The use of image analysis software increases the accuracy of the periacetabular osteotomy fragment placement

ABSTRACT The purpose of this study was to report on the use of image analysis technology to enhance accuracy of intra-operative imaging and evaluation of periacetabular osteotomy (PAO) correction. This was a retrospective study reporting on the first 25 cases of PAO performed with the use of an image analysis tool. This technology was used intra-operatively to assess the position of the supine coronal image in comparison to pre-operative standing images using a ratio of pelvic tilt (PT). Intra-operative PT, Tönnis angle, lateral center–edge angle (LCEA) and anterior wall index were compared to post-operative images. Post-operative radiographic parameters in the study group were compared with a control group of PAO cases performed prior to the implementation of the new software. The image analysis software was able to obtain intra-operative supine imaging that was equivalent to pre-operative standing imaging. When comparing the PAOs performed with the use of the software versus those without, the study group trended toward being more likely within the surgeon’s defined target range of radiographic values, which was statistically significant for LCEA. This tool can be used to assure the surgeon that the intra-operative image being used for surgical decision-making is representative of the functional radiograph. PAOs performed with the use of this technology showed enhanced accuracy of surgical correction for the parameters within our defined target ranges. This may increase the ability of the surgeon to place the acetabular fragment more precisely within his or her goal parameters for acetabular reorientation correction.

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.

629 Small Bowel Entrapment Secondary to An Acetabular Fracture: A Case Report

Bowel entrapment within a pelvic fracture is a rare clinical occurrence. The first reported case was documented in 1907, with only 24 further cases reported in the literature since. Entrapment usually involves mobile segments of bowel and various fracture sites within the pelvis have been implicated. We report a case of a 31-year-old ‘trauma alert’, who sustained pelvic fractures following a pedestrian vs car ‘RTC’. The patient was initially taken to theatre for an examination under anaesthesia, where an immobile acetabular fragment was identified, but the hip joint was felt to be stable. A Denham pin was placed in the distal femur and traction applied. Two days post admission they developed abdominal pain and vomiting. A subsequent CT scan demonstrated small bowel entrapment within the acetabular fracture causing a mechanical obstruction. Emergency laparotomy confirmed an intra-acetabular hernia which was released via an extra-peritoneal route. A section of necrotic bowel was resected, and a primary anastomosis performed. Bowel entrapment poses a difficult diagnostic challenge and there is often a delay in diagnosis. Despite advances in imaging, initial radiographic features can be subtle, and it can be difficult to distinguish clinically between mechanical bowel obstruction and adynamic ileus. This case highlights that bowel entrapment is an important consideration in patients with pelvic fractures following high energy trauma. Awareness of this rare complication and a high index of suspicion are key to early diagnosis and timely surgical intervention, which has the potential to prevent significant complications including bowel obstruction, acute peritonitis and death.

Comparative Biomechanical Study of Screw Fixation Techniques in Periacetabular Osteotomy

Periacetabular osteotomy (PAO) is a common surgical treatment for developmental dysplasia of the hip. To obtain the optimal method of fixation during PAO, different screw fixation techniques have been proposed for stabilizing the acetabular fragment. This study assesses the biomechanical performance of two popular 3-screw fixation techniques: iliac (IS) and transverse (IT) configurations, through finite element simulations. Additionally, different 2-screw combinations are simulated to investigate the biomechanical significance of each screw of the fixation configurations. The study findings show that yield load of the pelvic bone subject to gait loading for IT configuration is on average 7% higher compared to that of the IS. Although the yield load of the IT is predicted to be slightly higher, no significant difference in bone stiffness and displacement of the acetabular fragment are found between two configurations. Simulation results, therefore, do not demonstrate a significant biomechanical advantage of the IT configuration over the IS. Furthermore, the biomechanical comparison between the 2-screw combinations of IS and IT fixations demonstrates that the most anterior screw in IS, located at the iliac crest, and the most medial screw in the IT are the most critical elements in providing sufficient stability and support for acetabular fragment.

Is transverse screw fixation really necessary in PAO?—A comparative in vivo study

The optimal fixation technique in periacetabular osteotomy (PAO) remains controversial. This study aims to assess the in vivo stability of fixation in PAO with and without the use of a transverse screw. We performed a retrospective study to analyse consecutive patients who underwent PAO between January 2015 and June 2017. Eighty four patients (93 hips) of which 79% were female were included. In 54 cases, no transverse screw was used (group 1) compared with 39 with transverse screw (group 2). Mean age was 26.5 (15–44) in group 1 and 28.4 (16–45) in group 2. Radiological parameters relevant for DDH including lateral center edge angle of Wiberg (LCEA), Tönnis angle (TA) and femoral head extrusion index (FHEI) were measured preoperatively, post-operatively and at 3-months follow-up. All patients were mobilized with the same mobilization regimen. Post-operative LCEA, TA and FHEI were improved significantly in both groups for all parameters (P ≤ 0.0001). Mean initial correction for LCEA (P = 0.753), TA (P = 0.083) and FHEI (P = 0.616) showed no significant difference between the groups. Final correction at follow-up of the respective parameters was also not significantly different between both groups for LCEA (P = 0.447), TA (P = 0.100) and FHEI (P = 0.270). There was no significant difference between initial and final correction for the respective parameters. Accordingly, only minimal loss of correction was measured, showing no difference between the two groups for LCEA (P = 0.227), TA (P = 0.153) and FHEI (P = 0.324). Transverse screw fixation is not associated with increased fragment stability in PAO. This can be taken into account by surgeons when deciding on the fixation technique of the acetabular fragment in PAO.

Frequency of Acetabulum Retroversion Formation after Reorienting Pelvic Osteotomies in Children Over 7 Years Old with Developmental Dysplasia of the Hip

Background. One of the reasons for the development of the “pincer” type of femoroacetabular impingement are various reorienting pelvic osteotomies, which are widely used in the treatment of children with developmental dysplasia of the hip (DDH).The aim of the study was to evaluate the frequency of formation of retroversion of the acetabulum after reorienting pubic-iliac, iliac-sciatic and triple pelvic osteotomies in children over 7 years old with DDH I–II degree according to Crowe.Material and Methods. The retrospective study is based on the results of radiometry of 60 patients (69 hip joints) at an average age of 11.6±2.9 years with DDH I–II degree according to Crowe who underwent surgical treatment in 2014-2016. The patients were divided into three groups of 20 patients each. Group I underwent an iliac osteotomy. Group II underwent an ilio-sciatic osteotomy. In group III patients, the acetabulum was reoriented by triple (pubo-ilio-sciatic) pelvic osteotomy. In addition to standard radiometry of the hip joints, the following indicators were evaluated: signs of acetabular retroversion (“cross-over”, “posterior wall”, “ischial spine”), as well as the index of acetabular retroversion (ARI).Results. The assessment of the main radiometric parameters of the spatial position and the correction value of the acetabulum was carried out at least 36 months after the surgical treatment. There were no statistically significant differences in the radiometric parameters of the spatial orientation of the acetabulum in group I and II patients (p>0.05), except for the degree of bone coverage, which was significantly higher in group II patients (p<0.05) than in group II patients, which indicated the presence of hypercorrection. In patients of group III, the values of the above-mentioned indicators varied within the physiological values. Retroversion of the acetabulum was observed in more than half of the patients in group I and in almost all patients in group II. In group III patients, acetabular retroversion was observed in only 3 patients.Conclusion. In the vast majority of cases, a double pelvic osteotomy (pubo-iliac and ilio-sciatic) leads to the formation of hypercorrection of the acetabular fragment and its retroversion in comparison with a triple pelvic osteotomy. The pathological orientation of the acetabulum, despite the achieved stability of the hip joint, can be a morphological substrate for the development of femoro-acetabular impingement and, as a result, coxarthrosis. In the treatment of children with DDH over 7 years old the operation of choice is a triple pelvic osteotomy.

Augmented Reality Based Surgical Navigation of Complex Pelvic Osteotomies—A Feasibility Study on Cadavers

Augmented reality (AR)-based surgical navigation may offer new possibilities for safe and accurate surgical execution of complex osteotomies. In this study we investigated the feasibility of navigating the periacetabular osteotomy of Ganz (PAO), known as one of the most complex orthopedic interventions, on two cadaveric pelves under realistic operating room conditions. Preoperative planning was conducted on computed tomography (CT)-reconstructed 3D models using an in-house developed software, which allowed creating cutting plane objects for planning of the osteotomies and reorientation of the acetabular fragment. An AR application was developed comprising point-based registration, motion compensation and guidance for osteotomies as well as fragment reorientation. Navigation accuracy was evaluated on CT-reconstructed 3D models, resulting in an error of 10.8 mm for osteotomy starting points and 5.4° for osteotomy directions. The reorientation errors were 6.7°, 7.0° and 0.9° for the x-, y- and z-axis, respectively. Average postoperative error of LCE angle was 4.5°. Our study demonstrated that the AR-based execution of complex osteotomies is feasible. Fragment realignment navigation needs further improvement, although it is more accurate than the state of the art in PAO surgery.

Overcorrection of the acetabular roof angle or anterior center–edge angle may cause decrease of range of motion after curved periacetabular osteotomy

ABSTRACT The aim of this study was to evaluate the relationship between the correction of radiographic parameters and clinical range of motion (ROM) after periacetabular osteotomy (PAO). Sixty-nine patients with hip dysplasia were enrolled and underwent curved PAO. The pre- and post-operative 3D center–edge (CE) angles, total anteversion (acetabular and femoral anteversion), and radiographic acetabular roof angle were measured and compared with the post-operative ROM. The aim of surgery was to rotate the central acetabular fragment laterally without anterior or posterior rotation. Multiple linear regression analysis demonstrated that post-operative internal rotation at 90° flexion was significantly associated with the post-operative Tönnis sourcil angle (rr = 0.31, P = 0.02) and that the post-operative ROM of flexion and internal rotation at 90° flexion were significantly associated with the anterior CE (flex; rr = −0.44, P = 0.001, internal rotation at 90° flexion; rr = −0.44, P &lt; 0.001). However, we found no association between the lateral CE, femoral anteversion, or total anteversion and the post-operative ROM. We demonstrated that the overcorrection of the acetabular roof angle or anterior CE angle may cause a decrease in the range of motion after curved PAO. Therefore, surgeons need to be careful during surgery to prevent the overcorrection of the weight-bearing area and anterior acetabular coverage of the acetabular fragment to avoid femoroacetabular impingement after PAO.

Acetabular- and femoral orientation after periacetabular osteotomy as a predictor for outcome and osteoarthritis

Background Periacetabular osteotomy is a successful treatment for hip dysplasia. The results are influenced, however, by optimal positioning of the acetabular fragment, femoral head morphology and maybe even femoral version as well as combined anteversion have an impact. In order to obtain better insight on fragment placement, postoperative acetabular orientation and femoral morphology were evaluated in a midterm follow-up in regard to functional outcome and osteoarthritis progression. Methods A follow-up examination with 49 prospectively documented patients (66 hips) after periacetabular osteotomy (PAO) was performed after 62.2 ± 18.6 months. Mean age of patients undergoing surgery was 26.7 ± 9.6 years, 40 (82%) of these patients were female. All patients were evaluated with an a.p. pelvic x-ray and an isotropic MRI in order to assess acetabular version, femoral head cover, alpha angle, femoral torsion and combined anteversion. The acetabular version was measured at the femoral head center as well as 0.5 cm below and 0.5 and 1 cm above the femoral head center and in addition seven modified acetabular sector angles were determined. Femoral torsion was assessed in an oblique view of the femoral neck. The combined acetabular and femoral version was calculated as well. To evaluate the clinical outcome the pre- and postoperative WOMAC score as well as postoperative Oxford Hip Score and Global Treatment Outcome were analyzed. Results After PAO acetabular version at the femoral head center (31.4 ± 9.6°) was increased, the anterior cover at the 15 o’clock position (34.7 ± 15.4°) was reduced and both correlated significantly with progression of osteoarthritis, although not with the functional outcome. Combined acetabular and femoral torsion had no influence on the progression of osteoarthritis or outcome scores. Conclusion Long-term results after PAO are dependent on good positioning of the acetabular fragment in all 3 planes. Next to a good lateral coverage a balanced horizontal alignment without iatrogenic pincer impingement due to acetabular retroversion, or insufficient coverage of the anterior femoral head is important.

Three-dimensional acetabular orientation during periacetabular osteotomy: a video analysis of acetabular rim position using an external fixator as navigation tool during reorientation procedure

Introduction Bernese periacetabular osteotomy is an effective procedure for treating acetabular dysplasia. However, limited visual control of the acetabular position during surgery may result in under- or overcorrection with residual dysplasia or femoroacetabular impingement. Thus, we wanted to find a simple method to control the effect of correction in the sagittal and coronal plane. Method The acetabular coordinates are shown by two perpendicular tubes of an external fixator mounted onto a third tube that is fixed to the acetabular fragment with two Schanz screws. This method enables the isolated acetabular reorientation in the coronal, sagittal, and transverse plane. In a sawbone pelvis model, the acetabular rim is marked with a copper wire and a silicon adherent. To show the radiographic effect on acetabular parameters and the rim position, we visualized correction in the coronal and sagittal plane under fluoroscopic control. Results Lateral rotation of the acetabular fragment had the highest impact on radiographic lateral coverage of the femoral head. But also ventral coverage increased during isolated lateral rotation. Anterior rotation showed almost no effect on lateral coverage and just a little effect on ventral coverage but caused severe total acetabular retroversion. Conclusion Three-dimensional control of the acetabular orientation during periacetabular osteotomy is important to avoid over- and under-correction. Isolated lateral rotation of the acetabular fragment should be the predominant direction of correction during periacetabular osteotomy. Ambitious anterior correction may be the main source for severe acetabular retroversion following periacetabular osteotomy.