REIDER PART 2
89

Motor Examination

The spinał cord terminates at about the L1-L2 level, but its lower nerve roots continue distally as thc cauda equina. Each pair of nerve roots exits thc spine at thc ncu-ral foramen formed by the vertebra of the same number and thc one below. Thus, thc L4 ncrve root cxits at thc L4-L5 neuroforamen, the L5 nerve root exits at the L5-S1 neuroforamen, and so forth. However, when a lumbar disk herniation occurs, the disk tends to compress the next lower nerve root. Thus, thc L5-S1 disk, thc most common to herniate, usually compresscs thc SI ncrvc root. Similarly, thc L4-L5 disk usually compresses the L5 ncrve root, and the L3-L4 disk, the least common of thc three to herniate, usually compresses the L4 nerve root. Higher nerve roots are unlikely to be compressed by disk herniations. However, these higher nerve roots may be affected by other typcs of pathology, such as spinał frac-tures or dislocations; and congcnital malformations, such as spina bifida; tumors; and infections.

L1 andL2 Nerve Roots. The LI and L2 nerve roots sup-ply the iliopsoas muscle, the primary hip flexor. To test

_Charter 9_Lumbar Spine 349

the iliopsoas, the patient is seated with the knees flexed to 90° over the end or the side of the examination table. The patient is instructcd to raise the thigh off the examination table while maintaining flcxion of thc knee. The examiner then presses downward on the patienfs knee with both hands, asking the patient to resist as strongly as possible (Fig. 9-17). In a normal patient, the examiner should be able to overcome the iliopsoas with moderate difficulty.

L3 Newe Root The L3 nerve root is usually assessed by evaluating quadriceps strength, although the quadriccps is also innervated by L2 and L4. The quadriceps is also tested with the patient sitting on thc end or thc side of the examination table. The patient is asked to extend the knee fully and then to maintain the knee in fuli extension whilc thc examincr pushes downward on the lower leg just above the ankle (Fig. 9-18). In a normal patient, the examiner should be unable to overcomc the quadriceps and initiate knee flexion. In fact, in a strong patient, the examiner may begin to lift thc patient^łs pelvis off the examination table as the lower leg is pushed downward with the patient s knee locked in fuli extcnsion.