Skeletal muscle abnormalities and genetic factors related to vertical talus.

BACKGROUND/RATIONALE: Congenital vertical talus is a fixed dorsal dislocation of the talonavicular joint and fixed equinus contracture of the hindfoot, causing a rigid deformity recognizable at birth. The etiology and epidemiology of this condition are largely unknown, but some evidence suggests it relates to aberrations of skeletal muscle. Identifying the tissue abnormalities and genetic causes responsible for vertical talus has the potential to lead to improved treatment and preventive strategies.

QUESTIONS/PURPOSES: We therefore (1) determined whether skeletal muscle abnormalities are present in patients with vertical talus and (2) identified associated congenital anomalies and genetic abnormalities in these patients.

METHODS: We identified associated congenital anomalies and genetic abnormalities present in 61 patients affected with vertical talus. We obtained abductor hallucis muscle biopsy specimens from the affected limbs of 11 of the 61 patients and compared the histopathologic characteristics with those of age-matched control subjects.

RESULTS: All muscle biopsy specimens (n = 11) had abnormalities compared with those from control subjects including combinations of abnormal variation in muscle fiber size (n = 7), type I muscle fiber smallness (n = 6), and abnormal fiber type predominance (n = 5). Isolated vertical talus occurred in 23 of the 61 patients (38%), whereas the remaining 38 patients had associated nervous system, musculoskeletal system, and/or genetic and genomic abnormalities. Ten of the 61 patients (16%) had vertical talus in one foot and clubfoot in the other. Chromosomal abnormalities, all complete or partial trisomies, were identified in three patients with vertical talus who had additional congenital abnormalities.

CONCLUSIONS: Vertical talus is a heterogeneous birth defect resulting from many diverse etiologies. Abnormal skeletal muscle biopsies are common in patients with vertical talus although it is unclear whether this is primary or secondary to the joint deformity. Associated anomalies are present in 62% of all cases.