Wednesday, August 17, 2011

Revision surgery for failed shoulder replacement arthroplasty - humeral component revision, Part 13

Removal of a Humeral Implant

In some instances removal of the head of a modular component is sufficient to accomplish the desired revision including gaining access to the glenoid.

Often, however, revision requires removal of the entire humeral component. Extraction of a humeral prosthesis can be straightforward in the case where there is radiolucency in all 7 zones between the humeral endosteum on one hand and the prosthesis and any cement used to fix it on the other.

On the other hand, removal of a humeral prosthesis can be extremely challenging, for example when it has been thoroughly cemented to the bone of an osteopenic humerus or when an ingrowth or textured surface humeral component has been used.  Before embarking on the removal of a cemented humeral component, the difficulty and the necessity of the removal of cement needs to be anticipated.  The need for cement removal is influenced by the presence or absence of infection, the requirement to change prosthesis size and position, and the extent of the cementation.  In the absence of infection and when the cement is secure to the bone, we will often opt to work within the previous cement mantle (for example, using a component with a smaller diameter stem and recementing within the old cement) rather than running the risk of removing it.  The anticipated difficulty and the possibility of fracturing the humeral shaft or tuberosities during the removal are discussed with the patient in detail preoperatively.  The surgical inventory is carefully reviewed to assure that long stem implants of the appropriate diameters and head sizes are available for the subsequent reconstruction.

Our approach to prosthesis removal begins with the removal of soft tissue, bone ingrowth and cement from around the humeral head or, in the case of a modular prosthesis, from around the collar and from around the fins of the prosthesis.

If the prosthesis cannot be removed easily at this point, enough bone in the area of the bicipital groove is cut to allow the positioning of a bone tamp parallel to the shaft with one end beneath the collar or head 

The elbow is flexed to 90 degrees and the arm is stabilized to the thorax while the surgeon strikes the bone tamp so that a longitudinal impact is applied to the proximal prosthesis along the axis of the humeral shaft.  If reasonable impact does not dislodge the prosthesis, a longitudinal humeral osteotomy is started in the bicipital groove.

 When the bone is cut, the osteotome is twisted slightly to open up the endosteal cross section of the humerus.  Impact is applied as before with the bone tamp.  The linear osteotomy is continued sequentially with the osteotome twist each time until the prosthesis can be removed. 

If cement removal is necessary, this can be performed with the usual cement removal tools inserted down from the canal opening at the proximal humerus or through the humeral osteotomy.  In our hands, it seems more safe and effective to monitor the integrity of the bone by extending the incision sufficiently inferiorly so that the bone can be palpated during the cement removal rather than relying on intra operative fluoroscopy.  In any case, burrs and osteotomes tend to cut the often thin and soft bone preferentially to the hard cement; thus the surgeon must be prepared for bone penetration and its possible consequences (nerve damage, additional fracture, leakage of cement).

If a secure cement mantle remains after humeral component removal, the new humeral  component with a smaller diameter can be cemented into the old mantle.

If a cementless reconstruction is desired, the humerus can be reassembled using a long stem prosthesis press fit as far down the distal humerus as possible.

  At this point in the case the medullary canal can be divided into two components – the proximal section that was opened to retrieve the prosthesis and the distal aspect consisting of an intact cylinder.  The fixation of the prosthesis depends on this distal segment, especially in the circumstances where a cementless reconstruction is desired, for example after the debridement of an infected arthroplasty or because of concern regarding an adverse reaction to methylmethacrylate.  In this situation the cylindrical distal humeral segment is reamed with cylindrical reamers until the fit and fill of a cylindrical component stem is optimized. Since the quality of the fit depends on the length of the bone-prosthesis contact, the length of the prosthesis inserted into the cylindrical segment is maximized.  This is accomplished by extending the reaming as distally as possible and by maximizing the length of the prosthetic stem. We often start with a 300 mm stem of the proper diameter, insert it fully in the reamed canal and then measure how much of it needs to be trimmed for the articular surface to be in proper register with the glenoid.  The stem is then cut with a high-speed motorized disk and smoothed of any burrs remaining from the cut.  The prosthesis is then impacted into the distal cylindrical segment paying particular attention to the version.  The open proximal humeral segment is then folded around the prosthesis.  Because the posterior and medial periosteum and muscle attachments have been preserved, the osteotomized bone can be reconstructed by suturing the osteotomy closed using drill holes on either side (the 'bodice' repair).

Circlage can also be used, but care must be taken to protect the radial nerve that can be circlaged in its musculoskeletal groove. 


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