Current And Emerging Concepts With First MPJ Implants

Offering a closer look at the evolution of first MPJ arthroplasty, these authors discuss early implant designs, assess the pros and cons of unipolar and bipolar devices, and address common complications. 

Hallux rigidus is one of the most common forms of degenerative joint disease in the foot and it often leads to increased pain and rigidity in the first metatarsophalangeal joint (MPJ). Loss of the first MPJ’s ginglymus function and plantarflexion via the sesamoid apparatus lead to antalgia and compensation. Both of these can occur at a contracted infrapedal and suprapedal level, leading to a myriad of compensatory symptoms.

The term hallux rigidus, first introduced by Cotterill in 1877 and subsequently described by Nicoladoni in 1881, is a decrease in sagittal plane motion of the first MPJ.¹Degenerative joint disease is recognized as the most common cause of hallux rigidus.

However, other conditions (including inflammatory arthropathies or osteochondritis dissecans) may also be related to hallux rigidus, and hallux rigidus can also occur as a result of trauma.¹Biomechanical conditions, including metatarsus primus elevatus, a long first metatarsal, immobility of the first ray created by peritalar collapse and osteoarthritic hypermobility of the first ray can also play a role. Disease of the sesamoids themselves can also be associated with hallux rigidus.

When osteoarthritis surrounds the first metatarsal, further restriction of motion occurs through a buttressing or snowplow effect. As this sequela continues, mechanical impingement, eccentric cartilage wear, subchondral erosions and compression lead to metatarsal head flattening, loss of concentricity due to microsubcondral fracture and collapse during the repair process.

The clinical presentation of hallux rigidus most commonly includes a complaint of pain, which is worse during push-off or propulsion in gait, and increased activity often leads to abnormal gait mechanics. On radiographs, asymmetric narrowing of the joint space is typically visible with functional adaptation and flattening of the metatarsal head. Osteophyte formation occurs dorsally and laterally as the joint attempts to widen its contact area and dissipate stress. Osteophyte formation, head flattening and loss of concentricity further restrict dorsiflexion range of motion.

Multiple authors have proposed several classification systems of hallux limitus and one commonly used system is the classification devised by Drago, Oloff and Jacobs (see the table “A Closer Look At A Commonly Used Hallux Limitus Classification System” at right).²This classification defines hallux limitus in three stages with worsening severity with stage four progressing to hallux rigidus.

Treatment options for this condition remain controversial with options including first metatarsophalangeal joint arthrodesis, Keller arthroplasty, decompression osteotomy, arthrodiastasis, allomatrix interposition grafting, autograft soft tissue interposition, hemi-implants and total joint implants. While implant arthroplasty became in vogue in the 1970s, it still persists as a viable option in carefully chosen patients. The focus of this article is on the joint arthroplasty options in the treatment of hallux rigidus and clinical procedure selection.

A Quick Primer On The Origins And Evolution Of First MPJ Implant Arthroplasty

In Stage IV hallux limitus, joint destructive procedures are normally required. When deciding to perform an arthrodesis versus an arthroplasty, one should assess patient factors and comorbidities to provide the best chance for a favorable outcome. Patient factors to consider include age, activity level, severity of disease, presence of osteopenia, patient expectations and biomechanical factors that alter implant alignment. While first MPJ arthrodesis has been called the “gold standard,” a complete loss of first MPJ motion is not attractive to some patients and it is not without complications. Critical hallux interphalangeal joint motion must be present without arthrosis. Malunion, nonunion, painful hardware and risk of adjacent joint arthritis can lead to further revision surgery, and alter the clinical outcome.

First MPJ arthroplasty originated in the early 1950s. Endler described the use of an acrylic methacrylate design for the proximal phalanx in 1951.¹Similarly, Townley and Taranow designed a proximal phalanx hemi-implant.^1,3In the late 1960s to 1970s, researchers developed the silicone Swanson implant (Dow Corning Corporation) for surgeons to use in conjunction with the Keller arthroplasty procedure.1 However, researchers demonstrated poor results and decreased patient satisfaction.

Subsequently, the senior author saw the emergence of double-stemmed implants but they likewise had poor results and low patient satisfaction. Despite this, most of the findings were radiographic rather than clinical.

The senior author began using silastic implants in the early 1980s. Retrospectively, the amount of complications in his experience was quite low with most implants surviving nearly 40 years. Certainly, radiographs revealed concerns such as implant engulfment, hallux shortening, bone cysts (fibrous dysplasia) and some patients had “adjusting” metatarsal stress fractures secondary to a “cascade effect” created by detachment of the short flexor and loss of the windlass mechanism.

Recently, the use of titanium grommets to “protect” the implant from direct bony wear has somewhat resurrected the total silastic implant within the profession. Still, concerns of bone loss and complications of revision remain. Since then, several implants have emerged and offer varied results in terms of patient satisfaction.

Key Insights On Unipolar (Hemi) Implants

The first category of implants includes unipolar (hemi) implants designed for the articular surface of the proximal phalanx or the head of the first metatarsal. Although initial results were unfavorable, advances in implant design have led to increased patient outcomes and success rates of up to 95 percent in some studies.^1,4

Unipolar implants are designed for the proximal phalanx to improve motion and articulation with the first metatarsal head. However, initial designs were constructed from silicone and had a high rate of failure. Second-generation implants utilized various metal alloys. Titanium and cobalt chromium had improved success rates over the silicone design.

Surgeons would use the unipolar (non-constrained) implant for the proximal phalanx to maintain most of the first metatarsal head concentricity. The best results occur with unipolar implants designed to maintain the attachment of the flexor hallucis brevis to the proximal phalanx. This preserves the windlass mechanism, which is critical for the prevention of lateral overload.

The BioPro implant is a unipolar implant that acts as a “resurfacing” implant with minimal bone loss. A disadvantage is the “tight” fit with more on the first metatarsal head and clinically decreased ranges of motion. It is also critical that the surgeon does a full sesamoid release and in some cases fractional lengthening of the flexor hallucis brevis myotendinous junction. One also needs to address potential malalignment with the proximal phalanx subluxed plantarly to the metatarsal head. Ruff and colleagues demonstrated the use of cheilectomy in preparation of the implant to “reduce” this subluxation in the sagittal plane.⁵

One would also utilize unipolar metatarsal head implants when the articular surface of the metatarsal head appears compromised and the relative articular surface of the proximal phalanx remains viable.

What You Should Know About Unipolar Metatarsal Head Implants

Consideration with unipolar metatarsal head implants focus on the flat first metatarsal head created by subchondral microfracturing secondary to the disease process. The “resurfacing” implant re-establishes joint concentricity. For uses in which the proximal phalanx is also flattened, “cupping” may be necessary to allow movement. Again, release of the sesamoids is critical.

This design allows better freedom of countersinking and decompresses the joint without compromising length, and thus can ease the flexor contracture. Distinct advantages here are minimal bone loss and preservation of the windlass mechanism.

A recent advancement in implant design includes the Cartiva implant. This implant is comprised of polyvinyl alcohol, a biocompatible material that is classified as a hydrogel, and acts as an interpositional spacer.⁶A distinct advantage of the Cartiva implant is its ability to maintain first metatarsal length should an arthrodesis be required in the future. The Cartiva implant is available in 8 mm and 10 mm sizes, and the ideal protrusion of the implant should be between 2 to 4 mm.⁶As with other unipolar metatarsal head implants, one should perform an aggressive cheilectomy and sesamoid release in conjunction with the Cartiva implant.

In evaluating mid-term results with the Cartiva implant, Daniels and colleagues followed 27 patients at five years and demonstrated 96 percent survivorship and a significant improvement in the VAS pain scale, the SF-36 Physical Component Score (PCS) and the Foot and Ankle Ability Measure (FAAM).⁷Long-term results of the durability of this implant are to be determined but current results are promising.

Assessing The Impact And Potential Of Bipolar Total Joint Replacement Implants

Several companies have developed bipolar implants over the years. However, these implants have failed to achieve a wide acceptance among foot and ankle surgeons. This was in part due to the high failure rate with the first- and second-generation implant designs. Similar to total ankle arthroplasty, an improvement in implant design has led to more favorable outcomes despite the recognized potential complications.

In the senior author’s experience, the “bulk” of these implant failures lies in not preserving the windlass mechanism. Bipolar total joint replacement implants also act as “non-constrained” implants and are subject to triplanar biomechanical forces that can lead to an “edging” effect.

Two recent advances with bipolar joint implants include the Reference Toe System (In2Bones)  and the ToeMotion Total Toe Restoration System (Arthrosurface). The Reference Toe System is a silicone elastomer implant with titanium grommets. One advantage of this implant is the broach-less reamer system, which can decrease cortical stressors during implantation. The second advantage of the implant is the angled grommets that account for the first metatarsal declination angle, an improvement from previous silicone designs.

The ToeMotion Total Toe Restoration System is a two-component implant consisting of a cobalt-chromium alloy metatarsal implant and a titanium alloy phalanx implant with an ultra-high molecular weight polyethylene (UHMWPE) inlay. One advantage of this implant is its potential use for revision of a failed proximal phalanx arthroplasty. Also, due to the rigid fixation within the first metatsarsal and proximal phalanx, using this implant may help facilitate early range of motion that can lead to improved patient outcomes.

Recognizing The Potential And Drawbacks To First MPJ Implants

Total joint replacement of the first metatarsophalangeal joint remains controversial in the treatment of end-stage hallux rigidus. Patient outcomes vary. In first MPJ arthrodesis, the goal is to eliminate pain whereas with implant arthroplasty, the goals are eliminating pain and restoring motion to the first MPJ. No implant design available can restore normal first MPJ motion. Essentially, the implant acts as a “spacer” for pain relief with motion by offloading sensate subchondral bone.

Brewster and coworkers, in a 2010 systematic review of the literature comparing arthrodesis versus arthroplasty, found similar results in American Orthopaedic Foot and Ankle (AOFAS) scores (82 versus 83 respectively).⁸However, the authors noted patients had improved function in the arthroplasty group. In a recent study comparing first MPJ arthrodesis versus proximal phalanx hemi-arthroplasty, Beekhuizen and colleagues noted improved AOFAS hallux metatarsal interphalangeal scores among the hemi-arthroplasty group (89.7±6.6 versus 72.8± versus respectively) in patients treated for more than five years.⁹Accordingly, listening to the patient’s desired outcomes is important when deciding between arthrodesis and arthroplasty.

It is also important to recognize the risks and complications of first metatarsophalangeal joint arthroplasty. In 2012, Kim and colleagues found that heterotopic bone formation was the most common post-op complication with hemi-arthroplasty procedures.¹⁰

Surgeons must warn patients about potential complications and what further options are available if complications occur. The first is the implant itself. Surgeons can manage failure by “reimplantation” if available bone stock is present. This may also require bone graft augmentation. If further bone loss occurs, a revision arthrodesis is necessary. First MPJ arthroplasty is clearly a more complicated procedure than a primary arthrodesis. One can revise resurfacing implants to fusion usually without “block grafting” but by using a “back filling” technique. In cases of bone loss greater than 5 mm, transfer pain through the “cascade effect” to the second metatarsal may occur in 40 percent of these cases.^­11The objectives of bone block grafting are to restore first MPJ length and weightbearing for stabilization. However, the risks of delayed union and nonunion are near 30 percent.¹

Another complication includes an implant causing infection, which will require a two-stage procedure with implant removal, placement of an antibiotic-loaded spacer and a revision block allograft six to 12 weeks later. This is based on bone cultures, clinical and serologic parameters (normalization of C-reactive protein, erythrocyte sedimentation rate), and an absence of signs of infection.

Another complication is destabilization of the windlass mechanism when bone resection destabilizes the flexion apparatus. This also leads to what has been called the “cascade effect” or lateral transfer overload of the second and third metatarsals, plantar plate tears and hammertoe formation. This condition is very difficult to treat clinically and will often lend to further forefoot reconstruction.

In Conclusion

Surgeons should base the choice of implant arthroplasty on very careful clinical and radiographic parameters. One should ensure appropriate patient selection according to clinical, biomechanical and expectation factors. Implant arthroplasty is “time-honored” and often carries good results. However, patients must know the long-term consequences. The unipolar implants have led to much greater success due to limited bone resection and preservation of the windlass mechanism.

Dr. Visser is the Director of the SSM Health DePaul Hospital Foot and Ankle Surgery Residency in St. Louis. He is a Fellow of the American College of Foot and Ankle Surgeons.

Dr. Wolfe is a third-year resident with the SSM Health DePaul Hospital Foot and Ankle Surgery Residency in St. Louis.

Dr. McKee is a second-year resident with the SSM Health DePaul Hospital Foot and Ankle Surgery Residency in St. Louis.

Dr. Keeter is a second-year resident with the SSM Health DePaul Hospital Foot and Ankle Surgery Residency in St. Louis.

References

1.    Perler A, Nwosu V, Christie D, et al. End-stage osteoarthritis of the great toe/hallux rigidus. Clin Podiatr Med Surg.2013; 30(3):351-395.
2.    Townley C, Taranow W. Hemiarthroplasty resurfacing prosthesis for the hallux metatarsophalangreal joint. Foot Ankle Int. 1994;15(11):575-580.
3.    Drago J, Oloff L, Jacobs A. A comprehensive review of hallux limitus. J Foot Surg. 1984; 23(3):213-220.
4.    Endler F. Development of a prosthetic arthroplasty of the head of the first metatarsal bone, with a review of present indications. J Orthop Grenzeb.1951;80(3):480-487.
5.    Ruff J, Trotter K, Grady J. Nonimplant arthroplasty for the treatment of end-stage hallux rigidus. J Foot Ankle Surg. 2018;57(2):232-235.
6.    Chang TJ. The role of polyvinyl alcohol in cartilage repair of the ankle and first metatarsophalangeal joint. Clin Podiatr Med Surg. 2018; 35(1):133–43.
7.    Daniels TR, Younger AS, Penner MJ, et al. Midterm outcomes of polyvinyl alcohol hydrogel hemiarthroplasty of the first metatarsophalangeal joint in advanced hallux rigidus. Foot Ankle Int.2017; 38(3):243–47.
8.    Brewster M. Does total joint replacement or arthrodesis of the first metatarsophalangreal joint yield better functional results? A systematic review of the literature. J Foot Ankle Surg. 2010; 49(6):546-552.
9.    Beekhuizen S, Voskuijl T, Onstenk R. Long-term results of hemiarthroplasty compared with arthrodesis for osteoarthritis of the first metatarsophalangreal joint. J Foot Ankle Surg. 2018; 57(3):445-450.
10.    Kim P, Hatch D, DiDomenico L, et al. A multicenter retrospective review of outcomes for arthrodesis, hemi-metallic joint implant, and resectional arthroplasty in the surgical treatment of end-stage hallux rigidus. J Foot Ankle Surg. 2012; 51(1):50-56.
11.    Toth K, Huszanyik I, Kellermann P, et al. Metatarsalgia in the second through fourth rays after metatarsal osteotomy. Foot Ankle Int. 2007;28(1):61-63.

Editor’s note: For related articles, check out “Current Concepts With First MPJ Silicone Implants” in the March 2017 issue of Podiatry Today, the February 2017 online-exclusive article “A Closer Look At A First MPJ Hemi-Implant For The Treatment Of Hallux Limitus/Rigidus” (www.podiatrytoday.com/current-insights-first-mpjimplants ) or the April 2011 online-exclusive article “Current Insights On First MPJ Implants” (www.podiatrytoday.com/current-insights-first-mpjimplants ).