Emerging Insights On First MPJ Implant Arthroplasty

Arthritis of the first metatarsophalanageal joint (MPJ), or hallux rigidus, is the most common arthritic condition in the foot and ankle.¹ It typically involves progressive osteophyte formation and cartilage destruction resulting in joint pain, stiffness and restricted dorsiflexion of the first MPJ. The patient will often have swelling of the joint and difficulty wearing shoes. This pain often affects a patient’s activities of daily living and recreational activities. 

Hallux rigidus can result from progressive arthritis due to hallux valgus deformity, biomechanics, traumatic arthritis, gouty arthritis, rheumatoid arthritis and iatrogenic conditions.² 

With this in mind, let us take a closer look at salvage procedures for failed bunionectomies or failed first MPJ implants, and how the total first MPJ implant arthroplasty procedure could have an impact in enhancing results for revisional procedures of the first MPJ.

Surgeons have commonly utilized implant arthroplasty of the first MPJ for stage 3 and stage 4 hallux rigidus for many years. Over the years, the design and implant materials have changed. In the 1970s and early 1980s, there were a variety of non-articulating silicone-based implants. Initially, there was a high complication rate due to loss of the insertion of the flexor hallucis brevis tendon. The resulting loss of intrinsic stability of the joint apparently led to increased stress to the implant hinge, metatarsalgia to adjacent lesser MPJs and loss of hallux toe purchase.² This was primarily due to overresection of the base of the proximal phalanx and the straight orientation of the implant.

These earlier generations of silicone-based implants sometimes resulted in cystic changes to the bone and granulomatous reactions. The medical community deemed these questionable because of the silicone breast implant controversy at the time these were popular.

In the late 1990s, first MPJ implant development changed significantly. A combination of advanced computer modeling, improvement in the physical properties of silicone elastomers and more precise instrumentation led to the development of the Primus implant. Originally developed by Futura Biomedical, the implant is now owned and distributed by Integra LifeSciences. Many foot and ankle specialists in the United States and abroad use this implant but there has been very little research published in the last 25 years on outcomes with this implant. 

What The Research Reveals On One First MPJ Arthroplasty System 

In a 2013 retrospective study, Lawrence and Thuen assessed long-term results of the Primus First MPJ Implant (The implant has since been renamed the Integra Silicone 1^st MTP Toe Replacement System). The study reported on 54 patients (a total of 70 implants) who had an average follow-up of 66.4 months. The average age of the patients at the time of surgery was 66 and the average postoperative American Orthopaedic Foot and Ankle Society (AOFAS) score was 87.4. The most common complication was metatarsalgia under the second metatarsal (12.4 percent), which was transient for 23 of 25 patients and treated conservatively with orthotics, pads, modified shoe gear, NSAIDs and/or corticosteroid injections. Two patients required Weil osteotomies of the second metatarsal at a later date. Patients demonstrated asymptomatic medial deviation of the second toe at a rate of 27.1 percent. None of the first MPJ implants required removal or revisional surgery. There were no cases of sesamoiditis or synovitis, and three stress fractures of lesser metatarsals. The results revealed no signs of degradation or fracture of the implant, and no signs of a granulomatous reaction or loosening of the implant.³

The average post-op weightbearing range of the motion of the first MPJ was 65.3 degrees with weightbearing in a tip-toed position.³ There was less than seven percent of the patients revealed cystic changes at the stems of the implant on radiographic evaluation, but this was asymptomatic. Asymptomatic bony overgrowth over the dorsal hinge of the implant occurred in 10 percent of patients. Greater than five mm of hallux elevatus occurred in 14.2 percent of patients but this was also asymptomatic.

Most of the past research was based on older, less well-designed versions of the first MPJ implant. The Integra Silicone 1^st MTP Toe Replacement System implant has a unique and improved shape in that the implant stems are much shorter and have a smaller diameter than those of previous designs. The long axis of the implant is parallel to the long axis of the foot and eliminates most of the transverse plane stress on the hinge. The implant requires less bone resection off the base of the proximal phalanx and has an angled hinge, which allows for better hallux purchase and improved dorsiflexion.³ 

In recent years, there has been a shift toward employing first MPJ arthrodesis for the salvage of failed bunion surgeries and the treatment of stage 3 and 4 hallux rigidus over the years.^4,5 This is partially due to prior implant arthroplasty complications with older designs. The ability to correct for an abnormal increase in the first intermetatarsal angle in some patients with an arthrodesis versus an implant is also a factor along with the belief that arthrodesis patients can be more active than implant patients postoperatively. 

There is a lack of research assessing the Integra 1^st MTP Toe Replacement system in active patients. In addition, patients with osteoporotic bone are more difficult to fixate with screws or plate fixation, and older patients, smokers or people with diabetes may not fuse well.⁵ 

Key Patient Cases Examining The Utility Of First MPJ Implant Arthroplasty

That said, here are a few case study examples involving first MPJ implant arthroplasty to treat patients with failed bunion or implant procedures, or a severe bunion deformity. The goals of these revisional procedures are to alleviate pain, improve function/flexibility and return the patient to being active as soon as possible. The foot and ankle surgeon needs to consider the age of the patient, activity level, the need for flexibility of the joint and the patient’s ability to be non-weightbearing or wear a cast, or a wedge-type post-op shoe.

Case study #1: A 67-year-old female with type 2, insulin-using diabetes complained of pain to the right great toe joint. A year ago, she had a bunion surgery which included a first metatarsal osteotomy with bunionectomy and screw fixation. The joint pain improved minimally after this surgery and became progressively worse, limiting her daily activities. Despite second digit hammertoe repair one year ago as well, she related severe pain at the second MPJ with dorsal subluxation of the second toe.

The X-rays revealed asymmetric joint space narrowing of the first MPJ with flattening of the metatarsal head. There was abnormal elongation of the second metatarsal and second toe subluxation at the level of the MPJ. 

The revisional procedure included removal of the screw in the first metatarsal head, a Keller bunionectomy with total implant arthroplasty, second metatarsal osteotomy and flexor plate repair. The patient healed unremarkably and returned to full daily activities and walking for exercise. She has noted mild and occasional forefoot pain at the second MPJ, and no pain at the first MPJ.

Case study #2: A 65-year-old female complained of pain and muscle spasms to the left and right foot after minimal-incision bunion surgery eight months ago on the right foot and nine months ago on the left foot. She returned to her tennis shoes a few weeks after her prior surgery as instructed, and had chronic and progressive pain. The great toes were often in spasm and she was unable to wear closed-toed shoes. Instead, she has worn open-toed post-op shoes since her surgeries. She also related pain in the bilateral balls of the feet under the second and third metatarsals, and in the first MPJs. The patient was very anxious and depressed due to the dysfunction and pain in her great toes.

The X-rays revealed severe shortening of the first metatarsal, non-union of bone at the osteotomy sites and severe first metatarsal elevatus with hallux elevatus.

I initially had the patient use a below-knee CAM walker and Exogen® bone stimulator (Bioventus) for six weeks until the bone healed. We then performed a revisional surgery, which included a Keller bunionectomy with total implant arthroplasty. We minimized bone resection from the metatarsal as it was already very short. The hallux elevatus greatly improved but 10 degrees of elevatus was the final result.

The patient healed unremarkably with the right foot surgery taking place a few months before the left. We believed it was important for her to return to shoes and improve her muscle strength in the first foot and leg prior to operating on the opposite foot. The pain and muscle spasms resolved after the procedure and she returned to tennis shoes and walking for exercise without pain 6 weeks after the surgery. Her lesser metatarsalgia resolved after the implant arthroplasty and with use of soft over-the-counter insoles. 

Case studies #3 and #4: The following are two very similar patients. One was a 60-year-old male was a year out from surgery, which included a first MPJ joint cheilectomy and hemi-implant. The second patient is a 54-year-old male who had an Arthrosurface implant inserted one and a half years previously. Both patients still had severe hallux limitus with less than 10 degrees of dorsiflexion, severe joint pain when walking and sesamoiditis.

In both cases, I removed the implants and inserted the Integra Silicone 1^st MTP Toe Replacement System. Both patients healed unremarkably and returned to walking for exercise. The second patient returned to softball for exercise but had some residual metatarsalgia under the second and third metatarsals. However, the patient indicated the pain was minimal and tolerable with custom orthotics.

Case study #5: A 54-year-old female had prior McBride bunionectomy procedures bilaterally more than 10 years ago. Subsequently, the deformities recurred and continued to increase in size. The pain limited her daily and recreational activities, and she had difficulty wearing any closed-toed shoes. There was 20 degrees of dorsiflexion at the first MPJ with weightbearing and crepitus with range of motion. There was a severe bunion deformity with a first intermetarsal angle of 20 degrees and abnormal elongation of the second metatarsal on X-ray.

Due to the severity of the bunion deformity, the presence of a large osteochondral lesion and 50 percent erosion of the articular cartilage, I performed a Lapidus arthrodesis with bone graft and a Keller bunionectomy with an Integra first MPJ implant.  I also performed a second metatarsal osteotomy.

She healed unremarkably and returned to weightbearing in shoes at 10 weeks post-op. The patient proceeded to return to walking for exercise and all daily activities a few weeks later. Her pain resolved completely.

Final Perspectives

Although total implant arthroplasty of the first MPJ is common for stages 3 and 4 hallux rigidus, it can also be beneficial for revising prior failed surgeries due to progressive arthritis, pain and iatrogenic deformities. The implant can also enhance a foot surgeon’s outcomes in treating severe bunions and providing more post-op function and flexibility. 

Regardless of the surgeon’s preference for first MPJ arthrodesis versus a total implant arthroplasty, there are many patients who are not ideal patients for arthrodesis. Prior studies on first MPJ arthrodesis have often had a high percentage of patients who do not follow up for clinical evaluations. Therefore, post-op patient satisfaction and outcomes are likely underreported.^6,7 

After reviewing the medical literature and performing these procedures for 25 years, several studies on first MPJ arthrodesis are overly critical of implant arthroplasty due to the desire for longer-term follow up. However, several arthrodesis studies have only a short-term follow up.⁴ There are very few studies on the Integra first MPJ implant. Therefore, opinions on this procedure may be based on older generations of total implants.  

There are several long-term studies on implant arthroplasty using this older generation of implants (i.e. the Swanson total implant).^8,9 In both studies, which had average 13.4-year and 8.5-year follow-ups respectively, there was a greater than 90 percent satisfaction rate with minimal clinical complications. There were some abnormal findings on X-ray such as mild bony overgrowth or mild cystic changes at the implant stems but the patients did not exhibit symptoms. In my experience over the past 25 years, total implant arthroplasty has a very high success rate with minimal and rare complications. I am currently working on co-authoring an eight-year prospective study and hope to publish our group’s findings with longer-term follow up next year.

In my opinion, patients who are anxious or depressed from prior surgeries, or who would have difficulty wearing a cast and minimizing weight bearing for two months will not do well with an arthrodesis. If the patient has difficulty with balance due to his or her age, size or biomechanics, having more flexibility at the first MPJ will provide a more functional joint than a fusion. Most patients prefer a great toe that is more functional and more flexible.  

In order to have good long-term success with a first MPJ replacement, one must pay attention to the rebalancing of soft tissue structures and the realignment of severe bunions to minimize stress on the implant when the patient returns to being active. This includes adjunctive procedures such as an extensor hallucis brevis tenotomy, lateral capsular release and medial capsulorrhaphy. A release of hallux retrograde pressure will often reduce an increased intermetatarsal angle.¹⁰ Other soft tissue contractures of the Achilles tendon, flexor hallucis brevis, plantar fascia and flexor hallucis longus fibrosis all may necessitate release or lengthening to achieve an ideal result.^11,12 However, proximal osteotomies will be necessary for some patients. It is our preference to perform a Lapidus arthdrodesis for these patients as we can correct in both the transverse and sagittal planes. 

When considering revisional surgery with a patient after failed bunion or implant surgery, or patients with arthritic changes and a severe bunion, it is important to consider all options and what is best for the patient. Each patient has different goals and expectations when considering revisional surgery. It is a challenge to resolve a patient’s symptoms 100 percent after prior surgery. However, we can choose a procedure which will allow for a faster and easier recovery, and allow for the foot to be more functional. When one fuses a joint, it is difficult to revise the arthrodesis if it results in a non-union or other complication. If an implant wears out, one can replace it. If it creates a different problem, one can still remove it and fuse the joint with a bone graft. This is extremely rare in our experience as the Integra first MPJ total joint replacement system provides a good alternative for these patients.

Dr. Feit is board-certified by the American Board of Podiatric Surgery and is a past president of the American Diabetes Association in Los Angeles. Dr. Feit is in private practice in Torrance and San Pedro, Calif. He can be found online at www.precisionfootandanklecenters.com.

1. Vanore JV, Christensen JC, Kravitz SR, et al. Diagnosis and treatment of the first metatarsophalangeal joint disorders. Section 2: hallux rigidus. J Foot Ankle Surg. 2003;42(3):124-136.
2. Lawrence B. First metatarsophalangeal joint implant arthroplasty: then and now. Foot and Ankle Quarterly. 2013;24(1):1-9.  
3. Lawrence BR, Thuen E. A retrospective review of the Primus first mtp joint double-stemmed silicone implant. Foot Ankle Spec. 2013;6(2):94-100.
4. Asif M, Qasim SN, Kannan S, Bhatia M. A consecutive case series of 166 first metatarsophalangeal joint fusions using a combination of cup and cone reamers and crossed cannulated screws. J Foot Ankle Surg. 2018;57(3):462-465.
5. Stone OD, Ray R, Thomson CE, Gibson JNA. Long term follow up of arthrodesis vs total joint arthroplasty for hallux rigidus. Foot Ankle Int. 2017;38(4):375-380.
6. Rushing CJ, Rathnayake VR, Oxios AJ. Patient percieved recovery and outcomes after silastic implant arthroplasty. J Foot Ankle Surg. 2018;57(6):1080-1086.
7. Beekhuizen SR, Voskuijl T. long term results of hemiarthroplasty compared with arthrodesis for osteoarthritis of the first metatarsophalangeal joint. J Foot Ankle Surg. 2018;57(3):445-450.
8. Lemon B, Pupp GR. Long term efficacy of total silastic implants: a subjective analysis. J Foot Ankle Surg. 1997;36(5):341-346.
9. Bonet J, Taylor DT, Lam AT, Williams E, Keane LA. Retrospective analysis of silastic implant arthroplasty of the first metatarsophalangeal joint. J Foot Ankle Surg. 1998;37(2):128-134.
10. Durrant MN, Siepert KK. Role of soft tissue structures as an etiology of hallux limitus. J Am Podiatr Med Assoc. 1993;83(4):173-180.
11. Kirane YM, Michelson, JD, Sharkey NA. Contribution of the flexor hallucis longus to loading of the first metatarsophalangeal joint. Foot Ankle Int. 2008;29(4):367-377.