Intraoperativ Testing of Scapholunate Instability in Radius Fracture

Radius fractures are the most common fractures in adulthood and account for approximately 17.5% of all fractures. The most common distal radius fractures are approximately 57-66% extra-articular (AO type A), followed by completely articular fractures (AO type C) with 25-35% and the least rare partial articular fractures (AO type B) with 9-15%.

The fracture mechanism of distal radius fractures is in most cases a fall on the extended wrist, less often a high-energy trauma. It is not uncommon for there to be additional accompanying ligamental injuries, which are easily overlooked.

5-64% of intraarticular radius fractures are accompanied by injuries of the scapholunary ligament. However, most of these studies are carried out in smaller series, with only one exception. A scapholunary band lesion can occur in isolation or in combination with a distal radius fracture, scaphoid fracture or perilunary luxation. The prevalence of this ligament injury has not yet been sufficiently studied. Acute scapholunary ligament damage accompanying injury to a distal radius fracture, clinical testing of instability by means of the Watson provocation test is not possible due to pain. Thus, scapholunary dissociation is often initially overlooked. Additional later examinations by means of MRI or arthroscopy are necessary to diagnose the missed ligamentary injuries.

In 5-10% of cases, intraarticular radius fractures are associated with complete ruptures of the dorsal scapholunary band, which leads to symptomatic carpal instability with the simultaneous presence of a rupture of the dorsal ligamentum intercarpale (DIC). The number of untreated SL band lesions in distal radius fractures is largely unknown.

A scapholunary band lesion can be represented in different degrees of severity, depending on the still preserved portion of the scapholunary ligament and the surrounding extrinsical ligaments. Partial ruptures only lead to pain during movement and result in a slight restriction of scaphoid mobility. A scapholunary complete rupture, on the other hand, leads to a dissociation of ossa scaphoideum and lunatum, resulting in a Dorsal Intercalated Segment Instability (DISI). DISI malposition in turn leads in the long run to wrist osteoarthritis, called SLAC Wrist, with secondary development of osteoarthritis. The development of the full disease takes 10-20 years. The development of a SLAC Wrist can be counteracted preventively in which a scapholunary instability - also within the framework of a radius fracture - is detected at an early stage and correctly stabilized. However, the clinical relevance and the recommended treatment of scapholunary band rupture has not yet been definitively clarified.

A complete rupture of the scapholunary band alone does not necessarily lead to instability. Among other things, one study shows that the dorsal ligamentum intercaraple plays a very important role in the stabilization of the Os lunatum and the Os scaphoideum. Only with additional rupture of the ligamentum intercaraple dorsal, next to the ligamentum scapholunare, is there a Dorsal Intercalated Segment Instability.

The Os lunatum and the Os scaphoideum are coupled with each other by the scapholunary tape apparatus. With a complete rupture of the scapholunary band, both the os lunatum and the osscaphoideum follow the respective self-movement. The Os scaphoideum can no longer exert a force on the Os lunatum. Thus, without counter-action, there is a pulling force on the Os lunatum by the still intact ligamentum lunotriquetrale and da the Os lunatum palmar is wider than dorsal, the Os lunatum is pushed over time into a permanent position of the extension and palmaren dislocation. The Os scaphoideum, on the other hand, is anatomically "slanted" to the wrist axis and thus has a tendency towards flexion. The flexion of the Os scaphoideum leads to a dorsal subluxation of the os saphoideum to the fossa radialis. This phenomenone in turn leads to the Dorsal Intercalated Segment Instability (DISI). This is reflected by the flexion of the os scaphoideum and the extension of the os lunatum radiologically in the lateral uptake with an increase of the scapholunary angle > 60° (usually maximum 45)° and the radioscaphoidal angle >15° again. In the long run, this misalignment develops a wrist osteoarthritis called SLAC Wrist (Scapho-Lunate Advanced Collaps) with secondary development of osteoarthritis.

The effect of untreated scapholunary dissociation on wrist function is unknown despite abundant studies, but all with small series. However, it has been proven that they lead to symptomatic carpal instability, especially with additional rupture of the dorsal ligamentum intercarpale.

In a large study with 839 subjects, 25.6% of patients with distal radius fracture have scapholunary dissociation immediately after trauma, and only 13.4% continued to have a persi-sedate scpaholunary dissociation after repositioning and osteosynthesis. This can best be explained by stabilization due to the ligamentotaxis of the extrinsic carpal ligaments.

Another study showed an excellent long-term outcome in patients who were stable after volar plate osteosynthesis in distal radius fracture without surgical treatment of scapholunal dissociation in the functional test. Whereas a plaster cast leads to a worse outcome.

The Watson test, as used in clinical practice, is a provocation maneuver to diagnose a possible scapholic ligament lesion. Here, the Tubercel scaphoideum is fixed with the thumb and at the same time a wrist deviation from the radial duction and flexion into the ulnar duction and extension is performed. In the case of higher degree of instability in the sense of a complete rupture of the scapholunary band, the Watson test is positive if, in addition to pain, there is a palpable snap, due to a subluxation of the proximal scaphoid pole over dorsal radius at radial deviation and subsequent spontar position in the Fossa radii at Ulnadeviation. However, this test is not feasible with fresh radius fracture.

Accompanying scapholunary lesions in radius fractures are often underdiagnosed, although they are up to 54% in dislocated, distal radius fractures. A study shows that intraarticular radius fractures are twice more commonly associated with scapholic lesions than seen in radiological diagnostics, although there are conventional-radiological suggestive evidence for static scapholunary band lesions. It has been described that 60% of all scapholunary lesions show no abnormalities in conventional X-ray image and are therefore easily overlooked. A widened joint gap between Os scaphoideum and Os lunatum with a distance > 3mm as well as a tilting of the two carpalia to each other indicates apossible bandrupture but is not diagnostic. However, in patients with a distal radius fracture, more than half of patients with an SL distance > 3mm in ct also have an extension on the opposite side 38-52%. There are no uniform conventional-radiological criteria for determining the instability of the wrist and the scapholunary distance.

If none of the above abnormalities can be found in the conventional radiological images, however, a clinical suspicion of scpholunary dissociation leads to a MR tomography and an arthroscopy of the wrist. A computed tomography is not a sensitive modality for a band lesion. An arthro-CT, on the other hand, detects a ligament injury and is equivalent to arthro MRI with a sensitivity of 95%.

In current literature, the gold standard in the diagnosis of scapholunary ligament injuries is arthroscopy. Using wrist arthroscopy as an examination technique for scapholic ligamentions, 7-64% of all patients with a distal radius fracture show a rupture, in extra-articular radius fractures the incidence is lower with 7-33%. We do not require an indicative arthroscopy due to the increased risk of surgery and therefore also the risk of infection.

So far, there have been no studies that have used a clinical, dynamic functional test intraoperatively under screening, to assess scapholunary instability in intra-articular radius fractures. With intraoperative detection of an SL band lesion, this can be supplied surgically under the same anaesthesia with different methods such as a band seam, ossary reinsertion, carpal transfixing or combinations.

The core of the study is the actual intervention to which the patients commit themselves. In this case, patients receive a computed tomography of the affected wrist in distal, intra-articular radius fractures in order to preoperatively, in addition to fracture, diagnose possible concomitant ligamentic injuries, in particular of the scapholunary band rupture. Computed tomography without intraarticular contrast agent administration, on the other hand, is a standard for displaying the exact fracture curves in intraarticular, distal radius fractures.

Subsequently, the scpaholunary stability is checked under intraoperative investigation before and after osteosynthesis with a dynamic test modified by us. With the help of this test, a relevant, i.e. an unstable scpaholunary band lesion, is also to be diagnosed.

The aim of this study is to investigate scapholunous instability in distal, intraarticular radius fracture and thus to diagnose an accompanying scapholunary band rupture.

• Determination of the prevalence of scapholunary band lesions in distal, intraarticular radius fractures
• Detection of scapholic instability in distanceric, intraarticular radius fracture, with the intraoperative conduct of a modified, dynamic functional test under illumination

With the results, the intraoperative test will be able to be used in the future for the diagnosis of scapholunary band lesions and the detection of persistent carpal instability after osteosynthesis of radius fracture.