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

<img src="/images/thumb/5/5b/Thigh_muscles_back.png/150px-Thigh_muscles_back.png" _fck_mw_filename="Thigh muscles back.png" _fck_mw_location="right" _fck_mw_width="150" _fck_mw_type="thumb" alt="" class="fck_mw_frame fck_mw_right" />The hamstrings are comprised of three separate muscles located at the back of the thigh. The biceps Femoris, Semitendinosus and the Semimembranosus. These muscles start at the ischial tuberosity, extending down the back of the thigh and along either side of the knee . The Biceps Femoris exists out of two parts: the long head and the short head. 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 Semitendinosus starts at the Ischial tuberosity but unlike the Biceps Femoris, it lays at the medial side of the thigh and is attached to the upper medial surface of the tibia. The Semimembranosus is the most medial of the three hamstrings muscles . It also starts at the ischial tuberosity and is attached to the Pes Anserinus profundus.

Because the Hamstrings cross two joints, there functions are varied.The muscles function as movers and stabilizers of the hip and knee. Contractions of the hamstrings causes flexion of the knee and extension of the hip. The hamstrings help to get from a crouched position to an erect position. This reffers to movements like getting up from a chair or in sprinting, where the front leg in starting position has to bear the effect of the start.    

Epidemiology /Etiology

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.<span class="fck_mw_ref" _fck_mw_customtag="true" _fck_mw_tagname="ref" name="Sutton et al." />

Muscle strains can be divided into grades, dependable of their severity. The classification of hamstrings strains can be used to estimate the convalescent period and to design a rehabilitation program. <span class="fck_mw_ref" _fck_mw_customtag="true" _fck_mw_tagname="ref" name="Petersen et al." /> More information about classification: <a href="Muscle Injuries">Muscle Injuries</a>.

The cause of a hamstring muscle strains 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 <a href="Muscle spindles">muscles spindles</a> in the hamstrings. A strong contraction of the hamstrings 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 hamstrings 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 <span class="fck_mw_ref" _fck_mw_customtag="true" _fck_mw_tagname="ref" name="Sutton et al." /><span class="fck_mw_ref" _fck_mw_customtag="true" _fck_mw_tagname="ref" name="Petersen et al." />. 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 accumalation 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.<span class="fck_mw_ref" _fck_mw_customtag="true" _fck_mw_tagname="ref" name="9" />

Characteristics/Clinical Presentation

At the instant of an injury during sport activities, patients mostly report a sudden sharp pain in the posterior thigh. Also a “popping” or tearing impression can be described. The patients may complain of tightness, weakness and impaired range of motion like knee extension with the hip in a flexed postion. Sometimes swelling and ecchymosis are possible but they may be delayed for several days after the injury occurs. Rarely symptoms are numbness, tingling and distal extremity weakness. These symptoms require a further investigation into a sciatic nerve irritation.  Large hematoma or scar tissue can be caused by complete tears and avulsion injuries.

Differential Diagnosis

On examening the patient, the physiotherapist possibly has to differentiate between: adductor strains, avulsion injury, lumbosacral reffered pain syndrome, piriformis syndrome, sacroiliac dysfunction, sciatica, Hamstring tendinitis and ischial bursitis. 

Diagnostic Procedures

The purpose of the diagnosis is to determinate the location and severity of the injury. More information about the diagnostic procedures of a hamstring strain: <a href="Muscle Injuries">Muscle injuries.</a> (Diagnostic Procedures)

Outcome Measures

• VISA-H: Victorian Institute of Sport Assessment-Proximal Hamstring
• FASH: Functional Assessment Scale for Acute Hamstring Injuries
• <a href="http://www.physio-pedia.com/Lower_Extremity_Functional_Scale_(LEFS)">LEFS: Lower Extremity Functional Scale</a>
• SFMA: Selective Functional Movement Assessment
• <a href="http://www.physio-pedia.com/Patient_Specific_Functional_Scale">PSFS: Patient Specific Functional Scale</a>
• <a href="http://www.physio-pedia.com/Visual_Analogue_Scale">VAS: Visual Analog Scale</a>
• <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>