Dynamization at the near cortex in locking plate osteosynthesis by means of dynamic locking screws: an experimental study of transverse tibial osteotomies in sheep.

BACKGROUND: Locking plates are widely used in fracture fixation, mainly for meta-diaphyseal fractures, comminuted fractures, fractures with a critical-size bone defect, periprosthetic fractures, osteotomies, and fractures in osteoporotic bone. The aim of this animal study was to evaluate the effect on bone-healing of dynamization of locking plate constructs by means of new 5.0-mm dynamic locking screws (in the DLS group), which allow near-cortex micromotion, compared with a more rigid construct utilizing standard bicortical locking-head screws (in the LS group). Use of dynamic locking screws allows modulation of the stiffness of existing locking compression plate systems via parallel interfragmentary micromotion. METHODS: A standardized diaphyseal tibial osteotomy (90°, 3-mm fracture gap) was performed and stabilized with a six-hole large-fragment locking compression plate in twelve female sheep (six in each group). Radiographs were made postoperatively and then weekly from week three until sacrifice at nine weeks. Macroscopic, biomechanical, histologic, and radiographic assessments and microcomputed tomography were performed. RESULTS: The callus in the tested specimens in the DLS group had better biomechanical stability, with a significantly greater maximum failure moment (mean and standard deviation [SD] as a percentage of intact, 55.15 ± 20.65 compared with 26.80 ± 14.96 in the LS group; p = 0.021). The DLS group also had greater periosteal callus volume at the near cortex (mean volume and SD as a percentage of the tibial shaft volume, 36.21% ± 10.08% compared with 18.98% ± 8.61% in the LS group; p = 0.026) and in the intercortical region (mean volume and SD as a percentage of the bone volume of the tibial shaft, 3.56% ± 0.52% compared with 2.64% ± 0.98% in the LS group; p = 0.045), as shown by microcomputed tomography. The DLS group also had significantly greater torsional stiffness (mean and SD as a percentage of intact, 84.88 ± 13.51 compared with 58.89 ± 20.61 in the LS group; p = 0.027). CONCLUSIONS: Controlled micromotion and nearly homogeneous interfragmentary strain at the fracture site, together with the stable bicortical fixation achieved by the new dynamic locking screw, led to more uniform callus formation, significantly more callus formation at the near cortex, and biomechanically more competent bone-healing compared with use of rigid locking plate constructs with locking-head screws.

The dynamisation of locking plate osteosynthesis by means of dynamic locking screws (DLS)-an experimental study in sheep.

In this in vivo study a new generation of locking screws was tested. The design of the dynamic locking screw (DLS) enables the dynamisation of the cortex underneath the plate (cis-cortex) and, therefore, allows almost parallel interfragmentary closure of the fracture gap. A 45° angle osteotomy was performed unilaterally on the tibia of 37 sheep. Groups of 12 sheep were formed and in each group a different osteotomy gap (0, 1 and 3mm) was fixed using a locking compression plate (LCP) in combination with the DLS. The healing process was monitored radiographically every 3 weeks for 6, respectively 12 weeks. After this time the sheep were sacrificed, the bones harvested and the implants removed. The isolated bones were evaluated in the micro-computed tomography unit, tested biomechanically and evaluated histologically. The best results of interfragmentary movement (IFM) were shown in the 0mm configuration. The bones of this group demonstrated histomorphometrically the most distinct callus formation on the cis-cortex and the highest torsional stiffness relative to the untreated limb at 12 weeks after surgery. This animal study showed that IFM stimulated the synthesis of new bone matrix, especially underneath the plate and thus, could solve a current limitation in normal human bone healing. The DLS will be a valuable addition to the locking screw technology and improve fracture healing.

Rotator cuff muscles lose responsiveness to anabolic steroids after tendon tear and musculotendinous retraction: an experimental study in sheep.

BACKGROUND: Long-standing rotator cuff tendon tearing is associated with retraction, loss of work capacity, irreversible fatty infiltration, and atrophy of the rotator cuff muscles. Although continuous musculotendinous relengthening can experimentally restore muscular architecture, restoration of atrophy and fatty infiltration is hitherto impossible. HYPOTHESIS: Continuous relengthening with pharmacological stimulation of muscle growth using an anabolic steroid or insulin-like growth factor (IGF) can reverse atrophy and fatty infiltration as well as improve the work capacity of chronically retracted rotator cuff muscles in sheep. STUDY DESIGN: Controlled laboratory study. METHODS: Sixteen weeks after tenotomy of the infraspinatus (ISP) tendon, atrophy and fatty infiltration had developed in the retracted ISP muscle. The musculotendinous unit was continuously relengthened in 14 sheep during 6 weeks: Four sheep were treated without pharmacological stimulation, 4 with intramuscular administration of an anabolic steroid, and 6 with IGF before final repair and rehabilitation (12 weeks). Changes were documented by intraoperative measurements of muscle work capacity, histology, and computed tomography/magnetic resonance imaging. RESULTS: Musculotendinous relengthening by continuous traction resulted in gains of length ranging from 0.7 cm in the IGF group to 1.3 cm in the control group. Fatty infiltration progressed in all groups, and the muscle's cross-sectional area ranged from 71% to 74% of the contralateral side at sacrifice and did not show any differences between groups in weight, volume, histological composition, or work capability of the muscle. The contralateral muscles in the anabolic steroid group, however, showed significantly higher (mean ± standard deviation) muscle work capacity of 10 ± 0.9 N·m than the contralateral muscles of the control group (6.8 ± 2.4 N·m) (P < .05). This was accompanied by an increased mean muscle fiber area as well as by an unusual gain in the animals' weight after injection of the anabolic steroid. CONCLUSION: Subcutaneous continuous relengthening of a chronically retracted musculotendinous unit is feasible and advances the retracted musculotendinous junction toward its original position. This does not change the muscle work capacity. Whereas anabolic steroids have been shown to be effective in preventing classic degenerative muscle changes after tendon tears, neither an anabolic steroid nor IGF contributes to regeneration of the muscle once degenerative changes are established. CLINICAL RELEVANCE: The findings demonstrate that muscle cells lose reactiveness to an anabolic steroid and IGF once retraction has led to fatty infiltration and atrophy of the muscle. Retraction of the muscle after tendon tears must be avoided by early repair, particularly in an athlete, as no regeneration can be achieved by mechanical or pharmacological means at this time.

Device for lengthening of a musculotendinous unit by direct continuous traction in the sheep.

BACKGROUND: Retraction, atrophy and fatty infiltration are signs subsequent to chronic rotator cuff tendon tears. They are associated with an increased pennation angle and a shortening of the muscle fibers in series. These deleterious changes of the muscular architecture are not reversible with current repair techniques and are the main factors for failed rotator cuff tendon repair. Whereas fast stretching of the retracted musculotendinous unit results in proliferation of non-contractile fibrous tissue, slow stretching may lead to muscle regeneration in terms of sarcomerogenesis. To slowly stretch the retracted musculotendinous unit in a sheep model, two here described tensioning devices have been developed and mounted on the scapular spine of the sheep using an expandable threaded rod, which has been interposed between the retracted tendon end and the original insertion site at the humeral head. Traction is transmitted in line with the musculotendinous unit by sutures knotted on the expandable threaded rod. The threaded rod of the tensioner is driven within the body through a rotating axis, which enters the body on the opposite side. The tendon end, which was previously released (16 weeks prior) from its insertion site with a bone chip, was elongated with a velocity of 1 mm/day. RESULTS: After several steps of technical improvements, the tensioner proved to be capable of actively stretching the retracted and degenerated muscle back to the original length and to withstand the external forces acting on it. CONCLUSION: This technical report describes the experimental technique for continuous elongation of the musculotendinous unit and reversion of the length of chronically shortened muscle.

Osseointegration and biocompatibility of different metal implants--a comparative experimental investigation in sheep.

BACKGROUND: In the present study, 4 different metallic implant materials, either partly coated or polished, were tested for their osseointegration and biocompatibility in a pelvic implantation model in sheep. METHODS: Materials to be evaluated were: Cobalt-Chrome (CC), Cobalt-Chrome/Titanium coating (CCTC), Cobalt-Chrome/Zirconium/Titanium coating (CCZTC), Pure Titanium Standard (PTST), Steel, TAN Standard (TANST) and TAN new finish (TANNEW). Surgery was performed on 7 sheep, with 18 implants per sheep, for a total of 63 implants. After 8 weeks, the specimens were harvested and evaluated macroscopically, radiologically, biomechanically (removal torque), histomorphometrically and histologically. RESULTS: Cobalt-Chrome screws showed significantly (p = 0.031) lower removal torque values than pure titanium screws and also a tendency towards lower values compared to the other materials, except for steel. Steel screws showed no significant differences, in comparison to cobalt-chrome and TANST, however also a trend towards lower torque values than the remaining materials. The results of the fluorescence sections agreed with those of the biomechanical test. Histomorphometrically, there were no significant differences of bone area between the groups. The BIC (bone-to-implant-contact), used for the assessment of the osseointegration, was significantly lower for cobalt-chrome, compared to steel (p = 0.001). Steel again showed a lower ratio (p = 0.0001) compared to the other materials. CONCLUSION: This study demonstrated that cobalt-chrome and steel show less osseointegration than the other metals and metal-alloys. However, osseointegration of cobalt-chrome was improved by zirconium and/or titanium based coatings (CCTC, TANST, TAN, TANNEW) being similar as pure titanium in their osseointegrative behavior.

The influence of different osteosynthesis configurations with locking compression plates (LCP) on stability and fracture healing after an oblique 45° angle osteotomy.

BACKGROUND: Locking compression plates are used in various configurations with lack of detailed information on consequent bone healing. STUDY DESIGN: In this in vivo study in sheep 5 different applications of locking compression plate (LCP) were tested using a 45° oblique osteotomy simulating simple fracture pattern. 60 Swiss Alpine sheep where assigned to 5 different groups with 12 sheep each (Group 1: interfragmentary lag screw and an LCP fixed with standard cortex screws as neutralisation plate; Group 2: interfragmentary lag screw and LCP with locking head screws; Group 3: compression plate technique (hybrid construct); Group 4: internal fixator without fracture gap; Group 5: internal fixator with 3mm gap at the osteotomy site). One half of each group (6 sheep) was monitored for 6 weeks, and the other half (6 sheep) where followed for 12 weeks. METHODS: X-rays at 3, 6, 9 and 12 weeks were performed to monitor the healing process. After sacrifice operated tibiae were tested biomechanically for nondestructive torsion and compared to the tibia of the healthy opposite side. After testing specimens were processed for microradiography, histology, histomorphometry and assessment of calcium deposition by fluorescence microscopy. RESULTS: In all groups bone healing occurred without complications. Stiffness in biomechanical testing showed a tendency for higher values in G2 but results were not statistically significant. Values for G5 were significantly lower after 6 weeks, but after 12 weeks values had improved to comparable results. For all groups, except G3, stiffness values improved between 6 and 12 weeks. Histomorphometrical data demonstrate endosteal callus to be more marked in G2 at 6 weeks. DISCUSSION AND CONCLUSION: All five configurations resulted in undisturbed bone healing and are considered safe for clinical application.

Neer Award 2007: Reversion of structural muscle changes caused by chronic rotator cuff tears using continuous musculotendinous traction. An experimental study in sheep.

HYPOTHESIS: Chronic rotator cuff tears are associated with irreversible architectural muscle changes and a high rate of repair failure. The changes observed in man and their irreversibility with a single stage repair can be reproduced in sheep. It was the purpose of this experiment to test the hypothesis that slow, continuous elongation of a retracted musculotendinous unit allows reversal of the currently irreversible structural muscle changes. MATERIALS AND METHODS: The infraspinatus tendon of 12 sheep was released using a greater tuberosity osteotomy and allowed to retract for 4 months. Then, a new device was mounted on the scapular spine and used to extend the infraspinatus muscuculotendinous unit transcutaneously by 1 mm per day. Thereafter, the tendon was repaired back to the greater tuberosity. We assessed the muscular architecture using magnetic resonance imaging, macroscopic dissection, histology, and electron microscopy. Fatty infiltration (in Hounsfield units 1/4 HU) and muscular cross-sectional area (in % of the control side) were monitored with computed tomography at tendon release, initiation of elongation, repair, and at sacrifice. RESULTS: Sixteen weeks after tendon release, the mean tendon retraction was 29 +/- 6 mm (14% of original length, P = .008). In 8 sheep, elongation was achieved as planned (group I), but in 4, the elongation failed technically (group II). The mean traction time was 24 +/- 6 days with a mean traction distance of 19 +/- 4 mm. At sacrifice, the mean pennation angle in the infraspinatus of group I was not different from the control side (29.8 degrees +/-7.5 degrees vs. 30 degrees +/-6 degrees , P = .575). In group II, the pennation angle had increased from 30 degrees +/-6 degrees to 55 degrees +/-14 degrees (P = .035). There was no fatty infiltration at the time of tendon release. After retraction, there was a significant increase in fatty infiltration of the infraspinatus muscle and a decrease of its cross-sectional area to 57% of the contralateral side (P = .0001). During traction, the degree of fatty infiltration remained unchanged (36 HU to 38 HU, P = .381), and atrophy improved to a muscle square area of 78% of the contralateral side (P = .0001) in group I. In group II, an increase of fatty infiltration was measured from 36 HU to 28 HU; however, this increase was not significant (P = .144). Atrophy did not change in group II (57-55%, P = .946). At sacrifice, the remaining muscle mass was 64% in group I and 46% in group II (P = .019). DISCUSSION: Our preliminary results document, that continuous elongation of a retracted, fatty infiltrated and atrophied musculotendinous unit is technically feasible. CONCLUSION: In the sheep, continuous elongation can lead to restoration of normal muscle architecture, to partial reversal of muscle atrophy, and to arrest of the progression of fatty infiltration. LEVEL OF EVIDENCE: Basic science level 2; Prospective comparative therapeutic study.

Development of the Locking Compression Plate.

The development of the Locking Compression Plate (LCP) reflects the multilateral collaboration of clinicians, researchers, developers and industry. In retrospect, combining two completely different anchorage technologies into one implant is logical and the practical solution is simple. The clinical instructions for the new implant, which severely limited the constructive scope, proved to be critical for the project. Unlike an independent new development, compatibility with existing surgical techniques, instruments and implants had to be maintained. Industrial implementation of the LCP is only possible with the use of state-of-the-art production centres with up to five computer-controlled axes. The unlimited possibility of using the LCP as a compression plate, an internal fixator or in a specific combination allows ideal plate anchorage that is adapted to the bone. Combined with minimally invasive implant technology (MIPO), the indication spectrum of plate osteosynthesis can be expanded in a meaningful manner.