Femoral Pin Research Articles

Is bicortical femoral pin insertion safe for Image-based Robotic Knee Arthroplasty Surgery ? A comparative complications analysis in 970 Consecutive Cases

ObjectivesLimited data exists on complications associated with robotic image-based system in knee arthroplasty. This study aims to document complications in robotic arm-assisted knee arthroplasties, and evaluate the system’s safety by comparing two femoral pin insertion methods: bicortical diaphyseal with additional stab wounds, and unicortical metaphyseal placement through the main incision. MethodsAll patients undergoing primary knee arthroplasty with the image-based robotic system (Mako, Stryker, Mako Surgical Corp., Fort Lauderdale, FL, USA) from 1st March 2021 to 31st January 2024 with a minimum follow-up of 2 months were included. Demographics, system and non-system-related complications, as well as outcomes were recorded. Complications were categorized as either major (requiring a second surgical intervention) or minor. ResultsA total of 970 consecutive cases (median age 69.3 years) were analyzed. The unicortical group comprised 651 cases, while the bicortical group 319. The incidence of non-system-related complications was 2.37%, with the most common being joint stiffness (10 cases; 1.03%), followed by lateral femoral condyle fracture (4;0.41%). The overall incidence of system-specific complications was 1.03%. Pin-related femoral fractures occurred in 0.2% of cases, all postoperatively and in the unicortical group. There was no statistically significant difference between the femoral pin insertion-related complication rates among the two groups (0.3% in the unicortical, compared to 0% in the bicortical group; p-value= 0.3). Complications included tibia fracture (0.1%), delayed wound healing (0.2%), superficial wound infection (0.1%), tibia osteomyelitis (0.1%), and “exostosis” (0.2%). The major complications rate was 0.3% and minor 0.7%. ConclusionsMinimal system-specific overall complications indicate that robotic arm-assisted surgery is safe. The bicortical diaphyseal femoral pin insertion method does not increase the complication rates compared to the unicortical metaphyseal method. Level of evidenceIII

Staged treatment of bicondylar tibial plateau fractures: influence of frame configuration and quality of reduction on outcomes.

Despite evolving treatment, the surgical management of high-energy tibial plateau fractures (TPF) remains challenging, associating high rates of complications. In recent decades, staged management has emerged as an encouraging option. The main goal of our study was to evaluate the influence of bridging external fixation (EF) frame configuration and the resultant quality of reduction (QOR) on outcomes after staged-treatment of bicondylar TPF. A retrospective review was conducted of patients with bicondylar TPF treated at our level-I trauma center using a staged-treatment protocol from January 2010 to January 2020. Data on baseline characteristics, injuries, treatments, and clinical/radiological results were collected. The QOR was evaluated on CT images after EF and on plain films after ORIF. Sixty-eight patients were eligible for analysis. By our criteria, QOR was good in 57.4% and 70.6% after EF and ORIF, respectively. A squared EF configuration was associated with superior EF QOR (p = 0.032), while better EF QOR was linked to improved ORIF QOR (p = 0.016). No relationship between ORIF delay and ORIF QOR was identified. Postoperative complications were documented in 19 patients. Average ROM at one-year follow-up was 114.9 ± 12.6°, and non-influenced by anterior femoral pin placement. Staged management of bicondylar TPF resulted in a reasonable rate of complications. A direct relationship between QORs obtained with EF and after ORIF was found. Squared frames were associated with faster and better reductions, regardless of the surgeon's background. Considering our results, we advocate for the wider use of squared EF configurations in these patients.

Safe Zones and Trajectory of Femoral Pin Placement in Robotic Total Knee Arthroplasty.

Robotic-assisted total knee arthroplasty may result in array pin-related complications. Lack of knowledge on ideal pin placement results in varied insertion sites and trajectory, with unknown risks to surrounding neurovascular structures. This study included 10 lower-extremity magnetic resonance images. Images were subdivided into 6 zones of study. Zones consisted of a correlating axial image with femoral pin placement replicated by drawing a line angled 45° from the anterior to posterior reference in the anteromedial to posterolateral femoral quadrants. The distances from the pin paths to the neurovascular structures were measured. Zone 2C demonstrated femoral pin trajectory an average of 14 mm from the femoral artery/vein. In Zone 2B, proximity increased to an average of 30 mm to the femoral artery and 29 mm to the femoral vein. At Zone 1A, the popliteal artery and vein were on average 22 mm from the femoral pin, while the common peroneal nerve was an average of 21 mm. Placing pins in Zone 1A poses a high risk of injury to the genicular arteries. Women demonstrated greater proximity to neurovascular structures than men in 66% of the sites (P < .05). This classification system for safe zones and trajectory of femoral pin placement in robotic-assisted total knee arthroplasty demonstrates that proximally, the profunda femoris and femoral artery/vein are at risk of injury, while distally, the genicular arteries, common peroneal nerve, and popliteal artery/vein are at risk. Caution should be exercised if femoral pins are inserted with an angle less than 45°, especially in women.

Distal Femoral Tracker Pin Placement Prevents Delayed Pin Tract-Induced Fracture in Robotic-Assisted Total Knee Arthroplasty: Results of Minimum 1-Year Follow-Up.

The purpose of this study was to determine the outcomes of the placement of a pin tracker in the distal femur in robotic-assisted total knee arthroplasty (TKA) over a minimum follow-up period of 1 year. A consecutive series of 81 TKAs were performed in 59 patients using a robotic-assisted system (Mako) at our hospital. The mean follow-up period was 1.1 years (range, 1-1.2 years). No periprosthetic fracture at a pin tracker site was reported at a minimum of 1 year of follow-up. No patients reported minor or major complications associated with the distal femoral pins. In addition, unicortical pin-site drilling marks in all patients disappeared on one-postoperative-year follow-up radiographs. Our technique, which used unicortical pin placement in the distal femur in robotic-assisted TKA, demonstrated that it was a safe and reliable method at a minimum follow-up period of 1 year. The level of evidence is IV.

Distal Femoral Pin Tracker Placement Prevents Pin Tract-induced Fracture in Robotic-Assisted Total Knee Arthroplasty.

The purpose of this study was to determine the effectiveness of the placement of pin trackers in the medial sagittal plane of the distal femur in robotic-assisted total knee arthroplasty (TKA) over a minimum follow-up period of 3 months. From August 2020 to October 2020, a consecutive series of 81 TKAs were performed in 59 patients using the Triathlon posterior-stabilized total knee prosthesis with a robotic-assisted system (Mako) at our hospital. Patient charts were reviewed for complications associated with the pin sites, including fracture, infection, thigh pain, and the need for reoperation. No patients had any minor or major complications associated with distal femoral pins. This technique, which used pin trackers in the medial sagittal plane of the distal femur, could be a useful option for surgeons performing robotic-assisted TKA. This is a Level IV study.

Medial collateral ligament reconstruction graft isometry is effected by femoral position more than tibial position

PurposeThe purpose of this study was to examine the length change patterns of the native medial structures of the knee and determine the effect on graft length change patterns for different tibial and femoral attachment points for previously described medial reconstructions.MethodsEight cadaveric knee specimens were prepared by removing the skin and subcutaneous fat. The sartorius fascia was divided to allow clear identification of the medial ligamentous structures. Knees were then mounted in a custom-made rig and the quadriceps muscle and the iliotibial tract were loaded, using cables and hanging weights. Threads were mounted between tibial and femoral pins positioned in the anterior, middle, and posterior parts of the attachment sites of the native superficial medial collateral ligament (sMCL) and posterior oblique ligament (POL). Pins were also placed at the attachment sites relating to two commonly used medial reconstructions (Bosworth/Lind and LaPrade). Length changes between the tibiofemoral pin combinations were measured using a rotary encoder as the knee was flexed through an arc of 0–120°.ResultsWith knee flexion, the anterior fibres of the sMCL tightened (increased in length 7.4% ± 2.9%) whilst the posterior fibres slackened (decreased in length 8.3% ± 3.1%). All fibre regions of the POL displayed a uniform lengthening of approximately 25% between 0 and 120° knee flexion.The most isometric tibiofemoral combination was between pins placed representing the middle fibres of the sMCL (Length change = 5.4% ± 2.1% with knee flexion). The simulated sMCL reconstruction that produced the least length change was the Lind/Bosworth reconstruction with the tibial attachment at the insertion of the semitendinosus and the femoral attachment in the posterior part of the native sMCL attachment side (5.4 ± 2.2%). This appeared more isometric than using the attachment positions described for the LaPrade reconstruction (10.0 ± 4.8%).ConclusionThe complex behaviour of the native MCL could not be imitated by a single point-to-point combination and surgeons should be aware that small changes in the femoral MCL graft attachment position will significantly effect graft length change patterns. Reconstructing the sMCL with a semitendinosus autograft, left attached distally to its tibial insertion, would appear to have a minimal effect on length change compared to detaching it and using the native tibial attachment site. A POL graft must always be tensioned near extension to avoid capturing the knee or graft failure.

External fixator for temporary stabilization of complex periarticular knee fractures

Temporary stabilization of the knee joint in order to minimize soft tissue strain until definitive surgery is possible. Bicondylar distal femoral and tibial plateau fractures, additional vascular injury, open fractures (second or third degree), severe soft tissue damage, unicondylar fracture with contralateral ligament tear, (open) knee dislocation, polytrauma. Unsafe pin placement, severe osteoporosis. Two femoral and tibial pins are connected by two rods and are spanned over the knee with two additional longitudinal rods via atube-to-tube clamp. Alternatively, this can be facilitated by adirect connection of two rods in case of anteriorly placed femoral pins. Areasonable distance should be kept to open wounds, the fracture, and later operative approaches. The knee is fixed in 5-15° of flexion. Definitive treatment depending on patient well-being and amenable soft tissue.

ACL reconstruction using a quadruple semitendinosus graft with cortical fixations gives suitable isokinetic and clinical outcomes after 2years.

The objective of this single-center randomized single-blinded trial was to assess the hypothesis that anterior cruciate ligament reconstruction (ACLR) using a four-strand semitendinosus (ST) graft with adjustable femoral and tibial cortical fixation produced good outcomes compared to an ST/gracilis (ST/G) graft with femoral pin transfixation and tibial bioscrew fixation. Follow-up was 2years. Patients older than 16years who underwent primary isolated ACLR included for 1year until August 2017 were eligible. The primary outcome measures were the subjective International Knee Documentation Committee (IKDC) score, isokinetic muscle strength recovery, and return to work within 2years. The study was approved by the ethics committee. Of 66 eligible patients, 60 completed the study and were included, 33 in the 4ST group and 27 in the ST/G group. Mean age was 30.5 ± 8.9years in the 4ST group and 30.3 ± 8.5 in the ST/G group (n.s.). No significant between-group differences were found for mean postoperative subjective IKDC (4ST group, 80.2 ± 12.5; ST/G group, 83.6 ± 13.6; n.s.), side-to-side percentage deficits in isokinetic hamstring strength (at 60°/s: ST group, 17% ± 16%; ST/G group, 14% ± 11%; n.s.) or quadriceps strength (at 60°/s: ST group, 14% ± 12%; ST/G group, 19% ± 17%; n.s.), return to work, pain during physical activities, side-to-side differential laxity, balance, loss of flexion/extension, or surgical complications. This trial demonstrates that functional outcomes after 4ST for ACLR with cortical fixations could be as good, although not better, than those obtained using ST/G. The 4ST technique spares the gracilis tendon, which thus preserves the medial sided muscle and thereby could improve function and limit donor-side morbidity. Level I.

Safety of skeletal traction through the distal femur, proximal tibia, and calcaneus

Introduction: Skeletal traction provides pain relief and temporary stability in patients anticipating surgery for a variety of lower-extremity fractures. Recent literature suggests that distal femoral traction provides pain relief and is safe; however, data regarding proximal tibial and calcaneal pins are primarily historical and limited. The purpose of this study is to document complications associated with distal femur, proximal tibia, and calcaneal traction pin placement. Materials and Methods: We identified patients with the distal femur, proximal tibia, and calcaneal traction pin placement from January 2013 to June 2016. Chart review was utilized to identify any complications, including nerve or vascular injuries, need for revision, or infection. Results: Five hundred and nineteen traction pins were eligible for review, consisting of 120 calcaneal traction pins, 129 distal femoral pins, and 270 proximal tibia traction pins. Primary diagnosis was defined as 305 femur fractures (58.8%), 60 tibial shaft fractures (11.6%), 60 acetabular fractures (11.6%), 38 pilon fractures (7.3%), 30 pelvic ring injuries (5.8%), 21 tibial plateau fractures (4.0%), and 5 hip dislocations (1.0%). We identified 17 (3.3%) adverse events potentially attributable to traction pin insertion. Pins that became infected were found to have been in place for a significantly longer duration (18.3 days compared to 5.8 days, P = 0.0001). Conclusions: Traction pin placement for skeletal traction is generally an uncomplicated procedure. Duration of pin placement is significantly related to the likelihood of pin site infection.

Anatomic tunnel placement can be achieved with a modification to transtibial technique in single bundle anterior cruciate ligament reconstruction: A cadaver study.

Placing the tunnels in the anatomic positions is important for successful restoration of knee function after anterior cruciate ligament reconstruction (ACLR). It has been shown that it is difficult to place the tunnels in the anatomic position using the transtibial technique. The purpose of this study was to evaluate the effect of each step of our modified transtibial technique (mTT) on the positioning of the femoral tunnel so as to assess whether the mTT could achieve anatomic placements of the tunnels without tibial tunnel expansion. Ten fresh-frozen cadaveric knees were used. First, the tibial tunnel was created in the center of ACL footprint. Then, a pin was inserted through the tibial tunnel using a femoral guide by four stepwise techniques: transtibial technique, additional anterior drawer force applied to the proximal tibia, another additional varus force applied to the tibia and finally, additional external rotation of the tibia and the femoral guide (mTT). Then, tibial tunnel was re-reamed using mTT with 10mm-diameter reamer. The pin positions in each technique on the femur were evaluated by the quadrant method and shapes of the tibial tunnel apertures were evaluated. Femoral pin positions in the four techniques were 23.6±4.5%, 28.4±3.4%, 30.1±3.8%, 33.2±4.5% in the superior-inferior position, and 23.9±4.3%, 26.2±3.7%, 32.0±4.3%, 36.9±4.8% in the anterior-posterior position, respectively. Pin position shifted to more inferior and posterior position with each step of mTT (all p values comparing superior-inferior and anterior-posterior positions of each step with positions of previous step were 0.008 or less). Using mTT, tibial tunnel aperture was 10.5±0.3mm wide and 12.9±1.1mm long. In conclusion, anatomic placements of femoral tunnels in ACLR without excessive tibial tunnel expansion could be achieved using the mTT.

Are Distal Femoral Traction Pins Intra-Articular? A Cadaveric Study

To examine the frequency of intra-articular placement of distal femoral traction pins and their proximity to the superficial femoral artery (SFA). Wires were placed in the distal femurs of 28 cadaveric knees at the adductor tubercle (ADT), the superior pole of the patella (SPP), and 2 cm proximal to SPP (SPP+2). A lateral fluoroscopic image was obtained after injection of radiopaque contrast to assess for joint penetration. Dissection was performed to confirm or refute fluoroscopic findings. The distance from each wire to the SFA was measured. The percentage of intra-articular placement was higher (29%) at the ADT than the SPP+2 (0%) level. The mean (SD) distances from the ADT, SPP, and SPP+2 to the SFA were 7.4 (±1.8) cm, 5.7 (±1.7) cm, and 3.8 (±1.7) cm, respectively (P < 0.0001). None of the wires penetrated the femoral artery. The proportion of wires judged to be intra-articular was not statistically different whether judged by fluoroscopy or anatomic dissection (exact P = 1.0). Wires placed at the level of the ADT are at risk for capsular penetration. Risk of major vascular injury with transmedullary placement at all levels seems to be minimal. The optimum position for distal femoral pins remains unknown, but aiming >0.7 cm proximal to the ADT may lower the risk of intra-articular placement. No difference was detected between fluoroscopic arthrography and gross dissection.

A vascular complication in computer navigated total knee arthroplasty

The use of computer navigation has the potential to improve implant position in total knee arthroplasty (TKA), but pin fixation of reference arrays introduces an additional potential source of complications. We report a case of vascular injury related to the insertion of a femoral pin during navigated TKA.

Staged corrective surgery for complex adolescent kyphoscoliosis caused by back scalding during the childhood period

Adolescent scar contracture kyphoscoliosis is a very rare disease. Here, we present the case of a 21-year-old man who was scalded due to ebullient water when he was 10 years old. Moreover, kyphoscoliosis was found when he was 12 years old and developed rapidly. Thereafter, no management was proposed before his consultation at our center. On examination, kyphoscoliosis was detected in thoracolumbar, the trunk deviated to the right on standing view, extensive contractured scar presented on the right side of the back, abdomen, chest wall, hip, right thighs and armpit anterior, especially in the right flank. A one-stage correction was deemed too risky, we therefore released contractured scar during the first stage with the defect of soft tissue protected by vacuum sealing drainage and then performed skeletal traction with halo and bilateral femoral pins. A reasonable correction was achieved without any neurological deficits 1 month after traction. Next, a second-stage operation was taken to translate a free anterolateral thigh myocutaneous flap to overlay the extensive defect of soft tissue. 1.5 months later, a third posterior segmental pedicle screw instrumented fusion with Smith-Peterson osteotomy between T9 and L2 was performed. Postoperative recovery was uneventful and as there were no complications, he was discharged 10 days after the third surgery. At 2-year follow-up the patient's outcome is excellent with balance and correction of the deformity. Based this grand round case and relevant literature, we discuss the different options for the treatment of adolescent scar contracture scoliosis.

Magnesium alloys for temporary implants in osteosynthesis: In vivo studies of their degradation and interaction with bone

This study investigates the bone and tissue response to degrading magnesium pin implants in the growing rat skeleton by continuous in vivo microfocus computed tomography (μCT) monitoring over the entire pin degradation period, with special focus on bone remodeling after implant dissolution. The influence of gas release on tissue performance upon degradation of the magnesium implant is also addressed. Two different magnesium alloys – one fast degrading (ZX50) and one slowly degrading (WZ21) – were used for evaluating the bone response in 32 male Sprague–Dawley rats. After femoral pin implantation μCTs were performed every 4weeks over the 24weeks of the study period. ZX50 pins exhibited early degradation and released large hydrogen gas volumes. While considerable callus formation occurred, the bone function was not permanently harmed and the bone recovered unexpectedly quickly after complete pin degradation. WZ21 pins kept their integrity for more than 4weeks and showed good osteoconductive properties by enhancing bone accumulation at the pin surface. Despite excessive gas formation, the magnesium pins did not harm bone regeneration. At smaller degradation rates, gas evolution remained unproblematic and the magnesium implants showed good biocompatibility. Online μCT monitoring is shown to be suitable for evaluating materials degradation and bone response in vivo, providing continuous information on the implant and tissue performance in the same living animal.

Abducens Nerve (VI) Injury Caused by Halo-Femoral Traction: A Case Report

Stretch and traction on cranial nerves during surgery may cause localized ischemia or change of position of the cranial nerve leading to subsequent dysfunction. Cranial nerve palsies (VI, IX, X and XII) are the commonly affected nerves. Here we report a cranial nerve VI palsy from a halo-femoral suspension following a posterior spinal fusion. We present an 11-year-old girl with idiopathic scoliosis who was admitted for surgical correction. She had no neurological problems preoperatively. The initial video-assisted thoracoscopic anterior release and cranial bifemoral traction were uneventful. Postoperatively, ten-pound weights were added at the head and another ten were added for counter-traction. Weights were added daily in 5-pound increments. Postoperative day 2, the patient complained of “double vision” which resolved upon decreasing the traction weight only by 5 pounds. She underwent an uneventful posterior spinal fusion one week later with a total intravenous anesthesia technique; motor evoked potentials were adequate throughout the procedure. One day later, she again developed left sixth cranial nerve palsy with inability to gaze laterally. There were no other neurological deficits, headaches or even double vision. Neurology and ophthalmology consultations excluded hypoxia/hypoperfusion as possible etiologies. The femoral pins and occipital frame were removed on day 3 in order to obtain imaging and also to remove a potential source of infection. The left lateral rectus palsy was noted to improve that same day. Radiological imaging results were ultimately normal. There is a need for frequent neurological examinations in patients in halo-tractions and prompt removal of the instrument at the first sign of eye problems. doi:10.4021/jnr39e

Isokinetic muscle strength and knee function associated with double femoral pin fixation and fixation with interference screw in anterior cruciate ligament reconstruction

Intensive scheduling in sports requires athletes to resume physical activity shortly after injury. The purpose of this study was to investigate early isokinetic muscle strength and knee function on bone-patellar tendon-bone (BPTB) ACL reconstruction with double femoral pin fixation or interference screw technique. A prospective study was conducted from 2008 to 2009, with 48 athletes who received femoral BPTB fixation with interference screw (n = 26) or double pin (n = 22). Clinical (IKDC objective score and hop test) and isokinetic muscle strength (peak torque (PT), PT/body weight and flexion/extension rate (F/E) in 60 and 240°/s) were analyzed at 6 months of follow-up. Analysis at baseline showed no differences between groups before surgery related to age, gender, associated injury, Tegner or Lysholm score; thus showing that groups were similar. During follow-up, however, there were significant differences between the two groups in some of the isokinetic muscle strength: PT/BW 60°/s (Double Pin = 200% ± 13% vs. Interference Screw = 253% ± 16%*, *P = 0.01); F/E 60°/s (Double Pin = 89% ± 29%* vs. Interference Screw = 74% ± 12%, *P = 0.04). No statistical differences between groups were observed on IKDC objective score, hop test and complications. The significant muscle strength outcome of the interference screw group found in this study gives initial evidence that this fixation technique is useful for athletes that may need accelerated rehabilitation. Early return to sports ability signaled by isokinetic muscle strength is of clinical relevance as it is one of the main goals for athletes' rehabilitation.

Adjustment of leg length using imageless navigation THA software without a femoral tracker

BackgroundAdjustment of leg length discrepancy is an important factor influencing the outcome of total hip arthroplasty (THA). However, leg length discrepancy after THA has been reported to be associated with inferior clinical outcome in previous studies. A new version of the imageless navigation software “OrthoPilot THAplus” has been developed to assess the leg length adjustment and offset value. The clear advantage of this system is the elimination of the need for femoral pin insertion, which is associated with potential complications and additional surgical invasion. MethodsIn this study, the accuracy of this newly developed system was evaluated in 50 consecutive hips implanted with primary THA. The operative results of these 50 patients were compared with those of another 50 consecutive primary THA patients operated on with the previous navigation system that was not equipped with the leg length adjustment system. ResultsAfter surgery, the average leg length discrepancy in the THA plus group was 0.9 mm (range –5 to 5 mm), while the corresponding value in the other group with the older software was 2.9 mm (range –13 to 20 mm), showing a significant difference. ConclusionThe accuracy and reproducibility of new software added to the imageless THA navigation system in achieving equalization of leg length were assessed. Comparison of the surgical results as compared with the control group performed with the conventional navigation system showed the advantage of this system over the previous system.

Gas Gangrene as a Result of Femoral Traction Pin Placement

Treatment of adult femoral shaft fractures typically involves operative stabilization with intramedullary implants, external fixation, or a plate and screw construct. However, when stabilization is delayed for any reason, use of a traction pin is recommended to stabilize the fracture, prevent significant shortening, as well as to help with pain control. In this paper, we present the rare complication of a severe gas gangrene infection caused by Clostridium perfringens that led to several amputations and ultimately death. We also discuss risks of temporary skeletal traction and techniques to overcome the morbidity of such a procedure.

Stiffness of Knee-Spanning External Fixation Systems for Traumatic Knee Dislocations: A Biomechanical Study

The purpose of this study was to compare the relative stiffness of four common external fixation (XF) configurations used to span and stabilize the knee after knee dislocation. Synthetic composite femora and tibiae connected with cords were used to simulate a knee. Four configurations of external fixation were tested: anterior femoral pins with monotube (XF1), anterolateral femoral pins with monotube (XF2), anterolateral femoral pins with two connecting rods (XF3), and hinged ring fixator (XF4). Six specimens of each configuration were loaded nondestructively in varus/valgus, anterior-to-posterior shear, flexion/extension, axial compression, internal/external torsion, and failure in varus. XF2 was stiffer than XF1 in varus, valgus, and axial loading (P < 0.01) demonstrating that anterolateral pins provided greater stiffness than anterior femoral pins. XF3 was stiffer than XF2 in varus, valgus, and anterior-to-posterior shear (P < 0.002), indicating that two connecting rods provided greater stiffness than the monotube. XF4 was similar to the other configurations in anterior-to-posterior shear and torsion, indicating the hinged frame provided adequate stability. The average load to failure in varus mode was 250 N-m, which was far beyond the nondestructive loading of all specimens. There was no statistical difference between the different constructs in load to failure. The stiffest construct for external fixation of a knee dislocation was achieved when pins were placed anterior lateral on the femur and two connecting rods were used. A stiffer construct may provide a better clinical outcome and we therefore recommend this frame configuration.

Influence of cementing the pin on resistance to fracture in hip resurfacing

Background Since the introduction of modern hip resurfacing systems, there has been a controversy regarding the fixation of the centering pin in the femoral component. It has been suggested that cementing the pin may increase strength of the femoral neck. This in-vitro analysis investigated the influence of a cemented, femoral pin on resistance to fracture in the resurfaced hip. Methods Five pairs of cadaveric, fresh-frozen femora underwent hip resurfacing (ASR™) using a high viscosity cementing technique. In one side of each pair only the inner surface of the implant was cemented, in the other side, cement was additionally hand-pressurized down the pinhole prior to implantation of the femoral component. Specimen were then mounted on a material testing machine and cyclic loading with increasing load steps was applied until fracture of the femoral neck. Findings Fracture load was increased ( P = 0.013) in the cemented pin group (Median = 4200 N) when compared with the cementless pin group (Median = 2800 N). The number of cycles to failure in the group with the cemented pin (Median = 8072) was likewise higher ( P = 0.01) when compared to the group, in which the pin was not cemented (Median = 5906). Interpretation Cementing the pin may provide additional fixation in hips with low bone mineral density or osteonecrotic lesions, as resistance to fracture could be improved in the presented in-vitro scenario. Although this was shown for a specific hip resurfacing system, this effect might be extrapolated to other, similar implant designs.