Patterns of Hamstring Muscle Tears in the General Population: A Systematic Review

Introduction

Hamstring tears are commonly reported in professional sports players.[1–3] In contrast, the prevalence of hamstring tears in recreational-sporting and non-sporting situations is poorly defined. This lack of data is especially true for older individuals, who are known amongst clinicians to present to general practice and orthopaedic clinics with hamstring tears, yet their prevalence is unknown. Patients suffering a hamstring tear due to sport are mainly in the second and third decade of life.[4, 5] In contrast, the age range of patients with non-sporting or recreational injuries is much greater with hamstring tears reported in patients aged 60 years and over.[1, 6, 7]

A muscle strain is an anatomical and functional disruption of the muscle-tendon unit.[8] Severity of injury is based on the extent of tissue damage, inflammatory response and loss of function. The most common classification system defines a grade 1 injury as no appreciable tissue disruption, mild pain and swelling and no or minimal loss of function, Grade 2 injuries as an identifiable partial disruption of the tissue with moderate pain and swelling thereby leading to loss of function, and grade 3 as complete disruption or tear of the musculotendonous unit with severe pain and swelling and lack of function.[9]

Reports describing hamstring injury diagnosis and management highlight considerable time differences from injury to presentation from several hours to many years.[1, 10] Typical findings on examination include localised tenderness, swelling and a palpable defect. This marked heterogeneity in presenting signs and symptoms along with the sometimes insidious development may lead to delayed presentation and late diagnosis. Diagnosis is aided by imaging, either by plain X-ray to detect bony avulsion fractures or with MRI and ultrasound, which can detail the extent of the injury.[11–14]

Despite their high prevalence, there is a remarkable lack of consensus on hamstring injury management. Recent systematic reviews by Ropiak et al and Ahmad et al suggest that Grade 1 and Grade 2 injuries are typically treated non-operatively.[11, 15] This may encompass rest, ice, compression and progressive mobilization as well as the use of analgesia and non-steroidal anti-inflammatories. The outcome of these partial tears is considered to be varied and unpredictable. Grade 3 injuries and those presenting following failed conservative treatment are often repaired surgically. Good functional outcomes have been reported with operative repair.[1, 16, 17] Correct identification and treatment of suspected hamstring injuries is therefore of high importance.

The aim of this study was to determine the incidence of the injury in both professional and recreational sports people as well as in the remainder of the population, who do not play sport. In particular, our aim was to identify any differences in the type of injury between these groups.

Methods

Results

The mean age of patients across the study population was 31.1 (95% CI 30.1–32.3). Patient age ranged from 9 to 73 years. The majority (72.2%) of hamstring injuries reported were observed in patients in their 20s and 30s (Fig 2). Most injuries were reported in males (81.3%). Mean age at injury in males was lower (30.2, 95% CI 29.1–31.324) than in females (35.4, 95% CI 32.4–38.4) with this difference approaching significance (Students t-test, p = 0.06).

Discussion

Hamstring tears typically occur during rapid acceleration/deceleration involving sudden forced hip flexion concomitant with knee extension, and are well documented to occur as a result of sporting activities. [1, 16] Many studies have assessed the incidence, risk factors and severity of hamstring injuries in professional athletes, perhaps in whom there is a strong economic interest in defining the injury and expediting player return. [66, 67] Our review takes a different approach, assessing all reported hamstring injuries with defined mode of injury including those caused by non-sporting activities. By doing so the patient cohort extends across a much large range.

The principle findings of this systematic review of linked data was a population of individuals injuring their hamstrings in non-sporting situations. These ‘non-sporting injuries’ were more likely in females, in an older demographic and tended to be avulsions of the hamstring origins/insertions to the bone as opposed to tears of the muscle belly

As is typically reported, most hamstring injuries were due to sporting activities, however we highlight a proportion of injuries caused by simple low impact falls and slips; This has not been well described previously. We identified one report looking at non-athletes that described six patients where flexion of the hip with hyperextension of the knee during everyday activities such as missing a step during walking or gardening led to complete hamstring avulsions. [50]

The mean age of people sustaining a non-sporting injury was significantly greater than the age of those suffering sporting injuries. This is in keeping with the current literature, however, the heavily skewed demographic split towards females and the proportion of muscle injury/ avulsion injuries differing between sporting and non-sporting groups are new findings. It is of interest that the avulsions cluster in younger and older individuals, which is consistent witha possible association with skeletal maturity and bone mineral density (BMD). This association between BMD and avulsion/mid substance tendon tear has been previously recognized in different injury sites, namely the calcaneus/Achilles tendon and tibial tubercle/patella tendon; Wren et al demonstrated in a cadaver model that tendo-achilles avulsion injuries were related to reduced calcaneal bone density [68], a finding confirmed in osteoporotic bone and diabetic patients. [69–71] These are most commonly reported in the older patient and are typically the result of minor trauma such as accidental trips causing falls.[72] Similarly, the site where the extensor mechanism of the knee fails varies with age [73], with avulsions occurring at the tibial tubercle/inferior pole of the patella in immature patients and at the superior pole of the patella in older adults.

We suggest that the relatively small number of hamstring injuries reported in non-sporting situations may be a feature of selection bias and an under-representation of the true picture across the general population, as has been observed in other conditions [74]. This is compounded by problems with mis-diagnosis and coding. Hamstring injuries most commonly present with buttock pain, however the differential diagnosis of buttock pain is extensive and includes pathologies in the back, hip and groin. Referred pain from the lumbo-sacral spine may present as ill-defined posterior thigh or buttock pain and is a common presentation in general practice.[11, 75, 76] and may be confused with hamstring tears. In contrast, athletic and surgical cohorts are relatively well coded, in contrast coding of hamstring injuries in general practice is not well defined, again suggesting that hamstring tears in the community may be comparatively under-reported. In the sports medicine literature it is suggested that failing to diagnose a hamstring tear may lead to mismanagement, which may have a detrimental impact on outcome. Although surgical repair of chronic tears can be successful, the procedure is more complex, potentially requiring neurolysis of the sciatic nerve and the outcome is less predictable; consequently early repair is generally recommended [16, 77]. This though is in relation to athletes. The available literature does not confirm whether this same principle applies to the wider population.

Conclusion

This review highlights a largely unrecognised population of adults suffering hamstring injuries from low-impact activities. These tend to be avulsion injuries that cluster in the older female and skeletally immature patients suggesting a potential link to bone mineral density.

Supporting Information

Data Availability

All relevant data are within the data and its Supporting Information files.

Funding Statement

The authors have no support or funding to report.