Fractures of the proximal part of the humerus are common injuries that often occur in elderly osteoporotic patients. The decision process regarding the surgical technique is challenging because of the variety of treatment options1,2. Although locked plate fixation has become a popular surgical technique for many proximal humeral fractures, other techniques such as pinning, wiring, and intramedullary nailing are useful in certain situations. Less invasive techniques provide the advantage of incorporating the rotator cuff insertion to increase fixation in patients with poor bone quality, as well as preserving the soft-tissue envelope and vascularity to the humeral head. Closed or open-pin fixation techniques for proximal humeral fractures have potential pitfalls such as malunion, nonunion, loss of fixation, pin-track infection, and pin migration3.
We describe a case of late radial nerve palsy caused by pin migration in a patient treated with multiple pin fixation and tension-band wiring for a proximal humeral fracture. We also review the potential pitfalls of pin fixation and the technical details that can help avoid these complications. The patient was informed that data concerning the case would be submitted for publication, and she provided consent.
Despite advances in new implant designs, pin fixation with Kirschner wires is still an appropriate option for treatment of some fractures and dislocations around the shoulder. Percutaneous or open pinning techniques are cost-effective and have the potential advantage of preventing additional damage to the blood supply of the humeral head. However, pin fixation can be problematic, especially in osteoporotic elderly patients, in whom loss of fixation and related pin problems are not rare. Because patient compliance, especially during the rehabilitation period, is also very important, pinning is not recommended for patients with mental problems or substance abuse. Devastating complications of pin fixation around the acromioclavicular and sternoclavicular joints caused by pin migration to vital structures such as the lung, spinal cord, and major vessels have been reported4-7. Close follow-up is necessary, and the pins should be removed at the conclusion of therapy or whenever migration is noted.
Pinning is technically demanding, and experience with this surgical technique is important. Terminally threaded Kirschner wires should be inserted anterograde through the greater tuberosity to the medial humeral shaft and should penetrate the medial cortex to increase the purchase of the pins. Pins, implanted distally to proximally into the humeral head, should engage dense subchondral bone with the pin ends but should not penetrate the articular surface because articular penetration followed by retraction decreases the purchase of the pins and can lead to loosening and migration8. According to Koval et al.9, the diameter of the pins (2.5-mm Schanz pins) is important for providing additional stability. Pin configuration also is important for the construct stability. The parallel placement of pins increases stability compared with a convergent pin-placement pattern10. Increasing the number of pins that engage cortices adds additional stability10,11. Bending the pins under the skin may have a limited role in preventing pin migration.
In our case, we used four threaded and two smooth pins. One of the smooth pins migrated and caused a radial palsy. Because smooth pins tend to migrate, they should be used cautiously in osteoporotic bone around the shoulder girdle. Although the literature contains some isolated case reports on migration of pins after fixation of proximal humeral fractures, to our knowledge, this is the first report of a late radial nerve palsy caused by pin migration.
In our patient, the radial nerve palsy recovered within hours after the extraction of the migrated pin. This uncommon type of nerve lesion is referred to as “axonamonosis” and is not included in the traditional Seddon nerve injury classification12. To the best of our knowledge, this unusual type of nerve lesion was first described in three cases by Birch and St Clair Strange13. All of the nerve lesions in their report had complete and rapid recovery after the source of direct pressure was eliminated. Axonamonosis is a condition in which nerve conduction is blocked by direct pressure on a nerve, which results in a mechanical extrusion of the myelin. Although intact, the axon loses its myelin secondary to pressure. The myelin can return to normal when the pressure is removed.
Our case draws attention to some important issues that can arise when pins are used for the fixation of proximal humeral fractures. Meticulous compliance to principles of pin fixation during surgery is crucial. The use of pins in osteoporotic proximal humeral fractures requires careful follow-up. Unexpected complications can be avoided by close clinical and radiographic evaluation. Pin migration presents an orthopaedic emergency. Therefore, whenever follow-up radiographs show substantial migration of a pin, immediate removal is necessary to prevent serious complications.
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.