Aims. Accurate identification of the ankle joint centre is critical for estimating tibial coronal alignment in total knee arthroplasty (TKA). The purpose of the current study was to leverage artificial intelligence (AI) to determine the accuracy and effect of using different radiological anatomical landmarks to quantify mechanical alignment in relation to a traditionally defined radiological ankle centre. Methods. Patients with full-limb radiographs from the Osteoarthritis Initiative were included. A sub-cohort of 250 radiographs were annotated for landmarks relevant to knee alignment and used to train a deep learning (U-Net) workflow for angle calculation on the entire database. The radiological ankle centre was defined as the midpoint of the superior talus edge/tibial plafond. Knee alignment (hip-knee-ankle angle) was compared against 1) midpoint of the most prominent malleoli points, 2) midpoint of the soft-tissue overlying malleoli, and 3) midpoint of the soft-tissue sulcus above the malleoli. Results. A total of 932 bilateral full-limb radiographs (1,864 knees) were measured at a rate of 20.63 seconds/image. The knee alignment using the radiological ankle centre was accurate against ground truth radiologist measurements (inter-class correlation coefficient (ICC) = 0.99 (0.98 to 0.99)). Compared to the radiological ankle centre, the mean midpoint of the malleoli was 2.3 mm (SD 1.3) lateral and 5.2 mm (SD 2.4) distal, shifting alignment by 0.34. o. (SD 2.4. o. ) valgus, whereas the midpoint of the soft-tissue sulcus was 4.69 mm (SD 3.55) lateral and 32.4 mm (SD 12.4) proximal, shifting alignment by 0.65. o. (SD 0.55. o. ) valgus. On the intermalleolar line, measuring a point at 46% (SD 2%) of the intermalleolar width from the medial malleoli (2.38 mm medial adjustment from midpoint) resulted in knee alignment identical to using the radiological ankle centre. Conclusion. The current study leveraged AI to create a consistent and objective model that can estimate patient-specific adjustments necessary for optimal landmark usage in extramedullary and computer-guided navigation for tibial coronal alignment to match radiological planning. Cite this article: Bone Jt Open 2022;3(10):767–776

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

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

Background:. Conventional, extramedullary (EM) tibial alignment guides are only 65%–88% accurate in creating a tibial resection within 2° of perpendicular to the tibial mechanical axis in total knee arthroplasty (TKA). The purpose of this study was to compare the overall, tibial component alignment, and the surgeon's ability to achieve a specific, intraoperative goal for alignment between a portable, navigation system (KneeAlign™) and conventional, EM alignment guides. Methods:. One hundred patients were enrolled in a prospective, randomized controlled study. Fifty patients received a TKA using the KneeAlign™ to perform the tibial resection, and 50 patients an EM alignment guide. Standing AP hip-to-ankle radiographs and lateral knee-to-ankle radiographs were obtained at the first, postoperative visit. Results:. 95.7% of tibial components in the KneeAlign™ cohort were within 2° of perpendicular to the tibial mechanical axis, versus 68.1% in the conventional cohort (p < 0.001). 95.0% of the tibial components in the KneeAlign™ cohort were within 2° of a 3° posterior slope, versus 72.1% in the conventional cohort (p = 0.007). The absolute difference between the intraoperative goal (as recorded by the surgeon) and postoperative alignment for tibial component varus/valgus was 0.9° + 0.7° in the KneeAlign™cohort, versus 1.5° + 1.1° in the conventional cohort (p < 0.001). For posterior slope, the absolute difference was 0.9° + 1.2° in the KneeAlign™ cohort, versus 1.8° + 1.7° in the conventional cohort (p = 0.01). Conclusions:. A portable, navigation system improves tibial component alignment, and the surgeon's ability to achieve a specific, intraoperative goal, when compared to conventional, EM alignment guides in TKA. Level of Evidence: Level I, Prospective, randomized controlled study

We undertook a prospective, randomised study of 135 total knee arthroplasties to determine the most accurate and reliable technique for alignment of the tibial prosthesis. Tibial resection was guided by either intramedullary or extramedullary alignment jigs. Of the 135 knees, standardised postoperative radiographs suitable for assessment were available in 100. Correct tibial alignment was found in 85% of the intramedullary group compared with 65% of the extramedullary group (p = 0.019). We conclude that intramedullary guides are superior to extramedullary instruments for alignment of the tibial prosthesis

Abstract. Introduction. Controversy exists regarding the optimal tibial coronal alignment in total knee arthroplasty. Many believe navigation or robotics are required to set kinematic alignments or to ensure they remain within ‘safe’ limits e.g. maximum 5° varus on the tibia. Given most navigation or robotic systems require the surgeon to identify the ankle malleoli, this study aimed to radiographically analyse standardly used intra-operative landmarks around the ankle, assessing their value in achieving kinematic alignment / setting safety boundaries. Materials and Methods. Long leg alignment radiographs were analysed independently by two orthopaedic surgeons at two time points, eight weeks apart. Angles were measured between the long axis of the tibia (TB) and: 1. lateral malleolus (TB-LM), 2. lateral border of the talus (TB-LT) and 3. medial aspect of the medial malleolus (TB-MM). Intra- and inter-rater reliabilities were assessed. Results. One hundred and sixty-seven radiographs in 119 patients were analysed; mean age 71.6 years. Mean angles (95% CI) were: TB-LM 4.8° (4.7°- 4.8°), TB-LT 2.6° (2.5° - 2.6°) and TB-MM 4.2° (4.1° - 4.2°). Interrater reliability was good for TB-LM (ICC = 0.72) and TB-MM (ICC=0.67), and fair for TB-LT (ICC= 0.50). Intra-rater reliability was excellent for all measures (ICC >0.85). Conclusion. There are consistent angles between tibial alignment and ankle landmarks. Using these landmarks, with standard instrumentation and alignment checks, allows surgeons to define safe limits, e.g. maximum 4.8° tibial varus if aligned to the tip of the lateral malleolus or set a 2.5° varus cut, without the need for added technology

Background:

The axis of the fibula in the sagittal plane are known as a landmark for the extramedullary guide in order to minimize posterior tibial slope measurement error in the conventional total knee arthroplasty (TKA). However, there are few anatomic studies about them. We also wondered if the fibula in the coronal plane could be reliable landmark for the alignment of the tibia. This study was conducted to confirm whether the fibula is reliable landmark in coronal and sagittal plane.

INTRODUCTION

The alignment of components in total knee arthroplasty (TKA) is perceived to be one of the most influential factors in determining the long-term outcomes. A contemporary debate exists regarding the choice of the alignment method. As a vast majority of the surgeons support the basis of the mechanical alignment philosophy (MA), others believe in the concept of anatomical alignment theory (AA) to closely match the anatomy of the femur and the tibia of the native knee [1]. This study was intended to evaluate the accuracy of achieving a planned tibial resection target using either the MA or AA methods.

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

Objectives. Unicompartmental knee arthroplasty (UKA) is one surgical option for treating symptomatic medial osteoarthritis. Clinical studies have shown the functional benefits of UKA; however, the optimal alignment of the tibial component is still debated. The purpose of this study was to evaluate the effects of tibial coronal and sagittal plane alignment in UKA on knee kinematics and cruciate ligament tension, using a musculoskeletal computer simulation. Methods. The tibial component was first aligned perpendicular to the mechanical axis of the tibia, with a 7° posterior slope (basic model). Subsequently, coronal and sagittal plane alignments were changed in a simulation programme. Kinematics and cruciate ligament tensions were simulated during weight-bearing deep knee bend and gait motions. Translation was defined as the distance between the most medial and the most lateral femoral positions throughout the cycle. Results. The femur was positioned more medially relative to the tibia, with increasing varus alignment of the tibial component. Medial/lateral (ML) translation was smallest in the 2° varus model. A greater posterior slope posteriorized the medial condyle and increased anterior cruciate ligament (ACL) tension. ML translation was increased in the > 7° posterior slope model and the 0° model. Conclusion. The current study suggests that the preferred tibial component alignment is between neutral and 2° varus in the coronal plane, and between 3° and 7° posterior slope in the sagittal plane. Varus > 4° or valgus alignment and excessive posterior slope caused excessive ML translation, which could be related to feelings of instability and could potentially have negative effects on clinical outcomes and implant durability. Cite this article: K. Sekiguchi, S. Nakamura, S. Kuriyama, K. Nishitani, H. Ito, Y. Tanaka, M. Watanabe, S. Matsuda. Bone Joint Res 2019;8:126–135. DOI: 10.1302/2046-3758.83.BJR-2018-0208.R2

We wished to determine the most accurate and reliable technique for insertion of tibial prostheses, with tibial resection guided by either intramedullary (IM) or extramedullary (EM) alignment jigs. 135 consecutive AGC cemented total knee replacements in 126 patients in a single unit were performed by, or directly supervised by, four consultant surgeons. Ethical approval and patient consent was obtained. Intramedullary alignment was used for the femoral cuts and patients were randomised at the time of operation to have either IM or EM guides for resection of the proximal tibia, cut with a zero degree posterior slope in both. The protocol only entered patients into the trial if their knees were suitable for use with both IM and EM tibial alignment although, in the event, no patients were excluded. Long leg radiographs (standing hip to ankle) were taken by a standardised method three months after the surgery. A blinded assessor, unaware of the alignment method used, evaluated acceptable films and measured tibial component alignment. The proportion of tibial prostheses aligned within two degrees of 90 was the endpoint of the study. Of the 135 knees 100 suitable x-rays were assessed. Correct tibial alignment was more likely in the IM group (85%) than the EM group (65%), p=0. 019. Though mean alignment was similar, variation (standard deviation) was less in the IM group (2. 0 vv 2. 2). In the AGC knee, intramedullary alignment guides are superior to extramedullary guides for alignment of the tibial prosthesis. We recommend the routine use of intramedullary tibial alignment

INTRODUCTION. Cemented total knee arthroplasty (TKA) is a widely accepted treatment for end-stage knee osteoarthritis. During this procedure, the surgeon targets proper alignment of the leg and balanced flexion/extension gaps. However, the cement layer may impact the placement of the component, leading to changes in the mechanical alignment and gap size. The goal of the study was to assess the impact of cement layer on the tibial mechanical alignment and joint gap during cemented TKA. MATERIAL. Computer-assisted TKAs (ExactechGPS®, Blue-Ortho, Grenoble, FR) were performed by two fellowship trained orthorpaedic surgeons on five fresh-frozen non-arthritic pelvis-to-ankle cadaver legs. All the surgeries used a cemented cruciate retaining system (Optetrak Logic CR, Exactech, Gainesville, FL). After the bony resection, the proximal tibial resection plane was acquired by manually pressing an instrumented checker onto the resected tibial surface (resection plane). Once the prosthesis was implanted through standard cementing techniques, the top surface of the implanted tibial component was probed and recorded using an instrumented probe. A best fit plane was then calculated from the probed points and offset by the thickness of the prosthesis, representing the bottom plane of the component (component plane). The deviation of component alignment caused by the cement layer was calculated as the coronal and sagittal projection of the three-dimensional angle between the resection plane and the component plane. The deviation of the component height, reflecting a change in the joint gap, was assessed as the distance between the two planes calculated at the lowest points on the medial and lateral compartments of the proximal tibial surface. Statistical significance was defined as p≤0.05. RESULTS. The differences in alignment and component height between the tibial component placement and the ideal placement based on the bony resection are presented in Table 1. The magnitude of deviation in alignment was 1.2±0.9° for varus/valgus and 1.7±0.7° for posterior slope, with a tendency towards valgus (−0.2±1.6°) and reduced posterior slope (0.6±1.9°). The lateral compartment (2.4±0.9mm) had a generally higher increase in the height of the component compared to the medial compartment (1.0±0.9mm), the difference was close to being statistically significant (p=0.055). DISCUSSION. The finding of this study demonstrated that standard cement fixation during TKA may potentially influence the alignment and position of the tibial component. The formed cement layer generally results in elevated height, slightly more varus tibial alignment (overall limb valgus alignment) and less posterior slope in the implanted component. The results on the alignment are comparable to a previous study by Catani et al. [1]. More than 2°/2mm of deviation was found in the sagittal alignment (2 out of 5 knees), and medial (1 out of 5 knees) and lateral (3 out of 5 knees) component height, which may clinically impact the joint gap [2]. The varus/valgus alignment deviation found was clinically acceptable (≤3°). However when combined with other surgical variables, the accumulated impact on the alignment may warrant more investigation

Introduction. Using the tibial extramedullary guide needs meticulous attention to accurately align the tray in total knee arthroplasty (TKA). We previously reported the risk for varus tray alignment if the anteroposterior (AP) axis of the ankle was used for the rotational direction of the guide. The purpose of our study was to determine whether aligning the rotational direction of the guide to the AP axis of the proximal tibia reduced the incidence of varus tray alignment when compared to aligning the rotational direction of the guide to the AP axis of the ankle. Materials and Methods. Clinical Study. A total of 80 osteoarthritis (OA) knees after posterior stabilized TKA were recruited in this study. From 2002 to 2004, the rotational alignment of the guide was adjusted to the AP axis of the ankle (Method A: Figure 1, N = 40 knees). After 2005, the rotational alignment of the guide was adjusted to the AP axis of the proximal tibia (Method B: Figure 1, N = 40 knees). The AP axis of the proximal tibia was defined as the line connecting the middle of the attachment of the PCL and the medial third border of the attachment of the patellar tendon. The guide was set at a level of 10 mm distal to the lateral articular surface. Postoperative alignment was compared between the two groups using full-lengthanteroposterior radiograph. Computer simulation. Computer simulation was performed to determine the effect of ankle rotation on tibial tray alignment, using three-dimensional bone and skin model reconstructed from CT images of 75 OA knees (Figure 2). The position of the distal end of the guide in Method B was evaluated on the coronal plane perpendicular to the AP axis of the proximal tibia and of the ankle respectively. <Displacement> was the distance from the distal end of the guide to the midpoint-malleolar points (+: medial position). <Distance ratio> was the ratio of <Displacement> dividing by the entire width of the malleolar. Results. The results of the postoperative alignment for both methods from the clinical study are shown in Table 1. The number of the knees with more than 3 degrees of varus aligned tibial component significantly decreased with the Method B from the Method A. The computer simulation showed that the position of the guide varied great among individuals in the direction of the AP axis of the ankle joint. Discussion. When an extramedullary alignment guide is used in TKA, a rotational mismatch between the proximal part of the tibia and the ankle joint can induce a varus alignment of the tibial component. Computer simulation also supported our conclusion that the surgeon should not evaluate the distal end of the guide in the direction of the ankle joint to minimize the effects of anatomic variation for proper coronal alignment

Introduction

It has been reported that the tibial articular surface of coronal aligment is parallel to the floor in the whole-leg standing radiographs of the normal knee. The purposes of this study are to investigate the relationship between the tibial articular surface and the ground on the whole-leg standing radiographs after total knee arthroplasty(TKA).

Aim: The difficulty in accurately assessing coronal alignment of a total knee prosthesis (TKR) is widely accepted in the literature yet standard practice in the UK is to obtain AP and lateral knee views only; we compared standard AP knee films with long leg views of TKR in order to determine the most optimal way of assessment of the prosthetic knee alignment.

Methods: We included all patients who underwent TKR between January and September 2005 at Kings College Hospital under the care of one orthopaedic consultant. We excluded 11 patients with revision surgery, augmented prosthesis, high tibial osteotomies or severe tibiotalar joint arthritis.

We included 50 sets of radiographs from 48 patients (17 men and 31 women). The prostheses used were PFC (40) and Scorpio (10) and six of them were navigated and 44 were standard TKR.

We compared the difference between the angle of the tibial component with the mechanical axis of the tibia in the long leg image and the angle of the prosthesis with the midline of the visualised tibia in a standard antero-posterior knee view. Statistical analysis was carried out using the student t-test.

Results: The mean difference between the two views was 5.34o (range 1.9o – 12o) (p< 0.001). We did not find any difference between the Scorpio and PFC knees or between navigated and non navigated prostheses.

Conclusion:We concluded that the long leg views compared with the standard antero-posterior knee views provide more accurate information on the position and alignment of the tibial component of a TKR.

Although optimal alignment is essential for improved function and implant longevity after TKA, we have less bony landmarks of tibia relative to femur. Trans-malleolar axis (TMA) is a reference line of distal tibia in the axial plane, which externally rotated relative to a ML axis of proximal tibia. We originally defined another reference axis associated with the orientation of tibial plafond, and then measured tibial torsion in the 3D-coordinate system.

Three-dimensional CAD models of 20 tibiae were reconstructed based on pre-operative CT data from OA patients (16 females and 4 males, 73.8 ± 6.9 years old). TMA was a line connecting each apex of medial and lateral malleolus. The plafond axis (PLA) that we originally defined in this study was a line connecting each midpoint of medial and lateral margin of talocrural facet. In terms of interobserver correlation coefficiency and mean errors of the designated points to define those axes, TMA was found out to be 0.982, 3.14 ± 0.47 mm (medial), and 0.988, 4.88 ± 0.59 mm (lateral). Those of PLA were 0.997, 1.97 ± 0.53 mm (medial), and 0.995, 2.02 ± 0.44 mm (lateral). The tibial torsion was 16.3 ± 6.3°with reference to TMA, and 10.2 ± 8.4°to PLA.

Based on these results, as for the rotational reference axis in the axial plain of distal tibia, we consider the plafond axis to be another reliable and reproducible axis, which is expected to be applicable in preoperative planning in TKA to reduce outliers of coronal alignment.

Introduction. Varus alignment in total knee replacement (TKR) results in a larger portion of the joint load carried by the medial compartment. [1]. Increased burden on the medial compartment could negatively impact the implant fixation, especially for cementless TKR that requires bone ingrowth. Our aim was to quantify the effect varus alignment on the bone-implant interaction of cementless tibial baseplates. To this end, we evaluated the bone-implant micromotion and the amount of bone at risk of failure. [2,3]. Methods. Finite element models (Fig.1) were developed from pre-operative CT scans of the tibiae of 11 female patients with osteoarthritis (age: 58–77 years). We sought to compare two loading conditions from Smith et al.;. [1]. these corresponded to a mechanically aligned knee and a knee with 4° of varus. Consequently, we virtually implanted each model with a two-peg cementless baseplate following two tibial alignment strategies: mechanical alignment (i.e., perpendicular to the tibial mechanical axis) and 2° tibial varus alignment (the femoral resection accounts for additional 2° varus). The baseplate was modeled as solid titanium (E=114.3 GPa; v=0.33). The pegs and a 1.2 mm layer on the bone-contact surface were modeled as 3D-printed porous titanium (E=1.1 GPa; v=0.3). Bone material properties were non-homogeneous, determined from the CT scans using relationships specific to the proximal tibia. [2,4]. The bone-implant interface was modelled as frictional with friction coefficients for solid and porous titanium of 0.6 and 1.1, respectively. The tibia was fixed 77 mm distal to the resection. For mechanical alignment, instrumented TKR loads previously measured in vivo. [5]. were applied to the top of the baseplate throughout level gait in 2% intervals (Fig.1a). For varus alignment, the varus/valgus moment was modified to match the ratio of medial-lateral force distribution from Smith et al. [1]. (Fig.1b). Results. For both alignments and all bones, the largest micromotion and amount of bone at risk of failure occurred during mid stance, at 16% of gait (Figs.2,3). Peak micromotion, located at the antero-lateral edge of the baseplate, was 153±32 µm and 273±48 µm for mechanical and varus alignment, respectively. The area of the baseplate with micromotion above 40 µm (the threshold for bone ingrowth. [3]. ) was 28±5% and 41±4% for mechanical and varus alignment, respectively. The amount of bone at risk of failure at the bone-implant interface was 0.5±0.3% and 0.8±0.3% for the mechanical and varus alignment, respectively. Discussion. The peak micromotion and the baseplate area with micromotion above 40 µm increased with varus alignment compared to mechanical alignment. Furthermore, the amount of bone at risk of failure, although small for both alignments, was greater for varus alignment. These results suggest that varus alignment, consisting of a combination of femoral and tibial alignment, may negatively impact bone ingrowth and increase the risk of bone failure for cementless tibial baseplates of this TKR design

The current standard of practice following knee arthroplasty is to demonstrate the appropriate alignment of knee replacements using knee radiographs. Recent studies have suggested that standard knee radiographs provide adequate accuracy for tibial prosthesis alignment assessment as compared with long knee view radiographs which are more technically demanding and carry greater radiation exposure. In this study, we aim to address whether alignment measured on standard knee radiographs are reliable and reproducible over time. We examined a cohort of 80 patients 37 male (46%), 43 females (54%), mean age = 68 years) who underwent total knee arthroplasty (TKA). Standard knee anteroposterior radiographs performed within 2 days following surgery were compared to standard knee anteroposterior radiographs taken 1 year following the surgery in patients with well-functioning prosthesis. Tibial prosthesis alignment angles between the longitude of the tibial shaft and the tibial baseplate were calculated using Centricity Enterprise Web V3.0 software. The data was examined using R software. In well-functioning primary knee arthroplasties, tibial prosthesis alignment angles measured in the 1-year follow-up standard view knee radiographs were found to deviate from measurements obtained with the same radiographic specifications in the immediate post-operative period. A significant mean percentage difference was found between the two radiographs. Long knee view radiographs may be required in order to accurately assess tibial prothesis alignment following total knee arthroplasty