Dynamic Ultrasound of Pronator Quadratus to Evaluate Suitability of Anterior Interosseus for Nerve Transfer
Grzegorz Kwiecien, MD1, Dennis Alekseyenko, CPA2, Dennis Kao, MD2 and Megan Jack, MD, PhD2, 1Department of Plastic Surgery, Cleveland Clinic, Cleveland, OH, 2Cleveland Clinic, Cleveland, OH
Introduction
High ulnar nerve injuries result in poor functional recovery. Anterior interosseus nerve (AIN) to ulnar nerve transfer has recently gained popularity to preserve intrinsic function of the hand. However, it may be difficult to assess if the donor AIN is suitable for transfer. Clinical exam of the distal muscle innervated by the AIN - pronator quadratus (PQ) is subjective, EMG of this small, deep muscle is technically difficult and invasive, and static advanced imaging such as MRI or ultrasound may not detect its early changes. The goal of this study was to evaluate if dynamic ultrasound can be used to assess functional status of the PQ and thus indirectly distal AIN.
Materials & Methods
Twenty-four healthy volunteers (group 1), patients undergoing regional block including the AIN (group 2), and patients with known chronic AIN dysfunction (group 3) underwent dynamic sonographic evaluation. The superficial head of PQ was measured in the long with forearm in supination and active or passive pronation. The muscle width, thickness, and cross sectional area (CSA) was measured in each position. In addition, echodensity, intramuscular pattern and intramuscular blood flow were evaluated.
Results:
There were no significant differences in appearance of the PQ in forearm supinated. The thickness/CSA was 0.5±0.2cm/1.7±0.7cm2, 0.4±0.2cm/1.6±0.7cm2, 0.4±0.1cm/1.4±0.5cm2 for group 1, 2 and 3, respectively; ANOVA p>0.05) (Figure 1). Significant changes were observed with attempted forced pronation. The thickness/CSA was 0.9±0.3cm/3.5±1.0cm2, 0.6±0.2cm/2.1±0.9cm2, 0.5±0.2cm/1.7±0.8cm2 for group 1, 2 and 3, respectively; ANOVA p<0.05) (Figure 2). Thickness and CSA increased by at least 50% in all patients in group 1, in only two patients in group 2, and none in group 3. Increase in muscle contractility and reactive intramuscular blood flow was observed in normally innervated muscle (group 1) but not in the blocked muscle (group 2) or chronically denervated muscle (group 3).
Conclusions:
There are certain sonographic features that can differentiate between normal, acutely denervated, and chronically denervated PQ muscle. Bedside dynamic ultrasound may be a simple, time-efficient, and convenient method to assess the PQ muscle, and thus indirectly functionality of AIN before performing a nerve transfer.
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