The joints that are be treated are L4-L5 and L5-S1. Since radiofrequency ablation procedure are per facet joint. Then you would have to report 64635 64636.
L3,L4 medial branches would innervate the L4-L5 facet joint.
L3 medial branch would be blocked at L4 anatomical target site.
L4 medial branch would be blocked at L5 anatomical site.
L5 dorsal ramus would be blocked at the sacral ala.
The additional block I believe would represent the S1 communicating branch that would be considering it innervates L5-S1. It would be included in the L5-S1 level since RFA procedures of the facet joint nerves are reported per facet level. And the final level in the lumbar region is L5-S1.
Since there the facet joint receives dual innervation. From the medial branch at that level and from the level above you would the below chart of medial branch to facet joint relation
T11, T12 medial branches would innervate the T12-L1 Facet joint
T12, L1 medial branches would innervate L1-L2 Facet Joint
L1, L2 would innervate L2-L3 Facet joint
L2, L3 would.... L3-L4
L3,L4 would....L4-L5
L4, L5 would....L5-S1
So medial branches from L2-L5 (4 separate needles unilaterally) ((or L2-S1)) would be the three level block of the lower lumbar levels L3-4, L4-5, L5-S1
Below is from AMA CPT Assistant 2004
September 2004 page 1
The Facets of Paravertebral Facet Joint Procedures
There are four facet joints associated with each single vertebra in the spine below the level of C2 and above the level of S1. For example, at the L4 vertebral level, there is an L3-L4 facet joint at the upper end and also an L4-L5 facet joint at the inferior end.
Generally, each facet joint has dual innervation: one from the dorsal rami at the same level and one from the level above (eg, the L4-L5 lumbar facet joint is innervated by the medial branches of the dorsal rami from L3 and L4). Multiple injection levels are frequently performed when treating neck and upper back pain, as it is often difficult to isolate the exact joint level and two to three level injections may be performed at one sitting. Therefore, depending on the involved pathology, multiple-level facet joint and facet joint nerve blocks may be necessary for proper evaluation and management of chronic pain in a given patient.
Below is from AMA CPT Assistant 2010
August 2010 page 12
Surgery: Nervous System, 64490, 64491, 64492 (Q&A)
Question: Lumbar medial branch blocks were performed on the right at L3, L4, and L5. Would codes 64490, 64491, and 64492 be reported because three different levels were injected?
Answer: No. The L3, L4, and L5 medial branch nerves innervate the L4-L5 and L5-S1 facet joints. Therefore, code 64493, Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with image guidance (fluoroscopy or CT), lumbar or sacral; single level, is reported for the first joint injected or blocked (L4-L5). Code 64493 is reported for a single or initial level treated. Add-on code 64494, Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with image guidance (fluoroscopy or CT), lumbar or sacral; second level (List separately in addition to code for primary procedure), is reported for the second joint or level injected or blocked (L5-S1). In this specific instance only, CPT codes 64493 and 64494 should be used, provided the injections were performed in the lumbar spine with fluoroscopic (or CT) guidance, as required to use codes 64490-64495.
To further clarify, add-on code 64495, Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with image guidance (fluoroscopy or CT), lumbar or sacral; third and any additional level(s) (List separately in addition to code for primary procedure), is reported only once per day for injections at the third and any additional lumbar or sacral level(s) treated (which does not apply to this case). Codes 64494 and 64495 should only be used in conjunction with code 64493.
CPT codes 64490-64492 are reported in the same way for cervical-thoracic facet injections or blocks. In addition, add-on codes 64492, Injection(s), diagnostic or therapeutic agent, paravertebral facet (zygapophyseal) joint (or nerves innervating that joint) with image guidance (fluoroscopy or CT), cervical or thoracic; third and any additional level(s) (List separately in addition to code for primary procedure) and 64495 are reported once per day as a singular line item irrespective of the number of spinal levels treated.