Distribution of the subtendons in the midportion of the Achilles tendon revealed in vivo on MRI

Abstract

The aim of the study was to check if the subtendons of the Achilles tendon can be identified in vivo on MRI in the midportion of the tendon. The relation of the plantaris tendon to the Achilles tendon was also examined. A retrospective study of 200 MRI of ankle joints including the Achilles tendon was conducted. Statistical analysis of the correlation between the possibility of identifying the subtendons and the side, gender, presence of the central soleus tendon and plantaris tendon variation was performed. The inter-observer agreement between two reviewers in their evaluation of the subtendons was assessed using kappa statistics. The subtendon from the lateral head of the gastrocnemius muscle was identified in 65% (k = 0.63) and was located in the anterior part of the Achilles tendon. The subtendon from the soleus muscle was recognized in 12% (k = 0.75) comprising anterior part of the tendon. In 6% the subtendon from the medial head of the gastrocnemius muscle was identified (k = 0.58). The central soleus tendon was identified in 85% of cases. Statistical analysis shows the weak correlation of the presence of the central soleus tendon and the possibility of identifying the subtendon from the soleus muscle. The plantaris tendon was directly related to the insertion of the Achilles tendon in 42.5%. Identification of the subtendons of the Achilles tendon on MRI is challenging, and most often it is only possible to find the subtendon of the lateral head of the gastrocnemius muscle.

Figure 1

MRI right ankle, PD FS at the level of the talus. (a)—The highest section, (d)—the lowest section. A 42-year-old male with ankle sprain without trauma. The arrow marks a narrow septation between the subtendon from the lateral head of the gastrocnemius muscle and the other subtendons of the Achilles tendon.

Figure 2

MRI left ankle, PD FS at the level of the talus (a)—the highest section, (d)—the lowest section. A 35-year-old male 2 weeks after ankle sprain, pain laterally. The arrow marks the S-LGC.

Figure 3

MRI right ankle, PD FS at the level of the talus (a), superiorly to the calcaneus (b) and the Achilles tendon insertion (c). A 23-year-old male with a suspected anterior talofibular ligament rupture. 1—S-LGC, 2—S-Sol. It is not possible to clearly distinguish S-MGC.

Figure 4

MRI right ankle, PD FS at the level of the talus (a–c), (a)—the highest section, (d)—the lowest section and at the level of the deep calcaneal bursa just above the calcaneus (d). A 17-year-old female 1 week after ankle sprain, pain posteriorly to the lateral malleolus. 1—S-Sol, 2—S-LGC, 3—the plantaris tendon (type 4).

Figure 5

MRI left ankle, PD FS at the level of the talus; (a)—the highest section, (d)—the lowest section. A 48-year-old male presented with the anterior ankle pain. 1—S-Sol, 2—the plantaris tendon (type 5), 3—S-LGC.

Figure 6

MRI right ankle, PD FS at the level of the distal tibia (a–c); (a)—the highest section, (c)—the lowest section, and the talus (d). A 39-year-old female 4 weeks after ankle sprain. 1—S-Sol, 2—S-LGC, 3—S-MGC, 4—the plantaris tendon (type 4).

Figure 7

MRI left ankle, PD FS at the level of the distal tibia (a) is a slightly higher section than (b), the talus (c) and the calcaneus (d). A 37-year-old male with clinical suspicion of anterior conflict. The central tendon of the soleus muscle was absent. 1—S-LGC, 2—the plantaris tendon (type 4).

Figure 8

MRI left ankle, PD FS at the level of the distal tibia (a–e), the talus (f); (a)—the highest section, (f)—the lowest section. 1—T-Sol, 2—S-MGC, 3—S-LGC, 4—the plantaris tendon (type 3).

Figure 9

MRI right Achilles tendon, PD FS. The words medial and lateral are given for better orientation. (A,B) coronal picture of the right Achilles tendon. (C,D) transverse section at level shown on (B). 1—fibers from the soleus muscle, 2—fibers from the lateral head of the gastrocnemius muscle, 3—fibers from the medial head of the gastrocnemius muscle, 4—the plantaris tendon.

Figure 10

Two patients. One presented on (a,b) with the central tendon of the soleus muscle marked by an arrow. The other on (c,d) shows the absence of the central tendon of the soleus muscle.

Figure 11

Five variations of the plantaris tendon. The most common seen variations (a) (type 3) and (b) (type 4). The less often seen variations (c) (type 1), (d) (type 2) and (e) (type 5).