (mechanical method) and 8.0 years (kinematic method). Clinical outcome between two groups showed no significant difference in ROM, HSS, WOMAC, KSS pain score at last follow up. Varus and valgus laxity assessments showed no significant inter-group difference. We could not find any significant difference in mechanical alignment of the lower limb and perioperative complicatoin. In gait analysis, no significant spatiotemporal, kinematic or kinetic parameter differences including knee varus moment (mechanical=0.33, kinematic=0.16 P0.5) and knee varus force (mechanical=0.34, kinematic=0.37 P0.5) were observed between mechanical and kinematic groups. Conclusions. The results of this study show that mechanical and kinematic alignment method provide comparable clinical and radiological outcomes after robotic total knee arthroplasty in average 8 years follow-up. And no functional differences were found between two knee alignment methods during walking

Robotic-assisted technology in total knee arthroplasty (TKA) aims to increase implantation accuracy, with real-time data being used to estimate intraoperative component alignment. Postoperatively, Perth computed tomography (CT) protocol is a valid measurement technique in determining both femoral and tibial component alignments. The aim of this study was to evaluate the accuracy of intraoperative component alignment by robotic-assisted TKA through CT validation. A total of 33 patients underwent TKA using the MAKO robotic-assisted TKA system. Intraoperative measurements of both femoral and tibial component placements, as well as limb alignment as determined by the MAKO software were recorded. Independent postoperative Perth CT protocol was obtained (n.29) and compared with intraoperative values. Mean absolute difference between intraoperative and postoperative measurements for the femoral component were 1.17 degrees (1.10) in the coronal plane, 1.79 degrees (1.12) in the sagittal plane, and 1.90 degrees (1.88) in the transverse plane. Mean absolute difference between intraoperative and postoperative measurements for the tibial component were 1.03 degrees (0.76) in the coronal plane and 1.78 degrees (1.20) in the sagittal plane. Mean absolute difference of limb alignment was 1.29 degrees (1.25), with 93.10% of measurements within 3 degrees of postoperative CT measurements. Overall, intraoperatively measured component alignment as estimated by the MAKO robotic-assisted TKA system is comparable to CT-based measurements.

Purpose

To characterize the knee kinematic profiles of total knee arthroplasty patient knees intraoperatively, before implant insertion, using principal component analysis.

Introduction. Limb-length discrepancy (LLD) is a common postoperative complication after total hip arthroplasty (THA). This study focuses on the correlation between patients’ perception of LLD after THA and the anatomical and functional leg length, pelvic and knee alignments and foot height. Previous publications have explored this topic in patients without significant spinal pathology or previous spine or lower extremity surgery. The objective of this work is to verify if the results are the same in case of stiff or fused spine. Methods. 170 patients with stiff spine (less than 10° L1-S1 lordosis variation between standing and sitting) were evaluated minimum 1 year after unilateral primary THA implantation using EOS® images in standing position (46/170 had previous lumbar fusion). We excluded cases with previous lower limbs surgery or frontal and sagittal spinal imbalance. 3D measures were performed to evaluate femoral and tibial length, femoral offset, pelvic obliquity, hip-knee-ankle angle (HKA), knee flexion/hyperextension angle, tibial and femoral rotation. Axial pelvic rotation was measured as the angle between the line through the centers of the hips and the EOS x-ray beam source. The distance between middle of the tibial plafond and the ground was used to investigate the height of the foot. For data with normal distribution, paired Student's t-test and independent sample t-test were used for analysis. Univariate logistic regression was used to determine the correlation between the perception of limb length discrepancy and different variables. Multiple logistic regression was used to investigate the correlation between the patient perception of LLD and variables found significant in the univariate analysis. Significance level was set at 0.05. Results. Anatomical femoral length correlated with patients’ perception of LLD but other variables were significant (the height of the foot, sagittal and frontal knee alignment, pelvic obliquity and pelvic rotation more than 10°). Interestingly some factors induced an unexpected perception of LLD despite a non-significant femoral length discrepancy less than 1cm (pelvic rotation and obliquity, height of the foot). Conclusions. LLD is a multifactorial problem. This study showed that the anatomical femoral length as the factor that can be modified with THA technique or choice of prosthesis is not the only important factor. A comprehensive clinical and radiological evaluation is necessary preoperatively to investigate spinal stiffness, pelvic obliquity and rotation, sagittal and coronal knee alignment and foot deformity in these patients. Our study has limitations as we do not have preoperative EOS measurements for all patients. We cannot assess changes in leg length as a result of THA. We also did not investigate the degree of any foot deformities as flat foot deformity may potentially affect the patients perception of the leg length. Instead, we measured the distance between the medial malleolus and ground that can reflect the foot arch height. More cases must be included to evaluate the potential influence of pelvis anatomy and functional orientation (pelvic incidence, sacral slope and pelvic tilt) but this study points out that spinal stiffness significantly decreases the LLD tolerance previously reported in patients without degenerative stiffness or fusion

Purpose. Unicompartmental knee replacement (UKR) is an established, bone preserving surgical treatment option for medial compartment osteoarthritis (OA). Early revision rates appear consistently higher than those of total knee replacement (TKR) in many case series and consistently in national registry data. Failure with progression of OA in the lateral compartment has been attributed, in part, to surgical technical errors. In this study we used navigation assisted surgery to investigate the effects of improper sizing of the mobile bearing and malrotation of the tibial component on alignment and lateral compartment loading. Method. A total of eight fresh frozen cadaveric lower limbs were used in the study. After thawing overnight, a Brainlab navigation system with an Oxford (Biomet, Inc) medial UKR module was used to capture the native knee anatomy and alignment using a digitizing probe. Following registration, the case was performed with navigation verified neutral cuts and an ideal insert size was selected to serve as a baseline. The bearing thickness was subsequently increased by 2 mm increments to simulate progressive medial joint overstuffing. Excessive tibial internal rotation of 12 was also simulated at each of the intervals. Knee alignment in varus or valgus was recorded in real time for each surgical scenario with the knee in full extension and at 20 of flexion. Lateral compartment peak pressure was measured using a Tekscan pressure map. Results. Incremental overstuffing of the medial compartment with inserts of increasing thickness resulted in a progressive shift to more valgus knee alignment. Internally rotated sagittal cuts at 12 resulted in a further valgus shift for a given insert size. The valgus shift was detectable at full extension however it was more pronounced at 20 of flexion. Conclusion. The intentional technical errors of overstuffing and malrotation in UKR produced coronal valgus knee alignment and a greater load shift to the lateral compartment. These errors can be construed to contribute to the higher early failure rates associated with UKR when compared to TKR. Special care should be taken to ensure a neutral sagittal tibia cut and appropriate bearing selection. The Intra operative verification of knee alignment should be conducted at 20 of flexion where such errors will be easier for the surgeon to detect and rectify

Knee alignment is a fundamental measurement in the assessment, monitoring and surgical management of patients with osteoarthritis [OA]. In spite of extensive research into the consequences of malalignment, our understanding of static tibiofemoral alignment remains poor with discrepancies in the reported weight-bearing characteristics of the knee joint and there is a lack of data regarding the potential variation between supine and standing (functional) conditions. In total knee arthroplasty [TKA] the lower limb alignment is usually measured in a supine condition and decisions on prosthesis placement made on this. An improved understanding of the relationship between supine and weight-bearing conditions may lead to a reassessment of current surgical goals. The purpose of this study was to explore the relationship between supine and standing lower limb alignment in asymptomatic, osteoarthritic and prosthetic knees. Our hypothesis was that the change in alignment of these three groups would be different. A non-invasive infrared position capture system (accuracy ±1° in both coronal and sagittal plane) was used to assess the knee alignment for 30 asymptomatic controls and 31 patients with OA, both before and after TKA. Coronal and sagittal mechanical femorotibial (MFT) angles in extension (negative values indicating varus in the coronal plane and hyperextension in the sagittal plane) were measured with each subject supine and in bi-pedal stance. For the supine test, the lower limb was supported at the heel and the subject told to relax. For the standing position subjects were asked to assume their normal stance. The change in alignment between these two conditions was analysed using a paired t-test for both coronal and sagittal planes. To quantify the change in 3D, vector plots of ankle centre displacement relative to the knee centre from the supine to standing condition were produced. Alignment in both planes changed significantly from supine to standing for all three groups. For the coronal plane the supine and standing measurements (in degrees, mean(SD)) were 0.1(2.5) and −1.1(3.7) in the asymptomatic group, −2.5(5.7) and −3.6(6) in the OA group and −0.7(1.4) and −2.5(2) in the TKA group. For the sagittal plane the numbers were −1.7(3.3) and −5.5(4.9); 7.7(7.1) and 1.8(7.7); 6.8(5.1) and 1.4((7.6) respectively. This change was most frequently towards relative varus and extension. Vector plots showed that the trend of relative varus and extension in stance was similar in overall magnitude and direction between the three groups. Knee alignment can change from supine to standing for asymptomatic and osteoarthritic knees, most frequently towards relative varus and hyperextension. The similarities between each group did not support our hypothesis. The consistent kinematic pattern for different knee types suggests that soft tissue restraints rather than underlying joint deformity may be more influential in dynamic control of alignment from lying to standing. In spite of some evidence suggesting a difference between supine and standing knee alignment a mechanical femorotibial (MFT) angle of 0° is a common intra-operative target as well as the desired post-operative weight-bearing alignment. These results indicated that arthroplasties positioned in varus intra-operatively could potentially become ‘outliers’ (>3° varus) when measured weight-bearing. Mild flexion contractures may correct when standing, reducing the need for intra-operative posterior release. These potential changes should be considered when positioning TKA components on supine limbs as post-operative functional alignment may be different

Introduction. The influences of posterior tibial slope on the knee kinematics have been reported in both TKA and UKA. We hypothesized the posterior tibial slope (PTS) would affect the sagittal knee alignment after UKA. The influences of PTS on postoperative knee extension angle were investigated with routine lateral radiographies of the knee after UKA. Materials & Methods. Twenty-four patients (26 knees; 19 females, 7 males) underwent medial UKA were involved in this study. Average age was 74.8 ± 7.2 years. The mean preoperative active range of motion were − 4.1° ± 6.3°in extension and 123.2° ± 15.5° in flexion. All UKAs were performed using fixed bearing type UKA (Zimmer Biomet, ZUK), with adjusting the posterior slope of the proximal tibial bone cut according to the original geometry of the tibia. Routine lateral radiographies of the knee were examined preoperatively, 6 months after the surgery. PTS and knee extension angles with maximal active knee extension (mEXT) and one-leg standing (sEXT) were radiographically measured. We used the fibular shaft axis (FSA) for the sagittal mechanical axis of the tibia. PTS was defined as the angle between the medial tibial plateau and the perpendicular axis of FSA. Extension angles (mEXT and sEXT) were defined as the angles between FSA and distal femoral shaft axis (positive value for hyperextension). The changes of PTS and the influences of PTS on sEXT at each time period were analyzed using simple linear regression analysis (p<0.05). Results. The mean PTSs were 10.0° ± 3.0° and 9.9° ± 2.7° preoperatively, 6m after surgery respectively. The mean mEXTs were −4.1° ± 6.3° and −2.0° ± 5.4°, and sEXTs were −9.4° ± 7.6° and −7.3° ± 6.7° at each time period. Preoperative and postoperative PTS had positive correlation (r = −0.65). PTS significantly negatively correlated to sEXT at 6 months after the surgery (r = −0.63). Discussions. We found patient tended to stand with slight knee flexion (sEXT) which was smaller than the flexion contracture measured by mEXT. Interestingly, postoperative PTS significantly correlated to the knee flexion angle during one-leg standing. Patients with the higher PTS after UKA were more likely to stand with the higher knee flexion. The higher PTS had been reported to increase tibial anterior translation and strain or tear of the anterior cruciate ligament with load bearing in the normal knee. Slight knee flexion during one-leg standing would be beneficial to keep the joint surface parallel to the ground depending on PTS and reduce the anterior shearing force on the tibia after UKA. Conclusion. Postoperative posterior tibial slope reduced knee extension angle during one-leg standing after UKA. For any figures or tables, please contact authors directly

INTRODUCTION. In patients presenting with significant ligamentous instability/insufficiency and/or significant varus/valgus deformity of the knee, reproduction of knee alignment and soft tissue stability continues to be a difficult task to achieve. These complex primary total knee arthroplasty (TKA) candidates generally require TKA systems incorporating increasing levels of constraint due to the soft-tissue and/or bone deficiencies. In addition, achievement of “normal” gap symmetry through physiologic kinematics is challenging due to the complexity of the overall correction. Advancements in TKA design have not fully addressed the negative consequences of the increased forces between the degree of component constraint, the femoral box, and the tibial post. The purpose of this early feasibility study was to introduce the design characteristics of a primary TKA system that incorporates progressive constraint kinematics using a low profile trapezoidal femoral box, and to assess the short-term clinical and radiographic results of this patient cohort. METHODS. We retrospectively evaluated 22 consecutive, non-selected, complex primary TKA patients with a minimum of 3-years follow-up and varus deformity of > 20 degrees or valgus deformity of >15 degrees. The Progressive Constraint Kinematics® Knee System (PCK, MAXX Orthopedics, Norristown, PA) was used and provides a variable constraint profile, from high constraint in extension to less constraint in flexion through a novel trapezoidal femoral box. We evaluated patient demographics, pre- and post-operative serial radiography, range of motion (ROM), and total Knee Society Score (KSS – total score). General descriptive statistics and paired t-Test to assess the difference between means at p <0.05 level of significance. RESULTS. The average time to most recent follow-up was 40.5 ±3.5 months (range: 36.0 to 44.0 months). The PCK knee system had 100% survival rate at the most recent follow-up, with no reports of adverse events, subsequent corrective surgery, or revision. The average total KSS improved from 72.7 ±3.2 (range: 68 to 81) pre-operatively to 92.3 ±2.1 (range: 88 to 96) post-operatively (p < 0.001). Full post-operative arc of motion was 0 – 130° and there was no radiographic evidence of composite degradation, aseptic loosening or component malalignment. DISCUSSION/CONCLUSION. The PCK Knee System utilizes a trapezoidal shaped femoral box, where the narrower end is located anteriorly, allowing a valgus/varus tilt of 1–4 degrees and internal/external rotation of 2–7 degrees during flexion, while maintaining necessary soft-tissue constraint during extension. This variable constraint profile allows for fully tensed collaterals in extension, with a slight reduction in collateral tension through flexion. Furthermore, the combination of the condylar anatomy, trapezoidal femoral box and tibial post allows for adequate clearance through full flexion, while facilitating slightly progressive increases in tilt and rotation, thereby maintaining knee kinematics while dampening forces transmitted through the prosthetic composite. From this feasibility study we report promising short-term clinical and radiographic results in the absence of biomechanical failure in complex primary TKA cases. We recommend continuation of the use and further research of the PCK Knee System for complex primary TKA with the ultimate goal of further determining cost effectiveness and intermediate to long-term clinical relevance

Introduction. Coronal misalignment of the lower limbs is closely related to the onset and progression of osteoarthritis. In cases of severe genu varus or valgus, evaluating this alignment can assist in choosing specific surgical strategies. Furthermore, restoring satisfactory alignment after total knee replacement promotes longevity of the implant and better functional results. Knee coronal alignment is typically evaluated with the Hip-Knee-Ankle (HKA) angle. It is generally measured on standing AP long-leg radiographs (LLR). However, patient positioning influences the accuracy of this 2D measurement. A new 3D method to measure coronal lower limb alignment using low-dose EOS images has recently been developed and validated. The goal of this study was to evaluate the relevance of this technique when determining knee coronal alignment in a referral population, and more specifically to evaluate how the HKA angle measured with this 3D method differs from conventional 2D methods. Materials and methods. 70 patients (140 lower extremities) were studied for 2D and 3D lower limb alignment measurements. Each patient received AP monoplane and biplane acquisition of their entire lower extremities on the EOS system according the classical protocols for LLR. For each patient, the HKA angle was measured on this AP X-ray with a 2D viewer. The biplane acquisition was used to perform stereoradiographic 3D modeling. Valgus angulation was considered positive, varus angulation negative. Student's T-test was used to determine if there was a bias in the HKA angle measurement between these two methods and to assess the effect of flexion/hyperextension, femoral rotation and tibial rotation on the 2D measurements. One operator did measurements 2 times. Results. The average total dose for both acquisitions was 0.75mGy (± 0.11mGy). The 2D and 3D measurements are reported in table 1. Intraoperator reliability was >0,99 for all measurements. In the whole series, 2D–3D HKA differences were >2° in 34% of cases, >3° in 22% of cases, >5° in 9% of cases and >10° in 3% of cases >10°. We compared 2D and 3D measurements according to the degree of flessum/recurvatum (> or <5° and > or <10°). The results are reported in table 2. The statistical analysis of parameters influencing 2D/3D measurements is reported in table 3. Discussion and conclusion. The HKA angle is typically assessed from 2D long-leg radiographs. However, several studies highlighted that 2D assessment of this angle may be affected by patient's positioning. Radtke showed that lower limb rotation during imaging significantly affected measurements of coronal plane knee alignment. Brouwer showed that axial rotation had an even greater effect on the apparent limb alignment on AP radiographs when the knee was flexed. This last finding is particularly relevant as many lower extremities present some amount of flexion or hyperextension, especially in aging subjects. This low dose biplanar EOS acquisitions provide a more accurate evaluation of coronal alignment compared to 2D, eliminating bias due to wrong knee positioning. This study points out the interest of EOS in outliers patients and opens new perspectives for preoperative planning and postoperative control of deformity correction or knee joint replacement

Background. Coronal malalignment has been proposed as a risk factor for mechanical failure after total knee arthroplasty (TKA). In response to these concerns, technologies that provide intraoperative feedback to the surgeon about component positioning have been developed with the goal of reducing rates of coronal plane malalignment and improving TKA longevity. Imageless hand-held portable accelerometer technology has been developed to address some the limitations associated with other computer assisted navigation devices including line-of-sight problems, preoperative imaging requirements, extra pin sites, up-font capital expenditures, and learning curve. The purpose of this study was to compare the accuracy and precision of a hand-held portable navigation system versus conventional instrumentation for tibial and femoral resections in TKA. Methods. This study was a single-surgeon, retrospective cohort study. Consecutive patients undergoing TKA were divided into three groups: 1) tibial and femoral resections performed with conventional intra- and extramedullary resection guides (CON group; N=84), 2) a hand-held portable navigation system (KneeAlign, OrthoAlign Inc, Aliso Viejo, CA) for tibial resection only (TIBIA group; N=78), and 3) navigation for both tibial and distal femoral resections (BOTH group; N=80). Postoperative coronal alignment of the distal femoral and proximal tibial resection were measured based on the anatomic axis from standing AP radiographs and compared between the three groups for both precision and accuracy. Malalignment was considered to be greater than 3° varus/valgus from expected resection angle. Results. Preoperative age, sex, and knee axis alignment were similar between the three groups. Mean postoperative alignment of the distal femoral resection, proximal tibial resection, and knee axis did not differ between groups (Figure 1). Increased frequencies of malalignment (±3° varus/valgus) of the femoral resection (24% CON versus 5% TIBIA and 8% BOTH; p<0.001) and knee axis (31% CON versus 8% TIBIA and 6% BOTH; p<0.001) were observed with conventional resection guides compared to both navigation groups. Conclusion. Use of a hand-held portable navigation system improved precision of the distal femoral resection and overall anatomical knee alignment after TKA

In general, “alignment” refers to the position of all components in three dimensions. This discussion is limited to “varus-valgus” (v-v) alignment, or angulation in the frontal plane. This is largely determined by rotational position of the tibial and femoral components about the “z” (antero-posterior) axis. The earliest paper to note the importance of alignment, described only “valgus” on short x-rays. It is difficult to argue that knee alignment is irrelevant, as angulation increases, so does the lever arm at the knee. (Biomechanics) Alignment is relevant to the development of osteoarthritis, most likely as the result of load on the medial compartment with varus alignment. (Natural History of OA) The first knee arthroplasties were an attempt to resurface worn cartilage with biological tissue and then non-biological material. Alignment and biomechanics were not considered. (History). Frontal plane alignment can be depicted as “anatomic” (the angle between the femoral and tibial canals) on short radiographs or “mechanical” on full-length radiographs. Mechanical alignment may be reported in degrees or distance. Degrees describes the angle between a line from center of femoral head to center of knee (MA of the femur) with the line from center of knee to center of ankle (MA of tibia.) Alternately if a line is drawn form the center of the femoral head to the center of the ankle, MA may be described as the distance from the center of the knee to this axis along the joint line. Sometimes this is depicted by sectors in the knee. “Mechanical alignment” is a method of describing the angulation of the knee, not strictly a surgical technique. Long radiographs: Short radiographs, though perhaps cost effective in most clinical settings, are unreliable images for studies of alignment. Physiologists and astute surgeons have always considered the entire limb. When clinicians applied full-length radiographs to clinical practice, along with navigation technology, assumptions evolved about the most desirable alignment of an arthroplasty. Arbitrarily, a neutral mechanical axis, or a straight line from the centers of the hip, knee and ankle was promoted. This also means that a line from hip to ankle would pass through the center of the knee. Many surgeons have entertained the erroneous concept that a “neutral mechanical axis” represents “normal human alignment: it does not. Others contend that a neutral mechanical axis necessarily means that there will be equal load on medial and lateral compartments: it will not. Received wisdom about the necessity of a neutral mechanical axis has been questioned and yet malalignment and pre-operative deformity both appear to contribute to failure. Stability is clearly important, because it limits deviations in alignment, and a range of alignments are probably highly functional, just as the knee may be loaded in a variety of directions. Dynamic features of patient activity are undoubtedly important, as is pre-operative deformity

Introduction. Although Total Knee Arthroplasty (TKA) has been shown to correct abnormal frontal plane knee biomechanics, little is known about this effect beyond 6 months. The purpose of this study was to compare sequentially the knee adduction moment during level-walking before and after TKA in varus knees. We hypothesized that adduction moment would diminish after TKA proportionate to the tibio-femoral realignment in degrees. Methods. Fifteen patients (17 TKA's) with varus knees were prospectively enrolled and gait analysis performed prior to, 6 months and 1 year following TKA. Reflective markers were placed on the lower extremity and motion data collected using six infrared cameras (Qtrac, Qualysis). Ground reaction forces were recorded with a multicomponent force plate (Kistler). A repeated-measures ANOVA was used to compare changes in the peak adduction moment and peak dynamic varus angle over time. Results. TKA corrected static knee alignment from 2.2 (2.5) degrees varus to 3.5 (2.7) degrees valgus (P < 0.001). Peak dynamic varus angle during gait was reduced from 9.7 (6.5) degrees to 3.6 (5.8) degrees at 6 months and 5.2 (7.6) degrees at 1 year (Main Effect of Time; P=0.005). Peak adduction moment was significantly reduced to 85% of pre-op level at 6 months (P=0.037) but subsequently increased to 94% of pre-op level at 1 year (P = 0.539). Post-op improvement in static alignment did not correlate with the change in adduction moment at any follow-up period (P = 0.671). A significant correlation was found between the increase in dynamic varus angle and the subsequent increase in adduction moment from the six-month to the one-year follow-up (P = 0.008). Conclusion. TKA improves knee adduction moment at 6 months but this effect is lost with time (1 year). Despite restoration of static knee alignment and soft tissue balance, loading conditions at medial compartment remain high, predisposing to medial polyethylene wear, a finding reported by retrieval studies

Postoperative radiological assessment is used to evaluate the success of knee replacement procedures. Load-bearing long-standing anterior-posterior (AP) x-rays are typically used for this assessment. For knee replacement procedures the five landmarks that are identified are: 1) hip centre; 2) femoral knee centre; 3) tibial knee centre; 4) medial malleolus; and 5) lateral malleolus. These landmarks are used to identify the femoral and tibial reference mechanical axes. However, variations in the x-ray acquisition process and foot rotation can lead to errors in this assessment. In the past, researchers have studied the effect of foot rotation and flexion on estimation of knee alignment. In our study, the use of digitally reconstructed radiographs (DRRs) allows us to vary the x-ray acquisition parameters and observe the effect of these changes to estimations of the mechanical axes. We also measured the inter-user variability in these measurements. Our results show that AP x-rays can be used to accurately estimate the femoral and tibial mechanical axes

Background. Both minimally invasive surgery(MIS) and computer-assisted surgery(CAS) in total knee arthroplasty have been scientifically linked with surgical benefits. However, the long-term results of these techniques are still controversial. Most surgeons assessed the surgical outcomes with regard to knee alignment and range of motion, but these factors may not reflect subjective variables, namely patient satisfaction. Purpose. To compare satisfaction and functional outcomes between two technical procedures in MIS total knee arthroplasty, namely computer-assisted MIS and conventional MIS procedure, operated on a sample group of patients after 10 years. Methods. Seventy cases of posterior-stabilized total knee prostheses were implanted using a computer-assisted system and were compared to seventy-four cases of matched total knee prostheses of the same implant using conventional technique. Both groups underwent arthrotomy by 2 centimeter limited quadriceps exposure minimally invasive surgery (2 cm Quad MIS). At an average of ten years after surgery, self-administered patient satisfaction and WOMAC scales were administered and analyzed. Results. Demographic data of both groups including sex, age, preoperative WOMAC and post-operative duration were not statistically different. Post-operative WOMAC for the computer-assisted group was 38.94±5.68, while the conventional one stood at 37.89±6.22. The median of self-administered patient satisfaction scales of the computer-assisted group was 100 (min37.5-max100), while the conventional one was 100 (min25-max100). P-value was 0.889. There was 1 re-operative case in the conventional MIS group due to peri-prosthetic infection which was treated with debridement, polyethylene exchanged and intravenous antibiotics. Conclusion. The long-term outcomes of computer-assisted MIS total knee arthroplasty are not superior to that of the conventional MIS technique. Computer assisted MIS total knee arthroplasty is one of the treatment options for osteoarthritis of the knee that has comparable levels of satisfaction to the conventional MIS technique

The true results of revision total knee arthroplasty (TKA) are not fully understood, for a variety of understandable reasons. But it is has been clear for decades that revision without a diagnosis is likely to fail. The evaluation of the problem TKA should be systematic (follow the same scheme every time) and comprehensive (all possibilities should be considered even if one diagnosis seems obvious). Evaluation begins, as with all of medicine with a list of possible causes: the mechanisms of failure. John Moreland was the first to describe a coherent system which needed only one simple addition to be complete: 1.) Prosthetic joint infection; 2.) Extensor disruption; 3.) Patella and malrotation; 4.) Loose; 5.) Component breakage; 6.) PP fracture; 7.) Poor motion; and 8.) Tibial femoral instability. Evaluation begins with the history, where 10 questions in particular are useful: 1.) What seems to be the problem? 2.) Was the “knee” ever successful after surgery? If there was never pain relief, is the current pain, the same or different? 3.) Standard pain quality questions - Location, duration, frequency, quality, exacerbating, ameliorating. 4.) Swelling? 5.) Stiffness? 6.) Giving way? 7.) Weakness? 8.) Things “just don't feel right”? 9.) Possible sepsis questions - Fever, chills, sources, primary TKA healing. 10.) Mood, social situation?. The physical exam should cover these ten points: 1.) Active extension; 2.) Rising from chair; 3.) Gait: hip, knee alignment, knee instability; 4.) Hip (internal rotation); 5.) Inspection; 6.) Tenderness; 7.) ROM; 8.) Stability (extension and 30–45 degrees flexion; 9.) Sitting on edge of exam table (knee at 90 degrees); and 10.) Step up on low stool (stair). Investigations include: 1.) ESR + CRP; 2.) CBC; 3.) HGB- anemia; 4.) Lymphocytes- nutrition; 5.) GGT- alcohol abuse; 6.) Albumen- nutrition; 7.) HbA1c- diabetic control. Imaging includes: 1.) Single leg weightbearing AP; 2.) Lateral; 3.) Merchant; 4.) Full length (hip-knee-ankle); 5.) AP pelvis; 6.) CT scan; and 7.) (Technitium bone scan)

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