This is a two-part, Phase 2, multi-center, randomized, double-blind, placebo-controlled, parallel design study of CA-008 (vocacapsaicin) vs. placebo injected/instilled during an elective TKA.

This is a Phase 2, multi-center, randomized, double-blind, placebo-controlled, parallel design study evaluating, in a pilot stage of the study, up to 3 ascending dose level cohorts each evaluating a single dose of CA-008 vs. placebo injected/instilled during an elective TKA. Up to 54 subjects will be randomized in the pilot stage. During the optional second stage of the study, subjects will be randomized to one of either 2 or 3 CA-008 dose levels (to be determined) or placebo. The Sponsor made the decision not to proceed with the second stage.

Key Inclusion Criteria:

1. Plan to undergo an elective primary unilateral total knee arthroplasty (TKA or knee replacement), without collateral procedure or additional surgeries.
2. Be a reasonably healthy adult aged 18 - 80 years old, inclusive, with a BMI ≤ 36 kg/m2 and American Society of Anesthesiology (ASA) physical Class 1, 2 or 3 at the time of randomization.
3. Males and females must abstain from intercourse, use acceptable birth control methods or be sterile or otherwise incapable of having children.
4. Be willing and able to sign the informed consent form (ICF)
5. Be willing and able to complete study procedures and pain scales and to communicate meaningfully in English. Be able and willing to return for outpatient follow up visits as required.

Key Exclusion Criteria:

1. In the opinion of the Investigator,

   1. have a concurrent painful condition, other than pain in the knee to be replaced, that may require pain treatment during the study period.
   2. have active skin disease or other clinically significant abnormality at the anticipated site of surgery that could interfere with the planned surgery.

2. Have a known allergy to chili peppers, capsaicin or the components of CA-008, ropivacaine, ketorolac, acetaminophen, fentanyl, hydromorphone, morphine or oxycodone.

3. Have significant medical, neuropsychiatric or other condition.

4. The following are considered disallowed medications:

   1. tolerant to opioids as defined
   2. capsaicin-containing products or foods.
   3. central nervous system active agent as an analgesic adjunct medication
   4. antiarrhythmics except beta-blockers, digoxin, warfarin, lithium, or aminoglycosides or other antibiotics for an infection
   5. parenteral or oral corticosteroids.
   6. antianginal, antihypertensive agent or diabetic regimen at a dose that has not been stable for at least 30 days or which is not expected to remain stable while participating in the study.

5. Have positive results on the alcohol breath/saliva test indicative of alcohol abuse or urine drug screen indicative of illicit drug use at screening, and/or prior to surgery.

The reason for the difference in the analysis population versus the number of participants in Participant Flow is due to the participant in CA-008 15 mg Cohort 3 who was randomized but not treated with study drug. This participant discontinued early from the study (on the same day of randomization) due to an adverse event.

Adverse event data were collected up to 76 days for participants in the study. This was comprised of a screening period that could be up to 45 days and subsequent clinic visits through Day 29.

The definition of adverse event and/or serious adverse event, used to collect adverse event information in this study did not differ from the clinicaltrials.gov definitions.