Hamstring Muscles: When it comes to the Hamstrings do not get Hamstrung. Arlene Johnston January 24, 2014

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1 Hamstring Muscles: When it comes to the Hamstrings do not get Hamstrung. Arlene Johnston January 24, 2014 Abstract The muscles in the hind limbs of dogs, called the hamstrings are a very powerful and essential group of muscles made up of striated or voluntary muscle fibers. This paper will show what muscles are included in this group, called the hamstrings. Why is the group called the hamstrings, what actions these muscles have, their size, their sites of origin and insertion, the tendons and ligaments involved, and nerve and blood supplies involved in these very important muscles. When it comes to the hamstrings do not get hamstrung The hamstrings got their name from the way European butchers would hook through these muscles, behind the knee, to hang up legs of slaughtered pigs in their shops to sell, hence the ham and the stringing. This also correlated to the battle fields of swordsmen, and in Roman times, and as a form of torture. In battle lacerating through these muscles of men, with their swords, or their steeds, they were rendered helpless, unable to move, and the pain and blood loss that occurred, provided an effective means of torture. In modern times the term hamstrung is used to describe the inability to move forward, with regards to thinking or application of a project for example. The three main muscles of the hamstring group are the biceps femoris, semitendinous and semimembranous muscles (see figure1). There is also a fourth, less significant muscle of this group called the caudal crural abductor (see figure 2). This muscle is only present in carnivores and has the function to abduct the limb, with the origin being the sacrotuberous ligament and the insertion being the crural fascia (reference 1 ). The hamstrings cover the caudal side of the thigh and are involved with many of the functions of the hind limb joints. They begin as high as the ischium and end as low as the tibia. The main action of this group of muscles is to extend the hip joint (reference 1). Biceps femoris. The largest of the hamstrings is the femoral biceps; it is superficial covered only by the skin and fascia. The origin of the biceps femoris, the semitendinous and semimembranous is the ischial tuber and adjacent sacrotuberous ligament. The insertion point of the biceps is the patella and stifle ligaments, via the femoral and crural fascia. Tendons of the bicep also join tendons from the superficial digital flexor and gastocnemus to form the common calcanean tendon (see figure 2).The function of the biceps is the extension and abduction of the limb. It causes tarsal extension. The cranial part extends the hip and stifle, though the caudal part extends the hip but flexes the stifle (reference 3 and 4 ) Semitendinous. Page 1

2 The function of the semitendenous muscle is to extend the hip, stifle and tarsus when the foot makes contact with the ground, therefore propelling the dog forward. On a non-weight bearing leg it flexes the stifle and rotates the leg back and out. The origin for this muscle is the pelvic head and the insertion is the medial proximal tibia and a tendinous insertion on the calcaneal tuberosity, through joining the tendons from the superficial digital flexor and gastocnemius to form the common calcanean tendon (see figure 2), (references 3 and 4). Semimembranous. This is the most medial of the hamstring group and has the function to extend the hip and stifle in a weight bearing stance and on non-weight bearing limbs, it adducts and retracts the limb. The origin of the semimembranous muscle, as with the other two hamstring muscles, is the pelvic head. The cranial insertion is onto the medial femoral condyle and the caudal is onto the medial tibial condyle (references 3 and 4) Blood supply The abdominal aorta ends by splitting into the internal and external iliac arteries. (see figure 3). The internal iliac artery has a branch, the caudal gluteal (see figure 3), that serves the proximal hamstring muscles (reference 4). The external iliac is the main artery of the hindlimb, it has a number of branches as it decends the limb, the branch which is the main server to the biceps femoris, semitendinous and semimembranous is the distal caudal femoris ( see figure 3). The veins that return the blood up the hind limb coincide with the names of their arteries. The main veins that are connected to the hamstrings are, distal to proximal, the distal caudal femoral, to the femoral vein, to the external iliac and then into the caudal caval vein (see figure 3). Nerve supply The main nerve that serves the hamstrings is the sciatic nerve and its branches (see figure 4). The origin of the sciatic nerve is lumbar nerves L6 and L7 and sacral nerves S1 and S2. The sciatic nerve provides motor innervations to the femoral biceps, semitendinous and semimembranous muscle group. The sensory innervations from the sciatic nerve to the hamstrings are provided by way of the fibula and tibial branches of the sciatic. Move forward and work those thigh muscles. These large muscles are straightforward to find and feel on a dog and when healthy the muscles feel smooth with a consistent temperature. In a dog that is very active or that jumps/bounces allot, the hamstrings may feel enlarged or even look out of proportion due to their constant use, building the mass of the muscle. Hamstring muscles are used for all running and jumping activities and therefore can be susceptible to tearing and pulling just like human muscles. Page 2

3 A canine massage therapist can perform work on the hamstring muscles to help reduce the risk of common injuries. Massage can be done to prevent injuries, after an injury has occurred or after surgery to correct an issue. As with human muscle when injuries occur there is pain, inflammation and possible internal bleeding. Massage strokes, rocking and stretching can help address injuries and weaknesses in the muscles. The injured muscle may feel swollen and hot to the touch and the dog could express discomfort when the area is touched. Under the consult of a veterinarian, massage work can be done to reduce the inflammation, pain and discomfort of the dog. Muscle strain is commonly seen in canine athletes that perform activities that result in sudden acceleration, turns, and jumping ( ). Keeping the hamstrings strong and flexible can reduce the risk of common injuries in dogs undertaking any exercise. References Anatomy of the dog (Google ebook) by Klaus Dieter Budras, Manson Publishing, Sep 13, 2007, page Kainer, Robert A., DVM, MS and McCracken, Thomas O., MS. (2003) Dog anatomy, a coloring atlas. Plates 31, 33 and 34. Page 3

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