Written by: Lee R. Benaroch, BSc, MD student
Edited by: Jesse A. Morse, MD, MBA, CAQSM
Over the course of this NFL season, we will be beginning a new segment of bringing you articles detailing the physiological aspects of common injuries. We will be discussing how they occur, how they can be prevented, ways to treat them and medical imaging of the injured muscle, ligament or bone. We hope you enjoy! First up, the dreaded hamstring injury.
A study conducted in 2011 looked at 10 years’ worth of NFL injury data and found that the hamstring strain was the most common injury in the NFL, occurring on average 172 times per season*. More than half of these hamstring injuries end up taking place during training camp, preseason or the early weeks of the regular season. Why is that?
Many theorize that the athletes increase their usage of their hamstrings from 50% in the offseason to 100% in training camp and the muscle is not able to tolerate that overload. This year in particular, COVID-19 has caused a shortened training camp further intensifying the issue.
On top of that, why is it that during every NFL year, it feels like every team has a minimum of one impactful player go down with a hamstring injury? Already this year we’ve seen the likes of Tampa Bay’s Mike Evans, Detroit Lions’ Kenny Golladay, Philadelphia Eagles’ Miles Sanders, Atlanta Falcons’ Julio Jones and many more, struggle with a hamstring injury. Is it a previous injury history? Is it the strength and conditioning program? Or is it just luck?
The hamstrings are made up of three individual muscles located on the back of the thigh: the biceps femoris, semimembranosus and semitendinosus. All three muscles originate on the back of the hip and insert onto the back of the knee. The main function of the hamstrings is to primarily flex the knee joint and secondarily extend the hip joint.
A hamstring strain, like any other muscle strain, is graded based on its severity. Grade 1 is a mild strain but no tear. Grade 2 – a partial muscle tear and grade 3 – a complete muscle tear. It causes a sharp pain, weakness, swelling and bruising within the injured muscle.
Grade 1 strains are usually caused by overuse of the muscles which lead to friction at the insertion site, in turn leading to bursitis (i.e. bursae are small fluid-filled sacs that cushion the bones, tendons and muscles around joints – bursitis is an inflammation of these sacs). The problem with grade 1 strains is that injury to the tendon can develop, called tendinopathy. This can and often leads to repetitive pain and a potentially grade 2+ tear.
Where most of the NFL players run into issues is during a traumatic non-contact eccentric contraction/stretch of the hamstring beyond its physiological capabilities. This can occur either during knee flexion or hip extension and cause a partial or complete tear of the hamstring. One of the most common sites for these tears is at the origin point of the biceps femoris at the hip. These grade 2+ tears are usually caused by one of the following issues:
Poor Eccentric Strength – Eccentric strength is when a muscle lengthens under tension. One of the jobs of the hamstring is to stretch the knee and decelerate the lower leg of the player after sprinting. If the player’s hamstring lacks sufficient strength to do so, then the muscles can’t slow down the leg and an injury can follow.
Muscle Imbalances – The quadriceps and hamstrings oppose the actions of one another. If a player has much stronger quads than they do hamstrings, then the lower leg will swing forward at a speed that the hamstring cannot handle, ultimately leading to extensive pressure on the hamstring and a possible tear. This is a common cause of hamstring injury in the NFL as many players tend to be quad dominant.
Prevention of these hamstring strains is essential for any NFL player and there are many techniques that can help with it. However, one of the most common techniques used in European soccer, and that has been found to reduce the overall injury risk of a hamstring strain to athletes, is the Nordic Hamstring Exercise (NHE). The NHE involves kneeling on a pad and lowering under control while the ankles are held in place by a partner, a loaded barbell, or any other immovable object.
The athlete would then extend the hamstring muscles by leaning forward from the knee and not the hip. Van Dyk et al. (2019) found that when including NHE in injury prevention programs for athletes, the risk of hamstring injury was reduced by 50% when compared to usual training or other prevention programs. Therefore, NFL teams and strength coaches can do a great deal of good by making sure they include NHE in their strength and conditioning programs in order to help prevent a hamstring strain.
When it comes to treatment of a hamstring strain, the options are dependent on the severity of the injury. Ultimately there are two treatments available; the conservative or surgical method.
If the strain is mild, a Grade 1, the doctor may suggest simple rest, ice and use of crutches for 3 to 5 days. This will be followed up with rehabilitation to re-establish strength and flexibility of the hamstring.
If the injury is more severe, a grade 2, or the patient wants to be really aggressive (like an NFL athlete trying to return to the field quicker), then injections can be considered. An injection into the muscle or where the tendon inserts into the bone can further help with pain relief, healing, and recovery. Yong Soo Park et al., (2019) found that Platelet-Rich Plasma (PRP) injections (extracted from patient’s blood) provided a more favorable response when compared to steroid injections. They could be used as a conservative treatment choice for grade 2 proximal hamstring injuries with the added benefit of short-term pain relief.
While the quality of cells and growth factors in PRP is very good, often times these can take a couple of injections to see significant improvement. Extracting cells and growth factors from either bone marrow or amniotic tissue (provided from a company that extracts it safely from the placenta of a woman delivering a baby via a C-section) have significant better success rates. In some studies, the number of cells and growth factors found in bone marrow is 3x that found in PRP. The numbers for amniotic tissue are even better than bone marrow.
If the injury is more severe, the acute traumatic tear of the hamstring can be surgically treated. Surgery for a hamstring strain is quite rare. If the muscle completely tore off the bone and managed to take a piece of bone with it (Grade 3) then surgery is an option. Nonetheless, it is usually the last resort.
Most NFL hamstring injuries tend to be treated with the conservative method, as the tear is usually either a Grade 1 or 2. However, where most players run into issues is the fact that even though the hamstring may feel healed, most players and teams do not give the hamstring enough time to properly heal.
A 2007 study was done on professional sprinters with moderate strains that showed 20-55% of the original injury had not fully healed after 6 weeks. However, a 2011 study conducted by Cohen et al., found that players with a grade 1 hamstring strain missed only 1.1 week on average, those with a grade 2 strain missed 1.7 weeks on average, and those with a grade 3 strain missed 6.4 on average.
It is clear to see that both players and teams alike are willing to ignore the data and rush their players back following a hamstring injury. However, this is the precise reason why 16.2% of NFL players with hamstring injuries re-injure themselves.
Ultrasound Images (of Hamstring injuries) Written by Jesse A. Morse, MD
Ultrasound is a fantastic way to evaluate the severity of hamstring injuries, even if an MRI doesn’t show much. Below are a bunch of fantastic images that were borrowed (source below) from one of the best Musculoskeletal Ultrasound Imaging books.
The first image (Figure 6.75) is showing damage to one of the main hamstring tendons, but not a significant tear, this is called tendinosis.
Figure 6.76 is showing the most common area of injury in the hamstring, called the Conjoined Tendon, where two tendons come together. This demonstrates tendinosis, which is essentially early damage to the tissue, and not a large tear, which is what Figure 6.77 shows. Compare Figures 6.76 and 6.77, there is a clearer distinction between the amount of swelling (dark fluid) and the injured tissues look very different then the surrounding tissue.
Figure 6.78 demonstrates a very large tear, likely a moderate ‘Grade 2.’ So, think of this image when you hear a player suffered a ‘Grade 2 hamstring injury.’ All of the black within the white arrows is blood that has filled the area after the injury. It’s not supposed to be there. As you can tell the tissues look completely different than the tissues above and below it.
Figures 6.79 & 6.80 demonstrate tears of multiple hamstring tendons. There is significant damage at the muscle and these injuries are going to take at least 6-10 weeks to properly heal, likely much longer.
Figure 6.81 demonstrates a chronic tendon injury, which has scar tissue within it. This scar tissue is not as strong or as flexible as regular muscle tissue, so it often tears much easier. Chronic ‘microtears,’ which I often describe to my patients like a rope that is trying to hold a boat to a dock for the past 20 years. The rope is the tendon, the boat is the bone. That rope is going to be beat up and while still holding the boat on, like the tendon attached to the bone, it is not as strong as it used to be. A large force on that tendon will cause it to tear, sometimes off of the bone.
Hope this was helpful!
All ultrasound images were taken from Jacobson’s Fundamentals of Musculoskeletal Ultrasound
*Starting in 2012, the NFL started compiling and publishing sports injury data through the Play Smart Play Safe initiative and the concussion has now been recorded as the most common NFL injury coming in at 200-280 times per season.
Jacobson, Jon. Fundamentals of Musculoskeletal Ultrasound. Elsevier Science, 2018.
Are AC Joint sprains serious?-Dr. Morse
Currently both Tampa Bay Buccaneers QB Jameis Winston and Detroit Lions WR Golden Tate are dealing with a common football injury, a sprained AC joint. What does this mean? A sprained AC joint, also known as the acromioclavicular joint, is commonly referred to as a ‘separated shoulder.’ This is an injury where there is a sprain of the supporting ligaments (acromioclavicular and coraco-clavicular ligaments) of the AC joint. Typically, this injury occurs when striking another player with the point of the shoulder, or in Winston‘s case, when a player lands directly on the point of their shoulder, often while being tackled/sacked.
The initial presentation of an AC joint sprain reveals exquisite tenderness over the AC joint, which is in between the tip of your shoulder and your neck, just above where the clavicle is (see picture). X-rays are typically ordered to evaluate for a clavicle fracture, which Green Bay Packers Aaron Rodgers just suffered, and to it as well is to assess the degree of AC separation. Pulling down on the arm of a player with a possible AC joint sprain is an easy way to evaluate the joint, as it will widen the AC joint, causing pain.
Management of this condition typically focuses on control of the inflammation and pain with ice, rest, and a sling, often for about three weeks. Integrating the use of protection with padding, early restoration of range of motion, and the preservation of the shoulder strength are all-important as well. If conservative options are still failing to control the pain, an ultrasound-guided AC joint steroid injection can be considered.
To keep it simple, there are basically three types of AC joint sprains, grades 1, 2, and 3. Mild AC joint sprains (Grade 1) involve just a mild sprain of the AC joint capsule and AC ligament, normal x-rays, with a return to play of about 1 to 2 weeks.
Moderate sprains (Grade 2) involve rupture of the AC capsule as well as the ligaments. X-rays will show upward displacement of the collarbone/clavicle, but the C-C ligaments are normal. These take about 3 to 4 weeks to fully heal. Grade one and two AC joint sprains often only result in the patient wearing a sling.
High-grade AC sprains (Grade 3) often do not require surgery, but there is complete AC joint dislocation, and complete rupture of both the AC and C-C ligaments. Grade 3 AC joint sprains typically heal in about 6 weeks. Some athletes, especially at the elite level, may decide to surgically stabilize their joint to help speed up their return to play. About 30 to 50% of patients who suffer an AC joint sprain will have residual pain at the AC joint. Surprisingly, patients who undergo surgery have a higher rate of AC joint arthritis than those who to choose a more conservative route.
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