25 Open Surgery for Chronic Scapholunate Injury
Abstract
A wrist is unstable when it gives way under physiologic loads. Injury to the scapholunate (SL) ligament tends to cause wrist instability particularly when the so-called helical antipronation ligaments (HAPLs) cannot send proper proprioceptive information to the intracarpal supinator muscles, the ultimate SL joint stabilizers. Several HAPL reconstructions using local tendons have been proposed. Those tendon grafts, however, do not contain active mechanoreceptors. Furthermore, it is not known whether a properly vascularized and innervated environment will help new receptors to grow into the graft and reinitiate the process of joint stabilization. This chapter will explain commonly used SL reconstructions, with the understanding that these need to be still regarded as experimental at this point in time.
25.1 Introduction
This chapter should not start without first clarifying some carelessly used terminology. Particularly problematic are the concepts of wrist misalignment and carpal instability. There are two meanings for the term “stability”: one derives from the verb “to stand,” that is, to be capable of resisting loads; the other, rather different, comes from the verb “to stay,” that is, to remain permanently unaltered. If we believe that both meanings are complementary descriptions of one single condition, we are creating the basis for misleading expressions such as “static instability.” The problem is not only semantic. If all malalignments were to be considered permanently unstable, all should be surgically intervened, and this, obviously, would be dangerously wrong. Reality is less dramatic, fortunately. Most carpal instabilities deteriorate with time. After carpal collapse, most capsules and allied soft tissues undergo a process of contraction, all empty spaces fill up with fibrosis, and the wrist becomes osteoarthritic. In fact, down the line, most misaligned wrists become stiff and, in many instances, asymptomatic. (▶Fig. 25.1). Certainly, clarifying what is unstable and what is not becomes a practical necessity. 1
25.1.1 Terminology
Instability is defined as the inability of a load-bearing structure to resist normal amount of loads without collapsing. A wrist is stable when it is capable of bearing physiologic loads without yielding. If it gives way when loaded, a wrist is unstable. If an alteration of forces induces the carpus to collapse, that wrist is by definition unstable, despite being well aligned.
Misalignment refers to an improper position of one of many elements of a load-bearing structure in the three-dimensional space. A misaligned wrist may become evident by the presence of a widened SL gap or by increased angulation of an SL angle. However, it is important to understand that “instability” and “misalignment” are not synonyms. Instability is a dynamic term that cannot be measured in static terms (millimeter of a gap or degrees of an SL angle). Only carpal misalignment may be quantified this way. Therefore, the wrist with an SL injury may be both misaligned and unstable, either or neither.
Stiffness is a clinical sign experienced by a patient whose wrist has had an abnormal reduction in the range of motion. Hence, stiffness and instability are mutually exclusive wrist dysfunctions. A joint may be unstable or stiff but not both.
Clinical symptoms are usually the reason why patients seek attention. In other joints, symptoms are directly proportional to the severity of the case. This, however, cannot be always said if we assess carpal dysfunctions. The symptoms of pain and instability may not exist even in the presence of severe misalignment. Indeed, the rate of asymptomatic osteoarthritic wrists is unknown but certainly more common than usually assumed. For this reason, we propose including clinical symptoms as another variable to consider for the assessment and treatment of carpal dysfunctions.
25.1.2 Ligaments Involved in Scapholunate Instability
Ligaments are not merely static cables binding bones together, but complex arrangements of dense collagen fibers that contain sensorial elements (mechanoreceptors) able to detect changes in carpal bone position, and transmit this information to the sensorimotor system for centralized control of neuromuscular joint stabilization. 1 , 2 , 3 , 4 Depending upon the direction of their fascicles, some carpal ligaments are naturally aligned to detect one particular type of intracarpal displacement, while others are ready for a different type of torque. The so-called helical antipronation ligaments (HAPLs) are specialized in preventing carpal collapse when the distal row is torqued into pronation. 5 While the dorsal and volar ligaments are considered primary SL stabilizers, the HAPLs have a secondary, yet very important role in wrist stabilization (▶Fig. 25.2, ▶Fig. 25.3).
25.2 Indications
For an SL-dissociated wrist to be a good candidate for carpal realignment using neighboring tendon,
The dissociation must be complete and nonrepairable.
Carpal misalignment must be easily reducible.
The periscaphoid cartilages must be normal.
The injury must be the only cause of unpleasant symptoms such as pain, weakness, and/or a giving way sensation.
When all the above coexist in a wrist with normal radiolunate relationship (no ulnar translocation and no excessive rotation of the lunate), the so-called three-ligament tenodesis extensor carpi radialis longus (3LT-ECRL) tendon ligamentoplasty is indicated. 6 , 7
When the lunate exhibits an abnormal coronal and/or sagittal misalignment, indicating the presence of an unstable SL dissociation plus a radiocarpal derangement, the so-called spiral ECRL technique will be preferred. 8
An SL gap is not an indication for surgery without clinical findings.
Treatment during early stages of the condition, in which alignment is maintained by secondary stabilizers, should be directed at restoration of neuromuscular control of SL joint stability. 4 In these cases, surgery is not indicated.
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