Can a Subcostal Nerve Block Add Benefit to a Lateral Femoral Cutaneous Nerve Block for Open Hip Surgery

Hip replacement and hemiarthroplasty of the hip for neck of femur fracture are common orthopaedic procedures. The National Joint Registry in 2017 reported that 96.3% of hip replacements were performed using the anterolateral and posterior approach. NICE guidelines have suggested to utilise the anterolateral approach for hip fracture hemiarthroplasty due to decrease dislocation rates and thus, cost savings.

Despite these two commonly use approaches, the traditional incisions have, in the investigators experience, been modified. This is to accommodate the increasing evidence and emphasis on the acetabular components. Besides that, in hemiarthroplasty, various incisions have been described for the 'anterolateral' approach, such as direct lateral, curved posteriorly. 'Mini' and 'micro' incisions of the posterior approach has also been described all with the aim as tissue-sparing procedures, improving outcomes and length of stay.

In this study, the investigators aim to describe the 'traditionally' described posterior and anterolateral incisions to the hip by Moore and Hardinge:

1. Posterior - 5cm distally from the greater trochanter along the femoral diaphysis, curving the incision proximally 3-8cm towards the PSIS
2. Anterolateral - 3cm distally from the greater trochanter along the femoral diaphysis, continuing proximally 3-8cm along the femoral diaphysis

The cutaneous innervation for this area is largely supplied by the lateral femoral cutaneous nerve of the thigh; however some anatomical texts also describe contribution to this area from the subcostal nerve, or the lateral branches of the iliohypogastric nerve.

The lateral femoral cutaneous nerve can be readily identified using ultrasound, and has recently been categorised into 3 distinct types; the 'Sartorius', Posterior' and the 'Fan' types. The Sartorius type, accounting for roughly one-third, describes a dominant anterior branch running along the border of the Sartorius muscle, with no or few posterior branches.

The posterior type, accounting for roughly one-third, describes a strong posterior branch, equal in thickness to, or thicker than, the anterior branch running laterally and crossing the medial border of the tensor fasciae latae muscle immediately distal to the ASIS.

The fan type, accounting for roughly one-third, describes multiple nerve branches of equal thickness spreading over the anterolateral region of the proximal aspect of the thigh, crossing over the tensor fasciae latae muscle and the lateral border of the sartorius.

The lateral femoral cutaneous nerve can readily be identified using ultrasound and is readily blocked.

The subcostal nerve describes the distal continuation of the twelfth intercostal nerve.

Its lateral cutaneous branch perforates the obliquus internus and externus, descends over the iliac crest in front of the lateral cutaneous branch of the iliohypogastric, and is distributed to the skin of the front part of the gluteal region, extending as low as the greater trochanter.

The iliohypogastric nerve is usually a branch of the lumbar plexus originating from the L1 ventral ramus. Above the iliac crest, it enters the posterior part of the transversus abdominis. Between the transversus abdominis and internal oblique it divides into lateral and anterior cutaneous branches. The lateral cutaneous branch runs through the internal and external oblique above the iliac crest, a little behind the iliac branch of the T12 spinal nerve. It is distributed to the posterolateral gluteal skin. The iliohypogastric nerve usually gives communicating branches to the subcostal and ilioinguinal nerves. The iliac branch of the iliohypogastric nerve can be absent, replaced by the lateral cutaneous branch of the subcostal nerve. The iliohypogastric nerve is sometimes derived from the twelfth thoracic nerve and can also receive a root from the eleventh. Anloague and Huijbregts (2009) demonstrated the absence of the iliohypogastric nerve in 20.6% of the lumbar plexuses they investigated.

Anaesthesia for this incision can therefore only partly be achieved by a lateral femoral cutaneous nerve block; however this is not always complete for the territory of the incision, particularly if the incision is longer and extending more proximally. Due to the variation and sharing between the subcostal and iliohypogastric nerves, and their similar course, we will consider sonographically identified descending nerves to the gluteal region as a single entity, referred to as the subcostal nerve.

The Investigators have identified the subcostal nerve using ultrasound on volunteers and found it to lie above the superficial fascia directly above gluteus medius at the cranial aspect of the buttock, originating from the lateral abdominal wall musculature, where it can be tracked proximally to visualise its descent through the muscle layers of the lateral abdominal wall.

The investigators hypothesise that a lateral femoral cutaneous nerve block alone will not reliably provide cutaneous anaesthesia to the territory of our commonly observed incisions for hip arthroplasty. Our secondary hypothesis is that a blockade of the subcostal nerve will extend the cutaneous anaesthesia to reliably cover that area.

This study is to be conducted in three parts. Firstly, surgeons within the investigators department will be canvassed to mark out their likely line of incision for a routine elective primary hip arthroplasty. Pictorial evidence and variation will be gathered for overlay. Secondly, on volunteers, the lateral femoral cutaneous nerve will be identified using ultrasound in its course distal to the inguinal ligament, and the relevant type will be ascertained. The nerve will then be blocked using a short-acting local anaesthetic, and the area of numbness demarcated. Pictorial evidence will be gathered.

Thirdly, the subcostal nerve will be identified, and blocked using a short-acting local anaesthetic. The resulting area of numbness will be further demarcated, and further pictorial evidence gathered.

The relevant demarcated areas and incisions will be then be compared for analysis.