Use of 3D Printed Models to Determine Accurate Bone Cuts during a Periacetabular Osteotomy for Developmental Hip Dysplasia

The periacetabular osteotomy (PAO) is a powerful tool to delay the progression of hip arthritis by reorienting the acetabulum. This study aimed to use three-dimensional (3D)-printed models of the pelvis, reconstructed from the computed tomography (CT) scans of patients, to model how the level of dysplasia and its location ilium osteotomy affect radiographic outcomes following PAO. This pilot study aims to determine if preoperative 3D printing/planning can assist in predicting radiographic outcomes. We performed a retrospective review of five patients with differing levels of hip dysplasia for whom we had obtained CT scans before PAO surgery. For each patient, we printed two pelvis models that would undergo standardized cuts of the PAO procedure, with variations only in the distance of the ilium start point (one-third of the distance between the anterior superior iliac spine and anterior inferior iliac spine [AIIS] vs. two-thirds of the distance). We then mobilized the acetabular fragment into eight reproducible positions in space by moving the ilium cut a combination of 0, 1, or 2 cm anterior/lateral. Each position of the newly realigned acetabula was examined under fluoroscopy to obtain a standardized anteroposterior view, and to obtain standardized radiographic measurements in the form of lateral center edge angle (CEA), acetabular depth, Tonnis angle, and acetabular inclination. We performed 80 simulations of the PAO with varying degrees of acetabular mobilization. On average, in the models where the supra-acetabular cut was closer to the AIIS, we found more significant degrees of radiographic correction, regarding Tonnis angles (12.91 vs. 7.95, p = 0.0175), acetabular inclination (20.25 vs. 9.875, p = 0.027), and lateral CEA (11.75 vs. 2.5, p = 0.061). Patients who had greater dysplasia also had more significant degrees of radiographic Tonnis angle correction with the same mobilization movements of the acetabula (p = 0.005). When utilizing 3D printing to model PAO in dysplasia pelvises, we found that both a higher level of preoperative dysplasia and starting the supra-acetabular osteotomy closer to the AIIS were associated with more powerful corrections following smaller manipulations.

Adverse loading effects on tribocorrosive degradation of 28 mm metal-on-metal hip replacement bearings

Following the high clinical failure rates of metal-on-metal total hip replacements much work has been undertaken to investigate their poor performance. So called adverse loading scenarios such as acetabular inclination and microseparation have been attributed to indicators for failure of the implants. The ISO hip simulation standards (ISO 14242:1) still rely on gravimetric and ex situ analysis, considering only the total wear during articulation. Live in situ sensing can provide valuable insight into the degradation mechanisms of metallic interfaces under such scenarios. Clinical 28 mm diameter metal-on-metal components were articulated in a full-ISO hip simulator. The bearings were subjected to increasing angles of acetabular inclination and retroversion over short-term periods of articulation. Corrosive degradation was monitored during sliding by means of an in situ three-electrode cell. Changing acetabular inclination from 30° to 50° resulted in greater cathodic shifts in OCP upon the initiation of sliding; from −50 mV to as much as −150 mV. Under anodic polarisation (0 mV vs. Ag/AgCl) the resultant currents at the initiation of sliding also increased significantly with inclination; from approximately 4–10 µA to over 120 µA. Increased retroversion of 20° also resulted in increased anodic currents of 55–60 µA. Changing the nature of articulation demonstrated increased corrosive material loss compared to a standard ISO 14242 profile. The sole use of gravimetric assessment to determine a wear rate for hip replacement bearings under simulation can therefore neglect important degradation mechanisms, such as tribocorrosive loss in devices with metal sliding interfaces.

DIFFERENCES IN RADIOGRAPHIC MEASUREMENTS ON STANDING VERSUS SUPINE PELVIC RADIOGRAPHS

Background: Accurate pelvic radiographic measurements is of clear clinical importance, as these measurements can drive the indications for surgery, the surgical approach utilized, and/or the degree of correction during hip preservation surgery. Currently, there are a large number of measurements available and reported on the literature when referencing anterior-posterior (AP) pelvic radiographs. However, there is no standardization of whether these pelvic radiographs are obtained in the standing or supine position. Hypothesis/Purpose: Standing vs. Supine radiographs, obtained in the same patient, will result in different value for standard radiographic measurements used in making hip pathology diagnoses. Methods: All new patients who presented for evaluation of hip pain between September 2016 and July 2018 were retrospectively reviewed. Inclusion criteria included age 18-50, no prior hip surgery/injury, and both standing and supine AP pelvis radiographs dated within 2 years of each other. Measurements were obtained on 26 radiographs (52 hips), blinded to patient demographics and standing versus supine radiograph. Measurements included minimum joint space, lateral center edge angle (LCEA), acetabular depth, acetabular inclination, Tönnis Grade, crossover sign, posterior wall sign, ischial spine sign. Results: Standing films resulted in significantly lower LCEA and acetabular depth measurements, and higher acetabular inclination. Supine measurements for crossover sign were 5.69 times more likely to be positive than standing measurements. Similarly, supine measurements for ischial spine were 7.93 times more likely to be positive (see Table 1). Conclusion: Based on our study, supine films are almost 6 times more likely to give a positive crossover sign and almost 8 times more likely to give a positive ischial spine sign than a standing film in the same patient. Additionally, LCEA, acetabular depth will be lower and acetabular inclination will be higher on standing films. As such, our recommendation is to obtain standing AP pelvis radiographs to obtain the most accurate pelvic radiographic measurements in hip preservation patients. Tables: [Table: see text]

ASSESSMENT OF ACETABULAR COVERAGE IN BORDERLINE ACETABULAR DYSPLASIA: ARE PLAIN RADIOGRAPHIC PARAMETERS ACCURATELY ESTIMATES OF THREE-DIMENSIONAL COVERAGE?

Introduction: Assessment of anterior acetabular coverage is commonly done with measurement of the anterior center edge angle (ACEA) or anterior wall index (AWI). This is particularly important in cases of borderline acetabular dysplasia where it may influence treatment decisions. However, the ACEA and AWI has been poorly validated. Purpose: The purpose of the current study was to investigate the correlation between plain radiographic measurements and three-dimensional femoral head coverage on low-dose CT in borderline acetabular dysplasia. Methods: Seventy consecutive hips with borderline acetabular dysplasia (LCEA 20-25°) were included in the current study. Radiographic evaluation was performed prospectively including LCEA, acetabular inclination, and AWI on AP pelvis radiographs, and ACEA on false profile radiographs. The mean LCEA was 22.1±1.4°, while the mean acetabular inclination was 10.3±3.3. All patients underwent low-dose pelvic CT assessment for preoperative planning. The radial acetabular coverage was calculated according to the standardized clock-face position [measured at 12:00 (lateral), 1:00, 2:00, 3:00 (anterior), and 4:00] as described by Larson et al. Statistical analysis determined the correlation between ACEA and radial coverage. Results: The mean ACEA in the group was 25.3±5.8° (range 10.1-43.9), with 16% having ACEA≤20° and 50% having ACEA≤25°. The mean radial coverages were 63.5%±1.7 (12:00), 60.7%±2.2 (1:00), 50.8%±3.2 (2:00), 37.0%±3.3 (3:00), and 27.9%±3.1 (4:00). The ACEA had poor correlation with radial coverage at all positions from 12:00 to 4:00 (range –0.068-0.173). The AWI had moderate correlation with radial coverage at 3:00 (PCC 0.499) and 4:00 (PCC 0.573). Comparing hips with an ACEA <20° versus >20°, there was no difference between the mean radial acetabular coverage at any position 12:00-4:00 (p=0.18-0.95). Comparing hips with an ACEA <25° versus >25°, there was no difference between the mean radial acetabular coverage at any position 12:00-4:00 (p=0.12-0.71). No significant difference in AWI was present between subgroups with normal and deficient radial coverage from 12:00 to 4:00 (p=0.09-0.72). Discussion: The current study demonstrates poor correlation of the ACEA measurement with true anterior femoral head coverage as evaluated at clock-face positions from 12:00 to 4:00. The AWI demonstrated moderate correlation for 3:00-4:00 coverage but fails to differentiate hips with normal and deficient coverage. In the setting of borderline acetabular dysplasia, anterior and anterolateral femoral coverage should be assessed via low-dose CT rather than ACEA or AWI.

Can We Discriminate Symptomatic Hip Patients From Asymptomatic Volunteers Based on Anatomic Predictors? A 3-Dimensional Magnetic Resonance Study on Cam, Pincer, and Spinopelvic Parameters

Background: Given the high prevalence of patients with hip deformities and no ongoing hip dysfunction, understanding the anatomic factors predicting the symptomatic state is critical. One such variable is how the spinopelvic parameters (SPPs) may interplay with hip anatomic factors. Hypothesis/Purpose: SPPs and femoral- and acetabular-specific parameters may predict which patients will become symptomatic. The purpose was to determine which anatomic characteristics with specific cutoffs were associated with hip symptom development and how these parameters relate to each other. Study Design: Cohort study (Diagnosis); Level of evidence, 2. Methods: 548 participants were designated either symptomatic patients (n = 176, scheduled for surgery with hip pain and/or functional limitation) or asymptomatic volunteers (n = 372, no pain) and underwent 3-dimensional magnetic resonance imaging. Multiple femoral (α angle, Ω angle, neck angle, torsion), acetabular (version, coverage), and spinopelvic (pelvic tilt, sacral slope [SS], pelvic incidence) parameters were measured semiautomatically. Normative values, optimal differentiating thresholds, and a logistic regression analysis were computed. Results: Symptomatic patients had larger cam deformities (defined by increased Ω angle and α angle), smaller acetabular coverage, and larger pelvic incidence and SS angles compared with the asymptomatic volunteers. Discriminant receiver operating characteristic analysis confirmed that radial 2-o’clock α angle (threshold 58°-60°, sensitivity 75%-60%, specificity 80%-84%; area under the curve [AUC] = 0.831), Ω angle (threshold 43°, sensitivity 72%, specificity 70%; AUC = 0.830), acetabular inclination (threshold 6°, sensitivity 65%, specificity 70%; AUC = 0.709), and SS (threshold 44°, sensitivity 72%, specificity 75%; AUC = 0.801) ( P < .005) were the best parameters to classify participants. When parameters were entered into a logistic regression, significant positive predictors for the symptomatic patients were achieved for SS, acetabular inclination, Ω angle, and α angle at 2-o’clock, correctly classifying 85% of cases (model sensitivity 72%, specificity 91%; AUC = 0.919). Conclusion: Complex dynamic interplay exists between the hip and SPPs. A cam deformity, acetabular undercoverage, and increased SPP angles are predictive of a hip symptomatic state. SPPs were significant to discriminate between participants and were important in combination with other hip deformities. Symptomatic patients can be effectively differentiated from asymptomatic volunteers based on predictive anatomic factors.

The impact of surgeon handedness in total hip replacement

Introduction Total hip replacement (THR) is successful and performed commonly. Component placement is a determinant of outcome. Influence of surgeon handedness on component placement has not been considered previously. This study was a radiographic assessment of component positioning with respect to handedness. Early data from 160 patients are reported. Methods Overall, 160 primary THRs for osteoarthritis were included. Equal numbers of left and right THRs were performed by four surgeons, two right-handed and two left-handed. Postoperative radiography was assessed for THR component position by measurement of leg length inequality, acetabular inclination and centre of rotation. Surgeons’ handedness was assessed using the Edinburgh inventory. Results For leg length inequality, no significant interaction was seen between hip side and surgeon handedness. Acetabular inclination angles showed a statistically significant difference, however, depending on hand dominance, with higher inclination angles recorded when operating on the dominant side. There was a trend towards greater medialisation of the centre of rotation on the non-dominant side although this did not reach statistical significance. Conclusions Surgeon handedness appears to influence acetabular component position during THR but it is one factor of many that interact to achieve a successful outcome.