Direct repair of Spondylolysis with the Hook Screw

Transcription

1 Direct repair of Spondylolysis with the Hook Screw Principles Surgical Technique Clinical Findings Implants and Instruments Principles Surgical Technique Clinical Findings Implants and Instruments Original Instruments and Implants of the Association for the Study of Internal Fixation AO/ASIF

2 Spondylolysis Hook Screw Principles Both spondylolisthesis and spondylolysis can cause back pain. Fur ther more, they must be con sid ered to be sig ni fi cant factors of morbidity even though they are by no means ne ces sa ri ly sym ptom-lin ked. The overwhelm ing majo rity of symp to mat ic spon dy lo lis the ses can be suc - cess ful ly trea ted sympto matically applying conser vative me thods. The cause and location of pain in cas es of spond y lolisthe - sis are by no means uniform. The pain de vel ops mainly in the spondylolysis and in the in ter ver te bral disc. The younger the pa tient, the more likely spondylolysis is the cause of the pain. The objective of any therapy is complete res to ra tion. As spon dy lo ly sis is the cause of isthmic spon dy lo lis the sis, direct repair of spon dy lo ly sis is the log i cal therapy. Thus, in contrast to spondylodesis (spinal fusion), a stiffening of the motion segment system can be avoided. In 1970, Buck was the first to suggest direct repair of spon dy lolysis by ost eo syn the sis using a screw. In 1974, we started carrying out this type of direct repair using a 2.7 mm screw. There are tech ni cal difficulties, however, with this method of direct screw ing in trying to secure the screw in cases of the neural arch dys pla sia and Spina bifida. The in ci dence of the latter is thirteen times higher in pa tients with spondylolisthesis than in the general population. A further disadvantage is that the screw crosses the spon dy lo ly sis and thus occupies the space where bone consolidation should take place. In addition, we ob served a re la ti ve ly high number of bro ken screws. 2

3 The Spondylolysis Hook Screw The disadvantages associated with or di nary screw fixa tion led us to develop the hook screw. This system consists of a specially-shaped hook, a screw with various thread forms, a compression spring, and two nuts. The hook has an off-centre opening which ensures that the not ching lies close to the base of the neural arch and thus cannot in vade the spinal canal. The inside of the hook open ing has an ad di tio nal spur which prevents lateral shifting of the hook from taking place. The spond y - lol y sis hook is available in two sizes, 6 mm, and 8 mm. In the front part, the spondylolysis screw has a can cel lous thread of 4 mm in diameter and is avai la ble in lengths of 45, 50, 55, and 60 mm. The end of the screw is trian gu - lar and can be screwed into the base of the superior articular process with a spe cial triangular sock et wrench. To maintain compression of ost eo syn the sis, a com pres - sion spring is placed between the hook and the nut. Synthes 3

4 Spondylolysis Hook Screw Surgical Technique Indication Indications for surgery in gen er al is giv en when conserva - tive meth ods in treating pain have failed, or have been without success in curing neu ro lo gi cal symp toms, and when dis location is progressive. However, af ter the 18th to 20th year of life, the risk of an in crease in progression is very slight. Direct repair of spondylolysis is only indicated in cases of spondylolyses or spondylolistheses grade 1. Surgical re - sults were similar in spon dy lo lis the ses with a dislocation of less than 5 mm and those of more than 5 mm. On the other hand, it is obviously much easier to achieve a firm consolidation in young er patients than in adults. The in ci - den ce of pseudoarthrosis (i.e. mis sing consolidation) was 6% in pa tients under 20 years of age and 30% in patients over 20 years. There was also no cor re la tion between the de gree of olisthesis and the in ci dence of pseudo arthrosis. Positioning of Patient and Approach Under general anaesthesia, the pa tient is in the prone position, pre fe ra bly on a frame that leaves the ab do men free. A midline incision is made between spinous proc ess L4 and S1 (for spon dylolysis L5 and S1). The mus cu la tu re is ab la ted subperiosteally to both sides and the entire neu - ral arch, the spondylolysis, and the entire in fe rior cir cum - fe ren ce of the upper inter-ver te bral joint are ex po sed. A clear ex po su re of the afo re-men tio ned struc tures is a man datory pre-re qui si te for avoiding tech ni cal sur gi cal faults. The spondylolysis is thoroughly pre pa red and the pseudo arthritic con nec tive tissue is removed. The spon dylolysis is freshened. Afterwards, the joint capsule is opened in its cau dal cir cu - mference, and the tip of the in fe rior ar tic u lar proc ess of the vertebra above is resected ac cord ing to Sail lant. This tip of the articular process presses on the in ter ar ticu lar portion of the ver te bral arch like a pair of pin cers when lor do sis takes place and is thought to play an im por tant role in the pa tho ge ne sis of spon dy lo ly sis. Implantation Technique The spondylolysis hook is slid over the vertebral arch from caudal by means of the special holding for ceps, with the screw directed towards the base of the superior articular pro cess (Figs. 1 and 2). Before this happens, the Ligamen - tum flavum must be par tial ly removed from the anterior surface of the neural arch. The caudal area of the neural arch is slightly not ched using a Lueur bore. This pre vents la te ral slipping of the hook. Figure 1 Figure 2 When the base of the superior ar ti cu lar process has been precisely iden ti fied, a hole for the hook screw is dril led in the base of this articular process with the 2.5 mm drill through the hole of the hook (Fig.3). Be cau se the drill is in tro du ced through the hole of the hook, it is ensured that the entry point of the screw will come to lie posteriorly outside the spon dy lo ly sis, di rect ly at the base of the superior ar ti cu lar pro cess of the spon dy lo ly tic vertebra. Figure 3 4

5 Anatomical in ve sti ga tions have shown that, when this technique is used, there is no risk of damage to nervous struc tu res. Up to now, there have not been any com pli ca - tions of this nature, although the drill must pe ne tra te the entire breadth of the base of the ar ti cu lar process. The length of the drilled canal is mea sured. Nor mal ly it is approximately 18 mm long. The thread length of all screws is uni form ly 20 mm. Thus it is easy to determine how deep the screw is inserted. In every case, the screw must penetrate the two cor ti ces and project anteriorly by 1 2 mm over the circumference of the base of the arti - cular process. Before the osteosynthesis is com pres sed by means of the compression spring and nuts, fresh can cel lous bone which can be taken out of the iliac crest through the same incision, is inserted into and along the lateral side of the spondylolysis. Care must be tak en to ensure that af - ter wards, when the hook is tigh te ned and the can cel lous bone is com pres sed in the spon dy lo ly sis, no bone frag - ments are pressed anteriorly against the ner ve root or to - wards the spinal canal. If the gap of the spondylolysis is relati vely lar ge, com pres - si on should be car ried out by tightening the nuts on both sides after both implants are in situ. Thus a twi sting of the vertebra is avoided. By direct repair and com pres sion, re - set ting of spond y lolisthe sis is achieved at least partially. Furthermore, care should be taken to ensure that, when the second nut is being tightened with the hexagonal wrench, the first (com pres sing) screw is held in place using an o ther hex ag o nal wrench. This is to avoid the screw from being inserted fur ther thus pre vent ing ex ces - si ve compression from taking place. The thread pro jec ting over the nuts is cut off. After Treatment It is advisable to confine the patient to bed for one week after surgery. The lumbar corset (prepared preo pe ra ti ve ly) should be worn for 4 6 months, i.e., until definite consolidation of the spond y lol y sis has taken place. Both implants in situ. Synthes 5

6 Spondylolysis Hook Screw Clinical Findings A follow-up examination carried out in 1989 on 33 pa - tients, who had been ope ra ted on using the hook screw, showed a good or excellent re sult in 88% of pa ti ents under 20 years of age (N=16) and 71% of pa tients over 20 years of age (N=17). The difference in results between young er and older patients was due to the fact that, in the latter, a de ge ne - ra tion of the intervertebral disc, and not spondylolysis, caused the pain. Thus direct repair is con train di cat ed when the ver te bral disc starts to degenerate. In this case, a con ven tion al anterior or po ste ro la te ral or com bined an - te ro po ste rior spinal fu sion is indicated. If it is not sure wheth er degeneration of the ver te bral disc has taken place, ma gne tic resonance imaging is recom mended. Conclusions The results of direct repair of spon dy lo ly sis using the spon dy lo ly sis hook screw are better in patients under the age of 20 than those over 20. This is due to the fact that, in older patients, the pain is caused by the degene ration of the ver tebral disc which is there fore a con tra indication to direct repair. The incidence of non-union is also higher in older patients. There is no correlation bet ween this and the de gree of olisthesis. However, the ope ra tion is only indicated in the case of pure spon dy lo ly sis and slipping of a slight de gree (gra de 1). Author: Prof. Dr. E. Morscher Department of Orthopaedic Surgery, University of Basle, Switzerland Warning: This description is not sufficient for an immediate application of the instrumentation. An instruction by an experienced surgeon in handling this instrumentation is highly recommended. Spondylolysis Hook Screw The Spondylolysis Hook Screws consist of: one hook, large or small (No or 42), one Spondololysis Screw (Nos ), one compression spring (No ), two nuts (Nos ). These components are required in pairs but have to be ordered separately. 6

7 Spondylolysis Hook Screw Implants and Instruments Implants Spondylolysis Screw, Shaft M 3 triangular, cancellous thread 4 mm dia. Instruments Triangular Socket Wrench for spondylolysis screws length 45 mm length 50 mm length 55 mm length 60 mm Tubular Hexagonal Wrench 5.5 mm for Nuts No Compression Spring for spondylolysis hook Hexagonal Wrench 5.5 mm, angled Hexagonal Nut M 3 two required per spondylolysis screw Holding Forceps for Hooks Spondylolysis Hook 6 mm 8 mm small, 6 mm large, 8 mm Subject to alterations. Synthes 7

8 Manufacturer: Stratec Medical Eimattstrasse 3, CH-4436 Oberdorf Presented by: 0123 Art. No SM_ AA Stratec Medical 2004 Printed in Switzerland GRA Subject to modifications.