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To compare the kinematic effects of the dorsal fiber-splitting approach for scapholunate ligament repair to a dorsal “window” approach that spares all ligaments.
Methods
We randomized 24 fresh-frozen paired cadaveric forearms to either the dorsal fiber-splitting capsulotomy approach (FSC) or the dorsal window approach (window) following scapholunate interosseous ligament (SLIL) division. Loaded fluoroscopic radiographs were obtained after each of the 4 testing conditions following cyclic loading (200 cycles; 71 N): (1) intact SLIL, (2) SLIL-division, (3) surgical approach, and (4) closure. FSC specimens were randomly allocated to 2 subgroups for closure with either a suture anchor (n = 6) or a simple running suture closure (n = 6). Radiographic parameter measurements included the scapholunate gap, radiolunate angle, scapholunate angle, and dorsal scaphoid translation.
Results
Following the FSC, there were significant alterations in all radiographic parameters when compared with the intact and SLIL-division conditions. The window approach did not result in significant changes in any radiographic parameter. When compared to the window approach, all radiographic parameters of the FSC approach were significantly altered. Following closure with suture anchors in the FSC group, radiographic parameters improved, whereas with standard closure they failed to do so. Despite anchor closure, dorsal scaphoid translation, radiolunate angle, and scapholunate angle all remained elevated compared with scapholunate-divided wrists.
Conclusions
The FSC produced significant changes in carpal posture under load, including scapholunate diastasis, dorsal intercalated segment instability, and dorsal scaphoid translation in SLIL-deficient wrists. The window approach preserved the critical dorsal ligament stabilizers and did not produce changes in carpal posture.
Clinical relevance
The FSC may create iatrogenic changes in carpal posture that cannot be fully corrected with standard or anchor closure. The window approach does not alter carpal posture and should be considered when performing surgical procedures on the scaphoid or lunate.
Multiple dorsal approaches to the wrist have been described, including transverse, longitudinal, T-shape, L-shape, rectangular, or oblique incisions, which all involve sectioning of the dorsal intracapsular ligaments.
There is limited information as to the effects of these surgical approaches on carpal alignment or kinematics.
The fiber-splitting capsulotomy (FSC) was developed with the intent of preserving the dorsal ligaments of the proximal carpal row and is one of the most commonly used approaches.
This approach splits the dorsal radiocarpal ligament (DRC) and the dorsal intercarpal ligament (DIC), maintaining the integrity of their proximal and distal fibers in parallel with the arthrotomy incision for subsequent closure. While this approach preserves the ligament insertions of the DRC and DIC on the triquetrum, the radial reflection of the central flap may disrupt important insertions on the lunate and proximal scaphoid.
demonstrated the critical importance of the lunate and scaphoid attachments of the DIC in stabilizing the proximal carpal row in a cadaveric model; however, the importance of these insertions has not yet been defined in the context of a surgical approach to the carpus.
The purpose of our study was threefold. Our primary aim was to measure the effects of the FSC on the alignment of a scapholunate (SL) ligament–deficient proximal carpal row. Our second aim was to propose and investigate an alternate capsular “window” technique that spares the lunate and scaphoid insertions of the DIC ligament and the lunate insertion of the DRC ligament. Our third aim was to clarify whether the described capsular closure technique or an alternate suture anchor repair would successfully mitigate any adverse effects of the FSC on carpal posture. We hypothesized that the FSC would further destabilize a SL interosseous ligament (SLIL)–deficient wrist and result in proximal carpal row postural changes. We further hypothesized that the window exposure would not result in carpal postural changes in an SLIL-deficient wrist. Lastly, we hypothesized that reestablishing the lunate and scaphoid insertions of the DIC and DRC during closure of the FSC would improve carpal alignment compared to the described side-to-side capsular closure.
We studied 12 matched pairs of fresh-frozen cadaveric forearms (n = 24; 16 male, 8 female), with a mean age of 63 years (range, 32–85 years). Wrists were randomized on the basis of laterality among the FSC and window groups, and 1 wrist from each matched pair was allocated to each group. All wrists underwent a baseline radiographic assessment prior to testing, with posteroanterior (PA) and lateral radiographs to eliminate any specimens with carpal malalignment (radiolunate angle [RLA] ≥ 15°, SL angle > 60°, SL gap > 2 mm) or osteoarthritis. Criteria for carpal malalignment were defined by the International Wrist Investigators’ Workshop.
Forearms were mounted vertically in neutral pronosupination in a previously validated custom carpal testing frame, using a previously validated loading and testing protocol (Fig. 1).
A clenched-fist position was simulated by loading the wrist extensors and digital flexor tendons with a combined 71 N load; a 26.7 N load was applied to the extensor carpi radialis longus and brevis together, 26.7 N was applied to the extensor carpi ulnaris, and 17.6 N was applied to the flexor digitorum superficialis and profundus.
Figure 1Custom loading jig: the forearms were mounted vertically on a test frame by introducing 5-mm external fixator pins into the medullary canals of the radius and ulna. A 5-mm transverse pin secured the forearm in neutral pronation-supination. Tendons were loaded with 71 N to maintain a gripped fist position.
Loaded PA and lateral fluoroscopic radiographs (Fluoroscan, Hologic) were obtained for the intact condition and were repeated for each additional testing condition. Spot radiographs were standardized under live fluoroscopy such that the PA image demonstrated neutral coronal alignment and a true profile of the SL joint (Fig. 2A); neutral lateral radiographic still images were taken in scaphopisocapitate alignment (Fig. 2B–D), as defined by Yang et al.
A radiopaque marker was included to adjust for magnification. To precondition the wrists, the examiner manually moved the wrist through a full range of passive motion with 75 cycles of flexion-extension and 25 cycles of radial-ulnar deviation before imaging each testing condition as per Pérez et al.
Cycling was performed in the loading frame by disengaging the digits from the frame crossbar, and then cycling the wrist under 71 N load, at 1 Hz.
Figure 2A The SL gap is the distance between the scaphoid (S) and lunate (L; blue line) at the midpoints of Gilula lines (red lines) for the proximal carpal row.
B The longitudinal axis of the radius was defined by a bisector at points 2 and 5 cm proximal to the radiocarpal joint (blue line), as defined by Larsen et al.
The RLA is formed by the radial axis (blue line) and a line (yellow solid line) perpendicular to the tangent of the dorsal and palmar poles of the lunate (yellow dotted line).
C The SL angle is formed by a tangent (pink line) to the volar surface of the scaphoid and the axis of the lunate (yellow solid line). D The DST is the distance between a line tangential to the proximal articular surface of the scaphoid (green line) and parallel to the longitudinal axis of the radius (blue solid line) and a line drawn through the dorsal scaphoid facet of the distal part of the radius (blue dotted line).
Radiographic measurements were made by a single examiner after importing the loaded PA and lateral images into Osirix (version 11.0.1, Pixmeo Company). Radiographic axes of the carpals were used as defined by Larsen et al,
and as detailed in Figure 2, to measure the amount of carpal postural change generated after the 4 testing conditions. Using the function/tool “angle measurement” of the Osirix software, we inserted the axes according to the Larsen et al
criteria, and angular measurements were performed automatically by Osirix. The measured SL gap distances on the PA radiograph were adjusted proportionately using the radiopaque marker of known dimension.
Testing conditions
The 4 different testing conditions were: (1) intact, (2) SLIL-division, (3) surgical approach, and (4) closure. All surgical procedures and mechanical testing were performed by a fellowship-trained orthopedic hand surgeon using 3.5 magnification loupes. The wrists were tested at room temperature.
Intact
Intact wrists underwent unloaded and loaded radiographic assessments and measurements following cycling.
SLIL-division
The skin was incised longitudinally, and the extensor retinaculum was divided between the third and the fourth dorsal compartments to allow access to the dorsal capsule and intracapsular wrist ligaments. A 1-cm transverse arthrotomy, distal and radial to the Lister tubercle and radial to the origin of the DRC, was performed to divide the SL ligament. The dorsal, proximal, and volar components of the SLIL were sharply divided using a number 11 blade and a Hook Knife (Arthrex, Inc, Naples, FL) to ensure complete division of all 3 components of the SL ligament. No other dorsal or volar stabilizers of the proximal row were divided. The wrists were cycled, and the images of the loaded wrists were captured for carpal posture measurement.
Surgical approach
One specimen of each forearm pair was randomized to either the FSC or the window approach. Fiber-splitting capsulotomy was performed as originally described by Berger et al.
The midlines of the DRC and DIC were divided in line with their ligament fibers, meeting at a single point on the dorsal tubercle of the triquetrum (Fig. 3A). The DRC incision was continuous with the 1-cm dorsal rim incision that was used previously to divide the SLIL and was extended radially beneath the wrist extensors toward the radial styloid. The DIC was split in its midline from the triquetral tubercle to the distal scaphoid. The intervening capsuloligamentous flap was elevated radially, maintaining the dissection in the same plane as the dorsal cortex of the scaphoid and lunate, just superficial to the fibers of the dorsal SL ligament, and exposing the scaphoid dorsal ridge (Fig. 3B).
Figure 3The 2 different approaches to the dorsal wrist. The FSC performed on a left wrist, with the flap A in place and B elevated. The window approach performed on another left side wrist, with the C radiocarpal joint and D midcarpal joint. The opening of the capsule is delimited by a solid black line; the synovial capsular surface is highlighted by gray hatched lines. C, capitate; H, hamate; L, lunate; S, scaphoid.
The window approach was performed by making 2 separate capsulotomies to expose the proximal row at the radiocarpal and midcarpal joints (Figs. 3C, D and 4). The radiocarpal window extended the prior 1-cm capsulotomy radially toward the styloid, as in the FSC approach. The capsular incision was extended ulnarly from the Lister tubercle by angling sharply to follow the distal edge of the DRC fibers, maintaining the entire DRC ligament in continuity with its radial, lunate, and triquetral attachments (Figs. 3C and 4B). The flap was carefully raised distally without dividing the dorsal capsuloscapholunate septum,
or the scaphoid or lunate insertions of the DIC (Figs. 3C and 4C) and was preserved for later closure. The midcarpal window was similarly established via a transverse capsulotomy along the distal edge of the DIC in the radial to ulnar direction, preserving the entire DIC (Fig. 3D). The distally based capsular flap was lifted until visualization of the scaphocapitate joint, the capitate head, and the “4-corner” joint (lunate-capitate-hamate-triquetrum) was achieved (Figs. 3D and 4C). The flap was carefully preserved for subsequent closure.
Figure 4Steps of the window approach. A The DRC and DIC ligaments, B radiocarpal and midcarpal window incisions are identified in red, C radiocarpal and midcarpal open windows, and D closure.
The FSC group was randomly assigned to either dorsal ligament repair with suture anchors (anchor group; n = 6) or standard closure (standard group; n = 6).
In the anchor group, 1 suture anchor (Juggerknot 1 mm, ZimmerBiomet, Warsaw, IN) was placed at the DIC insertion of the scaphoid and a second was placed at the dorsal “bare area” of the lunate (the portion devoid of cartilage where the DIC and DRC insert).
The DIC and DRC fibers were affixed to bone at these points with the anchor’s 2-0 synthetic braided suture. The remainder of the fiber split was closed with a 2-0 running synthetic braided suture. The remaining 6 were closed by a running synthetic braided 2-0 suture (standard group) as originally described by Berger et al.
All capsular windows in the window approach were closed with running 2-0 synthetic braided suture (Fig. 4D). Following completion of the entire testing cycle, the specimens were dissected to confirm complete transection of the SLIL.
Statistical analysis
Data from a similar study indicated that a sample size of 10–12 per group would enable an 80% chance of detecting an increase in the RLA of 15° with a .05 probability, assuming an SD in RLA of 5°.
A post hoc power analysis using this study’s data set determined that a sample size of 6 was sufficient to achieve 95% power when comparing RLAs between FSC subgroups (standard closure versus anchor). Differences in SL angle, RLA, SL gap, and dorsal scaphoid translation (DST) baseline measurements between groups were assessed using one-way analysis of variance. Either Pearson χ2 or Fisher's exact test was used to compare differences in categorical variables between groups. To compare radiographic measurements within and between surgical approaches (groups), a series of generalized estimating equation models using robust variance estimates were constructed. The Bonferroni correction was used to adjust for multiple comparisons. All 4 generalized estimating equation models controlled for age and sex. The α value for statistical significance was predetermined at a P value < .05.
Results
Intact
Age, sex, and loaded/unloaded radiographic measurements of the intact wrists were similar (Table 1).
Table 1Measurements of Radiographic Parameters by Surgical Approach and Testing Condition
Following SLIL-division, the SL gap increased by an average of 0.6 mm (−0.3 to 2.4 mm, P < .05) in both the window and the FSC groups under load, and this difference was significant in the FSC group, but not in the window group. There was no statistically significant difference in SL gaps between the divided FSC group and the divided window group (P > .05). No other radiographic parameters measured after SLIL-division alone differed significantly from the intact condition in either group, and there were no significant differences in any parameter following SLIL-division between the groups (Table 1). Importantly, we identified no incomplete SLIL-divisions at the final open inspection.
Approach
Following the FSC approach, there were significant increases in all radiographic parameters compared to both intact wrists and SLIL-division (P < .05). The window approach did not result in significant changes in any of the measured radiographic parameters. The radiographic parameters in the FSC group were also significantly different from those in the window group (P < .05; Table 1; Fig. 5). Additionally, 9 of the 12 wrists in the FSC group developed DISI, whereas none of the 12 wrists in the window group demonstrated DISI (P < .05).
Figure 5The changes in the A SL gap (mm), B RLA (°), C SL angle (°), and D DST (mm) following each testing condition, according to the different steps of the approaches to the wrists in the FSC (standard and anchor closure) and window groups. ∗A P value < .05 represents significant difference from SLIL-division state.
Following closure of the FSC approach with suture anchors, all radiographic parameters significantly improved, whereas standard closure failed to achieve a significant improvement of any radiographic parameter (Table 2; Fig. 5). While closure with suture anchors improved radiographic parameters following the FSC approach, SL angle, RLA, and DST all remained significantly greater than in the SLIL-division condition (P < .05).
Table 2Measurements of Anatomic Structures by Surgical Approach, Closure Technique Among 24 Cadaveric Wrists
Following the FSC in the SLIL-division condition, we identified a significant increase in SL gap, RLA, SL angle, and DST. The FSC produced DISI in 9 of 12 SLIL-divided wrists, with an average increase of RLA greater than 20°. In contrast, the window approach did not alter carpal posture or produce DISI. While the described standard closure following FSC failed to improve the postural alteration, closure with suture anchors significantly improved alignment. It is important to note, however, that differences in DST, SL angle, and RLA persisted following anchor closure when compared to the intact and SLIL-division conditions.
described lunate insertions of the DRC and DIC in 90% of individuals. Several biomechanical studies have shown the importance of the dorsal extrinsic and intrinsic ligaments to lunate stability in cadaveric models.
noted that SLIL-division with concomitant interruptions of the lunate insertion of the DIC caused increased lunate extension but not DISI. Similarly, Elsaidi et al,
in an arthroscopic sectioning study, showed that concomitant division of the SLIL, the DRC, and the DIC produced a significant increase in the capitolunate angle. Overstraeten et al
demonstrated increased European Wrist Arthroscopy Society grade instability when the dorsal capsuloscapholunate septum capsular arches from the DIC to the bone-ligament junction of the dorsal SLIL were divided arthroscopically in 10 cadavers. Pérez et al
demonstrated the importance of the DIC’s lunate and scaphoid attachments to prevent DISI in a cadaveric model of SL dissociation. Taken together, there is growing evidence to designate the DIC and DRC as “critical stabilizers” of the carpus rather than “secondary stabilizers,” given their fundamental role in wrist stability.
cautioned that any repair or reconstructive technique for the SLIL must reestablish the DIC ligament attachments to both the scaphoid and the lunate. An improved understanding of the anatomy and mechanics of the dorsal ligament complex may enable novel approaches to SL ligament injuries, repairs, and reconstructions. Recently, Binder et al
successfully treated 9 of 10 patients with dynamic SL instability and arthroscopically identified avulsion of the DIC using an arthroscopic repair technique for the dorsal ligament complex. In their 5 patients with DISI and abnormal SL angles, both radiographic parameters were improved to normal values by reestablishing the DIC insertion to the scaphoid and lunate via arthroscopic capsuloplasty. This repair technique emphasizes the importance of the proximal carpal row attachments of the dorsal ligament complex. The findings of Binder et al
were corroborated by our demonstration of improved proximal row posture after reconstitution of the DIC and DRC with open suture anchor repair following the FSC approach.
in 1995, gained popularity because of its wide exposure of the dorsal wrist, while theoretically maintaining the integrity of the DRC and DIC. However, while the approach maintains the parallel fibers of the ligaments, it violates the lunate insertions of these important structures. Our study demonstrates that the FSC is associated with carpal malalignment in the setting of SLIL incompetence, by dividing the DIC ligament insertions on both the lunate and scaphoid.
Our study has several limitations common to cadaveric studies and to those that previously used this cadaveric model: a small sample size, subject ages, and an inability to study ligament healing. We used fluoroscopic radiographs to assess carpal alignment and concede that this may be subject to measurement error. We recognize that the detected increase in the SL gap of 0.6 mm in the FSC group following SL ligament transection could be subject to error, as could the decrease in gap of 0.3 mm in 1 specimen; however, these submillimeter differences are not likely to be clinically significant. Radiographic measurement of carpal angles and distances remains the most widely used and clinically relevant measure with which to evaluate symptomatic and normal carpal posture, and has been previously shown to be reliable by Larsen et al.
Though it could be argued that simultaneous repair of the SLIL would be of clinical relevance, we did not want to confound the focused comparison of surgical approaches by the added variable of SL ligament repair. Finally, the number of cycles used in our study (200) could be questioned, as protocols with as many as 1000 cycles have been used to induce ligament attenuation following SLIL-division.
Similar cadaveric mechanical studies have used 200 or fewer preconditioning cycles to simulate the effects of soft-tissue creep and allow the specimens to reach a steady stage following each cutting sequence, which were our goals.
In conclusion, we recommend that surgeons be mindful of the limitations of the FSC approach, as it necessitates detachment of the insertions of the critical dorsal stabilizing ligaments and has the potential to create iatrogenic carpal instability. If it is necessary to expose the carpus with such a wide approach, it is important to repair the anatomic DIC insertions on the scaphoid and lunate with bone anchors to improve carpal alignment. The window approach offers a simple, ligament-sparing alternative to the FSC for exposure of the proximal row that does not alter carpal stability. Increasing surgeons’ awareness of the complex dorsal ligament anatomy and the consequences of its disruption has clinical utility.
Acknowledgments
Funding for the study was provided in part by The American Society for Surgery of the Hand (Resident Fast Track Grant #2236), a Hospital for Special Surgery Surgeon-in-Chief Grant, and The French Orthopaedic Society Fellowship Grant.
We acknowledge the insights and cadaveric observations of Ubaldo Ayala Gamboa, MD, from Mexico City, who brought our attention to the critical insertions of the dorsal intercarpal ligament and dorsal radiocarpal ligament to the dorsal lunate, and developed an arthroscopic surgical repair technique. We thank Jinseong Kim for his assistance in the biomechanical laboratory during testing and Emmanuel Laurent for the graphic design. We acknowledge Gotham Surgical for their in-kind funding of sutures, hook blades, and supplies.
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