Three dimensional, radiosteriometric analysis (RSA) of equine stifle kinematics and articular surface contact: a cadaveric study.

REASONS FOR PERFORMING STUDY: Studies examining the effect of stifle joint angle on tibial rotation, adduction-abduction angle and articular contact area are lacking. OBJECTIVES: To test the hypothesis that tibial rotation, adduction-abduction angle and articular contact area change with stifle joint angle. STUDY DESIGN: Descriptive study of normal kinematics and articular contact patterns of the equine stifle through the functional range of motion using 3 dimensional (3D) radiosteriometric analysis (RSA) and equine cadaver stifles. METHODS: Multiple, radiopaque markers were embedded in the distal femur and proximal tibia and sequential, biplanar x-rays captured as the stifle was passively extended from 110° to full extension. Computer-programmed RSA was used to determine changes in abduction-adduction and internal-external rotation angles of the tibia during stifle extension as well as articular contact patterns (total area and areas of high contact) through the range of motion. RESULTS: The tibia rotated externally (P < 0.001) as the stifle was extended. Tibial abduction occurred from 110-135° of extension (P < 0.001) and tibial adduction occurred from 135° through full extension (P = 0.009). The centre of joint contact moved cranially on both tibial condyles during extension with the lateral moving a greater distance than the medial (P = 0.003). Articular contact area decreased (P = 0.001) in the medial compartment but not in the lateral compartment (P = 0.285) as the stifle was extended. The area of highest joint contact increased on the lateral tibial condyle (P < 0.001) with extension but decreased (P = 0.001) on the medial tibial condyle. CONCLUSIONS: Significant changes occur in tibial rotation, adduction-abduction angle and articular contact area of the equine stifle through the functional range of motion. Understanding the normal kinematics of the equine stifle and the relationship between joint positions and articular contact areas may provide important insight into the aetiology and location of common stifle joint pathologies (articular cartilage and meniscal lesions).

Low-dose CT imaging of radio-opaque markers for assessing human rotator cuff repair: accuracy, repeatability and the effect of arm position.

Previous studies have used radiostereometric analysis (RSA) to assess the integrity and mechanical properties of repaired tendons and ligament grafts. A conceptually similar approach is to use CT imaging to measure the 3D position and distance between implanted markers. The purpose of this study was to quantify the accuracy and repeatability of measuring the position and distance between metallic markers placed in the rotator cuff using low-dose CT imaging. We also investigated the effect of repeated or variable positions of the arm on position and distance measures. Six human patients had undergone rotator cuff repair and placement of tantalum beads in the rotator cuff at least one year prior to participating in this study. On a single day each patient underwent nine low-dose CT scans in seven unique arm positions. CT scans were analyzed to assess bias, precision and RMS error of the measurement technique. The effect of repeated or variable positions of the arm on the 3D position of the beads and the distance between these beads and suture anchors in the humeral head were also assessed. Results showed the CT imaging method is accurate and repeatable to within 0.7 mm. Further, measures of bead position and anchor-to-bead distance are influenced by arm position and location of the bead within the rotator cuff. Beads located in the posterior rotator cuff moved medially as much as 20 mm in abduction or external rotation. When clinically relevant CT arm positions such as the hand on umbilicus or at side were repeated, bead position varied less than 4 mm in any anatomic direction and anchor-to-bead distance varied +2.8 to -1.6 mm (RMS 1.3 mm). We conclude that a range of ± 3 mm is a conservative estimate of the uncertainty in anchor-to-bead distance for patients repeatedly scanned in clinically-relevant arm positions.

Evaluation of an electromagnetic position tracking device for measuring in vivo, dynamic joint kinematics.

An electromagnetic position tracking device was evaluated to determine its static and dynamic accuracy and reliability for applications related to measuring in vivo joint kinematics. The device detected the position and orientation of small coiled sensors, maintained in an electromagnetic field. System output was measured against known translations or rotations throughout the measurement volume. Average translational errors during static testing were 0.1 +/- 0.04, 0.2 +/- 0.17, and 0.8 +/- 0.81 mm (mean+/-SD) for sensors 50, 300, and 550 mm away from the field generator, respectively. Average rotational errors were 0.4 +/- 0.31 degrees, 0.4 +/- 0.21 degrees, and 0.9 +/- 0.85 degrees (mean +/- SD) for sensors located at the same distances. Since we intended to use this system in an animal walking on a treadmill, we incrementally moved the sensors under various treadmill conditions. The effects of treadmill operation on translational accuracy were found to be negligible. The effects of dynamic motions on sensor-to-sensor distance were also assessed for future data collection in the animal. Sensor-to-sensor distance showed standard deviations of 2.6 mm and a range of 13 mm for the highest frequency tested (0.23 Hz). We conclude that this system is useful for static or slow dynamic motions, but is of limited use for obtaining gait kinematics at higher speeds.

A noncontact, nondestructive method for quantifying intratissue deformations and strains.

The function of soft connective tissues is frequently characterized by quantifying tissue strain (e.g., during joint motion). Conventional techniques for quantifying tendon and ligament strain typically provide surface measures, using markers, stain lines or instrumentation that may influence the tissue. An alternative approach is to quantify intratendinous strain by applying texture correlation analysis to magnetic resonance (MR) images. This paper reports the accuracy and reproducibility of this approach by (1) assessing the reproducibility of MR images, (2) assessing texture correlation accuracy using simulated displacements, and (3) comparing texture correlation measures of displacement and strain from MR images to conventional techniques.

Total strain fields of the antero-inferior shoulder capsule under subluxation: a stereoradiogrammetric study.

The antero-inferior capsule (AIC) is the primary restraint to antero-inferior glenohumeral dislocation. This study utilizes a biomechanical model to determine the total strain field of the AIC in a subluxed shoulder. Strains were calculated from two capsule states: a nominal strain state set by inflation and a strained state set by subluxation. Marker coordinates on the AIC were reconstructed from stereoradiographs and strain fields calculated. Peak strain on the glenoid side of the AIC was significantly greater than the humeral side and strain fields were highly variable. This study reports an accurate method for measuring planar strains in a three-dimensional membrane.

Ligamentous restraints to external rotation of the humerus in the late-cocking phase of throwing. A cadaveric biomechanical investigation.

The late-cocking phase of throwing is characterized by extreme external rotation of the abducted arm; repeated stress in this position is a potential source of glenohumeral joint laxity. To determine the ligamentous restraints for external rotation in this position, 20 cadaver shoulders (mean age, 65 +/- 16 years) were dissected, leaving the rotator cuff tendons, coracoacromial ligament, glenohumeral capsule and ligaments, and coracohumeral ligament intact. The combined superior and middle glenohumeral ligaments, anterior band of the inferior glenohumeral ligament, and the entire inferior glenohumeral ligament were marked with sutures during arthroscopy. Specimens were mounted in a testing apparatus to simulate the late-cocking position. Forces of 22 N were applied to each of the rotator cuff tendons. An external rotation torque (0.06 N x m/sec to a peak of 3.4 N x m) was applied to the humerus of each specimen with the capsule intact and again after a single randomly chosen ligament was cut (N = 5 in each group). Cutting the entire inferior glenohumeral ligament resulted in the greatest increase in external rotation (10.2 degrees +/- 4.9 degrees). This was not significantly different from sectioning the coracohumeral ligament (8.6 degrees +/- 7.3 degrees). The anterior band of the inferior glenohumeral ligament (2.7 degrees +/- 1.5 degrees) and the superior and middle glenohumeral ligaments (0.7 degrees +/- 0.3 degrees) were significantly less important in limiting external rotation.

The mechanism of creation of superior labrum, anterior, and posterior lesions in a dynamic biomechanical model of the shoulder: the role of inferior subluxation.

Lesions of the superior glenoid labrum are a source of shoulder disease. However, the mechanisms of injury to this region are unknown, and controversy exists regarding the role of shoulder instability in creation of this lesion. With a cadaver model that simulates physiologic rotator cuff forces and produces traction on the biceps tendon, the creation of type II superior labrum, anterior, and posterior (SLAP) lesions and the role of glenohumeral subluxation were investigated: Left and right shoulders from each of 8 paired cadavers (age 62 +/- 7.2 years, 5 male and 3 female) were randomized to be tested in either a 20 mm inferiorly subluxed position or in a reduced position. The long head of the biceps tendon was held near the musculotendinous junction with a novel cryogenic clamp. Traction on the long head of the biceps tendon was applied at a fast rate of 12.7 cm/sec with a servohydraulic testing machine. A load cell was used to monitor the biceps tendon load. After testing to failure, the presence or absence of a type II SLAP lesion was determined by 2 experienced shoulder surgeons masked to the test group. The production of type II SLAP lesions differed significantly (P = .03) between reduced shoulders (2 SLAP lesions out of 8 tests) and the shoulders with inferior subluxation (7 SLAP lesions out of 8 tests). This experiment has shown that traction on the biceps tendon in this biomechanical model can reproducibly create type II SLAP lesions, and inferior subluxation facilitates the generation of such lesions.

Quantification of elastic resistance knee rehabilitation exercises.

Elastic resistance exercises are frequently used for knee rehabilitation following injury and/or surgery. The evidence supporting this mode of rehabilitation is primarily anecdotal, and no biomechanical assessment of elastic resistance exercises has been previously published. The purpose of this project was to quantify muscle activation levels, knee joint angles, and applied force during five rehabilitation exercises utilizing an elastic resistance device. Twelve subjects with no previous knee injury performed double knee dip, hamstring pull, leg press, single knee dip, and side-to-side jump exercises while sagittal plane kinematics, applied force from the elastic resistance device, and electromyographic activity of eight lower extremity muscles were collected. The muscle activation patterns suggest a progressive continuum of rehabilitation exercises that can be applied to nonoperative injuries as well as anterior cruciate ligament reconstructions.

Electromyographic activity and applied load during shoulder rehabilitation exercises using elastic resistance.

Muscle activity (measured by electromyography) and applied load were measured during seven shoulder rehabilitation exercises done with an elastic resistance device. Nineteen men with no shoulder abnormalities performed seven exercises: external and internal rotation, forward punch, shoulder shrug, and seated rowing with a narrow, middle, and wide grip. Qualitative video (60 Hz) was synchronized with the electromyography data from eight muscles (2000 Hz). Fine-wire intramuscular electrodes were inserted into the supraspinatus and subscapularis muscles, and surface electrodes were placed over the anterior deltoid, infraspinatus, pectoralis major, latissimus dorsi, serratus anterior, and trapezius muscles. Ten trials per subject were analyzed for average and peak amplitude, and the results were expressed as a percentage of maximum voluntary contractions. The peak loads for all exercises ranged from 21 to 54 N. The muscle activity patterns suggest that these shoulder rehabilitation exercises incorporating elastic resistance, controlled movements, and low initial loading effectively target the rotator cuff and supporting musculature and are appropriate for postinjury and postoperative patients.