Evaluation of Four-Dimensional Computed Tomography as a Technique for Quantifying Carpal Motion

Delayed diagnosis of dynamic carpal instability often occurs because early changes in bone alignment and movement are difficult to detect and manifest mainly during a dynamic/functional task. Current diagnostic tools are only able to examine the carpal bones under static or sequential-static conditions. Four-dimensional (three dimensions + time) computed tomography (4DCT) enables quantification of carpal mechanics through 3D volume sequences of the wrist in motion. A comprehensive understanding of carpal mechanics is needed to define normal function and structure and provide targets for treatment of carpal injuries. In this study, measurements of scaphoid translation and joint congruency were taken by creating models from the CT scans of the carpals in extreme frames of motion, registering those models to the neutral position, transforming the models into a local coordinate system, and using software to calculate the joint surface areas (JSA). Results indicated that the centroid of the scaphoid translated 6.4 ± 1.3 mm and extended from extreme radial to extreme ulnar deviation. Results are consistent with the literature. An additional study was performed to measure the responsiveness of the 4DCT technique presented. Bone models from each frame of motion for radio ulnar deviation (RUD) and flexion extension (FE) were created and distinct differences between their JSA were measured qualitatively and quantitatively. The results show that there was statistically significantly different JSA within carpal joints between RUD and FE. These studies provide the first step in developing the methodology when using 4DCT scanning to measure subtle abnormalities in the wrist.

The Natural History of Scaphoid Fracture Malunion: A Scoping Review

Background A scaphoid malunion occurs when a scaphoid fracture heals in a nonanatomic position or when the fracture is fixed without correction of the sagittal angular deformity. Although altered carpal mechanics and early osteoarthritis have been suggested as natural sequelae, the natural history and clinical outcomes are debatable. Purposes The purpose of this study is to review and summarize the available literature regarding clinical, functional, and radiographic outcomes of patients with scaphoid malunion. Methods A systematic search of the MEDLINE/PubMed, EMBASE, Cochrane Library, and Web of Science was performed to identify published studies concerning the clinical and radiological results of scaphoid malunion following either acute scaphoid fracture or surgically treated nonunions. Results Five publications with a total of 83 malunions were included in the final synthesis. The diagnosis of malunion was based on computed tomography by calculating the lateral intrascaphoid angle (threshold of 35 or 45 degrees) or height/length ratio (threshold of 0.6). Self-reported and clinical evaluation techniques varied between the studies and direct comparison was not possible between the different outcome measures. Most patients demonstrated arthritic changes; however, correlation with pain and functional results was not always present. Conclusions This scoping review confirmed that patients with malunited scaphoids seem to have higher likelihood of post traumatic arthritis. However, clinical implications remain uncertain and better methods for assessing and defining scaphoid deformity are required.

Does Wrist Laxity Influence Three-Dimensional Carpal Bone Motion?

Previous two-dimensional (2D) studies have shown that there is a spectrum of carpal mechanics that varies between row-type motion and column-type motion as a function of wrist laxity. More recent three-dimensional (3D) studies have suggested instead that carpal bone motion is consistent across individuals. The purpose of this study was to use 3D methods to determine whether carpal kinematics differ between stiffer wrists and wrists with higher laxity. Wrist laxity was quantified using a goniometer in ten subjects by measuring passive wrist flexion–extension (FE) range of motion (ROM). In vivo kinematics of subjects' scaphoid and lunate with respect to the radius were computed from computed tomography (CT) volume images in wrist radial and ulnar deviation positions. Scaphoid and lunate motion was defined as “column-type” if the bones flexed and extended during wrist radial–ulnar deviation (RUD), and “row-type” if the bones radial–ulnar deviated during wrist RUD. We found that through wrist RUD, the scaphoid primarily flexed and extended, but the scaphoids of subjects with decreased laxity had a larger component of RUD (R2 = 0.48, P < 0.05). We also determined that the posture of the scaphoid in the neutral wrist position predicts wrist radial deviation (RD) ROM (R2 = 0.46, P < 0.05). These results suggest that ligament laxity plays a role in affecting carpal bone motion of the proximal row throughout radial and ulnar deviation motions; however, other factors such as bone position may also affect motion. By developing a better understanding of normal carpal kinematics and how they are affected, this will help physicians provide patient-specific approaches to different wrist pathologies.

3D Dynamic Analysis of the Wrist

With advances in imaging and computing technology the greater capacity to diagnose, plan and deliver care to patients with hand and wrist disorder is being realised. Work in our laboratory, has been able to identify certain specific rules that control wrist motion, and is a step on the pathway to creating a unified theory of carpal mechanics which will incorporate a kinetic biomechanical model. This will allow more precise anatomically based as well as quantitative diagnoses, but also an ability to test a proposed intervention in a “what if” scenario.

Unifying model of carpal mechanics based on computationally derived isometric constraints and rules-based motion – the stable central column theory

This study was part of a larger project to develop a (kinetic) theory of carpal motion based on computationally derived isometric constraints. Three-dimensional models were created from computed tomography scans of the wrists of ten normal subjects and carpal spatial relationships at physiological motion extremes were assessed. Specific points on the surface of the various carpal bones and the radius that remained isometric through range of movement were identified. Analysis of the isometric constraints and intercarpal motion suggests that the carpus functions as a stable central column (lunate–capitate–hamate–trapezoid–trapezium) with a supporting lateral column (scaphoid), which behaves as a ‘two gear four bar linkage’. The triquetrum functions as an ulnar translation restraint, as well as controlling lunate flexion. The ‘trapezoid’-shaped trapezoid places the trapezium anterior to the transverse plane of the radius and ulna, and thus rotates the principal axis of the central column to correspond to that used in the ‘dart thrower’s motion’. This study presents a forward kinematic analysis of the carpus that provides the basis for the development of a unifying kinetic theory of wrist motion based on isometric constraints and rules-based motion.

X-Ray Analysis after Repair of Scaphoid Non-Union through a Dorsal Approach

The consequences of non-union of the scaphoid with or without deformity were evaluated before and after surgery with non-parametric tests, MANOVA and discriminant analysis, and Spearman correlation and contingency tables. 18 consecutive cases of scaphoid non-union, operated upon through a dorsal approach preserving the carpal ligaments since 1987, were used for measurements. Carpal height, radio-lunate and radio-scaphoid angles, lunate covering ratio, and apparent translation of the capitate and lunate were analyzed on standard views of the wrist before and after scaphoid repair. We found that the lunate covering ratio combined with the radio-lunate angle was the main indicator of deformity before the repair as suggested by the strong correlation between the radio-lunate angle and lunate covering ratio ( P= 0.0001). After repair, the only indicator of mal-union was the apparent translation of the lunate on frontal views (P= 0.0033) as suggested by the strong correlation between real-union and lunate translation ( P= 0.0001). Translation of both the lunate and capitate correlated well before and after repair. Radio-scaphoid angle and carpal height showed no significant changes and are not informative in the presence of subtle carpal alteration. Repair of the scaphoid produced an improvement in the radio-lunate angle in all cases, even in the presence of mal-union. However, full restoration was never achieved even in the absence of mal-union. More precise techniques of measurement might contribute to a better understanding of the carpal mechanics in relation to wefi-defined diagnoses such as scaphoid non-union.

Kinematic and Kinetic Analysis of the Human Wrist by Stereoscopic Instrumentation

A three-dimensional kinematic and kinetic analysis of the human wrist can lend useful data to understand carpal mechanics. This data would also be useful in implant design and evaluating surgical reconstructive procedures. A stereoscopic photographic technique using light-emitting diodes (LED’s) is described that records on film three-dimensional relative motion between two bone segments. The LED’s are inserted into the carpal bones at key ligamentous attachments. Kinetic data is generated by use of a force transducer. LED frames are mounted on both sides of the wrist joint and to the calibrated transducer so that the three-dimensional motion and force (moment) information is recorded at the same time. Wrist motion is generated both passively and dynamically by motors attached to the principle wrist tendons. The kinematic and kinetic data, recorded on film, is then digtized and analyzed by computer. Knowledge of the relative three-dimensional motion of the intercarpal and radiocarpal joints and the relative forces that are distributed through the various wrist ligaments will be produced by this instrumentation. Output computer graphics routines, including screw axis data, have been developed.