Chapter 016. Back and Neck Pain (Part 4) The neurologic examination includes a search for focal weakness or muscle atrophy, focal reflex changes, diminished sensation in the legs, and signs of spinal cord injury. The examiner should be alert to the possibility of breakaway weakness, defined as fluctuating strength during muscle testing. Breakaway weakness may be due to pain or a combination of pain and underlying true weakness. Breakaway weakness without pain is due to lack of effort. In uncertain cases, electromyography (EMG) can determine whether or not true weakness is present. Findings with specific nerve root lesions are shown in Table 16-2 and are discussed below. Table 16-2 Lumbosacral Radiculopathy—Neurologic Features Examination Findings Lumbo sacral Nerve Roots Reflex Sen sory Motor Pain Distribution L2 a — Up per anterior thigh Psoas (hip flexion) Anteri or thigh L3 a — Lo wer anterior thigh Ant erior knee Psoas (hip flexion) Quadriceps (knee extension) Thigh Anteri or thigh, knee adduction L4 a Quadriceps (knee) Me dial calf Quadriceps (knee extension) b Thigh adduction Tibialis anterior (foot dorsiflexion) Knee, medial calf Antero lateral thigh L5 c — Dor sal surface— foot Lat eral calf Peroneii (foot eversion) b Tibialis anterior (foot dorsiflexion) Gluteus Lateral calf, dorsal foot, posterolateral thigh, buttocks medius (hip abduction) Toe dorsiflexors S1 c Gastrocnemi us/soleus (ankle) Pla ntar surface— foot Lat eral aspect— foot Gastrocnemi us/soleus (foot plantar flexion) b Abductor hallucis (toe flexors) b Gluteus maximus (hip extension) Botto m foot, posterior calf, posterior thigh, buttocks a Reverse straight leg–raising sign present—see "Examination of the Back." b These muscles receive the majority of innervation from this root. c Straight leg–raising sign present—see "Examination of the Back." . Chapter 016. Back and Neck Pain (Part 4) The neurologic examination includes a search for focal weakness or muscle atrophy, focal reflex changes, diminished sensation in the legs, and. during muscle testing. Breakaway weakness may be due to pain or a combination of pain and underlying true weakness. Breakaway weakness without pain is due to lack of effort. In uncertain cases,. in Table 16-2 and are discussed below. Table 16-2 Lumbosacral Radiculopathy—Neurologic Features Examination Findings Lumbo sacral Nerve Roots Reflex Sen sory Motor Pain Distribution