Eric K. Wong

Biomechanical Analysis of an Anatomic Anterior Cruciate Ligament Reconstruction

Background: The focus of most anterior cruciate ligament reconstructions has been on replacing the anteromedial bundle and not the posterolateral bundle. Hypothesis: Anatomic two-bundle reconstruction restores knee kinematics more closely to normal than does single-bundle reconstruction. Study Design: Controlled laboratory study. Methods: Ten cadaveric knees were subjected to external loading conditions: 1) a 134-N anterior tibial load and 2) a combined rotatory load of 5-N·m internal tibial torque and 10-N·m valgus torque. Resulting knee kinematics and in situ force in the anterior cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for 1) intact, 2) anterior cruciate ligament deficient, 3) single-bundle reconstructed, and 4) anatomically reconstructed knees. Results: Anterior tibial translation for the anatomic reconstruction was significantly closer to that of the intact knee than was the single-bundle reconstruction. The in situ force normalized to the intact anterior cruciate ligament for the anatomic reconstruction was 97% ± 9%, whereas the single-bundle reconstruction was only 89% ± 13%. With a combined rotatory load, the normalized in situ force for the single-bundle and anatomic reconstructions at 30° of flexion was 66% ± 40% and 91% ± 35%, respectively. Conclusions: Anatomic reconstruction may produce a better biomechanical outcome, especially during rotatory loads. Clinical Relevance: Results may lead to the use of a two-bundle technique.

Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads

The anterior cruciate ligament (ACL) can be anatomically divided into anteromedial (AM) and posterolateral (PL) bundles. Current ACL reconstruction techniques focus primarily on reproducing the AM bundle, but are insufficient in response to rotatory loads. The objective of this study was to determine the distribution of in situ force between the two bundles when the knee is subjected to anterior tibial and rotatory loads. Ten cadaveric knees (50 ± 10 years) were tested using a robotic/universal forcemoment sensor (UFS) testing system. Two external loading conditions were applied: a 134 N anterior tibial load at full knee extension and 15°, 30°, 60°, and 90° of flexion and a combined rotatory load of 10 N m valgus and 5 N m internal tibial torque at 15° and 30° of flexion. The resulting 6 degrees of freedom kinematics of the knee and the in situ forces in the ACL and its two bundles were determined. Under an anterior tibial load, the in situ force in the PL bundle was the highest at full extension (67 ± 30 N) and decreased with increasing flexion. The in situ force in the AM bundle was lower than in the PL bundle at full extension, but increased with increasing flexion, reaching a maximum (90 ± 17 N) at 60° of flexion and then decreasing at 90°. Under a combined rotatory load, the in situ force of the PL bundle was higher at 15° (21 ± 11 N) and lower at 30° of flexion (14 ± 6 N). The in situ force in the AM bundle was similar at 15° and 30° of knee flexion (30 ± 15 vs. 35 ± 16 N, respectively). Comparing these two external loading conditions demonstrated the importance of the PL bundle, especially when the knee is near full extension. These findings provide a better understanding of the function of the two bundles of the ACL and could serve as a basis for future considerations of surgical reconstruction in the replacement of the ACL.

Use of robotic technology for diathrodial joint research

Knowledge of diarthrodial joint mechanics and specific function of the ligaments are needed in order to understand injury mechanisms, improve surgical procedures and design better post-surgical rehabilitation protocols. To facilitate these needs, a robotic/universal force-moment sensor (UFS) testing system was developed to measure joint kinematics in multiple degree-of-freedom and the in situ forces in the ligaments. When operated in the position control mode, the testing system applies a known load to the intact joint while the motion and force data are recorded. After transection of a ligament, the recorded motion for the intact joint is repeated and new force and moment data is recorded by the UFS. Since the robot reproduces the identical initial position as well as path of joint motion before and after a ligament is transected, the in situ force in the ligament is the difference between the two sets of force and moment data. In force control mode, a known force is applied to the intact knee while the kinematics are recorded. After ligament transection, the same force is applied while the changes in kinematics are again recorded. Testing in this mode is similar to a clinical examination that diagnoses ligament injury. To date, this testing system has been used for experimental studies that examine the anterior cruciate ligament & posterior cruciate ligament of the knee and ligaments of the shoulder. A three-dimensional finite element model has also been constructed based on CT/MRI scans of a knee specimen and validated using data obtained with the testing system. Once in vivo kinematics (such as during gait analysis or throwing activities) are available, the robotic/UFS testing system can be programmed to reproduce these joint kinematics on young human cadaveric specimens in order to generate a database for in situ forces in the ligaments, or Ligament replacement grafts. With appropriate computational models, the stresses and strains in these tissues in vivo can also be determined. Potential applications of this combined approach include pre-operative surgical planning, improvement of surgical procedures as well as development of appropriate post-operative rehabilitation protocols.

Epidemiology of Cytokines The Women On the Move through Activity and Nutrition (WOMAN) Study

Using multiplex technology, the authors investigated the laboratory and biologic variation of a panel of cytokines (interleukin (IL)-1a, IL-1 receptor antagonist, IL-4, IL-6, IL-8, IL-10, interferon-inducible protein-10, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha) over 18 months and their relations to cardiovascular disease risk factors, hormone therapy, and weight loss. Data were obtained from the Woman On the Move through Activity and Nutrition (WOMAN) Study, a randomized clinical trial investigating the effect of nonpharmacologic interventions on subclinical atherosclerosis among overweight, postmenopausal women in Pennsylvania. The present analysis (February 2002-August 2005) comprised 290 women aged 52-62 years (mean age = 57 years). Most of the cytokines were detectable in a majority of the samples, and the between-individual biologic variation was greater than the within-individual biologic and laboratory variation. There was little association between use of hormone therapy at baseline or change in hormone therapy by 18 months and cytokine levels. Weight loss was associated with a decrease in levels of IL-1 receptor antagonist, IL-6, and C-reactive protein. The results suggest that a wide panel of cytokines may be measured simultaneously from one sample. There is large unexplained variability in cytokine levels that is probably due to genetic-environmental associations.

An Analytical Approach to Determine the in Situ Forces in the Glenohumeral Ligaments

The purpose of this study was to use an analytical approach to determine the forces in the glenohumeral ligaments during joint motion. Predictions from the analytical approach were validated by comparing them to experimental data. Using a geometric model, the lengths of the four glenohumeral ligaments were determined during anterior-posterior loading simulations and forward flexion-extension. The corresponding force in each structure was subsequently calculated based on length data via load-elongation curves obtained experimentally. During the anterior loading simulation at 0 deg of abduction, the superior glenohumeral ligament carried up to 71 N at the maximally translated position. At 90 deg of abduction, the anterior band of the inferior glenohumeral ligament had the highest force of 45 N during anterior loading. These results correlated well with those found in previous experimental studies. We believe that this validated analytical approach can be used to predict the forces in the glenohumeral ligaments during more complex joint motion as well as assist surgeons during shoulder repair procedures.

Use of robotic technology to study the biomechanics of ligaments and their replacements

A robotic universal force-moment sensor (UFS) testing system has been developed in our research center to study joint kinematics as well as the in situ forces in ligaments and their replacements by using cadaveric knee and shoulder joints. In vitro data on the major ligaments of the intact, injured, and reconstructed joints have been obtained in response to various external loading conditions as well as simulated muscle loads. Furthermore, data provided by the testing system could also be used to validate computational models of these diarthrodial joints.

Canadian computed tomography head rule and its impact on Singaporean practice

Introduction We aim to determine the usefulness of the Canadian Computed Tomography (CT) Head Rule in patients who present with minor and minimal head injury to the emergency department. Methods Clinical information was retrospectively collected and the need for CT head was evaluated. The primary outcome measure was the requirement for neurological intervention. The secondary outcome measure was brain injury requiring admission or neurological follow-up. Results A total of 1127 cases were reviewed. About 6.3% had clinically important brain injury; and 1.2% required neurological intervention. The high-risk factors were 45.2% sensitive (95% confidence interval [CI]=27.8-63.7%) and 76.2% specific (95% CI=73.5-78.7%) for predicting need for neurological intervention. All seven risk factors were 73.2% sensitive (95% CI=61.2-82.7%) and 69.8% specific (95% CI=66.9-72.5%) for predicting clinically important brain injury. Overall, the rule had a positive predictive value of 14.0 (95% CI=10.7-18.1) and negative predictive value of 97.5 (95% CI=96.0-98.4). Conclusions In this retrospective validation of the Canadian CT Head Rule in the Singaporean context, we conclude that the lower sensitivity of the rule could be attributed to local neurosurgical practice, lack of application of the rule among clinicians and inclusion of patients with minimal head injury. Practically, the high NPV will mean that patients who do not fulfill the rule can be safely discharged with head injury advice, without the need for a scan. The judicious use of CT head can achieve savings for our health-care system. (Hong Kong j.emerg.med. 2015;22:359-363)

Focused Assessment with Sonography in Trauma (FAST): Experience of a Tertiary Hospital in Southeast Asia

Objective This study compares the positive predictive value (PPV) and negative predictive value (NPV) of focused assessment with sonography in trauma (FAST) versus abdominal-pelvic computed tomography scans (CTAP) after blunt abdominal injury as well as the need for abdominal surgery. We also sought to determine if any false negative ultrasound studies were associated with significant morbidity. The results were compared with other studies. Design Retrospective cross-sectional study. Setting A tertiary hospital. Methods Cases were retrieved from the trauma registry and electronic medical records in a tertiary hospital in Singapore over a two year period from 1 January 2009 to 31 December 2010. Exclusion criteria included penetrating trauma and burns. The sonographic finding, computed tomography finding, and the outcome of the patients were retrieved. Diagnostic characteristics including predictive values were calculated. Results A total of 476 patients were enrolled. Four hundred fifty-nine patients had FAST performed with fifty (10.9%) being positive. Forty-nine patients (21.7%) out of 226 patients had CTAP which showed abnormalities and nineteen (4.0%) patients underwent surgery. Comparing FAST to detect abnormalities on CTAP, the PPV and NPV were 0.590 and 0.863 respectively. Comparing FAST with the need for surgery, the PPV and NPV were 0.280 and 0.990 respectively. Four patients (0.98%) had negative FAST but required surgery. There were no significant adverse outcomes or surgical intervention in patients with normal vital signs, normal initial physical examination and negative FAST findings but who did not have a CTAP. Conclusions In patients with an initial normal physical examination and negative FAST, emergent CTAP may be avoided. (Hong Kong j.emerg.med. 2014;21:230-236)

Ligaments of the Knee in Sports Injuries and Rehabilitation

Increased athletic participation in high impact and high risk sports has increased the occurrence of soft tissue injuries in the knee. It has been estimated that the annual incidence of knee ligament injuries in the United States is 70,000 anterior cruciate ligament (ACL), 40,000 medial collateral ligament (MCL), and 20,000 combined ACL/MCL injuries [1, 2]. Seventy percent of all ACL injuries are sports-related [3]. In fact, an ACL injury occurs during every 1500 h of football, basketball, and soccer that are played [4]. A study from 1972 to 1987 concluded that an ACL tear occurs on approximately 1 out of 20,000 skier days [5]. Overall, 72% of all ACL injuries occur in males because they participate in sports more than females [6]. However, females have a proportionally much higher rate of ACL injury than males. Almost three times as many female basketball players and over two times as many female soccer players as their male counterparts injure their ACL [7]. Overall, the serious knee injury rate in all female athletes has increased to twice the level of that in males [8]. As the management of such ligamentous injuries occurs with greater frequency, elucidation of ligament function has become more emergent.