873 The Keystone Challenge- Volar Displaced Intra-Articular Distal Radius Fractures with Lunate Fossa Fragment

Aim Volar displaced fractures of the distal radius are unstable and warrant operative management. A subset of patients with volar displaced fractures also has a separate lunate fossa fragment, a specific injury with greater instability that may precipitate carpal subluxation. We aim to review our long-term experience in the management of this complex injury, exploring surgical technique which may improve treatment. Method We retrospectively reviewed all volar displaced distal radius fixations between 2015 and 2020. Inclusion criteria: any displaced intra-articular volar distal radius fracture with lunate fragment involvement undergoing volar fixation and over 16 years of age. Exclusion criteria: shaft fractures, extra-articular fractures, open fractures, fractures fixed using k-wires or external fixation, revision surgery and patients without follow-up. We adapted our surgical approach in order to address this more complex fracture pattern, and all operations were performed by specialist hand surgeons. Results 468 distal radius fractures were assessed, of which 29 (6%) cases included a lunate fossa fragment. 20 (69%) of patients were female, mean age was 59 years (SD 12.4). Mean length of stay was 5 hours and mean operative time was 96 mins (range 79-95). No patients had carpal subluxation, fracture fixation failure or return to theatre for any reason. Conclusions From our experience as a specialist orthopaedic institution, we recommend the extended FCR approach and intra-focal exposure to manage this complex injury. In particular, the lunate fossa fragment is the keystone which requires dedicated reduction prior to tackling the remaining fracture configuration.

Radiocarpal Contact Pressures Are Not Altered after Scapholunate Ligament Tears

Background The scapholunate interosseous ligament (SLIL) couples the scaphoid and lunate, preventing motion and instability. Prior studies suggest that damage to the SLIL may significantly alter contact pressures of the radiocarpal joint. Questions/Purposes The purpose of this study was to investigate the contact pressure and contact area in the scaphoid and lunate fossae of the radius prior to and after sectioning the SLIL. Methods Ten cadaveric forearms were dissected distal to 1-cm proximal to the radiocarpal joint and a Tekscan sensor was placed in the radiocarpal joint. The potted specimen was mounted and an axial load of 200 N was applied over 60 seconds. Results Sectioning of the SLIL did neither significantly alter mean contact pressure at the lunate fossa (p = 0.842) nor scaphoid fossa (p = 0.760). Peak pressures were similar between both states at the lunate and scaphoid fossae (p = 0.301–0.959). Contact areas were similar at the lunate fossa (p = 0.508) but trended toward an increase in the SLIL sectioned state in the scaphoid fossa (p = 0.055). No significant differences in the distribution of contact pressure (p = 0.799), peak pressure (p = 0.445), and contact area (p = 0.203) between the scaphoid and lunate fossae after sectioning were observed. Conclusion Complete sectioning of the SLIL in isolation may not be sufficient to alter the contact pressures of the wrist. Clinical Relevance Injury to the secondary stabilizers of the SL joint, in addition to complete sectioning of the SLIL, may be needed to induce altered biomechanics and ultimately degenerative changes of the radiocarpal joint.

112 Trans-Scaphoid Perilunate Dislocation. Two Atypical Presentations with Enucleation of The Proximal Pole

This article describes two cases of tran-scaphoid perilunate dislocation, both of which have an atypical presentation. In both cases, the proximal pole of the scaphoid was enucleated, one into the carpal tunnel, the other into the distal forearm. In addition, the capitolunate alignment was preserved, with dorsal dislocation of the entire carpus. These cases are presented for educational purposes, as these injuries are highly unstable, and require a different operative approach to a typical perilunate dislocation. In a typical Mayfield II perilunate dislocation, the lunate remains within the lunate fossa, and acts as a 'keystone' for fixation of the dislocated carpus. These cases do not fit the classic Mayfield classification. Given the lunate was also unstable, K-wires were placed through the distal radius into lunate, then from the scaphoid into the lunate. Another learning point for all training levels is that the referring orthopaedic hospital referred one of these injuries incorrectly as a 'lunate dislocation'. This article provides an opportunity to re-cap the Mayfield classification, and clarify the distinction between lunate and perilunate dislocation. In all cases, stringent monitoring for any carpal tunnel syndrome is required, and urgent decompression should be performed if there is any concern.

Perilunate instability: A rare variant

Perilunate dislocations and perilunate fracture dislocations are rare injuries that occur as a result of high energy trauma. We describe a case of a volar fracture dislocation of the proximal pole of the scaphoid with an associated scapholunate and lunotriquetral ligament disruption as well as a lunate fossa fracture of the distal radius. These injuries are serious injuries that require a high degree of clinical acumen and radiographic scrutiny to allow for prompt treatment in order to avoid the sequelae of long-term complications that can arise. This case serves as a reminder of the complexity of these injuries and their associated mechanics.

Bony Anatomy around the Watershed Line of the Distal Radius

Background An important surgical landmark in the distal radius is the watershed line. The watershed line is a landmark for the positioning of volar locking plates (VLP) in the distal radius. Inconsistencies remain in the literature as to the presence and dimensions of landmarks in this compact area. We studied the detailed anatomy and dimensions of the distal radius with reference to bony anatomy around the watershed line, with special attention to the area between the pronator quadratus (PQ) and radial styloid. Materials and Methods The distal radius regions of 31 cadavers (23 right sided and 8 left sided) were dissected and studied. The heights at the junction of the scaphoid and lunate fossa, at the radial styloid, at the midpoint in between, and the widths of the PQ line, scaphoid, and lunate fossa were measured. The angle subtended by the pronator fossa and the radial styloid was also recorded. Results The mean heights at the junction of the scaphoid and lunate fossa, radial styloid, and midpoint in between were 5.1, 15.7, and 8.2 mm, respectively. The widths of the PQ line, scaphoid, and lunate fossa were 27, 19.4, and 10.6 mm, respectively. The mean angulation between the pronator fossa and the radial styloid was 128.9 degrees. Conclusion The area between the PQ and watershed line comprises a narrow area of bone which tapers to a point at its medial extent largely below the lunate fossa, thus it can hardly contain any implant proximal to the lunate fossa. The anterior orientation of this area and the concave anatomy of the articular surface mean careful screw direction is imperative to avoid inadvertent joint penetration. An angulation exists between the pronator fossa and the radial styloid, below the scaphoid fossa.

Salvage of advanced carpal collapse: proximal row carpectomy with pyrocarbon resurfacing of the capitate versus four-corner arthrodesis

In this retrospective study we report on two comparable groups of patients with advanced carpal arthritis treated with either proximal row carpectomy combined with a pyrocarbon resurfacing of the capitate (31 patients) or a four-corner arthrodesis and dorsal plating (26 patients). Follow-up time was 46 months (24–118). Except for a modestly higher radial wrist deviation in the patients treated with four-corner arthrodesis, there were no significant differences in outcomes between the groups. Asymptomatic progression of osteoarthritis in the lunate fossa was observed in four cases in both groups. Two cases were converted to a total wrist arthrodesis in the pyrocarbon group compared with one case in the four-corner arthrodesis group. Although four-corner arthrodesis remains the reference standard in the treatment of wrist osteoarthritis with involvement of the midcarpal joint, proximal row carpectomy combined with pyrocarbon resurfacing of the capitate is an alternative option. It can even be used in selected cases with erosion of the lunate fossa. Level of evidence: III

Lateral Center-Edge Angle Is Not Predictive of Acetabular Articular Cartilage Surface Area: Anatomic Variation of the Lunate Fossa

Background: Surgical treatment of symptomatic femoroacetabular impingement (FAI) and dysplasia requires careful characterization of acetabular morphology. The lateral center-edge angle (LCEA) is often used to assess lateral acetabular anatomy. Previous work has questioned the LCEA as a surrogate for acetabular contact/articular cartilage surface area because of the variable morphology of the lunate fossa. Hypothesis: We hypothesized that weightbearing articular cartilage of the acetabulum would poorly correlate with LCEA secondary to significant variation in the size of the lunate fossa. Study Design: Cohort study (Diagnosis); Level of evidence, 3. Methods: Patients with 3D CT imaging undergoing either hip arthroscopy or periacetabular osteotomy for FAI or symptomatic hip instability were retrospectively identified. The LCEA and femoral head diameter were measured on an anteroposterior pelvis radiograph. Patients were grouped according to their lateral acetabular coverage as undercoverage (LCEA, <25°), normal coverage (LCEA, 25°-40°), or overcoverage (LCEA, >40°). Patients were randomly identified until each group contained 20 patients. The articular surface area was measured from preoperative 3D CT data. Linear regression analysis was performed to examine the relationship between articular surface area and LCEA. Continuous and categorical data were analyzed utilizing analysis of variance and chi-square analysis. Statistical significance was set at P < .05. Results: No difference in age ( P = .52), body mass index (BMI) ( P = .75), or femoral head diameter ( P = .66) was noted between groups. A significant difference in articular surface area was observed between patients with undercoverage and those with overcoverage (20.4 cm2 vs 24.5 cm2; P = .01). No significant difference was identified between the undercoverage and normal groups (20.4 cm2 vs 23.3 cm2; P = .09) or the normal and overcoverage groups (23.3 cm2 vs 24.5 cm2; P = .63). A moderate positive correlation was observed between LCEA and articular surface area across all patients ( r = 0.38; P = .002) but not when patients with undercoverage were excluded ( r = 0.02; P = .88). Significant variation in surface area was observed within each group such that no patient in any group was outside of 2 SDs of the means of the other groups. When patients were categorized into quartiles established by the articular surface area for the entire population, 40% of patients with overcoverage were observed in the first or second quartile (lower area). Conclusion: Lateral acetabular undercoverage based on the LCEA (<25°) correlates with decreased acetabular surface area. Normal or increased acetabular coverage (LCEA, >25°), however, is not predictive of increased, normal, or decreased acetabular surface area.

Quantitative three-dimensional assessment of Madelung deformity

In the diagnostic work-up of Madelung deformity conventional radiographic imaging is often used, assessing the three-dimensional deformity in a two-dimensional manner. A three-dimensional approach could expand our understanding of Madelung deformity’s complex wrist anatomy, while removing inter- and intra-rater differences. We measured previous two-dimensional-based and newly developed three-dimensional-based parameters in 18 patients with Madelung deformity (28 wrists) and 35 healthy participants (56 wrists). Madelung deformity wrists have increased levels of ulnar tilt, lunate subsidence, lunate fossa angle, and palmar carpal displacement. The lunate fossa is more concave and irregular, and angles between scaphoid, lunate, and triquetral bones are decreased. These findings validate the underlying principles of current two-dimensional criteria and reveal previously unknown anatomical abnormalities by utilizing novel three-dimensional parameters to quantify the radiocarpal joint.