Research Review By Dr. Brynne Stainsby©

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Date Posted:

March 2019

Study Title:

Dimensional changes of the carpal tunnel and the median nerve during manual mobilization of the carpal bones

Authors:

Bueno-Gracia E, Ruiz-de-Escudero-Zapico A, Malo-Urries M et al.

Author's Affiliations:

Department of Physiatry and Nursery, Faculty of Health Sciences, University of Zaragoza, Spain; Neurodynamic Solutions, Adelaide, Australia.

Publication Information:

Musculoskeletal Science and Practice 2018; 36: 12-16.

Background Information:

The carpal tunnel (CT) is a fibro-osseous structure bound by the scaphoid, trapezium, pisiform and hook of the hamate, and encased ventrally by the flexor retinaculum. The cross-sectional area (CSA) of the tunnel is influenced by the anatomy of the carpal bones and also by flexion and extension of the wrist (1). Passing through the CT with the flexor tendons, the median nerve is particularly vulnerable to compression, which is known clinically as carpal tunnel syndrome (CTS). CTS is the most common neuropathy of the upper limb, with prevalence ranging between 3-6% of the adult population (2-4).

Surgical release has been used to modify the size of the CT (5, 6), however, it may or may not alter symptoms of CTS. Conservative treatment may have clinical value, but the mechanism remains unclear. Therefore, the aim of this study was to quantify change in the cross-sectional dimensions and area of the CT and median nerve during manual mobilization of the carpal bones in healthy subjects.

Pertinent Results:

  • Eighteen volunteer subjects participated in the study (three wrists were excluded due to anatomical variations and a previous fracture), for a total of 33 wrists included in the investigation.
  • For the carpal tunnel (CT), the cross-sectional area (CSA) had an average value of 153 mm2, the anteroposterior diameter (APD) was 8 mm and the transverse diameter (TD) was 22 mm. The flattening ratio (defined as TD/APD) was 2.94 and the circularity was 0.65 (the flattening ratio and circularity measures indicated roundness of the CT and median nerve, suggesting possible changes in their morphology with the mobilization). All CT shape descriptors were significantly modified by mobilization, particularly the flattening ratio decreased from 2.94 to 2.06.
  • For the median nerve, all shape descriptors showed similar findings to the CT. The flattening ratio decreased from 3.6 to 3.09 during mobilization.

Clinical Application & Conclusions:

This study is the first to quantify the effects of manual mobilization (transverse force application) on asymptomatic subjects, demonstrating that mobilizations resulted in morphological changes of the CT, specifically increases in CSA of the median nerve and CT. Previous modelling studies have demonstrated similar changes. This was a simple yet very interesting study that helps us understand at least part of the mechanism of effect of manual therapy applied to the wrist.

Previous research has indicated that increased pressure on the nerve in the CT causes a decrease in blood supply to the nerve resulting in ischemia, local metabolic disturbances and disorders of neural function (7-9). The results of this study suggest that increase in the CT CSA produced by mobilization may reduce the pressure on the nerve. In symptomatic patients, this may be even more relevant as previous studies have indicated higher pressure on the nerve in patients compared to asymptomatic controls (10-12). Further research is needed to determine if manual mobilization results in clinically meaningful outcomes in symptomatic patients.

Study Methods:

  • This was a cross-sectional study in asymptomatic individuals, aged 18-65 with no previous or current pathology in the upper limbs.
  • Each participant was placed comfortably in a seated position with their forearm placed on a firm support with 90° of elbow flexion, forearm supination and the hand and wrist in neutral.
  • To perform mobilization, the researcher’s thumb was placed on the dorsal aspect of the scaphoid and trapezium, and the index finger on the dorsal side of the triquetrum and the hamate. A transverse and ventral force was applied until marked resistance was felt (and the technique was comfortable for the subject). The mobilization was performed three times while the forearm was stabilized with the researchers other hand ventrally.
  • The investigator who performed the mobilization was blinded to the ultrasound images which measured the CT and median nerve in the initial position and during mobilization. Three images were captured during each mobilization repetition.
  • A single investigator with training in musculoskeletal ultrasound imaging analyzed the images for each trial. Continuous tracing technique was used to measure the CSA of the CT and median nerve, along with measurement of the anteroposterior and transverse diameters (APD and TD) of the CT and the median nerve in order to calculate nerve perimeter, the flattening ratio and circularity.

Study Strengths / Weaknesses:

Strengths:
  • Though preliminary in nature, this study quantified measurements of the CT and median nerve in vivo during manual mobilization – pretty cool!
  • Though not an interventional study, blinding was employed to protect the integrity of the ultrasound measurements.
  • Manual forces were applied to the clinical endpoint of the subjective resistance (as determined by the clinician) and tolerated by the patient, replicating a clinical interaction and increasing the external validity of the study.
Weaknesses:
  • The greatest limitation of this study is its preliminary nature, as clinical relevance cannot be determined. It is important to note however that this project provides a critical foundation for future work on the mechanisms of manual therapy applied to the wrist.
  • Comments on sample size calculation were not provided, however, the results were consistent and did achieve statistical significance.

Additional References:

  1. Garcia-Elias M, Sanchez-Freijo JM, Salo JM et al. Dynamic changes of the transverse carpal arch during flexion-extension of the wrist: effects of sectioning the transverse carpal ligament. J Hand Surg Am 1992; 17: 1017–1019.
  2. Ibrahim I, Khan WS, Goddard N et al. Carpal tunnel syndrome: a review of the recent literature. Open Orthop 2012; 6: 69–76.
  3. Keith MW, Masear V, Chung KC et al. American academy of orthopaedic surgeons clinical practice guideline on diagnosis of carpal tunnel syndrome. J Bone Joint Surg 2009; 91(10): 2478–2479.
  4. Atroshi I, Gummesson C, Johnsson R et al. Prevalence of carpal tunnel syndrome in a general population. JAMA 1999; 282(2): 153–158.
  5. Lee C, Kim T, Yoon E. Postoperative morphologic analysis of carpal tunnel syndrome using high-resolution ultrasonography. Ann Plast Surg 2005; 54: 143–146.
  6. Richman JA, Gelberman RH, Rydevik BL et al. Carpal tunnel syndrome: morphologic changes after release of the transverse carpal ligament. J Hand Surg Am 1989; 14: 852–857.
  7. Kobayashi S, Shizu N, Suzuki Y et al. Changes in nerve root motion and intraradicular blood flow during an intraoperative straight-leg-raising test. Spine 2003; 28: 1427–1434.
  8. Alfonso C, Jann S, Massa R et al. Diagnosis, treatment and follow-up of the carpal tunnel syndrome: a review. Neurol Sci 2010; 31: 243–252.
  9. Hartz C, Linscheid R, Gramse R et al. The pronator teres syndrome: compressive neuropathy of the median nerve. J Bone Joint Surg 1981; 63: 863–872.
  10. Coppieters MW, Schmid AB, Kubler PA et al. Description, reliability and validity of a novel method to measure carpal tunnel pressure in patients with carpal tunnel syndrome. Man Ther 2012; 17: 589–592.
  11. Gelberman R, Hergenroeder P, Hargens A et al. The carpal tunnel syndrome: A study of carpal canal pressures. J Bone Joint Surg Am 1981; 63: 380–383.
  12. Seradge H, Jia Y, Owens W. In vivo measurement of carpal tunnel pressure in the functioning hand. J Hand Surg 1995; 20: 855–859.