Management of femur fractures with self-made polymethylmethacrylate plates, stainless steel plates, intra-medullar pins and interlocking nails in dogs

P. Mukherjee1†, D. Ghosh1, S. Roy1 and S. Basu2
West Bengal University of Animal and Fishery Sciences,
37, K. B. Sarani, Kolkata-700 037, India.

1. Department of Veterinary Surgery & Radiology.
2 Department of Veterinary Gynaecology and Obstetrics.

† Corresponding author
Dr. Prasenjit Mukherjee
Senior Research Fellow
Department of Veterinary Surgery and Radiology
West Bengal University of Animal and Fishery Sciences,
Kolkata- 700 037, India.

SUMMARY

This is a retrospective study of 24 femur diaphyseal transverse fractures stabilized with intra-medullar pinning, steel bone plating, fabricated polymethylmethacrylate (PMMA) plates and intra-medullar interlocking nailing (ILN). Four groups, each including 6 animals, were followed-up for 9 weeks in the perspective of postoperative complications and fracture healing. Routine physical examinations assessed limb function, joint involvement and condition of the operative site. Serum calcium and phosphorus showed no significant change. Full limb function was obtained quicker using fabricated PMMA plates, followed, in the order, by ILN, steel bone plating and intra-medullar pinning. Fabricated PMMA and steel bone plates showed earlier radiographic disappearance of fracture lines and earlier formation of direct bridging callus. The use of fabricated PMMA plates showed promising results for the management of the femur transverse fracture in dogs considering the advantages of lower cost, easy fabrication and actual adaptation to the specific contour of the bone.

Key words: bone plating, canine, femur fracture, intra-medullar interlocking nailing, intra-medullar pinning, polymethylmethacrylate plate.

INTRODUCTION

Among the long bones, the incidence of femur fractures is highest (45.87%) (Gahold et al, 2002) mostly seen in diaphysis and distal metaphysis (Roy et al, 2005). Internal fixation provides mechanical stability to a fractured bone, allowing weight bearing, early use of the limb and rapid healing. The selection of internal fixation is based on mechanical, biologic and clinical parameters associated with each patient and fracture, not just the fracture pattern itself (Aron et al, 1995). Intra-medullar pinning is most widely used because provides axial alignment and resists bending forces but not the shear and rotational forces (Vasseur et al, 1984). Less surgical exposure and dissection is needed to place intra-medullar interlocking nails compared to placement of bone plates. Therefore, the use of intra-medullar interlocking nail may result in preservation of more periosteal vascularity (Heitemeyer et al, 1990), promoting biological osteosynthesis (Reems et al, 2003). Bone plating resists tension, compression, shearing and rotational forces, and depending upon their placement resist bending forces. However, it is a more traumatic procedure (Stiffler, 2004), and demands extreme professional skills to achieve dynamic compression. The present study was carried out to assess the feasibility of using bone plates which contributes to dynamic compression but devoid of some complications like accurate proficiency in contouring plate with bone interface, as well as easy affordability. To this purpose we adopted an extremely versatile thermoplastic polymeric material, polymethylmethacrylate (PMMA), firstly introduced by Charnley (1960), used for decades as "filler" material in total-hip insertion and recently for internal fracture-fixation plates, to more evenly distribute forces over the plate-bone interface, thereby combating premature plate failure (Moursi et al, 2002).

MATERIAL AND METHODS

Aims
To evaluate the efficacy of fabricated polymethylmethacrylate (PMMA) plating as a method of internal fixation in canine diaphyseal femur fractures and to compare it with ILN, intra-medullar pinning and steel plating in view of bone healing and complications.
Study design
The study was conducted on twenty four (24) clinical cases of femur diaphyseal transverse fractures in dogs between the age group 2-5 years of either sex. The cases were randomly divided in to four groups and treated with four internal fixation devices (Gr. A- Intramedullary pinning; Gr. B- Bone Plating; Gr. C- Bone plating with fabricated PMMA plates and Gr. D- Intramedullary Interlocking nailing) comprising six animals in each group. Each animal of different groups were subjected to physical (condition of the operative site, assessment of full limb function, affection of joint as per the method described by Branden and Brinker, 1973) (Table I) and radiological examinations (14 mAs; 50Kvp and 90 cm FFD) throughout the study period. The decision for adopting any one of the internal fixation technique following the standard procedures (DeYoung and Probst, 1985; Conzemius and Swainson, 1999 and Raghunath and Singh, 2002) was randomly adopted.
Fabrication of polymethylmethacrylate (PMMA) bone plate
For fabrication of PMMA plates of appropriate thickness, two parts polymer of methylmethacrylate powder was mixed with one part of liquid monomer methylmethacrylate . Different sizes of femur from canine cadaver of different body weights were taken as negative cast. Then the PMMA was applied over the lateral side of the femur to achieve 6-8 mm thickness and kept till drying as a cast. The plates then were removed and grounded with sand paper into desired shape and finish and drilled with 3.5 mm drill bit to make six hole plates of different sizes (Fig. 1). Sterilization of fabricated plate was achieved by autoclaving. At the time of surgical intervention, different plates were taken corresponding to the size and body weight similar to patient under the study.

Table: I. Clinical evaluation of functional limb usage

Grade	Limb use description	Definition
I	Nonuse	No functional use of the limb; carries the limb most of the time.
II	Slight use	Some functional use; will set limb down to stand or walk; carries limb when running; does not bear weight on limb.
III	Limp	Functional use of limb; partial weight bearing.
IV	Normal	Full function for standing, walking, running; full weight bearing.

Anaesthesia preoperative preparation and surgical procedure
The dogs were pre-anaesthetized with subcutaneous injection of atropine sulphate @ 0.04 mg/kg body weight 15 minutes before the administration of injection xylazine hydrochloride @ 1 mg/kg body weight intramuscularly. After proper sedation, the dogs were placed to the operation table and operation was performed with intraoperative administration of injection ketamine hydrochloride @10 mg/ kg body weight and injection diazepam @ 0.5 mg/ kg body weight intravenously for maintenance of anaesthesia. Preoperatively, operative site was aseptically prepared with routine application of antiseptic solution, scrubbing and painting.
Anesthesia was performed using atropine sulphate (0.04 mg/kg), xylazine hydrochloride (1 mg/kg), ketamine hydrochloride (10 mg/ kg) and diazepam (0.5 mg/ kg).
The decision for adopting any one of the internal fixation technique following the standard procedures (DeYoung and Probst, 1985; Conzemius and Swainson, 1999 and Raghunath and Singh, 2002) was randomly adopted.
Postoperative care
Robert-Jone’s bandage was applied in all the cases postoperatively for 3 days to alleviate movement and the soft tissue swelling. Animals were intramuscularly administered with injection ceftriaxone @ 10 mg/ kg body weight for 7 days and injection meloxicam @ 0.3 mg/kg body weight for 3 days. Post operative dressing was carried out on 3rd, 5th and 7th day and as and when required. Removal of cutaneous sutures was done after complete healing of the wound in 10th postoperative day. The movements of the animals were restricted over the post operative period for 7-10 days. Implants were kept in situ over the entire study period.
Statistical analysis
The data were analyzed statistically by general linear model with univariate data by Tukey HSD multiple comparison test (Tukey, 1953) using SPSS 10.0 version for windows.

RESULTS

The anaesthetic regimen provided adequate anaesthesia. None of the animals showed untoward complication due to anesthesia and operative procedures.

Physical examination
Postoperative physical examination showed marked soft tissue swelling mostly up to 1st week of operation and in some cases extent of swelling persisted little bit more i.e. up to 2nd week in the animals of all four groups. The postoperative results of limb function viz. range of motion of stifle joint and full functional limb usage have been shown in Table II and III. The clinical evaluation of functional limb usage showed a remarkable difference amongst the study groups being earliest in Gr. C.

Table: II. Results of limb function and Range of Motion of the Stifle Joint (ROMSJ)

	1st week	3rd week	5th week	7th week	9th week	ROMSJ
Gr. A (n= 6)	Grade- I: (n=6)	Grade- II: (n=6)	Grade- II: (n=4) III: (n=2)	Grade- III: (n=6)	Grade- III: (n=4) IV: (n=2)	A5 week: (n=6)
Gr. B (n= 6)	Grade- I: (n=6)	Grade- II: (n=2) III: (n=4)	Grade- II: (n=1) III: (n=5)	Grade- II: (n=1) IV: (n=5)	Grade- II: (n= 1) IV: (n= 5)	A7 week: (n=1)
Gr. C (n= 6)	Grade- I: (n=5) II: (n=1)	Grade- II: (n=1) III: (n= 5)	Grade- III: (n=4) IV: (n=2)	Grade- IV: (n=6)	Grade- IV: (n=6)	N
Gr. D (n= 6)	Grade- I: (n=6)	Grade- II: (n=1) III: (n=5)	Grade- II: (n=1) III: (n=4) IV: (n=1)	Grade- II: (n=1) IV: (n=5)	Grade- II: (n= 1) IV: (n= 5)	A7 week: (n=1) A9 week: (n=2
A= ankylosis, N=normal, ROMSJ= range of motion of stifle join

Table: III. Mean ± S.E. of achievement of Grade IV (full functional) limb usage in days
Groups Days
Gr. A 63.00 ± 0.00
Gr. B 49.00 ± 0.00
Gr. C 44.33 ± 2.95
Gr. D 46.20 ± 2.80

Radiographic findings
Radiographically, fabricated polymethylmethacrylate plated animals showed early disappearance of fracture line and formation of direct bridging callus, whereas in intramedullary pinning, animals exhibited formation of excess external callus and more remodeling time. In intramedullary interlocking nailing, though did not show appreciably noticeable excess external callus formation, they took more remodeling time than steel bone plating and fabricated polymethylmethacrylate plating but lesser than intramedullary pinning. The 9th week post operative diagram of femur fracture of dog managed with intramedullary pin showed no radiographic signs of soft tissue swelling, pin migration or distortion. The radiodensity of the callus at the fracture side was uniform to that of cortical bone, suggesting maturation and remodeling. The medullary cavity was noticed reestablished in proximal and distal fragments of the fracture except at the site of union, which still represented the presence of dense callus packing the medullary canal. The remodeling was yet to be completed though, process found to be in advance stage as evidenced by irregularly arranged hypo dense callus at the periphery of the union site (Figure 2). The end stage radiograph at the 9th week of fracture immobilization in group -B, showed intact radiodense stainless steel plate and screws. The fracture gap was completely obliterated and remodeled imparting uniformity in radiographic features to that of proximal and distal bone fragments. The thickness of cortex at the union site was similar to that of normal in transcortical site (Figure 3). After the 9th week of fracture treatment with PMMA plate the radiograph showed presence of plate and all screws in situ without any materialistic abnormalities. The medullary cavity was established with uniformity of diameter throughout the length of bone. The remodeling was completed which was evidenced by absence of extra callus in the exterior or interior of the cortex at the junctional zone (Figure 4). After 9 weeks of fracture immobilization with ILN in the radiograph, fracture was found completely obliterated with organized callus. The nail and screws were found intact without any distortion, bending or breakage. The medullary canal looked uniform in diameter even at the junctional site to that of proximal and distal fragments (Figure 5).

DISCUSSION

Formation of pre-molded PMMA concave plate was very convenient without much difficulty due to its some inherent biomechanical properties like noncorrosiveness and nonabsorption or degradation of the material within the system (Vécsei and Starlinger, 1982). Marked soft tissue swelling during 1st postoperative week, irrespective of the groups, was due either to the preoperative trauma by the bone fragments and severity of the soft tissue injury during surgery. In group C and B the more duration of perceptible soft tissue swelling was due to more injury inflicted upon the tissue at the time of surgery. Moreover, more number of screw tips which crossed the transcortex might had also resulted more sustained trauma to the muscle mass in comparison to other two groups, where either no screw or less numbers of screws were used. The early ambulation of the affected limbs in the animals treated with PMMA plate in group C, followed by group D (ILN), B (steel plate) and A (intramedullary pinning) were also suggestive of quality of healing in those group in a same order as, weight bearing is considered to be one of the most important gross observable parameter for assessing the quality of fracture healing (Hutzschenreuter et al, 1969). The animals of group A treated with intramedullary pinning showed nonuse of limb for a longer duration (table-II). might have resulted due to the painful swelling of the operated limb which improved in course of time. The more duration of nonuse of the limb by the same animals might be due to incomplete neutralization of the forces as the rotational forces never are neutralized as a result of which slight rotational instability persisted in early phase of fracture healing. Similar to the animals of group A, the femur fracture of dogs immobilized with steel bone plate in group B also showed nonuse of the affected limb during the 1st week of operation which might be due to the inflammatory reaction of tissue at the site. The observation of grade-II and grade-III limb use on 3rd week as well as full functional limb use on 7th week of fracture immobilization indicated the positive correlation of better fracture immobilization and fracture healing with limb use. The use of bone plate for internal immobilization results to rigid fixation, resisting tension, compression, shearing and rotational forces (Stiffler, 2004). The use of PMMA plate for internal fixation of fracture is comparatively a newer concept with variable success (Kallmes and Jensen, 2003). The postoperative physical finding after using PMMA plates for management of femur fracture in the present study should be graded as promising as, such treated dog showed early ambulation, weight bearing and uneventful recovery which obviously might had resulted from optimum rigid fixation and qualitative fracture healing. Femur fractures were treated with interlocking nail as internal fixation device also showed grade- I limb function in first week which suggested the similar grade of tissue trauma to other groups while the surgical intervention was undertaken for fixing the internal fixation device. Subsequently, the dogs showed better grades of limb ambulation which reached to its best i.e. grade-IV, earliest at 5th to 7th postoperative weeks. Intramedullary pinning in long bone in animals undoubtedly results to better fixation stability barring its incapability for resisting the rotational force which can be overcome by using the ILN (Dueland et al, 1999). The addition of screws or bolts increases the ability of the pin to resist the rotational, shearing and compressive forces at the fracture site. The early and full limb ambulation is one of the criteria on the basis of which apparently quality of callus formation and fracture healing can be assessed, was satisfactorily observed in the animals of the Group D treated with ILN.
Intramedullary interlocking nailing does not require perfect anatomic fracture reduction of fracture for stability as such fracture with intramedullary interlocking nail undergoes indirect bone healing as interfragmentary load sharing is not usually obtained (Stiffler, 2004). In the instant study, presence of moderate quantities of external bridging callus in group A and D, is indicative of secondary bone healing with stability of fracture. As compression fixation was not attained by interlocking nailing as well as due to prevention of rotational stability of pin by screwing, the exuberant callus formation was not observed which has also been reported by many workers (Wiss et al, 1986 and Brumback et al, 1988). Radiographically, the fracture fragments were found perfectly aligned, retained without any remarkable anomalies in group B and C. The prefabricated concave plate, when used for immobilization of the bone with convex surface, coupled perfectly covering almost 1/3rd of the circumference, which provided very good gripping when fixed with cortical screws in the present study that might be attributed to the reasons for good alignment , retention of fracture fragments in postoperative observation period. In group B, type of periosteal reaction and formation of callus are in conformity of normal bore healing (Dambacher and Ruegsegger, 1994). At all stages of radiography in both the groups , the minimum external callus formation was observed with quickest symptoms of remodeling. The quality and quantity of fracture callus formation mostly depends on type and accuracy of fracture fixation; more the rigidity and stability in the fixation, minimum is callus formed (Beale, 2004). In the present study, due to rigid fixation, fracture healed by primary union, where direct osteon to osteon union of fragments occured (Stiffler, 2004; Vasseur et al, 1984).

CONCLUSIONS

Based on the above findings it may be concluded that bone plating is considered to be best option than any other immobilization devices but, self fabricated PMMA plate seems promising result in veterinary orthopedic surgery considering its cost, fabrication and facilities for imparting the specific contour of the questioned bone to be repaired, which provide the efficacy of using dynamic compression of fracture healing.

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First Published November 2008

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