The ROCKY REHAB trial will provide a pragmatic approach to evaluate if incorporating a rocky, uneven terrain treadmill into the proprioceptive rehabilitation received during physical therapy can improve outcomes and reduce reinjury rates in patients with ankle instability.

Lower limb sprains and strains are three-times more prevalent than any other acute injury in the Armed Forces, with lateral ankle sprains being the most common injury sustained during active-duty. Many individuals who experience an ankle sprain will go on to develop chronic ankle instability. Training and rehabilitation programs that incorporate proprioceptive training are particularly effective at improving outcomes and reducing re-injury rate. However, current programs do not help individuals "train to the tasks" that will be encountered once those individuals leave physical therapy. The proposed intervention evaluates the use of a rocky, uneven terrain treadmill that specifically targets aspects of the real-world environment for restoring and improving short-term function and performance and reducing the long-term risk of re-injury. This trial will randomly allocate 312 individuals with ankle sprains and chronic ankle instability to standard of care physical therapy or the standard of care supplemented with the uneven treadmill intervention. Patient reported outcome, performance measures, and biomechanical measures of muscle activations and plantar pressures will be evaluated. Patient reported outcomes and reinjury rates will be tracked for 18 months.

Inclusion Criteria

1. Aged 18-49.

2. Score < 24 on the Cumberland Ankle Instability Tool.

3. Foot and Ankle Ability Measure Activities of Daily Living score ≤ 90 and Sports score ≤ 80 indicating substantial ankle-foot impairment and activity limitation.

4. Able to attend treatment sessions for approximately a 6-week period.

5. Passed most recent physical fitness test (Active duty only).

6. Acute lateral ankle sprain specific inclusion criteria:

   1. history of a first-time ankle sprain that resulted in activity limitation that lasted at least one day.
   2. chronicity of 2-6 weeks prior to consent.

7. Chronic ankle instability specific inclusion criteria:

   1. history of at least one significant ankle sprain within the 12 months prior to enrollment that interrupted physical activity for 1+ days.
   2. most recent ankle sprain in the past 2-12 weeks.
   3. history of the previously injured ankle joint "giving way" and/or recurrent sprain and/or ''feelings of instability.''

8. Individual is about to start care with physical therapy.

Exclusion Criteria

1. Unable to walk at the point of study enrollment.
2. Non-removable casting.
3. History of previous surgeries to the musculoskeletal structures (i.e., bones, joint structures, nerves).
4. History of fracture in either limb of the lower extremity requiring realignment.
5. Acute injury to musculoskeletal structures of other joints of the lower extremity within the previous three months, which impacted joint integrity and function resulting in at least one interrupted day of physical activity.
6. Pregnant.
7. Self-reported disability due to neuromuscular impairment in the lower extremity, neurological or vestibular impairment that affected balance.
8. Connective tissue disorder (e.g. Marfan Syndrome or Ehlers-Danlos syndrome).
9. Anyone separating from the military within 12 months (other than normal military retirement), pending a medical evaluation board, discharge from the military for medical reasons, or pending or undergoing any litigation for an injury.

De-identified primary outcome data will be published. Additional outcome data may also be included.

Roughly 12 months after data collection completion as part of study publications.

Assessors will be blinded to group assignment