Posterior Approach to the Sacrum (Sacrectomy)

What it exposes. The posterior sacral approach gives direct dorsal access to the sacrum, the posterior sacral foramina and sacral nerve roots, the sacrotuberous and sacrospinous ligaments, and the posterior sacroiliac complex. It is the workhorse exposure for en-bloc resection of primary sacral tumours - above all sacral chordoma, the single most common primary malignant sacral tumour and the prototype for sacrectomy. Primary indications. - Primary sacral tumours requiring en-bloc resection - chordoma (the classic indication), chondrosarcoma, osteosarcoma.

• Giant cell tumour of bone of the sacrum where en-bloc or extended intralesional curettage is warranted.
• Locally advanced rectal and other pelvic malignancies involving the sacrum (multidisciplinary, often abdominosacral resection).
• Metastatic disease of the sacrum with intractable pain, impending sacral plexus compromise, or spinopelvic instability (more often palliative stabilisation). Why posterior. The dorsal sacrum, the sacral roots posterior to the foramina, the sacroiliac ligamentous attachments, and the posterior sacroiliac complex are all best exposed from behind. A posterior midline incision gives direct access to the dorsal sacrum, the posterior sacral foramina, the piriformis and gluteal origins, and the sacrotuberous and sacrospinous ligaments. For tumours whose anterior margin cannot be safely developed from the back - large high tumours adherent to rectum, presacral vessels, or visceral structures - a combined anterior and posterior approach is used. The central decision is the resection level. The level of sacral resection, defined by the most proximal sacral level transected, is the single most important determinant of both function and the need for reconstruction.

• Mid resections require careful individual root management to preserve any continence.
• High resections sacrifice the lumbosacral junction, dissociating the spine from the pelvis, and demand spinopelvic reconstruction plus colostomy and urostomy. Pre-operative assessment. Document a careful neurological and sphincter baseline: per-rectal examination of tone and sensation (S2-S4 function), lower-limb motor (hip abductors L5-S1, ankle plantarflexion S1-S2), perineal and saddle sensation (S2-S4), and the anal wink and bulbocavernosus reflexes (the sacral reflex arc). Palpate for a presacral mass (often felt on rectal exam), assess the biopsy site (it must be excised en bloc), and assess fitness for prolonged prone surgery and major blood loss. Imaging drives the plan. MRI (sagittal and axial T1 and T2) is essential - it defines the cephalad extent, nerve root involvement, presacral spread, and the relationship to the rectum and iliac vessels, and determines whether an anterior stage is required. CT complements MRI for bony detail and osteotomy planning. CT chest/abdomen/pelvis or PET-CT excludes metastatic disease. CT angiography of the internal iliac system is used when anterior vascular control is planned; some centres embolise the internal iliac arteries pre-operatively to reduce blood loss.

Treatment philosophy. Primary malignant sacral tumours are treated with wide en-bloc resection when feasible - a wide margin is the dominant predictor of local control and survival, with adjuvant radiotherapy considered for close or marginal margins (and for chordoma). Metastatic disease with intractable pain, impending plexus compromise, or instability may instead be managed by palliative stabilisation, decompression, or cement augmentation. The biopsy tract must be excised en bloc with the specimen, taken posteriorly/trans-gluteally along the planned incision. Contraindications. Medical unfitness for prolonged prone surgery and major blood loss (among the most physiologically demanding operations in orthopaedic oncology); unresectable distant metastatic disease where the goal is purely palliative; tumour encasing the rectum or major vessels without a safe plane and without general-surgical or vascular support for a combined case; and active local infection over the operative field. Alternative and complementary approaches. - Anterior (transabdominal) approach - for proximal vascular control, ligation of internal iliac vessels, presacral dissection, rectum mobilisation, and anterior osteotomy cuts.

• Combined anterior-posterior (staged or same anaesthetic) - standard for mid and high sacrectomy.
• Lateral approach - rarely used, for selected lateral sacral mass lesions.
• Percutaneous sacroplasty or cement augmentation - for palliative metastatic disease not requiring resection.

Work prone through a midline incision over the sacrum, raising gluteal myocutaneous flaps, reflecting gluteus maximus laterally to reach the posterior sacrum and the sacrotuberous and sacrospinous ligaments, then developing the lateral and anterior planes to deliver the specimen en bloc. There is no true internervous plane - this is an oncological en-bloc resection dictated by tumour margins, not a compartmental exposure; the useful cleavage is the midline raphe between the two gluteus maximus origins, an avascular plane down to the dorsal sacrum. Position and landmarks. Prone on a radiolucent table (Jackson frame or parallel rolls), freeing the abdomen to reduce epidural and presacral venous engorgement, with the hips extended slightly to preserve lumbar lordosis and aid imaging. Wide preparation runs from the mid-lumbar spine to the perineum and across both iliac crests (potential graft and flap harvest sites), with image-intensifier access confirmed. Key landmarks: the posterior superior iliac spines (the palpable dimples defining the upper sacrum and sacroiliac joints), the median sacral crest (the midline rail), the sacral hiatus and coccyx (palpable in the natal cleft), the iliac crests (the lumbopelvic junction), and the sciatic notch (the lateral exit of the sacral roots). The gluteal cleft is centred over the midline sacrum and coccyx.

Key ligamentous anatomy encountered. Dividing the pelvic ligaments is what mobilises the sacrum, so the surgeon must know each one.

Structures at risk, by layer.

Nerve injury and functional consequences. - Bilateral loss of S2 and below: loss of voluntary bladder and bowel control, and sexual dysfunction.

• Unilateral S2-S3 sacrifice: many patients retain some continence.
• S1 sacrifice: weak ankle plantarflexion and an altered gait.
• All roots sacrificed (high or total sacrectomy): complete loss of sacral autonomic and somatic function, requiring stomas. Extensile options. - Combined anterior stage - for mid and high sacrectomy: anterior laparotomy for internal iliac control, rectal mobilisation, ureteric protection, and anterior osteotomy cuts; it reduces posterior bleeding, protects viscera, and enables en-bloc margins for proximal tumours.
• Triradiate or inverted-Y incision - extends the midline incision laterally over the iliac crests for wide exposure of the sacroiliac complex and raising of large gluteal flaps; useful for total sacrectomy.
• Proximal extension along the lumbar spine - access for lumbopelvic reconstruction (lumbar pedicle screws and iliac bolts in a Galveston-type construct).
• Lateral extension along the ilium - develops the plane along the sacroiliac joint for high resections and structural bone-graft harvest. Reconstruction. Resection above S1 dissociates the spine from the pelvis and mandates lumbopelvic reconstruction to restore spinopelvic continuity and allow sitting and walking - typically a Galveston-type construct of bilateral iliac screws, lumbar pedicle screws (L4, L5), rods (with or without a cross-link), and a structural graft or cage between L5/S1 and the pelvis. The biomechanical goal is to transmit axial load from the lumbar spine to the ilia across the defect. Low and most mid resections leave spinopelvic continuity intact and need no bony reconstruction. Closure. Reconstruct first (if required), then close the large posterior dead space with mobilised gluteal advancement flaps, using a VRAM (vertical rectus abdominis myocutaneous) flap or other tissue transfer for large defects or irradiated fields. Obliterate dead space, place deep drains, and close the fascia, subcutaneous tissue, and skin meticulously; apply a pressure-relieving post-operative surface to protect the incision. Complications.

• En-bloc sacrectomy for primary sacral tumours - the principal operation: wide resection for chordoma, chondrosarcoma, and osteosarcoma.
• Extended intralesional curettage or resection for sacral giant cell tumour, where en-bloc resection is not feasible.
• Abdominosacral resection for locally advanced rectal or pelvic malignancy involving the sacrum, with general surgical and vascular support.
• Palliative stabilisation, decompression, or cement augmentation for metastatic sacral disease with pain, plexus compromise, or instability.
• Lumbopelvic reconstruction and soft-tissue flap coverage are performed through the same exposure when resection is above S1.

The posterior approach to the sacrum for sacrectomy is performed prone through a midline incision over the sacrum and natal cleft, designed to excise the biopsy tract en bloc. The gluteus maximus origins are reflected laterally to expose the posterior sacrum and the sacrotuberous and sacrospinous ligaments, which are divided to mobilise the sacrum. There is no true internervous plane - this is an oncological en-bloc resection. The critical structures are the sacral nerve roots (continence trade-off by level; preserve at least one S2 and S3 root where the margin allows), the presacral venous plexus and internal iliac vessels (the dominant bleeding risk, often controlled via an anterior stage), and the rectum anteriorly. Mid and high resections usually require a combined anterior and posterior approach, and resection above S1 dissociates the spine from the pelvis, mandating lumbopelvic reconstruction.

High-yield viva questions.

Outcomes and recovery. Good prognostic factors are a low resection with S2 roots preserved (near-normal continence and gait), a wide surgical margin, no visceral or major vascular involvement, and a primary rather than recurrent tumour. Poor prognostic factors are a high or total sacrectomy with loss of all sacral roots, a marginal or intralesional margin, rectal involvement requiring abdominosacral resection, and recurrent disease or prior radiotherapy.

Guidelines, Registries & Global Practice Sacrectomy is performed at specialist orthopaedic oncology and spinal centres worldwide, and the principles converge across examination systems. En-bloc wide resection for primary sacral malignancy, the resection-level approach to nerve root management, and combined anterior-posterior surgery for high lesions are near-universal tenets. Side-by-side principles (where guidance converges): | Body | Position on sacral tumours and sacrectomy |

|------|-------------------------------------------| | NCCN (US) | En-bloc wide resection with a healthy margin is the mainstay for chordoma and chondrosarcoma; adjuvant radiotherapy is considered for close or marginal margins and for unresectable disease | | AO Foundation / Spine Oncology | Enneking-appropriate margins; the WBB system guides en-bloc excision planning; anterior-posterior combined approaches for high lesions; lumbopelvic reconstruction restores spinopelvic continuity | | European consensus (EFORT / spine oncology groups) | Multidisciplinary management, careful nerve root preservation where oncologically safe, flap closure of the large dead space to prevent wound breakdown | Global practice variation. In high-resource centres, pre-operative internal iliac embolisation, neuronavigated osteotomy, neuromonitoring of sacral roots, and dedicated lumbopelvic implants are routine. In resource-limited settings, the same oncological principles are applied with more limited instrumentation, greater reliance on packing for venous bleeding, and selective use of adjuvant radiotherapy where reconstruction hardware is scarce. Consent (globally applicable). Discuss the magnitude of blood loss and transfusion, loss of bowel and bladder continence requiring stomas (for high resections), sexual dysfunction, wound breakdown and infection, the need for spinopelvic reconstruction, and the risk of local recurrence mandating long-term surveillance.