Analysis of skull bone thickness during growth: an anatomical guide for safe pin placement in halo fixation.

PURPOSE: To assess skull bone thickness from birth to skeletal maturity at different sites to provide a reference for the correct selection of pin type and pin placement according to age. METHODS: 270 children and adolescents (age: 0-17 years) with a normal CT scan obtained at Emergency Department for other medical reasons were included. Skull thickness was measured on the axial plane CT scans at eight different sites of the vault: midline anterior (A) and posterior (P), right and left lateral (L), antero-lateral (AL), postero-lateral (PL). RESULTS: From birth to skeletal maturity, L thickness was increased significantly less (+ 58%) compared with AL (+ 205%), P (+ 233%), PL (+ 247%), and A (+ 269%) thickness (P < 0.01). At the end of growth, the thickest and thinnest points of the vault (absolute value) were found at the P and L measurement sites, respectively (P < 0.01). Children aged < 4 years exhibited the highest variability in AL and PL skull bone thickness, with thickness < 3 mm observed in 85% (64/75 patients) and 92% (69/75 patients) of cases, respectively. CONCLUSION: We recommend that the tip of the pin should not exceed 2-3 mm in children aged < 4, and 4 mm in children aged 4-6 years, to decrease the risk of inner table perforation. After the age of 7 years and 13 years, standard-sized pin tips (5 and 6 mm, respectively) may be safely used. Children aged < 4 years show significant variability in skull thickness, and therefore a CT scan may be required for this particular age group.

Correction to: Analysis of skull bone thickness during growth: an anatomical guide for safe pin placement in halo fixation.

Unfortunately, the author group has been incorrectly listed by the first name instead of the family name in the original publication. The complete correct author group should read as follows.

An accessory belly of the abductor digiti minimi muscle: a case report and embryologic aspects.

Accessory fasciculi of the hypothenar muscles have been involved in vascular and nerve compressions. During a routine dissection an accessory belly of the abductor digiti minimi muscle arising from the tendon of the palmaris longus muscle was found in the lower third of the forearm. The accessory fasciculus ran through Guyon's canal enclosing the ulnar nerve and vessels. It was attached by means of two tendons where the fibres of the abductor digiti minimi muscle ended in a single pennate form. This anatomic variation was associated with a marked reduction of the caliber of the fourth tendon of the flexor digitorum superficialis muscle and a split of the median nerve. The nerve supply arose from the ulnar nerve. A fibrous band originating from this accessory muscular belly was found covering the median nerve. Based on the development of muscles and fibrous structures within the hand and forearm, as well as on our results, we consider the present anomalies as an unusual persistence of an undifferentiated group of mesenchymal cells. These belong to the superficial muscular anlagen layer of the hand, just between the flexor digitorum superficialis muscle blastema (which has the capacity of migration) and that for the abductor digiti minimi muscle.