Salvage

The most important problem to avoid is that of persistent maltracking of the patella. Provided careful attention to detail has been undertaken in the performance of the operation, the incidence of maltracking is extremely low (less than 2 %) - refer to technique. In the event of there being significant recurrent subluxation or dislocation a distal soft tissue realignment using the Roux Goldthwaite or a tubercle osteotomy with the Elmslie procedure will usually correct this problem.

Disease progression in the tibiofemoral joint

In cases that develop persistent pain, investigation with x-rays and then an arthroscopy of both the tibiofemoral joint and from the supero lateral portal of the patello-femoral joint will exclude or identify any specific causes.The most usual cause of persistent pain is disease progression and some improvement can be obtained with arthroscopic debridement, partial meniscectomy and chondrectomy. If the disease process continues to give troublesome symptoms then the patient will become eligible for a total knee replacement.

Unexplained persistant pain

If there are continuing symptoms of pain particularly associated with some dysfunction of the patellofemoral mechanism and tibio femoral disease progression problems have been excluded then further investigation is warranted.  It has now been established that a small number of cases have persistent symptoms due to minor misplacements of the components.

The most common of these technical errors is an extended anterior cut leading to elevation of the trochlear prosthesis and symptoms of tightness due to overstuffing or overstretching of the patellofemoral compartment.

A second and extremely subtle technical error is insufficient external rotation of the femoral component which can lead to overtightness of the lateral part of the patellofemoral joint and on occasions clicking symptoms due to problems with the patellar button smoothly engaging the trochlear groove.  The reference points for judging rotation of the prosthesis are poorly defined and it is difficult to judge the three to four degrees of external rotation which is so helpful in facilitating correct patellar tracking.

The third technical error that has been identified is when the femoral component has not been sufficiently inset on the medial and lateral femoral condyles leaving a small step which can result in clicking symptoms in flexion.  There should be a smooth transition from normal femoral condylar articular cartilage onto the metallic prosthesis on both medial and lateral condyles and these should be balanced as symmetrically as possible.  The overall alignment of the prosthesis does, therefore, sometimes vary depending on the underlying anatomy of the particular patient.

When such technical errors have been identified often with the help of a suppression CT scans revision of the femoral component by repositioning it on the femur and possibly downsizing the prosthesis has successfully solved these problems.  Revision to a total knee replacement in these circumstances is unlikely to solve the problem.

Revision

Revision to a total knee replacement is a straightforward procedure. The Avon patella button is identical to that of the Kinemax Plus total knee replacement and thus a modular procedure using the Kinemax Plus system is the simplest solution to the problem. Alternatively if another total knee replacement system is used then one must either accept a mismatch of the button with the trochlea or replace the button completely. The Avon button is a good match with other total knees, including the Duracon and Scorpio knees.

Removal of the trochlea is straightforward. A thin oscillating saw allows the cement prosthesis interface to be fatigued and the component will usually lift off after judicious use of a sharp thin 5mm osteotome to fatigue the edges of the cement prosthesis interface around the condyles. After removal of the trochlea, the anterior cut is identical to that of a standard total knee replacement. After completion of the other femoral cuts there is seldom more than the four small defects corresponding to the pegs of the trochlea component. The rest of the procedure is a standard primary total knee replacement

References

1. Ackroyd CE, Newman JH, Evans R, Eldridge JDJ, Joslin CC.  The Avon patellofemoral arthroplasty five year survivorship and functional results.  J Bone Jt Surg. 2007; 89-B: 310-15.
2. Porteous AJ, Mulford JS, Newman JH, Ackroyd CE.  A review of revision patellofemoral arthroplasty patients. J Bone Jt Surg. 2008; 90B; (Suppl 3) 575.
3. Mulford JS, Porteous AJ, Ackroyd CE, Newman JH. Clinical results after revision of patellofemoral arthroplasty. Current Orthopaedic Practice 2009. In press.
4. Lonner JH, Jasko JE, Booth RE Jnr:  Revision of a failed patellofemoral arthroplasty to a total knee replacement.  J. Bone & Jt. Surg. 2006; 88 –A: 2337-42