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Wheeless' Textbook of Orthopaedics

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.



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, October 4, 2012 12:53 pm