Complications in Lower Extremity Soft Tissue Surgery in Neuromuscular Patients

Introduction

Soft tissue pathology in the lower extremities of children with neuromuscular diseases, particularly those with spasticity (most commonly cerebral palsy [CP]), can lead to significant impairment in gait in ambulatory children and function-limiting deformities affecting limb and trunk position in nonambulatory children. The deformity and gait disturbances that stem from spasticity and contracture can be debilitating, often necessitating surgical intervention. Depending on the child’s clinical presentation, there are a number of soft tissue lengthening and transfer procedures designed to address the affected structure(s) that can be employed in isolation or in conjunction with select bony procedures, as dictated by the patient’s needs. Soft tissue procedures in this patient population are powerful tools that can lead to marked reduction in deformity and functional gains, but great care is required to avoid complications. Most pressingly, many of the targeted musculotendinous units, such as the iliopsoas, adductors, and hamstrings, are intimately associated with critical neurovascular structures, and an in-depth knowledge of local anatomy is required to avoid iatrogenic injury. In addition, a thorough physical exam and, in some cases, instrumented gait analysis are necessary to properly indicate patients for the appropriate surgical procedure at the most beneficial time in their disease process. Finally, incomplete releases may lead to deformity recurrence and the need for revision or repeat surgery. This chapter will review potential complications associated with the most common soft tissue procedures in the neuromuscular pediatric population and strategies for avoiding them.

Hip Flexors

The psoas muscle and iliopsoas tendon are commonly addressed surgically to treat excessive hip flexion, which has deleterious effects on hip development, gait, and spinopelvic alignment in patients with neuromuscular disease. Although the rectus, sartorius, tensor fascia lata, and anterior half of the gluteus medius may also play a role in hip flexion, biomechanical and clinical studies have largely identified the iliopsoas complex as the primary functional contributor and pathology generator. The lever arm of the iliopsoas insertion along with the cross-sectional area of the muscle contribute to the strong hip flexor function of the iliopsoas. Contracture of the iliopsoas can contribute to crouch gait in the ambulatory child and may lead to hip subluxation or dislocation in both ambulatory and nonambulatory children.

Understanding the anatomy of the iliacus and psoas muscles and iliopsoas tendon is the key to safely performing a successful recession or tenotomy. The iliacus originates in the iliac fossa, while the psoas originates from the vertebral discs and bodies of T12 to L5. They most commonly converge into a single iliopsoas tendon (97.5% of cases) that inserts onto the lesser trochanter of the femur. The iliopsoas can be addressed at its insertion at the lesser trochanter, at the level of the pelvic brim, or over the pelvic brim. It was previously reported that releasing the iliopsoas tendon at the lesser trochanter may lead to weakness in hip flexion in ambulatory children, and, resultantly, some authors strongly recommended against it ; however, more recent evidence has demonstrated that release at the lesser trochanter may result in a more effective clinical response without producing demonstrable weakness in excess of that seen in over-the-brim or at-the-brim release. As such, this procedure release at the lesser trochanter––should be considered when managing spastic hip flexion contractures.

Despite its inherent risks, the over-the-brim technique is still widely employed clinically. In utilizing this approach, the operating surgeon should be acutely aware of the proximity of the lateral femoral cutaneous nerve (LFCN). Although quite variable, this sensory nerve courses medial to the anterior superior iliac spine (ASIS) and superficial to the sartorius muscle belly. Care needs to be taken during the dissection to identify and protect this nerve if it lies in the surgical field. Damage to the LFCN causes paresthesias to the lateral thigh but no motor deficits, as it is a purely sensory nerve. Deeper within the dissection, the femoral neurovascular bundle may be encountered. There are limited data on the incidence of damage to the bundle during the over-the-brim operation, but one must be cognizant of the relationship between the iliacus, psoas, and femoral neurovascular bundle at all times during this operation. Magnetic resonance imaging (MRI) and cadaveric studies have identified the mean distance between the psoas tendon and the neurovascular bundle at 1 cm, with a range of 4 mm to 2 cm. This is in contrast to a mean distance of 3.1 cm between the iliopsoas tendon and neurovascular bundle (range 1.4–5.5 cm) at the level of the lesser trochanter.

Published techniques differ as to whether the bundle should be identified and protected or avoided entirely, but there are several important technical pearls that will minimize potentially catastrophic iatrogenic injury to the bundle. Prior to incision, the femoral artery should be palpated and marked for any iliopsoas release at or over the brim. This allows surgeons to remain mindful of their anatomic location within the surgical field throughout the surgery, which is especially prudent when operating on younger, smaller patients. If the approach is medial to the sartorius or the iliac fascia is divided medially, familiarity with the anatomy of the neurovascular bundle is key. The femoral nerve is the most lateral structure, and it branches at the level of the inguinal ligament, so it should be protected at that level or proximally. If the neurovascular bundle is identified and dissected, use of a soft retracting tool such as a rubber vessel loop for gentle medial retraction is recommended.

Alternatively, the surgeon may begin their approach more laterally, starting just lateral to the ASIS and dissecting along the inner brim of the pelvis. In this approach, the neurovascular bundle will not be directly encountered. The surgeon should remain deep to the iliopsoas muscle belly, dissecting along the periosteum of the inner table. This ensures that the nerve will remain superficial to the dissecting plane, within the muscular body of the iliopsoas muscles. The surgeon should continue the dissection along the deep side of the iliopsoas muscle, and a right-angle retractor should be utilized to medially retract the neurovascular bundle within the muscle belly. Placing the retractor deep to the muscle belly at this level, the surgeon will slowly lift the retractor until the tendon belly is palpated along or just proximal to the brim. The surgeon can then dissect the fascia from the suspected psoas tendon bluntly, utilizing a “peanut,” until the tendon is visualized. Placing the knee on a bump places the hip in a flexed and externally rotated position that will relax the tendon, aiding in identification and isolation, as will visualizing the tendon during internal and external rotation of the hip. Finally, using electrocautery or a handheld nerve stimulator to gently stimulate the tendon prior to resection and observing for quadriceps contracture will confirm that the identified structure is indeed the psoas tendon and not the femoral nerve. This technique can be utilized prior to resection at any level.