The Positions of Bony Protrusion Where Bone-Neck Impingements Occur by 4 Different Movements.
+*Yoshimine, F.
+*Tokyo Metropolitan Health and Medical Treatment Corporation Ohkubo Hospital, Shinjukuku, Tokyo, Japan
[email protected]
Introduction: Total Hip Arthroplasty (THA) tends to have more
frequent impingements and more dislocations than normal hip joints.
Bony impingements take place before prosthetic (cup and neck)
impingements. Prosthetic impingements and bony impingements lead to
subluxation and dislocation and prosthetic loosening, especially for a
patient with good hip movement. Bone and neck impingements by bony
protrusions left alone around the cup edge can be avoided by excising
during the THA operation. The position of the prosthetic impingement
on the cup edge is not known. Where prosthetic impingements occur on
the cup edge was analyzed for 4 different movements in different cup &
neck positions in both total hip prostheses with different technical ROM
( ) of 120° and 135°.
Methods: Prosthetic impingement points were shown as the coordinates
(x,y,z) in mathematical calculations. The reference point (R) was
defined as the distal one of the two intersections between the cup edge
and the coronal plane through the rotation center (C). The impingement
points on the cup anterior edge (L) and the cup posterior edge (M) were
indicated by the angles of LCR and MCR (Fig.1). Cup abduction
( ) 35°,45°,55°, Cup anterior opening(radiographic)( ) 10°,20°,30° and
Neck anteversion (b) 10°, 20°, 30° were selected. In the 27 combinations
of these 3 factors, the prosthetic impingement locations for flexion (FL),
internal rotation at 90° flexion (IRfl90), extension (EXT ) and external
rotation (ER) were calculated for the THP with ( ) of 120° and 135°.
The criteria of essential ROMs were defined as: more than 120° FL,
more than 45° IRfl90, more than 30° EXT and more than 40° ER, and
the number of combinations which fulfilled all the criteria of ROM were
checked.
Result: In ( ) 120°, the area of prosthetic impingement ranges from
117° to 150° anteriorly in FL, from 117° to 129° anteriorly in IRfl90,
from 52° to 80° posteriorly in ER and from 71° to 110° posteriorly in
EXT(Fig.2, Table 1). In ( ) 135°, the area of the prosthetic impingement
ranges from 122° to 157° anteriorly in FL, from 123° to 130° anteriorly
in IRfl90, from 43° to 80° posteriorly in ER and from 78° to 114°
posteriorly in EXT(Fig.3, Table 1). When ( ) enlarged from 120° to
135°, the prosthetic impingement locations of FL, IRfl90, ER moved
proximally by only 5° or 6° and the prosthetic impingement locations of
EXT moved distally by only 5° or 6°. Only 1 combination of cup and
neck position fulfilled all the criteria of ROM in 120° ( ), but 14
combinations of cup and neck position fulfilled all the criteria of ROM
in 135° ( ), (Fig. 2, 3).
Discussion: A total hip prostheses with a technical ROM greater than
135° ( ) is necessary to maintain a good ROM without prosthetic
impingement. Osteophytes along the cup edge where prosthetic
impingements occur, might become one of the causes of bony
impingement before prosthetic impingement. Therefore osteophytes at
the antero-superior quadrant (110° to 160° anteriorly from the distal end)
and the posterior quadrant (40° to 120° posteriorly from the distal end)
along the cup should be removed during the THA operation (Table 1:
Fig.4).
FL
impinge
150
EXT impinge
129
117
110
IRfl90
117 impinge
ER
impinge
80
71
52
R
Technical ROM 120°
Fig. 2: 1/27 fulfill all the criteria of ROM. (Neck-stem angle 135°)
FL
impinge
157
EXT impinge
130
122
123
114
IRfl90
impinge
ER
impinge
71
78
43
R
Technical ROM 135°
Fig. 3: 14/27 fulfill all the criteria of ROM. (Neck-stem angle 135°)
Technical ROM 120°
Impingement points FL
number
averageዊSD
range
IRfl90
EXT
ER
27
27
27
27
131ዊ9° 121ዊ4° 93ዊ10° 63ዊ9°
117°-150° 117°-129° 71°-110° 52°-80°
Technical ROM 135°
Impingement points FL
number
averageዊSD
range
IRfl90
EXT
ER
27
27
27
27
137ዊ9° 126ዊ2° 99ዊ9° 57ዊ9°
122°-156° 123°-130° 78°-114° 43°-73°
Table 1
Z
L
C
:cup abduction
M
Y
Osteophyte
around
cup edge
Fig. 4
R
Left Hip AP view
Fig. 1
Poster No. 2060 • 55th Annual Meeting of the Orthopaedic Research Society