Oral Presentation 51st International Society for the Study of the Lumbar Spine Annual Meeting 2025

Surgical outcome of drop foot caused by degenerative lumbar disorders - prediction using calf circumference differences (115126)

Hiroyuki Aono 1 , Shota Takenaka 2
  1. Orthopedic Surgery, Osaka Global Orthopedic Hospital, Osaka, 日本
  2. Orthopedic Surgery, JCHO Osaka Hospital, Osaka

Introduction

Drop foot can result from several etiologies causing claudication known as steppage gait. Some reports regarding drop foot caused by lumbar degenerative disorders indicate that a shorter duration of palsy is key to recovery1-3. However, it is difficult to confirm the exact duration of palsy due to recall bias. We conducted a prospective study to evaluate recovery after surgery for drop foot by assessing the differences in calf circumference.

Methods

This study consisted of 63 patients who presented with unilateral drop foot preoperatively and underwent lumbar spine surgery for degenerative lumbar disorders. Drop foot was defined as motor weakness of the tibialis anterior (TA) with a manual muscle testing (MMT) score of less than 3 out of 5. The mean age at surgery was 58 years, and the mean follow-up period was 4 years (range, 2 to11). Preoperative TA strength was 0-1 in 17 patients and 2-3- in 46 patients. The preoperative difference in calf circumference compared to the normal side was 1cm (range, 0 to 4).

We divided the patients into groups Group A (patients with final TA strength MMT 4 or 5) and Group B: (patients with final TA strength less than MMT 3). The preoperative factors we studied were age, gender, severity of palsy, and diagnosis (herniated disc or canal stenosis). The threshold for preoperative difference in calf circumference, which would be classified as Group A, was evaluated using receiver operating characteristic curve analysis. The area under the curve was used to determine the diagnostic performance, and values greater than 0.75 represented good performance.

Results

Forty-five patients recovered from drop foot, which means TA strength recovered more than 3 out of 5, and 34 patients experienced complete recovery of TA strength.

Forty-four patients were categorized into Group A and 19 into Group B. Multivariate analysis revealed that calf circumference was the only factor significantly affecting surgical outcome (p=0.012).

The area under the curve for the preoperative difference in calf circumference was 0.971, with an estimated cut-off value of 2 cm.

Discussion

In previous reports concerning surgical outcomes for drop foot caused by lumbar degenerative diseases, longer duration and more severe palsy were factors affecting outcomes. 1-3 However, it is very difficult to accurately determine the duration of palsy, especially in patients with longer duration due to recall bias. From this study, we can easily predict surgical outcomes by assessing differences in calf circumference, if patients had unilateral drop foot. In conclusion, surgical recovery of drop foot due to lumbar degenerative disease is predictable by measuring differences in calf circumference. If patients had a difference of less than 2cm, recovery from drop foot can be expected regardless of the duration and severity of palsy, age, gender, and diagnosis.

  1. 1. Girardi FP, Cammisa FP Jr, Huang RC, et al. Improvement of preoperative foot drop after lumbar surgery. J Spinal Disord Tech 2002; 15:490–4. 2. Postacchini F, Giannicola G, Cinotti G. Recovery of motor deficits after microdiscectomy for lumbar disc herniation. J Bone Joint Surg Br 2002; 84:1040–5. 3. Aono H, Iwasaki M, Ohwada T, Okuda S, Hosono N, Fuji T, et al: Surgical outcome of drop foot caused by degenerative lumbar diseases. Spine 32: E262–E266, 2007