Relevance of bone anomalies in patients with thoracic outlet syndrome.

BACKGROUND: Skeletal anomalies are recognized as potential causes of thoracic outlet syndrome (TOS); however, there is a paucity of information regarding the specific bone anomalies associated with TOS and their relative incidence among the different clinical types of TOS. This study describes the prevalence of bone anomalies in a population with TOS.
METHODS: A retrospective chart review of the clinical records and imaging studies of all patients who were surgically treated at our institution for TOS between 1991-2011 was conducted. A descriptive analysis of the cohort of patients with associated bone anomalies was performed and compared with the cohort of patients without bone anomalies.
RESULTS: During the study period, 400 patients underwent operative procedures for TOS. Of these, 115 (29%) harbored a bone anomaly and the remaining 285 did not. The bone anomalies included 80 (69%) cervical ribs, 25 (22%) clavicular anomalies, and 10 (9%) isolated first rib aberrations. Ninety (78%) of the bone anomalies were congenital, while 25 (22%) were posttraumatic. The bone anomaly cohort was predominantly female (76%), with an average age of 36 years. The distribution of neurogenic, arterial, and venous types of TOS in the cohort with bone anomalies was 63%, 33%, and 4%, respectively, while it was 51% neurogenic, 11% arterial, and 38% venous in the cohort without bone anomalies. These distributions were significantly different (chi-squared: 56.75; P < 0.0001). The likelihood of neurogenic compression was roughly equivalent between the 2 cohorts (odds ratio [OR]: 1.6; P = 0.03), while the likelihood of arterial compression was much higher in the presence of a bone anomaly (OR: 4.0; P < 0.001) and the likelihood of venous compression was much lower in the presence of bone anomaly (OR: 0.07; P < 0.001). Conversely, 33% of all neurogenic TOS cases, 54% of all arterial TOS cases, and 4% of all venous TOS cases were associated with a bone anomaly.
CONCLUSIONS: In our experience, the incidence of bone anomalies among patients treated for TOS was 29%, which is higher than previously reported. Cervical ribs were present in 20% of our patients with TOS, an estimated 40 times higher prevalence than that in the general population. However, acquired clavicular deformities and isolated abnormal first ribs were found in 9% of our patients, accounting for almost one-third of all bone anomalies present in this TOS population. The incidence of bone anomalies is rather different among the subtypes of TOS. The strongest association with the presence of a bone anomaly occurs in patients with arterial TOS, although 46% of all our arterial TOS cases did not have a bone anomaly. The presence of bone anomalies does not seem to influence the occurrence of neurogenic TOS, while venous TOS likely has no association with congenital bone anomalies, but occasionally mid and medial clavicular fracture calluses may cause venous TOS.