One surgeon performed 20 of the THRs. For two dogs, THR was performed at other hospitals using the same technique and system.

1) fracture groups

2) non-fracture groups

Medical records evaluated:

Radiographs

Ventrolateral and mediolateral of the affected femur. Pre- and postop during follow-up visits, fracture healing, and periodically after fractures were healed until either the patient died or the study ended.

Evaluated/identified

Interval between THR and femur fracture, orientation of fracture lines, events that occurred at fracture and treatment methods.

Patient information

Fixation method, joint alignment, bone healing implant integrity, bone-cement interface, implant-cement interface.

Limb function

Evaluated by examination and client interview and classified as either normal or good.

Mean, median and range of numerical values were calculated for variables such as age, body weight, body score, bone healing and follow-up intervals.

T-tests to compare fracture group and non-fracture group.

To report femur fracture as a complication of THR and to report the incidence, predisposing factors, treatment options and outcome.

Age at THR

Dogs that had femur fractures were significantly older (7.4 years) at THR than dogs that did not sustain femur fractures (4.9 years) (p=0.0063).

Predisposing factors

Osteopathy (n=5) iatrogenic fissures created during reaming (n=9) and previous hip surgery.

Fracture characteristics

Fracture occurrence

22 after original THR, 1 after revision, 1 after explanation:

• traumatic events in 17 dogs
• osteopathy present at THR in 5 dogs
• cortical thinning secondary to aseptic loosening in 3 dogs

Fracture treatment:

• plate and screw fixation (10 with and 7 without cerclage wires) resulted in the most favourable outcome - healing occurred in 6-10 weeks
• full cerclages wires in 3 dogs
• strict confinement in 3 dogs
• euthanasia in 1 dog

Outcome:

• 22 fractures healed and there were no non-unions
• two fractures that did not heal: 1 dog died 16 days after surgery of an unrelated illness and 1 dog was euthanised without treatment
• 20 clients with a dog with a healed fracture were interviewed > 65 days after surgery: 12 dogs were alive at the end of the study - 15 clients (75%) reported normal limb function and 5 (25%) reported good limb function

Old dogs with osteopathies, dogs that have had previous hip surgery, and dogs that have intraoperative fissures should be recognised as potentially being at greater risk of femoral fracture.

• retrospective study
• different surgeons, different hospitals
• surgeon experience was not evaluated as a risk factor
• different follow-up
• 10 dogs (45.5%) with fractures were followed until death
• client interview

1) fracture group (n=11)

2) non-fracture group (n=73)

Inclusion criteria

Cases with preoperative, immediate postoperative and initial follow-up radiographs.

Exclusion criteria

Dogs without complete surgery reports, dogs in the non-fracture group without documentation of absence of femoral fracture on recheck radiographs at least 4 weeks postoperatively.

Dog factors analysed

Age, breed, sex, weight, canal flare index (CFI), indication for arthroplasty, intraoperative fissure, cerclage usage, implant size.

Statistical analysis:

• preliminary univariate tests were performed and any factors with p>.30 were excluded for further consideration
• continuous variables: non parametric Wilcoxon’s rank sum test
• binary variables: Fisher’s exact test
• factors included for multicollinearity were entered in to the logistic equation
• previously deleted factors were singly added to the final model to reassess significance

• documented postoperatively 13.1% (11 of 84)
• with complete statistical analysis 13.5% (7 of 52)

This is higher than previously reported. It may partially represent a selection bias (dogs with complications are more likely to be seen for follow-up) and patients operated during the earlier part of the period were more likely to have incomplete medical records, this resulted in the exclusion of 12 dogs in the non-fracture group.

Dog factors:

• Age was positively associated with femoral fracture. Mean dog age was 7.3±0.69 years for fracture group and 4.77±0.37 years for non-fracture group (p=0.022).
• CFI was negatively associated with fracture. Mean CFI was 1.80±0.09 for the fracture group and 1.98±0.04 for the non-fracture group (p=0.045).
• Body weight, intraoperative fissure, cerclage use, implant size, position and canal fill did not influence the occurrence of femoral fracture.

Operative factors

Indications for THA:

• coxofemoral osteoarthritis (OA) secondary to canine hip dysplasia (CHD) (n=78)
• traumatic craniodorsal coxofemoral luxation (n=4)
• coxofemoral OA secondary to capital physeal fracture (n=1)
• femoral neck fracture malunion (n=1)

Intraoperative fissures

Reported in 3 cases. None of these dogs had femoral fractures. All fissures were addressed with cerclage wires.

Radiographic evaluation

None of the measures of implant positioning or canal fill were associated with risk of femoral fractures.

• retrospective study
• small number of dogs in the fracture group (may have led to type II error)
• different surgeons with 2 slightly different methods, 2 different hospitals and surgeon experience was not evaluated as a risk factor
• partial selection bias possible
• quality of radiographic positioning varied among patients
• radiographs not evaluated from a board diplomate in radiology
• canal flare index (CFI) not always available
• length of radiographic and clinical follow-up varied
• body score missing

At least 8 weeks of documented postoperative radiographic and orthopaedic evaluations.

Exclusion criteria

THR performed as the second procedure in dogs operated bilaterally, previous ipsilateral coxofemoral surgery, cases without sufficient client communication.

Medical records of dogs

Sex, breed, age, body weight, body condition score, side of arthroplasty, date of surgery, history of previous contralateral coxofemoral surgery, urinalysis results, intraoperative surgical site culture results, lameness score at presentation (0=no lameness, 1=slight lameness, 2=obvious weight-bearing lameness, 3=intermittent non-weight bearing lameness, 4=continuous non-weight-bearing lameness) size of prostheses implanted, duration of surgery.

Complications were separated into:

• intraoperative (IOC)
• short-term (STC)
• long-term (LTC)

Bivariate and multivariate statistical analysis was used to compare complications.

Procedures were performed by 10 different surgeons.

Prior femoral head and neck ostectomy (FHO) or cemented-THR in the contralateral joint was identified as a negative prognostic indicator for successful outcome (p<0.05).

IOC

overall IOC rate = 11%

• fracture of the femoral diaphysis (n=12)=7.4%
• fracture of the greater trochanter (n=3)
• lost screw in soft tissue (n=1)
• excessive haemorrhage (n=1)
• immediate revision of acetabular cup placement (n=1)

STC

overall STC rate=6.75%

• coxofemoral luxation (n=6)
• transient neuraprexia (n=2)
• fracture of the femoral diaphysis (n=2)(1.2%)
• fracture of the acetabulum (n=1)

LTC

overall LTC rate=10.4%

• septic loosening (n=6)
• coxofemoral luxation (n=6)

implant failure (n=4)

fracture of the femoral diaphysis (n=1)(0.6%)

• retrospective
• surgery performed by 10 different surgeons
• follow-up performed in different ways and by different persons
• relatively short scheduled radiographic follow-up (8 weeks)
• 50 cases in which the 8 week follow-up was not performed by board certified specialists (surgery and radiology), body score not evaluated in all dogs
• increased rate of complications higher than previous studies. Likely influenced in part by varying degrees of Z-THR experience (technical error)
• surgeon’s experience not evaluated as prognostic factor
• no evaluation of technical errors immediately post operatively

Signalement, body weight, body condition score, diagnosis at the time of surgery, history of previous or subsequent hip surgery.

Complications

• intraoperative (IOC)
• short term (STC)
• long term (LTC)

Evaluation of radiographs

2-view radiographic hip studies pre-operatively, immediately post-operatively and at the longest follow-up were evaluated by one investigator.

Pre-operatively

Severity of osteoarthritis (OA) was graded (0=normal, 1=subtle, 2=grade 0 or 1 with severe subluxation or luxation, 3=mild OA, 4=moderate OA, 5=severe OA).

Immediately post-operatively

Surgical technique (implant size, implant position, cement quality) and technical errors.

Radiographs at the longest available follow-up and at least at 8 weeks post-operatively

Evaluated and compared to the immediate post-operative films (fracture of cement, medullary infection, loosening of the acetabular component, prosthetic luxation, fracture of the femoral diaphysis or greater trochanter and infection).

Statistical analysis:

• categorical data: chi-square or Fisher’s exact test
• logistic regression analysis to access the independent contribution of possible risk factors

Surgery performed by various board certified surgeons

12.1% after primary cTHR

Pre-operative radiographs:

• available for 79 dogs
• majority had severe OA

Post-operative radiographs (primary cTHR) (n=97):

• available for 87 dogs
• 69 dogs had appropriately sized femoral implants
• 60 dogs had eccentrically placed implants
• angle of lateral opening of acetabular component was appropriate in 40 dogs

Post-operative radiographs (secondary cTHR) (n=8):

• available for 8 dogs
• 7 dogs had appropriately sized femoral implants
• 5 dogs had eccentrically placed implants
• angle of lateral opening of acetabular component was appropriate in 3 dogs

Technical errors:

• primary cTHR - ≥1 technical errors in 43 dogs
• secondary cTHR - technical errors in 50% of the dogs

STC

1. primary cTHR available in 77 dogs ≥1 STC in 7 dogs
2. secondary cTHR (n=8) STC in 2 dogs. Luxation (n=1) and infection (n=1)

LTC

1. primary cTHR available for 63 dogs 59 dogs with radiographic changes in the bone, cement or prosthesis
2. secondary cTHR available for 5 dogs, all had radiographic changes

Revision surgery:

1. primary cTHR 12.1% (11/90) six had the implant removed, five had a revision (one femoral fracture)
2. secondary cTHR two dogs had a revision

Risk and protective factors:

• after primary cTHR dogs were more likely to have a revision surgery if the femoral implant was eccentrically placed (p=0.01)
• presence of radiolucent lines at the femoral cement-bone interface in the long-term period was positively associated with revision surgery (p=0.02)

male dogs were more likely to have revision surgery on the primary cTHR (p=0.05)

• retrospective (medical records incomplete, limited follow-up)
• different surgeons with different experience
• surgeon’s experience not evaluated as risk factor
• complications that were treated elsewhere or left untreated would not have been detected
• variable radiographic technique and patient positioning (may have affected implant assessment)
• some radiographic films with inadequate quality for evaluation
• some body condition scores (BCS) were missing

Inclusion criteria:

Medical records of the first 100 consecutives cases with 2^nd generation ZCTHR were reviewed. Only those dogs that had clinical and radiographic evaluation with ≥ 6 months follow-up.

Signalement data:

• age, breed, body weight, gender
• indication for THR
• hip dysplasia and secondary coxarthrosis (n=59), failure of conservative and/or surgical management of traumatic coxofemoral luxation (n=5), old Salter-Harris fracture of the proximal femoral physis (n=1)
• date of surgery and operated size
• cup position (angle lateral opening ALO, angle of inclination AI)

Longest clinical and radiographic follow-up (presence of pain on manipulation of the hip joint, range of motion (ROM), muscle mass compared with the contralateral size, lameness). Evaluated using a score: excellent, good, fair, poor or failed.

Complications:

• intraoperative (n=1) femoral fissure during reaming
• post-operative (n=11) femoral fracture (1), prosthesis luxation (7), cup loosening (2), implant failure (1)

Management of complications and outcome 

Nine cases were successfully revised. Explanation of implants was performed in one case because of infection, one dog was euthanised after a new luxation.

22.68+/- 16.75 months

Clinical outcome:

• of 65 ZCTHR, 60 were considered to have an excellent outcome, 3 a good outcome, and 2 as failed
• 97% good or excellent outcome at an average of 2 years post-operatively (similar to previous reported rates of 91-96%)
• 17% needed one or more revision

Radiographic findings:

Findings compatible with bone ingrowth fixation were observed for all acetabular and femoral implants.

Focal radiolucent zones were observed in the acetabular component of 23 cases and none of the THR had a complete radiolucent zone around the cup or the stem.

Complications:

(n=11, 17%)

Previous complication rates 6.3%-20.3%.

Luxation in cemented and cementless systems is the most frequently reported complication 1.1-11.8%, in this study: 11% (n=7).

Femoral fracture

(n=1) well-reported complication after THR in dogs, and appears to be more common in old animals because of nonuse of the leg or other pathologic conditions. This single femoral fracture compares similarly with fractures occurring with cemented THR systems.

Increased femoral cortical thickening was observed along the medial cortex and distal to the stem in most cases. This bone remodeling and apposition may prevent occurrence of femoral fractures in the long-term that occur with cemented THR because of cortical thinning.

Component loosening

(acetabular component n=1)

Implant stresses are higher in the ZCTHR stem compared with cemented stems, reaching a maximum in the neck region of the implant, with a second peak at the level of the most proximal screw.

• retrospective descriptive case series study, no control groups, variable follow-up
• two ZCTHR were not evaluated radiographically

Variables evaluated:

• age, body weight, breed, indication for THR and prosthesis

Statistical analysis:

• association between each variable and the incidence of complications were assessed using logistic regression
• Mann-Whitney U-Test was performed to assess the significance of total lameness scores before and after THR

Owner outcomes assessment questionnaire was used additionally to collect data from owners.

Divided in 4 sections:

• Section A assessed information regarding length of ongoing mobility problem, medications received, and other concurrent medical history unrelated to hip dysplasia (HD).
• Section B assessed activity and willingness to exercise before THR.
• Section C assessed date of surgery, overall owner satisfaction and complications.
• Section D assessed activity and willingness to exercise after THR.

Surgical implants

CFX (BioMedtrix), BFX, Helica, Kyon

Incidence: 9.4%:

• luxation (n=5)
• femoral fractures (n=3)
• minor wound dehiscence
• (n=1) wound sepsis, (n=1) protrusion acetabuli, (n=1) acetabular cup displacement, (n=1) suspected pulmonary thromboembolism and death at the end of surgery
• (n=1) femoral pain, (n=1) femoral subsidence, (n=1) siatic paresis and luxation (n=5), femoral fracture (n=3), minor wound dehiscence (n=1)

No statistical significance was identified between weight, age, gender, breed, indication for THR, surgical technique and prosthesis and incidence of complications.

Client questionnaire:

A total of 51% response rate to the online owner assessment questionnaire was achieved. 82% described their satisfaction with the outcome of THR as “very good”, 12% “good”, 7%”fair”, 0% “poor”, 0% “very poor”.

A total of 20% complication rate was reported statistically significant difference in owner-assessed lameness scores before and after THR (p<0.001).

• client assessment subjective, no controls with force platform peak vertical force for example
• 51% response rate to the online owner assessment questionnaire
• different complications rate between owners and surgeons
• THR was most frequently performed on dogs ≤ 1year (39%)
• limited ability to fully evaluate the risk factors for THR complications to date, probably because most studies are single-center and have limited power
• BVOA-CHR does not currently include imaging data