Techniques for DDH Cup and Femur
Kush Raj Shrestha
Steven J. MacDonald
INDICATIONS
Total hip replacement (THR) in the setting of developmental dysplasia of the hip (DDH) is indicated in symptomatic patients after failed conservative and nonarthroplasty options. Patients are counseled regarding pros and cons of the procedure.
CONTRAINDICATIONS
Severe neuromuscular disorders and inability for patients to follow postoperative rehabilitation are relative contraindications for any THR procedure. Absolute contraindications include active infection and neurovascular dysfunction precluding a satisfactory result.
PREOPERATIVE PREPARATION
THR in DDH involves detailed evaluation and preparation of patients including adequate history, physical examination, and relevant investigations. The purpose of this evaluation is to determine whether the patient is an appropriate candidate for surgical intervention.
HISTORY
History taking should adequately elucidate the patient’s main presenting symptoms. The impact of pain and stiffness on daily and recreational activities and relevant past medical and surgical history should be investigated. It is important to document any childhood hip disorders, previous hip surgeries (open/closed hip reductions and femoral or pelvic osteotomies), prior surgical complications (especially prior infection), as well as relevant medications and allergies. Consultation and collaboration with internal medicine or anesthesia colleagues should be undertaken prior to surgery.
EXAMINATION
A thorough examination should be undertaken including general patient features such as spinal deformity, gait analysis, hip range of motion and strength evaluation (making note particularly of any abductor weakness), and leg length discrepancy. Leg length discrepancy should be accurately measured using a tape measure and confirmed with blocks under the short limb. In addition, the neurovascular status of the limb, with particular attention to the sciatic nerve function, should be well documented. The hip should be examined for prior surgical scars, range of motion, and fixed deformities. Surgeries to the contralateral limb (e.g., epiphysiodesis) should also be noted.
INVESTIGATION
Every patient should be investigated with plain radiographs of anteroposterior (AP) projection pelvis and lateral x-rays of the involved hip. Radiographs should take into account the magnification of the images and be reviewed to look for deformities around the hip joint.
Although each DDH patient presents with varying degrees of deformities, the acetabulum is usually characterized by deficiencies in the anterior column and superior dome. Similarly, the common deformities of the proximal femur are increased anteversion, a metaphyseal/diaphyseal mismatch with a relatively reduced intramedullary canal size, and coxa valga. Special attention should be taken of thin cortical diameters, which combined with smaller canal width make the femur prone to intraoperative fractures.
The hip can be classified according to the Crowe classification (1). This system radiographically divides dysplastic hips into four categories based on the extent of proximal migration of the femoral head compared to the contralateral normal head (Table 19-1).
In addition to the radiographic assessment, adequate blood work and urinary cultures should be carried out to prepare patients for surgical intervention. Computed tomography (CT) scans are not usually required; however, they can be used to accurately define femoral anteversion and acetabular bone stock.
TABLE 19-1 Crowe Classification | ||||||||||
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SURGERY
Approach
Anterolateral, direct lateral, and posterior approaches can all be utilized for THR. However, for increased postoperative stability, the anterolateral approach is the preferred approach by this author. A posterior approach is recommended if the deformity is very severe and sciatic nerve monitoring is anticipated.
Position
The patient is positioned in the lateral decubitus position on a radiolucent table, with the affected side up. The underlying leg is flexed to reduce the degree of lumbar lordosis and secured in such a way as to allow leg length assessment during surgery through palpation of both heels and knees. All bony prominences are protected and the trunk and pelvis appropriately stabilized. The pelvis is squared and adequately secured with bolsters.
Incision
A longitudinal incision is centered over the greater trochanter (GT), 4 cm proximal to and 6 cm distal to the GT, in line with the midshaft of the femur. Dissection is carried down to the fascia lata, and fat is swept away both anteriorly and posteriorly.
Deep Dissection
Using the GT as a landmark, the iliotibial band is incised beginning at the GT and extended distally. An index finger is then inserted under the fascia lata to separate it from the underlying tensor fascia lata fascia and the gluteus maximus fascia proximally. This internervous plane is utilized to dissect the fascia lata.
The dissected fascia lata layers are retracted using Charnley retractors, ensuring the sciatic nerve is not caught with posterior retractor. An abductor split is made at the level of GT 2/3 and 1/3 junction. The dissection is curved anteriorly over the GT and headed toward the vastus lateralis leaving a thick cuff of tissue over the GT for satisfactory closure later. The abductor muscles are lifted anteriorly off the GT and distally from the proximal femur.
The gluteus minimus is identified proximally after dissection through gluteus medius. A layer of fat helps to identify this layer. This fat layer is swept away, and an incision is made in this minimus layer in line with the neck toward the superior rim of the acetabulum. This dissection is connected distally to the gluteus medius dissection at the GT. The whole anterior layer of the capsule and muscles are dissected off the femoral neck to the level of the lesser trochanter. All the soft tissues are removed proximally and distally around the femoral head and neck to ensure femoral head dislocation.
Prior to dislocation, a leg length/offset guide is used to determine baseline measurements. A long Steinmann pin is inserted over the iliac crest, and a mark is made over GT with a Bovie and a marking pen. The offset guide is used to measure the length and limb offset from the iliac crest pin to this mark and fixed to compare the length and offset later.
Dislocation of the femoral head is then performed after ensuring adequate release of the capsule up to the acetabulum and proximal femoral neck. The femoral neck is cut as per preoperative templating, usually about 1 cm above the lesser trochanter. This neck cut can vary in dysplastic patients dependent upon reconstructive plans and proposed femoral component selection. The remainder of the surgery depends on the severity of the dysplasia and the deformities seen (Table 19-2).
TABLE 19-2 Summary of Surgical Options as per Crowe Classification | ||||||||||
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