David L. Churchill

The transepicondylar axis approximates the optimal flexion axis of the knee

The traditional understanding of knee kinematics holds that no single fixed axis of rotation exists in the knee. In contrast, a recent hypothesis suggests that knee kinematics are better described simply as two simultaneous rotations occurring about fixed axes. Knee flexion and extension occurs about an optimal flexion axis fixed in the femur, whereas tibial internal and external rotations occur about a longitudinal rotation axis fixed in the tibia. No other translations or rotations exist. This hypothesis has been tested. Tibiofemoral kinematics were measured for 15 cadaveric knees undergoing a realistic loadbearing activity (simulated squatting). An optimizing technique was used to identify the locations of the optimal flexion and longitudinal rotation axes such that simultaneous rotations about them could best represent the measured kinematics. The optimal flexion axis was compared with the transepicondylar axis defined by bony landmarks. The longitudinal rotation axis was found to pass through the medial joint compartment. The optimal flexion axis passed through the centers of the posterior femoral condyles. No significant difference was found between the optimal flexion and transepicondylar axes. To an average accuracy of better than 3.4 mm in translation, and 2.9° in orientation, knee kinematics were represented successfully by simple rotations about the optimal flexion and longitudinal rotation axes. The optimal flexion axis is fixed in the femur and can be considered the true flexion axis of the knee. The transepicondylar axis axis, which is identified easily by palpation, closely approximates the optimal flexion axis.

Mechanical signaling through connective tissue: a mechanism for the therapeutic effect of acupuncture

The mechanism of action of acupuncture remains largely unknown. The reaction to acupuncture needling known as ‘de qi’, widely viewed as essential to the therapeutic effect of acupuncture, may be a key to understanding its mechanism of action. De qi includes a characteristic needling sensation, perceived by the patient, and ‘needle grasp’ perceived by the acupuncturist. During needle grasp, the acupuncturist feels pulling and increased resistance to further movement of the inserted needle. We hypothesize that 1) needle grasp is due to mechanical coupling between the needle and connective tissue with winding of tissue around the needle during needle rotation and 2) needle manipulation transmits a mechanical signal to connective tissue cells via mechanotransduction. Such a mechanism may explain local and remote, as well as long‐term effects of acupuncture.—Langevin, H. M., Churchill, D. L., Cipolla, M. J. Mechanical signaling through connective tissue: a mechanism for the therapeutic effect of acupuncture. FASEB J. 15, 2275–2282 (2001)

Evidence of connective tissue involvement in acupuncture

Acupuncture needle manipulation gives rise to “needle grasp,” a biomechanical phenomenon characterized by an increase in the force necessary to pull the needle out of the tissue (pullout force). This study investigates the hypothesis that winding of connective tissue, rather than muscle contraction, is the mechanism responsible for needle grasp. We performed 1) measurements of pullout force in humans with and without needle penetration of muscle; 2) measurements of pullout force in anesthetized rats, with and without needle rotation, followed by measurements of connective tissue volume surrounding the needle; 3) imaging of rat abdominal wall explants, with and without needle rotation, using ultrasound scanning acoustic microscopy. We found 1) no evidence that increased penetration of muscle results in greater pullout force than increased penetration of subcutaneous tissue; 2) that both pullout force and subcutaneous tissue volume were increased by needle rotation; 3) that increased periodic architectural order was present in subcutaneous tissue with rotation, compared with no rotation. These data support connective tissue winding as the mechanism responsible for the increase in pullout force induced by needle rotation. Winding may allow needle movements to deliver a mechanical signal into the tissue and may be key to acupunctures therapeutic mechanism.

Subcutaneous tissue fibroblast cytoskeletal remodeling induced by acupuncture: Evidence for a mechanotransduction‐based mechanism

Acupuncture needle rotation has been previously shown to cause specific mechanical stimulation of subcutaneous connective tissue. This study uses acupuncture to investigate the role of mechanotransduction‐based mechanisms in mechanically‐induced cytoskeletal remodeling. The effect of acupuncture needle rotation was quantified by morphometric analysis of mouse tissue explants imaged with confocal microscopy. Needle rotation induced extensive fibroblast spreading and lamellipodia formation within 30 min, measurable as an increased in cell body cross sectional area. The effect of rotation peaked with two needle revolutions and decreased with further increases in rotation. Significant effects of rotation were present throughout the tissue, indicating the presence of a response extending laterally over several centimeters. The effect of rotation with two needle revolutions was prevented by pharmacological inhibitors of actomyosin contractility (blebbistatin), Rho kinase (Y‐27632 and H‐1152), and Rac signaling. The active cytoskeletal response of fibroblasts demonstrated in this study constitutes an important step in understanding cellular mechanotransduction responses to externally applied mechanical stimuli in whole tissue, and supports a previously proposed model for the mechanism of acupuncture involving connective tissue mechanotransduction. J. Cell. Physiol.

Tibial Axis and Patellar Position Relative to the Femoral Epicondylar Axis during Squatting

A laboratory-based study was performed to describe the tibial axis and patellar position relative to the femoral epicondylar (FE) axis during squatting. During the squat, the angle between the tibial and FE axes averaged 90.5 degrees, and 66% of internal rotation of the tibia occurred before 15 degrees flexion. In the mid-sagittal plane of the femur, the patella followed a circular arc, and mediolateral patellar shift averaged 4.3 mm. These findings can be used as the basis for development of new total knee arthroplasty components that recreate normal patellofemoral kinematics, and may provide important guidelines for alignment of the tibial and femoral components. The perpendicular relationship between the tibial and the FE axes may be useful in locating the FE axis intraoperatively. The reduced mediolateral shift of the patella suggests that alignment of the femoral component with the FE axis will aid patellar tracking about a circular arc with small deviations in the medial-lateral direction.

Measurement of a spinal motion segment stiffness matrix

The six-degrees-of-freedom elastic behavior of spinal motion segments can be approximated by a stiffness matrix. A method is described to measure this stiffness matrix directly with the motion segment held under physiological conditions of axial preload and in an isotonic fluid bath by measuring the forces and moments associated with each of the six orthogonal translations and rotations. The stiffness matrix was obtained from the load-displacement measurements by linear least squares assuming a symmetric matrix. Results from a pig lumbar spinal motion segment in an isotonic bath, with and without a 500 N axial preload, showed a large stiffening effect with axial preload.

A new device to measure knee laxity during weightbearing and non-weightbearing conditions.

The Vermont knee laxity device (VKLD) was developed to evaluate anterior—posterior (A—P) displacement of the tibia relative to the femur (A—P laxity) during weightbearing and non‐weightbearing conditions. The purposes of this study were to determine the repeatability and reliability of the VKLD measurements of A—P laxity and to compare them with two devices currently in clinical use: the KT‐1000 knee arthrometer and planar stress radiography. Two independent examiners tested six subjects with no history of knee injury. A—P laxity was measured on three separate days with the KT‐1000 and the VKLD. With the VKLD, A—P laxity was measured in the weightbearing and non‐weightbearing conditions. In addition, one examiner measured A—P laxity in each subject on each day using a planar stress radiography technique. Similar A—P laxity values were obtained with the KT‐1000 and the VKLD; however, the planar stress radiography technique measured less A—P laxity compared to the VKLD (9.2 ± 2.2 mm versus 13.3 ± 2.9 mm, P = 0.0004). None of the three devices showed significant differences in measuring A—P laxity between days. During weightbearing, A—P laxity was reduced by 65–70% compared to the non‐weightbearing condition (P = 0.0001). Future investigations will use the VKLD to study subjects that have suffered injury to the anterior and posterior cruciate ligaments.

The Effect of Anterior Cruciate Ligament Deficiency and Functional Bracing on Translation of the Tibia Relative to the Femur during Nonweightbearing and Weightbearing

Background Much of what is known about functional bracing is derived from studies of the knee during unweighted or weightbearing conditions, whereas little is known about the transition between these postures. Hypothesis Bracing the anterior cruciate ligament-deficient knee during nonweightbearing, throughout the transition to weightbearing, and during weightbearing reduces the abnormal translations of the tibia relative to the femur to within the limits of normal. Study Design Controlled laboratory study. Methods Subjects with chronic anterior cruciate ligament tears were studied with and without braces. Anteroposterior shear and compressive loads were applied to the knee, and translations of the tibia relative to the femur were measured while subjects were nonweightbearing, throughout the transition to weightbearing, and during weightbearing. Results Bracing the anterior cruciate ligament-deficient knee resulted in a significant reduction of anteroposterior laxity values, to a level within the limits of the normal knee during nonweightbearing and weightbearing postures. In contrast, when the anterior cruciate ligament-deficient knees transitioned from nonweightbearing to weightbearing, the anterior translation of the tibia relative to the femur was 3.5 times greater than in the normal knee, and bracing did not reduce this to within the limits of normal. Conclusions Bracing a knee with a chronic anterior cruciate ligament tear was effective in reducing abnormal anteroposterior laxity during nonweightbearing and weightbearing; however, braces were not effective in reducing the abnormal anterior translations produced by the change between these postures. Clinical Relevance This study explains why subjects with anterior cruciate ligament tears gain partial control of pathologic anteroposterior laxity with the use of a brace but may continue to experience abnormal translations during activity.

Femoral stem insertion generates high bone cement pressurization.

Adequate bone cement pressurization is critical in obtaining optimal femoral cement mantles during total hip arthroplasty. Pressurization can be generated during insertion of the femoral stem into the cement-filled canal. This may be clinically useful in augmenting conventional cement gun pressurization. Two factors, which were expected to influence the amount of insertion-induced pressurization, are the cement’s cure state (viscosity) at the time of insertion and the femoral stem profile. This study evaluated the effect of these factors on cement pressurization during stem insertion. Femoral stems were inserted at a controlled rate into a reusable, simulated femoral canal. Intramedullary pressures were monitored at four locations along the canal’s medial midline. The intrusion factor quantity, which accounts for pressure magnitude, duration of pressurization, and cement viscosity, was developed to quantify pressurization. Stem insertion into late cure stage (high viscosity) cement resulted in significantly higher intramedullary pressures (as much as 187% higher) and intrusion factors (as much as 43% higher) as compared with early stage (low viscosity) cement. The highest pressures and intrusion factors were found in the distal canal. A tapered stem profile resulted in significantly higher pressures (as much as 65%) and higher intrusion factors (as much as 63%) than a straight stem.

Breast milk odor via olfactometer for tube-fed, premature infants.

Human newborns use odor cues to orient to their source of nutrition. However, tube-fed, premature infants have restricted chemosensory experience. New methods of introducing breast milk odor to tube-fed premature infants will permit empiric tests of the effect of controlled exposure to nutrient odor. We therefore developed an infant olfactometer and piloted its use in 7 tube-fed, premature infants in the neonatal intensive care unit. Since nonnutritive sucking shortens the amount of time required to wean from tube-feeding, we tested the effect of breast milk odor on nonnutritive sucking. Six out of 7 subjects responded to breast milk odor with an increase in number of sucks. Statistical analysis supported the hypothesis that breast milk odor reinforces nonnutritive sucking. These results indicate the feasibility and potential of this experimental approach, and warrant further study of the effect of controlled nutrient odor exposure on feeding behavior of premature infants.