The case of the intramuscular tendon

A recent narrative review by Brukner and Connell1 has highlighted that, although athletes often present with the ‘typical’ musculotendinous injury, damage may sometimes extend into the intramuscular tendon. Intramuscular (also described as central)2 refers to the part of the tendon onto which muscle fibres insert (as opposed to the ‘free’ tendon). Brukner and Connell contend this has implications for treatment and prognosis.1 Not everybody agrees.

Are they really different?

The ‘traditional’ strain injury typically involves the musculotendinous junction, while the newly proposed injury subtype extends into the tendinous tissue. Tendon healing, characterised by a slow metabolic rate due to lower oxygen consumption, is a more time-consuming process than muscle healing.3 Hamstring and rectus femoris injuries involving the free tendon are associated with a longer time to return to preinjury level.4 Hamstring injuries with intramuscular tendon involvement take longer to heal2 5 and are more susceptible to reinjury.5 Considering the different anatomical location and prognosis, it appears that we might be faced with an altogether different type of injury.

However, the current body of evidence is entirely retrospective and consists of 27 cases. More importantly, treating physicians were not blinded to MRI results in these studies (i.e., presence of tendon involvement), and as a result there is high risk of bias in the return to play decision making. Although there are clues that involvement of the intramuscular tendon has implications for prognosis and possibly management, it would be infelicitous to conclude that we are faced with a distinctly ‘new’ clinical entity. Could you identify another subtype of injury or illness in general medicine (with just 27 cases described) that justify a review, several conference lectures and numerous editorials?

Why what happens next matters to you

As is often the case with the ‘appearance’ of potential new entities, clinicians lack evidence to guide their risk profiling, prevention and management strategies. To develop an evidence-based approach requires prospective studies with large sample sizes and low risk of bias.6

Muscle injury registry: strength in numbers

A concerted effort is needed to establish a number of (large) well-planned sequential investigations. This calls for a detailed muscle injury registry (including hamstrings, quadriceps and calf muscles) across all sporting codes. Such a registry would ideally provide information about the mechanism, clinical presentation and treatment of the injury, as well as data on outcome measures such as return to play or recurrence rate, as already implemented by UEFA.7 This integration of information might also lead to a more accurate muscle injury grading system.

There is strength in numbers. Similar projects have led to remarkable achievements in general medicine. Data collection on malaria mortality has been challenging and is relatively sparse in sub-Saharan Africa. An ensemble of different microsimulation data models (leveraging data collation and the relationships between different metrics) was developed and used together with high-resolution population maps. This approach led to greater understanding of the clinical incidence and how to direct prevention efforts.8 We could achieve similar results in sports medicine.

It will require collaboration between sporting organisations (from national clubs across different sporting codes to International bodies such as FIFA, International  Association of Athletics Federations, UEFA and the IOC), their affiliated teams, researchers and practitioners like you to allow for the appropriate scientific and clinical veracity needed to make meaningful conclusions. Collating data might also overcome pressure on resources, such as data analyses and recruitment difficulties.

We have identified four key steps to move this project forward:

• identify the main priorities (use one muscle group i.e. hamstrings to initiate project)

• funding must be secured (within formal research funding bodies as well as corporate/commercial collaboration)

• leverage technology through data processing platform and app-based data collection

• Create awareness and build capacity to connect with as many partners as possible (from formal institutions and teams to clinical practitioners in the field).

Prominent research groups from four different countries (Aspetar Sports Medicine and Orthopaedic Hospital, Oslo Sport Trauma Research Centre, Australian Catholic University Hamstring Injury Group and Academic Centre for Evidence-Based Sports Medicine) have already shown their interest and initiated the first step.

It is time to leverage our collective strength and share our resources. Implementing such joint data analytics will advance management of muscle injuries. We appeal to international leaders to heed the call from athletes and clinicians. Please prioritise team science focused on superior athlete outcomes.