I recently had a patient with a musculotendinous junction injury. Also known as the muscle-tendon junction (MTJ), it acts like a bridge to transfer forces from the muscle via the tendon to the connecting bone the muscle attaches to. This allows for movement to take place.
It's a common site for injury as the MTJ undergoes some stress during daily activities and substanstial stress while playing sports. MTJ injury is often accompanied with both muscle and tendon injuries leading to restricted force trasmission.
Due to it's highly specialized structure, it does not often heal well after injury. Conservative treatment are mostly effective for minor MTJ sprains while partial tears and complete ruptures will require surgical intervention.
It can happen during a fall leading to trauma to the area. It often occurs due to repeated overload, usually from high intensity training in young athletes or overuse in middle age or older adults. My observations are MTJ injuries usually happen after a period of rest/ decreased muscle use followed by a period of intense muscle activity.
An example who be my patient mentioned above. He went on holiday for 3 weeks with no exercise and resumed his weekly basketball game on returrn and promptly tore his hamstrings at the MTJ. These tears occur frequently during eccentric muscle loading.
They are usually complete muscle. In hamstring injuries this account for 14.4% of all bicep femoris injuries. The supraspinatus muscle has the highest incidence of the tendon midsubstance injuries (11.4%). Complete tendon avulsions are more frequent in the triceps brachii and pectoralis major.
Conservative treatmant options like rest, ice and compression etc helps in the initial stages if the tear is small. Several studies have indicated that surgical treatment yields better results in terms of function, strength, patient ratings and recovery to pre-injury performance for the more serious tears.
Continous development of tissue engineering that focuses on regenerating new tissue from cells are now helpful to MTJ injuries by utilizing biological and synthetic scaffold-based tissue. This helps in the repair and healing of MTJ tears. However it is not easy to fully mimic the unique characteristics of our muscles, tendons and the MTJ itself.
Hopefully, newer polymers and scaffolds will help with healing of MTJ injuries in the future. For now, please be vigilant in your exercise after a period of rest. Avoid exercising at higher intensities initially while allowing for your muscles to adapt again. Note that the calf, pectoralis major (chest) and hamstrings are the most vulnearble areas.
Reference
Tong Sm Sun Y, Kuang B et al (2024). A Comprehensive Review Of Muscle-Tendon Junction: Structure, Function, Injury And Repair. Biomedicines 12, 243. DOI: 10.3390/biomedicines12020423
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