Computed tomography assessment of the accuracy of in vivo placement of artificial discs in the lumbar spine including radiographic and clinical consequences

Influence of positioning of L4-5 disc prostheses on functional outcomes and sagittal balance: 2-year follow-up of a cohort of 38 patients

OBJECTIVE

The main objective of this study was to evaluate the influence of L4-5 total disc replacement (TDR) positioning on functional outcome at the 2-year follow-up. The secondary objective was to assess its influence on sagittal balance.

METHODS

Prospective data were compiled for 38 single-level L4-5 ProDisc-O TDRs. Anteroposterior placement (APP) was the distance between the center of the implant and the center of the L5 endplate divided by the total length of the L5 endplate. This ratio was expressed as a percentage (APP 0%-49%, anterior off-centering; 50%, perfect centering; and 51%-100%, posterior off-centering). The patients were divided into 3 groups depending on the APP and using quartile values: group 1, anterior placement (APP 0%-46%); group 2, central placement (APP 46.1%-52%, the 2 central quartiles); and group 3, posterior placement (APP 52.1%-100%). The sagittal balance parameters assessed were overall lordosis, segmental lordosis, and pelvic incidence. Adequate lordosis was defined for each patient according to their pelvic incidence. The Oswestry Disability Index and visual analog scale (VAS) scores for back and leg pain were assessed.

RESULTS

The average APP was 48% (range 40%-64%). There were 10 patients in group 1, 18 in group 2, and 10 in group 3. There was a significant difference in functional outcomes among the 3 groups. APP influenced the VAS back (p = 0.04) and VAS leg (p = 0.05) scores. Group 1 consistently showed the highest performance scores. No significant association between APP and the sagittal balance parameters was found. Patients who had preoperative sagittal imbalance or those who significantly modified their balance after the surgery had the poorest outcomes.

CONCLUSIONS

Disc prostheses at L4-5 seem to provide better functional outcome when they are positioned anteriorly to the center of the vertebral body.

Changes in flexion-relaxation phenomenon and lumbo-pelvic kinematics following lumbar disc replacement surgery

BACKGROUND

A single group prospective study. Disc prostheses are believed to contribute to the restoration of the segmental movement and the preservation of the adjacent segments. The study's main objective was to determine if changes in neuromuscular patterns assessed using the flexion-relaxation phenomenon (FRP) can be observed following disc replacement surgery.

METHODS

Fifteen subjects participated in this study; they were evaluated before and after lumbar disc replacement surgery. Both assessments included ten repetitions of a trunk flexion and extension movement (with and without a load), where the surface electromyography (EMG) and kinematic data were recorded.

RESULTS

Following the disc replacement procedure (17.3 weeks ± 8.4), participants reported a significant reduction in their ODI and FABQ - physical activity scores. Increases in pelvic flexion as well as in erector spinae (ES) muscle activity at L5 in the flexion phase were observed. Following the disc replacement surgery, ES activity at L2 decreased during the quiet standing position.

CONCLUSION

The results of this study suggest that although improvements in disability scores and fear-avoidance related to physical activities scores were noted after a disc replacement surgery, the lumbar ROM was not modified. Nevertheless, a significant increase in the hip ROM during the flexion-extension task as well as an increase in ES muscle activity in flexion was observed following surgery. The VAS, FABQ I and ODQ scores were positively correlated with change in the muscular activities during the FRP.

ProDisc-L learning curve: 24-Month clinical and radiographic outcomes in 44 consecutive cases

Background

Total disc replacement (TDR) promises preservation of spine biomechanics in the treatment of degenerative disc disease but requires more careful device placement than tradition fusion and potentially has a more challenging learning curve.

Methods

A cohort of 44 consecutive patients had 1-level lumbar disc replacement surgery at a single institution by a single surgeon. Patients were followed up clinically and radiographically for 24 months. Patients were divided into 2 groups of 22 sequential cases each. Clinically, preoperative and postoperative Oswestry Disability Index, visual analog scale, Short Form 12 (SF-12) Mental and Physical Components, and postoperative satisfaction were measured. Radiographically, preoperative and postoperative range of motion (ROM) dimensions, prosthesis deviation from the midline, and disc height were measured. TDR-related complications were noted. Logarithmic curve–fit regression analysis was used to assess the learning curve.

Results

Operative time decreased as cases progressed, with an asymptote after 22 cases. The operative time for the later group was significantly lower (P < .0005), but hospital stay was significantly longer (P = .03). There was no significant difference in amount of blood loss (P = .10) or prosthesis midline deviation (P = .86). Clinically, there was no significant difference in postoperative scores between groups in Oswestry Disability Index (P = .63), visual analog scale (P = .45), SF-12 Mental Component (P = .66), SF-12 Physical Component (P = .75), or postoperative satisfaction (P = .92) at 24 months. Radiographically, there was no significant difference in improvement between groups in ROM (P = .67) or disc height (P = .87 for anterior and P = .13 for posterior) at 24 months. For both groups, there was significant improvement for all clinical outcomes and disc height over preoperative values. One patient in the later group had device failure with subluxation of the polyethylene, which required revision.

Conclusions/level of evidence

Early experience can quickly reduce operative time but does not affect clinical outcomes or ROM significantly (level IV case series).

Clinical relevance

Lumbar TDR is a rapidly learnable technique in treatment of degenerative disc disease.

Subsidence and malplacement with the Oblique Maverick Lumbar Disc Arthroplasty: technical note

BACKGROUND

The A-Mav (Medtronic, Sofamor Danek, Memphis, TN) is a well-established lumbar total disc arthroplasty device. The O-Mav (Medtronic) is a more recent innovation designed to minimize the potential vascular complications associated with A-Mav insertion at L4/5. No study has hitherto studied the relative accuracy or safety of the two techniques.

PURPOSE

To compare the accuracy of lumbar disc arthroplasty placement by using the anterior technique (A-Mav) with the oblique (O-Mav) technique.

STUDY DESIGN

Technical report.

PATIENT SAMPLE

Fourteen patients.

OUTCOME MEASURES

Implant placement accuracy on high-resolution computed tomography scan. Comparative morbidity, mortality, blood loss, and operating time were also assessed.

METHODS

Patients were considered for lumbar disc arthroplasty who had suffered chronic discogenic low back pain unresponsive to nonoperative management for at least 6 months. All patients were operated on at the L4/5 level. A-Mavs were inserted in 7 patients and O-Mavs in 7. Implant placement was analyzed postoperatively by using computer software on high-resolution computed tomography scan with respect to four parameters: (1) off-center malplacement, (2) axial rotational malplacement, (3) coronal tilt, and (4) vertebral body susbsidence. Comparative morbidity, mortality, blood loss, and operating time were also assessed.

RESULTS

Subsidence, off-center malplacement, and rotational malplacement were significantly increased in O-Mavs compared with A-Mavs (4.3+/-0.6 mm vs. 1.6+/-0.6 mm, p=.008; 3.1+/-0.4 mm vs. 1.3+/-0.4 mm, p=.006; 6.5 degrees +/-1.2 degrees vs. 3.8 degrees +/-0.4 degrees , p=.046). No significant differences were found between O-Mavs and A-Mavs in tilt, operating time, blood loss, or morbidity and mortality.

CONCLUSIONS

O-Mav insertion appears to be complicated by significantly greater vertebral body subsidence and malplacement than A-Mav insertion. A-Mav insertion therefore appears to be more accurate and less complicated yet equally as safe as O-Mav insertion.

An evidence-based medicine approach in determining factors that may affect outcome in lumbar total disc replacement

STUDY DESIGN

Literature research.

OBJECTIVE

To analyze the available evidence about a variety of factors that might affect outcome of lumbar artificial disc replacement.

SUMMARY OF BACKGROUND DATA

Evaluating the scientific merit of new technology is important for a clinician considering incorporating these techniques. An evidence-based medicine approach can aid in this decision-making process.

METHODS

Eleven questions were asked about patient selection issues, surgical accuracy of placement, and evidence that motion preservation alters the natural history of degeneration. Studies where answers were found were ranked according to their level of evidence.

RESULTS

The majority of studies found were level IV, with only limited numbers of higher level studies. Only lower level studies with conflicting results assess the effect on outcomes of single versus multilevel surgery, L4-L5 versus L5-S1 implantations, patient's age, and history of previous surgery. One lower level study suggests that mild-to-moderate facet degeneration does not influence outcomes. The extent of preoperative facet degeneration that can be accepted remains unclear, as level IV studies report degradation of facet degeneration after implantation. Higher level studies support the importance of surgical precision on clinical outcome and lower level studies give mixed results on the same issue. A level III prognostic study suggests that higher range of motion of the implanted segment may be associated with better outcomes, whereas 2 level IV therapeutic studies provide conflicting results. The incidence of adjacent level degeneration in lower level studies ranges between 17% and 28.6%, and can require additional surgery in 2% to 3% of patients. Two level IV studies suggest that preservation of motion may have a prophylactic effect on adjacent discs.

CONCLUSION

Existing evidence does not provide definite conclusions in the majority of the questions regarding indications and factors that may affect outcomes. Where feasible, conclusions are mainly drawn from lower level, least reliable evidence. Highest quality data are short-term whereas longer-term data are of lower quality and in many instances conflicting. More high level studies with long-term follow-up are necessary to shed light to important clinical issues.

The accuracy and validity of "routine" X-rays in estimating lumbar disc arthroplasty placement

STUDY DESIGN

Original study.

OBJECTIVE

To compare the accuracy of radiograph (XR) estimates of lumbar total disc arthroplasty placement with high-resolution computed tomography (CT).

SUMMARY OF BACKGROUND DATA

Most lumbar disc arthroplasties are inserted and subsequently analyzed using anteroposterior and lateral XR: XR estimates are often correlated with clinical outcomes. No study has hitherto assessed the relative accuracy of XR estimates with CT.

METHODS

Patients (N = 36) had recently undergone uncomplicated lumbar total disc arthroplasty for unresponsive discogenic back pain. Interpedicular midline malplacement and vertebral body penetration (VBP) were estimated after surgery, by "blinded" independent review, using computer software on both nonrotated XR and high-resolution CT at the same clinic attendance.

RESULTS

Results were obtained in N = 36 patients. No significant differences were found between XR and CT in the mean +/- standard error estimation of either midline malplacement (1.7 +/- 0.2 mm vs. 1.8 +/- 0.2 mm, P = 0.86) or VBP (1.5 +/- 0.3 mm vs. 1.6 +/- 0.3 mm, P = 0.79). However, the correlation between XR and CT for midline malplacement appeared strong (r = 0.72, P < 0.001), whereas the correlation between XR and CT for VBP was poor (r = 0.23 P > 0.10). The standard deviation of XR-CT differences for VBP (2.2 mm) was almost twice that for midline malplacement (1.2 mm). XR-CT differences exceeded the 95% limit of agreement in 6% of midline placement estimates, and in 8% for VBP.

CONCLUSION

Nonrotated XR permitted an accurate and valid estimate of midline malplacement relative to CT in most cases. However, the correlation was biased toward XR underestimation of CT-derived malplacement, and highly significant XR-CT differences occurred in 6% of estimates: early postoperative CT is therefore recommended to enhance the estimation of midline placement. XR-CT agreement for VBP was poor: CT is therefore indicated in all cases for this parameter. This is the first study to compare the accuracy of XR in estimating lumbar total disc arthroplasty placement with CT.