Ruby, a two-year-old female spayed Labrador retriever had a traumatic diaphragmatic hernia repair and a shearing wound/right tarsocrural instability stabilized with an external fixator. Over the next month, the tarsal injury required debridement, treatment for infection, and bandage changes. Eight weeks after her injury, a full thickness mesh skin graft, harvested from her lateral abdomen, was placed atop the granulation tissue on her right tarsus. One week later the external fixator was removed. She had only partial weight bearing of the right hind leg, and once released from exercise restriction she began to run and play Frisbee on three legs. She remained three-legged lame despite rehabilitation therapies for the next four months when she was referred to the Pain Consultation and Referral Service at Cummings School to explore alternatives to amputation of the limb.
Diagnosis and Treatment
Upon presentation, she carried her right hind leg with the stifle near her abdomen, stood and walked with her spine bowed out to the left. (See video) Tight, abnormally firm muscle bands were palpated in her quadriceps, gluteal, and hamstring muscle groups as well as bilaterally along her entire spine and in both shoulders. These “contractured” muscles limited range of motion, preventing normal extension of her coxofemoral, stifle and hock joints. With a presumptive diagnosis of myofascial trigger points (MTPs, or MTrPs), treatment with trigger point dry needling was recommended to release the MTPs and permit normal muscle lengthening. Under sedation with butorphanol and dexmedetomidine, 32-gauge, one-inch acupuncture needles were inserted into the palpable taut bands of muscle in numerous muscle groups, followed by passive stretch and hold. Immediately after needling, softening of the muscles and improvement in range of motion / extension of her stifle, hock and hip could be appreciated. After reversal of sedation, Ruby was able to drop her left stifle away from her abdomen and place her foot on the ground. She walked out of the clinic using the leg to walk about 60 % of her strides. Home therapy with application of warmth, massage and passive stretch was prescribed. Subsequent treatment sessions were performed two more times at 2 – 3 week intervals, at which point she was using the leg approximately 90% of the time. Additional treatments were declined until several months later when she was injured while playing and became lame again. At this point, a tapering course of gabapentin and amantadine to reduce central sensitization was started, and two additional sessions of dry needling were performed. Also, the scar from her skin graft was treated with conventional acupuncture and massage. Her activity was changed from active Frisbee and beach running to long daily leash walks. Eighteen months after her final treatment session, her gait abnormality is almost entirely resolved – she has some residual tarsal instability and is unable to place the heel of her left hind foot entirely on the ground due to tissue restrictions of her lower limb, but is back to playing Frisbee and medication free. (See video) Her owner says, “Ruby is doing terrific! She lets us know when she has had enough and takes her Frisbee inside with her!”
What are myofascial trigger points?
MTPs are hyperirritable foci within skeletal muscle that are found along taut bands of muscle. Histologically, they are reportedly nodular, rounded, and contain large diameter muscle fibers. They are said to form in response to a variety of physical stimuli, such as eccentric contraction, deep intramuscular injections, limb immobility or muscle compression by bandages, or scars, from local muscle ischemia and other metabolic conditions. There are many excellent reviews of the etiology and pathology of trigger points. The most important things to understand about MTPs are: 1) they may arise in response to pain; 2) they may be a cause of significant pain; 3) they may also be responsible for muscle dysfunction, including weakness; and 4) effective treatment of MTPs may eliminate pain and restore muscle function. Myofascial pain accompanies a number of clinical syndromes in dogs, including osteoarthritis, IVDD, post-surgery, trauma, or following protracted immobilization. The author has found that, when a specific cause for pain is not discernable (i.e. joint instability), or successful surgical intervention fails to resolve pain and restore function adequately, and conventional pain relievers are not effective, that examination and treatment of MTPs may in many cases resolve, or be associated with resolution of pain. Canine sports medicine and rehabilitation professionals are versed in the theory and application of treatments for MTPs; however some typical rehabilitative therapies, such as passive stretch and aqua therapy, may exacerbate MTPs and fail to resolve pain and dysfunction unless MTPs are also treated.
What were potential causes of Ruby’s MTPs?
In Ruby’s case, she had many instigating and perpetuating reasons for having myofascial pain:
She had injury followed by prolonged pain from trauma, surgical interventions, and infection
She had her tarsus immobilized for 9 weeks, which prevented her from extending the stifle and hip normally.
She had a tight, adhered scar from her skin graft donor site that very likely “grabs” her when she moves, and scars may contain entrapped nerves/neuromas that fire abnormally when tugged on.
She was an enthusiastic athlete who was, once released from exercise restriction, playing extreme Frisbee, running in sand and jumping in and out of her pool, thus re-instigating MTPs by causing eccentric contraction (think “pogo-stick”) of her muscles.
Factors A and C are well-recognized causes of chronic pain, characterized by central sensitization – abnormal impulse generation and propagation by the central nervous system. Factor B favored contracture and D simply acted to habitually “reset” some of her trigger points.
What types of treatment for MTPs can be considered?
The medical literature for MTP related pain and dysfunction contains several possible modalities for treating trigger points. Many of them will have similar bases – the muscle knots and resulting taut, restrictive bands of muscle are influenced by physical means such as massage, careful stretch, low level laser, therapeutic ultrasound, shock wave, acupuncture and trigger point dry needling. However, it is necessary to know “where to treat,” as random application of physical methods will yield random results. Trigger point dry needling, while performed with acupuncture needles, differs from conventional acupuncture in that the points treated are found by a process of palpation and consideration of muscle forces/range of motion. Dry needling can produce immediate and dramatic increases in muscle length and function. Medications, while useful in reducing the pain perceived due to MTP and dysfunction, are seldom able to achieve resolution of trigger points. However, in Ruby’s case, the course of gabapentin and amantadine were instituted because, after four months of non-weight-bearing, and nearly 12 months of chronic pain, the contribution of the now quite pathological state of her nervous system in maintaining muscle dysfunction was deemed to be a perpetuating factor as well.