Progressive Adult Spinal Deformity Following Placement of Intrathecal Opioid Pump: a Report of Four Cases

Abstract

Introduction

Placement of intrathecal opioid pumps (ITOP) for chronic pain is a rare, but described cause of progressive spinal deformity. Over the last two decades there has been several suspected cases at our institution. In this case series, we described the apparent association between placement of an intrathecal opioid pump and progression of spinal deformity.

Methods

The medical records of a single surgeon working at a single institution were retrospectively queried for patients seen between 1995-2010 to identify patients with spinal deformity and an ITOP. All hospital records including notes, radiographs, and labs were reviewed and analyzed. Spine radiographs were measured using standard techniques and reported as Cobb angles. This project was IRB approved and no external funding was used.

Results

In total, we identified four patients with spinal deformity after placement of an ITOP. These patients were adults, two males and two females (ages: 48-80 years), with a unique medical history. Each participant's radiographs showed a progression of the spinal deformity following placement of ITOP. All patients underwent subsequent posterior spinal fusion for treatment of their progressive spinal deformities.

Conclusion

In this series, we have shown an apparent association between the placement of ITOP and progression of deformity in both patients with and without existing spinal deformity. While it is impossible to discern causality, all patients in our series had radiographic and clinical evidence of spinal deformity progression after placement of intrathecal pumps. These findings may raise awareness of this rare, but major, complication. In those performing pump placement, we recommend continued clinical and radiographic monitoring, through routine follow-up.

Level of Evidence

Level 4 - Case series; case control study (diagnostic studies); poor reference standard; analyses with no sensitivity analyses.

Introduction

Intrathecal opioid pumps (ITOP) have been available for use since the mid-1990s when they received FDA approval for the intrathecal (IT) infusion of morphine in the treatment of chronic intractable pain^1,2. Neurosurgeons and anesthesiologist have placed ITOP for the treatment of chronic pain from conditions such as cancer, back or leg pain, complex regional pain syndrome, and painful neuropathy. Contraindications for ITOP include infection (i.e. meningitis, ventriculitis, or bacteremia), insufficient body habitus (pump must be implanted deeper than 2.5 cm from skin surface), or history of spinal anomalies. From August 2003 to October 2008, the Implantable Systems Performance Registry followed 3,786 patients who had IT drug delivery system for the following indications: non-malignant pain (53%), intractable spasticity (29.3%), and malignant pain (17.7%)³. This subset of patients were then followed to evaluate adverse effects and overall pump survival. Most of the adverse effects associated with IT pumps are secondary to the delivery of the medications, like morphine⁴. Other adverse effects include: infection, cerebrospinal fluid leakage, migration of catheter tip and formation of catheter associated granuloma^4,5,6.

A rarely described iatrogenic cause of progressive spinal deformity is the placement of an ITOP. Sciubba et al. introduced this concept with a case report describing a single patient who developed scoliosis following ITOP placement⁴. A similar concept of progressive spinal deformity has been described in spastic cerebral palsy patients receiving baclofen therapy with an IT pump^7,8. Our objective is to describe an apparent association between placement of an ITOP and the development of spinal deformity. With the lack of a national device registry, it is essential to report potential adverse effects through small case series.

Materials and Methods

We retrospectively reviewed four cases of spinal deformity progression following the placement of an ITOP. All study participants presented to a single spine surgeon due to progressive spinal deformity and pain. Each patient had prior placement of an ITOP for chronic pain by a different spine surgeon. Study design approval was obtained from Institutional Review Board at the medical institutions. There was no funding required or used for the review of this study. There was no conflict of interest related to this study. Informed consent was obtained from each participant. Patient's age, gender, health co-morbidities, ITOP placement, number of ITOP revision operations, history of spine surgery, and eventual spinal fusion was obtained. Serial radiographs were reviewed. Cobb angle measurements as described by Spinal Deformity Radiographic Measurement Manual⁹ were measured to evaluate the magnitude of deformity before and after placement of ITOP Pre-pump rate progression was calculated by comparing the oldest known radiograph to the radiograph prior to or at the time of pump placement, and then post-pump progression was determined.

Case reports

Case #1

Patient 1 is an 80-year-old female with history of osteoporosis, who had no spinal deformity prior to spine surgery. She underwent a L3-4 and L4-5 microdiskectomy and posterior lumbar interbody fusion with titanium cages in 1997. She also had anterior cervical diskectomy and fusion of C4-5, C5-6, and C6-7 in 1998. In June 2005, she underwent another spine surgery which included a right L2-3 foraminotomy and L2-3 posterolateral fusion with autologous iliac crest bone graft and pedicle screw instrumentation. Initial radiographs after the June 2005 surgery showed a 17 degree convexity to the right at L1-4 (Figure 1a). Subsequent radiographs in 2005 and 2006 showed no change from initial measurements. She had an ITOP placed in September 2006 for chronic post-surgical low back pain or so-called “failed back syndrome”. Follow-up radiographs in December 2007 began to show progression of spinal deformity with an increase to 25 degree convexity to the right at L1-4. Four months later, her spinal deformity progressed to 42 degrees at L1-4 (Figure 1b). The rate of change in spinal deformity prior to placement of IT pump was 1.1 degrees per year. After placement, the rate of change increased to 12.5 degrees per year. She underwent correction of her spinal deformity in July 2008 with posterior spinal fusion of T6-S1 with instrumentation and extension to the pelvis.

Figure 1. a) Pre-pump radiographs from June 2005 showed a 17 degree convexity to the right at L1-L4. Hardware from prior lumbar fusion with instrumentation is seen and appears without complication. b) Post-pump radiograph showed progression of spinal deformity to 42 degrees at L1-L4 approximately nineteen months following the placement of ITOP. There was a progression of 12.5 degrees per year following placement of the ITOP.

Case #2

Patient 2 is a 61-year-old female who had a 10 degree convexity to the right at L1-4 in 1994. She had no previous history of spine surgery. She had an initial ITOP placed in 2003 for severe fibromyalgia associated with chronic low back pain. Initial radiographs at the time of pump placement showed a 14 degree convexity to the right at L1-4 (Figure 2a). Four years following the pump placement, radiographs displayed a progression of spinal deformity to 41 degree convexity to the right at T12-L3 (Figure 2b). The rate of change in spinal deformity prior to placement of IT pump was 0.4 degrees per year. After placement, the rate of change increased to 6.5 degrees per year. She underwent correction of her spinal deformity in May 2007 with posterior spine fusion with instrumentation from T9-L5.

Figure 2. a) Radiograph at the time of ITOP placement showed a 14 degree convexity to the right at the L1-L4 level. b) Four years following the placement of ITOP, there was a progression of spinal deformity to 41 degrees from T12-L3, representing a rate of progression of 6.5 degrees per year after placement of ITOP.

Case #3

Patient 3 is a 62-year-old male with two previous spine surgeries in 1977 including a laminectomy and diskectomy at L4-L5 and L5-S1, and spinal fusion from L4-S1. Initial radiographs in 2002 showed no signs of spinal deformity. He had an ITOP placed in August 2002 for post-laminectomy syndrome with intractable low back and bilateral lower limb pain. Subsequent radiographs in 2007 started to show the development of spinal deformity with an 18 degree Cobb angle from T7-L2 and lateral Cobb angle from T11-L4 of 39 degrees. The rate of change in spinal deformity prior to IT pump was zero degrees per year. After placement, the rate of change was 3.6 degrees per year. The most profound change was in the patient's sagittal spine balance. His thoracolumbar kyphosis progressed from 0 to 39 degrees. He had a revision of his ITOP in September 2007 and eventually went on to have spinal deformity correction with posterior spinal fusion with instrumentation from T7-L5 in October 2007.

Case #4

Patient 4 is a 48-year-old male with no previous history of spinal deformity. He had an extensive history of low back pain for which he had placement of spinal cord stimulator (SCS) in 1998. In 2000, he had his SCS removed and underwent placement of an ITOP for chronic low back pain. Pre-pump radiographs were destroyed by the health system as part of their routine management of films older than seven years. In 2004, he had a 21 degree Cobb angle to the right from T12-L4 (Figure 3a). He had two revisions of his IT pain pump in 2006 and 2007 due to device malfunction. Subsequent radiographs in early 2007 showed no significant progression with a 23 degree convexity to the right at the same levels. Later in 2007, he had a significant progression of his spinal deformity to a 38 degree convexity to the right at T12-L4 (Figure 3b). His rate of change from 2004 to 2006 was 3.5 degrees per year, but following the first revision of his ITOP, his progression rate increased to 10 degrees from 2006 to 2007. He underwent corrective surgery with posterior spinal fusion and instrumentation from T9-L5 in December 2007 for his progressive spinal deformity.

Figure 3. a) In radiographs from four years following the placement of the ITOP, there was a 21 degree convexity to the right from T12-L4. b) After two ITOP revision surgeries, the spinal deformity progressed to a 38 degree convexity from T12-L4.

Results

The study population consisted of four adult patients, two males and two females (ages 48-80 years), with unique medical history (Table 1). All participants showed progression of the spinal deformity following placement of ITOP (Table 1). Three out of the four cases had a revision of their ITOP with a mean pump survival of 5.6 years (range: 1-6 years). Pre-pump placement progression for the population was 1.1, 0.4, 0.0, and 3.5 degrees/year, respectively. Following the placement of ITOP, the rate of progression increased dramatically to 12.5, 6.5, 3.6, and 10.0 degrees/year, respectively. All patients underwent subsequent posterior spinal fusion for treatment of their progressive deformities (Table 1).

Table 1.

Summary of patient cohort, including prior medical history. Overall, there was an increase in curve progression following the placement of an ITOP.

Case	Age	Gender	Prior Spine Surgery	Baseline Spinal deformity	ITOP revision	Spinal cord stimulator	Co-morbidities	Curve progression: pre-ITOP (degrees/yr)	Curve progression: post-ITOP (degrees/yr)	Management of progressive deformity
1	80	F	Yes	No	No	No	Osteoporosis, hypertension, atrial fibrillation, irritable bowel syndrome.	1.1	12.5	T6-S1 posterior spinal fusion with instrumentation and extension to the pelvis
2	61	F	No	Yes	Yes	No	Depression, anxiety, fibromyalgia with chronic low back pain.	0.4	6.5	T9-L5 posterior spine fusion with instrumentation
3	62	M	Yes	No	Yes	No	Osteoarthritis, depression, hypertension	0.0	3.6	T7-L5 posterior spine fusion with instrumentation
4	48	M	No	Yes	Yes	Yes	Hypertension, myocardial infarction, depression, smoker	3.5	10.0	T9-L5 posterior fusion with transforaminal interbody fusion at L1-2 and L2-3.

Discussion

The proposed theory of placement of an ITOP contributing to progressive spinal deformities is based upon a pattern recognized within a single spine deformity surgeon's practice. To our knowledge, there has only been one other published case report describing this association with ITOP⁴. Our article reinforces the possible relationship between ITOP and progressive spinal deformities.

The mechanism by which IT drugs, specifically opioids, might cause progressive spine deformity is unclear. The paraspinal muscles play an essential role in providing major stability for the spine¹⁰. Paraspinal muscle imbalance by the indirect inhibition of motor neurons via polysynaptic nociceptive reflex pathways may constitute an etiology for progression of deformity^1,4,11. However, intrathecally administered drugs are cleared from the CSF by diffusion into the epidural space which means nearly 70% of intrathecal opioids, particularly morphine, is cleared into the systemic circulation from the epidural space¹². Therefore, a systemic effect on muscles may provide potential etiology.

Our case report has several inherent weaknesses. First, this cohort represents a minute fraction of the total number of patients receiving ITOP within the authors' community and only a careful longitudinal analysis of a large consecutive series of patients would allow understanding of the breadth of the problem. However, as with many medical devices in the United States, the lack of a national device registry often necessitates the identification of rare complications through small case series. Due to complex spine histories, it is difficult to explain whether the progressive spine deformity is related to ITOP or other possible causes like adjacent segment disease or the natural history of pre-existing spinal deformity^{13,14,15,16,17,18}.

In conclusion, we described four cases of progressive spinal deformity following the placement of an ITOP. At present, there exists only an association between the use of an ITOP and the progression of a spinal deformity. Intrathecal opioids appear to be playing a role, but these drugs can only be considered an association, not a cause. Physicians or other pain specialists recommending the implantation of an ITOP should be aware of a possible association with progression of spinal deformities. We recommend careful monitoring, through routine follow- up radiographs, of patients with an ITOP for development of spinal deformities.