Neurovascular Injuries : Prevention, Diagnosis, and Treatment

Peripheral Nerve Injury

Peripheral nerve injury following primary THA has been reported to have a prevalence that ranges from 0.1% (1 palsy in 1287 cases) to 1.9% (7 palsies in 360 cases). The risk for a nerve palsy following primary THA is increased if the indication for surgery is congenital hip dislocation, severe hip dysplasia, or if there is otherwise a need for a large degree of leg lengthening. Schmalzried et al. reviewed 3126 consecutive THAs and reported the overall rate of nerve injury to be 1.3% for diagnosis other than hip dysplasia and 5.2% in those patients receiving a primary THA for hip dysplasia (9 palsies in 172 cases). In the same study, nerve injury following a revision THA was reported to be 3.2%; however, that number has been reported to be as high as 7.5% in other series (5 palsies in 66 revision cases). Weber et al. performed preoperative and early postoperative electromyograms (EMGs) in 30 hips to determine the incidence of subclinical nerve injury following THA and found that asymptomatic injury to peripheral nerves may be as high as 70% (21 abnormal EMGs in 30 asymptomatic hips).

The most frequently injured nerves following THA are the sciatic, femoral, obturator, and superior gluteal nerves ( Table 110.1 ). Peripheral nerve injuries generally occur in isolation; however, multiple nerve injuries can occur. Injury to the sciatic nerve remains the most common, accounting for up to 90% percent of all post-THA nerve palsies. The peroneal fibers of the sciatic nerve are affected in 94% to 99% of sciatic nerve injuries, while up to 41% have tibial nerve involvement as well. Isolated tibial nerve injury is rare, however, comprising between 0.5% and 2% of sciatic nerve injuries while isolated peroneal nerve injury comprises between 47% and 65% of sciatic nerve injuries. The peroneal nerve is at increased risk due to a combination of factors, including the density of nerve fibers at the hip, the proximity of the peroneal distribution to retractors (it lies lateral), and the susceptibility to tethering or compression. Female sex, hip dysplasia, leg lengthening greater than 2.7 cm, revision surgery, a history of lumbar radiculopathy or peripheral neuropathy, excision of heterotopic bone, a deficient posterior wall, posterior surgical approach, and the use of a cementless femoral implant increase the risk of sciatic nerve injury ( Table 110.2 ). Lumbar stenosis and radiculopathy are important preoperative risk factors for nerves that can exacerbate intraoperative nerve damage through a double crush phenomenon in which impingement to the affected nerve proximally leaves it susceptible to damage at the surgical site. A history of lumbar spine disease should be noted in the preoperative visit, as it may change the course or timing of treatment for a postoperative nerve palsy.

The femoral nerve is the second most commonly injured nerve following a THA, comprising 13% of all peripheral nerve injuries (32 out of 243 palsies). The most common cause of acute injury is direct compression by aberrant placement of a retractor anterior to the acetabulum. Increased risks of femoral nerve palsy are an anterior surgical approach, deficient anterior acetabular bone, or a previously released or absent psoas tendon. Expanding hematomas are found in up to 11% of patients with diagnosed nerve palsy and is the most common cause of delayed femoral nerve palsy. Schmalzried found that simultaneous femoral and sciatic nerve injuries occur in 5.8% of nerve injuries.

Superior gluteal nerve palsies may be increasing in prevalence owing to the increasing use of anterior approaches for primary THA. The incidence of superior gluteal injury may be as high as 23% using a Hardinge approach. The exact incidence of superior gluteal nerve dysfunction is difficult to assess because patients present with abductor weakness similar to an abductor avulsion and may have a Trendelenburg gait.

Obturator nerve injury is extremely rare, only 1.6% of all nerve palsies (4 out of 243 palsies) with a prevalence of 0.016% of all cases (4 out of 24,469 hips). Obturator nerve injury was probably more common when cemented acetabular components were routinely used, with extravasated cement into the obturator foramen being the main cause. Difficulty in diagnosis of this entity may contribute to its low reported incidence.

The direct anterior approach to THA has gained increasing popularity in recent years. Grob et al. have examined its impact on the neurovascular structures to the anterior aspect of the hip in a cadaveric study. They found that distal extension of the anterior approach compromises the nerve supply to the anterolateral quadriceps and the placement of a cable passer through this anterior approach will endanger the nerve branches to the vastus lateralis and intermedius as well as branches of the lateral femoral circumflex artery.

Central Nervous System Injury

Central nervous system injury is much less common than peripheral nervous system injury and is typically associated with fat embolism syndrome (FES). The incidence for FES is not known following THA but occurs as high as 1% to 11% in the trauma population. FES is associated with femoral canal manipulation, such as reaming, cementing, and implant impaction. In addition to FES, ischemic stroke was noted to occur in 3.9% of patients within 1 year of hip arthroplasty (67 cerebrovascular accidents of 1606 patients) in one large study. Ischemic stroke is associated with a number of factors, including history of atrial fibrillation, hip fracture, and previous history of stroke.