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PubMed2005

Lag screws for hip fracture fixation: Evaluation of migration resistance under simulated walking.

Previous mechanical studies concerning cut-out of lag screws for pertrochanteric hip fractures have relied on static or dynamic uniaxial loading regimens to induce construct failure by varus collapse and superior cut-out. However, the hip is loaded in a multiplanar, dynamic manner during normal gait. We designed a hip implant performance simulator (HIPS) system to evaluate lag screw cut-out under multiplanar loading representative of normal gait. Five surrogate pertrochanteric fracture specimens with lag screw fixation were loaded up to 20,000 cycles using a biaxial rocking motion (BRM) gait simulation protocol. Another five specimens were loaded using a standard uniaxial loading protocol. The BRM loading group exhibited combined varus collapse (5.4+/-2.9 degrees ) and backward rotation (7.2+/-2.8 degrees ). The uniaxial loading group exhibited four times less varus collapse (1.4+/-1.1 degrees ) as compared to the BRM group, and only negligible rotation. For correlation of lag screw migration in surrogate specimens to that in native bone, six human cadaveric specimens were subjected to BRM loading. The degree of varus collapse (8.5+/-7.7 degrees ) and rotation (7.2+/-6.4 degrees ) in cadaveric specimens were comparable to that in surrogate specimens, with the surrogate specimens showing significantly less variability. The results demonstrate that accounting for clinically realistic multiplanar loading vectors significantly affects implant migration, and therefore should be considered when evaluating the fixation strength of hip screw implants.

Biomechanical Phenomena↗

PubMed1998

Angulated screw placement in the lateral condylar buttress plate for supracondylar femoral fractures.

Certain supracondylar femoral fractures are not amenable to internal fixation with fixed angle devices. In these instances, the condylar buttress plate is the recommended alternative; however, this is a less rigid device. Because of the decreased rigidity and strength of this device, there is a tendency toward varus angulation and malunion. In six fresh-frozen human knee specimens, segmental osteotomies were created to mimic supracondylar femoral fractures. The medial cortex was completely removed to make the fracture unstable to varus deformity. The fracture was fixed with a lateral condylar buttress plate using 4.5 mm screws. Each specimen was tested once with all the screws installed perpendicular to the plate, and again with the middle screw, just proximal to the fracture, angled 45 degrees diagonally across the fracture into the subchondral bone of the medial femoral condyle. For the construct with all screws placed perpendicular to the buttress plate, the initial stiffness was 410 N/mm, and after 1000 cycles it was 230 N/mm. With a screw placed diagonally across the fracture site, stiffness increased to 833 N/mm on the first cycle, and 796 N/mm after 1000 cycles. In all specimens with the screws placed perpendicular to the plate, the distal fragment had a permanent varus deformity after 1000 cycles, under no load, of 0.91 mm. For the diagonal screw condition, the average magnitude for all six specimens was 0.42 mm. This simple means of screw angulation in the plate strengthened the overall construct to resist the tendency toward varus deformity. The attractive features include the ease of application, and the use of an existing construct.

Aged↗

PubMed2002

The effects of tibial component inclination on bone stress after unicompartmental knee arthroplasty.

Unlike the case with total knee arthroplasty, the femorotibial angle (FTA) after unicompartmental knee arthroplasty (UKA) does not directly depend on the inclination of the tibial component when the height of the joint line is maintained. This study analyzed the effects of the inclination of the tibial component in the coronal plane on the contact pressure of the implant-bone surface and the stresses on the proximal tibia. A two-dimensional, coronal plane model of the proximal tibia was subjected to finite-element analysis. Sixteen patterns of finite-element models of equal FTA were developed in which the inclination of tibial components ranged from 5 degrees valgus to 10 degrees varus in increments of 1 degrees. Stress concentration at the proximal medial diaphyseal cortex gradually increased as the inclination changed from valgus to varus. Maximum contact pressure on the metal-bone interface similarly changed and shifted from the lateral edge to the medial edge of the implant as the inclination changed to varus. It was found that even without changing FTA, the inclination of the tibial component might affect stress concentration and contact pressure in the proximal tibia after UKA. The results suggested that slight valgus inclination of the tibial component might be preferable to varus and even to 0 degrees (square) inclination so far as the stress distribution is concerned.

Arthroplasty, Replacement, Knee↗

PubMed2005

[Difficulties and reproducibility of radiological measurement of the proximal tibial axis according to Lévigne].

PURPOSE OF THE STUDY: The angle between the anatomic axis of the tibia and the tangent to the superior borders of the tibial plateaus is, on average, tilted 3 degrees in the varus position. If there is no bone wear, this angle measures the constitutional epiphyseal axis of the proximal tibia. When degenerative joint disease modifies the aspect of the tibial plateaus, this angle measures the sum of the constitutional varus and the bone wear, without distinguishing between the two. It is known however that the respective contribution of these two deformations can have therapeutic implications, particularly when tibial osteotomy for valgus correction or implantation of a unicompartmental prosthesis is proposed. Lévigne proposed a radiographic measurement of the proximal tibial axis to distinguish between these two sources of tibial deformation. We studied the intra- and interobserver reproducibility of these measurements. MATERIAL AND METHODS: Fifty volunteers free of knee disease were chosen at random among a population of patients undergoing upper limb surgery. All patients provided their informed consent for participation in the study. Full-limb radiographs of one lower limb (chosen at random) were obtained using a standardized technique. The proximal tibial axis was measured according to the Lévigne technique using a manual goniometer graduated in degrees. One operator performed two series of measures independently on the same films. Two other operators performed a series of measurements on each film. The intra- and inter-observer reproducibility was determined with the interclass coefficient of correlation (rho). RESULTS: The proximal epiphyseal axis of the tibia could not be determined on 7 to 18 films, depending on the operator. All three operators were able to make the all measurements (four per film) for only 25 patients. The mean epiphyseal axis varied from 2.5 degrees to 4.7 degrees for the four series of measurements. Intra-observer reproducibility was considered good (rho=0.62). Inter-observer reproducibility was considered moderate (rho=0.41). DISCUSSION: The Lévigne technique is to our knowledge the only method described in the literature distinguishing the relative contribution of constitutional varus and bone wear of the proximal tibia. According to the advocates of this method, the angle between the epiphyseal axis linking the center of the tibial plateaus and the center of the proximal growth cartilage scare, and the anatomic axis of the tibia is a measurement of constitutional varus. The average is 3 degrees . The angle between a line perpendicular to the epiphyseal axis and the tangent of the superior borders of the tibial plateaus measures the deformation related to bone wear. In the present work, we found that this technique enables acceptable intra-observer reproducibility but that inter-observer reproducibility is low. The differences observed are certainly related to uncertain identification of the growth cartilage scar. This illustrates the difficulty in generalizing this technique for measuring healthy knees. Such difficulties would be even greater for degenerative knees. CONCLUSION: The Lévigne technique does not appear to be a reliable method for defining indications for different surgical procedures according to the morphology of the proximal tibia.

Anthropometry↗

PubMed2005

[Mid-term results of Wallaby I posterior cruciate retaining total knee arthroplasty: a prospective study of the first 425 cases].

PURPOSE OF THE STUDY: Posterior Wallaby I is a fixed polyethylene tibial plateau prosthesis enabling preservation of the posterior cruciate ligament (PCL). Its asymmetrical and divergent femoral condyles articulate with also asymmetrical tibial plateaus. The purpose of this prospective study was to analyze outcome of the first 425 Wallaby I prosthesis of the Guepar group implanted for first-intention treatment. MATERIALS AND METHODS: These 425 prostheses were implanted from December 1992 to February 1995 by senior and junior surgeons. Mean patient age at implantation was 70.5 years. 91% had primary or secondary osteoarthritis and only 8.9% had inflammatory rheumatoid disease. The mean preoperative IKS score was 25.34 points and the IKS function score was 29.04. 10.35% of knees were aligned normally (mechanical axis between 2 degrees varus and 3 degrees valgus) according to the IKS criteria (Ewald), 24% presented valgus > or = 4 degrees and 65.6% varus > or = 3 degrees. All tibial and patellar components (except one) were cemented, 5.8% of the femoral pieces were inserted without cement. All but 11 patellae were resurfaced. Clinical outcome was assessed with the IKS score and radiological outcome with the IKS criteria. The patella was considered to be tilted when the alpha angle was > 5 degrees and dislocated when the AA' distance was > 5 mm. The chi-square test was used for comparison of quantitative variables (significance set at 0.05). RESULTS: Early postoperative complications were rare: two infections cured with debridement-lavage and antibiotics without removal of the prosthesis, one peronal nerve palsy which regressed partially, ten late unions without clinical consequence (particularly in the inflammatory rheumatoid patients). Twenty-six prostheses were followed less than one year (eight patients died and eighteen were lost to follow-up) and 84 less than five years (27 patients died and 57 lost to follow-up before five years). 315 prostheses were followed for more than five years (5-9 years) with a mean follow-up of 6.3 years. Among the 399 prostheses followed for one year or more, we noted: four infections including three requiring change of the prosthesis (one cured by arthroscopic lavage), two aseptic loosenings which were revised (one global one tibial), one tibial loosening and three patellar loosenings which were not revised, and two femoral ossifications limiting joint motion but improved by arthrolysis and resection of the ossifications. Three patients experienced anterior pain requiring secondary patellar resurfacing in two and section of the lateral patellar wing in one. Ninteen patellar fractures (4.7%) were noted, including 17 with no significant functional impact which were not revised. The mean IKS knee score among prostheses followed for five years was 90.5 points, with mean motion 110.5 degrees. Mean IKS function score was 61.63 points. 72.9% of the knees were aligned, 22.2% in varus and 4.9% in valgus. The mechanical axis of 94.3% of the knees was between 5 degrees varus and 5 degrees valgus. Prosthesis survival at eight years (Kaplan-Meier method) was 97.7% considering all reasons for prosthesis removal and 98.5% for removal for aseptic loosening. CONCLUSION: This prospective multicentric study demonstrated that the results obtained with the Wallaby I prosthesis are as good as those obtained with other prostheses sparing the PCL and published in the literature. Preservation of the PCL enables better knee stability, correct motion (110.5 degrees in our series) with almost no radiological wear of the tibial polyethylene at eight years. The only worrisome complication is patellar fracture.

Adult↗

PubMed2004

Anatomical analysis of the femoral condyle in normal and osteoarthritic knees.

It is important to understand anatomical feature of the distal femoral condyle for treatment of osteoarthritic knees. Detailed measurement of the femoral condyle geometry, however, has not been available in osteoarthritic knees including valgus deformity. This study evaluated femoral condyle geometry in 30 normal knees, 30 osteoarthritic knees with varus deformity, and 30 osteoarthritic knees with valgus deformity using radiographs and magnetic resonance imaging (MRI). In radiographic analysis in the coronal plane, the femoral joint angle (lateral angle between the femoral anatomic axis and a tangent to femoral condyles) was 83.3 degrees in the normal knees, 83.8 degrees in the varus knees, and 80.7 degrees in the valgus knees. In MRI analysis in the axial plane, the posterior condylar tangent showed 6.4 degrees of internal rotation relative to the transepicondylar axis in the normal knees, 6.1 degrees in the varus knees, and 11.5 degrees in the valgus knees. These results suggested that there was no hypoplasia of the medial condyle in the varus knees, but the lateral condyle in the valgus knees was severely distorted. Surgeons should take this deformity of the lateral femoral condyle into account when total knee arthroplasty is performed for a valgus knee.

Aged↗

PubMed1995

Loose-hinge total elbow arthroplasty. An experimental study of the effects of implant alignment on three-dimensional elbow kinematics.

A previous study suggested that the kinematics of a loose-hinge total elbow arthroplasty (TEA) are those of a truly semiconstrained joint. This study addresses the effects of malposition of the implant. The three-dimensional elbow kinematics during simulated active motion were studied in six cadaver specimens using an electromagnetic tracking device. In addition to simulated active elbow flexion, flexion arcs were obtained under an elbow varus or valgus moment, to calculate the structural varus-valgus laxities. The results after four different Coondrad-Morrey TEA positions of implantation were compared with those of the intact elbow. The flexion-extension amplitudes were not significantly decreased after TEA implantation, except with external rotation of the ulnar component, which resulted in a loss of extension. In the intact elbow and after TEA implantation in any position, the mean varus-valgus deviations throughout elbow flexion were in a narrower range than the structural limits imposed by the ligaments (intact elbow) or the TEA hinge design. With internal malrotation of the humeral component over 10 degrees, however, the valgus structural limit was reached and, conversely, the varus limit with external rotation over 10 degrees. The clinical improvement observed with the semiconstrained TEA is derived from the benefits of the less constrained articulation. The proximodistal changes of TEA implantation have no consequence on the kinematic pattern. Rotational malpositioning of either humeral or ulnar component should be avoided, the first because it changes the kinematic pattern toward the structural limits of the implant and, therefore, may lead to excessive stresses at the bone-cement-implant interfaces and to early loosening, and the latter because it causes loss of extension.

Biomechanical Phenomena↗

PubMed1992

The effect of preoperative knee deformity on the initial results of cruciate-retaining total knee arthroplasty.

Between November 1985 and June 1987, 751 posterior cruciate-sparing total knee arthroplasties were performed on 523 patients who exhibited fixed varus or valgus deformities. Patients excluded from this study included the following: those with a postoperative follow-up period of less than 2 years (including patients who had died), patients who became infected, and patients with previous failed total knee arthroplasty in the same knee. A total of 473 knees left for evaluation. All arthroplasties were measured using anatomic axis for alignment measurement. The Hospital for Special Surgery scoring system was used to determine the clinical scores prior to the end of each follow-up examination. All ligament releases were performed sequentially, including balancing of the posterior cruciate ligament. All arthroplasties were divided into six separate groups depending upon the degree of varus or valgus deformity. Kaplan-Meier curves were constructed using three methods of failure definition. Curves were then compared between groups. The mean Hospital for Special Surgery score was no different between any of the groups, except for the group of 6 degrees-10 degrees varus, which was significantly higher than the mean score of the 11 degrees and higher valgus group. All other groups were the same statistically. It is concluded that severe varus and valgus deformities may be satisfactorily corrected with the use of a cruciate-retaining type of total knee arthroplasty.

Adult↗

PubMedDate not supplied

Lateral collateral ligament of the elbow joint: anatomy and kinematics.

The structure and kinematics of the lateral collateral ligament of the elbow joint were investigated in 10 cadaveric specimens. The lateral collateral ligament was observed to be a distinct part of the lateral collateral ligament complex. It contains posterior fibers that pass through the annular ligament and insert on the ulna. Three-dimensional kinematic measurements in different forearm rotations showed that joint puncture induced a 1 degree joint laxity significant in forced varus from 30 degrees to 80 degrees of flexion and in forced external rotation from 30 degrees to 120 degrees of flexion. Division of the posterolateral capsule caused no further laxity. Cutting the lateral collateral ligament induced a maximum laxity of 11.8 degrees at 110 degrees of flexion in forced varus and a maximum laxity of 20.6 degrees at 110 degrees of flexion in forced external rotation. The corresponding maximal posterior radial head translation was observed at 80 degrees to 100 degrees of flexion and was 5.7 mm in forced varus and 8.1 mm in forced external rotation. This study suggests the lateral collateral ligament to be an important stabilizer of the humeroulnar joint and the radial head in forced varus and external rotation. The humeroulnar stability is independent of forearm rotation.

Aged↗

PubMed2002

[Kinematic changes after bicondylar resurfacing knee arthroplasty].

AIM: Knee joint motion appears as a hinge movement around the flexion - extension axis. But corresponding to the rolling-sliding-mechanism and alternative models of knee joint kinematics an instant center pathway must be expected. Objective of the study was the comparison of this pathway when assessed in the sagittal plane in patients with preoperative varus or valgus deformity. METHOD: A total of 40 patients either with varus or valgus deformity (20 in each group) were examined before and 6 months after implantation of PFC(R)-SIGMA prostheses. Apart from the influence of knee joint deformity (35 degrees varus to 24 degrees valgus), a so called soft tissue ratio was investigated. Therefore the relation of thigh and femur as well as lower limb and tibia diameters was calculated and combined in one value. The examination by means of photogrammetry consisted of a standardized chair with passive knee joint movement (90 degrees to 0 degrees flexion) supported by an electric motor. The position of defined skin markers was assessed by digital camara with online transmission to PC. The instant center pathway was then evaluated applying the Reuleaux-technique based on the changes of skin marker positions. RESULTS: Results showed a dependence of the course and dimension of the instant center pathway on the extent of soft tissue ratio as well as knee joint deformity. Small values of the ratio (W = 2.9) were represented by round or oval courses of the pathway whereas increasing ratios (W = 4.0) led to triangular and slightly increased dimensions of the courses. Varus deformitywas primarily combined with an increase of the pathways dimension and in contrast, valgus deformity showed decreased pathways. In each case, dimension normalized after prostheses implantation. CONCLUSION: The instant center pathway of knee joint motion showed for both patient groups characteristic phenomen. They were clearly combined with constitutional and clinical features of each patient.

Aged↗

PubMed1986

Os calcis osteotomy in the management of deformities of the hindfoot in spinal dysraphism.

The results of 52 primary os calcis osteotomies in 44 patients with spinal dysraphism are reviewed. There were 42 varus hindfoot deformities and ten valgus hindfoot deformities. The results indicate that the operation is simple and uncomplicated, but over a mean 5.8 year follow-up for the varus feet and 6.5 years for the valgus feet, over 50% of the feet developed either a moderate or severe recurrence of deformity. Os calcis osteotomy appeared from this series to be a moderately successful interim operation for the equinus varus foot, delaying the need for premature triple arthrodesis, but the long-term results in cavo-varus feet with claw toes were uniformly poor. Furthermore, it appeared to be unsatisfactory in the mobile flail valgus foot unless the subtalar joint had been stabilised by fusion. Correction of proximal joint or bone deformity and muscle imbalance is considered necessary if satisfactory results are to be achieved from the osteotomy.

Adolescent↗

PubMedDate not supplied

Single-strand ligament reconstruction of the medial collateral ligament restores valgus elbow stability.

The purpose of this study was to determine the contribution of the central portion of the anterior bundle of the medial collateral ligament (MCL) to elbow stability and to evaluate the effectiveness of a single-strand MCL reconstruction in restoring elbow stability. Testing of 11 fresh-frozen upper extremities was first performed on the intact elbow and then with the capsule, flexor-pronator muscle group, posterior bundle, anterior or posterior band, and central band cut sequentially. Next, a single-strand reconstruction of the MCL was performed. The elbow was moved passively through a full arc of flexion in both varus and valgus gravity-loaded positions. Ulnar movement with respect to the humerus was analyzed by means of an electromagnetic tracking system. Maximum varus-valgus laxity throughout the arc of supinated flexion and pronated flexion was 6.6 degree plus minus 2.4 degree and 7.4 degree plus minus 2.0 degree, respectively, for the intact specimen, 34.2 degree plus minus 5.6 degree and 37.7 degree plus minus 11.8 degree for the specimen with all of the medial valgus elbow stabilizers cut, and 9.0 degree plus minus 2.5 degree and 10.5 degree plus minus 2.7 degree for the reconstructed specimen. Maximum varus-valgus laxity was not significantly different among any of the sectioning sequences until the central band was cut (P <.0001). There was no significant difference in maximum varus-valgus laxity between the intact and reconstructed elbows (P <.05). Our results demonstrate that the central band is an important valgus stabilizer of the elbow and that a simplified single-strand reconstruction is able to restore stability to the MCL-deficient elbow.

Aged↗

PubMed1990

Relationship of foot deformity to ulcer location in patients with diabetes mellitus.

The purpose of this study was to determine whether a relationship existed between type of foot deformity and the location of ulcers in patients with diabetes and insensitive feet. Forty-two ulcerated feet were examined in 40 patients. All patients had severely decreased or absent sensation. Foot deformities were classified according to operational definitions as 1) Charcot's foot, 2) a compensated forefoot varus, or 3) an uncompensated forefoot varus or forefoot valgus. The plantar surface of the midfoot and forefoot was divided into three regions. Six of the 7 patients with a Charcot's foot showed ulceration at the midfoot. Nine of 18 patients with a compensated forefoot varus showed ulceration at the second, third, or fourth metatarsal head. Fifteen of 17 patients with an uncompensated forefoot varus or forefoot valgus showed ulceration at the first or fifth metatarsal. A significant relationship was found between foot deformity and location of ulcer. These results support the hypotheses 1) that insensitivity, coupled with increased, repetitive pressure, is a primary cause of plantar ulcers and 2) that certain foot types are associated with characteristic patterns of pressure distribution and callus formation.

Diabetic Neuropathies↗

PubMed2000

Does axial limb rotation affect the alignment measurements in deformed limbs?

The long-term outcome of total knee arthroplasty and femoral or tibial osteotomy is related to the ability of the surgeon to achieve the desired alignment based on preoperative planning. This study evaluates the effect of axial rotation on measured tibiofemoral angles and the angle formed between the anatomic and mechanical axes of the femur in lower extremities with valgus and varus deformities. A comparison study of the measured tibiofemoral angles indicated a statistically significant effect in models with severe vagus or varus deformity when rotated 10 degrees internally or externally. In the second part of the study, the measured angle between the anatomic and mechanical axes of the femur never varied by more than 1 degree, despite a 40 degrees are of rotation. The results of the study indicate the tibiofemoral angle measurements are more sensitive to axial limb rotation in lower extremities with valgus or varus deformity than are normally aligned limbs. In preoperative planning of total knee arthroplasty, the measured angle between the anatomic and mechanical axes of the femur is less effected by limb rotation, regardless of the degree of valgus or varus deformity.

Arthroplasty, Replacement, Knee↗

PubMed2002

Importance of a radial head component in Sorbie unlinked total elbow arthroplasty.

The effects of a radial head component on total elbow arthroplasty kinematics and stability were evaluated using an anatomic design unlinked total elbow prosthesis. An electromagnetic tracking device recorded motion and varus and valgus displacements under various conditions in 10 cadaveric elbows. The motion patterns of the intact elbows and the Sorbie-Questor total elbow prostheses with a radial head component were similar, as both tended to have a valgus position in extension, varus at midflexion, and more valgus toward full flexion. Under conditions of simulated muscle loading, the maximum valgus and varus laxity of the elbow prosthesis was, on average, 8.6 degrees +/- 4.0 degrees greater than normal. Without the radial head component, however, significant kinematic disturbances and instabilities were seen. The varus and valgus displacements were 13.3 degrees +/- 5.5 degrees greater than the intact elbows. One total elbow arthroplasty without a radial head dislocated during testing. Increasing the muscle loading across the elbow significantly enhanced dynamic stability of the total elbow arthroplasties, especially in the extension half of elbow motion where instability is greatest. However, this dynamic enhancement of stability was seen only in those elbows in which the radial head component had been implanted. The radial head component is an important stabilizer, particularly in extension for this prosthesis, and possibly for other unlinked total elbow prostheses. Although instability of unlinked prostheses depends on the prosthetic design, the use of a radial head replacement may be an important factor in preventing such instability. Perhaps even more importantly, a radial head component balances the load distribution across the articulation, which could decrease stress on the ulnohumeral articulation and therefore possibly reduce polyethylene wear, osteolysis, and loosening.

Aged↗

PubMed2002

Diagnosis and treatment of posterolateral knee injuries.

Posterolateral knee injuries can be very debilitating. It is important to understand the complex anatomy and pertinent diagnostic tests to properly treat posterolateral knee injuries. The fibular collateral ligament, popliteus tendon, and the popliteofibular ligament are the main static stabilizers against abnormal varus and posterolateral translational moments. Important radiographic imaging studies for the posterolateral knee include full length anteroposterior radiographs, taken with the patient standing, to assess for varus alignment in patients with chronic injuries and high field (1.5 tesla or higher) magnetic resonance imaging with specific posterolateral knee sectioning. A physical examination that includes the external rotation recurvation test, varus stress test at 30 degrees, dial test at 30 degrees and 90 degrees, posterolateral drawer test, reverse pivot shift, and an assessment for a varus thrust gait are essential to properly diagnose a posterolateral knee injury. Patients with acute (< 3 weeks) anatomic repairs of Grade III posterolateral knee injuries have the best functional outcome. Although various surgical reconstruction techniques have been developed to treat chronic or irreparable acute posterolateral knee injuries, these techniques have not achieved outcomes comparable with the treatment of other ligament injuries of the knee. Techniques for anatomic reconstructions of these structures are just being developed. Improved education of clinicians as to the proper diagnosis of posterolateral knee injuries is necessary because a large number of these injuries still are missed on initial examinations. In addition, additional research into the most optimal posterolateral knee reconstruction techniques and outcome studies are needed to improve the treatment of this debilitating knee injury.

Arthroscopy↗

PubMed1990

The role of Ender rodding in tibial fractures with an intact fibula.

Thirty-three patients with tibia fractures and intact fibula were studied to determine the efficacy of Ender rod fixation in preventing a varus deformity of the tibia. Twenty-one patients were treated nonoperatively with five (23.8%) developing a significant varus angulation (greater than five degrees). No varus malunions were noted in those patients treated with Ender rods. Those patients treated with Ender rods and early weight-bearing had a shorter average time to union than those treated nonoperatively. We therefore feel that Ender rod fixation is a viable treatment modality in tibia fractures with an intact fibula. In these fractures the use of Ender rods helps prevent significant varus malunion and allows early weight-bearing, thus permitting early mobilization of the traumatized patient.

Adult↗

PubMed1995

Mechanics of retrograde nail versus plate fixation for supracondylar femur fractures.

Two common types of internal fixations for the supracondylar femur fractures--the retrograde intramedullary nail and the 95 degrees sideplate and screw--were mechanically tested in synthetic composite femur bones to determine the quantitative differences in their inherent rigidity. The medial and lateral femoral condyles were separated by a sagittal osteotomy, and a standardized medial segmental shaft defect was created at the distal shaft. The osteotomized specimens were stabilized using one of the two implants and were tested in different modes of loading. The bending stiffness of both constructs were not significantly different in varus compression, medial bending (pure varus), and bending in flexion. The plate and screw implant was three times stiffer in lateral bending (pure valgus) and 1.2 times stiffer in valgus compression than the retrograde supracondylar nail (p < 0.01). The torsional stiffness of the plate and screw implant was significantly higher, 1.6 times that of the nail. Clinically, the most important and common cause of implant failure is varus loadings due to loss of medial cortical contact. Although the retrograde nail was less rigid in other physiologically less critical modes of loading, it had a rigidity comparable to that of the plate in varus loading. Therefore, a supracondylar nail may be considered a mechanically possible alternative to plate fixation.

Biomechanical Phenomena↗