When Arsenal football club announced new signing Jurrien Timber faced a lengthy spell on the sidelines due to a serious knee injury sustained on his Premier League debut, sports fans questioned why so many top professionals have been struck down with the same injury in recent weeks.
The Dutch defender, who signed for the North London club only last month, faces lengthy rehabilitation and a similar recovery programme to Real Madrid stars Thibaut Courtois and Eder Militao, who also damaged their anterior cruciate knee ligaments (ACL) during pre-season training.
And they are not the only ones.
Christopher Nkunku, one of Chelsea’s many star summer signings, has a similar injury, while teammate Wesley Fofana had surgery on his ACL last month.
Aston Villa defender Tyrone Mings was another who crumpled to the floor on the opening day of the Premier League season after sustaining a serious ACL injury.
The Women’s World Cup in Australia and New Zealand, which draws to a close on Sunday, has been without 30 top players because of ACL tears, including England stars Leah Williamson and Beth Mead.
This year's Rugby World Cup will be without one of its biggest stars – France fly-half Romain Ntamack – who has been ruled out with a ruptured ACL.
This may seem like a mini-pandemic in the world of top-level sport, but experts say there is little evidence to suggest the injury is becoming more common.
“The incidence of these type of injuries has not changed, but we may see them more commonly because more people are active and involved in collision-type sports,” said Dr Erik Hohmann, an orthopaedic surgeon who has worked with Australian professional rugby teams and FC Bayern Munich.
“Football is big and the injury has a high incidence but the absolute number of ACL injuries per hours played has not changed.”
The ACL in the knee connects the shin bone to the thigh bone and is vital for pivoting, jumping and landing.
Women more at risk
While a series of high-profile ACL injuries may be a freak occurrence this summer, studies have shown the injury is becoming more common in young people, while women are also more susceptible.
Research by the University of Minnesota Medical School showed ACL tears in people aged six-18 have increased by 2.3 per cent a year over the past two decades.
Data showed girls reported higher rates of ACL tears, peaking at age 16 with 392 injuries per 100,000 people per year.
In the male population, ACL injuries peaked at age 17, with 422 injuries per 100,000.
There are on average 200,000 reported ACL tears per year in the US.
“Females in general are more vulnerable, maybe as much as eight times, due to a couple of factors,” said Dr Hohmann, who now works at Burjeel Hospital for Advanced Surgery in Dubai.
“Men have more testosterone and women have more oestrogen that makes the tissue more elastic and [leads to] a higher risk of injury.
“If we look at the hormonal cycle of women, as soon as there is a high oestrogen push and they are ovulating, they are at more risk of an ACL injury.
“When they perform jumping sports like handball or basketball, women have different landing patterns.
“They are landing with knock-knees so are extending their knees more and they are not bending as much [as men].
“These are risk factors, whereas men are more bow-legged and bend their knees more, with more muscle strength per square cm, so it is a hormonal, anatomical and biomechanical problem.”
While that could explain the high number of injuries at the Women’s World Cup, there are still questions over the recent spate of injuries in men’s football.
When a player has to undergo surgery to repair a damaged ACL, doctors will often look at several options.
Repairs can be made with tendons extracted from the hamstring or patella or even with a synthetic alternative.
Each option has different properties and recovery times, said Dr Hohmann.
“The patella tendon is generally stiffer and heals faster, which is why we take this option with professional athletes,” he said.
“In recreational athletes, we tend to use hamstrings and recovery is slow.”
While some professional players may return to top-level sport after about six months, they are more at risk of developing osteoarthritis in later life.
The advice for most people, without the commercial pressures of professional sport, is usually a slower recovery of about 15 months.
One of those is Andrei Comsa, 30, a physiotherapist in Dubai, who had surgery in 2018 after first suffering a meniscus and ACL tear while playing football seven years earlier.
“It happened on a synthetic pitch while I was taking a shot, and my standing leg just gave way,” said Mr Comsa, who played semi-professionally for Metalul Aiud in the third tier of Romanian football as a right-sided defender.
“I had no issues while playing on a full-size grass pitch, but it was a problem on the artificial surface.
“I went through a period of rehabilitation and continued to play until 2018 when my meniscus had gradually deteriorated and I required an operation.
“I was able to walk without sticks after a few months and since then it has been perfect.
“The only way you could tell I had an operation is the scars around my knee.”
Mr Comsa underwent knee reconstruction, with surgeons using extracts from his patella to create new ligaments.
Since then he has retrained as a physiotherapist and personal trainer and he moved to Dubai 12 months ago, working at J-Club Emirates Towers.
Many of his clients are recovering from similar knee injuries.
“It is an area I have an interest in, particularly as it is something that I have also been through,” said Mr Comsa, who is from Cluj in Romania.
“Most of my clients have been women, as they seem to be more vulnerable to these kind of injuries, due to their hip structure and anatomy.
“But the rehabilitation they must go through is the same as men, it can be a long process.”
Stem cell injections
Techniques to rebuild and repair knee injuries have remained unchanged in recent years, although the development of stem cell therapy could offer a more robust alternative.
Stem cells reset the joint environment, promote healing by reducing pain and swelling and improve the range of motions and quality of life.
Stem cell therapy also helps patients undecided about surgery or those medically unfit for a full knee replacement.
While there is little scientific data to support the therapy in professional sport, experts at Abu Dhabi Stem Cells Centre (ADSCC) said it could be used more widely in the general population.
“Studies have shown that such procedures usually take long recovery time and the patient might have residual painful knee due to incomplete healing,” said Dr Ashok Kumar, an orthopaedic surgeon at ADSCC.
“Surgical augmentation with stem cell injections enhances the strength of repaired or reconstructed tissues.
“It promotes early recovery and delays the ligament and cartilage degenerations in the knee joint.”
Stem cells have the unique ability of self-renewal and promote accelerated healing by replacing the damaged local tissue.
They are harvested from the bone marrow at the time of surgery or taken from patients' own stored stem cell and injected into the desired site.
"Combining stem cells with conventional knee surgery provides better tissue at the site of repair or reconstruction,” said Dr Kumar.
“It accelerates the early recovery and delays the further degeneration of the affected tissues. We proudly perform these procedures at ADSCC.”