Journal of Orthopaedic Surgery 2013;21(1):23-7
Position of the patella in adults in central
India: evaluation of the Insall-Salvati ratio
Sachin Upadhyay, HKT Raza, Pranay Srivastava
Department of Orthopaedics, Netaji Subhas Chandra Bose Medical College Jabalpur, (MP), India
ABSTRACT
Purpose. To assess the Insall-Salvati ratio in normal
Indian adults to determine its applicability and
the incidence of patella alta and baja in Indian
populations.
Method. 800 knees in 200 men and 200 women aged
18 to 50 (mean, 30) years were evaluated using lateral
radiographs. The knee was set in semi-flexion (30º) to
enable good visualisation of the patellar tendon and
its insertion into the tibia on radiographs. The length
of the patellar tendon (LT) over the length of the
patella (LP)—the Insall-Salvati ratio—was measured,
using a vernier caliper.
Results. The mean LT/LP ratio was 1.14 (standard
deviation, 0.18). Based on the 95% confidence
interval, the ratio was considered normal if within
±40%. The LT/LP ratio was significantly higher in
females than males (1.17 vs. 1.12, p<0.01). The cut-off
point of patella alta was significantly greater in our
Indian subjects than in western subjects (>1.5 vs. >1.2,
p<0.0001). In the present cohort, the frequencies of
patella alta (ratio, >1.5) and patella baja (ratio, <0.7)
were 2.8% and 1%, respectively.
Conclusion. The use of the Insall-Salvati ratio to
determine the patellar position is less applicable to
Indian populations in which squatting, sitting crosslegged, and kneeling are customs. We propose that
the normal range of the ratio for squatters among
Indian populations be 0.7 to 1.5.
Key words: patella; patellar ligament
INTRODUCTION
The patella is an integral component of the extensor
mechanism of the knee joint. It increases the efficiency
of the quadriceps muscle by increasing its leverage.1,2
It lengthens the extension moment arm throughout
the range of motion. The patellar height is an
imperative structural measurement.3 It is the length
of the patellar tendon (LT) over the length of the
patella (LP) and is termed the Insall-Salvati ratio.4 In
a study by Insall and Salvati,4 the mean LT/LP ratio
was 1.02 (standard deviation [SD], 0.13), and patella
Address correspondence and reprint requests to: Dr Sachin Upadhyay, 622, “Poonam” Sneh Nagar, State Bank Colony Jabalpur
482002 MP, India. Email: drsachinupadhyay@gmail.com
24
Journal of Orthopaedic Surgery
S Upadhyay et al.
baja and patella alta were indicated when the ratio
were <0.80 and >1.20, respectively. This ratio remains
the same in almost all degrees of knee flexion.5
A high-riding patella (patella alta) may be
associated with recurrent lateral dislocation and
subluxation of the patella,6–9 chondromalacia
patellae,10–13 patellar ligament rupture and SindingLarsen-Johansson disease,9,14 and patellar and
quadriceps
tendonitis
and
Osgood-Schlatter
disease.15,16 A low-riding patella (patella baja) may
be associated with quadriceps tendon rupture,
neuromuscular disorders, achondroplasia, and
postoperative advancement of the tibial tuberosity.17–19
We assessed the Insall-Salvati ratio (LT/LP) in
normal Indian adults to determine its applicability
and the incidence of patella alta and baja in Indian
populations, in which squatting, sitting cross-legged,
and kneeling are customs.
MATERIALS AND METHODS
Between September 2005 and September 2006, 800
knees in 200 men and 200 women aged 18 to 50 (mean,
30) years were evaluated using lateral radiographs.
Those with a history of knee surgery, underlying knee
pathology, knee pain during walking or squatting,
or trauma in lower limbs were excluded. This study
was approved by our institutional review board, and
informed consent was obtained from each subject.
Radiographs of the knee were taken, with
the knee set in semi-flexion (30º) with the aid of a
goniometer. This enabled good visualisation of the
patellar tendon and its insertion into the tibia. The
X-ray was perpendicular to the film and centered
on the joint at a distance of 100 cm. A 0.5-mm-thick
lead sheet was placed over the genitalia to reduce the
scatter dose by a factor of 100.20
Measurements were made using a vernier caliper.
The LT was measured from its origin on the lower pole
of the patella to its insertion into the tibial tubercle. A
well-defined notch suggestive of the insertion point
was used as a benchmark if the tendon could not be
adequately visualised. The LP was measured from
the articular superior to the non-articular inferior
pole (Fig.).
Parametric values reported in the present and
previous studies were compared using the Student’s
t test. An alpha value of 0.05 was considered for the
level of significance. Data were verified for normal
distribution before parametric test of analysis.
RESULTS
LP
The mean LT/LP ratio was 1.14 (SD, 0.18). Based on
the 95% confidence interval, the ratio was considered
normal if within ±40%. The cut-off point of patella
alta was significantly greater in our Indian subjects
than in western subjects (>1.5 vs. >1.2, p<0.0001).
The LT/LP ratio was significantly higher in females
than males (1.17 vs. 1.12, p<0.01, Table 1). In the
present cohort, the frequencies of patella alta (ratio,
>1.5) and patella baja (ratio, <0.7) were 2.8% and
1%, respectively (Table 2). The LT/LP ratio was
10% higher in our Indian subjects than in western
populations4,21–23 (p<0.0001, Table 3).
DISCUSSION
LT
Figure
Measurements of the length of the patellar tendon
(LT) and the length of the patella (LP).
Patella alta and patella baja represent the 2 ends of the
scale of the LT/LP ratio. Anomalies in patella position
are associated with derangements of patellofemoral
function such as chondromalacia10–13 and recurrent
subluxation or dislocation of the patella.6–9 Lateral
patellar subluxation is coupled with diminished
lateralisation of the patella-femoral junction contact
area, which increases lateral patellofemoral junction
stress and results in patellofemoral osteoarthritis.24
Vol. 21 No. 1, April 2013
Position of the patella in adults in central India
Table 1
Measurements of the ratio of the length of the patellar
tendon (LT) over the length of the patella (LP)
Parameter
LT (cm)
Male
Female
Both
LP (cm)
Male
Female
Both
LT/LP ratio
Male
Female
Both
Mean
Standard deviation
5.16
4.44
4.80
0.96
0.39
0.67
4.63
3.80
4.22
0.34
0.31
0.32
1.12
1.17
1.14
0.23
0.13
0.18
p Value
<0.0001
<0.0001
<0.01
Table 2
Distribution of subjects in terms of the ratio of the length of
the patellar tendon (LT) over the length of the patella (LP)
LT/LP ratio
<0.8
0.8–1.0
1.0–1.2
1.2–1.4
>1.4
Frequency (%)
12 (3)
140 (35)
170 (43)
53 (13)
25 (6)
Table 3
Comparison of studies in terms of the ratio of the length of
the patellar tendon (LT) over the length of the patella (LP)
Study
Present study
Insall and Salvati4
Schlenzta and Schwesinger21
Ahmed22
Theodore et al.23
Mean±SD LT/LP ratio
1.14±0.18*
1.02±0.13
1.00±0.14
1.02±0.13
1.00±0.2
* p<0.0001, Student’s t test
Realignment achieves satisfactory outcome in those
with mal-alignment or malposition of the patella.25
Shifting the tendon insertion both medially and distally
is important when performing a patellar tendon
transfer for patella subluxation.7,26,27 Patellofemoral
arthritis may result if the patellar tendon is rerouted
too far distally, as the articular surface of the patella
is forced against the femoral condyles. Patellar
tendon transfer (to restore the normal patellofemoral
relationship) should be performed only when the
height of the patella is clearly abnormal. Thus, this
demands a clear definition of the normal position of
the patella in the knee.
The insertion of patellar tendon is subject to
25
muscular traction. During growth of a bone, ligaments
and tendons migrate in different rates for different
insertions. The nearer the insertion to the extremity
of the bone, the greater is the migration.28,29 During
migration of the patellar tendon, its deeper layer is
constantly lengthened at the insertion site, whereas
its superficial layer slides over the surface of the tibial
tuberosity.30 In an experimental study,30 migration
of ligaments and tendons is due to the growth of
the periosteum dragging the insertions during its
stretching by the activity of the epiphyseal plates.
Squatting and sitting cross-legged are common
activities of daily living in Indian cultures. The InsallSalvati ratio is often restricted to chair-sitting western
populations and may not be generalised to others.
The patellar position is empirical for evaluation of
the anatomic alignment of the knee and anterior knee
pain.31,32 A patella alta may cause pain secondary to
patellar instability33–36 or chondromalacia patellae10–13
that results from abnormal patellofemoral junction
contact stress.37 Following knee trauma or surgery,38–40
particularly harvesting of a patellar tendon
autograft,17,18 progressive shortening of the patellar
tendon may lead to patella baja.10
Several techniques have been described for
radiological evaluation of the patellar height.5,41–45
The Insall-Salvati ratio4 is easy to calculate and
independent of the degree of knee flexion.5,23 The
normal ratio is 1.02±0.13; values >1.2 are suggestive
of patella alta and values <0.8 are suggestive of
patella baja.17,18 For the Blackburne-Peel method,44
the patellar ligament was not considered in assessing
the patellar height. Squatters have greater range
of knee flexion.46 The presence of the quadricipital
groove, which results from patellar ligament pressure
against the upper end of the tibia, makes projecting a
forward line along the tibial plateau difficult.46 The
Blackburne-Peel method gives different results for
squatters. Thus, grading the patellar level in relation
to the tibial plateau is not appropriate for assessing
the patellar position in squatters.
In the current study, the LT/LP ratio was
significantly greater in females than males (p<0.01),
which was consistent with findings of other
studies.47–50 We therefore disagreed with studies that
conclude the ratio to be independent of sex.4,21–23 The
lengths of the patella and the patellar ligament were
shorter in Indian females than males. For Indian
subjects, patella alta was indicated when the ratio
was >1.5, which was significantly greater than that
reported in other studies (p<0.0001).4,21,22
In a southern Chinese population, the position
of patella is 15 to 20% higher than that in western
populations.51 A patella alta index of >3.4 is considered
26
Journal of Orthopaedic Surgery
S Upadhyay et al.
abnormal in these population.51 This might be due to
the constant stretching effect over the patellar tendon
during squatting, sitting cross-legged, and kneeling,
which are common activities in India, Japan, China,
South-East Asia, and the Middle East.28–30
One limitation of the current study was that it
lacked a cohort with pathological conditions of the
knee, particularly chondromalacia and dislocation
of the patella. Moreover, the LT/LP ratio was not
applicable in children, because their bones are mainly
cartilaginous and not clearly visible on radiographs.
The use of the Insall-Salvati ratio to determine
the patellar position is less applicable to Indian
populations in which squatting, sitting cross-legged,
and kneeling are customs. We propose that the
normal range of the ratio for squatters among Indian
populations be 0.7 to 1.5.
DISCLOSURE
No conflicts of interest were declared by the authors.
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