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.

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.

Sensitivity of knee soft-tissues to surgical technique in total knee arthroplasty.

Restricted range of motion and excessive laxity are both potential complications of total knee arthroplasty (TKA). During TKA surgery, the surgeon is frequently faced with the question of how tightly to implant the prosthesis. The most common method of altering implantation tightness is to vary the thickness of the polyethylene inlay after the bone cuts have been made and the trial components inserted. We have sought to quantify how altering the polyethylene thickness may affect post-operative soft tissue tension for a range of prosthetic designs. Four different prosthetic designs were implanted into fresh-frozen cadaveric knee joints. All four designs were implanted in the standard manner, with a 100 Newton distraction force used to set soft tissue balance. The tibiofemoral force was then recorded at 15° intervals throughout the passive flexion range. After the standard implantation of each prosthesis, the tibial component was raised or lowered to mimic increasing and decreasing the polyethylene thickness by 2mm and the force measurements repeated. Tibiofemoral force in extension correlated with implantation tightness for all prosthesis designs. Between 15° and 90° of knee flexion, all four designs were insensitive to changes in implantation tightness. Beyond 90° the effect was more notable in rotating platform mobile-bearing and cruciate-retaining prostheses than in posterior-stabilised mobile-bearing designs. The findings of this research may be useful in assisting surgical decision-making during the implantation of TKA prostheses.

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.

Assessment of isometricity before and after total knee arthroplasty: a cadaver study.

Total knee arthroplasty (TKA) relies on soft tissue to regulate joint stability after surgery. In practice, the exact balance of the gaps can be difficult to measure, and various methods including intra-operative spreaders or distraction devices have been proposed. While individual ligament strain patterns have been measured, no data exist on the isometricity of the soft tissue envelope as a whole. In this study, a novel device was developed and validated to compare isometricity in the entire soft tissue envelope for both the intact and TKA knee. A spring-loaded rod was inserted in six cadaver knee joints between the tibial shaft and the tibial plateau or tibial tray after removing a 7 mm slice of bone. The displacement of the rod during passive flexion represented variation in tissue tension around the joint. The rod position in the intact knee remained within 1 mm of its initial position between 15 degrees and 135 degrees of flexion, and within 2 mm (+/-1.2 mm) throughout the entire range of motion (0-150 degrees). After insertion of a mobile-bearing TKA, the rod was displaced a mean of 6 mm at 150 degrees (p<0.001). The results were validated using a force transducer implanted in the tibial baseplate of the TKA, which showed increased tibiofemoral force in the parts of the flexion range where the rod was most displaced. The force measurements were highly correlated with the displacement pattern of the spring-loaded rod (r=-0.338; p=0.006). A simple device has been validated to measure isometricity in the soft tissue envelope around the knee joint. Isometricity measurements may be used in the future to improve implantation techniques during TKA surgery.

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.

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.

Tibiofemoral force following total knee arthroplasty: comparison of four prosthesis designs in vitro.

Despite ongoing evolution in total knee arthroplasty (TKA) prosthesis design, restricted flexion continues to be common postoperatively. Compressive tibiofemoral force during flexion is generated through the interaction between soft tissues and prosthesis geometry. In this study, we compared the compressive tibiofemoral force in vitro of four commonly used prostheses: fixed-bearing PCL (posterior cruciate ligament)-retaining (PFC), mobile-bearing posterior-stabilized (PS), posterior-stabilized with a High Flex femoral component (HF), and mobile-bearing PCL-sacrificing (LCS). Fourteen fresh-frozen cadaver knee joints were tested in a passive motion rig, and tibiofemoral force measured using a modified tibial baseplate instrumented with six load cells. The implants without posterior stabilization displayed an exponential increase in force after 90 degrees of flexion, while PS implants maintained low force throughout the range of motion. The fixed-bearing PFC prosthesis displayed the highest peak force (214 +/- 68 N at 150 degrees flexion). Sacrifice of the PCL decreased the peak force to a level comparable with the LCS implant. The use of a PCL-substituting post and cam system reduced the peak force up to 78%, irrespective of whether it was a high-flex or a standard PS knee. However, other factors such as preoperative range of motion, knee joint kinematics, soft tissue impingement, and implantation technique play a role in postoperative knee function. The present study suggests that a posterior-stabilized TKA design might be advantageous in reducing soft tissue tension in deep flexion. Further research is necessary to fully understand all factors affecting knee flexion after TKA.

Patella intraosseous blood flow disturbance during a medial or lateral arthrotomy in total knee arthroplasty: a laser Doppler flowmetry study.

Patella complications are recognized sequelae of total knee arthroplasty (TKA). Disruption of blood flow to the patella and adjacent soft tissues during surgery may contribute to reduced viability of the bone and patella ligament tissue. The effect on genicular blood flow to the medial and lateral patella was compared for a medial (MA) and lateral arthrotomy (LA) during TKA. Laser Doppler flowmetry was used to measure both baseline and postarthrotomy flow in vivo for 16 primary TKA patients. Flow in the lateral patella was reduced approximately 20% for both MA and LA. Conversely, the use of MA resulted in substantial reduction in flow to the medial patella (53%) compared to the lateral approach (27%). A large standard deviation of scores was evident in all cases. Although there was a tendency for LA to disturb the patellar blood flow less, the difference was not significant. It was concluded that neither approach is superior regarding the blood flow preservation to the patella. Hence, a lateral approach might only have an advantage in knee joints that are likely to need a lateral release in combination with an MA-e.g., a valgus deformity or preoperative patella maltracking.

Numerical analysis of maximal bat performance in baseball.

Metal baseball bats have been experimentally demonstrated to produce higher ball exit velocity (BEV) than wooden bats. In the United States, all bats are subject to BEV tests using hitting machines that rotate the bat in a horizontal plane. In this paper, a model of bat-ball impact was developed based on 3-D translational and rotational kinematics of a swing performed by high-level players. The model was designed to simulate the maximal performance of specific models of a wooden bat and a metal bat when swung by a player, and included material properties and kinematics specific to each bat. Impact dynamics were quantified using the finite element method (ANSYS/LSDYNA, version 6.1). Maximum BEV from both a metal (61.5 m/s) and a wooden (50.9 m/s) bat exceeded the 43.1 m/s threshold by which bats are certified as appropriate for commercial sale. The lower BEV from the wooden bat was attributed to a lower pre-impact bat linear velocity, and a more oblique impact that resulted in a greater proportion of BEV being lost to lateral and vertical motion. The results demonstrate the importance of factoring bat linear velocity and spatial orientation into tests of maximal bat performance, and have implications for the design of metal baseball bats.

A numerical model for risk of ball-impact injury to baseball pitchers.

INTRODUCTION: Metal baseball bats produce higher ball exit velocity (BEV) than wood bats, increasing the risk of impact injuries to infield players. In this paper, maximum BEV from a wood and a metal bat were determined using the finite element method. METHODS: Three-dimensional (3-D) bat kinematics at the instant of impact were determined from high-speed videography (N = 17 high-performance batters). A linear viscoelastic constitutive model was developed for stiffer and softer types of baseballs. The risk of impact injury was determined using available movement time data for adult pitchers; the data indicate that 0.400 s is required to evade a batted ball. RESULTS: The highest BEV (61.5 m.s(-1)) was obtained from the metal bat and the stiffer ball model, equating to 0.282 s of available movement time. For five impacts along the long axis of each bat, the "best case scenario" resulted from the wood bat and the softer ball (46.0 m.s(-1), 0.377 s). CONCLUSIONS: The performance difference between the bats was attributed to the preimpact linear velocity of the bat impact point and to differences in orientation on the horizontal plane. Reducing the swing moment of the baseball bat, and the shear and relaxation modulii of the baseball, increased the available movement time.

Impact injuries in baseball : prevalence, aetiology and the role of equipment performance.

Baseball has one of the highest impact injury rates of all sports. These injuries are primarily attributed to impact by a ball after it has been hit, pitched or thrown. This paper will review the incidence and causal factors for impact injuries in baseball. Attention is given to the design and material properties of bats, in light of evidence suggesting balls hit into the infield from metal bats can reach velocities potentially lethal to defensive players. The distribution of bat mass along the long axis of the implement appears a major factor in the greater performance potential of metal bats over wooden bats of equal length and mass. The dynamic behaviour of baseballs has also been implicated in the severity of head and chest injuries experienced by players. Balls of greatly reduced stiffness have been introduced for junior play, but debate still remains over their performance and impact characteristics. The behaviour of the ball during high-speed impact with the bat has been the subject of relatively limited research, and the effect of manipulating baseball material properties to decrease batted-ball velocity is unclear. The value of batting helmets is evident in the observed reduction of head injuries in baseball, but the use of protective vests to decrease the incidence and severity of cardio-thoracic trauma appears to be contraindicated.