Macnab, J Bone Joint Surg Am 1971 - Negative Disc Exploration. An Analysis of the Causes of Nerve-Root Involvement in Sixty-Eight Patients

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Negative Disc Exploration. An Analysis of the Causes of Nerve-Root Involvement in Sixty-Eight Patients

Macnab·J Bone Joint Surg Am·1971·851 citations·Case series

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Macnab analyzed 68 patients from 842 lumbar spine explorations who had no disc herniation found at surgery despite classic signs of nerve root compression. The study asks: where is the compression actually coming from? All identified lesions resided in the 'hidden zone' — the nerve root segment between surgical exposure and the intervertebral foramen.

Key Findings

Of 842 lumbar explorations, 68 patients (8%) had no disc herniation despite classic radicular signs — and in 50 of those 68, a hidden-zone lesion was the true cause:
- Articular-process (facet) impingement: 19 cases (most common)
- Pedicular kinking: 12 cases
- Foraminal disc fragment migration: 9 cases
- Segmental spinal stenosis at L4–5: 8 cases
- Extraforaminal lateral disc herniation: 2 cases
A taut nerve root that cannot be displaced medially is the key intraoperative signal that compression exists distal to your exposure — stop, extend the dissection, and follow the root into the foramen.
Prior surgery dramatically worsens outcomes: for facet impingement, 12/15 first explorations yielded excellent or good results versus only 1/4 re-explorations. Each prior operation adds scarring that tethers the root independently of the original lesion.
Segmental stenosis at L4–5 required hemilaminectomy plus medial facetectomy of both adjacent articular processes — simple laminotomy is insufficient — yet with adequate decompression, 7/8 patients were completely relieved.
In 18 early cases no cause was found, but Macnab attributes this entirely to inadequate exposure rather than true absence of pathology — the hidden zone was never entered, not empty.

Board PearlWhen the disc looks normal but the nerve root is taut and immobile, follow it into Macnab's hidden zone — five treatable causes live there.

Negative Disc Exploration. An Analysis of the Causes of Nerve-Root Involvement in Sixty-Eight Patients.

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|

Negative Disc Exploration. An Analysis of the Causes of Nerve-Root Involvement in Sixty-Eight Patients

Macnab·J Bone Joint Surg Am·1971·851 citations·Case series

|

Macnab analyzed 68 patients from 842 lumbar spine explorations who had no disc herniation found at surgery despite classic signs of nerve root compression. The study asks: where is the compression actually coming from? All identified lesions resided in the 'hidden zone' — the nerve root segment between surgical exposure and the intervertebral foramen.

Key Findings

Of 842 lumbar explorations, 68 patients (8%) had no disc herniation despite classic radicular signs — and in 50 of those 68, a hidden-zone lesion was the true cause:
- Articular-process (facet) impingement: 19 cases (most common)
- Pedicular kinking: 12 cases
- Foraminal disc fragment migration: 9 cases
- Segmental spinal stenosis at L4–5: 8 cases
- Extraforaminal lateral disc herniation: 2 cases
A taut nerve root that cannot be displaced medially is the key intraoperative signal that compression exists distal to your exposure — stop, extend the dissection, and follow the root into the foramen.
Prior surgery dramatically worsens outcomes: for facet impingement, 12/15 first explorations yielded excellent or good results versus only 1/4 re-explorations. Each prior operation adds scarring that tethers the root independently of the original lesion.
Segmental stenosis at L4–5 required hemilaminectomy plus medial facetectomy of both adjacent articular processes — simple laminotomy is insufficient — yet with adequate decompression, 7/8 patients were completely relieved.
In 18 early cases no cause was found, but Macnab attributes this entirely to inadequate exposure rather than true absence of pathology — the hidden zone was never entered, not empty.

Board PearlWhen the disc looks normal but the nerve root is taut and immobile, follow it into Macnab's hidden zone — five treatable causes live there.

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