Current Concepts With First MPJ Silicone Implants

Surgeons have used first metatarsophalangeal joint (MPJ) implants for over six decades with widespread availability beginning in the 1970s.¹ Patients with hallux rigidus have been the primary beneficiaries of implant arthroplasty. Other indications for these implants have included rheumatoid arthritis, hallux valgus with associated arthritis, and an unstable or painful joint from previous surgery. With the advent of computer-engineered implant designs, geriatric bunions have also become an indication for first MPJ silicone implants.

Historically, the various designs have included hemi-implants for either the metatarsal or phalanx side of the joint, and total joint implants with either a flexible double-stemmed design or two rigid components. The earliest generation implants were primarily joint spacers or modified hand implants. There was no specific instrumentation available. Surgical technique varied and the results were inconsistent. Often, there was postoperative joint instability, a loss of hallux toe purchase and lateral migration of weightbearing. Complications such as detritic synovitis and fibrous hyperplasia were common with silicone hemi-implants, and led to their removal from the market.      

The next generation of implants was prevalent in the 1980s and early 1990s. Several were hinged, double-stemmed, silicone elastomer implants. These implants provided better joint stability and range of motion. Concern over possible complications from the use of silicone breast implants caused a significant transition away from silicone first MPJ implants to arthrodesis or two-component systems of metal and ultra-high molecular weight polyethylene. These procedures were technically more difficult to perform and the results were mixed. Postoperative pain and limited range of motion were common.²  

When many experienced surgeons encountered various concerns and complications, they eventually abandoned the use of these implants, opting for alternative procedures instead. Other surgeons, realizing the benefit that many patients experienced, worked with manufacturers to create a newer generation of implants, using computer modeling around joint specific anatomy. These implants incorporated advanced materials, improved physical properties and redesigned instrumentation for greater accuracy. Recent advances include a single use instrumentation system that eliminates the need for cutting jigs and broaches.

Various authors have published studies demonstrating a high level of mid- to long-term successful outcomes with an implant arthroplasty procedure in appropriately selected patients.^3-6 Recently, there has been an increased usage of silicone double-stemmed first MPJ implants along with corresponding interest in greater education on the appropriate use of these implants.     

A Guide To Pertinent Indications And Contraindications For First MPJ Silicone Implants

Generally, middle age and older, less active patients with painful hallux rigidus, hallux valgus with degenerative arthritis, traumatic arthritis, rheumatoid arthritis, iatrogenic conditions or a geriatric bunion may be candidates for a double-stemmed silicone implant. The preoperative consultation should include all surgical options for correcting these deformities as part of informed consent.  

The addition of grommets will increase the durability of the implant by shielding the softer silicone material from abrasive wear from the adjacent harder bone.^7,8 When surgeons utilize grommets, there is generally less ectopic bone formation. We strongly recommend the use of grommets for most patients.

The general contraindications of implant use have not changed throughout history. This includes patients who have osseous, musculotendinous or adjacent soft tissue structures that cannot provide adequate support or fixation for the prosthesis. This may be attributed to disease, infection or prior surgery. Silicone first MPJ implants are not indicated for patients with very high activity levels or skeletal immaturity.

Addressing The Challenges Of Geriatric Bunions

Geriatric bunions can be challenging because of the frequent high angular deformities and often somewhat osteoporotic bone. These patients frequently do not easily handle limited or non-weightbearing. Surgeons commonly use the Keller procedure for correcting this deformity.⁹ However, there is often a post-op loss of joint stability and functional strength with the Keller procedure. The shorter stems on newer generation silicone double-stemmed implants, in combination with more anatomic designs, make implant arthroplasty a good alternative for these patients unless there is a rigid deformity.  

Often, it was not possible to use earlier generation implants due to longer stems not being tolerated with high intermetatarsal and hallux abductus angles. When one is using a current implant design, the important angle to consider is not the intermetatarsal angle but rather the angle at the intersection of the long axis of the implant and the second metatarsal bisection. If this angle is close to 0 degrees, there will be minimal stress on the implant. Placement of the implant in this alignment requires reaming the medullary canal of the first metatarsal parallel to the long axis of the second metatarsal rather than along the first metatarsal long axis.

Implants are not intended to correct angular deformities. Due to the high angular deformities in these patients, the surgeon needs to release significant soft tissue contractures. This frequently includes release of the lateral head of the flexor hallucis brevis tendon from its insertion into the base of the proximal phalanx. It is helpful to free the medial joint capsule from the subcutaneous tissues, beginning at the dorsal incision and continuing plantarly to the inferior aspect of the tibial sesamoid. This release mobilizes the joint capsule and the flexor complex from the subcutaneous tissues. Combining this dissection with the excision of the redundant dorsal medial capsule allows for excellent reduction of the angular deformity.  

It is recommended that surgeons use sizers to select the appropriate size implant. After inserting the appropriate size grommets, use the trial implant to check range of motion and joint alignment. One should evaluate the patient with the foot in a loaded position. Any jamming or twisting of the trial sizer indicates inadequate bone removal or soft tissue release.        

Loss of hallux toe purchase may occur from intrinsic instability of the joint. When using an implant that requires a vertical cut on the base of the proximal phalanx of the hallux, it is easy to weaken or sever the insertion of the flexor hallucis brevis tendon. One should assess the tendon on all patients before inserting the prosthesis. If there is significant weakness or complete release of the tendon from the base of the phalanx, the surgeon should consider a flexor tenodesis procedure. You may suture the flexor hallucis longus tendon to the base of the proximal phalanx using a non-absorbable suture through a drill hole in the inferior aspect of the phalanx. Then one sutures the flexor hallucis brevis tendon to the flexor hallucis longus tendon. This helps to prevent retraction of the sesamoid apparatus and provides additional intrinsic stability of the joint.  

Keys To Postoperative Management

The postoperative management is similar to that of other first MPJ procedures. If the surgeon performs no additional surgical procedures, one only applies a sterile compression dressing. Patients may be weightbearing immediately in a splint type, surgical shoe. Initially, there should be elevation of the foot above the level of the hips with frequent brief periods of weightbearing. The patient may increase ambulation to tolerance with intermittent elevation during the first few weeks following surgery. One removes sutures at approximately 14 days post-op. Early active and passive range of motion exercises are recommended to minimize joint stiffness. Encourage patients to perform weightbearing tip toe exercises when they can tolerate doing so. Shoe gear is permitted when discomfort and postoperative edema allow.

Clinical Tips And Pearls With First MPJ Silicone Implants

1.  The distal cut on the first metatarsal head should be approximately perpendicular to the long axis of the second metatarsal.

2.  One should perform reaming of the medullary canal of the first metatarsal parallel to the long axis of the second metatarsal, not along the long axis of the first metatarsal.

3.  After using the sizer to select the appropriate size implant, insert grommets. Utilize the trial implant to check range of motion and joint alignment with the foot loaded prior to inserting the implant.

4.  One may need to perform flexor tenodesis procedures if the flexor hallucis brevis tendon insertion has been compromised.

5.  Capsulorrhaphy needs to completely cover the joint implant in order to avoid possible dislocation of the prosthesis.

6.  Encourage early active and passive range of motion exercises to the patient in order to maintain joint mobility.      

Dr. Lawrence is a Fellow of the American College of Foot and Ankle Surgeons. Dr. Lawrence has disclosed that is the Executive Chairman and Chief Strategy Officer for In2Bones Global. He has also disclosed that he is the surgeon inventor of five implants for the first MPJ with current implants being marketed by Wright Medical, and Integra LifeSciences.

Dr. Lepow is a Fellow and Past President of the American College of Foot and Ankle Surgeons. He is an Associate Clinical Professor at Baylor College of Medicine and McGovern Medical School–University of Texas Health Science Center at Houston. He is the Director of Harris Health Ambulatory Services–Podiatry and is the Residency Director at St. Joseph Medical Center in Houston. He is a consultant to In2Bones USA.

Dr. Thuen is a Fellow of the American College of Foot and Ankle Surgeons, and is in private practice in Oceanside, Calif. He is a consultant to In2Bones USA.

References

1. Lawrence BR. First metatarsophalangeal joint implant arthroplasty: then and now. Foot Ankle Quarterly. 2013;24(1):1-9.
2. Gerbert J, Chang TJ. Clinical experience with two-component first metatarsal phalangeal joint implants. Clin Podiatr Med Surg. 1995;12:403.
3. Smetana M, Vencalkova A. Use of a silicone metatarsophalangeal joint endoprosthesis in hallux rigidus over a 15-year period. Acta Chir Orthop Traumatol Cech. 2003;70(3);177-181.
4. Sung W, Weil L Jr, Weil LS Sr, Stark T. Total first metatarsophalangeal joint implant arthroplasty: a 30-year retrospective. Clin Podiatr Med Surg. 2011;28(4);755-761.
5. Morgan S, Ng A, Clough T. The long-term outcome of silastic implant arthroplasty of the first metatarsophalangeal joint: a retrospective analysis of one hundred and eight feet. Int Ortho. 2012;36(9):1865-9.
6. Lawrence BR, Thuen E. A retrospective review of the Primus 1st MTP joint double stemmed silicone implant. Foot Ankle Spec. 2013;6(2):94-100.
7. Swanson AB, Swanson GG, Ishikawa H. Use of grommets for flexible implant arthroplasty of the metacarpophalangeal joint. Clin Orthop Relat Res. 1997:342;22-33.
8. Swanson AB, Swanson GG, Maupin BK, et al. The use of a grommet bone liner for flexible hinge implant arthroplasty of the great toe. Foot Ankle. 1991:12(3);149-55.
9. Keller WL. The surgical treatment of bunions and hallux valgus. NY Med J. 1904;80:741-742.