Lumbar Functional Instability
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Adopted: 8/10 Lumbar Functional Instability (AKA, Lumbar: Clinical Instability, Segmental Instability, Joint Instability) Note: In the 4-part diagnosis format used for musculoskeletal cases in the UWS clinic system, functional instability is not usually listed as a primary diagnosis. More commonly it will be accounted for as a significant contributor to a primary diagnosis linked by the phrase “complicated by lumbar functional instability.” Its presence is meant to identify one type of case that may be particularly suited for stabilization exercises. Severe traumatic instability and pathological instability are not included here. Definition Discussion Functional instability of the lumbar spine has The stabilization system of the spine can be been proposed as a distinct subset of patients divided into three subsystems: passive, active with LBP (Dellitto 1995, Demoulin 2007). and neural (Demoulin 2007, Panjabi 2003). The Lumbar functional instability (LFI)* is a clinical passive system consists of the discs, bony and diagnosis based on history and physical ligamentous structures and is primarily examination findings. It is a painful disorder responsible for resistance at the end range of hypothesized to result from a loss of the motion. The active system is composed of spine’s ability to maintain appropriate muscles and their tendinous attachments. This mechanical stiffness** in neutral, midrange, or component plays a major role in maintaining end-range movements. The most widely cited neutral zone stability. Multiple muscles definition is a “significant decrease in the contribute to spinal stability. (Kavcic 2004, capacity of the stabilizing system of the spine McGill 2003) The deep segmental muscles to maintain the intervertebral neutral zones (especially multifidi and transverse abdominis) within the physiological limits so that there is have been proposed as central players by some no neurological dysfunction, no major researchers (Hebert 2010) although whether deformity and no incapacitating pain.” (Panjabi they play a unique role is challenged by others. 1992) (Kavcic 2004, McGill 2002) The neural or motor control subsystem consists of the central and Functional instability is not synonymous with peripheral nervous system and integrates hypermobility or radiographic proprioceptive input from mechanoreceptors instability/hypermobility. Hypermobility and located in soft tissue structures and radiographic instability may be asymptomatic. coordinates activation of stabilizer muscles. LFI These terms denote circumstances where joint is postulated to result from dysfunction of this motion is excessive but may not be associated stabilization system. with qualitative (aberrant) alterations in physiologic motion. (Demoulin 2007) Neutral Zone Instability/Motor Control Insufficiency (MCI) The neutral zone is defined as the component ** LFI is used throughout this document for functional lumbar of physiologic intervertebral motion that can instability, but it is not a generally recognized abbreviation and is not suitable for charting. be induced with minimal internal resistance (Panjabi 2003). It is measured from the joint’s * * In biomechanical terms, spinal stiffness refers to the starting position up to the elastic zone (Panjabi spine’s ability to prevent unwanted movement or buckling. 1992). The elastic zone represents the elastic LUMBAR FUNCTIONAL INSTABILITY Page 1 of 16 capacity of the joint’s soft tissue structures activities potentially hazardous for the and the small amount of additional motion that functionally unstable spine. is available toward the end range of joint motion. Movement into the elastic zone Excessive end range motion/ hypermobility encounters more resistance and is dependent Excessive spinal joint end-range motion has on forced muscular effort on the part of the historically been labeled as either patient or by additional overpressure by an hypermobility or instability. However, examiner. When the forces applied at this point excessive end range motion is not necessarily are removed, the joint springs back from its associated with instability and the terms elastic limits. should not be used interchangeably. For the purposes of this document joint hypermobility Neutral zone instability is postulated to result and radiographic instability will be considered from expansion of the neutral zone or as isolated exam findings. Segmental or deficiencies in motor control with or without regional joint hypermobility is not clinically measurable excessive end range motion. problematic unless it is associated with pain or Expansion of the neutral zone is theorized to perceived as a risk factor for injury. Joint result from degeneration or attenuation in the hypermobility may be body wide or affect passive stabilizers (ligaments and the disc). specific spinal regions or joints. Joint hypermobility does not cross into the realm of Motor control insufficiency (MCI) refers to a instability unless it is inadequately break down in the neuromuscular system that compensated for by the motor system resulting provides the requisite stiffness needed by a in the characteristic signs and symptoms of functioning spine. MCI can result from poorly functional instability. conditioned muscles or from errors in the neurological control and programming of the Excessive end range motion results primarily muscles. It can be seen as a cause of functional from a loss of integrity of segmental spinal instability. This disorder is usually not ligaments, intervertebral disc or bony associated with marked structural deformity, stabilizing structures. This excessive end range excessive end range radiographic hypermobility motion may result from high load traumatic or neurologic deficits. (Panjabi 1992) Therefore events, repetitive microtrauma, a dynamic radiographs will typically not reveal developmental byproduct of activities such as any significant abnormalities of quantitative dance or sports (e.g., gymnastics) or, most movement. commonly, from significant spinal degeneration (degenerative spondylisthesis). Spinal MCI and neutral zone instability are associated degeneration is thought to have a strong with poor coordination of movement, lack of genetic factor (Battié 2009). proper stabilization and episodes of momentary aberrant motion. These events can cause Although there may be clues from a patient’s abnormal tissue loading (e.g., spinal history and physical examination (i.e., “buckling”) and local injury. Immediate palpation) suggesting hypermobility, it can only triggers of painful episodes include sustained be definitively demonstrated on dynamic postures, repetitive low load activities, or a radiographs by excessive listhesis at end range. single repetition of an ordinary activity of A variety of radiographic measures and ranges daily living. Based on biomechanical research, has been proposed (see diagnostic imaging). The National Institute for Occupational Safety There is, however, little agreement on a and Health (NIOSH) suggests that the spine can clinically useful cut point dividing excessive safely accommodate compressive loads at least from normal range of motion (Demoulin 2007). up to 3,400 Newtons during lifting tasks. In the absence of established standards, (Waters 1993) However, in vitro experiments increased end-range segmental motion must be have demonstrated that, in the absence of associated with clinical findings to be muscles and motor control systems, the passive considered significant. Dynamic radiographic elements of the spine alone cannot withstand evaluation is neither routine nor recommended loads of more than 90 Newtons (approximately as a screening tool for the identification of 9.2 kg) (Crisco 1991), making even common possible joint hypermobility. LUMBAR FUNCTIONAL INSTABILITY Page 2 of 16 Excessive end range motion may be also be motion on fluoroscopic video in one study associated with generalized joint laxity. In such (Teyhen 2007). cases it is associated with an increase in gross ROM throughout the body and can be identified Most of the other clinical signs and symptoms by an instrument like the Beighton Ligamentous frequently cited are based on expert opinion Laxity Scale. (See Appendix I.) and extrapolation from biomechanical research. In 2006, using a Delphi methodology, Finally, end range joint motion may be clearly a group of experts identified 15 subjective and excessive and if there is significant disability 14 objective identifiers for instability reflecting and/or significant neurologic deficits, current practice profiles (Cook 2006). The orthopedic consultation and potential surgical clinical clues most cited appear to derive from fusion may be appropriate. 1) the onset and behavior of the symptoms, 2) assessment of the quality of regional and segmental motion, and 3) indicators of poor Diagnosis motor control. The diagnosis of functional instability is made solely on clinical grounds. At this time there is Coding note no clearly established consensus on the criteria Functional instability does not have its own ICD for diagnosing LFI (Cook 2006, Demoulin 2007). code and there does not appear to be a There are, however, certain patterns of commonly used code used in the profession. presentation that suggest that the patient’s However, including functional instability in a spine may have a higher probability of being diagnosis and coding for it may help functionally unstable or would benefit from a communicate that the patient has a more spinal stabilization exercise program (Hicks complex