1. The concept of degenerative lumbar instability and slippage
Lumbar spine motion segment instability refers to abnormal motion function of one or more motion segments of the lumbar spine (two adjacent vertebrae and the intervertebral discs between them). Alterations in these components of stability due to any of these causes may lead to lumbar instability, and those with concomitant clinical symptoms are referred to as degenerative lumbar instability and are commonly seen in middle-aged and older patients. From the mechanical point of view, instability should be a dynamic change, i.e., the instability segment is displaced with the change of stress, which is manifested in imaging as a change in the position and angle of the vertebral body question in the typical lumbar hyperflexion and hyperextension position.
In contrast, degenerative lumbar spondylolisthesis is due to further aggravation of disc degeneration, increased abnormal intervertebral activity, and displacement of the upper and lower vertebrae of the diseased segment. This is manifested on imaging as a static slippage. Most degenerative lumbar spondylolisthesis stops between I and II degrees.
2.Diagnosis of degenerative lumbar instability and slippage
(1) Clinical symptoms and signs
The clinical manifestations of degenerative lumbar instability are diverse, with many symptoms. The signs are few. Patients mostly report lumbar pain related to position changes, with or without radiating pain in the lower limbs. Some patients may have intermittent claudication of the lower extremities alone without lumbar pain, a manifestation of lumbar spinal stenosis. Some patients exhibit lumbar pain after activity or position change, and spasm or tension in the lumbar musculature. Physical examination: localized pressure pain, percussion pain and swaying pain. Local palpation in the standing position can reveal a “step” shape of the spinous process and changes in local muscle hypertrophy, tension or even spasm.
The clinical manifestations can be categorized into three types: mechanical low back pain, intermittent claudication due to spinal stenosis, and nerve root pain.
(2) X-ray diagnosis
Lumbar instability in the frontal and lateral radiographs mainly shows degenerative changes such as mild narrowing of the intervertebral space, sclerosis of the end plate and formation of peri-vertebral bony redundancy, especially distraction bony redundancy. In contrast, power radiographs (hyperextension and hyperflexion) have characteristic changes, such as slippage ≥3 mm in sagittal power radiographs; disc angle change ≥12° (with additional criteria of 3 mm, 10° and 4 mm, 20°). Or the angle between each two vertebrae in L1 to 4 ≥ 15°, L4.5 ≥ 20°, and L5S1 ≥ 25°.
(3) Other examinations
CT can clearly show the degenerative changes of the lumbar disc in the unstable segment, as well as the ligaments and muscles around the lumbar spine. MRI has the advantage of showing the soft tissues and can be used to show the degenerative changes of the lumbar disc, as well as the ligaments and muscles around the lumbar spine.
The diagnosis should include both imaging and clinical manifestations, one without the other. Pain due to lumbar instability has the following characteristics: the pain is circumferential, the patient has a definite pain arc from sitting to standing, aggravated by exertion, relieved by rest, and relieved by complete standing; plain and power radiographs of the lumbar spine are the most basic and important diagnostic tools for diagnosing degenerative lumbar instability and slippage. Although MRI is of limited use in diagnosing the degree of displacement between degenerative lumbar spine vertebrae, it is of great use in determining the degree of disc degeneration and spinal stenosis.
3.Treatment of degenerative lumbar instability and slippage
Some lumbar instability is self-limiting, and some patients can obtain better results with conservative treatment, so conservative treatment should be carried out first. It includes: lumbar braking, lumbar back muscle and abdominal muscle training, weight reduction, and avoidance of lumbar rotation activities. If conservative treatment is ineffective, and the nerve canal produces substantial bony stenosis during the degeneration process and continues to worsen, there are progressive aggravation of radicular irritation symptoms, pain, sensory and motor disorders and cauda equina syndrome in the clinic, and there is imaging evidence compatible with it can be considered for surgical treatment.
(1) Indications for surgery
①Lumbar pain with or without lower extremity neurological symptoms, which seriously affects the patient’s work or life and has been ineffective after 3″ to 6 months of strict conservative treatment, and the patient requires active treatment.
②The lumbar hyperextension and hyperflexion radiographs support degenerative lumbar instability, and the radiographs show signs of lumbar spine slippage.
(3) CT or MRI of the lumbar spine suggests disc degeneration, thickening of the ligamentum flavum, bilateral small joint hyperplasia, formation of bone redundancy at the anterior edge of the vertebral body and narrowing of the intervertebral space and lumbar spinal canal.
(2) Decompression and fusion surgery
Decompression is an important element to address the compression of the nerve root or cauda equina in degenerative slippage to improve the patient’s neurological symptoms. Fusion is mainly to address the low back pain due to instability. The purpose of internal fixation is to improve the rate of fusion or correction of the slippage. Overall, a large body of literature has demonstrated better long-term outcomes with fusion plus decompression than with decompression alone.
In patients with low back pain as the primary symptom, stabilization is the goal and can be achieved by fusion fixation; therefore, fusion is the primary treatment principle. Commonly used methods are: transforaminallumbarinterbodyfusion (TLIF), posteriorlumbarinterbodyfusion (PLIF) or anteriorlumbarinterbodyfusion ( anteriorlumbarinterbodyfusion (ALIF).
With the continuous improvement of internal fixation instrumentation, the use of internal fixation systems for the treatment of degenerative lumbar instability has become increasingly available. The arch nail a rod system can achieve peak strong fixation of the three columns of the spine to improve the fusion rate of the lumbar spine, and is the internal fixation instrument widely used in clinical practice.
(3) Non-fusion surgery
Due to the problems of fusion surgery such as degeneration of adjacent segments, non-fusion techniques have been used in the clinic in recent years. Non-fusion techniques include artificial disc replacement, artificial nucleus pulposus replacement, interspinous internal fixation implants and other methods.
The main indications for artificial lumbar disc replacement surgery are: simple lumbar disc herniation; degenerative instability of the lumbar spine; degenerative changes in adjacent segments due to spinal fusion; and age below 50 years. And its main contraindications include: patients of advanced age, or patients with osteochondrosis or osteoporosis that easily cause vertebral collapse; patients with severe lumbar spondylolisthesis or with arch fracture; patients with poor mobility due to surgical scar or other causes of lumbar spine fusion and adhesion; patients with severe destruction of the posterior lumbar spine structure and posterior structural instability that are prone to dislocation after replacement; patients with intervertebral space infection, adhesive arachnoid inflammation.
Interspinous internal fixation implants restore posterior column height, withstand load transfer, while relieving pressure on the anterior and posterior spinal structures and cushioning the painful motion present in the implanted segment. Typical representatives of these include the Wallis system and the XSTOP system.
Because nonfusion techniques have been available for a short time, their long-term clinical efficacy remains to be seen.