Patent Publication Number: US-2005119756-A1

Title: Disposable articulated spacing device for surgical treatment of joints of the human body

Description:
TECHNICAL FIELD  
      The present invention is generally applicable to surgical treatment of articulations of the human body and in particular relates to a disposable spacing device for temporary replacement of joint prosthesis which have to be explanted due to unsuccessful septic or aseptic implantation of artificial joints.  
      According to the well known surgical “dual stage” method, the above spacing device can be maintained in the joint seat as long as necessary for re-establishing the most favourable conditions of implantation of the new artificial joint prosthesis.  
     BACKGROUND ART  
      It is known how artificial joints, such as knee, hip, heel and elbow joints often have to be removed for various reasons and mainly following local infections after a surgical implant.  
      In such a case, it is not possible to replace immediately the unsuccessful prosthesis with a new one, but the seat of the joint must be treated with suitable antibiotics before a new surgical operation can be performed.  
      In the meantime, the space within the joint must be maintained in order to prevent a reduction in the articular space, retraction of the tissues, atrophying of the joint and loss of muscular elasticity and tone.  
      Spacing devices used in the two-stage implant of artificial joints, for treatment of both the hip and the knee, are known.  
      Italian patent application No. VR95A000072 describes a disposable spacing device for an artificial hip joint, essentially characterized in that it is made of a biocompatible base material of the type used for bone cements.  
      Spacing devices for knee joints which are manually made by the surgeon at the time of the surgical operation are also known, these devices being made from blocks of bone cement of standard shape, optionally containing active constituents.  
      A drawback of these known methods of treatment is that they do not allow the space within the joint to be kept apart in an ergonomically and anatomically correct manner. Moreover, the long time required for preparation increases the difficulties for the surgeon and reduces the probability of success of the operation.  
      In order to overcome these drawbacks, spacing devices have been made using suitable anatomically and ergonomically shaped moulds which are filled with bone cement in situ. However, these known spacing devices do not allow mobilisation of the joint and result in the need for a long rehabilitation after reimplanting the permanent prosthesis.  
      In still other cases, the spacing devices have been obtained by lining a permanent metal prosthesis with bone cement. Although this solution allows a temporary articulation, it is difficult to prepare and in spite of use of cement-lined prostheses requires that such devices are positioned in infected seats, which most of the surgeon consider a worsening infection factor.  
     DISCLOSURE OF THE INVENTION  
      The main object of the present invention is to provide surgeons with a disposable and ready-to-use articulated spacing device, able to be directly implanted in the articulation seat for example of knee, hip, hell or elbow joints in case of replacement of a pre-existing prosthesis which must be removed due to septic or aseptic failures.  
      A further object is to provide a disposable articulated spacing device which allows to maintain a in a healing environment a suitable articular space for the time necessary to successfully re-implant a new permanent prosthesis.  
      A further object is to provide a disposable articulated spacing device which allows correct articulation and an anatomical and ergonomic form of the temporary implant.  
      Yet another object is to provide a disposable articulated spacing device which can be easily implanted and explanted into/from the location of the joint.  
      Yet another object is to provide a disposable articulated spacing device with limited articular friction so as to allow considerable mobility of the joint and improve the quality of life of the patient during hospitalisation.  
      These and other objects which will be more apparent hereinafter are achieved by a disposable articulated spacing device for the temporary replacement of a joint of the human body which, in accordance with claim  1 , comprises at least one first member able to be secured to a first articulation end and at least one second member able to be secured to a second articulation end, both said members being pre-formed and entirely made of biological compatible and porous material suitable to be added with pharmaceutical and therapeutical products, said pre-formed members being able to be reciprocally coupled in an articulated manner to maintain a suitable joint space and at least partial articulated mobility for the time necessary to perform the further implantation of a new permanent joint prosthesis.  
      Preferably, the above mentioned biologically compatible and porous material is chosen among metals, metallic alloys, organo-metals, ceramics, glasses, plastics materials, bone cements and combinations thereof.  
      The pre-formed members of the device may be previously charged with suitable pharmaceutical and therapeutical products. As alternative, the pre-formed members are initially free of the same products and are added immediately prior of their implantation by contact absorption or by filling of suitable cavities formed on their other surface.  
      Advantageously, the pharmaceutical and therapeutical products may be chosen among medical active principles, antibiotics and radiopacifier and may be added in the pre-formed members.  
      In case that the articulated spacing device replaces a knee joint, the pre-formed members may comprise a femoral member consisting of a body substantially shell-shaped and reproducing the femoral condyles, and tibial members consisting of a prismatic body able to replace the resected tibial flat portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Further features and advantages of the invention will, be more clearly understood in the light of the following detailed description of a disposable articulated spacing device furnished by way of a non-limiting example with the aid of the accompanying drawings, in which:  
       FIG. 1  shows a front view of a first detail of a spacing model according to the invention;  
       FIG. 2  shows a side view of the detail according to  FIG. 1 ;  
       FIG. 3  shows a top view of the detail according to  FIG. 1 ;  
       FIG. 4  shows a front view of another detail of the spacing device according to the invention;  
       FIG. 5  shows a side view of the detail according to  FIG. 4 ;  
       FIG. 6  shows a top view of the detail according to  FIG. 4 ;  
       FIGS. 7 and 8  show perspective views, from the top and bottom, of the detail of the device illustrated in FIGS.  1  to  3 ;  
       FIGS. 9 and 10  show a side view and a top perspective view of the detail according to FIGS.  4  to  6 ;  
       FIG. 11  shows a perspective view of the two details of the preceding figures in aligned positions; and  
       FIG. 12  shows a side view of an alternative embodiment of the spacing device according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      With reference to the above mentioned figures, there is shown a disposable articulated spacing device for the temporary replacement of a joint prosthesis explanted from a human body.  
      The articulated spacing device, generally indicated with the reference number  1 , comprises at least one first member  2  able to be secured to a first joint end and at last one second member  3  able to be secured to a second joint end.  
      According to the invention, both members  2 ,  3  are pre-formed and entirely made of a biological compatible and porous material and are mutually coupled in an articulated manner so as to maintain in a healing environment a suitable joint space and at least partial mobility of the joint for the time necessary to permit the further re-implantation of a new permanent joint prosthesis.  
      Preferably, the biological compatible and porous material may be chosen among metals, metallic alloys organo-metals, ceramics, glasses, plastics materials and combinations thereof.  
      Specifically, the above plastics material may be chosen among thermoplastic polymers, such as acrylic resins, polyethylene, polypropylene, thermoformable e.g. by blow moulding or injection moulding.  
      As alternative, the plastics material may be chosen among cold-formable resins curable by means of free radical polymerisation such as acrylic resins and polyesters.  
      In a per se known manner, free radical polymerisation may be accelerated either by suitable chemical catalysts and initiators, such as benzoyl peroxide, or physical accelerators such as ionizing radiation, gamma-rays, UV-rays.  
      In the particularly preferred embodiment the biological compatible and porous material forming the members  2 ,  3  is a bone-cements, e.g. that used in the Italian patent application no. VR95A000072 filed by the same applicant.  
      The pre-formed members  2 ,  3  may be previously added with suitable pharmaceutical and therapeutical products chosen among active medical principles, antibiotics and radiopacifiers.  
      In alternative, the pharmaceutical and therapeutical products may be added to the pre-formed members immediately prior of implantation thereof either by direct contact absorption or by filling of suitable cavities formed on their outer surfaces.  
      The pharmaceutical and therapeutical products in the form of liquid solutions may be easily absorbed by the device thanks to the porosity of their basic material and then released after implantation in the joint seat.  
      Advantageously, the pre-formed members  2 ,  3  may be shaped in different sizes to be correctly adapted to the different patients. Moreover, these members may present anchoring means for their fixation to the joint ends.  
      The embodiment of the spacer device  1  shown in the figures is designed to be inserted in the knee joint.  
      The pre-formed member  2  is a tibial member and the pre-formed member  3  is a femoral member.  
      In particular, the femoral part  3  consists of a first proximal body  4  designed to occupy the space left by an explanted metal prosthesis. Preferably, the body  4  has a shape, in plan view, approximately in the form of a “U” or horseshoe, with side portions  4 ′,  4 ″ and a central recess  5 . The external contact surface  6  of the body  4  has a curvature able to reproduce that of the femoral condyles.  
      The tibial member  2  consists of a second proximal body  7  which is approximately prismatic, slightly curved and of suitable thickness. The body  7  also has a shape, in plan view, approximately in the form of a “U” or horseshoe, with a curved internal contact surface  8  and an internal recess  9  so as to simulate the resected tibial flat portion.  
      The contact surfaces  6 ,  8  of members  2 ,  3  are formed so as to allow a roto-translatory movement during the flexing/extending movement of the limb.  
      Moreover, the surfaces  6 ,  8  may have an excellent surface finish with a low coefficient of friction so as to allow a considerably degree of articular mobility.  
      Both members  2 ,  3  may be provided with respective projections or rod-shaped distal portions  10 ,  11  for securing to the respective joint ends, e.g. by means of bone cement.  
      In use, the surgeon initially removes the previous infected joint prosthesis and cleans the articulation space. The surgeon further chooses the suitable spacing device with pre-formed members  2 ,  3  adapted of the size of the patient.  
      If the pre-formed members are already previously charged with active principles and pharmaceutical and therapeutical products upon formation thereof, the surgeon implants them taking care that they are fixedly secured to the joint ends and are mutually articulately coupled to allow at least partial mobilisation of the joint.  
      If on the contrary the members are not yet charged as above, the surgeon either impinges them in a solution of active principles or fills with them several outer cavities formed in situ or pre-shaped on their outer surfaces, and finally implants the members in the articulation seat, securing them to the joint ends through appropriate anchoring means or bone cement.