Entheses (insertion sites, osteotendinous junctions, osteoligamentous junctions) are sites of stress concentration at the region where tendons and ligaments attach to bone. Consequently, they are commonly subject to overuse injuries (enthesopathies) that are well documented in a number of sports. In this review, we focus on the structure-function correlations of entheses on both the hard and the soft tissue sides of the junction. Particular attention is paid to mechanical factors that influence form and function and thus to exploring the relationship between entheses and exercise. The molecular parameters indicative of adaptation to mechanical stress are evaluated, and the basis on which entheses are classified is explained. The application of the 'enthesis organ' concept (a collection of tissues adjacent to the enthesis itself, which jointly serve the common function of stress dissipation) to understanding enthesopathies is considered and novel roles of adipose tissue at entheses are reviewed. A distinction is made between different locations of fat at entheses, and possible functions include space-filling and proprioception. The basic anchorage role of entheses is considered in detail and comparisons are explored between entheses and other biological 'anchorage' sites. The ability of entheses for self-repair is emphasized and a range of enthesopathies common in sport are reviewed (e.g. tennis elbow, golfer's elbow, jumper's knee, plantar fasciitis and Achilles insertional tendinopathies). Attention is drawn to the degenerative, rather than inflammatory, nature of most enthesopathies in sport. The biomechanical factors contributing to the development of enthesopathies are reviewed and the importance of considering the muscle-tendon-bone unit as a whole is recognized. Bony spur formation is assessed in relation to other changes at entheses which parallel those in osteoarthritic synovial joints.

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Where tendons and ligaments meet bone: attachment sites (‘entheses’) in relation to exercise and/or mechanical load

Background. Degenerative disc disease may cause severe low-back pain, a large public health problem with significant economicandlifequalityimpact.Chroniccasesoftenrequiresurgery,whichmayleadtobiomechanicalproblemsand accelerated degeneration of the adjacent segments. Cell-based therapies may circumvent these problems and have exhibitedencouragingresultsinvitroandinanimalstudies.Wedesignedapilotstudytoassessfeasibilityandsafetyand to obtain early indications on efficacy of treatment with mesenchymal stem cells (MSC) in humans. Methods. Ten patients with chronic back pain diagnosed with lumbar disc degeneration with intact annulus fibrosus were treated with autologous expanded bone marrow MSC injected into the nucleus pulposus area. Clinical evolution wasfollowedfor1yearandincludedevaluationofbackpain,disability,andqualityoflife.Magneticresonanceimaging measurements of disc height and fluid content were also performed. Results. Feasibility and safety were confirmed and strong indications of clinical efficacy identified. Patients exhibited rapid improvement of pain and disability (85% of maximum in 3 months) that approached 71% of optimal efficacy. This outcome compares favorably with the results of other procedures such as spinal fusion or total disc replacement. Although disc height was not recovered, water content was significantly elevated at 12 months. Conclusions. MSC therapy may be a valid alternative treatment for chronic back pain caused by degenerative disc disease. Advantages over current gold standards include simpler and more conservative intervention without surgery, preservation of normal biomechanics, and same or better pain relief.

Intervertebral disc repair by autologous mesenchymal bone marrow cells: a pilot study.

Disc prosthesis surgery is rapidly becoming an option in treating patients with symptomatic degenerative disc disease. Only short-term and midterm results are described in the literature. Most operated patients belong to the age group of 30-50 years. In these active patients, complications can be expected to increase with longer follow-up, similar to total joint replacements in the extremities. Reported here is a series of 27 patients from another institution, who presented with unsatisfactory results or complications after SB Charite disc replacement. The objective of this work was to describe the possible short- and long-term unsatisfactory results of disc prosthesis surgery. Twenty-seven patients were seen in a tertiary university referral center with persisting back and leg complaints after having received a Charite disc prosthesis. All patients were operated on in a neighboring hospital. Most patients were operated on at the L4-L5 and /or the L5-S1 vertebral levels. The patients were evaluated with plain radiography, some with flexion-extension x-rays, and most of them with computed tomography scans. The group consisted of 15 women and 12 men. Their mean age was 40 years (range 30-67 years) at the time of operation. The patients presented to us a mean of 53 months (range 11-127 months) following disc replacement surgery. In two patients, an early removal of a prosthesis was required and in two patients a late removal. In 11 patients, a second spinal reconstructive salvage procedure was performed. Mean follow-up for 26 patients with mid- and long-term evaluation was 91 months (range 15-157 months). Early complications were the following: In one patient, an anterior luxation of the prosthesis after 1 week necessitated removal and cage insertion, which failed to unite. In another patient with prostheses at L4-L5 and L5-S1, the prosthesis at L5-S1 dislocated anteriorly after 3 months and was removed after 12 months. Abdominal wall hematoma occurred in four cases. Retrograde ejaculation with loss of libido was seen in one case and erection weakness in another case. A temporary benefit was experienced by 12 patients, while 14 patients reported no benefit at all. Main causes of persistent complaints were degeneration at another level in 14, subsidence of the prosthesis in 16, and facet joint arthrosis in 11. A combination of pathologies was often present. Slow anterior migration was present in two cases, with compression on the iliac vessels in one case. Polyethylene wear was obvious in one patient 12 years after operation. In eight cases, posterior fusion with pedicle screws was required. In two cases, the prosthesis was removed and the segment was circumferentially fused. These procedures resulted in suboptimal long-term results. In this relatively small group of patients operated on with a Charite disc prosthesis, most problems arose from degeneration of other lumbar discs, facet joint arthrosis at the same or other levels, and subsidence of the prosthesis. It is to be expected that many more patients will be seen with late problems some years after this operation as the survivorship will decrease with time.

Complications of artificial disc replacement: a report of 27 patients with the SB Charité disc.

Osteoarthritis (OA) of the spine involves the facet joints, which are located in the posterior aspect of the vertebral column and, in humans, are the only true synovial joints between adjacent spinal levels. Facet joint osteoarthritis (FJ OA) is widely prevalent in older adults, and is thought to be a common cause of back and neck pain. The prevalence of facet-mediated pain in clinical populations increases with increasing age, suggesting that FJ OA might have a particularly important role in older adults with spinal pain. Nevertheless, to date FJ OA has received far less study than other important OA phenotypes such as knee OA, and other features of spine pathoanatomy such as degenerative disc disease. This Review presents the current state of knowledge of FJ OA, including relevant anatomy, biomechanics, epidemiology, and clinical manifestations. We present the view that the modern concept of FJ OA is consonant with the concept of OA as a failure of the whole joint, and not simply of facet joint cartilage.

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Osteoarthritis of the spine: the facet joints

In recent years, nonfusion stabilization of the lumbar spine has gained more and more popularity. These nonfusion systems intend to maintain or restore the intersegmental motions to magnitudes of the intact spine and have no negative effects on the segments adjacent to the stabilized one. This study investigated the DYNESYS, a dynamic nonfusion system, which is designed to stabilize the bridged segments while maintaining the disc and the facet joints. To determine the magnitude of stabilization and the effect of the stabilization on the adjacent segment, six lumbar cadaver spines were fixed in a spine tester and loaded with pure moments in the three main motion planes. For each spine, four different stages were tested: intact, defect of the middle segment, fixation with the DYNESYS, and fixation with the internal fixator. Intersegmental motions were measured at all levels. For the bridged segment, the DYNESYS stabilized the spine and was more flexible than the internal fixator. This difference between the internal fixator and the DYNESYS was most pronounced in extension (P < 0.05), with the DYNESYS restoring the motion back to the level of the intact spine. The motion in the adjacent segments was not influenced by either stabilization method. Our results suggest that the DYNESYS provides substantial stability in case of degenerative spinal pathologies and can therefore be considered as an alternative method to fusion surgery in these indications while the motion segment is preserved.

Dynamic stabilization of the lumbar spine and its effects on adjacent segments: an in vitro experiment.

Study design Prospective clinical study enrolled in 2 centers (Munich and Liberec) as part of a prospective European multicenter study with ProDisc C (Synthes Inc., Paoli, PA). Objectives The first goal of the study was to evaluate the rate of heterotopic ossifications identified with plain radiograph following total cervical disc replacement (TCDR). The second goal was to show whether segmental motion can be preserved, and whether TCDR can provide improvement of the patient's ability to perform activities of daily living as well as a decrease of pain. Summary of background data Only a few reports about the radiologic outcome after TCDR are published so far. Heterotopic ossification is a well-known phenomenon after total hip arthroplasty. The rate of heterotopic ossification following TCDR is unclear. Methods The radiographs of 54 patients (in total, 77 implanted prostheses) were analyzed 1 year after TCDR with a ProDisc C prosthesis. We classified the heterotopic ossification in 5 grades according to a recently published classification system for lumbar total disc replacement. For clinical parameters, the visual analog scale and the Neck Disability Index were evaluated preoperatively and 1 year postoperatively. The Student t test and Wilcoxon test were used for statistical analysis. Results In 26 treated segments (33.8%), no heterotopic ossification was detectable. Grade 1 ossifications were present in 6 levels (7.8%). A total of 30 segments (39.0%) showed grade 2 ossifications. Heterotopic ossifications that led to restrictions of the range of motion were present in 8 cases (10.4%). One year postoperatively, 7 cases (9.1%) had a spontaneous fusion of the treated segment. The clinical parameters improved significantly and were similar to previous reports about TCDR. Conclusions Only 33.8% of the patients did not show any signs of heterotopic ossification, and the rate of spontaneous fusion after TCDR 1 year after surgery was unexpectedly high. There were 49.4% of the patients with grade 2-3 ossification, which lets us suspect an even higher rate of spontaneous fusion after long-term follow-ups. Motion preservation after TCDR is only guaranteed if spontaneous fusion can be prevented. Thus, mobility of the implanted segments needs to be further studied.

Heterotopic ossification in total cervical artificial disc replacement.

STUDY DESIGN Prospective study analyzing midterm clinical results of total lumbar disc replacement (ProDisc II) for different indications OBJECTIVES To assess functional outcome after total lumbar disc replacement (TDR) treated for varying indications SUMMARY OF BACKGROUND DATA Despite its frequent use and increasing popularity, indications and contraindications for TDR have not been defined precisely at this stage and remain a matter of debate, leading to disc replacement procedures in a variety of pathologies that have not yet been evaluated and compared separately METHODS Patients meeting inclusion criteria were evaluated prospectively according to Visual Analogue Scale (VAS), Oswestry Questionnaire, SF-36, and numerous clinical parameters Indications included degenerative disc disease (DDD), DDD with accompanying soft disc herniation (nucleus pulposus prolapse, NPP), osteochondrosis following previous discectomy, and DDD with presence of Modic changes Postoperative improvement was recorded and analyzed for influence of preoperative diagnosis RESULTS Overall, 92 patients from four groups with a mean follow-up of 342 months (minimum, 24 months) achieved significant and maintained improvement from preoperative levels (P < 0001) Patients with DDD + NPP achieved results significantly better than patients from the other groups (P < 005) Presence of Modic changes or previous discectomy did not influence outcome negatively Improvement was achieved for both monosegmental and bisegmental disc replacements (P < 005), nevertheless with significantly inferior results for bisegmental interventions at 12- and 24-month follow-up and considerably higher complication rate While older patients were still highly satisfied with postoperative outcome, better functional outcome was observed in younger patients CONCLUSION Present data suggest beneficial clinical results of TDR for treatment of DDD in a highly selected group of patients Better functional outcome was obtained in younger patients under 40 years of age and patients with degenerative disc disease in association with disc herniation Multilevel disc replacement had significantly higher complication rate and inferior outcome Results are significantly dependent on preoperative diagnosis and patient selection, number of replaced segments, and age of the patient at the time of operation Because of significantly varying outcomes, indications for disc replacement must be defined precisely

Clinical results of total lumbar disc replacement with ProDisc II: three-year results for different indications.

Total disc replacement has become an option for the treatment of degenerative disc disease of the lumbar spine A new generation of implants has been developed that can be implanted through minimally invasive anterior approaches to the lumbar levels L2/3, L3/4, L4/5 and L5/S1 However mid- and long-term data are still lacking This paper describes the minimally invasive surgical approach – techniques as well as the preliminary results of our first 34 consecutive patients The intervertebral spaces L5/S1, L4/5, L3/4 and L2/3 were each approached through slightly different, but standardized, mini-laparotomies either through a retroperitoneal or a transperitoneal route The clinical results with a follow-up of up to 1 year show satisfactory outcomes in about 80% of the patients Oswestry score as well as VAS values show significant changes during the postoperative course There have been three complications (88%), two of which were specific to the implantation process, but were resolved with a good clinical outcome in both patients The preliminary results suggest that total disc replacement may become a reasonable alternative to spinal fusion under the selection criteria used in this study

Minimally invasive total disc replacement: surgical technique and preliminary clinical results.

STUDY DESIGN Prospective study analyzing midterm clinical results of total lumbar disc replacement (TDR) with ProDisc II performed at different lumbar motion segments. OBJECTIVES To assess the influence of the disc level and number of discs replaced following TDR on postoperative outcome. SUMMARY OF BACKGROUND DATA Multisegmental disc replacement procedures belong to the so-called "off-label" indications for disc replacement, which still lack evidence of noninferiority when compared with fusion procedures. Results from uncontrolled clinical trials regarding monosegmental versus multisegmental disc replacements are contradictory. METHODS The influence of the level and the number of lumbar discs replaced on postoperative outcome was analyzed prospectively according to Visual Analogue Scale (VAS), Oswestry Disability Index (ODI), and numerous clinical parameters. Post-TDR pain patterns were analyzed with fluoroscopically guided spine infiltrations. RESULTS A total of 99 patients from 3 treatment groups with a mean follow-up of 25.8 months (range, 12.1-57.5 months) achieved significant improvement of preoperative VAS and ODI levels (P < 0.05). Best results and highest patient satisfaction rates (90.9%) were achieved in patients with monosegmental TDR at L4-L5 (n = 22). Results deteriorated when monosegmental TDR was performed at the lumbosacral junction (n = 57) with a tendency toward statistical significance at 24-month follow-up (P = 0.07). Postoperative outcome was significantly inferior following bisegmental disc replacements at L4-L5 + L5-S1 (n = 20) with a considerably higher complication rate when compared with monosegmental TDR procedures. Fluoroscopically guided spine infiltrations confirmed that the incidence of postoperative pain from posterior joint structures was 9.1% (n = 2) for L4-L5 TDR, 28.1% (n = 16) following L5-S1, and 60.0% (n = 12) for bisegmental-TDR at L4-L5 + L5-S1, respectively. CONCLUSION The level and the number of lumbar disc replacements influence postoperative outcome significantly. Satisfactory outcome was achieved for monosegmental L4-L5 and L5-S1 disc replacement procedures with best results achieved following TDR at L4-L5. For bisegmental TDR, complication rates are significantly higher and inferior postoperative results are to be expected. The incidence of postoperative pain originating from facet and/or iliosacral joints is currently underestimated and will require further investigation.

Total lumbar disc replacement: different results for different levels.

Background
During the last 20 years several less-invasive anterior approaches to the lumbar spine have become standard, including the extreme lateral transpsoas approach. Although it is associated with a lower risk of vascular injury compared with anterior midline approaches, neuromonitoring is considered mandatory to avoid neurologic complications. Interestingly, despite neuromonitoring, the reported risk of neurologic deficits with the extreme lateral transpsoas approach is greater than observed with other anterior approaches. An alternative lateral, oblique, psoas-sparing approach, recently named the oblique lumbar interbody fusion, uses the anatomic pathway between the abdominal vessels anteriorly and the lumbar plexus laterally to decrease the risk of neurologic and vascular injury; however, as yet, little on this new approach has been reported.

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Andreas Korge

Papers

Heterotopic ossification in total cervical artificial disc replacement.

Clinical results of total lumbar disc replacement with ProDisc II: three-year results for different indications.

Minimally invasive total disc replacement: surgical technique and preliminary clinical results.

Total lumbar disc replacement: different results for different levels.

The Oblique Anterolateral Approach to the Lumbar Spine Provides Access to the Lumbar Spine With Few Early Complications