How Accurate are Anatomical Surface Topography Parameters in Indicating the Presence of a Scoliosis?

STUDY DESIGN: Retrospective analysis of a longitudinal cohort. OBJECTIVE: To identify the presence of a scoliosis from surface data. SUMMARY OF BACKGROUND DATA: Identifying AIS can be difficult. Screening is not universal for reasons including high false positive and negative rates. These difficulties can lead to some adolescents missing out on bracing. METHODS: Logistic regression analysis of ISIS2 surface topography images only was performed. The x,y positions of the shoulders (Sh), axillae (Ax), waist (Waist) and the x,y,z positions of the most prominent points over the posterior torso (Scap) were used for the thoracic, thoracolumbar / lumbar and whole spine. The models were used to identify the presence of a 20° or larger scoliosis. Differences in the position of the landmarks were analysed comparing left and right, with the suffix 'Ht' representing a difference in the y coordinate,'Off' the x coordinate and 'Depth', the z coordinate. Model accuracy was assessed as both percentages and ROC curves with the coefficients as odds ratios. RESULTS: There were 1283 images (1015 females and 268 males) all with a diagnosis of AIS. The models identified a scoliosis in the thoracic spine with an 83% accuracy (AUC 0.91), thoracolumbar / lumbar spine 74% accuracy (AUC 0.76) and whole spine 80% accuracy (AUC 0.88). Significant parameters were AxDiffHt, AxDiffOff, WaistDiffHt, ScapDiffOff and ScapDiffHt for the thoracic curves, AxDiffHt, AxDiffOff, WaistDiffHt for the thoracolumbar / lumbar curves and AxDiffHt, AxDiffOff, WaistDiffHt and ScapDiffHt for the whole spine. CONCLUSIONS: The use of fixed anatomical points around the torso, analysed using logistic regression, has a high accuracy for identifying curves in the thoracic, thoracolumbar / lumbar and whole spines. Whilst coming from surface topography images, the results raise the future use of digital photography as a tool for the identification of a small scoliosis without using other imaging techniques.

The relationship between minor coronal asymmetry of the spine and measures of spinal sagittal shape in adolescents without visible scoliosis.

The purpose of this work is to identify what features of overall spinal sagittal shape are associated with coronal asymmetry in those without scoliosis. Using a longitudinal analysis of Integrated Shape Imaging System 2 (ISIS2) surface topography images of those without scoliosis, measures of coronal asymmetry, along with measures of spinal sagittal shape (kyphosis, lordosis and sagittal imbalance, which is a measure of the position of the top of the thoracic spine relative to the sacrum) were analysed using linear mixed effect models (LMEM), which is a method of analysing the components of a complex model (such as that describing overall spinal shape), to ascertain the relative relationships between the parameters. Data was also analysed when subdivided for the anatomical level of coronal asymmetry (thoracic or thoracolumbar/lumbar pattern). There were 784 measures from 196 children. Kyphosis had little effect on coronal asymmetry for males and females, lordosis increased with coronal asymmetry in females only and sagittal imbalance increased with coronal asymmetry in males only. The results of the LMEM modelling were that the parameters related to coronal asymmetry were lordosis and sagittal imbalance. In thoracic coronal asymmetry, whilst lordosis was predominant, kyphosis played more of a role. In thoracolumbar/lumbar coronal asymmetry, lordosis and sagittal imbalance were the larger coefficients. Coronal asymmetry of the spine in those without scoliosis is related to features of spinal sagittal shape, particularly lordosis and sagittal imbalance. This knowledge adds to the understanding of the aetiology of adolescent idiopathic scoliosis.

The anatomical growth of the thoracic cage in adolescents with specific reference to axial growth comparing the right and left hemithorax.

This study has demonstrated the changing volume of both the anterior and posterior thorax in normal adolescents (without spinal or thoracic deformity), differentiating for both sex and age, to further understand how the thorax grows, along with the differences in growth between the anterior and posterior thorax. The thorax was measured on axial CT slices at every vertebral level from T3 to T12 in a series of scans previous taken for routine clinical care. Measurements taken were the anteroposterior thoracic distance and the area of the anterior and posterior rib prominences on either side of the thorax. Data was analyzed per vertebral level, differentiating for age and sex. There were 486 CT scans analyzed (257 males and 229 females) between the ages of 8 and 18 years. The analysis identified that for the anterior thorax, there are three phases of growth with an initial slow increase in volume, followed by a stabilization of little growth, followed by another phase of a more rapid increase in volume. For the posterior thorax, there was a gradual increase in area with increasing age. This study demonstrates that the shape of the thorax is age and sex dependent, with males having both a greater width and depth of thorax compared to females. Of particular note is the difference in patterns of growth between the anterior and posterior thorax. This information will add to the understanding of normal growth, which will aid in the management of conditions where that growth is disturbed.

The kyphosis-lordosis difference parameter and its utility in understanding the pathogenesis of adolescent idiopathic scoliosis.

OBJECTIVE: The relationship of sagittal spinal shape in the pathogenesis of adolescent idiopathic scoliosis (AIS) is recognised. What is not clear is the relationship between the sagittal shape of those without scoliosis and the potential development of AIS, including the greater prevalence in females. The use of a new parameter, the kyphosis-lordosis (KL) difference, was developed to explore this further. RESULTS: The KL difference was calculated for 117 males and 79 females over seven years with 831 measures made. For females, the KL difference, between the ages of 9 and 12 ½ years, decreases from 5° to nearly 0° until starting to climb again from the age of 14 years, back to 5° by the age of 16 ½ years. For males, there is a gradual decline from 9° at age 9 years to 5° at age 17 years. Both age and sex were statistically significant in the development of the parameter. When comparing to previously published data around the true, de-rotated, sagittal shape of the scoliotic spine, the KL difference has utility in explaining the female predominance in the prevalence of AIS. This adds to the weight of evidence behind understanding why AIS develops.

Statistical modelling of how the sagittal alignment of the cervical spine is affected by adolescent idiopathic scoliosis and how scoliosis surgery changes that.

The relationship between the sagittal shape of the cervical spine and that of the thoracolumbar spine is established in the normal spine. Adolescent idiopathic scoliosis (AIS) is recognised as a change in the shape of the spine in both the coronal and sagittal planes. The effects of AIS on the alignment of the cervical spine, including the effects of surgery, has been less well studied. The objective of this study was to identify, using regression analysis, the significant relationships between the alignment of the thoracolumbar spine, in both the coronal and sagittal planes, and the sagittal alignment of the cervical spine in AIS. This study used coronal and sagittal radiographic measures from a group with AIS, both pre and post-operatively, which were analysed using multiple linear regression methods to identify significant parameters that explain the sagittal shape of the cervical spine. There were 51 pairs of pre and post-operative radiographs analysed, 40 of which were Lenke 1 curves and 11 Lenke 3 curves. Posterior spinal fusion was performed for all. The significant parameters pre-operatively were T1 slope, thoracic kyphosis, lumbar lordosis and SVA with an R2 value of 78%. Post-operatively, the significant parameters were T1 slope, thoracic kyphosis, lumbar lordosis and thoracolumbar scoliosis with an R2 of 63%. The sagittal alignment of the cervical spine in AIS is related to the shape of key parameters in the rest of the spine. Changes in the cervical sagittal shape occur to compensate for changes in shape to the rest of the spine that occur as a consequence of surgery. This has implications for the understanding of how the compensatory mechanisms of the spine are used to maintain a horizontal gaze, along with prediction of the effects of surgery on the shape of the spine.

The use of statistical modelling to identify important parameters for the shape of the torso following surgery for adolescent idiopathic scoliosis.

The surgical strategy in adolescent idiopathic scoliosis (AIS) aims to recreate the symmetry of the torso. This requires the minimisation of both the size of the scoliosis and the angulation between the sides of the torso, along with the recreation of a normal thoracic kyphosis. This study uses predictive modelling to identify the significance of the value of the pre-operative parameters, and the change in the magnitude of the parameters as a result of an operation on the shape of the torso using the 'most prominent points'; two areas of maximum prominence on either side of the spine with x, y and z coordinates. The pre-operative values, and the change in magnitude between the pre and post-operative values, for scoliosis, kyphosis and skin angulation from a group of Lenke 1 convex to the right AIS were analysed with measures collected using Integrated Spine Imaging System 2 surface topography and compared with those without visible spinal deformity. The models best explained the z coordinate and least well explained the x coordinate, although there was a contribution to all of the models that remained unexplained. The parameters that affected the position of the coordinates in the model differed between the models. This confirms that surgically altering the shape of the spine and torso whilst correcting an AIS does not lead to a symmetrical torso. There are as yet, undefined factors which contribute to the shape of the torso and which if identified and corrected surgically would lead to greater symmetry post-operatively.

The resting coronal and sagittal stance position of the torso in adolescents with and without spinal deformity.

The purpose of this work is to identify the resting stance of the torso, defined as the position of the C7 vertebral body relative to the sacrum in a 'birds eye view', as the coronal and sagittal offset, in those without spinal deformity, those with pre and post-operative AIS, and those with Scheuermann's kyphosis (SK). Using ISIS2 surface topography, the coronal and sagittal offset were measured in a prospective manner in all groups. With bivariate ellipses, a mean and 95% confidence ellipse of the data was developed. Statistical analyses was performed to examine the distribution of the data from the groups. A graphical representation of the data was developed. There were 829 without spinal deformity, 289 in both the pre and post-operative with AIS and 59 with SK. The results showed that the mean coronal offset for all groups was between 2 and 6 mm and the sagittal offset was 12 and 26 mm. Statistically significance was seen for both measures between the non-scoliotic and both AIS groups, along with the pre-operative AIS coronal offset and post-operative AIS sagittal offset and the SK measures. However, all mean values were within the 95% confidence ellipse for all of the groups. Regardless of the size or type of spinal deformity, the position of the C7 vertebral body and sacrum remain within the 95% confidence ellipse of that seen in those without spinal deformity. This work defines the Minimally Clinically Important Difference for all of the groups.

A cluster analysis describing spine and torso shape in Lenke type 1 adolescent idiopathic scoliosis.

PURPOSE: The purpose of this work is to identify the variability and subtypes of the combined shape of the spine and torso in Lenke type 1 adolescent idiopathic scoliosis (AIS). METHODS: Using ISIS2 surface topography, measures of coronal deformity, kyphosis and skin angulation (as a measure of torso asymmetry) in a series of children with Lenke 1 convex to the right AIS were analyzed using k-means clustering techniques to describe the combined variability of shape in the spine and torso. Following this, a k-nearest neighbor algorithm was used to measure the ability to automatically identify the correct cluster for any particular datum. RESULTS: There were 1399 ISIS2 images from 691 individuals available for analysis. There were 5 clusters identified in the data representing the variability of the 3 measured parameters which included mild, moderate and marked coronal deformity, mild, moderate and marked asymmetry alongside normal and hypokyphosis. The k-nearest neighbor identification of the correct cluster had an accuracy of 93%. CONCLUSION: These clusters represent a new description of Lenke 1 AIS that comprises both coronal and sagittal measures of the spine combined with a measure of torso asymmetry. Automated identification of the clusters is accurate. The ability to identify subtypes of deformity, based on parameters that affect both the spine and the torso in AIS, leads to as better understanding of the totality of the deformity seen.

The variability in location of the most prominent points on the posterior torso of those without abnormal surface topography, those with Adolescent Idiopathic Scoliosis and those with Scheuermann's Kyphosis: a seven year longitudinal analysis.

The correction of adolescent scoliosis involves the recreation of torso symmetry. A symmetrical torso has equivalent areas of shape on either side of the midline. The posterior torso has two areas of prominence, known as the 'most prominent points' on either side of the midline which can be used as reference points to measure symmetry of the posterior torso. This study used the three-dimensional (3D) coordinates of the most prominent points, measured using ISIS2 surface topography and standardised by torso size, in children without abnormal surface topography, with adolescent idiopathic scoliosis (AIS) (right thoracic curves) and with Scheuermann's kyphosis (SK). The purpose was to demonstrate the variability of the position of the points in these three groups. The variability of the 3D coordinates was calculated for each group (mean, standard deviation and range in millimetres) and the standardised data were illustrated using 3D 95% confidence interval ellipsoids. In those without deformity, the position of the left and right point was mirrored with little difference. The AIS group showed a difference between the left and right points, with the right becoming further from the midline and more prominent than the left but with the left becoming more superior than the right. For the SK cohort, both left and right points moved inwards towards the midline and became more prominent. Linear mixed effect modelling was used to examine the contribution of age, kyphosis and scoliosis to the position of the most prominent points. In the cohort without abnormal surface topography, the x parameter increases with the covariates of age and kyphosis, with the covariate of age likely reflecting torso growth. The left side becomes more prominent and inferior compared to the right. In the AIS cohort, age follows the cohort without abnormal surface topography. This is added to by the scoliosis which is observed to make the right side more lateral, less inferior and more prominent, whereas the left becomes more medial, less inferior and less prominent. Kyphosis in the AIS cohort leads to the right point becoming more lateral, less inferior and less prominent whereas in the left becomes more lateral, more inferior and more prominent. In the SK cohort, the effects of the covariates of age and kyphosis are not clear reflecting the small number of cases with more than one surface topography image over time.

The relationship between measures of spinal deformity and measures of thoracic trunk rotation.

BACKGROUND: Adolescent idiopathic scoliosis (AIS) is associated with both asymmetry of the torso (rib hump) and vertebral body rotation (VBR). Current surgical techniques aim to reduce the VBR and rib hump. However, it is not clear how the vertebral rotation and thoracic asymmetry are linked. METHODS: A retrospective cohort study was performed in which all adolescent patients with a diagnosis of AIS (Lenke curve type one to four only), a minimum 2-year follow up and a complete data set of radiographs, Integrated Shape Imaging System 2 (ISIS2) surface topography and axial imaging within a 6-week period were included. The Cobb angle was obtained from the radiograph, the maximum VBR was measured from the axial imaging using the Aaro and Dahlborn technique and the largest maximum skin angle (MSA) was taken from the ISIS2 topography. MSA is the ISIS2 parameter and is similar in nature to a scoliometer. RESULTS: From the surface topography database of AIS, 51 met the inclusion criteria. There were 6 males and 45 females with a mean age of 14.6 years (SD 1.4, range, 11.2 to 17.7). The mean Cobb angle was 54.4° (SD 13.8°, range, 29° to 92°). Mean MSA was 11.7° (SD 4.0°, range, 4° to 23°). Mean VBR was 14.3° (SD 4.3°, range, 8° to 24°). Through linear regression techniques, the relationships between Cobb angle, MSA and VBR were examined. The R2 between Cobb angle and MSA was 9%, between Cobb angle and VBR was 23% and between MSA and VBR was 16%. A multiple regression analysis did not improve these results. CONCLUSIONS: Whilst AIS features both VBR and torso asymmetry, they are poorly related to each other. This may help to explain why surgical de-rotation of the spine does not fully address the rib hump as other factors, yet to be defined, must be involved.

The effectiveness of blood metal ions in identifying bilateral metal-on-metal total hip arthroplasty patients at risk of adverse reactions to metal debris.

We investigated whether blood metal ions could effectively identify bilateral metal-on-metal total hip arthroplasty (THA) patients at risk of adverse reactions to metal debris (ARMD). Whole blood metal ions were sampled in 50 patients with bilateral 36mm Corail-Pinnacle THAs. Patients were divided into ARMD (n=10) and non-ARMD groups (n=40), with optimal ion thresholds for identifying ARMD determined using receiver operating characteristic analysis. Maximum cobalt or chromium produced the highest area under the curve (71.8%). The optimal ion threshold for distinguishing between patients with and without ARMD was 4.0µg/l (90.0%=sensitivity, 65.0%=specificity, 39.1%=positive predictive value, 96.3%=negative predictive value). Fixed regulatory authority thresholds missed more patients with ARMD (10%-12% missed) compared to our threshold (2% missed). Bilateral THA patients with blood metal ions below our threshold were at low-risk of ARMD. Compared to currently recommended fixed authority thresholds, our threshold appears preferable for managing patients with these particular implants.

The Development of Kyphosis and Lordosis in the Growing Spine.

STUDY DESIGN: A longitudinal cohort study. OBJECTIVE: The aim of this study was to do the analysis of the development of kyphosis and lordosis in the growing spine. SUMMARY OF BACKGROUND DATA: Previous studies have measured kyphosis and lordosis in different ways with differing techniques. None of the previous literature has a truly longitudinal design and there is disagreement as to whether there exists a difference between the development of kyphosis and lordosis between males and females. METHODS: Repeated measures using Integrated Shape Imaging System Integrated Shape Imaging System 2 surface topography over 5 years of a group of children aged 5 to 16 years without spinal deformity. Longitudinal analysis was performed using linear mixed effects modeling. RESULTS: There were 638 measures in 194 children. Both kyphosis and lordosis increased with age in both males and females (P < 0.001 for kyphosis and P = 0.002 for lordosis). There was no statistical difference in the development of kyphosis between males and females (P = 0.149). However, there was a significant difference in lordosis between males and females (P < 0.001) with female lordosis larger than that seen in males. Kyphosis and lordosis increased in a nonlinear fashion with age. CONCLUSION: Kyphosis and lordosis increase as children age. Between males and females there is no difference in the increase in the size of kyphosis, but there is difference in the size of lordosis with females having greater lordosis versus males at the same age. LEVEL OF EVIDENCE: 2.

Do the SRS-22 self-image and mental health domain scores reflect the degree of asymmetry of the back in adolescent idiopathic scoliosis?

BACKGROUND: Patient-reported outcomes are becoming increasingly recognised in the management of patients with adolescent idiopathic scoliosis (AIS). Integrated Shape Imaging System 2 (ISIS2) surface topography is a validated tool to assess AIS. Previous studies have failed to demonstrate strong correlations between AIS and patient-reported outcomes highlighting the need for additional objective surface parameters to define the deformities associated with AIS. The aim of this study was to examine whether the Scoliosis Research Society-22 (SRS-22) outcome questionnaire reflects the degree of measurable external asymmetry of the back in AIS and thus is a measure of patient outcome for external appearance. METHODS: A total of 102 pre-operative AIS patients were identified retrospectively. Objective parameters were measured using ISIS2 surface topography. The associations between these parameters and the self-image and mental health domains of the SRS-22 questionnaire were investigated using correlation coefficients. RESULTS: All correlations between the parameters of asymmetry and SRS-22 self-image score were of weak strength. Similarly, all correlations between the parameters of asymmetry and SRS-22 mental health score were of weak strength. CONCLUSION: The SRS-22 mental health and self-image domains correlate poorly with external measures of deformity. This demonstrates that the assessment of mental health and self-image by the SRS-22 has little to do with external torso shape. Whilst the SRS-22 assesses the patient as a whole, it provides little information about objective measures of deformity over which a surgeon has control.

The effects of scoliosis and subsequent surgery on the shape of the torso.

BACKGROUND: Adolescent idiopathic scoliosis (AIS) causes asymmetry of the torso, and this is often the primary concern of patients. Surgery aims to minimise the visual asymmetry. It is not clear how scoliosis makes the torso asymmetric or how scoliosis surgery changes that asymmetry when compared to the distribution of asymmetries seen in a non-scoliotic group of normal controls. METHODS: Surface topography images were captured for a group with AIS both pre-operatively and post-operatively. Identifiable points were compared between the images to identify the effects of AIS on the shape of the torso by looking at the relative heights and distances from the midline of the shoulders, axillae and waist in a two-dimensional coronal view. This was then compared to a previously reported group of normal non-scoliotic children to analyse whether surgery recreated normality. RESULTS: There were 172 pairs of images with 164 females and 8 males, mean age at pre-operative scan of 13.7 years. The normal group was 642 images (237 females and 405 males) from 116 males and 79 females, mean age of 12.5 years.The curve patterns seen in the scoliotic group matched the patterns of a main thoracic curve (n = 146) and main thoracolumbar curve (n = 26). The asymmetries seen in both shoulders, axillae and waist were different between the two different types of curve. Across both groups, the shoulder asymmetry was less than that of the corresponding axillae.There was a statistically significant reduction in all asymmetries following surgery in the main thoracic group (p < 0.001). This was not seen in the main thoracolumbar group, thought to be due to the small sample size. In the main thoracic group, there were statistically significant differences in the asymmetries between the post-operative and normal groups in the shoulders and axillae (p < 0.001) but not the waist. CONCLUSIONS: This paper demonstrates quantitatively the range of asymmetries seen in the AIS torso and the degree to which surgery alters them. Surgery does not recreate normality but does cause a statistically significant change in torso shape towards that seen in a non-scoliotic group.

What is the variability in shoulder, axillae and waist position in a group of adolescents?

The clinical assessment of scoliosis is based on the recognition of asymmetry. It is not clear what the degree of asymmetry is in a population without scoliosis, which could make the differentiation between abnormal and normal uncertain. This study defines the range of normality in certain parameters of torso shape that are also associated with the clinical assessment of scoliosis. This was done by analysing the surface topography of a group of 195 children serially measured over a 5-year period. The analysis considered both the spinal curvature and the relative position of shoulders, axillae and waist on each side. The bivariate relationships were examined using 95% confidence interval data ellipses. Our results showed that a degree of spinal curvature was seen, either as a main thoracic or main thoracolumbar curve. The distribution of the data about a mean point is illustrated by 95% confidence interval (CI) data ellipses with shoulder, axilla and waist data plotted against spinal curvature. The mean values were close to zero (exact symmetry) for all of the measured parameters, with the ellipses showing little differences in the distributions. We conclude that mild asymmetry of the measured torso parameters is normal. These results define what is normal and beyond what point asymmetry becomes abnormal. This information is of use for those managing and counselling patients with scoliosis both before and after surgery.

Erratum to: The use of growth standards and corrective formulae to calculate the height loss caused by idiopathic scoliosis.

[This corrects the article DOI: 10.1186/s13013-016-0068-9.].

The use of growth standards and corrective formulae to calculate the height loss caused by idiopathic scoliosis.

BACKGROUND: Loss of trunk height caused by scoliosis has been previously assessed using different mathematical formulae. However, these are of differing algebraic construction and will give a range of values for the same size of scoliosis curve. As such, the following study attempted to determine the most valid published formulae for calculating height loss caused by idiopathic scoliosis based on reported growth charts. METHODS: The height and sitting height for a group with idiopathic scoliosis were measured. These were plotted on published growth standards. The size of the coronal curves and the thoracic kyphosis was measured. Height was corrected for the size of the scoliosis using the formulae and replotted on the growth standards. The data spread on the standard was analysed for significant differences between the median and the 5th or 95th centile, and between data outside the 5th and 95th centile. RESULTS: The sitting to standing height ratio growth standard was used in the analysis as it minimised errors across the different growth standards, given that these standards come from different original populations. In the female group significant differences in the data spread were seen using the formulae of Bjure, Ylikoski and Hwang. Non-significant results were seen for the Kono and Stokes formulae. All formulae caused no significant differences in data spread across the growth standard in the males group. CONCLUSIONS: When assessing against growth standards, the formulae of Kono and Stokes are the most valid at determining height loss caused by idiopathic scoliosis.

The measurement of the normal thorax using the Haller index methodology at multiple vertebral levels.

The Haller index is a ratio of thoracic width and height, measured from an axial CT image and used to describe the internal dimensions of the thoracic cage. Although the Haller index for a normal thorax has been established (Haller et al. 1987; Daunt et al. 2004), this is only at one undefined vertebral level in the thorax. What is not clear is how the Haller index describes the thorax at every vertebral level in the absence of sternal deformity, or how this is affected by age. This paper documents the shape of the thorax using the Haller index calculated from the thoracic width and height at all vertebral levels of the thorax between 8 and 18 years of age. The Haller Index changes with vertebral level, with the largest ratio seen in the most cranial levels of the thorax. Increasing age alters the shape of the thorax, with the most cranial vertebral levels having a greater Haller index over the mid thorax, which does not change. A slight increase is seen in the more caudal vertebral levels. These data highlight that a 'one size fits all' rule for chest width and depth ratio at all ages and all thoracic levels is not appropriate. The normal range for width to height ratio should be based on a patient's age and vertebral level.

The Effectiveness of Blood Metal Ions in Identifying Patients with Unilateral Birmingham Hip Resurfacing and Corail-Pinnacle Metal-on-Metal Hip Implants at Risk of Adverse Reactions to Metal Debris.

BACKGROUND: We investigated whether blood metal ions could effectively identify patients with metal-on-metal hip implants with two common designs (Birmingham Hip Resurfacing [BHR] and Corail-Pinnacle) who were at risk of adverse reactions to metal debris. METHODS: This single-center, prospective study involved 598 patients with unilateral hip implants (309 patients with the BHR implant and 289 patients with the Corail-Pinnacle implant) undergoing whole blood metal ion sampling at a mean time of 6.9 years. Patients were classified into two groups, one that had adverse reactions to metal debris (those who had to undergo revision for adverse reactions to metal debris or those with adverse reactions to metal debris on imaging; n = 46) and one that did not (n = 552). Three metal ion parameters (cobalt, chromium, and cobalt-chromium ratio) were compared between groups. Optimal metal ion thresholds for identifying patients with adverse reactions to metal debris were determined using receiver operating characteristic analysis. RESULTS: All ion parameters were significantly higher (p < 0.0001) in the patients who had adverse reactions to metal debris compared with those who did not. Cobalt maximized the area under the curve for patients with the BHR implant (90.5%) and those with the Corail-Pinnacle implant (79.6%). For patients with the BHR implant, the area under the curve for cobalt was significantly greater than that for the cobalt-chromium ratio (p = 0.0005), but it was not significantly greater than that for chromium (p = 0.8483). For the patients with the Corail-Pinnacle implant, the area under the curve for cobalt was significantly greater than that for chromium (p = 0.0004), but it was similar to that for the cobalt-chromium ratio (p = 0.8139). Optimal blood metal ion thresholds for identifying adverse reactions to metal debris varied between the two different implants. When using cobalt, the optimal threshold for identifying adverse reactions to metal debris was 2.15 µg/L for the BHR group and 3.57 µg/L for the Corail-Pinnacle group. These thresholds had good sensitivities (88.5% for the BHR group and 80.0% for the Corail-Pinnacle group) and specificities (84.5% for the BHR group and 76.2% for the Corail-Pinnacle group), high negative predictive values (98.8% for the BHR group and 98.1% for the Corail-Pinnacle group), and low positive predictive values (34.3% for the BHR group and 20.0% for the Corail-Pinnacle group). The authority thresholds proposed by the United States (3 µg/L and 10 µg/L) and the United Kingdom (7 µg/L) missed more patients with adverse reactions to metal debris at 2.0% to 4.7% (twelve to twenty-eight patients) compared with our implant-specific thresholds at 1.2% (seven patients missed). CONCLUSIONS: Patients who underwent metal-on-metal hip arthroplasty performed with unilateral BHR or Corail-Pinnacle implants and who had blood metal ions below our implant-specific thresholds were at low risk of adverse reactions to metal debris. These thresholds could be used to rationalize follow-up resources in asymptomatic patients. Analysis of cobalt alone is acceptable. Implant-specific thresholds were more effective than currently recommended fixed authority thresholds for identifying patients at risk of adverse reactions to metal debris requiring further investigation. LEVEL OF EVIDENCE: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Mid-term results for hip resurfacing in patients under 30 years old with childhood hip disorders.

The aim of our study was to assess survivorship and function in young patients with hip resurfacing for degenerative arthritis secondary to childhood hip diseases. Data was collected retrospectively using the institutional database and patient notes. Between 1999 and 2012, there were 156 hip resurfacings performed in 143 patients (82 females, 73 males). Mean age at the time of surgery was 21.4 years (12.3 to 30.0). The main indications for surgery included; DDH, AVN, Perthes' and SUFE. Median follow-up was 4.1 years (1.0 to 13.2). Median Oxford scores improved from 54.2 pre-op to 18.8 post-op at a minimum of 2 years follow-up. There were 14 failures. Median head size was 46 mm (45 mm in the failures) For the failures, median cup inclination was 44.4 degrees and anteversion 7.6 degrees. We report the largest single surgeon series of resurfacing hip arthroplasty in the under 30's for childhood hip disorders. 90% 5-year survivorship and good functional outcome can be achieved.