Paul I. J. M. Wuisman

Pelvis-thorax coordination in the transverse plane during walking in persons with nonspecific low back pain

Study Design. Transverse pelvis and thorax rotations were studied during walking in 39 patients with nonspecific low back pain and 19 healthy participants. Objectives. To gain insight into the consequences of low back pain for gait and to identify clinically useful measures for characterizing the quality of walking in patients with low back pain. Summary of Background Data. Gait studies in patients with low back pain have reported a decrease in walking velocity. In normal gait, in-phase pelvis-thorax coordination (synchronicity) evolves toward antiphase coordination (counterrotation) as walking velocity increases. This study examined the effect of walking velocity on pelvis and thorax rotations in patients with low back pain. Methods. Amplitudes of pelvis and thorax rotations were calculated, and spectral analyses were performed. Pelvis-thorax coordination was characterized in terms of relative Fourier phase, and coupling strength was assessed by means of cross-spectral analysis. Results. In comparison with healthy participants, relative Fourier phase was significantly smaller in low back pain patients for walking velocities of 3.8 km/h and higher, whereas coupling strength was significantly higher for velocities from 1.4 to 3.0 km/h. No significant group differences were found in amplitude or spectral content of individual pelvis and thorax rotations. Conclusion. In comparison with healthy participants, the gait of patients with low back pain was characterized by a more rigid, less flexible pelvis-thorax coordination in the absence of significant differences in the kinematics of the component rotations. This result suggests that coordination measures are more adequate in assessing quality of walking in patients with low back pain than are kinematic measures pertaining to the individual segment rotations, and that conservative therapy should use methods aimed at improving intersegmental coordination.

Total sacrectomy and reconstruction: Oncologic and functional outcome

The oncologic and functional outcomes of nine patients who were treated by total sacrectomy through L5 (three cases) or L5-S1 (six cases) were reviewed. Histologic diagnoses were one osteosarcoma, two giant cell tumors, two chondrosarcomas, and four chordomas. Patients’ ages ranged from 17 to 70 years (mean age, 44.5 years). Resection margins were intralesional (giant cell tumors) in two, marginal in one, and wide in six patients (one contaminated). Reconstruction was performed using polymethylmethacrylate in two, screw and plate fixation in one, and a custom-made device in one. In five patients no reconstruction was performed. Five patients (45.5%) had wound complications: one had a wound dehiscence and two had deep infection; all needed surgical reintervention. In addition, in one a ventral and in another a dorsal hernia developed; only the ventral hernia was revised successfully. One patient had a deep vein thrombosis that was treated with a Coumadin derivate. Three patients (33%) died after 14, 18, and 50 months postoperatively respectively. One died of lung and widespread metastases, and two died of local recurrence and metastases. One patient with a giant cell tumor had a solitary lung metastasis. After resection the patient has been disease-free more than 90 months. At followup, six patients had no evidence of disease (mean followup, 73 months; range, 30–120 months). Functionally, there was no correlation between patients who had a reconstruction and those who had not. Total sacrectomy is a valuable procedure to secure local tumor control and overall survival, despite potential complications and neurologic and sexual dysfunction.

The effect of cage stiffness on the rate of lumbar interbody fusion: an in vivo model using poly(l-lactic Acid) and titanium cages.

Study Design. A goat interbody fusion model using poly-(L-lactic acid) and titanium cages was designed to evaluate the effect of cage stiffness on lumbar interbody fusion. Objective. To investigate the effect of cage stiffness on the rate of interbody fusion. Summary of Background Data. Various types of cages considerably exceed the stiffness of vertebral bone, which ultimately may lead to postoperative complications. To avoid these complications, poly-(L-lactic acid) cages with limited stiffness have been designed. The mechanical integrity of the cages remains intact for at least 6 months. Methods. Interbody fusions were performed at L3–L4 of 15 Dutch milk goats, and one of three cages was randomly implanted: 1) a titanium cage (n = 3), 2) a stiff poly-(L-lactic acid) cage (n = 6), or 3) a flexible poly-(L-lactic acid) cage (n = 6). Interbody fusion was assessed radiographically by three independent observers 3 and 6 months after surgery. Results. At 3 months, all the poly-(L-lactic acid) specimens showed ingrowth of new bone, but with radiolucency in the fusion mass. At 6 months, solid arthrodesis was observed in four of six poly-(L-lactic acid) specimens, advanced ingrowth in one specimen, and infection in one specimen. Titanium cages showed ingrowth of bone, but with radiolucency in the fusion mass. Interbody fusion using poly-(L-lactic acid) cages showed a significantly higher rate statistically (P = 0.016) and more complete fusion than titanium cages of the same design. Conclusions. The reduced stiffness of poly-(L-lactic acid) cages showed enhanced interbody fusion, as compared with titanium cages after 6 months. Bioabsorbable poly-(L-lactic acid) cages thus may be a viable alternative to current interbody cage devices, thereby avoiding the concomitant problems related to their excessive stiffness. However, the bioabsorbability of the poly-(L-lactic acid) cages awaits investigation in a long-term study currently underway.

Disorders in trunk rotation during walking in patients with low back pain: a dynamical systems approach

OBJECTIVE (1) To introduce an evaluation tool for the assessment of walking disorders in low back pain patients. (2) To investigate whether walking patterns in low back pain patients are different from those of control subjects. DESIGN Relative phase measures of movement coordination are applied in the assessment of trunk function in a small group of patients with non-specific low back pain and in control subjects. BACKGROUND Normal subjects change the coordination of pelvic and thoracic rotations from an in-phase to an out-of-phase pattern with increasing walking speed. Low back pain patients may have a reduced ability to counter rotate pelvis and thorax at higher walking speeds (from 1.0 m/s onwards) as a result of hyperstable coordination patterns. METHODS Six patients with non-specific low back pain and six healthy control subjects walked on a treadmill at comfortable walking speeds and during a systematic variation of the treadmill velocity. Coordination of arm and leg movements as well as of pelvic and thoracic rotations was analyzed using a relative phase algorithm. RESULTS AND CONCLUSIONS The comfortable walking speed was reduced in the patient group. In contrast to the control subjects, four of the six patients were not able to establish an out-of-phase coordination pattern between thorax and pelvis at higher walking speeds. This coincided with an increased stability of movement coordination, indicating guarded behavior. In addition, an increased asymmetry between the phase-relations of left and right side of the body was found in some of the patients.

The use of bioabsorbable implants in the spine

BACKGROUND CONTEXT Bioabsorbable implants are commonplace in sports medicine surgeries, especially in shoulder and knee ligamentous reconstruction. Their use is now expanding to the realm of spinal reconstructive surgery. Newer polymers offer reduced incidence of the side effects of aseptic sterile sinus formation and have appropriate resorption time parameters for spine use. These new bioabsorbable materials confer initial and intermediate-term stability that is adequate for stable bony healing in various applications. The majority of human clinical applications in the spine that have been documented involve bone graft harvest site reconstruction, posterior spinal graft containment, anterior interbody reconstruction and anterior cervical and lumbar spine tension band plating. PURPOSE The purpose of this review article is to highlight the indications and outcomes of the use of bioabsorbable implants in specific spinal applications. STUDY DESIGN A comprehensive literature review of the English and non-English literature on bioabsorbable implant technology. METHODS A comprehensive literature review was performed to gather basic science, animal and human data on the use of bioabsorbable implants in spinal surgery. RESULTS Bioabsorbable implants have demonstrated strength and resorption characteristics commensurate with the physiologic and biomechanical requirements of the human spinal axis. Histologic sampling has demonstrated successful time-patterned resorption accompanied by bony replacement and remodeling of intervertebral cage devices in the animal model. CONCLUSION Bioresorbable compounds appear to have a role in specific spinal reconstructive procedures. Their radiolucent nature improves image assessment of fusion healing, and their time-engineered resorption characteristics allow controlled dynamization in interbody and plate applications. Their widespread use and acceptance may increase dramatically as further research and clinical studies report on their safety and efficacy.

Experimental intervertebral disc degeneration induced by chondroitinase ABC in the goat

Study Design. In 2 studies, the injection of chondroitinase ABC into intervertebral discs of mature goats was evaluated as an experimental disc degeneration model. The first study analyzed the development of degeneration in time; the second study determined the optimal enzyme concentration. Objectives. To develop reproducible, slowly progressive disc degeneration in a large animal model. Summary of Background Data. Currently available, small animal models of intervertebral disc degeneration have shortcomings in the comparability to humans in terms of size, geometry, and cell population. Also, the methods to induce degeneration in the current models do not mimic human degeneration, which starts with the loss of proteoglycans. Injecting the enzyme chondroitinase ABC into the nucleus pulposus mimics the loss of proteoglycans. Methods. In Study 1, lumbar intervertebral discs of 17 goats were injected with chondroitinase ABC (0.25 U/mL) or phosphate-buffered saline. Degeneration was analyzed with radiograph analysis, MR imaging, and macroscopic and histologic scoring at 5 different time points (4, 8, 12, 18, and 26 weeks). Six control goats were analyzed. The second study used 6 goats in which 4 different concentrations of chondroitinase ABC (0.2–0.35 U/mL) or phosphate-buffered saline were injected. After 12 weeks, similar analyses as in Study 1 were performed. Results. After 12 weeks, degenerative signs were observed in all parameters in Study 1. The degeneration increased up to 18 weeks and leveled off after 26 weeks. The variability, however, was high. The second study showed a concentration dependent effect of chondroitinase ABC with all analyzed parameters. The injection of 0.25 U/mL chondroitinase ABC resulted in disc degeneration after 12 weeks without signs of severe degeneration. Conclusion. Injection of chondroitinase ABC in the caprine intervertebral disc results in mild, slowly progressive disc degeneration. This effect was optimal at a concentration of 0.25 U/mL. This is a promising model of disc degeneration that deserves further study.

Bioresorbable polymers: heading for a new generation of spinal cages

The use of polymer-based bioresorbable materials is now expanding to the realm of spinal interbody fusion. Bioresorbable polymers have important advantages over metals, because they are temporary, much less stiff, and radiolucent. Most promising is a group of α-polyesters, in particular polylactide acids (PLAs). Their biocompatibility is excellent, and they have sufficient stiffness and strength to provide initial and intermediate-term stability required for bone healing. However, polylactides have characteristics that make them vulnerable to complications if not properly controlled. Degradation rate strongly depends on polymer type, impurities, manufacturing process, sterilization, device size, and the local environment. The fact that larger implants degrade faster is contra-intuitive, and should be considered in the design process. Also optimal surgical techniques, such as careful bone bed preparation, are required for a successful application of these materials. The purpose of this paper is to highlight the specific properties of these bioresorbable polymers and to discuss their potential and limitations. This is illustrated with early preclinical and clinical data.Bioresorbable cage technology is just emerging: their time-engineered degradation characteristics allow controlled dynamization in interbody applications, facilitating spinal fusion. Their radiolucency improves image assessment of fusion healing. Acceptance and use of bioresorbable implants may increase as further research and clinical studies report on their safety, efficacy, and proper usage.

Bioabsorbable Poly-L-Lactic Acid Cages for Lumbar Interbody Fusion : Three-Year Follow-up Radiographic, Histologic, and Histomorphometric Analysis in Goats

Study Design. Long-term evaluation was performed for bioabsorbable poly-L-lactic acid cages in a goat interbody fusion model. Objective. To assess the radiographic, histologic, and histomorphometric characteristics of poly-L-lactic acid cages during 3 years of follow-up evaluation. Summary of Background Data. Failed cage fusions may be related to cage design and material in addition to the surgical technique used. To overcome material-related complications and to explore the potential benefits of bioabsorbable cages, poly-L-lactic acid cages have been designed. Methods. For this study, 36 Dutch milk goats underwent a lumbar interbody fusion procedure (L3–L4). Two types of custom-made cage devices were impacted with bone graft and implanted: poly-L-lactic acid cages (n = 30) and titanium cages (n = 6). Sequential harvesting of surgically managed motion segments (intervals: 3, 6, 12, 24, and 36 months) was performed for analysis. Results. In poly-L-lactic acid specimens, permanent interbody fusion could be achieved within 6 months after surgery with maintenance of cage height. Titanium specimens showed no interbody fusion within this period. Radiographic follow-up evaluation (6–36 months) showed interbody fusion in 86% (19/22) of poly-L-lactic acid specimens, as compared with 33% (2/6) of titanium specimens. After 36 months of implantation, in one half of the specimens, poly-L-lactic acid cages were completely absorbed. Bone histomorphometry showed complete bone remodeling after 2 years of follow-up evaluation. During the study period, no local or distant adverse histologic effects were observed. Conclusions. The current in vivo study showed that poly-L-lactic acid cage devices are feasible for lumbar interbody fusion. New poly-L-lactic acid cages designed for clinical practice might be a viable alternative to current nonabsorbable cage devices.

Reproducible long-term disc degeneration in a large animal model

Study Design. Twelve goats were chemically degenerated and the development of the degenerative signs was followed for 26 weeks to evaluate the progression of the induced degeneration. The results were also compared with a previous study to determine the reproducibility. Objectives. The purpose of this study was determine whether this Chondroitinase ABC (CABC) induced goat model is reproducible and to study the development of the degeneration in time up to 26 weeks. Summary of Background Data. Injecting CABC into goat intervertebral discs results in mild disc degeneration after 12 weeks. Spontaneous recovery or leveling off of the degeneration has been reported before and is relevant when the goat model is used in regeneration studies. Reproducibility of the induced degeneration is relevant as well. Methods. Twelve goats were used in this study. The development of degeneration was studied after the injection of 0.25 U/mL CABC intradiscally. The development of degenerative signs was studied after 18 (n = 6) and 26 (n = 6) weeks by means of radiograph, magnetic resonance imaging, macroscopic analysis, and histology and biochemical evaluation. The induced degeneration was compared with the results from a previous study, in which degeneration was induced similarly and analysis was performed after 12 weeks. Results. The severity of the degenerative signs was mild and was consequently present in all parameters analyzed. When compared with the results after 12 weeks, the degeneration was similar in the present study. Spontaneous recovery was not observed up to 26 weeks. Conclusion. The injection with CABC in the intervertebral disc reproducibly results in mild disc degeneration in the goat. These findings corroborate the goat model as a suitable large animal model to evaluate mild disc degeneration and potential new therapies.

In vitro gentamicin release from commercially available calcium-phosphate bone substitutes influence of carrier type on duration of the release profile

BackgroundPolymethyl-methacrylate (PMMA) beads releasing antibiotics are used extensively to treat osteomyelitis, but require surgical removal afterwards because they do not degrade.MethodsAs an alternative option, this report compares the in vitro gentamicin release profile from clinically used, biodegradable carrier-materials: six injectable cements and six granule-types. Cement cylinders and coated granules containing 3% gentamicin were submerged in dH2O and placed in a 48-sample parallel drug-release system. At regular intervals (30, 90, 180 min. and then every 24 h, for 21 days), the release fluid was exchanged and the gentamicin concentration was measured. The activity of released gentamicin was tested on Staphylococcus aureus.ResultsAll combinations showed initial burst-release of active gentamicin, two cements had continuous-release (17 days). The relative release of all cements (36–85%) and granules (30–62%) was higher than previously reported for injectable PMMA-cements (up to 17%) and comparable to other biodegradable carriers. From the cements residual gentamicin could be extracted, whereas the granules released all gentamicin that had adhered to the surface.ConclusionThe high release achieved shows great promise for clinical application of these biodegradable drug-carriers. Using the appropriate combination, the required release profile (burst or sustained) may be achieved.