Issues in Revision Total Knee Replacement

Donald T. Reilly, MD. PhD


Introduction
At the recent State of the Art Update in Orthopaedics 2000 in Whistler, British Columbia, Donald T. Reilly, MD, PhD, moderated a group of presentations on issues in revision total knee arthroplasty (TKA).


Identifying Bony Landmarks in Revision Total Knee Replacement
Revision total knee replacement poses problems for the orthopedic surgeon because the loosening process destroys many anatomical landmarks. The first mutation to ascertain is that of full extension. Kenneth A. Krackow, MD, described a modification of his positioning jigs with a perpendicular marker from the femoral component with which to define full extension.


Soft tissue cannot be used as a guide for rotational alignment of the femoral component in revision surgery because the loosening process changes tissue tension, especially in the flexion space. External rotation of the femoral component closes the lateral flexion space and moves the asymmetry that is created by a perpendicular tibial cut. This femoral rotation can cause a varus or valgus malalignment in flexion. Krackow suggested using the epicondylar axis as the bony landmark to avoid excessive external rotation of the femoral component. The epicondylar axis should be ascertained independent of the bony condyles because these change dramatically in the revision setting. Soft tissue release for alignment in extension causes external rotation of the bony femur. As such, posterior bony cuts must not follow component positioning via this technique.


Tibial component rotation takes into account the (medial-lateral) M-L axis, A-P axis, and tibial tubercle. The foot is a poor landmark for tibial rotation because common deformities can significantly change its alignment. Instead, the tibial component should be matched in rotation to the femoral component in extension, with the soft tissue being used as a secondary guide for tibial orientation.


Soft Tissue Balancing on Revision Total Knee Replacement
Chitranjan S. Ranawat, MD, proposed that revision soft tissue balancing is similar to primary knee balancing. He described his method of creating medial lateral subperiosteal sleeves for exposing a stiff knee. This method releases essentially all soft tissue medially and laterally from the femur, allowing exposure of the distal femur for implantation. If there is a discrepancy in the soft tissue balancing between flexion and extension, then a constrained component is used with this exposure.


A tibial ion rod is used for the tibial cut, and axial rotation of the tibial component is deferred until the femoral component position is fixed. In revision surgery, tibial components that are smaller than the femoral component are often required. For the femoral side, Ranawat urges preservation of distal femoral bone. The joint line should be approximately 25 mm distal to the medial collateral attachment. The tibial insert should be of sufficient thickness to place tension on the soft tissue sleeve.


For valgus knees, Ranawat suggests lengthening the iliotibial band by using a "pie crust" technique with multiple stab incisions until a balanced knee is achieved. Releases should be done to allow a springiness of 2 to 4 mm in extension and 2 to 4 mm in flexion, both medially and laterally with distraction. Flexion instability is compensated for by a TC-3-type component. Ranawat emphasized the importance of wide exposure, preservation of bone with extraction, and use of modularity.


Revision of the Patellofemoral Joint
Although the patellar-femoral joint accounts for only 1% to 12% of complications in most TKA series, it causes of 40% to 50% of revisions in those series. James A. D'Antonio, MD, discussed revision resulting from patellofemoral joint problems, including fracture, loosening, pain, and instability of the patella.


D'Antonio and colleagues evaluated a series of 161 TKAs with resurfaced patella. At 5-year follow-up, the complication rate in the patellar-femoral joint was 5%. Improvement of patella complications is dependent on the cause. Prosthetic component placement, soft tissue problems, malposition of the femoral component, and design (especially metal back patellar components) are the most common causes of patella complications.


At least 5 to 6 mm of bone stock are required for surfacing in the revision setting. If less than 5 mm are available, patelloplasty must be done, according to D'Antonio. He believes that extensor malalignment should be addressed distally so that smaller bony changes can be performed. Treatment of patella fracture depends on the integrity of the extensor mechanism and whether the prosthetic patella is loose.
The series by Berry and Rand was presented, showing that patellar-femoral complications were the reason for 33% of revisions and that the revisions were subsequently associated with a relatively high complication rate. Patella-backed components should not be used.


Allograft for Bone Loss
Bone defects in the tibial plateau present technical problems in primary knee replacement surgery. However, variety of techniques are available to solve these problems. Lester S. Borden, MD, finds classification systems for bony defects such as that described by Rand[4] to be cumbersome and to lack utility in the revision setting. Borden proposed 20 mm as the size from which the differential between graft and augmentations should be decided. He stressed the importance of retaining as much cortical rim as possible and emphasized that surgeons performing revision should start with conservative bone cuts. Cancellous allograft impaction techniques can be used with cavitary defects and the component should have maximum coverage without overhang. Cancellous morsalized grafts should be avoided in segmental defects.
Whiteside[5] used morsalized cancellous allograft to fill large femoral and/or tibial defects in 63 patients (63 knees) who had revision surgery for failed arthroplasty between September 1988 and January 1993. Fourteen of the 63 revisions required yet another procedure between 3 weeks and 37 months after the revision surgery for loosening, wound avulsion, wound hematoma, painful wires, patellar tendon avulsion from the tibial tubercle, patellar subluxation, or late-onset instability.


Cement can be used for small defects that are less than 20 mm in depth and account for less than 50% of the surface area of revised tibia.[5] Lotke and colleagues[6] followed 59 patients treated with a cement fill for an average of 7.1 years. Only 1 of the fills failed, but 43 had radiolucent lines. Radiolucent lines were not correlated with clinical symptoms.


Windsor and colleagues[7] found that autograft in primary knees healed well in a series of 50 knees with defects. Wedges or blocks used for tibial defects showed the same pattern of strain[8]. The shape of the augmentation should be based on the shape of the defect.


Borden noted that although femoral bone loss is rare in primary TKA, it occurs in 25% of revisions. Grafting or augmentation to fill these defects is important to maintain the joint line. In young patients with large defects, a "tumor" type of approach should be avoided and bulk allografts should be used for stock augmentation. In summary, cavitary lesions should have cancellous grafting, and modularity has replaced the need for most bone grafts in segmental defects smaller than 20 mm.


Cases You Would Rather Refer
Joseph C. McCarthy, MD,[9] discussed particularly challenging cases in revision TKA. Poor outcomes in TKA are associated with:
• previous trauma
• previous surgery
• extensor mechanism failure
• osteoporosis
• compromised skin
• severe deformity
• neuropathic joints
• drug dependence
• morbid obesity.


McCarthy discussed postoperative reflex sympathetic dystrophy and stressed that inclusion of a pain service in treatment is very important. Loss of the extensor mechanism can be treated with allograft augmentation[10]; however, this procedure is associated with many complications, including extensor weakness and poor range of motion.


McCarthy discussed the role of Workers' Compensation in TKA. Mont and colleagues studied the influence of Workers' Compensation on the outcome of TKA in 42 patients who had been managed between January 1980 and December 1993. These patients were matched with a group of 32 patients who were not receiving compensation. After a mean time of 80 months, patients receiving compensation had a mean Knee Society score of 64 points. The patients who were not receiving compensation had a mean Knee Society score of 93 points. The difference between the two groups with regard to fair or poor results and revisions was significant (P <.01). Surgeons should be aware that Workers' Compensation is one of several variables that may have an untoward influence on the perceived outcome of total knee arthroplasty.



References
1. Krackow KA. Identifying bony landmarks in revision total knee replacement. State of the Art Update in Orthopedics 2000. Whistler, BC: February 12-16, 2000.
2. Ranawat CS. Soft tissue balancing on revision total knee replacement. State of the Art Update in Orthopedics 2000. Whistler, BC: February 12-16, 2000.
3. Antonio JA. Revision of the patellofemoral joint . State of the Art Update in Orthopedics 2000. Whistler, BC: February 12-16, 2000.
4. Rand JA. Bone deficiency in total knee arthroplasty. Use of metal wedge augmentation. 1991;271:63-71.
5. Whiteside LA, Bicalho PS. Radiologic and histologic analysis of morselized allograft in revision total knee replacement. Clin Orthop. 1998;357:149-156.
6. Lotke PA, Wong RY, Ecker ML The use of methylmethacrylate in primary total knee replacements with large tibial defects. Clin Orthop. 1991;270:288-294.
7. Windsor RE, Insall JN, Sculco TP Bone grafting of tibial defects in primary and revision total knee arthroplasty. Clin Orthop. 1986;205:132-137.
8. Fehring TK, Peindl RD, Humble RS, Harrow ME, Frick SL. Modular tibial augmentations in total knee arthroplasty. Clin Orthop. 1996;327:207-217.
9. McCarthy JC. Cases you would rather refer away. State of the Art Update in Orthopedics 2000. Whistler, BC: February 12-16, 2000.
10. Emerson RH Jr, Head WC, Malinin TI. Extensor mechanism reconstruction with an allograft after total knee arthroplasty. Clin Orthop. 1994;303:79-85.
11. Mont MA, Mayerson JA, Krackow KA, Hungerford DS. Total knee arthroplasty in patients receiving Workers' Compensation. J Bone Joint Surg Am. 1998;80:1285-1290.