Osteoarthritis is a leading cause of pain and disability affecting all the three compartments of the knee. The patellofemoral joint is a complex articulation and a very critical factor for patient satisfaction after total knee arthroplasty [1]. Almost 25.7% of the causes of the first revision TKA are due to patellofemoral problem [2]. Management of defective patella with altered morphology is challenging and is more commonly encountered in revision surgeries [3]. Extensor mechanism impairment and anterior knee pain are often the sequelae in patients with patellar defects who undergo resurfacing during revision TKA [4]. The literature available for management of patellar defect in primary TKA is limited. The patellar defect encountered in a primary TKA is commonly a sequelae of patella-femoral malalignment which needs to be addressed, unlike those in revision arthroplasty where the patellar defect is usually the sequelae of implant removal [5].

Here, we present a novel surgical management of egg-shell patellar defect in primary knee arthroplasty. The patient displayed a good range of motion with no complaints and anntact extensor mechanism performing activities of daily living at 1-year follow-up.

The patient was informed that the data concerning the case would be submitted for publication, and she provided consent.

Patellar resurfacing in defective patella undergoing revision total knee arthroplasty has been well reported in the literature, but management of patellar defects in primary knee arthroplasty is rare. We believe our report to be one of the earliest, to the best of our knowledge, highlighting a novel approach for the management of patellar shell-like defect in primary arthroplasty.

Abdel et al. showed satisfactory results and good bone resorption in revision TKA using autologous bone graft harvested from box cuts of femur to fill patellar cavitary defects [4]. We used the similar principle of using autologous bone graft harvested from the proximal tibial cut for filling the patellar cavitary defect. Unlike Abdel et al., we secured the graft using screws, which we believe would not only prevent the future collapse of construct due to resorption/remodeling but also secure the graft allowing early ROM of knee [4, 9]. At 1-year follow-up on CT imaging, the patellar thickness was be well maintained.

A thin patella before resurfacing has an increased risk of fracture and osteonecrosis which has a disastrous effect with potentially long-standing disability for the patient [8]. A remnant of at least 12 mm is suggested to be ideal, regardless of the initial thickness to prevent patellar complications [10, 11]. Thus, we achieved a patellar thickness of 16 mm with adequate bone stock for patellar prosthesis, of reasonable thickness, and above the fracture risk threshold [12, 13]. In addition, restoring the patellar thickness post-resurfacing is critical for the quadriceps lever arm mechanism and a thickness of 20 mm and more is suggested to be ideal [4]. In our case, the final patellar thickness after resurfacing was 24.5 mm. We recommend further resection of patella if the flexion of knee is restricted, but it was not so in our case. An increased post-patellar thickness also improves the overall function in activities of high demand like negotiating stairs; hence, we believe it to be one of the reasons for a drastically improved post-operative functional score [10].

The ROM/self-adjustment method was a key step in identifying the ideal tibial axis for patellofemoral tracking due to var y ing anatomical landmark s in patients w ith patellofemoral dysplasia [7]. The tibial axis determined by ROM/self-adjustment method is primarily depends on the femoral component rotation and is considered being relevant only if adapted to each patient, which in our case was patient specific anatomy based on pre-operative CT-based planning [7]. The tibial component was noted to be more externally rotated compared to the Akagi’s line, which is in lieu of the increased external rotation in relation to native tibia seen in valgus knee [7]. Thus, a detailed patient specific pre-operative evaluation is essential in valgus deformity knee. We believe, the externally rotated alignment in this patient also improved our clinical outcome and results, including the patient’s ability to kneel without pain [14, 15]. The aim of patellar resurfacing is not only to relieve anterior knee pain but also to restore normal patellofemoral mechanics [10]. Restored patellofemoral mechanics are important for activities of high demand such as squatting, stairs ascent, and descent, thus patellar resurfacing was very crucial in our patient considering her younger age and higher demands.

We have presented a rare case of a combination of patellar defect in an osteoarthritic knee which was managed by modified gapbalancing technique of TKA with a novel method of patellar resurfacing in a single stage with good functional results at 1- year postoperatively. This case improves our understanding of management of such complex scenarios and more importantly raises the questions our understanding and need of classification of such patellar defects in a primary arthritic knee.