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Background

Several studies have reported that the transverse acetabular ligament (TAL) can be used to orient the acetabular component during total hip arthroplasty and that it can be identified in nearly all patients.

Questions/purposes

We attempted to determine how often the TAL could be identified during primary THA and its accuracy as a guide for acetabular component positioning.

Methods

In a prospective series of 63 patients (64 hips) undergoing primary THA, two surgeons attempted to identify the TAL and, if it was found, to use it for acetabular component orientation. Patients in whom the TAL was identified served as the study group and the ligament was used for cup orientation in those patients; the remaining patients in whom the ligament could not be identified served as a control group and had free-hand cup positioning. Anteversion was determined by radiographic measurement from true lateral views.

Results

The TAL was identified in only 30 hips (47%) and was more likely to be found in patients who did not have inferior acetabular osteophytes. Acetabular position was not improved using this ligament for reference.

Conclusions

The TAL could not be routinely identified at surgery and when used for cup orientation it was no more accurate for cup positioning than free-hand technique.

Background

Although surgical navigation reduces the rate of malpositioned acetabular cups in total hip arthroplasty (THA), its use has not been widely adopted. As a result of our perceived need for simple and efficient methods of navigation, we developed a mechanical navigation device for acetabular cup orientation.

Questions/purposes

We assessed accuracy of cup orientation (mean error of cup inclination and anteversion) of a novel mechanical navigation device, percentage of outliers, length of operation, and compared the results with a series of CT-based computer-assisted THAs.

Methods

Cup orientation of 70 THAs performed using the mechanical navigation device was compared with a historical control group of 146 THAs performed using CT-based computer navigation. Postoperative cup orientation was measured using a validated two-dimensional/three-dimensional matching method. An outlier was defined outside a range of ± 10° from the planned inclination and/or anteversion.

Results

Using the mechanical navigation device, we observed a decrease in the errors of inclination (1.3° ± 3.4° [range, −6.6° to 8.2°] versus 3.5° ± 4.2° [−12.7° to 6.9°]), errors of anteversion (1.0° ± 4.1° [−8.8° to 9.5°] versus 3.0° ± 5.8° [−11.8° to 19.6°]), percentages of outliers (0% versus 9.6%), and length of operation (112 ± 22 [78–184] minutes versus 132 ± 18 [90–197] minutes) compared with CT-based navigation.

Conclusions

Compared with CT-based surgical navigation, navigation of acetabular cup orientation using a mechanical device can be performed in less time, lower mean errors, and minimal equipment.

Background

Increasingly, acetabular retroversion is recognized in patients undergoing hip arthroplasty. Although prosthetic component positioning is not determined solely by native acetabular anatomy, acetabular retroversion presents a dilemma for component positioning if the surgeon implants the device in the anatomic position.

Questions/purposes

We asked (1) whether there is a difference in ROM between surface replacement arthroplasty (SRA) and THA in the retroverted acetabulum, and (2) does increased femoral anteversion improve ROM in the retroverted acetabulum?

Methods

Using a motion analysis tracking system, we determined the ROM of eight cadaveric hips and then created virtual CT-reconstructed bone models of each specimen. ROM was determined with THA and SRA systems virtually implanted with (1) the acetabular component placed in 45° abduction and matching the acetabular anteversion (average 23° ± 4°); (2) virtually retroverting the bony acetabulum 10°; and (3) after anteverting the THA femoral stem 10°.

Results

SRA resulted in ROM deficiencies in four of six maneuvers, averaging 25% to 29% in the normal and retroverted acetabular positions. THA restored ROM in all six positions in the normal acetabulum and in four of the six retroverted acetabula. The two deficient positions averaged 5% deficiency. THA with increased femoral stem anteversion restored ROM in five positions and showed only a 2% deficiency in the sixth position. Compared with the intact hip, ROM deficits were seen after SRA in the normal and retroverted acetabular positions and to a lesser extent for THA which can be improved with increased femoral stem anteversion.

Conclusion

Poor ROM may result after SRA if acetabular retroversion is present.

Total hip arthroplasty restores lost mobility to patients suffering from osteoarthritis and acute trauma. In recent years, navigated surgery has been used to control prosthetic component placement. Furthermore, there has been increasing research on what constitutes correct placement. This has resulted in the definition of a safe-zone for acetabular cup orientation. However, there is less definition with regard to femoral anteversion and how it should be measured. This study assesses the validity of the femoral anteversion measurement method used in imageless navigation, with particular attention to how the neutral rotation of the femur is defined. CT and gait analysis methodologies are used to validate the reference which defines this neutral rotation, i.e., the ankle epicondyle piriformis (AEP) plane. The findings of this study indicate that the posterior condylar axis is a reliable reference for defining the neutral rotation of the femur. In imageless navigation, when these landmarks are not accessible, the AEP plane provides a useful surrogate to the condylar axis, providing a reliable baseline for femoral anteversion measurement.

Background

Minimally invasive total hip arthroplasty (MITHA) remains considerably controversial. Limited visibility and prosthesis malposition increase the risk of post-surgical complications compared to those of the traditional method.

Methods

A meta-analysis was undertaken of all published databases up to May 2011. The studies were divided into four subgroups according to the surgical approach taken. The radiological outcomes and complications of minimally invasive surgery were compared to traditional total hip arthroplasty (TTHA) using risk ratio, mean difference, and standardized mean difference statistics.

Results

In five studies involving the posterolateral approach, no significant differences were found between the MITHA groups and the TTHA groups in the acetabular cup abduction angle (p = 0.41), acetabular anteversion (p = 0.96), and femoral prosthesis position (p = 0.83). However, the femoral offset was significantly increased (WMD = 3.00; 95% CI, 0.40–5.60; p = 0.02). Additionally, there were no significant differences among the complications in both the groups (dislocations, nerve injury, infection, deep vein thrombosis, proximal femoral fracture) and revision rate (p>0.05). In three studies involving the posterior approach, there were no significant differences in radiological outcomes or all other complications between MITHA or TTHA groups (p>0.05). Three studies involved anterolateral approach, while 2 studies used the lateral approach. However, the information from imaging and complications was not adequate for statistical analysis.

Conclusions

Posterior MITHA seems to be a safe surgical procedure, without the increased risk of post-operative complication rates and component malposition rates. The posterolateral approach THA may lead to increased femoral offset. The current data are not enough to reach a positive conclusion that lateral and anterolateral approaches will result in increased risks of adverse effects and complications at the prosthesis site.

Hip resurfacing is femoral bone preserving, but there is controversy regarding the amount of bone removed at the acetabular side. We therefore compared the implanted acetabular cup sizes in primary THAs between two resurfacing devices and a conventional press-fit cup using a series of 2134 THAs (Allofit® cup 1643 hips, Durom® Hip Resurfacing 249 hips, and Birmingham Hip® Resurfacing 242 hips). The effects of patient demographics and cup position in the horizontal plane also were assessed. After controlling for gender, patients were matched for height, weight, body mass index, and age. The mean size for Allofit® cups was smaller than the sizes for Durom® and Birmingham Hip® Resurfacing cups in women (49.9 mm, 51.6 mm, 52.3 mm, respectively) and men (55.1 mm, 56.7 mm, 57.8 mm; respectively). Although patient height was associated with the implanted cup size, the cup position in the horizontal plane had no effect on the size used. Larger cups were used with hip resurfacing than for THA with a conventional press-fit cup. However, additional studies are needed to determine whether these small differences have any clinical implications in the long term. The association of cup size and patient height should be considered in future studies comparing component sizes among different implants.

Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Purpose

At present, the indications for femoral derotational osteotomy remain controversial due to the inconsistent findings in femoral neck anteversion in developmental dysplasia of the hip (DDH). Moreover, combined anteversion is not assessed in unilateral DDH using three dimensional-CT. Therefore, the purposes of our study were to observe whether the femoral neck anteversion (FA), acetabular anteversion (AA) and combined anteversion (CA) on the dislocated hips were universally presented in unilateral DDH according to the classification system of Tönnis.

Methods

Sixty-two patients with unilateral dislocation of hip were involved in the study, including 54 females and eight males with a mean age of 21.63 months (range, 18–48 months). The FA, AA and CA were measured and compared between the dislocated hips and the unaffected hips.

Results

Although no significant difference was observed in FA between the dislocated hips and the unaffected hips (P = 0.067, 0.132, respectively) in Tönnis II and III type, FA was obviously increased on the dislocated hips compared with the unaffected hips in Tönnis IV type. Increased AA on the dislocated hips was a universal finding in Tönnis II, III and IV types. Meanwhile, a wide safe range of CA from 24° to 62° was demonstrated on the unaffected hips.

Conclusion

Femoral derotational osteotomy seems not to be necessary in Tönnis II and III types in unilateral DDH. Femoral derotational osteotomy should be considered in DDH, especially in Tönnis IV type, if the CA is still above 62° and the hip joints present instability in operation after abnormal acetabular anteversion, acetabular index and acetabular coverage of the femoral head are recovered to normal range through pelvic osteotomy.

The size of the femoral head and acetabular anteversion are crucial for stability in total hip replacements. This study examined the effects of head diameter and acetabular anteversion on the posterior instability after total hip replacement in an in vivo setting. The acetabular shell was inserted at 0–20° of anteversion at five degree intervals. By using different head sizes (28 mm, 32 mm, 36 mm), the degrees of dislocation were recorded by computer navigation. The 36-mm group consistently showed better stability compared with the 32- and 28-mm groups, regardless of the degree of cup anteversion. Within each group of head size, the hip was significantly more stable when the cup anteversion increased from 0° to 10°. The difference became insignificant when it increased from 15° to 20°.

There is limited morphological data on the sex differences between the commonly used pelvic parameters. This study analysed the CT scans of 100 consecutive Caucasian patients, 61 males and 39 females, undergoing hip resurfacing arthroplasty surgery for hip osteoarthritis in one institution.

There were no sex differences in femoral torsion/anteversion, femoral neck angle and acetabular inclination. Males had a mean femoral torsion/anteversion of 8 degrees (range -5 to 26 degrees), a mean femoral neck angle of 129 degrees (range 119 to 138 degrees) and a mean acetabular inclination of 55 degrees (range 40 to 86 degrees). Females had a mean femoral torsion/anteversion of 9 degrees (range -2 to 31 degrees), a mean femoral neck angle of 128 degrees (range 121 to 138) and a mean acetabular inclination of 57 degrees (range 44 to 80 degrees). Females had a significantly greater acetabular version of 23 degrees (range 10 to 53) compared with 18 degrees in males (range 7 to 46 degrees (p = 0.02) and males had a significantly greater femoral offset of 55 mm (range 42 to 68 mm) compared with 48 mm (range 37 to 57 mm) in females (p = 0.00). There were no significant differences between measurements taken from each patient's right and left hips.

These findings may be useful for the future design and the implantation of hip arthroplasty components.

Several studies have demonstrated a correlation between the acetabular cup position and the risk of dislocation, wear and range of motion after total hip arthroplasty. The present study was designed to evaluate the accuracy of the surgeon’s estimated position of the cup after freehand placement in total hip replacement. Peroperative estimated abduction and anteversion of 200 acetabular components (placed by three orthopaedic surgeons and nine residents) were compared with measured outcomes (according to Pradhan) on postoperative radiographs. Cups were placed in 49.7° (SD 6.7) of abduction and 16.0° (SD 8.1) of anteversion. Estimation of placement was 46.3° (SD 4.3) of abduction and 14.6° (SD 5.9) of anteversion. Of more interest is the fact that for the orthopaedic surgeons the mean inaccuracy of estimation was 4.1° (SD 3.9) for abduction and 5.2° (SD 4.5) for anteversion and for their residents this was respectively, 6.3° (SD 4.6) and 5.7° (SD 5.0). Significant differences were found between orthopaedic surgeons and residents for inaccuracy of estimation for abduction, not for anteversion. Body mass index, sex, (un)cemented fixation and surgical approach (anterolateral or posterolateral) were not significant factors. Based upon the inaccuracy of estimation, the group’s chance on future cup placement within Lewinnek’s safe zone (5–25° anteversion and 30–50° abduction) is 82.7 and 85.2% for anteversion and abduction separately. When both parameters are combined, the chance of accurate placement is only 70.5%. The chance of placement of the acetabular component within 5° of an intended position, for both abduction and anteversion is 21.5% this percentage decreases to just 2.9% when the tolerated error is 1°. There is a tendency to underestimate both abduction and anteversion. Orthopaedic surgeons are superior to their residents in estimating abduction of the acetabular component. The results of this study indicate that freehand placement of the acetabular component is not a reliable method.

The anatomic femoral component and Harris-Galante porous II (HGPII) cup were developed to provide more reliable bone ingrowth. We performed 20 cementless total hip arthroplasties (THAs) with anatomic stem/HGPII cup with 22-mm head in 14 consecutive patients, and evaluated the clinical and radiological results for a mean follow-up of 12.8 years. The all-anatomically designed stem provided excellent clinical and radiographic results. Four acetabular components underwent revision: three for fracture of the locking mechanism and wear of the polyethylene liner and one for the locking mechanism failure with dislocation of the HGPII cup. The abduction angles of the four revised acetabular components were apparently higher. The survivorship 13 years after surgery was 78%. Our findings show good long-term results using the anatomic femoral component, while the HGPII cup combined with 22-mm head seems to have poor durability due to locking mechanism failure.

Background

Appraisal of the orientation of implants in THA dislocations currently is based on imaging done with the patient in the supine position. However, dislocation occurs in standing or sitting positions. Whether measured anteversion differs in images projected in the position of dislocation is unclear.

Questions/purposes

We compared measured acetabular cup orientations on axial CT scans taken with the patient in a supine position with those from CT sections at angles to the sacral slope reflecting standing and sitting positions.

Methods

We retrospectively reviewed the radiographs of 328 asymptomatic patients who had THAs. Anatomic acetabular anteversion (AAA) was measured from the plain CT scan (supine position, axial CT sections). The AAA also was measured on reformatted CT scans in which the orientation was adjusted individually to the sacral slope on lateral radiographs with patients in the standing and sitting positions.

Results

The mean/(SD) AAA changed from 24.2° (6.9°) in the supine position to 31.7° (5.6°) and 38.8° (5.4°) in simulated standing and sitting positions, respectively. The supine AAA correlated with the standing AAA (r = 0.857) but not with the sitting AAA (r = 0.484).

Conclusions

These data suggest measurement of the AAA on a plain CT scan used in current practice is biased. In patients with recurrent posterior dislocation from a sitting position, accounting for the functional variations in measurement of the position of the acetabular cup provides more relevant information regarding component positioning.

Precise evaluation of acetabular cup version is necessary for patients with recurrent hip dislocation after THA. We retrospectively studied 42 patients, who underwent THAs, with multiple cross-table lateral radiographs and CT scans to determine whether radiographic or CT measurement of acetabular component version is more accurate. One observer measured cup version on all radiographs. CT scans were interpreted by one observer. Twenty radiographs were measured twice each by two observers to determine intraobserver and interobserver reliability. We implanted cups in four model pelvises using navigation and compared measurements of anteversion made with radiographs and CT scans. Intraclass correlation coefficients (ICC) for anteversion measurements of two observers were 0.9990 and 0.9998, respectively, when comparing measurements of identical radiographs (intraobserver). Paired values for two observers measuring the same radiograph had an ICC of 0.9686 (interobserver) compared with 0.7412 for measurements from serial radiographs of the same component. The ICC comparing radiographic versus CT-based measurements was 0.6981. CT measurements had stronger correlations with navigated values than radiographic measurements. Accuracy of anteversion measurements on cross-table radiographs depends on radiographic technique and patient positioning whereas properly performed CT measurements are independent of patient position.

Level of Evidence: Level III, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Background:

Abnormal femoral neck anteversion (FNA) and/or acetabulum anteversion (AA) have long been implicated in the etiogenesis of hip osteoarthritis (OA), developmental dysplasia of the hip (DDH), and impingement, instability and wear in total hip arthroplasty (THA). Since studies on the Indian population are sparse on this topic, the purpose of this study was to report the normal values of FNA, AA and the combined anteversion (CA= FNA+ AA) in Indian adults.

Materials and Methods:

FNA, AA and CA were prospectively measured in 172 normal hips in 86 Indian adults using standardized computed tomographic (CT) methods and this data was compared with the established Western values.

Results:

The median values and interquartile ranges were 8° (6.5-10.0°) for FNA, 19° (16.0-22.0°) for AA and 27° (23.5-30.0°) for CA. AA and CA values were significantly (P<0.05) lower in males, and there was also a trend towards lower FNA in males. Although a negative correlation was observed between the FNA and AA, this was not strong and may not be clinically relevant.

Conclusion:

When compared with the Western data, the FNA values were 3-12° lower and the CA values were 3-5° lower in Indian adults. The AA values were comparable, but were skewed towards the higher side. Further studies are needed to assess the clinical relevance of our basic science data in pathogenesis of OA, and to validate it in relation to hip surgeries like corrective osteotomies and THA.

Objective: In order to achieve accurate implantation of the acetabular prosthesis in total hip arthroplasty (THA), we designed individual templates based on a three-dimensional (3D) model generated from computed tomography (CT) scans. Methods: Individual templates were designed for 12 patients who underwent THA. A physical template was designed to conform to the contours of the patient’s acetabulum and to confirm the rotation of the acetabular center. This guided the acetabular component orientation. Results: The preoperative and postoperative X-ray and CT scans were obtained to assess the location with respect to the accuracy of the acetabular component. For all patients, the abduction angle of the acetabular component was 46.7° to 54.3° and the anteversion angle was 11.3° to 18.5°. Conclusions: The assessment of postoperative CT scans demonstrated higher accuracy of the acetabular component bore when used with the individual template. Therefore, the individual template can be an alternative to the computer-assisted navigation systems, with a good cost-performance ratio.

Several studies support the concept that, for optimum range of motion in THA, the combined femoral and acetabular anteversion should be some constant or fall within some “safe zone.” When using a cementless femoral component, the surgeon has little control of the anteversion of the component since it is dictated by native femoral anteversion. Given this constraint, we asked whether the surgeon should use the native anteversion of the acetabulum as a target for implant position in THA. Forty-six patients scheduled for primary THA underwent CT scanning and preoperative planning using a computer workstation. The native acetabular anteversion and the native femoral anteversion were measured. Prosthetic femoral anteversion was measured on the workstation by three-dimensional templating of a straight-stemmed tapered implant. The mean of the sum of the native acetabular anteversion and native femoral anteversion was 28.9°; however, 17% varied by 10° to 15° and 11% by more than 15°. The mean of native femoral anteversion and prosthetic femoral anteversion was 13.8° (range, −6.1°–32.7°) and 22.5° (range, 1°–39°), respectively. Based on our data, we believe the surgeon should not use the native acetabular anteversion as a target for positioning the acetabular component.

Rapidly destructive osteoarthritis (RDO) of the hip is a rare condition characterized by rapid joint degeneration and destruction similar to findings of infection, osteonecrosis, or Charcot disease but without a definitive diagnosis. The cause and natural history of RDO are unclear, but total hip arthroplasty has been utilized as a treatment modality due to the severity of the symptoms. We reviewed retrospectively the records of total hip arthroplasties performed between 1990 and 2003 and identified ten hips in eight patients who fit the profile of the diagnosis of RDO. The mean age at time of surgery was 70. Nine hips were treated with total hip arthroplasty with a hybrid configuration; one hip was treated with a non-cemented total hip arthroplasty. Average follow-up was 6 years with no radiographic evidence of acetabular loosening or osteolysis and no evidence of asymmetric cup wear. One femoral component had evidence of loosening but has not been revised. RDO is an idiopathic condition with no single diagnostic laboratory, pathological, or radiographic finding. A complete preoperative work-up for other causes of hip disease prior to arthroplasty for suspected RDO is necessary to rule out treatable disease. Our series of patients with RDO responded well to hybrid and non-cemented total hip arthroplasty with good clinical and radiographic results.

Malalignment of the cup in total hip arthroplasty (THA) increases the risks of postoperative complications such as neck cup impingement, dislocation, and wear. We asked whether a tailor-made surgical guide based on CT images would reduce the incidence of outliers beyond 10° from preoperatively planned alignment of the cup compared with those without the surgical guide. We prospectively followed 38 patients (38 hips, Group 1) having primary THA with the conventional technique and 31 patients (31 hips, Group 2) using the surgical guide. We designed the guide for Group 2 based on CT images and fixed it to the acetabular edge with a Kirschner wire to indicate the planned cup direction. Postoperative CT images showed the guide reduced the number of outliers compared with the conventional method (Group 1, 23.7%; Group 2, 0%). The surgical guide provided more reliable cup insertion compared with conventional techniques.

Level of Evidence: Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

We studied 105 patients who received a total hip arthroplasty between June 1985 and August 2001 using freehand positioning of the acetabular cup. Using pelvic CT scan and the hip-plan module of SurgiGATE-System (Medivision, Oberdorf, Switzerland), we measured the angles of inclination and anteversion of the cup. Mean inclination angle was 45.8°±10.1° (range: 23.0–71.5°) and mean anteversion angle was 27.3°±15.0° (range: −23.5° to 59.0°). We compared the results to the “safe” position as defined by Lewinnek et al. and found that only 27/105 cups were implanted within the limits of the safe position. We conclude that a safe position as defined by Lewinnek et al. [13] was only achieved in a minority of the cups that were implanted freehand.

A CT-based navigation system is helpful to evaluate the reamer shaft and the impactor position/orientation during unilateral total hip arthroplasty (THA). The main objective of this study is to determine the accuracy of the Navitrack system by measuring the implant's true anteversion and inclination, based on pre- and postoperative CT scans (n = 9 patients). The secondary objective is to evaluate the clinical validity of measurements based on postop anteroposterior (AP) radiographs for determining the cup orientation. Postop CT-scan reconstructions and postop planar radiographs showed no significant differences in orientation compared to peroperative angles, suggesting a clinical validity of the system. Postoperative AP radiographs normally used in clinic are acceptable to determine the cup orientation, and small angular errors may originate from the patient position on the table.

Background and purpose Total hip arthroplasties in young patients have lower long-term survival rates than in older patients. We evaluated the use of a unique treatment protocol in patients aged between 40 and 50 years. In all cases we used a cemented THA, and for acetabular deficiencies we also used impacted bone grafts together with a cemented cup.

Methods In 140 consecutive patients who were between 40 and 50 years of age at index surgery, 168 cemented total hip prostheses were evaluated after a mean follow-up time of 10 (2–19) years. Acetabular deficiencies were reconstructed with wire meshes and impacted bone grafts with a cemented cup (70 hips). During follow-up, 18 patients died (27 hips); in this group 3 hips (3 patients) had been revised. None of the patients were lost to follow-up. In all surviving patients, clinical assessment was performed with hip-score questions and all radiographs were evaluated.

Results All clinical questionnaires showed an improved clinical hip score. 29 hips (17%) were revised after a mean of 8 (0.3–18) years. Kaplan-Meier survival analysis showed a survival of 88% (95% CI: 82–94) after 10 years with revision of either component for any reason. Survival with endpoint revision for aseptic loosening of either component was 94% (95% CI: 90–99) after 10 years.

Interpretation Cemented implants in young patients have satisfying long-term results. Reconstruction of acetabular deficiencies with impacted bone grafts show promising results.

The centre of rotation of the hip can be displaced in hip dysplasia and revision arthroplasty. This study examined the effect of artificial femoral head load after acetabular component displacement in total hip arthroplasty. Sixteen total hip arthroplasty models of human cadaver specimens were reconstructed, and under different acetabular component position, the load around the femoral head was evaluated by strain gages. The results showed that the load was higher in the same specimens when the cup was moved 2 mm inward or upward, especially after the cup was moved more than 6 mm, and the load had an increasing effect in the inward group. In the upward group, an increasing effect happened at 8 mm upward displacement, but the stress value decreased from 4 mm to 6 mm upward displacement. In the same moving distance, the stress of inward displacement is obviously higher than upward displacement. Altogether, the results suggested that for both inward displacement and upward displacement of the acetabular cup, the load around the femoral head increased gradually, while the distance of the inward displacement and the superior displacement was increased. The greater the displacement, the bigger the loading contact stress. The upward displacement caused less stress change on the femoral head. The stress of the 6 mm upward position was lower than nearby positions; perhaps this site represented a stress buffering zone.

Purpose

Biomechanic factors play a role in the pathogenesis of knee osteoarthritis. The aim of the study was to find out whether there is a relation between femoral, acetabular anteversions, anterior, posterior acetabular coverages and primary osteoarthritis of the knee.

Methods

Thirty patients with primary osteoarthritis of the knee and 29 control subjects were enrolled into the study. Femoral anteversion, acetabular anteversion, McKibbin’s instability index, anterior acetabular sector and posterior acetabular sector angles were measured using tomographic scanograms.

Results

There was no difference between groups for each parameter (P > 0.05).

Conclusion

This study did not show any relationship between the axial plane changes in the hip joint and primary knee osteoarthritis.

In image-free navigation systems, cup orientation is determined in the pelvic coordinate by registration of bony landmarks. While the value of navigation relates primarily to the reliability and accuracy of cup placement, the reliability of registration plays a role in cup placement. We therefore examined intra- and intersurgeon variability in registration and the distance between registration points in each bony landmark. Thirty-seven THAs were performed in the lateral position and 15 THAs in the supine position. The cup was fixed using a navigation system. The registration was repeated two more times by operator and assistant, and the intra- and intersurgeon variability of cup abduction angle and anteversion was analyzed by ICC (intraclass correlation coefficients). In 25 hips, the distance between intrasurgeon registration points and between intersurgeon registration points in each landmark were calculated. The ICC in the lateral position ranged between 0.59 and 0.81, and between 0.85 and 0.95 in the supine position. The ICCs of cup abduction angle for the intra- and intersurgeon variability were 0.92 and 0.95 for the supine position and 0.65 and 0.59 for the lateral position. Those of anteversion were 0.93, 0.85, and 0.81, 0.72, respectively. The variability in locating the ASIS in the lateral position was greater than that in the supine position. The variability of registration points depended on bony landmarks and patient position but the range of variability we found would not likely result in a large variability in cup placement.

Background

CT allows for accurate measurement of acetabular orientation and shape, but malpositioning of the pelvis may lead to measurement variance.

Purpose

We therefore sought to determine: (1) whether acetabular anteversion measurements using the femoral head centers differed from those using the posterior ischia, and (2) the extent to which changing obliquity, rotation, and tilt of a pelvis in a CT scanner affected the measurement of acetabular variables.

Methods

A radiopaque human pelvis model with articulated hips was suspended from a plastic sheet as part of an adjustable frame. Changes in the transverse and sagittal planes created rotation and tilt, while rotating the frame in the coronal plane created obliquity. CT scans were obtained, varying the combinations of obliquity, rotation, and tilt by intervals of 5°, up to 20°. Acetabular anteversion (AA), anterior acetabular sector angle (AASA), posterior acetabular sector angle (PASA), and horizontal acetabular sector angle (HASA) were measured.

Results

The two methods for measuring AA yielded values differing by 1° to 4° but correlated (r = 0.981) across the spectrum of pelvis positioning. Pelvic obliquity and tilt were linearly associated with changes in the measurements. For each 1°-increase in pelvic obliquity, AA changed −0.4°, and AASA, PASA, and HASA changed 1.93°, 0.99°, and 2.80°, respectively. For each 1°-increase in pelvic tilt, AA changed 0.8°, and AASA, PASA, and HASA changed −1.07°, 0.52°, and −0.51°, respectively. Rotation had no affect on the variables.

Conclusions

Small changes in pelvic obliquity and tilt were associated with variances in acetabular measurements. The measured changes were directly proportional to the changes in obliquity and tilt, and were additive. Pelvic rotation created no changes in measurement.

Clinical Relevance

Incorrect interpretation of acetabular anteversion and coverage may lead to unsatisfactory acetabular fragment positioning during reorientational surgery. Although intraoperative positioning of an acetabular fragment may not be as precise as the tools for preoperative planning, it is important for a surgeon to have the most precise data available for planning a procedure, and know where error can occur in collecting the data.