Evaluation of risk factors for luxation after total hip replacement in dogs

Complications and outcomes of total hip arthroplasty in dogs with luxoid hip dysplasia: 18 cases (2010-2022)

OBJECTIVE

To describe the complications and outcomes in dogs with luxoid hip dysplasia (LH) undergoing total hip arthroplasty (THA) and compare complication rates with THA in non-LH dogs.

STUDY DESIGN

Retrospective study.

SAMPLE POPULATION

Client-owned dogs (n = 217) undergoing primary THA (n = 238).

METHODS

Medical records (2010-2022) of dogs undergoing THA were reviewed, and LH was defined as complete dorsal displacement of the femoral head from the acetabulum on lateral projection radiographs. Major or catastrophic complications, revisions, and outcomes were recorded for all dogs and they were compared between LH and non-LH groups.

RESULTS

Eighteen cases met the subcriterion for the LH group and 220 cases met the subcriterion for inclusion in the non-LH group. There were 14 complications in 13/18 dogs with LH; seven were intraoperative (femoral fissure/fracture) and seven were postoperative (dorsal luxation, n = 5; femoral fracture, n = 1; acetabular cup septic loosening, n = 1). Revisions were performed for all LH dogs that encountered complications; satisfactory outcomes were achieved in 12/13 dogs. Overall, LH dogs had a higher risk of developing complications (p < .001), including intraoperative fracture (p < .001) and postoperative dorsal luxation (p = .019) when compared with non-LH dogs.

CONCLUSION

Luxoid hip dysplasia was associated with a higher risk of major complications following THA in dogs, specifically intraoperative fissure/fracture and postoperative dorsal luxation. Despite the increased risk, revisions typically yielded satisfactory outcomes.

CLINICAL SIGNIFICANCE

Luxoid hip dysplasia is an important risk factor for the development of major complications in dogs undergoing THA.

A case report of a cementless total hip replacement performed in a pelvic limb amputee after a failed surgical reduction of a traumatic coxo-femoral luxation with a toggle rod

Coxo-femoral luxation is the most common luxation seen in dogs after road traffic accidents. There are multiple surgical techniques to repair the luxation. These range from a capsular reconstruction to a total hip replacement. This case report describes a total hip replacement to repair a failed toggle rod repair of a coxo-femoral luxation in a Greyhound pelvic limb amputee. The dog returned to normal activity as a household pet three months post-surgery and at the last follow-up consultation at 12 months post-surgery the dog was able to maintain an acceptable activity level as an amputee with no radiographic signs of complications.

Total hip replacement in a cat with contralateral pelvic limb amputation

Case summary

A 10-year-old male neutered domestic shorthair cat, which had previously had its contralateral pelvic limb amputated, was treated for coxofemoral degenerative joint disease (DJD) with a total hip replacement. The long-term outcome was favourable and no complications were recorded. Interestingly, the contralateral coxofemoral joint left at the time of the previous amputation developed DJD and became a source of pain for the cat and was subsequently excised.

Relevance and novel information

This case report shows that total hip replacement is a viable option in cats with coxofemoral DJD and a contralateral limb amputation. Retained joints in amputated limbs may develop osteoarthritis and be a source of pain for a cat.

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.

Three-Dimensional Morphometry of the Canine Pelvis: Implications for Total Hip Replacement Surgery

OBJECTIVES

 Two-dimensional measurements of acetabular geometry are widely used for the assessment of acetabular component orientation following total hip replacement (THR). With the increasing availability of computed tomography scans, there is an opportunity to develop three-dimensional (3D) planning to improve surgical accuracy. The aim of this study was to validate a 3D workflow for measuring angles of lateral opening (ALO) and version, and to establish reference values for dogs.

METHODS

 Pelvic computed tomography scans were obtained from 27 skeletally mature dogs with no radiographic evidence of hip joint pathology. Patient-specific 3D models were built, and ALO and version angles were measured for both acetabula. The validity of the technique was determined by calculating intra-observer coefficient of variation (CV, %). Reference ranges were calculated and data from left and right hemipelves were compared using a paired t-test and symmetry index.

RESULTS

 Measurements of acetabular geometry were highly repeatable (intra-observer CV 3.5-5.2%, inter-observer CV 3.3-5.2%). Mean (± standard deviation) values for ALO and version angle were 42.9 degrees (± 4.0 degrees) and 27.2 degrees (± 5.3 degrees) respectively. Left-right measurements from the same dog were symmetrical (symmetry index 6.8 to 11.1%) and not significantly different.

CONCLUSIONS

 Mean values of acetabular alignment were broadly similar to clinical THR guidelines (ALO of 45 degrees, version angle of 15-25 degrees), but the wide variation in angle measurements highlights the potential need for patient-specific planning to reduce the risk of complications such as luxation.

Serum acute-phase protein concentrations following uncomplicated total hip arthroplasty in dogs

OBJECTIVES

To establish preoperative and postoperative serum C reactive protein (CRP) and serum amyloid A (SAA) levels in dogs undergoing uncomplicated total hip arthroplasty (THA).

STUDY DESIGN

Prospective clinical trial.

ANIMALS

Eighteen client-owned dogs.

METHODS

Dogs undergoing THA were recruited. Serum CRP and SAA levels were measured in all dogs the day prior to surgery, and 3 and 6 months following surgery. All dogs received a physical examination and underwent radiography at each visit, and dogs with complications were excluded from the study. For continuous numeric data, histograms were generated and evaluated for normality. A 1-way repeated measures ANOVA was performed to find differences between time points.

RESULTS

No complications were encountered in any of the recruited dogs. Median age was 30 months (12-66), and the median bodyweight was 27.3 kg (22.3-40.2). Mean CRP concentrations in the preoperative, 3-month, and 6-month periods were 3.8 mg/L ± 4.4, 0.8 mg/L ± 1.9, and 1.4 mg/L ± 1.4, respectively. The mean SAA concentrations in the preoperative, 3-month, and 6-month periods were 13.9 mg/L ± 8.8, 14.1 mg/L ± 12.6, and 18.4 mg/L ± 15.1, respectively. There were no differences for each parameter between time points.

CONCLUSION

C-reactive protein and SAA levels were consistent with levels previously established for noninflammatory and normal conditions in dogs.

CLINICAL SIGNIFICANCE

Postoperative CRP and SAA concentrations were low by 3 months following uncomplicated THA.

Clinical outcomes of canine total hip replacement utilizing a BFX lateral bolt femoral stem: 195 consecutive cases (2013-2019)

OBJECTIVE

To evaluate the clinical outcomes of total hip replacements (THR) utilizing a BFX lateral bolt stem in dogs with coxofemoral joint disease.

STUDY DESIGN

Retrospective study.

SAMPLE POPULATION

A total of 149 dogs representing 195 THR.

METHODS

Consecutive THRs utilizing a BFX lateral bolt stem were studied. Preoperative, immediate postoperative, 1-, 2-, 3-, 4-, and 12-month postoperative radiographs were performed. All major and minor complications, revisions, outcomes, subsidence, canal flare index (CFI) were recorded.

RESULTS

An intraoperative complication rate of 11.8% was observed. The postoperative complication rate was 13.6%, with 9.2% major and 4.4% minor complications. Complications included: postoperative femur fractures (3.6%), coxofemoral luxation (3.6%), stem failure (0.5%), septic loosening (0.5%), aseptic loosening (0.5%), and acetabular fracture (0.5%). Three dogs underwent prophylactic plating after subjective assessment of cortical thickness. Five of 195 (2.6%) cases underwent explant of their prostheses (median = 3 months). Mean stem subsidence at 1 month postoperatively was 1.22 ± 0.16 mm. An increased CFI was associated with postoperative femur fractures (p < .05). A total of 190 of 195 (97.4%) cases returned to normal function in the long-term follow-up period.

CONCLUSION

Use of the BFX lateral bolt stem resulted in minimal postoperative subsidence, a low femoral stem complication rate, and a high rate of achieving normal limb function.

CLINICAL SIGNIFICANCE

The BFX lateral bolt stem should be considered in canine THR as the femoral failure rate is low and the long-term success rate is high.

Case factors for selection of femoral component type in canine hip arthroplasty using a modular system

OBJECTIVE

To describe a femoral stem selection process based on case features in dogs treated with total hip replacement (THR) by an expert surgeon, compare complications between implant types, and develop an algorithm for stem type selection.

STUDY DESIGN

Retrospective study.

ANIMALS

128 dogs, 135 THR.

METHODS

Data collected included breed, age, weight, canal flare index (CFI), and implant type: cementless (BFX), cementless with a collared stem (BFX-C), hybrid (cementless acetabular component with cemented stem), and cemented (CFX).

RESULTS

Of the 135 THRs, 69 BFX, 47 hybrid, and 18 BFX-C were performed. Dogs receiving hybrid (mean 5.5 years) were older than those receiving BFX (2.5 years, p < .0001) and BFX-C implants (2.5 years, p = .0014). The mean weights of dogs with hybrid, BFX, and BFX-C implants were 40.0, 31.0, and 35.3 kg, respectively, with dogs receiving hybrid heavier than those receiving BFX (p < .0001). Mean CFI for hybrid (1.52) was lower than for BFX (1.79, p < .0001) and BFX-C (1.76, p = .0021). Total complication rate was 14.0% with catastrophic complications in 1.5% and no association between implant type and risk of complications (p = .36). Femur fractures occurred in 2.9% of all cases and 1.1% of cementless THR cases.

CONCLUSIONS

Dogs receiving hybrid THR were older with lower CFI than dogs receiving BFX and BFX-C and heavier than dogs receiving BFX. There was no difference in complications between groups. Catastrophic complications and femur fractures occurred less frequently compared to recent studies of BFX THR.

CLINICAL SIGNIFICANCE

Careful preoperative assessment and implant selection can reduce complications of canine THR.

Greater trochanter osteotomy as a component of cementless total hip replacement: Five cases in four dogs

OBJECTIVE

To describe the surgical technique and report the long-term outcome of greater trochanteric osteotomy (GTO) as a component of cementless total hip replacement (THR) in dogs with severe medialization of the greater trochanter or chronic craniodorsal hip luxation.

STUDY DESIGN

Short case series.

ANIMALS

Four dogs treated with five THRs.

METHODS

Data collected from medical records included signalment, indication for THR, duration of clinical signs, body weight, pre- and post-operative radiographic assessment, surgical templating, osteotomy technique, THR implant selection, surgical time, complications, and long-term clinical and radiographic follow-up. Clinical outcomes were determined based on in-hospital history, orthopedic examination, and radiographic evaluation.

RESULTS

All five surgical procedures resulted in satisfactory long-term clinical results at follow-up a median of 48.2 months (range, 34-56 months) after THR. There were no minor complications and one major complication. One dog experienced post-operative luxation unrelated to the GTO and was successfully treated with a cup revision.

CONCLUSION AND CLINICAL RELEVANCE

GTO was effective in facilitating cementless THR in dogs with either severe medialization of the greater trochanter or chronic craniodorsal luxation.

Ventral acetabular augmentation for management of caudoventral luxation following total hip replacement in dogs

OBJECTIVE

To report ventral acetabular augmentation with an internal fixator for management of caudoventral luxation following total hip replacement in dogs and to report clinical outcomes.

MATERIALS AND METHODS

Clinical records from three UK-based referral hospitals were reviewed retrospectively between 2010 and 2020 to identify dogs with caudoventral hip luxation managed by ventral acetabular augmentation. Hip prosthesis component orientation was radiographically assessed to identify potential risk factors associated with the luxation. Clinical and radiographic assessments were performed at short-term (≤12 weeks) and long-term (>12 months) follow-up and all complications were recorded. A standardised owner telephone questionnaire was used to assess long-term outcomes when a clinical assessment was unavailable.

RESULTS

Nine dogs were included. Risk factors contributing to the luxation could not be defined. Implants used included a string-of-pearls plate (6/9), a polyaxial locking plate combined with a polyethylene implant (1/9) or a polyethylene implant alone (2/9). Complications occurred in two of nine dogs, including recurrent luxation and femoral stem loosening; both dogs had received a polyethylene implant alone, of which one received explantation of the hip prosthesis. Median long-term follow-up was 39 months (range 13.5-62). Seven dogs who received a ventral acetabular plate achieved full function of the operated limb and the overall outcome was good for eight dogs. Follow-up radiographs revealed stable hip prostheses in dogs who received a ventral plate, with the longest assessment at 37 months postoperatively. Owner satisfaction was good for all cases.

CLINICAL SIGNIFICANCE

Ventral acetabular augmentation can successfully manage caudoventral luxation following total hip replacement in dogs.

Zurich Cementless Dual Mobility Cup for Canine Total Hip Prosthesis: Implant Characteristics and Surgical Outcome in 105 Cases

Dislocation after total hip arthroplasty (THA) remains a troublesome complication, and a source of frustration for the owner and the surgeon. The dislocation rate of hip prostheses in dogs is reported to range from 4 to 15%, representing the most common short-term complication. This is especially true in large and giant breed dogs, usually requiring revision surgery. With the increase in the number of THA being performed in veterinary surgery, reducing or preventing complications such as postoperative THA dislocation will be of paramount importance. The Zurich cementless dual mobility (DM) system allows impingement-free range of angulation of 80 to 132 degrees between the ceramic head and the polyether ether ketone (PEEK) cup when combined with the range of the PEEK cup in the outer metal cup. In this article, we review the use of the DM cup in THA in large and giant breed dogs, in terms of its history, biomechanics, outcomes and complications based on 105 cases.

Total hip replacement in dogs with contralateral pelvic limb amputation: A retrospective evaluation of 13 cases

OBJECTIVE

To report the clinical characteristics, surgical management, and medium-term outcomes of total hip replacement (THR) performed in dogs with previous contralateral pelvic limb amputation.

ANIMALS

Thirteen client-owned dogs.

STUDY DESIGN

Multi-institutional retrospective clinical study.

METHODS

Data recorded from medical records included signalment, indication for amputation and THR, and surgical complications. Implant positioning and complications were assessed on radiographs. Clinical outcomes were evaluated during follow-up examinations by one of the authors and through a mobility- and lifestyle-based questionnaire completed by owners.

RESULTS

All 13 dogs had satisfactory clinical results at follow-up a median of 3 months (range, 2-36) after THR. No postoperative luxation was recorded. Four dogs had minor complications that did not require additional treatment. The only major complication was one failure of osseointegration of a cementless acetabular cup, and it was successfully revised.

CONCLUSION

Total hip replacement resulted in satisfactory clinical results and acceptable morbidity in this population.

CLINICAL SIGNIFICANCE

Total hip replacement should be considered in dogs with severe coxofemoral joint disease and contralateral pelvic limb amputation.

Measurement of Acetabular Component Position in Total Hip Arthroplasty in Dogs: Comparison of a Radio-Opaque Cup Position Assessment Device Using Fluoroscopy with CT Assessment and Direct Measurement

OBJECTIVES

 The aim of this study was to compare measurements of angle of lateral opening (ALO) and version determined using a radioopaque cup position assessment device imaged with fluoroscopy to measurements obtained by CT and direct measurement in a cadaveric model. Our null hypothesis was that there would not be any difference in the angles measured by the techniques.

METHODS

 Six cadavers were implanted with BFX acetabular components. The CPAD was placed and images were obtained with fluoroscopy. Measurements were obtained from the radiopaque marker bars on the CPAD device, and version and ALO were calculated. The ALO and version were determined by CT and DM. Comparisons were made using a two-way analysis of variance and a generalized linear model procedure analysis.

RESULTS

 There were no significant differences between the measurements for ALO (p = 0.275) or version (p = 0.226). Correlation between methods was 0.948 and 0.951 for ALO and version, respectively. The mean difference (standard deviation [SD], and 95% confidence interval [CI]) for ALO were: CT versus CPAD 1.85 degrees (± 2.32 degrees [-2.99-3.31]), CT versus DM 1.96 degrees (± 1.99 degrees [-2.2-4.27]), CPAD versus DM1.74 degrees (±2.21 degrees [-1.13 and 5.24]). The mean difference (SD [CI]) for version was CT versus CPAD 2.86 degrees (±1.56 degrees [ -2.63-1.69]), CT versus DM 1.10 degrees (±1.42 degrees [-1.57-2.09]), CPAD versus DM 1.07 degrees (±0.76 degrees [0.13-2.09]).

CLINICAL RELEVANCE

 The results demonstrate that intraoperative imaging in cadaveric specimens with the CPAD is an accurate method to determine ALO and version of the acetabular component.

Estimation of the effects of inset heights and slit configurations in an acetabular cup on the pull-out behavior of an artificial hip joint with a structure for preventing dislocation using finite element analysis

Joint dislocation is a critical problem of total hip replacement. We have newly proposed an artificial hip joint with a structure that prevents dislocation. The proposed joint has a simple form with a femoral head partially covered with an acetabular cup. In the present study, the effects of inset heights and slit configurations of the cup on the pull-out forces of the joint were evaluated using finite element analysis. Joint models with different inset heights and those with or without a slit in the cup were used for the analyses to estimate the pull-out forces of the joint. In the case without the slit, the maximum pull-out force of the joint with 1.0 and 1.5 mm of the inset height was approximately 12 and 40 N, respectively. In the case of 1.0-mm inset height, the maximum force of the joint with and without the slit was approximately 9 and 12 N, respectively. These results reveal that the maximum force is markedly changed by the inset height and is moderately affected by the slit. Thus, we can gain insights into a strategy to optimally design an artificial joint in which dislocation does not occur easily. Graphical abstract.

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.

Outcome and complications after dual mobility total hip replacement

Objectives: To report the clinical and radiographic outcome of a canine total hip prosthesis with a dual mobility acetabular component, with a minimum of six months follow-up.

Methods: The outcome of dogs that underwent primary cemented unilateral dual mobility hip prosthesis surgery by one of the authors for hip dysplasia or trauma, and which had a minimum of six months clinical and radiologic follow-up, was evaluated.

Results: Fifty dogs were included in the study. Follow-up ranged from six to 38 months (mean 14.4 months). Perioperative complications were acetabular collapse (n = 1) and greater trochanter fracture (n = 1), both of which were successfully managed perioperatively. Postoperative complications were aseptic loosening of the acetabular component (n = 2; both surgically revised), implant sepsis (n = 3; all explanted), acetabular fracture (n = 1; conservatively managed), greater trochanter fracture (n = 1; conservatively managed) and sciatic neurapraxia (n = 1). No cases of postoperative luxation or femoral implant aseptic loosening were encountered. Outcome was poor for three cases (3 implant sepsis), fair for three cases (including 1 acetabular component loosening and 1 acetabular fracture), and good or excellent for 44 cases (88%).

Clinical significance: There were not any cases of postoperative coxofemoral luxation observed in this series of 50 dogs with dual mobility hip prosthesis. Studies with more patients and longer follow-up are needed to confirm the satisfactory results observed to date with this implant.

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.

Dislocation of a dual mobility total hip replacement following fracture of the polyethylene liner

An eight-year-old male English Setter was referred for management of a dislocation of a cemented dual mobility canine total hip prosthesis that occurred four months after the initial surgery. Revision surgery showed that the dislocation was associated with fracture of the ultra-high molecular weight polyethylene liner. The dislocation was successfully reduced after replacing the liner. A dual mobility acetabular component is composed of a mobile polyethylene liner inside a metallic cemented cup. Chronic wear of the components of a canine dual mobility total hip replacement has not been described previously. The use of this type of implant is fairly recent and limited long term follow-up of the implanted cases may be the explanation. Acute rupture of a polyethylene liner has never been described in humans, the only case of rupture of a polyethylene liner occurred 10 years after implantation. The case presented here of rupture of the polyethylene liner of a dual mobility total hip replacement is a hitherto unreported failure mode in this model of acetabular cup in the dog.

INNOPLANT Total Hip Replacement System

Total hip replacement is a salvage procedure that is done to alleviate discomfort secondary to osteoarthritis in the hip, which is most often a result of hip dysplasia. Commercially available total hip replacement implants for small animal patients are classified as cemented or cementless. The INNOPLANT Total Hip Replacement system includes modular, screw-in cementless components that were developed to improve implant stability by maintaining as much normal anatomic structure, and by extension biomechanics of the coxofemoral joint, as possible. As a newer system, there are few data and no long-term studies available in the veterinary literature.

Feline hip dysplasia

Practical relevance:

The reported incidence of hip dysplasia (HD) in cats varies dramatically between studies, but the condition is likely more common than we realise. There is little doubt that cats with HD and associated osteoarthritis (OA) suffer pain, and this warrants appropriate therapy.

Diagnostic challenges:

Clinical signs of HD in cats are often gradual in onset, making them difficult to appreciate, but may include inactivity, pelvic limb lameness, difficulty jumping and climbing stairs, and reluctance to squat to defecate. Often lameness is bilateral, and can be particularly difficult to recognise. The most common radiographic finding is an abnormally shallow acetabulum. Subluxation, however, is not consistently associated with OA in cats and therefore the role that joint laxity plays in disease progression remains uncertain. Degenerative changes of the femoral head and neck seem to develop later than in the dog, and are less marked.

Therapeutic challenges:

The majority of cats respond to non-surgical management with environmental modulation, physical therapy, dietary modulation, weight loss, nutraceuticals and drug therapy. Should non-surgical management not provide sufficient relief, two salvage surgical options are available: femoral head and neck excision (FHNE) and total hip replacement (THR). While there is a risk of complications with micro-THR, the positive outcomes that have been reported indicate that it should be considered in the treatment of coxofemoral pathology in cats in the same way that THR is considered for larger dogs, especially given the inconsistent results associated with FHNE. Monitoring the effect of treatment is challenging as the assessment of pain in cats is complex and there is no validated scoring system or owner-completed questionnaire yet available for cats.

Evidence base:

There is a paucity of clinical reports focusing solely on HD in cats. The author draws on a combination of published studies, in cats, dogs and humans, as well as personal clinical experience.

Acetabular cup liner and prosthetic head exchange to increase the head diameter for management of recurrent luxation of a prosthetic hip in two dogs

Component malalignment and impingement are possible causes of recurrent luxation following total hip replacement in the dog. In the two cases presented in this report, luxation that was probably due to impingement was managed by exchanging the standard 17 mm prosthetic head for a 24 mm prosthetic head. This required removal of the original acetabular cup liner and placement of a new polyethylene liner that would accept the 24 mm head into the stable acetabular shell. In the first case, a 50 kg Malamute dog, recurrent luxation was initially managed by component alignment revision, iliofemoral suture, triple pelvic osteotomy and a novel lasso technique, without long-term success. After exchanging the head and cup liner, luxation did not recur over a 12-month period. In the second case, a 65 kg Newfoundland dog, impingement was suspected after a second luxation event. Luxation did not recur during the nine months after exchange of the head and cup liner. The larger prosthetic head used in these two cases increased the impingement-free range-of-motion of the joint and increased the translation distance required for luxation (jump distance).

Risk factors for loosening of cementless threaded femoral implants in canine total hip arthroplasty

OBJECTIVE

To determine the incidence and potential risk factors of femoral implant loosening in the canine Helica® total hip replacement (THR) system.

METHOD

Sixteen dogs with a Helica THR were included. Medical records were reviewed for signalment and size of implants. Stem angle, stem collar to lateral cortex distance, tip to cortex distance, stem collar to lateral cortex distance at a stem angle of 150°, lever arm distance, and the distance on the diaphysis measurements were calculated from the one year postoperative radiographs. Three ratios were determined from these measurements to take into account the size of the femur in relation to the size of the implant. Femoral implant loosening was identified by radiographic and clinical signs, and confirmed at the time of surgical explantation. Differences in the successful and femoral stem failure groups were compared using either a students t-test or a Mann Whitney test. Significance was set at p <0.003.

RESULTS

Six of the 16 dogs had loosening of the femoral prostheses within one year post-implantation. One dog had evidence of a septic cause for loosening. No significant risk factors could be identified in this group of dogs with Helica stem loosening.

CLINICAL SIGNIFICANCE

Helica femoral stem loosening was a common complication within one year post-implantation in this group of dogs. No risk factors were identified to potentially decrease the incidence of loosening. Therefore, due to this unacceptably high complication rate, the authors do not recommend this model of the Helica THR.

Evaluation of ranges of motion of a new constrained acetabular prosthesis for canine total hip replacement

Background

Total hip replacement (THR) is considered to be the most effective treatment option for advanced osteoarthritis of the hip in large breed dogs. However, a proportion of post-THR patients suffer prosthesis dislocation for various reasons, which may be addressed by a constrained acetabular prosthesis design. The study proposed a new THR with constrained acetabular component that aimed to decrease the incidence of postoperative dislocation while maintaining the necessary range of motion (ROM); and, through computer-simulated implantations, evaluated the ROM of the THR with and without malpositioning of the acetabular component.

Methods

A new THR with a constrained acetabular component that had an inward eccentric lining and a 60° cut-out on the dorsal side was designed, and its computer-aided design models were implanted into the pelvic and femoral models reconstructed from the computed tomography data of six healthy Labrador Retriever dogs. The allowable and functional ROM of the implanted THR were determined via computer simulations. The contact patterns between the bone or the prosthetic components at extreme positions of the THR were analyzed. Influence of malpositioning of the acetabular component on the ROM was assessed.

Results

The means (SD) of the functional ranges for flexion, extension, adduction, abduction, internal rotation and external rotation were 51.8° (6.6°), 163.3° (7.3°), 33.5° (5.7°), 74.0° (3.7°), 41.5° (8.3°) and 65.2° (9.9°), respectively. Malpositioning of the acetabular component by 20° in one direction was found to reduce ROM in other directions (reducing lateral opening: flexion: 12°, adduction: 20°, internal/external rotations: < 20°; increasing lateral opening: extension and abduction: < 16°; reducing retroversion: extension: < 20°, abduction: 15°, external rotation: < 20°; increasing retroversion: flexion: < 20°, abduction, adduction and internal rotation: 20°).

Conclusions

From the computer-aided surgical simulations, the new THR was found to have sufficient functional ranges for flexion, extension, abduction, adduction and external rotation for Labrador Retrievers. Analysis of the malpositioning of the acetabular component suggests that accurate placement of the acetabular component is critical for achieving desirable ROM for daily activities.

Biomechanical evaluation of the helica femoral implant system using traditional and modified techniques

OBJECTIVE

To determine the effect of implant placement on proximal femoral axial bone strains, implant subsidence, implant motion, and failure mechanical properties of Helica implants.

STUDY DESIGN

In vitro biomechanical study.

SAMPLE POPULATION

Cadaveric canine femora (n = 8 pairs).

METHODS

Femora instrumented with strain gauges and kinematic markers were cyclically loaded in axial compression before (intact femora) and after implantation with a Helica prosthesis that engaged only cancellous bone (traditional technique) or cancellous bone and lateral cortex (modified technique) to evaluate bone strains, subsidence, and motion; femora were then loaded to failure to evaluate failure mechanical properties.

RESULTS

After implantation, modified femoral prosthesis angle was 5% less than intact femora and 5.7% less than traditional implanted femora. Medial femoral bone strain was lower (P ≤ .05) for intact (-570 µ strain) than modified (-790), but not (P = .08) traditional (-700) implanted femora. High-load implant subsidence was present but small (-0.087 mm) for the modified technique. Motion (traditional and modified) increased (P = .05) during cyclic loading (-0.17 and -0.328 mm) and failure (P = .04) (-2.121 and -3.390 mm); remaining yield and failure properties revealed no significant findings (P ≤ .05).

CONCLUSIONS

The modified technique resulted in a smaller neck angle and minimal subsidence. Bone strain was minimally altered so stress shielding may be less compared to findings with traditional implants. Motion detected during cyclic and failure testing may lead to implant loosening in vivo.

An ex vivo investigation of the effect of the TATE canine elbow arthroplasty system on kinematics of the elbow

OBJECTIVE

To devise a kinematic technique to objectively ascertain the location and orientation of the centre of rotation of the canine elbow and to compare this axis following arthroplasty with the first generation TATE™ prosthesis in an ex vivo model.

METHODS

Five pairs of cadaveric forelimbs were obtained and proximal limb soft tissues removed. Pin-mounted reflective markers were applied to the humerus and ulna. Limbs were mounted on a frame and six trials of the elbow manually cycled through its sagittal range of motion captured using 4 Qualisys cameras at 120 Hz. Radiography was performed to identify marker position. TATE™ cartridges were implanted and kinematic analysis repeated. Kinematic data were imported into custom software and the three-dimensional joint centre of rotation defined using a closed-form solution for absolute orientation. Paired t tests were performed to determine if the centre of rotation of the elbow differed significantly (P<0·05) pre- and postoperatively and between left and right limbs.

RESULTS

There was no significant difference in three-dimensional orientation of the elbow axis between pre and postoperative measurements or between left and right limbs.

CLINICAL SIGNIFICANCE

A critical factor in obtaining a successful functional outcome following elbow arthroplasty in humans is accurate reconstruction of the anatomic centre of rotation. The first generation TATE canine elbow arthroplasty cartridge and its instrumentation accurately reconstructed the anatomic centre of rotation in 8 of the 10 elbows assessed in this ex vivo model.

Nano total hip replacement in 12 dogs

OBJECTIVE

To determine the short-term clinical outcome of nano total hip replacement (NanoTHR) in dogs.

STUDY DESIGN

Retrospective case series.

ANIMALS

Dogs (n = 12).

METHODS

Medical records (2009-2011) of dogs that had nano-THR were reviewed for signalment, weight, clinical signs, side, age, prosthesis sizes, concurrent surgeries performed, complications, operative time, 3-month postoperative pelvic radiograph results, and lameness scores.

RESULTS

Breeds were Yorkshire Terriers (n = 6), Toy Poodles (2), with 1 each of Maltese, Pomeranian, Cavalier King Charles Spaniel, and Shih-Tzu. Median body was 4.87 kg (range, 2.5-5.90 kg) and median age, 35.75 months (range, 12-144 months). Radiographs were taken in 4 dogs at 12 days (n = 2), 14 days (1), and 30 days (1) after surgery because of presentation for an acute grade 5 lameness. Three dogs had femoral fractures distal to the femoral implant tip and 1 dog displaced the acetabular implant medially. After revision surgery, all femoral fractures were assessed as healed with intact plate fixation. The dog with the medially displaced acetabular component responded to conservative management including strict confinement and analgesic administration. Eight dogs (58%) were assigned a grade 1 lameness and 4 dogs were grade 2 (33%) at 12-week examination. The 3 dogs with grade 5 lameness scores found to have femoral fractures within 1 month after surgery, subsequently improved to grade 1 (n = 1) and 2 (2) 12 weeks after revision surgery. The dog with medial acetabular displacement improved to a grade 2 lameness 12 weeks after conservative management.

CONCLUSIONS

Although all 12 dogs had good-to-excellent outcomes, 33% experienced significant complications associated with the technique. As improvements in instrumentation and refinements in the technique are developed, NanoTHR can be considered an alternative to the femoral head and neck ostectomy (FHO) or medical management of coxofemoral disease for toy breed dogs. Further studies with a larger number of dogs and longer follow-up times are required.

Advances in total joint replacement in small animals

Total joint replacement is now considered a routine surgical option for small animals with advanced joint disease. This review highlights the current state of the art in total hip, elbow and knee replacement in small animals, as well as the potential for application to other joints such as the intervertebral discs, hock and shoulder. Advances in cementless fixation, the use of less-invasive, bone-sparing procedures, and the development of custom implant options for revision surgery and oncologic reconstruction will be discussed. As growth in this field continues, it is important that future developments in total joint replacement are built on a foundation of detailed laboratory evaluation of new implant designs and surgical techniques, objective assessment of clinical outcomes, and a comprehensive, coordinated retrieval program that evaluates both well-functioning and failed joint replacements.

Complications and owner assessment of canine total hip replacement: a multicenter internet based survey

OBJECTIVE

To assess the variables associated with the complications of total hip replacement (THR) and report owner-assessed outcomes, through surgeon-based registration of cases via an online database, informed owner consent, and prospective outcomes assessment using a client-administered clinical metrology instrument.

STUDY DESIGN

Prospective case series

ANIMALS

Dogs (n = 170)

METHODS

Entries into the British Veterinary Orthopaedic Association-Canine Hip Registry (BVOA-CHR) between January 2010 and August 2011 were reviewed. Variables evaluated included dog age, body weight, breed, and indication for THR and prosthesis. Associations between each variable and the incidence of complications were assessed using logistic regression. Additionally, an on-line, owner-administered outcomes assessment questionnaire (modified from the Liverpool Osteoarthritis in Dogs (LOAD) questionnaire) was used to collect data from owners.

RESULTS

One hundred and seventy cases met the inclusion criteria. Surgical indications included hip dysplasia and coxofemoral osteoarthritis (n = 150), Legg-Calves-Perthes disease (7), coxofemoral luxation (6), fracture (4), slipped capital physis (2), and femoral head and neck ostectomy revision (1). Surgical implants were from 4 systems. The incidence of surgeon-reported complication was 9.4%. No significant association was identified between weight, age, sex, breed, indication for THR, surgical technique and prosthesis, and the incidence of complications. In 82% of the cases, owners described their satisfaction with the outcome of THR as "very good" and a total of 20% complication rate was reported. There was a statistically significant improvement in owner-assessed questionnaire score before and after THR (P < .001).

CONCLUSIONS

The BVOA-CHR offers a novel framework for the prospective studies on THR and on a national/international scale. Initial complication rates from the BVOA-CHR are similar to previous studies.

Biomechanical evaluation of screw-in femoral implant in cementless total hip system

OBJECTIVE

To compare (1) proximal femoral axial strains, (2) femoral head deflection, and (3) failure mechanical properties, between Helica head and neck prosthesis implanted femora and normal femora.

STUDY DESIGN

In vitro study.

SAMPLE POPULATION

Cadaveric canine femora (n = 5 pair).

METHODS

Femoral bone strains and head displacement during in vitro simulation of midstance of the gallop were evaluated using cadaveric femurs cyclically loaded in vitro. Strains and displacements were compared within femurs, before and after, prosthesis implantation; and throughout cycling to seek evidence of movement with cyclic loading. Subsequently, implanted femurs and contralateral, intact femurs were loaded to failure to compare failure mechanical properties and modes of failure.

RESULTS

Proximal femoral axial strains were significantly different between intact and implanted femora on all 4 cortical surfaces (P < .05). Compressive strains were lower in the implanted femur on all cortical surfaces, except on the caudal surface which was higher. No difference was noted for femoral head angle under an axial load corresponding to gallop (P > .05). Vertical head displacement was ∼0.1 mm greater for implanted femora than intact femora (P < .05). Yield and failure loads and yield energy of implanted femora were 39-54% lower than those for intact femora (P < .05). Mode of failure for both the intact and implanted femora did not appear to be different.

CONCLUSION

Helica femoral prosthesis alters strain distribution in the proximal aspect of the femur and exhibits initial micromotion. Failure load in axial compression of the Helica-implanted femur is less than that of the normal femur, but greater than that expected in vivo.

Modular hybrid total hip arthroplasty. Experimental study in dogs

Background

This prospective experimental study evaluated the surgical procedure and results of modular hybrid total hip arthroplasty in dogs.

Methods

Ten skeletally mature healthy mongrel dogs with weights varying between 19 and 27 kg were used. Cemented modular femoral stems and uncemented porous-coated acetabular cups were employed. Clinical and radiographic evaluations were performed before surgery and at 30, 60, 90, 120, 180 and 360 days post-operation.

Results

Excellent weight bearing was noticed in the operated limb in seven dogs. Dislocation followed by loosening of the prosthesis was noticed in two dogs, which were therefore properly treated with a femoral head osteotomy. Femoral fracture occurred in one dog, which was promptly treated with full implant removal and femoral osteosynthesis.

Conclusions

The canine modular hybrid total hip arthroplasty provided excellent functionality of the operated limb.

Use of the cumulative summation technique to quantitatively assess a surgical learning curve: canine total hip replacement

OBJECTIVE

To quantitatively assess a surgical "learning curve" using the cumulative summation (CUSUM) score technique.

STUDY DESIGN

Application of a CUSUM technique to a consecutive series of surgical cases.

ANIMALS

Consecutive primary cemented total hip replacement (THR; n=116) in 106 dogs.

METHODS

Records of all dogs that had primary canine THR were reviewed. Data retrieved included date of surgery, postoperative complications, and duration of follow-up. The 12-week outcome was analyzed graphically and with a CUSUM technique.

RESULTS

One hundred and one (87%) procedures were "successful" and 15 (13%) developed major complications within 12 weeks (failures). The CUSUM chart clearly demonstrated an initial "learning curve" of ∼44 THR.

CONCLUSION

The CUSUM technique can be used to demonstrate the learning curve for canine THR surgery.

Does the degree of preoperative subluxation or soft tissue tension affect the incidence of postoperative luxation in dogs after total hip replacement?

OBJECTIVE

To investigate whether preexisting coxofemoral subluxation/luxation predisposes to postoperative total hip replacement (THR) luxation.

STUDY DESIGN

Case series.

ANIMALS

Dogs (n=100) that had cemented THR (n=109); 23 normal controls.

METHODS

A preliminary study was performed to validate our methods of assessing luxation and laxity by comparing dogs with severe hip dysplasia with a control population of normal dogs. For the main study, the records and radiographs of all dogs that had primary THR were reviewed. Measurements taken from preoperative radiographs to quantify hip subluxation/laxity included the Norberg angle, subluxation index, and 2 new measures: acetabular depth ratio (ADR) and dorsal acetabular rim ratio (DARR). Differences between groups that had luxation within 8 weeks and those that did not were investigated.

RESULTS

Postoperative luxation occurred in 13 dogs (12%) within 8 weeks of surgery. Luxation was significantly associated with various measurements (including Norberg angle, ADR, DARR) thought to reflect degree of subluxation/soft tissue tension.

CONCLUSION

Luxation after canine THR is a multifactorial problem but preexisting subluxation/soft tissue laxity is a significant risk factor for this complication.

Femoral medullary infarction prevalence with the Zurich Cementless Canine Total Hip arthroplasty

OBJECTIVE

To document the prevalence of femoral medullary infarction associated with the Zurich Cementless Total Hip Replacement (ZCTHR) system in dogs.

STUDY DESIGN

Case series.

ANIMALS

Dogs (n=35) with 41 ZCTHR implants.

METHODS

Medical records (February 1999-December 2002) were reviewed for dogs that had ZCTHR and at least 1 year follow-up with radiographic evaluation. Thirty-five dogs (41 ZCTHR) met the inclusion criteria. Femoral morphologic data, implant to bone relationships, and medullary infarcts were recorded. Data were analyzed for associations between infarct occurrence and morphologic details and dog characteristics.

RESULTS

Eight of 41 femurs had radiographic evidence of infarcts (19.5%). Dogs with infarcts were significantly younger (mean [+/-SD] age, 18.5+/-5.2 months) compared with those without infarction (mean age, 44.4+/-5.6 months; P=.027). None of the other variables were significantly different between dogs with and without infarcts. Three femurs with infarcts ultimately developed stem loosening.

CONCLUSION

A higher prevalence of femoral medullary infarcts was identified with ZCTHR compared with incidence reported for other total hip systems. Younger dogs were more likely to develop infarction.

CLINICAL RELEVANCE

Femoral infarction appears to be associated with stem loosening. Adjustments in surgical technique or delaying surgery beyond 18 months of age may reduce incidence of infarction but needs further evaluation.