Canine Total Hip Replacement
The main design objective of the KYON Zurich Cementless THR, a proprietary system of implants, instruments and a surgical technique for canine total hip replacement, was to provide for an immediate and indefinitely stable anchorage of the prosthetic components. Total hip replacement techniques fall into two categories: Cemented and Cementless. Cemented THR provides fine short term, but less satisfactory long term outcomes. Aseptic loosening, the most common reason for long term failure of THR, is responsible for 75% of revisions in human patients. Conventional press-fit cementless THR’s have taken about 50% of the market, but the revision rates in all categories of human patients remain higher than with cemented THR. The femoral and acetabular components of the Zurich Cementless THR reflect different, both novel, approaches to addressing the most common complications of canine total hip replacement.
In 1999, after six years of clinical experience, Prof. Pierre M. Montavon, Head of Small Animal Surgery at the School of Veterinary Medicine, University of Zurich, and Slobodan Tepic, Dr. Sci., Dipl.Ing., of the AO Research Institute, Davos, Switzerland, with the participation and advice of Dr. Aldo Vezzoni, DVM, Dipl. ECVS, Cremona, Italy, initiated an international, multi-center clinical study, to collect well-documented, broad-based clinical performance data on the Zurich Cementless Total Hip Replacement. Data contributed by fourteen surgeons from eight countries on over 750 cases is in the final stages of preparation for publication. Collection of the surgical reports and clinical follow-up were coordinated by Prof. Randy Boudrieau, DVM, Dipl. ACVS, Prof. of Surgery, Cummings School of Veterinary Medicine, Tufts University, Massachusetts, USA.
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By the end of 2009, the Zurich Cementless THR had been used in over 9,000 dogs by more than 150 surgeons in Europe, the United States, Australia, and Japan. KYON holds an exclusive, worldwide patent license in the veterinary field for the anchorage of the THR femoral component from SCYON Orthopaedics AG.
- Immediate and permanent proprietary locking-screw fixation
- Near-physiolological loading of the proximal femur – absence of stress shielding
- Full range of impingement free motion
- Minimal disruption of methaphysial cancellous bone
- Rapid bone ingrowth into a highly compliant acetabular cup
- Absence of wear-particle induced lysis
- Titanium and titanium alloy for supreme biocompatibility and reduced risk of infection
- Titanium plasma porous coating for micro-interlock
- Proprietary, hydraulically open, compliant, double shell metal backing for the cup
- Amorphous Diamond Like Coating (ADLC) on the Head-Necks, harder, smoother, and more lubricious than conventional coatings, insuring superb articulation
- Proprietary, wear-reducing geometry for the poly inlay
 – Annual Report 2007, The Swedish National Hip Arthroplasty Register, Dept. of Orthopaedics, Sahlgrenska University Hospital, February 2005, www.jru.orthop.gu.se
Hip Dysplasia & Osteoarthritis:
A normal hip is a tightly joined “ball and socket” joint. The normal hip joint enables the hind leg to move smoothly in a full range of motion and allows a dog to rise, walk, run, jump, and turn effectively. In the diseased hip, the “ball and socket” become irregular, rough, and deformed, causing pain and decreased range of motion.
Total hip replacement (THR) surgery replaces a painful and dysfunctional hip joint with an artificial prosthesis, in order to provide a pain-free, fully functional joint. This surgery is typically performed on a dog with severe hip pain due to conditions called hip dysplasia and osteoarthritis. Total hip replacement can also be considered for a dog with a painful and abnormal hip due to fracture, luxation (dislocation), or necrosis (severe degeneration) of the femoral head.
Hip dysplasia, meaning abnormal growth of the hip, is a common problem in dogs. Dysplastic hips are painful and lack smooth movements; therefore the dog’s quality of life can be severely affected. Selection of the appropriate treatment option for this condition is dependent on many factors such as: age, severity of hip dysplasia, development of osteoarthritis, degree of pain/discomfort, and owner’s expectation and financial ability.
Treatment Options and Methods:
Many dogs with pain and lameness associated with hip dysplasia can be effectively managed with conservative methods. Conservative methods include: weight management, moderation of excessive exercise/activity, providing warm comfortable bedding, and the use of non-steroidal anti-inflammatory drugs, physical rehabilitation, and oral supplements as needed.
If the dog has severe hip pain and the quality of life is decreased, and if conservative methods are not effective, surgical treatment should be considered.
 – Hayashi, Kei, DVM, MS, PhD, DACVS – Total Hip Replacement In Dogs (ACVS)
MAIN DESIGN OBJECTIVES
(1) Provide an immediate and indefinitely stable bone anchorage of the femoral and acetabular components.
(2) Minimize wear of the artificial joint.
The Zurich Cementless THR stem achieves permanent anchorage on the femoral side through bony ingrowth from the medial cortex without coupling to the lateral cortex. Stability required for ingrowth is guaranteed by locking screw fixation of the stem to the cortex from the inner side of the bone**. This results in near physiological loading of the proximal femur, i.e. absence of stress shielding.
On the acetabulum side, the outer shell of the cup is manufactured from perforated, highly compliant, titanium, with an inner non-perforated shell and an ultra-high molecular weight polyethylene (UHMWPE) inner lining to receive the head of the stem. The double-shelled design** provides for rapid and consistent integration of the acetabular bone into the outer shell of the cup.
Minimizing wear reduces the risk of bone lysis mediated aseptic loosening. Instead of a conventional spherical shape, an artificial Fossa™** provides an articulating surface that minimizes contact with the femoral head and improves hydrodynamic lubrication within the cup. This modified geometry of the contact area between the head of the prosthesis and the polyethylene liner reduces the contact stresses several fold. A new amorphous diamond-like coating (ADLC) provides increased hardness and lubricity to the head/cup interface, also reducing wear.
INNOVATION AND DEVELOPMENT
Achieving the previously stated design objectives required solving two, partially coupled problems:
(1) Eliminating load-induced movement at the bone-implant interfaces, and
(2) Minimizing stress shielding of the bone, particularly the shielding caused by conventional, stemmed femoral components.
Bone cement in a Charnley-type cemented THR accomplishes both: stability of the interface by an in situ polymerized interlock; and well defined load distribution through a compliant cement mantle. This is fine for the near term, but less satisfactory on a long term basis. Aseptic loosening is the most common reason for long-term failure of THR surgery. This is well documented for human hip surgery and has been recently demonstrated to be even more so for canine THR. The high aseptic loosening rates of cemented hips has been the main driving force behind development of cementless THR. However, clinical performance with sufficient follow-up of all the different types of cementless THRs shows this technique to be inferior to that of a well-designed and well cemented THR. In most cases, cementless prostheses have replaced the soft cement mantle by adding more stiff metal to an already stiff core element. This exacerbates both problems. A higher mismatch in stiffness leads to more pronounced stress shielding and higher shear loads at interfaces, increasing the risk of micromotion. The femoral and acetabular components of KYON THR reflect different, novel approaches to the design objectives.
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ANCHORAGE OF THE FEMORAL COMPONENT:
During normal cycling, the femur is subjected to compression loading on the medial side and tension forces on the lateral side. The femur is naturally more compliant than a solid, canal-filling metal prosthesis. Physiological loading generates high interface shear stresses, which can be resisted initially by friction alone. It has been shown by theoretical analysis that canal-filling, press-fitted, metal stems cannot be stable at all contact areas with the femur under physiological-level loading. Should any motion occur before the interface is secured by bone adaptation to the implant (by ongrowth and/or ingrowth), true, solid anchorage of the prosthesis will fail.
Preparation of the medullary canal for implantation kills about two thirds of the cortex with the endosteal blood supply to the bone inevitably destroyed. About 10 to 12 weeks after surgery, remodeling of this dead bone will lead to its peak porosity. During this period, and then longer still to allow for the bone to refill and gain some strength, the hip should be protected from (over) loading. This is at best difficult, and in most cases impossible. As a consequence, most, if not all, of press-fit implants get loose at some stage and are then subjected to a chancy process of bone remodeling which may eventually form a stable interface at some areas, with soft connective tissue covering most of the implant.
In departure from the press-fit/bony ingrowth concept, the KYON Zurich Cementless THR deploys screw-based primary fixation of the femoral component. The Zurich Cementless THR uses locking screws. Conventional screws, used for hip prosthesis fixation in the 1950s, caused bone remodeling around the screws, resulting in loss of stability and implant failure. But with screws safely locked in the stem, the mechanics is similar to the extensively researched PcFix plating system of AO/ASIF. Remodeling can proceed without a major risk of loosening, without bone resorption occurring around all of the screws at the same time. The Zurich Cementless THR is fixed by mono-cortical screws to the medial cortex only. Screws are passed through the access holes in the lateral cortex, all drilling and fixation is performed with the aid of a drill guide attached to the stem. Since the stem does not touch the lateral cortex, it can move freely, does not transfer any load to the cortex, and does not cause bone resorption. Avoiding coupling between the medial and lateral cortices is the most important, distinguishing characteristic of the Zurich Cementless THR.
If any bone is to eventually bridge the gap and grow to direct apposition with the implant, it may do so under ideal conditions of stability. To facilitate the process of integration the stem is plasma coated with pure titanium.
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ANCHORAGE OF THE ACETABULAR COMPONENT:
In conventional cementless acetabular components, the subchondral shell is either completely removed in designs aiming for bone ingrowth, or partially retained in various threaded-type designs. The metal backing is usually a very stiff structure leading to a huge mismatch in compliance and seriously reducing the chances of a complete, long-lasting bony integration.
In most cases, the metal backing of conventional cups engage bone with a textured surface, sometimes with interconnected pores running some depth into the material, but ending in closed, dead-end holes. Our preoccupation with the role of convective transports in bone growth and remodeling has led us to propose the concept of a hydraulically open implant – the acetabular component of the Zurich Cementless THR being the first embodiment of this concept.
The polyethylene (UHMWPE) insert is suspended within a double layer of titanium. The first layer is a thin smooth surface to prevent the proginator cells from interacting with the polyethylene material. The outer layer is a densely perforated titanium shell leaving about 1 millimeter of free space between the inner wall of the metal shell and the outer wall of the smooth titanium insert, i.e. bone is free to grow past the shell into this space. Ingrowth is accelerated by convective fluid currents, set in motion by cyclic pressure gradients caused by the physiological loading of the bone. This is perhaps the main functional distinction over the perforated, cylindrical implants developed by Franz Sutter (who has also supported our early efforts) of the Straumann Institute, Waldenburg, Switzerland, mostly for dental, but also for orthopedic applications. Fluid convection is presumed to increase mass transport of important bone ingrowth promoting factors emanating from the extant cancellous bone surrounding the implant.
The surface of the outer titanium shell is plasma, titanium coated for an additional microinterlock with the bone. For improved press-fit the shell incorporates small protrusions running circumferentionally just below the equator. The pole of the shell is slightly flattened to avoid the cups bottoming out at the pole without a full engagement at the equator.
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The design objective for articulation is to maximize the range of impingement-free motion by minimizing the neck diameter, with maximum head coverage. This objective has been met in steps, with the final optimization of the neck shape to reduce stress concentration and the UHMWPE insert providing approximately 200° of cover. The combination allows for over 120°, now 135° with BIG HEADs, of impingement-free angulation. The average luxation rate is about 5% with several surgeons reporting it as low as 1%. We have found a new challenge in meeting stability criteria in very young – 6-10 months – dysplastic dogs, which typically show a great range of motion, and therefore an increased risk of luxation. A series of intra-operative stability tests, and appropriate corrective measures, if any lack of stability is detected, provide a strong guarantee against postoperative luxation.
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 – Annual Report 2002, The Swedish National Hip Arthroplasty Register, Dept. of Orthopaedics, Sahlgrenska University Hospital, April 2003, www.jru.orthop.gu.se
 – Skurla CP, Pluhar GE, Frankel DJ, Egger EL, James SP – Assessing the dog as model for human total hip replacement. Analysis of 38 canine cemented femoral components retrieved at post-mortem.
J Bone Joint Jurg Br. Jan;87(1):120-7, 2005
VetSurg 38: 1-22, 2009 (p.8)
 – Tepic S, Remiger AR, et al., – Strength Recovery in Fractured Sheep Tibia Treated with a Plate or an Internal Fixitor: An Experimental Study with a Two-Year Follow-up,
J Orthop Trauma 11(1):14-23, 1997
 – Vuillemin T, Raveh J, Sutter F, – Mandibular Reconstruction with the Titanium Hollow Screw Reconstruction Plate (THORP) System: Evaluation of 62 Cases
Plast Reconstr Surg 82(5):804-14,1988
In 1999, after six years of clinical experience, Prof. Pierre M. Montavon, Head of Small Animal Surgery at the School of Veterinary Medicine, University of Zurich, and Slobodan Tepic, Dr. Sci., Dipl.Ing., of the AO Research Institute, Davos, Switzerland, with the participation and advice of Dr. Aldo Vezzoni, DVM, Dipl. ECVS, Cremona, Italy, initiated an international, multi-center clinical study, to collect well-documented, broad-based clinical performance data on the Zurich Cementless Total Hip Replacement, a novel THR concept. Data contributed by fourteen surgeons from eight countries on over 750 cases is in the final stages of preparation for publication. Collection of the surgical reports and clinical follow-up were coordinated by Prof. Randy Boudrieau, DVM, Dipl. ACVS, Prof. of Surgery, Cummings School of Veterinary Medicine, Tufts University, Massachusetts, USA.
By the end of 2009, with over 16 years of clinical experience, the Zurich Cementless THR had been used in over 9,000 dogs by more than 150 surgeons in Europe, the United States, Australia, and Japan. The goal of providing an immediately and indefinitely stable THR is within reach.
Kyon holds an exclusive, worldwide patent license in the veterinary field for the anchorage system of the THR femoral component from SCYON Orthopaedics AG.
Please contact firstname.lastname@example.org to update contact information.
Use of a revision cup for treatment of Zurich cementless acetabular cup loosening. Surgical technique and clinical application in 31 cases.
Vet Comp Orthop Traumatol. 2013;26(5):408-15. doi: 10.3415/VCOT-13-02-0029. Epub 2013 Jun 26.
1Aldo Vezzoni, DVM Diplomate ECVS, Clinica Veterinaria Vezzoni, Via Massarotti 60/A, 26100 Cremona, Italy, Phone: +39 0372 23451, Fax: +39 0372 20074, E-mail: email@example.com.
Hummel DW1, Lanz OI, Werre SR.
Complications of cementless total hip replacement. A retrospective study of 163 cases.
Vet Comp Orthop Traumatol. 2010;23(6):424-32. doi: 10.3415/VCOT-09-07-0071. Epub 2010 Sep 9.
1Virginia-Maryland Regional Regional College of Veterinary Medicine, Blacksburg, VA, USA. firstname.lastname@example.org
Andreoni A1, Guerrero TG, Hurter K, Montavon PM.
Revision of an unstable HELICA endoprosthesis with a Zurich cementless total hip replacement.
Vet Comp Orthop Traumatol. 2010;23(3):177-81. doi: 10.3415/VCOT-09-08-0083. Epub 2010 Apr 26.
1Vetsuisse Faculty, University of Zurich, Clinic of Small Animal Surgery, Winterthurerstrasse 260, 8057 Zurich, Switzerland. email@example.com
Guerrero TG1, Montavon PM.
Zurich cementless total hip replacement: retrospective evaluation of 2nd generation implants in 60 dogs.
Vet Surg. 2009 Jan;38(1):70-80. doi: 10.1111/j.1532-950X.2008.00466.x.
1Department of Small Animal Surgery, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 260, Zurich, Switzerland. firstname.lastname@example.org
Lauer SK1, Nieves MA, Peck J, Pool RR, Hosgood G, Lazar T, Swanson E.
Descriptive histomorphometric ingrowth analysis of the Zurich cementless canine total hip acetabular component.
Vet Surg. 2009 Jan;38(1):59-69. doi: 10.1111/j.1532-950X.2008.00443.x.
1Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA.
Haney DR1, Peck JN.
Influence of canal preparation depth on the incidence of femoral medullary infarction with Zurich Cementless Canine Total Hip arthroplasty.
Vet Surg. 2009 Aug;38(6):673-6. doi: 10.1111/j.1532-950X.2008.00474.x.
1Affiliated Veterinary Specialists, Maitland, FL 32751, USA. email@example.com
Marsolais GS1, Peck JN, Berry C, Johnson A.
Femoral medullary infarction prevalence with the Zurich Cementless Canine Total Hip arthroplasty.
Vet Surg. 2009 Aug;38(6):677-80. doi: 10.1111/j.1532-950X.2009.00569.x.
1Monterey Peninsula Veterinary Surgical Service, Carmel, CA, USA.
Tidwell SA1, Graham JP, Peck JN, Berry CR.
Incidence of pulmonary embolism after non-cemented total hip arthroplasty in eleven dogs: computed tomographic pulmonary angiography and pulmonary perfusion scintigraphy.
Vet Surg. 2007 Jan;36(1):37-42.
1Affiliated Veterinary Specialists, Maitland, FL 32751, USA. firstname.lastname@example.org
Hanson SP1, Peck JN, Berry CR, Graham J, Stevens G.
Radiographic evaluation of the Zurich cementless total hip acetabular component.
Vet Surg. 2006 Aug;35(6):550-8.
1Affiliated Veterinary Specialists PA and Central Florida Veterinary Radiology PA, Maitland, 32751, USA.
Annual Report 2005, The Swedish National Hip Arthroplasty Register, Department of Orthopaedics, Sahlgrenska University Hospital
Department of Orthopaedics, Sahlgrenska University Hospital
Skurla CP1, Pluhar GE, Frankel DJ, Egger EL, James SP.
Assessing the dog as a model for human total hip replacement. Analysis of 38 canine cemented femoral components retrieved at post-mortem.
J Bone Joint Surg Br. 2005 Jan;87(1):120-7.
1Department of Engineering, Baylor University, Waco, Texas 76798-7356, USA.
Skurla CP1, James SP.
Postmortem retrieved canine THR: femoral and acetabular component interaction.
Biomed Sci Instrum. 2004;40:255-60.
1Baylor University, Department of Engineering, PO Box 97356, Waco, TX 76798, USA.
Femur fractures associated with canine total hip replacement.
Vet Surg. 2004 Mar-Apr;33(2):164-72.
Gulf Coast Veterinary Specialists, 1111 West Loop South, Houston, TX 77027, USA. Billliska@aol.com
Montavon PM, Tepic S
Zurich Cementless – a new concept in canine total hip replacement Principles of anchorage, surgical technique and results after five years of clinical experience
School of Veterinary Medicine, University of Zurich