Surgical Technique for the Hip Joint Replacement

MEDIN OVAL MO MEDIN OVAL MODULAR MOM

MUDr. Ivan Landor, CSc.

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Introduction

The oval cup MEDIN is used in clinic praxis since the 1999 year. During the period of two years it has been used for more than 1000 patients.The hip joint cup replacement consists of two basic components (the anchoring part and the polyethylene articulating insert). The hip joint cup is applied without using any bone cement.

Titanium anchoring part has oval shape with the ovality of 6 or 12 mm and which is made of titanium alloy Ti6Al4V (ISO 5832/3). The primary fixation is provided by means of impact combined with additional fixation by the bone screws, for which are in the anchoring part of cup created the corresponding holes. For increasing of the osteointegration quality is on the anchoring cup surface applicated the macroporous surface layer, which enables a more prosperous mechanical binding by means of growing the bone tissue into labyrinth of the porous surface and besides that it also supports chemical binding by means of the binding osteogenesis. The surface is created by a layer of the porous titanium alloy of the same chemical composition like the basic material of the anchoring part. Over this subjacent layer is applied the hydroxyappatite ( Ca10 (PO4)6 (OH)2 ) sprayed coating. Both layers are deposited by means of the plasma spraying technique. The anchoring part is delivered in 6 sizes for each ovality.

The hip joint articulating insert is made of the low pressure high-molecular polyethylene (UHMWPE) with the commercial marking „Chirulen“, according to the ISO 5834 standard.

The cup articulating insert is delivered in versions with or without offsets for heads Dia 28 and 32 mm and also with centric or eccentric position of the rotation centre. In the metallic part it is anchored by dressing of the external edge by means of a rim, which will be after inserting firmly locked into the metallic part.All presented individual components are in the whole production process kept in strict evidence (registered), i.e. starting from the raw material until packing and sterilizing.In the production process are all dimensions of parts 100 % inspected. Each product is marked by a code number, which enables its traceability back through the production operations as far as to the raw material. On the sterilized components is also made the check for sterility and air-tightness.

Instructions for use

For aplication of the above presented hip joint cup replacement it is necessary to use the set of instruments delivered by the producer of implant and to follow the operation procedure.When handling the product it is necessary to prevent the contact areas against damages, which may adversely affect properties and service life of the product, especially it may cause an increased friction wear of the polyethylene insert. In any case the individual components shall be not used for test-setting as for this purpose are intended the testing templates, incorporated in the instruments set. Bedding of the components shall be done on the definitely shaped areas only.When handling the HA coated components, special care should be given to protection of the areas provided with the sprayed coatings.

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Conditions for sterilization.

Implants producer delivers the metallic parts either in sterilized condition with the marked date of sterilization, or in not sterilized condition, which is expessively marked on the packing. Eventual re-sterilization may be done by the available methods, for example by means of steam sterilization, hot air sterilization, gamma radiation e.t.c. Polyethyléne parts are delivered in the sterilized condition with the date of sterilization and in case of the packing damage it is not possible to make a re-sterilization. Such product is not allowed to be used any more !

Indications:

The implant is intended for use as an acetabular component in case of re-implanting of the TP replacement of the hip joint in a defective terrain, or in case of prime implanting of the acetabular component in heavy dysplastic terrain. Indications are also the otherwise not solvable posttraumatic stages. It is applicated by the impact method without using the bone cement.Primary fixation of the implant is reinforced by inserting of several spongious self-cutting screws. The component shall be combined with use of the bone transplants.

Contraindications:

- Infectious diseases, or local infection.- Heavy neuromuscular or vein diseases.- Bad quality of the bone structures- According to the type of implant - alergy to titanium or polyethyléne.

Caution:

Indications shall be cerfully evaluated and in case of the passed infections, marked overweight and patients with hard physical strain or addicted to narcotics and alcohol.

Recommendation

Before execution it is recommended to exclude possible alergy to titanium or UHMWPE.

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The oval cup is produced in 12 sizes with the ovality of 6 mm and 12 mm. The polyethylene articulating insert for the 6 mm ovality is delivered for Dia 28 mm and Dia 32 mm heads in the symetric version only. For the 12 mm ovality are besides the previous sets also available the asymetric inserts enabling distaling of the rotation centre by 6 mm.

Palette No. I and No. II - MS/MO

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Next two instrument sets are creating a logical set of tools for handling with patterns and for the following inserting of the oval cup replacement.

Palette No. II and No. III - MO

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I m p l a n t I n d i c a t i o n s :

Primary implantation:

In cases of dysplastic acetabula the implant enables optimum using of the acetabular fixation potencial, without necessity of any additional bone plastic.

Revision operation:

Segmental defects in case of revision of the loosened cup of the total hip joint replacement. It enables perfect fixation in upper and lower vault of the acetabular tissue with the possibility of

the additional bone plastic operations. It is indicated especially in cases with defects consisting of heavy damaged acetabula bone bed sphericity (See Paprosky III), or in cases of the bottom defects, when it enables to by-pass the defect by anchoring in the bone tissue with good quality. (Paprosky II C).

Surgical Approach :

Surgical approach shall be selected according to the own experience with the hip joint operation and according to the given diagnosis (results of medical examination). Generally spoken it always should deal in providing maximum clearliness in the operation field and fully evident boundaries of the bone bed. The author himself prefers in most cases the transgluteal operational access according to Bauer in his own modification, which is used by Hardinge. Patient lies on the operation table on his back, the skin cut starts about 7 - 10 cm distal from the top of the large trochanter and continues across the top about 7 cm in proximal direction (see Fig. A). The gluteus medius area shall be cut along the fibre in the proximal direction in the distance of 5 cm as max. from the top of the large trochanter to prevent the n. gluteus superior damage. We shall divide the vastus lateralis tendon in the extend of about 7 cm (Fig. B and C). The tendons gluteus medius and vastus lateralis shall be then folded up forward (Fig. D).In case of the continuity of the both tendineous parts it is preferable to reinforce its strength by cutting it away of the thin bone plate from the front part of the trochanteric mass. In such way is enabled sufficient approach to the acetabular as well as to the femoral component and is also given sufficient clearness in process of the bone bed preparation for oval component and its further inserting and fixation by screws. The lobe suture is recommended to be done by means of the transoseal stitch for providing perfect stability of the implanted hip joint.

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References:

Bauer R., Kerschbaumer F., Poisel S., Oberthaler W.: The Transgluteal Approach to the Hip Joint. Arch. Orthop. Trauma. Surg. 95: 47 - 49 (1979).Hardinge K.: The Direct Lateral Approach to the Hip J. Bone Joint Surg. Br. 1982; 64:17.

The Implant Size Selection

The first step after extraction of the original implant is selection of the oval cup size. When selecting the implant size we must take into account as small bone tissue removal as possible and at the same time also as much complete shape of the new oval bone cup as possible.The size of the implant is characterised by the transversal and longitudinal dimensions of the original bone bed. The transversal dimension is given by the longest distance between the front and the rear wall of the bone bed ( dimension A). According to the transversal dimension shall be also determined the diameter of the reamer, which will be used for final fitting of the bone bed for the new implant. The longitudinal dimension is determined by the distance between the upper and the lower vault of the bone bed (dimension B).

Preparation of the Bone Bed

Reaming of the bone bed shall be done by the reamer of the suitable size, taken from the first set of instruments. In process of acetabula reaming is the basic requirement to prepare the bone bed as close to the corresponding shape of implant as possible. Besides certain equalization and cleaning-up of the bone bed it deals mainly in perfect preparation of the acetabular proximal and distal vault. Maximum

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diameter of the used reamer shall not exceed the selected acetabular transversal diameter.

Testing with trial components

Into the prepared bone bed we settle the trial component. Handling with the trial component shall be done by means of the striking tool with special extension piece, which enables the component orientation in declination and anteversion. The trial component must fit after striking into the bone bed comparatively firmly.

Through the holes in the bottom of the testing component shall be checked the fitting of the cup, i.e. the range the cavitary defects. It is important to evaluate also the relation between the trial and the basic acetabular bones and to check the extend of its contact with the bone bed. In the distal and proximal vault must have full bone cover, in the front and rear part is acceptable a partial overlap of the trial component.

After introducing of the teflon testing articulation component we can repose the joint head of the femoral component and review the function and stability of the joint.

Extraction of the teflon testing Extraction of the testing metalliccomponent by special hook component by special hook

Application of Bone Grafts

Then follows application of the homologeous morselised bone graft in the quantity corresponding to the extend of cavitary defects.

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Morselised bone is compressed into defects best of all by means of the extension piece for inserting of the anchoring component.

The distal and proximal vault of the bone bed shall be kept free (see the arrow). Presence of the morselised homograft in the bone bed vaults can seriously weaken stability of the new implant. The quantity of

the morselised bone should correspond to the extend of cavitary defects. If it would be excessive, it may cause a disadvantageous lateral position of the implant and besides that also a retarded integration of such amount of bone graft may cause loosening of the implant.

The inserted implant shall be stable after impact.

Introduction of Screws

Stability of implant is further reinforced by means of introduction of the titanium screws. The screws shall be introduced into all three bones creating acetabulum, in most cases their number is four. Great attention shall be paid to the screw, which is introduced into the pubic bone (see the red arrow) and which is out of the so called safe zone, but has substantial importance for the implant stability.

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The holes for screws shall be prepared by using the flexible drill Dia 3,75 to 5 mm according to the bone tissue quality. Orientation of the drill shall be controlled by means of the aimer.

By the flexible gauge is measured the possible length of the screw which can be used.

Flexible screwdriver is used for introduction of the selected screws.

Alternatively we can use the screwdriver with Cardan joint. Total fastening shall be done after inserting of all considered screws to prevent undesirable deviation of the implant or weakening of its primary stability.

The screw which does not hold properly is of no use for the implant fixation. Screws as the additional fixation shall be used in all cases of the oval cup application

Introduction of the PE Articulating Insert

The polyethylene articulating component is introduced into the anchoring component from the top downwards to catch it on the rim in the distal part of the anchoring component (see the arrow).

The articulating component is locked in the anchoring component by strike using the special pressing tool.

Reduction

The last phase is reduction of the joint, introduction of drains and the wo

und closure.

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Postoperative Treatment

Rehabilitation in most cases does not anyhow differ from the cases of primary implantation of the hip joint. Exception is only in the duration of the weight- bearing. Full weight relief, i.e. walking on two classical crutches supported on the arm-pits is recommended approximately for 12 weeks. The partial weight-bearing on the French crutches shall be indicated according to results of the inspection and shall last for further 6 to 12 weeks.

Revision oval cup with modules

Six different shape modules for accessory fixation of the proximalpart of the socket

Individual set solves the individual finding

Simple fitting

Firm module anchoring by meanings of the imbuss screws

Operation procedure very similar to the MEDIN OVALoperation :

- eventuality of larger amount of the spongioplasty

- the only distal acetabular vault contact is sufficient

The strong stability reinforcement

The indication enlargement

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The screws are loaded in followed order :

1. distal part of the socket

2. proximal modules

3. proximal part of the socket

Anchorage part of MEDIN OVAL MODULAR

Distalized PE insert about 6mm

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A. Oval shape socket with large spongioplasty without the modulesB. Loosening two years after the procedureC. Revision surgery with the modular oval shaped socked and the solid homograft

roofing

A B C

A. Acetabular dysplasia Crowe IV.B. Solid homograft is fixed thru proximal models of the socketC. X ray twelve months after the procedure

A B C