Stefanie Erhart

The effect of in situ augmentation on implant anchorage in proximal humeral head fractures

INTRODUCTION Fracture fixation in patients suffering from osteoporosis is difficult as sufficient implant anchorage is not always possible. One method to enhance implant anchorage is implant/screw augmentation with PMMA-cement. The present study investigated the feasibility of implant augmentation with PMMA-cement to enhance implant anchorage in the proximal humerus. MATERIALS AND METHODS A simulated three part humeral head fracture was stabilised with an angular stable plating system in 12 pairs of humeri using six head screws. In the augmentation group the proximal four screws were treated with four cannulated screws, each augmented with 0.5ml of PMMA-cement, whereas the contra lateral side served as a non-augmented control. Specimens were loaded in varus-bending or axial-rotation using a cyclic loading protocol with increasing load magnitude until failure of the osteosynthesis occurred. RESULTS Augmented specimens showed a significant higher number of load cycles until failure than non-augment specimens (varus-bending: 8516 (SD 951.6) vs. 5583 (SD 2273.6), P=0.014; axial-rotation: 3316 (SD 348.8) vs. 2050 (SD 656.5), P=0.003). Non-augmented specimens showed a positive correlation of load cycles until failure and measured bone mineral density (varus-bending: r=0.893, P=0.016; axial-rotation: r=0.753, P=0.084), whereas no correlation was present in augmented specimens (varus-bending: r=0,258, P=0.621; axial-rotation r=0.127, P=0.810). CONCLUSION These findings suggest that augmentation of cannulated screws is a feasible method to enhance implant/screw anchorage in the humeral head. The improvement of screw purchase is increasing with decreasing bone mineral density.

Biomechanical effect of bone cement augmentation on rotational stability and pull-out strength of the Proximal Femur Nail Antirotation™

INTRODUCTION After surgical treatment of osteoporotic hip fractures, complications such as implant cut-out are reported to be high and implant failure often is associated with poor bone quality. As augmentation is reported to enhance implant anchorage, the aim of our study was to investigate the effect of bone cement augmentation on the rotational stability and the pull-out resistance of the Proximal Femur Nail Antirotation™ (PFNa) blade. MATERIALS AND METHODS A total of 18 fresh-frozen femoral heads (mean age 68 years, standard deviation (SD) 8.2) were scanned with quantitative computed tomography (qCT) for bone mineral density (BMD) measurements and instrumented with a PFNa blade. Nine specimens were augmented with a mean volume of 4.4 ml Traumacem V+. After cement consolidation, the blade was rotated for 60° for the rotational test. Subsequently, the blade was extracted from the specimens. Force, torque, displacement and angle were recorded constantly. RESULTS In the rotational test, the mean maximum torque in the augmented group (17.2 Nm, SD 5.0) was significantly higher (p=0.017) than in the non-augmented group (11.7 Nm, SD 3.5). The pull-out test also yielded a significant difference (p=0.047) between the augmented (maximum pullout force: 2315.2N, SD 1060.6) and the non-augmented group (1180.4N, SD 1171.4). DISCUSSION Augmentation of femoral heads yielded a significantly superior rotational stability, as well as an enhanced pull-out resistance, compared to the non-augmented state. However, the higher the BMD of the specimens, the lower was the effect of augmentation on the rotational stability. Therefore, augmentation can be a good clinical tool to enhance implant anchorage in osteoporotic bone.

Aspects of current management of distal radius fractures in the elderly individuals.

Diatal radius fractures (DRFs) are typical fractures of relatively fit persons with osteoporotic bone who remain active into older age. Traditionally, DRFs in older patients have been treated with closed reduction and cast immobilization. Considering the increasing life expectancy of the elderly population, appropriate management of these fractures is of growing importance. Decision making for surgical or nonsurgical approach to osteoporotic DRFs is difficult. These decisions are often made based on the data from treatments of much younger patients. The current literature concerning the treatment of DRFs in the elderly individuals is more controversial. Some investigators have recommended open reduction internal fixation (ORIF) as treatment for unstable DRFs in older patients, while others have suggested that elderly patients should be treated nonsurgically even if there is an unstable fracture situation because fracture reduction is not associated with functional outcomes as in younger patients. This article reviews the different treatment options for DRFs in the elderly individuals reported in the recent literature.

Measurement of intraarticular wrist joint biomechanics with a force controlled system

Pathologies of the wrist, such as fractures or instabilities, can lead to alterations in joint biomechanics. Accurate treatment of these pathologies is a frequent challenge for the surgeon. For biomechanical investigations, a test-setup that applies physiological loading of the wrist joint is necessary. A force controlled test-bench with agonistic and antagonistic muscle forces was built to move six fresh frozen human upper extremities through flexion and extension of the wrist joint. Tendon forces, range of motion, intraarticular contact area and contact pressure of the lunate and scaphoid facet as well as tendon excursion were investigated and compared with the current literature. During wrist motion the extensors exerted double the force of the flexors. Capsulotomy and sensor insertion decreased the range of motion from 63.4° (SD 14.1) to 45.9° (SD 23.7). The ratio of force transmitted through the radius and ulna was 77:23 and pressure distribution between the scaphoid and lunate facet showed a 70:30 relationship. The obtained data indicate a good agreement with the available literature. Therefore, the force controlled test-bench in combination with intraarticular radiocarpal measurements can be used to investigate the influence of wrist pathologies on joint biomechanics.

Is augmentation a possible salvage procedure after lateral migration of the proximal femur nail antirotation

IntroductionFailed fracture fixation of proximal femur fractures in the elderly usually results in prosthetic replacement. In case of the proximal femur nail antirotation (PFNA), during lateral blade migration or periimplant fracture at the femoral shaft, the femoral head remains intact and therefore a joint preserving procedure might be performed. However, implant anchorage in the femoral head after the second blade implantation generally results in reduced anchorage in the remaining cancellous bone. Therefore, we hypothesize that in the above mentioned cases augmentation of the PFNA blade could be a treatment option before prosthetic surgery has to be performed.MaterialsBiomechanical investigations were performed in eight fresh frozen femoral heads. Implant anchorage in case of blade extraction and reinsertion was investigated by rotation and pull out of a PFNA blade with a servohydraulic testing machine. After reinsertion of the blade and augmentation with bone-cement, the anchorage of the blade was investigated again to observe changes in torque and pull-out force.ResultsRotational stability of the implant significantly increased after augmentation of the prior extracted PFNA blade. Pull-out strength was higher in the revised case than in the initial tests but without statistical significance. After augmentation, correlation between bone mineral density and pull-out strength which was found during initial pull-out disappeared.DiscussionAugmentation of simulated blade exchange after lateral blade migration demonstrated a good anchorage. There was superior rotational stability in the revised case and no inferiority during pull out for the investigated specimens. Furthermore, augmentation could compensate for destroyed trabeculae and poor bone stock. It could furthermore be an option when a failed implant has to be replaced by a long PFNA in case of shaft fracture at the tip of the implant to increase anchorage in the femoral head. From a biomechanical point of view, reosteosynthesis and augmentation in selected cases of PFNA revision could be an alternative to initial prosthetic replacement. In the case of cut-out or medial implant protrusion, the suggested salvage technique is not feasible.

The biomechanical effects of a deepened articular cavity during dynamic motion of the wrist joint

BACKGROUND A deepened articular cavity of the distal radius due to a metaphyseal comminution zone is associated with early osteoarthritis and reduced joint motion. As this deformity has not been investigated biomechanically, the purpose of this study was to evaluate the effects of a deepened articular cavity on contact biomechanics and motion range in a dynamic biomechanical setting. METHODS Six fresh frozen cadaver forearms were tested in a force controlled test bench during dynamic flexion and extension and intact mean contact pressure and contact area as well as range of motion were evaluated. Malunion was then simulated and intraarticular as well as motion data were obtained. Intact and malunion data were compared for the scaphoid and lunate facet and the total radial joint surface. FINDINGS Due to malunion simulation, cavity depth increased significantly. Motion decreased significantly to 54-69% when compared to the intact state. Malunion simulation led to a significant decrease of contact area in maximum extension for all locations (by ~50%). In maximum flexion and neutral position, contact area decrease was significant for the scaphoid fossa (by 51-54%) and the total radial joint surface (by 47-50%). Contact pressure showed a significant increase in maximum extension in the scaphoid fossa (by 129%). INTERPRETATION Already a small cavity increase led to significant alterations in contact biomechanics of the radiocarpal joint and to a significant range of motion decrease. This could be the biomechanical cause for degenerative changes after the investigated type of malunion. We think that restoration of the normal distal radius shape can minimize osteoarthritis risk post trauma and improve radiocarpal motion.

Primary stiffness of a modified transforaminal lumbar interbody fusion cage with integrated screw fixation: cadaveric biomechanical study.

Study Design. In vitro biomechanical study using human fresh-frozen vertebrae. Objective. To investigate the influence of the additional screw fixation on the stability of a noncommercially available prototype transforaminal lumbar interbody fusion (TLIF) cage, when used as a stand-alone fusion device and in combination with pedicle screws (PSs). Summary of Background Data. Generally interbody fusion cages are supplemented by additional fixation devices such as PS. However, such posterior instrumented techniques are associated with additional soft-tissue trauma and potentially increased complication rate. To limit such drawbacks, a conventional posterior TLIF cage was modified to allow supplemental screw fixation to the adjacent vertebral bodies, to increase initial stiffness and possibly allow as a stand-alone posterior interbody cage. Methods. Six monosegmental lumbar spine segments were loaded in a spine simulator with pure bending moments of 7.5 Nm in lateral bending, flexion/extension, and axial rotation. The following paradigms were tested: intact spines; a destabilized spine (i.e., after discectomy and unilateral facetectomy); and the modified TLIF cage with (i.e., fixed TLIF cage) and without (i.e., TLIF cage) integrated screw fixation as a stand-alone model and with and without additional posterior fixation with bilateral PS. The range of motion (RoM) was recorded by a 3-dimensional motion analysis system. Results. The TLIF cage with integrated screw fixation had minimal additional stabilizing effect in all motion planes with or without supplemental PS fixation. Moreover, compared with the intact spines, the stand-alone TLIF cage with and without integrated screw fixation did not reduce the RoM in any of the 3 motion planes. Comparison of the TLIF cage with integrated screw fixation to the TLIF cage supplemented with PS showed a significantly greater RoM in all testing conditions (P < 0.05). Conclusion. In several testing paradigms, the prototype TLIF cage with the integrated screw fixation had limited effect in reducing RoM and providing stability. The PS was the main contributor in reducing RoM in the destabilized spine and remains the current “gold standard” in posterolateral spinal fixation. Level of Evidence: N/A

Clinical and biomechanical investigation of an increased articular cavity depth after distal radius fractures: effect on range of motion, osteoarthrosis and loading patterns

IntroductionAfter fracture, distal radius malunion with dissociation of the volar and dorsal ulnar fracture fragments can lead to an increased articular cavity.Patients and MethodsTo investigate its clinical impact we retrospectively analyzed the outcome of 81 patients and simulated this form of malunion in a biomechanical experiment with six cadaver specimens in a dynamic loading set-up.ResultsIn clinics, a higher arthritis stage was significantly correlated with an increased articular cavity depth and an increased anterioposterior distance. In cadaver specimens, a significantly decreased range of motion and significantly altered intraarticular contact characteristics were recognized for an increased cavity.ConclusionAlterations in contact biomechanics could be one reason for the higher incidence of posttraumatic osteoarthritis when a deeper central impaction of the distal radius is present. From a clinical and experimental point of view, restoration of the normal shape of the distal radius is considered to minimize the risk for posttraumatic radiocarpal osteoarthritis.

Restoring independency with an osteochondral graft of the navicular for coronoid process reconstruction

IntroductionThe coronoid is a crucial element for elbow stability. In case of posttraumatic instability or reduced range of motion, a complex reconstruction might be necessary.CaseWe present the case of a polytraumatized patient with complex upper extremity injury and initial poor outcome. Subluxation after initial surgery was treated by sublime tubercle reconstruction with a corticocancellous iliac crest graft. Due to massive ossification, the elbow remained stiff and the paraplegic patient was unable to use a manually propelled wheelchair. After arthrolysis, the unstable elbow was treated with an osteocartilaginous graft from the navicular of the foot as well as ulnar and radial collateral ligamentoplasties. At the time of follow-up, the patient had a stable joint and was able to independently perform activities of daily living.ConclusionAn autologous navicular graft seems to be an excellent option for our paraplegic patient as the shape matches the sublime tubercle of the ulna.

Does intra-articular load distribution change after lateral malleolar fractures? An in vivo study comparing operative and non-operative treatment

PURPOSE The impact of isolated malleolar fractures on the intra-articular load distribution within the ankle joint has been studied in several biomechanical cadaver studies during the last decades. Recently, computed tomography osteoabsorptiometry (CT-OAM) has been proposed as a valuable tool to assess intra-articular joint load distribution in vivo. The purpose of this retrospective matched pair analysis was to apply CT-OAM to evaluate in vivo changes of talar load distribution after lateral malleolar fractures in patients treated with open anatomic reduction and internal fixation (ORIF) compared to patients treated non-operatively. METHODS Ten matched pairs of patients with isolated lateral malleolar fractures with a maximum fracture dislocation of 3mm and a median follow-up of 42 month were included into the study. Patients were matched for age, gender, and fracture dislocation. Range of ankle motion (ROM), the AOFAS hindfoot score and the Short Form 36 (SF-36) were evaluated. CT-OAM analysis of the injured and the uninjured contralateral ankles were performed. RESULTS Patients treated with ORIF showed a significant lower ROM compared to the uninjured contralateral ankle. No differences were found regarding clinical scores between patients treated by ORIF and those treated non-operatively. CT-OAM analysis showed symmetrical distribution of subchondral bone mineralization in comparison to the uninjured contralateral ankles for both groups of patients. CONCLUSIONS The data of this study suggest that isolated lateral malleolar fractures with fracture gaps up to 3mm are not associated with a change of the tibio-talar joint load distribution in vivo. Therefore, patients with isolated minimally displaced lateral malleolar fractures may achieve good clinical long-term outcome following non-operative treatment. LEVEL OF EVIDENCE Level III, retrospective cohort study.