Evaluation of hip flexion strength following lateral lumbar interbody fusion

Lateral interbody fusion (LIF) is a minimally invasive procedure that is designed to achieve a solid interbody fusion while minimizing the damage to the surrounding soft tissue. Although short-term results have been promising, few data have been published to date regarding its risks and complication rate.

The aim was to evaluate the extent of injury to the psoas muscle after the LIF procedure by measuring hip flexion strength.

A prospective case series was used in the study.

Hip flexion strength was measured using a handheld digital dynamometer while the patient was seated on a chair; the examiner held the device against the patient's attempt to flex the hip. Both sides were measured to compare the operated and nonoperated psoas muscles. Each side was measured three times and the average amount (in pounds) was recorded. Measurements were done before and after surgery on Day 2-3, at 2 weeks, 6 weeks, and at 3 and 6 months.

Thirty-three patients were recruited for this study. Mean preoperative hip flexion strength values were 20.7±3.47 lb and 21.3±4.31 lb for operated and nonoperated legs, respectively, with no significant difference (p=.85). With a mean of 11.2±2.24 lb postoperative measurements on Day 2, the operated side showed statistically significant reduction of strength (p=.0001). The nonoperated side was also weaker postoperatively, but not significantly (mean=19.12±1.74 lb; p=.097). From the first follow-up visit at 2 weeks, the values on the operated leg had returned to baseline values (20.6, p=.97) and were not significantly different from preoperative values on either side.

Hip flexion was weakened immediately after the LIF procedure, which may be attributed to psoas muscle injury during the procedure. However, this damage was temporary, with almost complete return to baseline values by 2 weeks.