The first 12 weeks: why range of motion after knee replacement can't wait
Updated: Oct 6
Most patients do well after total knee replacement. A small but important group don't regain the bend they need, and for them the calendar is working against them.
How common is stiffness?
Postoperative stiffness is estimated to affect about 5% to 7% of patients after TKR, most often because of arthrofibrosis, an excess of scar tissue that limits movement (Mamarelis et al., Annals of Translational Medicine, 2015).
Why timing matters
When stiffness doesn't respond to physiotherapy, manipulation under anaesthesia is a common next step. The editorial cited above reviews a study comparing manipulation within 12 weeks of surgery with manipulation after that point:
Within 12 weeks: mean flexion gained 36.5°, final range of motion 119°.
After 12 weeks: mean flexion gained 17°, final range of motion 95°.
The early group gained roughly twice the flexion. The authors recommended early manipulation, within 12 weeks, as first line management for arthrofibrosis when there is no infection or technical problem.
The visibility problem
To act within 12 weeks, the care team first has to know a patient is falling behind. In many pathways, range of motion is measured only at scheduled reviews, often at six weeks and then again weeks later. A patient who plateaus at 80° in week four might not be picked up until the window is closing.
What helps
Set clear range of motion milestones for each stage of recovery and share them with the patient.
Measure more often. Frequent, simple measurement shows trends, not just snapshots.
Escalate early. Agree in advance when a slow trajectory should trigger a review with the surgeon.
Support daily practice. Consistent home exercise in the early weeks is the best protection against stiffness.
BIBO measures range of motion through the phone's camera during each session and reports it to the clinician, so a flattening trend can be seen between appointments rather than at them.
This article is general information for health professionals and is not clinical advice.
