Adjunctive Dorsal Spanning Plate Fixation for Perilunate Dislocations May Increase Load to Failure

The addition of dorsal spanning plate fixation in surgery for perilunate dislocations led to increased load-bearing capacity as well as a decreased change in scapholunate interval at time of failure compared to Kirschner wire (K-wire) fixation alone, according to a study presented at the AAOS 2024 Annual Meeting. The results were presented by Bradley J. Vivace, MD, third-year resident in the Orthopaedic Surgery Department at the University of Missouri.

The investigators of the study “hypothesized that that the addition of a dorsal spanning plate to Kirschner wire fixation of perilunate dislocations would allow for increased loads to be applied before construct failure and better maintain carpal alignment in a robotically tested cadaveric model.”

As Dr. Vivace told AAOS Now, “The idea came from a clinical study performed by Nguyen et al, where an adjunctive dorsal spanning plate was weight bearing following fixation. We wanted to investigate what potential biomechanical advantage this fixation strategy could provide in a cadaveric model.”

The study included 14 fresh-frozen cadaveric wrists that underwent simulated perilunate injury via sharp ligament division. The wrists were randomized to either wire fixation or dorsal spanning plate with wire fixation. Wire fixation involved five 0.045-inch wires (one scaphocapitate wire, two scapholunate wires, and two lunotriquetral wires), and the dorsal spanning plate was applied at the radius and third metacarpal.

The dorsal spanning plate was applied at the radius and third metacarpal, with repair of the dorsal scapholunate ligament using a suture anchor. The constructed models were subjected to testing on a robotic system (Fig. 1). The wire-only constructs underwent loading with a 50 N compressive force for 100 cycles of 10-degree extension and 15-degree flexion. Due to the dorsal spanning plate construct’s stiffness, cyclical loading was limited to a maximum of 3 Nm of torque in both flexion and extension when achieving 10-degree extension and/or when 15-degree flexion was not feasible.

Regarding the maximum cycle loading limit in the wire-only group, Dr. Vivace commented, “The rigidity of the dorsal spanning plate made it necessary to operate the robot in force control mode. Had we commanded the same range of motion on the plate group, the robot would apply whatever necessary force to move the specimen to the prescribed range, resulting in very large forces that would have destroyed the construct in very few cycles. The 3 Nm torque was chosen given similar values were observed in the K-wire-only group in the prescribed range of motion.”

Fluoroscopic images were captured at various stages: before simulated injury, after fixation, after 10 and 100 loading cycles, and at the point of construct failure (defined as capitolunate subluxation, hardware failure, and/or fracture). Data normality was confirmed with the Shapiro-Wilk test. Statistical analyses, including t-tests, compared differences in scapholunate and lunotriquetral intervals, as well as scapholunate and capitolunate angles, between constructs after fixation and following the application of forces.

After fixation, there were no statistically significant differences in carpal alignment parameters between the two groups. However, the dorsal spanning plate fixation group demonstrated a significantly higher load to failure (436 N versus 132 N, P <0.001). the scapholunate interval change at failure was also significantly lower in the dorsal spanning plate group (5.01 mm versus 2.9 mm,>P = 0.04). Other parameters suggested better maintenance of alignment with the dorsal spanning plate construct.

Regarding the results of the study, Dr. Vivace said he was surprised to find the significant decrease in scapholunate interval change at the time of failure, “given that failure load for the adjunctive dorsal spanning plate group was so much higher than that of the K-wire-alone group.”

He went on to say that the current study shows that, “Within the confines of a cadaveric model, an adjunctive dorsal spanning plate provides a fixation strategy that offers significant increased loads to failure and adds biomechanical support to previous clinical studies.”

As the study examined cadaveric wrists with simulated perilunate injuries tested robotically, “This model may not translate fully into the clinical realm,” Dr. Vivace said. He noted the challenges he and his colleagues faced when obtaining fluoroscopic views: “This modality of measuring the carpal parameters does not provide a dynamic view of the instability of the injury, but rather a snapshot at the time of the image.”

Future research in this area, according to Dr. Vivace, would benefit by adding biomechanical support to previous clinical research. “Further areas of exploration may be identifying which patients may benefit from undergoing adjunctive dorsal spanning plate fixation for this injury, with consideration that the required removal of the spanning plate at a later date is more involved than just removing K-wires,” he said.

The results suggest that adjunctive dorsal spanning plate fixation could be a valuable technique in specific clinical scenarios. As written by the authors, “This may be a useful technique in the polytraumatized patient, where providing back a weight-bearing extremity may be advantageous in the rehabilitation process.”

Dr. Vivace’s coauthors of “Adjunctive Dorsal Spanning Plate Fixation in the Stabilization of Perilunate Dislocations” are Ashwin Garlapaty; Daniel London, MD, MS; Evan B. Reeves, BS; and Will A. Bezold, BSME.

Cailin Conner is the associate editor of AAOS Now. She can be reached at cconner@aaos.org.

Reference

1. Nguyen DM, Boden AL, Allen MK, et al: Dorsal spanning plate for perilunate dislocations. J Wrist Surg 2021;11(1):16-20.