FLEXION | Newsletter for Orthopedic Surgeons Volume 4 - Number 1 September 1996
Enhanced Instrumentation for Removal of a Bone Plug and Cement in the Distal Canal
Jeffrey M. Hayer, MD
Attending Orthopaedic Surgeon
Franklin Medical Center
The Problem: Cement Removal in the Distal Canal
To the present, numerous systems have been devised and used to remove cement - Midas Rex, Anspach, Cebotome, Moreland, Gray Revision, manual chisels, and Origin.
Manual tools deal with cement extraction through the inherent principle of controlled methodical removal. Unfortunately, they do so at the expense of time. Manual tools serve well in the proximal canal, but are, however, less effective distally or on a varus cement ledge with limited visualization.
Power tools cut with vigor, but with no ability to differentiate between cement and bone, resulting in consistent breaching of the intact cortical envelope. Cannulated versions will work when a flat mantle presents and extensive fluoroscopy is employed to centralize a guide pin in the canal, with biplanar considerations. In the presence of an angulated mantle, or a lateral cortice violated by the distal stem, breach of the cortex becomes an enduring problem with guide pin placement. At that time, fluoroscopic control is definitely mandatory.
Figure 1. The flexible reamer is passed down first as a device so that the guide wire can be passed through and drilled into the plug.
Figure 2. The cannulated End Mill reamer is placed centering over a guide pin in the midfemur. A smaller wire is drilled into the cement plug and then the cannulated reamer is used to remove the plug.
The Origin system is a triumph of technology over reason, in that you are actually adding more glue and relying on an imperfect bond between old and new polymethylmethacrylate to remove the old implant. In my experience, this has proven not to be fully effective and actually may further compromise bone integrity by methylmethacrylate leaking through breaches in the old cement mantle.
From my experience, the primary challenge is to place a guide pin centrally in the cement column-plug complex without the use of fluoroscopy, ream over this guide pin without perforation, and extract the remaining cement tube without removing needed bone stock - all in a reasonable amount of time.
| CURRENT TECHNIQUE |
Following routine extraction of the loose femoral component, utilizing thin flexible osteotomes proximally, and various cement chisels in the metaphysis, I focus on the distal cement column with the use of current Howmedica instruments.
First, I size the distal end of the femoral component to ascertain its diameter, and follow with short flexible reamers (3211 series) wedged into the distal canal to act as a centralized drill guide (Fig. 1). A Gamma Guide pin (3371-1-060) is of sufficient length and diameter to be inserted into the cement and drilled across the distal complex. The flexible reamer is removed, and the distal cement is successively reamed over the Gamma Pin with Gray Cannulated End Mills (Fig. 2). If, following this process, a cement tube is maintained, I return to flexible reamers over a femoral guide pin and sequentially ream the residual cement (Fig. 3). This has been necessary when bone stock is reasonable, the cement interface is intact, or the bone plug is below the isthmus. With cement tubes in which the cement interface is compromised or the cement has fractured, a hook is passed through the reamed complex and the fragmented cement is extracted in a distal-to-proximal fashion.
It should be mentioned that I have not used imaging with this technique with any appropriate aligned cement mantle. With malaligned cement mantles, however, fluoroscopy is appropriate with the instruments at hand, using the reamer as initial placement of the guide wire. Therefore, it is imperative to proceed with centering jigs that would allow one to deal with malaligned cement mantles by reviewing preoperative AP and lateral radiographs to assess angulation and eccentricity of the distal plug. This would minimize the need for fluoroscopic control during this complex procedure.
If I were to draft design requirements to extend this technique, they would consist of the following enhanced instrumentation:
- Centering jigs to deal with angulated cement mantles
- A "disimpaction" instrument
| ENHANCED INSTRUMENTATION |
Two jigs of small diameter that receive external sizing collets (disposable) could be used to fill void between the canal and centering jig, to initiate centralization. One jig will have a central hole applicable to centralized distal mantles, the other jig an offset hole so the jig can be rotated 3600 to deal with an angulated mantle or enable the guide pin to pass internally past a cortical perforation. The jig and collets will be shaped like cones in a reverse fashion to achieve a friction fit between collet and jig.
Guide pins, mills, reamers
The current tips of the Guide Pins and End Mills appear sufficient. The reamers could, however, be designed with a sharper pitch. If all three items above incorporated an "auger" component, cement removal would be enhanced. An auger would expedite removal: When the End Mill is cutting through the cement mantle, the auger would then bring the cement out of the cutting plane, essentially clearing the path to minimize the amount of free body interface between the End Mill and the virgin cement that is being cut.
A disimpaction instrument similar in design to the Osteolock Sleeve extractor with an expanding distal diameter that can be slipped over the guide pin through the reamed complex is part of my design. This instrument may be expanded below the cement tube by turning a knob proximally, and it imparts proximal extraction forces through a slaphammer attached to the end of the "Disimpactor."
| CONCLUSION |
A centralized jig system used in cement removal, including reaming out the distal femoral cement mantle over a cannulated pin affords a safe and effective way of dealing with a very complex problem that often leads to breaching the cortex or fracturing the femoral shaft. The appropriate use of centering without the need for fluoroscopic control also minimizes the potential for contamination and increased infection rate and reduces an obvious radiation hazard to the surgeon and his/her colleagues. My experience at this time is with 14 cases, from which I can only conclude that this could be used more effectively for highly varus or valgus mantles or for mantles that are posteriorly or anteriorly angulated. What once was a cement removal procedure that often resulted in multiple cortical breachings by using standard techniques, and was characterized by a significant amount of time working in a poorly visualized window, now can be accomplished very efficiently and with a notable reduction of surgical time.
Midas Rex, Anspach, Cebotome, Moreland and Origin are not trademarks of Howmedica Osteonics, Inc.
QUESTIONS & ANSWERS
What is the best surgical approach in total hip replacement to prevent limp?
Guy H. Frumson, MD
Gait disturbances following total hip arthroplasty (THA) are primarily caused by disruption of the abductor musculature. The surgical approach that results in the least disruption of these muscles is the posterior or "southern" approach. Theoretically, a transtrochanteric approach should also not disrupt the abductor muscles. However, problems with trochanteric nonunion and painful trochanteric hardware may lead to an increased answers risk of limp, compared to the posterior approach. The direct lateral (Harding) or anterior lateral (Watson Jones) approach requires dissection of the anterior portion of the gluteus medius and minimus. Despite meticulous repair of these muscles, limp can occur with these approaches. Other causes of limp following THA such as leg length discrepancy, loss of abductor power secondary to shortening of the abductor lever arm, and painful prosthesis are independent of the surgical approach used.
Joseph A. Bosco III, MD
Figure 3. The End Mill reamer, tracking distally, in the process of reaming out the cement (top), and all cement removed (bottom).
Exposure for Total Knee Replacement With Consideration of Preoperative Deformity
The technique of total knee replacement requires accurate component placement and the re-creation of neutral alignment. Preoperative deformities typically cause contractures, making ligament balancing techniques a critical portion of the procedure. Typical methods of establishing a balanced knee involve release or lengthening of the contracted soft tissues on the concave side of the deformity. Care should be taken during the initial surgical exposure not to aggravate pre-existent ligament imbalances.
Conventional knee exposure for total knee replacement involves a medial tibial metaphyseal dissection. With certain valgus lenses where the concave side of the deformity is on the lateral side, a conventional medial exposure as performed for a varus knee could aggravate the imbalance of the deformity. This is particularly important in patients with type II deformities where the medial collateral ligament is stretched; in this circumstance, conventional medial exposure may necessitate a more drastic lateral ligament release, putting neurovascular structures at risk. Limiting medial exposure in valgus knees to the level of the medial collateral ligament and not proceeding with posterior medial dissections will lessen the amount of soft tissue release required laterally to accomplish neutral ligament balance.
A medial release as part of the initial exposure for a varus knee will enhance bony mobility and make bone exposure much easier to accomplish. Subluxation of the tibia anteriorly enhances tibial exposure and allows for easier component placement. Since a medial release will typically be required for a patient with a preoperative varus deformity, incorporating this release in the initial exposure will facilitate the procedure. Paying attention to preoperative deformity and incorporating this factor in the exposure methodology will enhance the surgeon's ability to correct deformities with minimal ligament releases, avoiding the complications of nerve injury and postoperative ligament instability.
John R. Schurman II, MD