Relationship between near infrared spectroscopy and intra-compartmental pressures.

BACKGROUND: Near infrared spectroscopy (NIRS) has been suggested as a possible means for detecting perfusion deficits in patients with acute compartment syndrome (ACS). STUDY OBJECTIVES: To longitudinally examine NIRS in an ACS model to determine its responsiveness to decreasing perfusion pressure. METHODS: A NIRS sensor pad was placed under a tourniquet over the anterior compartment in the mid-tibia region on 20 volunteers. Initial perfusion pressures and NIRS values were recorded. The tourniquet pressure was sequentially raised by 10 mm Hg in 10-min intervals until systolic pressure was surpassed. NIRS values and perfusion pressure were determined at the end of each 10-min interval. RESULTS: There was no change in mean NIRS values from the initial baseline until 30 mm Hg of perfusion pressure was reached. Additionally, a statistically significant drop in mean NIRS values was observed as perfusion pressures dropped from 10 mm Hg to 0 mm Hg, and again with subsequent decreases of 10 mm Hg perfusion pressure until systolic pressure was surpassed. CONCLUSIONS: These results coincide with previously published studies using alternative methods of measuring blood flow or perfusion. NIRS values were responsive to decreasing perfusion pressures over a longitudinal period of time in an ACS model. These results suggest that NIRS may be useful for continuous, non-invasive monitoring of patients for whom ACS is a concern. Additional studies on traumatized patients are required.

Ability of near infrared spectroscopy to measure oxygenation in isolated upper extremity muscle compartments.

PURPOSE: Near infrared spectroscopy (NIRS), a noninvasive means for monitoring muscle oxygenation, may be useful in the diagnosis of acute compartment syndrome, a condition characterized by poor tissue perfusion. This study used the decrease in muscle oxygenation caused by exercise to investigate the ability of anatomic placement of NIRS sensor pads over compartments of the forearm to isolate perfusion values of a specific compartment. METHODS: We recruited 63 uninjured volunteers from a private clinic-based setting and placed NIRS sensor pads over the dorsal, volar, and mobile wad compartments of 1 forearm. A total of 49 participants also had the contralateral forearm monitored, which served as an internal control. Participants performed a series of 3 exercises designed to sequentially activate the muscles of each compartment. A washout period separated each exercise to allow perfusion to return to baseline. We compared NIRS values of each compartment recorded during muscle contraction with baseline values. RESULTS: Mean NIRS values decreased significantly from baseline during muscle contraction for all compartments, whereas mean NIRS values of muscle compartments that remained at rest showed little or no change. We observed no changes in NIRS values of the contralateral arm, which remained at rest during the entire data collection period. CONCLUSIONS: Although lack of an existing method for quantifying muscle perfusion precludes validation of this technique against a reference standard, this study suggests that NIRS can provide oxygenation values that are both sensitive and specific to muscle compartments of the forearm. Future studies should investigate NIRS among patients with upper extremity injuries. TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic III.

Retrospective analysis of trends in surgery volumes between 2016 and 2019 and impact of the insurance deductible: Cross-sectional study.

BACKGROUND: Understanding trends in surgical volumes can help Ambulatory Surgery Centers (ASCs) prevent clinician burnout and provide adequate staffing while maintaining the quality of patient care throughout the year. Health insurance deductibles reset in January each year and may contribute to an annual rhythm where the levee of year-end deductibles is breached in the last few months of every year, resulting in a flood of cases and several accompanying challenges. This study aims to identify and analyze monthly and yearly surgical volume patterns in ASCs and explore a relationship with the deductible reset. METHODS: De-identified, aggregate visit data for 2016-2019 were obtained retrospectively from 14 ambulatory surgery centers within the same benchmarking consortium in the Southeast. The ASCs subspecialty types consisted of orthopedics, urology, otolaryngology, and multispecialty. Kaiser Family Foundation survey data from 2016 to 2019 was used to inform deductible trends. Augmented Dickey-Fuller tests, linear regressions, and two-sample T-tests were conducted to explore and establish patterns in surgical volume between 2016 and 2019. RESULTS: Overall, average orthopedic surgical volume increased 38.04% from January to December in 2016-2019 with an average difference of 64 cases (95% CI: 47-80), while that of all ASCs combined increased 19.24% within the same timeframe with an average difference of 37 cases (95% CI: 21-52). Average health insurance deductibles rose 12% from $1476 to $1655 within the same timeframe. Regression analysis showed a stronger association between year and volume for orthopedic ASCs (R (Claxton et al., 2019) [2] = 0.796) than for all ASCs combined (R (Claxton et al., 2019) [2] = 0.645). Regression analysis also showed a stronger association between month and volume for orthopedic ASCs (R (Claxton et al., 2019) [2] = 0.488-0.805) than for all ASCs combined (R (Claxton et al., 2019) [2] = 0.115-0.493). CONCLUSION: This study is first to identify regular and predictable yearly and monthly increases in orthopedic ASCs surgical volume. The study also identifies yearly increases in surgical volume for all ASCs. The combination of increasing yearly demand for orthopedic surgery and growing association between month and volume leads to an unnecessary year-end rush. The study aims to inform future policy decisions as well as help ASCs better manage resources throughout the year.

Suture Button Suspensionplasty in the Treatment of Carpometacarpal Arthritis: A Retrospective Analysis of One Surgeon's Experience Over 9 Years.

Purpose: Trapeziectomy with suture button suspensionplasty (SBS) to treat thumb carpometacarpal (CMC) arthritis has been proposed as an alternative to ligament reconstruction tendon interposition. There have been limited large-scale or long-term reports regarding SBS outcomes. Single-surgeon intermediate follow-up is reported. Methods: We conducted a retrospective review of patients undergoing SBS procedures by a single surgeon. Implant manufacturer and postoperative immobilization protocol were recorded. Surgical outcomes, complications, and revision procedures were identified. Postoperative Disabilities of the Arm, Shoulder, and Hand scores were collected. Results: A total of 242 SBS surgeries were included, involving 215 patients, average age 64.82 years (range, 42-86 years). Average follow-up was 35 ± 25 months. In all, 183 Arthrex and 59 Stryker systems were used, 42 of which were immobilized for 6 weeks after surgery and 200 of which were mobilized at 2 weeks afterward. Postoperative Disabilities of the Arm, Shoulder, and Hand surveys were completed by 122 patients (57%), with an average score of 12. No scaphometacarpal abutment was reported. Thirteen complications were reported (5%), 7 of which were implant-associated (3%) and 6 of which were not (2%). Implant-associated complications consisted of 3 suture button pull-outs, 2 thumb-index metacarpal abutments, one suture tail irritation, and one index metacarpal fracture. Operative revision was required in 4 of 7 implant-associated cases and 5 of 6 non-implant associated cases. No suture button pull-outs required revision surgery. Conclusions: Results for a large series of SBS for CMC arthroplasty with intermediate follow-up revealed excellent clinical outcomes and low complication rates. Clinical relevance: Suture button suspensionplasty as an alternative to ligament reconstruction tendon interposition may be a viable option for treating thumb CMC arthritis. In addition, a technique to manage thumb-index metacarpal abutment is described.

Basal joint arthritis of the thumb.

The carpometacarpal joint of the thumb is the second most common site of arthritis in the hand. Patients in whom conservative treatment fails benefit from surgical intervention, although no consensus exists as to the best method to provide maximum pain relief and functional outcomes. The pathophysiology of carpometacarpal arthritis is loss of the integrity of the palmar oblique ligament, which allows for dorsal subluxation of the metacarpal on the trapezium. Most treatments revolve around resection or replacement of the arthritic carpometacarpal joint and restoration of the palmar oblique ligament. A critical appraisal of the current evidence-based research offers no guidance in treatment in the early stages of carpometacarpal arthritis; however, several evidence-based studies exist for more advanced stages. Although these studies exhibit limitations in regard to validated outcomes, power analysis, and blinded assessment, their conclusions question the clinical benefits of ligament reconstruction and tendon interposition. Further research is needed to delineate the best treatment of early stages of arthritis as well as the clinical significance of metacarpal subluxation and subsidence. Further, a standardized set of outcome tools is needed for the interpretation and comparison of data in regard to clinical outcomes.

Tunnel convergence in combined anterior cruciate ligament and posterolateral corner reconstruction.

PURPOSE: To examine the geometric relationship between tunnels created in the lateral femoral condyle in reconstruction of the anterior cruciate ligament (ACL) and the posterolateral structures. METHODS: The geometric relationship between a standard ACL tunnel and 11 lateral femoral tunnel variations in synthetic femur specimens was examined. Tunnel collision frequency and tunnel separation were measured radiographically. Subsequent evaluation was performed on 7 paired cadaveric specimens (14 knees) to access the efficacy of 2 configurations. RESULTS: Phase I-Tunnel collision frequency was 0% and 58% for 25-mm and 30-mm tunnel depths, respectively. Axial angles greater than 40 degrees and coronal angles > or =20 degrees resulted in unsafe configurations. The safest position for lateral tunnel placement was straight lateral approach (0 degrees in the coronal plane) with increased axial plane orientation (hand dropped toward the floor 40 degrees). The safe zone for lateral tunnel configuration was determined to be between [0,0] and [0,40] ([coronal, axial]). Phase II--Control group ([0,0]) collision frequencies were 43% and 86% for the 25-mm 30-mm tunnels, respectively. Experimental group ([0,40]) collision frequencies were 29% and 43% for the 25-mm and 30-mm tunnel, respectively. In femoral condyles measuring <35 mm, collision rates were 100% versus 0% in the control group ([0,0]) versus the experimental group ([0,40]). In specimens where no collision was seen, tunnel separation distance was 4.5 +/- 4.4 mm and 5.8 +/- 2.2 mm for the control and experimental groups, respectively (P = .39). CONCLUSIONS: Tunnel collision occurred often. Tunnel collision is dependent on femoral condyle geometry, tunnel depth, and tunnel configuration. To minimize the potential for tunnel collision, the surgeon should maintain a neutral alignment in the coronal plane, limit lateral tunnel depth to < or =25 mm, and direct the lateral tunnel anteriorly in the axial plane to a maximum of 40 degrees. CLINICAL RELEVANCE: This study describes guidelines for tunnel placement to prevent tunnel collision when performing combined ACL and posterolateral corner reconstruction.

Use of Near-Infrared Spectroscopy to Detect Sustained Hyperaemia Following Lower Extremity Trauma.

INTRODUCTION: Patients who sustain lower extremity trauma are at highest risk for acute compartment syndrome (ACS) during the first 48 hours after surgical stabilization. Near-infrared spectroscopy (NIRS) may be a useful monitoring tool for ACS during this period; however, expected normal values have yet to be established. This study sought to evaluate whether the expected hyperaemic response is present 48 hours postoperatively, using NIRS. MATERIALS AND METHODS: Participants consisted of 25 cases with acute unilateral lower extremity fractures. NIRS measurements for hemoglobin saturated with oxygen (rSO2) were taken approximately 48 hours after surgical stabilization for each compartment bilaterally, using the contralateral (uninjured) leg as an internal control. RESULTS: Mean rSO2 values taken 48 hours from surgical stabilization from each compartment of the patients' injured legs were significantly higher than the mean values of the contralateral legs (injured = 70, 68, 72, 70; contralateral = 55, 54, 57, 56 for anterior, lateral, deep posterior, and superficial posterior compartments, respectively; p < 0.0001 for all compartments). CONCLUSIONS: These results suggest that the hyperaemic response to injury remains present at 48 hours after surgical stabilization, and that NIRS values in an injured extremity should be expected to remain elevated throughout the window of concern for ACS. NIRS may be a valuable tool in monitoring leg injuries during this critical time period.

Comparison of NIRS, serum biomarkers, and muscle damage in a porcine balloon compression model of acute compartment syndrome.

BACKGROUND: Near-infrared spectroscopy (NIRS) has been shown to aid in the diagnosis of extremity acute compartment syndrome (ACS), offering continuous real-time capability to monitor perfusion in extremities. Porcine models of ACS have been developed to attempt to aid in the understanding of the development of ACS and provide better methods of diagnosing ACS. The objective of the present study was to assess and correlate NIRS, tibial intracompartmental pressure (TICP), tibial intracompartmental perfusion pressure (TIPP), serum markers of inflammation and muscle injury in a balloon compression model of ACS. METHODS: Six swine were used. Balloon catheters were inflated below the cranial tibial muscle. Systolic, diastolic, and mean arterial pressures; compartmental pressures; and oximetry were measured before, during, and after balloon inflation/deflation. Cranial tibial muscle was collected for muscle damage scoring. Serum creatine kinase, myoglobin, tumor necrosis factor α, IL-1ß, and IL-6 were measured. Data analysis included comparing differences in TICP, NIRS, and TIPP measurements as well as creatine kinase, myoglobin, tumor necrosis factor α, IL-1ß, and IL-6 levels between time points. Pearson correlations were calculated for muscle degeneration and edema and NIRS. RESULTS: Increases in TICP and decreases in TIPP were found. Near-infrared spectroscopy detected significant changes in tissue oxygenation at all the same time points. Myoglobin significantly increased from 45.7 ± 13.0 ng/mL (baseline) to 219.5 ± 57.3-ng/mL (balloon deflation) and continued to increase over the duration of the study. Creatine kinase significantly increased 2 hours after balloon deflation. Cranial tibial muscle degeneration, necrosis, and edema scores were higher in the test than the control legs. CONCLUSIONS: Near-infrared spectroscopy of the compartment provided a reliable, sensitive measure of both an increase and decrease in TICP and TIPP in this porcine balloon model of ACS. Creatine kinase and myoglobin significantly increased following balloon removal. Significant correlations between muscle degeneration, edema, hemorrhage, and NIRS were found.

Cadaveric Study of Appropriate Screw Length for Distal Radius Stabilization Using Volar Plate Fixation.

We conducted a study to highlight areas of risk with distal radius fixation to prevent occurrence of extensor tendon injury without compromising the security and stability of the fixation. Twelve cadaveric forearms were used. The volar locking plate was placed to best anatomical and radiologic fit on the distal radius of each arm. All 7 holes in the plate were drilled, and bicortical length was measured using a depth gauge under fluoroscopy to estimate screw lengths. Screws were secured into place, and dorsal prominence was measured. The central screw positions had the least dorsal screw prominence, mean (SD) of 0.50 (1.06) mm, and were considered low-risk. The radial and ulnar screw positions had more dorsal screw prominence, 3.38 (1.38) mm and 1.03 (1.30) mm, respectively. Although only radial prominence was statistically significant, both radial and ulnar screw positions were considered high-risk and in need of screw length adjustments. The data suggest that screw length for this plate should be decreased by about 3 mm for the radial positions and by 1 mm for the ulnar positions to decrease the risk for tendon rupture and irritation secondary to dorsal screw prominence.

Correlation of near-infrared spectroscopy and direct pressure monitoring in an acute porcine compartmental syndrome model.

OBJECTIVE: To correlate near-infrared spectroscopy (NIRS) and the tibial intracompartmental perfusion pressure (TIPP) in an acute limb compartmental syndrome. METHODS: Landrace swine were subdivided into 2 groups: plasma infusion (n = 16) and blunt trauma plus plasma infusion (n = 15). NIRS sensors were placed over the craniolateral muscle compartment of proximal both tibiae. Albumin infusion elevated tibial intracompartmental pressures (TICP). Time-synchronized measures of systolic, diastolic, and mean arterial pressures, TICP, and percent oxygenation from each leg were collected. For the blunt trauma group, trauma was induced by dropping a 2-kg weight 30 times from 100 cm directly on the muscle compartment. For each group, a repeated-measures analysis of variance model was used to test differences in the TICP, TIPP, and oxygenation values. Pearson correlations were calculated between TICP and oxygenation and between TIPP and oxygenation. RESULTS: Both models created reproducible increases in TICP and decreases in TIPP. Trauma did not alter TICP, TIPP, or percent oxygenation in the model. NIRS was able to detect significant changes in tissue oxygenation at all the same time points. NIRS was able to detect decreased oxygenation at every TIPP decrease and subsequent increase after fasciotomies. An increase in percent oxygenation was seen in all cases once fasciotomy was performed and TICP was reduced. CONCLUSIONS: NIRS provided a sensitive measure correlating to both an increase and decrease in TICP and TIPP, respectively, in this infusion model. The addition of blunt trauma to the model did not alter the correlations of NIRS values with TICP and TIPP. Fasciotomy produced a rebound in oxygenation values.

Subcutaneous depth in a traumatized lower extremity.

BACKGROUND: Acute compartment syndrome is a rare but serious consequence of traumatic leg injury. Near-infrared spectroscopy (NIRS) is able to measure oxygenation to a depth of 2 cm to 3 cm below the skin, raising concerns over the ability of NIRS to accurately determine oxygenation of injured leg compartments in the presence of swelling and in the obese. The purpose of this study was to measure the thickness of the subcutaneous tissue overlying the posterior muscle compartment in subjects with tibia fractures to determine if it might compromise rSO2 measurement in the muscle. METHODS: Data were analyzed on 50 patients with severe leg injuries. Distance from the skin to the fascia in the superficial posterior compartment of both legs was measured on each patient using a portable ultrasound device. RESULTS: Subject age ranged from 18 years to 65 years (mean, 39 years), with 43 male and 7 female patients. The mean (SD) subcutaneous adipose tissue thickness (ATT) was 6.98 (3.17) mm for the injured leg and 7.06 (3.37) mm for the uninjured leg, and the mean body mass index for the group was 27.08 kg/m. No significant correlation was found between the ATT of the injured or uninjured legs and body mass index. Mean comparison testing revealed no difference in ATT between the injured and uninjured legs (null hypothesis: equal means, p > 0.05). Of the 50 subjects analyzed, no subject had a subcutaneous depth of more than 2 cm on the injured or uninjured leg. CONCLUSION: These data suggest that, within this traumatically injured population, symptoms associated with leg injury (such as swelling and edema) do not significantly affect the distance from the skin to the fascia. It is also notable that subcutaneous depth beyond the 2-cm mark (validated in previous studies) is a rare occurrence in this population. These results further support the use of continuous NIRS monitoring for diagnosis of acute compartment syndrome. LEVEL OF EVIDENCE: Therapeutic study, level IV.

What's new in acute compartment syndrome?

Acute compartment syndrome (ACS) after trauma is often the result of increased size of the damaged tissues after acute crush injury or from reperfusion of ischemic areas. It usually is not solely caused by accumulation of free blood or fluid in the compartment, although that can contribute in some cases. There is no reliable and reproducible test that confirms the diagnosis of ACS. A missed diagnosis or failure to cut the fascia to release pressure within a few hours can result in severe intractable pain, paralysis, and sensory deficits. Reduced blood circulation leads to oxygen and nutrient deprivation, muscle necrosis, and permanent disability. Currently, the diagnosis of ACS is made on the basis of physical examination and repeated needle sticks over a short time frame to measure intracompartmental pressures. Missed compartment syndromes continue to be one of most common causes of malpractice lawsuits. Existing technology for continuous pressure measurements are insensitive, particularly in the deep tissues and compartments, and their use is restricted to highly trained personnel. Newer concepts of the pathophysiology accompanied by new diagnostic and therapeutic modalities have recently been advanced. Among these are the concept of inflammatory mediators as markers and anti-inflammatories as medical adjunct therapy. New diagnostic modalities include near-infrared spectroscopy, ultrafiltration catheters, and radio-frequency identification implants. These all address current shortcomings in the diagnostic armamentarium that trauma surgeons can use. The strengths and weaknesses of these new concepts are discussed to allow the trauma surgeon to follow current evolution of the field.

Correlation between muscle oxygenation and compartment pressures in acute compartment syndrome of the leg.

BACKGROUND: Near-infrared spectroscopy estimates soft-tissue oxygenation approximately 2 to 3 cm below the skin. The purpose of the present study was to evaluate muscle oxygenation in the setting of an acute compartment syndrome of the leg and to determine if near-infrared spectroscopy is capable of detecting perfusion deficits. METHODS: Fourteen patients with unilateral lower extremity trauma were enrolled after the diagnosis of an acute compartment syndrome was made clinically and confirmed with intracompartmental pressure measurements. Lower extremity muscle compartments were evaluated with near-infrared spectroscopy, and near-infrared spectroscopy values of the uninjured, contralateral leg of each patient were used as internal reference values. The compartment perfusion gradient was calculated as the diastolic blood pressure minus the intracompartmental pressure. RESULTS: Intracompartmental pressures ranged from 21 to 176 mm Hg (mean, 79 mm Hg) and exceeded 30 mm Hg in all compartments but two (both in the same patient). Thirty-eight compartments had a perfusion gradient of < or = 10 mm Hg (indicating ischemia). Among ischemic compartments, near-infrared spectroscopy values in the anterior, lateral, deep posterior, and superficial posterior compartments of the injured limbs were decreased by an average 10.1%, 10.1%, 9.4%, and 16.3% in comparison with the corresponding compartments of the uninjured leg. Differences in near-infrared spectroscopy values (the near-infrared spectroscopy value for the injured leg minus the near-infrared spectroscopy value for the uninjured leg) were positively correlated with compartment perfusion gradient within each compartment (r = 0.82, 0.65, 0.67, and 0.62, for the anterior, lateral, deep posterior, and superficial posterior compartments, respectively; p < 0.05 for all). CONCLUSIONS: Normalized near-infrared spectroscopy values decrease significantly with decreasing lower limb perfusion pressures. Near-infrared spectroscopy may be capable of differentiating between injured patients with and without an acute compartment syndrome.

Near-infrared spectroscopy in lower extremity trauma.

BACKGROUND: Near-infrared spectroscopy measures the percentage of hemoglobin oxygen saturation in the microcirculation of tissue up to 3 cm below the skin. The purpose of this study was to describe the measurable response of normal tissue oxygenation in the leg after acute trauma with use of this technique. METHODS: Twenty-six patients with acute unilateral tibial fractures and twenty-five uninjured volunteer control subjects were enrolled. Near-infrared spectroscopy measurements were obtained for both legs in all four compartments: anterior, lateral, deep posterior, and superficial posterior. The twenty-six injured legs were compared with twenty-five uninjured legs (randomly selected) of the volunteer control group, with the contralateral limb in each patient serving as an internal control. RESULTS: The mean tissue oxygenation for each compartment in the injured legs was 69% (anterior), 70% (lateral), 74% (deep posterior), and 70% (superficial posterior). In the control (uninjured) legs, the average tissue oxygenation percentage in each compartment was 54%, 55%, 60%, and 57%, respectively. Repeated-measures analysis revealed that near-infrared spectroscopy values averaged 15.4 percentage points (95% confidence interval, 12.2 to 18.6 percentage points) higher for injured legs than for uninjured legs, controlling for the value of the contralateral limb (p < 0.0001). CONCLUSIONS: Tibial fracture produces a predictable increase in tissue oxygenation as measured by near-infrared spectroscopy. The corresponding compartment of the contralateral leg can provide strong utility as an internal control value when evaluating the hyperemic response to injury.

Porous tantalum implant in early osteonecrosis of the hip: preliminary report on operative, survival, and outcomes results.

Porous tantalum implants are used in early osteonecrosis of the hip. Device evaluation included surgical time, blood loss, hospitalization, patient-controlled analgesia use, transfusions, implant survival, and outcomes. Mean blood loss was 70 mL. Mean operative time was 36 minutes. Average hospitalization was less than 1 day. No patient required patient-controlled analgesia use or transfusions. Results were compared to a historical vascularized fibular graft population. All parameters were less than the fibular graft groups (P < .00001). All surviving implants (86%) resulted in good to excellent outcomes. Kaplan-Meier analysis at 39 months was 86% and 67% for the implant and fibular graft, respectively (P = .21). Early outcomes demonstrate that porous tantalum implants are a safe option for femoral head salvage. Continued follow-up is necessary to determine the long-term success.

Angiotensin II stimulates calcineurin activity in proximal tubule epithelia through AT-1 receptor-mediated tyrosine phosphorylation of the PLC-gamma1 isoform.

Angiotensin II (AngII) contributes to the maintenance of extracellular fluid volume by regulating sodium transport in the nephron. In nonepithelial cells, activation of phospholipase C (PLC) by AT-1 receptors stimulates the generation of 1,4,5-trisphosphate (IP(3)) and the release of intracellular calcium. Calcineurin, a serine-threonine phosphatase, is activated by calcium and calmodulin, and both PLC and calcineurin have been linked to sodium transport in the proximal tubule. An examination of whether AngII activates calcineurin in a model of proximal tubule epithelia (LLC-PK1 cells) was performed; AngII increased calcineurin activity within 30 s. An examination of whether AngII activates PLC in proximal tubule epithelia was also performed after first showing that all three families of PLC isoforms are present in LLC-PK1 cells. Application of AngII increased IP(3) generation by 60% within 15 s, which coincided with AngII-induced tyrosine phosphorylation of the PLC-gamma1 isoform also observed at 15 s. AngII-induced tyrosine phosphorylation was blocked by the AT-1 receptor antagonist, Losartan. Subsequently, an inhibitor of tyrosine phosphorylation blocked the AngII-induced activation of calcineurin, as did coincubation with an inhibitor of PLC activity and with an antagonist of the AT-1 receptor. It is therefore concluded that AngII stimulates calcineurin phosphatase activity in proximal tubule epithelial cells through a mechanism involving AT-1 receptor-mediated tyrosine phosphorylation of the PLC isoform.

Risk factors for pulmonary emboli after total hip or knee arthroplasty.

Because it is difficult to predict which patients may sustain a pulmonary embolism after total hip or knee arthroplasty, we assessed multiple thrombophilic and hypofibrinolytic parameters to identify risk factors. Twenty-nine patients who survived a known pulmonary embolism after total knee or total hip arthroplasty were matched by age, gender, race, arthritic diagnosis, procedure, and surgery date with 29 patient-controls who had a total hip or knee arthroplasty but who did not have a symptomatic known pulmonary embolism or deep vein thrombosis. Twenty-one serologic measures and five genes associated with thrombophilia, hypofibrinolysis, or both were assessed without knowledge of group assignment. All patients with pulmonary embolism had at least one abnormality of plasminogen activator inhibitor activity, dilute Russell's viper venom time, prothrombin time, or total cholesterol versus 13 of 27 (48%) control patients. Forty-seven percent of patients who experienced pulmonary embolism had at least two abnormalities of plasminogen activator inhibitor activity, dilute Russell's viper venom time, prothrombin time, or total cholesterol, versus 7% of control patients. Preoperatively, to identify patients at high risk of pulmonary embolism, plasminogen activator inhibitor activity, dilute Russell's viper venom time, prothrombin time, and cholesterol levels were most predictive. Using at least one abnormality of these four measures as a screening test to detect risk of pulmonary embolism, the test is sensitive (100%), and the predictive value of a negative test is high (100%). After additional prospective study, this may allow identification of patients at low risk (the majority of patients) in whom anticoagulation may not be required and a small group of patients at high risk for pulmonary embolism in whom prophylactic anticoagulation should be provided.