Introduction

Muscles in the foot and leg are at a challenging crossroads location as they are included in the referral patterns of multiple proximal muscles such as the gluteus minimus, medius and maximus muscles, the piriformis, tensor fasciae latae, adductors longus and brevis, vastus lateralis, sartorius, semitendinosus and semimembranosus, and biceps femoris muscles (Travell & Simons, 1992; Dejung et al., 2001). The links between proximal and distal muscles may have a predominant sensory pattern, whereby secondary hyperalgesia from proximal trigger points (TrPs) may be present in the leg and foot but may also be predominantly mechanical in nature. TrPs in the gluteal medius muscle, for example, may cause an altered gait pattern leading to overuse of the gastrocnemius muscle. Pain and dysfunction caused by TrPs in foot and calf muscles induce gait alterations that overload muscles higher in the lower limbs and in the spine (Lewit, 2010). For example, subjects with a lowered arch had significantly more TrPs in the flexor digitorum longus, tibialis posterior, and vastus medialis muscles compared with controls (Zuil-Escobar et al., 2015).

Often, patients experience mixed patterns combining biomechanical and sensory aspects. Cuccia (2011) described a direct link between dental occlusion and the plantar arch. Such correlations are not limited to the lower leg and foot. Several studies found correlations between mouth opening, TrP sensitivity, and stretching of the hamstring muscles (Bretischwerdt et al., 2010; Rodriguez-Blanco et al., 2015; Espejo-Antúnez et al., 2016). Even more intriguing is the finding that treating suboccipital muscles can increase hamstrings flexibility (Aparicio et al., 2009; Cho et al., 2015).

The muscles in the foot and leg are the first line of defense of any anatomical or biomechanical problems occurring in the foot and, consequently, become easily overloaded by these issues leading to development and activation of TrPs (Travell & Simons, 1992; Saggini et al., 1996). Joint dysfunctions and inappropriate shoes can also either cause or add to these problems. In other words, the treatment of TrPs in the leg and foot muscles is necessary but usually insufficient to fully solve our patients’ problems because proximal muscles, as well as several other perpetuating factors, must be addressed for a complete and long-lasting relief of the symptoms. A multimodal approach including dry needling (DN) is recommended over single modality treatment approaches (Segura-Perez et al., 2017).

The reliability of identifying TrPs in the lower leg has been confirmed by Sanz and colleagues (2016), who were able to reach acceptable pairwise interrater agreement for the presence or absence of TrPs and local twitch responses in the tibialis anterior muscle and for taut bands, referred pain, and the jump sign with the extensor digitorum longus muscle. The percent agreement for the fibularis brevis muscle varied. Latent TrPs are commonly found in asymptomatic individuals. The finding of a taut band and tender spot were the most reliable diagnostic criteria (Zuil-Escobar et al., 2016). Note that in the US nomenclature, the peroneal muscles are now referred to as the fibularis muscles. In this chapter, we use the US term.

Clinical relevance of trigger points in leg and foot pain syndromes

Pain syndromes in the leg and foot span from simple delayed onset muscle soreness to plantar fasciitis, including calf cramps, shin splints, Morton’s neuroma, tendinopathy of the Achilles tendon and other tendons, posterior tibial nerve or deep fibularis nerve entrapments, compartment syndromes, ankle or foot sprains, instability, complex regional pain syndrome type I (CRPS I), intermittent claudication, and metatarsalgia, among others. The contributions of TrPs in the leg and foot muscles to these conditions can be highly variable, but scientific evidence and clinical impressions support that TrPs often play an important role. Professional soccer players with ankle pain presented commonly with TrPs particularly in the tibialis anterior and fibularis muscles (Pérez Costa & Torres-Lacomba, 2016). Salom-Moreno and colleagues (2015) confirmed that TrPs in the fibularis muscles play a significant role in ankle instability. Adding DN of TrPs in the fibularis muscles to a proprioceptive and strengthening exercise program improved outcomes in pain and function even 1 month after therapy had been concluded. A case report of a patient with postsurgical knee pain mentioned that the combination of ultrasonography-guided pulsed radiofrequency, physiotherapy, medication, and DN of TrPs in the quadriceps, hamstrings, adductors, sartorius, gracilis, gastrocnemius, and popliteus, successfully resolved the patient’s pain for at least 6 months (Vas et al., 2014). A study of patients with a variety of foot problems, such as plantar fasciitis, metatarsalgia, hallux valgus and hallux rigidus, Morton’s neuroma, and longitudinal arch pain, among others, compared manual TrP treatments and customised orthotics with a treatment protocol with only soft prefabricated insoles. The combination of customised orthotics and TrP compression yielded significantly better results as assessed by the Foot Function Index and the Patients’ Perceived Improvement Score (Hains et al., 2015).

Moghtaderi and colleagues (2014) observed that the application of extracorporeal shock wave therapy for plantar fasciitis was more effective when TrPs in the gastrocnemius and soleus muscles were included in the therapy. In addition, clinical experience shows that symptoms arising from TrPs often mimic many of these conditions, inducing incorrect diagnoses that lead to erroneous and ineffective treatments. A combination of TrPs in the tibialis posterior, the soleus, and gastrocnemius muscles, for example, may mimic an Achilles tendinopathy. TrPs in the third dorsal interosseous muscle may reproduce the symptoms of a Morton’s neuroma, whereas TrPs in the fibularis muscles may imitate the pain of an ankle sprain, and so on.

Although many different possible aetiologies are proposed for calf cramps, TrPs in the calf muscles, particularly in the gastrocnemius, seem to be important contributors (Travell & Simons, 1992; Ge et al., 2008; Xu et al., 2010). A clinical trial with a small sample of 24 subjects showed that xylocaine injections of TrPs in the gastrocnemius muscle induced a significantly better long-term efficacy on calf cramps compared with oral quinine (Prateepavanich et al., 1999). TrPs in the gastrocnemius and soleus muscles were successfully treated with a multimodal approach consisting of TrP pressure release, TrP self-release, and a home stretching program (Grieve et al., 2013a). In another study, Grieve and colleagues (2013b) found that a single application of manual compression of TrPs in the gastrocnemius and soleus muscles combined with stretching improved ankle range of motion in 22 recreational runners with a clinically meaningful increase.

Plantar heel pain, often diagnosed as plantar fasciitis, is commonly due to TrPs in the calf and foot musculature. Several reports have shown this close relationship and proven that conservative treatment of TrPs in calf muscles is useful in the treatment of plantar heel pain and plantar fasciitis (Nguyen, 2010; Renan-Ordine et al., 2011). Ajimsha and colleagues (2014) found that myofascial release was helpful in reducing plantar heel pain. DN and injections of TrPs in the calf and foot muscles may be helpful in the management of this condition (Imamura et al., 1998; Kushner & Ferguson, 2005; Cotchett et al., 2010; Sconfienza et al., 2011; Akhbari et al., 2014). Cotchett and colleagues (2014) reported that DN significantly reduced plantar heel pain, although the level of minimally important difference was insufficient. Eftekharsadat and colleagues (2016) confirmed that TrP DN significantly reduced the pain of plantar fasciitis, but it had no significant effect on ankle dorsiflexion and eversion. A recent meta-analysis of seven randomised controlled trials has shown that TrP DN effectively reduced the pain associated with plantar fasciitis (He & Ma, 2017).

An older study attributed medial tibial stress syndrome (shin splints) to overload of the attachments of the soleus muscle (Michael & Holder, 1985). One study showed that tension in the soleus, tibialis posterior, and flexor digitorum longus muscles caused a tenting effect that exerted a force on the distal tibial fascia directed to its tibial crest insertion (Bouche & Johnson, 2007). Another study demonstrated that the plantar flexors of the ankle were significantly weaker in medial tibial stress syndrome (Madeley et al., 2007). Increased tension and weakness are two cardinal features of muscles affected by TrPs. Nevertheless, the possible involvement of TrPs in these muscles in medial tibial stress syndrome has not yet been established unequivocally, and no clinical trial to date has proven that TrP treatment can be of help in the management of this condition.

Although Travell and Simons (1992) suggested that there was a ‘a strong possibility that, in muscles prone to developing a compartment syndrome, TrPs may make a significant contribution’, there is no actual evidence in the literature. The safety of using DN, which could potentially cause some bleeding in the muscle, has also not been established in patients with compartment syndrome; hence, more aggressive DN approaches such as Hong’s fast-in and fast-out technique, screwed-in/out techniques, or DN with thick needles may be considered possible contraindications. The risk of bleeding is increased when patients take anticoagulants, but this is not an absolute contraindication to DN (Muñoz et al., in press). Yet there is some question as to whether needling of deeper muscles, such as the tibialis posterior muscle or the lateral pterygoid muscle, can be performed safely without ultrasound guidance considering their close proximity to major arteries. On the one hand, clinicians have been needling the posterior tibialis muscle without any evidence of injury, but it is at least conceivable that, in some individuals, there may be an increased risk of bleeding. A recent case report describing a 41-year-old female with a vertebral artery dissection after receiving acupuncture to the neck demonstrated that small filiform needles are able to damage blood vessels (Hong et al., 2017). As the location of the neurovascular bundles in the leg can vary substantially (Fig. 12.1), a clinician may never know the exact location; however, it is unknown what the actual risk is of damage to these deeper blood vessels. Upon review of other needling procedures, such as venipuncture, electromyography, and botulinum toxin injections, Muñoz and colleagues concluded that DN does not pose a severe risk, but some caution is nevertheless warranted (Muñoz et al., in press).

Allen and colleagues (1999) reported that 42% of patients with complex regional pain syndrome (CRPS) in the lower extremities presented with active TrPs in their proximal muscles. In this study, only the lumbar paraspinous and gluteal musculature were examined, which raises the question as to what percentage of active TrPs would have been found if other lower extremity muscles had been included in the examination (Allen et al., 1999). Early treatment of TrPs is usually recommended in patients with CRPS I to decrease their pain intensity and disability (Dommerholt, 2004). Although the use of DN has not yet been reported for CRPS, a recent report of two cases of upper limb CRPS I showed promising results with treatment of proximal TrPs with botulinum toxin injections (Safarpour & Jabbari, 2010). Chang (2017) described using TrP injections in several cases with CRPS.

TrPs in the popliteus, plantaris, and gastrocnemius can also contribute to posterior knee pain, which is more commonly attributed to knee joint problems. TrPs in the proximal part of the gastrocnemius muscle can be responsible for posterior knee pain in patients before (Mayoral et al., 2013) and after (Aceituno, 2003) total knee replacement surgery and after knee arthroscopy (Rodríguez et al., 2005). DN is used increasingly in the treatment of tendinopathies such as Achilles tendinopathy (see Chapter 3). Chaudhry (2017) suggested to combine ultrasound-guided, high volume, image-guided injections with DN for Achilles tendinopathy, but acknowledged the limited research.

Further research is needed to elucidate the possible contribution of TrPs to the previously mentioned conditions or to other structural problems such as hammer toes (Travell & Simons, 1992) or hallux valgus, or to different leg and foot nerve entrapments (Crotti et al., 2005; Saggini et al., 2007).