Surgical epicondylar axis is not orthogonal to the femoral mechanical knee axis in valgus knees with primary osteoarthritis: Three-dimensional analysis according to knee coronal alignment in 112 patients

BackgroundDuring total knee arthroplasty (TKA), most surgeons align the femoral component along the surgical epicondylar axis (SEA) considering it as orthogonal to the femoral mechanical axis. However, it is still unclear how SEA coronal alignment varies according to the native coronal knee alignment. The main goal of this study was to analyze the SEA orientation according to the native coronal knee morphotype.MethodsA total of 112 patients underwent a three-dimensional (3D) -planning-based TKA. The SEA was then determined by locating the epicondyles on 3D models. The 3D femoral and tibial mechanical axes were marked and the femoral (FMA) and tibial (TMA) mechanical angles were measured. The native HKA angle was measured as FMA + TMA. The SEA orientation angles were measured in the coronal (SEA-α) and axial (SEA-β) plane. SEA orientation was compared between the valgus, neutral, and varus knees.ResultsThe mean SEA-α angle was 90.2 ± 3° and the mean axial SEA-β angle was 92.2 ± 1.3°. The SEA-α angle was significantly higher in the valgus group compared with the neutral group (92.3 ± 2.9°, 90 ± 2.9°, P = 0.0009) whereas there was no significant difference in the SEA-α angle between the varus and the neutral group (89.7 ± 2.3°, 90 ± 2.9°, P = 0.32).ConclusionsIn contrast to the neutral and varus knees, the SEA was not orthogonal to the femoral mechanical axis in patients undergoing TKA for primary osteoarthritis. Our results suggest adapting the coronal alignment of the femoral component during TKA, while maintaining an average 2° valgus in valgus knees. By contrast, with varus and neutral knees, our data support the use of a mechanical alignment.     

Factors contributing to inherent varus alignment of lower limb in normal Asian adults: Role of tibial plateau inclination

PurposeThis prospective study aimed to evaluate radiographically, mechanical or hip–knee–ankle (HKA) axis in healthy, asymptomatic, Asian (Indian and Korean) adults between 20 and 40 years of age to determine the incidence of inherent varus (mechanical limb alignment of > 3° varus) and the factors influencing it.MethodsThree hundred and eighty-eight lower limbs were evaluated using full length, standing hip-to-ankle radiographs in 198 healthy, asymptomatic, Asian (Indian and Korean) adults between 20 and 40 years of age to assess the hip–knee–ankle (HKA) angle, medial proximal tibial angle (MPTA), femoral bowing and femoral neck–shaft angle to determine the incidence of inherent varus (mechanical limb alignment of > 3° varus) and the factors influencing it.ResultsOverall, the mean HKA angle was 177.6° ± 2.6° with 34.5% of limbs in inherent varus (mean HKA angle 174.9° ± 1.8°). The incidence of inherent varus was significantly higher (p = 0.01) in males (40%) compared to females (28%) but similar among Indian (34%) and Korean subjects (35%). The hip–knee–ankle (HKA) angle showed significant positive correlation (r = 0.82, p < 0.001) with only the medial proximal tibial angle (MPTA).ConclusionsInherent varus alignment of the lower limb is fairly common among asymptomatic, Asian adults. These results raise several pertinent questions regarding the role of inherent varus in the aetiopathogenesis of knee osteoarthritis and in lower limb realignment procedures.     

Erratum to “Greater postoperative relatively medial loose gap at 90° of flexion for varus knees improves patient-reported outcome measurements in anatomical bi-cruciate retaining total knee arthroplasty” [The Knee 27(5) (2020) 1534–1541]”

BackgroundThe purpose of the present study was to measure the intraoperative joint gap using tensor device and pre- and, postoperative joint stability at 0, 30 and 90° of flexion using stress radiography and to identify whether these factors influence patient-reported outcome measurement (PROM) in anatomical bi-cruciate retaining (BCR) knee arthroplasty (TKA).MethodsFifty-three knees with preoperative varus osteoarthritis of the knee underwent anatomical BCR TKA with oblique 3° angle femorotibial joint line. The intraoperative medial and lateral joint gap using a tensor device and gap difference (lateral minus medial; varus laxity) were also calculated. Postoperative joint stability was measured using stress radiographs. PROM was also evaluated at 1.5 years postoperatively. The effect of intraoperative and postoperative joint stabilities on PROMs were analyzed using Spearman’s rank correlation analysis.ResultsIntraoperative greater difference between medial joint gap at 140° and 0° of flexion showed significant positive correlation with postoperative function of patellofemoral joint. Intraoperative varus laxity at extension improved postoperative symptoms in 2011 Knee Society Score (2011 KSS); greater postoperative lateral stability at 30 and 90° of flexion with the varus stress test was associated with the better patient expectation in 2011 KSS. Postoperative medial laxity at 90° of flexion with the valgus stress test positively correlated with the patient expectation and satisfaction in 2011 KSS.ConclusionSurgeons should notice that the postoperative lateral stability and medial laxity at 90° of flexion improved PROM in anatomical BCR TKA.     

Greater postoperative relatively medial loose gap at 90° of flexion for varus knees improves patient-reported outcome measurements in anatomical bi-cruciate retaining total knee arthroplasty

BackgroundThe purpose of the present study was to measure the intraoperative joint gap using tensor device and pre- and, postoperative joint stability at 0, 30 and 90° of flexion using stress radiography and to identify whether these factors influence patient-reported outcome measurement (PROM) in anatomical bi-cruciate retaining (BCR) knee arthroplasty (TKA).MethodsFifty-three knees with preoperative varus osteoarthritis of the knee underwent anatomical BCR TKA with oblique three-degree angle femorotibial joint line. The intraoperative medial and lateral joint gap using a tensor device and gap difference (lateral minus medial; varus laxity) were also calculated. Postoperative joint stability was measured using stress radiographs. PROM was also evaluated at 1.5 years postoperatively. The effect of intraoperative and postoperative joint stabilities on PROMs were analyzed using Spearman's rank correlation analysis.ResultsIntraoperative greater difference between medial joint gap at 140° and 0° of flexion showed significant positive correlation with postoperative function of patellofemoral joint. Intraoperative varus laxity at extension improved postoperative symptoms in 2011 Knee Society Score (2011 KSS); greater postoperative lateral stability at 30 and 90° of flexion with the varus stress test was associated with the better patient expectation in 2011 KSS. Postoperative medial laxity at 90° of flexion with the valgus stress test positively correlated with the patient expectation and satisfaction in 2011 KSS.ConclusionsSurgeons should notice that the postoperative lateral stability and medial laxity at 90° of flexion improved PROM in anatomical BCR TKA.     

Comparison between navigated reported position and postoperative computed tomography to evaluate accuracy in a robotic navigation system in total knee arthroplasty

BackgroundComputer navigation increases reproducibility compared to non-navigated total knee arthroplasty (TKA). Robotics navigation is a branch of computer navigation technology that might further improve accuracy of implant placement. The aim of this study is to assess the accuracy achieved in TKA with a robotic navigation system.MethodsOne hundred seventy three knees. System studied: Omni navigation System (OMNI, Raynham, MA). Navigated femoral and tibial cuts were compared to postoperative computed tomography (CT). Measurements reviewed: femoral coronal alignment (FCA), femoral sagittal alignment (FSA), femoral rotational alignment (FRA), tibial coronal alignment (TCA), tibial sagittal alignment (TSA) and hip–knee–ankle (HKA) angle. Statistical analysis was made using R.ResultsThe mean differences between the navigated reported and the CT positions were: FCA: 0.1 ± 1.2° more varus (P = 0.58), FSA: 1.5 ± 0.3° more flexed (P < 0.001), FRA: 0.0 ± 1.7° (P = 0.93), TCA: 0.7 ± 1.1° more varus (P < 0.001), TSA: − 1.3 ± 1.5 more negative slope (P < 0.001), HKA angle: 0.4 ± 2.4 more varus (P < 0.049).The percentages of concordance inside a three degree difference were: FCA: 98% (169 knees), FSA: 100% (173 knees), FRA: 94% (162 knees), TCA: 99% (171 knees), TSA: 93% (161 knees) and HKA angle: 83% (144 knees).ConclusionsThe current study showed that the robotic navigation system studied is highly accurate regarding final implant positioning for FCA, FRA and TCA. It has less accuracy in FSA, TSA and the HKA angle.     

Pitfalls in assessing limb alignment affected by rotation and flexion of the knee after total knee arthroplasty: Analysis using sagittal and coronal whole-body EOS radiography

BackgroundInappropriate posture during radiographic assessment may lead to misunderstanding of postoperative alignment after total knee arthroplasty (TKA). The EOS system assesses coronal and sagittal alignment simultaneously. This study aimed to evaluate the effect of flexion and/or rotation on alignment, and identify the patterns of knee posture with serial follow-up using the EOS system.MethodsOne-hundred and fifteen patients of TKA and serial whole-body EOS were included. The hip–knee–ankle (HKA) angle in the coronal and sagittal planes, femoral component rotation ratio (FCR), tibial component rotation ratio (TCR), and fibular overlap ratio (FO) were measured immediately and at six months and one year postoperatively. Total and partial correlation, using flexion and rotation as a control variable was performed.ResultsThe mean HKA values and flexion immediately post-operation were different compared with the values noted at six months and one year postoperatively (for all, P < 0.05). The FCR and FO were correlated with the HKA angle during all periods (for both, P < 0.05). The Pearson correlation coefficients of the HKA angle with rotation parameters decreased when flexion was controlled.ConclusionsCombined rotation and flexion of the knee joint has a greater effect on coronal alignment compared with isolated flexion or rotation and was more frequently observed during the early postoperative period. Therefore, surgeons should be made aware of the potential knee rotation and flexion errors after TKA.     

Improving the accuracy of tibial component placement during total knee replacement in varus knees with tibial bowing: A prospective randomised controlled study

BackgroundLateral tibial bowing leads to varus placement of the tibial component during total knee replacement in varus knees. Lateralised tibial jig placement can improve the accuracy of the tibial cut.MethodsA total of 227 patients (300 knees) undergoing total knee replacements were randomised into two groups. In the study group, the point of intersection of the distal tibial diaphyseal line at the tibial plateau drawn on long films was represented by zones. Knees with femoral bowing > 5° (28%) were excluded. Tibial jig placement on the proximal tibia was lateralised according to the zones. In the control group, the mid-point of the tibial plateau was taken as a reference. Femoral and tibial bowing, postoperative limb alignment and component placement were assessed.ResultsOf the 216 knees that were studied, 106 were in the study group and 110 in the control group. Bowing ≥ 3° had a significant positive correlation with lateralisation of the proximal tibial reference (p < 0.001). The Incidence of tibial bowing ≥ 3° was 57.33%. The mean postoperative hip–knee–ankle (HKA) angle was 178.31 ± 2.88° and 176.53 ± 2.88° (p < 0.001), whereas the mean medial proximal tibial angle (MPTA) was 89.91 ± 1.42° and 88.79 ± 1.72° (p < 0.001) in the study and control groups, respectively. Considering bowed tibiae alone, HKA angle and MPTA in the study group were 178.08 ± 2.81° and 89.72 ± 1.39° compared with 175.88 ± 2.87° and 88.38 ± 1.38° in the control group (p < 0.001).ConclusionThere is a high incidence of tibial bowing in varus knees. Lateralised tibial jig placement improved tibial component placement and postoperative limb alignment in total knee arthroplasty in varus knees with tibial bowing.     

Can total knee arthroplasty restore the correlation between radiographic mechanical axis angle and dynamic coronal plane alignment during gait?

BackgroundTotal knee arthroplasty (TKA) is the treatment of choice for end-stage knee osteoarthritis. Postoperative static knee alignment has been recognized as a key component of successful surgery. A correction toward the kinematics of a native knee is expected after TKA, with an aim for neutral mechanical alignment. The evolution of frontal plane knee kinematics is not well understood.MethodsNineteen patients awaiting TKA were recruited. Three-dimensional knee kinematics during treadmill gait were assessed pre-operatively, 12 months after surgery, and compared to a control group of 17 asymptomatic participants.ResultsMean radiographic mechanical alignment was corrected from 5.4° ± 5.0 (Standard Deviation) varus pre-operatively to 0.1° ± 2.0 (Standard Deviation) valgus postoperatively (P = 0.002). Mean stance coronal plane alignment decreased from 6.7° ± 4.0 (Standard Deviation) varus per-operatively to 2.1° ± 3.8 (Standard Deviation) postoperatively (P = 0.001). Correlation between radiographic mechanical axis angle and dynamic frontal plane alignment during gait, before and after surgery, was weak (pre-operative R = 0.41; postoperative R = 0.13) compared to control (R = 0.88). In the sagittal plane, TKA patients maintained their pre-operative stiff knee gait adaptation. Postoperative transverse plane kinematics suggested restoration of external tibial rotation during swing after TKA compared to control (Pre-operative 3.1°, postoperative 6.8°, control 7.1°, P = 0.05).ConclusionThe lack of correlation between static and dynamic alignment suggests that static radiographic coronal alignment of the knee does not accurately predict dynamic behavior. In the sagittal plane, pre-operative gait adaptations were still present 12 months after surgery, supporting the need for a functional assessment to guide postoperative rehabilitation following TKA.     

Under-correction of preoperative varus alignment does not lead to a difference in in-vivo bone loading in 3D-SPECT/CT compared to neutral alignment

BackgroundThe aim was to investigate the correlation of bone tracer uptake (BTU) in SPECT/CT and changes in coronal knee alignment after total knee arthroplasty (TKA). We questioned if undercorrection of preoperative varus alignment leads to a difference in BTU compared to neutral alignment.MethodsConsecutive 66 patients who received SPECT/CT before and after TKA were retrospectively included. Adjusted mechanical alignment was the alignment target. The alignment of the knee was measured on 3D-CT by selecting standardized landmarks. Maximum (mean ± SD) and relative BTU (ratio to the reference) were recorded using a previously validated localization scheme (p < 0.05).ResultsIn the native group, 20 knees were aligned (30.3%) in valgus (HKA > 181.5°), 12 (18.2%) in neutral (178.5°-181.5°) and 34 (51.5%) in varus (HKA < 178°). Overall TKA changed the alignment towards neutral. 48.5% remained in the same groups, whereas 50% of native valgus and 33% of varus knees changed to neutral after TKA. In native varus alignment mean BTU was significantly higher in some medial tibial and femoral regions (fem1ia (p = 0.010), fem1ip (p = 0.002), tib1a.mid (p = 0.005), tib1a.tray (p = 0.000), tib1p.tray (p = 0.000)); in native valgus alignment mean BTU was higher in the corresponding lateral tibial and femoral regions (fem2ip (p = 0.001), tib2a.tray (p = 0.011), tib2p.tray (p = 0.002)). After TKA, a significant decrease in femoral and tibial BTU (femoral preoperative BTU 1.64 +/-0.69; femoral postoperative BTU 0.95 +/-0.42; p = 0.000// tibial preoperative BTU 1.65 +/- 0.93; tibial postoperative BTU 1.16 +/- 0.48; p = 0.000) and an increase in patellar BTU was observed (p = 0.025). Native varus alignment correlated with a higher medial BTU decrease medially. Undercorrection of preoperative varus alignment showed no higher BTU after TKA.ConclusionPreoperative varus alignment correlated with a higher decrease in BTU in specific femoral and tibial medial regions. Preoperative valgus alignment correlated with a higher decrease in the corresponding lateral regions. Undercorrection of preoperative varus alignment did not lead to higher bone loading reflected by BTU after TKA.     

Intraoperative assessment of midflexion laxity in total knee prosthesis

BackgroundSoft-tissue balancing of the knee is fundamental to the success of a total knee arthroplasty (TKA). In posterior-stabilized TKA, there is no stabilizer of the anterior–posterior translation in the midflexion range in which the cam-post mechanism does not engage yet. Therefore, instability in the midflexion range is suspected to occur in posterior-stabilized TKA. The purpose of this study was to measure the joint gap throughout a full range of motion and to analyze the joint gap laxity in the midflexion range after implantation of a mobile-bearing posterior-stabilized total knee prosthesis.MethodsJoint gap kinematics in 259 knees with varus osteoarthritis were measured during TKAs using a tensor device with the same shape of a total knee prosthesis of the same design was used. After the implantation of a mobile-bearing posterior-stabilized prosthesis and the reduction of the patellofemoral joint, the joint gap was measured at 0°, 30°, 60°, 90°, 120°, and 145° of flexion.ResultsThe center size of the joint gap was tight in extension and deep flexion and loose at midflexion ranges, especially at 30° of flexion (p < 0.001). The symmetry of the joint gap was varus at 0° and 145° of flexion (p < 0.001).ConclusionsOur results showed the joint gap laxity in the midflexion range after the implantation of a mobile-bearing posterior-stabilized prosthesis. Our new tensor device, which can attach the polyethylene insert trial, will provide the important information about the joint gap kinematics after implantation of total knee prostheses.Level of evidenceIV.     

Cartilage assessment using preoperative planning MRI for femoral component rotational alignment

BackgroundSurgical planning of posterior referencing total knee arthroplasty (TKA) using computed tomography (CT) might lead to over-rotation of the femoral component because CT could not detect cartilage thickness of the posterior femoral condyle. The purpose of this study was to examine the rotational alignment difference of the femoral component between magnetic resonance imaging (MRI) and CT.MethodsFor elderly varus osteoarthritic patients, 66 varus osteoarthritic knee patients that underwent primary TKA were selected. Twenty-seven young patients who underwent primary anterior cruciate ligament reconstruction were selected as control. After the transepicondylar axis (CEA), the surgical epicondylar axis (SEA) and the posterior femoral condylar line (PCL) were drawn on CT and on MRI at the same angles as CT. Then, the practical PCL was drawn on MRI considering the cartilage thickness (the cartilage PCL). The angle between the SEA and the cartilage PCL (the cartilage posterior condylar angle (PCA)) was measured as preoperative planning. To investigate the accuracy of preoperative MRI measurement, the cartilage thickness on posterior femoral condyles was directly measured during TKA.ResultsThe cartilage PCA for varus osteoarthritic patients averaged 1.3 ± 1.3°. The cartilage PCA was 1.8 ± 1.0° significantly smaller than the bone PCA (the PCA measured on CT). Meanwhile, the cartilage PCA was 0.2 ± 0.4° significantly larger than the bone PCA in young people. The preoperative angle measurement on MRI strongly correlated with the direct measurement of cartilage thickness during TKA.ConclusionThere was 1.8° of divergence between MRI and CT in varus osteoarthritic patients due to cartilage degeneration of the medial femoral condyle. Cartilage assessment using MRI was useful for femoral component rotational alignment.     

What is the relationship between the “Fujisawa point” and postoperative knee valgus angle? A theoretical,computer-based study

BackgroundThe purpose of this study was to determine the relationship between the Fujisawa point and postoperative knee valgus angle and the anatomical factors influencing this relationship.MethodsAn experimental study was conducted including 116 patients with medial compartment knee osteoarthritis undergoing treatment with open-wedge high tibial osteotomy (OWHTO). Each patient received simulated HTO through the Fujisawa point in the picture archiving and communication system (PACS). The preoperative hip-knee-ankle (HKA) angle and lower extremity anatomical parameters were recorded before the computerized HTO simulation. The postoperative knee valgus angle was measured after this procedure. A second simulation HTO was performed to adjust the mechanical axis to the optimal valgus angle (4.5°) and calculate the percentage of the tibial plateau width where the Mikulicz line crossed the knee. The Spearman correlation test and multivariate regression were used for analysis.ResultsThe median preoperative HKA varus angle of this study cohort was 174.1° (170.8, 176.2°). The median knee valgus angle after simulated osteotomy through the Fujisawa point was 2.4° (2.1, 2.7°). The valgus angle was positively correlated with the tibial plateau width (r = 0.23, p = .013) and preoperative HKA angle (r = 0.32, p < .001). Multivariate regression analysis showed that the preoperative HKA angle was a significant contributor to the postoperative valgus angle. When conducting the osteotomy with the optimal valgus angle (4.5°), the percentage of the Mikulicz line passing through the tibial plateau was 71.93% (67–78%).ConclusionsThe preoperative HKA angle affects the postoperative valgus angle after HTO. If the optimal valgus angle of 4.5° is desired, a more lateral position of the Fujisawa point should be targeted during OWHTO, which accounts for approximately 71.9% of the tibial plateau.     

The medial gap is a reliable indicator for intraoperative soft tissue balancing in posterior-stabilized total knee arthroplasty

BackgroundAppropriate soft tissue balance and accurate alignment are important for successful total knee arthroplasty (TKA). However, the optimal technique for establishing and measuring soft tissue balancing remains unclear. The aim of this study was to analyze the intraoperative medial and lateral gap pattern using digital knee balancer in posterior-stabilized (PS) TKA.MethodsThis study involved 55 patients with medial osteoarthritis who underwent a primary TKA using an image-free navigation system. The extension gap and the flexion gap at 90° knee flexion were assessed using an offset seesaw-type digital balancer. Continuous joint distraction force from 10 lb to 60 lb was applied. Medial gap, lateral gap, and varus angle were measured.ResultsThe medial bone gap difference between extension and flexion was constant regardless of the distraction force from 20 lb to 60 lb. The lateral bone gap was significantly greater than the medial bone gap in extension and flexion from 30 lb to 60 lb (P < 0.05). The varus angle changed depending on the distraction force, especially in flexion. The varus angle in flexion was significantly greater than that in extension from 40 lb to 60 lb (P < 0.05).ConclusionsThe medial bone gap is a reliable indicator unaffected by the distraction force during surgery and is useful for adjusting the medial gap in extension and flexion appropriately to ensure medial stability in PS-TKA. The digital knee balancer and navigation system support both precise gap assessment and surgery.     

Residual varus alignment after total knee arthroplasty increases knee adduction moment without improving patient function: A propensity score-matched cohort study

BackgroundTargeting residual varus alignment in total knee arthroplasty may be functionally beneficial to preoperative varus patients.MethodsBilateral TKA patients were enrolled. According to the postoperative hip-knee-ankle axis, patients were allocated into residual varus (3° ± 1°) alignment group or neutral (0° ± 1°) alignment group. Then, 1:2 propensity score matching was used to match preoperative variables. Finally, matched neutral (n = 45) and varus groups (n = 32) were followed-up for two years and compared. The primary outcome was the Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC). Secondary outcomes were range of motion (ROM), Knee Society knee score and function score, spatiotemporal gait parameters, dynamic alignment, knee flexion angle, knee adduction moment (KAM) and internal knee extension moment.ResultsAt two years after surgery, the mean difference of WOMAC score was 0.3 (95% CI, [? 3.1, 3.7]) between the two groups. All secondary outcomes, except KAM and dynamic alignment, showed no significant difference between the two groups. Residual varus alignment group showed increased KAM and maximum KAM was 19% higher (P = 0.006).ConclusionsResidual varus alignment showed no clinical benefits, and both groups of patients had a functionally identical knee gait biomechanics, except for increased KAM and varus alignment. The authors consider that even in patients with varus alignment, the first principle is still achieving neutral alignment, which is helpful for reducing the KAM.Level of evidenceIII, retrospective cohort study.     

Different targets of mechanical alignment do not improve knee outcomes after TKA

BackgroundAccurate alignment is a basic principle of TKA surgery, but achieving alignment within this target may not translate into superior outcomes after surgery.PurposeTo assess if neutral TKA mechanical alignment was associated with superior knee outcomes and to examine the effect of various aspects of pre-operative and post-operative alignment on knee function.MethodsAnalysis of a database of 444 TKA patients between June 2009 and October 2016. Knee outcomes (WOMAC, AKSS and knee range of motion) were collected before surgery and during follow-up at a minimum of six months.ResultsAnalysis included 444 TKA patients (62% female, mean age 66 years, mean follow-up 23 months). Deformity varied from 21° varus (mean = 7.9, SD = 2.8) to 17° valgus deformity (mean = 7.7, SD = 2.8). Pre-operatively, 101 (23%) knees were in native neutral mechanical alignment, while 278 (63%) were in varus and 65 (15%) were in valgus. Post-operatively, a group of 365 (82%) TKA were found to be in neutral mechanical alignment and a group of 79 (18%) TKA were noted to be ‘Outliers’ (17 [4%] TKA > 3° varus and 62 [14%] TKA > 3° valgus alignment). Restoration of the target of alignment of 0 ± 3° or 0 ± 1°, did not have better functional outcomes scores, range of motion or prosthesis longevity than those in the outlier range.ConclusionNeutral TKA alignment did not appear to be a significant contributing factor to the improvement in knee function in short-medium term follow-up.     

The effect of component alignment on clinical outcomes in fixed bearing unicompartmental knee arthroplasty

BackgroundThe aim of this study is to report component alignment in a series of ZUK fixed bearing unicompartmental knee arthroplasty (UKA) implants and compare this to clinical outcomes.MethodsThe radiographs, Knee Society Scores (KSS) and knee flexion of 223 medial UKAs were evaluated. The following alignment parameters were assessed; coronal and sagittal femoral component angle (c-FCA and s-FCA), coronal and sagittal tibia component angle (c-TCA and s-TCA) and the coronal tibiofemoral angle (c-TFA). Each alignment parameter was grouped at consecutive 2.5° intervals, mean KSS and knee flexion was then compared between the interval groups.Results96.4% of femoral components were between 7.5° of varus and valgus and 95.1% between 7.5° extension and 5° flexion. 89.6% of tibial components were between 7.5° of varus and 2.5° valgus and 97.3% between 2.5° and 15° flexion. There was no significant difference between the KSS or knee flexion between any of the incremental groups of component alignment. Mean c-TFA was 0.2 ± 3.0°, 92.4% were between −5° (varus) and 5° (valgus). KSS were significantly greater for two of the increments with slightly more varus. Linear regression analysis showed there was very weak correlation (R² = 0.1933) between c-TFA and c-TCA.ConclusionsThe results of this study show that fixed bearing UKA components are forgiving to accommodate some variation in tibial and femoral component position without effecting clinical outcome scores or knee flexion. Limb alignment matters more than component position and knees with slight varus tibiofemoral alignment have better clinical scores than those with valgus.     

Limb and component alignment after total knee arthroplasty comparing 28 consecutive iAssist and 28 conventional TKAs: A prospective study

BackgroundThe objective of this study was to assess limb and component alignment after total knee arthroplasty (TKA) on long leg X-rays and to compare the use of iAssist, an accelerometric based computer-assisted device (CAD), with conventional jigs.MethodsWe prospectively recruited 56 consecutive patients undergoing primary unilateral TKA by a single surgeon into this study. In the first 28 patients iAssist navigation system was utilized and in the following 28 conventional jigs were used. The groups were comparable with regard to age, sex distribution, body mass index and preoperative hip–knee–ankle (HKA) angle. Our aim was to restore neutral coronal alignment and a five degree tibial slope.ResultsThe mean postoperative mechanical axis was 179.4° in the CAD group and 180.1° in the conventional group (P = 0.187). There were five TKAs deviating more than three degrees from neutral (18.5%) in the conventional group and none in the CAD group (P = 0.051). The mean femoral mechanical-condyles-angle was significantly closer (P < 0.001) to our target of 90° in the conventional group but contained more outliers (P = 0.67). The sagittal tibial slope was closer (P = 0.047) to our target of 85° in CAD-navigated TKAs with fewer outliers (P < 0.0001). The Oxford Knee Score showed comparable (P = 0.271) and good clinical outcome in both groups. The mean operation time was significantly longer in the CAD group (P < 0.001).ConclusionsThis study shows that the use of iAssist accelerometric CAD facilitates comparable good leg alignment after TKA in the frontal plane and more accurate tibial slope with fewer outliers in the sagittal plane compared with a conventional technique. Our operation time was longer with CAD.     

Characteristic kinematics of floor-sitting activities after posterior-stabilized total knee arthroplasty determined using model-based shape-matching techniques

BackgroundDetailed kinematics of floor-sitting activities after total knee arthroplasty (TKA) have not been well explored. Knee kinematics of cross-legged sitting, seiza-sitting, and side-sitting after TKA were examined to clarify the differences in tibiofemoral kinematics of each activity.MethodsSubjects were 40 knees in 20 osteoarthritic patients who underwent bilateral TKA with a high-flexion fixed-bearing posterior-stabilized prosthesis. Dynamic radiographs of floor-sitting activities were taken, and the knee kinematics were compared among the three activities. The patients were also divided into two groups (possible/easy group and impossible/no-try group) for each activity, and group comparisons were conducted.ResultsThe maximum implant flexion angle was significantly greater in seiza-sitting. In valgus/varus rotation, seiza-sitting demonstrated neutral rotation, while cross-legged sitting showed varus of about 10°, and side-sitting exhibited valgus. In tibial internal/external rotation, seiza-sitting demonstrated a constant rotational angle, while cross-legged sitting showed tibial internal rotation with flexion, and side-sitting exhibited tibial external rotation with flexion. The kinematic pathway during deep flexion illustrated the medial pivot pattern in cross-legged sitting, a small amount of bicondylar rollback in seiza-sitting, and the weak lateral pivot pattern in side-sitting. A greater flexion angle was the important factor for the performance of each floor-sitting activity followed by varus laxity at 10° knee flexion.ConclusionsThis study successfully revealed characteristic kinematic patterns of TKA knees in three floor-sitting activities. Obtaining a greater knee flexion with adequate lateral laxity is the key to enhancing postoperative floor-sitting activities.     

Convincing long-term results independent from the postoperative leg alignment following cementless total knee arthroplasty

BackgroundCementless primary total knee arthroplasty shows numerous advantages compared with cemented implants (e.g., shorter operation time, preservation of the bone stock). Up to now an increasing number of clinical long-term studies exist. Despite this fact, there is no evidence about the influence of the postoperative leg alignment on the results of cementless knee arthroplasty. There is no work on the clinical outcome of the specific implant, which was used in this study (VANGUARD®, ZimmerBiomet). The purpose of this study was to assess the clinical and radiological long-term results after cementless knee arthroplasty in relation to the postoperative mechanical leg alignment.MethodsClinical and radiological results were retrospectively assessed in 83 patients at 10.3 years (ranging from 9.6 to 11.8 years) after implantation. Hip-knee-ankle angle (HKA) was measured, and the patients were separated into a corrected (HKA between three degrees of varus and three degrees of valgus, n = 60) and a varus/valgus (HKA > 3° of varus and valgus, n = 23) group.ResultsUp to the time of the clinical follow-up, three out of 83 patients already underwent a revision surgery due to a deep infection (3.6%). Tegner–Lysholm Knee scale was 89.1 in the corrected group and 88.8 in the varus/valgus group (p = .94). The mean Knee Injury and Osteoarthritis Outcome score (KOOS) was 81.2 in the corrected group and 82.4 in the varus/valgus group (p = .63).ConclusionsResults of this study showed convincing clinical and radiological results after primary cementless knee arthroplasty. Under- or overcorrected postoperative mechanical leg alignments did not influence the long-term clinical results.     

Navigation-based analysis of associations between intraoperative joint gap and mediolateral laxity in total knee arthroplasty

BackgroundNo data have demonstrated how joint gap measured under a distraction force is actually associated with mediolateral laxity evaluated under a varus–valgus force during total knee arthroplasty (TKA). This study aimed to investigate the correlations between them using a navigation system.MethodsA total of 113 primary navigated TKAs were included. After bone resection and soft-tissue balancing, the component gap was measured with a distraction force of 60 N and 80 N for both the medial and lateral compartment (i.e. a total of 120 N and 160 N) at 0°, 10°, 30°, 60°, 90°, and 120° knee flexion. After the final prosthetic implantation and capsule closure, mediolateral laxity under a maximum varus–valgus stress was recorded with image-free navigation at each knee flexion angle. The correlation between joint gap laxity (total differences between component gap and insert thickness in the medial and lateral compartment) and mediolateral laxity was analyzed using Spearman’s rank correlation coefficient.ResultsThe joint gap laxity under both distraction forces showed significant positive correlations with mediolateral laxity at 10°, 30°, 60°, and 90° flexion, whereas no correlation was observed at extension and 120° flexion. The correlations were stronger in gap measurement under 80 N than 60 N at all examined ranges. In patients with body mass indexes (BMIs) ≥ 30 kg/m², the correlation became non-significant.ConclusionIntraoperative joint gap laxity was associated with mediolateral laxity after TKA, especially at mid-flexion angles. The factors weakening the correlations were a lower applied distraction force for gap measurement and a larger BMI.