Introduction

Lumbar instability is believed to be a significant contributor to LBP-subgroups (prevalence ranging from 13-33%) and is often missed in clinical practice. Instability is defined as a decreased capacity of the spinal stabilizers to maintain the neutral zone within the physiological limits of movement. Up until now clinicians diagnosing clinical lumbar instability mostly rely on medical imaging, which is quite remarkable given that this imaging assumes structural instability. However, findings on medical imaging do not always correspond to pathology and therefore, this gold standard can be questioned. We highlight this paper as it made a significant effort to investigate not so much structural but rather clinical lumbar instability (CLI) from several findings and tests proposed in literature earlier on.

Methods

A cross-sectional study was conducted which included 200 participants between 40-60y with LBP over a period of 3 months. Patients were classified in 2 groups: a CLI group and a group of other spinal pathologies.

A cluster of 4 tests for diagnosing clinical lumbar instability was carried out by a physical therapist:

• Apprehension sign: A positive test was a feeling of lower back “collapse” with the sudden onset of LBP during ADL activities in the past week.
• Instability catch with and without the abdominal drawing in maneuver (ADIM): Bending forward as far as possible from standing and returning to the erect position. A test was positive when patients showed a limited ability to return upright without the ADIM compared with the ADIM.
• Painful catch sign with and without the (ADIM): Patients were supine on the examination bench and were asked to lift both legs as high as possible and lowering them slowly back again. This test was considered positive if a sudden LBP onset made it impossible to lower the legs slowly without the ADIM compared by the ability of slowly lowering both legs with the ADIM.
• Prone Instability Test (PIT): The examiner assesses segmental AP glide to the lumbar spine for stiffness and pain provocation with the patient lying with their upper body in prone and the feet supported on the ground. If a painful segment was found, patients had to straighten their legs to contract the back and hip musculature. This test was positive with the residing of pain provoked with the AP glide with the legs straightened. Click here for video description.

This cluster was then tested against a self-constructed reference standard containing 13 recommended history-taking signs and 6 physical examination findings as proposed in earlier studies. An orthopedic surgeon assessed whether these findings were present. The reference standard was considered positive when 7 and 3 signs from respectively the history-taking and physical examination were present.

• History signs: 1) reports feelings of ‘‘giving way’’ or back ‘‘giving out’’, 2) self manipulator, 3) frequent bouts or episodes of symptoms, 3) history of painful catching or locking during twisting or bending of the spine, 4) pain during transitional activities, 5) pain increased with sudden, trivial, or mild movements, 6) difficulty with unsupported sitting and better with supported backrest, 7) worse with sustained postures and a decreased likelihood of reported static position, 8) condition is progressively worsening, 9) long-term, chronic history of disorder, 10) temporary relief with back brace or corset, 11) reports frequent episodes of muscle spasms, 12) fear and decreased willingness to move, and 13) reports of previous back injury or trauma.
• Physical examinations findings: 1) the sign of hand walk up the thighs to return to the upright position, 2) reversal of lumbopelvic rhythm, 3) the posterior shear test, 4) passive intervertebral movement tests, 5) the active straight leg raise test, and 6) the Beighton scale.

Results

A cluster of 3/4 positive tests was the most accurate cluster of tests overall, with the highest LR+ (5.8) and the second highest specificity (91.7%) but the second lowest sensitivity (47.8%) and LR- (0.6). The cluster of two of four clinical tests showed the second highest sensitivity (89.1%), LR+ (2.4), and LR- (0.2).

Talk nerdy to me

While the authors have made a substantial effort to study the diagnosis of CLI, this study shows several flaws. First and foremost, participants were recruited from an orthopedic department in a hospital, which may cause that patients with more severe LBP have entered the study, thus limiting generalizability. A technique of “convenience sampling” was used, which recruits patients from a group that is easily accessible or highly interested in participating. Therefore, the sample may not fully reflect all LBP patients. Furthermore, patients presenting with an inability to actively move the lumbar spine due to severe pain/muscle spasms were excluded, which we think may be a sign of CLI. Also, it was not indicated whether the required sample size was determined a priori or a posteriori and the flow chart did not indicate how many patients in total were assessed for eligibility.

Further problems arise with the so-called “gold standard” reference test. As it is composed of several imperfect tests, we cannot ascertain the reference test being a true gold standard, possibly introducing imperfect reference standard bias, and thus caution with interpreting the diagnostic accuracy of the proposed cluster is warranted. Yet it was a good option to consider this composite reference standard as it avoided the diagnosis of CLI through structural findings as evaluated on medical imaging. The orthopedic surgeon evaluated the presence of a positive or negative result on the reference standard. This may be of an issue since orthopedic surgeons may look differently at LBP as physiotherapists do. Furthermore, it is unsure if the choice of 7 history findings and 3 physical examination findings having to be present for a positive reference standard was determined arbitrarily or based on proposed evidence from the literature. Last but not least the risk of incorporation bias is present as some of the index tests make part of the reference test.

Take home messages

• A cluster of at least 3 of 4 positive clinical tests was found to be useful for diagnosing clinical lumbar instability, however, in absence of a true clinical gold standard, this conclusion must be taken with caution.
• If a thorough history taking is performed, the proposed cluster may help to further evaluate the possibility of the presence of clinical lumbar instability.

Reference

Areeudomwong P, Jirarattanaphochai K, et al. Clinical utility of a cluster of tests as a diagnostic support tool for clinical lumbar instability. Musculoskelet Sci Pract. 2020 Dec;50:102224. doi: 10.1016/j.msksp.2020.102224.