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Predisposition to hamstring injury cannot be determined!

Topic for Summary and Critique - by Joanna Kelton

Statement of the Topic
Introduction
Literature Review
Conclusion
References
Short Answer Review Questions

Statement of the Topic

Introduction

Hamstring injury is a prevalent injury in sports involving jumping, running or a combination of both. It is the most common injury in Australian Football, and furthermore, recurs at an unacceptable rate of 35% (Orchard et al 1997). Hamstring muscle strain accounts for 16% of all playing time missed in elite Australian football (Orchard et al 1997) and for 14.2% of all track and field injuries (Bennell and Crossley 1996). With the increasingly professional nature of sport and the subsequent high cost of injury, it is paramount to identify potential risk factors and prevent potential injuries wherever possible. It has long been postulated that early identification of risk factors and subsequently, at risk players, may reduce the incidence of hamstring injury and the concomitant loss of increasingly more valuable playing time. This paper will review the hamstring anatomy and function, as well as the common mechanism of injury to the hamstring muscle group. Possible injury aetiology will be identified, and current literature regarding the risk factors of hamstring strain will be examined.

Anatomy

The hamstring muscle group is located in the posterior thigh. It is comprised of three distinct muscles. The biceps femoris is situated on the lateral aspect of the posterior thigh. Its long head arises from the ischial tuberosity and joins with the short head from the linea aspera to insert as a common tendon onto the head of the fibula. Medially, the semitendinosis and the semimembranosus arise from the ischial tuberosity of the innominate bone and insert on to the posterior and medial aspects of the tibia (Snell 1986). The muscle is diarthroidal, crossing and hence affecting both the hip and the knee joints. Its primary actions are to extend the hip and to flex the knee. The biceps femoris also externally rotates the tibia and the medial semimembranosus and semitendinosus internally rotate the tibia. When the muscles act together, the resultant action is stabilisation of the tibia. This occurs during the stance phase of the gait cycle (Sanders and Nemeth 1996, Snell 1986). The hamstring is primarily comprised of type II fast twitch muscle fibres (Sanders and Nemeth 1996).

Hamstring Function

According to Stanton and Purdam (1989) and Worrell et al (1992), the hamstrings are most active in the terminal phase of swing and the initial phase of stance during the gait cycle. During the swing phase, the hamstrings act eccentrically to decelerate the thigh and the lower leg. This action prepares the limb to support the weight of the body at the point of ground contact. During this eccentric muscle action, the hamstrings effectively absorb energy, which is stored as elastic potential energy and utilised to maximise the concentric muscle action that immediately follows. This is an example of the stretch shorten cycle (Stanton and Purdam 1989). Wood et al (1984) measured the peak torques during this phase at 150Nm at the knee and 250 Nm at the hip.

At the point of ground contact, the hamstring is lengthened over the hip and the knee. The muscle action changes to concentric to assist the gluteal muscles with hip extension and to stabilise the knee and prevent further knee extension. The hamstrings are cocontracting with the gluteals and the quadriceps (Stanton and Purdam 1989). It has been postulated that the hamstrings are susceptible to injury at this point in the cycle if there is a muscle imbalance within any of the aforementioned muscles (Knapik et al 1992, Jonhagen et al 1992). The peak torques at this point have been recorded at 160 Nm at the knee and 300Nm at the hip. This is significantly higher than during the swing phase. Orchard et al (1997) mention anecdotal evidence that most hamstring strains occur at this point within the gait cycle.

Muscle Injury

Muscle strain will occur at a point of increased tension in the muscle as denoted by the stress strain curve (Malone et al 1996). This may be an active increase in tension from overcontraction of the muscle, or a passive increase from overstretch. The increase in the muscle force correlates with an increased tension within the series elastic component of the muscle (Sanders and Nemeth 1996). Pathological forces may increase the tension too much and result in muscle strain.

Untrained or weak hamstring muscles may predispose the athlete to injury, as the muscle is less able to withstand potentially injurious forces. The muscle has a decreased capacity to generate active tension, and therefore may be subject to strain with lesser stress or loads (Bennell et al 1998, Jonhagen et al 1994, Orchard et al 1997).

Aetiology

Sanders and Nemeth (1996) describe a muscle strain as an indirect injury from increased force or stress on the muscle. They postulate that this may be from powerful contraction or forced lengthening of the muscle. These injuries are reported to be more common in diarthroidal muscles as they must lengthen over two joints resulting in increased passive tension. The hamstring muscle group crosses both the hip and the knee and is lengthened over both joints at the point of ground contact in the swing phase of the gait cycle.

Further to this, muscle strains are more common in muscles that function eccentrically as there is an increase in the active tension within the muscle. During the swing phase, the hamstring muscle action is eccentric. This type of muscle action is involved with energy absorption. The energy is stored as elastic potential energy and utilised during the concentric muscle action to augment the force generated by the muscle (Sanders and Nemeth 1996). An eccentric muscle action has higher force than a concentric muscle action. The force within the muscle is dependent on the velocity of the contraction according to the force velocity relationship. As the velocity of muscle action increases, then so does the difference in the maximum tension between eccentric and concentric work. As the speed of the sprint increases, the time of foot contact decreases. As this time decreases, then the speed of the hamstring muscle action must increase (Stanton and Purdam 1989). According to the force - velocity relationship, the force within the muscle must also increase. Therefore an increased speed of sprinting may predispose the athlete for injury. This theory is supported by Jonhagen et al (1994) who found that faster sprinters were more likely to sustain an injury to the hamstring muscle group.

Sanders and Nemeth (1996) also proposed that muscles which contain a higher proportion of type two muscle fibres are more susceptible to strain injury as they have a capacity to act at an increased rate, hence generate more force according to the force - velocity relationship.

Predisposition to injury has been suggested in a population that is unable to withstand the demands of passive or active tension. Therefore it has been postulated that predisposition to hamstring injury may be determined by testing the strength and flexibility of the athlete (Bennell and Crossley 1996, Bennell et al 1998, Heiser et al 1984, Hennessy and Watson 1993, Jonhagen et al 1994, Orchard et al 1997, Worrell et al 1991).

Worrell (1994) suggested that a complex interaction between several factors would increase the likelihood of hamstring injury. These factors included hamstring muscle strength, and strength imbalances between the hamstrings and quadriceps, hamstring flexibility, warm up and fatigue. He postulated that an athlete exposed to a combination of these factors was more susceptible to hamstring muscle strain than an athlete with a single risk factor.

Literature Review

Hamstring Flexibility

Many authors have proposed that an insufficient hamstring length may predispose an athlete to injury as the hamstring is unable to successfully withstand the increased passive tension as it lengthens (Hennessy and Watson 1993, Jonhagen et al 1994, Knapik et al 1992, Orchard et al 1997, Worrell et al 1991). Knapik et al (1992) describe flexibility as the amount of movement at a joint through its normal range of movement. Hamstring flexibility and its relationship to hamstring strain has been investigated by several authors. One prospective investigation has been carried out by Orchard et al (1997). They examined flexibility as tested by the sit and reach test on 37 elite level Australian Footballers. No significant interaction was found between the sit and reach measure and the hamstring muscle injury.

Several authors have retrospectively examined athletes with and without a history of hamstring strain and various methods of flexibility testing. Although the retrospective studies cannot differentiate between a condition that exists pre and post injury they may be useful to examine in relation to the high rate of recurrence of injury. Jonhagen et al (1994) and Hennessy and Watson (1993) used a straight leg raise (SLR) test to measure hamstring flexibility. Jonhagen et al (1994) found a significant difference between the injured and uninjured athletes and the injured and uninjured limbs of the athletes as measured by the SLR. This is contrast to the results of Hennessy and Watson (1993) who found no significant difference within or between groups. Worrell et al (1991) investigated hamstring flexibility using a passive knee extension test and found a significant loss of hamstring flexibility in the affected limb of the injured athletes.

The measures utilised to detect a loss of flexibility have differed between the studies. The sit and reach test does not differentiate between loss of hamstring and loss of lumbar spine mobility. The SLR may implicate neural structures. Both the lumbar spine and the neural tissue may contribute to hamstring injury or mimic the symptoms of hamstring injury (Worrell 1994). The investigations reveal varied results and are collectively unable to measure or quantify any deficit relating to predisposition to hamstring injury.

Hamstring Strength

Sapega (1990) has defined strength as the capacity of a muscle for the active development of tension. Alternatively, Knapik et al (1992) define strength as the maximum force or torque exerted by a muscle group in a single voluntary contraction. Testing of muscle strength is a measure of the capacity of a muscle to develop maximal voluntary tension (Sapega 1990). Isokinetic dynamometry has been utilised in all tests of hamstring strength in relation to hamstring injury. Sapega (1990) suggests that the use of such dynamometers is beneficial as they are intrinsically accurate and possess good to excellent test retest reliability. Pincivero et al (1997) demonstrated reliability and precision of isokinetic quadriceps and hamstring muscle testing using a Biodex System 2 dynamometer. Isokinetic dynamometry also results in quantifiable data for measures of torque that may be useful in determining exact measures of predisposition for injury.

Orchard et al (1997) performed a prospective study of elite Australian Footballers using a Cybex 340 dynamometer. Preseason measures of peak torque for the quadriceps and hamstrings were taken and analysed in relation to the incidence of hamstring injury during the season. 16% of the players sustained an injury to the hamstring muscles. A significant association was found between the injured hamstring and the opposite leg in absolute values and a quadriceps and hamstrings ratio. Orchard et al (1997) concluded that they were able to identify at risk players for hamstring injury and potentially reduce the incidence of injury by strengthening the muscle group.

Conversely, Bennell et al (1998) were unable to identify players at risk of injury in a similar study. They investigated 102 senior Australian Footballers playing across a broad range of competitive levels. Quadriceps and hamstrings were tested preseason using a KIN/COM dynamometer. Twelve of the participants in the investigation injured a hamstring during the season (12%). No significant difference could be identified within or between the uninjured and injured groups. Bennell et al (1998) concluded that it was not possible to directly discriminate Australian Footballers at risk of a hamstring injury.

Knapik and colleagues (1991) who investigated 158 female college athletes using a Cybex dynamometer have performed a further prospective study. Only one hamstring strain was suffered during the span of the investigation. No significant difference was identified in the peak torque measurement of the injured athlete and the remainder of the cohort.

Several retrospective analyses regarding the relationship between hamstring strength and injury have also been performed. Jonhagen et al (1994) investigated strength of 40 sprinters using a KIN/COM dynamometer. The results showed an increase in peak torque generated by members in the uninjured group. Conversely, Worrell et al (1991) was unable to detect a significant difference between or within injured and uninjured groups in peak torque measurements from KIN/COM testing. The conflicting results in the retrospective analyses further confuse the issue of predisposition to hamstring injury.

There exists controversy in the results of the investigations of the relationship between hamstring strength and the likelihood of hamstring strain. The results of Orchard et al (1997) and Jonhagen et al (1994) support the direct relationship between decreased hamstring strength and hamstring strain. Conversely, evidence from the investigations by Bennell et al (1998), Knapik et al (1991) and Worrell et al (1991) refute any directly quantifiable relationship between strength of the hamstrings and predisposition to hamstring muscle injury.

The inconsistencies in the results would indicate that there is currently insufficient evidence to suggest that a predisposition to hamstring injury can be identified in all population by preseason testing of isokinetic muscle strength. However, in the specific population of elite Australian Footballers, there is evidence to suggest that predisposition to injury of the hamstring muscle may be determined preseason by assessment of the quadriceps and hamstrings peak torques (Orchard et al 1997).

Orchard et al (1997) tested elite professional footballers. As previously discussed, faster sprinters may be more susceptible for injury as they are able to generate higher forces during the shortened stance phase of gait. The elite level players sustained a higher percentage of hamstring injuries than the senior players tested by Bennell et al (1998). The senior players may be more influenced than the elite players by other potential risk factors identified by Worrell (1994) such as fatigue, warm up and flexibility. Worrell (1994) suggested a multifactorial aetiology for hamstring injuries. Different population groups may be more or less influenced by varying degrees of the different aspects of the possible aetiologies. Orchard et al (1997) investigated a single population group who played the season of football together and were involved in similar training and warm up procedures. Further to this, the elite players may be less influenced by fatigue or inefficient warm up and more influenced by poor muscle strength or muscle imbalance between the quadriceps and the hamstrings. Conversely, the nonelite players investigated by Bennell et al (1998) may be more variable in the type and duration of warm up, as well as the type of in season training and fitness regimes. It may be pertinent to attempt to stratify competitors into level of competition and type of competition before attempting to identify predisposition to hamstring muscle injury.

Conclusion

In order to correctly predict predisposition to hamstring muscle injury, the risk factors must be correctly identified. Worrell (1994) suggested a complex multifactorial aetiology for hamstring injury involving not single factors, but the interplay of various factors. Results of investigations into the relationship between hamstring flexibility and hamstring strength and predisposition to hamstring injury to date have been conflicting. However, some significant relationships have been identified between preseason isokinetic strength assessment and predisposition to hamstring injury in the specific population group of a single team of Australian Footballers. Currently there is insufficient evidence to suggest that it is possible to predetermine susceptibility to hamstring injury in a broad range of athletes at various levels of participation. However it may be possible to determine predisposition to injury in specific stratified populations and by considering the possibility of a multifactorial aetiology.

References

Bennell KL and Crossley K (1996): Musculoskeletal injuries in track and field: Incidence, distribution and risk factors. Australian Journal of Science and Medicine in Sport 28:69-75.
Bennell KL, Wajswelner H, Lew P, Schall-Riacour A, Leslie S, Plant D and Cirone J (1998): Isokinetic strength testing does not predict hamstring injury in Australian rules footballers. British Journal of Sports Medicine 32:309-314.
Heiser TM, Weber J, Sullivan G, Clare P and Jacobs RR (1984): Prophylaxis and management of hamstring muscle injuries in intercollegiate football players. American Journal of Sports Medicine 12:368-370.
Hennessy L and Watson WS (1993): Flexibility and posture assessment in relation to hamstring injury. British Journal of Sports Medicine 27:243-246.
Jonhagen S, Nemeth G and Eriksson E (1994): Hamstring injuries in sprinters.The role of concentric and eccentric hamstring muscle strength and flexibility. American Journal of Sports Medicine 22:262-266.
Knapik JJ, Jones BH, Bauman CL and Harris JmcA (1992): Strength, flexibility and athletic injuries. Sports Medicine14:277-282.
Knapik JJ, Bauman CL, Jones BH, Harris JmcA and Vaughan L (1991): Preseason strength and flexibility imbalances associated with athletic injuries in female collegiate athletes. American Journal of Sports Medicine 19:76-80.
Krivickas LS and Feinberg JH (1996): Lower extremity injuries in college athletes: Relation between ligamentous laxity and lower extremity muscle tightness. Archives of Physical Medicine and Rehabilitation 77:1139-1143.
Malone TR, Garrett WE and Zachazewski JE (1996): Muscle: Deformation, injury and repair. In Zachazewski JE, Magee DJ and Quillen WS (eds) Athletic Injuries and Rehabilitation. Philadelphia: WB Saunders co., pp. 599-622.
Orchard J, Marsden J, Lord S and Garlick D (1997): Preseason hamstring muscle weakness associated with hamstring muscle injury in Australain footballers. American Journal of Sports Medicine 25:81-85.
Pincivero DM, Lephart SM and Karunakara RA (1997): Reliability and precision of isokinetic strength and muscular endurance for the quadriceps and hamstrings. International Journal of Sports Medicine 18:113-117.
Sapega AA ( 1990): Muscle performance evaluation in orthopaedic practice. Journal of Bone and Joint Surgery 72A:1562-1574.
Sanders B and Nemeth WC (1996): Hip and Thigh Injuries.In In Zachazewski JE, Magee DJ and Quillen WS (Eds): Athletic Injuries and Rehabilitation. Philadelphia: WB Saunders co., pp. 71-91.
Snell RS (1986): Clinical Anatomy for Medical Students.(3rd ed.) Boston: Little, Brown and Company.
Stanton P and Purdam C (1989): Hamstring injuries in sprinting the role of eccentric exercise. Journal of Orthopedic and Sports Physical Therapy 10:343-349.
Wilson GJ, Wood GA and Elliot BC (1991): The relationship between stiffness of the musculature and static flexibility: An alternative explanation for the occurence of muscular injury. International Journal of Sports Medicine 12:403-407.
Worrell TW (1994): Factors associated with hamstring injuries. Sports Medicine 17:338-345.
Worrell TW and Perrin DH (1992): Hamstring muscle injury: The influence of strength, warm-up and fatigue. Journal of Orthopedic and Sports Physical Therapy 16:12-18.
Worrell TW, Perrin DH, Gansneder BM and Gieck JH (1991): Comparison of isokinetic strength and flexibility measures between hamstring injured and non-injured athletes. Journal of Orthopedic and Sports Physical Therapy 13:118-125.

Short Answer Review Questions

In which phases of the gait cycle are the hamstrings most active?
Explain muscle strain using the stress - strain relationship?
Explain hamstring muscle injury during its change from eccentric to concentric action using a force - velocity relationship?
Why might faster sprinters be more susceptible to hamstring strain?
How might hamstring flexibility contribute to injury.
Describe two possible means of assessing hamstring flexibility.
How might hamstring strength be assessed? Outline potential benefits of the chosen method.
Describe how poor hamstring strength might predispose an athlete to injury?
Outline potential differences in predisposition for injury between professional and amateur athletes.
Would you recommend preseason strength and flexibility testing for athletes? Are there any other tests that you would utilise?
What muscles might compensate for hamstring muscle weakness? Do you think that this may contribute to the variability of results found by the different studies? Is there a method of testing for this potential confounding variable?