Evaluation of a Custom Device for the Treatment of Flexion Contractures after Total Knee Arthroplasty

Abstract

Knee flexion contractures can severely impair function after total knee arthroplasties. We evaluated the use of a custom-molded knee device to treat 47 patients who had knee flexion contractures (mean, 22°; range, 10°–40°) after primary or revision total knee arthroplasties and who had failed conventional therapeutic methods. The device was used for 30 to 45 minutes per session two to three times per day in conjunction with standard physical therapy modalities two to three times per week. Twenty-seven of 29 patients who underwent primary total knee arthroplasty and 13 of 18 patients who underwent revisions achieved full extension after a mean treatment time of 9 weeks (range, 6–16 weeks). Full knee extension was maintained at a minimum followup of 18 months (mean, 24 months; range, 18–36 months). The mean Knee Society knee and functional scores improved from 50 points and 34 points to 91 points and 89 points, respectively. This protocol had comparable rates of improvement in knee extension with less treatment time when compared with other nonoperative treatments reported in the literature. The custom knee device may be a useful adjunct to a physical therapy regimen for knee flexion contractures after total knee arthroplasty.
Level of Evidence: Level IV, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Full text

SYMPOSIUM: ADVANCED TECHNIQUES FOR REHABILITATION AFTER TOTAL HIP
AND KNEE ARTHROPLASTY
Evaluation of a Custom Device for the Treatment of Flexion
Contractures after Total Knee Arthroplasty
Mike S. McGrath MD, Michael A. Mont MD,
Junaed A. Siddiqui, Erin Baker PT, Anil Bhave PT
Published online: 31 March 2009
ÓThe Association of Bone and Joint Surgeons 2009
Abstract Knee flexion contractures can severely impair
function after total knee arthroplasties. We evaluated the
use of a custom-molded knee device to treat 47 patients
who had knee flexion contractures (mean, 22°; range, 10°–
40°) after primary or revision total knee arthroplasties and
who had failed conventional therapeutic methods. The
device was used for 30 to 45 minutes per session two to
three times per day in conjunction with standard physical
therapy modalities two to three times per week. Twenty-
seven of 29 patients who underwent primary total knee
arthroplasty and 13 of 18 patients who underwent revisions
achieved full extension after a mean treatment time of
9 weeks (range, 6–16 weeks). Full knee extension was
maintained at a minimum followup of 18 months (mean,
24 months; range, 18–36 months). The mean Knee Society
knee and functional scores improved from 50 points and 34
points to 91 points and 89 points, respectively. This pro-
tocol had comparable rates of improvement in knee
extension with less treatment time when compared with
other nonoperative treatments reported in the literature.
The custom knee device may be a useful adjunct to a
physical therapy regimen for knee flexion contractures
after total knee arthroplasty.
Level of Evidence: Level IV, prognostic study. See
Guidelines for Authors for a complete description of levels
of evidence.
Introduction
Considerable loss of range of motion of the knee may occur
in 1% to 15% of patients who have undergone primary
TKAs [12,17,18,23,31,34]. Additionally, the frequency
of knee stiffness may be even higher in patients who have
had revision TKA, especially after treatment of a peri-
prosthetic infection [2,32]. Fixed flexion deformities after
TKA are associated with greater levels of pain, gait
abnormalities, difficulty with climbing stairs, and poorer
function scores [7,25,26], all of which can severely impair
a patient’s quality of life.
Knee flexion contractures may be caused by one or more
of several soft tissue factors, including preoperative loss of
motion with adaptive muscle shortening [24]; inadequate
soft tissue balancing during the procedure [4,9,24]; scar
tissue adhesion formation from prior surgeries or infections
[4]; pain-induced quadriceps muscle inhibition [21]; ham-
string or gastrocnemius muscle tightness [27,33]; limb
length discrepancy, with the TKA limb longer than the
unaffected side resulting in knee flexion [31]; or peroneal
nerve entrapment resulting in a flexed knee posture to
reduce tension on the nerve [13,22].
A variety of rehabilitation techniques have been used to
treat knee flexion contractures. These include moist heat,
hamstring and gastrocnemius muscle stretching, extensor
mechanism strengthening exercises, and manipulation of
One of the authors (MAM) is a consultant for Stryker Orthopaedics
and Wright Medical Technology. The other authors have no external
sources of support. All authors certify that they have not signed any
agreement with a commercial interest which would in any way limit
or delay publication of the data generated for this study.
Each author certifies that his or her institution has approved the
human protocol for this investigation and that all investigations were
conducted in conformity with ethical principles of research, and that
informed consent for participation in the study was obtained.
M. S. McGrath, M. A. Mont, J. A. Siddiqui, E. Baker,
A. Bhave (&)
Rubin Institute for Advanced Orthopedics, Sinai Hospital
of Baltimore, 2401 West Belvedere Avenue, Baltimore,
MD 21215, USA
e-mail: abhave@lifebridgehealth.org; anilbhave@yahoo.com
123
Clin Orthop Relat Res (2009) 467:1485–1492
DOI 10.1007/s11999-009-0804-z

the joint as well as the soft tissues [6,20]. Other
approaches include neuromuscular electrical stimulation,
joint aspiration, corticosteroid and/or local anesthetic
injections into the joint, and botulinum toxin injections
into the hamstring and gastrocnemius muscles [31]. Var-
ious orthoses have also been used, including casts or
braces to hold the joint in extension [1]; low-load pro-
gressive stretch splints, which apply a constant low-grade
force to the joint to gradually extend it [29]; and static
progressive stretch splints, which hold the joint at pro-
gressively greater degrees of extension [5]. These methods
may require prolonged treatment times (e.g., 4 to
55 weeks). In an attempt to create a treatment option that
requires fewer rehabilitation visits, one of the senior
authors (AB) developed a custom knee device (CKD)
composed of polyester casting material, two hinges, and
an elastic band (Fig. 1). This device was intended as an
adjunct that patients can use at home to supplement their
physical therapy treatments.
The purpose of our study was to determine whether the
passive ranges of motion and Knee Society scores of
patients who had knee flexion contractures after TKA
improved after treatment with the CKD. We also statisti-
cally compared the results of the patients who had primary
and revision total knee arthroplasties.
Materials and Methods
Between July 2003 and June 2007, we treated 47 patients
who had flexion contractures with a CKD in conjunction
with a standardized physical therapy regimen. Inclusion
criteria consisted of flexion contractures greater than 10°
after TKA and at least 4 to 8 weeks of conventional
physical therapy with no improvement. We excluded
patients who had heterotopic ossification, prosthetic mal-
alignment, oversized components, or other motion-limiting
abnormalities of the bone or prosthesis. All patients who
met the inclusion and exclusion criteria agreed to begin the
CKD treatment and take part in the study. The patients
included 18 men and 29 women who had a mean age of
62 years (range, 47–71 years). Twenty-nine of the patients
had undergone primary TKA, and 18 patients had under-
gone revision TKA. These were from a pool of 439 patients
who underwent primary TKA and 139 patients who
underwent revision TKA during that time. The range of
motion before the index TKA or revision arthroplasty had
not been consistently recorded, so these could not be
reported. We measured the passive knee range of motion
once per week during treatment to determine whether
improvement was occurring. Additionally, we assessed the
Knee Society knee and functional scores [11], and satis-
faction ratings of each patient before and after treatment.
We compared these values with published studies of other
nonoperative treatment methods. The minimum followup
time was 18 months (mean, 24 months; range, 18–
36 months). The study received full Institutional Review
Board approval.
All of the TKAs were performed by one of the senior
authors (MAM). The primary TKAs utilized Triathlon
TM
cruciate-retaining knee systems (Stryker Orthopaedics,
Mahwah, NJ). The revisions used Triathlon
TM
posterior-
stabilized or total-stabilized knee systems (Stryker). The
revisions had been performed for periprosthetic infection
(11 patients), knee stiffness (four patients), and component
loosening (three patients).
Postoperatively all patients received inpatient physical
therapy twice per day (consisting of active and passive
range-of-motion exercises, full weight-bearing gait train-
ing, and teaching for home exercises) for the first 3 to 4
postoperative days. Twenty-four patients received addi-
tional physical therapy at an inpatient rehabilitation
hospital for 7 to 10 days. After discharge to home, 30
patients followed a home physical therapy protocol that
consisted of range-of-motion as well as weight-bearing
exercises twice per week, and 17 patients received outpa-
tient physical therapy services two to five times per week.
All patients were evaluated in the office approximately
6±2 weeks after their surgeries, where we determined
their passive ranges of motion and Knee Society scores. At
that time, patients who had passive knee flexion contrac-
tures greater than 10°and who met the inclusion/exclusion
criteria were referred to the physical therapy office, where
a CKD was custom built and the treatment began. Patients
who lived a long distance from our institution were referred
Fig. 1 The customized knee device is composed of polyester casting
material, two hinges, and an elastic band.
1486 McGrath et al. Clinical Orthopaedics and Related Research
123

to a local physical therapy office for the adjunctive thera-
peutic treatments. The mean pretreatment passive knee
flexion contractures were 22°(range, 10°–40°) and 24°
(range, 20°–30°) for the patients who had undergone pri-
mary and revision TKA, respectively. The pretreatment
Knee Society knee and functional scores were 50 points
(range, 25–76 points) and 34 points (range, 15–70 points),
respectively. Forty-five of the 47 patients began the CKD
treatment on the day of the followup visit. The remaining
two patients had peroneal nerve entrapment symptoms
(pain and numbness radiating to the dorsum of the foot and
exacerbated by knee extension as well as mild extensor
hallucis longus muscle weakness) in addition to the knee
flexion contracture, so they underwent surgical peroneal
nerve releases, and then they began the CKD treatment
approximately 7 weeks after the TKA.
All of the CKDs were designed using a standardized
technique. Polyester-based casting tape (Dynacast PII BSN
Medical, Charlotte, NC) was used to make the brace. The
patient was placed in a supine position and a stockinette
was applied. The knee axis was marked, and one layer of
casting tape was applied to the thigh and lower leg (Fig. 2).
Polycentric knee hinges were bent around the knee in
alignment with the axis to conform to the anatomy of the
patient (Fig. 3). The remaining layers of the cast were then
applied. Once the hinges were incorporated into the cast,
two proximal and two distal hooks were applied. These
hooks were then used as fulcrums to anchor an elastic band
for the application of tension. After the cast was suffi-
ciently dry, it was cut longitudinally and removed. Then
the edges were trimmed and lined with adhesive fleece for
patient comfort (Fig. 4). Patients were shown how to apply
and remove the brace (Fig. 5), and were advised to keep it
on only during each stretching session. In some patients,
the cast loosened after 4 to 8 weeks and was rewrapped
with new casting tape by a physical therapist. Each brace
took approximately 60 to 90 minutes to construct for each
patient, with a total charge to the patient (including cost of
materials and labor) of $235 to $275. All braces used in
this study were fabricated by one of the authors (AB), but
other physical therapists have successfully learned how to
build a CKD through an 8-hour course, with 4 hours of
hands-on training.
Fig. 2 The patient is placed in a supine position, a stockinette is
applied, the knee axis is marked, and one layer of polyester casting
tape is applied to the thigh as well as the lower leg.
Fig. 3 Polycentric knee hinges (arrow) are bent around the knee in
alignment with the axis to conform to the individual anatomy of the
patient.
Fig. 4 When the cast is dry, the edges are trimmed and lined with
adhesive fleece for patient comfort.
Fig. 5 A patient removes the brace after the completion of a
stretching session.
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A standardized protocol for use of the CKD was given to
all of the patients. We advised them to sit or lie supine and
to prop their heels on a pillow at the same height as the hip.
Next, they applied an elastic band (Thera-Band; The Hy-
genic Corporation, Akron, OH) to the hooks in a figure-of-
eight configuration, crossing the distal femur to provide
knee extension force (Fig. 6). Soft ankle weights (5 to
10 pounds each) were placed on the table immediately
adjacent to the lateral ankle, knee, and thigh as a physical
block to prevent the leg from rotating externally during
treatment. Each stretching session was performed for 30 to
45 minutes two to three times per day. On the days on
which physical therapy was performed, the patients were
encouraged to apply the CKD for 30 minutes prior to the
physical therapy session to relax the soft tissues. Ten of the
patients were unable to perform the stretching protocol by
themselves, so the patients visited the physical therapy
office daily as outpatients, where the device was applied by
a physical therapist for 30 minutes, then they underwent an
adjunct physical therapy session, then the device was
applied again for 30 minutes. The CKD protocol was
continued for 2 to 3 weeks after full extension was
achieved to maintain the correction. If a patient followed
the protocol for a minimum of 6 weeks with no improve-
ment in passive knee flexion contracture or symptoms, then
the device was discontinued.
An adjunctive physical therapy protocol was followed
concurrently with the CKD treatment. Two to three times
per week, each patient underwent a physical therapy regi-
men that included (1) moist heat; (2) soft tissue
mobilization of the posterior aspect of the knee (at the
distal hamstring and proximal gastrocnemius muscle
insertions) with the patient in a prone position and maximal
knee extension; (3) anteroposterior joint mobilization of
the femur with the patient in a supine position and the
proximal tibia supported by a bolster to promote end-range
knee extension; (4) gastrocnemius and hamstring muscle
stretching with the patient in a supine position with the heel
supported and the knee in maximum extension; (5) neu-
romuscular electrical stimulation with electrodes applied
over the vastus medialis obliquus and proximal vastus
lateralis muscles (20- to 30-minute duration, alternating
6 seconds on and 18 seconds off, waveform at 50 to 90
pulses per second, 400-lsec pulse duration, and maximally
tolerated intensity); and (6) weight-bearing exercises,
including leg press and end-range knee extension.
We measured various clinical outcome variables during
the course of treatment, after the completion of treatment,
and annually thereafter. Passive range of motion was
measured with a long-arm goniometer by two authors (EB
and AB, licensed physical therapists) with the patients
lying supine with 10°to 15°of hip flexion. Inter- and in-
traobserver reliability was examined by having each author
measure 10 patients three times each. The inter- and in-
traobserver measurements were within 3°of each other for
extension 100% of the time, and were within 3°of each
other for flexion 95% of the time. After the completion of
treatment, each patient followed up in the office, where we
determined the passive knee range of motion, the Knee
Society knee as well as functional scores [11], and the
overall treatment duration in weeks. Additionally, each
patient rated his or her satisfaction with the CKD treatment
using a Likert scale that ranged from zero to 10 points [14],
with zero points indicating complete dissatisfaction and 10
points indicating complete satisfaction.
We used a paired Student t test to compare the pre-
treatment and posttreatment knee flexion contractures and
Knee Society scores. We also used a Student t test to
compare the range of motion, Knee Society scores, and
satisfaction scores of the two patient cohorts (primary and
revision TKA). All of the data met the assumptions of
normality (p [0.05 by the Kolmogorov-Smirnov test with
Lilliefors’ correction) and equal variance (p =1.000 on
the Levene Median test). A Mann-Whitney-Wilcoxon test
was used to compare the duration of treatment of the two
groups, because the data did not pass the normality test. A
chi square test was used to compare the failure rates of the
two patient cohorts. All statistical analyses were performed
using SigmaStat, version 3.5 (SPSS, Chicago, IL).
Fig. 6 An elastic band is applied to the hooks in a figure-of-eight
configuration, crossing the distal femur to provide knee extension
force.
1488 McGrath et al. Clinical Orthopaedics and Related Research
123

Results
At the end of the treatment protocol (mean, 8 weeks; range,
6–16 weeks), 40 of 47 patients improved their flexion
contractures compared with the pretreatment values
(p \0.001), with a mean residual contracture of 1.4°
(range, 0°–15°). The mean Knee Society knee and function
scores improved to 91 points (range, 60 to 100 points) and
90 points (range, 60 to 100 points) (p \0.001).
There were substantial differences between the patients
who underwent primary and revision TKA, although the
mean Knee Society scores of the two cohorts were similar.
Patients who underwent primary TKA had shorter
(p =0.05) mean treatment times than did patients who
underwent revision TKA (9 weeks, range, 6–15 weeks
versus 11 weeks, range, 9–16 weeks, respectively). In the
primary TKA group, 27 of 29 patients (93%) achieved full
extension (defined as a flexion contracture of less than 5°).
In the revision TKA group, 13 of 18 patients achieved full
extension, while 15 of 18 patients had a flexion contracture
of 10°or less. The patients who achieved complete reso-
lution of the flexion contracture maintained full extension
at a final followup time of 18 months (range, 12–
24 months). The primary TKA cohort had a greater range
of motion (p \0.001) compared with the patients who had
undergone revisions. The mean Knee Society knee scores
of the primary and revision cohorts were similar
(p =0.167) at the final followup, with scores of 92 points
(range, 75–100 points) and 90 points (range, 60–100
points), respectively. The mean Knee Society function
scores of the primary and revision cohorts were also similar
(p =0.398), with scores of 91 points (range, 60–100
points) and 87 points (range, 60–100 points), respectively.
The mean satisfaction scores of the primary and revision
cohorts were also similar (p =0.809), with scores of 9
points (range, 6–10 points) and 8 points (range, 5–10
points), respectively.
Two patients who had received primary TKAs and who
failed the CKD protocol required additional surgical pro-
cedures. One patient, a 55-year-old man who had a
pretreatment passive knee flexion contracture of 30°,
experienced no improvement after 6 weeks with the CKD
treatment. A manipulation under anesthesia also failed to
improve his flexion contracture, so he ultimately underwent
a distal hamstring-lengthening procedure. At a followup
visit 2 years after surgery, his passive knee flexion con-
tracture was improved to 10°with Knee Society knee and
functional scores of 80 points each. Another patient who
had received a primary TKA, a 60-year-old woman who
had a passive knee flexion contracture of 20°, also failed to
improve after 6 weeks of CKD treatment. She eventually
underwent a polyethylene insert change and subsequently
achieved a passive arc of motion of 0°to 110°with Knee
Society knee and functional scores of 100 and 95 points,
respectively. Five patients who were in the revision TKA
cohort failed to achieve full extension after 6 weeks of
CKD treatment with passive flexion contractures ranging
from 10°to 30°. Three of those patients underwent
arthroscopic exploration with scar tissue releases, and at
final followup times of 2 to 3 years, all had passive flexion
contractures of less than 5°with Knee Society knee scores
ranging from 85 to 100 points and Knee Society functional
scores ranging from 70 to 90 points. The two remaining
patients declined further treatment. Their residual knee
flexion contractures measured 10°each after treatment
times of 16 and 13 weeks, respectively. Their Knee Society
knee scores were 81 and 86 points, respectively, and their
Knee Society functional scores were 80 and 90 points,
respectively, at followup times of 2 years.
Discussion
The treatment of knee flexion contractures after TKA can
be difficult. Standard physical therapy protocols may
require long periods of time and may not be sufficient to
restore range of motion [28]. Low-load, prolonged
stretching techniques with therabands and/or ankle weights
have been successfully used for years to treat knee flexion
contractures, but in our practice, these treatments appeared
to be less well-tolerated by patients than splints when
maintaining the joint in a stretched position for an
extended period of time. Commercial splints may cost
over $2000, and although some orthopaedic practices are
able to make arrangements with companies for lower
rates, many patients may have difficulty affording those
devices. In an attempt to address these problems, the
authors designed a customized knee device that used
simple materials, had a low cost, and could be used daily
by the patient at home. We then evaluated whether the
device could be utilized to achieve full knee extension in
patients who had knee flexion contractures after primary
and revision TKAs.
There were several limitations of this study. There was
no separate cohort of patients who were treated with
physical therapy alone for comparison, and the patients
who were enrolled in this study might potentially have
restored their passive ranges of motion with only standard
physical therapy modalities without the brace. Addition-
ally, there was no direct comparison to a commercial brace.
The type of endpoint of the contracture (hard or soft) was
not consistently documented, so it could not be used to
interpret the data, and this could have provided more
information about which contractures might have better
outcomes with this treatment. Finally, the physical thera-
pist who constructed and applied all of the braces also took
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part in measuring the range of motion of the patients,
which introduces potential bias, although both therapists
who performed the measurements attempted to be as
accurate and reliable as possible. Although we had no
control group, the experimental protocol did resolve the
flexion contractures in 27 of 29 patients who had primary
TKAs and 13 of 18 patients who underwent revision TKAs
after a mean treatment time of 9 weeks (range, 6–
16 weeks), compared with reports of physical therapy
alone, which were associated with longer treatment times
and/or a greater proportion of patients who failed the
treatment [15,19,28].
The literature review revealed that other nonoperative
treatment methods had comparable or inferior results as
well as longer mean treatment times (Table 1). The mean
final knee flexion contractures ranged from 0.6°to 3°in
published reports, and the mean treatment times ranged
from 6 months to 2 years. The success rate (the percentage
of patients who had a flexion contracture of 0°–5°at final
followup) was 85% in one study and was not described in
the other reports. Shoji et al. [28] examined 231 patients
who underwent conventional physical therapy techniques
daily for 2 to 4 weeks, then two to three times per week for
2 to 4 more weeks after primary TKA. They reported that
35 patients (15%) had knee flexion contractures ranging
from 5°to 15°at a mean followup time of 3.8 years
(range, 2–9 years). McPherson et al. [19] examined 29
patients who had a mean knee flexion contracture of 11°
(range, 5°–30°) after TKA. With standard physical therapy
treatments (range of motion treatments, soft tissue
manipulation, moist heat), the mean flexion contracture
decreased to 5°,2°,1°, and 1°at 3, 6, 12, and 24 months
postoperatively, respectively. Logerstedt and Sennett [16]
described the use of a drop-out cast, which held the knee in
extension without the application of elastic bands. The cast
was applied by the patient for 6 to 8 hours every night in
conjunction with stretching, exercise, and knee mobiliza-
tion, to treat four patients who had a mean age of 20 years
and who had recalcitrant knee flexion contractures after
anterior curciate ligament reconstruction. After a mean of
13 weeks of treatment (range, 11 to 16 weeks), the mean
knee extension and flexion improved by 7°each. The final
mean knee flexion contracture was 4°(range, 1 to 8°). We
found a mean final knee flexion contracture of 1.4°after a
mean of 9 weeks of treatment (range, 6–16 weeks) and a
93% success rate for patients who had primary TKA,
which was comparable to the results of other published
treatments, but with a fewer mean hours of treatment.
Surgical treatments, including manipulation under
anesthesia, soft tissue release, and revision TKA, have
been successfully used to treat knee flexion contractures
after TKA; however, they all have associated risks,
including skin damage, tendon injuries, bleeding, and
Table 1. Published results of other nonoperative treatments for knee flexion contractures after TKA
Author Year Number
of knees
Treatment Mean duration of
treatment (range)
Mean pretreatment
flexion contracture
in degrees (range)
Mean posttreatment flexion
contracture in degrees (range)
Tanzer and Miller [30] 1989 35 Intensive physiotherapy 55 weeks
(no range given)
14.6 (range not reported) 2.9 (range not reported)
Shoji et al. [28] 1990 231 Organized physical therapy 4–6 weeks Not reported 35 patients had posttreatment flexion
contractures (range, 5°–15°)at2to
9 years followup
McPherson et al. [19] 1994 29 Standard physical therapy 12 months 11 (5–30) 1
Lizaur et al. [15] 1997 83 Standard physical therapy 24 months (12–41) 8.8 (0–45) 0.6 (0–10)
Cheng et al. [8] 2007 323 Intensive physiotherapy 1 year 11 ±63±5
Bonutti et al. [5] 2008 21 Static progressive stretch orthosis 9 weeks (3–27) 15 (3–65) 6 (0–45)
Present study 2009 47 Custom knee device 9 weeks (6–16) 22 (10–40) 1.4 (0–15)
1490 McGrath et al. Clinical Orthopaedics and Related Research
123

infection, in addition to high costs, and they often do not
improve the contracture [3,4,10,12]. The treatment used
in the present study resulted in improvements in all
patients with no complications or operative risks.
The CKD was associated with improved passive knee
range of motion, Knee Society scores, and satisfaction of
patients who had knee flexion contractures after TKAs. The
current protocol cannot be directly compared with pub-
lished reports of other protocols due to differences in study
designs and patient populations, but it did resolve the
flexion contractures of a comparable proportion of patients
in a relatively short period of time. The brace differs from
other low-load progressive stretch techniques because it is
custom-designed for each patient, and it can be applied and
removed by most patients without assistance, so it can be
used at home. Other surgeons could train their physical
therapy staff to construct and utilize these braces at a rel-
atively low cost, although fabrication quality might be
variable. The effectiveness and cost of this brace have not
been directly compared with other regimens in a random-
ized controlled trial, so a prospective comparison study is
necessary to determine any relative benefits of this tech-
nique. In conclusion, this approach offers an alternative
regimen that may be incorporated into rehabilitation pro-
tocols for the treatment of knee flexion contractures after
TKA.
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