Hamstrings are a group of muscles present at the back of thigh. They extend from the sit bones in pelvis to just below the knee joint and play an important an important role is daily activities such as walking & running. The names of the individual three muscles included in hamstrings are semimembranosus, biceps femoris and the semitendinosus. These, work in opposition to the muscles in the front of the thigh (quadriceps) and the two group of muscles together stabilize movements of the knee and pelvis.
Hamstring injuries account for approximately 12–16% of all injuries in athletes. They are seen more commonly in sports that involve sprinting, acceleration, deceleration, rapid change in direction and jumping such as football, basketball, rugby and baseball. Runners, ballet dancers and older adults who do a lot of walking are also at increased risk. Reinjury rates are high and generally require more time away from the field. Although any injury for a sportsperson is painful, this one can be quite frustrating for both the sufferer and the treating physician.
Symptoms vary depending on the severity of the problem. When the upper part of hamstrings is involved the most common symptom is deep buttock pain or irritation at the back of thigh (minor sprains) associated with tightness or cramping sensation. Pain can radiate down the back of thigh and is generally aggravated by physical activity such as walking, running uphill, high speed or long distance running, leaning forwards, squats and sitting on a firm surface for long duration. Morning increase in severity of pain is not uncommon in this condition. In the early stages pain may reduce after warm up and then recur after activity. This changes with time with the pain persisting throughout the day.
Partial or complete tear of hamstrings may present with severe stabbing pain, bruising with inability to weight bear or walk. Sciatic nerve is present close by and its irritation can cause pain to radiate further down the leg. In severe cases the tendon may completely tear away, often taking a piece of bone with it and this is addressed as avulsion injury.
RISK FACTORS & BIOMECHANICS
Muscle attaches to the bone with the help of a special type of tissue called tendon. To simplify, you can look at these as ropes tying the muscles to the bones. Injuries can involve the muscles or the area where the muscle transforms into the tendon (myotendinous junction) or the tendon itself. Generally the closer the injury is to the pelvis / sit bones the longer it takes to heal. Of the three muscles, biceps femoris is the most commonly injured one.
The hamstrings cross two joints and help to bend the knee and move the hip backwards (extension). They play an important role in propelling the body forwards as we move. Hamstring injury may occur by high speed mechanisms such as running or low speed mechanisms such as stretching. Sudden loading of muscle while it is stretched as while kicking a football is also a common injury mechanism.
The risk factors most consistently associated with hamstring muscle strain-type injuries are age, previous hamstring injury and quadriceps peak torque. As mentioned previously hamstrings and quadriceps oppose each another and it is not uncommon to see imbalance between the two groups of muscles with the latter being stronger. This is expressed as low hamstring to quad ratio which essentially means weaker hamstrings. Weak hamstrings can quickly turn into tight hamstrings and require hamstring to work harder which tires them easily. Tight, tired and weak muscles are predisposed to injuries. When the hamstring are injured, other nearby body muscles are called into action such as those in lower back and hip predisposing them also to injuries/ pain.
Risk factors foe hamstring injury can be classifies into modifiable and non-modifiable ones.
Modifiable risk factors
- Volume of training and rapid variations
- Muscle fatigue
- Weak hamstrings
- Repeated overloading with insufficient warm-up
- Over striding during running or abruptly changing direction
- Lower back, core and pelvis weakness or trunk instability
- Prolonged sitting (work, cycling etc)
- Biomechanical issues such as unequal leg length
Non-Modifiable risk factors
- Previous hamstring injuries – most consistent risk factor with two to six times increased risk of recurrence. Most repeat injuries occur within two months of return to the sport but the risk remains elevated up to three times for an year after initial injury.
- Age – teens and young adults are more likely to experience hamstring injuries as muscles do not tend to grow at the same speed as bones. Aging adults are also at a higher risk possibly due to reduced muscle cross-sectional area.
- Genetics (collagen types)
HAMSTRING INJURY GRADES
Most hamstring injuries occur in the thick, central part of the muscle or where the muscle fibres join tendon. Muscle strains are graded from 1 to 3 depending on their severity
Grade 1 – or hamstring pull is most minor form and usually heals readily. Most patients with this are able to walk easily although may notice pain at the back of the leg after prolonged or quick walking.
Grade 2 – this is associated with more pain (often shooting type) and patients may struggle to walk / limp.
Grade 3 – represents more marked muscle tears including complete tears which present with more severe pain, swelling and difficulty weight bearing. These may require several months of rehabilitation.
MRI scans can help confirm the diagnosis, assess severity of the problem and estimate recovery time. Proximal injuries close to pelvis and those involving increased length and cross-sectional area require longer rehabilitation.
Ultrasound scans are an alternative although are not as reliable in assessing deep portions of the muscles and are unable to identify bone oedema.
Most hamstring injuries can be managed conservatively. This includes using a combination of rest, activity modification, physical therapy and medications such as anti-inflammatory drugs. Activity modification will depend on the severity of problem and does not imply complete inactivity. Approximately 20% of people with proximal hamstring tendinopathy have residual pain despite conservative management and may require further treatment such as injections.
Injection options include
- Percutaneous tenotomy
- Platelet Rich Plasma (PRP)
Ultrasound-Guided Percutaneous Needle Tenotomy
This is used for patients with refractory symptoms and is often in combination with the PRP treatment. It is an OPD procedure performed under local anaesthesia and ultrasound guidance. The aim of the procedure is to create an injury in the tendon by repeated punctures. As a result blood and platelets flow to the area increases, thereby promoting release of growth factors and promoting healing.
Ultrasound-Guided Platelet Rich Plasma (PRP) Injection
PRP injections are commonly used for treatment of hamstring tendinopathy and the evidence supporting their use is slowly accumulating. The procedure involves drawing out patient’s blood and placing it into a spinning machine which separates the platelets from the other blood components. This concentrated platelet layer containing growth factors is then injected into the problem area to induce tissue healing and regeneration. These injections take time to work with benefits becoming apparent 6 to 12 weeks after treatment. My practice is to perform PRP injections under ultrasound guidance and combine these with the needle tenotomy procedure mentioned previously. These injections are used in in combination with lifestyle modification and physical therapy.
Ultrasound-Guided Steroid Injection
These injections can be beneficial for some patients with chronic hamstring tendinopathy and are best avoided in treatment of acute hamstring injuries. Ultrasound guidance helps to improve the safety and accuracy of injections. The aim of thee injection is to deposit steroids in close proximity to the problem area- targeting the area around the tendon (peritendinous) and the overlying bursa. Steroids by their anti-inflammatory effects help to reduce pain, inflammation and improve sitting tolerance, provide a window of opportunity for rehabilitation.
This is an important component of treatment irrespective of whether injections are performed or not. Continuous exercise program focusing on progressive eccentric hamstring strengthening and core stabilization is commonly used with expected recovery times from 1-3 months in majority. Other treatment goals include correcting postural imbalances and improving tissue mobility. Working on the gluteal muscles is equally important, as these are the strongest hip extensors and can assist in reducing/ sharing the hamstring load.
Different phases of rehabilitation have been described for grade I and II hamstring strain injuries.
Phase 1: Focusses on protection, ice, anti-inflammatory drugs , improving soft tissue mobility via manual therapies and therapeutic exercises. In this phase one can initiate non-provocative core strengthening and gluteal and hamstring isometric exercises under guidance of a specialist. Isometric exercises contract muscles without moving them as while squeezing the buttcheeks. Progression to phase 2 occurs when able walk a normal stride without pain and when very low speed jogging is tolerated.
Phase 2: Different exercises called concentrics with shortening of muscles (such as hamstring curls) are added in this phase. End range movements are avoided.Anaerobic training and sports skills can be initiated with care, in the phase. Progression to next phase is considered when forward and backward jogging at 50% maximum speed is possible without pain.
Phase 3: In this phase the range of exercises in increased and eccentric exercises are added. Eccentric exercises are those in which a muscle is contracting while lengthening. An example would be when one is lowering the weights down in a controlled fashion during a hamstring curl. These exercises help in strengthening and remodelling of tendons.
Modalities such as soft tissue mobilization and Extracorporeal Shockwave Therapy (ESWT) may be utilised along with exercises. Shockwave therapy delivers a small amount of controlled micro-trauma to the affected tendon. In order to reinitiate the natural healing process. Generally 3-5 sessions are required toreduce pain.
Surgery may be required to deal with severe cases such as avulsion injuries orcomplete/extensive partial tears not responding to other treatment options.
CONNECT WITH US FOR MORE ON MANAGEMENT OF HAMSTRING INJURIES