Bioresorbability, porosity and mechanical strength of bone substitutes: what is optimal for bone regeneration?

Bone repair is a multi-dimensional process that requires osteogenic cells, an osteoconductive matrix, osteoinductive signalling, mechanical stability and vascularization. In clinical practice, bone substitute materials are being used for reconstructive purposes, bone stock augmentation, and bone repair. Over the last decade, the use of calcium phosphate (CaP) based bone substitute materials has increased exponentially. These bone substitute materials vary in composition, mechanical strength and biological mechanism of function, each having their own advantages and disadvantages. It is known that intrinsic material properties of CaP bone substitutes have a profound effect on their mechanical and biological behaviour and associated biodegradation. These material properties of bone substitutes, such as porosity, composition and geometry change the trade-off between mechanical and biological performance. The choice of the optimal bone substitutes is therefore not always an easy one, and largely depends on the clinical application and its associated biological and mechanical needs. Not all bone graft substitutes will perform the same way, and their performance in one clinical site may not necessarily predict their performance in another site. CaP bone substitutes unfortunately have yet to achieve optimal mechanical and biological performance and to date each material has its own trade-off between mechanical and biological performance. This review describes the effect of intrinsic material properties on biological performance, mechanical strength and biodegradability of CaP bone substitutes.     

Inguinal hernia: what is the optimal size of prosthetic patch?

The use of prosthetic material for hernia repair is steadily increasing although some surgeons consider this excessive. This shift in surgical practice seems inevitable given the advantages of mesh prosthetic repair, but one may wonder about the amount of prosthetic material left in place which varies widely from one technique to another. While it may be impossible to determine the ideal size of a mesh, it is nevertheless useful to evaluate the relative advantages and drawbacks of techniques using meshes of different sizes. This study provides some elements of reflection based on anatomical, technical, and clinical data. The myo-pectineal orifice of Fruchaud is divided in two parts by the ilio-pubic tract. While the lower part is occupied by the femoral nerve and vessels and the lacunar ligament, the upper part contains the zone of weakness through which most groin hernias protrude. This area is small in size and can be covered by a mesh 8-9 cm long and 5-6 cm wide. There is no difference in the rate of recurrence of repairs using a wide preperitoneal mesh and those using a smaller onlay mesh. The theoretical advantage of a wide preperitoneal mesh is to prevent the possible occurrence of a femoral hernia. Given the rarity of femoral hernia, this advantage must be balanced against the drawbacks of this technique which include the need for general anesthesia, a higher incidence of early postoperative complications, and particularly a higher risk of late complications due to adhesion of the mesh to bladder and iliac vessels. Small onlay mesh prostheses are preferrable in most cases; the use of a wide preperitoneal mesh should be reserved for those cases of inguinal hernia at high risk of recurrence, particularly if bilateral.     

Analysis of lumbar pedicle morphology in degenerative spines using multiplanar reconstruction computed tomography: what can be the reliable index for optimal pedicle screw diameter?

Purpose

The measurement of transverse pedicle width is still recommended for selecting a screw diameter despite being weakly correlated with the minimum pedicle diameter, except in the upper lumbar spine. The purpose of this study was to reveal the difference between the minimum pedicle diameter and conventional transverse or sagittal pedicle width in degenerative lumbar spines.

Methods

A total of 50 patients with degenerative lumbar disorders without spondylolysis or lumbar scoliosis of >10° who preoperatively underwent helical CT scans were included. The DICOM data of the scans were reconstructed by imaging software, and the transverse pedicle width (TPW), sagittal pedicle width (SPW), minimum pedicle diameter (MPD), and the cephalocaudal inclination of the pedicles were measured.

Results

The mean TPW/SPW/MPD values were 5.46/11.89/5.09 mm at L1, 5.76/10.44/5.39 mm at L2, 7.25/10.23/6.52 mm at L3, 9.01/9.36/6.83 mm at L4, and 12.86/8.95/7.36 mm at L5. There were significant differences between the TPW and MPD at L3, L4, and L5 (p < 0.01) and between the SPW and MPD at all levels (p < 0.01).

Conclusions

The MPD was significantly smaller than the TPW and SPW at L3, L4, and L5. The actual measurements of the TPW were not appropriate for use as a direct index for the optimal pedicle screw diameter at these levels. Surgeons should be careful in determining pedicle screw diameter based on plain CT scans especially in the lower lumbar spine.     

Learning curve of thoracic pedicle screw placement using the free-hand technique in scoliosis: how many screws needed for an apprentice?

Purpose

The purpose of this study is to evaluate the learning curve of thoracic pedicle screw (TPS) placement of an inexperienced apprentice in scoliosis with the free-hand technique.

Methods

The patients with scoliosis who underwent TPS inserted with the free-hand technique by the apprentice under the direction of a chief surgeon were included in this study. The TPS placement by the apprentice was evaluated by examining the assessed position in chronological subgroups of 30 screws. The TPS position was assessed on the postoperative computed tomography (CT) scan images using Zdichavsky grading evaluation system and pedicle breach. The rates of good and dangerous screw placement and the rates of pedicle breaches in each apprentice subgroup were compared with those in the chief surgeon group.

Results

Thirty-eight patients with 311 TPS were retrospectively analyzed in our study. Of all screws, 154 pedicle screws were inserted by the apprentice, and were divided chronologically into five subgroups. The rates of dangerous placement performed by the apprentice in the first two subgroups were 26.7 and 23.3%, respectively, and were significantly higher than 9.1% by the chief surgeon (P < 0.05). Meanwhile, the breach rate was 46.6% in subgroup 1 and 50.0% in subgroup 2, and was significantly higher than 29.3% in chief surgeon (P < 0.05). Furthermore, after the first 60 TPS placements, the assessed rates in apprentice reached to a stable level, and no significant difference could be found among the subgroups (subgroup 3, 4 and 5) and the chief surgeon group (P > 0.05).

Conclusions

For an apprentice, an experience of at least 60 screw placements under the direction of an experienced surgeon is needed for inserting the TPS in scoliosis using the free-hand technique independently.     

Triggered electromyography for placement of thoracic pedicle screws: is it reliable?

Reliable electromyography (EMG) thresholds for detecting medial breaches in the thoracic spine are lacking, and there is a paucity of reports evaluating this modality in patients with adolescent idiopathic scoliosis (AIS). This retrospective analysis evaluates the ability of triggered EMG to detect medial breaches with thoracic pedicle screws in patients with AIS. We reviewed 50 patients (937 pedicle screws) undergoing posterior spinal fusion (PSF) with intraoperative EMG testing. Postoperative CT scans were used for breach identification, and EMG values were analyzed. There were 47 medial breaches noted with a mean threshold stimulus of 10.2 mA (milliamperes). Only 8/47 breaches stimulated at 2–6 mA. Thirteen of the forty-seven screws tested at an EMG value ≤6 mA and/or a decrease of ≥65% compared with intraosseously placed screws. The sensitivity and positive predictive value for EMG was 0.28 and 0.21. A subanalysis of T10–T12 screws identified six of seven medial breaches. Using guidelines from the current literature, EMG does not appear to be reliable in detecting medial breaches from T2 to T9 but may have some utility from T10 to T12.     

Anterior subcutaneous internal fixation of the pelvis − what rod-to-bone distance is anatomically optimal?

IntroductionAnterior fixation of the pelvis using subcutaneous supra-acetabular pedicle screw internal fixation (INFIX) has proven to be a useful tool by avoiding the downsides of external fixation in patients where open fixation is not suited.The purpose of this study was to find a rod-to-bone distance for the INFIX that allows for minimal hazard to the inguinal neuro-vascular structures and, at the same time, as little as possible interference with the soft tissues of the proximal thigh when the patient is sitting.MethodsAn INFIX was applied to 10 soft-embalmed cadaver pelvises with three different rod-to-bone distances. With each configuration, the relations of the rod to the neuro-vascular and the muscular surroundings were measured in supine and sitting position.ResultsExcept for the femoral artery, vein and nerve, all investigated anatomical structures of the groin were under compression with a rod-to-bone distance of 1 cm. With a rod-to-bone distance of 2 cm most of the anatomical structures were safe in supine position, although less than with 3 cm. With hip flexion some structures got under compression, especially the lateral femoral cutaneous nerve (LFCN, 80%) and the anterior cutaneous branches of the femoral nerve (ACBFN, 35%). With a rod-to-bone distance of 3 cm almost all anatomical structures were safe in supine position, while with hip flexion most superficial structures of the proximal thigh got under compression, especially the LFCN (75%) and the ACBFN (60%).ConclusionsAiming for a rod-to-bone distance of 2 cm is the safest way with regard to compression of the femoral neuro-vascular bundle and at the same time leads to the least compression of more superficial structures like the LFCN, the ACBFN, or the sartorius and the rectus femoris muscles in sitting position.     

Percutaneous short-segment pedicle screw placement without fusion in the treatment of thoracolumbar burst fractures: is it effective?: comparative study with open short-segment pedicle screw fixation with posterolateral fusion

Background

Since introduction of the pedicle screw-rod system, short-segment pedicle screw fixation has been widely adopted for thoracolumbar burst fractures (TLBF). Recently, the percutaneous pedicle screw fixation (PPSF) systems have been introduced in spinal surgery; and it has become a popularly used method for the treatment of degenerative spinal disease. However, there are few clinical reports concerning the efficacy of PPSF without fusion in treatment of TLBF. The purpose of this study was to determine the efficacy and safety of short-segment PPSF without fusion in comparison to open short-segment pedicle screw fixation with bony fusion in treatment of TLBF.

Methods

This study included 59 patients, who underwent either percutaneous (n?=?32) or open (n?=?27) short-segment pedicle screw fixation for stabilization of TLBF between December 2003 and October 2009. Radiographs were obtained before surgery, immediately after surgery, and at the final follow-up for assessment of the restoration of the spinal column. For radiologic parameters, Cobb angle, vertebral wedge angle, and vertebral body compression ratio were assessed on a lateral thoracolumbar radiograph. For patient’s pain and functional assessment, the visual analogue scale (VAS), the Frankel grading system, and Low Back Outcome Score (LBOS) were measured. Operation time, and the amount of intraoperative bleeding loss were also evaluated.

Findings

In both groups, regional kyphosis (Cobb angle) showed significant improvement immediately after surgery, which was maintained until the last follow up, compared with preoperative regional kyphosis. Postoperative correction loss showed no significant difference between the two groups at the final follow-up. In the percutaneous surgery group, there were significant declines of intraoperative blood loss, and operation time compared with the open surgery group. Clinical results showed that the percutaneous surgery group had a lower VAS score and a better LBOS at three months and six months after surgery; however, the outcomes were similar in the last follow-up.

Conclusions

Both open and percutaneous short-segment pedicle fixation were safe and effective for treatment of TLBF. Although both groups showed favorable clinical and radiologic outcomes at the final follow-up, PPSF without bone graft provided earlier pain relief and functional improvement, compared with open TPSF with posterolateral bony fusion. Despite several shortcomings in this study, the result suggests that ongoing use of PPSF is recommended for the treatment of TLBF.     

Does keel size,the use of screws,and the use of bone cement affect fixation of a metal glenoid implant?

The objective of this study was to determine the effect of screws and keel size on the fixation of an all-metal glenoid component. A prototype stainless-steel glenoid component was designed and implanted in 10 cadaveric scapulae. A testing apparatus capable of producing a loading vector at various angles, magnitudes, and directions was used. The independent variables included six directions and three angles of joint load, and five fixation modalities-three different-sized cross-keels (small, medium, and large), screws, and bone cement. Implant micromotion relative to bone was measured by four displacement transducers at the superior, inferior, anterior, and posterior sites. The components displayed a consistent response to loading of ipsilateral compression and contralateral distraction. Use of progressively larger keels did not significantly improve implant stability. Stability decreased as the angle of load application increased (P <.05). Screw and cement fixation resulted in the most stable fixation (P <.05).     

Biomechanical analysis of single screw fixation for slipped capital femoral epiphysis: are more threads across the physis necessary for stability?

PURPOSE: To evaluate single screw fixation stability, in the treatment of slipped capital femoral epiphysis, as a function of screw thread distribution across the physis. STUDY DESIGN: In vitro biomechanical study. METHODS: Thirty porcine proximal femurs were sectioned through the physeal line and stabilized with a cannulated 7.3-mm stainless steel AO screw. The distal 16 mm of each screw was threaded (5 threads). The femurs were randomized into 5 groups (1, 2, 3, 4, or 5 threads across the physis) and biomechanically tested to determine failure load (N) and stiffness (N/mm). RESULTS: Femurs with 2 or 3 threads across the physis had a significantly greater load to failure and stiffness compared with femurs with 1, 4, or 5 threads across the physis (P < 0.05). CONCLUSIONS: Thread distribution across the physis seems to be important. When using screws with a 16-mm thread, greatest strength and stiffness are achieved when 40%-60% of threads engage the epiphysis, with a significant decrease when greater than 80% of threads cross the physis. Too few threads in the epiphysis as well as too few in the metaphysis both lead to decreased stability. CLINICAL RELEVANCE: This study challenges the belief that compression across the physis maximizes slipped capital femoral epiphysis fixation stability. We recommend equal distribution of threads across the physis when using 16-mm thread screws, and we postulate that screws with a greater thread length (32 mm or fully threaded) would increase fixation stability even further. Optimizing purchase may decrease the incidence of slip progression, especially as the prevalence of obesity increases in the adolescent population.     

Adenocarcinoma of the gastric cardia: what is the optimal surgical approach?

BACKGROUND: The incidence of adenocarcinoma of the gastric cardia is rising in Western countries. This study evaluates prognostic factors associated with surgical management of this cancer. STUDY DESIGN: Medical records of consecutive patients with gastric cardial cancer treated by surgical resection from 1991 through 2001 were reviewed. Survival was analyzed using the Kaplan-Meier method. Prognostic factors were evaluated using log-rank test and Cox regression. Mean followup period was 34 months. RESULTS: Eighty-two patients met study inclusion criteria. Median patient age was 65 years (range 86 to 22). Fifty-nine (72%) patients had type II tumors and 23 (28%) patients had type III tumors, according to the Siewert classification for gastroesophageal junction tumors. Twenty-seven (33%) patients underwent total esophagectomy, 24 (29%) patients underwent extended gastrectomy with thoracotomy, and 31 (38%) patients underwent extended gastrectomy without thoracotomy. Overall postoperative 5-year survival rate was 30%. On multivariate analysis, patient age 65 years and older, absence of lymph node metastasis, and R0 resection emerged as factors independently associated with improved postoperative survival. Frequency with which proximal resection margin was infiltrated with cancer was a function of gross margin length and T stage. Proximal gross margin length of at least 6 cm was required to achieve a microscopically negative proximal margin for T3 and T4 cancers. CONCLUSIONS: Achieving R0 resection should be the goal of surgical therapy for the gastric cardial cancer. The surgical approach should be tailored to individual patients to achieve this goal.     

Risk factors of fixation failure in basicervical femoral neck fracture: Which device is optimal for fixation?

BackgroundBasicervical femur neck fracture (FNF) is a rare type of fracture, and is associated with increased risk of fixation failure due to its inherent instability. The purpose of this study was (1) to investigate the incidence of fixation failure and (2) to determine risk factors for fixation failure in basicervical FNF after internal fixation.MethodsTo identify basicervical FNF with a minimum of 12 months follow-up, we retrospectively reviewed records of 3217 patients who underwent hip fracture surgery from May 2003 to March 2016. Among the identified 77 patients with basicervical FNF, 69 patients were followed up for at least 12 months. We evaluated the rate of collapse of fracture site and reoperation due to fixation failure. We performed a multivariable analysis to determine risk factors associated with fracture site collapse and fixation failure.ResultsAmong the 69 patients with basicervical FNF, 17 (24.6%) showed collapse of fracture site, and 6 (8.6%) underwent conversion to arthroplasty because of fixation failure. In the multivariable analysis, use of extramedullary plating with a sliding hip screw was an independent significant risk factor for both collapse of fracture site (odds ratio 6.84; 95% confidence interval 1.91–24.5, p = 0.003) and fixation failure (odds ratio 12.2; 95% confidence interval 1.08–137.7, p = 0.042).ConclusionsBasicervical FNF treated with extramedullary plate with a sliding hip screw is more likely to fail than that treated with intramedullary nail with a helical blade. Our results suggested that intramedullary nail with a helical blade is more recommended for basicervical FNF compared with extramedullary plate with a sliding hip screw.Level of evidenceIII, Retrospective cohort study.     

Trabecular bone structure analysis of the spine using clinical MDCT: can it predict vertebral bone strength?

Recent technical improvements have made it possible to determine trabecular bone structure parameters of the spine using clinical multi-detector computed tomography (MDCT). Therefore, the purpose of this study was to analyze trabecular bone structure parameters obtained from clinical MDCT in relation to high resolution peripheral quantitative computed tomography (HR-pQCT) as a standard of reference and to investigate whether clinical MDCT can predict vertebral bone strength. Fourteen functional spinal segment units between T7 and L3 were harvested from 14 formalin-fixed human cadavers (11 women and 3 men; age 84 ± 10 years). All functional spinal segment units were examined using HR-pQCT (isotropic voxel size of 41 μm³) and a clinical whole-body MDCT (interpolated voxel size of 146 × 146 × 300 μm³). Trabecular bone structure analyses (histomorphometric and texture measures) were performed in the HR-pQCT as well as MDCT images. Vertebral failure load (FL) of the functional spinal segment units was determined in an uniaxial biomechanical test. The HR-pQCT and MDCT derived trabecular bone structure parameters showed correlations ranging from r = 0.60 to r = 0.90 (p < 0.05). Correlations between trabecular bone structure parameters and FL amounted up to r = 0.86 (p < 0.05) using the HR-pQCT images, and up to r = 0.79 (p < 0.05) using the MDCT images. Correlation coefficients of FL versus trabecular bone structure parameters obtained with HR-pQCT and MDCT were not significantly different (p > 0.05). In this cadaver model, the spatial resolution of clinically available whole-body MDCT scanners was suitable for trabecular bone structure analysis of the spine and to predict vertebral bone strength.     

Endarterectomy vs stent angioplasty: what is the optimal treatment of carotid stenosis?

Very few operations have been subject to more scientific scrutiny than carotid endarterectomy (CEA). Since its introduction in the 1950s, CEAs have been performed in great numbers with the goal of preventing ischemic stroke. In the mid 1980s concern about over utilization of CEA and reports of excessive perioperative stroke morbidity and mortality prompted the initiation of several multicenter, randomized trials designed to evaluate the efficacy of CEA. As the results of these trials became available, the number and frequency of CEA in the United States increased significantly. However, now a new wave of uncertainty has arisen related to the availability of an alternative to CEA, carotid angioplasty and stent (CAS). Now, more than ever, there is uncertainty as to the proper management of carotid artery stenosis. In this review we summarize the existing data regarding the efficacy of CEA and compare these data to a critical analysis of the recent results of CAS.