Systematic Lateral Retinacular Release Does Not Reduce Post-Operative Anterior Knee Pain After Primary Total Knee Arthroplasty With Patellar Replacement
Phase: NA
Conditions: Anterior Knee Pain Syndrome
Sponsor: Hospital del Mar

Systematic lateral retinacular release does not reduce post-operative anterior knee 
pain after primary total knee arthroplasty with patellar replacement 
 
Study Protocol and Statistical Analysis Plan 
 
September 1, 2019 
 
 
 

INTRODUCTION 
Anterior knee pain (AKP) remains a common cause of persistent pain after total knee 
arthroplasty (TKA). The reported incidence varies from 8% to more than 50%, and it has 
a negative effect on patient quality of life and satisfaction. Many factors may contribute 
to AKP, but there is no clear consensus with regard to its etiology and treatment.  
Lateral retinacular release (LRR) has been proposed as a surgical option to prevent AKP 
syndrome. This is based on the fact that excessive lateral patellofemoral pressure due to 
a tight lateral retinaculum contributes to patellofemoral disorders like AKP, patellar 
chondral lesions, or patellofemoral osteoarthrosis. Some authors suggested that the origin 
of AKP can be found in the degenerative neuropathy seen in the lateral retinaculum of 
symptomatic patients. Therefore, its release would improve this pain by denervating the 
tissue.  
Accordingly, the mechanism by which lateral release relieves pain may be the reduction 
of lateral tension decreasing the surface pressure, as well as the denervation of the 
retinaculum. 
With TKA, forces and peak pressures significantly increase in the patellofemoral joint. 
For that reason, some authors are keen advocates of the lateral release with the intent to 
ease AKP. They perform it systematically even if the tracking is correct. A clinical 
randomized trial suggested that routine LRR can reduce AKP in TKA without patellar 
resurfacing. 
 
Objectives and hypothesis 
The primary objective of this prospective randomized double-blind trial is to evaluate the 
effect of LRR on AKP after TKA with patellar replacement when compared to the 
resurfaced patella without release.  
The secondary objectives are to assess and compare the functional and radiological 
outcomes between the groups after 12 months.  
The hypothesis is that LRR would decrease the incidence of AKP after TKA with patellar 
resurfacing, as well as it would improve functional outcomes. 
 
MATERIALS AND METHODS 
Study design and eligibility criteria 
A prospective, randomized, and double-blinded clinical trial is designed. All the patients 
that will undergo a primary TKA in our center from October 2019 through December 
2020 are included.  
The inclusion criteria are patients aged 40-90 years with a diagnosis of knee osteoarthritis 
who signed written informed consent.  
The exclusion criteria are patients with a prior major surgery on the same knee (high tibial 
or distal femoral osteotomy, patellar realignment), important preoperative malalignment 

(varus or valgus >15º or flexion deformity >15º), and an inability to sign informed 
consent. 
The study was approved by the Research Ethics Committee of our institution 
(2019/8993/I). 
A total of 220 patients are randomized into either the LRR group (Group A) or non-release 
group (Group B).  
 
Surgical procedure 
Computer-generated randomization sequencing will be conducted before the surgery.  
All the procedures will be performed by five experienced surgeons from the knee unit of 
our institution, using a midline anterior approach and a medial parapatellar arthrotomy. 
An extramedullary guide will be used for tibial cutting and intramedullary guide for 
femoral cutting, following mechanical alignment technique. The prosthetic components 
will be implanted in a one-stage cementing technique after standard bone cuts. The patella 
is going to be always replaced with a symmetric implant.  
In the release group (Group A), a retinacular release will be performed 2cm lateral to the 
lateral margin of the patella.  
The postoperative rehabilitation protocol will be the standardized for every total knee 
arthroplasty in our hospital.  
 
Data collection and outcome measures 
Preoperatively, demographic data regarding age, gender, body mass index and laterality 
will be recorded. At the preoperative visit and at the 1-year follow up, the following 
clinical and radiological data will be collected by an examinator blinded to the surgical 
technique performed:  
• Patellar pain and function are evaluated with the patellofemoral score designed by Feller 
et al. The score is distributed with a maximum of 15 points for the intensity of anterior 
knee pain, 5 points for quadriceps strength, 5 points for the ability to rise from a chair and 
5 points for stair-climbing ability.  
• The Knee Society Score (KSS) for both the Knee and the Function scores, 0 being the 
worst and 100 the best possible result in each section.  
• The pressure pain threshold (PPT) determined using pressure algometry (PA). The PPT 
is assessed 3 times in each knee, with a calibrated electronic algometer (Algometer, 
Somedic Sales, Hörby, Sweden) with a 1cm2 probe placed perpendicular to the skin in 
the center of the anterior aspect of patella. The evaluator increases the pressure 20 kPa/s 
until the sensation become painful and the patient says “stop”. The final PPT value taken 
is the average of the 3 measurements.  
• The Visual Analogue Scale (VAS) referred by the patients at rest, when walking and 
when going up and downstairs. 

• Patellar height. Measured in the lateral view using the Caton-Deschamps index and its 
application in TKA. 
 
    
 
 
• Patellar tilt. Defined in the axial view, as the angle subtended by the anterior 
intercondylar line and the equatorial line of the patella preoperatively or a line drawn 
through the prosthesis-bone interface postoperatively. 
 
    
 
 
 
Statistical analysis  
The sample size calculation of 110 patients in each group was based on assuming a 
minimum difference of 1 point in the VAS value with a standard deviation of 2.5. A 
probability level of 0.05, a power of 80% and a drop-out rate of 10% were assumed. 
Descriptive statistics were used for the demographic data. Continuous variables and 
measured scores were presented as mean and standard deviations and categorical 
variables as number and percentage. Between group comparisons were evaluated with the 
Mann–Whitney U test. These comparisons were performed with the preoperative and 
postoperative measurements. Differences between the groups in terms of changes or 
improvements (post vs. pre) were also assessed with the Mann–Whitney U test.  
Figure 2. Patellar tilt measurement.   
Figure 1. Patellar height measurement 
defined as the ratio of the length of the 
patellar articular surface (B) and the 
distance between the lower pole of 
patellar articular surface and the 
anterior border of the tibial plateau (A) 
preoperatively or the tibial component 
surface postoperatively (A’).  

STATA version 15.1 (StataCorp, College Station, TX, USA) was used for the statistical 
analysis with p values of 0.05 being considered statistically significant. 
For the calculation of intraclass correlation coefficients (ICC) two-way random-effects 
model approximation was performed, being in terms of Shrout and Fleiss notation 
ICC(2,1) for intrarater agreement and ICC(2,2) for interrater agreement.