Steven F. Viegas

Effects of distal radius fracture malunion on wrist joint mechanics.

An experimental model using a static positioning frame, pressure-sensitive film (Fuji), and a microcomputer-based videodigitizing system was used to measure contact areas and pressures in the wrist. Contact areas and pressures were compared in a group of wrists between the normal state and with simulated distal radius fracture malunions of varying degrees. In simulated malunions, radial shortening to any degree slightly increased the total contact area in the lunate fossa, and was significant at 2 mm of shortening. By angulating the distal radius more than 20 degrees either palmar or dorsal, there was a dorsal shift in the scaphoid and lunate high pressure areas, and the loads were more concentrated, but there was no change in the load distribution between the scaphoid and lunate. Decreasing the radial inclination shifted the load distribution so that there was more load in the lunate fossa and less load in the scaphoid fossa.

Wrist anatomy: Incidence, distribution, and correlation of anatomic variations, tears, and arthrosis

We dissected 393 wrists to evaluate the incidence and distribution of anatomic features, arthrosis, chondromalacia, and soft tissue lesions. The data were then analyzed for any statistically significant associations among the different variables. The most common (73%) lunate morphology had a separate medial facet on its distal surface for the hamate. The capitate had a separate facet for the fourth metacarpal in 86% of the wrists. Fourth metacarpals with a dorsal radial facet, either separate from or connected to the rest of the fourth metacarpal base, were the most common types of fourth metacarpal. Cartilage erosion with exposed subchondral bone was identified in 58% of the wrists. It was most commonly at the proximal pole of the hamate (28%). Tears of the ligaments and/or the triangular fibrocartilage complex were identified in 56% of the wrists. The triangular fibrocartilage complex was found torn in 36% of the wrists. The lunotriquetral interosseous ligament was torn in 36% of the wrists, and the scapholunate interosseous ligament was torn in 28% of the wrists. There was a communication between the proximal wrist joint and the pisotriquetral joint in 88% of the 76 wrists, which were further dissected to assess this issue. Statistical analysis of the data found a significant correlation between the presence of cartilage erosion at the proximal pole of the hamate and the presence of a lunate facet. There was also a significant correlation between the presence of a tear in the scapholunate interosseous ligament and the presence of cartilage erosion in the scaphoid-trapezium-trapezoid joint. Analysis of the paired wrists from 169 cadavers revealed that the same soft tissue tear or combination of tears was present bilaterally in 39% of the pairs. Cartilage erosion was present bilaterally in the same location or locations in 27% of the pairs.

Ulnar-sided perilunate instability: an anatomic and biomechanic study.

A staging system for ulnar-sided perilunate instability is presented based on a series of cadaver dissections and load studies. Stage I: partial or complete disruption of the lunotriquetral interosseous ligament, without clinical and/or radiographic evidence of dynamic or static volar intercalated segment instability deformity; stage II: complete disruption of the lunotriquetral interosseous ligament and disruption of the palmar lunotriquetral ligament, with clinical and/or radiographic evidence of dynamic volar intercalated segment instability deformity; and stage III: complete disruption of the lunotriquetral interosseous and the palmar lunotriquetral ligaments, attenuation or disruption of the dorsal radiocarpal ligament, with clinical and/or radiographic evidence of static volar intercalated segment instability deformity.

A Comprehensive Study of Pressure Distribution in the Ankle Joint with Inversion and Eversion

The understanding of load transfer characteristics is the baseline for biomechanics of the ankle joint. Changes in contact patterns of the articular cartilage from the norm may indicate pathologic conditions. Measurement of the contact in human cadaver ankles provides a direct measurement for this understanding. The force transfer characteristics of the three facets of the ankle joint were investigated. Five fresh-frozen cadaver lower extremities were tested in 12 positions under three axial loads of 490, 686, and 980 N. Fuji film served as the pressure transducer and the prints were analyzed by a computerized video digitizer. The results demonstrated that as the foot was moved into inversion or eversion with the ankle in neutral flexion or dorsiflexion, there was a decrease in total contact area and an increase in the average high pressure. In plantarflexion, the contact area was lower and the average high pressure was higher, indicating a greater force per unit area as compared with dorsiflexion and neutral flexion. In plantarflexion, however, little change was noted with inversion or eversion. In dorsiflexion, the total contact area was higher and the average high pressure slightly lower as compared with neutral flexion. With inversion, the contact area of the medial facet of the ankle increased and with eversion it increased on the lateral facet, especially in dorsiflexion. With an increase in loading, the pressure did not significantly increase but the contact area did increase. The centroid of the contact moved anteriorly to posteriorly on the talus as the joint moved from dorsiflexion to plantarflexion. The talar dome facet sustained 77% to 90% of the load, while the medial facet was loaded more during inversion (up to 22%) and the lateral facet was loaded more during eversion (up to 10.5%). No previous study has examined the relative contributions of the three main talar joint surfaces in multiple positions. The new information in this study includes the fibular and medial facet contribution and the variation of the load with position changes and loading increase. This study also provides a comprehensive evaluation of the pressure, contact area, and centroid of the ankle joint in its normal ranges of motion.

A comparison of double-plate fixation methods for complex distal humerus fractures

A modified method of fracture fixation of complex distal humeral fractures with medial and lateral plates and bolts was biomechanically tested and compared with previously described fixation techniques. Compressive stiffness coefficients were determined for three classes of fixation before and after fatigue cycling. This procedure was followed with compressive loading to failure. The results show that in the most unstable fracture type tested this new fixation method provides increased strength and stability. Early clinical follow-up examinations of patients treated with this technique show that this method is a reasonable fixation alternative for the complex distal humerus intercondylar fracture.

Load transfer characteristics of the wrist. Part I. The normal joint

A static positioning frame allows the positioning of unembalmed human upper extremities in any combination of wrist flexion/extension, radio/ulnar deviation, and pronation/supination. Pressure-sensitive film (Fuji) was used to study the contact areas, scaphoid-lunate area ratios, average high pressures, centroid positions, and intercentroid distances of five wrist joints under a uniform load of 103 Newtons (N) in 36 different positions. The contact areas accounted for only 20.6% of the available joint surface. They shift from a primarily palmar location to a primarily dorsal location when the wrist changes from flexion to extension. Overall the scaphoid contact area was 1.47 times that of the lunate and was generally greatest with the wrist in ulnar deviation. The scapho-lunate contact area ratio increased as wrist position changed from radial to ulnar deviation and/or from flexion to extension. For the constant load of 103 Newtons the high pressure averaged 3.17 megapascals (MPa). The scaphoid and lunate high pressure centroids shifted palmar when wrist position changed from 20 degrees of flexion to 20 degrees of extension and then shifted dorsal with further extension of the wrist. The intercentroid distance averaged 14.91 mm and ranged from 10 to 20 mm.

High-speed, three-dimensional kinematic analysis of the normal wrist.

Carpal kinematics during a wrist flexion/extension motion using high-speed videodata acquisition was investigated. A cadaver forearm was stabilized, allowing unconstrained excursion of the wrist for passive range of motion (ROM). The extensor and flexor pairs of the wrist were looped together and a 1-lb weight was attached to each pair, simulating synergistic muscle tension. Capitate/radius and third metacarpal/radius angles were calculated to determine which measurement would be best for determining global wrist angle. The average difference in capitate/radius and third metacarpal/radius angles at each respective flexion/extension wrist angle for all wrists was 1.1 degrees +/- 1.6 degrees (the maximum difference was 4 degrees). Hence, the capitate-third metacarpal joint can be considered rigid. Capitate/lunate motion as described by capitate-radius Euler angles ranged from -16.9 to 23.5 with total capitate/lunate motion of 40.5 (35%) in the 114 degrees total global wrist ROM measured. Radius/lunate motion as described by lunate-radius angle ranged from -8.2 to 48.4 with total radius/lunate motion of 56.5 (49%) in the 114 degrees total global wrist ROM measured. During global wrist motion, the radiolunate joint contributes more motion in flexion than the capitolunate joint and the capitolunate joint contributes more motion in extension than the radiolunate joint. The instantaneous screw axes (ISAs) were calculated for each third metacarpal position with respect to the radius. The average distance difference between ISAs for the 4 wrists tested was -1.23 +/- 14.97 pixels. The maximum distance was 56.51 pixels and the minimum was -24.09 pixels. This new combination of motion analysis and 3-dimensional reconstructions of computed tomography images affords a high-speed, dynamic analysis of kinematics. It shows that during wrist flexion/extension, normal carpal kinematics does not have an ISA fixed in or limited to the capitate. In addition, the ISA data provide evidence that translational motion is a real and measurable component of normal carpal motion. These findings alter the understanding of carpal kinematics obtained from the results of previous studies which suggested that the center of rotation was fixed in the capitate.

Extension block pinning for proximal interphalangeal joint fracture dislocations: Preliminary report of a new technique

The simple, percutaneous placement of a smooth pin into the head of the proximal phalanx creates an extension block, which prevents subluxation of the middle phalanx and allows early active flexion of the proximal interphalangeal joint. Three case reports involving this new treatment are presented along with a detailed description of the technique.

Carpal arch alteration and related clinical status after endoscopic carpal tunnel release

One hundred eight endoscopic carpal tunnel releases were performed by a modification of the technique described by Chow. Eighty-seven of the 108 cases were evaluated for quantitative postoperative widening of the transverse carpal arch. The average postoperative widening of the transverse carpal arch was 0.17 cm (7%), with a range of 0 to 0.5 cm. Seventy percent of the patients showed 0% to 10% widening, 26% showed 10% to 20% widening, and 4% showed more than 20% widening of the transverse carpal arch. Preliminary findings show that 3 weeks after endoscopic carpal tunnel release, pinch strength was at 102% and grip strength at 86% of preoperative values. Six weeks after surgery, pinch strength was 106% and grip strength was 121% of preoperative values. The complication rate in this series was 3%. The transverse dimension of the carpal arch generally widens after endoscopic carpal tunnel release but to a lesser degree than has been reported for open carpal tunnel release. The rate of improvement of pinch and grip strength after endoscopic release is faster than that reported in the literature after open release.

Load transfer characteristics of the wrist. Part II. Perilunate instability

An experimental model with a static positioning frame, pressure-sensitive film (Fuji), and a microcomputer-based video digitizing system, previously developed by the two senior authors, was used in this study to examine the effects of increasing perilunate instability on the load transfer characteristics of the wrist. These effects included a significant dorsal ulnar shift of the scaphoid centroid with increasing perilunate instability together with a less dramatic palmar ulnar shift of the lunate centroid. Overall, the scaphoid contact area was found to decrease as the stage of perilunate instability increased, even in ulnar deviation and/or extension, which in the normal wrist was found to be the positions that had the greatest scaphoid contact area. Average pressures in the high pressure zones were found to significantly increase in wrists with a stage III instability compared with normal wrists. An increase in the intercentroid (scaphoid/lunate) distance was most evident with the wrist in 20 degrees extension, neutral radioulnar deviation, and 90 degrees supination.