Two-dimensional rigid-body kinematics using image contour registration

Humeral head translation after a suprascapular nerve block

Subacromial impingement syndrome is the most common shoulder disorder. Abnormal superior translation of the humeral head is believed to be a major cause of this pathology. The first purpose of the study was to examine the effects of suprascapular nerve block on superior translation of the humeral head and scapular upward rotation during dynamic shoulder elevation. The secondary purpose was to assess muscle activation patterns during these motions. Twenty healthy subjects participated in the study. Using fluoroscopy and electromyography, humeral head translation and muscle activation were measured before and after a suprascapular nerve block. The humeral head was superiorly located at 60 degrees of humeral elevation, and the scapula was more upwardly rotated from 30 to 90 degrees of humeral elevation after the block. The differences were observed during midrange of motion. In addition, the deltoid muscle group demonstrated increased muscle activation after the nerve block. The study's results showed a compensatory increase in humeral head translation, scapular upward rotation, and deltoid muscle activation due to the nerve block. These outcomes suggest that increasing muscular strength and endurance of the supraspinatus and infraspinatus muscles could prevent any increased superior humeral head translation. This may be beneficial in reducing shoulder impingement or rotator cuff tears over time.

In vivo movement analysis of the patella using a three-dimensional computer model

We used three-dimensional movement analysis by computer modelling of knee flexion from 0° to 50° in 14 knees in 12 patients with recurrent patellar dislocation and in 15 knees in ten normal control subjects to compare the in vivo three-dimensional movement of the patella. Flexion, tilt and spin of the patella were described in terms of rotation angles from 0°. The location of the patella and the tibial tubercle were evaluated using parameters expressed as percentage patellar shift and percentage tubercle shift. Patellar inclination to the femur was also measured and patellofemoral contact was qualitatively and quantitatively analysed.

The patients had greater values of spin from 20° to 50°, while there were no statistically significant differences in flexion and tilt. The patients also had greater percentage patellar shift from 0° to 50°, percentage tubercle shift at 0° and 10° and patellar inclination from 0° to 50° with a smaller oval-shaped contact area from 20° to 50° moving downwards on the lateral facet.

Patellar movement analysis using a three-dimensional computer model is useful to clearly demonstrate differences between patients with recurrent dislocation of the patella and normal control subjects.

Carpal kinematics after proximal row carpectomy

PURPOSE

Proximal row carpectomy (PRC) is a clinically useful motion-sparing procedure for the treatment of certain degenerative conditions of the wrist. Clinical outcome studies after PRC have shown that wrist flexion-extension averages approximately 60% of that of the contralateral wrist. The purpose of this study was to determine how the kinematics of the wrist are altered after PRC.

METHODS

Eight fresh-frozen cadaver forearms were scanned with computed tomography before and after PRC. Forearms were scanned in 5 different wrist positions (neutral, extension, flexion, radial deviations, and ulnar deviation). Wrists were positioned dynamically and then held statically in a custom fixture through forces applied to the 4 wrist flexor/extensor tendon groups. Three-dimensional computer models of the radius, lunate, and capitate were generated from the computed tomographic images, and the kinematics of the capitate and lunate were calculated relative to the neutral position. For the intact wrist, the motion of the capitate was calculated relative to both the lunate (midcarpal motion) and the radius (overall wrist motion) and the motion of the lunate was calculated relative to the radius (radiocarpal motion). After PRC, only the movement of the capitate relative to the radius was calculated, which represents radiocapitate and overall wrist motion. All motions were plotted in 3 dimensions for purposes of qualitative visualization.

RESULTS

After PRC, the capitate articulated with the lunate fossa of the radius for all positions in all samples. Overall wrist motion decreased 28%, 30%, 40%, and 12% in flexion, extension, radial deviation, and ulnar deviation, respectively. Motion at the radiocarpal joint after PRC, however, was greater compared with motion at the radiocarpal and midcarpal joints of the intact wrist during flexion and extension. This was not the case in radial deviation because of impingement of the trapezoid on the radial styloid. In radial and ulnar deviation, motion of the capitate head changed from predominantly rotational in the intact wrist (midcarpal joint) to a combination of rotation and translation after PRC (radiocarpal joint).

CONCLUSIONS

Removal of the proximal carpal row decreased normal wrist flexion and extension. Although ulnar deviation was preserved, radial deviation was limited by impingement of the trapezoid on the radial styloid. Radiocapitate range of motion after PRC was greater than capitolunate range of motion in the intact wrists. Compared with previously published requirements, wrist range of motion observed after PRC was sufficient for activities of daily living.

Calculating the 2D motion of lumbar vertebrae using splines

In this study we investigate the use of splines and the ICP method [Besl, P., McKay, N., 1992. A method for registration of 3d shapes. IEEE Transactions on Pattern Analysis and Machine Intelligence 14, 239-256.] for calculating the transformation parameters for a rigid body undergoing planar motion parallel to the image plane. We demonstrate the efficacy of the method by estimating the finite centre of rotation and angle of rotation from lateral flexion/extension radiographs of the lumbar spine. In an in vitro error study, the method displayed an average error of rotation of 0.44 +/- 0.45 degrees, and an average error in FCR calculation of 7.6 +/- 8.5 mm. The method was shown to be superior to that of Crisco et al. [Two-dimensional rigid-body kinematics using image contour registration. Journal of Biomechanics 28(1), 119-124.] and Brinckmann et al. [Quantification of overload injuries of the thoracolumbar spine in persons exposed to heavy physical exertions or vibration at the workplace: Part i - the shape of vertebrae and intervertebral discs - study of a yound, healthy population and a middle-aged control group. Clinical Biomechanics Supplement 1, S5-S83.] for the tests performed here. In general, we believe the use of splines to represent planar shapes to be superior to using digitised curves or landmarks for several reasons. First, with appropriate software, splines require less effort to define and are a compact representation, with most vertebra outlines using less than 30 control points. Second, splines are inherently sub-pixel representations of curves, even if the control points are limited to pixel resolutions. Third, there is a well-defined method (the ICP algorithm) for registering shapes represented as splines. Finally, like digitised curves, splines are able to represent a large class of shapes with little effort, but reduce potential segmentation errors from two dimensions (parallel and perpendicular to the image gradient) to just one (parallel to the image gradient). We have developed an application for performing all the necessary computations which can be downloaded from http://www.claritysmart.com.

Metacarpophalangeal joint mechanics after 3 different silicone arthroplasties

PURPOSE

This study was performed to compare metacarpophalangeal (MCP) joint mechanics after arthroplasty with 3 currently available silicone implants and to determine how postarthroplasty mechanics compares with the mechanics of the intact joint.

METHODS

Planar 2-dimensional kinematic analysis was performed using digitized radiographs on 10 isolated fingers harvested from 5 fresh-frozen human cadavers. Radiopaque markers were affixed to the metacarpals and proximal phalanges, sewn to the flexor and extensor tendons, and placed into the stems and hinges of the implants. Each finger was tested intact, and after MCP joint replacement with 3 implants (Swanson [Wright Medical, Memphis, TN], Avanta [Avanta Orthopaedics, San Diego, CA], and NeuFlex [DePuy Orthopaedics, Warsaw, IN]). The fingers were secured to the test fixture and the flexor digitorum profundus flexor and extensor tendons were loaded with physiologic weights. Lateral radiographs were taken at approximately 10 degrees intervals and were digitized on a high-resolution scanner. Instantaneous center of rotation (ICR), tendon excursion, and tendon moment arm were calculated. Statistical analysis was performed using repeated measures one-way analysis of variance and Dunnett post tests.

RESULTS

The ICRs of the intact and implanted MCPs did not follow a smooth path. The variability of the ICRs of the intact MCP joints was 2.1 +/- 0.8 mm. The variations in the Avanta and DePuy implants were similar (3.1 +/- 1.0 mm and 3.5 +/- 1.5 mm, respectively), whereas the Swanson implant was higher (4.9 +/- 1.7 mm). Implant pistoning was most pronounced with the Swanson implant, which moved 2.40 +/- 0.97 mm over the full range of motion. The Avanta and DePuy implants pistoned significantly less than the Swanson implant (1.05 +/- 0.45 mm and 0.69 +/- 0.31 mm, respectively). Flexor tendon excursion was greater for the intact joint when compared with all 3 implants while extensor tendon excursion was similar for all. Flexor tendon moment arm was similar for the intact joint and the Avanta and NeuFlex implants whereas the Swanson implant was reduced significantly; extensor tendon moment arms were similar for all.

CONCLUSIONS

The ICR of the NeuFlex implant most closely matched that of the intact MCP joint. The Swanson implant had greater pistoning and dorsal-volar translation when compared with the intact joint and the Avanta and NeuFlex implants. The block-hinge type design of the Avanta and NeuFlex implants improved tendon moment arm overall when compared with the Swanson, likely imparting greater functional ability for finger motion. Overall the NeuFlex implant most closely matched the ICR, tendon excursion, and moment arm when compared with the intact native MCP joint.

A kinematic study of lateral unicompartmental arthroplasty

When the Oxford unicompartmental meniscal bearing arthroplasty (UCA) is used in the lateral compartment 10% of the bearings dislocate. A fluoroscopic study was performed to investigate if abnormal mid-sagittal plane kinematics was related to bearing dislocation. Video fluoroscopy is an accepted means of determining in-vivo knee kinematics in the sagittal plane. Video fluoroscopy was obtained of 5 Oxford lateral UCAs 10 years post-operatively and of five normal knees. Patellar tendon angle (PTA), derived from dynamic fluoroscopic images, was used to describe the joint kinematics. This in-vivo experiment demonstrated that the PTA/knee relationship for the Oxford lateral UCA is similar to the normal knee. Both the normal knee (r(2)=0.99) and the Oxford lateral UCA (r(2)=0.98) demonstrated a linear relationship between flexion angle and PTA. No significant difference in PTA was found between the normal knee and the Oxford lateral UCA. This study demonstrated normal kinematics, as indicated by PTA, ten years after implantation of the Oxford lateral UCA. It is therefore reasonable to suggest that abnormal kinematics is not a significant factor relating to meniscal bearing dislocation in the lateral compartment.

Using cine phase contrast magnetic resonance imaging to non-invasively study in vivo knee dynamics

We tested the accuracy and feasibility of using cine phase contrast magnetic resonance imaging (cine-PC MRI) to non-invasively measure three-dimensional, in vivo, skeletal velocity. Bone displacement was estimated by integrating the velocity measurements. Cine-PC MRI was originally developed to directly and non-invasively measure in vivo blood and heart velocity. Since no standard of reference exists for in vivo measurement of trabecular bone motion, a motion phantom (consisting of a series of paired gears that moved a sample box containing a human femoral bone sample) was built to assess the accuracy of tracking trabecular bone with cine-PC MRI. The in-plane, average absolute displacement errors were 0.55 +/- 0.38 and 0.36 +/- 0.27 mm in the x- and y-direction, respectively. Thus, estimates of bone position based on the integration of bone velocity measurements are affected little by the magnetic properties of bone [Majumdar and Genant (1995) Osteoporos International 5, 79-92]. The velocity profiles of the patella, femur and tibia were measured in five healthy subjects during leg extensions. Extension was resisted by a 34 N weight. Subjects maintained a consistent motion rate (35 +/- 0.5 cycles min(-1)) and motion artifacts were minimal. Our results indicate that patellar flexion lags knee flexion and the patella tilts laterally and then medially as the knee extends. We conclude cine-PC MRI is a promising technique for the non-invasive measurement of in vivo skeletal dynamics and, based on our previous work, muscular dynamics as well.

Kinematics of the scaphoid shift test

Twenty-five uninjured subjects (50 wrists) were examined clinically and fluoroscopically during performance of the scaphoid shift test. Wrists were placed into 3 groups on the basis of the degree of palpable carpal motion that occurred during the clinical examination. Kinematic parameters of rotation and displacement were calculated from digitized images of the carpals at rest and at maximum displacement. On clinical exam, 36% of normal individuals had positive findings on scaphoid shift test. Dorsal displacement of the scaphoid was not significantly associated with positive scaphoid shift test results in these subjects, while total displacement of the scaphoid (the sum of axial and dorsal displacement) was significantly associated with positive test results. The principle confounding factor appeared to be a high degree of displacement that occurred at the capitolunate joint in some individuals, termed a "midcarpal shift." The data demonstrate that despite a high prevalence of positive scaphoid shifts among uninjured individuals, the ability to accurately detect dorsal displacement of the scaphoid using the scaphoid shift test is limited. On the basis of their findings, the authors recommend that positive test results be confirmed fluoroscopically.

A non-invasive method for studying in vivo carpal kinematics

Seven uninjured and three injured patients were studied using midsagittal computed tomographic (CT) images at 10 degrees increments from full extension to full flexion. Each injured patient had a confirmed scapholunate ligament tear and normal radiographs. CT bony contours were digitized, and incremental motion determined using a specifically designed automated contour-matching algorithm. We expressed wrist motion as a ratio of lunocapitate (midcarpal) motion, and radiolunate (radiocarpal) motion. In normal wrists, motion occurred equally at the midcarpal and radiocarpal joints. In wrists with scapholunate ligament disruption, lunocapitate motion increased significantly throughout the arc of motion.

In vivo kinematics of cruciate-retaining and -substituting knee arthroplasties

A fluoroscopic measurement technique has been used to provide detailed three-dimensional kinematic assessment of knee arthroplasty function during a step-up activity. Three groups of knee arthroplasty subjects with excellent clinical outcomes and similar ranges of motion were evaluated. Each group received different prosthetic components and surgical treatments of the posterior cruciate ligament (PCL). Group 1 had relatively flat articular surfaces with retention of the bony insertion of the PCL, group 2 had similar articular geometry but recessed the PCL without retaining the bony insertion, and group 3 had prostheses with greater sagittal conformity and post/cam substitution of the sacrificed PCL. Although none of the knees exhibited normal knee kinematics, the ranges of axial rotation and condylar translation for group 1 were similar to ranges previously reported for normal and anterior cruciate-deficient knees. Axial rotations and condylar translations decreased when the PCL was surgically recessed or substituted. The smallest kinematic ranges were observed in group 3. The results indicate that both prosthetic component selection and surgical technique have a significant effect on prosthetic knee kinematics during functional activities.