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Failure of femoral head fixation: a cadaveric analysis of lag screw cut-out with the Gamma locking nail and the AO dynamic hip screw
ltjury
Vol.
29, No.
7, p. 569, 1998
0 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain ooze-1383198 $19.00+0.00
ELSEVIER
Letter to the Editor Injury,
Vol. 29, No. 7, 569, 1998
PII: SOO20-13&X3(98)00131-4
Failure of femoral head fixation: a cadaveric analysis of lag screw cut-out with the Gamma locking nail and the A0 dynamic hip screw The study of Haynes et al.’ on cut-out rates for 24 cadaveric femoral heads, implied that the Gamma nail had a lower risk of cut-out compared with the sliding hip screw (SHS). In addition there was bending of the lag screw in 5 out of 12 SHS cases. These results achieved in the laboratory do not equate to what is found in viz10 where both implants have been extensively evaluated. A summation of all randomised trials comparing the Gamma nail with the SHS,’ found a cut-out rate of 33 out of 951 cases (3.5%) for the Gamma nail and 31 out of 967 (3.2%) for the SHS. Furthermore, breakage or bending of the SHS lag screw is exceptionally rare. For the last 1148 SHS fixations performed in Peterborough there have been no observed cases of the lag screw bending or breaking. The conclusion of the study of Haynes and colleagues should therefore not be that the implants have a different risk of cut-out or breakage, but that cadaveric testing of dynamic hip fixation implants does not reflect what occurs in zlizjo. Martyn
J. Parker
References 1 Haynes R. C., Piill R. G., Miles Failure of femoral head fixation:
A. W. and Weston a cadaveric analysis
R. of
lag screw cut-out with the gamma locking nail and the A0 dynamic hip screw. Itzjury 1997: 28: 337-341. 2 Parker M. J., Handoll H. H. and Robinson C. M. Gamma nail versus Sliding Hip Screw for the treatment of extracapsular femoral fractures. In: Gillespie W. J., Madhok R., Murray G. D., Robinson C. M. and Swiontkowski M. F., eds. Musmloskeletal Injuries Module of the Cockrane Database of Systematic Rez&ws. Available in the Cochrane Library (database on disc and CD-ROM). The Cochrane Collaboration; issue 4. Oxford Update Software: 1997.
PII: SOO20-1383(98)00132-6 Authors reply We thank Mr Parker for his comments. We would, however, like to stress that our study was a controlled in vitro study on paired cadaveric bone. The implants were randomly assigned to left and right femoral heads and all were implanted by the same surgeon who had substantial clinical experience with both types of implants. We agree that lag screw bending is a rare clinical experience with the DHS, however, we only observed this in hard bone (5 out of 12 paired samples) which is not typical of the soft osteoporotic bone in which hip fractures occur. We did state that the failure mode in soft osteoporotic bone was entirely due to screw cut out and not bending. We further stand by our conclusion that in paired bone, the Gamma Nail demonstrated a higher resistance to screw cut out than the DHS. A. W. Miles
and R. C. Haynes
Vol.
29, No.
7, p. 569, 1998
0 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain ooze-1383198 $19.00+0.00
ELSEVIER
Letter to the Editor Injury,
Vol. 29, No. 7, 569, 1998
PII: SOO20-13&X3(98)00131-4
Failure of femoral head fixation: a cadaveric analysis of lag screw cut-out with the Gamma locking nail and the A0 dynamic hip screw The study of Haynes et al.’ on cut-out rates for 24 cadaveric femoral heads, implied that the Gamma nail had a lower risk of cut-out compared with the sliding hip screw (SHS). In addition there was bending of the lag screw in 5 out of 12 SHS cases. These results achieved in the laboratory do not equate to what is found in viz10 where both implants have been extensively evaluated. A summation of all randomised trials comparing the Gamma nail with the SHS,’ found a cut-out rate of 33 out of 951 cases (3.5%) for the Gamma nail and 31 out of 967 (3.2%) for the SHS. Furthermore, breakage or bending of the SHS lag screw is exceptionally rare. For the last 1148 SHS fixations performed in Peterborough there have been no observed cases of the lag screw bending or breaking. The conclusion of the study of Haynes and colleagues should therefore not be that the implants have a different risk of cut-out or breakage, but that cadaveric testing of dynamic hip fixation implants does not reflect what occurs in zlizjo. Martyn
J. Parker
References 1 Haynes R. C., Piill R. G., Miles Failure of femoral head fixation:
A. W. and Weston a cadaveric analysis
R. of
lag screw cut-out with the gamma locking nail and the A0 dynamic hip screw. Itzjury 1997: 28: 337-341. 2 Parker M. J., Handoll H. H. and Robinson C. M. Gamma nail versus Sliding Hip Screw for the treatment of extracapsular femoral fractures. In: Gillespie W. J., Madhok R., Murray G. D., Robinson C. M. and Swiontkowski M. F., eds. Musmloskeletal Injuries Module of the Cockrane Database of Systematic Rez&ws. Available in the Cochrane Library (database on disc and CD-ROM). The Cochrane Collaboration; issue 4. Oxford Update Software: 1997.
PII: SOO20-1383(98)00132-6 Authors reply We thank Mr Parker for his comments. We would, however, like to stress that our study was a controlled in vitro study on paired cadaveric bone. The implants were randomly assigned to left and right femoral heads and all were implanted by the same surgeon who had substantial clinical experience with both types of implants. We agree that lag screw bending is a rare clinical experience with the DHS, however, we only observed this in hard bone (5 out of 12 paired samples) which is not typical of the soft osteoporotic bone in which hip fractures occur. We did state that the failure mode in soft osteoporotic bone was entirely due to screw cut out and not bending. We further stand by our conclusion that in paired bone, the Gamma Nail demonstrated a higher resistance to screw cut out than the DHS. A. W. Miles
and R. C. Haynes