Does pheumatic tourniquet change patellar tracking when inflated on straight leg and maximally flexed knees?

Huang Gang-yong, Wei Yi-bing , Xia Jun ,Wu Jian-guo, Chen Fei-yan, Chen Jie, Wang Si-qun.

Department of Orthopeadics, Huashan Hospital, Fudan University, Shanghai, 200040, China

Address for Correspondence:
Xia Jun
Department of Orthopeadics, Huashan Hospital, Fudan University, No.12, Wulumuqi Road(Middle), Shanghai, 200040, China

E-mail: cormierhuang@yahoo.com.cn

Abstract:

Objective To compare the patellar tracking with pheumatic tourniquet inflated on straight leg and maximally flexed knees. Merterials and Methods  20 inpatients’ normal knees with consents were enrolled to the study. The Caton Index and trochlear angle were recorded at 30°flexion of the knees under general aneasthesia without tourniquet. We inflated the pheumatic thigh tourniquets on straight leg and maximally flexed knees as contrast groups, and the Laurin angle and Merchant congruent angle were recorded at 30°,45°,60°,90°and 120°knee flexion at sunrise view. These angles were compared to describe different patellar tracking. Results  At 30°flexion, Caton Index averaged 1.02±0.19 and trochlear angle was 138.9±7.4°. The Merchant congruent angle tends to be larger during knee flexing with most significant changes as the knee flexed from 30°to 45°. The Laurin angle presented no significant change at the whole range of knee flexion. The Merchant congruent angle and Laurin angle of patellofemoral joint show no significant difference with pheumatic tourniquet inflated on either straight leg or maximally flexed knees. Conclusion  For normal knees, the main kinematic effect of pheumatic tourniquet on the patellofemoral joint with different knee flexion are presented at the initial 45°flexion of knee which is observed as increasement of Merchant congruent angle, while Laurin angle keeps no significant change during the whole range of motion. The patellar tracking shows no significant difference with pheumatic tourniquet inflated on either straight leg or maximally flexed knees.

J.Orthopaedics 2009;6(3)e3

Keywords:

patellofemoral joint; Kinematics; Pheumatic tourniquet

Introduction:

The pneumatic tourniquet is widely used in knee surgery. It guarantees less blood loss and easier exposure of the surgical fields. On the other hand, the tourniquet restricts the smooth movement of the quadriceps, which might in turn change patellofemoral kinematics theoretically. It has been justified in total knee arthroplasties.¹ The emphasis should be attached to the patellofemoral congruency especially when doing the kinematic changing operations such as dealing with knee arthroplasty and patellofemoral instability. Could the modification of pneumatic tourniquet fixation and inflation diminish its influence on patellar tracking? This study aimed to compare the patellofemoral congruency values with pheumatic tourniquet secured and inflated on straight leg and maximally flexed knees in normal individuals.

Materials and Methods:

With approval of the ethical review board and consents of the patients, the study recuited 20 inhospital patients from the Orthopedics Ward without knee disorders or anterior knee pain complaints, whose age ranged from 18 to 45 years. There were 14 male cases and 6 female cases. The study was done when the patient undergone operation of the other skeletal structures except the knees under general anesthesia. Only one randomized knee of each patient was selected to undergo the study to protect the attendees from excessive X-ray exposure.

Firstly, the Caton Index² and trochlear angle were recorded at 30°flexion of knees. Then we set the pheumatic tourniquet at 120° flexed knees and inflated to 60Kpa on maximally flexed position (Group I), and the Laurin angle（figure 1）³ and the Merchant congruent angle（figure 2）⁴ were recorded at 30°,45°,60°,90°and 120°knee sunrise view. Ten minutes rest after these manipulations, the tourniquet was secured and inflated to 60Kpa at the same knee which was extensed fully (Group II ) and the Laurin Angle and the Merchant congruent angle were measured at different knee flexion as abovementioned. These angles were measured by two independent orthopaedic surgeons and the averaged values were used for analysis. These angles were compared to describe different patellar tracking. We used the Sirimobil Iso-C X-ray intensifier (Simens, Germany) to record the images. Paired samples t test was adopted to analyse the Laurin angle and Merchant congruency angle differences between flexed and extensed knee groups . One sample t test was adopted to analyse the changes of the Laurin angle and Merchant congruency angle among different degrees of knee flexion at each group. P<0.05 was considered statistically significant level.

Figure 1   Laurin angle

Figure 2   Merchant congruency angle

Results :

At the knees of 30°flexion, Caton Index averaged 1.02±0.19 and trochlear angle was 138.9±7.4°. The Merchant congruent angle tended to be larger during knee flexing, with most significant changes as the knee flexed from 30°to 45°. The Laurin angle presented no significant change at the whole range of knee flexion. The Merchant congruent angle and Laurin angle of patellofemoral joint show no significant difference with pheumatic tourniquet secured and inflated on either straight leg or maximally flexed knees.(table 1)

Table 1  Patellar tracking changes when flexing knees

Discussion :

The patellar tracking are mandatorily assessed by surgeons both in TKA and in intervention of patellofemoral disorders. Due to high tension of quadriceps by tourniquet inflation, No Thumb Test in the TKA operation may mislead to “lateral tilt of patella”. The same situation also appears in other patellofemoral management. ^5,6,7

To our knowledge, the patella is seated in suprapatellar bursa as the knee fully extenses. And it slides into femoral trochlear groove by the pull of medial vastus femoris and medial patellofemoral ligament as knee flexion reaches 15°to 20°. The patella is stabilized in deeper trochlear groove as knee flexion is larger than 70°and less chance is that instability or subluxation of patella occurs. Sunrise or Merchant view of patella at 20 °to 30°flexion of knee is vital to evaluate the development of trochlear and stability of patellofemoral joint . Most of knee X-ray indexes are assessed at this position, and the trochlear angle and Caton index of patella height are also measured at the same position.

Insall-Salvati index is widely used to evaluate the height of patella. In this study Caton index is used instead of Insall-Salvati index considering we always pay close attention to joint line level in joint surgery. The Laurin angle and Merchant congruency angle are used to see the stability at different knee flexion angles in this study. When we assess the patellar tilt the line connecting posterior condyles of femur is reliable and in most cases considered as one of the best references. The line connection the anterior condyles are always less reliable due to various development of distal femur. Based on the fact that we would put the patients under radiation exposure of CT if we measured patellar tilt with posterior condylar reference, the Laurin angle was chosen in this study . Additionally, the comparation of  Laurin angle of those patients’ same knees eliminated the adverse influence by anatomical varieties. The Merchant congruency angle can be accessible in various flexion of knee to assess the lateralization of patella and it keeps good application of clinical relevance. ^2,3

The results showed patellar height with 1.02±0.19 of Caton index and trochlear groove development with 138.9±7.4°of  trochlear groove angle. These are similar to the results of established knowledge , and it indicates application of ordinary population. The arcuated contour of trochlear brought difficulty to measurement and may exaggerate errors. It is known that patellar tilt will be more obvious when the tension of quadriceps of femoris are increased by tourniquet after the VMO and medial retinaculum have been recised. The performance of Laurin angle in this study indicates patella tilt has not been infuenced by different tourniquet fixation groups when retinacular structures were intact . The changes of Merchant congruency angle at the initial 45°flexion of knee in this study may caused by the process of patellar slide from suprapatellar bursa to trochlear groove. While in deep flexion of knee, the Merchant congruency angle presented no significant further change under any alteration of quadriceps tension.

With incised medial retinaculum the pneumatic tourniquet increases the tilt of patella so that inflation of tourniquet at maximally flexed knee has the potential advantage of less interference of quadriceps femoris which protects from patellar tracking changes. ^6,7 As a major result of this study, the Merchant congruent angle and Laurin angle of patellofemoral joint show no significant difference with pheumatic tourniquet inflated at either extensed or flexed knees. This should be interpreted as that with intact medial retinaculum the patellofemoral congruency does not change significantly caused by different position of pneumatic tourniquet.

This study has the potential advantage of reliability as an own-control study in vivo and objective indexes observed. To protect the enrolled cases from escessive exposure under radiation of X-ray we chose randomly one side of knee and we use C-arm auto-protection system of Siemens to guarantee the safety. Because the Laurin angle and Merchant congruency angle was not obtained in a continuous style and the three dimensional data can not be reached, it is only a preliminary attemptation to understand the kinematics of patellofemoral joint and further investigation can be done in a three dimensional pattern. 

Reference :

1. Thorey F, Colsman CS, Windhagen H, et al. The effect of tourniquet release timing on perioperative blood loss in simultaneous bilateral cemented total knee arthroplasty: a prospective randomized study. Technol Health Care. 2008;16(2):85-92.

2. Caton J, Deschamps G, Chambat P, et al. Les rotules basses: A propos de 128 observations.  Rev Chir Orthop. 1982;68:317-25.

3. Laurin CA, Dussault R, Levesque HP. The tangential x-ray investigation of the patellofemoral joint: X-ray technique, diagnostic criteria and their interpretation. Clin Orthop. 1979;144:16-26.

4. Merchant AC, Mercer RL, Jacobsen RH, et al. Roentgenogrphic analysis of patella-femoral congruence. J Bone Joint Surg. 1974;56A:1391-6.

5. Fu FH, Maday MG. Arthroscopic lateral release and the lateral patellar compression syndrome. Orthop Clin North Am. 1992;23:601-12.

6. Marson BM， Tokish JT. The effect of a tourniquet on intraoperative patellofemoral tracking during total knee arthroplasty. J Arthroplasty. 1999;14:197-9.

7. Husted H, Toftgaard JT. Influence of the Pneumatic Tourniquet on Patella Tracking in Total Knee Arthroplasty: A Prospective Randomized Study in 100 Patients. J Arthroplasty. 2005;20(6):694 –7.

This is a peer reviewed paper 

Please cite as: Xia Jun: Does pheumatic tourniquet change patellar tracking when inflated on straight leg and maximally flexed knees?

J.Orthopaedics 2009;6(3)e3

URL: http://www.jortho.org/2009/6/3/e3

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