Keywords:
Trauma, Athletic injuries, Acute, Imaging sequences, MR, Digital radiography, Musculoskeletal system, Musculoskeletal soft tissue, Extremities
Authors:
P. Mundada, T. Shimpi, E. S. Mahmoud, E.-L. H. J. Teo; Singapore/SG
DOI:
10.1594/essr2015/P-0081
Results
Results:
- The lateral radiograph of the left knee reveals a 1.5cm curvilinear fracture fragment in the popiteal fossa,
projected along the posterior aspect of the distal femoral metaphysis,
approximately 1 cm away from the cortex and just above the physis (Figure 1). Another irregular osseous fragment is seen at same location, closely related to the posterior femoral metaphyseal cortex (Figure 1).
The antero-posterior radiograph of the left knee is unremarkable.
- MRI shows complete avulsion of the medial head of gastrocnemius with a large bony fragment attached to the retracted tendon (Figure 2 and Figure 3). There is associated soft tissue oedema,
minimal effusion (figure 2 and Figure 3).
Focal marrow oedema is seen in the femoral metaphysis,
at the avulsion site (Figure 3).
The musculotendinous junction of the medial head of gastrocnemius is normal (figure 4).
No meniscal tear or ligamentous tear or acute osteochondral defect or joint effusio is seen.
Discussion:
The medial head gastrocnemius injury is quite common as a part of tennis leg syndrome.
Avulsion of the medial head of gastrocnemius muscle is uncommon and most often occurs in combination of other injuries.
It is very rare to have isolated avulsion fracture of the medial head of gastrocnemius.
-
Functional anatomy:
- The medial head of the gastrocnemius muscle originates from the posterior aspect of the medial femoral condyle (Figure 5 ),
and as it courses distally,
the medial head merges with the lateral head of the gastrocnemius.
The main function of the gastrocnemius muscle is to plantar flex the ankle,
but it also provides some knee flexion,
as well as contributes to the posterior stability of the knee and partially to the motion of the menisci with flexion/extension of the knee.
Throughout the belly of the muscle,
the medial gastrocnemius has several origins of tendinous formation.
- A tendinous sling of the semimembranosus insertion onto the posteromedial tibia also elevates the medial head of the gastrocnemius from the tibia during active knee flexion and passive external rotation (Figure 6) .
- Biomechanics of Medial gastrocnemius injury:
The medial gastrocnemius often gets injured at two locations.
-
Most commonly at musculotendinous junction and in the bulk of muscle belly as part of the ‘ tennis leg’ syndorme.
This injury occurs when an eccentric force is applied to the gastrocnemius muscle,
which usually happens when the knee is extended,
the ankle is dorsiflexed,
and the gastrocnemius attempts to contract in the already lengthened state.
This is the common position of the back leg in a tennis stroke,
and it results in the greatest force to the muscle unit.
-
The femoral origin of the medial head of the gastrocnemius get stressed during a combination of planter flexion of the ankle with extension of knee on a forcible externally rotated tibia.
- Possible biomechanism of medial gastrocnemius head avulsion during a standing broad jump:
- During a well-executed standing broad jump,
the foot is planter flexed and the knee is extended simultaneously during the mid-part of the jump,
before making the landing.
At the time of a well-executed landing,
the foot is getting in to dorsiflexion and the knee is getting flexed with most of the body with being transfered on back side (Figure 7 a to i and j1 & k2)) .
However,
it is unlikely to get medial head avulsion fracture during the mid-part of the jump as the tibia is not fixed and externally rotated.
- In our case,
it possible that the landing of the jump had gone wrong.
It is possible that after touching the ground,
the athlete fell forward and the whole weight was transferred anteriorly which lead to forcible planter flexion of the ankle and simultaneous forced extension of the knee while the tibia was fixed and forcibly externally rotated (Figure 7- j2 and k2 ).