Alexander A. Sapega

Optimizing tourniquet application and release times in extremity surgery. A biochemical and ultrastructural study.

Despite numerous studies investigating the pathophysiology of tourniquet ischemia, definitive data at the cellular level have been lacking and no consensus regarding safe tourniquet-application times in extremity surgery has emerged. In light of the particular vulnerability of skeletal muscle to ischemic injury, we determined the degree of muscular metabolic derangement and cell damage produced by seven different protocols of tourniquet application and release, each providing three hours of total tourniquet time. We performed thirty-six experiments on canine hind limbs, comparing the following time-patterns of tourniquet application: I--three sequential one-hour periods, II--two sequential one and one-half-hour periods, III--two hours followed by one hour, and IV--a single continuous three-hour application. Five and fifteen-minute reperfusion intervals between ischemic periods were compared for the first three time-patterns, creating a total of seven different tourniquet protocols. Muscular metabolic derangement and cell injury were evaluated by monitoring changes in the cellular bioenergetic state (high-energy phosphate profile), cell pH, post-ischemic leakage of creatine phosphokinase, and ultrastructural cell degeneration. At the intracellular level, the metabolic recovery of muscle during reperfusion was much faster than previous studies focusing on extracellular parameters have indicated. In all instances complete intracellular bioenergetic recovery occurred within five minutes after tourniquet release. The use of one or more five-minute reperfusion intervals significantly reduced the degree of ischemic cell injury, as indicated by a decrease in creatine phosphokinase leakage and myofibrillar destruction. No additional benefit was derived by extending the reperfusion periods to fifteen minutes. The longest period of continuous ischemia in each tourniquet-application protocol bore the closest relationship with the amount of cell damage produced. Within the spectrum of observed pathological changes, time-patterns I and II produced comparatively little muscle damage.

A comparative study of the tolerance of skeletal muscle to ischemia. Tourniquet application compared with acute compartment syndrome.

In this study, the tolerance of skeletal muscle to tourniquet application (ischemia) and to acute compartment syndrome (ischemia and pressure) was compared. In five animals, the cuff of a pneumatic tourniquet was inflated to 350 millimeters of mercury at the level of the thigh for three hours. In five other animals, an acute experimental compartment syndrome was created in one anterolateral compartment by autologous plasma infusion. The compartment pressure (measured by wick catheter) was maintained at a level equal to the mean arterial pressure for three hours. At three hours, reperfusion was established in both groups, either by tourniquet release or by decompressive fasciotomy and epimysiotomy. During both the ischemic period and a two-hour recovery period immediately thereafter, the mean intracellular pH and high-energy phosphate profile (levels of adenosine triphosphate and phosphocreatine) of the muscles of the anterolateral compartment were monitored non-invasively by phosphorus nuclear magnetic-resonance spectroscopy. Muscle biopsies were done the following day to take specimens for electron microscopic analysis of ultrastructural cellular degeneration. During ischemia, the cellular levels of phosphocreatine decreased at an identical rate in both groups. In contrast, the levels of adenosine triphosphate diminished rapidly in the animals with the compartment syndrome, but remained unchanged in the tourniquet group. Ischemic muscle acidosis was more severe in dogs with the compartment syndrome. In the tourniquet group, the phosphocreatine, adenosine triphosphate, and pH were all normal within fifteen minutes after release of the tourniquet, but these values remained depressed even two hours after fasciotomy in the group with compartment syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Testing for Isometry During Reconstruction of the Posterior Cruciate Ligament: Anatomic and Biomechanical Considerations

The change in the distance of linear separation be tween each pair of osseous fiber attachment sites of the posterior cruciate ligaments was measured and plotted as a function of the knee flexion angle from 0° to 120°. Data were collected under four sequential test conditions that had in common quadriceps relaxation, absence of tibial rotation forces, and horizontal femoral stabilization. The posterior cruciate ligament fibers were intact or transected (excursion wires left intact) with gravitational joint distraction of the lower leg un constrained or constrained. The small, posterior ob lique fiber region was the most isometric of the four tested fiber regions. Progressively increasing devia tions from isometry were seen in the posterior longitu dinal, central, and anterior fiber regions, in that order. Transection of the posterior cruciate ligament, com bined with unconstrained gravitational distraction of the knee joint, further increased the magnitude of deviation from isometry of the anterior and central fibers, but only changed the pattern of deviation for the more nearly isometric posterior fibers. Under simulated operative conditions, most of the posterior cruciate ligaments anatomic attachment sites exhibit nonisometric behav ior, with near isometry demonstrated only by the rela tively small posterior fiber attachment sites. If isometry alone is used for bone tunnel placement, the large anterior and central fiber regions will be left largely unreconstructed. Because the normal behavior of most of the fibers of the posterior cruciate ligament involves 4 to 6 mm of end-to-end length increase with progres sive knee flexion, this pattern and degree of deviation from isometry should be sought to approximate an anatomic reconstruction of the anterocentral bulk of the ligament.

Phosphorus nuclear magnetic resonance: a non-invasive technique for the study of muscle bioenergetics during exercise

Phosphorus nuclear magnetic resonance (31P NMR) spectroscopy is a non-destructive analytical laboratory technique that, due to recent technical advances, has become applicable to the study of high-energy phosphate metabolism in both animal and human extremity muscles (in vivo). 31P NMR can assay cellular phosphocreatine, ATP, inorganic phosphate, the phosphorylated glycolytic intermediates, and intra-cellular pH in either resting or exercising muscle, in a non-invasive manner. NMR uses non-perturbing levels of radio-frequency energy as its biophysical probe and can therefore safely study intact muscle in a repeated fashion while exerting no artifactual influence on ongoing metabolic processes. Compared with standard tissue biopsy and biochemical assay techniques, NMR possesses the advantages of being non-invasive, allowing serial in situ studies of the same tissue sample, and providing measurements of only active (unbound) metabolites. NMR studies of exercising muscle have yielded information regarding fatigue mechanisms at the cellular level and are helping resolve long-standing questions regarding the metabolic control of glycolysis, oxidative phosphorylation, and post-exercise phosphocreatine re-synthesis. NMR is also being utilized to measure enzymatic reaction rates in vivo. In the near future, other forms of NMR spectroscopy may also permit the non-invasive measurement of tissue glycogen and lactate content.

Magnetic Resonance Imaging of Knee Disorders Clinical Value and Cost-Effectiveness in a Sports Medicine Practice

To prospectively evaluate the clinical value of magnetic resonance imaging of the knee in a referral sports medicine practice, we performed a three-part study. First, we asked 72 consecutive patients a series of clinically relevant questions regarding the ordering of their magnetic resonance imaging scans. Second, we asked the treating physicians at our center if the mag netic resonance imaging findings changed the diagno sis or treatment. Third, we compared the clinical eval uation with the findings on magnetic resonance imaging scans for 37 patients who had arthroscopic confirmation. From the physicians perspective, in only three cases would the results of the scan have changed the diagnosis. Information from the scans was judged to contribute to patient treatment in only 14 of 72 patients. Finally, comparison of clinical evaluation and magnetic resonance imaging findings with findings during arthroscopic procedures showed that clinical evaluation had a sensitivity and specificity of 100% for diagnosis of anterior cruciate ligament injuries, whereas magnetic resonance imaging was 95% sen sitive and 88% specific. For isolated meniscal lesions, the clinical assessment had a sensitivity and specificity of 91 % compared with 82% and 87%, respectively, for magnetic resonance imaging. For evaluation of articu lar surface damage, the predictive value of a positive test was 100% for clinical assessment and 33% for the

Compartment syndrome: a quantitative study of high-energy phosphorus compounds using 31P-magnetic resonance spectroscopy.

The purpose of this study was to quantitate the intracellular high-energy phosphate compounds during 6 hours of tissue ischemia in the anterior tibial compartment of beagles subjected to an induced traumatized compartment syndrome. The goal of this work was to provide clinicians with objective criteria to augment clinical judgment regarding surgical intervention in the impending compartment syndrome. A beagle model was utilized in which the Delta pressure (difference between the mean arterial pressure and compartment pressure) could be controlled. The model, in conjunction with 31P-magnetic resonance spectroscopy (MRS), allowed a measure of high-energy phosphate compounds and pH in the compartment at various Delta pressures. The extent of ischemic metabolic insult in the compartment was then quantitated. Our data suggest the following: 1) lower Delta pressures result in a proportionally greater drop in the intracellular phosphocreatine ratio and pH; 2) at lower Delta pressures, there is proportionally greater decline in the percentage recovery post-fasciotomy; 3) blood pressure is extremely important and periods of hypotension may result in increased muscle damage at lower compartment pressures.

The effect of early versus late return to vigorous activities on the outcome of anterior cruciate ligament reconstruction

The effect of early (mean, 5 months) versus late (mean, 9 months) return to vigorous cutting activity on the long-term outcome of anterior cruciate ligament recon struction was evaluated retrospectively. Sixty-four re constructions, using a distally attached medial one-third patellar tendon, were reviewed on an average of 46 months postoperatively. After surgery, the timing of return to vigorous activity was based on biologic fixa tion of the graft, a negative Lachman test, absence of effusion, and the patients desire to return to previous activity. The 64 patients were retrospectively separated into two groups. The early group consisted of 31 patients who returned to activity 2 to 6 months after reconstruc tion, and the late group consisted of 33 patients who returned to activity 7 to 14 months after reconstruction. By clinical examination, KT-1000 arthrometer meas urements, subjective evaluation, and Cybex testing, there were no differences between the early and late return groups except for reestablishment of final range of motion. At an average followup of 46 months, this study indicates that an early return to vigorous physical cut ting activities after ACL reconstruction does not predis pose patients to reinjury or a less satisfactory long- term result.

The posteromedial portal in knee arthroscopy: An analysis of diagnostic and surgical utility

We reviewed 400 consecutive knee arthroscopy cases in a predominantly sports medicine practice to determine (1) the frequency of posteromedial portal usage under a prospectively established set of indications, and (2) the impact of posteromedial portal access on patient diagnosis and management. Diagnostic posteromedial portals were used in 22% of anterior cruciate ligament (ACL)-deficient knees, and in 11% of stable knees with nonpatellar (usually meniscal) lesions. When used, posteromedial portal visualization showed treatable lesions 64% of the time, the majority of which were repairable peripheral meniscus tears. In 63% of these cases, no definite lesion had been identified by initial routine anterior portal viewing and probing. Of the 22 patients with posteromedial meniscus tears that were discovered only via posteromedial portal access, 9 had recently undergone anterior portal arthroscopy by other surgeons, during which none of these tears were detected. Posteromedial surgical portals (19 cases) were most useful for synovectomy, posterior cruciate stump resection before arthroscopic reconstruction, and posterior horn medial meniscectomy in exceptionally tight knees. Posteromedial portal access is often useful diagnostically in cases where (1) posteromedial meniscal lesions are frequent (i.e., ACL-deficient knees) and/or suspected on the basis of preoperative symptoms or imaging studies, and (2) full, direct visualization of the entire superior meniscosynovial junction is not possible via standard anterior portals. The option of a surgical posteromedial portal should be entertained whenever frontal approaches for posteromedial instrument work prove inefficient or unsuccessful.

The effect of antecedent ischemia on the tolerance of skeletal muscle to increased interstitial pressure

This study used an experimental model (canine hind limb) of compartment syndrome, monitored with phosphorus 31 nuclear magnetic resonance spectroscopy, to determine the pressure threshold for metabolic deterioration in skeletal muscle previously subjected to ischemia. Our results show that muscle subjected to 6 h of antecedent ischemia has a lower tolerance to increased tissue pressure than otherwise normal muscle. The threshold was found to occur at a delta P (difference between mean blood pressure and limb compartment pressure) of 40 mm Hg, compared with a delta P of 30 mm Hg in muscle that was not subjected to antecedent ischemia. In addition, once the critical pressure threshold of postischemic muscle was crossed, there was a more rapid rate of high-energy phosphate depletion than that seen in normal muscle pressurized to the same degree beyond its delta P threshold. For compartment syndromes that appear after relatively atraumatic ischemia (i.e., drug overdose-induced limb compression, proximal arterial trauma causing distal limb ischemia, etc.), of < or = 6 h, fasciotomy should be performed at a delta P < or = 40 mm Hg. Compartment pressure elevation after local blunt muscle trauma and ischemia may well require earlier or even prophylactic fasciotomy. Fasciotomy in ongoing postischemic compartment syndromes should be considered particularly urgent owing to the rapid rate of metabolic deterioration that is observed once the critical delta P threshold is crossed. The type of compartment syndrome should always be considered when interpreting tissue pressure measurements as indications for fasciotomy.

Muscle ischemia and hypothermia: a bioenergetic study using 31phosphorus nuclear magnetic resonance spectroscopy.

UNLABELLED Following traumatic limb amputation it is common clinical practice to maintain the ischemic tissues in a hypothermic state until surgical reimplantation. Of all extremity tissues, muscle is the most sensitive to ischemia; it is therefore imperative that reperfusion be established before diffuse muscle necrosis. Although it has been shown both clinically and experimentally that hypothermia prolongs the viability of ischemic skeletal muscle, the presumed mechanism by which this occurs has not been confirmed at the cellular level. This study was undertaken to quantify the effect of conventional iced-saline hypothermia on anaerobic cell metabolism and high-energy phosphate depletion in traumatically devascularized muscle. METHODS Phosphorus nuclear magnetic resonance spectroscopy (31P NMR) was employed to noninvasively monitor cellular phosphocreatine (PCr), ATP, and intracellular pH over time in ischemic cat hindlimb muscle under room temperature (22 degrees C) and 1 degree C hypothermic conditions. RESULTS Muscular PCr depletion was significantly retarded by tissue hypothermia but the rate of ATP depletion was not. A progressive, severe cellular acidosis was observed in the room-temperature muscle. Iced tissue cooling produced a dramatic initial rise in cell pH which significantly reduced the absolute degree of subsequent acidotic changes. SIGNIFICANCE These findings question our understanding of hypothermic tissue preservation, which has generally been assumed to work on the basis of decreased tissue metabolism, thus conserving critical cellular ATP levels. The empirical benefit derived by cooling muscle in an iced medium may actually be related to the cellular alkalinization produced by tissue cooling, as this significantly mitigates the profound acidosis that would otherwise occur.