SLR - June 2018 - Nam T. Tran

Differential Motion and Compression Between the Plantaris and Achilles Tendons. A Contributing Factor to Midportion Achilles Tendinopathy?

Reference: Stephen J, Marsland D, Masci L, Calder J, El Daou H. Differential Motion and Compression Between the Plantaris and Achilles Tendons. A Contributing Factor to Midportion Achilles Tendinopathy? Am J Sports Med 2018 Mar; 46(4):955–960.

Scientific Literature Review

Reviewed By: Nam T. Tran, DPM
Residency Program: Medstar Washington Hospital Center, Washington DC

Podiatric Relevance: Midportion Achilles tendinopathy has long been a condition commonly seen and treated by foot and ankle surgeons. Treatments can include conservative modalities as well as surgical intervention. The plantaris tendon, despite its close proximity to the Achilles tendon, has not been extensively studied as a possible contribution to midportion Achilles tendinopathy. Identifying the contributing factors of the plantaris tendon to midportion Achilles tendinopathy can help providers better choose operative procedures and postoperative courses for the patient suffering from this condition. This study of 18 cadaveric ankles explored the possible correlation between the presence of a plantaris tendon and midportion Achilles tendinopathy.

Methods: This laboratory study included 22 fresh-frozen cadaveric feet and ankles. Specimens were all screened to exclude any specimens with history of surgery or disease. All tibiae were cut to equal lengths, and the limb was subsequently stabilized upright on the bench surface. Dissection was performed on all specimens to identify the plantaris, gastrocnemius and soleus muscles. Of the 22 specimens, only 18 had a plantaris tendon present. The insertion of the plantaris tendon was then identified as being either on the calcaneus or on the Achilles tendon. A Tekscan 4011 pressure sensor was implemented and placed between the Achilles tendon and plantaris tendon to measure the pressure and differential motion between the tendons during passive range of motion.

Results: In evaluating the data to measure the mean pressure between the Achilles tendon and plantaris tendon, the study found that the flexion angle of the ankle joint had a significant effect on the mean pressure. During plantarflexion, an increase of mean contact pressures was observed to increase from 0.18 ± 0.3 MPa to 0.37 ± 0.44 MPa. They also observed an increase in mean pressures when applying a hindfoot valgus force regardless of the amount of plantarflexion applied to the ankle joint.

When evaluating the data separating the specimens by the insertion of the plantaris tendon, the researchers found a significant difference in differential motion. The specimens with a calcaneal insertion of the plantaris were found to have a differential motion of 14 ± 4mm compared to a plantaris tendon with an Achilles insertion, 2 ± 2mm.  

Conclusion: This study shows the profound effect that a plantaris muscle and tendon can have on the pressures and differential motion between the plantaris and Achilles tendon. Limitations of the study include the cadaveric nature of the study. Another significant limitation of the study was the low sample size of the study. Despite the limitations of the study, the data raises important questions regarding the importance of plantaris tendon excision during surgical intervention for Achilles tendinopathy. This data also implicated modifying postoperative physical therapy courses to be more mindful of exercises that may introduce excessive plantarflexory and hind foot valgus forces. Larger future studies are necessary to further evaluate the correlation between the presence of a plantaris tendon on midportion Achilles tendinopathy.

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