Biomechanical analysis of two ulnar head prostheses

The biomechanical effectiveness of 2 ulnar head prostheses was evaluated in 5 fresh-frozen cadaver arms. By using electromagnetic sensors, the amount of forearm rotation, diastasis, and dorsal/palmar subluxation of the radius at the level of the sigmoid notch was measured with the forearm in neutral rotation, pronation, and supination with and without dorsal/palmar loading. Testing was done in the intact specimens and after insertion of 2 types of ulnar head prostheses. Dynamic forearm rotation was also achieved by applying loads in the line of action of the appropriate pronator or supinator muscles to obtain a centroidal path of the radius relative to the ulna. Overall after ulnar head replacement forearm rotation lessened in pronation, diastasis decreased in most forearm positions, and subluxation increased in supination compared with the intact specimen. Despite these changes, both prostheses maintained near-normal biomechanics of the distal radioulnar joint when compared with the irregular behavior occurring after distal ulna resection. Therefore these prostheses are suggested for restoration of distal radioulnar joint function.     

Changes in length of the radioulnar ligament and distal oblique bundle after Colles' fracture

Abstract

The purpose of this study was to investigate changes in length of the radioulnar ligament and distal oblique bundle (DOB) within the distal interosseous membrane after Colles' fracture and correlate the magnitude of the changes in length with clinical features. This study investigated 10 patients with malunion of a Colles' fracture. In three-dimensional computed tomography, the paths of the four limbs of the radioulnar ligament (superficial and deep, dorsal, and palmar limbs) and DOB were modelled and each path length was computed. Differences in length between the affected and contralateral unaffected side were calculated and correlated with the radiographic parameters of deformity on plain X-ray, subluxation of the DRUJ on CT, and limited range of forearm rotation in the clinical examination. In the malunited radius, the superficial and deep dorsal limbs of the radioulnar ligament were significantly elongated and DOB was significantly shortened compared with the contralateral side. These length changes correlated with radiographic radial shortening, subluxation of the DRUJ, and inversely correlated with limited range of forearm pronation. This study suggests that the dorsal radioulnar ligament would be overstretched and disrupted in Colles' fracture with severely increased radial shortening, producing laxity of the distal radioulnar joint that could negate limitation of pronation.     

In vivo three-dimensional displacement of the distal radioulnar joint during resisted forearm rotation

PURPOSE: The in vivo displacement of the distal radioulnar joint (DRUJ) while under resisted pronation or supination has never been previously quantified. Being a joint with 3 dimensions of motion (dorsopalmar translation, changes in ulnar variance, and radioulnar coaptation), our purpose was to determine its 3-dimensional (3D) displacement during resisted rotational torque. METHODS: Ten normal subjects (aged 31.8 years+/-7.8; F, 5; M, 5) were recruited. Computed tomography scans of a subjects' distal forearms were obtained while grasping the handles of a custom apparatus to keep the fist and forearm in neutral rotation. Scanning was performed in 3 conditions: no rotational torque (control), maximum isometric supination, and maximum isometric pronation. The 3D displacement of the DRUJ, using the ulnar fovea as the reference point, during isometric rotational torque was determined using markerless bone registration techniques. RESULTS: The mean 3D displacement of the ulnar fovea during maximum isometric pronation and maximum isometric supination was 3.09 mm+/-0.94 and 2.17 mm+/-1.55, respectively. During maximum isometric pronation, the ulnar fovea displaced a mean of 0.51 mm+/-1.79 dorsally. During maximum isometric supination, the ulnar fovea displaced a mean of 0.13 mm+/-2.07 volarly. In both conditions, ulnar variance increased (0.23 mm+/-2.52 for isometric pronation and 0.44 mm+/-1.57 for isometric supination), and there was increased radioulnar coaptation (0.37 mm+/-0.86 for isometric pronation, 0.039 mm+/-0.66 for isometric supination). CONCLUSIONS: Resisted rotational torque can be applied to the DRUJ while in neutral rotation during computed tomography imaging, producing measurable displacements in 3D. This technique of studying the DRUJ has the potential to improve our ability to detect and quantify instabilities of the DRUJ.     

Ulnar bursa distention following volar subluxation of the distal radioulnar joint after distal radial fracture: a rare cause of carpal tunnel syndrome

This report describes an eighty-four-year-old woman with persistent carpal tunnel syndrome attributable to an ulnar bursa distention associated with the subluxation of the distal radioulnar joint after distal radial fracture. During surgery, when the forearm was placed in supination, the ulna head with a sharp osteophyte was found to be displaced into the carpal tunnel through a defect of the ruptured capsule of the wrist joint. This volar subluxation of the ulnar head had caused distention of the ulnar bursa, causing compression of the median nerve, which resulted in carpal tunnel syndrome. In addition to reduce displaced fractured segment to obtain anatomic articular surface, original radial length and tilt, the anatomic restoration of the distal radioulnar joint is essential to maintain better long-term function after fracture of the distal radius.     

Three-dimensional in vivo kinematics of the distal radioulnar joint in malunited distal radius fractures

How malunion of the distal radius affects the kinematics of the distal radioulnar joint in vivo was evaluated. A novel computed tomography image-based technique was used to quantify radioulnar motion in both wrists of 9 patients who had unilateral malunited distal radius fractures. In the injured wrists dorsal angulation averaged 21 degrees +/- 6 degrees, radial inclination averaged 18 degrees +/- 5 degrees, and radial shortening averaged 21 +/- 3 mm. Clinically, the average range of motion of the injured wrists was 75 degrees +/- 25 degrees pronation and 73 degrees +/- 23 degrees supination. Kinematics of the radius during pronation and supination in the malunited forearms was indistinguishable from that in the uninjured forearms. In both the axis of rotation of the radius passed through the center of the ulnar head, although it shifted slightly ulnar and volar in supination and radial and dorsal during pronation. In contrast to previous in vitro biomechanical findings, there was no dorsovolar radial translation at the extremes of pronation or supination and no translation of the radius along the rotation axis. Soft tissues may play a larger role in limiting function than previously appreciated, and treatment may require correction of altered soft tissue structures as well as any abnormal bone anatomy.     

Ulnar-positive variance as a predictor of distal radioulnar joint ligament disruption

PURPOSE: Previous cadaveric data show that disruption of the triangular fibrocartilage complex (TFCC) at the wrist allows 0.5 to 3.0 mm of proximal radius migration. Anatomic studies have documented the presence of superficial and deep fibers of both the palmar and the dorsal distal radioulnar joint (DRUJ) ligaments. The aim of this study was to determine the contribution of the superficial and deep fibers of the DRUJ ligaments to longitudinal forearm stability as measured by ulnar-positive variance. METHODS: Eight fresh-frozen cadaver specimens were included in this study. Each specimen was secured with external fixation clamps to a sequential loading frame with the elbow in 90 degrees of flexion and the forearm and wrist in neutral pronation supination, neutral ulnar-radial deviation, and neutral volar-dorsal angulation. The radial head was resected and a force gauge was applied to the proximal radius. The peripheral TFCC was identified through an incision between the fifth and sixth extensor compartments and the dorsal capsulotomy of the DRUJ capsule. After baseline measurement sequential transection of the superficial and deep fibers of the TFCC was performed. Before and after each step load application and removal were performed by attaching an 88.90-N weight to the end of a force gauge and via longitudinal traction on the proximal part of the radius, and ulnar variance was measured with wrist fluoroscopy. RESULTS: Transection of the superficial TFCC fibers resulted in radius migration of 0.70 mm. This migration, however, was not significantly different from that observed at baseline. After both the superficial and deep TFCC fibers were transected the radius migrated proximately with load. This change of ulnar variance was significantly greater than that observed at baseline or after transection of only the superficial TFCC fibers. CONCLUSIONS: Traumatic injury to the TFCC with radiographic evidence of ulnar-positive variance may be an indication of disruption of the deep TFCC fibers.     

Condylar blade plate fixation of unstable fractures of the distal ulna associated with fracture of the distal radius

PURPOSE: To review the results of condylar blade plate fixation of unstable fractures of the distal ulna associated with fracture of the distal radius. METHODS: Twenty-four patients in whom a minicondylar blade plate was used to repair an unstable fracture of the distal ulna associated with a fracture of the distal radius were reviewed retrospectively an average of 26 months (range, 12-50 months) after injury. According to the Q modifier of the Comprehensive Classification of Fractures, there were 1 simple fracture of the ulnar neck (Q2), 20 comminuted fractures of the ulnar neck (Q3), and 3 fractures of the head and neck (Q5). Subsequent surgeries included repeat fixation and autogenous cancellous bone grafting in 2 patients with nonunion of the distal radius and 1 with nonunion of the distal ulna. Seven patients had a second operation to remove the ulnar plate secondary to discomfort from plate prominence. RESULTS: The final average motion was as follows: degrees of flexion (range, 30 degrees-80 degrees), 52 degrees of extension (range, 40 degrees-90 degrees), 76 degrees of pronation (range, 45 degrees-90 degrees), and 70 degrees of supination (range, 45 degrees-90 degrees). Grip strength averaged 64% of the contralateral, uninjured extremity (range, 35%-100%). Final radiographic measurements included an average palmar tilt of the distal articular surface of the radius of 8 degrees (range, 0 degrees-20 degrees of palmar tilt), ulnar inclination of 21 degrees (range, 15 degrees-25 degrees), and ulnar positive variance of 1 mm (range, 0-4 mm). There were no problems related to the distal radioulnar joint. According to the system of Gartland and Werley as modified by Sarmiento, there were 6 excellent, 15 good, and 4 fair results at final evaluation. CONCLUSION: For unstable fractures of the distal ulna associated with fracture of the distal radius, condylar blade plate fixation can achieve healing with good alignment, satisfactory function, and an acceptable rate of secondary surgery.     

Kinematics of the distal radioulnar joint

The kinematics of the normal distal radioulnar joint (DRUJ) in five fresh frozen cadavers were investigated by means of computerized tomography (CT). Rotation of the radius about the ulna is accompanied by translation so that in supination the ulna is somewhat palmar, and in pronation the ulna is more dorsal relative to the radius. The average ranges of motion of the hand and DRUJ were 260 degrees and 190 degrees, respectively. Significant carpal and metacarpal rotation occurred with pronation-supination of the hand. The DRUJ has both rotational and translational components of movement and does not have a single center of rotation. The pathway of the instantaneous centers of rotation, or centrode, of the DRUJ has a characteristic pattern. The centrode moves in a direction opposite that of the DRUJ movement and is located near the center of the ulnar head. A prosthetic joint for the DRUJ should not have a fixed axis of rotation but should allow the normal translatory motion of the ulna and radius if early joint failure is to be prevented.     

Biomechanics of the distal radioulnar joint.

The distal radioulnar joint (DRUJ) is a complex joint involved in pronosupination and ulnocarpal motion and support. The ulnar head, in a rolling, sliding motion, moves from the dorsal to the volar rim of the sigmoid notch as the joint moves from pronation to supination. The triangular fibrocartilage (TFC) is taut first dorsally and then volarly in the same sequence. The ulnar carpus is supported variably, as a function of ulnar length relative to the radial articular surface, by the pole of the distal ulna through the TFC. The TFC does not resist the pistonlike movement of the DRUJ, which occurs under dynamic loading. The coronal alignment of the DRUJ minimizes shear stress on the articular surfaces because of its alignment with the rotational axis of the forearm. Ulnar variance is a factor in the development of several clinical conditions.     

The role of osteoporosis in distal radius fractures

Our study was designed to establish whether the degree of osteoporosis of the distal forearm affects the outcome of distal radius fractures in elderly women. We assessed the Gartland and Werley score, wrist mobility, grip strength, ulnar variance, radial inclination and palmar tilt of both wrists in 27 postmenopausal women who had sustained a unilateral distal radius fracture following a simple fall. Bone mineral density of the contralateral uninjured wrist and mid-tibial ultrasound velocity were measured. The Gartland and Werley score, wrist mobility, loss of grip strength and the radiological results of the fractured wrist did not correlate with bone mineral density of the uninjured distal radius or with mid-tibial ultrasound velocity. These results may indicate that the influence of osteoporosis on the radiological and clinical outcome in distal radius fractures is not very important.     

Influence of the pronator quadratus and supinator muscle load on DRUJ stability

PURPOSE: To determine the effects of altering the load contributions of the pronator quadratus and supinator muscles on in vitro distal radioulnar joint (DRUJ) stability during pronation and supination and before and after ulnar head excision. METHODS: Multiple pronation trials were conducted with incremental loading of the pronator quadratus relative to the pronator teres muscle; supination trials were similarly conducted with incremental loading of the supinator relative to the biceps muscle. All trials were conducted using an upper-limb apparatus capable of simulating muscle/tendon loading and displacement. Stability measurements included dorsal-volar translations of the radius relative to the ulna and DRUJ diastasis and convergence. RESULTS: Increased pronator quadratus loading did not affect intact DRUJ stability but effects were noted after ulnar head excision when the forearm was positioned between neutral and full pronation. Incremental loading of the supinator muscle did not modify DRUJ stability in the intact or ulnar head excised state. CONCLUSIONS: Pronator quadratus muscle activity aggravates forearm instability after ulnar head excision. Immobilization of the forearm in mid- to full supination should minimize pronator quadratus activity and optimize soft-tissue healing. This information may be useful to develop in vitro muscle-loading scenarios and analytical forearm models.     

Distal radioulnar joint instability in distal radius fractures: the role of sigmoid notch and triangular fibrocartilage complex revisited

The stabilising effects of various structures of the distal radioulnar joint (DRUJ) have been heavily debated. This biomechanical cadaveric study examined the effects of the volar and dorsal lips of the sigmoid notch and the volar and dorsal aspects of the triangular fibrocartilage complex (TFCC) on DRUJ stability. Sequential fractures of the distal radius and sectioning of the TFCC were performed followed by measurements of ulnar translation with the forearm in pronation, neutral and supination. A dorsal lunate facet fracture created instability in pronation. Lunate facet fractures alone did not create instability in other forearm positions. Sectioning of the volar TFCC after loss of the dorsal TFCC by a dorsal lunate facet fracture caused DRUJ instability with the forearm in neutral position. Sectioning of the dorsal TFCC after loss of the volar TFCC due to a volar lunate facet fracture created instability in neutral and pronated positions.     

Dynamic splinting of forearm rotational contracture after distal radius fracture

The results of dynamic forearm rotational splinting for the treatment of forearm rotational contractures in patients with acceptably aligned, healed distal radius fractures are documented. Fifteen patients with distal radius fractures that healed with < or =+5 mm ulnar variance and < or =20 degrees dorsal tilt had dynamic forearm rotational splinting for contractures that had failed conventional hand therapy. Average pronosupination arc before splinting was 83 degrees. Dynamic forearm rotational splinting increased forearm rotation by 52% to an average of 126 degrees. Only one patient with development of ectopic bone in the interosseous space during splinting failed to obtain at least 30 degrees pronation and supination after splinting. Dynamic forearm rotational splinting effectively treats rotational contractures in patients who have healed distal radius fractures that are in acceptable alignment.     

Computerized tomography of the distal radioulnar joint: correlation with ligamentous pathology in a cadaveric model

The kinematics of the normal distal radioulnar joint (DRUJ) and the stabilizing function of various structures about the DRUJ were investigated in a study involving six fresh frozen cadavers. Sequential division of the supporting structures was correlated with abnormalities detected by computerized tomography (CT). The infratendinous portion of the extensor carpi ulnaris is a major restraint against dorsal and palmar subluxation. Division of the radioulnar ligaments and triangular fibrocartilage alone produced only minor changes. Lateral displacement was controlled by the interosseous membrane and the pronator quadratus. CT is a useful method of gaining objective and quantifiable information regarding incongruity of the DRUJ. Three scans--one each in pronation, neutral, and supination--would be optimal. The pronation scan is likely to detect palmar subluxation, while the neutral scan is sensitive for dorsal subluxation and DRUJ diastasis. The supination view should confirm reduction of any subluxation. An important observation of this study was the spontaneous reduction of palmar, dorsal, and lateral displacement in supination. This suggests that immobilization in supination may be indicated in cases of acute DRUJ injury.     

Patterns of subchondral bone mineralization in the distal radioulnar joint

PURPOSE: Studies have shown that it is possible to derive direct knowledge about the actual mechanical conditions of the wrist by analyzing the subchondral mineralization. The aim of the present study was to evaluate the distribution of the subchondral bone mineralization of the distal radioulnar joint (DRUJ) noninvasively in living subjects by using computed tomography (CT) osteoabsorptiometry to gain new information about the long-term loading conditions. METHODS: Twenty-two wrist joints were investigated in 11 healthy young subjects by means of CT osteoabsorptiometry. The CT scans of the DRUJ were taken in the axial plane in neutral position of the forearm and in both maximum pronation and supination. The CT datasets of 1.5-mm sections were obtained and then transferred to an image-analyzing system. The subchondral bone plate in each section was isolated, reconstructed in 3 dimensions, and converted into a false color series. RESULTS: The maximum subchondral bone density in the sigmoid notch of the radius was found along the distal border in all wrists. It was located dorsally in 10 wrists, palmarly in 8 wrists, and centrally in 4 wrists. The maximum bone density on the corresponding articular surface of the ulna was found dorsally in 10 cases, centrally in 8 cases, and palmarly in 4 cases. In 13 cases the maximum bone density was found in direct opposition on radius and ulna in neutral position. A statistically significant difference could not be detected in subjects with an ulna minus variance nor in those with a DRUJ angulation greater than 10 degrees . CONCLUSIONS: Our results show that in the sigmoid notch the load is transmitted through either the dorsal or palmar parts of the joint. In contrast the maximum bone density on the side of the ulna was found dorsally and centrally. We conclude that the ulna receives the maximum load in neutral position and supination, whereas because of the dorsopalmar translation of the ulnar head the radius may lead the ulna with either its palmar or dorsal borders during pronosupination. The ligamentous apparatus, the shape of the joint, and the ulna variance, however, may influence load transmission.     

The distal radioulnar joint in relation to the whole forearm.

The functional anatomy of the distal radioulnar joint was studied in relation to the whole forearm, using three fresh-frozen, above-elbow amputation specimens. The specimens demonstrate how the proximal and distal radioulnar joints together form a bicondylar joint of special character. The proximal "condyle," the radial head, rotates axially, whereas the distal "condyle," the ulnar head, is fixed with respect to rotation. The ordinary articulation of a bicondylar joint (pure axial rotation) is thereby changed into pronation-supination. Axial rotation is preserved proximally, while distally the radius swings around the ulnar head. The mobile radius is distally attached to the stable ulnar head by the dorsal and volar radioulnar ligaments, the dorsal ligament being tight for stabilization in supination and the volar ligament being tight in pronation. The ulnar head also serves as a keystone, carrying the load of the radius. Removal of the ulnar head allows the radius to "fall in" towards the ulna, with narrowing of the interosseous space.     

Palmar locking plate for treatment of unstable dorsal dislocated distal radius fractures

Introduction This study investigates the clinical and radiological results of open reduction and internal fixation of unstable distal radial fractures using a palmar placed interlocking plate system with no substitutes for treatment of the dorsal metaphyseal fracture void.Materials and methods Nineteen patients with a mean age of 61 years (range 49–78 years) and a dorsally displaced distal radial fracture were treated using a palmar placed 2.4 mm interlocking plate system. All 17 women and 2 men were followed up according to the study protocol. Standardised radiographs in anteroposterior and lateral projection were performed before reduction and at 2, 6, 12 and 24 weeks after surgery. Radiological measurements included palmar tilt, radial inclination and radial shortening as defined by ulnar variance and intra-articular steps. Clinical assessment included active range of motion (ARM) of the wrist, pain according to a visual analogue scale (VAS), grip power, working ability, Disability of Arm, Shoulder and Hand-Score (DASH Score) and Mayo Wrist Score.Results At final follow-up after a minimum of 11 months, the palmar tilt was +1°, radial inclination 19.8° and ulnar variance 1.0 mm. Mean loss of palmar tilt measured 1.9°, radial inclination 1.3° and ulnar variance 0.4 mm. Mean wrist extension measured 58°, wrist flexion 41°, pronation 83° and supination 84°. The Mayo Wrist Score showed 21% excellent, 58% good, 16% fair and 5% poor results.Conclusion The treatment of unstable, dorsally dislocated, distal radius fractures AO types A3, C1 and C2, with a palmar placed 2.4 mm interlocking plate system and without additional treatment of the metaphyseal defects showed good radiological and functional results with minimal loss of reduction.     

Motion of the distal radioulnar joint in extension and flexion of the wrist using axial CT imaging of healthy volunteers

BackgroundThe midcarpal joint and the radiocarpal joint contribute to the extension and flexion of the wrist. Little is known about the contribution of the distal radioulnar joint (DRUJ) to the extension and flexion of the wrist. This study evaluated the ulnar motion in extension and flexion of the wrist using computed tomography (CT) imaging.MethodsA total of 30 wrists of healthy volunteers were enrolled. CT images of the axial sections of the DRUJ were obtained with 3 different positions of the wrist: 0° of extension (straight position), maximum active extension, and maximum active flexion. Each wrist motion was performed with 3 different forearm positions: neutral, pronation, and supination. Ulnar position at the DRUJ level was measured and ulnar position with the wrist in straight position was defined as baseline. The ulnar position was recorded as positive value when the position of the ulnar head was volar side and negative value when the position of the ulnar head was dorsal side. The difference from baseline in a position of maximum extension and flexion was evaluated.ResultsIn forearm neutral position and pronation, a value of ulnar position in maximum wrist flexion is significantly negative compared to that in the wrist straight position: the ulnar head moved dorsally from the wrist straight position to wrist flexion. In forearm supination, a value of ulnar position in maximum wrist extension is significantly positive compared to that in the wrist straight position: the ulnar head moved to the volar side from the wrist straight position to wrist extension.ConclusionsThe ulnar head moves during extension and flexion of the wrist. The direction of the ulnar motion was different according to the wrist and forearm position.     

Effects of forearm rotation on the clinical evaluation of ulnar variance

Neutral rotation radiographs of the wrist are recommended to standardize the measurement of ulnar variance because it is known that changes in forearm rotation result in changes of this measurement. The purpose of this study was to examine whether there are clinically measurable differences in ulnar variance between radiographs in various degrees of forearm rotation in human subjects. Forty-five wrist radiographs of 15 normal adults were obtained in 3 positions: maximum forearm pronation, neutral rotation, and maximum supination. The ulnar variance on each view was measured by 3 independent observers using a standard millimeter ruler. The average absolute difference in ulnar variance was 0.4 mm between pronation, 0.6 mm between pronation and supination, and 0.2 mm between neutral and supination. Although we found a statistically significant difference in ulnar variance between the pronated and neutral positions, this difference may not be clinically significant and may not justify concerns of forearm position during the radiographic evaluation of ulnar variance.     

Remodeling capacity and functional outcome of palmarly versus dorsally displaced pediatric radius fractures in the distal one-third

Introduction The purpose of this retrospective study was to compare the remodeling capacity and functional outcome of palmarly and dorsally displaced pediatric radius fractures in the distal one-third.Materials and methods Fifty-three children with a residual dorsal angulation of 15° (range 10°–28°, ±SD 5.32) and 31 children with a residual palmar angulation of 15° (range 10°–30°, ±SD 4.88) at fracture healing were re-examined clinically and radiologically with a median follow-up time of 10 years (range 5–15 years).Results There was no difference in the remodeling capacity, palmar tilt, radial inclination, and ulnar variance between both groups at follow-up. Pain as well as flexion/extension of the wrist and pronation showed no difference in both groups. Palmarly displaced fractures showed a significantly higher restriction of supination (p=0.01).Conclusion We conclude that remodeling of residual palmar angulation occurs to the same extent as it does in dorsal angulation. Functional outcome differs in forearm supination.