Abstract

In recent years, machine learning (ML) and artificial neural networks (ANNs), a particular subset of ML, have been adopted by various areas of healthcare. A number of diagnostic and prognostic algorithms have been designed and implemented across a range of orthopaedic sub-specialties to date, with many positive results. However, the methodology of many of these studies is flawed, and few compare the use of ML with the current approach in clinical practice. Spinal surgery has advanced rapidly over the past three decades, particularly in the areas of implant technology, advanced surgical techniques, biologics, and enhanced recovery protocols. It is therefore regarded an innovative field. Inevitably, spinal surgeons will wish to incorporate ML into their practice should models prove effective in diagnostic or prognostic terms. The purpose of this article is to review published studies that describe the application of neural networks to spinal surgery and which actively compare ANN models to contemporary clinical standards allowing evaluation of their efficacy, accuracy, and relatability. It also explores some of the limitations of the technology, which act to constrain the widespread adoption of neural networks for diagnostic and prognostic use in spinal care. Finally, it describes the necessary considerations should institutions wish to incorporate ANNs into their practices. In doing so, the aim of this review is to provide a practical approach for spinal surgeons to understand the relevant aspects of neural networks.

Cite this article: Bone Joint J 2021;103-B(9):1442–1448.

The cost of clinical negligence in the UK has continued to rise despite no increase in claims numbers from 2016 to 2019. In the US, medical malpractice claim rates have fallen each year since 2001 and the payout rate has stabilized. In Germany, malpractice claim rates for spinal surgery fell yearly from 2012 to 2017, despite the number of spinal operations increasing. In Australia, public healthcare claim rates were largely static from 2008 to 2013, but private claims rose marginally. The cost of claims rose during the period. UK and Australian trends are therefore out of alignment with other international comparisons. Many of the claims in orthopaedics occur as a result of “failure to warn”, i.e. lack of adequately documented and appropriate consent. The UK and USA have similar rates (26% and 24% respectively), but in Germany the rate is 14% and in Australia only 2%. This paper considers the drivers for the increased cost of clinical negligence claims in the UK compared to the USA, Germany and Australia, from a spinal and orthopaedic point of view, with a focus on “failure to warn” and lack of compliance with the principles established in February 2015 in the Supreme Court in the case of Montgomery v Lanarkshire Health Board. The article provides a description of the prevailing medicolegal situation in the UK and also calculates, from publicly available data, the cost to the public purse of the failure to comply with the principles established. It shows that compliance with the Montgomery principles would have an immediate and lasting positive impact on the sums paid by NHS Resolution to settle negligence cases in a way that has already been established in the USA.

Cite this article: Bone Joint J 2020;102-B(5):550–555.

Continuous technical improvement in spinal surgical procedures, with the aim of enhancing patient outcomes, can be assisted by the deployment of advanced technologies including navigation, intraoperative CT imaging, and surgical robots. The latest generation of robotic surgical systems allows the simultaneous application of a range of digital features that provide the surgeon with an improved view of the surgical field, often through a narrow portal.

There is emerging evidence that procedure-related complications and intraoperative blood loss can be reduced if the new technologies are used by appropriately trained surgeons. Acceptance of the role of surgical robots has increased in recent years among a number of surgical specialities including general surgery, neurosurgery, and orthopaedic surgeons performing major joint arthroplasty. However, ethical challenges have emerged with the rollout of these innovations, such as ensuring surgeon competence in the use of surgical robotics and avoiding financial conflicts of interest. Therefore, it is essential that trainees aspiring to become spinal surgeons as well as established spinal specialists should develop the necessary skills to use robotic technology safely and effectively and understand the ethical framework within which the technology is introduced.

Traditional and more recently developed platforms exist to aid skill acquisition and surgical training which are described.

The aim of this narrative review is to describe the role of surgical robotics in spinal surgery, describe measures of proficiency, and present the range of training platforms that institutions can use to ensure they employ confident spine surgeons adequately prepared for the era of robotic spinal surgery.

Cite this article: Bone Joint J 2020;102-B(5):568–572.

The MAGnetic Expansion Control (MAGEC) system is used increasingly in the management of early-onset scoliosis. Good results have been published, but there have been recent reports identifying implant failures that may be associated with significant metallosis surrounding the implants. This article aims to present the current knowledge regarding the performance of this implant, and the potential implications and strategies that may be employed to identify and limit any problems.

We urge surgeons to apply caution to patient and construct selection; engage in prospective patient registration using a spine registry; ensure close clinical monitoring until growth has ceased; and send all explanted MAGEC rods for independent analysis.

The MAGEC system may be a good instrumentation system for the treatment of early-onset scoliosis. However, it is innovative and like all new technology, especially when deployed in a paediatric population, robust systems to assess long-term outcome are required to ensure that patient safety is maintained.

Cite this article: Bone Joint J 2017;99-B:708–13.

Objective:

The aim of this study was to define a method to identify the location of the great vessel bifurcation (GVB) in relation to the L5/S1 disc and measure the lumbo-sacral angle (LSA) at L5/S1 using routine lumbar spine MRI images on standard PACS software. The information can be used for surgical planning of anterior lumbar interbody fusion (ALIF) at L5/S1 with a plate and cage.

The effective capture of outcome measures in the healthcare setting can be traced back to Florence Nightingale’s investigation of the in-patient mortality of soldiers wounded in the Crimean war in the 1850s.

Only relatively recently has the formalised collection of outcomes data into Registries been recognised as valuable in itself.

With the advent of surgeon league tables and a move towards value based health care, individuals are being driven to collect, store and interpret data.

Following the success of the National Joint Registry, the British Association of Spine Surgeons instituted the British Spine Registry. Since its launch in 2012, over 650 users representing the whole surgical team have registered and during this time, more than 27 000 patients have been entered onto the database.

There has been significant publicity regarding the collection of outcome measures after surgery, including patient-reported scores. Over 12 000 forms have been directly entered by patients themselves, with many more entered by the surgical teams.

Questions abound: who should have access to the data produced by the Registry and how should they use it? How should the results be reported and in what forum?

Cite this article: Bone Joint J 2015;97-B:871–4.

Statement of Purposes

Functional Restoration (FR) and spinal fusion are both used as treatment for patients with chronic low back pain however opinions are divided over their long term efficacy. This study examines the 18 month to 8 year outcomes of stand-alone lumbar fusion (STALIF) at L5/S1 and FR in similar groups of patients.

Soon, UK surgeons will need to undergo regular revalidation and relicensing. As a part of this process they will need to collect accurate outcomes data. However, a lack of standardisation has led to numerous generic and disease specific outcome tools being available with increasing complexity in their administration and interpretation. In research and university settings these tools are easily administered, but in a busy general spinal practice with limited human and time resources, it may not be possible to use them reliably and consistently. Web-based systems remove some of these problems, but data-input can be time consuming.

This study evaluates the utility of a subjective Patient Satisfaction Evaluation Questionnaire (PSE) by comparing it to well-known outcome tools, the Oswestry disability Index (ODI) and the Low Back Outcome Score (LBOS).

The PSE (modified Odom’s Criteria) evaluates pain, the willingness to undergo surgery again in similar circumstances, the likelihood of recommending the operation undergone to a friend or family member and satisfaction with the process of care. Pain relief is ranked as “complete”, “good but not complete”, “little” or “no pain relief/pain worse than before surgery”. The responses are scored with three points allocated to complete relief of pain, down to none for no relief. The other questions score one for a positive and zero for a negative response. The maximum score is six. Four, five or six points count as success as long as the pain component is two or three. Nought to three, counts as failure, as does a score of four when pain is rated as “poor”.

The ODI, LBOS and PSE are not directly numerically comparable, but the results of them all can be grouped into “Success” and “Failure” which gives a basis for comparison of the tools.

150 consecutive patients who underwent lumbar spine surgery completed the three questionnaires independently of the treating surgeon. The scores were subjected to regression analysis (R square) and a Pearson’s correlation. Feedback was sought from the patients regarding the “user friendliness” of the questionnaires.

Results showed a good correlation between the ODI and LBOS with a Pearson’s value and R Square (RSQ) value of 0.86 and 0.75 respectively. The PSE compared to the ODI showed a Pearson’s value of 0.86 and RSQ of 0.74. The LBOS and PSE comparison had a Pearson’s value of 0.78 and RSQ of 0.61. The results show that the PSE in the form used correlates well with results from the ODI and LBOS. However, the patient feedback data indicated that the PSE was the most user friendly of the three tools.

The PSE was found to be a useful and user friendly tool, correlating well with recognised outcome measures, being easy to administer, document and interpret. If surgeons with limited resources cannot reliably use a more rigorous outcome tool, using the PSE should provide enough data to meet the standards that are likely to be required for revalidation and relicensing.

Introduction: Europe has no equivalent of the US Food and Drug Administration (FDA). As a result, spinal implants can be adopted into clinical use in Europe earlier than in the US with a lesser regulatory burden. This may benefit patients, but if a device fails due to design changes that are not fully evaluated, outcomes can be compromised. The classic example in the past was the Capital Hip. If Europe had an equivalent to the FDA, oversight of implant design and design changes might prevent such occurrences.

The Prosthetic Disc Nucleus (PDN) is an implant designed to replace the nucleus of the lumbar disc in early stage symptomatic disc degeneration. The PDN originally was a paired device. Due to technical difficulties encountered by surgeons these were converted to a single implant (PDN Solo range). Mechanical testing suggested the new device would function as well as the original paired device. However, the implant was introduced into clinical practice, outside of the US, without any clinical evaluation.

Study Design: Prospective cohort study with 3 to 5 year clinical and radiological follow-up.

Objective of Study: To review the outcome of PDN Solo implanted anteriorly in the lumbar spine, define the mode of failure and describe revision strategies.

Patients and Methods: PDN Solo was used in 35 patients from September 2002 to January 2005 with a median follow-up of 49 months. Patients with discogenic back pain causing significant disability were offered nucleus replacement after an extensive process of consent. The approach was anterior retroperitoneal with the exception of L5/S1 which was transperitoneal. 17 patients were treated with PDN alone and 18 with a PDN to treat a degenerate level adjacent to an interbody fusion. Outcome measures were the Low Back Outcome Score and a Patient Satisfaction Evaluation.

Results: 14 patients have needed PDN revision. The mean time to failure was 16.5 months. There were three early extrusions, two replaced with PDNs and one converted to a fusion. Revision procedures included seven conversions to STALIF, two circumferential fusions and five posterolateral fusions.

Four more unrevised patients were identified as clinical failures. The total failure rate was therefore 51.4%. In patients with a successful outcome there was a 33 point improvement in the mean LBOS score.

In all cases of failure the PDN jacket became disrupted with concomitant fragmentation of the hydrogel core

Conclusions: Modification of the paired PDN to a single device was introduced outside the US without any clinical evaluation. In the US, the original PDN and the Solo version failed to gain regulatory approval and following the failure of the Solo it has been redesigned again. This study raises questions regarding implant design, testing and approval considering that more than 4500 PDN replacements have been carried out worldwide since 1996. Do these events call for a European equivalent to the FDA?

Objective: To evaluate the outcome of treatment for adolescent disc disease (ADD) in individuals regularly involved in high class sport compared to relatively more sedentary adolescents.

Design: Retrospective observational study.

Setting: Private Spinal Orthopaedic Practice.

Patients: 52 individuals with confirmed ADD. 25 competing at county or national level in various sports (Group A). 27 moderately active individuals (Group B), but not elite sports players.

Interventions: History and clinical examination followed by radiological investigations were performed. Both groups were treated with oral medication including simple analgesia, muscle relaxants and NSAIDs as well as physiotherapy. Those with persistent pain were referred for pain management. Surgery was considered for refractory cases.

Main outcome measurements: The clinical and radiological evidence of disease progression, need for minimally invasive and invasive treatments as well as return to previous level of sport.

Results: 11 patients (44%) in group A had a non-invasive programme of treatment based on intensive physiotherapy. 11 (44%) needed minimally-invasive treatments in addition to physiotherapy. Three patients (12%) required surgery. One patient had to give up elite sport because of recurrent pain on significant exercise, but the others resumed their previous level of activity.

Nine patients (33%) in Group B were treated by physiotherapy alone while 13 (48%) had minimally-invasive treatment in addition to physiotherapy. Five patients (18.5%) required surgery. Two patients required revision surgery. All patients returned to their normal level of sporting activity.

Conclusion: Adolescents who play sport at a high level should not be discouraged by a diagnosis of ADD, as the outcomes of treatment are at least no worse than in their less active counterparts.

Study Design: Prospective observational study.

Objective: To establish the sensitivity, specificity and cost-effectiveness of motor evoked potential (MEP) monitoring of lower lumbar nerve roots during instrumented spinal fusion.

Subjects: 161 patients undergoing elective lumbar spinal fusion monitored with the Neurosign 800 machine.

Outcome Measures: MEP evidence of pedicle breaches and nerve root over-distraction. Symptoms and signs of new neurological deficits postoperatively. EMG confirmation of neurological deficits in symptomatic post-operative patients.

Results: True positive results consisted of pedicle breaches detected in 15 patients (9.3%). Nerve root irritation on distraction was found in 9 patients (5.6%). These results allowed modification of the surgical technique to prevent subsequent neural injury. True negative results on active pedicle probing occurred in 134 patients (83.2%) and in 146 patients (90.7%) on passive monitoring. False positive results were detected in 7 patients (4.3%). Four patients had electrical connection problems and in three patients pedicle probing was positive but direct screw testing was negative. True negative results consisted of a failure of monitoring to detect clinically significant neurological events in five patients (3.1%). In four the symptoms and signs were transient, resolving within six weeks of surgery. In one, revision decompression of the L5 nerve roots was required.

Conclusions: MEP monitoring in our hands has a specificity of 95.4% and a sensitivity of 75%. The cost per case is around £75.

Study Design: Prospective randomised controlled trial.

Objective: To determine whether topical application of autologous growth factors (AGF) and thrombin as a spray to large spinal wounds can reduce blood loss after lumbar spinal fusion.

Subjects: Seventy patients undergoing single or multi-level lumbar spinal fusion were randomised to receive a spray of AGF and thrombin to the raw surfaces of the wound as a haemostat or to receive no spray, immediately prior to wound closure.

Outcome Measures: Intra-operative swab and suction blood loss and post-operative loss into suction drains.

Results: The median intra-operative blood loss in the two groups was similar (665 ml in the AGF/Thrombin spray group and 500 ml in the non-spray group), but the post-operative loss in the AGF/Thrombin spray group was 34% less than in the controls when expressed as the ratio of intra- to post-operative blood loss (median postoperative loss in AGF / Thrombin spray group 315 ml; median loss in the non-spray group 360 ml). There was an even greater difference (44%) when intra-operative blood loss was more than 500ml (median loss in AGF/Thrombin spray group 340 ml; median loss in the non-spray group 520 ml).

Conclusions: AGF/Thrombin spray applied to lumbar spine wounds reduces blood loss generally, but more particularly when the intra-operative loss has been considerable. This effect is probably due to local replacement of haemostatic agents when these have been systemically depleted by the surgical procedure. This study provides evidence to support the use of AGF/Thrombin spray as an effective haemostatic agent in major spinal surgery.

Background and purposes of study The objective of this study is to report the preliminary clinical data from a stand-alone interbody fusion cage (Stabilis™) from two centres.

Methods and results This was a retrospective group comparative study. Anterior lumbar interbody fusion was performed using Brantigan (n=6) or Stabilis™ cages (n=19). Clinical assessment was performed using standardised questionnaires. Lumbar flexion/extension views were used to assess union and implant subsidence. There were no significant differences between the groups for ODI, VAZ, MZ and MSPQ pre-operatively. The Stabilis group showed an improvement in ODI (pre: 49.4; post: 39.3; p=0.024), VAS (pre: 76.1; post: 47.8; p< 0.01) and MZ (pre 32.9; post: 20.6; p< 0.01).

There was no statistical improvement in the Brantigan cage group. Despite clinical improvement, five patients in the Stabilis group failed to unite and six demonstrated subsidence of the implant. The relationship between non-union and subsidence was statistically significant (p = 0.017). Furthermore, the change in ODI between patients who united and those who did not was both statistically significant (p=0.03) and the difference in mean ODI between the two groups was considerable (21%).

Conclusions: Stand-alone cages show promise, involve a shorter operating time and less tissue trauma for the patient. This study has identified a high rate of non-union and implant subsidence. This did not appear to be clinically relevant.

Introduction: Tarlov first described the sacral perineural cyst in 1938 as an incidental finding at autopsy. There is very little data in the literature regarding the natural history of Tarlov cysts and consequently the recommendations for treatment are vague. Various operative treatments have been suggested including cyst aspiration, cyst decompression, micro-surgical cyst imbrication & cyst plication with cement filling of bony defects. We were first presented with the difficulty of managing a patient with a large symptomatic sacral cyst in 1997 and found little in the literature to help advise the patient. This paper presents the results of a prospective observational study and describes the clinical relevance of the different types of cyst, showing how a simple clinico-radiological classification can be used to help manage patients with cysts.

Methods: Between February 1997 and December 2002, 3935 patients underwent standard three sequence MRI scanning (T1 and T2 sagittals and T2 axials) for lumbosacral symptoms in our hospitals. 62 patients had cysts in their sacral canals, an incidence of 1.6%. Additional contiguous axial and coronal scan sequences were carried out to fully characterise them. Once identified, the clinical picture was correlated with the findings on MRI.

Results: Tarlov cysts can be classified according to whether or not their presence is related to clinical symptoms. Type 1 cysts (n=38; 61%) are small, often multiple and are found at the most distal sacral segments. They are entirely unrelated to the patients’ symptoms and require no specific treatment. This has been confirmed when the primary pathology has been treated and the patients symptoms have been alleviated. Type 2 cysts (n=13; 21%) are usually single, unilateral and occur at the same level as the main cause of the patients’ symptoms, often a prolapsed intervertebral disc at L5/S1 with a Tarlov cyst in the S1 root canal. As such, the cyst itself will not require any treatment, which should be directed at the main pathology. Type 3 cysts (n=11; 18%) are the main cause of the patients’ symptoms and may require specific treatment. We have found that more than half of the Type 3 cysts can be managed expectantly with serial clinical and MRI review. However, the majority of these cysts (9 of 11) are massive and can cause both erosion of bone and compression of the lower sacral nerve roots. Three have to date required decompression to treat cauda equina symptoms.

Conclusions: The majority of Tarlov cysts are incidental findings on MRI. They may, however, either contribute to, or be responsible for a patient’s symptoms. Our classification system addresses this and offers guidance on patient management.

Introduction: Recent evidence from the Swedish Lumbar Spine Group has confirmed the anecdotal opinions of many spinal surgeons that fusion for persistent back pain can be a very effective treatment. However, it is clear that many more variables operate in determining clinical success than just radiological evidence of solid fusion. The very careful selection of patients for low back surgery is, in the opinion of the authors, the most important predictor of success. This paper addresses this issue and presents data to show why clinical failure can coexist with radiological success.

Methods: Between October 1997 and January 2001, 3600 spinal fusion using Diapason pedicle screw instrumentation and Brantigan anterior interbody fusion cages was performed on 25 patients. During this period 5,850 new outpatients with back pain were assessed in the low back clinic. Patients were selected by the following criteria: Low back pain of two years or more duration; Pain resistant to all non-operative and minimally invasive treatments; Normal psychosocial profile; Normal body mass index; Non-Smokers; Single or two level disease on MRI proven to be painful by provocative discography; No current insurance or workers-compensation claims. Postal follow-up was at a minimum of 2 years post-surgery (mean 47 months) using the Low Back Outcome Score (LBOS) and x-rays taken at the two-year clinic follow-up were independently assessed to determine fusion.

Results: 24 patients returned the questionnaire (96%). Only 20 (83%) patients had ‘good’ or ‘excellent’ results, as defined by the LBOS. However, 92% of patients stated that they would opt to have a circumferential fusion again, if guaranteed the same post-operative result. The same number of patients stated they would recommend the treatment to friend or family member. Analysis of the post-operative radiographs revealed that spinal fusion (as defined by the Brantigan and Steffee criteria) was present in all 25 cases.

Conclusions: Our opinion that patient selection is the most important predictor of satisfactory outcome in spinal surgery is demonstrated in this study by the mismatch between the clinical and radiological results. We have identified the causes of clinical failure in this group of patients as: Multiple sites of musculoskeletal pain confounding the LBOS; Neuropathic leg pain that cannot respond to surgical treatment; More than two previous spinal operations; Excessive pre-operative disability and functional loss that confounds the LBOS; Poor psychosocial profile.

Stringent application of rigid selection criteria might improve outcomes in lumbar spinal fusion so that clinical and radiological results correlate more closely. However, even with adherence to such rigid criteria, the outcome tool (LBOS) may be confounded and a more holistic assessment of outcome, including a more sensitive subjective assessment of satisfaction, might be a better measure.

Introduction: The initial promise of stand-alone threaded anterior interbody fusion cages to treat chronic low back pain has not been maintained. In an attempt to overcome some of the problems associated with threaded fusion devices (endplate subsidence, failure to re-establish lordosis and displacement) a two-part ALIF cage was devised. The device consists of a rectangular frame that accommodates a threaded, open-weave cylinder holding bone graft material. The device addresses the biomechanical issues required for successful ALIF whilst providing a large area for bone in-growth and is a less invasive solution than a formal 3600 fusion.

Methods: From August 2001 to December 2002, 41 patients who fulfilled selection criteria for a single or two-level 3600 spinal fusion for low back and leg symptoms underwent ALIF using Stabilis. All patients had failed to improve with all non-invasive and minimally invasive treatments available to them. Prospective follow-up has continued for all cases using the Low Back Outcome Score and a Patient Satisfaction Score. Plain x-rays were taken at 3, 6 and 12 months post-operatively and the 12-month series included flexion and extension films.

Results: Ten patients (24.4%) have completed more than 12 months follow-up; 18 (43.9%) are between six and twelve months post surgery and the rest (31.7%) have less than six months follow-up. LBOS results for the first 10 showed 9 (90%) as excellent or good. LBOS results for the second group of 18 were excellent or good in 15 (83.3%). All but two of the 28 patients, would be prepared to undergo the procedure again and all would recommend the operation to a friend with similar trouble. Radiographic assessment at 6 months showed 16 patients had at least a partial anterior or posterior sentinel sign. Using motion criteria, all 10 cases at one year were fused on flexion and extension lateral x-rays. No devices migrated anteriorly or posteriorly and no lucent lines have been seen around the implants. Three of the two-level procedures showed some subsidence of the L4/5 implant into the L5 vertebral body, but none were symptomatic. No clear reasons have emerged to explain the clinical failure of 14% of the patients given the radiological success. In only one was there a mismatch in the LBOS outcome measure and the satisfaction rating.

Conclusions: Stabilis is a useful standalone ALIF device that not only addresses the theoretical biomechanical failures of anterior threaded interbody fusion cages, but has been shown in this early clinical and radiological evaluation to be effective, objectively and subjectively. It is likely that in the medium term future, fewer patients will require fusion to treat back and leg pain as the results from lumbar spine arthroplasty become established and non-fusion technologies become accepted. Until that time, experience in the UK and USA suggests that Stabilis is a good alternative to 3600 fusion.

Introduction: Discectomy for herniation of the nucleus pulposus is an effective procedure when conservative treatment has failed. However, a number of patients rapidly progress to symptomatic instability after discectomy. Those most likely to develop instability have central and multi-regional herniations. Therefore, primary posterior lumbar interbody fusion (PLIF) may be a better option than discectomy alone in this group. This paper presents the clinical and radiological outcome of a consecutive group of such patients treated in one centre by PLIF, but recognises that newer technologies may make such destructive spinal surgery unnecessary in the future.

Methods: Between June 1997 and December 2000, PLIF for central disc herniation presenting with acute, subacute and chronic back and leg pain, with or without neurological loss, using Diapason pedicle screw instrumentation and Ogival PEEK (Polyether-ether-ketone) Interbody Fusion cages was performed on 41 patients. Eight patients presented acutely with cauda equina symptoms and 33 patients had sub-acute or chronic symptoms. Formal clinic follow-up was continued for at least two years post-surgery and the final outcome at 2 to 5 years after operation was assessed using the Low Back Outcome Score (LBOS). Two independent orthopaedic surgeons assessed the radiological evidence of fusion on X-rays taken at least two years after surgery.

Results: 39 of the 41 patients completed the LBOS questionnaire (95%). One patient had died from an unrelated cause and the other could not be contacted having moved away. 34 (87%) of these had an excellent or good outcome according to the LBOS criteria. However, every patient who returned the questionnaire stated that they would undergo the operation again if guaranteed the same surgical result and all would recommend it to a friend for similar trouble. Four patients (9.7%) were dissatisfied with the process of care they experienced. Analysis of radiographs taken between two and four years post-operatively revealed that spinal fusion (as defined by the Brantigan and Steffee criteria) was present in 38 cases (92.7%). None of the patients with a non-union radiologically had a poor outcome.

Conclusions: Post-discectomy instability causing disabling low back and leg pain is more likely to occur in patients with an incompetent annulus than those with a largely intact annulus. The patients in this series all had good evidence on MRI of complete (pan-annular) failure. The decision to perform an acute single level PLIF was taken after discussion with the patients, presenting them with the option of having only a central discectomy and a later fusion if needed or of dealing with the problem at one operation. The outcomes described in this study show that this condition is a good indication for PLIF. However, newer technologies such as disc arthroplasty may be a better option for this group of patients in the future.