1 Introduction

Plantaris muscle lies in the superficial posterior leg compartment of leg having a small muscle belly and long tendon. It is commonly used as a tendon graft due to its length, tensile strength, expendable nature and simple harvesting technique.¹ Various anatomical variations about Plantaris have been reported including its absence in 7–20% in different ethnic groups.^2–4 Hence, knowledge of its prevalence and morphology are important. Most reported studies are from Western population or cadavers; this paucity of data from Indian population prompted us to conduct this ultrasound study in healthy Indian volunteers.

2 Material and methods

This study was conducted in Plastic Surgery Unit, Department of Surgery and Department of Radiology in a Teaching Hospital in Central India. Healthy individuals attending the OPD were randomly selected and included in the study. Individuals with a history of injury, surgery, disease or any anomalies of the lower limb were excluded from the study. Demographic details such as age, height, hand and foot dominance was recorded. Every individual was examined for the presence or absence of the plantaris tendon along with tendon length by ultrasound of the leg. The presence or absence of the tendon in relation to the person's hand and foot dominance and correlation of patient's height with tendon length was also analyzed.

Using ultrasound (Alpinion E-Cube i7 with linear probe of 7–12 Hz) Plantaris muscle was located in the proximal leg region as an oval shaped hyper echoic structure between Medial head of Gastrocnemius and Soleus muscle from where it was traced down to its attachment on to the medial aspect of Calcaneum or fusion with fibers of Tendo Achilles before its insertion. (Fig. 1-3)

Close

Fig. 1 USG image showing origin and insertion of plantaris tendon.

Export to PPT

Close

Fig. 2 USG image showing longitudinal section of plantaris tendon between gastrocnemius and soleus.

Export to PPT

Close

Fig. 3 USG image showing transverse section of plantaris tendon between gastrocnemius and soleus.

Export to PPT

3 Results

250 healthy individuals (148 male, 102 female) aged between 18 and 62 years (mean age 34.42 years) attending the OPD were randomly selected and included in the study. 28/250 (11.2%) had absence of Plantaris tendon, either unilaterally or bilaterally. Unilateral absence was in 16 legs (3.2%) (10 right, 6 left) and bilateral absence was in 24 legs (4.8%). The overall absence was in 40 legs (8%). (Fig. 4)

Close

Fig. 4 USG image showing absent plantaris tendon.

Export to PPT

In 173 people right hand and right foot was dominant. Unilateral presence of tendon corresponding to their hand and foot dominance and was found to be statistically significant (p = 0.02) and the probability of finding right plantaris tendon in right dominance was 92.3% and in left dominance was 89.7%. Absence of tendon of dominant hand and foot was a rare occurrence (p < 0.05).

Length of plantaris tendon ranged from 22.5 to 43.5 cm (mean-30.8 cm). Mean height of included population was 167.7 cm. Height of the person correlated with tendon length (Table 1, Figs. 5, 6).

Close

Fig. 5 Showing relation of Plantaris tendon length and height of individual in male volunteers.

Export to PPT

Close

Fig. 6 Showing relation of Plantaris tendon length and height of individual in female volunteers.

Export to PPT

4 Discussion

In this study we assessed the prevalence and morphology of Plantaris Tendon in 250 healthy Indian individuals by ultrasound and found it absent in 28/250 (11.2%), either unilaterally or bilaterally.

Plantaris muscle is an underdeveloped muscle that plays inconsequential role in gait biomechanics but has important proprioceptive role due to very high density of muscle spindles.⁵ In nonhuman primates it is used to grasp objects, but human evolution to a bipetal stance may have resulted in Plantaris becoming a vestigial muscle.⁶ Anatomists and embryologists consider Plantaris as a derivative of lateral head of the gastrocnemius and it represents the third head of gastrocnemius often termed as “gastrocnemius tertius”.⁷

Its clinical importance chiefly lies in its use as a tendon graft due to its expendable nature. It is also involved in differential diagnosis of calf pain and popliteal artery compression syndrome. Other sources of tendon grafts are from the upper limb using palmaris longus, flexor digitorum superficialis and extensor carpi radialis longus. However, besides palmaris longus other two tendons have a substantial functional contribution and frequent anatomical variations making them suboptimal for harvesting.⁸ As compared to Palmaris longus, the Plantaris muscle has many advantages: it has a more stable frequency, a two times longer mean length of 30 cm (range-30-45 cm) and a mean width of ∼4 mm.^9,10 Therefore, Plantaris tendon is an ideal source for ligament reconstruction as it is a long tendon, has high tensile strength, it is expendable, has no donor site morbidity and absence of vital structures around it makes it easier to harvest.¹¹ The Plantaris tendon has been used for reconstruction of posttraumatic flexor tendon, extensor tendon lesions due to rheumatoid tenosynovitis, lateral ankle ligaments, atrioventricular valve repair and replacement of the papillary muscle/chordae.^10,12,13

Clinical assessment of Plantaris is not reliable especially in obese patients or when the tendon is poorly developed or anomalous. This makes an ultrasound confirmation mandatory.² Although Magnetic resonance imaging (MRI) is better but is not cost-effective for every patient.¹⁴ USG is the only practical way of documenting the presence or absence of Plantaris tendon in large population. Ultrasound is non-invasive, without radiation, inexpensive and both legs can be examined and compared simultaneously. However, there is a learning curve for the radiologist. The sensitivity of ultrasound for detection of plantaris tendon is ∼86% and false-negative results occur due to thinned out (<2 mm) Plantaris tendons and hence considered inadequate for grafting. This lead to the sensitivity for detecting a tendon suitable for grafting to 95% and specificity of 100%.²

Our findings are not dissimilar to other Indian studies^15–17 and a meta-analysis based on 41 cadaveric studies in the Western population including 10062 leg specimens which yielded overall true prevalence of Plantaris tendon ∼93% and bilateral prevalence ∼92%.⁸ Studies like ours provide the much needed confirmatory ethnic morphological data of tendon anatomy and prevalence for Radiologists, Orthopaedic and Plastic Surgeons.¹⁸

5 Conclusion

Plantaris tendon was absent in ∼11%, either unilaterally or bilaterally, in this cohort of Indian population.

Funding/sponsorship

Nil.

Informed consent (Patient/Guardian)

Not applicable.

Institutional ethical committee approval

Obtained from Institutional Ethical Committee.

Author's contribution

BS- Data acquisition, Manuscript preparation, PA: Study design, Data acquisition, Manuscript preparation. DS- Study design, Data acquisition, Manuscript preparation, SP- Data acquisition, Manuscript preparation, JSD- Data acquisition, statistical analysis. RR-Data acquisition, Manuscript preparation.

All authors read and approved the final version of the manuscript.