Aims. Disorders of bone integrity carry a high global disease burden, frequently requiring intervention, but there is a paucity of methods capable of noninvasive real-time assessment. Here we show that miniaturized handheld near-infrared spectroscopy (NIRS) scans, operated via a smartphone, can assess structural human bone properties in under three seconds. Methods. A hand-held NIR spectrometer was used to scan bone samples from 20 patients and predict: bone volume fraction (BV/TV); and trabecular (Tb) and cortical (Ct) thickness (Th), porosity (Po), and spacing (Sp). Results. NIRS scans on both the inner (trabecular) surface or outer (cortical) surface accurately identified variations in bone collagen, water, mineral, and fat content, which then accurately predicted bone volume fraction (BV/TV, inner R. 2. = 0.91, outer R. 2. = 0.83), thickness (Tb.Th, inner R. 2. = 0.9, outer R. 2. = 0.79), and cortical thickness (Ct.Th, inner and outer both R. 2. = 0.90). NIRS scans also had 100% classification accuracy in grading the quartile of bone thickness and quality. Conclusion. We believe this is a fundamental step forward in creating an instrument capable of intraoperative real-time use. Cite this article: Bone Jt Open 2023;4(4):250–261

Purpose: Near-infrared spectroscopy (NIRS) detects changes in chromophore concentrations of oxygenated (O2Hb) and deoxygenated hemoglobin (HHb) in target tissues approximately 2 to 3 cm below the skin. The main purpose of this study was to non-invasively measure skeletal muscle oxygenation in the leg during and after tourniquet (TQ)-induced ischemia using continuous wave NIRS. Secondarily, we aimed to assess the sensitivity, specificity, and reliability of this optical technique for detection and continuous monitoring of changes in muscle oxygenation and hemodynamics during TQ-induced ischemia throughout orthopedic surgery. Method: Consented patients aged 19–69 (n=21) with unilateral ankle fracture requiring emergency or elective surgery at our institution were recruited. All patients underwent standard general anesthetic. A pair of NIRS probes was fixed over the midpoint of the tibialis anterior muscle (TA) of both the fractured and healthy legs. A thigh TQ was applied to the injured leg and inflated to 300 mmHg. Using the NIRS apparatus coupled to a laptop with data acquisition software, changes in O2Hb, HHb, and total hemoglobin (tHb) levels in the TAs of both legs were measured at 10 Hz before and during TQ inflation, and after release until values returned to baseline. In each surgery the TQ was released when arterial obstruction was no longer required by the clinical team. Data are reported as mean±SD. Results: Changes in O2Hb, HHb, and tHb were successfully collected, stored and transmitted for graphic display in all subjects. TQ time (ischemia interval) varied among subjects, from 1245 s to 4431 s (2753±854). NIRS measured a progressive increase in HHb (2.6±2 μmol/L) during the first minute of TQ inflation and a sharp increase in O2Hb (23.3±12 μmol/L) during the first minute of leg muscle reperfusion (after deflation). Following TQ inflation a progressive increase in HHb (24.2±10.3 μmol/L) with a concomitant decrease in O2Hb (mean – 24.4±8 μmol/L) in the under-TQ TA were consistent across subjects. These changes in ΔHHb and ΔO2Hb began to reverse immediately after TQ deflation. Significant correlations were observed between ischemia interval and, respectively, oxygenation recovery time (r2=0.84) and changes of deoxygenated hemoglobin (r2=0.57). Conclusion: We demonstrated that, following TQ inflation and deflation respectively, NIRS can sensitively monitor muscle deoxygenation and reoxygenation. Consistent patterns of ΔHHb and ΔO2Hb occurred during TQ-induced ischemia in all subjects. These data confirm that near infrared spectroscopy is useful for the non-invasive detection and monitoring of muscle ischemia. These results indicate that it may be useful to investigate the efficacy of NIRS in the early detection of muscle ischemia or hypoxemia in conditions such as compartment syndrome. FUNDING: MSFHR, COF, BC Lung

The detection and treatment of acute compartment syndrome following trauma is critical if contractures, delayed fracture healing and possible amputations are to be avoided. The current standard for monitoring relies on invasive compartment pressure measurements. These require an additional procedure and cause discomfort to the patient. This prospective clinical study investigates the relationship between the intra-compartmental pressure and soft tissue oxygenation (%StO. 2. ) measured non-invasively by near-infrared spectroscopy (NIRS) in patients at risk of acute compartment syndrome. Adults with acute tibial or radial diaphyseal fractures were recruited on admission to the orthopaedic trauma unit. Non-invasive and invasive monitoring over anterior tibial or volar forearm compartments was carried out from admission and continued post-operatively. The differential pressure (ΔDP) was calculated as the compartment pressure subtracted from the diastolic blood pressure. The threshold for fasciotomy was a ΔDP < 30mmHg. StO. 2. values were simultaneously recorded from the contralateral (uninjured) limb at the same site. All patients had the difference between the StO. 2. value on the injured and uninjured sides calculated (‘StO. 2. difference’). Sixty patients with tibial fractures and 5 patients with forearm fractures were recruited. The mean age was 39 years (S.D.18 years). Fourteen patients underwent a four-compartment lower leg fasciotomy determined by a ΔDP < 30mmHg. We have observed that the difference in StO. 2. between limbs (measured non-invasively) was significantly lower in patients undergoing a fasciotomy. This suggests that NIRS is able to detect a change in oxygenation of the soft tissues in trauma patients developing an acute compartment syndrome. We are optimistic that near-infrared spectroscopy (NIRS) will be a reliable new non-invasive technique for detection of an acute compartment syndrome

Despite advances in treating acute spinal cord injury (SCI), measures to mitigate permanent neurological deficits in affected patients are limited. Augmentation of mean arterial blood pressure (MAP) to promote blood flow and oxygen delivery to the injured cord is one of the only currently available treatment options to potentially improve neurological outcomes after acute spinal cord injury (SCI). However, to optimize such hemodynamic management, clinicians require a method to measure and monitor the physiological effects of these MAP alterations within the injured cord in real-time. To address this unmet clinical need, we developed a series of miniaturized optical sensors and a monitoring system based on multi-wavelength near-infrared spectroscopy (MW-NIRS) technique for direct transdural measurement and continuous monitoring of spinal cord hemodynamics and oxygenation in real-time. We conducted a feasibility study in a porcine model of acute SCI. We also completed two separate animal studies to examine the function of the sensor and validity of collected data in an acute experiment and a seven-day post-injury survival experiment. In our first animal experiment, nine Yorkshire pigs underwent a weight-drop T10 vertebral level contusion-compression injury and received episodes of ventilatory hypoxia and alterations in MAP. Spinal cord hemodynamics and oxygenation were monitored throughout by a transdural NIRS sensor prototype, as well as an invasive intraparenchymal (IP) sensor as a comparison. In a second experiment, we studied six Yucatan miniature pigs that underwent a T10 injury. Spinal cord oxygenation and hemodynamics parameters were continuously monitored by an improved NIRS sensor over a long period. Episodes of MAP alteration and hypoxia were performed acutely after injury and at two- and seven-days post-injury to simulate the types of hemodynamic changes patients experience after an acute SCI. All NIRS data were collected in real-time, recorded and analyzed in comparison with IP measures. Noninvasive NIRS parameters of tissue oxygenation were highly correlated with invasive IP measures of tissue oxygenation in both studies. In particular, during periods of hypoxia and MAP alterations, changes of NIRS-derived spinal cord tissue oxygenation percentage were significant and corresponded well with the changes in spinal cord oxygen partial pressures measured by the IP sensors (p < 0.05). Our studies indicate that a novel optical biosensor developed by our team can monitor real-time changes in spinal cord hemodynamics and oxygenation over the first seven days post-injury and can detect local tissue changes that are reflective of systemic hemodynamic changes. Our implantable spinal cord NIRS sensor is intended to help clinicians by providing real-time information about the effects of hemodynamic management on the injured spinal cord. Hence, our novel NIRS system has the near-term potential to impact clinical care and improve neurologic outcomes in acute SCI. To translate our studies from bench to bedside, we have developed an advanced clinical NIRS sensor that is ready to be implanted in the first cohort of acute SCI patients in 2022

This prospective clinical study investigates the relationship between intra-compartmental pressure and soft tissue oxygenation (StO2) measured non-invasively by near-infrared spectroscopy (NIRS) in patients at risk of acute compartment syndrome. Patients (over 13 years) with fractures of the tibial diaphysis or high-energy fractures of the forearm or distal radius, or patients with soft tissue injury were recruited. Non-invasive and invasive monitoring was carried out pre and post operatively. The ‘Delta P’ value (DP) was calculated as the compartment pressure subtracted from the diastolic blood pressure. The threshold for fasciotomy was a DP < 30mmHg. Non-invasive tissue saturation measurements and pressure measurements were taken from the same compartment (anterior tibial or volar forearm). StO2 values were simultaneously recorded from the contralateral (uninjured) limb at the same anatomical site. All patients had the difference between the StO2 value on the injured and uninjured sides calculated (‘StO2 difference’). 42 patients with tibial diaphyseal fractures, 2 patients with forearm fractures and one case with thigh swelling were recruited to the study. The mean age was 40 years (SD 17 years). 11 patients underwent a four-compartment lower leg fasciotomy determined by a DP < 30mmHg. Patients who required a fasciotomy had an ‘StO2 difference’ that was 20% lower (p = 0. 002) compared to those who did not develop acute compartment syndrome. This suggests that patients who require a fasciotomy have reduced StO2 values on their injured legs compared to the contralateral (uninjured) side. We have observed that non-invasive StO2 measurements for patients over 13 years at risk of acute compartment syndrome, correlates with the requirement for a fasciotomy as defined by P < 30mmHg. We are optimistic that near-infrared spectroscopy (NIRS) will be a reliable new non-invasive technique for detection of an acute compartment syndrome