Cementless Total Hip Replacement in an Alpaca

Objective— To report management of a chronic slipped capital femoral epiphysis (SCFE) in an alpaca using cementless total hip replacement (THR).
Study Design— Case report.
Animal— An 18-month-old, 47 kg alpaca male.
Methods— Cementless THR was performed in an alpaca with a chronic, right SCFE, and secondary osteoarthritis. Force plate gait analysis was performed before and 8 weeks after surgery. Outcome was determined through clinical evaluation, radiography, and force plate gait analysis.
Results— Cementless THR resulted in marked improvement in the alpaca's comfort level, degree of lameness, and range of motion. On preoperative force plate gait analysis there was decreased contact time ( P =.01) and vertical impulse ( P <.01) of the affected limb, whereas at 8 weeks postoperatively significant differences in gait analysis between pelvic limbs were not apparent.
Conclusion— THR using a BioMedtrix^® canine cementless modular prosthesis restored hip function in an alpaca with coxofemoral osteoarthritis from chronic SCFE.
Clinical Relevance— THR may be an appropriate treatment for selected traumatic and degenerative conditions of the coxofemoral joint in alpacas.     

Zurich Cementless Total Hip Replacement: Retrospective Evaluation of 2nd Generation Implants in 60 Dogs

Objective— To evaluate the results of application, and identify complications, of the 2nd generation of Zurich Cementless Total Hip Replacement (ZCTHR).
Study Design— Case series.
Animals— Client-owned dogs (n=60) that had ZCTHR (n=65).
Methods— Dogs with ZCTHR (2001–2003) with a minimum follow-up ≥6 months were evaluated. Data included signalment, cup position, longest follow-up, complications, management of complications and outcome.
Results— Mean follow-up was 22.68 months. Eleven cases (17%) had postoperative complications: femoral fracture (n=1; 1.5%), prosthesis luxation (7; 11%), cup loosening (2; 3%), and implant failure (1; 1.5%); 9 cases were successfully revised. Explantation of implants was performed in 1 case because of infection, and 1 dog was euthanatized after reluxation.
Conclusions— ZCTHR can restore function in dogs affected by disabling diseases of the coxofemoral joint. The press-fit fixation of the cup allowed for corrections in cases of incorrect positioning. Cases with aseptic loosening were revised successfully by impacting larger cups. Newer stems of this generation are shot peening treated to increase their resistance to breakage. In our cases, infection is a disastrous event, leading to implant removal. After resolution of complications, a successful final outcome was achieved in 97% of THR.
Clinical Relevance— ZCTHR offers a reliable alternative for treating dogs with disabling diseases of the hip joints.     

Technique for Canine Total Hip Replacement

Between August 1976 and April 1980, a total of 132 canine total hip replacements using a commercially available prosthesis, were performed on clinical patients at The Ohio State University Veterinary Hospital and Berwyn Veterinary Hospital, Chicago. The technique for total hip replacement is described. Details of preoperative evaluation, the operative procedure, and postoperative care are presented.     

Biomechanical Evaluation of Acetabular Cup Implantation in Cementless Total Hip Arthroplasty

Objective: To report biomechanical properties of the Biologic Fixation System (BFX) acetabular cup impacted into a normal canine pelvis and to compare the effect of implant positioned to and beyond the medial acetabular wall. Study Design: In vitro cadaveric study. Animals: Hemipelves of mature, large‐breed dogs (n=6). Methods: For each dog, 1 hemipelvis was reamed to the depth of the acetabular wall (group A) and 1 was reamed an additional 6 mm after penetration of the medial cortex of the acetabulum (group B). The hemipelves were implanted with acetabular cups and loaded in compression through a matching femoral prosthetic component until failure. Specimen stiffness, and failure displacement, load, and energy were determined from load and displacement data and results between groups compared with a paired t‐test. Results: Mean failure load was greater in group A (3812 ± 391 N) than group B (2924 ± 316 N; P<.014). No other differences (P>.05) were observed between groups. Bone fracture (n=5) and cup displacement (1) occurred in group A whereas in group B there were 3 fractures and 3 cup displacements. Conclusions: Although medial placement of the BFX cup affected compressive failure loads, failure loads for both groups exceeded normal physiologic loads. Clinical Relevance: Medial positioning of the acetabular cup does not appear to compromise acetabular implant‐pelvic stability under normal physiologic loads. Because arthroplasty candidates often have abnormal acetabular architecture, mechanical properties of the cup placed in acetabula without a dorsal rim should be investigated.     

Revision of Cemented Total Hip Arthroplasty with Cementless Components in Three Dogs

Objective— To report revision of cemented total hip arthroplasty failure with cementless components in 3 dogs.
Study Design— Clinical case reports.
Animals— Dogs with total hip arthroplasty failure (n=3).
Methods— Cementless total hip arthroplasty revision was performed in 3 dogs with previously cemented femoral and acetabular components. All dogs required revision of the femoral component and 1 dog also required revision of the acetabular component.
Results— Revisions resulted in a stable functional prosthesis with successful bone integration.
Conclusions— Use of cementless components may be a viable option for revision of loosened cemented prosthesis after explantation of failed cemented canine total hip replacements.
Clinical Relevance— Failed canine-cemented total hip arthroplasties can be successfully revised with cementless components.     

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±5.6months; 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.     

Descriptive Histomorphometric Ingrowth Analysis of the Zurich Cementless Canine Total Hip Acetabular Component

Objectives— To (1) determine bone contact with the outer surface and ingrowth into the perforated outer shell of the Kyon acetabular component at 2, 6, and 12 months after total hip replacement (THR) and (2) determine correlation between radiographic lucency surrounding the cup–bone interface and bone contact and ingrowth.
Study Design— Experimental study.
Animals— Large breed dogs (n=11) with and without hip dysplasia.
Methods— Force platform gait analysis was performed preoperatively and 2, 6, and 12 months after THR. Curvilinear length of lucency (CLL) was measured on pelvic radiographs. Tissue contact with the outer cup and ingrowth into the cup were determined histomorphometrically at 2, 6, and 12 months.
Results— Peak vertical force and vertical impulse of the treated and control hind limb were not significantly different at any time. Median bone contact with the outer cup surface was 77%, 48%, and 76% at 2, 6, and 12 months, respectively. Median bone ingrowth into the cup perforations was 50%, 20%, and 44% at 2, 6, and 12 months, respectively. Median bone ingrowth to the inner cup surface was minimal at any time. CLL did not correlate with bone ingrowth.
Conclusions— Bone ingrowth into cup perforations occurred in each dog and was already present 2 months after THR, but most of the inner cup space remained vacant.
Clinical Relevance— Radiographic lucency surrounding the cup–bone interface does not allow assessment of bone contact with the outer surface or bone ingrowth into the Kyon cup in dogs without clinical problems.     

The Effects of Interlocking a Universal Hip Cementless Stem on Implant Subsidence and Mechanical Properties of Cadaveric Canine Femora

Objective

To determine if an interlocking bolt would limit subsidence of the biological fixation universal hip (BFX^®) femoral stem under cyclic loading and enhance construct stiffness, yield, and failure properties.

Study Design

Ex vivo biomechanical study.

Animals

Cadaveric canine femora (10 pairs).

Methods

Paired femora implanted with a traditional stem or an interlocking stem (constructs) were cyclically loaded at walk, trot, and gallop loads while implant and bone motions were captured using kinematic markers and high‐speed video. Constructs were then loaded to failure to evaluate failure mechanical properties.

Results

Implant subsidence was greater (P = .037) for the traditional implant (4.19 mm) than the interlocking implant (0.78 mm) only after gallop cyclic loading, and cumulatively after walk, trot, and gallop cyclic loads (5.20 mm vs. 1.28 mm, P = .038). Yield and failure loads were greater (P = .029 and .002, respectively) for the interlocking stem construct (1155 N and 2337 N) than the traditional stem construct (816 N and 1405 N). Version angle change after cyclic loading was greater (P = .020) for the traditional implant (3.89 degrees) than for the interlocking implant (0.16 degrees), whereas stem varus displacement at failure was greater (P = .008) for the interlocking implant (1.5 degrees) than the traditional implant (0.17 degrees).

Conclusion

Addition of a stabilizing bolt enhanced construct stability and limited subsidence of a BFX^® femoral stem. Use of the interlocking implant may decrease postoperative subsidence. However, in vivo effects of the interlocking bolt on osseointegration, bone remodeling, and stress shielding are unknown.     

Radiographic Criteria for Evaluation of Uncemented Total Hip Replacement in Dogs

A zonal analysis system and corresponding nomenclature were developed to describe the location and nature of radiographic changes in canine uncemented total hip arthroplasties. Criteria to assess prosthetic component alignment, percentage of femoral canal fill, resorptive and formative bony changes, and alterations in the bone at the implant-bone interface were derived by studying serial radiographs of 100 consecutive canine uncemented total hip arthroplasties for up to 30 months after surgery.     

Evaluation of Functional Outcome After BFX® Total Hip Replacement Using a Pressure Sensitive Walkway

Objective— To evaluate stance phase limb use after cementless (BFX^®) total hip replacement (THR) in dogs and to relate postoperative radiographic variables to static bodyweight distribution after surgery.
Study Design— Prospective clinical study.
Animals— Dogs (n=35) that had THR.
Methods— THR was performed using the BFX^® THR technique. Postoperative pain management regimens were similar for all dogs. Standing bodyweight distribution (%BW_distrib) was measured using a pressure sensitive walkway and radiographs made before surgery and at 3, 6, and 12 months after surgery. Repeated measures models (with backwards-stepping to obtain the final model) were used for statistical analysis.
Results— Temporally, %BW_distrib to the operated limb increased ( P <.0001; normal by 3 months) and decreased to the unoperated limb ( P =.0001) and also increased to the pelvic limbs and decreased to the thoracic limbs. %BW_distrib to the unoperated limb was significantly less than the operated limb at 3, 6, and 12 months after surgery. Postoperative canal fill and femur flare were significantly negatively correlated with change in %BW_distrib (estimate=−0.24, P =.0413).
Conclusion— BFX^® THR results in normal %BW_distrib to the operated limb by 3 months after surgery. A greater fill of the proximal femur may be associated with a suboptimal outcome.
Clinical Relevance— BFX^® THR normalizes standing bodyweight distribution dogs with hip osteoarthritis. Objective evaluation of THR outcome and radiographic features may reveal factors that could be improved through changes in prosthesis design or surgical technique.     

Risk Factors for Femoral Fracture after Canine Press‐Fit Cementless Total Hip Arthroplasty

Objective: To evaluate risk factors for femoral fracture after porous‐coated cementless total hip arthroplasty (THA). Study Design: Case series. Animals: Dogs (n=74) that had cementless THA (n=84). Methods: Medical records of dogs from 2 referral hospitals were reviewed for occurrence of postoperative femoral fracture. Patient and operative (age, breed, sex, weight, and canal flare index [CFI], indication for arthroplasty, intraoperative fissure, cerclage usage, and implant sizes) factors were analyzed. Assessment of implant positioning and canal fill was performed on immediate postoperative radiographs. Femoral fractures (n=11) were evaluated and compared with 73 cases without fracture that met the inclusion criteria. Results: Mean (±SEM) age was 7.30±0.69 years for dogs with, and 4.77±0.37 years for dogs without femoral fracture. Age was positively associated with fracture (P=.022). Mean (±SEM) CFI was 1.80±0.09 for dogs with, and 1.98±0.04 for dogs without fracture. CFI was negatively associated with fracture (P=.045). Body weight, intraoperative fissure, cerclage use, implant size, position, and canal fill did not influence the occurrence of femoral fracture. Conclusions: Older dogs and dogs with lower CFI may be at increased risk for femoral fracture after porous‐coated cementless THA. Clinical Relevance: Risk factors exist for femoral fracture after cementless THA using porous‐coated implants, and should be critically evaluated during the patient selection. These risks should be weighed against the benefits of the system, and measures to minimize femoral fracture in at‐risk patients studied.     

Pharmacokinetic Disposition of Cefazolin in Serum and Tissue during Canine Total Hip Replacement

Intraoperative cefazolin concentrations were measured in serum, joint capsule, cancellous bone of the acetabulum, and proximal cancellous bone of the femur in 15 dogs undergoing total hip replacement. Cefazolin (22 mg/kg intravenously [IV]) was administered every hour for three doses. The mean peak serum concentrations (+/- SEM) were 387.79 +/- 27.56 micrograms/mL, 521.71 +/- 28.00 micrograms/mL, and 542.20 +/- 30.91 micrograms/mL, respectively. Mean serum concentrations just before administration of doses 2 and 3 were 51.77 +/- 2.39 micrograms/mL, and 64.84 +/- 3.46 micrograms/mL, respectively. The mean cefazolin concentrations in the joint capsule, cancellous bone of the acetabulum, and cancellous bone of the femur were 34.71 +/- 2.50 micrograms/g, 28.70 +/- 7.40 micrograms/g, and 36.20 +/- 3.80 micrograms/g, respectively. The minimum inhibitory concentration of cefazolin for 90% of the common contaminants (MIC90) in this clinic is less than or equal to 2 micrograms/mL or per gram of tissue. Serum concentrations never fell below 15 times the MIC90 (lowest trough, 35.93 micrograms/mL), and the lowest tissue concentration (6.57 micrograms/mL in cancellous bone from the acetabulum) was still more than 3 times the MIC90. The mean tissue concentration was 15 times the MIC90.