Application of screw displacement axes to quantify elbow instability

Testing of Novel Total Elbow Prostheses Using Active Motion Experimental Setup

PURPOSE

The goal of this study was to test a novel uncemented and unconstrained total elbow arthroplasty (Kaufmann total elbow) design that is stabilized through a ligament reconstruction.

METHODS

We quantified the implant stability after 25,000 cycles, which represents the time between implantation and when ligament and bone healing has occurred. We used an active motion experimental setup that applies tendon loads via pneumatic cylinders and reproduces the forearm-originating dynamic stabilizers of the elbow. The novel total elbow arthroplasty was actuated for 5,000 full flexion-extension cycles at 5 different shoulder positions. Four Sawbones and 4 cadaver elbows were employed. Angular laxity and implant stability were recorded prior to testing and after each 5,000-loading cycle.

RESULTS

Four Sawbones and 4 cadaver elbows were implanted with the uncemented total elbow arthroplasty and did not demonstrate fixation failure or substantial laxity after 25,000 cycles of loading imparted at different shoulder positions.

CONCLUSIONS

Our findings demonstrate that the Kaufmann total elbow replacement implanted into cadaver and Sawbones specimens did not exhibit fixation failure or excessive laxity after 25,000 cycles.

CLINICAL RELEVANCE

An uncemented, nonmechanically linked total elbow arthroplasty that gains component fixation using intramedullary screws and employs a ligament reconstruction to stabilize the elbow has the potential to be a valuable management option, particularly in younger patients.

Distal Humeral Trochlear Geometry Associated With the Spatial Variation of the Dynamic Elbow Flexion Axis

Background: The complexity of the spatial dynamic flexion axis (DFA) of the elbow joint makes the elbow prosthesis design and humeral component alignment challenging. This study aimed to 1) investigate the variations of the spatial DFA during elbow flexion and 2) investigate the relationship between the distal humeral trochlear geometry and the in vivo spatial variation of the DFA.

Methods: Ten healthy subjects participated in this study. Each subject performed a full elbow extension to maximum flexion with hand supination under dual fluoroscopic imaging system (DFIS) surveillance. The 2D fluoroscopic images and the 3D bone models were registered to analyze the in vivo elbow kinematics and DFAs. The spatial DFA positions were defined as inclination with the medial and lateral epicondyle axes (MLA) in the transverse and coronal planes. The range of the DFA positions was also investigated during different flexion phases. The Spearman correlation method was used to analyze the relationship between the distal humeral trochlear’s morphological parameters and the position of DFAs during different flexion phases.

Results: The pathway of the DFAs showed an irregular pattern and presented individual features. The medial trochlear depth (MTD) (r = 0.68, p = 0.03) was positively correlated with the range of the DFA position (2.8° ± 1.9°) in the coronal plane from full extension to 30° of flexion. Lateral trochlear height (LTH) (r = −0.64, p = 0.04) was negatively correlated with the DFA position (−1.4° ± 3.3°) in the transverse plane from 30° to 60° of flexion. A significant correlation was found between LTH with the DFA position in the coronal (r = −0.77, p = 0.01) and transverse planes (r = −0.76, p = 0.01) from 60° to 90° of flexion.

Conclusion: This study showed that the pathway of the dynamic flexion axis has an individual pattern. The medial and lateral trochlear sizes were the key parameters that might affect the elbow joint flexion function. When recovering complex distal humeral fractures or considering the implant design of total elbow arthroplasty, surgeons should pay more attention to the medial and lateral trochlea’s geometry, which may help restore normal elbow kinematics.

A method for measuring in vivo finger kinematics using electromagnetic tracking

Accurate in vivo measurement of finger joint kinematics is important for evaluation of treatment methods, implant designs, and for the development and validation of computer models of the hand. The main objective of this project was to develop a standardized finger kinematic measurement system employing electromagnetic (EM) tracking to measure in vivo finger motion pathways. A landmark digitization protocol was developed and used in vivo, in a biomechanical study using EM trackers secured to the finger segments. In vivo results for finger flexion/extension showed no significant differences between EM and goniometer results, 5°±3°; p = 0.735.

The Effectiveness of a Hinged Elbow Orthosis in Medial Collateral Ligament Injuries: An In Vitro Biomechanical Study

BACKGROUND

Medial collateral ligament (MCL) injuries are common after elbow trauma and in overhead throwing athletes. A hinged elbow orthosis (HEO) is often used to protect the elbow from valgus stress early after injury and during early return to play. However, there is minimal evidence regarding the efficacy of these orthoses in controlling instability and their influence on long-term clinical outcomes.

PURPOSE

(1) To quantify the effect of an HEO on elbow stability after simulated MCL injury. (2) To determine whether arm position, forearm rotation, and muscle activation influence the effectiveness of an HEO.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven cadaveric upper extremity specimens were tested in a custom simulator that enabled elbow motion via computer-controlled actuators and motors attached to relevant tendons. Specimens were examined in 2 arm positions (dependent, valgus) and 2 forearm positions (pronation, supination) during passive and simulated active elbow flexion while unbraced and then while braced with an HEO. Testing was performed in intact elbows and repeated after simulated MCL injury. An electromagnetic tracking device measured valgus angulation as an indicator of elbow stability.

RESULTS

When the arm was dependent, the HEO increased valgus angle with the forearm in pronation (+1.0°± 0.2°, P = .003) and supination (+1.5°± 0.0°, P = .006) during active motion. It had no significant effect on elbow stability during passive motion. In the valgus position, the HEO had no effect on elbow stability during passive or active motion in pronation and supination. With the arm in the valgus position with the HEO, muscle activation reduced instability during pronation (-10.3°± 2.5°, P = .006) but not supination (P = .61).

CONCLUSION

In this in vitro study, this HEO did not enhance mechanical stability when the arm was in the valgus and dependent positions after MCL injury.

CLINICAL RELEVANCE

After MCL injury, an HEO likely does not provide mechanical elbow stability during rehabilitative exercises or when the elbow is subjected to valgus stress such as occurs during throwing.

The effect of implant linking and ligament integrity on humeral loading of a convertible total elbow arthroplasty

BACKGROUND

Both unlinked and linked total elbow arthroplasty (TEA) implants have been employed with no consensus as to the optimal design. The present study aimed to evaluate the effect of collateral ligament integrity and implant linkage on wear-inducing loads in a convertible TEA.

METHODS

Eight fresh frozen upper extremities were tested in an elbow motion simulator. A convertible TEA with an instrumented humeral stem was inserted using computer navigation. Elbow kinematics and humeral loading were recorded with the TEA both linked and unlinked. The collateral ligaments were then sectioned and testing was repeated.

RESULTS

In the dependent position, there was no effect of implant linkage or ligament sectioning on humeral loading. Humeral loading was significantly greater following sectioning of the collateral ligaments but not after linking the TEA with the arm in the valgus position. Humeral loading was significantly greater after linking the TEA but not after sectioning of the collateral ligaments and with the arm in the varus position.

CONCLUSIONS

Collateral ligament integrity reduces wear-inducing loads for both an unlinked and linked TEA. Linkage of a convertible TEA increases humeral loading, which may have detrimental effects on implant longevity.

Where Is the Ulnar Styloid Process? Identification of the Absolute Location of the Ulnar Styloid Process Based on CT and Verification of Neutral Forearm Rotation on Lateral Radiographs of the Wrist

Background

The location of the ulnar styloid process can be confusing because the radius and the hand rotate around the ulna. The purpose of this study was to identify the absolute location of the ulnar styloid process, which is independent of forearm pronation or supination, to use it as a reference for neutral forearm rotation on lateral radiographs of the wrist.

Methods

Computed tomography (CT) images of 23 forearms taken with elbow flexion of 70° to 90° were analyzed. The axial CT images were reconstructed to be perpendicular to the distal ulnar shaft. The absolute location of the ulnar styloid process in this study was defined as the position of the ulnar styloid process on the axial plane of the ulnar head relative to the long axis of the humeral shaft with the elbow set in the position for standard lateral radiographs of the wrist. To identify in which direction the ulnar styloid is located on the axial plane of the ulnar head, the angle between “the line of humeral long axis projected on the axial plane of the ulna” and “the line passing the center of the ulnar head and the center of the ulnar styloid” was measured (ulnar styloid direction angle). To identify how volarly or dorsally the ulnar styloid should appear on the true lateral view of the wrist, the ratio of “the volar-dorsal diameter of the ulnar head” and “the distance between the volar-most aspect of the ulnar head and the center of the ulnar styloid” was calculated (ulnar styloid location ratio).

Results

The mean ulnar styloid direction angle was 12° dorsally. The mean ulnar styloid location ratio was 1:0.55.

Conclusions

The ulnar styloid is located at nearly the ulnar-most (the opposite side of the humerus with the elbow flexed) and slightly dorsal aspects of the ulnar head on the axial plane. It should appear almost midway (55% dorsally) from the ulnar head on the standard lateral view of the wrist in neutral forearm rotation. These location references could help clinicians determine whether the forearm is in neutral or rotated position on an axial CT/magnetic resonance imaging scan or a lateral radiograph of the wrist.

Use of the alpha shape to quantify finite helical axis dispersion during simulated spine movements

In biomechanical studies examining joint kinematics the most common measurement is range of motion (ROM), yet other techniques, such as the finite helical axis (FHA), may elucidate the changes in the 3D motion pathology more effectively. One of the deficiencies with the FHA technique is in quantifying the axes generated throughout a motion sequence. This study attempted to solve this issue via a computational geometric technique known as the alpha shape, which bounds a set of point data within a closed boundary similar to a convex hull. The purpose of this study was to use the alpha shape as an additional tool to visualize and quantify FHA dispersion between intact and injured cadaveric spine movements and compare these changes to the gold-standard ROM measurements. Flexion-extension, axial rotation, and lateral bending were simulated with five C5-C6 motion segments using a spinal loading simulator and Optotrak motion tracking system. Specimens were first tested intact followed by a simulated injury model. ROM and the FHAs were calculated post-hoc, with alpha shapes and convex hulls generated from the anatomic planar intercept points of the FHAs. While both ROM and the boundary shape areas increased with injury (p<0.05), no consistent geometric trends in the alpha shape growth were identified. The alpha shape area was sensitive to the alpha value chosen and values examined below 2.5 created more than one closed boundary. Ultimately, the alpha shape presents as a useful technique to quantify sequences of joint kinematics described by scatter plots such as FHA intercept data.

A Refined Technique to Calculate Finite Helical Axes From Rigid Body Trackers

Finite helical axes (FHAs) are a potentially effective tool for joint kinematic analysis. Unfortunately, no straightforward guidelines exist for calculating accurate FHAs using prepackaged six degree-of-freedom (6DOF) rigid body trackers. Thus, this study aimed to: (1) describe a protocol for calculating FHA parameters from 6DOF rigid body trackers using the screw matrix and (2) to maximize the number of accurate FHAs generated from a given data set using a moving window analysis. Four Optotrak® Smart Markers were used as the rigid body trackers, two moving and two fixed, at different distances from the hinge joint of a custom-machined jig. 6DOF pose information was generated from 51 static positions of the jig rotated and fixed in 0.5 deg increments up to 25 deg. Output metrics included the FHA direction cosines, the rotation about the FHA, the translation along the axis, and the intercept of the FHA with the plane normal to the jig's hinge joint. FHA metrics were calculated using the relative tracker rotation from the starting position, and using a moving window analysis to define a minimum acceptable rotational displacement between the moving tracker data points. Data analysis found all FHA rotations calculated from the starting position were within 0.15 deg of the prescribed jig rotation. FHA intercepts were most stable when determined using trackers closest to the hinge axis. Increasing the moving window size improved the FHA direction cosines and center of rotation accuracy. Window sizes larger than 2 deg had an intercept deviation of less than 1 mm. Furthermore, compared to the 0 deg window size, the 2 deg window had a 90% improvement in FHA intercept precision while generating almost an equivalent number of FHA axes. This work identified a solution to improve FHA calculations for biomechanical researchers looking to describe changes in 3D joint motion.

Altered helical axis patterns of the lumbar spine indicate increased instability with disc degeneration

Although the causes of low back pain are poorly defined and indistinct, degeneration of the intervertebral disc is most often implicated as the origin of pain. The biochemical and mechanical changes associated with degeneration result in the discs' inability to maintain structure and function, leading to spinal instability and ultimately pain. Traditionally, a clinical exam assessing functional range-of-motion coupled with T2-weighted MRI revealing disc morphology are used to evaluate spinal health; however, these subjective measures fail to correlate well with pain or provide useful patient stratification. Therefore, improved quantification of spinal motion and objective MRI measures of disc health are necessary. An instantaneous helical axis (IHA) approach provides rich temporal three-dimensional data describing the pathway of motion, which is easily visualized. Eighteen cadaveric osteoligamentous lumbar spines (L4-5) from throughout the degenerative spectrum were tested in a pure moment fashion. IHA were calculated for flexion-extension and lateral bending. A correlational study design was used to determine the relationship between disc measurements from quantitative T2* MRI and IHA metrics. Increased instability and out-of-plane rotation with diminished disc health was observed during lateral bending, but not flexion-extension. This new analysis strategy examines the entire pathway of motion, rather than simplifying spinal kinematics to its terminal ends of motion and provides a more sensitive kinematic measurement of disc health. Ultimately, through the use of 3D dynamic fluoroscopy or similar methods, a patient's functional IHA in lateral bending may be measured and used to assess their disc health for diagnosis, progression tracking, and treatment evaluation.

Reconstruction of the coronoid process using the tip of the ipsilateral olecranon

BACKGROUND

Autograft reconstruction of the coronoid using the tip of the olecranon has been described as a treatment option for comminuted coronoid fractures or coronoid nonunions that are not repairable. The purpose of this in vitro biomechanical study of the coronoid-deficient elbow was to determine whether coronoid reconstruction using the tip of the ipsilateral olecranon would restore elbow kinematics.

METHODS

An elbow motion simulator was used to perform active and passive extension of six cadaveric arms in the horizontal, valgus, varus, and vertical orientations. Elbow kinematics were quantified with use of the screw displacement axis of the ulna with respect to the humerus. Testing was performed with an intact coronoid, a 40% coronoid deficiency, and a coronoid reconstruction using the tip of the ipsilateral olecranon.

RESULTS

Creation of a 40% coronoid deficiency resulted in significant changes (range, 3.6° to 10.9°) in the angular deviations of the screw displacement axis relative to the intact state during simulated active and passive extension in the varus orientation with the forearm in pronation and in supination (p < 0.05). Reconstruction of the coronoid using the ipsilateral olecranon tip restored the angular deviations to those in the intact state (p > 0.05) with the arm in all orientations except valgus, in which there was a small but significant difference (0.4° ± 0.2°, p = 0.04) during passive motion with forearm supination.

CONCLUSIONS

Reconstruction of the coronoid using the tip of the ipsilateral olecranon was an effective method for restoring normal kinematics over a range of elbow motion from 20° to 120° in a cadaveric model of an elbow with a 40% coronoid deficiency. This reconstruction technique may prove beneficial for patients with elbow instability due to coronoid deficiency.

Measuring dynamic in-vivo elbow kinematics: description of technique and estimation of accuracy

BACKGROUND

The objectives of this study were to characterize the translational and rotational accuracy of a model-based tracking technique for quantifying elbow kinematics and to demonstrate its in vivo application.

METHOD OF APPROACH

The accuracy of a model-based tracking technique for quantifying elbow kinematics was determined in an in vitro experiment. Biplane X-ray images of a cadaveric elbow were acquired as it was manually moved through flexion-extension. The 3D position and orientation of each bone was determined using model-based tracking. For comparison, the position and orientation of each bone was also determined by tracking the position of implanted beads with dynamic radiostereometric analysis. Translations and rotations were calculated for both the ulnohumeral and radiohumeral joints, and compared between measurement techniques. To demonstrate the in vivo application of this technique, biplane X-ray images were acquired as a human subject extended their elbow from full flexion to full extension.

RESULTS

The in vitro validation demonstrated that the model-based tracking technique is capable of accurately measuring elbow motion, with reported errors averaging less than ±1.0 mm and ±1.0 deg. For the in vivo application, the carrying angle changed from an 8.3 ± 0.5 deg varus position in full flexion to an 8.4 ± 0.5 deg valgus position in full extension.

CONCLUSIONS

Model-based tracking is an accurate technique for measuring in vivo, 3D, dynamic elbow motion. It is anticipated that this experimental approach will enhance our understanding of elbow motion under normal and pathologic conditions.

Correction of severe wrist deformity following physeal arrest of the distal radius with the aid of a three-dimensional computer simulation

Growth arrest following physeal injury may result in severe limb deformity. We report a case of complex wrist deformity caused by injury to the distal radial physis resulting in radial shortening and abnormal inclination of the radial articular surface, which was successfully treated by gradual correction after computer simulation. The simulation enabled us to develop an appropriate operative plan by accurately calculating the axis of the three-dimensional (3D) deformity using computer bone models. In the simulative surgery with a full-size stereolithography bone model, an Ilizarov external fixator was applied to the radius such that its two hinges were located on the virtual axis of the deformity, which was reproduced in the actual surgery. This technique of 3D computer simulation is a useful alternative to plan accurate correction of complex limb deformities following growth arrest.

Defining the flexion-extension axis of the ulna: implications for intra-operative elbow alignment

The increased utilization of total elbow replacements has resulted in a correspondingly increased number of failed implants requiring revision. The most common reason for revision is aseptic loosening of the ulnar component due to polyethylene induced osteolysis. Implant malalignment is thought to be an important cause of bearing wear and implant failure. The ulnar flexion axis can be used to accurately align the ulnar component of the elbow implant; however, the optimal method of determining this axis intra-operatively is unknown. This in vitro study determined the relationship amongst kinematically and anatomically defined ulnar flexion axes in an effort to improve the accuracy of ulnar component positioning. Five different techniques were used to determine the ulnar flexion axis in 12 cadaveric specimens, 3 kinematic and 2 anatomic. The techniques were compared with the screw displacement axis from simulated elbow flexion. An anatomic measurement technique using the guiding ridge of the greater sigmoid notch of the ulna and the radial head was found to most accurately replicate the position and orientation of the screw displacement axis of the elbow (p<0.05). Because an anatomically derived flexion axis can be determined using both pre-operative imaging techniques, as well as with intra-operative guides, it is more practical than kinematically derived techniques requiring tracking systems for clinical application and should provide reliable and consistent results.

Morphologic analysis of the distal humerus with special interest in elbow implant sizing and alignment

This study determined the relationship between the medullary canal axis and the flexion-extension axis of the distal humerus as they relate to implant selection and design for elbow arthroplasty. Computed tomography scans of 40 fresh-frozen cadaveric specimens were analyzed with computer-aided design software. The anterior offset and cubital angle were measured between the 2 axes, and the cross-sectional area and diameter were measured for the medullary canal at various intervals. The anterior offset of the flexion-extension axis from the medullary canal axis was proportional to the length of canal used to determine the stem axis. No correlation was established among the width of the articular surface, anterior-posterior canal curvature, and cubital angle. These findings suggest that modular implants that allow for the variability in the natural anterior bow and articular offset of the distal humerus may enhance proper restoration of the flexion-extension axis of the elbow.

Locating the axis of rotation when fitting an elbow orthosis: a comparison of measurement and palpation

No other previously published studies consider the relative motion of orthotic components positioned on the upper arm and the forearm. This study therefore measured the location and direction of the axis of rotation of an orthotic component fixed to the forearm in relation to an orthotic component fixed to the upper arm, and compared the results with those obtained by palpation. A plane flexion or extension motion of the forearm component in relation to the component on the upper arm can be described as a pure rotation about a fixed centre. However, activation of the biceps or triceps shifts that centre by around 2 cm, due to a displacement of the humerus within the orthotic component on the upper arm. Within a range of approximately 1 cm, the location of the axis of rotation was similar to that obtained by palpation. Neither custom-made plastic/foam orthoses with their hinges aligned to the measured axis, nor orthoses with their hinges aligned to the palpated axis, exhibited any difference in the wearer's comfort. It is concluded that the best choice for the location of the axis of a hinge-type orthosis for the elbow constitutes a compromise between the axes for active flexion and active extension. In view of the large influence that muscle activation has on axis location, errors in the order of 1 cm seem to be negligible when adjusting the hinge of an orthosis in individual cases.

Sagittal curvature of total knee replacements predicts in vivo kinematics

BACKGROUND

It is known that in vivo kinematics after total knee replacement is influenced by the design of the implant. The goal of this study was to show that the sagittal curvature of two different knee prostheses differing in geometric design predicts their in vivo motion behavior.

METHODS

Three-dimensional tibio-femoral displacements of two prosthesis designs (single radius vs. dual radius) were measured during knee extension under weight bearing conditions by in vivo video fluoroscopy. Finite helical axes were computed to represent the tibio-femoral motions. Angular deviation alpha and the spatial localization deviation delta were used to characterize the motions. Angular deviation is the angle between each incremental finite helical axis and the medio-lateral axis of the femoral component of the prosthesis. The spatial localization deviation is the distance between each finite helical axis and the center of the femoral component of the prosthesis. Statistical comparisons were performed using the median and the interquartile range of the angular deviation and the spatial localization deviation.

FINDINGS

The single-radius design showed finite helical axes concentrated at a single axis near to the medio-lateral axis of the femoral component. The angular and spatial localization deviation of the dual radius design were larger compared to the single radius design, exhibiting finite helical axes varying between two axes.

INTERPRETATION

Video fluoroscopy in combination with finite helical axis analysis proved to be suitable methods to evaluate the in vivo kinematical behavior of total knee arthroplasty, which can be useful for implant designers. Knowledge of in vivo kinematics can also provide surgeons with more background information about the total knee arthroplasty models they implant.