Plantaris Release for Non-insertional Achilles Tendinopathy

Midportion Achilles tendinopathy has been found to have an incidence of 1.85 per 1000 in the general population and is reported to be a career-ending condition in up to 5% of professional athletes. The mainstay of treatment at present is typically prescription of eccentric strengthening exercises, activity modification and analgesia. If conservative intervention fails then surgery can be indicated, and a wide range of different procedures are described. Open Achilles surgery may be successful in 75-100% of patients but debridement with excision of areas of tendinosis weakens the tendon and can delay return to sport for up to 18 months.

There is currently a growing acceptance for the role of the plantaris tendon in the development of medial Achilles tendon (AT) pain and focal medial Achilles tendinopathy. The plantaris arises from the lateral aspect of the supracondylar line of the femur, passing from lateral to medial deep to medial gastrocnemius and superficial to soleus, inserting into the medial aspect of the calcaneus. However there is wide variation in the exact insertion of the plantaris tendon observed distally. A large study examining 750 limbs reported 4 types of distal insertion, a further study reported 3 different insertion sites, whilst a more recent study reported 9 variations. Consistently 10-20% of plantaris tendons are identified to have a direct structural attachment to the AT. This variety of insertion patterns may explain why some individuals are more prone to plantaris issues than others.

Friction of the plantaris tendon against the medial border of the Achilles tendon and subsequent pain and swelling is a significant problem in elite track and field athletes, with an annual injury incidence of 3.9-9.3% reported. Biomechanical studies have hypothesized that this is due to the plantaris tendon being stiffer and stronger than the Achilles tendon (AT), thus reducing its capacity to elongate in response to loading. This is thought to cause friction between the AT and plantaris contributing to peritendon inflammation, which can induce tendinopathy changes to the AT through either a neuro-inflammatory mediation or via a compressive mechanism.

Twenty nine percent of patients with NIAT fail to respond to conservative management and many have to give up sporting activities. Patients who continue to experience symptoms may be referred for a high volume injection of the paratenon under ultrasound scan (USS) guidance - this aims to strip the paratenon layer from the AT which often becomes adherent with fibrous bands. This also strips the neovascularization from the ventral surface of the AT - this abnormal tissue has nerve fibres within it and it is believed that this is a major pain generator in NIAT. However, it is recognised that a sub-group of patients with NIAT have isolated medially-located pain approximately 4-6cm from insertion into the os calcis. On USS and Magnetic Resonance Imaging (MRI) the plantaris tendon may be seen to attach to the medial aspect of the AT (either inserting into the side of the AT directly rather than the os calcis or becoming adherent with fibrous tissue to the AT medial border). This is at the level of the AT where it has undergone a 90 degree rotation and corresponds to the soleus part of the tendon. Since the plantaris tendon crosses 2 joints (originating above the knee and inserting into the os calcis) whereas the soleus only crosses one joint (the ankle) there may be a differential movement of the plantaris against the medial border of the AT creating a frictional syndrome with subsequent focal inflammation and then tendinosis of the AT.

The treatment for this "plantaris syndrome" if it fails to respond to conservative measures or USS guided injections is to remove the plantaris tendon and surgically strip the ventral aspect of the AT through a 3cm medial incision. This is performed in theatres under general anaesthetic with good or excellent results being reported in 90% and 94% of professional athletes returning to sport.3 However, there have been papers reporting on the successful treatment of patients purely cutting the plantaris tendon using a minimally invasive endoscopic technique.The plantaris tendon is easily visualized under USS and tenotomy of tendons under USS guidance is described elsewhere. Performing a tenotomy of the plantaris tendon under USS guidance would necessitate a 5mm incision and may be performed under local anaesthetic as an out-patient. Currently it is not known whether this is as good as the open surgical procedure performed in theatre and the investigators would propose a randomized study comparing the techniques.

The rationale for the current study therefore is to compare clinical outcomes and AT structural changes in patients with NIAT undergoing plantaris excision using an open surgical procedure to those undergoing a minimally invasive US guided procedure performed in an out-patient clinic. The former is known to provide good clinical outcomes however the latter could significantly reduce post-operative scarring, recovery times and surgical costs. Thus, if found to be comparable, treating these patients in the clinic with an ultrasound guided plantaris release would offer a desirable alternative to surgery and result in a change of current clinical interventions for this population.