Is a leg break worse than an ACL tear?

When Alexander Isak had to be helped to limp off the pitch immediately after putting Liverpool ahead against Tottenham, it was evident he had sustained a significant injury.

Reports have since speculated that he may have suffered a leg fracture, and could be ruled out for anywhere from a few weeks to several months.

On the surface, a leg break may sound like one of the worst injuries to recover from, but how does it actually compare to other common football injuries such as an anterior cruciate ligament (ACL) tear?

The simple answer when comparing a leg break to any other injury is that it depends which bone has been broken, and how badly.

The most common leg fractures in football occur in the lower leg bones - the tibia and fibula.

Fibular fractions are among the quickest forms of leg break to heal, as the fibula are the smaller of the two lower leg bones that form the outer part of the shin and are not weight-bearing. These fractures can heal relatively quickly, often in around six to eight weeks.

The tibula is the more substantial shin bone of the lower leg pair, and can take three to four months to heal from a fracture.

In much rarer occasions, the femur - thigh bone - can be fractured in a footballing injury. It is far stronger than the tibia and fibula, and is also less likely to be impacted during a game, which is why thigh bone fractures for footballers are not as common compared to lower leg breaks. These can also take three to four months to heal.

"It all depends on the level of severity," sports physiotherapist Nick Worth told BBC Sport.

"If it's a straightforward fibular fracture from a kick to the outside of his leg, he could be back playing within six weeks."

However he said anything involving the tibia could result in Isak being sidelined for "three to four months if treated conservatively".

"The severity will dictate whether there's a need for any surgery, or pins and plates. That would add on time, because they are trying to make the fracture stable and strong."

Adding metal pins and plates to the bone means that players can get started on rehabilitation more quickly, as their fracture has been stabilised.

An ACL injury is one of the most dreaded in sport, mainly because of the notoriously lengthy recovery period.

The ACL is a band of connective tissue in the knee joint that can be impacted from a player's sudden change in direction or landings from jumps.

"The extent of the ACL surgery and all that comes with reconstructing the knee, you have to take such a long time to allow the muscles to restrengthen up and to regain your stability," Worth adds.

"It's such an important structure, that because it holds the stability of the whole leg though the knee, reconstruction there would take nine to 12 months realistically.

"We often say six to eight months, but often to see someone back at their best takes longer than that."

ACL injuries have a historic reputation of being 'career-ending' for some players but surgical advancements, including kneecap and hamstring tendon transplants from donors, now mean ACL reconstruction is more effective than ever, and the majority of athletes can eventually return to professional play.

Hamstring injuries are another common football injury, but tend to require less invasive treatment than bone fractures or ACL tears.

They can be graded as one (mild strain with a few days recovery), two (partial tear with a few weeks recovery) or three (severe or complete tear with months of recovery).

Although a grade-three tear will require specialist care, in general a hamstring injury is less likely to require surgery than a fracture or ACL injury, unless it is an extreme case.

Arsenal's Kai Havertz has been sidelined since February following surgery for a severe hamstring tear, but his team-mate Bukayo Saka was recently only ruled out for a few weeks.

One of the reasons that leg breaks can be quicker to heal than ACL injuries is that players are able to treat fractures much earlier.

"You can do some work pretty early on with a fracture, because actually fractures heal through the lines of stress," Worth says.

"Often once fractures have calmed down and are not so sore, putting weight or pressure through it can actually stimulate more bone growth to make it heal better and quicker."

This is because trabecular bone - spongy, porous bone in a honeycomb-like structure found at the ends of long bones like the tibia and femur - grows through stress lines, so the more stress that is applied, the stronger it becomes.

"Initially you take your weight off the injury, but then weight bearing through the joint allows the bone to grow more effectively and heal quicker."

Conversely, an ACL injury requires long periods of rest in order for effective recovery.

"Once you've had surgery, there's a lot of trauma to the knee," sports physiotherapist Ben Warburton told BBC Sport.

"Once that's calmed down, you've got to take it easy for the first three months. When you get past that three-month mark, you can rehab.

"Then it's a case of conditioning and training, getting the leg strong and getting the player back to running, training and games. That's why it takes so long."

This article is the latest from BBC Sport's Ask Me Anything team.