Three-dimensional stiffness of the carpal arch

Non-Surgical Carpal Arch Space Augmentation for Median Nerve Decompression

The carpal tunnel is a tightly bounded space, making the median nerve prone to compression and eventually leading to carpal tunnel syndrome. Carpal tunnel release surgery transects the transverse carpal ligament to expand the tunnel arch space, decompress the median nerve, and relieve the associated symptoms. However, the surgical procedure unavoidably disrupts essential anatomical, biomechanical and physiological functions of the wrist, potentially causing reduced grip strength, pillar pain, carpal bone instability, scar tissue formation, and perineural fibrosis. It is desirable to decompress the median nerve without surgically transecting the transverse carpal ligament. This paper is to review several approaches we have developed for nonsurgical carpal arch space augmentation (CASA), namely, radio ulnar wrist compression, muscle-ligament interaction, palmar pulling, and collagenolysis of the transverse carpal ligament. Briefly summarized is the research work on the CASA topic about theoretical considerations, in vitro and in situ experiment, computational modeling, and human subject studies with asymptomatic and carpal tunnel syndrome hands.

Translation of 2-Dimensional Wrist Radiographic Measurements to 3-Dimensional CT Scans

Background: Anatomical structure affects function. The morphology of articulations dictates the way forces will travel through the joint. A better understanding of the structure and function of the wrist will enhance our ability to diagnose and treat wrist conditions. Two wrist types have been described based on the morphology of the midcarpal joint. Biomechanically it is important to see if these 2-dimensional (2D) observations reflect articular contact areas. Our purpose was to assess the correlation between measurements performed on wrist radiographs (2D) to measurements performed on 3-dimensional (3D) computed tomography (CT). Methods: Retrospective review of a database of normal wrist radiographs and corresponding normal CT scans. Only imaging pairs with normal carpal alignment and technically optimal imaging were included. Evaluations included lunate, capitate and wrist type, capitate circumference, percent capitate circumference and volume that articulates with the lunate, scapholunate ligament, scaphoid, hamate, trapezoid, base of the index and middle and ring metacarpal bones. Results: Midcarpal joint radiographic measurements were positively correlated with measurements on CT scans. Correlations were 0.51 for capitate type and 0.71 for lunate type with both p < 0.001. Percent contact of the lunate with the hamate: r was 0.74 p < 0.001. Using logistic regression analysis, percent lunate-hamate contact on CT was a significant predictor of radiographic lunate type 2 p < 0.001. Percent contact area between lunate and hamate > 7.8% on CT scan achieved a sensitivity of 100% and specificity 79.4% for a type 2 lunate. Conclusions: 1) Good correlations found between CT and plain radiographs in lunate type, capitate type, and midcarpal joint contact support the use of plain radiographs to describe contact between the carpal bones in the clinical setting. 2) The retrospective nature of this study limited the technical quality of the measurements. Volumetric analysis may aid in a more exact evaluation of surface contact area.

Carpal tunnel release with versus without flexor retinaculum reconstruction for carpal tunnel syndrome at short- and long-term follow up-A meta-analysis of randomized controlled trials

Background

Carpal tunnel syndrome is a common neuropathy disorder for which surgical treatment consists of release and reconstruction of the flexor retinaculum. Reports of postoperative clinical outcomes after carpal tunnel release with or without flexor retinaculum reconstruction in several studies are controversial. This meta-analysis aimed to compare the efficacy and safety of carpal tunnel release with or without flexor retinaculum reconstruction.

Methods

The PubMed, EMBASE, Web of Science, Ovid, Cochrane Library and Clinical Tri Org databases were searched for randomized controlled trials that compared carpal release with and without transverse carpal ligament reconstruction for carpal tunnel syndrome. Outcomes included postoperative Boston Carpal Tunnel Questionnaire Symptom Severity Scale (SSS), Functional Status Scale (FSS), grip strength and complications. The follow-up time was categorized into short-term (0-3mon) and long-term(>3mon).

Results

A total of 7 studies with 613 patients met the inclusion criteria and were analyzed in detail. Statistical analysis showed no significant difference between two groups on postoperative long-term grip strength (MD 5.85, 95% CI -1.05 to 12.76) long-term SSS (MD -0.31, 95% CI -0.75 to 0.13) and occurrence of complications (RR 1.14, 95% CI 0.84 to 1.54), whereas statistically significant difference was found between groups regarding short-term grip strength (MD 1.51, 95% CI 0.86 to 2.17) and long-term FSS (MD -0.34, 95% CI -0.47 to -0.21).

Conclusion

Carpal tunnel release with flexor retinaculum reconstruction for carpal tunnel syndrome may result in improved long-term functional status while there’s no advantage regarding grip strength, symptom severity and safety over individual carpal tunnel release in short- and long-term outcomes.

Distinct Wrist Patterns Founded on Measurements in Plain Radiographs

Background  In joints, structure dictates function and consequently pathology. Interpreting wrist structure is complicated by the existence of multiple joints and variability in bone shapes and anatomical patterns in the wrist. Previous studies evaluated lunate and capitate shape in the midcarpal joint, and two distinct patterns have been identified. Purpose  Our purpose was to further characterize the two wrist patterns in normal wrist radiographs using measurements of joint contact and position. Our hypothesis was that we will find significant differences between the two distinct anatomical patterns. Patients and Methods  A database of 172 normal adult wrist posteroanterior (PA) radiographs was evaluated for radial inclination, height, length, ulnar variance, volar tilt, radial-styloid-scaphoid distance, and lunate and capitate types. We measured and calculated percent of capitate facet that articulates with the lunate, scapholunate ligament, scaphoid, and trapezoid. These values were compared between the wrist types and whole population. Results  Type-1 wrists (lunate type-1 and spherical proximal capitate) were positively associated with a longer facet between capitate and distal lunate ( p  = 0.01), capitate and base of middle metacarpal ( p  = 0.004), and shorter facet between the capitate and hamate ( p  = 0.004). The odds ratio of having a type-1 wrist when the interface between the capitate and lunate measures >8.5 mm is 2.71 (confidence interval [CI] 1.07, 6.87) and when the line between the capitate and the base of middle metacarpal >9.5 mm is 3.5 (CI 1.38, 9.03). Conclusion  We characterized the two-wrist patterns using intracarpal measurements. Translating these differences into three-dimensional contact areas may help in the understanding of biomechanical transfer of forces through the wrist. Level of Evidence  This is a Level II, diagnostic study.

Trabecular bone patterning across the human hand

Hand bone morphology is regularly used to link particular hominin species with behaviors relevant to cognitive/technological progress. Debates about the functional significance of differing hominin hand bone morphologies tend to rely on establishing phylogenetic relationships and/or inferring behavior from epigenetic variation arising from mechanical loading and adaptive bone modeling. Most research focuses on variation in cortical bone structure, but additional information about hand function may be provided through the analysis of internal trabecular structure. While primate hand bone trabecular structure is known to vary in ways that are consistent with expected joint loading differences during manipulation and locomotion, no study exists that has documented this variation across the numerous bones of the hand. We quantify the trabecular structure in 22 bones of the human hand (early/extant modern Homo sapiens) and compare structural variation between two groups associated with post-agricultural/industrial (post-Neolithic) and foraging/hunter-gatherer (forager) subsistence strategies. We (1) establish trabecular bone volume fraction (BV/TV), modulus (E), degree of anisotropy (DA), mean trabecular thickness (Tb.Th) and spacing (Tb.Sp); (2) visualize the average distribution of site-specific BV/TV for each bone; and (3) examine if the variation in trabecular structure is consistent with expected joint loading differences among the regions of the hand and between the groups. Results indicate similar distributions of trabecular bone in both groups, with those of the forager sample presenting higher BV/TV, E, and lower DA, suggesting greater and more variable loading during manipulation. We find indications of higher loading along the ulnar side of the forager sample hand, with high site-specific BV/TV distributions among the carpals that are suggestive of high loading while the wrist moves through the 'dart-thrower's' motion. These results support the use of trabecular structure to infer behavior and have direct implications for refining our understanding of human hand evolution and fossil hominin hand use.

Finite element analysis for transverse carpal ligament tensile strain and carpal arch area

Mechanics of carpal tunnel soft tissue, such as fat, muscle and transverse carpal ligament (TCL), around the median nerve may render the median nerve vulnerable to compression neuropathy. The purpose of this study was to understand the roles of carpal tunnel soft tissue mechanical properties and intratunnel pressure on the TCL tensile strain and carpal arch area (CAA) using finite element analysis (FEA). Manual segmentation of the thenar muscles, skin, fat, TCL, hamate bone, and trapezium bone in the transverse plane at distal carpal tunnel were obtained from B-mode ultrasound images of one cadaveric hand. Sensitivity analyses were conducted to examine the dependence of TCL tensile strain and CAA on TCL elastic modulus (0.125-10 MPa volar-dorsally; 1.375-110 MPa transversely), skin-fat and thenar muscle initial shear modulus (1.6-160 kPa for skin-fat; 0.425-42.5 kPa for muscle), and intratunnel pressure (60-480 mmHg). Predictions of TCL tensile strain under different intratunnel pressures were validated with the experimental data obtained on the same cadaveric hand. Results showed that skin, fat and muscles had little effect on the TCL tensile strain and CAA changes. However, TCL tensile strain and CAA increased with decreased elastic modulus of TCL and increased intratunnel pressure. The TCL tensile strain and CAA increased linearly with increased pressure while increased exponentially with decreased elastic modulus of TCL. Softening the TCL by decreasing the elastic modulus may be an alternative clinical approach to carpal tunnel expansion to accommodate elevated intratunnel pressure and alleviate median nerve compression neuropathy.

Subject-specific finite element analysis of the carpal tunnel cross-sectional to examine tunnel area changes in response to carpal arch loading

BACKGROUND

Manipulating the carpal arch width (i.e. distance between hamate and trapezium bones) has been suggested as a means to increase carpal tunnel cross-sectional area and alleviate median nerve compression. The purpose of this study was to develop a finite element model of the carpal tunnel and to determine an optimal force direction to maximize area.

METHODS

A planar geometric model of carpal bones at hamate level was reconstructed from MRI with inter-carpal joint spaces filled with a linear elastic surrogate tissue. Experimental data with discrete carpal tunnel pressures (50, 100, 150, and 200mmHg) and corresponding carpal bone movements were used to obtain material property of surrogate tissue by inverse finite element analysis. The resulting model was used to simulate changes of carpal arch widths and areas with directional variations of a unit force applied at the hook of hamate.

FINDINGS

Inverse finite element model predicted the experimental area data within 1.5% error. Simulation of force applications showed that carpal arch width and area were dependent on the direction of force application, and minimal arch width and maximal area occurred at 138° (i.e. volar-radial direction) with respect to the hamate-to-trapezium axis. At this force direction, the width changed to 24.4mm from its initial 25.1mm (3% decrease), and the area changed to 301.6mm² from 290.3mm² (4% increase).

INTERPRETATION

The findings of the current study guide biomechanical manipulation to gain tunnel area increase, potentially helping reduce carpal tunnel pressure and relieve symptoms of compression median neuropathy.