New Study Uses Apple Health Mobility Data to Evaluate Outcome Measures Following Lower Extremity Surgery

SAN DIEGO, March 10, 2025 /PRNewswire/ -- The Apple Health app provides users with a wide range of metrics to track various health parameters, from heart rate and blood oxygen levels to fall risk and time spent in daylight. Now, Apple Health mobility data can help serve as a valuable tool for assessing patient recovery following lower extremity trauma surgery, such as tibial plateau, distal femur and femoral shaft fractures, according to a study presented at the 2025 Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS). Using mixed-effect models to compare certain Apple Health mobility parameters, the researchers were able to objectively measure improvement by using a patient's mobility data prior to injury as a baseline metric. 

"Our goal as orthopaedic surgeons is to help patients regain mobility and resume the activities they enjoy," said Dane J. Brodke, MD, MPH, 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, MD and Nathan O'Hara, PhD, MHA, aimed to assess whether the 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 reoperation.

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 portion of the gait cycle 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 following the injury, the team observed the following improvements:

• 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 orthopaedics at 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 that patients can download during their initial visit with their orthopaedic surgeon with the goal of enrolling more participants to track their Apple Health data. By leveraging this technology, the team hopes to empower patients with personalized insights that support their recovery and help them safely return to an active lifestyle.

2025 AAOS Annual Meeting Disclosure Statement

About the AAOS
With more than 39,000 members, the American Academy of Orthopaedic Surgeons is the world's largest medical association of musculoskeletal specialists. The AAOS is the trusted leader in advancing musculoskeletal health. It provides the highest quality, most comprehensive education to help orthopaedic surgeons and allied health professionals at every career level best treat patients daily. AAOS is the source of information on bone and joint conditions, treatments, and related musculoskeletal healthcare issues; and it leads the healthcare discussion on advancing quality.

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SOURCE American Academy of Orthopaedic Surgeons