Frederick W. Werner

Complications during wrist surgery may be related to poor bone quality. The goal of this study was to determine if radiographic assessment of upper extremity bone quality reflects the trabecular bone quality of carpal bones, as this could be used clinically to assess adequacy for carpal bone surgical fixation or reconstruction. The first goal was to determine the carpal trabecular bone volume fraction (bone volume/total volume; BV/TV) in capitates, lunates, and scaphoids using micro-computed tomography (micro-CT). A second goal was to determine if either ultradistal radius bone mineral density (UDBMD) or second metacarpal cortical percentage (2MCP) is related to the trabecular BV/TV in carpal bones. For 20 fresh-frozen cadaver forearms, dual-energy X-ray absorptiometry (DXA) measured UDBMD. X-rays were used to measure the cortical thickness and periosteal diameter of the second metacarpal for calculation of 2MCP (% cortical thickness/periosteal diameter). Capitates, lunates, and scaphoids were scanned using micro-CT to assess carpal cancellous bone BV/TV. To determine if UDBMD and 2MCP were predictors of BV/TV after accounting for the influence of age and sex, the contribution of each was compared using semipartial correlation coefficients (SPCC) in two multiple linear regression models. UDBMD, 2MCP, and age each correlated individually with the carpal BV/TV (R = +0.84, +0.74, and −0.66, respectively). When accounting for the influence of age and sex, the regression models demonstrated that 2MCP was not a significant predictor of BV/TV (SPCC = +0.257, p = 0.10) but that UDBMD was (SPCC = +0.40, p = 0.004). Both UDBMD and 2MCP correlate with BV/TV individually, but only UDBMD correlates with BV/TV after accounting for age and sex. This study serves as a first step in determining whether forearm DXA and/or 2MCP may be used as screening tools to predict surgical fixation outcomes in the wrist.

Background: There is no clear consensus regarding optimal surgical management of Bennett fractures of the thumb carpometacarpal joint. We aimed to assess the initial displacement of such fractures and directly compare the stability of 2 different Kirschner-wire (K-wire) fixation constructs, hypothesizing that both constructs would confer substantial stability and that a pin crossing the fracture site would be more resistant to subsidence at the joint than suspensory fixation alone. Methods: Bennett fractures were recreated using a sagittal saw in 8 paired fresh-frozen cadaveric specimens. Axial subsidence was then measured under a 100 N load of applied force. Specimens were then assigned to one of two 0.064” K-wire fixation methods: (1) an intermetacarpal suspensory method with 2 parallel K-wires between the diaphyses of the first and second metacarpals; and (2) an interfragmentary pin directly spanning the fracture site at the base of the first metacarpal with a second suspensory intermetacarpal pin. Specimens were then tested with cyclic loading to 25 N, 50 N, and 100 N. Axial subsidence between the two fragments was measured followed by paired statistical analysis. Results: The average axial subsidence of the fractures prior to fixation was 3.1 mm. There was less subsidence for the fracture-spanning fixation at 25 N and 50 N compared to suspensory fixation ( P = .0156 and P = .0078, respectively) but no difference at 100 N ( P = .37). Conclusion: Bennett fractures without fixation demonstrate clinically significant step off greater than 2 mm indicating a benefit from operative fixation. Both percutaneous K-wire fixation methods conferred acceptable stability, with interfragmentary fixation providing increased stability at lower loads.

Scapholunate dissociation is usually the result of failure of multiple wrist ligaments. With continued use other structures attenuate, which results in change in position of the carpal bones. It is presumed that load characteristics in the wrist joint change with changes in carpal bone position. This is thought to result in localized pressure overload and arthritic change.The purpose of this study was to evaluate radioscaphoid joint pressures and carpal kinematics after sectioning specific wrist ligaments. Our hypotheses are that there would be increased scaphoid flexion and ulnar deviation, increased lunate extension and radial deviation, increased contact pressure in the radioscaphoid fossa, and increased tendon forces.Eight cadaver wrists were instrumented with an electromagnetic motion tracking device and a pressure sensor was inserted into the radioscaphoid joint. Using a wrist joint motion simulator, motion and pressure data were obtained in the moving wrist in the intact state and after sectioning the dorsal radiocarpal, dorsal intercarpal, and scapholunate interosseous ligaments.After ligament sectioning there was increased scaphoid flexion, scaphoid ulnar deviation, lunate extension, and lunate radial deviation resulting in carpal instability. There was also an increase in pressure in the radioscaphoid fossa. Several specimens showed evidence of scaphoid subluxation.It is our conclusion that this combination of ligament sectioning produces scapholunate instability and increased pressures in the radioscaphoid fossa in the laboratory setting. We believe that if left untreated in the clinical setting, scapholunate advanced collapse could result.

Background Multiple techniques have been developed to detect a triangular fibrocartilage complex (TFCC) foveal detachment. One commonly used technique to evaluate TFCC integrity, the trampoline test, has had variable reliability. Questions/Purposes The purpose of this biomechanical experiment was to evaluate the suitability of the trampoline test in detecting TFCC foveal detachments. Materials and Methods In each of 10 cadaver arms, TFCC displacement near the ulnar fovea was measured using a plunger with increasing incremental loads in the intact wrist, after ulnar sectioning of the TFCC, and following TFCC repair. Results After the application of the eight incremental small weights, there was no significant difference in the relative displacement of the plunger between the intact case, after detachment of the ulnar aspect of the TFCC disc, and after repair (0.6 mm intact, 0.7 mm detached, and 0.7 repair). However, there were significant differences in the absolute ending point displacement referenced to the starting intact position (0.6 mm intact, 1.3 mm detached, and −0.9 mm after repair). Conclusion/Clinical Relevance This study suggests that the trampoline test may not be adequate to quantify displacement (bouncing) of the TFCC disc after injury.

Background Typically, metacarpal shaft fractures are treated with closed reduction percutaneous pinning, intramedullary nails, or plate fixation. Recently some surgeons have begun using intramedullary headless compression screws. Questions/Purposes The purpose of this study was to compare intramedullary screw fixation to K-wire fixation, which is the standard of care in a transverse metacarpal midshaft fracture, using a cadaveric model. Our hypothesis was that intramedullary screw fixation would have a biomechanical advantage (higher stiffness and peak load to failure) when compared with dual Kirschner wire fixation of transverse metacarpal shaft fractures. Methods Four-point bend testing was performed to compare stiffness and failure load values of seven paired 2nd and 3rd metacarpals instrumented with headless intramedullary compression screw fixation or Kirschner wire fixation. Similar testing was performed on 14 unpaired 4th metacarpals. Results There was no significant difference in peak load (p = 0.60) or stiffness (p = 0.85) between fixation groups for the 2nd and 3rd instrumented metacarpals. For the instrumented 4th metacarpals, there was no significant difference in peak load (p = 0.14), but the stiffness was significantly greater (p = 0.01) for the compression screw group compared with the Kirschner wire fixation. Conclusions/Clinical Relevance In this study, the load to failure was not different between the two fixation methods and likely both techniques can sustain physiologic loads needed for rehabilitation. The greater stiffness in the 4th metacarpal compression screw group may be related to the smaller canal morphology than in the 2nd and 3rd metacarpals. Larger diameter screws may be needed to obtain a better fit particularly in the 2nd and 3rd metacarpals.