In recent years, the plantaris tendon has been implicated in the development of chronic painful mid-portion Achilles tendinopathy. In some cases, a thickened plantaris tendon is closely associated with the Achilles tendon, and surgical excision of the plantaris tendon has been reported to be curative in patients who have not derived benefit following conservative treatment and surgical interventions.

The aim of this review is to outline the basic aspects of, and the recent research findings, related to the plantaris tendon, covering anatomical and clinical studies including those dealing with histology, imaging and treatment.

Cite this article: Bone Joint J 2016;98-B:1312–19.

Introduction. Traditionally Plantaris has been considered of little clinical importance and absent in 8–20% of the population. Recent evidence indicates that it is present in 98–100% of the population and that it may have a contributing role in Achilles tendinopathy due to its close anatomical relationship. The aim of this study was to establish whether Plantaris was present in a sample of cadaveric limbs, to establish its position in relation to the Achilles tendon and to conduct measures of its thickness and width. Materials and Methods. Forty eight cadaveric limbs which had been previously dissected were assessed. Plantaris was looked for in the region of the medial Achilles. If it could not be identified here, Gastrocnemius was reflected back to reveal Plantaris tendon beneath, and was then followed distally. All Plantaris tendon measurements were taken 2- 6 cm from the Achilles insertion using a vernier caliper. Results. Plantaris was present in all of the forty three limbs which were appropriate for assessment. Plantaris was positioned ventromedial to the Achilles tendon in 33 (77%) and medial to the Achilles in 9 (21%) of the limbs. The average width of the Plantaris tendon was 2.8mm (range 1.2–4.9mm) and its average thickness was 0.9mm (range 0.2–1.5mm). Discussion. Plantaris was present in all limbs in keeping with recent studies. This is the first known study, which measures Plantaris tendon in the region of the midportion Achilles. Future studies are planned to compare these measurements with tendinopathic plantaris tendons

Introduction

The mainstay of treatment in non-insertional Achilles tendinopathy is non-operative, however between 1/4 and 1/3 of patients fail this. The main symptom is pain which appears to be related to new nerve endings that grow into the tendon with the neovessels from the paratenon. Treatments which strip the paratenon from the tendon are showing promise including formal paratenon stripping via Achilles tendinoscopy. The pain and swelling in Achilles tendinopathy is usually on the medial side leading to the postulation that the plantaris tendon may have a role to play.

Background. The Plantaris Longus Tendon (PLT) may be implicated in Achilles (AT) tendinopathy. Different mechanical characteristics may be the cause. This study is designed to measure these. Methods. Six PLT and six AT were harvested from frozen cadavers (aged 65-88). Samples were stretched to failure using a Minimat 2000(tm) (Rheometric Scientific Inc.). Force and elongation were recorded. Calculated tangent stiffness, failure stress and strain were obtained. Averaged mechanical properties were compared using paired, one-tailed t-tests. Results. Mean stiffness was higher (p<0.001) in the PLT, measuring 5.71 N/mm (4.68-6.64), compared with 1.73 N/mm (1.40-2.22) in AT. Failure stress was also higher (p<0.01) in PLT: 1.42 N/mm. 2. (0.86-2.23) AT: 0.20 N/mm. 2. (0.16-0.25). Failure strain was less (p<0.05) in PLT: 14.1% (11.5-16.8) than AT: 21.8% (14.9-37.9). Conclusions. The PLT is stiffer, stronger than AT, demonstrating potential for relative movement under load. The stiffer PLT could tether AT and initiate an inflammatory response