Acute Lumbar Disc Prolapse: A Rare Complication of Lithotomy Position

Introduction

Lithotomy is a common position in various gynecologic, urologic, orthopedic, colorectal, and pediatric surgeries. Neurovascular complications are sometimes seen when patients are operated in the lithotomy position. Neurovascular injuries described with the lithotomy position depend on the degree of lithotomy, type of surgery, and duration of surgery. The more prolonged the surgery, the more chances of neurovascular damage. These injuries include aseptic necrosis of femur head, ligamentous relaxation of the back, peroneal nerve injury, tibial nerve injury, vessel compression, compartment syndrome, compression ulcers, and disc prolapse. There are few reports of common peroneal neuropathy leading to temporary dysfunction of the lower limbs.^1,2 In this study, we report two rare cases of acute lumbar intervertebral disc prolapse following surgery for uterovaginal prolapse.

Case 1

Mrs N, a 35-year-old P2+0 with third-degree cervical elongation, underwent Fothergill operation on April 28, 2014 under spinal anesthesia. She had no other comorbidities and was found to be absolutely fit in the preanesthesia assessment before surgery. The procedure lasted for 90 minutes and was uneventful. She was well during the immediate postoperative period with normal bladder and bowel functions. On the fifth postoperative day, she complained of low backache, pain radiating to the lateral aspects of both the lower limbs, and weakness in both lower limbs. A neurosurgery evaluation showed motor power of 4/5, weak knee extension, and absence of knee jerk in both the lower limbs. The sensory examination was normal. Contrast MRI of the lumbosacral spine showed lumbar spondylosis, diffuse disc bulge, and left foramina disc protrusion at the L5-S1 level causing mild secondary canal stenosis with right-sided mild and left-sided moderate neural foraminal stenosis. The patient was managed conservatively with the use of lumbosacral belt and spinal extension exercises. She symptomatically improved and regained full strength and reflexes in both her lower limbs over a period of 3 months.

Case 2

Mrs D, a 52-year-old postmenopausal woman with third-degree uterovaginal prolapse with HIV infection, underwent Ward Mayo's hysterectomy under spinal anesthesia on May 12, 2014. Patient was found fit for surgery in the preanesthesia evaluation. The procedure was uneventful and lasted for 100 minutes. The patient was well during the immediate postoperative period with normal bladder and bowel habits. She developed complaints of low backache and weakness in both lower limbs on the third postoperative day. A neurosurgery evaluation advised MRI of the lumbosacral spine with contrast. The MRI showed lumbar spondylosis with disc bulge and canal stenosis at L4/5. She was managed conservatively and advised physiotherapy with spinal extension exercises and supportive medications. The patient improved with this treatment and is presently asymptomatic.

Discussion

Nerve injuries are common in the lithotomy position and may range from transient and clinically minor injury to severe permanent injury. Commonly injured nerves are the ulnar nerve (28%), brachial plexus (20%), lumbosacral root (16%), and spinal cord (13%). ³ The patient may develop complaints of backache commonly after vaginal surgery done in the lithotomy position. The pathophysiology of backache in the postoperative period is uncertain. It involves several factors. The neuropathic symptoms may occur rapidly (within hours) or may be delayed by a few days to weeks after surgery. The nerve injury could be caused by direct nerve trauma, compression or stretch injury, ischemia, injected solution toxicity, or pre-existing nerve insult. ³ Mostly, the injury is transient (neurapraxia). Gumus et al. ⁴ assessed the incidence and risk factors associated with lower extremity neurapraxia in various operations performed in the lithotomy position. Of the 1170 patients operated in the lithotomy position, 12 (1.02%) developed postoperative neurapraxia. Age of the patient, type of operation, and duration of operation contributed to the development of neurapraxia. ⁴ Besides backache, various neurovascular complications have been seen following surgery in the lithotomy position. The vascular complications include thromboembolism ⁵ and, although rare, the dreaded compartment syndrome. ⁶ The common neurologic complications are neuropathies of the femoral,^7–9 sciatic,^10,11 and the peroneal nerves. ¹² Similar to our cases, Kishor Choudhari et al. reported a case of acute central disc prolapse at the L4/5 level superimposed on a mild degree of congenital spinal stenosis following vaginal hysterectomy in the lithotomy position. She had complaints of severe backache and bilateral sciatica radiating to the lateral aspect of both legs. The patient was treated with L4/5 microdiscectomy. ¹³ Fortunately, neither of our cases needed surgical intervention and both responded well to the conservative treatment. Acute disc prolapse is an extremely rare complication of the lithotomy position. The mechanisms postulated include a congenitally narrow spinal canal, inherently more vulnerable to the manipulations involved in the lithotomy position, resulting in a symptomatic disc protrusion. Flexion and abduction at the hips and flexion at the knees in the supine posture during lithotomy can be likened to similar joint movements in the erect posture encountered during the lifting of a heavy weight, which is known to be the commonest single precipitating factor for acute disc prolapse. However, because the force applied in the former is considerably less, only rarely is disc prolapse precipitated by the lithotomy position. ¹³ Another mechanism seems more likely. It is known that the upper and lower parts of lumbosacral plexuses can be stretched between their respective origins and exits, beneath the inguinal ligament and the greater sciatic foramen, respectively, by hyperabduction of the hip. ¹⁴ It is reported that simultaneous hip flexion and knee extension can stretch the sciatic nerve by ∼1.5 inches. ¹¹ By placing the patient in the lithotomy position, flexion and hyperabduction of the hips made the stretching of the lumbosacral nerve roots worse and converted an occult pre-existing asymptomatic disc bulge into a frank disc prolapse with intractable sciatica and sensory-motor deficits. ¹³ Patients with spinal stenosis are more susceptible to symptomatic disc prolapse with relatively minor provocation as has happened in one of our patients whose MRI showed lumbar canal stenosis.

Hence, it is concluded from these case discussions that apart from detailed history and examination during preoperative evaluation, one must be careful while positioning the patient in lithotomy for any surgery. The process of positioning should be smooth and simultaneous bilaterally to avoid neuropathies. In the postoperative period, MRI should be done to exclude disc prolapse if the patient's signs and symptoms suggest so. Conservative treatment should be tried first.