Hip Anterior Approach (Smith-Petersen)

What it exposes. The Smith-Petersen anterior approach gives direct access to the anterior hip capsule, femoral neck and acetabular rim, and — with the iliofemoral extension — to the entire acetabulum (anterior column, anterior wall, quadrilateral plate and superior dome). It is the workhorse exposure for anterior and both-column acetabular fractures, periacetabular osteotomy (PAO) and paediatric hip reconstruction, and underpins the direct anterior approach (DAA) for total hip arthroplasty. Why anterior. It is the only approach to the hip that uses a true internervous plane, so it tolerates extensive dissection without denervating muscle. Supine positioning is a major practical advantage: better respiratory mechanics for anaesthesia, the option of simultaneous bilateral procedures, easy C-arm access without repositioning, and — after DAA THA — no hip precautions. Historical context. Marius Nygaard Smith-Petersen described the approach in 1917 for hip arthrodesis. It was used through the mid-20th century for acetabular fractures and complex reconstruction, and was revived from the 2000s as the DAA for minimally invasive THA (the same interval, historically also termed the Hueter approach). Position & landmarks. The patient is supine on a radiolucent table (a specialised DAA traction table is optional for THA; a standard table suffices for acetabular work). Palpate and mark the anterior superior iliac spine (ASIS) — the primary landmark — the iliac crest, the greater trochanter laterally, and the femoral pulse medially. The incision is planned lateral to the femoral pulse; mark the pulse before draping and never deviate medially, where the femoral neurovascular bundle lies. The C-arm comes from the contralateral side for AP, and inlet/obturator-oblique views when needed.

The exposure is built on a true internervous plane and developed layer by layer, protecting the lateral femoral cutaneous nerve superficially and the femoral nerve medially, then ligating the ascending branch of the lateral circumflex femoral artery before opening the capsule.

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The internervous plane — the anatomical basis. The approach exploits the interval between the tensor fasciae latae (superior gluteal nerve) and sartorius (femoral nerve). A second, deeper internervous plane lies between rectus femoris (femoral nerve) medially and gluteus medius/minimus (superior gluteal nerve) laterally. Both are true internervous planes, which is what makes the approach safe for extensile dissection.

Structures at risk, by layer

Lateral femoral cutaneous nerve variability (cadaveric). The LFCN is highly variable and cannot always be preserved. Across cadaveric series it crosses the DAA skin incision in roughly 42–65% of specimens (Sugano 42%; Ukai 64.9%; Giang 50%); shortening the proximal extent of the incision lowers the crossing rate.

Complications

LFCN injury management. Most injuries are neuropraxic and recover over 6–12 months; permanent numbness occurs in only 5–10% and is usually well tolerated. Neuropathic pain may need gabapentin or pregabalin; surgical exploration is rarely indicated. Always distinguish LFCN injury (sensory only) from a femoral nerve injury (quadriceps weakness). Extensile option — the iliofemoral extension. For full acetabular access, extend the incision proximally along the iliac crest, detach the abdominal wall muscles (external oblique, internal oblique, transversus) from the crest, and reflect the iliacus subperiosteally from the inner table working lateral to medial. This exposes the pelvic brim, quadrilateral plate and anterior column and gives 360-degree acetabular visualisation. Both-column fractures can often be fixed through this single approach, because stabilising both columns to the intact ilium secures the fracture without a posterior approach. Closure. Repair the capsule (always, for fracture and paediatric cases; surgeon preference for THA), close the TFL–sartorius fascial interval if opened widely (absorbable suture), close dead space with attention to haemostasis (a drain is favoured for acetabular trauma), and close skin with a subcuticular suture or staples.

• Total hip arthroplasty via the direct anterior approach (DAA) — the principal elective operation; muscle-sparing, supine, and no hip precautions postoperatively. Femoral exposure is the limiting factor (hardest in muscular or obese patients, BMI over 35).
• Acetabular fracture ORIF — anterior column, anterior wall, both-column and anterior column/posterior hemitransverse patterns (Judet-Letournel). Elementary types: anterior wall, anterior column, posterior wall, posterior column, transverse. Associated types: both-column (the commonest associated pattern, ~25%), T-shaped, transverse + posterior wall, anterior column/posterior hemitransverse, anterior wall/posterior hemitransverse. Postoperatively: touch weight-bearing for 6 weeks and heterotopic ossification prophylaxis (indomethacin 75 mg daily for 3 weeks, or a single 700 cGy radiation dose).
• Periacetabular osteotomy (PAO), Pemberton osteotomy and DDH open reduction — standard exposure for acetabular reorientation and paediatric hip reconstruction.
• Hip arthrodesis — Smith-Petersen's original 1917 indication; rarely performed today.
• Iliopsoas tenotomy — for symptomatic iliopsoas impingement after THA, via lesser trochanter access.
• Anterior hip arthroscopy portal placement — uses the same landmarks and internervous plane.

Approach data across major joint registries (side by side)

Named-society guidance and global practice. AAOS (US) and NICE / BOA (UK) do not mandate a single surgical approach for primary THA — approach choice rests on surgeon expertise and patient factors, with equivalent long-term outcomes emphasised. AO Foundation / Letournel-Judet principles underpin the Smith-Petersen, iliofemoral and anterior intrapelvic approaches for anterior column and both-column acetabular fractures. Informed consent should specifically cover LFCN injury and meralgia paraesthetica, the learning-curve risk (intraoperative femoral fracture within the first roughly 30–50 cases), and the possibility of wound extension or approach conversion for difficult femoral exposure. Specialised DAA traction tables and femoral elevators are used in some centres; a standard radiolucent table is adequate for the classic Smith-Petersen and for acetabular work, and the underlying internervous anatomy is identical worldwide.