Apple Health Mobility Data Used to Evaluate Extremity Surgery Outcomes

The Apple Health app provides users with a broad range of metrics to track various health parameters, from heart rate and blood oxygen levels to fall risk and time spent in daylight. But Apple Health mobility data now can serve as a valuable tool for assessing patient recovery after lower extremity trauma surgery such as tibial plateau, distal femur, and femoral shaft fractures, according to a recent study. Using mixed-effect models to compare certain Apple Health mobility parameters, researchers objectively measured improvement by using patients’ mobility data before injury as a baseline metric.

“Our goal as orthopedic surgeons is to help patients regain mobility and resume the activities they enjoy,” said Dane J. Brodke, M.D., assistant professor, Oregon Health & Science University in Portland. “In cases of traumatic leg injuries, assessing functional recovery has traditionally been challenging due to a lack of objective data. Since smartphone-based platforms like Apple Health collect data passively in the background, we have a unique opportunity to measure mobility both before and after an injury, providing valuable context for patient recovery. This baseline information is vital to contextualizing a patient’s recovery and is generally unavailable with other functional outcome measures.”

The study, “The Future is Mobile: Validating Apple Health as a Novel Orthopaedic Trauma Outcome Metric” led by Dr. Brodke, Brian Shear, M.D., and Nathan O’Hara, Ph.D., aimed to assess whether outcome measures from Apple Health captured mobility changes associated with injury and early recovery, correlated with patient-reported outcomes (PROs), and could distinguish between patients with and without nonunion, when the bone doesn’t heal properly, requiring another procedure.

The cross-sectional study included adult patients with lower extremity fractures who owned iPhones and had at least six months of post-injury follow up. Participants shared Apple Health data and completed Patient Reported Outcomes Measurement Information System (PROMIS) surveys to analyze physical function and pain.

The key metrics analyzed included daily step count, walking asymmetry (the percentage of time steps are asymmetric), double support time (the gait cycle portion where both feet are on the ground), walking speed, and step length. Researchers used mixed-effects models to compare mobility parameters at three critical time points: pre-injury (28 days prior), acute post-injury (first 28 days after injury), and six months post-injury (days 152-180). Correlations between mobility parameters and PROMIS physical function and pain interference were assessed.

As the researchers expected, the study found that all five Apple Health mobility parameters showed significant changes from pre-injury to post-injury:

• Step count decreased by 93%
• Walking speed decreased by 9%
• Step length decreased by 6%
• Walking asymmetry increased by 88%
• Walking double support increased by 1%

Six months after the injury, the team discovered:

• The average daily step count was 2,430, a 655% increase from early post-injury, but a 52% decrease from before the injury.
• Walking speed and step length continued to decrease during the first six months of recovery, while walking asymmetry and double support time increased.
• Compared to pre-injury, walking asymmetry remained 198% higher and speed 15% lower.

Step count was the only mobility parameter to show a moderate or stronger correlation with patient-reported physical function. Notably, patients with nonunions demonstrated a 55% slower recovery in daily step counts compared to those who healed normally.

“These finding suggest that smartphone-measured step counts not only correlate with adverse clinical outcomes but may also predict them, allowing for earlier intervention and improved patient care,” said Dr. O’Hara, associate professor of orthopedics at the University of Maryland Medical System in Baltimore. “Conversely, when a patient’s recovery plateaus, it may indicate they have reached their maximum potential improvement. While the PROMIS survey offers valuable insights from a patient’s perspective, it remains subjective. For the first time, the objective data from Apple Health provides a clearer, more reliable understanding of a patient’s recovery.”

The team is currently developing an app patients can download at their initial surgical consultation so researchers can enroll more Apple Health data trackers. The team hopes to leverage this technology to give patients the personalized insights they need to support their recovery and safely return to an active lifestyle.