27.1.1 Tone Management

Hypertonia can manifest itself secondary to a number of different etiologies. Neuromuscular disorders such as cerebral palsy (CP) are the most common, but many other disorders such as traumatic/acquired brain injury, metabolic disorders, leukodystrophies, hydrocephalus, and spinal cord injuries are also associated with hypertonia. ¹ Hypertonia can cause impairments in quality of life and lead to problems with rehabilitation. ² It can present as spasticity, dystonia, rigidity, or a mixed combination. Spasticity is the most frequently observed form. It is an increased muscle tone as a result of an externally imposed muscle movement. ³ Dystonia is a less common but more complicated form of hypertonia. ¹ It consists of abnormal involuntary contractions in muscle groups causing abnormal posturing of the neck, torso, or extremities. ³ Both spasticity and dystonia can lead to rigidity or simultaneous contracture of muscle agonists and antagonists. ³ Often, there is a mixture of spasticity and dystonia in children with various tone disorders.

Management of hypertonia can involve both nonoperative and operative approaches. Nonoperative approaches include physical/occupational therapy, orthoses, casting, chemodenervation with botulinum toxin, and enteral medications such as benzodiazepines. One enteral medication that is frequently used is baclofen. Baclofen binds to GABA_B receptors (metabotropic transmembrane receptors for gamma-aminobutyric acid) and inhibits the release of excitatory neurotransmitters and substance P, which results in decreased spasticity. ⁴ The enteral form of baclofen can work very well but can also cause significant sedation, fatigue, and hypotonia. ¹ Sedation is reported to occur in 7 to 70% of patients on enteral baclofen. ²

Operative management of hypertonia consists of various orthopaedic surgeries (soft tissue and bony), dorsal rhizotomy, intrathecal baclofen, deep brain stimulation, and other methods. ¹ Intrathecal baclofen delivered by an implanted pump was first approved by the Food and Drug Administration in 1996 for the treatment of hypertonia. Intrathecal baclofen is approved for treatment of spasticity related to a number of disorders including CP. ⁵ Evidence for its efficacy in spastic and dystonic CP was first published by Butler et al ⁶ in 2000. It results in fewer systemic side effects than enteral baclofen and has a higher efficacy rate. ⁷ Due to systemic absorption of enteral baclofen, only small concentrations reach the spinal cord and cerebrospinal fluid (CSF) despite high doses. Intrathecal delivery of baclofen allows for high concentrations to diffuse into the superficial layers of the spinal cord dorsal horn, often avoiding the cerebral side effects. ⁸

27.1.2 Indications/Treatment Goals for Intrathecal Baclofen Pump

The indications for implantation of intrathecal baclofen pumps are primarily for intractable spasticity or spasticity not optimally managed by physical therapies, oral baclofen, or other medications including botulinum toxin injections. ^{9 ,​ 10} Additionally, patients with intolerable side effects to enteral baclofen may be good candidates. ⁹ Patients and their family members need to have the ability and motivation to attend regular follow-ups and monitoring. ¹⁰

The treatment goals and benefits of intrathecal baclofen are well documented in the neuromuscular population. Penn and Kroin ¹¹ first reported its use for severe spasticity with immediate reduction of muscle tone to near normal levels, and others have demonstrated the efficacy of intrathecal baclofen in children with CP. ¹² Multiple studies have shown benefits in patients with CP. Gooch et al ¹³ demonstrated improved satisfaction of care providers, ease of care, and decreased pain. Other studies have also found improved ease of care ¹⁴ as well as improved gait in ambulatory patients. ¹⁵ Additionally, Gerszten et al ¹⁵ demonstrated a decreased need for subsequent orthopaedic surgery for lower extremity spasticity. In summary, intrathecal baclofen pumps have the ability to improve spasticity, range of motion, ease of care, pain, caregiver satisfaction, hygiene, and gait. ^{9 ,​ 10}

27.1.3 Timing of Intrathecal Baclofen Implantation

Many patients who are candidates for intrathecal baclofen pumps are also at risk for the development of scoliosis. Thus, the timing for intrathecal baclofen pump and catheter placement is often discussed in reference to the timing of spinal fusion: before, during, or after scoliosis surgery. Although there is extensive literature discussing this timing, significant controversy remains as to whether insertion of an intrathecal baclofen pump causes progression of scoliosis. ^{16 ,​ 17 ,​ 18 ,​ 19 ,​ 20 ,​ 21 ,​ 22 ,​ 23 ,​ 24} There is also concern and debate as to whether prior placement of an intrathecal baclofen pump can further complicate CP scoliosis surgery and increase the risk for wound complications. ^{23 ,​ 24 ,​ 25} Specifically, there is concern that the intrathecal baclofen catheter can prevent complete closure of the fascia, result in a CSF leak, or interfere with placement of instrumentation.

Numerous studies have evaluated progression of scoliosis after placement of a baclofen pump. Two small series of patients reported accelerated scoliosis progression after baclofen pump placement. ^{17 ,​ 18} Segal et al, ¹⁷ in their series of five patients with a rapid curve progression, found a mean progression of 44 degrees over 11 months leading to spinal fusion in all patients. Burn et al ²⁰ found an annual progression of Cobb angle of 19 degrees in 32 patients after intrathecal baclofen pump placement. This study also found that the Cobb progression was higher in patients who were skeletally immature. Another study found an increase in scoliosis progression from 1.8 degrees per year prior to implantation to 10.9 degrees per year after implantation. ¹⁶

Despite these studies suggesting curve progression, two studies that compared matched cohorts of CP patients with and without a baclofen pump found no difference in the rate of scoliosis progression. ^{21 ,​ 22} Senaran et al ²¹ compared 25 matched patients with quadriplegic CP who had scoliosis (controls) who did not receive an intrathecal baclofen pump to 26 patients who did receive the pump. The average curve progression for the baclofen pump group after implantation was 16.3 degrees per year compared to 16.1 degrees per year in the control group. Shilt et al ²² also found that patients receiving an intrathecal baclofen pump experience a natural progression of scoliosis similar to that of patients without this therapy.

Timing of baclofen pump placement and spinal fusion has also been studied. Controversy exists as to whether the presence of a baclofen pump complicates posterior spinal fusion. Caird et al ²³ and Borowski et al ²⁴ both report single center experiences evaluating complications associated with intrathecal baclofen pump placement and spinal fusion. Caird et al ²³ compared 20 patients with spastic quadriplegic CP with baclofen who underwent posterior spinal fusion to 20 matched patients without a baclofen pump. They found increased reoperation and rehospitalization and a higher infection rate in the baclofen pump group (20 vs. 0%, p = 0.063). However, in this series, two patients who developed wound infection had a history of decubitus ulcers prior to the spinal fusion, and four patients who were readmitted postoperatively for complications had been previously hospitalized for pulmonary problems.

Borowski et al ²⁴ compared four groups of patients with CP. The four groups included: (1) posterior spinal fusion prior to baclofen pump placement (n = 26); (2) posterior spinal fusion and baclofen pump placement concurrently (n = 11); (3) posterior spinal fusion after baclofen pump placement (n = 25); and (4) baclofen pump placement only (n = 103). In all four groups, they found an infection rate of 8 to 9% with no differences between groups. There was also no difference in device or catheter complications between groups. They concluded that baclofen pumps can be implanted and managed without any increase in complication rate before, during, or after spinal fusion.

A recent multicenter study by Yaszay et al ²⁵ is the largest study to date comparing patients undergoing posterior spinal fusion with (N = 32) and without (N = 155) previously placed intrathecal baclofen pumps. This study found no difference between groups in OR (operating room) time or intraoperative EBL (estimated blood loss), and an overall wound complication rate was not significant between the baclofen pump group (16%) and the nonbaclofen pump group (15%). The deep infection rate was 6.3% in the baclofen pump group and 5.8% in the nonbaclofen pump group. Both of these complication rates compare favorably to that of Caird et al. ²³

Based on the studies by Borowski et al ²⁴ and Yaszay et al, ²⁵ while it may be inconvenient for the surgeon, baclofen pumps do not appear to increase the complexity of surgery or the risk for wound complications. Yaszay et al ²⁵ states that when counseling patients and their caregivers on the timing of pump placement, it does not appear to compromise the care of the patient if the baclofen pump is placed first.