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Parameters of the ulnar medullary canal for locked intramedullary nailing
Parameters of the ulnar medullary canal for locked intramedullary nailing A. G. McFarlane and L. T. Macdonald Department UK Received
of Anatomy,
Edinburgh
Medical School,
Teviot Place, Edinburgh
EH8 9AG,
April 1990, accepted August 1990
ABSTRACT 7’he development of a ‘one shot’ locked intramedullary device for rapid stabilization of adult ulnar fractures would benejt surgeon andpatient alike, but, before a prototype device can be manufactured, basic internal measurements of the ulnar medullay canal are needed. Various sections and measurements of 142 adult human cadaver ulnas were performed to determine the calibre, length and curvature of the medullary canal. These measurements revealed that thz device can be of one calibre but will need to be manufactured in three different lengths. Because of the minimal curvature of the ulnar medullq canal and the ability to lock the nail both proximally and distally, the nail can be straight and inserted loosely. A prototype design is described. Keywords:
Ulna fractures, locked intramedullary
nail, stabilization
Ulnar fractures are notorious1 difficult to unite, even when adequately plated. T B is begs the question, ‘could a better device be designed?’ Perhaps the use of a loose fitting, thin, intramedullary nail which could be locked at either end might suffice; its point of entry would be via the olecranon, this being subcutaneous and it would facilitate engagement of the distal fragments. The nail could be solid, thereby increasing its strength and stiffness, and in this form would obviate the need for prior guide-wire placement. The device could be manufactured with its own forward and side cutting tip to allow easier insertion, without the need for further tools, which would add to the cost. To manufacture prototype devices we need to know how long and how wide to make them, so that a range of implants be available for most adult patients who may require this form of treatment. (Children fortunately tend not to require this therapy.) This paper hopes to answer the questions: how long?, how wide?, and how bent? (if necessary) to manufacture the nail.
device
locations, which were determined following protocol (see Figure 7).
0141-5425/91/010074-03 74
J. Biomed. Eng. 1991, Vol. 13, January
to the
Cut 1. 5 cm distal from the olecranon. The cuts were all distal to the coronoid process. Cut 2. Halfway between cuts 1 and 3. Cut 3. Halfway along the total measured length of the intact bone. Cut 4. Halfway between cuts 3 and 5. Cut 5. 3 cm proximal to the ulnar styloid process. Cuts I and 5 were performed first. The medullary cavity was then reamed with a 3.6 mm diameter blunt reamer (a No 9 imperial knitting needle!) and then held up to a light source. If light could be detected shining directly along the shaft of the truncated ulna, it was deemed to be straight. The other cuts were then performed and the segments maximally reamed using the blunt reamer. The minimum reamed diameter at each level of cut was then measured to the nearest millimetre.
MA’IWUALS AND METHODS Caucasian adult cadaver ulnas (142; 73 right, 69 left) were obtained. No details were available of the sex of the adults prior to extirpation of the bones, which were cleaned and washed before examination. The overall length of each one and the minimum width between the olecranon and coronoid processes were measured to the nearest millimetre. Using statistical analyses the ulnas were divided into three groups: long, medium and short. A representative sample of ten ulnas was taken from each group. Each ulna was sectioned using a fine electric saw in five standardized 0 199I Butterworth-Heinemann for BES
according
I
d
5cm
Figure
2
3
4
5
3cm c---)
-
1
Sectioning
of ulna in five standardized
locations
Parameters of the ulnar medulby canal: A. G. McFarlune and L. T. Macdonald 30 r
0
200
210
220
230
240
250
Length
Figure 2
Frequency
distribution
260
270
280
290
0
300
<19
19
20
21
22
23
24
25
26
27
28
29
30 >30
OCD (mm1
(mm)
of ulnar length
Figure 3
Frequency
distribution
of olecrano-coronoid
distance
WCD)
Table 2 Relationship
STATISTICAL ANALYSIS Student’s t-test and x2 test were appropriate.
employed
where
overall
RESULTS The distribution of the lengths of the ulnas is ‘ven in Figure 2. The mean length was 249.2 mm 6 D= 20.95). Ulnas lying within one standard deviation of the mean were considered to be of normal length, those in excess of 270 mm long, and those of less than 228 mm short. In the cohort of 30 ulnas for transverse sectioning, 17 were noted to be straight after cuts 1 and 5 had been performed, and the bones reamed. Another 20 bones were selected at random and cuts 1 and 5 performed; 17 of these were found to be straight. In total, 34 out of 50 (68%) were found to be straight after reaming. The mean diameters at each level of cut in the three groups is given in Table 7. None of the segments of bone had a minimum reamed diameter of less than 4mm. Using Student’s t-test, the difference between the minimum reamed dia-
meters of the short cohort and the long and medium cohorts were highly statistically significant (P=O.OOl and P= 0.01, respectively). There was no statistically significant difference between the minimum reamed diameters of the long and medium cohorts. The distribution of the olecranon-coronoid distances is given in Figure 3. The mean value was 24.2 mm. A subsidiary hy otbesis was proposed that longer bones would ex Kibit eater olecranoncoronoid distances. Therefore, Y able 2 was constructed so as to give the number of bones longer or
Table
1 Mean
minimum reamed diameters (mm) canal at five levels of section along the shaft Cut 4
Cut 5
Index*
Cut 1
Short Medium Long
5.2
4.3
4.2
4.4
4.7
22.x
6.X
5.!)
4.6
5.1
52%
2x.2
ti.!)
5.7
4.x
5.3
5.6
28.3
diameter
Cut 3
of the
Length
*Mean cumulative
Cut 2
of the cohort
between
olecrano-coronoid
ulna
length
distance
(OCD) and
length OCD
Ulnar
medullary
ulnar
(mm)
<250 2.50 and >250
<25
(mm)
25 and >25
ii4
IX
21
49
shorter than 250 mm with olecranon-coronoid distances greater or less than 25mm. Using the x2 test, the difference between these oups was highly statistically significant (P= 0.00 !7).
DISCUSSION The use of intramedullary nails in the treatment of long bone fractures was first popularized by Kuntschner’ during the First World War. These were straight nails placed inside bent lower limb bones, which had to be over-reamed to take the nail. Despite initial failures due to metal fatigue, this form of fracture fixation has since enjoyed a variable success. During the last two decades the shape of the nail has changed to the pre-bent shape advocated by the A0 ASIF group of surgeons in Switzerland”. Many differing types of pre-bent femoral intramedullary nail have been manufactured, with differing radii of curvature, most of which are not physiological’! This has led to intraoperative problems, including comminution at the fracture site during nail placement’ and disengagement of the nail from the guide-wire, especially if the nail is inserted ‘closed’. The placement of ‘loose’ nails reduces the incidence of these problems; however, the practice of over-reaming by as little as 0.5 mm to ensure ‘trouble free’ nail placement does result in poor distal grip by the device, thus seriously compromising distal rotational stability. ‘Locking’ of the intramedullary nail by means of cross screws inserted from cortex to cortex of the bone passing through prepared holes in the nail was first introduced by Huckstep,’ and has more recently been improved by many workers, including Grosse and Kempf” and the A0 ASIF group. Locking allows
J. Biomed.
Eng. 1991, Vol. 13, January
75
Parameters of the ulnar mdullay canal: A. G. McFarlone and L. T. Macdonaid 3.6mm
175 - 240
Figure 4
4mm
mm
Proposed intramedullary reaming device
the nails to be inserted loosely and yet gain improved rotational stability, and is especially useful in extreme metaphyseal fractures and those involving extreme comminution of the shaft. The aim of internal fixation of adult forearm fractures is to restore the anatomy so as to allow full passive function to occur whilst union takes place. Once a decision has been taken to fix internally, the choice of fixation device is left to the operating this operation is technically surgeon. However, demanding, and takes significant operating time. If the ulna can be quickly and easily stablized by a device or technique that tends not to interfere with union, it could significantly reduce the operating time for the whole procedure and allow the surgeon to concentrate his efforts on the more difficult radial fracture. The subcutaneous nature of the ulna throughout its length and the ease of surgical access of the olecranon lends itself to the development of an intramedullary device. The use of loose fitting (Rush) pins does provide a method of stabilizing the fractured bone7, but this can be further improved by using the ‘one shot’ concept, i.e. the reaming device also acts as the definitive implant, thereby reducing any instabilities caused by prior over reaming4. Yet more stability can be gained if a method of locking is simultaneously introduced. This would also help to maintain the length of the bone should there be any tendency to shortening (oblique or cornminuted fractures). We propose the use of the device shown Figure 4. It has a number of salient features: The tip of the device has a forward cutting end with side cutting flutes, diameter 4.0 mm. 0 The shaft of the device has a diameter of 3.6 mm. This reduction in width allows for swarf cut from the tip to pass proximally during insertion. This swarf contains cells of known osteogenic otentialsg which will be deposited along the Pength of the bone including the fracture site. The metallurgical nature of the proposed device should allow for flexibility to side-to-side bending forces, so that it can easily negotiate the gentle curve of the ulna should it not be completely straight, and et resistant enough to axial rotational forces so x at 0
76
J. Biomed. Eng. 1991, Vol. 13, January
sufficient torque can be applied to insert the device. The proximal 5 cm of the nail expands gently to a diameter of 8 mm with a wide cancellous self tapping thread on the outside. The overall maximum diameter would be 10 mm. Once the nail was firmly screwed home it would grip the roximal ulna sufficiently to provide proximal Pocking. There will be provision for a ‘snap fit’ universal locking out-rigger to allow a cross screw to be placed accurately across the bone abutting the tip of the device. This would not constitute true distal locking but would prevent shortening. It is proposed that once the radius has been accurately fixed, any tendency for the fracture to elongate would be negated. As the distal ulna is relatively static during pronation/supination”, the lack of rotational fixation is also not thought to be of concern. The device is currently being manufactured and will be available in overall lengths of 175, 225 and 240 mm. The finding that olecrano-coronoid distances are in excess of 25 mm implies that the ulnar shaft is likely to be in excess of 250 mm in overall length, which is useful for pre-operative planning purposes as it can prevent use of one device and its subsequent rejection because of inappropriate length. Having been used once, a device is no longer suitable for subsequent implantation.
REFERENCES 1. Kuntscher G. Die Marknagelung von Knochenbruchen.
Clin Orthop 1968; 60: 5-12. 2. Muller ME, Allgower M, Schneider R, Willenegger H. Manual of Internal Ftiation. Berlin: Springer-Verlag, 1979. 3. Zuber K, Eulenberger J, Schneider E, Perren SM. Anatomical curvature of the femoral medullary canal for intramedullary rodding. Unfallchirurg 1988; 92: 423-8. 4. Tencer AF, Sherman MC, Johnson KD. Biomechanical factors affecting fracture stability and femoral bursting in closed intramedullary rod fixation of femur fractures. J Biomech Eng 1985; 107: 104-11. 5. Huckstep RL. Rigid intramedullary fixation of femoral shaft fractures with compression. J Bone Joint Surg 1972; 54-B: 204. 6. Kempf I, Grosse A, Beck G. Closed locked intramedullary nailing: its application to comminuted fractures of the femur. JBoneJoint Surg 1985; 67-A: 709-20. 7. Ono M, Bechtold J, Merkow R, Sherman R, Gustilo R. Rotational stability of diaphyseal fractures of the radius and ulna fixed with Rush pins and/or fracture bracing. Clin Orthop 1989; 240: 236-43. 8. Urist MR, McLean FC. Osteogenic potency and newbone formation by induction in transplants to the anterior chamber of the eye. JIBone Joint Surg 1952; 34-A: 443-76. 9. McFarlane AG. Helping bones to heal. London: University of London, 1990. MD Thesis (in preparation). 10. Last RJ. Anatomy, Regional and Applied. Edinburgh: Churchill Livingstone, 1978.
of Anatomy,
Edinburgh
Medical School,
Teviot Place, Edinburgh
EH8 9AG,
April 1990, accepted August 1990
ABSTRACT 7’he development of a ‘one shot’ locked intramedullary device for rapid stabilization of adult ulnar fractures would benejt surgeon andpatient alike, but, before a prototype device can be manufactured, basic internal measurements of the ulnar medullay canal are needed. Various sections and measurements of 142 adult human cadaver ulnas were performed to determine the calibre, length and curvature of the medullary canal. These measurements revealed that thz device can be of one calibre but will need to be manufactured in three different lengths. Because of the minimal curvature of the ulnar medullq canal and the ability to lock the nail both proximally and distally, the nail can be straight and inserted loosely. A prototype design is described. Keywords:
Ulna fractures, locked intramedullary
nail, stabilization
Ulnar fractures are notorious1 difficult to unite, even when adequately plated. T B is begs the question, ‘could a better device be designed?’ Perhaps the use of a loose fitting, thin, intramedullary nail which could be locked at either end might suffice; its point of entry would be via the olecranon, this being subcutaneous and it would facilitate engagement of the distal fragments. The nail could be solid, thereby increasing its strength and stiffness, and in this form would obviate the need for prior guide-wire placement. The device could be manufactured with its own forward and side cutting tip to allow easier insertion, without the need for further tools, which would add to the cost. To manufacture prototype devices we need to know how long and how wide to make them, so that a range of implants be available for most adult patients who may require this form of treatment. (Children fortunately tend not to require this therapy.) This paper hopes to answer the questions: how long?, how wide?, and how bent? (if necessary) to manufacture the nail.
device
locations, which were determined following protocol (see Figure 7).
0141-5425/91/010074-03 74
J. Biomed. Eng. 1991, Vol. 13, January
to the
Cut 1. 5 cm distal from the olecranon. The cuts were all distal to the coronoid process. Cut 2. Halfway between cuts 1 and 3. Cut 3. Halfway along the total measured length of the intact bone. Cut 4. Halfway between cuts 3 and 5. Cut 5. 3 cm proximal to the ulnar styloid process. Cuts I and 5 were performed first. The medullary cavity was then reamed with a 3.6 mm diameter blunt reamer (a No 9 imperial knitting needle!) and then held up to a light source. If light could be detected shining directly along the shaft of the truncated ulna, it was deemed to be straight. The other cuts were then performed and the segments maximally reamed using the blunt reamer. The minimum reamed diameter at each level of cut was then measured to the nearest millimetre.
MA’IWUALS AND METHODS Caucasian adult cadaver ulnas (142; 73 right, 69 left) were obtained. No details were available of the sex of the adults prior to extirpation of the bones, which were cleaned and washed before examination. The overall length of each one and the minimum width between the olecranon and coronoid processes were measured to the nearest millimetre. Using statistical analyses the ulnas were divided into three groups: long, medium and short. A representative sample of ten ulnas was taken from each group. Each ulna was sectioned using a fine electric saw in five standardized 0 199I Butterworth-Heinemann for BES
according
I
d
5cm
Figure
2
3
4
5
3cm c---)
-
1
Sectioning
of ulna in five standardized
locations
Parameters of the ulnar medulby canal: A. G. McFarlune and L. T. Macdonald 30 r
0
200
210
220
230
240
250
Length
Figure 2
Frequency
distribution
260
270
280
290
0
300
<19
19
20
21
22
23
24
25
26
27
28
29
30 >30
OCD (mm1
(mm)
of ulnar length
Figure 3
Frequency
distribution
of olecrano-coronoid
distance
WCD)
Table 2 Relationship
STATISTICAL ANALYSIS Student’s t-test and x2 test were appropriate.
employed
where
overall
RESULTS The distribution of the lengths of the ulnas is ‘ven in Figure 2. The mean length was 249.2 mm 6 D= 20.95). Ulnas lying within one standard deviation of the mean were considered to be of normal length, those in excess of 270 mm long, and those of less than 228 mm short. In the cohort of 30 ulnas for transverse sectioning, 17 were noted to be straight after cuts 1 and 5 had been performed, and the bones reamed. Another 20 bones were selected at random and cuts 1 and 5 performed; 17 of these were found to be straight. In total, 34 out of 50 (68%) were found to be straight after reaming. The mean diameters at each level of cut in the three groups is given in Table 7. None of the segments of bone had a minimum reamed diameter of less than 4mm. Using Student’s t-test, the difference between the minimum reamed dia-
meters of the short cohort and the long and medium cohorts were highly statistically significant (P=O.OOl and P= 0.01, respectively). There was no statistically significant difference between the minimum reamed diameters of the long and medium cohorts. The distribution of the olecranon-coronoid distances is given in Figure 3. The mean value was 24.2 mm. A subsidiary hy otbesis was proposed that longer bones would ex Kibit eater olecranoncoronoid distances. Therefore, Y able 2 was constructed so as to give the number of bones longer or
Table
1 Mean
minimum reamed diameters (mm) canal at five levels of section along the shaft Cut 4
Cut 5
Index*
Cut 1
Short Medium Long
5.2
4.3
4.2
4.4
4.7
22.x
6.X
5.!)
4.6
5.1
52%
2x.2
ti.!)
5.7
4.x
5.3
5.6
28.3
diameter
Cut 3
of the
Length
*Mean cumulative
Cut 2
of the cohort
between
olecrano-coronoid
ulna
length
distance
(OCD) and
length OCD
Ulnar
medullary
ulnar
(mm)
<250 2.50 and >250
<25
(mm)
25 and >25
ii4
IX
21
49
shorter than 250 mm with olecranon-coronoid distances greater or less than 25mm. Using the x2 test, the difference between these oups was highly statistically significant (P= 0.00 !7).
DISCUSSION The use of intramedullary nails in the treatment of long bone fractures was first popularized by Kuntschner’ during the First World War. These were straight nails placed inside bent lower limb bones, which had to be over-reamed to take the nail. Despite initial failures due to metal fatigue, this form of fracture fixation has since enjoyed a variable success. During the last two decades the shape of the nail has changed to the pre-bent shape advocated by the A0 ASIF group of surgeons in Switzerland”. Many differing types of pre-bent femoral intramedullary nail have been manufactured, with differing radii of curvature, most of which are not physiological’! This has led to intraoperative problems, including comminution at the fracture site during nail placement’ and disengagement of the nail from the guide-wire, especially if the nail is inserted ‘closed’. The placement of ‘loose’ nails reduces the incidence of these problems; however, the practice of over-reaming by as little as 0.5 mm to ensure ‘trouble free’ nail placement does result in poor distal grip by the device, thus seriously compromising distal rotational stability. ‘Locking’ of the intramedullary nail by means of cross screws inserted from cortex to cortex of the bone passing through prepared holes in the nail was first introduced by Huckstep,’ and has more recently been improved by many workers, including Grosse and Kempf” and the A0 ASIF group. Locking allows
J. Biomed.
Eng. 1991, Vol. 13, January
75
Parameters of the ulnar mdullay canal: A. G. McFarlone and L. T. Macdonaid 3.6mm
175 - 240
Figure 4
4mm
mm
Proposed intramedullary reaming device
the nails to be inserted loosely and yet gain improved rotational stability, and is especially useful in extreme metaphyseal fractures and those involving extreme comminution of the shaft. The aim of internal fixation of adult forearm fractures is to restore the anatomy so as to allow full passive function to occur whilst union takes place. Once a decision has been taken to fix internally, the choice of fixation device is left to the operating this operation is technically surgeon. However, demanding, and takes significant operating time. If the ulna can be quickly and easily stablized by a device or technique that tends not to interfere with union, it could significantly reduce the operating time for the whole procedure and allow the surgeon to concentrate his efforts on the more difficult radial fracture. The subcutaneous nature of the ulna throughout its length and the ease of surgical access of the olecranon lends itself to the development of an intramedullary device. The use of loose fitting (Rush) pins does provide a method of stabilizing the fractured bone7, but this can be further improved by using the ‘one shot’ concept, i.e. the reaming device also acts as the definitive implant, thereby reducing any instabilities caused by prior over reaming4. Yet more stability can be gained if a method of locking is simultaneously introduced. This would also help to maintain the length of the bone should there be any tendency to shortening (oblique or cornminuted fractures). We propose the use of the device shown Figure 4. It has a number of salient features: The tip of the device has a forward cutting end with side cutting flutes, diameter 4.0 mm. 0 The shaft of the device has a diameter of 3.6 mm. This reduction in width allows for swarf cut from the tip to pass proximally during insertion. This swarf contains cells of known osteogenic otentialsg which will be deposited along the Pength of the bone including the fracture site. The metallurgical nature of the proposed device should allow for flexibility to side-to-side bending forces, so that it can easily negotiate the gentle curve of the ulna should it not be completely straight, and et resistant enough to axial rotational forces so x at 0
76
J. Biomed. Eng. 1991, Vol. 13, January
sufficient torque can be applied to insert the device. The proximal 5 cm of the nail expands gently to a diameter of 8 mm with a wide cancellous self tapping thread on the outside. The overall maximum diameter would be 10 mm. Once the nail was firmly screwed home it would grip the roximal ulna sufficiently to provide proximal Pocking. There will be provision for a ‘snap fit’ universal locking out-rigger to allow a cross screw to be placed accurately across the bone abutting the tip of the device. This would not constitute true distal locking but would prevent shortening. It is proposed that once the radius has been accurately fixed, any tendency for the fracture to elongate would be negated. As the distal ulna is relatively static during pronation/supination”, the lack of rotational fixation is also not thought to be of concern. The device is currently being manufactured and will be available in overall lengths of 175, 225 and 240 mm. The finding that olecrano-coronoid distances are in excess of 25 mm implies that the ulnar shaft is likely to be in excess of 250 mm in overall length, which is useful for pre-operative planning purposes as it can prevent use of one device and its subsequent rejection because of inappropriate length. Having been used once, a device is no longer suitable for subsequent implantation.
REFERENCES 1. Kuntscher G. Die Marknagelung von Knochenbruchen.
Clin Orthop 1968; 60: 5-12. 2. Muller ME, Allgower M, Schneider R, Willenegger H. Manual of Internal Ftiation. Berlin: Springer-Verlag, 1979. 3. Zuber K, Eulenberger J, Schneider E, Perren SM. Anatomical curvature of the femoral medullary canal for intramedullary rodding. Unfallchirurg 1988; 92: 423-8. 4. Tencer AF, Sherman MC, Johnson KD. Biomechanical factors affecting fracture stability and femoral bursting in closed intramedullary rod fixation of femur fractures. J Biomech Eng 1985; 107: 104-11. 5. Huckstep RL. Rigid intramedullary fixation of femoral shaft fractures with compression. J Bone Joint Surg 1972; 54-B: 204. 6. Kempf I, Grosse A, Beck G. Closed locked intramedullary nailing: its application to comminuted fractures of the femur. JBoneJoint Surg 1985; 67-A: 709-20. 7. Ono M, Bechtold J, Merkow R, Sherman R, Gustilo R. Rotational stability of diaphyseal fractures of the radius and ulna fixed with Rush pins and/or fracture bracing. Clin Orthop 1989; 240: 236-43. 8. Urist MR, McLean FC. Osteogenic potency and newbone formation by induction in transplants to the anterior chamber of the eye. JIBone Joint Surg 1952; 34-A: 443-76. 9. McFarlane AG. Helping bones to heal. London: University of London, 1990. MD Thesis (in preparation). 10. Last RJ. Anatomy, Regional and Applied. Edinburgh: Churchill Livingstone, 1978.