The interstitial fluid of bone fluid flow is supplied by flowing blood. Blood flow is determined by three kinds of muscles: cardiac, smooth, and skeletal. Cardiac muscle establishes baseline blood pressure. Smooth muscle controls vessel diameter and skeletal muscle creates intermittent intravascular pressure pulses. For the tibia the relevant skeletal muscle is the gastrocnemius which functions as a muscle pump. This study tested the hypotheses: 1) skeletal muscle-caused pressure pulses increase cortical blood flow, 2) extravasation of vascular fluid and, consequently, interstitial bone fluid flow are enhanced by resultant increased microvascular pressure and 3) bone healing is enhanced by increased bone fluid flow. Eighteen skeletally mature female New Zealand white rabbits were implanted with bone chamber windows (BCIs) as described previously. The windows were exposed at three weeks and observed weekly until Week 10 using intravital microscopy. During observation, the subject was suspended in prone position in a mesh fabric torso sling jacket so as to eliminate gravity-based reaction forces. Electrodes of a transcutaneous electrical nerve stimulator (TENS) were gel-glued at each rabbits gastroc-soleus position; but activated only in the 11 experimentals. A 4Hz 2.8 ± 1.3V impulse was delivered for 60 minutes. Still and video images were obtained at 0, 2, and 60 minutes following injection of 1μm fluorescent microspheres. Each such injection was followed by injection of 70 kD FITC- or RITC-dextran to define vascularity and capillary filtration. Additional still images were obtained at 5, 30, and 55 minutes. Muscle contraction forces during TENS were obtained acutely following the Week 10 observation with a Futek force transducer cell through an attached nylon suture. Bone mineral density was obtained at Week 3 and Week 10 with a Stratec pQCT and associated software. Data were analyzed statistically using a Wilcoxon signed rank test.Introduction
Methods
Scientific truth is an oxymoron. The goal of modern science is an understanding of the natural world. Truth is the goal of empiricism. In orthopaedic research conflict develops between these goals because empiricists seek to discover ways to improve musculoskeletal health and scientists seek to understand how the musculoskeletal system functions. When resources are limited, a hard choice must be made concerning which path to pursue. The conflict actually has a long history in Western culture that can be traced to differences between Greek and Roman approaches to discovering truths about the natural world. For ancient Greeks, no truth was complete unless a cause-and-effect connection could be established following analysis of observations. For Romans, truths were empirical. They were solutions to solved problems; an aqueduct that did not leak or a healed fracture. Empirical approaches to problems have been a characteristic of Homo sapiens since the Stone Age. They defined the original methodology of medicine and so established it as a “truth” profession. The Romans added engineering to the list of truth professions, although they did not classify it as a profession. Engineering and medicine functioned as truth professions until the 20th century. Science was much slower to mature. The term “scientist” was not coined until 1834. It was not established as a distinct profession until it was freed from scholasticism by the natural philosopher, Francis Bacon, who introduced inductive logic, and Galileo Galilei in the 17th century. They and Isaac Newton launched the Enlightenment which stimulated scientific research for over a century. By the mid-19th century, progress in science was sufficient to convince many scientists that they were members of a truth profession that would eventually be able to explain all life functions in terms of physics and chemistry. This reductionist view prevailed until 1927, when it was shown to be invalid by Werner Heisenberg. As a consequence of his ‘Principle of Uncertainty’, science is no longer a “truth” profession. Instead, scientific analysis has become a statistical methodology devoid of final proofs. In place of proofs, the scientist must formulate falsifiable hypotheses that are the reverse of those being proposed. In this approach, developed mainly by Karl Popper, observations are analyzed statistically and if they significantly disagree with the falsifiable hypothesis it may be said to have been disproven and one can say that the data support the proposed hypothesis. Members of truth professions began to perform experiments and employ science as an approach to truth in the 20th century thereby developing an “empirical science”. Since these investigators are constrained by their profession to favor truths, they tend to minimize the Greek and maximize the Roman components of their research. The result has been a dichotomy in science between those whose research success is measured by its contribution to “cures” and those whose research success is measured by its contribution to understanding. In orthopaedics, the dichotomy separates analytical scientists from engineers and physicians. In addition, caught in between are the bioengineers. There is a need for better communication between all.
