Unconventional pedicle spinal instrumentation. The Bombay experience

Role of 'low cost Indian implants' in our practice: our experience with 1,572 pedicle screws

PURPOSE

As Indian spine surgeons, we have to choose between 'foreign implants' and 'Indian implants'. An Indian four pedicle screw rod construct costs 330 US dollars (one-third that of a similar foreign construct). About 60% of patients cannot afford expensive foreign implants. There is little written data evaluating how these Indian implants fare. The purpose of our study was to evaluate implant failure rate with Indian implants and compare it to foreign implants.

METHODS

We analysed results of 1,572 titanium pedicle screws used in 239 patients with a minimum 1-year follow-up. Patients were divided into Indian and foreign implant groups. Radiological failures were classified as (1) surgery and disease failure, (2) bone failure and (3) implant failure. The null hypothesis was that there is no difference between implant failure rate for Indian and foreign implants.

RESULTS

A total of 128 (53.56%) of patients could not afford foreign implants. We used 679 foreign and 893 Indian pedicle screws. In foreign implant group, there was a single incident of implant failure (0.15%). In Indian implant group, there were five such incidents (0.56%).

CONCLUSIONS

(1) Rate of failure for 'low cost' Indian implants is very low (approximately 1 implant complication for every 200 screws). (2) There is no statistically significant difference in failure rates for Indian implants and foreign implants (P-value = 0.2438). We recommend that Indian implants are a safe and viable option to make spine surgery cost effective in the Indian scenario.

Stem fracture after total facet replacement in the lumbar spine: a report of two cases and review of the literature

BACKGROUND CONTEXT

A randomized controlled multicenter investigational device exemption clinical trial comparing the total facet arthroplasty system (TFAS) (Archus Orthopedics, Redmond, WA, USA) with posterior fusion was discontinued because of financial reasons. To our knowledge, no clinical outcomes or complications have yet been presented for the TFAS, and no device-related complications have been reported for any other lumbar facet replacement system.

PURPOSE

To report and discuss two cases of stem fracture after total facet replacement in the lumbar spine.

STUDY DESIGN

Case report and literature review.

PATIENT SAMPLE

A 55-year-old man with a body mass index (BMI) of 40 underwent total facet replacement at L4-L5 for Grade 1 spondylolisthesis with stenosis. After 9 months of pain relief, he experienced gradually increasing pain and radiographs showed a broken stem. A 60-year-old woman with a BMI of 31 underwent total facet replacement at L4-L5 for Grade 1 spondylolisthesis with stenosis. She experienced stem fracture 27 months postoperatively.

OUTCOME MEASURES

Visual analog scale for pain, Oswestry Disability Index for function, and computed tomography and X-ray for imaging.

RESULTS

After TFAS stem breakage, both patients underwent interbody fusion through a transpsoas approach and have done well over 24- and 12-month follow-up periods, respectively.

CONCLUSIONS

These are the first cases of stem fracture reported after total facet replacement in the lumbar spine. Biomechanics of TFAS stem breakage may be similar to those of pedicle screw breakage, including fatigue and three-point bending stress. Further biomechanical studies and failure analyses however are needed for adequate understanding to improve the biomechanics of dynamic pedicle-based devices.

Pedicle screw placement accuracy: a meta-analysis

STUDY DESIGN

A meta-analysis of the published literature was conducted specifically looking at accuracy and the postoperative methods used for the assessment of pedicle screw placement in the human spine.

OBJECTIVES

This study specifically aimed to identify postoperative methods used for pedicle screw placement assessment, including the most common method, and to report cumulative pedicle screw placement study statistics from synthesis of the published literature.

SUMMARY OF BACKGROUND DATA

Safety concerns have driven specific interests in the accuracy and precision of pedicle screw placement. A large variation in reported accuracy may exist partly due to the lack of a standardized evaluation method and/or the lack of consensus to what, or in which range, is pedicle screw placement accuracy considered satisfactory.

METHODS

A MEDLINE search was executed covering the span from 1966 until 2006, and references from identified papers were reviewed. An extensive database was constructed for synthesis of the identified studies. Subgroups and descriptive statistics were determined based on the type of population, in vivo or cadaveric, and separated based on whether the assistance of navigation was employed.

RESULTS

In total, we report on 130 studies resulting in 37,337 total pedicle screws implanted, of which 34,107 (91.3%) were identified as accurately placed for the combined in vivo and cadaveric populations. The most common assessment method identified pedicle screw violations simply as either present or absent. Overall, the median placement accuracy for the in vivo assisted navigation subgroup (95.2%) was higher than that of the subgroup without the use of navigation (90.3%).

CONCLUSIONS

Navigation does indeed provide a higher accuracy in the placement of pedicle screws for most of the subgroups presented. However, an exception is found at the thoracic levels for both the in vivo and cadaveric populations, where no advantage in the use of navigation was found.

Treatment of Thoracolumbar Burst Fractures with Variable Screw Placement or Isola Instrumentation and Arthrodesis

BACKGROUND

The controversy of burst fracture surgical management is addressed in this retrospective case study and literature review.

METHODS

The series consisted of 40 consecutive patients, index included, with 41 fractures treated with stiff, limited segment transpedicular bone-anchored instrumentation and arthrodesis from 1987 through 1994.

RESULTS

No major acute complications such as death, paralysis, or infection occurred. For the 30 fractures with pre- and postoperative computed tomography studies, spinal canal compromise was 61% and 32%, respectively. Neurologic function improved in 7 of 14 patients (50%) and did not worsen in any. The principal problem encountered was screw breakage, which occurred in 16 of the 41 (39%) instrumented fractures. As we have previously reported, transpedicular anterior bone graft augmentation significantly decreased variable screw placement (VSP) implant breakage. However, it did not prevent Isola implant breakage in two-motion segment constructs. Compared with VSP, Isola provided better sagittal plane realignment and constructs that have been found to be significantly stiffer. Unplanned reoperation was necessary in 9 of the 40 patients (23%). At 1- and 2-year follow-up, 95% and 79% of patients were available for study, and a satisfactory outcome was achieved in 84% and 79%, respectively. These satisfaction and reoperation rates are consistent with the literature of the time.

CONCLUSIONS

Based on these observations and the loads to which implant constructs are exposed following posterior realignment and stabilization of burst fractures, we recommend that three- or four-motion segment constructs, rather than two motion, be used. To save valuable motion segments, planned construct shortening can be used. An alternative is sequential or staged anterior corpectomy and structural grafting.

Surgical treatment of traumatic fractures of the thoracic and lumbar spine: a systematic review of the literature on techniques, complications, and outcome

STUDY DESIGN

A systematic review of the literature, pertaining surgical treatment of traumatic thoracic and lumbar spine fractures, was performed.

OBJECTIVES

To provide information on surgical techniques for traumatic spine fracture management, their respective performance and complication rates, based on previously published information.

SUMMARY OF BACKGROUND DATA

The treatment of traumatic fractures of the thoracic and lumbar spine remains controversial. There is insufficient evidence in the literature to choose between the various surgical options. In absence of conclusive studies, a systematic review can be an alternative to obtain more convincing information.

METHODS

Full-text papers from 1970 until 2001 were included if strict inclusion criteria were met. Five surgical subgroups were recognized: posterior short-segment (PS), posterior long-segment (PL), reports on both posterior short- and long-segment (PSL), anterior (A), and anterior combined with posterior (AP) techniques. Clearly defined and generally accepted parameters were scored and subsequently analyzed. The preoperative injury severity of the surgical groups was compared. The neurologic, radiologic, and functional outcome and complications of all groups were assessed.

RESULTS

A total of 132 papers, the majority being retrospective case-series, were included representing 5,748 patients. The preoperative injury severity revealed an inequality between the subgroups. Partial neurologic deficits had the potential to resolve irrespective of treatment choice. None of the five techniques used was able to maintain the corrected kyphosis angle. The functional outcome after surgery seems to be better than generally believed. Complications are relatively rare.

CONCLUSIONS

In general, surgical treatment of traumatic spine fractures is safe and effective. Surgical techniques can only be compared using randomized controlled trials.

Comparison of the in vitro holding strengths of conical and cylindrical pedicle screws in a fully inserted setting and backed out 180 degrees

Previous investigations have suggested that conical and cylindrical pedicle screws have comparable holding strengths. So far, the remaining performance in screws turned back or loose as a result of other reasons has not been determined. Twenty-four cadaveric spines from 6- to 8-week-old calves were examined. After bone mineral density was determined, four pedicle screws (two conical and two cylindrical screws) were inserted. The screws were fully inserted and half of them turned back 180 degrees. Twenty-four axial pullout and 24 cyclic loading tests with subsequent pullout tests were conducted. The pullout strengths of conical screws turned back 180 degrees are significantly smaller (1.8 kN) than those of cylindrical screws (4.3 kN). After cyclic loading, the displacement of conical screws is significantly greater (6.9 mm) than that of cylindrical screws (4.7 mm). Pedicle screws, especially conical ones, need to be placed to a correct depth, and they should not have to be backed out.