Contact areas of the scaphoid and lunate with the distal radius in neutral and extension: correlation of falling strategies and distal radial anatomy

Biomechanics of Proximal Hamate Autograft in Scaphoid Nonunion

Purpose  Treatment of proximal scaphoid fractures remains a challenge with a risk of nonunions and avascular necrosis due to its retrograde blood supply. The ipsilateral proximal hamate has been described as a viable autograft option for osteochondral reconstruction of the proximal scaphoid. Our study evaluated the changes in the contact area and pressure of the radioscaphoid joint after proximal hamate autograft reconstruction. Methods  Thin sensors (Tekscan Inc., Boston, MA) were placed in the radiocarpal joints of six fresh-frozen cadaveric forearms. Each specimen's tendons were loaded to 150 N in neutral, 45-degree flexion/extension positions through five cycles. Through a dorsal wrist approach, the proximal 10 mm of the scaphoid and hamate was excised. The proximal hamate autograft was affixed to the scaphoid with K-wires. Peak contact pressures and areas at the scaphoid facet were determined and averaged across loading cycles. Results  At the radioscaphoid facet, peak contact pressures were equivalent, although an increasing trend in the neutral and extended wrist position was seen. At the radiolunate facet, contact pressure had an increasing trend in the hamate reconstructed wrists in all wrist positions. Contact areas had a decreasing trend and were nonequivalent at the radioscaphoid facet in the hamate reconstructed wrist. Conclusion  After hamate autograft, the contact areas were not equivalent between the native and reconstructed wrists but contact pressures were equivalent in the facets. The proximal hamate has a more pointed morphology compared with the proximal scaphoid, which would explain the change in contact area in the hamate autografted wrist. Our study suggests hamate autograft may present a viable reconstruction for the proximal pole of the scaphoid without significantly altering peak contact pressures at the radioscaphoid facet.

The Effect of Forearm Position on Wrist Joint Biomechanics

PURPOSE

All active motion wrist joint simulators have been designed to simulate physiologic wrist motion; however, a main difference among them is the orientation of the forearm (horizontal or vertical with respect to gravity). Moreover, the effect of forearm orientation on experimental results has yet to be quantified, but it may be an important variable. Thus, the purpose of this study was to determine the effect of forearm orientation on wrist kinematics and contact mechanics.

METHODS

Eight cadaveric upper limbs were cycled through a flexion-extension motion using an active motion wrist simulator. Motion trials were performed in 3 forearm orientations (gravity-neutral, gravity-flexion, and gravity-extension). A computed tomography-based joint congruency technique was used to examine radiocarpal joint contact and joint contact centroid translation in the 3 tested orientations.

RESULTS

At full wrist extension and wrist flexion, radioscaphoid contact area was greatest in the gravity-extension orientation. Radiolunate contact area was similar among all 3 forearm orientations. The radioscaphoid contact centroid was consistent among the 3 tested positions with the wrist in neutral wrist position. In contrast, the radioscaphoid contact centroid translated radially in the gravity-neutral position relative to the gravity-flexion position in extreme extension. There were no differences in radiolunate centroid contact position in the 3 forearm orientations.

CONCLUSIONS

This study demonstrates that forearm orientation affects contact mechanics and end-range carpal kinematics. Future biomechanical studies should report forearm orientation and discuss the implication of the forearm orientation used on the experimental results.

CLINICAL RELEVANCE

This study provides evidence that the wrist joint is sensitive to forearm positions consistent with activities of daily living and rehabilitation protocols.

Wrist and hand postures when falling and description of the upper limb falling reflex

INTRODUCTION

Falling studies, i.e. assessing what happens when an individual falls, have been conducted in controlled environments but not in field studies for ethical reasons; this potentially limits the validity and applicability of previous studies. We performed field studies on existing YouTube © videos of skateboarders falling. The aims of these studies were to measure the wrist angle at impact on videos of real unprotected falls and to study the dynamics of the upper limbs when falling.

METHODS

Youtube © videos of skateboarders falling were studied assessing the direction of the fall, the positions of both upper limbs and especially the wrists on impact quantitatively and qualitatively. This study would not be ethical by other means.

RESULTS

In study one (the more quantitative study) there were 48 men and 50 falls. The mean elbow flexion was 30⁰ (range 0⁰ to 80⁰) and the mean maximal wrist extension was 80⁰ (range 50⁰ to 110⁰). The second wrist extended less or the same in > 90%. The second wrist only once (of 31) extended > 90⁰ which should minimise the risk of toppling. Falls onto only one wrist gave significantly greater maximal wrist extension. In the second more qualitative study we observed the "upper limb falling reflex" where the response to falling is for the upper limb(s) to align the upper limb with the direction of falling of the body with the elbow mostly but not fully extended. Initially the wrists extend c. 40⁰-50⁰ with the fingers held mildly flexed. Immediately before impact the fingers hyper-extend with some compensatory wrist flexion to c. 30⁰ of extension. The fingertips impact the ground first followed by the hand.

CONCLUSION

These studies confirm wrist extension at impact around 80⁰ but the wrist(s) may hyper-extend risking toppling. Falls on both wrists minimise the risk of toppling. The "upper limb falling reflex" is defined; it is a rapid dynamic response leading to the fingers impacting the ground first on falling. Abnormalities with the upper limb falling reflex may indicate problems with development in young children and may increase the risk of injury in older people.

Force transmission through the wrist during performance of push-ups on a hyperextended and a neutral wrist

STUDY DESIGN

Cross-sectional cohort.

INTRODUCTION

Push-ups are used ubiquitously to evaluate and strengthen the upper body. They are usually performed in 1 of 2 main ways: with the wrist in hyperextension and with the wrist in a neutral position.

PURPOSE OF THE STUDY

The purpose of our study was to compare the dynamic forces in the wrist during the 2 push-up styles.

METHODS

Fourteen volunteers performed push-ups in 2 different patterns: on a hyperextended wrist and a neutral wrist (NW). Two force plates and a motion capture system were used to measure the ground reaction forces (GRFs) and the kinematics of the upper extremity during push-ups. Kinematic and kinetic analyses were performed using Matlab software (Mathworks, Natick, MA).

RESULTS

The GRF vector was distributed differently during the different types of push-ups. For both methods, the total GRF carried by the upper dominant extremity was larger than those of the nondominant extremity. In the NW configuration, the GRF vector was more uniform throughout the push-up in the vertical direction. The horizontal distance between the capitate bone location and the GRF origin was smaller in hyperextension. The forces traveled more dorsally over a wider area and more ulnarly in the hyperextended wrist.

DISCUSSION

Forces are transmitted differently through the wrist in the 2 methods. Push-ups on an NW are likely safer because ligaments may be preferentially loaded in hyperextension. Further study may delineate the differences in the anatomic location of force transmission and the long-term clinical effect on the wrist.

CONCLUSIONS

This study supports the performance of push-ups on a wrist in neutral flexion extension; both to enable patients after surgery or injury to strengthen the upper body and prevent injury and long-term wear in the wrist. The knowledge gained from this study may assist in outlining guidelines for push-up performance.

LEVEL OF EVIDENCE

Diagnostic level 2a.

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.

In vivo metacarpophalanageal joint collateral ligament length changes during flexion

We investigated the in vivo length changes of the collateral ligaments of metacarpophalangeal joint during flexion. We obtained computed tomography scans of index, middle, ring and little fingers at 0°, 30°, 60° and 90° of joint flexion from six hands of six healthy adult volunteers. Three of them had their dominant right hand studied, and the other three had their non-dominant left hand studied. We measured and analysed the radial and ulnar collateral ligaments of each metacarpophalangeal joint from the reconstructed images. We found that the dorsal and middle portions of the both radial and ulnar collateral ligament lengthened progressively during digital flexion and reached the maximum at 90° flexion. The length of the volar portion increased from 0° to 30° flexion and then decreased from 30° to 60° flexion, reaching the minimum at 90°. In conclusion, three portions of collateral ligaments on both sides of the metacarpophalangeal joint have variable length changes during flexion, which act to stabilize the joint through its flexion arc.

In Vivo Contact Characteristics of Distal Radioulnar Joint With Malunited Distal Radius During Wrist Motion

PURPOSE

To determine whether distal radioulnar joint (DRUJ) contact characteristics were altered in patients with malunited distal radius fractures.

METHODS

We obtained computed tomography scans at 5 positions of both wrists of 6 patients who had unilateral malunited distal radius fractures with dorsal angulation from 10° to 20° and ulnar variance less than 3 mm. We reconstructed 3-dimensional images and mapped contact regions of DRUJ by calculating the shortest distance between the 2 opposing bones. The contact areas of the DRUJ were measured and the contact region centers were calculated and analyzed. The values of the malunited side were compared with those of the contralateral uninjured side.

RESULTS

In the uninjured wrist, the contact areas of the DRUJ increased slightly from wrist flexion to extension and ulnar deviation. In the malunited wrist, we found the contact areas of DRUJ to be progressively reduced from 20° flexion to neutral, 40° extension, and 20° extension, to ulnar deviation. The centroid of this area on the sigmoid notch moved to distal from flexion to extension. Compared with the contralateral uninjured wrist, the contact area significantly decreased during wrist extension and ulnar deviation, and significantly increased during wrist flexion. The centroids of this area on sigmoid notch all moved volarly in all selected wrist positions.

CONCLUSIONS

The contact areas of the DRUJ and the centroid of contact area on sigmoid notch are altered in patients with malunited distal radius fractures. The contact area of the DRUJ increases during wrist flexion and decreases during wrist extension and ulnar deviation. The centroids of the contact area on sigmoid notch move volarly during wrist flexion-extension and ulnar deviation.

CLINICAL RELEVANCE

The in vivo findings suggest that alterations in joint mechanics may have an important role in the dysfunction associated with these injuries.

How does wrist position affect the length of the distal radioulnar ligament: a three-dimensional image study in vivo?

PURPOSE

This study was designed to investigate the length changes of the distal radioulnar ligament at different wrist positions and to determine the effect of hyperextension on the distal radioulnar ligament and to find out the most vulnerable position where the distal radioulnar ligament rupture and foveal avulsion.

METHODS

We obtained computed tomography scans of the wrists for 12 volunteers including two groups: hyperextension group and hyperextension with maximal rotation group. The images were reconstructed to the three-dimensional bone structures with customized software. The four portions of the distal radioulnar ligament were measured and analyzed statistically.

RESULTS

No significant differences were noted in the lengths of the each portion of the distal radioulnar ligament among neutral position, wrist hyperextension, and hyper-radial extension. From neutral position to hyperextension with maximal pronation, the lengths of the palmar superficial radioulnar ligament (psRU) and dorsal deep radioulnar ligament (ddRU) decreased significantly, whereas the dorsal superficial radioulnar ligaments (dsRU) and palmar deep radioulnar ligament (pdRU) increased significantly. From neutral position to hyperextension with maximal supination, the lengths of the pdRU and dsRU ligaments decreased significantly, and the lengths of psRU and ddRU ligaments changed little.

CONCLUSIONS

The factor of hyperextension has little effect on the length of the distal radioulnar ligament and the distal radioulnar ligament may be under great tension at the position of hyperextension with maximal pronation. These findings can provide more information to understand the pathomechanics of the triangular fibrocartilage complex injury caused by a fall on the outstretched hand and can provide information relevant to the distal radioulnar ligament restoration.

In Vivo length changes of the proximal interphalangeal joint proper and accessory collateral ligaments during flexion

PURPOSE

To investigate the length changes in proper collateral ligament (PCL) and accessory collateral ligament (ACL) during flexion of the proximal interphalangeal (PIP) joint in vivo and how portions of the PCL and ACL stabilize the PIP joint.

METHODS

We obtained computed tomography scans of the index, middle, and ring fingers of one hand from 6 volunteers at 0°, 30°, 60°, 90°, and full flexion of the PIP joint. Radial and ulnar PCL and ACL were measured and analyzed with computer modeling.

RESULTS

The data showed that during flexion the average length of the dorsal portion of the radial and ulnar PCL increased significantly and reached a maximum at 90°. The volar portion of the radial and ulnar PCL and the distal portion of the radial and ulnar ACL shortened continuously from extension to full flexion.

CONCLUSIONS

The proximal and middle portions of each ACL are nearly isometric, the dorsal portion of each PCL becomes taut only in flexion, and the volar portion of PCL and the distal portion of ACL become taut only in extension. The current findings indicate that the dorsal portion of PCL is the most stabilizing structure during flexion of the PIP joint, and that the volar portion of PCL and the distal portion of ACL provide the crucial lateral stability to the joint at extension.

CLINICAL RELEVANCE

The results may provide information relevant to the ligaments of PIP joint reconstruction and rehabilitation.

Length changes of scapholunate interosseous ligament at different wrist positions: an in vivo 3-dimension image study

PURPOSE

The scapholunate interossous ligament (SLIL) has a critical role in maintaining the proper kinematic relationship between the scaphoid and the lunate. We hypothesize that the length of SLIL changes significantly at wrist full extension and during forearm rotation. The aim of this study was to investigate the length changes of SLIL at wrist full extension and forearm rotation in vivo.

METHODS

Twelve volunteers were randomly divided to two groups. We obtained computed tomography scans of the wrists at different wrist positions. The three regions of the SLIL were measured and analyzed with computer modeling.

RESULTS

The results showed that from the neutral to full extension of the wrist, the length of volar SLIL and volar, middle portions of the proximal SLIL increased significantly. The volar and proximal SLIL increased significantly in maximal forearm pronation.

CONCLUSIONS

The lengths of the volar and proximal regions of SLIL increase substantially at wrist full extension, but only slightly at maximal forearm pronation. Clinically, wrist full extension may make the SLIL ligament vulnerable to disruption.