Rub on pain relief is effective.

According to a Cochrane review both diclofenac, ibuprofen, ketoprofen, and piroxicam rub on gels are effective in treating the pain from various causes.

The highlights are that

  • For strains and sprains, several topical non-steroidal antiinflammatory drugs (NSAIDs) helped reduce pain by at least half over about a week.  With the number needed to treat to give relief to one person (NNT) of 2 to 5.
  • For hand and knee osteoarthritis, topical diclofenac and topical ketoprofen reduced pain by at least half over at least 6 to 12 weeks with an NNT of 5 to 10.
  • For postherpetic neuralgia, a single application of topical high-concentration capsaicin reduced pain by at least half for 8 to 12 weeks (NNT* 12).

 

Importantly the study authors also commeted that "Serious side effects were uncommon".

 

Here's a bit more information on NNT from wikipedia

The number needed to treat (NNT) is an epidemiological measure used in communicating the effectiveness of a health-care intervention, typically a treatment with medication. The NNT is the average number of patients who need to be treated to prevent one additional bad outcome (e.g. the number of patients that need to be treated for one of them to benefit compared with a control in a clinical trial). It is defined as the inverse of the absolute risk reduction. It was described in 1988 by McMaster University's Laupacis, Sackett and Roberts.[1] The ideal NNT is 1, where everyone improves with treatment and no one improves with control. The higher the NNT, the less effective is the treatment.[2]

NNT is similar to number needed to harm (NNH), where NNT usually refers to a therapeutic intervention and NNH to a detrimental effect or risk factor.