Wrist-Spanning Fixation of Radiocarpal Dislocation: A Cadaveric Assessment of Ulnar Translation

Abstract

Background: Radiocarpal dislocations represent a high-energy wrist injury that can occur with or without concomitant fractures about the wrist. Poor outcomes are often due to radiocarpal instability and secondary ulnar translation. The purpose of this cadaveric study is to determine if there is any difference in the radiographic parameters in a wrist dislocation model given the different location of distal fixation. Methods: Ten paired fresh cadaver upper extremities were fluoroscopically evaluated with posterior-anterior (PA) and lateral views. We created a radiocarpal dislocation model and applied a dorsal bridge plate to either the second or third metacarpal. Repeat PA and lateral fluoroscopic views were obtained for evaluation of radial inclination, radial height, volar tilt, ulnar variance, radiolunate angle, radioscaphoid angle, scapholunate angle, radial rotation index, and four indices for ulnar translation (Taleisnik, Gilula, McMurtry, and Chamay). Results: Bridge plate application to the second metacarpal resulted in a significantly greater incidence of ulnar translation compared to the third metacarpal. Application to either metacarpal resulted in extension of the carpus relative to the radius. Conclusions: A more anatomic radiocarpal relationship was restored more often when distal fixation of the dorsal wrist-spanning bridge plate was applied to the third metacarpal. Further investigation is warranted to determine clinical relevance of these findings in conjunction with clinical and radiographic outcomes.

Introduction

Radiocarpal dislocations are rare high-energy wrist injuries that represent about 0.2% of all dislocations.^1,2 They are on a spectrum of injuries involving the distal end of the radius that can represent partial articular injuries. Our understanding of radiocarpal dislocations has evolved considerably, and we now recognize them as being on a spectrum of injuries involving the distal radius and ulna. Volar radiocarpal ligament tears and dorsal capsuloperiosteal avulsion associated with radiocarpal dislocations can lead to multi-directional radiocarpal instability and subsequent secondary ulnar translation.^3,4

The literature remains confounded with regard to the treatment of these rare injuries. Treatment options include closed versus open reduction followed by cast immobilization, percutaneous Kirschner wire (K-wire) fixation, internal fixation, wrist-spanning external and/or internal fixation, soft-tissue repair and/or reconstruction, and limited wrist arthrodesis and ligament reconstruction. ⁵ Dumontier et al ⁶ presented their series of 27 cases, the largest published series to date, as well as a classification system to facilitate treatment. They noted a high rate of secondary ulnar translation of the carpus in patients with a ligamentous radiocarpal dislocation. These findings have been mirrored by multiple small series and case reports.^3,4,7-9

Wrist-spanning plate fixation is a novel approach to radiocarpal dislocations. Potter et al ¹⁰ published their experience and found encouraging clinical and radiographic results without carpal translation at 1 year. The author’s attribute the successful outcome to a well-maintained relationship between the carpus and the radius until the soft tissue repair had healed. The spanning plate is transfixed to the shaft of the radius bone and distally to the second or third metacarpal. There is little evidence to show which mode of distal fixation can provide the best reduction. The purpose of this cadaveric study is to determine if there is any difference in the radiographic parameters in a wrist dislocation model given the different location of distal fixation.

Materials and Methods

Ten fresh cadavers were provided by our institution’s fresh tissue dissection lab. Fluoroscopic evaluation of the forearm, wrist, and hand did not demonstrate any preexisting pathology. To control for anatomic variations, the upper extremities of each cadaver were paired. There were a total of 20 specimens, 10 paired wrists, each only used once for this study. Distal fixation of the second or third metacarpal was randomly assigned to either the right or left extremity for each cadaver. A 2.4-mm/2.7-mm dorsal wrist-spanning bridge plate (Depuy-Synthes, West Chester, PA) was used for all cadaveric specimens.

Specimen Preparation

Prior to dissection, a fluoroscopic posterior-anterior (PA) and lateral wrist radiograph was obtained. Superimposition of the volar and dorsal lips of the sigmoid notch of the radius was used to standardize the PA view. The lateral view was standardized by having the pisiform project directly over the distal pole of the scaphoid, with the long axis of the third metacarpal and radius parallel.

A circumferential incision was made at the level of the wrist joint. Skin and subcutaneous tissue were elevated proximally and distally. Volar and dorsal tendons as well as neurovascular structures were dissected and protected to allow for visualization of the radiocarpal ligaments. All volar radiocarpal ligaments (radioscaphocapitate, long radiolunate, and short radiolunate) and dorsal radiocarpal capsuloligamentous structures were divided to create an injury pattern necessary radiocarpal dislocation and ulnar translation. ¹¹ The carpus were translated ulnarly relative to the radius and the radiocarpal joint was dislocated both volar and dorsal. The gross instability of the radio-carpal joint was confirmed under fluoroscopy (Figure 1). Following closed reduction of the radiocarpal joint, a bridge plate was applied distally to the designated metacarpal and proximally to the radial shaft as described by Lewis et al ¹² (Figure 2). The plate was positioned along the longitudinal axis of the metacarpal and radius diaphysis in order to ensure bicortical fixation and was secured distally with 2.4-mm bicortical non-locking screws and proximally with 2.7-mm bicortical non-locking screws. The wrist was held in neutral position during fixation. Repeat PA and lateral radiographs of the wrist were then obtained.

Figure 1.

Fluoroscopic images illustrating gross instability following division of volar radiocarpal ligaments and dorsal radiocarpal capsuloligamentous structures. (a) Ulnar translation, (b) volar dislocation, and (c) dorsal dislocation.

Figure 2.

Upper extremity cadaveric specimen after volar and dorsal dissection, dislocation, and application of dorsal wrist-spanning bridge plate with distal fixation to the third metacarpal.

Radiographic Measurements

Radiographic measurements included radial inclination, radial height, volar tilt, ulnar variance, radiolunate angle, radioscaphoid angle, scapholunate angle, and radial rotation index.

Four indices for ulnar translation described by Taleisnik, ¹³ Gilula,^14,15 McMurtry, and Chamay ¹⁶ were compared pre- and post-radiocarpal dislocation and application of bridge plate to assess for the presence of ulnar translation. Taleisnik ¹³ described two types of ulnar translation. Type 1 involves complete translation of the carpus, sparing the relationship between the carpus resulting in widening of >2.0-mm between the radial styloid and the scaphoid (Figure 3a). Type II is associated with scapholunate dissociation. For this study, only Type 1 ulnar translation was assessed given the known injury pattern that was replicated. The method described by Gilula et al¹⁴ indicates that ulnar translation is present when >50% of the proximal articular surface of the lunate is uncovered by the lunate facet of the radius. This method involves measurement of the Lo/Lw ratio where Lo represents the lunate overhang and Lw represents the width of the lunate (Figure 3b).^14,17 The method of McMurtry et al is the ratio (L₃/L₁) of the distance separating the center of the head of the capitate from the longitudinal axis of the ulna, L₃, to the length of the third metacarpal, L₁, normal is 0.3 ± 0.03 (Figure 3c).^15,17 The carpal translation index described by Chamay et al. represents the ratio (L₃/L₁) of the distance separating the center of the head of the capitate from a line parallel to the longitudinal axis of the radius projecting through the radial styloid, L₃, to the length of the third metacarpal, L₁, normal is 0.28 ± 0.03 (Figure 3d).^9,16,17

Figure 3.

Ulnar translation indices. (a) The method of Taleisnik. Ulnar translation is present if there is >2.0 mm between the radial styloid and the scaphoid. (b) The method of Gilula. Ulnar translation is present with >50% of the proximal articular surface of the lunate is uncovered by the lunate facet of the radius. (c) The method of McMurtry. The ratio (L₃/L₁) of the distance separating the center of the head of the capitate from the longitudinal axis of the ulna (L₃) to the length of the third metacarpal (L₁), normally 0.3 ± 0.03. (d) The method of Chamay. The ratio (L₃/L₁) of the distance separating the center of the head of the capitate from a line parallel to the longitudinal axis of the radius projecting through the radial styloid (L₃) to the length of the third metacarpal (L₁), normally 0.28 ± 0.03.

Statistical Methods

A power analysis was performed. For 80% power with 95% confidence, 7 specimens per group (metacarpal) were required; 10 specimens per group were used. Continuous variables, such as radial inclination, radial height, and radial styloid-scaphoid distance were compared using an unpaired two-tailed t test. Categorical variables were compared using Fisher’s exact test.

Results

A total of 10-paired specimens were used for this study. The averages of the baseline radiographic measurements include radial inclination 22.9 (range: 18.4-27.1) degrees, radial height 11 (range: 8.1-14) mm, volar tilt 11 (range: 1.8-18.5) degrees, ulnar variance -0.5 (range: -2.7 to 1.9) mm, radiolunate angle 3.4 (range: -3.2 to 13.2) degrees, radioscaphoid angle 55.4 (range: 42.9-68.4) degrees, scapholunate angle 52.2 (range: 38.6-65) degrees, and radial rotation index 119.1 (108.3-126.7) degrees (Table 1). There was no significant difference between the second and third metacarpal groups at baseline (Table 2).

Table 1.

Mean Radiographic Parameters.

	Overall	Second metacarpal		Third metacarpal
Radiographic Measurement	Pre	Pre	Post	Pre	Post
Radial inclination (degrees)	22.9 ± 2.9 (18.4-27.1)	22.4 ± 2.9 (18.4-26.6)	22.3 ± 2.7 (17.7-26.0)	23.4 ± 3.1 (18.4-27.1)	23.3 ± 3.2 (17.6-27.4)
Radial height (mm)	11.0 ± 1.7 (8.1-14.0)	10.8 ± 1.7 (8.3-14)	10.9 ± 1.6 (8.1-13.0)	11.2 ± 1.7 (8.1-13.8)	11.2 ± 1.8 (7.9-13.7)
Volar tilt (degrees)	11.0 ± 3.4 (1.8-18.5)	10.2 ± 3.7 (1.8-15.9)	10.6 ± 3.6 (2.2-14.4)	11.7 ± 3.0 (8.1-18.5)	12.3 ± 3.5 (8.3-19.6)
Ulnar variance (mm)	−0.5 ± 1.5 (-2.7-1.9)	−0.6 ± 1.5 (-2.3-1.6)	−0.64 ± 1.4 (-2.1-1.4)	−0.4 ± 1.5 (-2.7-1.9)	−0.4 ± 1.5 (-2.4-1.8)
Radiolunate angle (degrees)	3.4 ± 5.6 (-3.2-13.2)	4.5 ± 6.2 (-3.2-14.1)	−4.2 ± 6.7 (-12.2-10.4)	2.4 ± 5.0 (-3.0-12.3)	−8.2 ± 7.8 (-26.2-0.5)
Radioscaphoid angle (degrees)	55.4 ± 6.7 (42.9-68.4)	54.1 ± 4.7 (47.2-62.3)	45.5 ± 7.6 (30.2-58.4)	56.8 ± 8.4 (42.9-68.4)	45.5 ± 8.5 (36.1-57.4)
Scapholunate angle (degrees)	52.2 ± 7.7 (38.6-65.0)	49.4 ± 7.8 (38.6-61.4)	50.2 ± 9.2 (37.9-66.2)	54.9 ± 6.8 (45.4-65.0)	54.0 ± 7.8 (45.3-65.7)
Radial rotation index (degrees)	119.1 ± 4.9 (108.3-126.7)	119.4 ± 4.9 (111.2-126.7)	119.4 ± 4.4 (113.9-127.6)	118.7 ± 5.2 (108.3-123.6)	127.6 ± 6.3 (115-137.2)
Radial styloid-scaphoid distance (mm)	1.8 ± 0.3 (1.0-2.8)	2.0 ± 0.3 (1.7-2.8)	3.8 ± 1.4 (1.8-6.6)	1.7 ± 0.4 (1.0-2.2)	1.5 ± 0.4 (0.8-1.9)

Mean radiographic measurements ± standard deviation (range). “Overall” includes measurements of all specimen, from both metacarpal groups, prior to radiocarpal dislocation and fixation. Negative (-) values for angular measurements represents relative extension with the reference line parallel to the longitudinal axis of the radius. Positive (+) values for angular measurements represents relative flexion with the reference line parallel to the longitudinal axis of the radius.

Table 2.

Comparison of Radiographic Parameters (P values).

Radiographic Measurement	Second pre vs third pre	Second pre vs third post	Third pre vs third post	Second post vs third post
Radial inclination	0.4493	0.9433	0.9389	0.4737
Radial height	0.5813	0.8406	0.9900	0.7258
Volar tilt	0.3299	0.8143	0.6955	0.2937
Ulnar variance	0.7720	0.9274	0.9298	0.7584
Radiolunate angle	0.4117	0.0076*	0.0020*	0.2337
Radioscaphoid angle	0.3850	0.0070*	0.0078*	0.9847
Scapholunate angle	0.1072	0.8323	0.7898	0.3261
Radial rotation index	0.7529	0.9697	0.0029*	0.0032*
Radial styloid-scaphoid distance	0.1748	0.0009*	0.1822	0.0001*

Comparison of the radiographic parameters with distal fixation to the second and third metacarpal prior to radiocarpal dislocation and following dorsal bridge plate fixation. Fixation of the dorsal bridge plate to either the second or third metacarpal resulted in extension of the carpus relative to the radius with a statistically significant decrease in radiolunate angle and radioscaphoid angle when compared to baseline. However, there was not a statistically significant difference between the two groups. Radial rotation index significantly increased with distal fixation to the third metacarpal.

^*Statistically significant difference (P < .05), t test.

There was no statistically significant difference when comparing baseline to post-fixation, or second versus third metacarpal fixation for radial inclination, radial height, volar tilt, ulnar variance, and scapholunate angle. Fixation of the dorsal bridge plate to either the second or third metacarpal resulted in a statistically significant decrease in radiolunate angle (P < 0.01) and radioscaphoid angle (P <.01) when compared to baseline, however, there was not a statistically significant difference between the two groups (P > .05). Radial rotation index significantly increased with distal fixation to the third metacarpal (P < .01) (Table 2).

Taleisnick

The average baseline radial styloid – scaphoid distance was 1.8 (range, 1 to 2.8) mm. One of the 10 cadavers had a baseline radial styloid – scaphoid distance >2.0 mm, bilaterally. There was no statistically significant difference between the two groups at baseline. Measurements after dorsal bridge plate fixation demonstrated that distal fixation to the second metacarpal resulted in greater radial styloid – scaphoid distance compared to third metacarpal fixation (P = .0001). A positive Taleisnick index was found in eight wrists with distal fixation to the second metacarpal, and none of the wrists with distal fixation to the third metacarpal (P = .0007) (Table 3).

Table 3.

Ulnar Translation Indices.

Ulnar Translation Index	Second metacarpal	Third metacarpal	P value
Taleisnick (Type 1)	8	0	.0007*
Gilula	6	1	.0573
McMurtry	8	0	.0007*
Chamay	6	0	.0108*

Comparison of the incidence of ulnar translation with distal fixation to the second versus third metacarpal with sample size of 10 specimens per group (n = 10). Distal fixation to the third metacarpal restored radiocarpal alignment more consistently. Ulnar translation was found to be present in 60% to 80% of specimen with distal fixation to the second metacarpal.

^*Statistically significant difference (P < .05), Fisher Exact test.

Gilula

A positive Gilula index (> 50% lunate overhang) was found in six wrists with distal fixation to the second metacarpal, and one wrist with distal fixation to the third metacarpal (P = .0573) (Table 3).

McMurtry

A positive McMurtry index was found in eight wrists with distal fixation to the second metacarpal, and none of the wrists with distal fixation to the third metacarpal (P = .0007) (Table 3).

Chamay

A positive Chamay index was found in six wrists with distal fixation to the second metacarpal, and none of the wrists with distal fixation to the third metacarpal (P = .0108) (Table 3).

Discussion

The treatment of radiocarpal dislocations has evolved since first being described by Malle in 1838 and Voillemier in 1839.^18,19 A major challenge to treating this injury is providing a stable radiocarpal articulation in the setting of ligamentous injury. Late ulnar translation of the carpus has been a recurrent issue with many of the current treatment options, leading to a lack of consensus in the literature.

A thorough comprehension of wrist anatomy and biomechanics is necessary to understand the pathophysiology of the injury and to formulate a thoughtful approach to treatment. Berger and Landsmeer ²⁰ provided first description of the short radiolunate ligament as well as further detailing the radioscaphocapitate and long radiolunate ligaments. Further work by Rayhack demonstrated that the radiolunate ligaments provide the primary soft tissue restraint against volar translation, while the radioscaphocapitate ligament prevents ulnar translation of the carpus. ⁹ Viegas’ biomechanical study suggests ulnar translation is secondary to a global ligament disruption of the soft tissue restrains about the volar and dorsal aspect of the radiocarpal joint. ⁷ This is consistent with multiple studies suggesting radiocarpal dislocations with an associated ulnar translocation require all volar radiocarpal ligaments to be torn in conjunction with posterior radiocarpal ligament disruption or capsuloperiosteal avulsion.^3,4,6,11

Moneim et al ² and Dumontier et al ⁶ classified radiocarpal dislocations based on intercarpal involvement and extent of radial styloid involvement, respectively. Dumontier Group 1 injuries include pure ligamentous radiocarpal dislocations with or without a fracture of only the tip of the radial styloid. Group 2 injuries include dislocations with a fracture of the radial styloid involving more than one-third of the width of the scaphoid fossa. Treatment approach included variations of closed/open reduction, plaster immobilization, percutaneous K-wire fixation, external fixator, and ligamentous repair. In their series of 27 radiocarpal dislocations, Group 1 injuries posed a greater challenge due to their inherent instability. All but one of the patients had secondary ulnar translation regardless of treatment method. The patient without recurrent instability had temporary radiolunate fixation. Both acute and secondary translation has been frequently reported, in addition to poor functional results and late arthritis.^{3,4,7-9,21-24}

Potter et al ¹⁰ first reported a case study utilizing a wrist-spanning plate for the treatment of radiocarpal dislocations in 2014 with encouraging radiographic and functional results at 1 year. The use of dorsal wrist-spanning plates has primarily been used in the setting of comminuted distal radius fractures with intra-articular extension in the setting of poor bone quality not amenable to volar fixation. These implants provide greater stability and early forearm weight bearing and rotation while avoiding the complications associated with external fixation, such as pin site infection and hand stiffness.^25-27 Radiographic and functional outcomes have also been comparable to traditional fixation methods.^28-30 Distal implant fixation can be to the second or third metacarpal, depending on surgeon preference, fracture pattern, soft tissue injury, and alignment. There is evidence of increased risk of superficial radial nerve injury with distal fixation to the second metacarpal, while fixation to the third metacarpal was found to have increased risk of tendon entrapment/contact while providing greater construct stiffness.^12,31,32

In the current study, dorsal bridge plate application to the second or third metacarpal of our radiocarpal dislocation model did not result in any changes with regard to intercarpal relationships. However, there was notable extension of the carpus relative to the radius for both distal fixation methods. This is likely attributed to plate positioning over Lister’s tubercle and/or the slight flare of the distal radius in the sagittal plane requiring relative wrist extension to obtain bone-plate contact distally (Figure 4). A technical concern with an extended wrist position is a resultant increased distance between volar ligament origin and insertion, compromising the ability to perform an adequate ligament repair by limiting bone-ligament apposition. Given that the volar radiocarpal ligaments and dorsal capsuloligamentous structures are taut through midrange wrist motion and are within 5% of their maximum length throughout the range of wrist motion, then accurate repairs maybe difficult.^33,34 A technique to mitigate this effect includes removal of Lister’s tubercle with a rongeur prior to plate application.

Figure 4.

Illustration of carpal extension secondary to plate position over Lister’s tubercle or flare of the distal radius (dots). Metacarpal-plate contact can result in secondary extension of the carpus (arrow) relative to the radius seen with distal fixation to both the second and third metacarpals.

Another interesting observation was the effect of distal fixation on radial rotation index. This measurement serves as a surrogate for wrist deviation. We found that fixation to the third metacarpal resulted in greater radial deviation compared to distal fixation to the second metacarpal. Prior biomechanical studies have shown shortening of the radioscaphocapitate ligaments and lengthening of the dorsal radiocarpal ligament with radial deviation of the wrist.^35-37

Radiocarpal instability with secondary ulnar translation following radiocarpal dislocation is a frequently characterized failure pattern with no agreed upon solution.^{3,4,7-9,21-24} Rayhack et al ⁹ reviewed 8 cases of posttraumatic ulnar translation and concluded that soft tissue augmentation alone resulted in a high failure rate, and recommended the addition of bony stabilization or limited arthrodesis. In the setting of purely ligamentous radiocarpal dislocations, bony stabilization was limited to temporary radiolunate fixation or radiolunate arthrodesis.^6,9

Potter et al is the first to report findings using dorsal wrist-spanning bridge plate in the setting of volar ligament repair. Their findings are promising, however, the study is limited to single patient. One consideration for why patients with temporary bony stabilization have improved outcomes without recurrence of ulnar translation is that the radiocarpal relationship is appropriately maintained allowing the soft tissue to heal without substantial stress. Early stress of acute ligamentous injuries, ligament repairs and reconstructions can result in ligament incompetence secondary to viscoelastic creep.^38,39 A dorsal wrist-spanning bridge plate can provide the temporary bony stabilization needed to allow the soft tissues to heal, while avoiding violation of the radiocarpal joint with radiolunate K-wire fixation. We therefore sought to evaluate the ability of a dorsal wrist-spanning bridge plate to restore radiocarpal alignment, specifically ulnar translation, comparing distal fixation to the second versus third metacarpal.

Four different methods were used to determine if ulnar translation was present after closed reduction and bridge plate application. Distal fixation to the third metacarpal was found to restore radiocarpal alignment more consistently. Distal fixation to the second metacarpal resulted in a significant increase in radial styloid-scaphoid distance, whereas fixation to the third metacarpal restored baseline distance. Additionally, ulnar translocation was found to be present in 60% to 80% of specimens with distal fixation to the second metacarpal.

Distal fixation to the third metacarpal restored radiocarpal alignment in all ten specimens based on the Taleisnick, McMurtry, and Chamay indices. However, Chamay index determined ulnar translation to be present in 1 of 10 specimens with distal fixation to the third metacarpal. This resulted in a statistically significant greater incidence of ulnar translation with fixation to the second metacarpal for all methods, except the Gilula index, which was trending toward, but did not reach, statistical significance.

Limitations of this study include that it was a cadaveric study. The radiocarpal dislocation model used in this study involved transection of the volar and dorsal radiocarpal ligaments to create an unstable radiocarpal joint. However, in the clinical setting there is a more significant soft tissue trauma that we are unable to capture in a cadaveric model. This includes intercarpal injuries, bony avulsions, and variations to the pattern of ligament injury and severity of ligament injury. Also, as with other studies of this nature, we are not able to extrapolate long-term clinical outcomes. Determination of whether this is a meaningful adjunct to allow soft tissues to heal will require clinical studies. Additionally, ligament repair was not performed in this study. Although meticulous ligamentous repair is an essential part of the treatment of this injury, the aim of this study was to characterize the distinctive effect of distal fixation on carpal alignment. Further investigation is warranted to determine the clinical effects of distal fixation on ligament repair with regard to ulnar translation and gapping of the volar radiocarpal ligaments.

There are strengths of this study. First, the cadavers used were fresh and therefore were more physiologically accurate than fresh-frozen. Second, we used a standardized fluoroscopic protocol to obtain views that were reproducible to allow for a more accurate comparison. Third, we used four different indices to evaluate for ulnar translation to improve reliability of our findings. Lastly, to control for anatomic variations, the extremities of each cadaver were paired to serve as an internal control.

Conclusion

In conclusion, the radiocarpal relationship was restored more often when distal fixation of the dorsal wrist-spanning bridge plate was applied to the third metacarpal; however, native anatomy was restored in several instances with distal fixation to the second metacarpal. With this in mind, goals of surgery should remain a concentric reduction and restoration of the radiocarpal relationship utilizing a stable construct to allow for anatomic soft tissue repair and healing. Distal fixation should therefore be determined on a case-by-case basis keeping in mind the unique anatomy of the patient, implant design, and concomitant injuries. In addition, we should keep in mind that congruent reduction of the radio-carpal joint can be difficult given the complex nature and variations in articular anatomy. Further investigation is warranted to determine clinical relevance of these findings in conjunction with clinical and radiographic outcomes.