TKR: Patellar Resurfacing Technique: - Wheeless' Textbook of Orthopaedics

- See: Patella in TKR

- Discussion:
- indications for patellar resurfacing
- patellar malalignment:
- lateral retinacular release:

- Technique:
- start by everting the patella laterally and reflecting the fat pad & synovium from around its periphery;
- remove any overhanging osteophytes;
- note propensity for subluxatation: (see patellar subluxation));
- prior to pataller resurfacing take the knee thru several ROM and note whether subluxation is present;
- if subluxation is present (and the tibial component is properly rotated), then the patellar
component should be medialized as much as possible (to minimize subluxation);
- determine geometric center: (see patellar anatomy);
- align geometric center of prosthetic patellar implant w/ geometric center of patella (not w/ central ridge, which is medial to geometric center);
- this ridge orients the longitudinal axis of the patella;
- in cases of pre-existing propensity for patellar subluxation, the central point of reaming should be moved medially;
- pitfalls: asymmetric resurfacing
- in some cases the medial patellar facet will be overgrown by synovium or will be eroded by arthrosis;
- do not confuse the lateral patellar facet for the main patellar surface;
- use the cautery to carefully demarcate the medial and lateral articular borders of the patellar facet;
- in the report by Pagnano et al, 300 consecutive TKAs were reviewed for presence of asymmetric patella resurfacing using a postop Merchant view;
- 21 knees in 14 patients were found to have the patella asymmetrically resurfaced;
- asymmetric resurfacing typically involved inadvertent excessive resurfacing of lateral facet w/ underresection of bone from medial patellar facet;
- all patients underwent follow-up for a minimum of 5 years, with a mean follow-up of 7.5 years;
- of the 21 knees, 3 revisions were required for patellar complications;
- one patellar component was loose on radiographs and there was marked patellofemoral pain in 6 knees;
- 11 / 21 knees (52%) underwent revision or were recommended for revision for patellar complications or had anterior knee pain that limited activities;
- ref: Asymmetric patella resurfacing in total knee arthroplasty. Pagnano MW et al Am J Knee Surg 2000 Fall;13(4):228-33.
- select component size:
- component should cover cut surface;
- patella is usually wider in the medial lateral dimension than in the proximal-distal dimension;
- make certain that there is no overhang, esp. proximally & distally;

- Depth of Patellar Resection:
- before resecting any bone, it is helpful to measure the thickness of patella, with a caliper;
- note that the average thickness of the male patella is 25 mm and that of the female 22 mm;
- it is important to exactly replace articular surface, that is resect neither to much or too little;
- amount of patella resection should equal thickness of patellar implant;
- to avoid increased patellar strains, bone patella should not be cut to a thickness of less than 12 to 15 mm;
- always know the thickness of the patellar implant before the cut is made;
- too little resection:
- height of the patella will be increased;
- altering biomechanics of quadriceps;
- may limit flexion;
- too much resection:
- worst error;
- results in a thin and mechanically weak patella that is prone to patellar fracture;
- to avoid increased patellar strains, bone patella should not be cut to thickness of less than 12 to 15 mm;
- references:
- The Effect of Patellar Thickness on Intraoperative Knee Flexion and Patellar Tracking in Total Knee Arthroplasty.
- Patellofemoral overstuff and its relationship to flexion after total knee arthroplasty.
- The effect of patellar thickness on intraoperative knee flexion and patellar tracking in total knee arthroplasty.
- Measurement of patellar thickness in relation to patellar resurfacing.
- Influence of patellar thickness on results of total knee arthroplasty: does a residual bony patellar thickness of
- Patellar resection during total knee arthroplasty: effect on bone strain and fracture risk.

- Onset Technique of Patellar Resection:
- with this method, the articular surface of the patella is resected to flat base and the patellar implant affixed on this base;
- prior to resection any rim osteophytes or surrounding synovial overgrowth (esp in RA pt) should be
removed so that the exact dimensions of the bone can be ascertained;
- hazards:
- avoid inadvertent cutting of either the patellar ligament or the quadriceps tendon;
- cut should be flat and should not remove too much bone, lest fracture of the patella develop;
- avoid making asymmetrically directed cuts;
- note that the medial facet is usually thicker than the lateral facet, which leads to a common error
of cutting off equal amounts of bone from both facets (ie too much bone is taken from the lateral facet);
- this creates an abnormal tilt to the patella;
- the proper method is to "under-resect" the lateral facet, removing only the subchondral bone, and continuing the cut
into the the substance of the medial facet;
- in the report by Pagnano et al, 300 consecutive primary, cemented, condylar TKAs were reviewed for
the presence of asymmetric patella resurfacing using a postop Merchant or sunrise patellar radiograph;
- 21 knees in 14 patients were found to have the patella asymmetrically resurfaced.
- asymmetric resurfacing typically involved the inadvertent preferential resurfacing
of the lateral facet with underresection of bone from the medial patellar facet;
- all patients underwent follow-up for a minimum of 5 years, with a mean follow-up of 7.5 years;
- of the 21 knees, 3 revisions were required for patellar complications;
- one patellar component was loose on radiographs and there was marked patellofemoral pain in 6 knees;
- overall, 11 of 21 knees (52%) underwent revision or were recommended for revision for patellar complications
or had anterior knee pain that limited activities;
- ref: Asymmetric patella resurfacing in total knee arthroplasty.
Pagnano MW, Trousdale RT. Am J Knee Surg 2000 Fall;13(4):228-33

- Inset Technique of Patellar Resection:
- in this technique, the patella is held by a patella clamp, and thru clamp a channel is reamed
into which patellar implant is inset;

- Access Patellar Tracking:
- with all trial components in place, the knee is taken through a series of ROMs, and the surgeon
assesses for patellar subluxation and lateral tilt;
- with frank subluxation, the surgeon must reassess for component malrotation and considers lateral release;

- Johnson and Johnson: