Mini-Open Achilles Tendon Repair: Perspective 2

Emilio Wagner

Cristian Ortiz

ANATOMY

The gastrocnemius muscle merges with the soleus muscle to form the Achilles tendon, which inserts onto the calcaneus.
- The gastrocnemius muscle is the most superficial muscle and is responsible of plantarflexion of the ankle and propelling the body forward. The soleus muscle is a postural muscle, with no action on the knee joint (it inserts only on the tibia), and also acts as a peripheral vascular pump.
- The Achilles tendon is approximately 15 cm long, flattened at both its proximal and distal end but rounded in the middle portion. On its anterior surface receives muscular fibers from the soleus up to its insertion.⁵
The Achilles tendon is enclosed by a paratenon, which is a thin gliding membrane, continuous proximally with fascia overlying muscles and distally continuous with the periosteum of the calcaneus. This structure is the most important regarding blood supply to the middle portion of the tendon. Most blood vessels arise from the anterior aspect of the paratenon, which is also the area where neovascularization occurs in tendinopathic patients. A relatively avascular area of the tendon is described near its insertion. Regarding vascular density, the middle portion of the tendon possesses the lesser density compared to its proximal or distal parts.⁵

PATHOGENESIS

The Achilles tendon transmits all the tension generated by the gastrocnemius-soleus complex to the calcaneus. The tendon is elastic and has the capability of deforming and recovering its original length if the strain does not exceed 4%. If the strain is between 4% and 8%, the tendon fibers start to become damaged. At a strain level of approximately 8%, the Achilles tendon may rupture.⁴
The exact reason why the Achilles tendon ruptures is not known, but there are two main theories, one a degenerative theory and one a mechanical theory. In the mechanical theory, the tendon just suffers strain which exceeds its limit with subsequent failure of the collagen fibrils. In the degenerative theory, a chronic degeneration of the tendon leads to rupture without the need of applying excessive loads.
Degenerative tendinopathy is present in most histologic samples from spontaneous tendon ruptures.⁶ It can be assumed that degenerated tendons will have less tensile strength and rupture under physiologic forces. It has been shown that ruptured tendons have more advanced intratendinous changes than tendinopathic tendons. Degenerative changes are described as hypoxic, mucoid, tendolipomatous, and calcific changes. These changes are found just in 31% of control tendons.⁴
The origin of tendinopathy is the subject of debate, but the overload theory is the most accepted one, where repeated loading of a musculotendinous unit may result in weakening of the structure and, in some cases, a failure of tendon tissue. If the overload persists and the tendon is unable to heal and/or respond to load over time, this weakening may increase and compromise a higher percentage of the total tissue.⁶ The failed healing response of the tendon may relate to numerous factors, such as genetics, age, and gender, among others.
Other reasons for Achilles tendon ruptures relate to drugrelated effects. Corticosteroids (local and systemic) have been described as risk factors for tendon ruptures. Fluoroquinolone antibiotic use is also a risk factor for Achilles tendon ruptures. Inflammatory conditions, collagen abnormalities, infectious diseases, and hyperlipidemia have also been associated with tendon ruptures.

NATURAL HISTORY

When left untreated, Achilles ruptures are named chronic ruptures and they cause great difficulty with ankle plantarflexion. Besides atrophy of the muscle belly, the tendon sheath becomes thickened and adherent to the tendon ends. There is a scar tissue bridging the defect, but this tissue is of poor quality, not as strong as the intact tendon, and may elongate with time.³
Chronic ruptures of the Achilles tendon are mainly surgically treated and conservative measures such as ankle-foot orthoses are only used in low-demand individuals or if the surgery is contraindicated.

PATIENT HISTORY AND PHYSICAL FINDINGS

Almost all the time, patients present with a typical history of feeling suddenly a “pop“ in the calf, often believing that they were hit by someone or somebody. After that, they feel pain and weakness to bear weight. Achilles tendon ruptures can be missed in up to 25% of patients.⁴ The diagnosis is clinical, and physical examination is paramount.

The identification of loss of physiologic equinus of the ankle will ascertain the diagnosis of a complete Achilles tendon rupture.

This can be evaluated by the knee flexion test, where the patient is prone holding his knee flexed and the foot falls into neutral or dorsiflexion position.

FIG 1 • Patient positioned prone at the end of the table. Observe normal physiologic equinus position of the ankle at the left of the picture compared to the nonphysiologic dorsiflexed position of the ankle at the right side, representing a complete Achilles tendon rupture.

This same test can be performed prone but with the knee extended, and the relative equinus of the ankle can be compared between the healthy and injured side. Any difference in the plantarflexion resting position of the ankle will indicate a loss of continuity of the Achilles tendon (FIG 1). A gap can be palpated in the rupture site, but this maneuver can be painful.
The Thompson test can also be performed, where squeezing of the calf should produce ankle plantarflexion. The test is positive when there is no or limited plantarflexion of the ankle, indicating an Achilles tendon rupture.

IMAGING AND OTHER DIAGNOSTIC STUDIES

Generally speaking, no diagnostic studies are needed to complete the diagnosis of Achilles tendon ruptures.
Ultrasonography and magnetic resonance imaging (MRI) have been used as an adjunct to assure clinical diagnosis, but they should be used to evaluate other diagnoses which may individually change the approach.
- Tendinopathy can be evaluated by MRI, which may have a role for follow-up studies.
- Ultrasonography may have a role when long-standing ruptures are being evaluated, as it will show if there still is hematoma left at the rupture site. If not, this may hinder a minimally invasive approach and incline the surgeon to perform an open repair. Also, ultrasound will detect the presence of deep vein thrombosis, which may delay the operative intervention.
Sometimes, imaging studies could be misleading when they show partial continuity of the tendon. In these cases, clinical diagnosis based on loss of physiologic equinus confirms the diagnosis.