Acetabular Component Orientation Research Articles

The effect of posterior capsule repair upon post-operative hip dislocation following primary total hip arthroplasty

BackgroundHerein, we evaluated, retrospectively, the effect of posterior capsular repair upon postoperative hip dislocation subsequent to total hip arthroplasty (THA) incorporating a posterolateral approach.MethodsA total of 181 patients undergoing 204 primary non-complicated THA surgical procedures in the period from January 2000 to October 2005 inclusively were included in this study. The patients were separated into two groups by whether the posterior capsular repair had been incorporated in the surgical procedure. For the surgeon did not commence repairing the posterior capsule until July, 2003, all members in the group that did not undergo posterior capsular repair (142 hips from 131 patients) were collected since January, 2000 to July, 2003, while the members in the group that underwent posterior capsular repair (62 hips from 52 patients) were followed since July, 2003, to October, 2005. With a minimum follow-up period of 12 months, we evaluated the early post-operative dislocation rate.ResultsThe early postoperative hip-dislocation rate for the group who did not undergo posterior capsular repair appeared to be substantially greater (6.38% versus 0%) than the corresponding figure for the group the members of which underwent posterior capsular repair. In addition, patient demographics and the orientation of acetabular components for the replaced hip joints, as presented in postoperative radiographs, did not differ between the two groups.ConclusionThus, surgeons should include posterior capsular repair as an important step in the surgical procedures of posterolateral approach for all THA in order to reduce the likelihood of early hip dislocation subsequent to THA.

Squeaking in Ceramic-on-Ceramic Hips: The Importance of Acetabular Component Orientation

Audible squeaking in total hip replacements with ceramic-on-ceramic bearings is a rare problem. Acetabular component orientation was compared for 17 squeaking hips and 17 matched controls. Ninety-four percent of control hips were in a range of 25° ± 10° anteversion and 45° ± 10° inclination, but only 35% of squeaking hips were in this range ( P = .0003). Eight hips squeak with bending. Four hips squeak with walking, and 5 hips squeak after prolonged periods of walking. Hips that squeaked with walking had acetabular components that were more anteverted (40°) than hips that squeaked with bending (19°) ( P = .001) or prolonged walking (18°) ( P = .020). The hips started squeaking after an average of 14 months. Patients with squeaking hips were younger, heavier, and taller than patients with silent hips.

Comparison of Conventional Versus Computer-Navigated Acetabular Component Insertion

This retrospective study compared the efficacy of computer navigation and conventional freehand techniques to place acetabular component orientation in the target position of acetabular cup inclination of 45° and anteversion of 20°. We selected 69 patients who had undergone total hip arthroplasty with freehand cup insertion who had computed tomography (CT) to plan for acetabular cup placement of the contralateral side. This group was compared with 98 patients who underwent CT-based cup insertion, and all had postoperative CT. After CT-based cup placement, average cup position was 43° inclination (95% confidence interval [CI], 0.97; range, 30°-58°) and 22.2° anteversion (95% CI, 1.72; range, 5°-38°). For freehand, average cup position was 45.7° inclination (95% CI, 2.63°; range, 26°-64°) and 28.5° anteversion (95% CI, 3.80°; range, 9°-53°). F ratio was 5.56 for inclination and 3.67 for anteversion (P < .0001). This study demonstrated substantial statistical improvement in accuracy of cup placement using CT-based navigation compared with freehand methods.

Acetabular Component Orientation in 834 Total Hip Arthroplasties Using a Manual Technique

Acetabular component orientation during total hip arthroplasty affects dislocation, range of motion, polyethylene wear, pelvic osteolysis, and component migration. New total hip arthroplasty navigation systems have been introduced to avoid the errors reported after acetabular component orientation using a manual technique. We investigated acetabular component orientation in 834 consecutive primary total hip arthroplasties performed by one surgeon using a manual technique. We examined the relationship between dislocation and a defined safe range. Vertical tilt and planar anteversion were 44.4 +/- 6.5 and 17.9 +/- 6.3 (mean +/- standard deviation), respectively. The error of vertical tilt and planar anteversion were 5.2 +/- 3.9 and 5.3 +/- 4 (mean +/- standard deviation), respectively. Two hundred thirty-three of 834 hips (27.8 %) were outside the safe range. Logistic regression analysis showed that patients with Group IV class according to the classification system of Crowe et al and right hips had a greater risk of being outside the safe range. Navigation systems should be considered, especially in patients with highly dislocated hips. We found no relationship between risk of dislocation and the safe range. Factors other than acetabular component orientation also might affect dislocation. Prognostic Study, Level IV (case series).

Biomechanics of Large Femoral Heads

The stability and durability of total hip reconstruction is dependent on many factors that include the design and anatomic orientation of prosthetic components. An analysis of femoral component head size and acetabular component orientation shows an interdependency of these variables and joint stability. Increased femoral component head size can increase hip stability by increasing the prosthetic impingement-free range of hip motion and by increasing the inferior head displacement required before hip dislocation. Increasing the femoral head size from 22 mm to 40 mm increases the required displacement for dislocation by about 5 mm with the acetabular component at 45 degrees of abduction; however, increasing acetabular component abduction greatly diminishes this stability advantage of larger femoral heads. Vertical acetabular component orientation and femoral component head subluxation are each predicted to more than double the tensile stress with acetabular component polyethylene compared with components at 45 degrees of abduction. With a desirable acetabular component orientation, the use of larger femoral heads may result in improved joint stability and durable use of polyethylene. With high abduction acetabular component orientation, the use of larger femoral heads contributes little to joint stability and contributes to elevated stress within the polyethylene that may result in implant failure.

Relation Between Vertical Orientation and Stability of Acetabular Component in the Dysplastic Hip Simulated by Nonlinear Three‐dimensional Finite Element Method

In acetabular dysplasia, more vertical orientation of the acetabular component is often used to minimize the superolateral bone grafting. This study was designed to determine the effects of vertical orientation of the cup on the stability and polyethylene wear of the acetabular component in uncemented total hip arthroplasty (THA). Three-dimensional finite element models of the hemipelvis with dysplastic acetabulum were developed. Metal-backed hemispherical cups were placed in the true acetabulum with abduction angles of 35, 45, 55, and 65 degrees. It was found that more vertical orientation of the cup was associated with larger relative motion of the metal shell between the acetabulum and metal shell. Furthermore, tilting and torsional shear stresses in the model of the cup abduction angle of 65 degrees were found to be 1.7 times larger than that in the model with 35 degrees at the bone-metal shell interface. More vertically oriented cups caused larger contact stresses at the articulating surfaces of the polyethylene liners. The results suggest that the abduction angle of the acetabular component significantly influences cup loosening and polyethylene wear in THA.

Effects of acetabular component orientation on dislocation propensity for small-head-size total hip arthroplasty

Objective. Examine the role of surgical orientation of the acetabular cup on posterior dislocation propensity for small-head-size total hip arthroplasty. Design. A finite element model of a widely used total hip arthroplasty system was examined for peak resisting moment and range-of-motion prior to impingement, as well as prior to onset of posterior dislocation. Acetabular component surgical orientation was varied. Background. Dislocation is a leading cause of total hip replacement failure, with an incidence between 2% and 11%. Clinical registries imply acetabular component orientation to be a leading predictor of dislocation. The finite element method permits this complex kinetic behavior to be addressed systematically. Methods. Twenty-five combinations of cup abduction (five angles) and anteversion (five angles) were studied, with the resultant resisting moment about the cup center being tracked in each case. Key events were benchmarked, and a novel dislocation resistance index was developed for multi-factor comparison. Results. Increasing tilt and/or anteversion resulted in a monotonically increasing range-of-motion prior to impingement, as well as increased peak resisting moment. Range of motion was more sensitive to tilt, while peak resisting moment was more sensitive to anteversion. Peak resisting moment for 22-mm head size was nearly 25% less than that for a 26-mm head. Conclusions. Increased cup tilt and anteversion discourage posterior dislocations of small-head-size components. Relevance Pre-existing soft tissue compromise and untoward patient motions/postures are largely beyond surgeon control. However, other factors being equal, especially for small-head-size components, many posterior dislocations that would otherwise occur might be prevented by suitable tilt and anteversion of the acetabular component.

Acetabular component orientation as an indicator of implant luxation in cemented total hip arthroplasty.

To determine the sensitivity and specificity with which acetabular component angles of inclination and version could be used, alone or in combination, to predict luxation of cemented total hip arthroplasties (THA). Comparison of retrospectively selected cases and controls All THA performed at the University of Florida between 1991 and 1998 with the BioMedtrix system and for which at least 2 months of radiographic follow-up were available. All THA performed at the University of Georgia with the BioMedtrix system which subsequently luxated. Acetabular component inclination angle (IA) and acetabular version angle (VA) were determined for each THA. Data were grouped according to outcome - luxation or no luxation - with the luxated cases from the 2 institutions pooled. Receiver operator characteristic (ROC) analysis was used to evaluate decision rules for using IA and VA as tests for detecting postoperative luxation. Sensitivity and specificity for luxation and 95% confidence bounds were computed with selected values of IA and VA as cut-points. The nonluxation group consisted of 68 THA with a median follow-up time of 5 months (range, 2-60 months). The luxation group consisted of 12 THA with a mean time to luxation of 36 days. The nonluxation group had a mean +/- standard deviation (SD) IA and VA of 40.3 degrees +/- 8.9 degrees and 71.1 +/- 13.6 degrees, respectively, whereas the luxation group had a mean +/- SD IA and VA of 34.7 degrees +/- 12.6 degrees and 72.9 degrees +/- 16.6 degrees, respectively. An IA cut-point of 37.8 degrees achieved 58.3% sensitivity and 57.4% specificity. A VA cut-point of 73 degrees achieved 75.0% sensitivity and 51.5% specificity. IA and VA considered simultaneously achieved a 50.0% sensitivity and 88.2% specificity. ROC analysis indicated that both IA and VA considered individually or simultaneously were poor indicators of luxation. Although extreme values of IA may predict luxation with high specificity, the potential for luxation cannot be excluded based on apparently appropriate values of IA and VA. The results of this study also indicate that a successful outcome is possible with a wide range of acetabular component positions.

Definition and determination of acetabular component orientation in cemented total hip arthroplasty.

To describe the spatial orientation of the cemented acetabular component in cemented total hip arthroplasty, based on a ventrodorsal and lateral radiographic projection of the pelvis. Equations were derived by using trigonometric relationships that describe the radiographic rotation about the longitudinal pelvic axis (alpha), transverse pelvic axis (beta), acetabular inclination (phi), acetabular inclination corrected for longitudinal pelvic rotation, version (phiC), acetabular version (theta), acetabular version corrected for longitudinal pelvic rotation (thetaC), acetabular inclination corrected for transverse pelvic rotation (phi(beta)), and acetabular version corrected for transverse pelvic rotation (theta(beta)) Alpha was calculated by using the equation alpha = sin(-1) (x/y) where x is the transverse distance between the dorsal spinous processes and the center of the pubis on a ventrodorsal radiograph and y is the distance from the pubis to the dorsal aspect of the first coccygeal vertebra perpendicular to the long axis of the pelvis on a lateral radiograph. Phi was calculated from the long axis (LA) and short axis (SA) of the ellipse formed by the radiopaque acetabular marker ring by using the equation phi = sin(-1) (SA/LA). phiC was calculated by using the equation phiC = phi +/- (alpha - tan(-1) (tan alpha cos thetaC)). Theta was determined as previously described. ThetaC was calculated by using the equation thetaC = tan(-1) (tan theta cos alpha). Theta(beta) and theta(beta) were calculated with the equations phi(beta) = tan(-1) (tan theta cos beta) and theta(beta) = theta - tan(-1) (sin beta), respectively. Beta could not be accurately determined from ventrodorsal and lateral pelvic radiographs. These techniques allow for more accurate postoperative radiographic assessment of acetabular component positioning. This information can then be used in retrospective or prospective analyses examining that effects of implant positioning on clinical outcome.

Postoperative dislocation of the head of the hip endoprosthesis and ways to prevent it

428 primary and 20 revision hip arthroplasties (384 patients) were performed during 1992-1998 at Republic Center of Arthroplasty. Hip dislocation was observed in 10 patients. Seven of those hips dislocated during the second postoperative week. Two cases of the recurrent and one case of old dislocation are described. It is shown that the incorrect orientation of acetabular component contributes to hip dislocation. Reduction should be performed under anesthesia with musculature relaxation. In case of recurrent or old dislocations open reduction is indicated. Prevention of hip dislocation must be performed both during intra- and postoperative period.

Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration

We retrospectively reviewed 75 total hip arthroplasties to examine the effect of acetabular component position. In group A, 38 of the components were implanted according to manufacture's instructions with all peripheral fins in contact with acetabular bone; as such, the acetabular components were in a relatively vertical position with a mean angle of inclination of 61.9°. Three of these patients developed recurrent dislocations necessitating revision of the acetabular component. In group B, 37 hips, a more horizontal orientation was used despite the fact that all of the peripheral fins of the acetabular component did not engage acetabular bone; in this group the mean angle of inclination was 49.7°. Only one of these hips recurrently dislocated and required revision. There were no problems in this group associated with provisional component stability caused by inadequate peripheral fixation. Radiographs of all patients were obtained at 4 years after surgery (range, 4.0 – 4.3 years). Pelvic osteolysis had occurred in 24% of hips in group A and 13% of group B. Asymmetric polyethylene wear was observed in 5.1% of the hips in group A; no hip in group B showed wear asymmetry. Acetabular component migration developed in 19% of group A hips and 5% of group B hips. The Mayo clinical hip score was excellent in both groups: group A 71 80 , group B 73 80 . At an intermediate follow-up it is clear that significant problems can be encountered when this component is positioned in a relatively vertical position to facilitate engaging all four peripheral fins in bone. We have addressed this problem by placing the cup in a more anatomic position of inclination while maintaining provisional rim fixation. This has resulted in a decreased incidence of pelvic osteolysis and fewer complications overall.

Analysis of optimal range of socket orientations in total hip arthroplasty with use of computer-aided design simulation.

A three-dimensional computer-aided design model of a total hip replacement was used to study the effects of anteversion and abduction of the acetabular component and anteversion and varus-valgus angulation of the femoral component on the range of hip flexion and extension that could be obtained without component impingement. Impingement of the component was defined as impingement between the neck of the femoral component and the edge of the acetabular component. To achieve an angle of hip flexion greater than 90 degrees and an extension angle greater than 30 degrees without component impingement, the optimal angulations were found to be between 1 and 30 degrees of anteversion and 30 and 50 degrees of abduction of the acetabular component, as well as 10 degrees of anteversion of the femoral component. When the valgus angulation of the femoral component was reduced from 7 to 0 degrees, the allowable range of flexion without impingement increased under the same conditions of acetabular-component orientation and femoral-component anteversion. Significant inverse correlations were found between the anteversion angle of the acetabular component and both the lumbar lordosis angle and the sacrohorizontal angle.