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Background: We aimed to analyze the surface morphology of the distal femur in three dimensions for the healthy elderly, based on the concept that the surgical epicondylar axis (SEA) is a better surrogate for the flexion-extension axis of the knee joint., Methods: We studied 77 healthy elderly volunteers (40 males and 37 females; age, 68 ± 6 years). The medial and lateral contact lines were calculated three-dimensionally, using the highest points of the medial and lateral condyles in 201 cross-sectional planes around the SEA (every 1°, -60° (hyperextension) to 140° (flexion)). A piecewise fitting function consisting of two linear segments was applied to detect the inflection point of the constant radii in the sagittal plane. The main assessment parameters were knee flexion angle at the inflection point of the radius (inflection angle), mean radius from 0° to the inflection angle (constant radius), and coronal tilt angle of the contact line., Results: The inflection angles, constant radii, and coronal tilt angles were 78.2 ± 8.6°, 26.1 ± 2.3 mm, and -0.6 ± 3.2° and 65.6 ± 9.2°, 23.9 ± 2.2 mm, and 6.2 ± 3.2° in the medial and lateral condyles, respectively (all, P < 0.001). The coronal alignment was 88.7 ± 2.2°., Conclusions: The medial and lateral femoral condyles showed asymmetrical morphologies with the almost 'constant' radius of sagittal curvature from 0° to around 80° and 65° of knee flexion, respectively., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Purpose: The purpose of this study was to three-dimensionally analyse the size and shape of the femoral posterior condyles of the normal knee., Methods: A total of 62 healthy Japanese volunteers (37 males and 25 females) providing a sample of 124 normal knee joints, who had no knee-related symptoms and no history of major trauma, underwent computed tomography scans of the bilateral femur and tibia. Three-dimensional digital models of the femur were constructed from computed tomography data using visualisation and modelling software. The following parameters were evaluated: (1) the radii of the posterior condyles approximated to spheres and (2) the inclination angle of the posterior condyles in the coronal plane of the femoral coordinate system., Results: The radii of the medial and lateral condyles approximated to spheres were 17.0 ± 1.6 and 17.1 ± 1.8 mm, respectively and were not different. The inclination angles of the medial and lateral condyles in the coronal plane were - 0.6° ± 4.6° and 9.7° ± 5.7°, respectively. The medial condyle was almost vertical, whereas the lateral one was medially tilted., Conclusions: This study found an asymmetrical inclination between medial and lateral condyles. This may be related to the asymmetrical motion of the knee, which is known as medial pivot motion. This finding provides valuable morphological information and may be useful for implant designs for total knee arthroplasty., Level of Evidence: IV.

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.

Background: Sports injury prevention training programs have been reported to be effective in decreasing the incidence of injuries. The aim of this study was to evaluate the effects of a 6-month training period, using part 2 of the FIFA11+ program (the Fédération Internationale de Football), on the activation and strength of core and lower limb muscles and on static and dynamic balance performance., Study Design: Case series; level of evidence, 4., Methods: Eight college male soccer players, aged mean 20.4 ± 0.5 years old, completed the FIFA11+ program at least three times per week for 6 months. The following variables were measured both before and after the 6-month training program: activities of more than 30 muscles (core and lower limb muscles), measured using the standardized uptake values of 18F-fluorodeoxyglucose on positron emission tomography; isokinetic strength of the knee flexor and extensor and hip abductor muscles, measured at 60° s -1 ; static balance over a 60-s period, measured using a gravicorder; and dynamic balance, measured using the star excursion balance test., Results: Training improved the activity levels of core (obliquus externus abdominis and erector spinae) and lower limb (tibialis anterior) muscles ( p ≤ 0.03), corrected the between-limb difference in the activation of the semimembranosus and improved dynamic balance, with a greater training effect on the nondominant limb ( p ≤ 0.02). Training also improved the knee flexor force of the nondominant lower limb ( p = 0.02)., Conclusion: Routine performance of the FIFA11+ program can improve the activation of core and lower limb muscles, with a concomitant improvement in dynamic balance. These improvements could be beneficial in lowering the risk of sports-related injuries.

The wear rate of five types of cruciate-retaining artificial knee joint ultrahigh-molecular-weight polyethylene (UHMWPE) inserts was examined using two custom-made knee joint simulators satisfying ISO 14243-1 (load control) and ISO 14243-3 (displacement control). The wear rate of knee joints composed of a UHMWPE insert and a Co-Cr-Mo alloy or oxidized zirconium femoral component linearly increased with increasing number of wear cycles, and the volumetric wear rate per million cycles was approximately 6-18 mm 3 /Mc. The wear rate was the lowest in the highly crosslinked knee joint irradiated at 90 kGy (Scorpio) among the five UHMWPE inserts. The extent of oxidation in UHMWPE after a knee simulator test of up to 5 × 10 6 cycles was small. The load-controlled wear rates measured in this work were close to the displacement-controlled wear rates reported in the literature. The effect of the control method on the wear rate was small for Nexgen and Scorpio knee joints. However, it was larger for the PFC Sigma knee joint having a high curvature of the surface. The wear rate of various knee joints made of highly crosslinked UHMWPE (XLPE) markedly decreased when they were subjected to a radiation dose of 40 kGy or more. The 10-year cumulative percentage revision rate since the primary operation slightly decreased with decreasing volumetric knee simulator wear rate for conventional UHMWPE (CPE) and XLPE knee joint inserts. The XLPE knee joint was shown to exhibit reduced in vivo wear and lower rates of revision for total knee replacement. On the other hand, Nexgen and PFC Sigma (both CPE) knee joints showed the lowest revision rate in the AOA and NJR national joint replacement registries. The volumetric wear rates of 3 mm 3 /Mc for XLPE and 15 mm 3 /Mc for CPE knee joint inserts are recommended as a goal for the development of new knee joints., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Purpose: Abnormalities of lower extremity alignment (LEA) in recurrent patella dislocation (RPD) have been studied mostly by two-dimensional (2D) procedures leaving three-dimensional (3D) factors unknown. This study aimed to three-dimensionally examine risk factors for RPD in lower extremity alignment under the weight-bearing conditions., Methods: The alignment of 21 limbs in 15 RPD subjects was compared to the alignment of 24 limbs of 12 healthy young control subjects by an our previously reported 2D-3D image-matching technique. The sagittal, coronal, and transverse alignment in full extension as well as the torsional position of the femur (anteversion) and tibia (tibial torsion) under weight-bearing standing conditions were assessed by our previously reported 3D technique. The correlations between lower extremity alignment and RPD were assessed using multiple logistic regression analysis. The difference of lower extremity alignment in RPD between under the weight-bearing conditions and under the non-weight-bearing conditions was assessed., Results: In the sagittal and coronal planes, there was no relationship (statistically or by clinically important difference) between lower extremity alignment angle and RPD. However, in the transverse plane, increased external tibial rotation [odds ratio (OR) 1.819; 95% confidence interval (CI) 1.282-2.581], increased femoral anteversion (OR 1.183; 95% CI 1.029-1.360), and increased external tibial torsion (OR 0.880; 95% CI 0.782-0.991) were all correlated with RPD. The tibia was more rotated relative to femur at the knee joint in the RPD group under the weight-bearing conditions compared to under the non-weight-bearing conditions (p < 0.05)., Conclusions: This study showed that during weight-bearing, alignment parameters in the transverse plane related to the risk of RPD, while in the sagittal and coronal plane alignment parameters did not correlate with RPD. The clinical importance of this study is that the 3D measurements more directly, precisely, and sensitively detect rotational parameters associated with RPD and hence predict risk of RPD., Level of Evidence: III.

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., (Copyright © 2018 Elsevier Inc. All rights reserved.)

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.

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.

Purpose: Evaluating pivot shift phenomenon is difficult due to its subjectivity, wide variation of testing manoeuvres, and difficulty in evaluating patients while awake. The purpose of this study was to evaluate the pivot shift phenomenon using a triaxial accelerometer by two different manoeuvres, the pivot shift test as representative of flexion manoeuvre and N test as a representative of extension manoeuvre, and in two different conditions, awake and under anaesthesia., Methods: Twenty-nine patients with unilateral anterior cruciate ligament (ACL)-injured knee were included. Pivot shift test and N test were performed for both injured and uninjured legs while awake and under anaesthesia, with the acceleration measurements using a triaxial accelerometer (KiRA). The tests were also subjectively graded on a scale of 0-6 based on the modification of IKDC criteria., Results: Under anaesthesia, acceleration of ACL-injured knees was greater than that of uninjured knees in both pivot shift test (P < 0.001) and N test (P < 0.001) , whereas the acceleration value was greater in the N test. Furthermore, there were significant positive correlations between the acceleration and subjective grading in both tests, whereas the N test was more significant than the pivot shift test. On the other hand, there was no statistical significance in acceleration between ACL-injured and uninjured knees in either test while the patient was awake., Conclusion: The triaxial accelerometer was useful to objectively detect and quantitatively evaluate the pivot shift phenomenon by both the pivot shift test and N test under anaesthesia. The acceleration of ACL-injured knees was greater than that of uninjured knees, and the acceleration was correlated with the subjective manual grading, especially in the N test. On the other hand, its use while the patient was awake was likely limited., Levels of Evidence: Diagnostic study of non-consecutive patients without a universally applied gold standard, Level III.

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., (Copyright © 2017 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)

Background: Analysis of dynamic knee loading during gait is essential to prevent mechanical failures following total knee arthroplasty. External knee adduction moment during gait is the primary factor producing medial joint reaction force, and an increase in the moment is directly related to an increase in the medial compartment load on the knee., Methods: Knee adduction moment during gait in 39 knees of 32 female patients following a posterior stabilized knee replacement with a single surgeon was evaluated at 1.3months following surgery. A cut-off moment was determined as mean+1 standard deviation (SD) of the moment from 10 healthy subjects, and patients' knees were divided into high- and normal-moment groups. Significant differences in clinical assessments and gait parameters between the two groups were assessed., Results: Based on the cut-off moment, 23 knees were grouped into normal knees and 16 knees were grouped into high-moment knees. High-moment knees showed identical femorotibial angles and knee society scores but had greater toe-out angles and medially directed ground reaction forces compared to normal-moment knees. High-moment knees showed strong correlations between peak moment and knee adduction angle, and frontal plain moment arm., Conclusions: The clinical significance of a high knee adduction moment following total knee arthroplasty remains unclear, but dynamic frontal alignment during gait is one of the key factors for residual high-moment knees following surgery., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Purpose: Although studies support the clinical importance of the fibres from the horns of lateral meniscus (LM), few studies have investigated the detailed anatomy. This anatomic study was conducted to analyse the structural details of LM with special reference to (1) the attachment area of the fibres from the anterior and posterior horns and (2) the positional relationship between these fibres and the anterior cruciate ligament (ACL)., Methods: A total of 24 cadaveric knees were used in the macroscopic investigation, and six knees were used in the histological investigation. Micro-computed tomography analysis was also performed to assess the anatomy of the posteriormost fibre from the posterior horn of LM., Results: Based on the macroscopic investigations, the outer fibres from the anterior horn of LM extended to ACL and seemed to intermingle with ACL fibres. However, the histological investigations showed a distinct border between the fibres and ACL. The inner fibres from the anterior horn of LM attached to the lateral intercondylar tubercle serving as a lateral margin of ACL attachment. Fibres from the posterior horn of LM were separated into anterolateral and posteromedial crura which attached to the posterior aspect of the lateral and medial intercondylar tubercles, respectively. These two crura formed the posterior margin of the ACL attachment, except for the central part of ACL., Conclusion: The outer fibres from the anterior horn of LM adjoined ACL. The inner fibres from the anterior horn of LM and two crura from the posterior horn of LM formed the border of the attachment area of ACL. The distinctive fibre anatomy from LM could provide a surgical landmark during arthroscopic surgery.

Background: The extensor mechanism may be the key to kinematic alignment of total knee arthroplasty. The purpose of this study was to determine any differences in the direction of the quadriceps vector based on gender or ethnicity and to determine which anatomically derived alignment axis is closest to the quadriceps vector., Methods: Computed tomography scans and patient records for 14 Caucasians (9 men and 5 women) and 40 Japanese (19 men and 21 women) were evaluated. Three axes of alignment-anatomic, mechanical, and spherical-were identified, measured, and compared to the quadriceps vector in each case. Principal component analysis was used to determine the quadriceps vector by using 3-dimensional models of muscles on computed tomography scans., Results: No statistically significant differences in the orientation of the quadriceps vector were found based on gender or ethnicity, and the quadriceps vector was most closely aligned with the spherical axis., Conclusion: Because the quadriceps is the primary knee extensor, the spherical axis therefore may be a ubiquitous guide to alignment of the arthroplasty knee based on motion., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: Anterior cruciate ligament (ACL) injury often leads to symptoms of instability, which may cause meniscus injury, osteochondral lesions, and degenerative changes. For thorough evaluation of the effects of abnormal motion of ACL-deficient (ACLD) knees on the meniscus and articular cartilage, it is necessary to assess tibiofemoral motion in the medial and lateral compartments separately. Our aim was to determine if in vivo three-dimensional (3D) dynamic motion of ACLD knees differs from that of contralateral uninjured knees by assessing knee motion in the medial and lateral compartments respectively., Methods: A total of 22 patients with an isolated ACL-injured knee were examined. 3D to two-dimensional registration was used to determine 3D knee motion during squatting from full knee extension to full flexion for both ACLD and contralateral uninjured knees. The knee motion was evaluated by the movement of the geometric center axis of the femur projected onto the tibial axial plane., Results: In ACLD knees the lateral femoral condyle was located significantly more posteriorly during nearly full extension than in contralateral uninjured knees. The range of anteroposterior translation of the medial femoral condyle was significantly greater than those of contralateral uninjured knees. Almost all of the contralateral uninjured knees demonstrated medial pivot motion, while the ACLD knees showed higher variance., Conclusions: The ACLD knees exhibited a motion pattern different from those of contralateral uninjured knees with higher variance. During nearly full extension of the ACLD knees, the lateral femoral condyle translated posteriorly and the screw-home movement seemed to be impaired. The ACL might have an important role in maintaining normal knee function, especially during the early flexion phase. The larger range of anteroposterior translation of the medial femoral condyle in ACLD knees may be associated with a risk of secondary meniscal injury and degenerative change in the articular cartilage., Level of Evidence: Level IV., (Copyright © 2015 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)

Purpose: The purpose of this study was to investigate the hypothesis that a medial unicompartmental knee arthroplasty might restore the functional flexion axis of a knee to normal. The flexion axis can be indirectly identified by tracking the vertical translation of anatomic landmarks that basically move around the flexion axis during a knee motion. If a unicompartmental knee could help restore the normal flexion axis, the anatomic landmarks after the arthroplasty would show the vertical translation similar to those of normal knees during a knee flexion., Methods: While performing a squatting motion, the kinematics of 17 knees were determined before and after a medial unicompartmental arthroplasty to calculate the vertical translation of a clinical epicondylar axis, using a three- to two-dimensional registration technique through a single-plane fluoroscopic system incorporating a biplanar static radiography. The results were compared with a normal data, and a statistical analysis including a two-way repeated-measured analysis of variance was performed., Results: For the medial end, from 10° to 100° knee flexion, normal, osteoarthritic, and unicompartmental knees had the average superior vertical translation of 7.3 ± 4.2, 4.3 ± 7.2, and 2.4 ± 3.1 mm, respectively, with statistical significance between normal and unicompartmental knees (p < 0.001). The vertical translation did not return to normal post-implantation., Conclusions: A unicompartmental knee could not reproduce the normal flexion axis. As for clinical relevance, the changes of the implant design and surgical procedure may be necessary to obtain the normal flexion axis reproducing a normal motion., Level of Evidence: IV.

Purpose: To determine the initial minimal tension for restoring knee stability during double-bundle anterior cruciate ligament (ACL) reconstruction in vivo., Methods: Patients who underwent primary double-bundle ACL reconstruction with an autologous semitendinosus tendon during 2012 were included. The bundles were fixed to a graft-tensioning system during surgery. Initial graft tensions were set to the following tensions per 6 mm in graft diameter: (1) 30 N, (2) 25 N, and (3) 20 N. Bundle tension was recorded during knee flexion-extension and in response to anterior or rotatory loads. In addition, anterior knee laxity was measured with the KT-1000 arthrometer (MEDmetric, San Diego, CA), and the pivot-shift test was evaluated., Results: Sixty patients were evaluated. The tension curves of both bundles among different initial tension settings were significantly different (P < .0001), with the tension in the 30-N setting being highest and that in the 20-N setting being lowest. The tension in both bundles showed reciprocal pattern during flexion-extension (P = .019). The tension of the posterolateral bundle graft was significantly lower than that of the anteromedial bundle graft in response to the anterior load at all settings (P = .0017, P = .0019, and P = .0021 at 30° in the 30-N, 25-N, and 20-N settings, respectively, and P < .0001 at 90° at all settings), whereas the tensions in both bundles in response to rotatory loads were equivalent. Two cases showed a grade 1 pivot shift in the 20-N setting, whereas no case showed a positive pivot shift in the other settings. KT measurements in the 30-N and 25-N settings showed no difference., Conclusions: In double-bundle ACL reconstruction, initial tension could be set as low as 25 N; however, initial tension of 20 N is not recommended because it might result in residual pivot shift in some cases, although the pivot-shift difference was not significant., Level of Evidence: Level IV, therapeutic case series., (Copyright © 2015 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Purpose: To evaluate a novel approach for femoral tunnel creation, a behind-remnant approach, in remnant-preserving double-bundle anterior cruciate ligament (ACL) reconstruction through comparison with a standard approach., Methods: Sixty patients who underwent remnant-preserving double-bundle ACL reconstruction were included. Thirty patients with a standard approach were classified as the standard group, and 30 patients with a behind-remnant approach as the behind-remnant (BR) group. The anteromedial bundle (AMB) and posterolateral bundle (PLB) were provisionally fixed at 20° and 45° of flexion to a graft tensioning system during surgery. Bundle tension was recorded during knee flexion-extension and in response to anterior or rotatory loads. Femoral tunnel positions were then assessed using the quadrant method., Results: During flexion-extension, the BR group showed equivalent tension curves between AMB and PLB, while the standard group showed reciprocal tension curves. The tension on the PLB was lower than the AMB in response to anterior or rotatory loads in the BR group, while the AMB and PLB shared equivalent loads in the standard group. Tunnel position of the AMB in the BR group was lower and deeper, with smaller variances, than that in the standard group. Tunnel position of the PLB in the BR group was lower than that in the standard group., Conclusions: In remnant-preserving double-bundle ACL reconstruction, a behind-remnant approach can be achieved without any removal of the remnant tissue, and could create a deeper and lower AMB tunnel and a lower PLB tunnel with higher reproducibility, showing equivalent tension curves between the AMB and PLB., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Purpose: To evaluate the effect of the femoral tunnel position of the anteromedial bundle (AMB) and the posterolateral bundle (PLB) on the graft tension curves and knee stability in anatomic double-bundle anterior cruciate ligament (ACL) reconstruction., Methods: Forty-five patients who underwent anatomic double-bundle ACL reconstruction were included. AMB and PLB were provisionally fixed to a graft tensioning system in the following settings during surgery: (1) AMB at 20° and PLB at 0° (A20P0), (2) AMB at 20° and PLB at 20° (A20P20), and (3) AMB at 20° and PLB at 45° (A20P45). Bundle tension was recorded during knee flexion-extension. A pivot shift test was also evaluated. Femoral tunnel positions of the AMB and PLB were then assessed by three-dimensional computed tomography, and the correlation between femoral tunnel position and tension change pattern or residual pivot shift was evaluated., Results: The depth of the PLB tunnel position was correlated with the extent of tension reduction in the PLB between 0° and 30° irrespective of graft fixation settings, while neither the AMB tunnel position nor the height of the PLB tunnel position affected the tension change pattern. Ten cases showed grade 1 pivot shift only in the A20P0 setting. The PLB tunnel position in the pivot shift-positive cases was significantly deeper than that in the pivot shift-negative cases (27.5 ± 6.2 and 34.1 ± 5.5%, respectively, P = 0.002)., Conclusions: In anatomic double-bundle reconstruction, deeper PLB tunnel position was correlated with the larger tension reduction in the PLB between 0° and 30°. Fixation of the AMB at 20° and the PLB at 0° resulted in residual pivot shift phenomenon in 10/45 cases, and the PLB tunnel position in the pivot shift-positive cases was significantly deeper than that in the pivot shift-negative cases. In anatomic double-bundle reconstruction, the placement of PLB femoral tunnel must not be too deep, as it might lead to significant tension reduction in the PLB near extension and thus insufficient tension in the PLB, resulting in residual pivot shift phenomenon., Level of Evidence: IV.

Purpose: It is common to assert that restoration of normal knee kinematics is essential for the best functional result after knee arthroplasty. Previous studies using the progression of the geometric centre axis have suggested that kinematics after unicompartmental arthroplasty is markedly different from the normal. For this study, the transepicondylar axis was used because this axis is closer to the flexion axis and should be a better reference for motion. The following hypothesis was tested: the transepicondylar axis would again show that the postoperative kinematics does not restore normal motion and is closer to that before replacement., Methods: Seventeen osteoarthritic knees were tested before and after unicompartmental arthroplasty using a three-dimensional to two-dimensional registration technique tracking the transepicondylar axis to calculate translation and rotation of this axis. Results were compared for the seventeen knees before and after arthroplasty and were compared to the normal knee as measured in our previous study., Results: Similar motion patterns in the pre- and postoperative knees were shown but both the pre- and postoperative motion were markedly different from the normal knee., Conclusions: This result supported our hypothesis. The clinical relevance is that medial unicompartmental arthroplasty cannot restore the motion of the knee to normal in the living knee. Therefore, it would be expected that the patient for unicompartmental knee might not feel normal. It may not be possible depending on ligaments alone to restore the knee to normal, and the changes in the articular shapes and the surgical procedure may also be necessary.

Background: The effects of notchplasty on the clinical outcome after anatomic double-bundle anterior cruciate ligament (ACL) reconstruction remain unclear., Hypothesis: Anatomic ACL reconstruction with notchplasty would result in less risk of loss of extension and would provide adequate space for better graft healing, leading to better knee stability compared with anatomic ACL reconstruction without notchplasty., Study Design: Cohort study; Level of evidence, 3., Methods: A total of 137 patients who underwent anatomic double-bundle ACL reconstruction were included. Seventy-three patients without notchplasty were classified as the control group, and 64 patients with 2-mm notchplasty were classified as the notchplasty group. The following evaluation methods were used: loss of extension, patient's subjective feeling of limited extension and pain at passive full extension, muscle strength, manual laxity tests, KT-1000 arthrometer measurement, patellofemoral joint findings, Tegner score, Lysholm score, subjective scores, and time to return to sports. Tearing of the reconstructed ACL and additional synovectomy were recorded. Both tibial and femoral tunnel positions were measured using 2-view radiographs: a Rosenberg and a lateral view., Results: Loss of extension was larger in the notchplasty group compared with controls (at 6 months: 0.8° vs 1.4°, P = .012; at 2 years: 0.4° vs 0.9°, P = .0053). The number of patients with a feeling of limited extension was also larger in the notchplasty group (at 6 months: 13 patients graded 1+ [somewhat limited] and 2 patients graded 2+ [very limited] vs 18 graded 1+ and 6 graded 2+, P = .015; at 2 years: 2 graded 1+ and 0 graded 2+ vs 4 graded 1+ and 5 graded 2+, P = .011). Six patients in the notchplasty group required additional synovectomy because of the prolonged loss of extension, whereas no patient in the control group required additional synovectomy. There were no differences between groups regarding muscle strength, patellofemoral findings, Lysholm score, Tegner score, subjective scores, or time to return to sports. The KT-1000 arthrometer measurement was better in the notchplasty group (1.2 vs 0.4 mm, P = .0017). However, 6 patients in the notchplasty group showed an overconstrained knee (KT-1000 measurement ≤-2 mm), compared with only 1 patient in the control group. There were no differences between groups in the other manual laxity tests or the tunnel positions., Conclusion: In anatomic double-bundle ACL reconstruction, anterior stability was improved and there were no harmful effects on patellofemoral joint findings by 2-mm notchplasty; however, notchplasty likely caused overconstrained knee, leading to a need for additional synovectomy in some patients. In contrast, anatomic double-bundle ACL reconstruction without notchplasty did not increase the incidence of loss of extension or of graft failure., (© 2014 The Author(s).)

Background: The functional flexion axis (FFA) is the principal axis around which the knee moves and thus, by definition, does not move in vertical displacement relative to the tibia. The transepicondylar axis (TEA) has been reported to coincide with the FFA. If that is not true, the TEA should show vertical displacement during motion, and this hypothesis was investigated., Methods: Three-dimensional knee kinematics of 20 healthy volunteers were determined during a squatting motion via a 3-dimensional to 2-dimensional image registration technique by calculating the vertical displacement of the clinical epicondylar axis (CEA) through the full range of motion., Results: From 0° to 90° knee flexion, the average vertical displacement of the lateral end of the CEA was <3 mm, whereas that of the medial end was large (7.6 mm)., Discussion: The large vertical displacement of the medial end of the CEA suggests that the CEA is not the FFA. This finding implies that the CEA may not be an appropriate axis for a TKA prosthesis having a "single radius" design., Evidence Level: Level IV.

Purpose: The purpose of this study is to evaluate the morphology of the mid-substance and fan-like extension fibres of ACL during knee motion with reference to the femoral attachment., Methods: This study used six fresh-frozen cadaveric knees and 22 embalmed cadaveric knees to macroscopically evaluate morphological changes in the ACL attachment during knee motion. Three embalmed specimens fixed at knee extension and another three specimens fixed at 120° flexion were used for histologic observations., Results: The fan-like extension fibres were adhered to the bone surface and the fibre location and orientation in relation to the femoral surface did not change, regardless of the knee flexion angle, while the orientation of the mid-substance fibres in relation to the femur did change during knee motion. During knee flexion, a fold in the ACL femoral attachment was observed at the border between the mid-substance and the fan-like extension fibres. The attachment of the mid-substance fibres was significantly smaller than the attachment of the fan-like extension fibres., Conclusion: The present study clarified anatomic and histologic character of the mid-substance fibres and fan-like extension fibres, and provided critical information for future clinical and biomechanical studies concerning both two different fibres. Specifically for ACL reconstruction, it is difficult to reconstruct the natural fan-like extension fibres by creating a tunnel at the femoral and tibial ends of each fibre bundle, although the mid-substance fibres can be reconstructed by such procedures.

Purpose: The transepicondylar axis (TEA) has been used as a flexion axis of the knee and a reference of the rotational alignment of the femoral component. However, no study has showed dynamic normal knee kinematics employing TEA as the evaluation parameter throughout the full range of motion in vivo. The purpose of this study was to analyze dynamic kinematics of the normal knee through the full range of motion via the 3-dimensional to 2-dimensional registration technique employing TEA as the evaluation parameter., Methods: Dynamic motion of the right knee was analyzed in 20 healthy volunteers (10 female, 10 male; mean age 37.2 years). Knee motion was observed as subjects squatted from standing with knee fully extended to maximum flexion. The following parameters were determined: (1) Anteroposterior translations of the medial and lateral ends of the TEA; and (2) changes in the angle of the TEA on the tibial axial plane (rotation angle)., Results: The medial end of the TEA demonstrated anterior translation (3.6 ± 3.0 mm) from full extension to 30° flexion and demonstrated posterior translation (18.1 ± 3.7 mm) after 30°, while the lateral end of the TEA demonstrated consistent posterior translation (31.1 ± 7.3 mm) throughout knee flexion. All subjects exhibited femoral external rotation (16.9 ± 6.2°) relative to the tibia throughout knee flexion., Conclusion: Compared to previously used parameters, the TEA showed bicondylar posterior translation from early flexion phase. These results provide control data for dynamic kinematic analyses of pathologic knees in the future and will be useful in the design of total knee prostheses.

Purpose: To date, there is no consensus on the detailed anatomy of the posterior cruciate ligament (PCL) and the most appropriate PCL reconstruction method. The purpose of this study is the detailed observation of separate small PCL bundles for better comprehension of detailed PCL anatomy to facilitate the design of anatomic PCL reconstruction., Methods: Twelve cadaveric knees were used in this study. PCL was divided into anterolateral and posteromedial (PM) sections and then separated into about 20 small bundles of 1 mm in diameter while maintaining preservation of their attachment sites marked with fine coloured marker pens. The positional relationship between the femoral and tibial attachments of each small bundle was investigated., Results: The small bundles of tibial and femoral attachments showed a topographical correlation. The anterior-posterior aligned bundles in the tibia corresponded to the bundles aligned in a low-high direction in flexion in the femur. The femoral attachment pattern was relatively similar in each specimen. However, the tibial attachment showed two patterns of small bundle footprint location: a parabolic type (6 of 12) and a transverse type (6 of 12). The posterior portion of the PM bundle was separately attached to the medial and lateral portions in the tibial attachment., Conclusion: Small bundles of PCL showed a relatively layered arrangement between tibial and femoral attachments. Therefore, anatomic PCL reconstruction cannot be completed simply performed merely with straight bundles and circular bone tunnels.

Purpose: To evaluate the effect of posterolateral bundle (PLB) graft fixation angles on graft tension curves and load sharing between the anteromedial bundle (AMB) and the PLB in double-bundle anterior cruciate ligament (ACL) reconstruction., Methods: Twenty-four patients who underwent double-bundle ACL reconstruction were included in this study. AMB and PLB were provisionally fixed to a graft tensioning system during surgery. The graft fixation settings were as follows: (1) AMB at 20° and PLB at 0° (A20P0), (2) AMB at 20° and PLB at 20° (A20P20), and (3) AMB at 20° and PLB at 45° (A20P45). Bundle tension was recorded during knee flexion-extension and in response to anterior or rotatory loads. A pivot-shift test, as well as factors affecting the residual pivot-shift, was also evaluated., Results: A20P45 created reciprocal tension curves and load sharing, in which the tension in both bundles was equivalent during flexion-extension and during each loading test at 30°. In A20P0, the tension of the AMB was constantly higher than that of the PLB. Seven patients showed grade 1 pivot-shift phenomenon in A20P0, whereas no patient showed a positive pivot-shift at other settings. Larger tension reduction of the PLB between 0° and 30° and smaller load sharing of the PLB were significant factors affecting residual pivot-shift., Conclusions: In double-bundle ACL reconstruction, fixation of the AMB at 20° and the PLB at 45° created reciprocal tension curves and load sharing between the bundles. Fixation of the AMB at 20° and the PLB at 0° led to insufficient tension in the PLB, resulting in a residual pivot-shift phenomenon in 7 of 24 patients., Level of Evidence: Level IV, therapeutic case series., (Copyright © 2013 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Background: Pre- and postoperative knee kinematics in unicompartmental knee arthroplasty (UKA) can be theoretically related to clinical outcome and longevity after UKA with regard to ligament function and the degree of arthritic changes. However, the preoperative knee kinematics of patients indicated for UKA remain to be elucidated, and it is also unclear whether the preoperative kinematics can be maintained by the UKA procedure. The objective of this study was to examine the in vivo pre- and postoperative three-dimensional knee kinematics in UKA while referencing the normal knee kinematics reported in our previous study., Methods: We analyzed the knee kinematics in 17 knees (14 patients) undergoing UKA via a three-dimensional to two-dimensional registration technique employing femoral condylar translation and femoral axial rotation. The pre- and postoperative knee kinematics during squat motion were evaluated in the same subjects, employing consistent evaluation parameters., Results: On average, both pre- and postoperative knee kinematics in the range 10-100° of knee flexion demonstrated near-consistent femoral external rotation and anterior translation of the medial condyle and posterior translation of the lateral condyle. However, the mean femoral external rotation angle and the posterior translation of the lateral condyle postoperatively were significantly smaller than the values observed preoperatively., Discussion: Although the patterns of preoperative knee motion were similar to those seen in normal knees, the magnitude of this motion varied widely between patients, so it was not necessarily representative of normal knees. These variations may be due to the varying degrees of arthritic changes caused by osteoarthritis. Although the patterns of knee kinematics were largely maintained by the UKA procedure, the causes of the significant reductions in the magnitude of motion upon performing the UKA procedure should be investigated in subsequent studies with a larger number of patients.

Background: Analysis of the movement of anatomically defined reference axes at the femoral condyles relative to the tibia is appropriate for evaluating knee kinematics. However, such parameters have been previously employed only in studies utilizing stop-motion techniques. The purpose of this study was to evaluate in vivo dynamic kinematics for full range of motion in normal knees using the three-dimensional to two-dimensional registration technique and to compare them with previously reported normal knee kinematics obtained via stop-motion techniques., Methods: Dynamic motion of the right knee was analyzed in 20 healthy volunteers (10 female, 10 male; mean age 37.2 years). Knee motion was observed when subjects squatted from standing with the knee fully extended to maximum flexion. We determined the following parameters: (1) changes to angles of the geometric center axis (GCA) on the tibial axial plane (rotation angle); (2) anteroposterior translations of the medial and lateral ends of the GCA; and (3) motion patterns in each phase during knee flexion., Results: All subjects exhibited femoral external rotation (26.1°) relative to the tibia throughout knee flexion. The medial femoral condyle demonstrated anterior translation (5.5 mm) from full extension to 100° flexion, and demonstrated posterior translation (3.9 mm) after 100°, while the lateral femoral condyle demonstrated consistent posterior translation (15.6 mm) throughout knee flexion. All subjects showed medial pivot motion from full extension to nearly 120° flexion. From 120° flexion, bicondylar rollback motion was observed., Discussion: Although the behavior of the medial femoral condyle in our analysis differed somewhat from that seen in previous cadaver studies, the results obtained using dynamic analysis were generally equivalent to those obtained in previous studies employing stop-motion techniques. These results provide control data for future dynamic kinematic analyses of pathological knees.

We report the case of a patient requiring total knee arthroplasty (TKA) due to massive knee bone deformities caused by rheumatoid arthritis (RA) complicated with polyostotic fibrous dysplasia. Reconstruction of the knee with large osseous defect was achieved with conventional TKA by impaction bone grafting. Benign tumor-like conditions such as fibrous dysplasia may be treated with conventional TKA instead of endoprosthesis, custom-made knee prosthesis, or osteoarticular allografting.

Objective: Synovial mesenchymal stem cells (MSCs) are an attractive cell source for cartilage regeneration because of their high chondrogenic ability. In this study, we examined the synovium of patients with medial compartment knee osteoarthritis (OA) to determine the proportion of MSCs in relation to cellular compartmentalization, and to identify the culture parameters that could affect the chondrogenic potential of synovial MSCs., Methods: Human synovium was collected from 4 different harvest sites in the knees of patients with medial compartment OA. Each synovial tissue sample was divided into 2 parts, one for histologic assessment and the other for analysis of the cell size, surface epitopes, and chondrogenic potential of colony-forming cells in vitro., Results: The numbers of alpha-smooth muscle actin-positive vessels and CD31+ endothelial cells were higher in the medial outer region than in the other regions of OA synovial tissue. The numbers of these cells correlated with the number of colony-forming cells. In parallel with increasing duration of the preculture period, the size of the cells increased, while the chondrogenic potential decreased, and this was correlated with expression of CD90., Conclusion: Medial compartment knee OA demonstrates variability in the distribution of vessels, which results in a varying distribution of MSCs. The preculture period should be utilized to assess both the potential for expansion and the chondrogenic potential of MSCs.

Controversy persists concerning around posterior cruciate ligament (PCL) retention in total knee arthroplasty (TKA) for patients with rheumatoid arthritis (RA). This study investigated factors affecting anteroposterior (AP) instability following cruciate-retaining (CR)-TKA. In a consecutive series of 70 knees from 52 RA patients, total displacement (TD) was measured using a KT-2000 arthrometer before and after CR-TKA under anesthesia, and changes in TD were defined as DeltaTD. TD was also measured under anesthesia in 65 knees from 48 RA patients at a mean of 7.5 years after CR-TKA. Mean postoperative TD was 9.4+/-0.95 mm, representing an increase of about 1.5-1.8 mm compared to preoperative TD, and possibly reflecting resection of the anterior cruciate ligament. Correlation analysis revealed significant negative correlations between DeltaTD and both preoperative flexion angle (r=-0.67, p<0.001) and preoperative extension angle (r=-0.63, p<0.001), suggesting that TD in knees with flexion contracture increased postoperatively. At medium-term follow-up, no patients displayed AP instability, and mean TD was 8.3+/-0.48 mm. A significant correlation was found between TD and permissible flexion angle (r=0.61, p<0.001). These results indicate that TD is basically maintained during the course of CR-TKA in RA, but may be slightly affected by factors other than the PCL itself.

We conducted a study to assess the predictive factors for total knee arthroplasty (TKA) in a cohort of rheumatoid arthritis (RA) patients recruited and followed prospectively for 5 years. A linked registry study using information from a large observational cohort of RA patients followed at the Institute of Rheumatology, Tokyo Women's Medical University (IORRA) was done. Baseline routine clinical and laboratory assessments were recorded. The data were analyzed using the multivariate piecewise-linear Cox (PL-Cox) regression model; the model initially included variables such as gender, age, duration of the disease, visual analog scale (VAS) generated by physicians (VAS-physician), patient-reported VAS for pain (VAS-pain), VAS for general health (VAS-GH), disability level using the Japanese version of the Health Assessment Questionnaire (J-HAQ), C-reactive protein, erythrocyte sedimentation rate, rheumatoid factor (RF), and hemoglobin. Of the 3945 patients registered at baseline, 955 (24.2%) had pain or tenderness in their knee joints, and 114 (11.9%) had TKA surgery in one or both knee joints. On PL-Cox regression, the variables with positive coefficients were J-HAQ, VAS-pain, VAS-physician, and RF positive; advanced age was associated with a reduced risk of TKA. The hazard ratios were: 0.920 for age >60 years; 2.64 for J-HAQ <1.5; 1.01 for J-HAQ >1.5; 1.47 for VAS-pain >6 (cm); 1.20 for VAS-physician >4 (cm); and 2.08 for RF positive. The consistently predictive factors for TKA in RA were age, J-HAQ, VAS-pain, VAS-physician, and RF positive. Age greater than 60 years was associated with a decreased risk of TKA, while J-HAQ from 0 to 1.5, VAS-pain >6 (cm), and VAS-physician >4 (cm) were associated with an increased risk for TKA surgery. These results suggest that, when treating RA patients, physicians should pay particular attention to pain complaints, the patient's daily activity level, and the RF factor status.

The aim of this study was to improve surgical techniques for arthroscopically-assisted anterior cruciate ligament (ACL) reconstruction with minimal sensory disturbance in the infrapatellar and anterior lower leg regions. Thirteen patients with sensory disturbance were examined neurologically, and 51 lower limbs of 26 adult cadavers were examined anatomically to investigate the nerve branches supplying the regions. The region of sensory disturbance was supplied by branches of the medial femoral cutaneous nerve and the saphenous nerve, and the nerves showed a complementary distribution area. After detailed investigation of the positional relationships between the nerve branches and the skin incisions of the operative procedure, it was found that at least one branch of both nerves ran across the longitudinal skin incision (80%) for tendon harvest in the above-mentioned reconstruction. The complicated anatomic variations of the nerve branches preclude their absolute avoidance in any surgical incision, and a completely safe zone could not be found in the present study. However, an oblique incision for the tendon harvest rather than the typical longitudinal incision should be considered to minimize the sensory disturbance.