Sub-continental-scale carbon stocks of individual trees in African drylands.

The distribution of dryland trees and their density, cover, size, mass and carbon content are not well known at sub-continental to continental scales1-14. This information is important for ecological protection, carbon accounting, climate mitigation and restoration efforts of dryland ecosystems15-18. We assessed more than 9.9 billion trees derived from more than 300,000 satellite images, covering semi-arid sub-Saharan Africa north of the Equator. We attributed wood, foliage and root carbon to every tree in the 0-1,000 mm year-1 rainfall zone by coupling field data19, machine learning20-22, satellite data and high-performance computing. Average carbon stocks of individual trees ranged from 0.54 Mg C ha-1 and 63 kg C tree-1 in the arid zone to 3.7 Mg C ha-1 and 98 kg tree-1 in the sub-humid zone. Overall, we estimated the total carbon for our study area to be 0.84 (±19.8%) Pg C. Comparisons with 14 previous TRENDY numerical simulation studies23 for our area found that the density and carbon stocks of scattered trees have been underestimated by three models and overestimated by 11 models, respectively. This benchmarking can help understand the carbon cycle and address concerns about land degradation24-29. We make available a linked database of wood mass, foliage mass, root mass and carbon stock of each tree for scientists, policymakers, dryland-restoration practitioners and farmers, who can use it to estimate farmland tree carbon stocks from tablets or laptops.

Polyethylene Wear Testing of a Non-Mechanically Linked Total Elbow Replacement.

BACKGROUND: The objective of this study was to perform a polyethylene wear test on a non-mechanically linked total elbow arthroplasty implant using a clinically relevant in-vitro elbow wear test methodology that simulated ten years of use in the light to moderate activity of daily living range. MATERIALS AND METHODS: The test protocol applied an 80° arc of ulnohumeral motion beginning at 30° shy of full extension and progressing to 110° of flexion. Force was applied at 7° to recreate a valgus load on the elbow. A variable joint load profile at a frequency of 0.5 Hz was employed. The implants were tested for 5 million cycles (Mc) in a bovine serum lubricant. Implant component failure was characterized and polyethylene wear was determined gravimetrically. RESULTS: After 5 Mc the small polyethylene bushing wear rate was 0.56 mg/Mc. The medium size wear rate was 0.28 mg/Mc. Three large sizes were tested and the average wear rate was 0.39 ± 0.07 mg/Mc. No implant failure was identified. CONCLUSION: The test recreated an in vivo loading environment and measured polyethylene wear rates at specified cycle counts. The test demonstrated less wear than other joint replacements. Further clinical evaluation is necessary to determine if this translates into reduced complications of total elbow replacement associated with wear.

Static stability of novel uncemented elbow hemiarthroplasty stabilized with ligament reconstruction.

BACKGROUND: The purpose of this study was to create a model to simulate treatment of unreconstructable distal humerus fractures with hemiarthroplasty. Stability was restored with a latest plate-system that simultaneously tensions medial and lateral collateral ligament grafts. MATERIALS AND METHODS: Static varus and valgus elbow stability was tested in 11 cadaver elbows with intact ligaments and capsule at 5 flexion angles (0°, 30°, 60°, 90°, 120°). The elbows were then destabilized via release of all ligaments and capsular attachments. The distal humerus articular cartilage was excised and replaced with an uncemented hemiarthroplasty. Ligament reconstruction was subsequently performed, and elbow stability was measured and compared to the native state. Dimensions of the hemiarthroplasty component were compared to native elbow dimensions to assess and quantify any existing relationship to elbow stability. RESULTS: A hemiarthroplasty was implanted in all specimens. A size mismatch occurred between the distal humerus trochlea and the olecranon fossa in all specimens and averaged 6.3 mm. Following ligament reconstruction, specimens reproduced the flexion angle-dependent stability of native elbows to both varus and valgus stress. On the medial side, elbow joint stability in mid-flexion was approximately 7% tighter after hemiarthroplasty. Laterally, the elbow was approximately 15% tighter after hemiarthroplasty and demonstrated peak stability in full flexion. The 3 assessed hemiarthroplasty components and bony dimensions did not exhibit any relationship between implant-bone mismatch and elbow stability after ligamentous reconstruction. CONCLUSION: Cadaveric elbow specimens underwent uncemented hemiarthroplasty with soft tissue stabilization with a novel technique for ligament reconstruction. Following hemiarthroplasty and ligament reconstruction, these specimens maintained secure fixation between ligament and bone. Static stability was maintained at varying degrees of elbow flexion regardless of variable mismatch between the hemiarthroplasty component and the native olecranon fossa.

Antimicrobial efficiency and cytocompatibility of different decontamination methods on titanium and zirconium surfaces.

OBJECTIVES: The purpose of this study was to investigate the efficiency of different implant-decontamination methods regarding biofilm modification and potential cytotoxic effects. Therefore, the amount of biofilm reduction, cytocompatibility, and elementary surface alterations were evaluated after decontamination of titanium and zirconium surfaces. MATERIAL AND METHODS: Titanium and zirconium disks were contaminated with a newly developed high-adherence biofilm consisting of six microbial species. Decontaminations were performed using titanium curette, stainless steel ultrasonic scaler (US), glycine (GPAP) and erythritol (EPAP) powder air-polishing, Er:YAG laser, 1% chlorhexidine (CHX), 10% povidone-iodine (PVI), 14% doxycycline (doxy), and 0.95% NaOCl solution. Microbiologic analysis was done using real-time qPCR. For assessment of cytocompatibility, a multiplex assay for the detection of cytotoxicity, viability, and apoptosis on human gingival fibroblasts was performed. X-ray photoelectron spectroscopy (XPS) was used to evaluate chemical alterations on implant surfaces. RESULTS: Compared with untreated control disks, only GPAP, EPAP, US, and Er:YAG laser significantly reduced rRNA counts (activity) on titanium and zirconium (p < .01), whereas NaOCl decreased rRNA count on titanium (p < .01). Genome count (bacterial presence) was significantly reduced by GPAP, EPAP, and US on zirconium only (p < .05). X-ray photoelectron spectroscopy analyses revealed relevant re-exposure of implant surface elements after GPAP, EPAP, and US treatment on both materials, however, not after Er:YAG laser application. Cytocompatibility was impaired by CHX, PVI, doxy, and NaOCl. CHX and PVI resulted in the lowest viability and doxy in the highest apoptosis. CONCLUSIONS: Within the limits of this in vitro study, air-polishing methods and ultrasonic device resulted in effective biofilm inactivation with surface re-exposure and favorable cytocompatibility on titanium and zirconium. Chemical agents, when applied on implant surfaces, may cause potential cytotoxic effects.

Flexor Tendon Repair in Zone II Augmented With an Externalized Detensioning Suture: Protected Flexor Tendon Repair.

Flexor tendon repair in zone II benefits from early finger motion to prevent stiffness. This article presents a technique that serves to augment a zone II flexor tendon repair with an externalized detensioning suture that can be used following any commonly employed repair method. This simple technique enables early active motion and is suited for patients who are less likely to be compliant after surgery or when the soft-tissue injury to the finger and hand is substantial. Although this technique substantially strengthens the repair, a possible drawback is that the tendon excursion distal to the repair is limited until the externalized suture is removed, which may lead to less motion of the distal interphalangeal than what may have occurred without the detensioning suture.

Testing of a Novel Method for Securing Ligaments Against Bone During Simultaneous Medial and Lateral Elbow Ligament Reconstruction.

PURPOSE: A ligament reconstruction method that simultaneously tensions the medial and lateral sides of the elbow and maintains tension with compression plates on the proximal ulna is proposed for the treatment of bidirectional elbow ligament instability. Graft slippage, catastrophic failure, and excessive displacement were evaluated. Biomechanical stability without graft slippage was hypothesized. METHODS: Eight cadaveric ligament reconstruction simulations were created through the dissection of three cadaver arms. Each reconstruction was statically tested with 160 N in a manner where it was first augmented with an absorbable suture and then without. Then, 3 more ligament reconstruction simulations were created for dynamic testing with each undergoing testing at 80 N for 2,000 cycles at 2 Hz. Construct displacement and graft slippage were recorded for each load application. RESULTS: No grafts failed catastrophically and no graft slippage was observed with either static or dynamic loading. Under static loading, the mean change in displacement between augmented and nonaugmented ligament reconstruction simulations was 28.7% ± 21% (augmented 3.95 ± 1.81 mm vs nonaugmented 4.89 ± 2.22 mm). The mean stiffness was 66.6 ± 26.6 N/mm for augmented and 64.6 ± 23.2 N/mm for nonaugmented simulations. With dynamic loading, the mean displacement for augmented graft ligament reconstruction simulations was 1.55 ± 0.16 mm compared with 2.18 ± 0.77 mm for nonaugmented reconstruction simulations. CONCLUSIONS: This method of fixation to the proximal ulna for the simultaneous reconstruction of medial and lateral elbow ligaments successfully prevented graft slippage without excessive construct displacement during static and dynamic testing. Ligament augmentation with absorbable sutures decreased the construct displacement. CLINICAL RELEVANCE: This ligament fixation method may be a viable alternative for the treatment of concomitant medial and lateral elbow instability.

Testing of Novel Total Elbow Prostheses Using Active Motion Experimental Setup.

PURPOSE: The goal of this study was to test a novel uncemented and unconstrained total elbow arthroplasty (Kaufmann total elbow) design that is stabilized through a ligament reconstruction. METHODS: We quantified the implant stability after 25,000 cycles, which represents the time between implantation and when ligament and bone healing has occurred. We used an active motion experimental setup that applies tendon loads via pneumatic cylinders and reproduces the forearm-originating dynamic stabilizers of the elbow. The novel total elbow arthroplasty was actuated for 5,000 full flexion-extension cycles at 5 different shoulder positions. Four Sawbones and 4 cadaver elbows were employed. Angular laxity and implant stability were recorded prior to testing and after each 5,000-loading cycle. RESULTS: Four Sawbones and 4 cadaver elbows were implanted with the uncemented total elbow arthroplasty and did not demonstrate fixation failure or substantial laxity after 25,000 cycles of loading imparted at different shoulder positions. CONCLUSIONS: Our findings demonstrate that the Kaufmann total elbow replacement implanted into cadaver and Sawbones specimens did not exhibit fixation failure or excessive laxity after 25,000 cycles. CLINICAL RELEVANCE: An uncemented, nonmechanically linked total elbow arthroplasty that gains component fixation using intramedullary screws and employs a ligament reconstruction to stabilize the elbow has the potential to be a valuable management option, particularly in younger patients.

The Effect of Elbow Flexion On Valgus Carrying Angle.

PURPOSE: This study aimed to examine the effect of flexion on valgus carrying angle in the human elbow using a dynamic elbow testing apparatus. METHODS: Active elbow motion was simulated in seven cadaveric upper extremities. Six electromechanical actuators simulated muscle action, while 6 degrees-of-freedom joint motion was measured with an optical tracking system to quantify the kinematics of the ulna with respect to the humerus as the elbow was flexed at the side position. Repeatability of the testing apparatus was assessed in a single elbow over five flexion-extension cycles. The varus angle change of each elbow was compared at different flexion angles with the arm at 0° of humerothoracic abduction or dependent arm position. RESULTS: The testing apparatus achieved excellent kinematic repeatability (intraclass correlation coefficient, >0.95) throughout flexion and extension. All elbows decreased their valgus carrying angle during flexion from 0° to 90° when the arm was maintained at 0° of humerothoracic abduction. Elbows underwent significant total varus angle change from full extension of 3.9° ± 3.4° (P = .007), 7.3° ± 5.2° (P = .01), and 8.9° ± 7.1° (P = .02) at 60°, 90°, and 120° of flexion, respectively. No significant varus angle change was observed between 0° and 30° of flexion (P = .66), 60° and 120° of flexion (P = .06), and 90° and 120° of flexion (P = .19). CONCLUSIONS: The dynamic elbow testing apparatus characterized a decrease of valgus carrying angle during elbow flexion and found that most varus angle changes occurred between 30° and 90° of flexion. All specimens underwent varus angle change until at least 90° of flexion. CLINICAL RELEVANCE: Our model establishes the anatomic decrease in valgus angle by flexion angle in vitro and can serve as a baseline for testing motion profiles of arthroplasty designs and ligamentous reconstruction in the dependent arm position. Future investigations should focus on characterizing motion profile change as the arm is abducted away from the body.

Do Intramedullary Screws Provide Adequate Fixation for Humeral and Ulnar Components in Total Elbow Arthroplasty? A Cadaveric Analysis.

PURPOSE: The objective of this study was to determine the structural properties of the cadaver bone-screw interface for cementless intramedullary screw fixation in the context of total elbow arthroplasty. METHODS: The intramedullary canals of seven humerus and seven ulna specimens from fresh-frozen cadavers were drilled using custom drill bits until the inner cortex was reached and then hand tapped for the corresponding thread size. Titanium screws were advanced into the tapped holes until securely seated. The bones were potted and then mounted on a uniaxial material testing machine. A tensile load was applied, and end-of-test elongation, failure load, energy absorbed, and stiffness were determined. End-of-test load and elongation were defined as the elongation and load experienced by the structure at 3,000 N or failure. Each specimen was inspected for evidence of pullout, loosening, or visible fractures. RESULTS: The end-of-test load and elongation for the humerus specimens were 2721 ± 738 N and 3.0 ± 0.9 mm, respectively. The ulna specimens reached 92% of the humerus specimens' end-of-test load at 2,514 ± 678 N and 120% of their end-of-test elongation (3.6 ± 0.6 mm). The stiffness of the humerus specimens was 1,077 ± 336 N/mm, which was 1.3 times greater than the stiffness of the ulna specimens (790 ± 211 N/mm). Lastly, the energy absorbed by the humerus samples was 3.6 ± 1.6 J, which was 92% of the energy absorbed by the ulna samples at 3.9 ± 1.1 J. One humerus and three ulnas failed before the end-of-test load of 3,000 N. Two failures were caused by screw pullout and two by bone fracture. CONCLUSIONS: Our findings demonstrate that intramedullary screw fixation is successful in withstanding forces that are greater than required for osseointegration. CLINICAL RELEVANCE: Uncemented fixation may be beneficial in elbow arthroplasty.

Stress Shielding of Ligaments Using Nonabsorbable Suture Augmentation May Influence the Biology of Ligament Healing.

Nonabsorbable suture augmentation of ligament reconstruction has seen an increase in use over the past several years with the goal of protecting the newly reconstructed ligament while allowing early rehabilitation for a potential earlier return to activity and sport. By spanning the joint with a durable nonabsorbable suture, this construct shares the stress and load seen by the reconstructed ligament, thereby protecting it from forces that could result in an early failure during the early ligamentization phase of the tendon graft. However, stress shielding of the ligament via nonabsorbable suture augmentation is also a double-edged sword, as a reduction in the stress and load seen by the ligament during this healing phase may ultimately have an impact on the final strength and composition of the reconstructed ligament. Although the long-term effects of this stress shielding have yet to be studied or reported in human subjects, multiple biomechanical and animal studies have demonstrated overall changes in architecture, tensile strength, and mechanical properties of a stress-shielded autograft ligament reconstruction.

Strength of Humeral and Ulnar Intramedullary Screw Fixation.

PURPOSE: The goal of this study was to test the pullout strength of intramedullary (IM) screws from within the humerus to establish their ability to seat an uncemented elbow arthroplasty. METHODS: Six humerus and 6 ulna Sawbones specimens were drilled with a drill bit diameter of 5/16 inches, and the inner cortex was hand tapped for a ⅜-16 thread. A ⅜-16 custom-made titanium screw with an outer bolt diameter of 3/8 inches and 16 threads per inch was inserted by hand into the tapped holes. The specimens were then axially tensile loaded at a rate of 5 mm per minute until either the screw began to pull out from the bone or a fracture was noted. RESULTS: Intramedullary screw fixation in the humerus achieved an average pullout strength of 1,439 pound-force (6,401 N), and IM screw fixation in the ulna achieved an average pullout strength of 882 pound-force (3,923 N). A fracture was noted in 3 humeral specimens, with 3 screws pulling out. In the ulna, the IM axial load caused a fracture in 5 specimens, and in 1 specimen, the screw pulled out. CONCLUSIONS: Our findings demonstrate that IM screw fixation can create a tensile force within the screw that is greater than that required to generate the calculated level of compression between the implant and bone. CLINICAL RELEVANCE: This may be beneficial in ensuring fixation between arthroplasty components and bone.

A New Consideration for Corticosteroid Injections: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2/COVID-19) Vaccination.

Corticosteroid injection (CSI) is a commonly used tool in hand surgery that is often given little consideration as a potential detriment to vaccination efficacy. The authors reviewed guidelines issued by relevant societies for the timing of CSI around the severe acute respiratory syndrome coronavirus 2 vaccination period and the evidence used to support them. Ultimately, providers and patients should be adequately educated on the theoretical risks and benefits before proceeding with CSI immediately before, during, or immediately after coronavirus disease 2019 vaccination.

Spatial heterogeneity of climate change as an experiential basis for skepticism.

We postulate that skepticism about climate change is partially caused by the spatial heterogeneity of climate change, which exposes experiential learners to climate heuristics that differ from the global average. This hypothesis is tested by formalizing an index that measures local changes in climate using station data and comparing this index with survey-based model estimates of county-level opinion about whether global warming is happening. Results indicate that more stations exhibit cooling and warming than predicted by random chance and that spatial variations in these changes can account for spatial variations in the percentage of the population that believes that "global warming is happening." This effect is diminished in areas that have experienced more record low temperatures than record highs since 2005. Together, these results suggest that skepticism about climate change is driven partially by personal experiences; an accurate heuristic for local changes in climate identifies obstacles to communicating ongoing changes in climate to the public and how these communications might be improved.

Elbow Biomechanics: Soft Tissue Stabilizers.

The elbow positions the hand in a stable manner relative to the trunk while allowing flexion and extension as well as forearm rotation at varying shoulder positions. Its ability to perform this task without joint subluxation is accomplished through a combination of bony congruency, ligamentous restraint, and dynamic stabilization. Elbow stability is challenged repeatedly during everyday activities, particularly when the arm is abducted. Traumatic injuries that lead to an elbow dislocation or the microtrauma associated with pitching are frequent situations that destabilize the elbow. This article reviews the soft tissue stabilizers that contribute to elbow kinematics and stability.

Elbow Biomechanics: Bony and Dynamic Stabilizers.

The elbow positions the hand in a stable manner relative to the trunk while allowing flexion and extension as well as forearm rotation at varying shoulder positions. Its ability to perform this task without joint subluxation is accomplished through a combination of bony congruency, ligamentous restraint, and dynamic stabilization. This article reviews the bony and dynamic contributors to elbow stability and kinematics. Bony stability is conferred through the morphology of the humeroulnar, humeroradial, and radioulnar joints. Depending on the arm position relative to the trunk and the degree of elbow flexion, the bony contribution will vary. Dynamic elbow stabilizers confer stability through the activation of various muscles that cross the elbow. These forces help resist valgus and varus forces and may also increase bony stability by generating compressive forces. The goal of this article is to review the literature surrounding the biomechanics of bony and dynamic stabilizers of the elbow while drawing clinically relevant biomechanical observations.

Doctor, when can I drive? - Range of functional ankle motion during driving.

BACKGROUND: Driving a motor vehicle needs a specific joint mobility and yet only limited knowledge exists regarding the necessary ankle range of motion. The goal of this study is to characterize the sequence and range of ankle motion. METHODS: The arc of plantarflexion/dorsiflexion and supination/pronation was recorded in the right and left ankle using electrogoniometers while thirty laps were driven by fifteen healthy participants around a course in a manual transmission car with a left sided steering wheel. The driver was required to perform the following maneuvers during each lap: (I) Vehicle acceleration and gear change, (II) Sudden evasion, (III) Routine turning, (IV) Rapid turning, (V) Vehicle acceleration followed by emergency braking. RESULTS: Driving required the right ankle to plantarflex 13±9 and dorsiflex 22±7 while supinating 15±7 degrees and pronating minimally. The left ankle plantarflexed 19±10and dorsiflexed 17±10 while supinating 15±7 degrees and pronating minimally. The right ankle dorsiflexed significantly more (p=0.00), and yet the left ankle had a significantly higher maximum plantarflexion and range of plantarflexion/dorsiflexion (p=0.00). Emergency braking resulted in a significantly higher maximum plantarflexion as well as plantarflexion/dorsiflexion range when compared to other maneuvers. CONCLUSION: This study describes the range of ankle motion identified to drive a car with a manual transmission and a left-sided steering wheel. The right and left ankle exhibit different arcs of motion during driving. This knowledge may assist when evaluating a patient's driving capability. Further studies are needed to investigate whether movement restrictions impair driving. LEVEL OF EVIDENCE: Basic science study.

Total Elbow Arthroplasty: Elbow Biomechanics and Failure.

Total elbow arthroplasty (TEA) has lower revision-free survivorship than other major joint replacement. Despite this, elbow replacement has remained popular. Surgical technique for TEA destabilizes the elbow by removing the medial and lateral collateral ligaments and, frequently, the radiocapitellar articulation. Current semiconstrained implants aim to allow for physiological varus and valgus motion by employing a sloppy hinge; however, over time, these designs fail owing to nonanatomic force transmission. Nonanatomic force transmission results from ligament release, force transmission primarily to the humeral and ulnar shafts, and radial head resection. These altered biomechanics may be the source of complications seen in semiconstrained arthroplasty. These complications perpetuate the cycle of failure and ultimately have poor salvage options.

Doctor, when can I drive?-the range of elbow motion while driving a car.

BACKGROUND: Immobilization of the upper extremity after an acute injury or postoperatively affects an individual's ability to safely operate a motor vehicle. The elbow is particularly sensitive to immobilization, with subsequent stiffness leading to functional limitations. Most activities of daily living are successfully achieved within a "functional arc" of elbow motion between 30° and 130° of flexion. No objective guidelines exist regarding the range of motion needed to safely operate a vehicle. In this study, we measured the range of motion of right and left elbows while driving a manual-transmission car. MATERIALS AND METHODS: Using electro-goniometers, we measured the flexion and extension, as well as pronation and supination, of the right and left elbows in 20 healthy, right hand-dominant subjects while driving a car. These measurements were recorded on (1) city streets, (2) country roads, and (3) highways. RESULTS: For city streets, the range of motion in terms of flexion and pronation/supination was 15°-105° and 0°-45°/0°-35°, respectively, for the right elbow and 20°-95° and 0°-45°/0°-40°, respectively, for the left. For country roads, it was 10°-100° and 0°-40°/0°-35°, respectively, for the right elbow and 20°-95° and 0°-30°/0°-30°, respectively, for the left. For highways, it was 5°-100° and 0°-40°/0°-35°, respectively, for the right elbow and 20°-90° and 0°-30°/0°-25°, respectively, for the left. Mean pronation was significantly higher for the right elbow (P < .01). CONCLUSION: This study describes the range of elbow motion identified to drive a car with a manual transmission and a left-sided steering wheel. Mean pronation of the right elbow is significantly higher than that of the left. Further studies are needed to investigate the relevance of movement restrictions as they relate to handedness, steering-wheel side, and driving impairment.

Optimal Oblique Radiographs to Identify Fifth Carpometacarpal Dorsal Subluxations: A Cadaveric Study.

PURPOSE: Carpometacarpal (CMC) joint subluxations of the fifth finger are rare injuries and are notoriously difficult to diagnose due to severe swelling and overlapping of bones on radiographs. Various radiographic studies have been suggested to identify these injuries. We hypothesize that there will be no difference between various oblique radiographs for detection of a fifth finger CMC subluxation. METHODS: Using 4 cadaveric specimens, we took radiographs at various angles (0°, 30°, 45°, and 60°) with the fifth metacarpal in anatomic position, subluxated 25% and 50% dorsally. Radiology and orthopedic residents, fellows, and attending physicians viewed each image to determine whether a subluxation was present. Data were analyzed using area under the receiver operating curve, sensitivity, and specificity. RESULTS: A total of 36 responses were obtained from 9 radiologists (4 residents, 3 fellows, 2 attendings) and 27 orthopedic surgeons (16 residents, 8 fellows, 3 attendings). Radiographs taken at 60° were more sensitive and specific (Sn 85, Sp 60) than at 0° (Sn 64, Sp 33), 30° (Sn 84, Sp 47), or 45° (Sn 80, Sp 49). Area under the receiver operating curve was also higher for 60° (0.87) than 0° (0.59), 30° (0.75), and 45° (0.75). CONCLUSIONS: Sensitivity, specificity, and area under the receiver operating curve were highest for 60° radiographs. We recommend obtaining radiographs of the hand in 60° of pronation from the lateral if there is suspicion for a fifth CMC subluxation or dislocation. CLINICAL RELEVANCE: This study suggests a simple radiographic view to enhance the diagnosis of fifth CMC subluxations.

Hyperspectral remote sensing of foliar nitrogen content.

A strong positive correlation between vegetation canopy bidirectional reflectance factor (BRF) in the near infrared (NIR) spectral region and foliar mass-based nitrogen concentration (%N) has been reported in some temperate and boreal forests. This relationship, if true, would indicate an additional role for nitrogen in the climate system via its influence on surface albedo and may offer a simple approach for monitoring foliar nitrogen using satellite data. We report, however, that the previously reported correlation is an artifact--it is a consequence of variations in canopy structure, rather than of %N. The data underlying this relationship were collected at sites with varying proportions of foliar nitrogen-poor needleleaf and nitrogen-rich broadleaf species, whose canopy structure differs considerably. When the BRF data are corrected for canopy-structure effects, the residual reflectance variations are negatively related to %N at all wavelengths in the interval 423-855 nm. This suggests that the observed positive correlation between BRF and %N conveys no information about %N. We find that to infer leaf biochemical constituents, e.g., N content, from remotely sensed data, BRF spectra in the interval 710-790 nm provide critical information for correction of structural influences. Our analysis also suggests that surface characteristics of leaves impact remote sensing of its internal constituents. This further decreases the ability to remotely sense canopy foliar nitrogen. Finally, the analysis presented here is generic to the problem of remote sensing of leaf-tissue constituents and is therefore not a specific critique of articles espousing remote sensing of foliar %N.