Comparison of knee kinematics and ligament forces in single and multi-radius cruciate-retaining total knee arthroplasty: A computer simulation study.

BACKGROUND: The single-radius design in total knee arthroplasty has been designed to develop a more fixed flexion-extension axis without mid-flexion instability compared with the multi-radius design. It remains unclear whether differences between the multi-radius and single-radius designs can affect kinematics and collateral ligament forces. This study aimed to simulate knee kinematics and kinetics between single-radius and multi-radius models using a musculoskeletal computer model. METHODS: The single-radius and multi-radius femoral components were virtually implanted in a computer simulation using the same tibial insert. The effects of implant design on kinematics and medial collateral ligament forces during squatting and gait activities were analyzed. RESULTS: During squatting, the multi-radius model exhibited paradoxical anterior translation on both the medial and lateral flexion facet center where peak anterior translation was 2.4 mm for medial flexion facet center and 2.2 mm for the lateral flexion facet center, while the peak anterior translation of the single-radius model was less than 1 mm at early flexion. A rapid decrease in medial collateral ligament tension was observed in the early flexion phase in the multi-radius model, which occurred simultaneously with paradoxical anterior translation, whereas the relatively constant medial collateral ligament tension was observed in the single-radius model. During gait activity, the single-radius model exhibited a more posterior position than the multi-radius model. CONCLUSION: These suggest that abrupt changes in the medial collateral ligament force influence anterior sliding of the femur, and that the single-radius design is a reasonable choice for prevention of mid-flexion instability.

Excessive flexed position of the femoral component causes abnormal kinematics and joint contact/ ligament forces in total knee arthroplasty.

Poor clinical outcomes are reported in excessive flexion of the femoral component in total knee arthroplasty (TKA), but their mechanisms have not yet been elucidated. This study aimed to investigate the biomechanical effect of flexion of the femoral component. Cruciate-substituting (CS) and posterior-stabilised (PS) TKA were reproduced in a computer simulation. The femoral component was then flexed from 0° to 10° with anterior reference, keeping the implant size and the extension gap. Knee kinematics, joint contact, and ligament forces were evaluated in deep-knee-bend activity. When the femoral component was flexed 10° in CS TKA, paradoxical anterior translation of the medial compartment was observed at mid-flexion. The PS implant was best stabilised with a 4° flexion model in mid-flexion range. The medial compartment contact force and the medial collateral ligament (MCL) force increased with the flexion of the implant. There were no remarkable changes in the patellofemoral contact force or quadriceps in either implant. In conclusions, excessive flexion of the femoral component yielded abnormal kinematics and contact/ligament forces. Avoiding excessive flexion and maintaining mild flexion of the femoral component would provide better kinematics and biomechanical effects in CS and PS TKA.

Biomechanical Comparison of Kinematic and Mechanical Knee Alignment Techniques in a Computer Simulation Medial Pivot Total Knee Arthroplasty Model.

Several concepts may be used to restore normal knee kinematics after total knee arthroplasty. One is a kinematically aligned (KA) technique, which restores the native joint line and limb alignment, and the other is the use of a medial pivot knee (MPK) design, with a ball and socket joint in the medial compartment. This study aimed to compare motions, contact forces, and contact stress between mechanically aligned (MA) and KA (medial tilt 3° [KA3] and 5° [KA5]) models in MPK. An MPK design was virtually implanted with MA, KA3, and KA5 in a validated musculoskeletal computer model of a healthy knee, and the simulation of motion and contact forces was implemented. Anteroposterior (AP) positions, mediolateral positions, external rotation angles of the femoral component relative to the tibial insert, and tibiofemoral contact forces were evaluated at different knee flexion angles. Contact stresses on the tibial insert were calculated using finite element analysis. The AP position at the medial compartment was consistent for all models. From 0° to 120°, the femoral component in KA models showed larger posterior movement at the lateral compartment (0.3, 6.8, and 17.7 mm in MA, KA3, and KA5 models, respectively) and larger external rotation (4.2°, 12.0°, and 16.8° in the MA, KA3, and KA5 models, respectively) relative to the tibial component. Concerning the mediolateral position of the femoral component, the KA5 model was positioned more medially. The contact forces at the lateral compartment of all models were larger than those at the medial compartment at >60° of knee flexion. The peak contact stresses on the tibiofemoral joint at 90° and 120° of knee flexion were higher in the KA models. However, the peak contact stresses of the KA models at every flexion angle were <20 MPa. The KA technique in MPK can successfully achieve near-normal knee kinematics; however, there may be a concern for higher contact stresses on the tibial insert.

Static Mediolateral Tilt of the Joint Line after Total Knee Arthroplasty Does Not Reflect Dynamic Tilt during a Stair Ascent Activity.

The correlation between static and dynamic mediolateral (ML) tilts of the joint line in the coronal plane remains unknown after total knee arthroplasty (TKA). The purpose was to evaluate the ML tilt as measured by two-dimensional to three-dimensional registration during stair ascent in TKA patients, and to examine the correlation between the dynamic ML tilt and radiographic measurements of static indices. Thirty-two knees that underwent TKA using the mechanical alignment method were included. Continuous sagittal fluoroscopy was taken from before initial contact (IC) until after the toe-off (TO) phase during the stair ascent. The ML tilt of the tibial component relative to the ground was analyzed in terms of dynamic alignment using image-matching techniques, whereas static alignment was measured using standing long-leg radiographs. The correlation between static and dynamic ML tilts was evaluated. In the fluoroscopic analysis, the joint line was neutral (0.0 degree, standard deviation [SD] = 3.4 degrees) around IC phases, then was tilted valgus (5.5° valgus, SD = 2.6 degrees) in the mid-stance (MS) phase. After the TO phase, the joint line became almost neutral (0.4 degrees valgus, SD = 3.1 degrees). The dynamic ML tilt was significantly more varus during the IC phase and significantly more valgus in MS and TO phases than the static ML tilt (1.4 degrees valgus, SD = 2.0 degrees). No correlation was found between static and dynamic ML tilts in weight-bearing phases. During stair ascent, the static tilt had no correlation with the dynamic tilt in weight-bearing phases despite being in the same range. Static lower limb alignment does not reflect coronal alignment during motion. Further research should be conducted to determine whether the horizontal dynamic ML tilt can improve long-term durability and clinical outcomes after TKA.

Patellar medial-lateral position can be used to correct the effect of leg rotation on preoperative planning in total knee arthroplasty for varus knees.

BACKGROUND: Lower limb malrotations can be observed in long leg radiographs, affecting the measurement of the angle between the mechanical and anatomical axes. The purposes were to analyze the effect of limb rotation and to evaluate the accuracy of the corrected angle between the mechanical and anatomical axes based on the patellar ML position. HYPOTHESIS: The hypothesis was that the correction of the angle between the mechanical and anatomical axes according to the patellar ML position can reduce the error from the angle in the true AP view in most of the knees. PATIENTS AND METHODS: A total of 100 consecutive knees with varus deformity undergoing primary total knee arthroplasty were included. Computed tomography images were digitally reconstructed in the neutral position, and internally and externally rotated at 10° and 20°, respectively. The patellar ML position relative to the medial (0%) and lateral (100%) epicondyles and the angle between the mechanical and anatomical axes of the femur were measured. The corrected angle between the mechanical and anatomical axes was calculated using the averaged translational ratio. RESULTS: In the neutral position, the patellar center position was 56.1% (standard deviation [SD]=4.7%), which was 31.4% (SD=7.2%) and 80.2% (SD=5.4%) in the 20° internal and external rotation, respectively. The angle between the mechanical and anatomical axes was 2.6° (SD=2.0°) and 8.1° (SD=2.1°) in the 20° internal and external rotation, respectively. On average, if the patellar center shifted 10%, the change of the angle between the mechanical and anatomical axes of the femur was 1.13°. Applying the corrected angle, a discrepancy from the neutral position decreased. CONCLUSION: The method to correct the angle between the mechanical and anatomical axes according to the patellar ML position can be used to reduce the measurement error for preoperative planning using a long leg radiograph. LEVEL OF EVIDENCE: III.

How does asymmetric tibial insert affect tibiofemoral kinematics and contact stresses in total knee Arthroplasty?

BACKGROUND: Asymmetric tibial insert design is expected to restore normal knee kinematics better than symmetric design. A tri-condylar implant has asymmetric and symmetric tibial inserts with a ball-and-socket joint to replace the post-cam mechanism. The purpose of this study was to compare the knee kinematics of the two designs and to measure tibiofemoral contact stresses, including that of the ball-and-socket joint. METHODS: Using a computer simulation, the anteroposterior position and axial rotation of the femoral component were simulated during a weight-bearing deep knee bend for six validated models. Contact forces were simultaneously simulated in the medial, lateral, and ball-and-socket compartments. The relative position and the magnitude and direction of each contact force were applied to aforce/displacement control knee simulator. The contact stresses were measured individually using a pressure sensor. RESULTS: The asymmetric tibial insert demonstrated a more posterior position of the femoral component in the lateral compartment during the entire range of motion and greater external rotation of the femoral component, compared to the symmetrical tibial insert. The mean peak contact stress of the medial and lateral compartments was < 9 Mpa, with no significant differences between the two designs except at 0°. The contact stress of the ball-and-socket joint was < 5 MPa. CONCLUSIONS: Asymmetry of the tibial insert shows significant kinematic difference and has little influence on the peak contact stress, which is considerably lower than the yield strength of polyethylene. The asymmetric tibial insert can lead to clinical benefits owing to its kinematic and kinetic properties.

Kinematic comparison between asymmetrical and symmetrical polyethylene inserts during deep knee bend activity.

BACKGROUND: The in vivo kinematic benefit of an asymmetrical polyethylene insert is still unknown in comparison with that of a symmetrical insert with the same femoral component design. The purpose of this study was to analyze the kinematic differences between symmetrical and asymmetrical polyethylene inserts and to detect the kinematic benefit in the asymmetrical polyethylene insert. The hypotheses are that greater axial rotation and more posterior rollback are observed in the asymmetrical polyethylene insert. METHODS: The patients were randomly allocated to the following two groups: total knee arthroplasty with a symmetrical insert and with an asymmetrical insert. In vivo knee kinematics was analyzed in asymmetrical (17 knees) and symmetrical (16 knees) inserts using an image matching technique. The symmetrical polyethylene insert had the same geometry on both sides, whereas the asymmetrical polyethylene insert had a flat surface on the postero-lateral side. The anterior/posterior position and axial rotation were compared between the two polyethylene inserts. RESULTS: The femoral component was significantly positioned posteriorly at 70° (p = 0.016) and 80° (p = 0.040) of knee flexion and externally rotated at 80° of knee flexion (p = 0.040) in the asymmetrical polyethylene insert as compared to the position of the symmetrical polyethylene insert. Femoral rollback and axial rotation from full extension to maximum flexion were greater in the asymmetrical polyethylene insert, although the difference was not significant. CONCLUSIONS: In the asymmetrical polyethylene insert, slight kinematic benefit with greater axial rotation and more posterior rollback was observed in comparison with the symmetrical polyethylene insert. Further research should be required whether the kinematic benefit of an asymmetrical polyethylene insert will lead to better patient satisfaction and function.

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 new femoral fixation device for anterior cruciate ligament reconstruction using the outside-in technique and hamstring tendon graft: A comparison between two devices in cadaveric human knee models.

BACKGROUND: A new device (T-anchor) was developed for ACL reconstruction and is implanted via the outside-in technique using hamstring grafts. The purpose of this study was to compare the T-anchor with the EndoButton Direct. METHODS: This study was conducted on 30 cadaveric knees (15 matched pairs). There were two groups of 15 each in the T-anchor and EndoButton Direct groups. After the harvest of grafts, fixation site profile and graft length were measured by loading the grafts onto both devices. They were then tested on a universal testing machine to assess elongation after cyclic loading, load to failure, ultimate load, and mode of failure. RESULTS: The fixation site profile was lower in the T-anchor group than in the EndoButton Direct group (2.3±0.4mm vs. 4.7±1.0mm, P<0.001). The length of the graft-device complex of the T-anchor specimens was longer than that of the EndoButton Direct specimens (125.0±8.9mm vs. 115.0±8.7mm, P<0.001). The mean cyclic elongation was lower for the T-anchor group when compared with the EndoButton Direct group (2.4±0.6mm vs. 3.9±2.6mm, P=0.015). There was no statistically significant difference in ultimate load and load to failure between the T-anchor and EndoButton Direct groups. For mode of failure, the T-anchor fared better (P=0.013) with all failures attributed to specimens. CONCLUSIONS: In this cadaveric study, the new device, T-anchor, performed better than the EndoButton Direct with respect to the above-mentioned study parameters except for ultimate load and load to failure.

Active Flexion in Weight Bearing Better Correlates with Functional Outcomes of Total Knee Arthroplasty than Passive Flexion.

PURPOSE: Correlations between maximum flexion and functional outcomes in total knee arthroplasty (TKA) patients are reportedly weak. We investigated whether there are differences between passive maximum flexion in nonweight bearing and other types of maximum flexion and whether the type of maximum flexion correlates with functional outcomes. MATERIALS AND METHODS: A total of 210 patients (359 knees) underwent preoperative evaluation and postoperative follow-up evaluations (6, 12, and 24 months) for the assessment of clinical outcomes including maximum knee flexion. Maximum flexion was measured under five conditions: passive nonweight bearing, passive weight bearing, active nonweight bearing, and active weight bearing with or without arm support. Data were analyzed for relationships between passive maximum flexion in nonweight bearing by Pearson correlation analyses, and a variance comparison between measurement techniques via paired t test. RESULTS: We observed substantial differences between passive maximum flexion in nonweight bearing and the other four maximum flexion types. At all time points, passive maximum flexion in nonweight bearing correlated poorly with active maximum flexion in weight bearing with or without arm support. Active maximum flexion in weight bearing better correlated with functional outcomes than the other maximum flexion types. CONCLUSIONS: Our study suggests active maximum flexion in weight bearing should be reported together with passive maximum flexion in nonweight bearing in research on the knee motion arc after TKA.

Does surgical reconstruction produce better stability than conservative treatment in the isolated PCL injuries?

INTRODUCTION: The purpose of this study was to conduct a systematic review to address the stability outcome from reconstruction and conservative treatments. MATERIALS AND METHODS: Inclusion criteria were as follows: (1) English language, (2) human subject, (3) measures of stability outcomes, and (4) patients with isolated PCL injuries. We did not limit the type of study design (interventional or non-interventional study) and included all published systematic reviews. The following data were extracted: the number of study populations, year of publication, baseline characteristics of patients, follow-up period, and outcome data. The primary outcome variable was side-to-side difference (STSD). RESULTS: In the conservative treatment, the average STSD ranged from 3.5 to 5.3 mm on Telos™ (range 0.7-12.0 mm) and from 3.0 to 5.2 mm on KT-1000™ (range 0.5-10 mm). Among reconstructive treatment, the average STSD ranged from 2.0 to 3.7 mm on Telos™ (range 0-7 mm) and 0.7-5.9 mm on KT-1000™ (range -1 to 11.8 mm). In the conservative treatment, the estimated weighted mean STSD difference was 3.49 [95 % confidence interval (CI): 0.95-6.03] on Telos™ and 2.64 (95 % CI 0.76-4.51) on KT-1000™. On the other hand, in the reconstructive treatment, the estimated mean STSD difference was 8.09 (95 % CI 7.11-9.07) on Telos™ and 8.45 (95 % CI 6.44-10.47) on KT-1000™. CONCLUSIONS: This systematic review noted more satisfactory and consistent stability in the reconstructive treatment group. However, more complications and small differences of stability between groups should be also considered.

Can Serum Albumin Level and Total Lymphocyte Count be Surrogates for Malnutrition to Predict Wound Complications After Total Knee Arthroplasty?

BACKGROUND: Although the serum albumin level and total lymphocyte count (TLC) have been reported as valid and reliable markers for defining malnutrition, their cutoff levels and predictive values for wound complications in patients undergoing total knee arthroplasty (TKA) remain questionable. METHODS: A total of 3169 TKAs performed between April 2003 and December 2013 were retrospectively reviewed. We determined the prevalence of malnutrition on applying different definitions, with various cutoff values of serum albumin and TLC and analyzed the variations in outcome. The differences between groups with and without malnutrition in terms of functional outcome and complications were determined using Student's t test and analysis of variance. Multivariate logistic regression analysis was conducted to identify the independent risk factors. RESULTS: Among all the patients (N = 3169), the serum albumin level and TLC varied widely, with means of 4.1 g/dL and 2189 cells/mm(3), respectively. The prevalence of malnutrition (21%) as per the conventional definition (serum albumin level <3.5 g/dL or a serum TLC <1500 cells/mm(3)) dropped to only 1.6% when malnutrition was defined as serum albumin <3.5 g/dL "and" TLC <1500/mm(3), indicating a very small overlap between the 2 markers. No differences were observed between 2 groups in functional outcomes and incidence of wound complications. CONCLUSION: Our findings call into question the values of serum albumin level and TLC as a surrogate of malnutrition for predicting wound complications after TKA.

Correlation between dorsovolar translation and rotation of the radius on the distal radioulnar joint during supination and pronation of forearm.

This study aimed to describe the patterns of movements about radius and ulna in individual degrees of forearm rotation. And, we also determined the effect of forearm rotation on translation and rotation of the radius with reference to the ulna, and to measure the relationship between forearm rotation, translation and rotation of the radius. Computed tomography of multiple, individual forearm positions, from 90° pronation to 90° supination, was conducted in 26 healthy volunteers (mean age, 43.9 years) to measure dorsovolar translation and rotation of the radius in the DRUJ in each forearm position. The mean dorsovolar translations were within 1.99 mm at 90° pronation to -2.03 mm at 90° supination. The rotations of the radius were 71.20° at 90° pronation and -46.63° at 90° supination. There were strong correlations between degrees of forearm rotation and dorsovolar translation (r=0.861, p<0.001) and rotation of the radius (r=0.960, p<0.001), suggesting that the DRUJ, carpal joints, and rotatory laxity of the carpal ligament, especially in supination, contribute to forearm supination and pronation. These findings provide an understanding of wrist kinematics, are may be useful in reconstructive wrist surgery to achieve normal range of motion, and are may be helpful for the design of DRUJ reconstruction using prostheses.

Multilevel Thoracolumbar Spondylolysis with Spondylolisthesis at L4 on L5.

A 24-year-old male patient was initially evaluated for persistent back pain. The visual analogue scale (VAS) score was 7 points. Physical examination revealed a decreased range of lumbar spinal motion, which caused pain. Simple X-ray revealed Meyerding grade 1 spondylolisthesis at L4 on L5, with mild dome-shaped superior endplate and consecutive multilevel spondylolysis at T12-L5. Standing anteroposterior and lateral views of the entire spine revealed normal balance of sagittal and coronal alignment. A computed tomography scan revealed bilateral spondylolysis at T12-L4, left unilateral spondylolysis at L5, and spina bifida at L5 to sacral region. Magnetic resonance imaging revealed mild dural ectasia at the lumbar region. Due to the absence of any neurological symptoms, the patient was managed conservatively. He was rested a few weeks with corset brace and physiotherapy. After treatment, his back pain improved, VAS score changed from 7 to 2, and he was able to return to normal activity.

Is Knee Magnetic Resonance Imaging Overutilized in Current Practice?

PURPOSE: To determine what proportion of patients visiting a tertiary knee clinic had pre-obtained knee magnetic resonance imaging (MRI) and to assess the impact of pre-obtained knee MRI on the selection of treatment plans. MATERIALS AND METHODS: Six hundred and eighty patients were enrolled from patients who visited our knee clinic during a 6-month period. The proportion of patients with pre-obtained knee MRI was calculated, and associations of sociodemographic factors, disease category, and finally selected treatment options with knee MRI pre-obtainment were investigated. A utility assessment panel of five orthopaedic surgeons was formed and established utility assessment criteria. Two rounds of utility assessment (before and after MRI review) were performed. RESULTS: Of the 680 patients, 185 (27%) had pre-obtained knee MRI. In the first round of utility assessment, 39%, 18%, and 43% of the 185 knee MRIs were evaluated as useful, equivocal, and arguably useless, respectively, and almost identical results were obtained in the second round. The proportion of assessed 'useful MRI' was higher in sports related injury (84%) and other conditions (91%) than in degenerative joint disease (18%) and nonspecific knee pain (31%). Utility assessment results among panels varied little for practice patterns and education duration. CONCLUSIONS: This study suggests clinicians should reconsider and counsel patients the expected utility of knee MRI acquisition.

Patients still wish for key improvements after total knee arthroplasty.

PURPOSE: Our goals were to rigorously document and explore the interrelationships of various parameters in the aftermath of total knee arthroplasty (TKA), including patient characteristics, clinical scores, satisfaction levels, and patient-perceived improvements. MATERIALS AND METHODS: A questionnaire addressing sociodemographic factors, levels of satisfaction, and "wished-for" improvements was administered to 180 patients at least 1 year post primary TKA. Both satisfaction levels and wished-for improvements were assessed through nine paired parameters. Patients responded using an 11-point visual analogue scale (VAS) and the results were summarized as mean VAS score. Correlations between clinical scores and satisfaction levels and between satisfaction levels and desired improvements were analyzed. RESULTS: Patient satisfaction levels were only modest (mean score, 4-7) for eight of the nine parameters, including pain relief and restoration of daily living activities, the top two ranked parameters in wished-for improvement while high-flexion activity constituted the top source of discontent. Wished-for improvement was high in seven parameters, the top three being restoration of daily living activities, pain relief, and high-flexion activity. The effects of sociodemographic factors on satisfaction levels and wished-for improvement varied. Satisfaction levels correlated positively with functional outcomes, and satisfaction in pain relief and restoration of daily living activities correlated more often and most strongly with clinical scores. CONCLUSIONS: Following TKA, patient satisfaction is not high for a number of issues, with improvements clearly needed in restoring daily living activities and relieving pain. Continued efforts to achieve better surgical outcomes should address patient-perceived shortcomings.

Continuous Improvements of a Clinical Pathway Increased Its Feasibility and Improved Care Providers' Perception in TKA.

PURPOSE: We aimed to determine 1) whether dropout rate decreased and 2) whether health care providers' perceptions were changed with continued improvements of contents of clinical pathway (CP) for total knee arthroplasty (TKA). MATERIALS AND METHODS: This retrospective study included two separate analyses of patients and health care providers. In the analysis of patients, dropout rates and reasons were evaluated in two cohorts of patients who underwent TKA with CP applied at two different time periods (384 patients from 2009 to 2010 and 242 patients from 2012 to 2013). Contents of CP were continuously improved during the 3-year interval. Self-administered questionnaire surveys targeted to health care providers were carried out twice (2010 and 2013) and compared. RESULTS: Dropout rate decreased from 19.1% in the first time period to 10.4% in the second time period. Although overall satisfaction of care providers was high at both time-points, doctors had more favorable perceptions than nurses; most positive changes of perception were noted in nurses. The health care providers' perceptions for potential concerns of CP were improved while the perceptions for potential benefits and satisfaction were maintained. CONCLUSIONS: Continuously improved CP has increased feasibility for TKA patients and reduced health care providers' concern about its value. We propose that CP can be implemented and actively used to improve the outcomes and efficacy of patient care for TKA, regardless of the rotation of care providers.