Post-traumatic myotendinous junction injury of tibialis posterior: A case report

Abstract

Background:

Post-traumatic calf injuries most commonly involve the medial head of the gastrocnemius muscle. In contrast, injuries to the tibialis posterior muscle, particularly at the myotendinous junction, are rare.

Case Report:

We present the case of a healthy young male who experienced a fall, followed by pain and swelling in the posterior calf. Radiographs excluded a fracture, and subsequent ultrasound evaluation identified an injury at the myotendinous junction of the tibialis posterior muscle.

Discussion:

Traumatic injuries to the calf typically affect the medial gastrocnemius and soleus muscles, which form part of the triceps surae complex. Ultrasound imaging proved instrumental in localising the injury and allowed for dynamic assessment. This modality is reproducible and facilitates monitoring the healing process. To our knowledge, similar cases involving the tibialis posterior myotendinous junction have not been documented in the literature.

Conclusion:

Ultrasound evaluation of a post-traumatic calf injury revealed a rare myotendinous lesion of the tibialis posterior, highlighting the importance of comprehensive imaging in atypical presentations.

Background

The tibialis posterior muscle and tendon play a critical role in ankle and foot biomechanics. The long muscle belly is located deep within the posterior compartment of the leg and originates from the posterior surface of the interosseous membrane, the superior two-thirds of the posterior and medial aspect of the fibula, and the proximal portion of the tibia. It was documented that the muscle has his own fascial compartment, separated from the posterior compartment. ¹ The tendon courses through the tarsal tunnel, positioned just posterior to the medial malleolus, and continues along the plantar aspect of the foot. Functionally, the tibialis posterior acts as the primary inverter of the foot, serves as a secondary plantar flexor, and provides dynamic support to the medial longitudinal arch.

Pathologies affecting the myotendinous unit of the tibialis posterior encompass a range of conditions. Acute tendon injuries typically result from high-impact activities, whereas chronic or repetitive stress may initiate a tendinopathic cascade, potentially leading to posterior tibial tendon dysfunction (PTTD). The muscle belly may also be implicated in acute compartment syndrome of the deep posterior compartment—a post-traumatic complication that may occur following fractures, direct external compression, or intramuscular haematomas. In such cases, the muscle becomes entrapped within a fibro-osseous compartment; elevated intracompartmental pressures compromise tissue perfusion, resulting in structural damage to both muscles and associated neurovascular structures.^2,3

Case report

A 36-year-old otherwise healthy man presented with posterior lower leg and ankle pain and swelling, 2 weeks after falling from approximately 1 m. The injury occurred when he landed first on his left foot, then on the right. He reported experiencing a sudden, sharp, stabbing pain in the posterior left calf and ankle, accompanied by immediate swelling. He was unable to bear weight on the affected leg due to severe pain. Initial evaluation in the emergency department included plain radiographs of the calf and foot, which revealed no osseous abnormalities. Active foot movements were severely limited, with a reduced range of motion and significant pain, rated 7–8 on the Visual Analogue Scale (VAS, 0–10). The Thompson test was negative, and localised tenderness was noted over the posterior calf and ankle.

The primary differential diagnoses considered in the emergency setting included deep vein thrombosis, tendon rupture—most notably of the Achilles tendon—or muscle rupture, particularly involving the medial head of the gastrocnemius or soleus muscle. Given these concerns, an ultrasound examination was performed to further evaluate the soft tissue structures.

The ultrasound examination was performed using a Samsung HS70A system equipped with an 8–18 MHz linear transducer, utilising both greyscale and colour Doppler modalities. The patient was positioned prone, with the foot hanging freely over the edge of the examination table to allow for optimal posterior access. The posterior calf was scanned in a longitudinal sweep, beginning at the popliteal fossa and extending distally to the Achilles tendon. Subsequently, the medial aspect of the ankle was evaluated with the transducer in a transverse orientation, using the medial malleolus as a bony anatomical landmark.

Ultrasound evaluation of the posterior calf revealed no structural abnormalities. Examination then focused on the medial aspect of the ankle. The transducer was initially positioned in a transverse plane, aligned parallel to the plantar surface, with one edge placed on the medial malleolus. From this point, the probe was moved proximally, above the medial malleolus, in both transverse and longitudinal planes, and subsequently distally, below the medial malleolus in the longitudinal plane (Figure 1a). In the initial transverse section, the tarsal tunnel was visualised (Figure 1b), demonstrating short-axis views of the tibialis posterior and flexor digitorum longus tendons. The tibialis posterior tendon was surrounded by a small amount of anechoic fluid, forming a halo-like appearance suggestive of peritendinous effusion. As the probe was moved proximally, the muscular belly of the tibialis posterior came into view, and the amount of surrounding fluid increased (Figure 1c).

Figure 1.

Figure 1a. Medial aspect of the ankle showing the position of the probe for the images b, c, d, e. Figure 1b. Transverse section of the tarsal tunnel with medial malleolus (MM), tibialis posterior tendon (star) with surrounding fluid (arrows), flexor digitorum longus tendon (circle). Figure 1c. Transversal section above the medial malleolus, with tibialis posterior tendon (star) and muscle (two stars), increased amount of fluid (arrows), flexor digitorum longus tendon (circle) and muscle (two circles). Figure 1d. Long axis view on tibialis posterior tendon (star) and muscle (two stars), with bell-clapper sign (arrowhead) and fluid (arrows). Figure 1e. Longitudinal section under the medial malleolus, centered on the sustentaculum tali (ST), with short-axis view on the tibialis posterior tendon (star) and surrounding fluid (arrow), short-axis view of flexor digitorum longus (circle).

With the probe in a longitudinal orientation, a partial detachment of the tibialis posterior muscle belly from its tendon was observed. The resulting gap was filled with anechoic fluid, indicating a myotendinous junction injury. A “bell-clapper sign” was also noted (Figure 1d, arrowhead), further supporting the diagnosis of a myotendinous tear.

The bell-clapper sign has been described by some authors as an ultrasound feature characterised by retracted, echogenic muscle fragments surrounded by a hypoechoic haematoma, typically observed in grade II (partial) muscle ruptures.^4–6

As the probe was advanced distally below the medial malleolus and centered over the sustentaculum tali (ST), two tendons were clearly visualised: the tibialis posterior tendon located superiorly, and the flexor digitorum longus tendon positioned laterally, just superficial to it. The tibialis posterior tendon was surrounded by a significant amount of anechoic fluid, likely representing distally tracking fluid from the proximal myotendinous rupture (Figure 1e).

Throughout the entire examination, no colour Doppler signal was detected, indicating the absence of hyperaemia or active inflammation.

Discussion

The paper presents the case of a patient with trauma on the lower leg and a sudden pain in the posterior and inferior calf. He was cleared for fracture and an ultrasound exam performed 2 weeks later revealed a partial detachment of the muscle belly from its tendon, with a surrounding fluid area, presumably an old haematic collection.

The tibialis posterior muscle is the deepest muscle of the deep posterior compartment of the lower leg. It is continuous with a tendon located just behind the medial malleolus, in a sulcus, under the flexor retinaculum, in the tarsal tunnel. ⁷ At this level, it is close to flexor digitorum longus tendon, the vasculo-nervous bundle of tibial nerve, artery and veins, and hallucis longus tendon. The tibialis posterior tendon continues under the malleolus, toward ST, where it is located on the superior side. The tendon has its own synovial sheet which starts about 6 cm proximally to the malleolus and continues 7 to 9 cm distally, toward the navicular bone. ⁸ It courses deeply into the plantar aspect of the foot, and it splits into three fascicles, primary, plantar, and recurrent.

It acts as an inverter and plantar flexor of the foot, and it supports the medial arch of the foot. It is a stabiliser of the medial ankle and acts like a shock absorber.

It is subject of injury in acute settings, after a fall or a high-impact sport. Usually, the tendon suffers acutely, taking the form of tendinitis. In the chronic, recurrent trauma, tendinopathic changes take place and tibialis posterior dysfunction occurs. ¹

Acute trauma on the tibialis posterior muscle may lead to tendon injury (tendinitis), tendon rupture, posterior compartment syndrome. Tendon rupture is suspected when a high-impact loading is followed by generalised medial ankle pain and swelling. ⁹ In some circumstances, tendon rupture accompanies closed malleolar or distal tibial fractures. ¹⁰ The mechanisms were the presence of medial bone flakes from avulsion injury or the interposition of the tendon in the fracture site. ¹¹

Muscle acute injuries are reported as a consequence of strenuous exercise, taking the form of an acute strain. Pain and an achy sensation, followed by difficulty when climbing the stairs were the main complaints. Therapy was conservative, rest and rehabilitation. ¹²

Myotendinous injuries of the tibialis posterior may progress to complete rupture, typically presenting with increased pain, swelling, and an acute loss of ankle and foot alignment during stance. Over time, this can lead to chronic dysfunction, manifesting as tibialis posterior tendon insufficiency (TPTI). This condition is characterised by a complex pattern of static misalignment, beginning with collapse of the medial longitudinal arch, internal rotation of the tibia and talus, subtalar joint eversion, calcaneal valgus, and talonavicular abduction. As a compensatory mechanism, the forefoot adopts a varus deformity. With disease progression, adjacent hindfoot structures may become involved. The Achilles tendon, for example, may shift laterally relative to the subtalar joint axis, potentially leading to shortening and altered biomechanics. In addition, the fibular malleolus may impinge on the lateral wall of the calcaneus, creating another potential source of pain. The resulting loss of eversion affects both terminal stance and pre-swing phases, impairing forward propulsion and leading to shortening of the swing phase during gait.

Although the current case involves a rare myotendinous injury, multiple risk factors can contribute to the development of TPTI, including obesity, diabetes mellitus, chronic corticosteroid use, and seronegative arthropathies.

Ultrasound plays a critical role in the diagnosis of soft tissue injuries, particularly those involving muscle and tendon. It is a readily accessible, cost-effective, and repeatable imaging modality that enables dynamic evaluation and longitudinal follow-up. Muscular injuries can be graded sonographically:

• Grade I: Involves <5% of muscle fibers, with minimal loss of strength and function.

• Grade II: Involves the myotendinous junction, with visible tearing and a marked reduction in strength.

• Grade III: Represents a complete rupture, associated with total loss of strength and function.^13,14

Therapy was conservatory, rest, and immobilisation in a walking boot for 3 to 4 weeks, followed by referral to a rehabilitation center to follow a program centered on physical exercises. ¹⁵

Conclusion

This paper presents a rare case of a post-traumatic myotendinous lesion of the tibialis posterior, a clinical condition requiring careful differentiation from more common post-traumatic injuries such as fractures and triceps surae muscle injuries. Ultrasound examination played a crucial role in establishing the diagnosis by accurately localising the lesion and excluding other potential causes of posterior calf pain and dysfunction.