Three-dimensional in vivo dynamic motion analysis of anterior cruciate ligament-deficient knees during squatting using geometric center axis of the femur

Anterior cruciate ligament-deficient knee induces a posterior location of the femur in the medial compartment during squatting

Although an anterior cruciate ligament (ACL) deficiency induces knee osteoarthritis, particularly in the medial compartment, the kinematics remains partially unclear. This study investigated the in vivo knee kinematics of ACL-deficient and normal knees by comparing them during squatting. This prospective comparative study included 17 ACL-deficient knees and 20 normal knees. The kinematics was investigated under fluoroscopy using a two- to three-dimensional registration technique. The anteroposterior (AP) translation of the medial and lateral sides of the femur, axial rotation of the femur relative to the tibia, and kinematic pathways were evaluated and compared. At first, the medial AP position of the femur translated anteriorly from 0° to midflexion, afterward it translated posteriorly in both ACL-deficient and normal knees. However, the medial AP position of the femur in the ACL-deficient knees was located significantly posteriorly compared with normal knees at 0-110° flexion. The lateral AP position of the femur translated posteriorly from 0° to 150° flexion in both ACL-deficient and normal knees. The lateral AP position of the femur in the ACL-deficient knees was located significantly posteriorly compared with that in normal knees at 0-10° flexion. The femur showed external rotation from 0° to 150° flexion in both ACL-deficient and normal knees. A medial pivot motion and subsequent bicondylar rollback were observed in both knees in the kinematic pathway. In conclusion, the AP position of the femur relative to the tibia was altered due to ACL deficiency, particularly in the medial compartment.

Four-dimensional computed tomographic analysis of screw home movement in patients with anterior cruciate ligament deficient knee - a 3D-3D registration technique

OBJECTIVE

The tibia externally rotates to the femur during the last 20° of the knee extension motion. This kinematic phenomenon is well known as screw home movement (SHM). The purpose was to clarify the SHM in anterior cruciate ligament deficient (ACLD) knee using four-dimensional computed tomography (4DCT).

MATERIALS AND METHODS

Six patients with a unilateral isolated ACLD knee participated. In the static position, CT scan of the both limbs of the femur and tibia were performed. Then, 4DCT was performed around knee. In the CT gantry, subjects were positioned in supine position with 45° of knee flexion on a triangle pillow and were asked to extend the knee to full extension within 10 s on each limb. The CT data were accumulated in digital imaging and communication in medicine (DICOM) data format. From the static CT and 4DCT DICOM data, three-dimensional surfaces of the knee joint were reconstructed. The whole tibia surface was matched into the partial tibia surface of that frame using 3D-3D registration technique. After the assessment of coordination system of the whole leg, knee flexion, abduction, and external rotation angle were calculated.

RESULTS

Knee external rotation angle was significantly smaller on the ACLD side than on the contralateral unaffected side in 0-15° of knee flexion (P < 0.05 in 0, 5, 10, and 15 degrees), while the angle was similar during 15-60° of knee flexion.

CONCLUSION

The absence of SHM in ACLD knee was detected using 3D-3D registration technique based on 4DCT.

Translation and rotation analysis based on stress MRI for the diagnosis of anterior cruciate ligament tears

BACKGROUND

Due to the increasing need for a detailed biomechanical analysis of anterior cruciate ligament (ACL) lesions, the aim of the study was to develop a method of direct measurement of the three-dimensional tibial translation and rotation based on stress MRI.

METHODS

For the purpose of the study, thirty patients with acute ACL rupture and 17 healthy control subjects were selected. Based on clinical examination, they were qualified for MRI examination using the Arthroholder Device prototype to perform anterior tibial translation. Each examination was performed at 30° of knee flexion, initially without tibia translation and then using the force applied to the calf of 80 N. The femur and tibia were separately registered using rigid local SimpleITK landmark refinement; translation and rotation parameters were then calculated using the 3D transformation algorithms. The significance level was set at 0.05.

RESULTS

Initially, the device and method for obtaining the parameters of the 3D translation and rotation were validated. The pooled Standard Deviation for translation parameters was 0.81 mm and for rotation parameters 0.87°. Compared to the control group, statistically significant differences were found in parameters such as Anterior Shift [(median ± interquartile range) 3.89 mm ±6.55 vs. 0.90 mm ±2.78, P=0.002238] and External Rotation (-0.55° ±3.88 vs. -2.87° ±2.40, P=0.005074). Statistically significant correlations were observed in combined groups between Anterior Shift and parameters such as External Rotation (P=0.001611), PCL Tibial Attachment Point (pPCL) Anterior Shift (<0.000001), Rolimeter Measurement (P=0.000016), and Side-to-Side Difference (SSD) (P=0.000383). A significant statistical correlation was also observed between External Rotation and parameters such as Rolimeter (P=0.02261) and SSD (P=0.03458).

CONCLUSIONS

The analysis of the anterior tibia translation using stress MRI and the proposed three-dimensional calculation method allows for a detailed analysis of the tibial translation and rotation parameters. The correlations showed the importance of external rotation during anterior tibial translation.

Postoperative femoral anteroposterior position while standing correlates with the posterior tibial slope and posterior femoral condylar offset in medial pivot total knee arthroplasty

BACKGROUND

After total knee arthroplasty (TKA), the femur tends to be located posteriorly under weight-bearing (WB) conditions, and a paradoxical femoral anterior motion occurs, leading to joint instability.

OBJECTIVE

We aimed to clarify factors which affect the postoperative femoral anteroposterior position relative to the tibia under WB conditions (A-P position) in medial pivot (MP) TKA.

METHODS

Among 126 knees (81 women) with primary TKA using MP prosthesis for varus osteoarthritic knees, 70 knees had cruciate-retaining inserts (CR) with the reduced conformity and 56 knees had cruciate-substituting inserts (CS) with the full conformity. Using the three-dimensional (3D) assessment system, the associations between the A-P position and the factors including pre- and postoperative lower extremity alignment, component positions, and posterior femoral condylar offset (PCO), were assessed regarding the type of inserts.

RESULTS

Significant correlations were seen between the A-P position and posterior tibial slope (PTS), medial PCO, and lateral PCO. Regarding the difference between the two inserts, the PTS, medial PCO, and lateral PCO significantly correlated with the A-P position in the CR, but only the PTS correlated in the CS.

CONCLUSIONS

The increased PTS and decreased PCO were the dominant factors for the A-P position in MP TKA.

New evaluation indices for rotational knee angles in standing anteroposterior knee radiographs

BACKGROUND

Identifying the time course of rotational knee alignment is crucial for elucidating the etiology in knee osteoarthritis.

OBJECTIVE

The aim of this study was to propose new rotational indices for calculating the change in relative rotational angles between the femur and tibia in standing anteroposterior (AP) radiographs.

METHODS

Forty healthy elderly volunteers (20 women and 20 men; mean age, 70 ± 6 years) were assessed. The evaluation parameters were as follows: (1) femoral rotational index: the distance between the sphere center of the medial posterior femoral condyle and the lateral edge of the patella, and (2) tibial rotational index: the distance between the medial eminence of the tibia and the lateral edge of the fibula head. The indices were standardized by the diameter of the sphere of the medial posterior femoral condyle. This study (1) identified the relationship between changes in rotational indices and the simulated rotational knee angles in the standing position, (2) proposed a regression equation for the change in relative rotational angles between the femur and tibia in standing AP radiographs, and (3) verified the accuracy of the regression equation.

RESULTS

The rotational indices increased in direct proportion to simulated rotational knee angles (femoral index: r > 0.9,p < 0.0001; tibial index: r > 0.9, p < 0.0001). Based on the results, the regression equation with the accuracy of 0.45 ± 0.26° was determined.

CONCLUSIONS

The proposed regression equations can potentially predict the change in relative rotational angles between the femur and tibia in a pair of standing AP radiographs taken at different dates in longitudinal studies.

Association between the toe angle and bony factors in the transverse plane for osteoarthritic knees compared with healthy knees

BACKGROUND

The association between the toe angle and bony rotational factors is critical to explain issues related to the onset and progression of knee osteoarthritis (OA).

OBJECTIVE

The study aimed to clarify the association between the toe angle and each of the femoral and tibial transvers direction relative to gait direction, rotational knee alignment, and bony torsional deformity for the subjects with knee OA.

METHODS

This study evaluated 58 knees in 24 healthy elderly (72 ± 5 years) and 34 varus knee OA (72 ± 6 years). A three-dimensional (3D) assessment system was used on 3D models and biplanar long-leg radiographs with the toe angle reflecting gait direction, applying a 3D-to-2D image registration technique. The main parameters on the transverse plane were: (1) toe angle, (2) transverse direction of the femur and tibia relative to the gait direction, (3) femoral neck anteversion, (4) condylar twist angle, (5) tibial torsion, and (6) rotational knee alignment.

RESULTS

The alignment parameters, except for the tibial transverse direction, were different between healthy and osteoarthritic knees. In knee OA, the femoral neck anteversion - femoral transverse direction (p = 0.001), femoral transverse direction - tibial transverse direction (p < 0.001), and tibial transverse direction - toe angle (p < 0.001) were associated.

CONCLUSIONS

The osteoarthritic knees showed that the femoral neck anteversion was associated with the femoral transverse direction, which determined the tibial transverse direction by adjusting the rotational knee alignment, leading to the toe angle.

Validation of a portable marker-based motion analysis system

BACKGROUND

The Opti_Knee system, a marker-based motion capture system, tracks and analyzes the 6 degrees of freedom (6DOF) motion of the knee joint. However, the validation of the accuracy of this gait system had not been previously reported. The objective of this study was to validate and the system. Two healthy subjects were recruited for the study.

METHODS

The 6DOF kinematics of the knee during flexion-extension and level walking cycles of the knee were recorded by Opti_Knee and compared to those from a biplanar fluoroscopy system. The root mean square error (RMSE) of knee kinematics in flexion-extension cycles were compared between the two systems to validate the accuracy at which they detect basic knee motions. The RMSE of kinematics at key events of gait cycles (level walking) were compared to validate the accuracy at which the systems detect functional knee motion. Pearson correlation tests were conducted to assess similarities in knee kinematic trends between the two systems.

RESULTS

In flexion-extension cycles, the average translational accuracy (RMSE) was between 2.7 and 3.7 mm and the average rotational accuracy was between 1.7 and 3.8°. The Pearson correlation of coefficients for flexion-extension cycles was between 0.858 and 0.994 for translation and 0.995-0.999 for angles. In gait cycles, the RMSEs of angular knee kinematics were 2.3° for adduction/abduction, 3.2° for internal/external rotation, and 1.4° for flexion/extension. The RMSEs of translational kinematics were 4.2 mm for anterior/posterior translation, 3.3 mm for distal/proximal translation, and 3.2 mm for medial/lateral translation. The Pearson correlation of coefficients values was between 0.964 and 0.999 for angular kinematics and 0.883 and 0.938 for translational kinematics.

CONCLUSION

The Opti_Knee gait system exhibited acceptable accuracy and strong correlation strength compared to biplanar fluoroscopy. The Opti _Knee may serve as a promising portable clinical system for dynamic functional assessments of the knee.

Intraoperative rotational kinematics and its influence on postoperative clinical outcomes differ according to age in Unicompartmental knee Arthroplasty

Background

Although Oxford unicompartmental knee arthroplasty (UKA) is used in patients of wide age ranges, there is no clear information regarding the age differences in terms of intraoperative femorotibial rotational kinematics and its influence on clinical outcomes. Therefore, this study was conducted to examine the age differences in terms of intraoperative rotational kinematics and postoperative clinical outcomes and to analyze their relationship with classification according to the age group.

Methods

We investigated 111 knees of patients who underwent Oxford UKA using a navigation system and divided them into two groups: elderly (aged ≥75 years; 48 knees) and nonelderly (aged < 75 years; 63 knees). Intraoperative tibial internal rotational angles relative to the femur during passive knee flexion were measured using a navigation system, and clinical outcomes were evaluated using knee range of motion, the Knee Injury and Osteoarthritis Outcome Score (KOOS), and the Knee Society Functional Score at 2 years postoperatively. The relationships between intraoperative tibiofemoral rotational angles and clinical outcomes were also evaluated in the two groups.

Results

The intraoperative tibial internal rotational angle relative to the femur during knee flexion was significantly larger in the nonelderly group (13.5°) than in the elderly group (9.0°). The intraoperative tibial internal rotational angle showed a positive correlation with the pain subscale of KOOS only in the nonelderly group.

Conclusion

Intraoperative rotational kinematics and its influence on clinical outcomes were different between elderly and nonelderly patients, and the tibial internal rotational angle could be a more important factor for successful UKA in nonelderly patients.

Lower limb kinematics of single-leg squat performance in patients with anterior cruciate ligament deficiency

[Purpose] This study investigated the parameters that characterize the knee, hip, and pelvic kinematics during a single-leg squat in preoperative anterior cruciate ligament rupture injury. [Participants and Methods] Overall, 15 patients with unilateral anterior cruciate ligament deficiency were enrolled in this study. For each single-leg squat, data from two-dimensional video cameras and three-dimensional motion analysis were collected. Measurement indices included the articular angles of the knee, hip, and trunk. The anterior cruciate ligament-injured leg was compared with the uninjured leg. [Results] The maximum knee valgus and flexion angles during a single-leg squat were smaller in the injured leg than in the uninjured leg. During the single-leg squat, the effect of "compensatory mechanisms" appeared as knee valgus and flexion movements. In particular, the knee valgus angle decreased in the anterior cruciate ligament-injured leg compared to that in the uninjured leg. [Conclusion] This phenomenon suggests that it is possible to utilize recurrence prevention training for anterior cruciate ligament injury.

Articular surface of the medial proximal tibia is aligned parallel to the ground in three-dimensional space under weight-bearing conditions in healthy and varus osteoarthritic knees

PURPOSE

To test the hypothesis that an inclined articular surface on the medial proximal tibia is aligned more parallel to the ground in three-dimensional (3D) space under weight-bearing (WB) conditions (parallel phenomenon) than under non-WB (NWB) conditions in healthy and varus osteoarthritic knees.

METHODS

We examined 55 healthy knees (26 women, 29 men; mean age, 70 ± 6 years) and 108 varus osteoarthritic knees (66 women, 16 men; mean age, 74 ± 7 years). For the evaluation under WB conditions, a 3D assessment system was used on biplanar long-leg radiographs and 3D bone models using a 3D-to-2D image registration technique. In addition, the least square method was used to determine the approximation plane. The angles between the normal vector for the approximation plane of an articular surface on the medial proximal tibia and each axis of the tibial or world coordinate system were calculated.

RESULTS

Morphologically, the inclination of the approximation plane was steeper in osteoarthritic knees than in healthy knees (p < 0.0001). The approximation plane was aligned more parallel to the ground under WB conditions than under NWB conditions in healthy (p < 0.0001) and osteoarthritic knees (p < 0.0001).

CONCLUSIONS

The parallel phenomenon in the medial proximal tibia was confirmed for healthy and varus osteoarthritic knees. The medial proximal tibia plays an important role in the parallel phenomenon, assumingly associated with varus alignment and varus thrust. The inclination of the medial proximal tibia may become a new parameter for imaging investigations.

LEVEL OF EVIDENCE

III.

Functionally Oriented Alignment of the Lower Extremity Reflecting the Direction of Gait for Healthy Elderly, Knee Osteoarthritis, and Total Knee Arthroplasty Subjects

Purpose

The objective of this study was to evaluate the functional lower extremity alignment based on both position and motion [functionally oriented alignment (FOA)] of the knee in healthy elderly, varus osteoarthritis (OA), and total knee arthroplasty (TKA) subjects.

Methods

This study evaluated 87 knees in 24 healthy elderly (72 ± 5 years), 39 varus OA (72 ± 6 years), and 24 TKA (75 ± 4 years) subjects. A 3D assessment system was used on 3D models and biplanar long-leg radiographs with the toe angle reflecting gait direction, by applying a 3D-to-2D image registration technique. In the world coordinate system, the y-, z-, and x-axes were defined as gait direction, gravity direction, and the cross product of y- and z-axes, respectively. The parameters were: (a) coronal inclination, sagittal inclination, and transverse direction of the femur and tibia relative to the ground and (b) the difference between the yz-plane of the world coordinate system (functional plane) and the yz-plane of the femoral or tibial coordinate system (anatomical plane).

Results

The femur had more medial and posterior inclination and the tibia had more lateral and anterior inclination in osteoarthritic knees as compared to healthy knees, and TKA knees had inclinations similar to healthy knees. Rotation was similar or different in the anatomical and functional planes among the subjects with the healthy, knee OA, and TKA.

Conclusions

The association between the anatomical and functional planes and the position of each bone relative to gravity varied depending on the condition of the knees.

Level of Evidence: Level of III

Length of anterior cruciate ligament affects knee kinematics and kinetics using a musculoskeletal computer simulation model

Introduction

The tension of anterior cruciate ligament (ACL) graft has an important role in antero-posterior (AP) and rotational stability of the knee. The purposes of this study were to analyze the kinematics and kinetics of normal knee models with loose and tight ACL tension, and to evaluate the effect of the tension of ACL on knee kinematics and kinetics.

Materials and methods

Slack and tight ACL models were constructed in a musculoskeletal computer simulation. The effect of ACL tension on kinematics, and femorotibial contact force during various activities was analyzed.

Results

During stair descent activity in the slack ACL models, the lateral femoral condyles were positioned posterior, and more external rotation of the femur was observed in comparison with the normal model. The contact forces at the lateral compartment in the tight models increased during all activities, and the tension of the medial collateral ligament (MCL) in the slack models increased during the stair descent activity, compared with the normal knee model.

Conclusion

AP and rotational instability and excessive MCL tension were observed in the ACL slack knees especially during stair descent movement, whereas the tibiofemoral contact force of the lateral compartment increased in the tight ACL knees.

A comparative study of weight-bearing and non-weight-bearing 3-dimensional lower extremity alignment in knee osteoarthritis

BACKGROUND

Lower extremity alignment is an important variable with respect to the development and progression of knee osteoarthritis. It is very essential for the preoperative planning of realignment surgeries such as total knee arthroplasty and high tibial osteotomy. Nevertheless, there have been no reports comparing 3D lower extremity alignment between weight-bearing upright and non-weight-bearing horizontal states in osteoarthritic knees in the same subject. Therefore, we determined whether the alignment of the lower extremity in the weight-bearing upright state differed from that in the non-weight-bearing horizontal or supine position in patients with knee osteoarthritis.

METHODS

Adduction-abduction, flexion-extension, and rotational angle of osteoarthritic knees were assessed in weight-bearing upright and non-weight-bearing supine positions. Knee alignment in the supine position was determined from preoperative computed tomography data. In the weight-bearing upright state, alignment was determined using a technique that utilized 2D-3D image-matching with biplanar computed radiography and 3D bone models of the complete lower extremity rebuilt using computed tomography-based information.

RESULTS

We assessed 81 limbs from osteoarthritic knee patients (74 women, 7 men; mean age 75.3 years, range 59-86 years). In the coronal plane, there were varus deformities in both the supine and standing positions, while there was flexion in both the supine upright state and position at the sagittal plane. In the axial plane, the rotation of the tibia to the femur was neutral in the supine position and internal in the upright state.

CONCLUSION

Patient position significantly affects lower extremity alignment in osteoarthritic knees. This study provides important data regarding the preoperative evaluation of realignment surgery in total knee arthroplasty and high tibial osteotomy. We believe that these results are an important contribution to the knowledge regarding knee osteoarthritis.

Effect on inclined medial proximal tibial articulation for varus alignment in advanced knee osteoarthritis

BACKGROUND

The inclination of the medial compartment of the proximal tibia (MCT) is assumed to be a critical factor for varus alignment in advanced knee osteoarthritis (OA). This study was aimed at investigating; (1) whether the inclination of MCT is aligned parallel to the ground under weight-bearing (WB) conditions; (2) whether this is associated with the change in alignment and the relative position between the bones; and (3) whether the tibia or femur mainly contributes to the changes.

METHODS

We examined 102 knees (84 women, 18 men; mean 75 years). A three-dimensional (3D) assessment system was applied on biplanar whole lower extremity radiographies using 3D-to-2D image registration technique. The evaluation parameters were 1) MCT angle, 2) femorotibial angle (FTA), 3) medial-lateral femoral location to the tibia (M-L femoral location), 4) WB line passing point, and 5) tibial position to WB line (tibial position) and 6) femoral postion to WB line (femoral position). Each parameter was evaluated in non-WB and WB conditions, and the differences (Δ-parameters).

RESULTS

MCT angle in the world coordinate system was larger than that in the tibial coordinate system (p <  0.0001). ΔMCT angle was correlated with ΔFTA (p = 0.002) and ΔM-L femoral location (p = 0.004). The tibial position was the more dominant factor for ΔMCT angle (p = 0.001), ΔFTA (p <  0.0001), and ΔWB line passing point (p <  0.0001) .

CONCLUSIONS

The inclination in MCT was aligned parallel to the ground under WB conditions (tibial parallel phenomenon). The parallel phenomenon was associated with the change of alignment and the relative position between the bones in the coronal plane. These phenomena were produced mainly by the tibia, not the femur.

LEVEL OF EVIDENCE

Level IV.

Correlation between posterior tibial slope and sagittal alignment under weight-bearing conditions in osteoarthritic knees

INTRODUCTION

Posterior tibial slope (PTS) and sagittal alignment are important factors in the etiology of knee osteoarthritis and knee surgery. Clinically, sagittal alignment, which indicates flexion contracture of the knee, contributes to knee function in weight-bearing (WB) conditions. PTS and sagittal alignment under WB conditions in varus osteoarthritic knees are presumed to affect each other, but their association remains unclear. In this study, we aimed to clarify the association.

MATERIAL AND METHODS

In total, 140 osteoarthritic varus knees were investigated. Under WB conditions, a three-dimensional (3D) alignment assessment system was applied via biplanar long-leg X-rays, using 3D-to-2D image registration technique. The evaluation parameters were as follows: 1) 3D mechanical flexion angle (3DMFA) in regards to sagittal alignment, 2) passing point in the WB line (PP), and 3) medial and lateral PTS.

RESULTS

The medial and lateral PTS showed a positive correlation with 3DMFA and PP, respectively (medial PTS-3DMFA, p = 0.001; medial PTS-PP, p < 0.0001; lateral PTS-3DMFA, p < 0.0001; lateral PTS-PP, p = 0.002). The flexion contracture group with 3DMFA >5° demonstrated greater PTS than non-flexion contracture group (medial PTS, p = 0.006; lateral PTS, p = 0.006).

CONCLUSIONS

Both medial and lateral PTS were correlated with sagittal alignment under WB conditions and were larger in the flexion contracture group. This finding can explain the function to take the load articular surface parallel to the ground for holding the balance in WB conditions in the sagittal plane for osteoarthritic knees. Moreover, surgeons may be required to decrease the PTS during knee arthroplasty to restore full extension in knees of patients with fixed flexion contracture.

Contribution of sex and body constitution to three-dimensional lower extremity alignment for healthy, elderly, non-obese humans in a Japanese population

BACKGROUND

Humans support their bodies exclusively by vertical balance in bipedal locomotion, and the body, especially the lower extremity, generally changes with age. Sex and body constitution are assumed to be associated with lower extremity alignment, but this association remains to be elucidated. This study sought to clarify this association in healthy, elderly, non-obese humans in a Japanese population.

METHODS

The present study investigated 55 healthy volunteers (mean age: 70 ± 6 years). A 3D extremity alignment system was applied under weight-bearing conditions on biplane long lower extremities X-rays using a 3D-to-2D image registration technique. The evaluation parameters included 3D hip-knee-ankle angle (3DHKA) alignment in the coronal (coronal alignment) and sagittal planes (sagittal alignment) and rotational alignment between the femur and tibia. The influences of sex and body constitution on all the alignment were analyzed.

RESULTS

Multiple linear regression analysis with the dependent variable of each alignment showed that sex was the dominant factor for coronal and rotational alignment (coronal: p <  0.01; rotational: p <  0.01), and body weight was the dominant factor for sagittal alignment (p <  0.01).

CONCLUSIONS

The association of sex with coronal and rotational alignment and of body constitution with sagittal alignment were proved in healthy, elderly, non-obese humans in a Japanese population. This finding can lead to further understanding of the etiology of many diseases and age-related changes.

Extrinsic Factors as Component Positions to Bone and Intrinsic Factors Affecting Postoperative Rotational Limb Alignment in Total Knee Arthroplasty

BACKGROUND

This study aimed to identify the factors affecting postoperative rotational limb alignment of the tibia relative to the femur. We hypothesized that not only component positions but also several intrinsic factors were associated with postoperative rotational limb alignment.

METHODS

This study included 99 knees (90 women and 9 men) with a mean age of 77 ± 6 years. A three-dimensional (3D) assessment system was applied under weight-bearing conditions to biplanar long-leg radiographs using 3D-to-2D image registration technique. The evaluation parameters were (1) component position; (2) preoperative and postoperative coronal, sagittal, and rotational limb alignment; (3) preoperative bony deformity, including femoral torsion, condylar twist angle, and tibial torsion; and (4) preoperative and postoperative range of motion (ROM).

RESULTS

In multiple linear regression analysis using a stepwise procedure, postoperative rotational limb alignment was associated with the following: (1) rotation of the component position (tibia: β = 0.371, P < .0001; femur: β = -0.327, P < .0001), (2) preoperative rotational limb alignment (β = 0.253, P = .001), (3) postoperative flexion angle (β = 0.195, P = .007), and (4) tibial torsion (β = 0.193, P = .010).

CONCLUSION

In addition to component positions, the intrinsic factors, such as preoperative rotational limb alignment, ROM, and tibial torsion, affected postoperative rotational limb alignment. On a premise of correct component positions, the intrinsic factors that can be controlled by surgeons should be taken care. In particular, ROM is necessary to be improved within the possible range to acquire better postoperative rotational limb alignment.

No differences in objective dynamic instability during acceleration of the knee with or without subjective instability post-total knee arthroplasty

INTRODUCTION

Instability after total knee arthroplasty is a critical problem. The purpose of this study was to clarify the stability of implanted knees during walking by comparing differences in dynamic instability during knee acceleration between individuals with or without previously experienced subjective instability, as measured by self-reported questionnaire.

MATERIALS AND METHODS

We examined 92 knees with medial pivot implants. Mean patient age and follow-up duration were 78.4 years and 32.8 months, respectively. An accelerometer was used to investigate the accelerations along three axes; that is, vertical (VT), mediolateral (ML), and anteroposterior (AP) directions in 3-dimensional (3D) space. The analysis in the stance phase and gait cycle was performed by: (1) root mean square (RMS) values of acceleration and (2) frequency domain analysis using fast Fourier transformation (FFT). A self-reported knee instability score was used for the subjective feeling of instability.

RESULTS

A total of 76 knees did not feel unstable (group 0), but 16 knees felt unstable (group 1) in patients during activities of daily living. Regarding the RMS, there were no differences in each direction between the groups. For FFT, the cumulative amplitude in the frequency < 30 Hz also showed no significant differences in all directions between the groups during the stance phase (VT, p = 0.335; ML, p = 0.219; AP, p = 0.523) or gait cycle (VT, p = 0.077; ML, p = 0.082; AP, p = 0.499).

DISCUSSION

Gait analysis based on the acceleration data showed that there were no between-group differences in objective dynamic instability during acceleration of the knee, with or without reports of previously experienced subjective instability, as assessed by the self-reported questionnaire.

Association between anteroposterior laxity in mid-range flexion and subjective healing of instability after total knee arthroplasty

PURPOSE

Flexion instability following total knee arthroplasty (TKA) is a common indication of early revision. The association between the objective anteroposterior (AP) laxity direction in mid-range flexion and the subjective healing of instability remains unclear; thus, this study aimed to clarify this association.

METHODS

In this study, 110 knees (74 females, 92 knees; 16 males, 18 knees) with medial pivot implants were examined with a median age of 79 (range 60-92) years for a median follow-up duration of 22 (range 6-125) months. AP laxity was measured using a KT-1000 arthrometer. Self-reported knee instability score was used for the subjective healing of instability.

RESULTS

Eighty-seven knees did not feel unstable (Group 0), whereas 23 knees felt unstable (Group 1). There was a significant difference in AP displacement [Group 0: median 6 mm; range 2-15 mm and Group 1: median 8 mm; range 4-14; p < 0.0001]. The threshold value of 7 mm was determined using the area under receiver operating characteristic curve of 0.79 [95% confidence interval (CI) 0.69-0.88, p < 0.0001]. In multivariate analysis, AP displacement of ≥7 mm was an independent risk factor for feelings of instability (odds ratio 7.695; 95% CI 2.306-25.674; p = 0.001).

CONCLUSIONS

AP laxity of ≥7 mm represents a known cause of feelings of instability. By controlling AP laxity in TKAs, without stiffness in the knee, it is possible to prevent feelings of instability. The clinical relevance is that AP laxity of <7 mm is one of the target areas in TKA.

LEVEL OF EVIDENCE

IV.

External torsion in a proximal tibia and internal torsion in a distal tibia occur independently in varus osteoarthritic knees compared to healthy knees

INTRODUCTION

The relative torsional angle of the distal tibia is dependent on a deformity of the proximal tibia, and it is a commonly used torsional parameter to describe deformities of the tibia; however, this parameter cannot show the location and direction of the torsional deformity in the entire tibia. This study aimed to identify the detailed deformity in the entire tibia via a coordinate system based on the diaphysis of the tibia by comparing varus osteoarthritic knees to healthy knees.

METHODS

In total, 61 limbs in 58 healthy subjects (age: 54 ± 18 years) and 55 limbs in 50 varus osteoarthritis (OA) subjects (age: 72 ± 7 years) were evaluated. The original coordinate system based on anatomic points only from the tibial diaphysis was established. The evaluation parameters were 1) the relative torsion in the distal tibia to the proximal tibia, 2) the proximal tibial torsion relative to the tibial diaphysis, and 3) the distal tibial torsion relative to the tibial diaphysis.

RESULTS

The relative torsion in the distal tibia to the proximal tibia showed external torsion in both groups, while the external torsion was lower in the OA group than in the healthy group (p < 0.0001). The proximal tibial torsion relative to the tibial diaphysis had a higher external torsion in the OA group (p = 0.012), and the distal tibial torsion relative to the tibial diaphysis had a higher internal torsion in the OA group (p = 0.004) in comparison to the healthy group.

CONCLUSION

The reverse torsional deformity, showing a higher external torsion in the proximal tibia and a higher internal torsion in the distal tibia, occurred independently in the OA group in comparison to the healthy group. Clinically, this finding may prove to be a pathogenic factor in varus osteoarthritic knees.

LEVEL OF EVIDENCE

Level Ⅲ.

Sex differences in femoral deformity determined using three-dimensional assessment for osteoarthritic knees

PURPOSE

To characterize femoral deformities and determine sex differences in varus knee osteoarthritis (OA), femoral morphology and limb alignment were evaluated by using three-dimensional (3D) assessment, comparing healthy, elderly volunteers with osteoarthritic knees.

METHODS

A total of 178 lower limbs of 169 subjects with knee osteoarthritis (136 women, 33 men; mean age 74.9 ± 5.2 years) and 80 lower limbs of 45 healthy, elderly subjects (24 women, 21 men; mean age 65 ± 4.9 years) were examined. A 3D extremity alignment assessment system was used to examine the subjects under weight-bearing conditions on biplanar long-leg radiographs using a 3D-to-2D image registration technique. The evaluation parameters were (1) femoral bowing in the coronal plane, (2) femoral bowing in the sagittal plane, (3) femoral neck anteversion, (4) hip-knee-ankle angle, and (5) femoral torsion.

RESULTS

Higher femoral lateral bowing and slightly higher femoral internal torsion in the proximal diaphysis were observed in women with OA compared with healthy subjects. No difference in the higher varus malalignment, no alteration in the femoral anterior bowing, and no difference in the lower femoral neck anteversion were found between men and women when comparing healthy and OA subjects.

CONCLUSIONS

The higher femoral lateral bowing and slightly higher femoral internal torsion in the proximal diaphysis in women are possibly a structural adaptation to mechanical use. The clinical significance is that the femoral deformities and the sex differences in knee OA have the potential to improve the understanding of the aetiology of primary varus knee OA.

LEVEL OF EVIDENCE

IV.