Landmarks
• Central landmark – the greater trochanter
• The anterior superior iliac spine and the femoral shaft are also palpable and act as useful reference points.
Incision
A straight 15 cm incision is created, parallel to the femoral shaft and centred on the anterior half of the greater trochanter (Fig. 10.6).
Superficial dissection
The incision is continued through subcutaneous fat and down to fascia lata. The fascia lata is incised in line with the skin incision overlying the lateral femur (Fig. 10.7). At this point a self- retaining retractor is inserted.
Deep dissection
The incision continues in line with the skin incision. This begins proximally within the fibres of the gluteus medius and must be limited to a point 3 cm above the tip of the greater trochanter to avoid damage to the superior gluteal nerve. The
Structures at risk
Superior gluteal nerve – between the gluteus medius and minimus; this may be as close as 3 cm above the tip of the greater trochanter.
Gluteus medius Greater tronchanter Quandratus femoris Sciatic nerve Ischial tuberosity Inferior gemellus Superior gemellus Obturator internus Piriformis
Figure 10.5 The path of the sciatic nerve over the external rotators of the hip
Greater trochanter
Figure 10.6The skin incision for the lateral approach to the hip
incision continues distally, in the line of the fibres of the gluteus medius and across the greater trochanter, entering the vastus lateralis. The fibres of the vastus lateralis overlying the greater trochanter are split.
The incision develops an anterior flap, consisting of the anterior fibres of the gluteus medius and gluteus minimus above the greater trochanter and the anterior fibres of the vastus lateralis lying over and below the greater trochanter. This is elevated off the greater trochanter subperiosteally, with either a scalpel or cutting diathermy. A cuff of gluteus medius is left posteriorly on the greater trochanter, allowing reattachment at the time of closure.
The incision progresses anteriorly, detaching the insertion of the gluteus medius and minimus onto the greater trochanter, to reveal the capsule of the hip. The anterior flap is retracted by placing a Hohmann retractor. The capsule is incised in a T shape, with the downstroke of the T lying in line with the femoral neck and the bar of the T running under the femoral head (Fig. 10.8).
• Dislocation and retractor positioning – This must be done gently as excess force can fracture the femur (typically a spiral fracture running from the subtrochanteric region down the shaft). In younger patients, the ligamentum teres can remain intact, preventing full dislocation; if this occurs it can be easily divided with a scalpel. If the dislocation is difficult, further capsule can be excised; remove any more visible labrum and remove any acetabular osteophytes with nibblers or an osteotome. If
the hip can still not be removed with minimal force, division of the femoral neck in situ and removal the head with a corkscrew is recommended.
• Posterior approach dislocation and retraction– The hip joint can now be dislocated. This is performed by placing the hip in adduction and flexion then internally rotating it, bringing the calf to lie vertically and the foot pointing towards the ceiling. A bone hook can be carefully passed around the femur, at the level of the lesser trochanter, and used to ease the femoral head away from the acetabulum.
• Lateral approach dislocation and retraction – The hip can be dislocated with adduction, flexion and external rotation, again with a blunt bone hook around the femoral neck. The leg is then placed in the leg bag, i.e. the foot pointing to the floor, on the opposite side of the operating table.
Procedure
Structures at risk
• Femoral nerve – injudicious placement of anterior retractors may, rarely, damage the femoral nerve
• Sciatic nerve – vulnerable posteriorly
• Obturator arterial branches – large branches are present below the transverse acetabular ligament; cutting them should be avoided
Primary total hip arthroplasty 149
Tendon of gluteus medius
Fascia lata
Figure 10.7 Dissection of the lateral approach to the hip
Joint capsule Greater trochanter
Vastus lateralis Fascia lata
Gluteus medius
Hohmann retractors are inserted around the superior and inferior aspects of the femoral neck, supporting and stabilizing the proximal femur and exposing the whole of the intertrochanteric line. Any soft tissues along this line are removed until the superior portion of the lesser trochanter is seen.
The planned femoral osteotomy site is marked with an osteotome. A number of hip replacement sets have a specific instrument to aid identification of the right site for this osteotomy; use of a trial prosthesis or a rasp as a guide is recommended in those sets without a neck cutting guide. This is particularly important with collared stems. Templating will have provided a guide to the height above the lesser trochanter that the osteotomy should pass through the calcar (typically, this is around 15 mm above the lesser trochanter). An oscillating saw is used to perform the osteotomy, with the Hohmann retractors protecting the surrounding soft tissues. The cut is made with the saw blade 45° to the femoral shaft and in the plane of the tibia. If the line of the osteotomy passes into the greater trochanter, the osteotomy is stopped before entering the trochanter and a second osteotomy carried vertically down from the piriformis fossa to meet the lateral extent of the first osteotomy (Fig. 10.9). The femoral head is removed and kept in case of its later requirement as graft.