Validation of the Artificial Floor Technique in First Metatarsophalangeal Joint Arthrodesis.

BACKGROUND: Patient function after arthrodesis of the first metatarsophalangeal joint (MTPJ) relies on proper positioning of the first MTPJ. To maximize the likelihood of good postoperative function, the dorsiflexion angle, referred to as the fusion sagittal angle, should range between 20° and 30°, corresponding to 10° to 15° of dorsiflexion off the weightbearing axis. However, achieving appropriate sagittal alignment intraoperatively is challenging. The artificial floor technique (AFT) uses a rigid, flat surface to simulate the weightbearing position of the foot intraoperatively to accurately position the first MTPJ without fluoroscopy. This technique has been previously described and is commonly used but, to our knowledge, it has never been validated. QUESTIONS/PURPOSES: (1) Is the AFT a valid and repeatable technique for positioning the fusion sagittal angle between 20° and 30° of dorsiflexion from the first metatarsal? (2) Does the fusion sagittal angle obtained using the AFT vary with foot size?
METHODS: In this retrospective study, a search was performed using Current Procedural Terminology codes for patients undergoing first MTPJ arthrodesis by one surgeon between June 2012 and June 2020. The surgical technique used during this time did not vary and consisted of the use of a rigid, flat, sterile surface. The entire foot was placed flat on the surface, simulating the weightbearing position and allowing for an evaluation of the fusion sagittal angle of the first MTPJ. The target sagittal alignment was achieved when the soft tissue of the plantar surface at the distal-most aspect of the proximal phalanx was measured (using a sterile ruler) as 1 cm off the artificial floor. The recommended fusion sagittal angle falls within a range of 20° to 30°, which allows for 1-mm to 2-mm variations in measuring the elevation of the proximal phalanx off the artificial floor. Fixation was achieved with two 2.8-mm threaded, double-pointed Steinmann pins placed through the intramedullary canal of the proximal and distal phalanges and into the first metatarsal. Once fixation was achieved, the fusion sagittal angle was confirmed with the AFT without using fluoroscopy. Postoperatively, patients were allowed to bear weight fully on their heels in a postoperative, rigid-soled shoe. During the study period, 117 patients (135 feet) underwent first MTPJ arthrodesis utilizing the AFT for either first MTPJ arthritis/hallux rigidus, hallux valgus, or inflammatory arthropathy. Of those, we considered patients with preoperative AP and lateral weightbearing radiographs and patients with AP and lateral weightbearing radiographs at 3 months postoperatively after the removal of the internal fixation construct as eligible for analysis. Based on these criteria, 84% (113 of 135) of feet were included in the final radiographic analysis. Sixteen percent (22 of 135) of the feet were excluded because postoperative radiographs demonstrating the removal of the internal fixation construct were absent from the Picture Archiving and Communication System (PACS) in these cases. The length of the whole foot, first metatarsal, and proximal phalanx were measured on preoperative weightbearing radiographs. In addition, fusion sagittal angles were measured on weightbearing radiographs after removal of internal fixation construct at a minimum of 3 months postoperatively (mean 3.5 ± 2.2 months). No patients were lost to follow-up before obtaining those radiographs. Two qualified reviewers independently evaluated each radiograph. We ascertained inter- and intraobserver reliability using intraclass correlation coefficients (ICCs). We determined whether the fusion sagittal angle obtained using the AFT varied with foot size by using a multiple linear regression model.
RESULTS: In the entire study group, the mean fusion sagittal angle using the AFT was 27° ± 4°. The interobserver ICC of the fusion sagittal angle measurements was 0.92 (95% confidence interval [CI] 0.56 to 0.97; p < 0.001). The intraobserver ICC for reviewer 1 was 0.95 (95% CI 0.92 to 0.97; p < 0.001) and the intraobserver ICC for reviewer 2 was 0.97 (95% CI 0.88 to 0.98; p < 0.001). Ninety-one percent (103 of 113) of the study group fell within the acceptable range of 20° to 30° ± 2°. The multiple linear regression analyses demonstrated that the preoperative lengths of the whole foot (β =-0.05 [95% CI -0.12 to 0.02]; p = 0.16), proximal phalanx (β =-0.13 [95% CI -0.46 to 0.20]; p = 0.44), and first metatarsal (β = 0.13 [95% CI -0.10 to 0.35]; p = 0.27) were not independently associated with the postoperative fusion sagittal angle.
CONCLUSION: The AFT allows for accurate and reproducible positioning of the first MTPJ within the appropriate functional range of dorsiflexion, regardless of foot size. Additionally, this technique can be performed without fluoroscopy and so avoids radiation exposure to the patient and the surgical team. LEVEL OF EVIDENCE: Level III, therapeutic study.