Partial Trapeziotrapezoid Resection and Thumb Range of Movement After Trapeziometacarpal Joint Fusion-A Biomechanical Study.

PURPOSE: Trapeziometacarpal (TMC) joint arthrodesis is an effective treatment for stage III osteoarthritis. Although this procedure alleviates thumb pain and restores grip power and pinch strength, persistent limitation of thumb movement is inevitable. This biomechanical study aimed to investigate the altered kinematics of thumb circumduction motion after TMC joint arthrodesis and subsequent excision of the trapeziotrapezoid (TT) and trapezio-second metacarpal (T-2MC) joint spaces. METHODS: Eight cadaver upper extremities were mounted on a custom testing apparatus. The hand and carpal bones were fixed to the apparatus, except for the first metacarpal bone, trapezium, and trapezoid. A 50-g load was applied at the tip of the first metacarpal head to generate passive thumb circumduction. An electromagnetic tracking system measured the angular and rotational displacement of the first metacarpal. All specimens were tested in 4 conditions: intact, after simulated TMC joint fusion, after subsequent excision of 3 mm of bone at the TT joint space, and after additional 3 mm resection at the T-2MC joint space. RESULTS: After simulated TMC arthrodesis, the range of angular motion of thumb circumduction decreased to 25% that of the intact thumb. Subsequent resections at the TT and T-2MC joint spaces increased circumduction ranges to 49% (TT joint) and 73% (TT plus T-2MC joints) that of the intact thumb. The range of thumb rotational motion showed a similar trend. CONCLUSIONS: Trapeziometacarpal arthrodesis decreased the range of both angular and rotational motion during thumb circumduction. Subsequent resections at the paratrapezial space increased the range of thumb motion, suggesting that hypermobility of the paratrapezial joints increases thumb mobility after TMC joint fusion. CLINICAL RELEVANCE: Patients with hypermobile paratrapezial joints may have larger thumb movement after TMC joint fusion. Additional resections of the TT and T-2MC joint spaces may further mobilize the thumb in patients who complain of stiffness after TMC fusion.

Biomechanical Effects of Radioscapholunate Fusion With Distal Scaphoidectomy and Triquetrum Excision on Dart-Throwing and Wrist Circumduction Motions.

PURPOSE: Distal scaphoid and triquetrum excisions can improve the range of wrist motion after radioscapholunate (RSL) fusion, but little is known about the kinematics of dart-throwing and global circumduction motions. We hypothesized that these excisions could increase the range of motion without causing midcarpal instability. METHODS: Seven fresh-frozen cadaver upper extremities were mounted on a testing apparatus after isolation and preloading of the tendons of the flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis, and extensor carpi ulnaris. Sequential loadings of the flexor carpi ulnaris and extensor carpi radialis simulated active dart-throwing motion. Passive circumferential loading produced the wrist circumduction motion. We measured the range of wrist motions with an electromagnetic tracking system in 4 experiments: intact, simulated RSL fusion, RSL fusion with distal scaphoid excision, and RSL fusion with distal scaphoid and total triquetrum excisions. To evaluate midcarpal stability, we conducted passive mobility testing of the distal carpal row in the radial, volar, ulnar, and dorsal directions. RESULTS: Radioscapholunate fusion decreased the dart-throwing motion to a mean of 46% of the baseline value; distal scaphoid and triquetrum excisions increased the mean arc to 50% and 62%, respectively. Radioscapholunate fusion diminished the wrist circumduction to a mean of 43% of the baseline value, which increased to a mean of 58% and 74% after distal scaphoid and triquetrum excision, respectively. A significant increase in radial deviation was noted after distal scaphoid excision, and subsequent triquetrum excision significantly increased motion in the ulnar-palmar direction. Regarding midcarpal stability, dorsal translation significantly increased after distal scaphoid and triquetrum excisions. CONCLUSIONS: Distal scaphoid and triquetrum excision after RSL fusion improved both dart-throwing and circumduction motions, but dorsal midcarpal instability occurred. CLINICAL RELEVANCE: Subsequent carpal excisions may improve short-term outcome by increasing motions in a RSL-fused wrist; however, a potential risk of midcarpal instability should be considered.

Tamai Zone 1 Fingertip Amputation: Reconstruction Using a Digital Artery Flap Compared With Microsurgical Replantation.

PURPOSE: The surgical treatment of fingertip amputations is controversial. This study was designed to compare the clinical results of 2 surgical procedures for fingertip amputation: reconstruction with a digital artery flap and microsurgical replantation. METHODS: Between 2003 and 2015, 37 patients with Tamai zone 1 fingertip amputation of the index or middle finger were treated by reconstruction with a digital artery flap (n = 23) or microsurgical replantation (n = 14). Data for these patients were evaluated retrospectively. Nerve suture was not conducted in microsurgical replantation because spontaneous sensory recovery is expected in zone 1 replantation. Primary outcomes included hand dexterity (Purdue Pegboard Test), and disability of the upper extremity (Disabilities of the Arm, Shoulder, and Hand score). Secondary outcomes included strength (key pinch), digital sensitivity (Semmes-Weinstein test), and finger mobility (% total active motion). RESULTS: The average follow-up period was 34 months. There was no significant difference in the primary outcomes between the 2 groups. The reconstruction group showed significantly better results for the secondary outcomes. CONCLUSIONS: This study suggests that the 2 procedures were comparable regarding postoperative activities of daily living and hand performance, but reconstruction using a digital artery flap gave better objective functional outcomes than microsurgical replantation. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Arthroscopic Distal Scaphoid Resection for Isolated Scaphotrapeziotrapezoid Osteoarthritis.

PURPOSE: To investigate the radiographic and clinical results of arthroscopic distal scaphoid resection for isolated scaphotrapeziotrapezoid (STT) osteoarthritis and analyze the radiographic parameters associated with the functional outcomes. METHODS: From 2008 to 2014, 17 wrists with symptomatic isolated STT osteoarthritis without carpal deformity underwent arthroscopic distal scaphoid resection. We evaluated visual analog scale (VAS) scores for pain, grip strength, pinch strength, and Patient-Rated Wrist Evaluation (PRWE) scores before surgery and at the final follow-up. We analyzed correlations between the resection height and the radiographic and functional outcomes. RESULTS: The average follow-up period was 42 months. The average VAS score improved from 6.1 ± 2.3 before surgery to 1.7 ± 1.9 after surgery. The average grip strength improved from 18 ± 6 to 19 ± 9 kg, pinch strength from 2.5 ± 1.1 to 4.4 ± 1.7 kg, and PRWE score from 52 ± 23 to 32 ± 24. Carpal deformity (C-L angle of > 15°) was seen in 2 patients at the final follow-up. The deformity was more likely to occur when the resection height was greater than 3 mm. CONCLUSIONS: Arthroscopic distal scaphoid resection alone can reduce pain and improve functional outcomes for early to mid-stage isolated STT osteoarthritis in patients without dorsal intercalated segment instability deformity. Resection of greater than 3 mm of the distal scaphoid may result in carpal malalignment. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Three-Dimensional Kinematic Analysis of the Distal Radioulnar Joint in the Axial-Loaded Extended Wrist Position.

PURPOSE: To assess the wrist joints of healthy volunteers in extended and loaded states versus the unloaded state by using computed tomography (CT) to analyze the in vivo 3-dimensional movements in the distal radioulnar joint (DRUJ). METHODS: The dominant arms of 9 volunteers with healthy wrists were studied. We mounted a compression device onto the elbows in an inverted position. A 0-kg and 7-kg load each was applied during low-dose radiation CT imaging and a bone model was produced. We marked the insertion sites for the 4 radioulnar ligaments stabilizing the DRUJ: palmar superficial radioulnar ligament (PS-RUL), dorsal superficial radioulnar ligament (DS-RUL), dorsal deep radioulnar ligament (DD-RUL), and palmar deep radioulnar ligament (PD-RUL). Using Marai's method, each ligament was virtualized and the length of each simulated ligament was measured. We also computed the 3-dimensional displacement and corresponding rotation of the distal ulna where it comes into contact with the radius in the sigmoid notch. RESULTS: The lengths of palmar ligaments (PS-RUL and PD-RUL) increased significantly under loaded conditions, and although not significant, the length of dorsal ligaments (DS-RUL and DD-RUL) tended to increase. When the wrist was loaded, the ulna rotated toward the open palmar side. CONCLUSIONS: The length of simulated radioulnar ligaments increased when the wrist joint was loaded in an extended position. This kinematic movement of DRUJ separation under a loading condition is different from physiological active movement. CLINICAL RELEVANCE: The 3-dimensional kinematic analysis revealed that palmar radioulnar ligaments were stretched during axial loading, suggesting that a tear of the palmer ligament can result from a fall on an outstretched hand.

Predictors of Hand Dexterity after Single-Digit Replantation.

BACKGROUND: Microsurgical replantation of the thumb and digits has become an increasingly familiar technique in clinical practice worldwide. However, successful digit replantation does not always provide better hand function than revision amputation. Little information is available regarding predictors of motor skill activities of replanted hands. Therefore, we retrospectively evaluated hand dexterity after single-digit replantation at a minimum follow-up of 1 year and analyzed the factors influencing dexterity. METHODS: This retrospective cohort study included 23 patients treated for amputation injuries at our institution from 2014 to 2015. Patients with amputations from Tamai's zone 2 to 5 of the thumb (3 patients), index finger (11 patients), or middle finger (9 patients) who underwent digital replantation surgery and were followed up for more than 1 year were included. Follow-up evaluations were conducted at an average of 23 months postoperatively (range: 13-25 months). We hypothesized that possible factors influencing hand dexterity after single-digit replantation were patient age, injured finger, key pinch strength, Semmes-Weinstein test result, and percentage of total active motion. Relationships between the outcome variable, which was the result of the Purdue Pegboard Test of hand dexterity, and explanatory variables were analyzed using Spearman's correlation coefficient. A p-value of < 0.05 indicated statistical significance. RESULTS: No postoperative complications occurred. Univariate analysis indicated that decreased hand dexterity after single-digit replantation was significantly associated with older age (p = 0.001) and poor recovery of sensation, as shown by the Semmes-Weinstein test (p = 0.012). CONCLUSION: Patient age was a risk factor for low hand dexterity after replantation surgery. Recovery of finger sensitivity enhanced dexterity of motor skill activities following finger replantation surgery.

Magnetic resonance imaging analysis of the extensor carpi ulnaris tendon and distal radioulnar joint in triangular fibrocartilage complex tears.

BACKGROUND: We compared the incidence of extensor carpi ulnaris (ECU) tendon and distal radioulnar joint (DRUJ) abnormalities using magnetic resonance imaging (MRI) between patients with triangular fibrocartilage complex (TFCC) tears and subjects without ulnar wrist pain. Additionally, we aimed to identify potential predictors of these MRI lesions. METHODS: The TFCC group comprised 70 consecutive patients with TFCC tears. The control group comprised 70 age- and sex-matched subjects without ulnar wrist pain. We evaluated the presence or absence of fluid collection in the DRUJ and ECU peritendinous area and longitudinal ECU tendon splitting. Dimensions of the fluid collection area around the ECU tendon were measured to evaluate the severity. The incidences of these abnormal MRI findings were compared between the two groups. We analyzed the correlation between the presence of ECU tendon and DRUJ lesions and variables including age, magnitude of ulnar variance, and type of TFCC tear. RESULTS: Significant differences were found between the two groups in the incidence of fluid collection of the DRUJ and ECU peritendinous area, and longitudinal ECU tendon splitting. Among the 70 patients with TFCC tears, age and the magnitude of ulnar variance were significantly correlated with the severity of fluid collection around the ECU tendon. The magnitude of ulnar variance in patients with DRUJ fluid collection was significantly larger than that in patients without fluid collection. There was a significant correlation between the presence of disc tears and DRUJ fluid collection. CONCLUSION: We found a higher incidence of accompanying abnormal MRI findings of the ECU tendon and DRUJ in patients with TFCC tears than in the control group. The presence of disc tears, the magnitude of ulnar variance, and age may be risk factors for these MRI lesions associated with TFCC tears.

Biomechanical study of isolated radial head dislocation.

BACKGROUND: Isolated radial head dislocation is a rare injury with an unclear pathomechanism, and the treatment is controversial. The purpose of the present study was to investigate the biomechanical contributions of the annular ligament, quadrate ligament, interosseous membrane, and annular ligament reconstructions to proximal radioulnar joint stability. METHODS: Five fresh frozen cadaveric upper extremities were amputated above the elbow and solidly fixed on a customized jig. Radial head dislocation was reproduced by sequential sectioning of ligamentous structures and passive mobility testing. Radial head displacement during mobility testing was measured with an electromagnetic tracking device in three forearm rotation positions. The data were compared among different sectioning stages and between two types of simulated ligamentous reconstruction. RESULTS: Lateral displacement of the radial head significantly increased in the neutral forearm rotation after annular ligament sectioning (46 ± 10%, p < 0.05). After quadrate ligament sectioning, we found significant posterior (67 ± 36%, p < 0.05) and lateral (74 ± 24%, p < 0.01) displacement in neutral forearm rotation and pronation. Significant radial head displacement was found in all directions and in all forearm positions after sequential sectioning of the proximal half of the interosseous membrane. Anatomical annular ligament reconstruction stabilized the proximal radioulnar joint except for anterior laxity in neutral forearm rotation (15 ± 6%, p < 0.05). The radial head with Bell Tawse procedure was significantly displaced in all directions. CONCLUSION: The direction of radial head instability varied depending on the degree of soft tissue sectioning and specific forearm rotation. Anterior radial head dislocation may involve more severe ligament damage than other types of dislocation. Anatomical annular ligament reconstruction provided multidirectional radial head stability.

Predictors of Proximal Interphalangeal Joint Flexion Contracture After Homodigital Island Flap.

PURPOSE: To identify independent predictors of postoperative proximal interphalangeal (PIP) joint contracture after direct-flow homodigital island flap transfer. METHODS: Forty-four fingertip amputations in 39 patients treated with oblique triangular flaps were evaluated at a minimum of 1 year after surgery. Five variables were examined: patient age, injured finger, mechanism of injury, flap advancement distance, and time required for wound healing. Univariate and multivariate linear regression analyses were performed to identify the extent to which these variables affected the flexion contracture of the PIP joint. RESULTS: The average reduction in the passive extension angle of the PIP joint was 16° at final follow-up. Univariate analysis indicated significant correlations of PIP joint flexion contracture with age, injured finger, and time for wound healing, but no significant correlation with the distance the flap was advanced. Multivariate analysis indicated that the age and duration of wound healing were independent predictors of the flexion contracture of the PIP joint. CONCLUSIONS: Elderly people and cases with delayed wound healing are at risk for postoperative PIP joint contracture after homodigital flap transfer. Intervention with early hand therapy and orthotics may be useful in elderly patients with delayed wound healing. TYPE OF STUDY/LEVEL OF EVIDENCE: Prognostic II.

Pressure and tendon strain in the sixth extensor compartment of the wrist during simulated provocative maneuvers for diagnosing extensor carpi ulnaris tendinitis.

BACKGROUND: Various provocative maneuvers for diagnosing extensor carpi ulnaris (ECU) tendinitis have been reported; however, it remains unclear which maneuver is the most sensitive to detect ECU tendinitis. To clarify this, we investigated and compared the extratendinous pressure and ECU tendon strain in the sixth extensor compartment of the wrist during various provocative maneuvers for diagnosing ECU tendinitis. METHODS: Nine upper extremities from nine fresh-frozen cadavers were examined. We investigated extratendinous pressure in the ECU fibro-osseous tunnel of the distal ulna and ECU tendon strain during eight forearm positions-neutral rotation, pronation, supination, pronation with wrist flexion, supination with wrist flexion, supination with wrist extension, both hand and forearm supination, and supination with ECU full loading-to simulate provocative maneuvers reported to detect ECU tendinitis. RESULTS: Pressure was significantly higher during both hand and forearm supination (carpal supination test) and during supination with wrist extension (prayer's hand supination test) than during neutral rotation. The pressure during the carpal supination test was 3 times higher than that during the prayer's hand supination test and 27 times higher than that during the neutral position. Strain was significantly higher during the carpal supination test and during supination with ECU full loading (the ECU synergy test) than during other maneuvers. CONCLUSIONS: Both pressure and tendon strain increased most notably during the carpal supination test compared to the other maneuvers, which suggests that the carpal supination test is the most sensitive for the detection of ECU tendinitis.

The utility of the phosphate binder, ferric citrate hydrate (JTT-751), about phosphorus absorption-reducing effect in normal rats.

Hyperphosphatemia is a risk factor for arterial calcification contributing to the high-cardiovascular mortality in patients with chronic kidney disease (CKD). Ferric citrate hydrate (JTT-751) is being developed as a treatment for hyperphosphatemia with chronic renal failure and has shown a serum phosphorus-lowering effect in CKD patients. In this study, we evaluated the combination effect of JTT-751 with the phosphorus absorption-reducing effect of calcium carbonate and compared phosphorus absorption-reducing efficacy between three phosphate binders including JTT-751. Normal rats were fed a diet containing either 1% calcium carbonate, 1% JTT-751 or 1% JTT-751 with 1% calcium carbonate, for 7 days. Both 1% calcium carbonate and 1% JTT-751 alone reduced urinary phosphorus excretion, and the combined treatment reduced it more than each single-treatment, without clearly influencing calcium or iron-metabolism. Next, normal rats were fed a diet containing either 0.3, 1 and 3% lanthanum carbonate or 2.3% JTT-751, for 7 days. Either 3% lanthanum carbonate or 2.3% JTT-751 reduced urinary phosphorus excretion. Finally, we compared the reduced amount of urinary phosphorus excretion per dose of compound, of which JTT-751 is comparable to that of calcium carbonate and is greater than that of the lanthanum carbonate. In conclusion, JTT-751 showed an additive effect on the phosphorus absorption-reducing effect of calcium carbonate without influencing calcium- and iron-metabolism, and had a phosphorus absorption-reducing efficacy comparable to or greater than other existing phosphate binders.

Symptomatic Congenital Coalition of the Pisiform and Hamate - A Case Report.

We describe a 13-year-old boy with piso-hamate coalition confirmed by X-ray. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed type 1 coalition according to the classification of DeVilliers Minnaar. Piso-hamate coalition is rare, and suspicions should be raised in instances of chronic ulnar-sided wrist pain, particularly in individuals with a history of elevated hand usage, especially amongst athletes engaging in intensive hand grip activities. Surgical resection of the synchondrosis site between the pisiform and the hamate is an efficacious intervention that can mitigate pain. Level of Evidence: Level V (Therapeutic).

Characterization of pathological stages in a mouse model of progressive multiple sclerosis.

The purpose of this study was to analyze and elucidate the mechanisms of non-obese diabetes-experimental autoimmune encephalomyelitis (NOD-EAE), an animal model of progressive multiple sclerosis (MS), and to compare the pathological features with those observed in human progressive MS. Pathological analysis, flow cytometry analysis, immunohistochemical staining, and transcriptome analysis were performed at each pathological stage of the NOD-EAE mice to characterize each pathological stage in the lesion. The NOD-EAE mice showed a biphasic pattern of disease progression once in remission. The longitudinal profile of demyelination and inflammatory cell infiltration in the spinal cord was consistent with the pathological score. In the chronic phase of the disease, fibrosis and lymph follicle formation, characteristic of progressive human MS, were observed. Here we describe the pathological profile and transcriptome analysis of the NOD-EAE mice and verify that this model has similar features to those of human progressive MS. Our findings suggest that this model recapitulates lymph follicle formation, a disease hallmark of progressive MS, and fibrosis, a feature complicating the pathogenesis of MS in the chronic phase. This model may be useful for evaluating the efficacy of therapeutic agents and for mechanistic analysis.

Ferric citrate hydrate, a new phosphate binder, prevents the complications of secondary hyperparathyroidism and vascular calcification.

BACKGROUND/AIMS: Ferric citrate hydrate (JTT-751) is being developed as a treatment for hyperphosphatemia in chronic kidney disease patients, and shows serum phosphorus-reducing effects on hyperphosphatemia in hemodialysis patients. We examined whether JTT-751 could reduce phosphorus absorption in normal rats and prevent the progression of ectopic calcification, secondary hyperparathyroidism and bone abnormalities in chronic renal failure (CRF) rats. METHODS: Normal rats were fed a diet containing 0.3, 1 or 3% JTT-751 for 7 days. The effects of JTT-751 on phosphorus absorption were evaluated with fecal and urinary phosphorus excretion. Next, a CRF model simulating hyperphosphatemia was induced by feeding rats a 0.75% adenine diet. After 21 days of starting the adenine diet feeding, 1 or 3% JTT-751 was administered for 35 days by dietary admixture. The serum phosphorus levels and mineral parameters were measured. Calcification in the aorta was examined biochemically and histopathologically. Hyperparathyroidism and bone abnormalities were evaluated by histopathological analysis of the parathyroid and femur, respectively. RESULTS: In normal rats, JTT-751 increased fecal phosphorus excretion and reduced phosphorus absorption and urinary phosphorus excretion. In CRF rats, JTT-751 reduced serum phosphorus levels, the calcium-phosphorus product and calcium content in the aorta. Serum intact parathyroid hormone levels and the incidence and severity of parathyroid hyperplasia were also decreased. JTT-751 reduced femoral bone fibrosis, porosity and osteoid formation. CONCLUSIONS: JTT-751 could bind with phosphate in the gastrointestinal tract, increase fecal phosphorus excretion and reduce phosphorus absorption. JTT-751 could prevent the progression of ectopic calcification, secondary hyperparathyroidism and bone abnormalities in rats.

AQDnet: Deep Neural Network for Protein-Ligand Docking Simulation.

We have developed an innovative system, AI QM Docking Net (AQDnet), which utilizes the three-dimensional structure of protein-ligand complexes to predict binding affinity. This system is novel in two respects: first, it significantly expands the training dataset by generating thousands of diverse ligand configurations for each protein-ligand complex and subsequently determining the binding energy of each configuration through quantum computation. Second, we have devised a method that incorporates the atom-centered symmetry function (ACSF), highly effective in describing molecular energies, for the prediction of protein-ligand interactions. These advancements have enabled us to effectively train a neural network to learn the protein-ligand quantum energy landscape (P-L QEL). Consequently, we have achieved a 92.6% top 1 success rate in the CASF-2016 docking power, placing first among all models assessed in the CASF-2016, thus demonstrating the exceptional docking performance of our model.

Reliability and clinical importance of teardrop angle measurement in intra-articular distal radius fracture.

PURPOSE: The teardrop angle (TDA) is a newly characterized radiographic parameter that some authors propose as an indicator of articular incongruity of the lunate facet. The purposes of this study were to investigate intra-observer and interobserver reliability of the measurements of the TDA and to determine whether the TDA is a reliable indicator of articular step and gap formation after distal radius fracture. METHODS: We studied radiographs of 24 uninjured wrists and 24 wrists with intra-articular distal radius fractures. On standard and 10° tilt views of lateral wrist radiographs, the teardrop represents the volar rim of the lunate facet, and the TDA is defined as the angle between the central axis of the teardrop and the radial shaft. We examined interobserver and intra-observer reliability for 3 observers using the intraclass correlation coefficient (ICC) for measurements of the uninjured and fractured wrists. For subjects with fractures, we determined correlation of the TDA-volar tilt with the articular step and gap measured by computed tomography using simple linear regression. RESULTS: There was almost perfect intra-observer (ICC = 0.95) and interobserver (ICC = 0.93) reliability in the fractured wrists. We observed substantial intra-observer (ICC = 0.64) and fair interobserver (ICC = 0.28) reliability in the uninjured wrists on the standard lateral radiographs. On the 10° tilt views, intra-observer and interobserver reliability in the uninjured wrists increased to substantial levels (ICC = 0.76 and 0.61, respectively). The TDA-volar tilt was significantly associated with articular step and gap on computed tomography. CONCLUSIONS: The TDA, measured on the lateral radiograph of the wrist, exhibits higher intra-observer and interobserver reliability in fractured wrists compared with uninjured wrists. On the 10° tilt views, the reliability increased in the uninjured wrists. Measurement of the TDA in plain radiographs may allow direct estimation of articular incongruity as seen on sagittal computed tomography reconstruction images.

Distal radioulnar joint stress radiography for detecting radioulnar ligament injury.

PURPOSE: To determine the reliability and efficacy of clenched-fist stress radiographs in patients with radioulnar ligament injury. METHODS: We examined 30 patients with chronic radioulnar ligament injury. These patients underwent stress radiography, which included clenched-fist posteroanterior (PA) views in forearm pronation and computed tomography in pronation. We measured distal radioulnar joint (DRUJ) gap distance and ulnar variance using clenched-fist PA views. We measured the radioulnar ratio with pronated computed tomography to quantify dorsal translation of the ulnar head. We analyzed these radiographic data and compared them between the injured and contralateral sides. We examined test-retest reliability and interobserver and intraobserver reliability using intraclass correlation coefficients as a measurement of the DRUJ gap distance in clenched-fist PA views. RESULTS: The DRUJ gap distance observed with clenched-fist PA views in injured wrists was significantly greater than in the contralateral side. The DRUJ gap distance observed with stress radiography significantly correlated with the magnitude of the radioulnar ratio in forearm pronation. We found a significant test-retest reliability for measuring DRUJ gap distance using clenched-fist PA views, as well as a significant level of intraobserver and interobserver reliability. CONCLUSIONS: The DRUJ gap distance observed with clenched-fist PA radiography in forearm pronation was a reliable parameter and may be useful for evaluating DRUJ instability. TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic II.

Ulnar variance: its relationship to ulnar foveal morphology and forearm kinematics.

PURPOSE: It is unclear how individual differences in the anatomy of the distal ulna affect kinematics and pathology of the distal radioulnar joint. This study evaluated how ulnar variance relates to ulnar foveal morphology and the pronosupination axis of the forearm. METHODS: We performed 3-dimensional computed tomography studies in vivo on 28 forearms in maximum supination and pronation to determine the anatomical center of the ulnar distal pole and the forearm pronosupination axis. We calculated the forearm pronosupination axis using a markerless bone registration technique, which determined the pronosupination center as the point where the axis emerges on the distal ulnar surface. We measured the depth of the anatomical center and classified it into 2 types: concave, with a depth of 0.8 mm or more, and flat, with a depth less than 0.8 mm. We examined whether ulnar variance correlated with foveal type and the distance between anatomical and pronosupination centers. RESULTS: A total of 18 cases had a concave-type fovea surrounded by the C-shaped articular facet of the distal pole, and 10 had a flat-type fovea with a flat surface without evident central depression. Ulnar variance of the flat type was 3.5 ± 1.2 mm, which was significantly greater than the 1.2 ± 1.1 mm of the concave type. Ulnar variance positively correlated with distance between the anatomical and pronosupination centers. CONCLUSIONS: Flat-type ulnar heads have a significantly greater ulnar variance than concave types. The pronosupination axis passes through the ulnar head more medially and farther from the anatomical center with increasing ulnar variance. CLINICAL RELEVANCE: This study suggests that ulnar variance is related in part to foveal morphology and pronosupination axis. This information provides a starting point for future studies investigating how foveal morphology relates to distal ulnar problems.

Biomechanical study of the extensor carpi ulnaris as a dynamic wrist stabilizer.

PURPOSE: To investigate the dynamic stabilizing effect of the extensor carpi ulnaris (ECU) on the distal radioulnar joint (DRUJ) and the ulnocarpal joint in a simulated model of triangular fibrocartilage complex (TFCC) injury. METHODS: Using 8 fresh-frozen cadavers, we fixed the humerus and ulna at 90° of elbow flexion, and the radius and hand were allowed to rotate freely around the ulna. Passive mobility was tested by translating the radiocarpal unit relative to the ulna along dorsal-palmar directions. Unit displacement was measured by an electromagnetic tracking device in different forearm rotations and under varied loading to the wrist motor tendons. Magnitudes of displacement were compared between different loading patterns of the prime wrist movers in the TFCC-sectioned wrists. The effect of sectioning the ECU subsheath was analyzed. RESULTS: When physiological loads were applied to all of the prime wrist movers, the magnitude of displacement during passive mobility testing decreased in supination and neutral rotation. After ECU tendon loading was released, mobility increased again in supination and neutral rotation. When the load was applied only to the ECU tendon, mobility decreased in supination and neutral rotation as compared with unloaded. Little change in the mobility was found in pronation regardless of the tendon loading pattern. After sectioning of the ECU subsheath, the stabilizing effect of the ECU decreased in neutral rotation. CONCLUSIONS: In a neutral wrist position with complete sectioning of the TFCC, the ECU dynamically stabilized the DRUJ and the ulnocarpal joint in supination and neutral forearm rotation. The ECU subsheath assisted ECU tendon stabilization on the ulnar side of the wrist, especially in the neutral rotation. CLINICAL RELEVANCE: Maintaining the ECU and its subsheath may reduce DRUJ instability in patients with TFCC injuries.

Predictors of distal radioulnar joint instability in distal radius fractures.

PURPOSE: A tear of the triangular fibrocartilage complex (TFCC) is the most frequent soft tissue injury associated with fractures of the distal radius, and repair of the deep ligamentous portion of the TFCC is considered when the tear contributes to instability of the distal radioulnar joint (DRUJ). The purpose of this prospective cohort study was to identify predictors of DRUJ instability accompanying unstable distal radius fractures. METHODS: Between 2002 and 2007, we prospectively treated 163 consecutive patients with unstable distal radius fractures with the volar locking plating system. Complete radioulnar ligament tears representing DRUJ instability were present in 11 of 163 distal radius fractures. We tested univariate associations between DRUJ instability and potential predictors and conducted multivariate analysis to establish independent predictors of instability. We applied receiver operating characteristics curves within the significant risk factors to determine threshold values. RESULTS: In univariate analyses, only the radial and sagittal translation ratios of the fracture site were significant predictors of DRUJ instability. Multivariate logistic regression analysis confirmed that the radial translation ratio, which corresponds to a normalized DRUJ gap, was a significant risk factor. According to the receiver operating characteristics curve for the radial translation ratio, the area under the curve was 0.89. A cutoff value of 15% for the radial translation ratio showed the highest diagnostic accuracy rate. CONCLUSIONS: A radiographic finding of a normalized DRUJ gap on posteroanterior views was the most important predictor to identify DRUJ instability accompanying unstable distal radius fractures. The relative risk of instability increases by 50% when the ratio of DRUJ widening increases by 1%.