Rita M. Patterson

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 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.

Muscle balance at the knee-moment arms for the normal knee and the ACL-minus knee

Forces, moments and stresses at the knee are dependent upon external and internal loading factors including muscle forces, segmental position and velocity, load carried, and the moment arms (mechanical advantage) of the muscle-tendon units. Requisite to prediction of forces and moments is a detailed understanding of effective moment arms throughout the knee range-of-motion (ROM). Existing muscle models for the knee are based upon limited static studies of only a few preserved specimens. The objectives of this report are to develop a comprehensive description of muscle-tendon moment arms for the normal knee and the anterior cruciate ligament (ACL)-minus knee during flexion-extension motion. Recent research results describe two nonorthogonal, nonintersecting axes of motion for the knee--one describing flexion-extension (FE) and the other longitudinal rotation (LR, equivalent to internal-external rotation). The effective flexion-extension moment arms of the muscles crossing the knee were developed with respect to the FE axis in 15 fresh, hemi-pelvis cadaver specimens. The normal moment arms for each of 13 muscles plus the patellar tendon exhibited variable, yet repeatable and recognizable patterns throughout the ROM. For most muscles there was no significant difference between the normal and ACL-minus moment arms. The results provide a basis for more accurate predictions of joint reaction forces and moments as well as useful knowledge for practitioners and therapists to assist in the assessment of muscle balance at the knee following injury, repair, and throughout rehabilitation.

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.

The effects of various load paths and different loads on the load transfer characteristics of the wrist

An experimental model that incorporated a static positioning frame, pressure-sensitive film, and a microcomputer-based videodigitizing system was used to analyze the effects of different loading pathways and various loads on the contact area and pressures within the wrist joint. There was no statistically significant difference in loading the wrist with comparable weights through the second and third metacarpals, through all five metacarpals, or through weights suspended from the wrist flexor and extensor tendons. A nonlinear relation was discovered between increasing loads and greater overall contact areas. The general distribution of the contact between the scaphoid and the lunate contact areas was consistent at all of the loads tested with 60% of the total contact area involving the scaphoid contact area and 40% involving the lunate contact area. Loads greater than 46 pounds were not found to significantly increase the overall contact areas implying that the cartilage of the wrist joint was maximally compressed at loads of this magnitude. At loads higher than 46 pounds it appears that average high pressures increase in a more direct correlation with the increase in weight. The overall contact area even at the highest loads tested were not more than 40% of the available joint surface. The contact areas were not concentric or symmetric as is characteristic of the incongruance of the radio/triangularfibrocartilage (ulna)/carpal joint.

Extrinsic wrist ligaments in the pathomechanics of ulnar translation instability.

A description of the various combinations of ligament disruptions necessary for ulnar translation instability is presented based on a series of cadaver dissections and load studies. Dissections and load studies demonstrated that major ligament disruption, even to the extent that only the dorsal ulnolunate, the palmar ulnolunate or the radioscaphocapitate, and the long radiolunate ligaments were left intact, failed to result in meaningful ulnar translation of the carpus. The radioscaphocapitate ligament alone could not prevent significant ulnar translation. Palmar translation instability was evident with less ligament disruption than that needed for ulnar translation and was always evident if there was ulnar translation. These studies imply that ulnar translation represents a much more global ligament disruption and instability than previously suggested in the literature.

Anatomy and pathomechanics of ring and small finger carpometacarpal joint injuries.

PURPOSE The purpose of this study was to detail the pathomechanics and pathoanatomy of fracture dislocations of the ring finger and small finger carpometacarpal (CMC) joint by duplicating the pathomechanics of the fist blow. METHODS A custom-made jig was used to position 20 fresh-frozen cadaver upper extremities in forearm neutral rotation, 90 degrees of elbow flexion, 20 degrees of wrist extension, and 20 degrees and 30 degrees of flexion at the ring and small finger CMC joint, respectively. First 7.7 kg of weight were dropped from a height of 0.76 m to 1.1 m to axially load the ring and small metacarpal (MC) heads through a custom-made apparatus. Fluoroscopic examination before and after loading, and detailed dissection after loading, were used to identify any osseous and/or ligamentous injuries. RESULTS The most common fractures were a dorsal capitate fracture and a middle MC dorsal base fracture. The most common combinations of fractures were the dorsal capitate and dorsal hamate fractures. Multiple fractures often were identified in a number of locations including dorsally: the capitate, hamate, and index through small metacarpal bases, and volarly: the hook of the hamate and the middle through the small MC bases. CONCLUSIONS The patterns of injuries encountered at the ring and small CMC joints can be explained by the direction and force of the applied load, position of the CMC joint at the time of loading, and the constraints imposed by specific CMC ligaments. A detailed analysis of the fracture patterns and associated ligament anatomy suggests that the typical ring and small carpometacarpal fracture dislocations are a more complex combination of fractures than identified by plain radiographs alone. The complexity of these injuries is greater than previously recognized and is most likely the result of a combination of axial load and shear stresses resulting in carpal fractures and ligament avulsions as well as fracture dislocations. This study suggests that computed tomography may be the preferred diagnostic imaging method for complete assessment of these injuries.

Relation of residency selection factors to subsequent orthopaedic in-training examination performance.

Objectives: Orthopaedic surgery remains one of the most competitive specialties, with more than a 99% match fill rate in the past several years. An oversupply of qualified applicants leads to intense competition for these residency spots, allowing program directors to be more selective in choosing their future residents. Although many previous studies have documented factors important to program directors in the admission process, less is known about how preselection factors correlate with subsequent performance in a residency program. Methods: The relation of both demographic and academic factors with subsequent performance on the Orthopaedic In-Training Examination (OITE) were studied. These factors include United States Medical Licensing Examination (USMLE) step I scores, Alpha Omega Alpha (AOA) status, research publications, age entering residency, marital status, and medical school affiliation. Results: In this study, the only statistically significant correlations to OITE scores were USMLE step I performance and marital status. Those residents who had previously scored above 220 on the USMLE step I had higher average OITE scores than those scoring below 220. Residents who were married also had higher average OITE scores. A trend with regard to AOA status also was found, with residents scoring slightly higher on the OITE if they were members of AOA. Conclusions: Few preresidency variables correlate to success during an orthopaedic residency.