Posteromedial vertical capsulotomy selectively expands the intraoperative extension gap in cruciate-retaining total knee arthroplasty.

PURPOSE: Effective soft-tissue balancing procedures for expanding the extension gap (EG) are needed in cases of gap mismatch in total knee arthroplasty (TKA). A posteromedial vertical capsulotomy (PMVC) is performed to restore mobility in a knee with a flexion contracture. The purpose of this study was to evaluate the effectiveness and safety of PMVC for intraoperative gap adjustment in cruciate-retaining TKA. METHODS: A total of 120 consecutive knees undergoing cruciate-retaining TKA for varus osteoarthritis were examined. The EG and flexion gap (FG) with a trial femoral component were measured using spacer blocks before and after PMVC. PMVC was performed when the first FG was larger than the first EG by > 2 mm. RESULTS: Sixty-five knees underwent PMVC, and the mean EG significantly increased by 2.4 mm (p < 0.001). This increase was significantly larger than that of the FG by 2.0 mm (p < 0.001). The preoperative extension range of motion (ROM) was negatively correlated with the EG change after PMVC (r = - 0.39, p = 0.001). A receiver operating characteristic (ROC) curve indicated a preoperative extension ROM cut-off of -10° for predicting PMVC (sensitivity 72.3%, specificity 56.4%). No associated complications were observed during a minimum 2-year follow-up period, and there was no difference in the postoperative Knee Society Score between the PMVC and non-PMVC groups. CONCLUSION: PMVC may be a useful soft-tissue treatment for gap adjustment with a selective EG expansion in TKA, especially in cases of a limited preoperative extension of - 10° or less. LEVEL OF EVIDENCE: Therapeutic study, level III.

The distance between the femoral nerve and anterior acetabulum is significantly shorter in hip osteoarthritis than in non-osteoarthritis hip.

BACKGROUND: The appropriate position of retractors to minimize the risk of femoral nerve palsy remains uncertain. The purpose of this imaging study was to evaluate the distance between the femoral nerve (FN) and anterior acetabulum (AA) in hip osteoarthritis (OA). METHODS: Forty-one patients with unilateral hip OA underwent magnetic resonance imaging. Three measurement levels were defined and the minimum distance between the femoral nerve (FN) margin and anterior acetabulum (AA) rim was measured on axial T1-weighted images on the OA and normal sides at each level, with reference to an advanced neurography view. The cross-sectional area (CSA) of the iliopsoas muscle was also measured at each level bilaterally by three observers. Distances and CSAs were compared between the OA and normal side. Multiple regression analysis was performed to identify variables associated with the distance in OA. RESULTS: The mean minimum FN to AA distances in OA were 19.4 mm at the top of the anterior inferior iliac spine (AIIS), 24.3 mm at the bottom of the AIIS, and 21.0 mm at the tip of the greater trochanter. These distances were significantly shorter than in normal hips at the top and bottom of the AIIS, with mean differences of 1.6 and 5.8 mm, respectively (p = 0.012, p < 0.001). CSAs of the iliopsoas in OA were significantly smaller at all levels (all p < 0.001), with reductions of 10.5 to 17.9%. The CSA of the iliopsoas at the bottom of the AIIS was associated with the FN to AA distance at the same level (p = 0.026). Interobserver reliabilities for measurements were very good to perfect (intraclass correlation coefficients 0.897 to 0.966). CONCLUSIONS: To minimize the risk of femoral nerve palsy, surgeons should consider the change of the femoral nerve to anterior acetabulum distance in osteoarthritic hip surgery.

Interpretable and Lightweight 3-D Deep Learning Model for Automated ACL Diagnosis.

We propose an interpretable and lightweight 3D deep neural network model that diagnoses anterior cruciate ligament (ACL) tears from a knee MRI exam. Previous works focused primarily on achieving better diagnostic accuracy but paid less attention to practical aspects such as explainability and model size. They mainly relied on ImageNet pre-trained 2D deep neural network backbones, such as AlexNet or ResNet, which are computationally expensive. Some of them tried to interpret the models using post-inference visualization tools, such as CAM or Grad-CAM, which lack in generating accurate heatmaps. Our work addresses the two limitations by understanding the characteristics of ACL tear diagnosis. We argue that the semantic features required for classifying ACL tears are locally confined and highly homogeneous. We harness the unique characteristics of the task by incorporating: 1) attention modules and Gaussian positional encoding to reinforce the seeking of local features; 2) squeeze modules and fewer convolutional filters to reflect the homogeneity of the features. As a result, our model is interpretable: our attention modules can precisely highlight the ACL region without any location information given to them. Our model is extremely lightweight: consisting of only 43 K trainable parameters and 7.1 G of Floating-point operations per second (FLOPs), that is 225 times smaller and 91 times lesser than the previous state-of-the-art, respectively. Our model is accurate: our model outperforms the previous state-of-the-art with the average ROC-AUC of 0.983 and 0.980 on the Chiba and Stanford knee datasets, respectively.

Comparison study of bone strength of the proximal femur with and without hip osteoarthritis by computed tomography-based finite element analysis.

Proximal femoral fractures are common in elderly osteoporosis patients; however, its prevalence is clinically rare in hip fracture patients with hip osteoarthritis (OA). This study aimed to evaluate bone strength of the proximal femur with or without hip OA and proximal femoral fracture risk using computed tomography (CT)-based finite element analysis (FEA). A retrospective analysis was done on CT data of 20 patients who underwent total hip arthroplasty for unilateral hip OA. Furthermore, the fracture load between OA and contralateral sides was compared and the association between fracture load and risk factor was analyzed. The fracture load was significantly higher in the OA side than that in the contralateral side (3819.5 ± 1557.8 N vs. 3224.5 ± 943.7 N, respectively; P = 0.0405). There was no significant difference in fracture load between OA and the contralateral side in Kellgren-Lawrence (KL)-3 and KL-4 grade, but the KL-4 fracture load tends to be high (P = 0.2461 and P = 0.0527, respectively). Moreover, there was no significant association between fracture load and OA severity or age. The study findings may assist in predicting bone strength and proximal femur fracture risk. The results of this FEA study indicate the bone strength of the proximal femur was affected by the severity of the osteoarthritis.

Anatomical Implications Regarding Femoral Nerve Palsy During a Direct Anterior Approach to Total Hip Arthroplasty: A Cadaveric Study.

BACKGROUND: Femoral nerve palsy is a serious neurological complication following total hip arthroplasty (THA) via a direct anterior approach. One hypothesis is that the nerve injury is caused by malpositioning of retractors over the anterior wall of the acetabulum. The purpose of this cadaveric study was to clarify the anatomical features of the femoral nerve around the anterior acetabular rim and the potential risk of nerve injury during a direct anterior approach to THA. METHODS: We dissected 84 cadaveric hips from 44 formalin-embalmed cadavers. When the cadavers were supine, the iliopsoas muscle and the femoral nerve were exposed and the anterior joint capsule and labrum were resected. The measurement points were determined along the acetabular rim every 30°, and a reference line was drawn from the anterior superior iliac spine to the center of the acetabulum, with the intersection of the rim at 0°. The minimum distance to the femoral nerve margin was measured from 0° to 150° (6 points). Other anatomical structures were measured to determine their association with the distance of the shortest measurement points. RESULTS: The mean minimum distances to the femoral nerve were 33.2 mm at 0°, 24.4 mm at 30°, 18.4 mm at 60°, 16.6 mm at 90°, 17.9 mm at 120°, and 23.2 mm at 150°, showing that the distance at 90° was the shortest (p < 0.001). The thickness of the iliopsoas muscle and the femoral length were positively associated with the distance to the femoral nerve at 90°. CONCLUSIONS: In this cadaveric study, the femoral nerve was within 16.6 to 33.2 mm of the acetabular rim at points from 0° to 150° of a line drawn from the anterior superior iliac spine. The nerve was closest to the rim at 90°, indicating that this is an area of high risk during retractor placement. CLINICAL RELEVANCE: Retractor placement at 90° to the anterior acetabular rim should be avoided to reduce the risk of femoral nerve injury.

Predictive value of magnetic resonance imaging for multifocal osteonecrosis screening associated with glucocorticoid therapy.

Objectives: The goals of this study were to elucidate the distribution of multifocal osteonecrosis associated with glucocorticoid therapy using magnetic resonance imaging (MRI) and to establish a MRI screening method.Methods: Between 1986 and 2018, 107 patients underwent MRI screening of their hips, knees, shoulders and ankle joints (856 joints in total) after systemic glucocorticoid therapy.Results: Osteonecrosis was observed in hip (68%), knee (44%), ankle (17%) and shoulder (15%) joints. Patients with bilateral osteonecrosis in their hips were likely to have bilateral osteonecrosis in their knees, whereas patients without osteonecrosis in both hips were unlikely to have osteonecrosis in both knees (p = .0299). Osteonecrosis was never evident in the ankle or shoulder joints when a patient did not have osteonecrosis in both hip and knee joints.Conclusion: In this study, MRI - as a screening method for multifocal osteonecrosis associated with glucocorticoid therapy - showed the sites affected first are hips and knees followed by ankles and shoulders. If osteonecrosis is absent in hip and knee joints, further screening of the ankles and shoulders is unnecessary. Any osteonecrosis observed in the hip and/or the knee joints warrants a second MRI screening of the ankles and shoulders.

Intra- and interobserver reliability and agreement in three-dimensional computed tomography measurements of component positions after total knee arthroplasty.

BACKGROUND: Accurate evaluation of the postoperative position of total knee arthroplasty (TKA) components is crucial in the analysis of the association of alignments with clinical outcomes. The aim of this study was to investigate the reliability of measurements of component positions after TKA using three-dimensional computed tomography (3D-CT) reconstruction. METHODS: Two independent orthopedic surgeons (an attending surgeon and a fellow) examined 30 knees after primary TKA. The coronal, sagittal, and rotational positions of the femoral and tibial components were measured twice at an interval of six weeks on 3D-CT images reconstructed using ZedKnee software. Mean intra- and interobserver differences of measured angles were calculated, and the intra- and interobserver reliability was determined using intraclass correlation coefficients (ICCs), with agreement assessed by Bland-Altman analysis. RESULTS: The mean intraobserver difference between alignment measurements for femoral and tibial components was <2° (range 0.23-1.17°) and the mean interobserver difference was <1° (range 0.22-0.97°). The intra- and interobserver ICCs were >0.8 for all component positions. The only systematic bias found in the intra- and interobserver agreements occurred for the sagittal position of the femoral component. CONCLUSION: Three-dimensional-CT measurements of component positions after TKA showed good intra- and interobserver reliability for the femoral and tibial components in coronal, sagittal and rotational positions. The intra- and interobserver agreements were favorable for all but the sagittal position of the femur. These results suggest that 3D-CT can be used to evaluate the alignment of all TKA components except for the sagittal position of the femur.

Preoperative planned distance between the skin surface and the guide rod provides accurate posterior tibial slope in total knee arthroplasty.

BACKGROUND: Although sagittal tibial alignment in total knee arthroplasty (TKA) is important, no landmark exists to achieve reproducible slope. It is theoretically demonstrated that the preoperative planned distance between the skin surface and the rod can be a useful guide for the tibial slope in the previous imaging study. We conducted this retrospective study to confirm whether the results of the study are repeatable in an intra-operative situation. METHODS: Fifty-five consecutive TKAs using the distance from the extramedullary cutting guide rod to the skin surface as a reference guide for the tibial slope were performed and tibial component positioning was compared with 55 knees performed using the accelerometer-based portable navigation. The tibial component alignment was evaluated with a computed tomography (CT)-based three-dimensional (3D) software. RESULTS: The absolute mean deviation from the targeted slope in the proposed method was significantly smaller than the portable navigation (1.0° and 1.7°, respectively, p = 0.0025). The outlier rate beyond 3° was 0% in the proposed technique (16.4% in the portable navigation, p = 0.0014). CONCLUSIONS: The preoperative planned distance between the skin surface and the guide rod is a useful technique to provide accurate posterior tibial slope in TKA.

An accelerometer-based navigation did not improve the femoral component positioning compared to a modified conventional technique of pre-operatively planned placement of intramedullary rod in total knee arthroplasty.

INTRODUCTION: Although the most commonly used method of femoral component alignment in total knee arthroplasty (TKA) is intramedullary (IM) guides, this method demonstrated a limited degree of accuracy. Because of the femoral anterior bowing, the tip of the guide rod will impinge on the anterior cortex if a long rod is inserted. We hypothesized that the pre-operative planned insertion depth of the rod could increase the accuracy of the femoral component positioning in conventional TKA (modified conventional technique). Accelerometer-based, portable navigation device has been postulated to have better accuracy than conventional TKA in component positioning. The purpose of this study was to compare the post-operative femoral component alignment of TKA using the modified conventional technique with the accelerometer-based navigation. MATERIALS AND METHODS: Fifty-five knees underwent TKA using the modified conventional technique and femoral component positioning was compared with 55 knees performed using the accelerometer-based navigation device. The femoral component alignment was evaluated with a CT-based three-dimensional software. RESULTS: The mean absolute deviation from targeted alignment in the sagittal plane was significantly less in the modified conventional cohort than in the accelerometer-based navigation cohort (1.1° vs 2.6°, P < 0.001). In the modified conventional cohort, 96.4% had an alignment within 3° of a targeted angle in the coronal plane (vs 89.1% with the accelerometer-based navigation, P = 0.14), and 96.4% in the sagittal plane (vs 74.5% with the accelerometer-based navigation, P < 0.001). CONCLUSION: The modified conventional technique is a simple and equal to or more accurate method than the accelerometer-based navigation in positioning the femoral component in TKA at a mid-volume hospital.

Diffusion tensor imaging of the sciatic and femoral nerves in unilateral osteoarthritis of the hip and osteonecrosis of femoral head: Comparison of the affected and normal sides.

Objective: The aim was to compare the fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of the sciatic and femoral nerves in patients with unilateral osteoarthritis of the hip (OA) and osteonecrosis of the femoral head (ONFH) using diffusion tensor imaging (DTI) and to investigate the mechanism of hip pain. Methods: Forty-four patients (22 OA and 22 ONFH) underwent DTI of the sciatic and femoral nerves at the level of the hip joint and the S1 roots to visualize the tractography and quantify the FA and ADC values. Results: The tractography of the femoral and the sciatic nerves on the affected side with OA and ONFH were similar to those on the normal side. The mean FA values of the sciatic and femoral nerves, and the S1 roots were 0.542, 0.551, and 0.316 with OA, 0.568, 0.560, and 0.318 with ONFH on the affected side, and 0.559, 0.560, and 0.315 on the normal side, respectively, and did not show significant differences. The FA values of the sciatic nerve on the affected side with OA decreased with longer pain duration. Conclusion: The FA and ADC values of the sciatic and femoral nerves in patients with unilateral OA and ONFH showed no significant differences between the affected and normal sides.

Finite element analysis of the femoral diaphysis of fresh-frozen cadavers with computed tomography and mechanical testing.

BACKGROUND: The purpose of this study was to validate a diaphyseal femoral fracture model using a finite element analysis (FEA) with mechanical testing in fresh-frozen cadavers. METHODS: We used 18 intact femora (9 right and 9 left) from 9 fresh-frozen cadavers. Specimens were obtained from 5 males and 4 females with a mean age of 85.6 years. We compared a computed tomography (CT)-based FEA model to diaphyseal femoral fracture loads and stiffness obtained by three-point bending. Four material characteristic conversion equations (the Keyak, Carter, and Keller equations plus Keller's equation for the vertebra) with different shell thicknesses (0.3, 0.4, and 0.5 mm) were compared with the mechanical testing. RESULTS: The average fracture load was 4582.8 N and the mean stiffness was 942.0 N/mm from actual mechanical testing. FEA prediction using Keller's equation for the vertebra with a 0.4-mm shell thickness showed the best correlations with the fracture load (R2 = 0.76) and stiffness (R2 = 0.54). Shell thicknesses of 0.3 and 0.5 mm in Keller's equation for the vertebra also showed a strong correlation with fracture load (R2 = 0.66 for both) and stiffness (R2 = 0.50 and 0.52, respectively). There were no significant correlations with the other equations. CONCLUSION: We validated femoral diaphyseal fracture loads and stiffness using an FEA in a cadaveric study.

Transitional changes in the incidence of osteonecrosis in systemic lupus erythematosus patients: focus on immunosuppressant agents and glucocorticoids.

Objective: The purpose of this study was to investigate transitional changes in the incidence of glucocorticoid-associated osteonecrosis in SLE patients, with a focus on immunosuppressive agent and glucocorticoid consumption. Methods: We retrospectively registered 185 SLE patients with 740 joints, who were newly diagnosed and hospitalized for initial high-dose glucocorticoid therapy from 1986 to 2015. Immunosuppressive agent, glucocorticoid dose, age, sex, organ lesion at hospitalization, complement (C3, C4, CH50) and anti-DNA antibody before initial glucocorticoid therapy, the frequency of use of anticoagulant and antilipidemic drugs, and incidence of osteonecrosis were documented. Results: Based on trends in immunosuppressive agent use, 116 patients treated from 1986 to 1999, before calcineurin inhibitors were introduced, comprised the past group, and 69 patients treated from 2000 to 2015 comprised the recent group. Patient characteristics (age, sex and organ lesion at hospitalization, complement, anti-DNA antibody, the frequency of use of anticoagulant and antilipidemic drugs) were similar between groups. Glucocorticoid doses were significantly lower in the recent group than in the past group (highest daily glucocorticoid dose, 45.7 vs 59.0 mg/day, respectively; dose per weight, 0.88 vs 1.16 mg/day/kg, respectively; and cumulative dose at 3 months, 3118 vs 3985 mg). The incidence of osteonecrosis was significantly lower in the recent group than in the past group (26.4 vs 41.0%, respectively), particularly in the knee (25.4 vs 46.6%, respectively). Conclusion: The incidence of glucocorticoid-associated osteonecrosis in SLE patients decreased in association with a decrease in glucocorticoid administration after introduction of immunosuppressant agents.

Case-related factors affecting cutting errors of the proximal tibia in total knee arthroplasty assessed by computer navigation.

PURPOSE: The aim of this study was to determine factors that contribute to bone cutting errors of conventional instrumentation for tibial resection in total knee arthroplasty (TKA) as assessed by an image-free navigation system. The hypothesis is that preoperative varus alignment is a significant contributory factor to tibial bone cutting errors. METHODS: This was a prospective study of a consecutive series of 72 TKAs. The amount of the tibial first-cut errors with reference to the planned cutting plane in both coronal and sagittal planes was measured by an image-free computer navigation system. Multiple regression models were developed with the amount of tibial cutting error in the coronal and sagittal planes as dependent variables and sex, age, disease, height, body mass index, preoperative alignment, patellar height (Insall-Salvati ratio) and preoperative flexion angle as independent variables. RESULTS: Multiple regression analysis showed that sex (male gender) (R = 0.25 p = 0.047) and preoperative varus alignment (R = 0.42, p = 0.001) were positively associated with varus tibial cutting errors in the coronal plane. In the sagittal plane, none of the independent variables was significant. CONCLUSION: When performing TKA in varus deformity, careful confirmation of the bone cutting surface should be performed to avoid varus alignment. The results of this study suggest technical considerations that can help a surgeon achieve more accurate component placement. LEVEL OF EVIDENCE: IV.

Diffusion tensor imaging and tractography of the sciatic and femoral nerves in healthy volunteers at 3T.

BACKGROUND: The aim was to clarify the normal fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of the sciatic and femoral nerves at the level of the hip joint and to visualize the neural tracts with diffusion tensor imaging (DTI). METHODS: Twenty-four healthy volunteers (12 men and 12 women, age 20-29 years) underwent DTI for visualization with tractography and quantification of FA and ADC values on a 3 Tesla MRI (b value = 800 s/mm2, motion probing gradient, 11 directions, time to repeat/echo time = 9000/72.6 ms, axial slice orientation, slice thickness = 3.0 mm with no inter-slice gap, field of view = 320 × 320 mm, 96 × 192 matrix, 75 slices, number of acquisitions = 4). Regions of interest in the sciatic nerve were defined at the femoral head, the S1 root, and the midpoint levels. The femoral nerve was evaluated at 3-4 cm proximal to the femoral head level. RESULTS: The tractography of the sciatic and femoral nerves were visualized in all participants. The mean FA values of the sciatic nerve were increased distally from the S1 root level, through the midpoint, and to the femoral head level (0.314, 0.446, 0.567, p = 0.001, respectively). The mean FA values of the femoral nerve were 0.565. The mean ADC values of the sciatic nerves were significantly lower in the S1 root level than in the midpoint and the femoral head level (1.481, 1.602, 1.591 × 10-3 × 10-3 mm2/s, p = 0.001, respectively). The ADC values of the femoral nerve were 1.439 × 10-3 mm2/s. FA and ADC values showed moderate to substantial inter- and intra-observer reliability without significant differences in gender or laterality. CONCLUSION: Visualization and quantification of the sciatic and femoral nerves simultaneously around the hip joint were achieved in healthy young volunteers with DTI. Clinical application of DTI is expected to contribute to hip pain research.

Revision Total Hip Arthroplasty Using a Cementless Cup Supporter and Iliac Autograft: A Minimum of 15-Year Follow-Up.

BACKGROUND: Bone deficiency in revision total hip arthroplasty is a surgical challenge. The Murata-Chiba cup supporter (MC support ring) is an acetabular component supporter for a cementless porous-coated cup. The purpose of this study is to examine the clinical and radiographic outcomes of reconstruction of acetabular bone deficiency using iliac autografts supported by an MC support ring in a revision setting with minimum 15-year follow-up. METHODS: Fifty-nine consecutive revision total hip arthroplasties (57 patients) using the MC support ring were followed for a minimum of 15 years. Nine hips had American Academy of Orthopaedic Surgeons type II deficiency and 24 had type III defects of the acetabulum. Clinical outcomes were evaluated using the Harris hip score. Radiographic evaluation included assessment for loosening and bone graft incorporation. Kaplan-Meier survival analysis was performed. RESULTS: At a minimum 15-year follow-up (mean, 17.6 years), 32 patients (33 hips) were alive, 17 patients (18 hips) were deceased, and 8 patients (8 hips) were lost to follow-up. The mean Harris hip score improved from 44.3 to 77.2 at final follow-up. Four hips required reoperation due to deep infection (2 hips) and liner dissociation (2 hips), but no acetabular components were revised for aseptic loosening. Incorporation of the bone graft occurred in all cases. One unrevised patient had radiographic failure. Survivorship at 15 years with re-revision or radiographic failure as the end point was 90.6% (95% confidence interval, 83.0%-98.8%). CONCLUSION: The reconstruction of acetabular bone deficiency using autografts supported by an MC support ring provided satisfactory clinical and radiological results at 17.6 years postoperatively.

The rectangular flexion gap is associated with an increased knee flexion angle in a cruciate-sacrificing rotating platform mobile-bearing total knee arthroplasty.

BACKGROUND: The knee flexion angle after a total knee arthroplasty is an important indicator of clinical outcome. However, there is little appropriate information about the correlation between the ligament balancing and knee flexion angle after total knee arthroplasty. The purpose of this study was to investigate the effect of the ligamentous balance in extension and flexion on knee flexion angle one year after posterior cruciate ligament sacrificing rotating platform total knee arthroplasty. METHODS: Eighty-five total knee arthroplasties in 71 patients were investigated in this study. The postoperative knee flexion angle and the percentage of improvement in the balanced group in which the difference between varus and valgus was less than 2° and the unbalanced group in extension and the rectangular group in which the asymmetry of the flexion gap was within 2° and the trapezoidal group in flexion were compared. The factors affecting postoperative knee flexion angle were also investigated in a forced entry multiple regression analysis. RESULTS: The mean flexion angle improved significantly from 116.2° to 122.5° in the rectangular group. By contrast, in the trapezoidal group, no significant improvement was seen (from 115.5° to 117.4°). The statistically significant difference was found between the rectangular and trapezoidal group in flexion in terms of the improvement of the knee flexion angle while there was no difference between the balanced and unbalanced group in extension. The multiple regression analysis showed that the asymmetry of the flexion gap was a predictor of the postoperative knee flexion angle. CONCLUSIONS: Asymmetric flexion gap affected negatively the postoperative knee flexion angle after posterior cruciate ligament sacrificing rotating platform total knee arthroplasty. A gap balancing technique is recommended for this type of implant.

Increase of TRPV1-immunoreactivity in dorsal root ganglia neurons innervating the femur in a rat model of osteoporosis.

PURPOSE: Transient receptor potential vanilloid 1 (TRPV1) is a ligand-gated nonselective cation channel, which can be activated by capsaicin and other noxious stimuli. Recently, an association between bone pain and TRPV1 has been reported. However, the influence of osteoporosis on TRPV1 in the sensory system innervating the femur has not been reported. MATERIALS AND METHODS: TRPV1-immunoreactive (ir) in dorsal root ganglia (DRG) neurons labeled with neurotracer [Fluoro-Gold (FG)] innervating the femurs of Sprague Dawley rats were examined in control, sham, and ovariectomized (OVX) rats. We evaluated osteoporosis in the femurs and compared the proportion of TRPV1-ir DRG neurons innervating femur between the 3 groups of rats. RESULTS: OVX rats showed osteoporotic cancellous bone in the femur. FG labeled neurons were distributed from L1 to L6 DRG, but there was no significant difference in the proportion of labeled neurons between the 3 groups (p>0.05). The proportions of FG labeled TRPV1-ir DRG neurons were 1.7%, 1.7%, and 2.8% of DRG neurons innervating the femur, in control, sham-operated, and OVX rats, respectively. The proportion of TRPV1-ir neurons in DRG innervating the femur in OVX rats was significantly higher than that in control and sham-operated rats (p<0.05). CONCLUSION: Under physiological conditions, DRG neurons innervating femurs in rats contain TRPV1. Osteoporosis increases the numbers of TRPV1-ir neurons in DRG innervating osteoporotic femurs in rats. These findings suggest that TRPV1 may have a role in sensory perception of osteoporotic femurs.

Transient receptor potential vanilloid 1-immunoreactive innervation increases in fractured rat femur.

PURPOSE: Pain from vertebral or femoral neck fractures is a particularly important problem in clinical orthopaedics. Transient receptor potential vanilloid 1 (TRPV1) is a ligand-gated nonselective cation channel, and there are recent reports on an association between bone pain and TRPV1. However, an increase in TRPV1 activity has not been reported following femoral fracture. MATERIALS AND METHODS: We applied a neurotracer [Fluoro-gold (FG)] onto femur to detect dorsal root ganglia (DRGs) innervating the cortex of the femur in 30 Sprague Dawley rats. Seven days after application, a closed mid-diaphyseal fracture of the femur was performed. FG labeled TRPV1-immunoreactive (ir) DRGs innervating the femur were examined in nonfractured controls, and 3 days, 1 week, 2 weeks, and 4 weeks after fracture. We evaluated bone healing of the femur and compared the ratio of TRPV1-ir DRG neurons innervating the femur at the time points. RESULTS: Four weeks after fracture, complete bone union was observed. There was no significant difference in the ratio of FG labeled DRG neurons to total DRG neurons at each time point. The percentages of TRPV1-ir neurons in DRGs innervating the femur at 3 days and 1 week after fracture were significantly higher than those in control, 2 weeks, and 4 weeks after fracture (p<0.05). CONCLUSION: Fracture induced an increase of TRPV1-ir neurons in DRGs innervating the fractured femur within 3 days, and decreased during bone healing over 4 weeks. These findings show that TRPV1 may play a role in sensory sensation of bone fracture pain.

Vertebral compression exacerbates osteoporotic pain in an ovariectomy-induced osteoporosis rat model.

STUDY DESIGN: Basic pain study using osteoporotic rodent models. OBJECTIVE: To examine alterations in distribution of pain-related neuropeptides after compressive force on osteoporotic vertebrae and their chronic pain-related properties. SUMMARY OF BACKGROUND DATA: We previously reported significantly increased production of calcitonin gene-related peptide (CGRP), a marker of inflammatory pain, in the dorsal root ganglia (DRG) of vertebrae in osteoporosis-model ovariectomized (OVX) rats. Here, we hypothesized that longitudinal compressive force on vertebrae can affect osteoporotic pain properties, which has not been examined yet. METHODS: OVX rats were used as the osteoporosis model. Female Sprague-Dawley rats were prepared and Fluoro-Gold (FG) neurotracer was applied to the periosteal surface of the Co5 vertebra. After FG labeling, the animals were divided into 4 groups: Control, Control + compression, OVX, and OVX + compression. The Control groups were not ovariectomized. In the compression groups, K-wires were stabbed transversely through Co4 and Co6 with Co5 compressed longitudinally by rubber bands bridged between the 2. One, 2, 4, and 8 weeks after surgery, bilateral S1 to S3 DRGs were excised for immunofluorescence assays. Expression of CGRP and activating transcription factor 3, a marker of neuronal injury, were compared among the 4 groups. RESULTS: Sustained upregulation of CGRP in DRG neurons was observed after compression of the Co5 vertebra, and Co5 compression caused significant increase in CGRP production in DRG neurons, whereas a greater level of activating transcription factor 3 upregulation was observed in DRGs in OVX rats after dynamic vertebral compression 8 weeks after surgery, implying potential neuropathic pain. CONCLUSION: There was sustained upregulation of CGRP and activating transcription factor 3 in DRGs in osteoporotic model rats compared with controls, and levels were further enhanced by dynamic vertebral compression. These findings imply that dynamic compression stress on vertebrae can exacerbate osteoporotic pain by inducing both inflammatory and neuropathic pain mediators. LEVEL OF EVIDENCE: N/A.