Does the cement stiffness affect fatigue fracture strength of vertebrae after cement augmentation in osteoporotic patients?

Purpose

Normal progression of osteoporosis or the rigid reinforcement of the fractured vertebral body with polymethyl methacrylate (PMMA) cement is being discussed as a cause for adjacent-level fractures after vertebroplasty. The purpose of this study was to investigate whether augmentation with low stiffness cement can decrease the risk of adjacent-level fractures in low-quality bone.

Methods

Eighteen female osteoporotic lumbar specimens (L1–L5) were harvested and divided into three groups according to bone mineral density: (I) native; (II) PMMA; (III) modified PMMA (lower stiffness). For the PMMA and modified PMMA groups, a compression fracture was first mechanically induced in L3, and then the fracture received vertebroplasty treatment. The cement stiffness reduction of the modified PMMA group was achieved via an addition of 8 mL of serum to the typical PMMA base. All specimens were exposed to cyclic loading (4 Hz) and a stepwise increasing applied peak force. Cement stiffness was tested according to ISO 5833.

Results

A 51 % decrease in cement stiffness was achieved in the modified PMMA group (954 ± 141 vs. 1,937 ± 478 MPa, p < 0.001). Fatigue fracture force (the force level during cyclic loading at which the deformation experienced a sudden increase; FFF) was significantly affected by bone quality (r ² = 0.39, p = 0.006) and by the initial fracture force (the force necessary to create the initial fracture in L3 prior to augmentation; r ² = 0.82, p < 0.001). Using initial fracture force as a covariate, the FFF of the modified PMMA group (1,764 ± 49 N) was significantly higher than in the PMMA group (1,544 ± 55 N; p = 0.03).

Conclusions

A possible method to reduce adjacent-level fractures after vertebroplasty in patients with reduced bone quality could be the use of a lower modulus cement. Therefore, mixing cement with biocompatible fluids could prove useful to tailor cement properties in the operating theater.     

Calcium homeostasis influences radiological fracture healing in postmenopausal women

Introduction

Recent studies suggest that calcium and 25-[OH]-cholecalciferol represent substantial co-factors in fracture healing. However, there still seems to be no sustainable consensus regarding the influence on fracture healing patterns. In this study, the influence of calcium and vitamin D levels on fracture callus formation was prospectively analysed using pQCT scan.

Methods

94 postmenopausal females with distal radius fractures and consecutive surgery were included. Calcium, 25-[OH]-cholecalciferol, parathyroid hormone and bone-specific alkaline phosphatase levels were obtained prior surgical treatment and after 6 weeks. A pQCT scan was performed on both sites. Bone mineral density and fracture callus area were determined after detecting the outer border contour at a threshold of 280 mg/ccm. Patients received daily supplements of 1000 mg calcium and 880 IU 25-[OH]-cholecalciferol.

Results

Mean 25-[OH]-cholecalciferol level was 19.61 ± 21.87 ng/ml, mean parathyroid hormone level was 52.6 ± 58.9 ng/l and mean Ca level was 2.23 ± 0.35 mmol/l. After 6 weeks of supplementation a significant increase of calcium (p < 0.001) and 25-[OH]-cholecalciferol (p < 0.001), and a significant decrease of parathyroid hormone (p < 0.001) levels were observed. Sixth week follow-up fracture callus area correlated significantly with postoperative normal range calcium levels on the fractured site (p = 0.006). Bone mineral density correlated with age (p < 0.001), but not with calcium and 25-[OH]-cholecalciferol levels after 6 weeks. All fractures presented timely adequate callus formation.

Conclusion

Calcium and parathyroid hormone serum levels influence fracture callus area interpreted as fracture callus formation patterns. Calcium levels within physiological range accounted for highest fracture callus area. Therefore, a balanced calcium homeostasis is required for appropriate callus formation.     

Tantalum Acetabular Augments in One-stage Exchange of Infected Total Hip Arthroplasty: A Case–control Study

During the one-stage exchange procedure for periprosthetic joint infection (PJI) after total hip arthroplasty (THA), acetabular defects challenge reconstructive options. Porous tantalum augments are an established tool for addressing acetabular destruction in aseptic cases, but their utility in septic exchange is unknown. This retrospective case–control study presents the initial results of tantalum augmentation during one-stage exchange for PJI. Primary endpoints were rates of re-infection and short-term complications associated with this technique. Study patients had no higher risk of re-infection with equivalent durability at early follow-up with a re-infection rate in both groups of 4%. In conclusion, tantalum augments are a viable option for addressing acetabular defects in one-stage exchange for septic THA. Further study is necessary to assess long-term durability when compared to traditional techniques for acetabular reconstruction.     

Biomechanical advantage of C1 pedicle screws over C1 lateral mass screws: a cadaveric study

Purpose

The established technique for posterior C1 screw placement is via the lateral mass. Use of C1 monocortical pedicle screws is an emerging technique which utilizes the bone of the posterior arch while avoiding the paravertebral venous plexus and the C2 nerve root. This study compared the relative biomechanical fixation strengths of C1 pedicle screws with C1 lateral mass screws.

Methods

Nine human C1 vertebrae were instrumented with one lateral mass screw and one pedicle screw. The specimens were subjected to sinusoidal, cyclic (0.5 Hz) fatigue loading. Peak compressive and tensile forces started from ±25 N and constantly increased by 0.05 N every cycle. Testing was stopped at 5 mm displacement. Cycles to failure, displacement, and initial and end stiffness were measured. Finally, CT scans were taken and the removal torque measured.

Results

The pedicle screw technique consistently and significantly outperformed the lateral mass technique in cycles to failure (1,083 ± 166 vs. 689 ± 240 cycles), initial stiffness (24.6 ± 3.9 vs. 19.9 ± 3.2 N/mm), end stiffness (16.6 ± 2.7 vs. 11.6 ± 3.6 N/mm) and removal torque (0.70 ± 0.78 vs. 0.13 ± 0.09 N m). Only 33 % of pedicle screws were loose after testing compared to 100 % of lateral mass screws.

Conclusions

C1 pedicle screws were able to withstand higher toggle forces than lateral mass screws while maintaining a higher stiffness throughout and after testing. From a biomechanical point of view, the clinical use of pedicle screws in C1 is a promising alternative to lateral mass screws.     

Pertrochanteric fractures: tips and tricks in nail osteosynthesis

Introduction

Intramedullary fixation of intertrochanteric fractures has become the standard method of fixation especially in unstable fracture types. Even though there have been developments on implant design and technology, the surgical technique of reduction and implant positioning remains the mandatory factor in treating these fractures successfully. The advantages of nailing in the mainly elderly patients sustaining intertrochanteric femur fractures are a short lever arm and a lateral support in the trochanter supplied by the nail. The disadvantages are that it is often harder to achieve a closed reduction of a displaced fracture and to maintain the reduction with the intramedullary implant.

Tips and tricks

To obtain and maintain anatomic reduction and a secure fracture fixation, the surgical approach and fixation technique is of great importance. It starts with correct patient positioning, fracture reduction (accounting for varus dislocation and dislocation of flexed fragments), choosing the correct nail entry point and perfect lag screw positioning within the head-neck fragment and distal locking. To maintain the reduction achieved intraoperatively, the decision has to be made to use a cerclage wiring or to tolerate fracture gaps in the metaphyseal area. Intraoperative controlled compression of the neck or the subtrochanteric area is of great importance to reduce delayed unions or nonunions.

Summary

Intramedullary fixation of unstable per-, inter- or subtrochanteric fractures shows biomechanical advantages compared to extramedullry fixation techniques. Even though there have been several amendments and developments of implants, a better implant does not compensate for an inadequate surgical approach or deficient surgical techniques which are paramount for successful treatment. When fixing fractures with intramedullary nailing systems, the surgeon should always try to achieve anatomic reduction and a perfect implant positioning to allow immediate full weight bearing without an increased risk of cut-out, non-union and implant failure.     

Customised osteotomy guides and endoprosthetic reconstruction for periacetabular tumours

Purpose

We sought to analyse clinical and oncological outcomes of patients after guided resection of periacetabular tumours and endoprosthetic reconstruction of the remaining defect.

Methods

From 1988 to 2008, we treated 56 consecutive patients (mean age 52.5 years, 41.1 % women). Patients were followed up either until death or February 2011 (mean follow up 5.5 years, range 0.1–22.5, standard deviation ± 5.3). Kaplan–Meier analysis was used to estimate survival rates.

Results

Disease-specific survival was 59.9 % at five years and 49.7 % at ten and 20 years, respectively. Wide resection margins were achieved in 38 patients, whereas 11 patients underwent marginal and seven intralesional resection. Survival was significantly better in patients with wide or marginal resection than in patients with intralesional resection (p = 0.022). Survival for patients with secondary tumours was significantly worse than for patients with primary tumours (p = 0.003). In 29 patients (51.8 %), at least one reoperation was necessary, resulting in a revision-free survival of 50.5 % at five years, 41.1 % at ten years and 30.6 % at 20 years. Implant survival was 77.0 % at five years, 68.6 % at ten years and 51.8 % at 20 years. A total of 35 patients (62.5 %) experienced one or more complications after surgery. Ten of 56 patients (17.9 %) experienced local recurrence after a mean of 8.9 months. The mean postoperative Musculoskeletal Tumor Society (MSTS) score was 18.1 (60.1 %).

Conclusion

The surgical approach assessed in this study simplifies the process of tumour resection and prosthesis implantation and leads to acceptable clinical and oncological outcomes.     

Molecular mechanisms underlying ectopic otoconia-like particles in the endolymphatic sac of embryonic mice

Otoconin-90, the principal otoconial matrix protein, provided a tool to investigate the molecular mechanism of otoconial morphogenesis. The endolymphatic sac of the embryonic chick and guinea pig contain otoconia. Here, we show that the embryonic mouse transiently expresses ectopic otoconia in the endolymphatic sac. Massive precipitate of otoconin-90-positive material is detectable in the lumen of the endolymphatic sac between embryonic day 14.5 and 17.5 with frequent accretion into more heavily staining otoconia-like particles. Otoconin-90 was also localized at the surface and the interior of epithelial cells lining the endolymphatic sac as well as incorporated into free floating cells. In contrast, in situ hybridization failed to detect mRNA in the endolymphatic duct and sac, even though the adjacent nonsensory vestibular structures are heavily stained. Because of ample expression of otoconin-90 protein in the absence of the corresponding mRNA, we conclude that the luminal otoconin-90 is imported via longitudinal flow from the vestibular compartments, where both mRNA and protein are strongly expressed. Because of absence of mRNA, the expression of the corresponding protein by the epithelia lining the endolymphatic sac can only be explained by a resorptive process, as previously proposed on the basis of the movement of luminal macromolecules. The data do not support the previous hypothesis that the transient expression of otoconia-like particles of the endolymphatic sac represents a vestigial phenomenon from the amphibian stage, since amphibia express ample mRNA encoding otoconin-22 in the endolymphatic sac system.     

BMP‐7 protects against progression of cartilage degeneration after impact injury

In vivo studies were used to characterize a model of cartilage injury leading to osteoarthritis progression in the medial femorotibial joint of sheep. In three subsequent studies, bilateral impact injuries were created and one joint received intraarticular injections of 340 µg of rhBMP‐7 protein in a collagen particle carrier while the contralateral knee received the vehicle alone. Sheep were allocated to three groups that received intraarticular injections on day 0 (group A), 21 (group B), or 90 (group C) after experimental knee injury. In each group the, joints were evaluated for signs of osteoarthritis progression 90 days after the last treatment using India ink stained area, OARSI histological scoring, cartilage sGAG content, immunostaining for apoptosis (TUNEL), caspase‐3, collagen degradation (Col 2 3/4C short collagen epitope), and the endogenous (pro‐) form of BMP‐7 protein. Knee joints that received rhBMP‐7 immediately after injury had small focal lesions at the injury site that did not progress into the surrounding cartilage. Joints that received BMP‐7 3 weeks after injury were improved and had limited progression compared to controls, but joints that received the protein 12 weeks after injury had no statistically significant improvement. These studies suggest that BMP‐7 may be chondroprotective after traumatic injury in patients if it is administered within 3 to 4 weeks of the index injury. The mechanism of protection after sublethal injury appeared to be an increased survival of chondrocytes that are able to participate in the repair process. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 602–611, 2009     

Technique and proof of patency of microsurgical lympho‐lymphonodular anastomoses: A study in the rat model

Background: Lymphedemas due to local lymphatic blocks can be treated by microsurgical transplantation or transposition of lymphatic vessels. Here, the anastomoses are usually made end‐to‐end between lymphatics, but occasionally appropriate lymphatic recipient vessels are missing. In such cases, reconstructing lymph drainage by connection to a lymph node could be another technical option. The purpose of this study was to examine the patency rate of such lympho‐lymphonodular anastomoses in an experimental animal model. Methods: Male Sprague–Dawley rats were anesthetized, and the retroperitoneum was exposed. Patent blue dye was injected into the left foot to stain lymphatic structures. In group A (n = 8), the left lumbar trunk was cut centrally, the distal part was turned over to the right lumbar lymph node, and a microsurgical lympho‐lymphonodular anastomosis was performed. In group B (n = 8), the left lumbar trunk was cut. After 8 weeks, the lumbar region was surgically re‐explored, and the lymphatic drainage was examined by injection of Patent blue dye into the left lumbar lymph node. Results: In 8/8 animals of group A, patent transposed lymphatics were found. The patency of the anastomosis was proven directly by observation of blue dye transit and indirectly by observation of blue staining of the right lumbar lymph node. In 6/8 animals of group B, no lymphatic connection to the right lumbar lymphatic system was observed. Conclusions: This is the first report of the microsurgical technique and the proof of patency of lympho‐lymphonodular anastomoses. The novel animal model for testing the patency of transposed lymphatics is discussed. © 2009 Wiley‐Liss, Inc. Microsurgery, 2009.