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1 Department of Orthopedic Surgery, Schulthess Clinic, Lenggstrasse 2, Zurich
CH-8008, Switzerland.
2 Present address: Department of Orthopedic Surgery, St. Vinzenz Hospital,
Schloss Strasse 85, Düsseldorf D-40477, Germany.
3 Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse
340, Zürich CH-8008, Switzerland.
Received April 14, 2003;
accepted after revision August 12, 2003.
Address correspondence to J. Hodler.
Abstract
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SUBJECTS AND METHODS. From a consecutive cohort of more than 3,000 mobilebearing total knee arthroplasties, 44 cases (1.5%) with arthrofibrosis were identified, of which 38 were recruited for a clinical and sonographic investigation. A control group of 38 patients with a well-functioning total knee arthroplasty was matched. Synovial hypertrophy, presence of neovascularity, patellar tendon thickness, and extent of effusion were assessed.
RESULTS. Synovial membrane thickness was significantly (p
< 0.001) increased in the arthrofibrosis group (medial, 3.4 mm; lateral,
3.0 mm; suprapatellar, 3.1 mm) when compared with the control group (medial,
2.0 mm; lateral, 2.0 mm; suprapatellar, 1.9 mm). When a cutoff of 3.0 mm was
used, sonography had a sensitivity of 84% and a specificity of 82% for
detecting arthrofibrosis. Neovascularity (rated as grades 0–3) of the
synovial membrane and Hoffa's fat pad was significantly (p 
0.003) more pronounced in the arthrofibrosis group (medial, 1.1; lateral, 1.2;
suprapatellar, 1.0; Hoffa's fat pad, 1.1) than in the control group (medial,
0.1; lateral, 0.3; suprapatellar, 0.2; Hoffa's fat pad, 0.1). No significant
difference was seen between study groups with regard to the amount of joint
effusion at three locations and with regard to patellar tendon thickness.
CONCLUSION. Synovial membrane thickening and neovascularity are characteristic sonographic findings for the diagnosis of arthrofibrosis associated with total knee arthroplasty.
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All patients with total knee arthroplasty performed at our department are routinely followed up clinically and with standard radiography after 1 week, 6 weeks, 6 months, 1 year, 5 years, and whenever complications occur.
Forty-nine knees (1.6%) were diagnosed with arthrofibrosis on the basis of the following criteria: reduced range of motion (maximal range of motion of < 80°, an extension deficit of > 10°, or a total range of motion of < 80°); knee pain with no known reasons; palpable synovial thickening; an interval of more than 12 months after the last surgical intervention (to exclude physiologic postoperative changes); and absence of infection, hemarthrosis, and extraarticular abnormalities (including deep vein thrombosis). Clinical and laboratory tests or joint aspiration was performed whenever appropriate. This assessment was performed by two experienced senior knee surgeons who each perform more than 250 knee arthroplasties per year.
Five of the 49 patients had died at the time of this investigation. Six patients could not be motivated to attend the follow-up examinations for personal reasons (n = 2), distance between home and the hospital (n = 2), illness not relating to total knee arthroplasty (n = 1), and revision surgery performed at another institution (n = 1). Therefore, 38 (86%) of the surviving 44 total knee arthroplasties were included in the study. The investigation was approved by the responsible institutional review board and informed consent was obtained from all patients.
The mean age of the patients with arthrofibrosis was 65 years (range, 49–76 years). The range of motion of the knees that underwent surgery was 40–80° (mean, 70°). The 38 knees had been treated by one to five manipulations (mean, 1.9 manipulations) with the patient under anesthesia at the time of follow-up. At least one surgical revision had been performed in 36 (95%) of the 38 knees, including open débridement in 26 (72%), arthroscopic débridement in 15 (42%), bearing exchange in six (17%), tibial component revision in four (11%), resurfacing of a primarily nonoperated patella in three (8%), repositioning of the tibial tuberosity in three (8%), and patellar component removal in one (3%) knee.
Control Subjects
A control group of 38 individuals with well-functioning LCS knee
arthroplasties were matched with regard to age, sex, body mass index, and
follow-up period. Inclusion criteria for the control group were range of
motion of more than 100°, lack of peri- or postoperative complications,
and excellent or good clinical results according to a published clinical knee
arthroplasty score [4]. During
a period of 8 months, all patients who were scheduled for a routine follow-up
visit at least 1 year after surgery were invited to enter the control group
until the appropriate number of the matched group was obtained. None of the
eligible patients rejected study participation. The mean age of the control
patients was 67 years (range, 54–77 years). Fourteen patients were men
and 24 were women. The range of motion in the control group was
100–135° (mean, 115°). Age, sex, body mass index, diagnosis, and
type of prosthesis were not significantly different in the arthrofibrosis and
control groups.
Sonography
The patients were examined by one of two consultant musculoskeletal
radiologists who have worked at the same institution for 8 years; both have
more than 10 years of experience in sonography of the musculoskeletal systems.
Before the start of the study, they examined a few patients not included in
the investigation to make sure that the same imaging technique and image
criteria were used. The radiologists were unaware of the patients' symptoms.
The radiologists were asked not to talk to the patient about the knee during
the examination but rather about technical aspects of sonography. The patients
were placed in the supine position with the knees extended (90° flexion)
for examination of the patellar ligament. A 7.5-MHz linear transducer on an
Elegra scanner (Siemens Medical Solutions, Erlangen, Germany) was used.
Measurements were obtained during the examination with the electronic calipers
of the sonographic equipment. The output on the screen (to the nearest 1/10 of
a millimeter) was used for calculations. Such numbers probably overstate the
precision of sonographic measurements but do not introduce a bias in favor of
either patient group. For the power Doppler examinations, the color gain was
adjusted until no color signal was present deep in relation to the cortical
bone of the femoral condyle. The pulse repetition frequency was maintained at
1,250 Hz in all cases. Hard copies and digital (JPEG) images were obtained for
documentation.
Synovial hypertrophy (in millimeters), neovascularity of synovial membrane
and Hoffa's fat pad (grades 0–3), patellar tendon thickness (in
millimeters), and the extent of effusion (in millimeters squared) were
assessed. Synovial hypertrophy and neovascularity were separately assessed in
the suprapatellar, medial, and lateral parapatellar recesses. When synovial
thickness was variable in a specific compartment, the thickest part was
measured. The amount of effusion was measured in the same three compartments.
From the largest transverse (craniocaudal for the suprapatellar recess) and
anteroposterior diameters, a cross-sectional area was calculated with the 2D
ellipsoid formula (
x a x b / 4, with
a and b representing the two measured diameters). This is
only an estimation of the amount of effusion. However, because of the
complicated form of the synovial recesses, the true volume would have been
complicated to calculate, presumably without changing the message.
Neovascularity was graded as 0 for not detectable, 1 for minimal (one or two
vessels visible in the field of view), 2 for moderate (three or more vessels
in field of view, flow signal covering < 50% of the section even in the
most vascularized parts of the synovial membrane), and 3 for prominent (three
or more vessels in the field of view, flow signal covering > 50% of the
section in the most vascularized parts of the synovial membrane). The same
grading was used for vascularity of Hoffa's fat pad. The anteroposterior
diameter of the patellar ligament was measured at mid distance between the
patellar and tibial insertions.
Statistical Analysis
Continuous data in both groups were normally distributed (one-sample
Kolmogorov-Smirnov test), and an unpaired Student's t test was
performed. For the grading of neovascularity, Mann-Whitney tests were used.
Significance was set at the 5% level.
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Sonography
Results are presented in Table
1. Synovial thickness was significantly increased in the
arthrofibrosis group (Fig. 2)
in comparison with the control group (Fig.
3). When a cutoff of 3.0 mm was used, sonography had a sensitivity
of 84% and a specificity of 82% for detecting arthrofibrosis. Synovial
membrane and Hoffa's fat pad hypervascularity were significantly more
pronounced in the arthrofibrosis group than in the control group. Thirty-three
knees had a vascularity of grade 2 or more
(Fig. 2) in at least two
regions versus three in the control group
(Fig. 3). Differences with
regard to joint effusion and patellar tendon thickness were not significant. A
significantly (p < 0.04) increased synovial thickness (mean, 3.5
mm) was seen in patients who had previously been treated with open
débridement compared with those with previous arthroscopic
débridement (mean, 2.9 mm). However, neovascularity of the synovial
membrane was not significantly different for these two groups.
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2 weeks); closed manipulation; arthroscopic débridement; and open
procedures, including revision surgery with exchange of prosthetic components.
The etiology of arthrofibrosis is a subject of debate. Biochemical and
immunologic factors, genetically determined predisposition, reflex sympathetic
dystrophy, complex regional pain syndrome, metal-related allergy, lowgrade
infection, and mechanical factors have been discussed
[1,
5–8].
Histopathologic analysis has shown massive connective tissue proliferation
with deposition of disordered matrix proteins and increased expression of type
VI collagen in the subsynovia as well as around capillary walls
[6–8]. According to our data, sonography can differentiate total knee arthroplasty patients with arthrofibrosis from those with an uncomplicated postoperative course on the basis of synovial membrane thickness and neovascularity. Therefore, sonography may be useful in the assessment of the postoperative knee. Previously published papers have not focused on the specific diagnosis of arthrofibrosis but support the potential role of postoperative sonography. Grobbelaar et al. [9] have emphasized both the economic and diagnostic potential of power Doppler sonography in assessing synovial structures. Giovagnorio et al. [10] have shown that power Doppler sonography of the knee is useful for identification of synovial thickening and hypervascularity and that it differentiates joint capsule from synovial membrane and effusion. Sonography has also been used for the qualitative assessment, grading, and follow-up of a number of synovial and other joint abnormalities [11–19].
We acknowledge that the precision and reproducibility of the sonographic measurements and gradings have not been assessed. We believe, however, that any errors would be identical for both groups of patients and would not change our conclusions. At the institution of the orthopedic coauthors, sonography is used for surgical planning in patients with arthrofibrosis. The amount, diameter, and localization of hypertrophic tissues in the knee are relevant when deciding whether to perform open versus arthroscopic surgery. In addition, because synovial and capsular tissue cannot easily be differentiated intraoperatively, sonography assists in tissue-sparing synovectomy, thereby avoiding injury to capsular tissue.
In conclusion, synovial membrane thickening and neovascularity are characteristic sonographic findings for the diagnosis of arthrofibrosis associated with total knee arthroplasty.
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