Analysis of ulnar variance as a risk factor for developing scaphoid nonunion.

OBJECTIVE: Ulnar variance may be a risk factor of developing scaphoid non-union. METHODS: A review was made of the posteroanterior wrist radiographs of 95 patients who were diagnosed of scaphoid fracture. All fractures with displacement less than 1mm treated conservatively were included. The ulnar variance was measured in all patients. RESULTS: Ulnar variance was measured in standard posteroanterior wrist radiographs of 95 patients. Eighteen patients (19%) developed scaphoid nonunion, with a mean value of ulnar variance of -1.34 (-/+ 0.85) mm (CI -2.25 - 0.41). Seventy seven patients (81%) healed correctly, and the mean value of ulnar variance was -0.04 (-/+ 1.85) mm (CI -0.46 - 0.38). A significant difference was observed in the distribution of ulnar variance (p<.05). These results remained significant after adjusting for age, with an OR of 0.69 (CI 0.49 to 0.95). The patients were categorized into two groups: ulnar variance less than -1mm, and ulnar variance greater than -1mm. It appears that patients with ulnar variance less than -1mm had an OR 4.58 (CI 1.51 to 13.89) with p<.007. DISCUSSION: Desai et al. concluded that radiological features of acute scaphoid fractures cannot be used to predict the likelihood of fracture union. For this reason, the existence of other risk factors was analysed. According to the results of the present study, it can be concluded that patients with scaphoid fracture and ulnar variance less than -1mm have a greater risk of developing scaphoid nonunion, OR 4.58 (CI 1.51 to 13.89) with p<.007.

[Muscular control of scapholunate instability. An experimental study]. / Control muscular de la inestabilidad escafolunar. Estudio experimental.

PURPOSE: As long as the neuromuscular stabilizers are intact, a lesion of the scapholunate ligament may or may not progress to a carpal instability. The mechanisms by which the muscles compensate this defect are not very well known. We designed an experimental study with the aim of clarifying these mechanisms. MATERIAL AND METHOD: Using 10 fresh wrists, with no pre-existing lesions, we studied the movements of the scaphoid, triquetrum and capitate produced by the isometrical loading of the muscles which move the wrist, each of them isolated or combined, before and after cutting off the scapholunate ligaments. To do this, we placed sensors in each of these bones and used the Fastrack system to record these movements. RESULTS: The simultaneous loading of the muscles of the wrist produce rotational movements in flexion and supination of the proximal carpal row. After cutting off the scapholunate ligaments, the scaphoid rotates in pronation and flexion, while the triquetrum rotates in pronation and extension. In this situation of a scapholunate lesion, the muscles that worsen the carpal dexasation are the extensor carpi ulnaris and flexor carpi ulnaris. On the other hand, the isolated loading of the radial muscles reduce the scapholunate diastasis, thus improving the carpal alignment. CONCLUSION: In dynamic scapholunate instabilities, isometric contraction of the ulnar carpal muscles must be avoided, as it promotes the scapholunate diastasis. The rest of the muscles have the opposite effect, stabilizing the carpus when primary stabilizers have failed.

[Carpal dynamic stability mechanisms. Experimental study]. / Mecanismos de estabilización dinámica del carpo. Estudio experimental.

OBJECTIVE: To evaluate, experimentally in cadavers, the effect of the motor muscles in the wrist in the kinetic behaviour of the carpal, under axial load, and the wrist in a neutral position. MATERIAL AND METHOD: The changes in the spatial orientation of the carpal bones were recorded with a movement trajectory gauge that functions with electromagnetic fields. A total of 30 fresh cadaver wrists were used, in which the principal motor tendons were isolated and subjected to loads proportional to the area of the physiological section of each muscle. The experiment was performed under isometric load conditions of all the tendons, and separately from each tendon. RESULTS: The simultaneous load of all the tendons studied caused a three-dimensional change of the carpal bones. The flexor carpi radialis led to supination of the scaphoids and pronation of the pyramidal. Conversely, the isolated load of the flexor carpi ulnaris, abductor pollicis longus and the extensor carpi radialis longus, caused a supination movement of the 2 carpal rows. Only the extensor carpi ulnaris led to a marked pronation of the carpal. COMMENTS AND CONCLUSIONS: The forearm muscles, as well as the movements of the wrist, cause pronation/supination/supination, flexion/extension and radial/cubital inclination movements. It is proposed that the most important movements in the dynamic stabilisation of the carpal are the intercarpal pronation and supination movements provoked by these muscles. Depending on the carpal injury mechanism or instability, the stimulating of one muscle group or the other may be beneficial.

Role of the extensor carpi ulnaris and its sheath on dynamic carpal stability.

Ten cadaveric forearms were tested using a wrist testing apparatus specifically designed to investigate the mechanisms of muscle stabilization of the wrist. The specimens were set in a jig allowing the distal row to migrate proximally and rotate around the axis of pronosupination. The extensor carpi ulnaris (ECU) was loaded with specific weights. Reactive rotations of the scaphoid, triquetrum, and capitate were measured by an electromagnetic motion tracking device. Loading the ECU caused pronation of both proximal and distal rows. After sectioning its sheath, the overall direction of the movement remained unchanged, but there was a 40% and 50% decrease of the pronation power over the distal and proximal carpal row, respectively. In addition to stabilizing the distal radiolunar joint, the ECU is an important structure that contributes to the dynamic stability of the wrist. Furthermore, its sheath plays a crucial role in maintaining the effect of the ECU muscle on the carpus.

Effects of forearm muscles on carpal stability.

Thirty cadaveric forearms were tested using a wrist testing apparatus specifically designed to investigate the mechanisms of muscle stabilization of the wrist. The specimens were set in a jig allowing the distal row to migrate proximally and to rotate around the pronosupination forearm axis. Five wrist motor tendons (FCR, FCU, ECU, ECRL and APL) were loaded with specific weights. Reactive rotations of the scaphoid, triquetrum and capitate were measured by an electromagnetic motion tracking device. When all five tendons were loaded simultaneously, the capitate supinated and the proximal row predominantly supinated and flexed. By contrast, when the ECU was loaded in isolation, it caused pronation to both proximal and distal rows. The FCR exhibited a mixed effect pronating the capitate and triquetrum, whilst supinating the scaphoid. Based on this, a hypothesis is proposed linking wrist stability to the balance of wrist pronators (ECU and FCR) and supinators (FCU, ECRL and APL).

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.

[Metastasis of an adenocarcinoma of the colon to the 1st metacarpal bone]. / Métastases d'un adénocarcinome du côlon au premier métacarpien.

The authors report a clinical case of metastasis to the first metacarpal arising from carcinoma of the colon, treated surgically four years previously. Clinical examination revealed painful swelling over the right thenar eminence. The diagnosis was established by radiology and needle biopsy. No treatment was administered and the patient died one month later. Metastases of the hand are uncommon and, according to the review of the international literature concerning bone metastases in the hand conducted by Kerin (1987), are usually secondary to lung, renal and breast cancers. Only a few cases have been described in the literature of bone metastases of the hand from carcinoma of the colon. The authors feel that some of these cases probably remain undiagnosed, as they are of secondary importance in view to the severity of the disease.