High-yield overview

Post-surgical stiffness | TKA & ACL | Cyclops lesion | MUA

ScarExcess intra-articular collagen

TGF-betaKey fibrotic pathway

MUABest within 6-12 weeks

CyclopsFibrous nodule blocks extension

PATTERNS

Global (diffuse)

PatternPan-capsular scarring, loses flexion and extension

TreatmentTherapy then MUA or arthroscopic release

Localised - Cyclops

PatternAnterior nodule on/near ACL graft, blocks extension

TreatmentArthroscopic excision

Infrapatellar contracture

PatternPatella baja, fat pad and tendon scarring

TreatmentDifficult - aggressive therapy, release

Secondary (treatable cause)

PatternMalposition/oversize implant, infection, CRPS

TreatmentTreat the underlying cause first

Critical Must-Knows

Arthrofibrosis is a diagnosis of exclusion - rule out infection, component malposition/oversizing, CRPS and poor rehab first
Driven by aberrant myofibroblasts depositing type I collagen in a proinflammatory joint; TGF-beta is the best-established pathway
Manipulation under anaesthesia (MUA) works best early - typically within 6-12 weeks of the index surgery, before scar matures
Cyclops syndrome = fibrous nodule anterior to the ACL graft causing a painful, springy loss of terminal extension
Prevention beats cure - good pain control, early range of motion, correct surgical technique and avoiding graft malposition

Clinical Pearls

"
MUA after ~3 months is far less effective and risks fracture/extensor disruption
"
No biopsy and no biomarker confirms arthrofibrosis - it is clinical plus exclusion
"
Cyclops = LOSS OF EXTENSION; global arthrofibrosis = loss of flexion AND extension
"
Patella baja on lateral film suggests infrapatellar contracture - a poor-prognosis pattern

Clinical Imaging

Imaging Gallery

Four-panel MRI and arthroscopic figure of a cyclops lesion after ACL reconstruction — Four panels (A-D). Panels A and B are sagittal MRI images of the knee after ACL reconstruction: a focal nodule (arrowheads/arrows) sits at the anterior aspect of the graft. Panel C is a further sagittal MRI; panel D is an arthroscopic view of the intercondylar notch showing the corresponding fibrous nodule. This is the classic cyclops lesion - localised anterior arthrofibrosis that blocks terminal extension.Credit: Dhanda S et al. via Indian J Radiol Imaging via Open-i (NIH) (Open Access (CC BY))

Single sagittal MRI of a knee after ACL reconstruction showing an anterior fat pad nodule — Single sagittal proton-density MRI of a knee after ACL reconstruction. The tibial tunnel and interference screw are visible, with a hypointense soft-tissue mass anteriorly in the infrapatellar fat pad region - a cyclops lesion sitting in front of the graft.Credit: Draghi F et al. via Insights Imaging via Open-i (NIH) (Open Access (CC BY))

Three-panel sagittal MRI of a cyclops lesion anterior to an ACL graft — Three sagittal MRI panels (A-C) of the same knee. In A and B a hypointense-to-isointense nodule (arrowhead/arrow) lies immediately anterior to the ACL graft; panel C shows the anterior intercondylar region. The nodule's anterior position is what causes mechanical impingement and loss of full extension.Credit: Dhanda S et al. via Indian J Radiol Imaging via Open-i (NIH) (Open Access (CC BY))

Critical Arthrofibrosis Concepts

It Is Exclusion

Never call stiffness 'arthrofibrosis' until you have excluded treatable causes. Infection, component malposition or oversizing, instability, CRPS and inadequate rehabilitation all mimic it and need different treatment.

Timing Is Everything

Act on stiffness early. Manipulation under anaesthesia is most effective within roughly 6-12 weeks while the scar is immature. After 3 months it is less effective and the risk of periprosthetic fracture or extensor rupture rises.

Cyclops Pattern

Loss of EXTENSION after ACL reconstruction. A firm, sometimes audible/palpable block at terminal extension suggests a cyclops nodule anterior to the graft. Confirm on MRI; treat with arthroscopic excision.

Biology

Myofibroblast-driven type I collagen deposition in a proinflammatory joint, with TGF-beta as the best-established signalling pathway. No biomarker or biopsy confirms the diagnosis.

Arthrofibrosis - Quick Decision Guide

Pattern	Setting	Motion Lost	First-line Treatment
Diffuse arthrofibrosis	After TKA	Flexion and extension	Therapy; MUA if early; release if late
Cyclops lesion	After ACL reconstruction	Terminal extension	Arthroscopic excision
Infrapatellar contracture	After major knee surgery	Flexion, patella baja	Aggressive therapy, release (poor prognosis)
Secondary stiffness	Any (correctable cause)	Variable	Treat the cause (infection/malposition)

Mnemonic

STIFFExclude Before Diagnosing

S	Sepsis Exclude infection (bloods, aspirate)
T	Technical Component malposition/oversizing, overstuffing
I	Instability Mimics and worsens stiffness
F	Failed rehab Pain control and physiotherapy inadequate
F	Funny pain (CRPS) Complex regional pain syndrome

S	Sepsis Exclude infection (bloods, aspirate)	F	Failed rehab Pain control and physiotherapy inadequate
T	Technical Component malposition/oversizing, overstuffing	F	Funny pain (CRPS) Complex regional pain syndrome
I	Instability Mimics and worsens stiffness

Hook:A STIFF knee needs every other cause excluded before you blame scar.

Mnemonic

EYESCyclops Lesion Features

E	Extension lost Springy, painful block to full extension
Y	Yields a clunk Audible/palpable clunk near terminal extension
E	Eccentric nodule Fibrous nodule anterior to the ACL graft
S	Scope to excise Arthroscopic resection is curative

E	Extension lost Springy, painful block to full extension	E	Eccentric nodule Fibrous nodule anterior to the ACL graft
Y	Yields a clunk Audible/palpable clunk near terminal extension	S	Scope to excise Arthroscopic resection is curative

Hook:The CYCLOPS has one EYE - and it blocks the knee from straightening.

Mnemonic

TIPSDrivers of Fibrosis

T	TGF-beta Best-established profibrotic pathway
I	Inflammation Proinflammatory joint environment
P	Proliferation Aberrant myofibroblast proliferation
S	Scar collagen Excess type I collagen deposition

T	TGF-beta Best-established profibrotic pathway	P	Proliferation Aberrant myofibroblast proliferation
I	Inflammation Proinflammatory joint environment	S	Scar collagen Excess type I collagen deposition

Hook:TIPS for why scar forms - TGF-beta, Inflammation, Proliferation, Scar collagen.

Overview and Epidemiology

Arthrofibrosis is the formation of excessive scar tissue within and around the knee that mechanically restricts movement, causing stiffness, pain and functional loss. According to PubMed, a critical analysis review describes it after total knee arthroplasty (TKA) as new formation of excessive scar tissue producing limited range of motion, pain and functional deficits (Ramos et al., JBJS Reviews 2023; DOI).

It is best thought of as a spectrum:

Diffuse (global) arthrofibrosis - pan-capsular scarring after arthroplasty or major trauma, losing both flexion and extension.
Localised arthrofibrosis - most importantly the cyclops lesion after ACL reconstruction, a discrete anterior nodule that blocks extension.
Infrapatellar contracture syndrome - dense scarring of the fat pad and patellar tendon, often with patella baja.

Why It Matters

A stiff knee is one of the most disabling outcomes after otherwise technically sound surgery. Patients cannot manage stairs, get out of chairs or walk normally, and revision for stiffness alone is notoriously unsatisfying.

Definition First

Arthrofibrosis = pathological scar causing restricted motion AFTER excluding other causes of stiffness. It is a clinical diagnosis of exclusion, not a radiological or histological one.

Frequency

After TKA, clinically significant stiffness requiring manipulation occurs in roughly 2-5% of knees in modern series.
According to PubMed, a multimodal pain-management cohort reported manipulation rates falling from 4.75% to 2.24% with a multimodal protocol (Lavernia et al., J Arthroplasty 2008; DOI).
After ACL reconstruction, cyclops lesions are seen in up to a quarter of second-look arthroscopies, but symptomatic cyclops syndrome is far less common - around 3-11% depending on the series.

Pathophysiology

Arthrofibrosis is fundamentally a dysregulated wound-healing response. Normal healing resolves; arthrofibrosis is healing that fails to switch off.

The Fibrotic Cascade

Surgical/injury trigger - tissue damage and bleeding create a proinflammatory environment.
Inflammation - cytokines recruit fibroblasts and activate them.
Myofibroblast transformation - fibroblasts differentiate into contractile myofibroblasts.
Excess matrix - myofibroblasts deposit large amounts of type I collagen.
Contraction and maturation - the scar contracts and cross-links, mechanically tethering the joint.

According to PubMed, the pathophysiology is multifactorial and centres on aberrant activation and proliferation of myofibroblasts that primarily deposit type I collagen in response to a proinflammatory environment, with transforming growth factor-beta (TGF-beta) signalling the best-established pathway (Ramos et al., JBJS Reviews 2023; DOI).

Key Pathway

TGF-beta drives the myofibroblast. It is the central, best-established profibrotic signal in knee arthrofibrosis. There is currently no validated biomarker and no diagnostic biopsy.

The Cyclops Lesion

The cyclops lesion is a localised variant. According to PubMed, second-look studies describe it as a fibroproliferative nodule arising from tibial-tunnel drilling debris, ACL stump remnants or broken graft fibres, sometimes from repeated graft impingement on the notch in terminal extension (Delince et al., Arthroscopy 1998; DOI). Its bluish, vascular arthroscopic appearance with surrounding reddish tissue ("eyes") gives it the name.

Contributory Factors

Surgical - graft malposition or oversizing, notch impingement, retained drilling debris, overstuffed patellofemoral joint, haematoma.
Patient - tendency to aggressive scarring, prior surgery, diabetes, lower pain threshold.
Rehabilitation - inadequate pain control and delayed mobilisation allow scar to mature unopposed.

Classification

There is no single universally accepted classification. The most useful exam frameworks are by pattern and by whether a treatable cause is present.

By Pattern

Patterns of Knee Arthrofibrosis

Pattern	Key Feature	Motion Affected	Prognosis
Diffuse / global	Pan-capsular scar	Flexion + extension	Variable
Localised - cyclops	Anterior graft nodule	Extension	Good after excision
Infrapatellar contracture	Patella baja, fat pad scar	Flexion mainly	Poor
Posterior capsular	Posterior contracture	Extension	Variable

Primary vs Secondary

Primary (idiopathic) arthrofibrosis - an exaggerated fibrotic response with no identifiable mechanical cause.
Secondary arthrofibrosis - stiffness driven by a correctable problem (malpositioned/oversized component, instability, infection, CRPS, poor rehab). Identifying secondary causes is the single most important step because they change management completely.

Classification Principle

Examiners want to hear you separate primary scar from secondary stiffness. Always say: "First I would exclude a treatable cause before labelling this primary arthrofibrosis."

Clinical Presentation

History

Persistent stiffness despite a technically satisfactory operation and appropriate rehabilitation.
Pain - often disproportionate, worse at the extremes of motion.
Functional loss - difficulty with stairs, sit-to-stand, kneeling.
Cyclops syndrome - after ACL reconstruction, a painful loss of full extension, sometimes with an audible or palpable clunk near terminal extension.

Examination

Range of Motion

Document active and passive flexion and extension, and compare to the other side. Global arthrofibrosis loses both; cyclops loses terminal extension with a springy, sometimes clunking end-feel.

Effusion and Warmth

A warm, hot or persistently swollen knee should raise suspicion of infection or active inflammation rather than mature scar.

Stability

Assess ligamentous stability - instability mimics and aggravates stiffness, and an unstable knee will not respond to manipulation.

Patella

Check patellar height and tracking. Patella baja suggests infrapatellar contracture, a poor-prognosis pattern.

Red Flags - Do Not Manipulate Yet

A hot, swollen, painful knee with raised inflammatory markers may be infected. Never manipulate or release a knee until infection has been excluded - manipulating a septic joint is dangerous and worsens outcomes.

Investigations

Investigations serve mainly to exclude other causes - there is no test that proves arthrofibrosis.

Bloods

CRP, ESR, white cell count - screen for periprosthetic or septic joint infection.
Consider joint aspiration for cell count, differential and culture if infection is suspected.

Imaging

Plain films assess component position and size, alignment, patellar height (baja) and loosening. Overstuffing of the patellofemoral joint and malrotation are key technical mimics to identify.

According to PubMed, in the TKA setting the review is explicit that imaging helps rule out specific causes of stiffness, biopsy is not indicated and no biomarkers of arthrofibrosis exist (Ramos et al., JBJS Reviews 2023; DOI).

Cyclops on MRI

A focal nodule anterior to the ACL graft that is low-to-intermediate signal, in a patient with loss of extension, is the radiological signature of a symptomatic cyclops lesion.

Management

Management is staged and escalating: optimise rehabilitation, then manipulation, then surgical release - and always treat any secondary cause first.

Step 1 - Prevention and Rehabilitation

Multimodal analgesia and early aggressive physiotherapy to keep the knee moving while scar is immature.
Address swelling, encourage extension as well as flexion, and set range-of-motion milestones.

According to PubMed, a multimodal pain-management protocol reduced the manipulation rate after TKA from 4.75% to 2.24%, supporting good analgesia as primary prevention (Lavernia et al., J Arthroplasty 2008; DOI). Adjuncts at the index operation have also been explored - according to PubMed, autologous platelet gel and fibrin sealant improved early range of motion and reduced the incidence of arthrofibrosis and forced manipulation in one controlled study (Everts et al., Knee Surg Sports Traumatol Arthrosc 2007; DOI).

Step 2 - Manipulation Under Anaesthesia (MUA)

Indicated for diffuse stiffness that fails to progress with therapy, ideally early (within ~6-12 weeks).
Performed gently under full muscle relaxation with the hand close to the joint to minimise lever-arm forces.

MUA Timing and Risk

MUA is most effective early while scar is immature. Performed late (after ~3 months) it is less effective and carries a real risk of periprosthetic fracture, patellar tendon avulsion or wound dehiscence. Manipulate gently, with the hand high on the tibia.

Step 3 - Arthroscopic Management

Cyclops lesion - arthroscopic excision of the nodule (with notchplasty if there is impingement) reliably restores extension.
Diffuse arthrofibrosis - arthroscopic lysis of adhesions and selective release, often combined with a gentle manipulation at the same sitting.

Step 4 - Open Surgery / Revision

Open release / quadricepsplasty for severe or recurrent diffuse scar resistant to arthroscopic treatment.
Revision arthroplasty is reserved for stiffness due to component malposition or oversizing - and according to PubMed is typically a last resort when scar alone is the problem (Ramos et al., JBJS Reviews 2023; DOI).

Treat the Cause

If stiffness is due to a malpositioned or oversized component, no amount of manipulation or release will help - the implant must be revised. Diagnose this before operating for "arthrofibrosis".

Reassurance on Arthroscopy After TKA

According to PubMed, knee arthroscopy after ipsilateral TKA (commonly for patellar clunk/synovial hyperplasia or arthrofibrosis) was not associated with an elevated risk of periprosthetic joint infection in a registry-matched study, so arthroscopic treatment of post-TKA stiffness is a reasonable option (Wahlig et al., J Arthroplasty 2024; DOI).

Complications

Recurrence

Scar can re-form, especially after late or repeated intervention. Aggressive post-procedure physiotherapy is essential to hold the gains made.

MUA Injuries

Forceful or late manipulation can cause periprosthetic fracture, patellar tendon avulsion, wound dehiscence and haemarthrosis.

Persistent Pain / CRPS

Some patients have ongoing pain out of proportion; complex regional pain syndrome both mimics and complicates arthrofibrosis.

Functional Disability

A stiff knee impairs stairs, transfers and gait, and patient satisfaction after revision for stiffness alone is often modest.

Evidence and Key Studies

Arthrofibrosis After TKA: Critical Analysis Review

Level 5 (Review)

Ramos MS et al. • JBJS Reviews (2023)

Key Findings:

Arthrofibrosis is a clinical diagnosis of exclusion
No biopsy and no biomarker confirms it
Myofibroblasts deposit type I collagen; TGF-beta is the key pathway
Revision arthroplasty is reserved as a last resort

Clinical Implication: Exclude treatable causes, escalate from therapy to MUA to release, and reserve revision for component-related stiffness.

Verify on PubMed (PMID 38079496)

Multimodal Pain Management and Arthrofibrosis

Level 3

Lavernia C et al. • J Arthroplasty (2008)

Key Findings:

Manipulation rate fell from 4.75% to 2.24% with multimodal analgesia
Better early pain control allows earlier mobilisation
Supports prevention over later intervention
Recommends multimodal protocols for TKA

Clinical Implication: Good multimodal analgesia and early motion are primary prevention against arthrofibrosis.

Verify on PubMed (PMID 18722306)

Risk Factors for Manipulation After TKA

Level 3

Pfefferle KJ et al. • J Arthroplasty (2014)

Key Findings:

Overall MUA rate after TKA was 1.51%
Younger age (under 60) is a strong risk factor (RR 3.46)
Obesity and nicotine dependence increase risk
Diabetes and depression were not significant risk factors

Clinical Implication: Identify high-risk patients (younger, obese, smokers) preoperatively to plan intensive rehabilitation and early follow-up.

Verify on PubMed (PMID 24927868)

Multifactorial Etiopathogenesis of the Cyclops Lesion

Level 4

Delince P et al. • Arthroscopy (1998)

Key Findings:

Cyclops is a fibroproliferative nodule, multifactorial in origin
Drilling debris and stump remnants are key sources
Graft malposition causing notch impingement contributes
Arthroscopic resection (plus notchplasty) restores extension

Clinical Implication: Meticulous debris removal and correct graft placement at index ACL surgery help prevent the cyclops lesion.

Verify on PubMed (PMID 9848601)

Cyclops Syndrome After Double-Bundle ACL Reconstruction

Level 4

Sonnery-Cottet B et al. • Arthroscopy (2010)

Key Findings:

Symptomatic cyclops syndrome occurred in 3.61%
More common with quadriceps than hamstring graft
Mean extension loss ~6 degrees with early quad dysfunction
Arthroscopic debridement restored motion in most

Clinical Implication: Suspect cyclops syndrome when extension is lost early after ACL reconstruction; arthroscopic excision is reliably effective.

Verify on PubMed (PMID 20875722)

Intercondylar Notch Size and Cyclops Formation

Level 4

Fujii M et al. • Knee Surg Sports Traumatol Arthrosc (2014)

Key Findings:

Cyclops lesions in 27.3% but symptomatic in only 10.9%
Smaller intercondylar notch predisposes to cyclops formation
Higher tunnel-to-notch ratio in the cyclops group
Most cyclops lesions are asymptomatic incidental findings

Clinical Implication: A narrow notch is a risk factor; many cyclops lesions are asymptomatic, so treat the patient (extension loss), not the MRI.

Verify on PubMed (PMID 24549261)

Exam Viva Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

Scenario 1: Stiff Knee After TKA

CLINICAL PROMPT

"A 58-year-old woman is 10 weeks after a primary TKA. She has poor range of motion (5 to 75 degrees) despite physiotherapy and is in pain. How do you assess and manage her?"

PRACTICAL APPROACH

My priority is to determine whether this is true arthrofibrosis or stiffness from a treatable cause - this is a diagnosis of exclusion. 1. History and examination: confirm range of motion (active and passive) versus the other side, look for effusion, warmth, instability and patellar height. 2. Exclude infection: CRP, ESR, white cell count, and aspirate if any suspicion. 3. Exclude technical causes: radiographs and, if needed, CT for component position, rotation and sizing; exclude overstuffing and malrotation. 4. If no treatable cause and she is failing to progress at 10 weeks, this is the window for manipulation under anaesthesia - it works best within roughly 6 to 12 weeks before scar matures. 5. MUA is done gently under full relaxation with the hand high on the tibia to avoid periprosthetic fracture or extensor disruption, followed immediately by intensive physiotherapy. If she presented much later, MUA is less effective and I would consider arthroscopic lysis of adhesions.

KEY CLINICAL POINTS

Arthrofibrosis is a diagnosis of exclusion

Exclude infection and component malposition first

MUA is most effective early (within 6-12 weeks)

Manipulate gently to avoid fracture/extensor injury

COMMON PITFALLS

Manipulating before excluding infection

Missing a malpositioned or oversized component

Manipulating forcefully or too late

FURTHER QUESTIONS

"What are the risks of MUA?"

"What would change if her CRP was raised?"

"When would you choose arthroscopy over MUA?"

CLINICAL SCENARIOStandard

Scenario 2: Loss of Extension After ACL Reconstruction

CLINICAL PROMPT

"A 24-year-old man is 4 months after hamstring ACL reconstruction. He cannot fully straighten the knee, has anterior pain and a palpable clunk near terminal extension. What is your diagnosis and management?"

PRACTICAL APPROACH

The loss of terminal extension with anterior pain and a clunk strongly suggests a cyclops lesion - a fibrous nodule anterior to the graft causing mechanical impingement. 1. Examination: confirm a fixed or springy block to full extension and compare with the other side using prone heel-height. 2. Imaging: MRI to confirm a focal nodule anterior to the graft and to assess graft position and notch impingement. 3. Rehabilitation: first optimise extension with focused physiotherapy. 4. If a discrete symptomatic cyclops lesion is confirmed and extension loss persists, the treatment is arthroscopic excision of the nodule, with notchplasty if there is impingement. Outcomes are reliably good - most patients regain full extension. I would counsel him that many cyclops lesions seen on MRI are asymptomatic, so I am treating his extension loss, not just an imaging finding.

KEY CLINICAL POINTS

Cyclops syndrome = loss of EXTENSION after ACL reconstruction

Confirm a focal anterior nodule on MRI

Arthroscopic excision is reliably effective

Treat the patient, not an incidental MRI nodule

COMMON PITFALLS

Confusing it with graft failure (that causes instability, not stiffness)

Excising an asymptomatic incidental cyclops

Ignoring graft malposition contributing to impingement

FURTHER QUESTIONS

"Why does a cyclops form?"

"What is the role of notch size?"

"How would you prevent it at the index surgery?"

CLINICAL SCENARIOChallenging

Scenario 3: Recurrent Stiffness and Patella Baja

CLINICAL PROMPT

"A 45-year-old man has had two prior knee operations and now has severe stiffness with patella baja on the lateral radiograph. Manipulation has already failed once. How do you proceed?"

PRACTICAL APPROACH

The combination of multiple prior surgeries, patella baja and failed manipulation suggests infrapatellar contracture syndrome - a dense, poor-prognosis pattern of arthrofibrosis. 1. Re-exclude treatable causes: infection screen and assessment of any implant for malposition. 2. Set realistic expectations: this pattern responds poorly and recurrence is common. 3. Given failed MUA, repeated forceful manipulation is unwise - I would consider arthroscopic lysis of adhesions, and if scar is extensive, open release or quadricepsplasty to address the contracted extensor mechanism and capsule. 4. The key to any gain is an aggressive, supervised rehabilitation programme immediately afterwards to prevent re-scarring. 5. If component malposition or oversizing is the driver, release alone will fail and revision is required. I would counsel him carefully that outcomes for stiffness surgery in this setting are modest.

KEY CLINICAL POINTS

Patella baja signals infrapatellar contracture - poor prognosis

Re-exclude infection and implant problems

Avoid repeat forceful MUA; consider open release/quadricepsplasty

Aggressive rehab and realistic counselling are essential

COMMON PITFALLS

Repeating forceful manipulation after a failure

Promising a good outcome for infrapatellar contracture

Missing component malposition needing revision

FURTHER QUESTIONS

"What is patella baja and why does it matter?"

"When is revision arthroplasty justified?"

"What is the role of quadricepsplasty?"

MCQ Practice Points

Diagnosis

Q: How is arthrofibrosis diagnosed? A: Clinically and by exclusion. There is no confirmatory biopsy and no biomarker - rule out infection, malposition, instability and CRPS first.

Key Pathway

Q: What is the best-established profibrotic pathway? A: TGF-beta signalling, driving myofibroblast activation and type I collagen deposition.

MUA Timing

Q: When is manipulation under anaesthesia most effective after TKA? A: Early - within roughly 6 to 12 weeks, before scar matures. Late MUA is less effective and riskier.

Cyclops

Q: What motion does a cyclops lesion typically block? A: Terminal extension. It is a fibrous nodule anterior to the ACL graft, treated by arthroscopic excision.

Risk Factors

Q: Which patients are at higher risk of needing MUA after TKA? A: Younger (under 60), obese and smokers. Younger age is a particularly strong independent risk factor.

Guidelines, Registries & Global Practice

Global Epidemiology

Clinically significant stiffness needing manipulation after TKA occurs in roughly 1.5-5% of knees worldwide; younger, obese and smoking patients are over-represented.
Cyclops lesions appear in up to ~27% of second-look arthroscopies after ACL reconstruction, but symptomatic cyclops syndrome affects only ~3-11%.
A narrow intercondylar notch and graft malposition are recognised anatomical/technical risk factors for cyclops formation.

Side-by-Side Guidance

How Major Bodies Frame Post-Surgical Knee Stiffness

Body	Stance	Emphasis
AAOS (US)	Prevention and staged escalation	Early ROM, multimodal analgesia, MUA before scar matures
BOA / BOAST (UK)	Optimise rehab pathways	Pain control and physiotherapy to prevent stiffness after TKA/ACL
ESSKA (Europe)	ACL focus	Correct graft placement and debris removal to prevent cyclops; arthroscopic excision when symptomatic
General principle (global)	Exclude treatable cause first	Never label stiffness arthrofibrosis until infection/malposition excluded

Registry and Outcome Data

Arthroplasty registries (NJR, AJRR, AOANJRR) capture manipulation and reoperation for stiffness as quality indicators, consistently showing higher rates in younger TKA recipients.
Registry and cohort data confirm stiffness is a leading non-infective reason for early reoperation after TKA.

High- vs Limited-Resource Practice

Well-Resourced Settings

Multimodal analgesia, rotational CT, MRI for cyclops, and arthroscopic lysis/excision are routinely available, enabling early diagnosis and staged, joint-preserving treatment.

Limited-Resource Settings

Where MRI and arthroscopy are scarce, diagnosis is clinical and treatment leans on physiotherapy and manipulation. Late presentation with mature scar worsens outcomes, underscoring the value of prevention through good early rehabilitation.

KNEE ARTHROFIBROSIS

Clinical summary

Key Concepts

•Pathological scar restricting knee motion
•Diagnosis of exclusion - no biopsy, no biomarker
•Myofibroblast + type I collagen; TGF-beta key pathway
•Spectrum: diffuse (TKA) to localised (cyclops)

Exclude First

•Infection (CRP/ESR/aspirate)
•Component malposition or oversizing
•Instability
•CRPS and inadequate rehabilitation

Cyclops Lesion

•After ACL reconstruction
•Loss of terminal EXTENSION + clunk
•Fibrous nodule anterior to graft on MRI
•Arthroscopic excision (+ notchplasty)

Management Ladder

•Prevention: analgesia + early ROM
•MUA: best within 6-12 weeks
•Arthroscopic lysis of adhesions
•Open release / revision (last resort)

Risk Factors

•Younger age (under 60) - strong
•Obesity, smoking
•Multiple prior surgeries
•Narrow notch (cyclops)

Pattern

Setting

Motion Lost

First-line Treatment

Diffuse arthrofibrosis

After TKA

Flexion and extension

Therapy; MUA if early; release if late

Cyclops lesion

After ACL reconstruction

Terminal extension

Arthroscopic excision

Infrapatellar contracture

After major knee surgery

Flexion, patella baja

Aggressive therapy, release (poor prognosis)

Secondary stiffness

Any (correctable cause)

Variable

Treat the cause (infection/malposition)

Pattern

Key Feature

Motion Affected

Prognosis

Diffuse / global

Pan-capsular scar

Flexion + extension

Variable

Localised - cyclops

Anterior graft nodule

Extension

Good after excision

Infrapatellar contracture

Patella baja, fat pad scar

Flexion mainly

Poor

Posterior capsular

Posterior contracture

Extension

Variable

Management is staged and escalating: optimise rehabilitation, then manipulation, then surgical release - and always treat any secondary cause first.

Step 1 - Prevention and Rehabilitation

Multimodal analgesia and early aggressive physiotherapy to keep the knee moving while scar is immature.
Address swelling, encourage extension as well as flexion, and set range-of-motion milestones.

Step 2 - Manipulation Under Anaesthesia (MUA)

Indicated for diffuse stiffness that fails to progress with therapy, ideally early (within ~6-12 weeks).
Performed gently under full muscle relaxation with the hand close to the joint to minimise lever-arm forces.

MUA Timing and Risk

Step 3 - Arthroscopic Management

Cyclops lesion - arthroscopic excision of the nodule (with notchplasty if there is impingement) reliably restores extension.
Diffuse arthrofibrosis - arthroscopic lysis of adhesions and selective release, often combined with a gentle manipulation at the same sitting.

Step 4 - Open Surgery / Revision

Open release / quadricepsplasty for severe or recurrent diffuse scar resistant to arthroscopic treatment.
Revision arthroplasty is reserved for stiffness due to component malposition or oversizing - and according to PubMed is typically a last resort when scar alone is the problem (Ramos et al., JBJS Reviews 2023; DOI).

Treat the Cause

If stiffness is due to a malpositioned or oversized component, no amount of manipulation or release will help - the implant must be revised. Diagnose this before operating for "arthrofibrosis".

Reassurance on Arthroscopy After TKA

Body

Stance

Emphasis

AAOS (US)

Prevention and staged escalation

Early ROM, multimodal analgesia, MUA before scar matures

BOA / BOAST (UK)

Optimise rehab pathways

Pain control and physiotherapy to prevent stiffness after TKA/ACL

ESSKA (Europe)

ACL focus

Correct graft placement and debris removal to prevent cyclops; arthroscopic excision when symptomatic

General principle (global)

Exclude treatable cause first

Never label stiffness arthrofibrosis until infection/malposition excluded