Factors affecting fracture healing after intramedullary nailing of the tibial diaphysis for closed and grade I open fractures.

As there is little information on the factors that influence fracture union following intramedullary nailing of the tibia we retrospectively investigated patient-, injury- and treatment-related factors in 161 patients with closed or grade I open fractures of the tibial diaphysis. The patients were reviewed until clinical and radiological evidence of union at a mean of 13.3 months (4 to 60). Multivariate statistical analysis using a Cox proportional hazards model showed that the risk of failure of union increased by 2.38 times for highly comminuted fractures, by 3.14 times when nail dynamisation was applied, and by 1.65 times when the locking screws failed. In fractures with no or only minimal comminution the risk of nonunion increased if the post-reduction gap was > or = 3 mm.

Correlation between radiological parameters and patient-rated wrist dysfunction following fractures of the distal radius.

The present study investigates the correlation between radiological parameters of wrist fractures and the clinical outcome expressed by objective clinical parameters and the level of patient-rated wrist dysfunction. Thirty consecutive cases of unstable distal radial fractures treated with closed reduction and percutaneous fixation were prospectively studied for a period of one year. The outcome parameters included objective clinical and radiological parameters and the previously described and validated patient-rated wrist evaluation (PRWE) score. Analysis showed that for unstable (AO classification types 23-A2, -A3, -C1 and -C2) fractures the fracture type affects the range of wrist palmarflexion (p=0.04) and that the presence of postoperative articular 'step-off' affects the range of wrist dorsiflexion and the patient-rated wrist function at the final time of the study (p<0.01 and p=0.02, respectively). It is also shown that permanent radial shortening and loss of the palmar angle were associated with prolonged wrist pain (p<0.01 and p=0.03, respectively). Our finding that residual articular incongruity correlates with persisting loss of wrist dorsiflexion and wrist dysfunction contradicts the view that loss of articular congruity is associated with late development of articular degeneration but not with early wrist dysfunction. Additionally, this study failed to show any association between the fracture type and the functional outcome as rated by the patients.

Association between objective clinical variables and patient-rated disability of the wrist.

Although the outcome of fractures of the distal radius is traditionally assessed using objective clinical variables such as grip strength and range of movement of the wrist, the extent to which they reflect function and outcomes of importance for the patient is uncertain. This may cause considerable inconsistencies in the assessment of outcome using current scoring systems. We prospectively studied 31 patients recovering from unstable fractures of the distal radius in order to investigate the association between objective variables and the level of post-traumatic disability of the wrist as measured by the patient-rated wrist evaluation (PRWE) score. Multiple regression showed considerable differences in the extent to which limitations in specific objective clinical variables reflected the level of disability of the wrist. Grip strength was shown to be a significant predictor of the PRWE score (regression coefficient -1.09, 95% confidence interval -1.76 to -0.42, p < 0.01) and thus appears to be a sensitive indicator of return of function of the wrist. Forearm rotation and flexion and extension of the wrist were not significantly associated with the PRWE score. These observations should be taken into account during the evaluation of methods of treatment and in constructing future clinical outcome scoring systems.

A technique for accurate reproduction of the femoral anteversion during primary total hip arthroplasty.

Accurate reproduction of the femoral anteversion is important in achieving stability of the prosthetic joint in total hip arthroplasty (THA), while placement of the femoral stem in excessive anteversion or retroversion results in an increased incidence of dislocation. Due to a number of factors, the current surgical technique results in significant variation between the anatomical and the surgically reconstructed femoral anteversion. This technical note describes a method to reproduce the normal anatomical femoral anteversion accurately in any case of primary THA. The method is based on the idea that the initial stages of femoral canal preparation can be completed before the femoral neck is osteotomised and therefore at a stage when the femoral head and neck are still accessible and can be used as landmarks for accurate reconstruction of the femoral anteversion. The described technique for accurate reconstruction of the anatomical version of the femoral head is indicated for all cases of primary THA where reproduction of the normal anatomical centre of rotation of the hip joint is a principal aim.

Initial rotational stability of distal tibial fractures nailed without proximal locking: the importance of fracture type and degree of cortical contact.

Although distally locked (dynamic) nailing is generally recommended for fractures below the isthmus of the tibia in the presence of adequate proximal nail-bone contact, rotational stability in the above situation appears to be a major concern and can increase the risk of malunion. However, there is no published experimental evidence to quantify this mechanical parameter or to relate factors such as the fracture pattern with the final clinical outcome. This in-vitro biomechanical experimental study was set out to measure the initial rotational stability of dynamically nailed fractures of the distal tibial diaphysis. Using a composite tibial model, three non-comminuted types (spiral, oblique and transverse) and various comminuted patterns (comminution, 0-85%) of dynamically nailed fractures of the distal tibial diaphysis were tested. Using a special rig to simultaneously apply axial and torsional loading measurements of torsional stiffness and the previously described "spring-back angle" were carried out. Our results showed that in terms of torsional stiffness and the "spring-back" angle oblique fractures are the most stable followed by transverse and spiral fractures. Furthermore, when testing of the above parameters against the degree of comminution was carried out, a significant reduction of rotational stability was evident with comminution of 50% or above. It is concluded that oblique fractures of the distal tibial third that can be reduced with at least 50% cortical apposition present the optimal rotational stability following dynamic nailing.

Quantified kinematics of the injury to the posterior cruciate ligament: a computer-aided design simulation study.

OBJECTIVE: To quantify the kinematics of the injury to the posterior cruciate and the other major knee ligaments as a function of the knee flexion angle at the moment of impact. DESIGN: Computer-aided design modelling was used to investigate the strain response of all major knee ligaments during antero-posterior abnormal tibio-femoral translation at 0-90 degrees knee flexion. BACKGROUND: It is generally believed that the likelihood of injury to the posterior cruciate ligament following anterior impact is higher in the flexed knee. However, there are no kinematical studies to quantify this clinical observation or investigate the role of the other knee ligaments in the above situation. METHODS: Computer calculations of the individual ligament strain were plotted against the magnitude of posterior tibial translation. Additionally, the strain rate for each ligament (defined as the ligament strain produced per mm of posterior tibial linear translation) was calculated as the slope of the strain-displacement curve for all tested degrees of knee flexion. RESULTS: The posterior cruciate ligament has been shown to be the primary restraint to posterior tibial translation in all degrees of knee flexion. However, at 90 degrees of knee flexion the strain rate of the posterior cruciate ligament is approximately half that in the fully extended knee and the posterior cruciate ligament is the only ligament to resist posterior tibial translation. CONCLUSIONS: The strain behaviour of the posterior cruciate ligament during injury is highly dependent on the knee flexion during the moment of impact. Forced posterior tibial translation in the 90 degrees flexed knee may result in isolated posterior cruciate ligament deficit rather than a complex ligament disruption. The strain rate of a ligament as introduced in the present study is a quantified parameter related to the resistance that the ligament imposes to an abnormal joint movement. Relevance. This study provides insight into the differential strain of the knee ligaments during impacts that result in posterior cruciate ligament injury. Studies that quantify the strain behaviour of individual knee ligaments are important to the understanding, diagnosis and prevention of injuries sustained during contact sports and high-energy road traffic accidents.

Biomechanical considerations in 'biological' femoral osteosynthesis: an experimental study of the 'bridging' and 'wave' plating techniques.

Although traditional compression plate fixation aims to abolish interfragmentary movement and achieve primary bone healing, the more recent 'biological' plate fixation methods such as the 'bridging' and wave' plate techniques aim to maintain fracture alignment without absolute stability and promote union by callus formation. Furthermore, some mechanical advantages have been attributed to the 'wave' plate fixation. Since no data have been published on the mechanical characteristics of the 'bridging' and 'wave' plate fixation methods, the aim of this biomechanical comparative study was to investigate the rigidity of those fixation methods in various types of femoral diaphyseal fractures. Using a composite femoral model, the rigidity characteristics of three fixation methods (short DCP, 'bridging' and 'wave' plates) were investigated. The results showed that when cortical contact between the main fragments is present, a 'bridging' plate can be equally rigid to the 'wave' plate in mediolateral bending by displaying a similar tension-band effect. Furthermore, in the absence of cortical contact, the axial fixation rigidity of the long 'bridging' plate is superior to that of the 'wave' plate. Both methods showed a significant 'stress-shielding' effect on the intact femur. In conclusion, this in vitro study failed to show any significant mechanical advantages of the 'wave' plate technique over the 'bridging' plating method. It appears that the 'bridging' plate fixation may be the mechanically optimal 'biological' plating method for the femoral diaphysis.

Computer modeling in bone research.

Computer modeling has had an undoubtedly enormous impact on the field of bone research in recent years. Development of advanced computer based models has permitted researchers to explore a vast area of musculoskeletal science from the complex biophysical stimuli at the cellular level to the mechanical behavior of heterogeneous skeletal structures. Furthermore, computer modeling has given significant impetus to the impressive progress of modern bone implant development. With recent advances in computers, faster hardware and increasingly sophisticated software, the prospects for the future of computer-based bone research appear more exciting than ever.

Variations in serum angiotensin-converting enzyme activity following lung resection: a controlled study in a clinical setting.

Angiotensin-converting enzyme (ACE) plays an important role in post-operative cardiovascular control, especially in critical illness. Since the pulmonary endothelium is the major site of ACE production it would seem probable that surgical resection of lung tissue would significantly influence serum ACE (sACE) activity. The aim of this study was to investigate the effect of surgery on early post-operative sACE activity in patients undergoing lung resection (n = 18) and a control group of patients (n = 18) undergoing thoracotomy for other reasons. An early post-operative, sustained sACE fall without significant difference in sACE activity between the two groups was observed 6 h after the operation. Furthermore, there was no correlation between post-operative sACE variations and the amount of lung tissue resected. It appears that surgical removal of lung tissue does not significantly affect the post-operative sACE response. This may be due to the presence of important extra-pulmonary ACE-producing sites or to the compensation of the remaining pulmonary vascular endothelium.

Axial preload in external fixator half-pins: a preliminary mechanical study of an experimental bone anchorage system.

OBJECTIVE: To demonstrate the effect of axial preload achieved with an experimental external fixator pin prototype on the initial stability of the pin-bone interface. DESIGN: An in vitro mechanical study comparing pin stability of an axially-preloaded experimental pin and a radially-preloaded conventional external fixation pin. BACKGROUND: The most common problem in clinical practice of external fixation is pin site failure. An experimental external fixator half-pin has been designed introducing axial preload as an alternative method of achieving a stable pin-bone interface. METHODS: Standardized measurements of pin insertion and removal torque comparing the experimental pin prototype and a conventional external fixator pin in a synthetic composite material and ovine tibial cortical bone. RESULTS: There is a positive correlation between axial preload and torque resistance of the coaxial experimental half-pin as well as significantly increased torque resistance of the axially-preloaded experimental pin over the conventional pin tested. In addition, significantly lower insertion torque of the experimental pin was observed with the applied insertion technique. CONCLUSIONS: 'Axial preload' achieved with appropriately-designed half pins might represent an effective biology-sparing method of increasing the mechanical stability of the pin-bone interface in unilateral external fixator frames. RELEVANCE: Several aspects of the current external fixator pin design and insertion technique have been implicated for the significant incidence of failure at the pin-bone interface manifested as pin loosening, pin track infection or even osteomyelitis. An axially-preloaded bone fastener system may be mechanically and biologically superior and therefore clinically advantageous.

"Biological" internal fixation of long bone fractures: a biomechanical study of a "noncontact" plate system.

Based on existing knowledge of noncontact plates, an experimental prototype of a nonperiosteal contact internal fixation implant ("noncontact internal fixator") has been designed. The construct rigidity of osteotomised synthetic composite femora, fixed with the noncontact fixator and a reamed, statically-locked intramedullary nail were compared in axial compression, two plane bending and torsion in four types of diaphyseal fractures. With the exception of axial loading in the presence of extensive comminution, the fixation stability provided by the noncontact fixator is significantly higher than that of the tested intramedullary nail. Any degree of cortical contact between the two main fragments is important for the stability of this nonperiosteal contact fixation system under axial load. Appropriately-designed "internal fixators" could provide not only a number of biological and technical advantages, but also fixation stability comparable and in certain aspects superior to that of other fixation methods.

Unusual patellar tendon injury in an adolescent runner with generalised ligamentous laxity.

A case is reported of an acute traction injury of the patellar tendon in a boy of 14 with joint hypermobility. Such injuries are unusual but early diagnosis and surgical repair lead to a good long term outcome. In adolescents participating in sports, the awareness of the possibility of a rare knee extensor mechanism injury is essential for a successful outcome.