Anatomic study suggests that the morphology of the plantaris tendon may be related to Achilles tendonitis

Abstract

Purpose: Achilles tendinopathy is a significant clinical lower limb issue observed in recent years. Neither the location nor the mechanism behind the pain has yet been sufficiently explained. Patients frequently experience pain on the medial side of the calcaneal tendon, and between 2 and 7 cm above the calcaneal tuberosity, which may suggests that the plantaris tendon plays an important role. The purpose of this study was to determine the anatomical relationships between the course of the plantaris tendon and the calcaneal tendon, as well as the type of insertion of the plantaris tendon.

Methods: The tests were carried out on 50 randomized lower limbs (23 left and 27 right) fixed in 10 % formalin solution.

Results: Five insertion types of the plantaris tendon were identified in relation to the calcaneal tendon: four with their insertion on the calcaneal tuberosity (Types 1, 2, 3, 5), while the fifth (Type 4) had its insertion in the crural fascia. In addition, two variants of the course of the plantaris tendon were identified, the most common being termed Variant A, in which the tendon crosses the space between the gastrocnemius and the soleus muscles, thus reaching the medial crural region, and is located on the medial side of the calcaneal tendon (84 % cases). The course of the Variant B is similar to the course of the Variant A, but upon leaving the space located between the gastrocnemius and soleus muscle, it turned to the medial crural region and ran directly anterior to the calcaneal tendon (12 %). The plantaris muscle was found to be absent in two lower limbs (4 %). The most frequent insertion type of the plantaris tendon into the calcaneal tuberosity is fan-shaped, occurring on the medial side of the Achilles tendon (Type 1-44 % cases).

Conclusion: The course of the plantaris tendon and its mobility range in relation to the calcaneal tendon may be likely to affect the occurrence of pains in the lower medial part of the leg (Achilles tendinopathy).

Keywords: Calcaneal tendon; Mid-portion Achilles tendinopathy; Plantaris muscle; Plantaris tendon.

Fig. 1

Tendon of the plantaris muscle. a Type 1 of plantaris tendon insertion to the calcaneal tuberosity (the most common). Medial view of the right leg. The course of the plantaris muscle tendon visible on the medial part of the calcaneal tendon. b Type 4 of the plantaris tendon insertion (the less common). Posteromedial view of the right leg. The figure shows the atypical insertion of the plantaris tendon to the deep fascia of the leg. The lack of the insertion located on the calcaneal bone is visible. AT Achilles tendon, CT calcaneal tuberosity, PT plantaris tendon

Fig. 2

Tendon of the plantaris muscle. Schematic representation of the major types of the plantaris tendon insertion. Medial view of the right leg. a Type 1 (44 %), b Type 2 (18 %), c Type 3 (8 %), d Type 4 (4 %), e Type 5 (22 %). Black arrowhead plantaris tendon

Fig. 3

Variable anatomical relationships of the plantaris tendon. a Variant A of the plantaris tendon course. b Variant B of the plantaris tendon course. AT Achilles tendon, GM gastrocnemius muscle, SM soleus muscle, PT plantaris tendon