1. SLIDING HIP SCREW FIXATION FOR PROXIMAL FEMUR FRACTURES: AN ANALYSIS OF THE PREDICTIVE FACTORS OF FAILURE
Dr Tao Shan Lim MBBS Grad Dip Surg Anat
Mr Karl Stoffel MD
Dr Rochelle Nicholls PhD
Dr Bianca Billik MBBS
Fremantle Orthopaedic Unit
Fremantle Hospital
Western Australia
Mr Chairman, ladies and gentlemen, this paper is a radiological analysis of failures of sliding hip screw fixation from a series of 731 proximal femur fractures.

2. The Sliding Hip Screw Trochanteric region #’s
Maximises healing potential
Elderly / co-morbidities
The sliding hip screw is designed for fractures of the neck and trochanteric region of the proximal femur. The patients are often elderly with multiple co-morbidities and are not a good candidates for re-operation.

3. Failure 8 – 23% Bone quality Fragment geometry Reduction
Implant placement
Thus it’s concerning that the literature reports failure rates of between 8 and 23 percent, which is quite a high figure. Several predictive factors have been proposed however there is no clear consensus as to which is most important.
Kaufer, Clinical Orthopaedics 1980, Jan-Feb:53–61.
Dodds & Baumgaertner, Current Opinion in Orthopedics 2004, Feb:12-17

4. Baumgaertner, 1995 Tip – Apex Distance > 25mm
19 failures in 198 fractures (9.6%)
16 cut out
Baumgaertner’s landmark paper published in 1995 introduced a new measurement, the Tip Apex distance. When over 25mm it is strongly associated with hip screw cut out.
Baumgaertner et al, J Bone Joint Surg Am Jul;77(7):

5. Baumgaertner, 1995 Tip – Apex Distance > 25mm
19 failures in 198 fractures (9.6%)
16 cut out
5 different devices
142 sliding hip screw (3 manufacturers)
56 intramedullary nail (2 manufacturers)
What is often overlooked is that the results were derived from five different implants.
Baumgaertner et al, J Bone Joint Surg Am Jul;77(7):

6. Study Aims Local experience of use Identify failures
Dynamic Hip Screw
Exclusive use since March 2001
Identify failures
Identify predictive factors
The aim of our study was to describe the local experience of the Dynamic Hip Screw, and to identify failures and predictive factors. This implant is the only sliding hip screw in use at the three Western Australian Tertiary Hospitals.

7. Study Design Retrospective radiological audit 731 cases 701 patients
2002 – 2004
We performed a retrospective radiological audit of 731 consecutive cases in 701 patients, over a three year period from 2002 to 2004.

8. Inclusion Criteria New adult proximal femur fracture Adequate imaging
Preoperative
Implant
Inclusion criteria was a new adult proximal femur fracture with adequate imaging.

9. Methods Theatre database Ortho techs PACS Revision Cause
A case listing from the theatre database was accompanied by implant data from the orthopaedic technicians’ files. All radiographs were assessed on the PACS system. Revision procedure was the recognized end point, and its’ cause identified as failure.

10. PACS Picture Archiving Computer System Fremantle Hospital
2001
Sir Charles Gairdner Hospital
2004
Royal Perth Hospital
For consistency we included cases with imaging on the statewide Picture Archiving Computer System. This had been in place at Fremantle Hospital since 2001, and at Sir Charles Gairdner and Royal Perth Hospitals since 2004.

11. Fracture Classification
AO / Muller
Evan’s
All fractures were classified according to the AO / Muller classification,
Müller et al; Manual of internal fixation: techniques recommended by the AO-ASIF group, ed 3, Berlin, 1991, Springer-Verlag

12. Fracture Classification
AO / Muller
Evan’s
As well as Evan’s method, which assesses position after fixation as stable or unstable.
Evan E. J Bone Joint Surg 1949;31B:190–203

13. X-rays 1. Reduction Alignment AP Normal or slight valgus
Alignment Lateral
Less than 20 degrees tilt of femoral head
We assessed implant imaging in three ways in a similar manner to Baumgaertner’s paper. Reduction consisted of two items: alignment and displacement. The former requires avoidance of valgus and excessive head fragment tilt.

14. X-rays 1. Reduction Displacement
Less than 5mm displacement of any bone fragment
The latter required less than 5mm displacement of any fracture fragment. Combining the two gives a good, acceptable or poor reduction.

15. X-rays 1. Reduction 2. Tip – Apex Distance
In addition, The Tip-Apex distance as per Baumgaertner…
Baumgaertner et al, J Bone Joint Surg Am Jul;77(7):

16. X-rays 1. Reduction 2. Tip – Apex Distance
3. Position of screw in femoral head
And the position of the screw in the femoral head, by Cleveland’s method, were also recorded.
Cleveland et al, J Bone Joint Surg Am Dec;41-A:

17. Exclusion Criteria Not a fracture Inadequate imaging 1 case (myeloma)
11 cases
12 patients were excluded from the study, one without a fracture and 11 with inadequate imaging.

18. Demographics 387 Females, 120 Males Mean age 80.9 years
Female : Male : 1
Mean age 80.9 years
Range 15.0 – 106.2
SD 13.0
The eligible study population consisted of 538 females and 193 males, with a mean age was 82 years.

19. Age
Over 90 percent of the patients were aged over 70…

20. ASA Score
And the mean American Society of Anaesthesiologists score was 2.78.

21. Radiological Follow Up
Intraoperative only
25.3%
Postoperative X-ray within 2 weeks
33.8%
X-ray between 2 weeks and 3 months
17.9%
X-ray after 3 months
23.0%
Current practice is to do follow up imaging on clinical grounds only, thus only 23% of cases had imaging after 3 months.

22. Surgeon Consultant 10.7% 41 min Fellow 1.8% 43 min Training registrar
50.6%
39 min
Service registrar
36.9%
50 min
Training and service registrars performed the bulk of the cases, 51 and 36 percent respectively.

23. Surgeon Consultant 10.7% 41 min Fellow 1.8% 43 min Training registrar
50.6%
39 min
Service registrar
36.9%
50 min
P < 0.001
The mean operating time was 43 minutes, with service registrars taking significantly longer than more senior staff.

24. Fracture Region 22.4% 76.3% 1.2% N = 164 N = 407 N = 9
Looking at fracture classification, about 22 percent occurred in the femoral neck and the remainder in the trochanteric region. We will discuss results of trochanteric group in this presentation.
22.4% % %
N = N = N = 9

25. Trochanter vs Neck Age (years) ASA Contralateral #NOF 82.7 2.85 11.5%
75.1
2.52
6.7%
Patients with trochanteric fracture were of older age and poorer medical status than patients with femoral neck fracture, and were more likely to have had a previous contralateral fracture.

26. AO / Muller Classification
266
46.9%
235
41.4% 57
10.1%
N = 9
Using the AO classification, pertrochanteric fractures accounted for nearly 90 percent of cases. Half of these were simple and half were multi-fragmentary.

27. AO / Muller Classification
266
46.9%
235
41.4% 57
10.1%
N = 9
True intertrochanteric fractures made up the remainder.

28. AO / Muller Classification
266
46.9%
235
41.4% 57
10.1%
N = 9
There were very few subtrochanteric and reverse oblique cases.

29. Evan’s Classification
According to Evan’s classification, only 26% of fractures in this series were unstable.
73.7%
N = 418
26.3%
N = 149

30. Reduction Good 336 59.3% Acceptable 125 22.0% Poor 106 18.7%
Here is an example of a poor reduction, with varus alignment and fragment displacement. This occurred in 18 percent of cases.

31. Cleveland Zone
This diagram indicates the hip screw locations in the femoral head. about two thirds of hip screws were placed in the desired central central location. The remainder were three times more likely to be posterior than anterior.

32. Tip – Apex Distance Mean 20mm Stable ≈ unstable Range 5 to 44 SD 6.1
20 vs 22 mm
The mean tip-apex distance was 21 millimetres, with a range of 5 to 44 millimetres. In both stable and unstable fractures a similar mean distance was achieved.

33. Tip – Apex Distance
More than three quarters of cases had a Tip – Apex distance of less than 25mm.

34. Failures 14 revisions - 2.5% 10 cut out 4 failures of plate screws
In 567 cases!
10 cut out
Superior breach of femoral head
4 failures of plate screws
“Reverse cut out”
We found only 11 failures requiring revision in this group of 414 trochanteric region fractures, a failure rate of 2.7%.

35. Failures 14 revisions - 2.5% 10 cut out 4 failures of plate screws
In 567 cases!
10 cut out
Superior breach of femoral head
4 failures of plate screws
“Reverse cut out”
There were 10 cases of cut out, requiring revision to total or hemi arthroplasty

36. Failures 14 revisions - 2.5% 10 cut out 4 failures of plate screws
In 567 cases!
10 cut out
Superior breach of femoral head
4 failures of plate screws
“Reverse cut out”
And 4 failures of plate screws, requiring redo fixation.

37. Cut Out - TAD
P < 0.001
Cases of cut out had a mean Tip Apex Distance which was significantly higher, 32mm compared to 20 millimetres.

38. Cut Out - TAD Cut Out TAD < 25 TAD ≥ 25 Yes 10 No 437 120 Total 0%10 No
437
120
Total 0%
7.7%
A tip apex distance of 25mm or more had a 7.7% chance of cut out, compared to zero for those under 25mm.

39. Cut Out Evan’s Unstable Displacement > 4mm Varus reduction 10 of 10
All ten cases of cut out occurred in unstable fractures in which there was unacceptable displacement; and eight of ten had a varus reduction.

40. Cut Out – Cleveland Zone
This diagram shows cases of cut out by screw position in the femoral head. I will draw attention to a few crucial locations; here in the superior anterior zone 3 screws were placed and one cut out…

41. Cut Out – Cleveland Zone
In the posterior zones there were four cases of cut out. While the posterior direction are advocated by some authors these screws were quite a long way off from the central cylinder of the head here. To the right we can see some of the consequences of such positioning.

42. Cut Out – Cleveland Zone

43. Cut Out – Cleveland Zone

44. Bivariate Regression Rank Variable P value 1 Tip-Apex Distance2
Evan’s Unstable
9.10 x 10 -8 3
Poor Reduction
5.25 x 10 -7 4
Inferior Posterior Hip Screw
9.85 x 10 -6 5
Superior Anterior Hip Screw
3.11 x 10 -5
Bivariate regression revealed Tip Apex distance as having the strongest relationship to cut out. This was followed by Evan’s unstable fracture, poor reduction, inferior posterior hip screw position and superior anterior hip screw position, Variables with no relationship included age, gender, medical status, surgeon level and plate angle.

45. Multivariate Regression
Rank
Variable
P value 1
Tip-Apex Distance
1.58 x 10 -6 2
Evan’s Unstable
4.30 x 10 -3 3
Poor Reduction
6.21 x 10 -1
A three variable model found tip-apex distance of over 25mm to be the most significantly associated with cut out.

46. Failure Rate of 2.5%? Choice of implant Quality of results
Less unstable
Quality of results
Mean TAD 20mm (Baumgaertner 25mm)
Computerised PACS
Statewide tertiary catchment
One might wonder, why is the failure rate so low, less than three percent? Firstly some positive explanations. There is growing awareness that not all trochanteric region fractures are the same. 74% of fractures in this series were stable, compared to 45% in Baumgaertner’s series from a decade ago. The remainder may be getting an intramedullary device instead.

47. Failure Rate of 2.5%?
To illustrate, here is a sample of usage of the Synthes Proximal Femoral Nail at Fremantle Hospital, during the same period.

48. Failure Rate of 2.5%? Choice of implant Quality of results
Less unstable
Quality of results
Mean TAD 20mm (Baumgaertner 25mm)
Computerised PACS
Statewide tertiary catchment
With a mean Tip Apex Distance of 21mm, this series was more “on target” than Baumgaertner’s. The benefits of a single model of implant include better staff performance and validity of results.

49. Failure Rate of 2.5%? Choice of implant Quality of results
Less unstable
Quality of results
Mean TAD 20mm (Baumgaertner 25mm)
Computerised PACS
Statewide tertiary catchment
The computerised PACS system provided high quality images and a state wide catchment; this may explain why the exclusion rate in this series is far lower than many others.

50. Study Weaknesses Level IV evidence Observer bias
Loss of failures to the private sector
? X-rays on clinical need
Now for the negatives. Our study has a number of weaknesses. It is level IV evidence and we cannot control for observer bias at this stage. 15% of patients were insured, and failures in this group may have been lost to the private sector. By not routinely imaging patients after three months we may be missing further failures.

51. Summary Accurate reflection of experience
Captures all complications and revisions in Western Australian tertiary centres
To conclude, we feel that this study is an accurate reflection of the local clinical experience with the Dynamic Hip Screw. It shows a low failure rate and captures all the complications and revisions at tertiary centres in the state of Western Australia.

52. Thank you.

53. Acknowledgements Synthes Australia
Ben Fraser
FH, SCGH, RPH Orthopaedic Technicians
Particularly Steve and Ken from Fremantle
My wife May
Data entry!

54. Insurance Status Insurance N % HO 591 80.8% VA 80 10.9% PI 38 5.2% MV14
1.9% OV 6
0.8% WC 2
0.3%
Backup slide plate angles

55. Plate Length Length N % 2 hole 15 2.6% 4 hole 522 92.1% 5 hole 16 2.8%11
1.9%
8 hole 2
0.4%
12 hole 1
0.2%
Backup slide plate angles

56. Plate Angle Angle N % 130 deg 122 21.5% 135 deg 386 68.1% 140 deg 4610
1.8%
150 deg 3
0.5%
Backup slide plate angles

57. DHS Extras Implant N % Trochanteric Side Plate 12 2.1%
Antirotation Screw 7
1.2%
Backup slide plate angles