Beyond PROs: Why Digital Outcome Metrics (DOMs) Are the Real Frontier of Functional Recovery
Every orthopedic surgeon wants the same answer after surgery: Did this patient actually get better? Today, we mostly answer that question by handing the patient a survey. We ask them to rate their pain, check a few boxes about stiffness, and tell us how far they can walk. Then we use those numbers to judge outcomes, benchmark procedures, and guide the next wave of care.
At Surgeon Decision Intelligence, we think that approach has run out of road. Patient-reported outcomes (PROs) gave us a starting point, but they cannot carry us into the next era of orthopedic care. Digital Outcome Metrics (DOMs) can.
The Limitations of Patient-Reported Outcomes (PROs)
PROs sound objective because we put them on a scale. But the scores come from a human memory on a specific afternoon and that makes them deeply variable.
PROs shift with mood, pain tolerance, and expectations. A patient who slept poorly or argued with a family member before the appointment will rate the same knee differently than a patient who just had a good day. Socioeconomic stress, cultural background, and personal expectations all color the answer before the patient picks up the pencil.
PROs can change based on what patients did five minutes earlier. A 2019 study on the QuickDASH PROM showed that simply asking patients to complete functional tasks before filling out the survey changed their scores. The hand did not change. The questionnaire did not change. Only the order changed. And the "outcome" moved with it [1]. If the order of a clinic visit can move a score, we cannot call that score a reliable measure of function.
PROs suffer from inconsistent follow-up. Patients skip surveys, especially at 6, 12, and 24 months when we need long-term data the most. Response rates drop, missing data piles up, and we end up comparing complete early scores to spotty late scores. That skews every benchmark we build on top.
PROs miss the recovery curve. A survey at week 6 and another at month 6 gives us two dots on a graph. Recovery does not happen in two dots. It happens every day, in thousands of small movements, and PROs never see those.
What Digital Outcome Metrics Actually Are
When surgeons first hear "DOMs," many picture a step counter on a smartwatch. Steps matter, but they are one slice of a much bigger picture. DOMs include every stream of digital data a patient passively generates as they recover. We group them into six categories.
Activity and mobility covers the familiar metrics: daily step count, active minutes, stair climbs, and workout sessions. These show whether a patient is actually moving through their life, not just telling us they are.
Gait and pose biomechanics goes deeper. Modern phones and wearables measure gait velocity, stride symmetry, cadence, and joint range of motion. Researchers have called walking speed the "sixth vital sign" because it predicts function, independence, and even mortality across populations [2]. A hip replacement that restores gait velocity is a hip replacement that worked.
Sleep and physiologic recovery captures what happens when the patient is not moving. Sleep quality, heart rate variability, and resting heart rate all reflect how the body is healing. Tissue repair, inflammation control, and nervous system recovery all show up here long before they show up in a clinic visit.
Geographic mobility may be the most underrated DOM category we track. Using anonymized location data from a patient's phone, we can measure how many unique places they visit each week, how far they travel from home, how long they spend outside the house, and whether they are returning to meaningful destinations like workplaces, grocery stores, gyms, and places of worship. These patterns matter because orthopedic surgery is fundamentally about restoring a patient's ability to move through their world. A post-op knee patient whose travel radius stays at 500 meters three months after surgery is telling us something a questionnaire never will. Geographic data also captures recovery milestones that activity counts miss - the first trip back to work, the first long drive, the first vacation. Independence is not a number on a pain scale. It is a map that starts expanding again.
Social engagement pulls from communication patterns: calls made, messages sent, time spent in social apps, community participation. A patient who starts calling friends again is recovering in a way no knee exam can measure.
Anatomic signals close the loop by linking digital data to biology. Muscle volume, pose estimates, alignment paramaters- often captured through sensors- give us the anatomic truth underneath the behavior.
Why DOMs Are the Real Frontier of Function
DOMs do four things PROs cannot.
They measure function objectively. A step count does not care about the patient's mood. A gait velocity does not depend on how the question was worded. A travel radius does not change based on expectations. Systematic reviews of wearable devices in total joint arthroplasty show that passive sensors can track recovery trajectories with a granularity PROs simply cannot match [3].
They track recovery continuously. Instead of two dots on a graph, DOMs give us a full curve every day after surgery. We can watch a patient's travel radius grow from the driveway to the block to the full neighborhood. We can see exactly when a patient plateaus, regresses, or breaks through.
They detect change before the patient notices it. Subtle drops in gait symmetry, stride length, or time spent outside the home often appear weeks before a patient reports new pain. DOMs act as an early-warning system for complications, re-tears, and failing hardware.
They enable true predictive power. When we train models on thousands of patient recovery trajectories — combining activity, biomechanics, sleep, geographic mobility, and social engagement - DOMs let us forecast reoperation risk, return-to-function timelines, and implant survivorship with accuracy PROs cannot approach. Recent work on digital biomarkers in spine care shows how these signals are already reshaping outcome measurement across musculoskeletal medicine [4].
Paired with anatomic imaging biomarkers, DOMs give surgeons something we have never had before: a real-time, objective, continuous view of how each patient is actually recovering - and whether our surgical decisions are delivering the function we promised.
The Path Forward
We are not arguing that PROs should disappear. Patient voice still matters, and some things - pain, satisfaction, quality of life - must come from the patient. But PROs can no longer stand alone as the gold standard of outcome measurement in orthopedics. The evidence, the technology, and the patients themselves have all moved past that.
At Surgeon Decision Intelligence, we are building the infrastructure to collect, synthesize, and act on DOMs at the point of care. We want every surgeon to open a dashboard and see, in real time, whether their patients are walking faster, sleeping better, reaching farther, and returning to the lives surgery was supposed to give back.
That is the next frontier of understanding function.
References
[1] Shapiro LM et al. Can the QuickDASH PROM be Altered by First Completing the Tasks on the Instrument? Clin Orthop Relat Res. 2019 Apr 27;477(9):2062–2068.
[2] Fritz S & Lusardi M. White Paper: “Walking Speed: the Sixth Vital Sign”. J Geriatr Phys Ther. 2009;32(2):46–49.
[3] Hall RR III et al. Use of Wearable Devices to Augment Traditional Measurements of Postoperative Outcomes Following Total Joint Arthroplasty: Systematic Review. JMIR Rehabil Assist Technol. 2026 Apr 17;13:e84671.
[4] Bi CL et al. Digital Biomarkers and the Evolution of Spine Care Outcomes Measures: Smartphones and Wearables. Neurosurgery. 2023;93(4):745–754.