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

Poor success rates with double pelvic osteotomy for craniodorsal luxation of total hip prosthesis in 11 dogs

OBJECTIVE

To report the outcome of double pelvic osteotomy (DPO) for craniodorsal luxation of total hip replacement (THR).

STUDY DESIGN

Retrospective case series.

ANIMALS

Eleven client-owned animals.

METHODS

Dogs with craniodorsal luxation of THR and high angle of lateral opening (ALO) were considered candidates for DPO. The ALO and the version angle (VA) were measured on pre- and post-DPO radiographs. Pre- and post-DPO ALO and VA were compared using a Wilcoxon signed-rank test. Clinical and radiographic outcomes were assessed at 2 and 6 months post-DPO.

RESULTS

Eleven DPOs were performed on 11 dogs after THR luxation. The ALO was reduced from a median of 66.2° (range 37.3-73.1°) to 55.9° (range 13.2-60.0°) (p ≤ .001), and VA increased from a median of 25.6° (range 6.8-51.9°) to 35.3° (range 15.1-51.7°) (p ≤ .03). Craniodorsal luxation recurred in five dogs and was managed with closed reduction (one dog), capsulorrhaphy (one dog), or repositioning of the acetabular cup (three dogs). The median clinical follow-up duration was 19.7 months (range 3.4-73.0). In the long term, seven dogs required explantation (five aseptic loosenings, two infections) (median 8.2 months, range 2.6-50.6).

CONCLUSION

Reluxation was frequent after DPO, 5/11 dogs requiring additional procedures, including three cup revisions. The long-term outcome was considered to be poor due to frequent explantation.

CLINICAL SIGNIFICANCE

Double pelvic osteotomy may be considered to avoid cup replacement when managing craniodorsal THR luxations in dogs but is not recommended due to high complication rates.

Fluoroscopic Categorization of Cementless Acetabular Component Positioning

OBJECTIVES

 The purpose of this study was to evaluate a fluoroscopic method of angle of lateral opening (ALO) categorization based on identification of the visible portion of a pre-existing, circular recess within the metal shell of the BioMedtrix BFX acetabular component, which projects as an ellipse at clinically relevant ALO values. Our hypothesis was that there will be an association between the actual ALO and the categorization of ALO based on identification of the visible portion of the elliptical recess on a lateral fluoroscopic image at clinically relevant values.

METHODS

 A custom plexiglass jig was fitted with a two-axis inclinometer and a 24 mm BFX acetabular component attached to its tabletop. Fluoroscopic reference images were obtained with the cup positioned at an ALO of 35, 45 and 55 degrees with a fixed 10 degrees of retroversion. Thirty study fluoroscopic images (10 images at each ALO) were obtained based on randomization at an ALO of 35, 45 and 55 degrees (±0.5 degrees) with 10 degrees of retroversion. The order of the study images was randomized, and a single, blinded observer categorized the 30 study images as representing an ALO of 35, 45 or 55 degrees by comparison to the reference images.

RESULTS

 Analysis showed perfect (30/30) agreement with a weighted kappa coefficient of 1 (95% confidence interval: -0.717 to 1).

CLINICAL RELEVANCE

 The results demonstrate that accurate categorization of ALO can be achieved using this fluoroscopic method. This method may prove to be a simple but effective method of estimating intraoperative ALO.

Management of total hip replacement luxation with triple pelvic osteotomy

OBJECTIVE

To report the outcome of dogs treated with triple pelvic osteotomy (TPO) for dorsal luxation after total hip replacement (THR).

STUDY DESIGN

Retrospective clinical case series.

ANIMALS

Seventeen client-owned animals.

METHODS

Medical records were searched at a single institution for dogs that had been treated with TPO for dorsal THR luxation. The angle of lateral opening (ALO), version angle (VA), and inclination angle (IA) were measured from radiographs after THR and TPO and corrected for pelvic rotation. A paired t test was performed to compare cup orientation after THR and TPO. Functional outcome was assessed at follow-up examination and during telephone interviews.

RESULTS

Eighteen TPOs were performed in 17 dogs, and radiographs were available for 15 cases. Open and/or closed hip reduction with additional stabilization was attempted unsuccessfully in 6 dogs prior to TPO. Triple pelvic osteotomy reduced the ALO by a mean of 23.0 ° ± 10.9 ° (P ≤ .001), increased VA by 9.0 ° ± 4.9 ° (P < .001), and increased IA by 2.9 ° ± 5.8 ° (P = .126). An excellent or good outcome was achieved in 12 dogs. Ventral luxation occurred in 3 dogs, and dorsal luxation occurred in 1 dog after TPO. Triple pelvic osteotomy excessively reduced ALO in 2 dogs with ventral luxation.

CONCLUSION

Triple pelvic osteotomy with cup retention is a viable alternative to cup revision for treatment of dorsal luxation of cemented and cementless THR. Triple pelvic osteotomy significantly reduces ALO and increases VA. Careful patient selection is recommended because excessive ventroversion can lead to ventral luxation.

CLINICAL SIGNIFICANCE

Triple pelvic osteotomy offers a revision option that preserves the implant-bone interface and significantly reduces ALO. This technique may be appropriate in dogs with high ALO, luxoid hips, and prior failed revision attempts.

Effects of antebrachial torsion on the measurement of angulation in the frontal plane: A cadaveric radiographic analysis

Objectives: To quantify the effect of antebrachial torsion on the miscalculation of radial valgus measured radiographically and to assess a radiographic positioning method used to mitigate torsion-associated artifactual miscalculation of concurrent frontal plane angulation.

Methods: A canine cadaveric forelimb was used to model different combinations of valgus and external torsion. Valgus was induced in the limb in increments of five degrees, radiographic images were taken at each increment, and the observed radiographic valgus was measured. Various angles of torsion were then induced and the process was repeated for a range of torsional angles at 15° increments. For the second objective, the study was repeated with the forelimb rotationally re-positioned to mirror the degree of the induced torsion of the deformity at each valgus and torsion iteration.

Results: Both zero degrees and 15° torsional iterations possessed mean artifactual valgus (AV) values between zero and five degrees for every valgus increment. With torsion of 30° and higher, mean AV values varied widely and did not fall within the zero to five degree accepted range. Rotationally re-positioning the limb in an attempt to alleviate the AV discrepancies resulted in the 30° torsional group having acceptable AV values for valgus values between zero and 20°.

Clinical significance: Increasing antebrachial torsion interferes with accurate radiographic measurement of frontal plane deformities. Radiographically repositioning the limb allows the accurate calculation of more valgus and torsion combinations, but still results in miscalculations of more complex deformities.

Inter- and intra-observer variability of radiography and computed tomography for evaluation of Zurich cementless acetabular cup placement ex vivo

Objective: To evaluate the inter- and intra-observer variability in measurement of the angle of lateral opening (ALO) and version angle measurement using digital radiography and computed tomography (CT).

Methods: Each hemipelvis was implanted with a cementless acetabular cup. Ventrodorsal and mediolateral radiographs were made of each pelvis, followed by CT imaging. After removal of the first cup, the pelves were implanted with an acetabular cup in the contra-lateral acetabulum and imaging was repeated. Three surgeons measured the ALO and version angles three times for each cup from the mediolateral radiographic projection. The same measurements were made using three-dimensional multiplanar reconstructions from CT images. Two anatomical axes were used to measure pelvic inclination in the sagittal plane, resulting in six measurements per cup. Two-way repeated measures analysis of variance evaluated inter- and intra-observer repeatability for radiographic and CT-based measurements.

Results: Version angle based on radio-graphic measurement did not differ within surgeons (p = 0.433), but differed between surgeons (p <0.001). Radiographic measurement of ALO differed within surgeons (p = 0.006) but not between surgeons (p = 0.989). The ALO and version angle measured on CT images did not differ with or between surgeons.

Clinical significance: Assessment of inter-and intra-observer measurement of ALO and version angle was more reproducible using CT images than conventional mediolateral radiography for a Zurich cementless acetabular cup.

Total hip replacement with dorsal acetabular rim augmentation using the SOP(TM) implant and polymethylmethacrylate cement in seven dogs with dorsal acetabular rim deficiency

OBJECTIVE

To describe a surgical technique for reinforced augmentation of the dorsal acetabular rim (DAR) using a string-of-pearls (SOP™) locking plate and polymethylmethacrylate (PMMA) bone cement, and to report clinical outcome in 7 dogs.

STUDY DESIGN

Case series.

ANIMALS

Dogs (n=7).

METHODS

Medical records (November 2009-April 2010) of 7 dogs with large DAR deficits, that had total hip replacement (THR) with reinforced augmentation of the DAR using a SOP™ plate and PMMA were evaluated retrospectively. Reinforced augmentation of the DAR involved anchorage of a precontoured 2.0 or 2.7 mm SOP™ plate dorsal to the acetabulum followed by application of PMMA cement to cover the reamed acetabulum and plate. Cemented acetabular components were used. Implant associated complications were recorded and ≥6-month follow-up obtained.

RESULTS

In all dogs, lameness improved at medium-term reassessment (median, 8 months; range, 6-11 months). Complications included transient sciatic neurapraxia in 2 dogs, which resolved by 3 months.

CONCLUSIONS

Reinforced augmentation of the DAR using a SOP™ plate and PMMA cement may facilitate placement of acetabular THR component implantation in dogs with severe DAR insufficiency.

Personalized image-based templates for precise acetabular prosthesis placement in total hip arthroplasty: a pilot study

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 degrees to 54.3 degrees and the anteversion angle was 11.3 degrees to 18.5 degrees .

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.

Evaluation of the effect of pelvic tilt in the coronal plane on the Norberg angle measured in ventrodorsal radiographic views of a canine hip joint bone model

OBJECTIVE

To determine the effect of pelvic tilt on the Norberg angle (NA) measured in ventrodorsal radiographic views of a hip joint in a canine femoral-pelvic bone model.

SAMPLE POPULATION

Radiographic views of a femoral-pelvic bone model with 1 articulated hip joint (without evident laxity).

PROCEDURES

The bone model was placed on a radiography table. With the joint fully extended, the pelvic coronal plane was tilted from 0° in 5° increments caudally and cranially to a maximum of 30° in each direction (femoral frontal plane was maintained parallel with the radiograph cassette); a digital ventrodorsal radiographic view was obtained at each tilt position. In each image, the NA was measured 3 times by 2 observers (operators). The effect of pelvic tilt on the NA was evaluated by use of a repeated-measures analysis; within-and between-operator variances were also assessed.

RESULTS

Within-operator repeatability was excellent for assessments of hip joint NAs in radiographic views obtained when cranial or caudal tilt was applied to the femoral-pelvic model; replicate measurement variation was < 2.5% (coefficient of variation < 5%). Mean NA values determined by the 2 operators in cranial or caudal tilt views did not differ. Mean between-operator difference in caudal tilt measurements was -0.55° (95% confidence interval, -1.69° to 0.59°) and in cranial tilt measurements was -0.13° (95% confidence interval, -1.33° to 1.06°). Cranial or caudal pelvic tilt did not affect measurement of the NA.

CONCLUSIONS AND CLINICAL RELEVANCE

Model-derived results indicated that pelvic tilt during acquisition of ventrodorsal radiographic views of the hip joints of a dog should not affect measurement of the NA.

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

OBJECTIVE

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).

STUDY DESIGN

Comparison of retrospectively selected cases and controls

SAMPLE POPULATION

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS AND CLINICAL RELEVANCE

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.