Last week I discussed the muscle linings of the Cutaneous Trunci. This week, I’d like to focus on another superficial muscle close to it: The Tensor Fascia Latea.
The Tensor Fasciae Latae is a superficial muscle located in the horse’s hindquarter. It is complex in nature due to its multiple attachments. The muscle originates at the Tuber Coxae [Point of Hip] - sharing a partial partnership with the Superficial Gluteal. It has direct insertions at the Fascia Latae and Crural Fascia of the Limb as well as indirect insertions due to fascial tissue connections, at the Patella, Lateral Patellar Ligament and Tibia Crest.
The TFL flexes the hip joint and extends the stifle whilst tensing the Fascia Latae and acts in opposition to the Semitendinosus that extends the hip and hock joints while flexing the stifle. It is also part of the myofascial Spiral Line and Functional Line that is related to the movement around the sagittal axis i.e., rotation of the spine as well as the Lateral Line which is related to the movement around the vertical axis. It has to work with the vertebral column both in extension and flexion. During walk and trot, activity of the TFL usually begins in the middle of the stance phase and ceases in the early period of the swing phase. During canter, the TFL of either loading limb or trailing limb is usually active from the early period of the stance phase to the end of the stance phase or the early period of the swing phase. The longer activity of the TFL in canter can be explained by the necessity of more support and stabilisation for the joints in faster gaits. It is important to understand the TFL is closely connected to surrounding muscles such as the Biceps Femoris, Quadriceps and it is considered to be part of the so-called ‘ventral’ chain which provides support and maintains posture. In most horses, the TFL shows a higher amplitude of activity in the stance phase than in the swing phase, which would indicate that the muscle acts stronger as an extensor or stabiliser of the stifle than as a hip flexor during locomotion.
In some horses, the action of the Tensor Fascia Latae upon the extension phase of the hind limb shows with some ‘strands’ as if pulling a plastic bag. On the opposite, the muscle might show a big ‘blob’ during the flexion phase of the hind limb – especially in canter. This results in a ‘blob’ – ‘strain’ – ‘blob’ – ‘strain’ pattern.
What is causing this phenomom? 1. Dysfunction. Sometimes it is as simple as that! Although the muscle although the muscle should tense the Fascia Latae upon extending the stifle, it should do so smoothly. If the muscle is functional, but simply underdeveloped, the muscle action is just weak, but still pure. This is acceptable, especially in the young horse that has not been trained a lot yet. The muscle should then gradually strengthen and develop with proper exercise in conjunction with the other muscles in the hindquarters. However, if the muscle shows up with ‘strands’, it is not just weak, but dysfunctional. It is tight and trying to hang on. The Fascia can sometimes tear. Some horses shows one ‘strand’ coming up from low point on the Tubercoxae, some horses show a double pattern on both the upper and lower part of the Tubercoxae.
The cause of dysfunction can be multiple: 1. Injury / Dysfunctional anatomy. It is commonly caused by underlying issues or restrictions in the lower back, hip, hock and stifle. It is thus key to check and restore functionality and mobility as much as possible in these joints to improve the muscle tone of the TFL. 2. Overuse. Training needs to be build up progressively. If this is not done correctly, naturally the abovementioned joints and surrounding structures will also start to struggle, but then mobilizing through treatment will not be enough as without adaptations in the training, the problem will re-occur. 3. Lack of oxygen. This is a general cause that can have a genetical link and underlying problems such as cardio-vascular issues or lung problems or pathologies such as Equine Exertional Rhabdomyolysis. Faster gaits require more oxygen and thus more contraction of the FTL as already mentioned earlier and thus this could be a problem. On the other hand, weak muscles in general can also cause oxygen deprivation as the diaphragm is weaker to support deep breathing. 4. Neurological compression. This is also a more general cause. Muscles are innervated by neurons. Hence, compression of the nervous system could alter the functionality of muscles.
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