A 58-year-old lady was referred for imaging studies after suffering a pedestrian accident three weeks before. She had twisted her right foot with an audible snap, as she had slipped off the kerb.
X-rays of the right foot in two planes (Fig. 1) showed pronounced soft-tissue swelling at the lateral foot border, most prominently at the level of the calcaneocuboid joint. A proximally displaced os peroneum (OP) with an irregular distal contour was present. More distally, at the level of the cuboid notch, some tiny bone fragments appeared within the soft-tissue opacity, probably representing bony avulsions. Given the patient's history and the radiographic findings, peroneus longus tendon (PLT) injury was suspected, and an MRI of the right foot and ankle was performed, showing replacement of the normally dark tendon by diffuse T1- and T2-hyperintense signal, that extended from the retracted sesamoid down to the cuboid notch. The distance of the OP to the calcaneocuboid joint measured on sagittal MR images was about 12 mm (Fig. 2). Coronal T2-weighted images showed complete discontinuity of the PLT on several contiguous slices (Fig. 3).
The os peroneum (OP) is a sesamoid bone of variable shape and size in the peroneus longus tendon (PLT). It is normally situated at the lateral calcaneocuboid joint, proximally to the plantar inflection of the tendon. In old-world monkeys, the OP is a regular bone of the foot, articulating with a facet of the cuboid, whereas in humans, it has undergone regression with the loss of hallux opposability [1]. Its prevalence has been reported between 4.7 and 30% [2, 3]. The OP may rarely be affected by, or associated with, acute traumatic or chronic attrition injuries of the PLT, especially with inversion stress in a cavovarus foot [4]. However, the mere presence of an OP apparently does not predispose to degenerative disease [3]. PLT tears are injuries, that are commonly overlooked, and the final diagnosis may be delayed up to several months or even years [5]. Complete tears are more likely to occur in the distal PLT segment at the cuboid notch [6]. Foot mechanics may be seriously impaired by these ruptures. However, asymptomatic cases have also been described [7]. PLT ruptures typically present either as a fracture through the OP with diastasis of the fragments or as posterior dislocation of the whole OP [8]. Radiographic measurements of fragment separation and displacement relative to the calcaneocuboid joint have been carried out by Brigido and co-workers. Accordingly, a gap between fragments of 6 mm or more or proximal OP displacement of 10 mm or more are indicative of a full-thickness tear of the PLT [9].
MRI is very accurate in predicting partial or complete PLT tears, especially if oblique coronal T2-weighted images, perpendicular to the tendon course, are included [6, 10]. Although comparative studies with ultrasound are lacking, MRI is probably the imaging method of choice to secure a suspected PLT rupture or to detect alternative causes of lateral foot pain, not only in the setting of acute trauma.
Complete peroneus longus tendon rupture
(1) X-ray:
On the lateral side of the right foot, near the calcaneocuboid joint, a small, roughly circular or split-shaped bony shadow can be observed, suggesting the presence of an accessory ossicle in this region (i.e., the Os Peroneum, OP). In some cases, fragmentation or clear separation of the two parts may be visible.
Overall, the bony structures of the foot appear fundamentally normal, with no obvious bone collapse or joint dislocation. However, an abnormal gap or discontinuity can be seen near the OP, indicating possible tearing of the Peroneus Longus Tendon (PLT) or an associated avulsion fracture.
(2) MRI:
Coronal and sagittal T2-weighted images show abnormal soft tissue signals around the level of the OP. Localized high signal intensity, irregular shape, or a partial tendon interruption can be observed in the Peroneus Longus Tendon; in some cases, a small amount of fluid or edema signal may be present around the tendon. If the distance between the two OP fragments is ≥6 mm, or the proximal fragment is displaced ≥10 mm proximally, it often suggests a full-thickness tear of the Peroneus Longus Tendon.
Based on the imaging findings and the patient’s history of trauma, consider the following possibilities:
Taking into account the patient’s age (58 years), history of trauma (sprain with a “click” sound), and the characteristic imaging findings (fragmentation or separation of the OP, high signal intensity indicative of tendon discontinuity), the most likely diagnosis is:
Peroneus Longus Tendon Tear with Fracture/Fragmentation of the Os Peroneum (OP)
If there is still uncertainty, high-resolution ultrasound or additional clinical examinations and physical evaluations can be considered to rule out other foot pathologies. If necessary, surgical exploration can provide further confirmation.
(1) Conservative Treatment:
For mild or partial tears, a short period of immobilization with a cast or protective brace may be considered, limiting weight-bearing activities and supplementing with anti-inflammatory and analgesic medications to control pain and swelling. During this phase, avoid any movements that may cause excessive traction on the Peroneus Longus Tendon.
(2) Surgical Indications:
If there is a definite tendon rupture, significant displacement of bony fragments (fragment separation ≥6 mm), or if symptoms persist and affect foot function after conservative treatment, surgical repair of the Peroneus Longus Tendon and management of the fragmented OP should be considered. Postoperative rehabilitation is necessary to gradually restore ankle and foot strength and stability.
(3) Rehabilitation and Exercise Prescription (FITT-VP Principles):
① Initial Phase (Postoperative or Acute Phase):
• Frequency: 1–2 sessions of mild activity per day, such as small-range ankle flexion and extension exercises.
• Intensity: Very low intensity, avoiding significant increase in pain or swelling.
• Time: 5–10 minutes per session, without causing fatigue.
• Type: Passive ankle movements, seated ankle pump exercises, combined with ice therapy and limb elevation if necessary.
• Progression: Gradually increase the range of motion based on pain and swelling recovery.
② Recovery Phase (After Removing Protective Gear):
• Frequency: 3–4 sessions per week.
• Intensity: Low to moderate intensity; may include resistive band exercises for ankle inversion, eversion, dorsiflexion, and plantar flexion.
• Time: 15–20 minutes per session.
• Type: Balance training (e.g., single-leg stance) and core stability exercises.
• Progression: Increase the frequency and weight resistance in ankle exercises and reduce external support as foot stability and strength improve.
③ Strengthening Phase (Functional Reconstruction):
• Frequency: 3–5 sessions per week.
• Intensity: Moderate intensity, gradually transitioning to moderate-to-high intensity; add more complex lower limb proprioceptive exercises (e.g., small jumps, change-of-direction drills).
• Time: 20–30 minutes per session.
• Type: Combine gentle treadmill running or functional exercises to strengthen the small foot muscles.
• Progression: Depending on improvement in joint stability and pain relief, progressively return to normal walking, climbing stairs, slow running, and low-intensity sports.
For a 58-year-old female patient, special attention is required regarding bone density and potential degenerative changes in the foot and ankle. Adjust training intensity and frequency dynamically based on tolerance. If persistent pain, swelling, or discomfort occurs, timely follow-up and reassessment of the rehabilitation plan are recommended.
This report is a reference analysis based on imaging and clinical information. It cannot replace an in-person consultation or professional medical advice. The final diagnosis and treatment plan should be determined based on the patient’s specific condition, further clinical examinations or pathological results, and the comprehensive evaluation by a qualified physician.
Complete peroneus longus tendon rupture
