ReviewBiomechanical and anatomical consequences of carpal tunnel release
Section snippets
Introduction and clinical significance
Carpal tunnel syndrome is one of the most common orthopedic conditions, with an estimated incidence of nearly 1% annually in the United States (Einhorn and Leddy, 1996), which translates into almost 2.8 million new cases per year. If conservative therapy fails, surgical release of the carpal tunnel is the preferred method of treatment. Though the majority of patients have relief of symptoms postoperatively, there are still a significant number of patients who experience disabling postoperative
Anatomy
The carpal bones and intercarpal ligaments at its medial, lateral, and posterior borders form the carpal tunnel. The anterior border is formed by the transverse carpal ligament and flexor retinaculum (Hoppenfeld Sd, 1984; Tanabe and Okutsu, 1997). The terms “flexor retinaculum” and “transverse carpal ligament” have been considered synonyms, however, Cobb et al. demonstrated that they are distinct structures (Cobb et al., 1993). The flexor retinaculum as a whole can be divided into three parts
Carpal tunnel anatomic variations
Phalen originally reported on his 17-year experience in 1966, suggesting that thickening of the flexor synovium was the most common direct cause of median nerve compression and carpal tunnel syndrome in his patients (Phalen, 1996). Tanzer, however, noted three of 21 patients with cystic masses in the carpal tunnel and seven of these 21 hands had various congenital anomalies (Tanzer, 1959). Singer retrospectively looked for anatomic variations in 147 hands undergoing carpal tunnel release via an
Pressure changes and mechanism of relief after carpal tunnel release
When considering complete release of the carpal tunnel, one must consider the relevant anatomy (Tanabe and Okutsu, 1997; Cobb et al., 1993); neglecting to release the distal part of the flexor retinaculum or the proximal part described above may fail to completely relieve pressure on the median nerve or may result in failure of surgery to relieve symptoms of carpal tunnel syndrome (Tanabe and Okutsu, 1997; Phalen, 1996; Cobb and Cooney, 1994). Tanabe noted that release of only the transverse
Surgical techniques
To serve as background for understanding the biomechanical and anatomic changes after different types of carpal tunnel release, a brief review is presented here. A thorough review of the methods for carpal tunnel release and their pros and cons is beyond the scope of this paper.
Potential biomechanical complications of carpal tunnel release
Generally reported complications of carpal tunnel release include incomplete release, neuropraxia or injury to the median or ulnar nerve, and inadvertent entrance into Guyon’s canal, injury to digital nerves, the ulnar artery and the superficial palmar arch (Lee et al., 1992; Seiler et al., 1992). However, there exist several biomechanical changes after carpal tunnel release, which may be considered “complications”, not merely “expected” postoperative, changes.
The phenomenon of pillar pain is a
Biomechanical change after carpal tunnel release
A number of studies have examined the effect of dividing the transverse carpal ligament on the carpal arch. The transverse carpal ligament has been shown to serve three functions: anchor thenar and hypothenar musculature, provide transverse stability to the carpus, and act as a pulley for the flexor tendons (Seradge and Seradge, 1989; Garcia-Elias et al., 1989b). Thus, division of this ligament could alter the normal function of the wrist and contribute to such postoperative complications as
Carpal arch and carpal tunnel volume
Cobb et al. (1993) determined normal carpal tunnel dimensions by injecting contrast material into the carpal tunnel and examining antero-posterior (AP) radiographs. On the AP view, the carpal tunnel is shaped like an hourglass (Fig. 4), with the narrowest part at the level of the hook of the hamate. The mean width of the carpal tunnel was 25 ± 1.2 mm proximally, 20 ± 1.2 mm at the hook of the hamate, and 25 ± 1.5 mm at its distal extent, a significant difference (P<0.0001). This is an important
Conclusion
Carpal tunnel surgery has been performed for nearly 80 years, yet despite the majority of patients who recover without complication, there are still a significant number that suffer postoperative pain and weakness. A successful decompression of the median nerve provides symptomatic relief of carpal tunnel symptoms, and generally allows patients to return to activities of daily living and employment. However, complete release of the carpal tunnel probably has a small but significant effect on
Acknowledgements
We would like to thank Ted Trafton for his tireless illustrative effort.
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