Peroneal Tendonitis

**Peroneal tendonitis** is inflammation or degeneration of the **peroneal tendons** — two tendons that run from the lower leg muscles, behind the lateral malleolus (outer ankle bone), and attach to the outside of the foot. These tendons are critical for ankle stability and lateral foot function. **The Two Peroneal Tendons:** 1. **Peroneus brevis** — Runs behind the fibula and attaches to the base of the 5th metatarsal (the bony bump on the outside midfoot). Its primary function is foot eversion (turning the sole outward). **More commonly affected** (70% of cases). 2. **Peroneus longus** — Runs behind the fibula alongside the brevis, then crosses under the foot to attach on the medial cuneiform and 1st metatarsal base. It everts the foot AND stabilizes the first ray during push-off. Less commonly affected but important for arch support. **Their Critical Function:** The peroneal tendons serve as the **primary dynamic stabilizers** of the lateral ankle. They actively resist ankle inversion (the motion that causes the classic ankle sprain). When you walk on uneven terrain, the peroneals fire rapidly to keep the ankle from rolling outward. This is why: - **After ankle sprains**, the peroneals are overworked compensating for damaged ligaments → tendonitis - **On uneven terrain** (trail running, hiking), the peroneals are constantly active → overuse - **With high arches**, the foot is inherently inverted → chronic peroneal overload **The Spectrum of Peroneal Tendon Pathology:** - **Tendonitis** — Acute inflammation from overuse (early, reversible) - **Tendinosis** — Chronic tendon degeneration with collagen disorganization (similar to [medial epicondylitis](/condition/medial-epicondylitis)) - **Tendon tears** — Partial or complete tears (the brevis tendon is prone to longitudinal "split tears" where it is compressed against the fibula) - **Tendon subluxation** — The tendon slips out of its groove behind the fibula during ankle motion, causing a snapping sensation. This usually requires surgical repair of the superior peroneal retinaculum.

Peroneal tendonitis results from **mechanical overload** of tendons designed for ankle stabilization: **The Biomechanical Vulnerability:** The peroneal tendons pass through a **fibro-osseous tunnel** behind the lateral malleolus — held in place by the superior peroneal retinaculum. In this tunnel: - The tendons change direction sharply, creating friction - The peroneus brevis is compressed between the peroneus longus and the fibula - This zone has relatively poor blood supply — a "watershed zone" similar to other tendinopathies **The Overload-Degeneration Cycle:** 1. **Repetitive loading** — Each step requires peroneal activation; running and trail activities dramatically increase loading 2. **Microtrauma accumulation** — The tendon sustains microscopic damage faster than it can repair 3. **Tendinosis** — Collagen becomes disorganized, neovascularization develops, and the tendon weakens 4. **Increased tear risk** — The degenerated tendon is susceptible to partial tears, especially the brevis (which is compressed against the fibula) **The Ankle Instability Connection:** This is the most important clinical association. After an ankle sprain: - The lateral ankle ligaments (ATFL, CFL) are damaged → ankle becomes unstable - The peroneal tendons must work HARDER to stabilize the ankle → chronic overload - Up to **60% of chronic ankle instability** patients have concurrent peroneal tendon pathology - This creates a vicious cycle: weak ligaments → overworked tendons → tendonitis → ankle feels more unstable → more tendon stress **High Arch (Pes Cavus) Connection:** High arches create a **varus hindfoot alignment** — the heel tilts inward. This: - Shifts weight to the lateral foot border - Places the peroneals in a mechanically disadvantaged, chronically stretched position - Increases the workload on the peroneal tendons with every step - Explains why high-arched individuals are predisposed to peroneal problems

Treatment follows a **conservative-first approach** succeeding in 85-90% of cases: **Phase 1: Acute Management (Weeks 1-4)** - **Relative rest** — Modify activities to reduce peroneal loading. Avoid running on uneven surfaces, trail running, and lateral sports. Continue low-impact activities (swimming, cycling). - **Ice** — 15-20 minutes to the lateral ankle, 3-4 times daily - **NSAIDs** — Short-term (1-2 weeks) for pain and inflammation. Topical diclofenac gel directly over the tendon is effective with fewer systemic effects. - **Ankle bracing** — Lace-up ankle brace or taping to reduce tendon excursion and stress during daily activities. Particularly important if ankle instability is present. - **Immobilization** — Walking boot for 2-4 weeks in severe cases or suspected tendon tear **Phase 2: Rehabilitation (Weeks 4-12)** - **Peroneal strengthening** — THE cornerstone of treatment: - **Resistance band eversion**: Sit with foot on floor, loop band around forefoot, slowly turn sole outward against resistance. 3 sets of 15, twice daily. - **Eccentric eversion**: Stand on the affected foot, slowly lower from a slightly everted to neutral position. 3 sets of 15. - **Single-leg balance**: Stand on affected foot on flat surface → progress to foam pad → progress to wobble board. 30 seconds, 3-5 reps, 3 times daily. - **Calf stretching** — Wall stretch, 30 seconds, 3 reps, 3-4 times daily. Tight calves alter ankle mechanics and increase peroneal tendon load. - **Proprioception training** — Critical for lateral ankle stability: single-leg stance, eyes open → eyes closed; balance board; perturbation training. - **Gradual return to running** — Start on flat, even surfaces; add terrain complexity gradually; follow the 10% rule. **Phase 3: Refractory Cases (3-6 Months of Failed Conservative Treatment)** - **Corticosteroid injection** — Ultrasound-guided injection around (not into) the tendon sheath. Provides short-term relief. Caution: risk of tendon weakening and rupture. Maximum 1-2 injections. - **PRP injection** — Emerging evidence for chronic peroneal tendinosis. - **Custom orthotics** — Lateral wedge or varus posting to reduce hindfoot varus and peroneal overload. Essential if high arches are contributing. **Surgery (10-15% of Cases):** - **Peroneal tendon debridement** — Cleaning up degenerated tendon tissue. For chronic tendinosis with partial tears. - **Peroneal tendon repair** — For significant longitudinal (split) tears of the peroneus brevis. - **Superior peroneal retinaculum repair** — For recurrent tendon subluxation. The retinaculum is deepened or reconstructed to keep tendons in their groove. - **Lateral ankle ligament reconstruction (Brostrom)** — If underlying ankle instability is driving peroneal overload. Addresses the root cause. - **Surgical outcomes**: 80-90% good to excellent results. **Prognosis:** - 85-90% resolve with conservative treatment - Addressing underlying ankle instability is key to preventing recurrence - High-arched patients need long-term orthotic support