The accuracy of an automasking algorithm in plantar pressure measurements.

Masking algorithms provide a way to analyze plantar pressure parameters based on distinct anatomical regions of the foot. No study has addressed their accuracy. The purpose of this study was to determine the accuracy of the Novel® ten-region standard masking algorithm in both dynamic and static measurements in normal feet. Static and dynamic plantar pressure measurements were collected from ten normal subjects (20 ft) with and without 10-mm radiopaque markers placed under the first through fifth metatarsal heads, fifth metatarsal base, and first proximal phalanx. The automask was then applied to subdivide the foot into distinct anatomical areas. Weight-bearing AP radiographs were obtained with and without markers. Plantar pressures and radiographs were overlaid. The percent accuracy of each marker within its appropriate mask region was calculated. The average accuracies of the automasking algorithm regions for dynamic and static measurements, respectively, were 98.8% and 90.4% (1MH), 89.9% and 80.6% (2MH), 98.6% and 81.4% (3MH), 96.8% and 82.3% (4MH), 93.1% and 80.8% (5MH), 97.3% and 92.5% (5MB), and 91.2% and 64.2% (1PPH). Marker presence did not alter foot structure or function as determined by intermetatarsal angles (range, p = 0.361 to p = 0.649) and the center of pressure excursion index (p = 0.727), respectively. The automasking algorithm accurately identifies most foot regions in normal feet, particularly in gait. Such accuracy may be reduced in the setting of foot deformity. Understanding the accuracy of masking algorithms may help guide the interpretation of plantar pressure measurements and ultimately both conservative and operative treatment decisions.

Assessment of lateral hindfoot pain in acquired flatfoot deformity using weightbearing multiplanar imaging.

BACKGROUND: The etiology of lateral hindfoot pain in flatfoot deformity can be difficult to assess on plain radiographs. We hypothesized that multiplanar measurements obtained in a fully upright, weightbearing position would reliably demonstrate an increase in lateral hindfoot arthrosis and/or impingement in a cohort of flatfoot patients with lateral hindfoot pain compared to a cohort without pain. MATERIALS AND METHODS: Ten consecutive patients with flexible flatfoot deformity and lateral hindfoot pain (mean age, 55.5 +/- 13.9) were compared to 10 consecutive patients with flexible deformity but no pain (mean age, 61.0 +/- 8.6). Conventional radiographs and weightbearing multiplanar images were performed on all patients before surgical reconstruction. Flatfoot, hindfoot impingement, and arthrosis parameters were interpreted in a blinded fashion by two musculoskeletal radiologists. Interrater reliability was determined with intraclass correlation coefficients (ICC). All parameters were compared between groups with a Wilcoxon rank sum test (p < 0.05). RESULTS: A significant increase in posterior facet subtalar arthrosis (p = 0.006) and combined anterior and posterior facet subtalar arthrosis (p = 0.022) was evident in the pain group. Calcaneofibular impingement and calcaneocuboid arthritis were increased in the pain group, but did not reach significance (p = 0.057 and p = 0.067 respectively). The multiplanar imaging parameters demonstrated good (ICC = 0.60 to 0.73) to excellent (ICC >or= 0.74) reliability for most impingement and arthrosis parameters and for many of the standard flatfoot parameters. CONCLUSION: The results indicate that weightbearing, multiplanar imaging provides a reliable means of assessing lateral pain in patients with flexible flatfoot deformity.

Plantar pressures in patients with and without lateral foot pain after lateral column lengthening.

BACKGROUND: Lateral column lengthening, a commonly used adjuvant for the reconstruction of adult flatfoot deformity, can lead to postoperative complaints of lateral plantar pain or discomfort. We hypothesized that patients with such symptoms would have increased lateral plantar pressures when compared with matched controls without these symptoms. METHODS: Ten subjects who had undergone lateral column lengthening and were experiencing pain or discomfort in the plantar-lateral aspect of the foot were selected. Controls who had undergone lateral column lengthening but who were not experiencing such symptoms were matched for age, sex, accessory reconstructive procedures, and time from surgery. At the time of the present study, the patients had been followed for at least two years after the reconstruction and had had removal of hardware. Radiographs of each foot were assessed before and after surgery. The patients completed the Short Form-36 (SF-36) and Foot and Ankle Outcome Score surveys, and standing plantar pressure measurements were obtained. Average mean pressure, peak pressure, and maximum force were assessed at twelve anatomic regions and the two groups were compared. RESULTS: There were no significant preoperative differences between the two groups in terms of radiographic parameters. Patients with pain had significantly lower SF-36 Physical Health Summary scores (p < 0.05), SF-36 Physical Function Subscale scores (p < 0.05), and average Foot and Ankle Outcome Scores (p < 0.05). Patients with pain had significantly higher lateral midfoot average mean pressure (p < 0.05), peak pressure (p < 0.05), and maximum force (p < 0.05). No differences were found in the hindfoot or forefoot regions. CONCLUSIONS: Patients who have undergone lateral column lengthening and who experience lateral plantar pain have increased plantar pressure values in the lateral aspect of the midfoot. The increased pressures in this area cannot be accounted for solely by radiographic or demographic factors.

New radiographic parameters assessing forefoot abduction in the adult acquired flatfoot deformity.

BACKGROUND: Stage II flatfoot secondary to posterior tibial tendon insufficiency may be subclassified into mild (IIa) and severe (IIb) deformity based on the degree of talonavicular abduction. Current assessment of this abduction is difficult. We hypothesized that two new anteroposterior radiographic parameters, the lateral talonavicular incongruency angle (IA) and incongruency distance (ID) would demonstrate good reliability, correlate with current abduction parameters, and differ in IIb deformity, IIa deformity, and controls. MATERIALS AND METHODS: Preoperative radiographs for consecutive patients undergoing flatfoot reconstruction were reviewed and subdivided into those with a Stage IIb (n = 32) or Stage IIa (n = 8) deformity. A third group of patients without flatfoot served as control (n = 30). Radiographs were measured blindly by two investigators. Reliability was assessed with intraclass correlation coefficients (ICC), correlation with existing parameters with Pearson coefficients, and comparison between groups with analysis of variance. RESULTS: The mean intrarater and interrater ICC's for the IA (0.88 and 0.81, respectively) were high. The IA correlated well with the coverage angle (r = 0.86) and uncoverage percent (r = 0.76). The IA was higher in the IIb versus IIa patients (p = 0.007) and in the IIb group versus control (p < 0.001). The ID demonstrated excellent reliability (ICC's of 0.83 and 0.83), but correlated poorly with the two other abduction parameters (r = -0.59 and -0.49) and failed to differentiate between the three groups (p = 0.0528). CONCLUSION: This data suggests that the IA is reliable and may help subclassify Stage II flatfoot deformity.