AN45.1-3 | Posterior abdominal wall — Gate Quiz

Correct! Middle layer of TLF → transverse processes + intertransverse ligaments (forms the intermuscular septum between erector spinae posteriorly and quadratus lumborum anteriorly). Posterior layer → spinous processes. Anterior layer → anterior transverse processes.

TLF middle layer = transverse processes. This creates a compartment for erector spinae (between posterior and middle layers) and one for quadratus lumborum (between middle and anterior layers).

Incorrect. TLF layers: posterior → spinous processes; middle → transverse processes + intertransverse ligaments; anterior → anterior surfaces of transverse processes.

Correct! Femoral nerve (L2,3,4) supplies quadriceps femoris (knee extension), sartorius, and sensation over anterior + medial thigh (via saphenous nerve). The knee jerk (L3,4) is mediated via the femoral nerve → absent. The femoral nerve runs lateral to the psoas within the iliacus compartment — retroperitoneal haematoma compresses it here.

Femoral nerve palsy: unable to extend knee (quadriceps paralysis), absent knee jerk, numb anterior and medial thigh. Key cause: retroperitoneal haematoma or psoas abscess compressing the nerve within the iliacus fossa.

Incorrect. Knee extension weakness + anterior/medial thigh numbness + absent knee jerk = femoral nerve (L2,3,4). The sciatic nerve supplies posterior thigh + entire leg. The obturator nerve supplies medial thigh and adductors. LFCN is purely sensory to lateral thigh.

Correct! Obturator nerve = L2, L3, L4 (anterior divisions). It emerges from the medial border of psoas, crosses the pelvic brim, and exits through the obturator foramen to supply the medial compartment of the thigh (adductors longus, brevis, magnus, gracilis, obturator externus).

Femoral nerve = L2,3,4 (posterior divisions). Obturator nerve = L2,3,4 (anterior divisions). Same roots, different fibre divisions. Obturator exits via obturator foramen; femoral exits under inguinal ligament in muscular lacuna.

Incorrect. Obturator nerve = L2, L3, L4 (anterior divisions of lumbar plexus). Femoral nerve also L2,3,4 but posterior divisions. The identical root value (L2,3,4) for both femoral and obturator is because they share roots — divided into anterior (obturator) and posterior (femoral) divisions.

Correct! All intrinsic (deep) back muscles — including erector spinae and the transversospinalis group — are supplied by the dorsal primary rami (posterior rami) of the spinal nerves at each segmental level. The anterior primary rami supply the limbs and anterolateral trunk.

Rule: posterior/deep back muscles (erector spinae, transversospinalis) → dorsal primary rami. Anterior abdominal wall muscles → anterior primary rami. The genitofemoral nerve is a lumbar plexus branch; the long thoracic nerve supplies serratus anterior.

Incorrect. Intrinsic back muscles = dorsal primary rami (posterior rami). This is a general rule: muscles of the back (posterior compartment) are supplied by posterior rami; muscles of the limbs and trunk are supplied by anterior rami.

Correct! The MOST important distinguishing feature is the ABSENCE of motor deficit. The LFCN (L2,3) is a purely sensory nerve — no motor supply. Meralgia paraesthetica causes sensory symptoms (burning, numbness, tingling) in the lateral thigh with completely preserved motor function. L3 root compression would cause quadriceps weakness and a diminished knee jerk.

LFCN = purely sensory nerve (L2,3). Meralgia paraesthetica: lateral thigh sensory symptoms, NO motor deficit. L3 root: anterior/lateral thigh pain + quadriceps weakness (unable to extend knee against gravity) + diminished knee jerk.

Incorrect. The critical differentiator is absent motor deficit in meralgia paraesthetica (LFCN is purely sensory). L3 root compression → quadriceps weakness + reduced knee jerk + dermatomal sensory loss. LFCN entrapment → sensory only, no motor change.

Correct! A psoas abscess from Pott's disease tracks within the fascial sheath of the psoas major (part of the anterior layer of the TLF/iliacus fascia) from the lumbar vertebrae, under the inguinal ligament, to the femoral triangle. Gravity and the closed fascial compartment direct the pus inferiorly.

Psoas abscess: pus from lumbar TB → psoas fascia sheath → under inguinal ligament → femoral triangle. Presents as fluctuant groin swelling with hip held in flexion (iliopsoas spasm). Classical features: non-tender, non-erythematous (cold), fluctuant — differentiates from pyogenic abscess.

Incorrect. A cold (psoas) abscess from spinal TB tracks within the psoas major fascial sheath — which is an extension of the anterior thoracolumbar fascia. It passes under the inguinal ligament medially to present in the femoral triangle as a fluctuant, non-tender, non-erythematous swelling.

Correct! The cremasteric reflex arc: Afferent = ilioinguinal nerve (L1) or femoral branch of genitofemoral nerve (sensory, medial thigh skin). Efferent = genital branch of genitofemoral nerve (motor to cremaster muscle). The reflex is absent in testicular torsion and upper motor neuron lesions.

Cremasteric reflex: afferent (sensory) via ilioinguinal/femoral branch of GFN; efferent (motor) via genital branch of GFN → cremaster. Absent reflex on side of testicular torsion — important emergency sign.

Incorrect. Cremasteric reflex efferent = genital branch of genitofemoral nerve (L1,2) → motor to cremaster. Afferent = ilioinguinal or femoral branch of genitofemoral (sensory, medial thigh). Reflex absent in testicular torsion (emergency) and UMN lesions.

Correct! Multifidus provides approximately 2/3 of the segmental stiffness of the lumbar facet joints — it is the primary stabiliser of individual lumbar motion segments. Its atrophy after disc injury dramatically reduces lumbar stability, predisposing to recurrent episodes. Rehabilitation specifically targets multifidus reactivation (deep abdominal bracing exercises).

Multifidus = primary lumbar joint stabiliser. Spans 2–4 segments (short lever, maximum stiffness per segment). Atrophies ipsilateral to disc lesion → loss of stability → recurrence. Core stability exercises (drawing-in manoeuvre, four-point kneeling) specifically target multifidus.

Incorrect. Multifidus provides the greatest contribution to lumbar intervertebral joint stiffness among all deep back muscles — hence it is the primary rehabilitation target. It spans only 2–4 segments (not the greatest) and is not the largest back muscle.

Correct! Obturator hernia passes through the obturator canal and can compress the obturator nerve (L2,3,4). Howship-Romberg sign: pain referred along the medial thigh (obturator distribution), aggravated by hip extension, abduction, or medial rotation. More common in elderly thin women (reduced obturator canal fat).

Obturator hernia: elderly thin women, intestinal obstruction + medial thigh pain (Howship-Romberg sign from obturator nerve compression). Often missed clinically; diagnosed on CT. The obturator canal is bounded by the obturator membrane and groove of the superior pubic ramus.

Incorrect. An obturator hernia passes through the obturator canal and compresses the obturator nerve → Howship-Romberg sign (medial thigh pain on hip extension/rotation). This is an obturator nerve sign.

Correct! Rectus abdominis originates from the pubic symphysis and pubic crest — it does not originate from the thoracolumbar fascia. Transversus abdominis, internal oblique, and latissimus dorsi all have significant attachments to the TLF.

TLF origins: TA, IO, latissimus dorsi, and also serratus posterior inferior. Rectus abdominis is a vertical muscle with pubic origin — it does not have a TLF attachment.

Incorrect. TLF provides origin for: transversus abdominis, internal oblique, and latissimus dorsi. Rectus abdominis is NOT TLF-attached — it originates from the pubic crest and pubic symphysis and inserts into xiphisternum/costal cartilages.