Secondary motions of the knee during weight bearing and non-weight bearing activities.

The objective of this study was to test the hypothesis that during a weight bearing activity such as walking, a dynamic range (envelope of motion) exists in the relationship between the secondary knee motions (anterior-posterior (AP) translation, internal-external (IE) rotation, and abduction-adduction (Ab-Adduction)) and knee flexion angle. In addition differences in the envelope of motion between a weight bearing and non-weight bearing activity were tested. The hypothesis was evaluated by testing for differences (offsets) in secondary displacements at specific knee flexion angles during the walking cycle and seated leg extension (non-weight bearing). Kinematic measurements were obtained using a previously developed point cluster technique to analyze the six-degrees of freedom movement of the knee. During walking, phase plots of the IE rotation and AP translation versus knee flexion demonstrated significant offsets from one phase of the gait cycle to another at the same flexion angle. During the non-weight bearing activity, no significant offset in the secondary movement was found; the knee followed the same pathway of motion during the flexion and extension phase of this activity. The characteristics of the secondary motions during walking indicated that secondary knee movements are caused by the external forces (muscle, inertial and gravitational) that act on the knee during the various phases of the walking cycle. The boundaries of the envelope appear to reflect the characteristics of the passive restraints. The weight bearing secondary motion AP and IE rotation seen during a walking activity demonstrated an envelope of dynamic laxity that could potentially be used to evaluate functional instabilities at the knee.     

Motion of a mobile bearing knee allowing translation and rotation.

The kinematics of a mobile bearing knee, which allowed +/-20 degrees of rotation and 4.5 mm of anteroposterior translation, was measured for ascending and descending a step, deep-knee bend, normal walking, and twisting. A fluoroscopic technique was used, analyzed by 2 different methods. The rotations and displacements during the activities were similar to those of moderate-to-high constrained fixed bearing knees. The motion patterns were variable among test subjects and in general did not reproduce normal knee motion. Because of the freedom of anteroposterior translation and rotation in the design, however, each knee could determine its own neutral position and its own axis of internal-external rotation, depending on the activity.     

The kinematics of fixed- and mobile-bearing total knee arthroplasty

The success of any total knee arthroplasty (TKA) is influenced by a complex interaction between component geometry and the surrounding soft tissues. The objective of this study was to investigate posterior femoral translation and tibial rotation in a single design posterior-stabilized TKA offering fixed- and mobile-bearing tibial components. Specifically, we examined whether mobile-bearing TKA restores normal knee translation and rotation better than fixed-bearing TKA design. Eleven human knee specimens retrieved postmortem were tested using a robotic system. The translation and rotation of the intact and reconstructed knees were compared. The data indicate that for all knees, posterior femoral translation occurs along the passive path and under muscle loading conditions. Furthermore, increasing flexion angle corresponded with increased internal tibial rotation. Femoral translation and tibial rotation for fixed- and mobile-bearing posterior-stabilized TKAs were similar despite component design variations. However, both arthroplasties only partially restored intact knee translation and rotation. The data presented here may serve as an aid in the development of a rationale for additional improvement in surgical techniques and prosthesis design, so that normal knee function may be restored.     

Demonstration of Rotatory Instability in Injured Knees by Stress Radiography

Rotatory instability of injured knees may be demonstrated by stress radiography by recording the different movements of the medial and lateral tibial condyle at pull or push with the knee in 90 degrees flexion. The displacements of the condyles are expressed in millimetres, not degrees. Comparison with the healthy knee is always used. The displacement of a tibial condyle has to exceed 3.0 mm in relation to the healthy knee to be defined as pathological. If the movements of both condyles exceed the movements in the healthy knee by more than 3.0 mm in the same direction a drawer sign is present - if only one of them moves, an abnormal rotation is present. When a drawer sign is present there may still be a greater displacement of one of the tibial condyles which means a rotatory instability added to the drawer sign, designated a complex rotatory instability. All types of rotatory instabilities, simple and complex, are defined and discussed, in relation to the classification of Nicholas, Trickey and Slocum & Larson. Forty-one cases of abnormal rotation were demonstrated in this series by stress radiography. The direction of rotation and the type of instability are described and compared with the operative findings. The findings are in agreement with those of the above-mentioned authors and the experimental work of Warren et al.     

Comparison of posterior-stabilized,cruciate-retaining,and medial-stabilized knee implant motion during gait

Accurate knowledge of knee joint motion is needed to evaluate the effects of implant design on functional performance and component wear. We conducted a randomized controlled trial to measure and compare 6-degree-of-freedom (6-DOF) kinematics and femoral condylar motion of posterior-stabilized (PS), cruciate-retaining (CR), and medial-stabilized (MS) knee implant designs for one cycle of walking. A mobile biplane X-ray imaging system was used to accurately measure 6-DOF tibiofemoral motion as patients implanted with PS (n = 23), CR (n = 25), or MS (n = 26) knees walked over ground at their self-selected speeds. Knee flexion angle did not differ significantly between the three designs. Relative movements of the femoral and tibial components were generally similar for PS and CR with significant differences observed only for anterior tibial drawer. Knee kinematic profiles measured for MS were appreciably different: external rotation and abduction of the tibia were increased while peak-to-peak anterior drawer was significantly reduced for MS compared with PS and CR. Anterior-posterior drawer and medial-lateral shift of the tibia were strongly coupled to internal-external rotation for MS, as was anterior-posterior translation of the contact center in the lateral compartment. MS exhibited the least amount of paradoxical anterior translation of the femur relative to the tibia during knee flexion. The joint center of rotation in the transverse plane was located in the lateral compartment for PS and CR and in the medial compartment for MS. Substantial differences were evident in 6-DOF knee kinematics between the healthy knee and all three prosthetic designs. Overall, knee kinematic profiles observed for MS resemble those of the healthy joint more closely than PS and CR.     

Kinematics of medial osteoarthritic knees before and after posterior cruciate ligament retaining total knee arthroplasty

Total knee arthroplasty (TKA) is a widely accepted surgical procedure for the treatment of patients with end‐stage osteoarthritis (OA). However, the function of the knee is not always fully recovered after TKA. We used a dual fluoroscopic imaging system to evaluate the in vivo kinematics of the knee with medial compartment OA before and after a posterior cruciate ligament‐retaining TKA (PCR‐TKA) during weight‐bearing knee flexion, and compared the results to those of normal knees. The OA knees displayed similar internal/external tibial rotation to normal knees. However, the OA knees had less overall posterior femoral translation relative to the tibia between 0° and 105° flexion and more varus knee rotation between 0° and 45° flexion, than in the normal knees. Additionally, in the OA knees the femur was located more medially than in the normal knees, particularly between 30° and 60° flexion. After PCR‐TKA, the knee kinematics were not restored to normal. The overall internal tibial rotation and posterior femoral translation between 0° and 105° knee flexion were dramatically reduced. Additionally, PCR‐TKA introduced an abnormal anterior femoral translation during early knee flexion, and the femur was located lateral to the tibia throughout weight‐bearing flexion. The data help understand the biomechanical functions of the knee with medial compartment OA before and after contemporary PCR‐TKA. They may also be useful for improvement of future prostheses designs and surgical techniques in treatment of knees with end‐stage OA. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:40–46, 2011     

Kinematics of the knee at high flexion angles: an in vitro investigation.

Restoration of knee function after total knee, meniscus, or cruciate ligament surgery requires an understanding of knee behavior throughout the entire range of knee motion. However, little data are available regarding knee kinematics and kinetics at flexion angles greater than 120 degrees (high flexion). In this study, 13 cadaveric human knee specimens were tested using an in vitro robotic experimental setup. Tibial anteroposterior translation and internal-external rotation were measured along the passive path and under simulated muscle loading from full extension to 150 degrees of flexion. Anterior tibial translation was observed in the unloaded passive path throughout, with a peak of 31.2+/-13.2 mm at 150 degrees. Internal tibial rotation increased with flexion to 150 degrees on the passive path to a maximum of 11.1+/-6.7 degrees. The simulated muscle loads affected tibial translation and rotation between full extension and 120 degrees of knee flexion. Interestingly, at high flexion, the application of muscle loads had little effect on tibial translation and rotation when compared to values at 120 degrees. The kinematic behavior of the knee at 150 degrees was markedly different from that measured at other flexion angles. Muscle loads appear to play a minimal role in influencing tibial translation and rotation at maximal flexion. The results imply that the knee is highly constrained at high flexion, which could be due in part to compression of the posterior soft tissues (posterior capsule, menisci, muscle, fat, and skin) between the tibia and the femur.     

Custom-fit versus premanufactured braces

Custom-made and off-the-shelf functional knee orthoses from four manufacturers were evaluated. Anterior tibial translation testing was performed using a pneumatic mechanical surrogated knee. The mechanical surrogate was interfaced with a servohydraulic materials testing system, which applied all anterior/posterior displacements to an ultimate anterior load of 400 N. Comparison of the individual custom versus premanufactured braces showed that the custom braces demonstrated a statistically significant difference for restraining anterior displacement (P=.0001 to P=.0005). Pooled data from all tests showed that the custom brace measurements as a group restrained anterior displacement better than the premanufactured brace group by a mean difference of 0.84 mm (P=.0001). The authors question whether such small, sub-millimeter findings between custom and off-the-shelf functional derotation braces represent any clinically significant differences.     

Intraoperative passive kinematics of osteoarthritic knees before and after total knee arthroplasty.

Total knee arthroplasty is a successful procedure to treat pain and functional disability due to osteoarthritis. However, precisely how a total knee arthroplasty changes the kinematics of an osteoarthritic knee is unknown. We used a surgical navigation system to measure normal passive kinematics from 7 embalmed cadaver lower extremities and in vivo intraoperative passive kinematics on 17 patients undergoing primary total knee arthroplasty to address two questions: How do the kinematics of knees with advanced osteoarthritis differ from normal knees?; and, Does posterior substituting total knee arthroplasty restore kinematics towards normal? Osteoarthritic knees displayed a decreased screw‐home motion and abnormal varus/valgus rotations between 10° and 90° of knee flexion when compared to normal knees. The anterior–posterior motion of the femur in osteoarthritic knees was not different than in normal knees. Following total knee arthroplasty, we found abnormal varus/valgus rotations in early flexion, a reduced screw‐home motion when compared to the osteoarthritic knees, and an abnormal anterior translation of the femur during the first 60° of flexion. Posterior substituting total knee arthroplasty does not appear to restore normal passive varus/valgus rotations or the screw motion and introduces an abnormal anterior translation of the femur during intraoperative evaluation. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1607–1614, 2006     

In Vivo Knee Kinematics in Patients With Bilateral Total Knee Arthroplasty of 2 Designs

Many younger and highly active patients desire to achieve high flexion after total knee arthroplasty. This study's purpose was to determine if a contemporary total knee arthroplasty design improved functional knee flexion compared with a traditional total knee arthroplasty in patients living a Western lifestyle. Ten patients with bilateral total knee arthroplasty of 2 types were studied during weight-bearing lunge, kneeling, and stair activities using fluoroscopic imaging. There were no differences in maximum knee flexion during lunging or kneeling. Statistically significant differences in tibial rotation and condylar translation were observed during the 3 activities. Although several joint kinematic differences were observed, no important functional differences were observed in clinically excellent, high performing subjects with bilateral total knee arthroplasty of 2 types.     

Stress changes of lateral collateral ligament at different knee flexion with or without displaced movements: a 3-dimensional finite element analysis

Objective: To create a 3-dimensional finite element model of knee ligaments and to analyse the stress changes of lateral collateral ligament (LCL) with or without displaced movements at different knee flexion conditions.Methods: A four-major-ligament contained knee specimen from an adult died of skull injury was prepared for CT scanning with the detectable ligament insertion footprints,locations and orientations precisely marked in advance. The CT scanning images were converted to a 3-dimensional model of the knee with the 3-dimensional reconstruction technique and transformed into finite element model by the software of ANSYS. The model was validated using experimental and numerical results obtained by other scientists.The natural stress changes of LCL at five different knee flexion angles (0°, 30°, 60°, 90°, 120°) and under various motions of anterior-posterior tibial translation, tibial varus rotation and internal-external tibial rotation were measured.Results: The maximum stress reached to 87%-113%versus natural stress in varus motion at early 30° of knee flexions. The stress values were smaller than the peak value of natural stress at 0° (knee full extension) when knee bending was over 60° of flexion in anterior-posterior tibial translation and internal-external rotation.Conclusion: LCL is vulnerable to varus motion in almost all knee bending positions and susceptible to anterlor-posterior tibial translation or internal-external rotation at early 30° of knee flexions.     

Diagnosis and management of a patient with knee pain using the movement system impairment classification system

STUDY DESIGN: Case report. BACKGROUND: Selecting the most effective conservative treatment for knee pain continues to be a challenge. An understanding of the underlying movement system impairment that is thought to contribute to the knee pain may assist in determining the most effective treatment. Our case report describes the treatment and outcomes of a patient with the proposed movement system impairment (MSI) diagnosis of tibiofemoral rotation. CASE DESCRIPTION: The patient was a 50-year-old female with a 3-month history of left anteromedial knee pain. Her knee pain was aggravated with sitting, standing, and descending stairs. A standardized clinical examination was performed and the MSI diagnosis of tibiofemoral rotation was determined. The patient consistently reported an increase in pain with activities that produced abnormal motions or alignments of the lower extremity in the frontal and transverse planes. The patient was educated to modify symptom-provoking functional activities by restricting the abnormal motions and alignments of the lower extremity. Exercises were prescribed to address impairments of muscle length, muscle strength, and motor control proposed to contribute to the tibiofemoral rotation. Tape also was applied to the knee in an attempt to restrict tibiofemoral rotation. OUTCOMES: The patient reported a cessation of pain and an improvement in her functional activities that occurred with correction of her knee alignment and movement pattern. Pain intensity was 2/10 at 1 week. At 10 weeks, pain intensity was 0/10 and the patient reported no limitations in sitting, standing, or descending stairs. The patient's score on the activities of daily living scale increased from 73% at the initial visit to 86% at 10 weeks and 96% at 1 year after therapy was discontinued. DISCUSSION: This case report presented a patient with knee pain and an MSI diagnosis of tibiofemoral rotation. Diagnosis-specific treatment resulted in a cessation of the patient's pain and an improved ability to perform functional activities.     

全膝关节置换股骨假体植入定位参数有限元分析及优化

目的通过有限元分析,结合正交试验方法,优化膝关节股骨假体植入的定位参数,有助于降低聚乙烯衬垫表面压应力峰值以减少磨损。方法依据全膝关节置换(TKA)基本原则,构建TKA膝关节有限元模型,以股骨假体外翻角度、外旋角度以及内外平移量作为正交试验的影响因素,对模型进行材料属性定义、边界条件建立并施加载荷,以聚乙烯衬垫上表面压应力峰值为研究指标,进行有限元分析,并对分析结果进行极差和方差分析,比较各因素变化对聚乙烯衬垫上表面压应力分布的影响,确定聚乙烯衬垫上表面压应力峰值最小的股骨假体植入定位参数的最优组合。结果通过有限元分析获得不同参数组合下9个TKA膝关节有限元模型聚乙烯衬垫上表面的压应力峰值,由极差分析,明确内外平移对分析结果影响最大,其次是外旋角度,外翻角度影响最小。确定股骨假体植入定位参数最优组合为外翻6°、外旋3°、平移0 mm。结论聚乙烯衬垫所受的压应力峰值受股骨假体位置变化影响,微小的植入位置变化可导致股骨-聚乙烯衬垫假体间的应力异常分布,提示术中要对股骨假体进行精确定位。     

Polyethylene contact stresses, articular congruity, and knee alignment.

Increased conformity at the tibiofemoral articulation increases contact area and reduces contact stresses in total knee arthroplasty. Malalignment, however, can increase polyethylene contact stresses. The effect of knee alignment and articular conformity on contact stresses was evaluated in a finite element model. The polyethylene insert and femoral component were modeled in high- and low-conformity conditions. An axial tibial load of 3000 N was applied across the tibiofemoral articulation at different knee positions ranging from 0 degrees, to 90 degrees, flexion, 0 to 10 mm anteroposterior translation, 0 degrees to 10 degrees axial rotation, and coronal plane angulation (liftoff). Increased conformity significantly reduced contact stresses in neutral alignment (by 44% at 0 degrees flexion and 36% at 60 degrees and 90 degrees flexion). Liftoff significantly increased contact stresses in low- and high-conformity conditions, but to a lesser degree in the high-conformity condition. Malalignment in rotation was most detrimental especially with the high-conformity insert design. Overall, increasing articular conformity reduced stresses when the knee was well-aligned. However, malalignment in axial rotation was detrimental. Mobile-bearing knee designs with increased articular congruity may result in lower contact stresses, especially the rotating-bearing designs that theoretically minimize rotational malalignment.     

Intraoperative measurement of knee kinematics in reconstruction of the anterior cruciate ligament

Our objectives were to establish the envelope of passive movement and to demonstrate the kinematic behaviour of the knee during standard clinical tests before and after reconstruction of the anterior cruciate ligament (ACL). An electromagnetic device was used to measure movement of the joint during surgery. Reconstruction of the ACL significantly reduced the overall envelope of tibial rotation (10 degrees to 90 degrees flexion), moved this envelope into external rotation from 0 degrees to 20 degrees flexion, and reduced the anterior position of the tibial plateau (5 degrees to 30 degrees flexion) (p < 0.05 for all). During the pivot-shift test in early flexion there was progressive anterior tibial subluxation with internal rotation. These subluxations reversed suddenly around a mean position of 36 +/- 9 degrees of flexion of the knee and consisted of an external tibial rotation of 13 +/- 8 degrees combined with a posterior tibial translation of 12 +/- 8 mm. This abnormal movement was abolished after reconstruction of the ACL.     

Can Joint Contact Dynamics Be Restored by Anterior Cruciate Ligament Reconstruction?

Background

Rotational kinematics has become an important consideration after ACL reconstruction because of its possible influence on knee degeneration. However, it remains unknown whether ACL reconstruction can restore both rotational kinematics and normal joint contact patterns, especially during functional activities.

Questions/purposes

We asked whether knee kinematics (tibial anterior translation and axial rotation) and joint contact mechanics (tibiofemoral sliding distance) would be restored by double-bundle (DB) or single-bundle (SB) reconstruction.

Methods

We retrospectively studied 17 patients who underwent ACL reconstruction by the SB (n = 7) or DB (n = 10) procedure. We used dynamic stereo x-ray to capture biplane radiographic images of the knee during downhill treadmill running. Tibial anterior translation, axial rotation, and joint sliding distance in the medial and lateral compartments were compared between reconstructed and contralateral knees in both SB and DB groups.

Results

We observed reduced anterior tibial translation and increased knee rotation in the reconstructed knees compared to the contralateral knees in both SB and DB groups. The mean joint sliding distance on the medial compartment was larger in the reconstructed knees than in the contralateral knees for both the SB group (9.5 ± 3.9 mm versus 7.5 ± 4.3 mm) and the DB group (11.1 ± 1.3 mm versus 7.9 ± 3.8 mm).

Conclusions

Neither ACL reconstruction procedure restored normal knee kinematics or medial joint sliding.

Clinical Relevance

Further study is necessary to understand the clinical significance of abnormal joint contact, identify the responsible mechanisms, and optimize reconstruction procedures for restoring normal joint mechanics after ACL injury.     

Die In-vivo-Biomechanik von unikondylären Knieprothesen in minimal-invasiver Technik

Disturbed kinematics of the knee plays an important role in early failure of a unicondylar knee prosthesis (UNI). Recent studies on kinematics have shown that an intact anterior cruciate ligament (ACL) is important for a successful UNI. In this study, in vivo fluoroscopic analysis of knee kinematics was performed for 30 patients with a successful medial UNI implanted with the use of minimally invasive technique. The three-dimensional data of the CAD model were used for evaluating the sagittal translation as well as the axial rotation during deep knee bending and one gait cycle. The anteroposterior translation for flexion was, on average, -5.3 mm (-15.7-3.3; standard deviation 5.3). In most cases, the contact point was more posterior compared with the normal knee. During gait, the average anteroposterior translation was 0.8 mm, which is comparable to that of the normal knee. Axial rotation for deep knee bending was, on average, 8 degrees (-1.3-22.0; standard deviation 5.7), whereas 28 of the 30 knees showed normal axial rotation. During gait, an average axial rotation of 0.94 degrees was observed. The kinematic pattern of each of the subjects did not replicate the average pattern in most of the patients. An insufficient ACL may be suspected as the cause of the pathological kinematic pattern observed in some of these patients.     

Knee motion after tibial osteotomy for arthrosis: Kinematic analysis of 7 patients

The in vivo kinematics of the knee in 7 patients with moderate medial gonarthrosis was analyzed before and 6 months after high tibial osteotomy using roentgen stereophotogrammetric analysis. The inclination of the femorotibial helical axis of rotation did not change with knee flexion or after surgery. The femorotibial rotation increased after surgery. No consistent change in patellar position after surgery was found. Patella translated laterally as the knee was flexed with a maximum patellar translation of about 15 mm and rotated internally with a maximum patellar internal rotation of about 15°. There was no significant change in patellar translation or rotation after surgery. There was a good concordance regarding the size of the tibial wedge removed during surgery, calculated from the Hip-Knee-Ankle radiographs and from the roentgen stereophotogrammetric measurements.     

Comparison of the syndesmotic staple to the transsyndesmotic screw: a biomechanical study

BACKGROUND: Controversy still exists about treatment of syndesmotic injuries. This study compared the fixation strengths and biomechanical characteristics of two types of ankle fracture syndesmotic fixation devices: the barbed, round staple and the 4.5-mm cortical screw. METHODS: Cadaveric testing was done on 21 fresh-frozen knee disarticulation specimens in biaxial servohydraulic Instron testing equipment. Submaximal torsional loads were applied to specimens in intact and Weber C bimalleolar fracture states. The specimens were then fixed with one of two techniques and again subjected to submaximal torsion and torsion to failure. Biomechanical parameters measured included tibiofibular translation and rotation, maximal torque to failure, and degrees of rotation at failure. RESULTS: Compared to the intact state before testing, the staple held the fibula in a more anatomic position than the screw for mediolateral and anterior displacements (p < 0.01). With submaximal torsional testing, the staple restored 85% of the tibiofibular external rotation and all of the posterior translation values as compared to the intact state. The screw resulted in 203% more tibiofibular medial translation and 115% more external rotation than the intact state. The degree of tibial rotation during submaximal torsional loading was restored to within 15% of intact values but was 21% less with the screw. There was no statistical difference between the screw and staple when tested in load to failure. Tibiotalar rotation at failure was statistically different with the staple construct, allowing more rotation as compared to the screw. CONCLUSION: The staple restored a more physiologic position of the fibula compared to the syndesmotic screw. Both provided similar performance for the load to failure testing, while the screw reduced tibial rotation more after cyclic loading. There was more tibial rotation before failure for the staple, suggesting a more elastic construct. This study provides biomechanical data to support the clinical use of the syndesmotic staple.     

A three-dimensional MRI analysis of knee kinematics.

PURPOSE: To quantify normal, in vivo tibio-femoral knee joint kinematics in multiple weight bearing positions using non-invasive, high-resolution MRI and discuss the potential of developing future kinematic methods to assess patients with abnormal joint pathologies. METHODS: Ten volunteers with clinically normal knees pushed inferiorly on the footplate of a weight bearing apparatus inside the MR scanner. The volunteers held the weight (133 N) for five scans as the knee motion was evaluated from 0 degrees to 60 degrees of flexion. Full extension was set as the zero point for all measured parameters. Using 3D reconstructions, tibia motion relative to the femur and flexion angle was measured as varus-valgus angle, axial rotation, anterior-posterior translation, and medial-lateral translation. Medial and lateral compartment tibio-femoral contact areas were examined and centroids of the contract areas were calculated. RESULTS: Tibial internal rotation averaged 4.8 degrees at 40 degrees of flexion and then decreased. Tibial valgus increased by 8 degrees at 60 degrees of flexion. Femoral roll back also increased to 18.5 mm average at 60 degrees of flexion, while the tibia translated medially 2.5 mm. Medial compartment femoro-tibial contact area started at 374 mm2 and decreased to 308 mm2 with flexion of 60 degrees, while lateral compartment contact area did not change significantly from 276 mm2. CONCLUSIONS: Results correlate with previous studies of knee kinematics while providing greater three-dimensional detail. MR imaging allows excellent non-invasive evaluation of knee joint kinematics with weight bearing. This tool may potentially be used for assessing knee kinematics in patients with knee pathology.