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Os Trigonum / Posterior Talar Impingement

- See:
- Diff Dx: Posterior Ankle Pain
- Fractures of Posterior Talar Process

- Discussion:
- accessory bone found just posterior to talus (accessory ossification center of the posterior process of the talus);
- it may be considered a non united portion of the lateral tubercle;
- os trigonum is round, oval, or triangular and of variable size;
- present in 2.5% to 14% of normal feet;
- arises from separate ossification center just posterior to lateral tubercle of posterior talar process;
- it may fuse w/ lateral tubercle or remain as separate ossicle;
- may be injured with forced dorsiflexion injuries - causing disruption of the synchondrosis bewteen the Os and the Talus;
- signs and symptoms:
- symptoms are worse when she assumes the en pointe position
- tenderness to palpation at posterolateral aspect of ankle posterior to the peroneal tendons which is made worse with passive plantar flexion;
- operative management through a medial approach;

- Radiographs:
- edges appear smooth, with dense cortical bone;
- need to distinguish between ossicle & frx of lateral tubercle;
- MRI:
- look for fluid surrounding the Os and associated marrow edema (absence of talar marrow edema)
- if there is marrow edema in the talus then consider posterior talar process fracture;
- in the report by Sopov et al, the authors sought to determine the clinical significance of an increased uptake of 99mTc methylene-diphosphonate (Tc-MDP) in the os trigonum region seen on bone scintigrams of soldiers on active duty;
- radionuclide whole-body skeletal imaging and physical examination of the foot were carried out in 100 consecutive soldiers on active duty referred for evaluation of suspected stress-injury of the lower limbs, back pain, and different skeletal trauma;
- lateral radiographs of the foot were performed in those with increased uptake of Tc-MDP at the site of os trigonum;
- among 200 feet, 27 (13.5%) showed an increased uptake of Tc-MDP in the os trigonum region;
- right side was affected in six patients, the left side in 11 and five patients had bilaterally increased uptake;
- on X-rays, 31 of 44 feet showed the os trigonum. Only 10 of these 27 feet (37%) had a symptomatic os trigonum;
- increased uptake of Tc-MDP in the os trigonum region is a frequent finding among active soldiers and is of limited value in detecting symptomatic os trigonum;
- Bone scintigraphic findings of os trigonum: a prospective study of 100 soldiers on active duty.

- Posterior Compression Syndrome: (see: diff dx);
- arises from forced plantar flexion in Ballet dancers;
- impingement of posterior aspect of talus between tibia & calcaneus may cause block to plantar flexion;
- results in painful lateral compression between calcaneus and posterior aspect of tibia;
- forceful passive plantar flexion should reproduce the patients symptoms;
- in contrast, both FHL tendinitis and posterior tibial tendinitis cause posteromedial tenderness;
- a differential lidocaine/steroid injection (injected laterally at the posterior process of the calcaneus) should relieve symptoms;
- note that this condition may occur along with FHL tendonitis;

- non-operative treatment:
- local steroid injections can be effective;
- cast immobilization might reduce soft tissue swelling, but it will not reduce block to motion;

- operative treatment:

- excision of bony block will often improve motion and eliminate pain;
- for isolated posterior impingement, consider lateral approach;
- performed at the level of the ankle joint, just posterior to the peroneal tendons;
- identify the sural nerve and the FHL tunnel;
- after a capsulotomy has been performed, identify the os trigonum or the offending osteophyte;
- an adequate decompression should allow the foot to be plantar flexed w/ no bony impingement

Anatomy of the os trigonum.

Stenosing tenosynovitis of the flexor hallucis longus tendon and posterior impingement upon the os trigonum in ballet dancers.

Outcome of Resection of a Symptomatic Os Trigonum.

Bilateral os trigonum syndrome associated with bilateral tenosynovitis of the flexor hallucis longus muscle.