Weight-bearing Flexion Research Articles

A comparative study on effectiveness of patellar resurfacing against non-resurfacing in total knee arthroplasty

To investigate the effectiveness of total knee arthroplasty (TKA) with or without patellar resurfacing. Between March 2013 and August 2015, 30 patients (60 knees) with osteoarthritis who met the inclusion criteria were recruited in the study. Of 30 cases, 24 were male and 6 were female with an average age of 57.2 years (range, 37-65 years). The body mass index ranged from 19.5 to 40.3 kg/m 2 (mean, 28.2 kg/m 2). According to Kellgren-Lawrence grading, there were 8 cases at grand Ⅲ and 22 cases at grand Ⅳ. All patients underwent primary bilateral TKA. The patellar resurfacing was done at the unilateral knee randomly (resurfacing side); the opposite treatment was done at the other side (non-resurfacing side). The indexes of 2 groups were recorded and compared, including the intraoperative blood loss, operation time, knee society score (KSS), "Forgotten Joint" scale (FJS), anterior knee pain, anterior patellar spirant, knee constraint feeling, anterior patellar clunk, muscle power of knee extension, and ability of up and down stairs, weight-bearing flexion, squatting down, cross-legged, knee down, knee extension, and patient satisfaction. Radiographic examination was used to analyze the prosthesis position. The operation time were (126±14) minutes and (112±11) minutes in resurfacing side and non-resurfacing side, respectively, showing significant difference between two sides ( t=5.103, P=0.030); and there was no significant difference in intraoperative blood loss between two sides ( t=3.431, P=0.800). All patients were followed up 2-4 years (mean, 2.6 years). There was no significant difference ( P>0.05) between two sides in KSS clinical and functional scores at preoperation and 6 weeks, 6 months, and 2 years after operation; in visual analogue scale (VAS) score of anterior knee pain at preoperation and 6 weeks after operation; in incidences of anterior patellar spirant, knee constraint feeling, anterior patellar clunk, and muscle power of knee extension at 6 weeks, 6 months, and 2 years after operation; in incidences of disability of up and down stairs, weight-bearing flexion, squatting down, cross-legged, knee down, and knee extension at 6 weeks, 6 months, and 2 years after operation; in ratio of FJS score at 2 years after operation. The VAS scores at 6 months and 2 years after operation in resurfacing group were significantly lower than those in non-resurfacing group ( Z=-1.997, P=0.046; Z=-2.197, P=0.028). Patient satisfaction of resurfacing side was superior to the non-resurfacing side at 6 weeks after operation ( χ2=4.271, P=0.039). Radiographic examination showed no prosthesis loosing occurred. The effectiveness of TKA with patellar resurfacing is better than that with non-resurfacing in patients satisfaction.

Posterior Condyle Offset and Maximum Knee Flexion Following a Cruciate Retaining Total Knee Arthroplasty.

Inconsistent data has been reported on the effect of the femoral posterior condyle offset (PCO) on the maximal knee flexion after total knee arthroplasty (TKA). This study investigated the relationship between the postoperative changes of the PCO and the changes of maximal knee flexion after a cruciate retaining (CR) TKA. Nine patients with medial osteoarthritis (OA) in one knee were investigated. Before operation, each index knee was magnetic resonance imaging (MRI) scanned for construction of a three-dimensional (3D) knee model. The patient then performed a maximal weight-bearing (WB) flexion and the index knee flexion was measured using a dual fluoroscopy technique. At an average of 8 months after a CR TKA, all patients performed the same WB knee flexion. The postoperative changes of the PCO, the posterior cruciate ligament (PCL) elongation, and the posterior tibial slope (PTS) were determined. The postoperative changes of maximal knee flexion were determined by comparing with the preoperative maximal flexion angles of the knee. The correlations of the postoperative changes of PCO and PTS with the postoperative changes of the maximal flexion angle and PCL elongation of the knee were analyzed. The preoperative PCO (28.5 ± 4.5 mm) was significantly smaller than the postoperative PCO (31.1 ± 5.1 mm) (p < 0.05). The increasing of PCO after surgery is correlated with the decreasing of maximal knee flexion angle (r = 0.74) and the increasing of PCL elongation (r = 0.64) after the TKA. The PTS was not found to change significantly after the TKA and was not significantly correlated to the maximal knee flexion angle and PCL elongation. The postoperative increases of the PCO were shown to cause overstretching of the PCL and poor flexion angle of the knee after the CR TKA. Restoration of PCO could help optimize the maximal flexion of the knee after the TKA with consideration about PCL tension.

In Vivo Kinematic Comparison of a Bicruciate Stabilized Total Knee Arthroplasty and the Normal Knee Using Fluoroscopy

BackgroundThe bicruciate stabilized (BCS) total knee arthroplasty (TKA) features asymmetrical bearing geometry and dual substitution for the anterior cruciate ligament and posterior cruciate ligament (PCL). Previous TKA designs have not fully replicated normal knee motion, and they are characterized by lower magnitudes of overall rollback and axial rotation than the normal knee. MethodsIn vivo kinematics were derived for 10 normal knees and 40-second generation BCS TKAs all implanted by a single surgeon. Mobile fluoroscopy and three-dimensional-to-two-dimensional registration was used to analyze anterior-posterior motion of the femoral condyles and femorotibial axial rotation during weight-bearing flexion. Statistical analysis was conducted at the 95% confidence level. ResultsFrom 0° to 30° of knee flexion, the BCS subjects exhibited similar patterns of femoral rollback and axial rotation compared to normal knee subjects. From 30° to 60° of knee flexion, BCS subjects experienced negligible anterior-posterior motions and axial rotation while normal knees continued to rollback and externally rotate. Between 60° and 90° the BCS resumed posterior motion and, after 90°, axial rotation increased in a normal-like fashion. ConclusionSimilarities in early flexion kinematics suggest that the anterior cam-post is supporting normal-like anterior-posterior motion in the BCS subjects. Likewise, lateral femoral rollback and external rotation of the femur in later flexion provides evidence for appropriate substitution of the PCL via the posterior cam-post. Being discrete in nature, the dual cam-post mechanism does not lend itself to adequate substitution of the cruciate ligaments in mid-flexion during which anterior cruciate ligament tension is decreasing and PCL tension is increasing in the normal knee.

Kneeling and standing up from a chair as performance-based tests to evaluate knee function in the high-flexion range: a randomized controlled trial comparing a conventional and a high-flexion TKA design

BackgroundWe compared the functional outcome between conventional and high-flexion total knee arthroplasty (TKA) using kneeling and sit-to-stand tests at 1 year post-operative. In addition, the patient’s daily functioning, pain and satisfaction were quantified using questionnaires.MethodsWe randomly assigned 56 patients to receive either a conventional or a high-flexion TKA. Primary outcomes were maximum flexion angle and maximum thigh-calf contact measured during kneeling at 1 year post operatively. Secondary outcomes were the angular knee velocity and ground reaction force ratio measured during sit-to-stand performance tests, and questionnaires.ResultsAt one year post-operative, maximum knee flexion during kneeling was higher for the high-flexion TKA group (median 128.02° (range 108–146)) compared to the conventional TKA group (119.13° (range 72–135)) (p = 0.03). Maximum thigh-calf contact force was higher for the high flexion TKA group (median 17.82 N (range 2.98–114.64)) compared to the conventional TKA group (median 9.37 N (range 0.33–46.58))(p = 0.04). The sit-to-stand tests showed a significantly higher angular knee velocity in the conventional TKA group (12.12 rad/s (95%CI 0.34–23.91); p = 0.04). There were no significant differences between groups in ground reaction force ratios and patient-reported outcome scores.ConclusionAlthough no differences were found in patient-reported outcome scores, differences in performance-based tests were clearly apparent. Standing up from a chair at 90° of knee flexion appeared to be easier for the conventional group. The kneeling test revealed significantly higher weight-bearing knee flexion for the high-flex group. Hence, if kneeling is an important activity for a patient a high-flex design may be recommendable.Trial registrationThe study was retrospectively registered in ClinicalTrials.gov under identifier NCT00899041 (date of registration: May 11, 2009).

In-vivo Elongation Patterns of the Anteromedial and Posterolateral Bundles of the ACL at Low Flexion Angles

The kinematics of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) in hyperextension was not well understood. This study investigated elongations of the two bundles in hyperextended knee. Twenty living knees were CT-scanned and fluoroscopy-imaged during a weight-bearing flexion–extension cycle from hyperextension to maximal flexion. The knee positions and the relative elongations of the two bundles were reproduced along the motion path using a combined fluoroscopic imaging and CT modeling technique. Results showed the elongation patterns of the two bundles were distinctively different (p < 0.01). The elongation of the PL bundle was slightly higher than that of the AM bundle at hyperextension and then decreased sharply with flexion. The elongation of the AM bundle was highest between the full extension and 10° flexion, and then decreased gradually with flexion angles. In every 10° from hyperextension to 30° flexion, the increasing rates of the PL bundle elongation were significantly higher than those of the AM bundle (p < 0.01). These data may provide important implications for selection of knee flexion angles for fixation of the AM and PL graft bundles in an anatomic ACL reconstruction that can help prevent over-stretching of the graft and reduce the risk of graft failure.

Effect of tibial slope changes on femorotibial contact kinematics after cruciate-retaining total knee arthroplasty.

The present study was undertaken to evaluate the effect of tibial slope (TS) changes on the femorotibial articular contact kinematics in subjects undergoing posterior cruciate-retaining total knee arthroplasty (CRTKA). Eighteen knees in nine patients with medial osteoarthritis who underwent CRTKA using the same size prosthesis were analysed preoperatively and 2years after TKA. TS changes were calculated on lateral radiographs taken before and after TKA. Knees were classified into two groups according to the change in TS obtained by subtracting the post-operative value from the preoperative value: group 1 (>3°) and group 2 (<3°). The femorotibial articular contact kinematics of knees during weight-bearing flexion were compared between the two groups by two-dimensional/three-dimensional registration. Group 1 showed a continuous posterior translation of the medial femoral condyle during the process of knee flexion, whereas in group 2 the medial femoral condyle experienced paradoxical anterior motion from 20° to 90° of knee flexion. The lateral femoral condyle continuously moved posteriorly in both groups. A greater reduction in TS after TKA compared with preoperative TS reduces paradoxical medial femoral condylar movement. This may contribute to improved patient satisfaction after CR TKA. III.

In Vivo Length Changes of the Anterolateral Ligament and Related Extra-articular Reconstructions

Background: Both anatomic anterolateral ligament (ALL) and nonanatomic anterolateral reconstructions are performed to improve the stability of anterior cruciate ligament (ACL)–deficient patients. However, the in vivo length change patterns and isometry of these anterolateral reconstructions are unknown. Purpose: To measure the theoretical length change patterns of the ALL and various anterolateral extra-articular reconstructions in healthy and ACL-deficient knees during in vivo weightbearing flexion. Study Design: Controlled laboratory study. Methods: Ten patients with an ACL injury in 1 knee and the contralateral side intact were included. By use of magnetic resonance and dual fluoroscopic imaging techniques, the changes in length of the ALL, modeled with its femoral attachment either anterior or posterior-proximal to the fibular collateral ligament (FCL) attachment, and nonanatomic extra-articular reconstructions were measured as a function of knee flexion and were compared between the intact and ACL-deficient knees. Results: The ALL, with its femoral attachment anterior to the FCL attachment, showed a consistent length increase of approximately 50% from 0° to 90° of knee flexion. The length change of the ALL was 20% ± 6% when its femoral attachment was placed posterior-proximal to the FCL. ACL deficiency did not affect ALL length. Even minor shifts in position around the rotational axis of the femur resulted in contrary ligament kinematic patterns. An extra-articular reconstruction with the femoral attachment proximal to the lateral epicondyle and the tibial attachment on the Gerdy tubercle increased 15% ± 4% in length from 0° to 60° and shortened at 90° of flexion. When the tibial fixation of the anatomic ALL with its femoral attachment posterior to the FCL was moved to the Gerdy tubercle, a 30% ± 4% length increase over 90° occurred, without the decrease in length at 90°. A significant length increase of both theoretical reconstruction grafts was seen at 0° in ACL-deficient knees. Conclusion: An anatomic ALL reconstruction as modeled based on recent anatomic studies was not isometric during in vivo knee flexion and was not affected by ACL deficiency. The nonanatomic extra-articular reconstructions demonstrated more biomechanically favorable length change patterns with the smallest percentage increase in elongation during knee flexion. Clinical Relevance: This study presents the first in vivo biomechanical data on the ALL, in both healthy and ACL-deficient knees, and provides surgical information that may be valuable for restoring normal anterolateral stability.

Relationships between lumbar inter-vertebral motion and lordosis in healthy adult males: a cross sectional cohort study.

BackgroundIntervertebral motion impairment is widely thought to be related to chronic back disability, however, the movements of inter-vertebral pairs are not independent of each other and motion may also be related to morphology. Furthermore, maximum intervertebral range of motion (IV-RoMmax) is difficult to measure accurately in living subjects. The purpose of this study was to explore possible relationships between (IV-RoMmax) and lordosis, initial attainment rate and IV-RoMmax at other levels during weight-bearing flexion using quantitative fluoroscopy (QF).MethodsContinuous QF motion sequences were recorded during controlled active sagittal flexion of 60° in 18 males (mean age 27.6 SD 4.4) with no history of low back pain in the previous year. IV-RoMmax, lordotic angle, and initial attainment rate at all inter-vertebral levels from L2-S1 were extracted. Relationships between IV-RoMmax and the other variables were explored using correlation coefficients, and simple linear regression was used to determine the effects of any significant relationships. Within and between observer repeatability of IV-RoMmax and initial attainment rate measurements were assessed in a sub-set of ten participants, using the intra-class correlation coefficient (ICC) and standard error of measurement (SEM).ResultsQF measurements were highly repeatable, the lowest ICC for IV-RoMmax, being 0.94 (0.80–0.99) and highest SEM (0.76°). For initial attainment rate the lowest ICC was 0.84 (0.49–0.96) and the highest SEM (0.036). The results also demonstrated significant positive and negative correlations between IV-RoMmax and IV-RoMmax at other lumbar levels (r = −0.64–0.65), lordosis (r = −0.52–0.54), and initial attainment rate (r = −0.64–0.73). Simple linear regression analysis of all significant relationships showed that these predict between 28 and 42 % of the variance in IV-RoMmax.ConclusionsThis study found weak to moderate effects of individual kinematic variables and lumbar lordosis on IV-RoMmax at other intervertebral levels. These effects, when combined, may be important when such levels are being considered by healthcare professionals as potential sources of pain generation. Multivariate investigations in larger samples are warranted.Electronic supplementary materialThe online version of this article (doi:10.1186/s12891-016-0975-1) contains supplementary material, which is available to authorized users.

Relationships between Paraspinal Muscle Activity and Lumbar Inter-Vertebral Range of Motion.

Control of the lumbar spine requires contributions from both the active and passive sub-systems. Identifying interactions between these systems may provide insight into the mechanisms of low back pain. However, as a first step it is important to investigate what is normal. The purpose of this study was to explore the relationships between the lumbar inter-vertebral range of motion and paraspinal muscle activity during weight-bearing flexion in healthy controls using quantitative fluoroscopy (QF) and surface electromyography (sEMG). Contemporaneous lumbar sEMG and QF motion sequences were recorded during controlled active flexion of 60° using electrodes placed over Longissimus thoracis pars thoracis (TES), Longissimus thoracis pars lumborum (LES), and Multifidus (LMU). Normalised root mean square (RMS) sEMG amplitude data were averaged over five epochs, and the change in amplitude between epochs was calculated. The sEMG ratios of LMU/LES LMU/TES and LES/TES were also determined. QF was used to measure the maximum inter-vertebral range of motion from L2-S1, and correlation coefficients were calculated between sEMG amplitude variables and these measurements. Intra- and inter-session sEMG amplitude repeatability was also assessed for all three paraspinal muscles. The sEMG amplitude measurements were highly repeatable, and sEMG amplitude changes correlated significantly with L4-5 and L5-S1 IV-RoMmax (r = −0.47 to 0.59). The sEMG amplitude ratio of LES/TES also correlated with L4-L5 IV-RoMmax (r = −0.53). The relationships found may be important when considering rehabilitation for low back pain.

Articular Cartilage Degenerates After Subtotal/Total Lateral Meniscectomy but Radiographic Arthrosis Progression Is Reduced After Meniscal Transplantation

Background: Little is known about the degree of articular cartilage degeneration after subtotal/total lateral meniscectomy in patients who later undergo isolated lateral meniscal allograft transplantation (LMAT). It has not yet been studied whether arthritic changes as shown on radiographs were lower during the posttransplantation period than during the meniscus-deficient period. Hypothesis: Articular cartilage will significantly degenerate during the meniscus-deficient period, but the progression in radiographic arthrosis is reduced after LMAT. Study Design: Case series; Level of evidence, 4. Methods: This study retrospectively reviewed 49 patients who underwent subtotal/total lateral meniscectomy before isolated LMAT performed over 1 year later by the same surgeon. International Cartilage Repair Society (ICRS) grades of the femorotibial joint at the time of subtotal/total meniscectomy and at LMAT were compared. Radiographic evaluation was performed at the time of initial meniscectomy, LMAT, and the latest follow-up in 38 patients (after 11 patients whose radiographs showed incomplete ossification at the time of meniscectomy were excluded). Arthrosis, based on Kellgren-Lawrence (K-L) grades, was determined on standing anteroposterior views. Joint space width (JSW) was measured on weightbearing flexion posteroanterior views. Results: Over a mean meniscus-deficient period of 4.5 years (range, 1-13 years), articular cartilage significantly degenerated on the femoral and tibial sides (P < .001). Grade ≥3 degeneration on the lateral tibial plateau was observed in 13 patients (27%) at the time of initial meniscectomy; this incidence doubled to 28 patients (57%) by the time of LMAT. The K-L grades worsened (P < .001) and JSWs narrowed significantly (–0.65 ± 1.09 mm; P = .001) during the mean meniscus-deficient period of 3.1 years. At radiographic assessment, however, the K-L grades (P = .097) and JSWs (4.06 ± 1.19 vs 3.92 ± 1.21 mm; mean difference, –0.14 ± 0.68 mm; P = .213) did not significantly change during the mean posttransplantation period of 3.8 years. The changes in ICRS grade and JSW during the meniscus-deficient period were not associated with age, body mass index, mechanical axis deviation, or Tegner activity level (P > .05 for all relationships). Conclusion: Patients who underwent isolated LMAT showed substantial articular cartilage degeneration at the time of initial subtotal/total lateral meniscectomy, and this degeneration progressed thereafter. Further progression of radiographic arthrosis was delayed after LMAT.

Knee alignment in the transverse plane during weight-bearing activity and its implication for the tibial rotational alignment in total knee arthroplasty

BackgroundThe alignment of the knee in the transverse plane is important to the biomechanical functions of the lower limb, and is also associated with the outcomes of the total knee arthroplasty. This study aimed to evaluate the dynamic tibiofemoral alignment in the transverse plane during a weight-bearing activity. MethodsKnee kinematics of weight-bearing flexion from 0° to 120° was obtained in 16 healthy subjects utilizing biplanar radiography and 3D–2D registration techniques. The anteroposterior axes of the femur at multiple flexion angles in the range of knee motion were used to calculate the anteroposterior axis of motion using the least square method. The latter was compared to six surface-derived anatomical axes in the proximal tibia which were most commonly reported in the literature. The relationship between the anteroposterior axis of motion and the tibial tubercle was also quantified. FindingsThe anteroposterior axis of motion did not coincide with any of the six anatomical axes tested. Their orientations varied from 10.3° of external rotation to 9.9° of internal rotation in relation to the former. The anteroposterior axis of motion tended to intersect the tibial tubercle between the medial border and the medial 1/3 point. InterpretationInstead of any of the tested anatomical axes, the transverse knee alignment during functional movements is associated with the medial 1/3 portion of the tibial tubercle. This region may be helpful for the rotational alignment of the tibial components in total knee arthroplasty.

No Superiority of High-Flexion vs Standard Total Knee Arthroplasty: An Update Meta-Analysis of Randomized Controlled Trials

This meta-analysis was performed using a Cochrane systematic review approach to examine published data with an aim to clarify whether standard or high flexion prostheses increase the range of knee motion and clinical outcomes. 1778 patients from 17 randomized controlled trials were identified. No significant differences in the range of motion, weight-bearing flexion and hip functions scores were found between treatment groups. We also found no significant differences in complications with regard to revision, component loosening, deep infection, anterior knee pain, stiffness, post-operative bone fracture and post-operative patella clunk syndrome, but the high flexion prostheses group had a higher incidence of deep venous thrombosis. The results do not support the proposition that high flexion knee prostheses provide substantial clinical advantages over standard knee prostheses.

In vivo length change patterns of the medial and lateral collateral ligaments along the flexion path of the knee.

The knowledge of the function of the collateral ligaments-i.e., superficial medial collateral ligament (sMCL), deep medial collateral ligament (dMCL) and lateral collateral ligament (LCL)-in the entire range of knee flexion is important for soft tissue balance during total knee arthroplasty (TKA). The objective of this study was to investigate the length changes of different portions (anterior, middle and posterior) of the sMCL, dMCL and LCL during in vivo weightbearing flexion from full extension to maximal knee flexion. Using a dual fluoroscopic imaging system, eight healthy knees were imaged while performing a lunge from full extension to maximal flexion. The length changes of each portion of the collateral ligaments were measured along the flexion path of the knee. All anterior portions of the collateral ligaments were shown to have increasing length with flexion except that of the sMCL, which showed a reduction in length at high flexion. The middle portions showed minimal change in lengths except that of the sMCL, which showed a consistent reduction in length with flexion. All posterior portions showed reduction in lengths with flexion. These data indicated that every portion of the ligaments may play important roles in knee stability at different knee flexion range. The soft tissue releasing during TKA may need to consider the function of the ligament portions along the entire flexion path including maximum flexion. III.

Does lumbar disk degeneration increase segmental mobility in vivo? Segmental motion analysis of the whole lumbar spine using kinetic MRI.

This is a retrospective analysis of lumbar segmental motion using Kinetic magnetic resonance imaging(KMRI). The aim of the study was to investigate lumbar segmental motion in functional (ie, standing weight-bearing flexion and extension) positions and examine the effects of lumbar disk degeneration on lumbar segmental motion. Various biomechanical studies using cadaveric specimens have demonstrated the effects of disk degeneration on lumbar motion. However, the studies did not determine the effect of disk degeneration on segmental motion in the functional, living spine. Segmental range of motion (ROM) was calculated and disk degeneration was graded in patients who had undergone KMRI in weight-bearing neutral, 60 degrees of flexion, and 20 degrees of extension. Patients (n=262) were categorized as having normal disks (n=94), single-level degeneration at L4–L5 (n=28) or L5–S1 (N=71), or double-level degeneration at L4–L5–S1 (N=69). Angular ROM, contribution (%)of each segment to total lumbar motion, and contribution of motion from upper (L1–L3) and lower (L4–S1) lumbar levels were compared. Mean ROMo f the lumbar spine in the normal group was 41.3±13.3 degrees. The L4–L5 degeneration group (36.1±12.4 degrees) and the L4–L5–S1 degeneration group (37.1±12.5 degrees) showed significantly decreased total lumbar ROM compared with the normal group. The ROM in upper lumbar segments was significantly larger than that in the lower segments in the normal group and similar in the degeneration groups. The contribution of L5–S1 to total lumbar motion was the smallest of all segments, and no significant difference was found between all groups. In functional positions assessed utilizing weight bearing KMRI, segmental motion at levels with degenerated disks was decreased. The contribution of upper lumbar segments to the total lumbar motion was not smaller than that of the lower segments. The L5–S1 level showed the smallest ROM in lumbar motion.

In vivo femoro-tibial kinematic analysis of a tri-condylar total knee prosthesis

BackgroundAn alternative tri-condylar implant has been designed to incorporate necessary posterior stability without a post, but has not been evaluated. The purpose of the current study was to determine the in vivo three dimensional femoro-tibial kinematics of a tri-condylar implant during a weight bearing deep knee bend activity. MethodsFluoroscopy based in vivo femoro-tibial kinematics of the tri-condylar implant was assessed for 66 knees during a deep knee bend activity, using a three dimensional to two dimensional model fitting approach. FindingsAverage range of motion was 125.5° (standard deviation (SD)=20.5°) in sagittal plane, and 42 knees (63.6%) experienced at least 120° of weight-bearing knee flexion. The average amount of posterior femoral movement (PFM) was 8.7mm (SD=4.3mm) for the medial condyle and 11.2mm (SD=5.4mm) for the lateral condyle. PFM of the medial condyle was significantly smaller than that of the lateral condyle. The average amount of femoro-tibial axial rotation was 5.7° (SD=6.4°), and 56 knees (84.8%) experienced a normal axial rotation pattern. Condylar lift-off, mostly occurring in deep flexion range, was experienced in 16 knees (24.2%). InterpretationKnees in the current study did achieve high weight-bearing flexion, more normal-like greater posterior femoral movement of lateral condyle than the medial condyle and a normal axial rotation pattern, albeit, less in magnitude than the normal knee.

Abnormal Axial Rotations in TKA Contribute to Reduced Weightbearing Flexion

Previous in vivo fluoroscopy studies have documented that axial rotation for patients having a TKA was significantly less than those having a normal knee. In fact, many subjects having a TKA experience a reverse axial rotation pattern where the femur internally rotates with increasing flexion. However, no previous studies have been conducted to determine if this reverse axial rotation pattern affects TKA performance. The purposes of this study were: (1) Do normal and reverse axial rotation patterns of a TKA affect the maximum flexion angle postoperatively? (2) Does the axial rotation angle of the knee at maximum flexion during weightbearing impact the magnitude of the maximum flexion achieved in weightbearing? One hundred twenty patients having TKA, previously analyzed under in vivo conditions using fluoroscopy and a three-dimensional model-fitting software package, were further evaluated to determine if reverse axial rotation patterns limit weightbearing TKA flexion. In this retrospective cohort, we identified 58 patients who had a normal axial rotation pattern (greater than 15° normal rotation). Sixty-two patients experienced greater than 3° of reverse axial rotation, defined as internal rotation of the femur relative to the tibia. Patients having a normal axial rotation achieved greater weightbearing knee flexion than those with reverse axial rotation (115° versus 109°, p = 0.02). Additionally, patients with greater than 3° of normal axial rotation at maximum flexion had more flexion than those with less than 3° of normal axial rotation at ending flexion (115° versus 107°, p < 0.001). These findings show reverse axial rotation and a smaller magnitude of normal axial rotation reduce weightbearing knee flexion. This is likely the result of increased posterior movement of the lateral condyle and is an important consideration in future implant designs.

In vivo kinematics of the knee during weight bearing high flexion

Achieving high flexion is an objective of contemporary total knee arthoplasty; however little is known on the knee biomechanics at high flexion under weight-bearing conditions. This study investigates the 6DOF kinematics and tibiofemoral cartilage contact biomechanics of the knee during weight-bearing flexion from full extension to maximal flexion. Eight knees from seven healthy subjects with no history of injuries or chronic pain were recruited. The knees were MRI scanned to create 3D models of the tibia and femur, including their articular cartilage surfaces. The subjects were then imaged using a dual fluoroscopic image system while performing a weight-bearing quasi-static single-legged lunge from full extension to maximal flexion. The 6DOF kinematics and the articular cartilage contact locations were measured along the flexion path of the knee. The result indicated that the internal tibial rotation increased sharply at low flexion angles (full extension to 30°), maintained a small variation in the middle range of flexion (30–120°, and then sharply increased again at high flexion angles (120° to maximal flexion). The contact point moved similarly in the medial and lateral compartments before 120° of flexion, but less on the medial compartment at high flexion angles. The results indicated that the knee motion could not be described using one character in the entire range of flexion, especially in high flexion. The knee kinematic data in the entire range of flexion of the knee could be instrumental for designing new knee prostheses to achieve physical high flexion and improving rehabilitation protocols after knee injuries.

Clinical and Kinematic Outcomes of A Rotating Platform Posterior Stabilized Total Knee System

Early post-operative clinical outcomes were analyzed for subjects having a rotating platform (RP) posterior stabilized (PS) total knee arthroplasty (TKA); a subset of which underwent in vivo kinematics and produced kinematic results that compare well with subjects in previous fluoroscopic studies that were deemed excellent in nature. In total, 153 subjects (180 knees) were enrolled in the prospective clinical study. TKAs were performed by three surgeons at three North American centers. Ten subjects were randomly chosen and evaluated under fluoroscopic surveillance. Average active flexion increased from 113.3 (SD=16.6) degrees before surgery to 118.3 (SD=9.9) degrees 12-months post-operatively. American Knee Society (AKS) function score increased from an average of 57.6 (SD=18.8) points pre-operatively to 85.3 (SD=16.6) points 12-months post-operatively. For the kinematic subset, post-operative weight-bearing flexion was 115.9 (SD=8.4),while subjects achieved an average posterior femoral rollback of their lateral condyle of −5.4mm. The average femorotibial axial rotation from full extension to maximum weight-bearing flexion was 3.9 degrees (SD=3.9). Certain kinematic parameters were deemed statistically significant when determining early post-operative clinical success.

Gender differences in tibio-femoral kinematics and quadriceps muscle force during weight-bearing knee flexion in vitro

Females have a higher risk in terms of anterior cruciate ligament injuries during sports than males. Reasons for this fact may be different anatomy and muscle recruitment patterns leading to less protection for the cruciate- and collateral-ligaments. This in vitro study aims to evaluate gender differences in knee joint kinematics and muscle force during weight-bearing knee flexions. Thirty-four human knee specimens (17 females/17 males) were mounted on a dynamic knee simulator. Weight-bearing single-leg knee flexions were performed with different amounts of simulated body weight (BW). Gender-specific kinematics was measured with an ultrasonic motion capture system and different loading conditions were examined. Knee joint kinematics did not show significant differences regarding anteroposterior and medial-lateral movement as well as tibial varus-valgus and internal-external rotation. This applied to all simulated amounts of BW. Simulating 100 N BW in contrast to AF50 led to a significant higher quadriceps overall force in female knees from 45° to 85° of flexion in contrast to BW 50 N. In these female specimens, the quadriceps overall force was about 20 % higher than in male knees being constant in higher flexion angles. It is indicated by our results that in a squatting movement females compared with males produce higher muscle forces, suggesting an increased demand for muscular stabilization, whereas tibio-femoral kinematics was similar for both genders.

Tibiofemoral cartilage contact biomechanics in patients after reconstruction of a ruptured anterior cruciate ligament

We investigated the in vivo cartilage contact biomechanics of the tibiofemoral joint in patients after reconstruction of a ruptured anterior cruciate ligament (ACL). A dual fluoroscopic and MR imaging technique was used to investigate the cartilage contact biomechanics of the tibiofemoral joint during in vivo weight-bearing flexion of the knee in eight patients 6 months following clinically successful reconstruction of an acute isolated ACL rupture. The location of tibiofemoral cartilage contact, size of the contact area, cartilage thickness at the contact area, and magnitude of the cartilage contact deformation of the ACL-reconstructed knees were compared with those previously measured in intact (contralateral) knees and ACL-deficient knees of the same subjects. Contact biomechanics of the tibiofemoral cartilage after ACL reconstruction were similar to those measured in intact knees. However, at lower flexion, the abnormal posterior and lateral shift of cartilage contact location to smaller regions of thinner tibial cartilage that has been described in ACL-deficient knees persisted in ACL-reconstructed knees, resulting in an increase of the magnitude of cartilage contact deformation at those flexion angles. Reconstruction of the ACL restored some of the in vivo cartilage contact biomechanics of the tibiofemoral joint to normal. Clinically, recovering anterior knee stability might be insufficient to prevent post-operative cartilage degeneration due to lack of restoration of in vivo cartilage contact biomechanics.