- Mucoid ACL degeneration (MDACL) is a common incidental MRI finding where the ACL appears thickened and ill-defined with mucinous material separating its longitudinal fibers. It is often associated with ACL ganglions and subchondral bone cysts. - While the correlation between MDACL, ganglions, and bone cysts is still poorly understood, it seems to represent progressive structural ACL degeneration. MDACL may be related to early osteoarthritis and synovial inflammation exacerbated by repetitive knee trauma. - Patients typically present with medial or posterior knee pain out of proportion to physical findings, and MRIs show the characteristic MDACL appearance along with secondary osteoarthritic changes. Ar

1. Mucoid ACL Degeneration, ACL
Ganglions & Subchondral Cysts
(an update from ACL SG Åre 2016)
Vladimir Bobić, MD, FRCSEd
Consultant Orthopaedic Knee Surgeon
Chester Knee Clinic, Chester, UK
ACL Study Group 2023
St Kits, 29th January to 2nd February 2023

2. ESKA - AOSSM Fellowship, Cleveland 1991

3. … except the last minute update:

4. Not me! I vigorously deny this.

5. MR
Images:
Dave
Ritchie,
Glasgow,
UK
• This is somewhat esoteric observational and
speculative study based on one simple
question: why do people develop
MDACL?
• We noticed quite high MRI incidence of
MDACLs, ACL ganglions and subchondral
cysts long time ago but, as we treat
symptoms and not MRI findings, we did not
pay much attention because of no
correlation with instability.
• However, most people had seemingly
unrelated symptoms which we associated
with almost ubiquitous meniscal findings
and chondral/subchondral MRI findings
(bone marrow oedema and cysts), which
were often disproportionate.
• Some of those had progressive and
persistently severe pain which did
correlate with progressive MRI findings
of further MDACL and bone marrow
oedema. Why?
Mucoid ACL Degeneration
(MDACL)

6. What is Mucoid ACL Degeneration?
Mucoid ACL degeneration is “simply a biological and structural failure because of
progressive ACL degeneration with acquired synovial tissue entrapment between ACL
fibres”. True, but not entirely. ACL injury does not seem to be related to progressive
mucoid degeneration but may play a role in the development of ACL ganglions.
CKC UK

7. 2013 Update: MDACL is not infrequent incidental MRI diagnosis in our practice (70 reported
since 2016, approx. 50% with associated ACL cysts and 30% with tibial or femoral intra-
osseous cysts, almost all in 40-60 age group, gender difference: F40% M60%).
Mucoid ACL, ACL Cysts and Bone Cysts
The correlation is still poorly understood but seems to be associated with progressive
structural ACL degeneration, formation of ACL ganglions and local femoral or tibial
subchondral marrow oedema and intraosseous cysts (progressive degeneration but on
different point on the same timeline?).
CKC UK

8. Features of Mucoid ACL Degeneration
• Clinical Presentation: Patients usually present
with medial or posterior knee pain, mechanical
locking, clicking and swelling or restricted
movement. Instability or giving way are rare
complaints and clinical signs of ACL laxity are
often absent.
• MRI: most cases are incidental and
asymptomatic. The appearance can mimic acute
or chronic interstitial partial tears of the ACL. The
ACL is thickened and ill-defined with a “celery
stalk” appearance. Its low signal longitudinal fibres
are separated from each other by higher signal
mucinous material, best seen on T2 weighted
images. Its signal is increased on all sequences.
Intact fibres are best seen on T2-weighted
sequences.
• Secondary signs of ACL injury or deficiency (bone
bruising and bone marrow oedema, meniscal
tears, anterior subluxation of the tibia and other
ligament injuries) are usually absent.
• We have observed a significant number of
associated mucoid degeneration of both menisci.
CKC UK

9. Arthroscopic Features
Early stages appear as “degloved” ACL (missing synovial envelope and
blood vessels), sometimes misdiagnosed as partially torn ACL
CKC UK

10. Arthroscopic Features
… more often as “bare” but bulky appearance with diffuse separation
and fragmentation of fibre clusters
CKC UK

11. Features of Mucoid ACL Degeneration
• Arthroscopy: MDACLs are always more voluminous than normal ACL, often shredded
with open internal structure, clearly structurally dysfunctional, with moderate instability
on EUA.
• Histology: typically distorted collagen fibres with multifocal scanty myxomatous
degeneration (generally very vague findings, in our practice)
CKC UK

12. Mucoid ACL + Ganglion Cyst
Ganglia and synovial cysts technically are different entities: ganglia have a
connective-tissue capsule and viscous contents, whereas synovial cysts are a
membrane-lined collection of synovial fluid. The terms are often used interchangeably
or even in combination (ganglion cyst), as they are essentially identical from a clinical
perspective.
CKC UK

13. Incidence associated with
increased posterior tibial
slope
CKC UK

15. Treatment Options:
ACL “Deconstruction”
• Electrothermal debridement
but beware as it may induce
more pain because of
“electrostimulation” of remaining
ACL nerves and receptors.
• Reductionplasty or ”
Debulking”: arthroscopic
debridement and partial excision
of torn fibres and ganglions.
• Notchplasty: makes spatial
sense but may cause extended
chondral damage.
• Total excision: only if the
patient is desperate (numerous
concerns: instability, leading to
meniscal and chondral
deficiency, proprioceptive
deficit). Don’t do it!
• Leave alone, if not too painful
and/or mechanically
troublesome, do periodic FU
MRIs. Seems to work as well as
any of the options above.
MR Images: Albert van Kampen

16. Does PRP Help?
(not much in our experience)

17. • ACL mucoid degeneration is a relatively common cause of
incidental increased MRI signal within the ACL, rarely entirely
asymptomatic
• Possibly “senescent”, but the causation of mucoid ACL
degeneration and correlation with ganglion and bone cysts is
suggestive of OA at work.
• It is possible that ganglion cysts are a byproduct of mucoid
degeneration of the connective tissue or a cause of herniation
of synovial tissue through a defect in ACL’s synovial sheet or joint
capsule.
• Discrete intraosseous cysts were observed in 66% of other
studies with intrasubstance ACL ganglia and 77% of patients
with mucoid ACL degeneration.
• In our review intraosseous cysts (often at the femoral and tibial
attachments of the ACL) appear to be histologically similar to soft-
tissue ganglia, consisting largely of gel-like myxoid material, but
they generally have no identifiable communication with the
articular surface or joint cavity.
CKC UK
MDACL 2023 Update:

18. The Key: MDACL & OA

19. Cross-talk Between Articular Cartilage,
Subchondral Bone and ACL
• Our focus now is on the role of enthesitis which seems to be the key to the start of the
inflammatory and subsequently degenerative processes of the ACL.
• MRI analyses indicates that the localization of bone marrow oedema in early OA is often
associated with ligament attachment site, the enthesis, which seems to play a central role.
• The intimate cross-talk between synovitis, articular cartilage, ACL and subchondral bone is
no doubt the main feature of MDACL.
• The aetiology is also suggestive of disrupted neuromuscular network and joint homeostasis
at several intra-articular levels.
CKC UK

20. MDACL 2023 Update:
• MDACLs do not heal: FU MRIs look progressively worse over a long
period of time (more diffuse volume) + more BME (more MTC than
MFC) but subchondral cysts remain unchanged.
• We observed transient exacerbation of symptoms in this group
(over 50% of recent patients), following the COVID-19 vaccine,
further suggestive of metabolic and inflammatory origin.
• There is strong association between MDACL and chondral
lesions (82%) and between MDACL and meniscal tears (69%),
which may support the theory that MDACL is a slow early stage
degenerative process.
• MDACL is a metabolic consequence, clearly associated with early
OA and synovial inflammation possibly exacerbated with repetitive knee
trauma.
• MDACL is differentiated from synovial cysts of the ACL where, in
MDACL, mucoid tissue intermingles within ACL fibres and is not
contained within a cyst.
• MRI, arthroscopic and histological findings are suggestive of
major structural failure of the ACL, uniformly confirming
degenerative and biologically failed tissue.
• And yet, and this is still difficult to explain, functional
instability is seldom a problem, although most people have
moderate clinically demonstrable laxity!
CKC UK

21. Thank you
vbobic@kneeclinic.info
CKC UK