Smartphones are often equipped with inertial sensors capable of measuring individuals' physical activities. Their role in monitoring the patients' physical activities in telemedicine, however, needs to be explored. The main objective of this study was to explore the correlation between a participant's daily step counts and the daily step counts reported by their smartphone. This prospective observational study was conducted on patients undergoing lower limb orthopedic surgery and a group of non-patients. The data collection period was from 2 weeks before until four weeks after the surgery for the patients and two weeks for the non-patients. The participants' daily steps were recorded by physical activity trackers employed 24/7, and an application recorded the number of daily steps registered by the participants' smartphones. We compared the cross-correlation between the daily steps time-series taken from the smartphones and physical activity trackers in different groups of participants. We also employed mixed modeling to estimate the total number of steps. Overall, 1067 days of data were collected from 21 patients (11 females) and 10 non-patients (6 females). The cross-correlation coefficient between the smartphone and physical activity tracker was 0.70 [0.53–0.83]. The correlation in the non-patients was slightly higher than in the patients (0.74 [0.60–0.90] and 0.69 [0.52–0.81], respectively). Considering the ubiquity, convenience, and practicality of smartphones, the high correlation between the smartphones and the total daily step time-series highlights the potential usefulness of smartphones in detecting the change in the step counts in remote monitoring of the patient's physical activity.

Total hip arthroplasty (THA) in the young patient has been associated with higher rates of revision and perioperative complications. For clinicians and patients alike, there remains a desire to better characterize the durability of THA in young patients. We reviewed secondary data from our institutional database for all patients who underwent primary THA from January 2000 to May 2015. Patients were identified using ICD-9 procedure code 81.51. Our primary interest was the survival of implants in patients 30 years of age or younger (n=167) while using a contemporaneous cohort of patients age 60 and older as a control (n=1359). Failure was defined as revision THA for any reason. Cox regression with robust standard errors was used to calculate hazard ratios. A population-averaged Poisson regression analysis was used to compare complication rates.

The rate of all-cause revision THA was 2.4 times greater (95% CI 1.10 – 5.37, p=0.028) in young patients (7%, 12/167) undergoing primary or conversion to THA compared to their elderly counterparts (3.7%, 50/1,359). Survival at 10 years was 89% (95% CI 82 – 94) in the young cohort and 96% (94 – 97) in the elderly cohort. The primary reasons for revision in young that patients compared to their elderly counterparts included metal-on-metal implants (IRR 8.12, 95% CI 2.04 – 32.38, p=0.003).

These data demonstrate that patients 30 years of age and younger substantially benefit from THA but should be warned of higher risk of subsequent revision.