Heterotopic ossification: a comparison between reamed and unreamed femoral nailing

ELSEVIER

Injury Vol. 28, No. 1, pp. 9--14, 1997 Copyright © 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0020-1383/97 $17.00 + 0.00

PII: S0020-1383(96)00147-7

Heterotopic ossification: a comparison between reamed and unreamed femoral nailing A. J. Furlong, P. V. Giannoudis and R. M. Smith Department of Orthopaedics and Trauma Surgery, St James's University Hospital NHS Trust, Leeds, UK

Heterotopic ossification in the abductor region of the hip following reamed intramedullary femoral nailing has an incidence as high as 68 per cent. A definitive triggering factor [or heterotopic ossification remains obscure, but it has been suggested that there may be both local and systemic influences. Previous work has only been able to show a statistical correlation with systemic factors. Sixty antegrade femoral nailings were performed in 58 patients, of which 32 were unreamed. There was no significant diffi,rence between the two groups for systemic risk factors known to have statistical correlation with the formation of heterotopic bone. The incidence qf heterotopic oss(fication in the reamed nail group was 35.7 per cent and 9.4 per cent in the unreamed nail group (P=O.01). The difference in the incidence of heterotopic bone formation seems to be due to local factors, in particular the generation of osteogenic reaming debris, which are important in the pathophysiology of heterotopic ossification seen in femoral intramedullary nailing. © 1997 Elsevier Science Ltd.

Injury, Vol. 28, No. 1, 9-14, 1997

Introduction Heterotopic ossification is well documented following closed intracranial injury ~.2, spinal cord injury ~, blunt injury 4, total joint arthroplasty ~7, and fracture 2.~. Heterotopic ossification in the abductor region of the hip following intramedullary nailing of the femur was not initially felt to be a problem and when it did occur, its functional significance was disregarded ~,1''. More recently, heterotopic ossification following reamed femoral nailing has been recognized as a significant complication of the procedure with a reported incidence as high as 68 per cent 11 '~. The aetiology of heterotopic ossification is not well understood. Factors implicated in the formation of heterotopic bone around the hip in femoral intramedullary nailing can be broadly grouped into those which are acting locally and those which act systemically. Systemic factors implicated in the formation of ectopic bone in femoral nailing are the presence of an associated closed head injury ~2,1~, early and

prolonged intubation ~2'~, male sex ~3, and a long delay between injury and surgery'L An elevated Injury Severity Score (ISS) has also been suggested to be an important systemic factor, but of the three major studies in this field l' ~3, only one has been able to show statistical significance le. Local contributing factors to heterotopic ossification may include the osteogenic reamings which spill into the soft tissues at the time of operation, anatomic location, and damage to the gluteal muscles during reaming. The reamings consist predominantly of bone marrow and fine particulate bone matter, which are known to be highly osteogenic 14. In an attempt to reduce the osteogenic stimulus from these intramedullary reamings, Brumback et al." undertook a trial using pulsatile lavage irrigation of the wound with 31 of normal saline solution. He was unable to show that wound lavage affected the incidence or severity of heterotopic ossification after femoral intramedullary nailing. Since March 1994, our unit has been using the AO Synthes unreamed femoral nail system as the standard form of treatment for subtrochanteric fractures, ipsilateral femoral neck and shaft fractures, and femoral shaft fractures. Since this is an unreamed nailing system, it should not generate the same amount of osteogenic debris as with a reamed femoral nail. Therefore, a retrospective study was undertaken comparing the unreamed femoral nail with the reamed femoral nails routinely used in this unit before March 1994 to determine if there was a difference in the incidence of heterotopic ossification.

Patients and methods The records and radiographs of patients who underwent primary antegrade femoral nailing in our unit between May 1990 and January 1996 were reviewed. Patients with medical conditions predisposing to heterotopic bone formation, such as metabolic bone disease, ankylosing spondylitis, or diffuse idiopathic skeletal hyperostosis, were excluded. Two patients who died as a result of multiple injuries before radiological union had occurred were also excluded,

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as were two patients who did not have adequate clinical or radiographic follow up. Those patients who had a revision femoral nailing for non-union were excluded because of the possible stimulatory effect of a second procedure on the incidence of heterotopic bone formation. Patients with pathological femoral shaft fractures were excluded as a proportion of these patients did not survive long enough to reach radiological union. Some of these patients had received radiotherapy to the fracture site following intramedullary nailing, and irradiation is known to reduce the incidence of heterotopic bone formationC This left 60 primary antegrade femoral nailing operations performed in 58 patients who had been followed up until radiological union of the femoral fracture. Twenty-six patients had undergone 28 reamed femoral nailings (two bilateral), and 32 patients underwent unreamed femoral nailing. Information was collected on age, sex, mechanism of injury, presence of other injuries (including closed head injury and associated pelvic fracture), ISS, time to operation from injury, prolonged intubation, fracture side, AO fracture classification, femoral nail used, and the time to radiological fracture union. In the reamed femoral nail group, the mean age of patients was 37.4 years (range, 17-88 years) and in the unreamed femoral nail group, the mean age was 51.7 years (range, 17-90). Nineteen men (73.1 per cent) had a reamed femoral nail inserted and 21 (65.6 per cent) had an unreamed femoral nailing. Road traffic accidents accounted for 34 (56.7 per cent) femoral fractures, crush injuries caused three (5 per cent), and the remaining 23 (38.3 per cent) resulted from slipping on ice or falling over. The ISS for both groups ranged from 9 to 27 (mean 12.6 in the reamed femoral nail group; mean 11.7 in the unreamed femoral nail group). Three patients had CT-proven head injuries in the reamed nail group,

and four in the unreamed nail group. Three patients had an associated pelvic fracture in the reamed nail group, as did four patients in the unreamed nail group. There were two open femoral fractures (one in each group). Thirty-two (53.3 per cent) fractures were of the right femur. The distribution of femoral fractures in both groups according to the AO classification is shown in Figure 1. (Note that one patient in the unreamed group had a femoral neck fracture and an ipsilateral femoral shaft fracture.) All operations in both groups were performed by a consultant or senior registrar; with 25 (89.3 per cent) reamed femoral nailings, and 24 (75 per cent) unreamed being performed on the same day as the fracture was sustained. The remaining patients had their operations within 48 h of injury, except for two patients surgery was not performed until 12 days after their fracture (one in each group). Fifty-three (88.3 per cent) patients were extubated within 12 h of their operation. In the reamed nail group, 24 AO femoral nails, and four Russell Taylor reconstruction femoral nails were inserted. All patients in the unreamed group had an AO unreamed femoral nail inserted. All nails in both groups were statically locked. All patients had been followed up at regular intervals in the outpatient department at least until radiological fracture union. Fracture union was defined as painless full weight-bearing in the presence of circumferential callus in two planes on radiographs. The mean time to radiological union for the reamed nail group was 20.9 weeks (range, 14-32 weeks), and for the unreamed nail group was 24.5 weeks (range, 14-40 weeks). The diagnosis of heterotopic bone formation was based on the anteroposterior (AP) radiograph of the proximal femur taken at the time of discharge or at the time of fracture radiological union (whichever

i• Reamed

Figure 1. Distribution o[ fcmoral ffacturcs (AO classification).

Furlong et al.: Heterotopic ossification

was latest). The severity of heterotopic ossification was classified according to the system of Brumback et al. ~ based on the distance between the proximal end of the nail and the most proximal tip of the heterotopic bone. This classification has five grades: • grade 0, no evidence of heterotopic ossification; • grade I, a small nidus of heterotopic ossification, not more than 1 cm in length; • grade II, heterotopic ossification between 1 and 2 cm in length; • grade III, heterotopic ossification more than 2 cm in length, without extension to the pelvis; • grade IV, severe heterotopic ossification with evidence of nearly complete or complete osseous ankylosis of the hip. Examples are given in Figures 2-5. The results were computerized. Data were then analysed using a statistical package by Student's t-test, the X2 test, the two-tailed Fisher exact probability test, and the non-parametric Wilcoxian Mann-Whitney U-test.

Figure 2. Grade I heterotopic ossification in a patient with an unreamed femoral nail.

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Results There were no significant differences between the two groups with regard to sex (Z 2 test, P=0.54), presence of an associated CT-proven head injury or pelvic fracture (Fisher exact probability, P=0.93), ISS ( M a n n - W h i t n e y U-test, P = 0.10), and time to extubation from surgery (Fisher exact probability, P=0.52). However, a significant difference between the two groups with regard to age was found to occur at the 5 per cent level (Student's t-test, P=0.02). In the reamed femoral nail group, 10 cases of heterotopic ossification (incidence 35.7 per cent) were seen on AP radiographs of the hip; while in the u n r e a m e d femoral nail group, only three cases of heterotopic ossification occurred (incidence 9.4 per cent). The difference in the incidence of heterotopic bone formation between the two groups was highly

Figure 3. Grade I hctcrotopic ossification in a patient with a reamed femoral nail.

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significant (12 test, P=0.01). The severity of heterotopic ossification for the two groups is shown in Table I.

closed head injury, prolonged intubation, male sex, long delay to surgery, and ISS. N o n e of these studies was able to show a correlation between the presence of heterotopic ossification and local contributory

Discussion A definitive triggering factor for heterotopic ossification remains obscure; but it has been suggested that heterotopic bone formation may d e p e n d on a fine balance of osteogenic and osteo-inhibitory influences acting both locally and systemically 1~. Previous work looking at factors that might contribute to the formation of heterotopic ossification with intramedullary femoral nailing has only been able to show statistical correlation with systemic influences ~2,~3. These are the presence of an associated

Figure 5. Grade III heterotopic ossification in a patient with a

reamed temoral nail.

Table I. Severity of heterotopic ossification (Brumback classification) Ossification

Figure 4. Grade 11 heterotopic ossification in a patient with a

rcamcd femoral nail.

Grade Grade Grade Grade Grade Total

0 I II III IV

Reamed nails

Unreamed nails

18 3 5 2 0 28

29 3 0 0 0 32

Furlong et al.: Heterotopic ossification factors such as prominence of the nail, fracture pattern, and w o u n d drainage. All previous studies involved the use of a reamed femoral nail. Brumback et al. ~ recognized the possible stimulatory effects of the osteogenic reaming debris that spilled into the abductor muscles of the hip during reamed femoral nailing. Despite their attempts to reduce the presence of this reaming debris with pulsatile lavage of the w o u n d , they were unable to demonstrate any reduction in the incidence of heterotopic bone formation. A recent study from H a n n o v e r '~ reporting early results with the AO u n r e a m e d femoral nail in 57 cases, did not include information on the incidence of heterotopic ossification. However, it would seem reasonable to postulate that the absence of reaming debris should alter the incidence of heterotopic ossification if local factors do have a role to play in the pathophysiology of this condition. This study demonstrates significantly different incidences in heterotopic ossification w h e n comparing reamed femoral nailing with u n r e a m e d femoral nailing. The two groups were otherwise similar in their demographic characteristics except for a difference in the mean age. In our opinion the higher mean age in the u n r e a m e d group is likely to reflect the greater versatility and application of the unreamed femoral nail system, particularly its use in the stabilization of subtrochanteric femoral fractures (see Figure 1). Furthermore, it has not been shown statistically that age affects the incidence of heterotopic ossification in intramedullary nailing of the femur. Both groups had similar characteristics for systemic risk factors previously shown to be important in the d e v e l o p m e n t of heterotopic ossification. The difference in the incidence of heterotopic ossification is likely to be a result of locally acting factors. There are several possible explanations that may account for the reduced rate of heterotopic ossification seen with u n r e a m e d femoral nailing. Firstly, it has been our experience that a much smaller incision is n e e d e d for u n r e a m e d nail insertion than is possible with the reamed nail; and this is confirmed in the H a n n o v e r report '7. Furthermore, tissue damage is no longer produced by the passage of reamers through the abductor muscles. Secondly, osteogenic debris should be much less than is seen with reamed femoral nails. However, while the reduced production of osteogenic debris may play a part in the reduced incidence of heterotopic ossification seen with the u n r e a m e d femoral nail it may also have other implications, namely a prolonged fracture union time due to less 'autografting' of the fracture siteC In conclusion, this study has shown a statistically reduced incidence of heterotopic bone formation with the u n r e a m e d femoral nail compared with the reamed femoral nail. We feel that this difference demonstrates that local factors particularly the generation of reaming debris are important in the pathophysiology of heterotopic ossification in femoral intrameduUary nailing.

13 Acknowledgements Dr P. V. Giannoudis was supported by a grant from AO International. We would also like to acknowledge the support of all the Trauma & Orthopaedic Consultants at St James's University Hospital.

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17 Krettek C, Rudolf J, Schandelmaier P, Guy P, Konemann B and Tscherne H. Unreamed intramedullary nailing of femoral shaft fractures: operative technique and early clinical experience with the standard locking option. Injury 1996; 27: 233. 18 Giannoudis PV, Furlong AJ, MacDonald DA and Smith RM. Reamed against unreamed nailing of the femoral diaphysis: a retrospective study of healing time. Injury 28: 15.

Paper accepted 29 October 1996.

Requests for reprints should be addressed to: Mr R. M. Smith, Department of Orthopaedics and Trauma Surgery, St James University Hospital NHS Trust, Beckett Street, Leeds LS9 7TF, UK.