Axial 'anchor' screw (lag screw with biconcave washer) or 'slanted-screw' plate for osteosynthesis of fractures of the mandibular condylar process Christian Krenkel

Department of Maxillofacial Surgery- LKA Salzburg (Head: Univ.-Prof. Dr Helene Matras MD, DMD), Salzburg, Austria.

SUMMARY. Almost a quarter of aH mandibular fractures are located in the condylar neck region and generally lead to disturbances of occlusion. Because they still possess active growth centres, children and adolescents can take advantage of the joint's remodelling capacity following conservative treatment of these fractures. Fractures with displacement of the condylar head in adults can interfere with function if they are not surgically reduced (Krenkel and Strobl, 1989). In addition, a compensatory overloading of the non-fractured side, which originally goes unnoticed, can bring about disc pathology and chronic pain years later. For this reason, a surgical technique was developed for the management of mandibular condylar neck fractures. A new axial/oblique-axial lag screw (anchor screw) with biconcave washers (anchor washer) makes it possible to carry out standardized osteosynthesis in the region of the thin mandibular condyle neck. Functional exercises can be initiated immediately after the operation. There are three operative procedures using an extraoral approach (I-3) and two using an intraoral approach (4-5), depending on the type and severity of the fracture: I. Direct anchor screw osteosynthesis with closed gliding hole. 2. Indirect anchor screw osteosynthesis with open gliding groove and safety plates. 3. Osteosynthesis with a 'slanted-screw' plate for longer oblique fractures. 4. Intraoral anchor screw method. 5. Intraoral anchor screw method with intraoral 'slanted-screw' plate. The functional long-term results of conservatively and surgically treated mandibular condylar neck fractures were objectively documented by means of mechanical and electronic axiography. The functional long-term results of the condylar neck fractures treated surgically were significantly better than those treated conservatively. The compensatory overload on the non-fractured side in the conservatively treated group, confirmed by axiography, predisposes this joint to disc pathology and secondary joint damage due to overstretching of the capsular ligaments. Therefore, osteosynthesis of condylar neck fractures not only serves to restore anatomical conditions, but also acts as a preventive measure against overloading the non-fractured side.

INTRODUCTION

from penetrating the spongiosa or the triangular fragment from breaking off (Fig. 1) (Krenkel, 1992). It has been demonstrated (Kuttner, 1989) that lag screws with biconcave washers (anchor washers) can be turned twice as tightly as screws without washers before cracks in the bone occur. Consequently, thinner

Lag screw osteosynthesis is a performance-proven technique. Its application, however, is limited by the fact that the spherical head of the screw acts as a wedge. Combining this screw with a biconcave washer (anchor washer), which we will refer to as an 'anticrack' or 'anchor' screw has broadened the range of indications for lag screw osteosynthesis in the maxillofacial region (Krenkel, 1988). The biconcave washer causes the wedging forces underneath the screw head to be rotated through 90 degrees, which results in these forces being transformed into pressur e forces which the bone is better able to tolerate. The 3dimensional anchorage of the screw head in the cortical bone achieved with the aid of the biconcave washer (anchor washer) also prevents the screw head

Dedicated to Primarius Doz. Dr F. Clementschitsch on the occasion of his 80th birthday.

Fig. 1 - Longitudinal cut of wooden model of oblique/axial lag screw with biconcave washer (' a n c h o r ' screw). 348

Axial 'anchor' screw or 'slanted-screw' plate for osteosynthesis of fractures of the mandibular condylar process 349 screws can be used (~b = 2 mm). The use of biconcave washers (anchor washers) has made it possible to position lag screws obliquely and even parallel to the surface of the cortical bone. This is one of the prerequisites for the new axial/oblique axial ' a n c h o r ' screw osteosynthesis technique for treating condylar neck fractures.

A second indication is a fracture in the condylar neck region in which the fracture line runs obliquely inwards in a caudal direction. These fractures have a

MATERIALS AND METHODS

121 patients with 143 mandibular condylar neck fractures were treated in the Department of Maxillofacial Surgery in Salzburg, Austria between 1985 and 1989. The theoretical and practical research into the operative management of mandibular condylar neck fractures resulted in the establishment of five basic osteosynthesis techniques. The fracture is exposed via a submandibular (Risdon) incision in the upper cervical fold. Using specially designed instruments, the severely displaced condylar process can be centred in the fossa and the fracture reduced exactly. Depending on the type of fracture, three different extraoral methods are used (Krenkel, 1992). The type of fracture and degree of dislocation can be ascertained by means of computerised tomographic recordings and orthopantomography and by means of X-rays at 3 levels (Krenkel, 1987): Runstrom-IV-X-ray (transverse plane, Runstrom, 1933). Individual oblique/lateral transcranial X-ray (sagittal plane, Krenkel and Grunert, 1988). X-ray of the ramus according to Clementschitsch (frontal plane, Clementschitsch, 1941; 1951; 1963).

Fig. 2 - Mandibular neck fracture with direct axial 'anchor' screw with 'anchor' washer (closed gliding hole).

Direct axial 'anchor' screw osteosynthesis (Fig. 2)

This is the best and most stable osteosynthesis method, since the closed gliding hole reliably prevents lateral displacement of the fracture ends after the operation. Indirect axial ' anchor' screw osteosynthesis (Fig. 3)

This method is applied in the case of dislocated fractures that are difficult to reduce. The lag screw with the biconcave washer (anchor washer) is secured in the proximal fragment, which has not yet been reduced, in order to obtain an extension of the condylar process for better leverage when repositioning. The displaced condyle can then b e easily straightened and kept centred. The gliding groove and countersink for the biconcave washer ('anchor' washer) are cut secondarily into the distal fragment. The shaft of the °anchor' screw is fixed with the aid of the biconcave washer (' anchor' washer). This lateral anchorage effect, however, becomes lost after minimal resorption in the fracture gap as the screw slips slightly. For this reason the shaft of the screw must be additionally secured with one or two safety plates in the open gliding groove. The safety plates turn this into a closed gliding groove.

Fig. 3 - Mandibular neck fracture with indirect axial ' anchor'

screw with 'anchor' washer and safety plate (closed gliding groove).

350 Journal of Cranio-Maxillo-Facial Surgery

Fig. 4 Schematicrepresentation of the mandibular neck region, frontal view, with transverse fracture (1), medial (2) and lateral (3) oblique downward fracture drawn inwards. 'anchor' screw and slanted-screwplate depicted.

tendency to deviate medially and caudally after they have been reduced and this can be prevented by using the indirect axial ' a n c h o r ' screw osteosynthesis method. An additional two-hole tension band plate placed in the region of the sigmoid notch is an additional safeguard against torsion.

Osteosynthesis with 'slanted-screw' plates (Fig. 4) The idea behind the slanted-screw plate technique is that the plate screws can be positioned at angles of between 90 and 20 degrees to the surface of the plate. The long access from the submandibular region to the condylar neck usually allows only a very shallow view of the outer surface of the mandibular ramus. Consequently, in order to protect the soft tissue, the plate screws must be placed at very low angles. This can keep the soft tissue from being overstretched and the marginal branch of the facial nerve from being damaged by pressure. Indications for slanted-screw plates include comminuted fractures or oblique fracture lines running outwards and caudally. In the case of a displaced deep condylar neck fracture without condylar head dislocation out of the fossa, a lag screw osteosynthesis or a slanted-screw plate osteosynthesis can be carried out (4 and 5) to avoid having to make an extraoral incision (Krenkel, 1992).

Fig. 5 - Intraoperative view of a sagittal ' anchor' screw placed intraorally for osteosynthesis of a low fracture of the left condylar neck (arrow).

Direct sagittal ' anchor' screw osteosynthesis with biconcave washer (' anchor' washer) from an intraoral approach (Fig. 5) The surgical approach in this method is the same as that of the Obwegeser sagittal split technique (1957). The screw is positioned parallel to the occlusal plane, or just above this plane, starting from the anterior margin of the mandibular ramus (distal fragment) above the mandibular foramen, through the fracture gap to the posterior margin of the proximal fragment. Since the thin cortical bone of the inner side of the delicate ramus is very susceptible to splitting, the anchorage effect of the biconcave washer is very important for the security of the screw head.

Direct sagittal 'anchor' screw osteosynthesis with biconcave washer (' anchor' washer) and osteosynthesis with 'slanted-screw' plates from an intraoral approach (Fig. 6) In treating a mandibular fracture of the condylar neck intraorally, a direct sagittal anchor-screw osteosynthesis must first be performed before the slantedscrew plate is fitted i n t r a o r a l l y - without using the transbuccal t e c h n i q u e - to secure the osteosynthesis. Problems which may arise are as follows:

Axial ' a n c h o r ' screw or 'slanted-screw' plate for osteosynthesis of fractures of the mandibular condylar process

351

holes running lengthwise are fitted as a tension band close to the point of incision. Once the screws in these plates have been tightened, the sagittal anchor screw can also be tightened since there is now no danger of the oblique fracture ends overriding each other. Special instruments have been designed for bone preparation and reduction to facilitate this surgical technique. FOLLOW-UP

Fig. 6 - Intraoperative view of a sagittal ' a n c h o r ' screw and a direct slanted-screw plate placed intraorally for osteosynthesis of a low fracture of the right condylar neck (arrows).

Repositioning Access through the open mouth of the patient makes operating easier. Specially designed instruments for repositioning and holding facilitate the exact repositioning of the fracture ends.

The shape of the mandibular ramus The buccal surface of the mandibular ramus can sometimes be so concave that a sagittal screw, if it is to reach as far as the dorsal cortical layer of the ramus, is bound to protrude through the buccal cortical surface. When the screw is tightened, this concavity is increased thus causing a valgus shape and the body of the mandible is shifted to the nonfractured side and produces disturbance of the occlusion.

Oblique fractures When axial lag screws are used to reduce extremely oblique fractures, the fracture ends will still slip apart because the screw cannot be inserted vertically enough to the fracture line. The screw cannot, therefore, be immediately tightened. It does, however, serve as an anchorage point for the fixation of intraoral slantedscrew plates and thus stops the fragments from overriding each other. Slanted-screw plates with transverse holes can be fitted at the dorsal border of the mandibular ramus. Slanted-screw plates with the

We have treated dislocated and displaced mandibular condylar neck fractures with the foregoing methods in the Department for Maxillofacial Surgery, Salzburg since 1985. A first report was given in 1988 at the 9th Congress of the EACMFS (Krenkel and Lixl, 1988). We conducted a follow-up study on the patients operated on up to the middle of 1989. 64 condylar neck fractures were treated with direct and 13 with indirect lag screw osteosynthesis. 42 miniplate osteosyntheses were carried out with the plates fixed as slanted-screw plates. Three fractures were stabilized with sagittal ' a n c h o r ' screws via an intraoral approach. In another 2 cases, an intraoral sagittal ' a n c h o r ' screw together with an intraoral slantedscrew plate were used. In 5 cases circumferential wires were used. Three cases were stabilized with Kirschner wires (Timmel, 1981). In 8 cases, the fracture was so close to the capitulum that osteosynthesis could not be carried out, and in another 6 cases the radiographic findings revealed intracapsular fractures, making fracture reduction and osteosynthesis impossible. RESULTS Of these patients, 20 osteosyntheses with ' a n c h o r ' screws were followed-up by clinical and radiographic examination using axiography (Slavicek and Mack, 1982) for an average period of 1 year and 7 months. The control group comprised 10 patients with dislocated fractures treated conservatively, in whom the fracture had occurred more than 5 years previously. These patients were followed up in the same manner as the group managed surgically, however, for an average period of 5 years and 6 months. At follow-up, the results of clinical and radiographic examinations, as well as the instrumental findings, were remarkably consistent. For example, in axiographs the condylar outlines after conservative treatment were irregular, corresponding to the irregular X-ray findings of the joints with the formation of nearthrosis, which can develop into an ankylosis. It could be demonstrated that the patients in the group treated conservatively gradually got used to the functional restrictions experienced on the side of the fracture. The findings of axiographic analyses showed considerable differences between the two groups. Among the conservatively treated unilateral fractures (n = 10) there was hyperfunction in protrusion (x = 13.75 mm = + 38 %) and mediotrusion (x = 18 mm = + 29 %) in comparison with the group treated by osteosynthesis (n = 20). Dysfunction could best be demonstrated by a comparison of the lengths of the function lines between

352 Journal of Cranio-Maxillo-Facial Surgery

the fractured and the non-fractured side. The function of the fractured side following conservative treatment and after an average follow-up period of 5 years and 6 months was only 50.9 % for protrusion (x = 7.9 mm) and 44.9% for mediotrusion (x = 8.08 mm) and showed an irregular curve. After osteosynthesis, up to 80.8 % for protrusion and 91.9 % for mediotrusion could be reached after an average period of 1 year and 7 months. In other words, in the cases of condylar neck fractures treated by osteosynthesis, we attained almost symmetrical function with regular curves. Reduced mobility was observed on both sides in the group treated conservatively, with maximum opening of ~ = 7.30 mm on the fractured side and ~ = 11.44 mm on the nonfractured side. The group treated surgically retained sufficient maximum opening (osteosynthesis side = 10.77 mm; non-fractured side ~ = 13.94 mm). The good clinical, radiological and functional findings, in 128 osteosyntheses of the mandibular condylar neck fractures from 1983 to 1990, have been proven (Leindecker, 1991).

A

He. St. Re

Li

B Fig. 7 - (A) Frontal tomogram showing bilateral mandibular neck fracture dislocations. (B) Postoperative orthopantomograph with osteosyntheses.

CASE STUDY (Fig. 7A and 7B) A male patient, had a bicycle accident on June 22, 1989 and sustained bilateral dislocated fractures (Fig. 7A) combined with a mandibular midline fracture.

Therapy On June 23, 1989 bilateral reduction of the condylar processes was carried out using a submandibular approach and osteosynthesis with one direct ' a n c h o r ' screw for each side (Fig. 7B). The mandibular midline fracture was stabilized with two parallel oblique-axial ' a n c h o r ' screws and an alloy wire was utilised as a tension band bonded to the anterior teeth on both sides of the fracture line. Jaw exercises were commenced on the first day after the operation. Because of the small size and biocompatibility of the titanium implants, they do not have to be removed. A second operation is therefore not necessary.

D I S C U S S I O N AND C O N C L U S I O N Much has been published on the surgical management of condylar neck fractures. Petzel (1982) paved the way for the methods I have described in performing submandibular osteosyntheses starting from the mandibular border using long lag screws. The same technique was also used by Eckelt (1984). Timmel (1981) was the first to report on fixation with Kirschner wires starting from in front of the auricle, which, however, required a transarticular approach. Takenoshita et al. in 1989 introduced a combined operative procedure proceeding preauricularly and submandibularly using Kirschner wires. An intraoral lag screw method was described by Kitayama in 1989. The method of axial anchor screw osteosynthesis sets itself apart from all these techniques in that the screws are anchored so securely that they do not have to pass through the entire length of the ascending ramus of the jaw, a factor which facilitates the procedure enormously. The Kirschner wire method does not withstand function and requires at least 14 days intermaxillary immobilisation. Consequently, early mobilisation to prevent adhesions is not possible. If we compare the intraoral lag screw method described by Kitayama with the one which is presented here, we can see that the screw is much thicker and the idea of a 3.5 mm thread going through the very delicate ramus is disconcerting. The secure anchorage of the anchor screw head, made possible by the washer, makes 2 mm screws sufficient, and this in turn makes the anchor screw osteosynthesis easier and more reliable. What are the advantages of operative management over conservative treatment ? 1. Patients are free of pain immediately following the stable osteosynthesis and therefore can begin exercising the jaw on the first day after the operation. 2. Since there is no intermaxillary fixation no restrictions have to be placed on diet.

Axial 'anchor' screw or 'slanted-screw' plate for osteosynthesis of fractures of the mandibular condylar process

3. The convalescent period is considerably reduced. 4. Function on the fractured side can be fully restored so that there is no danger of overloading the non-fractured side as a result of compensation. The results we have obtained support operative treatment of condylar neck fractures with condyles dislocated out of the joint cavity or of severely dislocated condylar neck fractures with severe shortening. The restrictions associated with the method apply only to children and adolescents or to patients in whom surgery under anaesthesia would pose an unacceptable risk. The risk of danger to the marginal ramus of the facial nerve in the submandibular approach is negligible. We did not observe any lasting nerve lesions among our patients. However, caution is advised in patients who have a tendency to develop keloids. Since 1986, the use of axial/oblique axial anchor-screw osteosynthesis has not only been used in the condylar neck region but also tested successfully in nearly 1000 osteosyntheses performed in the Department of Maxillofacial Surgery of the LKA in Salzburg, Austria. The anchor-screw osteosynthesis has proved successful both in mandibular and mid-face fractures. Particularly in the mandible, the plate osteosynthesis hitherto used (over 90 %), has now in most cases been replaced by the anchor-screw osteosynthesis in 70-80 % of cases. This means that instead of 1 or 2 plates fixed with 6-8 screws, now only 2 or 3 anchor-screws are used (Knoll, 1991)- a reduction of implant material of approximately 70%. As a result, the anchor-screw osteosynthesis system is very economical. Anchor-screws, as opposed to the plate-osteosynthesis system, do not cover the surface of the bone which of course speeds up bony union. Anchor-screws do not lead to atrophy of the bone and do not need to be removed routinely. Therefore a second operation to remove the metal does not need to be performed routinely, which also avoids further morbidity. The operative processes involved in fitting and removing the screws are less complicated and less time-consuming, compared with plate osteosynthesis. Not only that, but such operations can be carried out under local anaesthesia, on an out-patient basis. The anchor-screw system, as opposed to plates, is an osteosynthesis technique with a great future since the development of resorbable implant materials.

References Clementschitsch, F. : Mitteilung einer symmetrischen Aufnahme

beider Kiefergelenke in posterior anteriorer Richtung. 0st. Z. Stomat. 23 (1941) 877 Clementschitsch, F. : Die R6ntgendarstellung des GesichtsscMdels. Urban & Schwarzenberg, Wien 1951

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Clementschitsch, F. : Die R6ntgendarstellung der Kiefergelenke.

In O. Olssen, F. Strnad, H. Vieten, A. Zuppinger (eds): Handbuch der Medizinischen Radiologie. Springer, Berlin 1963 (S. 819) Eckelt, U.." Zur funktionsstabilen Osteosynthese bei Unterkiefergelenkfortsatzfrakturen. Dissertation, Medizinische Akademie 'Carl Gustav Carus' Dresden, 1984. Kitayama, S..' A New Method of Intra-Oral Open Reduction Using a Screw Applied Through the Mandibular Crest in Condylar Fractures. J. Cranio Max. Fac. Surg. 17 (1989) 16 Knoll, M.." Klinische Ergebnisse der Versorgung yon Unterkiefercorpusfrakturen mit Ankerschrauben. Dissertation, Leopold Franzens Universit~it Innsbruck 1991. Krenkel, Ch. : Darstellbarkeit der Kiefergelenkregion in verschiedenen Projektionsebenen. Fortschr. Kiefer Gesichtschir. 32 (1987) 16 Krenkel, Ch., L Grunert : Das individuelle, reproduzierbare Kiefergelenkr6ntgen. Zahn~irztl. Prax. 39 (1988) 6; 56 Krenkel, Ch. : Die tangentiale Zugschraube mit Krallenunterlegscheibe--eine Variante der intramedull~iren Osteosynthese. 4. Internationales Maxillo-Faciales Osteosynthese-Symposion, 2.-5. M~irz 1988, St. Anton/Arlberg/Austria Krenkel, Ch., G. Lixl." Axial lag screws with double-contoured washers. 9th Congress of the European Association for Cranio-Maxillo-Facial Surgery, 5th-9th September 1988, Athens-Greece Krenkel, Ch., V. Strobl : Sp~.tfolgen einer funktionell behandelten, doppelseitigen hohen Kollumfraktur. Ost. Z. Stomatol. 86 (1989) 401 Krenkel, C. : Axial 'Anchor' Screw (Lag Screw with Biconcave Washer) or 'Slanted-Screw' Plate for Osteosynthesis of Fractures of the Mandibular Condylar Neck (Biomechanics and Osteosynthesis Technique). Habilitation, Universit~t Wien, Quintessenz Verlags-GmbH, 1993, English (in press) Kuttner, P. : Untersuchungen zur physikalischen Dynamik yon Zug- und Tandemschrauben mit bikonkaven Unterlegscheiben am Unterkiefer. Dissertation, Leopold Franzens Universit~it Innsbruck 1989. Leindecker, B..' Klinische Ergebnisse der Versorgung von Unterkiefercollumfrakturen mit Zugschrauben und Miniplatten. Dissertation, Leopold Franzens Universitfit Innsbruck 1991. Obwegeser, H. L. : The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. Oral Surg. 10 (1957) 677 Petzel, J. R. : Die Zugschraubenosteosynthese der UnterkieferGelenkfortsatzfrakturen-Biomechanik-Instrumentarium-Klinik. Habilitation, Rheinisch-Westf~ilische Techniscbe Hochschule Aachen 1982 Runstrom, G. : A roentgenological study of acute and chronic otitis media. Wez~ta Wald. Zachrisson Boktryckeri A.-B., O6teborg 1933 Slavicek, R., H. Mack: Der Axiograph. Inf. Orthod. Kieferorthop. 14 (1982) 53 Takenoshita, Y., M. Oka, H. Tashiro : Surgical Treatment of Fractures of the Mandibular Condylar Neck. J. Cranio Max. Fac. Surg. 17 (1989) 119 Timmel, R.: Die Osteosynthese yon Luxationsfrakturen des Kiefergelenkes mittels Kirschner-Drahtung. Dtsch. Z. Mund. Kiefer GesichtsChir. 5 (1981) 243 OA Dr. Christian Krenkel M D D M D Abteilung fiir Kiefer- und Gesichtschirurgie der LKA Salzburg Mfillner HauptstraBe 48 A-5020 Salzburg Austria Paper received 5 April 1991 Accepted 17 July 1992

Axial 'anchor' screw (lag screw with biconcave washer) or 'slanted-screw' plate for osteosynthesis of fractures of the mandibular condylar process.

Almost a quarter of all mandibular fractures are located in the condylar neck region and generally lead to disturbances of occlusion. Because they sti...
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