Location, Location, Location: a Key Consideration in Hamstring Rehabilitation

LOCATION, LOCATION, LOCATION

A KEY CONSIDERATION IN HAMSTRING REHABILITATION

FEATURE / FEARGHAL KERIN

Leinster Rugby, Ireland University College Dublin, Ireland

Homogenising hamstrings

The evolution in the physical demands of football - challenging athletes to go faster and further, than ever before - continues unabated. As a result, despite all advances in technology, science, and rehabilitation, hamstring re-injury rates remain consistently high and remain a frustration to both athletes and medics charged with managing the injury quickly and safely back to the field of play. This challenge has perhaps been compounded by the post-pandemic fixture congestion over the past number of years.

UEFA injury study data have described reinjury rates of 13% in the first two months following return to play1. After such a re-injury, one of most difficult challenges is determining which component of the rehabilitation was to blame for the failure. The likes of muscle strength, neuromuscular control, or apparently pathological running mechanics are often deemed the culprit.

However, the spotlight over the past decade has shifted somewhat from the functional diagnosis to the anatomy of the injury. This is due to the realisation that not all hamstring strain injuries are the same. Within the hamstring complex, there are three (or four if including short head) distinct muscles, each with proximal and distal components. In addition, the musculotendinous unit is made up of peripheral muscle fibres, the attachment of muscle to the intramuscular tendon (or musculotendinous junction) and the intramuscular tendon itself – the connective tissue that is analogous to the rachis of a feather. Within these, there are multiple potential locations for injury - each have their own appropriate timelines for return to play, and each benefitting from bespoke management.

Intramuscular Tendon Injuries

An analysis (currently under review) of the hamstring injuries at Leinster Rugby over 5 seasons found that 20% of hamstring strain injuries involved the intramuscular tendon. In a similar study predominantly involving footballers, van der Made, et al.2 found intramuscular tendon disruption in 39% of hamstring strain injuries. This suggests that this type of injury forms a significant proportion of the hamstring strain injuries seen by practitioners at clubs and warrants consideration.

This was highlighted in a review in the BJSM by Brukner and Connell3 where they named intramuscular tendon injuries as ‘a more serious type of thigh strain’ and this concept has evolved thereafter. Comin, et al.4 were the first to our knowledge to describe prolonged recovery in Australian Football players who had disrupted their intramuscular tendon. In 2014, Noel Pollock

of British Athletics published the British Athletics Muscle Injury Classification, which is now in almost ubiquitous use in elite football.5 The classification grades injury by their location within the musculotendinous unit in ascending severity - ‘a’ (peripheral myofascial injury), ‘b’ (musculotendinous junction) and the most severe, ‘c’ (intramuscular tendon injury). They later validated the scale when they demonstrated ‘c’ type injuries required prolonged rehabilitation and faced a 60% re-injury rate6 .

Given each sport is unique, with different demands and different potential mechanisms of injury, there has since been several welcome analyses to attempt to determine whether this BAMIC scale does indeed cause similar challenges in football as well as athletics. Shamji, et al. 7 reported intramuscular tendon disruption in 21.3% of all hamstring strain injuries. These injuries were seen to take significantly longer time (36 days versus 24 days) and risked higher recurrence rate (38.5% versus 12.5%) than ‘a’ and ‘b’ type injuries which though more frequent, are likely to be outnumbered by ‘c’ type.7 Research conducted at Liverpool FC, however, found no association with injury location and outcomes8 . Another recent paper by Tears, et al. 9 at Sunderland AFC found a small difference between BAMIC grade and time to return to play.

What is certain is that track and field is not football and that it wouldn’t be appropriate to transpose the findings directly across regarding the BAMIC. In addition, in a group of sub-elite athletes, van der Made, et al. 10 showed no difference in re-injury rate at 12 months. What is noteworthy about that work is that the clinicians and athletes were blinded to the imaging findings – raising the possibility that expectations of a difficult recovery following MRI may impact upon outcomes. However, there are pockets of evidence to support the hypothesis that ‘c’ type injuries are more severe. In truth, to expand our understanding of these injuries in the future, everyone would benefit from a collaborative approach to data sharing when cataloguing these injuries.

Bespoke Rehabilitation

In 2019, Macdonald, et al. 11 described the principles the British Athletics group had designed in respect of the high re-injury rates they were suffering following ‘c’ type injury. For ‘a’ type injury, though these may initially be quite painful due to the highly innervated fascia, these were progressed quickly as the musculotendinous unit is largely intact. The authors continue to allow their athletes to train through some degree of pain in the first week for this reason, and running is re-introduced early. While ‘b’ type injuries may be considered ‘typical’ hamstring injuries, ‘c’ type injuries are argued to benefit from completely bespoke management. The authors advocate delayed running, delayed eccentrics, and delayed speed, to give respect to the slower healing process for tendons. By utilising this approach, the authors were able to significantly reduce their recurrence rate for ‘c’ type injuries to 0%.8 It is critical to note that the approach used took similar time to return to play as previously, so it is not overly cautious in terms of holding the athletes out longer. The point of difference in this case is the structured rehabilitation which gives respect and attention to the specific tissues. These results are demonstrated in Table 1.

Table 1: Time to return to full training and number of reinjuries in the different BAMIC classes following a location specific approach to rehabilitation (reproduced from Pollock et al 2022)

Time to return to full training in the different BAMIC classes

BAMIC Number of Injuries Number of re-injuries Median TRFT (days (IQR, range))

0 16 9 (4.3, 4-17)

1a 6 1 12 (4.0, 9-16)

1b 19 17 (10.3, 8-32)

2a 4 19 (3.5, 14-21)

2b 11 1 19 (3.5, 11-36)

2c 7 35 (9.5, 25043)

3a 1

3c 6 17

51.5 (23.8, 28-70)

Figure 1: Reproduced from Entwisle et al. The anterolateral epimyseal surface of the long head (L) condenses to form the proximal portion of the distal musculotendinous junction. The opposing epimyseal condensations at the anterolateral aspect of the long head (L, large arrow) and the posterolateral aspect of the short head (S, small arrow) form the midportion of the distal musculotendinous junction that appears T-Shaped.

T-Junction Injuries

It is not just intramuscular tendon injuries that have particularly high re-injury rates. Consideration needs to be given also to the distal hamstring, which may have its own characteristics. Kenneally-Dabrowski, et al. 12 noted that amongst a group of professional rugby players, distal hamstring injuries were the injuries typically classified as more severe. Entwisle, et al. 13 was the first to describe what is now known as the T-Junction of the distal hamstring. This is the confluence of the epimyseal surfaces of the biceps femoris long head and short head (Figure 1). These authors report re-injury rates for this sub-type of hamstring injury at 70% for the higher grade injuries, which must be the highest reported re-injury rate for any muscle injury.13 Similarly, Kayani, et al. 14 noted 55% recurrence rates from conservatively managed injuries to this area. Shamji, et al. 7 in their group of professional footballers at Aston Villa found that most of the re-injuries they had, were indeed in the region of the T-Junction.

All in all, the existing data, and our experience, suggest that these are a particularly challenging injury too - perhaps even more challenging than intramuscular tendon injuries. These are not rare injuries – 18% of all hamstring injuries at Leinster Rugby over a 5-year period involved the T-Junction. These injuries are difficult to diagnose without imaging. It is characteristic of T-Junction injuries that they present well early (perhaps due to limitations in clinical assessment in appropriately straining the T-Junction) and it is only when they progress through rehabilitation and reinjure that the severity becomes clear.

Thus, it is advocated that any acute distal hamstring injury should be treated with suspicion. The T-Junction confluence can be palpated in prone, located at the most distal component of long head where the short head condenses - usually 5cm (range 1.5-10) proximal to the knee joint space. A distal to proximal approach to palpation is advocated, to reach the thickening where the common insertion broadens to form two muscles, with short head the more lateral. While this is often a tender area even in an uninjured athlete, a side-to-side comparison should be a part of every hamstring assessment. In more severe injuries, an experienced practitioner may detect a defect.

While much of our understanding of the mechanism of hamstring injury comes from the likes of Thelen, et al. 15 who have described the kinematics of upright treadmill running, evasion sports such as football involve a mix of stretching and sprinting, in addition to stretching, reaching, changing direction and responding to opponents. Interestingly, a recent study Gronwald, et al. 16 described using video analysis the mechanism of 52 hamstring injuries in elite German soccer. It was noteworthy that 27 of these were stretch type, and often occurred following contact from an opponent. This matches our own findings in rugby union, where trunk flexion and ipsilateral rotation were frequently associated with hamstring injury17 .

In addition, while other authors have suggested that sprint type injuries tend to cause injury to the biceps femoris, and slow stretch type injuries to cause injury to semimembranosis,18 19 our group have repeatedly detected a theme amongst athletes with T-Junction injuries (see Figure 2, reproduced from Kerin, et al. 17). Frequently these injuries occur during late swing phase (or early stance), with a rapid ipsilateral trunk rotation (often to catch a pass, make a tackle, reach for a ball or to look behind). If this is confirmed to be a pathognomic mechanism, it could be helpful in aiding clinicians and athletes in both detecting and optimally managing these challenging injuries. If this position is the position of injury, then we may consider ipsilateral trunk rotation in trunk flexion, hip flexion and knee extension a position of ‘end stage’ rehabilitation and periodise our exercise selection accordingly.

Figure 3: Reproduced from Pieters et al (2021). Following muscle injuries, footballers typically return after 2 to 3 weeks, several weeks before the end point of healing. This should surely impact upon some aspects of load management, exercise selection and rehabilitation planning.

Table 2: Specific exercise and running suggestions for a moderate to high grade T-Junction at 0-4, 4-6 and 6 weeks plus.

Table 3: Suggested exercises at Early, Mid and Late Stages of rehabilitation of T-Junction injury

Management of T-Junction Injuries

Pieters, et al. 17 (Figure 3) note that most athletes return to play following hamstring injury after 2-3 weeks, well before the optimal time point for healing. This time point is no doubt of particular importance in an injury like the T-Junction, with high re-injury rates, primarily in the early weeks. Respect must be given to pathology and healing time.

A strength of the tailored approach described by Macdonald, et al. 11 is that they were specific to the injured tissues with consideration of intramuscular tendon versus other areas, but they did not differentiate between T-Junction and non-T-Junction injuries in their 2022 study. Nonetheless, they still achieved a miniscule re-injury rate, suggesting that this approach will work well for all injuries if consideration is given to BAMIC grading. It is still worthy of further consideration however, as to whether further modifications to the rehabilitation approach should be advocated given that the T-Junction has some unique characteristics, not least the contribution of the uniarticular short head muscle.

Rehabilitation

The return to sport process begins with the clinical assessment. Mechanisms associated with trunk rotation that present with symptoms in the distal half of the hamstring should be considered potential T-Junction injuries. Palpation of the confluence of the short and long head should be carried out, though sometimes it is generally a tender area even on the non-injured limb. In some more severe cases, the area can be boggy and swollen. Deep palpation may reveal a divot or loss of tension.

Hip Dominant

0-4 Moderate range isos and eccentrics - temp loading

4-6 Through range isos and eccentrics with multiplanar focus

6+ Unanticipated and rapid focus

Knee Dominant Running

Moderate range isos and eccentrics - tempo loading Delayed - <70% linear only

Through range isos and eccentrics

Through range isos and eccentrics <80% linear only

Curve, sport specific and 80%+

Early Stage Session

Knee Dominant Val Slide Curl to 3/4 range Single leg Natera Isometric - bent knee Prone Tempo Curl to 3/4 range

Hip Dominant GHR Isometric Rack Pull from above knees

Hip Extension Hip Thruster

Glute Glute Work as Indicated

Horizontal Force Heavy Sled Pushes

Linear Mechanics/ Angular Velocity

Mid Strange Session

Straight Leg Hamstring Bridge (load as appropriate) Single leg Natera Isometric weighted straight knee Seated Temp Hamstring Curl

GHR through Range RDL/Rack Pull/SL RDL

Hip Thruster

Glute Work as Indicated

Sled Acceleration

Marching and Skipping

Late Stage Session

Cable eccentrics in hip flexion Single leg Isometric switches with trunk rotation Heavy eccentric tempo curls

GHR with ball bounce or catch Bound to SL RDL

Hip Thruster

Glute Work as Indicated

Speed

OH A or B Skips

A major challenge of T-Junction injuries is that the initial examination may not reveal the extent of the injury, and the symptoms that do exist typically ease quickly. This may contribute to the high rate of early re-injuries, with athletes progressing too quickly as symptoms settle quickly and assessment normalises. It is possible that typical hamstring strength tests like single leg bridge and prone curl are simply not provocative enough to stress the T-Junction, either because they are not of sufficient rate of force development or because they are in a single plane. This is certainly one area for further research and conversation.

MRI is the probable imaging type of choice to confirm diagnosis, although dynamic ultrasound is also useful. Synchronous movement of the short and long heads during an isometric prone curl can be assessed and monitored as either a prognostic or progress indicator, though a reliable and valid protocol has yet to be described.

The suggested principles of a Grade 2 or 3 T-Junction injury are similar to those recommended by Macdonald, et al. 11 for intramuscular tendon injuries, and are described in Tables 2 and 3. Regardless of clinical presentation, running is delayed for about two weeks, and subsequent running should be below 70% until 4 weeks post injury20 21. From 6 weeks, the athlete should gradually progress speed from 80 to 100% across several sessions, with the integration of curvilinear and reactive training (given the likely mechanism).

Hip and knee dominant exercises should be introduced early, using both isometric and eccentric exercises with the goal of maintaining eccentric strength and fascicle length to maintain the athlete’s hamstring conditioning in preparation for return to more challenging field-based activities. Suggestions for exercises across the stages are provided in Tables 2 and 3. In the early phase, range of motion should be capped in all exercises to avoid over stressing the healing area. Knee dominant exercises are likely to bias the distal hamstring and in particular the short head, so for this type of injury, these are considered high load 22. Slower, tempo-based exercises (both hip and knee dominant) are recommended to achieve time under tension and specific adaptation in both the proximal and distal hamstrings. Additional neuromuscular control, hip extension (thruster) and speed mechanics exercises should also supplement the hamstring specific exercises throughout23 24 .

Given these injuries typically settle quickly, monitoring progression can be somewhat difficult. As a result, it is key to carry out a complete battery of assessment to guide progression, particularly ahead of the final phase of running (Figure 4). Strength deficits on the Nordic hamstring exercises or at outer range during isokinetic dynamometry have been noted following these injuries, while rate of force development during long lever bridges may be an area to further explore. Range of motion can sometimes be impacted, and the MHFAKE test should be monitored regularly25 .

Conclusion

• The anatomical location of hamstring injury (particularly the intramuscular tendon and distal T-Junction) may be associated with delayed return to play and higher re-injury rate • Specific rehabilitation strategies have been shown by other authors to greatly reduce re-injury risk following intramuscular tendon injuries • T-Junction injuries are a particular challenge to manage, given there is little evidence to guide conservative management

Figure 4: Key Progression Indicators used to guide rehabilitation of T-Junction injury

Speed - multiple exposures on curve and straight

No tenderness

Synchrony on Ultrasound

SL Iso on Force Plate (Force and RFD)

Key Progression Indicators

Pain free bridge

IKD - concentric and eccentric

Split Stance Rack Pull Force on Force Plate Nordic

1. Ekstrand J, Walden M, Hagglund 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(12):731-7. doi: 10.1136/bjsports-2015-095359 [published Online First: 2016/01/10] 2. van der Made AD, Almusa E, Reurink G, et al. Intramuscular tendon injury is not associated with an increased hamstring reinjury rate within 12 months after return to play. 2018(1473-0480 (Electronic)) 3. Brukner P, Connell D. ‘Serious thigh muscle strains’: beware the intramuscular tendon which. Br J Sports Med 2016;50(4):205-8 LID - 10.1136/ bjsports-2015-095136 [doi]. 4. Comin J, Malliaras P, Baquie P, et al. Return to competitive play after hamstring injuries involving disruption of the central tendon. Am J Sports Med 2013;41(1):111-5. doi: 10.1177/0363546512463679 [published Online First: 2012/11/01] 5. Pollock N, James SL, Lee JC, et al. British athletics muscle injury classification: a new grading system. Br J Sports Med 2014;48(18):1347-51. doi: 10.1136/bjsports-2013-093302 [published Online First: 2014/07/18] 6. Pollock N, Patel A, Chakraverty J, et al. Time to return to full training is delayed and recurrence rate is higher in intratendinous (‘c’) acute hamstring injury in elite track and field athletes: clinical application of the British Athletics Muscle Injury Classification. Br J Sports Med 2016;50(5):305-10. doi: 10.1136/bjsports-2015-094657 [published Online First: 2016/02/19] 7. Shamji R, James SLJ, Botchu R, et al. Association of the British Athletic Muscle Injury Classification and anatomic location with return to full training and reinjury following hamstring injury in elite football. BMJ open sport & exercise medicine 2021;7(2):e001010. doi: 10.1136/ bmjsem-2020-001010 [published Online First: 2021/05/28] 8. McAuley S, Dobbin N, Morgan C, et al. Predictors of time to return to play and re-injury following hamstring injury with and without intramuscular tendon involvement in adult professional footballers: A retrospective cohort study. Journal of science and medicine in sport 2022;25(3):216-21. doi: 10.1016/j.jsams.2021.10.005 [published Online First: 2021/11/07] 9. Tears C, Rae G, Hide G, et al. The British Athletics Muscle Injury Classification grading system as a predictor of return to play following hamstrings injury in professional football players. Physical Therapy in Sport 2022;58:46-51. doi: https://doi.org/10.1016/j.ptsp.2022.08.002 10. van der Made AD, Almusa E, Reurink G, et al. Intramuscular tendon injury is not associated with an increased hamstring reinjury rate within 12 months after return to play. Br J Sports Med 2018;52(19):1261-66. doi: 10.1136/bjsports-2017-098725 [published Online First: 2018/04/15] 11. Macdonald B, McAleer S, Kelly S, et al. Hamstring rehabilitation in elite track and field athletes: applying the British Athletics Muscle Injury Classification in clinical practice. Br J Sports Med 2019;53(23):1464-73. doi: 10.1136/bjsports-2017-098971 [published Online First: 2019/07/14] 12. Kenneally-Dabrowski C, Serpell BG, Spratford W, et al. A retrospective analysis of hamstring injuries in elite rugby athletes: More severe injuries are likely to occur at the distal myofascial junction. Phys Ther Sport 2019;38:192-98. doi: 10.1016/j.ptsp.2019.05.009 [published Online First: 2019/06/09] 13. Entwisle T, Ling Y, Splatt A, et al. Distal Musculotendinous T Junction Injuries of the Biceps Femoris: An MRI Case Review. Orthop J Sports Med 2017;5(7):2325967117714998. doi: 10.1177/2325967117714998 [published Online First: 2017/08/11] 14. Kayani B, Ayuob A, Begum F, et al. Surgical Repair of Distal Musculotendinous T Junction Injuries of the Biceps Femoris. Am J Sports Med 2020;48(10):2456-64. doi: 10.1177/0363546520938679 [published Online First: 2020/08/02] 15. Thelen DG, Chumanov ES, Hoerth DM, et al. Hamstring muscle kinematics during treadmill sprinting. Med Sci Sports Exerc 2005;37(1):10814. doi: 10.1249/01.mss.0000150078.79120.c8 [published Online First: 2005/01/06] 16. Gronwald T, Klein C, Hoenig T, et al. Hamstring injury patterns in professional male football (soccer): a systematic video analysis of 52 cases. Br J Sports Med 2022;56(3):165-71. doi: 10.1136/bjsports-2021-104769 [published Online First: 2021/12/09] 17. Kerin F, Farrell G, Tierney P, et al. Its not all about sprinting: mechanisms of acute hamstring strain injuries in professional male rugby union-a systematic visual video analysis. Br J Sports Med 2022;56(11):608-15. doi: 10.1136/bjsports-2021-104171 [published Online First: 2022/01/21] 18. Askling CM, Tengvar M, Saartok T, et al. Acute first-time hamstring strains during slow-speed stretching: clinical, magnetic resonance imaging, and recovery characteristics. Am J Sports Med 2007;35(10):1716-24. doi: 10.1177/0363546507303563 [published Online First: 2007/06/15] 19. Askling CM, Tengvar M, Saartok T, et al. Acute first-time hamstring strains during high-speed running: a longitudinal study including clinical and magnetic resonance imaging findings. Am J Sports Med 2007;35(2):197-206. doi: 10.1177/0363546506294679 [published Online First: 2006/12/16] 20. Dorn TW, Schache AG, Pandy MG. Muscular strategy shift in human running: dependence of running speed on hip and ankle muscle performance. J Exp Biol 2012;215(Pt 11):1944-56. doi: 10.1242/jeb.064527 [published Online First: 2012/05/11] 21. Schache AG, Dorn TW, Blanch PD, et al. Mechanics of the human hamstring muscles during sprinting. Med Sci Sports Exerc 2012;44(4):64758. doi: 10.1249/MSS.0b013e318236a3d2 [published Online First: 2011/09/14] 22. Hegyi A, Csala D, Peter A, et al. High-density electromyography activity in various hamstring exercises. Scand J Med Sci Sports 2019;29(1):3443. doi: 10.1111/sms.13303 [published Online First: 2018/09/20] 23. Sugiura Y, Saito T, Sakuraba K, et al. Strength Deficits Identified With Concentric Action of the Hip Extensors and Eccentric Action of the Hamstrings Predispose to Hamstring Injury in Elite Sprinters. Journal of Orthopaedic & Sports Physical Therapy 2008;38(8):457-64. doi: 10.2519/jospt.2008.2575 24. Mendiguchia J, Edouard P, Samozino P, et al. Field monitoring of sprinting power-force-velocity profile before, during and after hamstring injury: two case reports. Journal of sports sciences 2016;34(6):535-41. doi: 10.1080/02640414.2015.1122207 [published Online First: 2015/12/10] 25. Whiteley R, van Dyk N, Wangensteen A, et al. Clinical implications from daily physiotherapy examination of 131 acute hamstring injuries and their association with running speed and rehabilitation progression. Br J Sports Med 2018;52(5):303-10. doi: 10.1136/bjsports-2017-097616 [published Online First: 2017/11/01]