Apple Health mobility data can be valuable for assessing patient recovery following lower extremity trauma surgery, according to a study presented at last week’s annual meeting of the American Academy of Orthopaedic Surgeons (AAOS) in San Diego.

Using mixed-effect models to compare certain Apple Health mobility parameters, the researchers were able to measure improvement objectively by using a patient’s mobility data prior to injury as a baseline metric.

Lower extremity trauma surgery could include tibial plateau, distal femur and femoral shaft fractures.

“Our goal as orthopaedic surgeons is to help patients regain mobility and resume the activities they enjoy,” said Dane Brodke, assistant professor at the 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 contextualising a patient’s recovery and is generally unavailable with other functional outcome measures.”

The study led by Brodke, Brian Shear and Nathan O’Hara 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 PRO Measurement Information System (Promis) surveys to analyse physical function and pain.

The key metrics analysed 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 to 180). Correlations between mobility parameters and Promis physical function and pain interference were assessed.

As the researchers expected, the study found all five Apple Health mobility parameters showed significant changes from pre-injury to post-injury: step count decreased 93%; walking speed decreased 9%; step length decreased 6%; walking asymmetry increased 88%; and walking double support increased 1%.

Six months following the injury, the team observed the following improvements:

• The average daily step count was 2430, 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 with 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 with 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 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 provide a clearer, more reliable understanding of a patient’s recovery.”

The team is 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 personalised insights that support their recovery and help them safely return to an active lifestyle.

With more than 39,000 members, the American Academy of Orthopaedic Surgeons (www.aaos.org) is the world’s largest medical association of musculoskeletal specialists.