## 4 Discussions  
Although TKR has become a well-established treatment for end stage degenerative disease of the knee with good survivorship [2], a great number of patients remain dissatisfied following the procedure [1]. AKP represents a leading cause of dissatisfaction that can be associated with PFJ complications which ultimately require revision surgery [3,4]. Restoring physiologic soft tissue tension and balance of the PFJ during TKR and thereby avoiding patella \"over-stuffing\" or \"under-tensioning\" should be a primary objective during surgery; however, few if any advancements in surgical strategies to address PFJ balancing have been made. At present, limited understanding exists on how to address the specific PFJ anatomy of each individual patient, and significant variation exists by surgeon on whether patellar resurfacing is performed. Furthermore, there is limited agreement on what constitutes adequate patellar resurfacing, with many surgeons performing the procedure using a freehand technique [15]. The findings of this preliminary cadaveric study revealed that a novel force sensor device is capable of recording PFJ loads in four quadrants intraoperatively. No previously published studies have assessed the feasibility of utilizing this device, and we present findings validating its use in both a knee model and cadaveric specimen. Furthermore, we demonstrated how these measurements can guide surgical planning, with the ability to adjust the patella resection to achieve more physiologic, native loading and balance during TKR. Following assessment of the native PFJ loads in this study compared with TKR trial components in place, PFJ loads increased significantly with use of greater thickness adjustment shims. Angled adjustment shims revealed differential loads in the superior and lateral quadrant, which could guide adjustment cuts to \"fine-tune\" the preliminary patella using custom cutting guides with adjustable thickness and angles. Furthermore, we observed in our left knee study that performing an angled adjustment cut based on shim measurements could reproduce expected loads when re-measured with a neutral shim matched in resection thickness. Our study also observed the effects of under-stuffing or under-tensioning the patella, as uniformly reduced PFJ loads were measured after a large 4 mm adjustment cut was made in our right knee study. PFJ loads increased significantly with greater shim thickness with TKR trial components in place compared to the native PFJ load measurements. Soft tissue tension in the extensor hood of the soft tissue structures surrounding the patella, quadriceps muscle and tendon, medial and lateral retinaulum and patella tendon, have been implicated in AKP [7]. Patella resection remains one of the least controlled aspects of TKR and it is widely acknowledged in the literature that improved surgical accuracy would reduce the risk of postoperative patella complications [16]. Amongst experienced surgeons, errors in patella resection occur in 10% of cases [17]: with increased patellar resection angle reported to be the sole independent risk factor for AKP [18]. Inaccurate surgical patella resection, which is confounded by a lack of consensus, is responsible for a high incidence of patella-related complications, with some studies reporting that up to 80% of resurfaced patella are greater in size than their pre-surgical measurement with associated post-operative AKP [19]. \"Over-stuffing\" the PFJ through under-resection of the patella can lead to AKP following TKR [20]. While over-resection of the patella should be avoided due to the risk of fracture, [8] the quad sense device allowed for characterization of PFJ loads for comparison to the patient-specific native PFJ loads. This provides the surgeon with the ability to make