assessment of limb length in hip arthroplasty

1. LIMB LENGTH
DISCREPENCY IN HIP
ARTHROPLASTY
DR RAVINDRA CHAURASIA
DEPARTMENT OF ORTHOPAEDICS
MAX HOSPITAL VAISHALI

2. INCIDENCE OF POSTOPERATIVE LLD
• Range from 1 % to 27 %.
• Lengthening is more frequent than shortening.
• The LLD is reported to vary from 3 to 70 mm.
• The postoperative LLD was less than 5 mm in 75%,
5-7 mm in 12.5%
7-10 mm in 2% of patients
(In a study conducted at the Rothman Institute, in which the direct lateral approach in the supine position was used).
• However, when care is taken to minimize LLD, the difference is
less than 10 mm in 97% of cases.

3. TRUE LLD
• Caused by lengthening of the prosthetic head-neck
distance. can be measured
1. A line drawn from the center of the femoral head to the
ankle center on full-length AP radiographs.
2. A vertical line drawn from the interteardrop line to the
lesser trochanter .
3. By comparing the position of the medial malleoli of the
patient in the supine position.

4. PREOPERATIVE MEASUREMENT.
• In full-length AP standing radiograph
LLD is measured as the difference in
length of the line segments extending
from the top of the femoral head to the
center of the ankle on each side.
• This length is modified in patients
with flexion contracture of the hip or
knee.

5. Estimation of lower limb
length discrepancy
related to the hip.
a: Biischial line
b: Interteardrop line
c: Pelvic obliquity is a
less reliable criterion:
although the hips are at
the same level, the pelvis
is oblique.

6. FUNCTIONAL LLD
• Caused by the tightness of the soft tissues about the hip
or scoliosis of the lumbar spine, causing obliquity of the
pelvis.
• Functional LLD is typically assessed when the patient is
standing and feels a sense of imbalance.
• To measure this discrepancy, measuring blocks are
placed under the short limb until the legs feel equal.

7. ACCEPATBLE LLD
• Small leg-length discrepancies (1 cm or less) are usually
well tolerated by patients and may go unnoticed.
• Discrepancies between 1 and 2 cm have been shown to
affect functional outcome scores.
• Discrepancies greater than 2 cm may lead to greater
patient dissatisfaction, nerve palsy, and back pain.

8. CONSEQUENCES OF POSTOPERATIVE LLD
• Altered balancing/ hip instability
• Back pain
• Gait disturbance
• Generalized hip pain
• Nerve pain
• Sciatic nerve palsy
• Ipsilateral knee pain
• Aseptic prosthesis loosening
• The need for a shoe lift
• Revision surgery

9. PREOPERATIVE LLD
• The short side: loss of the articular cartilage,
superior migration of the femoral head,
Requiring the surgeon to lengthen the affected limb.
• Ranawat et al showed that preoperative LLD ranges
from a 24 mm of shortening to a 5 mm of lengthening
of affected limb (mean 4.04 mm short).

10. CAUSES OF POSTOPERATIVE LIMB SHORTENING
• Inaccurate preoperative planning based on the
radiographs at several different magnifications.
• Flexion contracture of the hip joint before the surgery
• Excessive acetabular reaming during the surgery
• Sinking of the collarless stem

11. METHODS TO OVERCOME LLD
1. Preoperative Templating.
2. Intraoperative pelvic or femoral markers for reference.
3. Computer-assisted surgery or navigation or CT.

12. PREOPERATIVE TEMPLATING
• Several studies had concluded that correct sizing of
components match in only up to 60 % of Cases.

13. TWO-DIMENSIONAL TEMPLATING
• Two-dimensional templating using radiographs remains
a standard method.
• Linear measurements and calculations from plain X-
rays are susceptible to error, due to variations in
positioning of the pelvis relative to the plane of the film
and the divergence of the X-ray beams.
• The magnification issues raised by radiograph can be
overcome by using templating software.

14. USING TRACING PAPER
• The principle consists in drawing the contralateral hip
on tracing paper.
• The traces are then used to replicate the positioning of
the selected components on the abnormal hip.
• When both hips are abnormal, the Amstutz index can
be used which guides the implant positioning
according to eliminate the risk of limping.

15. THREE-DIMENSIONAL TEMPLATING
• Is performed using software developed initially to
design custom-made stems for THA. The software
compensates for poor patient positioning during
image acquisition.

16. Influence of rotation in x ray and CT

17. PROXIMAL FEMUR TEMPLATING IN THE THREE
PLANES USING CT-BASED SOFTWARE.

18. GOALS OF AN IDEAL REFERENCING SYSTEM
• Improve the accuracy of component position
• Minimize errors of leg length
• Eliminate instability
• Maximize range of motion (ROM)
• Minimize component impingement
• Improve hip mechanics and functionality

19. ACETABULAR COMPONENT
• Concerns involving the acetabular component include cup
position, cup version, and cup tilt (abduction angle).
• The most important radiographic landmark is the teardrop
reference point, which is a guide to the inferior acetabulum.
• This is important in restoring leg length, as well as optimizing the
hip center of rotation and minimizing impingement of the
components.

20. ACETABULAR COMPONENT
• Intraoperative landmarks include the superior, anterior,
and posterior rims of the acetabulum, the sciatic notch,
and the transverse acetabular ligament.
• The anterior and posterior rims of the acetabulum are
useful as guides to the anteroposterior positioning of
the cup, as well as providing a sense of the anteversion.

21. TRANVERSE ACETABULAR LIGAMENT
• Defines the line from the posteroinferior to the anteroinferior
acetabulum. Placing the reamer parallel to the TAL represents
the patient’s native anteversion.
• The height and depth of the component positioning have also
been described relative to the TAL, with the component
optimally sitting just underneath the TAL, as does the native
acetabulum.

22. FEMORAL COMPONENT
The femoral component concerns include stem version, stem offset,
and neck length. The landmarks used for the femoral component are
various aspects of the proximal femur.

23. MODULAR NECKS ALLOWING THE INDEPENDENT
ADJUSTMENT OF LENGTH, OFFSET, AND ANTEVERSION

24. INTRAOPERATIVE TECHNIQUES
• Based on the distance between 2 reference points
marked on the pelvis and femur.
• Traditionally, the greater trochanter is used as an
intraoperative landmark.
• The pelvic reference can be iliac fixation pins,
intraoperative callipers, infracotyloid pins, and fixed
suture lengths.

25. INTRAOPERATIVE FIXED BONY LANDMARKS
• These landmarks are unreliable, as they may be removed
and replaced between measurements.
• Hip position must be replicated accurately in all three
planes before and after implantation of the prosthesis,
which is challenging.
• Variations in femoral abduction/adduction of only 5◦to
10◦result in measurement errors of 8 to 17 mm.
• It is believed the supine position is more reliable.

26. COTYLOID GROOVE

27. • Mcgee and Scott were the first to describe a simple
intraoperative technique to correct LLD in THA.
They used a fine guide wire to bend in ‘U’ shape to
act as a device to mark referencing points.
• Though they mention it has been successfully used in
200 patients, they fail to substantiate their claim with
any radiological or clinical data.

28. • Woolson and Harris later described another technique
by using a calliper device, which is more time
consuming and difficult to adopt.
• Using this device they achieved postoperative
lengthening of <6 mm in 89 % of patients. They also
fail to correlate their results to any functional
outcome.

29. Transosseous pin method. Two Kirshner wires are inserted parallel to 1 another and
perpendicular to the floor, 1 in the greater trochanter and the other in the supra-
acetabular ridge of the ilium. The caliper is placed on the pins. Intraoperative LLD is
calculated by summing the preoperative LLD with the change in length demonstrated
by the caliper

30. PCA limb lengthening gauge (Stryker, Mahwah, NJ, USA). The
left pin goes into the acetabulum, and the right pin into the femur.
A stopper and a thread cutting are added to the pin for the
acetabulum.
The disadvantage of this device is loosening of the pins in patients with osteoporotic bones,
The inaccurate abduction/adduction repositioning of the femur with respect to the pelvis
also can cause substantial error in the measurement of the length and can offset changes.

31. INTRAOPERATIVE PHOTOGRAPH
(A)The lengthening axis is marked and the device is placed.
(B) A scheme showing the location of the device.

32. • Takigami et al described another technique using a
dual pin retractor for measuring the LLD. Though this
is well validated by radiological and functional
outcome.

33. The calipers dual pin retractor (CDPR). Dual pins for retracting the gluteal muscle are
connected at the “shoulder” of the CDPR. The base of the measuring ruler arm fits over the
guide pin and is removed easily after the measurement. CDPR inserted into the pelvis, about
2 to 3 cm proximal to the acetabulum

34. • Though techniques by using large Steinmann pin
have been described in literature , they have been
criticized as unreliable as they are recommended to
be removed and replaced during the surgery in
between the measurements.

35. Picture illustrating intraoperative assessment of limb
length by pin and thread technique

36. • Naito et al , Bose, and Shiramizu et al described techniques
using a Steinman pin and adjustable calliper to achieve
intraoperative limb length correction.
• Both these techniques describe a cumbersome and
expensive device used as an adjunct in routine THA. Also
there is a need for a larger or a separate incision to
accommodate these devices for their pelvic reference

37. • Ranawat et al used vertical Steinman pin at the
infracotyloid groove of the acetabulum.
• They alluded that the points of reference are close to
center of rotation of hip, making less variations in
measurements resulting from different limb positions.
• The main limitation of this technique making it
unreliable is the difficulty in accurate positioning of
the pin due to large osteophytes at the posterior lip of
acetabulum.

38. • A simple technique described by Cuckler by using an
umbilical tape and knots to reference the bony
landmarks like ASIS.
• It is very unreliable, it is very difficult to identify the
bony prominence under surgical drapes especially in
obese patients.

39. • Matsuda et al used a ruler intraoperatively
• The main disadvantage of this method was the
difficult evaluation of acetabular component position.

40. • Another simple technique using a skin suture below
the iliac crest has been described without any clinical
or radiological correlation.
• This technique is unlikely to be reliable as the skin is
not a fixed point and differential tension on the suture
between length assessments will lead to significant
error.

41. A simple technique is by using a Judd pin (Judd
Medical, Braintree, Essex, UK) or any stout pin into the
ileum just superior to the acetabulum. A thread/suture is
then securely tied to this pin, and a knot tied in the
suture and a reference mark made with diathermy on the
greater trochanter at the level of the knot, which is then
used as a guide to either lengthen or maintain the same
length based on preoperative templating.

42. LIMITATION OF TECHNIQUES
• Linear measurements are basically based on accurate
repositioning of the leg in abduction, flexion, and
rotation.
• Hence small errors in femur repositioning can lead to
substantial errors in assessing the leg length and
offset, as the fixed reference points used is away from
center of rotation of the hip joint.

43. INTRAOPERATIVE TEST
• Shuck test, described by Charnley and involving in-line lower
limb traction in the distal direction
• Drop kick test, with the hip held in extension and the knee
flexed to 90◦; and leg-to-leg comparison of length based on the
heels or medial malleoli
• To assess soft-tissue tension and length
• The results are influenced by surgeon experience; type of
anesthesia, the approach, the patient position.

44. Abductor shuck method. The electrocautery tip indicates the abductor
musculotendinous unit, which is tensioned by a tag suture onto the greater trochanter.
The gap (or overlap) between the tenotomized ends of the abductor is measured as the
amount of limb lengthening (or shortening).

45. Preoperative photographs of the patella lead method: front view
(A) and side view (B).

46. The ILMOD is made of two main parts –a measuring ruler
arm ① and a femoral osteotomy guide ②

47. ①The femoral head was taken out, and then an anatomical reduction of femoral neck fracture
was achieved and fixed by K-wire temporarily; ② The ILMOD was seated on the lesser
trochanter. The guide pin was pressed on the highest point of the femoral head; ③ The saw was
guided by cutting surface of osteotomy guide to create a flat resection on the femoral neck; ④
The guide pin was pressed on the highest point of the trial component

48. COMPUTER NAVIGATION
• The navigation technique has several limitations of
not only being cumbersome and expensive but also
has a steep learning curve.
• Though the measurements are calculated precisely,
the precision largely depends upon mapping and
referencing points, which are surgeon controlled,
hence the possibility of LLD remains.

49. COMPUTER NAVIGATION SYSTEMS
Quite sophisticated intraoperative support systems
• Manzotti et al used image-free navigation and
reported that the postoperative LLD was 5.06 ± 2.99
mm and the LLD was within 12 mm in all of their
patients.
• Murphy and Ecker used CT-based navigation and
reported that postoperative LLD was ranging from –5
to 3.9 mm.

50. CONCLUSIONS
• LLD is a common and recognized complication
following THA
• To overcome LLD from the numerous methods
described
• The combined use of templating to predict the
necessary length correction and plan femoral neck
osteotomy level and the intraoperative use of a simple
pelvic reference pin with accurate positioning of the
leg during measurements will provide better result
without compromising the stability of the hip.

51. • Iagulli ND, Mallory TH, Berend KR, et al. A simple and accurate method for
determining leg length in primary total hip arthroplasty. Am J Orthop (Belle Mead
NJ). 2006; 35:455- 457.
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Clin Orthop Relat Res. 1977; (123):27-28.
• Kurtz WB. In situ leg length measurement technique in hip arthroplasty. J
Arthroplasty. 2011; 27:66-73.