Lumbar Arthroplasty (Disc Replacement)
Dr Ales Aliashkevich is a strong advocate for motion-preserving spinal surgery. He has been using lumbar disc replacement as an alternative to spinal fusion to maintain segmental mobility in hundreds of patients with chronic back pain and radiculopathy since 2012. The validity of this approach was confirmed by the excellent surgery results with very low complication rates. Over the years, he has gained extensive experience in single and multilevel arthroplasty and hybrid procedures.
Goals of lumbar disc replacement include:
– reduction of back and radicular leg pain,
– medication reduction,
– prevention of disc and facet joint degeneration,
– improved posture, lower back and leg function,
– improved work and recreational capacity,
– improved life quality,
– return to normal activities.
Lumbar Disc Disease
The human spine is a complex structure with multiple intervertebral discs playing a crucial role in its mobility and stability. They act as shock absorbers and contribute to the flexibility and motion of the spinal column. The lumbar discs bear the weight of the whole body and are much larger than the discs in the neck or thoracic spine. The facet joints at each level provide additional stability and prevent discs from excessive translation (spondylolisthesis).
The discs are made up of the inner jelly-like portion (nucleus pulposus), and outer fibrous material called the annulus fibrosus, which supports the inner nucleus. The annulus is innervated by multiple pain receptors, which signal any injuries, tears or cracks. With disc degeneration, the nucleus material can bulge out and press on the nerves causing referred radicular pain. The lower two discs of the spine (L4/5 and L5/S1) bear the most weight and are exposed to considerable stress and pressure. They are the most frequently damaged discs with injuries and prone to degenerate faster than other discs.
It is estimated that 70-80% of all people experience low back pain at some point in their lives. Lumbar pain can be caused by degenerated discs, facet joints, disc herniations, spondylolysis and spondylolisthesis with or without compression of the nerve roots. Accurate identification of the primary pain generator is critical. Natural ageing of the disc (degeneration) or trauma can affect its mobility and cause reduction of its cushioning function. Structurally, it may manifest in a disc protrusion of formation of bone spurs (osteophytes) causing pressure on the neural structures and resulting in back and hip/leg pain, numbness or weakness.
IMPROVED SURGICAL OUTCOME
Goals of Lumbar Disc Replacement
Lumbar arthroplasty is aimed at restoring the shock-absorbing function of the damaged or degenerated intervertebral disc with simultaneous decompression of the spinal cord and nerve roots. Similar to the well-established hip and knee joint replacement procedures, the evolution of artificial disc prostheses may also result in a dramatic improvement of patient’s quality of life and achieve high levels of patient satisfaction.
The initial treatment of lumbar disc disease involves rest, gentle physical therapy, painkillers or anti-inflammatory medications. Sometimes, spinal nerve root injections with local anaesthetic or steroid can be applied. Surgical treatment is taken into consideration only as the very last resort to manage intractable pain or neurological deficit. Different types of surgery can address lumbar disc pathology, starting from a simple decompressive procedure (microdiscectomy or laminotomy) and going to more complex interventions which involve implants (fusion or Lumbar disc replacement). Decompression of the spinal canal and nerve roots is primarily indicated to deal with neuropathic symptoms, like leg pain. They are less efficient if the lower back pain dominates. In patients with intractable and disabling low back pain, lumbar disc replacement and fusion are taken into consideration. Fusing vertebrae into a solid bone (arthrodesis) helps to eliminate discogenic of facetogenic pain in carefully selected patients but prevents normal movements in the spine and puts additional stress on the segments above and below. Other potential issues include failure to achieve a solid bone fusion (pseudarthrosis) and complications at the bone donor site (usually the iliac crest). Some patients with radiologically confirmed lumbar fusion may still end up with no improvement of their back pain because of increased biomechanical stress. Hence, the motion-preserving lumbar arthroplasty had established as an alternative option for chronic low back pain. Although lumbar total disc replacement (TDR) and fusion are similar in approach, technique and initial results, the differences are becoming more obvious over time, in particular after more than five years when adjacent segment disease becomes symptomatic as a result of the fusion-induced accelerated degeneration.
The goals of a lumbar disc replacement include:
– Reduction of back pain
– Medication reduction
– Prevention of disc and facet joint degeneration
– Improved posture, lower back and leg function
– Improved work and recreational capacity
– Improved quality of life
The chance of obtaining a significant benefit from surgery depends upon a wide variety of factors which will be discussed at your appointment with Dr Aliashkevich.
The meta-analysis study of Deng-Yan Bai et al. (Medicine (Baltimore). 2019 Jul;98(29): Total disc replacement versus fusion for lumbar degenerative diseases – a meta-analysis of randomized controlled trials) stated:
Compared to lumbar fusion, total Lumbar disc replacement significantly improved ODI, VAS, SF-36, patient satisfaction, overall success, reoperation rate, ODI successful, reduced operation time, shortened duration of hospitalization, decreased postsurgical complications.
The long-term outcome studies also showed that the disc replacement reduces the chances of the symptomatic adjacent segment degeneration by more than 50% when compared to fusion. Multiple other investigations have shown superior patient outcomes, higher patient satisfaction rates, reduced rate of re-operations, fewer complications and reduced costs after lumbar arthroplasty when compared with spinal fusion in properly selected candidates.
MATERIALS AND DESIGNS
Decades of biomechanical research, engineering and meticulous clinical studies were required to achieve advances in medical device technology and to produce a current line of artificial intervertebral discs. Modern artificial lumbar disc replacement implants are available in variable shapes, sizes, heights and articulation types. It means that there is still no ideal implant available to mimic the biomechanical properties of a healthy natural disc and perfectly cushion and transfer loads in the lumbar spine. The perfect artificial disc should achieve the following goals:
– distribute loads evenly across the front, back and sides of the vertebrae
– provide stability and natural lumbar spine movements in different postures;
– bear prolonged loads of the bodyweight;
– unload facet joints;
– restore healthy anatomy and space between the vertebrae;
– restore foraminal height decompressing the nerve roots;
– be biologically compatible, corrosion-resistant, and able to last for the patient’s lifetime.
Extensive biomechanical wear and motion tests are performed to simulate varying loads and movements and to ensure the durability of the implants and their components. It is assumed that the human spine undergoes more than 100 million bending/extending cycles during a lifetime. For the minimal life length of an artificial disc implant of 40-50 years, it should be able to tolerate at least 40 million load cycles.
The implants can be classified into constrained, semi-constrained, and unconstrained. A constrained disc has a mechanical stop that limits its range of motion and provides physical stability. Semi-constrained devices can move slightly outside of the physiological range of motion, and unconstrained prostheses rely only on natural limiters of segmental mobility like spinal ligaments and facet joints.
Titanium is the most common disc implant material used, followed by cobalt alloys. Special surface treatment increases its integration with the vertebral bones:
– large footprint to cover the maximum area of the vertebral endplate;
– keels, spikes and screws;
– specialised coatings (calcium phosphate, plasma-sprayed titanium, aluminium oxide, hydroxyapatite).
The metallic components may produce distortions (artifacts) on magnetic resonance imaging (MRI) but because they are fixed to the bone, should not be considered as a contraindication for a scan.
ADVANCED SPINAL TECHNOLOGY
There are several types of artificial lumbar disc replacement prostheses available on the market. Here are some examples:
– LP-ESP (Elastic Spine Pad) disc (FH Orthopedics) is a one-piece implant which has titanium alloy endplates covered by hydroxyapatite with spikes to improve bone fixation. The core consists of concentric inner and outer parts made from elastomeric polycarbonate urethane. It has a variable centre of rotation adaptive to natural movements and no surface bearing for an increased lifetime.
– Charité Artificial Disc: This was the first artificial lumbar disc approved by the FDA in the United States. It is made of two metal endplates and a polyethylene core.
– ProDisc-L: This is a two-piece device that consists of a cobalt chromium alloy endplate and a polyethylene core. It is designed to mimic the natural movement of the lumbar spine.
– Maverick Disc: This device is made of a cobalt chromium alloy endplate and a polyurethane core. It is designed to be implanted without the need for cement or screws.
– Kineflex/SpineArt: This is a one-piece device that consists of a titanium endplate and a polyurethane core. It is designed to provide motion in all directions.
– M6-L: This is a artificial disc that is designed to mimic the natural movement of the cervical spine. It is made of a titanium alloy endplate and a high molecular weight polyethylene core.
It is important to note that the choice of prosthesis is typically made by a surgeon based on the specific needs of the patient and their medical history.
Please refer to the following website for more information and examples of available disc prostheses:
INDICATIONS AND CONTRAINDICATIONS FOR ARTHROPLASTY
Who can be a candidate for lumbar disc replacement?
Patients with chronic back pain and lumbar radiculopathy should be carefully selected before consideration of disc replacement. All conservative treatment options (rest, medications, physical therapy, steroid injections) should be exhausted before the discussion of surgery. Intractable radicular leg pain and neurological deficits (tingling, numbness, weakness, loss of balance, trouble with coordination or walking) caused by a damaged disc are the most common indications for lumbar disc replacement. Apart from a thorough neurological examination, patients require MRI to visualise the anatomy of the intervertebral discs and nerve roots. Flexion/extension x-rays are routinely required to estimate the mobility of the affected segment. SPECT/CT may be needed to rule out inflammation in the facet and sacroiliac joints.
If imaging shows problems with several discs, clinical correlation, neurophysiological testing (EMG and nerve conduction tests), diagnostic nerve blocks or provocative discography are required to identify which level should be considered as the dominant source of the problem.
The final decision with regards to surgery is always prerogative of the patient.
In Australia, the United States and many other countries, lumbar disc replacement is only approved for use at one level. Two-level disc replacement is not covered by Medicare or private health insurance. In some exceptional circumstances, insurances may consider some funding. Usually, the two-level disease is dealt with by a hybrid procedure, in which one disc is replaced and another fused.
Based on MBS protocols, (http://www9.health.gov.au/mbs/search.cfm?q=51130) it can be used for a patient who:
(i) has not had prior spinal fusion surgery at the same lumbar level; and
(ii) does not have vertebral osteoporosis; and
(iii) has failed conservative therapy.
total Lumbar disc replacement might be a suitable alternative to fusion for young patients suffering from disc-related chronic back pain of more than 6 months duration without significant facet joint degeneration, deformity, instability, or osteopenia. Disc arthroplasty can also be used for the treatment of symptomatic adjacent segment disease above or below the previous fusion.
Contraindications for lumbar disc replacement surgery
The procedure should not be performed in patients younger than 16 years (skeletally immature), in the presence of significant osteoporosis (reduced bone density), impaired motion due to segmental fusion (e.g., ankylosing spondylitis), an active infection or advanced malignancy. It is contraindicated if abnormal motion (e.g., spondylolisthesis with translation on flexion/extension lateral views) or instability is present at the affected level. The goal of lumbar disc replacement arthroplasty is to preserve but not to recreate motion, and severe degeneration of the facet joints with loss of mobility on flexion/extension x-rays or significantly reduced disc height (less than 3 – 4 mm) would make fusion more appropriate. Kyphotic or scoliotic spine deformity cannot be reliably corrected by Lumbar disc replacement. Patients with a high pelvic incidence (more than 65°) are prone to have back pain due to facet arthropathy and may not respond well to a disc replacement. It may also be contraindicated by certain vascular anomalies or conditions that would make the necessary surgical approach unsafe. Possible allergy to the device material should also be taking into consideration during preoperative planning.
ADVANCED SPINAL TECHNOLOGY
Preparing for lumbar arthroplasty
To maximise the benefit from surgery, patients are usually advised:
– to take sufficient time to consider all available treatment options;
– to have an assessment of general health and fitness for general anaesthesia;
– to discuss their medications with the surgeon and anaesthetist;
– to quit smoking (if applicable);
-not to eat or drink at least 8 hours before the scheduled surgery.
Lumbar arthroplasty is usually performed via the anterior approach. This technique avoids splitting large back muscles and prevents scar formation around the spinal nerves. It allows for complete removal of the damaged intervertebral disc, restoration of its height and placement of a large-footprint implant to cover the surface of the vertebral endplates. The muscles that maintain spinal posture and stability of the lower back remain undisturbed, and the spinal nerves can be decompressed directly from the front. Before surgery, assessment of the individual vascular anatomy is routinely performed by abdominal ultrasound and CT-angiography.
Dr Aliashkevich usually performs the procedure together with an experienced vascular approach surgeon to minimise the risk of injury to the major vessels in front of the lumbar spine (aorta, inferior vena cava and iliac arteries and veins). The vascular surgeon assesses all patients to confirm their suitability for this approach. Slight variations of the surgical technique are possible, depending on the individual anatomy and type of the implant. Before surgery, sequential compression stockings are fitted to maintain blood circulation is in the legs and to minimise the risk of deep venous thrombosis. The patient is positioned face-up on the operating table. Pulse oximeters are attached to the big toes for continuous monitoring of blood circulation and to rule out ischemia from the short-term compression of the iliac arteries by retractors or vertebral pins. The CellSaver autologous blood recovery system is used to collect any possible blood lost during surgery and to avoid unnecessary allogeneic transfusions. After induction of general anaesthesia, a bladder catheter is placed to reduce the tension of the lower abdomen, to monitor urine output and to make postoperative voiding easier.
The level of surgery is visualised with intraoperative x-ray (fluoroscopy). The surgical approach can be performed from the left or right side, depending on the level of surgery and individual anatomy. A left retroperitoneal approach is usually recommended in L4/5 and L3/4 to avoid excessive retraction of the aorta. A right-sided approach can be preferred for the L5/S1 level in males to avoid injury to the superior hypogastric plexus on the left side of the pelvic promontory, which may cause retrograde ejaculation. Another advantage of accessing L5/S1 disc from the right side is to preserve the left-sided retroperitoneal plane intact for possible interventions in the future.
After disinfecting and draping the skin in the anterior abdominal wall, the local anaesthetic is injected. The incision is made, and the subcutaneous fat tissue is divided. The fascial muscle sheath is raised, and the abdominal rectus muscles are separated in the midline. The transversalis fascia is divided, and the retroperitoneal structures are approached by retraction of the bowels in the peritoneal envelope. The ureter is identified and carefully retracted. The retroperitoneal dissection allows exposure of the ventral spine and bifurcations of the aorta and inferior vena cava. Moderate prevertebral adhesions were found requiring extensive dissection. Ligation and suturing of several venous branches were performed.
Exposure of the target disc is created by mobilising the vessels (the aorta/common iliac arteries and inferior vena cava/left common iliac vein). The midline is marked, and the anterior longitudinal ligament is incised and opened in H-shape fashion. Discectomy is performed by separating the cartilage from the vertebral endplates and using rongeurs. Decompression of the nerve roots can be achieved using Kerrison rongeurs and curettes. The endplates are carefully prepared using various sizes of curettes and raspatorium. The posterior longitudinal ligament and protruded disc material can be removed. Possible venous bleeding can be controlled with bipolar coagulation or various haemostatic agents. The disc implant trials are used to size the height, width, and depth of the implant. The artificial disc should have the largest possible footprint to cover the surface of the vertebral endplates. The height of the prosthesis should match the discs above and below. The appropriately sized disc implant is positioned in the middle of the intervertebral disc space with some tension allowing its snug fit. Initial fixation is reached through the implant teeth or a keel, but screws can be used to secure its position and prevent the risk of migration if needed. The implant position is confirmed using X-Ray. The meticulous haemostasis is obtained, and the wound is closed in a multilayer fashion. The skin edges are approximated using absorbable Monocryl suture, and a sterile dressing is attached. The average duration of uncomplicated lumbar disc replacement surgery is 1.5-2 hours.
RECOVERY AFTER LUMBAR ARTHROPLASTY
After surgery, patients are taken to the recovery room to monitor their neurological function, to control postoperative pain and to keep an eye on the heart rate, blood pressure and blood oxygen saturation. About an hour later, they are taken to the ward and allowed to mobilise. Physiotherapy and gentle exercises are usually commenced the next day after surgery. Early mobilisation allows for quicker rehabilitation and recovery.
X-rays of the lower back are performed within the first 24 hours after surgery to confirm implant position. The urinary catheter is removed the next day, and blood thinning medication commenced to prevent deep venous thrombosis. Compression stockings are used until full mobility and discharge. Some patients may experience mild trouble with opening their bowels or bloating for a few days and could receive laxatives. Discharge can be planned after 3 or 4 nights, depending on postoperative progress and physiotherapist assessment. A lumbar brace is usually not required.
For the first days at home, patients are recommended to avoid lifting weights over 2 kg and to engage in any strenuous or repetitive activities that may affect the back or cause discomfort. Regular short walks, gentle stretching and a healthy diet, are recommended during the first weeks after surgery.
It is not uncommon to have mild pain in the lower back, buttock, leg or around the wound. It should respond to prescribed painkillers and improve in the first weeks. Occasionally, a short course of oral steroid medication can be required to reduce the nerve swelling. Laxatives can be continued to avoid constipation. Most patients are capable of returning to their normal activities and light work within a few weeks of surgery. Local driving for up to 20 minutes can be resumed after discontinuing strong pain medications. Patients are advised to participate in a rehabilitation program and an appropriate low-impact physical therapy.
Incision care is straightforward, and the dressing applied in the hospital should be kept dry and clean for 10 – 14 days. The absorbable sutures placed beneath the skin don’t require removal. The stitching material will dissolve with time. Dressing changes are usually not required. Taking showers is possible with an additional plastic occlusive dressing applied on top. Allowing water to soak the dressing or wound for a few minutes is not a problem but scrubbing or scratching should be avoided, and the incision must be kept dry. It is important not to leave a wet dressing on the wound or soak the wound in a bath or swimming pool during the first two weeks. A follow-up appointment with Dr Aliashkevich is usually arranged six weeks following the procedure to plan ongoing care and individual prospects of recovery and return to work.
RISKS AND COMPLICATIONS
Risks of Lumbar Arthroplasty
Lumbar arthroplasty is a safe procedure, but not without risks. The chances of minor complications (e.g., superficial wound infection) are around 3-4%, and the risk of significant or permanent complications is 1-2%. Candidates for surgery are provided with the explicit information materials and requested to sign a consent form before entering the operating theatre.
General surgery risks include:
– excessive blood loss,
– postoperative heamatoma,
– adverse reaction to medications,
– deep venous thrombosis,
– pulmonary embolism,
– heart attack
– pressure injuries,
– eye or teeth injuries,
– stroke, and
– other unpredictable complications/mortality.
Specific risks associated with the area of intervention may include:
– implant migration or subsidence,
– spontaneous fusion/heterotopic ossification,
– adjacent segment disease,
– ongoing or worsening pain,
– material failure,
– adverse reaction to implant material,
– adjacent segment disease,
– cerebrospinal fluid leakage,
– injury of the spinal structures, nerves, vessels, bowels, kidney, ureter and other vital organs,
– recurrent laryngeal nerve injury causing hoarseness of the voice,
– tetraplegia, hemiplegia,
– bladder/bowel problems,
– sexual problems (retrograde ejaculation which occurs into the bladder, rather than out into the penis),
– erectile dysfunction,
– incisional hernia,
– ileus (slowing of bowel movements),
– other unpredictable morbidities and mortality.
Some factors may increase the risk:
– poor general health,
– chronic cardiac or pulmonary disease,
– chronic kidney problems,
– chronic pain condition,
– the prolonged and severe neurological deficit,
– intake of blood-thinning medications such as anticoagulants or antiplatelets,
– mental health problems,
– multi-level surgery,
– advanced pre-existing degenerative disease,
– long-term intake of steroids, immunosuppressants and stronger painkillers,
Fortunately, the above complications are extremely rare. The lumbar disc replacement surgery is well-established, and the quality of care and materials used are very robust. The likelihood of any implant-related complications is extremely low because the natural range of movements and stresses applied to the lumbar intervertebral discs are significantly less than in other joints such as the hip and knee.
WHAT TO EXPECT FROM LUMBAR ARTHROPLASTY
Outcomes of Lumbar Disc Replacement
Postoperative pain is usually moderate and subsides markedly within 7-14 days. Recovery times can vary in different patients, depending on their age and individual medical conditions. The longer the problems existed before surgery, the longer it may take to notice a benefit. In some cases, the final recovery can take a few months.
Most patients recover well from lumbar arthroplasty and can expect the improvement of lower back and leg pain in a few weeks or months. It is realistic to expect significant pain reduction after successful surgery, but its complete elimination is rare. Restoration of muscle strength may require several weeks of rehabilitation and physical exercises. Muscle wasting may take up to 6-12 months to improve. The muscle may never recover its normal bulk if the nerve compression had been too severe. Preoperative sensory loss, tingling or pins and needles may take 3-9 months to recover fully. In rare situations, neurological deficits may persist for over a year after surgery or become permanent.
Possible outcomes if no treatment is undertaken
If the lumbar disc replacement degeneration is not treated appropriately, the possible outcomes may include:
– Chronic back and leg pain
– Problems with mobility
– Weakness, numbness
– Problems with bladder/bowels/sexual functions
– Depression and anxiety
ADVANTAGES OF LUMBAR ARTHROPLASTY
Comparing lumbar disc replacement with anterior lumbar interbody fusion (ALIF)
Both artificial lumbar disc replacement and anterior lumbar interbody fusion (ALIF) improve pain, but may not eliminate it. Both procedures offer very favourable short- and medium-term clinical outcomes reaching satisfaction rates higher than 80 – 90% in appropriately selected patients. However, the difference may become apparent after longer follow-up. Fusion decreases spinal mobility and causes more stress to the adjacent levels creating new problems and accelerating spinal degeneration. The ability of the bone to “fuse” varies in different patients. Failure of consolidation (non-union) may be associated with persisting pain.
The advantages of motion-preserving surgery include:
– maintaining natural back mobility;
– reducing the chances of adjacent segment degeneration above and below operated disc;
– reduced need for re-operations;
– eliminating potential problems with bone graft harvesting;
– eliminating the risk of pseudoarthrosis or non-union;
– no need to wait for solid fusion;
Potential benefits of ALIF include:
– applicability to a wider range of patients, including cases where disc replacement is contraindicated;
– the ability to address multi-level pathology;
– wider insurance cover (some insurance plans don’t include joint replacements);
As a general rule, Dr Aliashkevich would recommend considering lumbar disc replacement as the preferred choice over fusion. Only if it is not feasible, e.g. in multi-level pathology consideration may be given to a hybrid procedure where disc replacement in one level is combined with fusion in another.