Iliocapsularis and Long Head of Triceps Brachii Innervation: Not Such “Textbook” Cases

Abstract

Anatomy instructors rely on accurate anatomical texts to facilitate instruction. While the understanding of anatomy continues to evolve, recent advancements are most reliably reflected in the vast amount of peer‐reviewed literature (PRL). Adjustments in anatomy textbooks (TBs), however, may take years to occur due to the publishing constraints such as illustrations and content vetting procedures. Consequently, TBs tend to lag behind the PRL with respect to new content. Subsequently, anatomy instruction may be dated despite the well‐intentioned instructor. Here we highlight two musculoskeletal‐focused discrepancies in anatomical PRL and TB literature: the presence of the Iliocapsularis (IC) and the innervation of the Long Head of Triceps Brachii (LHTB). To explore potential discrepancies, we used convenience sampling and audited 16 widely‐used TBs published within the past 10 years (3.1 ± 2.8 years) to determine the presence of IC and the innervation of the LHTB. We also analyzed PRL published within the past 18 years (5.4 ± 6.7 years) which focused on studies that used MRI or dissection to determine the presence of IC, and dissection only to explore the innervation of LHTB to the triceps. We conducted human dissection to verify the literature audit findings. To better evaluate the presence of IC, we dissected 22 anterior hips on preserved limbs in 11 cadavers and 5 unpreserved limbs in 3 cadavers. To better assess the innervation of the LHTB, we dissected the posterior shoulder and arm on 5 preserved limbs in 5 cadavers and 3 unpreserved limbs in 3 cadavers, with the aim of completing LHTB dissections on a minimum of 20 limbs. Out of 16 TBs reviewed, only 1 suggested the presence of IC and all reported the radial nerve as the innervation of LHTB (Table 1). Conversely, 4 PRL studies used dissection or MRI to assess the presence of IC and 3 studies used dissection to assess the innervation of LHTB by nerves other than the radial nerve (namely the axillary nerve) (Table 2). When pooling the individuals assessed in PRL, 100% were found to have an IC (n=271) and 72.2% were found to have a LHTB innervated by the axillary nerve. Our dissections of the anterior hips revealed that the IC was present in 100% of the 27 limbs. Our dissections of the posterior shoulder and arm revealed that the axillary nerve innervated the LHTB in 50% of the 8 bodies, including 2 of the 5 preserved limbs and 2 of the 3 unpreserved limbs. This study demonstrates that recently published TBs are not in alignment with the anatomical findings of our dissections or, more importantly, with the PRL. These findings suggest that anatomist instructors, as well as clinicians, should be familiar with recently published PRL and not rely solely on anatomical TBs.Support or Funding InformationNoneThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.