Weak or Absent Ankle Dorsiflexion: The Most Sensitive Indicator of Motor Deficits Following Spinal Deformity Surgery

Abstract

Study Design

A retrospective, single-center review of all spinal deformity surgeries at the authors’ institution.

Objectives

To determine the most sensitive physical examination finding as a test for motor deficits after spinal deformity surgery.

Background

Despite both reported false negatives of neuromonitoring and the potential for development of delayed deficits, the literature has paid relatively little attention to the postoperative evaluation and monitoring of neurologic integrity after correction of spinal deformity.

Methods

A retrospective, single-center review of 1,274 consecutive spinal deformity surgeries from 2003 to 2011 was performed. Patients with limited neurologic function or an inability to undergo an examination preoperatively were excluded. A total of 1,023 patients were included in the analysis. Records were analyzed for postoperative motor deficit.

Results

A total of 12 patients had a motor deficit in the perioperative period. Eight had a deficit on the immediate postoperative exam; 6 had absent ankle dorsiflexion and 2 had weak ankle dorsiflexion; And 4 developed a delayed motor deficit: 3 with absent ankle dorsiflexion and 1 with weak ankle dorsiflexion. There were no cases of a motor deficit in which ankle dorsiflexion was not weak or absent. Of the 12 patients with a deficit, 8 had complete loss of motor function. Of the 4 patients with incomplete neurologic injury, loss of ankle dorsiflexion was the only common physical examination finding. In this review, ankle dorsiflexion was 100% sensitive (12 of 12) and 100% specific (1,011 of 1,011) for neurologic injury.

Conclusions

Ankle dorsiflexion was the most sensitive test for lower extremity motor function after spinal deformity surgery, both for immediate and delayed deficits. Without testing ankle dorsiflexion specifically, neurologic motor deficits may be missed.