Prediction of Worse Functional Status After Surgery for Degenerative Cervical Myelopathy: A Machine Learning Approach.

BACKGROUND: Surgical decompression for degenerative cervical myelopathy (DCM) is one of the mainstays of treatment, with generally positive outcomes. However, some patients who undergo surgery for DCM continue to show functional decline. OBJECTIVE: To use machine learning (ML) algorithms to determine predictors of worsening functional status after surgical intervention for DCM. METHODS: This is a retrospective analysis of prospectively collected data. A total of 757 patients enrolled in 2 prospective AO Spine clinical studies, who underwent surgical decompression for DCM, were analyzed. The modified Japanese Orthopedic Association (mJOA) score, a marker of functional status, was obtained before and 1 yr postsurgery. The primary outcome measure was the dichotomized change in mJOA at 1 yr according to whether it was negative (worse functional status) or non-negative. After applying an 80:20 training-testing split of the dataset, we trained, optimized, and tested multiple ML algorithms to evaluate algorithm performance and determine predictors of worse mJOA at 1 yr. RESULTS: The highest-performing ML algorithm was a polynomial support vector machine. This model showed good calibration and discrimination on the testing data, with an area under the receiver operating characteristic curve of 0.834 (accuracy: 74.3%, sensitivity: 88.2%, specificity: 72.4%). Important predictors of functional decline at 1 yr included initial mJOA, male gender, duration of myelopathy, and the presence of comorbidities. CONCLUSION: The reasons for worse mJOA are frequently multifactorial (eg, adjacent segment degeneration, tandem lumbar stenosis, ongoing neuroinflammatory processes in the cord). This study successfully used ML to predict worse functional status after surgery for DCM and to determine associated predictors.

Clinical outcomes of nonoperatively managed degenerative cervical myelopathy: an ambispective longitudinal cohort study in 117 patients.

OBJECTIVE: Degenerative cervical myelopathy (DCM) is among the most common pathologies affecting the spinal cord but its natural history is poorly characterized. The purpose of this study was to investigate functional outcomes in patients with DCM who were managed nonoperatively as well as the utility of quantitative clinical measures and MRI to detect deterioration. METHODS: Patients with newly diagnosed DCM or recurrent myelopathic symptoms after previous surgery who were initially managed nonoperatively were included. Retrospective chart reviews were performed to analyze clinical outcomes and anatomical MRI scans for worsening compression or increased signal change. Quantitative neurological assessments were collected prospectively, including modified Japanese Orthopaedic Association (mJOA) score; Quick-DASH; graded redefined assessment of strength, sensation, and prehension-myelopathy version (GRASSP-M: motor, sensory, and dexterity); grip dynamometer; Berg balance scale score; gait stability ratio; and gait variability index. A deterioration of 10% was considered significant (e.g., a 2-point decrease in mJOA score). RESULTS: A total of 117 patients were included (95 newly diagnosed, 22 recurrent myelopathy), including 74 mild, 28 moderate, and 15 severe cases. Over a mean follow-up of 2.5 years, 57% (95% CI 46%-67%) of newly diagnosed patients and 73% (95% CI 50%-88%) of patients with recurrent DCM deteriorated neurologically. Deterioration was best detected with grip strength (60%), GRASSP dexterity (60%), and gait stability ratio (50%), whereas the mJOA score had low sensitivity (33%) in 50 patients. A composite score had a sensitivity of 81% and a specificity of 82%. The sensitivity of anatomical MRI was 28% (83 patients). CONCLUSIONS: DCM appears to have a poor natural history; however, prospective studies are needed for validation. Serial assessments should include mJOA score, grip strength, dexterity, balance, and gait analysis. The absence of worsening on anatomical MRI or in mJOA scores is not sufficient to determine clinical stability.

Spinal Cord Signal Change on Magnetic Resonance Imaging May Predict Worse Clinical In- and Outpatient Outcomes in Patients with Spinal Cord Injury: A Prospective Multicenter Study in 459 Patients.

Prognostic factors for clinical outcome after spinal cord (SC) injury (SCI) are limited but important in patient management and education. There is a lack of evidence regarding magnetic resonance imaging (MRI) and clinical outcomes in SCI patients. Therefore, we aimed to investigate whether baseline MRI features predicted the clinical course of the disease. This study is an ancillary to the prospective North American Clinical Trials Network (NACTN) registry. Patients were enrolled from 2005-2017. MRI within 72 h of injury and a minimum follow-up of one year were available for 459 patients. Patients with American Spinal Injury Association impairment scale (AIS) E were excluded. Patients were grouped into those with (n = 354) versus without (n = 105) SC signal change on MRI T2-weighted images. Logistic regression analysis adjusted for commonly known a priori confounders (age and baseline AIS). Main outcomes and measures: The primary outcome was any adverse event. Secondary outcomes were AIS at the baseline and final follow-up, length of hospital stay (LOS), and mortality. A regression model adjusted for age and baseline AIS. Patients with intrinsic SC signal change were younger (46.0 (interquartile range (IQR) 29.0 vs. 50.0 (IQR 20.5) years, p = 0.039). There were no significant differences in the other baseline variables, gender, body mass index, comorbidities, and injury location. There were more adverse events in patients with SC signal change (230 (65.0%) vs. 47 (44.8%), p < 0.001; odds ratio (OR) = 2.09 (95% confidence interval (CI) 1.31-3.35), p = 0.002). The most common adverse event was cardiopulmonary (186 (40.5%)). Patients were less likely to be in the AIS D category with SC signal change at baseline (OR = 0.45 (95% CI 0.28-0.72), p = 0.001) and in the AIS D or E category at the final follow-up (OR = 0.36 (95% CI 0.16-0.82), p = 0.015). The length of stay was longer in patients with SC signal change (13.0 (IQR 17.0) vs. 11.0 (IQR 14.0), p = 0.049). There was no difference between the groups in mortality (11 (3.2%) vs. 4 (3.9%)). MRI SC signal change may predict adverse events and overall LOS in the SCI population. If present, patients are more likely to have a worse baseline clinical presentation (i.e., AIS) and in- or outpatient clinical outcome after one year. Patients with SC signal change may benefit from earlier, more aggressive treatment strategies and need to be educated about an unfavorable prognosis.

Inter-rater Reliability of the Modified Japanese Orthopedic Association Score in Degenerative Cervical Myelopathy: A Cross-sectional Study.

STUDY DESIGN: Prospective cross-sectional blinded-assessor cohort study. OBJECTIVE: The aim of this study was to determine the inter-rater reliability of the modified Japanese Orthopaedic Association (mJOA) score in a large cohort of degenerative cervical myelopathy (DCM) patients. SUMMARY OF BACKGROUND DATA: The mJOA score is widely accepted as the primary outcome measure in DCM; it has been utilized in clinical practice guidelines and directly influences treatment recommendations, but its reliability has not been established. METHODS: A refined version of the mJOA was administered to DCM patients by two or more blinded clinicians. Inter-rater reliability was measured using intraclass correlation coefficient (ICC), agreement, and mean difference for mJOA total score and subscores. Data were also analyzed with analysis of variance for differences by mJOA severity (mild: 15-17, moderate: 12-14, severe: <12), assessor, assessment order, previous surgery, age, and sex. RESULTS: One hundred fifty-four DCM patients underwent 322 mJOA assessments (183 paired assessments). ICC was 0.88 for total mJOA, 0.79 for upper extremity (UE) motor, 0.84 for lower extremity (LE) motor, 0.63 for UE sensation, and 0.78 for urinary function subscores. Paired assessments were identical across all four subscores in 25%. The mean difference in mJOA was 0.93 points between assessors, and this differed by severity (mild: 0.68, moderate: 1.24, severe: 0.87, P = 0.001). Differences of ≥ 2 points occurred in 19%. Disagreement between mild and moderate severity occurred in 12% of patients. Other variables did not demonstrate significant relationships with mJOA scores. CONCLUSION: The inter-rater reliability of total mJOA and its subscores is good, except for UE sensory function (moderate). However, the vast majority of assessments differed between observers, indicating that this measure should be interpreted carefully, particularly when near the threshold between severity categories, or when a patient is reassessed for deterioration. Further efforts to educate clinicians on administration and to refine the UE sensory subscore may enhance the reliability of this tool.Level of Evidence: 1.

In-hospital Course and Complications of Laminectomy Alone Versus Laminectomy Plus Instrumented Posterolateral Fusion for Lumbar Degenerative Spondylolisthesis: A Retrospective Analysis of 1804 Patients from the NSQIP Database.

STUDY DESIGN: Retrospective analysis of data from the National Surgical Quality Improvement Program (NSQIP). OBJECTIVE: We sought to compare the short-term outcomes of laminectomy with/without fusion for single-level lumbar degenerative spondylolisthesis (DS). SUMMARY OF BACKGROUND DATA: Lumbar DS is a common cause of low back and radicular pain. Controversy remains over the safety and efficacy of fusion in addition to standard decompressive surgery. METHODS: Patients with lumbar DS who underwent laminectomy alone or laminectomy plus posterolateral fusion at a single level were identified from the 2012-2017 NSQIP database. Outcomes included 30-day mortality, major complication, reoperation, readmission, as well as operative duration, need for blood transfusion, length of stay (LOS), and discharge destination. Outcomes were compared between treatment groups by multivariable regression, adjusting for age, sex, and comorbidities (modified Frailty Index). Effect sizes were reported by adjusted odds ratio (aOR) or mean difference (aMD). RESULTS: The study cohort consisted of 1804 patients; of these, 802 underwent laminectomy alone and 1002 laminectomy plus fusion. On both unadjusted and adjusted analyses, there was no difference in 30-day mortality, major complications, reoperation, or readmission. However, laminectomy plus fusion was associated with longer operative time (170.0 vs. 152.7 minutes; aMD 16.00 minutes, P < 0.001), longer hospital LOS (3.2 vs. 2.5 days; aMD 0.68, P < 0.001), more frequent need for intra- or postoperative blood transfusion (6.8% vs. 3.1%; aOR 2.24, P = 0.001), and less frequent discharge home (80.7% vs. 89.2%; aOR 0.46, P < 0.001). CONCLUSION: We found single-level laminectomy plus fusion for lumbar DS to have a comparable short-term safety profile to laminectomy alone. However, fusion was associated with longer operative time and LOS, higher risk of blood transfusion, and greater need for inpatient rehabilitation. These factors should be recognized by clinicians and discussed with patients in the context of their values when weighing surgical treatment of lumbar DS.Level of Evidence: 3.

Quantitative Assessment of Gait Characteristics in Degenerative Cervical Myelopathy: A Prospective Clinical Study.

It is challenging to discriminate the early presentation of Degenerative Cervical Myelopathy (DCM) as well as sensitively and accurately distinguishing between mild, moderate, and severe levels of impairment. As gait dysfunction is one of the cardinal symptoms of DCM, we hypothesized that spatiotemporal gait parameters, including the enhanced gait variability index (eGVI), could be used to sensitively discriminate between different severities of DCM. A total of 153 patients recently diagnosed with DCM were recruited and stratified on the basis of DCM severity grades, as measured using the modified Japanese Orthopedic Association (mJOA) scale. Demographic information and neurological status were collected. Gait assessments were performed using an 8 m walkway. Spearman rank correlation was used to identify relationships between gait parameters and mJOA values as well as the mJOA lower extremity (LE) subscore. Kruskal-Wallis H test was performed to evaluate differences between severity groups, as defined by mJOA classification. A significant and relatively strong correlation was found between the mJOA score and eGVI, as well as between the LE subscore of the mJOA and eGVI. Significant differences in the eGVI (X2(2, N = 153) = 55.04, p < 0.0001, ε2 = 0.36) were found between all groups of DCM severity, with a significant increase in the eGVI as DCM progressed from mild to moderate. The eGVI was the most discriminative gait parameter, which facilitated objective differentiation between varying severities of DCM. Quantitative gait assessments show promise as an accurate and objective tool to diagnose and classify DCM, as well as to potentially evaluate the impact of therapeutic interventions.

Predicting Outcomes After Surgical Decompression for Mild Degenerative Cervical Myelopathy: Moving Beyond the mJOA to Identify Surgical Candidates.

BACKGROUND: Patients with mild degenerative cervical myelopathy (DCM) represent a heterogeneous population, and indications for surgical decompression remain controversial. OBJECTIVE: To dissociate patient phenotypes within the broader population of mild DCM associated with degree of impairment in baseline quality of life (QOL) and surgical outcomes. METHODS: This was a post hoc analysis of patients with mild DCM (modified Japanese Orthopedic Association [mJOA] 15-17) enrolled in the AOSpine CSM-NA/CSM-I studies. A k-means clustering algorithm was applied to baseline QOL (Short Form-36 [SF-36]) scores to separate patients into 2 clusters. Baseline variables and surgical outcomes (change in SF-36 scores at 1 yr) were compared between clusters. A k-nearest neighbors (kNN) algorithm was used to evaluate the ability to classify patients into the 2 clusters by significant baseline clinical variables. RESULTS: One hundred eighty-five patients were eligible. Two groups were generated by k-means clustering. Cluster 1 had a greater proportion of females (44% vs 28%, P = .029) and symptoms of neck pain (32% vs 11%, P = .001), gait difficulty (57% vs 40%, P = .025), or weakness (75% vs 59%, P = .041). Although baseline mJOA correlated with neither baseline QOL nor outcomes, cluster 1 was associated with significantly greater improvement in disability (P = .003) and QOL (P < .001) scores following surgery. A kNN algorithm could predict cluster classification with 71% accuracy by neck pain, motor symptoms, and gender alone. CONCLUSION: We have dissociated a distinct patient phenotype of mild DCM, characterized by neck pain, motor symptoms, and female gender associated with greater impairment in QOL and greater response to surgery.

A comparison of the perioperative outcomes of anterior surgical techniques for the treatment of multilevel degenerative cervical myelopathy.

OBJECTIVE: Degenerative cervical myelopathy (DCM) is the most common cause of spinal cord dysfunction in adults. Multilevel ventral compressive pathology is routinely managed through anterior decompression and reconstruction, but there remains uncertainty regarding the relative safety and efficacy of multiple discectomies, multiple corpectomies, or hybrid corpectomy-discectomy. To that end, using a large national administrative healthcare data set, the authors sought to compare the perioperative outcomes of anterior cervical discectomy and fusion (ACDF), anterior cervical corpectomy and fusion (ACCF), and hybrid corpectomy-discectomy for multilevel DCM. METHODS: Patients with a primary diagnosis of DCM who underwent an elective anterior cervical decompression and reconstruction operation over 3 cervical spinal segments were identified from the 2012-2017 National Surgical Quality Improvement Program database. Patients were separated into those undergoing 3-level discectomy, 2-level corpectomy, or a hybrid procedure (single-level corpectomy plus additional single-level discectomy). Outcomes included 30-day mortality, major complication, reoperation, and readmission, as well as operative duration, length of stay (LOS), and routine discharge home. Outcomes were compared between treatment groups by multivariable regression, adjusting for age and comorbidities (modified Frailty Index). Effect sizes were reported by adjusted odds ratio (aOR) or mean difference (aMD) and associated 95% confidence interval. RESULTS: The study cohort consisted of 1298 patients; of these, 713 underwent 3-level ACDF, 314 2-level ACCF, and 271 hybrid corpectomy-discectomy. There was no difference in 30-day mortality, reoperation, or readmission among the 3 procedures. However, on both univariate and adjusted analyses, compared to 3-level ACDF, 2-level ACCF was associated with significantly greater risk of major complication (aOR 2.82, p = 0.005), longer hospital LOS (aMD 0.8 days, p = 0.002), and less frequent discharge home (aOR 0.59, p = 0.046). In contrast, hybrid corpectomy-discectomy had comparable outcomes to 3-level ACDF but was associated with significantly shorter operative duration (aMD -16.9 minutes, p = 0.002). CONCLUSIONS: The authors found multiple discectomies and hybrid corpectomy-discectomy to have a comparable safety profile in treating multilevel DCM. In contrast, multiple corpectomies were associated with a higher complication rate, longer hospital LOS, and lower likelihood of being discharged directly home from the hospital, and may therefore be a higher-risk operation.

Degenerative cervical myelopathy - update and future directions.

Degenerative cervical myelopathy (DCM) is the leading cause of spinal cord dysfunction in adults worldwide. DCM encompasses various acquired (age-related) and congenital pathologies related to degeneration of the cervical spinal column, including hypertrophy and/or calcification of the ligaments, intervertebral discs and osseous tissues. These pathologies narrow the spinal canal, leading to chronic spinal cord compression and disability. Owing to the ageing population, rates of DCM are increasing. Expeditious diagnosis and treatment of DCM are needed to avoid permanent disability. Over the past 10 years, advances in basic science and in translational and clinical research have improved our understanding of the pathophysiology of DCM and helped delineate evidence-based practices for diagnosis and treatment. Surgical decompression is recommended for moderate and severe DCM; the best strategy for mild myelopathy remains unclear. Next-generation quantitative microstructural MRI and neurophysiological recordings promise to enable quantification of spinal cord tissue damage and help predict clinical outcomes. Here, we provide a comprehensive, evidence-based review of DCM, including its definition, epidemiology, pathophysiology, clinical presentation, diagnosis and differential diagnosis, and non-operative and operative management. With this Review, we aim to equip physicians across broad disciplines with the knowledge necessary to make a timely diagnosis of DCM, recognize the clinical features that influence management and identify when urgent surgical intervention is warranted.

Efficacy and Safety of Surgery for Mild Degenerative Cervical Myelopathy: Results of the AOSpine North America and International Prospective Multicenter Studies.

BACKGROUND: There is controversy over the optimal treatment strategy for patients with mild degenerative cervical myelopathy (DCM). OBJECTIVE: To evaluate the degree of impairment in baseline quality of life as compared to population norms, as well as functional, disability, and quality of life outcomes following surgery in a prospective cohort of mild DCM patients undergoing surgical decompression. METHODS: We identified patients with mild DCM (modified Japanese Orthopaedic Association [mJOA] 15 to 17) enrolled in the prospective, multicenter AOSpine CSM-NA or CSM-I trials. Baseline quality of life Short Form-36 version 2 (SF-36v2) was compared to population norms by the standardized mean difference (SMD). Outcomes, including functional status (mJOA, Nurick grade), disability (NDI [Neck Disability Index]), and quality of life (SF-36v2), were evaluated at baseline and 6 mo, 1 yr, and 2 yr after surgery. Postoperative complications within 30 d of surgery were monitored. RESULTS: One hundred ninety-three patients met eligibility criteria. Mean age was 52.4 yr. There were 67 females (34.7%). Patients had significant impairment in all domains of the SF-36v2 compared to population norms, greatest for Social Functioning (SMD -2.33), Physical Functioning (SMD -2.31), and Mental Health (SMD -2.30). A significant improvement in mean score from baseline to 2-yr follow-up was observed for all major outcome measures, including mJOA (0.87, P < .01), Nurick grade (-1.13, P < .01), NDI (-12.97, P < .01), and SF-36v2 Physical Component Summary (PCS) (5.75, P < .01) and Mental Component Summary (MCS) (6.93, P < .01). The rate of complication was low. CONCLUSION: Mild DCM is associated with significant impairment in quality of life. Surgery results in significant gains in functional status, level of disability, and quality of life.

Minimum Clinically Important Difference in SF-36 Scores for Use in Degenerative Cervical Myelopathy.

STUDY DESIGN: Post-hoc analysis of 606 patients enrolled in the AOSpine CSM-NA or CSM-I prospective, multicenter cohort studies. OBJECTIVE: The aim of this study was to determine the minimum clinically important difference (MCID) in SF-36v2 Physical Component Summary (PCS) and Mental Component Summary (MCS) scores in patients undergoing surgery for degenerative cervical myelopathy (DCM). SUMMARY OF BACKGROUND DATA: There has been a shift toward focus on patient-reported outcomes (PROs) in spine surgery. However, the numerical scores of PROs lack immediate clinical meaning. The MCID adds a dimension of interpretability to PRO scales; by defining the smallest change, a patient would consider meaningful. METHODS: The MCID of the SF-36v2 PCS and MCS were determined by distribution- and anchor-based methods comparing preoperative to 12-month scores. Distribution-based approaches included calculation of the half standard deviation and standard error of measurement (SEM). Change in Neck Disability Index (NDI) served as the anchor: "worse" (ΔNDI>7.5); "unchanged" (7.5≥ΔNDI>-7.5); "slightly improved" (-7.5≥ΔNDI>-15); and "markedly improved" (ΔNDI ≤-15). Receiver operating characteristic (ROC) analysis was performed to determine the change score for the MCID with even sensitivity and specificity to distinguish patients who were "slightly improved" versus "unchanged" on the NDI. RESULTS: The MCID for the SF-36v2 PCS and MCS were 4.6 and 6.8 by half standard deviation and 2.9 and 4.3 by SEM, respectively. By ROC analysis, the MCID was 3.9 for the SF-36v2 PCS score and 3.2 for the SF-36v2 MCS score. Using a cutoff of 4 points, the SF-36v2 PCS had a sensitivity of 72.2% and specificity of 68.1%, and MCS 61.9% and 64.6%, respectively, in separating patients who were "markedly improved" or "slightly improved" from those who were "unchanged" or "worse." CONCLUSION: We found the MCID of the SF-36v2 PCS and MCS to be 4 points. This will facilitate use of the SF-36v2 as an outcome in future studies of DCM. LEVEL OF EVIDENCE: 3.

Patient phenotypes associated with outcome following surgery for mild degenerative cervical myelopathy: a principal component regression analysis.

BACKGROUND CONTEXT: Predictors of outcome after surgery for degenerative cervical myelopathy (DCM) have been determined previously through hypothesis-driven multivariate statistical models that rely on a priori knowledge of potential confounders, exclude potentially important variables because of restrictions in model building, cannot include highly collinear variables in the same model, and ignore intrinsic correlations among variables. PURPOSE: The present study aimed to apply a data-driven approach to identify patient phenotypes that may predict outcomes after surgery for mild DCM. STUDY DESIGN: This is a principal component analysis of data from two related prospective, multicenter cohort studies. PATIENT SAMPLE: The study included patients with mild DCM, defined by a modified Japanese Orthopaedic Association score of 15-17, undergoing surgical decompression as part of the AOSpine CSM-NA or CSM-I trials. OUTCOME MEASURES: Patient outcomes were evaluated preoperatively at baseline and at 6 months, 1 year, and 2 years after surgery. Quality of life (QOL) was evaluated by the Neck Disability Index (NDI) and Short Form-36 version 2 (SF-36v2). These are both patient self-reported measures that evaluate health-related QOL, with NDI being specific to neck conditions and SF-36v2 being a generic instrument. MATERIALS AND METHODS: The analysis included 154 patients. A heterogeneous correlation matrix was created using a combination of Pearson, polyserial, and polychoric regressions among 67 variables, which then underwent eigen decomposition. Scores of significant principal components (PCs) (with eigenvalues>1) were included in multivariate logistic regression analyses for three dichotomous outcomes of interest: achievement of the minimum clinically important difference [MCID] in (1) NDI (≤-7.5), (2) SF-36v2 Physical Component Summary (PCS) score (≥5), and (3) SF-36v2 Mental Component Summary (MCS) score (≥5). RESULTS: Twenty-four significant PCs accounting for 75% of the variance in the data were identified. Two PCs were associated with achievement of the MCID in NDI. The first (PC 1) was dominated by variables related to surgical approach and number of operated levels; the second (PC 21) consisted of variables related to patient demographics, severity and etiology of DCM, comorbid status, and surgical approach. Both PC 1 and PC 21 also correlated with SF-36v2 PCS score, in addition to PC 4, which described patients' physical profile, including gender, height, and weight, as well as comorbid renal disease; PC 6, which received large loadings from variables related to cardiac disease, impaired mobility, and length of surgery and recovery; and PC 9, which harbored large contributions from features of upper limb dysfunction, cardiorespiratory disease, surgical approach, and region. In addition to PC 21, a component profiling patients' socioeconomic status and support systems and degree of physical disability (PC 24) was associated with achievement of the MCID in SF-36 MCS score. CONCLUSIONS: Through a data-driven approach, we identified several phenotypes associated with disability and physical and mental health-related QOL. Such data reduction methods may separate patient-, disease-, and treatment-related variables more accurately into clinically meaningful phenotypes that may inform patient care and recruitment into clinical trials.

Determining phosphorus release rates to runoff from selected Alberta soils using laboratory rainfall simulation.

Phosphorus losses from agricultural land can cause accelerated eutrophication of surface water bodies. This study evaluated the use of soil test phosphorus (STP) levels to predict dissolved inorganic phosphorus (DIP) concentrations in runoff water from agricultural soils using laboratory rainfall simulation. The objectives of this study were to determine (i) to what extent STP concentrations can be used as a basis to predict P losses from Alberta soils and (ii) how extended rainfall simulation run times affected DIP losses. Soil samples collected from a total of 38 field sites, widely scattered throughout the southern half of Alberta, were subjected to rainfall simulation in the laboratory. The STP concentrations were determined using Miller-Axley, Norwest, Kelowna, Modified Kelowna Mehlich-III, and distilled water extraction methods. Each rainfall simulation event lasted for at least 90 min. Runoff samples were collected in time series for the duration of each simulation, during two distinct runoff intervals: (i) for the first 30 min of continuous runoff (T30) and (ii) for 40 min during runoff equilibrium (Teq). For all the STP extractants and both runoff intervals, the relationship with DIP-flow-weighted mean concentration (FWMC) was linear and highly significant with r2 values ranging from 0.74 to 0.96. However, the slopes of the resulting regression lines were, on average, 1.85 times greater for the T30 runoff interval over those computed for the Teq interval. Thus experimental methodology greatly influenced regression parameters, suggesting that more work was needed to verify these relationships under natural conditions. In addition, with many of the r2 values greater than 0.90 there would be little, if any, benefit derived by including soil properties in regression analysis.