Liu et al.

Journal of Orthopaedic Surgery and Research (2015) 10:69

DOI 10.1186/s13018-015-0213-9

RESEARCH ARTICLE Open Access

Effects of knee position on blood loss following

total knee arthroplasty: a randomized, controlled
study
Jun Liu1,2*†, Yao-min Li1,3†, Jian-gang Cao2† and Lei Wang2

Abstract
Objective: Blood loss following total knee arthroplasty is a serious side-effect of surgery and impacts on patient
recovery and quality of life. The aim of this study was to assess the effect of postoperative knee position during
recovery on blood loss and range of motion.
Methods: One hundred consecutive patients, with stage III or IV degenerative osteoarthritis, were enrolled in the
study and randomized equally between two treatment groups: flexion and extension. In the flexion group, the
affected leg was elevated postoperatively by 45° at the hip, with 45° flexion at the knee, while patients in the
extension group had the knee extended fully. Blood loss, pre- and postoperative hemoglobin levels, and range
of motion were recorded together with duration of hospital stay and complications.
Results: Calculated blood loss, hidden blood loss, and postoperative hemoglobin levels between the two groups
were significantly different, with patients in the flexion group experiencing lower blood loss than those in the
extension group (P < 0.05). After 6-week rehabilitation, patients from both groups attained a similar range of
motion in the joint. Duration of hospital stay was shorter in the flexion group by 1.6 days. Wound infection
rates were similar in both groups, and we observed no proven deep vein thrombosis.
Conclusions: Postoperative elevation of the hip by 45°, with 45° knee flexion, is an effective and simple method
of reducing blood loss and hospital stay following unilateral primary total knee arthroplasty.
Keywords: Total knee arthroplasty, Blood loss, Knee position

Introduction disease, transfusion-related acute lung injury, hemolytic

With an increasing number of aged people suffering reactions, fluid overload, increased rate of postoperative
from degenerative osteoarthritis of the knee, total knee infection [1], and immunosuppression [2]. In addition,
arthroplasty (TKA) has become an important method allogenic blood transfusions can also lengthen the duration
for relieving pain and improving quality of life. The of hospital stay and increase the cost of treatment.
procedure involves extensive soft tissue release and Clinically, blood loss influences the restoration of a
bone incisions, resulting in significant blood loss. The functional range of motion (ROM), an important factor
resulting reduction in hemoglobin level may have a when evaluating the success of TKA, because different
serious impact on patient health, especially for older ROMs are needed for different types of activity. For
individuals with lower hematopoietic ability. Allogenic example, 67° of flexion are required for the swing phase of
blood transfusions are generally used to prevent post- gait, 83° to climb stairs, 90° to descend stairs, and at least
operative anemia. However, transfusions are associated 93° to rise from a chair. Recovery of a good range of motion
with additional risks, such as transmission of infectious is vital for an optimal result, and small changes in
maximum flexion can have profound effects on functional
* Correspondence: drliutka@163.com capability [3]. The greatest improvement in flexion has
†
Equal contributors
1
Tianjin Medical University, 30070 Tianjin, China
been found at the time of patients discharged and 6 weeks
2
Center for Joint Diseases, Tianjin Hospital, 300211 Tianjin, China postoperatively. Postoperative knee swelling, mainly due to
Full list of author information is available at the end of the article

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unless otherwise stated.
Liu et al. Journal of Orthopaedic Surgery and Research (2015) 10:69 Page 2 of 4

hidden hemorrhage around the knee joint, impedes early Table 1 Demographics and baseline measurements
rehabilitation. Therefore, minimizing blood loss following Flexion group Extension group P value
surgery has a positive impact on both clinical recovery Age (years) 73.1 ± 5.1 72.4 ± 4.6 0.68
and in reducing the need for transfusion, avoiding the Gender (female/male) 34/16 32/18 0.67
associated risks [4].
Affected side (L/R) 22/28 24/26 0.69
Various procedures have been used to reduce blood
loss associated with TKA, including tourniquet use Preoperative Hb (g/dL) 13.3 ± 1.4 12.8 ± 1.7 0.34
during surgery [5], drain placement protocols [6], bipolar Preoperative ROM 93.9 ± 18.9 92.3 ± 21.5 0.80
sealers [7], autologous platelet gels [8], and the most L left, R right, Hb hemoglobin, ROM range of motion
important method is using tranexamic acid by intravenous
or intra-articular injections [9]. Postoperative limb posi- affecting clotting function were terminated prior to surgery
tioning has also been investigated in several studies but has for 7 days.
shown conflicting results [5, 10–15]. A systematic review
of these studies concluded that a 48–72-h postoperative Surgical procedure
knee flexion protocol should be implemented as a simple All operations were performed under spino-epidural
and inexpensive method of reducing blood loss and anesthesia by the same group of surgeons skilled in
increasing ROM following TKA [16]. TKA. Tourniquets were not used during the procedure. All
There is no definitive consensus upon whether it is surgery was performed via a medial parapatellar approach,
exact limb position or duration of flexion which contributes incising the quadriceps tendon along the medial border.
most to the benefits seen with postoperative flexion The synovial capsular reflection and patellar tendon fat pad
protocols. The aim of the present study was therefore were excised. Osteophyte excision and soft tissue release
to examine the effect of knee position on blood loss and were performed where necessary. The implant used
related parameters at 48 h following total knee arthroplasty, was a posterior cruciate ligament-substituting, total knee
during a randomized, prospective comparative study. prosthetic component (GENESIS II, Smith & Nephew Inc.,
Memphis, TN, USA). The patella was reshaped to better
Materials and methods match the shape of the femoral component trochlea. To
Study design reduce blood loss from the femoral hole, an intramedullary
This study was approved by the ethics committee of plug with bone grafts was used prior to wound closure. A
hospital [Tianjin Hospital], and we obtained informed high-elasticity bandage was applied to compress the
consent from all patients, after explaining the benefits and wound. No drain was placed.
risks of the study. We conducted a prospective, randomized
clinical study, between June 2013 and June 2014, including Rehabilitation program
patients diagnosed with stage III or IV degenerative All patients received standard thromboprophylaxis in the
osteoarthritis of the knee. Diagnosis was based on form of enoxaparin (40 mg), with the first dose adminis-
medical history, clinical examination, and X-ray of the tered 12-h preoperatively and continued throughout hos-
standard weight-bearing knee. Patients were excluded pital stay. If required, a patient-controlled analgesia system
based on the following criteria: history of knee trauma or machine was provided for up to 48 h postoperatively, and
knee surgery, inflammatory polyarthritis (e.g., rheumatoid thereafter, NSAID-based analgesia was used to control post-
arthritis), neuromuscular diseases, disorders of the hips, operative pain. Wound dressings were changed at 48 h, and
metabolic bone disease, and other serious medical condi- the bandage was not wrapped so tightly as to hinder blood
tions (for example, neoplasms, chronic atrial fibrillation, circulation in the extremities. Active isometric quadriceps,
or diabetes mellitus). initiative straight leg raises, and extension–flexion motion
One hundred patients were enrolled in the study. An were encouraged 48 h postoperatively, and ambulation with
equal number of patients were randomly allocated to partial weight bearing was permitted under the supervision
either flexion or extension groups, using a random of a physical therapist. During the later part of hospital stay,
number list generated at the end of surgery. In the the affected leg would always be placed back in the flexion
flexion group, the affected leg was elevated 45° at the or extension position after physical therapy. The transfusion
hip using an inactive continuous passive motion trigger was defined as a hemoglobin level of less than 8 g/dl
machine with 45° of flexion at the knee, while patients in at 48 h postsurgery, with additional anemia symptoms, such
the extension group had the knee extended fully. The as tachycardia and dizziness, measured.
two groups were well matched for age, gender, affected
side, preoperative hemoglobin (Hb) levels, and ROM of the Follow-up assessment
knee. Patient demographics and baseline measurements Patients were assessed by a surgeon blinded to the post-
are summarized in Table 1. Aspirin and other agents operative limb position grouping, with affected legs left
Liu et al. Journal of Orthopaedic Surgery and Research (2015) 10:69 Page 3 of 4

in extension at the time of examination. Calculated total Discussion

blood loss (CBL) was obtained using the formula reported Blood loss following TKA is thought to be one of the
by Gross [17]. Hb levels were measured preoperatively major contributing factors to a better functional outcome.
and at 48 h postoperatively. Hidden blood loss (HBL) was Many methods have therefore been employed to decrease
calculated by subtracting intraoperative blood loss and blood loss and aid good postoperative ROM. The aim of
postoperative wound blood loss (obtained by weighing the present study was to examine the effect of adopting a
soiled dressings) from the CBL at the 48th postoperative postoperative knee flexion position after TKA: our results
hour. The ROM was measured preoperatively and at 6 showed that this position had a positive impact on surgery
weeks postoperatively. The length of hospital stay was outcome. Using a 45° hip elevation and 45° knee flexion
recorded as an economic factor. All other complications position for 48 h postoperatively resulted in significantly
were recorded, including wound infection and deep vein lower blood loss than that seen in the knee extension
thrombosis (DVT). Any clinical suspicion of DVT was group.
investigated by Doppler ultrasound. Previous studies have examined the effect of a greater
angle of hip elevation and have shown no significant
Statistical analysis difference in total blood loss and hemoglobin levels
Statistical analysis was performed using SPSS for Windows [10, 13–15]; however, this may be due to femoral and
11.5 software (SPSS, Chicago, Illinois). Continuous data popliteal veins being so curved as to hinder venous
were expressed as means (± standard deviation). A return [5]. Patients may be more uncomfortable while
two-tailed Student’s t test was used to compare continuous on the flexion regime, due to increased immobility,
variables, while chi-square test was used for nominal data. increased wound stretch, and pain receptor stimulation in
The level of significance was set at P < 0.05. flexion [14]. To avoid this, we elevated the hip by 45° and
put the knee into a 45° flexion position, showing similar
Results results to the study of Li et al. [5]. Blood loss after wound
Study outcomes are summarized in Table 2. We observed closure comes from extensive soft tissue release in the
a significant difference in CBL, HBL, and postoperative early postoperative period, and passive motion during this
Hb levels between the two groups (P < 0.05). Based on time also influences blood coagulation. The greatest blood
transfusion criteria, three patients in the flexion group loss following TKA has previously been reported in
and nine patients in the extension group required patients who had immediate continuous passive motion
transfusions, although this difference was not statistically following surgery [18]. One hypothesis for the reason why
significant. After 6 weeks of rehabilitation, both groups flexion can reduce bleeding is that vessel angulation
had a similar ROM without statistical difference and occurs with knee flexion, resulting in increased local
overall patients in the flexion group spent less time tension and decreased venous return. This mechanism is
in hospital than those in the extension group. The most thought to be effective only for flexion protocols of 48 h
common postoperative complications were wound or longer [16]. Compression was also maintained for
infections: three superficial infections occurred in the 48 h postoperatively because patients treated by 48 h
flexion group and two in the extension group, and compression with high-elasticity bandages have shown
two deep infections occurred in the flexion and one quicker postoperative recovery, with shorter hospital
in the extension groups. There were no cases of DVT stays and a greater range of flexion on discharge [19].
observed in this study. Based on these findings, all the patients’ affected legs
in our study were maintained in flexion or extension
Table 2 Clinical outcome and complications for 48 h postoperatively. After this period, continuous
Flexion group Extension group P value passive motion was then encouraged. Suction drainage
CBL (ml) 1008.4 ± 102.6 1212.0 ± 113.9 0.00 was not used, as it may have negated any tamponade
HBL (ml) 505.1 ± 28.0 617.5 ± 52.4 0.00 effect from the reduction in intra-articular knee volume.
Postoperative Hb (g/dL) 10.8 ± 1.1 10.0 ± 1.3 0.04 Tourniquets were also not used because TKA without
Transfusion 3 9 0.06
tourniquet shows superior early postoperative rehabilita-
tion, fewer thromboembolic events, and other related com-
ROM 105.8 ± 11.6 104.5 ± 9.2 0.70
plications [20]. Duration of hospital stay was also shorter
Duration 10.1 ± 1.1 11.7 ± 1.3 0.00 in the flexion group by only 1.6 days. The reason why
Complications 0.46 decreased length of stay was seen in the flexion group
Superficial/deep infection 3/2 2/1 which what we speculated was that these patients had less
DVT 0 0 blood loss with better general health and more confidence
CBL calculated total blood loss, HBL hidden blood loss, Hb hemoglobin,
of physical practice. These results were in accordance with
ROM range of motion, DVT deep vein thrombosis results of a previous study, in which increasing knee
Liu et al. Journal of Orthopaedic Surgery and Research (2015) 10:69 Page 4 of 4

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Author details
1
Tianjin Medical University, 30070 Tianjin, China. 2Center for Joint Diseases,
Tianjin Hospital, 300211 Tianjin, China. 3Department of Rehabilitation, Tianjin
Hospital, 300211 Tianjin, China.

Received: 3 November 2014 Accepted: 4 May 2015