Addressing the biomechanics of the first metatarsophalangeal joint (MPJ) as well as the first ray are the keys to any surgical correction of first metatarsal pathology. According to Rootian theory, the principal etiologies of hallux limitus are as follows.1 • A long first metatarsal or when the position of the first metatarsal head is relative to the second. When the first metatarsal is long, there will be jamming of the metatarsophalangeal joint during the initiation of the propulsive phase of gait. This causes a reduction in the range of dorsiflexion of the hallux and increases the ground reactive forces in the joint, resulting in early arthritic joint changes.2,3 • Hypermobility of the first ray. This occurs when pronation of the subtalarjoint removes the mechanical advantage of the peroneous longus tendon on the first metatarsal, unlocking it and allowing dorsiflexion through midstance and propulsion. This leads to improper articulation at the first metatarsophalangeal joint and subsequent arthritic changes.1 • Metatarsus primus elevatus. Metatarsus primus elevatus, a dorsally positioned first metatarsal relative to the lesser metatarsals, causes destruction of the joint, similar to hypermobility. • An immobilized first ray. Either bony ankylosis of the first metatarsocuneiform joint or congenital coalition may cause immobility of the first metatarsophalangeal joint. This causes the hallux to accept part or all of the normal first metatarsocuneiform joint motion in its articulation with the first metatarsal.1 • Arthritic joint changes and trauma. Generalized degenerative joint disease— whether it is traumatic in origin or brought on by a multitude of other causes (hallux valgus, systemic arthritidies-rheumatoid) — will also stress the range of hallux dorsiflexion during gait. Generalized degenerative joint disease is usually the presenting clinical/symptomatic diagnosis for the patient with hallux limitus, regardless of the biomechanical etiology. Although not a primary etiology of hallux limitus, the presence and degree of metatarsus primus adductus requires the utmost attention in order to achieve surgical success. Determining the nature of the articulation of the first metatarsocuneiform joint and whether this joint is stable can further affect the overall outcome of a total first metatarsophalangeal joint arthroplasty. In conjunction with resurfacing the diseased articular cartilage, it is necessary to correct any structural abnormalities present. If the joint is unstable, a repositional arthrodesis of the first metatarsocuneiform joint or a repositional osteotomy of the first metatarsal may be required for a successful outcome. Why First Metatarsophalangeal Joint Implants Fail Over the years, there have been many first metatarsophalangeal joint implants, hemi and total, that have attempted to resolve the aforementioned pathologies (see “An Overview Of Previous First Metatarsophalangeal Implants” below). Unfortunately, most of these implants have failed to provide long-term relief of symptoms. There are a variety of reasons for these implant failures. Very few constrained (single component) silicone-based implants — and even some implants made of alloy materials — are capable of withstanding the forces transmitted through the first metatarsophalangeal joint. When this occurs, implant destruction or osseous degeneration about the implant follows. Joint biomechanics are another issue. The natural anatomy of the first MPJ allows for specific fluidities of motion for given levels of activity. Any implant must likewise adapt for those varying activity levels or the implant will fail. The complexity of the surgical procedure also factors into the equation. Many first MPJ implant procedures are technically complicated and surgeons may be less likely to choose a total joint replacement when a joint destructive procedure, although less gratifying to the patient, will require less operative time and less potential postoperative complications. A Closer Look At The Bio-Action Total Joint Implant After a review of previous findings and a desire to avoid past implant failures, the Bio-Action® Total Joint Implant was created. The two-component implant was designed to address diseased cartilage surfaces and pain involving the first metatarsophalangeal joint. Made of titanium and cobalt chrome, the implant’s components act as intramedullary endoprostheses with the roughened stems applied into medullary bone. The implant, which also features an ultra-high molecular weight polyethylene interface in the phalangeal component, replicates normal physiologic first MPJ biomechanics without sacrificing excessive articular cartilage or osseous contours. Utilizing the implant also does not require secondary fixation techniques. The implant requires minimal osseous resection, preserves the flexor/extensor apparatus and does not interfere with the sesamoid apparatus. It maintains stable hallucal ground purchase and provides unaltered plantar articular surfaces to facilitate immediate postoperative motion and ambulation. In the event of implant failure, surgeons are not left with a first metatarsal that is excessively short or extensively modified. Accordingly, one has options available for a successful joint salvage procedure. These options include the interposition of capsular tissue in the event of removal of both components or the use of the metatarsal component alone as an endoprosthesis, also utilizing the interposition of soft tissue. Arthrodesis of the first metatarsophalangeal joint with bone graft remains an option as well. This system is designed to provide unchallenged, stress-free motion in all three cardinal planes for the following conditions and scenarios: • hallux limitus or rigidus with degenerative joint disease; • hallux abductovalgus with associated arthritis; • rheumatoid arthritis with inflammatory joint disease; • osteoarthritis; • repair of subluxation and/or dislocation of the joint in conjunction with a repositional osteotomy and/or fusion of the first ray to repair metatarsus primus varus; • a painful or unstable joint from prior surgery; • revision of failed silicone arthroplasty; and • difficult management situations in which clinical experience indicates that continued conservative efforts are likely to render unsatisfactory results. The Bio-Action Implant is contraindicated in the presence of infection, inadequate vascularity, severe osteopenia, physiological or psychological patient compromise or irreparable tendon system function. Assessing Long-Term Outcomes In a randomized retrospective review of 11 patients who received the Bio-Action implant between 1991 and 1994, we found encouraging long-term outcomes. The average implant age was 9.1 years. The mean patient age was 74.6 years with the patients ranging in age between 51 and 82. Eight of the patients were female and three were male. Ten of 11 patients or 91 percent reported that they were satisfied with the joint replacement surgery. The average pain level prior to surgery was reported as 4.63 out of 5 with 5 being the highest. After surgery, the pain level was reported as 1.45 out of 5. The average subjective range of motion within the first MPJ before the surgery was stated as 1.27 out of 5 (with 5 being a full range of motion). At the time of the interview, patients related an average range of motion of 4.63 out of 5. Prior to surgery, 45.5 percent of the patients described themselves as sedentary, 45.5 percent said they were moderately active and 9 percent stated they were highly active. At the time of the interview, only 9 percent described themselves as sedentary, 45.5 percent were moderately active and 45.5 percent were highly active. The interviews of 11 patients reveal that eight regularly wear closed toe or dress shoes, nine regularly wear sandals and 10 regularly wear athletic shoes. Further questioning revealed that three of eight female patients are able to wear high-heeled shoes and the average age of these patients is 70. After more than nine years, the patients in this retrospective study report a decrease in pain from 91 percent (preoperative) to 27 percent (postoperative). When one also considers the maintained restoration of range of motion, this indicates that the Bio-Action Implant has a proven history of durability. Granted, these statistics may be affected by the inability of patients to measure their pain and range of motion accurately and objectively. For precisely this reason, we made the questionnaire as simple as possible. By allowing the patients to assess their own relative conditions, the study naturally acquires a selective perspective. However, given the average length of time (9.1 years) since the implants were placed, we felt this type of questioning would be sufficient to demonstrate either the success or failure of the implant. Step-By-Step Pearls For Using The Bio-Action Implant To begin, make a dorsal curvilinear incision over the first MPJ, exposing the head of the metatarsal and the base of the proximal phalanx. Perform a dorsal capsulotomy according to one’s preference. Once the head of the first metatarsal and the base of the proximal phalanx are exposed, one may remove the hypertrophic changes about the first metatarsal head and rasp the remaining bone smooth. A key component to the success of the Bio-Action Implant is the position of the metatarsal component relative to the second metatarsal head. One must remove enough bone from the metatarsal in order to preserve and/or restore the natural metatarsal parabola. However, minimal osseous resection is critical in order to preserve the sesamoid apparatus as well as the flexor/extensor function. Since this is a joint destructive procedure, surgeons must resect the prominent dorsolateral, dorsal, dorsomedial and medial aspects of the metatarsal to exactly match the circumference of the metatarsal component. Removing this bone will minimize the possibility of osseous impingement and diminish the potential for recurrent bony overgrowth. Mark the center of the respective medullary canals with an awl through the centering guides in order to facilitate acceptance of the implant stems. Drill a guide hole with a football/egg shaped burr parallel to the shaft of the respective bone. One may make this evacuation in the presence of any previous fixation or other implanted device (wire/anchor), provided there is sufficient osseous structure for the implant stem support. Use the implant sizers to ensure proper implant selection and to estimate the range of motion within the joint. When there are some questions as to which implant size to choose (large or small), we feel the best outcome is achieved with the smaller size. This allows the surgeon to skive off any additional overhanging bone, further minimizing the possibility of bony overgrowth. Following proper implant selection, proceed to resect any overhanging bone on the metatarsal about the trial flanges to prevent impingement. When properly seated, the head of the metatarsal component should be slightly shorter clinically than the second metatarsal head. This allows for minimal disruption of the weightbearing surface of the first metatarsal and preserves the metatarsal parabola. Double-check the range of motion within the joint. Copiously irrigate the operative side and place the implants within the appropriate impactor. Again, check the range of motion within the joint and close the capsule with the suture of choice. If the extensor hallucis is contracted, one may lengthen it to a functional position. Close the tissue layers and secure them according to preference. Apply a mild compression with the hallux placed in a functional position. Another key to the success of the Bio-Action Implant is immediate, postoperative, passive range of motion. Daily sagittal plane range of motion exercises, performed by the patient or caregiver, are crucial to minimizing the length of the overall recovery period. Case Study: When A First MPJ Arthrodesis Fails To Relieve Pain A 67-year-old female presented with the chief complaint of difficulty ambulating and pain in the area of her left great toe joint. She related no acute trauma nor an accident. The patient did have a 25-year history of rheumatoid arthritis. She noted that she had previously undergone first MPJ arthrodesis of the left foot two years ago but it did not relieve her symptoms. In fact, she had more pain in the great toe due to a fixed malalignment of the first ray. Her goal was to become as pain free as possible and to have some range of motion restored in her great toe joint. A physical exam of the left foot revealed a solid fusion of the first MPJ with a slight valgus rotation. The lesser MPJs exhibited a decreased range of motion with some fibular deviation. Neurovascular status was intact and within normal limits as were the rearfoot and ankle joint range of motion. Radiographs demonstrated a four-hole plate using the load-screw technique with little anatomical shaping to accommodate adequate fusion position in the first MPJ area. We also noted resection of the lesser metatarsal heads. After a full evaluation of the patient’s treatment options, including the risks and complications of surgical intervention, the patient decided to undergo surgery to remove the malaligned hardware, reduce the fusion and utilize the Bio-Action Implant to help improve alignment and restore some of her joint function. We proceeded to perform an osteotomy of the fusion at a level where the length of the first metatarsal with the implant would approximate that of the previous joint line and maintain the proper metatarsal parabola. Postoperatively, the patient began immediate passive range of motion exercises and wore a below-knee cam-walker boot for two weeks. At two weeks, the patient was relatively pain-free and able to progress to athletic shoes. At recovery, the patient had resumed her normal activities and demonstrated approximately 75 degrees of unrestrained dorsiflexion at the first MPJ. In Conclusion Based on the results of the study, we believe the Bio-Action Implant is capable of providing at least nine years of satisfactory, relatively pain-free range of motion to a previously painful and non-functioning joint. By minimizing the amount of bone resection and preserving the plantar articulating/weightbearing surfaces, those who utilize the implant can maintain the flexor tendon function and sesamoid apparatus, and improve biomechanical function of the first ray. Dr. Zang is a Fellow of the American College of Foot and Ankle Surgeons. He practices in Mesa, Ariz. Dr. Seuferling practices in Oregon. Dr. Burks is a Fellow of the American College of Foot and Ankle Surgeons and is board certified in foot and ankle surgery. Dr. Burks practices in Little Rock, Ark. For related articles, see “How To Salvage A Failed First MPJ Implant” in the May 2005 issue of Podiatry Today or “How To Select The Right Procedure For Hallux Limitus” in the December 2003 issue. 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References 1. Root ML, Orien WP, Weed JH. Normal and abnormal function of the foot: clinical biomechanics, vol. 2. Los Angeles, Clinical Biomechanics Corp., 1977. 2. Vilaseca RR, Ribers ER. The growth of the first metatarsal bone. Foot and Ankle 1:117-122, 1980. 3. Ogden JA. Skeletal injuries in the child. Philadelphia, Lea and Febiger, 1982, pp 621-624.