April D. Armstrong

Reliability of range-of-motion measurement in the elbow and forearm***

The purpose of this study was to examine intratester, intertester, and interdevice reliability of range of motion measurements of the elbow and forearm. Elbow flexion and extension and forearm pronation and supination were measured on 38 subjects with elbow, forearm, or wrist disease by 5 testers. Standardized test methods and a randomized order of testing were used to test groups of patients with universal standard goniometers, a computerized goniometer, and a mechanical rotation measuring device. Intratester reliability was high for all 3 measuring devices. Meaningful changes in intratester range of motion measurements taken with a universal goniometer occur with 95% confidence if they are greater than 6 degrees for flexion, 7 degrees for extension, 8 degrees for pronation, and 8 degrees for supination. Intertester reliability was high for flexion and extension measurements with the computerized goniometer and moderate for flexion and extension measurements with the universal goniometer. Meaningful change in interobserver range of motion measurements was expected if the change was greater than 4 degrees for flexion and 6 degrees for extension with the computerized goniometer compared with 10 degrees and 10 degrees, respectively, if the universal goniometer was used. Intertester reliability was high for pronation and supination with all 3 devices. Meaningful change in forearm rotation is characterized by a minimum of 10 degrees for pronation and 11 degrees for supination with the universal goniometer. Reliable measurements of elbow and forearm arm movement are obtainable regardless of the level of experience when standardized methods are used. Measurement error was least for repeated measurements taken by the same tester with the same instrument and most when different instruments were used.

Two-dimensional glenoid version measurements vary with coronal and sagittal scapular rotation.

BACKGROUND Accurate analysis of osseous glenoid morphology is important in treating glenohumeral arthritis and instability. Two-dimensional computed tomography scans are used to evaluate glenoid alignment. Accuracy of this method is dependent on the angle of axial reconstruction in relation to the position of the scapula. The purpose of this study was to investigate the effect of scapular rotation in the coronal and sagittal planes on glenoid version as measured on two-dimensional images. METHODS Computer-generated three-dimensional models of scapulae from computed tomography scans of thirty-six shoulders in whole-body cadavers were generated. The anatomic geometry of these models had been previously validated. The position of the scapulae relative to the gantry was determined. The three-dimensional models were rotated in 1 degree increments in the coronal and sagittal planes. Glenoid version was measured on two-dimensional images for each of the rotation increments. Version variability at each rotation increment was calculated. RESULTS The anatomic glenoid version (independent of the resting position of the scapula) was an average (and standard deviation) of 2.0 degrees +/- 3.8 degrees of retroversion. The average difference between anatomic glenoid version and clinical glenoid version (depending on the position of the scapula on the original computed tomography axial images) was 6.9 degrees +/- 5.6 degrees (range, 0.1 degrees to 22.5 degrees). Version variability with coronal or sagittal rotation was significant for all degrees of rotation (p < 0.0001). Scapular abduction had the greatest effect on version variation and resulted in 0.42 degrees of relative anteversion for every 1 degree of abduction in the coronal plane. In the sagittal plane, internal rotation resulted in relative anteversion. CONCLUSIONS Any malalignment of > or = 1 degree of the scapula in the coronal or sagittal plane will create inaccuracies in measuring glenoid version. The plane of axial reconstruction should be aligned with the scapula when two-dimensional computed tomography images are used to measure glenoid version. These findings support the use of three-dimensional models to evaluate glenoid version.

Comparison of standard two-dimensional and three-dimensional corrected glenoid version measurements

HYPOTHESIS There is concern regarding the accuracy of 2-dimensional (2D) computed tomography (CT) for measuring glenoid version. Three-dimensional (3D) CT scan reconstructions can properly orient the glenoid to the plane of the scapula and have been reported to accurately measure glenoid version in cadaver models. We hypothesized that glenoid version measured by correcting 2D CT scans to the plane of the scapula by 3D reconstruction would be significantly different compared with standard 2D CT scan measurement of the glenoid in a clinical patient population. MATERIALS AND METHODS Thirty-four patients underwent dedicated axial 2D CT scan of the shoulder with 3D reconstruction. The 2D glenoid version was measured on unmodified midglenoid axial cuts, and the 3D glenoid version measurement was corrected to be perpendicular to the plane of the scapula and then measured in the axial plane. Three observers repeated each measurement on 2 different days. RESULTS The difference between the overall average 2D and 3D measurements was not statistically significant (P = .45). In individual scapulae, 35% of 2D measurements were 5° to 10° different and 12% were greater than 10° different from their corresponding 3D-corrected CT measurement (P < .001 to P = .045). Reproducibility of both 2D and 3D-corrected measurements was good. DISCUSSION Although 2D and 3D corrected methods showed a high degree of both intraobserver and interobserver reliability in this series, axial 2D images without correction were 5 to 15 degrees different than their 3D-corrected counterparts in 47% of all measurements. Correcting 2D glenoid version by 3D reconstruction to the transverse plane perpendicular to the scapular body allows for an accurate assessment of glenoid version in spite of positioning differences and results in increased accuracy while maintaining high reliability. CONCLUSIONS Owing to the variability in scapular position, the axial 2D CT scan measurement was significantly different from 3D-corrected measurement of glenoid version. Averaging the version measurements across patients did not reflect this finding.

Anatomy and Biomechanics of the Elbow

The elbow is a complex, highly constrained joint that provides critical range of motion to the upper extremity needed for performing the normal activities of daily living. The elbow is protected by a fortress of individual static and dynamic constraints that function together to provide stability. Knowing the identity and specific functions of each stabilizing structure facilitates appropriate diagnosis and treatment of the acutely injured elbow.

Patellar position after total knee arthroplasty: Influence of femoral component malposition

Patellar shift, tilt, and rotation were analyzed in 7 cadaveric knee specimens during simulated quadriceps loading, in the intact knee, and after implant reconstruction. Femoral component medialization, lateralization, and external rotation were also investigated. Relative motion of the patella with respect to the femur was measured using an electromagnetic tracking system. The spatial position of the patella did not change with standardized total knee arthroplasty (P <.05). After malpositioning of the femoral component, patellar rotation also did not change (P >.05); however, patellar tilt was altered by femoral component external rotation malposition (P <.05), and patellar shift was affected by all femoral component malpositions (P <.05). The spatial position of the patella relative to the femoral shaft was changed with any femoral component malposition, suggesting that the soft tissues were abnormally tensioned. This could result in subsequent wear on the patellar component and, therefore, early failure.

Validation of three-dimensional models of in situ scapulae

A principal challenge in creating accurate models of in situ scapulae is delineating bone from surrounding soft tissues. Computed tomography scans were obtained of both shoulders of 20 embalmed cadavers. Each shoulder was rescanned after repositioning of the cadavers to test for rescan reliability. After scans were complete, all scapulae were excised and stripped of all soft tissue. Thresholding, region growing, and manual processing were used to create computer-generated 3-dimensional (3D) models. Seven anatomic measurements were performed on each scapula and 3D model. Mean differences between corresponding measurements of specimen and model were small (<3 mm). Intraobserver and interobserver reliability for cadaveric measurements and rescan and interobserver reliability for model measurements were all excellent (R(2) = 0.99). Patient positioning was not a significant source of error in obtaining measurements from 3D models. Results from this work verify that accurate and reproducible 3D models can be created from in situ scapulae by use of effective segmentation.

The Medial Collateral Ligament of the Elbow Is Not Isometric An In Vitro Biomechanical Study

Background The anterior bundle of the medial collateral ligament (AMCL) of the elbow has been shown to be the most important valgus stabilizer of the elbow. However, the isometry of this band has not been quantified. Hypothesis Isometric fibers exist within the AMCL, and these fibers are located within its central region. Study Design Controlled laboratory study. Methods Twelve cadaveric elbow specimens were mounted in a testing apparatus in a valgus gravity-loaded orientation. Passive supinated flexion was performed and the motion recorded using an electromagnetic tracking device. Hundreds of attachment points for the AMCL of the elbow were recorded on the medial epicondyle and ulna. The overall change in length between each point on the ulna to every humeral point, throughout the arc of motion, was quantified (. L = Lmax – Lmin). The locations of the smallest. L values were determined relative to the attachment site of the AMCL on the medial epicondyle. Results True isometry was not found throughout the arc of flexion. The smallest. L values averaged 2.8 ± 1.2 mm (range: 0.7 mm to 5.2 mm). Isometric fibers do not exist within the AMCL; however, “nearly” isometric areas are located on the lateral aspect of the attachment site of the AMCL on the medial epicondyle, near the anatomic axis of rotation. Conclusions We postulate that these nearly isometric areas would be the most ideal location for graft attachment during reconstruction of the AMCL.

Location of the optimized centerline of the glenoid vault: a comparison of two operative techniques with use of three-dimensional computer modeling.

BACKGROUND The three-dimensional vault geometry beneath the glenoid face reduces to a narrow width in many individuals, creating a risk of perforation of the glenoid component pegs or keel in total shoulder arthroplasty. The purpose of this study was to introduce the concept of a centerline of the glenoid vault determined by computed optimization and to compare this centerline geometry against two existing surgical methods for orienting the glenoid component. METHODS Thirty-four subject-specific computer models of three-dimensional scapular geometry were created from computed tomography scans. The glenoid vault centerline was calculated by slicing the vault into a series of cross sections, determining the center of each section, and fitting a centerline with use of optimization. Vault centerline orientations were compared with the drill-line orientations determined by two surgical techniques, the face plane technique, which drills perpendicular to the glenoid face, and the neutralization technique, which drills parallel to the scapular body resulting in 0 degrees of glenoid version. Distances between the drill lines and the vault wall, throughout the vault depth, were also calculated. RESULTS The vault centerline intersected the articular surface of the glenoid at an intersubject average (and standard deviation) of 1.1 +/- 0.8 mm posterior to the glenoid face center point. In comparison with the neutralization direction, the centerline was oriented an average of 9.4 degrees +/- 5.1 degrees posteriorly and the face plane perpendicular direction was oriented an average of 7.3 degrees +/- 4.0 degrees posteriorly. Minimum distances between the centerline and the vault wall averaged 5.1 mm (minimum, 2.6 mm), whereas they averaged 4.4 mm (minimum, 1.0 to 1.4 mm) for the center peg drill lines of both surgical techniques. CONCLUSIONS The normal glenoid vault centerline is directed from lateral-posterior to medial-anterior, and it crosses, on the average, close to the glenoid face center. The neutralization direction, on the average, anteverts the glenoid relative to the vault centerline and the face plane perpendicular. Relationships between these directions vary across the subjects.

Preoperative and intraoperative infection workup in apparently aseptic revision shoulder arthroplasty

The possibility of infection should be considered in every revision shoulder arthroplasty even in the absence of clinical symptoms and signs of infection because indolent infection is prevalent. Detection of infection in apparently aseptic failed arthroplasties poses a diagnostic challenge as the conventional principles and criteria used for hip and knee arthroplasty are not generally applicable. Propionibacterium acnes and Staphylococcus epidermidis are among the infectious organisms most commonly identified in such situations. Serum inflammatory markers are essential but are often unreliable as they have poor sensitivity in the shoulder. Preoperative shoulder joint aspiration culture is an important step but is subject to high false-negative rates. Lower cutoff values of synovial fluid analysis are used for detection of periprosthetic infection than for native joint infection as demonstrated in the knee literature. Intraoperatively, frozen section should be considered when a diagnosis of infection has not been established even in the presence of clinical suspicion. Gram stain is currently not recommended because of its low sensitivity and negative predictive value. Intraoperative culture is critical and should be performed whenever there is clinical suspicion of infection. Unexpected positive intraoperative cultures are not uncommon, and 6% to 25% of them appear to represent true infection as demonstrated with positive follow-up cultures or subsequent development of infection. In revision shoulder arthroplasty, determining the presence of infection can be difficult. A standardized approach is needed to determine the best course of treatment in this particular clinical setting.

Application of screw displacement axes to quantify elbow instability

OBJECTIVES To determine if screw displacement axis patterns describing elbow joint motion: (1) change after ligament transection in vitro; (2) can reflect subtle changes in stability as a function of forearm position; (3) can reflect dynamic stabilization of the ligament insufficient elbow provided by muscle activity.Design. An in vitro kinematic study of eighteen cadaveric specimens tested in a joint simulator. BACKGROUND In the elbow joint, screw displacement axes have been employed for proper positioning and design of endoprostheses. The effect of instability on screw displacement axes has not been previously reported. METHODS Passive and simulated active flexion, with the forearm maintained in both pronation and supination, was performed on eighteen intact and ligament insufficient elbows. Instability was produced by transection of the medial collateral or lateral collateral ligament complexes. Kinematics were recorded using an electromagnetic tracking device and analyzed with a repeated measures design. RESULTS During passive motion, division of either ligament caused deviation of screw displacement axes compared to the intact state (P<0.05). Transection of the medial/lateral collateral ligament generated greater instability with the forearm maintained in pronation/supination compared to supination/pronation (P<0.05). Muscle activation increased stability similar to the intact state (P>0.05). CONCLUSIONS These results are consistent with observations determined using traditional kinematic descriptors. Screw displacement axes can readily detect changes in stability due to ligament sectioning. RELEVANCE Clinicians can employ the screw displacement axis technique as a succinct descriptor of motion to readily detect elbow instability.