In vivo kinematic comparison before and after mobile-bearing unicompartmental knee arthroplasty during high-flexion activities

BackgroundMany patients who undergo unicompartmental knee arthroplasty (UKA) have an expectation that their knee flexion would increase following its replacement. Additionally, the survival rate of mobile-bearing UKA (MB-UKA) is high. However, the effect on the patient's kinematics remains unknown. This study aimed to clarify the kinematic effect of MB-UKA knees during high-flexion activities by comparing the in vivo kinematics before and after surgery.MethodsA squatting motion was performed under fluoroscopic surveillance in the sagittal plane before and after MB-UKA. To estimate the spatial position and orientation of the knee, a two-dimensional/three-dimensional registration technique was used. The femoral rotation and varus–valgus angle relative to the tibia and anteroposterior (AP) translation of the medial and lateral side of the femur on the plane perpendicular to the tibial mechanical axis in each flexion angle were evaluated.ResultsRegarding the varus–valgus angle, the preoperative knees indicated a significant varus alignment compared with the postoperative knees from 10° to 60° of flexion. There were no significant differences in the femoral rotation angle, AP translation, and kinematic pathway before and after MB-UKA in the mid-flexion of the range of motion.ConclusionThere were differences between the varus–valgus knee kinematics before and after MB-UKA, from 10 to 60° of flexion, but no difference from midrange of flexion to deep flexion. In addition, the rotational knee kinematics before and after MB-UKA was not significantly different.     

Rotational kinematics differ between mild and severe valgus knees in total knee arthroplasty

BackgroundThere is no consensus regarding femorotibial rotational kinematics in total knee arthroplasty (TKA) for valgus knee deformity. Additionally, whether the degree of valgus deformity influences intraoperative rotational kinematics and postoperative clinical scores remains unclear. The objectives of this study were to investigate whether the valgus angle is associated with intraoperative rotational kinematics in TKA for valgus knee deformity and to examine the relationship between rotational kinematics and postoperative clinical results.Materials and methodsA total of 24 knees with valgus deformity for TKA were included in this study and were divided into two groups depending on the femorotibial angle (FTA); there were 11 knees in the severe valgus group (FTA < 160°) and 13 knees in the mild valgus group (FTA ≥ 160°). Intraoperative femorotibial rotational kinematics from knee extension to flexion were evaluated using an image-free navigation system and postoperative clinical results (range of motion and subjective outcomes) were evaluated 1 year postoperatively. All parameters were compared between the two groups.ResultMild valgus knee showed tibial internal rotation during knee flexion before implantation, whereas severe valgus knee showed tibial external rotation during knee flexion before implantation. The postoperative flexion angle was positively correlated with the tibial internal rotation angle after implantation in the mild valgus group only.ConclusionIntraoperative rotational kinematics before implantation differed between mild and severe valgus knee deformity in TKA. Intraoperative tibial rotation influenced the postoperative knee flexion angle in mild, but not severe, valgus knee deformity. Ideal postoperative rotational kinematics may be different between the two groups and the difference may be taken into consideration in implant selections and surgical techniques.     

Association of knee flexion angle after posterior-stabilized total knee arthroplasty with postoperative tibial external position relative to the femur and the extent of tibial internal rotation from knee extension to flexion

BackgroundThis study evaluated the relationship between preoperative and postoperative knee kinematics, moreover, investigated tibial rotational position and the extent of tibial internal rotation from knee extension to flexion as factors to obtain significant knee flexion after total knee arthroplasty (TKA).MethodsFifty-four patients (60 knees total; 15 males, 16 knees; 39 females, 44 knees) who underwent posterior-stabilized TKA using a navigation system were included. Intraoperative knee kinematics involving tibial rotational position relative to the femur and the extent of tibial internal rotation were examined at two time points: 1) after landmarks registration (pre-TKA) and 2) after skin closure (post-TKA). The relationship between the knee flexion angle at one year postoperatively and intraoperative tibial rotational position, or the extent of tibial rotation among several knee flexion angles calculated with a navigation system were investigated.ResultsThe postoperative knee flexion angle was positively associated with the preoperative flexion angle and intraoperative knee kinematics at post-TKA involving tibial external position relative to the femur at knee extension and the extent of tibial internal rotation from extension to 90° of flexion or to maximum flexion. There was a positive relationship between the extent of tibial internal rotation at pre-TKA and that at post-TKA.ConclusionsThe intraoperative kinematics of the extent of tibial internal rotation at post-TKA was influenced by that at pre-TKA. The greater external position of the tibia relative to the femur at knee extension and the greater extent of tibial internal rotation at post-TKA might lead to good knee flexion angle.     

Intraoperative kinematics of bicruciate-stabilized total knee arthroplasty during high-flexion motion of the knee

BackgroundIt is unknown whether intraoperative kinematics of bicruciate-stabilized total knee arthroplasty (BCS-TKA) are different for different activities. It has also not been established whether intraoperative high-flexion motions correlate with postoperative patient-reported outcome measures (PROMs). We aimed to clarify the intraoperative kinematics of BCS-TKA during high-flexion activities and describe the relationship between intraoperative and postoperative patient-reported outcomes.MethodsWe examined 33 knees from 31 patients who underwent BCS-TKA and measured intraoperative knee kinematics, passive knee flexion, and cross-legged flexion using a navigation system. We also calculated knee flexion, varus-valgus, and rotation angles. As a secondary evaluation, we divided the patients into two clusters based on the PROMs and compared the kinematics between them.ResultsThe valgus moved by 1.3 ± 1.3° beyond 90° knee flexion during passive flexion. In contrast, during cross-legged flexion, the varus moved by 4.6 ± 5.1° beyond 30° flexion. This indicated significantly increased varus alignment in the cross-legged flexion as compared with passive flexion. Beyond 60° of flexion, the femur displayed 8.8 ± 4.8° of external rotation relative to the tibia. In cross-legged flexion, the femur displayed 9.2 ± 6.5° of external rotation relative to the tibia beyond 45° of flexion. At 90° of flexion, the cross-legged knees rotated more externally. There were no significant postoperative differences between the high- and low-score clusters.ConclusionThe intraoperative knee kinematics after BCS-TKA during high-flexion motions differed depending on the performance of an individual. This will be useful for physicians who might recommend BCS-TKA to new patients.     

In vivo kinematic analysis of posterior-stabilized total knee arthroplasty for the valgus knee operated by the gap-balancing technique

BackgroundMost in vivo kinematic studies of total knee arthroplasty (TKA) report on the varus knee. The objective of the present study was to evaluate in vivo kinematics of a posterior-stabilized fixed-bearing TKA operated on a valgus knee during knee bending in weight-bearing (WB) and non-weight-bearing (NWB).MethodsA total of sixteen valgus knees in 12 cases that underwent TKA with Scorpio NRG PS knee prosthesis and that were operated on using the gap balancing technique were evaluated. We evaluated the in vivo kinematics of the knee using fluoroscopy and femorotibial translation relative to the tibial tray using a 2-dimensional to 3-dimensional registration technique.ResultsThe average flexion angle was 111.3° ± 7.5° in WB and 114.9° ± 8.4° in NWB. The femoral component demonstrated a mean external rotation of 5.9° ± 5.8° in WB and 7.4° ± 5.2° in NWB. In WB and NWB, the femoral component showed a medial pivot pattern from 0° to midflexion and a bicondylar rollback pattern from midflexion to full flexion. The medial condyle moved similarly in the WB condition and in the NWB condition. The lateral condyle moved posteriorly at a slightly earlier angle during the WB condition than during the NWB condition.ConclusionsWe conclude that similar kinematics after TKA can be obtained with the gap balancing technique for the preoperative valgus deformity when compared to the kinematics of a normal knee, even though the magnitude of external rotation was small. Level of evidence: IV.     

Insufficient lateral joint laxity after bicruciate-retaining total knee arthroplasty potentially influences kinematics during flexion: A biomechanical cadaveric study

BackgroundSoft tissue balancing in bicruciate-retaining (BCR) total knee arthroplasty (TKA) is a challenge that must be overcome to achieve excellent clinical outcomes. However, the optimal degree of joint laxity has yet to be clarified. This cadaveric study sought to examine joint laxity after BCR TKA using a navigation system.MethodsKnee joint laxity was quantified using an image-free navigation system in 8 intact fresh frozen cadavers under three conditions: the native knee, BCR TKA knee, and BCR TKA knee after anterior cruciate ligament resection. Rotational kinematics in the BCR TKA knee during flexion were compared according to whether joint laxity was increased or decreased.ResultsKnee joint laxity after BCR TKA under varus-valgus movement, anterior translation, and internal-external rotation loadings was similar to that of the native knee. However, lateral joint laxity was decreased during flexion in some cases. BCR TKA-treated knees with decreased lateral joint laxity at 90° of flexion demonstrated more limited tibial internal rotation in deep flexion than the native knee (p < 0.05). The loss of internal rotation in deep flexion was partly recovered by using a lateral insert with a posterior slope of +3°.ConclusionsRestoring optimal joint laxity was not always straightforward in BCR TKA if the 4 ligaments were preserved. Lateral joint laxity was potentially decreased in BCR TKA and may result in kinematic conflict during flexion. Surgeons should be aware of the need to achieve sufficient lateral joint laxity in this type of BCR TKA.     

Bi-cruciate substituting total knee arthroplasty provides varus–valgus stability throughout the midflexion range

Background

Proper soft tissue balance is crucial for a successful clinical outcome after total knee arthroplasty (TKA). Bi-cruciate substituting (BCS)-TKA has been developed to more closely approximate normal knee characteristics. The purpose of the present study was to evaluate midflexion laxity before and after BCS-TKA using a navigation system, and assess the correlation between intraoperative laxity and the maximum flexion angle after surgery.

In vivo weight-bearing kinematics with medial rotation knee arthroplasty

Knee arthroplasties are designed to accommodate flexion, axial rotation and anteroposterior (AP) translation. Axial rotation during extension varies, with some rotating platform devices allowing unrestricted rotation while some conforming fixed-bearing designs almost none. The purpose of this study was to examine in vivo kinematics of a fixed-bearing medial rotation-type arthroplasty (MRK) during weight-bearing activities. Fifteen knees with a medial pivot TKA design were studied during step and pivot activities using lateral fluoroscopy and model-image registration. Average knee kinematics during the step activity showed little AP translation or rotation from 0°–100° flexion. During the pivot activity, the mean tibial internal rotation in individual knees was 7° (3°–19°). Mean condylar translations for individual knees were 3 mm medially and 5 mm laterally. The medial pivot prosthesis design provides anteroposterior stability during demanding activities, and exhibits a medial pivot motion pattern when subjected to twisting.     

Anterior cruciate ligament repair versus reconstruction: A kinematic analysis

BackgroundThe purpose of this study was to compare the biomechanical properties of an anterior cruciate ligament (ACL) anatomic repair of a true femoral avulsion to an anatomic ACL reconstruction. It was hypothesized that the ACL repair and ACL reconstruction would have comparable biomechanical behavior when compared to the native knee.MethodsTen paired fresh-frozen cadaveric knees (n = 20) were used to investigate knee kinematics when an anterior drawer force, varus, valgus, internal, and external rotational moment were applied at 0, 15, 30, 45, 60, and 90 degrees of flexion. Displacement and rotation were recorded in the following conditions: ACL-intact, ACL-deficient, and ACL-repaired vs reconstructed.ResultsSectioning of the ACL significantly increased anterior tibial translation (0°, 15°, 30° and 45°) compared to the intact state. The mean anterior displacement difference from intact was lower in the ACL-repaired knees compared to reconstructed knees at 30° and 90°. There were no significant differences between conditions in varus, valgus, internal, or external rotations.ConclusionACL repair and ACL reconstruction procedures restored knee anterior tibial translation in matched paired specimens. There were no differences in valgus, varus, internal, or external rotation. Although, ACL-repaired knees (avulsion model) demonstrated less anterior tibial translation when compared to ACL-reconstructed knees, this difference was less than one millimeter. Based on the findings of this study, repair and reconstruction procedures both restored anterior tibial translation in matched-pair specimens. This suggests that the initial functionality of both techniques is similar and that further clinical studies are needed to compare the long-term stability.     

Laxity and contact forces of total knee designed for anatomic motion: A cadaveric study

Background

Total knee designs that attempt to reproduce more physiological knee kinematics are gaining attention given their possible improvement in functional outcomes. This study examined if a total knee designed for anatomic motion, where the soft tissue balancing was intended to replicate anatomical tibiofemoral contact forces, can more closely reproduce the laxity of the native knee.

Comparison of the joint laxity of total knee arthroplasty evaluated by the distraction force and the varus–valgus force

BackgroundComponent gap (CG) measurement help surgeons evaluate intraoperative soft-tissue balance. One technique is measuring the CG using tensioner devices with distraction force. Another is to evaluate the laxity under a varus–valgus force using navigation or robotics. The aim was to compare the JL evaluated by CG and varus–valgus force between the different types of total knee arthroplasties.MethodsForty-three bi-cruciate stabilized (BCS) knees and 33 bi-cruciate retaining (BCR) knees were included. After bone resection and soft tissue balancing, the CG was measured and after the final implantation and capsule closure, JL under a maximum varus–valgus stress was recorded with navigation. JL evaluated by the CG (JLCG) was defined as CG minus selected thickness of the tibial component and JL under varus–valgus force (JLVV) was defined as difference between varus–valgus angles without stress and maximum varus–valgus angles under varus–valgus force. The evaluations were performed at flexions of 10°, 30°, 60° and 90°.ResultsAlthough JLCGs of lateral compartment of BCS were larger than those of BCR, no difference was found between JLVVs of BCS and BCR. Although JLCGs of lateral compartment did not change at each knee flexion angle in both BCS and BCR, JLVVs of lateral compartment increased by 3° from 10° to 90° knee flexion.ConclusionJLVVs of BCS and BCR were equivalent, whereas BCS showed larger JLCGs of lateral compartment. JLVVs of lateral compartment increased by 3° in the range from 10° to 90° knee flexion whereas JLCGs remained stable.     

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.     

In vivo kinematics of a newly updated posterior-stabilised mobile-bearing total knee arthroplasty in weight-bearing and non-weight-bearing high-flexion activities

BackgroundThe purpose of this study was to clarify the in vivo kinematics of a newly updated posterior-stabilised (PS) mobile-bearing total knee arthroplasty during high-flexion activities in weight-bearing (WB) and non-weight-bearing (NWB) conditions. The hypothesis was that the kinematics would differ between the WB and NWB conditions, and the kinematics would be affected by the WB condition.MethodsThe kinematics of 19 knees were investigated under fluoroscopy during squatting (WB) and active-assisted knee flexion (NWB) with two- and three-dimensional registration technique. Accordingly, the range of motion, anteroposterior (AP) translation of the medial and lateral contact points, axial rotation of the femoral component relative to the tibial component, and kinematic pathway were evaluated.ResultsThere was no difference in the knee’s range of motion between the WB and NWB conditions. The medial AP translation of the femur did not differ in each flexion angle between WB and NWB conditions except for flexions of 70°. There was no difference in the lateral AP translation of the femur at all tested flexion angles between the WB and NWB conditions. The external femoral rotation and the medial pivot motion were observed throughout all flexion angles in WB conditions. The clinical relevance is that this implant could produce ideal medial AP stability and medial pivot motion.ConclusionThe medial AP translation of the femur was stable for AP direction when it was in both WB and NWB conditions. In WB conditions, the medial pivot motion was observed throughout all flexion angles.Level of Evidence: III.     

Lateral subvastus lateralis versus medial parapatellar approach for total knee arthroplasty: A cadaveric biomechanical study

BackgroundThe standard of care for total knee arthroplasty (TKA) is a medial parapatellar approach (MPA). We aimed to study a novel lateral subvastus lateralis approach (SLA), which offers the benefit of keeping the extensor mechanism and medial soft tissues intact. To ensure the approach could be used safely in vivo, a biomechanical study was performed to assess whether the joint kinematics would be preserved after performing a TKA.MethodsA biomechanical study was conducted using 14 fresh-frozen cadaveric knees, with seven specimens each for the MPA and SLA. After a single radius, cemented cruciate retaining TKA was performed, specimens were tested on a VIVO joint motion simulator to measure and compare anterior/posterior, internal/external, and varus/valgus kinematics and laxity.ResultsThere was no significant difference in joint kinematics or laxity between the SLA and MPA groups.ConclusionBoth the SLA and MPA offer similar knee kinematics and laxity based on a cadaveric model. Although the surgical approach was different, inherently releasing different ligaments, both approaches resulted in a stable knee. This suggests that either approach will enable the surgeon to provide a stable knee, and that the implant itself may contribute a significant portion of the knee’s kinematics.     

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.     

Variability in static alignment and kinematics for kinematically aligned TKA

Background

Total knee arthroplasty (TKA) significantly improves pain and restores a considerable degree of function. However, improvements are needed to increase patient satisfaction and restore kinematics to allow more physically demanding activities that active patients consider important. The aim of our study was to compare the alignment and motion of kinematically and mechanically aligned TKAs.

Patellar resurfacing has minimal impact on in vitro tibiofemoral kinematics during deep knee flexion in total knee arthroplasty

BackgroundWhile patellar resurfacing can affect patellofemoral kinematics, the effect on tibiofemoral kinematics is unknown. We hypothesized that patellar resurfacing would affect tibiofemoral kinematics during deep knee flexion due to biomechanical alteration of the extensor mechanism.MethodsWe performed cruciate-retaining TKA in fresh-frozen human cadaveric knees (N = 5) and recorded fluoroscopic kinematics during deep knee flexion before and after the patellar resurfacing. To simulate deep knee flexion, cadaver knees were tested on a dynamic, quadriceps-driven, closed-kinetic chain simulator based on the Oxford knee rig design under loads equivalent to stair climbing. To measure knee kinematics, a 2-dimensional to 3-dimensional fluoroscopic registration technique was used. Component rotation, varus-valgus angle, and anteroposterior translation of medial and lateral contact points of the femoral component relative to the tibial component were calculated over the range of flexion.ResultsThere were no significant differences in femoral component external rotation (before patellar resurfacing: 6.6 ± 2.3°, after patellar resurfacing: 7.2 ± 1.8°, p = 0.36), and less than 1° difference in femorotibial varus-valgus angle between patellar resurfacing and non-resurfacing (p = 0.01). For both conditions, the medial and lateral femorotibial contact points moved posteriorly from 0° to 30° of flexion, but not beyond 30° of flexion. At 10° of flexion, after patellar resurfacing, the medial contact point was more anteriorly located than before patellar resurfacing.ConclusionDespite the potential for alteration of the knee extensor biomechanics, patellar resurfacing had minimal effect on tibiofemoral kinematics. Patellar resurfacing, if performed adequately, is unlikely to affect postoperative knee function.     

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.     

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.