Microneurolysis of constrictions aids anterior intraosseous nerve syndrome recovery
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Microneurolysis aids recovery of strength in patients with persistent anterior interosseous nerve syndrome and hourglass constrictions, leading researchers to say the constrictions may represent therapeutic targets, a presenter said.
Karthik R. Krishnan, MD, MS, who presented the findings at the American Society for Surgery of the Hand Annual Meeting, said this is also what he and his colleagues at the Center for Brachial Plexus and Traumatic Nerve Injury at Hospital for Special Surgery, where the study was performed, hypothesized would happen.
“Our definition for [anterior interosseous nerve syndrome] AINS was a complete AIN palsy with 0 out of 5 [Medical Research Council] MRC strength of the flexor pollicis longus (FPL) and/or the flexor digitorum profundus (FDP) of the index finger along with electromyogram (EMG) evidence of subtotal or complete axonal denervation,” Krishnan said.
Microneurolysis was performed in 10 patients who met the inclusion criteria and had MRI or ultrasound evidence of one to four hourglass constrictions. In addition, to undergo microneurolysis, patients needed lack of recovery 12 months after onset of AINS or complete or nearly complete denervation or lack of recovery at 9 months after onset with successive clinical and EMG examinations that showed complete denervation. Surgery was performed at 13.2 months after onset of AIN.
Primary outcome was a difference in MRC scale for muscle strength of the FPL and FDP-2 at 3 months minimum postoperatively compared with preoperative values.
“Our data do suggest that hourglass constrictions are a common feature of patients with persistent AINS and that they may represent a therapeutic target. We found that microneurolysis of hourglass constrictions in AINS was associated with clinical recovery as documented by MRC strength,” Krishnan said.
The constrictions in nine of the 10 patients were at or proximal to the medial epicondyle compared with the forearm, which is where they had formerly been believed to be located, he said.
At the latest follow-up, which was at an average of 16.8 months postoperatively, six of the 10 patients with FPL palsies recovered to a score of at least MRC 3.
“Nine out of 10 recovered to at least MRC 3 with respect to FDP-2; four of five recovered to MRC 4 and all five recovered to at least MRC 3,” Krishnan said, however he noted limitations of the study were its small sample size and retrospective design.
Perspective
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The authors present an excellent study of AINS, which can be challenging to treat. Their review identified 24 patients with AINS and 12 of them underwent microneurolysis for hourglass constrictions (HGCs) at an average of 12.6 months post-onset for failed nonoperative treatment. The results were encouraging with five of six patients with FDP2 and six of 11 patients with FPL denervation recovering at least four out of five for MRC strength.
In my experience, most patients with AINS are treated with observation, although nerve recovery can be unpredictable. I suspect patients with HGCs are more likely to fail nonoperative treatment, so detecting these lesions with high-resolution imaging would offer useful prognostic information. I would, thus, strongly consider earlier surgical intervention for AINS patients with EMG findings and HGCs on imaging, and earlier surgical intervention may lead to even better nerve recovery.
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Krishnan KM, et al. Paper 34. Presented at: American Society for Surgery of the Hand Annual Meeting. Sept.30 - Oct. 2, 2021; San Francisco (hybrid meeting).
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