Intramuscular hamstring tendon injury: prognosis, surgical repair and rehabilitation

Adam Smith explores the anatomy of intramuscular hamstring tendons, outlines an injury classification system and using a case study, provides treatment and rehab options following surgical repair.

Hamstring injuries are the most common muscular injury in athletes with most injuries occurring at the musculotendinous junction^(1-3). There is some evidence that injuries that involve the intramuscular tendon require a longer rehabilitation period and have higher recurrence rates⁽²⁾. Imaging is useful to determine the location and severity of injury, and with improved MRI resolution, the astute clinician can also determine whether a muscle injury involves the intramuscular tendon.

Traditionally all hamstring injuries – with the exception of large proximal tendon ruptures/avulsions – have been treated with conservative management. However surgical repair of injuries that involve the intramuscular tendon is now possible, and leading to some good results⁽³⁾.

Hamstring tendon anatomy

The hamstring muscle group is comprised of three separate muscles: the biceps femoris (short and long head), semimembranosus and the semitendinosus (see figure 1). The proximal tendon of the semimembranosus originates from the lateral facet of the ischial tuberosity; the semitendinosus and the biceps femoris meanwhile share the common tendon origin on the medial facet of the ischial tuberosity⁽³⁾.

Figure 1: Hamstring tendon anatomy

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If both the proximal and distal portions of the bicep femoris are considered, the muscle tendon junction of the bicep femoris extends the full length of its muscle belly⁽²⁾. The proximal tendon comprises approximately 60% of the length of the muscle⁽²⁾. The free part of the proximal tendon (which has no inserting muscle fascicles) extends approximately 6.5 cm distally, with its long musculotendinous junction spanning 45% of the muscle length, to terminate deep within the muscle belly⁽²⁾. The distal tendon and muscle-tendon junction extends up to 66% of the muscle length⁽²⁾. Similarly, the semimembranosus has a proximal tendon and distal tendon that extends approximately 78% and 52% respectively into the muscle. The proximal tendon of the semitendinousus is the shortest of all the hamstring muscles, and extends about 30% of the length of the muscle.

The role of imaging

Clinically, some hamstring injuries resolve quickly whilst others take longer to recover (or may even fail conservative treatment and reoccur). One factor that has been thought to explain this is involvement of the intramuscular tendon⁽²⁾. On MRI, the tendon may be seen to maintain its structural integrity, or it may lose its integrity and take on a irregular, wavy contour, or it may be frankly disrupted.

The British Athletics Muscle Injury Classification System (BAMICS) was developed to help clinicians determine not only the severity of a soft tissue injury, but also the type of tissue involved. This system is based on MRI findings and categorises the injury numerically by severity (1=small, 2=moderate, 3=extensive, 4=complete tear) and alphabetically by site (a=myofascial, b= myotendinous, c=intratendinous).

Researchers studying a series of hamstring injuries in AFL players showed that those with bicep femoris injuries without tendon disruption had a recovery time of 21 days, whereas those with tendon disruption treated non operatively recovered in 72 days. Those with tendon disruption requiring surgery recovered in 91 days⁽²⁾.

In a study of track and field athletes, Pollock et al found similar results; when the injury extended into the tendon, athletes took longer to return to full activity (3c injuries took 84 days while 2b injuries took 21 days). They also has a higher rate of recurrence (2c injuries 63%; 3c injuries 57%; 2b injuries 6%)⁽²⁾. Interestingly, there were no significant differences between injury grades 1 and 2 or classification a and b. This demonstrate that MRI is a useful tool with regard to hamstring injuries in the clinical setting as it identifies possible tendon involvement, which influences injury prognosis and management.

Case study of a cricketer

A 26-year old elite cricketer (wicket keeper) suffered a hamstring strain whilst playing a game of touch football during pre season training. The player had no history of hamstring or lumbar spine injury. The injury occurred when he was sprinting to catch an opposition player who had made a ‘break’, and while he was reaching forward to touch him.

The player felt sudden pain in his hamstring and fell to the ground. He was unable to walk so was assisted off the field. At the time, he described a feeling like a ‘balloon deflating’ in his hamstring. His pain was localised to the proximal one third of the hamstring, approximately 5-10cm from the origin.

A MRI scan was conducted the following day, showing a full thickness rupture of the biceps femoris tendon 78mm from its origin with 31mm retraction (see figure 2). Considering it was full thickness tear (grade 4 on BAMICS), a surgical opinion was advised. The player was reviewed with a surgeon three days post injury, and underwent surgery to repair the ruptured tendon the following day. There is no consensus on the best management of injuries that involve the intramuscular tendon⁽⁴⁾. However, surgery was recommended as the return to play timeframes with conservative management and surgical management were similar, and the risk of recurrence was significantly lower with surgery.

Figure 2: MRI scan

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Returning to play

Initially the aim was to return to playing elite domestic cricket at 12 weeks post surgery. Considering the specific injury and the demands of a game, return-to-play criteria were established, which outlined key physical parameters (clinical and functional measures) that needed to be met prior to returning to play (see table 1).

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Table 1: Return-to-play criteria

	Test	Description of test and goal	Result and date of previous best	Date achieved
Range of movement and clinical tests:	Knee extension ROM	Supine 90/90	70 deg L and R 20/6/18	72deg 22nd August
	Hamstring bridge endurance test	Endurance (>18reps 90% of screening score)	20 reps 20/6/18	20 reps 20th August
	Isometric hamstring in prone	Pain and strength >308N (90% previous score at 30deg)	L 301N, R343N 9/7/18	431 N 10th Sept
	Nordic test	More than 433 (90% of previous score)	L 472N, R 482N 8/6/18	L 501, R466. 17th Aug
Functional milestones:	Resume normal walking - ADL's	Gait pattern		6th August
	Start jogging	No pain walking		10th August
	High-speed running - *most critical*	More than 25kph - GPS - minimum 5 sessions		5th session completed 18th Sept
	Chronic GPS loads	Three consecutive weeks achieving all velocity band loads equivalent to Shield match		17th Sept - high loads last 3 weeks (wks 5-7)
	Batting - throw downs	Throw downs		Commenced 17th August
	Batting - nets (unrestricted)	If no issues during previous week		Achieved 30th August
	Stationary catching/keeping	Above knee high catches to start - progress as able		Commenced 17th August
	Unrestricted keeping- (centre wicket)	Complete 5 full sessions		Achieved 18th August
	2km TT	7mins:30 or less	7min 13/7/18	7:18 -17th Sept
	Counter movt Vertical Jump	More than 61cm (90% of previous score)	67cm (20/7/18)	62cm -17th Sept
	Run a quick single	Reach HSR with lunge for crease	>26kph	Achieved 11th Sept
	Mid thigh pull	More than 4.64 relative force (90% of previous score)	5.15 relative force 2/7/18	4.8- 19th Sept

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The running criteria were based on GPS data obtained from the previous years data to ensure adequate capacity was achieved. Table 2 shows GPS data from a competition week for a one day tournament in the previous year for this player (including 2 games and training). Consistent high speed running is protective against hamstring injuries so it was deemed as a critical component to help mitigate the risk of re-injury when he returned to playing.

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Table 2: GPD data

Total Distance	Vel Band 1 (0-11.02km/hr)	Vel Band 2 (11.02km-14km/hr)	Vel Band 3 (14-20.99 km/hr)	Vel Band 4 (20.99-25.99km/hr)	Vel Band 5 (26+km/hr)	Max Velocity
42 250m	33 489m	4 515m	3 391m	671m	184m	30.7km/hr

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The post operative instructions initially were as follows:

• Focus on wound healing.
• Weight bear as tolerated – avoid striding out on hills or on stairs beyond comfort.
• Commence double leg bridging.
• Commence bike and jogging when comfortable.

The initial phase of rehabilitation progressed very well (table 3 outlines the progression in the early phases of rehabilitation).

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Table 3: Early phase of rehab

Week	Subjective	Clinical observations / tests	Specific hamstring exercises	Training
1	Able to walk without pain - still having difficulty putting pants on due to lack of hip function (feels wound, gets tight) otherwise ADLs going really well Hip F ROM (supine)- 80deg Hamstring length in supine 25 deg (at 80deg hip F)	Significant bruising. Hip F ROM (supine)- 80deg Hamstring length in supine 25 deg (at 80deg hip F)	Bridge- up on 2 legs hold on 1. Standing and prone hamstring curls	ADLs only
2	Going really well much better walking and putting pants on able to bike and do boxing today	Hip F ROM (supine) -90deg hamstring length in supine at 90deg hip F- 25deg. DL squat to 90deg no concerns. HHD strength in prone (30deg) to P1 L 299, R 105 able to do hamstring curl in prone 2kg.	BW squat, hamstring curl prone 2kg. Hip abd/add Theraband work in standing	Bike and boxing for fitness. Commenced graduated return to run from day 14.
3	Going well saw surgeon happy to progress as pain allows	No restrictions with ADL's HHD strength in prone0deg  L 235, R 132 ,30deg L 325, R 140, 90deg L 206, R 114		Progress running, commence batting and keeping drills

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Hamstring exercises were commenced as pain allowed and were broken into a couple of phases. In the later stages, the emphasis was on eccentric loading to help protect against re-injury. Examples of hamstring exercises used in each phase were:

Initial phase (0-2 weeks)

• BW squat
• DL bridge on bed
• Hamstring curl prone
• Standing hamstring curl

Phase two (2-4 weeks)

• Isometric holds in prone against resistance (various ranges)
• Single leg bridge on box
• Monster walks
• RDL

Phase three (weeks 4-8)

• DL hamstring slide outs progressed to SL
• 45 deg DL hip ext progressed to SL
• SL bridge with band resistance
• GHR Straight leg SL hip ext

At four weeks post operation, the patient developedsome intermittent sharp stabbing pain in the gym when was doing a reverse lunge to step up. An ultrasound was arranged which showed some slight neural tethering around scar. The player was able to continue to training but modified his speed work when running. These symptoms then resolved with soft tissue treatment and neural mobilisation techniques by week six.

Hamstring strength

Hamstring strength was deemed to be an important criterion to determine the player’s readiness for return to play. To monitor strength progressions, hamstring strength testing was done through isometric testing (see table 4) and single leg bridge (based on the pre-season screening test). On pre-season testing for hamstring endurance two months prior to injury, the player was able to achieve 20reps for the single-leg bridge. At four weeks post operation, he was able to achieve the same result of 20 reps.

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Table 4: Hamstring strength testing

Test	Pre-injury	Week 2	Week 3	Week 4	Week 5	Week 6	Week 7
HHD at 30deg prone	Best (June 2018) L) 418 R) 418	L) 343 R) 149	L) 330 R)202	L) 319 R) 283	L) 404 R) 431	L) 369 R) 356	L) 400 R) 413

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Finally, from a specific hamstring strength and injury protection point of view, a Nordic hamstring test was performed seven weeks post surgery. The results were L) 501, R) 466N. This was slightly lower than his previous best a year beforehand (L) 472, R) 482) but showed good strength and symmetry.

As well as specific strengthening, running was an important component of his rehabilitation. Running was progressed as pain allowed, and by 5 weeks post op he was able to recommence HSR running (>26km/hr). By day 51, the player had completed his return-to-play criteria and returned to club cricket. He was able to bat for 25 overs. One week later, he was cleared to play a domestic 1-day game. Since then he has continued to play both 1-day cricket , 20/20 cricket and 4-day cricket without any recurrence of hamstring pain.

References:

1. British Journal of Sports Medicine 51: 1021-1028
2. British Journal of Sports Medicine 0: 1-5
3. Orthopaedic Journal of Sports Medicine. 3 (10): 1-7
4. British Journal of Sports Medicine. Vol0, No 0: 1-4