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John Vanore, DPM
Faculty, Podiatry Institute
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Implant arthroplasty is a commonly performed procedure at the level of the first MTP joint. There are a good number of first metatarsal phalangeal joint implants available today and prior to utilization, it is incumbent upon surgeons to be familiar with some basic principles.
Production of this present lecture was made possible by an educational grant from Integra, Limit Uncertainty.
John Vanore: Implant arthroplasty is not a new phenomenon and has been practiced at the level of first MTP joint for the last 40 or so years. We’ve learned a few things about implant arthroplasty over these years and as a senior member of our profession, who has investigated implants more than 30 years, my goal is to try and impart to you some of the important aspects of implant surgery that I have learned during that time. I'll try and identify what has worked and what has not worked with regard to implant surgery. Our discussion of implants does need to include a few basic principles. Just like histology, physiology, pathology are necessary prerequisites for the practice of medicine our study of joint implantation must include a discussion about materials, implant design, indications for use of the implant and appropriate patient selection.
The author has contributed to numerous textbook chapters, reviewing these topics and refers to participant to the three editions of McGlamry's textbook, Comprehensive Textbook of Foot and Ankle Surgery for a more in-depth discussion. Materials used in the design of implants include a host of polymers and metals. Generally hemi-arthroplasty with a single component consists of a solitary material, while two component or total joint implant systems are fabricated of more than one material, which generally include both the metal and a polymeric component. Use of polymer biomaterials was common in the performance of hemi-arthroplasty and silicone materials was one of the initial choices.
Silicone is a relatively soft polymer and was popularized by Alfred Swanson for use as an inter-positional device that allowed movement between diseased joint segments. Silicone rubber as was often referred to, due to its soft, but elastic physical properties. Implant arthroplasty with the use of silicone type interposition devices became very popular in the 1970s, but suffered a decline in usage in the 1980s with reports of complications associated with silicone detritus and difficulties associated with fragmentation and subsequent host reactions, generally involving foreign body granulomatous reactions.
Polyethylene was another choice amongst polymeric materials, but is a harder biomaterial compared to silicone. Polyethylene is generally the material of choice for articulation with a metal component during the performance of total joint arthroplasty. Unfortunately, ultra-high-molecular-weight polyethylene, although still in common use is also subjected to particle abrasion or micro-fragmentation and subsequent reactive phenomena, including host reactions of detritic synovitis. Use of this material has been particularly important in large joint orthopedics as a bearing surface with a metal typically for total joint replacement.
Ultra-high-molecular-weight polyethylene was also the initial material chosen for subtalar arthroereisis. Several metallic biomaterials have been utilized in the performance of joint arthroplasty. Amongst the most common metals is a cobalt chromium alloy, where cobalt is the dominant element with lesser degrees of chromium and nickel. Cobalt chromium alloys generally possess superior bearing surface characteristics, meaning that it possesses an extremely low coefficient of friction with an opposing biomaterial, such as ultra-high-molecular-weight polyethylene. Titanium may be utilized in either its pure metallic form or more commonly an alloy with vanadium and aluminum.
Both are extremely inert and resistant to corrosion and have similar elastic moduli although the alloy is considered less brittle. Titanium is light in weight compared to cobalt chrome and stainless steel and is generally considered to have excellent characteristics with regard to osseous compatibility and biointegration. Titanium alloys are often chosen for fabrication of implant stems or trays to hold articulating surfaces such as polyethylene.
Titanium is usually not considered for articulating surfaces due to its higher coefficient of friction and its tendency to get erosion and production of wear debris. Ceramics utilized for orthopedic purposes include the crystalline ceramics, silica, and aluminum. Generally, there are two classes of bioceramics, the bio-stable or inert and the bioactive or degradable. The former group has application as a component of a joint system, while the latter is used as a coating to enhance osseous integration. Ceramics are excellent materials for situations of compression loading and articulation as a bearing surface. Ceramics do have a reputation as a relatively brittle material and low resistance to crack propagation.
A synovial joint is a system that allows movement between the osseous lever arms, allows smooth transmission of forces and does so with an incredible efficiency and a minimum of wear. Most joints possess a changing or dynamic joint axis, the first MTP joint requires a stable hallux, wherein the first metatarsal rotates in plantar flexes upon the sesamoid complex. Why implant arthroplasty? Interpositional arthroplasty was initially championed by Alfred Swanson as an adjunct to resection arthroplasty. Swanson was an advocate of interpositional arthroplasty in an effort to avoid the complications of resection arthroplasty such as painful, stiff and unstable joints.
In the foot, the Keller Resection Arthroplasty was associated with instability of the interphalangeal joint as well as the first MTP joint. A short unstable great toe and frequent lesser metatarsalgia, implant arthroplasty was meant to augment the resection arthroplasty in an effort to avoid these biomechanical faults. Swanson believed in the integrity of the joint space and was an advocate of interpositional arthroplasty or in joint resection, reestablish the joint space and a biomaterial spacer maintain the joint space and provide it for joint motion.
He believed that interposition of the soft, flexible material would maintain the joint space created by the resection arthroplasty and a fibrous capsule would develop, that would stabilize and maintain alignment. Implant arthroplasty of the first metatarsal phalangeal joint may be performed by a variety of techniques. Initially hemi-interpositional arthroplasty was performed with the silicone device followed by a double-stem hinged implant. Early attempts at two component joint arthroplasty were not encouraging and hemi-arthroplasty with resurfacing techniques of the proximal phalangeal base advocated.
Later metatarsal resurfacing was introduced. Today all these techniques are practiced with the exception of hemi-silicone arthroplasty which is no longer available. Swanson initially tried implantation of the first metatarsal head, but found that interpositional arthroplasty with the silicone intramedullary stem device was more stable when placed on the non-weightbearing side of the joint. The 3-D graph on the right, illustrates the original design, Swanson great toe implant, five years postoperative, all the while modified design with an angled base is present in the radiograph to the left.
Silicone interpositional arthroplasty may be performed with a double-stemmed hinged implant. The metatarsal stem was somewhat longer and the hinge allowed for constrained motion, essentially only in the sagittal plane. And attempts to improve the durability of the bone silicone interface, titanium grommets were later introduced. Hemi-arthroplasty then migrated from silicone to metal implants with Swanson simply changing materials, but keeping his basic design.
Later resurfacing techniques with thin metal articular surfaces generally of a cobalt chromium alloy were designed to articulate with the first metatarsal head and predominated first MTP joint implant arthroplasty. As you may notice, a wide variety of different intra-medullary stems were proposed to provide osseous stabilization of the implant. Hemi-arthroplasty may also be performed on the metatarsal side of the joint. The first metatarsal head generally possesses the greater degree of osteoarthritic changes and reconstruction on the side of the joint appears logical.
The metatarsal head implants have been proposed with a large variety of features, which varied the shape of the articulating surface, coating the presence of a flange usually dorsal to the variations of the size and shape of the intra-medullary stem. Reconstruction of the first metatarsal phalangeal joint may also be performed by total joint replacement, which generally consists of separate metatarsal and phalangeal components, which when implanted allow for resection of pathologic joint surfaces and restoration of physiologic movement at the first MTP joint.
Many systems have been introduced over the past 20 years and three different implant systems are illustrated. Indications for implant arthroplasty have changed little over the past 40 years, these include osteoarthrosis to the first metatarsal phalangeal joint, whether due to hallux rigidus or arthrosis due to prior surgery or trauma. Hallux valgus and the arthritides such as rheumatoid arthritis have also been in indication when combined with arthritic pathology. Implant arthroplasty is a joint destructive procedure and the pathology should warrant a joint destructive procedure.
Hallux rigidus is the most ideal indication for implant arthroplasty. Reconstructive techniques with large inter-metatarsal angles or a large hallux abductus angle make the reconstruction more difficult and require adjunctive procedures. Hemi-arthroplasty on either side of the joint or total joint replacement are all appropriate reconstructive techniques for hallux rigidus. With regard hallux rigidus, the reader is directed to the American College of Foot and Ankle Surgeon’s first [Indiscernible] [0:12:22] clinical practice guideline for a full discussion of the pathology and its surgical management.
Joint preservation techniques are appropriate in cases of lesser degrees of arthrosis and primary joint reconstruction should be considered. Implant arthroplasty is a joint destructive procedure and is appropriate in patients with significant or end-stage arthrosis where the joint is deemed to be in such poor condition, that primary joint reconstruction is unlikely to provide a pain-free alternative. Besides implant arthroplasty, joint destructive techniques for hallux rigidus include resection arthroplasty as well as arthrodesis.
The treatment of painful hallux valgus with hemi-arthroplasty was over utilized in the 1970s and 1980s and led to numerous problems including recurrent deformity and host reactions to silicone detritus. Constrained implants such as double-stem silicone hinge have been utilized with success in patients with hallux valgus deformities and concomitant arthrosis of the first MTP joint. The size of the intermetatarsal angle is an important element in these patients and the use of these implants may require a separate osteotomy and/or metatarsal-cuneiform fusion, which also increases the complexity of the surgical procedure.
Longevity of the silicone implant particularly in the younger and more active patient has generally been questioned and should be avoided. Literature searches will reveal numerous papers, demonstrating use of implants in patients with rheumatoid arthritis. Traditionally, these have been reconstructions utilizing the silicone hinge implant in combination with panmetatarsal head resections. Patients with poor bone stock should not be considered for implant arthroplasty. Additionally, use of non-constrained implants generally will not provide adequate stability at the first MTP joint for a reduction of the inter-metatarsal angle which is generally quite high and may require a separate procedure.
Alternatively, first MTP joint arthrodesis provides for a reduction of both, the hallux abductus deformity as well as the intermetatarsal angle and does so providing stability to the medial column. Implant arthroplasty has been utilized in other pathologies, but may present with very difficult clinical situations. A patient with chronic tophaceous gout may possess very poor bone stock and yield difficulty with implant stability. In the case of hallux varus, some cases show very unstable capsular ligamentous structures and make reconstruction with alternatives such as arthrodesis more likely successful.
As with any other surgical procedure, there are contraindications to surgery in general and some more specific to implant arthroplasty. Obviously, if the patient has poor circulation, limited skin and soft tissue coverage in the area of surgery or has had a recent infection or local osteomyelitis, surgery should probably be avoided. The stability of any implant is dependent upon secure osseous stability, and poor bone stock certainly must be considered. Implant arthroplasty fabricated of any materials, which the patient has a known allergy is a definite contraindication.
Patient selection is a very important consideration for the performance of implant arthroplasty. Implant arthroplasty with intra-positional devices went out of favor in the 1980s in good part due to the overutilization. Pathology is emphasized and should warrant a joint destructive procedure. Younger patients with greater activity demands are more likely to place greater stress upon the reconstruction and potential for complications. Women are more often concerned with first MTP joint movement with regard to the types of shoes they would like to wear, particularly in regard to heel height. The surgical technique for implant arthroplasty may appear rather simple.
The details of the individual procedures will be stressed in part two of this lecture. Surgeons are cautioned that revision of the failed implant arthroplasty may be very difficult and more complicated than the original surgery.
The surgeon must be able to provide alternatives and perform revision surgery if necessary. The age of the individual undergoing joint reconstruction with implant arthroplasty has been a concern since the 1980s and the large number of case reports of complications associated with silicone arthroplasty. Hemi-metallic arthroplasty has been shown to be a much more durable reconstruction. First MTP joint arthrodesis is believed to be the most durable reconstruction and once full-bone union has been achieved and is indicated in individuals of all ages.
The message today is that implant arthroplasty of the first MTP joint is okay and is a well accepted procedure. When performed for the proper indications, in an appropriate patient, implant arthroplasty can be expected to be successful. The second portion of this lecture will deal mainly with the specific techniques of implant arthroplasty.