Two-Incision Minimally Invasive Approach to the Hip

What it is. The two-incision minimally invasive total hip arthroplasty performs a hip replacement through two small incisions, both guided by fluoroscopy. The acetabulum is prepared through an anterior Smith-Petersen and Hueter interval incision, and the femur is prepared through a separate posterolateral stab incision over the greater trochanter, with broaches passed to the piriformis fossa. The intended prize was a muscle-sparing, tissue-sparing replacement with faster recovery and a more stable hip than a posterior approach, because the posterior capsule and short external rotators are not divided. Primary indications. - Selected primary total hip arthroplasty in a patient with suitable anatomy and a near-virgin hip.

• Patients motivated by and suited to a rapid-recovery, tissue-sparing pathway.
• Surgeons trained specifically in the technique, with fluoroscopy and the dedicated instruments available. Contraindications. - Obesity - retractor reach and fluoroscopic imaging both fail, with a high conversion-to-open rate; a high body mass index is the commonest reason to deselect the approach (many use a threshold around 30 to 35).
• Prior hip surgery, or multiple abdominal and pelvic incisions distorting the anterior planes.
• Severe hip dysplasia, protrusio, a high-riding greater trochanter, or a stiff ankylosed hip.
• Complex acetabular reconstruction needed (cages, grafting, impaction grafting).
• Poor femoral bone stock or a very large canal that raises broaching and fracture risk.
• Surgeon inexperience with the technique and its fluoroscopy dependency. Relative cautions. A very muscular or athletic build crowds the anterior interval; a flexion contracture greater than 20 degrees makes supine femoral preparation harder; and a significant leg-length inequality to correct is difficult to judge on fluoroscopy alone. Alternative approaches.

Why the two-incision technique has fallen out of favour. The procedure is technically demanding: early in a surgeon's experience there is a well-documented rise in intra-operative femoral fracture, nerve injury, wound problems and operative time, and a meaningful rate of conversion to a standard incision. Every step is fluoroscopy-guided, which adds operative time, requires a radiolucent table and a skilled radiographer, exposes patient and staff to radiation, and is unforgiving if the pelvis is not flat and neutral - a tilted pelvis makes the apparent cup inclination and anteversion wrong. Comparative studies and randomised trials showed that, while early postoperative function can be modestly faster, the advantage narrows and largely disappears by one to two years against standard approaches. Finally, the single-incision direct anterior approach on a specialised orthopaedic table delivers the same muscle-sparing anterior interval through one incision, with simpler femoral preparation and without a second wound - it absorbed the two-incision technique's rationale and most of its adopters.

The exposure sets up on a radiolucent table, exploits the anterior internervous plane to reach the capsule and acetabulum, then turns to a separate posterolateral portal for the femur - every step checked on fluoroscopy.

Position and fluoroscopy setup. - Supine on a fully radiolucent table - no metal side-rails through the imaging field.

• Both hips laid flat so the pelvis is neutral, not tilted or rotated.
• Operative leg free to be moved into extension, adduction and external rotation for femoral preparation.
• C-arm brought in from the contralateral side, with true AP and cross-table lateral fluoroscopy verified before draping.
• Arms secured across the chest or out on armboards away from the imaging arc.

Surface landmarks and incision planning. - Anterior superior iliac spine (ASIS) - the reference for the anterior incision.

• Greater trochanter - the landmark for the posterolateral femoral incision.
• Anterior incision - placed 2 cm lateral and distal to the ASIS, angled toward the fibular head, typically 4 to 5 cm; deliberately offset from the ASIS to avoid the lateral femoral cutaneous nerve, which passes under the inguinal ligament roughly 1 cm medial to the ASIS and branches across the interval.
• Posterolateral incision - a 2 to 3 cm stab over the posterior aspect of the greater trochanter, localised intra-operatively with a fluoroscopy-guided guide pin placed into the piriformis fossa. Muscular layers of the anterior interval. | Layer | Muscle | Nerve supply | Role in the approach | |-------|--------|--------------|----------------------| | Superficial medial | Sartorius | Femoral nerve | Medial boundary, retracted medially | | Superficial lateral | Tensor fasciae latae | Superior gluteal nerve | Lateral boundary, retracted laterally | | Deep medial | Rectus femoris | Femoral nerve | Swept medially off the capsule | | Deep lateral | Gluteus medius and minimus | Superior gluteal nerve | Retracted laterally, protected | Neurovascular anatomy in play. | Structure | Location | Clinical significance | |-----------|----------|----------------------| | Lateral femoral cutaneous nerve | Under inguinal ligament near ASIS, crosses the interval | Commonest nerve injury - anterolateral thigh numbness | | Ascending branch of lateral circumflex femoral artery | Deep in the sartorius-TFL interval | Must be coagulated or it bleeds briskly | | Femoral nerve and vessels | Anteromedial, lateral to the femoral sheath, over the capsule | Anterior retractor pressure causes quadriceps weakness | | Sciatic nerve | Posterior to the hip, deep to piriformis | Stretched by external rotation and adduction of the femur | | Superior gluteal nerve | Exits greater sciatic notch, above piriformis | At risk with deep posterior or trochanteric dissection | The internervous plane. - Anterior (true internervous): between sartorius (femoral nerve) medially and tensor fasciae latae (superior gluteal nerve) laterally, deepened between rectus femoris (femoral nerve) medially and gluteus medius and minimus (superior gluteal nerve) laterally to expose the anterior capsule. This plane allows access to the anterior hip without denervating either muscle.
• Posterolateral femoral portal (muscle split, not internervous): there is no classical internervous plane here. The portal is developed by bluntly splitting the gluteus maximus fibres and passing between or just posterior to gluteus medius and minimus to reach the piriformis fossa. The abductors are retracted and protected rather than divided.

Structures at risk, by layer.

Nerve injury management. - LFCN numbness - usually transient; observe and reassure; rare need for intervention.

• Femoral nerve palsy - remove compressive dressings, exclude a hematoma; most recover; physiotherapy for quadriceps.
• Sciatic palsy - urgent review to exclude a compressive hematoma or dislocation; foot-drop splint; EMG at 3 weeks; consider exploration if complete with no recovery. Extensile options. - Proximal extension of the anterior incision along the iliac crest converts toward a full Smith-Petersen approach for acetabular column or complex revision work; the LFCN becomes more at risk as the incision extends medially.
• Distal extension of the posterolateral portal into a standard lateral or posterior approach is the fallback when exposure, fracture, or instability demand it. Conversion to a standard approach is the correct response to an intra-operative complication, not a failure. When to convert. Inadequate exposure or visualisation despite all measures; an intra-operative femoral fracture requiring open reduction and cabling or plating; or an inability to achieve stable, well-positioned components. Closure and post-operative care. Anterior capsulorrhaphy using the tag sutures improves stability; close the tensor fascia lata fascia, subcutaneous layer and skin of the anterior incision and the posterolateral incision in layers; confirm haemostasis - the ascending branch LFCA and the femoral and sciatic regions should be dry; obtain a post-operative AP pelvis and lateral hip before discharge. On an accelerated pathway patients weight-bear as tolerated on the day of surgery, sometimes with same-day discharge in selected patients, supported by multimodal analgesia and local infiltration. Posterior precautions are generally not required because the short external rotators are not divided, but extremes of rotation and adduction are avoided early given the posterolateral portal. Heterotopic ossification prophylaxis (indometacin or single-fraction radiotherapy per institutional protocol) is considered in higher-risk patients given abductor handling at the greater trochanter. Common complications and their management.

• Primary total hip arthroplasty - the principal and essentially only operation designed for this exposure, in carefully selected patients with a near-virgin hip.
• The technique was conceived specifically as a muscle-sparing, fluoroscopy-guided method of performing a primary THA through internervous and intermuscular planes; it is not used for revision, dysplasia, or complex reconstruction, which are contraindications.

Guidelines, registries and global practice. The two-incision minimally invasive total hip arthroplasty is not a guideline-driven standard of care but a surgical technique of historical importance, so registry and society guidance frames it indirectly through the broader evidence on minimally invasive and direct anterior hip replacement. AAOS supports patient-centred approach selection and informed consent for surgical approach, component positioning, and the recognised risks of dislocation, nerve injury, infection and thromboembolism; NICE and the BOA-BOAST guidance emphasise evidence-based approach choice, venous thromboembolism prophylaxis, enhanced recovery, and infection prevention rather than any single minimally invasive technique; EFORT and European consensus hold that approach selection should follow surgeon competence and patient factors, and that minimally invasive techniques demand training and carry a learning curve. Major joint registries (NJR, AOANJRR, AJRR, SHAR, Norwegian, NZJR) report arthroplasty outcomes by bearing and fixation rather than by surgical approach alone, so they do not single out the two-incision technique; their broader message is that implant survivorship in hip arthroplasty is driven by component design, fixation, bearing surface and patient factors rather than by the incision strategy. In high-resource settings the single-incision direct anterior approach on an orthopaedic table is now the dominant muscle-sparing option, while the two-incision technique is rarely practised outside the centres that originated it; in resource-limited settings the choice is driven by instrument and table availability, and a standard posterior or anterolateral approach remains the pragmatic default. Consent (globally applicable) should cover the lateral femoral cutaneous nerve and anterolateral thigh numbness, femoral and sciatic nerve injury, intra-operative periprosthetic fracture, dislocation, infection, leg-length inequality, heterotopic ossification and thromboembolism, as well as the technique's learning curve and the small chance of conversion to a standard incision.