Skip to main content
NCBI home page
Clinical Orthopaedics and Related Research logoLink to Clinical Orthopaedics and Related Research
. 2008 Feb 9;466(5):1169–1176. doi: 10.1007/s11999-008-0133-7

Reliable Angle Assessment During Periacetabular Osteotomy with a Novel Device

Anders Troelsen 1,✉, Brian Elmengaard 1, Lone Rømer 2, Kjeld Søballe 1
PMCID: PMC2311482  PMID: 18264742

Abstract

We developed and assessed a measuring device for intraoperative assessment of the acetabular index and center edge angle during acetabular reorientation in periacetabular osteotomy. We asked whether reliable assessment of angles could be made using the device; to be reliable we presumed the variability of angle measurements should not exceed that of inherent variability when assessing angles on radiographs (± 5°). The device was mounted bilaterally on the pelvis, and using fluoroscopy, angle measurements were obtained with adjustable measuring discs. We conducted a cadaver study to assess intraobserver and interobserver variability of the device and to assess if pelvic positioning influenced variation of measurements. Intraoperative measurements of 35 consecutive patients were compared with measurements on postoperative radiographs. Intraoperatively obtained angle measurements differed less than ± 5° from measurements on postoperative radiographs and the intraobserver and interobserver variability of the device were confined within ± 5°. Positioning did not influence the variation of angle measurements beyond intraobserver variability of the device when applying arcs of tilt and rotation of ± 12.5°. We believe the device is a potentially helpful tool in the periacetabular osteotomy. It is simple to use and facilitates repeated reliable angle measurements during acetabular reorientation, making intraoperative radiographs unnecessary.

Introduction

Developmental dysplasia of the hip (DDH) is characterized by an excessively oblique and shallow acetabulum with insufficient coverage of the femoral head laterally and anteriorly [1, 10, 19]. The periacetabular osteotomy is a well-established treatment for DDH in young adults [6, 20, 21, 24, 32, 33]. In this procedure, the acetabulum is reoriented to enhance coverage of the femoral head and the aim is to achieve congruity, to stabilize the joint, to medialize the joint center, and to reduce contact pressures [6, 7, 13, 31]. This will relieve pain and improve function and is likely to prevent additional overload of the labrum, cartilage, and soft tissues, thereby delaying or preventing the development of osteoarthritis [20, 21, 24, 32, 33]. Undercorrection or overcorrection of the acetabulum can cause symptoms such as the feeling of instability and impingement, respectively [9, 18, 25]. One study reported a postoperative acetabular index (AI) outside the interval of 0° to 10° negatively influenced the outcome after periacetabular osteotomy [24], and another study found the postoperative center edge (CE) angle averaged 29° for hips that had an increase in the apparent joint space compared with an average 21° in hips that did not [33]. Although not thoroughly investigated, it seems warranted to consider acetabular reorientation an important step in surgical decision making when performing periacetabular osteotomy.

The AI and the CE angle are commonly used to characterize the dysplastic anatomy of the hip [1, 10, 19, 26, 29, 34]. In the dysplastic hip undergoing a periacetabular osteotomy, these angles must be assessed intraoperatively to ascertain whether the intended reorientation of the acetabulum has been achieved [5, 6, 17, 20, 25, 31]. One way to assess the AI and the CE angle intraoperatively is by taking anteroposterior pelvic radiographs during reorientation of the acetabulum. Several radiographs may be necessary and the surgeon must wait for the radiographs to be developed and the angles to be measured. Alternatively, assessment can be made by eye using fluoroscopy, but this approach is qualitative and might only be reliable for an experienced surgeon. Image-guided techniques seemingly facilitate surgery but without improving acetabular correction, and are relatively expensive [8, 14, 15].

The senior author (KS) developed a measuring device that allows intraoperative assessment of the AI and the CE angle during acetabular reorientation when performing periacetabular osteotomy. The device is mounted bilaterally at the anterior superior iliac spines and angle measurements are performed with adjustable measuring discs using fluoroscopy.

The primary research question was whether the measuring device could assist the surgeon in obtaining good correction of the acetabulum in terms of reliable intraoperative determination of the AI and the CE angle. We also determined (1) the variability between angle measurements obtained with the device and angle measurements on postoperative radiographs of the same patients, (2) whether this variability was increased compared with the intraobserver variability of angle measurements obtained on postoperative radiographs, (3) the intraobserver and interobserver variability when using the device for angle measurements, and (4) whether patient positioning in terms of differing pelvic tilt and rotation influenced variation of angle measurements.

Materials and Methods

Prospective intraoperative assessment of the AI and the CE angle was made in 35 patients undergoing unilateral periacetabular osteotomies performed by the senior author (KS) from May 2006 to March 2007. Intraoperative angle measurements were performed by the senior author (KS) using the measuring device. Indications for surgery were symptomatic DDH defined by persistent hip pain, a CE angle less than 25°, a congruent joint, Tönnis osteoarthritis Grade 0 to 1, hip flexion greater than 110°, and internal rotation greater than 15°. The study group consisted of 31 females and four males with a median age of 30 years (range, 14–57 years). Double measurements of the AI and the CE angle were performed on the patients’ postoperative anteroposterior pelvic radiographs by one author (AT). We presumed the device satisfactory from clinical and radiographic points of view if the measurements differed less than ± 5° from measurements on postoperative radiographs and if intraobserver and interobserver variability of the device were within ± 5°. We selected this level as it corresponds approximately to the inherent variability of AI and CE angle measurements on plain radiographs [2, 11, 22, 30]. In a cadaver study, measurements of the AI and the CE angle were made by two authors (AT, KS) in a setup mimicking differing tilt and rotation of the pelvis.

The landmarks for the CE angle [34] are the center of the femoral head and the most lateral point of the sclerotic acetabular roof. For the AI [29], the landmarks are the most medial and lateral points of the sclerotic acetabular roof. Intraoperative and postoperative measurements on anteroposterior pelvic radiographs demand alignment of the pelvis using a line of reference (Fig. 1).

Fig. 1.

Fig. 1

Open in a new tab

Drawing a line of reference precedes construction of radiographic angles. It is constructed by drawing a line going through the most caudal points on the inferior ramus bilaterally. The acetabular index (AI) is constructed by drawing a line from the most lateral to the most medial limit of the sclerotic acetabular roof and from there another line parallel to the line of reference. The center edge (CE) angle is constructed by drawing a line from the most lateral limit of the sclerotic acetabular roof to the center of the femoral head and another line perpendicular to the line of reference and through the center of the femoral head.

The measuring device is used under fluoroscopy in the anteroposterior plane. It is mounted bilaterally at the anterior-superior iliac spines and the position is secured by inserting small spikes. To secure alignment of the pelvis for angle measurement, a rod connects the spikes (Fig. 2). Adjustable angle measuring discs can be mounted on the alignment rod. We use two different angle measuring discs: (1) the disc for AI measurement is positioned and adjusted until it is placed correctly in relation to the most medial and lateral points of the sclerotic acetabular roof (Fig. 3A); and (2) the disc for CE angle measurement is positioned and adjusted until it is placed correctly in relation to the center of the femoral head and the most lateral point of the sclerotic acetabular roof (Fig. 3B). If fine-tuning of the reorientation is necessary, the measuring discs are easily adjusted for new assessment of the angle measurements. Version of the acetabulum cannot be measured using the device but is equally important and must be addressed to achieve an appropriate anteversion [20, 30]. This is accomplished by identifying the anterior and posterior acetabular rim (Fig. 3A). In appropriate anteversion, it is observed (1) the posterior rim is lateral to the anterior rim and the center of the femoral head and (2) the anterior rim is medial to the center of the femoral head [16, 20, 31]. Crossing of the anterior and posterior rim (crossover sign) is a sign of inappropriate anteversion or retroversion [12, 16]. Acetabular version, that is, the appearance of the acetabular rims, is dependent on the pelvic tilt [12, 23, 28, 30]. We attempt to minimize intraoperative misinterpretation of the acetabular version by ensuring the pelvic tilt intraoperatively corresponds to that of the anteroposterior pelvic radiograph used for diagnosis and preoperative planning. Pelvic tilt can be assessed in the anteroposterior plane measuring the distance from the symphysis to the sacrococcygeal joint [23, 27, 28]. We use fluoroscopy to obtain an approximate measure intraoperatively. The aim of the reorientation is to achieve an AI between 0° and 10° and CE angle between 30° and 40°. To achieve appropriate coverage, we approximate the AI to 0°. We avoid a negative value of the AI and a CE angle greater than 40° when approximating the AI to 0°. A negative AI, a CE angle greater than 40°, or the crossover sign are indicators for overcorrection and it is recognized impingement and reduced range of motion can result from a periacetabular osteotomy [9, 18, 25]. We routinely assess range of motion intraoperatively after reorientation. If the CE angle becomes excessive, it is adjusted to 40° or less and the AI is adjusted keeping it between 0° and 10°, which in our experience is possible in almost every case. Also, in some patients, the hip is too dysplastic to achieve a CE angle greater than 30° when approximating the AI to 0°. Using the above guidelines, the senior author (KS) decided when optimal reorientation was achieved during surgery; the AI (range, 0°–10°) and CE angle (range, 23°–36°) measurements then were registered. After becoming familiar with the measuring device, mounting and adjusting the discs for measurement of the AI and the CE angle take approximately 2 to 3 minutes.

Fig. 2A–B.

Fig. 2A–B

Open in a new tab

The measuring device is used under fluoroscopy in the anteroposterior plane. It is mounted bilaterally at the anterior-superior iliac spines. The position is secured by inserting small spikes. To secure alignment of the pelvis for angle measurement, a rod connects the spikes. (A) The measuring device is mounted on a sawbones model with the disc for CE angle measurement. (B) The measuring device is mounted during surgery with the disc for CE angle measurement.

Fig. 3A–B.

Fig. 3A–B

Open in a new tab

(A) The disc for AI measurement is positioned and adjusted until it is placed correctly in relation to the most medial (Arrow 1) and lateral (Arrow 2) points of the sclerotic acetabular roof. The AI in this case is 1° (Arrow 3). The anterior (row of white arrows) and posterior (row of black arrows) acetabular rims are seen in the anteroposterior fluoroscopic view. The fluoroscopic view is rotated slightly clockwise, but alignment is secured by the measuring device. (B) The disc for CE angle measurement is positioned and adjusted until it is placed correctly in relation to the center of the femoral head (Arrow 1) and the most lateral point of the sclerotic acetabular roof (Arrow 2). The CE angle in this case is 35° (Arrow 3). 0° on the measuring disc is marked. The fluoroscopic view is rotated slightly clockwise, but alignment is secured by the measuring device.

Anteroposterior pelvic radiographs were taken on the first or second postoperative day and were stored digitally. Using a workstation allowing digital management of radiographs, the AI (range, −1°–9°) and the CE angle (range, 24°–36°) were measured by one blinded observer (AT). To assess intraobserver variability, a second blinded measurement of the AI and the CE angle was performed by the same observer 4 weeks later. Angle measurements obtained with the device were compared with angle measurements on postoperative radiographs to assess the variability. We also compared intraobserver variability with the variability when comparing angle measurements obtained intraoperatively with those obtained on postoperative radiographs.

To assess intraobserver and interobserver variability and evaluate the effect of pelvic tilt or rotation on the AI and CE angle measurements, we did a cadaver study. The female cadaver specimen was partial and consisted of the pelvis, hips, thighs, and knees with intact skin and soft tissues. Initially, the spikes and alignment rod of the measuring device were mounted as described previously. The position of the pelvis then was adjusted until it was in a neutral position. This was confirmed by achieving a foramen obturator index of 1.0 and a distance between the pubic symphysis and the sacrococcygeal joint of 4 cm on an anteroposterior pelvic radiograph (the tube was oriented perpendicular to the table and the tube to film distance was 110 cm, resulting in a magnification of 15%).

Measurement of the AI and the CE angle using the measurement device was done as described previously. Two observers (Observer 1: KS, experienced with the device; Observer 2: AT, inexperienced with the device) performed the angle measurements on the right hip of the cadaver. The C-arm of the fluoroscope was tilted in 2.5° increments to the left and to the right of the cadaver in an arc totaling 25°. In this way, 11 measurements of both angles were done from an angle of 12.5° to the left and to 12.5° to the right of the cadaver (Table 1). An angle of 0° indicates the anteroposterior plane. Another 11 measurements of both angles were performed similarly tilting the C-arm of the fluoroscope in 2.5° increments in the cranial and caudal directions in an arc totaling 25° (Table 1). For each measurement, the femoral head was focused in the middle of the image. The observers were blinded to each other’s measurements and to the actual position of the C-arm. The order of measurements was random with respect to the position of the C-arm. We assessed intraobserver and interobserver variability of angle measurements obtained using the device.

Table 1.

Angle measurements in the cadaver study

Angle Observer Tilting of the C-arm Number of measurements Range Mean Standard deviation
Acetabular index 1* Right, 12.5°; left, 12.5° 11 1°–4° 2.73° ± 1.01°
Cranial, 12.5°; caudal, 12.5° 11 1°–5° 3.00° ± 1.18°
2 Right, 12.5°; left, 12.5° 11 2°–3° 2.36° ± 0.50°
Cranial, 12.5°; caudal, 12.5° 11 0°–3° 1.64° ± 0.92°
Center edge 1* Right, 12.5°; left, 12.5° 11 34°–37° 35.73° ± 0.90°
Cranial, 12.5°; caudal, 12.5° 11 32°–37° 34.27° ± 1.90°
2 Right, 12.5°; left, 12.5° 11 35°–38° 36.27° ± 1.10°
Cranial, 12.5°; caudal, 12.5° 11 35°–38° 36.09° ± 1.14°
Open in a new tab

*Observer 1 did double measurements to determine intraobserver variability.

We determined the variability between intraoperatively and postoperatively obtained AI and CE angle measurements and present data as mean of the difference with standard deviation (SD) and 95% limits of agreement presented in a Bland-Altman plot [3, 4]. The intraobserver variability of angle measurements on postoperative radiographs and intraobserver and interobserver variability of angle measurements in the cadaver study were assessed and presented the same way. We compared the intraobserver variability of angle measurements on postoperative radiographs with (1) the variability between angle measurements obtained intraoperatively and on postoperative radiographs and (2) the intraobserver and interobserver variability of angle measurements in the cadaver study; for this comparison we used Pitman’s variance ratio test. Angle measures of the different series in the cadaver study are presented as range, mean, and SD. The variability of these series of measurements is compared with the intraobserver variability of the device using Pitman’s variance ratio test. Analyses were performed using the Stata® software package (Intercooled Stata version 9.2; StataCorp LP, College Station, TX).

Results

We found the measuring device assisted the surgeon in obtaining good correction of the acetabulum as the intraoperatively obtained angle measurements differed less than ± 5° from measurements on postoperative radiographs and the intraobserver and interobserver variability of the device were confined within ± 5° (Table 2; Fig. 4).

Table 2.

Comparison of angle measurements

Compared measurements Angle Number of measurements Mean of the difference Standard deviation 95% Limits of agreement Pitman’s variance ratio test
Perioperative versus postoperative AI 35 0.06° ± 2.22° −4.30°–4.42° AI: p = 0.14; CE: p = 0.24
CE 35 −0.03° ± 2.43° −4.80°–4.74°
Postoperative versus postoperative AI 35 −0.09° ± 1.72° −3.46°–3.28°
CE 35 −2.09° ± 2.02° −6.05°–1.87°
Cadaver study Observer 1 versus Observer 2 AI 22 0.86° ± 1.21° −1.51°–3.23° AI: p = 0.39; CE: p = 0.13
CE 22 −1.18° ± 1.84° −4.79°–2.43°
Cadaver study Observer 1 versus Observer 1 AI 22 −0.77° ± 1.45° −3.60°–2.06°
CE 22 0.55° ± 1.30° −2.00°–3.10°
Open in a new tab

AI = acetabular index; CE = center edge.

Fig. 4A–B.

Fig. 4A–B

Open in a new tab

Bland-Altman plots of difference against average for measurements of (A) AI and (B) CE angle on postoperative radiographs and with the device intraoperatively are shown. The mean of differences (solid line), the SD of differences (dotted line), and the 95% limits of agreement (dashed line) are presented. The 95% limits of agreement show we can expect 95% of differences between the two measurement methods to lie (A) between −4.3° and +4.4° for the AI and (B) between −4.8° and +4.7° for the CE angle. Because inherent variability of radiographic angle assessment is ± 5°, the reported levels are satisfactory for reliable intraoperative angle assessment.

We found 95% of differences between angle measurements obtained with the device and angle measurements on postoperative radiographs were between −4.3° and +4.4° for the AI and between −4.8° and +4.7° for the CE angle (Table 2; Fig. 4).

The level of variability (device versus postoperative) did not differ (AI, p = 0.14; CE angle, p = 0.24) from the intraobserver variability assessed on double measurement of angles on postoperative radiographs (Table 2). With intraobserver variability assessment on postoperative radiographs, we found 95% of differences between two repeated measurements would be expected to lie between −3.5° and +3.3° for the AI and between −6.1° and +1.9° for the CE angle (Table 2).

For intraobserver and interobserver variability we found 95% limits of agreement for both angle measures were confined between −4.8° and +3.3° (Table 2). We also found intraobserver and interobserver variability when using the measuring device did not differ from each other (AI, p = 0.39; CE angle, p = 0.13) (Table 2) or from the intraobserver variability assessed on double measurements on postoperative radiographs (AI, p = 0.45–0.96; CE angle, p = 0.06–0.92).

Patient positioning (differing pelvic tilt and rotation) did not influence the variation of angle measurements beyond intraobserver variability of the device, within the arcs (± 12.5°) of tilt and rotation applied in this study. The different series of angle measurements performed by both observers in the cadaver study showed variations (expressed as ± SD) for AI measurement between ± 0.5° and ± 1.2° and for CE angle measurement between ± 0.9° and ± 1.9° (Table 1). These variations either did not differ from intraobserver variability (AI, p = 0.65–0.81; CE angle, p = 0.17–0.52), or in one series of AI measurement by Observer 2 variation actually was less (p = 0.03) than the intraobserver variability.

Discussion

Periacetabular osteotomy with reorientation of the acetabulum is a well-established treatment to relieve pain, increase function, and delay or prevent development of osteoarthritis in young adults with DDH [20, 21, 24, 32, 33]. The AI and the CE angle are commonly used to describe the morphologic characteristics of DDH [1, 10, 19, 26, 29, 34] and are assessed intraoperatively to ascertain whether the intended reorientation has been achieved [5, 6, 17, 20, 25, 31]. The senior author developed a measuring device for intraoperative assessment of the AI and the CE angle using fluoroscopy. We asked whether the device could assist the surgeon in obtaining good correction of the acetabulum in terms of reliable intraoperative determination of the AI and the CE angle.

Perhaps the major limitation of our study is that we had no gold standard against which to compare angles using the measuring device. Measurements of the AI and the CE angle using three-dimensional imaging techniques could be considered a gold standard, although for example, computed tomography scanning is unlikely to be conducted postoperatively. We therefore judged our measurements against the variability of the measures, presuming the correct (accurate) measure was within those ranges. It seems meaningful to compare the angle measurements obtained with the device with those on postoperative radiographs as this is the commonly used imaging technique to evaluate the result of the acetabular reorientation.

We found the measuring device was able to assist the surgeon in obtaining good correction of the acetabulum as the intraoperatively obtained AI and CE angle measurements differed less than ± 5° from measurements on postoperative radiographs and the intraobserver and interobserver variability of the device were confined well within ± 5°. The limit for a satisfactory result of the variability assessment of ± 5° was chosen from clinical and radiographic points of view. Using a two-dimensional imaging technique for assessment of the AI and the CE angle, there are some inherent problems adding to variability: (1) identification of the center of the femoral head; (2) identification of the medial and lateral limits of the sclerotic acetabular roof; and (3) construction of the line of reference. Previously, variability of AI and CE angle measurements were confined to ± 5° [2, 11, 22, 30]. The device is built to mimic construction of the AI [29] and the CE angle [34] when they are drawn on an anteroposterior pelvic radiograph. Therefore, the expectation was not to find decreased variability when using the device, but to make sure it did not exceed existing variability of angle assessment using two-dimensional imaging techniques. The intraobserver and interobserver variability of the device did not differ from each other, suggesting the device is equally reliable in the hands of an inexperienced (Observer 2) and experienced (Observer 1) user. This is likely attributable to the simple construction and straightforward use of the device.

One way to assess angles intraoperatively is by recording anteroposterior pelvic radiographs. This is time-consuming and several radiographs might be needed before the intended correction has been achieved. An advantage is that assessment of angles can be made constructing a line of reference (Fig. 1) securing pelvic alignment. Using the device, this is achieved by a rod connecting the bilaterally and symmetrically inserted spikes. Also, the device is used under fluoroscopy, which allows fast and easy repeated measurements during fine-tuning of acetabular correction without exposing patients to heavy radiation of conventional radiographs. A potential disadvantage when using the device is the insertion of spikes in the anterior-superior iliac spine. In our experience, it does not convey specific site-related postoperative pain or skin problems.

Another way is intraoperative assessment of the AI and the CE angle by eye using fluoroscopy. In our opinion, this can be done only by someone very experienced, if at all. The surgeon using this approach for angle assessment can evaluate postoperative radiographs to see if surgery resulted in the intended reorientation, but to our knowledge, there is no study evaluating whether this is a reliable approach for AI and CE angle assessment, either for the experienced or less experienced surgeon.

Computer-assisted and image-guided techniques using preoperative computed tomography scans have been introduced as potentially helpful and eliminate or reduce the need for radiographs in acetabular reorientation surgery [8, 14, 15]. However, these techniques are relatively expensive and have not been shown to improve the achieved acetabular correction compared with a conventional approach [8]. Our measuring device is relatively inexpensive and, in our opinion, simple and fast to use. In our hands, mounting and adjusting the discs for both angle measurements takes approximately 2 to 3 minutes. Also, the device can assist the surgeon in making a reliable intraoperative determination of the AI and the CE angle, with variability at the same level as angle measurements made on conventional radiographs.

The appearance of acetabular version on two-dimensional radiographic imaging depends on pelvic tilt [12, 23, 28, 30]. Radiographic dysplastic parameters, such as the AI and the CE angle, generally are only affected beyond inherent measuring error if the image is severely distorted [2, 11, 22, 34]. We wanted to make sure the measuring device did not add variability to angle measurements when tilting and rotating the pelvis. This could introduce a potential risk of misinterpreting the achieved angle measurements. We found patient positioning, in terms of differing pelvic tilt and rotation, did not influence variation of angle measurements beyond intraobserver variability of the device, within the arcs (± 12.5°) of tilt and rotation applied in this study.

The measuring device is a potentially helpful tool during acetabular reorientation. Using the device, one can obtain reliable measures of the AI and the CE angle with a variability confined well within that of angle measurements on conventional radiographs. Compared with existing techniques for intraoperative AI and CE angle assessment, it has the advantages of (1) being simple to use, (2) being relatively inexpensive, (3) making conventional intraoperative radiographs unnecessary, (4) facilitating fast repeated angle measurements during fine-tuning of correction, and (5) being equally reliable in the hands of inexperienced and experienced users.

Acknowledgments

We thank associate professor Peter Holm-Nielsen from the Institute of Anatomy, Faculty of Health Sciences, Aarhus University, Denmark, for providing access to the cadaver specimen.

Footnotes

One or more of the authors (AT) have received funding from a grant from the Danish Rheumatism Association during conduction of this study.

Each author certifies that his or her institution has approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.

References

  • 1.Anda S, Terjesen T, Kvistad KA, Svenningsen S. Acetabular angles and femoral anteversion in dysplastic hips in adults: CT investigation. J Comput Assist Tomogr. 1991;15:115–120. [DOI] [PubMed]
  • 2.Ball F, Kommenda K. Sources of error in the roentgen evaluation of the hip in infancy. Ann Radiol (Paris). 1968;11:298–303. [PubMed]
  • 3.Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1:307–310. [PubMed]
  • 4.Bland JM, Altman DG. Applying the right statistics: analyses of measurement studies. Ultrasound Obstet Gynecol. 2003;22:85–93. [DOI] [PubMed]
  • 5.Clohisy JC, Barrett SE, Gordon JE, Delgado ED, Schoenecker PL. Periacetabular osteotomy in the treatment of severe acetabular dysplasia. J Bone Joint Surg Am. 2006;88(suppl 1, pt 1):65–83. [DOI] [PubMed]
  • 6.Ganz R, Klaue K, Vinh TS, Mast JW. A new periacetabular osteotomy for the treatment of hip dysplasias: technique and preliminary results. Clin Orthop Relat Res. 1988;232:26–36. [PubMed]
  • 7.Hipp JA, Sugano N, Millis MB, Murphy SB. Planning acetabular redirection osteotomies based on joint contact pressures. Clin Orthop Relat Res. 1999;364:134–143. [DOI] [PubMed]
  • 8.Hsieh PH, Chang YH, Shih CH. Image-guided periacetabular osteotomy: computer-assisted navigation compared with the conventional technique: a randomized study of 36 patients followed for 2 years. Acta Orthop. 2006;77:591–597. [DOI] [PubMed]
  • 9.Hussell JG, Rodriguez JA, Ganz R. Technical complications of the Bernese periacetabular osteotomy. Clin Orthop Relat Res. 1999;363:81–92. [PubMed]
  • 10.Jacobsen S, Rømer L, Søballe K. The other hip in unilateral hip dysplasia. Clin Orthop Relat Res. 2006;446:239–246. [DOI] [PubMed]
  • 11.Jacobsen S, Sonne-Holm S, Lund B, Søballe K, Kiær T, Rovsing H, Monrad H. Pelvic orientation and assessment of hip dysplasia in adults. Acta Orthop Scand. 2004;75:721–729. [DOI] [PubMed]
  • 12.Jamali AA, Mladenov K, Meyer DC, Martinez A, Beck M, Ganz R, Leunig M. Anterior pelvic radiographs to assess acetabular retroversion: high validity of the “cross-over-sign.” J Orthop Res. 2007;25:758–765. [DOI] [PubMed]
  • 13.Kralj M, Mavcic B, Antolic V, Iglic A, Kralj-Iglic V. The Bernese periacetabular osteotomy: clinical, radiographic and mechanical 7–15-year follow-up of 26 hips. Acta Orthop. 2005;76:833–840. [DOI] [PubMed]
  • 14.Langlotz F, Bächler R, Berlemann U, Nolte LP, Ganz R. Computer assistance for pelvic osteotomies. Clin Orthop Relat Res. 1998;354:92–102. [DOI] [PubMed]
  • 15.Langlotz F, Stucki M, Bächler R, Scheer C, Ganz R, Berlemann U, Nolte LP. The first twelve cases of computer assisted periacetabular osteotomy. Comput Aided Surg. 1997;2:317–326. [DOI] [PubMed]
  • 16.Mast JW, Brunner RL, Zebrack J. Recognizing acetabular version in the radiographic presentation of hip dysplasia. Clin Orthop Relat Res. 2004;418:48–53. [DOI] [PubMed]
  • 17.Mechlenburg I, Nyengaard J, Rømer L, Søballe K. Changes in load-bearing area after Ganz periacetabular osteotomy evaluated by multislice CT scanning and stereology. Acta Orthop Scand. 2004;75:147–153. [DOI] [PubMed]
  • 18.Myers SR, Eijer H, Ganz R. Anterior femoroacetabular impingement after periacetabular osteotomy. Clin Orthop Relat Res. 1999;363:93–99. [DOI] [PubMed]
  • 19.Nakamura S, Yorikawa J, Otsuka K, Takeshita K, Harasawa A, Matsushita T. Evaluation of acetabular dysplasia using a top view of the hip on three-dimensional CT. J Orthop Sci. 2000;5:533–539. [DOI] [PubMed]
  • 20.Peters CL, Erickson JA, Hines JL. Early results of the Bernese periacetabular osteotomy: the learning curve at an academic medical center. J Bone Joint Surg Am. 2006;88:1920–1926. [DOI] [PubMed]
  • 21.Pogliacomi F, Stark A, Wallensten R. Periacetabular osteotomy: good pain relief in symptomatic hip dysplasia, 32 patients followed for 4 years. Acta Orthop. 2005;76:67–74. [DOI] [PubMed]
  • 22.Portinaro NM, Murray DW, Bhullar TP, Benson MK. Errors in measurement of acetabular index. J Pediatr Orthop. 1995;15:780–784. [DOI] [PubMed]
  • 23.Siebenrock KA, Kalbermatten DF, Ganz R. Effect of pelvic tilt on acetabular retroversion: a study of pelves from cadavers. Clin Orthop Relat Res. 2003;407:241–248. [DOI] [PubMed]
  • 24.Siebenrock KA, Schöll E, Lottenbach M, Ganz R. Bernese periacetabular osteotomy. Clin Orthop Relat Res. 1999;363:9–20. [DOI] [PubMed]
  • 25.Søballe K. Pelvic osteotomy for acetabular dysplasia. Acta Orthop Scand. 2003;74:117–118. [DOI] [PubMed]
  • 26.Tallroth K, Lepistö J. Computed tomography measurement of acetabular dimensions: normal values for correction of dysplasia. Acta Orthop. 2006;77:598–602. [DOI] [PubMed]
  • 27.Tannast M, Murphy SB, Langlotz F, Anderson SE, Siebenrock KA. Estimation of pelvic tilt on anteroposterior x-rays: a comparison of six parameters. Skeletal Radiol. 2006;35:149–155. [DOI] [PubMed]
  • 28.Tannast M, Zheng G, Anderegg C, Burckhardt K, Langlotz F, Ganz R, Siebenrock KA. Tilt and rotation correction of acetabular version on pelvic radiographs. Clin Orthop Relat Res. 2005;438:182–190. [DOI] [PubMed]
  • 29.Tönnis D. Congenital Dysplasia and Dislocation of the Hip in Children and Adults. Berlin, Germany: Springer; 1987.
  • 30.Troelsen A, Jacobsen S, Rømer L, Søballe K. Weightbearing anteroposterior pelvic radiographs are recommended. Clin Orthop Relat Res. 2008; DOI: 10.1007/s11999-008-0156-0. [DOI] [PMC free article] [PubMed]
  • 31.Trousdale RT, Cabanela ME. Lessons learned after more than 250 periacetabular osteotomies. Acta Orthop Scand. 2003;74:119–126. [DOI] [PubMed]
  • 32.Trousdale RT, Ekkernkamp A, Ganz R, Wallrichs SL. Periacetabular and intertrochanteric osteotomy for the treatment of osteoarthrosis in dysplastic hips. J Bone Joint Surg Am. 1995;77:73–85. [DOI] [PubMed]
  • 33.Trumble SJ, Mayo KA, Mast JW. The periacetabular osteotomy: minimum 2 year followup in more than 100 hips. Clin Orthop Relat Res. 1999;363:54–63. [DOI] [PubMed]
  • 34.Wiberg G. Studies on dysplastic acetabula and congenital subluxation of the hip: with special reference to the complication of osteoarthritis. Acta Chir Scand. 1939;83(suppl 58):5–135.

Articles from Clinical Orthopaedics and Related Research are provided here courtesy of The Association of Bone and Joint Surgeons

RESOURCES