Characteristics of three different patellar implant designs in total knee arthroplasty.
BACKGROUND
Despite 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.


METHODS
The 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.


RESULTS
The 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.


CONCLUSION
Onlay-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.
['Gharaibeh|Monther A|MA|0000-0001-6637-3801', 'Chen|Darren B|DB|', 'Wood|Jil A|JA|', 'MacDessi|Samuel J|SJ|']
D019645:Arthroplasty, Replacement, Knee D006801:Humans D007720:Knee Prosthesis D010329:Patella D011474:Prosthesis Design D012086:Reoperation D016896:Treatment Outcome
implant knee arthroplasty patella