Digging Deeper into the Patello – Femoral Joint: Patello – Femoral Composite - A New Dimension for Overstuffing of Patello – Femoral Joint

Abstract

Introduction: Patello–femoral complications are the most common complications in postoperative Total Knee Arthroplasty (TKA) patients especially overstuffing of Patello – Femoral Joint (PFJ). So, to study the effects of overstuffing of PFJ in postoperative TKA patients we put forth a new dimension - “PATELLO - FEMORAL COMPOSITE (PFC)”. This is the maximum distance between anterior cortical line of femur shaft and the anterior cortex of patella with knee in full extension. Aim: To calculate chances of overstuffing of PFJ in postoperative TKA patients and document the effect of overstuffing of PFJ on the passive knee Range of Motion (ROM) in post- op TKA patients. Materials and Methods: This was a prospective observational study which included 51 consecutive primary TKAs. Preoperative and postoperative (24 weeks) passive knee ROM was measured. Preoperative and postoperative radiological parameters {PFC, Anterior Femur Offset (AFO), Patellar thickness (PT)} was recorded using Computed Tomography (CT) Scanogram image of patient in lateral view with knee in full extension and perfect overlap of both femur condyles, using DICOM format of the CT Scanogram image on the DICOM viewer. Results: The postoperative PFC was more than its preoperativevalue in 80.39% TKAs. Patients who had increased postoperative PFC had significantly less preoperative AFO. Female patients in our study had significantly less preoperative AFO compared to males. Thus, we deduced that female patients with lesser preoperative AFO undergoing TKA had increased postoperative PFC than male patients. PFC not only accounted for the overstuffing of the PFJ because of the patellar component, but also because of the femoral component; thus was a better measure of PFJ overstuffing compared to isolated PT. Passive knee ROM in the postoperative TKA patients approximately decreased by 2 degrees for every 1 mm increase in PFC compared to its preoperative-value in the patients with PFJ overstuffing. Conclusion: We conclude that overstuffing of the PFJ in postoperative TKA is present in 80.39% patients. Higher chances of postoperative PFJ over stuffing are present in female patients and those with thinner anterior cortex of distal femur. Postoperative passive knee ROM decreases significantly in patients with postoperative PFJ overstuffing (Every 1 mm increase in the postoperative PFC, passive knee ROM decreased by approximately 2 degrees).

Keywords

• anterior knee offset
• overstuffing of patello-femoral joint
• patellar thickness
• range of motion
• total knee arthroplasty