Can plate osteosynthesis of periprosthethic femoral fractures cause cement mantle failure around a stable hip stem? A biomechanical analysis.

Periprosthetic femoral fractures (PFF) are a serious complication after total hip arthroplasty. Plate fixation with screws perforating the cement mantle is a common treatment option. The study objective was to investigate hip stem stability and cement mantle integrity under dynamic loading. A cemented hip stem was implanted in 17 composite femur models. Nine bone models were osteotomised just distal to the stem and fixed with a polyaxial locking plate the other eight constructs served as the control group. All specimens were tested in a bi-axial material testing machine (100000 cycles). There were no statistically significant differences in axial nor in medial (varus) stem migration. No cement cracks were detected in both groups. Plate fixation of a PFF with a stable, cemented prosthesis did not lead to cement mantle failure in this in vitro study.

The treatment of periprosthetic fractures with locking plates: effect of drill and screw type on cement mantles: a biomechanical analysis.

INTRODUCTION: Periprosthetic fractures after cemented hip replacement are a challenging problem to manage. Biomechanical studies have suggested the benefit of using locking screws for plate fixation, but there are concerns whether screws damage the cement mantle and promote crack propagation leading to construct failure. METHOD: In this biomechanical study, different screw types were implanted into the cement mantle after pre-drilling holes of different sizes, in unicortical and bicortical configuration. The presence of cracks and the pull-out resistance of these screws were then evaluated. RESULTS: No unicortical screw induced cracks. Screws with a shortened tip, smaller flutes and double threads were significantly better for pull-out resistance. Bicortical screws were associated with a risk of local cement mantle damage, but also with a significantly greater holding power. By increasing the drill diameter, the onset of cracks decreased, but so does the pull-out resistance.

A new technique for cement augmentation of the sliding hip screw in proximal femur fractures.

BACKGROUND: Fractures of the osteoporotic proximal femur are a significant source of mortality and morbidity in today's ageing population. Even with modern fixation techniques such as the sliding hip screw, a certain percentage of fixations will fail due to cut-out of the screw. This study presents a new method for augmenting hip screws with cement to reinforce the fixation. METHODS: Unstable pertrochanteric fractures were created in paired osteoporotic cadaver femora (n=10). The fractures were fixed using either standard fixation techniques (dynamic hip screw), or using a dynamic hip screw augmented with cement. Cement was introduced using a customised jig to guide cement into a region superior to the screw in the femoral head. Cut-out resistance was assessed using a biaxial material testing machine, with loading applied in compression until failure. FINDINGS: The new cement augmentation technique significantly improved the cut-out strength of the fixation (mean 42%; P=0.032). The failure mechanism for both groups was the same, with failure occurring through compression of the cancellous bone superior to the screw. The mean increase in temperature at the femoral neck was 3.7 degrees C in augmented bones, which is much lower than values previously reported for polymethylmethacrylate cements. INTERPRETATION: Several benefits with this technique have emerged. The method is technically straightforward. The risk of cement penetration into the joint is reduced, and cement is targetted to the areas of the femoral head where it is most needed. The exothermic reaction is minimised by reducing the volume of cement used. The first clinical results are promising.

Mid-term results of revision total hip arthroplasty with an uncemented modular femoral component.

INTRODUCTION: During revision total hip arthroplasty (THA), the surgeon commonly faces deficient proximal femoral bone. In this situation, distal fixation of the prosthesis is required. The aim of the current retrospective study is to assess the clinical and radiographic mid-term outcome of revision total hip arthroplasty using a modular uncemented, tapered, grit-blasted, distal straight stem system. METHODS: This retrospective study included 70 femoral revisions that were performed in 67 patients using the device of interest. All patients were operated on via an extended trochanteric osteotomy. 60 revisions were performed as 1-stage (12 infected) and 10 as 2-stage (all infected) revisions. At 3 months postoperatively and at final follow-up, patients were assessed radiographically for the presence of osteolysis and for distal integration. RESULTS: The mean follow-up time was 4.3 (2.0-7.6) years. 4 patients had a removal of at least 1 prosthetic component. Stem survival for any reason was 92% after 5 years (95% confidence interval [CI], 83%-100%). With aseptic loosening of the stem as the endpoint of interest, survival after 5 years was 96% (95% CI, 88%-100%). A postoperative subsidence rate of 14.7% was found. No perioperative femoral fractures were found in the current patient series. CONCLUSIONS: This study showed excellent mid-term survival and good clinical and radiographic outcomes in patients who had undergone revision THA with a modular uncemented, tapered, straight design.

Intraosseous blood flow of the everted or laterally-retracted patella during total knee arthroplasty.

Patellofemoral problems are relatively common sequelae of total knee arthroplasty (TKA), and many factors contribute to these complications. Vascular compromise has been identified as a possible contributing factor, and was selected for further investigation in the present study. Laser Doppler Flowmetry was used to quantify patella intraosseous blood flow in vivo during TKA surgery without the use of a tourniquet. Flow was measured after medial parapatellar arthrotomy, and compared to flow during patella eversion and lateral retraction. Patella blood flow during eversion was reduced to 13% of baseline values (p<0.05). A significantly greater proportion of flow was preserved during lateral retraction (53%), although the reduction from baseline was still significant (p<0.05). A statistically significant difference in flow (60% of baseline) was also noted when the leg was flexed from full extension to 90 degrees (p<0.05) with the patella in its normal anatomical alignment. In this study, we have demonstrated the sensitivity of the patella blood supply to knee flexion angle and patella dislocation technique, particularly to patella eversion. These may be important findings with regard to surgical technique for TKA.

Biomechanical properties of a posterior fully threaded positioning screw for cannulated screw fixation of displaced neck of femur fractures.

OBJECTIVES: Displaced intracapsular neck of femur fractures (NOF) in younger patients are usually fixed with partially-threaded cannulated screws. However posterior comminution may lead to construct failure. We hypothesised that a posterior fully threaded positioning screw would enhance stability. METHODS: A total of 16 left composite femora (Sawbone) were used for testing. To mimic a subcapital fracture with posterior comminution, a subcaptial osteotomy was performed and a posterior wedge was resected from the neck. Group A (n=8) was fixed using 3 partially threaded cancellous screws. In Group B (n=8), a fully threaded positioning screw instead of a partially threaded was used posteriorly. The specimens were tested for bending (antero-posterior=A-P) and axial stiffness. Finally, they were axially loaded up to failure or up to 10,000 cycles and the final displacement was measured at the site of the resected neck. More than 5mm of displacement was considered as a failure of the construct. RESULTS: Group B showed significantly higher average A-P stiffness (665±17N/mm compared to 414±41N/mm, p=0.0004); whereas axial stiffness did not significantly differ between the two groups (p=0.301). In Group B, the mean final displacement after cyclic axial loading was 0.51±0.13mm and none of the specimens failed, whereas 7 of 8 constructs failed in Group A (p=0.001). CONCLUSIONS: This biomechanical study points out a potential benefit of replacing the posterior partially threaded cancellous screw with a fully threaded positioning screw in subcapital NOF with posterior comminution. The construct with the fully threaded screw significantly improved the A-P stiffness and reduced the collapse of the fracture.

Does a bipolar hemiprosthesis offer advantages for elderly patients with neck of femur fracture? A clinical trial with 261 patients.

BACKGROUND: Previous studies comparing unipolar and bipolar hemiarthroplasty for treatment of displaced intracapsular femoral neck fractures in elderly patients have often lacked methodological power and yielded conflicting clinical results. The objective of this study was to compare the clinical outcomes from each implant in a randomized cohort of elderly patients with intracapsular fracture of the femoral neck treated with a cemented hemiprosthesis. METHODS: This study is a clinical trial of 261 patients (82.0 ± 7.9 years) who were randomly assigned to one of the two treatment groups: group 1 (n = 133) received a cemented bipolar implant and group 2 (n = 128) received a unipolar head with the same stem. At 12 months post-surgery, pain and functional abilities were quantified by blinded assessors using the Oxford and Harris Hip Scores, Verbal Numerical Rating Score and Six-Minute Walk. The Mann-Whitney U-test and t-test for independent samples were used to compare results between the groups (P < 0.05). RESULTS: There were no significant differences in any clinical scores between the groups. Results from the Six-Minute Walk indicated no difference in functional walking ability or endurance (P = 0.446) between the groups. Self-selected pain ratings also did not differ between groups (P = 0.236). Patients receiving the unipolar prosthesis had significantly reduced abduction (P = 0.0001) and internal rotation (P = 0.047) in the operated hip compared to the non-operated hip. CONCLUSION: These short-term results suggest that unipolar implants share many of the advantages of the bipolar prosthesis but can be manufactured at substantially lower cost. These implants may be appropriate for the less-active elderly patient, particularly when used with bone cement.

Periprosthetic fractures around polished collarless cemented stems: the effect of stem design on fracture pattern.

BACKGROUND: Predictable patterns of periprosthetic fracture have been observed around polished double tapered stems. Finite element studies have suggested that triple-tapered stems cause less cement strain in torsion compared to double-tapered stems. Hence, we hypothesised that the in vitro behaviour of implanted double- and triple-tapered polished stems, like the CPT (Zimmer, Warsaw, USA) or C-Stem (DePuy, Leeds, U.K.) when subjected to pathological torsional loads may cause different patterns of periprosthetic fractures. METHODS: Ten double-tapered stems (CPT) and ten triple-tapered stems (C-Stem) were cemented into synthetic femur bones. A constant axial compression load of 100 N and a torsional pre-load of 0.1 N.m were applied using a biaxial testing machine. The distal femur was then loaded in external rotation at 45 degrees until failure. RESULTS: Seven of the 10 CPT stems fractured at the level of the stem body while fracturing the cement mantle at the same level. In three of ten of the CPT stems and all ten C-Stems, the synthetic bone fractured at the tip of the prosthesis while the cement mantle remained intact. This was significant for the resulting fracture pattern (P=0.001). There was no significant difference between the groups for either torque (P=0.13) or angle at failure (P=0.49). INTERPRETATION: This biomechanical study indicates that the CPT and C-Stem create a different fracture pattern under the same loading condition. The C-Stem (a triple tapered stem) may produce lower strain in torsion to the cement mantle of a cemented THA. However, fractures that do occur may be more difficult to treat than those produced around a stem like the CPT subjected to comparable loading.

The comminuted midshaft clavicle fracture: a biomechanical evaluation of plating methods.

BACKGROUND: The optimal plate location and fixation method for midshaft fractures of the clavicle remains undetermined. The objective of this study was to develop a realistic biomechanical model with which to compare superior with inferior-medial plate placement, and the failure resistance of locked and against non-locked constructs. METHODS: We estimated implant loads for operated patients in early rehabilitation utilising 3-D mathematical model of the shoulder. During simulation of upper limb motion associated with eating, the fracture opened in an inferior and frontal direction. The peak X, Y, and Z loads from the simulation were reproduced using a materials testing machine. A one centimetre transverse osteectomy was created at the midshaft of forty composite clavicles. Each specimen was then fixed with either (1) non-locked superior plating (n=10), (2) locked superior plating (n=10), (3) non-locked inferior-medial plating (n=10), or (4) locked inferior-medial plating (n=10). Specimens were loaded at 20 N/s in four-point bending for 50 cycles to the peak X, Y, Z moment obtained from the computational model (-3.50, 2.46, and -1.00 N m), then loaded to failure at 20 N/s. FINDINGS: Inferior-medial unlocked plates were significantly stiffer than superior locked plates (P=0.046). INTERPRETATION: Operative fixation of midshaft clavicle fractures is controversial, though becoming more widely accepted. Few biomechanical data are available to assist surgical decision-making. Inferior plates may be better equipped to resist the in vivo loads experienced by the clavicle during early rehabilitation after internal fixation, particularly during the shoulder flexion motions associated with eating.

Trabecular bone texture detected by plain radiography and variance orientation transform method is different between knees with and without cartilage defects.

The objective of this work is to evaluate differences in trabecular bone (TB) texture between subjects with and without tibiofemoral cartilage defects using a variance orientation transform (VOT) method. A case-control study was performed in subjects without radiographic knee osteoarthritis (OA) (K&L grade <2) matched on sex, BMI, age, knee compartment, and meniscectomy where cases (n = 28) had cartilage defects (grade ≥2) and controls (n = 28) had no cartilage defects (grade <2). Cartilage defects were assessed from MRI using validated methods. The VOT was applied to TB regions selected on medial and lateral compartments in knee X-rays and fractal signatures (FS) in the horizontal (FS(H) ) and vertical (FS(V) ) directions, and along the roughest part of TB (FS(Sta) ) and texture aspect ratio signatures (StrS), at different trabecular image sizes (0.30-0.70 mm) were calculated. Compared with controls, FS(V) for cases were higher (p < 0.011) at image sizes 0.30-0.40 mm and 0.45-0.55 mm in the medial compartment. In the lateral compartment, FS(H) and FS(Sta) for cases were higher (p < 0.028) than those for controls at 0.30-0.40 mm and 0.45-0.55 mm, while FS(V) was higher (p < 0.02) at 0.30-0.40 mm. TB texture roughness was greater in subjects with cartilage defects than in subjects without, suggesting thinning and fenestration of TB occur early in OA and that the VOT identifies changes in TB in knees with early cartilage damage. No differences in StrS (p > 0.05) were found.

Effect of ankle taping on knee and ankle joint biomechanics in sporting tasks.

INTRODUCTION: Prophylactic taping is commonly used to prevent ankle injuries during sports. However, unnatural constraint of the ankle joint may increase the risk of injury to proximal joints such as the knee. The association between ankle taping and knee joint loading during open sporting tasks has not been quantified. This research aimed to measure changes in knee and ankle kinetics and kinematics during dynamic athletic activities undertaken with and without ankle taping. METHODS: A kinematic and inverse dynamics model was used to determine ankle and knee joint motion and loading in 22 healthy male participants undertaking running and sidestepping tasks. Both tasks were randomized to planned and unplanned conditions and undertaken with and without the use of ankle tape. RESULTS: At the knee, peak internal rotation moments (P < 0.001) and peak varus moments (P < 0.05) were significantly reduced during all running and sidestepping trials (planned and unplanned) when undertaken with ankle tape. Internal rotation impulse (P < 0.001) was reduced for sidestepping tasks. Varus impulse during unplanned sidestepping maneuvers (P = 0.04) was reduced with the use of ankle tape. However, there was a trend toward increased valgus moments and impulse for planned sidestepping trials undertaken with ankle tape(P = 0.056). Taping reduced the range of motion at the ankle in all three planes (P < 0.05). Peak inversion (P < 0.001) was reduced for running trials only. Average eversion and peak dorsiflexion moments were significantly reduced in sidestepping tasks by use of taping. CONCLUSIONS: By limiting motion at the ankle, taping increased mechanical stability at this joint. Ankle taping also provided protective benefits to the knee via reduced internal rotation moments and varus impulses during both planned and unplanned maneuvers. Medial collateral and anterior cruciate ligament injuries may, however, occur through increased valgus impulse during sidestepping undertaken with ankle tape.

Radiological findings and clinical results of 102 thrust-plate femoral hip prostheses: a follow-up of 2 to 8 years.

We report the radiological and clinical outcome of 102 consecutive femoral hip arthroplasty we prospectively followed up in 84 patients using the third generation of the thrust-plate prosthesis with a mean period of follow-up of 58 (range, 26-100) months. Four implants were revised: 2 because of an infection and 2 because of aseptic loosening. The thrust-plate prosthesis, which allows preservation of part of the femoral neck, was used in younger patients, 80% were younger than 60 years. In 95 implants, contact was maintained between thrust plate and underlying bone, and in only 3 instances, without any clinical manifestation, did the bone retract from the thrust plate to the extent that a gap appeared. The extent of radiologically evident bone contact with the flat surface of the thrust plate, as a consequence of the bone remodeling behavior, is described and retrospectively classified. The average Harris hip score increased from 51 points preoperatively to 96 points postoperatively at the last follow-up. Survivorship analysis according to Kaplan-Meier showed a survival rate of 98% after 6 years, with no further losses up to the end of the 8-year follow-up period.