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PubMed1999

Mechanical and histological analysis of bone-pedicle screw interface in vivo: titanium versus stainless steel.

OBJECTIVE: To investigate the differences in bone interface between titanium and stainless steel pedicle screws in the lumbar spine. METHODS: Eighteen adult mini-pigs that underwent total laminectomy, posterolateral spinal fusion (L4-L5) were randomly selected to receive stainless steel (9) or titanium pedicle screw devices (9). In both groups, the devices were CCD (Sofamore Danek) type with the same size and shape. The postoperative observation time was 3 months. Screws from L4 were harvested along their long axis of pedicle for histomorphometric study. Bone-screw interface and bone volume from thread were examined using linear intercept techniques. Mechanical testing (torsional test and pull-out test) was performed on the screws from L5. RESULTS: The titanium screw group had a significantly higher maximum torque (P < 0.05) and angle related stiffness (P < 0.05) measured by torsional test. In the pull-out tests, no differences were found between the two groups in relation to the maximum load, stiffness and energy to failure. Direct bone contact with the screw in percentage was 29.4% for stainless steel and 43.8% for titanium (P < 0.05). No differences in the bone purchase between the vertebral body part and pedicle part were found. CONCLUSION: Pedicle screws made of titanium have a better bone-screw interface binding than screws made of stainless steel. Torsional tests are more informative for bone-screw interface study. Pull-out tests seem less valuable when comparing bone purchase of screws made from different materials.

Animals↗
PubMed1994

Correlations between screw hole preparation, torque of insertion, and pullout strength for spinal screws.

The bone-screw interface is critical in the use of spinal instrumentation. The purpose of these experiments described here was twofold. First, to determine whether a correlation existed between torque generated during screw insertion and the pullout strength. Second, to determine how differing surgical methods of screw hole preparation influenced torque of insertion and screw pullout strength. A series of experiments were carried out in which screws were inserted into synthetic bone (experiment 1) and into calf vertebrae (experiment 2). The method of screw hole preparation (i.e., diameter of entrance hole and pilot hole) was varied while the resulting torque of insertion and the pullout strength of the screw was measured in each case. A torque screwdriver was used to measure the torque of insertion of the screws. Screw pullout strength was measured using a materials testing machine. Two important results emerged from these experiments. First, a higher torque of insertion correlated with a higher screw pullout force. This correlation may be useful intraoperatively in evaluating fixation. Second, torque of insertion and pullout force were more influenced by cortex over-drill diameter than pilot hole diameter. These experiments show the importance of the dorsal cortex in pedicle screw fixation.

Animals↗
PubMed2001

Analysis of the osseous/metal interface of drill free screws and self-tapping screws.

AIM: A comparison of metal/osseous interface and bone remodelling after insertion of different types of titanium bone screws in vivo. MATERIAL: Samples of five of each of the following bone screw types were inserted into the anterior wall of the frontal sinus of five Göttingen minipigs: self-tapping micro- (1.5mm) and miniscrews (2.0 mm) or drill free micro- (1.5 mm) and miniscrews (2.0 mm) (Martin Medizintechnik, Tuttlingen, Germany). Screw length was 7mm. METHODS: Sequential intraperitoneal injections of fluorochromes were performed between the second and ninth postoperative week. After 6 months the pigs were sacrificed, the screw-bone-blocks resected, and microradiographic, histological and fluorescence microscopical examinations were carried out. RESULTS: Using drill free screws, mean screw/bone contact was 88.4% (miniscrews), or 93.8% (microscrews). With self-tapping miniscrews it was 54.9%, but in microscrews 81%; the differences were statistically significant (t-test: p<0.05). By fluorescence microscopy, the amount of bone remodelling (ratio of residual vs. newly formed bone) was measured. Significantly more of the residual bone was found in the region of the screw threads using drill free screws (miniscrews: mean 71.8%, microscrews: mean 67.9%) than in the region of screw threads with self-tapping screws (miniscrews: mean 33.1%, microscrews: mean 42.4%). CONCLUSION: The present data support the view that screw/bone contact with drill free screws was superior to that of self-tapping screws; the greater amount of original bone in the threads of drill free screws demonstrated that the insertion of drill free screws did not cause harm to the surrounding bone. Both results are important for osteosynthesis in regions where thin cortical bone is present, such as the central midface.

Animals↗
PubMed2001

Analysis of the osseous/metal interface of drill free screws and self-tapping screws.

Aim: A comparison of metal/osseous interface and bone remodelling after insertion of different types of titanium bone screws in vivo. Material: Samples of five of each of the following bone screw types were inserted into the anterior wall of the frontal sinus of five Göttingen minipigs: self-tapping micro- (1.5 mm) and miniscrews (2.0 mm) or drill free micro- (1.5 mm) and miniscrews (2.0 mm) (Martin Medizintechnik, Tuttlingen, Germany). Screw length was 7 mm. Methods: Sequential intraperitoneal injections of fluorochromes were performed between the second and ninth postoperative week. After 6 months the pigs were sacrificed, the screw-bone-blocks resected, and microradiographic, histological and fluorescence microscopical examinations were carried out. Results: Using drill free screws, mean screw/bone contact was 88.4% (miniscrews), or 93.8% (microscrews). With self-tapping miniscrews it was 54.9%, but in microscrews 81%; the differences were statistically significant (t -test: p<0.05). By fluorescence microscopy, the amount of bone remodelling (ratio of residual vs. newly formed bone) was measured. Significantly more of the residual bone was found in the region of the screw threads using drill free screws (miniscrews: mean 71.8%, microscrews: mean 67.9%) than in the region of screw threads with self-tapping screws (miniscrews: mean 33.1%, microscrews: mean 42.4%). Conclusion: The present data support the view that screw/bone contact with drill free screws was superior to that of self-tapping screws; the greater amount of original bone in the threads of drill free screws demonstrated that the insertion of drill free screws did not cause harm to the surrounding bone. Both results are important for osteosynthesis in regions where thin cortical bone is present, such as the central midface. Copyright 2001 European Association for Cranio-Maxillofacial Surgery.

Journal Article↗
PubMed2001

A fracture movement monitoring system to aid in the assessment of fracture healing in humans.

This paper presents a new design for a device to monitor the motion of fracture fragments in diaphyseal tibial fractures. The device measures the motion that occurs at the fracture site when loaded by gait or by manipulation. It has undergone rigorous calibration and acceptance trials. The device has been used in ethically approved research clinics held at the North Staffordshire Hospital (40 patients). The paper presents a selection of results obtained using the new device. The results demonstrate several new ways of assessing fracture healing by examining fracture site motion. The following conclusions were drawn: 1. If fracture monitoring devices are to be attached to bone screws, it is essential to minimize bone screw errors. To do this, each patient must have similar bone screw lengths, orientations, alignment and siting. This is only achievable using a peroperative reduction device. 2. If fracture stiffness is to be used as a measure of fracture healing, load rate should be controlled; at the very least strain rate should be controlled. 3. It is imperative that fracture stiffness be measured in more than one plane by a biplanar device so that asymmetry may be accommodated. 4. Fracture stiffness, on its own, is probably not a sufficiently rigorous measure of healing end-point. The quantifiably viscoelastic properties of healing callus should be taken into account.

Bone Screws↗
PubMed2004

Lumbar spinal fusion. Outcome in relation to surgical methods, choice of implant and postoperative rehabilitation.

Chronic low back pain (CLBP) has become one of the most common causes of disability in adults under 45 years of age and is consequently one of the most common reasons for early retirement in industrialised societies. Accordingly, CLBP represents an expensive drain on society's resources and is a very challenging area for which a consensus for rational therapy is yet to be established. The spinal fusion procedure was introduced as a treatment option for CLBP more than 70 years ago. However, few areas of spinal surgery have caused so much controversy as spinal fusion. The literature reveals divergent opinions about when fusion is indicated and how it should be performed. Furthermore, the significance of the role of postoperative rehabilitation following spinal fusion may be underestimated. There exists no consensus on the design of a program specific for rehabilitation. Ideally, for any given surgical procedure, it should be possible to identify not only possible complications relative to a surgical procedure, but also what symptoms may be expected, and what pain behaviour may be expected of a particular patient. The overall aims of the current studies were: 1) to introduce patient-based functional outcome evaluation into spinal fusion treatment; 2) to evaluate radiological assessment of different spinal fusion procedures; 3) to investigate the effect of titanium versus stainless steel pedicle screws on mechanical fixation and bone ingrowth in lumbar spinal fusion; 4) to analyse the clinical and radiological outcome of different lumbar spinal fusion techniques; 5) to evaluate complications and re-operation rates following different surgical procedures; and 6) to analyse the effect of different rehabilitation strategies for lumbar spinal fusion patients. The present thesis comprises 9 studies: 2 clinical retrospective studies, 1 clinical prospective case/reference study, 5 clinical randomised prospective studies and 1 animal study (Mini-pigs). In total, 594 patients were included in the investigation from 1979 to 1999. Each had prior to inclusion at least 2 years of CLBP and had therefore been subjected to most of the conservative treatment leg pain, due to localized isthmic spondylolisthesis grades I-II or primary or secondary degeneration. PATIENT-BASED FUNCTIONAL OUTCOME: Patients' self-reported parameters should include the impact of CLBP on daily activity, work and leisure time activities, anxiety/depression, social interests and intensity of back and leg pain. Between 1993 and 2003 approximately 1400 lumbar spinal fusion patients completed the Dallas Pain Questionnaire under prospective design studies. In 1996, the Low Back Pain Rating scale was added to the standard questionnaire packet distributed among spinal fusion patients. In our experience, these tools are valid instruments for clinical assessment of candidates for spinal fusion procedures. RADIOLOGICAL ASSESSMENT: It is extremely difficult to interpret radiographs of both lumbar posterolateral fusion and anterior interbody fusion. Plain radiographs are clearly not the perfect media for analysis of spinal fusion, but until new and better diagnostic methods are available for clinical use, radiographs will remain the golden standard. Therefore, the development of a detailed reliable radiographic classification system is highly desirable. The classification used in the present thesis for the evaluation of posteroalteral spinal fusion, both with and without instrumentation, demonstrated good interobserver and intraobserver agreement. The classification showed acceptable reliability and may be one way to improve interstudy and intrastudy correlation of radiologic outcomes after posterolateral spinal fusion. Radiology-based evaluation of anterior lumbar interbody fusion is further complicated when cages are employed. The use of different cage designs and materials makes it almost impossible to establish a standard radiological classification system for anterior fusions. BONE-SCREW INTERFACE: Mechanical binding at the bone-screw interface was significantly greater for titanium pedicle screws than it was for stainless steel. This could be explained by the fact that the titanium screws had superior bone on-growth. There was no correlation between screw removal torques and pull-out strength. Clinically, the use of titanium and titanium-alloy pedicle screws may be preferable for osteoporotic patients and those with decreased osteogenesis. OUTCOME: The present series of studies observed significant long-term functional improvement for approximately 70% of patients who had undergone lumbar spinal fusion procedure. Solid fusion as determined from radiographs ranged from 52% to 92% depending on the choice of surgical procedure. The choice of surgical procedure should relate to the diagnosis, as patients with isthmic spondylolisthesis (Grades I and II) are best served with posterolateral fusion without instrumentation, and patients with disc degeneration seem to gain most from instrumented posterolateral fusion or circumferential fusion. COMPLICATIONS: The number of perioperative complications increased with the use of pedicle screw systems to support posterolateral fusions and increased further with the use of circumferential fusions. There was no significant association between outcome result and perioperative complications. The risk of reoperation within 2 years after the spinal fusion procedure was, however, significantly lower for those who had received circumferential fusion in comparison to posterolateral fusion with instrumentation. Furthermore, the risk of non-union was found to be significantly lower for patients who had received circumferential fusion as compared to posterolateral fusion with and without instrumentation. The complications of sexual dysfunction and fusion at non-intended levels were found to be significant but without influence on the overall outcome. REHABILITATION: The patients in the Back-café group performed a succession of many daily tasks significantly better and moreover had less pain compared with both the Video and Training groups 2 years after lumbar spinal fusion. The Video group had significantly greater treatment demands outside the hospital system. This study demonstrates the importance of the inclusion of coping schemes and questions the role of intensive exercises in a rehabilitation program for spinal fusion patients.

Activities of Daily Living↗
PubMed1990

[Stability of screw fixation following sagittal splitting osteotomy of the mandibular ramus].

Recently, sagittal splitting osteotomy of the mandibular ramus is frequently performed in orthognathic surgeries of mandibular deformities. Although the surgical technique has been established. Methods for osteosynthesis following sagittal spitting of mandibular ramus still remain unestablished. Osteosynthesis is usually achieved by circumferencial wiring, interosseous wiring or screw fixation. It is unknown which of these three methods is best suited from dynamic and clinical point of view. The author carried out a simulation study of screw fixation using acrylic resin plate models and sagittally split air-dried human mandibles. The following result were obtained: 1) In the fixation experiment using an acrylic resin plate and AO cortical bone screws, a significantly smaller displacement was recorded by S3E type fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, S3D type fixation required a significantly larger stress, compared with other modes of fixation. 2) In the destruction experiment using an acrylic resin plate and AO cortical bone screws, the critical displacement measured was significantly smaller by S3E type fixation compared with other modes of fixation S3C type fixation required a significantly larger amount of stress to cause destruction. 3) In the fixation experiment using the air-dried human mandibles and alumina ceramic screws, a significantly smaller displacement was recorded by 2-alumina ceramic screw fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, 3-alumina ceramic screw fixation required a larger stress, compared with other modes of fixation. 4) In the fixation experiment using the air-dried human mandible and AO cortical bone screws, a significantly smaller displacement was recorded by 2-AO cortical bone screw fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, 3-AO cortical bone screw fixation required a larger stress, compared with the 2-AO type of fixation. The above experimental results suggest that when the sagittally split proximal cortical plate retains enough thickness for tapping, clinical application of screw fixation either with alumina ceramic or AO cortical bone screws produces an adequately high anti-displacement effect, even if only 2 screws are used. However, when stability is evaluated in terms of the resistance to stress, 3-screw fixation is considered to amply satisfy the resistance required.

Acrylic Resins↗
PubMed1999

Fracture fixation with screws and bone plates.

The treatment goal of fracture fixation is to restore the patient to normal function as quickly as possible. Fracture fixation can be accomplished by various means; fixation with screws and bone plates is not only a popular but a successful technique. In this article, the authors provide concepts that a surgeon must understand for successful screw and bone plate use. In addition, case examples demonstrating the application of many of the concepts are included.

Animals↗
PubMed1994

Sacral fixation using iliac instrumentation and a variable-angle screw device. Technical note.

Secure fixation of the sacrum is technically challenging. The bone of the dorsal sacral surface is often thin, making hook fixation tenuous. The use of bone screws in the sacral pedicles has gained popularity, but rigidity is often not achieved and screw pullout is common. Solid constructs have been achieved using angled rods to stabilize the ilium, but these methods are technically difficult and time-consuming to perform. A technique is described that achieves rigid sacral fixation by adding a bone screw placed through both cortical surfaces of the ilium. This bone screw is a new type that allows attachment to a rod at variable angles. It permits easy attachment to an appropriately contoured rod, which is affixed to sacral hooks or screws. The resulting configuration of the bone-metal interface creates a tripod for load distribution. Additionally, the splayed geometry of these purchase sites provides a significant biomechanical advantage preventing the instrument from being pulled out. The technique for this fixation method, particularly for patients with complex spinal disorders, is described. Use of this new technique provides significant advantages to the spine surgeon in situations in which substantial sacral fixation integrity is necessary.

Biomechanical Phenomena↗
PubMed2001

Biomechanical evaluation of anterior spinal instrumentation systems for scoliosis: in vitro fatigue simulation.

STUDY DESIGN: A biomechanical study was designed to assess the bone-screw interface fixation strength among five anterior spinal instrumentation systems for scoliosis before and after a fatigue simulation. OBJECTIVES: The objectives of the current study were twofold: 1) evaluate the static (initial) strength at the bone-screw interface and 2) evaluate dynamic (post fatigue) strength of the bone-screw interface after a fatigue simulation to investigate a possible mechanism for postoperative loss of correction. SUMMARY OF BACKGROUND DATA: Although the recent advancement of anterior instrumentation for scoliosis has permitted shorter fusion segments and improved surgical correction, the loss of correction over the instrumented segments still has been reported in one-rod systems. Little is known about the mechanism for loss of correction. METHODS: Twenty-five fresh-frozen calf spines (T6-L6) were used. A total of five instrumentation systems included the following: Anterior ISOLA (ISOLA), Bad Wildungen Metz (BWM), Texas Scottish Rite Hospital system (TSRH), Cotrel-Dubousset Hoph (CDH), and Kaneda Anterior Scoliosis System (KASS). Screw pullout and rotational tests in the sagittal plane using a single vertebra were performed to investigate bone-screw interface fixation strength before and after a fatigue simulation. To simulate cyclic loading that the spine could undergo in vivo, a fatigue simulation using compressive-flexion loading up to 24,000 cycles was carried out. RESULTS: Mean maximum tensile pullout force decreased in the following order: KASS > CDH > BWM > TSRH > ISOLA (F = 29.91, P < 0.0001). KASS blunt tip screw was 26% stronger in pullout force than KASS sharp tip screw (P < 0.05). The one-rod system demonstrated a positive correlation between pullout force and both bone mineral density and screw insertional torque. For fatigue analysis the rotational strength at the most cephalad and caudal segments significantly decreased after a fatigue simulation in the one-rod system (P < 0.05). The two-rod system showed no significant decrease after a fatigue simulation. CONCLUSIONS: Simulating the cyclic loading to the construct, screw loosening at the bone-screw interface was produced in the one-rod system. This screw loosening may elucidate one mechanism for loss of correction in the one-rod system. The two-rod system may have the potential to minimize the risk of loss of correction.

Analysis of Variance↗
PubMed1986

Expanding applications for the Herbert scaphoid screw.

A distinctive new bone screw developed for the management of scaphoid fractures and nonunions promises to have expanding applicability. Its utilization for osteochondral fractures, small joint arthrodeses, osteochondritic lesions, and fractures involving small bones is described. Its unique design affords significant advantages over more conventional management techniques of these problems.

Arthrodesis↗
PubMed2000

Use of small cannulated screws for fixation in foot surgery.

Use of cannulated bone screws, as compared with use of traditional bone screws, has been reported to decrease surgical time, allow for more precise screw placement, and reduce sources of error. Cannulation of the smaller-size screws that are routinely used in foot surgery has not been available until the last few years. This article reports on the use of the small cannulated screws manufactured by Alphatec Manufacturing, Inc (Palm Desert, California). The screw sizes available in the Mini Lag Screw System are 2.7, 3.5, and 4.0 mm. A long-term clinical and radiographic prospective evaluation of 70 procedures performed on 49 patients was conducted. The follow-up time for all patients was 2 years. None of the 70 implants fractured, and seven procedures (in seven patients) resulted in some type of implant-fixation failure. All of the fixation failures, however, appeared to be related to an untoward event or patient noncompliance. These smaller cannulated screws proved to be a reliable and effective means of fixation in foot surgery.

Bone Screws↗
PubMed1997

Does the anchorage form and depth influence the pull-out strength of screws from bone cement? An experimental study.

The pull-out strengths of cortical screws inserted into soft, unpolymerised Refobacin Palacos bone cement (procedure S) and into hardened polymerised cement into which a hole had been drilled and tapped (procedure P) were compared. Cortical screws 58 mm in length, outer diameter 4.5 mm and inner diameter 2.95 mm were used. Screws were inserted into cement cylinders at 5 mm incremental depths between 10 and 30 mm. At a screw depth of less than 25 mm, the screws pulled out, and at a depth of greater than 25 mm, the screws broke in both procedures. There was no statistically significant difference in pull-out strength leading to burst or break between the two procedures for screws inserted to comparable depths, but there was a statistically significant difference regarding the screwing depth regardless of the procedure of screw insertion chosen. The average material stability (sigma) of the cortical screws used was calculated to be 1191 N/mm2, and the elasticity limit was 5137 N. This study demonstrated that the material stability and not the depth of screw insertion was the limiting parameter in screw anchorage in bone cement while static testing. To avoid screw breakage due to fatigue during continuous alternate loading, the screws should not be loaded above this value.

Analysis of Variance↗
PubMed1996

Effects of radiation therapy on reconstruction of mandibular defects with a titanium reconstruction plate.

Titanium fixation plates are commonly used in reconstruction of mandibular defects resulting from tumor resections in head and neck surgery. The effects of radiation therapy on the interface of bone, plate, and soft tissue were examined in this in vivo study. Four conditioned beagles had 1-cm segmental mandibular defects that were reconstructed with titanium plates. Two of the four also had placement of vascularized bone grafts. Healing was evaluated with or without postoperative radiotherapy. After collection of tissues using histologic methods and analysis with energy-dispersive spectroscopy, we found that the effects of radiation on bone-plate and bone-screw interfaces is minimal. Although radiation decreased the bone density and the rate of bone repair at the bone-screw interface, this did not appear to affect stability of the plate repair or the viability of bone tissue.

Animals↗
PubMed2004

New implant designs for fracture fixation in osteoporotic bone.

Screws are one of the limiting factors for fixation of implants, particularly in poor bone quality. A class of new implants with an implant-bone-interface optimized regarding load transition by increasing the peripheral area might improve the anchorage of implants in osteoporotic bone. However, the shape of these implants requires new technologies for insertion. The goal of the work presented here was to analyze the relevant parameters regarding implant geometry and to demonstrate the effect of new procedures for their insertion. The investigation was divided into three parts: 1) implant design optimisation, 2) efficiency of cortical bone ablation, and 3) implant insertion technology. Finite element analysis (FEA) was performed to investigate the influence of the number of lobes, the radius of the outer curvature and additional milling to remove any sharp changes of section around the lobe. Opening of the cortical bone with an Er:YAG laser was studied using calf cortex from 2 to 7 mm thickness. The effect of a) pulse energy and pulse duration, b) cortical thickness, c) wet or dry boundary conditions on volume and geometry of ablated bone, time required to penetrate the cortical bone and local bone tissue damage was quantified. Pneumatic and ultrasound based insertion were compared in the third experiment. The cortical bone was prepared in the following ways: a) no opening, b) predrilling of three holes (1 mm diameter each) and c) exact pre-cutting of the whole contour. Increasing the radius of the outer curvature from 2 to 5 mm reduces the peak stresses during loading in all planes in the implant as well as in the adjacent cortical bone by about 30-40%. An increase in the number of lobes from two to three decreases the mean peak stress by about 46% (alpha < 0.001) and the range between the minimal and maximal peak stresses for different loading directions by about 83%. Penetration of cortical bone with an Er:YAG laser was possible up to a cortical thickness of 6 mm with fewer than 100 pulses. The ablation rate per pulse increased more with increasing duration than with increasing energy. Signs of bone damage such as melting were only visible when high pulse energies and durations were used. Insertion of the prototype was possible with all devices, but only when the whole contour was cut out of the cortical bone. However, the use of the ultrasound vibrator led to heating up of the tissue fluid and subsequently to water evaporation and tissue damage. Insertion of the prototype was possible with both pneumatic vibrators, but only when the whole contour was cut out of the cortical bone. New implant designs may lead to reduced stress peaks in the surrounding bone and might be inserted with the help of new insertion technologies, namely laser cutting of cortical bone and pneumatic vibration. Further studies are required to optimize these technologies prior to clinical use.

Animals↗
PubMed2006

Volar fixed-angle plating of distal radius extension fractures: influence of plate position on secondary loss of reduction--a biomechanic study in a cadaveric model.

PURPOSE: Treatment of extension fractures of the distal radius with volar fixed-angle plates has become increasingly popular in the past 2 years. It has been observed clinically that placement of the distal screws as close as possible to the subchondral zone is crucial to maintain radial length after surgery. The purposes of this study were (1) to evaluate radial shortening after plating with regard to plate position and (2) to evaluate whether plate position has an influence on the strength and rigidity of the plate-screw construct. METHODS: An extra-articular fracture (AO classification, A3) was created in 7 pairs of fresh-frozen human cadaver radiuses. The radiuses then were plated with a volar distal radius locking compression plate. Seven plates were applied subchondrally; 7 plates were applied 4.5 mm to 7.5 mm proximal to the subchondral zone. The specimens were loaded with 800-N loads for 2,000 cycles to evaluate radial shortening in the 2 groups. Each specimen then was loaded to failure. RESULTS: Radial shortening was significantly greater when the distal screws were placed proximal to the subchondral zone. The amount of shortening after cyclic loading correlated significantly with the distance the distal screws were placed from the subchondral zone. Rigidity of the plate systems was significantly higher in radiuses in which the distal screws were placed close to the subchondral zone. CONCLUSIONS: To maintain radial length after volar fixed-angle plating, placement of the distal screws as subchondral as possible is essential. The subchondral plate-screw-bone constructs showed significantly greater rigidity, indicating higher resistance to postoperative loads and displacement forces.

Aged↗