Qi-yi Li, Jin Jin,Xi-sheng Weng, Jin Lin, Yi-dan Zhang, and Gui-xing Qiu

Department of Orthopaedics, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China

ARTHRITIS of the first metatarsophalangeal joint is a common and painful condition, with trea- tment being determined by the disease severity, the extent of any associated deformity, the patient's age and activity level.1Surgical treatments for severe disease include arthrodesis,2osteotomies,3resection arthroplasty,4and joint replacement.5,6With the development of joint replacement technique, arthroplasty with prosthesis has been used more and more widely. Though satisfactory clinical results have been reported,6-9surgical te- chnique, implant design, materials, and patient selection re- main areas of heated debate and ongoing research. This retr- ospective study was therefore performed to evaluate the pri- mary clinical outcomes of joint replacement with double-stem silicone implant for the first metatarsophalangeal arthritis.

PATIENTS AND METHODS

Patients

From July 2001 to December 2003, a total of 12 patients (15 feet) were treated in our department. There were 2 males and 10 females. The average age was 61.4 years old (range, 56-75). Nine cases (11 feet) were hallux valgus with senile osteoarthritis； 1 case (2 feet) rheumatic arthritis； 2 cases (2 feet) post traumatic arthritis.

The inclusion criteria in our study were: (1) severe senile osteoarthritis with hallux valgus of the first metatarsophalangeal joint； (2) severe rheumatic or rheumatoid arthritic hallux valgus of the first metatarsophalangeal joint, in which X-ray showed joint-space narrowing or signs of bone erosion or bone cyst formation； (3) degenerative or traumatic arthritis of the first metatarsophalangeal joint； (4) pain with motion of the first metatarsophalangeal joint； (5) adequate bone density to accept stems and stresses of an implant device； (6) age over 50 years old with less postoperative activity demand； (7) no infective process, and no allergy to implant material.

All of the patients suffered severe pain caused by the first metatarsophalangeal arthritis. The other symptoms and signs include swelling, callus, degeneration, malformation, and walking-distance limitation with need for larger shoes. No patients suffered from primary talipes adductus, flat foot or talipes cavus. Preoperative X-ray indicated that 9 patients (11 feet) of hallux valgus and 1 patient (2 feet) of rheumatoid arthritis had notable malformation, different degrees of subluxation, degeneration and medial osteophyte formation of the first metatarsophalangeal joint. Patients of traumatic arthritis mainly represented with the narrowing and proliferative sclerosis of the joint space. All the patients in the group were senile and had moderate to severe hallux valgus with degeneration of the joint and with less postoperative activity demand. Patients with larger first-second intermetatarsal angle, or patients with higher postoperative activity demand were excluded in the study.

Operative technique

All patients underwent the first metatarsophalangeal joint replacement using the double-stemmed Swanson hinge silicone implant (Wright Medical Technology Inc., TX, USA). The size of the implant was properly selected according to the preoperative radiographic images and prosthesis templates. The incision was slightly curved, longitudinal over the dorsomedial aspect of the first metatarsophalangeal joint. Care must be taken to avoid injury to the small dorsal sensory nerves and veins in the area. The fascia and medial capsule of the joint were exposed and incised medial to the extensor hallucis longus tendon to prepare a capsuloligamentous flap for later closure and correction of the deviation deformity. The head of the first metatarsal was excised distal to the metaphyseal flare with a 10 degree valgus angle maintaining. A portion of the base of the proximal phalanx was removed to provide a wider joint space. The intramedullary canals were shaped in a rectangular fashion to accept the implant stem. Bone edges were carefully smoothened. A preliminary reduction with a trial implant was done to check the proper size of the implant, the effectiveness of the realignment, the balance of soft tissue and the motion of the toe. Then the implant was carefully placed in the canals. With the toe held in proper alignment including rotation and maintained the medial and lateral soft tissue balance, the medial fascial-capsular flap was firmly sutured. Then we must check the tension and balance of the soft tissue around the joint. After the cutaneous incision was closed, a sterile dressing held the toe in the correct position for 3 to 4 weeks. Early exercise started mandatory on the 3rd postoperative day, while weight-bearing exercise was mandatory 3 weeks after the operation.

Definition of evaluation criteria

We evaluated both the subjective and the objective results according to the forefoot surgery evaluation criteria.10Subjective evaluation included pain, walking ability and phalangeal function, with a total score of 10 points. The higher the score was, the better the effectiveness of the operation was. Patient satisfaction was classified into complete satisfaction partial satisfaction, and dissatisfaction. Objective evaluation included hallux valgus angle and change of flexion and extension angle of the metatarsophalangeal joint. We also monitored the appearance of the foot, the position of implant and the change of bone mass around the implant by radiographic evaluations.

Statistical analysis

The results were presented as± s. Our data were an- alyzed with SAS. P value less than 0.01 was considered statistically significant.

RESULTS

All of the patients were followed up regularly with an average of 24.7 months, ranging from 12 to 38 months (Table 1). No early postoperative complications were found. The symptoms including pain, walking ability and phalangeal function were all improved significantly (P＜0.01). Ten patients (13 feet) were completely satisfied (Fig. 1)； 1 patient (1 foot) partially satisfied； and 1 patient (1 foot) unsatisfied with the result. The partially satisfied one was a senile arthritic patient with hallux valgus who underwent bilateral replacements of the feet. He felt weakness in one foot while walking after the operation. The unsatisfied one was a traumatic arthritic patient of the first metatarsophalangeal joint. He still had pain in the joint when weight-bearing and could not walk long distance. The radiography of 3 years postoperation showed severe hyperostosis around the osteotomy surface of the metatarsophalangeal joint, accompanied by osteolysis around the implant (Fig. 2). No revision surgery has so far been performed or planned.

Postoperative radiography follow-up showed 2 patient(2 feet) had hyperostosis on the osteotomy surface of th metatarsophalangeal joint. One was quite slight and wa asymptomatic, the other one was severe with painful hy perostosis and osteolysis around the prosthesis. And ther was another 1 patient (1 foot) with osteolysis around th silicon rubber implant but without symptom. No loosening dislocation, or fracture of the implant was noted.

Table 1. Preoperative and follow-up results of 15 feet of 12 patients undergoing the first metatarsophalangeal joint replacement with double-stemmed hinge silicone implant§ (n=15)

Figure 1. Radiographs of a 68-year-old female with hallux valgus of left foot. A. Preoperative radiograph shows 29° hallux valgus angle with appearance of osteoarthritis. B. Postoperative radiograph shows correction of the hallux valgus after Swanson implant replacement. C. Radiograph shows satisfactory result after 30 months of follow-up.

Figure 2. Radiographs of a 61-year-old male with traumatic arthritis of the left first metatarsophalangeal joint. A. Preoperative radiograph shows narrowing of the joint space. B. Radiograph one month after the Swanson implant replacement. C. Hyperostosis and osteolysis occur around the implant after 37 months of follow-up.

DISCUSSION

The first metatarsophalangeal joint replacement was first developed in the 1950s as an alternative solution for patients in whom the arthrodesis, metatarsal osteotomy, or excisional arthroplasty was not the ideal choice.11Over time, it had become clearer that certain implant designs, implant materials, and patient characteristics were associated with poorer outcomes.12Since 1974, Swanson recommended the use of double-stem hinged implant in patients with severe hallux valgus with arthritic destruction on both sides of the joint, as in some patients with rheumatoid arthritis and in the elderly.13One advantage of the Swanson system design is the compatibility between the flexible implant and the grommet, so will the survival rate of the prostheses be longer. This system has been widely used in the treatment of rheumatoid arthritis, degenerative or post traumatic arthritis nowadays.14

The double-stemmed Swanson hinge silicone implant is a kind of constrained implant composed of two parts: the flexible implant and the titanium grommet. The implant is made of silicone elastomer with two stems fit into the intramedullary canal of the metatarsal and phalanx. The flexural concavity or open portion of the hinge is placed superiorly or dorsally to allow greater range of extension of the toe. The proximal and distal stems have a rectangular cross section to help provide rotational stability in the intramedullary canals. The titanium shield grommet is designed for use in patients where cutting or abrasion of the flexible implant from contact with thin, sharp bone edges can occur, or in patients who have high activity demands. The grommet can protect the implant from sharp bone ends in areas where abrasion, wear, and cutting are most likely to occur due to forces exerted on the implant during flexion and extension. In a meta-analysis of the first metatarsophalangeal joint replacement, the constrained total silicone implant showed best estimated effect of 89.7%.15

Smetana et al16reported that the subjective satisfaction rate of the patients who had undergone this kind of operation was 79%. The average extension and flexion angles were 19° and 10° respectively. And the total range of joint motion was 29°. Postoperative radiographs showed that 17.5% of feet had osteolysis at the bone head； 15.5% of the feet had calcification around the implant； osteophyte was formed in 67% of the feet at the proximal end of the phalanx and the distal end of the metatarsal bone. Bankes's cohort study of 45 consecutive patients with a minimum 5-year follow-up showed that the Swanson implant provided high levels of patient satisfaction in lower activity demand patients.1There were significant improvements in scores for pain, ambulation, function and shoe wear (P＜0.0001). The mean hallux valgus angle decreased from 37.9° to 24.1° (P＜0.0001). In Granberry's study,17a series of 90 consecutive total joint replacements of the first metatarsophalangeal joint with a flexible hinged prosthesis were reviewed. Subjective responses showed favorable over-all ratings were associated with relief of pain (P＜0.05) and with the ability to wear cosmetically acceptable shoes (P＜0.05). Although the average range of motion was from 26° of extension to 13° of flexion, 22 feet of the 73 feet (30%) had flexion of less than 15°. The range of motion of the toe did not change markedly with the duration of implantation of the prosthesis and did not correlate with the severity of postoperative pain or the distance that the patient was able to walk.

In our study, the overall satisfaction rate was 83.3% (10 in 12 patients). All of the patients could wear any shoes as wished. The postoperative radiographs showed that the hallux valgus angle and the malformations of the metatarsophalangeal joints were well corrected. The postoperative average extension and flexion angles were 19.2° and 11.9° respectively. And the postoperative range of joint motion was 31.1°, which had no significant difference from the preoperative range of motion (P＞0.05). The results might be caused by the bias of etiological distribution in which senile osteoarthritis accounted for a dominant portion of our cases. In this way, patients who had high expectation on postoperative activity were not recommended to undergo this kind of replacement according to our study.

The key points and goals of the surgery are to realign the joint and balance the soft tissue function. The operation technique was very important for good results since most of the patients were hallux valgus with osteoarthritis. We should not place too much emphasis on radiographic measurements and miss the finer points of clinical soft tissue examination since the stability of the artificial joint relied on it. Preoperative and intraoperative evaluation of the capsule, tendons and soft tissue around the joint will ultimately determine the long-term results of the surgery. In our study, the medial capsule of the first metatarsophalangeal joint was incised in a V-shaped fashion, leaving a distally based flap on the proximal phalanx for later closure and correction of the valgus deformity.

Although a meta-analysis of 47 studies showed that this kind of total silicone implant had the best estimated effect among the implants made of all kinds of materials,15all long follow-up studies reported an increased number of implant failures and complications.18-20The complications after silastic joint replacement surgery include soft tissue inflammatory reaction simulating infection, silicone particulate synovitis, osteolysis, surrounding hyperostosis and calcification, prosthetic wear and fragmentation with proximal migration of silicone particles causing inguinal lymphadenopathy.6,17,18,21In our group of patients, hyperostosis occurred in 2 cases (2 feet), including 1 case (1 foot) of severe hyperostosis accompanied by surrounding osteolysis, and the patient's subjective evaluation was unsatisfied. Another 1 case (1 foot) appeared osteolysis around the silicone prosthesis, but the patient had no discomfort and the follow-up was still carrying on. No other complications had been discovered by far. If we chose revision as the end point, the patients of our group had 100% survival rate of the prosthesis at an average of 2 years. But this only indicated primary good results, longer follow-up and more studies will be needed.

The indication of the silastic metatarsophalangeal joint replacement had long been debated.22We thought that the biggest advantage of this replacement was that the implant worked as a spacer to maintain the range of motion of the joint and the normal length of the great toe, so ordinary function of the forefoot was salvaged. Some trials using the double-stemmed Swanson hinge silicone implant had also been conducted domestically,23-25most of which showed preferable result.

In conclusion, the joint replacement with the double-stemmed Swanson hinge silicone implant was a preferable method in salvaging the advanced metatarsophalangeal destruction under the condition of proper indication evaluation, complete preoperative preparation and cautious operation procedure.

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