World Rugby has been asked to consider reducing the legal height for a tackle after a seventh successive season of increased incidents of concussion in the English professional game.
The Professional Rugby Injury Surveillance Project, jointly commissioned by the Rugby Football Union and Premiership Rugby, with the support of the Rugby Players' Association, reported injury data for the 2016-17 season on Monday.
The report showed concussion was the most commonly reported match injury for a seventh straight year, contributing 22 percent to the total.
And it suggested a World Rugby directive -- to increase sanctions on tackles and take a zero tolerance approach to contact with the head, introduced in January 2017 -- made "no difference" to the incidence of all injuries and concussion.
RFU medical services director Dr Simon Kemp said World Rugby was making its own analysis of data to consider a reduction in the legal height of a tackle which, RFU professional rugby director Nigel Melville said, has "become a bit of a grey area".
Kemp said: "We would like World Rugby to give consideration to thinking about reducing the legal height for the tackle.
"There's very little margins for error with the permitted height of the tackle at the line of the shoulders.
"It's for World Rugby to consider and we know they're doing that at the moment."
Melville added: "It's become a bit of a grey area at times.
"What we're looking for is consistency across the refereeing. It's challenging for World Rugby, with referees coming from different hemispheres, from different competitions and you get a lack of consistency.
"That's difficult for fans and people watching to know what's right and what's wrong."
The report, in its 14th season and delivered by researchers at the University of Bath, showed concussion cases requiring more than a three-month absence had increased in number. That was attributed to "a trend to more conservative management of players who have sustained two or more concussions in a 12-month period".
For the first time, hamstring injuries and concussion appear alongside anterior cruciate ligament knee injuries in the top three match injuries resulting in an absence of 84 days or more.
For the 2016-17 Premiership season, there were 3.8 injuries per match (1.9 per team), on average.
Of the 169 concussions reported, 22 players suffered more than one concussion. One player suffered four and one player three.
The average severity of match injuries (measured by the time taken to return to play) for the same campaign was 32 days.
The report showed 47 percent of all match injuries are associated with the tackle, with an almost equal split between tackler and the ball carrier.
Concussion accounted for 43 percent of injuries to the tackler and 19 percent to the ball carrier.
An eight-point Professional Game Action Plan was announced alongside the publication of the injury project.
As well as addressing the tackle height, the plan vowed to undertake or continue research in player load, training injury risk and the impact of artificial grass pitches.
Three of 12 Premiership teams played their home matches on artificial turf in 2016-17 and the report showed "the incidence and burden (days absence) of match injury on artificial turf was significantly higher than that of natural grass".
There were 608 and 170 injuries on grass and artificial turf, respectively.
The report also said combining data for the four seasons in which Premiership matches have been played on artificial surfaces "indicates that neither injury incidence or severity differ between surfaces".