[Modification of the Blackburne-Peel ratio for improved application in total knee arthroplasty].
BACKGROUND
The methods currently used to measure patella height in relation to the tibiofemoral joint line after total knee arthroplasty are not easily reproducible. For this reason we modified the Blackburne-Peel ratio.


METHODS
Instead of taking the tibial joint line as the reference line, we constructed a tangent on the femoral condyle. In addition, we took the greatest diameter of the patella from the tip of the patella as a measuring line.


RESULTS
Compared with the classic Blackburne-Peel and Caton-Deschamps ratios, it was much easier to determine the patella height in osteoarthritic knees and after total knee replacement using this modified Blackburne-Peel ratio. Factors such as the height of the polyethylene inlay, the slope of the tibial component, and superimposition of the patellar joint line can be disregarded. Preoperative and postoperative reference lines can be compared readily. Furthermore, the classic Blackburne-Peel ratio shows a greater tendency to interpret the measurements after total knee arthroplasty as pseudo-patella baja. The interobserver variability was good for all ratios.


CONCLUSIONS
We can therefore recommend the modified Blackburne-Peel ratio for measuring patella height in relation to the tibiofemoral joint line after total knee arthroplasty.
Classen
T
T
Klinik für Orthopädie, Universität Duisburg-Essen, Essen, Deutschland. timclassen@gmx.de
Wegner
A
A
von Knoch
M
M
D000465:Algorithms; D019645:Arthroplasty, Replacement, Knee; D005269:Femur / Q000000981:diagnostic imaging*; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D017063:Outcome Assessment, Health Care / Q000379:methods*; D011859:Radiography; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
Clin Orthop Relat Res. 2001 Nov;(392):46-55
11716424
J Arthroplasty. 1988;3(2):177-80
3397748
Clin Orthop Relat Res. 1982 Oct;(170):152-5
7127941
J Bone Joint Surg Am. 1979 Sep;61(6A):879-83
479233
J Bone Joint Surg Br. 1977 May;59(2):241-2
873986
Clin Orthop Relat Res. 1982 Oct;(170):141-6
7127939
Z Orthop Ihre Grenzgeb. 1984 Mar-Apr;122(2):159-66
6720040
Knee Surg Sports Traumatol Arthrosc. 2000;8(4):231-6
10975264
Am J Sports Med. 1996 Mar-Apr;24(2):218-21
8775124
J Bone Joint Surg Am. 2003 Feb;85(2):259-65
12571303
J Arthroplasty. 2002 Jan;17(1):66-9
11805927
Radiologe. 2009 Jun;49(6):533-7
19468704
Clin Orthop Relat Res. 1982 Oct;(170):116-22
7127936
Radiology. 1971 Oct;101(1):101-4
5111961
Orthop Clin North Am. 1998 Apr;29(2):355-60
9553581
Rev Chir Orthop Reparatrice Appar Mot. 1982;68(5):317-25
6216535
J Arthroplasty. 1991 Jun;6(2):169-77
1875209
Clin Sports Med. 1985 Apr;4(2):247-57
3986927
Rev Chir Orthop Reparatrice Appar Mot. 1995;81(4):286-95
8559997
J Bone Joint Surg Br. 2006 Apr;88(4):484-8
16567783
Clin Orthop Relat Res. 1992 Sep;(282):170-6
1516309