Hamstring Strain

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Definition/Description

Hamstring strains are caused by a rapid extensive contraction or a violent stretch of the hamstring muscle group which causes a high mechanical stress. This results in varying degrees of rupture within the fibres of the musculotendinous unit.
Hamstring strains are common in sports with a dynamic character like sprinting, jumping, etc.,... where quick eccentric contractions are regular. In soccer it is the most frequent injury. 
The hamstrings consist of three muscles : The biceps femoris, the semitendinosus and the semimembranosus.

Clinically Relevant Anatomy

The hamstrings are a group of muscles which are comprised of three separate muscles located at the back of the thigh. The M. Biceps Femoris, M. Semitendinosus and the M. Semimembranosus. These muscles start at the ischial tuberosity, extending down the back of the thigh and along either side of the knee .

The M. Biceps Femoris exists out of two parts: the long head and the short head (Caput longum and Caput breve). These two parts are both attached to the head of the fibulae, but only the long head starts at the ischial tuberosity. The other part, the short head, starts at the lateral lip of the linea Aspera on the posterior aspect of the femur . The Caput Breve and Longum are innervated by 2 different nerves. The Caput Longum is innervated by the N. Tibialis, while the Caput Breve is innervated by the N. Fibularis, who are both originating from the spine segment L5-S2 .

The M. Semitendinosus starts at the ishial tuberosity but unlike the M. Biceps Femoris, it lays at the medial side of the thigh and is attached to the upper medial surface of the tibia, also called Pes Anserinus.

The M. Semimembranosus is the most medial of the three hamstring muscles . It also starts at the ishial tuberosity and is attached to the Condylus Medialis Tibiae . It’s also connected to the Lig. Popliteum Obliquum, and the fascia cruris .
  
This shows that all of the three hamstring muscles start at the same origin, but have different insertions .
Schematic Review of structural anatomy:
- M. Biceps Femoris:
              o Caput Breve:
                      § O: Labium Laterale Lineae Aspera, Septum Intermusculare Laterale
                      § I: Caput Fibula

              o Caput Longum:
                      § O: Tuber Ishiadicum
                  § I: Caput fibula

- M. Semimtendinosus:
              o O: Tuber ishidadicum
              o I: Pes Anserinus (facies Medialis Tibiae)

- M. Semimembranosus:
             o O: Tuber Ishiadicum
             o I: Condylus Medialis Tibiae, Lig. Popliteum Obliquum, Fascia Cruris

Because the hamstrings cross 2 joints (the knee and the hip), their functions are varied.
The muscles function as movers and stabilizers of the hip and knee. The hamstrings are used to flex the knee, and extent the hip. The hamstrings help to get from a crouched position to an erect position. This refers to movements like getting up from a chair or in sprinting, where the front leg in starting position has to bear the effect or the start .

Because of the insertion of the muscles, the secondary function of the hamstrings is endo and exorotation of the knee. This makes the hamstrings extremely important muscles if it comes to walking and running .

Schematic review of functional anatomy:

- M. Biceps Femoris:
           o Extension Hip
           o Flexion Knee
           o Exorotation Bottom Leg

- M. Semitendinosus:
           o Extension Hip
           o Flexion Knee
           o Endorotation Bottom Leg

- M. Semimebranosus:
           o Extension Hip
           o Flexion Knee
           o Endorotation Bottom Leg

Epidemiology /Etiology

Despite the clinical importance, there isn’t a lot of research dealing with classifying muscle injuries. However, if we look at what researchers usually do when they need to separate groups of people according to muscle injury, we see that they usually classify this based on the mechanics of the trauma.  
There are 2 categories of muscle injuries if we base them on mechanics of trauma:
- Acute (traumatic muscle injuries): these muscle injuries are the result of a sudden trauma which causes a problem in the muscle.
- Chronic (injury because of overuse): happens because of tiring a muscle which results in said muscle being damaged.
Hamstring strains are caused by a rapid contraction or a violent stretch of the hamstring muscle group which causes varying degrees of rupture within the musculotendinous unit . A hamstring strain can be categorised in both groups, as both mechanics of injury can happen to cause a hamstring strain.

Hamstring and other muscle strains can be divided into grades, dependable of their severity. The classification of hamstring strains can be used to estimate the convalescent period and to design a rehabilitation program . If you need a summary of these grades, you can find it in Clinical Representation.

The cause of a hamstring muscle strain is often obscure. In the late forward swing phase, the hamstrings are at their greatest length and at this moment, they generate maximum tension . In this phase, hamstrings contract eccentrically to decelerate flexion of the hip and extension of the lower leg . At this point, a peak is reached in the activity of the muscle spindles in the hamstrings. A strong contraction of the hamstring and relaxation of the quadriceps is needed. According to “Klafs and Arnheim”, a breakdown in the coordination between these opposite muscles can be a cause for the hamstring to tear .

Predisposing Factors/Risk Factors

There are several predisposing factors to hamstring strains like fatigue, poor posture( anterior tilt of the pelvis), muscle strength imbalances, leg length inequality, non-flexibility and an insufficient warm-up . So reported Worrel et al. that the hamstring-injured group was significantly less flexible than the non-injured group. These factors have an influence on the tenderness of the hamstrings.
During activities like running and kicking, hamstring will lengthen with concurrent hip flexion and knee extension, this lengthening may reach the mechanical limits of the muscle or lead to accumulation of microscopic muscle damage. Biceps femoris muscle has a dual nerve supply, with long head innervated by tibial portion of sciatic nerve and short head innervated by common peroneal division of sciatic nerve. There is a possibility that hamstring injuries may arise secondary to the potential uncoordinated contraction of biceps femoris muscle resulting from dual nerve supply. Another debate is on hamstring variation in muscle architecture. BFS possess longer fascicles (which allow for greater muscle extensibility and reduce the risk of over lengthening during eccentric contraction) and a much smaller CSA compared to BFL. Whereas BFL presents with shorter fascicles compared to BFS which undergo repetitive over lengthening and accumulated muscle damage. Excessive anterior pelvic tilt will place the hamstring muscle group at longer lengths and some studies proposed that this may increase risk of strain injury.
There are various proposed risk factors which may play a role in hamstring injuries. Increased age, previous hamstring injury, limited hamstring flexibility, increased fatigue, poor core stability and strength imbalance have been listed as possible risk factors for hamstring strain injuries.

Characteristics/Clinical Presentation

Hamstring strains mostly occur due to a powerful eccentric contraction or overstretching of the hamstrings. The hamstrings consists of 3 parts. Those parts provide flexion of the hip and extension of the knee. The Hamstring strain is caused by repeated eccentric muscle contractions of the muscle.
It occurs when the muscle fibers tear due to extensive mechanical stress.

This results in a sudden sharp pain in the posterior thigh when it occurs during sport activities. Also a "popping" or tearing impression can be described. The patients may complain of tightness and improved range of motion like knee extension and hip flexion. Sometimes swelling and ecchymosis are possible but they may be delayed for several days after the injury occurs.[15] Rarely symptoms are numbness, tingling and distal extremity weakness. These symptoms require a further investigation into sciatic nerve irritation.[15] Large hematoma or scar tissue can be caused by complete tears and avulsion injuries.
Other possible symptoms:
· Pain
· Tenderness
· Loss of motion
· Decreased strength on isometric contraction
· Decreased length of the hamstrings

Hamstring strains are categorised in 3 groups, according to their severity.:

· Grade 1 (mild): just a few fibres of the muscle are damaged or have ruptured. This rarely influences the muscle's power and endurance. Pain and sensitivity usually happen the day after the injury (depends from person to person). Normal patient complains are stiffness on the back side of the leg. Patients can walk fine. There can be a small swelling, but the knee can still bend normally.

· Grade 2 (medium): approximately half of the fibres are torn. Symptoms are acute pain, swelling and a mild case of function loss. The walk of the patient will be influenced. Pain can be reproduced by applying precision on the hamstring muscle or bending the knee against resistance.

· Grade 3 (severe): ranging from more than half of the fibres ruptured to complete rupture of the muscle. Both the muscle belly and the tendon can suffer from this injury. It causes massive swelling and pain. The function of the hamstring muscle can't be performed anymore and the muscle shows great weakness.

Differential Diagnosis

On examining the patient, the physiotherapist possibly has to differentiate between different injuries e.g. adductor strains, avulsion injury, lumbosacral referred pain syndrome, piriformis syndrome, sacroiliac dysfunction, sciatica, Hamstring tendinitis and ischial bursitis. 
Other sources of posterior thigh pain could also be confused with hamstring strains and should be considered during the examination process. Specific tests and imaging are used to asses and exclude those different pain source possibilities.
Sciatic nerve mobility limitations can contribute to posterior thigh pain and adverse neural tension could in some cases be the only source of pain without any particular muscular injury. In certain cases it is difficult to determinate whether it are the Hamstrings or other muscle groups like hip adductors (eg. M. Gracilis and M. Adductour magnus and longus.) that are injured due to their proximity. Sometimes imaging procedures may be required to determinate the exact location of the injury.

Other conditions with similar presentations as hamstring strains are strained popliteus muscle, tendonitis at either origin of the gastocnemius, sprained posterior cruciate ligament, apophysitis-pain in ischial tuberosity, Lumbar spine disorders and lesions of the upper tibio-fibular joint.

Diagnostic Procedures

Most of the acute injuries can easily be found by letting the patient tell how the injury occured. To be sure they must do a little investigation of the hamstrings as well.

When the therapist Isn't too sure, he can ask for medical imaging. This will exclude al other possibilities.

- Radiographs: a good thing about radiographs is that with that kind of imaging, its possible to differentiate the etiology of the pain. It can differentiate in muscular disease (e.g muscle strain) or a disease of the bone (e.g. Stress fracture).

- Ultrasound (US): this kind of imaging is used a lot because it is a cheap method. It is also a good method because it has the ability to image muscles dynamically. A negative point about Ultrasound is that it needs a skilled and experienced clinician.

- Magnetic Resonance Imaging (MRI): MRI gives a detailed view of the muscle injury. But sometimes it may not be clear according to the images. If that happens, the therapist must rely on the story that the patient told him (see characteristics/clinical presentation).

Outcome Measures

• VISA-H: The final version, named Victorian Institute of Sport Assessment-Proximal Hamstring Tendons (VISA-H), consisted of ten questions that measured the domains of pain, function and sporting activity. It evaluates proximal hamstring tendinopathy. Not validated yet.[22][23]
  

• FASH: The FASH questionnaire is a self-administered questionnaire which now can only be used in Greek, English and German languages. Because hamstring injuries represent the most common football injury, they tested the validity and reliability of the FASH-G (G = German version) questionnaire in German-speaking footballers suffering from acute hamstring injuries.
  The FASH-G questionnaire was tested on 16 footballers with hamstring injuries (patients’ group) , 19 field hockey players (at risk-group) and a healthy group: 77 asymptomatic footballers. For measuring the validity of the test they compared the total FASH-G score of the non-injured and injured groups. Reliability of the FASH-G questionnaire was analysed in 18 asymptomatic footballers using the intra-class coefficient.
  The FASH (Functional Assessment Scale for Acute Hamstring Injuries) questionnaire:
  · They came to the result there were significant differences between injured and non-injured participants.
  · No statistical differences were found between healthy athletes (p = 0.257), but patients’ groups (footballers with hamstring injuries) and at-risk groups (hockey players) presented scoring differences(p = 0.040 and <0.001, respectively).
  So we can conclude that the FASH-G is a valid and reliable instrument to assess and determine the severity of hamstring injuries, in this case tested on German footballers. [18][19][20]

• <a href="http://www.physio-pedia.com/Lower_Extremity_Functional_Scale_(LEFS)">LEFS: Lower Extremity Functional Scale</a>

• SFMA: The Selective Functional Movement Assessment (SFMA) is a clinical assessment system designed to identify musculoskeletal dysfunction by evaluation of fundamental movements for limitations or symptom provocation.[24]

• PSFS: Patient Specific Functional Scale <a href="http://www.physio-pedia.com/Patient_Specific_Functional_Scale">PSFS: Patient Specific Functional Scale</a>

• VAS: Visual Analog Scale <a href="http://www.physio-pedia.com/Visual_Analogue_Scale">VAS: Visual Analog Scale</a>

• NPRS: Numerical Pain Rating Scale  <a href="http://www.physio-pedia.com/Numeric_Pain_Rating_Scale">NPRS: Numerical Pain Rating Scale</a>

Examination

The physical examination begins with an examination of the running gait. Patients with a hamstring strain usually show a shortened walking gait. Swelling and ecchymosis aren’t always detectable at the initial stage of the injury because they often appear several days after the initial injury <span class="fck_mw_ref" _fck_mw_customtag="true" _fck_mw_tagname="ref" name="Frontera et al." />. The physical examination also exists of visible examination. The posterior thigh is inspected for asymmetry, swelling, ecchymosis and deformity. When there is a palpable defect, it indicates a more severe injury, mostly with a full rupture of the muscle. Also the active and passive range of motion should be tested and compared with the other leg.

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Clinical tests

1. Puranen-Orava test – Actively stretching the hamstring muscles in standing position with hip flexed at about 90*, the knee fully extended and foot on a solid surface. Positive – exacerbation of symptoms. (SN 0.76, SP 0.82, +LR 4.2, -LR 0.29)

2. Bent-Knee stretch test (SN 0.84, SP 0.87, +LR 6.5, -LR 0.18)

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3. Modified Bent-knee stretch test (SN 0.89 SP 0.91, +LR 9.9, -LR 0.12)
4. Taking off the shoe test/hamstring-drag test (SN 1.00, SP 1.00, +LR 280.0, -LR 0.00)
5. Active ROM test (SN 0.55, SP 1.00, +LR 154.6, -LR 0.50)
6. Passive ROM test (SN 0.57, SP 1.00, +LR 160.6, -LR 0.43)
7. Resisted ROM test (SN 0.61, SP 1.00, +LR 170.6, -LR 0.40)

Tests Summery

Test	Sensitivity	Specificity	+LR	-LR
Puranen-Orava	0.76	0.82	4.2	0.29
Bent-Knee stretch	0.84	0.87	6.5	0.18
Modified Bent-knee stretch	0.89	0.91	9.9	0.12
Taking off the shoe	1.00	1.00	280	0.00
Active ROM	0.55	1.00	154.6	0.50
Passive ROM	0.57	1.00	160.6	0.43
Resisted ROM	0.61	1.00	170.6	0.40

Medical Management

Surgical intervention is an extremely rare procedure after a hamstring strain. Only in case of a complete rupture of the hamstrings, surgery is recommended. Almost all patients believed that they had improved with surgery. A study  shows that 91% was satisfied after surgery and rated their happiness with 75% or better. Hamstrings endurance tests and hamstring strength tests were better and highly scored after an surgical procedure. The muscle strength testing after surgery ranged from 45% until 88%. The hamstrings endurance testing ranged from 26% to 100% .The physical examination and follow-up reveals that all repairs stayed intact.

Physical Therapy Management

The primary objective of physical therapy and the rehabilitation program is to restore the patient’s functions to the highest possible degree and/or to return the athlete to sport at the former level of performance and this with minimal risk of reinjury.

Rehabilitation programs are mostly based on the tissue’s theoretical healing response. More information: <a href="Healing">Healing</a>

Taping may be effective, as well as dry needling/imtramuscular stimulation (IMS).

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Rehabilitation protocol

Phase I (week 0-3)

• Goals

1. Protect healing tissue
2. Minimize atrophy and strength loss
3. Prevent motion loss

• Protection

1. Avoid excessive active or passive lengthening of hamstring
2. Avoid antalgic gait pattern

• Rehab

1. Ice – 2-3 times daily
2. Stationary bike
3. Sub maximal isometric at 90, 60 and 30
4. Single leg balance
5. Balance board
6. Soft tissue mobs/IASTM
7. Pulsed ultrasound (Duty cycle 50%, 1 MHz, 1.2 W/cm2)
8. Progressive hip strengthening
9. Painfree isotonic knee flexion
10. Active sciatic nerve flossing
11. Conventional TENS

• Criteria for progession to next phase

1. Normal walking stride without pain
2. Pain-free isometric contracton against submaximal (50%-75%) resistance during prone knee flexion at 90.

Phase 2 (week 3-12)

• Goals

1. Regain pain-free hamstring strength, progressing through full ROM
2. Develop neuromuscular control of trunk and pelvis with progressive increase in movement and speed preparing for functional movements

• Protection

1. Avoid end-range lengthening of hamstring if painful

• Rehab

1. Ice – post exercise
2. Stationary bike
3. Treadmill at moderate to high intensity pain-free speed and stride
4. Isokinetic eccentrics in non-lengthened state
5. Single limb balance windmill touches without weight
6. Single leg stance with perturbations
7. Supine hamstring curls on theraball
8. STM/IASTM
9. Nordic hamstring Ex
10. Shuttle jumps
11. Prone leg drops
12. Lateral and retro bandwalks
13. Sciatic nerve tensioning

• Eccentric protocol

1. Once non-weight bearing exercises are tolerated start low-velocity eccentric activities such as stiff leg dead lifts, eccentric hamstring lowers/Nordic hamstring Ex, and split squats

• Criteria for progression

1. Full strength 5/5 without pain during prone knee flexion at 90
2. Pain-free forward and backward, jog, moderate intensity
3. Strength deficit less than 20% compared against uninjured limb
4. Pain free max eccentric in a non-lengthened state

Phase 3 (week 12+)

• Goals

1. Symptom free during all activities
2. Normal concentric and eccentric strength through full ROM and speed
3. Improve neuromuscular control of trunk and pelvis
4. Integrate postural control into sport-specific movements

• Protection

1. Train within symptoms free intensity

• Rehab

1. Ice – Post exercise – as needed
2. Treadmill moderate to high intensity as tolerated
3. Isokinetic eccentric training at end ROM (in hyperflexion)
4. STM/IASTM
5. Plyometric jump training
6. 5-10 yard accelerations/decelarations
7. Single-limb balance windmill touches with weight on unstable surface
8. Sport-specific drills that incorporate postural control and progressive speed

• Eccentric protocol

1. Include higher velocity eccentric Ex that include plyometric and sports specific activities
2. Examples include squat jumps, split jumps, bounding and depth jumps
3. Single leg bounding, backward skips, lateral hops, lateral bounding and zigzag hops and bounding
4. Plyometric box jumps, eccentric backward steps, eccentric lunge drops, eccentric forward pulls, single and double leg deadlifts, and split stance deadlift (good morning Ex)

• Return to sport criteria

1. Full strength without pain in the lengthened state testing position
2. Bilateral symmetry in knee flexion angle of peak torque
3. Full ROM without pain
4. Replication of sport specific movements at competition speed without symptoms.
5. Isokinetic strength testing should be performed under both concentric and eccentric action conditions. Less than a 5% bilateral deficit should exist in the ratio of eccentric hamstring strength (30d/s) to concentric quadriceps strength (240d/s).
   

Resources

• <a href="https://www.youtube.com/channel/UCjSI7l2zSkZCpEod8qQY5Tg">KT Tape YouTube Channel</a>
  

Recent Related Research (from <a href="http://www.ncbi.nlm.nih.gov/pubmed/">Pubmed</a>)

http://www.ncbi.nlm.nih.gov/entrez/eutils/erss.cgi?rss_guid=1pwP1t1nr4XhjCZxQim64K0Sb4uq4Evw0ahSWz06Y95ZCyYMOk%7Ccharset=UTF-8%7Cshort%7Cmax=10

References

<span class="fck_mw_references" _fck_mw_customtag="true" _fck_mw_tagname="references" />

<a _fcknotitle="true" href="Category:Injury">Injury</a> <a _fcknotitle="true" href="Category:Sports_Injuries">Sports_Injuries</a> <a _fcknotitle="true" href="Category:Thigh">Thigh</a> <a _fcknotitle="true" href="Category:Thigh_Injuries">Thigh_Injuries</a> <a _fcknotitle="true" href="Category:Musculoskeletal/Orthopaedics">Musculoskeletal/Orthopaedics</a> <a _fcknotitle="true" href="Category:Vrije_Universiteit_Brussel_Project">Vrije_Universiteit_Brussel_Project</a>