The Achilles tendon and the plantar fascia – strangers or friendly neighbors?

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Though plantar fasciitis makes up only 1% of the visits to orthopedic doctors, it is one of the hardest-to-treat ailments⁽¹⁾. Because 80% of those diagnosed with plantar fasciitis present with a tight Achille’s tendon (AT), researchers in New Zealand sought to understand better the relationship between the two structures⁽¹⁾. The known biomechanical relationship between the plantar-flexor tendon and the medial longitudinal arch’s primary support structure – the plantar facia (PF) – made them wonder if they were more closely related. They examined 18 feet obtained from cadaver specimens and conducted radiographic and histological exams on them.

The measurements obtained included:

1. Measurement of the thickness of both tendons at their calcaneal insertion.
2. Measurement of the thickness of both tendons at equal distances from their point of insertion.
3. Insertional length of each tendon – how much of the tendon was attached to the bone.
4. Cross-sectional area (CSA) of each tendon at 10mm distal and proximal to their attachment.
5. The CSA of each tendon at the point of insertion.
6. The CSA of the insertional length of each tendon.

Practical implications

The researchers found that the AT and the PF’s CSA correlated strongly and significantly at all points measured. When they examined the tendons’ insertional site, they found that in some of the samples, the paratenon of the AT merged with the periosteum of the calcaneus and continued on as part of the PF. The continuity of the tissue provides evidence of a link between the two structures. Therefore, these findings support current recommendations to stretch the AT as part of the conservative treatment of PF.

This study suggests that the blending of the soft tissue fibers with the superficial layer of bone allows the calcaneus to act as a fulcrum between the two structures. They further propose that the calcaneus acts more like a sesamoid bone, similarly to the patella, serving this biomechanical function. Further exploration of this region’s anatomical makeup may influence treatment approaches, including greater attention to the neuromuscular function and strength of the calf muscles in treating plantar fasciitis.

Limitations to this study include a small sample size. The researchers obtained the samples from Caucasian cadavers only. The mean age of each cadaver at the time of death was 79 years. The authors could not control for the impact that embalming and slicing had on the integrity of the prosections. In addition, they could not rule out distortion in the quality of the radiographic images.

Reference

1. Sci Rep. 2021;11:5986. https://doi.org/10.1038/s41598-021-85251-0