Ex vivo postimplantation biomechanical properties of a press-fit cementless femoral stem with transfixation pin for canine total hip replacement.

OBJECTIVE: To compare ex vivo postimplantation biomechanical characteristics of 3 implants for canine total hip replacement: a cementless press-fit femoral stem with a pin in the femoral neck (p-pfFS), a press-fit cementless femoral stem without this pin (pfFS), and a cemented femoral stem (cFS). SAMPLE: 18 cadaveric femurs from 9 dogs. PROCEDURES: Femurs were assigned randomly to 3 groups, and biomechanical testing was performed by measuring vertical displacement during cyclic loading and resistance to failure with compression parallel to the longitudinal axis of the femur. Force-displacement curves were assessed for failure tests, and work necessary for failure was calculated. RESULTS: No significant differences were observed in vertical displacement during cyclic loading (P = .263) or work necessary for failure (P = .079). Loads to failure for cFS and p-pfFS implants were significantly greater than that for the pfFS, but no significant difference in load to failure was observed between cFS and p-pfFS implants (P = .48). CLINICAL RELEVANCE: Cementless femoral stems with a transfixation pin offer significantly greater immediate resistance to failure to compressive loads parallel to the longitudinal axis of the femur than standard cementless stems, and a level of stability comparable to that of cemented stems. p-pfFS implants may be valuable in total hip replacement, potentially reducing the risk of fracture during the early postoperative period prior to osteointegration.

Limb-Sparing Surgery in Two Cats Using a Femoral Endoprosthesis with an Integrated Total Knee Replacement Implant.

OBJECTIVE: The aim of this study was to describe a novel limb-sparing technique for the management of feline bone neoplasia using a custom-made femoral endoprosthesis in combination with a total knee replacement (TKR) prosthesis. METHODS: Two cats with distal femoral bone tumours underwent pelvic limb salvage procedures with custom-made implants designed from patient-specific computed tomography images to replace the distal femur and the stifle. In case 1, the first-generation implant was a combination of a cemented femoral endoprosthesis with a uniaxial hinged cemented TKR prosthesis. Due to aseptic loosening of the endoprosthesis, revision was performed with a second-generation femoral endoprosthesis modified with a short intramedullary peg and a lateral bone plate for immediate stability. In case 2, a third-generation endoprosthesis with an intramedullary peg and two orthogonal bone plates for immediate stability, combined with a custom-designed rotationally hinged cemented TKR prosthesis, was used. Clinical and radiographic follow-up was recorded. RESULTS: After revision surgery in case 1 and with the third-generation implant in case 2, no complications were encountered. Both cats showed minor mechanical restriction of stifle range of motion and good clinical long-term outcome without local tumour recurrence. CONCLUSION: The combination of a femoral endoprosthesis and a TKR prosthesis can be a viable alternative for distal femoral limb salvage in cats.

Effect of Stem Positioning on Biomechanical Performance of a Novel Cementless Short-Stem Canine Total Hip Implant.

OBJECTIVE: The aim of this study was to evaluate the effect of stem positioning on the biomechanical performance of a novel, collared, short-stem total hip implant under compression and torsion ex vivo. STUDY DESIGN: Six canine cadaveric femurs were implanted with a collared short-stem femoral implant. Canal flare index (CFI), stem angle, absolute and relative cut heights and relative size were measured radiographically and used as independent variables. Biomechanical performance of the construct was evaluated using physiologic loading (loading) and supraphysiologic loading (failure) protocols. RESULTS: During loading protocols, compressive stiffness was influenced by absolute cut height (p = 0.018). During failure protocols, peak torque was influenced by CFI (p = 0.004) and craniocaudal relative size (p = 0.005). Peak load and torsional stiffness were not impacted by any of the radiographic variables (p > 0.05). Three of six femurs developed longitudinal fractures originating at the medial calcar at the time of failure. CONCLUSION: The biomechanical performance of the collared short-stem implant was positively impacted by preserving more of the femoral neck, having a higher CFI and using a smaller implant size relative to the femoral neck isthmus.

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.

Custom-made artificial eyes using 3D printing for dogs: A preliminary study.

Various incurable eye diseases in companion animals often result in phthisis bulbi and eye removal surgery. Currently, the evisceration method using silicone balls is useful in animals; however, it is not available to those with impaired cornea or severe ocular atrophy. Moreover, ocular implant and prostheses are not widely used because of the diversity in animal size and eye shape, and high manufacturing cost. Here, we produced low-cost and customized artificial eyes, including implant and prosthesis, using computer-aided design and three-dimensional (3D) printing technique. For 3D modeling, the size of the artificial eyes was optimized using B-mode ultrasonography. The design was exported to STL files, and then printed using polycaprolactone (PCL) for prosthesis and mixture of PCL and hydroxyapatite (HA) for ocular implant. The 3D printed artificial eyes could be produced in less than one and half hour. The prosthesis was painted using oil colors and biocompatible resin. Two types of eye removal surgery, including evisceration and enucleation, were performed using two beagle dogs, as a preliminary study. After the surgery, the dogs were clinically evaluated for 6 months and then histopathological evaluation of the implant was done. Ocular implant was biocompatible and host tissue ingrowth was induced after in vivo application. The custom-made prosthesis was cosmetically excellent. Although long-term clinical follow-up might be required, the use of 3D printed-customized artificial eyes may be beneficial for animals that need personalized artificial eye surgery.

Custom acetabular prosthesis for total hip replacement: A case report in a dog with acetabular bone loss after femoral head and neck ostectomy.

OBJECTIVE: To describe the application of a custom acetabular prosthesis (CAP) for total hip replacement (THR) in a dog 20 months after femoral head and neck ostectomy (FHNO). STUDY DESIGN: Case report. ANIMAL: A 10-year-old, male, castrated, Labrador retriever with progressive lameness and pain after FHNO. METHODS: Acetabular bone stock was assessed as insufficient for conventional THR, so a biflanged CAP was designed and three-dimensionally printed in titanium to bridge the bone defect. The CAP had a porous surface for long-term biologic fixation on the backside and was anchored to the ilium and ischium with screws. A polyethylene cup was cemented into the CAP, and a bolted cementless femoral stem was inserted. RESULTS: The loss of the conventional anatomic landmarks complicated intraoperative orientation and led to eccentric reaming and 5-mm malalignment of the CAP. Reduction of the prosthetic joint was difficult because of periarticular fibrosis, loss of functional muscle length, and thickness of the CAP, and intraoperative shortening of the stem neck was required. Postoperative complications included sciatic neurapraxia, which resolved with time and conservative management. Absence of pain and improvement of range of motion were observed at clinical examination 12 months after surgery; however, moderate hind limb lameness persisted due to muscle tension. No evidence of implant loosening was noted on radiographs acquired 24 months after surgery. CONCLUSION: Femoral head and neck ostectomy with poor functional outcome was ameliorated by using a CAP in this dog. CLINICAL SIGNIFICANCE: Use of a CAP can be considered to treat acetabular defects in dogs.

A Biomechanical Comparison of Four Hip Arthroplasty Designs in a Canine Model.

OBJECTIVE: The aim of this study was to develop an in vitro biomechanical protocol for canine cementless hip arthroplasty that represents physiological gait loading (compression and torsion) and to evaluate if three alternative implant designs improve fixation compared with the traditional collarless, tapered stem in the clinically challenging case of moderate canal flare index. STUDY DESIGN: Twenty-four (six/group) laboratory-prepared canine constructs were tested using a simulated gait and overload (failure) protocol. Construct stiffness, failure load/displacement and migration were measured as outcome variables. RESULTS: Simulated gait loading did not show any significant differences between implant types for peak displacement, peak rotation, torsional stiffness, subsidence or inducible displacement. The collared and collarless stem groups were stiffer in compression compared with the collarless with a lateral bolt and short-stem groups. Increasing the loading above simulated gait showed significant reductions in compressive and torsional stiffness for all implant constructs. Despite the reductions, the short-stem group showed significantly higher stiffness compared with the other three groups. CONCLUSION: Peak failure loads (compressive and torsional) in this study were approximately four to seven times the simulated gait loading (430 N, 1.6 Nm) regardless of implant type and highlight the importance of limiting activity level (trotting, jumping) following hip replacement in the postoperative period and during the osseointegration of the implant.

Design and Use of a 3D Prosthetic Leg in a Red-lored Amazon Parrot ( Amazona autumnalis).

A three-dimensional (3D) prosthesis was designed and built for a red-lored Amazon parrot ( Amazona autumnalis) with a pre-existing amputation of the distal left leg at the tibiotarsal-tarsometatarsal joint and injuries to the right leg caused by cage companion aggression. The prosthesis consisted of a straight main imprint, with a round element at both ends to provide stability, and a bridge connecting this to a socket without a bottom where the stump could be accommodated and held securely with self-adhesive bandaging. Over a 4-month period, 3 different 3D prosthetic models were made and evaluated. The first model was fitted, but the parrot would only use the tip of the main imprint to stand and walk. The second model was designed with a semicircular imprint with only 1 round element at the cranial end, a different bridge to accommodate the change to the main imprint, and the same socket. With these changes, the parrot was able to place the imprint of the prosthesis on the floor to stand and move freely around its enclosure. To accommodate morphologic changes on the stump, a third model was created consisting of the same imprint and bridge, but the socket was cut vertically all the way on one side to allow distention on its diameter and provide a long-lasting fit to the stump over time.

Bony ingrowth potential of 3D-printed porous titanium alloy: a direct comparison of interbody cage materials in an in vivo ovine lumbar fusion model.

BACKGROUND CONTEXT: There is significant variability in the materials commonly used for interbody cages in spine surgery. It is theorized that three-dimensional (3D)-printed interbody cages using porous titanium material can provide more consistent bone ingrowth and biological fixation. PURPOSE: The purpose of this study was to provide an evidence-based approach to decision-making regarding interbody materials for spinal fusion. STUDY DESIGN: A comparative animal study was performed. METHODS: A skeletally mature ovine lumbar fusion model was used for this study. Interbody fusions were performed at L2-L3 and L4-L5 in 27 mature sheep using three different interbody cages (ie, polyetheretherketone [PEEK], plasma sprayed porous titanium-coated PEEK [PSP], and 3D-printed porous titanium alloy cage [PTA]). Non-destructive kinematic testing was performed in the three primary directions of motion. The specimens were then analyzed using micro-computed tomography (µ-CT); quantitative measures of the bony fusion were performed. Histomorphometric analyses were also performed in the sagittal plane through the interbody device. Outcome parameters were compared between cage designs and time points. RESULTS: Flexion-extension range of motion (ROM) was statistically reduced for the PTA group compared with the PEEK cages at 16 weeks (p-value=.02). Only the PTA cages demonstrated a statistically significant decrease in ROM and increase in stiffness across all three loading directions between the 8-week and 16-week sacrifice time points (p-value≤.01). Micro-CT data demonstrated significantly greater total bone volume within the graft window for the PTA cages at both 8 weeks and 16 weeks compared with the PEEK cages (p-value<.01). CONCLUSIONS: A direct comparison of interbody implants demonstrates significant and measurable differences in biomechanical, µ-CT, and histologic performance in an ovine model. The 3D-printed porous titanium interbody cage resulted in statistically significant reductions in ROM, increases in the bone ingrowth profile, as well as average construct stiffness compared with PEEK and PSP.

The in vivo response to a novel Ti coating compared with polyether ether ketone: evaluation of the periphery and inner surfaces of an implant.

BACKGROUND CONTEXT: Increasing bone ongrowth and ingrowth of polyether ether ketone (PEEK) interbody fusion devices has the potential to improve clinical outcomes. PURPOSE: This study evaluated the in vivo response of promoting new bone growth and bone apposition with NanoMetalene (NM) compared with PEEK alone in a cancellous implantation site with an empty aperture. STUDY DESIGN: This is a randomized control animal study. METHODS: Implants and funding for this study were provided by SeaSpine (60,000 USD). Cylindrical dowels with two apertures were prepared as PEEK with a sub-micron layer of the titanium (NM). The titanium coating was applied over the entire implant (Group 1) or just the apertures (Group 2). Polyether ether ketone implants with no coating served as controls (Group 3). Implants were placed in the cancellous bone of the distal femur or proximal tibia with no graft material placed in the apertures in eight adult sheep. Bone ongrowth to the surface of the implant and ingrowth into the apertures was assessed at 4 and 8 weeks after surgery with micro-computed tomography (CT) and undecalcified histology. RESULTS: The apertures in the implants were notably empty in the PEEK group at 4 and 8 weeks. In contrast, new bone formation into the apertures was found in samples coated with NM even though no graft material was placed into the defect. The bone growing into the aperture tracked along the titanium layer. Apertures with the titanium coating demonstrated significantly more bone by micro-CT qualitative grading compared with PEEK with average bone coverage scores of Group 1 (NM) 1.62±0.89, Group 2 (NM apertures only) 1.62±0.77, and Group 3 (PEEK) 0.43±0.51, respectively, at 4 weeks (p<.01) and Group 1 (NM) 1.79±1.19, Group 2 (NM apertures only) 1.98±1.18, and Group 3 (PEEK) 0.69±0.87, respectively, at 8 weeks (p<.05). The amount of bone in the apertures (ingrowth) quantified using the volumetric data from the micro-CT supported an overall increase in bone volume inside the apertures with the titanium coating compared with PEEK. Histology showed newly formed woven bone tracked along the surface of the titanium in the apertures. The PEEK interface presented the typical nonreactive fibrous tissue inside the apertures at 4 weeks and some focal contact with bone on the outside at 4 weeks and 8 weeks. CONCLUSIONS: Micro-CT and histology demonstrated bone ongrowth to the surfaces coated with NM where the newly formed bone tracked along the thin titanium-coated surfaces. Polyether ether ketone surfaces presented the nonreactive fibrous tissue at the interface as previously reported in preclinical scenarios.

Use of an Electron Beam Melting Manufactured Titanium Collared Cementless Femoral Stem to Resist Subsidence After Canine Total Hip Replacement.

OBJECTIVES: To evaluate the effect of a collared electron beam melting (EBM)-manufactured titanium cementless femoral stem on implant subsidence after total hip replacement (THR). STUDY DESIGN: Prospective study ANIMALS: Dogs (n = 26); 33 THR. METHODS: Records were maintained on the first 110 consecutive THR using an EBM collared femoral stem. Radiographs on the first 33 THR that had 6-months follow-up were evaluated for implant subsidence. These results were compared to 27 dogs with subsidence after THR with a Co Cr collarless stem. RESULTS: Dogs that had EBM collared stem THR had a mean body weight of 35.4 kg, body condition score (BCS) of 6.21, and mean canal flare index (CFI) of 1.56. EBM stem sizes used (number implanted) were #7 (13), #8 (10), #9 (8), and #10 (2). Subsidence of collared stems did not occur if the collar was in contact with cortical bone during surgery. Subsidence of 1-3 mm occurred closing a gap between the collar and bone if contact was not made during surgery, but subsidence stopped once contact was made. No major complications directly related to the EBM collared stem were encountered. CONCLUSIONS: A collar on a cementless femoral stem in contact with cortical bone resists subsidence.

Development and validation of a canine radius replica for mechanical testing of orthopedic implants.

OBJECTIVE: To design and fabricate fiberglass-reinforced composite (FRC) replicas of a canine radius and compare their mechanical properties with those of radii from dog cadavers. SAMPLE: Replicas based on 3 FRC formulations with 33%, 50%, or 60% short-length discontinuous fiberglass by weight (7 replicas/group) and 5 radii from large (> 30-kg) dog cadavers. PROCEDURES: Bones and FRC replicas underwent nondestructive mechanical testing including 4-point bending, axial loading, and torsion and destructive testing to failure during 4-point bending. Axial, internal and external torsional, and bending stiffnesses were calculated. Axial pullout loads for bone screws placed in the replicas and cadaveric radii were also assessed. RESULTS: Axial, internal and external torsional, and 4-point bending stiffnesses of FRC replicas increased significantly with increasing fiberglass content. The 4-point bending stiffness of 33% and 50% FRC replicas and axial and internal torsional stiffnesses of 33% FRC replicas were equivalent to the cadaveric bone stiffnesses. Ultimate 4-point bending loads did not differ significantly between FRC replicas and bones. Ultimate screw pullout loads did not differ significantly between 33% or 50% FRC replicas and bones. Mechanical property variability (coefficient of variation) of cadaveric radii was approximately 2 to 19 times that of FRC replicas, depending on loading protocols. CONCLUSIONS AND CLINICAL RELEVANCE: Within the range of properties tested, FRC replicas had mechanical properties equivalent to and mechanical property variability less than those of radii from dog cadavers. Results indicated that FRC replicas may be a useful alternative to cadaveric bones for biomechanical testing of canine bone constructs.

Biomechanical comparison of the pullout properties of external skeletal fixation pins in the tibiae of intact and ovariectomised ewes.

The pin-bone interface is the least stable component of the external skeletal fixator. Concerns exist regarding the ability to obtain adequate implant purchase in poor quality bone. Consequently, reduced bone quality has been viewed as a contra-indication for the use of external skeletal fixators. The aim of this study was to investigate the holding power of two different fixator pin designs in bone from entire and ovariectomised sheep. Thirty-two aged ewes were divided into two groups. Group 1 were controls, and Group 2 were ovariectomised (OVX). The ewes were sacrificed 12 months post-ovariectomy and five pairs of tibiae were harvested from each group. The holding power of cortical and cancellous fixator pins was assessed at five standardised locations on each tibia. An increase in mean cortical thickness was noted in the OVX group. The holding power of cancellous fixator pins was superior to that of cortical pins, irrespective of whether or not ovariectomy had been performed. Cancellous pins had an increased holding power in post ovariectomy bone compared to control bone. Cortical pin performance was not affected by ovariectomy. There was a lack of correlation between the incidence of insertional fractures of the far cortex and implant holding power. The results raise questions over the effectiveness of ovariectomy in establishing osteopaenic bone suitable for assessing implant performance, hence further investigations are warranted.

Use of a pulsatile ventricular assist device (Berlin Heart EXCOR) and an interventional lung assist device (Novalung) in an animal model.

Pulsatile ventricular assist devices (VADs) are used in pediatric patients mainly as a bridge to heart transplantation. If severe respiratory failure occurs, extracorporeal membrane oxygenation (ECMO) is currently the treatment of choice. ECMO has the potential for severe complications. Interventional lung assist (iLA) devices, e.g., the Novalung, are used in patients with isolated lung failure. This study aimed to show the feasibility of the combined use of the EXCOR VAD (10 ml and 30 ml blood pumps) and the Novalung. There were two separate experiments within this study. First, a bench test was carried out to analyze pressure and flow through both devices. Second, 10 kg and 30 kg pigs received support with the VAD and iLA in series. Pressures and flow were measured systemically before and after the iLA. Flow was unaffected by the iLA. The mean arterial pressure was reduced (mean of 13 mm Hg) by the iLA. There were no obvious difficulties observed within the interaction of VAD and iLA. The combined use of both devices is feasible and able to provide sufficient perfusion pressures. Oxygenation and CO2 clearance was effectively supported by the iLA. Patients with myocardial and respiratory failure may benefit from this setup.

Assistive devices, orthotics, and prosthetics.

Deciding on which supportive device, orthotic, or prosthetic is best suited for a given patient is a complex process involving many different factors. The ability to manage biomechanical abnormalities successfully may be enhanced by an understanding of the properties of the various materials that comprise these devices, their effect on functional performance, and other associated patient factors. Veterinary health care providers are faced with the challenge of effectively addressing the physiologic and fiscal needs of the patient in a rapidly changing patient care environment.

Total joint replacement in the dog.

Total joint replacement has evolved over the past 50 years from a concept that was first attempted in people suffering from osteoarthritis to a commonly applied practice in veterinary medicine. Although many questions have been answered, several controversies still exist, with many implant and technical options being explored. Currently, total hip and elbow replacement are commercially available options viable for use in dogs. These options are detailed in this article. Joint replacement for other canine joints (ie, knee, hock, shoulder) that develop osteoarthritis likely will be developed in the near future.

The effects of femoral stem and neck length on cement strains in a canine total hip replacement model.

OBJECTIVE: To determine the effects of femoral prosthesis stem length and head size on cement strains in a canine hip replacement system. STUDY DESIGN: An in vitro experimental model. SAMPLE POPULATION: (1) Three standard and 3 1-cm shortened femoral implants with +3 femoral heads. (2) Two standard implants with +0, +3, and +6 femoral heads. METHODS: Femoral stems were embedded in polymethylmethacrylate cement. A uniaxial proximodistal-oriented strain gauge was applied to the cement on the medial and lateral aspects of the construct 1.5 cm, 6.0 cm and 7.0 cm distal to the collar. Each construct with a +3 femoral head was mounted in a materials testing system. An axial compressive load (0-200 N) was applied to the femoral head and cement strains were recorded. Additionally, 2 standard length constructs were also tested with +0 and +6 femoral heads. The effects of stem length and neck length on cement strains were assessed with analysis of variance. RESULTS: Strains increased at all locations with increasing loads for all constructs. Shorter implants had higher strains by 152% and 171%, lateral (P =.003) and medial (P =.0025) to the stem tip. No significant strain differences were noted, at any strain gauge location, between different neck lengths (P values ranged from.20 to.67). CONCLUSIONS: Although a shorter implant stem has a potential to improve implant fit, it led to significantly higher cement strains that may increase the risk for aseptic loosening. Changes in femoral neck length did not significantly affect cement strains under the conditions tested. CLINICAL RELEVANCE: Shortening of the femoral stem currently cannot be recommended in canine total hip replacement. The existing use of variable neck lengths likely does not increase the risk of failure of the femoral stem.

Amputation and prosthesis.

Amputation of a limb is a drastic therapy in cattle and should be considered as a last resort in the treatment of limb injuries. Even though the surgical technique for amputation is simple, daily limb management, prosthesis manufacture, and adaptation of the animal to the prosthesis are difficult and time consuming. Dedication of the owner to the aftercare required for the rest of the animal's life is extremely important. Amputation of a limb with prosthesis application is a method of saving valuable animals for breeding purposes or animals of sentimental value. The author reviews his experience with partial foreleg amputation and prosthesis application in three heifers.