Anatomical Considerations of Intramedullary Humeral Nailing and Lengthening

Abstract

Intramedullary lengthening, in cases of extensive humeral shortening, offers the advantages of preventing external-fixator-associated problems. The humeral cavity, as the main parameter in nailing, however, has been neglected in recent literature. It was hypothesized that available implants might be too large and therefore increase the risk of intraoperative fractures. The aim of this cross-sectional study was to describe the humeral canal and how it might affect the choice of implant and the surgical approach. Thirty humeri (15 female, 15 male) from clinical patients and anatomical specimens were studied. Specifically, the medullary cavity width (MCW), cortical thickness (CoT), and the course of the medullary canal were examined. The smallest MCW diameters were found at the distal third of the humeral shaft with mean diameters of 10.15 ± 1.96 mm. CoTs of female humeri were significantly smaller than those of male humeri (p < 0.001). The mean angles of the pro- and recurvatum were 4.01 ± 1.68° and 10.03 ± 2.25°, and the mean valgus bending was 3.37 ± 1.58°. Before implanting a straight lengthening nail into a doubly curved humerus, X-rays and, in selected cases, CT-scans should be performed. The unique size and course of the humeral canal favors an antegrade approach in cases of intramedullary lengthening.

Keywords: cortical thickness; humerus; intramedullary lengthening; medullary cavity.

Figure 1

Left humerus, lateral (left) and anteroposterior (AP) radiograph (right). (a) Measurement levels from the surgical neck to the beginning of the medial supracondylar ridge are marked in black as 1–7. (b) The axis of the medullary canal is marked in white, and the corresponding angles are marked in red. While the slight valgus bending seems irrelevant, pro- and especially recurvatum angles should be considered both in ante- and retrograde nailing.

Figure 2

Left humerus, PRECICE UNYTE nail, comparison of ante-(left) and retrograde (right) nailing. Discrepancies in retrograde nailing of the MCW and nail sizes at the distal third of the humerus are demonstrated. The area at risk regarding iatrogenic fractures at the distal humerus.