Methods, difficulties and inaccuracies in the study of human joint kinematics and pathokinematics by the instant axis concept. Example: the knee joint

Functions and Effectiveness of Unloader, Patellofemoral, and Knee Sleeve Orthoses: A Review

Background

Knee orthoses have been extensively used as a nonsurgical approach to improving knee deficiencies. Currently, arthritic knee conditions remain the leading cause of disability, and this number is expected to increase. As the use of knee orthoses varies widely, so has their effectiveness which is still largely debatable. Here, we present the functions and effectiveness of the three most prominent knee orthotic models dedicated to supporting knee osteoarthritis-unloader, patellofemoral, and knee sleeves.

Purpose/Research Question

Considering the depth and diversity of the many clinical studies and documented laboratory reports published to date, this literature review was created to educate the clinician, patient, and researcher on common knee orthoses used for the management of arthritic knee conditions. In doing so, we discuss their design, biomechanical effects, and clinical efficacy, as well as broader outcomes, limitations, and recommendations for use.

Results/Synthesis

The knee orthoses discussed within the scope of this paper are dedicated to protecting the knee against strenuous compressive loads that may affect the patellofemoral and tibiofemoral joints of the knee. Since the knee has multiple axes of motion and articulating surfaces that experience different loads during functional activities, it can be implied that, to a large extent, knee brace designs can differ drastically. Unloader knee orthoses are designed to decrease tibiofemoral and patellofemoral joint pressures. Patellofemoral knee orthoses are designed to decrease strain on the patellofemoral and quadriceps tendons while stabilizing the patella. Knee sleeves are designed to stabilize movements, reduce pain in joints, and improve proprioception across the knee joint.

Conclusion

Although patients often report benefits from wearing braces, these benefits have not been confirmed by clinicians and scientific investigators. Results from these three orthosis types show that clinical efficacy is still elusive due to the different methodologies used by researchers.

Layman Summary

Knee orthoses also referred to as knee brace are commonly used for support and stability of the knee. Unloader knee braces are designed to relieve and support those suffering from knee osteoarthritis by improving physical impairment and reducing pain. Patellofemoral knee braces aim to help patients manage patellofemoral pain syndrome. Rehabilitative compression sleeves, also known as knee sleeves, are often used to assist patients suffering from knee pain and laxity. Important findings on the three knee braces discussed show discrepancies in results. Their effectiveness and validity are yet to be understood.

Effect of center of rotation of angulation-based levelling osteotomy on instantaneous center of rotation ex vivo

Cranial cruciate ligament rupture is a common cause of femorotibial instability in dogs. Despite numerous techniques being described for achieving joint stabilization, no consensus exists on the optimal management strategy. This ex vivo study utilized the path of the instantaneous center of rotation (ICR) to compare normal, pathological and treated joints. Fluoroscopic recordings of seven limbs from a previous study of canine stifle joint stability following center of rotation of angulation-based levelling osteotomy (CBLO) with and without hamstring loading were analyzed using least-squares approximation of the ICR and estimation of percentage gliding (vs. rolling) to determine if alterations in ICR path and gliding caused by CCL transection and following meniscal release could be normalized by CBLO. In intact joints, the ICR path was located mid-condyle, but this shifted significantly proximally and caudally following CCL transection and medial meniscal release (p < 0.007, p < 0.04). Hamstring loading resulted in qualitative and some quantitative improvements in joint movement based on percentage gliding movement analysis. The ICR path after CBLO remained significantly different to the intact location with or without a hamstring load (p < 0.02, p < 0.04), potentially consistent with CBLO aims of mild residual instability. CBLO resulted in percentage gliding characteristics not significantly different to intact joints (p > 0.08). Qualitative improvements in ICR path and percentage gliding quantities and variability suggest that hamstring loading positively influences joint biomechanics and that further investigation of this role ex vivo and clinically is warranted.

Instantaneous center of rotation in the canine femorotibial joint: Ex vivo assessment of a tool to evaluate joint stabilization surgeries

Cranial cruciate ligament rupture is a common cause of femorotibial joint instability in the dog. Numerous techniques including several tibial osteotomies have been described for stabilization, but there is no current consensus on the best method. The instantaneous center of rotation (ICR) can aid investigations of pathological joint movement, but its use is problematic in the femorotibial joint due to combined rotation and translation during flexion and extension. Using fluoroscopic images from an earlier cadaveric study of canine joint stability, an interpolation method was used to create repeatable rotational steps across joint situations, followed by least squares approximation of the ICR. The ICR in intact joints was located mid-condyle but displaced significantly (P < 0.001) proximally following cranial cruciate ligament transection and medial meniscal release. Individual joints appear to respond differently to destabilization. Triple tibial osteotomy partially restored ICR location during early movement from flexion to extension. Joint instability significantly altered the proportions of rolling and gliding movement at the joint surface (P < 0.02), which triple tibial osteotomy partially improved. While triple tibial osteotomy restores joint stability ex vivo and clinically, normal biomechanics of the joint are not restored. The methods described here may prove useful for comparison of osteotomy techniques for stabilization of the cranial cruciate ligament deficient femorotibial joint in dogs.

Comparison of Knee Kinematics and Kinetics during Stair Descent in Single- and Multi-Radius Total Knee Arthroplasty

Despite continuing advances, nearly 20% of patients remain dissatisfied with their total knee arthroplasty (TKA) outcomes. Single-radius (SR) and multiradius (MR) TKA designs are two commonly used knee replacement designs based on competing theories of the flexion/extension axis of the knee. Our aim was to characterize stair descent kinematics and kinetics in SR and MR TKA subjects. We hypothesized that 1 year after TKA, patients who received SR TKA will more closely replicate the knee kinematics and kinetics of healthy age-matched controls during stair descent, than will MR TKA patients. SR subjects (n = 12), MR subjects (n = 12), and age-matched controls (n = 12) descended four stairs affixed to force platforms, while 10 infrared cameras tracked markers attached to the body to collect kinematic and kinetic data. Both patient groups had improvements in stair descent kinetics and kinematics at the 1-year postoperative time point. However, SR TKA subjects were indistinguishable statistically from age-matched controls, while MR TKA subjects retained many differences from controls. Similar to previous reports for level walking, the SR knee design performs closer to healthy controls than MR knees during stair descent. This study demonstrates that patients who receive SR TKA have more improved kinematic normalization during stair descent postoperatively than those who received an MR TKA.

Raising the Joint Line in TKA is Associated With Mid-flexion Laxity: A Study in Cadaver Knees

BACKGROUND

In a typical osteoarthritic knee with varus deformity, distal femoral resection based off the worn medial femoral condyle may result in an elevated joint line. In a setting of fixed flexion contracture, the surgeon may choose to resect additional distal femur to obtain extension, thus purposefully raising the joint line. However, the biomechanical effect of raising the joint line is not well recognized.

QUESTIONS/PURPOSES

(1) What is the effect of the level of the medial joint line (restored versus raised) on coronal plane stability of a TKA? (2) Does coronal alignment technique (mechanical axis versus kinematic technique) affect coronal plane stability of the knee? (3) Can the effect of medial joint-line elevation on coronal plane laxity be predicted by an analytical model?

METHODS

A TKA prosthesis was implanted in 10 fresh frozen nonarthritic cadaveric knees with restoration of the medial joint line at its original level (TKA0). Coronal plane stability was measured at 0°, 30°, 60°, 90°, and 120° flexion using a navigation system while applying an instrumented 9.8-Nm varus and valgus force moment. The joint line then was raised in two steps by recutting the distal and posterior femur by an extra 2 mm (TKA2) and 4 mm (TKA4), downsizing the femoral component and, respectively, adding a 2- and a 4-mm thicker insert. This was done with meticulous protection of the ligaments to avoid damage. Second, a simplified two-dimensional analytical model of the superficial medial collateral ligament (MCL) length based on a single flexion-extension axis was developed. The effect of raising the joint line on the length of the superficial MCL was simulated.

RESULTS

Despite that at 0° (2.2° ± 1.5° versus 2.3° ± 1.1° versus 2.5° ± 1.1°; p = 0.85) and 90° (7.5° ± 1.9° versus 9.0° ± 3.1° versus 9.0° ± 3.5°; p = 0.66), there was no difference in coronal plane laxity between the TKA0, TKA2, and TKA4 positions, increased laxity at 30° (4.8° ± 1.9° versus 7.9° ± 2.3° versus 10.2° ± 2.0°; p < 0.001) and 60° (5.7° ± 2.7° versus 8.8° ± 2.9° versus 11.3° ± 2.9°; p < 0.001) was observed when the medial joint line was raised 2 and 4 mm. At 30°, this corresponds to an average increase of 64% (3.1°; p < 0.01) in mid-flexion laxity with a 2-mm raised joint line and a 111% (5.4°; p < 0.01) increase with a 4-mm raised joint line compared with the 9-mm baseline resection. No differences in coronal alignment were found between the knees implanted with kinematic alignment versus mechanical alignment at any flexion angle. The analytical model was consistent with the cadaveric findings and showed lengthening of the superficial MCL in mid-flexion.

CONCLUSIONS

Despite a well-balanced knee in full extension and at 90° flexion, increased mid-flexion laxity in the coronal plane was evident in the specimens where the joint line was raised.

CLINICAL RELEVANCE

When recutting the distal and posterior femur and downsizing the femoral component, surgeons should be aware that this action might increase the laxity in mid-flexion, even if the knee is stable at 0° and 90°.

Synthesis of a Knee Joint Endoprosthesis is Based on Pure Rolling

One of the major contributing factors to the life of knee endoprostheses is wear resulting from sliding of the mating surfaces. Although this is not considered the primary cause for failure of the prosthesis, the importance of reducing wear becomes more pronounced with the increase of life expectancy of the patients. Sliding mechanisms are subjected to wear significantly more than rolling mechanisms. It was therefore suggested to develop a prosthetic knee joint in which the mating surfaces will roll one on top of the other. For this purpose an experimental study was carried out aimed at the investigation of the natural knee centrodes. Rolling of the natural centrodes on each other is bound to retain the natural kinematics of the knee elements and that of the soft tissues. Since the natural centrodes were found mechanically inadequate for reproduction, synthetic surfaces were postulated and examined. The various surfaces were subjected to kinematic optimization and the optimal surfaces from structural and kinematic reproduction aspects were selected. Finally, a conceptual configuration of the joint is suggested taking into account the necessary constraints for the performance of the rolling function.

Primary and coupled motions of the native knee in response to applied varus and valgus load

BACKGROUND

Knowledge of the complex kinematics of the native knee is a prerequisite for a successful reconstructive procedure. The aim of this study is to describe the primary and coupled motions of the native knee throughout the range of knee flexion, in response to applied varus and valgus loads.

METHODS

Twenty fresh-frozen cadaver knees were affixed to a six degree of freedom robotic arm with a universal force-moment sensor, and loaded with a 4Nm moment in varus and valgus at 0, 15, 30, 45, and 90° of knee flexion. The resulting tibiofemoral angulation, displacement, and rotation were recorded.

RESULTS

For each parameter investigated, the knee joint demonstrated more laxity at higher flexion angles. Varus angulation increased progressively from zero (2.0° varus) to 90 (5.2° varus) degrees of knee flexion (p<0.001). Valgus angulation also increased progressively, from zero (1.5° valgus) to 90 (3.9° valgus) degrees of knee flexion (p<0.001). At all flexion angles, the magnitude of tibiofemoral angle deviation was larger with varus than with valgus loading (p<0.05).

CONCLUSIONS

We conclude that the native knee exhibits small increases in coronal plane laxity as the flexion angle increases, and that the knee has generally more laxity under varus load than with valgus load throughout the Range of Motion (ROM). Larger differences in laxity of more than 2 to 3°, or peak laxity specifically during the range of mid-flexion, were not found in our cadaver model and are not likely to represent normal coronal plane kinematics.

LEVEL OF EVIDENCE

Level V, biomechanical cadaveric study.

Accuracy and repeatability of quantitative fluoroscopy for the measurement of sagittal plane translation and finite centre of rotation in the lumbar spine

Quantitative fluoroscopy (QF) was developed to measure intervertebral mechanics in vivo and has been found to have high repeatability and accuracy for the measurement of intervertebral rotations. However, sagittal plane translation and finite centre of rotation (FCR) are potential measures of stability but have not yet been fully validated for current QF. This study investigated the repeatability and accuracy of QF for measuring these variables. Repeatability was assessed from L2-S1 in 20 human volunteers. Accuracy was investigated using 10 consecutive measurements from each of two pairs of linked and instrumented dry human vertebrae as reference; one which tilted without translation and one which translated without tilt. The results found intra- and inter-observer repeatability for translation to be 1.1mm or less (SEM) with fair to substantial reliability (ICC 0.533-0.998). Intra-observer repeatability of FCR location for inter-vertebral rotations of 5° and above ranged from 1.5mm to 1.8mm (SEM) with moderate to substantial reliability (ICC 0.626-0.988). Inter-observer repeatability for FCR ranged from 1.2mm to 5.7mm, also with moderate to substantial reliability (ICC 0.621-0.878). Reliability was substantial (ICC>0.81) for 10/16 measures for translation and 5/8 for FCR location. Accuracy for translation was 0.1mm (fixed centre) and 2.2mm (moveable centre), with an FCR error of 0.3mm(x) and 0.4mm(y) (fixed centre). This technology was found to have a high level of accuracy and with a few exceptions, moderate to substantial repeatability for the measurement of translation and FCR from fluoroscopic motion sequences.

Impact of dynamic alignment, motion, and center of rotation on myelopathy grade and regional disability in cervical spondylotic myelopathy

OBJECT

Cervical stenosis is a defining feature of cervical spondylotic myelopathy (CSM). Matsunaga et al. proposed that elements of stenosis are both static and dynamic, where the dynamic elements magnify the canal deformation of the static state. For the current study, the authors hypothesized that dynamic changes may be associated with myelopathy severity and neck disability. This goal of this study was to present novel methods of dynamic motion analysis in CSM.

METHODS

A post hoc analysis was performed of a prospective, multicenter database of patients with CSM from the AOSpine North American study. One hundred ten patients (34%) met inclusion criteria, which were symptomatic CSM, age over 18 years, baseline flexion/extension radiographs, and health-related quality of life (HRQOL) questionnaires (modified Japanese Orthopaedic Association [mJOA] score, Neck Disability Index [NDI], the 36-Item Short Form Health Survey Physical Component Score [SF-36 PCS], and Nurick grade). The mean age was 56.9 ± 12 years, and 42% of patients were women (n = 46). Correlations with HRQOL measures were analyzed for regional (cervical lordosis and cervical sagittal vertical axis) and focal parameters (kyphosis and spondylolisthesis between adjacent vertebrae) in flexion and extension. Baseline dynamic parameters (flexion/extension cone relative to a fixed C-7, center of rotation [COR], and range of motion arc relative to the COR) were also analyzed for correlations with HRQOL measures.

RESULTS

At baseline, the mean HRQOL measures demonstrated disability and the mean radiographic parameters demonstrated sagittal malalignment. Among regional parameters, there was a significant correlation between decreased neck flexion (increased C2–7 angle in flexion) and worse Nurick grade (R = 0.189, p = 0.048), with no significant correlations in extension. Focal parameters, including increased C-7 sagittal translation overT-1 (slip), were significantly correlated with greater myelopathy severity (mJOA score, Flexion R = −0.377, p = 0.003; mJOA score, Extension R = −0.261, p = 0.027). Sagittal slip at C-2 and C-4 also correlated with worse HRQOL measures. Reduced flexion/extension motion cones, a more posterior COR, and smaller range of motion correlated with worse general health SF-36 PCS and Nurick grade.

CONCLUSIONS

Dynamic motion analysis may play an important role in understanding CSM. Focal parameters demonstrated a significant correlation with worse HRQOL measures, especially increased C-7 sagittal slip in flexion and extension. Novel methods of motion analysis demonstrating reduced motion cones correlated with worse myelopathy grades. More posterior COR and smaller range of motion were both correlated with worse general health scores (SF-36 PCS and Nurick grade). To our knowledge, this is the first study to demonstrate correlation of dynamic motion and listhesis with disability and myelopathy in CSM.

Analysis of knee functional flexion axis in navigated TKA: identification and repeatability before and after implant positioning

PURPOSE

Providing correct rotational alignment of femoral component in total knee arthroplasty (TKA) is mandatory to achieve correct kinematics, good ligament balance and patellar tracking. The purpose of this study was to evaluate potential clinical applications of functional flexion axis (FFA) by analysing the differences between pre- and post-implant placement. This evaluation was supported by the analysis of repeatability, assessing the robustness of the proposed method.

METHODS

Anatomical acquisitions and passive kinematics were acquired on 87 patients undergoing TKA using a commercial navigation system. Knee FFA was estimated, before and after implant positioning, from three flexion-extension movements between 0 and 120°. The angle between FFA and transepicondylar axis was analysed in frontal and axial planes. Repeatability coefficient and intraclass correlation coefficient (ICC) were used to analyse the reliability and the agreement in identifying the axis.

RESULTS

The analysed angle presented differences between pre- and post-operative conditions only in the frontal plane (from -8.3 ± 5.5° to -2.8 ± 5.3°) (p < 0.0001). There was good intraobserver reliability and agreement. Repeatability coefficient ranged between 4.4° (3.7-4.9°) and 3.4° (2.9-3.8°), the ICC between 0.87 (0.83-0.91) and 0.93 (0.90-0.95) and the standard deviation ranged between 1.3 and 1.0°.

CONCLUSIONS

The present study demonstrated that TKA affected the estimation of FFA only in the frontal plane. This method reported good repeatability, demonstrating its usefulness for clinical purposes particularly to evaluate rotational positioning of the femoral component in the axial plane.

LEVEL OF EVIDENCE

Case series, Level IV.

Sensitivity, reliability and accuracy of the instant center of rotation calculation in the cervical spine during in vivo dynamic flexion-extension

The instant center of rotation (ICR) has been proposed as an alternative to range of motion (ROM) for evaluating the quality, rather than the quantity, of cervical spine movement. The purpose of the present study was to assess the sensitivity, reliability and accuracy of cervical spine ICR path calculations obtained during dynamic in vivo movement. The reliability and sensitivity of in vivo cervical spine ICR calculations were assessed by evaluating the effects of movement direction (flexion versus extension), rotation step size, filter frequency, and motion tracking error. The accuracy of the ICR path calculations was assessed through a simulation experiment that replicated in vivo movement of cervical vertebrae. The in vivo assessment included 20 asymptomatic subjects who performed continuous head flexion-extension movements while biplane radiographs were collected at 30 frames per second. In vivo motion of C2 through C7 cervical vertebrae was tracked with sub-millimeter accuracy using a volumetric model-based tracking technique. The finite helical axis method was used to determine ICRs between each pair of adjacent vertebra. The in vivo results indicate ICR path is not different during the flexion movement and the extension movement. In vivo, the path of the ICR can reliably be characterized within 0.5mm in the SI and 1.0mm in the AP direction. The inter-subject variability in ICR location averaged ±1.2mm in the SI direction and ±2.2mm in the AP direction. The computational experiment estimated the in vivo accuracy in ICR location was between 1.1mm and 3.1mm.

Is femoral component rotation in a TKA reliably guided by the functional flexion axis?

BACKGROUND

The position of the femoral component in a TKA in the axial plane influences patellar tracking and flexion gap symmetry. Errors in femoral component rotation have been implicated in the need for early revision surgery. Methods of guiding femoral component rotation at the time of implantation typically are derived from the mean position of the flexion-extension axis across experimental subjects. The functional flexion axis (FFA) of the knee is kinematically derived and therefore a patient-specific reference axis that can be determined intraoperatively by a computer navigation system as an alternative method of guiding femoral component rotation. However, it is unclear whether the FFA is reliable and how it compares with traditional methods.

QUESTION/PURPOSES

We asked if the FFA could be measured reproducibly at different stages of the operative procedure; (2) where it lies in relation to a CT-derived gold standard; and (3) how it compares with more traditional methods of judging femoral component rotation.

METHODS

Thirty-seven patients undergoing elective TKAs were recruited to the study. Preoperative CT scans were obtained and the transepicondylar axis (TEA) was identified. The TKA then was performed using computer navigation. The FFA was derived before incision and again after the surgical approach and osseous registration. The navigation system was used to register the surgical TEA. The FFA and surgical TEA then were compared with the CT-derived TEA.

RESULTS

The mean preincision FFA was similar to the intraoperative FFA and therefore deemed reproducible. We observed no differences in variability between surgical TEA and preincision FFA. The FFA was different from the CT-TEA and judged similar in accuracy to the surgical TEA.

CONCLUSION

The reliability and accuracy of the FFA were similar to those of other intraoperative methods. Further evaluation is required to ascertain whether the FFA improves on currently available methods for determining the ideal rotation of the femoral component during TKA.

Knee functional flexion axis in osteoarthritic patients: comparison in vivo with transepicondylar axis using a navigation system

PURPOSE

No study, up to now, has examined the effect of arthritis on pathologic subjects using functional flexion axis (FFA). The purpose of this study is to understand whether arthritis affects somehow the FFA evaluation and to assess whether the FFA could be considered a usable reference for implant positioning for osteoarthritic knees.

METHODS

Using a navigation system, FFA orientation was evaluated intraoperatively (computed with the mean helical axis method) in three different ranges of motion (0°-120°; 35°-80°; 35°-120°) and in two different planes (coronal and axial), for 111 osteoarthritis patients undergoing total knee arthroplasty. The results were compared with a control group of 60 patients that underwent ACL reconstruction. The angle between the transepicondylar axis (TEA) and FFA was computed.

RESULTS

Results showed in arthritic knees on frontal plane, an average difference between TEA and FFA of -2.8° ± 5.0° while on axial plane it was 0.6° ± 4.7°. No statistical difference was found between the three ranges in axial view, whereas some difference was found in frontal view (P < 0.0001). The TEA-FFA angle was not correlated with limb alignment on axial plane, while it was, even if poor, in frontal plane. In the control group, in frontal and in axial view, no statistical difference was found for the angle between TEA and FFA.

CONCLUSIONS

FFA can be used as reference for implant positioning in axial plane also in pathologic knees, while for the frontal plane further investigations are required.

Anatomical Study of the Radius and Center of Curvature of the Distal Femoral Condyle

In this anatomical study, the anteroposterior curvature of the surface of 16 cadaveric distal femurs was examined in terms of radii and center point. Those two parameters attract high interest due to their significance for total knee arthroplasty. Basically, two different conclusions have been drawn in foregoing studies: (1) The curvature shows a constant radius and (2) the curvature shows a variable radius. The investigations were based on a new method combining three-dimensional laser-scanning and planar geometrical analyses. This method is aimed at providing high accuracy and high local resolution. The high-precision laser scanning enables the exact reproduction of the distal femurs—including their cartilage tissue—as a three-dimensional computer model. The surface curvature was investigated on intersection planes that were oriented perpendicularly to the surgical epicondylar line. Three planes were placed at the central part of each condyle. The intersection of either plane with the femur model was approximated with the help of a b-spline, yielding three b-splines on each condyle. The radii and center points of the circles, approximating the local curvature of the b-splines, were then evaluated. The results from all three b-splines were averaged in order to increase the reliability of the method. The results show the variation in the surface curvatures of the investigated samples of condyles. These variations are expressed in the pattern of the center points and the radii of the curvatures. The standard deviations of the radii for a 90 deg arc on the posterior condyle range from 0.6 mm up to 5.1 mm, with an average of 2.4 mm laterally and 2.2 mm medially. No correlation was found between the curvature of the lateral and medial condyles. Within the range of the investigated 16 samples, the conclusion can be drawn that the condyle surface curvature is not constant and different for all specimens when viewed along the surgical epicondylar axis. For the portion of the condylar surface that articulates with the tibia during knee flexion-extension, the determined center points approximate the location of the centers of rotation. The results suggest that the concept of a fixed flexion-extension axis is not applicable for every specimen.

The influence of sequential debridement in total knee arthroplasty on the flexion axis of the knee using computer-aided navigation

The effects of osteophyte debridement, bony cuts, and soft tissue releases on the functional flexion axis of the knee can be assessed by evaluating 3D kinematics following each step of a total knee arthroplasty. Using a navigated knee system with dedicated software, the functional flexion axis (helical axis) can be determined after each step. Five paired fresh-frozen cadaveric knees were used with a CT scan performed on each specimen identifying implanted fiducial markers. Kinematics data were recorded during each step of sequential osseous cuts and soft tissue releases for both an unloaded and loaded limb by each of three surgeons. The functional helical (flexion/extension) axis was identified for all specimens. The internal/external rotation angle (theta) of the helical axis differed from the transepicondylar axis by -8.3 degrees to +6.7 degrees for the unloaded condition. theta ranged from -7.2 degrees to +7.4 degrees with distraction. Soft tissue releases had no effect on theta; until a bony cut of the articular surface, which increased theta from -0.3 degrees to +9.7 degrees. Implantation of cruciate retaining prosthetic components subsequently reduced the theta range -7.3 degrees to +4.0 degrees. Thus, soft tissue releases had minimal effect on theta of the helical axis except for resection of the proximal tibia. Implantation of the CR prosthesis reduced è close to that of the intact knee. In a minority of knees, the helical axis did not coincide exactly with the transepicondylar axis. Interspecimen and left/right variability of theta were significant, although interinvestigator variability and an applied distraction force were insignificant.

Development of a hinge compatible with the kinematics of the knee joint

This study aims to present a new concept of a knee hinge based on a crossed four-bar linkage mechanism which has been designed to optimally follow a motion curve representing the knee kinematics in the position at which the knee hinge should be placed. The methodology used to determine the optimal knee hinge is based on the optimization of certain variables of the crossed four-bar mechanism using genetic algorithms in order to follow a certain motion curve, which was determined using a biomechanical model of the knee motion. Two current, commercially available knee hinges have been used to theoretically determine their motion by means of the path performed by their instantaneous helical axis. Comparison between these two different knee hinges, Optimal Knee Hinge and the theoretical motion performed by a human knee reveals that a common monocentric hinge has a maximum misalignment of up to 27.2 mm; a polycentric hinge has a maximum misalignment of 23.9 mm. In contrast, the maximum misalignment produced by the Optimal Knee Hinge is 1.99 mm. The orthotic joint presented significantly improves the kinematical compatibility and the adjustment between orthotic and human joint motion, and should provide several advantages in terms of comfort and safety. Furthermore, the determination of the instantaneous helical axis for a particular user, by means of human movement measurement techniques, will enable the optimal crossed four-bar mechanisms to be determined in a customized and personalized manner. As a consequence, this new concept of orthotic knee joint design may improve the adaptability of lower limb orthoses for the user, and may lead to significant advantages in the field of orthotics for the lower limb.

Recognizing knee pathologies by classifying instantaneous screws of the six degrees-of-freedom knee motion

We address the problem of knee pathology assessment by using screw theory to describe the knee motion and by using the screw representation of the motion as an input to a machine learning classifier. The flexions of knees with different pathologies are tracked using an optical tracking system. The instantaneous screw parameters which describe the transformation of the tibia with respect to the femur in each two successive observation is represented as the instantaneous screw axis of the motion given in its Plücker line coordinates along with its corresponding pitch. The set of instantaneous screw parameters associated with a particular knee with a given pathology is then identified and clustered in R(6) to form a "signature" of the motion for the given pathology. Sawbones model and two cadaver knees with different pathologies were tracked, and the resulting screws were used to train a classifier system. The system was then tested successfully with new, never-trained-before data. The classifier demonstrated a very high success rate in identifying the knee pathology.

The functional flexion-extension axis of the knee corresponds to the surgical epicondylar axis: in vivo analysis using a biplanar image-matching technique

We investigated the concept that the knee has a fixed flexion-extension axis in the posterior femoral condyles and that this functional axis corresponds to the surgical epicondylar axis in vivo. We used a biplanar image-matching technique to perform the in vivo analysis of 9 normal knees to determine the location of the functional flexion-extension axis of the knee using an optimization technique. The functional flexion-extension axis passed through the sulcus of the medial epicondyle and the prominence of the lateral epicondyle. Flexion and extension of the knee could be represented as a rotation around a fixed axis, and this functional axis corresponded to the surgical epicondylar axis during a 0 degrees to 90 degrees flexion. This study assists more understanding of knee kinematics and provides useful information for the design and positioning of the prostheses used in total knee arthroplasty.

The movement of the normal tibio-femoral joint

This review describes the anatomy of the articular surfaces and their movement in the normal tibio-femoral joint, together with methods of measurement in volunteers. Forces and soft tissues are excluded. To measure movement, the articular surfaces and natural or inserted movement markers must be imaged by some combination of MRI, CT, RSA or fluoroscopy. With the aid of computer-imaging, the movements can then be related to an anatomy-based co-ordinate system to avoid kinematic cross-talk. Methods of depicting these movements which are understandable to engineers and clinicians are discussed. The shapes of the articular surfaces are reported. They are relevant to landmarks and co-ordinate systems and form a basis for inferring the nature of the movements which take place in the knee. The movements of the condyles are described from hyperextension to full passive flexion. Medially the condyle hardly moves antero-posteriorly from 0 degrees to 120 degrees but the contact area transfers from an anterior pair of tibio-femoral surfaces at 10 degrees to a posterior pair at about 30 degrees . Thus because of the shapes of the bones, the medial contact area moves backwards with flexion to 30 degrees but the condyle does not. Laterally the femoral condyle and the contact area move posteriorly but to a variable extent in the mid-range causing tibial internal rotation to occur with flexion around a medial axis. From 120 degrees to full flexion both condyles roll back onto the posterior horn so that the tibio-femoral joint subluxes.

Can normal knee kinematics be restored with unicompartmental knee replacement?

BACKGROUND

Unicompartmental replacement can be an alternative to tibial osteotomy in younger, active patients with unicompartmental knee disease. In unicompartmental replacement, the other compartments and knee ligaments are largely untouched. Therefore, it was hypothesized that the knee kinematics after unicompartmental replacement may also be unchanged. To test this hypothesis, knee kinematics and quadriceps tension were recorded before and after replacement with a unicompartmental design and then with a tricompartmental design.

METHODS

Six human cadaver knees were tested before implantation, after implantation with a bicruciate-retaining unicompartmental knee prosthesis, and after implantation with a posterior cruciate-retaining tricompartmental knee prosthesis. The unicompartmental prosthesis was initially implanted, and it was then revised to a total condylar knee replacement. The knee kinematics were measured with use of an electromagnetic tracking device while the knee was put through dynamic simulated stair-climbing under peak flexion moments of approximately 40 N-m. Quadriceps tension was also measured for all three conditions.

RESULTS

No significant differences in tibial axial rotation were noted between the intact and unicompartmental conditions. However, tricompartmental replacement significantly affected tibial axial rotation (p = 0.001). Femoral rollback was not significantly affected by either unicompartmental or tricompartmental arthroplasty. Quadriceps tension was also similar among all three conditions.

CONCLUSIONS

In this in vitro cadaver study, the tricompartmental replacement significantly changed knee kinematics while the unicompartmental replacement preserved normal knee kinematics.

Development of the concepts of knee kinematics

OBJECTIVES

To review the experimental evidence and development of concepts in knee kinematics and to present a synthesis of current theories.

DATA SOURCES

Historical literature from private collections and published journals, from Galen in 160 AD, and Weber and Weber in 1860, through to current research in knee kinematics, sourced through MEDLINE and CINAHL.

STUDY SELECTION

Studies of the healthy human knee in vivo and in vitro were included. Other studies were included when relevant, for example, when knee surgery methods have led to a change in kinematic concepts. Of 285 items, 94 were included based on their contribution to original research. When relevant, authors were contacted to resolve issues.

DATA EXTRACTION

Sources included were descriptive studies, anatomic dissections, controlled experimental designs, editorials, and review articles.

DATA SYNTHESIS

The axes of rotation of the knee are fundamental to kinematic models. The hinge model is contradicted by the ellipsoid shape of the femoral condyles, which results in a moving instant center of motion. However, the "instant center of motion" model was based on analysis of sagittal sections, oblique to the plane of movement and neglecting rotation. The four-bar linkage theory linked cruciate ligament isometry with the roll and glide pattern of knee motion. Recently, however, studies of the biomechanics and histology of the knee ligaments have enabled more accurate kinematic modeling. Three-dimensional imaging and computer modeling have made possible analysis of kinematics parallel to the planes of motion and incorporation of conjoint rotation. Femoral roll back is now described as the manifestation of longitudinal rotation during knee flexion.

CONCLUSIONS

Current research concludes that the knee has 4 independent axes: patella, posterior condylar, distal condylar, and longitudinal axes. The axes combine to produce the characteristic helical motion of the knee.

Tibiofemoral Joint-Surface Motions in Weight-Bearing and Non-Weight-Bearing Movement

Context:

Analyses of the path of instant center of rotation (PICR) can be used to infer joint-surface rolling and sliding motion (arthrokinematics). Previous PICR research has not quantified arthrokinematics during weight-bearing (WB) movement conditions or studied the association of muscle activity with arthrokinematics.

Objective:

To examine tibiofemoral arthrokinematics and thigh-muscle EMG during WB and non-weight-bearing (NWB) movement.

Design:

2 x 9 repeated-measures experiment.

Setting:

Laboratory.

Participants:

11 healthy adults (mean age 24 years).

Main Outcome Measures:

Tibiofemoral percentage rolling arthrokinematics and quadriceps: hamstring EMG activity.

Results:

WB percentage rolling (76.0% ± 4.7%) exceeded that of NWB (57.5% ± 1.8%) through terminal knee extension (F8,80= 8.99,P< .001). Quadriceps:hamstring EMG ratios accounted for 45.1% and 34.7% of the variance in arthrokinematics throughout the WB and NWB movement conditions, respectively (P< .001).

Conclusions:

More joint-surface rolling occurs through terminal knee extension during WB movement and is associated with an increase in hamstring activity.

The instantaneous axis of rotation (IAOR) of the foot and ankle: a self-determining system with implications for rehabilitation medicine application

A noninvasive method for determining the instantaneous axis of rotation (IAOR) of the foot and ankle during human ambulation has been developed. The algorithm uses three-dimensional (3-D) external marker trajectories to describe the IAOR of the calcaneus with respect to the tibia. Multiple optimization techniques were used to fit a plane and a sphere to the marker trajectories, with the constraint that the center of the sphere lie on the plane. The IAOR was defined perpendicular to the plane and passed through the center of the sphere. The results from validation procedures have demonstrated the applicability of the method. Experimental IAOR data acquired from normal adult subjects indicated the ability to track the IAOR during gait. This self-determining system for locating a patient's foot and ankle IAOR during gait may benefit rehabilitation applications in pedorthic and prosthetic design, surgical and nonsurgical treatment, and rehabilitative approaches to suprasegmental functional accommodation.

Helical axis errors affect computer-generated occlusal contacts

A helical axis describing mandibular motion can be calculated from two distinct positions of the mandible; however, as these positions come closer together, calculation errors increase. This study investigated the effects of errors in the calculated helical axis on simulated mandibular motion by the measurement of changes in occlusal contacts. A standard helical axis was calculated from a simulated lateral movement. A series of digital interocclusal records from centric to a 5 degree mandibular rotation about the standard helical axis was created. Digital dental cast models were aligned to the interocclusal records. Helical axis parameters and occlusal contacts calculated with the use of the aligned digital models were compared with those of the standard. Helical axes calculated from mandibular positions separated by 1.5 degrees to 5.0 degrees yielded equivalent occlusal contacts. Qualitatively, contacts for helical axes calculated from jaw rotations of 0.7 degrees or larger were nearly identical to those of the standard.

Quadriceps moment arm and quadriceps forces after total knee arthroplasty

Knee prosthetic designs that increase quadriceps moment arm can reduce quadriceps tension and patellofemoral compressive forces. Six knees from cadavers were tested on the Oxford knee rig, which simulates closed chain knee extension under load. Three conditions were tested sequentially for each knee: Normal, Control (implanted with the Osteonics 7000 knee design), and Scorpio (implanted with the Osteonics Scorpio design). The center of flexion-extension of the Scorpio design was 10 mm posterior to that of Control that served to lengthen the quadriceps moment arm. An electromagnetic tracking system measured dynamic knee kinematics, and a uniaxial load cell measured quadriceps tension. The Scorpio design reduced quadriceps tension when compared with the Normal or Control knee ranging from 5% to 20%. This was statistically significant at flexion angles greater than 50 degrees. In three knees, the patellar component was instrumented with a triaxial load cell that measured patellofemoral forces. Patellofemoral forces were lower with the Scorpio design compared with the Control. Increasing quadriceps lever arm reduces quadriceps forces and can facilitate activities of daily living and enhance patient rehabilitation. Reduced quadriceps forces may result in reduced patellofemoral forces that can have a beneficial effect on anterior knee pain, patellar component wear, and loosening.

Relationship between frontal knee alignment and reference axes in the distal femur

The two transepicondylar axes (the clinical and surgical epicondylar axes), the posterior condylar axis, and the anteroposterior axis were constructed using computed tomography scans in 111 (66 patients) knees with symptomatic arthritis. The relationships between angles made by these reference axes and two angles indicating frontal knee alignment (the tibiofemoral valgus angle and the femoral valgus angle) were investigated. In Y of the knees, the surgical epicondylar axis could not be constructed because the sulcus of the medial epicondyle was not recognizable. The condylar twist angle was almost constant and averaged 6 degrees when the femoral valgus angle was 9 degrees or less, but increased gradually when the angle was greater than 9 degrees. The difference between the condylar twist angle and the posterior condylar angle was constantly 3 degrees. The anteroposterior axis was almost at right angles to the clinical epicondylar axis, and the relationship between these axes was constant, independent of the femoral valgus angle. With 3 degrees to 6 degrees external rotation relative to the posterior condylar axis, the femoral component could be set parallel to the transepicondylar axis in common varus or neutral knees. In cases with a larger femoral valgus angle, the anteroposterior axis would be a more reliable reference axis. Preoperative computed tomography scans are recommended for patients with knees with severe valgus deformity or severe hypertrophic osteoarthritis.

Estimation of the finite center of rotation in planar movements

The finite center of rotation (FCR) is often used to assess joint function. It was the purpose of this study to compare the accuracy of the procedure of Crisco et al. [4] for estimating the FCR with a procedure which uses least-squares principles. The procedures were evaluated using noisy data rotated about a known FCR. Both procedures demonstrated increasing accuracy of FCR estimation with increasing rotation angle. As the centroid of a pair of markers was moved further from the FCR, accuracy of its location decreased. Noise levels had a strong influence on FCR estimation accuracy, with the least-squares procedure being better able to cope with noise. Increasing the number of landmarks increased FCR estimation accuracy. The accuracy of the procedure of Crisco et al. [4] increased when multiple estimates of the FCR were averaged. On all of the evaluations performed, the least-squares procedure gave small improvements in the accuracy of estimating the FCR, but was not able to circumvent the inaccuracies which arise when landmarks are not appropriately positioned, numerous, or if the rotation angle is small.

Neandertal knees: power lifters in the Pleistocene?

It has been proposed (Trinkaus, 1983 a; Miller & Gross, 1998) that the marked thickness of Neandertal patellae and/or the posterior displacement of their tibial condyles increased their relative M. quadriceps femoris moment arms, thereby making their legs powerful in extension. However, it is necessary to compare these reflections of muscle moment arm length to appropriate measures of the body weight moment arm and body mass estimates, both of which are influenced by ecogeographically determined body proportions. Reassessment of tibial condylar displacement and patellar thickness, as well as patellar height, relative to an appropriate measure of the moment arm for the baseline load on the knee (body weight), to that moment arm times estimated body mass, and to that moment arm times a skeletal reflection of body mass (femoral head diameter) rejects the hypothesis that the Neandertals had exceptionally powerful knee extension. Relative tibial condylar displacement remains above that of a modern industrial society sample, but similar to that of the Broken Hill tibia, Late Pleistocene early modern humans and a recent human nonindustrial sample. Relative patellar thickness is similar to that of early modern humans, who have relatively thick patellae compared to the late Holocene human samples. Consequently, once body proportions are taken into account, there is little difference between the Neandertals and other later Pleistocene humans in knee extensor mechanical advantage, and all of these fossil hominids are similar in the more important proximal tibial proportions to those of nonindustrial recent humans.

Three-dimensional dynamical capabilities of the human masticatory muscles

Many habitual human jaw movements are non-symmetrical. Generally, it is observed that when the lower incisors move to one side the contralateral condyle moves forwards onto the articular eminence, whereas the ipsilateral condyle stays in the mandibular fossa, moving slightly to the ipsilateral side. These jaw movements are the result of contractions of active masticatory muscles and guided by the temporomandibular joints, their ligaments and passive elastic properties of the muscles. It is not known whether the movements are primarily dependent on passive guidance, active muscle control or both. Therefore, the objective of this study was to analyse the interplay between these factors during non-symmetrical jaw movements. A six-degrees-of-freedom dynamical biomechanical model of the human masticatory system was used. The movements were not restricted to a priori defined joint axes. Jaw movement simulations were performed by unilateral activity of the muscles. The ligaments or the passive elastic properties of the muscles could be removed during these simulations. Laterodeviations conform to naturally observed ones could be generated by unilateral muscle contractions. The movement of the lower incisors was hardly affected by the absence of passive elastic muscle properties or temporomandibular ligaments. The latter, however, influenced the movement of the condyles. The movements could be understood by analysing the combination of forces and torques with respect to the centre of gravity of the lower jaw. In addition, the loading of the condyles appeared to be an important determinant for the movement. This analysis emphasizes that the movements of the jaw are primarily dependent on the orientation of the contributing muscles with respect to this centre of gravity and not on the temporomandibular ligaments or passive elastic muscle properties.

Knee joint motion: description and measurement

Knee joint motion has been described in various ways in the literature. These are explained and commented on. Two methods for describing knee joint motion with 6 degrees of freedom (DOF)--Euler angle and the helical axis of motion--are discussed. Techniques to measure joint motion which can either approximate the motion to less than 6 DOF or fully measure the spatial motion are identified. These include electrical linkage methods, radiographic and video techniques, fluoroscopic techniques and electromagnetic devices. In those cases where the full spatial motion is measured, the data are available to describe the motion in simpler terms (or with less DOF) than three rotations with three translations. This is necessary for clinical application and to facilitate communication between the clinician and the engineer.

Prediction of mandibular autorotation

PURPOSE

The purpose of this investigation was to test the hypothesis that the mandible rotates around the same point during maxillary impaction surgery as during initial jaw opening. This point, called the center of mandibular autorotation (CAR), could then be used to predict mandibular position and to decide whether only maxillary impaction would be needed to correct the occlusion and the facial profile.

PATIENTS AND METHODS

Preoperatively, two lateral cephalograms were obtained from a consecutive series of 20 patients who underwent maxillary impaction without concomitant mandibular ramus osteotomy. One cephalogram was taken with the mandible in centric relation using a wax bite wafer and another with a jaw opening of 10 mm using a fabricated acrylic bite block with the mandible manipulated to its most retruded position. The CAR was calculated before and after jaw opening using the Rouleaux method on the lower incisor and gonion point. A third lateral cephalogram was taken within 2 days postoperatively. The postoperative lower incisal point was then transferred to the first cephalogram using cranial base superimposition.

RESULTS

When the preoperative and postoperative distances between CAR and incisal point were compared, there was no significant difference between these distances, proving the hypothesis.

CONCLUSIONS

The method used is a practical and precise way to determine the center of mandibular autorotation on an individual basis. The center of rotation during initial jaw opening is the same as during impaction surgery.

The transepicondylar axis approximates the optimal flexion axis of the knee

The traditional understanding of knee kinematics holds that no single fixed axis of rotation exists in the knee. In contrast, a recent hypothesis suggests that knee kinematics are better described simply as two simultaneous rotations occurring about fixed axes. Knee flexion and extension occurs about an optimal flexion axis fixed in the femur, whereas tibial internal and external rotations occur about a longitudinal rotation axis fixed in the tibia. No other translations or rotations exist. This hypothesis has been tested. Tibiofemoral kinematics were measured for 15 cadaveric knees undergoing a realistic loadbearing activity (simulated squatting). An optimization technique was used to identify the locations of the optimal flexion and longitudinal rotation axes such that simultaneous rotations about them could best represent the measured kinematics. The optimal flexion axis was compared with the transepicondylar axis defined by bony landmarks. The longitudinal rotation axis was found to pass through the medial joint compartment. The optimal flexion axis passed through the centers of the posterior femoral condyles. No significant difference was found between the optimal flexion and transepicondylar axes. To an average accuracy of better than 3.4 mm in translation, and 2.9 degrees in orientation, knee kinematics were represented successfully by simple rotations about the optimal flexion and longitudinal rotation axes. The optimal flexion axis is fixed in the femur and can be considered the true flexion axis of the knee. The transepicondylar axis axis, which is identified easily by palpation, closely approximates the optimal flexion axis.

Joint kinematics simulation from medical imaging data

A method for joint kinematics simulation is described. Kinematics parameters are determined from the relative displacement of marker sets placed on anatomical landmarks of surface models generated from medical imaging contour data. The landmarks are identified manually on fingers in multiple positions. A mathematical algorithm was then used to ascertain the kinematics axes of motion of the fingers. Once these axes are located, they are used as the base of a real time interactive simulation of the finger. The entire simulation was accomplished in a high-resolution graphics environment. A full complement of interactive tools (virtual dials and buttons controlled via mouse) was used to enhance the user interface. The development of the system, the model and the advantages and disadvantages of the method are discussed.

Description of mandibular finite helical axis pathways in asymptomatic subjects

Despite wide use of systems to record jaw motion with six degrees of freedom, most studies have analyzed only the movement of a single mandibular point. The finite helical axis (FHA) is a mathematical model which can be used to describe comprehensively the movements of a rigid body. The aim of this investigation was to describe the FHA of the mandible during habitual jaw movements. Thirty subjects (13 females, 17 males; mean age, 26 years; range, 18 to 34 years) without myoarthropathies of the masticatory system participated in the study. Opening and closing movements, performed at 1-Hz frequency, were recorded with the optoelectronic system Jaws-3D. Three opening and closing movements were recorded from the right side and three from the left side of the jaw. The movement data were low-pass-filtered for noise reduction prior to the computation of the finite helical axis by means of a software program developed in our laboratory. The following parameters were calculated: the rotation of the FHA, its spatial orientation, and the translation along it, as well as its position and distance relative to an intracondylar point. In addition, methodological errors of the model were calculated. During opening and closing, the group mean FHA rotation was 24.3 degrees +/- 4.2 degrees. The group mean of the maximum total translation along the FHA was 0.9 +/- 0.7 mm. The group mean distance between the FHA and the intracondylar point was 48.9 +/- 9.9 mm. The FHA pathways were smooth and varied between individuals. Furthermore, the finite helical axes were never localized within the condyle, and often were located outside of the mandible. The analysis of the FHA pathways yields more information on whole mandibular movements than simply the movements of a single condylar point.

Analytical study on the kinematic and dynamic behaviors of a knee joint

A knee model in the sagittal plane is established in this study. Specifically, the model is used to study the effects of inertia, articular surfaces of the knee joint, and patella on the behaviors of a knee joint. These behaviors include the joint surface contact point, ligament forces, instantaneous center and slide/roll ratio between the femur and tibia. Model results are compared to experimental cadaver studies available in the literature, as well as between the quasistatic and dynamic models. We found that inertia increases the sliding tendency in the latter part of flexion, and lengthens the cruciate ligaments. Decreasing the curvature of the femur surface geometry tends to reduce the ligament forces and moves the contact points towards the anterior positions. The introduction of the patellar ligament in the model seems to stabilize the behaviors of the knee joint as reflected by the behavior of the instant centers and the contact point pattern on the tibia surface. Furthermore, we found that different magnitudes of the external load applied to the tibia do not alter the qualitative behaviors of the knee joint.

The mobility of the sacroiliac joints in healthy volunteers between 20 and 50 years of age

The nature and amplitude of movement in the sacroiliac joint (SIJ) is still open to controversy. Whereas some authors using modern measuring techniques have reported on the range of motion in the SIJ of patients and in embalmed elderly humans, the following is a presentation of our observations related to healthy individuals between 20 and 50 years of age. Using a three-dimensional stereophotogrammetric method, the motion in the joints of 15 males and nine females was investigated with change in posture from the upright standing position. The general description of spatial motion, as obtained through the helical axis concept, has been used. For comparison of the results obtained, the motion is also specified as components of rotation about vertical, anteroposterior and transverse axes, or in horizontal, frontal and sagittal planes respectively. The average values for total rotation and translation were low, being 1.7 degrees and 0.7 mm respectively. One of the test subjects who was known to have occasional trouble with his sacroiliac joints exhibited more than 6 degrees rotation. No statistically significant differences could be demonstrated with respect to sex, age, or parturition. RELEVANCE:--No data are available in the literature on the motion of the sacroiliac joints of healthy men and women in the age group 20-50 years. Measurements were carried out with the aid of percutaneously introduced external markers, using conventional light photography. This is a definite advantage over the use of X-rays and radio-opaque markers that would probably remain implanted in the bone indefinitely. Therefore this method might also be considered for future use in clinical research involving the mobility of the SIJ in patients.

A videofluoroscopy method for optical distortion correction and measurement of knee-joint kinematics

Image distortion in video and image intensifier X-ray systems requires appropriate distortion correction methods to obtain accurate biomechanical quantitative measurements for joint kinematics applications. This paper presents an algorithm for coordinate reconstruction and distortion correction using a modified polynomial method. This algorithm was used for the measurement of patellar tendon moment arm, tibial plateau-tibial axis angle and patellar tendon-tibial axis angle during knee extension using videofluoroscopy in vivo. These parameters allow the determination of a two-dimensional biomechanical model of the knee for the measurement of muscle and joint forces during dynamic activities. Five males without knee joint injury history participated in the study. The mean measurement error obtained using an image intensifier-video system was 0.246 +/- 0.111 mm over a 180-mm x 180-mm field of view. The mean maximum patellar tendon moment arm was 39.87 mm at 44.9 degrees of knee flexion. The patellar tendon-tibial plateau angle was 112.9 degrees at full extension and decreased linearly to 87.6 degrees at 90 degrees of knee flexion. The mean angle between the tibial plateau and the tibial long axis was 84.8 degrees. Applications of the method include motion analysis using video and X-ray fluoroscopy systems with non-linear distortion problems. RELEVANCE: Accurate measurement of anatomical parameters from videofluoroscopy systems is important for the determination of joint biomechanical models and measurement of muscular and joint forces.

Visualization and quantitative analysis of talocrural joint kinematics

The three dimensional (3D) in vivo kinematic behavior of the ankle joint was evaluated using spiral volumetric CT scanning of a normal adult foot. The CT data were reconstructed and interpolated to create an isotropic 3D data volume. These data were rendered, visualized, segmented into their bony elements, labeled, and exported to disk using Mayo Analyze software. The labeled 3D CT datasets were analyzed to determine relative orientation, translation, and rotation of the tibia-talus, tibia-calcaneus and calcaneus-talus. Using these results, the 3D motion characteristics during normal adult foot flexion/extension were described quantitatively.

The distal hindlimb musculature of the cat: multiaxis moment arms at the ankle joint

The cat hindlimb muscles have been classified, traditionally, as flexors and extensors, based on their actions in the parasagittal plane and their patterns of recruitment during locomotion and reflex responses. This study provides a detailed examination of the relative magnitudes of the various moment arms of the cat ankle muscles and the interdependent effects of position in the various axes of motion. We used a method based on observing small sliding movements of tendon in response to small angular displacements of the joint. Surprisingly, we found that the ankle joint of the cat permits substantial motion in three axes (eversion/inversion and abduction/adduction as well as extension/flexion) and many muscles crossing the ankle joint have their largest moment arms about axes other than extension/flexion. These moment arms often depended on the joint position in the axis of the moment arm and, to a lesser degree, on the extension/flexion angle as well. For some muscles (notably peroneus longus) there was sufficient variability that the predominant action in neutral posture (axis with the largest moment arm) could change from animal to animal, which may be related to heterogeneities of locomotor and reflex recruitment reported in the companion paper.

Location of the mandibular center of autorotation in maxillary impaction surgery

Controversy exists about the location of the center of autorotation of the mandible after maxillary impaction surgery. This investigation focuses on the problems associated with locating that center of autorotation and identifies factors that can increase the probability of accurately identifying its location for predicting surgical outcomes. The reliability of the Rouleaux technique for calculating the centers of rotation is established and is shown to be acceptable, as long as the landmarks used for determining the center are properly selected, and the magnitude of the rotation required is sufficient. The location of the centers of autorotation of the mandibles after maxillary impaction surgery for 46 patients was used to investigate the errors associated with landmark selection and amounts of rotation. Although there is much variation in its location, the center does not lie within the body of the condyle but instead lies away from the condyle. Guidelines for maximizing the reliability of predicting surgical outcomes on the basis of autorotation of the mandible after maxillary impaction surgery are given.

Effects of radial deformity on distal radioulnar joint mechanics

A cadaver experiment was performed to study the effects of radial deformity on the kinematics of the distal radioulnar joint and the anatomic configuration of the triangular fibrocartilage. Radial shortening caused the greatest disturbance in kinematics and the most distortion of the triangular fibrocartilage. Decreased radial inclination and dorsal angulation caused intermediate changes. Dorsal displacement produced minimal changes. Radial deformity did not produce distal radioulnar joint dislocation. These results provide biomechanical evidence of an important relationship between radial malunion and persistent symptoms in the distal radioulnar joint.

Partial excision of the triangular fibrocartilage complex articular disk: a biomechanical study

A cadaver study was performed to evaluate the effects of partial and complete excisions of the articular disk of the triangular fibrocartilage complex on the kinematics of the distal radioulnar joint and the structural integrity of the triangular fibrocartilage. An excision that did not violate the peripheral 2 mm of the disk and that comprised less than two thirds of the disk area resulted in no significant kinematic or structural changes, but larger excisions produced measurable changes. These results provide further support for limited excision of central triangular fibrocartilage complex tears.

Instantaneous axes of rotation of the typical cervical motion segments: II. optimization of technical errors

The reliability of a modified protocol for plotting the instantaneous axes of sagittal rotation for the cervical spine was evaluated by measuring the observer differences when the process was performed separately by two observers, and by a single observer, on two separate occasions. Small observer differences were found both for individual steps in the process and for the process as a whole. These differences were substantially less than those found using the conventional technique for plotting the instantaneous axes of rotation. The improvement in the technique was resultant from the use of stricter criteria for recognizing and tracing vertebral landmarks.

Instantaneous axes of rotation of the typical cervical motion segments: I. an empirical study of technical errors

The reliability of the conventional technique for determining the instantaneous axes of rotation of the cervical motion segments was evaluated by comparing the determinations made by two observers and the same observer on two separate occasions. Different observers found the same mean location for the instantaneous axis at each segment in a test population of 17 normal subjects, but for any given subject the interobserver and intraobserver differences were large, with a relative variation of up to 35%. Thus, while reliable for determining the mean location of the instantaneous axis of rotation in a population, the technique was not reliable for determining the axis in a given subject. Qualitative analysis suggested that the identification of the radiographic images of the vertebrae and their tracing is the greatest source of error for this technique.