Optimal detection of scapholunate ligament tears with MRI.

Background Scapholunate interosseous ligament (SLIL) injuries can often be difficult to detect using magnetic resonance imaging (MRI), especially with older 1.0 and 1.5 Tesla magnets. Wrist arthroscopy is the gold standard for diagnosis of SLIL injuries, but is an invasive procedure with associated risks. Purpose To assess whether SLIL injuries can be more accurately detected using axial MRI sequences instead of coronal sequences. Material and Methods An institutional review board approved retrospective analysis of arthroscopic wrist surgeries performed at our institution. Patients that had a preoperative MRI performed at our university center using a 1.5 Tesla scanner with a dedicated wrist coil were included in the study. Three fellowship-trained musculoskeletal radiologists reviewed the axial sequences and coronal sequences independently. The accuracy of the coronal and axial sequences was compared with the arthroscopic/surgical findings. Result Twenty-six patients met the inclusion criteria. The sensitivity for SLIL tears was 79% and 65% for the axial and coronal sequences, respectively. The specificity was 82% for the axial and 69% for the coronal sequences, respectively. The positive and negative predictive values for the axial sequences were 76% and 84% respectively, compared to 68% and 71% for the coronal sequences, a statistically significant difference. Conclusion SLIL tears are more readily detectable on axial MRI sequences than coronal. Clinically, patients with radial-sided wrist pain and suspicion for SLIL tears should have the axial sequences scrutinized carefully. An otherwise normal study with the axial sequence being degraded by motion or other MRI artifacts might need repeat imaging.

Computer-assisted navigation for dorsal percutaneous scaphoid screw placement: a cadaveric study.

PURPOSE: To investigate computer-assisted surgery (CAS) for dorsal insertion of percutaneous scaphoid screws and to compare operative time, accuracy, and fluoroscopy time with the traditional mini C-arm method. We hypothesized that CAS techniques would improve accuracy, reduce actual K-wire insertion time, and decrease fluoroscopy time. METHODS: Ten fresh cadaveric upper limbs were randomized to either CAS or traditional dorsal percutaneous scaphoid screw placement by a single surgeon. Custom orthoses were applied to the CAS arms followed by intraoperative computed tomography (CT) scan and navigation calibration. Time was recorded for the portion of setup that required surgeon input, ideal guide wire placement, and fluoroscopy. Postoperative CT scans of the CAS arms were obtained to confirm accuracy. Two-tailed unpaired Student t test was used to analyze the outcome variables. RESULTS: The CAS group required on average 4.8 ± 0.8 minutes longer for setup. The time for placement of the guidewire in the ideal position was 4.6 ± 1.5 minutes in the CAS group compared with 11.8 ± 4.4 minutes in the control group. Fluoroscopy time was 18 ± 4 seconds for the CAS group and 114 ± 38 seconds for the control group. Postoperative CT scans demonstrated 1.5 ± 0.6 mm maximum deviation from the planned ideal screw. No significant differences were found in the accuracy between methods, the number of guidewire attempts, or the total surgical time. CONCLUSIONS: Computer-assisted surgery navigation of dorsal percutaneous scaphoid screw placement takes on average 5 minutes longer to set up, but leads to significantly reduced guidewire placement time and no differences in overall procedural time. This CAS method was as accurate as the traditional method and resulted in an approximate 6-fold reduction in fluoroscopy time. CLINICAL RELEVANCE: This is an effective imaging alternative to the mini C-arm for scaphoid fixation using existing intraoperative CT scanners and navigation software.

Comparison of 2 forearm reconstructions for longitudinal radioulnar dissociation: a cadaver study.

PURPOSE: We present the results of a cadaveric study of 2 forearm reconstructions with radial head replacement for longitudinal radioulnar dissociation injuries. METHODS: We created a simulated longitudinal radioulnar dissociation injury in 8 cadaver forearms. Two reconstructions were performed alternately on each arm: patellar tendon interosseous ligament complex reconstruction and the Herbert sling extensor retinaculum plication. We performed mechanical testing in a materials testing machine with and without a radial head replacement, and measured ulnocarpal impaction force through 2 distal ulna strain gauges. We determined relative radioulnar displacement using live fluoroscopic analysis of implanted stainless-steel beads. RESULTS: Relative radioulnar longitudinal displacement in the destabilized forearms was 10.7 compared with 0.7 mm before creating the injury. A prosthetic radial head replacement alone decreased the displacement by 75% to 2.7 mm. Interosseous ligament reconstruction alone reduced the displacement to 5.1 mm and to 1.3 mm when combined with a radial head implant. The Herbert sling alone did not improve longitudinal stability. The distal ulna force in the native arm was 17 N, or 17% of the force across the wrist. The interosseous ligament reconstruction restored the force to 21 N, whereas the Herbert sling only marginally decreased the ulna impaction force to 45 N. Adding a radial head decreased the distal ulna force to 7 N for the patellar tendon interosseous ligament reconstruction, and 2 N for the Herbert sling. CONCLUSIONS: In longitudinal radioulnar dissociation injuries, the radial head is an important stabilizer and should be repaired or replaced to minimize radial shortening and ulnar impaction force. Patellar tendon interosseous ligament reconstruction effectively restores the ulnocarpal force distribution and markedly reduces longitudinal instability at the distal radioulnar joint. Combined with radial head arthroplasty, the construct has stability similar to an intact forearm. The Herbert sling did not improve longitudinal stability in this testing construct. CLINICAL RELEVANCE: Treatment of longitudinal radioulnar dissociation may benefit from radial head replacement and interosseous ligament reconstruction using a patellar tendon graft.

Ulnar nerve component to innervation of thumb carpometacarpal joint.

PURPOSE: Thumb carpometacarpal (CMC) joint arthritis is one of the most common problems addressed by hand surgeons. The gold standard of treatment for thumb CMC joint arthritis is trapeziectomy, ligament reconstruction and tendon interposition. Denervation of the thumb CMC joint is not currently used to treat arthritis in this joint due to the failure of the procedure to yield significant symptomatic relief. The failure of denervation is puzzling, given that past anatomic studies show the radial nerve is the major innervation of the thumb CMC joint with the lateral antebrachial nerve and the median nerve also innervating this joint. Although no anatomic study has ever shown that the ulnar nerve innervates the CMC joint, due to both the failure of denervation and the success of arthroscopic thermal ablation, we suspect that previous anatomic studies may have overlooked innervation of the thumb CMC joint via the ulnar nerve. METHODS: We dissected 19 formalin-preserved cadaveric hand-to-mid-forearm specimens. The radial, median and ulnar nerves were identified in the proximal forearm and then followed distally. Any branch heading toward the radial side of the hand were followed to see if they innervated the thumb CMC joint. RESULTS: Eleven specimens (58%) had superficial radial nerve innervation to the thumb CMC joint. Nine specimens (47%) had median nerve innervation from the motor branch. Nine specimens (47%) had ulnar nerve innervation from the motor branch. CONCLUSIONS: We believe this is the first study to demonstrate that the ulnar nerve innervates the thumb CMC joint This finding may explain the poor results seen in earlier attempts at denervation of the thumb CMC, but the more favorable results with techniques such as arthroscopy with thermal ablation.

Suture-button construct for interosseous ligament reconstruction in longitudinal radioulnar dissociations: a biomechanical study.

PURPOSE: Longitudinal radioulnar dissociation is a triad of injuries consisting of distal radioulnar joint disruption, interosseous ligament complex (IOLC) tear, and radial head fracture. This renders the forearm longitudinally unstable, resulting in proximal migration of the radius and ulnar-sided wrist degeneration. We hypothesized that reconstruction of the central band of the IOLC in cadaver forearms using a Mini-TightRope suture-button construct would restore native forearm stability. METHODS: We implanted 8 fresh-frozen cadaver arms with steel beads into the distal radius and ulna, mounted them on an MTS machine, and cyclically loaded them from 13 N distraction to 130 N compression. Bead motion was recorded fluoroscopically and analyzed using Image-Pro Express software. We measured distal ulnar forces using strain gauge transducers. Longitudinal radioulnar dissociation injuries were created by radial head excision and complete IOLC and triangular fibrocartilage complex disruption. At each stage, arms were tested with and without a radial head implant. We reconstructed the central band of the IOLC using a Mini-TightRope and tightened until the distal radioulnar joint was reduced fluoroscopically. We used multiple-comparison analysis of variance with Tukey's Honestly Significant Difference test for statistical analysis. RESULTS: The intact arms had an average radioulnar axial displacement of 0.7 ± 0.8 mm and distal ulnar impaction force of 16.7 ± 11.1 N (per 100 N of axial load on the forearm). After destabilization, the radioulnar displacement increased to 10.7 ± 3.9 mm (p < .001) and ulnar load increased 312%, to an average of 52.2 ± 25.7 N (p < .001). After IOLC reconstruction, average displacement decreased to 2.2 ± 0.9 mm with a distal ulnar load of 19.05 ± 13.5 N (not significantly different from intact arms). CONCLUSIONS: In this cadaveric study, Mini-TightRope IOLC reconstruction with or without a radial head prosthesis significantly reduced distal ulnar impaction forces to that of the native forearm, while limiting radioulnar displacement to near-anatomic levels.

Correlation of strain and loads measured in the long bones with observed kinematics of the lower limb during vehicle-pedestrian impacts.

The purpose of this study is to determine the loads in the long bones of the lower extremities during vehicle-pedestrian impact tests, and to correlate load data with observed kinematics in an effort to understand how stature and vehicle shape influence pedestrian response. In tests with a large sedan and a small multi-purpose vehicle (MPV), four post mortem human surrogates (PMHS) in mid-stance gait were struck laterally at 40 km/h. Prior to the tests, each PMHSwas instrumented with four uniaxial strain gages around the mid-shaft cross section of the struck-side (right) tibia and the femora bilaterally. After the tests, the non-fractured bones were harvested and subjected to three-point bending experiments. The effective elastic moduli were determined by relating the applied bending loads with the measured strains using strain gage locations, detailed bone geometry, and elastic beam theory. Using the strains measured in the vehicle-pedestrian tests and the calculated effective elastic moduli, the axial load and bending moments in the instrumented bone cross-sections were calculated. Peak longitudinal strains in the mid-shaft cross-sections approached 1% in the right tibiae and exceeded 0.5% in the right femora with peak strain rates of 200%s(-1)-750%s(-1) in the right tibiae and 100%s(-1)-170%s(-1) in the femora. While peak axial forces were consistent for both vehicles and ranged from 1 kN to 3 kN, bending moments in the right lower extremity exceeded 300 Nm in the sedan impacts but were substantially lower in impacts with the MPV. The right tibia bent predominantly in the medial direction during the impact whereas bi-modal patterns were observed in the sagittal bending moment time histories of the femora. Stature differences caused variations in hip and knee impact locations relative to the hood edge and bumper of each vehicle that may have been a contributing factor resulting in more severe struck-side lower extremity injuries in the tall subject tested with the MPV, and more severe struck-side lower extremity injuries in the shorter subject tested with the sedan.