Intramuscular Pressure Measurements Research Articles

Ultrasound-guided fasciotomy in forearm chronic exertional compartment syndrome: Preliminary results in 12 cases

IntroductionForearm chronic exertional compartment syndrome is a rare condition in athletes and musicians who perform repeated prolonged forced gripping movements. It mainly affects young men, and presents with cramp-like pain, beginning on the anteromedial side of the forearm and progressively extending to the entire circumference, and may be associated with muscle weakness and neurologic symptoms. The objective of this study was to report preliminary results of ultrasound-guided fasciotomy in the treatment of forearm chronic exertional compartment syndrome. Material and methodsA single-center retrospective observational study was conducted. Forearm chronic exertional compartment syndrome was diagnosed on clinical presentation and pathological intramuscular pressure measurement, defined as >30 mmHg at 1 min after effort. The series comprised 7 men, with bilateral involvement. Mean age was 30 years. All patients were motorcyclists. The mean preoperative intramuscular pressure at 1 min after effort was 60.75 mmHg (range: 30−81 mmHg). The main study endpoint was change in pain on visual analogic scale. Secondary endpoints comprised patient satisfaction, change in competitive sports level, and time to return to sport. Complications were noted. ResultsSix patients (12 forearms) were evaluated. Mean follow-up was 22.5 months (range: 3–48 months). Mean pain rating was 7.3/10 (range: 6–9) preoperatively, and 0/10 postoperatively. All patients were satisfied with the procedure. Mean time to return to sports was 25.5 days (range: 21–30 days). No patients decreased their competitive sports level after the procedure. One patient presented a postoperative hematoma, not requiring surgery. ConclusionUltrasound-guided fasciotomy in the treatment of Forearm chronic exertional compartment syndrome is an innovative technique with promising preliminary results. Level of EvidenceIV; retrospective cohort.

Chronic Exertional Compartment Syndrome in Athletes: An Overview of the Current Literature.

Chronic exertional compartment syndrome is an incapacitating condition that primarily affects athletes and individuals with high activity levels. The exact etiology of the condition is unknown to date, but multiple factors play a role in its occurrence. The clinical presentation includes pain, tightness, muscle weakness, paresthesia, and cramps. Common tools utilized during the diagnostic approach include intramuscular compartment pressure measurement, advanced imaging to exclude other disorder entities, near-infrared spectrometry, and shear wave elastography, with the clinical diagnosis being the gold standard. Management includes both conservative and surgical options. Conservative treatment includes gait re-training and botulinum toxin injections. Further, the operative treatment has variable approaches and may be combined with conservative modalities. This article reviews the literature on chronic exertional compartment syndrome and elucidates future recommendations.

Intramuscular Pressure and Patient-Reported Outcomes in Patients Surgically Treated for Anterior Chronic Exertional Compartment Syndrome.

Chronic exertional compartment syndrome (CECS) causes exercise-induced leg pain. The diagnosis is confirmed by intramuscular pressure (IMP) measurements. Fasciotomy has been demonstrated to be a successful treatment for CECS; however, few studies have examined postoperative IMP and long-term outcomes. To evaluate long-term outcomes and postoperative IMP in patients surgically treated for anterior CECS, and to identify possible preoperative or postoperative factors associated with overall satisfaction with treatment at follow-up. Case-control study; Level of evidence, 3. A consecutive series of 209 patients who underwent fasciotomy of the anterior compartment for CECS between 2009 and 2019 and had at least 1 year of follow-up were approached for inclusion. A total of 144 patients (69%), with a follow-up time of 1 to 11.5 years, were ultimately included. All patients underwent preoperative and postoperative 1-minute postexercise IMP measurements of the anterior compartment and completed a questionnaire covering pain and activity parameters at both time points. The follow-up questionnaire included an additional question on overall satisfaction with treatment, and surgical details were collected from the patient's medical records. The median IMP was significantly lower at follow-up than at baseline (17 mm Hg [range, 5-91 mm Hg] vs 49 mm Hg [range, 25-130 mm Hg]; P < .001). The overall satisfaction rate was 77%, and 83% reported a decreased pain level. The group of patients who were satisfied with the treatment included more men and had a higher ΔIMP and a lower revision rate (P < .05). Among the 16 patients (11%) who had undergone revision fasciotomies before follow-up, the satisfaction rate was 56%, and 64% reported a decrease in pain level. Fasciotomy significantly reduced 1-minute postexercise IMP in patients with CECS and resulted in satisfaction and decreased pain in more than three-quarters of the patients at long-term follow-up. The male sex and a significant decrease in IMP were both positively associated with treatment satisfaction. Patients who underwent revision surgery before the follow-up had lower satisfaction rates and less pain reduction than the overall group.

Extremity compartment syndrome: A review with a focus on non-invasive methods of diagnosis.

The article deals with an overview of acute extremity compartment syndrome with a focus on the option of non-invasive detection of the syndrome. Acute extremity compartment syndrome (ECS) is an urgent complication that occurs most often in fractures or high-energy injuries. There is still no reliable method for detecting ECS. The only objective measurement method used in clinical practice is an invasive measurement of intramuscular pressure (IMP). The purpose of this paper is to summarize the current state of research into non-invasive measurement methods that could allow simple and reliable continuous monitoring of patients at risk of developing ECS. Clinical trials are currently underway to verify the suitability of the most studied method, near-infrared spectroscopy (NIRS), which is a method for measuring the local oxygenation of muscle compartments. Less explored methods include the use of ultrasound, ultrasound elastography, bioimpedance measurements, and quantitative tissue hardness measurements. Finding a suitable method for continuous non-invasive monitoring of the syndrome would greatly improve the quality of care for patients at risk. ECS must be diagnosed quickly and accurately to prevent irreversible tissue damage that can occur within hours of syndrome onset and may even warrant amputation if neglected.

The effect of gender on intramuscular pressure in patients with chronic exertional compartment syndrome of the lower leg.

This study aimed to compare intramuscular pressure (IMP) in all four compartments of the lower leg between men and women in patients with suspected chronic exertional compartment syndrome (CECS), and to assess possible effects of gender in relation to covariation factors. A consecutive series of patients with exertional leg pain (n=962, median age 27years, 56.2% women) underwent IMP measurements between 2009 and 2019. The CECS diagnosis was confirmed (n=491, 48% women) or ruled out (n=471, 65% women) based on the patient's history, clinical examination, and IMP measurements. IMP values of the compartments were compared between genders. A multiple linear regression analysis was performed for IMP in the anterior and lateral compartments, where the number of patients was large enough to investigate the possible impact of other factors such as height, age, and duration of pain. Among those with a confirmed CECS diagnosis, one-minute post-exercise IMP was significantly lower in women than in men for all four muscle compartments: anterior (median [range] mmHg 44 [24-120] vs. 50 [24-130]), lateral (35 [20-89] vs. 40 [26-106]), deep posterior (31 [25-36] vs. 34 [24-53]), and superficial posterior (32 [27-39] vs. 37 [22-54]). In the multiple regression analysis, gender differences remained significant in the anterior compartment but not the lateral compartment, where only height remained a significant predictor of IMP. Gender should be considered when using cut-off values for IMP in diagnosing CECS, especially for the anterior compartment.

Intramuscular pressure of human tibialis anterior muscle detects age-related changes in muscle performance

Intramuscular pressure (IMP) reflects forces produced by a muscle. Age is one of the determinants of skeletal muscle performance. The present study aimed to test whether IMP mirrors known age-related muscular changes. We simultaneously measured the tibialis anterior (TA) IMP, compound muscle action potential (CMAP), and ankle torque in thirteen older adults (60–80 years old) in vivo by applying different stimulation intensities and frequencies. We found significant positive correlations between the stimulation intensity and IMP and CMAP. Increasing stimulation frequency caused ankle torque and IMP to increase. The electromechanical delay (EMD) (36 ms) was longer than the onset of IMP (IMPD) (29 ms). Compared to the previously published data collected from young adults (21–40 years old) in identical conditions, the TA CMAP and IMP of older adults at maximum intensity of stimulation were 23.8% and 39.6% lower, respectively. For different stimulation frequencies, CMAP, IMP, as well as ankle torque of older adults were 20.5%, 24.2%, and 13.2% lower, respectively. Surprisingly, the EMD did not exhibit any difference between young and older adults and the IMPD was consistent with the EMD. Data supporting the hypotheses suggest that IMP measurement is an indicator of muscle performance in older adults.

Sensor Anchoring Improves the Correlation Between Intramuscular Pressure and Muscle Tension in a Rabbit Model.

Intramuscular pressure (IMP) shows promise for estimating individual muscle tension in vivo. However, previous pressure measurements show high variability during isometric contraction and poor correlation with tension during dynamic contraction. We hypothesized that enhanced sensor anchoring/orientation would improve tension estimation and thus developed a novel pressure sensor with a barbed housing. Sensors were inserted into the tibialis anterior (TA) of New Zealand White rabbits (N = 8) both parallel and perpendicular to the fiber orientation. We measured muscle stress and IMP during both isometric and dynamic contractions. Passive stress showed good agreement for both insertion directions across muscle lengths (ICC > 0.8). Active stress and IMP agreement were good (ICC = 0.87 ± 0.04) for perpendicular insertions but poor (ICC = 0.21 ± 0.22) for parallel insertions across both dynamic contractions and isometric contractions within the muscle's range of motion. These findings support use of IMP measurements to estimate muscle tension across a range of contraction conditions.

Significantly lower intramuscular pressure in the posterior and lateral compartments compared with the anterior compartment suggests alterations of the diagnostic criteria for chronic exertional compartment syndrome in the lower leg

PurposeTo investigate distributions and identify possible differences in intramuscular pressure (IMP) values at 1 min post-exercise between the four muscle compartments of the lower leg, in patients with exertional leg pain with or without chronic exertional compartment syndrome (CECS).MethodsA consecutive series of patients seeking orthopaedic consultation for exertional leg pain underwent IMP measurements between 2009 and 2018. The diagnosis of CECS was confirmed (n = 442) or ruled out (n = 422), based on the patient’s history, clinical examination, and IMP measurements.ResultsThe median (range) 1 min post-exercise IMP values in affected compartments in the patients diagnosed with CECS were 33 (25–53) mmHg (deep posterior), 35 (27–54) mmHg (superficial posterior), 40 (26–106) mmHg (lateral), and 47 (24–120) mmHg (anterior). In patients with no CECS, the median (range) 1 min post-exercise IMP values in the compartments were 12 (2–28) mmHg (deep posterior), 12 (2–27) mmHg (superficial posterior), 14 (2–26) mmHg (lateral), and 18 (4–34) mmHg (anterior). The IMP was significantly lower in the lateral and both posterior compartments than in the anterior compartment in both patients diagnosed with CECS and patients without CECS.ConclusionThe study demonstrates significantly lower IMP values in the posterior and lateral compartments compared to the anterior compartments. These findings suggest a lowering of the IMP 1 min post-exercise cut-off value for diagnosing CECS in the lateral and both posterior compartments, which may lead to improved treatment of patients with suspected CECS in the lower leg.Level of evidenceLevel II.

Surgical outcomes for chronic exertional compartment syndrome following improved diagnostic criteria

IntroductionChronic exertional compartment syndrome (CECS) presents with pain during exercise, most commonly within the anterior compartment of the lower limb. A diagnosis is classically made from a typical history and...

Noninvasive diagnostics for extremity compartment syndrome following traumatic injury: A state-of-the-art review.

Acute compartment syndrome (ACS) is a serious medical condition that can occur following traumatic injury to an extremity. If left undiagnosed, ACS can eventuate in amputation of the limb or even death. Because of this, fasciotomy to release the pressure within the muscle and restore tissue perfusion is often performed upon suspicion of ACS, as the sequelae to fasciotomy are less severe than those associated with not performing the fasciotomy. Currently, the "gold standard" of diagnosis is based on clinical assessment of such symptoms as pain out of proportion to the injury, obvious high pressure and swelling, pain on passive stretch of the muscles in the affected compartment, and deficits in sensory and/ormotor functions. Diagnosis is often confirmed using invasive measurements of intramuscular pressure (IMP); however, controversy exists as to how direct IMP measurement should be accomplished and threshold pressures for accurate diagnosis. Because of this and the attendant issues with invasive measurements, investigators have been searching over the last 25 years for a noninvasive means to quantitatively measure IMP or perfusion to the limb. The purpose of this review is to summarize the current state of the art of noninvasive devices that could potentially be used to diagnose ACS accurately and objectively. To do this, we divide the discussion into those medical devices that primarily measure mechanical surrogates of IMP (e.g., tissue hardness or myofascial displacement) and those that primarily measure indices of tissue perfusion (e.g., tissue oxygen saturation via near-infraredspectroscopy). While near-infrared spectroscopy-basedtechnologies have shown the most promise, whether such technologies will be of diagnostic benefit await the completion of ongoing clinical trials. LEVEL OF EVIDENCE: Systematic Review, level II.

Intramuscular Pressure of Human Tibialis Anterior Muscle Reflects in vivo Muscular Activity.

Intramuscular pressure (IMP) is the fluid hydrostatic pressure generated within a muscle and reflects the mechanical forces produced by a muscle. By providing accurate quantification of interstitial fluid pressure, the measurement of IMP may be useful to detect changes in skeletal muscle function not identified with established techniques. However, the relationship between IMP and muscle activity has never been studied in vivo in healthy human muscles. To determine if IMP is able to evaluate electromechanical performance of muscles in vivo, we tested the following hypotheses on the human tibialis anterior (TA) muscle: (i) IMP increases in proportion to muscle activity as measured by electrical [Compound Muscle Action Potential (CMAP)] and mechanical (ankle torque) responses to activation by nerve stimulation and (ii) the onset delay of IMP (IMPD) is shorter than the ankle torque electromechanical delay (EMD). Twelve healthy adults [six females; mean (SD) = 28.1 (5.0) years old] were recruited. Ankle torque, TA IMP, and CMAP responses were collected during maximal stimulation of the fibular nerve at different intensity levels of electrical stimulation, and at different frequencies of supramaximal stimulation, i.e., at 2, 5, 10, and 20 Hz. The IMP response at different stimulation intensities was correlated with the CMAP amplitude (r2 = 0.94). The area of the IMP response at different stimulation intensities was also significantly correlated with the area of the CMAP (r2 = 0.93). Increasing stimulation intensity resulted in an increase of the IMP response (P < 0.001). Increasing stimulation frequency caused torque (P < 0.001) as well as the IMP (P < 0.001) to increase. The ankle torque EMD [median (interquartile range) = 41.8 (14.4) ms] was later than the IMPD [33.0 (23.6) ms]. These findings support the hypotheses and suggest that IMP captures active mechanical properties of muscle in vivo and can be used to detect muscular changes due to drugs, diseases, or aging.

Continuous Near-Infrared Spectroscopy Demonstrates Limitations in Monitoring the Development of Acute Compartment Syndrome in Patients with Leg Injuries.

We recorded measurements of muscle perfusion using near-infrared spectroscopy (NIRS) and intramuscular pressure (IMP) in a study designed to develop a decision rule for predicting acute compartment syndrome (ACS). The purpose of this study was to report our experience measuring NIRS data in the context of this broader investigation and to explore factors related to variations in data capture. One hundred and eighty-five patients with lower-leg injuries had data consisting of continuous NIRS measurement of the O2 saturation in the anterior compartment of the injured limb and the contralateral (control) limb, and continuous IMP recording in the anterior and deep posterior compartments of the injured leg as part of their participation in an institutional review board-approved multicenter trial. All monitoring was done for a prescribed period of time. For both types of data, the percentage of valid data capture was defined as the ratio of the minutes of observed data points within a physiological range to the total minutes of expected data points. Clinically useful NIRS data required simultaneous data from the injured and control limbs to calculate the ratio. Statistical tests were used to compare the 2 methods as well as factors associated with the percent of valid NIRS data capture. For the original cohort, clinically useful NIRS data were available a median of 9.1% of the expected time, while IMP data were captured a median of 87.6% of the expected time (p < 0.001). Excluding 46 patients who had erroneous NIRS data recorded, the median percentage was 31.6% for NIRS compared with 87.4% for IMP data (p < 0.00001). Fractures with an associated hematoma were less likely to have valid data points (odds ratio [OR], 0.53; p = 0.04). Gustilo types-I and II open fractures were more likely than Tscherne grades C0 and C1 closed fractures to have valid data points (OR, 1.97; p = 0.03). In this study, NIRS data were not collected reliably. In contrast, IMP measurements were collected during >85% of the expected monitoring period. These data raise questions about the utility of current NIRS data capture technology for monitoring oxygenation in patients at risk of ACS.

Modeling Skeletal Muscle Stress and Intramuscular Pressure: A Whole Muscle Active-Passive Approach.

Clinical treatments of skeletal muscle weakness are hindered by a lack of an approach to evaluate individual muscle force. Intramuscular pressure (IMP) has shown a correlation to muscle force in vivo, but patient to patient and muscle to muscle variability results in difficulty of utilizing IMP to estimate muscle force. The goal of this work was to develop a finite element model of whole skeletal muscle that can predict IMP under passive and active conditions to further investigate the mechanisms of IMP variability. A previously validated hypervisco-poroelastic constitutive approach was modified to incorporate muscle activation through an inhomogeneous geometry. Model parameters were optimized to fit model stress to experimental data, and the resulting model fluid pressurization data were utilized for validation. Model fitting was excellent (root-mean-square error or RMSE <1.5 kPa for passive and active conditions), and IMP predictive capability was strong for both passive (RMSE 3.5 mmHg) and active (RMSE 10 mmHg at in vivo lengths) conditions. Additionally, model fluid pressure was affected by length under isometric conditions, as increases in stretch yielded decreases in fluid pressurization following a contraction, resulting from counteracting Poisson effects. Model pressure also varied spatially, with the highest gradients located near aponeuroses. These findings may explain variability of in vivo IMP measurements in the clinic, and thus help reduce this variability in future studies. Further development of this model to include isotonic contractions and muscle weakness would greatly benefit this work.

Effects of anterior compartment fasciotomy on intramuscular compartment pressure in patients with chronic exertional compartment syndrome

BackgroundPatients with chronic exertional compartment syndrome (CECS) have pain during exercise that usually subsides at rest. Diagnosis is usually confirmed by measurement of intramuscular compartment pressure (IMCP) following exclusion of...

Barefoot plantar pressure measurement in Chronic Exertional Compartment Syndrome

BackgroundPatients with Chronic Exertional Compartment Syndrome (CECS) have exercise-limiting pain that subsides at rest. Diagnosis is confirmed by intramuscular compartment pressure (IMCP) measurement. Accompanying CECS, subjective changes to gait (foot slap) are frequently reported by patients. This has not previously been investigated. The aim of this study was to investigate differences in barefoot plantar pressure (BFPP) between CECS cases and asymptomatic controls prior to the onset of painful symptoms. Methods40 male military volunteers, 20 with symptoms of CECS and 20 asymptomatic controls were studied. Alternative diagnoses were excluded with rigorous inclusion criteria, magnetic resonance imaging and dynamic IMCP measurement. BFPP was measured during walking and marching. Data were analysed for: Stance Time (ST); foot progression angle (FPA); centre of force; plantarflexion rate after heel strike (IFFC-time); the distribution of pressure under the heel; and, the ratio between inner and outer metatarsal loading. Correlation coefficients of each variable with speed and leg length were calculated followed by ANCOVA or t-test. Receiver operating characteristic (ROC) curves were constructed for IFFC-time. ResultsCaseshad shorter ST and IFFC-times than controls. FPA was inversely related to walking speed (WS) in controls only. The area under the ROC curve for IFFC-time ranged from 0.746 (95%CI: 0.636–0.87) to 0.773 (95%CI: 0.671–0.875) representing ‘fair predictive validity’. ConclusionPatients with CECS have an increased speed of ankle plantarflexion after heel strike that precedes the onset of painful symptoms likely resulting from a mechanical disadvantage of Tibialis Anterior. These findings provide further insight into the pathophysiology of CECS and support further investigation of this non-invasive diagnostic. The predictive value of IFFC-time in the diagnosis of CECS is comparable to post-exercise IMCP but falls short of dynamic IMCP measured during painful symptoms.

Muscle Microvascular Blood Flow, Oxygenation, pH, and Perfusion Pressure Decrease in Simulated Acute Compartment Syndrome.

The current gold standard for diagnosing acute compartment syndrome (ACS) is an assessment of clinical signs, invasive measurement of intramuscular pressure (IMP), and measurement of local perfusion pressure. However, IMP measurements have several shortcomings, including pain, risk of infection, risk of technique error, plugging of the catheter tip, lack of consensus on the diagnostic pressure threshold, and lack of specificity and sensitivity. The objective of this study was to evaluate muscle hemodynamics, oxygenation, and pH as diagnostic parameters in a human model of ACS. We hypothesized that as IMP increases, muscle microvascular blood flow, oxygenation, and pH decrease in the anterior compartment of a leg at heart level and that they decrease significantly more when the leg is elevated further. An external pneumatic leg pressure chamber, combined with a venous stasis thigh cuff, was used to increase IMP and simulate ACS. Eight healthy subjects (5 males and 3 females; mean age, 26 years) had photoplethysmography and near-infrared spectroscopy-pH sensors placed over the middle aspect of the tibialis anterior muscle of the right (experimental) and left (control) legs. Leg chamber pressure conditions (40, 50, and 60 mm Hg) were applied in a randomized order after baseline measurements were taken. Data were collected continuously for each 11-minute pressure condition, with an 11-minute recovery period after each condition, and the average of the last 6 minutes was used for data analyses. The same protocol was repeated with each subject's legs elevated 12 cm above heart level. Data were analyzed using repeated-measures analysis of variance (ANOVA). As IMP increased, muscle microvascular blood flow (p = 0.01), oxygenation (p < 0.001), and pH (p < 0.001) all decreased significantly in the experimental leg compared with the control leg. At all IMP levels, leg elevation significantly decreased muscle oxygenation (p = 0.013) and perfusion pressure (p = 0.03) compared with the control leg at heart level. These results indicate that muscle microvascular blood flow, oxygenation, pH, and perfusion pressure decrease significantly as IMP increases in a human model of ACS. This study identifies hemodynamic and metabolic parameters as potential noninvasive diagnostic tools for ACS.

Acute compartment syndrome

Acute compartment syndrome is a well-known complication of tibial fractures, yet it remains difficult to diagnose and the only effective treatment is surgical fasciotomy. Delayed fasciotomy is the most important factor contributing to poor outcomes, and as a result, treatment is biased towards performing early fasciotomy. Current diagnosis of ACS is based on clinical findings and intramuscular pressure (IMP) measurement, and is targeted at identifying safe thresholds for when fasciotomy can be avoided. Since clinical findings are variable and difficult to quantify, measurement of IMP – ideally continuously – is the cornerstone of surgical decision – making. Numerous investigators are searching for less invasive and more direct measurements of tissue ischemia, including measurement of oxygenation, biomarkers, and even neurologic monitoring. This article provides a brief but thorough review of the current state of the art in compartment syndrome diagnosis and treatment.

Design Considerations of a Fiber Optic Pressure Sensor Protective Housing for Intramuscular Pressure Measurements.

Intramuscular pressure (IMP), defined as skeletal muscle interstitial fluid pressure, reflects changes in individual muscle tension and may provide crucial insight into musculoskeletal biomechanics and pathologies. IMP may be measured using fiber-optic fluid pressure sensors, provided the sensor is adequately anchored to and shielded from surrounding muscle tissue. Ineffective anchoring enables sensor motion and inadequate shielding facilitates direct sensor-tissue interaction, which result in measurement artifacts and force-IMP dissociation. The purpose of this study was to compare the effectiveness of polyimide and nitinol protective housing designs to anchor pressure sensors to muscle tissue, prevent IMP measurement artifacts, and optimize the force-IMP correlation. Anchoring capacity was quantified as force required to dislodge sensors from muscle tissue. Force-IMP correlations and non-physiological measurement artifacts were quantified during isometric muscle activations of the rabbit tibialis anterior. Housing structural integrity was assessed after both anchoring and activation testing. Although there was no statistically significant difference in anchoring capacity, nitinol housings demonstrated greater structural integrity and superior force-IMP correlations. Further design improvements are needed to prevent tissue accumulation in the housing recess associated with artificially high IMP measurements. These findings emphasize fundamental protective housing design elements crucial for achieving reliable IMP measurements.

Analysis of fluid movement in skeletal muscle using fluorescent microspheres.

Regional variability in interstitial fluid pressure confounds use of intramuscular pressure measurement to assess muscle force. It is hypothesized that interstitial flow is dependent on intramuscular pressure. The goal of this study was to assess the feasibility of using fluorescent microspheres to evaluate movement of interstitial fluid in skeletal muscle. Two diameters of fluorescent microspheres were injected into the rat tibialis anterior during both static (n = 6) and passively lengthened (10% strain) experimental conditions (n = 6). Microsphere dispersion was evaluated using confocal imaging of transverse muscle sections. Fluorescent microspheres tracked interstitial fluid while not penetrating the muscle fiber. When compared with the static condition, significantly greater dispersion (P = 0.003) was seen with passively lengthened conditions (17 ± 9% vs. 31 ± 7%, respectively). Dispersion did not differ for the 2 microsphere sizes (P = 0.811). Fluorescent microspheres track movement of interstitial fluid, and dispersion is dependent on passive lengthening. Muscle Nerve 54: 444-450, 2016.

Evaluation of a fiber-optic technique for recording intramuscular pressure in the human leg.

To evaluate a forward-sensing fiber-optic pressure technique for recording of intramuscular pressure (IMP) in the human leg and investigate factors that may influence IMP measurements used in diagnosing compartment syndromes. IMP in the tibialis anterior muscle was recorded simultaneously by a fiber-optic technique and needle-injection technique in 12 legs of 7 healthy subjects. Both measurement catheters were placed in parallel with the muscle fibers to the same depth, as verified by sonography. IMP recordings were performed at rest before, during and after applying a model of abnormally elevated IMP (simulated compartment syndrome). IMP was elevated by venous obstruction induced by a thigh tourniquet of a casted leg. IMP was also measured during injections of 0.1ml of saline into the muscle through the catheters. IMP at baseline was 5.1 (SD=2.6) mmHg measured with the fiber-optic technique and 7.1 (SD=2.5) mmHg with the needle-injection technique (p<0.001). It increased to 48.5 (SD=6.9) mmHg and 47.6 (SD=6.6) mmHg respectively, during simulated compartment syndrome. IMP increased significantly following injection of 0.1ml of saline, measured by both techniques. It remained increased 1min after injection. The fiber-optic technique was able to record pulse-synchronous IMP oscillations. The fiber-optic technique may be used for IMP measurements in a muscle with both normal and abnormally elevated IMP. It has good dynamic properties allowing for measurement of IMP oscillations. Saline injection used with needle-injection systems to ensure catheter patency compromises IMP readings at least one minute after injection.