Radiographic rotational profiles of the proximal and distal humerus: analysis of 46 computed tomography scans with 3-dimensional simulation.

BACKGROUND: To date, no study has investigated the radiographic rotational profiles (RRPs) of the proximal and distal humerus. However, malrotation after minimally invasive surgery for humeral fracture has been an unsolved problem. Therefore, we aimed to investigate the RRPs of the proximal and distal humerus that linearly correlate with rotational status and show significant differences as the rotational status changes. METHODS: Forty-six computed tomography scans of the humerus were 3-dimensionally reconstructed, and 5 rotational statuses (20° and 10° of internal rotation; neutral; and 10° and 20° of external rotation) were simulated. Seven candidate RRPs of the proximal humerus and 4 candidates of the distal humerus were measured for each rotational status. The overall differences and trends in the RRPs as the rotational status changed were evaluated, and multiple comparisons were performed between the RRPs for each of the 5 rotational statuses. Moreover, the correlations between the RRPs and rotational status with adjustment of retroversion were analyzed. Finally, interobserver and intraobserver reliabilities were evaluated. RESULTS: The following proximal and distal RRPs were linearly correlated with rotational status, differed significantly between the rotational statuses, and showed a relatively low prediction error and excellent interobserver and intraobserver reliabilities: the distance from the tip of the lesser tuberosity to the lateral margin of the proximal humerus (PL1) and the medial margin of the head (PL2), as well as the PL1 to PL2 ratio (PRL), in the proximal humerus; and the distance from the medial margin of the olecranon process to the medial epicondyle (DOP), the widest width of the overlapped olecranon fossa (DOF), and the distance from the lateral margin of the capitellum to the lateral epicondyle (DC) in the distal humerus. CONCLUSION: Our findings suggest that PL1, PL2, and PRL in the proximal humerus and DOP, DOF, and DC in the distal humerus are potentially useful and reproducible RRPs for restoring the intrinsic rotational alignment in humeral fractures.

Stress fracture after implant removal from the tibia reconstructed by the induced membrane technique: A case report.

Background: The induced membrane technique promotes vascularization and corticalization of the grafted bone and has become one of the mainstays in treatment of segmental bone defects. However, there are clinical concerns regarding the quality of bony consolidation using the induced membrane technique including a thin cortex formation and cortical notching after consolidation. We present the case of a tibial stress fracture in the bone reconstructed by the induced membrane technique after implant removal. Case: A 49-year-old male presented post-traumatic osteomyelitis of the right tibia and was treated with staged segmental bone resection leading to an 11 cm defect which was reconstructed using the induced membrane technique. The patient requested implant removal at 33 months after bony consolidation. Four months after implant removal, he developed acute, atraumatic leg pain due to a tibial stress fracture caused by small notching in the reconstructed tibial segment. His stress fracture treated with intramedullary nailing and later healed uneventfully. Conclusion: Caution is warranted prior to implant removal from bone reconstructed by the induced membrane technique as cortical notching may result in stress fractures.

Effect of Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2) with Hydroxyapatite Carrier in Induced Membrane Technique: A Retrospective Propensity Score-Matched Study.

OBJECTIVES: To determine the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) with hydroxyapatite (HA) carrier augmentation in managing critical-sized bone defect (CSBD) with induced membrane technique (IMT). DESIGN: Retrospective comparative study. SETTING: Academic level I trauma center. PATIENTS/PARTICIPANTS: The study included 14 patients who underwent rhBMP-2 with HA carrier (rhBMP-2/HA) augmentation in IMT for managing CSBD (BMP group). Moreover, 14 patients who underwent IMT without rhBMP-2 augmentation were matched by propensity score analysis (non-BMP group). INTERVENTION: IMT with or without rhBMP-2/HA augmentation. MAIN OUTCOME MEASUREMENT: Changes in quality and quantity measurements of grafted bone to regenerated bone using serial computed tomography. RESULTS: In the BMP and non-BMP groups, the changes in densities from grafted bone to regenerated bone were +379.63 Hounsfield unit and +248.55 Hounsfield unit (P = 0.034), changes in dense bone percentage were +37.52% and +23.31% (P = 0.027), corticalization rates under the plate were 79.70% and 39.30% (P = 0.007), changes in volume were -20.77% and -23.35% (P = 0.812), union rates were 85.71% and 78.57% (P = 0.622), numbers of patients requiring additional procedures were 4 and 3 (P = 0.663), and time to union were 316.3 and 585.45 days (P = 0.040), respectively. CONCLUSIONS: RhBMP-2/HA augmentation increases the density of regenerated bone, enhances corticalization under the plate, and shortens the time to union while managing CSBD with IMT. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Percutaneous two unilateral iliosacral S1 screw fixation for pelvic ring injuries: a retrospective review of 38 patients.

Purpose: Percutaneous iliosacral (IS) screw fixation for pelvic ring injuries is a minimally invasive technique that reduces the amount of blood loss and shortens the procedure time. Moreover, two unilateral IS S1 screws exhibit superior stability to a single IS screw and are also safer for neurological injuries than an S2 screw. Therefore, this study aimed to evaluate fixation using percutaneous two unilateral IS S1 screws for pelvic ring injuries and its subsequent clinical outcomes. Methods: We retrospectively reviewed 38 patients who underwent percutaneous two unilateral IS S1 screw fixation for pelvic ring injuries. The procedure time, blood loss, achievement of bone union, radiological outcomes (Matta and Tornetta grade), and postoperative complications were evaluated. Results: The mean procedure time, hemoglobin loss, bone union rate, and time to union were 40.1 minutes (range, 18-102 minutes), 0.6 g/dL (range, 0.3-1.0 g/dL), 100%, and 153.2 days (range, 61-327 days), respectively. The Matta and Tornetta grades were excellent, good, and fair in 24 (63.1%), 11 (28.9%), and three patients (7.9%), respectively, and the postoperative complications were S1 screw loosening, widening of the symphysis pubis (2.3 and 2.5 mm), lumbosacral plexopathy, and S1 radiculopathy in one (2.6%), two (5.3%), one (2.6%), and one patient (2.6%), respectively. However, all neurological complications recovered spontaneously. Conclusions: Percutaneous two unilateral IS S1 screw fixation was useful for treating pelvic ring injuries. In particular, it involved a short procedure time with little blood loss and also led to 100% bone union and good radiological outcomes.

Outcome of multi-staged induced membrane technique based on post-debridement cultures for the management of critical-sized bone defect following fracture-related infection.

The authors' institution utilizes multi-staged induced membrane technique protocol based on post-debridement culture in treating patients with critical-sized bone defect in lower extremity due to infected nonunion or post-traumatic osteomyelitis. This study aimed to evaluate the success rate of this limb reconstruction method and which risk factors are associated with recurrence of infection. 140 patients were treated with multi-staged induced membrane technique from 2013 to 2018 and followed up more than 24 months after bone grafting. The primary success rate of limb reconstruction was 75% with a mean follow-up of 45.3 months. The mean Lower Extremity Functional Scale in success group improved from 12.1 ± 8.5 to 56.6 ± 9.9 after the treatment. There were 35 cases of recurrence of infection at a mean of 18.5 months after bone grafting. Independent risk factors for recurrence of infection were infected free flap, surprise positive culture, deviation from our surgical protocol, and elevated ESR before final bone graft procedure. In conclusion, this study showed that multi-staged induced membrane technique protocol based on post-debridement culture resulted in 75% success rate and revealed a number of risk factors for recurrence of infection.

The difference in the corridor of the antegrade posterior column screw according to the presence of pelvic dysmorphism.

INTRODUCTION: Antegrade posterior column screw (aPCS) fixation via the anterior approach has been widely used for separated the posterior columns in acetabular fracture treatment. Although the relationship between pelvic dysmorphism and sacroiliac screws has been widely studied, no studies have reported on the clinical impact of pelvic dysmorphism on acetabular fractures. This study aimed to reveal the difference in the insertion angle and entry point of aPCS between the dysmorphic and normal pelvises. METHODS: Patients diagnosed with unilateral acetabular fractures and who underwent pelvic computed tomography scans between 2013 and 2019 in two institutes were enrolled in this study. Patients were divided into the dysmorphic and control groups according to the sacral dysmorphic score, which predicts the presence of pelvic dysmorphism, and each group enrolled 130 patients. The semitransparent 3D hemipelvis model was reconstructed using a 3D reconstruction program. The sagittal and coronal angles of a virtual cylinder that fill the safe corridor of the column screw the most were measured. The surface area of the safe corridor and distance of the optimal entry point from the anterior border of the sacroiliac joint were analyzed. The measurements were compared between the dysmorphic and control groups. RESULTS: The average sacral dysmorphic score in the normal and dysmorphic pelvis groups was 56.1 and 81.0, respectively. There were no significant differences in demographic data, including age, sex, height, weight, and body mass index, between the dysmorphic and control groups. There was a significant difference in the average sagittal insertion angle of PCs, which was 38.3° in the control group and 27.2° in the dysmorphic group (P < 0.001). The coronal insertion angles were not significantly different. The dysmorphic group presented longer straight distances (25.9 vs 24.8 mm, P = 0.026) and had a smaller aPCS surface area (685 vs 757 mm2, P < 0.001) than the control group. CONCLUSION: The present study describes a difference in the corridor of aPCS between the dysmorphic and normal pelvis. Insertion of aPCS in the dysmorphic pelvis requires a more acute angular trajectory in the sagittal plane than that in the normal pelvis.

Treatment of Critical-Sized Bone Defects Involving the Ankle Joints: Staged Tibiotalocalcaneal Arthrodesis With Induced Membrane Technique and Intramedullary Nail.

OBJECTIVES: To report the outcomes of staged tibiotalocalcaneal (TTC) arthrodesis for critical-sized bone defects involving the ankle joints. DESIGN: Retrospective review of case series. SETTING: Two academic Level 1 trauma centers. PATIENTS/PARTICIPANTS: The study included 20 patients with critical-sized (≥2 cm) segmental bone defects around the ankle joints. INTERVENTION: Staged TTC arthrodesis was performed with induced membrane technique and retrograde intramedullary nail. MAIN OUTCOME MEASUREMENTS: We investigated the radiological evaluation, including modified radiographic union scale for tibia fractures score, time to union, and leg length discrepancy, and functional outcomes using foot and ankle outcome score and American Orthopaedic Foot and Ankle Society ankle-hindfoot score. RESULTS: The average bone defect was 6.4 cm (range: 2.4-12.3). Two of the 20 (10%) patients developed recurrence of infection. Fifteen patients (75%) achieved primary healing. Three patients (15%) were treated with repeated bone grafting and additional plating. The average time to union and leg length discrepancy were 10 months (range: 5-21) and 9 mm (range: 0-31), respectively. The mean foot and ankle outcome score and American Orthopaedic Foot and Ankle Society ankle-hindfoot score were 63 (range: 52-71) and 74 (range: 64-81), respectively. CONCLUSIONS: Staged TTC arthrodesis with induced membrane technique and intramedullary nail can be an effective treatment method for critical-sized bone defects involving the ankle joints. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The impact of COVID-19 on trauma patients and orthopedic trauma operations at a single focused training center for trauma in Korea.

Purpose: The objective of this study was to determine the effects of coronavirus disease 2019 (COVID-19) on the volume of trauma patients, the number of orthopedic trauma operations, and the severity of injuries. We also investigated the correlations between social distancing and these variables. Methods: This was a retrospective review of trauma patient cases at a single focused training center for trauma in Korea from January 2017 to April 2021. The COVID-19 group included patients treated from January 1 to April 30 in 2020 and 2021, and the control group included patients treated during the same months from 2017 to 2019. The volume of trauma patients according to the level of social distancing was evaluated among patients treated from August 2, 2020 to November 23, 2020. Results: The study included 3,032 patients who presented to the emergency department with traumatic injuries from January to April 2017 to 2021. The average number of patients was 646.7 and 546.0 in the control and COVID-19 groups, respectively. The percentage of patients injured in traffic accidents (TAs) decreased from 25.0% to 18.2% (P<0.0001). The proportions of in-car TAs and pedestrian TAs also decreased from 6.7% and 10.8% to 3.5% and 6.0%, respectively (P=0.0002 and P<0.0001). The percentage of bicycle TAs increased from 2.4% to 4.0% (P=0.0128). The proportion of patients with an Injury Severity Score above 15 and the mortality rate did not change significantly. As the level of social distancing increased, the number of trauma patients and the number of trauma injuries from TAs decreased. The number of orthopedic trauma operations also depended on the social distancing level. Conclusions: The number of trauma patients presenting to the emergency department decreased during the COVID-19 period. The volume of trauma patients and orthopedic trauma operations decreased as the social distance level increased.

Combined Transfibular and Anterior Approaches Increase Union Rate and Decrease Non-Weight-Bearing Periods in Ankle Arthrodesis: Combined Approaches in Ankle Arthrodesis.

The transfibular approach is a widely used method in ankle arthrodesis. However, it is difficult to correct coronal plane deformity. Moreover, it carries a risk of nonunion and requires long periods of non-weight-bearing because of its relatively weak stability. We hypothesized that the transfibular approach combined with the anterior approach in ankle arthrodesis wound yield a higher fusion rate and shorter non-weight-bearing period. This study was performed to evaluate the clinical and radiographic results and postoperative complications in ankle arthrodesis using combined transfibular and anterior approaches in end-stage ankle arthritis. Thirty-five patients (36 ankles) with end-stage ankle arthritis were consecutively treated using ankle arthrodesis by combined transfibular and anterior approaches. The subjects were 15 men and 20 women, with a mean age of 66.5 years (46-87). Clinical results were assessed using the visual analog scale (VAS) for pain, the American Orthopaedic Foot and Ankle Society (AOFAS) scores, and the ankle osteoarthritis scale (AOS) preoperatively and at the last follow-up. Radiographic results were assessed with various radiographic parameters on ankle weight-bearing radiographs and hindfoot alignment radiographs. All clinical scores significantly improved after surgery. Union was obtained in all cases without additional surgery. Talus center migration (p = 0.001), sagittal talar migration (p < 0.001), and hindfoot alignment angle (p = 0.001) significantly improved after surgery. One partial skin necrosis, two screw penetrations of the talonavicular joint, and four anterior impingements because of the bulky anterior plate occurred after surgery. In conclusion, combined transfibular and anterior approaches could be a good method to increase the union rate and decrease the non-weight-bearing periods in ankle arthrodesis.

Comparison of sliding distance of lag screw and nonunion rate according to anteromedial cortical support in intertrochanteric fracture fixation: A systematic review and meta-analysis.

INTRODUCTION: We compared the sliding distance of the lag screw, change in neck-shaft angle (NSA), and nonunion rates according to the anteromedial cortical support on anteroposterior (AP) and lateral view radiographs post intertrochanteric fracture reduction. MATERIAL AND METHODS: In this systematic review and meta-analysis, MEDLINE, Embase, and Cochrane Library databases were searched systematically for studies published before September 26, 2020. We performed synthetic analyses of the amount of lag screw sliding, change in NSA, and incidence of nonunion following reduction of intertrochanteric fractures by extramedullary reduction (EMR), neutral reduction (NR), and intramedullary reduction (IMR). The combined data of EMR and NR comprised the non-IMR group. RESULTS: Our study enrolled eight studies, representing 1,363 patients who underwent surgery for intertrochanteric fractures. A pooled analysis showed a larger sliding distance in the IMR group than in the non-IMR group (standard mean difference [SMD] = 1.47, 95% confidence interval [CI]: 0.73-2.20; P < 0.0001 and SMD = 1.27, 95% CI: 0.56-1.99; P = 0.0005, respectively) in both AP and lateral views. The pooled mean difference of change in NSA in the IMR group was -3.11° and differed significantly from that of the non-IMR group (95% CI: -4.07 to -2.16; P < 0.0001). In the lateral view, the nonunion rate was significantly higher in the IMR group than in the non-IMR group (odds ratio [OR] = 11.61; 95% CI, 3.32-40.62; P = 0.0001). In the subgroup analysis, the NR group showed a larger sliding distance than that of the EMR group in the AP view (SMD = 0.40, 95% CI: 0.04-0.76; P = 0.03); however, the reverse was true in the lateral view (SMD = 0.68, 95% CI: 0.38-0.97; P < 0.00001). CONCLUSION: In the current meta-analysis, larger sliding distances, more varus in NSA, and higher nonunion rates were observed in the IMR group than the non-IMR group, in both AP and lateral views. However, in the comparison between EMR and NR, it was difficult to conclude which of them was the ideal reduction method because of inconsistent results.

Usefulness of the obturator hook technique for guiding the initial trajectory control in infra-acetabular screw placement.

PURPOSE: Proper placement of infra-acetabular screws is technically demanding; there is a limited safe zone for screw fixation because of the complexity of the bone anatomy around the hip joint and the vulnerability of the major neurovascular bundles in the pelvic cavity. We aimed to present the obturator hook technique as a surgical technique for infra-acetabular screw placement in acetabular and pelvic fractures and report its radiological outcomes. METHODS: Patients treated with infra-acetabular screw placement using the obturator hook technique between January 2015 and August 2020 were enrolled in this study. We collected data on demographics, surgical approach, reduction status, complications, and outcomes. The radiological outcomes of infra-acetabular screw placement based on computed tomography findings were evaluated as follows: success, articular penetration, or out of the bone. RESULTS: Thirty-five patients underwent infra-acetabular screw placement (26 men, 9 women; mean age, 55 years; range, 27-90 years). One patient underwent bilateral infra-acetabular screw placement; therefore, 36 infra-acetabular screws were inserted in all patients. An ideal placement was achieved with 27 infra-acetabular screws (27/36, 75%). Seven infra-acetabular screws (7/36, 19%) showed articular penetration, and two infra-acetabular screws (2/36, 6%) were placed outside the bone. One patient with articular penetration and mechanical symptoms of the hip joint required screw replacement. No other complications, including obturator nerve and vascular injuries, were observed. CONCLUSION: The obturator hook technique could be a favorable and individualized method for infra-acetabular screw placement in patients with acetabular and pelvic fractures. LEVEL OF EVIDENCE: IV, retrospective descriptive study.

Proximal tibia with an inserted nail can be an available donor site for harvesting cancellous bone.

INTRODUCTION: A pre-existing implant at the harvesting site might dissuade the surgeon from considering the site as available for bone harvesting. This study aimed to investigate the quantity of cancellous bone graft that can be harvested from a proximal tibia with an inserted nail and to report the clinical outcomes of this bone graft harvesting technique. HYPOTHESIS: Our hypothesis was that a certain amount of cancellous bone graft could be harvested from a proximal tibia with an inserted nail without compromising the surrounding environment and outcome of nonunion treatment. MATERIAL AND METHODS: Bone grafting from an ipsilateral proximal tibia with an inserted nail was performed in 32 patients for treating defect nonunion. The amount of harvested bone was measured using three parameters (weight, height, and volume). The effects of the proximal locking screw position on the quantity and location of bone graft harvest were analyzed. Clinical outcomes were evaluated by assessing the radiologic healing of the bone graft site and by assessing the donor site complications. RESULTS: The mean bone defect volume in the nonunion site was 31.1±18.3 (range, 10.6-87.0) cm3. The mean quantity of harvested bone from proximal tibias with an inserted nail was 21.2g, height was 3.9cm, and volume was 26.3 cm3. A positive correlation was found between the quantity of harvested bone and the level of the lateral oblique interlocking screw hole in the tibial nail. All grafted bone successfully consolidated in all cases at an average of 5.8 months postoperatively. However, joint penetration during bone harvesting occurred in one case. DISCUSSION: The bony defect, which measured about 14.3 cm3 could be filled with cancellous bone from a PT with an existing IM nail, without additional bone graft requirements. Even if an intramedullary nail exists inside the proximal tibia, harvesting cancellous bone at this site can be a viable option without serious complications. LEVEL OF EVIDENCE: IV; Retrospective descriptive study.

Multifragmentary patellar fracture has a distinct fracture pattern which makes coronal split, inferior pole, or satellite fragments.

The present study aimed to map the location and frequency of fracture lines on the coronal articular and sagittal planes in multifragmentary patellar fractures. 66 multifragmentary patellar fractures were digitally reconstructed using the 3D CT mapping technique. The coronal articular surface and midsagittal fracture maps were produced by superimposing each case over a single template. Each fracture line was classified based on the initial displacement and orientation. We evaluated the frequency and direction of the fracture line, coronal split fragment area, and satellite and inferior pole fragment presence. Coronal articular surface fracture mapping identified primary horizontal fracture lines between the middle and inferior one-third of the articular surface in 63 patients (95.4%). Secondary horizontal fracture lines running on the inferior border of the articular facet were confirmed (83.3%). Secondary vertical fracture lines creating satellite fragments were mostly located on the periphery of the bilateral facet. Midsagittal fracture mapping of primary and secondary horizontal fracture lines with the main coronal fracture line revealed a predominantly X-shaped fracture map. The consequent coronal split fragment and inferior pole fracture were combined in most cases. In conclusion, the multifragmentary patellar fracture has a distinct pattern which makes coronal split, inferior pole, or satellite fragments.

More weighted cancellous bone can be harvested from the proximal tibia with less donor site pain than anterior iliac crest corticocancellous bone harvesting: retrospective review.

BACKGROUND: Iliac crest is the most preferred autogenous bone graft harvesting donor site while it has sorts of complications like prolonged pain, hematoma, and fracture. Harvesting cancellous bone from proximal tibia is also increasingly being used because of lower complications and less donor site pain. However, there are lack of studies to compare these two donor sites in detail. Thus, we proposed to investigate the available amount of autogenous bone graft from the proximal tibia. METHODS: Fifty-one patients who underwent simultaneous bone graft harvest from the PT and the AIC to fill up the given critical sized bone defects were enrolled in this study. We prospectively collected data including the weight of the harvested bone, donor site pain using the visual analog scale (VAS) score, and complications between the two sites. RESULTS: The mean weight of cancellous bone harvested from the PT was greater than AIC (33.2g vs. 27.4g, p = 0.001). The mean VAS score was significantly lesser in the PT up to 60 days after harvesting (p < 0.001). There was persistent pain up to 90 days in four PT patients and in seven AIC patients. The major complication was reported only in AIC patients (11.8%). CONCLUSIONS: Harvesting cancellous bone from the PT is an acceptable alternative to the AIC for autogenous bone grafting owing to availability of more weighted graft bone and less donor site pain.

Efficacy of Open Debridement and Polyethylene Exchange in Strictly Selected Patients with Infection after Total Knee Arthroplasty.

Purpose: To assess the efficacy of open debridement and polyethylene exchange (ODPE) combined with proper antibiotic therapy in strictly selected patients with infection after total knee arthroplasty (TKA) and analyze factors associated with treatment failure. Materials and Methods: From January 2010 to January 2014, 25 cases that underwent ODPE under the diagnosis of infection within four weeks after TKA or acute hematogenous infection within five days of symptom onset were reviewed in this study. Results: Treatment was successful in 22 out of 25 cases (88.0%). Factors associated with failure were accompanying infection (periprosthetic infection in the ipsilateral foot, cervical parotid abscess, and masticator space abscess) and diagnosis of rheumatoid arthritis (RA) before TKA. Resistant bacteria did not entail a risk. On clinical results, the mean postoperative Lysholm score and Korean Knee score were 81.4 and 79.4, respectively, the knee range of motion was 115.4°±12.9°, and duration of hospitalization was 32.3±8.4 days. On radiographic results, 3.47±1.56 mm joint line elevation and a valgus change of 0.61°±2.35° in knee alignment were observed. Conclusions: ODPE combined with appropriate antibiotics therapy could be a useful treatment method for infection after TKA if the procedure is performed within a symptom duration of five days or less in the absence of accompanying infection in patients whose indication for TKA was not RA.

Significance of Coronal Proset Magnetic Resonance Imaging to Detect Hidden Zone of the Mid-Zone Stenosis in the Lumbar Spine and Morphometric Analysis of the Mid-Zone Stenosis.

STUDY DESIGN: Retrospective exploratory imaging study. PURPOSE: To investigate the significance of the coronal magnetic resonance imaging (MRI) using Proset technique to detect the hidden zone in patients with mid-zone stenosis by comparing with conventional axial and sagittal MRI and to explore the morphologic characteristic patterns of the mid-zone stenosis. OVERVIEW OF LITERATURE: Despite advancements in diagnostic modalities such as computed tomography and MRI, stenotic lesions under the pedicle and pars interarticularis, also called the mid-zone, are still difficult to definitely detect with the conventional axial and sagittal MRI due to its inherited anatomical peculiarity. METHODS: Of 180 patients scheduled to undergo selective nerve root block, 20 patients with mid-zone stenosis were analyzed using MRI. Characteristic group patterns were also explored morphologically by comparing MRI views of each group after verifying statistical differences between them. Hierarchical cluster analysis was performed to classify morphological characteristic groups based on three-dimensional radiologic grade for stenosis at all three zones. RESULTS: At the mid-zone, the stenosis of grade 2 or more was found in 14 cases in the coronal image,13 cases in the sagittal image, and 9 cases in the axial image (p<0.05). Especially, mid-zone stenosis was not detected in six of 20 cases at the axial images. At the entrance and exit-zone, coronal image was also associated with more accurate detection of hidden zone compared to other views such as axial and sagittal images. After repeated statistical verification, the morphological patterns of hidden zone were classified into 5 groups: 6 cases in group I; 1 case in group II; 4 cases in group III; 7 cases in group IV; and 2 cases in group V. CONCLUSIONS: Coronal MRI using the Proset technique more accurately detected hidden zone of the mid-zone stenosis compared to conventional axial and sagittal images.