A knee replacement should give you a joint that bends, straightens and carries you through the day without pain. If your knee still feels tight or "stuck" weeks after surgery, you may hear the word arthrofibrosis. It is a recognised complication of knee replacement, studied in large reviews, and in most cases it is not caused by a surgical error [1, 2].

This guide explains what arthrofibrosis is, how common it is, how it is diagnosed, and how it is treated, from physiotherapy to manipulation under anaesthesia (MUA) and surgery.

What is arthrofibrosis after total knee replacement?

Arthrofibrosis is the formation of too much scar tissue in and around the knee after surgery, which limits movement, causes pain and makes daily tasks harder [2]. Some scarring is a normal part of healing. In arthrofibrosis, healing overshoots.

At the cell level, cells called myofibroblasts become over-activated and lay down excess type I collagen in an inflamed environment [2]. A signalling pathway called TGF-beta is the best-established driver [2]. The extra tissue thickens the joint capsule, glues tissue layers together, and blocks bending (flexion) and, in more severe cases, straightening (extension).

Researchers increasingly separate stiffness (a measurement) from arthrofibrosis (the scar-tissue cause behind some stiff knees). A widely used research definition of "acquired idiopathic stiffness" is a range of motion below 90° lasting more than 12 weeks after surgery, when other causes such as infection, implant problems or pre-existing stiffness have been ruled out [3].

How common is it?

About 4 in every 100 patients develop stiffness of this kind after a first knee replacement. That is the pooled figure from a 2019 systematic review and meta-analysis in the Journal of Bone and Joint Surgery [3]. A separate study of 1,216 knee replacements found 3.7% had less than 90° of bend at one year [4].

Published figures range more widely, from about 1% to over 10%, mainly because studies define "stiff" differently [1, 3]. Arthrofibrosis is one of the leading causes of readmission and of knee-replacement failure [1], and a long-term Mayo Clinic series confirms it remains a common failure mode even with modern implants [5].

Why does it happen?

Every knee replacement involves cutting bone and releasing soft tissue, which sets off an inflammatory healing response. In most people this settles and leaves organised, flexible scar. In arthrofibrosis, the response is prolonged and exaggerated, leaving dense, disorganised scar and adhesions between layers that should glide [1, 2].

Some patients form a cyclops lesion, a nodule of fibrous tissue at the front of the knee that blocks full straightening. Low-grade infection can also cause stiffness, which is why infection must be ruled out before stiffness is labelled arthrofibrosis [2, 3].

Who is at higher risk?

The evidence is strongest for the first few factors below. Others are commonly cited but less consistent across studies.

Women and people with obesity (BMI 30 or above): both had a higher rate of stiffness in the 2019 meta-analysis [3].
Younger age: patients under 75 were more likely to need surgery to release adhesions in a study of over 100,000 Medicare and Humana patients [14].
Previous surgery on the same knee: knee arthroscopy within two years before replacement was linked to more MUA, adhesion release and revision in a 2026 matched study (conference abstract, not yet peer-reviewed in full) [16].
Stiffness in the other knee: patients whose first knee replacement needed MUA had a nearly 14-fold higher risk of needing MUA on the second knee [19].
A stiff knee before surgery: pre-operative range of motion is one of the strongest predictors of range after surgery [9, 4].
Poor pain control and delayed rehabilitation: pain stops patients moving the knee during the early window when scar is still soft [1].
Implant position or sizing problems: these cause stiffness for mechanical reasons and must be checked on X-ray [2].
Diabetes and smoking: often listed because they impair healing. The evidence that they specifically cause arthrofibrosis is mixed.

Knowing your risk lets your team plan closer follow-up and earlier physiotherapy from the first day.

Signs and symptoms

Tightness that stops improving, or gets worse, despite regular physiotherapy
The knee feels "stuck" past a certain angle
Inability to fully straighten the knee, so you walk with a slight bend
Pain or swelling that is out of proportion to your stage of recovery
Growing difficulty with stairs, low chairs, or getting in and out of a car

Many Indian patients first notice it when they cannot sit cross-legged, squat, use an Indian-style toilet, or kneel for prayer. If these feel blocked well beyond the first two to three months, tell your surgeon. Do not assume it is "normal stiffness".

How much knee bend do you actually need?

Most Western daily tasks need less than 90° to about 120° of bend. Floor-based activities common in India need much more. One study suggests 110° as a sensible rehabilitation goal for Western-style living [10].

Activity	Approximate knee flexion needed	Source
Walking on level ground	about 67°	[10]
Climbing stairs	about 83°	[10]
Descending stairs	about 90°	[10]
Rising from a standard chair	about 93°	[10]
Getting in and out of a bath	about 135°	[10]
Sitting cross-legged on the floor	about 106° to 165° (varies with technique and body build)	[12, 13]
Kneeling (including prayer)	about 127° to 141°	[13, 22]
Full squatting	about 127° to 157° (157° for heels-up squat in healthy Indian adults)	[11, 13]

These figures come from healthy people. After a knee replacement, average maximum flexion in published series is roughly 115° to 125° [24]. That is enough for chairs and stairs, but often not for deep squatting or comfortable floor sitting.

Discuss your floor-sitting, squatting and prayer needs with your surgeon before surgery. This shapes implant choice, rehabilitation targets, and how you judge whether recovery is on track.

How is arthrofibrosis diagnosed?

No single blood test or scan confirms arthrofibrosis. A biopsy is not routinely needed, and no biomarker exists yet [2]. The diagnosis rests on your recovery timeline and examination, after other causes are ruled out [2, 3].

Examination: active and passive range of motion measured with a goniometer and compared with expected milestones.
X-rays: to check implant position, alignment, sizing and loosening.
Blood tests (such as ESR and CRP) and sometimes joint aspiration: to rule out infection, a key cause of a stiff, painful knee.
CT or MRI: occasionally, to assess component rotation or soft-tissue scarring.

Normal stiffness or arthrofibrosis?

Some stiffness in the first few weeks is expected. If your bend improves week on week with physiotherapy, even slowly, that is usually normal healing.

Arthrofibrosis becomes more likely when progress plateaus or reverses despite consistent therapy, typically between 6 and 12 weeks after surgery. Range below 90° persisting beyond 12 weeks meets the research definition of stiffness [3]. Do not wait until then to ask: the best results from manipulation come within the first 12 weeks [6, 7].

Treatment: a stepwise approach

Treatment starts with the least invasive option and escalates only if motion does not improve. Physiotherapy is the most used treatment, and revision surgery is kept as a last resort [2].

1. Supervised, structured physiotherapy

Supervised physiotherapy is the first line of defence against arthrofibrosis [1]. Results depend on getting the timing, intensity and progression right for your pain level [1]. A good programme includes:

Progressive stretching for both bending and straightening
Hands-on soft-tissue and joint mobilisation by an experienced physiotherapist
Quadriceps and hamstring strengthening
Pain control that lets you work through therapy rather than guard the knee
Splinting where needed: static progressive stretch splints improved range of motion in patients with arthrofibrosis after knee replacement [17]

Continuous passive motion (CPM) machines are widely used, but a Cochrane review found their effect on range of motion is too small to be clinically worthwhile [23]. Active, supervised exercise matters more. See our guide to total knee replacement exercises.

2. Manipulation under anaesthesia (MUA)

If supervised physiotherapy is not working, MUA is usually the next step. Under regional or general anaesthesia, the surgeon carefully bends the knee to break up immature scar tissue. There is no incision.

Timing matters most. In a study of 144 manipulations, MUA within 12 weeks gained an average of 36.5° of flexion and reached 119° overall. MUA after 12 weeks gained 17° and reached 95° [6, 18]. A systematic review of 22 studies (1,488 patients) also found the best results within 12 weeks [7].

Late MUA is not useless. Another series found average gains of at least 11° even beyond three months, and sometimes beyond a year [8]. Outcomes after 26 weeks are generally less satisfactory [6].

Physiotherapy must continue straight after MUA, or the knee can stiffen again. As Dr. Naveen Kumar's clinical notes explain, the manipulation is quick, but the therapy afterwards sustains the gain.

Risks are uncommon but include bleeding into the joint, fracture around the implant, and injury to the tendons that straighten the knee [20]. Patients who need MUA also have a higher rate of later revision surgery, likely reflecting the underlying stiffness [15].

3. Arthroscopic or open release of adhesions

If MUA fails, or scar tissue is already mature, the surgeon can cut adhesions directly, using keyhole (arthroscopic) instruments or an open incision. This also allows removal of a cyclops lesion that blocks straightening. It is needed in a small minority: about 0.56% of patients within one year in a study of over 100,000 people [14]. Those patients had a higher risk of later revision, so expectations need careful discussion [14]. Our arthroscopic debridement guide explains the keyhole approach.

4. Revision knee replacement

For severe, long-standing stiffness, especially when implant position or size contributes, revising the implant may be needed [2, 20]. It is reserved as a last resort [2]. See our guide on revision total knee replacement.

Emerging treatments

Research is targeting the biology of scarring, including the TGF-beta pathway, to develop antifibrotic drugs [2]. None is yet standard care. They are likely to support, not replace, physiotherapy, MUA and surgery.

Can arthrofibrosis be prevented?

It cannot be eliminated, but these steps lower the risk:

Choose an experienced surgeon and centre, so implant sizing and alignment are right
Start moving early, often the same day or day after surgery, when your team clears you
Commit to supervised physiotherapy in the first six to twelve weeks
Keep pain well controlled so you can move the knee fully
Discuss floor sitting, squatting and kneeling goals before surgery
Manage weight, blood sugar and smoking before surgery to support healing
If you have had stiffness or MUA in your other knee, tell your surgeon: your risk is higher [19]

Still deciding on surgery? Read our pages on knee arthritis and when to consider surgery, and types of total knee replacement.

When should you contact your surgeon?

Contact your surgeon promptly if:

Your bend or straightening has not improved for one to two weeks despite regular physiotherapy
Pain, warmth, redness or swelling is increasing (this needs checking for infection)
The knee feels progressively tighter rather than looser
By six weeks you still struggle to rise from a chair or climb one flight of stairs

Early action keeps every option open, including the most effective window for MUA within 12 weeks [6, 7].

Conclusion

Arthrofibrosis affects roughly 4% of knee replacements and is a well-studied complication with a clear treatment pathway [3]. The single most important factor you can influence is time: recognise a plateau early, and act within the first 12 weeks.

At Sports Orthopedics Institute, Dr. Naveen Kumar L.V. and team plan surgery and rehabilitation around Indian lifestyle needs such as floor sitting, squatting and kneeling, not just Western benchmarks. If your recovery does not feel on track, book a consultation for a full assessment.

Frequently asked questions

Mark up this section with FAQPage schema.

What is arthrofibrosis after total knee replacement? It is excessive scar tissue in and around the replaced knee that causes stiffness, pain and limited bending or straightening, beyond what normal healing produces [2].

How common is arthrofibrosis after knee replacement? About 4% of patients develop this kind of stiffness, according to a 2019 meta-analysis. Individual studies range from about 1% to over 10% because they define stiffness differently [3].

How do I know if my stiffness is normal or arthrofibrosis? If your bend improves week by week, that is usually normal healing. Be concerned if progress stalls or reverses despite physiotherapy, usually between 6 and 12 weeks, or if pain and swelling stay high [3].

What is manipulation under anaesthesia (MUA), and when is it best done? MUA is a procedure without incisions in which the surgeon bends the knee under anaesthesia to break up scar tissue. Results are best within 12 weeks of surgery [6, 7].

Can MUA still help after three months? Sometimes. Studies report average gains of at least 11° even beyond three months, though results are generally less satisfactory after six months [6, 8].

Can arthrofibrosis be treated without surgery? Yes, often. Supervised physiotherapy is the first-line treatment, and splinting can add benefit [1, 17]. MUA involves no incision and helps most patients when physiotherapy alone is not enough [7].

Does a CPM machine prevent stiffness? The evidence says its benefit is too small to matter clinically. Active, supervised exercise is more important [23].

What happens if arthrofibrosis is left untreated? Scar tissue matures and tightens over time, making MUA less effective and surgery more likely [6, 18].

Can I sit cross-legged or squat after knee replacement? It depends on how much bend you regain. Squatting and floor sitting typically need 106° to over 150°, while average bend after knee replacement is about 115° to 125° [11, 13, 24]. Discuss your goals with your surgeon before surgery.

Is arthrofibrosis caused by a surgical mistake? Usually not. It mainly reflects an individual's exaggerated healing response [1, 2]. Implant position or sizing can occasionally contribute, which is why X-rays are part of the assessment.

Which doctor should I see for a stiff knee after replacement? See an orthopaedic surgeon experienced in knee replacement and revision surgery, ideally your operating surgeon or a specialist joint-replacement centre.

References

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Ramos MS, Pasqualini I, Surace PA, et al. Arthrofibrosis after total knee arthroplasty: a critical analysis review. JBJS Rev. 2023;11(12):e23.00140.
Tibbo ME, Limberg AK, Salib CG, et al. Acquired idiopathic stiffness after total knee arthroplasty: a systematic review and meta-analysis. J Bone Joint Surg Am. 2019;101(14):1320–1330.
Gandhi R, de Beer J, Leone J, et al. Predictive risk factors for stiff knees in total knee arthroplasty. J Arthroplasty. 2006.
Owen AR, Tibbo ME, van Wijnen AJ, et al. Acquired idiopathic stiffness after contemporary total knee arthroplasty: incidence, risk factors, and results over 25 years. J Arthroplasty. 2021;36(8):2980–2985.
Issa K, Banerjee S, Kester MA, et al. The effect of timing of manipulation under anesthesia to improve range of motion and functional outcomes following total knee arthroplasty. J Bone Joint Surg Am. 2014.
Efficacy of manipulation under anesthesia for stiffness following total knee arthroplasty: a systematic review. J Arthroplasty. 2018;33(5). PMID 29290334.
Colacchio ND, Abela D, Bono JV, et al. Efficacy of manipulation under anesthesia beyond three months following total knee arthroplasty. Arthroplasty Today. 2019;5(4):515–520.
Rowe PJ, Myles CM, Nutton R. The effect of total knee arthroplasty on joint movement during functional activities and joint range of motion with particular regard to higher flexion users. J Orthop Surg. 2005;13(2):131–138.
Rowe PJ, Myles CM, Walker C, Nutton R. Knee joint kinematics in gait and other functional activities measured using flexible electrogoniometry: how much knee motion is sufficient for normal daily life? Gait Posture. 2000;12(2):143–155.
Hemmerich A, Brown H, Smith S, et al. Hip, knee, and ankle kinematics of high range of motion activities of daily living. J Orthop Res. 2006;24(4):770–781.
Mulholland SJ, Wyss UP. Activities of daily living in non-Western cultures: range of motion requirements for hip and knee joint implants. Int J Rehabil Res. 2001.
Knee range of motion required for daily activities in a healthy Southeast Asian urban population. Front Rehabil Sci. 2024. doi:10.3389/fresc.2024.1446389.
Lysis of adhesion for arthrofibrosis after total knee arthroplasty is associated with increased risk of subsequent revision total knee arthroplasty. J Arthroplasty. 2021;36(1):339–344.
Werner BC, et al. Manipulation under anesthesia after total knee arthroplasty is associated with an increased incidence of subsequent revision surgery. J Arthroplasty. 2015;30:72.
Mirahmadi A, Lawand JJ, Momenzadeh K, et al. Scoping out the risks: arthrofibrosis and failure after total knee arthroplasty in patients with prior arthroscopy. AAOS Annual Meeting 2026 (abstract).
Bonutti PM, et al. Static progressive stretch improves range of motion in arthrofibrosis following total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2010;18:194.
Mamarelis G, Sunil-Kumar KH, Khanduja V. Timing of manipulation under anaesthesia for stiffness after total knee arthroplasty. Ann Transl Med. 2015.
Chandi SK, Hawes JD, Kolin DA, et al. Nearly 14-fold increased risk of manipulation under anesthesia after total knee arthroplasty when previous contralateral total knee arthroplasty required manipulation under anesthesia. J Arthroplasty. 2024;39(9S2):S449–S453.
Haffar A, Goh GS, Fillingham YA, et al. Treatment of arthrofibrosis and stiffness after total knee arthroplasty: an updated review of the literature. Int Orthop. 2022;46(6):1253–1279.
Further reading: Akhtar M, Razick D, Seibel A, et al. Outcomes of early versus delayed manipulation under anesthesia for stiffness following total knee arthroplasty: a systematic review and meta-analysis. J Arthroplasty. 2024;39(11):2872–2879.
Acker SM, Cockburn RA, Krevolin J, et al. Knee kinematics of high-flexion activities of daily living performed by male Muslims in the Middle East. J Arthroplasty. 2011.
Harvey LA, Brosseau L, Herbert RD. Continuous passive motion following total knee arthroplasty in people with arthritis. Cochrane Database Syst Rev. 2014;(2):CD004260.
Lee TQ. Biomechanics of hyperflexion and kneeling before and after total knee arthroplasty. Clin Orthop Surg. 2014;6(2):117.

This article is for general education and does not replace an in-person consultation with an orthopaedic specialist. Every knee recovery needs individual clinical assessment before treatment decisions are made.

Stiff knee after TKR? Evidence-based guide to arthrofibrosis, MUA timing and regaining the bend needed for squatting and floor sitting.