RESUMO
INTRODUCTION: Matching into orthopaedic residency has become difficult, and the US Medical Licensing Examination Step 1 transition to pass/fail scoring has complicated the process. Advisors' ability to mentor students has decreased, and program directors may rely on Step 2 Clinical Knowledge (CK) scores in selecting which candidates to interview. This study aims to offer a method to predict Step 2 CK outcomes based on preadmission and preclinical performance. METHODS: The study investigated 486 students from a US medical school who enrolled in 2017 and 2018. Data on demographics, preadmission, and preclinical performance were collected. Before model creation, it was found that sex, Medical College Admission Test scores, Comprehensive Basic Science Examination performance, and preclinical curriculum performance produced optimal models. Multivariate ordinal logistic regression models were built to predict probabilities of four outcome levels of Step 2 CK: <235, 235 to 249, 250 to 265, and >265. Finally, nomograms were created to visualize probability calculations. RESULTS: Each model's odds ratios revealed that female sex, higher MCAT scores, and better Comprehensive Basic Science Examination and preclinical performance were associated with an increased likelihood of being in higher Step 2 CK scoring groups. Preclinical performance had a profound effect, especially for those in the top 1/3. Models were successful in assigning higher probabilities to students in higher Step 2 CK scoring groups in more than 80% of instances. Nomograms presented provide examples of how to apply these models to an individual student. DISCUSSION: This study presents a novel method for predicting probabilities of Step 2 CK outcomes that can be used to mentor students at a time point when Step 1 previously filled this role. It may assist in identifying orthopaedic hopefuls at risk of performing poorly on Step 2 CK and can foster the development of individualized guidance and mitigation strategies.
RESUMO
OBJECTIVE: Lumbar lateral interbody fusion (LLIF) allows placement of large interbody cages while preserving ligamentous structures important for stability. Multiple clinical and biomechanical studies have demonstrated the feasibility of stand-alone LLIF in single-level fusion. We sought to compare the stability of 4-level stand-alone LLIF utilizing wide (26 mm) cages with bilateral pedicle screw and rod fixation. METHODS: Eight human cadaveric specimens of L1-5 were included. Specimens were attached to a universal testing machine (MTS 30/G). Flexion, extension, and lateral bending were attained by applying a 200 N load at a rate of 2 mm/sec. Axial rotation of ± 8° of the specimen was performed at 2°/sec. Three-dimensional specimen motion was recorded using an optical motion-tracking device. Specimens were tested in 4 conditions: (1) intact, (2) bilateral pedicle screws and rods, (3) 26-mm stand-alone LLIF, (4) 26-mm LLIF with bilateral pedicle screws and rods. RESULTS: Compared to the stand-alone LLIF, bilateral pedicle screws and rods had 47% less range of motion in flexion-extension (p < 0.001), 21% less in lateral bending (p < 0.05), and 20% less in axial rotation (p = 0.1). The addition of bilateral posterior instrumentation to the stand-alone LLIF resulted in decreases of all 3 planes of motion: 61% in flexion-extension ( p < 0.001), 57% in lateral bending (p < 0.001), 22% in axial rotation (p = 0.002). CONCLUSION: Despite the biomechanical advantages associated with the lateral approach and 26 mm wide cages, stand-alone LLIF for 4-level fusion is not equivalent to pedicle screws and rods.
RESUMO
Background: Chondral defects in the knee have biomechanical differences because of defect size and location. Prior literature only compares the maximum stress experienced with large defects. Hypothesis: It was hypothesized that pressure surrounding the chondral defect would increase with size and vary in location, such that a size cutoff exists that suggests surgical intervention. Study Design: Controlled laboratory study. Methods: Isolated chondral defects from 0.09 to 1.0 cm2 were created on the medial and lateral femoral condyles of 6 human cadaveric knees. The knees were fixed to a uniaxial load frame and loaded from 0 to 600 N at full extension. Another defect was created at the point of tibiofemoral contact at 30° of flexion. Tibiofemoral contact pressures were measured. Peak contact pressure was the highest value in the area delimited within a 3-mm rim around the defect. The location of the peak contact pressure was determined. Results: At full extension, the mean maximum pressures on the medial femoral condyle ranged from 4.30 to 6.91 MPa at 0.09 and 1.0 cm2, respectively (P < .01). The location of the peak pressure was found posteromedial in defects between 0.09 and 0.25 cm2, shifting anterolaterally at sizes 0.49 and 1.0 cm2 (P < .01). The maximum pressures on the lateral femoral condyle ranged from 3.63 to 5.81 MPa at 0.09 and 1.0 cm2, respectively (P = .02). The location of the peak contact pressure point was anterolateral in defects between 0.09 and 0.25 cm2, shifting posterolaterally at 0.49 and 1.0 cm2 (P < .01). No differences in contact pressure between full extension and 30° of flexion were found for either the lateral or medial condyles. Conclusion: Full-thickness chondral defects bilaterally had a significant increase in contact pressure between defect sizes of 0.49 and 1.0 cm2. The location of the maximum contact pressures surrounding the lesion also varied with larger defects. Contact area redistribution and cartilage stress change may affect adjacent cartilage integrity. Clinical Relevance: Size cutoffs may exist earlier in the natural history of chondral defects than previously realized, suggesting a lower threshold for intervention.