Characteristics of three different patellar implant designs in total knee arthroplasty

Abstract

BackgroundDespite debate over the role of patellar resurfacing in total knee arthroplasty, many surgeons feel it decreases re‐operation rates and anterior pain, and an increasing number are adopting resurfacing. This study compares intra‐operative characteristics of different patellar implants to assist surgeons in gaining better understanding of these implants.MethodsThe three most commonly used patellar implants (inset, onlay round and onlay oval) were allocated randomly to 120 patients undergoing total knee arthroplasty. We compared the groups in terms of implant size, bone coverage, lateral underhang (uncovered lateral facet) and need for partial lateral facetectomy. We also compared the patient‐reported outcome measures between the groups at 6 months post‐operatively.ResultsThe inset, onlay round and onlay oval designs had bone coverage of 48.5%, 65.9% and 85.9%, respectively (P < 0.01). Similarly, the onlay‐oval implant was found to have the smallest lateral underhang of all three designs (inset 11.6 mm; onlay round 6.9 mm, onlay oval 1.6 mm, P < 0.01). The onlay‐oval design was the largest implant with a median size of 35 mm, compared to 23 mm for the inset and 32 mm for the onlay round (P < 0.01). In addition, patellae using onlay‐oval implants required significantly fewer lateral facetectomies due to improved bone coverage (inset 95%; onlay round 87%; onlay oval 3%; P < 0.01). Finally, comparison of patient‐reported outcome measures between the groups showed no difference at an early assessment of 6 months.ConclusionOnlay‐oval design allows for the use of a larger implant, improving bone coverage and reducing the need for partial lateral facetectomy; however, early assessment of outcomes shows no difference between the three designs.

Patellar management during total knee arthroplasty: a review

“… 20 , 80 There is some disagreement in the literature regarding the clinical benefit of patella-friendly designs. 20 , 81 , 82 …”

“…Gharaibeh et al compared three different designs in terms of intraoperative characteristics and patient-reported outcomes and found no difference between implants. 82 Additionally, Pavlou et al conducted a meta-analysis of 7075 cases of resurfacing and non-resurfacing TKA using both patella-friendly and non-patella-friendly designs. The authors found no difference in the incidence of reoperation or anterior knee pain between patellar-friendly and unfriendly designs regardless of resurfacing status, and concluded that prosthetic design had no effect of clinical outcome of TKA.…”

Management of the Patella During Total Knee Arthroplasty

“…Inlay patellar designs are embedded into the patella after it is reamed. Onlay patellar designs are laid flat onto an evenly cut patella 53 . Inlay designs have larger bone-cement and implant-cement interfaces; however, they have not been proven to be biomechanically superior or to decrease rates of loosening 54,55 .…”

“…Additionally, onlay designs can have either a symmetric or an asymmetric patellar component. The proposed advantage of an asymmetric onlay design is increased patellar coverage due to the native oval shape of the patella 53 . Lastly, patellar components come in a variety of thicknesses.…”

Does Choice of Patellar Implant in Total Knee Arthroplasty Matter?

“…The articular surface is formed solely by the implant dome 10 . With the use of round implants (either IN or OR), some surgeons perform a lateral facetectomy to reduce the risk of lateral compression and to improve patellar tracking 11 , 12 OO implants replicate the asymmetrical retropatellar surface, aiming to improve bone coverage and to minimize the need for patellar lateral facetectomy 10 . A recent report from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) 5 demonstrated lower revision rates with onlay implants compared with inlay designs.…”