CHAPTER SYNOPSIS:
The periacetabular osteotomy is an effective procedure for correcting the structural abnormalities and dynamic instability associated with acetabular dysplasia. Mid- and long-term clinical results from multiple centers are now available and demonstrate the success of this surgical procedure for most patients. It is a technically challenging operation, and focused surgical training in the procedure is essential to optimize clinical results. This chapter summarizes the indications, surgical technique, and pitfalls of this surgical procedure.
IMPORTANT POINTS:
- 1
The periacetabular osteotomy is indicated for the treatment of symptomatic acetabular dysplasia.
- 2
Optimal candidates for surgery are younger than 50 years and have well-maintained range of motion and minimal secondary osteoarthritis.
- 3
Acetabular reorientation is the most challenging aspect of the procedure, and care must be taken to optimize the reduction intraoperatively.
- 4
Maintaining functional hip motion (flexion, internal rotation, and adduction) and avoiding secondary femoroacetabular impingement are believed to enhance clinical results.
- 5
Consideration for concomitant osteochondroplasty (common) and/or proximal femoral osteotomy (uncommon) should be included in the preoperative surgical planning.
- 6
Major potential complications of the procedure include malpositioning of the acetabulum, intraarticular fracture, and neurovascular injury.
CLINICAL/SURGICAL PEARLS:
- 1
Select patients with symptoms of structural instability.
- 2
Patients must have adequate preoperative range of motion.
- 3
A subgroup of patients will have combined structural instability and concurrent impingement.
- 4
Severe hip joint irritability, rapid progression of symptoms, and/or moderate radiographic osteoarthritis may indicate secondary joint disease too advanced for joint preservation.
- 5
Continuous electromyographic monitoring may minimize nerve injury risk.
- 6
Intraoperative fluoroscopy and plain radiographs can be helpful in guiding osteotomy cuts and reduction.
- 7
Avoid excessive retraction of soft tissues during the superior pubic ramus cut because of the presence of the neurovascular bundle.
- 8
Avoid excessive lateral osteotome penetration during posterior column and ischial cuts because of sciatic nerve proximity.
- 9
Check osteotomy cuts and soft tissue attachments if the acetabular fragment does not mobilize.
- 10
Acetabular reduction includes internal rotation, extension (forward tilt), medial translation, and adduction.
- 11
Acetabular reduction should be carefully assessed intraoperatively.
- 12
Ensure 90 degrees or more of flexion and 30 degrees or more abduction of hip intraoperatively. If not present, reposition the acetabulum.
- 13
Consider anterior arthrotomy and femoral head-neck junction osteochondroplasty if insufficient offset.
CLINICAL/SURGICAL PITFALLS:
- 1
Acetabular reorientation may fail early if preoperative secondary osteoarthritis is dominant.
- 2
Clinical factors, including obesity, osteoporosis, and tobacco use, may compromise the surgical procedure or clinical result. These factors should be considered during the patient selection process.
- 3
Patient noncompliance with the rehabilitation protocol may compromise the surgical result.
- 4
Patients must understand the treatment and prolonged rehabilitation period.
- 5
Excessive traction of the femoral nerve occurs during the superior ramus cut.
- 6
Fracturing of the posterior column or intraarticular osteotomy extension is possible.
- 7
Incomplete osteotomies can prevent acetabular fragment mobilization.
- 8
Acetabular fragment retroversion is a common learning curve mistake.
- 9
Acetabular reduction must be carefully assessed intraoperatively.
- 10
Excessive loss of flexion (need 90 degrees after fixing fragment) can compromise the clinical result because of secondary femoroacetabular impingement.
INTRODUCTION
Developmental dysplasia of the hip is one of the main causes of secondary osteoarthritis. Many patients have prolonged hip symptoms and functional limitations before the development of advanced joint degeneration. The periacetabular osteotomy (PAO) (Bernese) was developed in an attempt to improve the surgical technique of correcting acetabular hip dysplasia. With this technique, the posterior column is left intact, providing improved inherent stability in the immediate postoperative period. The PAO is performed near the acetabulum, allowing comprehensive correction of severe deformities. Despite the relatively extensive mobilization of the large periacetabular fragment, clinical experience to date has revealed minimal risk of the occurrence of avascular necrosis of the acetabular fragment. The osteotomy can be safely performed in the mature and near skeletally mature pelvis.
INDICATIONS AND CONTRAINDICATIONS
The Ganz PAO is indicated in a skeletally or near skeletally mature patient with symptomatic, acetabular-based hip dysplasia. The ideal patient is younger than 50 years with early hip symptoms and minimal secondary osteoarthritis. Preoperative symptoms include initially lateral (greater trochanteric) hip pain characteristically aggravated by weight-bearing activities. With time, medial (groin) hip pain often is experienced. On physical examination patients typically have a positive Trendelenburg sign. Hip range of motion is variable. Hip flexion often is more than 100 degrees, and hip abduction is 35 degrees or more in young patients with severe dysplasia. On the other hand, hip flexion is often less than 100 degrees and abduction less than 35 degrees in patients with symptoms of both dysplasia and impingement (groin pain, pain aggravated with sitting). The anterior hip impingement test result (pain with passive flexion to 90 degrees and internal rotation adduction at 90 degrees) is positive in patients with impingement as well as structural instability. Radiographs will reveal variable acetabular hip dysplasia. On the standing anteroposterior radiograph Shenton’s line is broken. The hip joint center often is lateralized. Acetabular inclination and lateral acetabular deficiency are assessed by measuring the angle of the weight-bearing acetabulum (normal is 0 to 10 degrees) and the lateral center-edge angle (normal is 25 degrees or more), respectively. Anterior deficiency is assessed on the false profile radiograph. It often is deficient (normal is 20 degrees or more).
A supine anteroposterior hip radiograph with the hip in flexion/abduction assesses how congruently the femoral head reduces into the acetabulum. In turn, it predicts how effectively the osteotomized acetabular fragment could be redirected over the femoral head. The supine frog-leg lateral radiograph also demonstrates congruence and profiles the anterolateral head-neck offset, typically deficient in acetabular-based hip dysplasia. The degree of degenerative changes is assessed by the 0 to 3 grading system of Tönnis. Indications for a PAO are the presence of acetabular dysplasia in a symptomatic patient without major secondary osteoarthritis. However, dysplasia caused by neuromuscular disease (e.g., cerebral palsy), Charcot-Marie-Tooth disease, skeletal dysplasia, and Down syndrome also are potential candidates. Contraindications include advanced degenerative joint disease affecting function of the involved hip. Recent progression in pain, increased pain with all parts of the assessment of range of motion, marked limitation in hip motion, and marked incongruity on radiographic assessment may be contraindications for performing a PAO. Obesity and history of recent smoking are relative contraindications.
SURGICAL TECHNIQUE
The patient is positioned supine on an x-ray translucent operating table and administered general anesthesia with combined epidural anesthesia for postoperative pain management. A soft bump is placed under the posterior ilium and lower lumbar spine, creating a 5- to 10-degree tilt of the pelvis toward the unoperated side. A foot rest is secured on the table on the operated side to support the lower extremity during the procedure when the hip and knee are both flexed approximately 50 to 70 degrees. A large U-shaped sterile adhesive drape is applied vertically along the midline of the abdomen, then posteriorly to cover the perineum and proximally again in a vertical direction onto the buttock and lower back. An additional adhesive drape is placed horizontally across the lower rib cage, sealing off the surgical prepped area from the rest of the torso. The entire involved lower extremity and adjacent torso are surgically prepped and draped. If continuous electromyographic monitoring is to be performed, appropriate electrodes are strategically placed at this time on the involved lower extremity.
A modified Smith-Petersen surgical approach is used. The incision starts at a point just lateral to the proximal iliac crest and parallels the iliac crest, extending distally to the anterior superior iliac spine and then gradually turning laterally and extending down the thigh for several centimeters. Subcutaneous flaps are elevated to identify the abductors, the tensor, sartorius, and external oblique. Care is taken to not penetrate through the sartorius fascia and inadvertently injure branches of the lateral femoral cutaneous nerve. The muscular interval between the tensor and the sartorius is developed through a fascial incision starting from the anterior superior iliac spine and extending laterally over the tensor muscle ( Fig. 6-1 ). Once the fascia has been incised, Metzenbaum scissors are used to develop the interval between the medial edge of the tensor muscle and the adjacent lateral edge of the sartorius muscle. Deep to this muscle interval, the lateral edge of the rectus muscle is exposed deep to an overlying fatty tissue layer. Next, the lateral edge of the thin external oblique aponeurosis is carefully incised with a knife, starting at the posterior corner of the lateral iliac crest and extending anteriorly across the anterior superior iliac spine. The aponeurosis and the external oblique muscle are reflected from lateral to medial off the iliac crest. In skeletally immature patients the aponeurosis is carefully elevated off the apophyseal growth cartilage. After completion of the osteotomy the aponeurosis and the attached external oblique muscle will be reattached to the lateral edge of the iliac crest, covering it and the screws, which will secure the acetabular fragment.
The sartorius muscle is detached from the pelvis together with a 1 × 1.5 cm fragment of bone (anterior superior iliac spine) with a straight half-inch osteotome and reflected distally ( Fig. 6-2, A ). Similarly, the adjacent iliacus muscle is detached from the distal inner pelvis with a 1 × 2 cm bone fragment. Osteotomized surfaces are covered with bone wax.
The interval between the rectus and the tensor is developed laterally, as is the interval between the rectus and the sartorius medially, exposing the rectus tendon. A large right-angle clamp is placed around the rectus tendon from medial to lateral. The rectus is transected at a point just distal to the conjoined straight and reflected heads. The distal tendon and broad expanse of the rectus muscle are reflected distally off the lateral, anterior, and medial hip joint capsule. Medial to and often inseparable from the rectus muscle are the adjacent fibers of the iliocapsularis muscles. This muscle and the contiguous iliopsoas muscle are reflected medially off the capsule. With further dissection, the interval between the capsule laterally and the iliopsoas medially is further developed (see Fig. 6-2, B ). Slight hip flexion will facilitate this extracapsular dissection in a medial, then posterior, direction. Long, large Mayo-type scissors are quite useful in completing this dissection around the anterior medial capsule posteriorly down to the intraacetabular groove. Once the ischium can be readily probed with the tips of the scissors, a small hip skid is inserted into the interval. The hip skid facilitates passing the osteotome through the soft tissue interval. The ischium is probed with the osteotome, identifying the medial and lateral edges of the same ( Fig. 6-3, A ). A C-arm fluoroscope is now brought into the operative field across from the surgeon and an anteroposterior image is taken to verify the location of the osteotome on the ischium (see Fig. 6-3, B ). The medial ischium is cut first. The C-arm fluoroscope is then rotated 45 to 50 degrees away from the surgeon to obtain an oblique image of the inferior acetabulum and adjacent ischium. From the oblique view the correct point of beginning the ischial osteotomy (5 to 10 mm inferior to the edge of the acetabulum within the infracotyloid groove) is confirmed (see Fig. 6-3, C ). The ischial osteotomy extends posteriorly and proximally around the acetabulum. The curve of the modified (Mast/Ganz) osteotome facilitates making this curved ischial cut toward the base of the ischial spine. The medial cut will extend approximately 15 to 20 cm into the ischium. The central cut extends to a depth of approximately 2.5 to 3.0 cm. Care also should be taken to not break through the posterior column as the osteotome is advanced into the ischium. The most lateral cut is made with caution; the cortical wall falls off laterally and, as the osteotome is advanced, the static nerve is located just lateral to the osteotome. To minimize the possibility of static nerve injury, the osteotome is not advanced as far laterally as it is more medially. In addition, the extremity is abducted and externally rotated while the lateral ischial cut is being made. Three well-positioned adjacent cuts typically ensure that the inferoacetabular ischial cut has been satisfactorily completed.
