Abstract
PurposeThe aim of the study was to examine the ligaments of the os trigonum.MethodsThe ankle joint magnetic resonance imaging (MRI) of 104 patients with the os trigonum (experimental group) and 104 patients without the os trigonum (control group) were re-reviewed. The connections of the os trigonum and posterior talofibular ligament (PTFL), the fibulotalocalcaneal ligament (FTCL), the paratenon of the Achilles tendon, the posterior talocalcaneal ligament (PTCL), the osteofibrous tunnel of the flexor hallucis longus (OF-FHL) and the flexor retinaculum (FR) were studied.ResultsThe os trigonum is connected to structures. The posterior part of the PTFL inserted on the os trigonum in 85.6% of patients, whereas in all patients in the control group, the posterior part of the PTFL inserted on the posterior talar process (p < 0.05). The connection of the PTCL was seen in 94.2% of patients in the experimental group, while it was seen in 90.4% of patients in the control group (p > 0.05). The connection to the FTCL in the experimental group was 89.4%, while in the control group, it was 91.3% (p > 0.05). The communication with the paratenon was seen more often in the control group compared to that in the experimental group (31.7% vs. 63.8%, p < 0.001). The FTCL was prolonged medially into the FR in 85.6% of patients in the experimental group and in 87.5% of patients in the control group (p > 0.05). The flexor hallucis longus (FHL) run at the level of articulation between the os trigonum 63.5% and the posterior process of the talus 25% and less often on the os trigonum 11.5%.ConclusionThe os trigonum is connected with all posterior ankle structures and more connections than previously reported.
Highlights
The os trigonum is the second most common accessory bone present in the foot and is often the cause of posterior ankle impingement [34]
We found connections between the os trigonum and posterior talofibular ligament (PTFL), posterior talocalcaneal ligament (PTCL), OF-flexor hallucis longus (FHL), paratenon and fibulotalocalcaneal ligament (FTCL), and flexor retinaculum (FR) both in the experimental and control group (Table 1)
In all cases in the control group, the PTFL inserted on the posterior process of the talus (Table 1)
Summary
The os trigonum is the second most common accessory bone present in the foot and is often the cause of posterior ankle impingement [34]. Different authors provide various frequencies (2–13%) of the occurrence of the os trigonum [1, 2, 11, 34]. The posterior part of the talofibular ligament inserts on the os trigonum [8]. PTCL is present in about 80% of cases and connects the posterior process or os trigonum with the superior and medial part of the calcaneus. The formation of the letter “V” can seldom be seen, because the ligament is formed from two fascicles originating from the medial and lateral tubercles on the posterior process of the talus, with the apex on the calcaneus [9, 17]. When the os trigonum is present, the PTCL is usually formed from one fascicle; some authors call it the trigonocalcaneal ligament [17]
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