Segmental avascularity of the humeral diaphysis after reamed intramedullary nailing.

Although the clinical experience with reamed intramedullary nailing has been successful for the treatment of femur and tibia fractures, similar success has not been duplicated when this technique has been applied in the humerus. Although the cortical vascular response to nailing of the humerus is presently assumed to be similar to that of the femur, the response of the humerus to reaming has not been documented in vivo. The following case depicts avascularity of the humeral diaphyseal cortex as a complication of reamed intramedullary nailing and illustrates the sensitivity of the humerus to this treatment.

Strength recovery in fractured sheep tibia treated with a plate or an internal fixator: an experimental study with a two-year follow-up.

OBJECTIVES: Comparison of fracture healing with two different implants: a conventional Dynamic Compression Plate (DCP) and a new internal Point Contact Fixator (PC-Fix). DESIGN: Randomized, prospective study in experimental animals. Observation times: 12, 24, 48 and 96 weeks, with six sheep per group. SETTING: Following surgery, animals were kept with unrestricted weight-bearing in individual stalls for 12 weeks, thereafter in groups. ANIMALS: 56 adult Swiss mountain sheep. INTERVENTION: A standardized oblique fracture of the sheep tibia was reduced and compressed by a lag screw and "neutralized" with one of the implants. MAIN OUTCOME MEASUREMENTS: Standard radiographs were used for callus size measurements. After sacrifice the implant was removed and both the treated bone and the contralateral bone were tested for static strength in bending with the plate side under tension. Broken bones were processed for histological evaluation. RESULTS: In the DCP group all six bones failed through the original fracture at 12 weeks. At 24 and 48 weeks two out of six, at 96 weeks one out of six bones failed through the original fracture, others through one of the screw holes. In the PC-Fix group there were no failures through the original fracture with a single exception at 96 weeks. The strength values in the PC-Fix groups of 12 and 96 weeks were significantly higher then in the corresponding DCP groups. CONCLUSIONS: Healing of simple diaphysial fractures treated by PC-Fix was superior to that achieved by conventional plating. The histological evaluation suggested that the observed differences can be accounted for by the absence of implant-related cortical necrosis and by the circumferentially uninterrupted (if smaller) callus in the PC-Fix group.

A simple technique for creating hybrid fixators using a modified AO single adjustable clamp.

Hybrid external fixators with limited internal fixation have become popular in the treatment of complex intraarticular fractures of the tibia. A wide variety of hybrid external fixation systems are commercially available, but these frames are expensive and not always readily available. The authors present a simple hybrid frame constructed from the AO tubular and Ilizarov type external fixator sets using a modified AO single adjustable clamp. This hybrid frame is easy to apply, versatile, and significantly less expensive than other commercially available adaptors and frames.

The torsional strength of bones with residual screw holes from plates with unicortical and bicortical purchase.

OBJECTIVE: To evaluate the effect of unicortical and bicortical screw holes on residual bone strength by comparing the in vitro torsional strength of cadaveric sheep tibiae with screw holes from plates with unicortical and bicortical purchase relative to each other and to intact bone. DESIGN: The paired tibiae were grouped randomly and torsion tested to failure as follows: Group I -- unicortical screw holes versus intact bone; Group II -- bicortical screw holes versus intact bone; and Group III -- bicortical versus unicortical screw holes. BACKGROUND: Recently the point contact fixator, or PC-Fix (using screws with unicortical purchase), was designed to minimize bone devascularization beneath the plate compared to the conventional dynamic compression plate, or DCP (bicortical purchase), and possibly reduce refracture rates after plate removal. However, the effects of unicortical versus bicortical residual screw holes on potential refracture are unknown. METHODS: Screw holes were drilled and tapped through either a 7-hole bicortical DCP or a unicortical PC-Fix in 18 paired cadaveric sheep tibiae. The bones were then tested in torsion. RESULTS: The average decreases in the torsional strength of unicortical screw holes versus intact bone, bicortical screw holes versus intact bone, and bicortical versus unicortical screw holes were 21.6, 31.4, and 26.7% respectively. Mean torque values to failure were statistically significant within each of the three groups: P<0.01, 0.001, and 0.001 respectively. CONCLUSIONS: Bones with unicortical screw holes are significantly weaker in torsion than intact bones, but significantly stronger than bones with bicortical holes. RELEVANCE: Refracture after hardware removal is a recognized clinical complication of the traditional bicortical screw fixation. In combination with the demonstrated biological advantages, implants with unicortical purchase may be associated with less risk for early refracture upon removal.

The pinless external fixator--relevance of experimental results in clinical applications.

The pinless external fixator was intended as a stable, temporary, minimally invasive fixator for severe tibial fractures ensuring safer conversion to an intramedullary nail. An in vitro study showed that the pinless fixator was mechanically not as stiff as the conventional AO tubular device, the main problem being low axial stiffness. This study involving initial clinical trials with the pinless fixator on tibial fractures in St. Gall is based on the experimental work and previous clinical experience of the main author. From June 1992 to June 1994 10 tibial fractures (eight II degrees and III degrees open, one closed with compartment syndrome, one infected non-union) were temporarily stabilized with a pinless fixator. In another patient a calcaneal traction device was applied. The pinless fixator was applied immediately in eight cases and three times as a secondary measure. All patients were scheduled for a secondary change of treatment. The tibiae were stabilized with four clamps and one anterior rod. The clamps were inserted via transverse stab incisions. Intraoperatively the pinless fixator was easy to handle and complications did not occur. Seven different surgeons needed an average of 20 minutes for insertion. Postoperative care was the same as for conventional fixators. Six patients were treated secondarily with an i.m. nail, three with an external fixator on average after 12 days. One patient died on day 1. The pinless fixator failed twice in one patient (incorrect insertion, fall). Reversible pain in the tendons of the foot extensor muscles was noticed. One superficial clamp track infection was seen. All clamps were reused more than three times. The pinless fixator is stable enough for temporary fracture fixation of the tibia in a four clamp one bar construction. A prerequisite for stability is the proper application technique ("grab test", rocking movements). Weight-bearing should be limited to a minimum and needs a compliant patient. The application technique is easy to learn suggesting that the pinless fixator could be an ideal tool for emergency stabilization. The primary application of this fixator leaves all further treatment modalities open (repeated debridements, evaluation of the open fracture). It may also be of particular value to many clinicians working with reamed nails as their only secondary treatment option for open tibial fractures.

Mechanical properties of the Pinless external fixator on human tibiae.

UNLABELLED: In the treatment of either acute severe open tibial fractures or their sequelae, a convenient external fixator is desirable. The conventional transosseous fixation with pins entering the medullary cavity is associated with problems such as pin loosening and pin track infection. Due to the bacterial contamination of the medullary space via the pin track the change of treatment from primary external fixation to secondary medullary nailing is an infection risk. In order to minimize these problems an external clamp fixator, the Pinless, was created. Medullary penetration is avoided by substitution of the conventional pins with clamps. The latter are inserted by hand (removable handles) and anchored only in the bone cortex. The medullary cavity stays intact. But is this clamp fixation stable enough for clinical use? MATERIAL AND METHODS: On paired human cadaver tibiae, we compared the mechanical properties of the experimental Pinless, the conventional AO-tubular fixator and the Ultra-X fixator. Clamps differing in size (small/large) and material (steel/titanium) were used and compared to Schanz screws (steel, 5.0 mm diameter). We measured the stiffness of comparable configurations (1 or 2 bars) under axial compression, four-point-bending in two planes, and torsion. The pull-out force of the different clamps in relation to the bone diameter and number of rocking movements during insertion was also determined. RESULTS: The Pinless configurations with small clamps and 1 bar showed stiffness values as follows (as a percentage of the corresponding AO-tubular fixator): 42/36% (steel/titanium clamp) axial stiffness, 61/43% bending stiffness perpendicular to the reference plane, 78/79% bending stiffness parallel to the reference plane, and 90/95% torsional stiffness. The corresponding Ultra-X device was not as stiff as the Pinless. The use of two longitudinal rods increased the relative stiffness only under axial compression. The mean pull-out force on the proximal tibia was 1011 N for the small steel clamp, 717 N for the large steel clamp, 681 N for the small and 777 N for the large titanium clamp. At the lowest tibial diameter the values were reduced by 10 to 43%. The rocking movements doubled the pull-out force, e.g. there was a pull-out force for the large clamp of 600 N with five rocking movements compared to 310 N without. DISCUSSION: The Pinless was not as stiff as the conventional AO-tubular device but stiffer than the clinically used Ultra-X, especially in sagittal bending, the main load on a tibial fracture in the first weeks after trauma.(ABSTRACT TRUNCATED AT 400 WORDS)