Anatomical landmarks to define a safe zone for percutaneous K-wire fixation in acute peri lunate dislocations with a diamond configuration: A cadaveric correlation

Introduction

The conventional treatment for acute perilunate injuries involves open reduction and ligamentous repair. ¹ However, treatment with closed reduction and K-wire fixation without ligament repair or reconstruction has yielded favourable results, particularly in cases of acute presentation.^2,3 Intraoperatively, it is extremely difficult without a mini open incision to determine whether the percutaneous K-wire path caused any damage to soft tissue structures, such as extensor tendons, sensory branches of the radial and ulnar nerves, and radial artery branches, as no safe zones have been described for this technique. There are established safe zones for K-wire insertion into the radius for distal radius fractures. These safe zones are based on anatomical landmarks and aim to minimize the risk of injury to extensor tendons and branches of the superficial radial nerve during the procedure. ⁴ In a cadaveric study to better define the clinical anatomy of the radial aspect of the wrist, Steinberg et al. identified a consistent safe zone in the anatomical snuff box for K-wire insertion into the carpal bones (scapholunate and scaphocapitate) and radius. ⁵ Similarly, Naik et al., in their cadaveric study, recommended safe techniques for pinning ulnar-sided wrist structures, particularly the lunotriquetral and fifth metacarpal bases, to avoid injury to the dorsal sensory branch of the ulnar nerve. ⁶ The concept of the diamond K wire construct for peri-lunate dislocation has gained popularity because of the work of Özyürekoğlu and Acar, ⁷ which is supported by a biomechanical rationale. However, no research has identified safe landmarks and trajectories for K-wire insertion in the percutaneous reduction of acute perilunate dislocation. Our study aimed to determine the anatomical landmarks for safe zones at the wrist that could be used to pass the K-wires. Our objective was to correlate the same with landmarks in cadaveric anatomy and to look for any complications.

Methodology

To establish secure fixation of the carpal bones in closed reduction and fixation of peri lunate dislocation, the senior author devised a surgical technique that utilizes a precise sequence, orientation, and arrangement of Kirschner wire placement. After approval from our institutional ethical committee, 10 consecutive patients with acute closed perilunate dislocation underwent closed reduction and percutaneous K wire pinning under an image intensifier. Patients with pure ligamentous injury were included in the study and ones with fracture of the scaphoid/ radial styloid were excluded. Patients had no other injuries apart from a closed perilunate dislocation. Accurate landmarks for K wire entry were marked with normal bony prominences as a guiding source. The borders of the distal radius with the radial styloid, surface marking of the first extensor compartment tendons : extensor pollicis brevis, abductor pollicis longus and the extensor pollicis longus tendon, radial and the ulnar borders of the distal ulna and the ulnar styloid, and the radial and the ulnar borders of the fifth metacarpal were marked around the wrist joint (Figure 1(a)–(d)). On the radial side, the X axis is the horizontal line across the dorsum of the wrist in line with the radial styloid tip till midline. The Y axis is along the dorsal edge of the radial styloid (Figure 1(e)). On the ulnar side, the X¹ axis is the line across the dorsum of the wrist in line with the ulna styloid till midline. The Y¹ axis is along the dorsal edge of the ulna styloid, which continues along the ulnar border of the fifth metacarpal (Figure 1(f)). We then proceeded to the diamond configuration with the following wire trajectories and order.(Table 1) Initially the Linscheid manoeuvre with a radio lunate wire was performed to facilitate reduction and to perform the subsequent K wire fixation.OPEN IN VIEWER

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Table 1.

Summary of K-wire entry points and trajectories in the diamond Configuration.

Wire	Entry point	Angle to axis	Direction of trajectory	Target joint
Wire 1	1.5 cm distal to radial styloid tip, in line with dorsal edge (Y axis)	30° oblique to X axis	Proximal, toward radiocarpal joint	Scapholunate joint
Wire 2	1.5 cm distal to ulnar styloid tip, in line with dorsal edge (Y1 axis)	45° oblique to X1 axis	Proximal, toward ulnocarpal joint	Lunotriquetral joint
Wire 3	At tip of ulnar styloid (intersection of X1 and Y1 axes)	30° oblique to X1 axis	Distal, toward carpometacarpal joint	Triquitrocapitate joint
Wire 4	At tip of radial styloid (intersection of X and Y axes)	45° oblique to X axis	Distal, toward carpometacarpal joint	Scaphocapitate joint

Scapholunate wire (Wire 1): The scapholunate wire is inserted obliquely at 30° to the horizontal X axis and 1.5 cm distal to the radial styloid tip in line with the Y axis which is directed towards the radiocarpal joint proximally aiming at the scapholunate joint (Figure 2).We measure the angle by eyeballing in relation to the horizonal axis.OPEN IN VIEWER

The lunotriquetral wire (Wire 2) is inserted obliquely at 45° to the horizontal X¹ axis and 1.5 cm distal to the ulna styloid tip in line with the Y¹ axis, which is directed towards the ulnocarpal joint proximally aiming at the lunotriquetral joint (Figure 3).OPEN IN VIEWER

Triquitrocapitate wire (Wire 3) is inserted at the tip of the ulna styloid, where the X¹- and Y¹-axes on the ulnar side meet and 30° obliquely to the X¹-axis and is directed towards the carpometacarpal joint distally aiming at the triquitrocapitate joint (Figure 4).OPEN IN VIEWER

Scaphocapitate wire (Wire 4) is inserted at the tip of the radial styloid, where the X- and Y-axes on the radial side meet and 45° obliquely to the X-axis directed towards the carpometacarpal joint distally aiming at the scaphocapitate joint . (Figure 5). All the wires were passed with wrist in posteroanterior position without any ulnar or radial deviation. Once the reduction is maintained by the diamond construct the radio lunate wire was removed.OPEN IN VIEWER

Accurate joint purchase was confirmed by visualizing the trajectory of each wire across the intended carpal joint space without extraosseous protrusion. The trajectory angle and diamond configuration was evaluated on the C arm in real time for wire orientation symmetry and convergence at the mid-carpal and radiocarpal levels (Figure 6). Particular attention was paid to the restoration of carpal alignment and the correction of any dorsal intercalated segment instability (DISI), a common sequela of perilunate injuries.OPEN IN VIEWER

We then performed the same procedure using five cadaveric wrists for correlation in accordance to the above-mentioned landmarks and trajectories. The scapholunate joint, lunotriquetral joint, scaphocapitate, and triquetrocapitate joints were percutaneously pinned using smooth 1.5 mm Kirschner wires applied with a wire driver (Figure 7(a)). The five cadaveric wrists were then radiographed to assess the accuracy of the K-wire trajectory and the purchase of the joints leading to the diamond configuration with respect to the anatomical landmarks (Figure 7(g) and (h)).We meticulously dissected the five wrists to identify the actual trajectory of the K wire and whether any structures, such as the superficial radial nerve, dorsal sensory branch of the ulnar nerve and extensor tendons, were violated during this process. The underlying anatomic structures were meticulously preserved while the skin and subcutaneous tissues were dissected (Figure 7(b)). The superficial radial sensory nerve (Figure 7(c)) and the dorsal sensory ulnar nerve (Figure 7(d)) were identified. The extensor tendons were visualized once the extensor retinaculum had been raised (Figure 7(e)). To confirm the presence of bone in the K wire trajectory, the superficial layer of the carpal bones was scraped (Figure 7(f)). The average distance from the K wires to the soft tissue structures were also measured during each of the above-mentioned steps. The clinical cohort was clinically evaluated for any neuro tendinous involvement postoperatively.OPEN IN VIEWER

Results

Radiographs of the cadaveric wrist revealed that all five wrists had accurate K-wire trajectories leading to the diamond configuration, aligning perfectly with the anatomical landmarks in both the PA and lateral views. On cadaveric dissection, the K wires were found to spare the ulnar sensory nerve, radial sensory nerve and extensor tendons in all five wrists, where the landmarks and trajectories were followed. (Figure 7)

On the radial side, the mean distance from scapholunate wire (wire 1) to the extensor pollicis longus tendon was 0.48 ± 0.09 cm and scaphocapitate wire (wire 4) to the 1st extensor compartment muscles was 0.58 ± 0.05 cm (Figure 8(a)), and that from scaphocapitate wire( wire 4) to the main sensory branch of the radial nerve was 0.5 ± 0.08 cm (Figure 8(c)). On the ulnar side, the mean distance from triqitrocapitate wire (wire 3) to the dorsal sensory branch of the ulnar nerve was 0.45 ± 0.05 cm (Figure 8(c)), and that from lunotriquetral wire (wire 2) to the extensor digiti minimi tendon was 0.53 ± 0.09 cm (Figure 8(b)). A total of 10 patients who underwent percutaneous K wire fixation were clinically evaluated postoperatively to determine the presence of a sensory deficit in the dorsum of the hand within the sensory nerve territories of the radial and ulnar nerves as well any complications related to extensor tendon. None of the patients exhibited any sensory loss or any finger extension lag, suggesting the safety of the trajectories and the wire placements. All patients demonstrated restoration of normal carpal angles without residual DISI deformity, further supporting the radiological accuracy of this techniqueOPEN IN VIEWER

Discussion

The primary treatment objective in acute perilunate dislocation is to reestablish carpal alignment, allowing the intercarpal ligaments to heal and regain stability. ⁸ A contentious debate exists regarding the most appropriate approach to achieve reduction and the optimal method for preserving carpal alignment in terms of closed reduction and pinning versus open reduction and ligament repair. ⁹ A study conducted by Inoue and Kuwahata (1997) ¹⁰ involving 14 patients evaluated the efficacy of closed reduction versus open reduction and ligamentous repair. This investigation revealed no statistically significant difference in outcomes between the two groups. ¹⁰ Percutaneous K-wire fixation following closed reduction is a highly effective approach for treating acute closed perilunate dislocation, as long as precise anatomical carpal realignment is achieved.^2,3 The studies conducted by Hildebrand et al. (2000) ¹¹ and Sotereanos et al. (1997) ¹² involved the execution of perilunate dislocation treatment with a fixation technique that employed two K-wires for the fixation of both the scapholunate (SL) and lunotriquetral (LT) ligaments exclusively involving the proximal row. Most patients experienced satisfactory pain alleviation, improved functional motion, and increased grip strength following this surgery. A further investigation by Herzberg (2008) ¹³ and Malovic et al. (2011) ¹⁴ revealed favourable outcomes by the use of a K-wire for fixation at the proximal row and midcarpal joints. The utilization of a diamond-shaped arrangement consisting of four K-wires for the treatment of Peri lunate dislocation was initially reported in a study conducted by Bhatia D. N. (2016)15 and subsequently gained popularity through the work of Özyürekoğlu & Acar. (2021). ⁷ This configuration indicates the most effective stabilisation can be accomplished by using non-parallel K-wires through each bone segment, reducing dislocation and unloading adjacent rows. The design offers strength by stabilising dislocated joints in the proximal row and stabilising the proximal row against the distal carpal row. In a cadaveric study by Steinberg et al. (1995) ⁵ to denote safe zone on the radial side of the wrist, three percutaneous Kirschner wires were inserted into the upper extremities through the anatomic snuff box with fluoroscpic guidance. One Kirschner wire was inserted into the radial styloid, one across the scapholunate joint, and one across the scaphocapitate joint. They revealed a persistent safe zone for the insertion of K wires from the radial aspect of the wrist, with a mean area of 0.682 cm around the anatomical snuff box, bordered by branches from the superficial radial nerve, tendons forming the first dorsal compartment, the radial artery and its branches, and the radial styloid. Specific neurovascular and musculotendinous structures, including the ulnar nerve, ulnar artery, extensor digiti minimi, extensor carpi ulnaris, and flexor carpi ulnaris, are at risk for iatrogenic damage during the percutaneous pinning of ulnar-sided structures (Mok D et al., 2006). ¹⁶ A study by Naik et al. (2016) ⁶ demonstrated that two of the 11 ulnar styloid pins directly penetrate the distal superficial branch of the ulnar nerve (DSBUN) and that one of the 11 lunotriquetral pins directly penetrates the DSBUN. These findings highlight the potential risk of nerve injury associated with the placement of the ulnar styloid and lunotriquetral pins. However, the precise landmarks and trajectories for K wire insertion were not specified in the clinical and cadaveric studies previously discussed. While wire placement accuracy was confirmed intraoperatively and through cadaveric dissection, this study quantified safety rather than finding a “ideal” intraosseous position. Our study’s chosen landmarks and trajectories effectively avoided damage to essential structures during K-wire insertion. These findings indicate that the technique used in this study can be considered safe and reliable for future clinical applications. This may reduce the use of image intensifiers and decrease the amount of radiation exposure associated with their use.

The study’s primary shortcomings include its small sample size, its lack of a correlation between genders, and its exclusion of contributing anthropometric variables like hand size. However, the cadaveric correlation in our study offers insightful information on anatomical features, enabling a more thorough comprehension of the results. During cadaveric validation, we observed a distinct learning curve, evidenced by enhanced wire placement accuracy following the initial two specimens. As familiarity increased, the duration for wire placement decreased, and trajectory errors lessened, indicating that the method is readily teachable and reproducible with limited fluoroscopic support. Additionally, the inclusion of clinical evaluation of the patients postoperatively ensures that the study’s conclusions are supported by real-world observations and not limited to theoretical implications.More inclusive research with a larger sample size is needed to make it applicable to diverse demographic groups and a more diverse patient population. In addition, considering a potential variability in anatomical landmarks would also provide a balanced perspective. This study is the first of its kind in terms of safe anatomical landmarks for K-wire fixation of perilunate dislocation. A comparative analysis would place our findings in context and highlight the advancements our study offers over current practices. In clinical practice, reliable radiographic accuracy and the lack of iatrogenic damage further validate that the procedure may be safely implemented following initial supervised training.