Research Article| Volume 23, SUPPLEMENT 3, S28-S43, 1992

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5. Mechanical properties of the Pinless external fixator on human tibiae

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      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): Math Eq % (steel/titanium clamp) axial stiffness, Math Eq % bending stiffness perpendicular to the reference plane, Math Eq % bending stiffness parallel to the reference plane, and Math Eq % 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 suffer than the clinically used Ultra-X, especially in sagittal bending, the main load on a tibial fracture in the first weeks after trauma. A certain number of rocking movements improve the anchorage of the clamps in the cortex tremendously. In clinical trials the Finless appeared to be mechanically sufficient for temporary tibial fracture stabilisation in patients not bearing weight and for support of the lower leg during management of soft tissue traumata (burn injury, compartment syndrome, soft tissue reconstruction). Furthermore, the clamp proved ideal as a traction device.
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        • Aho AJ
        • Nieminen SJ
        • Nylamo El
        External fixation by Hoffmann-Vidal-Adrey osteotaxis for severe tibial fractures.
        Clin. Orthop. 1983; 181: 154-164
        • Bastiani G.De
        • Aldeghieri R
        • Brivio LR
        The treatment of fractures with a dynamic axial fixator.
        J. Bone Joint Surg. 1984; 66B: 538-545
        • Behrens F
        • Johnson WD
        • Koch TW
        • Kovacevic N
        Bending stiffness of unilateral and bilateral fixator frames.
        Clin. Orthop. 1983; 178: 103-110
        • Behrens F
        • Searls K
        External fixation of the tibia. Basic concepts and prospective evaluation.
        J. Bone Joint Surg. 1986; 68B: 246-254
        • Behrens F
        • Johnson W
        Unilateral external fixation. Methods to increase and reduce frame stiffness.
        Clin. Orthop. 1989; 241: 15-23
        • Blachut PA
        • Meek RN
        • O'Brien PJ
        External fixation and delayed intramedullary nailing of open fractures of the tibial shaft A sequential protocol.
        J. Bone Joint Surg. 1990; 72A: 729-735
        • Bone L
        • Johnson K
        Treatment of tibial fractures by reaming and intramedullary nailing.
        J. Bone Joint Surg. 1986; 68A: 877-887
        • Braune W
        • Fischer O
        Über den Schwerpunkt des menschlichen Körpers mit Rücksicht auf die Ausrüstung des deutschen Infanteristen.
        Abhandlung K.Sächs, 1889
        • Braune W
        • Fischer O
        Maquet PGJ Furlong R On the centre of gravity of the human body. Springer Verlag, 1985
        • Briggs BT
        • Chao EYS
        The mechanical performance of the standard Hoffmann-Vidal external fixation apparatus.
        J. Bone Joint Surg. 1982; 64A: 566-573
        • Brooker AF
        Biomechanics of external fixation.
        in: Brooker AF Principles of external fixation. Williams and Wilkins, Baltimore1983: 165-199
        • Burstein AH
        • Currey I
        • Frankel VH
        Bone strength: The effect of screw holes.
        J. Bone Joint Surg. 1972; 54A: 1143-1156
        • Chao EYS
        • Aro HT
        • Lewallen DG
        • Kelly PJ
        The effect of rigidity on fracture healing in external fixation.
        Clin. Orthop. Rel. Res. 1989; 241: 24-35
        • Churches AE
        • Tanner KE
        • Harris JD
        The Oxford external fixator: Fixator stiffness and the effects of bone pin loosening.
        MEP Ltd. 1985; 14: 3-11
        • Claes L
        • Burri H
        • Gerngross H
        Vergleichende Stabilitätsuntersuchungen an symmetrischen und einseitig ventromedialen Fixateur-externe-Osteosynthesen an der Tibia.
        Unfallchirurgie. 1981; 7: 194-197
        • Claudi B
        • Oedekoven G
        Biologische Osteosynthesen.
        Der Chirurg. 1991; 62: 367-377
        • Edwards CC
        Staged reconstruction of complex open tibial fractures using Hoffmann external fixation.
        Clin. Orthop. 1983; 178: 130-161
        • Edwards CC
        • Simmons SC
        • Browner BD
        • Weigel MC
        Severe open tibial fractures. Results treating 202 injuries with external fixation.
        Clin. Orthop. 1988; 230: 98-115
        • Etter C
        • Burri C
        • Claes L
        • Kinzl Raible M
        Treatment by external fixation of open fracture associated with severe soft tissue damage of the leg.
        Clin. Orthop. 1983; 178: 80-87
        • Evans M
        • Kenwright J
        • Tanner KE
        Analysis of single-sided external fracture fixation.
        Engineering Med. 1979; 8: 133-137
        • Finlay JL
        • Eng P
        • Moroz TK
        • Rorabeck CH
        • Davey JR
        • Bourne RB
        Stability of ten configurations of the Hoffmann external fixation frame.
        J. Bone Joint Surg. 1987; 69A: 734-744
        • Fischer MD
        • Gustilo RB
        • Varecka TF
        The time of flap coverage, bone grafting and intramedullary nailing in patients who have a fracture of the tibial shaft with extensive soft tissue injury.
        J. Bone Joint Surg. 1991; 73A: 1316-1322
        • Frigg R.
        Pinless external fixator.
        1992 (International patent, pending)
        • Green SA
        Complications of external skeletal fixation.
        Clin. Orthop. Rel. Res. 1983; 180: 110-116
        • Gustilo RR
        • Anderson JT
        Prevention of infection in the treatment of one-thousand and twenty-five open fractures of long bones.
        Joint Surg. 1976; 58A: 453-458
        • Hammer R
        External fixation of tibial shaft fractures. A review of 42 fractures treated by the Hoffmann-Vidal-Adrey external fixation system.
        Arch. Orthop. Trauma Surg. 1985; 104: 271-274
        • Hecht P
        Ausreisstests mit Schanzschen Schrauben.
        Internal Report. 1990;
        • Johnson EE
        • Marder RA
        Open intramedullary nailing and bone grafting for non-union of tibial diaphyseal fracture.
        J. Bone Joint Surg. 1987; 69A: 375-380
        • Johnson EE
        • Simpson LA
        • Helfet DL
        Delayed intramedullary nailing after failed external fixation of the tibia.
        Clin. Orthop. Rel. Res. 1990; 253: 251-257
        • Karlstoem G
        • Olerud S
        Percutaneous pin fixation of open tibial fractures.
        J. Bone Joint Surg. 1975; 56B: 915-924
        • Karlstroem G
        • Olerud S
        External fixation of severe open tibial fractures with the Hoffmann frame.
        Clin. Orthop. 1983; 180: 68-78
        • Kempson GE
        • Campbell B
        The comparative stiffness of external fixation frames.
        Injury. 1981; 12: 297-304
        • Mast J
        • Jakob R
        • Ganz R
        Planning and reduction technique in fracture surgery.
        Springer Verlag, 1989
        • Matter Th
        • Rahn BA
        • Cordey J
        • Mikuschka-Galgoczy E
        Die Beziehung zwischen Röntgendichte und maximal erreichbarer Axialkraft von AO-Schrauben im Knochen.
        Unfallheilkunde. 1977; 80: 165-167
        • Maurer DJ
        • Merkow RL
        • Gustilo RB
        Infection after intramedullary nailing of severe open tibial fractures initially treated with external fixation.
        J. Bone Joint Surg. 1989; 71A: 835-838
        • McCoy MT
        • Chao EYS
        • Kasman RA
        Comparison of mechanical performance in four types of external fixators.
        Clin. Orthop. 1983; 180: 23-33
        • McGraw JM
        • Lim EVA
        Treatment of open tibial shaft fractures. External fixation and secondary intramedullary nailing.
        J. Bone Joint Surg. 1988; 70A: 900-911
        • Moroz TK
        • Finlay JB
        • Rorabeck CH
        • Bourne RB
        External fixation: Choosing a system based on biomechanical stability.
        J. Orthop. Trauma. 1989; 24: 284-296
        • Müller ME
        • Allgöwer M
        • Schneider R
        • Willenegger H
        Manual of internal fixation. Springer Verlag, Heidelberg1977
        • Müller ME
        • Allgöwer M
        • Schneider R
        • Willenegger H
        Manual of internal fixation. Springer Verlag, 1991: 367
        • Oedekoven G
        • Ascherl R
        • Scherer M
        • Langhammer H
        • Güssregen B
        • Blümel G
        Die unaufgebohrte Marknagelung: Vorteile bei der corticalen und medullären Vaskularisation? Experimentelle Untersuchungen am Hund.
        in: Chirurgisches Forum 1992 für experim. u. klin. Forschung. Springer Verlag, Heidelberg1992: 73-76
        • Puno RM
        • Teynor JT
        • Nagano J
        • Gustilo RB
        Critical analysis of the results of treatment of 201 tibial shaft fractures.
        Clin. Orthop. 1986; 212: 113-121
        • Raschke M
        • Mann J
        • Oedekoven G
        • Claudi B
        Segmental transport after unreamed tibial nailing. The monorail procedure: A preliminary report.
        Clin. Orthop. Rel. Res. Sept. 1992; (in press)
        • Rommens P
        • Broos P
        • Gruwez JA
        External fixation of tibial shaft fractures with severe soft tissue injuries by Hoffmann-Vidal-Adrey osteotaxis.
        Arch. Orthop. Trauma Surg. 1986; 105: 170-174
        • Törnqvist H
        Tibia nonunions treated by interlocked nailing: Increased risk of infection after previous external fixation.
        J. Orthop. Trauma. 1990; 4: 109-114
        • Tscherne H
        • Oestern H.I.
        Die Klassifizierung des Weichteilschadens bei offenen und geschlossenen Frakturen.
        Unfallheilkunde. 1982; 85: 111-115
        • Wu JJ
        • Shyr HS
        • Chao EYS
        • Kelly PJ
        Comparison of osteotomy healing under external fixation devices with different stiffness characteristics.
        J. Bone Joint Surg. 1984; 66A: 1258-1264