Plantaris tendon resection increases ankle dorsiflexion independently of knee position, with greater effect in tendons inserting close to the Achilles.

BACKGROUND

Equinus deformity, defined as limited ankle dorsiflexion, is a frequent clinical finding with implications in multiple foot and ankle disorders. While gastrocnemius tightness is considered the main dynamic cause, the plantaris tendon (PT) has been proposed as an additional restrictor of ankle mobility. Its anatomical variability and proximity to the Achilles tendon may influence ankle dorsiflexion.

METHODS

Eighteen cadaveric feet from nine donors were examined to confirm the presence of a plantaris tendon (PT) and classify its insertion type. Ankle dorsiflexion and plantarflexion were measured with the knee fully extended and flexed at 90 °, both before and after complete PT resection. Standardized lateral photographs were used for angular measurements, which were independently assessed by two blinded observers. Statistical analyses evaluated the influence of knee position, PT insertion type, and baseline range of motion on post-resection dorsiflexion gain.

RESULTS

The PT was identified in all specimens, with insertional types distributed as follows: type 1 (33%), type 2 (28%), type 3 (17%), type 4 (11%), and type 5 (11%). PT resection resulted in a significant dorsiflexion increase with the knee extended (8.6 ° ± 4.8 °; p = 0.002) and flexed at 90 ° (7.6 ° ± 4.2 °; p = 0.02), without affecting plantarflexion. Knee position had no significant effect on dorsiflexion gain (p = 0.82). Insertions adjacent to the Achilles tendon (types 1, 2, 5) were associated with greater dorsiflexion improvement compared with anterior insertions, both with the knee extended (10.2 ° ± 5.6 ° vs. 4.4 ° ± 1.7 °; p = 0.03) and flexed at 90 ° (9.1 ° ± 4.4 ° vs. 3.6 ° ± 1.9 °; p = 0.04). Baseline dorsiflexion correlated with post-resection gain only with the knee flexed (ρ = 0.58; p = 0.01).

CONCLUSION

Plantaris tendon resection significantly increased ankle dorsiflexion independently of knee position or baseline mobility, with greater effect when the tendon inserted adjacent to the Achilles tendon. These findings support the potential role of the PT as an independent restrictor of ankle dorsiflexion.

LEVEL OF EVIDENCE: IV; Basic Science Study.