The most common entrapment syndrome of a peripheral nerve is carpal tunnel syndrome, first described by Paget in 1854 [6, 19]. The cause of the damage to the median nerve lies in persistent pressure damage in the carpal tunnel. In addition to the median nerve, the flexor digitorum superficialis, profundus, and flexor pollicis longus muscles are also affected.
Incidence and Prevalence
The incidence of CTS is approximately 3 cases per 1000 inhabitants [19]. In a southern Swedish cohort, there was a prevalence of about 2.7% for clinically and electrophysiologically confirmed CTS [6]. Women are affected three to four times more frequently, and the risk is increased in occupational groups with frequent stress on the wrists (e.g., cleaning staff, gardeners, locksmiths, etc.). Prevalence is highest between the 40th and 60th year of life. However, younger adults and children can also be affected, such as during pregnancy (often in the third trimester) or in childhood with metabolic diseases like mucopolysaccharidosis. CTS often occurs bilaterally, with the dominant hand more frequently affected.
Causes
Distal radius fractures, local space-occupying lesions (e.g., ganglia), diseases of the rheumatic spectrum, and metabolic disorders can rarely lead to CTS. Associations exist between CTS and dialysis-dependent renal insufficiency, diabetes mellitus, and an elevated body mass index (BMI) [11, 14]. Another important risk factor is pregnancy. In the third trimester, up to 40% of pregnant women show electrophysiological signs of CTS [29]. Long-term pressure increases in the carpal tunnel, caused among other things by edematous swelling of the synovialis, are of crucial importance for the pathogenesis of CTS [10]. This results in ischemia in the epi- and perineurium of the median nerve with edema formation and focal demyelinations, which mainly affect the strong myelinated fibers [17]. Over time, axonal degeneration can occur.
Diagnostics
Medical history and clinical examination are crucial for the diagnosis of carpal tunnel syndrome. Electrophysiological examination can confirm the clinical diagnosis and demonstrate the reduced nerve conduction velocity of the median nerve. The distal motor latency of the median nerve in the carpal tunnel is determined. A value of > 4.2 ms is pathological (distance between stimulation and recording electrode 6.5 cm) [1]. Pathological measurement results without matching clinical findings are not an indication for surgery but should be monitored over time [5, 13]. Conversely, decompression can be beneficial for patients with typical medical history and clinical findings of carpal tunnel syndrome even with normal nerve conduction velocity [9, 16].
Conservative Treatment
Conservative treatment is recommended if the symptoms are mild. The symptoms can possibly be reduced by the following measures [2, 3, 4, 5, 15]:
- Occupational therapy: manual techniques, thermal applications, and sensitivity training.
- Wrist splint at night for symptom relief
- Oral corticosteroid preparation
- Perineural infiltration of a corticosteroid crystal suspension under neurosonographic control
In case of unsuccessful conservative treatment and the presence of sensory or motor disturbances, surgical treatment is indicated [19].
Surgical Treatment
Indications
Painful paresthesias as well as persistent sensory or motor deficits, such as loss of abduction and opposition strength of the thumb, are indications for surgery [5]. The electrophysiological proof of reduced nerve conduction velocity of the median nerve confirms the clinical diagnosis and facilitates the indication. Measurement of nerve conduction velocity is generally recommended before elective carpal tunnel surgery [5]. In acute carpal tunnel syndrome, e.g., following a distal radius fracture, emergency decompression of the carpal tunnel is required without electrophysiological examination.
A several-day postoperative immobilization in a wrist splint in 20° dorsal extension of the wrist is optional. Studies showed no advantage for immobilization [18].
Approximately 300,000 procedures for carpal tunnel syndrome are performed each year in Germany. Decompression of the carpal tunnel can be performed through a standard approach, via one or two mini-incisions, or endoscopically [5, 8, 23, 30]. Mini-incisions increase the risk of incomplete retinaculum division and iatrogenic lesions of the median and ulnar nerves [5].
Endoscopic decompression of the median nerve leads to less postoperative scar pain than open carpal roof division due to smaller skin incisions. Overall, the long-term results are similar for both methods [26]. However, the surgical risk with endoscopic procedures appears to be significantly higher [7].
The open decompression remains the standard method, as a possible faster load-bearing capacity and lower scar pain do not justify the surgical risk for iatrogenic nerve lesions and the higher costs with endoscopic procedures [13, 26].
Comparison of CTS Surgical Techniques
| Technique | Features | Risks |
|---|---|---|
| Open Surgery |
|
|
| Open Surgery with Mini-Incision |
|
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| Endoscopic Surgery, Monoportal (Agee Technique) |
|
|
| Endoscopic Surgery, Biportal (Chow Technique) |
|
|
Source: Gelderblom, M., Antoniadis, G. Diagnostics and Therapy of Carpal Tunnel Syndrome. InFo Neurology 24, 32–43 (2022).
Advantages of Open Standard Surgery
- Lower risk of incomplete retinaculum division.
- Lower risk of iatrogenic lesions of the median and ulnar nerves.
- Uncomplicated inspection of the surgical site
- Uncomplicated synovectomy of the flexor tendons (e.g., in rheumatic diseases), ganglion extirpation within the carpal tunnel, etc.
- If necessary, exposure and decompression of the motor branch of the median nerve
Disadvantages of Open Standard Surgery
- Scar pain in the access area due to lesions of cutaneous nerve branches [22].
- Postoperative reduction in hand strength in manually active patients, possibly due to the loss of the flexor retinaculum, an important component of the pulley system of the finger flexor tendons, as well as a postoperative widening of the transverse bony carpal arch (Canalis carpi), which has been discussed in the literature [24].
Complications
- Injury to the palmar branch of the median nerve: microsurgical coaptation [21].
- Injury to the motor branch of the median nerve: microsurgical coaptation. In case of absent re-innervation of the muscles innervated by the median nerve over time, possibly motor replacement surgery [28].
- Postoperatively persistent carpal tunnel syndrome due to incomplete division of the flexor retinaculum: revision with complete decompression [5].
- Opening of Guyon's canal with risk to the ulnar vascular/nerve bundle: strictly vertical preparation from the skin incision described above downward toward the retinaculum.
CTS surgery has a low complication rate. Postoperative bleeding or wound infections are well below 1%. Nerve injuries are rare with experienced surgeons; they can occur more frequently in the learning phase with endoscopic procedures. A survey among American surgeons (6,833 procedures) showed that the complication rate was 0.8% with open technique and 1.6% in endoscopically operated patients [25]. In a literature review of 9,516 operations, Boeckstyns reported an irreversible nerve lesion of 0.3% in endoscopic and 0.2% in open operations [7].
Postoperatively, pain in the palm can occur, known as "pillar pain." This may be caused by the divergence of the distal end of the flexor retinaculum after division. The symptoms can occur after both open and endoscopic operations and usually disappear after six months. With properly performed operations, complex regional pain syndrome (CRPS I) is extremely rare [2].
Results
Haupt et al. examined 60 patients with carpal tunnel syndrome after retinaculum division with a mean follow-up time of 5.5 years (2 to 11 years). In 26% of cases, there was a complete resolution of symptoms and normalization of electrophysiological parameters. In 45% of cases, there was a significant improvement in pain, function, and electrophysiological parameters, while in 15% of cases there was only slight improvement, in 7% no improvement, and in 7% clinical deterioration. Accordingly, in 86% of cases, the clinical and electrophysiological findings improved postoperatively to varying degrees [12]. In a retrospective study, Mühlau et al. examined 157 individuals with electrophysiologically confirmed carpal tunnel syndrome. A significant improvement was found in 86% of the 85 surgically treated patients. However, symptoms also improved significantly in 32% of the non-operated patients [20].
Comparison of Surgical and Conservative Treatments
In a meta-analysis by Verdugo et al., four randomized controlled trials with a total of 317 patients were examined, comparing the outcome of surgery and conservative therapy for carpal tunnel syndrome. After 3 and 6 months as well as after 1 year, advantages of surgical therapy were shown for clinical outcome and electrophysiological measurements compared to conservative measures [27].