Standardized artificially created stable pertrochanteric femur fractures present more homogenous results compared to osteotomies for orthopaedic implant testing

Background

With regard to biomechanical testing of orthopaedic implants, there is no consensus on whether artificial creation of standardized bone fractures or their simulation by means of osteotomies result in more realistic outcomes. Therefore, the aim of this study was to artificially create and analyze in an appropriate setting the biomechanical behavior of standardized stable pertrochanteric fractures versus their simulation via osteotomizing.

Methods

Eight pairs of fresh-frozen human cadaveric femora aged 72.7 ± 14.9 years (range 48–89 years) were assigned in paired fashion to two study groups. In Group 1, stable pertrochanteric fractures AO/OTA 31-A1 were artificially created via constant force application on the anterior cortex of the femur through a blunt guillotine blade. The same fracture type was simulated in Group 2 by means of osteotomies. All femora were implanted with a dynamic hip screw and biomechanically tested in 20° adduction under progressively increasing physiologic cyclic axial loading at 2 Hz, starting at 500 N and increasing at a rate of 0.1 N/cycle. Femoral head fragment movements with respect to the shaft were monitored by means of optical motion tracking.

Results

Cycles/failure load at 15° varus deformation, 10 mm leg shortening and 15° femoral head rotation around neck axis were 11324 ± 848/1632.4 ± 584.8 N, 11052 ± 1573/1605.2 ± 657.3 N and 11849 ± 1120/1684.9 ± 612.0 N in Group 1, and 10971 ± 2019/1597.1 ± 701.9 N, 10681 ± 1868/1568.1 ± 686.8 N and 10017 ± 4081/1501.7 ± 908.1 N in Group 2, respectively, with no significant differences between the two groups, p ≥ 0.233.

Conclusion

From a biomechanical perspective, by resulting in more consistent outcomes under dynamic loading, standardized artificial stable pertrochanteric femur fracture creation may be more suitable for orthopaedic implant testing compared to osteotomizing the bone.

Bone cement augmentation of femoral nail head elements increases their cut-out resistance in poor bone quality- A biomechanical study

The aim of this study was to analyze biomechanically the impact of bone cement augmentation on the fixation strength and cut-out resistance of Proximal Femoral Nail Antirotation (PFNA) and Trochanteric Fixation Nail Advanced (TFNA) head elements within the femoral head in a human cadaveric model with poor bone quality. Methodology: Fifteen pairs of fresh-frozen human cadaveric femoral heads were randomized to three sets of five pairs each for center-center implantation of either TFNA blade, TFNA screw, or PFNA blade. By splitting the specimens of each pair for treatment with or without bone cement augmentation, six study groups were created. All specimens were biomechanically tested under progressively increasing cyclic loading featuring a physiologic loading trajectory in a setup simulating a reduced intertrochanteric fracture with lack of posteromedial support. Number of cycles to 5° varus collapse was evaluated together with the corresponding load at failure. Results: Compared to the non-augmented state, all types of implants demonstrated significantly higher numbers of cycles to failure and load at failure following augmentation, p ≤ 0.03. Augmented TFNA blades resulted in highest numbers of cycles to failure and loads at failure (30492; 4049 N) followed by augmented PFNA blades (30033; 4003 N) and augmented TFNA screws (19307; 2930 N), p = 0.11. Augmented TFNA screws showed similar numbers of cycles to failure and loads at failure compared to both non-augmented TFNA and PFNA blades, P = 0.98. From a biomechanical perspective, bone cement augmentation significantly increases the cut-out resistance of instrumented TFNA and PFNA head elements and is a valid supplementary treatment option to these nailing procedures in poor bone quality.

Surgical Skills Training Using Simulation for Basic and Complex Hip and Knee Arthroplasty

Skills training is important in an arthroplasty curriculum and can focus either on "part tasks" or on full procedures. The most commonly used simulations in orthopedics including arthroplasty are anatomic specimens, dry bone models, and virtual or other technology-enhanced systems. A course curriculum planning committee must identify the gaps to address, define what learners need to be able to do, and select the most appropriate simulation modality and assessment for delivery. Each simulation must have a clear structure with learning objectives, steps, and take-home messages. Feedback from learners and faculty must be integrated to improve processes and models for future learning.

Comminuted patellar fractures: The role of biplanar fixed angle plate constructs

Background

Comminuted patellar fractures represent a challenging clinical problem. Treatment aims to restore the integrity of the extensor mechanism and the congruity of patellofemoral joint. Controversy exists regarding the ideal fixation method. Metallic constructs aiming to convert pulling forces on the anterior aspect of the patella into compression forces across the fracture site are the standard of care. More recently, low profile plates have been described in the management of comminuted patellar fractures. The aims of this study were to (1) develop a novel unstable patellar fracture model and (2) to compare biomechanically three different constructs for fixation comminuted patellar fractures. We hypothesized that an orthogonal biplanar disposition of the screws within an anteriorly placed locking plate provides the best biomechanical properties in the management of comminuted fractures.

Methods

Six-part complex AO 34–C3 patella fractures were simulated in 18 human cadaveric knees by means of osteotomies including comminution around the distal patellar pole. The specimens were randomly assigned to 3 fixation techniques (n ​= ​6) for either anterior plating, antero-lateral plating, or tension band wiring (TBW). Biomechanical testing was performed over 5000 cycles in active extension and passive flexion, followed by ultimate destructive quasi-static testing. Interfragmentary movements were captured by means of optical motion tracking.

Results

Displacement between the proximal and distal medial patella fragments was lower after anterior plating compared to both antero-lateral plating (P ​= ​0.084) and TBW (P ​< ​0.001). Moreover, displacement between the proximal and distal lateral fragments was significantly lower after anterior plating compared to both other techniques (P ​≤ ​0.032). In addition, it was significantly lower for antero-lateral plating versus TBW (P ​< ​0.001). Rotation around the medio-lateral axis between the proximal and distal medial fragments was significantly lower after anterior plating compared to TBW (P ​= ​0.017).

Conclusions

Anterior mesh plating with biplanar placement of locking screws provides superior stability for fixation of comminuted patellar fractures when compared to both antero-lateral mesh plating and TBW. The latter is associated with considerably inferior performance.

Biomechanical evaluation of the docking nail concept in periprosthetic fracture fixation around a stemmed total knee arthroplasty

Intramedullary femoral nails provide an ideal mechanical axis for periprosthetic fracture fixation. Slotted nails allow a connection to a total knee arthroplasty (TKA) stem. This study aims to compare implant and construct stiffness, interfragmentary movement and cycles to failure between an antegrade slotted femoral nail construct docked to a TKA stem and a distal femoral locking plate in a human periprosthetic femoral fracture model. In eight pairs of fresh-frozen human femora with stalked TKA, a 10 mm transverse osteotomy gap was set simulating a Rorabeck type II, Su type I fracture. The femora were pairwise instrumented with either an antegrade slotted nail coupled to the prosthesis stem, or a locking plate. Cyclic testing with a progressively increasing physiologic loading profile was performed at 2 Hz until catastrophic construct failure. Relative movement at the osteotomy site was monitored by means of optical motion tracking. In addition, four-point bending implant stiffness, torsional implant stiffness and frictional fit of the stem-nail connection were investigated via separate non-destructive tests. Intramedullary nails exhibited significantly higher four-point bending and significantly lower torsional implant stiffness than plates, P < 0.01. Increasing difference between nail and stem diameters decreased frictional fit at the stem-nail junction. Nail constructs provided significantly higher initial axial bending stiffness and cycles to failure (200 ± 83 N/mm; 16'871 ± 5'227) compared to plate constructs (93 ± 35 N/mm; 7'562 ± 1'064), P = 0.01. Relative axial translation at osteotomy level after 2'500 cycles was significantly smaller for nail fixation (0.14 ± 0.11 mm) compared with plate fixation (0.99 ± 0.20 mm), P < 0.01. From a biomechanical perspective, the docking nail concept offers higher initial and secondary stability under dynamic axial loading versus plating in TKA periprosthetic fracture fixation.

Periprosthetic fractures of the proximal femur: beyond the Vancouver classification

The majority of periprosthetic femoral fractures are treated surgically.

Surgical treatment may be revision only, revision in combination with open reduction and internal fixation (ORIF), or ORIF only.

The treatment decision is dependent on whether the stem is loose or not, but loose stems are not always identified, resulting in unsatisfactory treatments.

This article presents an algorithmic approach to identifying loose stems around proximal femoral periprosthetic fractures, taking patient history, stem design, and plain radiographs into consideration. This approach may help identifying loose stems and increase the probability of effective treatments.

Cite this article: EFORT Open Rev 2020;5:449-456. DOI: 10.1302/2058-5241.5.190086

Higher stability and more predictive fixation with the Femoral Neck System versus Hansson Pins in femoral neck fractures Pauwels II

Objectives

To evaluate the biomechanical performance of the Femoral Neck System (FNS) versus the Hansson Pin System (Hansson Pins) with two parallel pins in a Pauwels II femoral neck fracture model with posterior comminution.

Methods

Forty-degree Pauwels II femoral neck fractures AO 31-B2.1 with 15° posterior wedge were simulated in fourteen paired fresh-frozen human femora, followed by instrumentation with either FNS or Hansson Pins in pair-matched fashion. Implant positioning was quantified by measuring shortest implant distances to inferior cortex (DI) and posterior cortex (DP) on anteroposterior and axial X-rays, respectively. Biomechanical testing was performed in 20° adduction and 10° flexion with simulated iliopsoas muscle tension. Progressively increasing cyclic loading was applied until construct failure. Interfragmentary femoral head-to-shaft movements were measured with optical motion tracking.

Results

Cycles to 10° varus deformation were significantly higher for FNS (23007 ​± ​5496) versus Hansson Pins (17289 ​± ​4686), P ​= ​0.027. Cycles to 10° femoral head dorsal tilting (FNS: 12765 ​± ​3425; Hansson Pins: 13357 ​± ​6104) and cycles to 10° rotation around the femoral neck axis (FNS: 24453 ​± ​5073; Hansson Pins: 20185 ​± ​11065) were comparable between the implants, P ​≥ ​0.314. For Hansson Pins, the outcomes for varus deformation and dorsal tilting correlated significantly with DI and DP, respectively (P ​≤ ​0.047), whereas these correlations were not significant for FNS (P ​≥ ​0.310).

Conclusions

From a biomechanical perspective, by providing superior resistance against varus deformation and performing in a less sensitive way to variations in implant placement, the angular stable Femoral Neck System can be considered as a valid alternative to the Hansson Pin System for the treatment of Pauwels II femoral neck fractures.

Level of evidence

therapeutic, Level V.

The Translational potential of this article

The translational potential of this article is to compare the performance of the FNS with Hansson Pins in a AO 31-B2.1 fracture model featuring a 15 posterior wedge to show the implants behavior concerning the dorsal tilting tendency.

An excellent 5-year survival rate despite a high incidence of distal femoral cortical hypertrophy in a short hip stem

BACKGROUND

Although reported results on short stems sound very promising, the occurrence of distal femoral cortical hypertrophy is often observed. The aim of the present study was to report 5-year survival data of a commercially available trochanter sparing short stem and investigate the clinical impact of distal femoral cortical hypertrophy on the outcome.

METHODS

123 total hip arthroplasties were performed on 120 patients from April 2008 to May 2010 (mean age 62, range 29-89 years; 71 hips from male patients, 58%). Clinical and radiological data were collected preoperative, at 6 weeks, 1, 2, 3, and 5 years postoperative to assess the outcome. Radiographs taken immediately postoperative as well as 1 and 5 years postoperative were used to identify and assess cortical hypertrophy.

RESULTS

1 stem had to be revised due to aseptic loosening, resulting in a Kaplan-Meier survival analysis with endpoint for stem revision of 99.2% (95% Confidence Interval 94.1-99.9) at 5 years. 96 radiological and 95 clinical follow-ups were analysed 5 years postoperative. 68 (71%) hips showed distal femoral cortical hypertrophy after 5 years. The average Harris Hip Score and Oxford Hip Score improved 33 (standard deviation (SD) 15.1, range 2-70), 18 (SD 12.1, range -10-43) points, respectively. Overall 16% of the patients reported thigh pain, unrelated to the presence of cortical hypertrophy.

DISCUSSION

This short stem shows an excellent 5-year survival rate and good clinical outcome despite a high incidence of cortical hypertrophy. However, the question of the mechanism of load transfer arises.

Prospective 5-year study with 96 short curved Fitmore™ hip stems shows a high incidence of cortical hypertrophy with no clinical relevance

Background

An increased occurrence of cortical hypertrophy (CH) was observed 1–2 years after implanting short curved Fitmore hip stems. There are no published data about either the clinical relevance or the progression of CH over the long term.

Methods

Ninety-six primary total hip arthroplasties were performed between 2008 and 2010 using the Fitmore hip stem. Clinical and radiological parameters were recorded preoperatively and at 1, 2, 3, and 5 year follow-up.

Results

CH appeared mainly on antero-posterior radiographs in Gruen Zones 2, 3, 5, and 6. After 1 year, the diameter was 10 ± 2 mm and remained constant thereafter. The CH rate after 1 year was 69% and after 5 years 71%. Subsidence after 1 year was 1.6 ± 1.55 mm and 1.93 ± 1.72 mm after 5 years. Cortical thinning was 46% after 1 year and 56% after 5 years, mainly in Gruen Zones 7 and 8. In the first year radiolucencies were found in 51% in all Gruen Zones, and in 20% after 5 years. Patient, implant, and surgical factors did not correlate with radiological outcomes except that larger stems had more CH. After 5 years, the Harris Hip Score had improved from 59 to 94 and the Oxford Hip Score from 22 to 41. Radiographic parameters, notably CH, were not associated with clinical outcomes except that cortical thinning correlated with lower outcome scores.

Conclusions

CH correlated neither with clinical outcome nor with patient, surgical or implant factors, except for a positive correlation with stem size. The Fitmore hip stems settled within the first year to a stable fixation and then remained almost unchanged. However, cortical thinning is common in Gruen Zone 7 and 8 meaning that there is stress-shielding.

LagLoc-a new surgical technique for locking plate systems

Treatment of oblique and spiral fractures remains challenging. The aim of this study was to introduce and investigate the new LagLoc technique for locked plating with generation of interfragmentary compression, combining the advantages of lag screw and locking-head-screw techniques. Oblique fracture was simulated in artificial diaphyseal bones, assigned to three groups for plating with a seven-hole locking compression plate. Group I was plated with three locking screws in holes one, four, and seven. The central screw crossed the fracture line. In group II the central hole was occupied with a lag screw perpendicular to fracture line, whereas holes one and seven were occupied with locking screws. Group III was instrumented applying the LagLoc technique as follows. Hole four was predrilled perpendicularly to the plate, followed by overdrilling of the near cortex and insertion of a locking screw-crossing the fracture line-whose head was covered by a holding sleeve to prevent temporarily the locking in the plate hole and generate interfragmentary compression. Subsequently, the screw head was released and locked in the plate hole. Holes one and seven were occupied with locking screws. Interfragmentary compression in the fracture gap was measured using pressure sensors. All screws in the three groups were tightened with 4 Nm torque. Interfragmentary compression in group I (167 ± 25 N) was significantly lower in comparison to groups II (431 ± 21 N) and III (379 ± 59 N), p ≤ 0.005. The difference in compression between groups II and III remained not significant (p = 0.999). The new LagLoc technique offers an alternative tool to generate interfragmentary compression with the application of locking plates by combining the biomechanical advantages of lag screw and locking screw fixations. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2886-2891, 2018.

Is augmented LISS plating biomechanically advantageous over conventional LISS plating in unstable osteoporotic distal femoral fractures?

Treatment of complex osteoporotic distal femur fractures with the Less Invasive Stabilization System (LISS) has been associated with high complication rates. The aim of this study was to investigate the biomechanical competence of two different techniques of augmented versus conventional LISS plating. Unstable distal femoral fracture AO/OTA 33-A3 was created via osteotomies in artificial femora simulating osteoporotic bone. Three study groups, consisting of 10 specimens each, were created for fixation with either LISS plate, LISS plate with additional polylactide intramedullary graft, or LISS plate plus medial locking plate (double plating). All specimens were non-destructively tested under axial (20-150 N) and torsional (0-4 Nm) quasi-static loading. Each bone-implant construct was tested with two different working length (WL) configurations (long and short) of the LISS plate. Relative movements between the most medial superior and inferior osteotomy aspects were investigated via three-dimensional motion tracking analysis. Double plating revealed significantly smaller longitudinal and shear displacement than the other two techniques (p ≤ 0.001). In addition, LISS plus graft fixation was with significantly less longitudinal displacement in comparison to conventional LISS plating (p < 0.001). Long WL resulted in significantly higher longitudinal and shear displacement compared to short WL for LISS and LISS plus graft (p ≤ 0.032), but not for double plating (p > 0.999). In conclusion, intramedullary grafting resulted in significantly increased fracture stability under axial loading in comparison to conventional LISS plating. Although it was not efficient enough to provide comparable stability to double plating, intramedullary grafting may be considered as a useful biological alternative to the latter in a surgeon's armamentarium. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2604-2611, 2018.

Direct anterior approach to the hip joint in the lateral decubitus position for joint replacement

SURGICAL PRINCIPLE AND OBJECTIVE

The direct anterior approach for total hip arthroplasty is associated with higher complication rates and difficult femoral component positioning. Performing a modified technique in the lateral position allows secure component positioning.

INDICATIONS

Primary hip replacement (including femoral neck fracture) and cup revision without bone deficiency.

CONTRAINDICATIONS

Destruction/deformities of proximal femur or acetabulum, bone deficiency or malignancy.

SURGICAL TECHNIQUE

Strict lateral decubitus position. Straight anterior incision of 10-12 cm, starting 2 cm lateral to the anterior superior iliac spine. Incision of the fascia over the tensor fascia lata muscle (TFL). Lateral retraction of the TFL. Incision of the fascia and medial retraction of rectus femoris. Ligation of the ascending branch of the lateral femoral circumflex artery. Detachment of the iliocapsularis muscle from the capsule in a medial direction. Anterior capsule excision. Femoral neck osteotomy and removal of the head. Reaming of the acetabulum; insertion the acetabular component. Exposure of the femur. Incision/excision of the capsule medial to the greater trochanter for easy anteriorization of the femur. Reaming and implantation of femoral component.

POSTOPERATIVE MANAGEMENT

Weight bearing on day one with crutches for 4 weeks; deep vein thrombosis prophylaxis.

RESULTS

In all, 138 patients (72 women, 66 men, mean age of 67 years) were followed up over 2 years. Overall complication rate was 3.6%: 3 patients (2.2%) with grade III complications required additional intervention. Acetabular cup inclination: 35-50° in 88% of patients. Neutral femoral stem position observed in 99% of patients. Mean Harris hip score improved from 61 preoperatively to 97 after 2 years. Patient satisfaction on a visual analogue scale improved from 3.7 to 9.5.

Quality of fracture reduction assessed by radiological parameters and its influence on functional results in patients with pilon fractures-A prospective multicentre study

INTRODUCTION

The management of pilon fractures remains a challenging issue. Due to the complexity of factors that influence the outcome, it has been questioned if anatomical reductions of articular fracture are relevant. The lack of a commonly accepted assessment of quality of fracture reduction compounded the uncertainty of the importance of anatomical reduction in pilon fracture. The current study aimed to define parameters that can better assess the reduction quality and to investigate the influence of reduction quality on functional outcomes.

METHODS

Patients with unilateral pilon fracture of the AO/OTA type 43-B or 43-C were consecutively recruited to the study and followed up for 2 years after surgery. Postoperative radiographs of the injured and the contralateral joints were evaluated and 13 radiological parameters measured by 2 independent surgeons. The reliability of the measurements for each parameter was assessed by the Intraclass Correlation Coefficient (ICC), and 4 parameters with the highest ICC scores were deemed most reliable and were selected for further analyses. Functional outcome was assessed by the Foot and Ankle Ability Measure (FAAM) for daily living and sports activities. The 4 most reliable radiologic parameters, together with 3 possible baseline confounders (age, AO/OTA fracture type, and open versus closed injury), were analysed using both univariable and multivariable analysis for their association with the FAAM scores. Secondary outcome measures including pain, ankle range of motion (ROM), quality of life (QoL), and adverse events were also reported.

RESULTS

The length of lateral malleolus (LLM), anterior distal tibia angle, anterior talar shift, and length of medial malleolus scored highest on reliability in ICC assessment (ICC=0.76, 0.72, 0.58, and 0.45, respectively). Only LLM exhibited statistical significant association with the 2-year FAAM results. At the 2-year follow-up, the injured joints on average achieved a ROM of 70.7% (95% CI=63.9-77.6) when compared to the contralateral joints, and patients did not regain the pre-injury QoL overall.

CONCLUSION

The multivariable analysis showed that LLM (independent of age, AO/OTA fracture type, and open/closed injury) was a reliable indicator of reduction quality and a prognostic factor for patient outcome in pilon fracture surgery.

Biomechanical evaluation of the tension band wiring principle. A comparison between two different techniques for transverse patella fracture fixation

PURPOSE

The aim of this study was to investigate the validity of the dynamic compression principle of tension band wiring in two techniques for patella fracture treatment.

METHODS

Twelve human cadaveric knees with simulated transverse patella fractures were assigned to two groups for treatment with tension band wiring using either Kirschner (K-) wires or cannulated screws. Biomechanical testing was performed over three knee movement cycles between 90° flexion and 0° full extension. Pressure distribution in the fracture gap and fracture site displacement were evaluated at the 3^rd cycle in 15° steps, namely 90°-75°-60°-45°-30°-15°-0° extension phase and 0°-15°-30°-45°-60°-75°-90° flexion phase.

RESULTS

Mean anterior / posterior interfragmentary pressure in the groups with K-wires and cannulated screws ranged within 0.16-0.40MPa / 0.12-0.35MPa and 0.37-0.59MPa / 0.10-0.30MPa, respectively. These changes remained non-significant for both groups and loading phases (P≥0.171). Mean anterior / posterior fracture site displacement for K-wires and cannulated screws ranged within -0.01-0.53mm / 0.11-0.74mm and 0.11-0.55mm / -0.10-0.50mm, respectively. Anterior displacement remained without significant changes for both groups and loading phases (P≥0.112). However, posterior displacement underwent a significant increase in the course of knee extension for K-wires (P≤0.047), but not for cannulated screws (P≥0.202). Significantly smaller displacement at the posterior fracture site was detected in the group with cannulated screws compared to K-wires at 60° and 75° extension phase (P≤0.017), as well as at 45°, 60° and 75° flexion phase (P≤0.018). The critical value of 2mm displacement at the posterior fracture site was not reached for any specimen and fixation technique. Knee extension was accompanied by synchronous increase in quadriceps pulling force.

CONCLUSIONS

Tension band wiring fulfills from a biomechanical perspective the requirements for sufficient stability of transverse patella fracture fixation. It should, however, rather be considered as a static fixation principle than a dynamic one. Tension band wiring with cannulated screws was found advantageous over Kirschner wires in terms of interfragmentary movements at the posterior fracture site.

Femoral neck fracture osteosynthesis by the biplane double-supported screw fixation method (BDSF) reduces the risk of fixation failure: clinical outcomes in 207 patients

INTRODUCTION

Osteosynthesis of femoral neck fractures is related up to 46% rate of complications. The novel method of biplane double-supported screw fixation (BDSF; Filipov's method) offers better stability using three medially diverging cannulated screws with two of them buttressed on the calcar. Biomechanically, the most effective component is the distal screw placed at steeper angle and supported on a large area along the distal and posterior cortex of the femoral neck following its spiral anterior curve. Thereby, BDSF achieves the strongest possible distal-posterior cortical support for the fixation construct, which allows for immediate full weight-bearing. The aim of this study was to evaluate the outcomes from the first 5-year period of BDSF clinical application.

MATERIALS AND METHODS

Subject of this retrospective study were 207 patients with displaced Garden III-IV femoral neck fractures treated with BDSF. Three 7.3-mm cannulated screws were laid in two medially diverging oblique planes. The distal and the middle screws were supported on the calcar. The distal screw had additional support on the posterior neck cortex.

RESULTS

The outcomes in 207 patients were analysed in 29.6 ± 16.8 months follow-up. Bone union occurred in 96.6% of the cases (males 97.6%, females 96.4%, P = 0.99). Rate of nonunion was 3.4%, including fixation failure (2.4%), pseudoarthrosis (0.5%) and nonunion with AVN (0.5%). Rate of AVN was 12.1% (males 4.8%, females 13.9%, P = 0.12). Modified Harris hip score was 86.2 ± 18.9 (range 10-100), with no significant difference between genders, P = 0.07. Older patients were admitted with significantly more comorbidities (P = 0.001), and on follow-up they were significantly less mobile (P = 0.005) and had significantly more difficulties to put socks and shoes on (P < 0.001).

CONCLUSIONS

By providing additional cortical support, the novel BDSF method enhances femoral neck fracture fixation strength.

The influence of the operation technique and implant used in the treatment of periprosthetic hip and interprosthetic femur fractures: a systematic literature review of 1571 cases

INTRODUCTION

A systematic literature review on periprosthetic/interprosthetic fracture fixation after hip arthroplasties was performed to summarize available clinical data. Operation techniques and implants used were evaluated as possible risk factors for outcomes.

MATERIALS AND METHODS

MEDLINE and Cochrane databases were searched. Articles describing patients with postoperative periprosthetic femur fractures sustained around a hip arthroplasty and with interprosthetic fractures treated with plates, nails, screws and/or cerclage were included. Considered articles were from 2000 or newer. Eligible abstracts were screened by two independent persons and discrepancies were resolved by consensus. Absolute numbers of complications and/or reoperation events along with their corresponding rates were calculated according to operation technique and type of implant. Relative risks of having a complication and/or a reoperation according to the operation technique and the type of implant used were estimated.

RESULTS

Available data from 49 prospective and retrospective studies were analyzed. Of 1574 fractures, 81.7 % were treated with plating. For 83.0 % of all fractures, an open approach was applied. The overall complication rate was 14.3 %. Fixation failure and nonunion were most often reported (fixation failure: 4.4 %; nonunion: 3.9 %). Nonunion and refracture occurred more often after open approaches than after minimal invasive osteosynthesis (nonunion: 4.5 vs. 0.0 %, p = 0.001; refracture: 3.8 vs. 0.6 %. p = 0.024). The relative risk for nonunion was 11.9 (95 % CI 4.5-31.5) times higher (p < 0.0001) for non-locking plates (13.0 %) than for locking plates (1.1 %).

CONCLUSIONS

The clinical evidence of published studies dealing with periprosthetic/interprosthetic fractures after hip arthroplasty is generally low. This literature search suggested higher rates of nonunion and refracture after an open approach and a higher risk of nonunion for non-locking plates compared to locking plates. Based on the available clinical evidence, no treatment recommendations can be given.

Enhancing fixation strength in periprosthetic femur fractures by orthogonal plating-A biomechanical study

Orthogonal plate osteosynthesis enhances fixation stability in periprosthetic femur fractures. Another option are locking attachment plates (LAP) allowing bicortical locking screw placement lateral to the prosthesis stem. Stability of lateral plate osteosynthesis with two LAP (2LAP) was compared to anterolateral orthogonal plate osteosynthesis (OP) with one LAP in a periprosthetic femur fracture model. In six pairs of fresh frozen human femora with cemented Charnley hip prosthesis, a transverse osteotomy was set distal to the tip of the prosthesis simulating a Vancouver type B1 fracture. Each pair was instrumented using a plate tensioner with either one lateral plate and two LAP, or two orthogonal anterolateral plates and one LAP. Stiffness was determined in a four-point-bending test prior to cyclic testing (2Hz) with physiologic profile and progressively increasing load up to catastrophic construct failure. Paired t-test and Wilcoxon-signed-rank test were used for statistical evaluation at a level of significance p = 0.05. The OP construct exhibited a significantly higher number of cycles and load to failure (39,627 cycles ± 4,056; 4,463 N ± 906) compared to the 2LAP construct (32,927 cycles ± 3,487; 3,793 N ± 849), p < 0.01. Mediolateral bending and torsional stiffness of the OP (1610 N/mm ± 249; 16.9 Nm/mm ± 6.3) were significantly higher compared to 2 LAP (1077 N/mm ± 189; 12.1 Nm/mm ± 3.9), p = 0.03 for both comparisons. Orthogonal plate osteosynthesis is a valuable option in periprosthetic fracture surgery, offering increased stability compared to a single lateral plate fixed with two LAP.

Prospective clinical and radiostereometric analysis of the Fitmore short-stem total hip arthroplasty

INTRODUCTION

Uncemented short, curved femoral stems may help save proximal bone stock during total hip arthroplasty (THA) and facilitate insertion in minimal invasive surgery. The aim of this 2 year, prospective, single-center study was to examine the stability and migration of the Fitmore (®) stem in THA using model-based radiostereometric analysis (RSA), and thus predict the implant's long-term survival. In addition, we evaluated the stem's clinical performance using standard clinical measures.

PATIENTS AND METHODS

We conducted a prospective cohort study of 34 THA patients who received the short Fitmore Hip Stem (Zimmer, Winterthur, Switzerland). At 3, 6, 12 and 24 months postoperatively, the patients underwent clinical evaluation and radiostereometric analysis (RSA) to measure stem migration.

RESULTS

RSA analysis revealed a mean subsidence of -0.39 mm (95 % CI -0.60 to -0.18) at 3 months with no further migration after 2 years. Mean internal rotation along the longitudinal axis was 1.09° (95 % CI 0.52-1.66) at 2 years, versus 0.85° (95 % CI 0.44-1.26) at 3 months. The Harris hip score improved from 60 (range 30-80) preoperatively to 99 (range 83-100) after 2 years. Three patients underwent revision due to deep infection, non-specific thigh pain and aseptic loosening in one case.

CONCLUSION

We conclude that the Fitmore Hip Stem stabilizes after 3 months and achieves good short-term clinical results in most cases.

What is the underlying mechanism for the failure mode observed in the proximal femoral locking compression plate? A biomechanical study

PURPOSE

Recently, several cases of clinical failure have been reported for the Proximal Femoral Locking Compression Plate (PF-LCP). The current study was designed to explore biomechanically the underlying mechanism and to determine whether the observed failure was due to technical error on insertion or to implant design.

METHODS

A foam block model simulating an unstable intertrochanteric fracture was created for 3 study groups with 6 specimens each. Group C was correctly instrumented according to the manufacturer's guidelines. In Group P and Group A, the first or second proximal screw was placed with a posterior or anterior off-axis orientation by 2° measured in the transversal plane, respectively. Each construct was cyclically tested until failure using a test setup and protocol simulating complex axial and torsional loading. Radiographs were taken prior to and after the tests. Force, number of cycles to failure and failure mode were compared.

RESULTS

A screw deviation of 2° from the nominal axis led to significantly earlier construct failure in Group P and Group A in comparison to Group C. The failure mode was characterised by loosening of the off-axis screw due to disengagement with the plate, resulting in loss of construct stiffness and varus collapse of the fracture.

CONCLUSIONS

In our biomechanical test setup, the clinical failure modes observed with the PF-LCP were reproducible. A screw deviation of 2° from the nominal axis consistently led to the failure. This highlights how crucial is the accurate placement of locking screws in the proximal femur.

Angular stable lateral plating is a valid alternative to conventional plate fixation in the proximal phalanx. A biomechanical study

BACKGROUND

Dorsal plating is commonly used in proximal phalanx fractures but it bears the risk of interfering with the extensor apparatus. In this study, dorsal and lateral plating fixation methods are compared to assess biomechanical differences using conventional 1.5mm non-locking plates and novel 1.3mm lateral locking plates.

METHODS

Twenty-four fresh frozen human cadaveric proximal phalanges were equally divided into four groups. An osteotomy was set at the proximal metaphyseal-diaphyseal junction and fixed with either dorsal (group A) or lateral (group B) plating using a 1.5mm non-locking plate, or lateral plating with a novel 1.3mm locking plate with bicortical (group C) or unicortical (group D) screws. The specimens were loaded in axial, dorsovolar and mediolateral direction to assess fixation stiffness followed by a cyclic destructive test in dorsovolar loading direction.

FINDINGS

Axial stiffness was highest in group D (mean 321.02, SEM 21.47N/mm) with a significant difference between groups D and B (P=0.033). Locking plates (groups C and D) were stiffer than non-locking plates under mediolateral loading (P=0.007), no significant differences were noted under dorsovolar loading. Furthermore, no significant differences were observed under cyclic loading to failure between any of the study groups.

INTERPRETATION

No considerable biomechanical advantage of using a conventional 1.5mm dorsal non-locking plate was identified over the novel 1.3mm lateral locking plate in the treatment of proximal phalanx fractures. Since the novel low-profile plate is less disruptive to the extensor mechanism, it should be considered as a valid alternative.

Assessment of ankle and hindfoot stability and joint pressures using a human cadaveric model of a large lateral talar process excision: a biomechanical study

Lateral talar process fragment excision may be followed by hindfoot instability and altered biomechanics. There is controversy regarding the ideal fragment size for internal fixation versus excision and a concern that excision of a large fragment may lead to significant instability. The aim of this study was to assess the effect of a simulated large lateral talar process excision on ankle and subtalar joint stability.A custom-made seesaw rig was designed to apply inversion/eversion stress loading on 7 fresh-frozen human cadaveric lower legs and investigate them in pre-excision, 5 cm and 10 cm lateral talar process fragment excision states. Anteroposterior radiographs were taken to assess ankle and subtalar joint tilt and calculate angular change from neutral hindfoot alignment to 10-kg forced inversion/eversion. Ankle joint pressures and contact areas were measured under 30-kg axial load in neutral hindfoot alignment.In comparison to the pre-excision state, no significantly different mediolateral angular change was observed in the subtalar joint after 5 and 10 cm lateral talar process fragment excision in inversion and eversion. With respect to the ankle joint, 10-cm fragment excision produced significantly bigger inversion tibiotalar tilt compared with the pre-excision state, P = .04. No significant change of the ankle joint pressure and contact area was detected after 5 and 10-cm excision in comparison with the pre-excison state.An excision of up to 10 cm of the lateral talar process does not cause a significant instability at the level of the subtalar joint but might be a destabilizing factor at the ankle joint under inversion stress. The latter could be related to extensive soft tissue dissection required for resection.

Biomechanical evaluation of interfragmentary compression at tibia plateau fractures in vitro using different fixation techniques: a CONSORT-compliant article

Reliable osteosynthesis of intraarticular fractures depends on lasting interfragmentary compression. Its amount differs in the applied fixation method. The interfragmentary compression of cancellous and cortical lag screws and angle stable locking plates was quantified in an osteoporotic and non-osteoporotic synthetic human bone model.A split fracture of the lateral tibia plateau (AO/OTA type 41-B1.1) was mimicked by an osteotomy in right adult synthetic human tibiae with hard or soft cancellous bone. Specimens were fixed with either two 6.5 mm cancellous, four 3.5 mm cortical lag screws, or 3.5 mm LCP proximal lateral tibia plate preliminary compresed by a reduction clamp (n = 5 per group). A pressure sensor film was used to register the interfragmentary compression. One-way analysis of variance (ANOVA) with Bonferroni post hoc correction was performed for statistical analysis (p < 0.05).Interfragmentary compression under reduction clamp was 0.59 ± 0.12 MPa in the non-osteoporotic and 0.55 ± 0.14 MPa in the osteoporotic group. The locking plate itself maintained the compression in non-osteoporotic (0.53 ± 0.11 MPa) and osteoporotic bone (0.50 ± 0.14 MPa). Four 3.5 mm cortical lag screws provided a compression of 1.69 ± 0.65 MPa in non-osteoporotic bone, being not significantly different to the osteoporotic bone group (1.43 ± 0.47 MPa, P = 1.0). Two 6.5 mm cancellous lag screws showed a significantly higher compression in non-osteoporotic (2.1 ± 0.59 MPa) compared to osteoporotic (0.77 ± 0.21 MPa, P < 0.01) bone.Angle stable locking plates maintained the compression preliminarily applied by a reduction clamp. Two 6.5 mm cancellous lag screws are especially suited for non-osteoporotic bone, whereas four 3.5 mm cortical screws exhibited comparable compression in both bone qualities.

Comparison of two intraoperative assessment methods for injuries to the ankle syndesmosis. A cadaveric study

BACKGROUND

Intraoperative stress testing is required for the detection of syndesmosis instability following an ankle fracture. The present study compared two stress tests for the detection of syndesmotic injury.

METHODS

A true mortise radiograph of the ankle was made for fourteen cadaver joints. Specimens were randomized into two groups to simulate ligament and syndesmosis injury on the basis of the Danis-Weber classification system. In the first group, the anterior inferior tibiofibular ligament was divided first (Weber B(r)), followed sequentially by division of the interosseous membrane (Weber C) and the deltoid ligament. In the second group, the deltoid ligament was divided first, followed by the anterior inferior tibiofibular ligament. Radiographs were made at each stage with use of two methods of stressing the ankle mortise: (1) external rotation of the foot with an external moment of 7.5 Nm, and (2) application of a lateral force of 100 N. Tibiofibular overlap, tibiofibular clear space, and medial clear space were measured.

RESULTS

Lateral stress produced a significantly greater increase in the tibiofibular clear space than did the external rotation test for Weber C injuries and Weber C plus deltoid ligament injuries. A greater increase in the tibiofibular clear space was noted during the lateral stress test when both the deltoid and the anterior inferior tibiofibular ligament had been sectioned (p < 0.05). The external rotation stress test produced a significant increase in the medial clear space in the presence of isolated anterior inferior tibiofibular ligament and deltoid ligament injuries (p < 0.05).

CONCLUSIONS

For the detection of syndesmotic instability at the site of ankle fractures on stress radiographs, the lateral stress test appeared to be superior to the external rotation stress test in this cadaver model.

Early results in the treatment of proximal humeral fractures with a polyaxial locking plate

OBJECTIVES

We report early results using a second generation locking plate, non-contact bridging plate (NCB PH((R)), Zimmer Inc. Warsaw, IN, USA), for the treatment of proximal humeral fractures. The NCB PH combines conventional plating technique with polyaxial screw placement and angular stability.

DESIGN

Prospective case series.

SETTING

A single level-1 trauma center.

PATIENTS

A total of 50 patients with proximal humeral fractures were treated from May 2004 to December 2005.

INTERVENTION

Surgery was performed in open technique in all cases.

MAIN OUTCOME MEASURES

Implant-related complications, clinical parameters (duration of surgery, range of motion, Constant-Murley Score, subjective patient satisfaction, complications) and radiographic evaluation [union, implant loosening, implant-related complications and avascular necrosis (AVN) of the humeral head] at 6, 12 and 24 weeks.

RESULTS

All fractures available to follow-up (48 of 50) went to union within the follow-up period of 6 months. One patient was lost to follow-up, one patient died of a cause unrelated to the trauma, four patients developed AVN with cutout, one patient had implant loosening, three patients experienced cutout and one patient had an axillary nerve lesion (onset unknown). The average age- and gender-related Constant Score (n = 35) was 76.

CONCLUSIONS

The NCB PH combines conventional plating technique with polyaxial screw placement and angular stability. Although the complication rate was 19%, with a reoperation rate of 12%, the early results show that the NCB PH is a safe implant for the treatment of proximal humeral fractures.