Introduction / Definition

Achilles tendon pathologies span a broad clinical spectrum ranging from overuse degenerative changes to complete structural failure. Pathology is broadly split into:

1. Midportion tendinopathy: Degenerative changes located 2 to 6 cm proximal to the calcaneal insertion in the hypovascular watershed zone.
2. Insertional tendinopathy: Enthesopathy at the calcaneal insertion, frequently associated with retrocalcaneal bursitis, superficial adventitial bursitis, and a posterolateral calcaneal prominence (Haglund deformity).
3. Acute Achilles tendon rupture: Sudden full-thickness discontinuity of the tendon fibres, typically occurring during explosive push-off or sudden eccentric loading.
4. Chronic / neglected rupture: Ruptures presenting beyond 4 to 6 weeks, characterised by tendon edge retraction, fibrous gap formation, gastrocnemius-soleus atrophy, and lengthened muscle-tendon architecture.

Epidemiology

• Acute Rupture: Incidence ranges from 18 to 37 per 100,000 person-years, with a bimodal peak (most commonly active males aged 30–45, "weekend warriors", and a secondary peak in elderly patients). Up to 25% of acute ruptures are initially misdiagnosed or missed in primary care.
• Risk Factors: Episodic intense sporting activity (racquet sports, football, athletics), fluoroquinolone antibiotic exposure, systemic or local corticosteroid administration, inflammatory arthritides, hypercholesterolaemia, hyperuricaemia, and advancing age.
• Tendinopathy: Highly prevalent in running athletes (lifetime incidence up to 24%), but up to one-third of individuals presenting with midportion tendinopathy are sedentary, reflecting microvascular and metabolic compromise.

Relevant Anatomy

• Composition: Conjoint tendon of the gastrocnemius (spanning knee and ankle) and soleus (spanning ankle only), with variable contribution from the plantaris medially.
• Fibre Rotation: Fibres spiral internally by approximately 90 degrees as they descend; gastrocnemius fibres insert posterolaterally on the posterior calcaneus, while soleus fibres insert posteromedially. This twist creates a mechanical energy storehouse but concentrates internal shear stresses.
• Blood Supply: Longitudinal branches from the posterior tibial artery medially and the peroneal (fibular) artery laterally provide paratenon flow. The watershed hypovascular zone exists 2 to 6 cm proximal to the calcaneal insertion, which correlates with the most frequent site of both degenerative tendinopathy and acute tear.
• Envelope: The Achilles tendon lacks a true synovial sheath; instead, it is surrounded by a vascularised paratenon composed of an epitenon and peritenon that facilitates excursion.
• Neurological Relation: The sural nerve courses from central-posterior in the calf to run laterally along the lateral margin of the Achilles tendon roughly 8 to 10 cm above the calcaneal tuberosity, making it particularly vulnerable during lateral portal placement or percutaneous repair passes.

Pathophysiology & Classification

Tendinopathy: Cook and Purdam Continuum Model

• Reactive Tendinopathy: Non-inflammatory proliferative response to acute tensile or compressive overload; cell-mediated thickening with increased proteoglycans.
• Tendon Disrepair: Progression towards matrix breakdown, chondroid metaplasia, microvascular proliferation, and neurovascular ingrowth (neovascularisation).
• Degenerative Tendinopathy: Extensive areas of cellular apoptosis, disordered collagen fibrils, large collections of ground substance, and loss of tensile architecture; predisposes to acute catastrophic rupture.

Kuwada Classification (Achilles Ruptures)

Devised to guide surgical decision-making based on the gap magnitude following debridement of non-viable tissue:

• Type I: Partial rupture (managed conservatively or with local repair).
• Type II: Complete tear with gap ≤ 3 cm (direct primary end-to-end repair).
• Type III: Complete tear with defect between 3 and 5 cm (requires synthetic/autologous augmentation or tendinous turn-down / gastrocnemius V-Y lengthening).
• Type IV: Complete tear with defect > 5 cm (requires free or local dynamic tendon transfer, e.g. Flexor Hallucis Longus [FHL], peroneus brevis, combined with gastroc-soleus turn-down flab or structural allograft).

Clinical Presentation & Examination

Acute Rupture

• History: Sudden, severe "gunshot" or "kick" sensation to the back of the calf, audible snap, followed by immediate weakness. Pain often diminishes rapidly after complete tear.
• Resting Angle (Matles Test): With the patient prone and knees flexed to 90 degrees, the injured foot hangs in increased passive dorsiflexion compared to the resting gravity equinus of the uninjured contralateral foot.
• Palpable Gap (Hatchet Sign): Distinct soft tissue depression in the watershed zone.
• Simmonds-Thompson Calf Squeeze Test: Squeezing the calf belly fails to produce passive ankle plantarflexion. Pathognomonic for full-thickness disruption.
• Active Plantarflexion Fallacy: Active plantarflexion may remain partially intact through preserved function of posterior tibial, peroneal, and long toe flexor muscles; however, push-off power is critically lost.
• Copeland's Sphygmomanometer Test: A blood pressure cuff inflated to 100 mmHg around the calf fails to register a pressure increase during passive dorsiflexion.

Tendinopathy

• Midportion: Morning stiffness, tenderness, and nodular fusiform swelling 2–6 cm above calcaneus. Pain moves with tendon excursion (differentiating it from fixed paratenonitis, known as the Royal London Hospital Test).
• Insertional: Pain at bone-tendon junction, aggravated by dorsiflexion impingement; local prominence (Haglund's deformity), positive two-finger squeeze anterior to tendon over retrocalcaneal bursa.

Investigations

• Plain Radiographs (AP, Lateral, Axial Calcaneal): Rule out calcaneal avulsion fractures, demonstrate posterior cortical enthesophytes, or calculate Fowler-Philip angle (> 75°) / Chauveaux-Liet angle in Haglund deformity.
• Diagnostic Ultrasound: Operator-dependent, highly sensitive modality for confirming full-thickness gap, distinguishing partial tears, and evaluating dynamic tendon apposition in equinus.
• Magnetic Resonance Imaging (MRI): Gold standard for chronicity evaluation, estimating gap size for surgical planning, assessing degenerative changes, and ruling out flexor tendon pathologies.

Management

Acute Achilles Tendon Rupture

1. Non-operative Functional Rehabilitation

• Evidence Base: Landmark trials by Willits et al. (JBJS Am 2010) and Olsson et al. (Am J Sports Med 2013) demonstrated that with modern functional weight-bearing protocols in gravity equinus, non-operative management achieves equivalent functional outcomes and re-rupture rates (approx. 3–5%) compared to open surgical repair, avoiding wound complication risks.
• Protocol: Immediate immobilisation in resting equinus (> 20° plantarflexion) using a rigid boot with heel wedges. Progressive serial wedge removal every 2 weeks, transitioning to neutral by 6–8 weeks, with early controlled weight-bearing commenced within 2 to 4 weeks under physiotherapeutic guidance.

2. Operative Management

• Indications: High-demand athletes, delayed presentation (> 7–14 days), lack of apposition on ultrasound in equinus, recurrent rupture, or patient preference.
• Open End-to-End Repair: Postero-medial longitudinal incision (to avoid sural nerve injury). Non-absorbable, heavy core locking sutures (modified Krakow, Bunnell, or Kessler) using #2 or #5 sutures with fine epitenon continuous running suture for edge apposition.
• Percutaneous / Minimally Invasive Repair: e.g., Achillon or PARS (Percutaneous Achilles Repair System) jig devices. Delivers lower wound infection rates compared to open repair but carries an elevated risk of sural nerve injury/entrapment if nerve course is not safeguarded.

Chronic / Neglected Ruptures

• Gap < 2-3 cm: Direct debridement and end-to-end repair with heavy non-absorbable sutures.
• Gap 2-5 cm: Gastrocnemius-Soleus V-Y advancement (apical cut at the musculotendinous junction with superficial tendinous limb incision, leaving underlying muscle fibres intact) or single/double Lindholm / Bosworth turn-down fascial flaps.
• Gap > 5 cm: Dynamic Flexor Hallucis Longus (FHL) transfer. FHL tendon is harvested either through a single posterior incision (short harvest above knot of Henry) or a dual incision medial foot approach (long harvest at the master knot of Henry). Transferred into the calcaneal tuberosity via an interference screw or transosseous bone tunnel directly anterior to the Achilles insertion, matching axis of pull and firing synchronously during gait.

Achilles Tendinopathy

• Conservative (First-Line):
  • Relative rest, biomechanical correction, heel raises (unloads tendon).
  • Alfredson Eccentric Loading Protocol: 180 repetitions per day (3 sets of 15 repetitions, twice daily, with both straight and bent knee) over 12 weeks. High success rate in midportion disease.
  • Caution with Injections: Corticosteroid injections into the tendon substance are strictly contraindicated due to disastrous rupture rates. High-volume image-guided saline injections (HVIGI) stripping neovessels from paratenon show variable success.
  • Extracorporeal Shockwave Therapy (ESWT) holds NICE interventional procedure guidance support for chronic refractory cases.
• Surgical Intervention: Indicated only after failure of ≥ 6 months exhaustive conservative care. Includes longitudinal tenotomies, excision of degenerative tendon core, debridement of retrocalcaneal bursa, and resection of Haglund prominence with re-anchoring of the insertional footprint using suture anchors.

Complications

• Re-rupture: Approximately 2–3% in operative repairs; 3–5% in accelerated functional non-operative regimens (historically up to 10–12% in rigid non-weight-bearing cast series).
• Wound Necrosis and Deep Infection: 5–10% in open procedures. Greatest risk factors: smoking, diabetes, female gender, corticosteroid use. Often necessitates salvage with free flap transfer (e.g. anterolateral thigh flap) due to sparse soft tissue envelope.
• Sural Nerve Neuropraxia / Neuroma: Elevated in percutaneous repairs (2–5%).
• Deep Vein Thrombosis (DVT) / Pulmonary Embolism: 5–11% incidence across both operative and non-operative groups; thromboprophylaxis risk stratification is mandatory.
• Tendon Lengthening: Results in chronic calf weakness, loss of push-off power, and abnormal gait kinetics.

Exam Pearls

• Thompson's Test: Squeeze upper third of calf; absence of passive plantarflexion is diagnostic. Plantarflexion produced by toe flexors or posterior tibialis does not rule out complete Achilles discontinuity.
• Matles Test Reliability: Increased dorsiflexion of the affected foot with knee flexed to 90 degrees in the prone position is often the most reliable early physical sign of acute structural rupture.
• Sural Nerve Anatomy: Exits lateral to the Achilles tendon roughly 8 to 10 cm proximal to the calcaneus, making the proximal-lateral percutaneous stitch the most hazardous step.
• Kuwada Thresholds: 3 cm and 5 cm defects differentiate primary repair, local advancement (V-Y / turn-down), and distant transfer (FHL / peroneus brevis).
• FHL Transfer Mechanics: Harvested at the Master Knot of Henry for maximum length; FHL acts as an ideal motor substitute because it is an ankle plantarflexor that fires in phase with the gastrosoleus complex.