Introduction

Myofascial trigger point (TP) pain is a common painful muscle disorder. Travell and Simons have defined a trigger point as “a hyperirritable spot in skeletal muscle that is associated with a hypersensitive palpable nodule in a taut band. The spot is tender when pressed and can give rise to characteristic referred pain, motor dysfunction, and autonomic phenomena” [1]. Skeletal muscles are the largest single organ in the human body, accounting for approximately 50% of body weight. Any one of these muscles can develop a myofascial TP which is the hallmark physical exam sign of myofascial pain (Figure 63.1a,b). Compression of a TP may elicit local tenderness, referred pain, or local twitch response.

Acute trauma or repetitive microtrauma, inflammation and other factors may result in the development of a TP [2]. Injection on the TP is one of the most effective treatment modalities to loosen the taut bands and relieve pain promptly [3]. It is known as a low-risk procedure; however, serious adverse effects are observed. TPs frequently appear in musculoskeletal disorders such as myofascial pain syndrome, fibromyalgia, and temporomandibular joint disorders [4]. They may also occur in patients with cervicogenic headache, migraine, post-traumatic, and other headache disorders [5].

Myofascial pain syndrome (MPS) is defined as a musculoskeletal pain disorder caused by one or more myofascial TPs and their associated reflexes. MPS typically involves myofascial TPs found within the belly muscle of one or more muscles or muscle groups, but they can also be found in ligaments, periosteum, scar tissue, skin, and tendons. MPS may be the most common cause of persistent musculoskeletal pain, including chronic low back, head, neck, and shoulder pain. This syndrome is also associated with other chronic pain conditions, such as osteoarthritis, rheumatoid arthritis, migraine, and tension-type headaches, complex regional pain syndrome and whiplash-associated disorders.

Indications

• Myofascial pain syndrome
  
• Whiplash associated pain
  
• Chronic abdominal wall pain
  
• Cervicogenic headache
  
• Tension headache
  
• Post-traumatic headache
  
• Migraine headaches
  
• Rheumatism
  
• Fibromyalgia.

Contraindications

Absolute:

• Presence of local or systemic infection
  
• Acute muscle injury
  
• Patient refusal
  
• Allergy to the drug of injection
  
• Children under 18 (with some exceptions e.g. rheumatoid arthritis).

Relative:

• Bleeding disorders or being on anticoagulant therapy
  
• Diabetes
  
• Pregnant patient
  
• Immunosuppression
  
• Poorly controlled psychiatric disorders
  
• Large tendinopathies
  
• Needle-phobic.

Substances Potentially Injectable into Joints and Soft Tissues for Therapeutic Effect

Technique

1. Patient preparation
   
   
   
   • Medical history and examination
     
   • Discard contraindications
     
   • Informed written consent, signed and supervised
     
   • Discuss possible side effects with patient
     
   • Comfortable position for injection.
   
   
2. Select injection type
   
   
   
   • Dose and volume according to the structure
     
   • Check labels and expiry dates.
   
   
3. Equipment
   
   
   
   • Aseptic environment, preferably an operating theater
     
   • Rigorous sterile material
     
   • Iodine/alcohol preparation of skin
     
   • Sterile in-date needle
     
   • Correct gauge-length of needle/cannula
     
   • Check for allergy
     
   • Ultrasound (US) guidance vs. X-ray.

Palpate the TP in the taut band and place the muscle in a slightly stretched position to prevent it from moving. Once a TP has been located and the overlying skin has been cleansed with alcohol, the clinician isolates the point with a pinch between the index and middle finger or presses the point by the index or middle finger of the non-dominant hand to find the taut band and most sensible site. The clinician then holds the needle which is attached to the 3- or 5-ml syringe by the dominant hand and inserts the needle into the TP at an angle of 30–45° to the skin. Before advancing the needle into the TP, the physician should warn the patient of the possibility of sharp pain, muscle twitching or an unpleasant sensation as the needle contacts the taut muscular band. A small amount (0.2–1 ml) of medication is injected once the needle is inside the TP. Lidocaine 0.5–1% is commonly used. Other substances such as corticosteroids, botulinum toxin type A (Botox), and PRP (platelet-rich plasma) have been chosen in TP injections. Needling the area in multiple directions is suggested by inserting and retracting the needle repeatedly without completely withdrawing the needle from the muscle until the local twitch response is no longer elicited. Pressure is then applied to the injected area for two minutes to avoid bleeding [7, 8] (Figures 63.2a,b and 63.3a,b).

US-guided TP injection is recommended to confirm the desired structure and depth while avoiding neurovascular and visceral structures which is a serious issue [9, 10].