The Use of Physiotherapy in the Conservative Treatment of Cubital Tunnel Syndrome: A Critical Review of the Literature

Background: The lack of a clear answer regarding the efficacy of physiotherapy in the treatment of cubital tunnel syndrome (CuTS) has led to attempts to critically assess the scientific studies conducted to date. Materials and Methods: Two databases (MEDLINE via PubMed and PEDro) and Google Scholar were used to search for papers. The inclusion criteria were randomized controlled trials, case series, and case reports that evaluate the effects of physiotherapy in the treatment of patients with CuTS. Results: A total of 18 studies met the eligibility criteria, capturing a total of 425 participants. Seven papers were randomized controlled trials, three more described prospective studies without a control group, and eight papers contained case reports. An analysis of the literature evaluating the effectiveness of various forms of broadly defined physiotherapy indicates that their use can have a beneficial effect in reducing many subjective and objective symptoms and improving function. In the majority of papers included in this review, their authors indicated positive therapeutic effects. Only one randomized controlled trial reported no change following therapy. It can therefore be stated that the results of the research conducted so far are optimistic. However, only 7 of the 18 papers were randomized controlled trials, while 3 were prospective studies, and 8 papers were case studies, in which 23 people with CuTS were studied. Conclusions: The small number of randomized clinical trials and their considerable heterogeneity do not allow firm conclusions to be drawn about the effectiveness of physiotherapy in the conservative treatment of CuTS.


Introduction
Cubital tunnel syndrome (CuTS) is the second most common upper limb peripheral neuropathy in clinical practice after carpal tunnel syndrome [1,2].The incidence of CuTS is estimated at an average of 21-24 cases per 100,000 patients per year [3] (2-6% in the general population) [4].The typical clinical picture is characterized by sensory abnormalities in the early phase of the condition in the form of paresthesia and mild hypoesthesia, occurring paroxysmally and mainly related to the position of the elbow.Over time, sensory symptoms worsen, and motor disturbances gradually appear (weakness and atrophy of the intrinsic muscles of the hand) [5,6], which can lead to permanent sensory disturbances, paresis, and joint contractures [7].McGowan identified three stages of CuTS related to the severity of symptoms, ranging from paroxysmal subjective sensory symptoms (Stage 1), significant sensory loss and weakness of the intrinsic muscles of the hand (Stage 2), to severe sensorimotor deficits with muscle atrophy (Stage 3) [8].Failure to provide immediate and correct clinical diagnosis and appropriate timely treatment can result in significant impairment of hand function [9].This, in turn, can have a significant impact on activities of daily living, work, and perceptions of overall quality of health, which is not only a medical problem but also a social and economic one [10].
The diagnosis of CuTS is based on the medical history, physical examination, electrophysiological assessment, and ultrasound examination [9].However, with anatomical differences, a wide spectrum of symptoms, and the need to differentiate this problem from other neuropathies of the ulnar nerve, diagnosis often poses many problems [9].Forms of CuTS are often divided into primary (idiopathic) and secondary (symptomatic) [11].In the case of idiopathic CuTS, a specific morphological cause cannot be determined, making a correct diagnosis difficult [11].In the secondary form, on the other hand, there are multiple causes (trauma, degenerative changes, cysts, ganglions, etc.) [1,12] and multiple sites of compression of the ulnar nerve (arcade of Struthers, the medial intermuscular septum, the medial epicondyle, the cubital tunnel, and the deep flexor-pronator aponeurosis) [13].Such a variety of causes, sites of compression, and sometimes a lack of a tangible cause makes it significantly more difficult not only to diagnose but also to choose the most optimal form of therapy.
Both conservative and surgical approaches used in the treatment of CuTS [14].Conservative treatment is recommended in mild to moderate forms of CuTS [6].This usually includes pharmacological treatment [15,16], immobilization with elbow night splints [17], and education of the patient on how to change their habits at work and activities of daily living, with particular emphasis on avoiding prolonged elbow flexion [16].Physiotherapy is also often implemented and includes manual therapy with neurodynamic techniques [18,19], short wave diathermy [20], low-level laser therapy [21], extracorporeal shock wave therapy [22], and even dry needling [23].Unfortunately, as reported by Mezian et al. [9], conservative treatment of CuTS is based more on empirical experience than on a significant amount of high-quality scientific research.Surgical intervention is used in cases of advanced CuTS or when conservative treatment has failed.The most commonly used surgical methods are simple decompression [24], endoscopic techniques [25], medial epicondylectomy [26], or one of the anterior transposition methods: subcutaneous [27], intramuscular [28], or submuscular [29].However, there are no scientific reports indicating that any of these techniques can produce better results than the others [30,31].Palmer and Hughs emphasized that, to date, a 'gold standard' in the surgical treatment of CuTS has not been developed [1].Therefore, there is a lack of scientifically supported treatments for CuTS.This concerns both surgical and conservative treatment, including physiotherapeutic management.Few randomized controlled trials have examined the effectiveness of physiotherapy in CuTS [19][20][21] and the results and conclusions fail to unequivocally demonstrate the beneficial effects of the various physiotherapy methods.Other studies are mostly case reports or case series with a low number of patients studied [18,22,23], which have shown an improvement in the patient's condition but had a low level of reliability (they are not randomized controlled trials) and should therefore be approached with caution.To the best of our knowledge, there are no recommendations for the physiotherapeutic management of CuTS that are supported by strong scientific evidence.The lack of a clear answer regarding the efficacy of physiotherapy in the treatment of CuTS leads to the attempts to critically assess the scientific studies conducted to date on the use of various forms of physiotherapy in the conservative treatment of this neuropathy.This will help to identify areas that need such research and to deepen or extend the scientific research on the possibility of using different forms of physiotherapy in the conservative treatment of CuTS.

Materials and Methods
The literature review was conducted in December 2023.Two electronic databases (MEDLINE via PubMed and PEDro) and the Google Scholar search engine were used to search for papers.The search strategy for database papers was based on the use of key phrases and/or abbreviations, taking into account their respective English wording.The following terms were used: cubital tunnel syndrome, CuTS, physiotherapy, physical therapy, PT, electrostimulation, ES, ultrasound, US, magnet therapy, MT, shock wave therapy, RSW, shortwave diathermy, laser, neuromobilization, neurodynamic techniques, neurodynamic treatment, neurodynamic mobilization, nerve gliding exercises, neurodynamics, manual therapy, conservative treatment, and splitting.
Studies that met the following criteria were included in the review: (1) the participant had clinically and/or electrophysiologically diagnosed CuTS, and (2) any form of physical stimulus was used in the study.All papers were accepted regardless of the year of publication.The search was limited to papers published in English.
The titles and abstracts of the retrieved papers were analyzed to assess whether they met the inclusion criteria.Those that did not show relevance to the subject area studied were excluded, e.g., those that contain surgical treatment approaches.The bibliographies of the included papers were also analyzed to check whether other papers meeting the criteria had not been omitted (Figure 1).Studies that met the following criteria were included in the review: (1) the participant had clinically and/or electrophysiologically diagnosed CuTS, and (2) any form of physical stimulus was used in the study.All papers were accepted regardless of the year of publication.The search was limited to papers published in English.
The titles and abstracts of the retrieved papers were analyzed to assess whether they met the inclusion criteria.Those that did not show relevance to the subject area studied were excluded, e.g., those that contain surgical treatment approaches.The bibliographies of the included papers were also analyzed to check whether other papers meeting the criteria had not been omitted (Figure 1).
Randomized controlled trials have the lowest risk of bias, so they provide the most objective and reliable results.Most of the randomized controlled trials included in this review reported beneficial effects of the therapy (in 6/7 papers) [19,21,32,33,40,42].However, it should be emphasized that in only four papers [19,21,33,40] the diagnosis of CuTS was based on medical history, orthopedic examination, and electrophysiological examination, which is considered a 'gold standard' in the diagnosis of compression syndromes [43].In other studies, the diagnosis was based only on the medical history and orthopedic examination [20,32,42], which, of course, is very often sufficient in combination with an ultrasound examination, but, without an ultrasound and electrophysiological examination, other causes cannot be excluded, such as Guyon canal syndrome, cervical radiculopathy, or brachial plexopathy, which can produce similar symptoms [9].Special attention should also be paid to the different methodologies used in all eligible randomized controlled trials.The majority of the papers assessed pain complaints (5/7 papers) [19][20][21]32,40], but although pain is the predominant symptom, it is not necessarily specific to CuTS.While several studies investigated muscle strength [19][20][21]32,42], function [20,32,40], and sensation [21], only one analyzed the overall quality of health [20].The large spectrum of parameters studied makes it significantly more difficult to compare the results obtained from different studies.A similar observation can be made for the multitude of different physiotherapy interventions.In fact, different physiotherapy programs were used in each paper selected for review.In three out of seven papers [21,32,42], one of the groups used ultrasounds as one of the components of physiotherapy programs, and in two papers, it was used as the only form of therapy [21,42].Also, in three papers, the common element of the physiotherapy program was neurodynamic techniques [19,32,42], but the other components of the physiotherapy program were different.Neurodynamic mobilizations to enhance ulnar nerve gliding include sliding techniques and, to a lesser extent, tensioning techniques.A sliding technique is an alternation of combined movements of (at least) two joints in which one movement loads the peripheral nervous system while the other movement simultaneously unloads the nervous system.These techniques facilitate nerve gliding without intensely challenging the nervous system.This process allows gliding to take place inside the nerve itself and between the surrounding tissues.The patient is in a supine position with a contralateral side bending position of the neck.External rotation is 90 • abduction, and the shoulder is positioned in depression.The therapist executes passive forearm pronation and supination whereas the elbow is flexed to 90 • .In the second step, the therapist pronates the forearm and conducts passive elbow flexion from 90 • to 140 • from the first position.Third, the therapist conducts shoulder depression from 90 • to 120 • of abduction, beginning from the final position obtained with the elbow in 90 • flexion [18,32,42].Also, in three papers, limb immobilization with a splint was used as the only therapy or as one of the components of a therapy program [19,33,42].Other studies used short-wave diathermy [20], laser [21], shock wave [40], and strengthening exercises [32].
Benincá et al. [44] describe diathermy as the use of high-frequency electromagnetic currents to induce heat.It has many applications, such as producing tissue damage during surgery, hyperthermia treatment in oncology, and as a deep heating method in rehabilitation.The heating effects include pain relief, increased nerve conduction velocity, blood flow, local metabolism, tissue elasticity, and muscle relaxation.One form of diathermy used by physical therapists that achieves these effects is shortwave diathermy (SWD), which produces shortwave electric and magnetic fields in the tissue.SWD can be delivered by an inductive technique, in which the greatest amount of heat occurs in deep tissue, or by a capacitive technique, in which the greatest amount of heat occurs in superficial tissue.Inductive types of electrodes consist of a current flowing through a coiled cable that may be contained within drum or sleeve electrodes.Capacitive electrodes consist of two air plates or pad electrodes that allow for three arrangements: coplanar (electrodes placed side by side, tissues parallel to the current), anti-planar (electrodes on either side of the body part, tissues in series to the current), or longitudinal (electrodes placed at each end of the limb on opposite sides of the body part, tissues in series to the current).Each technique can be continuous (CSWD) or pulsed (PSWD), the continuous mode being used primarily for thermal effects, while the pulsed mode is used primarily for non-thermal effects.
Low-level laser therapy (LLLT) is described by Glazov et al. [45] as a light source treatment that may act via non-thermal or photochemical reactions in cells.It includes laser acupuncture, which involves focused irradiation at specific points, most commonly traditional acupuncture points, with a low-intensity laser.LLLT for pain relief in medicine remains controversial with claims that apparent efficacy is due to the placebo effect.Multiple mechanisms for LLLT analgesia may exist.There is experimental evidence suggesting that laser irradiation induces peripheral neural blockade, suppresses central synaptic activity, modulates neurotransmitters, reduces muscle spasm and interstitial oedema, and exerts anti-inflammatory effects.
Extracorporeal shock wave therapy (ESWT) was described by Yao et al. [46] as a non-invasive procedure in which acoustic waves are focused on targeted sites within the body to facilitate pain relief and healing.In general, ESWT is considered safe, non-invasive, easy to apply, and well tolerated by most patients, and so has been widely used for many musculoskeletal conditions over the last 25-30 years.Although the exact mechanisms for analgesic and functional effects are still incompletely understood, it is suggested that shock waves accelerate tissue regeneration, reduce calcification, and inhibit pain receptors.This wide variation in the therapeutic programs in the randomized clinical trials conducted to date considerably complicates the comparison of study results.Therefore, the results obtained should be viewed with some caution.It should also be emphasized that only two out of seven randomized clinical trials performed a longitudinal evaluation of the effectiveness of the applied physiotherapy program [19,33], which indicated the achieved effects of the applied therapy were maintained after six months.The remaining five studies evaluated the effectiveness of the therapy program directly [32,42] or a maximum of 3 months [20,21,40] after its completion, so it cannot be assumed that the effects would be sustained over a longer period of time, and it seems that maintaining sustained improvements is most important from the point of view of its effectiveness.
In all three prospective studies without a control group included in this review, some improvements were obtained in patients with CuTS [17,37,39].Improvements were documented in all participants in the first study [17], 88% of participants in the second [39], and 73% in the third [37].Neurophysiological assessment was also performed in all studies, although subjects with normal nerve conduction who showed typical CuTS symptoms were also included [39].Sensory threshold and discriminative sensation were assessed in two studies [17,37], while only discriminative sensation was assessed in one study [39], and pain intensity was assessed in one study [17].Two out of three papers measured muscle strength [37,39], and one study evaluated the degree of disability [39] and general quality of health [39].In all three studies, the main component of therapy was an elbow night splinting [17,37,39].Two studies employed additionally provided instruction on changing habits during activities of daily living.All studies examined not only the effects immediately after the therapy but also the long-term effects one year later [17,37,39].Although orthoses were used in all of these studies, unfortunately, the angle of flexion varied in each study (from the elbow in full extension to flexion up to 60 • ), which was not justified in any way.Unfortunately, the main limitation of all these studies was the lack of a control group.Therefore, it is impossible to verify whether the effects obtained result from the therapy used, spontaneous recovery, or the placebo effect.
Positive effects of the applied therapy were obtained in all case studies [18,22,23,[34][35][36]38,41].The studies reported a reduction in pain [18,22,23,36,38,41], improved function [18,22,23,38,41], increased muscle strength [23,34,38], and reduced symptoms in provocation tests [18,34,35,38].Evaluation of therapeutic effects occurred immediately after therapy but in 6/8 papers also much later: 3 [22,36,41], 6 [18,23,36,41], and even 12 months [38,41] after the intervention.Unfortunately, the small number of study participants (23 people in all studies), the very large methodological variation, and the use of different physiotherapy programs require considerable caution in drawing conclusions about the effectiveness of the therapy used.The studies assessed pain [18,23,35,36,38], range of motion [18,35], sensation [38], muscle strength [34,38], and hand dexterity [22,38,41], conducted provocation tests [18,34,35,38].Therapeutic interventions varied from neurodynamic techniques, spinal and rib manipulation [18], manual therapy [35], electric therapy [36,41], ultrasound [38], shock wave [22], and dry needling [23].Dry needling as described by Gattie et al. [47] is a technique in which a fine needle is used to penetrate the skin, subcutaneous tissues, and muscle with the intention of mechanically disrupting the tissue without the use of an anesthetic.Dry needling is often used to treat myofascial trigger points (MTrPs), which are described as localized hypersensitive areas within a palpable taut band of muscle.These hypersensitive areas can be classified as active MTrPs when they elicit spontaneous pain and, on palpation, reproduce the pain known to the patient.Latent MTrPs do not elicit spontaneous pain and are painful only on palpation.Myofascial trigger points are commonly seen in patients with musculoskeletal pain.The physiologic mechanism underlying the action of dry needling remains to be elucidated.However, it has been suggested that dry needling may induce both local and central neural responses to restore homeostasis at the MTrP site, resulting in a reduction in both peripheral and central pain sensitivity.Centrally, dry needling may activate descending control mechanisms in the brain or spinal cord.Dry needling has been shown to immediately increase pressure pain threshold and range of motion, reduce muscle tension, and reduce pain in patients with musculoskeletal disorders.
The number of therapy sessions also varied and equaled 1 [36], 3 [41], 5 [18], or 11 [34].Unfortunately, in the vast majority of these papers, the diagnosis of CuTS was based only on medical history and/or orthopedic examination [18,22,23,34,35,38,41], while electrophysiological examination was performed in only three cases [18,22,36], including one that was within normal values [18].It is therefore difficult to confirm whether in all case studies the patients actually had CuTS or whether the symptoms had another cause.Also, in case study research, the lack of comparison with non-therapy cases may indicate that the effects obtained after therapy are the result of spontaneous recovery or a placebo effect.It should also be emphasized that case studies are subjected to a high risk of bias, and therefore the results obtained from the physiotherapy programs used should be approached with caution.
Techniques that may be useful in treating CuTS include interferential current (IFC), transcutaneous electrical nerve stimulation (TENS), neuromuscular electrical stimulation (NMES), and deep oscillation procedures.According to Rampazo and Liebano [48], IFC therapy involves the transcutaneous application of two medium-frequency alternating currents (>1 kHz to <10 kHz) out of phase to deliver current to deep tissues.For example, one of the alternating currents may have a fixed frequency of 4000 Hz, while the frequency of the other alternating current may be set between 4000 and 4250 Hz.The two medium-frequency currents "interfere" in the tissue and produce an amplitudemodulated low-frequency "beat" (0-250 Hz) which is the difference between the values of the two applied currents.IFC is an example of a pulse-modulated sinusoidal alternating current, also known as kilohertz alternating current, and is reportedly more comfortable, reaches deeper tissues, and produces greater muscle torque than low-frequency pulsed currents.There are several parameters that can be adjusted in IFC devices, including the carrier frequency, amplitude modulated frequency, sweep frequency, sweep mode or swing pattern (slope), application type (bipolar or quadripolar application), and application time and intensity.
Mokhtari et al. [49] describe TENS as a noninvasive pain relief technique that activates peripheral nerves by delivering electrical impulses to the intact skin surface, which can modulate the transmission of nerve impulses by inhibiting presynaptic nociceptive information.In practice, TENS can be implemented using different stimulus parameters in terms of frequency, intensity, and electrode placement.Since TENS with different stimulus parameters can activate different populations of nerve fibers, this technique can be divided into different types, including conventional TENS (low intensity and high frequency), acupuncture-like TENS (high intensity and low frequency), and intensive TENS (high intensity and high frequency).
As described by Doucet et al. [50], neuromuscular electrical stimulation, used interchangeably with electrical stimulation (ES), is typically delivered at higher frequencies (20-50 Hz) with the express purpose of producing tetany and muscle contraction that can be used for "functional" purposes.The frequencies of electrical stimulation used can vary widely depending on the goals of the task or intervention, but most clinical regimens use patterns of 20-50 Hz to achieve optimal results.To avoid fatigue or discomfort, a constant low-frequency stimulation that produces a smooth contraction at low force levels is typically used.Electrical stimulation devices deliver pulses in waveforms that are often represented by geometric shapes such as a square, spike, or sine wave.Controversy regarding optimal electrode placement is common in the literature, with most debates centering on whether the muscle belly or the motor point is the preferred location.Program duration has ranged from 30 min once a day to an hour in each session three times daily.The total treatment period ranged from 2 weeks to 3 months.
Deep Oscillation (DO), as described by Villalba-Meneses et al. [51], is a patented manual therapy that produces mechanical vibrations in the skin and deep tissues.This device uses repeated electrostatic oscillations to relieve the pain and swelling of a specific area by moving the swelling through the lymphatic system.DO therapy builds up a pulsating electrostatic field of low intensity (100-400 V; 150 µA) and low frequency  between the hand applicator and the affected tissue.Its low-frequency electrostatic field produces a throbbing effect in the underlying tissues that improves wound healing and anti-inflammatory effects, stimulates lymphatic flow, stimulates collagen production, and cell regeneration, and ensures more blood reaches the affected area.Both the patient and the physical therapist are connected to the deep oscillation device, which serves as a source of tension with high internal resistance.The impulse of the voltage produces an electrostatic attraction on the tissue and rhythmic frictions are generated when massaging the oedema.These rhythmic frictions result in oscillations of the local tissue (skin, conductive tissue, subcutaneous adipose tissue, muscles, blood, and lymphatic vessels) and increase the vascular circulation of the area concerned.Each session of deep oscillation therapy follows a rigorous clinical protocol.In most medical trials, therapy begins with 15 min of conventional manual lymphatic drainage.Later, the DO equipment is used for 10 min at 200-250 Hz in the area to be treated, and oscillations of 85 Hz are administered for 10 min to finish.The physiological effects of deep oscillation therapy in the treatment of low back pain will depend on the frequency and intensity applied.Clinical studies have reported that DO therapy restores mobility between fibers, repairs affected tissue, exerts anti-inflammatory effects, reduces oedema, improves drainage channels, and accelerates wound healing.
It must be emphasized that, from the broader perspective, studies to date on the effectiveness of physiotherapy in the conservative treatment of CuTS have found beneficial effects, although no clear far-reaching conclusions can be drawn at this stage.This is mainly due to the small number of randomized clinical trials, the significant methodological discrepancies regarding both the diagnosis of CuTS and the parameters studied, and the significant variety of therapeutic programs used.Therefore, high-quality randomized controlled trials evaluating the effectiveness of different physiotherapy measures in the conservative treatment of CuTS are needed.Due to the frequent occurrence of CuTS, case studies do not seem to be relevant.Since positive therapeutic effects were documented in most of the papers included in this review, similar therapeutic programs based on manual therapy incorporating neurodynamic techniques, ultrasound therapy, low-level laser, or other measures that had a beneficial effect on the patient's condition could be used in further studies.It would also be advisable to conduct studies with blinding of participants and investigators.
This critical review of studies evaluating the effectiveness of physiotherapy in the conservative treatment of CuTS has some limitations.Only two databases and the Google Scholar search engine were used to search for papers for the review.This was limited to English-language papers only, so other valuable studies might have been likely omitted, especially randomized controlled trials that have evaluated the effectiveness of physiotherapy in the conservative treatment of CuTS.Another limitation is that we have only managed to cover a limited number of the existing physiotherapy procedures with positive effects on CuTS.

Conclusions
A review of studies to date evaluating the effectiveness of physiotherapy in the conservative treatment of CuTS leads to the conclusion that beneficial therapeutic effects were achieved in the majority of these studies.The small number of randomized clinical trials and their considerable heterogeneity do not allow firm conclusions to be drawn about the effectiveness of physiotherapy in the conservative treatment of CuTS.

Future Directions
High-quality randomized controlled trials evaluating the effectiveness of different physiotherapy programs in the conservative treatment of CuTS are needed.
Pain (VAS), Tinel's sign, disability questionnaire of the arm, shoulder and hand (DASH), and grip and side grip strength (JAMAR ® dynamometer (Lafayette Instrument Company, Lafayette, LA, USA)) COPM-Canadian Occupational Performance Measure; VAS-Visual Analogue Scale; NCS-Nerve Conduction Study; DASH-Disabilities of the Arm, Shoulder, and Hand Outcome Measure; MRC-Medical Research Council; MGS-McGowan scale; SQUNE-Self-administered Questionnaire of Ulnar Neuropathy at the Elbow; NMUS-Neuromuscular Ultrasonography; SF-36-Short-Form Health Survey with 36 questions.

Table 2 .
Characteristics of papers describing prospective studies without a control group.

Table 3 .
Characteristics of papers with case reports.