The role of the flexor carpi radialis muscle in scapholunate instability.

PURPOSE: The flexor carpi radialis (FCR) muscle has been suggested to act as a dynamic scaphoid stabilizer. Because the FCR tendon uses the scaphoid tuberosity as a pulley to reach its distal insertion onto the second metacarpal, it has been hypothesized that FCR muscle contraction generates a dorsally directed vector that resists the scaphoid from rotating into flexion. The purpose of the present study was to validate that hypothesis and clarify the role of the FCR as a dynamic scaphoid stabilizer. METHODS: Ten fresh cadaver wrist specimens were tested. A custom-designed testing apparatus was used to hold the forearm and wrist vertically, in neutral forearm rotation. A 6-degree-of-freedom, electromagnetic motion-tracking device, with sensors attached to the scaphoid, triquetrum, capitate, and radius, was used to monitor spatial changes in carpal alignment as a result of isometrically loading the FCR in 5 different wrist positions. RESULTS: In all specimens and all wrist positions, the scaphoid consistently rotated into flexion when the FCR was loaded. It also exhibited variable degrees of pronation or supination, depending on whether the wrist was in flexion or extension. When the wrist was loaded in neutral position, the scaphoid consistently supinated and the triquetrum pronated, these differences being statistically significant (p < .05). CONCLUSIONS: The scaphoid consistently rotated into flexion and supination when the FCR was loaded, while the triquetrum rotated in flexion and pronation. The positive effects of FCR muscle re-education in dynamic scapholunate instabilities can be explained not by this muscle's capability of extending the scaphoid, as has often been hypothesized, but by its ability to induce supination to the scaphoid and pronation to the triquetrum. Such opposite rotations are likely to result in a dorsal coaptation of the scapholunate joint with relaxation of the dorsal scapholunate ligament.

Wrist kinetics after scaphoidectomy.

BACKGROUND: The scaphoid cannot be excised without generating substantial carpal dysfunction. The extent and nature of such a destabilizing procedure, however, has never been properly studied in the laboratory. METHODS: We used a six-degrees-of-freedom motion tracking device to quantify the changes in carpal alignment produced by isometric simultaneous loading of five wrist motor tendons in 12 fresh normal cadaver arms, before and after excising the entire scaphoid. FINDINGS: In the intact wrist, tendon loading consistently extended and supinated the capitate while flexing the triquetrum. After scaphoidectomy, the opposite rotations were always found: the capitate collapsed into flexion and pronation, whereas the triquetrum migrated proximally, while extending and radial deviating. All these changes were statistically significant. INTERPRETATION: Unless it is supplemented by some sort of midcarpal stabilization, scaphoidectomy alone is much too aggressive as a procedure to be considered a treatment option for wrist osteoarthritis. LEVEL OF EVIDENCE: Laboratory study. Not applicable.

[Radio-scapho-lunate arthrodesis with distal scaphoid excision]. / Arthrodèse radioscapholunaire avec excision du scaphoïde.

Painful dysfunction of the radio-scapho-lunate joint may occur secondary to a number of post-traumatic, inflammatory and non-inflammatory conditions. When symptomatic, this problem may necessitate fusing the radio-scapho-lunate joint. The goal of this study is to describe precisely the technical steps of radio-scapho-lunate fusion with distal scaphoidectomy and to present the results in a clinical series. Sixteen patients presented with degeneration of the radio-scapho-lunate joint combined with a normal midcarpal joint. Radio-scapho-lunate fusion with distal scaphoidectomy was performed in all patients. At an average follow-up of 37 months, complete relief of pain was obtained in 10 patients, three had slight pain with strenuous loading, and three had occasional pain with regular activities. The average range of passive motion at follow-up was 32 degrees of flexion and 35 degrees of extension. The average postoperative grip strength was 76%. In all cases a solid fusion was obtained. In two patients who had originally suffered a perilunate dislocation, midcarpal degenerative arthritis was noted. We suggest that in cases of radio-scapho-lunate osteoarthritis without degenerative change in the midcarpal joint, radio-scapho-lunate fusion is a possible solution. However, it is necessary to perform distal scaphoidectomy in order to avoid scapho-trapezo-trapezoid impingement. Provided all the technical principles are respected, complications such as ulnocarpal impingement or nonunion, are rare.

Divergent Axial Carpal Dislocation and Its Pathomechanics.

Background Axial carpal dislocations and fracture dislocations are 1.4 to 2.08% of all the fractures and dislocations of the wrist. These injuries are caused by high-energy blast or compression mechanisms. Only 11 cases of axial-radial-ulnar (ARU) fracture dislocations have been described in the literature. Case Description We describe a case with a traumatic transtrapezoid, peritrapezium, transhamate, peripisiform ARU in a patient with acute compartment syndrome, traumatic transverse flexor retinaculum (TFR) rupture, and radial nerve palsy. Literature Review The ARU fractures are injuries where the carpus is torn into three columns. ARU injuries have a high incidence of neurovascular, soft-tissue cover, and muscular-associated injuries. Depending on the injuries mentioned earlier, a bad functional prognosis can be expected. Nearly without exception, in ARU cases, a traumatic TFR rupture takes place. Garcia-Elias mentioned that the injury pattern is given by the speed, magnitude, and energy entry point. Clinical Relevance We describe a case of an ARU injury which has not been previously described. In an analysis of the 12 ARU cases previously reported, we observed that when two or more applied forces converge, an ARU injury pattern can occur. That suggests that in ARU injuries, one side of the injury occurs before the other. Due to the extensive carpal damage, in patients with ARU, a restricted range of motion is more likely to happen than residual instability. Thus, in all these cases, an early mobilization and intensive rehabilitation is highly necessary.

Histological assessment of the triangular fibrocartilage complex.

The morphological structure of the seven components of triangular fibrocartilage complexes of 11 cadaver wrists of elderly people was assessed microscopically, after staining with Hematoxylin-Eosin and Elastica van Gieson. The articular disc consisted of tight interlaced fibrocartilage without blood vessels except in its ulnar part. Volar and dorsal radioulnar ligaments showed densely parallel collagen bundles. The subsheath of the extensor carpi ulnaris muscle, the ulnotriquetral and ulnolunate ligament showed mainly mixed tight and loose parallel tissue. The ulnolunate ligament contained tighter parallel collagen bundles and clearly less elastic fibres than the ulnotriquetral ligament. The ulnocarpal meniscoid had an irregular morphological composition and loose connective tissue predominated. The structure of the articular disc indicates a buffering function. The tight structure of radioulnar and ulnolunate ligaments reflects a central stabilizing role, whereas the ulnotriquetral ligament and ulnocarpal meniscoid have less stabilizing functions.

The effect of individual isometric muscle loading on the alignment of the base of the thumb metacarpal: a cadaveric study.

Stability of the thumb carpometacarpal joint relies upon equilibrium between its ligaments, muscular support and joint congruity. We wanted to identify the muscles important in preventing or increasing dorsoradial subluxation of this joint. In ten cadaveric hands, a Fastrak® motion tracking device was used to assess the effects of individual isometric muscle loading on the base of the thumb metacarpal relative to the radius and to the base of the middle finger metacarpal. We found that the first dorsal interosseous muscle caused the least dorsoradial translation and highest distal migration of the base of the first metacarpal, whereas abductor pollicis longus was the primary destabilizer, increasing dorsoradial misalignment. The findings show different impacts of these muscles on joint alignment and stability, which suggests that treatment should be targeted to enhance the action of the primary stabilizing muscle, the first dorsal interosseous muscle.

Tendinopathies of the Extensor Carpi Ulnaris.

To improve its mechanical advantage, the extensor carpi ulnaris (ECU) muscle uses, as if it was a pulley, the 6(th) extensor compartment, a dorsal fibro-osseous tunnel formed by the ulnar sulcus and the ECU tendon sub-sheath. Rupture or insufficiency of that sheath may allow anteromedial ECU tendon subluxation and subsequent destabilization of the distal radioulnar and ulnocarpal joints. Sometimes, it is not sheath problem, but excessive friction between the sheath and the tendon what causes a painful degeneration of the tendon (tendinosis) with or without tendon entrapment. The term "ECU tendinopathy" has been chosen to designate all painful ECU anomalies resulting from a dysfunctional 6(th) extensor compartment. ECU tendinopathies are frequent among sportsmen using bats, sticks or clubs. There are 2 major types of tendinopathy: 1) constrained tendinopathies, where there is entrapment of a thickened overused tendon, and 2) unconstrained tendinopathies, where a ruptured ECU sub-sheath allows the ECU to sublux in a volar direction, a position precluding all its stabilizing potential. In the first type, the goal of the treatment is to avoid further degeneration and subsequent rupture of the diseased tendon; in the second, to re-establish the normal connections between the ulna and the ECU tendon. This article reviews the management of the most frequent ECU tendinopathies.

Transverse stability of the carpus. An analytical study.

The stabilizing structures of the transverse carpal arch were studied utilizing an analytical model based on a rigid body spring model theory. This method was used to calculate the relative motion between carpal bones, the distribution of compressive forces in the intercarpal joints, and the tensions in the ligaments under simulated dorsopalmar compression. The contribution of each ligament against the effect of compression was determined by removing ligaments from the model. A multivariate analysis of variance disclosed that sectioning the flexor retinaculum alone does not significantly modify the distribution of forces in ligaments and joints (p = 0.33), and decreases dorsopalmar carpal stiffness by only 7.8%. In contrast, isolated removal of the palmar hamate-capitate ligament causes a pronounced weakening of the carpal structure, from an average of 232 to 131 N/mm (p less than 0.01). If the flexor retinaculum is removed in addition to releasing one palmar intercarpal ligament, a gross instability of the carpal arch is created.

Axial loading induces rotation of the proximal carpal row bones around unique screw-displacement axes.

The changes in carpal bone alignment secondary to the application of an axial compressive load through the major wrist motor tendons while the wrist is kept in neutral position (isometric loading) have been investigated on 13 fresh cadaver specimens using a biplanar radiographic method of kinematic analysis. The scaphoid, lunate and triquetrum rotate an average of 5.1, 4.2, and 3.8 degrees, respectively, around different screw displacement axes, all implying flexion, radial deviation and supination. Based on these findings, a new interpretation of the mechanism by which the wrist remains stable under physiologic loads is provided.

Non-union of a fractured coracoid process after dislocation of the shoulder. A case report.

A patient with a fractured coracoid process in association with a dislocation of the shoulder is reported. The fracture was not recognised initially, and early mobilisation was encouraged; the widely separated fracture did not heal and a painful pseudarthrosis developed. We believe that this association may not be as rare as generally supposed, and emphasise the importance of careful clinical examination in patients with shoulder dislocation. If a coracoid fracture is suspected, lateral or oblique radiographs should be taken to confirm the diagnosis. A further radiograph after reduction is a useful precaution.

Crush injury of the carpus.

Severe crush injuries affecting the bones of the carpus are rare. We review the nine cases that have previously been described and report four additional cases which we have treated and followed up. All 13 present remarkable similarities, with disruption of the carpal arch through the capitate-hamate articulation distally and the piso-triquetral joint proximally. Three slightly different variations of this pattern of fracture-dislocation are identified. The flexor retinaculum must be involved to allow the displacement which is seen, and there is usually an extensive laceration of the thenar eminence. Treatment by closed reduction is usually successful. Long-term follow-up shows that, in the absence of nerve or vascular damage, the results are surprisingly good.

Failed ulnar head resection: prevention and treatment.

Distal ulnar head resections may cause a painful impingement of the distal ulnar stump against the radius during loaded forearm rotation. Different soft-tissue procedures have been suggested to solve this difficult problem, but none has demonstrated clear superiority over the others. The introduction of a variety of ulnar head and total radio-ulnar joint prostheses has provided a new method of addressing this problem, but there is presently no evidence that these implants produce long-lasting results. This paper critically reviews these different options, and emphasizes techniques which may help to minimize the risk of complications when excision of the ulnar head is unavoidable.

Dynamic radial translation instability of the carpus.

We report a case of a dynamic radial translation instability of the carpus, secondary to avulsion of the ulnocarpal ligaments and attenuation of the short radiolunate ligament. In addition, there was a peripheral detachment of the distal radioulnar ligaments causing distal radioulnar instability. Reattachment of the avulsed ligaments combined with a Sauvé-Kapandji procedure resulted in an excellent function, which was maintained 10 years after surgery.

Combined fracture of the hook of the hamate and palmar dislocation of the fifth carpometacarpal joint.

A case of fracture of the hook of the hamate associated with a palmar dislocation of the fifth carpometacarpal joint is described. Surgical exploration revealed that the different elements of the flexor carpi ulnaris musculotendinous unit, which includes the pisiform, the pisohamate and pisometacarpal ligaments, were displaced proximally together with the avulsed fragment of the hook of the hamate and the fifth metacarpal. These findings suggest that such an injury results from a sudden, violent contraction of the flexor carpi ulnaris against the fixed wrist. It was successfully treated by open reduction and fixation of the hook of the hamate fracture and stabilization of the carpometacarpal joint.

Relationship between joint laxity and radio-ulno-carpal joint morphology.

The relationships between wrist laxity, ulnar variance, sigmoid notch inclination, and lunotriquetral motion were analysed in 60 normal volunteers. A strong correlation between ulnar length and sigmoid notch inclination was found for the entire group. Joint laxity was found to correlate with ulnar variance and lunotriquetral mobility in women, but not in men. The greater the laxity, the shorter the ulna and the greater the lunotriquetral motion during radial to ulnar deviation. These results support the concept that laxity increases the vulnerability of the wrist to injury.

Influence of joint laxity on scaphoid kinematics.

Excessively lax wrists more frequently become symptomatic if overloaded or injured than normal joints. Whether this is the consequence of biological or mechanical factors or both remains unknown. This study evaluates the relationship between the degree of joint laxity and scaphoid kinematic behaviour during radio-ulnar deviation of the wrist in 60 normal volunteers. There is a significant linear relationship between the direction of scaphoid rotation and the amount of wrist joint laxity. During lateral deviation of the wrist, joints that are more lax have a scaphoid rotating mainly along the sagittal plane of flexion and extension, with little lateral deviation. In contrast, the scaphoid of volunteers with decreased laxity rotate mostly along the frontal plane of radioulnar deviation with minimal flexion extension. These results support the concept of increased out-of-plane scaphoid rotation as a factor of increased vulnerability during over-work or injury.

Resection of the distal scaphoid for scaphotrapeziotrapezoid osteoarthritis.

Twenty-one patients with symptomatic scaphotrapeziotrapezoid osteoarthritis were treated with partial distal scaphoid excision. In 12 wrists the joint defect was filled with either capsular or tendinous tissue, while in nine no fibrous interposition was done. At an average follow-up time of 29 (range, 12-61) months, 13 wrists were painfree, while eight had occasional mild discomfort. Mean wrist flexion-extension was 119 degrees. Grip and pinch strength improved by an average of 26% and 40% respectively compared with their preoperative status. Fifteen patients returned to their original jobs, while six, who were unemployed, felt unrestricted for activities of daily living. Although patient satisfaction was comparable for both types of treatment, the wrists without fibrous interposition showed significantly greater wrist flexion-extension than patients with soft-tissue interposition. Removal of the distal scaphoid resulted in a DISI pattern of carpal malalignment in 12 wrists. At follow-up, none of these wrists showed further joint deterioration due to residual malalignment.

Bennett's fracture combined with fracture of the trapezium. A report of three cases.

Three cases are reported in which open reduction and internal fixation were required to stabilize an unstable first carpometacarpal joint with simultaneous fracture of the trapezium and Bennett's fracture. The results were good in terms of range of movement and radiological appearance, all of them returning to normal activities, including heavy manual work.

Kinetic analysis of carpal stability during grip.

When the wrist is grasping an object, at least four mechanisms of carpal stabilization are involved-one for each carpal row (proximal and distal), one for the midcarpal joint, and one for the radiocarpal joint. These mechanisms are based on the general principle that, under load-bearing conditions, any bone tends to rotate into a specific direction depending upon several factors, including the position of the wrist at the time of loading, the direction of the forces being transferred, and the inclination and shape of the articular surfaces on which the bone stands. Such an attempted displacement is initially guided and later neutralized by appropriately oriented ligaments, with which a new equilibrium is achieved. An injury or disease affecting any one of these mechanisms results in a specific type of carpal instability, depending upon which mechanism(s) has been violated. Only through a thorough understanding of these mechanisms of wrist stabilization will our ability to successfully treat these problems be enhanced.

Soft-tissue anatomy and relationships about the distal ulna.

The author investigates the complex anatomic relationship between the ulnar head and adjacent osseous structures (radius and carpus). Special attention is directed to the orientation and shape of the articular surfaces the constraining effects of specific membranes and ligaments (radio-ulnar and ulnocarpal), the shock-absorbing function of the triangular fibrocartilage, and the dynamic action of specific muscles (pronator quadratus and extensor carpi ulnaris) The anatomy of other nonstabilizing structures (meniscus homologue and prestyloid recess) is also discussed.