The most common entrapment syndrome of a peripheral nerve is carpal tunnel syndrome, first described by Paget in 1854 [6, 19]. The cause of damage to the median nerve is persistent compression in the carpal tunnel. This affects not only the median nerve but also the flexor digitorum superficialis, profundus, and flexor pollicis longus muscles.
Incidence and Prevalence
The incidence of CTS is approximately 3 cases per 1000 inhabitants [19]. In a southern Swedish cohort, the prevalence of clinically and electrophysiologically confirmed CTS was about 2.7% [6]. Women are three to four times more frequently affected, and the risk is increased in occupations with frequent wrist strain (e.g., cleaners, gardeners, locksmiths, etc.). The prevalence is highest between the ages of 40 and 60. However, younger adults and children, such as during pregnancy (often in the third trimester) or in childhood with metabolic disorders like mucopolysaccharidosis, can also be affected. CTS often occurs bilaterally, with the dominant hand more frequently affected.
Causes
Distal radius fractures, local space-occupying lesions (e.g., ganglia), rheumatic diseases, and metabolic disorders can rarely lead to CTS. Associations exist between CTS and dialysis-dependent renal insufficiency, diabetes mellitus, and an increased body mass index (BMI) [11, 14]. Another important risk factor is pregnancy. Up to 40% of pregnant women show electrophysiological signs of CTS in the third trimester [29]. Long-term pressure increases in the carpal tunnel, caused among other things by edematous swelling of the synovium, are crucial for the pathogenesis of CTS [10]. This results in ischemia in the epi- and perineurium of the median nerve with edema formation and focal demyelination, mainly affecting the large myelinated fibers [17]. Over time, axonal degeneration may occur.
Diagnostics
History and clinical examination are crucial for diagnosing 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 stimulus and recording electrode 6.5 cm) [1]. Pathological measurements without corresponding clinical symptoms are not an indication for surgery but should be monitored over time [5, 13]. Conversely, decompression may benefit patients with typical history and clinical findings of carpal tunnel syndrome even with normal nerve conduction velocity [9, 16].
Conservative Treatment
Conservative treatment is recommended if symptoms are mild. Symptoms can potentially be reduced by the following measures [2, 3, 4, 5, 15]:
- Occupational therapy: manual techniques, thermal applications, and sensory training.
- Wrist splint at night for symptom relief
- oral corticosteroid preparation
- perineural infiltration of a corticosteroid crystal suspension under neurosonographic control
If conservative treatment is unsuccessful and there are sensory or motor disturbances, surgical treatment is indicated [19].
Surgical Treatment
Indications
Painful paresthesias and persistent sensory or motor deficits, such as loss of thumb abduction and opposition strength, are indications for surgery [5]. Electrophysiological evidence of reduced nerve conduction velocity of the median nerve confirms the clinical diagnosis and facilitates indication. Measurement of nerve conduction velocity is generally recommended before elective carpal tunnel surgery [5]. In acute carpal tunnel syndrome, e.g., due to a distal radius fracture, emergency decompression of the carpal tunnel is required without electrophysiological examination.
A multi-day postoperative immobilization in a wrist splint in 20° dorsiflexion of the wrist is optional. Studies showed no advantage for immobilization [18].
Approximately 300,000 procedures for carpal tunnel syndrome are performed annually 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 results in less postoperative scar pain due to smaller skin incisions compared to open carpal roof division. Overall, long-term outcomes are similar with both methods [26]. However, the operative risk with endoscopic procedures appears to be significantly higher [7].
The open decompression remains the standard method, as the potential for faster load-bearing and reduced scar pain does not justify the operative risk for iatrogenic nerve lesions and the higher costs associated 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. Diagnosis and Therapy of Carpal Tunnel Syndrome. InFo Neurology 24, 32–43 (2022).
Advantages of the Open Standard Surgery
- Lower risk of incomplete retinaculum division.
- Lower risk of iatrogenic lesions of the median and ulnar nerves.
- Inspection of the surgical site without issues
- Uncomplicated synovectomy of the flexor tendons (e.g., in rheumatic diseases), ganglion excision within the carpal tunnel, etc.
- If necessary, visualization and decompression of the motor branch of the median nerve
Disadvantages of the Open Standard Surgery
- Scar pain in the access area due to lesions of skin nerve branches [22].
- Postoperative reduction in hand strength in manual workers, 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 (carpal canal), 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. If reinnervation of the muscles innervated by the median nerve does not occur, a motor substitution operation may be necessary [28].
- Postoperative persistent carpal tunnel syndrome due to incomplete division of the flexor retinaculum: revision with complete decompression [5].
- Opening of the Guyon's canal with risk to the ulnar vascular/nerve bundle: strictly vertical dissection from the described skin incision into the depth towards the retinaculum.
The CTS surgery has a low complication rate. Postoperative bleeding or wound infections are well below 1%. Nerve injuries are rare with experienced surgeons, but they can occur more frequently during the learning phase of endoscopic procedures. A survey of American surgeons (6,833 procedures) showed a complication rate of 0.8% for open technique and 1.6% for endoscopically operated patients [25]. In a literature review of 9,516 operations, Boeckstyns reported an irreversible nerve lesion rate of 0.3% for endoscopic and 0.2% for open surgeries [7].
Postoperatively, pain in the palm, known as "pillar pain," may occur. This may be due to the gaping of the distal end of the flexor retinaculum after division. The symptoms can occur after both open and endoscopic surgeries and usually disappear after six months. A complex regional pain syndrome (CRPS I) is extremely rare when surgeries are performed properly [2].
Results
Haupt et al. studied 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 a slight improvement, in 7% there was no improvement, and in 7% there was a clinical deterioration. Accordingly, in 86% of cases, 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 significantly improved in 32% of 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 outcomes of surgery and conservative therapy for carpal tunnel syndrome. After 3 and 6 months and after 1 year, the clinical outcomes and electrophysiological measurements showed advantages of surgical therapy compared to conservative measures [27].