Patients needing hip or knee replacements face a "lottery" over when their operations will be carried out, according to a new report.
Nearly 11,500 more knee and hip replacements were performed by the NHS in March compared with April over the last 10 years, c oinciding with the end of the financial year, researchers found
The figures suggested health trusts forecasting an under-spend were carrying out more procedures in March because they were "incentivised" to spend their budget limit to avoid losing those funds, the report said.
The Medical Technology Group, which conducted the research, also found a "pronounced postcode lottery" over surgery waiting times, with a difference of up to 30 days in some parts of the country for hip and knee replacements.
Patients in London waited an average of 121 days for a hip replacement last year compared to 91 days for patients in the East Midlands, researchers found.
Meanwhile, Londoners waited an average of 121 days for knee joint replacements in 2012, compared with 93 days in the East Midlands.
Barbara Harpham, chairman of the Medical Technology Group, said: "If you need a new hip or knee, it shouldn't matter when in the year it is, or where in the country you live.
"There is a postcode lottery and a time-of-year lottery, and it isn't good enough for patients. It is vital that the Government stops restrictions on knees and hips operations for people who need them."
Nearly 140,000 hip and knee joint replacements on the NHS took place in 2012 - a 92% increase over the last decade - making them among the most frequently undertaken medical interventions, the report found.
Some 49,351 knee procedures were performed in March from 2004 to 2013, compared to 42,944 in April over the same period - a 13% difference.
A total of 46,501 hip procedures were performed in March over the last decade, compared to 41,519 in April - an 11% difference.
The study claimed t he difference in hip and knee replacement procedures in March and April implied " financial calendars for trusts are driving access for patients".
Patients starting the average 15-week wait for a new hip or knee were better starting their wait before Christmas than just after the festive period because March was the busiest month for operations, it added.
"In the public sector, organisations forecasting that they may under-spend at the end of the financial year are incentivised to spend up to their delegated limit," the report's authors said.
"Therefore they will conduct additional activity at the end of financial year.
"This financial calendar-led allocation of procedures is highly unlikely to be the best model through which to fund equitable and consistent healthcare."