The APTA recently released the clinical practice guideline “Hamstring Strain Injury in Athletes”[1] in JOSPT. This, as with all of the APTA’s CPGs, is a great source and summary of the current recommendations and evidence surrounding hamstring strain injuries (HSI). This CPG is open access through JOSPT.org and I highly recommend you look into this one and others that the APTA has released.
I read the article to freshen up on these injuries and wanted to share my thoughts on the current state of evidence, as well as how I’ll look to implement the recommendations through a rehabilitative framework.
In this post I’ll detail a bit of basic information and characteristics on HSIs and summarize the chief goals and considerations of the examination. In subsequent posts I’ll detail the continuum of care and associated interventions with HSIs.
The Nature of Hamstring Strain Injuries:
In thinking about the hamstring muscle group the main word that comes to mind is “elastic.” Additionally, when thinking of strain injuries I believe it’s easiest to think of these as “stretch injuries.” With that said, considering the volume of rapid stretch shortening cycles the hamstrings undergo during sporting activities like sprinting, jumping, and kicking the common mechanism of injury for this muscle group is clear. As detailed in the CPG, HSIs are most commonly seen in sports like “track and field, soccer, Australian rules football, American football, and rugby.” [1] There is also evidence that these injuries are increasing in incidence since the early 2000s.[2] Without quoting all of the statistics associated with incidence, prevalence, and injury rates, it is clear that these are common injuries you can expect to see in your outpatient orthopedic/sports physical therapy setting.
These injuries are also responsible for significant time lost due to injury “generally ranging from 3 to 28 days depending on injury severity.”[1] The CPG also notes that re-injury rates are high ranging from 13.9% to 63.3%.[1] These two stats summarize the importance of managing these injuries appropriately to avoid excessive strain on the healthcare system and to improve patient outcomes.
Healing timeline is variable and dependent on the degree of injury. This highlights the importance of identifying the degree of injury in your examination to assist in providing guidance on patient prognosis (more on this later). See the chart below for a rough guideline of tissue healing timelines which may help decision making.
When considering the healing process it is important to recall the phases of healing. The inflammatory phase is typically <7-10 days and is characterized by pain, localized swelling, and limited function. The proliferative phase generally lasts between 2-3 weeks and is characterized by the initial processes of “rebuilding” damaged tissue. During this phase function gradually returns although pain may still be evident. The final stage is titled the remodeling phase. During the final stage the newly built tissues accommodate and respond to applied stress and mature. Appreciate that these phases occur on a continuum and modify future treatments accordingly with consideration for the degree of injury.[3]
Examining Hamstring Strain Injuries:
The goals of the evaluative process and examination include: establish the severity of injury, determine the need for referral, rule out red flags, determine current activity limitations, establish current status relative to several KPIs, and to initiate a plan of care.
In gathering a subjective history, your suspicion for a HSI should peak when the athlete reports a sudden sharp pain in the posterior thigh during activity. This may commonly be associated with a pop. Suspect a hamstring injury when the patient participates in a field or sprinting based sport, and has a history significant for prior hamstring injury.[1]
In those patients without these findings, care should be taken to perform a comprehensive exam that looks to rule in or out the following differential diagnoses:[1]
- Lumbar radiculopathy
- SI dysfunction
- Deep gluteal syndrome with nerve entrapment
- Ischial tunnel syndrome
- Adductor muscle strain
- Contusion
- Compartment syndrome
- Thrombosis
Other findings that may require referral include point tenderness over the ischial tuberosity, fibular head, or other bony landmarks. Clinicians should also consider the possibility of tendinous injury as part of their differential diagnosis profile when symptoms occur closer to the origin or insertion of the muscle.[1]
As mentioned above, the goal of this post is to highlight several key performance indicators that will serve to guide progress in care. These may be performed at initial examination as symptoms allow. The following tests provide insight into pain-free muscle length, muscle strength and performance (in multiple positions), area of injury, prognosis, and current functional status.
Active Knee Extension Test:
The Active Knee Extension Test is performed by having the subject positioned in supine, the involved hip flexed to 90o. Have the subject extend their knee slowly until they are limited by pain or tightness in the posterior thigh. Measure the angle of the knee and record the finding. Grade I injuries are characterized by having <15o of extension lacking. Grade II injuries are characterized by 16o to 25o of extension lacking. Grade III injuries are characterized by lacking 26o to 35o of knee extension.[4]
It is recommended that those athletes exhibiting findings associated with a grade III injury be referred for further examination.[1] Not only does this test provide immediate feedback as to injury severity and prognosis, but it is an easily replicable test that can be measured throughout a plan of care.
| Degrees of Knee Extension Lacking | Average Days of Rehabilitation Required | |
| Grade I | <15 degrees lacking | 25.9 days of rehabilitation on average |
| Grade II | 16-25 degrees lacking | 30.7 days of rehabilitation on average |
| Grade III | 26-35 degrees lacking | 75 days of rehabilitation on average |
Muscle Strength and Performance:
The CPG recommends that clinicians quantify hamstring muscle strength as part of the examination at a grade of “A.” Specifically, they mention using the gold standard of isokinetic testing and hand held dynamometry.[1] Let’s appreciate that not all clinics have access to this equipment, so we must look to identify other viable options for examining muscle strength and performance.
When looking to test the strength of the hamstring, we must appreciate that the hamstring is a two-joint muscle performing the actions of extension at the hip and flexion at the knee. This means we must test muscle performance in two positions to account for these actions. In an effort to standardize these measures we will measure muscle performance in prone with 150 knee flexion (termed the mid-range)[5], and in supine with the hip flexed to 90o and the knee fully extended (outer range).[6]
In our clinic at Rehab 2 Perform, we utilize the Tindeq device to quantify strength. If a dynamometer or Tindeq device is not available to you, you should at least perform manual resistance in these positions to establish muscle performance. Using manual resistance allows you to establish whether the muscle is “strong and painful/pain-free,” or “weak and painful/pain-free.” Using this classification system you may add credence to your exam finding with the AKE exam and continue to establish the severity of injury. This also provides meaningful information as to what sorts of therapeutic exercises may be appropriate as part of the initial home program.
Isometric testing tells us only part of the story, however. Should a patient test strong and relatively pain-free with isometric testing, I suggest clinicians also examine hamstring muscle endurance and tissue tolerance using the single leg elevated hamstring bridge endurance test.[7] The results of this study demonstrate that limited performance on the single leg bridge may be indicative of increased risk of future hamstring strain injury. This gives us meaningful information as to how the hamstring tolerates repeated loads and whether it is prepared for more intense activity. Additionally, it provides a benchmark to guide criterion-based decision making in return to play situations.
Area of Tenderness:
The CPG suggests clinicians “map” the area of tenderness and note the point of maximal tenderness along the hamstrings at a grade of “C.” There is low grade evidence (level II B) that suggests those injuries with longer areas of tenderness relative to the length of the hamstring muscle to be predictive of greater time to RTS.[8] Again, this provides a nice metric to track progress in terms of symptom irritability and sensitivity early in care.
Establishing Current Functional Status:
Level II evidence provided by Hickey et al suggests the utilization of an activity progression of pain-free walking, pain-free normal jogging, running linearly at 70% maximum perceived speed, pain-free change of direction, and pain-free 100% linear running.[9] Depending on the preceding examination findings, I feel it appropriate to perform this progression to establish which activities may be permitted both in and out of the clinic as part of the plan of care utilizing progressive exercise-based activity.
Conclusion:
The purpose of the examination is to identify key limitations and low hanging fruits to help initiate a plan of care. Testing should consist of easily replicated measures that may guide progress, confirm/disconfirm your hypothesis, and be specific to the suspected condition to guide initial interventions. The AKE test, muscle performance testing, mapping of tenderness, and completion of progressively intense activities within the examination as appropriate accomplish these goals.
In coming posts I’ll outline interventions for the early, mid-, and late phases of hamstring strain injuries. Throughout these posts I’ll include information regarding hamstring strain injury risk mitigation upon return to sport for the rehabilitative and strength and conditioning professional.
Citations:
[1] Martin, R. L., Cibulka, M. T., Bolgla, L. A., Koc, T. A., Loudon, J. K., Manske, R. C., Weiss, L., Christoforetti, J. J., & Heiderscheit, B. C. (2022). Hamstring strain injury in athletes. Journal of Orthopaedic & Sports Physical Therapy, 52(3). https://doi.org/10.2519/jospt.2022.0301
[2] Ekstrand J, Waldén M, Hägglund M. Hamstring injuries have increased by 4% annually in men’s professional football, since 2001: a 13-year longitudinal analysis of the UEFA Elite Club injury study. Br J Sports Med. 2016;50:731-737. https://doi.org/10.1136/bjsports-2015-095359
[3] Laumonier T, Menetrey J. Muscle injuries and strategies for improving their repair. J Exp Orthop. 2016;3:15. https://doi.org/10.1186/ s40634-016-0051-7
[4] Smirnova L, Derinov A, GlazkovaI. Hamstring structural injury in futsal players: the effect of active range of motion (AROM) deficit on rehabilitation period. Muscles Ligaments Tendons J. 2020;10:645-650. https://doi. org/10.32098/mltj.04.2020.12
[5] Reurink G, Goudswaard GJ, Moen MH, Tol JL, Verhaar JA, Weir A. Strength measurements in acute hamstring injuries: intertester reliability and prognostic value of handheld dynamometry. J Orthop Sports Phys Ther. 2016;46:689-696. https://doi.org/10.2519/jospt.2016.6363
[6] Whiteley R, van Dyk N, Wangensteen A, Hansen C. Clinical implications from daily physiotherapy examination of 131 acute hamstring injuries and their association with running speed and rehabilitation progres- sion. Br J Sports Med. 2018;52:303-310.
[7] Freckleton G, Cook J, Pizzari T. The predictive validity of a single leg bridge test for hamstring injuries in Australian Rules Football players. Br J Sports Med. 2014;48:713-717. https://doi.org/10.1136/bjsports-2013-092356
[8] Schmitt BM, Tyler TF, Kwiecien SY, Fox MB, McHugh MP. Mapping tenderness to palpation predicts return to play following acute hamstring strain. Int J Sports Phys Ther. 2020;15:421-428.
[9] Hickey JT, Timmins RG, Maniar N, Williams MD, Opar DA. Criteria for progressing rehabilitation and determining return-to-play clearance following hamstring strain injury: a systematic review. Sports Med. 2017;47:1375- 1387. https://doi.org/10.1007/s40279-016-0667-x
