The development of an intraoperative plantar pressure assessment device

Development of Intraoperative Plantar Pressure Measurement System Considering Weight Bearing Axis and Center of Pressure

To prevent postoperative complications in corrective surgery for foot deformities such as hallux valgus and pes planus, it is critical to quantitatively predict the postoperative standing-position plantar pressure distribution during the operation. The authors have previously proposed an intraoperative plantar pressure measurement system (IPPM) that allows for the measurement of a supine patient’s plantar pressure distribution that is equivalent to that in the standing position. This system consists of an IPPM device comprising of a force plate and pressure distribution sensor, an optical three-dimensional position measurement device, a navigation monitor, and a PC. The plantar pressure distribution in the standing position is reproduced by navigating the operator, as he or she presses the IPPM device against the patient’s sole so that the weight-bearing axis (floor reaction force vector) and femoral head center are as close to each other as possible. However, in our previous study, the reproducibility of the standing position plantar pressure distribution was insufficient. Therefore, in the present study, we add a navigational function that can be used to bring the centers of pressure in the standing position and under measurement, as well as to correct the IPPM’s self-weight in the measured force. The improved device was used in an experiment with nine healthy subjects, and the similarity of the plantar pressure distribution in the standing and supine positions was evaluated using normalized cross-correlation, yielding an average of 0.90. Furthermore, in an evaluation experiment with ten orthopedic surgeons, it was observed that using the system reproduced the plantar pressure distribution significantly better than when the system was not used. These results indicate that the present system can predict the plantar pressure distribution in the standing position. We believe that this system can contribute to reducing complications after foot surgery.

Assessment of Hindfoot Alignment: Intraoperative Fluoroscopy Versus Standing Radiograph

Few intraoperative assessments are available for hindfoot alignment. In the current study, we demonstrated the feasibility of hindfoot alignment via intraoperative fluoroscopy. We retrospectively compared measurements of heel alignment obtained via intraoperative fluoroscopy with those acquired using standard radiographs. Two observers compared the heel alignment ratios and angles derived from 100 pairs of images. The effects of age, sex, laterality, and body mass index on the discrepancy between fluoroscopic images and radiographs were analyzed. The heel alignment ratio revealed a strong correlation between standing radiograph and intraoperative fluoroscopy, based on a correlation coefficient of 0.844 (p < .001). The heel alignment angle also showed significant correlation based on a correlation coefficient value of 0.667 (p < .001). None of the demographic factors showed any significant effect on the discrepancy between the 2 sets of images. Our study showed that the heel alignment determined via intraoperative fluoroscopy was comparable to that of a standard standing radiograph without any significant association with demographic factors.

Development of intraoperative plantar pressure measuring system considering weight bearing axis

PURPOSE

Surgical reconstructions in three dimensions are needed for treatment of foot and ankle deformities. However, surgical results might be influenced by the skill and experience of doctors which complement the limited information for reconstructions in three dimensions. To solve these, studies were carried out to measure plantar pressure distribution during surgery. Though, it was impossible to accurately measure plantar pressure distribution accurately during operation. Therefore, we proposed an intraoperative plantar pressure measurement (IPPM) device that enables proper navigation in the push direction.

METHODS

For this purpose, first, we investigated how the physiological load axis passes through the human body to identify the pushing direction of the pressure sensor of the device toward the patient's foot. In particular, we hypothesized that the physiological load axis passes through the femoral head center and we evaluated this in a measurement experiment with nine healthy subjects. Second, based on these results, we developed the IPPM device that has two force sensors to identify the pushing direction toward the femoral head center and a conductive ink sensor to measure plantar pressure distribution. Finally, we conducted the experiments with nine healthy subjects and two users.

RESULTS

From the first experimental results, the physiological load axis was found to pass through the femoral head center in normal standing posture. From the evaluation experiment, there are no significant differences statistically in plantar pressure distributions between the conditions of using IPPM device and without using it for both a medical student and a surgeon. However, in some cases the plantar pressure distribution can be reproduced similarly to that of the standing posture, and also from the evaluation experiment concerning the relation between CoP position and NCC, the NCC tends to increase when the position of the CoP is closer to that at the standing posture.

CONCLUSION

The IPPM device has possibility to reproduce the plantar pressure distribution during surgery and prevent the recurrence of surgical complications.

In Vivo Plantar Pressures in Adult-Acquired Flatfoot Compared to Control Using an Intraoperative Pedobarographic Device

BACKGROUND

Intraoperative pedobarography has the potential to aid surgical decisions, but no parameters exist to guide its use.

QUESTIONS/PURPOSES

This study compared supine plantar pressures between flatfoot patients and controls using a previously validated intraoperative pedobarographic device and examined associations between supine, walking, and standing plantar pressures.

METHODS

Ten preoperative patients with stage II adult-acquired flatfoot deformity (AAFD) were compared to ten healthy controls. Supine plantar pressures were assessed using the pedobarographic device. Standing and walking plantar pressures were assessed with an EMED-XT sensor array (Novel). Maximum force (MF) and peak pressure (PP) were calculated for nine anatomical foot regions adjusting for age and BMI.

RESULTS

No differences in plantar pressures were found between flatfoot patients and controls in the supine or standing positions. During walking, flatfoot patients had greater MF of the first, second, and third metatarsals (p ≤ 0.018) and greater PP of the first and second metatarsals than controls (p ≤ 0.010). Supine MF and PP were both strongly positively correlated with their respective pressure measurements for both standing and walking in multiple foot regions (p ≤ 0.05, all analyses). Correlations in the first metatarsal region were generally weak and not statistically significant.

CONCLUSION

This device did not show differences in supine plantar pressures of flatfoot patients and healthy subjects, highlighting the limitations of intraoperative devices in guiding flatfoot correction. The differences between flatfoot and controls during walking and the correlations between supine and walking conditions suggest that dynamic plantar pressures are a more useful parameter in guiding flatfoot reconstruction.

Sensitivity of plantar pressure and talonavicular alignment to lateral column lengthening in flatfoot reconstruction

BACKGROUND

Lateral column lengthening (LCL) of the calcaneus is commonly performed as part of correction of the adult acquired flatfoot deformity. Increases in postoperative lateral plantar pressure associated with pain in the lateral aspect of the foot have been reported. The aim of this study was to investigate changes in pressures in the lateral aspect of the forefoot with increments of 6, 8, and 10 mm of LCL in a cadaveric flatfoot model. The hypothesis was that increasing the LCL incrementally by 2 mm will linearly increase the plantar pressures in the lateral aspect of the forefoot.

METHODS

Eight fresh-frozen cadaveric foot specimens were used. A robot compressively loaded the foot to 400 N with a 310-N tensile load applied to the Achilles tendon. A flatfoot model was created by resecting the medial and inferior soft tissues of the midfoot, followed by axial load of 800 N for 100 cycles. Kinematic and plantar pressure data were gathered after the different amounts of LCL (6, 8, and 10 mm) were achieved.

RESULTS

The talonavicular joint demonstrated a median abduction angle of 4.4° in the axial plane and -2.6° in the sagittal plane in the flatfoot condition as compared with the intact condition. The 6, 8, and 10-mm LCLs showed axial correction of talonavicular alignment by -1.4°, -4.9°, and -9.2° beyond that of the intact foot, and sagittal correction of -0.1°, 1.3°, and 2.9°, respectively. LCL of 6, 8, and 10 mm showed consistently increasing lateral forefoot average mean pressure, peak pressure, and contact area.

CONCLUSIONS

LCL in 2-mm increments consistently reduced talonavicular abduction and consistently increased plantar pressure in the lateral aspect of the forefoot.

CLINICAL RELEVANCE

The lateral column should be lengthened judiciously, as a 2-mm difference leads to significant difference not only in angular correction of the talonavicular joint but also with regard to pressure in the lateral aspect of the forefoot.

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.

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.