Intraoperative Electrical Stimulation Can Identify Potential Ulnar Nerve Injury from Crossed Pinning of a Supracondylar Humerus Fracture

Abstract

Treatment of Gartland type III supracondylar fractures using reduction and crossed Kirschner wire fixation is considered the most stable method; however, there is a risk of iatrogenic ulnar nerve injury during medial pin placement. We describe a technique for intraoperative detection of such nerve injury.

An inexpensive disposable nerve stimulator is set at 2 mA and applied directly to the Kirschner wires after placement, alerting the surgeon intraoperatively if a wire contacts the ulnar nerve. A positive response involves any finger motion with Kirschner wire stimulation. We recommend this novel method of intraoperative Kirschner wire stimulation using an inexpensive disposable nerve stimulator for simple, quick, safe, effective, and cost-efficient prevention of nerve injury during surgeries for supracondylar humerus fractures.

Key Concepts

• (1)Cross pinning with lateral and medial Kirschner wires provides optimal stability for treating type III supracondylar humerus fractures but there is a risk of ulnar nerve injury.
• (2)A novel technique using intraoperative electrical stimulation of Kirschner wires allows surgeons to safely identify nerve contact and prevent iatrogenic ulnar nerve injury.
• (3)This method uses a cost-effective disposable nerve stimulator and can be easily incorporated into standard surgical procedures without using excessive time or resources.

Level of Evidence

IV

Introduction

Supracondylar fractures of the humerus are the most common elbow fractures in children [1]. The original Gartland classification system organizes these fractures into three major groups based on the pattern of displacement. Gartland type III fractures are present in 29% of these fractures, which correspond to higher risk of neurological and vascular injury and require surgical management with reduction and percutaneous pinning [[1], [2], [3]] (Fig. 1A).

Figure 1.

A: Anteroposterior and lateral radiographs of a right elbow demonstrating a type III supracondylar fracture. The images reveal complete displacement of the distal humerus. B: Intraoperative fluoroscopic images of the right elbow showing the “cross-pinned” fixation of this type III supracondylar fracture using crossed Kirschner wires.

This technique for operative fixation, which involves two Kirschner wires placed in parallel across the fracture from a starting point on the lateral distal humerus, was first described by Swenson in 1948 [4]. In response to concerns regarding the stability of this construct, alternate Kirschner wire fixation techniques were developed [5,6]. A widely used technique involves Kirschner wires placed in a “cross-pinned” orientation with either one to two lateral and one medial starting points (Fig. 1B) [7]. Biomechanical analyses of these constructs have confirmed the advantages of lateral and medial starting points and bicolumnar fixation, especially in stability with rotational forces. However, they also are more likely to result in iatrogenic ulnar nerve injury [8,9]. The trade-off of increased biomechanical stability with a cross-pinned technique reportedly is a 2%-12% risk of iatrogenic ulnar nerve injury [10,11]. There are several fracture patterns, such as a comminuted medial column or oblique pattern where a medial pin may be essential.

Strategies for reducing the risk of ulnar nerve injury with medial and lateral cross-oriented constructs have been proposed. These include prone patient positioning, intraoperative exploration or transposition of the ulnar nerve, a mini-open incision, and “thumb blocking” for localization of the ulnar nerve [[12], [13], [14], [15]]. Widespread adoption of these techniques has been limited by their efficacy and safety, as well as practical issues. Prone positioning of the child risks airway and anesthesia safety [12]. Thumb blocking–palpation for localization of the ulnar nerve–lacks the ability to confirm that the pin is not near the nerve [15]. Anterior transposition of the ulnar nerve is invasive and has not decreased the risk of iatrogenic ulnar nerve injury [13]. Although intraoperative exploration provides direct visualization of the ulnar nerve, it is also invasive and time- and labor-intensive. The mini-open technique has yielded lower rates of ulnar neuropraxia at the expense of soft tissue disruption and infection risk [14].

In 2002, we described the use of a cost-effective disposable stimulator for intraoperative nerve localization, safe Kirshner wire fixation, and nerve injury prevention [16]. The stimulator, when directly applied to a 27-gauge needle inserted adjacent to the ulnar nerve, elicited twitching of the small and ring fingers in all 34 patients, thus confirming the ability of this device to detect the location of the ulnar nerve [16]. Following percutaneous placement, the medial Kirschner wires were located at an average of 8 mm from the ulnar nerve as determined by the nerve stimulator. In one case, stimulation of the medial pin elicited twitching of the small and ring fingers, so the pin was successfully replaced. Based on these results, we reasoned that intraoperative stimulation of Kirschner wires following placement would give a reliable assessment if a wire was touching the ulnar nerve with intraoperative Kirshner wire stimulation following medial and lateral cross-oriented Kirschner wire fixation. We have since used this technique in our clinical practice treating severely displaced pediatric supracondylar humerus fractures. The purpose of this study was to describe our surgical technique of using an inexpensive disposable intraoperative nerve stimulator to assure that the medial pin does not injure the ulnar nerve.

Methods

Technique description

The anesthetized patient is supine, with the C-arm image intensifier supporting the elbow. After confirming adequate fracture reduction with fluoroscopic imaging, we place the first Kirschner wire percutaneously through a lateral humeral condyle starting point, with the elbow fully flexed as described by Kocher et al. [7] The Kirschner wire is inserted onto the capitellum and directed medially and posteriorly within the lateral column. For children older than three years, we use larger diameter wires (either 5/64 or 3/32 inches) based on their age and size. A second Kirschner wire is inserted up the lateral column, especially if the fracture is highly unstable. Once lateral fixation and stability is confirmed by fluoroscopy, a medial pin is placed. The lateral pins provide initial stability, allowing the elbow to be slightly extended to about 90°, which relaxes the ulnar nerve [7]. As the capitellum is an anterior structure, the lateral pins start anteriorly and are directed posteriorly. This anatomical consideration further ensures the safety and efficacy of the pin placement. Since the medial epicondyle is invariably palpable, the medial Kirschner wire is inserted onto the tip of the epicondyle and confirmed by fluoroscopy. Since the medial epicondyle is a more posterior structure, the medial pin is directed more transversely and in an anterior direction, thus reducing the likelihood of compromising the ulnar nerve. Our technique emphasizes obtaining good pin spread on the anteroposterior view, with the pins extending up their respective column. If there is any concern about the ulnar nerve overlying the medial epicondyle, based on our 2002 study, a 27-gauge needle can be inserted, and the nerve stimulator was used to stimulate the needle before actual Kirschner wire placement [16].

Before using the nerve stimulator, we confirm with the anesthesiologist that any muscle paralytic medication is no longer active and that the patient exhibits muscle twitches in response to stimulation. Nerve stimulation testing of all Kirschner wires is performed by placing the grounding wire percutaneously and then stimulating each Kirschner wire at 2 mA (Fig. 2). We prefer the VARI-STIM® III Nerve Locator (Medtronic, Minneapolis, MN, USA) for its availability, efficiency, and low cost ($49.00). A positive response indicating ulnar nerve compromise would be flexion of the small and ring fingers with pin stimulation. However, all pins are stimulated to be sure that the median and radial nerves are also not irritated or compromised. Once we confirm there is no nerve compromise, the Kirschner wires are bent to 90° and cut short. Marcaine 0.25% with epinephrine can be injected into the facture site or intraarticular for pain relief, thus avoiding postoperative narcotic medication. A well-padded thin fiberglass cast is applied at less than 90° of elbow flexion and then bivalved to accommodate for swelling.

Figure 2.

Intraoperative application of the VARI-STIM® III Nerve Locator (Medtronic, Minneapolis, MN, USA) to the K-wires with a grounding wire in the distal triceps brachii muscle.

Clinical experience

We have treated 128 consecutive patients with a Gartland type 3 fracture treated with two lateral pins inserted first, followed by a single medial pin. No finger movement was observed in any case upon Kirschner wire stimulation at 2 mA. There were no iatrogenic ulnar nerve injuries, one loss of fixation due to migration of the pins (0.8%) that did not require a return to the operating room, and six (4.7%) wire-related superficial site infections that responded to oral antibiotics and outpatient pin removal. There were no other complications recorded. Follow-up at three to four weeks postoperatively revealed no further complications.

Discussion

Our technique involving intraoperative electrical stimulation of the medial pin during fixation of type III supracondylar humerus fractures provides a simple, safe, quick, and cost-effective solution to detect iatrogenic ulnar nerve injury when using the more stable crosswire construct [5]. This method provides real-time feedback on the proximity of the ulnar nerve to the Kirschner wires, allowing for prompt pin removal and replacement [16,17]. We utilize palpation of the medial epicondyle prior to Kirschner wire insertion, with the option to stimulate the intended wire entry site with a 27-gauge needle if there is uncertainty regarding the ulnar nerve’s position during palpation. The medial pin is inserted with the ulnar nerve relaxed by having the elbow extended to 90° after placement of two lateral pins. We recommend stimulation of each of the Kirschner wires, assuring that no nerve irritation or injury has occurred from any of the wires. In the case of a positive twitch response, this would alert the surgeon to reposition the Kirschner wire.

Limitations to this method

• 1.While the cost of the nerve stimulator (50 dollars) is additional, the extra time and potential morbidity to perform a mini-open incision and medial pin placement would justify this expense.
• 2.The fact that we experienced no ulnar nerve injury suggests that this is an improvement over traditional percutaneous cross pinning. However, it is unclear whether this method is safer than using a mini-open approach and placing a medial pin. Further research with a larger patient group and comparative studies would help determine how much this technique reduces the risk of ulnar nerve injury compared to a mini-open approach.

Author contributions

Lucas A. Georger: Writing – review & editing, Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. McKenna C. Noe: Writing – review & editing, Writing – original draft, Validation, Methodology, Investigation, Formal analysis, Data curation. Richard M. Schwend: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Project administration, Methodology, Investigation, Formal analysis, Conceptualization.

Ethics approval and consent

The author(s) declare that no patient consent was necessary as no images or identifying information are included in the article.

Additional links

• •POSNA Study Guide: Supracondylar Humerus Fractures
• •POSNA Resident Review: 5 Tips for Pinning a Supracondylar Humerus Fracture

Funding

The authors have no relevant financial or nonfinancial interests to disclose. No funds, grants, or other support was received for this study. This study involving human participants met the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The human investigation committee (IRB) of Children’s Mercy Kansas City approved this study.

Declaration of competing interests

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Consultant, OrthoPediatrics. Past President POSNA. I occasionally review for JPOSNA®. The other two authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.