Kinematic adjustability of unilateral external fixators for fracture reduction and alignment of axial dynamization

Bone fracture reduction and bone axial dynamization are important operations which effectiveness can be further enhanced by the use of a unilateral external fixator. By design, axial dynamization can be performed through reciprocating one of its translational joints. However, non-axial dynamization may occur after correcting residual fracture deformity. To explore and to maximize its full potential, the joint adjustment constraint equations for fracture reduction and alignment of axial dynamization under unilateral external fixation are derived. Their physical implications and criteria on the kinematic structure of a fixator are then established. In order to correctly make the alignment of axial dynamization with the proper fracture reduction, this study shows that the linkage of a bone–fixator system should have a minimum of eight degrees-of-freedom (DOFs) with at least two nonparallel rotational DOFs adjacent to both ends of the designated single translational DOF for axial dynamization. Thus, the adjustment of the connection between bone pin/pin clamp of Othofix^® fixator is required, while the alignment of one of the translational joints of Dynafix^® fixator with its bone segment axis during fracture stabilization procedure is a crucial step. A conceptual fixator that requires neither an adjustment of the pin/pin clamp connection nor special pre-alignment is demonstrated. Based on the constraint equations and criteria developed throughout this study, the creation of an effective frame design of external fixation device becomes feasible.     

Development and validation of a new approach for computer-aided long bone fracture reduction using unilateral external fixator

An innovative computer-aided method to plan and execute long bone fracture reduction using Dynafix unilateral external fixator (EF) is presented and validated. A matrix equation, which represents a sequential transformation from proximal to distal ends, was derived and solved for the amount of rotation and translation required at each EF joint to correct for a displaced fracture using a non-linear least square optimization method. Six polyurethane-foam models of displaced fracture tibiae were used to validate the method. The reduction accuracy was quantified by calculating the residual translations (xr, yr, zr), the residual displacement (dr), and the residual angulations (alphar, betar, gammar) based on the X-Y-Z Euler angle convention. The experiment showed that the mean+/-S.D. of alphar, betar, gammar, xr, yr, zr and dr were 1.57+/-1.14 degrees, 1.33+/-0.90 degrees, 0.71+/-0.70 degrees, 0.98+/-1.85, 0.80+/-0.67, 0.30+/-0.27, and 0.50+/-0.77 mm, respectively, which demonstrated the accuracy and reliability of the method. Instead of adjusting the fixator joints in-situ, our method allows for off-site adjustment of the fixator joints and employs the adjusted EF as a template to guide the surgeons to manipulate the fracture fragments to complete the reduction process. Success of this method would allow surgeons to perform fracture reduction more objectively, efficiently and accurately yet reduce the radiation exposure to both the involved clinicians and patients and lessen the extent of periosteum and soft tissue disruption around the fracture site.     

Measurement of fracture movement in patients treated with unilateral external skeletal fixation

Axial movement occurring at the fracture site has been determined in a group of healing tibial fractures treated by external skeletal fixation. Fracture movement was determined via a strain gauge transducer which was attached to the column of the external fixator and measured the deflection of the bone screw adjacent to the fracture site and the active loading or weight bearing given by the patient to the fractured limb was monitored using a force platform. The results for 27 subjects show that, with a rigid unilateral fixator, the axial movement occurring at the fracture site was initially small (mean = 0.28 mm at 5 weeks post fracture). This movement increases to reach a mean maximum value of 0.43 mm at 11 weeks post-fracture and then decreases, despite increased weight bearing, as fracture healing progresses. In the early stages of healing, the movement can be increased slightly if the fixator is fitted with a module which permits additional fracture site movement, although the resultant increase in movement is only a small proportion of the potential available with this module.     

Primary correction of the unilateral cleft nasal deformity

An 18-year experience with the management of the unilateral cleft nasal deformity in 1200 patients is presented. A primary cleft nasal correction was performed at the time of lip repair in infancy; a secondary rhinoplasty was done in adolescence after nasal growth was complete. The technical details of the authors' primary cleft nasal correction are described. Exposure was obtained through the incisions of the rotation-advancement design. The cartilaginous framework was widely undermined from the skin envelope. The nasal lining was released from the piriform aperture, and a new maxillary platform was created on the cleft side by rotating a "muscular roll" underneath the cleft nasal ala. The alar web was then managed by using a mattress suture running from the web cartilage to the facial musculature. In 60 percent of cases, these maneuvers were sufficient to produce symmetrical dome projection and nostril symmetry. In the other 40 percent, characterized by more severe hypoplasia of the cleft lower lateral cartilage, an inverted U infracartilaginous incision and an alar dome supporting suture (Tajima) to the contralateral upper cartilage were used. Residual dorsal hooding of the lower lateral cartilage was most effectively managed with this suture. This primary approach to the cleft nasal deformity permits more balanced growth and development of the ala and domal complex. Some of the psychological trauma of the early school years may be avoided. Also, because of the early repositioning of the cleft nasal cartilages, the deformity addressed at the time of the adult rhinoplasty is less severe and more amenable to an optimal final result.     

Computational simulation of bone fracture healing under inverse dynamisation

Adaptive finite element models have allowed researchers to test hypothetical relationships between the local mechanical environment and the healing of bone fractures. However, their predictive power has not yet been demonstrated by testing hypotheses ahead of experimental testing. In this study, an established mechano-biological scheme was used in an iterative finite element simulation of sheep tibial osteotomy healing under a hypothetical fixation regime, “inverse dynamisation”. Tissue distributions, interfragmentary movement and stiffness across the fracture site were compared between stiff and flexible fixation conditions and scenarios in which fixation stiffness was increased at a discrete time-point. The modelling work was conducted blind to the experimental study to be published subsequently. The simulations predicted the fastest and most direct healing under constant stiff fixation, and the slowest healing under flexible fixation. Although low fixation stiffness promoted more callus formation prior to bridging, this conferred little additional stiffness to the fracture in the first 5 weeks. Thus, while switching to stiffer fixation facilitated rapid subsequent bridging of the fracture, no advantage of inverse dynamisation could be demonstrated. In vivo data remains necessary to conclusively test this treatment protocol and this will, in turn, provide an evaluation of the model’s performance. The publication of both hypotheses and their computational simulation, prior to experimental testing, offers an appealing means to test the predictive power of mechano-biological models.     

The residual unilateral cleft lip nasal deformity: a three-phase correction technique

The author presents a three-phase correction technique for the residual unilateral cleft lip nasal deformity. This procedure involves a sculpting excision of the alar rim, use of this alar rim as an interpositional flap in lengthening the columella, and augmentation of the nasal tip and perialar sulcus with a free ear conchal cartilage graft. The concept has been incorporated in the revisionary surgery program of 74 patients over a period of 5 years with a minimal follow-up of 2 years. The majority of the patients are operated on between the ages of 5 and 7 years based on the concept of a need for a "tidy appearance" by first grade.     

Radical correction of secondary nasal deformity in unilateral cleft lip patients presenting late

It is universally acknowledged that correction of a cleft lip nasal deformity continues to be a difficult problem. In developing countries, it is common for patients with cleft lip deformities to present in their early or late teens for correction of severe secondary lip and nasal deformities retained after the initial repairs were carried out in infancy or early childhood. Such patients have never had the benefit of primary nasal correction, orthodontic management, or alveolar bone grafting at an appropriate age. Along with a severe nasal deformity, they present with alveolar arch malalignments and anterior fistulae. In the study presented here, a strategy involving a complete single-stage correction of the nasal and secondary lip deformity was used.In this study, 26 patients (nine male and 17 female) ranging in age from 13 to 24 years presented for the first time between June of 1996 and December of 1999 with unilateral cleft lip nasal deformity. Eight patients had an anterior fistula (diameter, 2 to 4 mm) and 12 patients had a secondary lip deformity. An external rhinoplasty approach was used for all patients. The corrective procedures carried out in a single stage in these patients included lip revision; columellar lengthening; repair of anterior fistula; augmentation along the pyriform margin, nasal floor, and alveolus by bone grafts; submucous resection of the nasal septum; repositioning of lower lateral cartilages; fixation of the alar cartilage complex to the septum and the upper lateral cartilages; augmentation of nasal dorsum by bone graft; and alar base wedge resections. Medial and lateral nasal osteotomies were performed only if absolutely indicated. The median follow-up period was 11 months, although it ranged from 5 to 25 months. Overall results have been extremely pleasing, satisfactory, and stable.In this age group (13 years of age or older), it is not fruitful to use a technique for nasal correction that corrects only one facet of the deformity, because no result of nasal correction can be satisfactory until septal deviations and maxillary deficiencies are addressed along with any alar repositioning. The results of complete remodeling of the nasal pyramid are also stable in these patients because the patients' growth was nearly complete, and all the deformities could be corrected at the same time, leaving no active deforming vector. These results would indicate that aesthetically good results are achievable even if no primary nasal correction or orthodontic management had been previously attempted.     

Primary correction of unilateral cleft lip nasal deformity: a 10-year review

A 10-year follow-up of patients who underwent primary correction of their cleft lip nasal deformity is presented. These are the first 10 consecutive patients who were treated following a change in treatment plan in 1973. Primary correction of the cleft lip nasal deformity essentially consists in elevating the displaced alar cartilage at the time of lip repair. There has been no interference with nasal growth, and the position of the alar cartilages and nasal tip has been maintained.     

Primary correction of unilateral cleft lip nasal deformity in Asian patients: anthropometric evaluation

Previously it was thought that primary correction of nasal deformity in cleft lip patients would cause developmental impairment of the nose. It is now widely accepted that simultaneous correction of the cleft lip nasal deformity has no adverse effect on nasal growth. Thus, the authors tried to evaluate the results of primary correction of cleft lip in Asian patients. Of 412 cases of cleft lip, 195 cases were corrected by means of the conventional method from June of 1992 to June of 1997, and 217 cases were corrected by simultaneous rhinoplasty from July of 1997 to October of 2001. The average patient age was 3 months. Photographs and anthropometric evaluation were used to evaluate the results. Nasal tip projection, columellar length, and nasal width were measured in 60 randomized normal children, 30 randomized children treated with the conventional method, and 30 randomized children with primary nasal repair. Data were analyzed using t tests, and the level of significance was 5 percent (p < 0.05). In cases of simultaneous repair, nasal tip projection and columellar length were increased 24.8 percent and 28.8 percent, respectively. Nasal width was increased 12.3 percent in the cases of simultaneous repair and 12.6 percent in the cases without primary rhinoplasty. Simultaneous repair of cleft lip and nasal deformity in Asian patients showed that more symmetry of nostril and nasal dome projection and better correction of buckling and alar flaring were achieved. More balanced growth and development of the alar complex was achieved, and no interference with nasal growth was encountered.     

Resorbable internal splint: an adjunct to primary correction of unilateral cleft lip-nasal deformity

There is usually some relapse in position of the alar cartilage after primary repair of unilateral cleft lip. Therefore, preoperative or postoperative external splinting has been recommended to supplement either closed or open suspension of the alar cartilage. The authors present a method using a resorbable internal nostril splint to shield the positioned alar cartilage from deformational forces caused by scar, and thus avoiding the problems associated with external splinting. An internal nasal splint was placed in 15 infants during repair of unilateral complete cleft lip and nasal deformity. The nasal morphology was compared with that of 15 control patients who had the same nasolabial procedure without internal splinting. Average follow-up time was 20.4 months (range, 4 to 30 months). Photogrammetric analysis showed that asymmetry of the alar contours averaged 8.6 percent in the splinted patients, as compared with 23 percent for controls (p <0.01). Thus, alar asymmetry was decreased two-thirds in the splinted group. An internal resorbable nasal splint is an adjunct to open alar suspension in primary repair of the unilateral cleft lip nasal deformity. An internal nasal splint protects the corrected alar cartilage longer than an external splint and eliminates drawbacks, such as necrosis, cutaneous depression of the nostril sill, and patient noncompliance. This strategy of temporary internal support of healing cartilage has other applications.     

Nonsurgical correction of nasal deformity in unilateral complete cleft lip: a 6-year follow-up.

Nasal deformity in unilateral cleft lip and palate patients increases with time, tongue malposition being one of the causes. Some authors have emphasized the role of nasal and adjacent facial musculature as active extrinsic agents. Another cause of alar deformity can be the lack of a proper foundation because of a maxillary hypoplasia in the region of the pyriform foramen. If alar collapse occurs, the septum bends convexly toward the cleft side. Tissues are soft and plastic during the neonatal period. Once the infant is about 3 months of age, it becomes difficult to correct the nasal deformity. Therefore, any resource used from the first day, and mainly during the first 15 days of life, will be useful to prevent the increasing deformity and to avoid the surgical correction. A controlled clinical trial was planned to compare the anthropometric measurements of the nasal region in two series of patients with unilateral complete cleft lip. In the first group, we included 44 patients who came to our clinic during the first 2 days of life and the second group consisted of 47 patients who were more than 15 days of age at the time of the first consultation. To provide control data for the evaluation of the results after 6 years of follow-up in both series of cleft patients, we also included a third group of 48 healthy 6-year-old children. A nasal component added to the occlusal prostheses was only used in the first group up to the time of surgery. The same surgeon performed a Millard II procedure with muscular reposition as described by Delaire in all the patients. Nasal measurements taken with a caliper, obtained directly from plaster models by using surface impressions of the babies, were confirmed by a laser three-dimensional measuring device. The statistical comparison between both series showed a significant increase of the columellar length in the first group. A 6-year follow-up to compare growth and cosmetic results of the nose revealed a better and permanent nasal nostril symmetry and no alar cartilage luxation in the patients who had had the nasal component. These results highlight the importance of the early treatment and allow us to suggest the nasal prostheses as a way to prevent the increasing nasal deformity, to help nasal remodeling, to obtain columellar elongation, and to avoid or decrease the need for primary surgery of the cleft nose.     

Rigidity and stress analyses of external fracture fixation devices—A theoretical approach

The rigidity and stresses in external fracture fixation devices were studied by means of the finite element method. Different geometries and material parameters were simulated using a beam element model. Axial, bending and torsional loads were applied through the bone ends and the displacement obtained at the fracture sites was used to calculate the fracture fixation stiffness. The key parameters which increased fixation rigidity were identified. High pin stresses were predicted under certain application conditions. Possible clinical implications for the use of such apparatus are discussed in the light of bone fracture healing. The present results are expected to have a significant impact on future design modifications and clinical applications of this popular instrument in orthopedic surgery and traumatology.     

Design and experimental evaluation of adjustable bone plates for mandibular fracture fixation

Conventional bone plates are commonly used for surgical mandibular fracture fixation. Improper alignment between bone segments, however, can result in malocclusion. Current methods of fixation require a surgeon to visually align segments of bone and affix a metal plate using bone screws, after which little can be done to adjust alignment. A method of adjusting fracture alignment after plate placement, without screw removal, presents an improvement over costly and risky revision surgery. A modified bone plate has been designed with a deformable section to give surgeons the ability to reduce misalignments at the fracture site. The mechanics of deformation for various adjustment mechanisms was explored analytically, numerically, and experimentally to ensure that the adjustable plate is comparable to conventional bone plates. A static force of 358.8 N is required to deform the adjustable bone plate, compared with predicted values of 351 N using numerical simulation and 362 N using a simple beam theory. Dynamic testing was performed to simulate in vivo loading conditions and evaluate load-capacity in both deformed and un-deformed bone plates. Results indicate that bending stiffness of a rectangular bone plate is 709 N/mm, compared with 174 N/mm for an octagonal plate and 176 N/mm for standard plates. Once deformed, the rectangular and octagonal plates had a stiffness of 323 N/mm and 228 N/mm, respectively. Un-deformed and deformed adjustable bone plates have efficacy in bone segment fixation and healing.