Keywords
Adductor - distal avulsion - magnus
Introduction
The adductor magnus is the largest and deepest medial thigh muscle. It is a fan-shaped
muscle that is rarely injured. The adductor muscles are the second commonest muscle
group to be injured after the hamstrings. Of these, the adductor longus is the most
commonly injured muscle accounting for 62–90’ of the cases.[[1]] Avulsion injuries of the adductor muscles are uncommon and most frequently involve
the proximal origin rather than the distal insertion. We present a case of avulsion
fracture of the adductor tubercle at the distal adductor magnus insertion in a 20-year-old
skier which is the first reported case in the literature.
Case Report
A 20-year-old male presented with medial right knee pain for a week following a fall
whilst skiing. Clinically, the patient presented with a tender swelling on the medial
aspect of the lower thigh and had an antalgic gait. MRI of the right knee demonstrated
a minimally displaced distal avulsion fracture of the adductor tubercle with diffuse
marrow edema along the medial femoral condyle and a tear of the distal adductor magnus
myotendinous junction [[Figure 1]]. The posteromedial corner of the knee was otherwise intact. The patient was conservatively
managed.
Figure 1 (A-D): STIR sagittal (A), axial (B and C), and T1 coronal (D) showing avulsion fracture
(arrow) of the adductor tubercle at the site insertion of adductor magnus with marked
osseous edema
Discussion
Lower limb injuries account for approximately 90’ of all sports-related injuries[[2]] and of these, involvement of the knee is relatively common. The menisci and ACL
are most frequently injured. Avulsion injuries are relatively uncommon; however, their
incidence continues to rise as the population becomes increasingly involved in sporting
and other athletic activities.[[3]] The knee is particularly susceptible to avulsion injuries due to the numerous ligamentous,
tendinous, and meniscal attachments. The commonest avulsion injuries specific to the
knee joint include the Segond fracture, reverse Segond fracture, cruciate ligament
avulsion fractures, and ilio–tibial band avulsion fractures that rarely occur in isolation.
Whilst proximal adductor magnus avulsion has previously been reported, isolated distal
adductor magnus insertion avulsion injury is rare and the authors are not aware of
any reported cases in the literature. Proximal adductor muscle strains and avulsions
are more prevalent than distal injuries and most commonly occur in high-intensity
kicking sports as a result of rapid uncoordinated movements. The adductor longus tendon
is the commonest adductor muscle to be injured followed by the adductor magnus muscle.[[4], [5]] The exact mechanism of distal adductor magnus avulsion is unknown. Adductor insertion
avulsion syndrome (AIAS) (thigh splints) is an uncommon osseous fatigue injury resulting
from repetitive avulsive stresses at the tendinous insertion of the adductor longus
and/or adductor brevis tendons onto the proximal and mid femur.[[6]] The clinical presentation and imaging features of AIAS are different to avulsion
injuries which have an acute onset. AIAS presents with vague activity-related groin
pain that is relieved by rest. MRI demonstrates periosteal high signal on fluid-sensitive
sequences along the insertion of the adductor longus and brevis tendons.
The medial knee has a relatively complex anatomy, which may preclude a diagnosis on
radiographs or clinical examination and warrant an MRI. The adductor magnus is the
most complex adductor muscle, which stabilizes the posteromedial compartment and plays
a role in the flexion and extension movements of the hip joint. The muscle has pubofemoral
and ischiofemoral heads [[Figure 2]]. The pubofemoral muscle fibers/adductor parts are directed horizontally that insert
along the plane between the greater trochanter and linea aspera and are innervated
by the posterior branch of the obturator nerve. The ischiofemoral fibers/hamstring
part have vertical and lateral fibers that insert onto the linea aspera and adductor
tubercle[[7]] and are innervated by the sciatic nerve. The adductor tubercle [AT] is a bony protuberance,
situated just cranial to the medial epicondyle of femur and is the caudal most point
of the medial supracondylar line serving as the insertion point of the ischiofemoral
portion of the adductor magnus muscle.[[8], [9]] The adductor magnus myotendinous junction occurs approximately at the level of
the junction of the middle and distal thirds of the femur. As a result, the distal
tendon has a long course to its insertion onto the adductor tubercle. On routine knee
MRI, this tendon appears as a thin low signal structure on all sequences and is thus
often overlooked.
Figure 2: Coronal diagram showing the pubofemoral (AM1) and ischiocondylar (AM2) parts of adductor
magnus. ADT (adductor tubercle)
There are multiple ligamentous and tendinous attachments in close proximity to the
adductor magnus insertion onto the AT. The medial patellofemoral ligament (MPFL) attaches
at a triangular area located anterior to the AT.[[8], [10]] The posterior oblique ligament originates slightly posteroinferiorly to the AT
and is directed caudally, blending distally with the semimembranosus tendon.[[9], [11]] The gastrocnemius tubercle is located distal and posterior to AT, giving attachment
to the medial head of gastrocnemius.[[9], [10]] The medial collateral ligament (MCL) arises from the medial epicondyle just distal
to AT [[Figure 3]].
Figure 3 (A and B): Diagrams (A and B) of attachments of various structures in the medial aspect of the
distal femora. MPT (medial patellotibial ligament), ADD MAGN (adductor magnus), MCL
(medial collateral ligament), MED GAST (medial gastrocnemius), and sMCL (superficial
MCL)
An avulsion fracture occurs when there is detachment of a bony fragment from the forces
applied to a ligament, tendon, or joint capsule insertion onto the bone. Radiographically,
a tiny osseous fragment located close to where the expected attachment of the ligament
or tendon inserts maybe visualized. Other secondary signs including a joint effusion
for intra-articular fractures or soft tissue swelling may also be present. Whilst
computed tomography is useful in demonstrating the dimensions of the bony fragment,
MRI is the modality of choice for knee injuries as it depicts the extent of both the
bony and associated soft tissue injuries. In the context of distal adductor magnus
avulsion, on MRI, the avulsed fragment should be visible with a small rim of fluid
between the fragment and medial femoral condyle. Bone marrow edema maybe visualized
in the medial femoral condyle. The adductor magnus tendon maybe unremarkable or torn
to various degrees. There may be associated injuries to the remaining structures of
the posteromedial corner such as the semimembranosus tendon, MCL, POL, and medial
meniscus.[[11]] The likely mechanism of injury of the avulsion of distal adductor magnus is due
to the forced eccentric contraction of the ischiofemoral ligament with knee in flexion.
Summary
Isolated adductor tubercle avulsion is a rare cause of medial knee pain in patients
presenting with sport-related injuries. Evaluation of the distal adductor magnus insertion
is vital when assessing the posteromedial corner.
Declaration of patient consent
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In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
