Is DISI Deformity Related to Presence of a Medial Lunate Facet in Patients with Scapholunate Dissociation?

Background Lunate morphology has been suggested to influence carpal kinematics. Purpose We investigate a possible relation between presence of a medial lunate facet and dorsal intercalated segment instability (DISI) of the wrist in patients with a scapholunate (SL) dissociation. Methods We retrospectively reviewed patients diagnosed with SL dissociation between 2000 and 2017. Lunate morphology was categorized based on radiographs and magnetic resonance imaging (MRI), as type I or II according to Viegas and Galley. DISI was defined as radiolunate angle > 15 degrees and SL instability as SL angle > 60 degrees. SL distance > 3 mm was considered as widening and carpal height ratio < 0.5 was considered as carpal collapse. We used descriptive statistics to report on SL instability and DISI in patients with Viegas type I and type II lunates. We calculated kappa to determine agreement between radiographs and MRI and to determine inter- and intraobserver agreement. Results Of 119 patient files, 79 wrists met the inclusion criteria of which 25 were type I lunates and 54 type II. Similar spreading of the data of both groups was found regarding DISI, SL instability, and SL widening based on radiographic classification of the lunate, even after adding MRI findings. In the presence of carpal collapse, capitate-to-triquetrum distance was higher. We found a substantial inter- and intraobserver agreement for lunate classification. Conclusion Our results suggest a similar prevalence of DISI deformity or enlarged SL angle in patients with type I or II lunate in presence of SL dissociation. The Viegas classification is a reliable and reproducible classification system. Level of evidence This is a Level III, cross-sectional study design.

How Much Scaphoid Can be Safely Resected? A Biomechanical Analysis of the Effects of Distal Scaphoid Resection

Background: Resection of the distal pole of the scaphoid has been advocated as a simple alternative to other wrist salvage procedures for scaphoid nonunion advanced collapse and scaphotrapezio-trapezoid arthritis. However, the extent of scaphoid that may be resected without adversely affecting carpal kinematics has never been clearly defined. Methods: Seven cadaveric upper extremities were tested in a custom motion wrist simulator. A 3-stage sequential sectioning of the distal scaphoid protocol was performed in 25% increments then cyclic active wrist flexion-extension and dart thrower’s motion trials were recorded. Results: The extent of distal scaphoid resection had no effect on overall wrist range of motion. The lunate assumed a more extended position following resection of the distal scaphoid compared to intact. At 25%, 50%, and 75% of distal scaphoid resection, the lunate extended to 13.32° ± 9.4°, 23.43° ± 7.5°, and 15.81° ± 16.9°, respectively. The capitate migrated proximally with 25% and 50% distal scaphoidectomy, and proximally and radially with 75% of the scaphoid resected. Resection of 75% of the scaphoid resulted in unstable wrist kinematics. Conclusions: Resection of up to 25% of the distal scaphoid did not significantly influence carpal kinematics and induced mild lunate extension deformity. Resection of 50% of the scaphoid induced further and potentially clinically significant lunate extension and dorsal intercalated segment instability. Further removal of 75% of the distal scaphoid induced capitate migration radially and unpredictable wrist kinematics. Consequently, removal of over 25% of the scaphoid should be avoided or supplemented with partial wrist fusion.

The Effect of Lunate Morphology in Carpal Disorders: Review of the Literature

Variation in lunate morphology can exist based on the absence (Type I) or presence (Type II) of medial facet on the distal articular surface of the lunate that contacts the proximal pole of the hamate. This additional lunatohamate articulation can affect load transmission across the radiocarpal joint and exert an influence on carpal kinematics. A Type II lunate is protective against carpal instability patterns associated with scaphoid nonunions and scapholunate dissociations. It may also play a role in the progression of carpal collapse that occurs in Kienböck disease. This review summarizes the effect of lunate morphology in the outcomes of non-operative and operative treatment of carpal disorders.

Quantifying in vivo scaphoid, lunate, and capitate kinematics using four-dimensional computed tomography

Objective We aimed to establish a quantitative description of motion patterns and establish test-retest reliability of the four-dimensional CT when quantifying in vivo kinematics of the scaphoid, lunate, and capitate. Materials and methods We assessed in vivo kinematics of both wrists of 20 healthy volunteers (11 men and 9 women) between the ages of 20 and 40 years. All volunteers performed active flexion-extension and radial-ulnar deviation with both wrists. To test for reliability, one motion cycle was rescanned for both wrists approximately 15 min after the first scan. The coefficient of multiple correlation was used to analyze reliability. When two motion patterns are similar, the coefficient of multiple correlation tends towards 1, whereas in dissimilar motion patterns, it tends towards 0. The root mean square deviation was used to analyze the total motion patterns variability between the two scans. Results Overall, mean or median coefficient of multiple correlations were higher than 0.86. The root mean square deviations were low and ranged from 1.17° to 4.29°. Conclusion This innovative non-invasive imaging technique can reliably describe in vivo carpal kinematics of uninjured wrists in healthy individuals. It provides us with a better understanding and reference values of carpal kinematics of the scaphoid, lunate, and capitate.

The Effects of Capitate Height Alteration on Dorsal Intercalated Segment Instability

Question/Purpose Carpal kinematics may be influenced by the manipulation of carpal dimensions. This may provide a surgical alternative to unpredictable soft tissue reconstruction for scapholunate dissociation. The purpose of this study was to determine if altering capitate height can correct dorsal intercalated segment instability (DISI). Materials and Methods Five cadaveric wrists had baseline radiolunate (RL) angles and scapholunate (SL) intervals measured fluoroscopically, confirming no baseline DISI. We simulated open- and clenched-fist testing via a constant load of the wrist extensors and sequential loading of the digital flexors. We confirmed no baseline static/dynamic DISI. The SL ligament and secondary stabilizers (scapho-trapezio-trapezoid [STT] and dorsal intercarpal ligaments) were transected. Repeat loading and fluoroscopic measurements confirmed creation of static DISI. Capitate height was altered in three interventions: 2 mm shortening osteotomy of capitate waist, 7 mm shortening osteotomy of capitate waist, and 2 mm lengthening of original capitate height by insertion of a spacer at capitate waist. The osteotomized capitate was stabilized with a Kirschner wire; RL angles and SL intervals were measured via fluoroscopy during open- and clenched-fist testing. Primary and secondary outcomes were change in RL angle and SL interval, from the DISI stage to each capitate shortening and lengthening stage. Results SL ligament and secondary stabilizers sectioning created a DISI pattern, with abnormal RL angles (>15°) and widened SL intervals. Neither capitate shortening nor overexpansion corrected RL angles or SL intervals in any DISI-induced wrists. Conclusions Under the conditions studied, isolated capitate shortening or lengthening did not correct radiographic DISI posturing of the lunate following sectioning of the SL and STT interosseous ligaments. Further study of carpal kinematics with more substantial bone changes and loading of adjacent joints may be beneficial. Clinical relevance Surgeons performing capitate shortening osteotomy in isolation should not expect to improve DISI.

Carpal Kinematics following Sequential Scapholunate Ligament Sectioning

Background The scapholunate ligament (SLL) is the most commonly injured intercarpal ligament of the wrist. It is the primary stabilizer of the scapholunate (SL) joint, but the scaphotrapeziotrapezoid (STT) and radioscaphocapitate (RSC) ligaments may also contribute to SL stability. The contributions of SL joint stabilizers have been reported previously; however, this study aims to examine their contributions to SL stability using a different methodology than previous studies. Purpose The purpose of this in vitro biomechanical study was to quantify changes in SL kinematics during wrist flexion and extension following a previously untested sequential sectioning series of the SL ligament and secondary stabilizers. Methods Eight cadaveric upper extremities underwent active wrist flexion and extension in a custom motion wrist simulator. SL kinematics were captured with respect to the distal radius. A five-stage sequential sectioning protocol was performed, with data analyzed from 45-degree wrist flexion to 45-degree wrist extension. Results Wrist flexion and extension caused the lunate to adopt a more extended posture following sectioning of the SLL and secondary stabilizers compared with the intact state (p < 0.009). The isolated disruption to the dorsal portion of the SLL did not result in significant change in lunate kinematics compared with the intact state (p > 0.05). Scaphoid kinematics were altered in wrist flexion following sequential sectioning (p = 0.013). Additionally, disruption of the primary and secondary stabilizers caused significant change to SL motion in both wrist flexion and wrist extension (p < 0.03). Conclusions The SLL is the primary stabilizer of the SL articulation, with the STT and RSC ligaments playing secondary stabilization roles. Clinical Relevance Understanding the role primary and secondary SL joint stabilizers may assist in the development of more effective treatment strategies and patient outcomes following SLL injuries.