Pain and Patellofemoral Functionality in Total Knee Arthroplasty

A Comparative Cohort Study of Two Prosthesis Designs

Luis Miguel Cely, MD; Cesar Hernando Rocha, MD


Curr Orthop Pract. 2021;32(1):53-57. 

In This Article

Materials and Methods

Study Design and Ethical Review

After institutional review board approval was obtained from Fundacion Cardioinfantil Instituto de Cardiologia (IRB00007736, minutes No. 17–2019), we conducted an observational analytical cohort study. Informed consent was not required by the institutional review board since this was an observational study with no patient intervention.

Patient Selection

Patients who underwent total knee replacement surgery with Optetrak PS and Optetrak Logic from January 2015 to August 2019 were included. Data were taken from medical records and face-to-face interviews of patients. Patients with incomplete data and with whom it was not possible to carry out the physical examination were excluded. The total sample was 130 patients (132 knees: 66 with Optetrak Logic and 66 with Optetrak PS). The Optetrak Logic prosthesis was first marketed in Colombia in April 2018. Prior to this date, the prosthesis that was used was the Optetrak PS, and after April 1, 2018, the Optetrak Logic prosthesis was the only one used, which makes the size of the samples equal.

Surgical Procedures

All surgeries were performed by a single surgeon (CR), using a standardized surgical technique and perioperative care. Pneumatic tourniquets were not used; however, a 1000-mg dose of intravenous tranexamic acid was administered prior to incision for each patient. In all patients, a medial parapatellar approach was performed. In addition, the gap balance technique was combined with bone cuts to improve knee kinematics. A total knee replacement with a posterior-stabilized prosthesis was performed in all patients. Patellar replacement was performed in all patients and adequate patellar tracking, stability, and mobility of the knee were verified prior to soft-tissue closure. The closure of the arthrotomy and the surgical wound was performed with continuous suture for all planes.

Data Collection

A detailed physical examination was performed to measure the degrees of mobility of the operated knees. Joint instability, the Oxford Knee Score,[22] Knee Society Score (KSS),[23] and Kujala[24,25] scales in addition to demographic variables such as gender, age, operated knee, presurgical knee alignment, type of prosthesis, and approximate follow-up time (minimum of 12 mo) were considered. The average measurement of flexion and extension was taken and was evaluated both actively and passively. In order to measure objectively, a goniometer was used. Instability grades were categorized as: grade 0, no degree of instability; grade 1, 0 mm to 5 mm instability; grade 2, 6 mm to 10 mm instability; and grade 3, greater than 10 mm instability. Assessments were made only by the two researchers.

Both intragroup and intergroup comparisons of the results were made. The mobility of the knee was evaluated in the preoperative and postoperative periods with the two types of prostheses; intragroup comparison helped to determine if the difference was significant in terms of joint mobility. Preoperative and postoperative pain and functionality were determined using objective assessment scales; intragroup comparison helped to determine if the difference was significant in terms of pain and functionality.

Intergroup comparison was made of the two types of prostheses in the postoperative period. This was used to determine if one type of prosthesis was superior to the other in terms of joint mobility, pain, and functionality which were measured using objective scales.

Statistical Analysis

Since the results with previous studies of the two prosthesis comparisons were not known, a sample size calculation was not performed. Qualitative variables were described with frequencies and proportions. Quantitative variables were described with mean and standard deviation or median with interquartile ranges. To evaluate differences within each prosthesis group between the preoperative and the postoperative period, the Student t-test was applied for related samples in the case of quantitative variables, Wilcoxon test was applied for ordinal qualitative variables, and McNemar for dichotomous qualitative variables. For the comparison between the two groups of prostheses, the Student t-test was used for independent samples, Mann-Whitney and Chi-square were used according to normality criteria. The data were processed in the IBM SPSS program version 14.0 (SPSS Inc., Chicago, Illinois). A significant P value of less than 0.05 was considered significant.