Peroneal Tendon Subluxation is NOT Ankle Laxity
Peroneal tendon subluxation is a distinct pathological entity involving instability of the peroneal tendons within the retromalleolar groove, not a form of ankle joint laxity. These are separate anatomical and clinical conditions that require different diagnostic and therapeutic approaches.
Understanding the Distinction
Peroneal Tendon Subluxation
- Peroneal tendon subluxation occurs when the peroneal tendons displace anteriorly from the retromalleolar groove, typically due to disruption of the superior peroneal retinaculum (SPR) 1, 2
- The pathology involves the fibro-osseous tunnel system that contains the tendons, not the ankle joint ligaments themselves 3
- Intrasheath subluxation can occur where tendons remain in the groove but move abnormally within their sheath, distinct from SPR tears 4
Ankle Laxity (Instability)
- Ankle laxity refers to excessive motion at the ankle joint itself, typically involving disruption of lateral collateral ligaments (anterior talofibular ligament, calcaneofibular ligament) or deltoid ligaments 5
- MRI demonstrates 97% diagnostic accuracy for anterior talofibular ligament injury and 96% sensitivity for deep deltoid ligament tears 5
Important Clinical Relationship
These Conditions Commonly Coexist
- Peroneal tendon subluxation is commonly associated with lateral ankle instability because disruption of lateral collateral ankle ligaments places considerable strain on the superior peroneal retinaculum 3
- This explains why patients with ankle sprains may develop both conditions simultaneously, leading to diagnostic confusion 1, 6
- Peroneal tendon subluxation is often misdiagnosed as an ankle sprain 2, 6
Diagnostic Approach to Differentiate
Clinical Examination Findings
- In peroneal subluxation, patients report a popping or snapping sensation, and tendons may be visibly subluxing anteriorly on the distal fibula during ankle circumduction in eversion and dorsiflexion 3, 6
- With SPR tears, tendons dislocate from the peroneal groove; with intrasheath laxity, tendons remain in the groove but move abnormally 4
- Ankle laxity presents with joint instability on stress testing (anterior drawer, talar tilt) without tendon displacement 5
Imaging Strategy
- Ultrasound is the superior modality for peroneal tendon subluxation, allowing dynamic assessment with 100% positive predictive value compared with surgical findings 5, 7
- MRI has only 66% accuracy for assessing tendon subluxation compared to ultrasound's superior capability 5, 7
- For ankle ligamentous laxity, MRI demonstrates 77-92% accuracy for chronic lateral ligament tears and 100% accuracy for tibiofibular ligament tears 5
Clinical Pitfalls to Avoid
- Do not assume ankle instability symptoms are solely due to ligamentous injury—always assess for concurrent peroneal tendon pathology 3
- History of previous ankle injury "misdiagnosed as a sprain" should raise suspicion for peroneal subluxation 3, 6
- Ultrasound results are operator-dependent, so expertise is critical for accurate diagnosis 5
- Up to 34% of asymptomatic patients may have peroneus brevis tendon tears on MRI, so clinical correlation is essential 5