We present a study done to measure the change of angle of the acetabulum or cup, due to leg length discrepancy, deformity of hip and spine on standing. In 1998 a 3-dimensional reconstruction of hip model was prepared on CAD and the change of angle of the cup was measured as Functional Acetabular Inclination Angle (FAIA) with patient standing without squaring the pelvis. The FAIA on standing was compared with angle of the cup with patient in supine position with squared pelvis. The position of the cup changed on weight bearing due to multiple issues. The results showed that one centimetre of leg lengthening changed FAIA by 3°, 10° of abduction deformity resulted in apparent lengthening of 2.87 cm and loss of lordosis anteverted the cup on loading and vice-versa. We conclude that fixed hip deformities, leg length discrepancy and spine deformities can affect the angle of cup in hip replacement surgery and may prone to dislocations, impingement and segmental wear of the cup

The spinopelvic alignment is often assessed via the Pelvic Incidence-Lumbar Lordosis (PI-LL) mismatch. Here we describe and validate a simplified method to evaluating the spinopelvic alignment through the L1-Pelvis angle (L1P). This method is set to reduce the operator error and make the on-film measurement more practicable. 126 standing lateral radiographs of patients presenting for Total Hip Arthroplasty were examined. Three operators were recruited to label 6 landmarks. One operator repeated the landmark selection for intra-operator analysis. We compare PI-LL mismatch obtained via the conventional method, and our simplified method where we estimate this mismatch using PI-LL = L1P - 90°. We also assess the method's reliability and repeatability. We found no significant difference (p > 0.05) between the PI-LL mismatch from the conventional method (mean 0.22° ± 13.6) compared to L1P method (mean 0.0° ± 13.1). The overall average normalised root mean square error (NRMSE) for PI-LL mismatch across all operators is 7.53% (mean -3.3° ± 6.0) and 6.5% (mean -2.9° ± 4.9) for the conventional and L1P method, respectively. In relation to intra-operator repeatability, the correlation coefficients are 0.87 for PI, 0.94 for LL, and 0.96 for L1P. NRMSE between the two measurement sets are PI: 9.96%, LL: 5.97%, and L1P: 4.41%. A similar trend is observed in the absolute error between the two sets of measurements. Results indicate an equivalence in PI-LL measurement between the methods. Reproducibility of the measurements and reliability between operators were improved. Using the L1P angle, the classification of the sagittal spinal deformity found in the literature translates to: normal L1P<100°, mild 100°<L1P<110°, and severe L1P>110°. Surgeons adopting our method should expect a small improvement in reliability and repeatability of their measurements, and a significant improvement of the assessment of the mismatch through the visualisation of the angle L1P

Purpose. The aim of this study was to compare the accuracy of limb alignment and component positioning after total knee arthroplasty(TKA) performed using fixed or individual distal femoral valgus correction angle(VCA)in valgus knees. Materials and Methods. One hundred and twenty-four patients were randomised to undergo TKA with either of the clinical baseline, radiological outcomes and subsequent outcome such as knee HSS scores, knee range of motion (ROM) and visual analogue scale (VAS) scores were assessed. Knees in the individual group (n=62) were performed with a tailored VCA. Knees in the fixed group (n=62) were performed utilizing a 4°VCA. Results. The distribution of distal femoral valgus cut angle used in the individual group range from 3° to 8°. There were statistically significant differences between groups in post-operative hip-knee-ankle angle (individual: 180.0°±3.8°; fixed: 178.5°±2.9°; P=0.00). 86.9% of patients in the individual group had a post-operative mechanical axis deviation within ± 3°compared to 70.7% in the fixed group (P = 0.03). Patients in the fixed group had a higher percentage of postoperative residual deformity than in the individual group, and this difference was statistically significant (p=0.03). No significant differences were observed between the groups in terms of femoral and component alignment except coronal femoral component angle (α), although the size of the difference was very small(individual: 90.12°±1.61°; fixed: 88.97°±2.50°), the difference was statistically significant (P=0.00). There were no differences in HSS scores, knee ROM, or VAS pain scores in the early phase after surgery between groups. Conclusions. This study demonstrated that the VCA in patients with knee valgus deformities are smaller than normal or varus knee. Individual VCA for distal femoral resection could enhance the accuracy of postoperative neutral limb alignment in the coronal plane. Both individual and fixed VCA place the components with the similar accuracy

Abstract. Aim. This study aims to Inter and intra observer reliability compare, use of a standard goniometer (SG) to measure intermetacarpal angle (degrees) vs use of a new technique of using a digital vernier calliper (DVC) (mm) to measure the distance between the first and second metacarpal head. Method. Maximal active abduction and extension of both thumbs was measured in 20 healthy volunteers on two occasions at least one week apart by two assessors. Results. The inter and intra-observer agreement was higher & the variance of the data was lower using the DVC with the new technique than the SG for both thumb abduction and extension. Additionally, the correlation between measurement of extension and abduction was higher using the DVC than the SG. Conclusion. Whilst both tools provide acceptable intra and inter-observer agreement, the new technique using a DVC is consistently better and more reliable than a SG in measuring thumb abduction and extension. The study also supports our hypothesis that the thumb rotates around the second metacarpal head with a consistent radius

Introduction. During its conception, Ilizarov advocated a fine wire tension of between 900N and 1200N for circular frame construction. Wire tension can be achieved via a tensioning device or ‘Russian tensioning’ (a fixed wire lengthening around a bolt). There is limited information on the latter technique. This study aimed to explore the tensions achieved via Russian tensioning and report the impact of a second wire on construct tension. Materials and Methods. A single 160mm stainless-steel ring was constructed, then 1.8mm stainless steel wires secured using a Russian fixation bolt and Russian tensioned with a 2nd bolt. The angle subtended by tensioning using the 2nd bolt was measured using a goniometer. Angles of 45°, 70° and 90° were repeated in triplicates, with wire tension measured using a calibrated tensiometer. A 2nd orthogonal wire was placed on the opposite side and tensioned to the same angle. Tensions of both wires were remeasured and recorded. Statistical comparison using unpaired t-tests was used to compare mean tensions. A value of p<0.05 was considered significant. Results. Russian wire tensioning at all angles was insufficient to achieve the target range of 900–1200N (range 99–110N). The addition of a second orthogonal wire changed frame dynamics such that a 90° angle resulted in both wires achieving adequate tension (mean 1143N, SD 307N). Increases were significant across all tensioning angles (p–<0.002) however only biomechanically relevant for 90°. Conclusions. Russian tensioning is insufficient with a single wire, however the addition of an orthogonal wire increases tension in both wires, which reaches the target range at 90° deflection. This phenomenon is explained by force transmission initially into ring deflection, which is then balanced out by the second wire. Further study of this phenomenon using wire tensioners is warranted, and also the impact of non-orthogonal wire constructs

The use of shorter humeral stems in reverse shoulder arthroplasty has been reported as safe and effective. Shorter stems are purported to be bone preserving, easy to revise, and have reduced surgical time. However, a frequent radiographic finding with the use of uncemented short stems is stress shielding. Smaller stem diameters reduce stress shielding, however, carry the risk of varus or valgus malalignment in the metadiaphyseal region of the proximal humerus. The aim of this retrospective radiographic study was to measure the true post-operative neck-shaft (N-S) angle of a curved short stem with a recommended implantation angle of 145°. True anteroposterior radiographs of patients who received RTSA using an Ascend Flex short stem at three specialized shoulder centres (London, ON, Canada, Lyon, France, Munich, Germany) were reviewed. Radiographs that showed the uncemented stem and humeral tray in orthogonal view without rotation were included. Sixteen patients with proximal humeral fractures or revision surgeries were excluded. This yielded a cohort of 124 implant cases for analysis (122 patients, 42 male, 80 female) at a mean age of 74 years (range, 48 – 91 years). The indications for RTSA were rotator cuff deficient shoulders (cuff tear arthropathy, massive cuff tears, osteoarthritis with cuff insufficiency) in 78 patients (63%), primary osteoarthritis in 41 (33%), and rheumatoid arthritis in 5 (4%). The humeral component longitudinal axis was measured in degrees and defined as neutral if the value fell within ±5° of the humeral axis. Angle values >5° and < 5 ° were defined as valgus and varus, respectively. The filling-ratio of the implant within the humeral shaft was measured at the level of the metaphysis (FRmet) and diaphysis (FRdia). Measurements were conducted by two independent examiners (SA and TW). To test for conformity of observers, the intraclass correlation coefficient (ICC) was calculated. The inter- and intra-observer reliability was excellent (ICC = 0.965, 95% confidence interval [CI], 0.911– 0.986). The average difference between the humeral shaft axis and the humeral component longitudinal axis was 3.8° ± 2.8° (range, 0.2° – 13.2°) corresponding to a true mean N-S angle of 149° ± 3° in valgus. Stem axis was neutral in 70% (n=90) of implants. Of the 34 malaligned implants, 82% (n=28) were in valgus (mean N-S angle 153° ± 2°) and 18% (n=6) in varus position (mean N-S angle 139° ± 1°). The average FRmet and FRdiawere 0.68 ± 0.11 and 0.72 ± 0.11, respectively. No association was found between stem diameter and filling ratios (FRmet, FRdia) or cortical contact with the stem (r = 0.39). Operative technique and implant design affect the ultimate positioning of the implant in the proximal humerus. This study has shown, that in uncemented short stem implants, neutral axial alignment was achieved in 70% of cases, while the majority of malaligned humeral components (86%) were implanted in valgus, corresponding to a greater than 145° neck shaft angle of the implant. It is important for surgeons to understand that axial malalignment of a short stem implant does influence the true neck shaft angle

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

In the setting of traumatic elbow injuries involving coronoid fractures, the relative size of the coronoid fragment has been shown to relate to the stability of the joint. Currently, the challenge lies in accurately classifying the amount of bone loss in coronoid fractures. In comminuted fractures, bone loss is difficult to measure with plain radiographs or computed tomography. The purpose of this study is to describe a novel radiographic measure, the Coronoid Opening Angle (COA), on lateral elbow radiographs. We demonstrate the relationship of the COA to coronoid height and describe how this measure can be used to estimate bone loss and potentially predict elbow instability following coronoid fracture. Radiographs were drawn from a regional database in a consecutive fashion. Candidate radiographs were excluded on the basis of radiographic evidence of degenerative changes, previous surgery or injury, bony deformity, and inadequate lateral view of the elbow. The COA was measured as the angle between the long axis of the ulna at the level of the trochlear notch, and the tip of coronoid, from a common origin at the posterior cortex of the olecranon. Images were reviewed by a fellowship trained upper extremity surgeon, an upper extremity fellow, and a junior resident. Normal COA, coronoid height, and calculated COA at varying amounts of bone loss were calculated by three reviewers. A sensitivity analysis was performed to determine how the COA can most effectively predict bone loss at varying coronoid heights. Intraclass correlation coefficient (ICC) was calculated for 39 subjects. Seventy-two subjects were included for analysis (M=40, F=32). The normal coronoid opening angle is 33.19 degrees [32.2 – 34.2]. Coronoid height is 18.8 mm [18.1 – 19.6]. Extrapolating this baseline data, the COA at 20%, 33%, and 50% of coronoid bone loss was calculated to be 27.5, 23.5, and 18 degrees, respectively. ICC was found to be 0.90 or higher. Cutoff values were determined to maximize the sensitivity of the COA. A cutoff value of 21 degrees has a 92% sensitivity in detecting a minimum of 50% bone loss. The COA with similar sensitivity in predicting 20% and 33% bone loss are 32 and 27 degrees. The coronoid opening angle is a novel technique that can be used on a lateral elbow radiograph to predict the minimum coronoid bone loss. This can be used to guide clinical decision making and potentially predict instability. Future research will aim to validate this tool in the clinical setting in predicting instability

Background. The Q angle is an index of the vector of combined pull of the quadriceps and the patellar tendon. However, the Q angle is traditionally measured with the knee extended and static. The indexation of the Q angle measured using the traditional method therefore is questionable. Questions/purposes. We asked if the Q angle would change when the knee flexed; if it did change, how it changed; and if it changed with different patterns in females and males. Methods. We studied 30 volunteers' right lower extremities. To define the dynamic Q angle, we measured each volunteer's spatial position of the anterior superior iliac spine, patella center, tibial tuberosity, hip joint center, knee joint center, and ankle joint center. The Q angles were calculated with the knees at different angles of knee flexion. Results. The Q angle was dynamic, and it was correlated with the knee flexion angle (P < 0.001). It decreased when the knee flexion angle increased and finally approached 0° when the flexion angle was larger than 90°. The dynamic Q angle in males and females had no significant difference (P = 0.066). Conclusions. The Q angle is dynamic, and it approaches 0° when the knee is highly flexed. Additional studies are needed to further clarify the difference of Q angles in males and females

Introduction. One of the objectives of total hip arthroplasty is to restore femoral and acetabular combined anteversion. It is desirable to reproduce both femoral and acetabular antevesions to maximize the acetabular cup fixation coverage and hip joint stability. Studies investigated the resultant of implanted femoral stem anteversion in western populations showed that the implanted femoral stems had only a small portion can meet the desirable femoral anteversion angle. 1. , and anteversion angle increases after the implantation of an anatomical femoral stem with anteverted stem neck comparing to anatomical femoral neck. 2. The purpose of this study was to anatomically measure the anteversion angular difference between metaphyseal long axis and femoral neck in normal Chinese population. The metaphyseal long axis represents the coronal fixation plane of modern cementless medial-lateral cortical fitting taper stem. This angular difference or torsion Δ angle provides the estimation of how much the neck antevertion angle of femoral stem would be needed to match for desirable anatomical femoral neck version. Methods. 140 (77 male and 63 female) anonymous normal adult Chinese CT data with average age of 54.6 (male 54.6, female 54.5, P=0.95) were segmented and reconstructed to 3D models in Trauson Orthopeadic Modeling and Analytics (TOMA) program. Femoral head center, femoral neck axis and center point of diaphyseal canal 100mm bellow calcar formed the femoral neck plane. The metaphyseal stem implantation plane was determined by the center point of medial calcar, proximal canal central axis formed by femoral neck plane and the center point of diaphyseal canal 100mm bellow calcar. [Fig. 1] The angle between two planes was the torsion Δ angle between femoral placement plane and anatomical femoral neck. [Fig. 2] The torsion Δ angles were measured for all 140 cases. The traditional anteversion angle for anatomical femoral neck was also measured by Murphy's method. Student T test was perform to compare the angles for male and female. The 98% confidence level was assumed. Results. The average torsion Δ angle for whole population was 4.9°(0.04°-15.6°), SD=3.52°, male: 4.6° (0.42°-13.9°), SD=3.09°; female: 5.3° (0.04°-15.6°), SD=3.98°. There was no statistical significant difference between genders. P=0.28. All metaphyseal stem placement planes were less anteverted than anatomical femoral neck plane. [Fig. 3] The average anatomical femoral neck anteversion angle for total population was 18.6° (0.27°-42.6°), SD=7.54°; male: 18.6° (0.27°-32.9°), SD=7.37°; female: 18.7° (1.74°-42.6°), SD=7.81°. There was no statistical significance between male and female P=0.92. Only 26% of study population or 37 cases with unadjusted implant neck version had normal anteversion angle of 10°-15° (Tönnis). Discussion. The study suggested femoral stem neck anteversion angle adjustments up to 11° was necessary to match anatomical femoral neck for 94% of cases in Chinese population. And the adjustments of 0°-7° represented the 76% majority of population. This finding was in agreement with the published data in western population. 2. . Significance. Variable femoral stem neck anteversion angles up to 11° are necessary to reproduce the anatomical anteversions for 94% of normal Chinese population. For any figures or tables, please contact the authors directly

Purpose. Factors influencing flexion angle of the knee before and after PS-TKA were assessed. Methods. In 368 PS-TKA cases (71 males and 297 females) by means of modified gap control technique with Stryker NRG system, multi-variance analysis was performed to assess factors influencing flexion angle before TKA and flexion angle 3 weeks after TKA. Their mean age was 74.1 years old. Operative techniques and angle of the components were included as the factors. Results. Factors that influenced the flexion angle before TKA were BMI (standard regression coefficient, −0.166), standing femoro-tibial angle (−0.140), external rotation angle of the femoral component relative to the posterior condylar line (0.220) and resurfacing the patella (−0.225). Factors that influenced the flexion angle after TKA were flexion angle before TKA (0.491), medial soft tissue releases (−0.116) and patellar lateral release (−0.130). In cases with high BMI, severe deformity and patella damage, flexion angle before TKA was smaller. In cases in that medial soft tissues release and/or patella lateral release were necessary, flexion angle after TKA was smaller. Conclusion. In cases with contractures and deformities, flexion angle before TKA was smaller and it was hard to obtain deep flexion angle after TKA

Introduction. Modular junctions in total hip replacement (THR) have been a primary source of fretting and corrosion which can lead to implant failure. Fretting is a result of unintended micromotion between the femoral head and stem tapers and is suspected to result after improper taper seating during assembly. Two design factors known to influence in-vitro taper assembly mechanics are relative taper alignment—mismatch angle—and the surface finish—micro-grooves. However, these factors have not been systematically evaluated together. Objective. The objective of this study was to employ a novel, micro-grooved finite element (FEA) model of the hip taper interface and assess the role of taper mismatch angle and taper surface finish—smooth and rough—on the modular junction mechanics during assembly. Methods. A two-dimensional, axisymmetric model of a CoCrMo femoral head taper and Ti6Al4V stem taper was created using median measurements taken from over 100 retrieved implants. Micro-grooves on the stem and head taper were modeled using a sinusoidal function with amplitude and period corresponding to median retrieval measurements. To evaluate effects of a “smooth” head taper surface finish, additional models were run with a head taper having a flat edge (no micro-grooves). Lastly, mismatch between the stem and head taper was varied between distal-locked, no mismatch, and proximal-locked. To simulate assembly during surgery, boundary conditions were applied to move the femoral head taper at a constant velocity onto the stem taper until a 4kN reaction load was achieved. Models were assembled and meshed in ABAQUS Standard (v 6.17) using four-node linear hexahedral, reduced integration elements. Contact was modeled between the stem and head taper using surface-to-surface formulation with penalty contact and a coefficient of friction of 0.2. Forty simulations (5 mismatch angles x 2 head taper surface types x 4 stem taper surface finishes) were run. Outcome variables included contact area, contact pressure, equivalent plastic strain, and number of micro-grooves undergoing plasticity. Results. As expected, taper mismatch angle drove the location of contact to the distal or proximal ends. Increasing taper mismatch led to significant decreases in contact area for both micro-grooved and flat head taper models (Figure 1A). Taper mismatch had minimal effects on contact pressure (∼2.15 GPa) with the “rough” head taper surface finish but influenced the range of contact pressures (1.30 – 1.91 GPa) in the “smooth” head taper models (Figure 1B). Stress at the micro-grooves varied depending on the stem taper surface finish (Figure 2). Significant plastic deformation of the micro-grooves was only found in models with the “rough” head taper surface finish. Conclusion. Regardless of the taper surface finish, contact area decreased by 30% – 58% when going from a 3’ – 12’ mismatch. Reduced contact area may significantly influence the long-term stability of the implant. Modeling the taper micro-grooves led to plastic deformation consistent with those found from retrieved implants—indicating the importance of modeling the surface finish of tapers. These models will be used to identify the optimal design factors to maximize stability of the modular taper junctions. For any figures or tables, please contact authors directly

Purpose. Posterior pelvis tilt (PPT) would affect lumbar lordosis and lead to hip flexion, which causes difficulties walking and standing in patients with hip disorders. Hip flexion movement associated with PPT is well known. We investigated the effect of the angle of hip flexion without the movement of PPT in the supine position. Methods. The study enrolled 24 healthy males with an average age of 20.5 ± 2.3 years. Two pelvic positions in the supine position were investigated: (1) the limited position of the PPT by 500ml PET bottle with water placed under their low back, and (2) the position without placing a PET bottle. We assessed unilateral hip flexion angle with photos taken with a digital camera. For reference, we took an X-ray of a healthy female and observed the lumbo-sacral from the sagittal plane in the supine position. Analysis. Data was processed by Image analysis software (Image J 1.42, NIH). Paired t-tests were used to assess the range of motion of individual joints in each position in the sagittal plane. MEPHAS software (Oosaka University. Japan) was used for all statistical processing, and the level of significance was set at P < 0.05. In addition, we also measured the lumbo-sacral angle (LSA), the lumbo-lordotic angle (LLA) and the sacral slope angle (SSA) with the X-ray. Results. The angle of hip flexion decreased 22.9±6.04 degrees on average in the limited position with a PET bottle compared with the position without a bottle (P<0.01). The angle of pelvis decreased 4.8±2.0 degrees on average. Discussion. The angle of hip flexion significantly decreased in the limited position with a PET bottle. Our results suggest the association movement of the PPT with hip flexion movement in the supine position. This suggests that movements of the LLA and SSA are involved greatly in hip flexion. Significance of study. Our results provide evidence that could lead to more effective way of measurement of the primary hip joint (coxal femoral joint) flexion in the supine position for the patients with hip diseases. If we can measure primary hip joint (coxal femoral joint) flexion, it may also be measured mobility of the pelvis. Measurement of the hip joint flexion should consider the movement of the lumbar vertebrae and the sacral slope

Introduction. Pre-clinical assessment of total knee replacements (TKR) can provide useful information about the constraint provided by an implant, and therefore help the surgeon decide the most appropriate configurations. For example, increasing the posterior tibial slope is believed to delay impingement in deep flexion and thus increase the maximal flexion angle of the knee, however it is unclear what effect this has on anterior-posterior (AP) constraint. The current ASTM standard (F1223) for determining constraint gives little guidance on important factors such as medial- lateral (M:L) loading distribution, flexion angle or coupled secondary motions. Therefore, the aim of the study was to assess the sensitivity of the ASTM standard to these variations, and investigate how increasing the posterior tibial slope affects TKR constraint. Methods. Using a six degree of freedom testing rig, a cruciate-retaining TKR (Legion; Smith & Nephew) was tested for AP translational constraint. In both anterior and posterior directions, the tibial component was displaced until a ‘dislocation limit’ was reached (fig. 1), the point at which the force-displacement graph started to plateau (fig. 2). Compressive joint loads from 710 to 2000 N, and a range of medial-lateral (M:L) load distributions, from 70:30% to 30:70% M:L, were applied at different flexion angles with secondary motions unconstrained. The posterior slope of the tibial component was varied at 0°, 3°, 6° and 9°. Results. AP translation was significantly larger at 60° and 90° flexion (22 ± 1 mm and 24 ± 1 mm respectively) than at 0° (14 ± 1 mm), whilst increasing the compressive joint load increased the force required to translate the tibia to limits of AP constraint at all flexion angles tested. When the M:L load distribution was shifted medially, a coupled internal rotation was observed with anterior translation and external rotation with posterior translation; this was reversed with a lateral shift in load distribution. It was also found that increasing the posterior slope of the tibial tray moved the neutral position of the tibia relative to the femur more anteriorly at all flexion angles tested. The constraint under anterior drawer was then reduced with increasing slope, which meant that the tray dislocated at lower drawer force and translations. Conclusions. When intraoperative tibial bone cuts are made, surgeons should be aware that by increasing posterior slope angles the TKR may offer less anterior constraint under body-weight loads, therefore relying more heavily on surrounding soft-tissue and muscle action to prevent dislocation. The ASTM test protocol could be refined to stipulate the variation of the M:L loading distribution. It has been shown to vary between patients and activities, and the AP constraint and associated secondary motions in this study were very sensitive to this distribution. The secondary motions observed should be measured and recorded to provide more information about the device's stability characteristics. The tests could also be extended to include a higher axial load such as 2000 N, approximately three times body weight, in order to investigate coupled rotations and M:L distribution effects whilst under normal walking gait loads

INTRODUCTION. Several papers have reported the efficacy of an imageless navigation system in acetabular cup orientation during total hip arthroplasty (THA). Also, an imageless navigation system is useful for recovering leg length discrepancy. However, no study has evaluated the accuracy of the stem antetorsion angle (SAA) with an imageless navigation system in THA. The purpose of this study was to evaluate the accuracy of the stem antetorsion angles, which were measured by CT with the CT-free navigation system. Also, we evaluate the factors that affect the inaccuracy. MATERIALS AND METHODS. CT evaluation was performed in 60 patients (60 joints) who underwent primary THA from December 2011 to March 2014. Fifty-nine patients were female. The mean age at surgery was 67 years. The mean BMI at surgery was 24.0 kg/m2. Fifty-four patients had osteoarthrosis, 5 patients had osteonecrosis, and 1 patient had femoral neck fracture. All surgeries were performed in the supine position with the direct anterior approach. The OrthoPilot imageless navigation system was used during surgery. An Excia stem was used in 47 patients and a Bicontact stem was used in the other 13. Evaluation of SAA was carried out. Instead of SAA, the navigation indicates the rasp antetorsion angle based on the hip-knee-ankle plane during surgery. SAA based on the posterior condylar plane was measured with CT by using 3D THA plannning software. The accuracy of the imageless navigation system was evaluated by comparison of the navigation values obtained during surgery with the CT measured values. Correlations were analyzed with Pearson correlation analysis. RESULTS. The rasp antetorsion angle was 28.1±9.6 degrees [range 7.7–49.2 degrees]. The mean SAA was 29.9±8.9 degrees [10.7–49.7 degrees] in CT. Strong correlation was found between the rasp antetorsion angle and SAA (p<0.001, r=0.858, Figure). The difference between SAA and the rasp antetorsion angle (SAA – rasp antetorsion angle) was 1.8±4.7 degrees [-6.7–11.9 degrees]. The mean absolute difference between the rasp antetorsion angle and SAA was 4.0±3.1 degrees [0.2–11.9 degrees]. Forty-five cases (75%) showed less than 5 degrees of difference between SAA and the rasp antetorsion angle. Five cases (8.3%) showed more than 10 degrees of difference. In these five cases, SAAs were greater than the rasp antetorsion angles. Patients’ age, height, weight, and BMI did not affect the difference. Deformity of the femoral head, osteoarthrosis of the hip with subluxation, and osteoarthrosis of the knee were found in the patients who showed more than 5 degrees of difference between SAA and the rasp antetorsion angle. DISCUSSION. This study demonstrated that imageless navigation showed good accuracy for determining SAA during operation. This helps surgeons to recognize combined anteversion during surgery, and to avoid impingement after THA. This navigation system determines rasp antetorsion angle based on the hip-knee-ankle plane. The hip center is defined by setting the trial cup on the acetabulum. The knee center and the ankle center are defined by pointing over the skin. Therefore, deformity of the acetabulum or femoral head may affect the accuracy of the rasp antetorsion angle

In total hip arthroplasty (THA), acetabular cup orientation is critical for avoiding edge-loading and implant-implant impingement, which may lead to serious complications such as dislocation, mechanical loosening, accelerated wear, or implant breakage. Many studies recommended to place the acetabular cup radiographically at an inclination of <50° to avoid edge-loading. Simultaneously, larger prosthetic ROMs than the patients’ ROM during daily activities are needed to minimize impingement related complications. Several three-dimensional computer simulation studies have been done for optimal cup orientation to avoid prosthetic impingement within possible hip ROMs in the late 1990s. However, the reference angles in the directions of flexion, extension, external rotation and internal rotation at 90 ° flexion as possible hip ROMs have not been consistent in previous simulation studies. Thus, different reference angles of hip ROMs resulted in different optimal cup orientation. Therefore, to give accurate information about the reference hip ROM, we measured passive hip ROMs intraoperatively using a navigation system in 91 patients. Pelvic and femoral coordinate systems referred a functional pelvic plane in the supine position and a retrocondylar plane, respectively. The neutral position of the hip ROM was defined as the position in which corresponding axes of the pelvic and femoral coordinate systems were parallel. Maximum flexion, extension, external rotation and abduction were 120°, 36 °, 43 ° and 55 °, respectively. Moreover, we investigated the hip ROM during five traditional Japanese hip positions which required large hip flexion and internal rotation angles in five healthy female volunteers by a 3D image matching technique using an open-configuration MRI. Maximum flexion was 122 ° and maximum internal rotation was 40 ° at more than 90 ° of flexion position. Therefore, we recommended using 120 ° for flexion, 40 ° for extension, 40 ° for external rotation and 40 ° for internal rotation at 90 ° flexion as the reference ROM when calculating an optimum cup orientation. We calculated radiographic cup anteversion, when radiographic cup inclination was 40 °, without prosthesis impingement in the reference hip ROMs using computer aided design models of prosthesis, which included a cementless CentPillar stem with a head 32mm in diameter and cementless Trident cup with a flat liner. The results showed the optimal cup target zone existed when the stem anteversion was between 20 ° and 45 °. The size of the target zone was widest when the stem anteversion was 30 °, and then it was plus or minus 5 ° of inclination and anteversion from the center of the zone. To eliminate outliers of cup orientation form the target zone, a computer assisted system such as navigation is recommended

INTRODUCTION. Normal kinematics have not been achieved in TKA design. Recently, knee simulation studies have suggested that a medial pivot TKA can achieve the anatomic pathway that reduce mid-flextion rollback and increase lateral rotation. However, the influence of postoperative flextion angle associated with medial tightness for guide motion TKA remains poorly understood. The purpose of this study was to investigate the effect of postoperative flextion angle and clinical outcomes associated with tightness for medial component gap (MCP). METHODS. We evaluated 79 patients who underwent 84 medial pivot The Journey.2. Bi-Cruciate Substituting (BCS) TKA using the measured resection tequnique, from June 2014 to March 2016. We measured the gaps after implantation from extension to full flextion with reduced patella by constant distraction force (120N). A new tensor has the same articular shapes as that the tibial liner, including anterior and posterior structure. RESULTS. There were no patients with midflextion instability for varus ligament balance. Postoperative knee flextion angle was positively corrected with preoperative knee flextion angle (r=0.62, p=0.001). The MCP difference (max-mini)(r=0.66, p=0.002) and Lateral minus medial component gap (varus angle) (r=0.43, p=0.001)from extension to full flextion was negative correlations with postoperative flextion angle. DISCUSSION AND CONCLUSIONS. Medial tightness and no lateral laxity as well as joint component gap at extension throughout full flex is the most important factors affecting postoperative flextion angle in guided motion TKA

Introduction. Proper alignment of the components and soft tissue balance are the two factors that determine the long term outcome of total knee arthroplasty (TKA). On the femoral side a distal cut made perpendicular to the MA will restore the MA of the leg. Different methods are commonly used to resect the femur perpendicular to its MA. In uncomplicated cases, most surgeons routinely use a fixed valgus cut angle (VCA) of 5° or 6°. Various studies have questioned the use of fixed valgus angle resection to restore the mechanical axis. The purpose of this prospective study is to analyze the variability in the valgus angle following computer assisted TKA. Materials and methods. Twenty-three patients who underwent computer assisted TKA in our institution in 2009 were involved in the study. A total of 40 knees were available for analysis. All the knees underwent a CT scanogram postoperatively. Each scanogram was analyzed using the Amrita medvision(r) software. The angle subtended between the mechanical axis and the distal femoral anatomic axis is the valgus angle. Two independent observers calculated all the values and the interobserver reliability was calculated. Results. The average age of the patients was 65.6 years. The kappa coefficient of agreement was 0.8, which shows good interobserver reliability. The average angle formed by the femoral component with the mechanical axis was 91.6. 0. and the average valgus angle calculated was 7.41. 0. 14 knees out of 40 (35%) were lying within the range of 4 - 7 degrees. In 25 knees (65%) valgus angle was more than 7 degrees. In one case the valgus angle was less than 4 degrees. Conclusions. Fixed valgus angle resection is not reliable in restoring mechanical axis in total knee arthroplasty. In the absence of facilities for surgical navigation, a pre operative planning with long leg films is extremely important to achieve long-term success

Introduction. Taper corrosion and fretting has been identified to be a major problem in total hip replacement during the past years. Taper design and manufacturing are not been standardised, and therefore it can be assumed that the tapers vary among different implant manufacturers. This can lead to variable contact situations and stresses in the taper junction depending on the combination. It can be assumed that the taper strength will influence the occurrence and magnitude of micromotions which are known to influence corrosion. Therefore, the aim of this study was to assess the influence of the taper angle clearance on the taper connection strength. Material & Methods. For the investigation stem dummys with different taper angles were used that were manufactured from titanium alloy. The stem dummys were combined with ceramic heads with identically taper angles. Out of this, there were seven groups ranging from distal contact through full contact up to proximal contact. Three samples were used in each group and five repetitive measurements per samples were performed. All taper connections were impacted with different forces (1 kN, 3 kN, 6 kN and 10 kN) and afterwards an increasing torque was applied until the head disconnected. The maximal torque off value was used as a measure for the taper strength. Results. A greater taper clearance leads to a higher taper strength (Fig. 1). However, this effect is also influenced by the assembly force and becomes even stronger with higher assembly forces. When comparing a distal, full and proximal contact situation the full contact shows the lowest taper strength, whereas the distal contact situation leads to the highest taper strength. Discussion and conclusion. The design variability in taper connections influences its strength. A smaller contact area leads to higher local contact pressure. It is assumed that this increases local plastic deformations of the surface structure which is beneficial for this self-locking mechanism of the junction. However, the effect of the assembly force seems to overcome the effect of the taper clearance. Therefore taper junctions should be firmly connected in total hip replacements. Furthermore, surgeons should be aware that in a clinical case of a Mix & Match the taper strength may be reduced depending on the combined components. For figures/tables, please contact authors directly.

Materials and Methods. We treated 60 hips in 60 patients (8 males and 52 females) with cementless THA that were performed from January 2007 to December 2009 in our hospital. 48 osteoarthritis hips, 5 rheumatoid arthritis hips and 7 idiopathic osteonecrosis hips were included. All patients were performed THA with VectorVision Hip navigation system (BrainLAB, Feldkirchen, Germany). We used AMS HA cups and PerFix stems (KYOCERA Medical co., Osaka, Japan). The mean age of surgery was 61 years old (35–79 years old). The pelvic inclination angles (PIA) were measured with anteroposterior radiographic image in accordance with the Doiguchi's method. Results. The amount of change of the pelvic inclination angle between supine and standing position was 0.6 degrees prior to surgery, 0.7 degree at 1 year after surgery and 2.4 degrees at 5 years after surgery. 7 patients prior to surgery, 7 patient at 1 year after surgery and 18 patient at 5 year after surgery changed more than 5 degrees between supine and standing position. The pelvic inclination angles of 23 patients prior to surgery, 19 patients at 1 year after surgery and 35 patients at 5 years after surgery changed in the retroverted direction with posture change. It tended to increase after surgery. Discussions and Conclusions. When we place the acetabular component, it is important that the pelvic inclination angle in supine position according to preoperative planning and the change of pelvic inclination angle with posture change. The amount of change of PIA tended to increase at 5 year after surgery compared to 1 year after surgery. Moreover, we experienced some patients the amount of change of pelvic inclination angle between supine and standing position changed more than 10 degrees. If the pelvic inclination angle changes widely, it requires more attention because of a narrow safe margin for placing the acetabular component