The authors entered patients into a randomised trial to compare the results of the use of cemented and cementless acetabular prostheses between 1993 and 1995. The results of mid-term wear studies at average follow up of eight years were reported in the journal in 2004. We now present long-term results to show the eventual fate of the hip replacements under study.

The initial study group of 162 patients was randomly assigned to a modular titanium cup with a polyethylene liner or an all polyethylene cemented cup. All patients received a cemented stem with a 26 mm head and a standardised surgical technique. The polyethylene wear was estimated via head penetration measurement and the mid-term results showed a significantly higher wear rate in the cementless cups compared to the cemented cups (0.15mm/yr vs. 0.07mm/yr p<0.0001). The prediction was that this would lead to a higher rate of aseptic loosening in the cementless group.

Patients have now been re-examined at an average of 15 years with the main emphasis on prosthesis survival. Wear studies were also performed.

There were exclusions from the initial study because of death and reoperation for reasons other than aseptic loosening. The number of patients in this longer-term study had decreased as a result of death and loss to follow up. Revisions for aseptic loosening did not follow the path as suggested by the mid term wear studies. There were five cup revisions in the cemented group and one cup revision in the cementless group for aseptic loosening. No femoral stem was revised for aseptic loosening. Details of the long-term wear studies will be presented and osteolysis rates and extent documented.

Despite the statistically significant difference in wear rates at the mid term, an incorrect prediction of eventual loosening rates was made. The authors believe that there are many factors other than wear rates involved in longevity of fixation. We also believe there are many weaknesses in long term prospective, randomised trials in joint replacement and question whether they are, in fact, level 1 evidence in the age of evidence based medicine.

Introduction: The role of spinal fusion in patients suffering degenerative spine disease may be scrutinized more as costs of surgical treatment rise. Health-related quality of life (HRQL) measurement instruments enable outcome comparisons following treatment of different medical conditions. Rampersaud et al (1) recently presented the results of a comparative study of HRQL outcomes after surgery for lumbar spinal stenosis and hip and knee total joint arthroplasty. The latter are now accepted benchmarks for improvement in patient health.

Methods: A retrospective, observational cohort study was undertaken of 12-item Short Form Health Survey (SF-12) outcome data of 105 consecutive patients of two surgeons (1st and 2nd authors) who underwent single level Posterior Lumbar Interbody Fusion (PLIF) for lumbar spinal stenosis associated with degenerative spondylolisthesis. Minimum 12-month (F/U) data was available for 98 patients (93%). Comparison was made with published SF-12 results of hip and knee total joint arthroplasty (THR and TKR) and with age-related Australian population norms. Analyses were performed using XLSTAT version 7.5.3. Non-parametric statistics were used for assessment of skewed continuous variables. Overlappng 95%CIs were interpreted as indicating lack of significant difference in outcomes between patient and population groups.

Results: Median follow-up was 24months (range: 12–60months). Median age was 65 (Interquartile range: 59–75) years. Male:female ratio 2.8:1

Mean (95%CI) pre-op Physical Component Summary score (PCS) was 28.1 (26.6–29.5). This increased at last F/U to 39.3 (36.9–41.7, P< 0.0001). Mean Mental Component Summary score (MCS) was 47.8 (45.5–50.1) pre-op and 52.3 (50.2–54.5) at last F/U (P=< 0.0001).

While there was no difference in patient demographics, a significant difference existed in the pre-op SF-12 scores between the patients of the two surgeons (mean PCS: 24.9 (22.7–27.0) vs. 29.6 (27.8–31.5) and MCS: 44.0 (39.3–48.6) vs. 49.5 (46.8–52.1)). No significant difference was found in the improvements in mean SF-12 scores between these two patient groups (PCS: 12.3 (7.6–17.1) vs. 10.8 (8.3–13.3) and MCS: 6.3 (1.8–10.8) vs. 3.0 (0.3–5.6)) or in the SF-12 scores at 12-months (PCS: 37.2 (32.8–41.6) vs. 40.2 (37.2–43.2) and MCS: 52 (48.3–55.7) vs. 52.3 (50.1–54.4)). No significant difference was found between post-op PCS of the less disabled patient group or MCS scores of either group and published SF-12 age-matched population norms (65–74 years: mean PCS of 44.4 (42.7–46.1) and MCS of 53.8 (52.7–55.0)).

Three published series (869 patients) were located providing SF-12 data for TKR surgery. Weighted mean age was 69 years and pre-op PCS was 30 (range:27–34). 12-month improvement in PCS was 7.0 (range:7–8.5). For THR, one paper (147 patients from 3 hospitals) containing SF-12 data was found. Mean age was 68 years (range:36–89). Mean pre-op PCS and MCS of 30.5 and 41.4, increased to 45.6 and 49.7 at one year.

Discussion: The current study shows that spinal fusion can return patients’ HRQL to that of age-matched population norms and yield outcomes comparable to those of total hip and knee arthroplasty. Strict comparison with the arthroplasty literature was problematic however owing to variations in the methodology of their data presentation. Prospective collaboration with surgical colleagues in other disciplines is required.

Introduction: Total disc arthroplasty’s (TDA) fall into two groups – constrained ball and socket and sliding core devices. It is commonly theorized that sliding core devices offer the advantage of being able to adapt to varying centres of rotation (COR) of the functional spinal unit (FSU), however no rigorous justification has, so far, been tendered for this. Despite the perceived advantage, differing clinical results have been reported in the lumbar spine, possibly with better results with ball and socket devices. Furthermore abnormal motion with a large hysteresis effect has been identified in in vitro flexibility testing with a physiological preload in the lumbar spine. The purpose of this paper was to develop an understanding of the kinematics of sliding core TDA’s, their ability to match variable COR’s of a normal FSU, and to gain an understanding of theoretical load displacement behaviour when implanted.

Methods: The motion of a biconvex sliding core prosthesis was observed to define the motion as a linked kinematic chain. By the use of sequential multiplication by appropriate transformation matrices that described this kinematic chain, equations for the position and orientation of the upper vertebrae were established. By a similar method equations for the position and orientation of the upper vertebrae were developed for a physiological simple rotation around the FSU COR. Attempts were made to solve these two sets of equations simultaneously to see if motion of the biconvex core prosthesis could match either the position, orientation or both position and orientation of the normal physiological motion. Functions defining the length of the load vector through the COR were obtained. By considering a physiological load in the direction of this vector, a function describing potential energy was defined. This was further modified by the addition of ligament constraints with a “J” shaped non linear load displacement behaviour that approximated normal ligament stiffness. Sensitivity analysis was then performed to establish the behaviour of the prosthesis under differing loads, ligament strains and malplacements and the outcomes were compared to published in vitro results.

Results: The motion of the device could be modeled as a ‘two bar linkage’. Attempts to find simultaneous solutions for the equations for the two bar linkage and physiological movement showed that a solution was possible when matching either position or orientation but not both. The biconvex core prosthesis best approximated the normal motion by a change in the length of the vector joining the FSU COR to the vertebrae above. When the potential energy caused by this change in length was plotted as a two dimensional surface, a ‘saddle shape’, indicating an unstable high energy equilibrium position at neutral was found. The addition of functions to simulate ligament structures showed a ‘metastable’ energy surface with two stable minimum equilibrium positions with an intervening unstable high energy equilibrium position. Sensitivity analysis showed that the prosthesis could adapt quite well to changes in vertical position of the FSU COR though had limited ability to adapt to anteroposterior malplacement.

Discussion: The theoretical potential energy function for a biconvex core prosthesis predicts significant hysteresis with a high energy unstable central position. The equations predict abnormal load behaviour that is similar to observed in vitro testing. This may explain the difference in clinical results.

Introduction: Vertebral end plate is both inervated and has been shown to be a source of pain. Clinical experience shows some degree of end plate subsidence, usually posteriorly, in cases of total disc arthroplasty (TDA). It follows therefore that this may be a cause of pain. It is theorized that in quiet standing, a prosthesis with a posteriorly placed centre of rotation (COR) will have maximal end plate stresses posteriorly unless the centroid of the prosthesis end plate lies over the COR of the prosthesis. The rationale is that a posteriorrly weighted non uniform static end plate stress distribution will be produced in order to satisfy the static requirement that the sum of all moments be zero. It is further theorized that removal of portions of anterior end plate to move the centroid closer to the pivot point will make the stress distribution more normal.

Methods: A ball and socket prosthesis with a posterior articulation was subjected to static compression with an Instron testing machine against a foam block (Sawbones 1522-11) with the lower part of the specimen on rollers to allow lateral translation. Load was applied normal to the lower end plate in displacement control at a constant rate of 3 mm/min. Load displacement curves, lateral translation of the lower endplate and subsidence angle into the foam was measured. The experiment was repeated with various shaped end plates with the same outside footprints, though with various cutouts of the endplate footprint, such that the footprint area was reduced though with the centroid now lying over the prosthesis COR.

Results: With the standard prosthesis subsidence was noted to be associated with a translatatory movement of the inferior assembly and tilting, with the posterior portion subsiding more than the anterior portion. The prosthesis continued to subside with an increase in the tilt angle and liftoff of the anterior portion of the end plate until the calculated centroid of the subsidence footprint in the foam was over the prosthesis COR. With an end plate cutout the inferior assembly did not translate and the prosthesis subsided in a parallel fashion. This behavior was unchanged by varying the geometry of the cutout. The area of the modified cutout prosthesis was 69% (564 sq mm cf 817 sq mm) of the area of the original end plate, while the yield load was 89% (2.34 kN cf 2.62 kN) of the original. The Yield stress was higher in the modified prosthesis (4.13 MPa cf 3.21 MPa)

Discussion: A potential reason for end plate subsidence in TDA’s may be mismatch between the position of the end plate centroid and the COR. In static loading this causes a tendency to posterior subsidence and tilting. Removal of part of the end plate footprint such that the centroid is moved closer to the COR results in less of reduction in yield load than would be anticipated by loss of surface area alone. There is also abolition of subsidence by tilting.

Introduction The management of severe pain associated with progressive adult scoliosis remains a challenging problem. Radicular symptoms are often caused by bony foraminal stenosis and significant global and segmental imbalance may exist in both the sagittal and coronal planes. The patients are often elderly and have intercurrent medical conditions. The use of disc space distraction, pedicle screw instrumentation and posterior lumbar interbody fusion (PLIF) with Insert and Rotate prostheses has been shown to be effective in the correction of sagittal plane deformity (1). The current study examines the safety, clinical and radiological efficacy of this technique in the management of adult multilevel scoliosis.

Methods A prospective single cohort observational study of 15 consecutive patients with a degenerative scoliosis of 20 degrees or greater managed using an Insert and Rotate PLIF technique between October 2000 and July 2003. The minimum follow-up was 2 years. Clinical outcome measures included VAS pain score, SF-12, LBOS and Patient Satisfaction survey. Pre- and post-operative measures of radiological sagittal and coronal deformity were manually obtained. Wilcoxon signed-ranks test and Spearman’s non parametric test for correlation were used with significance set at 0.05.

Results The median age was 72 years (range: 56–80). Male: female ratio was 6:9. PLIF was carried out at 2 levels in 7 patients, 3–5 levels in 8 patients. Median blood loss was 1100mls for 2 level patients and 2550mls for 3–5 level patients. Operating time was 345mins and 545mins in the 2 and 3–5 level cases respectively. Median pre-operative scoliosis was 31degrees (range: 20–65) and post-operatively measured 14degrees (range: 0–30, p=0.001). Median pre-op VAS of 53 reduced to 20 (p=0.003). LBOS improved from 24 to 37 (p=0.004). A correlation was found between the amount of pre-operative coronal plane deformity and the post-operative VAS (r=0.6, p=0.003). 13 of the 15 patients considered the procedure was worthwhile and that they would have it again under similar circumstances. Early post-operative complications included electrolyte/fluid disturbance in 2 patients, 2 cardiac arrhythmias, one DVT/PE and 2 returns to the O.R. for pain caused by a misplaced pedicle screw or bone graft. One patient developed a progressive scoliosis above the fusion and one a pathological wedge compression fracture. 4 patients required late surgery including 2 who had been fused down to L5 and required extension of their fusion to the sacrum for pain associated with an L5/S1 foraminal stenosis and one who developed a painful non-union.

Discussion PLIF with an Insert and Rotate technique following disc space distraction for severe and progressive adult scoliotic deformity is technically difficult and can be associated with significant peri-operative morbidity. Nevertheless, the reported satisfaction rates by the patients in this small series are encouraging and the procedure appears to have achieved substantial correction of global and segmental deformity in both the coronal and sagittal planes. Whether this will be beneficial in the long term requires further study.

Introduction Sagittal balance is a combination of a balance function (T1 maintained vertically over S1) that partially constrains the spine, the passive constraints provided by soft tissues and the active constraints – muscle force and gravity. Normal standing posture is likely to be the posture of minimum muscle activity and soft tissue energy. Observed deviation from this position would require muscle action. A mathematical model describing spinal balance without muscle activity is described.

Methods The spine was modeled as a series of articulations between the hip and T1 that were controlled by a third degree polynomial ‘spring’ function that approximates the force displacement curves as measured by Panjabi et al. T1 was constrained to remain over S1. Geometric data imported from the erect radiograph of a 34 female without back pain was used to set the zero point for the stiffness functions. All spring functions except the hip function were identical. The system was then perturbed by changing the rest disc space (or hip) angles. An initial smoothing function was used to ‘distribute’ this perturbation amongst several adjacent vertebrae as a guess. The model then minimized the total soft tissue energy to find the new position by treating the system as a series of damped rotational spring – mass constructs. Minimization was achieved using Euler’s method to solve a system of second order nonlinear ordinary differential equations. The iterations were run until oscillations ceased. The model was then perturbed by creating a series of kyphotic deformities at multiple levels and the results were observed.

Results Most perturbations converged to a minimum solution almost instantly. With the hip fixed, it was found that kyphotic deformities in the lower and mid lumbar spine led to compensatory lordosis at most other levels – particularly at the apex of the thoracic kyphosis. The spine tended to straighten and lengthen (possibly causing a rise in the centre of mass of the body). This tendency was substantially mitigated by allowing the hip joint to move. By trial and error, a spring function with of one tenth of the stiffness allowed the centre of gravity to move minimally and the compensatory lordosis occurred at segments closer to the induced kyphosis. When an apical thoracic kyphosis was applied with a fixed hip, the spine shortened with compensation being mostly by lordosis in the upper lumbar spine. When the hip was allowed to flex the tendency was for some of the compensation to occur at hip and for the spine to shorten further. The compensatory lordosis that developed at the level above an induced lumbar kyphosis could be partially corrected by applying a flexion moment. However as there is no muscle that is capable of applying such a moment over a single segment an alternative approach suggested that the hyperlordosis could be reduced by applying an extension moment to multiple segments above the hyperlordotic level.

Discussion Sagittal Spinal balance is complex. A minimum energy stiffness model may lead to further understanding of spinal balance. The prototype model suggests that the hip joint may have a role in preventing excessive lengthening (with a rise in the centre of gravity) of the spine. The model predicts extensor muscle contraction more than one level above a lumbar kyphosis.

Introduction Current evidence suggests that, in the short and medium term, total disc arthroplasty (TDA) is at least as good as fusion for the management of discogenic low back pain. The optimum kinematic design of TDA, however, at this stage has not been identified. This paper compares the clinical outcomes of two TDA prostheses with different kinematic properties.

Methods A randomised comparative clinical study with prospective data collection was performed. Two groups of patients with low back pain who were treated surgically with TDA were compared. All patients had primary symptoms of low back pain without significant facet degeneration. All patients had MRI evidence of disc degeneration and positive discography at the target level. The two surgical groups were treated consecutively by the one surgeon. The first chronological group consisted of 23 cases of SB Charité (CHR) prostheses (DePuy Spine) and the second group consisted of 18 cases of Maverick (MAV) disc replacements (Medtronic Sofamor Danek). The CHR group consisted of 16 males and 7 females with an average age of 37.1 years. The MAV group consisted of 10 males and 8 females with an average age of 41.3 years. 17 (74%) of the CHR group were single level cases. 6 (24%) cases were performed at the same time as an adjacent level anterior fusion. There were no two level prostheses performed. One case in the CHR group was lost to follow-up. 10 (55%) of the MAV group were single level cases. 7 (38%) of the MAV group were double level prosthesis cases. There was 1 case performed adjacent to a fusion in this group. Patients were assessed by visual analogue pain scores (VAS), Low-Back outcome score (LBOS), and SF12 health outcomes that were collected preoperatively and at 6 months.

Results There was a mean improvement of 3.4 VAS points with the CHR group compared to a mean improvement of 5.1 points with the MAV group (p=0.039). There was a mean percentage improvement in VAS scores of 42.1% with the CHR group compared to a 70.1% improvement in the MAV group (p=0.003). The mean LBOS scores improved by 12.3 points in the CHR group, compared to an improvement of 25.6 points in the MAV group (p=0.016). Percentage improvement in LBOS score was 67.8% for the CHR group compared to 210% for the MAV group (p=0.006). The mean improvement in the PCS score of the SF12 measure was 7.3 for the CHR group compared to 15.6 for the MAV group (p=0.055). The percentage improvement in PCS scores was 23.1% for the CHR group compared to 56.0% for the MAV group (p=0.047). There was no significant difference in the improvement in MCS score of the SF12 measure (6.3 compared to 8.1 p=0.7).

Discussion On all outcome measures of pain and physical disability the MAV cases improved by a statistically greater amount than the CHR cases. This difference appears to be clinically important. There are a number of possible reasons for this difference, including the fact that the cases were not performed concurrently (learning curve affect) and that there were a number of fusions performed simultaneously in the CHR group. However one possible explanation is the difference in the kinematic behaviour of the two prostheses.

Introduction and Aims: Zirconia heads were introduced into hip replacement surgery with in vitro reports of lower wear on polyethylene compared with metal. Over 400,000 zirconia heads have been implanted worldwide and yet clinical studies have varied in their results. The aim of this study was to compare the radiological wear rate of zirconia and stainless steel heads on polyethylene.

Method: Between March 1998 and August 2001, 186 patients having a hip replacement by one of the two authors were entered into a randomised trial to receive either a 26mm stainless steel head, a 28mm stainless steel head or a 28mm zirconia head. In all patients a posterior approach and a cemented Exeter femoral stem were used. One surgeon used a cementless cup in patients under 65. All other patients received an all-polyethylene cemented cup. An upper age limit of 75 was chosen to hopefully allow at least 10 years follow-up. The penetration of the heads into the polyethylene was then assessed by the modified Livermore technique.

Results: Sixty-seven hips were randomised to receive a 26mm metal head, 58 a 28mm metal head and 61 a 28mm ‘HIPed’ zirconia head. The average radiological follow-up was 48 months. The penetration rate on the all-polyethylene cup for the 26mm metal head was 0.06mm/yr. This was equivalent to a previous study using the same components. This compared with a penetration rate of the 28mm metal head of 0.07mm/yr and the 28mm zirconia head of 0.13mm/yr. There was considerable variation in the latter, which is consistent with the theory that some zirconia heads may undergo phase transformation that in turn increases the surface roughness.

Conclusion: Although we have only a short follow-up, this study already shows a statistically significant difference in the penetration rates produced by zirconia femoral heads on polyethylene when compared with stainless steel heads. This agrees with several other clinical studies, but to our knowledge is the first reported randomised trial.

Introduction The early clinical results of cervical disc replacement surgery are encouraging but the in vivo kinematics of prostheses remains poorly understood. Two recent published reports suggest that use of a prosthesis with an unconstrained (over normal range of motion) biconvex nucleus (Bryan Cervical Disc® – Medtronic Sofamor Danek, Memphis, TN) can be associated with post-operative segmental kyphosis.

This study examines post-operative kyphosis and segmental imbalance following cervical disc replacement using the Bryan Cervical Disc prosthesis and factors which may influence this. In particular, the influence of change in disc space height as a result of surgery was studied.

Methods 67 patients underwent prosthetic disc replacement by one of three surgeons (19, 25 and 23 patients, respectively) using the Bryan prosthesis. 46 single, 20 double and 1 triple level were operated. Neutral pre- and post-op erect and intra-operative x-rays were examined manually and using digital image analysis software (Medical Metrics, Inc. Houston, TX). Possible contributing factors to segmental alignment were studied including: pre-op alignment, angle of prosthesis insertion, disc space degeneration and sacrifice of the posterior longitudinal ligament (PLL). Particular attention was given to changes in disc space height and factors which may influence this.

Inter- and intra-observer agreement was assessed. Non-parametric tests were used for assessment of categorical and skewed continuous variables. Multivariate linear regression was used to adjust significant correlation coefficients. Significance was set at p< 0.05.

Results The median pre-op focal lordosis of +0.5° (range: 21 to −14°, −ve = kyphotic) changed by −1° (+14 to −17°), to post-op: 0° (+11.5 to −16°).

There was a significant difference in the median change in focal lordosis for surgeon 1 (−3°) vs. surgeons 2 & 3 (−1°) (p< 0.005) and in the loss of disc space height. Median loss of disc space height for surgeon 1 was 22% vs. 8% for surgeons 2 & 3 (p< 0.002). Correlation co-efficient (Spearman) for change in disc space height vs. change in disc space angulation was 0.67 (p< 0.0001). No single pre- or intra-operative factor was found to clearly correlate with subsequent loss of disc space height apart from a trend towards a weak correlation with the angle of prosthesis insertion (r=0.24, p=0.06).

Discussion The median change (loss) in focal lordosis was −1.5° but there was considerable range: from +14° to −17°. Attempts to identify contributing factors suggest that a number may be involved but there did appear to be a highly significant correlation between loss of disc space height following surgery and subsequent focal kyphosis.

While the difference in outcomes between Surgeon 1 and Surgeons 2 & 3 is probably not clinically significant, it does suggest that intra-operative factors such as the angle of prosthesis insertion may be important. We are continuing to study these factors.

Introduction A prospective, randomised, controlled study has been conducted to compare the clinical outcomes of patients treated with a Presige® artificial cervical disc (Medtronic Sofamor Danek, Memphis, TN) to patients who receive fusion after cervical discectomy for the treatment of primary cervical disc disease. It is hypothesized that maintenance of motion after anterior cervical discectomy will prevent the high rate of adjacent level premature degeneration. The primary purposes of the study are to (1) prove equivalence (non inferiority) of outcome of the disc prosthesis in the short term compared with fusion; and (2) to asses the ability of the prosthesis to maintain motion. Enrolment has closed and this is a report of the data with 50 cases with 6 month follow-up and 9 cases having reached 24 month final follow-up.

Methods In four centres, 52 patients with primary, single level cervical disc disease producing radiculopathy and/or myelopathy were randomised prospectively to receive anterior cervical discectomy with either fusion or artificial cervical disc replacement. The patients were evaluated with pre and postoperative serial flexion-extension cervical x-rays at 6 weeks, 3, 6, 12, and 24 months. At the same intervals, the patients had pre and postoperative neck disability indexes, visual pain analogue scales, European myelopathy scores, SF-36 general health scores, and neurological status examinations assessing the patient’s reflex, motor and sensory function.

Results At 6 weeks the neck disability index reduced by 34.1 for the investigational group compared to 35.2 for the fusion group. The improvement seen in the treatment groups was statistically equivalent (p < 0.05, non-inferiority margin = 10) up to the 24-month follow-up interval. The pain score had reduced by 7.7 for the investigational group and by 9.7 for the control group. Both groups improved statistically from preoperatively though statistical equivalence could not be shown. This improvement appeared to be maintained until the 12 month follow-up. Mean arm pain scores improved in both groups with statistical equivalence being demonstrated (p < 0.05, non-inferiority margin = 10). The adverse events in both groups were similar. Analysis of range motion showed a mean preoperative range of motion in the arthroplasty group of 5.9 degrees and 6.3 degrees in the fusion group. At twelve months the arthroplasty group had a mean range of motion of 5.9 degrees and the fusion group had a mean range of motion of 1.1 degrees

Discussion Anterior cervical discectomy and fusion has a good short term outcome though there is a high incidence of failure at adjacent levels over time. It is hypothesised that the maintenance of motion of a segment will prevent adjacent premature degeneration. It will take long term follow-up studies however to prove this. In the mean time, the justification to insert artificial cervical prostheses rests on being able to prove equivalence of outcome between fusion and prosthesis in the short term. This paper shows that, in the short to medium term, the clinical outcomes appear to be equivalent to fusion. And that range of motion is maintained.

Introduction: A prospective, randomized, controlled study has been conducted to compare the clinical outcomes of patients treated with an artificial cervical disc to patients who receive fusion after cervical discectomy for the treatment of primary cervical disc disease. It is hypothesized that maintenance of motion after anterior cervical discectomy will prevent the high rate of adjacent level premature degeneration. The primary purpose of the study is to prove equivalence (non inferiority) of outcome of the disc prosthesis in the short term compared with fusion. Enrolment has closed and this is a report of the data with 50 cases with 6 month follow-up and 9 cases having reached 24 month final follow-up.

Methods: In four centres, 52 patients with primary, single level cervical disc disease producing radiculopathy and/or myelopathy were randomised prospectively to receive anterior cervical discectomy with either fusion or artificial cervical disc replacement. The patients were evaluated with pre- and post-operative serial flexion-extension cervical x-rays at 6 weeks, 3, 6, 12, and 24 months. At the same intervals, the patients had pre and postoperative neck disability indexes, visual pain analogue scales, European myelopathy scores, SF-36 general health scores, and neurological status examinations assessing the patient’s reflex, motor and sensory function.

Results: At 6 weeks the neck disability index reduced by 34.1 for the investigational group compared to 35.2 for the fusion group. The pain score had reduced by 7.7 for the investigational group and by 9.7 for the control group. This improvement appeared to be maintained until the 12 month follow-up. The mean pain scores at 24 months were similar (4.3 and 5.6 respectively) In general there appeared to be a slightly better outcome for the investigational group, though the investigational group showed slightly less preoperative pain (p=0.091) and disability (p=0.055) than the fusion group. Both pain score and disability scores improved statistically significantly compared to the pre op scores (p< 0.001 all comparisons). Analysis of non-inferiority of outcome for the investigational group using ANCOVA with the preoperative score as the covariate and a non-inferiority margin of 5 points (5%) showed statistical significance at 12 weeks for Neck Disability Index.

Discussion: Anterior cervical discectomy and fusion has a good short-term outcome though there is a high incidence of failure at adjacent levels over time. It is hypothesized that the maintenance of motion of a segment will prevent adjacent premature degeneration. It will take long term follow-up studies however to prove this. In the mean time, the justification to insert artificial cervical prostheses rests on being able to prove equivalence of outcome between fusion and prosthesis in the short term. This paper shows that the outcomes appear to be equivalent. Though there is insufficient power to prove equivalence with a clinical margin of 5%.

We selected randomly a consecutive series of 162 patients requiring hip replacement to receive either a cementless, hemispherical, modular, titanium acetabular cup or a cemented, all-polyethylene cup. These replacements were performed by two surgeons in four general hospitals. The same surgical technique was used and a 26 mm metal-head femoral component was used in every case.

After exclusions, 115 hips were studied for differences in rates of wear and osteolysis. The mean clinical follow-up was eight years and the mean radiological follow-up, 6.5 years. The cementless cups wore at a mean rate of 0.15 mm per year and the cemented cups at 0.07 mm per year. This difference was significant (p < 0.0001).

Our findings in this mid-term study suggest that cementless cups wear more than cemented cups.

Introduction: Surgical management of discogenic low back pain has in the past been limited to spinal fusion. Recently disc arthroplasty has become available. The rationale for disc arthroplasty is that it may avoid the long term consequences of adjacent segment degeneration. Avoidance of long term consequences is of no value unless the short term outcome is at least equivalent between fusion and arthroplasty.

Methods: A series of patients with chronic low back pain with concordant lumbar discography and a negative control discogram were surgically treated. Prospective data was collected preoperatively and at regular intervals during the post-operative period for a historical series of combined anterior and posterior lumbar fusion (n =24), a series of SB Charité (DePuy Spine) disc replacements (n =23), and recently, a series of Maverick (Medtronic Sofamor Danek) artificial disc replacements (n =9). Self assessed outcome measures of visual analog pain score (VAS), Low Back Outcome Score (LBOS) and SF12 general health data was obtained at intervals after the surgery. This paper presents the results of the consecutive series that have a minimum of 3 months follow-up.

Results: The data for the two groups of arthroplasty was combined and compared to the fusion group. The mean age for the fusion group was 37.6 years and the mean age for the arthroplasty group was 38.6 years. There were 5 compensation cases (20.8 %) in the fusion group and 5 cases (15.6 %) in the arthroplasty group. Both groups had 69% male patients. The mean VAS dropped from 7.5 to 3.7 (p< 0.001) in the arthroplasty group and from 7.3 to 3.5 (p< 0.001) in the fusion group. The mean LBOS improved from 22.0 to 36.5 (p< 0.001) in the arthroplasty group and from 19.6 to 37.1 (p< 0.001) in the fusion group.

There was no apparent difference between the clinical improvement in VAS and LBOS (p=0.91 and p=0.45 respectively) for each group. Analysis of the power of the comparison showed an 86% power for comparison of VAS improvement using a clinically important difference (delta) of 1 VAS point and there was 98% power for the LBOS improvement comparison using a clinically important difference (delta) of 10 LBOS points. Complications appeared higher in the arthroplasty group with foraminal encroachment requiring revision in 3 cases and one case of polyethylene failure in the Charité group at 3 years. This case occurred with an 8mm polyethylene insert (since removed from inventory by the manufacturer)

Discussion: Disc arthroplasty in the lumbar spine appears to offer similar short term results to that of fusion for chronic low back pain. The surgical complication rate may be higher in the early learning curve of the procedure.

Introduction: A prospective, randomized, controlled study has been conducted to compare the clinical outcomes of patients treated with an Artificial Cervical Disc to patients who receive fusion after cervical discectomy for the treatment of primary cervical disc disease. It is hypothesized that maintenance of motion after anterior cervical discectomy will prevent the high rate of adjacent level premature degeneration. The primary purpose of the study is to prove equivalence (non inferiority) of outcome of the disc prosthesis in the short term compared with fusion.

Methods: In four centers, 60 patients with primary, single level cervical disc disease producing radiculopathy and/or myelopathy are randomized prospectively to receive anterior cervical discectomy with either fusion or artificial cervical disc placement. The patients are evaluated with pre and postoperative serial flexion-extension cervical x-rays at 6 weeks, 3, 6, 12, and 24 months. At the same intervals, the patients have pre and postoperative neck disability indexes, visual pain analogue scales, European myelopathy scores, SF-36 general health scores, and neurological status examinations assessing the patient’s reflex, motor and sensory function.

Results: Data is presented for the first 47 patients. At 6 weeks the neck disability index reduced by 36.1 for the investigational group compared to 34.8 for the fusion group. The pain score had reduced by 8.2 for the investigational group and by 9.9 for the control group. This improvement appeared to be maintained until the 12 month followup. In general there appeared to be a slightly better outcome for the investigational group. Both pain score and disability scores improved statistically significantly compared to the pre op scores (p< 0.001 all comparisons). Analysis of non inferiority of outcome for the investigational group using ANCOVA with the preoperative score as the covariate and a non inferiority margin of 5 points showed statistical significance at 6 and 12 weeks for Neck disability index. Operative time appeared slightly less (2.3 hrs) for the investigational group compared to the fusion group(2.5hrs). Blood loss also appeared higher in the fusion group (165 mls compared to 91 mls). Hospital stay was equivalent (2.8 days and 2.9 days).

Discussion: Anterior cervical discectomy and fusion has a good short term outcome though there is a high incidence of failure at adjacent levels over time. It is hypothesized that the maintenance of motion of a segment will prevent adjacent premature degeneration. It will take long term followup studies however to prove this. In the mean time, the justification to insert artificial cervical prostheses rests on being able to prove equivalence of outcome between fusion and prosthesis in the short term. This paper shows that the outcomes appear to be equivalent. Early statistical evidence is available for some of the outcome measures at early post op followup. Further statistical power will be available when the full 60 cases are available for study and this may give further weight to the hypothesis of equivalence of outcome.

Introduction: Posterior interbody fusion (PLIF) can be performed for a variety of indications and by a variety of methods. This paper presents a prospective observational study of the outcome for PLIF using an insert and rotate lordotic implant with pedicle screws for the indication of neurological compression caused by segmental deformity.

Methods: Prospective data was collected preoperatively and at regular intervals during the post operative period. Self assessed outcome measures of visual analog pain score (VAS), Low Back Outcome Score (LBOS) and SF12 general health data was obtained at intervals after the surgery. This paper presents the results of a consecutive series who have a minimum of 6 months followup. All surgery was performed by the two authors. Implants used were a carbon fibre composite ramp (DePuy AcroMed), a titanium mesh lordotic cage (Medtronic Sofamor Danek) or a lordotic PEEK spacer (R90, Medtronic Sofamor Danek).

Results: One hundred and twenty eight cases were performed. The mean age was 61.5 yrs(sd 15.1), 63 (49% ) were female and 65(51%) were male. Thirteen cases (10%) were workers compensation. Eighty seven (69%) had a single level fused, thirty three (26%) had 2 levels fused. Six cases had three or more levels fused. Forty cases had had one or more previous decompressive procedures at the target level. All cases had leg pain due to neurological compression associated with some form of deformity. Fifty three percent had a spondylolisthesis, 20 % had degenerative scoliosis with collapse of the disc space being the most common other deformity. The mean pre operative VAS pain score dropped from 6.95 (sd 2.0) to 3.2 (sd 2.4). (p< 0.0001 paired t test). The mean percentage VAS improvement was 49.7% (95% ci 42.4% to 57.1%). Twenty seven percent achieved greater then 80% pain improvement with 47% achieving greater than 60% pain improvement. The mean LBOS score rose from 21.8 (95% ci 19.6 to 24.0) to 37.9 (95% ci 35.1 to 40.6) (p< 0.001 paired t test). The mean percentage improvement in LBOS was 120.7% (95% ci 94.6% to 146%).

Complications consisted of 3 cases of minor wound drainage that settled, a possible deep infection that settled with antibiotics. There were 4 cases of transient leg weakness that recovered and one case of postoperative extradural heamatoma requiring evacuation for partial cauda equina lesion (near full recovery). Unexplained persistence of leg pain or new leg pain was present 8 cases. Three cases resolved spontaneously , 2 cases were due to screw malposition and required revision and 3 cases required re-exploration for further foraminal decompression. Other medical problems included pulmonary embolus (1), chest infection/atelectasis (2), confusional state (2), paralytic ileus (3), Atrial fibrillation (2), myocardial infarction (1).

Discussion: Posterior lumbar interbody fusion with insert an rotate implants for neural compression gives reasonable pain relief and reduction in disability with a low complication rate for the target (elderly) population.

INTRODUCTION: A prospective, randomised, controlled study has been conducted to compare the clinical outcomes of patients treated with an Artificial Cervical Disc to patients who receive fusion after cervical discectomy for the treatment of primary cervical disc disease. It is hypothesised that maintenance of motion after anterior cervical discectomy will prevent the high rate of adjacent level premature degeneration. The primary purpose of the study is to prove equivalence (non inferiority) of outcome of the disc prosthesis in the short term compared with fusion.

METHODS: In four centres, 60 patients with primary, single level cervical disc disease producing radiculopathy and/or myelopathy are randomised prospectively to receive anterior cervical discectomy with either fusion or artificial cervical disc placement. The patients are evaluated with pre- and post-operative serial flexion-extension cervical X-rays at six weeks, three, six, 12, and 24 months. At the same intervals, the patients have pre- and post-operative neck disability indexes, visual pain analogue scales, European myelopathy scores, SF-36 general health scores, and neurological status examinations assessing the patient’s reflex, motor and sensory function.

RESULTS: Data are presented for the first 47 patients. At six weeks the neck disability index reduced by 36.1 for the investigational group compared to 34.8 for the fusion group. The pain score had reduced by 8.2 for the investigational group and by 9.9 for the control group. This improvement appeared to be maintained until the 12 month follow-up. In general there appeared to be a slightly better outcome for the investigational group. Both pain score and disability scores improved statistically significantly compared to the pre-operative scores (p< 0.001 all comparisons). Analysis of non inferiority of outcome for the investigational group using ANCOVA with the pre-operative score as the covariate and a non inferiority margin of five points showed statistical significance at six and 12 weeks for Neck disability index. Operative time appeared slightly less (2.3 hours) for the investigational group compared to the fusion group (2.5 hours). Blood loss also appeared higher in the fusion group (165 mls compared to 91 mls). Hospital stay was equivalent (2.8 days and 2.9 days).

DISCUSSION: Anterior cervical discectomy and fusion has a good short term outcome though there is a high incidence of failure at adjacent levels over time. It is hypothesised that the maintenance of motion of a segment will prevent adjacent premature degeneration. It will take long term follow-up studies however to prove this. In the meantime, the justification to insert artificial cervical prostheses rests on being able to prove equivalence of outcome between fusion and prosthesis in the short term. This paper shows that the outcomes appear to be equivalent. Early statistical evidence is available for some of the outcome measures at early post-operative follow-up. Further statistical power will be available when the full 60 cases are available for study and this may give further weight to the hypothesis of equivalence of outcome.

INTRODUCTION: Posterior interbody fusion (PLIF) can be performed for a variety of indications and by a variety of methods. This paper presents a prospective observational study of the outcome for PLIF using an insert and rotate lordotic implant with pedicle screws for the indication of neurological compression caused by segmental deformity.

METHODS: Prospective data were collected pre-operatively and at regular intervals during the post-operative period. Self assessed outcome measures of visual analog pain score (VAS), Low Back Outcome Score (LBOS) and SF12 general health data were obtained at intervals after the surgery. This paper presents the results of a consecutive series who have a minimum of six months follow-up. All surgery was performed by the two authors. Implants used were a carbon fibre composite ramp (DePuy AcroMed), a titanium mesh lordotic cage (Medtronic Sofamor Danek) or a lordotic PEEK spacer (R90, Medtronic Sofamor Danek).

RESULTS: One hundred and twenty eight cases were performed. The mean age was 61.5 years (sd 15.1), 63 (49% ) were female and 65 (51%) were male. Thirteen cases (10%) were workers compensation. Eighty seven (69%) had a single level fused, thirty three (26%) had two levels fused. Six cases had three or more levels fused. Forty cases had had one or more previous decompressive procedures at the target level. All cases had leg pain due to neurological compression associated with some form of deformity. Fifty three percent had a spondylolisthesis, 20% had degenerative scoliosis with collapse of the disc space being the most common other deformity. The mean pre-operative VAS pain score dropped from 6.95 (sd 2.0) to 3.2 (sd 2.4). (p< 0.0001 paired t test). The mean percentage VAS improvement was 49.7% (95% ci 42.4% to 57.1%). Twenty seven percent achieved greater than 80% pain improvement with 47% achieving greater than 60% pain improvement. The mean LBOS score rose from 21.8 (95% ci 19.6 to 24.0) to 37.9 (95% ci 35.1 to 40.6) (p< 0.001 paired t test). The mean percentage improvement in LBOS was 120.7% (95% ci 94.6% to 146%).

Complications consisted of three cases of minor wound drainage that settled, a possible deep infection that settled with antibiotics. There were four cases of transient leg weakness that recovered and one case of post-operative extradural haematoma requiring evacuation for partial cauda equina lesion (near full recovery). Unexplained persistence of leg pain or new leg pain was present in eight cases. Three cases resolved spontaneously, two cases were due to screw malposition and required revision and three cases required re-exploration for further foraminal decompression. Other medical problems included pulmonary embolus (1), chest infection/atelectasis (2), confusional state (2), paralytic ileus (3), atrial fibrillation (2), myocardial infarction (1).

DISCUSSION: Posterior lumbar interbody fusion with insert and rotate implants for neural compression gives reasonable pain relief and reduction in disability with a low complication rate for the target (elderly) population.

Introduction: posterior lumbar interbody fusion can theoretically allow neural decompression directly and by restoration of disc height and appropriate lumbar lordosis. The technique of insertion of a trapezoidal lordotic wedge spacer (ramp) into the disc space before rotating it into position theoretically will obtain both an increase in disc height and allow correction of lordosis. However observations suggest that incongruity between a flat implant and a curved end plate, and possible settling of the implant into the vertebral body may limit the ability of the technique to achieve its full theoretical potential. This paper attempts to establish the capacity of this technique to (1) restore disc height, and (2) alter segmental lordosis.

Methods: pre- and post-operative lateral radiographs were obtained from 34 patients who had undergone posterior lumbar interbody fusion using carbon fibre spacers with a lordotic angle of five degrees. Supplemental pedicle screws were used in all cases. The procedure was performed at l2/3 in one case, at l3/4 in two cases, at l4/5 16 cases and l5/1 in 15 cases. Measurements of pre- and post-operative lordosis, anterior and posterior disc height, slip percentage and anterior and posterior positioning of the prosthesis were made. To allow for comparison of length measurements the raw data were normalised by dividing by the inferior end plate length.

Results: stepwise multiple linear regression showed the only variable to be related to final post-operative lordosis was pre-operative lordosis (p = 0.026). There was no relationship between final lordosis and implant placement or slip percentage. The regression line suggested that small pre-operative segmental angles (less than 7.5 degrees) were increased post-operatively while large pre-operative angles (greater than 7.5 degrees) were reduced. This suggests that the segment is attempting to accommodate to the five-degree implant. The regression equation only explains 14% of the total variance (r² = 0.144). The mean normalised posterior disc height increased significantly by 55% (0.1195 to 0.1844) (paired t test p < 0.0001) and the mean normalised anterior disc height increased by 18% (0.27151 to 0.32251) (paired t test p < 0.007). Changes in both anterior and posterior disc height were highly correlated with pre-operative disc height (r = −0.6729 p < 0.0001, r = −0.7402 p < 0.0001).

Discussion: posterior lumbar interbody fusion using a five degree wedged spacer can lead to significant improvements in anterior and posterior disc height when the disc space is narrowed and maintain disc height when the disc height is normal. The insertion of a wedged implant causes the segment to approximate the lordosis of the implant. The variation is however large. Possible causes for this variation are a mismatch between the flat implant and a curved end plate and end plate subsidence. Having a curved implant end plate and a selection of lordotic angles may possibly reduce the former effect.