Biomedical subjects

Karen D Gordon

Publications and source records attributed to Karen D Gordon.

12 recordsLinked to original sources

PubMed2006

Effect of simulated muscle activity on distal radioulnar joint loading in vitro.

This study investigated the relationship between simulated forearm muscle loads and the joint reaction force in the distal radioulnar joint using an in vitro model. Seven fresh frozen cadaveric specimens were mounted in an upper extremity joint simulator capable of applying pneumatic loads to various (muscle) tendons while restraining the forearm in the three positions of pronation, supination, and neutral rotation. Loads were applied to model four forearm muscles (biceps, pronator teres, pronator quadratus, and supinator) in 10 N increments ranging from 10 N to 80 N for the biceps and pronator teres and in 10 N increments from 10 N to 50 N for the pronator quadratus and the supinator. Distal ulnar arthroplasty was performed on each specimen with a custom instrumented ulnar head replacement implant that quantified loads (via strain gauge instrumentation). The relationship between increasing muscle load and joint load was found to be positive and quasilinear in most cases. The biceps had the greatest influence on the distal radioulnar joint reaction force with a joint force in the range of 8% to 33% of the applied muscle load. The pronator teres, supinator, and pronator quadratus were less influential with a joint reaction force ranging between 6% to 19%, 4% to 9% and 2% to 10% of the applied muscle load, respectively.

Aged↗

PubMed2006

Design and implementation of an instrumented ulnar head prosthesis to measure loads in vitro.

The development of a novel instrumented implant for ulnar head replacement is presented in this study. This implant was instrumented with strain gauges to quantify bending moments about the anatomic axes of the distal ulna, and subsequently the distal radioulnar joint (DRUJ) reaction force magnitude. The implant was surgically inserted in seven cadaveric upper extremities, which were subsequently mounted in a custom joint simulator. Simulated active unresisted pronation and supination motion trials were conducted using computer-controlled pneumatic actuators to simulate forearm musculature. Passive (unloaded) trials were also conducted. The reaction force across the DRUJ ranged from 2 to 10 N in magnitude during this unresisted motion. Increased bending moment magnitudes were measured when the forearm was positioned in supination compared to pronation. The magnitude of joint bending moments showed a consistent pattern with forearm position, regardless of simulated active or passive rotation, or supination and pronation motion trials. This result illustrates that the primary influence on joint load is likely the position and contact with the radial articulation. This study of DRUJ loading should be useful for biomechanical modeling, implant design considerations and improved knowledge of articular mechanics.

Aged↗

PubMed2005

Comparison of distal radioulnar joint reconstructions using an active joint motion simulator.

PURPOSE: Distal radioulnar joint (DRUJ) instability can result in pain and functional disability. Numerous DRUJ reconstructive options have been described with minimal biomechanical analysis. The purpose of this study was to evaluate the ability of 4 well-described DRUJ reconstructions to restore joint kinematics using a dynamic, motion-controlled simulator. METHODS: Eleven cadaveric upper extremities had computer-controlled simulated active forearm rotation. Joint kinematics were quantified by using an electromagnetic tracking system. We compared the passive and simulated active kinematics of the intact, unstable, and reconstructed DRUJ (capsular repair, 2 described radioulnar ligament reconstructions, and a radioulnar tethering procedure). RESULTS: All reconstructions improved significantly the kinematics of the unstable DRUJ. The capsule repair restored simulated active joint kinematics closest to the intact DRUJ. CONCLUSIONS: All 4 reconstructions improved DRUJ stability significantly. The capsule repair most closely matched intact DRUJ kinematics and the radioulnar ligament reconstructions were found to be superior to a radioulnar tethering procedure.

Adult↗

PubMed2005

The effect of radial head fracture size on elbow kinematics and stability.

This study determined the effect of radial head fracture size and ligament injury on elbow kinematics. Eight cadaveric upper extremities were studied in an in vitro elbow simulator. Testing was performed with ligaments intact, with the medial collateral (MCL) or lateral collateral (LCL) ligament detached, and with both the MCL and LCL detached. Thirty degree wedges were sequentially removed from the anterolateral radial head up to 120 degrees . Valgus angulation and external rotation of the ulna relative to the humerus were determined for passive motion, active motion, and pivot shift testing with the arm in a vertical (dependent) orientation. Maximum varus-valgus laxity was calculated from measurements of varus and valgus angulation with the arm in horizontal gravity-loaded positions. No effect of increasing radial head fracture size was observed on valgus angulation during passive and active motion in the dependent position. In supination, external rotation increased with increasing fracture size during passive motion with LCL deficiency and both MCL and LCL deficiency. With intact ligaments, maximum varus-valgus laxity increased with increasing radial head fracture size. With ligament disruption, elbows were grossly unstable, and no effect of increasing radial head fracture size occurred. During pivot shift testing, performed with the ligaments intact, subtle instability was noted after resection of one-third of the radial head. In this in vitro biomechanical study, small subtle effects of radial head fracture size on elbow kinematics and stability were seen in both the ligament intact and ligament deficient elbows. These data suggest that fixation of displaced radial head fractures less than or equal to one-third of the articular diameter may have some biomechanical advantages; however, clinical correlation is required.

Aged↗

PubMed2004

Soft-tissue stabilizers of the distal radioulnar joint: an in vitro kinematic study.

PURPOSE: Distal radioulnar joint (DRUJ) stability is dependent on osseous anatomy, soft-tissue stabilizers, and muscle activity. The relative importance of DRUJ soft-tissue stabilizers remains controversial and has not been examined in the more physiologic setting of simulated muscle loading in the intact specimen. The purpose of this study was to examine the role of static stabilizers on the kinematics of the DRUJ during active simulated motion. METHODS: Twelve cadaveric upper extremities underwent computer-controlled, simulated, active forearm rotation. Joint kinematics were measured in the intact specimen and after sequential sectioning of soft-tissue stabilizers including the dorsal and palmar radioulnar ligaments (RULs) and the triangular fibrocartilage (TFC), dorsal and palmar capsule, ulnocarpal ligaments (UCL), extensor carpi ulnaris (ECU) subsheath, pronator quadratus (PQ), and the interosseous membrane (IOM). RESULTS: After sectioning of soft tissues significant changes in the DRUJ kinematics were observed. With a distal to proximal sectioning sequence significant alterations in kinematics were not identified until sectioning of the IOM; with a proximal to distal sectioning sequence intact DRUJ kinematics were maintained until the final soft-tissue (RULs and TFC) sectioning. CONCLUSIONS: Sectioning of all soft-tissue stabilizers produced significant DRUJ instability and abnormal joint kinematics. The RULs and TFC play a key role in DRUJ kinematics because they can help to maintain normal joint rotation in the absence of all other soft-tissue stabilizers. With the preservation of other soft-tissue stabilizers, however, the RULs and TFC are not essential for the maintenance of normal kinematics of the DRUJ.

Adult↗

PubMed2004

Electromyographic activity and strength during maximum isometric pronation and supination efforts in healthy adults.

There exists a lack of quantitative data in the literature related to the torque produced during axial forearm rotation and the electromyographic (EMG) activity of the muscles involved. Therefore, the purpose of this study was to compare the relative EMG activity of four forearm muscles during resisted forearm rotation. A custom-built device capable of measuring torque in the absence of grip was employed. Fourteen healthy volunteers performed maximum isometric voluntary contractions in five positions of axial forearm rotation for both pronation and supination. EMG data were collected simultaneously from the supinator, biceps, pronator quadratus (deep and superficial heads), and pronator teres muscles using fine-wire bipolar electrodes. Data were analyzed to determine the contributions of each muscle to pronation and supination torque over five positions of forearm rotation. In the absence of grip no significant difference was found between supination and pronation torque in neutral position. Supination torque generation was greater in the pronated forearm positions, and pronation torque was greater in the supinated positions (p<0.05). A root-mean-square EMG analysis verified the major contributions of the pronator teres and both heads of the pronator quadratus muscle to pronation torque, and supinator and biceps to supination torque. The deep head of the pronator quadratus was active during both pronation and supination, lending support to the theory that it may act primarily as a dynamic distal radioulnar joint stabilizer. This information may be helpful in upper extremity modeling, surgical treatments, and rehabilitation strategies.

Adult↗

PubMed2004

The effect of radial head excision and arthroplasty on elbow kinematics and stability.

BACKGROUND: Radial head fractures are common injuries. Comminuted radial head fractures often are treated with radial head excision with or without radial head arthroplasty. The purpose of the present study was to determine the effect of radial head excision and arthroplasty on the kinematics and stability of elbows with intact and disrupted ligaments. We hypothesized that elbow kinematics and stability would be (1) altered after radial head excision in elbows with intact and disrupted ligaments, (2) restored after radial head arthroplasty in elbows with intact ligaments, and (3) partially restored after radial head arthroplasty in elbows with disrupted ligaments. METHODS: Eight cadaveric upper extremities were studied in an in vitro elbow simulator that employed computer-controlled actuators to govern tendon-loading. Testing was performed in stable, medial collateral ligament-deficient, and lateral collateral ligament-deficient elbows with the radial head intact, with the radial head excised, and after radial head arthroplasty. Valgus angulation and rotational kinematics were determined during passive and simulated active motion with the arm dependent. Maximum varus-valgus laxity was measured with the arm in a gravity-loaded position. RESULTS: In specimens with intact ligaments, elbow kinematics were altered and varus-valgus laxity was increased after radial head excision and both were corrected after radial head arthroplasty. In specimens with disrupted ligaments, elbow kinematics were altered after radial head excision and were similar to those observed in specimens with a native radial head after radial head arthroplasty. Varus-valgus laxity was increased after ligament disruption and was further increased after radial head excision. Varus-valgus laxity was corrected after radial head arthroplasty and ligament repair; however, it was not corrected after radial head arthroplasty without ligament repair. CONCLUSIONS: Radial head excision causes altered elbow kinematics and increased laxity. The kinematics and laxity of stable elbows after radial head arthroplasty are similar to those of elbows with a native radial head. However, radial head arthroplasty alone may be insufficient for the treatment of complex fractures that are associated with damage to the collateral ligaments as arthroplasty alone does not restore stability to elbows with ligament injuries.

Aged↗

PubMed2003

Influence of the pronator quadratus and supinator muscle load on DRUJ stability.

PURPOSE: To determine the effects of altering the load contributions of the pronator quadratus and supinator muscles on in vitro distal radioulnar joint (DRUJ) stability during pronation and supination and before and after ulnar head excision. METHODS: Multiple pronation trials were conducted with incremental loading of the pronator quadratus relative to the pronator teres muscle; supination trials were similarly conducted with incremental loading of the supinator relative to the biceps muscle. All trials were conducted using an upper-limb apparatus capable of simulating muscle/tendon loading and displacement. Stability measurements included dorsal-volar translations of the radius relative to the ulna and DRUJ diastasis and convergence. RESULTS: Increased pronator quadratus loading did not affect intact DRUJ stability but effects were noted after ulnar head excision when the forearm was positioned between neutral and full pronation. Incremental loading of the supinator muscle did not modify DRUJ stability in the intact or ulnar head excised state. CONCLUSIONS: Pronator quadratus muscle activity aggravates forearm instability after ulnar head excision. Immobilization of the forearm in mid- to full supination should minimize pronator quadratus activity and optimize soft-tissue healing. This information may be useful to develop in vitro muscle-loading scenarios and analytical forearm models.

Aged↗

PubMed2003

Development of a motion-controlled in vitro elbow testing system.

Joint simulators can be used to study motion pathways of a human joint, to investigate changes in joint stability following injury, and to formulate improved reconstructive and rehabilitative procedures. Our objectives were: to develop a laboratory-based, motion-controlled elbow testing apparatus capable of simulating tendon (muscle) loading and displacement in a cadaveric specimen; to describe its performance while testing stable and unstable elbows; and to compare its operation to that of a previously designed load-controlled device. Velocity control of a pneumatic actuator was achieved using a custom-written, closed-loop feedback controller. This actuator was incorporated into an elbow testing system that used additional pneumatic actuators and a combination of motion- and load-control to achieve desired motions. Simulations achieved with this apparatus demonstrated small magnitudes of error in actuator position and highly repeatable flexion pathways with the specimens positioned in vertical, varus, and valgus orientations. The repeatability in motion pathways generated in both a stable and unstable elbow model was equivalent to or better than for similar tests performed using the load-controlled system, and the velocity of the resulting elbow motion was more reproducible.

Biomechanical Phenomena↗

PubMed2003

Mechanical properties of subchondral cancellous bone of the radial head.

OBJECTIVE: To quantify the mechanical properties of subchondral bone of the radial head, with special interest in the regional variations in bone stiffness and strength. DESIGN: Transverse subchondral cancellous bone slices obtained from the proximal radial head were subjected to indentation tests. SETTING: Biomechanics laboratory with a servohydraulic materials testing machine. SPECIMENS: Thirteen previously frozen, cadaver proximal radii of mean age 69 +/- 9 years. MAIN OUTCOME MEASUREMENTS: The mean indentation modulus and local yield strength were calculated for the anteromedial (AM), anterolateral (AL), posteromedial (PM), and posterolateral (PL) quadrants of the radial head. RESULTS AND CONCLUSIONS: There were no differences in mean indentation modulus across all 4 quadrants (AL, 55.56 +/- 16.20 MPa; AM, 53.48 +/- 20.67 MPa; PM, 49.20 +/- 18.31 MPa; PL, 49.96 +/- 14.97 MPa) (P > 0.05). The AM quadrant had higher local yield strength than the PL and PM quadrants, as did the AL compared with the PL quadrant (AL, 24.89 +/- 8.52 Mpa; AM, 28.39 +/- 10.52 Mpa; PM, 23.01 +/- 6.99; PL, 20.62 +/- 4.83 MPa) (P < 0.05). This suggests that the high frequency of radial head fractures in the AL quadrant is likely not due to the local strength of cancellous bone. Rather, the location of fracture may be influenced by the composite strength or the mechanisms of loading at the radiocapitellar and proximal radioulnar joints. The modulus results suggest that similar screw purchase can be achieved in all areas of the radial head during internal fixation of fractures. These results may also influence implant design and fixation. This study was limited to an older population and may not be representative of a younger population.

Age Factors↗

PubMed2002

An anthropometric study of the distal ulna: implications for implant design.

Arthroplasty of the distal ulna is frequently used for distal radioulnar joint disorders; however, prosthetic failures are common. An implant replicating the ulna may be advantageous from the viewpoint of joint kinematics, wear, and fixation. The geometry of 40 distal ulnas was quantified by computed tomography scanning and radiography. Ulnar head diameter (16.8 +/- 1.6 mm), canal diameter (8.3 +/- 1.6 mm), eccentricity of the head relative to the shaft (2.5 +/- 1.4 mm), and angle of articulation (176 degrees +/- 29 degrees ) were measured. No correlation was found between the diameters of the ulnar head and intramedullary canal (R(2) = 0.2). A modular head-stem system with an eccentric offset may best reproduce the geometry of the distal ulna.

Adult↗

PubMedDate not supplied

Kinematics and stability of the fractured and implant-reconstructed radial head.

Controversy exists as to the optimal management of radial head fractures. Biomechanical studies have been conducted to quantify elbow stability for simulated wedge fractures, head excision, and head replacement, with and without the integrity of the collateral ligaments. Our in vitro studies have demonstrated that in the ligamentously intact elbow, kinematics and stability are slightly altered with simulated depressed wedge fractures up to 120 degrees of the radial head, markedly altered with head resection, and improved after radial head replacement. Radial head excision decreases elbow stability in the ligament-deficient elbow, and radial head replacement improves stability similar to that of the native radial head. The ligaments have the most marked influence on stability, particularly when the upper limb is positioned such that valgus and varus gravity loads are applied to the elbow. Whereas the radial head acts as a secondary stabilizer to the collateral ligaments with the arm in these positions, its relative role is greater when the arm is in the dependent position and elbow flexion is simulated, particularly in extension. Further studies are needed to elucidate the complex interaction of the radial head with the capitellum, the ulnohumeral joint, and the ligamentous structures for different activities of daily living.

Biomechanical Phenomena↗