Introduction

The combination of tendon pain, swelling, and impaired performance should be given the clinical label of tendinopathy, and should include the histopathological entities peritendinitis and tendinosis. The most common clinical diagnosis of Achilles overuse injuries is paratendinopathy and/ or tendinopathy (55-65%), followed by insertional problems like retrocalcaneal bursitis and insertional tendinopathy (20-25%).

Differentiation between tendinopathy of the main body of the Achilles tendon and paratendinopathy may be confusing, and frequently these entities coexist in the chronic phase. There is no consensus on which causes the pain, the peritendineum, the tendon proper, or a combination of both.

Degeneration of the body of the Achilles tendon has been found during autopsies in 34% of tendons in patients without complaints7. This finding was confirmed in a study by Khan and co-workers who identified abnormal tendon morphology in 37 of the 57 symptomatic tendons (65%) and abnormal morphology in 9 of 28 asymptomatic tendons (32%) using ultrasound. Another study concluded that there was no relationship between symptoms and ultrasonographic intratendinous abnormalities in elite gymnasts. These studies imply that degeneration of the Achilles tendon proper may not be the cause of pain.

Since neovascularisation and enhanced neurovascular growth into the peritendineum and myofibroblasts responsible for the formation of permanent scarring and the shrinkage of peritendinous tissue have been shown in patients with chronic complaints of pain and stiffness of their Achilles tendon, we postulate that the peritendineum is the main cause of complaints.

This part of ankleplatform describes the endoscopic management of a combination of mid-portion tendinopathy and paratendinopathy, and isolated paratendinopathy: Achilles tendoscopy.

Anatomy

The anatomy of the Achilles tendon is different from that of other tendons inserting into the foot. It lacks a true synovial sheath but rather has a paratenon. The paratenon functions as an elastic sleeve and permits free movement of the tendon within the surrounding tissues. The paratenon forms a thin space between the tendon and crural fascia. Under the paratenon, the entire Achilles tendon is surrounded by a fine, smooth connective tissue sheath called the epitenon. On its outer surface, the epitenon is in contact with the paratenon. The inner surface of the epitenon is continuous with the endotenon, which binds the collagen fibers and fiber bundles together. 

The paratenon is richly vascularized, and provides blood supply to the Achilles tendon itself. The neural supply to the Achilles tendon and the surrounding paratenon is provided by nerves from the attaching muscles and by small fasciculi from cutaneous nerves, in particular the sural nerve. The number of nerves and nerve endings is relatively low, and many nerve fibers terminate in the paratenon or on the tendon surface. These nerves follow the vascular channels within the long axis of the tendon, anastomose via obliquely and transversely oriented fibers, and finally terminate in sensory nerve endings. Achilles paratendinopathy involves inflammation of the peritendinous tissues. In patients with Achilles tendon overuse injury, the sensory nerve endings accompany the paratendinous neovascularization.

History & Physical Examination

Symptoms exist of pain and swelling around the Achilles tendon which often increase with activity in patients with paratendinopathy. The tendon is diffusely swollen and on palpation, tenderness is usually greatest in the middle third of the tendon. The pain is often most prominent on the medial side. On physical examination, a paratendinopathy manifests itself as peritendinous crepitus as the tendon tries to glide within the inflamed covering.
Typically, in patients with acute symptoms, the area of swelling and tenderness does not move when the ankle joint is dorsiflexed. Areas of increased erythema, local heat, and palpable tendon nodules or defects may also be present at clinical examination. In addition, ankle instabilities and malalignment of the lower extremity, especially in the foot, should be sought in patients with Achilles complaints. 
In chronic Achilles paratendinopathy, exercise-induced pain is still the cardinal symptom while crepitation and swelling diminish.

A tender, nodular swelling usually indicates tendinopathy of the main body of the tendon and these focal tender nodules move as the ankle is dorsi- and plantarflexed. Tendinopathy and patratendinopathy often co-exist.

Differential diagnoses of paratendinopathy are tendinopathy, a combination of both, partial rupture, an insertional disorder, anomalous soleus muscle and complete rupture. All these show a marked overlapping of the findings in history and physical examination. In clinical practice overuse injuries often do have features of more than one pathophysiological entity, however in most cases thorough history taking and physical examination should provide with the correct diagnosis.

Diagnostic Imaging

In the acute phase of Achilles tendinopathy, ultrasonography reveals fluid surrounding the tendon. In its more chronic form, peritendinous adhesions can be seen as thickening of the hypo-echoic paratenon with poorly defined borders. Discontinuity of tendon fibers, focal hypo-echoic intratendinous areas, and localized tendon swelling, and thickening are the most characteristic ultrasonographic findings in patients with surgically verified intratendinous lesion of the Achilles tendon. Ultrasound imaging is known as a cost-effective and accurate to evaluate disorders of the Achilles tendon.

MRI has been used extensively to visualize tendon pathology as it satisfies two fundamental principles of imaging. It provides high intrinsic tissue contrast, which is able to separate normal from abnormal tendons, and gives high spatial resolution that can identify detailed anatomic structures. The ability of MRI to acquire images from multiple planes (axial, sagittal, coronal) is also a clear advance, and is especially important for pre-operative planning. In the acute phase of Achilles paratendinopathy MRI shows high signal around the Achilles tendon on Short Tau Inversion Recovery (STIR) and T2 (hyper- intense signal in water rich regions) weighted images. In the chronic phase the paratenon is thickened on MRI. The disadvantages of MRI are its relatively high cost, limited availability in some countries, time-consuming scanning, and slow and often incomplete resolution of signal changes after operative intervention.

Surgical Treatment

Surgical management is recommended to those patients who do not adequately respond to 3 to 6 months of conservative management. However, no prospective randomized studies comparing operative and conservative management of Achilles tendinopathy and/ or -paratendinopathy have been published and most of our knowledge on management efficacy is based on clinical experience and descriptive studies.

We have been performing Achilles tendoscopy for isolated paratendinopathy and combined chronic Achilles tendinopathy and paratendinopathy over the last decennium. It comprises a release of the peritendineum, hereby ‘denervating' it, leaving the tendon proper untouched. This technique renders good short- and midterm results, as described in a retrospective study by Steenstra and co-workers. A prospective series is currently under investigation. With this procedure the intratendinous changes cannot be addressed, so when on physical examination the tendon proper seems to cause the majority of complaints, Achilles tendoscopy should not be performed. 

Post-operative rehabilitation

The patient can be discharged the same day of surgery and weightbearing is allowed as tolerated. The patient is instructed to perform active dorsiflexion of the ankle to the neutral position (knee slightly bent). This exercise should be performed 2 or 3 days times per hour for the first days after surgery. The patient is instructed to elevate the foot when not walking to prevent edema. The dressing is removed 3 days post-operative. Normal walking without crutches at 4 - 5 days post surgery. Patients with limited range of motion are directed to a physiotherapist. Running can be started when range of motion is normal and in absence of swelling. This can on avarage be expected at 3 weeks post surgery. Sport resumption can on average be expected at 6 weeks post surgery. 

Recommended literature

Steenstra F, van Dijk CN. Achilles tendoscopy. Foot Ankle Clin. 2006 Jun;11(2):429-38, viii. 

Van Sterkenburg MN, Kerkhoffs GM, van Dijk CN. Good outcome after stripping the plantaris tendon in patients with chronic mid-portion Achilles tendinopathy. Knee Surg Sports Traumatol Arthrosc. 2011 Aug;19(8):1362-6.

Van Sterkenburg MN, van Dijk CN. Mid-portion Achilles tendinopathy: why painful? An evidence-based philosophy. Knee Surg Sports Traumatol Arthrosc. 2011 Aug;19(8):1367-75.