All patients were assessed with the Short Form-36 Health Survey (SF-36)27 and the American Orthopaedic Foot and Ankle Society (AOFAS) clinical rating system for the hallux.12 The SF-36 Health Survey is a self administered, patient-based scoring system. It consists of 36 questions with eight scales leading to two summary measures describing physical and mental health, respectively. This summary outcomes measure has been validated to have internal and external consistency and reliability and has increasingly been used to assess orthopaedic conditions.7,25 The AOFAS clinical rating system is a 100-point physician-based scale with scoring based on pain (40 points), function (45 points), and alignment (15 points). Patients were asked to grade their pain as no pain, mild, moderate, or severe. Preoperative and postoperative ROM were measured with a standard goniometer (Howmedica, Rutherford, NJ). Preoperative ROM was measured by the operating surgeon, and postoperative measurements were made by the two principle investigators (JK, FC) who were not the primary surgeons to reduce bias.
Two-tailed p values were used to establish significant differences. The relationship of outcome to age, gender, and disease grade was examined by multiple regression analysis. A p value < 0.05 was considered significant. We used the Spearman correlation coefficient to find associations between the SF-36 and AOFAS scores. Correlation was expressed as the coefficient of determination and assigned r2. All data were analyzed using statistical software (SPSS 12.0, SPSS Inc, Chicago, IL).
All 18 patients had less pain than they experienced preoperatively.
Sixteen of 18 patients stated they had little or no pain. Two patients stated they had moderate pain on exercise, but that pain was less than preoperatively. The mean pre-operative ROM in the first metatarsophalangeal joint was 27° (range, 5°-35°). The mean postoperative ROM in the first metatarsophalangeal joint was 64° (range, 25°-70°). All 18 patients were satisfied with the position and appearance of their first toe.
The mean postoperative AOFAS score was 78.4 points (range, 49-100 points). The mean postoperative SF-36 score was 96.3 points (range, 64.91-115.7 points). When split into the two outcome measure scores, the mean physical outcome score was 47.3 (range, 25.2-60.3), and the mean mental outcome measure score was 49.1 (range, 37.6-61.5). The SF-36 correlated (r2 = 0.62) with the AOFAS hallux score. Gender, age at the time of surgery, and radiographic grade had no influence on outcome.
There were few reported complications. Restricted motion of the first metatarsophalangeal joint less than 20° occurred in two patients postoperatively. One of these patients required manipulation under anesthesia to improve motion. This occurred 2 months after the index procedure, and the patient was satisfied with the outcome. At the latest followup, the patient has a painless joint with 32° motion. The patient who reported stiffness postoperatively continues to have a painless joint at the latest followup. However, the arc of motion is restricted to 30° when passively moved and was restricted to 20° when the patient was asked to actively range the joint. The patient was not satisfied with the final ROM, and did not want manipulation or any other procedure to address the limitation in motion. Transfer metatarsalgia occurred in one patient who subsequently had a stress fracture of the second metatarsal shaft develop. This was secondary to a relatively short first ray after resection of the joint and an excess of mobility of the first tarsometatarsal joint. This produced an excess of force through the overloaded second metatarsal. The stress fracture healed without surgical intervention within 10 weeks.
Before the introduction of interposition arthroplasty, surgical treatment of moderate to severe hallux rigidus was confined to excision arthroplasty, prosthetic replacement, or arthrodesis. These methods of treatment have substantial functional limitations and complication rates.2,4,5,8,11,13,20,22,23 The goal of any surgical intervention for an arthritic joint should be establishment of a pain-free and functional joint. We found interposition arthroplasty can satisfy these criteria. The procedure also had a low rate of complications compared with rates in historical reports for traditional surgical treatments (Table 1).5,9,14,15,23,29
Our study has several limitations. Patients did not complete an AOFAS score or SF-36 score preoperatively; therefore, conclusions cannot be made regarding improvement in postoperative scores. All 18 patients reported improvements in pain compared with preoperatively. This is an objective measurement that cannot be biased by the investigators and validates the subjective postoperative AOFAS and SF-36 scores. Inherent bias by nonblinded data collection also may confound the results reported. This is a problem in many retrospective studies but should not diminish the comparative impact of the investigation when judged against other nonblinded retrospective studies.9,14
Studies detailing differences from the technique described by Hamilton et al,9 have yielded satisfactory outcomes.1,19,23 However, these studies were limited by small sample size and lack a standardized or validated outcome score.1,19,23 In the absence of standardized outcome scoring, meaningful comparison could not be made with other investigations. Data supporting the use of the interposition arthroplasty are sparse and inconclusive. We found interposition arthroplasty can be a useful procedure for treatment of hallux rigidus by using standardized and validated outcome scales. These outcome scores have shown content validity in evaluating outcomes in hallux rigidus by the correlation shown between the AOFAS and the SF-36 scores, underscoring the value of this technique.
Lau and Daniels14 found interposition arthroplasty did not perform well in comparison with cheilectomy using the AOFAS and SF-36 outcome analyses. In one group of 19 patients, cheilectomy was used whereas the second group of 11 patients had interposition arthroplasties. Their technique of interposition arthroplasty was similar to that described by Hamilton et al.9 Meaningful data analysis is confounded by the comparison between two methods of treatment in patients who were not matched in severity of disease. The group of 11 patients treated with interposition arthroplasty seemed to have more severe disease, judging from the radiologic grading. However, there was no mention of the degree of joint destruction at the time of surgery. The authors did conclude that comparison between the two treatment modalities was difficult based on the difference in degree of disease at presentation. They suggested cheilectomy is the preferred method of treatment for moderate hallux rigidus, and interposition arthroplasty should be regarded as a salvage procedure for severe degenerative changes.14 Our indications for the interposition arthroplasty agree with those of Lau and Daniels.14 However, we do not think the data presented should implicate the interposition arthroplasty as a salvage procedure alone. The majority of patients treated with interposition arthroplasty had good to excellent AOFAS scores.
The patients in our study had few complications, unlike patients in other studies who had alternative methods of treatment and where incidences of transfer metatarsalgia and malposition were reported to be as much as 27% and 38%, respectively.4,5,11,13,30 There was no evidence of malposition in our patients, and only one patient had transfer metatarsalgia. The low rates of complication in our patients are not solely determined by the surgery, but also by the selection criteria of patients suitable for surgery. Selection criteria are critical for patients before interposition arthroplasty. Patients with longer second and third rays in comparison with the first metatarsal are more likely to have transfer metatarsalgia develop than patients with longer first rays.9 Excluding these patients from having interposition arthroplasties has reduced this complication. These patients can be treated with fusion of the joint. By resecting just 10% of the base of the proximal phalanx, the correct tension of the soft tissues about the joint is maintained. This prevents the malposition that can occur with the traditional Keller's excision arthroplasty, where 25% of the base is resected.29
Selecting recreational athletes rather than elite athletes also could have contributed to the successful outcomes in the active patients. No data are available regarding outcomes after any surgical treatment for hallux rigidus in the elite athlete; however, we were concerned that a soft tissue interposition in this cohort would have been compromised by the level of stress and wear on the graft. Patients who were more sedentary also were excluded from the study population. As such, results of our study suggest interposition arthroplasty can be used in an active population that anticipates continued activity postoperatively. This activity level can be substantiated by the physical component score of the SF-36. The physical component score has four subscales that include physical function, physical role, general health, and bodily pain. These domains most accurately reflect the activity of the patient and are the most responsive to surgical intervention.27 The patients in our study reported vitality similar to that of the general population of similar age measured by the physical component score subscale score. The data suggest this population was active, but was not at an elite level of activity that would be reflected by at least two standard deviations above the norm.27
We identified two patients with joint motion less than 20°. We initially hypothesized inadequate resection of less than 10% of the base of the proximal phalanx or of the dorsal or lateral osteophytes may have been responsible for the postoperative lack of motion. However, there were no clear radiologic differences between these two patients and the remainder of the cohort with respect to the amount of bone resected. When the two patients were examined, there was a reduced arc of motion of the central metatarsophalangeal joints and the first metatarsophalangeal joint on the surgically treated foot and on the contralateral side. Whether this occurred because of surgery, or whether it was a contributing factor to postoperative stiffness is not clear. It may be that there is a subset of patients with restricted motion in the metatarsophalangeal joints, and these patients are more prone to have postoperative stiffness.
Interposition arthroplasty of the first metatarsophalangeal joint is indicated for treatment of advanced hallux rigidus with joint destruction. The original interpositional arthroplasty as described by Hamilton et al9 has reproducible outcomes evaluated by contemporary outcome scoring systems. Increased motion of the first metatarsophalangeal joint and excellent pain relief are indications for interposition arthroplasty to be used in patients with advanced hallux rigidus.
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