The treatment of vertebral and chest wall deformities with expandable thoracoplasty and a prosthetic expandable implant.

BACKGROUND: Expansion thoracoplasty is a temporary solution to allow complete pulomonary development in the setting of vertebral and rib cage deformities. After thoracoplasty, an expandable implant is needed to maintain the correction. The Growing Spine Profiler (GSP) is a new type of readjustable rib distracter. The purpose of this study was to evaluate the experiences of surgeons in Europe with the implantation of the GSP. METHODS: We retrospectively reviewed 44 patients that underwent placement of the GSP at 15 sites throughout Europe. The mean age at the time of surgery was 6.24 years. Basic demographic data and postoperative management were reviewed. All patients received an opening-wedge thoracostomy with device implantation and expansion thoracoplasty. Retrospectively, the original indications for implantation were determined. Digital images of the radiographs were used to measure coronal and sagittal parameters. RESULTS: The most common diagnoses for implantation were hemivertebrae (9), hemivertebrae with chest wall deformity (10), and unilateral bar (8). Outcomes were available for 43 patients with a mean follow-up period of 3.07 years. There were 23 patients that had an adverse event. Rib fractures were the most common adverse event, with 8 incidents in 7 patients. Radiographically, coronal curve magnitudes were maintained, whereas sagittal kyphosis gradually increased. CONCLUSIONS: The GSP was effective in the maintenance of deformity, while providing a moderate complication rate. Further studies need to be performed to determine the safety and efficacy of this implant.

Determination of the in vivo posterior loading environment of the Coflex interlaminar-interspinous implant.

BACKGROUND CONTEXT: The in vivo loading environment of load-bearing implants is generally largely unknown. Loads are typically approximated from cadaver tests or biomechanical calculations for the preclinical assessment of a device's safety and efficacy. PURPOSE: To determine the actual in vivo loading environment of an elastic interlaminar-interspinous implant (Coflex). STUDY DESIGN: A retrospective radiographic study to noninvasively measure the in vivo implant loads of 176 patients. METHODS: For this study, neutral, flexion, and extension radiographs were quantitatively analyzed using validated image analysis technology. The angle between the Coflex arms was measured for each radiograph and statistically evaluated. Separately, the Coflex implant was characterized using mechanical test data and finite element analysis, which resulted in a load-deformation formula that describes the implant load as a function of its size and elastic deformation. Using the formula and the elastic implant deformation data obtained from the radiographic analysis, the exact implant load was calculated for each patient and each posture. For statistical analysis, the patients were grouped by indication and procedure, which resulted in 12 different groups. The determined loads were compared with the strength of the posterior lumbar spinal elements obtained from the literature and with the static and dynamic mechanical limits of the Coflex interlaminar-interspinous implant. RESULTS: The force data were independent of implant size, diagnosis (with one exception), number of levels of the decompression procedure, number of levels of implantations (one or two), and follow-up time. The median compressive force acting on the Coflex implant was found to be 45.8 N. The maximum load change between flexion and extension was 140 N; the maximum overall load exceeded 239 N in extension. CONCLUSIONS: The average loads exerted by the Coflex implant on the spinous process and lamina are 11.3% and 7.0% of their respective static failure load. The implant fatigue strength is significantly higher than the measured median force, which explains the extremely rare observation of a Coflex fatigue failure.

A biomechanical evaluation of an interspinous device (Coflex) used to stabilize the lumbar spine.

A biomechanical study of an interspinous stabilization spinal implant (Coflex) was carried out using eight human lumbar L4/L5 motion segments. Each motion segment was tested in compression, then flexion/extension, then lateral bending, and then axial rotation at five conditions: 1) intact; 2) partial destabilization (by cutting the supraspinous and interspinous ligaments, the ligamentum flavum, the facet capsules, and 50% of the inferior bony facet bilaterally); 3) stabilization with the Coflex device; 4) complete destabilization with total laminectomy; and 5) stabilization with pedicle screws and rods. The most important result is that the motion segment after destabilization and insertion of the Coflex device does not allow significantly more or less motion than the intact specimen in either flexion/extension or axial rotation. Thus the Coflex offers nonrigid fixation and can return a partially destabilized specimen back to the intact condition in terms of motion in flexion/extension and axial rotation.

AcroFlex design and results.

The AcroFlex prosthesis is unique when compared to other current devices, as it has an elastomeric core sandwiched between two titanium endplates. The purpose of this design was to optimize shock absorption qualities. This paper reviews the design of the AcroFlex Disc and relevant design and outcomes of two pilot studies carried out on 28 patients using the AcroFlex prosthesis. Although clinical outcomes of the pilot studies were successful, the pivotal randomized trial has not been carried out due to detection of mechanical failure of the elastomer on thin cut CT scans. The implications of this for the AcroFlex and other arthroplasties are discussed.

Two-year fusion rate equivalency between Grafton DBM gel and autograft in posterolateral spine fusion: a prospective controlled trial employing a side-by-side comparison in the same patient.

STUDY DESIGN: Multicenter, prospective equivalency trial with each patient serving as his/her own control. OBJECTIVES: To compare the effectiveness of a Grafton DBM gel composite with iliac crest autograft in posterolateral spine fusion. SUMMARY OF BACKGROUND DATA: While autograft remains the preferred graft material to facilitate spine fusion, the supply is limited and harvesting produces undesirable clinical consequences. METHODS: A total of 120 patients underwent posterolateral spine fusion with pedicle screw fixation and bone grafting. Iliac crest autograft was implanted on one side of the spine and a Grafton DBM/autograft composite was implanted on the contralateral side in the same patient. An independent, blinded reviewer evaluated anteroposterior and lateral flexion-extension radiographs. The fusion mass lateral to the instrumentation on each side was judged fused or not, and the mineralization of the graft was rated absent, mild, moderate, or extensive. The degree of correspondence in outcomes between sides was estimated by computing the percentage agreement and kappa statistic. RESULTS: Nearly 70% of patients (81 of 120) provided complete 24-month radiographic studies. The bone graft mass was fused in 42 cases (52%) on the Grafton DBMside and in 44 cases (54%) on the autograft side. The overall percentage agreement for fusion status between sides was approximately 75% (61 of 81), indicating moderately strong statistical correspondence (kappa = 0.51, P < 0.0001). Bone mineralization ratings also were similar between treated sides. Perfect agreement was realized in almost 60% of patients (48 of 81) with moderate statistical correspondence (weighted kappa = 0.54, P < 0.0001). CONCLUSIONS: Grafton DBM can extend a smaller quantity of autograft than is normally required to achieve a solid spinal arthrodesis. Consequently, a reduced amount of harvested autograft may be required, potentially diminishing the risk and severity of donor site complications.

Arterial complications following anterior lumbar interbody fusion: report of eight cases.

The objective of this study is to report eight cases of arterial complication following anterior lumbar interbody fusion (ALIF) and to analyze the data in order to identify possible risk factors. The authors have encountered six cases of common iliac artery occlusion and two cases of acute vasospasm as a complication of ALIF using two different approaches to spine: hypogastric-midline-transperitoneal approach at one center and minimally invasive muscle-sparing retroperitoneal approach at the other. All cases involved surgery at the L4-L5 level. All patients were smokers, and three had an existing history of vascular disease. The left iliac and common femoral arteries were involved in seven cases, while the right common iliac was involved in one case. Five patients had thromboembolism, one patient had an intimal tear and two had functional vasospasm. Circulation to the lower limb was restored by thrombectomy (five patients) and arterioplasty for the intimal tear (one patient). One of the vasospasm cases was explored (false-positive), while the other was treated conservatively. One of the patients with thrombosis developed rhabdomyolysis resulting in fatal acidosis. All but the first case at each center was diagnosed either intraoperatively or within 2 h of surgery. We believe that awareness of this potentially serious complication will lead to precautionary measures for prevention of the problem as well as early diagnosis and management of the complication if it does occur. Intraoperative monitoring of lower limb blood flow by measuring the toe oxygenation with a pulse oxymeter can prove to be helpful in early diagnosis.

Histology of tissues within retrieved human titanium mesh cages.

STUDY DESIGN: Histologic documentation of contents within retrieved, failed human titanium mesh cages. OBJECTIVES: The purpose of this study is to describe the contents of a series of retrieved, clinically failed titanium mesh cages from human patients. SUMMARY OF BACKGROUND DATA: The use of interbody fusion cages is gaining rapid acceptance, but there is little histologic documentation of tissue within retrieved cages. METHODS: Eleven Titanium Surgical Mesh Cages (Harms; DePuy AcroMed, Raynham, MA) retrieved from 10 patients were histologically analyzed. Indications for cage retrieval included failed fusion or failed fusion with instrumentation failure. The cages had been in situ from 2 to 47 months. Histologic sections were reviewed qualitatively, and the approximate percent of area in the cage occupied by viable bone, necrotic bone, fibrocartilage, hyaline cartilage, fibrous tissue, and bone graft substitute was visually estimated. Particles of metal debris were estimated by a semiquantitative scoring system. RESULTS: All cages except one showed evidence of vascular ingrowth and areas of histologically viable bone, representing incorporating bone graft. At least a few particles of debris were present in 9 of 11 cages. Fibrocartilage of probable intervertebral disc origin ranged from 0% to 70% of the available area. Several cages contained small seams of fibrocartilage connecting segments of bone in a pattern that suggested a response to motion. CONCLUSIONS: Mean viable bone area within 11 retrieved, human titanium mesh cages was approximately 31%. Seams of fibrocartilage within the cages may represent tissue differentiation in response to bending or compressive load.

Total disc replacement arthroplasty using the AcroFlex lumbar disc: a non-human primate model.

Using a non-human primate model, the current study was undertaken to investigate the efficacy of the AcroFlex lumbar disc as an intervertebral disc prosthesis, based on biomechanical, histopathologic and histomorphometric analyses. A total of 20 mature male baboons (Papio cynocephalus, mean weight 30 kg) were randomized into two equal groups based on post-operative time periods of 6 (n=10) and 12 months (n=10). Each animal underwent an anterior transperitoneal surgical approach to the lumbar spine, with intervertebral reconstructions performed at L3-L4 and L5-L6 using the following techniques: (1) tricortical iliac autograft and (2) AcroFlex lumbar disc. The two treatments were equally randomized between the non-contiguous operative lumbar levels. Post-mortem analysis included histopathologic assessment of the systemic reticuloendothelial tissues, multi-directional flexibility testing of the operative functional spinal units and quantitative histological analysis of trabecular bone coverage at the prosthesis endplates. Data were statistically compared using a one-way ANOVA with the Student-Newman-Keuls test. All animals survived the operative procedure and post-operative interval without significant intra- or peri-operative complications. Histopathologic analysis of the paraffin-embedded systemic reticuloendothelial tissues indicated no significant pathologic changes at the 6- or 12-month intervals. Plain film radiographic analysis showed no lucencies or loosening of any prosthetic vertebral endplate. Biomechanical testing of the 6-month autograft, reconstructions with AcroFlex lumbar disc and non-operative control (n=10) intact motion segments indicated no significant differences in peak range of motion (ROM) in axial compression. However, axial rotation produced significantly lower ROM for the autograft treatment compared to the intact and AcroFlex groups (P<0.05). The most significant differences in peak ROM were noted between all treatment groups under flexion/extension and lateral bending loading modalities (P<0.05). By 12 months, the intact condition indicated significantly more motion in all bending modes compared to the AcroFlex and autograft treatments, which were not statistically different from each other (P>0.05). Gross histopathologic analysis of the AcroFlex disc prosthesis demonstrated excellent ingrowth at the level of the implant-bone interface, without evidence of fibrous tissue or synovium. BioQuant histomorphometric analysis at the metal-bone interface (bone contact area/total endplate area) indicated the mean ingrowth was 54.59+/-13.24% at 6 months and 56.79+/-5.85% at 12 months. Radiographic analysis showed no lucencies or loosening of the AcroFlex vertebral endplate. Based on multi-directional flexibility testing, motion was preserved in axial rotation, but significantly diminished in the other bending modalities, particularly at the 12-month interval. This effect may be secondary to the limited surface area of device-vertebral endplate contact. Histomorphometric analysis of porous ingrowth coverage at the vertebral bone-metal interface was more favorable for total disc arthroplasty compared to historical reports of cementless femoral components. This project serves as the first comprehensive in vivo investigation into the AcroFlex disc prosthesis, and establishes an excellent research model in the evaluation of total disc replacement arthroplasty.