Knee Mobility · Stage 02
Knee stiffness exercises, done in the right order.
"Knee stiffness exercises." "How to get knee bend back after surgery." "Knee won't fully straighten." If a search like that brought you here, this page covers how mobility loss happens after knee surgery and injury, what the current evidence says about restoring it, and why the right approach depends on what caused the stiffness in the first place.
Assessment + treatment from session one · $750 MXN · Zona Rio, Tijuana.
By Leonardo Machado, LFT · Licensed Physiotherapist · issuing institution name pending publication
A knee that won't bend past a certain point, or won't fully straighten, is one of the more frustrating problems in rehabilitation — because it's visible, it's measurable, and progress can feel slow. Mobility loss shows up in two very different contexts, and they are not treated the same way: stiffness following surgery (ACL reconstruction, meniscus repair, total knee replacement), and stiffness that develops without any surgery at all.
This is educational information, not a personalized program. What your knee needs specifically — how far to push range, how fast to progress, what to avoid — depends on your surgery type, your surgeon's protocol if applicable, and what assessment finds. If you've had surgery, your treating surgeon's specific restrictions always take priority over general information here.
Why it happens
Two different problems that both look like "a stiff knee."
Post-surgical stiffness.
After ACL reconstruction, meniscus repair, or knee replacement, some early loss of motion is expected while tissue heals and swelling resolves. Modern rehabilitation protocols deliberately start range-of-motion and weight-bearing work early and progressively, rather than immobilizing the knee for an extended period — that shift is one of the more established changes in ACL rehab over the past several decades.
Non-surgical stiffness.
Knee stiffness without surgery is usually one part of a broader movement or load picture — often grouped clinically with conditions like patellofemoral pain. Generic stretching for everyone is not the right default here; the right intervention depends on which impairment pattern is actually present.
The approach
Criterion-based, not calendar-based.
Instead of "you should be able to bend your knee to X degrees by week Y," a criterion-based approach sets targets that need to be met before progressing, regardless of exactly how many days have passed. For the early phase after ACL reconstruction, commonly used early-phase targets include working toward roughly 0–115° of flexion or more, keeping swelling controlled, and restoring a normal walking pattern before adding more demanding loading work.
Meniscus repair is handled more conservatively than an ACL reconstruction alone — protocols commonly limit flexion range and weight-bearing for the first several weeks before progressing toward fuller range and loading. It's worth being direct here: there is no single agreed-upon protocol for meniscus repair restrictions across the field, and the evidence behind specific numbers is limited. Your surgeon's specific instructions for your repair type should always be the deciding factor, not a general timeline found online.
One point worth correcting directly: early motion and early loading are not what causes arthrofibrosis (excessive post-surgical scarring and stiffness). The factors more consistently linked to that complication include things like patient sex and — importantly — how quickly early stiffness is recognized and addressed when it does start to develop. That's part of why we track mobility closely in the early weeks rather than waiting to see if it resolves on its own.
Evidence
What the evidence says.
Rehabilitation after ACL reconstruction has shifted decisively toward early range-of-motion and weight-bearing work rather than prolonged immobilization, without an increase in complications (Melick N et al., "Anterior cruciate ligament reconstruction rehabilitation: Decades of change," Knee Surgery, Sports Traumatology, Arthroscopy, 2025; Shelbourne KD & Nitz P, "Accelerated rehabilitation after anterior cruciate ligament reconstruction," American Journal of Sports Medicine, 1990).
Early-phase recovery is typically defined by targets such as flexion of roughly 0–115° or more, effusion controlled to a mild level, and a normalized gait pattern before advancing (Petterson S et al., "Recovery Stages After Anterior Cruciate Ligament Reconstruction," Arthroscopy, 2025; APKASS 2024 Consensus Statement on ACL Reconstruction Part III: Return to Play, 2024).
Known risk factors for excessive post-surgical scarring and stiffness are multifactorial and include patient sex and delayed recognition or treatment of early stiffness — not the timing of early motion work itself ("Arthrofibrosis risk factors after anterior cruciate ligament reconstruction," Frontiers in Sports and Active Living, 2023).
Clinical practice guidelines for patellofemoral pain recommend classifying patients into subgroups — including a specific mobility-impairment subgroup — rather than applying the same stretching or mobility program to every patient with anterior knee stiffness (Willy RW et al., "Patellofemoral Pain: Clinical Practice Guidelines Linked to the ICF," Journal of Orthopaedic & Sports Physical Therapy, 2019).
Post-operative protocols after isolated meniscus repair commonly restrict flexion and weight-bearing for the first several weeks, but a recent systematic review found no true consensus on the exact restrictions, based on generally low-level evidence — reinforcing why the treating surgeon's specific instructions should guide this stage (Bouchard MD et al., "Postoperative Rehabilitation Protocol After Isolated Meniscal Repair: A Systematic Review," Orthopaedic Journal of Sports Medicine, 2025).
Watch
Video walkthrough.
A video walkthrough of knee mobility rehabilitation will be added here.
Related
Next steps.
Understanding, mobility, strength, and return to sport — the complete phased approach to knee rehabilitation.
Once mobility milestones are met, strength becomes the priority — quadriceps, hamstring, and hip capacity.
ACL, meniscus, patellofemoral pain, and post-surgical presentations — how assessment identifies what's actually driving the problem.
Not sure what your knee needs
Ask Leonardo, or book a mobility assessment.
Assessment + treatment from session one. $750 MXN. Zona Rio, Tijuana.