Modern Hamstring Tendon Injury Management

Alistair Mayne, MBChB, MSc FRCS, UNITED KINGDOM Peter Samuel Edward Davies, MBChB, FRCS, UNITED KINGDOM Shahbaz S. Malik, BSc, MB BCh, MSc (Orth Engin), LLM, FRCS (Tr&Orth), UNITED KINGDOM Randeep Singh Aujla, MBChB ChM FRCS (Tr&Orth) MFSEM, UNITED KINGDOM Nikolaos K. Paschos, MD, PhD, UNITED STATES Peter Edwards, PhD, AUSTRALIA Jay R. Ebert, PhD, AUSTRALIA Peter D'Alessandro, MBBS (Hons), FAOrthA, FRACS, AUSTRALIA

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Introduction

Hamstring tendon injuries occur more commonly than might be perceived in the community, generally involving combined eccentric hip flexion/knee extension. Overall, hamstring injuries are most prevalent in athletes participating in sports that combine high velocity and significant lower-limb forces in vulnerable positions. However, specific injury patterns are more common in the middle-aged population where the most common mechanism of injury is a simple slip and or fall leading to hip hyperflexion and tearing of tendinopathic tendons. Over the past decade, there has been a significant increase in our understanding of hamstring tendon injuries and treatment options, with a resultant increase in the volume of patients managed surgically in an attempt to minimise loss of function and provide a more predictable return to pre-injury levels of activity and sport.

Anatomy

The hamstring muscle group comprises 3 muscles (semimembranosus, semitendinosus, and biceps femoris) with 4 origins (the biceps femoris has a short head arising from the femur). The long head of biceps femoris and semitendinosus arise together as the conjoint tendon from the ischial tuberosity, along with semimembranosus. The hamstring muscles are in close proximity to the sciatic nerve, and care must be taken to identify and protect the nerve during any surgical repair (Figure 1). The biceps femoris and semimembranosus muscle bellies contain an intramuscular tendon (IT) that provides a large insertional area for muscle fibres. This IT may run within the muscle belly or alongside it. During activity, the IT acts as a central strut and amalgamates asynchronous motor units to optimise muscular contraction.

Fig. 1 Legend Diagram Describing Proximal Hamstring Anatomy and the Relationship to the Sciatic Nerve

Hamstring Tendon Injuries

In general, hamstring tendon injuries can be divided into 3 groups: (1) proximal avulsions from the ischial tuberosity, (2) musculotendinous junction/central tendon injuries, and (3) distal hamstring insertion injuries.

Mechanism of Injury

Proximal hamstring avulsions most commonly arise from eccentric contraction, usually at the end of the swing phase during running or during a fall/slip with significant forced hip flexion. Patients usually report a sudden onset of pain in the posterior thigh, which is often associated with a “pop” sensation, after which there is often extensive bruising down the thigh and significant pain with concentric hamstring contraction or eccentric lengthening. This injury is most commonly seen in moderate-demand patients between the ages of 40 and 65 years, although it also can occur in athletes as well as in adolescents as part of an ischial apophyseal avulsion.

Assessment, Imaging, and Classification

Magnetic resonance imaging (MRI) is the gold-standard method for the evaluation of proximal hamstring avulsions as it allows for the determination of the extent of injury (1, 2, or 3 tendons) as well as the extent of retraction. This information is essential for determining treatment, and we recommend early MRI (and avoidance of ultrasound, which is often non-diagnostic and a cause for delay in diagnosis).

At our institution, early MRI and orthopaedic assessment within 2 weeks after the injury is considered an acceptable timeframe for management. A close relationship with our hospital emergency departments, primary care physicians, and physiotherapists plays a very important role in our management of these injuries. Education as to the likely diagnosis based on history and examination findings leads to a “triggering” of our Perth Sports Injury Pathway, with early direct referral to the Sports Fellow for the organisation of MRI and an appointment with the Sports Trauma clinic within 2 weeks after the injury. This allows for surgical management (if indicated) in an appropriate timeframe of ideally 2-4 weeks.

David Wood and colleagues developed an MRI-based classification system for proximal hamstring avulsions that is based on the location of the injury, the degree of avulsion and retraction, and the presence of sciatic nerve tethering (Figure 2). We have documented the different injury types and their classification in Table 1, along with our own management approach to each of these injury types¹.

Fig. 2 Legend MRI Scan Showing a Displaced Proximal Hamstring Avulsion Injury

Table 1. Wood Classification with Perth Sports Surgery Management Algorithm

Surgical Repair and Rehabilitation

While some hamstring tendon injuries can be managed nonoperatively, especially in lower-demand patients with partial injuries, it is widely agreed that complete proximal hamstring avulsions with retraction are best treated with surgical repair in the majority of patients. Nonoperative treatment has been associated with poor functional results in terms of patient-reported outcome scores, hamstring strength, and the likelihood of returning to the preinjury levels of function and sports activity² In contrast, operative management has been shown to lead to high patient satisfaction levels, good restoration of hamstring strength, and high rates of return to the preinjury levels of function and sports activity, even in moderate-demand patients, with the peak incidence of these injuries being between the ages of 40 and 65 years. Early surgical intervention (ideally within 2-4 weeks post-injury) is recommended as it makes the surgery technically less complex (particularly with respect to adherence of the torn tendon complex to the sciatic nerve) and has been associated with a greater improvement in surgical outcomes¹. That said, in many locations, proximal hamstring injuries are commonly missed or assumed to be appropriately managed nonoperatively, meaning that first imaging/assessment by the Sports Orthopaedic Team is often delayed. These delayed presentations often contribute to a perception of a “missed” surgical window and nonoperative management by default. That said, in our experience, satisfactory primary repair of displaced avulsion injuries can be achieved even up to 4-6 months post-injury, albeit with increased surgical difficulty. More delayed surgical interventions often require a graft reconstruction.

Surgery: Surgical repair generally involves a transverse incision in the gluteal crease with mobilisation of gluteus maximus and penetration of the deep gluteal fascia. In more chronic cases, or in large patients, an extensile longitudinal approach is utilised. The sciatic nerve is first identified and careful neurolysis is performed, mobilising the nerve along its length to allow protection during tendon repair and to minimise traction-related injury. This is often the most challenging part of the procedure. The ischium is identified and dissected to define the surfaces. The lateral wall is prepared to create a bleeding bone surface that is ready for tendon reattachment. Repair generally involves reattachment of the avulsed tendon to the ischial tuberosity tendon bed ,usually with use of 3-4 suture anchors in a double-row configuration. We use 2 double-loaded distal anchors with sutures that are whipstitched with locking Krakow sutures (8 strands) into the tendon, which is then reduced to the ischium with use of sliding knots. One or two proximal anchors are then used to create a compressive force in a suture-bridge construct, with forces being distributed evenly over the entire ischium.

Rehabilitation: Traditional rehabilitation protocols after hamstring repair have involved protected weight-bearing (or even non-weight-bearing), often with a knee brace to restrict knee extension, for a period of up to 6 weeks or longer. We recently undertook a randomised controlled trial (PHARRLAP Trial) in which this traditional conservative regimen was compared with an accelerated protocol in which patients were allowed to mobilise early with weight-bearing as tolerated with crutches as required and no brace3. The majority of patients in the accelerated group were fully weight-bearing unaided by 2 weeks. The primary outcome measure was peak isokinetic hamstring torque at 6 months, and we found improved early strength and better early quality-of-life scores in this cohort, with no increase in the rate of reinjury. We concluded that accelerated rehabilitation is at least noninferior to the more conservative approach, and accelerated rehabilitation is now our “standard” protocol and is our recommendation for rehabilitation after surgical repair. The early data from this research were presented at ISAKOS 2023, with further presentations and publications planned for 2025.

Intramuscular Hamstring Tendon Injuries

Hamstring injuries are the most common soft-tissue injury and cause of recurrent injury in the Australian Football League (AFL). Most hamstring muscle injuries in athletes recover completely after a period of appropriate rehabilitation, but concurrent injury to the intramuscular tendon may occur in up to 27% of all hamstring injuries. Concurrent injury can occur anywhere from the conjoint tendon, to the proximal musculotendinous junction, to the central intramuscular tendon (most commonly biceps but also to the semimembranosus), to the distal musculotendinous “T” junction. In our experience, particularly in the AFL, the rate of recurrence after tendon injury is high, with any recurrent injury often being of greater severity and requiring prolonged rehabilitation. These injuries are therefore significant both because of their morbidity and time away from play at the time of initial injury as well as because of the high potential for recurrence. Additionally, the subsequent fear of further reinjury may significantly impair athletic performance.

Assessment, Imaging, and Classification

A high index of suspicion following a significant hamstring injury in athletes (high velocity, significant pain, difficulty weight-bearing, extensive bruising) is important. However, clinical examination cannot diagnose the involvement of the IT, making MRI essential for the confirmation of diagnosis and grading of extent. High-grade injury to the IT causes detensioning of the distal tendon-muscle complex (seen on MRI as a “wavy” appearance of distal low-signal tendon) and in our experience has been associated with increased time to return to play along with higher reinjury rates (Figure 3). This has led us to implement a more proactive approach to surgical repair of intramuscular hamstring tendon injuries in an attempt to provide a more predictable return to play while minimising recurrence. The British Athletics Muscle Injury Classification (BAMIC) is a 5-point MRI-based classification system that is used to grade muscular injuries. This system frequently has been applied to hamstring injuries and is summarized in the table below for its application to IT injuries, along with our current management algorithm in athletes⁴.

Fig. 3 Legend MRI Scan Showing a High Grade Intramuscular Hamstring Tendon Injury with Tendon Separation and Distal Dentensioning

Table 2. BAMIC Classification with Perth Sports Surgery Management Algorithm

Surgical Repair and Rehabilitation

Given the higher reinjury rates seen across the literature with involvement of the IT, we recommend early MRI scanning of all high-level athletes with hamstring injuries. For athletes with high-grade tendon injuries, we advocate surgical repair with the primary aims being to anatomically align the tendon, recreate distal tension, and increase the chance of tendon-healing rather than scar/fibrous tissue formation that may become a vulnerable site for recurrent injury. Ideally, this will reduce the risk of recurrence and provide a more predictable return to play (Figure 4). Our initial report on the early surgical repair of acute of 11 high-grade acute IT injuries in professional athletes was the first in the literature on this topic; this treatment led to successful return to play at a mean of 3.1 months (range, 2-6 months) and no reinjuries at a median follow up of 33.7 months (range, 16-65 months)⁵. All but one athlete returned to their preinjury level of competition. We are now following a series of 44 athletes who were managed in the same way (pending publication). After a mean follow-up of 18 months, all athletes have returned to the same level of sports activity, with no games lost to reinjury. Ninety-four percent of the athletes can sprint with 0/10 pain, while two patients have reported 1/10 “awareness” of their hamstring without clinical significance. Ninety-` percent can perform Nordic curls equal to their preinjury strength.

Fig. 4 MRI Scan Showing Combined Intramuscular Hamstring Tendon Injuries, with Tearing of Both the Semi-Tendinosus and SemiMembranosus Tendons at Different Levels

Surgery: Surgical repair involves use of a longitudinal incision, identification and protection of the posterior cutaneous nerve of the thigh. The sciatic nerve (along with 1-2 branches to the biceps tendon) are carefully identified and protected. Identification and re-approximation of the IT with sutures to restore tendon anatomy and distal muscle tension (Figure 5). Our preferred technique is to use core 1 PDS sutures in a 4-strand Krakow technique (with between 2 and 4 strands generally being used, depending on length of longitudinal tearing), along with several 2-0 vicryl circumferential sutures to assist with tendon tubularisation. As these injuries do not involve the proximal hamstring origin, no suture anchors are used. We always use absorbable sutures as we aim to create a “normal” tendon environment post successful repair in our aim to minimise scar formation and sciatic nerve tethering (Figure 6).

Fig. 5 Intra-operative Image of a High Grade Intramuscular Hamstring Tendon Injurym showing Separation of the Tendon Ends and the Close Relationship to the Sciatic Nerve

Fig. 6 Legend Intraoperative Image of the Tendon in Figure 5 after Repair has been completed, showing Restoration of Tendon Coninuity and Tension, Using Absorbable Sutures

Rehabilitation: Crutches are used until the patient’s gait has normalised with weight-bearing as tolerated, generally for <1 week postoperatively. Patients are not braced, and early range of motion is encouraged, although patients are advised to be aware of combined hip flexion/knee extension. Early isometric strengthening is followed by concentric and eccentric strengthening. Return to running is determined by restoration of strength and is generally achieved at 4 weeks postoperatively. Patients follow a graduated return to activity and exercise and may return to sports once hamstring strength and running velocity have returned to 90% of baseline with careful reintroduction of sport-specific training and vulnerable positions as managed by the club high-performance team. The mean return to play in our series was 12.1 weeks.

Distal Hamstring Injuries

Isolated distal hamstring tears are uncommon. The biceps femoris insertion may be involved as part of a posterolateral corner knee ligament injury, but this is outside the scope of this article. Isolated injuries of the semitendinosus insertion are uncommon. For elite athletes, we favour surgical repair, and we have treated a small series of these injuries as part of pes anserinus avulsions in athletes (along with the distal gracilis tendon), with successful return to play achieved at 13-14 weeks.

Summary

Hamstring tendon injuries that may require surgical repair are more common than perceived, and our understanding of their management has improved significantly in recent years. Early MRI scanning with avoidance of ultrasound is crucial in any suspected significant high-grade hamstring injury to guide management in an appropriate timeframe.

With regard to treatment, we believe the majority of displaced proximal hamstring avulsions are best treated surgically, even in moderate-demand patients, who will benefit from an accelerated rehabilitation protocol. High-grade intramuscular tendon injuries in high-level athletes should be considered for surgical intervention in order to provide a predictable return to sport with low recurrence.

Awareness of these injuries is paramount. Formal orthopaedic assessment and MRI imaging that allows for early decision-making and primary surgical repair if indicated are critical to achieve what we believe is best-practice management of these patients.

References

1. Wood D, French SR, Munir S, Kaila R. The surgical repair of proximal hamstring avulsions: does the timing of surgery or injury classification influence long-term patient outcomes? Bone & Joint Journal. 2020 Oct 3;102-B(10):1419–27.
2. Chang JS, Kayani B, Plastow R, Singh S, Magan A, Haddad FS. Management of hamstring injuries: current concepts review. Bone & Joint Journal. 2020 Oct 3;102-B(10):1281–8.
3. Cecchi S, Aujla R, Edwards P, Ebert J, Annear P, Ricciardo B, D'Alessandro P et al. A RANDOMIZED CONTROLLED TRIAL ASSESSING TRADITIONAL VERSUS DYNAMIC REHABILITATION REGIMES FOLLOWING SURGICAL REPAIR OF A PROXIMAL HAMSTRING TENDON AVULSION. Orthop Proc. 2023 Feb 23;105-B(SUPP_3):91–91.
4. Pollock N, James SLJ, Lee JC, Chakraverty R. British athletics muscle injury classification: a new grading system. Br J Sports Med. 2014 Sep;48(18):1347–51.
5. Aujla RS, Cecchi S, Koh E, D’Alessandro P, Annear P. Surgical treatment of high-grade acute intramuscular hamstring tendon injuries in athletes leads to predictable return to sports and no re-injuries. Knee Surg Sports Traumatol Arthrosc. 2023 Oct;31(10):4601–6.

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