Early postoperative step count and walking time have greater impact on lower limb fracture outcomes than load-bearing metrics.

INTRODUCTION: Weight-bearing protocols for rehabilitation of lower extremity fractures are the gold standard despite not being data-driven. Additionally, current protocols are focused on the amount of weight placed on the limb, negating other patient rehabilitation behaviors that may contribute to outcomes. Wearable sensors can provide insight into multiple aspects of patient behavior through longitudinal monitoring. This study aimed to understand the relationship between patient behavior and rehabilitation outcomes using wearable sensors to identify the metrics of patient rehabilitation behavior that have a positive effect on 1-year rehabilitation outcomes. METHODS: Prospective observational study on 42 closed ankle and tibial fracture patients. Rehabilitation behavior was monitored continuously between 2 and 6 weeks post-operative using a gait monitoring insole. Metrics describing patient rehabilitation behavior, including step count, walking time, cadence, and body weight per step, were compared between patient groups of excellent and average rehabilitation outcomes, as defined by the 1-year Patient Reported Outcome Measure Physical Function t-score (PROMIS PF). A Fuzzy Inference System (FIS) was used to rank metrics based on their impact on patient outcomes. Additionally, correlation coefficients were calculated between patient characteristics and principal components of the behavior metrics. RESULTS: Twenty-two patients had complete insole data sets, and 17 of which had 1-year PROMIS PF scores (33.7 ± 14.5 years of age, 13 female, 9 in Excellent group, 8 in Average group). Step count had the highest impact ranking (0.817), while body weight per step had a low impact ranking (0.309). No significant correlation coefficients were found between patient or injury characteristics and behavior principal components. General patient rehabilitation behavior was described through cadence (mean of 71.0 steps/min) and step count (logarithmic distribution with only ten days exceeding 5,000 steps/day). CONCLUSION: Step count and walking time had a greater impact on 1-year outcomes than body weight per step or cadence. The results suggest that increased activity may improve 1-year outcomes for patients with lower extremity fractures. The use of more accessible devices, such as smart watches with step counters combined with patient reported outcome measures may provide more valuable insights into patient rehabilitation behaviors and their effect on rehabilitation outcomes.

Early weight bearing after lower extremity fractures in adults.

Weight-bearing protocols should optimize fracture healing while avoiding fracture displacement or implant failure. Biomechanical and animal studies indicate that early loading is beneficial, but high-quality clinical studies comparing weight-bearing protocols after lower extremity fractures are not universally available. For certain fracture patterns, well-designed trials suggest that patients with normal protective sensation can safely bear weight sooner than most protocols permit. Several randomized, controlled trials of surgically treated ankle fractures have shown no difference in outcomes between immediate and delayed (≥6 weeks) weight bearing. Retrospective series have reported low complication rates with immediate weight bearing following intramedullary nailing of femoral shaft fractures and following surgical management of femoral neck and intertrochanteric femur fractures in elderly patients. For other fracture patterns, particularly periarticular fractures, the evidence in favor of early weight bearing is less compelling. Most surgeons recommend a period of protected weight bearing for patients with calcaneal, tibial plafond, tibial plateau, and acetabular fractures. Further studies are warranted to better define optimal postoperative weight-bearing protocols.

Load Monitoring System for Partial Weight Bearing Therapy for rehabilitation of lower extremity fractures.

Partial Weight Bearing Therapy (PWB) is used during in rehabilitation of lower-extremity fractures, but optimal outcomes are limited by the paucity of data supporting the current standard of care, the inability of clinicians to assess patients' compliance to the prescribed therapy, and by the patient's inability to apply clinical loading guidelines. To address these needs a Load Monitoring System (LMS) was developed using a novel long-term load measuring technology coupled with consumer electronics for storing and reporting of patient limb loading data. The project was planned as a staged effort and the results of the first stage development are presented here. During the first stage of this project, the LMS insole load sensor was developed for 6-week standalone operation. The LMS was subjected to bench-testing, demonstrating low static and dynamic drift.

The effect of partial weight bearing in a walking boot on plantar pressure distribution and center of pressure.

Physicians routinely prescribe partial weight bearing in a walking boot following fractures of the lower limbs in order to produce the needed mechanical environment to facilitate healing. Plantar pressure measurements can provide key information regarding the mechanical environment experienced by lower limb bones. The effect of walking boots on plantar pressure distribution has been well reported, however, the combined effects of partial weight bearing and walking boots on plantar pressure distribution and center of pressure is unknown. Thirteen healthy volunteers with no known gait pathologies were fitted with a multi-pressure sensor insole that recorded their plantar pressure distribution during four walking trials: (i) normal walking, (ii) full weight bearing in a walking boot, (iii) 27 kg partial weight bearing in a walking boot and (iv) 9 kg partial weight bearing in a walking boot. Results demonstrated that changing from trial (i) to (iv) resulted in a posterior shift in weight distribution; the percentage of total weight experienced at the heel increased while the percentage of total weight experienced at the forefoot (both medial and lateral) and the hallux decreased. Center of pressure trajectories also shifted more posteriorly. Additionally, while in a walking boot the gait during full and partial weight bearing resulted in more even foot loading.

Sensor packaging design for continuous underfoot load monitoring.

Continuous force measurement can provide valuable insight to the efficacy of limb loading regimes during fracture rehabilitation. Currently there is no load monitoring device that is capable of more than 1 h of continuous recording. To enable continuous underfoot load monitoring a piezoresistive pressure sensor was encapsulated in a non-compressible silicone gel. This basic approach to signal transduction was implemented in three continuous underfoot load sensor designs. Design I constrained the gel in a rigid urethane housing. Design II constrained the gel in a silicone elastomer bladder. Design III utilized a hybrid approach by constraining the gel with a rigid upperplate inside of an elastomeric bladder. All three designs were subjected to bench and human testing. Design I outperformed the other two designs showing high linearity (correlation coefficient of 1), low static drift (<1%) and low dynamic drift (<3%) and captured the largest percentage of weight during human testing (35%). The sensor was designed, tested and shown to be durable and accurate for a 2 week window of time. This sensor has the low cost and high performance required for large scale clinical tests to correlate limb loading and fracture healing rates.

An insole sensor for recording weight bearing behavior during tibial fracture rehabilitation.

Partial weight bearing prescriptions for tibial fracture care are made with little data to support their efficacy. To provide long term tibial load data that can be used to study, guide, and monitor partial weight bearing, we developed a novel load sensor that can record the load placed on an injured limb over a two-week period of time. The prototype load sensor demonstrated high linearity, low hysteresis and low static and dynamic drift. Preliminary human testing on the load sensor demonstrated the ability of the load sensor to capture load profile during underfoot recording. Presented are the bench testing and human testing data on the prototype load sensor verifying the design of an economic and durable system that allows for 2 weeks of recording of normal loads experienced by the tibia. This design motivates a next generation approach for use in clinical trials that will enable clinicians and researchers to improve current partial weight bearing prescriptions, thus improving tibial fracture outcomes.