The dislocation of the stent on the back of the metacarpophalangeal joint is commonly encountered in rheumatoid arthritis, but more rarely in rheumatoid arthritis. a traumatic context as evidenced by the few publications on the subject and the frequency of misunderstanding of the diagnosis. The lesion of the extensor apparatus in Verdan Zone 5, which is the cause, is sometimes referred to as boxer ‘ s knuckle by its relative greater frequency in the boxer.
The instability of the stenting device results, in fact, from the failure of the tensioning mechanism of the sagittal strips.
Their lesion may be isolated or associated with that of collateral ligaments of the metacarpophalangeal joint.
The instability of the extensor apparatus is, moreover, not systematic, but results from the extent of the lesion. In the majority of cases, it is a closed trauma of the dominant major with a forced flexion of the finger (mechanism of blow – depoing) causing a rupture of the radial sagittal fibers and an ulnar dislocation in the intermetacarpal valley of the extensor tendon.
The sagittal strips (BS) are part of the cylindrical retinacular complex around the metacarpal head and the metacarpophalangeal joint (MP) embedded in a functional complex including palmar plate, collateral ligaments and intermetacarpal ligaments. They constitute the main dynamic stabilizer of the extensor device on the back of the MP.They accompany the extensor tendons in their longitudinal sliding whereas the orientation of the transverse fibers varies with the stretch tendon stretch and the degree of flexion of the MP. Perpendicular to the axis of the stent in neutral position, they have an angulation of 25 to 45 ° of flexion of the MP and of 55 ° in complete flexion. The pressure exerted on the BS also varies as a function of the position of the MP, maximum in high flexion and increased by a component of radial inclination, it is minimal around 45 ° but increases in full extension.
From a pathological point of view, the section of the ulnar BS does not destabilize the extensor apparatus while the proximal (and non – distal) section of the radial BS causes dislocation in the intermétacarpian valley.
This lesion is more readily observed on the first two long fingers than the fifth, although the anatomical studies have observed a greater thickness of the sagittal strips.
The exceptional nature of this lesion explains its frequent initial misconception and the underestimation of its frequency. The posttraumatic painful functional impotence on the back of a hematic metacarpophalangeal lesion without radiographic lesion must evoke the diagnosis, particularly if the history relates a punch in a boxer (more often in training than in the match , because strapping and gloves usually protect from this type of trauma). It ‘s the classic boxer ‘ s knuckle of Anglo-Saxon literature.
A careful clinical examination can show the dislocation of the tendon extensor in the intermetacarpal valley, ulnar most often (but not always) and painful. The examination is sensitized by full bending of the MP or by resistance extension.The active extension is often limited, if not impossible, by the loss of the moment of action of the luxated stent and projecting at the center of rotation of the MP. Clinical examination can be repeated after a few days of immobilization, during the time that the inflammatory phenomena retrocede, to refine the diagnosis and to adapt the treatment. The stability of the extensor tendons of the other fingers as well as of the contralateral hand should also be systematically assessed in order to to unmask an instability that can sometimes be congenital and not pathological.
The clinical examination and the circumstances of occurrence are usually sufficient for positive diagnosis. A lateral or rotational traumatic component should also cause suspected association with the lesion of a collateral ligament and testing of the stability of the MP must be systematic in extension but especially in flexion.
In case of doubt, an ultrasound scan or MRI can be performed, these examinations being of a fairly good sensitivity including ultrasound which can be dynamic. Nevertheless, MRI performed by means of specific antennas allows a perfect exploration of the extensor apparatus and an accurate lesion diagnosis.
A classification of lesion was proposed by Rayan and Murray in three types:
* type 1: simple contusion without rupture of the transverse fibers, without instability of the tendon extensor;
* type 2: tendonous subluxation which nevertheless remains in contact with the metacarpal condyle in flexion;
* type 3: intermetacarpal dislocation of the tendon with sensations of painful blockages of the extension of the MP.
When the diagnosis was made early, the treatment can be orthopedic in a disciplined patient.
The immobilization is strictly semi – bending (zone of less pressure exerted on the BS) of the metacarpophalangeal, for three to four weeks, the interphalangeals are left free and mobile. After this period of restraint, the rehabilitation is carried out without splint, but it must be kept at night and between sessions for another three to four weeks. The adherence of the treatment is not always very good, especially since the pain disappears rapidly and that the few functional signs felt by the patient contribute to the trivialization of his lesion. The results are often correct on the pain but sometimes allow a tendon sweeping effect to persist, which can be troublesome in a patient requiring functional recovery as are the top athletes.
In most cases, we prefer surgical treatment consisting in suturing the injured sagittal strip after reduction of the stretch tendon.
An intra-articular exploration must be systematic (chondral lesions, collateral ligaments … ). An immobilization at 45° of flexion of the MP (less pressure on the BS) must be preserved for four weeks and then relayed by a syndactylization on the side of the lesion that is retained for an additional month (rehabilitation period) and during the resumption of sport activities example: syndactylisation 2 – 3 for a lesion of the radial backbone on the back of the MP3 with ulnar dislocation of the extensor). A boxer can resume typing with strapping and gloves from the second month. Diagnostic delay of several weeks does not contraindicate this type of suture often possible until the third posttraumatic month.
If the lesion is only diagnosed later, a retinaculum plasty can be performed.
The complications of these techniques are rare and are limited to a few adhesions. Stabilization is often very good with the simple persistence of a cicatricial pad, rarely troublesome.
The best treatment is preventive, especially in the boxing halls by prohibiting any work with the bag without protection.The strapping must be meticulous and systematic, and develop specific protections of the metacarpophalangeal joints.
Finally, sports doctors and traumatologists must be sensitized to this pathology that is still too often neglected and treated with delay requiring more complex surgical management (capsular plasties, Mac Coy type tendinous or dorsal retinaculum) with results often less rewarding.