Articular cartilage deformation following experimental synovitis in the rabbit hip.

The development of transient synovitis in the hips of young children occurs quite frequently. This experiment examined the effects of a model synovitis on the deformability of articular cartilage of the immature rabbit hip. At 1, 2, 3, and 4 weeks following synovitis, there was an increase of cartilage deformability on both the acetabular and femoral sides of the joint. This increased deformability may alter force transmission to the underlying bone and its contained vascular structures.

Recovery of the dog quadriceps after 10 weeks of immobilization followed by 4 weeks of remobilization.

Skeletal muscle fiber areas were measured in three heads of the dog quadriceps after 10 weeks of immobilization followed by 4 weeks of remobilization. Two-way analysis of variance demonstrated a significant decrease in both type 1 (p less than 0.005) and type 2 (p less than 0.001) fiber area. However, there was no significant difference among the three heads of the quadriceps (p less than 0.2). Although muscle fiber areas had not returned to control levels following remobilization, the area fraction of perimysial and epimysial connective tissue was not significantly different from control values (p greater than 0.15). These data suggest that although the degree of muscle atrophy following 10 weeks of immobilization is severe and muscle specific, following 4 weeks of remobilization, muscles uniformly recover to about 70% of control values.

An animal model for the study of neuromuscular injury induced beneath and distal to a pneumatic tourniquet.

A well-controlled animal model is presented for the study of neuromuscular injury induced by a pneumatic tourniquet. This model comprises a curved tourniquet surrounded by a stiff exterior shell, both of which were specifically designed to fit the conical and oblong shape of the rabbit hindlimb. Computed tomographic imaging was used to assess transverse tissue displacement induced by tourniquet compression. The curved tourniquet/shell configuration occluded the distal arterial blood flow to the extremity at a significantly lower cuff inflation pressure than a straight tourniquet of equal width. The magnitude and distribution of tissue pressures in the subcutaneous and deep tissues beneath the tourniquet were similar to those recorded in previous human cadaver studies of tourniquet compression. This animal model will facilitate the quantitation and analysis of tissue injury induced beneath and distal to a pneumatic tourniquet. Such data can help define the critical pressure and time limits for the safe use of pneumatic tourniquets in extremity surgery.

Comparison of functional deficits in the rabbit tibialis anterior following tourniquet ischemia and tourniquet compression.

The purpose of this study was to measure the contractile properties of skeletal muscle after direct compression with a tourniquet and to compare these properties with those found after a similar period of tourniquet ischemia. A rabbit model of tourniquet compression of the tibialis anterior was developed and tested for this investigation. Fifty-seven animals then were divided into four protocol groups: (a) thigh tourniquet (ischemia) at 350 mm Hg (46.7 kPa), (b) leg tourniquet (compression) at 350 mm Hg (46.7 kPa), (c) leg tourniquet at 125 mm Hg (16.7 kPa), and (d) controls. A significant decrease in maximum tetanic tension was demonstrated in all three experimental groups. Direct compression at 350 mm Hg resulted in the greatest decline in maximum tetanic tension (22.6% of control), followed by compression at 125 mm Hg (30.5%) and ischemic injury (40.2%). In addition, direct compression at 350 mm Hg resulted in a significantly greater loss of force-generating capacity when compared with the ischemic group (p < 0.01). A similar pattern was noted for the rate of rise in maximum tetanic tension. Gross histologic examination of the tibialis anterior sections was consistent with the results of functional testing, with the more severe abnormalities noted in the compressed specimens. These results clearly demonstrate that tourniquet compression injury results in a more significant loss of functional strength and contractile speed than tourniquet ischemia. Further investigations on the safe limits of tourniquet use thus should be directed toward measuring the effect of the pneumatic tourniquet on the underlying soft tissues.

Viscoelastic shear properties of the equine medial meniscus.

Recent studies have shown that the meniscus is highly anisotropic in tension and that its compressive creep behavior can be modeled using biphasic theory. In this study, an alternative approach is used, where viscoelastic shear properties of the meniscal fibrocartilage are measured to determine the anisotropy and inhomogeneity of this tissue with respect to specimen location and fiber orientation. Medial menisci were obtained from eight skeletally-mature horses. Nine test specimens were taken from the circumferential midsubstance of each meniscus, at three circumferential and three axial positions. The magnitude of the complex shear modulus and the phase angle were determined for each specimen from 100-800 Hz, in 100 Hz increments. Data were gathered shearing parallel and perpendicular to the circumferentially-oriented fibers. The magnitude of the shear modulus and the phase angle were both found to be frequency dependent, anisotropic, and inhomogeneous. The magnitude of the shear modulus increased with frequency, and was greatest in specimens from the posterior superior region, shearing parallel to the fibers. The phase angle decreased slightly with frequency and was lowest in specimens from the midsubstance of the anterior region, shearing perpendicular to the fibers. Our data demonstrated that collagen fibers substantially stiffen the meniscus in the direction of its fibers and that the solid matrix of the meniscus, like articular cartilage, behaves largely as an elastic material.

Delayed use of hyperbaric oxygen for treatment of a model anterior compartment syndrome.

This study examines the effect of delayed exposure to hyperbaric oxygen on muscle necrosis and edema development following compartment syndromes in the canine hindlimb. Compartment syndromes (100 mm Hg for 8 h) were generated in one anterolateral compartment of six anesthetized dogs. After a 2-h delay, three 1-h hyperbaric oxygen treatments (2 atm absolute pure oxygen) were given during the next 12 h. Two days later, technetium-99m stannous pyrophosphate (99mTc Sn-PYP) was injected intravenously; 3 h later, samples were obtained from the pressurized and contralateral control muscles, weighed for edema development, counted for 99mTC Sn-PYP uptake, and evaluated histologically. Hyperbaric oxygen treatments, even when delayed 2 h, reduced muscle necrosis and intramuscular edema to negligible levels (p less than 0.05) compared with untreated animals. In addition, muscle morphology remained essentially normal in all hyperbaric oxygen-treated animals. We conclude that even if hyperbaric oxygen treatments are delayed 2 h, edema and muscle necrosis are reduced significantly in a model compartment syndrome.

Increased transsynovial transport with continuous passive motion.

Thirteen freshly killed immature rabbits were used to study the effect of continuous passive motion (CPM) on regional nutritional pathways of the medial and lateral menisci and the transport of a solute from synovial fluid to the patellar tendon. A bolus of 35SO4 was injected into each knee joint cavity. The right knee underwent CPM for 1 h, whereas the left knee was immobilized (rest extremity). Both knees were then rapidly resected and immediately frozen. The medial and lateral menisci were removed and sectioned into anterior, middle, and posterior thirds for Group 1 animals; in Group 2 animals a portion of patellar tendon was harvested. Radioactivity as counts per minute per milligram of tissue was counted in a scintillation counter. The posterior portion of the lateral meniscus in the rest extremity had significantly higher uptake than the extremity that underwent CPM (p less than 0.001). In the extremity at rest, the posterior third of the lateral meniscus had a significantly higher uptake than that of the middle third (p = 0.04). In Group 2 rabbits, the patellar tendon of the knee undergoing CPM had significantly higher uptake as compared with the patellar tendon of the knee at rest (p = 0.02). These results indicate that diffusion from synovial fluid to meniscal cells is an important mechanism of transport for low-molecular-weight nutrients such as sulfate; CPM does not facilitate this mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Local compression patterns beneath pneumatic tourniquets applied to arms and thighs of human cadavera.

Distributions of tissue fluid pressure were examined beneath a standard pneumatic tourniquet in six upper extremities and six lower extremities of fresh human cadavera, disarticulated at the shoulder and hip, respectively. A standard 8-cm-wide tourniquet cuff was applied at mid-humerus or mid-femur position. Tissue fluid pressures were measured by 100-cm-long slit catheters inserted parallel to the bone at four tissue depths: subcutaneous, subfascial, mid-muscle, and adjacent to bone. All arms and thighs were studied at the following cuff pressures: 100, 150, 200, 250, 300, 400, and 500 mm Hg. Tissue fluid pressure was always maximal in subcutaneous tissue at mid-cuff. Transmission of cuff pressures to deeper tissues was significantly less (p less than 0.01) in the thighs with a girth of 40-52 cm than in the arms with a girth of 22-33 cm. At the four tissue depths studied, tissue fluid pressures fell steeply in a longitudinal direction near the cuff edge to levels near zero at points 1-2 cm outside each cuff edge. Our results suggest that wider cuffs are required on thighs than on arms to provide a bloodless field during limb surgery and to minimize underlying tissue injury associated with high cuff pressures. Our recommendation for wider tourniquet cuffs than those presently used during orthopaedic surgery is contrary to recent prevailing knowledge.

Long-term measurement of muscle function in the dog hindlimb using a new apparatus.

The objective of this study was to develop an apparatus for reliable, reproducible, and minimally invasive measurements of long-term, myoneural function. Twenty conditioned dogs were anesthetized and placed supine with one hindlimb secured in a boot apparatus. The hindpaw was attached to a force transducer that was connected to a recorder for continuous monitoring of torque. Muscles within the anterolateral compartment were stimulated by percutaneous electrodes over the peroneal nerve near the fibular head. This elicited isometric dorsiflexion of the hindpaw. Twitch and tetanic torques correlated positively with dog weight whereas other skeletal-muscle function parameters (time to peak tension, one-half relaxation time, and endurance) were independent of dog weight. Muscle function results were consistent with an overall compartmental composition of 30% Type I and 70% Type II fibers. Repetitive testing of twitch and tetanic torques in the dog legs yielded coefficients of variance of 3-4% (intraday) and 7% (interday). Thus, about one-half of the interday variability may be accounted for by diet, exercise, and other physiological conditions that change daily. The apparatus was also used to detect myoneural degeneration following tourniquet ischemia. The results indicate that this procedure for evaluating muscle function yields reliable and quantitative results noninvasively, and thus allows long-term testing of muscle function in normal and diseased hindlimbs of dogs.

Intraarticular pressure during continuous passive motion of the human knee.

Intraarticular pressure (IAP) was continuously monitored during continuous passive motion (CPM) of five normal and 11 abnormal human knees using a new fiberoptic, transducer-tipped Camino catheter. IAP varied in a consistent hysteresis pattern in the normal knees, with subatmospheric pressures recorded at intermediate angles of joint flexion. A similar pattern was recorded in the abnormal knees without cruciate ligament pathology, whereas considerable variability was noted in the knees with cruciate ligament abnormality. IAP was lower in the extension to flexion than in the flexion to extension portion of the CPM cycle, providing evidence of intraarticular fluid flow during portions of the CPM cycle. IAP changes were consistent with "physiologic compartmentation" within the knee at extremes of joint position. Capsular viscoelastic changes and/or synovial fluid volume changes were observed during CPM. The therapeutic mechanism of continuous passive motion may be related to cyclic variation of the intraarticular pressure.

Kappa Delta Award paper. Tissue fluid pressures: from basic research tools to clinical applications.

The two basic research tools developed to measure tissue fluid pressure (wick catheter) and osmotic pressure (colloid osmometer) have undergone extensive validation and refinement over the past 20 years. Using these techniques, basic science investigations were undertaken of edema in Amazon reptiles, pressure-volume relations in animals and plants, adaptive physiology of Antarctic penguins and fishes, edema in spawning salmon, tissue fluid balance in humans under normal conditions and during simulated weightlessness, and orthostatic adaptation in a mammal with high and variable blood pressures--the giraffe. Following and sometimes paralleling this basic research have been several clinical applications related to use of our colloid osmometer and wick technique. Applications of the osmometer have included insights into (a) reduced osmotic pressure of sickle-cell hemoglobin with deoxygenation and (b) reduced swelling pressure of human nucleus pulposus with hydration or certain enzymes. Clinical uses of the wick technique have included (a) improvement of diagnosis and treatment of acute and chronic compartment syndromes, (b) elucidation of tissue pressure thresholds for neuromuscular dysfunction, and (c) development of a better tourniquet design for orthopaedics. This article demonstrates that basic research tools open up areas of basic, applied, and clinical research.

Growth hormone secretagogue increases muscle strength during remobilization after canine hindlimb immobilization.

Twenty-two beagles were divided into two equal groups, and the right hindlimb of each animal was immobilized at 105 degrees of knee flexion by external fixation. After 10 weeks of fixation, the device was removed, allowing free mobility for the following 5 weeks. Each day throughout the 15 weeks, one group received a growth hormone secretagogue (treatment) at a dose of 5 mg/kg, and the other received a lactose placebo (control). At weeks 0, 10, and 15, strength as indicated by maximum isometric extension torque was measured in the right hindlimb, biopsies of the vastus lateralis muscle were taken, and the dogs were weighed. Weekly blood samples were analyzed for insulin-like growth factor-1, blood urea nitrogen, and creatine phosphokinase. Between weeks 0 and 10, tetanic torque declined by about 60% (p < 0.001) in both groups, with no significant difference between the groups (p > 0.7). Between weeks 10 and 15, tetanic torque in the treated group increased by 0.81 Nm; this was significantly greater than the increase of 0.25 Nm in the placebo group (p < 0.05). The diameters of slow (type-1) and fast (type-2) fibers measured from the vastus lateralis muscle followed the same trend. At all time points, fiber diameter correlated strongly with torque; this argues against nonmuscular causes such as nerve injury for strength loss. The mean levels of insulin-like growth factor-1 increased 100% by week 4 in the treated group and remained elevated by about 60% throughout the experiment. Levels of insulin-like growth factor-1 in the placebo group decreased 30% within week 1 and remained depressed throughout the experiment. Our interpretation of these data suggests that the growth hormone secretagogue elevated levels of serum insulin-like growth factor-1, which in turn increased the size and strength of the quadriceps muscle during remobilization. These data may ultimately have therapeutic application to humans during rehabilitation after prolonged inactivity.

Regional nutrition and cellularity of the meniscus. Implications for tear and repair.

The knee menisci are relatively avascular and must rely to a large degree on synovial sources of nutrition. Lack of nutrition may lead to degenerative changes and may inhibit any potential repair capabilities of the menisci. Continuous passive motion applied to the knee stimulates greater activity and/or transport of nutrients to the meniscal fibrochondrocytes. However, in an avascular model, solutes within the synovial fluid are lost by their convective transport from the joint. Regional differences in transport of a low molecular weight nutrient like sodium sulphate exist such that cells in the central core region of the meniscus are poorly supplied with nutrients by the synovial fluid and/or are less active. These conditions may be the cause of a relatively high incidence of degenerative changes in the central core region.

Arthrographic findings in Legg-Calvé-Perthes disease and transient synovitis of the hip.

Bilateral arthrography of the hip was performed in thirty-seven patients with unilateral Legg-Calvé-Perthes disease. Measurements made on the plain roentgenograms and on the arthrograms of the diameter of the femoral head, the width of the medial joint space, and the thickness of the acetabular cartilage were compared. The acetabulum-head quotients also were calculated. When present, evidence of flattening of the femoral head cartilage and of pooling of the contrast material also was noted. These data showed that in the early stages of Legg-Calvé-Perthes disease the articular cartilage is thickened, and that the cartilaginous femoral head is deformed and protrudes from the acetabulum. Arthrograms made with the hip in different positions also indicated the extent and location of collapse of the (osteochondroal) femoral head and therefore proved useful as a means to determine the best therapeutic position of the hip to provide coverage of the head. In three patients with severe transient synovitis, thickening of the articular cartilage resembling that seen in Legg-Calvé-Perthes disease was demonstrated.

Effect of ankle position and a plaster cast on intramuscular pressure in the human leg.

Intramuscular pressure was measured with transducer-tipped catheters that had been inserted into the anterior and deep posterior compartments of the leg in seven healthy adults. Intramuscular pressure increased three to sevenfold (depending on the position of the ankle) in both compartments after the application of a plaster cast from the proximal part of the thigh to the malleoli. While the cast was in place, the baseline intramuscular pressure was elevated by the inflation of a tourniquet, which was located on the proximal part of the thigh, to a pressure of sixty millimeters of mercury (8.00 kilopascals). The intramuscular pressure in both the anterior and the deep posterior compartments was found to be lowest when the ankle joint was between the neutral and the resting positions (between 0 and 37 degrees of flexion). After the cast was bivalved and the opening on each side was spread approximately one-half centimeter, there was a significant decrease in intramuscular pressure of 47 per cent in the anterior compartment and of 33 per cent in the deep posterior compartment (p < 0.05 for both).

Intramuscular deoxygenation during exercise in patients who have chronic anterior compartment syndrome of the leg.

Currently, the definitive diagnosis of chronic compartment syndrome is based on invasive measurements of intracompartmental pressure. We measured the intramuscular pressure and the relative oxygenation in the anterior compartment of the leg in eighteen patients who were suspected of having chronic compartment syndrome as well as in ten control subjects before, during, and after exercise. Chronic compartment syndrome was considered to be present if the intramuscular pressure was at least fifteen millimeters of mercury (2.00 kilopascals) before exercise, at least thirty millimeters of mercury (4.00 kilopascals) one minute after exercise, or at least twenty millimeters of mercury (2.67 kilopascals) five minutes after exercise. Changes in relative oxygenation were measured with use of the non-invasive method of near-infrared spectroscopy. In all patients and subjects, there was rapid relative deoxygenation after the initiation of exercise, the level of oxygenation remained relatively stable during continued exercise, and there was reoxygenation to a level that exceeded the pre-exercise resting level after the cessation of exercise. During exercise, maximum relative deoxygenation in the patients who had chronic compartment syndrome (mean relative deoxygenation [and standard error], -290 +/- 39 millivolts) was significantly greater than that in the patients who did not have chronic compartment syndrome (-190 +/- 10 millivolts) and that in the control subjects (-179 +/- 14 millivolts) (p < 0.05 for both comparisons). In addition, the interval between the cessation of exercise and the recovery of the pre-exercise resting level of oxygenation was significantly longer for the patients who had chronic compartment syndrome (184 +/- 54 seconds) than for the patients who did not have chronic compartment syndrome (39 +/- 19 seconds) and the control subjects (33 +/- 10 seconds) (p < 0.05 for both comparisons).

A comparison of conventional radiography and computed tomography in the evaluation of spiral fractures of the tibia.

Spiral fractures of the distal third of the tibial shaft can have problems of malunion or non-union that may be related to inability to assess the quality of the initial reduction of the fracture. We created typical two-fragment torsional tibial fractures in cadaver bones. The fracture fragments were mounted in a specially constructed jig that allowed simulation of various malreduction positions including varus and valgus angulation, antecurvatum, recurvatum, malrotation, and shortening. Anteroposterior and lateral radiographs and computed tomographic scans of the specimens were made. Measurements of the fracture gap were made at defined distances along the fractures, directly on the specimens as well as on the radiographs and computed tomographic scans. Excellent correlation was obtained between measurements of the gap on the specimens and on the computed tomographic scans, but plain radiographic measurements in thirty of thirty-four instances underestimated the true width of the gap. When shortening was introduced larger maximum gaps (of as much as eighteen millimeters) as well as greater discrepancies between measurements on the scans and plain radiographs were seen. The sizes of the fracture gaps were also greater for a given degree of shortening when the pitch of the spiral fracture was greater.

Experimental models to promote healing of tears in the avascular segment of canine knee menisci.

Longitudinal tears were created in canine lateral menisci and techniques were applied to induce healing by removal of a core of tissue from the periphery of the meniscus to the tear or by implantation of a vascularized synovial flap into the tear. The meniscal tears did not heal in knees that were not immobilized, and they healed poorly and sporadically in knees that were immobilized in a cast but bore some weight. However, a higher percentage of tears that were treated by the core-removal or synovial-flap technique healed when the knee was firmly immobilized and weight-bearing was prevented by the use of an external skeletal fixator across the joint for eight to twelve weeks. Neovascularization and access to a source of reparative cells appear to be important in the healing process.

Ankle and knee position as a factor modifying intracompartmental pressure in the human leg.

The objective of this study was to examine the effect of position of the knee and ankle on intracompartmental pressures in the leg. Slit catheters were introduced bilaterally into all four muscle compartments of the lower extremities of six healthy volunteers. Intracompartmental pressures were monitored with the catheters while the ankle joint was passively held in full dorsiflexion, full plantar flexion, or neutral with the knee flexed 90 or 10 degrees or fully extended. Statistical analysis revealed that intracompartmental pressure increased significantly in all four compartments when the ankle was passively dorsiflexed. Pressure in the superficial posterior and lateral compartments was dependent on knee position and in the deep posterior and anterior compartments it was independent of knee position. In addition, pressure in the deep posterior compartment decreased significantly when the ankle was placed in full plantar flexion, and that finding was independent of knee position. Anterior compartment pressure was not significantly elevated by full passive plantar flexion of the ankle.

Hyperbaric oxygen reduces edema and necrosis of skeletal muscle in compartment syndromes associated with hemorrhagic hypotension.

This study examined the effect of exposures to hyperbaric oxygen on the development of the edema and necrosis of muscle that are associated with compartment syndromes that are complicated by hemorrhagic hypotension. A compartment syndrome (twenty millimeters of mercury for six hours) was induced by infusion of autologous plasma in the anterolateral compartment of the left hind limb of seven anesthetized dogs while the mean arterial blood pressure was maintained at sixty-five millimeters of mercury after 30 per cent loss of blood volume. These dogs were treated with hyperbaric oxygen (two atmospheres of pure oxygen) and were compared with six dogs that had an identical compartment syndrome and hypotensive condition but were not exposed to hyperbaric oxygen. Forty-eight hours later, edema was quantified by measuring the weights of the muscles (the pressurized muscle compared with the contralateral muscle), and necrosis of muscle was evaluated by measuring the uptake of technetium-99m stannous pyrophosphate. The ratio for edema was significantly (p = 0.01) greater in dogs that had not been exposed to hyperbaric oxygen (1.15 +/- 0.01) than in the dogs that had been treated with hyperbaric oxygen (1.01 +/- 0.03), and the ratio for necrosis of muscle was also significantly (p = 0.04) greater in dogs that had not had hyperbaric oxygen (1.96 +/- 0.41) than in those that had been treated with hyperbaric oxygen (1.05 +/- 0.11). Comparisons were also made with the muscles of four normal control dogs and separately with the muscles of six normotensive dogs that had an identical compartment syndrome and normal blood pressure and were not treated with hyperbaric oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)