How To Address Predislocation Syndrome Of Lesser MPJs

     Metatarsalgia is a diagnostic term used to describe pain in the ball of the foot. Gerard V. Yu, DPM, eloquently described and illustrated predislocation syndrome in 1995. What Dr. Yu described was a clinical syndrome characterized by focal pain under a lesser metatarsophalangeal joint (MPJ), most often affecting the second toe joint.1      Subjective symptoms reported by those afflicted with this syndrome would be described as a “grape-like” swelling under the affected toe joint, and a feeling as if there were a stone bruise on the ball of the foot. More often than not, the patient would be apologetic about wasting the doctor’s time with what seemed trivial as there was no obvious problem looking at the foot.      Clinical findings with predislocation syndrome include pain upon palpation of the plantar plate, and subtle dorsal and/or transverse plane subluxation of the toe (exacerbated with loading of the foot) without frank hammertoe formation. Usually, there is no callus but one may see mild edema in the region of the plantar plate. With this condition, the clinician will also note that range of motion of the metatarsophalangeal joint is painful with end-range plantarflexion of the digit.      In contrast to metatarsalgia without predislocation syndrome, there is pain upon palpation of the metatarsal head, which is more proximal than the plantar plate. One would also usually see callus formation and note that range of motion of the metatarsophalangeal joint is not painful. In these cases, podiatrists may also note a lack of fat padding and a longstanding, non-reducible hammertoe deformity.      Essentially, predislocation syndrome describes the evolution of a hammertoe deformity if it is left untreated. Inflammation of the plantar structures of the metatarsophalangeal joint can eventually lead to attenuation or rupture of the stabilizing plantar structures, which leads to ensuing deformity of the toe. As the plantar capsular structures rupture, the proximal phalanx will eventually dorsally migrate and the flexor tendons may deviate medially. If you think of the plantar plate as analogous to the sesamoid apparatus of the great toe joint, then you can appreciate that where the plantar plate migrates, the flexor tendons migrate in similar fashion.      This ultimately can lead to a flexion contracture and transverse plane drift of the toe. If there is concomitant hallux valgus, then the mechanical force of the crowding great toe will undermine the second toe, encouraging it to sit on top of the great toe. This process can exacerbate the medial drift of the second toe.

Getting A Strong Grasp On Lesser MPJ Anatomy

     Understanding the anatomy of the lesser metatarsophalangeal joint is necessary to appreciate the syndrome. The normal anatomy has been well described in the literature.2-4 Yao has described pathological findings on MRI.5 The plantar plate is a thickening of the plantar capsule consisting of a fibrocartilage material. This provides a shock-absorbing weightbearing structure. The distal attachment of the plantar plate is to the base of the proximal phalanx, which is relatively strong, and the proximal attachment site is behind the condyles of the metatarsal neck, which is the weakest attachment.      Despite the relatively strong attachment of the plantar plate distally, most plantar plate ruptures occur there. According to Blitz, et. al., consistent findings of plantar plate ruptures are located just proximal to the strong phalangeal base attachment.6 The plantar fascia sends attachment slips to the plantar plate and therefore contributes to the overall function of the windlass mechanism of the foot. The collateral ligaments are blended into the capsule, reinforcing the medial and lateral sides. According to Liu, et. al., cadaveric studies show that sectioning of the collateral ligaments may destabilize the toe more than sectioning of the plantar plate.7 In addition, the deep intermetatarsal ligament attaches to the medial and lateral walls of the plantar plate for added stability.      Other supporting structures of the MPJ include the flexor tendons that are intimate with the plantar plate, and the intrinsic muscles medially and laterally provide minimal support. The extensor hood apparatus and tendons reinforce the dorsal capsule.

How To Diagnose Predislocation Syndrome

     One would essentially diagnose predislocation syndrome via the clinical examination. To confirm the diagnosis, one can utilize other diagnostic studies such as arthrography, MRI and ultrasound. The physical exam should include careful palpation of each of the lesser metatarsal heads, each interspace and finally, the plantar plates.      Neuroma formation can be a source of metatarsalgia. Typically, though, with a neuroma, pain will be in the third interspace and rarely in the second. Pain is greatest between the metatarsal heads, and not in the region of the plantar plate. The cause of pain in the second intermetatarsal space is more likely to be due to an intermetatarsal bursitis rather than a neuroma. Diagnostic injections into the interspace are of little clinical value. If the digital nerve is anesthetized, all pain regardless of the etiology will be masked.      Additional maneuvers for evaluating for predislocation syndrome include range of motion of the affected joint(s). With mechanical metatarsalgia (i.e., callus formation under the metatarsal head), there should be no pain with range of motion of the MPJ. In predislocation syndrome, the range of motion may be painful, especially with plantarflexion. An arthritic condition of the MPJ can also have the same physical exam findings with range of motion.      Another physical exam maneuver should include the Lachman test (dorsal drawer test), which one essentially performs by stabilizing the metatarsal head with one hand and attempting to translate the phalanx base dorsally with the other hand. If the toe dorsally elevates more than 2 mm, then this is a positive test confirming MPJ instability, which is most likely derangement of the plantar plate and collateral ligaments. If the patient has ligamentous laxity, then consider performing the same Lachman test on the same MPJ on the contralateral foot.      Regardless of the pathology that you are dealing with, always compare both feet. Order plain film radiographs to rule out Freiberg’s infraction or other arthritic conditions. The information you gather from the X-ray should include whether or not there is an arthritic process (i.e. joint space narrowing), an abnormal metatarsal parabola, and/or malalignment of the toe (i.e. transverse and/or sagittal plate deviation). Also, one can rule out unusual causes of pain such as bone neoplasm or fracture.      In simplistic terms, the cause of predislocation syndrome is excessive plantar pressures to the MPJ. This may be a functional etiology from lesser metatarsal overload caused by hallux valgus or a hypermobile first ray. There may be a structural cause such as a short first ray (relatively long second ray). It is important to understand the cause of increased pressures to the affected MPJ, especially if one is considering surgery for treatment.

Pertinent Pointers On Conservative Treatment

     All of us have guidelines and protocols that we implement in the treatment of various podiatric disorders. I will review my personal treatment protocol for predislocation syndrome. After making the appropriate diagnosis, one would begin conservative treatment by stabilizing the MPJ and providing appropriate offloading of the joint. The clinician can do this by applying a crossover taping of the toe with 1/2-inch cloth tape (or one may use a commercially available hammertoe regulator splint) and a felt accommodation pad to the foot or to the insole of the shoe. I will prescribe oral antiinflammatory medication as well. I will recommend an Achilles tendon stretching regimen as equinus can also contribute to high forefoot pressures during gait. Encourage icing of the affected area with an ice cube in a Ziplock bag.      A thorough review of appropriate shoe gear is paramount. I will have patients avoid barefoot and slipper walking around the house. I encourage women to avoid high heels. I recommend stiff-soled shoes (that resist bending and twisting) to reduce forefoot pressures. Orthoses are also recommended and I will typically incorporate a metatarsal pad directed proximal to the affected MPJ (i.e. one may medialize the pad if the problem is at the second MPJ). I also incorporate an accommodative cutout pad to the affected joint(s).      I will generally try the aforementioned treatment strategies for at least one to two months. If there has been little or no improvement, then I will consider cortisone. I have a frank discussion with patients regarding a cortisone injection around the MPJ. First, I discuss that cortisone can help resolve pain around the joint. However, it can also cause worsening of a hammertoe deformity by contributing to further instability of the toe. I also discuss that stabilizing the toe with taping is critical and mandatory following the injection. If the patient is not willing to do the taping, then I will not do the cortisone injection. I have found that dorsally directed injections into the interspace are of little value.      Instead, I will inject directly into the flexor sheath from a plantar approach. I use phosphate-based steroids as the acetate-based steroid would probably be too destructive for such a small joint. The technique that I use involves performing a digital block with lidocaine. Then I will inject 2 mg of dexamethasone phosphate into the plantar aspect of the base of the proximal phalanx. As I insert the needle, I will touch the bone and then retract the needle slightly to inject the steroid. One can subsequently tape the toe in neutral position and instruct the patient to continue taping daily for a couple of weeks and follow up in the office. The patient should also continue with accommodative padding or orthotic use, wearing appropriate shoes, icing and calf stretching.      Generally speaking in my practice, cortisone is the last attempt to resolve pain prior to surgery. In my mind, if the patient is not responding to other conservative measures and the only other option is surgery, then I feel cortisone is warranted. Over the years, I have seen too many patients who were previously treated with cortisone injections to a lesser MPJ, and then presented to my office with a frank rupture of the plantar plate with ensuing crossover deformity. If there is one message that I can emphasize to readers of this article, it is to be very cautious with cortisone when dealing with lesser MPJ pathology.

Which Surgical Options Are Effective?

     During the course of treatment, if conservative care should fail to provide adequate pain relief for the patient, then one should discuss surgery. The dogma for surgical intervention of an unstable MPJ has traditionally been hammertoe surgery to include arthrodesis of the proximal interphalangeal joint with extensor hood recession, dorsal MPJ capsule release and then, if necessary, a flexor tendon transfer. The flexor tendon transfer has been the procedure of choice in the surgical treatment of an unstable MPJ.6      In recent years, however, others have suggested primary repair of the plantar plate with or without adjunctive digital procedures.7,9 Others have suggested lesser metatarsal osteotomies, such as the Weil osteotomy for the treatment of metatarsalgia, and even arthrodesis of the MPJ for advanced dislocation of the toe.10-14 In a recent publication by Co, et. al., a retrospective radiographic study examining various procedures on the lesser MPJ showed no clear cut advantages of fusion of the toe with or without flexor tendon transfer, plantar plate repair, MPJ arthroplasty with syndactyly, or metatarsal osteotomy.15 Arguably, each one of those procedures has its place in lesser MPJ stabilization surgery.      Once we have decided to proceed with surgery, I will determine the underlying cause of lesser metatarsal overload. For example, if there is any pathology of the first ray such as hallux valgus, then I will recommend addressing the first ray in addition to the lesser MPJ. However, if there is no pathology of the first ray, I will consider surgery of the digit(s), MPJ and possibly the metatarsal. If there is a normal metatarsal parabola, then I will, generally speaking, perform an arthrodesis of the digit with K-wire fixation and a MPJ release. If the Kelikian push-up test reveals residual sagittal or transverse plane deformity, I will attempt a more aggressive soft tissue rebalancing maneuver at the MPJ to include a plantar medial capsule release and lateral capsulorrhaphy (assuming a medial transverse plane deformity). I will use a non-absorbable suture such as a 4-0 fiberwire for the capsulorrhaphy.      If the toe still does not sit in an acceptable position, then I will transfer the long flexor tendon to the extensor tendon by releasing the tendon from the arthrodesis site, splitting the tendon in half and yoking the tendon arms dorsally. Varying the tension of either arm of the tendon can help balance any residual transverse plane deformity. The flexor tendon transfer will usually resolve any remaining dorsal elevation of the toe as well.      In cases where there is a structural abnormality of the metatarsal, such as a long metatarsal, then I will perform a Weil shortening osteotomy. I typically do the digital work first. Then I can better appreciate whether I need to perform the metatarsal osteotomy. In cases in which there is a significant transverse plane deformity, a shortening osteotomy is often required to relax the MPJ. I prefer to use 2.0-mm snap-off screws for fixation. If I have room, then I insert two screws to prevent any rotation of the metatarsal head. The most common complication of a shortening metatarsal osteotomy is a lack of toe purchase.16 To that end, I will generally do a flexor tendon transfer in conjunction with the osteotomy to help prevent a floating toe. Always remember that a floating toe is rarely due to problems of dorsal structures such as scarring or a tight extensor tendon, it has to do with lack of flexor function.

In Conclusion

Predislocation syndrome is a very common disorder affecting the forefoot. Careful examination will differentiate it from other causes of metatarsalgia. Most clinicians will agree that treatment is difficult and can frustrate the patient when progress is slow. Often, predislocation syndrome will ultimately require surgical intervention. Unfortunately, surgical outcomes are sometimes unpredictable with recurrence of deformity and/or inability to completely resolve the deformity.      Whatever your treatment protocol is for predislocation syndrome, one should employ sound judgment for surgical procedures. I look forward to seeing more research published on the topic of lesser MPJ instability. Hopefully some day, we can build a better mousetrap for the elusive second toe.      Dr. Fishco is board-certified in foot surgery and reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. He is in private practice in Phoenix. He is also a faculty member of the Podiatry Institute.
 

References:

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10. Trnka HJ, Muhlbauer M, Zettl R, Myerson MS, Ritschl P. Comparison of the results of the Weil and Helal osteotomies for the treatment of metatarsalgia secondary to dislocation of the lesser metatarsophalangeal joints. Foot Ankle Int. 1999: 20, 72-9.
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